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1

Redox reactions and complex formation of transplutonium elements in solutions  

SciTech Connect

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

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

1986-01-01

2

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

3

Kinetics of actinide complexation reactions.  

National Technical Information Service (NTIS)

Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In li...

K. L. Nash J. C. Sullivan

1997-01-01

4

Reaction time dependent formation of Pd(II) and Pt(II) complexes of bis(methyl)thiasalen podand.  

PubMed

Thiasalen podand 9 having S2N2 donor set has been synthesized by the condensation of 2-methylthiobenzaldehyde with ethylenediamine. The reaction of the thiasalen podand ligand with Pd(II) afforded two complexes depending on the reaction time. Shorter reaction time (5 min) afforded thioether complex 10; whereas with increase in reaction time (4 h) thioether-thiolate complex 11 was obtained via cleavage of one of the two S-C(Me) bonds of bis(methyl)thiasalen podand upon complexation. The reaction of 9 with Pt(II) afforded only thiolate-thioether complex 12 independent of the reaction time. The cleavage of both the S-C(Me) bonds of bis(methyl)thiasalen to afford bisthiolate complexes has never been observed. The structures of thiasalen podands and all three complexes have been determined by single crystal X-ray diffraction analysis. All three complexes possess a square planar geometry around the metal centres. Weak van der Waals interactions through C-H···F interactions are present in all three complexes leading to the formation of supramolecular synthons and the supramolecular structures are stabilized by aromatic ?···? interactions, which leads to the formation of 3D pseudo-double helical network packing. Under similar conditions bis(methyl)salen did not form any complexes with Pd(II) and Pt(II). PMID:23073301

Dutta, Pradip Kr; Panda, Snigdha; Krishna, G Rama; Reddy, C Malla; Zade, Sanjio S

2012-10-17

5

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

6

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

7

Intermediates in Reactions of Copper(I) Complexes with N-Oxides: From Formation of Stable Adducts to Oxo Transfer  

PubMed Central

Reactions of Cu(I) complexes of bidentate N-donor supporting ligands with pyridine- and trimethylamine-N-oxides or PhIO were explored. Key results include the identification of novel Cu(I)-N-oxide adducts, aryl substituent hydroxylation, and bis(?-oxo)dicopper complex formation via a route involving oxo transfer.

Hong, Sungjun; Gupta, Aalo K.; Tolman, William B.

2009-01-01

8

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

PubMed

The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems. PMID:22466785

Kalita, Apurba; Kumar, Pankaj; Mondal, Biplab

2012-03-30

9

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

10

A complex cortical reaction leads to formation of the fertilization envelope in the lobster, Homarus.  

PubMed

We have examined the formation of the fertilization envelope in the lobsters Homarus americanus and H gammarus. Oocytes were fixed for electron microscopy either in the ovary or following extrusion from the gonopore. Mature ovarian oocytes are surrounded by a coat (envelope 1), which is comprised of small electron-dense granules and structures resembling "bottlebrushes." At least part of this coat is synthesized by the follicle cells of the ovary. The cortex of ovarian oocytes contains four types of vesicles that we refer to as high-density vesicles (HDV), low-density vesicles (LDV), moderately dense vesicles (MDV), and ring vesicles (RV). Oocytes that were electrically extruded from the gonopore and fixed immediately had an envelope identical to that of ovarian oocytes. The cortex of gonopore oocytes contained the four types of vesicles found in ovarian oocytes. When unfertilized gonopore oocytes were allowed to incubate in sea water, the oocyte cortex appeared unaltered, but envelope 1 swelled and the bottlebrushes dispersed. When recently fertilized oocytes were fixed during natural spawning or following in-vitro fertilization, each type of vesicle was released in sequence from the cortex of the oocyte. The contents of the HDV and LDV appeared first in the perivitelline space, but their fate could not be determined at later times. The ring-shaped elements of the RV and the moderately electron-dense material of the MDV were released exocytotically somewhat later; these materials coalesced in the perivitelline space to form a new coat (envelope 2). Envelope 1 subsequently condensed to its original thickness and appeared firmly attached to envelope 2. Our results show that the fertilized lobster egg is surrounded by two discrete coats. The outer coat, which is formed in the ovary, undergoes a swelling/condensation cycle at spawning. The inner coat originates from a complex cortical reaction. Together these coats comprise the fertilization envelope of the lobster egg. PMID:3198040

Talbot, P; Goudeau, M

1988-01-01

11

The thermochemical characteristics of complex formation reactions between 3 d transition metal ions and L-serine in aqueous solution  

NASA Astrophysics Data System (ADS)

The heat effects of complex formation between nickel(II), cobalt(II), cadmium (II), and zinc(II) ions and L-serine in aqueous solution over the ionic strength range 0.25-0.75 (background electrolyte KNO3) were determined calorimetrically at 298.15 K. The heats of dilution of solutions of metal nitrates with solutions of the background electrolyte were measured under identical conditions for the introduction of the corresponding corrections. The thermodynamic characteristics of complex formation between 3 d transition metals and L-serine were calculated. The results were analyzed using the Herny theory. The complex-forming ability of transition metals in reactions with the ligand was characterized with the use of the Irving-Williams series.

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

2009-11-01

12

Reactions of guanine with methyl chloride and methyl bromide: O6-methylation versus charge transfer complex formation  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) at the B3LYP/6-31+G* and B3LYP/AUG-cc-pVDZ levels was employed to study O6-methylation of guanine due to its reactions with methyl chloride and methyl bromide and to obtain explanation as to why the methyl halides cause genotoxicity and possess mutagenic and carcinogenic properties. Geometries of the various isolated species involved in the reactions, reactant complexes (RCs), and product complexes (PCs) were optimized in gas phase. Transition states connecting the reactant complexes with the product complexes were also optimized in gas phase at the same levels of theory. The reactant complexes, product complexes, and transition states were solvated in aqueous media using the polarizable continuum model (PCM) of the self-consistent reaction field theory. Zero-point energy (ZPE) correction to total energy and the corresponding thermal energy correction to enthalpy were made in each case. The reactant complexes of the keto form of guanine with methyl chloride and methyl bromide in water are appreciably more stable than the corresponding complexes involving the enol form of guanine. The nature of binding in the product complexes was found to be of the charge transfer type (O6mG+ · X-, X dbond Cl, Br). Binding of HCl, HBr, and H2O molecules to the PCs obtained with the keto form of guanine did not alter the positions of the halide anions in the PCs, and the charge transfer character of the PCs was also not modified due to this binding. Further, the complexes obtained due to the binding of HCl, HBr, and H2O molecules to the PCs had greater stability than the isolated PCs. The reaction barriers involved in the formation of PCs were found to be quite high (?50 kcal/mol). Mechanisms of genotoxicity, mutagenesis and carcinogenesis caused by the methyl halides appear to involve charge transfer-type complex formation. Thus the mechanisms of these processes involving the methyl halides appear to be quite different from those that involve the other strongly carcinogenic methylating agents.

Shukla, P. K.; Mishra, P. C.; Suhai, S.

13

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

14

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

PubMed

Dehydration/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects of pH, divalent cation binding and osmotic stress. Experimental variables included temperature, water activity and hydrolysis of the resulting ester product, providing insights into the environmental conditions that would favor the formation and stability of this more evolved amphiphile. At temperatures exceeding 50 degrees C, the ester product formed even in the presence of bulk water, suggesting that the reaction occurs at the liquid interface of the two reactants and that the products segregate in the two immiscible layers, thereby reducing hydrolytic back reactions. This implies that esterification reactions were likely to be common in the prebiotic environment as reactants underwent cycles of wetting and drying on rare early landmasses at elevated temperatures. PMID:16228646

Apel, Charles L; Deamer, David W

2005-08-01

15

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: kOH+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 kOH+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 kOH+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%: kOH+DME = 8.45 × 10(-18) (T/K)(2.07) exp(262.2 K/T) cm(3) s(-1). For kOH+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

2013-08-20

16

Reactions of a Chromium(III)-Superoxo Complex and Nitric Oxide That Lead to the Formation of Chromium(IV)-Oxo and Chromium(III)-Nitrito Complexes.  

PubMed

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr(III)(14-TMC)(O2)(Cl)](+), with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr(IV)(14-TMC)(O)(Cl)](+), via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [Cr(III)(14-TMC)(NO2)(Cl)](+). The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally. PMID:24066924

Yokoyama, Atsutoshi; Cho, Kyung-Bin; Karlin, Kenneth D; Nam, Wonwoo

2013-09-30

17

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 C(8)H(7)(+) and C(10)H(9)(+) 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 C(8)H(7)(+) adduct as 2-phenyl-ethenylium ion, the most stable C(8)H(7)(+) 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 C(10)H(9)(+) containing a four-membered ring connected to the phenylium ion. Evidence for rearrangement of the C(10)H(9)(+) 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 H(2) 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

2012-08-28

18

Radical-Molecule Reaction Mechanisms: Role of Electron Delocalization, Complex Formation, and Intramolecular Energy Transfer  

Microsoft Academic Search

This thesis presents: (1) measurements of the kinetics of the reactions of the OH radical with several molecules by the discharge flow technique, (2) reactivity trend analysis, electronic structure, and transition state calculations, (3) molecular beam electric deflection experiments of hot polyatomics. A synthesis of these studies demonstrates that radical-molecule reactions frequently involve an indirect mechanism and are not necessarily

Manvendra Krishna Dubey

1994-01-01

19

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

Microsoft Academic Search

G protein coupled receptors catalyze the GDP\\/GTP exchange on G proteins, thereby activating them. The ternary complex model, designed to describe agonist binding in the absence of GTP, is often extended to G protein activation. This is logically unsatisfactory as the ternary complex does not accumulate when G proteins are activated by GTP. Extended models taking into account nucleotide binding

David J Roberts; Magali Waelbroeck

2004-01-01

20

Formation of carbonato and hydroxo complexes in the reaction of platinum anticancer drugs with carbonate.  

PubMed

The second-generation Pt(II) anticancer drug carboplatin is here shown to react with carbonate, which is present in blood, interstitial fluid, cytosol, and culture medium, to produce platinum-carbonato and -hydroxo complexes. Using [(1)H-(15)N] HSQC NMR and (15)N-labeled carboplatin, we observe that cis-[Pt(CBDCA-O)(OH)(NH(3))(2)](-), cis-[Pt(OH)(2)(NH(3))(2)], cis-[Pt(CO(3))(OH)(NH(3))(2)](-), and what may be cis-[Pt(CO(3))(NH(3))(2)] are produced when 1 is allowed to react in 23.8 mM carbonate buffer. When (15)N-labeled carboplatin is allowed to react in 0.5 M carbonate buffer, these platinum species, as well as other hydroxo and carbonato species, some of which may be dinuclear complexes, are produced. Furthermore, we show that the carbonato species cis-[Pt(CO(3))(OH)(NH(3))(2)](-) is also produced when cisplatin is allowed to react in carbonate buffer. The study outlines the conditions under which carboplatin and cisplatin form carbonato and aqua/hydroxo species in carbonate media. PMID:19113934

Di Pasqua, Anthony J; Centerwall, Corey R; Kerwood, Deborah J; Dabrowiak, James C

2009-02-01

21

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

Microsoft Academic Search

Dehydration\\/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of

Charles L. Apel; David W. Deamer

2005-01-01

22

Intracluster reactions: The formation of hydrazine complexes from ammonia clusters following ArF excimer laser excitation  

Microsoft Academic Search

We have found a novel intracluster reaction proceeding in large ammonia or ammonia\\/argon clusters upon excitation with ArF excimer laser radiation which leads to the formation of unprotonated and prototaned hydrazine clusters, (N2H4)+n and (N2H4)nH+ (n=1–4). To our knowledge it is the first time that the production of bareclustersofadifferentchemicalspecies has been observed as a result of an intracluster reaction. Besides

Matthias Färber; Friedrich Huisken

1996-01-01

23

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

PubMed

Reactions of ruthenium complexes having 2-pyridinecarboxylato and 2,2'-bipyridine ligands with sodium azide in alcohol afforded nitrido-bridged diruthenium complexes, [{Ru(OR)(pyca)(bpy)}2(mu-N)](+) (R = CH3, C2H5). Diruthenium complexes showed diamagnetic properties, a linear Ru-N-Ru coordination configuration, and two irreversible oxidation waves and two reversible reduction waves. PMID:18788795

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

2008-09-13

24

Reaction of Cp*RuCl(PPh 3) 2 with dioxygen and formation of a neutral complex Cp*RuCl(O 2)(PPh 3)  

Microsoft Academic Search

Reaction of Cp*RuCl(PPh3)2 (1) with atmospheric oxygen occurs at room temperature in the presence of acetone or methylene chloride leading to Cp*RuCl(O2)(PPh3) (2). This complex is remarkably stable in the solid state and it can also release, under not unduly harsh conditions, the activated oxygen molecule, which can oxidize the phosphite L=MeOP[(OCHMe)2CH2] to the corresponding phosphate, along with formation of

J Román Torres-Lubián; M Esther Sánchez-Castro; Patricia Juárez-Saavedra; Javier Hernández-Mart??nez; Bárbara Gordillo-Román; M Angeles Paz-Sandoval

2002-01-01

25

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

NASA Astrophysics Data System (ADS)

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

Wang, Yun; Stone, Alan T.

2006-09-01

26

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

SciTech Connect

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

Groot, Marie-Louise; Paa lsson, Lars-Olof; Pribic, Radmila; Stokkum, Ivo H. van; Dekker, Jan P.; Grondelle, Rienk van [Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

1996-04-01

27

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

SciTech Connect

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

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

1986-02-05

28

Thermodynamic and kinetic properties of the formation reactions of the donor-acceptor complexes HXPY (X=Al, B; Y=H, Cl, SH)  

NASA Astrophysics Data System (ADS)

The optimized geometries, complexation energies, and transferred charges, etc. of the donor-acceptor complexes HXPY (X=Al, B; Y=H, Cl, SH) have been studied at the B3LYP/6-311+G (d, p), MP2/6-311+G (d, p) and/or CCSD(T)/6-311 +G (d, p) levels. The research results show that HBPY is more stable than the corresponding HAlPY (Y=H, Cl, SH), and Cl (or SH) substitution on phosphorus results in decreasing the stability of the complexes. The general statistical thermodynamics and Eyring transition state theory with Wigner correction were used to examine the thermodynamic and kinetic properties of these donor-acceptor complexes formation reactions. It is concluded that within the temperature range 200 800 K, the formation of HBPY is thermodynamically favored over that of the corresponding HAlPY especially at low temperature, and is kinetically favored over that of the relevant HAlPY (Y= H, Cl, SH) especially at high temperature.

Yin, Ping; Zhou, Taoyu; Kong, Lingyan; Sun, Yanzhi; Zhang, Ying; Xu, Xiaohui

2006-07-01

29

Complex formation reactions of uranyl(VI) with neutral N-donors in dimethyl sulfoxide. Influence of small amounts of water  

SciTech Connect

Quantitative information about the existence and thermodynamic stability of uranyl(VI) ion complexes based solely upon nitrogen coordination has been obtained in the solvent dimethyl sulfoxide. Calorimetric, potentiometric, and FT-IR investigations, under controlled anhydrous conditions, show that the uranyl(VI) ion can form both mono and bis chelates with the ethylenediamine ligand and only a mono chelate of rather low stability with propylenediamine. With the monodentate ligand n-butylamine only a very weak metal-ligand interaction has been detected. The stability constants and the enthalpy and entropy changes have been calculated for the identified coordinated species. All data refer to 25.0{degree}C and a tetraethylammonium perchlorate medium of ionic strength 0.1 M. All the complexes are enthalpy stabilized whereas the entropy contributions oppose the complex formation. Calorimetric and FT-IR measurements carried out to investigate the effects of small amounts of water present show that a very low water concentration, comparable to that of the coordinating metal ion, can give rise to hydrolysis reactions that may compete with complex formation. This is due to the combined action of different factors that are discussed. 39 refs., 6 figs., 1 tab.

Cassol, A.; Di Bernardo, P.; Zanonato, P. (Universita di Padova (Italy)); Portanova, R.; Tolazzi, M. (Universita di Udine (Italy) CNR, Padova (Italy))

1990-03-07

30

Reaction in alphavirus mRNA capping: formation of a covalent complex of nonstructural protein nsP1 with 7-methyl-GMP.  

PubMed Central

After the start of transcription, the 5' ends of eukaryotic mRNA molecules are modified by the addition of a guanylyl residue to form a cap structure, G(5')ppp(5')N. The guanylyltransferase (GTP:mRNA guanylyltransferase, EC 2.7.7.50) reaction responsible for cap formation usually proceeds via a covalent enzyme-GMP intermediate. We have studied the alphavirus-specific guanylyltransferase by incubating lysates from Semliki Forest and Sindbis virus-infected cells with [alpha-32P]GTP, using vaccinia virus and mock-infected cells as controls. One additional 32P-labeled protein was detected in alphavirus-infected cells but only in the presence of S-adenosylmethionine. This protein was identified as the nonstructural protein nsP1. The properties of the covalent enzyme-guanylate complex were studied with Semliki Forest virus nsP1 expressed in recombinant baculovirus-infected cells. S-Adenosylmethionine and divalent cations were required for the complex formation. The reaction was specific for guanylate nucleotides (GTP, dGTP) and was inhibited by pyrophosphate. nsP1 could be labeled with S-adenosyl[methyl-3H]methionine but only under conditions in which the nsP1-guanylate complex was formed. 7-Methyl-GMP was released from the nsP1-guanylate complex by treatment with acid or acidic hydroxylamine. Similar treatment of vaccinia virus capping enzyme released GMP. These findings suggest that in the capping of alphavirus mRNAs the guanine is methylated before linkage to the mRNA molecule. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Ahola, T; Kaariainen, L

1995-01-01

31

Reactions of methyl(phenyl)silylene with CO and PH 3—the formation of acid–base complexes  

Microsoft Academic Search

The thermal reaction of methyl(phenyl)silylene 1a with CO and PH3, respectively, was investigated using matrix isolation spectroscopy in combination with DFT calculations. The silylene 1a was produced by UV irradiation (?>400 nm followed by ?>350 nm) of (phenyl)silyldiazomethane 2 in high yields. The thermal reaction of 2 with CO in CO-doped argon matrices produces the acid–base adduct 3 which was

Holger Bornemann; Wolfram Sander

2002-01-01

32

Labelling Studies to Determine Product Formation from Reactions of CO and Hydrogen Catalysed by Ru Clusters and Rh Complexes  

Microsoft Academic Search

Reaction of CO with hydrogen in the presence of [Ru3(CO)12], KI and N-methylpyrrolidone produces small amounts of methanol under mild conditions. Using D2 the methanol is CD3OD confirming that it is a product of CO hydrogenation. In the presence of added H2O, CH\\u000a x\\u000a D1-y\\u000a OH\\/D (y=0–3) are produced. Carrying out the same reaction in the presence of MeI water

Martin J. Lofthouse; Evert Ditzel; Andrew J. Poole; David J. Cole-Hamilton

2006-01-01

33

Reinvestigation of the reaction of tert-butyllithium with uranium tetrachloride: formation of catalytically active uranium(III) hydride complexes  

Microsoft Academic Search

The reaction of UClâ with t-CâHâLi in alkane solvents has been reinvestigated in detail by quantitative collection and identification of gaseous products and by spectral, analytical, and chemical characterization of the solid uranium products. Treatment of UClâ with 4 equiv of t-CâHâLi generates 1.5 to 1.8 equiv of 2-methylpropane and 2-methylpropene in a 2.5-3 to 1 ratio and a solid

William J. Evans; Donald J. Wink; David R. Stanley

1982-01-01

34

Catalytic reactions of chlorite with a polypyridylruthenium(II) complex: disproportionation, chlorine dioxide formation and alcohol oxidation.  

PubMed

cis-[Ru(2,9-Me(2)phen)(2)(OH(2))(2)](2+) reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite. PMID:22064846

Hu, Zongmin; Du, Hongxia; Man, Wai-Lun; Leung, Chi-Fai; Liang, Haojun; Lau, Tai-Chu

2011-11-07

35

Electrospray ionization of uranyl-citrate complexes: Adduct formation and ion-molecule reactions in 3D ion trap and ion cyclotron resonance trapping instruments  

Microsoft Academic Search

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes

Árpád Somogyi; Sofie P. Pasilis; Jeanne E. Pemberton

2007-01-01

36

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

Microsoft Academic Search

Dehydration\\/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into protocellular structures. As a model of such reactions, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate. This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects

C. L. Apel; D. W. Deamer

2004-01-01

37

Reactions of d(0) tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations.  

PubMed

(Me3SiCH2)3(Me3SiC[triple bond, length as m-dash])W?O[double bond, length as m-dash]PMe3 (), an adduct between (Me3SiCH2)3W[triple bond, length as m-dash]CSiMe3 () and O[double bond, length as m-dash]PMe3, reacts with O2 to give O[double bond, length as m-dash]W(OSiMe3)(CH2SiMe3)3 () and CO2. Reaction of with H2O yields and the trimer [(?-O)W(CH2SiMe3)2([double bond, length as m-dash]O)(THF)]3 (). In the reaction of D2O with , and methane isotopologues CH2D2, CHD3 and CD4 have been observed. PMID:24036498

Morton, Laurel A; Miao, Maozhong; Callaway, Tabitha M; Chen, Tianniu; Chen, Shu-Jian; Tuinman, Albert A; Yu, Xianghua; Lu, Zheng; Xue, Zi-Ling

2013-09-24

38

Complex formation of uranyl ion with triphenylphosphine oxide and its ligand exchange reaction in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid.  

PubMed

Complex formation of the uranyl ion (UO(2)(2+)) with triphenylphosphine oxide (OPPh(3)) in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ([BMI][NfO]) ionic liquid was investigated by means of (31)P NMR spectroscopy. In [BMI][NfO], coordination of OPPh(3) to UO(2)(2+) was found, and its coordination number was 4.1 +/- 0.2, indicating UO(2)(OPPh(3))(4)(2+). From the [BMI][NfO] solution containing UO(2)(2+) and OPPh(3), yellow crystals of UO(2)(OPPh(3))(4)(ClO(4))(2) deposited, and its molecular and crystal structures were determined by using single-crystal X-ray analysis. An OPPh(3) exchange reaction of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] was also examined. The apparent first-order rate constant (k(obs)) showed the first-order dependence on [OPPh(3)] (k(obs) = k(4)[OPPh(3)](free)), suggesting the "associative" (A) mechanism. Its activation parameters were DeltaH(4)(++) = 55.3 +/- 2.8 kJ mol(-1) and DeltaS(4)(++) = 16.1 +/- 7.9 J mol(-1) K(-1). To compare the reactivity of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] with that in an ordinary organic solvent, the same reaction in CD(2)Cl(2) was studied. In the CD(2)Cl(2) system, an equilibrium between UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) was observed. The k(obs) values of the OPPh(3) exchange reactions in UO(2)(OPPh(3))(4)(2+) (k(4obs)) and UO(2)(OPPh(3))(5)(2+) (k(5obs)) in CD(2)Cl(2) are expressed as k(4obs) = k(4)[OPPh(3)](free) and k(5obs) = k(5), respectively, indicating that the exchange reactions in UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) are categorized in A and "dissociative" (D) mechanisms, respectively. The activation parameters of these reactions were also estimated (UO(2)(OPPh(3))(4)(2+): DeltaH(4)(++) = 7.1 +/- 0.3 kJ mol(-1) and DeltaS(4)(++) = -122 +/- 1 J mol(-1) K(-1), UO(2)(OPPh(3))(5)(2+): DeltaH(5)(++) = 62.4 +/- 1.0 kJ mol(-1) and DeltaS(5)(++) = 68.4 +/- 4.2 J mol(-1) K(-1)). A large difference in the reactivity of UO(2)(OPPh(3))(4)(2+) was found between [BMI][NfO] and CD(2)Cl(2). This was explained by the formation of a specific solvation barrier of NfO(-) around UO(2)(OPPh(3))(4)(2+) in [BMI][NfO]. PMID:19138105

Takao, Koichiro; Takahashi, Takafumi; Ikeda, Yasuhisa

2009-02-16

39

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

40

Formation and stability of 3-5 atom gold clusters from gold complexes during the catalytic reaction: dependence on ligands and counteranions.  

PubMed

Gold complexes and salts decompose to catalytically active 3-5 atom gold clusters during the one-pot acylation-hydration of propargyl alcohols. Kinetic and spectroscopic studies show that released ligands and counteranions exert a direct effect on the formation and stability of the clusters. PMID:23900257

Oliver-Meseguer, Judit; Leyva-Pérez, Antonio; Al-Resayes, Saud I; Corma, Avelino

2013-09-14

41

Mechanistic and kinetic investigation on the formation of palladacyclopentadiene complexes. A novel interpretation involving a bimolecular self-reaction of a monoalkyne intermediate  

Microsoft Academic Search

The stoichiometric reaction between the complex [Pd(eta(2)-dmfu)(BiPy)] (dmfu = dimethylfumarate; BiPy = 2,2'-bipyridine) and the deactivated alkynes dmbd (dimethyl-2-butynedioate) and pna (methyl (4-nitrophenyl)propynoate), providing the respective palladacyclopentadienes, was investigated. The mechanism leading to the palladacyclopentadiene derivative involves a bimolecular self-rearrangement of the monoalkyne intermediate [Pd(eta(2)-alk)(BiPy)] (alk = dmbd, pna), followed by the customary attack of the free alkyne on the

A. Holuigue; J. M. Ernsting; F. Visentin; C. Levi; L. Canovese; C. J. Elsevier

2008-01-01

42

Reactions of coordinated dinitrogen. 8. Formation of ammonia by protonation of a molybdenum-dinitrogen complex and isolation and characterization of the molybdenum-containing product  

SciTech Connect

This is the first reported conversion of metal-coordinated dinitrogen into ammonia in which the fate of the metal has been determined. This reaction is shown in the following equation, where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/ and L = PPh/sub 3/:2Mo(N/sub 2/)/sub 2/(triphos)(L) + 8HBr ..-->.. 2NH/sub 4/Br + 2MoBr/sub 3/(triphos) + 3N/sub 2/ + 2L. The metal complex which is a new subclass of bis(dinitrogen) complexes of molybdenum, reacted in tetrahydrofuran (THF) solution with anhydrous hydrogen bromide to produce ammonium bromide. No hydrazine or hydrazinium bromide was detected among the reaction products. Ammonium bromide was detected by infrared spectroscopy among the reaction products after solvent and excess HBr had been removed in vacuo. The yield of ammonia was determined quantitatively by the indophenol method after either aqueous, nonaqueous (ethanol), or two-phase (dichloromethane-water) extraction of ammonium bromide from the residue. The molybdenum-containing product slowly decomposed during the dichloromethane-water extraction step. Isolation of pure MoBr/sub 3/(triphos) was carried out in a separate experiment in which only N/sub 2/ evolution was measured. All volatiles were removed from the reaction vessel and the resulting yellow solid was washed with ethanol and dried. Its identity was confirmed by elemental analysis.

Baumann, J.A.; George, T.A.

1980-09-10

43

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

2011-09-26

44

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

45

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

2008-01-01

46

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

47

Methods for forming complex oxidation reaction products including superconducting articles  

SciTech Connect

This patent describes a method for producing a superconducting complex oxidation reaction product of two or more metals in an oxidized state. It comprises positioning at least one parent metal source comprising one of the metals adjacent to a permeable mass comprising at least one metal-containing compound capable of reaction to form the complex oxidation reaction product in step below, the metal component of the at least one metal-containing compound comprising at least a second of the two or more metals, and orienting the parent metal source and the permeable mass relative to each other so that formation of the complex oxidation reaction product will occur in a direction towards and into the permeable mass; and heating the parent metal source in the presence of an oxidant to a temperature region above its melting point to form a body of molten parent metal to permit infiltration and reaction of the molten parent metal into the permeable mass and with the oxidant and the at least one metal-containing compound to form the complex oxidation reaction product, and progressively drawing the molten parent metal source through the complex oxidation reaction product towards the oxidant and towards and into the adjacent permeable mass so that fresh complex oxidation reaction product continues to form within the permeable mass; and recovering the resulting complex oxidation reaction product.

Rapp, R.A.; Urquhart, A.W.; Nagelberg, A.S.; Newkirk, M.S.

1992-04-07

48

Methods for forming complex oxidation reaction products including superconducting articles  

SciTech Connect

This patent describes a method for producing a complex oxidation reaction product of two or more metals in an oxidized state. Positioning a parent metal source comprising at least one first metal of the two or more metals adjacent to a permeable mass comprising at least one metal-containing compound capable of reaction to form the complex oxidation reaction product, the metal component of the at least one metal-containing compound comprising at least a second of the two or more metals, and orienting the parent metal source and the permeable mass relative to each other so that formation of the complex oxidation reaction product will occur in a direction towards and into the permeable mass; heating the parent metal source in the presence of a vapor-phase oxidant; and recovering the resulting complex oxidation reaction product.

Rapp, R.A.; Urquhart, A.W.; Nagelberg, A.S.; New Kirk, M.S.

1990-09-11

49

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

50

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

PubMed

Oxygen conversion process between O? and H?O by means of electrochemistry or photochemistry has lately received a great deal of attention. Cobalt-phosphate (Co-Pi) catalyst is a new type of cost-effective artificial oxygen-evolving complex (OEC) with amorphous features during photosynthesis. However, can such Co-Pi OEC also act as oxygen reduction reaction (ORR) catalyst in electrochemical processes? The question remains unanswered. Here for the first time we demonstrate that Co-Pi OEC does be rather active for the ORR. Particularly, Co-Pi OEC anchoring on reduced graphite oxide (rGO) nanosheet is shown to possess dramatically improved electrocatalytic activities. Differing from the generally accepted role of rGO as an "electron reservoir", we suggest that rGO serves as "peroxide cleaner" in enhancing the electrocatalytic behaviors. The present study may bridge the gap between photochemistry and electrochemistry towards oxygen conversion. PMID:23877331

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

2013-01-01

51

Pattern Formation and Complexity Emergence  

NASA Astrophysics Data System (ADS)

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

Berezin, Alexander A.

2001-03-01

52

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

PubMed

Reaction of alpha-P(2)W(15)O(56)(12-) and Fe(III) in a saturated NaCl solution produces a trisubstituted Wells-Dawson structure with three low-valent metals, alpha-(Fe(III)Cl)(2)(Fe(III)OH(2))P(2)W(15)O(59)(11-) (1). Dissolution of this species into 1 M NaBr (Br(-) is non-coordinating) gives the triaquated species alpha-(Fe(III)OH(2))(3)P(2)W(15)O(59)(9-) (2). Ionic strength values of 1 M or greater are necessary to avoid decomposition of 1 or 2 to the conventional sandwich-type complex, alpha beta beta alpha-(Fe(III)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(12-) (3). If the pH is greater than 5, a new triferric sandwich, alpha alpha beta alpha-(NaOH(2))(Fe(III)OH(2))Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (4), forms rather than 3. Like the previously reported Wells-Dawson-derived sandwich-type structures with three metals in the central unit ([TM(II)Fe(III)(2)(P(2)W(15)O(56))(P(2)TM(II)(2)W(13)O(52))],(16-) TM = Cu, Co), this complex has a central alpha-junction and a central beta-junction. Thermal studies suggest that 4 is more stable than 3 over a wide range of temperatures and pH values. The intrinsic Jahn-Teller distortion of d-electron-containing metal ions incorporated into the external sites of the central multi-metal unit impacts the stoichiometry of their incorporation (with a consequent change in the inter-POM-unit connectivity, where POM = polyoxometalate). Reaction of non-distorting Ni(II) with the diferric lacunary sandwich-type POM alpha alpha alpha alpha-(NaOH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(16-) (5) produces alpha beta beta alpha-(Ni(II)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (6), a Wells-Dawson sandwich-type structure with two Ni(II) and two Fe(III) in the central unit. All structures are characterized by (31)P NMR, IR, UV-vis, magnetic susceptibility, and X-ray crystallography. Complexes 4 and 6 are highly selective and effective catalysts for the H(2)O(2)-based epoxidation of alkenes. PMID:11978116

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

2002-05-01

53

Structural determinants for the formation of sulfhemeprotein complexes  

PubMed Central

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

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

2010-01-01

54

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

55

[Kinetics of DNA-distaxin complex-formation].  

PubMed

Kinetics of DNA--distaxines complexes formation was studied spectrophotometrically by means of the stop--flow method. It has been found that increase of number of bulky pyrrolcarboxamide group in the row of distaxines: -0, -1, -2, - slows down the binding reactions and increases the number of their stages. PMID:3814634

Sizova, I A; Poletaev, A I

56

Extraposition via Complex Domain Formation  

Microsoft Academic Search

We propose a novel approach to extraposition in German within an alternative conception of syntax in which syntactic structure and linear order are mediated not via encodings of hierarchical relations but instead via order domains. At the heart of our proposal is a new kind of domain formation which affords analyses of extraposition constructions that are linguistically more adequate than

Andreas Kathol; Carl Pollard

1995-01-01

57

Kinetics of rouleau formation. II. Reversible reactions.  

PubMed Central

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

Samsel, R W; Perelson, A S

1984-01-01

58

Spray formation with complex fluids  

NASA Astrophysics Data System (ADS)

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

Lustig, S.; Rosen, M.

2011-05-01

59

Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase  

SciTech Connect

The reactions of anhydrous HBr and HCl with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PR/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/(PR/sub 3/ = PPh/sub 3/(1), PMePh/sub 2/ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of N/sub 2//mol of 1 and routinely ca. 0.72 mol of NH/sub 3//mol of 1, respectively, and MoBr/sub 3/(triphos) (greater than or equal to94% yield). No more than a trace of hydrazine was detected. Total nitrogen balance was increased to 100% when amounts of HBr were added periodically during the reaction. The reaction of 1 or 2 with HBr or HCl led to the rapid loss of 1 mol of N/sub 2/ and the formation of a pair of isomeric hydrazido(2-) complexes, (MoX(NNH/sub 2/)(triphos)(PR/sub 3/))X (PR/sub 3/ = PPh/sub 3/ for 1 A(X) and 1 B(X), PPh/sub 2/Me for 2A(X) and 2B(X); X = Br, Cl). The same mixtures were formed in the absence of solvent. The presence of two isomers was the result of the position of the phenyl group on the central phosphorus atom of the triphos ligand relative to the hydrazido(2-) ligand. 48 references, 3 figures, 3 tables.

Baumann, J.A.; Bossard, G.E.; George, T.A.; Howell, D.B.; Koczon, L.M.; Lester, R.K.; Noddings, C.M.

1985-10-23

60

C-C bond formation in diiron complexes.  

PubMed

The growing effort to design new sustainable synthetic methodologies, based on readily available and environmentally friendly transition metals, has boosted research on iron complexes. This review article focuses on C-C-bond-forming reactions occurring at bridging ligands in diiron complexes, aimed at evidencing distinctive aspects and advantages associated with the presence of two adjacent iron centres. A number of diiron-mediated C-C-bond-forming reactions reported in the literature, including nucleophilic and electrophilic additions and insertion and cycloaddition reactions, have been accumulated over the years, which, together with more recent developments, indicate that diiron complexes might provide promising alternatives to precious metals in the challenging field of metal-promoted C-C bond formation. PMID:22760971

Mazzoni, Rita; Salmi, Mauro; Zanotti, Valerio

2012-07-03

61

Reaction-diffusion controlled growth of complex structures  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

62

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

PubMed

Reaction mixtures, containing Al atoms and methylethyl ether (MEE) or diethyl ether (DEE) in an adamantane matrix, were prepared with the aid of a metal-atom reactor known as a rotating cryostat. The EPR spectra of the resulting products were recorded from 77-260 K, at 10 K intervals. Al atoms were found to insert into methyl-O, ethyl-O, and C-C bonds to form CH(3)AlOCH(2)CH(3), CH(3)OAlCH(2)CH(3), and CH(3)OCH(2)AlCH(3), respectively, in the case of MEE while DEE produced CH(3)CH(2)AlOCH(2)CH(3) and CH(3)AlCH(2)OCH(2)CH(3), respectively. From the intensity of the transition lines attributed to the Al atom C-O insertion products of MEE, insertion into the methyl-O bond is preferred. The Al hyperfine interaction (hfi) extracted from the EPR spectra of the C-O insertion products was greater than that of the C-C insertion products, that is, 5.4% greater for the DEE system and 7% greater for the MEE system. The increase in Al hfi is thought to arise from the increased electron-withdrawing ability of the substituents bonded to Al. Besides HAlOH, resulting from the reaction of Al atoms with adventitious water, novel mixed HAlOH:MEE and HAlOH:DEE complexes were identified with the aid of isotopic studies involving H(2)(17)O and D(2)O. The Al and H hfi of HAlOH were found to decrease upon complex formation. These findings are consistent with the nuclear hfi calculated using a density functional theory (DFT) method with close agreement between theory and experiment occurring at the B3LYP level using a 6-311+G(2df,p) basis set. PMID:22299675

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

2012-03-01

63

Thermal reactions in interstellar ice: A step towards molecular complexity in the interstellar medium  

NASA Astrophysics Data System (ADS)

Complex organic molecules are widely observed in star-forming regions, although their formation mechanisms are not well understood. Solid-state chemistry is thought to play an important role, but the solid-state reaction network is poorly known. We provide a list of purely thermal reactions involving electronically stable reactants to complement existing grain chemistry networks. The kinetic parameters of the reactions are given when available. These reactions lead to the formation of complex organic molecules, which were not considered previously. Eventually, these complex molecules are either released into the gas phase or incorporated into the organic residue found in meteorites. Thermal reactions are important because they are not limited by the UV flux or the slow diffusion of the radicals, and because they involve both surface and mantle molecules. Thermal reactions represent an important step in the formation of complex organic molecules that constitute the primitive material of comets and asteroids.

Theulé, P.; Duvernay, F.; Danger, G.; Borget, F.; Bossa, J. B.; Vinogradoff, V.; Mispelaer, F.; Chiavassa, T.

2013-10-01

64

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

65

[Significance of the immune complex reaction in internal medicine].  

PubMed

A review is given concerning occurrence, identification, and pathogenetic effects of immune complexes. The formation of immune complexes by interaction of antigen with antibody, is a component of the normal immune response. In cases with inefficient clearance by the mononuclear phagocyte system only, pathological consequences will be expected, in particular by immune complexes formed with moderate excess of antigen. For the identification of immune complexes in biological fluids many methods have been developed. The methods are based mostly on biological activities of immune complexes, e.g. interaction with complement or rheumatoid factor and reactivity with cellular receptors. These antigen-nonspecific methods do not allow to discriminate between true immune complexes and nonspecifically aggregated immunoglobulins. Circulating immune complexes become fixed to basement membranes of the body. They can produce an acute inflammatory reaction by activation of complement and inflammatory cells and also interfere with the immune response. Circulating immune complexes have been detected in some human diseases, e.g. autoimmune diseases (LEV, RA), infectious diseases, malignancies, serum sickness syndrome, immune-complex glomerulonephritis, and after transplantation. The possibilities for management of immune complex diseases are discussed. PMID:6447414

Jäger, L; Herrmann, D

1980-01-15

66

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

PubMed

M(NMe(2))(4) (M = Ti, Zr, Hf) were found to react with H(2)SiR'Ph (R' = H, Me, Ph) to yield H(2), aminosilanes, and black solids. Unusual amide hydride complexes [(Me(2)N)(3)M(mu-H)(mu-NMe(2))(2)](2)M (M = Zr, 1; Hf, 2) were observed to be intermediates and characterized by single-crystal X-ray diffraction. [(Me(2)N)(3)M(mu-D)(mu-NMe(2))(2)](2)M (1-d(2), 2-d(2)) were prepared through reactions of M(NMe(2))(4) with D(2)SiPh(2). Reactions of (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) with H(2)SiR'Ph were found to give aminosilanes and (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6). These reactions are reversible through unusual equilibria such as (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) + H(2)SiPh(2) right arrow over left arrow (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6) + HSi(NMe(2))Ph(2). The deuteride ligand in (Me(2)N)(2)Zr(D)Si(SiMe(3))(3) (6-d(1)) undergoes H-D exchange with H(2)SiR'Ph (R' = Me, H) to give 6 and HDSiR'Ph. The reaction of Ti(NMe(2))(4) with SiH(4) in chemical vapor deposition at 450 degrees C yielded thin Ti-Si-N ternary films containing TiN and Si(3)N(4). Ti(NMe(2))(4) reacts with SiH(4) at 23 degrees C to give H(2), HSi(NMe(2))(3), and a black solid. HNMe(2) was not detected in this reaction. The reaction mixture, upon heating, gave TiN and Si(3)N(4) powders. Analyses and reactivities of the black solid revealed that it contained -H and unreacted -NMe(2) ligands but no silicon-containing ligand. Ab initio quantum chemical calculations of the reactions of Ti(NR(2))(4) (R = Me, H) with SiH(4) indicated that the formation of aminosilanes and HTi(NR(2))(3) was favored. These calculations also showed that HTi(NH(2))(3) (3b) reacted with SiH(4) or H(3)Si-NH(2) in the following step to give H(2)Ti(NH(2))(2) (4b) and aminosilanes. The results in the current studies indicated that the role of SiH(4) in its reaction with Ti(NMe(2))(4) was mainly to remove amide ligands as HSi(NMe(2))(3). The removal of amide ligands is incomplete, and the reaction thus yielded "=Ti(H)(NMe(2))" as the black solid. Subsequent heating of the black solid and HSi(NMe(2))(3) may then yield TiN and Si(3)N(4), respectively, as the Ti-Si-N materials. PMID:11506557

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

2001-08-22

67

Complex formation processes in 3d metal hexacyanoferrate(II) gelatin-immobilised matrices  

Microsoft Academic Search

Data on nontraditional complex formation reactions in iron(II, III), cobalt(II), cobalt(III), nickel(II), and copper(II) hexacyanoferrate(II) gelatin-immobilised matrixes with fixation of the immobilised substances by intermolecular forces are surveyed and described systematically. Such reactions proceed when the matrices come into contact with aqueous solutions of nitrogen-, oxygen-, and sulfur-containing polydentate ligands. The practical possibilities for complex formation reactions in metal hexacyanoferrate(II)

Oleg V. Mikhailov

1995-01-01

68

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

69

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

70

Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase  

Microsoft Academic Search

The reactions of anhydrous HBr and HCl with trans-(Mo(Nâ)â(triphos)(PRâ)), where triphos = PhP(CHâCHâPPhâ)â(PRâ = PPhâ(1), PMePhâ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of Nâ\\/mol of 1 and routinely ca. 0.72 mol of NHâ\\/mol of 1,

J. A. Baumann; G. E. Bossard; T. A. George; D. B. Howell; L. M. Koczon; R. K. Lester; C. M. Noddings

1985-01-01

71

The catalytic role of uranyl in formation of polycatechol complexes  

PubMed Central

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

2011-01-01

72

Characterizing the dynamics of functionally relevant complexes of formate dehydrogenase  

PubMed Central

The potential for femtosecond to picosecond time-scale motions to influence the rate of the intrinsic chemical step in enzyme-catalyzed reactions is a source of significant controversy. Among the central challenges in resolving this controversy is the difficulty of experimentally characterizing thermally activated motions at this time scale in functionally relevant enzyme complexes. We report a series of measurements to address this problem using two-dimensional infrared spectroscopy to characterize the time scales of active-site motions in complexes of formate dehydrogenase with the transition-state-analog inhibitor azide (). We observe that the frequency–frequency time correlation functions (FFCF) for the ternary complexes with NAD+ and NADH decay completely with slow time constants of 3.2 ps and 4.6 ps, respectively. This result suggests that in the vicinity of the transition state, the active-site enzyme structure samples a narrow and relatively rigid conformational distribution indicating that the transition-state structure is well organized for the reaction. In contrast, for the binary complex, we observe a significant static contribution to the FFCF similar to what is seen in other enzymes, indicating the presence of the slow motions that occur on time scales longer than our measurement window.

Bandaria, Jigar N.; Dutta, Samrat; Nydegger, Michael W.; Rock, William; Kohen, Amnon; Cheatum, Christopher M.

2010-01-01

73

Some reactions of an eta3-tetracyanobutadienyl-ruthenium complex.  

PubMed

In the eta(3)-butadienyl complex Ru{eta(3)-C(CN)(2)CPhC=C(CN)(2)}(PPh(3))Cp 1, which is formed from Ru(C[triple bond]CPh)(PPh(3))(2)Cp and tcne, a CN group reacts with MeO(-) to give the methoxy-amide Ru{NH=C(OMe)C(CN)=CCPh=C(CN)(2)}(PPh(3))Cp 2, in which the NH has displaced the C=C from the Ru centre with formation of a RuC(3)N ring. "Click addition" of azide to a CN group in 1 gives the oligomeric tetrazolato complex Ru{N(3)N[Na(OEt(2))]=CC(CN)=CCPh=C(CN)(2)}(PPh(3))Cp 3, also containing a RuC(3)N ring. Salt-elimination reactions of 3 with MeOTf, FeCl(dppe)Cp, RuCl(dppe)Cp* and trans-PtCl(2){P(tol)(3)}(2) result in selective substitution at one nitrogen atom of the RuC(3)N ring. Geometries of 1 and the anion in 3 were computed by DFT methods. Preferences for CN groups attacked in the nucleophilic and cycloaddition reactions of 1 are supported by NBO calculations. Alkylation of 1 in reactions with 1,2-dimethoxyethane gave two isomers of Ru{N(3)[CH(CH(2)OMe)(OMe)]N=CC(CN)=CCPh=C(CN)(2)}(PPh(3))Cp 8 and 9, differing in the sites of attachment of the alkyl group, likely by radical processes. The molecular structures of eight complexes are reported, including a re-determination of 1. Computed NMR chemical shifts are used to reassign the butadienyl carbon resonances in the (13)C NMR spectrum of 1. PMID:20354629

Bruce, Michael I; Fox, Mark A; Low, Paul J; Skelton, Brian W; Zaitseva, Natasha N

2010-03-11

74

Proton transfer and complex formation of angiotensin I ions with gaseous molecules at various temperature  

NASA Astrophysics Data System (ADS)

Proton transfer reactions of angiotensin I ions for +2 charge state, [M + 2H]2+, to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of the reaction rate constants was measured. Remarkable change was observed for distribution of product ions and reaction rate constants. Proton transfer reaction was enhanced or reduced by complex formation of [M + 2H]2+ with gaseous molecules. The results relate to conformation changes of [M + 2H]2+ with change of temperature, which are induced by complex formation and or by thermal collision with He. Proton transfer reactions of angiotensin I ions for +3 charge state, [M + 3H]3+, were also studied. The reaction rates did not depend on temperature so definitely.

Nonose, Shinji; Yamashita, Kazuki; Sudo, Ayako; Kawashima, Minami

2013-09-01

75

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in this article problems of non- equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanos- tructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because

Y. De Decker; A. S. Mikhailov

2006-01-01

76

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

PubMed

In order to address problems such as aging, cell death, and cancer, it is important to understand the mechanisms behind reactions causing DNA damage. One specific reaction implicated in DNA oxidative damage is hydroxyl free-radical attack on adenine (A) and other nucleic acid bases. The adenine reaction has been studied experimentally, but there are few theoretical results. In the present study, adenine dehydrogenation at various sites, and the potential-energy surfaces for these reactions, are investigated theoretically. Four reactant complexes [A···OH]* have been found, with binding energies relative to A+OH* of 32.8, 11.4, 10.7, and 10.1 kcal mol(-1). These four reactant complexes lead to six transition states, which in turn lie +4.3, -5.4, (-3.7 and +0.8), and (-2.3 and +0.8) kcal mol(-1) below A+OH*, respectively. Thus the lowest lying [A···OH]* complex faces the highest local barrier to formation of the product (A-H)*+H(2)O. Between the transition states and the products lie six product complexes. Adopting the same order as the reactant complexes, the product complexes [(A-H)···H(2)O]* lie at -10.9, -22.4, (-24.2 and -18.7), and (-20.5 and -17.5) kcal mol(-1), respectively, again relative to separated A+OH*. All six A+OH* ? (A-H)*+H(2)O pathways are exothermic, by -0.3, -14.7, (-17.4 and -7.8), and (-13.7 and -7.8) kcal mol(-1), respectively. The transition state for dehydrogenation at N(6) lies at the lowest energy (-5.4 kcal mol(-1) relative to A+OH*), and thus reaction is likely to occur at this site. This theoretical prediction dovetails with the observed high reactivity of OH radicals with the NH(2) group of aromatic amines. However, the high barrier (37.1 kcal mol(-1)) for reaction at the C(8) site makes C(8) dehydrogenation unlikely. This last result is consistent with experimental observation of the imidazole ring opening upon OH radical addition to C(8). In addition, TD-DFT computed electronic transitions of the N(6) product around 420 nm confirm that this is the most likely site for hydrogen abstraction by hydroxyl radical. PMID:20878802

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

2010-10-18

77

Complexation and Demetalation Reactions of Porphyrins  

Microsoft Academic Search

The mechanisms by which porphyrins form metal complexes in nature are of interest because of the importance of both the iron complexes, the active sites of hemoproteins, and the magnesium complexes, the chlorophylls. Currently there is interest in using chelated radioactive metal isotopes as diagnostic imaging and therapeutic agents; porphyrins are excellent candidates because of their extremely high stability constants

David K. Lavallee

1986-01-01

78

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

79

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

80

The Activated Complex in Chemical Reactions  

Microsoft Academic Search

The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the

Henry Eyring

1935-01-01

81

Formation and reactivity of (octaethyltetraazaporphyrinato)rhodium complexes  

SciTech Connect

A series of (octaethyltetraazaporphyrinato)rhodium, (OETAP)Rh, complexes including (OETAP)Rh-I, (OETAP)Rh-CH[sub 3], and [(OETAP)Rh][sub 2] were prepared for comparison with the corresponding (octaethyltetraazaporphyrinato)rhodium, (OEP)Rh, derivatives. [(OETAP)Rh][sub 2] (1) reacts like [(OEP)Rh][sub 2] (2) with CH[sub 3]I, CH[sub 3]NC, (CH[sub 3]O)[sub 3]P, and CH[sub 2]=CH[sub 2] in forming (OETAP)Rh-CH[sub 3] and (OETAP)Rh-I, (OETAP)Rh(NC)(CH[sub 3]NC), (OETAP)Rh-P(O)(OCH[sub 3])[sub 2], and (OETAP)Rh-CH[sub 2]CH[sub 2]-Rh(OETAP), respectively, but reactions of 1 are invariably much slower than those of 2. [(OETAP)Rh][sub 2] fails to react with H[sub 2], CO, CH[sub 3]CHO, and CH[sub 3]C[sub 6]H[sub 5], which participate in prominent substrate reactions for 2. Reactivity and equilibrium studies indicate that a substantially larger Rh-Rh bond dissociation enthalpy for 1 compared with 2 is primarily responsible for the slower rates and reduced scope of substrate reactions for [(OETAP)Rh][sub 2]. Dissolution of 1 in pyridine results in formation of a persistent OETAP anion radical complex of Rh(III), (OETAP[sup [sm bullet][minus

Ni, Y.; Fitzgerald, J.P.; Carroll, P.; Wayland, B.B. (Univ. of Pennsylvania, Philadelphia, PA (United States) United States Naval Academy, Annapolis, MD (United States))

1994-04-27

82

Synthesis and decarbonylation reactions of the triiron phosphinidene complex [Fe3Cp3(?-H)(?3-PPh)(CO)4]: easy cleavage and formation of P-H and Fe-Fe bonds.  

PubMed

The binuclear phosphine complex [Fe(2)Cp(2)(?-CO)(2)(CO)(PH(2)Ph)] (Cp = ?(5)-C(5)H(5)) reacted with the acetonitrile adduct [Fe(2)Cp(2)(?-CO)(2)(CO)(NCMe)] in dichloromethane at 293 K to give the trinuclear hydride-phosphinidene derivative [Fe(3)Cp(3)(?-H)(?(3)-PPh)(CO)(4)] as a mixture of cis,anti and trans isomers (Fe-Fe = 2.7217(6) Å for the cis,anti isomer). In contrast, photochemical treatment of the phosphine complex with [Fe(2)Cp(2)(CO)(4)] gave the phosphide-bridged complex trans-[Fe(3)Cp(3)(?-PHPh)(?-CO)(2)(CO)(3)] as the major product, along with small amounts of the binuclear hydride-phosphide complexes [Fe(2)Cp(2)(?-H)(?-PHPh)(CO)(2)] (cis and trans isomers), which are more selectively prepared from [Fe(2)Cp(2)(CO)(4)] and PH(2)Ph at 388 K. The photochemical decarbonylation of either of the mentioned triiron compounds led reversibly to three different products depending on the reaction conditions: (a) the 48-electron phosphinidene cluster [Fe(3)Cp(3)(?-H)(?(3)-PPh)(?-CO)(2)] (Fe-Fe = 2.592(2)-2.718(2) Å); (b) the 50-electron complex [Fe(3)Cp(3)(?-H)(?(3)-PPh)(?-CO)(CO)(2)], also having carbonyl- and hydride-bridged metal-metal bonds (Fe-Fe = 2.6177(3) and 2.7611(4) Å, respectively); and (c) the 48-electron phosphide cluster [Fe(3)Cp(3)(?-PHPh)(?(3)-CO)(?-CO)(2)], an isomer of the latter phosphinidene complex now having three intermetallic bonds (Fe-Fe = 2.5332(8)-2.6158(8) Å). PMID:21981036

Alvarez, Celedonio M; Alvarez, M Angeles; García, M Esther; González, Rocío; Ramos, Alberto; Ruiz, Miguel A

2011-10-07

83

[Formation of a new type of dinitrosyl iron complexes bound to cysteine modified with methylglyoxal].  

PubMed

It has been shown that interaction of cysteine dinitrosyl iron complexes with methylglyoxal leads to the formation of a new type of dinitrosyl iron complexes., EPR spectrum of these complexes essentially differs from spectra of dinitrosyl iron complexes containing unmodified thiol. The products of the cysteine reaction with methylglyoxal are hemithioacetals, Schiff bases and thiazolidines, which most likely serve as ligands for the new type of dinitrosyl iron complexes. It has been shown that the new type of dinitrosyl iron complexes as cysteine dinitrosyl iron complexes, which are physiological donors of nitric oxide, exert a vasodilator effect. It has also been found that the oxidative destruction of the new type of dinitrosyl iron complexes occurs at normal oxygen partial pressure, but these dinitrosyl iron complexes remain rather stable under hypoxia modeling. An assumption that the destruction of the new type of dinitrosyl iron complexes is caused by the formation of a bound peroxynitrite-containing intermediate is made. PMID:23755548

Shumaev, K B; Gubkina, S A; Vanin, A F; Burbaev, D Sh; Mokh, V P; Topunov, A F; Ruuge, E K

84

[Kinetics of the formation of AT-specific DNA-distamin complex].  

PubMed

Kinetics of DNA--distamin complex formation was studied by means of the stop-flow method. It has been found that the binding reaction is much faster than in the case with distamycin A and has only two stages. The differences in kinetic properties of the complexes of distamin and distamycin A with DNA has been interpreted as resulting from the formation of different bonds by protonated positively charged N-containing groups of ligands with negatively charged DNA phosphates. PMID:3778954

Sizova, I A; Poletaev, A I

85

Mechanisms of reactions of organoaluminium compounds with alkenes and alkynes catalyzed by Zr complexes  

NASA Astrophysics Data System (ADS)

The results of studies dealing with mechanisms of hydro-, carbo- and cycloalumination of alkenes and alkynes catalyzed by zirconium complexes are generalized and systematized for the first time. Data about the structures of intermediates responsible for the formation of the target compounds are presented and the available data on the effect of the structure of organoaluminium compounds and the electronic and steric factors determining the catalytic activity of metal complexes in these reactions are considered in detail. Much attention is paid to studies of the influence of reaction conditions on the chemo-, regio- and stereoselectivity of the Zr-containing complex catalysts. The bibliography includes 217 references.

Parfenova, L. V.; Khalilov, Leonard M.; Dzhemilev, Usein M.

2012-06-01

86

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in article problems of non-equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanostructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because of their small

Y. D. Decker; A. S. Mikhailov

2006-01-01

87

Complex formation of elements of the third group of the periodic system with chromazurol s  

SciTech Connect

An attempt is made to establish the composition and spectrophotometric characteristics of colored complexes of elements of the third group of the periodic system, produced with chromazurol S purified according to the procedure described. For a comparison of data on complexes of various elements with this reagent the authors used published results of an investigation of the complex formation of aluminium and those results they themselves obtained. The complex formation of aluminum, gallium, indium, scandium, yttrium, lanthanum, and cerium (III) were studied with the chromazurol S. The mechanism of the reaction of aluminum, gallium, scandium, and yttrium with chromazurol S was examined.

Tikhonov, V.N.

1985-03-01

88

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

89

Photosynthetic Reaction Center Complexes from Heliobacteria (Abstract Only).  

National Technical Information Service (NTIS)

Photosynthetic reaction centers are pigment-protein complexes that are responsible for the transduction of light energy into chemical energy. Considerable evidence indicates that photosynthetic organisms were present very early in the evolution of life on...

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

1991-01-01

90

Transition Metal Complexes as Mediators in Photochemical and Chemiluminescence Reactions  

Microsoft Academic Search

Transition metal complexes can play the role of photosensitizes in light driven electron transfer reactions and the role of chemiluminescence inducers in exoergonic electron transfer reactions. A unifying view of these processes is given and their relevance concerning the interconversion of light, chemical energy and electrical energy is emphasized. Ru(bpy) is presently the most used photosensitizer and chemiluminescence inducer. Several

Vincenzo Balzani; Fabrizio Bolletta

1983-01-01

91

Formation of amorphous metals by solid-state reactions  

Microsoft Academic Search

Until recently, amorphous metals were closely associated with rapid quenching, since they were usually prepared by a quenching technique and were therefore regarded as quenched-in liquids. In 1983, it was found that amorphous metals can also be prepared by a reaction within the solid state during an isothermal annealing below the crystallization temperature. The glass formation can be due to

L. Schultz

1990-01-01

92

Formation of superheavy elements in cold fusion reactions  

Microsoft Academic Search

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,

Robert Smolanczuk

2001-01-01

93

Formation of superheavy nuclei in cold fusion reactions  

SciTech Connect

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

Feng Zhaoqing [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Gesellschaft fuer Schwerionenforschung mbH (GSI), D-64291 Darmstadt (Germany); Jin Genming; Li Junqing [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Scheid, Werner [Institut fuer Theoretische Physik der Universitaet, D-35392 Giessen (Germany)

2007-10-15

94

Reactions of the simple nitroalkanes with hydroxide ion in water. Evidence for a complex mechanism.  

PubMed

Conventional kinetic analysis of the reactions of nitromethane (NM), nitroethane (NE) and 2-nitropropane (2-NP) with hydroxide ion in water revealed that the reactions are complex and involve kinetically significant intermediates. Kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel indicate the evolution and decay of absorbance characteristic of the formation of reactive intermediates. The deviations from 1st-order kinetics were observed to increase with increasing extent of reaction and in the reactant order: NM < NE < 2-NP. The apparent deuterium kinetic isotope effects for proton/deuteron transfer approach unity near zero time and increased with time toward plateau values as the reaction kinetics reach steady state. It is proposed that the initially formed preassociation complexes are transformed to more intimate reactant complexes which can give products by two possible pathways. PMID:21519607

Li, Zhao; Cheng, Jin-Pei; Parker, Vernon D

2011-04-26

95

Suppressing the formation of stable intermediates in hydride destabilization reactions  

NASA Astrophysics Data System (ADS)

Comprehensive computational screening efforts have identified numerous candidates for hydride destabilization reactions with reaction enthalpies that fall in the range of interest for engineering requirements (20 to 40 kJ/mol H2). Less certain are the actual kinetic pathways of the solid--state reactions under consideration. Of particular interest are LiBH4--based reactions. We have studied a number of destabilization reactions based on LiBH4 and note that the B12H12 closo--borane is a commonly formed intermediate. Moreover, formation of M2/nB12H12 phases as major intermediate species is observed in hydrogen desorption reaction of various M(BH4)n systems before further conversion to either MBn or B+MHn. We have also examined a number of possible reactions that might destabilize B12H12 phases using reactions suggested in the recent literature but even under severe processing conditions, this closo--borane phase remains. Our inability to destabilize the closo--borane is particularly puzzling given that the initial work of Vajo on the LiBH4--MgH2 with dehydrogenation into several bar pressure showed complete reversibility. Our work however has generally been done under static vacuum. We have re-examined the reactions in the LiBH4--MgH2 and through the use of ^11B NMR, note that when dehydrogenated under 4 bar hydrogen pressure, no amorphous boron or B12H12 can be detected. When dehydrogenated into pressures below 1.5 bar hydrogen however, the closo--borane structure is formed. We will discuss these results and consider other possible reaction pathways that dictate the way in which these solid--state reaction experiments are conducted.

Ahn, Channing

2010-03-01

96

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

97

On the Formation of "Hypercoordinated" Uranyl Complexes  

SciTech Connect

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

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

2011-09-05

98

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

99

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

SciTech Connect

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

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

1996-12-01

100

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

101

Reaction mechanism governing formation of 1,3-bis(diphenylphosphino)propane-protected gold nanoclusters.  

PubMed

This report outlines the determination of a reaction mechanism that can be manipulated to develop directed syntheses of gold monolayer-protected clusters (MPCs) prepared by reduction of solutions containing 1,3-bis(diphenylphosphino)propane (L(3)) ligand and Au(PPh(3))Cl. Nanocluster synthesis was initiated by reduction of two-coordinate phosphine-ligated [Au(I)LL'](+) complexes (L, L' = PPh(3), L(3)), resulting in free radical complexes. The [Au(0)LL'](•) free radicals nucleated, forming a broad size distribution of ligated clusters. Timed UV-vis spectroscopy and electrospray ionization mass spectrometry monitored the ligated Au(x), 6 ? x ? 13, clusters, which comprise reaction intermediates and final products. By employing different solvents and reducing agents, reaction conditions were varied to highlight the largest portion of the reaction mechanism. We identified several solution-phase reaction classes, including dissolution of the gold precursor, reduction, continuous nucleation/core growth, ligand exchange, ion-molecule reactions, and etching of colloids and larger clusters. Simple theories can account for the reaction intermediates and final products. The initial distribution of the nucleation products contains mainly neutral clusters. However, the rate of reduction controls the amount of reaction overlap occurring in the system, allowing a clear distinction between reduction/nucleation and subsequent solution-phase processing. During solution-phase processing, the complexes undergo core etching and core growth reactions, including reactions that convert neutral clusters to cations, in a cyclic process that promotes formation of stable clusters of specific metal nuclearity. These processes comprise "size-selective" processing that can narrow a broad distribution into specific nuclearities, enabling development of tunable syntheses. PMID:21928777

Hudgens, Jeffrey W; Pettibone, John M; Senftle, Thomas P; Bratton, Ryan N

2011-09-19

102

Formation of cis-enediyne complexes from rhenium alkynylcarbene complexes.  

PubMed

Dimerization of the alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(3) (8) occurs at 100 degrees C to give a 1.2:1 mixture of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(3))=C(CH(3))C(triple bond)CTol] (10-Eand 10-Z), showing no intrinsic bias toward trans-enediyne complexes. The cyclopropyl-substituted alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CC(3)H(5) (11) dimerizes at 120 degrees C to give a 5:1 ratio of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)C(C(3)H(5))C=C(C(3)H(5))C(triple bond)CTol] (12-E and 12-Z); no ring expansion product was observed. This suggests that if intermediate A formed by a [1,1.5] Re shift and having carbene character at the remote alkynyl carbon is involved, then interaction of the neighboring Re with the carbene center greatly diminishes the carbene character as compared with that of free cyclopropyl carbenes. The tethered bis-(alkynylcarbene) complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(2)CH(2)CH(2)C(triple bond)CC(Tol)= Re(CO)(2)Cp (13) dimerizes rapidly at 12 degrees C to give the cyclic cis-enediyne complex [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(2)CH(2)CH(2))=CC(triple bond)CTol] (15). Attempted synthesis of the 1,8-disubstituted naphthalene derivative 1,8-[Cp(CO)(2)Re=C(Tol)C(triple bond)C](2)C(10)H(6) (16), in which the alkynylcarbene units are constrained to a parallel geometry, leads to dimerization to [Cp(CO)(2)Re](2)(eta(2),eta(2)-1,2-(tolylethynyl)acenaphthylene] (17). The very rapid dimerizations of both 13 and 16 provide compelling evidence against mechanisms involving cyclopropene intermediates. A mechanism is proposed which involves rate-determining addition of the carbene center of A to the remote alkynyl carbon of a second alkynylcarbene complex to generate vinyl carbene intermediate C, and rearrangement of C to the enediyne complex by a [1,1.5] Re shift. PMID:11890809

Casey, Charles P; Kraft, Stefan; Powell, Douglas R

2002-03-20

103

Formation of ATP by the adenosine triphosphatase complex from spinach chloroplasts reconstituted together with bacteriorhodopsin.  

PubMed

The energy-linked ATPase complex has been isolated from spinach chloroplasts. This protein complex contained all the subunits of the chloroplast coupling factor (CF1) as well as several hydrophobic compoenents. When the activated complex was reconstituted with added soybean phospholipids, it catalyzed the exchange of radioactive inorganic phosphate with ATP. Sonication of the complex into proteoliposomes together with bacteriorhodopsin yield vesicles that catalyzed light-dependent ATP formation. Both the 32Pi-ATP exchange reactions and ATP formation were sensitive to uncouplers such as 3-tert-butyl-5,2'-dichloro-4'-nitrosalicylanilide, bis-(hexafluoroacetonyl)acetone and carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone, that act to dissipate a proton gradient. The energy transfer inhibitors dicyclohexylcarbodiimide, triphenyltin chloride and 2-beta-D-glucopyranosyl-4,6'-dihydroxydihydrochalcone were also effective inhibitors of both reactions. PMID:141938

Winget, G D; Kanner, N; Racker, E

1977-06-01

104

Steric Aspects of the Formation of Metal Chelate Complexes  

NASA Astrophysics Data System (ADS)

The geometrical and thermodynamic aspects of the formation of complexes between metal cations and organic ligands are examined theoretically from the standpoint of conformational analysis. Particular attention has been devoted to the problem of the selectivity of the complex formation, which is of practical importance. It is shown that the selectivity of complex formation is largely determined by the steric factor. The advantages and disadvantages of the available methods for the quantitative allowance for the steric factor as well as methods of calculation of the structure of coordination compounds are analysed. The bibliography includes 105 references.

Dashevskii, V. G.; Baranov, A. P.; Kabachnik, Martin I.

1983-02-01

105

Minimum energy spin crossings for an O-O bond formation reaction  

NASA Astrophysics Data System (ADS)

The O-O bond formation reaction in the synthetic O 2 formation catalyst, [(terpy)(H 2O)Mn IV(?-O) 2Mn III(H 2O)(terpy)] 3+ (terpy = 2,2':6,2?-terpyridine), goes through a transition between two spin surfaces. Using DFT with the B3LYP functional, three different minimum energy crossing points have been located for this redox reaction. The system is predicted to perform the spin crossing close to (+0.1 kcal/mol) the low-spin Mn III-OOH product and this transition does not significantly affect the kinetics. The location of spin crossings in this system is relevant for discussions of O-O bond formation in the oxygen evolving complex of photosystem II.

Lundberg, Marcus; Siegbahn, Per E. M.

2005-01-01

106

Reaction of gallium arsenide with concentrated acids: formation of arsine.  

PubMed

Crystalline particles of gallium arsenide (GaAs) (approximately 2 microns in diameter) react with concentrated hydrochloric acid (HCl) (11.6 to 9 M) to form highly toxic arsine (AsH3) gas. None of the other strong acids that were investigated reacted with gallium arsenide to form AsH3. A spectrophotometric method, based on the reaction of AsH3 with silver diethyldithiocarbamate in a chloroform solution containing morpholine, was used to detect AsH3 gas dissolved in aqueous solutions and to determine the AsH3 gas that was liberated by the reaction of GaAs with HCl. Active sites on the gallium arsenide surface initiate the reaction that forms AsH3 gas. Absorption of oxygen or ions from solution on these active sites inhibits the formation of AsH3. PMID:2756869

Scott, N; Carter, D E; Fernando, Q

1989-07-01

107

Formation and reactions of alkyl adamantanes in sediments: Carbon surface reactions  

Microsoft Academic Search

Diamondoids are hydrocarbons with a carbon skeleton that is superimposable on the diamond lattice. Adamantane is the cage-shaped primary unit of diamondoids and occurs widely in sediments and petroleum. The first report of adamantane isolated from petroleum extends back seven decades, but the precursors and reaction mechanisms for the formation of adamantane and related diamondoids in sediments has remained unclear.

Lyndon Berwick; Robert Alexander; Kieran Pierce

2011-01-01

108

Predictive gold nanocluster formation controlled by metal-ligand complexes.  

PubMed

The formation of ligand-protected gold nanoclusters during size-selective syntheses is seemingly driven by the inherent properties of the protecting ligands, but a general description of the product formation has not been presented. This study uses diphosphine-protected Au clusters as a model system to examine i) control of metal-ligand complex distributions in methanol-chloroform solutions, ii) role of solution perturbations, e.g., oxidation, and iii) nanocluster formation through reduction of characterized complex distributions. By selectively reducing complexes and monitoring cluster formation with electrospray ionization mass spectrometry and UV-vis, data show the distribution of complexes can be controlled through ligand exchange, and the reduction of specific complexes produce characteristic ligated gold clusters based on ligand class. Specifically, 1,n-bis(diphenylphosphino)n-alkane ligands, L(n), where n = 1 through 6, are classified into two distinct sets. The classes represent ligands that either form mainly [AuL(n)(2)](+) (Class I, n = 1-3) or bridged [Au(2)L(n)(2)](2+) (Class II, n = 4-6) complexes after complete ligand exchange with AuClPPh(3). Selectively reducing gold-phosphine ligand complexes allows mapping of product formation, resulting collectively in a predictive tool for ligated gold cluster production by simply monitoring the initial complex distribution prior to reduction. PMID:22228703

Pettibone, John M; Hudgens, Jeffrey W

2012-01-09

109

Efficient stochastic simulations of complex reaction networks on surfaces.  

PubMed

Surfaces serve as highly efficient catalysts for a vast variety of chemical reactions. Typically, such surface reactions involve billions of molecules which diffuse and react over macroscopic areas. Therefore, stochastic fluctuations are negligible and the reaction rates can be evaluated using rate equations, which are based on the mean-field approximation. However, in case that the surface is partitioned into a large number of disconnected microscopic domains, the number of reactants in each domain becomes small and it strongly fluctuates. This is, in fact, the situation in the interstellar medium, where some crucial reactions take place on the surfaces of microscopic dust grains. In this case rate equations fail and the simulation of surface reactions requires stochastic methods such as the master equation. However, in the case of complex reaction networks, the master equation becomes infeasible because the number of equations proliferates exponentially. To solve this problem, we introduce a stochastic method based on moment equations. In this method the number of equations is dramatically reduced to just one equation for each reactive species and one equation for each reaction. Moreover, the equations can be easily constructed using a diagrammatic approach. We demonstrate the method for a set of astrophysically relevant networks of increasing complexity. It is expected to be applicable in many other contexts in which problems that exhibit analogous structure appear, such as surface catalysis in nanoscale systems, aerosol chemistry in stratospheric clouds, and genetic networks in cells. PMID:17935419

Barzel, Baruch; Biham, Ofer

2007-10-14

110

Crk family adaptors–signalling complex formation and biological roles  

Microsoft Academic Search

Crk family adaptors are widely expressed and mediate the timely formation of signal transduction protein complexes upon a variety of extracellular stimuli, including various growth and differentiation factors. Selective formation of multi-protein complexes by the Crk and Crk-like (CRKL) proteins depends on specific motifs recognized by their SH2 and SH3 domains. In the case of the first SH3 domains [SH3(1)

Stephan M Feller

2001-01-01

111

Formation of the complex oxide NaNdTiO 4  

Microsoft Academic Search

The processes of phase formation in the Na2CO3-TiO2 and Na2CO3-TiO2-Nd2O3 systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process\\u000a of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO4 compound occurs through the reaction of the intermediate product Na8Ti5O14 with neodymium oxide in the temperature range 720–780°C.

I. A. Zvereva; O. I. Silyukov; A. V. Markelov; A. B. Missyul’; M. V. Chislov; I. A. Rodionov; D.-Sh. Li

2008-01-01

112

Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.  

NASA Astrophysics Data System (ADS)

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

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

113

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

ERIC Educational Resources Information Center

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

Horvath, Otto; Papp, Sandor

1988-01-01

114

Quantitative assessment of trihalomethane formation using simulations of reaction kinetics.  

PubMed

A modelling procedure with a time discretisation of 1 min is developed in order to study and simulate the kinetics of formation of total trihalomethanes (TTHM) in water treatment plants. This methodology was applied on two significant processing units of Athens (Galatsi Treatment Plant-GTP, Menidi Treatment Plant-MTP). The fundamental concept of the model was based on the representation of the water treatment plant as a mixed flow reactor, where the formation of TTHM was predicated on a generalised reaction of total halogens with an organic precursor. Differential rates of reactants and products were expressed in terms of the reaction stoichiometry. Volatilisation, flocculation, coagulation and sedimentation processes were also incorporated in the model in order to assess their distinct role. The most appropriate coefficient set was sought and it was found that a stoichiometric ratio of 0.5 for total halogen, 0.6 for organic substrate and 0.2 for TTHM (or 2.5:3:1) resulted in the best fit between simulated and experimental data. The present modelling approach should be considered as a promising methodological basis towards the realistic reproduction of the dynamics of water treatment plants and the development of reliable numerical tools for the accurate prediction of THM formation. PMID:12146874

Golfinopoulos, Spyros K; Arhonditsis, George B

2002-06-01

115

Dynamics of Lane Formation in Driven Binary Complex Plasmas  

SciTech Connect

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

Suetterlin, K. R.; Ivlev, A. V.; Raeth, C.; Thomas, H. M.; Rubin-Zuzic, M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany); Wysocki, A.; Loewen, H. [Heinrich-Heine-Universitaet Duesseldorf, 40225 Duesseldorf (Germany); Goedheer, W. J. [FOM-Institute for Plasma Physics Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F. [Joint Institute for High Temperatures, 125412 Moscow (Russian Federation)

2009-02-27

116

Transition-Metal Complex Formation with Phenyl Isocyanate.  

National Technical Information Service (NTIS)

Complex formation between phenyl isocyanate and cobalt or manganese naphthenate in benzene was determined by the mole ratio method. Complexes of 3:1 for cobalt and 2:1 for manganese were found. The method of analysis in this study utilized the characteris...

L. Rand J. A. McLean

1968-01-01

117

Image formation in the eye: very specified complexity  

Microsoft Academic Search

The formation of an image, and its correct interpretation by sighted living creatures, is a unique example of specified complexity unlike anything else in nature. While many of the functional aspects of living organisms are extremely complex, only an image requires a unique mapping process by the eye-brain system to be useful to the organism. The transfer of light from

David E. Stoltzmann

2005-01-01

118

Positronium formation in solid transition metal losartanates complexes  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

119

The stochastic separatrix and the reaction coordinate for complex systems.  

PubMed

We present a new approach to the identification of degrees of freedom which comprise a reaction coordinate in a complex system. The method begins with the generation of an ensemble of reactive trajectories. Each trajectory is analyzed for its equicommittor position or transition state; then the transition state ensemble is identified as the stochastic separatrix. Numerical analysis of the points along the separatrix for variability of coordinate location correctly identifies the components of the reaction coordinate in a test system of a double well coupled to a promoting vibration and a bath of linearly coupled oscillators. PMID:19388729

Antoniou, Dimitri; Schwartz, Steven D

2009-04-21

120

Nitro and Nitroso Metathesis Reactions with Monomeric Zirconium Imido Complexes  

PubMed Central

Summary The bis(cyclopentadienyl)(tert-butylimido)zir-conium complex 1 undergoes ambient-temperature metathesis reactions with nitro- and nitrosoarenes, providing a rare nonphotochemical synthesis of cis-azoxy and cis-azo compounds, respectively. 2-Nitro-2-methylpropane also undergoes metathesis to give trans-(tert-butylazoxy)-2-methylpropane. This reaction was studied kinetically, and the rate was found to be first order in both 1 and substrate and inversely proportional to the concentration of tetrahydrofuran, with activation parameters ?H‡ = 15 ± 2 kcal mol?1 and ?S‡ = ?26 ± 3 cal mol?1 K?1.

Blum, Suzanne A.; Bergman, Robert G.

2005-01-01

121

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

122

TAR RNA decoys inhibit tat-activated HIV-1 transcription after preinitiation complex formation.  

PubMed Central

The ability of the HIV-1 Tat protein to trans -activate HIV-1 transcription in vitro is specifically inhibited by a circular TAR RNA decoy. This inhibition is not overcome by adding an excess of Tat to the reaction but is partially overcome by adding Tat in combination with nuclear extract, suggesting that TAR RNA might function by interacting with a complex containing Tat and cellular factor(s). A cell-free transcription system involving immobilized DNA templates was used to further define the factor(s) that interact with TAR RNA. Preinitiation complexes formed in the presence or absence of Tat were purified on immobilized templates containing the HIV-1 promoter. After washing, nucleotides and radiolabelled UTP were added and transcription was measured. The presence of Tat during preinitiation complex formation resulted in an increase in the level of full-length HIV-1 transcripts. This Tat-activated increase in HIV-1 transcription was not inhibited by circular TAR decoys added during preinitiation complex formation but was inhibited by circular TAR decoys subsequently added during the transcription reaction. These results suggest that TAR decoys inhibit Tat-activated HIV-1 transcription after preinitiation complex formation, perhaps by interacting with components of transcription complexes.

Bohjanen, P R; Liu, Y; Garcia-Blanco, M A

1997-01-01

123

Grinding-induced equimolar complex formation between thiourea and ethenzamide.  

PubMed

We prepared and characterized a grinding-induced equimolar complex of thiourea with ethenzamide. When thiourea and ethenzamide were co-ground at a molar ratio of 3 : 1, new powder X-ray diffraction (PXRD) peaks were observed in addition to PXRD peaks of thiourea crystals. The optimum stoichiometry of the new structure was confirmed as 1 : 1 mol/mol. Effect of grinding time on the thiourea-ethenzamide equimolar complex formation was investigated by using PXRD, differential scanning calorimetry and Fourier transform infrared spectroscopy. The equimolar crystal structure was confirmed by X-ray diffraction measurements of the single crystal which was recrystallized from ethanol. It was found that the intermolecular hydrogen bond formations between thiourea and ethenzamide molecules contributed to the equimolar complex formation. The complex formation was not observed in the cases where benzamide, salicylamide or 3-ethoxybenzamide was co-ground with thiourea. 2-Alcoxyl benzamide structures should be required for the grinding-induced equimolar complex formation with thiourea. PMID:15133201

Moribe, Kunikazu; Tsuchiya, Masami; Tozuka, Yuichi; Yamaguchi, Kentaro; Oguchi, Toshio; Yamamoto, Keiji

2004-05-01

124

Activation of immobilized plasminogen by tissue activator. Multimolecular complex formation  

SciTech Connect

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

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

1985-08-25

125

Understanding bistability in complex enzyme-driven reaction networks.  

PubMed

Much attention has been paid recently to bistability and switch-like behavior that might be resident in important biochemical reaction networks. There is, in fact, a great deal of subtlety in the relationship between the structure of a reaction network and its capacity to engender bistability. In common physicochemical settings, large classes of extremely complex networks, taken with mass action kinetics, cannot give rise to bistability no matter what values the rate constants take. On the other hand, bistable behavior can be induced in those same settings by certain very simple and classical mass action mechanisms for enzyme catalysis of a single overall reaction. We present a theorem that distinguishes between those mass action networks that might support bistable behavior and those that cannot. Moreover, we indicate how switch-like behavior results from a well-studied mechanism for the action of human dihydrofolate reductase, an important anti-cancer target. PMID:16735474

Craciun, Gheorghe; Tang, Yangzhong; Feinberg, Martin

2006-05-30

126

Reactions of Aluminium Tribromide with Tetrakis(triphenylphosphine)nickel(0) and Tetrakis(triethylphosphite)nickel(0) Complexes  

Microsoft Academic Search

Reactions of aluminium tribromide with the Ni(0) phosphine and phosphite complexes are studied by EPR method. AlBr3was found to cause the oxidation of the transition metal in the (PPh3)4Ni complex to the univalent state with the formation of the tetracoordinated (PPh3)3NiBr complex. With an excess of AlBr3, the phosphine ligands are eliminated from the coordination sphere of Ni(I), and the

P. B. Kraikivskii; V. V. Saraev; D. A. Matveev; S. N. Zelinskii; V. S. Tkach

2003-01-01

127

Radionuclide reactions with groundwater and basalts from Columbia River basalt formations  

SciTech Connect

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

Barney, G.S.

1981-06-01

128

Formation of superheavy elements in cold fusion reactions  

SciTech Connect

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 {sup 209}Bi({sup 86}Kr, 1n){sup 294}119, {sup 208}Pb({sup 88}Sr, 1n){sup 295}120, and {sup 209}Bi({sup 88}Sr, 1n){sup 296}121, 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 {sup 136}Xe({sup 124}Sn, 1n){sup 259}Rf, {sup 136}Xe({sup 136}Xe, 1n){sup 271}Hs,{sup 138}Ba({sup 136}Xe, 1n){sup 273}110, and {sup 140}Ce({sup 136}Xe, 1n){sup 275}112. Although shell effects in the magic nuclei {sup 124}Sn, {sup 136}Xe, {sup 138}Ba, and {sup 140}Ce are not as strong as in {sup 208}Pb and {sup 209}Bi, they act on both the target and the projectile and lead to the prediction of measurable cross sections.

Smolanczuk, Robert

2001-04-01

129

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

SciTech Connect

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

Rehm, K.E.

1992-12-01

130

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

SciTech Connect

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

Rehm, K.E.

1992-01-01

131

Enhancing electrorheological behaviors with formation of ?-cyclodextrin supramolecular complex  

Microsoft Academic Search

According to the point that the host structure and the properties can be easily modified by the formation of host–guest complex, the supramolecular complexes of ?-cyclodextrin cross-linking polymer\\/1-(2-pyridlazo)-2-naphthol (?-CDP-PAN) particles were synthesized. Then the electrorheological properties of the suspensions of ?-CDP-PAN particles in silicone oil have been investigated under DC electric fields. It was found that the yield stress of

Xiaopeng Zhao

2003-01-01

132

Formation of ubiquitin dimers via azide-alkyne click reaction.  

PubMed

The conjugation of poly-ubiquitin chains is a widespread post-translational modification of proteins that plays a role in many different cellular processes. Notably, the biological function of the attached ubiquitin chain depends on which lysine residue is used for chain formation. Here, we report a method for the modular synthesis of site-specifically linked ubiquitin dimers, which is based on click reaction between two artificial amino acids. In this way, it is possible to synthesize all seven naturally occurring ubiquitin connectivities, thus giving access to all ubiquitin dimers. Furthermore, this method can be generally applied to link ubiquitin to any substrate protein or even to link any two proteins site specifically. PMID:22350914

Eger, Silvia; Scheffner, Martin; Marx, Andreas; Rubini, Marina

2012-01-01

133

New insights into formation of trivalent actinides complexes with DTPA.  

PubMed

Complexation of trivalent actinides with DTPA (diethylenetriamine pentaacetic acid) was studied as a function of pcH and temperature in (Na,H)Cl medium of 0.1 M ionic strength. Formation constants of both complexes AnHDTPA(-) and AnDTPA(2-) (where An stands for Am, Cm, and Cf) were determined by TRLFS, CE-ICP-MS, spectrophotometry, and solvent extraction. The values of formation constants obtained from the different techniques are coherent and consistent with reinterpreted literature data, showing a higher stability of Cf complexes than Am and Cm complexes. The effect of temperature indicates that formation constants of protonated and nonprotonated complexes are exothermic with a high positive entropic contribution. DFT calculations were also performed on the An/DTPA system. Geometry optimizations were conducted on AnDTPA(2-) and AnHDTPA(-) considering all possible protonation sites. For both complexes, one and two water molecules in the first coordination sphere of curium were also considered. DFT calculations indicate that the lowest energy structures correspond to protonation on oxygen that is not involved in An-DTPA bonds and that the structures with two water molecules are not stable. PMID:23152978

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

2012-11-15

134

Reactions of ?-dichlorobis(? 3-allyl)palladium(II) with bis(1 -H-benzo-triazolyl-methyl) selenide: Formation of unexpected polymeric structure with dormant Se donor site. Applications of the polymeric Pd-complexes in Heck coupling  

Microsoft Academic Search

Bis(1-H-benzotriazolylmethyl)selenide (L) has been synthesized by reacting Se2? generated in situ with 1-(chloromethyl)-1H-benzotriazole. Proton, C-13 and Se-77 NMR spectra of L are characteristic. ?-Dichlorobis(?3-allyl)palladium(II) reacts with L resulting in polymeric complexes which give single crystals of stoichiometry [Pd(?3-C3H5)(L)]·ClO4\\/PF6·CH3CN (1\\/2). The single crystal X-ray diffraction analyses of these polymeric species reveal that they have chain type of structures, and anions through

Dipanwita Das; Monika Singh; Ajai K. Singh

2009-01-01

135

A Function for the AP3 Coat Complex in Synaptic Vesicle Formation from Endosomes  

Microsoft Academic Search

Synaptic vesicles can be coated in vitro in a reaction that is ARF-, ATP-, and temperature-dependent and requires synaptic vesicle membrane proteins. The coat is largely made up of the heterotetrameric complex, adaptor protein 3, recently implicated in Golgi-to-vacuole traffic in yeast. Depletion of AP3 from brain cytosol inhibits small vesicle formation from PC12 endosomes in vitro. Budding from washed

Victor Faúndez; Jim-Tong Horng; Regis B Kelly

1998-01-01

136

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

PubMed

The hydroxyl radical (OH radical) formation rates from the photo-Fenton reaction in river and rain water samples were determined by using deferoxamine mesylate (DFOM), which makes a stable and strong complex with Fe(III), resulting in a suppression of the photo-Fenton reaction. The difference between the OH radical formation rates with and without added DFOM denotes the rate from the photo-Fenton reaction. The photoformation rates from the photo-Fenton reaction were in the range of 0.7 - 45.8 x 10(-12) and 2.7 - 32.3 x 10(-12) M s(-1) in river and rain water samples, respectively. A strong positive correlation between the OH radical formation rate from the photo-Fenton reaction and the amount of fluorescent matter in river water suggests that fluorescent matter, such as humic substances, plays an important role in the photo-Fenton reaction. In rain water, direct photolysis of hydrogen peroxide was an important source of OH radicals as well as the photo-Fenton reaction. The contributions of the photo-Fenton reaction to the OH radical photoformation rates in river and rain water samples were in the ranges of 2 - 29 and 5 - 38%, respectively. Taking into account the photo-Fenton reaction, 33 - 110 (mean: 80) and 42 - 110 (mean: 84)% of OH radical sources in river and rain water samples, respectively, collected in Hiroshima prefecture were elucidated. PMID:17878592

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

2007-09-01

137

The effect of carbonyl complexation on highly exothermic vanadium oxidation reactions  

NASA Astrophysics Data System (ADS)

The effects of CO complexation on highly exothermic vanadium oxidation reactions is evaluated. We study the chemiluminescent (CL) reaction products formed when vanadium vapor entrained in Ar or CO is oxidized by O 3 or NO 2. The multiple collision V+ Ar+ O3? VO*( C 4? -, 4? , 2X)+ Ar+ O2 reactive encounter yields two previously unreported VO excited states, whereas the V+Ar+NO 2?VO *+Ar+NO reactive encounter populates states up to and including VO* C 4? -. The multiple collision V+ nCO+O 3 reactive encounter would appear to form a VOCO excited state complex, emitting in the region 420-560 nm, via the formation and oxidation of V(CO) 2 viz. V(CO) 2+O 3?VOCO *+CO+O 2 and a relaxed VO excited state emitter via V+ nCO+O 3?VO *+ nCO+O 2 where the VO excited state excitation is mediated by V-CO complexation. In complement, the much less exothermic V-NO 2 encounter displays an emission which, in concert with previous studies of CO complexation, suggests the formation of a VO(CO) 2 excited state complex viz. V(CO) 2+NO 2?VO(CO) 2*+NO. The experiments characterizing CL are complemented by comparative laser-induced fluorescence studies of the VO X 4? -- CO and Ar interactions and their influence on the VO C 4? -- X 4? - laser-induced excitation spectrum. These studies, in conjunction with further attempts to excite LIF in the 420-560 nm region, suggest that the observed complex emissions result primarily from VO excited state interactions. Complementary time-of-flight mass spectroscopy of vanadium and vanadium-oxide-carbonyl complex formation demonstrates the formation of V(CO), V(CO) 2, V 2(CO), and VOCO, the latter three of which demonstrate clear metastable-ion dissociation peaks for the processes VOCO +?V ++CO 2, V(CO) 2+?V ++2CO, and V 2(CO) +?V 2++CO, suggesting that these vanadium complexes when formed in a reaction-based environment may be photodissociated with light in the visible and ultraviolet regions.

McQuaid, M. J.; Gole, James L.

2000-10-01

138

Isolation of a uranyl amide by "ate" complex formation.  

PubMed

The uranyl amide [{Li(DME)}(2)Cl][Li(DME)][UO(2)(NC(5)H(10))(3)](2) has been synthesised and structurally characterised. Its stability is attributed to the saturation of the uranyl coordination sphere by "ate" complex formation. PMID:20631946

Seaman, Lani A; Schnaars, David D; Wu, Guang; Hayton, Trevor W

2010-03-25

139

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

140

Geology of the Biwabik Iron Formation and Duluth Complex  

USGS Publications Warehouse

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

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

2008-01-01

141

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

2007-10-01

142

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

143

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, Agost Gyula; Peintler, Gábor; Forgo, Péter; Pálinkó, István; Sipos, Pál

2013-07-29

144

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

145

How to impose microscopic reversibility in complex reaction mechanisms.  

PubMed

Most, but not all, ion channels appear to obey the law of microscopic reversibility (or detailed balance). During the fitting of reaction mechanisms it is therefore often required that cycles in the mechanism should obey microscopic reversibility at all times. In complex reaction mechanisms, especially those that contain cubic arrangements of states, it may not be obvious how to achieve this. Three general methods for imposing microscopic reversibility are described. The first method works by setting the 'obvious' four-state cycles in the correct order. The second method, based on the idea of a spanning tree, works by finding independent cycles (which will often have more than four states) such that the order in which they are set does not matter. The third method uses linear algebra to solve for constrained rates. PMID:15189850

Colquhoun, David; Dowsland, Kathryn A; Beato, Marco; Plested, Andrew J R

2004-06-01

146

Theoretical mechanism studies on the electrocatalytic reduction of CO2 to formate by water-stable iridium dihydride pincer complex.  

PubMed

The reaction mechanism for electrocatalytic reduction of CO2 to formate by water-stable iridium dihydride pincer complex is studied using density functional theory (DFT). The reaction pathways are investigated in detail. The results suggest that the reaction proceeds in three steps: insertion of carbon dioxide into the Ir(III) pincer dihydride, elimination of formate ligand from the hydridoformatoiridium complex, and catalyst regeneration. The reduction potential of the electrode reaction is calculated and accords well with the experimental value. The solvent effect of MeCN and water on the reaction is explored. The results indicate that water has an important effect on CO2 transforming to HCOO(-). In addition, it also plays a critical role for regeneration of the catalyst via non-classical intermolecular hydrogen bonding. PMID:23450254

Cao, Linlin; Sun, Chuanzhi; Sun, Nan; Meng, Lin; Chen, Dezhan

2013-04-28

147

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds  

PubMed Central

Summary N-Arylated aliphatic and aromatic amines are important substituents in many biologically active compounds. In the last few years, transition-metal-mediated N-aryl bond formation has become a standard procedure for the introduction of amines into aromatic systems. While N-arylation of simple aromatic halides by simple amines works with many of the described methods in high yield, the reactions may require detailed optimization if applied to the synthesis of complex molecules with additional functional groups, such as natural products or drugs. We discuss and compare in this review the three main N-arylation methods in their application to the synthesis of biologically active compounds: Palladium-catalysed Buchwald–Hartwig-type reactions, copper-mediated Ullmann-type and Chan–Lam-type N-arylation reactions. The discussed examples show that palladium-catalysed reactions are favoured for large-scale applications and tolerate sterically demanding substituents on the coupling partners better than Chan–Lam reactions. Chan–Lam N-arylations are particularly mild and do not require additional ligands, which facilitates the work-up. However, reaction times can be very long. Ullmann- and Buchwald–Hartwig-type methods have been used in intramolecular reactions, giving access to complex ring structures. All three N-arylation methods have specific advantages and disadvantages that should be considered when selecting the reaction conditions for a desired C–N bond formation in the course of a total synthesis or drug synthesis.

Fischer, Carolin

2011-01-01

148

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds.  

PubMed

N-Arylated aliphatic and aromatic amines are important substituents in many biologically active compounds. In the last few years, transition-metal-mediated N-aryl bond formation has become a standard procedure for the introduction of amines into aromatic systems. While N-arylation of simple aromatic halides by simple amines works with many of the described methods in high yield, the reactions may require detailed optimization if applied to the synthesis of complex molecules with additional functional groups, such as natural products or drugs. We discuss and compare in this review the three main N-arylation methods in their application to the synthesis of biologically active compounds: Palladium-catalysed Buchwald-Hartwig-type reactions, copper-mediated Ullmann-type and Chan-Lam-type N-arylation reactions. The discussed examples show that palladium-catalysed reactions are favoured for large-scale applications and tolerate sterically demanding substituents on the coupling partners better than Chan-Lam reactions. Chan-Lam N-arylations are particularly mild and do not require additional ligands, which facilitates the work-up. However, reaction times can be very long. Ullmann- and Buchwald-Hartwig-type methods have been used in intramolecular reactions, giving access to complex ring structures. All three N-arylation methods have specific advantages and disadvantages that should be considered when selecting the reaction conditions for a desired C-N bond formation in the course of a total synthesis or drug synthesis. PMID:21286396

Fischer, Carolin; Koenig, Burkhard

2011-01-14

149

Reaction of monovalent gold complex salts with ferrocene thio derivatives  

SciTech Connect

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

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

1986-02-01

150

Snapshot of a reaction intermediate: analysis of benzoylformate decarboxylase in complex with a benzoylphosphonate inhibitor  

PubMed Central

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 stereocontrol in the carbon-carbon bond-forming reverse reaction, making it a useful biocatalyst for the production of chiral ?-hydroxyketones. The reaction of methyl benzoylphosphonate (MBP), an analogue of the natural substrate benzoylformate, with BFDC results in the formation of a stable analogue (C2?-phosphonomandelylThDP) of the covalent ThDP-substrate adduct C2?-mandelylThDP. 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 Å. 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

2009-01-01

151

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

152

Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide – Acetanilide  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

153

Mercury(ii) complex formation with N-acetylcysteine.  

PubMed

N-Acetylcysteine (H2NAC) is a potent antioxidant, a precursor for cysteine and glutathione, and a potential antidote against certain metal ions such as cadmium and mercury. Little is known about the structural aspects of complexes formed between Hg(ii) and N-acetylcysteine, despite many biological tests on its ability to bind to organic and inorganic mercury, and a few reports on formation constants for Hg(NAC)n (n = 1-3) complexes. We have combined several techniques, including Hg L3-edge EXAFS (extended X-ray absorption fine structure), (199)Hg NMR and Raman spectroscopy, to investigate the nature and structure of Hg(ii) N-acetylcysteine complexes formed in aqueous solution at pH 7.5 and 10.5. To allow measurements on the same samples, rather concentrated solutions containing CHg(ii) = 0.1 M and variable H2NAC/Hg(ii) mole ratios = 2.0-10.0 were used. At physiological pH, Hg(NAC)2(2-) and Hg(NAC)3(4-) complexes form, while in ligand excess and at alkaline pH (H2NAC/Hg(ii) > 4), a novel tetra-thiolate species Hg(NAC)4(6-) dominates. Comparison between the Hg(ii) complex formation with cysteine, penicillamine and N-acetylcysteine in alkaline aqueous solution has been made to elucidate the influence of the blocked amino group of N-acetylcysteine. PMID:23986393

Jalilehvand, Farideh; Parmar, Karnjit; Zielke, Stephen

2013-09-25

154

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

PubMed

The reaction of phthalazine with the binuclear organoplatinum complexes [Me(2)Pt(?-SMe(2))(?-dppm)PtR(2)], R = Me, Ph, 4-tolyl or R(2) = (CH(2))(4), dppm = bis(diphenylphosphino)methane, gives the corresponding complexes [Me(2)Pt(?-phthalazine)(?-dppm)PtR(2)] by displacement of the bridging dimethylsulfide ligand. The structures of [Me(2)Pt(?-SMe(2))(?-dppm)PtMe(2)] and [Me(2)Pt(?-phthalazine)(?-dppm)PtMe(2)] have been determined. Kinetic studies show that the reactions occur mostly by a second order reaction when R = Me or R(2) = (CH(2))(4) but entirely by a first order reaction when R = Ph or 4-tolyl. Evidence is presented that the reactions when R = Me or R(2) = (CH(2))(4) can occur by either associative or dissociative mechanisms but that the reactions when R = Ph or 4-tolyl occur only by an unusual dissociative mechanism involving formation of an intermediate with a donor-acceptor Pt-Pt bond. PMID:20712374

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

2010-09-20

155

Thermodynamic study of cyclodextrins complexation with benzimidazolic antihelmintics in different reaction media.  

PubMed

The main purpose of this work was to accomplish a comparative study about cyclodextrins complexation equilibria with three benzimidazolic antihelmintics: albendazole (Alb), mebendazole (Meb) and thiabendazole (Thiab). The complexation process with four different cyclodextrins (alpha-, beta-, gamma-, and HP-beta-CDs) was investigated under various temperatures and different reaction media (aqueous solution buffered at pH 7.5, dimethylsulfoxide (DMSO) and DMSO/water at 25/75, 50/50, 75/50 (w/w) mixtures). It was studied by electronic absorption and 1H NMR (NOESY) spectroscopy. Binding constants were determined by electronic absorption spectroscopic method, the DeltaH and DeltaS complexation values were evaluated and discussed according to the diverse factors that affect the chemical interactions in these systems. Solubility has also been determined by the Higuchi and Connors method. In general, albendazole and mebendazole exhibit similar complexation behavior, while thiabendazole acts differently. Classic and non-classic solvophobic effects are mainly the driving and stabilizing forces for complex formation, with the exception in some Thiab-CDs interactions. In all cases, DMSO, an aprotic solvent, should be considered as an active component of the reaction systems. PMID:18673253

Bernad-Bernad, María-Josefa; Gracia-Mora, Jesus; Díaz, David; Castillo-Blum, Silvia Elena

2008-06-01

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

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

158

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

159

Mechanism of formation of partially-crosslinked polyacrylamide complexes  

Microsoft Academic Search

A new type of partially-crosslinked polyacrylamide (PCPAM) which displays promising application in enhanced oil recovery (EOR) has been synthesized via aqueous solution polymerization under adiabatic conditions. Based on methods of real time infrared monitoring, two-dimensional infrared correlation spectroscopy and dynamic rheology measurement, an unusual complex formation mechanism of the PCPAM with the multi-functional initiator system is clearly disclosed. A process

Zhiqing Su; Zuming Jiang; Guangsu Huang; Li Li; Xiaoan Wang

2012-01-01

160

Single-stranded nucleic acids promote SAMHD1 complex formation.  

PubMed

SAM domain and HD domain-containing protein 1 (SAMHD1) is a dGTP-dependent triphosphohydrolase that degrades deoxyribonucleoside triphosphates (dNTPs) thereby limiting the intracellular dNTP pool. Mutations in SAMHD1 cause Aicardi-Goutières syndrome (AGS), an inflammatory encephalopathy that mimics congenital viral infection and that phenotypically overlaps with the autoimmune disease systemic lupus erythematosus. Both disorders are characterized by activation of the antiviral cytokine interferon-? initiated by immune recognition of self nucleic acids. Here we provide first direct evidence that SAMHD1 associates with endogenous nucleic acids in situ. Using fluorescence cross-correlation spectroscopy, we demonstrate that SAMHD1 specifically interacts with ssRNA and ssDNA and establish that nucleic acid-binding and formation of SAMHD1 complexes are mutually dependent. Interaction with nucleic acids and complex formation do not require the SAM domain, but are dependent on the HD domain and the C-terminal region of SAMHD1. We finally demonstrate that mutations associated with AGS exhibit both impaired nucleic acid-binding and complex formation implicating that interaction with nucleic acids is an integral aspect of SAMHD1 function. PMID:23371319

Tüngler, Victoria; Staroske, Wolfgang; Kind, Barbara; Dobrick, Manuela; Kretschmer, Stefanie; Schmidt, Franziska; Krug, Claudia; Lorenz, Mike; Chara, Osvaldo; Schwille, Petra; Lee-Kirsch, Min Ae

2013-01-31

161

Demixing-stimulated lane formation in binary complex plasma  

SciTech Connect

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

Du, C.-R.; Jiang, K.; Suetterlin, K. R.; Ivlev, A. V.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85748, Garching (Germany)

2011-11-29

162

Thermodynamic Studies of the Effects of Solvents on Molecular Complex Formation Equilibria; Orientation of Water Around Nonpolar Solutes in Aqueous Solutions.  

National Technical Information Service (NTIS)

The effect of solvents on electron-donor-acceptor complex formation reactions has been studied thermodynamically. The nonpolar analog model (NPA) is examined theoretically and methods are developed for using it to predict thermodynamic properties of the t...

K. O. Yeo

1973-01-01

163

Terminal vanadium-neopentylidyne complexes and intramolecular cross-metathesis reactions to generate azametalacyclohexatrienes.  

PubMed

Four-coordinate vanadium complexes containing a terminal neopentylidyne functionality have been prepared by two consecutive alpha-hydrogen abstraction reactions both of which were induced by one-electron oxidations. Among these vanadium-alkylidyne complexes are the neutral and the cation (Nacnac)VCtBu(OTf) and [(Nacnac)VCtBu(THF)]+, respectively (Nacnac- = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3). The vanadium-alkylidynes have been characterized by 1H, 13C, 51V NMR spectroscopy and single-crystal X-ray diffraction and are consistent with a short VC bond. These alkylidynes were found to transform to azametalacyclohexatriene systems via an intramolecular cross-metathesis reaction. Kinetic studies of the transformation of (Nacnac)VCtBu(OTf) in C7D8 reveal the formation of the azametalacyclohexatriene to be independent of solvent (toluene vs THF) and the reaction to be first order in vanadium (k = 3.30(5) x 10-5 s-1 at 80 degrees C, with activation parameters DeltaH= 25.4(3) kcal/mol, DeltaS = -6(3) cal/molK). High-level DFT calculations on the full model suggest an intramolecular mechanism invoking only one transition state. The overall thermodynamic driving force for the reaction (DeltaG) in solution phase was estimated to be -21.3 kcal/mol. PMID:15327285

Basuli, Falguni; Bailey, Brad C; Brown, Douglas; Tomaszewski, John; Huffman, John C; Baik, Mu-Hyun; Mindiola, Daniel J

2004-09-01

164

Cu(I) Amido Complexes in the Ullmann Reaction. Reactions of Cu(I)-Amido Complexes with Iodoarenes with and without Autocatalysis by CuI  

PubMed Central

A series of Cu(I)-amido complexes both lacking ancillary ligands and containing 1,10-phenanthroline (phen) as ligand have been prepared. These complexes react with iodoarenes to form arylamine products, and these data are consistent with the intermediacy of such complexes in catalytic Ullmann amination reactions. The stoichiometric reactions of the Cu(I)-amido complexes with iodoarenes are autocatalytic, with the free CuI generated during the reaction serving as the catalyst. Such autocatalytic behavior was not observed for reactions of iodoarenes with Cu(I)-amidates, -imidates and -phenoxides. The selectivity of these complexes for two sterically distinct aryl halides under various conditions imply that the autocatalytic reaction proceeds by forming highly-reactive [CuNPh2]n lacking phen. Reactions with radical probes imply that the reactions of phen-ligated Cu(I)-amido complexes with iodoarenes occur without the intermediacy of aryl radicals. DFT calculations of the oxidative addition of iodoarenes to Cu(I) species are consistent with faster reactions of iodoarenes with CuNPh2 species lacking phen in DMSO than with phen-ligated LCuNPh2. The free energy barrier computed for reaction of PhI with (DMSO)CuNPh2 was 21.8 kcal/mol, while the free energy barrier computed for reaction of PhI with (phen)CuNPh2 was 33.4 kcal/mol.

Giri, Ramesh; Hartwig, John F.

2010-01-01

165

Mercury(II) Penicillamine Complex Formation in Alkaline Aqueous Solution  

SciTech Connect

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

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

2009-06-01

166

Catecholase activity of a mu-hydroxodicopper(II) macrocyclic complex: structures, intermediates and reaction mechanism.  

PubMed

The monohydroxo-bridged dicopper(II) complex (1), its reduced dicopper(I) analogue (2) and the trans-mu-1,2-peroxo-dicopper(II) adduct (3) with the macrocyclic N-donor ligand [22]py4pz (9,22-bis(pyridin-2'-ylmethyl)-1,4,9,14,17,22,27,28,29,30- decaazapentacyclo -[22.2.1(14,7).1(11,14).1(17,20)]triacontane-5,7(28),11(29),12,18,20(30), 24(27),25-octaene), have been prepared and characterized, including a 3D structure of 1 and 2. These compounds represent models of the three states of the catechol oxidase active site: met, deoxy (reduced) and oxy. The dicopper(II) complex 1 catalyzes the oxidation of catechol model substrates in aerobic conditions, while in the absence of dioxygen a stoichiometric oxidation takes place, leading to the formation of quinone and the respective dicopper(I) complex. The catalytic reaction follows a Michaelis-Menten behavior. The dicopper(I) complex binds molecular dioxygen at low temperature, forming a trans-mu-1,2-peroxo-dicopper adduct, which was characterized by UV-Vis and resonance Raman spectroscopy and electrochemically. This peroxo complex stoichiometrically oxidizes a second molecule of catechol in the absence of dioxygen. A catalytic mechanism of catechol oxidation by 1 has been proposed, and its relevance to the mechanisms earlier proposed for the natural enzyme and other copper complexes is discussed. PMID:16208496

Koval, Iryna A; Belle, Catherine; Selmeczi, Katalin; Philouze, Christian; Saint-Aman, Eric; Schuitema, Anna Maria; Gamez, Patrick; Pierre, Jean-Louis; Reedijk, Jan

2005-11-08

167

Monte Carlo simulations of oscillations, chaos and pattern formation in heterogeneous catalytic reactions  

Microsoft Academic Search

Experimental studies employing surface science methods indicate that kinetic oscillations, chaos, and pattern formation in heterogeneous catalytic reactions often result from the interplay of rapid chemical reaction steps and relatively slow complementary processes such as oxide formation or adsorbate-induced surface restructuring. In general, the latter processes should be analysed in terms of theory of phase transitions. Therefore, the conventional mean-field

Vladimir P. Zhdanov

2002-01-01

168

Mechanism of Acyl-Enzyme Complex Formation from the Henry-Michaelis Complex of Class C ?-Lactamases with ?-Lactam Antibiotics.  

PubMed

Bacteria that cause most of the hospital-acquired infections make use of class C ?-lactamase (CBL) among other enzymes to resist a wide spectrum of modern antibiotics and pose a major public health concern. Other than the general features, details of the defensive mechanism by CBL, leading to the hydrolysis of drug molecules, remain a matter of debate, in particular the identification of the general base and role of the active site residues and substrate. In an attempt to unravel the detailed molecular mechanism, we carried out extensive hybrid quantum mechanical/molecular mechanical Car-Parrinello molecular dynamics simulation of the reaction with the aid of the metadynamics technique. On this basis, we report here the mechanism of the formation of the acyl-enzyme complex from the Henry-Michaelis complex formed by ?-lactam antibiotics and CBL. We considered two ?-lactam antibiotics, namely, cephalothin and aztreonam, belonging to two different subfamilies. A general mechanism for the formation of a ?-lactam antibiotic-CBL acyl-enzyme complex is elicited, and the individual roles of the active site residues and substrate are probed. The general base in the acylation step has been identified as Lys67, while Tyr150 aids the protonation of the ?-lactam nitrogen through either the substrate carboxylate group or a water molecule. PMID:24010547

Tripathi, Ravi; Nair, Nisanth N

2013-09-23

169

GABAergic complex basket formations in the human neocortex.  

PubMed

Certain GABAergic interneurons in the cerebral cortex, basket cells, establish multiple connections with cell bodies that typically outline the somata and proximal dendrites of pyramidal cells. During studies into the distribution of the vesicular GABA transporter (VGAT) in the human cerebral cortex, we were struck by the presence of a very dense, pericellular arrangement of multiple VGAT-immunoreactive (-ir) terminals in certain cortical areas. We called these terminals "Complex basket formations" (Cbk-formations) to distinguish them from the simpler and more typical pericellular GABAergic innervations of most cortical neurons. Here we examined the distribution of these VGAT-ir Cbk-formations in various cortical areas, including the somatosensory (area 3b), visual (areas 17 and 18), motor (area 4), associative frontal (dorsolateral areas 9, 10, 45, 46, and orbital areas 11, 12, 13, 14, 47), associative temporal (areas 20, 21, 22, and 38), and limbic cingulate areas (areas 24, 32). Furthermore, we used dual or triple staining techniques to study the chemical nature of the innervated cells. We found that VGAT-ir Cbk-formations were most frequently found in area 4 followed by areas 3b, 13, and 18. In addition, they were mostly observed in layer III, except in area 17, where they were most dense in layer IV. We also found that 70% of the innervated neurons were pyramidal cells, while the remaining 30% were multipolar cells. Most of these multipolar cells expressed the calcium-binding protein parvalbumin and the lectin Vicia villosa agglutinin. PMID:21031559

Blazquez-Llorca, Lidia; García-Marín, Virginia; DeFelipe, Javier

2010-12-15

170

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

171

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

172

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

173

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

Microsoft Academic Search

Collisions between two heavy nuclei produce a diverse spectrum of reaction modes which is much wider than that observed in light ion studies. For the latter case, two processes are observed: direct reactions and compound nucleus formation. Heavy ion reaction studies on the other hand have identified additional processes such as deep-inelastic scattering, incomplete fusion, and quasi-fission reactions. While the

K. E. Rehm

1992-01-01

174

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

National Technical Information Service (NTIS)

Collisions between two heavy nuclei produce a diverse spectrum of reaction modes which is much wider than that observed in light ion studies. For the latter case, two processes are observed: direct reactions and compound nucleus formation. Heavy ion react...

K. E. Rehm

1992-01-01

175

Ribonucleoprotein complex formation by the human hepatitis B virus polymerase.  

PubMed

Human hepatitis B virus (HBV) polymerase (pol or RT), when expressed in Xenopus oocytes upon injection of synthetic minimal pol RNA (RT RNA), assembles into a higher molecular weight complex with the characteristics of a ribonuclear protein (RNP) complex. In vitro RNA competition binding data suggest that RT RNA is preferentially packaged into this complex even though it lacks the authentic viral encapsidation signal, epsilon, and viral capsid protein sequences. Consistent with this finding, the in vitro polymerase reaction performed in pol-expressing oocyte extracts generates primarily HBV-specific DNAs even when the pol template is challenged with a coinjected non-HBV competitor RNA. These results suggest that interaction between pol and its cognate RNA can be mediated by sequences other than the known packaging elements. We speculate that HBV RNP complexes containing at least polymerase and viral RNA may play a role in viral nucleocapsid assembly and may help to segregate HBV reverse transcription from the cellular milieu in vivo. PMID:8724861

Seifer, M; Standring, D N

1995-01-01

176

Caldera formation in the Rum Central Igneous Complex, Scotland  

NASA Astrophysics Data System (ADS)

The Northern Marginal Zone of the Rum Central Igneous Complex in NW Scotland represents part of the early, felsic phase of the volcano. The marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks. Its formation has been explored through field examination of the ring fracture system of the Complex and its pyroclastic and epiclastic intracaldera facies. A sequence of magmatic tumescence and chamber growth caused initial doming, followed by the formation of a collapse structure without accompanying volcanism. This collapse structure, circular in plan, is akin in origin to a salt basin formed by crustal stretching above a rising diapir. We call this the proto-caldera. Collapse breccias, which represent the slumping and sliding of megablocks, blocks and boulders of the Torridonian sandstones which form the walls of the basin, were the original infilling. Logs of these deposits reveal considerable variation in thickness of the breccias (from 80-170 m) in the Complex, indicating an uneven floor to the proto-caldera, consistent with piecemeal collapse. Following accumulation of up to >70 m thickness of breccia, thin interbedded rhyodacitic crystal tuffs (10-30 cm) record the earliest eruptions of felsic magma in the caldera. Caldera formation was then interrupted by a period of quiescence, recorded by the presence of an epiclastic sandstone of locally several metres thickness, formed by washout of fines from the breccias. Subsequent resurgence created a fracture pattern characteristic of doming, along which rhyodacite magma rose in dykes and erupted up to perhaps 10 km3 of rhyodacitic intracaldera ignimbrites. This major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber. Mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma.

Troll, Valentin R.; Emeleus, C. Henry; Donaldson, Colin H.

2000-08-01

177

Chemical proprieties of the iron-quinone complex in mutated reaction centers of Rb. sphaeroides  

NASA Astrophysics Data System (ADS)

We investigated type II bacterial photosynthetic reaction centers, which contain a quinone - iron complex (QA-Fe-QB) on their acceptor side. Under physiological conditions it was observed mainly in a reduced high spin state but its low spin ferrous states were also observed. Therefore, it was suggested that it might regulate the dynamical properties of the iron-quinone complex and the protonation and deprotonation events in its neighbourhood. In order to get insight into the molecular mechanism of the NHFe low spin state formation, we preformed Mössbauer studies of a wild type of Rb. sphaeroides and its two mutated forms. Our Mössbauer measurements show that the hydrophobicity of the QA binding site can be crucial for stabilization of the high spin ferrous state of NHFe.

Ha?as, Agnieszka; Derrien, Valerie; Sebban, Pierre; Matlak, Krzysztof; Korecki, Józef; Kruk, Jerzy; Burda, Kv?toslava

2012-03-01

178

Effects of wearing a mouth guard and movement complexity on simple reaction time  

Microsoft Academic Search

The purpose of the study was to determine how use of a mouth guard and movement complexity affect simple reaction time. The experiment consisted of three prescribed whole body movements of varying complexity. Participants were 12 college aged males who were free from injury and had some experience playing sports. Reaction time was determined using ground reaction force data and

Taijiro Hide

2011-01-01

179

Complex formation between uranyl and various thiosemicarbazide derivatives  

SciTech Connect

Complex formation between hexavalent uranium and salicylaldehyde thiosemicarbazone (H/sub 2/L), salicylaldehyde S-methyl-isothiosemicarbazone (H/sub 2/Q), S-methyl-N/sub 1/,N/sub 4/-bis(salicylidene)isothiosemicarbazide(H/sub 2/Z), and thiosemicarbazidodiacetic acid (H/sub 2/R) has been studied spectrophotometrically in solution. Stability constants for complexes having the composition UO/sub 2/A have been calculated. Solid uranyl derivatives having the composition UO/sub 2/L x 2H/sub 2/O, UO/sub 2/Q x 2H/sub 2/O, UO/sub 2/Z x 2H/sub 2/O, and UO/sub 2/R x 2H/sub 2/O have been obtained. These derivatives were isolated and their IR spectroscopic behavior and thermal properties were investigated.

Chuguryan, D.G.; Dzyubenko, V.I.

1987-01-01

180

Flower-like porous hematite nanoarchitectures achieved by complexation-mediated oxidation-hydrolysis reaction.  

PubMed

Flower-like porous hematite (?-Fe(2)O(3)) nanoarchitectures composed of ultra-thin nanoflakes were prepared by annealing the iron oxide precursor formed via the oxidation-hydrolysis reaction between Fe(II) ions and Tris(hydroxymethyl)aminomethane (abbreviated as Tris). The microstructure of the prepared FeOOH and hematite samples were fully characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier-transforming infrared spectra, thermogravimetric analysis, and nitrogen adsorption-desorption isotherm. Based on the influences of reactant concentrations, reaction time and reaction temperature on the morphologies of the resultant samples, a formation mechanism of etching was proposed, Fe(II)-Tris complexes were self-assembled via hydrogen bonds into brick-like building blocks, which then aggregated into rudimentary nanoparticles, and the synergistic effect between the crystallization of FeOOH and dissociation of Fe(II)-Tris complexes make the rudimentary nanoparticles evolve into the flower-like products. The as-prepared flower-like ?-Fe(2)O(3) nanostructures possessed a Brunauer-Emmett-Teller specific surface area of 191.63 m(2)g(-1), hierarchical pore distribution ranging from micropores to macropores, and good crystallinity, and excellent visible photocatalysis in terms of removing chemical oxygen demand of dimethyl sulfoxide industrial wastewater. The current work provides a reliable approach for building functional hierarchical nanoarchitectures and the prepared iron oxide nanomaterials demonstrate an excellent ability to remove toxic pollutants in industrial wastewater. PMID:21353233

Huang, Xing; Guan, Jianguo; Xiao, Zhidong; Tong, Guoxiu; Mou, Fangzhi; Fan, Xi'an

2011-02-24

181

Asymmetric hollow nanorod formation through a partial galvanic replacement reaction.  

PubMed

An asymmetric single hollow structure was generated from Ag-Au-Ag heterometal nanorods by a partial galvanic replacement reaction for the first time. The C(2)-symmetry breaking took place because of the random generation of a single pit on only one end of the silver domain at an early stage of the reaction. Careful control of the reaction kinetics could also yield a double-hollow structure on both ends of the silver domain. The resulting single- and double-hollow nanorods exhibited characteristic extinctions in the near-IR range. PMID:19994851

Seo, Daeha; Song, Hyunjoon

2009-12-30

182

Formation of octahedral iridium(III) dihydrides from the reaction of ortho-chelated aryliridium(I) compounds with dihydrogen  

Microsoft Academic Search

The reaction of Ir\\/sup I\\/(CHâNMeâ)-2-R¹-4-R²⁻⁶(COD) (COD = cyclooacta-1,5-diene) with dihydrogen in CDâClâ was monitored by ¹H NMR. At -20°C quantitative formation of the novel dihydride complexes Ir\\/sup III\\/Hâ(CâHâ(CHâNMeâ)-2-R¹-4-R²⁻⁶(COD) (R¹ = H, R² = CHâNMeâ (10), Me (11); R² = H, R¹ = H (12), Me (13), CHâNMeâ (14); R¹ = R² = CHâNMeâ (15)) occurs. Further reactions, the type of

Adolphus A. H. Van der Zeijden; Gerard. Van Koten; R. Lujik; David M. Grove

1988-01-01

183

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

184

Vancomycin: ligand recognition, dimerization and super-complex formation.  

PubMed

The antibiotic vancomycin targets lipid II, blocking cell wall synthesis in Gram-positive bacteria. Despite extensive study, questions remain regarding how it recognizes its primary ligand and what is the most biologically relevant form of vancomycin. In this study, molecular dynamics simulation techniques have been used to examine the process of ligand binding and dimerization of vancomycin. Starting from one or more vancomycin monomers in solution, together with different peptide ligands derived from lipid II, the simulations predict the structures of the ligated monomeric and dimeric complexes to within 0.1 nm rmsd of the structures determined experimentally. The simulations reproduce the conformation transitions observed by NMR and suggest that proposed differences between the crystal structure and the solution structure are an artifact of the way the NMR data has been interpreted in terms of a structural model. The spontaneous formation of both back-to-back and face-to-face dimers was observed in the simulations. This has allowed a detailed analysis of the origin of the cooperatively between ligand binding and dimerization and suggests that the formation of face-to-face dimers could be functionally significant. The work also highlights the possible role of structural water in stabilizing the vancomycin ligand complex and its role in the manifestation of vancomycin resistance. PMID:23298227

Jia, ZhiGuang; O'Mara, Megan L; Zuegg, Johannes; Cooper, Matthew A; Mark, Alan E

2013-02-11

185

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

SciTech Connect

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

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

2011-12-05

186

Thermodynamics and Complexation Reactions of Anionic Silicate Species  

SciTech Connect

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

Choppin, Gregory R.; Felmy, Andrew R.

2001-06-01

187

The role of the Maillard reaction in the formation of flavour compounds in dairy products--not only a deleterious reaction but also a rich source of flavour compounds.  

PubMed

Dairy products are heated both during processing and by consumers during food preparation; consumers place a high level of importance on flavour when assessing product acceptability. Of particular importance to the flavour of heated dairy products is the highly complex network of Maillard reactions. Much focus has been placed on the undesirable flavours generated through the Maillard reaction and how to minimise the formation of these flavours. However, beneficial flavours can also be formed by the Maillard reaction; dairy products, such as ghee, are formed by heating and are characterised by the unique flavour generated by this chemistry. This review looks at the Maillard reaction as a source of beneficial flavours for cooked dairy products and the application of models to the study of flavour formation in food systems. Models are typically used to study complex reactions in a simplified way; however, they are not always applicable to food systems. PMID:22948260

Newton, Angela E; Fairbanks, Antony J; Golding, Matt; Andrewes, Paul; Gerrard, Juliet A

2012-12-01

188

Kinetics of substitution reactions of Fe II-phosphine complexes with Cl ?, Br ? and SCN ? in acetonitrile. A comparative study of complexes containing bidentate and tripodal phosphines  

Microsoft Academic Search

The kinetics of formation of FeLX+ complexes from FeLan22+ and X? [L ? P(CH2CH2PPh2)3, N(CH2CH2PPh2)3, (Ph2PCH2CH2PPh2)2; X ? Cl, Br, SCN; an = acetonitrile] has been studied in acetonitrile at 25.0°C and Et4NBF4 (0.05 mol dm?3). All the reactions seem to go through initial substitution of one coordinated acetonitrile by X? to form FeLX+, although in some cases the reaction

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

1996-01-01

189

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

190

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

191

Thermally reversible single-crystal to single-crystal transformation of mononuclear to dinuclear Zn(ii) complexes by [2+2] cycloaddition reaction.  

PubMed

Two Zn(ii) complexes of trans-4-styrylpyridine ligands undergo [2+2] cycloaddition reaction forming Zn(ii) complex dimers in a single-crystal to single-crystal (SCSC) manner which were thermally reversible. The dimers are presumed to be the stable intermediates in the formation of 1D coordination polymers upon prolonged exposure to UV light. PMID:24022693

Medishetty, Raghavender; Yap, Terence Teck Sheng; Koh, Lip Lin; Vittal, Jagadese J

2013-09-24

192

Complex Formation of Yeast Rev1 with DNA Polymerase ??  

PubMed Central

In Saccharomyces cerevisiae, Rev1 functions in translesion DNA synthesis (TLS) together with polymerase ? (Pol?), comprised of the Rev3 catalytic and Rev7 accessory subunits. Rev1 plays an indispensable structural role in promoting Pol? function, and deletion of the Rev1-C terminal region that is involved in physical interactions with Rev3 inactivates Pol? function in TLS. In humans, however, Rev1 has been shown to physically interact with the Y-family polymerases Pol?, Pol?, and Pol?, 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? and not for Pol?, 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? 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.

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

2007-01-01

193

Photosynthetic Reaction Center Complexes from Heliobacteria (Abstract Only).  

National Technical Information Service (NTIS)

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...

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

1991-01-01

194

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

195

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

196

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

NASA Astrophysics Data System (ADS)

CaF2-structure CoSi2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi2 layers obtained by conventional solid phase growth (SPG). In the case of RDE, CoSi 2 formation occurred during Co deposition at elevated temperature while for SPG, Co was deposited at 25°C and silicidation took place during subsequent annealing. My results demonstrate that RDE CoSi2 layers are epitaxial with a cube-on-cube relationship, 001CoSi2 ?001Si and 100CoSi2 ?100 Si . In contrast, SPG films are polycrystalline with a mixed 111/002/022/112 orientation. I attribute the striking difference to rapid Co diffusion during RDE for which the high Co/Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. Initial formation of CoSi2(001) follows the Volmer-Weber mode with two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal <110> directions, bounded by four {111} CoSi2/Si interfaces, and grow with a cube-on-cube orientation with respect to Si(001). Platelet-shaped islands are bounded across their long <110> directions by {111} twin planes and their narrow <110> directions by 511CoSi2 ?111Si interfaces. The top and bottom surfaces are {22¯1}, with 22¯1 CoSi2?001 Si , and {1¯1¯1}, with 1¯1¯ 1CoSi2? 11¯1Si , respectively. The early stages of film growth (tCo ? 13 A) are dominated by the twinned platelets due to a combination of higher nucleation rates and rapid elongation along preferred <110> directions. However, at tCo ? 13 A, island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. Further island growth becomes dominated by the untwinned islands. I show that high-flux low-energy Ar+ ion irradiation during RDE growth dramatically increases the area fraction of untwinned regions from 0.17 in films grown under standard magnetically balanced conditions in which the ratio JAr+/JCo of the incident Ar> to Co fluxes is 1.4 to 0.72 with JAr+/JCo= 13.3. TEM analyses reveal that increasing JAr+/J Co results in larger values of both the number density and area of untwinned islands. The intense Ar+ ion bombardment under high-ion-flux conditions creates additional low-energy adsorption sites that favor the nucleation of untwinned islands and collisionally enhances the Co adatom surface mobility which, in turn, increases the probability of itinerant Co adatoms reaching these sites.

Lim, Chong Wee

197

Viewer Reactions to Content and Presentational Format of Television News  

Microsoft Academic Search

From the theoretical perspective of activation theory and using an on-line, real-time, computerized response system, the purpose of the present study was to investigate the pattern of viewer reactions to local television newscasts. Of specific concern was the overall interest pattern for the entire newscast, as well as comparative interest levels for the various component segments and the characteristics of

Ralph R. Behnke; Phyllis Miller

1992-01-01

198

Consumer reactions to different health claim formats on food labels  

Microsoft Academic Search

Health claims on foods act as health messages and have a role in communicating and educating the consumer about diet-disease related issues. Previous studies have suggested that different formats of health claims communicate differently with the consumer. The aim of our study was to investigate whether splitting of the claim (a brief claim at the front package directing consumers to

L. Singer; P. G. Williams; L. Ridges; S. Murray; A. McMahon

2006-01-01

199

Reaction of Atomic Hydrogen with Hydrogenated Porous Silicon - Detection of Precursor to Silane Formation.  

National Technical Information Service (NTIS)

The reaction of electrochemically formed porous silicon with atomic hydrogen or atomic deuterlum flas been studied at cryogenic temperatures and at room temperature. Cryogenic temperatures were chosen in order to kinetically suppress silane formation (sil...

J. A. Glass E. A. Wovchko J. T. Yates

1995-01-01

200

Fission and quasi-fission: insights into heavy element formation reactions  

SciTech Connect

Mass-angle distributions carry detailed information on the characteristics of quasi-fission, and thus of the dynamics of heavy element formation reactions. Recent experimental results are presented and discussed.

Hinde, D. J.; Rietz, R. du; Rafiei, R.; Dasgupta, M.; Diaz-Torres, A. [Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Thomas, R. G. [Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); B.A.R.C., Mumbai (India)

2009-03-04

201

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

202

Formation of Porous Surface Layers in Reaction Bonded Silicon Nitride During Processing.  

National Technical Information Service (NTIS)

An effort was undertaken to determine if the formation of the generally observed layer of large porosity adjacent to the as-nitride surfaces of reaction bonded silicon nitrides could be prevented during processing. Isostatically pressed test bars were pre...

N. J. Shaw T. K. Glasgow

1979-01-01

203

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

204

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

205

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

206

Pattern formation of Cu layer by photocatalytic reaction of ZnO thin film  

SciTech Connect

A new, fully additive-based, electroless plating process for the formation of fine Cu patterns without using a conventional photoresist has been developed which utilizes a photocatalytic reaction of ZnO thin films prepared on ceramic substrates for printed circuit boards. The ZnO layer serves both as an adhesive layer and as a photosensitive layer. The Cu patterns could be easily fabricated in an electroless Cu plating bath after Pd nuclei, which act as catalytic sites for the electroless plating, were patterned via an area-selective photocatalytic reaction. This was achieved by adsorbing Pd(II) onto the ZnO surface and selectively exposing the surface with UV light through a photomask. The unexposed regions can be freed of Pd(II) using ethylenediamine, which can form a stable complex with Pd(II). Cu patterns 17 {micro}m wide, with adhesion strengths suitable for practical use, have been achieved on alumina substrates with this electroless plating method.

Yoshiki, Hajime; Kitahara, Hiromitsu; Hashimoto, Kazuhito; Fujishima, Akira [Univ. of Tokyo (Japan). Dept. of Applied Chemistry

1995-12-01

207

Study of the Ternary Complex Formation Between Vanadium(III), Dipicolinic Acid and Small Blood Serum Bioligands  

Microsoft Academic Search

Ternary complex formation reactions were studied between vanadium(III), dipicolinic acid and small molecular weight blood\\u000a serum components: lactic, oxalic, citric and ortophosphoric acids. The electromotive force measurement permitted us to determine\\u000a the chemical speciation of the complexes formed. In the vanadium(III)–dipicolinic acid–lactic acid system the complexes detected\\u000a were: V(dipic)(lac), V(dipic)(lac)(OH)? and V(dipic)(lac). In the vanadium(III)–dipicolinic acid–oxalic acid system the observed

Freya Da Costa; Giuseppe Lubes; Mildred Rodríguez; Vito Lubes

2011-01-01

208

Image formation in the eye: very specified complexity  

NASA Astrophysics Data System (ADS)

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

Stoltzmann, David E.

2005-08-01

209

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

PubMed

Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor. NDMA was formed from the reaction between DMA and monochloramine indicating that it should be considered a potential disinfection by-product. The formation of NDMA increased with increased monochloramine concentration and showed maximum in yield when DMA was varied at fixed monochloramine concentrations. The mass spectra of the NDMA formed from DMA and 15N isotope labeled monochloramine (15NH2Cl) showed that the source of one of the nitrogen atoms in the nitroso group in NDMA was from monochloramine. Addition of 0.05 and 0.5 mM of preformed monochloramine to a secondarily treated wastewater at pH 7.2 also resulted in the formation of 3.6 and 111 ng/L of NDMA, respectively, showing that this is indeed an environmentally relevant NDMA formation pathway. The proposed NDMA formation mechanism consists of (i) the formation of 1,1-dimethylhydrazine (UDMH) intermediate from the reaction of DMA with monochloramine followed by, (ii) the oxidation of UDMH by monochloramine to NDMA, and (iii) the reversible chlorine transfer reaction between monochloramine and DMA which is parallel to (i). We conclude that reactions involving monochloramine in addition to classical nitrosation reactions are potentially important pathways for NDMA formation. PMID:11848351

Choi, Junghoon; Valentine, Richard L

2002-02-01

210

Polymer-supported Schiff base complexes in oxidation reactions  

Microsoft Academic Search

Polymer-supported Schiff base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff base was analyzed and presented in this review. The manganese(III) Schiff base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the

K. C. Gupta; Alekha Kumar Sutar; Chu-Chieh Lin

2009-01-01

211

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

PubMed

In this paper, we demonstrated a new convenient route for in situ fabrication of well separated small sized WO(3) nanoparticles in silica spheres, through a predeposition of surfactant encapsulated polyoxotungates as tungsten source, and followed by a calcination process. In a typical procedure, selected polyoxotungates with different charges were enwrapped with dioctadecyldimethylammonium cations through electrostatic interaction. Elemental analysis, thermogravimetric analysis, and spectral characterization confirmed the formation of prepared complexes with the anticipated chemical structure. The complexes were then phase-transferred into aqueous solution that predissolved surfactant cetyltrimethylammonium bromide, and finally incorporated into silica spheres through a joint sol-gel reaction with tetraethyl orthosilicate in a well dispersed state under the protection of organic layer for polyoxotungates from the alkaline reaction condition. Transmission electron microscopic images illustrated the well dispersed WO(3) nanoparticles in the size range of ca. 2.2 nm in the silica spheres after the calcination at 465 °C. The sizes of both the silica spheres and WO(3) nanoparticles could be adjusted independently through changing the doping content to a large extent. Meanwhile, the doped polyoxotungate complexes acted as the template for the mesoporous structure in silica spheres after the calcination. Along with the increase of doping content and surfactant, the mesopore size changed little (2.0-2.9 nm), but the specific surface areas increased quite a lot. Importantly, the WO(3)-nanoparticle-doped silica spheres displayed an interesting photovoltaic property, which is favorable for the funtionalization of these nanomaterials. PMID:20715875

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

2010-09-21

212

Kinetic study of the gas phase formation and decomposition reactions of nitrous acid  

Microsoft Academic Search

The kinetics of the gas phase decomposition and formation reactions of nitrous acid, 2HONO = NO + NOâ + HâO (kâ, kâ), have been investigated in a Pyrex reactor at HONO partial pressures of 0.05 to 1.0 Torr and total pressures of 5 to 50 Torr using a mass spectrometer detector. The reactions were determined to be heterogeneous under all

E. W. Kaiser; C. H. Wu

1977-01-01

213

Formation of Nnitrosodimethylamine (NDMA) from reaction of monochloramine: a new disinfection by-product  

Microsoft Academic Search

Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor. NDMA was formed from the reaction between DMA and monochloramine indicating that it should be considered a potential disinfection by-product. The formation of NDMA increased with increased monochloramine concentration and showed

Junghoon Choi; Richard L. Valentine

2002-01-01

214

In situ formation of titanium carbide in titanium powder compacts by gas–solid reaction  

Microsoft Academic Search

Porous titanium compacts of fine and coarse sponge titanium powders were reacted with methane gas to produce Ti–TiC in situ composites. The kinetics of titanium carbide formation during the reaction were studied in relation to powder size, reaction temperature and time, and methane flow rate. The titanium carbide was initially formed as a layer around each titanium powder and the

Y.-J. Kim; H. Chung; S.-J. L. Kang

2001-01-01

215

Nanocrystalline starch grafted palladium(ii) complex for the Mizoroki-Heck reaction.  

PubMed

Nanocrystalline starch produced from the acid hydrolysis of gelatinized starch has been used for the first time to support palladium(ii) ethylenediamine complex. The nanocrystalline starch supported Pd(ii) complex was found to be an efficient and efficiently recycled catalyst for the Mizoroki-Heck reaction of furans and thiophenes with styrenes under mild reaction conditions. PMID:23969940

Verma, Sanny; Le Bras, Jean; Jain, Suman L; Muzart, Jacques

2013-09-24

216

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

217

Palladium(II) complex formation by indole-3-acetate. Mixed ligand complexes involving a unique spiro-ring formed by cyclopalladation  

Microsoft Academic Search

Formation of mixed ligand palladium(II) complexes involving indole-3-acetate (IA) has been studied by synthetic, spectroscopic and X-ray crystallographic methods. Reaction of IA with Na2PdCl4 in methanol gave NaPd(IAH?1)Cl (1) (IAH?1=IA deprotonated from the indole ring), which reacted with pyridine (py) to give [Pd(IAH?1)(py)] (2) as orange crystals. Similar reactions carried out in the presence of water gave Pd(IAH?1)·1.5H2O (1?), which

Masako Takani; Hideki Masuda; Osamu Yamauchi

1995-01-01

218

The Griffin model, complex particles and direct nuclear reactions  

Microsoft Academic Search

The basic approximations of the Griffin model for nuclear reactions are reexamined. Proton-neutron distinguishability and the Pauli exclusion principle are treated in an improved way. Several improvements in the model input values are suggested. Direct reaction mechanisms are systematically considered, and semi-empirical descriptions are proposed for those not included in the Griffin model calculations (knockout and inelastic processes involving alpha

C. Kalbach

1977-01-01

219

Catecholase activity of dicopper(II)-bispidine complexes: stabilities and structures of intermediates, kinetics and reaction mechanism.  

PubMed

A mechanism for the oxidation of 3,5-di-tert-butylcatechol (dtbc) with dioxygen to the corresponding quinone (dtbq), catalyzed by bispidine-dicopper complexes (bispidines are various mono- and dinucleating derivatives of 3,7-diazabicyclo[3.3.1]nonane with bis-tertiary-amine-bispyridyl or bis-tertiary-amine-trispyridyl donor sets), is proposed on the basis of (1) the stoichiometry of the reaction as well as the stabilities and structures [X-ray, density functional theory (B3LYP, TZV)] of the bispidine-dicopper(II)-3,4,5,6-tetrachlorcatechol intermediates, (2) formation kinetics and structures (molecular mechanics, MOMEC) of the end-on peroxo-dicopper(II) complexes and (3) kinetics of the stoichiometric (anaerobic) and catalytic (aerobic) copper-complex-assisted oxidation of dtbc. This involves (1) the oxidation of the dicopper(I) complexes with dioxygen to the corresponding end-on peroxo-dicopper(II) complexes, (2) coordination of dtbc as a bridging ligand upon liberation of H(2)O(2) and (3) intramolecular electron transfer to produce dtbq, which is liberated, and the dicopper(I) catalyst. Although the bispidine complexes have reactivities comparable to those of recently published catalysts with macrocyclic ligands, which seem to reproduce the enzyme-catalyzed process in various reaction sequences, a strikingly different oxidation mechanism is derived from the bispidine-dicopper-catalyzed reaction. PMID:16964505

Born, Karin; Comba, Peter; Daubinet, André; Fuchs, Alexander; Wadepohl, Hubert

2006-09-09

220

The importance of classes of neutral-neutral reactions in the production of complex interstellar molecules  

NASA Astrophysics Data System (ADS)

The role of classes of neutral-neutral reactions in the gas-phase synthesis of complex interstellar molecules is determined via a series of model calculations. Reactions between O or N atoms and bare carbon clusters Cn appear to be critical in hindering the synthesis of complex species. Neutral-neutral reactions involving molecular hydrogen that occur via tunneling under potential energy barriers are shown to aid molecular synthesis. We demonstrate that, despite the existence of rapid neutral-neutral reactions, large abundances of complex molecules can be produced in dense clouds.

Bettens, R. P. A.; Lee, H.-H.; Herbst, Eric

1995-04-01

221

Catalytic Reactions of DNT and TNT Molecules on Porphyrin Complexes  

NASA Astrophysics Data System (ADS)

Reactions of molecules with substrates can be used to identify them, as in sensor applications. Here we examine reactions of DNT and TNT molecules on porphyrin and metal-porphyrin via first-principles DFT calculations. We find that the oxidation of DNT by O2 using Fe-porphyrin as a catalyst is exothermic. The affinity of O2 to Fe-porphyrin weakens the O2 intramolecular bond, which lowers the oxidation reaction barrier is lowered by ˜1 eV. Substrate effects on this process are accounted for. One way to use this selective oxidation reaction for DNT/TNT sensor applications is to exploit the metal-semiconductor transition in thin-film VO2 to detect the energy deposited by the exothermic reaction between the adsorbed molecules. This work was supported in part by DTRA grant HDTRA1-10-0047.

Warnick, Keith; Wang, Bin; Pantelides, Sokrates

2011-03-01

222

Stable pattern and standing wave formation in a simple isothermal cubic autocatalytic reaction scheme  

Microsoft Academic Search

The formation of stable patterns is considered in a reaction-diffusion system based on the cubic autocatalator, A+2B ? 3B, B ? C, with the reaction taking place within a closed region, the reactant A being replenished by the slow decay of precursor P via the reaction P ? A. The linear stability of the spatially uniform Steady state % MathType!MTEF!2!1!+-%

R. Hill; J. H. Merkin; D. J. Needham

1995-01-01

223

Reactions of Chelates with Macrocyclic Ligands. Complexation between Tetraphenylporphine and Cu(II) Complexes with ?-Amino Acids  

Microsoft Academic Search

The reactions of tetraphenylporphine (H2TPP) with copper(II) chelates in DMSO were studied. a-Amino acids (glycine, a-alanine, valine, leucine, tyrosine, and glutamine) were used as chelating ligands. The study of the reaction kinetics showed that Cu(II) chelates with alanine and the other amino acids are less reactive in these reactions than acetylacetonates, a-nitroso-ß-naphtholates, and hydroxyquinolates. The exception is a Cu(II) complex

B. D. Berezin; G. M. Mamardashvili

2002-01-01

224

Thermodynamics of the complex protein unfolding reaction of barstar.  

PubMed

The complex unfolding reaction of barstar has been characterized by studying the apparent rate of unfolding, monitored by intrinsic Trp fluorescence, as a function of temperature and guanidine hydrochloride (GdnHCl) concentration. The kinetics of unfolding and folding of wild-type (wt) barstar at 5 degrees C were first studied in detail. It is shown that when unfolding is carried out using concentrations of GdnHCl in the posttransition zone of unfolding, the change in fluorescence that accompanies unfolding occurs in two phases: 30% of the change occurs in a burst phase that is complete within 4 ms, and 70% of the change occurs in a fast phase that is complete within 2 s. In contrast, when the protein is unfolded at 25 degrees C, no burst-phase change in fluorescence is observed. To confirm that a burst-phase change in fluorescence indeed accompanies unfolding at low temperature, unfolding studies were also carried out on a marginally destabilized mutant form of barstar for which the burst-phase change in fluorescence is shown to be as high as 70%. These results confirm a previous report [Nath et al., (1996), Nat. Struct. Biol. 3, 920-923], in which the detection of a burst-phase change in circular dichroism at 222 nm during unfolding at 25 degrees C led to the inclusion of a rapidly formed kinetic intermediate, IU, on the unfolding pathway. To characterize thermodynamically the unfolding pathway, apparent unfolding rates were then measured at six different concentrations of GdnHCl in the range 2.6 to 5.0 M, at five different temperatures from 5 to 46 degrees C. The subsequent analysis was done on the basis of the observation that a preequilibrium between the fully folded state (F) and IU gets established rapidly before further unfolding to the completely unfolded state (U). The results indicate that IU has a specific heat capacity similar to that of F and therefore suggest that IU is as compact as F, with practically no exposure of the hydrophobic core. On the other hand, the transition state of unfolding has a 45% greater heat capacity than F, indicating that significant hydration of the hydrophobic core occurs only after the rate-limiting step of unfolding. PMID:9315868

Agashe, V R; Schmid, F X; Udgaonkar, J B

1997-10-01

225

Complexation in reactions of cycloalkane solvent holes. II. reactions of cis- and trans-decalin{lg_bullet}+ with benzene.  

SciTech Connect

Solvent holes in liquid cis- and trans-decalin form metastable complexes with benzene, which are probably solvation complexes of monomer radical cations of benzene. At 25 C, the rate constants of formation of the complexes are, for trans- and cis-decalin respectively 1.1 x 10{sup 11} and 3.6 x 10{sup 10} M{sup -1} s{sup -1}, and the natural lifetime of the complex is 7 ns for trans- and 50 ns for cis-decalin. Thermodynamic potentials for the complexation are determined. The heat of the complex formation is {approx}26 kJ/mol for trans- and {approx}-18 kJ/mol for cis-decalin. In cis-decalin, the complexes are more stable because of near-zero entropy of the complex formation. The complex decays by proton or H atom transfer with activation energy {approx}10 kJ/mol (which yields a benzonium cation) or in a reactive encounter with a second benzene molecule (which yields a benzene dimer cation). Laser excitation of the dimer cation with a 1.165- or 2.33 eV photon causes valence band electron transfer and injection of a free solvent hole.

Shkrob, I. A.; Sauer, M. C., Jr.; Trifunac, A. D.; Chemistry

2000-01-01

226

Effects of online advertising format and persuasion knowledge on audience reactions  

Microsoft Academic Search

In an experiment (N = 99), effects of subtle and prominent online advertising formats, respectively sponsored content and banner ads, on audience reactions toward the advertisement are tested. In addition, the role of several persuasion knowledge elements such as understanding of persuasive intent and ad skepticism in processing online advertising formats is investigated. Results show that participants find the sponsored content more

Karolina Tutaj; Eva A. van Reijmersdal

2012-01-01

227

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

228

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

229

Manganese(III)-promoted reactions for formation of carbon–heteroatom bonds  

Microsoft Academic Search

Manganese(III) reagent is an important one- electron oxidant for initiation of free-radical reactions and formation of carbon–carbon\\u000a bonds. The reactions are usually carried out under mild conditions, have high regio- and stereo-selectivities, and good functional\\u000a group tolerance. Summarized in this article are the developments of manganese (III)-based reactions for the formation of carbon–heteroatom\\u000a bonds including carbon–oxygen, carbon–phosphorus, carbon–sulfur, and carbon–nitrogen

Xiang-Qiang Pan; Jian-Ping Zou; Wei Zhang

2009-01-01

230

Possible self-complexity and affective reactions to goal-relevant evaluation.  

PubMed

The complexity of people's self-concept appears to be inversely related to the intensity of their reactions to evaluative feedback about present goals and abilities (Linville, 1985, 1987). The idea that the complexity of individuals' possible self-concept similarly mediates reactions to feedback regarding future goals was investigated. Two preliminary studies suggested that complexity of the actual self only explains 20% to 30% of the variance in possible self-complexity. Three studies were conducted. Support was found for the idea that possible self-complexity mediates affective reactions to evaluative feedback about future goals and actual self-complexity mediates affective reactions to evaluative feedback about present goals. The findings underscore the independent roles of the organization of actual and possible self-concepts in affective processes. PMID:1494985

Niedenthal, P M; Setterlund, M B; Wherry, M B

1992-07-01

231

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

NASA Astrophysics Data System (ADS)

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

Alavi, Saman; Taghikhani, Mahdi

2012-06-01

232

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

PubMed

EPR was used to study the influence of formate on the electron acceptor side of photosystem II (PSII) from Thermosynechococcus elongatus. Two new EPR signals were found and characterized. The first is assigned to the semiquinone form of Q(B) interacting magnetically with a high spin, non-heme-iron (Fe²(+), S=2) when the native bicarbonate/carbonate ligand is replaced by formate. This assignment is based on several experimental observations, the most important of which were: (i) its presence in the dark in a significant fraction of centers, and (ii) the period-of-two variations in the concentration expected for Q(B)(•-) when PSII underwent a series of single-electron turnovers. This signal is similar but not identical to the well-know formate-modified EPR signal observed for the Q(A)(•-)Fe²(+) complex (W.F.J. Vermaas and A.W. Rutherford, FEBS Lett. 175 (1984) 243-248). The formate-modified signals from Q(A)(•-)Fe²(+) and Q(B)(•-)Fe²(+) are also similar to native semiquinone-iron signals (Q(A)(•-)Fe²(+)/Q(B)(•-)Fe²(+)) seen in purple bacterial reaction centers where a glutamate provides the carboxylate ligand to the iron. The second new signal was formed when Q(A)(•-) was generated in formate-inhibited PSII when the secondary acceptor was reduced by two electrons. While the signal is reminiscent of the formate-modified semiquinone-iron signals, it is broader and its main turning point has a major sub-peak at higher field. This new signal is attributed to the Q(A)(•-)Fe²(+) with formate bound but which is perturbed when Q(B) is fully reduced, most likely as Q(B)H? (or possibly Q(B)H(•-) or Q(B)(²•-)). Flash experiments on formate-inhibited PSII monitoring these new EPR signals indicate that the outcome of charge separation on the first two flashes is not greatly modified by formate. However on the third flash and subsequent flashes, the modified Q(A)(•-)Fe²(+)Q(B)H? signal is trapped in the EPR experiment and there is a marked decrease in the quantum yield of formation of stable charge pairs. The main effect of formate then appears to be on Q(B)H? exchange and this agrees with earlier studies using different methods. PMID:21036139

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

2010-10-29

233

Methane formation in the reaction of carbon monoxide and hydrogen in the presence of iridium and osmium clusters  

SciTech Connect

In a previous publication, homogeneous solutions of Ir/sub 4/-(CO)/sub 12/ or Os/sub 3/(CO)/sub 12/ in toluene were reported to catalyze the formation of methane from carbon monoxide and hydrogen. Also, the rate of methane formation was found to be significantly enhanced by the addition of phosphorus ligands, especially trimethyl phosphite. In this paper, we report the results of a more quantitative investigation. Less than stoichiometric amounts of methane were formed by hydrogenation of carbon monoxide within a 5-day period. Isotopic labeling studies (/sup 13/C and /sup 2/H) have established that the enhanced formation of methane in the presence of trimethyl phosphite arises from a trimethyl phosphite and hydrogen reaction catalyzed by the iridium and osmium complexes.

Schunn, R.A. (E.I. du Pont de Nemours and Co., Wilmington, DE); Demitras, G.C.; Choi, H.W.; Muetterties, E.L.

1981-11-01

234

Deciphering complex soil/site formation in sands  

NASA Astrophysics Data System (ADS)

This paper summarizes aspects of the geoarchaeological research at two adjacent multi-component archaeological sites, 13JP86 and 13JP87, along Indian Creek in central Iowa, USA. The sites, both recently salvaged but now destroyed, formed in late Pleistocene sands reworked from glacial sediments that emanated from the wasting Des Moines Lobe glacier some 13,000-14,000 years ago. The soils contained shallowly dispersed and mixed artifacts that span the Paleoindian-to-historic cultural spectrum. In open areas, as at Indian Creek, site formation processes equate to natural soil genetic processes, plus human imprints. Cultural materials, once deposited, become part of the soil and subject to dynamic soil processes. These soils had reasonably well expressed Ap, A, and E horizons that collectively formed thick one-layered biomantles, underlain by well expressed argillic Bt horizons. The biomantles had been well bioturbated, deeply in some pedons, but still exhibited organized A and E horizons. The Bt horizons were also bioturbated, though less so, and consisted of multiple thin to thick sandy clay bands, termed illuvial clay lamellae (icl's). The icl's contained modest to appreciable amounts of illuvial clay as bridges between grains, and as diffuse splotches and blebs separated by less clayey, E horizon-like interlamellar sandy zones. Deeper and less bioturbated E-like sandy zones had accumulated so much clay that they had coalesced with icl's into thick, complexly banded argillic Bt horizons. The process histories of the sandy pedons were obviously extremely complex. The geoarchaeological aspects of the project, which were mainly complex pedologic ones, were largely interpreted by drawing on the genetic principles of dynamic denudation to explain soil/site evolution. Many questions were raised, and most were answered under these principles. New concepts and perspectives were gained in this study, and the resulting interpretive scenarios carry explanatory implications for sandy soils everywhere, whether charged with cultural materials or not.

Johnson, D. L.; Johnson, D. N.; Benn, D. W.; Bettis, E. A., III

2008-10-01

235

An efficient and recyclable water-soluble cyclopalladated complex for aqueous Suzuki reactions under aerial conditions  

Microsoft Academic Search

Several water-soluble cyclopalladated complexes with five- or six-membered rings have been prepared as air-stable solids from Schiff base ligands bearing an N-phenyl sulfonate groups. Cyclopalladated complexes with six-membered rings show high catalytic efficiency for the Suzuki reactions of aryl bromides with phenylboronic acid in aqueous solvents under mild conditions. Palladium complex 1 can be used for five reaction cycles in

Jin Zhou; Xiaoyan Li; Hongjian Sun

2010-01-01

236

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

2013-04-19

237

Polyelectrolyte complexes of chitosan: formation, properties and applications  

NASA Astrophysics Data System (ADS)

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.

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

2008-09-01

238

Adhesion and formation of microbial biofilms in complex microfluidic devices  

SciTech Connect

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

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

2012-01-01

239

In vivo analysis of synaptonemal complex formation during yeast meiosis.  

PubMed Central

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

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

2004-01-01

240

Simulating phase formation during exothermic reactions in Al/Ni and Al/Zr multilayered foils  

NASA Astrophysics Data System (ADS)

Reactive multilayered foils are composed of thousands of alternating micro- to nano- scale layers of elements which have a large negative enthalpy of mixing. When a small pulse of energy (such as an electric spark or a thermal pulse) is provided, highly exothermic, self-propagating chemical reactions can be triggered. Both theoretical models and experimental data indicate that even a relatively small amount of premixing can have a dramatic effect on the heats and velocities of the propagating reaction front. We have implemented molecular dynamics simulation to study the phase transformation sequence during multilayered reactions and to elucidate how premixing can affect the sequence of phase formation during such reactions.

Xu, Rong-Guang; Falk, Michael L.; Sheng, Hong-Wei

2011-03-01

241

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

242

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

PubMed

The synthesis of a new class of organogold species containing a peroxo moiety is reported. Complexes [Au(IPr)(OO(t)Bu)] and [Au(SIPr)(OO(t)Bu)] have been synthesised via a straightforward methodology using the parent gold(i) hydroxide complexes as synthons. These complexes have been successfully used in oxygen-transfer reactions to triphenylphosphine. PMID:24107923

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

2013-10-22

243

Photoinduced spin-polarized radical pair formation in a DNA photolyase.substrate complex at low temperature.  

PubMed

Electron spin polarization is a phenomenon characterized by anomalous line intensities (emission or enhanced absorption) in the EPR spectrum. It is highly diagnostic of radical pairs, such as those formed in photoinduced electron transfer reactions. Electron spin polarization behavior (E/A pattern) is observed in light-modulated EPR spectra obtained at 4 K with fully reduced DNA photolyase.substrate complexes. Similar results are obtained with complexes formed with native enzyme or reconstituted enzyme containing fully reduced flavin as its only chromophore. No signal is observed for fully reduced enzyme or substrate alone. The results suggest that the electron spin polarization signal is due to photoinduced formation of a flavin/substrate radical pair (FADH./T < > T.-); splitting of T < > T.- does not occur at 4 K, and the radical pair can only undergo back-electron-transfer reactions. The data are consistent with the proposal that electron transfer initiates DNA repair in the photolyase reaction. PMID:7857939

Rustandi, R R; Jorns, M S

1995-02-21

244

THE SHROUD OF TURIN: AN AMINO-CARBONYL REACTION (MAILLARD REACTION) MAY EXPLAIN THE IMAGE FORMATION  

Microsoft Academic Search

Summary. The Shroud of Turin is a large piece of linen that shows the faint image of a man on its surface: it has been claimed to be the shroud of Jesus. Here we report evidences that colour can be produced by reactions between reducing sugars, left on the cloth by the manufacturing procedure, and amines deriving from the decomposition

Raymond N. Rogers; Anna Arnoldi

245

Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation.  

PubMed Central

Islet amyloid polypeptide (IAPP), or 'amylin', is co-stored with insulin in secretory granules of pancreatic islet beta-cells. In Type 2 diabetes, IAPP converts into a beta-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop beta-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation.

Jaikaran, Emma T A S; Nilsson, Melanie R; Clark, Anne

2004-01-01

246

Substitution reactions in dinuclear Ru-Hbpp complexes: an evaluation of through-space interactions.  

PubMed

The synthesis of new dinuclear complexes of the general formula in,in-{[Ru(II)(trpy)(L)](?-bpp)[Ru(II)(trpy)(L')]}(3+) [bpp(-) is the bis(2-pyridyl)-3,5-pyrazolate anionic ligand; trpy is the 2,2':6',2?-terpyridine neutral meridional ligand, and L and L' are monodentate ligands; L = L' = MeCN, 3a(3+); L = L' = 3,5-lutidine (Me(2)-py), 3c(3+); L = MeCN, L' = pyridine (py), 4(3+)], have been prepared and thoroughly characterized. Further, the preparation and isolation of dinuclear complexes containing dinitrile bridging ligands of the general formula in,in-{[Ru(II)(trpy)](2)(?-bpp)(?-L-L)}(3+) [?-L-L = 1,4-dicyanobutane (adiponitrile, adip), 6a(3+); 1,3-dicyanopropane (glutaronitrile, glut), 6b(3+); 1,2-dicyanoethane (succinonitrile; succ), 6c(3+)] have also been carried out. In addition, a number of homologous dinuclear complexes previously described, containing the anionic bis(pyridyl)indazolate (bid(-)) tridentate meridional ligand in lieu of trpy, have also been prepared for comparative purposes. In the solid state, six complexes have been characterized by X-ray crystallography, and in solution, all of them have been spectroscopically characterized by NMR and UV-vis spectroscopy. In addition, their redox properties have also been investigated by means of cyclic voltammetry and differential pulse voltammetry and show the existence of two one-electron waves assigned to the formation of the II,III and III,III species. Dinitrile complexes 6a(3+), 6b(3+), and 6c(3+) display a dynamic behavior involving their enantiomeric interconversion. The energy barrier for this interconversion can be controlled by the number of methylenic units between the dinitrile ligand. On the other hand, pyridyl complexes in,in-{[Ru(II)(T)(py)](2)(?-bpp)}(n+) (T = trpy, n = 3, 3b(3+); T = bid(-), n = 1, 3b'(+)) and 3c(3+) undergo two consecutive substitution reactions of their monodentate ligands by MeCN.The substitution kinetics have been monitored by (1)H NMR and UV-vis spectroscopy and follow first-order behavior with regard to the initial ruthenium complex. For the case of 3b(3+), the first-order rate constant k(1) = (2.9 ± 0.3) × 10(-5) s(-1), whereas for the second substitution, the k obtained is k(2) = (1.7 ± 0.7) × 10(-6) s(-1), both measured at 313 K. Their energies of activation at 298 K are 114.7 and 144.3 kJ mol(-1), respectively. Density functional theory (DFT) calculations have been performed for two consecutive substitution reactions, giving insight into the nature of the intermediates. Furthermore, the energetics obtained by DFT calculations of the two consecutive substitution reactions agree with the experimental values obtained. The kinetic properties of the two consecutive substitution reactions are rationalized in terms of steric crowding and also in terms of through-space interactions. PMID:22242940

Planas, Nora; Christian, Gemma; Roeser, Stephan; Mas-Marzá, Elena; Kollipara, Mohan-Rao; Benet-Buchholz, Jordi; Maseras, Feliu; Llobet, Antoni

2012-01-13

247

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

2012-05-14

248

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

PubMed

A computational study of peptide bond formation from gas-phase ion-molecule reactions has been carried out. We have considered the reaction between protonated glycine and neutral glycine, as well as the reaction between two neutral glycine molecules for comparison purposes. Two different mechanisms, concerted and stepwise, were studied. Both mechanisms show significant energy barriers for the neutral reaction. The energy requirements for peptide bond formation are considerably reduced upon protonation of one of the glycine molecules. For the reaction between neutral glycine and N-protonated glycine the lowest energy barrier is observed for the concerted mechanism. For the reaction between neutral glycine and protonated glycine at carbonyl oxygen, the preferred mechanism is the stepwise one, with a relatively small energy barrier (23 kJ mol(-1) at 0 K) and leading to the lowest-lying protonated glycylglycine isomer. In the case that the reaction could be initiated by protonated glycine at hydroxyl oxygen the process would be barrier-free and clearly exothermic. In that case peptide bond formation could take place even under interstellar conditions if glycine is present in space. PMID:23817675

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

2013-08-21

249

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

250

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

251

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

PubMed

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 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°C and 300°C) surfaces at incident energies above about 50eV. This finding suggested an activation barrier or reaction endothermicity of the heterogeneous reaction of about 3-3.5 eV. The main process in N2+ or N+ interaction with the surfaces is ion neutralization; the probability of forming the reaction product HCN+ was very roughly estimated for both N2+ and N+ ions to about one in 104 collisions with the surfaces. PMID:23614645

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

2013-04-24

252

Binding of polyanions by biogenic amines. II. Formation and stability of protonated putrescine and cadaverine complexes with carboxylic ligands  

Microsoft Academic Search

The formation and stability of protonated diamines–carboxylic ligand complexes was studied potentiometrically (H+-glass electrode). Species formed are ALHr (A=cadaverine, putrescine, L=acetate, malate, tartrate, malonate, citrate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate and glutamate; r=1...m+1, where m is the maximum degree of protonation of the carboxylic ligand), and their stability is a function of charges involved in the formation reaction. For the equilibrium HiAi++HjL(j?z)=ALH(i+j?z)i+j the

Concetta De Stefano; Antonio Gianguzza; Roberta Maniaci; Daniela Piazzese; Silvio Sammartano

1998-01-01

253

Rate constants for the reactions of benzene-chlorine atom ?-complexes with alcohols in carbon tetrachloride  

Microsoft Academic Search

The reactivity and selectivity of benzene-chlorine atom ?-complexes for hydrogen atom abstraction from various alcohols were investigated. Benzene-chlorine atom ?-complexes were produced in liquid carbon tetrachloride using the technique of pulse radiolysis at room temperature. The effect of the concentration of benzene and absorbed doses on the formation and decay kinetics were examined and the equilibrium constant of the complex

T. Sumiyoshi

1997-01-01

254

Multiple Equilibria in Complex Chemical Reaction Networks: II. The Species-Reaction Graph  

Microsoft Academic Search

For mass action kinetics, the capacity for multiple equilibria in an isothermal homo- geneous continuous ?ow stirred tank reactor is determined by the structure of the underlying network of chemical reactions. We suggest a new graph-theoretical method for discriminating between com- plex reaction networks that can admit multiple equilibria and those that cannot. In particular, we associate with each network

Gheorghe Craciun; Martin Feinberg

2006-01-01

255

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

2012-02-22

256

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

PubMed

In this study, a mechanism for the uncatalyzed reaction between acetone and hydrogen peroxide is postulated. The reaction leads to the formation of the important homemade explosives collectively known as cyclic acetone peroxides (CAP). The proposed mechanistic scheme is based on Raman, GC-MS, and nuclear magnetic resonance measurements, and it is supported by ab initio density functional theory (DFT) calculations. The results demonstrate that the proposed mechanism for the uncatalyzed formation reaction of CAP occurs in three steps: monomer formation, polymerization of the 2-hydroperoxipropan-2-ol monomer, and cyclization. The temporal decay of the intensities of important assigned-bands is in excellent agreement with the proposed mechanism. Previous reports also confirm that the polymerization step is favored in comparison to other possible pathways. PMID:24050655

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

2013-10-04

257

Rate constants for reactions of alkyl radicals with water and methanol complexes of triethylborane.  

PubMed

Reactions of secondary alkyl radicals with triethylborane and several of its complexes were studied. The H-atom transfer reactions from Et3B-OH2 and Et3B-OD2 were suppressed by addition of pyridine to the reaction mixture. Rate constants for reactions of secondary alkyl radicals with triethylborane and its complexes with water, deuterium oxide, methanol, and THF at ambient temperature were determined by radical clock methods. Cyclization of the 1-undecyl-5-hexenyl radical and ring opening of the 1-cyclobutyldodecyl radical were evaluated as clock reactions. The cyclobutylcarbinyl radical ring opening had the appropriate velocity for relatively precise determinations of the ratios of rate constants for H-atom transfer trapping and rearrangement, and these ratios combined with an estimated rate constant for the cyclobutylcarbinyl radical ring opening gave absolute values for the rate constants for the H-atom transfer reactions. For example, the triethylborane-water complex reacts with a secondary alkyl radical in benzene at 20 degrees C with a rate constant of 2 x 10(4) M(-1) s(-1). Variable temperature studies with the Et3B-CH3OH complex in toluene indicate that the hydrogen atom transfer reaction has unusually high entropic demand, which results in substantially more efficient hydrogen atom transfer trapping reactions in competition with radical ring opening and cyclization reactions at reduced temperatures. PMID:17579450

Jin, Jing; Newcomb, Martin

2007-06-19

258

Production of complex particles in low energy spollation and in fragmentation reactions by in-medium random clusterization  

NASA Astrophysics Data System (ADS)

Rules for in-medium complex particle production in nuclear reactions are proposed. These rules have been implemented in two models to simulate nucleon-nucleus and nucleus-nucleus reactions around the Fermi energy. Our work emphasizes the effect of randomness in cluster formation, the importance of the nucleonic Fermi motion as well as the role of conservation laws. The concepts of total available phase-space and explored phase-space under constraint imposed by the reaction are clarified. The compatibility of experimental observations with a random clusterization is illustrated in a schematic scenario of a proton-nucleus collision. The role of randomness under constraint is also illustrated in the nucleus-nucleus case.

Lacroix, Denis; Durand, Dominique

2005-10-01

259

Reaction of a Copper(II)-Nitrosyl Complex with Hydrogen Peroxide: Phenol Ring Nitration through a Putative Peroxynitrite Intermediate.  

PubMed

Copper(II) complex, 1, with the histidine-derived ligand L (L = methyl 2-(2-hydroxybenzylamino)-3-(1H-imidazol-5-yl)propanoate) has been synthesized and characterized. Single-crystal structure determination reveals a diphenolato-bridged dicopper(II) core in 1. Addition of (•)NO to an acetonitrile solution of 1 affords the corresponding mononuclear copper(II)-nitrosyl complex, 2. In the presence of H2O2, 2 results in formation of the corresponding copper(I)-peroxynitrite. Formation of peroxynitrite ((-)OONO) intermediate is evident from its characteristic phenol ring nitration reaction which resembles the tyrosine nitration in biological systems. Further, isolation of nitrate (NO3(-)) as the decomposition product from 2 at room temperature also supports the involvement of (-)OONO intermediate. PMID:24059697

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

2013-09-23

260

Cyanogen bromide formation from the reactions of monobromamine and dibromamine with cyanide ion.  

PubMed

Cyanide ion (CN-) was found to reactwith monobromamine (NH2Br) and dibromamine (NHBr2) according to the reactions NH2Br + CN- + H20 --> NH3 + BrCN + OH- and NHBr2 + CN- + H20 --> NH2Br + BrCN + OH- with respective reaction rate constants of 2.63 x 10(4) M9-10 s(-1) and 1.31 x 10(8) M(-1) s(-1). These values were found to be 10(5)-10(6) times greater than those for the corresponding reactions between chloramine species and CN-. As a result, bromamines, even if present at relatively low concentrations, would tend to outcompete chloramines in reacting with CN-, and thus, the formation of BrCN would predominate that of ClCN through these reaction mechanisms. The NH2Br reaction was found to be general-acid-catalyzed. The third-order catalysis rate constants for H+, H2PO4-, HPO4(2-), H3BO3, and NH4+ correlated linearly with their corresponding acid dissociation constants, consistent with the Brønsted-Pedersen relationship. The NHBr2 reaction did not undergo catalysis. A model was developed to predict the concentrations of bromamines over time on the basis ofthe above two reactions with CN- and bromamine formation/decomposition reactions previously reported. PMID:16683592

Lei, Hongxia; Minear, Roger A; Mariñas, Benito J

2006-04-15

261

Automatic Method for Identifying Reaction Coordinates in Complex Systems †  

Microsoft Academic Search

To interpret simulations of a complex system to determine the physical mechanism of a dynamical process, it is necessary to identify the small number of coordinates that distinguish the stable states from the transition states. We develop an automatic method for identifying these degrees of freedom from a database of candidate physical variables. In the method neural networks are used

Ao Ma; Aaron R. Dinner

2005-01-01

262

Pattern formation in reaction-diffusion models with spatially inhomogeneous diffusion coefficients  

Microsoft Academic Search

Reaction-diffusion models for biological pattern formation have been studied extensively in a variety of embryonic and ecological contexts. However, despite experimental evidence pointing to the existence of spatial inhomogeneities in various biological systems, most models have only been considered in a spatially homogeneous environment. The authors consider a two-chemical reaction-diffusion mechanism in one space dimension in which one of the

PHILIP K. MAINI; DEBBIE L. BENSON; JONATHAN A. SHERRATT

1992-01-01

263

Ligand-induced formation of a transient tryptophan synthase complex with ??? subunit stoichiometry.  

PubMed

The prototypical tryptophan synthases form a stable heterotetrameric ???? complex in which the constituting TrpA and TrpB1 subunits activate each other in a bidirectional manner. The hyperthermophilic archaeon Sulfolobus solfataricus does not contain a TrpB1 protein but instead two members of the phylogenetically distinct family of TrpB2 proteins, which are encoded within (sTrpB2i) and outside (sTrpB2a) the tryptophan operon. It has previously been shown that sTrpB2a does not functionally or structurally interact with sTrpA, whereas sTrpB2i substantially activates sTrpA in a unidirectional manner. However, in the absence of catalysis, no physical complex between sTrpB2i and sTrpA could be detected. In order to elucidate the structural requirements for complex formation, we have analyzed the interaction between sTrpA (?-monomer) and sTrpB2i (??-dimer) by means of spectroscopy, analytical gel filtration, and analytical ultracentrifugation, as well as isothermal titration calorimetry. In the presence of the TrpA ligand glycerol 3-phosphate (GP) and the TrpB substrate l-serine, sTrpA and sTrpB2i formed a physical complex with a thermodynamic dissociation constant of about 1 ?M, indicating that the affinity between the ?- and ??-subunits is weaker by at least 1 order of magnitude than the affinity between the corresponding subunits of prototypical tryptophan synthases. The observed stoichiometry of the complex was 1 subunit of sTrpA per 2 subunits of sTrpB2i, which corresponds to a ??? quaternary structure and testifies to a strong negative cooperativity for the binding of the ?-monomers to the ??-dimer. The analysis of the interaction between sTrpB2i and sTrpA in the presence of several substrate, transition state, and product analogues suggests that the ??? complex remains stable during the whole catalytic cycle and disintegrates into ?- and ??-subunits upon the release of the reaction product tryptophan. The formation of a transient tryptophan synthase complex, together with the observed low affinity of sTrpB2i for l-serine, couples the rate of tryptophan biosynthesis in S. solfataricus to the cytosolic availability of l-serine. PMID:21090805

Ehrmann, Alexander; Richter, Klaus; Busch, Florian; Reimann, Julia; Albers, Sonja-Verena; Sterner, Reinhard

2010-12-06

264

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

265

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...

266

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

267

New reactions involving the oxidative O-, N-, and C-phosphorylation of organic compounds by phosphorus and phosphides in the presence of metal complexes  

Microsoft Academic Search

The mechanisms of new catalytic reactions leading to the formation of di-, and tri-alkyl phosphates, di- and tri-alkyl phosphites, phosphoramidites, phosphazenes, phosphines, and phosphine oxides from hydrogen, copper, and zinc phosphides and white and red phosphorus are analysed. The mechanisms of the activation of the reactants by metal complexes and of the reactions involving the oxidative P-O, P-N, and P-C

Ya A. Dorfman; M. M. Aleshkova; G. S. Polimbetova; L. V. Levina; T. V. Petrova; R. R. Abdreimova; D. M. Doroshkevich

1993-01-01

268

Conductive Anodic Filament Formation Part II: Electrochemical Reactions Leading to CAF  

NASA Astrophysics Data System (ADS)

Conductive anodic filament (CAF) formation has been studied for a number of years, but the mechanism of its formation has not previously been defined. In 2002, Ready identified CAF as atacamite, Cu2(OH)3Cl. Electrochemical studies have shown that both CuCl and CuCl{2/-} participate in the formation of Cu2(OH)3Cl, with the predominating species being CuCl. This paper proposes a mechanism for CAF formation based on x-ray photoelectron spectroscopy. The data show that CuCl is the precursor to the formation of Cu2(OH)3Cl in the presence of oxygen and water. Earlier, Meeker and Lu Valle had proposed that CAF failure is best represented by two competing reactions: the formation of a copper chloride corrosion compound (now identified as Cu2(OH)3Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single nonreversible reaction.

Caputo, Antonio; Turbini, Laura J.; Perovic, Doug D.

2010-01-01

269

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

PubMed Central

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

Stang, Erik M.; White, M. Christina

2011-01-01

270

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

PubMed

Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-?-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear metallohydrolases and use PAP, the OP-degrading enzyme from Agrobacterium radiobacter (OPDA), and GpdQ as representative systems because they illustrate both the diversity and similarity of the reactions catalyzed by this family of enzymes. The majority of binuclear metallohydrolases utilize metal ion-activated water molecules as nucleophiles to initiate hydrolysis, while some, such as alkaline phosphatase, employ an intrinsic polar amino acid. Here we only focus on catalytic strategies applied by the former group. PMID:22698580

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

2012-06-14

271

Catalytic oxidation reactions of aromatic diamines by transition metal complexes  

Microsoft Academic Search

The catalytic reactions of M(TPP)Cl (M = Fe (1), Mn (2)), Fe(TMP)Cl (3), and Fe(TDCPP)Cl (4) (H2TPP = 5,10,15,20-tetraphenylporphyrin; H2TMP = 5,10,15,20-tetramesitylporphyrin; H2TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin) with 2,4-diaminotoluene (5) and p-phenylenediamine (6) were carried out using t-BuOOH (3 M isooctane solution) as oxidant. With the former substrate, the nitro derivatives 2-amino-4-nitrotoluene (5a) and 2,4-dinitrotoluene (5b) (total yield of 5a + 5b

Francesca Porta; Fabio Colonna; Francesca Arciprete; Stefano Banfi; Fausta Coppa

1996-01-01

272

The thermodynamic characteristics of complex formation between Cd2+ and iminodisuccinic acid in aqueous solution  

NASA Astrophysics Data System (ADS)

The enthalpies of complex formation between iminodisuccinic acid (H4L) and the Cd2+ ion were determined calorimetrically at 298.15 K and ionic strengths 0.5, 1.0, and 1.5 (KNO3). The thermodynamic characteristics of formation of CdL2- and CdHL- complexes at fixed and zero ionic strength values were calculated.

Lytkin, A. I.; Chernyavskaya, N. V.; Litvinenko, V. E.; Nikol'Skii, V. M.

2010-06-01

273

Nidogen mediates the formation of ternary complexes of basement membrane components  

Microsoft Academic Search

Nidogen mediates the formation of ternary complexes of basement membrane components. Using a recombinant nidogen we have probed the calcium binding potential of various nidogen domains, examined the binding of nidogen to various basement membrane proteins and assessed the ability of nidogen to mediate the formation of ternary complexes between laminin and heparan sulfate proteoglycan and collagen IV and laminin.

Monique Aumailley; Cristina Battaglia; Ulrike Mayer; Dieter Reinhardt; Roswitha Nischt; Rupert Timpl; Jay W Fox

1993-01-01

274

Light saturation curves show competence of the water splitting complex in inactive Photosystem II reaction centers  

Microsoft Academic Search

Photosystem II complexes of higher plants are structurally and functionally heterogeneous. While the only clearly defined structural difference is that Photosystem II reaction centers are served by two distinct antenna sizes, several types of functional heterogeneity have been demonstrated. Among these is the observation that in dark-adapted leaves of spinach and pea, over 30% of the Photosystem II reaction centers

Ladislav Nedbal; Cynthia Gibas; John Whitmarsh

1991-01-01

275

Formation of Core-Shell Structured Composite Microparticles via Cyclic Gas-Solid Reactions.  

PubMed

This work reports a novel low-cost and environmental-friendly preparation strategy for core-shell structured composite microparticles and discusses its formation mechanism. Different from most conventional strategies, which involve coating or coating-like processes, this reported strategy uses irreversible solid-phase ionic diffusion in a gas-solid reaction cycle (e.g., reduction and oxidation of Fe) to gradually move the shell material from a core-and-shell material mixture microparticle to the surface. Without the need for solvent as do many conventional processes, this novel process only involves gas-solid reactions, which reduces environmental impact. To substantiate this conceived strategy, a micrometer-sized microparticle made up of a mixture of Fe2O3 and Al2O3 powders is first reduced by H2 and then oxidized by O2 over 50 cycles at 900 °C. These reactions are known to proceed mainly through the diffusion of solid-phase Fe cations. SEM and EDX analyses verify the formation of an Al2O3 core-Fe2O3 shell structure at the end of the 50 reaction cycles. If the cyclic reactions of a microparticle proceed mainly through the diffusion of gaseous-reactant-derived O anions such as the mixture of Fe2O3 and TiO2 instead of solid-phase Fe cation diffusion, no formation of the core-shell structure is observed in the resulting microparticle. These two opposing results underscore the dominating role of solid-phase ionic diffusion in the formation of the core-shell structure. A 2-D continuum diffusion model is applied to account for the inter-Fe-particle bridging and directional product layer growth phenomena during an oxidation reaction. The simulation further verifies the conceived core-shell formation strategy. PMID:24044419

Sun, Zhenchao; Zhou, Qiang; Fan, Liang-Shih

2013-09-27

276

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

NASA Astrophysics Data System (ADS)

Positronium formation in triphenylphosphine oxide (TPPO), triphenylmethanol (TPM), and systems [TPPO(1-X)?TPMX] has been studied. The low probability of positronium formation in complex [TPPO0.5?TPM0.5] was attributed to strong hydrogen bond and sixfold phenyl embrace interactions. These strong interactions in complex reduce the possibility of the n- and ?-electrons to interact with positrons on the spur and consequently, the probability of positronium formation is lower. The ?3 parameter and free volume (correlated to ?3) were also sensitive to the formation of hydrogen bonds and sixfold phenyl embrace interactions within the complex. For physical mixture the positron annihilation parameters remained unchanged throughout the composition range.

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

2012-06-01

277

Formation and use of poly-L-histidine-catalase complexes  

Microsoft Academic Search

Insoluble complexes of poly-L-histidine (polyhistidine) and catalase were prepared by mixing the two reactants together in solution at pH 5.5 and subsequently elevating the pH to approximately 7.0, at which point they precipitated. Complexes formed at optimal ratios of polyhistidine to catalase contained essentially all of the catalase present in the original solution. The catalase present in such complexes contained

Douglas Gibbs; James Varani; Isaac Ginsburg

1989-01-01

278

Reaction of a terminal phosphinidene complex with azulenes: eta1-complexes, C--H bond insertions, and 1,4-adducts.  

PubMed

Reaction of an in situ generated phosphinidene complex [PhPW(CO)(5)] with the aromatic azulene and guaiazulene leads to unexpected 1,4-adducts of the seven-membered ring and to C--H bond insertion of the five-membered ring. A DFT analysis suggests that the reaction is initiated by formation of a eta(1)-complex between the phosphinidene and the five-membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn- and anti-1,2-adducts. These undergo pericyclic 1,7-sigmatropic rearrangements with remarkably low barriers to give 1,4-adducts, with an inverted configuration at the phosphorus center. An X-ray crystal structure is presented for one of the 1,4-adducts of guaiazulene. The other two eta(1)-complexes insert with modest barriers into a C--H bond of the five-membered ring. PMID:15195304

Bulo, Rosa E; Ehlers, Andreas W; de Kanter, Frans J J; Schakel, Marius; Lutz, Martin; Spek, Anthony L; Lammertsma, Koop; Wang, Bing

2004-06-01

279

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

280

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

PubMed

The plasma concentration of the placentally derived proMBP (proform of eosinophil major basic protein) increases in pregnancy, and three different complexes containing proMBP have been isolated from pregnancy plasma and serum: a 2:2 complex with the metalloproteinase, PAPP-A (pregnancy-associated plasma protein-A), a 2:2 complex with AGT (angiotensinogen) and a 2:2:2 complex with AGT and complement C3dg. In the present study we show that during human pregnancy, all of the circulating proMBP exists in covalent complexes, bound to either PAPP-A or AGT. We also show that the proMBP-AGT complex constitutes the major fraction of circulating HMW (high-molecular weight) AGT in late pregnancy, and that this complex is able to further associate with complement C3 derivatives post-sampling. Clearance experiments in mice suggest that complement C3-based complexes are removed faster from the circulation compared to monomeric AGT and the proMBP-AGT complex. Furthermore, we have used recombinant proteins to analyse the formation of the proMBP-PAPP-A and the proMBP-AGT complexes, and we demonstrate that they are competing reactions, depending on the same cysteine residue of proMBP, but differentially on the redox potential, potentially important for the relative amounts of the complexes in vivo. These findings may be important physiologically, since the biochemical properties of the proteins change as a consequence of complex formation. PMID:23033876

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

2013-01-01

281

From snowflake formation to growth of bacterial colonies II: Cooperative formation of complex colonial patterns  

NASA Astrophysics Data System (ADS)

In nature, bacterial colonies must often cope with hostile environmental conditions. To do so they have developed sophisticated cooperative behaviour and intricate communication capabilities, such as direct cell- cell physical interactions via extra-membrane polymers, collective production of extracellular 'wetting' fluid for movement on hard surfaces, longrange chemical signalling such as quorum sensing and chemotactic (bias of movement according to gradient of chemical agent) signalling, collective activation and deactivation of genes and even exchange of genetic material. Utilizing these capabilities, the bacterial colonies develop complex spatio-temporal patterns in response to adverse growth conditions. We present a wealth of beautiful patterns formed during colonial development of various bacterial strains and for different environmental conditions. Invoking ideas from pattern formation in non-living systems and using generic modelling we are able to reveal novel bacterial strategies which account for the salient features of the evolved patterns. Using the models, we demonstrate how bacterial communication leads to colonial self-organization that can only be achieved via cooperative behaviour of the cells. It can be viewed as the action of a singular feedback between the microscopic level (the individual cells) and the macroscopic level (the colony) in the determination of the emerging patterns.

Ben-Jacob, Eshel

1997-03-01

282

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

283

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

2012-12-03

284

Surfactant-Induced Trans-Interface Transportation and Complex Formation of Giant Polyoxomolybdate-Based Clusters  

Microsoft Academic Search

The interaction and complex formation between cationic surfactants dimethyldioctadecylammonium Bromide (DODA-Br) and a polyoxomolybdate (POM)-based giant cluster {Mo72Fe30}, in its both single cluster (in aqueous solution, these clusters exist as anions) format and supramolecular format in aqueous solution, are studies by using laser light scattering (LLS) techniques. DODA\\/{Mo72Fe30} complexes containing basically single {Mo72Fe30} clusters are observed when the {Mo72Fe30} aqueous

Tianbo Liu

2003-01-01

285

Spectroscopic investigation of the novel charge-transfer complex [(phen)(TCNE) 12] formed in the reaction of phenacetin with tetracyanoethylene  

NASA Astrophysics Data System (ADS)

The charge-transfer (CT) interaction of the electron donor phenacetin (phen) and the ?-electron acceptor tetracyanoethylene (TCNE) has been studied in CH 2Cl 2. The results obtained indicate the formation of the novel CT-complex with the general formula [(phen)(TCNE) 12]. The 1:12 stoichiometry of the reaction was based on photometric titration, elemental analysis, infrared, thermal and cyclic voltametry measurements of the formed CT-complex.

AlQaradawi, Siham Y.; Nour, El-Metwally

2005-11-01

286

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

287

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

EPA Science Inventory

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

288

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...

289

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

290

Tandem Chain Extension-Iodomethylation Reactions: Formation of ?-Functionalized ?-Keto Carbonyls  

PubMed Central

Sequential exposure of a zinc-organometallic intermediate, generated through a zinc carbenoid-mediated chain extension reaction of a ?-keto carbonyl, to trimethylsilylchloride and iodine provided regioselective formation of an ?-iodomethyl-?-keto carbonyl. The iodomethyl functionality can be further manipulated to provide side chains that are potential mimics of ?-amino acid side chains.

Pu, Qinglin; Wilson, Emerald; Zercher, Charles K.

2008-01-01

291

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

PubMed

Reactions of DNBF with a series of 2-aminothiazoles (1 a-f) to afford thermodynamically stable C-bonded sigma-adducts have been investigated in acetonitrile. A most significant finding emerged on recording NMR spectra immediately after mixing of equimolar amounts of DNBF and the unsubstituted 2-aminothiazole (1 a) in Me2SO: namely, that the formation of 9 a is preceded by that of a short-lived intermediate species X. From the 1H NMR parameters characterizing this intermediate, as well as the dependence of its lifetime on the experimental conditions-the presence of excess DNBF over 1 a increases the lifetime of X while an excess of base (1 a) accelerates its conversion into 9 a--it is convincingly demonstrated that the structure of X combines the presence of a positively charged Wheland complex moiety (with regard to the thiazole ring) with that of a negatively charged Meisenheimer complex moiety (with regard to the benzofuroxan system). So far, only one intermediate of this type (noted WM) has been successfully characterized, in the reactions of DNBF with 1,3,5-tris(N,N-dialkylamino)benzenes. Among the key features supporting the intermediacy of X along the reaction coordinate leading to 9 a is the fact that the reactions of DNBF with 1 a in the presence of an alcohol (MeOH, EtOH, nPrOH) produce new adducts arising from the addition of an alcohol molecule to the thiazole moiety of WM-1 a. Reflecting the presence of three chiral centres, these species are formed as mixtures of several diastereomers that could all be characterized in their racemic forms in ethanol. These findings generalize the previous report on the formation of Wheland-Meisenheimer carbon-carbon complexes in homocyclic series. PMID:17868171

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

2007-01-01

292

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

293

Influence of Ge substrate crystallinity on Co germanide formation in solid-state reactions  

NASA Astrophysics Data System (ADS)

A strong influence of substrate crystallinity is observed for thin-film Co/Ge reactions. For the detected phases (CoGe, Co5Ge7, and CoGe2), 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 Co5Ge7 was not observed on a-Ge. It is likely that this is due to a promoted CoGe2 formation on a-Ge, resulting in a ~200 °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.; Detavernier, C.; van Meirhaeghe, R. L.; Lauwers, A.; Maex, K.; Lavoie, C.

2007-01-01

294

Double layer formation at the interface of complex plasmas  

SciTech Connect

Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.

Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany)

2008-08-15

295

Influence of complexing agents on texture formation of electrodeposited copper  

Microsoft Academic Search

Ethylenediaminetetraacetic acid (EDTA) and sodium citrate were used as complexing agents for copper coated on Ni–P substrate via the electrodeposited copper procedure. X-ray diffraction (XRD) has been used to examine the effect of complexing agents on the texture of copper films. The experimental results showed that copper films deposited without any additives have two different texture types, (111) and (110)

Bo Hong; Chuan-hai Jiang; Xin-jian Wang

2007-01-01

296

>Cognitive complexity and impression formation in informal social interaction  

Microsoft Academic Search

While awaiting the arrival of the experimenter, pairs of subjects participated in ten minutes of spontaneous casual interaction. The impression which each formed of the other was assessed. Analyses of these impressions compared subjects differing in initial level of cognitive complexity. High complexity subjects, in comparison with noncomplex subjects, formed more differentiated, more abstract, more highly organized, and less evaluatively

Jesse G. Delia; Ruth Anne Clark; David E. Switzer

1974-01-01

297

Bulk Density Logging with Radiations Produced by Fast Neutron Reactions with Formation Atoms. Final Report, February-September 1996.  

National Technical Information Service (NTIS)

This report presents the results of experiments conducted to prove the principle of logging earth formations for bulk density by detecting high-energy gamma rays produced by fast neutron reactions in formation atoms, principally oxygen atoms. This report ...

R. D. Wilson D. C. George J. L. Burnham

1998-01-01

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

SINDO1 study of photocatalytic formation and reactions of OH radicals at anatase particles  

SciTech Connect

Model calculations are performed with the semiempirical MO method SINDO1 to study the photocatalytic primary reactions at anatase particles in aqueous solution. The photochemical formation and migration of hydroxyl radicals is investigated at the particle surface, leading to the formation of hydrogen peroxide or peroxide groups. These reactions represent the first step of the oxidative part of the photocatalytic decomposition of water into oxygen and hydrogen. The anatase particles are simulated by (TiO[sub 2])[sub n](H[sub 2]O)[sub m] clusters with structures corresponding to the anatase solid-state structure. With these clusters the photophysical properties of the anatase particles and the photoreactions are calculated on the SCF and CI level. The photoreactions are described by potential curves along selected reaction coordinates. 44 refs., 16 figs., 3 tabs.

Bredow, T.; Jug, K. (Universitaet Hannover (Germany))

1995-01-05

300

Facile oxygenation reactions of ruthenium acetylide complex containing substituted olefinic group.  

PubMed

Reaction of the ruthenium acetylide complex Cp(dppe)RuC?CCH(OMe)CPh(2)-CH(2)CH=CMe(2) (5a) with oxygen readily gives acetone and the acyl complex 6 in almost quantitative yield. Protonation of 5a is followed by an elimination of MeOH and a hydroxyl addition at C? in the presence of water to give the hydroxycarbene complex 7a. The structures of the acyl complex 6 and the hydroxycarbene complex 7c are fully characterized by single crystal X-ray diffraction analysis. PMID:21380405

Yang, Hsuan; Chung, Chia-Pei; Lin, Ying-Chih; Liu, Yi-Hong

2011-03-04

301

Attaching high charge density metal ions to surfaces and biomolecules. Reaction chemistry of hypodentate cobalt diamine complexes.  

PubMed

Hypodentate diamine cobalt(iii) pentammine complexes [Co(NH3)5(NH2(CH2)nNH3)](ClO4)4 (: : n = 3; : n = 4; : n = 6; : n = 8) have been synthesized via the reaction of [Co(NH3)5(OTf)](OTf)2 (TfOH = CF3SO3H) with the corresponding diamines. The analogous t-boc protected diamine complexes [Co(NH3)5(NH2(CH2)nNHt-boc)](ClO4)3 () were prepared in 4-26% yield. Low yields for the formation of are due to competing side reactions which also gave [Co(NH3)6](3+). Complexes were deprotected using trifluoroacetic acid to give the corresponding hypodentate diamine complexes [Co(NH3)5(NH2(CH2)nNH3)](CF3CO2)0.5(ClO4)3.5 (). HBTU coupling of with N-(t-boc)-l-phenylalanine gave an amino acid functionalized cobalt pentammine complex [Co(NH3)5(NH2(CH2)6NHt-boc)-l-phenylalanine)](ClO4)3 (). All new complexes were characterized using UV-vis and (1)H NMR spectroscopy, and elemental analysis. Grafting of onto 2.4 mm poly(ethylene-co-acrylic acid) (PEAA) beads was achieved via amide coupling. Complex was coupled to thioctic acid via amide coupling and the resulting cobalt disulfide complex [Co(NH3)5(N-(6-aminohexyl)-5-(1,2-dithiolan-3-yl)pentanamide)](ClO4)3 () was attached to 10 nm Au nanoparticles. The amount of cobalt loading onto PEAA beads and Au nanoparticles was determined using ICP-MS and EDX. PMID:24037460

Funk, Aaron R; Goldberg, Efram; Chang, Eddie L; Trammell, Scott A; Knight, D Andrew

2013-10-22

302

The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.  

ERIC Educational Resources Information Center

Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)

Ibanez, Jorge G.; And Others

1988-01-01

303

The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.  

ERIC Educational Resources Information Center

|Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)|

Ibanez, Jorge G.; And Others

1988-01-01

304

Palladium(II) thiocarboxamide complexes: synthesis, characterisation and application to catalytic Suzuki coupling reactions.  

PubMed

A simple route to synthesise palladium(II) complexes from the reaction of N-substituted pyridine-2-thiocarboxamide ligands and PdCl(2)(PPh(3))(2) has been developed. The new complexes are very soluble in common solvents and have been fully characterised (elemental analysis, FT-IR, (1)H, (31)P, (13)C-NMR), including an X-ray diffraction analysis. The molecular structures of all the complexes were determined and reveal the presence of square planar geometry around Pd with little distortion. The complexes were tested in the Suzuki coupling of electronically deactivated aryl and heteroaryl bromides and were found to have much greater activity, without using any promoting additives or phase transfer agent under aerobic conditions. Higher reaction rates are obtained by varying R substituents on the aromatic ring of pyridine-2-thiocarboxamide. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported. PMID:22399145

Sindhuja, Elangovan; Ramesh, Rengan; Liu, Yu

2012-03-08

305

Solubility, complex formation, and redox reactions in the Tl2O3-HCN/CN(-)-H2O system. Crystal structures of the cyano compounds Tl(CN)3.H2O, Na[Tl(CN)4].3H2O, K[Tl(CN)4], and Tl(I)[Tl(III)(CN)4] and of Tl(I)2C2O4.  

PubMed

Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. Tl(III) is leached from its oxide both by aqueous solutions of hydrogen cyanide and by alkali-metal cyanides. The dominating cyano complex of thallium(III) obtained by dissolution of Tl2O3 in HCN is [Tl(CN)3(aq)] as shown by 205Tl NMR. The Tl(CN)3 species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN-/Tl(III) = 3. When aqueous solutions of the MCN (M = Na+, K+) salts are used to dissolve thallium(III) oxide, the equilibrium in liquid phase is fully shifted to the [Tl(CN)4]- complex. The Tl(CN)3 and Tl(CN)4- species have for the first time been synthesized in the solid state as Tl(CN)3.H2O (1), M[Tl(CN)4] (M = Tl (2) and K (3)), and Na[Tl(CN)4].3H2O (4) salts, and their structures have been determined by single-crystal X-ray diffraction. In the crystal structure of 1, the thallium(III) ion has a trigonal bipyramidal coordination with three cyanide ions in the equatorial plane, while an oxygen atom of the water molecule and a nitrogen atom from a cyanide ligand, attached to a neighboring thallium complex, form a linear O-Tl-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [Tl(CN)4]- unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by Tl(III)-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the Tl2O3-HCN-H2O system yielding thallium(I), while hydrogen cyanide is oxidized to cyanogen. The latter is hydrolyzed in aqueous solution giving rise to a number of products including (CONH2)2, NCO-, and NH4+ detected by 14N NMR. The crystalline compounds, Tl(I)[Tl(III)(CN)4], Tl(I)2C2O4, and (CONH2)2, have been obtained as products of the redox reactions in the system. PMID:15792470

Nagy, Péter; Fischer, Andreas; Glaser, Julius; Ilyukhin, Andrey; Maliarik, Mikhail; Tóth, Imre

2005-04-01

306

Redox reactions of Cu(II)-amine complexes in aqueous solutions  

NASA Astrophysics Data System (ADS)

A number of amines can be employed for all volatile treatment (AVT) of steam generator (SG) systems of nuclear power reactors. These amines form complexes with Cu2+ and Ni2+ ions which come into water due to corrosion. The redox reactions of a number of Cu(II)-AVT amine complexes and the stability of the transient species formed have been studied by pulse radiolysis technique. Rate constants for the reaction of eaq- with a number of Cu(II)-amine complexes have been determined by following the decay of eaq- absorption. Stability of Cu(I)-amine complexes was studied by following the kinetics of the bleaching signal formed at the ?max of the Cu(II) amine complex. Except for Cu(I)-triethanolamine complex all other Cu(I)-amine complexes were found to be stable. One-electron oxidation of Cu(II) amine complexes was studied using azidyl radicals for the oxidation reaction as OH radicals react with the alcohol groups present in the amines used in this study. Cu(III)-amine complexes were found to be unstable and decayed by second-order kinetics.

Kumbhar, A. G.; Kishore, Kamal

2003-03-01

307

Effect of fatty acid chain length and saturation on formation of the acylenzyme complex by the isolated aortic enzyme fraction.  

PubMed

Formation of acylenzyme complexes between the protein fraction isolated from pig thoracic aortas and palmitic, stearic, oleic, linoleic, linolenic and arachidic acid, was studied. The reaction brings about transformations of the periodically variable sinusoidal function of the enzyme absorbancy (energy level) depending on the kind of substrate utilized. Different changes in the enzyme energy level in the elementary process are induced by the saturated and polyunsaturated fatty acids and by oleic acid as demonstrated by the intermediate course of the function for oleylenzyme. The reaction rate constants were calculated and their negative curvilinear dependence upon molecular weight of the substrates has been shown. The differences in the acyl-enzyme reaction course and preferences are discussed with respect to the arterial metabolism and different accumulation of lipids. PMID:2641424

Swidzi?ska, K; Patelski, J; Szwajca, T

308

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

309

Study of Complex Formation and Precipitation Conditions of Beryllium Hydroxide.  

National Technical Information Service (NTIS)

The percentage of beryllium present under the form of different complex ions is established. Three analytical concentrations taken with pH are observed. Data study results of equilibrium conditions of the different ions in solution are presented. (Atomind...

J. F. Oliveira M. M. A. El-Naggar

1984-01-01

310

Functionalized organotin-chalcogenide complexes that exhibit defect heterocubane scaffolds: formation, synthesis, and characterization.  

PubMed

The synthesis of new functionalized organotin-chalcogenide complexes was achieved by systematic optimization of the reaction conditions. The structures of compounds [(R(1,?2) Sn)3 S4 Cl] (1, 2), [((R(2) Sn)2 SnS4 )2 (?-S)2 ] (3), [(R(1,?2) Sn)3 Se4 ][SnCl3 ] (4, 5), and [Li(thf)n ][(R(3) Sn)(HR(3) Sn)2 Se4 Cl] (6), in which R(1) =CMe2 CH2 C(O)Me, R(2) =CMe2 CH2 C(NNH2 )Me, and R(3) =CH2 CH2 COO, are based on defect heterocubane scaffolds, as shown by X-ray diffraction, (119) Sn?NMR spectroscopy, and ESI mass spectrometry analyses. Compounds 4, 5, and 6 constitute the first examples of defect heterocubane-type metal-chalcogenide complexes that are comprised of selenide ligands. Comprehensive DFT calculations prompted us to search for the formal intermediates [(R(1) SnCl2 )2 (?-S)] (7) and [(R(1) SnCl)2 (?-S)2 ] (8), which were isolated and helped to understand the stepwise formation of compounds 1-6. PMID:23963989

Eußner, Jens P; Barth, Beatrix E K; Leusmann, Eliza; You, Zhiliang; Rinn, Niklas; Dehnen, Stefanie

2013-08-21

311

Formation of protein complexes in crowded environments--from in vitro to in vivo.  

PubMed

Traditionally, biochemical studies are performed in dilute homogenous solutions, which are very different from the dense mixture of molecules found in cells. Thus, the physiological relevance of these studies is in question. This recognition motivated scientists to formulate the effect of crowded solutions in general, and excluded volume in particular, on biochemical processes. Using polymers or proteins as crowders, it was shown that while crowding tends to significantly enhance the formation of complexes containing many subunits, dimerizations are only mildly affected. Computer simulations, together with experimental evidence, indicate soft interactions and diffusion as critical factors that operate in a concerted manner with excluded volume to modulate protein binding. Yet, these approaches do not truly mimic the cellular environment. In vivo studies may overcome this shortfall. The few studies conducted thus far suggest that in cells, binding and folding occur at rates close to those determined in dilute solutions. Obtaining quantitative biochemical information on reactions inside living cells is currently a main challenge of the field, as the complexity of the intracellular milieu was what motivated crowding research to begin with. PMID:23337873

Phillip, Yael; Schreiber, Gideon

2013-01-18

312

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

NASA Astrophysics Data System (ADS)

We develop a microscopic theory for reaction-diffusion (RD) processes based on a generalization of Einstein's master equation [Ann. Phys.10.1002/andp.19053220806 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.

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

2012-02-01

313

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

314

Reactions of ruthenium vinylidene and acetylide complexes containing trichloromethyl groups: preparation of a cyclobutenonyl complex by solid-state photolysis.  

PubMed

Solid-state route to a cyclobutenone: Ruthenium perchlorocyclobutenonyl complex 2 is obtained by solid-state photoisomerization of ruthenium trichloroacetyl acetylide complex 1. The four-membered ring is sufficiently robust that transfer of the intact ligand could be readily achieved in a reaction of 2 with an enyne. Cyclobutenedionyl complex 3 was obtained by hydrolysis of 2 in H(2)O/THF.New reactions were observed for the cationic gamma-hydroxyvinylidene complex [Ru(2)]==C==CHC(OH)(CCl(3))(2) (+) (2, [Ru(2)]=CpRu(PPh(3))(2)). A rare chloroform elimination was observed when 2 was treated with nBu(4)NOH to give neutral acetylide complex [Ru(2)]--C[triple chemical bond]CC(==O)CCl(3) (3). Solid-state photoinduced isomerization of 3 generated ruthenium perchlorocyclobutenonyl complex [Ru(2)]--C(4)Cl(3)O (4) in high yield. This transformation was analyzed by DFT calculations, and 4 was found to be 4.22 kcal mol(-1) more stable in terms of Gibbs free energy than 3. In the coupling reaction of 4 with 2-methyl-1-buten-3-yne the four-membered cyclic ligand is transferred to the enyne to give substituted eta(3)-butadienyl complex 5 containing a cyclobutenonyl group. This coupling product could be removed from the metal by HCl. Deprotonation of 2 gave gamma-hydroxyacetylide complex [Ru(2)]--C[triple chemical bond]CC(OH)(CCl(3))(2) (9). In the photolysis of 9 phosphine dissociation is followed by addition of HCl to give neutral vinylidene complex Cl[Ru(1)]==C==CHC(OH)(CCl(3))(2) (10, [Ru(1)]=Cp(PPh(3))Ru). Complex 4 catalyzed the coupling reaction of dimethyl acetylenedicarboxylate with styrene yielding the diene PhCH==CHC(CO(2)Me)==CHCO(2)Me. Solid-state structures of 3-6 and 10 were determined by single-crystal X-ray diffraction analysis. PMID:19199302

Wu, Chung-Yeh; Chou, Hsien-Hsin; Lin, Ying-Chih; Wang, Yu; Liu, Yi-Hung

2009-01-01

315

Antibody formation in the mouse induced by hapten-carrier complexes.  

PubMed Central

The influence of hapten, carrier and their ratio in a complex on T-cell helper stimulation and antibody formation against the dinitrophenyl (DNP) hapten was studied. Complexes of DNP with bovine serum albumin (BSA), bovine gamma-globulin (BGG), isologous mouse immunoglobulin (MIG) and polyvinylpyrrolidone (PVP) as carriers were used. Optimal antibody formation against DNP was obtained with complexes with an intermediate hapten:carrier ratio (DNP 16-minusBSA, DNP 43-minusBGG and DNP 48-MINUSMIG). DNP-PVP complexes were not active either in the primary or in the secondary response. The anti-BSA titre was independent of the number of DNP groups on the complex used for immunization. Inhibition of DNP-plaque formation by spleen cells of immunized mice shows an increase of the inhibitory capacity of the complex with the increase of the hapten-carrier ratio. DNP 16-minusPVP was the only PVP complex which was inhibitory. These results suggest that helper cells involved in the antibody formation against BSA and DNP are reactive with different parts of the complex. Priming of mice with carrier or complex after cyclophosphamide (Cy) treatment followed by a secondary injection with complex 10 days later gave strong indications that there is a greater involvement in stimulation of helper T cells by determinants of the complex (new antigenic determinants (NAD) or NAP-DNP groups) or DNP, than by true BSA determinants. This holds for both the IgM and IgG responses.

Snippe, H; Graven, W G; Willems, P J

1975-01-01

316

Separations of olefins and heterocyclic organic compounds based on reversible complexation reactions  

SciTech Connect

While numerous biological processes utilize membranes that contain transporting agents (carriers) to separate molecular and ionic permeates, the potential of synthetic membranes for separations in commercial processes has not been fully realized. In principal, the phenomenon of facilitated transport (FT) in membranes, which relies on the reversible formation of a permeate:carrier complex, can provide selective and efficient separations. Recently, membranes and thin films derived from ion exchange materials have received considerable attention with respect to their structural, physical and chemical properties. The authors report the facilitated transport of 1-hexene and 1,5-hexadiene between two decane phases separated by thin, hydrated membranes (ca. 25 ..mu..m). The flux of olefin across the membranes is enhanced by factors of several hundred when silver ions are exchanged for sodium ions. Flux measurements were made using a two compartment cell arranged vertically and separated by the membrane which was held in place with o-rings and a clamp. The reactions described in this paper can be incorporated into a staged electrochemical separation process. Results for the removal of isoquinoline and pentamethyene sulfide from iso-octane and the subsequent concentration of these compounds is a second (waste) hydrocarbon phase are presented.

Koval, C.A.; Drew, S.; Spontarelli, T.; Noble, R.D. (Departments of Chemistry and Biochemistry and of Chemical Engineering, Univ. of Colorado, Boulder, CO (US))

1988-06-01

317

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

318

Glyoxal-methylglyoxal cross-reactions in secondary organic aerosol formation.  

PubMed

Glyoxal (G) and methylglyoxal (MG) are potentially important secondary organic aerosol (SOA) precursors. Previous studies of SOA formation by G and MG have focused on either species separately; however, G and MG typically coexist in the atmosphere. We studied the formation of secondary organic material in aqueous aerosol mimic mixtures containing G and MG with ammonium sulfate. We characterized the formation of light-absorbing products using UV-vis spectrophotometry. We found that absorption at 280 nm can be described well using models for the formation of light-absorbing products by G and MG in parallel. Pendant drop tensiometry measurements showed that surface tension depression by G and MG in these solutions can be modeled as a linear combination of the effects of G and MG alone. Product species were identified using chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol CIMS). Peaks consistent with G-MG cross-reaction products were observed, accounting for a significant fraction of detected product mass, but most peaks could be attributed to self-reaction. We conclude that cross-reactions contribute to SOA mass from uptake of G and MG, but they are not required to accurately model the effects of this process on aerosol surface tension or light absorption. PMID:20704215

Schwier, Allison N; Sareen, Neha; Mitroo, Dhruv; Shapiro, Erica L; McNeill, V Faye

2010-08-15

319

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

320

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

PubMed

An experimental investigation of phenyl radical pyrolysis and the phenyl radical + acetylene reaction has been performed to clarify the role of different reaction mechanisms involved in the formation and growth of polycyclic aromatic hydrocarbons (PAHs) serving as precursors for soot formation. Experiments were conducted using GC/GC-MS diagnostics coupled to the high-pressure single-pulse shock tube present at the University of Illinois at Chicago. For the first time, comprehensive speciation of the major stable products, including small hydrocarbons and large PAH intermediates, was obtained over a wide range of pressures (25-60 atm) and temperatures (900-1800 K) which encompass the typical conditions in modern combustion devices. The experimental results were used to validate a comprehensive chemical kinetic model which provides relevant information on the chemistry associated with the formation of PAH compounds. In particular, the modeling results indicate that the o-benzyne chemistry is a key factor in the formation of multi-ring intermediates in phenyl radical pyrolysis. On the other hand, the PAHs from the phenyl + acetylene reaction are formed mainly through recombination between single-ring aromatics and through the hydrogen abstraction/acetylene addition mechanism. Polymerization is the common dominant process at high temperature conditions. PMID:22339468

Comandini, A; Malewicki, T; Brezinsky, K

2012-03-02

321

Real-time observation of multiple-protein complex formation with single-molecule FRET.  

PubMed

Current single-molecule techniques do not permit the real-time observation of multiple proteins interacting closely with each other. We here report an approach enabling us to determine the single-molecule fluorescence resonance energy transfer (FRET) kinetics of multiple protein-protein interactions occurring far below the diffraction limit. We observe a strongly cooperative formation of multimeric soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes, which suggests that formation of the first SNARE complex triggers a cascade of SNARE complex formation. PMID:23808880

Bae, Woori; Choi, Mal-Gi; Hyeon, Changbong; Shin, Yeon-Kyun; Yoon, Tae-Young

2013-07-09

322

Dynamics of microtubule aster formation by motor complexes  

Microsoft Academic Search

The polymerisation of filaments and their moving by motor proteins contribute to the organisation of the cytoskeleton of higher cells. What a mixture of such elements is capable of doing, is not yet understood. Using computer simulations, we study here in a simple system the kinetics of aster formation by motors and growing microtubules. We find that the system can

François Nédélec; Thomas Surrey

2001-01-01

323

Caffeic acid inhibits the formation of 1-hydroxyethyl radical in the reaction mixture of rat liver microsomes with ethanol partly through its metal chelating activity  

PubMed Central

Effect of caffeic acid on the formation of 1-hydroxyethyl radicals via the microsomal ethanol-oxidizing system pathway was examined. The electron spin resonance spin trapping showed that 1-hydroxyethyl radicals form in the control reaction mixture which contained 0.17 M ethanol, 1 mg protein/ml rat river microsomes, 0.1 M ?-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 5 mM nicotinamide adenine dinucleotide phosphate and 30 mM phosphate buffer (pH 7.4). When the electron spin resonance spectra of the control reaction mixtures with caffeic acid were measured, caffeic acid inhibited the formation of 1-hydroxyethyl radicals in a concentration dependent manner. Gallic acid, dopamine, l-dopa, chlorogenic acid and catechin also inhibited the formation of 1-hydroxyethyl radicals. Above results indicated that the catechol moiety is essential to the inhibitory effect. Caffeic acid seems to chelate of iron ion at the catechol moiety. Indeed, the inhibitory effect by caffeic acid was greatly diminished in the presence of desferrioxamine, a potent iron chelator which removes iron ion in the Fe (III)-caffeic acid complex. Since Fe (III)-desferrioxamine complex is active for the 1-hydroxyethyl radicals formation, caffeic acid inhibits the formation of 1-hydroxyethyl radicals in the reaction mixture partly through its metal chelating activity.

Ikeda, Hideyuki; Kimura, Yuka; Masaki, Miho; Iwahashi, Hideo

2011-01-01

324

Complexation in reactions of cycloalkane solvent holes. I. reactions of Cis- and Trans-decalin{lg_bullet}+ with alcohols.  

SciTech Connect

It is shown that solvent holes in cis- and trans-decalin form complexes with aliphatic alcohols that live 1-100 ns, depending on the solute and the solvent temperature. This complexation has near-zero activation energy and occurs with rate constants of (1-1.2) x 10{sup 11} M{sup -1} s{sup -1} in trans-decalin and 3 x 10{sup 10} M{sup -1} s{sup -1} in cis-decalin. The metastable complex decays by proton transfer (for alcohols higher than ethanol); in concentrated solutions a diffusion-controlled reaction of the complex with a second alcohol molecule occurs. While the stability of the complex increases with the carbon number of the alcohol, the standard heat of the complexation decreases in the opposite direction ({Delta}H{sup o} changes from -39 kJ/mol for ethanol to -25 kJ/mol for tert-butanol). The decrease in the standard entropy is small ({Delta}S{sup o}{sub 298} > -80 J mol{sup -1} K{sup -1}), approaching zero for higher alcohols. We argue that this thermochemistry is due to the polaronic nature of the solvent holes.

Shkrob, I. A.; Sauer, M. C., Jr.; Tribunac, A. D.; Chemistry

2000-01-01

325

Formation of deuterated formaldehyde on low temperature surfaces: Isotope effect of quantum tunneling reactions  

NASA Astrophysics Data System (ADS)

The elucidation of formation pathways and mechanisms of deuterated species that have been detected by astronomical observations is important in studying chemical evolution in space. Formaldehyde and methanol are well-known molecules not only as reaction products on grain surfaces, but also as highly deuterated molecules. We have conducted experimental studies to clarify the formation mechanisms of deuterated formaldehyde and methanol on low temperature solid surfaces. In this paper, we summarize our experimental findings of the exposure of solid H2CO and D2CO on amorphous solid water to D and H atoms at 10-20 K, respectively. The isotope exchange reactions were observed in both reaction systems of D+H2CO and H+D2CO. In contrast, the addition reactions were only observed in the H+D2CO system because D addition to H2CO is much slower than isotope exchange. This isotope dependence on the reaction pathways can be explained by the quantum tunneling effect.

Hidaka, H.; Watanabe, M.; Kouchi, A.; Watanabe, N.

2013-06-01

326

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

327

Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways  

Microsoft Academic Search

The generation by combustion processes of airborne species of current health concern such as polycyclic aromatic hydrocarbons (PAH) and soot particles necessitates a detailed understanding of chemical reaction pathways responsible for their formation. The present review discusses a general scheme of PAH formation and sequential growth of PAH by reactions with stable and radical species, including single-ring aromatics, other PAH

H. Richter; J. B. Howard

2000-01-01

328

Reactions of group 4 amide guanidinates with dioxygen or water. Studies of the formation of oxo products.  

PubMed

Reactions of the zirconium amide guanidinates (R2N)2M[(i)PrNC(NR2)N(i)Pr]2 (R = Me, M = Zr, 1; M = Hf, 2; R = Et, M = Zr, 3) with O2 or H2O give products that are consistent with the oxo dimers {M(?-O)[(i)PrNC(NR2)N(i)Pr]2}2 (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr, 6) and polymers {M(?-O)[(i)PrNC(NR2)N(i)Pr]2}n (R = Me, M = Zr, 7; M = Hf, 8; R = Et, M = Zr, 9). Mass spectrometric (MS) analyses of the reactions of water in air with 1 and 2 show formation of the Zr monomer Zr(?O)[(i)PrNC(NMe2)N(i)Pr]2 (10), oxo dimers 4 and 5, and dihydroxyl complexes M(OH)2[(i)PrNC(NMe2)N(i)Pr]2 (M = Zr, 11; Hf, 12). Similar MS analyses of the reaction of diethylamide guanidinate 3 with water in air show the formation of Zr(?O)[(i)PrNC(NEt2)N(i)Pr]2 (13), Zr(OH)2[(i)PrNC(NEt2)N(i)Pr]2 (14), 6, and {(Et2N)Zr[(i)PrNC(NEt2)N(i)Pr]2}(+) (15). Kinetic studies of the reaction between 1 and a continuous flow of 1.0 atm of O2 at 80-105 °C indicate that it follows pseudo-first-order kinetics with ?H(?) = 8.7(1.1) kcal/mol, ?S(?) = -54(3) eu, ?G(?)358 K = 28(2) kcal/mol, and a half-life of 213(1) min at 85 °C. PMID:24060138

Sharma, Bhavna; Callaway, Tabitha M; Lamb, Adam C; Steren, Carlos A; Chen, Shu-Jian; Xue, Zi-Ling

2013-09-23

329

Formation of chromium(III) complexes with 8?hydroxyquinoline derivatives in nonionic micellar solutions  

Microsoft Academic Search

Due to the inertness of hydrated chromium ion, chromium(III) complexes are formed very slowly in aqueous solutions but not in surfactant solutions. Micelle effects were observed in the reaction of chromium(III) ion with 8?hydroxyquinoline or its derivatives. In nonionic surfactant solutions, reactions between chromium(III) ion and 8?hydroxyquinoline at 23 EC and 40 EC followed first?order kinetics. The reaction between chromium(III)

Chuhua Wang; Dean F. Martin; Barbara B. Martin

1998-01-01

330

Formation of hydrogen-vacancy complexes in alpha iron  

NASA Astrophysics Data System (ADS)

An extended variant of Smirnov statistic theory [12] is presented that describes the equilibrium concentrations of vacancy-hydrogen atom complexes as a function of temperature. Calculations based on the first-principle values of interaction energy show that, at low temperatures, the majority of vacancies are bound with several hydrogen atoms, and the concentration of vacancies sharply increases.

Mirzaev, D. A.; Mirzoev, A. A.; Okishev, K. Yu.; Shaburov, A. D.; Ruzanova, G. E.; Ursaeva, A. V.

2012-10-01

331

Photocatalytic CO2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes  

PubMed Central

Previously undescribed supramolecules constructed with various ratios of two kinds of Ru(II) complexes—a photosensitizer and a catalyst—were synthesized. These complexes can photocatalyze the reduction of CO2 to formic acid with high selectivity and durability using a wide range of wavelengths of visible light and NADH model compounds as electron donors in a mixed solution of dimethylformamide–triethanolamine. Using a higher ratio of the photosensitizer unit to the catalyst unit led to a higher yield of formic acid. In particular, of the reported photocatalysts, a trinuclear complex with two photosensitizer units and one catalyst unit photocatalyzed CO2 reduction (?HCOOH = 0.061, TONHCOOH = 671) with the fastest reaction rate (TOFHCOOH = 11.6 min-1). On the other hand, photocatalyses of a mixed system containing two kinds of model mononuclear Ru(II) complexes, and supramolecules with a higher ratio of the catalyst unit were much less efficient, and black oligomers and polymers were produced from the Ru complexes during photocatalytic reactions, which reduced the yield of formic acid. The photocatalytic formation of formic acid using the supramolecules described herein proceeds via two sequential processes: the photochemical reduction of the photosensitizer unit by NADH model compounds and intramolecular electron transfer to the catalyst unit.

Tamaki, Yusuke; Morimoto, Tatsuki; Koike, Kazuhide; Ishitani, Osamu

2012-01-01

332

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

2013-05-31

333

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

2013-03-01

334

Effect of Heavy Doping on Complex Formation and Diffusivity of Sb in Si.  

National Technical Information Service (NTIS)

The complex formation and diffusivity during rapid thermal annealing of low concentrations of ion-implanted Sb in silicon have been studied as functions of donor concentration by combination of Rutherford backscattering spectroscopy, Hall effect/resistivi...

A. N. Larsen P. Tidemand-Petersson P. E. Andersen G. Weyer

1988-01-01

335

[Characteristics of marketing complex formation in rendering of sanatorium resort services].  

PubMed

Basic positions in sanatorium resort marketing and its evolution with description of its main components are considered. Marketing research management in sanatorium resort institutions, marketing theory, analysis of services market, characteristics of marketing complex formation are presented. PMID:17004381

Kemalov, R F

336

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

337

Selective Covalent Bond Formation in Polypeptide Ions via Gas-Phase Ion/Ion Reaction Chemistry  

PubMed Central

Primary amines present in protonated polypeptides can be covalently modified via gas-phase ion/ion reactions using bifunctional reagent ions. The use of reagent anions with a charge bearing site that leads to strong interactions with the polypeptide, such as sulfonic acid, gives rise to the formation of a long-lived adduct. A distinct reactive functional group, an aldehyde in the present case, can then undergo a reaction with the peptide. Collisional activation of the adduct ion formed from a reagent with an aldehyde group and a peptide ion with a primary amine gives rise to water loss in conjunction with imine (Schiff base) formation. The covalently-bound modification is retained upon subsequent collisional activation. This work demonstrates the ability to selectively modify polypeptide ions in the gas-phase within the context of a multi-stage mass spectrometry experiment.

Han, Hongling; McLuckey, Scott A.

2009-01-01

338

Reaction-diffusion approach to prevertebrae formation: Effect of a local source of morphogen  

NASA Astrophysics Data System (ADS)

Periodic structure formation is an essential feature of embryonic development. Many models of this phenomenon, most of them based on time oscillations, have been proposed. However, temporal oscillations are not always observed during development and how a spatial periodic structure is formed still remains under question. We investigate a reaction-diffusion model, in which a Turing pattern develops without temporal oscillations, to assess its ability to account for the formation of prevertebrae. We propose a correspondence between the species of the reaction scheme and biologically relevant molecules known as morphogens. It is shown that the model satisfactorily reproduces experiments involving grafting of morphogen sources into the embryos. Using a master equation approach and the direct simulation Monte Carlo method, we examine the robustness of the results to internal fluctuations.

Dziekan, P.; Signon, L.; Nowakowski, B.; Lemarchand, A.

2013-09-01

339

Reaction-diffusion approach to prevertebrae formation: Effect of a local source of morphogen.  

PubMed

Periodic structure formation is an essential feature of embryonic development. Many models of this phenomenon, most of them based on time oscillations, have been proposed. However, temporal oscillations are not always observed during development and how a spatial periodic structure is formed still remains under question. We investigate a reaction-diffusion model, in which a Turing pattern develops without temporal oscillations, to assess its ability to account for the formation of prevertebrae. We propose a correspondence between the species of the reaction scheme and biologically relevant molecules known as morphogens. It is shown that the model satisfactorily reproduces experiments involving grafting of morphogen sources into the embryos. Using a master equation approach and the direct simulation Monte Carlo method, we examine the robustness of the results to internal fluctuations. PMID:24070279

Dziekan, P; Signon, L; Nowakowski, B; Lemarchand, A

2013-09-21

340

Formation of {eta}-mesic nuclei by the ({pi},N) reaction and properties of N*(1535) in medium  

SciTech Connect

We calculate formation spectra of the {eta}-nucleus systems in the ({pi},N) reactions with nuclear targets, which can be performed at existing and/or forthcoming facilities, including the Japan Proton Accelerator Research Complex, to investigate the {eta}-nucleus interaction. Based on the N*(1535) dominance in the {eta}N system, the {eta}-mesic nuclei are suitable systems for the study of in-medium properties of the N*(1535) baryon resonance, such as reduction of the mass difference of N and N* in the nuclear medium, which affects the level structure of the {eta} and N*-hole modes. We find that clear information on the in-medium N*- and {eta}-nucleus interactions can be obtained through the formation spectra of the {eta}-mesic nuclei. We also discuss the experimental feasibilities by showing several spectra of the ({pi},N) reactions calculated with possible experimental settings. Coincident measurements of the N{pi} pairs from the N* decays in nuclei help us to reduce backgrounds.

Nagahiro, Hideko [Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka, 567-0047 (Japan); Jido, Daisuke [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Hirenzaki, Satoru [Department of Physics, Nara Women's University, Nara, 630-8506 (Japan)

2009-08-15

341

Formation of stable iron/cobalt NHC complexes via unexpected ring opening and in situ generation of a tridentate ligand.  

PubMed

The reactions of FeCl(2) and CoCl(2) with a bistriazolium salt yields the NHC complexes [Fe(III)(L1)(2)]I·H(2)O, [Fe(III)(L2)(2)]PF(6)·CH(3)CN and [Co(III)(L1)(2)]I·0.5CH(3)CN, through an unusual ring opening of one of the triazoyl rings, which leads to the formation of C,N,O tridentate ligands L1 or L2. Furthermore, a Fe(ii) species [Fe(II)(L1)(2)]·CH(2)Cl(2) was also obtained. PMID:22885774

Wang, Gao-Feng; Song, Xiao-Jiao; Chen, Fei; Li, Yi-Zhi; Chen, Xue-Tai; Xue, Zi-Ling

2012-08-28

342

Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study  

Microsoft Academic Search

The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm-3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB2+ chelate. At 25 °C, the rates and activation parameters for the reactions NiII + AEB \\u000a$$\\\\xrightarrow{{k_f^L }}$$\\u000a NiAEB2+ and NiII + AEBH+\\u000a$$\\\\xrightarrow{{k_f^{HL} }}$$\\u000a NiAEB2+

Anadi C. Dash; Achyuta N. Acharya; Ramakanta Sahoo

1995-01-01

343

Heck reaction catalysed by pyridyl-imine palladium(0) and palladium(II) complexes  

Microsoft Academic Search

Three different palladium(II) complexes Pd(NN?)Cl2 and two different palladium(0) complexes Pd(NN?)(dmfu) (dmfu=dimethylfumarate) containing NN? pyridyl-imine ligands, have been prepared and used as pre-catalysts for the coupling between iodobenzene and methyl acrylate (Meac) (Heck reaction). All the reactions have been conducted in DMF at 80°C, using Et3N as base and a Pd:PhI:Meac:Et3N=1:1000:1100:1000 molar ratio. In all cases the complete conversion of

Paolo Pelagatti; Mauro Carcelli; Mirco Costa; Sandra Ianelli; Corrado Pelizzi; Dominga Rogolino

2005-01-01

344

Structural basis for cooperativity of CRM1 export complex formation  

PubMed Central

In eukaryotes, the nucleocytoplasmic transport of macromolecules is mainly mediated by soluble nuclear transport receptors of the karyopherin-? superfamily termed importins and exportins. The highly versatile exportin chromosome region maintenance 1 (CRM1) is essential for nuclear depletion of numerous structurally and functionally unrelated protein and ribonucleoprotein cargoes. CRM1 has been shown to adopt a toroidal structure in several functional transport complexes and was thought to maintain this conformation throughout the entire nucleocytoplasmic transport cycle. We solved crystal structures of free CRM1 from the thermophilic eukaryote Chaetomium thermophilum. Surprisingly, unbound CRM1 exhibits an overall extended and pitched superhelical conformation. The two regulatory regions, namely the acidic loop and the C-terminal ?-helix, are dramatically repositioned in free CRM1 in comparison with the ternary CRM1–Ran–Snurportin1 export complex. Single-particle EM analysis demonstrates that, in a noncrystalline environment, free CRM1 exists in equilibrium between extended, superhelical and compact, ring-like conformations. Molecular dynamics simulations show that the C-terminal helix plays an important role in regulating the transition from an extended to a compact conformation and reveal how the binding site for nuclear export signals of cargoes is modulated by different CRM1 conformations. Combining these results, we propose a model for the cooperativity of CRM1 export complex assembly involving the long-range allosteric communication between the distant binding sites of GTP-bound Ran and cargo.

Monecke, Thomas; Haselbach, David; Voss, Bela; Russek, Andreas; Neumann, Piotr; Thomson, Emma; Hurt, Ed; Zachariae, Ulrich; Stark, Holger; Grubmuller, Helmut; Dickmanns, Achim; Ficner, Ralf

2013-01-01

345

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

346

A Study on Advanced Maillard Reaction in Heated Casein\\/Sugar Solutions: Colour Formation  

Microsoft Academic Search

The Maillard reaction in its advanced state was studied with respect to colour formation in milk-resembling model systems (lactose–caseinate or glucose–caseinate solutions), heated between 110 and 150°C. Browning was measured spectrophotometrically (420nm) and via a tristimulus colorimeter. The pigments causing browning (measured at 420nm) were mainly bound to caseinate (brown pigments not bound to protein amounted to 5–6% of total

F. J. Morales

1998-01-01

347

Fuel-sodium reaction product formation in breached mixed-oxide fuel  

Microsoft Academic Search

The run-beyond-cladding-breach (RBCB) operation of mixed-oxide LMR fuel pins has been studied for six years in the Experimental Breeder Reactor-II (EBR-II) as part of a joint program between the US Department of Energy and the Power Reactor and Nuclear Fuel Development Corporation of Japan. The formation of fuel-sodium reaction product (FSRP), NaâMOâ, where M = U\\/sub 1-y\\/Pu\\/sub y\\/, in the

J. H. Bottcher; J. D. B. Lambert; R. V. Strain; S. Ukai; S. Shibahara

1988-01-01

348

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

349

Predicted formation of localized superlattices in spatially distributed reaction-diffusion solutions.  

PubMed

We study numerically the formation of localized superlattices in spatially distributed systems. We predict that in wide regions of the parameter space, stable localized, either bright or dark, superlattices may form in reaction-diffusion systems. Localized superlattices are patterns which consist of a piece of superlattice. Each single ring is surrounded by spots. The number of rings and their spatial distribution are determined by the initial conditions. The peak concentration remains unaltered for fixed values of the parameters. PMID:23214638

Tlidi, M; Sonnino, G; Bachir, M

2012-10-16

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

Kinetics of Ion Formation in the Volumetric Reaction of Methane with Air  

Microsoft Academic Search

The formation of ions in the volumetric reaction of methane and hydrogen with air is analyzed. In methane–air mixtures, the highest concentrations are observed for NO+, NO3-, CO3-, CO4-, OH-, and NO2- ions. In hydrogen–air mixtures, maximum concentrations are characteristic for NO+, OH-, H3O+, O-, and O2- ions. In both rich and lean mixtures after ignition there is a long

A. M. Starik; N. S. Titova

2002-01-01

353

Formation of 9,10-phenanthrenequinone by atmospheric gas-phase reactions of phenanthrene  

Microsoft Academic Search

Phenanthrene is a 3-ring polycyclic aromatic hydrocarbon which exists mainly in the gas-phase in the atmosphere. Recent concern over the presence of 9,10-phenanthrenequinone in ambient particles led us to study the products of the gas-phase reactions of phenanthrene with hydroxyl radicals, nitrate radicals and ozone. The formation yields of 9,10-phenanthrenequinone were measured to be ?3%, 33±9%, and ?2% from the

Lin Wang; Roger Atkinson; Janet Arey

2007-01-01

354

On the influence of the char gasification reactions on NO formation in flameless coal combustion  

SciTech Connect

Flameless combustion is a well known measure to reduce NO{sub x} emissions in gas combustion but has not yet been fully adapted to pulverised coal combustion. Numerical predictions can provide detailed information on the combustion process thus playing a significant role in understanding the basic mechanisms for pollutant formation. In simulations of conventional pulverised coal combustion the gasification by CO{sub 2} or H{sub 2} O is usually omitted since its overall contribution to char oxidation is negligible compared to the oxidation with O{sub 2}. In flameless combustion, however, due to the strong recirculation of hot combustion products, primarily CO{sub 2} and H{sub 2} O, and the thereby reduced concentration of O{sub 2} in the reaction zone the local partial pressures of CO{sub 2} and H{sub 2} O become significantly higher than that for O{sub 2}. Therefore, the char reaction with CO{sub 2} and H{sub 2} O is being reconsidered. This paper presents a numerical study on the importance of these reactions on pollutant formation in flameless combustion. The numerical models used have been validated against experimental data. By varying the wall temperature and the burner excess air ratio, different cases have been investigated and the impact of considering gasification on the prediction of NO formation has been assessed. It was found that within the investigated ranges of these parameters the fraction of char being gasified increases up to 35%. This leads to changes in the local gas composition, primarily CO distribution, which in turn influences NO formation predictions. Considering gasification the prediction of NO emission is up to 40% lower than the predicted emissions without gasification reactions being taken into account. (author)

Stadler, Hannes; Toporov, Dobrin; Foerster, Malte; Kneer, Reinhold [Institute of Heat and Mass Transfer, RWTH Aachen University, Eilfschornsteinstrasse 18, 52056 Aachen (Germany)

2009-09-15

355

Formation of covalent ?-linked carbohydrate–enzyme intermediates during the reactions catalyzed by ?-amylases  

Microsoft Academic Search

Porcine pancreatic and Bacillus amyloliquefaciens ?-amylases were examined for the formation of covalent carbohydrate intermediates during reaction. The enzymes were precipitated and denatured by adding 10 volumes of acetone. When these denatured enzymes were mixed with methyl ?-6-[3H]-maltooligosaccharide glycosides and chromatographed on BioGel P-2, no carbohydrate was found in the protein void volume peak. When the enzymes were added to

Seung-Heon Yoon; D. Bruce Fulton; John F. Robyt

2007-01-01

356

Subcellular location for the formation of the retinol/retinol-binding protein complex in rat liver  

SciTech Connect

Retinol complexes with retinol-binding protein (RBP) within the hepatocyte, however the subcellular location where complex formation occurs has not previously been identified. A model similar to that of lipoproteins formation has been hypothesized. The authors have identified the initial site of retinol/RBP complex formation. Furthermore, the authors have elucidated the progression of the complex through the subcellular organelles. Intravenous injections of /sup 3/H-retinol suspended in Tween 40 were administered to vitamin A depleted rats. After intervals of 2, 3, 4, 5, 10, 15, 20, and 30 minutes the rat livers were removed and fractions enriched in rough and smooth microsomes and Golgi apparatus were prepared. Extracts of these subcellular fractions were chromatographed on Sephadex G-100. Simultaneous elution of /sup 3/H-retinol and immunoreactive RBP indicated the presence of the complex. The retinol/RBP complex was observed in rough microsomes 2 minute after the injection of /sup 3/H-retinal. The complex appeared subsequently in smooth microsomes and Golgi apparatus. The complex was first detected serum around 10 minutes after injection. Based on the data, they believe that the retinol/RBP complex formation occurs in rough microsomes.

Crumbaugh, L.M.; Green, E.L.; Smith, J.E.

1986-03-01

357

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

358

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

359

Hydrogenation of carbon dioxide and aryl isocyanates by a tetranuclear tetrahydrido yttrium complex. Isolation, structures, and CO2 insertion reactions of methylene diolate and mu3-oxo yttrium complexes.  

PubMed

The reaction of carbon dioxide with a tetranuclear tetrahydrido yttrium complex [(C5Me4SiMe3)Y(mu-H)]4(L) (L = Me3SiCC(H)C(H)CSiMe3) (1) rapidly afforded the corresponding bis(methylene diolate) complex [(C5Me4SiMe3)Y]4(mu-O2CH2)2(L) (2), while the reactions of an aryl isocyanate with 1 led to selective formation of the mu3-oxo complex [(C5Me4SiMe3)Y]4(mu-O)( mu-H)2(L) (5) or [(C5Me4SiMe3)Y]4(mu-O)2(L) (7), depending on the substrate ratio. Both the methylene diolate and the oxo complexes can undergo CO2 insertion reactions to give the corresponding carbonate complexes. These reactions not only yield a new series of polynuclear yttrium complexes having novel structures but also shed new light on the mechanistic aspects of the heterogeneous hydrogenation of COmicron2. The high reactivity of the polynuclear mu3-oxo yttrium complexes 5 and 7 could also make them novel molecular models for study of metal oxide-supported catalysts. PMID:15225025

Tardif, Olivier; Hashizume, Daisuke; Hou, Zhaomin

2004-07-01

360

Relation between State-Selected or State-Averaged Cross Sections of Endothermic Reactions and Rate Constants of Exothermic Reactions. Application of Bimolecular Microcanonical Activated Complex Theory  

Microsoft Academic Search

An expression is derived relating state-selected or state-averaged molecular beam reaction cross sections of endothermic reactions to observed rate constants for the inverse (exothermic) reactions. An approximation of Anlauf, Maylotte, Polanyi, and Bernstein is used, together with bimolecular microcanonical activated complex theory [R. A. Marcus, J. Chem. Phys. 45, 2138 (1966)].

R. A. Marcus

1970-01-01

361

Enthalpies of formation of hexahalide complexes of uranium(III)  

Microsoft Academic Search

The enthalpies of solution of uranium-containing elpasolites in a solution of 4 M HCl + 0.005 M NaâSiFâ + 10⁻⁶ M HâPtClâ were measured with a calorimeter with an isothermal casing. The standard enthalpies of formation at 298.15°K from binary halides (and from the elements and gaseous bromine) were calculated in kJ\\/mole: -23.0 +\\/- 2.2 (-2184.4 +\\/- 4.0) for KâNaUClâ;

N. A. Aurov; D. E. Chirkst

2009-01-01

362

Formation of Complex Structures in Dusty Plasmas under Temperature Gradients  

SciTech Connect

Thermophoretic effects on dust structures under temperature gradients in glow and radio-frequency discharge plasmas are studied experimentally. The geometry of dust structures consisting of micrometer-sized polydisperse grains depends on heat release in the plasma. Thermophoretic forces associated with heat release can control the formation of dust structures of different geometries. A theoretical model is proposed to describe dust separation with respect to grain size caused by the effects of radial electrostatic and thermophoretic forces. The glow discharge currents under critical conditions for grain separation predicted by the model agree with those observed experimentally.

Vasilyak, L.M.; Vetchinin, S.P.; Polyakov, D.N.; Fortov, V.E. [Institute for High Energy Densities, Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 (Russian Federation)

2005-05-01

363

The reaction of amidinato(pyridine) complexes of molybdenum and tungsten with triethylborane adduct of N-heterocyclic carbene (NHC · BEt 3): Investigation on the reactivity of NHC · BEt 3 as carbene precursor toward transition metal complexes  

Microsoft Academic Search

The reaction of triethylborane adduct of N-heterocyclic carbene, NHC·BEt3, (NHC=IiPr=1,3-diisopropylimidazol-2-ylidene (IiPr·BEt3; 1a), NHC=IMes=1,3-dimesitylimidazol-2-ylidene (IMes·BEt3; 1b)), which was prepared by the reaction of the corresponding imidazolium salt with one equivalent of LiBEt3H, with amidinato(pyridine) complex, [M(?3-allyl){?2-(NPh)2CH}(CO)2(NC5H5)] (M=Mo; 2-Mo M=W; 2-W), was investigated. The reaction of compound 1 with complex 2 under toluene-reflux conditions resulted in the formation of carbene complex [M(?3-allyl){?2-(NPh)2CH}(CO)2(NHC)

Kenichi Ogata; Yoshitaka Yamaguchi; Taigo Kashiwabara; Takashi Ito

2005-01-01

364

Surface models and reaction barrier in Eley-Rideal formation of H2 on graphitic surfaces.  

PubMed

The exothermic, collinearly-dominated Eley-Rideal hydrogen formation on graphite is studied with electronic structure and quantum dynamical means. In particular, the focus is on the importance of the model used to describe the graphitic substrate, in light of the marked discrepancies present in available literature results. To this end, the collinear reaction is considered and the potential energy surface is computed for a number of different graphitic surface models using Density Functional Theory (DFT) for different dynamical regimes. Quantum dynamics is performed with wavepacket techniques down to the cold collision energies relevant for the chemistry of the interstellar medium. Results show that the reactivity at moderate-to-high collision energies sensitively depends on the shape of the PES in the entrance channel, which in turn is related to the adopted surface model. At low energies we rule out the presence of any barrier to reaction, thereby highlighting the importance of quantum reflection in limiting the reaction efficiency. PMID:21858337

Bonfanti, Matteo; Casolo, Simone; Tantardini, Gian Franco; Martinazzo, Rocco

2011-08-22

365

Photo-initiated thiol-ene click reactions as a potential strategy for incorporation of [M(I)(CO)3]+ (M = Re, (99m)Tc) complexes.  

PubMed

Click reactions offer a rapid technique to covalently assemble two molecules. In radiopharmaceutical construction, these reactions can be utilized to combine a radioactive metal complex with a biological targeting molecule to yield a potent tool for imaging or therapy applications. The photo-initiated radical thiol-ene click reaction between a thiol and an alkene was examined for the incorporation of [M(I)(CO)3](+) (M = Re, (99m)Tc) systems for conjugating biologically active targeting molecules containing a thiol. In this strategy, a potent chelate system, 2,2'-dipicolylamine (DPA), for [M(I)(CO)3](+) was functionalized at the central amine with a terminal alkene linker that was explored with two synthetic approaches, click then chelate and chelate then click, to determine the flexibility and applicability of the thiol-ene click reaction to specifically incorporate ligand systems and metal complexes with a thiol containing molecule. In the click then chelate approach, the thiol-ene click reaction was carried out with the DPA chelate followed by complexation with [M(I)(CO)3](+). In the chelate then click approach, the alkene functionalized DPA chelate was first complexed with [M(I)(CO)3](+) followed by the conduction of the thiol-ene click reaction. Initial studies utilized benzyl mercaptan as a model thiol for both strategies to generate the identical product from either route to provide information on reactivity and product formation. DPA ligands functionalized with two unique linker systems (allyl and propyl allyl ether) were prepared to examine the effect of the proximity of the chelate or complex on the thiol-ene click reaction. Both the thiol-ene click and coordination reactions with Re, (99m)Tc were performed in moderate to high yields demonstrating the potential of the thiol-ene click reaction for [M(I)(CO)3](+) incorporation into thiol containing biomolecules. PMID:23445468

Hayes, Thomas R; Lyon, Patrice A; Silva-Lopez, Elsa; Twamley, Brendan; Benny, Paul D

2013-02-27

366

OBSERVATION OF LOW ENERGY NUCLEAR REACTIONS INDUCED BY D2 GAS PERMEATION THROUGH PD COMPLEXES  

Microsoft Academic Search

Observation of low energy nuclear reactions induced by D2 gas permeation through Pd complexes, which consist of a thin Pd layer, alternating CaO and Pd layers and bulk Pd, is described. The Pd complex was located in a vacuum chamber and the elemental analysis was performed using an X-ray photoelectron spectroscopy (XPS) apparatus mounted on the chamber. When Cs was

Yasuhiro IWAMURA; Takehiko ITOH; Mitsuru SAKANO; Satoshi SAKAI

367

Molecular Interactions and Thermodynamic Aspects of the Complexation Reaction between Gentian Violet and Several Cyclodextrins  

Microsoft Academic Search

The complexation process between gentian violet (CV+) and four different cyclodextrins (a-, ß-, ?-, and HP-ß-CDs) has been investigated under different reaction conditions (pH, solvent, and temperature) by electronic absorption and 1H NMR (NOE and NOESY) spectroscopies. All the binding constants were determined by the direct spectroscopic method. The ?H and ?S complexation values have been evaluated and discussed according

M. J. Bernad Bernad; J. Gracia-Mora; D. Díaz; G. Mendoza DÍAZ

1999-01-01

368

Does enzyme-catalyzed formation of sulfate complexes cause oxygen isotope exchange during dissimilatory microbial sulfate reduction?  

NASA Astrophysics Data System (ADS)

We have experimentally tested the hypothesis that oxygen isotope exchange may occur between sulfate and water during enzyme-catalyzed formation of the sulfate complex adenosine phosphosulfate (APS). This reaction is the initial step in the dissimilatory microbial sulfate reduction process. It has been suggested that the enzyme-catalyzed formation of APS could facilitate oxygen isotope exchange between the cell internal water and the residual sulfate pool. This is important because only a fraction of the APS is then further reduced to sulfite, the remainder of which could be reintroduced to the sulfate pool, resulting in significant resetting of the sulfate oxygen isotope compositions. This study isolated the enzyme-catalyzed formation of APS in vitro, in a solution of 17O-labeled water, in order to quantify the degree of oxygen isotope exchange between the complexed sulfate and water. The use of ?17O as an indicator of exchange is more rigorous than the commonly used ?18O parameter. We observed no oxygen isotope exchange between the APS and water during a set of experimental runs at 30° C with time varying from 2 to 48 hours. A subsequent study will confirm and describe the dynamics of APS formation during this reaction using spectroscopic methods. The lack of oxygen isotope exchange between APS and water suggests that the discrepancy seen in the literature between the level of enrichment for ?34S vs. ?18O is not due to oxygen isotope exchange during APS formation, but other processes, i.e. the re-oxidation of sulfite to sulfate or oxygen exchange between sulfite and water during the later steps of dissimilatory microbial sulfate reduction.

Bao, H.; Kohl, I. E.

2006-12-01

369

Biofilm Formation and Acyl Homoserine Lactone Production in the Burkholderia cepacia Complex  

Microsoft Academic Search

Acyl homoserine lactone (acyl-HSL)-mediated gene regulation has been shown to influence biofilm formation in one Burkholderia cepacia cystic fibrosis isolate, but it is not known whether this relationship is a consistent feature of the several genomic species that make up the B. cepacia complex (BCC). We screened strains belonging to genomovars I to V of the BCC for biofilm formation

Barbara-Ann D. Conway; Vicnays Venu; David P. Speert

2002-01-01

370

Stable complex formation of thylakoidal processing peptidase and PGRL1.  

PubMed

The thylakoid-transfer signal is required for energy-dependent translocation of preproteins into the thylakoid lumen and is removed by the thylakoidal processing peptidase (TPP). PGRL1 is an essential component of antimycin A-sensitive photosynthetic cyclic electron flow in chloroplasts. Here we report that one of the TPP isoforms, Plsp1, forms a stable complex with PGRL1. Genetic data demonstrate that PGRL1 is not essential for Plsp1 activity in vivo, leading to a possibility that PGRL1 may act as a regulator of TPP. PMID:23727204

Endow, Joshua K; Inoue, Kentaro

2013-05-31

371

Synthesis of mono(dinitrogen) complexes of molybdenum. Formation of ammonia and hydrazine  

SciTech Connect

The synthesis and reactivity of a series of mono-N/sub 2/ complexes of molybdenum are reported. Reduction of MoCl/sub 3/(triphos), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/, with sodium amalgam in the presence of 2L or L/sub 2/ and with a regulated amount of N/sub 2/ led to the formation of Mo(N/sub 2/)(triphos)(L/sub 2/) (1-5): 1, L = PMe/sub 2/Ph; 2, L/sub 2/ = Me/sub 2/PCH/sub 2/PMe/sub 2/, dmpm; 3, L/sub 2/ = 1,2-(Me/sub 2/As)/sub 2/C/sub 6/H/sub 4/, diars; 4, L/sub 2/ = Ph/sub 2/PCH/sub 2/PPh/sub 2/, dppm; 5, L/sub 2/ = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/, dppe. Complexes 3 and 5 were each a mixture of two isomeric mono-N/sub 2/ complexes. Complexes 1-5 reacted with excess HX (X = Br, Cl) to afford varying yields of ammonia, hydrazine, and N/sub 2/ (and some H/sub 2/). Loss of N/sub 2/ occurred readily from 1 when it was evacuate in the solid state to give 7. Five-coordinate 7 reacted with H/sub 2/, CO, and C/sub 2/H/sub 4/ in the solid state to form MoH/sub 2/(triphos)(PMe/sub 2/Ph)/sub 2/ (8), Mo(CO)(triphos)(PMe/sub 2/Ph)/sub 2/ (9), and Mo(C/sub 2/H/sub 4/)(triphos)(PMe/sub 2/Ph)/sub 2/ (10), respectively. Reaction of solids 7, 8, and 10 with N/sub 2/ regenerated 1. Structural assignments of the new complexes are based upon /sup 31/P and /sup 1/H NMR spectral data. Triphos is shown to adopt both fac and mer configurations. 33 references, 1 table.

George, T.A.; Tisdale, R.C.

1988-08-24

372

Aqueous-Phase Reactions of Isoprene with Sulfoxy Radical Anions as a way of Wet Aerosol Formation in the Atmosphere  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols exhibit an important role in the environment. They have implications on human health and life, and - in the larger scale - on climate, the Earth's radiative balance and the cloud's formation. Organic matter makes up a significant fraction of atmospheric aerosols (~35% to ~90%) and may originate from direct emissions (primary organic aerosol, POA) or result from complex physico-chemical processes of volatile organic compounds (secondary organic aerosol, SOA). Isoprene (2-methyl-buta-1,3-diene) is one of the relevant volatile precursor of ambient SOA in the atmosphere. It is the most abundant non-methane hydrocarbon emitted to the atmosphere as a result of living vegetation. According to the recent data, the isoprene emission rate is estimated to be at the level of 500 TgC per year. While heterogeneous transformations of isoprene have been well documented, aqueous-phase reactions of this hydrocarbon with radical species that lead to the production of new class of wet SOA components such as polyols and their sulfate esters (organosulfates), are still poorly recognized. The chain reactions of isoprene with sulfoxy radical-anions (SRA) are one of the recently researched route leading to the formation of organosulfates in the aqueous phase. The letter radical species originate from the auto-oxidation of sulfur dioxide in the aqueous phase and are behind the phenomenon of atmospheric acid rain formation. This is a complicated chain reaction that is catalyzed by transition metal ions, such as manganese(II), iron(III) and propagated by sulfoxy radical anions . The presented work addresses the chemical interaction of isoprene with sulfoxy radical-anions in the water solution in the presence of nitrite ions and nitrous acid, which are important trace components of the atmosphere. We showed that nitrite ions and nitrous acid significantly altered the kinetics of the auto-oxidation of SO2 in the presence of isoprene at different solution acidity from 2 to 8.7. The presence of nitrogen-containing inorganic salts strongly impact the formation of novel organosulfur products, whereas no organonitrates were observed. A detailed characterization of these products with the triple-quadruple negative electrospray mass spectrometry (-)ESI-MS/MS revealed oxygenated polar species with C-5 skeleton bearing SO3H (MW 182, 180) and SO2H (MW 166, 164) moieties on the hydroxyl group. The structures of these products were firmly confirmed by comparison of their liquid chromatography and mass spectrometry behaviors with that corresponding to the synthesized model compounds. It is believed that newly discovered highly polar low molecular weight compounds may contribute to the growth of wet aerosol particles by the formation of higher molecular weight species.

Kuznietsova, I.; Rudzinski, K. J.; Szmigielski, R.; Laboratory of the Environmental Chemistry

2011-12-01

373

TraML--a standard format for exchange of selected reaction monitoring transition lists.  

PubMed

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

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

2011-12-12

374

Mechanistic Studies on the Reaction of Nitroxylcobalamin with Dioxygen: Evidence for Formation of a Peroxynitritocob(III)alamin Intermediate.  

PubMed

Studies by others suggest that the reduced vitamin B12 complex, cob(II)alamin, scavenges nitric oxide to form air-sensitive nitroxylcobalamin (NO(-)-Cbl(III); NOCbl) in vivo. The fate of newly formed NOCbl is not known. A detailed mechanistic investigation of the oxidation of NOCbl by oxygen is presented. Only base-on NOCbl reacts with O2, and the reaction proceeds via an associative mechanism involving a peroxynitritocob(III)alamin intermediate, Co(III)-N(O)OO(-). The intermediate undergoes O-O bond homolysis and ligand isomerization to ultimately yield NO2Cbl and H2OCbl(+)/HOCbl, respectively. Ligand isomerization may potentially occur independent of O-O bond homolysis. Formation of (•)OH and (•)NO2 intermediates from O-O bond homolysis is demonstrated using phenol and tyrosine radical traps and the characterization of small amounts of a corrinoid product with minor modifications to the corrin ring. PMID:24050193

Subedi, Harishchandra; Brasch, Nicola E

2013-09-19

375

Complexity, segregation, and pattern formation in rotating-drum flows  

NASA Astrophysics Data System (ADS)

Rotating-drum flows span a variety of research areas, ranging from physics of granular matter through hydrodynamics of suspensions to pure liquid coating flows. Recent years have seen an intensified scientific activity associated with this unique geometrical configuration, which has contributed to our understanding of related subjects such as avalanches in granules and segregation in suspensions. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences between the various flow realizations. Scaling laws expressing the importance of different mechanisms underlying the observed phenomena have been focused on. An emphasis is placed on pattern formation phenomena. Rotating-drum flows exhibit stationary patterns as well as traveling and oscillating patterns; they exhibit reversible transitions as well as hysteresis. Apart from the predominant cylindrical configuration, this review covers recent work done with tumblers having other geometries, such as the sphere and the Hele-Shaw cell.

Seiden, G.; Thomas, P. J.

2011-10-01

376

Adsorption of Pb(2+) ions on nanosized gamma-Fe(2)O(3): formation of surface ternary complexes on ligand complexation.  

PubMed

Adsorption of Pb(2+) ions on the combustion derived nanosized gamma-Fe(2)O(3) and its thiourea complex composite is reported. The adsorbents upon adsorption of Pb(2+) ions are characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and infrared spectroscopy techniques. The eluent is characterised by atomic absorption spectroscopy for the estimation of Pb(2+) ions. The reduction in the amount of lead after adsorption was estimated to be around 50% in case of complex composite adsorbent and around 15% in case of the gamma-Fe(2)O(3) adsorbents. Orthorhombic PbSO(4) precipitated out from the eluent and is reported with a model reaction. Adsorption of lead onto the complex composite is explained through the formation of a surface tertiary complex. The advantage of employing a thiourea-gamma-Fe(2)O(3) complex composite as solid adsorbent for the adsorption of heavy metal pollutants is envisaged in the present investigation. PMID:18969034

Mallikarjuna, N N; Venkataraman, A

2003-05-28

377

Neuronal inputs to hippocampal formation in Alzheimer's disease and in parkinsonism-dementia complex on Guam  

Microsoft Academic Search

This study concerns the expression of synaptophysin in the hippocampal formation of normal controls, of patients with Alzheimer's disease (AD) and of patients with parkinsonism-dementia complex on Guam (P-D complex). A monoclonal antibody was used to visualize synaptophysin, an integral component of presynaptic vesicle membranes. In the normal controls, a strong synaptophysin immunoreactivity was seen in the stratum pyramidale, stratum

S. Goto; A. Hirano

1990-01-01

378

Formation of complex impact craters - Evidence from Mars and other planets  

Microsoft Academic Search

An analysis of the depth vs diameter data of Arthur (1980), is given along with geomorphic data for 73 Martian craters. The implications for the formation of complex impact craters on solid planets is discussed. The analysis integrates detailed morphological observations on planetary craters with geologic data from terrestrial meteorite and explosion craters. The simple to complex transition for impact

R. J. Pike

1980-01-01

379

The nature and extent of synaptonemal complex formation in haploid barley  

Microsoft Academic Search

Normal synaptonemal complexes have been found in haploid barley meiotic prophase at stages equivalent to pachytene in diploids. Reconstructions of serially sectioned nuclei have shown that up to 60% of the haploid chromosomes may pair in either intra- or interchromosomal associations. The extent and nature of the synaptonemal complex formation suggest that the chromosome pairing is non-homologous. From the virtual

C. B. Gillies

1974-01-01

380

An electron microscopic study of synaptonemal complex formation at zygotene in rye  

Microsoft Academic Search

A spreading technique was used to allow ultrastructural analysis of seventeen zygotene nuclei of rye (Secale cereale). Twenty pachytene nuclei were also examined. Lateral element lengths of the haploid complements decreased from 742 µm at the beginning of zygotene to 451 µm at the end of zygotene. Variation in pachytene synaptonemal complex lengths was also noted. Zygotene synaptonemal complex formation

C. B. Gillies

1985-01-01

381

Dynamics of Nanoparticle-Protein Corona Complex Formation: Analytical Results from Population Balance Equations  

PubMed Central

Background Nanoparticle-protein corona complex formation involves absorption of protein molecules onto nanoparticle surfaces in a physiological environment. Understanding the corona formation process is crucial in predicting nanoparticle behavior in biological systems, including applications of nanotoxicology and development of nano drug delivery platforms. Method This paper extends the modeling work in to derive a mathematical model describing the dynamics of nanoparticle corona complex formation from population balance equations. We apply nonlinear dynamics techniques to derive analytical results for the composition of nanoparticle-protein corona complex, and validate our results through numerical simulations. Results The model presented in this paper exhibits two phases of corona complex dynamics. In the first phase, proteins rapidly bind to the free surface of nanoparticles, leading to a metastable composition. During the second phase, continuous association and dissociation of protein molecules with nanoparticles slowly changes the composition of the corona complex. Given sufficient time, composition of the corona complex reaches an equilibrium state of stable composition. We find analytical approximate formulae for metastable and stable compositions of corona complex. Our formulae are very well-structured to clearly identify important parameters determining corona composition. Conclusion The dynamics of biocorona formation constitute vital aspect of interactions between nanoparticles and living organisms. Our results further understanding of these dynamics through quantitation of experimental conditions, modeling results for in vitro systems to better predict behavior for in vivo systems. One potential application would involve a single cell culture medium related to a complex protein medium, such as blood or tissue fluid.

Darabi Sahneh, Faryad; Scoglio, Caterina; Riviere, Jim

2013-01-01

382

Effect of ligand basicity on the formation and dissociation equilibria and kinetics of Gd{sup 3+} complexes of macrocyclic polyamino carboxylates  

SciTech Connect

Formation and dissociation equilibria and reaction kinetics for Gd(III) complexes of GdL(L is HE-DO3A = 10-(2-hydroxyethyl)-1,4,7,10-tetraazacyclodecance-1,4,7-triacetic acid, HP-DO3A = 10-(2-hydroxyisopropyl)1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, AND HIP-DO3A = 10-(2-hydroxyisopropyl)-1,4,7,10-tetraazacyclododecnae-1,4,7-triacetic acid). Stability constants were measured and reaction kinetics were studied. Relationships of ligand basicity to reaction rate and stability was discussed.

Kumar, K.; Tweedle, M.F. [Bristol-Myers Squibb Pharmaceutical Research Inst., Princeton, NJ (United States); Tianzhu Jin; Xiangym Wang; Desreux, J.F. [Univ. of Liege (Belgium)

1994-08-17

383

The thermodynamic functions of formation and transfer of copper(II) and nickel(II) ethylenediaminetetraacetate complexes with ammonia in aqueous-ethanolic solutions  

NASA Astrophysics Data System (ADS)

The formation of mixed-ligand NiEdtaNH{3/2-} and CuEdtaNH{3/2-} complexes in an aqueous-ethanolic solvent with the mole fractions of ethanol 0.1 and 0.2 at 298.15 K and ionic strength I = 0.4 (KNO3) was studied calorimetrically. The thermodynamic characteristics of formation and transfer parameters of these complexes were calculated. The influence of the mixed solvent on the thermodynamic characteristics of these reactions was studied.

Khrenova, E. V.; Pyreu, D. F.; Kozlovskii, E. V.

2011-03-01

384

Formation of Nitriles in the Interstellar Medium via Reactions of Cyano Radicals, CN(X2?+), with Unsaturated Hydrocarbons  

NASA Astrophysics Data System (ADS)

Crossed molecular beam experiments of cyano radicals, CN(X2?+, ?=0), in their electronic and vibrational ground state reacting with unsaturated hydrocarbons acetylene, C2H2(X1?+g), ethylene, C2H4(X1Ag), methylacetylene, CH3CCH(X1A1), allene, H2CCCH2(X1A1), dimethylacetylene, CH3CCCH3(X1A1'), and benzene, C6H6 (X1A1g), were performed at relative collision energies between 13.3 and 36.4 kJ mol-1 to unravel the formation of unsaturated nitriles in the outflows of late-type AGB carbon stars and molecular clouds. In all reactions, the CN radical was found to attack the ? electron density of the hydrocarbon molecule with the radical center located at the carbon atom; the formation of an initial addition complex is a prevalent pathway on all the involved potential energy surfaces. A subsequent carbon-hydrogen bond rupture yields the nitriles cyanoacetylene, HCCCN (X1?+), vinylcyanide, C2H3CN (X1A'), 1-methylcyanoacetylene, CH3CCCN (X1A1), cyanoallene, H2CCCH(CN) (X1A'), 3-methylcyanoacetylene, HCCCH2CN(X1A'), 1,1-cyanomethylallene, H2CCC(CN)(CH3) (X1A'), and cyanobenzene, C6H5CN (X1A1). In case of acetylene and ethylene, a second reaction channel involves a [1, 2]-H atom shift in the initial HCCHCN and H2CCH2CN collision complexes prior to a hydrogen atom release to form cyanoacetylene, HCCCN (X1?+), and vinylcyanide, C2H3CN (X1A'). Since all these radical-neutral reactions show no entrance barriers, have exit barriers well below the energy of the reactant molecules, and are exothermic, the explicit identification of this CN versus H atom exchange pathway under single collision conditions makes this reaction class a compelling candidate to synthesize unsaturated nitriles in interstellar environments holding temperatures as low as 10 K. This general concept makes it even feasible to predict the formation of nitriles once the corresponding unsaturated hydrocarbons are identified in the interstellar medium. Here HCCCN, C2H3CN, and CH3CCCN have been already observed; since CH3CCH is the common precursor to H2CCCH(CN)/CH3CCCN and the latter isomer has been assigned unambiguously toward TMC-1 and OMC-1, H2CCCH(CN) is strongly expected to be present in both clouds as well. The formation of isonitrile isomers was not observed in our experiments. Since all reactions to HCCNC, C2H3NC, CH3CCNC, H2CCCH(NC), H2CCC(NC)(CH3), and C6H5NC are either endothermic or the exit barrier is well above the energy of the reactants, neutral-neutral reactions of cyano radicals with closed shell unsaturated hydrocarbons cannot synthesize isonitriles in cold molecular clouds. However, in outflow of carbon stars, the enhanced translational energy of both reactants close to the photosphere of the central star can compensate this endothermicity, and isonitriles might be formed in these hotter environments as well.

Balucani, N.; Asvany, O.; Huang, L. C. L.; Lee, Y. T.; Kaiser, R. I.; Osamura, Y.; Bettinger, H. F.

2000-12-01

385

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

PubMed

The transformation of two benzophenone UV filters (Oxybenzone and Dioxybenzone) was examined over the pH range 6-11 in the presence of excess aqueous chlorine. Under these conditions, both UV filters were rapidly transformed by aqueous chlorine just above circumneutral pH while transformation rates were significantly lower near the extremes of the pH range investigated. Observed first-order rate coefficients (k(obs)) were obtained at each pH for aqueous chlorine concentrations ranging from 10 to 75 ?M. The k(obs) were used to determine the apparent second-order rate coefficient (k(app)) at each pH investigated as well as determine the reaction order of aqueous chlorine with each UV filter. The reaction of aqueous chlorine with either UV filter was found to be an overall second-order reaction, first-order with respect to each reactant. Assuming elemental stoichiometry described the reaction between aqueous chlorine and each UV filter, models were developed to determine intrinsic rate coefficients (k(int)) from the k(app) as a function of pH for both UV filters. The rate coefficients for the reaction of HOCl with 3-methoxyphenol moieties of oxybenzone (OXY) and dioxybenzone (DiOXY) were k(1,OxY) = 306 ± 81 M?¹s?¹ and k(1,DiOxY) = 154 ± 76 M?¹s?¹, respectively. The k(int) for the reaction of aqueous chlorine with the 3-methoxyphenolate forms were orders of magnitude greater than the un-ionized species, k(2,OxY) = 1.03(±0.52) × 10? M?¹s?¹ and k(2_1,DiOxY) = 4.14(±0.68) × 10? M?¹s?¹. Also, k(int) for the reaction of aqueous chlorine with the DiOXY ortho-substituted phenolate moiety was k(2_2,DiOxY) = 2.17(±0.30) × 10³ M?¹s?¹. Finally, chloroform formation potential for OXY and DiOXY was assessed over the pH range 6-10. While chloroform formation decreased as pH increased for OXY, chloroform formation increased as pH increased from 6 to 10 for DiOXY. Ultimate molar yields of chloroform per mole of UV filter were pH dependent; however, chloroform to UV filter molar yields at pH 8 were 0.221 CHCl?/OXY and 0.212 CHCl?/DiOXY. PMID:23168312

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

2012-10-24

386

Characterizing Pyroxene Reaction Space in Calcium-Aluminum Rich Inclusions: Oxidation During CAI Rim Formation  

NASA Astrophysics Data System (ADS)

We define the reaction space that controls changes in pyroxene composition in CAIs and Wark-Lovering (WL) rims in an oxidizing solar nebula. Ti-rich pyroxenes in CAIs record a sub-solar oxygen fugacity (Ti3+/Ti4+~1.5). WL rim pyroxenes in the CAI Leoville 144A have a distinctly lower oxidation state.This difference supports WL rim condensation in an environment of increasing O2(g) and Mg(g) (Simon et al. 2005). We used the following phase components to identify four linearly independent reactions (Thompson 1982): diopside, CaTs (Al2Mg-1Si-1), T3 (Ti3+AlMg-1Si-1), T4 (Ti4+Al2Mg-1Si-2), En (MgCa-1), perovskite, O(g), Mg(g), SiO(g), and Ca(g). Compositional variation in this system is dominated by two reactions. The first is oxidation of Ti3+ via reaction with O and Mg in the gas phase: 1.5 O(g) + Mg(g) ? ¼ Di + [Ti4+Mg3/4Ti3+-1Ca-1/4Si-1/2] (1). Pyroxene is produced and En is introduced. The second reaction (2) is perovskite formation. It is observed in the WL rim of Leoville 144A, and experiments confirm that an elevated Ti component converts pyroxene to perovskite(Gupta et al. 1973). MgCa-1 is the third linearly independent reaction (3). They combine to give: ½ Di + x Ca(g)? x Mg(g)+ Pv + [Mg1/2-xSiTi4+-1Ca-1/2+x](2,3). Unlike (1), pyroxene is consumed in this reaction. The parameter x defines the extent of Mg-Ca exchange. When x > 0.5, WL rim formation occurs in an environment where Mg is volatile and Ca condenses. The reaction space defined by reactions (1) and (2,3) describes the transition from CAI interior to WL rims. WL rim pyroxene Ti contents, [CaTs], and Ca < 1 pfu are all explained in this space. The fourth linearly independent reaction is SiO(g):1/8 Di + ¼ Mg(g)? ¾ SiO(g) + [Mg3/8Ca1/8Ti4+Ti3+-1Si-1/2](4). Silica reduction forms Ti4+, releasing SiO(g). (4) does not describe the oxidation of Ti3+ in WL rim pyroxene, but (1) - (4) results in En formation directly from the gas phase. This may explain WL rim analyses that have Si contents in excess of those predicted from reactions (1) and (2,3). Simon et al. (2005) EPSL 41, 272-283; Thompson (1982)Rev. Min. 10, 33-52; Gupta et al. (1973) Contr. Mineral. Petrol. 41, 333-344 Reaction space for CAI pyroxene. Pyroxenes plotted using titanium contents.

Dyl, K. A.; Young, E. D.

2009-12-01

387

Mono- versus bis-chelate formation in triazenide and amidinate complexes of magnesium and zinc.  

PubMed

Magnesium and zinc complexes of the monoanionic ligands N,N'-bis(2,6-di-isopropylphenyl)triazenide, L1, N,N'-bis(2,6-di-isopropylphenyl)acetamidinate, L2, and N,N'-bis(2,6-di-isopropylphenyl)tert-butylamidinate, L3, have been synthesized, but only L3 possesses sufficient steric bulk to prevent bis-chelation. Hence, the reaction of L1H with excess ZnEt2 leads to the isolation of (L1)2Zn, 1; L1H also reacts with Bu2Mg in Et2O to afford (L1)2Mg(Et2O), 2. Similar reactivity is observed for L2H, leading to the formation of (L2)2Zn, 3, and (L2)2Mg, 4. The reaction of L2H with ZnR2 may also afford the tetranuclear aggregates {(L2)Zn2R2}2O, 5 (R=Me) and 6 (R=Et). By contrast, the tert-butylamidinate ligand was found to exclusively promote mono-chelation, allowing (L3)ZnCl(THF), 7, [(L3)Zn(micro-Cl)]2, 8, (L3)ZnN(SiMe3)2, 9, (L3)MgiPr(Et2O), 10, and (L3)MgiPr(THF), 11, to be isolated. X-ray crystallographic analyses of 1, 2, 3, 4, 5, 6, 8, and 10 indicate that the capacity of L3 to resist bis-chelation is due to greater occupation of the metal coordination sphere by the N-aryl substituents. PMID:17927169

Nimitsiriwat, Nonsee; Gibson, Vernon C; Marshall, Edward L; Takolpuckdee, Pittaya; Tomov, Atanas K; White, Andrew J P; Williams, David J; Elsegood, Mark R J; Dale, Sophie H

2007-10-10

388

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.

2013-09-01

389

Hydrolysis Reactions and Carbonate Complexation of Americium(III) In Natural Aquatic Systems.  

National Technical Information Service (NTIS)

The hydrolysis reaction and carbonate complexation of the Am exp 3+ and Eu exp 3+ have been investigated in the pH region of 3 - 13 by solubility measurements at the ionic strength of 0.1 and 25 +- 0.5 exp 0 C. The solubility products of M(OH) sub 3 , M(O...

J. I. Kim M. F. Bernkopf

1984-01-01

390

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…

Eskridge, Veronica L.

391

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.

392

A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction  

Microsoft Academic Search

Most extraoral appliances used for protracting small or retropositioned maxilla do not allow for variations in the point of force application or in its direction. This variation may be necessary to control vertical, anteroposterior, as well as transverse effects. The purpose of this study was to investigate the initial reaction of the maxillofacial complex according to force magnitude, force direction,

Kong-Geun Lee; Young-Kyu Ryu; Young-Chel Park; David J. Rudolph

1997-01-01

393

Triethylborane-induced radical allylation reaction with zirconocene-olefin complex.  

PubMed

[reaction: see text] Allylzirconium reagents are effective for radical allylation of alpha-halo carbonyl compounds. The key steps would be homolytic cleavage of the zirconium-carbon bond and halogen abstraction by the resulting Cp(2)ZrCl(III). Zirconocene-olefin complex can be also utilized for the allylation of alpha-halo compounds. PMID:14961631

Hirano, Koji; Fujita, Kazuya; Shinokubo, Hiroshi; Oshima, Koichiro

2004-02-19

394

Increasing complexity of a diterpene synthase reaction with a single residue switch.  

PubMed

Terpene synthases often catalyze complex reactions involving intricate series of carbocation intermediates. The resulting, generally cyclical, structures provide initial hydrocarbon frameworks that underlie the astonishing structural diversity of the enormous class of terpenoid natural products (>50,000 known), and these enzymes often mediate the committed step in their particular biosynthetic pathway. Accordingly, how terpene synthases specify product outcome has drawn a great deal of attention. In previous work, we have shown that mutational introduction of a hydroxyl group at specific positions within diterpene synthase active sites can "short circuit" complex cyclization and/or rearrangement reactions, resulting in the production of "simpler"' diterpenes. Here we demonstrate that the converse change, substitution of an Ile for Thr at the relevant position in a native pimaradiene synthase, leads to a dramatic increase in reaction complexity. Product outcome is shifted from the tricyclic pimaradiene to a rearranged tetracycle, aphidicol-15-ene. Thus, the nature of the residue at this position acts as a true switch for product outcome. In addition, the ability of aliphatic residue substitution to enable a more complex reaction emphasizes the importance of substrate conformation imposed by a largely inert active site. Furthermore, the profound plasticity of diterpene synthases exemplified by this single residue switch for product outcome is consistent with the screening/diversity-oriented hypothesis of natural products metabolism. PMID:18366162

Morrone, Dana; Xu, Meimei; Fulton, D Bruce; Determan, Mara K; Peters, Reuben J

2008-03-26

395

Improvement of the stoichiometric network analysis for determination of instability conditions of complex nonlinear reaction systems  

Microsoft Academic Search

Stoichiometric network analysis (SNA), a known method for analyzing complex reaction systems including biochemical ones, is improved and applied to a nonlinear process studied far from equilibrium in a continuously fed, well stirred tank reactor (CSTR). A particular attention is focused on the determination of the narrow range of the control parameter values where the main steady state is unstable

Ljiljana Kolar-Ani?; Željko ?upi?; Guy Schmitz; Slobodan Ani?

2010-01-01

396

20S cyclosome complex formation and proteolytic activity inhibited by the cAMP\\/PKA pathway  

Microsoft Academic Search

THE 20S cyclosome complex (also known as the anaphase-promoting complex) has ubiquitin ligase activity and is required for mitotic cyclin destruction1-3 and sister chromatid separation4,5. The formation and activation of the 20S cyclosome complex is regulated by an unknown mechanism. Here we show that Cut4 (ref. 6) is an essential component of the cyclosome in fission yeast. Cut4 shares sequence

Yukiko M. Yamashita; Yukinobu Nakaseko; Itaru Samejima; Kazuki Kumada; Hiroshi Yamada; David Michaelson; Mitsuhiro Yanagida

1996-01-01

397

Distinct domains of syntaxin are required for synaptic vesicle fusion complex formation and dissociation  

Microsoft Academic Search

Membrane fusion resulting in neurotransmitter secretion forms the basis of neural communication. Three multimeric complexes of the protein syntaxin are important in this process: syntaxin and n-sect; syntaxin, VAMP, and SNAP-25; and syntaxin, VAMP, SNAP-25, ?SNAP, and NSF (20S complex). In this report, we demonstrate that unique, yet overlapping, domains of syntaxin are required to form these complexes. The formation

Yun Kee; Richard C Lin; Shu-Chan Hsu; Richard H Scheller

1995-01-01

398

Oxidative double dehalogenation of tetrachlorocatechol by a bio-inspired CuII complex: formation of chloranilic acid.  

PubMed

Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1. PMID:18449873

Bruijnincx, Pieter C A; Viciano-Chumillas, Marta; Lutz, Martin; Spek, Anthony L; Reedijk, Jan; van Koten, Gerard; Klein Gebbink, Robertus J M

2008-01-01

399

Simulation of dual temperature ion-exchange separation process taking into account complex formation in solution  

SciTech Connect

A mathematical modeling of a dual temperature ion-exchange separation system is reported. The nonlinear nonequilibrium model created takes into account the following physicochemical processes: kinetics, ion-exchange reactions, complex formation accomplishing the chemical equilibria. The model was applied for a system containing Cu{sup 2+} and Zn{sup 2+} in acidic sulfate solutions and the iminodiacetic ion-exchange resin Amberlite IRC-718. Good agreement to the experimental data was found. The dependence of the separation efficiency on different factors was tested. The advantage of nonequilibrium operations for the effective separation was shown. The optimal separation cycle was calculated for a sulfate solution containing 1.5 mM Cu and 20 mM Zn at pH 2.05. An ion-exchange column can process 207 bed volumes of the treated solution during one cycle. The effluent is separated for three fractions. The first fraction (75 bed volumes) is the solution containing the 9 times reduced Cu concentration. The second one (36 bed volumes) is the concentrate of Cu. The third fraction is mixed and recycled for repeated treatment.

Tikhonov, N.A.; Zagorodni, A.A. [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Inorganic Chemistry

1998-03-01

400

Formation of BaSO4 fibres with morphological complexity in aqueous polymer solutions.  

PubMed

BaSO4 fibres with morphological complexity were formed in aqueous solution with polyacrylate and partially monophosphonated poly(ethyleneoxide)-block-poly(methacrylic acid) additives by a simple precipitation reaction. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2+:polymer molar ratio (R). At S = 60 to 80, and R = 3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although the yield was low. The nanofilaments were also organized into cone-shaped aggregates at S = 80, and at lower R values these formed higher-order structures that consisted of multiple cone-on-cone assemblies with remarkable self-similarity. Increasing the supersaturation produced ovoid or cross-shaped dendritic particles for the range of molar ratios studied. In contrast, BaSO4 crystallisation in the presence of a partially phosphonated block copolymer gave a high yield of BaSO4 fibres up to 100 microm in length, and consisting of co-aligned bundles of 30 nm-diameter defect-free single-crystal nanofilaments with a uniform growth tip. A model for the defect-free growth of BaSO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is proposed. PMID:11560323

Qi, L; Cölfen, H; Antonietti, M; Li, M; Hopwood, J D; Ashley, A J; Mann, S

2001-08-17

401

Method for inhibiting the formation of SET1 family core complexes  

US Patent & Trademark Office Database

Disclosed in this specification is a method for inhibiting the formation of SET1 family core complexes. A guanidinium-containing molecule is used to competitively inhibit the binding of the N-SET region of a SET1 protein to WDR5, thus inhibiting the formation of the SET1 family core complex. The guanidinium-containing molecule may be, for example, an arginine-containing peptide. When bound to WDR5, the guanidinium moiety is bound between the F-133 and F-263 residues of the WDR5 when a crystal structure of the bound complex is obtained.

2012-03-13

402

SOLUBILITY AND ION EXCHANGE METHODS FOR DETERMINING THE COMPLEX FORMATION OF PLUTONIUM AND AMERICIUM III IN AQUEOUS SOLUTIONS  

Microsoft Academic Search

The formation of Pu(IV) complexes in phosphoric acid solutions and the ; dissociation constants of Pu(IV) phosphate complexes were studied by solubility ; methods. The Me: addend ratio of various Pu(IV) phosphate complexes and ; complexes of other investigated systems tends to shift, with the increase of ; complex forming agent concentration, toward the side of complexes with larger ;

Moskin

1959-01-01

403

A new reaction mode of germanium-silicon bond formation: insertion reactions of H2GeLiF with SiH 3X (X?=?F, Cl, Br).  

PubMed

A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H2GeLiF with SiH3X (X?=?F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X?=?F), 95.28 (X?=?Cl), and 84.42 (X?=?Br) kJ mol(-1) for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH3-Br?>?SiH3-Cl?>?SiH3-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation. PMID:23949419

Yan, Bingfei; Li, Wenzuo; Xiao, Cuiping; Li, Qingzhong; Cheng, Jianbo

2013-08-16

404

Microbanded manganese formations; protoliths in the Franciscan Complex, California  

USGS Publications Warehouse

The Buckeye manganese deposit, 93 km southeast of San Francisco in the California Coast Ranges, preserves a geologic history that provides clues to the origin of numerous lenses of manganese carbonate, oxides, and silicates that occur with interbedded radiolarian chert and metashale of the Franciscan Complex. Compositionally and mineralogically laminated Mn-rich protoliths were deformed and dismembered, in a manner that mimics in smaller scale the deformation of the host complex, and then were incipiently metamorphosed at blueschistfacies conditions. Eight phases occur as almost monomineralic protoliths and mixtures: rhodochrosite, caryopilite, chlorite, gageite, taneyamalite, braunite, hausmannite, and laminated chert (quartz). Braunite, gageite, and some chlorite and caryopilite layers were deposited as gel-like materials; rhodochrosite, most caryopilite, and at least some hausmannite layers as lutites; and the chert as turbidites of radiolarian sand. Some gel-like materials are now preserved as transparent, sensibly isotropic relics of materials that fractured or shattered when deformed, creating curved surfaces. In contrast, the micrites flowed between the fragments of gel-like materials. The orebody and most of its constituent minerals have unusually Mn-rich compositions that are described by the system MnO-SiO2-O2-CO2-H2O. High values of Mn/Fe and U/Th, and low concentrations of Co, Cu, and Ni, distinguish the Buckeye deposit from many high-temperature hydrothermal deposits and hydrogenous or diagenetic manganese and ferromanganese nodules and pavements. This chemical signature suggests that ore deposition was related to fluids from the sediment column and seawater. Tungsten is associated exclusively with gageite, in concentrations as high as 80 parts per million. The source of the manganese is unknown; because basalts do not occur near the deposit, it was probably manganese leached from the sediment column by reducing solutions. Low concentrations of calcium (CaO approximately 0.6 weight percent) suggest that the host sediments formed beneath the carbonate-compensation depth. The most probable cause of the microbanding is changing proportions of chemical fluxes supplied to the sediment-seawater interface. The principal fluxes were biogenic silica from the water column, carbon dioxide from organic matter in the sediment column, O2 and other seawater constituents, and Mn +2-bearing fluid. The presence of Al2O3 and TiO2 (supplied by a detrital flux) in the metashale but not the ore lens suggests rapid ore deposition. Material supply-rate changes were probably due to a complex combination of episodic variations in the hydrothermal flux and periodic flows of radiolarian sand (silica and CO2 fluxes) that may be related to climate variations. The processes that form recent marine hydrothermal mounds may be the same as processes that formed the Buckeye deposit. Features common to both include the presence of Mn-oxyhydroxide crusts (corresponding to the Buckeye orebody), a large Mn/Fe ratio, low abundances of most minor elements, and small size. The most important differences are the absence of rhodochrosite and manganese silicates, interlayered with oxide, and the absence of adjacent chert in the contemporary deposits. These differences may be due to an absence of the debris of siliceous pelagic organisms, which accumulated in the Buckeye paleoenvironment. Periodic turbidity flows of chert-forming radiolarian sand could provide the changes in the fluxes of silica and organic matter necessary to form manganese carbonate and silicates. Turbidity flows of graywacke indicate proximity to an environment with high relief. A possible paleodepositional environment is an oceanic spreading center approaching a continental margin at which subduction occurred.

Huebner, J. Stephen; Flohr, Marta J.

1990-01-01

405

Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions  

PubMed Central

We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag-NHC) complexes. A set of four Ag-NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag-NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methyl-1H-imidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography, and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the ? isomer regardless of neighboring group effects.

Talisman, Ian J.; Kumar, Vineet; Deschamps, Jeffrey R.; Frisch, Mark

2011-01-01

406

Regulation of complement membrane attack complex formation in myocardial infarction.  

PubMed Central

Recent studies have suggested that the complement (C) system is involved in the development of tissue injury of myocardial infarction. As it is not known why the strictly controlled C system starts to react against autologous heart tissue, we have analyzed the expression of various membrane regulators of C (CR1, DAF, MCP, CD59, C8 binding protein) and the pattern of deposition of C components and plasma C regulators (C4b binding protein and vitronectin) in normal (n = 7) and infarcted (n = 13) human myocardium. In the infarcted myocardium deposits of the C membrane attack complex (MAC) were observed by immunofluorescence microscopy, and lesions resembling the transmembrane channels of MAC were detected by transmission electron microscopy. CD59 and C8 binding protein were strongly expressed by muscle cells of normal myocardial tissue. Little or no CR1, MCP, and DAF was observed on these cells. The assembly of MAC was accompanied by the deposition of vitronectin (S-protein) and C4b binding protein in the infarcted areas of myocardium. In accordance with our earlier results the expression of CD59 but not of C8 binding protein was clearly diminished in the lesions. The results show that C8 binding protein, vitronectin, and C4b binding protein do not prevent complement attack against the infarcted myocardium but rather become codeposited with the MAC. Ischemia-induced transformation of nonviable cells into complement activators, acquired loss of resistance to the MAC by shedding of CD59, and recruitment of multifunctional serum proteins by MAC could thus constitute a general process aimed at the clearance of injured tissue. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Vakeva, A.; Laurila, P.; Meri, S.

1993-01-01

407

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

National Technical Information Service (NTIS)

Rates of complex formation and dissociation in NpO(sub 2)(sup +)- Chlorophosphonazo III (2,7-bis(4-chloro- 2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studi...

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

1996-01-01

408

Fission and quasifission modes in heavy-ion-induced reactions leading to the formation of Hs{sup *}  

SciTech Connect

Mass and energy distributions of binary reaction products obtained in the reactions {sup 22}Ne+{sup 249}Cf,{sup 26}Mg+{sup 248}Cm, {sup 36}S+{sup 238}U, and {sup 58}Fe+{sup 208}Pb have been measured. All reactions lead to Hs isotopes. At energies below the Coulomb barrier the bimodal fission of Hs{sup *}, formed in the reaction {sup 26}Mg+{sup 248}Cm, is observed. In the reaction {sup 36}S+{sup 238}U, leading to the formation of a similar compound nucleus, the main part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier fusion-fission is the main process leading to the formation of symmetric fragments for both reactions with Mg and S ions. In the case of the {sup 58}Fe+{sup 208}Pb reaction the quasifission process dominates at all measured energies.

Itkis, I. M.; Kozulin, E. M.; Itkis, M. G.; Knyazheva, G. N.; Bogachev, A. A.; Chernysheva, E. V.; Krupa, L.; Oganessian, Yu. Ts.; Zagrebaev, V. I.; Rusanov, A. Ya.; Goennenwein, F.; Dorvaux, O.; Stuttge, L.; Hanappe, F.; Vardaci, E.; Goes Brennand, E. de [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Nuclear Physics of the National Nuclear Center of Kazakhstan, 050032 Almaty (Kazakhstan); Physikalisches Institut, Universitaet Tuebingen, D-72076 Tuebingen (Germany); Institut Pluridisciplinaire Hubert Curien and Universite de Strasbourg, F-67037 Strasbourg (France); Universite Libre de Bruxelles, CP229, B-1050 Bruxelles, Belgique (Belgium); Istituto Nazionale di Fisica Nucleare and Dipartimento di Scienze Fisiche dell'Universita di Napoli, Napoli (Italy); Departamento de Fisica, Universidade Estadual da Paraiba, 58109-753 Campina Grande (Brazil)

2011-06-15

409

Hierarchical network between the components of the multi-tRNA synthetase complex: implications for complex formation.  

PubMed

The macromolecular tRNA synthetase complex consists of nine different enzymes and three non-enzymatic factors. This complex was recently shown to be a novel signalosome, since many of its components are involved in signaling pathways in addition to their catalytic roles in protein synthesis. The structural organization and dynamic relationships of the components of the complex are not well understood. Here we performed a systematic depletion analysis to determine the effects of structural intimacy and the turnover of the components. The results showed that the stability of some components depended on their neighbors. Lysyl-tRNA synthetase was most independent of other components for its stability whereas it was most required for the stability of other components. Arginyl- and methionyl-tRNA synthetases had the opposite characteristics. Thus, the systematic depletion of the components revealed the functional reason for the complex formation and the assembly pattern of these multi-functional enzymes and their associated factors. PMID:17062567

Han, Jung Min; Lee, Min Ji; Park, Sang Gyu; Lee, Sun Hee; Razin, Ehud; Choi, Eung-Chil; Kim, Sunghoon

2006-10-24

410

Complexation Facilitated Reduction of Aromatic N-Oxides by Aqueous Fe(II)-Tiron Complex: Reaction Kinetics and Mechanisms.  

PubMed

Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom. PMID:23957215

Chen, Yiling; Zhang, Huichun

2013-09-09

411

Ligand substitution reactions of a phenolic quinolyl hydrazone; oxidovanadium (IV) complexes  

PubMed Central

Background Quinoline ring has therapeutic and biological activities. Quinolyl hydrazones constitute a class of excellent chelating agents. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have aimed to study the competency effect of a phenolic quinolyl hydrazone (H2L; primary ligand) with some auxiliary ligands (Tmen, Phen or Oxine; secondary ligands) towards oxidovanadium (IV) ions. Results Mono- and binuclear oxidovanadium (IV) - complexes were obtained from the reaction of a phenolic quinolyl hydrazone with oxidovanadium (IV)- ion in absence and presence of N,N,N',N'- tetramethylethylenediamine (Tmen), 1,10-phenanthroline (Phen) or 8-hydroxyquinoline (Oxine). The phenolic quinolyl hydrazone ligand behaves as monobasic bidentate (NO- donor with O- bridging). All the obtained complexes have the preferable octahedral geometry except the oxinato complex (2) which has a square pyramid geometry with no axial interaction; the only homoleptic complex in this study. Conclusion The ligand exchange (substitution/replacement) reactions reflect the strong competency power of the auxiliary aromatic ligands (Phen/Oxine) compared to the phenolic quinolyl hydrazone (H2L) towards oxidovanadium (IV) ion; (complexes 2 and 3). By contrast, in case of the more flexible aliphatic competitor (Tmen), an adduct was obtained (4). The obtained complexes reflect the strength of the ligand field towards the oxidovanadium (IV)- ion; Oxine or Phen >> phenolic hydrazone (H2L) > Tmen.

2011-01-01

412

Asymmetric 1,3-Dipolar Cycloaddition Reactions Catalyzed by Heterocycle-Based Metal Complexes  

NASA Astrophysics Data System (ADS)

Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, ?-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.

Suga, Hiroyuki

413

Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space  

NASA Astrophysics Data System (ADS)

Gas phase chemistry in the cold interstellar clouds is dominated by ion-molecule and radical-radical interactions, though some neutral-neutral reactions are also barrier-free and efficient at cold temperatures. It has been suggested that it is impossible to synthesize detectable abundances of the pre-biotic HCN oligomer adenine (H5C5N5) in the interstellar medium via successive neutral-neutral reactions. We attempted therefore to use quantum chemical techniques to explore if adenine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains. We report results of ab initio calculations for the formation of adenine starting from some of the simple neutral molecules and radicals detected in the interstellar space. The reaction path is found to be totally exothermic and barrier free, which increases the probability of occurrence in the cold interstellar clouds (10 - 50 K). We also estimated the reaction rates.

Gupta, V. P.; Tandon, P.; Rawat, P.; Singh, R. N.; Singh, A.

2011-04-01

414

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

NASA Astrophysics Data System (ADS)

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

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

1980-12-01

415

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

PubMed

A number of routes have been suggested for the prebiotic synthesis of uracil involving the reaction of urea with malic acid, propiolic acid, cyanoacetylene and others. Cyanoacetylene has been detected in the interstellar medium as well as simulated prebiotic experiments. It is therefore plausible that dicyanoacetylene and its hydrolytic product acetylene dicarboxylic acid (ADCA) may have played a role in chemical evolution. This aspect has been examined in the present work for the synthesis of uracil from ADCA and urea reaction. It was found that when ADCA reacted with urea, uracil was formed only in the presence of phosphoric acid and phosphates. ammonium phosphates gave higher yields of uracil than other phosphates. In the absence of phosphoric acid or phosphates no uracil formation took place. This type of synthesis could have taken place in prebiotic oceans which contained ammonium phosphates and other salts. PMID:7454254

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

1980-12-01

416

Monte Carlo simulation and linear stability analysis of Turing pattern formation in reaction-subdiffusion systems  

NASA Astrophysics Data System (ADS)

Subdiffusion is an important physical phenomenon observed in many systems. However, numerical techniques to study it, especially when coupled to reactions, are lacking. In this paper, we develop an efficient Monte Carlo algorithm based on the Gillespie algorithm and the continuous-time ra