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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

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

NASA Astrophysics Data System (ADS)

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

Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

2015-04-01

3

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

4

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

5

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

NASA Astrophysics Data System (ADS)

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

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

1996-11-01

6

Kinetics of actinide complexation reactions  

SciTech Connect

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

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

1997-09-01

7

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

NASA Astrophysics Data System (ADS)

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

Apel, Charles L.; Deamer, David W.

2005-08-01

8

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

PubMed

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

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

2013-09-01

9

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 Central

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [CrIII(14-TMC)(O2)(Cl)]+, with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [CrIV(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 EPR 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, [CrIII(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

2013-01-01

10

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

PubMed

Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO4, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe2(?-CysS)2(NO)4, a Roussin's red salt ester (Cys-RSE), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe(NO)2(CysS)2(-) (Cys-DNIC) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both Cys-RSE and Cys-DNIC are formed via a common intermediate Fe(NO)(CysS)2(-). Cys-DNIC and Cys-RSE interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the Cys-RSE formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant kNO = 6.9 × 10(7) M(-1) s(-1). In contrast, photolysis of the mononuclear-DNIC species Cys-DNIC formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS(•) radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes. PMID:25479566

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

2015-01-14

11

Theoretical study on the atmospheric reaction of SO2 with the HO2 and HO2·H2O complex formation HSO4 and H2SO3  

NASA Astrophysics Data System (ADS)

The influence of a single water molecule on the gas-phase reactivity of HO2 radical has been investigated by theoretical studying the reaction of SO2 with the HO2 radical and the HO2·H2O radical complex, respectively. The former leads to the formation of the HSO4 radical, while in the latter reaction the water slightly accelerates the SO2 + HO2 reaction to form HSO4·H2O radical complex and the HO2 acts as a positive catalyst for the formation H2SO3·HO2 complex in the SO2 + H2O reaction, respectively. The rate constants at 298 K are calculated using transition state theory.

Chen, Xiayu; Tao, Cen; Zhong, Li; Gao, Ya; Yao, Wei; Li, Shujin

2014-07-01

12

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

PubMed

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules. PMID:17899888

Mohamed, Mahmoud M A

2007-08-01

13

Formation of whey protein\\/ ?-casein complexes in heated milk: Preferential reaction of whey protein with ?-casein in the casein micelles  

Microsoft Academic Search

Studies of the formation of soluble ?-casein\\/whey protein (WP) complexes in heated (90°C10min?1) milk and related mixtures of proteins have been made. The use of milk samples containing different genetic variants, and having different compositions, allowed the effects of changing the natural protein balance on the formation of particles to be investigated. In addition, studies were made of the effects

Laurence Donato; Fanny Guyomarc’h; Sylvie Amiot; Douglas G. Dalgleish

2007-01-01

14

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

SciTech Connect

I. This study reports the rapid reaction under mild conditions of internal or terminal alkynes with methyl (acetyl~ acetonato) (triphenylphosphine) nickel (1) in either aromatic or ether solvents. In all cases vinylnickel products 2 are formed by insertion of the alkyne into the nickel=methyl bond. These complexes may be converted into a variety of organic products (e.g. alkenes, esters, vinyl halides) by treatment with appropriate reagents. Unsymmetrical alkynes give selectively the one regioisomer with the sterically largest substituent next to the nickel atom. In order to investigate the stereochemistry of the initial insertion, a x-ray diffraction study of the reaction of 1 with diphenylacetylene was carried out. This showed that the vinylnickel complex formed by overall trans insertion was the product of the reaction. Furthermore, subsequent slow isomerization of this complex, to a mixture of it and the corresponding cis isomer, demonstrated that this trans addition product is the kinetic product of the reaction. In studies with other alkynes, the product of trans addition was not always exclusively (or even predominantly) formed, but the ratio of the stereoisomers formed kinetically was substantially different from the thermodynamic ratio. Isotope labeling, added phosphine, and other experiments have allowed us to conclude that the mechanism of this reaction does involve initial cis addition. However, a coordinatively unsaturated vinylnickel complex is initially formed which can undergo rapid, phosphine-catalyzed cis-trans isomerization in competition with its conversion to the isolable phosphine-substituted kinetic reaction products. II. The reaction of CpMo(CO){sub 3}H (1a) with CpMo(CO){sub 3}R (2, R= CH{sub 3}, C{sub 2}H{sub 5}) at 50{degrees} C in THF gives the aldehyde RCHO and the dimers [CpMo(CO){sub 3}]{sub 2} (3a) and [CpMo(CO){sub 2}]{sub 2} (4a). Labeling one of the reactants with a methylcyclopentadienyl ligand it was possible to show that the mixed dimers MeCpMo(CO){sub 3}-(CO){sub 3}MoCp (3b) and MeCpMo(CO){sub 2}{triple_bond}(CO){sub 2}MoCp (4b) are the predominant kinetic products of the reaction. Additionally labeling the carbonyl ligands of 1a with {sup 13}CO led to the conclusion that all three of the carbonyl ligands in 1a end up in the tetracarbonyl dimers 4a if the reaction is carried out under a continuous purge of argon Trapping studies failed to find any evidence for the intermediacy of either [CpMo(CO){sub 3}]{sup -} or [CpMo(CO){sub 3}]{sup +} in this reaction. A mechanism is proposed that involves the initial migration of the alkyl ligand in 2 to CO forming an unsaturated acyl complex which reacts with 1a to give a binuclear complex containing a three center-two electron Mo-H-Mo bond. This complex then selectively looses a carbonyl from the acyl molybdenum, migrates the hydride to that same metal, and forms a metal-metal bond. This binuclear complex with the hydride and acyl ligands on one metal reductively eliminates aldehyde, and migrates a carbonyl ligand, to give 4a directly. The other product 3a is formed by addition of two molecules of free CO to 4a.

Huggins, John Mitchell

1980-06-01

15

Acceleration of enzymatic reaction of trypsin through the formation of water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid).  

PubMed

The amidase activity of bovine pancreas trypsin in water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid) (PEG-PAA) was evaluated by a colorimetric assay using L-lysine p-nitroanilide as a substrate. The enzymatic reaction of trypsin was accelerated through the complexation with PEG-PAA. By determining the kinetic parameters of the enzymatic reaction of trypsin, it was confirmed that the catalytic rate constant of the complexed trypsin was 15 times higher than that of the native trypsin. From the evaluation of pH dependence of initial reaction rate, it was indicated that this acceleration was induced by a stabilization of the imidazolium ion of the His residue in the catalytic site, the Asp-His-Ser triad, of trypsin due to the Asp units of PEG-PAA. The hydrogen bonded Asp-His pairs are critical constituents in several key enzymatic reactions including serine protease and apurinic endonucleases, and it was expected that the acceleration of the catalytic reaction might occur for other enzymes by the formation of water-soluble complexes with PEG-PAA. PMID:15762622

Kawamura, Akifumi; Yoshioka, Yuriko; Harada, Atsushi; Kono, Kenji

2005-01-01

16

Cathodic properties of a lithium-ion secondary battery using LiCoO 2 prepared by a complex formation reaction  

Microsoft Academic Search

A LiCoO2 precursor is prepared by a complex formation reaction in a solution that contains LiOH, Co(NO3)2, and humic acid it is used as a cathode for a lithium-ion rechargeable battery. Layered LiCoO2 powders are prepared in air at 700 or 850°C after preheating the precursor at 350 and 450°C, respectively. X-ray diffraction spectra of the powders display a high

Euh-Duck Jeong; Mi-Sook Won; Yoon-Bo Shim

1998-01-01

17

Bacterial formate hydrogenlyase complex  

PubMed Central

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

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

2014-01-01

18

Bacterial formate hydrogenlyase complex.  

PubMed

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

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

2014-09-23

19

Tracking the formation of a polynuclear Co16 complex and its elimination and substitution reactions by mass spectroscopy and crystallography.  

PubMed

We present the syntheses and structures of the biggest chiral cobalt coordination cluster, [Co16(L)4(H3L)8(N3)6](NO3)2·16H2O·2CH3OH (1, where H4L = S,S-1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol). 1 consists of two Co4O4 cubes (Co4(L)2(H3L)2) alternating with Co2(EO-N3)2Co2 (Co4(L)2(H3L)2(N3)2), bridged by the benzimidazole and azide nitrogen atoms to form a twisted ring. The ligand adopts both cis and trans forms, and all the rings have the same chiralilty. ESI-MS of 1 from a methanol solution of crystals reveals the fragment [Co16(L)4(H3L)8(N3)6+2H](4+), suggesting the polynuclear core is stable in solution. ESI-MS measurements from the reaction solution found smaller fragments, [Co4(H3L)4-H](3+), [Co4(H3L)4-2H](2+), [Co4(H3L)4(N3)2](2+), and [Co2(H3L)2](2+), and ESI-MS from a methanol solution of the solid deposit found in addition the Co16 core. These results and the dependence on the synthesis time allow us to propose the process for the formation of 1, which opens up a new way for the direct observation of the ligand-controlled assembly of clusters. In addition, the isolation of [Co4(H3L)4](NO3)4·4H2O (2) consisting of separate Co4O4 cubes with the ligands being only cis in crystalline form supports the proposal. Interestingly, N3(-) is replaced by either CH3O(-) or OH(-), and this is the first time that high-resolution ESI-MS is successfully utilized to examine both the step-by-step elimination and substitution of inner bridging ligands in such a high nuclear complex. Increasing the voltage results in stepwise elimination of azide from the parent cluster. The preliminary magnetic susceptibility of 1 indicates ferromagnetic cubes antiferromagnetically coupled to the squares within the cluster, though in a field of 2.5 kOe, weak and slow relaxation is observed below 4 K. PMID:23651120

Hu, Yue-Qiao; Zeng, Ming-Hua; Zhang, Kun; Hu, Sheng; Zhou, Fu-Fang; Kurmoo, Mohamedally

2013-05-29

20

Formation of interpolymer complexes  

Microsoft Academic Search

Interpolymer complex formations of poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) with oligocations as well as poly(ethylene oxide) (PEO), and poly-(N-vinyl-2-pyrrolidone of various chain lengths were studied. For the case of complexation between PMAA and oligocations, the standard free energy change for the complexation ?G° was found to be linearly dependent on the number of interacting sites, n. The stability

Eishun Tsuchida; Yoshihito Osada; Hiroyuki Ohno

1980-01-01

21

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

NASA Astrophysics Data System (ADS)

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

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

22

C-H activation and C=C double bond formation reactions in iridium ortho-methyl arylphosphane complexes.  

PubMed

The Vaska-type iridium(I) complex [IrCl(CO){PPh(2)(2-MeC(6)H(4))}(2)] (1), characterized by an X-ray diffraction study, was obtained from iridium(III) chloride hydrate and PPh(2)(2,6-MeRC(6)H(3)) with R=H in DMF, whereas for R=Me, activation of two ortho-methyl groups resulted in the biscyclometalated iridium(III) compound [IrCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)] (2). Conversely, for R=Me the iridium(I) compound [IrCl(CO){PPh(2)(2,6-Me(2)C(6)H(3))}(2)] (3) can be obtained by treatment of [IrCl(COE)(2)](2) (COE=cyclooctene) with carbon monoxide and the phosphane in acetonitrile. Compound 3 in CH(2)Cl(2) undergoes intramolecular C-H oxidative addition, affording the cyclometalated hydride iridium(III) species [IrHCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}] (4). Treatment of 2 with Na[BAr(f) (4)] (Ar(f)=3,5-C(6)H(3)(CF(3))(2)) gives the fluxional cationic 16-electron complex [Ir(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)][BAr(f) (4)] (5), which reversibly reacts with dihydrogen to afford the delta-agostic complex [IrH(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}][BAr(f)(4)] (6), through cleavage of an Ir-C bond. This species can also be formed by treatment of 4 with Na[BAr(f)(4)] or of 2 with Na[BAr(f)(4)] through C-H oxidative addition of one ortho-methyl group, via a transient 14-electron iridium(I) complex. Heating of the coordinatively unsaturated biscyclometalated species 5 in toluene gives the trans-dihydride iridium(III) complex [IrH(2)(CO){PPh(2)(2,6-MeC(6)H(3)CH=CHC(6)H(3)Me-2,6)PPh(2)}][BAr(f) (4)] (7), containing a trans-stilbene-type terdentate ligand, as result of a dehydrogenative carbon-carbon double bond coupling reaction, possibly through an iridium carbene species. PMID:17535000

Baratta, Walter; Ballico, Maurizio; Del Zotto, Alessandro; Zangrando, Ennio; Rigo, Pierluigi

2007-01-01

23

Dehydrocoupling reactions of borane-secondary and -primary amine adducts catalyzed by group-6 carbonyl complexes: formation of aminoboranes and borazines.  

PubMed

Photoirradiation of a solution of BH(3).NHR(2) (1a: R = Me, 1b: R = 1/2C(4)H(8), 1c: R = 1/2C(5)H(10), 1f: R = Et) containing a catalytic amount of a group-6 metal carbonyl complex, [M(CO)(6)] (M = Cr, Mo, W), led to dehydrogenative B-N covalent bond formation to produce aminoborane dimers, [BH(2)NR(2)](2) (2a-c, f), in high yield. During these reactions a borane sigma complex, [M(CO)(5)(eta(1)-BH(3).NHR(2))] (3), was detected by NMR spectroscopy. Similar catalytic dehydrogenation of bulkier amineboranes, BH(3).NH(i)Pr(2) (1d) and BH(3).NHCy(2) (1e, Cy = cyclo-C(6)H(11)), afforded monomeric products BH(2) horizontal lineNR(2) (4d, e). The reaction mechanism of the dehydrocoupling was investigated by DFT calculations. On the basis of the computational study, we propose that the catalytic dehydrogenation reactions proceed via an intramolecular pathway and that the active catalyst is [Cr(CO)(4)]. The reaction follows a stepwise mechanism involving NH and BH activation. Dehydrocoupling of borane-primary amine adducts BH(3).NH(2)R (1g: R = Me, 1h: R = Et, 1i: R = (t)Bu) gave borazine derivatives [BHNR](3) (5g-i). PMID:19772343

Kawano, Yasuro; Uruichi, Mikio; Shimoi, Mamoru; Taki, Seitaro; Kawaguchi, Takayuki; Kakizawa, Taeko; Ogino, Hiroshi

2009-10-21

24

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

PubMed

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

Rao, Radhika M; Aggarwal, Suresh K

2008-04-15

25

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

PubMed

The reaction of the dialdehyde N,N-di(?-formylpyrrolyl-?-methyl)-N-methylamine with two equiv. of 2,6-diisopropylaniline yielded two Schiff bases: bis(iminopyrrolylmethyl)amine () and its hydrolyzed monoimino compound () after column separation. The dimeric lithium complex [(HL)Li]2 () containing the monoanionic form of was obtained by treating with (n)BuLi. The presence of both proton donors and acceptors causes the diimino compound to undergo tautomerization to exhibit an amine-azafulvene structure, though the central amine nitrogen competes for a proton. As a result, in the presence of Pd(2+) ions, the cationic complex [Pd(Cl)(H2L)][Cl] () containing one pendant amine-azafulvene arm and the protonated central amine nitrogen was obtained. Its X-ray structure showed that the bond distances are reversed for the imino-pyrrole moiety relative to those in the structure of . However, the reaction of with [Pd(OAc)2] afforded the neutral complex [PdL] () containing the dianionic form of the ligand. The reaction of with [PdCl2(PhCN)2] yielded a zwitterionic complex [PdCl2(H2L')] () owing to the presence of the central amine nitrogen. The formation of these palladium complexes with the features mentioned above can be explained by invoking the Brønsted acid-base character of the Schiff base. Complex is fluxional owing to the up and down movements of the palladium square plane formed by two 5-membered palladacycles, which causes the interconversion of its enantiomers and is studied by the variable temperature (1)H NMR method. Furthermore, both complexes and are precatalysts for the Suzuki-Miyaura cross-coupling reaction in water. Sterically encumbered and electronically different substrates including activated aryl chlorides and benzyl halides gave the coupled products in very good yields. The reaction proceeds even at room temperature and in the presence of a large excess amount of mercury. PMID:25771810

Kumar, Rajnish; Mani, Ganesan

2015-04-01

26

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

NASA Astrophysics Data System (ADS)

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

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

27

Formation of coordination polymers or discrete adducts via reactions of gadolinium(III)-copper(II) 15-metallacrown-5 complexes with polycarboxylates: synthesis, structures and magnetic properties.  

PubMed

Reactions of the copper(II)-gadolinium(III) 15-metallacrown-5 complex [GdCu5(Glyha)5(NO3)2(H2O)6](NO3) (Glyha(2-) = dianion of glycinehydroxamic acid) with different di/tricarboxylates (1,3-phthalate, 1,4-phthalate, biphenyl-4,4'-dicarboxylate, citrate) resulted in formation of different types of products: {[(GdCu5(Glyha)5(H2O)2)(GdCu5(Glyha)5(H2O)3)(1,3-bdc)3]·16H2O}n (1), {[(GdCu5(Glyha)5(H2O)3)2(1,4-bdc)2](1,4-bdc)·8H2O}n (2), {[(GdCu5(Glyha)5(H2O)4)2(1,4-bdc)3]·8H2O}n (3), [GdCu5(Glyha)5(Citr)(H2O)4]·7H2O (4), {[GdCu5(Glyha)5(H2O)5](?2-CO3)[Cu(Fgg)]}·7H2O (5) and [Cu(Gly)2(H2O)]n (6) (where bdc(2-) is the corresponding phthalate (benzenedicarboxylate), Citr(3-) is citrate, Fgg(3-) is the trianion of [(N-formylaminoacetyl)amino]acetic acid and Gly(-) is glycinate). Complexes 1-5 contain the [GdCu5(Glyha)5](3+) cation. Complexes 2 and 3 possess the same composition but differ by the mode of p-phthalate coordination to the [GdCu5(Glyha)5](3+) unit. In compounds 1-3, metallacrown cations are linked by the corresponding phthalates in 1D, 1D and 2D polymers, respectively, whereas 4 and 5 are discrete molecules. Compound 5 is the product of a multistep reaction, which finally involves atmospheric CO2 capture. Hydrolysis of hydroxamate in this reaction is confirmed by isolation of a mononuclear copper glycine complex 6. The ?MT vs T data for 1 were fitted using a model based on the Hamiltonian ? (GdCu5) = -2J1(S1 × SGd + S2 × SGd + S3 × SGd + S4 × SGd + S5 × SGd) - 2J2(S1 × S2 + S2 × S3 + S3 × S4 + S4 × S1 + S5 × S1. The best fit corresponded to J1 = +0.60(2) cm(-1), J2 = -61.0(5) cm(-1) and zJ' = -0.035(4) cm(-1). Complex 1 is the first example of a 15-metallacrown-5 system, for which numerical values of exchange parameters have been reported. The isotherm for methanol absorption by compound 1 at 293 K was typical for microporous sorbents, whereas ethanol sorption was negligibly small. PMID:24422476

Pavlishchuk, Anna V; Kolotilov, Sergey V; Zeller, Matthias; Thompson, Laurence K; Addison, Anthony W

2014-02-01

28

Formation of molecular ?-complexes upon the mechanochemical reaction of the freshly formed surface of alkali halide crystals with some organic compounds  

Microsoft Academic Search

We have discovered that a solid-phase mechanochemical reaction proceeding upon the combined vibrational dispersion of LiF crystals with emulsified polyvinyl chloride (PVC) or maleic anhydride (MA) gives strong charge transfer complexes (CTC) on the freshly formed surface of the LiF particles. The binary LiF-PVC and LiF-MA systems containing from 0.5 to 10% PVC or MA were dispersed for 30 min

V. A. Kuznetsov; A. G. Lipson; D. M. Sakov; P. V. Fedenyuk; Yu. P. Toporov; Yu. S. Simakov

1988-01-01

29

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

30

Reverse hydrotropy by complex formation.  

PubMed

Self-aggregation of three di-N-alkylated diaza-18-crown-6 ethers (ACEs) was studied in non-polar solvents. The three ACEs differed by the length of the alkyl chain: n-decyl (ACE-10), n-hexadecyl (ACE-16) and n-tetracosane (ACE-24). From the previously reported interfacial tension isotherms, the formation of reverse micelles was expected above ACE concentrations of ?10(-3) M. However, the water content analysis in conjunction with Dynamic Light Scattering (DLS), Fluorescence Correlation Spectroscopy (FCS) and (1)H NMR Diffusion Ordered Spectroscopy (DOSY) do not provide any clear proof of the existence of aggregates. Only the Small Angle Neutron Scattering (SANS) of concentrated toluene ACE solutions reveals the existence of small reverse micelles (probably ACE dimers forming small cages hosting 1-2 water molecules). On the other hand, spectrophotometric and fluorescence dye dissolution studies using eosin Y, tropaeolin OO and methyl orange suggest that ACEs can dissolve these dyes without requiring the formation of aggregates. This discrepancy was interpreted assuming the dye-ACE complexation as the driving force for dye solubilisation, providing a possible mechanism of reverse hydrotropy ("lipotropy") in non-polar solvents. This example shows that special care should be taken when dye solubilisation is used to probe self-aggregation of an amphiphile in non-polar solvents. The amphiphile-dye complex formation might be responsible for false positive results and the aggregate formation should always be confirmed with other methods. PMID:25415596

Wojciechowski, Kamil; Gutberlet, Thomas; Raghuwanshi, Vikram Singh; Terry, Ann

2015-01-14

31

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

PubMed Central

Oxygen conversion process between O2 and H2O by means of electrochemistry or photochemistry has lately received a great deal of attention. Cobalt-phosphate (Co-Pi) catalyst is a new type of cost-effective artificial oxygen-evolving complex (OEC) with amorphous features during photosynthesis. However, can such Co-Pi OEC also act as oxygen reduction reaction (ORR) catalyst in electrochemical processes? The question remains unanswered. Here for the first time we demonstrate that Co-Pi OEC does be rather active for the ORR. Particularly, Co-Pi OEC anchoring on reduced graphite oxide (rGO) nanosheet is shown to possess dramatically improved electrocatalytic activities. Differing from the generally accepted role of rGO as an “electron reservoir”, we suggest that rGO serves as “peroxide cleaner” in enhancing the electrocatalytic behaviors. The present study may bridge the gap between photochemistry and electrochemistry towards oxygen conversion. PMID:23877331

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

2013-01-01

32

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

33

Transient kinetics of redox reactions of flavodoxin: effects of chemical modification of the flavin mononucleotide prosthetic group on the dynamics of intermediate complex formation and electron transfer.  

PubMed

The effects of structural modifications of the flavin mononucleotide (FMN) prosthetic group of Clostridium pasteurianum flavodoxin on the kinetics of electron transfer to the oxidized form (from 5-deazariboflavin semiquinone produced by laser flash photolysis) and from the semiquinone form (to horse heart cytochrome c by using stopped-flow spectrophotometry) have been investigated. The analogues used were 7,8-dichloro-FMN, 8-chloro-FMN, 7-chloro-FMN, and 5,6,7,8-tetrahydro-FMN. The ionic strength dependence of cytochrome c reduction was not affected by chlorine substitution, although the specific rate constants for complex formation and decay were appreciably smaller. On the other hand, all of the chlorine analogues had the same rate constant for deazariboflavin semiquinone oxidation. The rate constants for tetrahydro-FMN flavodoxin semiquinone reduction of cytochrome c were considerably smaller than those for the native protein. The implications of these results for the electron-transfer mechanism of flavodoxin are discussed. PMID:6307350

Simondsen, R P; Tollin, G

1983-06-01

34

Nuclear Reaction Rates and Carbon Star Formation  

E-print Network

We have studied how the third dredge-up and the carbon star formation in low-mass Asymptotic Giant Branch stars depends on certain key nuclear reaction rates. We find from a set of complete stellar evolution calculations of a 2Msun model with Z=0.01 including mass loss, that varying either the N14(p,g)O15 or the 3-alpha reaction rate within their uncertainties as given in the NACRE compilation results in dredge-up and yields that differ by a factor of 2. Model tracks with a higher rate for the 3-alpha rate and a lower rate for the N14(p,g)O15 reaction both show more efficient third dredge-up. New experimental results for the N14(p,g)O15 reaction rates are surveyed, yielding a rate which is about 40% lower than the tabulated NACRE rate, and smaller than NACRE's lower limit. We discuss the possible implications of the revised nuclear reaction stellar evolution calculations that aim to reproduce the observed carbon star formation at low mass, which requires efficient third dredge-up.

Falk Herwig; Sam M. Austin

2004-08-21

35

Reaction front formation in contaminant plumes  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

36

Photosynthetic reaction center complexes from heliobacteria  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

37

Reaction front formation in contaminant plumes.  

PubMed

The formation of successive fronts in contaminated groundwater plumes by subsoil bacterial action is a commonly accepted feature of their propagation, but it is not obviously clear from a mathematical standpoint quite how such fronts are formed or propagate. In this paper we show that these can be explained by combining classical reaction-diffusion theory involving just two reactants (oxidant and reductant), and a secondary reaction in which a reactant on one side of such a front is (re-)formed on the other side of the front via diffusion of its product across the front. We give approximate asymptotic solutions for the reactant profiles, and the propagation rate of the front. PMID:25461883

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

2014-12-15

38

Complex formation by phenols with tertiary amines in aprotic media  

Microsoft Academic Search

1.The equilibrium constants (Kg) and the enthalpies of formation of H-bonds in complex-formating reactions of phenols with tertiary amines in aprotic solvents fall with a rise in the polarity of the medium and in its capacity for specific solvation with the phenols.2.The introduction of the electron-accepting substituent chlorine into the para position of phenol leads to a considerable rise in

M. L. Keshtov; S. V. Vinogradova; V. A. Vasnev; V. V. Korshak

1980-01-01

39

Photosynthetic reaction center complexes from heliobacteria  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

40

Kinetic analysis of complex reactions using FEMLAB  

SciTech Connect

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

Cao, Chunshe; Wang, Yong

2005-06-07

41

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. PMID:23318678

SUZUKI, Toshinori

2013-01-01

42

Formation of Free Radicals from Molecular Complexes  

Microsoft Academic Search

The Review summarises results from various branches of chemistry having as a common theme the part played by donor-acceptor molecular complexes in the generation of free radicals. Attention is paid mainly to liquid-phase reactions. One section deals with polymerisations involving molecular complexes. A list of 200 references is included.

Gleb B. Sergeev; I. A. Leenson

1972-01-01

43

Formation of Free Radicals from Molecular Complexes  

Microsoft Academic Search

The Review summarises results from various branches of chemistry having as a common theme the part played by donor–acceptor molecular complexes in the generation of free radicals. Attention is paid mainly to liquid-phase reactions. One section deals with polymerisations involving molecular complexes. A list of 200 references is included.

Gleb B Sergeev; I A Leenson

1972-01-01

44

Reaction Dynamics of the Bromine-Bromoform Complex in Solution  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

45

Complex organic molecules and star formation  

NASA Astrophysics Data System (ADS)

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

Bacmann, A.; Faure, A.

2014-12-01

46

Characteristics of acid reaction in limestone formations  

Microsoft Academic Search

A kinetic model for the reaction of hydrochloric acid with limestone has been determined. Reaction order and rate constant for this model were calculated from experiments where acid reacted with a single calcium carbonate plate. Experiments were performed so that acid flow past the plate and mass transfer rate to the rock surface could be calculated theoretically. The resulting model,

D. E. Nierode; B. B. Williams

1970-01-01

47

Nitrene transfer reactions by late transition metal complexes  

E-print Network

This thesis presents nitrene transfer reactions that are catalyzed or mediated by late transition metal complexes. Sterically large, fluorinated supporting ligands are used to minimize potential side reactions. A new ...

Hamilton, Charles W., Ph. D. Massachusetts Institute of Technology

2007-01-01

48

Low-molecular-weight iron complexes and oxygen radical reactions in idiopathic haemochromatosis.  

PubMed

The sera of patients with idiopathic haemochromatosis and iron-overload have been found to contain low-molecular-weight iron complexes detectable in the 'bleomycin assay'. These complexes stimulate both the peroxidation of membrane lipids and the formation of the highly reactive and damaging hydroxyl radical. The iron chelator desferrioxamine interferes with these reactions. We suggest that oxygen radical reactions stimulated by iron salts are important in the pathology of idiopathic haemochromatosis. PMID:2578915

Gutteridge, J M; Rowley, D A; Griffiths, E; Halliwell, B

1985-04-01

49

Reactions and mass spectra of complex particles using Aerosol CIMS  

NASA Astrophysics Data System (ADS)

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

Hearn, John D.; Smith, Geoffrey D.

2006-12-01

50

Understanding Bond Formation in Polar One-Step Reactions. Topological Analyses of the Reaction between Nitrones and Lithium Ynolates.  

PubMed

The mechanism of the reaction between nitrones and lithium ynolates has been studied using DFT methods at the M06-2X/cc-pVTZ/PCM=THF level. After the formation of a starting complex an without energy barrier, in which the lithium atom is coordinated to both nitrone and ynolate, the reaction takes place in one single kinetic step through a single transition structure. However, the formation of C-C and C-O bonds takes place sequentially through a typical two-stage, one-step process. A combined study of noncovalent interactions (NCIs) and electron localization function (ELFs) of selected points along the intrinsic reaction coordinate (IRC) of the reaction confirmed that, in the transition structure, only the C-C bond is being formed to some extent, whereas an electrostatic interaction is present between carbon and oxygen atoms previous to the formation of the C-O bond. Indeed, the formation of the second C-O bond only begins when the first C-C bond is completely formed without formation of any intermediate. Once the C-C bond is formed and before the C-O bond formation starts the RMS gradient norm dips, approaching but not reaching 0, giving rise to a hidden intermediate. PMID:25803829

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

2015-04-17

51

Nonlinear Dynamics and Structure Formation in Complex Systems  

E-print Network

Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca - Complex behaviors AND STRUCTURE FORMATION IN COMPLEX SYSTEMS: CHALLENGES AND OPEN PROBLEM FOR MODERN PHYSICS September 21-22, 2009 ENEA, Frascati, Italy #12;Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca

Zonca, Fulvio

52

Pattern Formation with Reaction-Diffusion Systems  

E-print Network

th, 2006 #12;#12;Introduction Morphogenesis: development of pattern and form in biological organisms. Turing (1952): reaction-diffusion theory of morphogenesis Self-organization of adult stem cells #12 in 1D Higher dimensions: Are the dispersion relation and the eigenfunctions sufficient? Morphogenesis

Timmer, Jens

53

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

54

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. PMID:21396112

2011-01-01

55

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

56

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

57

Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome  

E-print Network

Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome Segregation and essential for reproduction. During the first meiotic division, homologous chromosomes pair, recombine the synaptonemal complex. The synaptonemal complex is a critical component for chromosome pairing, segregation

Nachman, Michael

58

Vortex formation in a complex plasma  

NASA Astrophysics Data System (ADS)

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

Ishihara, Osamu

59

EXFOR SYSTEMS MANUAL NUCLEAR REACTION DATA EXCHANGE FORMAT.  

SciTech Connect

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

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

60

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

61

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

PubMed

Recent reports have claimed a superior performance of HEPES buffer in comparison to alternative buffer systems for (67/68) Ga labeling in aqueous media. In this paper we report spectroscopic ((1) H and (71) Ga NMR), radiochemical, mass spectrometry and theoretical modeling studies on the Ga(3+)/HEPES system (HEPES = N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) performed with the aim of elucidating a potential contribution of HEPES in the (68/67) Ga radiolabeling process. Our results demonstrate that HEPES acts as a weakly but competitive chelator of Ga(3+) and that this interaction depends on the relative Ga(3+): HEPES concentration. A by-product formed in the labeling mixture has been identified as a [(68) Ga]Ga(HEPES) complex via chromatographic comparison with the nonradioactive analog. The formation of this complex was verified to compete with [(68) Ga]Ga(NOTA) complexation at low NOTA concentration. Putative chelation of Ga(3+) by the hydroxyl and adjacent ring nitrogen of HEPES is proposed on the basis of (1)H NMR shifts induced by Ga(3+) and theoretical modeling studies. PMID:23606430

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

2013-01-01

62

A Reaction Pathway for Nanoparticle Formation in Rich Premixed Flames  

E-print Network

A Reaction Pathway for Nanoparticle Formation in Rich Premixed Flames A. D'ANNA,* A. VIOLI, and A and A. F. SAROFIM Department of Chemical and Fuels Engineering, University of Utah, Salt Lake City, Utah of aromatic structures formed in rich premixed flames of ethylene at atmospheric pressure with C/O ratios

Utah, University of

63

Polarographic Study of Complex Formation Equilibria in Solutions  

NASA Astrophysics Data System (ADS)

Methods for the calculation of the coordination numbers and stability constants of complexes formed in solution from polarographic data are examined and methods for the determination of the parameters governing the formation of a single complex and stepwise complex formation as well as the formation of mixed and polynuclear complexes and complexonates are described. It is shown how kinetic and catalytic waves, the waves of the ligand, and the waves due to irreversible processes can be used for this purpose. Attention is drawn to the necessity to take into account the adsorption of the components of a system involving complex formation. The bibliography includes 64 references.

Mambetkaziev, E. A.; Zhdanov, Stepan I.

1980-04-01

64

Fluid pressure and reaction zone formation at a lithological interface  

NASA Astrophysics Data System (ADS)

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

Malvoisin, Benjamin; Podladchikov, Yuri

2014-05-01

65

Role of initial complexes in 1,2-addition reactions of disilene derivatives  

NASA Astrophysics Data System (ADS)

Mechanisms of four 1,2-addition reactions, H 2 Si - SiHMe + H 2 O, H 2 Si - SiHF + H 2 O, H2Si - SiH(C - CH) + H2O, H2Si - SiH(NH2) + HF, were investigated in detail by the ab initio MO method using a recent approach combined with frontier MO theory. Twelve reaction pathways were found. The initial step of each reaction is the formation of a weakly bonded complex. According to the structure and the charge distribution of the complexes, the reactions are categorized into two types. Reactions starting from electrophilic interaction between the LUMO of water (or hydrogen fluoride) and the HOMO of disilene always result in syn -adducts. On the other hand, nucleophilic interaction between the HOMO of the water and the LUMO of disilene leads both syn and anti adducts. Depending on the acidity of the reagent and the charge on the silicon to be attacked, the reactions proceed in simple one-step mechanisms or in two-step ones via a Lewis-type complex. The paired interacting orbitals of the initial complexes were examined in order to predict the reaction pathways.

Takahashi, Masae; Veszprémi, Tamás; Sakamoto, Kenkichi; Kira, Mitsuo

66

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

67

A new metalation complex for organic synthesis and polymerization reactions  

NASA Technical Reports Server (NTRS)

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

Hirshfield, S. M.

1971-01-01

68

Polyelectrolyte synthesis and in situ complex formation in ionic liquids.  

PubMed

For the first time, polyelectrolyte complex (PEC) capsules were prepared from a water insoluble polyanion, namely cellulose sulfates (CSs) with a degree of substitution (DS) below 0.2 in ionic liquids (IL). Capsules prepared via interaction with the polycation poly(dimethyldiallyammonium chloride) were free of residual IL and possessed an outer shell and a hollow inner core that made them ideal containers for enzyme mediated reactions. Due to the reestablished hydrogen bond system of the low substituted CS, the capsules showed increased stability, compared to the products obtained by application of the common aqueous preparation. Encapsulation of glucose oxidase demonstrated that the steps of CS preparation, PEC capsule formation, and encapsulation could be combined in a single pot, with the elimination of time and cost consuming isolation and purification steps. PMID:19754182

Gericke, Martin; Liebert, Tim; Heinze, Thomas

2009-09-23

69

EXFOR systems manual: Nuclear reaction data exchange format  

SciTech Connect

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

McLane, V. [ed.

1996-07-01

70

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

SciTech Connect

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

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

1988-05-20

71

Kinetics and mechanism of substitution reactions of complexes, XX  

Microsoft Academic Search

Thermal decomposition of 21 complexes of the type [Co(DH)2(amine)2]NCS has been studied under the conditions of thermogravimetric analysis, by using different heating rates. From the thermogravimetric curves apparent kinetic parameters of the pyrolysis reaction have been derived by means of the modified Doyle method. Apparent reaction order increases and apparent activation energy decreases with increasing heating rate. Thus, the obtained

J. Zsakó; E. Kékedy; Cs. Várhelyi

1969-01-01

72

Light induced electron transfer reactions of metal complexes  

SciTech Connect

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

Sutin, N.; Creutz, C.

1980-01-01

73

Microkinetics of oxygenate formation in the Fischer-Tropsch reaction.  

PubMed

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

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

2014-06-01

74

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

75

First stage of CoSi2 formation during a solid-state reaction  

NASA Astrophysics Data System (ADS)

The kinetics of CoSi2 formation via a solid-state reaction between CoSi and single crystal Si has been the object of many studies in the past. Because of the importance of nucleation, complex kinetics has been reported. In this work, we investigate CoSi2 formation kinetics with in-situ diffraction during isothermal annealing of CoSi films on Si (100). In-situ measurements allow capturing the initial stage of CoSi2 formation. An initial t3/2 time-dependent evolution is observed and attributed to 3D growth of individual nuclei. This first regime is followed after the coalescence of the nuclei by a classical parabolic t1/2 one-dimensional film growth. We evidence a marked influence of the initial Co thickness (50 nm vs 10 nm) on the growth kinetics. A significant slowdown of the CoSi2 formation kinetics is observed for the thinnest film, whereas the activation energy remains the same. These results shine a new light on the complex formation kinetics of CoSi2 during solid-state reaction between CoSi and single crystal silicon and bring new knowledge about what occurs in the ultra-thin film regime, which is important for nanotechnologies.

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

2014-12-01

76

DNA branch migration reactions through photocontrollable toehold formation.  

PubMed

Strand displacement cascades are commonly used to make dynamically assembled structures. Particularly, the concept of "toehold-mediated DNA branch migration reactions" has attracted considerable attention in relation to dynamic DNA nanostructures. However, it is a challenge to obtain and control the formation of pure 1:1 ratio DNA duplexes with toehold structures. Here, for the first time, we report a photocontrolled toehold formation method, which is based on the photocleavage of 2-nitrobenzyl linker-embedded DNA hairpin precursor structures. UV light irradiation (? ? 365 nm) of solutions containing these DNA hairpin structures causes the complete cleavage of the nitrobenzyl linker, and pure 1:1 DNA duplexes with toehold structures are easily formed. Our experimental results indicate that the amount of toehold can be controlled by simply changing the dose of UV irradiation and that the resulting toehold structures can be used for subsequent toehold-mediated DNA branch migration reactions, e.g., DNA hybridization chain reactions. This newly established method will find broad application in the construction of light-powered, controllable, and dynamic DNA nanostructures or large-scale DNA circuits. PMID:23642046

Huang, Fujian; You, Mingxu; Han, Da; Xiong, Xiangling; Liang, Haojun; Tan, Weihong

2013-05-29

77

Disulfide bond formation involves a quinhydrone-type chargetransfer complex  

E-print Network

Disulfide bond formation involves a quinhydrone-type charge­transfer complex James Regeimbal the spectral signal of a quinhydrone, a charge­transfer complex consisting of a hydroquinone and a quinone­benzoquinone pair that can be trapped on DsbB as a quinhydrone charge­transfer complex. Quinhydrones are known

Bardwell, James

78

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

79

Efficient transfer hydrogenation reaction Catalyzed by a dearomatized PN 3P ruthenium pincer complex under base-free Conditions  

Microsoft Academic Search

A dearomatized complex [RuH(PN3P)(CO)] (PN3PN, N?-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (3) was prepared by reaction of the aromatic complex [RuH(Cl)(PN3P)(CO)] (2) with t-BuOK in THF. Further treatment of 3 with formic acid led to the formation of a rearomatized complex (4). These new complexes were fully characterized and the molecular structure of complex 4 was further confirmed by X-ray crystallography. In complex 4, a

Li-Peng He; Tao Chen; Dong-Xu Xue; Mohamed Eddaoudi; Kuo-Wei Huang

80

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

PubMed Central

We describe how the use of the Python language improved the user interface of the program STEPS. STEPS is a simulation platform for modeling and stochastic simulation of coupled reaction-diffusion systems with complex 3-dimensional boundary conditions. Setting up such models is a complicated process that consists of many phases. Initial versions of STEPS relied on a static input format that did not cleanly separate these phases, limiting modelers in how they could control the simulation and becoming increasingly complex as new features and new simulation algorithms were added. We solved all of these problems by tightly integrating STEPS with Python, using SWIG to expose our existing simulation code. PMID:19623245

Wils, Stefan; Schutter, Erik De

2008-01-01

81

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

PubMed

We describe how the use of the Python language improved the user interface of the program STEPS. STEPS is a simulation platform for modeling and stochastic simulation of coupled reaction-diffusion systems with complex 3-dimensional boundary conditions. Setting up such models is a complicated process that consists of many phases. Initial versions of STEPS relied on a static input format that did not cleanly separate these phases, limiting modelers in how they could control the simulation and becoming increasingly complex as new features and new simulation algorithms were added. We solved all of these problems by tightly integrating STEPS with Python, using SWIG to expose our existing simulation code. PMID:19623245

Wils, Stefan; De Schutter, Erik

2009-01-01

82

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

NASA Astrophysics Data System (ADS)

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

Alonso, Sergio; John, Karin; Bär, Markus

2011-03-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

84

Formation of crystalline complexes between amylomaize dextrin and ceramide.  

PubMed

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

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

2014-01-30

85

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

PubMed Central

The regulation of enzyme activity through the transient formation of multiprotein assemblies plays an important role in the control of biosynthetic pathways. One of the first regulatory complexes to be discovered was cysteine synthase (CS), formed by the pyridoxal 5?-phosphate-dependent enzyme O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT). These enzymes are at the branch point of the sulfur, carbon, and nitrogen assimilation pathways. Understanding the mechanism of complex formation helps to clarify the role played by CS in the regulation of sulfur assimilation in bacteria and plants. To this goal, stopped-flow fluorescence spectroscopy was used to characterize the interaction of SAT with OASS, at different temperatures and pH values, and in the presence of the physiological regulators cysteine and bisulfide. Results shed light on the mechanism of complex formation and regulation, so far poorly understood. Cysteine synthase assembly occurs via a two-step mechanism involving rapid formation of an encounter complex between the two enzymes, followed by a slow conformational change. The conformational change likely results from the closure of the active site of OASS upon binding of the SAT C-terminal peptide. Bisulfide, the second substrate and a feedback inhibitor of OASS, stabilizes the CS complex mainly by decreasing the back rate of the isomerization step. Cysteine, the product of the OASS reaction and a SAT inhibitor, slightly affects the kinetics of CS formation leading to destabilization of the complex. PMID:20164178

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

2010-01-01

86

Thermodynamics of the formation of copper(II) complexes with L-histidine in aqueous solution  

NASA Astrophysics Data System (ADS)

The heat effects from the reaction between L-histidine solutions and Cu(NO3)2 solutions at 298.15 K in the 0.2 to 1.0 (KNO3) range of ionic strength are measured by means of direct calorimetry. The experimental data is treated with allowance for the simultaneous proceeding of several processes. The heat effects of the formation of complexes Cu(His)+, Cu(His)2, CuHHis2+, CuH(His){2/+} and CuH2(His){2/2+} are calculated from calorimetric measurements. The standard enthalpies of formation for complexes of L-histidine with Cu2+ ions are obtained via extrapolation to zero ionic strength. The relationship between the thermodynamic characteristics of the formation of complexes of copper(II) with L-histidine and their structure is determined.

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

2015-02-01

87

Lead(II) Complex Formation with Glutathione  

PubMed Central

A structural investigation of complexes formed between the Pb2+ ion and glutathione (GSH, denoted AH3 in its triprotonated form) the most abundant non2protein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and CPb2+ = 10 mM, and in the solid state. The Pb LIII-edge EXAFS oscillation for a solid compound with the empirical formula [Pb(AH2)]ClO4 was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 Å and 2.28 ± 0.04 Å, respectively. In addition Pb···Pb interactions at 4.15 ± 0.05 Å indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb2+ ions. In aqueous solution at the mole ratio GSH / Pb(II) = 2.0 (CPb2+ = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge transfer band (LMCT) S- ? Pb2+ at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 Å and 2.51 ± 0.04 Å, respectively, from a Pb LIII-edge EXAFS spectrum. For solutions with higher mole ratios, GSH / Pb(II) ? 3.0, ESI-MS spectra identified a trisglutathionyl lead(II) complex, for which Pb LIII-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS3 coordination, 207Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum an S- ? Pb2+ LMCT band appears at 335 nm. The complex persists at high excess of glutathione, and also at ~25 K in frozen glycerol (33%) / water glasses for GSH / Pb(II) mole ratios from 4.0 to 10 (CPb2+ = 10 mM) measured by Pb LIII-edge EXAFS spectroscopy. PMID:22594853

Mah, Vicky

2012-01-01

88

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

PubMed

Germinal center (GC) reaction is crucial in adaptive immune responses. The formation of GC is coordinated by the expression of specific genes including Blimp-1 and Bcl-6. Although gene expression is critically influenced by the status of chromatin structure, little is known about the role of chromatin remodeling factors for regulation of GC formation. Here, we show that the SWI/SNF chromatin remodeling complex is required for GC reactions. Mice lacking Srg3/mBaf155, a core component of the SWI/SNF complex, showed impaired differentiation of GC B and follicular helper T cells in response to T cell-dependent antigen challenge. The SWI/SNF complex regulates chromatin structure at the Blimp-1 locus and represses its expression by interacting cooperatively with Bcl-6 and corepressors. The defect in GC reactions in mice lacking Srg3 was due to the derepression of Blimp-1 as supported by genetic studies with Blimp-1-ablated mice. Hence, our study identifies the SWI/SNF complex as a key mediator in GC reactions by modulating Bcl-6-dependent Blimp-1 repression. PMID:25646472

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

2015-02-17

89

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

90

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes  

E-print Network

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes) Meunier, B., Ed. Biomimetic Oxidations Catalyzed by Transition Metal Complexes; Imperial College Press

Roth, Justine P.

91

Complex molecule formation around massive young stellar objects.  

PubMed

Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T = 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics--CH3CCH, CH3CN, CH3OCH3 and CH3CHO--in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history. PMID:25302375

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

2014-01-01

92

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

PubMed

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

Hashimoto, Takayoshi; Ohki, Yasuhiro; Tatsumi, Kazuyuki

2010-07-01

93

Direct electronic probing of biological complexes formation  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

94

Dinitrosyl intermediate for N{sub 2}O formation from reaction of NO on Mo(110)  

SciTech Connect

The adsorption and subsequent reaction of nitric oxide (NO) on Mo(110) has been studied by temperature programmed reaction, electron energy loss, and infrared reflectance absorbance spectroscopies. The predominant reaction pathway for a saturated NO overlayer is dissociation to atomic nitrogen and oxygen; in fact, for low NO coverages, dissociation is the only reaction and largely takes place below 300 K. At NO coverages above 65{percent} of {theta}{sub sat}, evolution of N{sub 2}O, N{sub 2}, and NO is also observed at low temperature. Temperature programmed reaction of isotopically mixed overlayers demonstrates that N{sub 2}O formation occurs via reaction of two intact NO molecules, suggestive of a dimeric surface intermediate. Electron energy loss and infrared spectroscopies identify three {nu}(NO) features which are assigned to three distinct species; the frequencies of the {nu}(NO) peaks in the infrared spectrum of a saturated {sup 14}NO overlayer at 100 K are 1860, 1821, and 1720thinspcm{sup {minus}1}. The 1860 and 1720thinspcm{sup {minus}1} features are assigned to monomeric NO. Based on the infrared spectrum of a mixed overlayer of {sup 14}NO and {sup 15}NO, and on comparison to reference spectra of NO adsorbed on MoO{sub 3}, the 1821thinspcm{sup {minus}1} peak is identified as {nu}{sub s}(NO) of a surface dinitrosyl complex, i.e., two NO molecules bound to one Mo site. The weakly bound NO with the stretch frequency of 1860thinspcm{sup {minus}1} is associated with NO desorption, while the dinitrosyl leads to low-temperature N{sub 2} and N{sub 2}O formation and some dissociation. {copyright} {ital 1997 American Institute of Physics.}

Queeney, K.T.; Friend, C.M. [Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138 (United States)

1997-10-01

95

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

96

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

97

Excitation energy transfer and carotenoid radical cation formation in light harvesting complexes — A theoretical perspective  

Microsoft Academic Search

Light harvesting complexes have been identified in all chlorophyll-based photosynthetic organisms. Their major function is the absorption of light and its transport to the reaction centers, however, they are also involved in excess energy quenching, the so-called non-photochemical quenching (NPQ). In particular, electron transfer and the resulting formation of carotenoid radical cations have recently been discovered to play an important

Michael Wormit; Philipp H. P. Harbach; Jan M. Mewes; Sergiu Amarie; Josef Wachtveitl; Andreas Dreuw

2009-01-01

98

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

99

Complex reaction networks in high temperature hydrocarbon chemistry.  

PubMed

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

Mutlay, I Combining Dot Above Brahim; Restrepo, Albeiro

2015-03-11

100

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

101

Disulfide bond formation involves a quinhydrone-type charge-transfer complex.  

PubMed

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge-transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone-benzoquinone pair that can be trapped on DsbB as a quinhydrone charge-transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge-transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L; Yu, Chang-An; Diwakar, Mithun; Ballou, David P; Bardwell, James C A

2003-11-25

102

Disulfide bond formation involves a quinhydrone-type charge–transfer complex  

PubMed Central

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge–transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone–benzoquinone pair that can be trapped on DsbB as a quinhydrone charge–transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge–transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L.; Yu, Chang-An; Diwakar, Mithun; Ballou, David P.; Bardwell, James C. A.

2003-01-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

104

Carbon–heteroatom bond formation catalysed by organometallic complexes  

PubMed Central

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

Hartwig, John F.

2010-01-01

105

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

PubMed

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

Holmes, William R

2014-01-01

106

Complex lane formation in a system of dipolar microswimmers  

E-print Network

Using Brownian Dynamics (BD) simulations we investigate the non-equilibrium structure formation of a two-dimensional (2D) binary system of dipolar colloids propelling in opposite directions. Despite of a pronounced tendency for chain formation, the system displays a transition towards a laned state reminiscent of lane formation in systems with isotropic repulsive interactions. However, the anisotropic dipolar interactions induce novel features: First, the lanes have themselves a complex internal structure characterized by chains or clusters. Second, laning occurs only in a window of interaction strengths. We interprete our findings by a phase separation process and simple force balance arguments.

Florian Kogler; Sabine H. L. Klapp

2015-02-13

107

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

PubMed Central

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

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

2014-01-01

108

Cation-induced formation of a macro-glucan synthase complex  

SciTech Connect

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

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

1990-05-01

109

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

SciTech Connect

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

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

2010-03-16

110

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

PubMed

The reaction of the ground state methylidyne radical CH (X(2)Pi) with pyrrole (C(4)H(5)N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 363 K, at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr(3)) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C(5)H(5)N) is identified as the product of the reaction and resolved from (79)Br atoms, and the result is consistent with CH addition to pyrrole followed by H-elimination. The photoionization efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C(5)H(4)DN and identified as deuterated pyridine (d-pyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as gas-phase combustion processes, are discussed. PMID:20463997

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

2010-08-21

111

Formation and characterization of polylactide and ?-cyclodextrin inclusion complex  

Microsoft Academic Search

Inclusion complex (ICs) of ?-cyclodextrin (?-CD) and polylactide (PLA) were prepared by a solution-ultrasonic technique. Results showed that the feeding ratios of ?-CD and PLA and the molecular weight of PLA had significant effects on the formation of the ICs, and the formed ICs could be dispersed in water when the molecular number weight (Mn) of PLA was lower than

D. M. Xie; K. S. Yang; W. X. Sun

2007-01-01

112

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, J.D., Jr.; Morey, G.B.

2008-01-01

113

Geology of the Biwabik Iron Formation and Duluth Complex.  

PubMed

The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. PMID:17997209

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

2008-10-01

114

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

PubMed Central

This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe2(SC5H11NO2)2(NO)4]SO4·5H2O (I) and glutathione- (GSH-) ligands [Fe2(SC10H17N3O6)2(NO)4]SO4·2H2O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)??k1 = (4.6 ± 0.1)·10?3?s?1 and the elimination rate constant of the penicillamine ligand k2 = (1.8 ± 0.2)·10?3?s?1 at 25°C in 0.05?M phosphate buffer, ?pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS? during decomposition of 1.5·10?4?M (I) in the presence of 10?3?M GSH, with 76% yield in 24?h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity. PMID:24790592

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

2014-01-01

115

Paper Number 15736-PA Title Reaction Kinetics of Fuel Formation for In-Situ Combustion  

E-print Network

Paper Number 15736-PA Title Reaction Kinetics of Fuel Formation for In-Situ Combustion Authors Abu believed to cause fuel formation for in-situ combustion have been studied and modeled. A thin, packed bed the approach of a combustion front. Analysis of gases produced from the reaction cell revealed that pyrolysis

Abu-Khamsin, Sidqi

116

Formation and in situ reactions of hypervalent iodonium alkynyl triflates to form cyanocarbenes.  

PubMed

The conversion of readily available silylalkynes, iodobenzene diacetate, and azide anions was utilized to form and react cyanocarbenes. A copper(ii)-catalyzed reaction was found to react in a different manner. Both of these methods benefit from the formation and in situ reaction of hypervalent iodonium alkynyl triflates in O-H insertion reactions. PMID:25558484

Dempsey Hyatt, I F; Nasrallah, Daniel J; Maxwell, Michael A; Hairston, A Christina F; Abdalhameed, Manahil M; Croatt, Mitchell P

2015-03-12

117

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

PubMed Central

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

2013-01-01

118

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

2013-10-01

119

Rosette: Understanding Star Formation in Molecular Cloud Complexes  

NASA Astrophysics Data System (ADS)

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

Wang, Junfeng

2010-09-01

120

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

PubMed Central

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

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

2010-01-01

121

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

PubMed Central

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

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

2013-01-01

122

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

123

Formation of complex and unstable chromosomal translocations in yeast.  

PubMed

Genome instability, associated with chromosome breakage syndromes and most human cancers, is still poorly understood. In the yeast Saccharomyces cerevisiae, numerous genes with roles in the preservation of genome integrity have been identified. DNA-damage-checkpoint-deficient yeast cells that lack Sgs1, a RecQ-like DNA helicase related to the human Bloom's-syndrome-associated helicase BLM, show an increased rate of genome instability, and we have previously shown that they accumulate recurring chromosomal translocations between three similar genes, CAN1, LYP1 and ALP1. Here, the chromosomal location, copy number and sequence similarity of the translocation targets ALP1 and LYP1 were altered to gain insight into the formation of complex translocations. Among 844 clones with chromosomal rearrangements, 93 with various types of simple and complex translocations involving CAN1, LYP1 and ALP1 were identified. Breakpoint sequencing and mapping showed that the formation of complex translocation types is strictly dependent on the location of the initiating DNA break and revealed that complex translocations arise via a combination of interchromosomal translocation and template-switching, as well as from unstable dicentric intermediates. Template-switching occurred between sequences on the same chromosome, but was inhibited if the genes were transferred to different chromosomes. Unstable dicentric translocations continuously gave rise to clones with multiple translocations in various combinations, reminiscent of intratumor heterogeneity in human cancers. Base substitutions and evidence of DNA slippage near rearrangement breakpoints revealed that translocation formation can be accompanied by point mutations, and their presence in different translocation types within the same clone provides evidence that some of the different translocation types are derived from each other rather than being formed de novo. These findings provide insight into eukaryotic genome instability, especially the formation of translocations and the sources of intraclonal heterogeneity, both of which are often associated with human cancers. PMID:20711256

Schmidt, Kristina H; Viebranz, Emilie; Doerfler, Lillian; Lester, Christina; Rubenstein, Aaron

2010-01-01

124

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

125

Reactions of NO 3 radicals with limonene and ?-pinene: Product and SOA formation  

NASA Astrophysics Data System (ADS)

Monoterpenes are ubiquitous in forested environments and are subject to reactions with OH radicals, NO 3 radicals and O 3 both within and above forest canopies. While reactions of monoterpenes with OH and O 3 have received considerable attention with regard to their reaction kinetics, reaction products and secondary organic aerosol (SOA) formation those with NO 3 have received relatively little consideration. To redress this imbalance and to try and assess the possible importance of NO 3+monterpene reactions within forest canopies investigations have been performed on selected monterpenes. The products and aerosol formation from the NO 3 radical initiated oxidation of limonene and ?-pinene have been investigated in the EUPHORE photoreactor facility, and the secondary chemistry of the observed major products was then investigated in a large volume laboratory photoreactor. In addition to large yields of yet unidentified organic nitrates, pinonaldehyde and endolim have been identified as the major reaction products of the NO 3 radical initiated oxidation of ?-pinene and limonene, respectively. The aerosol formation has been investigated in the presence of different seed aerosols and also water vapour. The reactions lead to the formation of SOA and the results indicate the importance of the chemical character of the seed aerosol in determining the SOA yield in NO 3+monoterpene reactions. The possible pathways leading to SOA formation and also their potential importance are discussed based on the laboratory results on the reaction of NO 3 with the two major products.

Spittler, M.; Barnes, I.; Bejan, I.; Brockmann, K. J.; Benter, Th.; Wirtz, K.

126

Olefin Metathesis Reactions Initiated by d2 Molybdenum or Tungsten Complexes  

E-print Network

Olefin Metathesis Reactions Initiated by d2 Molybdenum or Tungsten Complexes Richard R. Schrock species, behave as olefin metathesis catalysts. Recently we reported tungsten complexes that contain a Wd

Müller, Peter

127

Formation and stability of nucleotide complexes: Raman titration investigation  

NASA Astrophysics Data System (ADS)

In order to monitor the formation of complexes between modified and wild type nucleotides, a concept based on spectroscopic titration combined with factor analysis data treatment has been developed. A set of samples containing two homopolynucleotides with complementary bases at various concentration ratios has been prepared. Other conditions, i.e. total nucleotide concentration, temperature, ionic strength, divalent ions percentage and pH, were conserved. The series of Raman and UV-absorption spectra obtained from these samples have been treated by factor analysis and the results then fitted to the equilibrium equations of 1 : 1 and 1 : 2 complexes. By this way, spectra of individual unpaired nucleotides, 1 : 1 and 1 : 2 complexes, and values of the stability constants can be determined at the same time. While the former characterise the structure of the individual species, the latter parameters implicate their percentage in each sample. The approach has been tested on a poly(rA)-poly(rU) model system.

Hanuš, J.; Št?pánek, J.; Turpin, P.-Y.; Bok, J.

1999-05-01

128

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

129

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

130

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

PubMed

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

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

2015-02-01

131

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

132

Mercury(II) penicillamine complex formation in alkaline aqueous solution.  

PubMed

The complex formation between mercury(II) and penicillamine (H(2)Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH approximately 2) has been investigated with extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy. By varying the penicillamine concentration (C(H(2)Pen) = 0.2-1.25 M) in approximately 0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen)2](2-) and [Hg(Pen)3](4-) were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) A, respectively. The [Hg(Pen)2](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) A. The same type of coordination is also found for the corresponding [Hg(Cys)2](2-) complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) A and Hg-N 2.56(2) A. The relative amounts of the [Hg(Pen)2](2-) and [Hg(Pen)3](4-) complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their (199)Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen)3](4-) complex dominates already at moderate excess of the free ligand ([Pen(2-)] > approximately 0.1 M). PMID:17940647

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

2007-11-01

133

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

134

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

PubMed

The new monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(NR)(NR')C(NMe2)}] (R = R' = (i)Pr, 2; R = (t)Bu, R' = Et, 3) were obtained by the insertion reaction of either diisopropylcarbodiimide or 1-tert-butyl-3-ethylcarbodiimide with the triamido precursor [Nb(NMe2)3(N-2,6-(i)Pr2C6H3)] (1) bearing a bulky imido moiety. The ?-oxo derivative [{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NMe2)}(NMe2)Nb]2(?-O) (2a) was formed by an unexpected hydrolysis reaction of the amido niobium compound 2. Alternatively, monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NHR)}] (R = (i)Pr, 4, (n)Bu, 5) can be obtained by protonolysis of 1 with N,N',N''-alkylguanidines [(NH(i)Pr)2C(NR)] (R = (i)Pr, (n)Bu). Compound also reacts with either tert-butylisocyanide or 2,6-xylylisocyanide to give, by a migratory insertion reaction, the corresponding iminocarbamoyl compounds [Nb(NMe2)2{(NMe2)C=NR}{N(2,6-(i)Pr2C6H3)}] (R = (t)Bu, 6, Xy, 7). Addition of the neutral alkylguanidines to complex 6 results in a facile C-N bond cleavage at room temperature in a process directed by the formation of the stable chelate complex 4 or 5. Complex reacts with heterocumulenic CS2 to produce new imido dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}2{N(2,6-(i)Pr2C6H3)}] (8) and [Nb{S2C(NMe2)}3{N(2,6-(i)Pr2C6H3)}] (9). These complexes do not react with alkylguanines, although new mixed guanidinato dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}{(N(i)Pr)2C(NHiPr)}{N(2,6-(i)Pr2C6H3)}] (10) and [Nb{(S2C(NMe2)}2{(N(i)Pr)2C(NH(i)Pr)}{N(2,6-(i)Pr2C6H3)}] (11) can be obtained by reaction of complex 4 with one or two equivalents of CS2, respectively. All of the complexes were characterized spectroscopically and the dynamic behaviour of some of them was studied by variable-temperature NMR. The molecular structures of 2a, 3, 6 and 10 were also established by X-ray diffraction studies. PMID:25338231

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

2014-12-14

135

Complex reaction dynamics in the cerium-bromate-2-methyl-1,4-hydroquinone photoreaction.  

PubMed

Spontaneous oscillations with a long induction time were observed in the bromate-2-methyl-1,4-hydroquinone photoreaction in a batch reactor, where removal of illumination effectively quenched any reactivity. A substantial lengthening of the oscillatory window and a dramatic increase in the complexity of the reaction behavior arose upon the addition of cerium ions, in which separate bifurcation regions and mixed mode oscillations were present. The complexity has a strong dependence on the intensity of illumination supplied to the system and on the initial concentrations of the reactants. (1)H NMR spectroscopy measurements show that the photoreduction of 2-methyl-1,4-benzoquinone leads to the formation of 2-methyl-1,4-hydroquinone and the compound 2-hydroxy-3-methyl-1,4-benzoquinone. Spectroscopic investigation also indicates that the presence of methyl group hinders the bromination of the studied organic substrate 2-methyl-1,4-hydroquinone, resulting in the formation of 2-methyl-1,4-benzoquinone. PMID:25279948

Bell, Jeffrey G; Green, James R; Wang, Jichang

2014-10-23

136

FORMATION AND DISTRIBUTION OF NUCLEAR PORE COMPLEXES IN INTERPHASE  

PubMed Central

The possibility of nuclear pore formation in the interphase nucleus was investigated in control and phytohemagglutinin (PHA) stimulated lymphocytes by the freeze-etching technique. 48 hr after the addition of PHA, the newly formed blasts which had not as yet divided had at least twice the number of pores per nucleus as controls. This clearly demonstrates that in lymphocytes nuclear pore formation can take place during interphase. It has generally been assumed that the distribution of nuclear pore complexes in somatic animal cells is random. However, we have utilized freeze etched rat kidney cells and a computer program to evaluate pore distribution. We find a minimum pore center-to-center spacing of approximately 1300 A and multiples thereof with high frequency. This is strong evidence for a nonrandom distribution of nuclear pores. The nonrandomness may be related to an underlying chromosomal organization in interphase. Using three criteria for identifying prospective pore sites (membrane specialization, nonrandomness, and alteration of heterochromatin distribution), we have found forming pores in sectioned material from cultured human melanoma cells. While nuclear pore formation may take place in conjunction with reformation of the nuclear membrane, a mechanism also exists for their formation during interphase. PMID:5165267

Maul, Gerd G.; Price, Joseph W.; Lieberman, Michael W.

1971-01-01

137

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

138

Formation of mRNA 3' termini: stability and dissociation of a complex involving the AAUAAA sequence.  

PubMed Central

Formation of the 3' termini of mRNAs in animal cells involves endonucleolytic cleavage of a pre-mRNA, followed by polyadenylation of the newly formed end. Here we demonstrate that, during cleavage in vitro, the highly conserved AAUAAA sequence of the pre-mRNA forms a complex with a factor present in a crude nuclear extract. This complex is required for cleavage and polyadenylation. It normally is transient, but is very stable on cleaved RNA to which a single terminal cordycepin residue has been added. The complex can form either during the cleavage reaction, or on a synthetic RNA that ends at the polyadenylation site. Mutations which prevent cleavage also prevent complex formation. The complex dissociates during or after polyadenylation, enabling the released activities to catalyze a second round of cleavage. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. PMID:2438129

Zarkower, D; Wickens, M

1987-01-01

139

Formation and working mechanism of the picornavirus VPg uridylylation complex.  

PubMed

The initiation of picornavirus replication is featured by the uridylylation of viral protein genome-linked (VPg). In this process, viral RNA-dependent RNA polymerase (RdRp) catalyzes two uridine monophosphate (UMP) molecules to the hydroxyl group of the third tyrosine residue of VPg. Subsequently, the uridylylated VPg (VPg-pUpU) functions as the protein primer to initiate the replication of the viral genome. Although a large body of functional and structural works has been performed to define individual snapshots for particular stages of the VPg uridylylation process, the formation, dynamics and mechanism of the whole VPg uridylylation complex still requires further elucidation. We would like to provide an overview of the current knowledge of the picornaviral VPg uridylylation complex in this paper. PMID:25240314

Sun, Yuna; Guo, Yu; Lou, Zhiyong

2014-12-01

140

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

141

Optical and Modeling Studies of Sodium/Halide Reactions for the Formation of Titanium and Boron  

E-print Network

diffusion flame reactor. After the Cl is stripped from the metal chloride by the Na vapor, nanosize Ti or B flame model show that formation of TiB2 likely occurs by gas-phase clustering reactions involving both or K with metal halides to yield the metal and an alkali halide salt. Such reactions15,16 have been

Zachariah, Michael R.

142

Elementary Reactions of Boron Atoms with HydrocarbonssToward the Formation of Organo-Boron Compounds  

E-print Network

Boron Reactions 5112 2.3.1. Crossed Beam Machines with a Rotating QMS Detector 5113 2.3.2. Crossed BeamElementary Reactions of Boron Atoms with HydrocarbonssToward the Formation of Organo-Boron 96822 Received December 16, 2009 Contents 1. Introduction 5107 1.1. Organo-Boron Molecules in Combustion

Kaiser, Ralf I.

143

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

144

Molecular determinants of orexin receptor-arrestinubiquitin complex formation  

PubMed Central

Background and Purpose:?The orexin system regulates a multitude of key physiological processes, particularly involving maintenance of metabolic homeostasis. Consequently, there is considerable potential for pharmaceutical development for the treatment of disorders from narcolepsy to metabolic syndrome. It acts through the hormonal activity of two endogenous peptides, orexin A binding to orexin receptors 1 and 2 (OX1 and OX2) with similar affinity, and orexin B binding to OX2 with higher affinity than OX1 receptors. We have previously revealed data differentiating orexin receptor subtypes with respect to their relative stability in forming orexin receptor-arrestin-ubiquitin complexes measured by BRET. Recycling and cellular signalling distinctions were also observed. Here, we have investigated, using BRET, the molecular determinants involved in providing OX2 receptors with greater ?-arrestin-ubiquitin complex stability. Experimental Approach:?The contribution of the C-terminal tail of the OX receptors was investigated by bulk substitution and site-specific mutagenesis using BRET and inositol phosphate assays. Key Results:?Replacement of the OX1 receptor C-terminus with that of the OX2 receptor did not result in the expected gain of function, indicating a role for intracellular domain configuration in addition to primary structure. Furthermore, two out of the three putative serine/threonine clusters in the C-terminus were found to be involved in OX2 receptor-?-arrestin-ubiquitin complex formation. Conclusions and Implications:?This study provides fundamental insights into the molecular elements that influence receptor-arrestin-ubiquitin complex formation. Understanding how and why the orexin receptors can be functionally differentiated brings us closer to exploiting these receptors as drug targets. Linked Articles:?This article is part of a themed section on Orexin Receptors. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-2 PMID:24206104

Jaeger, Werner C; Seeber, Ruth M; Eidne, Karin A; Pfleger, Kevin DG

2014-01-01

145

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

PubMed

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

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

2014-04-23

146

Thermally induced oxidative decarboxylation of copper complexes of amino acids and formation of strecker aldehyde.  

PubMed

In the Maillard reaction, independent degradations of amino acids play an important role in the generation of amino-acid-specific products, such as Strecker aldehydes or their Schiff bases. Such oxidative decarboxylation reactions are expected to be enhanced in the presence of metals. Preliminary studies performed through heating of alanine and various metal salts (Cu, Fe, Zn, and Ca) under pyrolytic conditions indicated that copper(II) and iron(III) because of their high oxidation potentials were the only metals able to induce oxidative decarboxylation of amino acids and formation of Strecker aldehyde or its derivatives as detected by gas chromatography/mass spectrometry. Furthermore, studies performed with synthetic alanine and glycine copper complexes indicated that they constituted the critical intermediates undergoing free-radical oxidative degradation, followed by the loss of carbon dioxide and the generation of Strecker aldehydes, which were detected either as stable Schiff base adducts or incorporated in moieties, such as pyrazine or pyridine derivatives. PMID:25078730

Nashalian, Ossanna; Yaylayan, Varoujan A

2014-08-20

147

Characterization of Hydrogen Complex Formation in III-V Semiconductors  

SciTech Connect

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

Williams, Michael D.

2006-09-28

148

Nucleophile influence on the complex reaction network of 2-isopropylnaphthalene hydroperoxide decomposition  

Microsoft Academic Search

Acid-catalysed decomposition of 2-isopropylnaphthalene hydroperoxide (2-IPNHP), which is of industrial importance for the productions of 2-naphthol and acetone simultaneously, proceeds through a complex ionic reaction mechanism. Since two steps of the ionic reactions in series are nucleophilic reactions, the presence, character and concentration of nucleophile reagents in the decomposition reaction medium are important. In the present study, the effects of

Fatma Gül Boyaci; Serpil Takaç; Tunçer H. Özdamar

2005-01-01

149

Permanent Hydrophilic Surface Formation by Ion Assisted Reaction  

Microsoft Academic Search

Since totally wettable hydrophilic polymer surfaces from hydrophobic polymers (PMMA, PTFE, PET and PC) have been demonstrated for the first time at Materials Research Society meeting, 1995 Fall meeting, Boston, the application of ion assisted reaction (IAR), in which energetic ions (0.5~1.5 keV) are irradiated on materials with blowing reactive gases near the irradiating surfaces, has been extended to various

Ki-Hwan Kim; Jun Sik Cho; Sung Han; Young Whoan Beag; Byung Ha Kang; Samchul Ha; Seok-Keun Koh

2004-01-01

150

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

PubMed Central

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

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

2014-01-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

152

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

PubMed

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

Futera, Zden?k; Burda, Jaroslav V

2014-07-15

153

Preparation, characterization, and reaction of novel dioxoruthenium(VI) porphyrin cation radical complexes  

SciTech Connect

Novel dioxoruthenium(VI) porphyrin cation radicals were prepared in the stoichiometric oxidation of Ru[sup VI]TMP(O)[sub 2] (1) and Ru[sup VI]OEP(O)[sub 2] (2) with phenoxathiin hexachloroantimonate. [sup 2]H-NMR, UV-vis, and ESR were measured to determine the electronic structure of the oxidation products. The oxidation product (3) of 1 shows a broad Q band and a less intense and blue-shifted Soret band, suggestive of the porphyrin cation radical formation. Further, the single ESR signal for 3 at g = 2.002 at 77 K is a clear demonstration of one-electron oxidation of the porphyrin ring to form a free radical complex. The presence of two oxo ligands in 3 was confirmed in the reaction of 3 with Ph[sub 3]P under argon to give 2 mol equiv of Ph[sub 3]P[double bond]O. Very similar results were also obtained when 2 was oxidized under the same condition, and the oxidation product (4) was also assigned to be a dioxoruthenium(VI) prophyrin cation radical. The chemical shifts of 3 and 4 were determined by deuterium NMR using partially deuterated 3 and 4. On the basis of paramagnetic shifts, the radical orbitals of 3 and 4 were determined to be A[sub 1u]. Further, oxidation reactions of diphenyl sulfide and some olefins were carried out with high valent ruthenium complexes (1-4), and the results show that 3 and 4 exhibit greater reactivity than 1 and 2; however, the enhancement of the reactivities are less than those expected for the complexes bearing A[sub 2u] radical orbitals. 27 refs., 5 figs., 2 tabs.

Tokita, Yuichi; Yamaguchi, Kazuya; Watanabe, Yoshihito; Morishima, Isao (Kyoto Univ. (Japan))

1993-02-03

154

Incipient species formation in salamanders of the Ensatina?complex  

PubMed Central

The Ensatina eschscholtzii complex of plethodontid salamanders, a well-known “ring species,” is thought to illustrate stages in the speciation process. Early research, based on morphology and coloration, has been extended by the incorporation of studies of protein variation and mitochondrial DNA sequences. The new data show that the complex includes a number of geographically and genetically distinct components that are at or near the species level. The complex is old and apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. While the hypothesis that speciation is retarded by gene flow around the ring is not supported by molecular data, the general biogeographical hypothesis is supported. There is evidence of a north to south range expansion along two axes, with secondary contact and completion of the ring in southern California. Current research targets regions once thought to show primary intergradation, but which molecular markers reveal to be zones of secondary contact. Here emphasis is on the subspecies E. e. xanthoptica, which is involved in four distinct secondary contacts in central California. There is evidence of renewed genetic interactions upon recontact, with greater genetic differentiation within xanthoptica than between it and some of the interacting populations. The complex presents a full array of intermediate conditions between well-marked species and geographically variable populations. Geographically differentiated segments represent a diversity of depths of time of isolation and admixture, reflecting the complicated geomorphological history of California. Ensatina illustrates the continuing difficulty in making taxonomic assignments in complexes studied during species formation. PMID:9223261

Wake, David B.

1997-01-01

155

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

PubMed

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

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

2014-08-15

156

The ?-Effect and Competing Mechanisms: The Gas-Phase Reactions of Microsolvated Anions with Methyl Formate  

NASA Astrophysics Data System (ADS)

The enhanced reactivity of ?-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase SN2 reactions of the microsolvated HOO-(H2O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the ?-effect as we compare the gas-phase reactivity of the microsolvated ?-nucleophile HOO-(H2O) with that of microsolvated normal alkoxy nucleophiles, RO-(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO-(H2O) towards methyl formate, and clearly demonstrate the presence of an overall ?-effect for the reactions of the microsolvated ?-nucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the SN2 and BAC2 reactivity compared with the unsolvated analogs. HOO-(H2O) reacts with methyl formate exclusively via the BAC2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the BAC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction.

Thomsen, Ditte L.; Nichols, Charles M.; Reece, Jennifer N.; Hammerum, Steen; Bierbaum, Veronica M.

2013-12-01

157

Gas-phase ion-molecule reactions of transition metal complexes: the effect of different coordination spheres on complex reactivity.  

PubMed

Using a modified quadrupole ion trap mass spectrometer, a series of metal complex ions have been reacted with acetonitrile in the gas phase. Careful control of the coordination number and the type of coordinating functionality in diethylenetriamine-substituted ligands enable the effects of the coordination sphere on metal complex reactivity to be examined. The association reaction kinetics of acetonitrile with these pentacoordinate complexes are followed in order to obtain information about the starting complexes and the reaction dynamics. The kinetics and thermodynamics of acetonitrile addition to the metal complex ions are strongly affected by the chemical environment around the metal center such that significant differences in reactivity are observed for Co(II) and Cu(II) complexes with various coordination spheres. When thiophene, furan, or benzene moieties are present in the coordination sphere of the complex, addition of two acetonitrile molecules is readily observed. In contrast, ligands with better sigma donors react mainly to add one acetonitrile molecule. Among the ligands with good sigma donors, a clear trend in reactivity is observed in which complexes with nitrogen-containing ligands are the least reactive, sulfur-containing complexes are more reactive, and oxygen-containing complexes are the most reactive. In general, equilibrium and reaction rate constants seem to be consistent with the hard and soft acid and base (HSAB) principle. Interestingly, the presence of certain groups (e.g., pyridine and imidazole) in the coordination sphere clearly can change the acid character of the metal as seen by their effect on the binding properties of other functional groups in the same ligand. Finally, we conclude that because complexes with different coordination spheres react to noticeably different extents, ion-molecule (I-M) reactions may be potentially useful for obtaining coordination structure information for transition metal complexes. PMID:12148806

Combariza, Marianny Y; Vachet, Richard W

2002-07-01

158

Structure of Soybean Serine Acetyltransferase and Formation of the Cysteine Regulatory Complex as a Molecular Chaperone*  

PubMed Central

Serine acetyltransferase (SAT) catalyzes the limiting reaction in plant and microbial biosynthesis of cysteine. In addition to its enzymatic function, SAT forms a macromolecular complex with O-acetylserine sulfhydrylase. Formation of the cysteine regulatory complex (CRC) is a critical biochemical control feature in plant sulfur metabolism. Here we present the 1.75–3.0 ? resolution x-ray crystal structures of soybean (Glycine max) SAT (GmSAT) in apoenzyme, serine-bound, and CoA-bound forms. The GmSAT-serine and GmSAT-CoA structures provide new details on substrate interactions in the active site. The crystal structures and analysis of site-directed mutants suggest that His169 and Asp154 form a catalytic dyad for general base catalysis and that His189 may stabilize the oxyanion reaction intermediate. Glu177 helps to position Arg203 and His204 and the ?1c-?2c loop for serine binding. A similar role for ionic interactions formed by Lys230 is required for CoA binding. The GmSAT structures also identify Arg253 as important for the enhanced catalytic efficiency of SAT in the CRC and suggest that movement of the residue may stabilize CoA binding in the macromolecular complex. Differences in the effect of cold on GmSAT activity in the isolated enzyme versus the enzyme in the CRC were also observed. A role for CRC formation as a molecular chaperone to maintain SAT activity in response to an environmental stress is proposed for this multienzyme complex in plants. PMID:24225955

Yi, Hankuil; Dey, Sanghamitra; Kumaran, Sangaralingam; Lee, Soon Goo; Krishnan, Hari B.; Jez, Joseph M.

2013-01-01

159

Molybdenum alkylidene complexes : syntheses and applications to olefin metathesis reactions  

E-print Network

Chapter 1. Alkylimido Molybdenum Complexes: Synthesis, Characterization and Activity as Chiral Olefin Metathesis Catalysts. Molybdenum olefin metathesis catalysts that contain previously unexplored aliphatic 1- ...

Pilyugina, Tatiana

2007-01-01

160

Evidence for long formation times of near-barrier fusion reactions  

NASA Astrophysics Data System (ADS)

High energy ? rays from the decay of the giant dipole resonance built on highly excited states in 164Yb at Eex=49 MeV formed in two different reactions have been measured. While standard statistical model calculations can describe the ?-ray spectrum from the 16O + 148Sm reaction they fail to reproduce the ?-ray spectra from the more symmetric reaction 64Ni + 100Mo. Simple model calculations which include particle evaporation and ?-ray decay during the formation process suggest that the observed differences may be related to a long fusion time in the more symmetric reaction.

Thoennessen, M.; Beene, J. R.; Bertrand, F. E.; Baktash, C.; Halbert, M. L.; Horen, D. J.; Sarantities, D. G.; Spang, W.; Stracener, D. W.

1993-06-01

161

The formate-pyruvate exchange reaction by Streptococcus faecalis  

E-print Network

of these inter. . onversions kn . '. ; metabokksm are kinked ivkth derivatives of tetrehydrofolic acid. '}uennekens et al. (1958), emphasi'. ed the role of reduced folic acid as the co?nzyme or carrier of Ci groups. t, " right et al. (1958) showed, in a... bacterial system. that folic acid may be reduced to dihydrofolic acid by pyruvic ox}des?. Pine and Guthrie (1959) studied the influence of folic acid in the lncorporatlon of formats-C14 into the pyrimidine ring of thiagdne. ", 'hiteley et al. (1959) have...

Yeager, Robert Lee

1960-01-01

162

Cadmium(II) Complex Formation with Cysteine and Penicillamine  

PubMed Central

The complex formation between cadmium(II) and the ligands cysteine (H2Cys) or penicillamine (H2Pen = 3, 3?-dimethylcysteine) in aqueous solutions, containing CCd(II) ? 0.1 mol dm-3 and CH2L = 0.2 – 2 mol dm-3, was studied at pH = 7.5 and 11.0 by means of 113Cd-NMR and Cd K- and L3-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine mole ratios the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52 – 2.54 Å and 2.27 – 2.35 Å, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50 – 2.53 Å, but with the Cd-(N/O) bond distances in a similar wide range, 2.28 – 2.33 Å. For the mole ratio CH2L / CCd(II) = 2, the 113Cd chemical shifts, in the range 509 – 527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS2N(N/O) coordination geometry. With a large excess of cysteine (mole ratios CH2Cys / CCd(II) ? 10) complexes with CdS4 coordination geometry dominate, consistent with the 113Cd NMR chemical shifts, ? ? 680 ppm at pH 7.5 and 636 - 658 ppm at pH 11.0, and their mean Cd-S distances of 2.53 ± 0.02 Å. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)4]n-, while at higher pH the deprotonation of the amine groups promotes chelate formation, and at pH 11.0 a minor amount of the [Cd(Cys)3]4- complex with CdS3N coordination is formed. For the corresponding penicillamine solutions with mole ratios CH2Pen / CCd(II) ? 10, the 113Cd-NMR chemical shifts, ? ? 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances Cd-S 2.53 ± 0.02 Å and Cd-O 2.30 – 2.33 Å, indicate that [Cd(penicillaminate)3]n- complexes with chelating CdS3(N/O) coordination dominate already at pH 7.5, and become mixed with CdS2N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines are capable of capturing cadmium(II) ions, while penicillamine, clinically useful for treating the toxic effects of mercury(II) and lead(II) exposure, is not efficient against cadmium(II) poisoning. PMID:19469490

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

2009-01-01

163

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

164

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

PubMed

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

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

2015-02-11

165

Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs  

PubMed Central

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

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

2012-01-01

166

Biological pattern formation: from basic mechanisms to complex structures  

NASA Astrophysics Data System (ADS)

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

Koch, A. J.; Meinhardt, H.

1994-10-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

168

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

169

Quantitative NMR spectroscopy of complex technical mixtures using a virtual reference: chemical equilibria and reaction kinetics of formaldehyde–water–1,3,5-trioxane  

Microsoft Academic Search

Quantitative 1H NMR spectroscopy was used to study chemical equilibria and reaction kinetics of both the formation and decomposition of 1,3,5-trioxane in aqueous formaldehyde solutions. The reaction was homogeneously catalyzed with up to 0.10 g g?1 sulfuric acid at temperatures between 360 and 383 K so that most of the experiments had to be carried out pressurized. The studied mixtures were complex due

Michael Maiwald; Thomas Grützner; Eckhard Ströfer; Hans Hasse

2006-01-01

170

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

NASA Technical Reports Server (NTRS)

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

Devincent, Sandra M.; Michal, Gary M.

1992-01-01

171

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

NASA Technical Reports Server (NTRS)

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

Devincent, Sandra M.; Michal, Gary M.

1993-01-01

172

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...

173

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

174

IgA nephropathy: current views of immune complex formation.  

PubMed

Characteristic features of IgA nephropathy (IgAN) include IgA1-containing immune complexes (IC) in the circulation, urine, and renal mesangium. IC contain IgA1 deficient in hinge region-associated galactose (Gal) and antibodies specific for antigenic determinants present on the hinge region. The biological effects of IC are primarily related to their molecular size and composition: when added to a culture of human mesangial cells, large IC exhibit a proliferative effect while small complexes are inhibitory. These activities have been observed using IC obtained from sera of IgAN patients or generated in vitro. Specifically, various preparations of human IgA1 with modified glycan moieties formed IC in vitro when incubated with sera from IgAN patients or healthy individuals, cord blood serum, or tissue culture supernatants of EBV-immortalized peripheral blood B cells secreting IgG. Interestingly, IgG antibodies specific for the IgA1 Gal-deficient hinge region are commonly found in sera of hominoid as well as non-hominoid primates and many other vertebrate species, and suggest the evolutionary uniqueness of the human IgA1 hinge region. Because of the molecular defect in IgA1 glycosylation and its subsequent recognition by naturally-occurring antibodies, experimental approaches that diminish or prevent formation of large immunostimulatory IC should be further explored. PMID:17495438

Mestecky, Jiri; Suzuki, Hitoshi; Yanagihara, Takeshi; Moldoveanu, Zina; Tomana, Milan; Matousovic, Karel; Julian, Bruce A; Novak, Jan

2007-01-01

175

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

NASA Astrophysics Data System (ADS)

A new technique is described for probing the reaction dynamics of ``half-collisions'' in systems where ``full-collision'' chemical dynamics can also be studied. By selective laser excitation of an atom-molecule van der Waals complex, an electronically excited atom can be created at a known distance from, and with a known orbital symmetry with respect to, the reactive molecule. From spectra of the complex and from detection of nascent products in a state-resolved fashion, not only can a great deal be learned about the dynamics of the half-collision, but comparison can also be made with analogous full-collision dynamical information. Reported here are initial results involving the Hg?H2 van der Waals complex. When the Hg (6s 1S0)?H2 ground-state complex is excited to the Hg(6p 3P1)?H2 complex with frequencies near that of the Hg(6 1S0-6 3P1) free atom transition, the molecular product HgH(X 2?+) is readily detected. No fluorescence of the Hg(6p 3P1)?H2 complex is observed, nor is Hg(6p 3P0) detected as a major product. The two electronic configurations of the excited Hg(6p 3P1)?H2 complex, 3? and 3? (which correspond approximately to axial and perpendicular orientation, respectively, of the p orbital with respect to the freely rotating H2 molecule) exhibit different behavior. The reaction to form HgH (X 2?+) via the 3? complex is ``direct,'' i.e., occurs within 0.1 ps, since the HgH(X 2?+) action spectrum for 3? excitation is continuous. In contrast, there is rovibrational structure in the HgH (X2 ?+) action spectrum for 3? excitation, showing that HgH(X 2?+) formation in this case is ``indirect,'' i.e., occurs on a time scale between 2 ps and 1 ns. Furthermore, the HgH (X 2?+, v=0) rotational quantum-state distribution from 3? complex excitation is bimodal, with a major component quite similar to that resulting from excitation of the 3? complex, but with a minor component present at low N. Possible explanations of these results, which definitely show orbitally selective chemical reactivity, are discussed. Because the initial total angular momentum of the Hg?H2 complex is approximately zero in the cold supersonic jet, the distribution of exit-channel impact parameters could be determined from HgH (X 2?+, v=0) rotational state distributions. For 3? excitation the fairly narrow distribution is peaked at 1.2 Å, and geometrical considerations indicate that energy release into rotation most likely results from the angular dependence of the exit-channel potential surface of an H-Hg-H species and not from H-H bond-breaking impulsion. The angular dependence could result from transitions from the bent excited triplet to the linear ground-state singlet surface of H-Hg-H. The HgH (X 2?+, v=0) initial rotational state distribution from the thermal reaction Hg(6p 3P1) +H2 ? HgH(X 2?+)+H, measured independently at 300 K, was found to be similar to that for half-collision excitation of Hg?H2(3?), but somewhat broadened. This was interpreted to mean that the thermal reaction proceeds via insertive ? attack of the H-H bond, and that exit-channel forces, rather than initial orbital angular momentum, play the dominant role in determining rotational energy disposal in this reaction. From preliminary measurements of HgH (X 2?+, v=1,2) rotational state distributions, it is also proposed that the known Hg(1S)+H+H product channel in the 300 K thermal reaction results merely from the known predissociation of highly rotationally excited HgH (X 2?+, v=1,2) produced initially.

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

1986-02-01

176

Design of a New Cascade Reaction for the Construction of Complex Acyclic Architecture: The  

E-print Network

Design of a New Cascade Reaction for the Construction of Complex Acyclic Architecture: The Tandem of Technology Pasadena, California 91125 ReceiVed December 27, 2000 Tandem or domino reactions have long been Surprisingly, however, relatively few tandem strategies have been directed toward the production of acyclic

MacMillan, David W. C.

177

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS  

E-print Network

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS A Dissertation Presented by CRAIG G. BATES: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS MAY 2005 CRAIG G BATES, B.S., ROGER WILLIAMS UNIVERISTY

Venkataraman, Dhandapani "DV"

178

Copper, silver, and gold complexes in hydrosilylation reactions.  

PubMed

The reduction of diverse functional groups is an essential protocol in organic chemistry. Transition-metal catalysis has been successfully applied to the reduction of olefins, alkynes, and many carbonyl compounds via hydrogenation or hydrosilylation; the latter presenting several advantages over hydrogenation. Notably, hydrosilylation generally occurs under mild reaction conditions, and consequently over-reduced products are rarely detected. Moreover, the great majority of hydrosilanes employed in this reaction are easily handled, inexpensive, or both. A large number of multiple bonds can be involved in this context, and the hydrosilylation reaction can be regarded as a useful method for the synthesis of silicon-containing organic molecules or a convenient way of reducing organic compounds. Furthermore, the silyl group can also be retained as a protecting group, a strategy that can be of great usefulness in organic synthesis. Since the first Wilkinson's catalyst-mediated hydrosilylation of ketones in 1972, metals such as rhodium and iridium have attracted most of the attention in this area. A wide array of catalytic systems for hydrosilylation reactions is nowadays available, which has allowed for a great expansion of the synthetic scope of this transformation. After having been overlooked in the early years, group 11 metals (Cu, Ag, and Au), especially copper, have emerged as appealing alternatives for hydrosilylation. The use of a stabilized form of copper hydride, the hexameric [(Ph3P)CuH]6, by Stryker represented a breakthrough in copper-catalyzed reduction reactions. Nowadays, several copper-based catalytic systems compare well with a variety of reported rhodium-based catalysts, which generally suffer from the high cost of the catalyst. Tertiary phosphine ligands are the most widely used in these transformations. However, other families such as N-heterocyclic carbenes (NHCs) have shown promising activities. Compared with copper, little attention has been paid to silver- or gold-based catalysts. Silver salts have been considered inert towards hydrosilylation, and they are often employed as innocent anion exchange reagents for the in situ generation of cationic transition metal catalysts. Despite the rare reports available, they have already shown interesting reactivity profiles, for example, in the chemoselective reduction of aldehydes in the presence of ketones. Furthermore, 1,2-hydride delivery is favored over 1,4-reductions for alpha,beta-unsaturated carbonyl compounds, in contrast with most copper-based systems. PMID:18281951

Díez-González, Silvia; Nolan, Steven P

2008-02-01

179

Atomistic theory of mesoscopic pattern formation induced by bimolecular surface reactions between oppositely charged molecules  

NASA Astrophysics Data System (ADS)

The kinetics of mesoscopic pattern formation is studied for a reversible A+B rightleftharpoons 0 reaction between mobile oppositely charged molecules at the interface. Using formalism of the joint correlation functions, non-equilibrium charge screening and reverse Monte Carlo methods, it is shown that labyrinth-like percolation structure induced by (even moderate-rate) reaction is principally non-steady-state one and is associated with permanently growing segregation of dissimilar reactants and aggregation of similar reactants into mesoscopic size domains. A role of short-range and long-range reactant interactions in pattern formation is discussed.

Kuzovkov, V. N.; Kotomin, E. A.; Zvejnieks, G.

2011-12-01

180

Nitric oxide-forming reaction between the iron-N-methyl-D-glucamine dithiocarbamate complex and nitrite.  

PubMed

The objective of this study was to elucidate the origin of the nitric oxide-forming reactions from nitrite in the presence of the iron-N-methyl-D-glucamine dithiocarbamate complex ((MGD)(2)Fe(2+)). The (MGD)(2)Fe(2+) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. Although it is widely believed that only NO can react with (MGD)(2)Fe(2+) complex to form the (MGD)(2)Fe(2+).NO complex, a recent article reported that the (MGD)(2)Fe(2+) complex can react not only with NO, but also with nitrite to produce the characteristic triplet EPR signal of (MGD)(2)Fe(2+).NO (Hiramoto, K., Tomiyama, S., and Kikugawa, K. (1997) Free Radical Res. 27, 505-509). However, no detailed reaction mechanisms were given. Alternatively, nitrite is considered to be a spontaneous NO donor, especially at acidic pH values (Samouilov, A., Kuppusamy, P., and Zweier, J. L. (1998) Arch Biochem. Biophys. 357, 1-7). However, its production of nitric oxide at physiological pH is unclear. In this report, we demonstrate that the (MGD)(2)Fe(2+) complex and nitrite reacted to form NO as follows: 1) (MGD)(2)Fe(2).NO complex was produced at pH 7.4; 2) concomitantly, the (MGD)(3)Fe(3+) complex, which is the oxidized form of (MGD)(2)Fe(2+), was formed; 3) the rate of formation of the (MGD)(2)Fe(2+).NO complex was a function of the concentration of [Fe(2+)](2), [MGD], [H(+)] and [nitrite]. PMID:10636843

Tsuchiya, K; Yoshizumi, M; Houchi, H; Mason, R P

2000-01-21

181

Acid-base catalysis of chiral Pd complexes: development of novel catalytic asymmetric reactions and their application to synthesis of drug candidates.  

PubMed

Using the unique character of the chiral Pd complexes 1 and 2, highly efficient catalytic asymmetric reactions have been developed. In contrast to conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine and methylene compounds were activated to form chiral palladium enolates, which underwent enantioselective carbon-carbon bond-forming reactions such as Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid, formed concomitantly during the formation of the enolates to activate electrophiles, thereby promoting the C-C bond-forming reaction. This palladium enolate chemistry was also applicable to electrophilic enantioselective fluorination reactions, and various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, tert-butoxycarbonyl lactone/lactams, cyanoesters, and oxindole derivatives could be fluorinated in a highly enantioselective manner (up to 99% ee). Using this method, the catalytic enantioselective synthesis of BMS-204352, a promising anti-stroke agent, was achieved. In addition, the direct enantioselective conjugate addition of aromatic and aliphatic amines to alpha,beta-unsaturated carbonyl compound was successfully demonstrated. In this reaction, combined use of the Pd complex 2 having basic character and the amine salt was the key to success, allowing controlled generation of the nucleophilic free amine. This aza-Michael reaction was successfully applied to asymmetric synthesis of the CETP inhibitor torcetrapib. PMID:17015970

Hamashima, Yoshitaka

2006-10-01

182

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

183

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

PubMed

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

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

2014-08-18

184

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

PubMed Central

Reaction of nitrogen monoxide with a copper(I) complex possessing a tridentate alkylamine ligand gives a Cu(I)–(·NO) adduct, which when exposed to dioxygen generates a peroxynitrite (O=NOO?)–Cu(II) species. This undergoes thermal transformation to produce a copper(II) nitrito (NO2?) complex and 0.5 mol equiv O2. In the presence of a substituted phenol, the peroxynitrite complex effects oxidative coupling, whereas addition of chloride ion to dissociate the peroxynitrite moiety instead leads to phenol ortho nitration. Discussions include the structures (including electronic description) of the copper–nitrosyl and copper–peroxynitrite complexes and the formation of the latter, based on density functional theory calculations and accompanying spectroscopic data. PMID:19662443

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

2010-01-01

185

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

PubMed Central

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

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

2013-01-01

186

Photochromic polyelectrolyte-surfactant complexes via acid-base reactions  

Microsoft Academic Search

Polyelectrolytesurfactant complexes of tetradecyltrimethylammonium polyacrylate were formed from stoichiometric amounts of polyacrylic acid and tetradecyltrimethylammonium hydroxide in methanol. Photochromicity was introduced by exchanging a few percent of tetradecyltrimethylammonium hydroxide by various stilbazolium hydroxides. The materials obtained showed photochromic properties. Optical anisotropy due to mesogenic behavior was not found in dried samples, but appeared upon exposure to air. Certain changes in

Bernhard KLAUßNER; Jens Frommel; Thomas Wolff

1999-01-01

187

Aminomethylation reaction of ortho-pyridyl C-H bonds catalyzed by group 3 metal triamido complexes.  

PubMed

Tris[N,N-bis(trimethylsilyl)amido] complexes of group 3 metals, especially yttrium and gadolinium, served as catalysts for ortho-C-H bond addition of pyridine derivatives and N-heteroaromatics into the C?N double bond of nonactivated imines to afford the corresponding aminomethylated products. Addition of catalytic amounts of secondary amines, such as dibenzylamine, dramatically improved the catalytic activity through the formation of a mixed ligated complex such as [(Me3Si)2N]2Y(NBn2)(THF) (4). Furthermore, kinetic studies using the isolated complex 4 provided a plausible reaction mechanism by which coordination of two pyridine derivatives afforded a penta-coordinated species as a key step. PMID:25543453

Nagae, Haruki; Shibata, Yu; Tsurugi, Hayato; Mashima, Kazushi

2015-01-21

188

An alternative approach to aldol reactions: gold-catalyzed formation of boron enolates from alkynes.  

PubMed

A new method for enolate generation via the gold-catalyzed addition of boronic acids to alkynes is reported. The formation of boron enolates from readily accessible ortho-alkynylbenzeneboronic acids proceeds rapidly with 2 mol % PPh(3)AuNTf(2) at ambient temperature. The enolates undergo aldol reaction with an aldehyde present in the reaction mixture to give cyclic boronate esters, which can be subsequently transformed into phenols, biaryls, or dihydrobenzofurans via oxidation, Suzuki-Miyaura, or intramolecular Chan-Lam coupling, respectively. A combined gold/boronic acid catalyzed aldol condensation reaction of an alkynyl aldehyde was also successfully achieved. PMID:20380452

Körner, Cindy; Starkov, Pavel; Sheppard, Tom D

2010-05-01

189

Modeling of the formation of complex molecules in protostellar objects  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

190

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

PubMed

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

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

2012-08-01

191

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

SciTech Connect

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

McLane, V. [ed.] [comp.

1997-07-01

192

Ligand basicity and rigidity control formation of macrocyclic polyamino carboxylate complexes of gadolinium(III)  

SciTech Connect

The formation reaction rates of some macrocyclic polyamino carboxylate complexes of gadolinium, GdL (where L is DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, H[sub 3]L, HP-DO3A = 10-(hydroxyproyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, H[sub 3]L, and DO3MA = (1R,4R,7R)-[alpha],[alpha][prime],[alpha][double prime]-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-triacetic acid, H[sub 3]L), have been measured at 25.0 [+-] 0.1 [degrees]C and at a constant ionic strength of 1.0 (NaCl) by an indicator method. The formation reactions are first order in the limiting reagent (ligand) and nearly independent of the excess reagent (gadolinium ion). A mechanism of the formation of the gadolinium complexes involves the formation of a precursor (intermediate) complex, Gd(*HL), in an equilibrium step followed by its deprotonation and reorganization to the final product in the rate-determining step. The stability constants (log K[sub Gd(*HL)]) of the intermediate have been determined from the kinetic data and the values are 8.9 (DO3A), 9.0(HP-DO3A), and 10.7 (DO3MA). The nature of the intermediate is proposed in which the metal is coordinated to oxygens and at least one nitrogen of the ligand. Deprotonation and reorganization of the intermediate are specific-base assisted. The second-order rate constants (k[sub OH], M[sup [minus]1]s[sup [minus]1]) for the reorganization of the intermediate, Gd(*HL) (L are given in the parentheses), are (2.1 [+-] 0.1) x 10[sup 7] (DO3A), (1.23 [+-] 0.04) x 10[sup 7] (HP-DO3A), and (7.2 [+-] 0.3) x 10[sup 4] (DO3MA), compared to the literature data (7.1 [+-] 1) x 10[sup 7] (NOTA) and (5.9 [+-] 0.2) x 10[sup 6] (DOTA). The specific-base assisted rate of reorganization of the intermediate, Gd(*HL), is correlated with the ligand strain energy and its first protonation constant.

Kumar, K.; Tweedle, M.F. (Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, NJ (United States))

1993-09-29

193

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

PubMed

ortho-Phospho-l-serine (H2Psi, where Psi represents the serinephosphato ion), a constituent of salivary proteins, seems to play an important role in the mineralization of teeth. To understand the basic mechanism of this interaction, the uptake of o-phospho-l-serine from relatively concentrated aqueous solutions (up to 100 mmol/L) onto synthetic hydroxyapatite was studied. Previous studies have shown that in the dilute concentration range (<12.5 mmol/L) the uptake followed a regular Langmuirian adsorption plot. At higher concentrations the uptake curve increased steeply, but no formation of a separate phase in the reacted apatite was discernible, either by optical or by scanning electron microscopy. The dissolution of apatite released phosphate and calcium ions into the solution in amounts linearly related to the uptake of serine with P/Psi = 1 and Ca/Psi = 2. The charge and mass balance of the reaction can be reconciled with the formation of the surface complex (shown within brackets):Ca10(OH)2(PO4)6 + 6H2Psi --> [Ca6(HPsi)2(HPO4)2(PO4)2] + 4Ca2+ + 2HPsi1- + 2Psi2- + 2H2PO1-4 + 2H2O.The formation of two other surface complexes is possible; however, the complex shown above probably disrupts the apatite lattice the least. Traces of CaPsi·H2O precipitate out from the filtrates of highly concentrated solutions after 6 days. Copyright 1997 Academic Press. Copyright 1997Academic Press PMID:9367603

Misra

1997-10-01

194

Terminal Vanadium-Neopentylidyne Complexes and Intramolecular Cross-Metathesis Reactions to Generate Azametalacyclohexatrienes  

E-print Network

Terminal Vanadium-Neopentylidyne Complexes and Intramolecular Cross-Metathesis Reactions-carbon multiple bonds5 triggered the pursuit for the thus far unknown vanadium- alkylidyne functionality. Herein by this observation and realizing that vanadium- alkylidyne complexes are unknown, we alkylated (Nacnac)Vd CHt

Baik, Mu-Hyun

195

Synthesis and Reactions of Tungsten Alkylidene Complexes That Contain the 2,6-Dichlorophenylimido Ligand  

E-print Network

Synthesis and Reactions of Tungsten Alkylidene Complexes That Contain the 2,6-Dichlorophenylimido Institute of Technology, Cambridge, Massachusetts 02139 ReceiVed October 30, 2006 Tungsten alkylidene alkylidene bisalkoxide complexes of molybdenum or tungsten of the type M(NR)(CHR)(OR)2 are now established

Müller, Peter

196

Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention of short-circuiting  

E-print Network

Review Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention This review is focused on the mechanism of ubiquinol oxidation by the cytochrome bc1 complex (bc1: (i) the formed semiquinone anion remains bound to the reduced FeS domain and impedes its undocking

Steinhoff, Heinz-Jürgen

197

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

2013-10-01

198

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

PubMed

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

Gronert, Scott; O'Hair, Richard A J

2002-09-01

199

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

PubMed

Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation. PMID:15330667

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

2004-08-19

200

Formation and characterization of an insoluble polyelectrolyte complex: Chitosan-polyacrylic acid  

Microsoft Academic Search

Chitosan and polyacrylic acid mixtures were prepared in different mole ratios and at different pH values and ionic strengths (0.025–0.300). Complex formation was detected by turbidity measurement and quantified by weighing the freeze dried pellet recovered by centrifugation. No insoluble complex formation at pH=2 was detected. In the 3 to 6 pH range, the maximum complex formation occurred at different

Visith Chavasit; Carlos Kienzle-Sterzer; J. Antonio Torres

1988-01-01

201

Use of charge-transfer complex formation for the spectrophotometric determination of nortriptyline.  

PubMed

Three simple and selective methods are proposed for the determination of nortriptyline hydrochloride in bulk form and in tablets. The first two methods are based on the formation of charge-transfer complexes between the drug base as a n-donor and quinhydrone or p-chloranil as pi-acceptor. The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for quinhydrone and p-chloranil, respectively. The third method is based on the interaction of N-alkylvinylamine formed from the condensation of the free secondary amine group and acetaldehyde with p-chloranil to give a vinylamino substituted quinone. The coloured product exhibits an absorption maximum at 650 nm in dioxane. All variables were studied to optimize reaction conditions. Beer's law was obeyed and the relative standard deviations were found to be less than 1.5%. The methods have been applied to the analysis of nortriptyline hydrochloride in the bulk drug and in tablets. PMID:11204939

Attia, F M

2000-01-01

202

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

PubMed Central

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

Liu, Ben; Han, Lu; Che, Shunai

2012-01-01

203

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

PubMed

The helicity of DNA and its long-range chiral packing are widespread phenomena; however, the packing mechanism remains poorly understood both in vivo and in vitro. Here, we report the extraordinary DNA chiral self-assembly by silica mineralization, together with circular dichroism measurements and electron microscopy studies on the structure and morphology of the products. Mg(2+) ion and diethylenetriamine were found to induce right- and left-handed chiral DNA packing with two-dimensional-square p4mm mesostructures, respectively, to give corresponding enantiomeric impeller-like helical DNA-silica complexes. Moreover, formation of macroscopic impeller-like helical architectures depends on the types of polyamines and co-structure-directing agents and pH values of reaction solution. It has been suggested that interaction strength between negatively charged DNA phosphate strands and positively charged counterions may be the key factor for the induction of DNA packing handedness. PMID:24098845

Liu, Ben; Han, Lu; Che, Shunai

2012-10-01

204

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

Microsoft Academic Search

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

P. Del Castillo; A. R. Llorente; A. Gomez; J. Gosalvez; V. J. Goyanes; J. C. Stockert

1990-01-01

205

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

PubMed Central

Reaction of a nonheme iron(III)-peroxo complex, [FeIII(14-TMC)(O2)]+, with NO+, a transformation which is essentially isoelectronic with that for nitric oxide dioxygenases [Fe(III)(O2•?) + NO], affords an iron(IV)-oxo complex, [FeIV(14-TMC)(O)]2+, and nitrogen dioxide (NO2), followed by conversion to an iron(III)-nitrato complex, [FeIII(14-TMC)(NO3)(F)]+. PMID:24394960

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

2014-01-01

206

The function of supplements required for the formate-pyruvate exchange reaction in Streptococcus faecalis  

E-print Network

of the requirements for the degree of MASTER OF SCIENCE January l964 Major Subject: Microbiology THE FUNCTION OF SUPPLEMENTS REQUIRED FOR THE FORMATE-PYRUVATE EXCHANGE REACTION I. N STREPTOCOCCUS FAECALIS A Thesis By GORDON MARSH SMITH Approved as to styie... necessary for tbe incorporation of formate-C into pyruvate by Streptococcus faeca'lis (Wood and O'Kane, 14 1960). Since cell extracts can exchange formate without an additional factor other than a required O-R potent:ial (Oster, 196'), t. he factor...

Smith, Gordon Marsh

1964-01-01

207

Integrin activation and focal complex formation in cardiac hypertrophy  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

208

Star Formation in the Northern Cloud Complex of NGC 2264  

E-print Network

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

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

2006-01-01

209

Star Formation in the Northern Cloud Complex of NGC 2264  

E-print Network

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

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

2006-03-09

210

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

211

The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution  

NASA Astrophysics Data System (ADS)

Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO3). The formation of the CaL+ and CaHL2+ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO3). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.

Kurochkin, V. Yu.; Chernikov, V. V.; Orlova, T. D.

2011-04-01

212

Fiber-dependent amyloid formation as catalysis of an existing reaction pathway  

E-print Network

Fiber-dependent amyloid formation as catalysis of an existing reaction pathway Amy M. Ruschak component of a number of degenerative diseases is the deposition of protein as amyloid fibers. Self islet amyloid polypeptide. We show that nucleation occurs by two pathways: a fiber-independent (primary

Miranker, Andrew

213

Kinetics of Enol Formation from Reaction of OH with Propene Lam K. Huynh,,  

E-print Network

Kinetics of Enol Formation from Reaction of OH with Propene Lam K. Huynh,, Hongzhi R. Zhang*, Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112, Department of Chemical Engineering, UniVersity of Utah, Salt Lake City, Utah 84112

Utah, University of

214

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 ...

215

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

216

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

PubMed

The reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(?-Cl)2Li(THF)2] (1, BIPM(TMS) = {C(PPh2NSiMe3)2}) towards carbonyl and heteroallene substrates is reported. Reaction of 1 with benzophenone proceeds to give the metallo-Wittig terminal alkene product Ph2C=C(PPh2NSiMe3)2 (2); the likely "UOCl2" byproduct could not be isolated. Addition of the bulky ketone PhCOBu(t) to 1 resulted in loss of LiCl, coordination of the ketone, and dimerisation to give [U(BIPM(TMS))(Cl)(?-Cl){OC(Ph)(Bu(t))}]2 (3). The reaction of 1 with coumarin resulted in ring opening of the cyclic ester and a metallo-Wittig-type reaction to afford [U{BIPM(TMS)[C(O)(CHCHC6H4O-2)]-?(3)-N,O,O'}(Cl)2(THF)] (4) where the enolate product remains coordinated to uranium. The reaction of PhCOF with 1 resulted in C-F bond activation and oxidation resulting in isolation of [U(O)2(Cl)2(?-Cl)2{(?-LiDME)OC(Ph)=C(PPh2NSiMe3)(PPh2NHSiMe3)}2] (5) along with [U(Cl)2(F)2(py)4] (6). The reactions of 1 with tert-butylisocyanate or dicyclohexylcarbodiimide resulted in the isolation of the [2 + 2]-cycloaddition products [U{BIPM(TMS)[C(NBu(t)){OLi(THF)2(?-Cl)Li(THF)3}]-?(4)-C,N,N',N''}(Cl)3] (7) and [U{BIPM(TMS)[C(NCy)2]-?(4)-C,N,N',N''}(Cl)(?-Cl)2Li(THF)2] (8). Complexes 2-8 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR and FTIR spectroscopies, Evans method solution magnetic moments, variable temperature SQUID magnetometry, and elemental analyses. PMID:24798878

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

2014-10-14

217

Mobility-induced instability and pattern formation in a reaction-diffusion system  

NASA Astrophysics Data System (ADS)

Ions undergoing a reaction-diffusion process are susceptible to electric field. We show that a constant external field may induce a kind of instability on the state stabilized by diffusion in a reaction-diffusion system giving rise to formation of pattern even when the diffusion coefficients of the reactants are equal. The origin of the pattern is due to the difference in mobilities of the two species and is thus markedly different from that of deformed Turing pattern in presence of the field. While this differential flow instability had been shown earlier to result in traveling waves, we realize in the context of stationary pattern formation in a typical reaction-diffusion-advective system. Our analysis is based on a numerical simulation of a generic model on a two-dimensional domain.

Riaz, Syed Shahed; Kar, Sandip; Ray, Deb Shankar

2004-09-01

218

Catalytic C-N, C-O, and C-S Bond Formation Promoted by Organoactinide Complexes  

NASA Astrophysics Data System (ADS)

Throughout this last decade, we have witnessed impressively how the chemistry of electrophilic d0/fn actinides has been prospering either in their new synthetic approaches reaching very interesting compounds or in their use in stoichiometric and catalytic reactions leading to high levels of complexity. The unique rich and complex features of organoactinides prompted the development of this field toward catalysis in demanding chemical transformations. In this review, we present a brief and selective survey of the recent developments in homogenous catalysis of organoactinide complexes, especially toward the formation of new C-N, C-O, and C-S bonds. We start by presenting the synthesis and characterization of the corresponding organoactinide complexes, followed by the homogeneous catalytic chemical transformations that include the hydroamination of terminal alkynes, the polymerization of ?-caprolactone and L-lactide, the reduction of azides and hydrazines by high-valent organouranium complexes, the hydrothiolation of terminal alkynes, and the catalytic Tishchenko reaction. For each reaction, the scope and the thermodynamic, kinetic, and mechanistic aspects are presented.

Eisen, Moris S.

219

Lattice Boltzmann study of pattern formation in reaction-diffusion systems  

E-print Network

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

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

2010-07-19

220

Reactions of Complex Phenols on Aerosols with Gaseous Ozone  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

221

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

SciTech Connect

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

Fedorenko, S. G. [Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk (Russian Federation); Burshtein, A. I. [Weizmann Institute of Science, 76100, Rehovot (Israel)

2014-09-21

222

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

223

Mononuclear Phenolate Diamine Zinc Hydride Complexes and Their Reactions With CO2  

PubMed Central

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (1)/methoxy (2)/nitro (3)]-6-{[(2?-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes 4–6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes 7–9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes 10–12. The new complexes 4–12 have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (d8-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(?-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes 13–15. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer–dimer equilibrium that is dominated by the mononuclear species at 298 K. PMID:24882918

2014-01-01

224

Mononuclear Phenolate Diamine Zinc Hydride Complexes and Their Reactions With CO2.  

PubMed

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (1)/methoxy (2)/nitro (3)]-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes 4-6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes 7-9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes 10-12. The new complexes 4-12 have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (d 8-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(?-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes 13-15. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer-dimer equilibrium that is dominated by the mononuclear species at 298 K. PMID:24882918

Brown, Neil J; Harris, Jonathon E; Yin, Xinning; Silverwood, Ian; White, Andrew J P; Kazarian, Sergei G; Hellgardt, Klaus; Shaffer, Milo S P; Williams, Charlotte K

2014-03-10

225

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

PubMed

Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni(0), Ni(I), Ni(II), and/or Ni(III) oxidation states. In contrast, Ni(IV) intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic Ni(IV) complexes, accessed by the reaction of Ni(II) precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These Ni(IV) complexes undergo highly selective carbon(sp(3))-oxygen, carbon(sp(3))-nitrogen, and carbon(sp(3))-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions. PMID:25766226

Camasso, Nicole M; Sanford, Melanie S

2015-03-13

226

Development of an aquacatalytic system based on the formation of vesicles of an amphiphilic palladium NNC-pincer complex.  

PubMed

Two amphiphilic palladium NNC-pincer complexes bearing hydrophilic tri(ethylene glycol) chains and hydrophobic dodecyl chains were designed and prepared for the development of a new aquacatalytic system. In water, these amphiphilic complexes self-assembled to form vesicles, the structures which were established by means of a range of physical techniques. When the catalytic activities of the vesicles were investigated in the arylation of terminal alkynes in water, they were found to catalyze the reaction of aryl iodides with terminal alkynes to give good yields of the corresponding internal alkynes. The formation of a vesicular structure was shown to be essential for efficient promotion of this reaction in water. PMID:25820251

Sakurai, Fumie; Hamasaka, Go; Uozumi, Yasuhiro

2015-04-21

227

N-Heterocyclic Carbene Complexes of Rh: Reaction With Dioxygen Without Oxidation  

SciTech Connect

The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d{sup 8} metal complex, rather than the more common Rh(III) d{sup 6} peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 {angstrom} range.

Praetorius, J.M.; Allen, D.P.; Wang, R.; Webb, J.D.; Grein, F.; Kennepohl, P.; Crudden, C.M.

2009-05-21

228

Controlled formation of synthetic metal - transition metal conjugated complex systems  

Microsoft Academic Search

The controlled complexation of the emeraldine base of poly(o-toluidine) with palladium(II) compounds was achieved in an organic solvent to afford structurally defined conjugated polymer complexes. Two coordination sites are used for complexation in the case of Pd(OAc)2 or PdCl2(MeCN)2, in contrast to only one coordination site available for the palladium(II) complex bearing the tridentate ligand. Two imine moieties are capable

Toshikazu Hirao; Satoshi Yamaguchi; Shinya Fukuhara

1999-01-01

229

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

230

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

2012-03-15

231

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

232

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

PubMed

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

Wotal, Alexander C; Ribson, Ryan D; Weix, Daniel J

2014-10-27

233

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

234

Influence of entrance channels on the formation of superheavy nuclei in massive fusion reactions  

NASA Astrophysics Data System (ADS)

Within the framework of the dinuclear system (DNS) model, the production cross sections of superheavy nuclei Hs ( Z=108) and Z=112 combined with different reaction systems are analyzed systematically. It is found that the mass asymmetries and the reaction Q values of the projectile-target combinations play a very important role on the formation cross sections of the evaporation residues. Both methods to obtain the fusion probability by nucleon transfer by solving a set of microscopically derived master equations along the mass asymmetry degree of freedom (1D) and distinguishing protons and neutrons of fragments (2D) are compared with each other and also with the available experimental data.

Feng, Zhao-Qing; Jin, Gen-Ming; Li, Jun-Qing

2010-05-01

235

Atom-transfer radical addition reactions catalyzed by RuCp* complexes: a mechanistic study.  

PubMed

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom-transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero-order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate-limiting step of the reaction. PMID:19750528

Fernández-Zúmel, Mariano A; Thommes, Katrin; Kiefer, Gregor; Sienkiewicz, Andrzej; Pierzchala, Katarzyna; Severin, Kay

2009-11-01

236

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

NASA Astrophysics Data System (ADS)

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

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

1999-05-01

237

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

238

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

239

Mechanism of the production of light complex particles in nucleon-induced reactions  

NASA Astrophysics Data System (ADS)

The improved quantum molecular dynamics (ImQMD) model incorporated with the statistical decay model is successful in describing emission of the nucleons in the intermediate energy spallation reactions, but not good enough in describing productions of the light complex particles, i.e. d, t, 3He and 4He. To improve the description on emission of light complex particles, a phenomenological mechanism called surface coalescence and emission is introduced into the ImQMD model: nucleon ready to escape from the compound nuclei can coalesce with the other nucleon(s) to form light complex particle and be emitted. With updated ImQMD model, the description on the experimental data of light complex particles produced in nucleon-induced reactions are great improved.

Wei, Dexian; Wang, Ning; Ou, Li

2014-03-01

240

Formation of Kaonic Atoms and Kaonic Nuclei by In-flight ($K^-,p$) reactions  

E-print Network

We study the kaonic atom and kaonic nucleus formation by the in-flight ($K^-, p$) reactions for C, O, Si and Ca target cases theoretically. Deeply bound kaonic atoms were predicted to exist as quasi-stable states and were expected to be observed in some proper experimental methods. Kaonic nuclear states are also expected to exist with large decay widths. We evaluate the formation cross sections of the kaonic atoms and kaonic nuclei using an effective number approach. We show that the indications of the kaonic bound states can be observed in the outgoing proton energy spectra.

Junko Yamagata; Hideko Nagahiro; Yuko Okumura; Satoru Hirenzaki

2005-08-25

241

Enolization and racemization reactions of glucose and fructose on heating with amino-acid enantiomers and the formation of melanoidins as a result of the Maillard reaction  

Microsoft Academic Search

This study investigated the enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers\\u000a and the formation of melanoidins as a result of the Maillard reaction. The study measured reducing sugars and L- and D- amino acids using HPLC as an index for the amount of enolization of the sugars and isomerization of the amino acids.

Ji-Sang Kim; Young-Soon Lee

2009-01-01

242

Formation of bare UO2(2+) and NUO(+) by fragmentation of gas-phase uranyl-acetonitrile complexes.  

PubMed

In a prior study [Van Stipdonk; et al. J. Phys. Chem. A 2006, 110, 959-970], electrospray ionization (ESI) was used to generate doubly charged complex ions composed of the uranyl ion and acetonitrile (acn) ligands. The complexes, general formula [UO2(acn)n](2+), n = 0-5, were isolated in an 3-D quadrupole ion-trap mass spectrometer to probe intrinsic reactions with H2O. Two general reaction pathways were observed: (a) the direct addition of one or more H2O ligands to the doubly charged complexes and (b) charge-exchange reactions. For the former, the intrinsic tendency to add H2O was dependent on the number and type of nitrile ligand. For the latter, charge exchange involved primarily the formation of uranyl hydroxide, [UO2OH](+), presumably via a collision with gas-phase H2O and the elimination of a protonated nitrile ligand. Examination of general ion fragmentation patterns by collision-induced dissociation, however, was hindered by the pronounced tendency to generate hydrated species. In an update to this story, we have revisited the fragmentation of uranyl-acetonitrile complexes in a linear ion-trap (LIT) mass spectrometer. Lower partial pressures of adventitious H2O in the LIT (compared to the 3-D ion trap used in our previous study) minimized adduct formation and allowed access to lower uranyl coordination numbers than previously possible. We have now been able to investigate the fragmentation behavior of these complex ions completely, with a focus on tendency to undergo ligand elimination versus charge reduction reactions. CID can be used to drive ligand elimination to completion to furnish the bare uranyl dication, UO2(2+). In addition, fragmentation of [UO2(acn)](2+) generated [UO2(NC)](+), which subsequently fragmented to furnish NUO(+). Formation of the nitrido by transfer of N from cyanide was confirmed using precursors labeled with (15)N. The observed formation of [UO2(NC)](+) and NUO(+) was modeled by density functional theory. PMID:25121574

Van Stipdonk, Michael J; Michelini, Maria del Carmen; Plaviak, Alexandra; Martin, Dean; Gibson, John K

2014-09-11

243

Scale-dependent rates of uranyl surface complexation reaction in sediments  

NASA Astrophysics Data System (ADS)

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results show that the grain-scale rate constant of U(VI) surface complexation was over 3-10 orders of magnitude smaller than the rate constant calculated using the molecular simulations. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed that the rate of coupled diffusion and molecular surface complexation reaction in the intragranular porous domains was slower than either individual process alone. The results provide important implications for developing models to scale geochemical/biogeochemical reactions.

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien; Zachara, John M.; Zhu, Weihuang

2013-03-01

244

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

245

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

246

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

247

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

PubMed Central

We have investigated both the chemical reduction of (BDI)Nb(V) imido complexes (BDI = HC[C(Me)NAr]2; Ar = 2,6-iPr2-C6H3) to the formal Nb(III) oxidation state and the ability of these Nb(III) complexes to behave as two-electron reductants. The reduction of the Nb(V) species was found to depend heavily on the nature of available supporting ligands, but the chemistry of the reduced compounds proceeded cleanly with a number of unsaturated organic reagents. Accordingly, the novel Nb(V) bis(imido) complexes supported by the monoazabutadiene (mad) ligand (mad)Nb(NtBu)(NAr)(L?) (L? = py, thf) were formed by either KC8 reduction of (BDI)Nb(NtBu)Cl2(py) in the absence of strong ?-acids or by H2 reduction of the Nb(V) dimethyl complex (BDI)Nb(NtBu)Me2 in THF. These products are likely formed though an intramolecular, 2 e? reductive C–N bond cleavage, as has been observed previously for related Group 4 systems, suggesting that transient Nb(III) intermediates were present in both cases. In the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), KC8 reduction of (BDI)Nb(NtBu)Cl2(py) was arrested at the Nb(IV) oxidation state to give (BDI)Nb(NtBu)Cl(dmpe), which was characterized by solution-state EPR spectroscopy as a Nb-centered paramagnet with strong coupling to the two equivalent phosphorus nuclei (Aiso{93Nb} = 120.5×10?4 cm?1, Aiso{31P} = 31.0×10?4 cm?1, giso = 1.9815). When strong ?-acids were used to intercept the thermally unstable Nb(III) complex (BDI)Nb(NtBu)(py) prior to reductive cleavage of the ligand C–N bond, the thermally stable Nb(III) species (BDI)Nb(NtBu)(CX)2(L?) (X = O, L? = py; X = NXyl, L? = CNXyl; Xyl = 2,6-Me2-C6H3) were obtained in good yields. The Nb(III) complexes (BDI)Nb(NtBu)py, (BDI)Nb(NtBu)(CO)2(py) and (BDI)Nb(NtBu)(CO)2 were subsequently investigated for their ability to serve as two-electron reducing reagents for both metal-ligand multiple bond formation and for the reduction of organic ?-systems. The reduction of mesityl azide by (BDI)Nb(NtBu)(py) and diphenylsulfoxide by (BDI)Nb(NtBu)(CO)2 led to the monomeric bis(imido) and dimeric oxo complexes (BDI)Nb(NtBu)(NMes)(py) and [(BDI)Nb(NtBu)]2(?2-O)2, respectively. MeLi addition to (BDI)Nb(NtBu)(CO)2(py) resulted in the formation of a Nb-acylate via methide addition to one of the carbonyl carbons. The acylate product was revealed to have a short Nb–Cacylate bond distance (2.059(4) Å), consistent with multiple Nb–C bond character resulting from Nb(III) back-bonding into the acylate carbon. The interaction of (BDI)Nb(NtBu)(CO)2 with two equivalents of 4,4?-dichlorobenzophenone resulted in the clean, quantitative formation of the corresponding pinacol coupling product, but introduction of the ketone in 1: 1 molar ratios resulted in mixtures of the pinacol product and the starting material, suggesting that ketone coordination to the Nb(III) complex may be reversible. Relatedly, addition of 1-phenyl-1-propyne to (BDI)Nb(NtBu)(CO)2 formed a thermally unstable 1: 1 Nb/alkyne complex, as characterized by NMR and IR spectroscopies; reaction of this species with HCl/MeOH yielded a 2: 1 mixture of 1-phenyl-1-propene and the free alkyne, suggesting a high degree of covalency in the Nb–C bonds. PMID:21116450

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

2010-01-01

248

Halogenated metalloporphyrin complexes as catalysts for selective reactions of acyclic alkanes with molecular oxygen  

SciTech Connect

The authors have shown that halogenation of the porphyrin ring of a metalloporphyrin complex can convert a catalytically inactive material into an exceptionally active catalyst for the selective reaction of an alkane with molecular oxygen. The greater the degree of halogenation of the ring, the greater is the catalytic activity of the metal complex. The product profile, while characteristic of radical reactions, is sensitive to the nature of the metal center. Iron complexes are generally more active than those of cobalt, manganese, or chromium. The activity of iron complexes is directly related to the Fe(III)/(II) reduction potential of the porphyrin complex. There is also a similar correlation between the Fe(III)/Fe(II) reduction potential and the rate at which iron haloporphyrin complexes decompose alkyl hydroperoxides. These iron perhaloporphyrin complexes are not only the most active known liquid phase alkane air-oxidation catalysts, they are also the most active hydroperoxide decomposition catalysts known to date. The nature of the products formed is dependent on the structure of the aliphatic substrate that is oxidized and can be rationalized by a catalytic pathway that very efficiently generates alkyl and alkoxy radicals at low temperatures. The relationship between the electrochemical properties of these complexes and the rates of alkane oxidation and hydroperoxide decomposition lends insight into possible mechanisms of catalytic activity. 73 refs., 7 figs., 11 tabs.

Lyons, J.E.; Ellis, P.E. Jr.; Myers, H.D. Jr. [Sun Company, Marcus Hook, PA (United States)] [Sun Company, Marcus Hook, PA (United States)

1995-08-01

249

Catalytic C-N and C-F bond formation by organometallic group 11 complexes  

E-print Network

This thesis presents a study of the reaction between an (NHC)gold(I) fluoride complex (NHC = N-heterocyclic carbene) and alkynes (Chapter 1). Gold(I) and fluoride add trans across the triple bond of 3-hexyne and ...

Akana, Jennifer Anne

2007-01-01

250

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

2013-10-01

251

A calorimetric study of the hydrolysis and peroxide complex formation of the uranyl(VI) ion.  

PubMed

The enthalpies of reaction for the formation of uranyl(vi) hydroxide {[(UO2)2(OH)2](2+), [(UO2)3(OH)4](2+), [(UO2)3(OH)5](+), [(UO2)3(OH)6](aq), [(UO2)3(OH)7](-), [(UO2)3(OH)8](2-), [(UO2)(OH)3](-), [(UO2)(OH)4](2-)} and peroxide complexes {[UO2(O2)(OH)](-) and [(UO2)2(O2)2(OH)](-)} have been determined from calorimetric titrations at 25 °C in a 0.100 M tetramethyl ammonium nitrate ionic medium. The hydroxide data have been used to test the consistency of the extensive thermodynamic database published by the Nuclear Energy Agency (I. Grenthe, J. Fuger, R. J. M. Konings, R. J. Lemire, A. B. Mueller, C. Nguyen-Trung and H. Wanner, Chemical Thermodynamics of Uranium, North-Holland, Amsterdam, 1992 and R. Guillaumont, T. Fanghänel, J. Fuger, I. Grenthe, V. Neck, D. J. Palmer and M. R. Rand, Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, Amsterdam, 2003). A brief discussion is given about a possible structural relationship between the trinuclear complexes [(UO2)3(OH)n](6-n), n = 4-8. PMID:24301256

Zanonato, Pier Luigi; Di Bernardo, Plinio; Grenthe, Ingmar

2014-02-14

252

Formation and decay of 164Yb* in near- and below-barrier fusion reactions  

NASA Astrophysics Data System (ADS)

A consistent description of the formation and decay of 164Yb* in the fusion of 16O+148Sm and 64Ni+100Mo is presented in a bombarding energy range from near to well below the entrance channel Coulomb barrier. Fusion excitation functions and angular momentum distributions are described well with a recently proposed one-dimensional barrier penetration model with energy-dependent fusion barriers. The main features of fusion and angular momentum distribution data in 64Ni+100Mo are also reproduced with simplified coupled channel calculations. The statistical model accounts well for the decay of 164Yb* in the 16induced reaction and for most of the data in the 64induced reaction. The evaporation residue fractional cross sections as a function of the compound nucleus excitation energy show trends that correlate with the low- and high-spin regions of the compound nucleus angular momentum distributions populated in the two reactions.

Nicolis, N. G.; Sarantites, D. G.

1993-12-01

253

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

Microsoft Academic Search

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

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

2005-01-01

254

Formation of metamorphic core complex in inherited wedges: A thermomechanical modelling study  

E-print Network

Formation of metamorphic core complex in inherited wedges: A thermomechanical modelling study B Férollerie, 45071 Orléans cedex 02, France Abstract Metamorphic Core Complexes (MCCs) form when a thickened in a nappe stack involving continental basement. 1. Introduction A metamorphic core complex (MCC) corresponds

Paris-Sud XI, Université de

255

Pressure Dependence of Butyl Nitrate Formation in the Reaction of Butylperoxy Radicals with Nitrogen Oxide.  

PubMed

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

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

2014-11-21

256

SOA formation from partitioning and heterogeneous reactions: model study in the presence of inorganic species.  

PubMed

A predictive model for secondary organic aerosol (SOA) formation by both partitioning and heterogeneous reactions was developed for SOA created from ozonolysis of alpha-pinene in the presence of preexisting inorganic seed aerosols. SOA was created in a 2 m3 polytetrafluoroethylene film indoor chamber under darkness. Extensive sets of SOA experiments were conducted varying humidity, inorganic seed compositions comprising of ammonium sulfate and sulfuric acid, and amounts of inorganic seed mass. SOA mass was decoupled into partitioning (OM(P)) and heterogeneous aerosol production (OM(H)). The reaction rate constant for OM(H) production was subdivided into three categories (fast, medium, and slow) to consider different reactivity of organic products for the particle phase heterogeneous reactions. The influence of particle acidity on reaction rates was treated in a previous semiempirical model. Model OM(H) was developed with medium and strong acidic seed aerosols, and then extrapolated to OM(H) in weak acidic conditions, which are more relevant to atmospheric aerosols. To demonstrate the effects of preexisting glyoxal derivatives (e.g., glyoxal hydrate and dimer) on OM(H), SOA was created with a seed mixture comprising of aqueous glyoxal and inorganic species. Our results show that heterogeneous SOA formation was also influenced by preexisting reactive glyoxal derivatives. PMID:16719105

Jang, Myoseon; Czoschke, Nadine M; Northcross, Amanda L; Cao, Gang; Shaof, David

2006-05-01

257

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

258

Reliable Protein Folding on Complex Energy Landscapes: The Free Energy Reaction Path  

E-print Network

Reliable Protein Folding on Complex Energy Landscapes: The Free Energy Reaction Path Gregg Lois the dynamics of protein folding. The key insight is that the search for the native protein conformation. In the ``new view'' of protein folding (3,7), statistical fluctuations on an energy landscape give rise

O'Hern, Corey S.

259

Further study on mechanism of production of light complex particles in nucleon-induced reactions  

NASA Astrophysics Data System (ADS)

The Improved Quantum Molecular Dynamics model incorporated with the statistical decay model is used to investigate the intermediate energy nucleon-induced reactions. In our last work, by introducing a phenomenological mechanism called surface coalescence and emission into ImQMD model, the description on the light complex particle emission has been great improved. In this work, taking account of different specific binding energies and separation energies for various light complex particles, the phase space parameters in surface coalescence model are readjusted. By using the new phase space parameters set with better physical fundament, the double differential cross sections of light complex particles are found to be in better agreement with experimental data.

Wei, Dexian; Mao, Lihua; Wang, Ning; Liu, Min; Ou, Li

2015-01-01

260

SiC Formation Through Interface Reaction between C60 and Si in Plasma Environment  

NASA Astrophysics Data System (ADS)

The formation of SiC through the interface reaction between C60 and Si in a plasma-assisted chemical vapour deposition system (PACVD) is investigated with a C60 film previously deposited on Si wafers. The composition and structure of the deposited samples were characterized by micro-Raman spectroscopy and X-ray diffraction (XRD). The results showed that SiC film was formed successfully in hydrogen plasma at a substrate temperature of 800°C. The hydrogen atoms in plasma were found to enhance the production of SiC. Furthermore, the effects of the added CH4 on the formation of film were studied. Introduction of CH4 simultaneously with H2 at the beginning would suppress the formation of the initial layer of SiC due to a carbon-rich environment on the substrate, which would be disadvantageous to the further growth of the SiC film.

Ding, Fang; Meng, Liang; Zhu, Xiaodong

2007-02-01

261

Intimations of neck formation in heavy-ion subbarrier fusion reactions  

SciTech Connect

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

Stelson, P.H.

1990-07-01

262

Anionic tantalum dihydride complexes: heterobimetallic coupling reactions and reactivity toward small-molecule activation.  

PubMed

The anionic dihydride complex [Cp2TaH2](-) was synthesized as a well-defined molecular species by deprotonation of Cp2TaH3 while different solubilizing agents, such as [2.2.2]cryptand and 18-crown-6, were applied to encapsulate the alkali-metal counterion. The ion pairs were characterized by multiple spectroscopic methods as well as X-ray crystallography, revealing varying degrees of interaction between the hydride ligands of the anion and the respective countercation in solution and in the solid state. The [Cp2TaH2](-) complex anion shows slow exchange of the hydride ligands when kept under a D2 atmosphere, but a very fast reaction is observed when [Cp2TaH2](-) is reacted with CO2, from which Cp2TaH(CO) is obtained as the tantalum-containing reaction product, along with inorganic salts. Furthermore, [Cp2TaH2](-) can act as a synthon in heterobimetallic coupling reactions with transition-metal halide complexes. Thus, the heterobimetallic complexes Cp2Ta(?-H)2Rh(dippp) and Cp2Ta(?-H)2Ru(H)(CO)(P(i)Pr3)2 were synthesized and characterized by various spectroscopies and via single-crystal X-ray diffraction. The new hydride bridged tantalum-rhodium heterobimetallic complex is cleaved under a CO atmosphere to yield mononuclear species and slowly exchanges protons and hydride ligands when exposed to D2 gas. PMID:25669136

Ostapowicz, Thomas G; Fryzuk, Michael D

2015-03-01

263

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

PubMed

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-methylimidazolium 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. PMID:21911215

Talisman, Ian J; Kumar, Vineet; Deschamps, Jeffrey R; Frisch, Mark; Malhotra, Sanjay V

2011-11-01

264

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. PMID:21911215

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

2011-01-01

265

Direct formation of element chlorides from the corresponding element oxides through microwave-assisted carbohydrochlorination reactions.  

PubMed

A series of technically and economically important element chlorides-such as SiCl4, BCl3, AlCl3, FeCl2, PCl3 and TiCl4-was synthesized through reactions between hydrogen chloride and the corresponding element oxides in the presence of different carbon sources with microwave assistance. This process route was optimized for demonstration purposes for tetrachlorosilane formation and successfully demonstrates the broad applicability of various silicon oxide-containing minerals and materials for carbohydrochlorination. The chlorination reaction occurs at lower temperatures than with conventional heating in a tubular oven, with substantially shorter reaction times and in better yields: quantitatively in the case of tetrachlorosilane, based on the silicon content of the starting material. The experimental procedure is very simple and provides basic information about the suitability of element compounds, especially element oxides, for carbohydrochlorination. According to the general reaction sequence element oxide-->element-->element chloride used in today's technology, this one-step carbohydrochlorination with hydrogen chloride is considerably more efficient, particularly in terms of energy input and reaction times, avoiding the isolation of the pure elements required for chlorination to give the element chlorides with use of the more corrosive and toxic chlorine gas. PMID:18324655

Nordschild, Simon; Auner, Norbert

2008-01-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

267

Indene formation from alkylated aromatics: kinetics and products of the fulvenallene + acetylene reaction.  

PubMed

A novel reaction is described for formation of the polyaromatic hydrocarbon (PAH) indene in aromatic flames, via the reaction of fulvenallene with acetylene (C2H2). Fulvenallene has been recently identified as the major decomposition product of the benzyl radical, the dominant intermediate in the oxidation of alkylated aromatic hydrocarbons, yet it is not presently included in kinetic models for aromatic oxidation or PAH/soot formation. Ab initio calculations with the G3B3 theoretical method show that acetylene adds to fulvenallene with a barrier of around 27 kcal mol(-1). This forms an activated C9H8 adduct that can rearrange to indene and dissociate to 1-indenyl + H with energy barriers below that of the entrance channel. Master equation simulations across a range of temperature and pressure conditions demonstrate that for temperatures relevant to combustion indene is the dominant product at high pressures while 1-indenyl + H dominate at lower pressures. At low to moderate temperatures, the production of collision stabilized cyclopentadiene-fulvene intermediates is also significant. The results presented in this study provide a new pathway to cyclopenta-fused PAHs in aromatic combustion and are expected to improve modeling of PAH and soot formation. The formation of cyclopenta-fused C5-C6 structures is required to describe the flame synthesis of carbon nanoparticles like fullerenes and buckybowls (corannulene). Improved rate expressions are also reported for the 1-indenyl + H --> indene association reaction, and for the reverse dissociation, from variational transition state theory calculations. The new rate constants are significantly different than current estimates, primarily due to a re-evaluation of the indene C-H bond dissociation energy. PMID:19603772

da Silva, Gabriel; Bozzelli, Joseph W

2009-08-01

268

Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K  

E-print Network

The reactions of cold H atoms with solid O2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in-situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates. This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications.

N. Miyauchi; H. Hidaka; T. Chigai; A. Nagaoka; N. Watanabe; A. Kouchi

2008-05-01

269

Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K  

E-print Network

The reactions of cold H atoms with solid O2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in-situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates. This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications.

Miyauchi, N; Chigai, T; Nagaoka, A; Watanabe, N; Kouchi, A

2008-01-01

270

Evidence for methane {sigma}-complexes in reductive elimination reactions from Tp{prime}Rh(L)(CH{sub 3})H  

SciTech Connect

Two sets of experiments are describes that provide indirect evidence for the involvement of alkane {sigma}-complexes in oxidative addition/reductive elimination reactions of Tp{prime}Rh(L)(R)H complexes (Tp{prime} = tris-3,5-dimethylpyrazolylborate, L = CNCH{sub 2}CMe{sub 3}). First, the methyl deuteride complex Tp{prime}Rh(L)(CH{sub 3})D is observed to rearrange to Tp{prime}Rh(L)(CH{sub 2}D)H prior to loss of CH{sub 3}D. Similarly, Tp{prime}Rh(L)(CD{sub 3})H rearranges to Tp{prime}Rh(L)(CD{sub 2}H)D prior to loss of CD{sub 3}H. Second, the rate of elimination of methane from Tp{prime}Rh(L)(CH{sub 3})H in benzene/perfluorobenzene solvent mixtures is found to be dependent upon the concentration of benzene, indicating an associative component to the reductive elimination of methane. Both of these processes, and their rates, are accommodated by the reversible formation of alkane {sigma}-complexes prior to dissociation of alkane.

Wick, D.D.; Reynolds, K.A.; Jones, W.D. [Univ. of Rochester, NY (United States). Dept. of Chemistry] [Univ. of Rochester, NY (United States). Dept. of Chemistry

1999-04-28

271

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

272

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. PMID:21846387

2011-01-01

273

Reaction-path calculations of groundwater chemistry and mineral formation at Rainier Mesa, Nevada  

SciTech Connect

Reaction-patch calculations of groundwater chemistry and mineral formation at Rainier Mesa, Nevada, have been done using a model of volcanic-glass dissolution by water that is initially saturated with CO{sub 2}. In the reaction-path calculation, rate processes control the availability of species through dissolution of volcanic glass, and equilibrium processes distribute the species between the aqueous phase and mineral phases in equilibrium at each step in the reaction path. The EQ3/6 chemical-equilibrium programs were used for the calculation. Formation constants were estimated for three zeolites (clinoptilolite, mordenite, and heulandite), so they could be considered as possible mineral precipitates. The first stage of mineral evolution, from volcanic glass to a cristobalite, smectite clay, and zeolite mixture, was modeled quite well. Predicted aqueous-phase compositions and precipitates agree with observations at Rainier Mesa and other Nevada Test Site areas. Further mineral evolution, to quartz, clay, analcime, and albite mixtures, was also modeled. Decreasing aqueous silica activity from the first stage, where cristobalite precipitates, to later stages, where quartz is present, was the controlling variable in the mineral evolution. 30 references, 20 figures, 4 tables.

Kerrisk, J F

1983-12-01

274

Determination of citric acid by means of competitive complex formation in a flow injection system  

Microsoft Academic Search

A photometric method for the determination of citrate and other organic acids based on their ability to complex Fe3+-ions is presented. The red colored complex of [Fe(SCN)2]+, used as reagent, is destroyed upon contact with the sample because the organic acid complexes the Fe3+-ion. The decrease in absorption is monitored at 460 nm. The reaction is carried out in a

Achim Krug; Robert Kellner

1994-01-01

275

Simultaneous and stereoselective formation of planar and axial chiralities in enantiopure sulfinyl iron diene complexes.  

PubMed

[reaction: see text] Enantiopure (1Z,3E)-1-sulfinyl dienes bearing an o-dithianylphenyl group can be prepared and complexed with (bda)Fe(CO)(3) to afford the corresponding sulfinyl diene iron(0) tricarbonyl complexes. This diastereoselective complexation introduces planar and axial chirality simultaneously, with a high degree of facial selectivity as well as atropselectivity. Dynamic kinetic resolution is likely to be the origin of the atropselectivity. PMID:12556179

Paley, Robert S; Liu, Jane M; Lichtenstein, Bruce R; Knoedler, Vanessa L; Sanan, Toby T; Adams, Drew J; Fernández, Jorge; Rablen, Paul R

2003-02-01

276

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

SciTech Connect

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

Boxer, Matthew B.; Yamamoto, Hisashi (UC)

2008-04-02

277

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

DOE PAGESBeta

We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates (~1 K/s) using differential scanning calorimetry (DSC) traces to 725ºC. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 105 K/s) in high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (Tmax) are largely independent of foil chemistry at 0.6 ± 0.1 m/s and 1220 ± 50 K, respectively, and that the measured Tmax is more than 200 K lower than predicted adiabatic temperatures (Tad). The difference between Tmax and Tad is explained by the prediction that transformation to the final intermetallic phases occurs after Tmax and results in the release of 20-30 % of the total heat of reaction and a delay in rapid cooling.

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

2011-01-11

278

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

SciTech Connect

We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates ({approx}1 K/s) using differential scanning calorimetry traces to 725 deg. C. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 10{sup 5} K/s) in high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (T{sub max}) are largely independent of foil chemistry at 0.6{+-}0.1 m/s and 1220{+-}50 K, respectively, and that the measured T{sub max} is more than 200 K lower than predicted adiabatic temperatures (T{sub ad}). The difference between T{sub max} and T{sub ad} is explained by the prediction that transformation to the final intermetallic phases occurs after T{sub max} and results in the release of 20%-30% of the total heat of reaction and a delay in rapid cooling.

Barron, S. C.; Knepper, R.; Walker, N.; Weihs, T. P. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States)

2011-01-01

279

Reaction path in the formation of titanium diboride by a magnesium thermite process  

SciTech Connect

TiB{sub 2} was formed by a thermite reaction amongst Mg, amorphous B{sub 2}O{sub 3} and TiO{sub 2} powders. Mixtures consisting of 2Mg-TiO{sub 2}, 3Mg-B{sub 2}O{sub 3} and 5Mg-TiO{sub 2}-B{sub 2}O{sub 3} were heat treated using DTA and separately via ignition with a nichrome wire; product phases were identified using XRD. MgO and Ti were products from the first mixture reacted in argon, whereas an incomplete transformation forming Mg{sub 3}TiO{sub 4} occurred in air. For the second mixture, a reaction forming Mg{sub 3}B{sub 2}O{sup 6} occurred in air, but no reaction occurred in argon due to deficiency of oxygen. Minor amounts Of Mg{sub 3}B{sub 2}O{sub 6} and Mg{sub 2}TiO{sub 4} were detected in addition to the predicted product phases of MgO and TiB{sub 2} for the third mixture ignited both in air and argon. Based on available evidence, a path for this reaction was deduced; Mg particles in contact with TiO{sub 2} reacted to form Ti, which in turn reacted with B{sub 2}O{sub 3} to form TiB{sub 2}. TiB{sub 2} product particles from the reaction in argon had a more faceted appearance than those formed during the reaction in air. This was interpreted to be the result of glassy B{sub 2}O{sub 3} surface layer formation on TiB{sub 2} particles in air.

Sundaram, V.; Logan, K.V.; Speyer, R.F. [Georgia Inst. of Technology, Atlanta, GA (United States)

1995-12-31

280

Ferric-transferrin and ferric-transferrin-anion complexes: formation and characterization.  

E-print Network

FERRIC-TRANSFERRIN AND FFRRIC-TRANSFERRIN-ANION COMPLEXES'. FORMATION AND CHARACTERIZATION A Thesis by MICHAEL RAY SCHLABACH Submitted to the Graduate College of Texas A & M University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE December 1974 Major Subject: Biochemistry FERRIC ? TRANSFERRIN AND FERRIC-TRANSFERRIN-ANION COMPLEXES: FORMATION AND CHARACTERIZATION A Thesis MICHAEL RAY SCHLABACH Approved as to style snd content by: (' Chai of Committee) (He...

Schlabach, Michael Ray

1974-01-01

281

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

PubMed Central

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

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

2015-01-01

282

In--Flight ($K^-,p$) Reactions for the Formation of Kaonic Atoms and Kaonic Nuclei in Green function method  

E-print Network

We study theoretically the kaonic atom and kaonic nucleus formations in the in--flight ($K^-,p$) reactions using the Green function method, which is suited to evaluate formation rates both of stable and unstable bound systems. We consider $^{12}$C and $^{16}$O as the targets and calculate the spectra of the ($K^-,p$) reactions. We conclude that a no peak structure due to kaonic nucleus formation is expected in the reaction spectra calculated with the chiral unitary kaon--nucleus optical potential. In the spectra with the phenomenological deep kaon--nucleus potential, we may have possibilities to observe some structures due to kaonic nucleus states. For all cases, we have peaks due to the kaonic atom formations in the reaction spectra.

J. Yamagata; H. Nagahiro; S. Hirenzaki

2006-06-01

283

Spatiotemporal Pattern Formation and Chaos in the Belousov-Zhabotinsky Reaction in a Reverse Microemulsion  

NASA Astrophysics Data System (ADS)

We study the spatiotemporal behavior of the oscillatory Belousov-Zhabotinsky (BZ) reaction in a reverse microemulsion consisting of water, octane and the surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT). By varying the microemulsion composition, we can "tune" its structure, specifically the size and spacing between the nanometer-sized water droplets in which the polar BZ reactants reside. We find a remarkable array of pattern formation as the microemulsion structure and BZ chemistry are varied. Behaviors observed include stationary Turing patterns, traveling and standing waves, spirals, targets, antispirals and antitargets (which travel into rather than out from their center), and spatiotemporal chaos. A simple reaction-diffusion model, which accounts for the BZ chemistry and the differential diffusion of species within water droplets and in the bulk oil phase, is able to reproduce nearly all of the observed behavior.

Epstein, Irving R.; Vanag, Vladimir K.

2003-08-01

284

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments  

SciTech Connect

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

2013-03-15

285

Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces  

E-print Network

Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces R. G. Ford Metal sorption to clay minerals may lead to the formation of secondary precipitates structurally similar to the mineral takovite. Saturation with respect to this phase is promoted, in part

Sparks, Donald L.

286

Scale-invariance in reaction-diffusion models of spatial pattern formation.  

PubMed Central

We propose a reaction-diffusion model of spatial pattern formation whose solutions can exhibit scale-invariance over any desired range for suitable choices of parameters in the model. The model does not invoke preset polarity or any other ad hoc distinction between cells and provides a solution to the French flag problem without sources at the boundary. Furthermore, patterns other than the polar pattern that usually arises first in a growing one-dimensional system described by Turing's model can be obtained. Evidence is given that suggests that the model may apply in the slug stage of Dictyostelium discoideum. PMID:6933464

Othmer, H G; Pate, E

1980-01-01

287

Roles of Acetone and Diacetone Alcohol in Coordination and Dissociation Reactions of Uranyl Complexes  

SciTech Connect

Combined collision-induced dissociation mass-spectrometry experiments and DFT calculations were employed to elucidate the molecular structure of "hypercoordinated" species and the energetics of water-elimination reactions of uranyl acetone complexes observed in earlier work (Rios, D.; Rutkowski, P. X.; Van Stipdonk, M. J.; Gibson, J. K. Inorg. Chem. 2011, 50, 4781). It is shown that the "hypercoordinated" species contain diacetone alcohol ligands bonded in either bidentate or monodentate fashion, which are indistinguishable from (acetone)2 in mass spectrometry. Calculations confirm that four diacetone ligands can form stable complexes, but that the effective number of atoms coordinating with uranium in the equatorial plane does not exceed five. Diacetone alcohol ligands are shown to form mesityl oxide ligands and alkoxide species through the elimination of water, providing an explanation for the observed water-elimination reactions.

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

2012-12-03

288

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

PubMed

Mononuclear nonheme iron enzymes generate high-valent iron(IV)-oxo intermediates that effect metabolically important oxidative transformations in the catalytic cycle of dioxygen activation. In 2003, researchers first spectroscopically characterized a mononuclear nonheme iron(IV)-oxo intermediate in the reaction of taurine: ?-ketogultarate dioxygenase (TauD). This nonheme iron enzyme with an iron active center was coordinated to a 2-His-1- carboxylate facial triad motif. In the same year, researchers obtained the first crystal structure of a mononuclear nonheme iron(IV)-oxo complex bearing a macrocyclic supporting ligand, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecene), in studies that mimicked the biological enzymes. With these breakthrough results, many other studies have examined mononuclear nonheme iron(IV)-oxo intermediates trapped in enzymatic reactions or synthesized in biomimetic reactions. Over the past decade, researchers in the fields of biological, bioinorganic, and oxidation chemistry have extensively investigated the structure, spectroscopy, and reactivity of nonheme iron(IV)-oxo species, leading to a wealth of information from these enzymatic and biomimetic studies. This Account summarizes the reactivity and mechanisms of synthetic mononuclear nonheme iron(IV)-oxo complexes in oxidation reactions and examines factors that modulate their reactivities and change their reaction mechanisms. We focus on several reactions including the oxidation of organic and inorganic compounds, electron transfer, and oxygen atom exchange with water by synthetic mononuclear nonheme iron(IV)-oxo complexes. In addition, we recently observed that the C-H bond activation by nonheme iron(IV)-oxo and other nonheme metal(IV)-oxo complexes does not follow the H-atom abstraction/oxygen-rebound mechanism, which has been well-established in heme systems. The structural and electronic effects of supporting ligands on the oxidizing power of iron(IV)-oxo complexes are significant in these reactions. However, the difference in spin states between nonheme iron(IV)-oxo complexes with an octahedral geometry (with an S = 1 intermediate-spin state) or a trigonal bipyramidal (TBP) geometry (with an S = 2 high-spin state) does not lead to a significant change in reactivity in biomimetic systems. Thus, the importance of the high-spin state of iron(IV)-oxo species in nonheme iron enzymes remains unexplained. We also discuss how the axial and equatorial ligands and binding of redox-inactive metal ions and protons to the iron-oxo moiety influence the reactivities of the nonheme iron(IV)-oxo complexes. We emphasize how these changes can enhance the oxidizing power of nonheme metal(IV)-oxo complexes in oxygen atom transfer and electron-transfer reactions remarkably. This Account demonstrates great advancements in the understanding of the chemistry of mononuclear nonheme iron(IV)-oxo intermediates within the last 10 years. PMID:24524675

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

2014-04-15

289

Synthetic and Mechanistic Studies of Strained Heterocycle Opening Reactions Mediated by Zirconium(IV) Imido Complexes  

PubMed Central

The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp2Zr=N-t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles without accessible ?-hydrogens undergo insertion/protonation of the C–X bond to produce 1,2-amino alcohols (X = O) and 1,2-diamines (X = NR), whereas heterocycles with accessible ?-hydrogens undergo elimination/protonation to produce allylic alcohols (X = O) and allylic sulfides (X = S). Mechanistic investigations support a stepwise pathway with zwitterionic intermediates for the first reaction class and a concerted pathway for the second reaction class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi = ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)-Zr=NAr(THF) (Ar = 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of meso epoxides. PMID:16508693

Blum, Suzanne A.; Rivera, Vicki A.; Ruck, Rebecca T.; Michael, Forrest E.; Bergman, Robert G.

2005-01-01

290

Sharper graph-theoretical conditions for the stabilization of complex reaction networks.  

PubMed

Across the landscape of all possible chemical reaction networks there is a surprising degree of stable behavior, despite what might be substantial complexity and nonlinearity in the governing differential equations. At the same time there are reaction networks, in particular those that arise in biology, for which richer behavior is exhibited. Thus, it is of interest to understand network-structural features whose presence enforces dull, stable behavior and whose absence permits the dynamical richness that might be necessary for life. We present conditions on a network's Species-Reaction Graph that ensure a high degree of stable behavior, so long as the kinetic rate functions satisfy certain weak and natural constraints. These graph-theoretical conditions are considerably more incisive than those reported earlier. PMID:25600138

Knight, Daniel; Shinar, Guy; Feinberg, Martin

2015-04-01

291

On the formation and survival of complex prebiotic molecules in interstellar grain aggregates  

NASA Astrophysics Data System (ADS)

The aggregation of interstellar grains as a result of ballistic collisions produces loosely packed structures with much of their internal volume composed by vacuum (cavities). The molecular material present on the surfaces of the cavities gives rise to a series of reactions induced by cosmic rays, UV radiation, thermal shocks, etc., in high reducing conditions. Thus, a terrestrial type chemistry is given the possibility to evolve inside these cavities. The resulting products are different and of a wider range than those from gas-phase or surface chemistry in molecular clouds. Under conditions similar to those in the aggregate cavities, laboratory experiments have produced amino acids, sugars and other organic compounds from simple precursors. In dense star-forming regions, the molecular species inside aggregates are efficiently shielded against the local UV field. The same molecules were incorporated in the material which formed the Earth, as well as other planets, during the process of its formation and afterwards fell on the surface via comets, meteorites, interstellar dust, etc. This was the source material that can produce, under favorable circumstances, the biopolymers needed for life. The astronomical observations of organic molecules in star-forming regions and the results of analyses of meteorites and cometary dust seem to support the present hypothesis that complex prebiotic molecules form inside dust aggregates and therein survive the journey to planetary systems. The Miller experiment is revisited through innumerable repetitions inside dust grain aggregates.

Cecchi-Pestellini, Cesare; Scappini, Flavio; Saija, Rosalba; Iatì, Maria Antonia; Giusto, Arianna; Aiello, Santi; Borghese, Ferdinando; Denti, Paolo

2004-10-01

292

Search for reaction conditions and catalyst for selective prebiotic formation of Aldopentoses from Glycolaldehyde and Formaldehyde  

NASA Astrophysics Data System (ADS)

Formation of organic compounds from simple precursors appears to have been one of the first steps from geochemistry towards modern biochemistry. The Earth lagoons, hydrothermal springs, cosmic dust, meteorites, protoplanetary disk, etc. has been considered as the possible ``reactors'' in which the prebiotic synthesis could have taken place. The finding of reactions and reaction conditions which allow to produce the high yields of the biologically relevant substances from simple compounds could help us to verify different hypothesis of plausible prebotic conditions. In this work we have studied the formation of vitally important sugars, namely aldopentoses (ribose, xylose, lyxose and arabinose), from glycolaldehyde and formaldehyde over catalysts. Aldopentoses nowadays play the important roles as the components of polysaccharides, glycosides, nucleic acids and ATP. Glycolaldehyde is the simplest monosaccharide, which was found in the interstellar space [1], where it could be generated as a result of several processes, for instance, condensation of formaldehyde under UV-radiation [2]. In this work the peculiarities of interaction between glycolaldehyde and formaldehyde in the presence of soluble (phosphate and borate buffers) and solid (minerals apatite and montmorillonites) catalysts were studied. The dependences of composition of the reaction products on the catalyst nature, molar ratio of substrates, pH value of reaction mixture were revealed. The yields of aldopentoses amount to ca. 60-65% in the presence of borate catalyst under optimized reaction conditions. Borate acts not only as a catalyst, but also as the stabilizer of active intermediates and aldopentoses from side reactions [3]. Borates are present in some mineral and clays (serpentine, montmorillonite etc.) and in water of Cityhot springs (Geyser valley, placeKamchatka) in rather high concentrations. Therefore catalysis by borates could be considered as plausible prebotic condition. Acknowledgements. We thank Dr. S. Yashnik for providing the montmorillonite clays. The financial support of Program RAS (program ``Origin of biosphere and evolution biogeology systems'') is gratefully acknowledged. Hollis, J., Jewell, P., Lovas, F., et al., The Astrophysical Journal. 613, L45--L48, 2004 Pestunova, O., Simonov, A., Snytnikov, V., et al., Adv. Space Res. 36/2, 214-219, 2005. Ricardo, A., Carrigan, M.A., Olcott, A.N., Benner, S.A. Science. 303, 5655, 196, 2004.

Delidovich, Irina; Taran, Oxana; Parmon, Valentin; Gromov, Nikolay

2012-07-01

293

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

294

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

Microsoft Academic Search

Using a quadrupole ion trap mass spectrometer, trimethyl borate was allowed to react with dihydrogen phosphate, deprotonated\\u000a O-phosphoserine, and a set of hydrogen bonded complexes involving dihydrogen phosphate and neutral acids (phosphoric acid,\\u000a acetic acid, serine, and O-phosphoserine). The reactions show a consistent pattern in which the initial attack leads to addition\\u000a with the loss of one or two CH3OH

Scott Gronert; Richard A. J. O’Hair

2002-01-01

295

Acid\\/base reactions and Al(III) complexation at the surface of goethite  

Microsoft Academic Search

Acid\\/base reactions and Al(III) complexation at the geothite-solution interface have been investigated at 298.2 K in NaNOâ solutions at a constant ionic strength of 0.1 M. Equilibrium measurements were performed as potentiometric titrations using a glass electrode. The experimental data were evaluated on the basis of the constant capacitance model. The acid\\/base properties are described by the equilibria and the

L. Loevgren; S. Sjoeberg; P. W. Schindler

1990-01-01

296

Acid\\/base reactions and Al(III) complexation at the surface of goethite  

Microsoft Academic Search

Acid\\/base reactions and Al(III) complexation at the goethite-solution interface have been investigated at 298.2 K in NaNO 3 solutions at a constant ionic strength of 0.1 M. Equilibrium measurements were performed as potentiometric titrations using a glass electrode. The experimental data were evaluated on the basis of the constant capacitance model. The acid\\/base properties are described by the equilibria and

Lars Lövgren; Staffan Sjöberg; Paul W. Schindler

1990-01-01

297

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

E-print Network

Low temperature rate coefficients for the reaction of CHreaction rate coefficients of the bromomethylidyne radical (CBr) with alkenes and alkynes at room temperaturerate coefficient with increasing temperature. The reaction

Soorkia, Satchin

2010-01-01

298

The nature of the antigen-antibody complexes initiating the specific wheal-and-flare reaction in sensitized man.  

PubMed

To study the nature of the antigen-antibody complexes which initiate the specific wheal-and-flare (W & F) reaction in sensitized man, a homologous series of bivalent, oligovalent, and multivalent benzylpenicilloyl (BPO) haptens were quantitatively compared for their effectiveness in eliciting W & F in BPO-sensitized human subjects.A series of seven divalent haptens were capable of eliciting W & F, but these generally were not maximally effective elicitors. Of the divalent haptens, those with separation chains of 8 or 13 A were the most effective. Of the oligovalent haptens, maximal effectiveness was attained with BPO(6)-lysine(7), and not with BPO(2)-lysine(3) or BPO(4)-lysine(4), i.e., haptens which are 6- 3- and 4-valent, respectively, from a chemical point of view. However, evidence was obtained from quantitative precipitation experiments which indicated that BPO(6)-lysine(7) functions as a trivalent hapten immunologically, i.e., capable of binding three antibody molecules per mole hapten. Large molecularsized haptens with immunological valences of 7 or 12, but in which the haptenic groups were widely separated, were comparatively ineffective elicitors of W & F. In individual subjects, threshold W & F reactions were obtained with equimolar concentrations of the differently sized divalent, oligovalent, and multivalent haptens. The results demonstrate that for maximally effective elicitation of W & F by haptens, trivalency with optimal distances of separation of haptenic groups is necessary and sufficient. These results indicate the requirement for the formation of a high energy complex of two or three membrane-fixed skin-sensitizing antibody molecules closely bridged together by the elicitor hapten as the initiator of the W & F reaction. PMID:5637143

Levine, B B; Redmond, A P

1968-03-01

299

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

300

Diffusive leakage of carbon, variable migration rates of solutes, multiple reaction fronts: what happens when CO2 is injected into geologic formations  

NASA Astrophysics Data System (ADS)

A complex set processes occur when CO2-charged water resulting from CO2 injection into a geologic formation interacts with the resident formation water and sediment. First, the sequestration efficiency depends on the rate of CO2 injection and sediment texture (porosity and permeability). Second, acid and bicarbonates resulting from the hydration of CO2 interact with the resident water to create multiple solute migration fronts, and also simultaneously induce complex interactions with the resident minerals. All of these features, and accurate mass-balancing, can be achieved using a new water-rock interaction and reactive-transport simulator Sym.CS. Water-rock interaction and reactive transport modeling is an important tool for deciphering chemical and physical reactions occurring in sediments and rocks that are not accessible for monitoring. Traditional models solve a large set of conservation of mass equations written for aqueous solute species. Typically, reactions are solved separately from mass-transfer equations through loosely coupled sequentially iterated numerical algorithms. Resulting simulators therefore fall short of achieving the full extent of the theoretical accuracy and the nonlinearly of the reactive-transport and water-rock interaction phenomena. A new method is presented that uses conservation equations written for chemical elements, and tight coupling between mass-transfer and reactions. Derivation of the elemental conservation equation from the theoretically correct solute conservation equation involves one parametric conversion. The tight coupling between mass-transfer and reactions entails using explicitly discretized form of mass-transfer terms of the conservation equation when solving for the reactions. This explicitly coupled iteration method allows accurate solution of the conservation equations to be achieved. More importantly, this method allows (1) accurate bookkeeping of mass as effluents are injected and reactions progress among various phases, and (2) capturing the flow-reaction feedback that determines the efficiency of injection practice and reservoir capacity usage. The third component of the model is a composite media petrophysical model that allows the monitoring of changing reservoir characteristics as chemical and textural compositions evolve. The simulator Sym.CS, which includes all of above processes, is used to model interaction between CO2-charged water with formation water in sandstone reservoirs. Results demonstrate the utility of the model that preserves the nonlinearity of mass-transfer and reaction processes. Accurate mass-balance is also achieved and demonstrated. The results also show the importance of diffusive properties of highly reactive solutes, as they form one or more reaction fronts ahead of sweep fronts, as well as significant quantity of carbon to leak out of the reservoir.

Park, A. J.

2009-12-01

301

The kinetics of complex formation in the trithiadiazoletri[3,4-di(4- tert-butylphenyl)-pyrrole] macrocycle-copper(II) acetate-DMFA-H2O system  

NASA Astrophysics Data System (ADS)

The paper presents the results of a study of the kinetics of coordination of a macroheterocyclic compound with an increased coordination cavity of the (3 + 3) McH3 composition consisting of sequentially alternating 1,3,4-thiadiazole and 3,4-bis(4- tert-butylphenyl)pyrrole fragments to dehydrated Cu(OAc)2 in dimethylformamide with and without H2O admixtures. The reaction could be controlled spectrophotometrically over the salt and ligand concentration ranges (0.175-0.55) × 10-4 and (0.16-0.64) × 10-5 mol/l, respectively, at temperatures of 288-303 K. A kinetic equation of an unusual form with a negative order with respect to the salt was for the first time obtained experimentally for a macrocyclic ligand by the method of excess concentrations. The kinetics of the complex formation reaction was given a theoretical interpretation. Quantitative characteristics were obtained, and the role played by water in the kinetics of complex formation was studied. These data were of importance for practical applications, for the development of optimum conditions increasing the yield of complexes when they were synthesized in complex formation reactions.

Lomova, T. N.; Mozhzhukhina, E. G.; Danilova, E. A.; Islyaikin, M. K.

2009-10-01

302

Formation of nitrogen oxides via NO + O2 gas-solid reaction on cold surfaces  

NASA Astrophysics Data System (ADS)

The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O2 adsorbed on a cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO2. Via two molecular beams, O2 and NO molecules are aimed at a cold (10 K) sample held in a UHV chamber. NO2 is formed independently of the surface composition and morphology. We show that the NO + O2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO2, N2O3, N2O4).

Minissale, M.; Congiu, E.; Baouche, S.; Chaabouni, H.; Moudens, A.; Dulieu, F.; Manicó, G.; Pirronello, V.

2013-04-01

303

Thermodynamics of Lead(II) Halide Complex Formation in Calcium Nitrate Tetrahydrate -Acetamide Melts  

NASA Astrophysics Data System (ADS)

The complex formation between lead(II) ions and chloride and bromide ions in melts of C a(N 03) 2 • 4 H2O • ?CH3CONH2 has been studied at different temperatures between 30 and 70 °C. The formation constants of the complexes PbX+ and PbX2 (X = Cl, Br) were determined from em f measurements by means of Ag/AgX electrodes. The dependence of the formation constants for PbCl+ on the solvent melt composition has been analysed. The thermodynamic parameters ?H011 and ?S011 for PbX+ complex formation have been estimated. The parameters are compared with the literature data for the same process in dilute aqueous solutions and in some hydrated and anhydrous salt melts.

Gadzuric, S. B.; Zsigrai, I. J.; Nikolic, R. M.

2001-12-01

304

Landscape complexity influences route-memory formation in navigating pigeons.  

PubMed

Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations. PMID:24451267

Mann, Richard P; Armstrong, Chris; Meade, Jessica; Freeman, Robin; Biro, Dora; Guilford, Tim

2014-01-01

305

Formation of Molecular Bromine from the Reaction of Ozone with Deliquesced NaBr Aerosol: Evidence for Interface Chemistry  

E-print Network

Formation of Molecular Bromine from the Reaction of Ozone with Deliquesced NaBr Aerosol: Evidence modeling, and molecular dynamics simulations. The molecular bromine production in the chamber experiments on bromine formation in the marine boundary layer shows that several ppt of bromine could potentially

Dabdub, Donald

306

The complex interplay between semantics and grammar in impression formation.  

PubMed

We sought to bridge findings showing that (a) describing a person's behavior with the perfective verb aspect (did), compared to the imperfective aspect (was doing), increases processing of semantic knowledge unrelated to the target's action such as stereotypes and (b) an increased recognition of stereotypical thoughts often promotes a judgment correction for the stereotypes. We hypothesized an interplay between grammar (verb conjugation) and semantic information (gender) in impression-formation. Participants read a resume, attributed to a male or female, for a traditionally masculine job. When the resume was written in the imperfective, people rated a male (vs. female) more positively. When the resume was in the perfective, this pattern reversed. Only these latter effects of gender were influenced by cognitive load. Further, people more quickly indicated the applicant's gender in the perfective condition, suggesting an enhanced focus on gender during processing. PMID:24950389

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

2014-09-01

307

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

SciTech Connect

The reaction of Ir/sup I/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4-R/sup 2/-6)(COD) (COD = cyclooacta-1,5-diene) with dihydrogen in CD/sub 2/Cl/sub 2/ was monitored by /sup 1/H NMR. At -20/sup 0/C quantitative formation of the novel dihydride complexes Ir/sup III/H/sub 2/(C/sub 6/H/sub 2/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4-R/sup 2/-6)(COD) (R/sup 1/ = H, R/sup 2/ = CH/sub 2/NMe/sub 2/ (10), Me (11); R/sup 2/ = H, R/sup 1/ = H (12), Me (13), CH/sub 2/NMe/sub 2/ (14); R/sup 1/ = R/sup 2/ = CH/sub 2/NMe/sub 2/ (15)) occurs. Further reactions, the type of which depends on the bulkiness of the R/sup 1/ and R/sup 2/ groups, occur when these solutions are warmed to 0/sup 0/C. Complexes 12-14 (R/sup 2/ = H) lose H/sub 2/ to re-form Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R/sup 1/-4)(COD). In contrast, complexes 10, 11, and 15 (R/sup 2/ = alkyl) react further by means of C(aryl)-H reductive elimination. For complex 15 (R/sup 1/ = CH/sub 2/NMe/sub 2/) this results in quantitative formation of 1,3,5-(Me/sub 2/NCH/sub 2/)/sub 3/C/sub 6/H/sub 3/ and IrH(COD). In Ir/sup III/H/sub 2/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-6)(COD) (R = alkyl (10 and 11)), C(aryl)-H reductive elimination is followed by re-addition of another C(aryl)-H bond, which upon subsequent reductive elimination of H/sub 2/, yields the rearranged iridium(I) complexes Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-4)(COD). Since the rearrangement of Ir/sup I/(C/sub 6/H/sub 3/-(CH/sub 2/NMe/sub 2/)-2-R-6)(COD) to Ir/sup I/(C/sub 6/H/sub 3/(CH/sub 2/NMe/sub 2/)-2-R-4)(COD) can also be induced thermally at 60/sup 0/C, it is therefore being catalyzed by dihydrogen at 0/sup 0/C. None of these reactions with dihydrogen is attended by hydrogenation of the COD ligand.

van der Zeijden, A.A.H.; van Koten, G.; Lujik, R.; Grove, D.M.

1988-07-01

308

Reactions between vanadium ions and biogenic reductants of tunicates: Spectroscopic probing for complexation and redox products in vitro  

SciTech Connect

Several species of marine tunicates store oxygen-sensitive V{sup III} in blood cells. A sensitive colorimetric V{sup III} assay was used t survey the leading candidates for the native reducing agent of vanadate in tunicates (i.e., An-type tunichromes, glutathione, NADPH, and H{sub 2}S) in reactions with V{sup V} or V{sup IV} ions under anaerobic, aqueous conditions at acidic or neutral pH. Except for the case of An-1 and V{sup V} ions in pH 7 buffer, the assay results for the biogenic reducing agents clearly showed that appreciable quantities of V{sup III} products were not generated under the conditions tested. Therefore, the assay results place new limits on hypothetical mechanisms of V{sup III} formation in vivo. For reactions between An-1 and V{sup V} ions in pH 7 buffer, low levels of V{sup III} products could not be ruled out because of an interfering peak in the colorimetric assays. For similar reactions between V{sup V} ions and An-1, or an An-1,2 mixture, in mildly to moderately basic media, the product mixtures precipitated as greenish black solids. Analyses of the precipitated V/An mixtures using vanadium K-edge X-ray absorption spectroscopy (XAS) showed that the major products were tris(catecholate)-type V{sup IV} complexes (65 {plus_minus} 6%) and bis(catecholate)-type V{sup IV}O complexes (20 {plus_minus} 4%). XAS analysis of the V/An-1 product mixture also provided evidence of a minor V{sup III} component (9 {plus_minus} 5% of total V), notable for possible relevance to tunicate biochemistry. The combined results of XAS studies, spectrophotometric studies, and EPR studies consistently establish that reactions between tunichromes (Mm-1 or An-1) and V{sup V} ions generate predominantly V{sup IV}-tunichrome complexes in neutral to moderately basic aqueous media. 53 refs., 4 figs., 3 tabs.

Ryan, D.E.; Grant, K.B.; Nakanishi, K. [Columbia Univ., New York, NY (United States)] [and others] [Columbia Univ., New York, NY (United States); and others

1996-07-02

309

Identification of regions within the four small subunits of human replication factor C required for complex formation and DNA replication.  

PubMed

Replication factor C (RFC) and proliferating cell nuclear antigen (PCNA) are processivity factors for eukaryotic DNA polymerases delta and epsilon. RFC binds to a DNA primer end and loads PCNA onto DNA in an ATP-dependent reaction. The five RFC subunits p140, p40, p38, p37, and p36, all of which are required to form the active RFC complex, share regions of high homology including the defined RFC boxes II-VIII. RFC boxes III and V constitute a putative ATP binding site, whereas the function of the other conserved boxes is unknown. To study the individual subunits in the RFC complex and the role of the RFC boxes, deletion mutations were created in all subunits. Sequences close to the C terminus of each of the small subunits are required for formation of the five subunit complex. A N-terminal region of the small subunits, containing the RFC homology box II, plays a critical role in the function of these subunits, deletion of which reduces but does not abolish RFC activity in loading PCNA onto DNA and in supporting an RFC-dependent replication reaction. The N termini of p37 and p40, although highly homologous, are not interchangeable, suggesting unique functions for the individual subunits. PMID:9092550

Uhlmann, F; Gibbs, E; Cai, J; O'Donnell, M; Hurwitz, J

1997-04-11

310

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

PubMed

Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated. PMID:25420634

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

2014-12-16

311

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

PubMed

The secondary formation of HO(2) radicals following OH + aromatic hydrocarbon reactions in synthetic air under normal pressure and temperature was investigated in the absence of NO after pulsed production of OH radicals. OH and HO(x) (=OH + HO(2)) decay curves were recorded using laser-induced fluorescence after gas-expansion. The prompt HO(2) yields (HO(2) formed without preceding NO reactions) were determined by comparison to results obtained with CO as a reference compound. This approach was recently introduced and applied to the OH + benzene reaction and was extended here for a number of monocyclic aromatic hydrocarbons. The measured HO(2) formation yields are as follows: toluene, 0.42 ± 0.11; ethylbenzene, 0.53 ± 0.10; o-xylene, 0.41 ± 0.08; m-xylene, 0.27 ± 0.06; p-xylene, 0.40 ± 0.09; 1,2,3-trimethylbenzene, 0.31 ± 0.06; 1,2,4-trimethylbenzene, 0.37 ± 0.09; 1,3,5-trimethylbenzene, 0.29 ± 0.08; hexamethylbenzene, 0.32 ± 0.08; phenol, 0.89 ± 0.29; o-cresol, 0.87 ± 0.29; 2,5-dimethylphenol, 0.72 ± 0.12; 2,4,6-trimethylphenol, 0.45 ± 0.13. For the alkylbenzenes HO(2) is the proposed coproduct of phenols, epoxides, and possibly oxepins formed in secondary reactions with O(2). In most product studies the only quantified coproducts were phenols whereas only a few studies reported yields of epoxides. Oxepins have not been observed so far. Together with the yields of phenols from other studies, the HO(2) yields determined in this work set an upper limit to the combined yields of epoxides and oxepins that was found to be significant (?0.3) for all investigated alkylbenzenes except m-xylene. For the hydroxybenzenes the currently proposed HO(2) coproducts are dihydroxybenzenes. For phenol and o-cresol the determined HO(2) yields are matching the previously reported dihydroxybenzene yields, indicating that these are the only HO(2) forming reaction channels. For 2,5-dimethylphenol and 2,4,6-trimethylphenol no complementary product studies are available. PMID:22195640

Nehr, Sascha; Bohn, Birger; Wahner, Andreas

2012-06-21

312

Effect of OH radical scavengers on secondary organic aerosol formation from reactions of isoprene with ozone  

NASA Astrophysics Data System (ADS)

In order to understand the effect of OH radical scavengers on secondary organic aerosol formation, aerosol yields from the isoprene ozonolysis were measured in the presence of sufficient amounts of OH radical scavengers. Cyclohexane, CO, n-hexane, and diethyl ether were used as the OH radical scavengers. The aerosol yield was determined to be 0.002-0.023 for experiments without OH radical scavengers in the aerosol mass range 2-120 ?g m-3. Similar aerosol yields were observed in experiments using cyclohexane. The aerosol yield observed with n-hexane was close to that observed without scavengers at 120 ?g m-3, but this aerosol yield was slightly lower than those observed in reactions without scavengers in the range 3-83 ?g m-3. The offline aerosol samples obtained in experiments with cyclohexane or n-hexane contained oxygenated hydrocarbons with six or more carbon atoms. Aerosol formation in experiments that used cyclohexane or n-hexane as the scavenger was enhanced. This was caused by the oxidation products of the OH radical scavengers, although the increase in the yield could not be quantified. The aerosol yields were 0.002-0.014 for experiments with CO and diethyl ether in the aerosol mass range 4-120 ?g m-3. The reaction of CO with OH radicals forms HO2 radicals, whereas the reactions of cyclohexane, n-hexane, and diethyl ether, respectively, with OH radicals form organic peroxy (RO2) radicals. Present results show that the aerosol yield is independent of the HO2/RO2 ratio or that it decreases with increasing HO2/RO2 ratio. Since the HO2 concentration is much higher than the RO2 concentration in the atmosphere, the results obtained using CO in this study will be a good approximation of the aerosol yield from the ozonolysis of isoprene in the atmosphere.

Sato, Kei; Inomata, Satoshi; Xing, Jia-Hua; Imamura, Takashi; Uchida, Risa; Fukuda, Sayaka; Nakagawa, Kazumichi; Hirokawa, Jun; Okumura, Motonori; Tohno, Susumu

2013-11-01

313

Chemically Activated Formation of Organic Acids in Reactions of the Criegee Intermediate with Aldehydes and Ketones  

SciTech Connect

Reactions of the Criegee intermediate (CI, .CH2OO.) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between .CH2OO. and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48–51 kcal mol-1 lower in energy, formed via 1,3- cycloaddition of .CH2OO. across the CQO bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O–O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO o CH3CHO o CH3COCH3 (the highest yield being 10-4 times lower than the initial .CH2OO. concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

Jalan, Amrit; Allen, Joshua W.; Green, William H.

2013-08-08

314

Kinetics and mechanism for formation of enols in reaction of hydroxide radical with propene.  

PubMed

Recently, enols have been found to be the common intermediates in hydrocarbon combustion flames (Taatjes et al. Science 2005, 308, 1887), but the knowledge of kinetic properties for such species in combustion flames is rare. Therefore in this work, particular attention is paid to the formation of enols in combustion flames. Starting with HO and propene (CH(3)CH=CH(2)), the reaction mechanism involving eight product channels has been investigated systematically. It is revealed that the electrophilic addition of OH to the double bond of CH(3)CH=CH(2) is unselective and the chemically activated adducts, CH(3)CHOH=CH(2) and CH(3)CH=CH(2)OH, may undergo dissociation in competition with H-abstractions. The kinetics and product branching ratios of the HO and propene reaction have been evaluated in the temperature range of 200-3000 K by Variflex code, based on the weak collision master equation/microcanonical variational RRKM theory. Available experimental kinetic data can be quantitatively reproduced by this study, with a minor adjustment (1.0 kcal/mol) of the OH central addition barrier. From the theoretical calculations with multiple reflection correction included, the total rate constant is fitted to k(t) = 6.07 x 10(-5)T(-2.54) exp(108/T) cm(3) x molecule(-1) x s(-1) in the range of 200-800 K and k(t) = 7.11 x 10(-23)T(3.38) exp(-1097/T) cm(3) x molecule(-1) x s(-1) in the range of 800-3000 K, which are in close agreement with experimental data. The branching ratios of enol channels are consistent with the observation in low-pressure flames and hence the reaction mechanisms presented here provide valuable descriptions of enol formations in hydrocarbon combustion chemistry. PMID:19231829

Zhou, Chong-Wen; Li, Ze-Rong; Li, Xiang-Yuan

2009-03-19

315

Ion wake formation with dust charge fluctuation in complex plasma  

SciTech Connect

In complex plasma, the interaction mechanism among dust grains near the plasma sheath is significantly influenced by the downward ion flow towards the sheath and dust charge fluctuation over grain surface. Asymmetric ion flow towards the sheath gives rise to well known attractive wake potential in addition to repulsive Yukawa type of potential. The present work shows that the charging dynamics play a significant role in modification of plasma dielectric response function and hence the interaction mechanism among test dust particulates. The effective Debye length is found to be a characteristic of dust size and background plasma response towards the grain along with ion flow speed. The potentials thus obtained show a damping in strength of interaction in the presence of dynamical charging of dust as compared to that of constant charge dust grains. The result also shows decrease in focal length of ion lensing with increase in grain size.

Bhattacharjee, Saurav; Das, Nilakshi [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)] [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)

2013-11-15

316

Formation of nitroanthracene and anthraquinone from the heterogeneous reaction between NO2 and anthracene adsorbed on NaCl particles.  

PubMed

Oxidative derivatives of polycyclic aromatic hydrocarbons (PAHs), that is, nitro-PAHs and quinones, are classed as hazardous semivolatile organic compounds but their formation mechanism from the heterogeneous reactions of PAHs adsorbed on atmospheric particles is not well understood. The heterogeneous reaction of NO2 with anthracene adsorbed on NaCl particles under different relative humidity (RH 0-60%) was investigated under dark conditions at 298 K. The formation of the major products, 9,10-anthraquinone (9,10-AQ) and 9-nitroanthracene (9-NANT), were determined to be second-order reactions with respect to NO2 concentration. The rate of formation of 9,10-AQ under low RH (0-20%) increased as the RH increased but decreased when the RH was further increased in high RH (40-60%). In contrast, the rate of formation of 9-NANT across the whole RH range (0-60%) decreased significantly with increasing RH. Two different reaction pathways are discussed for the formation of 9,10-AQ and 9-NANT, respectively, and both are considered to be coupled to the predominant reaction of NO2 with the NaCl substrate. These results suggest that relative humidity, which controls the amount of surface adsorbed water on NaCl particles, plays an important role in the heterogeneous reaction of NO2 with adsorbed PAHs. PMID:24950458

Chen, Wenyuan; Zhu, Tong

2014-08-01

317

Programming in situ immunofluorescence intensities through interchangeable reactions of dynamic DNA complexes  

PubMed Central

The regulation of antibody reporting intensities is critical to various in situ fluorescence imaging analyses. While such control is often necessary to visualize sparse molecular targets, the ability to tune marker intensities is also essential for highly multiplexed imaging strategies where marker reporting levels must be tuned to both optimize dynamic detection ranges and minimize crosstalk between different signals. Existing chemical amplification approaches generally lack such control. Here, we demonstrate that linear and branched DNA complexes can be designed to function as interchangeable building blocks that can be assembled into organized, fluorescence reporting complexes. We show that the ability to program DNA strand displacement reactions between these complexes offer new opportunities to deterministically tune the number of dyes that are coupled to individual antibodies in order to both increase and controllably balance marker levels within fixed cells. PMID:23165916

Zimak, Jan; Schweller, Ryan M.; Duose, Dzifa Y.; Hittelman, Walter N.

2013-01-01

318

Programming in situ immunofluorescence intensities through interchangeable reactions of dynamic DNA complexes.  

PubMed

The regulation of antibody reporting intensities is critical to various in situ fluorescence-imaging analyses. Although such control is often necessary to visualize sparse molecular targets, the ability to tune marker intensities is also essential for highly multiplexed imaging strategies in which marker reporting levels must be tuned both to optimize dynamic detection ranges and to minimize crosstalk between different signals. Existing chemical amplification approaches generally lack such control. Here, we demonstrate that linear and branched DNA complexes can be designed to function as interchangeable building blocks that can be assembled into organized, fluorescence-reporting complexes. We show that the ability to program DNA-strand-displacement reactions between these complexes offers new opportunities to deterministically tune the number of dyes that are coupled to individual antibodies in order both to increase and controllably balance marker reporting levels within fixed cells. PMID:23165916

Zimak, Jan; Schweller, Ryan M; Duose, Dzifa Y; Hittelman, Walter N; Diehl, Michael R

2012-12-21

319

Probing ‘Spin-Forbidden’ Oxygen Atom Transfer: Gas-Phase Reactions of Chromium-Porphyrin Complexes  

PubMed Central

Oxygen-atom transfer reactions of metalloporphyrin species play an important role in biochemical and synthetic oxidation reactions. An emerging theme in this chemistry is that spin-state changes can play important roles, and a ‘two-state’ reactivity model has been extensively applied especially in iron-porphyrin systems. Herein we explore the gas phase oxygen-atom transfer chemistry of meso-tetrakis(pentafluorophenyl)porphyrin (TPFPP) chromium complexes, as well as some other tetradentate macrocyclic ligands. Electrospray ionization in concert with Fourier transform ion cyclotron resonance (FT-ICR) spectrometry has been used to characterize and observe reactivity of the ionic species [(TPFPP)CrIII]+ (1) and [(TPFPP)CrVO]+ (2). These are an attractive system to examine the effects of spin state change on oxygen atom transfer because the d1 CrV species are doublets while the CrIII complexes have quartet ground states with high-lying doublet excited states. In the gas phase, [(TPFPP)CrIII]+ forms adducts with a variety of neutral donors but O-atom transfer is only observed for NO2. Pyridine N-oxide adducts of 1 do yield 2 upon collision induced dissociation (CID), but the ethylene oxide, DMSO, and TEMPO analogs do not. [(TPFPP)CrVO]+ is shown by its reactivity and by CID experiments to be a terminal metal-oxo with a single vacant coordination site. It also displays limited reaction chemistry, being deoxygenated only by the very potent reductant P(OMe)3. In general, [(TPFPP)CrVO]+ species are much less reactive than the Fe and Mn analogs. Thermochemical analysis of the reactions points towards the involvement of spin issues in the lower observed reactivity of the chromium complexes. PMID:20218631

Fornarini, Simonetta; Lanucara, Francesco; Warren, Jeffrey J.

2010-01-01

320

Direct observation of R-loop formation by single RNA-guided Cas9 and Cascade effector complexes.  

PubMed

Clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems protect bacteria and archaea from infection by viruses and plasmids. Central to this defense is a ribonucleoprotein complex that produces RNA-guided cleavage of foreign nucleic acids. In DNA-targeting CRISPR-Cas systems, the RNA component of the complex encodes target recognition by forming a site-specific hybrid (R-loop) with its complement (protospacer) on an invading DNA while displacing the noncomplementary strand. Subsequently, the R-loop structure triggers DNA degradation. Although these reactions have been reconstituted, the exact mechanism of R-loop formation has not been fully resolved. Here, we use single-molecule DNA supercoiling to directly observe and quantify the dynamics of torque-dependent R-loop formation and dissociation for both Cascade- and Cas9-based CRISPR-Cas systems. We find that the protospacer adjacent motif (PAM) affects primarily the R-loop association rates, whereas protospacer elements distal to the PAM affect primarily R-loop stability. Furthermore, Cascade has higher torque stability than Cas9 by using a conformational locking step. Our data provide direct evidence for directional R-loop formation, starting from PAM recognition and expanding toward the distal protospacer end. Moreover, we introduce DNA supercoiling as a quantitative tool to explore the sequence requirements and promiscuities of orthogonal CRISPR-Cas systems in rapidly emerging gene-targeting applications. PMID:24912165

Szczelkun, Mark D; Tikhomirova, Maria S; Sinkunas, Tomas; Gasiunas, Giedrius; Karvelis, Tautvydas; Pschera, Patrizia; Siksnys, Virginijus; Seidel, Ralf

2014-07-01

321

Direct observation of R-loop formation by single RNA-guided Cas9 and Cascade effector complexes  

PubMed Central

Clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems protect bacteria and archaea from infection by viruses and plasmids. Central to this defense is a ribonucleoprotein complex that produces RNA-guided cleavage of foreign nucleic acids. In DNA-targeting CRISPR-Cas systems, the RNA component of the complex encodes target recognition by forming a site-specific hybrid (R-loop) with its complement (protospacer) on an invading DNA while displacing the noncomplementary strand. Subsequently, the R-loop structure triggers DNA degradation. Although these reactions have been reconstituted, the exact mechanism of R-loop formation has not been fully resolved. Here, we use single-molecule DNA supercoiling to directly observe and quantify the dynamics of torque-dependent R-loop formation and dissociation for both Cascade- and Cas9-based CRISPR-Cas systems. We find that the protospacer adjacent motif (PAM) affects primarily the R-loop association rates, whereas protospacer elements distal to the PAM affect primarily R-loop stability. Furthermore, Cascade has higher torque stability than Cas9 by using a conformational locking step. Our data provide direct evidence for directional R-loop formation, starting from PAM recognition and expanding toward the distal protospacer end. Moreover, we introduce DNA supercoiling as a quantitative tool to explore the sequence requirements and promiscuities of orthogonal CRISPR-Cas systems in rapidly emerging gene-targeting applications. PMID:24912165

Szczelkun, Mark D.; Tikhomirova, Maria S.; Sinkunas, Tomas; Gasiunas, Giedrius; Karvelis, Tautvydas; Pschera, Patrizia; Siksnys, Virginijus; Seidel, Ralf

2014-01-01

322

Isolation of a photoactive photosynthetic reaction center-core antenna complex from Heliobacillus mobilis.  

PubMed

A photoactive reaction center-core antenna complex was isolated from the photosynthetic bacterium Heliobacillus mobilis by extraction of membranes with Deriphat 160c followed by differential centrifugation and sucrose density gradient ultracentrifugation. The purified complex contained a Mr 47,000 polypeptide(s) that bound both the primary donor (P800) and approximately 24 antenna bacteriochlorophylls g. Time-resolved fluorescence emission spectroscopy indicated that the antenna bacteriochlorophylls g are active in energy transfer to P800, exhibiting a decay time of 25 ps. The complex contained 1.4 menaquinones, 9 Fe, and 3 labile S2- per P800. The complex was photoactive with an exponential decay time of 14 ms for P800+ yet showed no EPR-detectable Fe-S center signal in the g less than or equal to 2.0 region, either by chemical reduction to -600 mV or by illumination of reduced samples. The complex is similar to photosystem I of oxygen-evolving photosynthetic systems in that both the primary donor and a core antenna are bound to the same pigment-protein complex. PMID:2620065

Trost, J T; Blankenship, R E

1989-12-26

323

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

PubMed

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

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

2013-11-18

324

Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.  

PubMed

Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative. PMID:23967699

Povie, Guillaume; Renaud, Philippe

2013-01-01

325

Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami  

NASA Technical Reports Server (NTRS)

Zagami, a basaltic shergottite, contains several kinds of lithologies such as Normal Zagami consisting of Fine-grained (FG) and Coarse-grained (CG), Dark Mottled lithology (DML), and Olivine-rich late-stage melt pocket (DN). Treiman and Sutton concluded that Zagami (Normal Zagami) is a fractional crystallization product from a single magma. It has been suggested that there were two igneous stages (deep magma chamber and shallow magma chamber or surface lava flow) on the basis of chemical zoning features of pyroxenes which have homogeneous Mg-rich cores and FeO, CaO zoning at the rims. Nyquist et al. reported that FG has a different initial Sr isotopic ratio than CG and DML, and suggested the possibility of magma mixing on Mars. Here we report new results of petrology and mineralogy for DML and the Olivine-rich lithology (we do not use DN here), the most evolved lithology in this rock, to understand the relationship among lithologies and reveal Zagami s formation history

Niihara, T.; Misawa, K.; Mikouchi, T.; Nyquist, L. E.; Park, J.; Hirata, D.

2012-01-01

326

Formation of the diphenyl molecule in the crossed beam reaction of phenyl radicals with benzene  

SciTech Connect

The chemical dynamics to form the D5-diphenyl molecule, C{sub 6}H{sub 5}C{sub 6}D{sub 5}, via the neutral-neutral reaction of phenyl radicals (C{sub 6}H{sub 5}) with D6-benzene (C{sub 6}D{sub 6}), was investigated in a crossed molecular beams experiment at a collision energy of 185 kJ mol{sup -1}. The laboratory angular distribution and time-of-flight spectra of the C{sub 6}H{sub 5}C{sub 6}D{sub 5} product were recorded at mass to charge m/z of 159. Forward-convolution fitting of our data reveals that the reaction dynamics are governed by an initial addition of the phenyl radical to the {pi} electron density of the D6-benzene molecule yielding a short-lived C{sub 6}H{sub 5}C{sub 6}D{sub 6} collision complex. The latter undergoes atomic deuterium elimination via a tight exit transition state located about 30 kJ mol{sup -1} above the separated reactants; the overall reaction to form D5-diphenyl from phenyl and D6-benzene was found to be weakly exoergic. The explicit identification of the D5-biphenyl molecules suggests that in high temperature combustion flames, a diphenyl molecule can be formed via a single collision event between a phenyl radical and a benzene molecule.

Zhang Fangtong; Gu Xibin; Kaiser, Ralf I. [Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822 (United States)

2008-02-28

327

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

328

A common intermediate for N2 formation in enzymes and zeolites: side-on Cu-nitrosyl complexes  

SciTech Connect

Understanding the mechanisms of catalytic processes requires the identification of reaction centers and key intermediates, both of which are often achieved by the use of spectroscopic characterization tools. Due to the heterogeneity of active centers in heterogeneous catalysts, it is frequently difficult to identify the specific sites that are responsible for the overall activity. Furthermore, the simultaneous presence of a large number of surface species on the catalyst surface often poses a great challenge for the unambiguous determination of the relevant species in the reaction mechanism. In contrast, enzymes possess catalytically active centers with precisely defined coordination environments that are only able to accommodate intermediates relevant to the specific catalytic process. Here we show that side-on Cu+-NO+ complexes characterized by high magnetic field solid state magic angle spinning nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies are the key intermediates in the selective catalytic reduction of NO over Cu-SSZ-13 zeolite catalysts. Analogous intermediates have been observed and characterized in nitrite reductase enzymes, and shown to be the critical intermediates in the formation of N2 for anaerobic ammonium oxidation reactions.[1] The identification of this key reaction intermediate, combined with the results of our prior kinetic studies, allows us to propose a new reaction mechanism for the selective catalytic reduction of NO with NH3 under oxygen-rich environments over Cu-SSZ-13 zeolites, a key reaction in automotive emission control. The authors acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute.

Kwak, Ja Hun; Lee, Jong H.; Burton, Sarah D.; Lipton, Andrew S.; Peden, Charles HF; Szanyi, Janos

2013-09-16

329

Micelle formation in a dilute solution of block copolymers with a polyelectrolyte block complexed with oppositely charged linear chains  

NASA Astrophysics Data System (ADS)

The theory of micelle formation in a dilute solution mixture of polyelectrolyte/neutral diblock copolymers and oppositely charged linear chains has been developed. The core of the micelles is formed by the hydrophobic monomer units of polyelectrolyte complexes between the oppositely charged polyions while the hydrophilic uncharged blocks of the block copolymers comprise the micellar corona. The process of the formation of polyelectrolyte complexes and micelles in the solution has been described as sets of association-dissociation reactions with certain chemical constants and the concentration distribution of micellar aggregates of a given composition has been calculated for various concentrations of linear chains and block copolymer macromolecules in the solution. It was shown that the micelles are formed by nearly fully neutralized block copolymers, so that the micellar charge is close to zero. The aggregation number of the micelles and their charge slightly depend on the concentration of the block copolymers as well as the linear chains in the solution. Micelles in the solution coexist with single block copolymer chain/linear polymer complexes of different composition.

Kramarenko, E. Yu.; Khokhlov, A. R.; Reineker, P.

2003-09-01

330

Dissociation dynamics of sequential ionic reactions: heats of formation of tri-, di-, and monoethylphosphine.  

PubMed

The sequential ethene (C2H4) loss channels of energy-selected ethylphosphine ions have been studied using threshold photoelectron photoion coincidence (TPEPICO) spectroscopy in which ion time-of-flight (TOF) distributions are recorded as a function of the photon energy. The ion TOF distributions and breakdown diagrams have been modeled in terms of the statistical RRKM theory for unimolecular reactions, providing 0 K dissociation onsets, E0, for the ethene loss channels. Three RRKM curves were used to model the five measurements, since two of the reactions differ only by the internal energy of the parent ion. This series of dissociations provides a detailed check of the calculation of the product energy distribution for sequential reactions. From the determined E0's, the heats of formation of several ethylphosphine neutrals and ions have been determined: Delta(f)H degrees 298K[P(C(2)H(5))3] = -152.7 +/- 2.8 kJ/mol, Delta(f)H degrees 298K[P(C(2)H(5))3+] = 571.6 +/- 4.0 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2] = -89.6 +/- 2.1 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2+] = 669.9 +/- 2.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)] = -36.5 +/- 1.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)+] = 784.0 +/- 1.9 kJ/mol. These values have been supported by G2 and G3 calculations using isodesmic reactions. Coupled cluster calculations have been used to show that the C2H4 loss channel, which involves a hydrogen transfer step, proceeds without a reverse energy barrier. PMID:17201383

Kercher, James P; Gengeliczki, Zsolt; Sztáray, Bálint; Baer, Tomas

2007-01-11

331

Kinetics and Thermochemistry of ClCO Formation from the Cl + CO Association Reaction  

NASA Technical Reports Server (NTRS)

Laser flash photolysis of Cl2/CO/M mixtures (M = N2, CO, Ar, CO2) has been employed in conjunction with Cl((sup 2)P(sub J)) detection by time-resolved resonance fluorescence spectroscopy to investigate equilibration kinetics in the reactions Cl((sup 2)P(sub J)) + CO ClCO as a function of temperature (185-260 K) and pressure (14-200 Torr). The association and dissociation reactions are found to be in the low-pressure limit over the range of experimental conditions investigated. In N2 and/or CO buffer gases, the temperature dependences of the ClCO formation and dissociation reaction rate constants are described by the Arrhenius expressions k(sub 1) = (1.05 +/- 0.36) x 10(exp -34) exp[(810 +/- 70)/T] cm(exp 6)/molecules(exp 2).s and k(sub -1) = (4.1 +/- 3.1) x 10(exp -10) exp[(-2960 +/- 60)/T]cu cm/(molecule.s) (errors are 2 sigma). Second- and third-law analyses of the temperature dependence of the equilbrium constant (k/k-1) lead to the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -7.7 +/- 0.6 kcal/mol, Delta-H(sub 0) = -6.9 +/- 0.7 kcal/mol, Delta-S(sub 298) = -23.8 +/- 2.0 cal/mole.K, Delta-H(sub f,298)(ClCO) = 5.2 +/- 0.6 kcal/mol (errors are 2 sigma). The results repported in this study significantly reduce the uncertainties in all reported kinetic and thermodynamic parameters.

Nicovich, J. M.; Kreutter, K. D.; Wine, P. H.

1997-01-01

332

Freeze-induced reactions: formation of iodine-bromine interhalogen species from aqueous halide ion solutions.  

PubMed

Interhalide ion formation resulting from the freezing of dilute solutions containing components found in natural sea salt are investigated as a potential mechanism for the release of interhalogens to the polar atmosphere. Acidified solutions containing iodide, bromide, and nitrite ions have been frozen and then thawed, with changes in speciation analyzed using UV-visible spectrophotometry. The freezing process is shown to induce the formation of the important interhalide ion, IBr(2)(-). This species has previously been predicted to be a precursor of iodine monobromide, IBr, and represents a potentially important source of halogen atoms in the polar marine boundary layer. The reaction mechanisms that lead to the formation of IBr(2)(-) under freezing conditions are explored using both experimental and computational methodologies. The chemistry involved was subsequently modified in order to mimic naturally occurring conditions more closely and also incorporated the use of hydrogen peroxide as an oxidant. In contrast to previous studies, the freeze-induced production of IBr(2)(-) was thereby observed to occur up to pH <5.1, where the acidity levels are comparable to those found in the polar snowpack. PMID:21043531

O'Sullivan, Daniel; Sodeau, John R

2010-11-25

333

Oxidative peptide /and amide/ formation from Schiff base complexes  

NASA Technical Reports Server (NTRS)

One hypothesis of the origin of pre-modern forms of life is that the original replicating molecules were specific polypeptides which acted as templates for the assembly of poly-Schiff bases complementary to the template, and that these polymers were then oxidized to peptide linkages, probably by photo-produced oxidants. A double cycle of such anti-parallel complementary replication would yield the original peptide polymer. If this model were valid, the Schiff base between an N-acyl alpha mino aldehyde and an amino acid should yield a dipeptide in aqueous solution in the presence of an appropriate oxidant. In the present study it is shown that the substituted dipeptide, N-acetyl-tyrosyl-tyrosine, is produced in high yield in aqueous solution at pH 9 through the action of H2O2 on the Schiff-base complex between N-acetyl-tyrosinal and tyrosine and that a great variety of N-acyl amino acids are formed from amino acids and aliphatic aldehydes under similar conditions.

Strehler, B. L.; Li, M. P.; Martin, K.; Fliss, H.; Schmid, P.

1982-01-01

334

Interferogram formation in the presence of complex and large deformation  

USGS Publications Warehouse

Sierra Negra volcano in Isabela island, Gala??pagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a "rubber-sheeting" SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra. Copyright 2007 by the American Geophysical Union.

Yun, S.-H.; Zebker, H.; Segall, P.; Hooper, A.; Poland, M.

2007-01-01

335

Factors leading to the formation of arc cloud complexes  

NASA Technical Reports Server (NTRS)

A total of 12 mesoscale convective systems (MCSs) were investigated. The duration of the gust front, produced by each MCS, was used to classify the MCSs. Category 1 MCSs were defined as ones that produced a gust front and the gust front lasted for more than 6 h. There were 7 category 1 MCSs in the sample. Category 2 MCSs were defined as ones that produced a gust front and the gust front lasted for 6 h or less. There were 4 category 2 MCSs. The MCS of Case 12 was not categorized because the precipitation characteristics were similar to a squall line, rather than an MCS. All of the category 1 MCSs produced arc cloud complexes (ACCs), while only one of the category 2 MCSs produced an ACC. To determine if there were any differences in the characteristics between the MCSs of the two categories, composite analyses were accomplished. The analyses showed that there were significant differences in the characteristics of category 1 and 2 MCSs. Category 1 MCSs, on average, had higher thunderstorm heights, greater precipitation intensities, colder cloud top temperatures and produced larger magnitudes of surface divergence than category 2 MCSs.

Welshinger, Mark John; Brundidge, Kenneth C.

1987-01-01

336

An illustration of the complexity of continent formation  

NASA Technical Reports Server (NTRS)

It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated.

Burke, Kevin

1988-01-01

337

Inhibitory mechanism of pancreatic amyloid fibril formation: formation of the complex between tea catechins and the fragment of residues 22-27.  

PubMed

Islet amyloid polypeptide (IAPP) is a major component of pancreatic amyloid deposits associated with type 2 diabetes. Polyphenols contained in plant foods have been found to inhibit amyloid fibril formation of proteins and/or peptides. However, the inhibition mechanism is not clear for a variety of systems. Here the inhibition mechanism of green tea polyphenols, catechins, on amyloid fibril formation of the IAPP fragment (IAPP22-27), which is of sufficient length for formation of ?-sheet-containing amyloid fibrils, was investigated by means of kinetic analysis. A quartz crystal microbalance (QCM) determined that the association constants of gallate-type catechins [epicatechin 3-gallate (ECg) and epigallocatechin 3-gallate] for binding to IAPP22-27 immobilized on the gold plate in QCM were 1 order of magnitude larger than those of the free IAPP22-27 peptide, and also those of epicatechin and epigallocatechin. Kinetic analysis using a two-step autocatalytic reaction mechanism revealed that ECg significantly reduced the rate constants of the first nucleation step of amyloid fibril formation, while the rate of autocatalytic growth was less retarded. (1)H nuclear magnetic resonance studies clarified that a IAPP22-27/ECg complex clearly forms as viewed from the (1)H chemical shift changes and line broadening. Our study suggests that tea catechins specifically inhibit the early stages of amyloid fibril formation to form amyloid nuclei by interacting with the unstructured peptide and that this inhibition mechanism is of great therapeutic value because stabilization of the native state could delay the pathogenesis of amyloid diseases and also the toxicity of the small oligomer (protofibril) is reported to be greater than that of the mature fibril. PMID:23205879

Kamihira-Ishijima, Miya; Nakazawa, Hiromi; Kira, Atsushi; Naito, Akira; Nakayama, Tsutomu

2012-12-21

338

Effect of reaction pH and CuSO4 addition on the formation of catechinone due to oxidation of (+)-catechin.  

PubMed

A novel hair dyeing technique being milder and safer for a human body is desired. The oxidation product of (+)-catechin, catechinone, was invented as a safer dyestuff for hair colouring under such the situation. The preparation of catechinone by a chemical oxidation is a practical way and the objective of the study is clarify the effect of the solution pH and in the presence or absence of Cu(2+) on the formation rate and yield of catechinone in order to improve the efficiency of the dye formation. The catechinone formation was monitored by ultraviolet-visible spectroscopy. Catechinone was prepared chemically from (+)-catechin in aqueous solution with O2 gas introduced over a pH range of 7.1-11.7. The rate and amount of the dye formation increase with increasing pH. Dissociation of the hydroxyl group of the catechol part of (+)-catechin is significant for the oxidation of (+)-catechin and promotes the dye production. This is because the deprotonated (+)-catechin has a higher reactivity with O2 . The production of catechinone is accelerated by the addition of CuSO4 and the production rate reaches the maximum at pH = 8.8. (+)-Catechin - Cu(2+) complexes are formed and the formation promotes the oxidation of the catechol part of (+)-catechin at pH ? 8.8. On the other hand, the complex becomes too stable to proceed for the oxidation reaction at pH > 8.8. PMID:23574395

Matsubara, T; Wataoka, I; Urakawa, H; Yasunaga, H

2013-08-01

339

Recent advances in catalytic C-N bond formation: a comparison of cascade hydroaminomethylation and reductive amination reactions with the corresponding hydroamidomethylation and reductive amidation reactions.  

PubMed

The design and catalytic implementation of tandem reactions to selectively create nitrogen-containing products under mild conditions has encountered numerous challenges in synthetic chemistry. Several known classes of homogeneously catalyzed carbon-nitrogen bond formation including hydroamination, hydroamidation, hydroaminoalkylation, hydroaminomethylation and reductive amination were reported in the literature. More recently, a new class of C-N bond formation consisting of hydroamidomethylation and reductive amidation extended the applicability of these synthetic methodologies. The tandem reactions do considerably impact on the selectivity and efficiency of synthetic strategies. This review highlights and compares selected examples of the hydroaminomethylation, reductive amination, hydroamidomethylation and reductive amidation reactions, and thus consequently reveals their potential applications in synthetic chemistry as well as chemical industries. PMID:25098332

Raoufmoghaddam, Saeed

2014-10-01

340

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies  

SciTech Connect

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed.

Slavin, L.L.; Bose, R.N. (Chemistry Department, Kent State University, OH (USA))

1990-12-01

341

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies.  

PubMed

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed. PMID:2150856

Slavin, L L; Bose, R N

1990-12-01

342

Trichloramine reactions with nitrogenous and carbonaceous compounds: Kinetics, products and chloroform formation.  

PubMed

Trichloramine is a hazardous disinfection by-product that is of particular relevance in indoor swimming pools. To better understand its fate in pool waters, apparent second order rate constants (kapp) at pH 7 for its reaction with several model compounds were determined. kapp values at pH 7 for nitrogenous compounds were found to increase in the following order: ammonia ? amides (?10(-2)-10(-1) M(-1) s(-1)) < primary amines (?10(-1)-10(0) M(-1) s(-1)) < relevant body fluid compounds (l-histidine, creatinine) (?10(0)-10(1) M(-1) s(-1)) < secondary amines (?10(1)-10(2) M(-1) s(-1)) < trimethylamine (?10(3) M(-1) s(-1)). kapp values at pH 7 of trichloramine with hydroxylated aromatic compounds (?10(2)-10(5) M(-1) s(-1)) are higher than for the nitrogenous compounds and depend on the number and position of the hydroxyl groups (phenol < hydroquinone < catechol < resorcinol). The measurement of kapp as a function of pH revealed that mainly the deprotonated species react with trichloramine. The reaction of trichloramine with Suwannee River and Pony Lake fulvic acid standards showed a decrease of their reactivity upon chlorination, which can be related to the electron donating capacity and the SUVA254. Chlorinated nitrogenous compounds (e.g. uric acid) also have a reduced reactivity with trichloramine. Hence, the residual chlorine in pool water hinders a fast consumption of trichloramine. This explains why trichloramine degradation in pool water is lower than expected from the reactivity with the estimated bather input. Trichloramine also has the potential to form secondary disinfection by-products such as chlorinated aromatic compounds or chloroform by electron transfer or Cl(+)-transfer reactions. The chloroform formation from the reaction of trichloramine with resorcinol occurs with a similar yield and rate as for chlorination of resorcinol. Since the trichloramine concentration in pool water is commonly about one order of magnitude lower than the free chlorine concentration, its contribution to the disinfection by-product formation is assumed to be minor in most cases but might be relevant for few precursors (e.g. phenols) that react faster with trichloramine than with free chlorine. PMID:25655201

Soltermann, Fabian; Canonica, Silvio; von Gunten, Urs

2015-03-15

343

Accelerating the Computation of Detailed Chemical Reaction Kinetics for Simulating Combustion of Complex Fuels  

SciTech Connect

Combustion of hydrocarbon fuels has been a very challenging scientific and engineering problem due to the complexity of turbulent flows and hydrocarbon reaction kinetics. There is an urgent need to develop an efficient modeling capability to accurately predict the combustion of complex fuels. Detailed chemical kinetic models for the surrogates of fuels such as gasoline, diesel and JP-8 consist of thousands of chemical species and Arrhenius reaction steps. Oxygenated fuels such as bio-fuels and heavier hydrocarbons, such as from newer fossil fuel sources, are expected to have a much more complex chemistry requiring increasingly larger chemical kinetic models. Such models are beyond current computational capability, except for homogeneous or partially stirred reactor type calculations. The advent of highly parallel multi-core processors and graphical processing units (GPUs) promises a steep increase in computational performance in the coming years. This paper will present a software framework that translates the detailed chemical kinetic models to high- performance code targeted for GPU accelerators.

Grout, Ray W [ORNL

2012-01-01

344

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

SciTech Connect

We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates (~1 K/s) using differential scanning calorimetry (DSC) traces to 725ºC. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 105 K/s) in high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (Tmax) are largely independent of foil chemistry at 0.6 ± 0.1 m/s and 1220 ± 50 K, respectively, and that the measured Tmax is more than 200 K lower than predicted adiabatic temperatures (Tad). The difference between Tmax and Tad is explained by the prediction that transformation to the final intermetallic phases occurs after Tmax and results in the release of 20-30 % of the total heat of reaction and a delay in rapid cooling.

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

2011-01-11

345

Intra-Golgi formation of IgM-glycosaminoglycan complexes promotes Ig deposition.  

PubMed

Immune complexes arise from interactions between secreted Ab and Ags in the surrounding milieu. However, it is not known whether intracellular Ag-Ab interactions also contribute to the formation of extracellular immune complexes. In this study, we report that certain murine B cell hybridomas accumulate intracellular IgM and release large, spherical IgM complexes. The complexes (termed "spherons") reach 2 ?m in diameter, detach from the cell surface, and settle out of solution. The spherons contain IgM multimers that incorporate the J chain and resist degradation by endoglycosidase H, arguing for IgM passage through the Golgi. Treatment of cells with inhibitors of proteoglycan synthesis, or incubation of spherons with chondroitinase ABC, degrades spherons, indicating that spheron formation and growth depend on interactions between IgM and glycosaminoglycans. This inference is supported by direct binding of IgM to heparin and hyaluronic acid. We conclude that, as a consequence of IgM binding to glycosaminoglycans, multivalent IgM-glycan complexes form in transit of IgM to the cell surface. Intra-Golgi formation of immune complexes could represent a new pathogenic mechanism for immune complex deposition disorders. PMID:21841132

Khan, Salar N; Cox, John V; Nishimoto, Satoru K; Chen, Ching; Fritzler, Marvin J; Hendershot, Linda M; Weigert, Martin; Radic, Marko

2011-09-15

346

Binary role of an ylide in formation of a terminal methylidene complex of niobium.  

PubMed

The first structurally characterized niobium(v) complex possessing a terminal methylidene ligand is reported in high yield from the reaction of [(Ar'O)2Nb(CH3)2Cl] (Ar' = (2,6-CHPh2)2-4-tBu-C6H2) and two equivalents of H2CPPh3. PMID:24788367

Searles, Keith; Keijzer, Karlijn; Chen, Chun-Hsing; Baik, Mu-Hyun; Mindiola, Daniel J

2014-06-14

347

Reversible carbon-carbon bond formation between carbonyl compounds and a ruthenium pincer complex.  

PubMed

This communication describes the reversible reaction of a ruthenium pincer complex with a variety of carbonyl compounds. Both NMR spectroscopic and X-ray crystallographic characterization of isomeric carbonyl adducts are reported, and the equilibrium constants for carbonyl binding have been determined. PMID:23832007

Huff, Chelsea A; Kampf, Jeff W; Sanford, Melanie S

2013-08-18

348

UV-Vis, IR spectra and thermal studies of charge transfer complexes formed in the reaction of 4-benzylpiperidine with ?- and ?-electron acceptors  

NASA Astrophysics Data System (ADS)

The reactions of the electron donor 4-benzylpiperidine (4BP) with the ?-acceptor iodine and ?-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. Based on the obtained data, the charge-transfer complexes were formulated as [I3-, [(4BP)(DDQ)2], and [(4BP)(TBCHD)] for the donor (4BP) and the acceptors I2, DDQ and TBCHD. In the 4BP-TCNQ reaction, a short-lived CT complex is formed followed by rapid N-substitution by TCNQ forming the final reaction product 7,7,8-tricyano-8-benzylpiperidinylquinodimethane [TCBPQDM]. These products were isolated as solids and have been characterized through electronic and infrared spectra as well as elemental and thermal analysis measurements. The formation constants (KCT), charge transfer energy (ECT), molar extinction coefficients (?CT), free energy change ?G? and ionization potential IP of the formed CT-complexes [I3-, [(4BP)(DDQ)2] and [(4BP)(TBCHD)] were obtained.

Mostafa, Adel; El-Ghossein, Nada; Cieslinski, G. Benjamin; Bazzi, Hassan S.

2013-12-01

349

Time-dependent insulin oligomer reaction pathway prior to fibril formation: Cooling and seeding  

PubMed Central

The difficulty in identifying the toxic agents in all amyloid-related diseases is likely due to the complicated kinetics and thermodynamics of the nucleation process and subsequent fibril formation. The slow progression of these diseases suggests that the formation, incorporation and/or action of toxic agents is possibly rate limiting. Candidate toxic agents include precursors (some at very low concentrations), also called oligomers and protofibrils, and the fibrils. Here, we investigate the kinetic and thermodynamic behavior of human insulin oligomers (imaged by cryo-EM) under fibril forming conditions (pH 1.6 and 65°C) by probing the reaction pathway to insulin fibril formation using two different types of experiments – cooling and seeding – and confirm the validity of the nucleation model and its effect on fibril growth. The results from both the cooling and seeding studies confirm the existence of a time-changing oligomer reaction process prior to fibril formation that likely involves a rate-limiting nucleation process followed by structural rearrangements of intermediates (into ?-sheet rich entities) to form oligomers that then form fibrils. The latter structural rearrangement step occurs even in the absence of nuclei (i.e. with added heterologous seeds). Nuclei are formed at the fibrillation conditions (pH 1.6 and 65°C) but are also continuously formed during cooling at pH 1.6 and 25°C. Within the time-scale of the experiments, only after increasing the temperature to 65°C are the trapped insulin nuclei and resultant structures able to induce the structural rearrangement step and overcome the energy barrier to form fibrils. This delay in fibrillation and accumulation of nuclei at low temperature (25°C), result in a decrease in the mean length of the fibers when placed at 65°C. Fits of an empirical model to the data provide quantitative measures of the delay in the lag-time during the nucleation process and subsequent reduction in fibril growth rate resulting from the cooling. Also the seeding experiments, within the time-scale of the measurements, demonstrate that fibers can initiate fast fibrillation with dissolved insulin (fresh or taken during the lag-period) but not with other fibers. Qualitatively this is explained with a conjectual free energy-space plot. PMID:19408310

Sorci, Mirco; Grassucci, Robert A.; Hahn, Ingrid; Frank, Joachim; Belfort, Georges

2009-01-01

350

In situ investigations of bromine-storing complex formation in a zinc-flow battery at gold electrodes  

SciTech Connect

One of the most promising candidates for affordable energy storage systems for electric vehicles is the zinc/bromine battery. The reversible cell voltage of 1.82 V, a theoretical specific energy of 430 Wh kg{sup {minus}1}, robustness, high cycle life, unlimited standby periods in the charged or discharged state, low self-discharge rates, and operation at ambient temperature explain the scientific and industrial interest in this system. The storage reactions of the zinc/bromine battery are the cathodic deposition of zinc and the anodic formation of a nonaqueous polybromide phase. Quaternary ammonium cations, N-methylethylpyrrolidinium (MEP{sup +}) and N-methylethylmorpholinium (MEM{sup +}), store the bromine as polybromide complexes. The mechanism of this complicated reaction determines the polarization and self-discharge rate of the bromine electrode. Electrochemical in situ techniques, phase-stabilized electrochemical quartz microbalance, and in situ reflection-absorption Fourier transform infrared spectroscopy were employed for the first time to investigate these electrode processes. It was shown that specifically adsorbed polybromide anions (Br{sub n}{minus}) formed MEM-Br{sub n}. Therefore, a homogeneous chemical reaction of the dissolved MEP{sup +} cation with electrochemically generated bromine leads to the storage complex MEP-Br{sub n} much more rapidly than the heterogeneous electrochemical reaction of the strongly adsorbed MEM{sup +} to MEM-Br{sub n}. These results demonstrate that in situ techniques not only support the evaluation of the mechanism but also provide key information for battery development.

Kautek, W.; Conradi, A.; Sahre, M.; Fabjan, C.; Drobits, J.; Bauer, G.; Schuster, P.

1999-09-01

351

The conserved oligomeric Golgi complex is involved in double-membrane vesicle formation during autophagy  

PubMed Central

Macroautophagy is a catabolic pathway used for the turnover of long-lived proteins and organelles in eukaryotic cells. The morphological hallmark of this process is the formation of double-membrane autophagosomes that sequester cytoplasm. Autophagosome formation is the most complex part of macroautophagy, and it is a dynamic event that likely involves vesicle fusion to expand the initial sequestering membrane, the phagophore; however, essentially nothing is known about this process including the molecular components involved in vesicle tethering and fusion. In this study, we provide evidence that the subunits of the conserved oligomeric Golgi (COG) complex are required for double-membrane cytoplasm to vacuole targeting vesicle and autophagosome formation. COG subunits localized to the phagophore assembly site and interacted with Atg (autophagy related) proteins. In addition, mutations in the COG genes resulted in the mislocalization of Atg8 and Atg9, which are critical components involved in autophagosome formation. PMID:20065092

Yen, Wei-Lien; Shintani, Takahiro; Nair, Usha; Cao, Yang; Richardson, Brian C.; Li, Zhijian; Hughson, Frederick M.; Baba, Misuzu

2010-01-01

352

Formation of formaldehyde and methanol from the reactions of H atoms with solid CO at 10-20 K  

NASA Astrophysics Data System (ADS)

The reaction of H atoms with solid CO molecules was studied. The solid CO film deposited on the cold head of the cryocooler was reacted with H atoms by spraying the plasma-activated hydrogen gas over the surface of the sample. After the reaction, temperature-programmed mass spectra of the sample were measured. The formation of formaldehyde and methanol has been confirmed, i.e. the occurrence of consecutive H atom addition reactions, CO yields HCO yields HCHO yields HCHOH yields CH3OH. The rather low yield of the reaction products suggests either the small rate constants of the H atom addition reactions to CO and/or the occurrence of the hydrogen abstraction reaction H + HCO yields H2 + CO.

Hiraoka, Kenzo; Ohashi, Nagayuki; Kihara, Yosihide; Yamamoto, Kazuyosi; Sato, Tetsuya; Yamashita, Akihiro

1994-11-01

353

Real-time observation of polymer network formation by liquid- and solid-state NMR revealing multistage reaction kinetics.  

PubMed

The reaction rate for the end-cross-linking process of vinyl-terminated poly(dimethylsiloxane) by a cross-linker with four Si-H functionalities in the presence of solvent was studied by (1)H liquid-state NMR in dependence of the reaction temperature. The properties of the resulting polymer networks, i.e., the gel-point and the formation of the elastically effective network, were monitored in situ during the reaction by single-evolution-time (1)H double-quantum (SET-DQ) low-field NMR. It was found that the cross-linking kinetics shows no uniform reaction order for the conversions of the functional groups before the topological gelation threshold of the polymer network. The two NMR methods are combined to investigate the formation of the elastically effective network in dependence of the conversion of the functional groups of the precursor polymers and the cross-linker. The high chemical and time resolution of the experiments enabled an in-depth analysis of the reaction kinetics, allowing us to conclude on a multistage model for PDMS network formation by hydrosilylation-based end-linking in the presence of solvent. We found that the nonuniform network formation kinetics originates from a dependence of the apparent reaction rate on the number of the Si-H groups of the cross-linker that have already reacted during the progress of the reaction. The fastest overall reaction rate is observed in a range until each cross-linker has reacted once on average, and a uniform apparent overall reaction order of unity with respect to cross-linker concentration is only found at a later stage, when multiply reacted cross-linker molecules with similar reactivity dominate. PMID:22650309

Kovermann, Michael; Saalwächter, Kay; Chassé, Walter

2012-06-28

354

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

NASA Technical Reports Server (NTRS)

Microstructural examination of reaction bonded silicon nitride (RBSN) has shown that there is often a region adjacent to the as-nitrided surfaces that is even more porous than the interior of this already quite porous material. Because this layer of large porosity is considered detrimental to both the strength and oxidation resistance of RBSN, a study was undertaken to determine if its formation could be prevented during processing. All test bars studied were made from a single batch of Si powder which was milled for 4 hours in heptane in a vibratory mill using high density alumina cylinders as the grinding media. After air drying the powder, bars were compacted in a single acting die and hydropressed.

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

1979-01-01

355

Metabolic Intermediate Complex Formation of Human Cytochrome P450 3A4 by Lapatinib  

PubMed Central

Lapatinib, an oral breast cancer drug, has recently been reported to be a mechanism-based inactivator of cytochrome P450 (P450) 3A4 and also an idiosyncratic hepatotoxicant. It was suggested that formation of a reactive quinoneimine metabolite was involved in mechanism-based inactivation (MBI) and/or hepatotoxicity. We investigated the mechanism of MBI of P450 3A4 by lapatinib. Liquid chromatography-mass spectrometry analysis of P450 3A4 after incubation with lapatinib did not show any peak corresponding to irreversible modifications. The enzymatic activity inactivated by lapatinib was completely restored by the addition of potassium ferricyanide. These results indicate that the mechanism of MBI by lapatinib is quasi-irreversible and mediated via metabolic intermediate complex (MI complex) formation. This finding was verified by the increase in a signature Soret absorbance at approximately 455 nm. Two amine oxidation products of the metabolism of lapatinib by P450 3A4 were characterized: N-hydroxy lapatinib (M3) and the oxime form of N-dealkylated lapatinib (M2), suggesting that a nitroso or another related intermediate generated from M3 is involved in MI complex formation. In contrast, P450 3A5 was much less susceptible to MBI by lapatinib via MI complex formation than P450 3A4. In addition, P450 3A5 had a significantly lower ability than 3A4 to generate M3, consistent with N-hydroxylation as the initial step in the pathway to MI complex formation. In conclusion, our results demonstrate that the primary mechanism for MBI of P450 3A4 by lapatinib is not irreversible modification by the quinoneimine metabolite, but quasi-irreversible MI complex formation mediated via oxidation of the secondary amine group of lapatinib. PMID:21363997

Takakusa, Hideo; Wahlin, Michelle D.; Zhao, Chunsheng; Hanson, Kelsey L.; New, Lee Sun; Chan, Eric Chun Yong

2011-01-01

356

A quinhydrone-type 2 ratio 1 acceptor-donor charge transfer complex obtained via a solvent-free reaction.  

PubMed

A 2 : 1 2-methoxybenzoquinone (BQ(OMe))-hydroquinone (H2Q) complex (5), obtained as single crystals by a solvent-free reaction, combines dipolar and pi-pi interactions, as well as hydrogen bonding. PMID:16609793

Bouvet, Marcel; Malézieux, Bernard; Herson, Patrick

2006-04-28

357

Highly Z- and Enantioselective Ring-Opening/Cross-Metathesis Reactions Catalyzed by Stereogenic-at-Mo Adamantylimido Complexes  

E-print Network

The first highly Z- and enantioselective class of ring-opening/cross-metathesis reactions is presented. Transformations are promoted in the presence of <2 mol % of chiral stereogenic-at-Mo monoaryloxide complexes bearing ...

Ibrahem, Ismail

358

Reaction of Elemental Sulfur with a Copper(I) Complex Forming a trans--1,2 End-On Disulfide Complex: New Directions in Copper-Sulfur Chemistry  

E-print Network

Reaction of Elemental Sulfur with a Copper(I) Complex Forming a trans-µ-1,2 End-On Disulfide Complex: New Directions in Copper-Sulfur Chemistry Matthew E. Helton, Peng Chen, Partha P. Paul, Zolta, investigations into copper-sulfur interactions have been of marked interest in the research fields of copper

Chen, Peng

359

Spectrophotometric determination of doxazosin mesylate in tablets by ion-pair and charge-transfer complexation reactions.  

PubMed

Two accurate, easy spectrophotometric methods for the determination of doxazosin mesylate were described. The first method was based on the formation of ion-pair complexes with the acidic sulfophthalein dyes bromocresol purple (BCP) and bromophenol blue (BPB) in pH 3.3 and 4.5 citrate-phosphate buffer, respectively. The formed complexes were extracted into dichloromethane, and their absorbance was measured at 403 and 410 nm for BCP and BPB, respectively. The second method was based on the charge transfer reaction of the drug as an n-electron donor with either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) as pi-acceptors, to give colored radical anions. The absorbances of products were measured at 457 nm in acetonitrile and 838 nm in methanol for DDQ and TCNQ, respectively. Under the optimum reaction conditions, Beer's law was obeyed with a good correlation coefficient (r = 0.9997-0.9999) in the concentration ranges 3.0-18.0, 3.0-20.0, 15.0-95.0, and 10.0-100.0 microg/mL for the BCP, BPB, DDQ, and TCNQ methods, respectively. Limits of detection of the BCP, BPB, DDQ, and TCNQ methods were 0.314, 0.408, 1.935, and 1.610 microg/mL, respectively. The limits of quantification were 1.045, 1.360, 6.449, and 5.367 microg/mL, respectively. The parameters molar absorptivity, precision, accuracy, recovery, robustness, and stability constant were studied. The proposed methods were successfully applied for determination of the drug in tablets with good accuracy and precision. Statistical comparison of the results with those obtained by a reported method showed good agreement and indicated no significant difference in accuracy and precision. PMID:19382570

Aydo?mu?, Zeynep; Aydodmup, Zeynep; Barla, Asli

2009-01-01

360

The use of new ionic liquids in two-phase catalytic hydrogenation reaction by rhodium complexes  

Microsoft Academic Search

The reaction of 1-n-butyl-3-methylimidazolium chloride (BMIC) with sodium tetrafluoroborate or sodium hexafluorophosphate produced the room temperature-, air- and water-stable molten salts (BMI+)(BF4?) (1) and (BMI+)(PF6?) (2), respectively, in almost quantitative yield. The rhodium complexes RhCl(PPh3)3 and [Rh(cod)2][BF4] are completely soluble in these ionic liquids and they are able to catalyse the hydrogenation of cyclohexene at 10 atm and 25°C in

Paulo A. Z. Suarez; Jeane E. L. Dullius; Sandra Einloft; Roberto F. De Souza; Jairton Dupont

1996-01-01

361

URDME: a modular framework for stochastic simulation of reaction-transport processes in complex geometries  

PubMed Central

Background Experiments in silico using stochastic reaction-diffusion models have emerged as an important tool in molecular systems biology. Designing computational software for such applications poses several challenges. Firstly, realistic lattice-based modeling for biological applications requires a consistent way of handling complex geometries, including curved inner- and outer boundaries. Secondly, spatiotemporal stochastic simulations are computationally expensive due to the fast time scales of individual reaction- and diffusion events when compared to the biological phenomena of actual interest. We therefore argue that simulation software needs to be both computationally efficient, employing sophisticated algorithms, yet in the same time flexible in order to meet present and future needs of increasingly complex biological modeling. Results We have developed URDME, a flexible software framework for general stochastic reaction-transport modeling and simulation. URDME uses Unstructured triangular and tetrahedral meshes to resolve general geometries, and relies on the Reaction-Diffusion Master Equation formalism to model the processes under study. An interface to a mature geometry and mesh handling external software (Comsol Multiphysics) provides for a stable and interactive environment for model construction. The core simulation routines are logically separated from the model building interface and written in a low-level language for computational efficiency. The connection to the geometry handling software is realized via a Matlab interface which facilitates script computing, data management, and post-processing. For practitioners, the software therefore behaves much as an interactive Matlab toolbox. At the same time, it is possible to modify and extend URDME with newly developed simulation routines. Since the overall design effectively hides the complexity of managing the geometry and meshes, this means that newly developed methods may be tested in a realistic setting already at an early stage of development. Conclusions In this paper we demonstrate, in a series of examples with high relevance to the molecular systems biology community, that the proposed software framework is a useful tool for both practitioners and developers of spatial stochastic simulation algorithms. Through the combined efforts of algorithm development and improved modeling accuracy, increasingly complex biological models become feasible to study through computational methods. URDME is freely available at http://www.urdme.org. PMID:22727185

2012-01-01

362

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

E-print Network

The first broadly applicable set of protocols for efficient Z-selective formation of macrocyclic disubstituted alkenes through catalytic ring-closing metathesis (RCM) is described. Cyclizations are performed with 1.2–7.5?mol?% ...

Wang, Chenbo

363

Reaction path study of conformational transitions and helix formation in a tetrapeptide.  

PubMed Central

Conformational transitions between the 112 stable states of the tetrapeptide isobutyryl-Ala3-NH-methyl (IAN) are studied theoretically. The objective of the investigation is to advance the understanding of helix formation and of conformational transitions in polypeptides. The possible reaction paths between extended chain and helical configurations are examined in detail. The study of the multiple reaction paths in this 48-atom molecule became possible due to development of a new computational algorithm. It is shown that the helix-coil transitions in IAN follow a sequence of local dihedral flips and that the number of the available routes for the transition is significantly lower than in a random search. A quasi-melting point is obtained at 5 +/- 1 kcal (1 cal = 4.18 J)/mol above the lowest energy minimum. Below this point the molecule is trapped in one or very few minima, and above it the molecule hops between a large number of configurations. PMID:2780552

Czerminski, R; Elber, R

1989-01-01

364

Formation of cysteine-S-conjugates in the Maillard reaction of cysteine and xylose.  

PubMed

Cysteine-S-conjugates (CS-conjugates) occur in foods derived from plant sources like grape, passion fruit, onion, garlic, bell pepper and hops. During eating CS-conjugates are degraded into aroma-active thiols by ?-lyases that originate from oral microflora. The present study provides evidence for the formation of the CS-conjugates S-furfuryl-l-cysteine (FFT-S-Cys) and S-(2-methyl-3-furyl)-l-cysteine (MFT-S-Cys) in the Maillard reaction of xylose with cysteine at 100°C for 2h. The CS-conjugates were isolated using cationic exchange and reversed-phase chromatography and identified by (1)H NMR, (13)C NMR and LC-MS(2). Spectra and LC retention times matched those of authentic standards. To the best of our knowledge, this is the first time that CS-conjugates are described as Maillard reaction products. Furfuryl alcohol (FFA) is proposed as an intermediate which undergoes a nucleophilic substitution with cysteine. Both FFT-S-Cys and MFT-S-Cys are odourless but produce strong aroma when tasted in aqueous solutions, supposedly induced by ? -lyases from the oral microflora. The perceived aromas resemble those of the corresponding aroma-active thiols 2-furfurylthiol (FFT) and 2-methyl-3-furanthiol (MFT) which smell coffee-like and meaty, respectively. PMID:23790889

Cerny, Christoph; Guntz-Dubini, Renée

2013-11-15

365

ERK phosphorylation potentiates Elk-1-mediated ternary complex formation and transactivation.  

PubMed Central

Induction of the human c-fos proto-oncogene by mitogens depends on the formation of a ternary complex by p62TCF with the serum response factor (SRF) and the serum response element (SRE). We demonstrate that Elk-1, a protein closely related to p62TCF in function, is a nuclear target of two members of the MAP kinase family, ERK1 and ERK2. Phosphorylation of Elk-1 increases the yield of ternary complex in vitro. At least five residues in the C-terminal domain of Elk-1 are phosphorylated upon growth factor stimulation of NIH3T3 cells. These residues are also phosphorylated by purified ERK1 in vitro, as determined by a combination of phosphopeptide sequencing and 2-D peptide mapping. Conversion of two of these phospho-acceptor sites to alanine impairs the formation of ternary complexes by the resulting Elk-1 proteins. Removal of these serine residues also drastically diminishes activation of the c-fos promoter in epidermal growth factor-treated cells. Analogous mutations at other sites impair activation to a lesser extent without affecting ternary complex formation in vitro. Our results indicate that phosphorylation regulates ternary complex formation by Elk-1, which is a prerequisite for the manifestation of its transactivation potential at the c-fos SRE. Images PMID:7889942

Gille, H; Kortenjann, M; Thomae, O; Moomaw, C; Slaughter, C; Cobb, M H; Shaw, P E

1995-01-01

366

Computational Investigation of the Competition between the Concerted Diels-Alder Reaction and Formation of Diradicals in Reactions of Acrylonitrile with Non-Polar Dienes  

PubMed Central

The energetics of the Diels-Alder cycloaddition reactions of several 1,3-dienes with acrylonitrile, and the energetics of formation of diradicals, were investigated with density functional theory (B3LYP and M06-2X) and compared to experimental data. For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile, the concerted reaction is favored over the diradical pathway by 2.5 kcal/mol using B3LYP/6-31G(d); experimentally this reaction gives both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene with acrylonitrile is preferred computationally over the stepwise pathway by 5.9 kcal/mol; experimentally, only the Diels-Alder adduct is formed. For the reactions of (E)-1,3-pentadiene and acrylonitrile, both cycloaddition and copolymerization were observed experimentally; these trends were mimicked by the computational results, which showed only a 1.2 kcal/mol preference for the concerted pathway. For the reactions of (Z)-1,3-pentadiene and acrylonitrile, the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with previous experimental findings that only polymerization occurs. M06-2X is known to give more accurate activation and reaction energetics but the energies of diradicals are too high. PMID:23758325

James, Natalie C.; Um, Joann M.; Padias, Anne B.; Hall, H. K.; Houk, K. N.

2013-01-01

367

Computational investigation of the competition between the concerted Diels-Alder reaction and formation of diradicals in reactions of acrylonitrile with nonpolar dienes.  

PubMed

The energetics of the Diels-Alder cycloaddition reactions of several 1,3-dienes with acrylonitrile, and the energetics of formation of diradicals, were investigated with density functional theory (B3LYP and M06-2X) and compared to experimental data (Hall et al., J. Org. Chem.1993, 58, 7049-7058). For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile, the concerted reaction is favored over the diradical pathway by 2.5 kcal/mol using B3LYP/6-31G(d); experimentally, this reaction gives both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene with acrylonitrile is preferred computationally over the stepwise pathway by 5.9 kcal/mol; experimentally, only the Diels-Alder adduct is formed. For the reactions of (E)-1,3-pentadiene and acrylonitrile, both cycloaddition and copolymerization were observed experimentally; these trends were mimicked by the computational results, which showed only a 1.2 kcal/mol preference for the concerted pathway. For the reactions of (Z)-1,3-pentadiene and acrylonitrile, the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with previous experimental findings that only polymerization occurs. M06-2X is known to give more accurate activation and reaction energetics (Pieniazek, et al., Angew. Chem. Int.2008, 47, 7746-7749), but the energies of diradicals are too high. PMID:23758325

James, Natalie C; Um, Joann M; Padias, Anne B; Hall, H K; Houk, K N

2013-07-01

368

Complex formation between heme oxygenase and phytochrome during biosynthesis in Pseudomonas syringae pv. tomato.  

PubMed

The plant pathogen Pseudomonas syringae pv. tomato carries two genes encoding bacterial phytochromes. Sequence motifs identify both proteins (PstBphP1 and PstBphP2, respectively) as biliverdin IX? (BV)-binding phytochromes. PstbphP1 is arranged in an operon with a heme oxygenase (PstBphO)-encoding gene (PstbphO), whereas PstbphP2 is flanked downstream by a gene encoding a CheY-type response regulator. Expression of the heme oxygenase PstBphO yielded a green protein (?(max) = 650 nm), indicative for bound BV. Heterologous expression of PstbphP1 and PstbphP2 and in vitro assembly with BV IX? yielded the apoproteins for both phytochromes, but only in the case of PstBphP1 a light-inducible chromoprotein. Attempts to express the endogenous heme oxygenase BphO and either of the two phytochromes from two plasmids yielded only holo-PstBphP1. Relatively small amounts of soluble holo-PstBphP2 were just obtained upon co-expression with BphO from P. aeruginosa. Expression of the operon containing PstbphO:PstbphP1 led to an improved yield and better photoreactivity for PstBphP1, whereas an identical construct, exchanging PstbphP1 for PstbphP2 (PstbphO:PstbphP2), again yielded only minute amounts of chromophore-loaded BphP2-holoprotein. The improved yield for PstBphP1 from the PstbphO:PstbphP1 operon expression is apparently caused by complex formation between both proteins during biosynthesis as affinity chromatography of either protein using two different tags always co-purified the reaction partner. These results support the importance of protein-protein interactions during tetrapyrrole metabolism and phytochrome assembly. PMID:22415794

Shah, Rashmi; Schwach, Julia; Frankenberg-Dinkel, Nicole; Gärtner, Wolfgang

2012-06-01

369

Petrological and geochemical constraints on granitoid formation: The Waldoboro Pluton Complex, Maine  

SciTech Connect

The Waldoboro Pluton Complex (WPC) comprises seven units ranging from qtz-diorite to aplite. The country rocks are biotite-rich metagraywackes with minor shales mostly belonging to the Proterozoic Z-Ordovician Bucksport Formation. Field evidence strongly suggests that the WPC formed in-situ: contacts with the country rock are cryptic, transitional and concordant; restitic minerals in the granitoids are identical to those in the country rocks; prolific metasedimentary enclaves in the WPC are locally derived. Major and trace element data for country rock and the most voluminous units of the WPC define consistent linear trends suggesting limited melt segregation and retention of a high proportion of restite. Mixing models and partial melting models require 54--76% melting for generation of the gneissic granites and two-mica granites. Garnet-biotite geothermometry and garnet-Al[sub 2]SiO[sub 5]-SiO[sub 2]-plagioclase geobarometry indicate that the WPC formed at T = 740--780 C and P = 0.4--0.7 GPa. Published experimental data show that < 50% melting is likely under these conditions if melting is controlled by dehydration reactions. Bucksport lithologies contain < 20% biotite, suggesting that the maximum amount of melt that could have formed by dehydration melting is < 20%, even if all biotite was consumed during melting. It seems probable that a free fluid phase was required to generate the WPC. Migmatization is apparent in all lithologies (including amphibolites) in the vicinity of the WPC, consistent with fluid-present melting. Fluid may have ingressed along the St. George thrust, but the source of the fluid is unknown.

Barton, M. (Ohio State Univ., Columbus, OH (United States). Dept. of Geological Science); Sidle, W.S. (Oak Ridge National Lab., TN (United States))

1992-01-01

370

Donor functionalized ruthenium N-heterocyclic carbene complexes in alcohol oxidation reactions.  

PubMed

N-Pyridyl, N'-amido functionalized imidazolium bromides were obtained in high yields as an N-heterocyclic carbene (NHC) precursor and used as bidentate or a pincer ligands to obtain ruthenium complexes via a silver NHC transmetallation route. The incorporation of a phenyl group as an amido-N substituent (R = Ph) results in a bidentate coordination mode through the C(NHC) and N(pyridyl) donors, whereas in its absence (R = H) a pincer coordination mode was observed through the N(pyridyl)^C(NHC)^O(amido) donors. The ruthenium complex featuring a pincer type NCO coordination mode with a protic NH function adjacent to the coordinating O(amido) atom was found to efficiently catalyse the oxidation of activated alcohols effecting quantitative conversions within 30 minutes. However the oxidation of deactivated alcohols required longer reaction times to effect the quantitative transformation. PMID:24519541

Naziruddin, Abbas Raja; Zhuang, Chun-Shiuan; Lin, Wan-Jung; Hwang, Wen-Shu

2014-04-14

371

Study on formation of starch–lipid complexes during extrusion-cooking of almond flour  

Microsoft Academic Search

A blend containing almond and wheat flours (about 1:2.5, dry basis) was extruded through a co-rotating twin-screw extruder with a screw diameter of 25mm. The effects of barrel temperature (61.72–118.28°C) and feed moisture (21.17–26.83%) on starch–lipid complex formation (X-ray diffraction, melting enthalpy, and complexing index) as well as on fat loss (which occurs during extrusion processing), break strength, deformability and

Teresa De Pilli; Kirsi Jouppila; Jarno Ikonen; Jarno Kansikas; Antonio Derossi; Carla Severini

2008-01-01

372

reactions  

Microsoft Academic Search

Gene regulatory, signal transduction and metabolic networks are major areas of interest in the newly emerging field of systems biology. In living cells, stochastic dynamics play an important role; however, the kinetic parameters of biochemical reactions necessary for modelling these processes are often not accessible directly through experiments. The problem of estimating stochastic reaction constants from molecule count data measured,

S. Reinker; R. M. Altman; J. Timmer

373

Cobalt catalysis in the gas phase: experimental characterization of cobalt(I) complexes as intermediates in regioselective Diels-Alder reactions.  

PubMed

In situ-formed cobalt(I) complexes are proposed to act as efficient catalysts in regioselective Diels-Alder reactions of unactivated substrates such as 1,3-dienes and alkynes. We report the first experimental evidence for the in situ reduction of CoBr2(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane] by Zn/ZnI2 to [Co(I)(dppe)](+) by means of electrospray MS(n) experiments. Additionally, the reactivities of Co(II) and Co(I) dppe complexes toward the Diels-Alder substrates isoprene and phenylacetylene were probed in gas-phase ion/molecule reactions (IMRs). Isoprene and phenylacetylene were introduced into the mass spectrometer via the buffer gas flow of a linear ion trap. The IMR experiments revealed a significantly higher substrate affinity of [Co(I)(dppe)](+) compared with [Co(II)Br(dppe)](+). Furthermore, the central intermediate of the solution-phase cobalt-catalyzed Diels-Alder reaction, [Co(I)(dppe)(isoprene)(phenylacetylene)](+), could be generated via IMR and examined in the gas phase. Collision activation of this complex ion delivered evidence for the gas-phase reaction of isoprene with phenylacetylene in the coordination sphere of the cobalt ion. The experimental findings are consistent with the results of quantum-chemical calculations on all of the observed Co(I) dppe complex ions. The results constitute strong analytical evidence for the formation and importance of different cobalt(I) species in regioselective Diels-Alder reactions of unactivated substrates and identify [Co(I)(dppe)](+) as the active Diels-Alder catalyst. PMID:24044877

Fiebig, Lukas; Kuttner, Julian; Hilt, Gerhard; Schwarzer, Martin C; Frenking, Gernot; Schmalz, Hans-Günther; Schäfer, Mathias

2013-10-18

374

Condensation Reactions and Formation of Amides, Esters, and Nitriles Under Hydrothermal Conditions  

NASA Astrophysics Data System (ADS)

Hydrothermal pyrolysis experiments were performed to assess condensation (dehydration) reactions to amide, ester, and nitrile functionalities from lipid precursors. Beside product formation, organic compound alteration and stability were also evaluated. Mixtures of nonadecanoic acid, hexadecanedioic acid, or hexadecanamide with water, ammonium bicarbonate, and oxalic acid were heated at 300°C for 72 h. In addition, mixtures of ammonium bicarbonate and oxalic acid solutions were used to test the abiotic formation of organic nitrogen compounds at the same temperature. The resulting products were condensation compounds such as amides, nitriles, and minor quantities of N-methylalkyl amides, alkanols, and esters. Mixtures of alkyl amide in water or oxalic acid yielded mainly hydrolysis and dehydration products, and with ammonium bicarbonate and oxalic acid the yield of condensation products was enhanced. The synthesis experiments with oxalic acid and ammonium bicarbonate solutions yielded homologous series of alkyl amides, alkyl amines, alkanes, and alkanoic acids, all with no carbon number predominances. These organic nitrogen compounds are stable and survive under the elevated temperatures of hydrothermal fluids.

Rushdi, Ahmed I.; Simoneit, Bernd R. T.

2004-06-01

375

Photochemical reactions of divalent mercury with thioglycolic acid: formation of mercuric sulfide particles.  

PubMed

Mercury (Hg) is a key toxic global pollutant. Studies in aquatic environment have suggested that thiols could be important for mercury speciation. Thioglycolic acid has been detected in various natural water systems and used as a model compound to study the complicated interaction between mercury and polyfunctional dissolved organic matter (DOM). We herein presented the first evidence for mercury particle formation during kinetic and product studies on the photochemistry of divalent mercury (Hg(2+)) with thioglycolic acid at near environmental conditions. Mercuric sulfide (HgS) particles formed upon photolysis were identified by high-resolution transmission electron microscopy coupled with energy dispersive spectrometry and select area electron diffraction. Kinetic data were obtained using UV-visible spectrophotometry and cold vapour atomic fluorescent spectrometry. The apparent first-order reaction rate constant under our experimental conditions was calculated to be (2.3±0.4)×10(-5) s(-1) at T=296±2 K and pH 4.0. It was found that (89±3)% of the reactants undergo photoreduction to generate elemental mercury (Hg(0)). The effects of ionic strengths, pH and potassium ion were also investigated. The formation of HgS particles pointed to the possible involvement of heterogeneous processes. Our kinetic results indicated the importance of weak binding sites on DOM to Hg in photoreduction of Hg(2+) to Hg(0). The potential implications of our data on environmental mercury transformation were discussed. PMID:25094064

Si, Lin; Ariya, Parisa A

2015-01-01

376

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

E-print Network

Low temperature rate coefficients for the reaction of CHreaction rate coefficients of the bromomethylidyne radical (CBr) with alkenes and alkynes at room temperaturereaction is barrierless with a slight positive evolution of the rate coefficient with increasing temperature.

Soorkia, Satchin

2010-01-01

377

Quantitative NMR spectroscopy of complex technical mixtures using a virtual reference: chemical equilibria and reaction kinetics of formaldehyde-water-1,3,5-trioxane.  

PubMed

Quantitative 1H NMR spectroscopy was used to study chemical equilibria and reaction kinetics of both the formation and decomposition of 1,3,5-trioxane in aqueous formaldehyde solutions. The reaction was homogeneously catalyzed with up to 0.10 g g(-1) sulfuric acid at temperatures between 360 and 383 K so that most of the experiments had to be carried out pressurized. The studied mixtures were complex due to the formation of methylene glycol and poly(oxymethylene) glycols in aqueous formaldehyde and the presence of considerable amounts of ionized species. Most common internal standards are decomposed by the hot sulfuric acid and external standards were not applicable using the flow NMR probe or pressurizable NMR sample tubes. Therefore, for the quantification of the small trioxane signals, a novel procedure was applied, in which electronically generated NMR signals were used as highly stable Virtual References (VR). The NMR decoupler channel with wave-form generator was used as the source of the reference signal, which was irradiated into the probe using the lock coil. Details on the experimental procedure are presented. It is shown that the presented method yields reliable quantitative reaction data for the complex studied mixtures. PMID:16773212

Maiwald, Michael; Grützner, Thomas; Ströfer, Eckhard; Hasse, Hans

2006-07-01

378

Complexes in the Photocatalytic Reaction of CO2 and H2O: Theoretical Studies  

PubMed Central

Complexes (H2O/CO2, e–(H2O/CO2) and h+–(H2O/CO2)) in the reaction system of CO2 photoreduction with H2O were researched by B3LYP and MP2 methods along with natural bond orbital (NBO) analysis. Geometries of these complexes were optimized and frequencies analysis performed. H2O/CO2 captured photo-induced electron and hole produced e–(H2O/CO2) and h+–(H2O/CO2), respectively. The results revealed that CO2 and H2O molecules could be activated by the photo-induced electrons and holes, and each of these complexes possessed two isomers. Due to the effect of photo-induced electrons, the bond length of C=O and H-O were lengthened, while H-O bonds were shortened, influenced by holes. The infrared (IR) adsorption frequencies of these complexes were different from that of CO2 and H2O, which might be attributed to the synergistic effect and which could not be captured experimentally. PMID:21152274

Luo, Dongmei; Zhang, Ning; Hong, Sanguo; Wu, Huanwen; Liu, Zhihua

2010-01-01

379

Influence of iron and copper oxides on polychlorinated diphenyl ether formation in heterogeneous reactions.  

PubMed

Polychlorinated diphenyl ether (PCDE) has attracted great attention recently as an important type of environmental pollutant. The influence of iron and copper oxides on formation of PCDEs was investigated using laboratory-scale flow reactors under air and under nitrogen at 350 °C, a temperature corresponding to the post-combustion zone of a municipal solid waste incinerator. The results show that the 2,2',3,4,4',5,5',6-otachlorodiphenyl ether (OCDE) formed from the condensation of pentachlorophenol (PCP) and 1,2,4,5-tetrachlorobenzene (Cl4Bz) is the predominant congener formed on the SiO2/Fe2O3 surface with and without oxygen. This indicated that HCl elimination between PCP and 1,2,4,5-Cl4Bz molecules formed 2,2',3,4,4',5,5',6-OCDE in the presence of Fe2O3. On the other hand, decachlorodiphenyl ether, nonachlorodiphenyl ether, and OCDE were the dominant products on the SiO2/CuO surface without oxygen, although the 2,2',3,4,4',5,5',6-OCDE was the dominant product on the SiO2/CuO surface with oxygen. Therefore, the presence of Fe2O3 and CuO influences the formation and homologue distribution of PCDEs, which shifted towards the lower chlorinated species. Fe2O3 can promote both the condensation and dechlorination reaction without oxygen. On the contrary, with oxygen, Fe2O3 suppresses the condensation of chlorobenzene and chlorophenol to form PCDEs and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). CuO can increase the formation of lower chlorinated PCDEs and PCDDs without oxygen. In conclusion, the different fly ash components have a major influence on PCDE emissions. PMID:23440438

Liu, Wenxia; Shen, Lianfeng; Zhang, Fawen; Liu, Wenbin; Zheng, Minghui; Yang, Xitian

2013-08-01

380

Unexpected formation of fluorine-containing tetrahydrocarbazole during the reaction of indole, paraformaldehyde, and fluorine-containing ?-ketoesters  

Microsoft Academic Search

A surprise and mild method to prepare fluorine-containing indole derivatives through a one-pot three-component condensation reaction sequence is presented. To our surprise, during the reaction of preparation of fluorine-containing indole derivatives, unexpected formation of fluorine-containing tetrahydrocarbazole was found. Moreover, this method has been demonstrated in the preparation of functionalized polycyclic indole derivatives in a straightforward and atom-economical manner.

Wan Pang; Yong Xin; Shi-fa Zhu; Huan-feng Jiang; Shi-zheng Zhu

2011-01-01

381

Formation and alteration of complex amino acid precursors in cosmic dusts and their relevance to origins of life  

NASA Astrophysics Data System (ADS)

A wide variety of organic compounds including many kinds of amino acids have been detected in carbonaceous chondrites. It has been known that comets also bring complex organic compounds. The relevance of extraterrestrial organics to the origin of life is extensively discussed. There have been many scenarios of the origin of amino acids found in meteorites or comets, including the Strecker synthesis in the parent bodies of meteorites, the Fischer-Tropsch type reaction in the solar nebula and reactions in cosmic dusts. We examined possible formation of amino acids or their precursors in interstellar dust environments. When possible interstellar media (a mixture of carbon monoxide, ammonia and water) was irradiated with high energy protons, complex organic compounds whose molecular weights are thousands were formed [1], which gave amino acids after acid hydrolysis: Hereafter we will refer them simulated interstellar organics. It was suggested that complex amino acid precursors could be formed in ice mantles of interstellar dust particles in prior to the formation of the solar system. We are planning to irradiate simulated interstellar ices with high-energy heavy ions from the Digital Accelerator (KEK) to confirm the scenario. The simulated interstellar oraganics were so hydrophilic that they were easy to dissolve in water. Complex organics found in meteorites are generally so hydrophobic and are insoluble to water. Organics found in cometary dusts sampled by the Stardust Mission contains organics with various hydrophobicity. We irradiated the simulated interstellar organics with UV and/or soft X-rays. Soft X-rays irradiation of the simulated interstellar organics resulted in the formation of more hydrophobic compounds as seen in some of cometary dusts. It was suggested that organics of interstellar origin on dusts were altered when the solar system was being formed with soft X-rays from the young Sun in prior to the incorporation to planetesimals or comets. Dusts have another important role: Delivery of extraterrestrial organics to the primitive Earth. We are planning a novel astrobiology mission named Tanpopo by utilizing the Exposed Facility of Japan Experimental Module (JEM/EF) of the International Space Station (ISS). We will collect cosmic dusts by using ultra-low density silica gel (aerogel), and will analyze them after returning them to the Earth. Details will be presented in the other session of COSPAR 2014 [2]. [1] Y. Takano et al., Appl. Phys. Lett., 84 (2004) 1410-1412. [2] K. Kobayashi et al., COSPAR 2014, Session F31, #14256, Moscow, Russia.

Kobayashi, Kensei; Kaneko, Takeo; Mita, Hajime; Obayashi, Yumiko; Kawamoto, Yukinori; Kanda, Kazuhiro; Takayama, Ken; Shibata, Hiromi

382

Kinetics and mechanisms of the reactions of alkyl radicals with oxygen and with complexes of Co(III), Ru(III), and Ni(III)  

SciTech Connect

The kinetics of the reactions of C{sub 2}H{sub 5} radical with Co(NH{sub 3}){sub 5}X{sup 2+}, Ru(NH{sub 3}){sub 5}X{sup 2+}, and Co(dmgH){sub 2} (X) (Y) (X = Br, Cl, N{sub 3}, SCN; Y = H{sub 2}O, CH{sub 3}CN) complexes were studied using laser flash photolysis of ethylcobalt complexes. The kinetics were obtained by the kinetic probe method. Some relative rate constants were also determined by a competition method based on ethyl halide product ratios. The kinetics of colligation reactions of a series of alkyl radicals with {beta}-Ni(cyclam){sup 2+} were studied using flaser flash photolysis of alkylcobalt complexes. Again, the kinetics were obtained by employing the kinetic probe competition method. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H{sub 2}O{sup 2+} were studied. Activation parameters were obtained for the unimolecular homolysis of C{sub 2}H{sub 5}Ni(cyclam)H{sub 2}O{sup 2+}. Kinetic and thermodynamic data obtained from these reactions were compared with those for the {sigma}-bonded organometallic complexes. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H{sub 2}O{sup 2+} complexes were studied by monitoring the formation of the oxygen insertion product RO{sub 2}Ni(cyclam)H{sub 2}O{sup 2+}. The higher rate constants for the reactions of alkyl radicals with oxygen in solution, as compared with those measured in the gas phase, were discussed. 30 refs.

Kelley, D.

1990-10-08

383

Formation of copper complexes in landfill leachate and their toxicity to zebrafish embryos  

SciTech Connect

Toxic metal organic complexes have not been found in natural waters, although some organic acids form bioavailable lipophilic and metabolite-type metal complexes. Landfill leachates usually contain organic acids and in the urban environment these leachates, when mixed with storm waters containing Cu, could be a source of toxic Cu organic complexes in streams and estuaries. The authors investigated the formation of Cu complexes in the leachate from an active urban landfill and found that some of the complexes formed were toxic to zebrafish embryos. High and low nominal molecular weight (NMWT) fractions; >5,000 Da and <700 Da, of leachate both formed Cu complexes with almost identical Cu complexing characteristics but the toxicity was due solely to the low NMWT complexes formed in the <700 Da fraction. Chemical equilibrium modeling with MINTEQA2 and H and Cu complex conditional association constants and ligand concentrations obtained from pH and Cu titrations with a Cu ion-selective electrode and van den Berg-Ruzic analyses of the titration data was used to calculate the copper speciation in the embryo test solutions. This calculated speciation, which was confirmed by measurements of Cu{sup 2+} in the test solutions, enabled the toxicity due to the free Cu ion and to the Cu complexes to be distinguished.

Fraser, J.K.; Butler, C.A.; Timperley, M.H.; Evans, C.W.

2000-05-01

384

Stochastic waiting times of complex biochemical reactions may exhibit universal behavior  

NASA Astrophysics Data System (ADS)

To model cell regulatory pathways, one must understand completion times of complex, multistep, often reversible biochemical reactions. As transient properties, these completion (first passage) times are typically unobtainable from stationary behavior, and their distributions are known only for simple homogeneous network topologies. Here, we derive explicit formulas for first passage time distributions of various biological models, such as multi-site phosphorylation, kinetic proofreading, and discrete walks along an inhomogeneous line, and others. In many cases, as system size grows, the system behavior frequently becomes simpler, approaching an unexpected universality. Under many conditions, this limiting behavior is deterministic, under others it is a memoryless Markovian dynamics, and the two results are separated by a phase transition. For example, below a critical parameter, the time to complete a given complex multistep reaction obeys a narrow gamma distribution, and above this threshold, waiting times are exponentially distributed. These findings suggest first that possibilities to coarse-grain cellular networks are immense, and second that the common practice of arbitrarily replacing unknown dynamics with ballistic motion or exponential waiting times may be justified in a wide array of circumstances.

Munsky, B.; Bel, G.; Sinitsyn, N.; Nemenman, I.

2009-03-01

385

Chemistry of low-valent molybdenum phosphite complexes: Models of seven-coordinate reaction intermediates.  

PubMed

A simple synthesis of the zerovalent complex Mo[P(OCH(3))(3)](6) has been devised from a potassium reduction of MoCl(4)(tetrahydrofuran)(2) followed by reaction with trimethyl phosphite at 70 degrees . Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH(3))(3)](6) (+). The major product was an octahedral nonhydridic cation, Mo[P(OCH(3))(3)](5)P(OCH(3))(2) (+), derived from proton cleavage of the P-O phosphite ester bond. This octahedral cation was stereochemically nonrigid, apparently through facile methoxy group migration. Close packing by methoxy groups in this fluxional cation was established through an x-ray crystallographic study of Mo[P(OCH(3))(3)](5)P(OCH(3))(2) (+)-PF(6) (-). Extended reaction of trifluoroactic acid with Mo[P(OCH(3))(3)](6) yielded the seven-coordinate hydride, HMo[P(OCH(3))(3)](4)(O(2)CCF(3)), which was near pentagonal bipyramidal and was stereochemically nonrigid. PMID:16592505

Muetterties, E L; Kirner, J F; Evans, W J; Watson, P L; Abdel-Meguid, S; Tavanaiepour, I; Day, V W

1978-03-01

386

The significance of ACTH for the process of formation of complex heparin compounds in the blood during immobilization stress  

NASA Technical Reports Server (NTRS)

Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex.

Kudryashov, B. A.; Shapiro, F. B.; Lomovskaya, F. B.; Lyapina, L. A.

1979-01-01

387

Dynamics of cadherin\\/catenin complex formation: novel protein interactions and pathways of complex assembly  

Microsoft Academic Search

Calcium-dependent cell-cell adhesion is mediated by the cadherin family of cell adhesion pro- teins. Transduction of cadherin adhesion into cellular reorganization is regulated by cytosolic proteins, termed ct-, ~-, and qc-catenin (plakoglobin), that bind to the cytoplasmic domain of cadherins and link them to the cytoskeleton. Previous studies of cadherin\\/cate- nin complex assembly and organization relied on the coimmunoprecipitation of

Lindsay Hinck; Inke S. Ntithke; Jackie Papkoff; W. James Nelson

1994-01-01

388

Crystal Structure of an EAL Domain in Complex with Reaction Product 5?-pGpG  

PubMed Central

FimX is a large multidomain protein containing an EAL domain and involved in twitching motility in Pseudomonas aeruginosa. We present here two crystallographic structures of the EAL domain of FimX (residues 438–686): one of the apo form and the other of a complex with 5?-pGpG, the reaction product of the hydrolysis of c-di-GMP. In both crystal forms, the EAL domains form a dimer delimiting a large cavity encompassing the catalytic pockets. The ligand is trapped in this cavity by its sugar phosphate moiety. We confirmed by NMR that the guanine bases are not involved in the interaction in solution. We solved here the first structure of an EAL domain bound to the reaction product 5?-pGpG. Though isolated FimX EAL domain has a very low catalytic activity, which would not be significant compared to other catalytic EAL domains, the structure with the product of the reaction can provides some hints in the mechanism of hydrolysis of the c-di-GMP by EAL domains. PMID:23285035

Robert-Paganin, Julien; Nonin-Lecomte, Sylvie; Réty, Stéphane

2012-01-01

389

Communication: Structure, formation, and equilibration of ensembles of Ag-S complexes on an Ag surface  

SciTech Connect

We have utilized conditions of very low temperature (4.7 K) and very low sulfur coverage to isolate and identify Ag-S complexes that exist on the Ag(111) surface. The experimental conditions are such that the complexes form at temperatures above the temperature of observation. These complexes can be regarded as polymeric chains of varying length, with an Ag4S pyramid at the core of each monomeric unit. Steps may catalyze the formation of the chains and this mechanism may be reflected in the chain length distribution.

Russell, Selena M. [Ames Laboratory; Kim, Yousoo [RIKEN Advanced Science Institute; Liu, Da-Jiang [Ames Laboratory; Evans, J. W. [Ames Laboratory; Thiel, P. A. [Ames Laboratory

2013-02-15

390

Formation of MgF3 (-)-dependent complexes between an AAA(+) ATPase and ?(54.).  

PubMed

The widely distributed bacterial ?(54)-dependent transcription regulates pathogenicity and numerous adaptive responses in diverse bacteria. Formation of the ?(54)-dependent open promoter complex is a multi-step process driven by AAA(+) ATPases. Non-hydrolysable nucleotide analogues are particularly suitable for studying such complexity by capturing various intermediate states along the energy coupling pathway. Here we report a novel ATP analogue, ADP-MgF3 (-), which traps an AAA(+) ATPase with its target ?(54). The MgF3 (-)-dependent complex is highly homogeneous and functional assays suggest it may represent an early transcription intermediate state valuable for structural studies. PMID:23650585

Zhang, Nan; Buck, Martin

2012-01-01

391

Formation of MgF3?-dependent complexes between an AAA+ ATPase and ?54  

PubMed Central

The widely distributed bacterial ?54-dependent transcription regulates pathogenicity and numerous adaptive responses in diverse bacteria. Formation of the ?54-dependent open promoter complex is a multi-step process driven by AAA+ ATPases. Non-hydrolysable nucleotide analogues are particularly suitable for studying such complexity by capturing various intermediate states along the energy coupling pathway. Here we report a novel ATP analogue, ADP–MgF3?, which traps an AAA+ ATPase with its target ?54. The MgF3?-dependent complex is highly homogeneous and functional assays suggest it may represent an early transcription intermediate state valuable for structural studies. PMID:23650585

Zhang, Nan; Buck, Martin

2012-01-01

392

Stochastic dynamics of complexation reaction in the limit of small numbers.  

PubMed

We study stochastic dynamics of the non-linear bimolecular reaction A + B?AB. These reactions are common in several bio-molecular systems such as binding, complexation, protein multimerization to name a few. We use master equation to compute the full distribution of several stochastic equilibrium properties such as number of complexes formed (N(c)), equilibrium constant (K). We provide exact analytical and simpler approximate expression for equilibrium fluctuation quantities to quickly estimate the amount of noise as a function of reactant molecules and rates. We construct the phase diagram for a fluctuational quantity f, defined as the ratio of standard deviation to average (f=?(?N(c))(2)/N(c)), as a function of different number of reactant molecules and reaction rates. One of the striking result is, it is possible to have f as high as 45% or higher in significant regions of the phase diagram even when number of reactants involved are around 20-40, typical in biology. Our finding indicates studying averages alone using mass action law needs careful scrutiny. We also outline possible application of our findings in gene expression. Furthermore, we compute average and fluctuation properties of time dependent quantities and derive equations of motion for different moments such as N(c)(t) and N(c)(t)(2). While mean-field mass action law fails to reproduce the exact time dependence, approximate solutions of coupled equations of motions for different moments, capturing fluctuation, is in good agreement with exact results. This may be a way to compute time development of averages and fluctuations in such non-linear systems where mass action law breaks down. Moreover, for this reaction, we outline connection to variational principle of maximum caliber and other more traditional approaches such as chemical Langevin equation. We derive noise statistics for the equivalent Langevin equation and show possible departure from Gaussian white noise. We believe quantitative estimates of phase diagrams for noise, time dependent quantities, and simple analytical expression for equilibrium quantities will be particularly useful to guide experiments involving such non-linear reactions with small numbers of reactants that are often encountered in biology. PMID:21599088

Ghosh, Kingshuk

2011-05-21

393

Fluorimetric determination of some sulfur containing compounds through complex formation with terbium (Tb+3) and uranium (U+3).  

PubMed

Two simple, sensitive and specific fluorimetric methods have been developed for the determination of some sulphur containing compounds namely, Acetylcysteine (Ac), Carbocisteine (Cc) and Thioctic acid (Th) using terbium Tb+3 and uranium U+3 ions as fluorescent probes. The proposed methods involve the formation of a ternary complex with Tb+3 in presence of Tris-buffer method (I) and a binary complex with aqueous uranyl acetate solution method (II). The fluorescence quenching of Tb+3 at 510, 488 and 540 nm (lambda(ex) 250, 241 and 268 nm) and of uranyl acetate at 512 nm (lambda(ex) 240 nm) due to the complex formation was quantitatively measured for Ac, Cc and Th, respectively. The reaction conditions and the fluorescence spectral properties of the complexes have been investigated. Under the described conditions, the proposed methods were applicable over the concentration range (0.2-2.5 microg ml(-1)), (1-4 microg ml(-1)) and (0.5-3.5 microg ml(-1)) with mean percentage recoveries 99.74+/-0.36, 99.70+/-0.52 and 99.43+/-0.23 for method (I) and (0.5-6 microg ml(-1)), (0.5-5 microg ml(-1)), and (1-6 microg ml(-1)) with mean percentage recoveries 99.38+/-0.20, 99.82+/-0.28 and 99.93+/-0.32 for method (II), for the three cited drugs, respectively. The proposed methods were successfully applied for the determination of the studied compounds in bulk powders and in pharmaceutical formulations, as well as in presence of their related substances. The results obtained were found to be in agree statistically with those obtained by official and reported ones. The two methods were validated according to USP guidelines and also assessed by applying the standard addition technique. PMID:17440799

Taha, Elham Anwer; Hassan, Nagiba Yehya; Aal, Fahima Abdel; Fattah, Laila El-Sayed Abdel

2007-05-01

394

Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole  

NASA Astrophysics Data System (ADS)

UV-Vis, 1H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1-4) and to characterize the reaction products. The interactions of MQ1-4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations.

Ganesh, K.; Satheshkumar, A.; Balraj, C.; Elango, K. P.

2013-04-01

395

Reversibility of the inhibitory effect of atrazine and lindane on cytosol 5. alpha. -dihydrotestosterone receptor complex formation in rat prostate  

SciTech Connect

Once entering the bloodstream, most toxic substances, including pesticides, can reach organs involved in the reproductive system. They can cross the placenta, as well as the brain barrier, posing various risks to the reproductive processes. The organochlorine insecticide lindane and the s-triazine herbicide atrazine produce changes in hormone-dependent reactions in the rat hypothalamus, anterior pituitary, and prostate. Lindane also causes histological and biochemical alterations in the rat testis. In vivo treatment with atrazine produces a markedly inhibitory influence of 5{alpha}-dihydrotestosterone - receptor complex formation in rat prostate cytosol. Therefore, the aim of this study was to investigate whether such changes in the crucial step in the reproductive process are reversible. A parallel investigation using lindane was also undertaken.

Simic, B.; Kniewald, Z.; Kniewald, J. (Univ. of Zagreb, (Yugoslavia)); Davies, J.E. (Univ. of Miami, FL (United States))

1991-01-01

396

Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole.  

PubMed

UV-Vis, (1)H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1-4) and to characterize the reaction products. The interactions of MQ1-4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations. PMID:23416920

Ganesh, K; Satheshkumar, A; Balraj, C; Elango, K P

2013-04-15

397

Synthesis and structures of doubly-bridged dicyclopentadienyl dinuclear rhenium complexes, and their photochemical reactions with aromatic halides in benzene.  

PubMed

Reaction of the doubly-bridged biscyclopentadienes (C5H4(EMe2))(C5H4(SiMe2)) (E = Si(1a), or C(1b)) with Re2(CO)10 in refluxing mesitylene gave the corresponding dirhenium carbonyl complexes [(?(5)-C5H3)2(EMe2)(SiMe2)][Re(CO)3]2 (trans-2a,b and cis-2a,b), and the desilylated products [(?(5)-C5H4)2(EMe2)][Re(CO)3]2 (3a,b). Photolysis of trans-2a,b with a series of aryl halides in benzene results in the formation of biphenyl, together with the corresponding rhenium dihalide complexes trans-[(?(5)-C5H3)2(EMe2)(SiMe2)][Re(CO)3][Re(CO)2X2] (X = Cl, Br, I) (4, 6, 8, or 10) and trans-[(?(5)-C5H3)2(EMe2)(SiMe2)][Re(CO)2X2]2 (5, 7, or 9). Additional experiments indicate that one phenyl ring in the resulting biphenyl comes from aryl halides and the other phenyl ring comes from the solvent benzene. However, photolysis of trans-2a with benzyl chloride and n-hexyl chloride in benzene afforded the corresponding bibenzyl and n-dodecane, as well as the rhenium dichlorides 8 and 9. In addition, complex trans-2a can also activate the C-F bond on C6F6 to form the pentafluorophenyl rhenium fluoride trans-[(?(5)-C5H3)2(SiMe2)2][Re(CO)3][Re(CO)2(C6F5)F] (11). Molecular structures of cis-2a, cis-2b, trans-2b, 3b, 6, 7, 8, 11, and 12 determined by X-ray diffraction are also presented. PMID:25274024

Zhu, Bolin; Huang, Xinwei; Hao, Xiaoting

2014-11-28

398

Hexakis (PCP-Platinum and Ruthenium) Complexes by the Transcyclometalation Reaction and Their Use in Catalysis  

Microsoft Academic Search

Hexakis(PCP-pincer) complexes [C6{PtBr(PCP)}6] (5d) and [C6{RuCl(PCP)(PPh3)}6] (5e) were synthesized via the transcyclometalation (TCM) procedure. Mixing the hexakis(PCHP-arene) ligand 7 with six equivalents of [PtBr(NCN)] (1a) or [RuCl(NCN)(PPh3)] (1b), respectively, resulted in the selective metalation of all PCP-ligand sites and the concomitant formation of six equivalents of the NCHN-arene ligand. This procedure was found to be superior over existing metalation procedures.

H. P. Dijkstra; M. Albrecht; G. P. M. van Klink

2002-01-01

399

Flow partitioning in the lithosphere during core complex formation: An interactive evolutionary computation  

E-print Network

the dynamics of core complex formation in a three-layer model of the lithosphere. In this method a mathematical the Moho and topography flat across the detachments as observed in the Basin and Range (McKenzie et al model for an elastic-plastic upper crust. McKenzie et al. (2000) explored the nature of lower crustal

Boschetti, Fabio

400

Enthalpies of complex formation of boron and aluminum bromides with organic bases of high donor power  

SciTech Connect

By the calorimetric method enthalpies of complex formation were determined for boron and aluminum bromides with piperidine and hexamethylphosphoric triamide in benzene solutions and for boron bromide with pyridine in dichloroethane, and also enthalpies of solution were determined for BBr/sub 3/ and the adducts AlBr/sub 3/ x PPy and BBr/sub 2/ x Py in benzene and pyridine.

Grigor-ev, A.A.; Kondrat'ev, Y.V.; Suvorov, A.V.

1986-11-20

401

Photoinduced formation of stable Ag-nanoparticles from a ternary ligand-DNA-Ag(+) complex.  

PubMed

The combination of (i) the light-harvesting nature and excited-state redox reactivity of a cationic DNA intercalator, (ii) a conjugated Ag(+)-binding crown ether, and (iii) the stabilizing effect of DNA on AgNPs in one integral ternary complex enables the mild photoinduced formation of Ag nanoparticles. PMID:25690723

Berdnikova, Daria V; Ihmels, Heiko; Schönherr, Holger; Steuber, Marc; Wesner, Daniel

2015-03-11

402

In vivo dynamics of chromatin-associated complex formation in mammalian nucleotide excision repair  

Microsoft Academic Search

Chromatin is the substrate for many processes in the cell nucleus, including transcription, replication, and various DNA repair systems, all of which require the formation of multiprotein machineries on the chromatin fiber. We have analyzed the kinetics of in vivo assembly of the protein complex that is responsible for nucleotide excision repair (NER) in mammalian cells. Assembly is initiated by

M. J. Mone; T. Bernas; C. Dinant; F. A. Goedvree; E. M. M. Manders; M. Volker; A. B. Houtsmuller; J. H. J. Hoeijmakers; W. Vermeulen; Driel van R

2004-01-01

403

Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid  

E-print Network

Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid fluidlike vesicle to adhere to and encapsulate an oppositely charged spherical colloidal particle. The vesicle contains mobile charges that interact with the colloid and among themselves through a screened

Iglic, Ales

404

STUDY USING A THREE-DIMENSIONAL SMOG FORMATION MODEL UNDER CONDITIONS OF COMPLEX FLOW  

EPA Science Inventory

To clarify the photochemical smog formation mechanisms under conditions of complex flow, the SAI Urban Airshed Model was evaluated using a 1981 field observed data base. In the Tokyo Metropolitan Area higher O3 concentrations are usually observed near the shore in the morning. As...