Electron spin relaxation enhancement measurements of interspin distances in human, porcine, and Rhodobacter electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO).

Science.gov (United States)

Fielding, Alistair J; Usselman, Robert J; Watmough, Nicholas; Simkovic, Martin; Frerman, Frank E; Eaton, Gareth R; Eaton, Sandra S

2008-02-01

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S](2+,1+) cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S](+) cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S](+) between 8 and 18K and for semiquinone between 25 and 65K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S](+) were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S](+) and obtain point-dipole interspin distances of 18.6+/-1A for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present.

Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

Directory of Open Access Journals (Sweden)

Mário M. Q. Simões

2018-03-01

Full Text Available Carbene transfer reactions are very important transformations in organic synthesis, allowing the generation of structurally challenging products by catalysed cyclopropanation, cyclopropenation, carbene C-H, N-H, O-H, S-H, and Si-H insertion, and olefination of carbonyl compounds. In particular, chiral and achiral metalloporphyrins have been successfully explored as biomimetic catalysts for these carbene transfer reactions under both homogeneous and heterogeneous conditions. In this work the use of synthetic metalloporphyrins (MPorph, M = Fe, Ru, Os, Co, Rh, Ir, Sn as homogeneous or heterogeneous catalysts for carbene transfer reactions in the last years is reviewed, almost exclusively focused on the literature since the year 2010, except when reference to older publications was deemed to be crucial.

Evaluation of the electron transfer flavoprotein as an antibacterial target in Burkholderia cenocepacia.

Science.gov (United States)

Stietz, Maria S; Lopez, Christina; Osifo, Osasumwen; Tolmasky, Marcelo E; Cardona, Silvia T

2017-10-01

There are hundreds of essential genes in multidrug-resistant bacterial genomes, but only a few of their products are exploited as antibacterial targets. An example is the electron transfer flavoprotein (ETF), which is required for growth and viability in Burkholderia cenocepacia. Here, we evaluated ETF as an antibiotic target for Burkholderia cepacia complex (Bcc). Depletion of the bacterial ETF during infection of Caenorhabditis elegans significantly extended survival of the nematodes, proving that ETF is essential for survival of B. cenocepacia in this host model. In spite of the arrest in respiration in ETF mutants, the inhibition of etf expression did not increase the formation of persister cells, when treated with high doses of ciprofloxacin or meropenem. To test if etf translation could be inhibited by RNA interference, antisense oligonucleotides that target the etfBA operon were synthesized. One antisense oligonucleotide was effective in inhibiting etfB translation in vitro but not in vivo, highlighting the challenge of reduced membrane permeability for the design of drugs against B. cenocepacia. This work contributes to the validation of ETF of B. cenocepacia as a target for antibacterial therapy and demonstrates the utility of a C. elegans liquid killing assay to validate gene essentiality in an in vivo infection model.

The flavoprotein Mcap0476 (RlmFO) catalyzes m5U1939 modification in Mycoplasma capricolum 23S rRNA

DEFF Research Database (Denmark)

Lartigue, Carole; Lebaudy, Anne; Blanchard, Alain

2014-01-01

Efficient protein synthesis in all organisms requires the post-transcriptional methylation of specific ribosomal ribonucleic acid (rRNA) and transfer RNA (tRNA) nucleotides. The methylation reactions are almost invariably catalyzed by enzymes that use S-adenosylmethionine (AdoMet) as the methyl g...... specifically modifies m5U1939 in 23S rRNA, a conserved methylation catalyzed by AdoMet-dependent enzymes in all other characterized bacteria. The Mcap0476 methyltransferase (renamed RlmFO) represents the first folate-dependent flavoprotein seen to modify ribosomal RNA.......Efficient protein synthesis in all organisms requires the post-transcriptional methylation of specific ribosomal ribonucleic acid (rRNA) and transfer RNA (tRNA) nucleotides. The methylation reactions are almost invariably catalyzed by enzymes that use S-adenosylmethionine (AdoMet) as the methyl...... group donor. One noteworthy exception is seen in some bacteria, where the conserved tRNA methylation at m5U54 is added by the enzyme TrmFO using flavin adenine dinucleotide together with N5,N10-methylenetetrahydrofolate as the one-carbon donor. The minimalist bacterium Mycoplasma capricolum possesses...

Electron transfer reactions involving porphyrins and chlorophyll a

International Nuclear Information System (INIS)

Neta, P.; Scherz, A.; Levanon, H.

1979-01-01

Electron transfer reactions involving porphyrins (P) and quinones (Q) have been studied by pulse radiolysis. The porphyrins used were tetraphenylporphyrin (H 2 TPP), its tetracarboxy derivative (H 2 TCPP), the sodium and zinc compounds (Na 2 TPP and ZnTPP), and chlorophyll a (Chl a). These compounds were found to be rapidly reduced by electron transfer from (CH 3 ) 2 CO - . Reduction by (CH 3 ) 2 COH was rapid in aqueous solutions but relatively slow in i-PrOH solutions. Transient spectra of the anion radicals were determined and, in the case of H 2 TCPP - ., a pK = 9.7 was derived for its protonation. Electron-transfer reactions from the anion radical of H 2 TCPP to benzoquinone, duroquinone, 9,10-anthraquinone 2-sulfonate, and methylviologen occur in aqueous solutions with rate constants approx. 10 7 -10 9 M -1 s -1 which depend on the pH and the quinone reduction potential. Reactions of Na 2 TPP - ., ZnTPP - ., and Chl a - . with anthraquinone in basic i-PrOH solutions occur with rate constants approx. 10 9 M -1 s -1 . The spectral changes associated with these electron-transfer reactions as observed over a period of approx. 1 ms indicated, in some cases, the formation of an intermediate complex [P...Q - .]. 8 figures, 2 tables

Impact of mutations on the midpoint potential of the [4Fe-4S]+1,+2 cluster and on catalytic activity in electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO).

Science.gov (United States)

Usselman, Robert J; Fielding, Alistair J; Frerman, Frank E; Watmough, Nicholas J; Eaton, Gareth R; Eaton, Sandra S

2008-01-08

Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is an iron-sulfur flavoprotein that accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the Q-pool. ETF-QO contains a single [4Fe-4S]2+,1+ cluster and one equivalent of FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. Mutations were introduced by site-directed mutagenesis of amino acids in the vicinity of the iron-sulfur cluster of Rhodobacter sphaeroides ETF-QO. Y501 and T525 are equivalent to Y533 and T558 in the porcine ETF-QO. In the porcine protein, these residues are within hydrogen-bonding distance of the Sgamma of the cysteine ligands to the iron-sulfur cluster. Y501F, T525A, and Y501F/T525A substitutions were made to determine the effects on midpoint potential, activity, and EPR spectral properties of the cluster. The integrity of the mutated proteins was confirmed by optical spectra, EPR g-values, and spin-lattice relaxation rates, and the cluster to flavin point-dipole distance was determined by relaxation enhancement. Potentiometric titrations were monitored by changes in the CW EPR signals of the cluster and semiquinone. Single mutations decreased the midpoint potentials of the iron-sulfur cluster from +37 mV for wild type to -60 mV for Y501F and T525A and to -128 mV for Y501F/T525A. Lowering the midpoint potential resulted in a decrease in steady-state ubiquinone reductase activity and in ETF semiquinone disproportionation. The decrease in activity demonstrates that reduction of the iron-sulfur cluster is required for activity. There was no detectable effect of the mutations on the flavin midpoint potentials.

Identification of the electron transfer flavoprotein as an upregulated enzyme in the benzoate utilization of Desulfotignum balticum.

Science.gov (United States)

Habe, Hiroshi; Kobuna, Akinori; Hosoda, Akifumi; Kosaka, Tomoyuki; Endoh, Takayuki; Tamura, Hiroto; Yamane, Hisakazu; Nojiri, Hideaki; Omori, Toshio; Watanabe, Kazuya

2009-07-01

Desulfotignum balticum utilizes benzoate coupled to sulfate reduction. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) analysis was conducted to detect proteins that increased more after growth on benzoate than on butyrate. A comparison of proteins on 2D gels showed that at least six proteins were expressed. The N-terminal sequences of three proteins exhibited significant identities with the alpha and beta subunits of electron transfer flavoprotein (ETF) from anaerobic aromatic-degraders. By sequence analysis of the fosmid clone insert (37,590 bp) containing the genes encoding the ETF subunits, we identified three genes, whose deduced amino acid sequences showed 58%, 74%, and 62% identity with those of Gmet_2267 (Fe-S oxidoreductase), Gmet_2266 (ETF beta subunit), and Gmet_2265 (ETF alpha subunit) respectively, which exist within the 300-kb genomic island of aromatic-degradation genes from Geobacter metallireducens GS-15. The genes encoding ETF subunits found in this study were upregulated in benzoate utilization.

Impact of Mutations on the Midpoint Potential of the [4Fe-4S]+1,+2 Cluster and on Catalytic Activity in Electron Transfer Flavoprotein-ubiquinone Oxidoreductase (ETF-QO)†

Science.gov (United States)

Usselman, Robert J.; Fielding, Alistair J.; Frerman, Frank E.; Watmough, Nicholas J.; Eaton, Gareth R.; Eaton, Sandra S.

2011-01-01

Electron transfer flavoprotein - ubiquinone oxidoreductase (ETF-QO) is an iron-sulfur flavoprotein that accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the Q-pool. ETF-QO contains a single [4Fe-4S]2+,1+ cluster and one equivalent of FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. Mutations were introduced by site-directed mutagenesis of amino acids in the vicinity of the iron-sulfur cluster of Rhodobacter sphaeroides ETF-QO. Y501 and T525 are equivalent to Y533 and T558 in the porcine ETF-QO. In the porcine protein, these residues are within hydrogen bonding distance of the Sγ of the cysteine ligands to the iron-sulfur cluster. Y501F, T525A, and Y501F/T525A substitutions were made to determine the effects on midpoint potential, activity, and EPR spectral properties of the cluster. The integrity of the mutated proteins was confirmed by optical spectra, EPR g-values, and spin-lattice relaxation rates, and the cluster to flavin point-dipole distance was determined by relaxation enhancement. Potentiometric titrations were monitored by changes in the CW EPR signals of the cluster and semiquinone. Single mutations decreased the mid-point potentials of the iron-sulfur cluster from +37 mV for wild type to −60 mV for Y501F and T525A and to −128 mV for Y501F/T525A. Lowering the midpoint potential resulted in a decrease in steady-state ubiquinone reductase activity and in ETF semiquinone disproportionation. The decrease in activity demonstrates that reduction of the iron-sulfur cluster is required for activity. There was no detectable effect of the mutations on the flavin midpoint potentials. PMID:18069858

Complexation Key to a pH Locked Redox Reaction

Science.gov (United States)

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

2016-01-01

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

Quantitation of immunoadsorbed flavoprotein oxidases by luminol-mediated chemiluminescence.

Science.gov (United States)

Hinkkanen, A; Maly, F E; Decker, K

1983-04-01

The detection of the flavoenzymes 6-hydroxy-L-nicotine oxidase and 6-hydroxy-D-nicotine oxidase at the sub-femtomol level was achieved by coupling the reaction of the immunoadsorbed proteins to the peroxidase-catalysed oxidation of luminol. The H2O2-producing oxidases retained their full activity when bound to the respective immobilized antibodies. This fact allowed the concentration of the enzymes from very dilute solutions and the quantitative assay of their activities in the microU range. Due to strict stereoselectivity and the absence of immunological cross-reactivity, the two flavoproteins could be determined in the same solution. This method was used to measure the 6-hydroxy-D-nicotine oxidase and 6-hydroxy-L-nicotine oxidase activities in Escherichia coli RR1 and different Arthrobacter strains cultured under non-inducing conditions. The same activity ratio of 6-hydroxy-L-nicotine oxidase/6-hydroxy-D-nicotine oxidase as in D L-nicotine-induced cells of A. oxidans was observed in non-induced wild type and in riboflavin-requiring (rf-) mutant cells of this aerob.

Electron transfer reactions

CERN Document Server

Cannon, R D

2013-01-01

Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

5,5'-Dithiobis-(2-nitrobenzoic acid) as a probe for a non-essential cysteine residue at the medium chain acyl-coenzyme A dehydrogenase binding site of the human 'electron transferring flavoprotein' (ETF).

Science.gov (United States)

Parker, A; Engel, P C

1999-01-01

Human 'electron transferring flavoprotein' (ETF) was inactivated by the thiol-specific reagent 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB). The kinetic profile showed the reaction followed pseudo-first-order kinetics during the initial phase of inactivation. Monitoring the release of 5-thio-2-nitrobenzoate (TNB) showed that modification of 1 cysteine residue was responsible for the loss of activity. The inactivation of ETF by DTNB could be reversed upon incubation with thiol-containing reagents. The loss of activity was prevented by the inclusion of medium chain acyl-CoA dehydrogenase (MCAD) and octanoyl-CoA. Cyanolysis of the DTNB modified-ETF with KCN led to the release of TNB accompanied presumably by the formation of the thio-cyano enzyme and with almost full recovery of activity. Conservation studies and the lack of 100% inactivation, however, suggested that this cysteine residue is not essential for the interaction with MCAD.

Temperature-dependent kinetics of charge transfer, hydrogen-atom transfer, and hydrogen-atom expulsion in the reaction of CO+ with CH4 and CD4.

Science.gov (United States)

Melko, Joshua J; Ard, Shaun G; Johnson, Ryan S; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

2014-09-18

We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer.

Development of Novel Electrode Materials for the Electrocatalysis of Oxygen-Transfer and Hydrogen-Transfer Reactions

Energy Technology Data Exchange (ETDEWEB)

Simpson, Brett Kimball [Iowa State Univ., Ames, IA (United States)

2002-01-01

Throughout this thesis, the fundamental aspects involved in the electrocatalysis of anodic O-transfer reactions and cathodic H-transfer reactions have been studied. The investigation into anodic O-transfer reactions at undoped and Fe(III)[doped MnO₂ films] revealed that MnO₂ film electrodes prepared by a cycling voltammetry deposition show improved response for DMSO oxidation at the film electrodes vs. the Au substrate. Doping of the MnO₂ films with Fe(III) further enhanced electrode activity. Reasons for this increase are believed to involve the adsorption of DMSO by the Fe(III) sites. The investigation into anodic O-transfer reactions at undoped and Fe(III)-doped RuO₂ films showed that the Fe(III)-doped RuO₂-film electrodes are applicable for anodic detection of sulfur compounds. The Fe(III) sites in the Fe-RuO₂ films are speculated to act as adsorption sites for the sulfur species while the Ru(IV) sites function for anodic discharge of H₂O to generate the adsorbed OH species. The investigation into cathodic H-transfer reactions, specifically nitrate reduction, at various pure metals and their alloys demonstrated that the incorporation of metals into alloy materials can create a material that exhibits bifunctional properties for the various steps involved in the overall nitrate reduction reaction. The Sb₁₀Sn₂₀Ti₇₀, Cu₆₃Ni₃₇ and Cu₂₅Ni₇₅ alloy electrodes exhibited improved activity for nitrate reduction as compared to their pure component metals. The Cu₆₃Ni₃₇ alloy displayed the highest activity for nitrate reduction. The final investigation was a detailed study of the electrocatalytic activity of cathodic H-transfer reactions (nitrate reduction) at various compositions of Cu-Ni alloy electrodes. Voltammetric response for NO₃^- at the Cu-Ni alloy electrode is superior to

Nonperfect synchronization of bond-forming and bond-rupturing processes in the reaction H + H2 → H2 + H

International Nuclear Information System (INIS)

Chandra, A.K.; Rao, V.S.

1996-01-01

The simplest prototypical hydrogen transfer reaction, i.e., H + H 2 → H 2 + H, is studied by the quantum-mechanical ab initio methods. Results reveal that during this reaction free valence which almost equals the square of the spin density develops on the migrating hydrogen atom. Bond orders are calculated using Mayer's formalism. Both the variations of bond orders and bond lengths along the reaction path are examined. This analysis reveals that the bond formation and bond cleavage processes in this reaction are not perfectly synchronous. The bond clevage process is slightly more advanced on the reaction path. 38 refs., 6 figs., 2 tabs

The (3He,α) reaction mechanism. A study of the angular momentum transfer

International Nuclear Information System (INIS)

Guttormsen, M.; Bergholt, L.; Ingebretsen, F.; Loevhoeiden, G.; Messelt, S.; Rekstad, J.; Tveter, T.S.; Helstrup, H.; Thorsteinsen, T.F.

1994-01-01

The γ-rays emitted after the 163 Dy( 3 He,αxn) reactions at E( 3 He) = 45 MeV have been measured. The transferred angular momentum in the reaction is deduced from the side-feeding γ-intensities of the ground bands in the residual 162-x Dy isotopes. With decreasing α-energy the average spin transfer increases from similar 5h to similar 11h. The ( 3 He,α) reaction at these energies is dominated by direct processes. Even at the highest spin transfer the contribution from the compound reaction channel is negligible. ((orig.))

Conformational dependence of a protein kinase phosphate transfer reaction

Science.gov (United States)

Labute, Montiago; Henkelman, Graeme; Tung, Chang-Shung; Fenimore, Paul; McMahon, Ben

2007-03-01

Atomic motions and energetics for a phosphate transfer reaction catalyzed by the cAMP-dependent protein kinase have been calculated using plane-wave density functional theory, starting from structures of proteins crystallized in both the reactant conformation (RC) and the transition-state conformation (TC). In TC, we calculate that the reactants and products are nearly isoenergetic with a 20-kJ/mol barrier, whereas phosphate transfer is unfavorable by 120 kJ/mol in the RC, with an even higher barrier. Our results demonstrate that the phosphate transfer reaction occurs rapidly and reversibly in a particular conformation of the protein, and that the reaction can be gated by changes of a few tenths of an angstrom in the catalytic site [1]. [1] G.H. Henkelman, M.X. LaBute, C.-S. Tung, P.W. Fenimore, B.H. McMahon, Proc. Natl. Acad. Sci. USA vol. 102, no. 43:15347-15351 (2005).

Characterization of Two VAO-Type Flavoprotein Oxidases from Myceliophthora thermophila

Directory of Open Access Journals (Sweden)

Alessandro R. Ferrari

2018-01-01

Full Text Available The VAO flavoprotein family consists mostly of oxidoreductases harboring a covalently linked flavin cofactor. The linkage can be either monocovalent at position 8 with a histidine or tyrosine or bicovalent at position 8 with a histidine and at position 6 with a cysteine. Bicovalently bound flavoproteins show a preference for bulkier substrates such as oligosaccharides or secondary metabolites. The genome of the thermophilic fungus Myceliophthora thermophila C1 was found to be rich in genes encoding putative covalent VAO-type flavoproteins. Enzymes from this fungus have the advantage of being rather thermostable and homologous overexpression in M. thermophila C1 is feasible. Recently we discovered a new and VAO-type carbohydrate oxidase from this fungus: xylooligosaccharide oxidase. In this study, two other putative VAO-type oxidases, protein sequence XP_003663615 (MtVAO615 and XP_003665713 (MtVAO713, were expressed in M. thermophila C1, purified and characterized. Enzyme MtVAO615 was found to contain a bicovalently bound FAD, while enzyme MtVAO713 contained a monocovalent histidyl-bound FAD. The crystal structures of both proteins were obtained which revealed atypical active site architectures. It could be experimentally verified that both proteins, when reduced, rapidly react with molecular oxygen, a hallmark of flavoprotein oxidases. A large panel of alcohols, including carbohydrates, steroids and secondary alcohols were tested as potential substrates. For enzyme MtVAO713 low oxidase activity was discovered towards ricinoleic acid.

Polarization transfer in (p,n) reactions at 495 MeV

International Nuclear Information System (INIS)

Taddeucci, T.N.

1991-01-01

Polarization transfer observables have been measured with the NTOF facility at LAMPF for (p,n) reactions at 495 MeV. Measurements of the longitudinal polarization transfer parameter D LL for transitions to discrete states at 0 degrees show convincing evidence for tensor interaction effects. Complete sets of polarization transfer observables have been measured for quasifree (p,n) reactions on 2 H, 12 C, 40 Ca at a scattering angle of 18 degrees. These measurements show no evidence for an enhancement in the isovector spin longitudinal response. 19 refs., 10 figs

Heavy ion transfer reactions

International Nuclear Information System (INIS)

Weisser, D.C.

1977-06-01

To complement discussions on the role of γ rays in heavy ion induced reactions, the author discusses the role played by particle detection. Transfer reactions are part of this subject and are among those in which one infers the properties of the residual nucleus in a reaction by observing the emerging light nucleus. Inelastic scattering ought not be excluded from this subject, although no particles are transferred, because of the role it plays in multistep reactions and in fixing O.M. parameters describing the entrance channel of the reaction. Heavy ion transfer reaction studies have been under study for some years and yet this research is still in its infancy. The experimental techniques are difficult and the demands on theory rigorous. One of the main products of heavy ion research has been the thrust to re-examine the assumptions of reaction theory and now include many effects neglected for light ion analysis. This research has spurred the addition of multistep processes to simple direct processes and coupled channel calculations. (J.R.)

A quantum-rovibrational-state-selected study of the proton-transfer reaction H2+(X2Σ: v+ = 1-3; N+ = 0-3) + Ne → NeH+ + H using the pulsed field ionization-photoion method: observation of the rotational effect near the reaction threshold.

Science.gov (United States)

Xiong, Bo; Chang, Yih-Chung; Ng, Cheuk-Yiu

2017-07-19

Using the sequential electric field pulsing scheme for vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection, we have successfully prepared H 2 + (X 2 Σ: v + = 1-3; N + = 0-5) ions in the form of an ion beam in single quantum-rovibrational-states with high purity, high intensity, and narrow laboratory kinetic energy spread (ΔE lab ≈ 0.05 eV). This VUV-PFI-PI ion source, when coupled with the double-quadrupole double-octupole ion-molecule reaction apparatus, has made possible a systematic examination of the vibrational- as well as rotational-state effects on the proton transfer reaction of H 2 + (X 2 Σ: v + ; N + ) + Ne. Here, we present the integral cross sections [σ(v + ; N + )'s] for the H 2 + (v + = 1-3; N + = 0-3) + Ne → NeH + + H reaction observed in the center-of-mass kinetic energy (E cm ) range of 0.05-2.00 eV. The σ(v + = 1, N + = 1) exhibits a distinct E cm onset, which is found to agree with the endothermicity of 0.27 eV for the proton transfer process after taking into account of experimental uncertainties. Strong v + -vibrational enhancements are observed for σ(v + = 1-3, N + ) in the E cm range of 0.05-2.00 eV. While rotational excitations appear to have little effect on σ(v + = 3, N + ), a careful search leads to the observation of moderate N + -rotational enhancements at v + = 2: σ(v + = 2; N + = 0) quantum dynamics predictions. We hope that these new experimental results would further motivate more rigorous theoretical calculations on the dynamics of this prototypical ion-molecule reaction.

Studies on electron transfer reactions of Keggin-type mixed ...

Indian Academy of Sciences (India)

Administrator

(PV2) in aqueous phosphate buffer of pH 6 at ambient temperature. Electrochemical and optical studies show that the stoichiometry of the reaction is 1: 2 (NADH : HPA). EPR and optical studies show that HPA act as one electron acceptor and the products of electron transfer reactions are one elec- tron reduced heteropoly ...

Isotope effects for base-promoted, gas-phase proton transfer reactions

International Nuclear Information System (INIS)

Grabowski, J.J.; Cheng, Xueheng

1991-01-01

Proton transfer reactions are among the most basic, the most common and the most important of chemical transformations; despite their apparent simplicity, much is unknown about this most fundamental of all chemical processes. Active interest in understanding the underlying principles of organic proton transfer reactions continues because of efforts being made to develop the theory of elementary chemical processes, because of the resurgence of interest in mechanistic organic chemistry and because of the resurgence of interest in mechanistic organic chemistry processes, because of the resurgence of interest in mechanistic organic chemistry and because of the dynamic role played by proton transfers in biochemical transformations. As organic chemists, the authors have used the flowing afterglow technique to gain an appreciation of the fundamental issues involved in reaction mechanisms by examining such processes in a solvent-free environment under thermally-equilibrated (300 K) conditions. Recent characterization of the facile production of both acetate and the monoenolate anion from the interaction of hydroxide or fluoride with acetic acid reinforces the idea that much yet must be learned about proton transfers/proton abstractions in general. Earlier work by Riveros and co-workers on competitive H vs D abstraction from α-d 1 -toluenes and by Noest and Nibbering on competitive H vs D abstraction from α,α,α-d 3 -acetone, in combination with the acetic acid results, challenged the author's to assemble a comprehensive picture of the competitive nature of proton transfer reactions for anionic base-promoted processes

Temperature dependence of third order ion molecule reactions. The reaction H+3 + 2H2 = H+5 + H2

International Nuclear Information System (INIS)

Hiraoka, K.; Kebarle, P.

1975-01-01

The rate constants k 1 for Reaction (1): H + 3 +2H 2 = H + 5 +H 2 were measured in the temperature range 100--300 degreeK. The temperature dependence of k 1 has the form k 1 proportionalT - /subn/, where n=2.3. Pierce and Porter have reported a much stronger negative temperature dependence with n=4.6. The difference arises from a determination of k 1 at 300 degreeK obtained by Arifov and used by Porter. The present k 1 (300 degreeK) =9times10 -30 (cm 6 molecules -2 center-dotsec -1 ). This is more than an order of magnitude larger than the Arifov value. The temperature dependence of third body dependent association reactions like (1) is examined on the basis of the energy transfer theory and the recently proposed trimolecular complex transition state theory by Meot-Ner, Solomon, Field, and Gershinowitz. The temperature dependence of the rate constant for the reverse reaction (-1) is obtained from k 1 and the previously determined temperature dependence of the equilibria (1). k/sub -//sub 1/ gives a good straight line Arrhenius plot leading to k/sub -//sub 1/ =8.7times10 -6 exp(-8.4/RT) cm 3 molecules -1 center-dotsec -1 . The activation energy is in kcal/mole. The preexponential factor is much larger than the rate constant for Langevin collisions. This is typical for pyrolysis of ions involving second order activation

Binding of the human "electron transferring flavoprotein" (ETF) to the medium chain acyl-CoA dehydrogenase (MCAD) involves an arginine and histidine residue.

Science.gov (United States)

Parker, Antony R

2003-10-01

The interaction between the "electron transferring flavoprotein" (ETF) and medium chain acyl-CoA dehydrogenase (MCAD) enables successful flavin to flavin electron transfer, crucial for the beta-oxidation of fatty acids. The exact biochemical determinants for ETF binding to MCAD are unknown. Here we show that binding of human ETF, to MCAD, was inhibited by 2,3-butanedione and diethylpyrocarbonate (DEPC) and reversed by incubation with free arginine and hydroxylamine respectively. Spectral analyses of native ETF vs modified ETF suggested that flavin binding was not affected and that the loss of ETF activity with MCAD involved modification of one ETF arginine residue and one ETF histidine residue respectively. MCAD and octanoyl-CoA protected ETF against inactivation by both 2,3-butanedione and DEPC indicating that the arginine and histidine residues are present in or around the MCAD binding site. Comparison of exposed arginine and histidine residues among different ETF species, however, indicates that arginine residues are highly conserved but that histidine residues are not. These results lead us to conclude that this single arginine residue is essential for the binding of ETF to MCAD, but that the single histidine residue, although involved, is not.

Investigation of transition metal-catalyzed nitrene transfer reactions in water.

Science.gov (United States)

Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

2018-04-11

Transition metal-catalyzed nitrene transfer is a powerful method for incorporating new CN bonds into relatively unfunctionalized scaffolds. In this communication, we report the first examples of site- and chemoselective CH bond amination reactions in aqueous media. The unexpected ability to employ water as the solvent in these reactions is advantageous in that it eliminates toxic solvent use and enables reactions to be run at increased concentrations with lower oxidant loadings. Using water as the reaction medium has potential to expand the scope of nitrene transfer to encompass a variety of biomolecules and highly polar substrates, as well as enable pH control over the site-selectivity of CH bond amination. Copyright © 2018 Elsevier Ltd. All rights reserved.

Regulatory mechanism of the flavoprotein Tah18-dependent nitric oxide synthesis and cell death in yeast.

Science.gov (United States)

Yoshikawa, Yuki; Nasuno, Ryo; Kawahara, Nobuhiro; Nishimura, Akira; Watanabe, Daisuke; Takagi, Hiroshi

2016-07-01

Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. The regulatory mechanism of NO generation in unicellular eukaryotic yeast cells is poorly understood due to the lack of mammalian and bacterial NO synthase (NOS) orthologues, even though yeast produces NO under oxidative stress conditions. Recently, we reported that the flavoprotein Tah18, which was previously shown to transfer electrons to the iron-sulfur cluster protein Dre2, is involved in NOS-like activity in the yeast Saccharomyces cerevisiae. On the other hand, Tah18 was reported to promote apoptotic cell death after exposure to hydrogen peroxide (H2O2). Here, we showed that NOS-like activity requiring Tah18 induced cell death upon treatment with H2O2. Our experimental results also indicate that Tah18-dependent NO production and cell death are suppressed by enhancement of the interaction between Tah18 and its molecular partner Dre2. Our findings indicate that the Tah18-Dre2 complex regulates cell death as a molecular switch via Tah18-dependent NOS-like activity in response to environmental changes. Copyright © 2016 Elsevier Inc. All rights reserved.

Hydropersulfides: H-Atom Transfer Agents Par Excellence.

Science.gov (United States)

Chauvin, Jean-Philippe R; Griesser, Markus; Pratt, Derek A

2017-05-10

Hydropersulfides (RSSH) are formed endogenously via the reaction of the gaseous biotransmitter hydrogen sulfide (H 2 S) and disulfides (RSSR) and/or sulfenic acids (RSOH). RSSH have been investigated for their ability to store H 2 S in vivo and as a line of defense against oxidative stress, from which it is clear that RSSH are much more reactive to two-electron oxidants than thiols. Herein we describe the results of our investigations into the H-atom transfer chemistry of RSSH, contrasting it with the well-known H-atom transfer chemistry of thiols. In fact, RSSH are excellent H-atom donors to alkyl (k ∼ 5 × 10 8 M -1 s -1 ), alkoxyl (k ∼ 1 × 10 9 M -1 s -1 ), peroxyl (k ∼ 2 × 10 6 M -1 s -1 ), and thiyl (k > 1 × 10 10 M -1 s -1 ) radicals, besting thiols by as little as 1 order and as much as 4 orders of magnitude. The inherently high reactivity of RSSH to H-atom transfer is based largely on thermodynamic factors; the weak RSS-H bond dissociation enthalpy (∼70 kcal/mol) and the associated high stability of the perthiyl radical make the foregoing reactions exothermic by 15-34 kcal/mol. Of particular relevance in the context of oxidative stress is the reactivity of RSSH to peroxyl radicals, where favorable thermodynamics are bolstered by a secondary orbital interaction in the transition state of the formal H-atom transfer that drives the inherent reactivity of RSSH to match that of α-tocopherol (α-TOH), nature's premier radical-trapping antioxidant. Significantly, the reactivity of RSSH eclipses that of α-TOH in H-bond-accepting media because of their low H-bond acidity (α 2 H ∼ 0.1). This affords RSSH a unique versatility compared to other highly reactive radical-trapping antioxidants (e.g., phenols, diarylamines, hydroxylamines, sulfenic acids), which tend to have high H-bond acidities. Moreover, the perthiyl radicals that result are highly persistent under autoxidation conditions and undergo very rapid dimerization (k = 5 × 10 9 M -1 s -1 ) in

Enantioselective H-atom transfer reaction: a strategy to synthesize formaldehyde aldol products.

Science.gov (United States)

Sibi, Mukund P; Patil, Kalyani

2005-04-14

[reaction: see text] Enantioselective radical alkylation of Baylis-Hillman adducts furnished aldol products in good yield and selectivity. The results illustrate that the selectivity in the hydrogen atom transfer is dependent on the size of the ester substituent, with smaller substituents providing better enantioselectivity.

Theoretical characterizations of novel C2H5O+ reactions

Science.gov (United States)

Hudson, Charles E.; McAdoo, David J.

2004-03-01

Assorted reactions of C2H5O+ isomers are characterized by theory, including tracing their courses by means of intrinsic reaction coordinate computations. We establish that CH3CH=OH+ eliminates methane by transferring H from oxygen to a methyl hydrogen and then to the CC bond to produce CHO++CH4. This adds to the limited knowledge of the involvement of hypervalent structures in the reactions of cations in the gas phase. Second, we characterized the course of CH3CH=OH+-->H3O++HC[triple bond; length as m-dash]CH. In this dissociation, H first migrates from the methyl to the oxygen to give O-protonated vinyl alcohol, a stable intermediate. Then the H2O swings outward to over the middle of the CC bond while one of the two hydrogens on the non-O-bearing carbon revolves to between the oxygen and the two carbons, leading to formation of a [H3O+ HC[triple bond; length as m-dash]CH] complex. This complex contains sufficient energy to dissociate its partners because a high barrier is crossed in its formation. Third, we found that methane elimination from CH3O+=CH2 involves stretching of the CH3---O bond and then rotation of the methyl so that a methyl hydrogen is pointed directly toward the oxygen. This reaction is completed by further rotation of the methyl to abstract a methylene hydrogen to the opposite side of the methyl from that initially bonded to oxygen. This clearly establishes that this dissociation takes place through an ion-neutral complex. Each of the reaction coordinates for the three preceding reactions traverses a novel bonding stage involving H, evidence that such are not unusual in gas phase ion chemistry. Finally, we showed that in the rearrangement CH3O+=CH2-->CH2=O+CH3, before Ht is transferred CH2 rotates around the C=C bond from being in the skeletal plane to being perpendicular to it, and Ht remains in the skeletal plane throughout its transfer. This pathway appears to balance avoiding an orbital symmetry-forbidden suprafacial transition state with

Study of charge transfer reactions in a microbial fuel cell

Energy Technology Data Exchange (ETDEWEB)

Martin, E.; Savadogo, O. [Ecole Polytechnique, Montreal, PQ (Canada). Dept. de Genie Chimique; National Research Council of Canada, Montreal, PQ (Canada). Biotechnology Research Inst.; Tartakovsky, B. [National Research Council of Canada, Montreal, PQ (Canada). Biotechnology Research Inst.

2008-07-01

Electron transfer reactions in a microbial fuel cell (MFC) were evaluated. The MFC was inoculated with anaerobic mesophilic sludge and operated with carbon felt, carbon cloth, and platinum (Pt) coated carbon cloth. The MFC was then fed with either acetate or glucose as a source of fuel and operated at a temperature of 25 degrees C and a pH of 7. Scanning electron microscopy (SEM) micrographs demonstrated that the micro-organisms colonized the anodes. Cyclic voltammetry and polarization tests were conducted using different fractions of the anodophilic biofilm in order to determine charge transfer routes. The study characterized the electron transfer mechanisms used by the exoelectrogenic micro-organisms to produce electricity. It was concluded that further research is needed to characterize reaction transfer routes. 2 refs., 1 fig.

Nucleon transfer reactions with radioactive beams

Science.gov (United States)

Wimmer, K.

2018-03-01

Transfer reactions are a valuable tool to study the single-particle structure of nuclei. At radioactive beam facilities transfer reactions have to be performed in inverse kinematics. This creates a number of experimental challenges, but it also has some advantages over normal kinematics measurements. An overview of the experimental and theoretical methods for transfer reactions, especially with radioactive beams, is presented. Recent experimental results and highlights on shell evolution in exotic nuclei are discussed.

A polymorphic variant in the human electron transfer flavoprotein alpha-chain (alpha-T171) displays decreased thermal stability and is overrepresented in very-long-chain acyl-CoA dehydrogenase-deficient patients with mild childhood presentation

DEFF Research Database (Denmark)

Bross, P; Pedersen, P; Nyholm, M

1999-01-01

The consequences of two amino acid polymorphisms of human electron transfer flavoprotein (alpha-T/I171 in the alpha-subunit and beta-M/T154 in the beta-subunit) on the thermal stability of the enzyme are described. The alpha-T171 variant displayed a significantly decreased thermal stability, wher....... This is compatible with a negative modulating effect of the less-stable alpha-T171 ETF variant in this group of VLCAD patients that harbor missense mutations in at least one allele and therefore potentially display residual levels of VLCAD enzyme activity. Udgivelsesdato: 1999-Jun...

Polarization transfer in the 3H(rvec p,rvec n)3He reaction and the 0- level in 4He

International Nuclear Information System (INIS)

Walston, J.R.; Gould, C.R.; Haase, D.G.; Raichle, B.W.; Seely, M.L.; Walston, J.R.; Keith, C.D.; Gould, C.R.; Haase, D.G.; Raichle, B.W.; Seely, M.L.; Tornow, W.; Wilburn, W.S.; Keith, C.D.; Tornow, W.; Wilburn, W.S.; Hoffmann, G.W.; Penttilae, S.I.

1998-01-01

Longitudinal polarization-transfer coefficients for the 3 H(rvec p,rvec n) 3 He reaction have been measured at zero degrees for proton energies of 1.3 endash 2.8 MeV. The results show a striking resonance behavior for energies corresponding to excitation of the 0 - level in 4 He at 21.0 MeV. In agreement with R-matrix calculations, the value approaches unity at 1.52 MeV, the peak of the resonance. Near this same energy, at 1.62 MeV, the transverse polarization-transfer coefficient was measured to be consistent with zero. copyright 1998 The American Physical Society

Probing the semi-magicity of $^{68}$Ni via the $^{3}$H($^{66}$Ni,$^{68}$Ni)p two-neutron transfer reaction in inverse kinematics

CERN Multimedia

Reiter, P; Blazhev, A A; Kruecken, R; Franchoo, S; Mertzimekis, T; Darby, I G; Van de walle, J; Raabe, R; Elseviers, J; Gernhaeuser, R A; Sorlin, O H; Georgiev, G P; Bree, N C F; Habs, D; Chapman, R; Gaudefroy, L; Diriken, J V J; Jenkins, D G; Kroell, T; Axiotis, M; Huyse, M L; Patronis, N

We propose to perform the two-neutron transfer reaction $^{3}$H($^{66}$Ni, $^{68}$Ni)$p$ using the ISOLDE radioactive ion beam at 2.7 $A$ MeV and the MINIBALL + T-REX setup to characterize the 0$^{+}$ and 2$^{+}$ states in $^{68}$Ni.

Electron transfer reactions of macrocyclic compounds of cobalt

Energy Technology Data Exchange (ETDEWEB)

Heckman, R.A.

1978-08-01

The kinetics and mechanisms of reduction of H/sub 2/O/sub 2/, Br/sub 2/, and I/sub 2/ by various macrocyclic tetraaza complexes of cobalt(II), including Vitamin B/sub 12r/, were studied. The synthetic macrocycles studied were all 14-membered rings which varied in the degree of unsaturation,substitution of methyl groups on the periphery of the ring, and substitution within the ring itself. Scavenging experiments demonstrated that the reductions of H/sub 2/O/sub 2/ produce free hydroxyl radicals only in the case of Co((14)ane)/sup 2 +/ but with none of the others. In the latter instances apparently H/sub 2/O/sub 2/ simultaneously oxidizes the metal center and the ligand. The reductions of Br/sub 2/ and I/sub 2/ produce an aquohalocobalt(III) product for all reductants (except B/sub 12r/ + Br/sub 2/, which was complicated by bromination of the corrin ring). The mechanism of halogen reduction was found to involve rate-limiting inner-sphere electron transfer from cobalt to halogen to produce a dihalide anion coordinated to the cobalt center. This intermediate subsequently decomposes in rapid reactions to halocobalt(III) and halogen atom species or reacts with another cobalt(II) center to give two molecules of halocobalt(III). The reductions of halomethylcobaloximes and related compounds and diamminecobaloxime by Cr/sup 2 +/ were also studied. The reaction was found to be biphasic in all cases with the reaction products being halomethane (for the halomethylcobaloximes), Co/sup 2 +/ (in less than 100 percent yield), a Cr(III)-dimethylglyoxime species, a small amount of free dmgH/sub 2/, and a highly-charged species containing both cobalt and chromium. The first-stage reaction occurs with a stoichiometry of 1:1 producing an intermediate with an absorption maximum at 460 nm for all starting reagents. The results were interpreted in terms of inner-sphere coordination of the cobaloxime to the Cr(II) and electron transfer through the oxime N-O bond.

Hydrogen transfer reactions of interstellar Complex Organic Molecules

Science.gov (United States)

Álvarez-Barcia, S.; Russ, P.; Kästner, J.; Lamberts, T.

2018-06-01

Radical recombination has been proposed to lead to the formation of complex organic molecules (COMs) in CO-rich ices in the early stages of star formation. These COMs can then undergo hydrogen addition and abstraction reactions leading to a higher or lower degree of saturation. Here, we have studied 14 hydrogen transfer reactions for the molecules glyoxal, glycoaldehyde, ethylene glycol, and methylformate and an additional three reactions where CHnO fragments are involved. Over-the-barrier reactions are possible only if tunneling is invoked in the description at low temperature. Therefore the rate constants for the studied reactions are calculated using instanton theory that takes quantum effects into account inherently. The reactions were characterized in the gas phase, but this is expected to yield meaningful results for CO-rich ices due to the minimal alteration of reaction landscapes by the CO molecules. We found that rate constants should not be extrapolated based on the height of the barrier alone, since the shape of the barrier plays an increasingly larger role at decreasing temperature. It is neither possible to predict rate constants based only on considering the type of reaction, the specific reactants and functional groups play a crucial role. Within a single molecule, though, hydrogen abstraction from an aldehyde group seems to be always faster than hydrogen addition to the same carbon atom. Reactions that involve heavy-atom tunneling, e.g., breaking or forming a C-C or C-O bond, have rate constants that are much lower than those where H transfer is involved.

A single arginine residue is required for the interaction of the electron transferring flavoprotein (ETF) with three of its dehydrogenase partners.

Science.gov (United States)

Parker, Antony R

2003-12-01

The interaction of several dehydrogenases with the electron transferring flavoprotein (ETF) is a crucial step required for the successful transfer of electrons into the electron transport chain. The exact determinants regarding the interaction of ETF with its dehydrogenase partners are still unknown. Chemical modification of ETF with arginine-specific reagents resulted in the loss, to varying degrees, of activity with medium chain acyl-coenzyme A dehydrogenase (MCAD). The kinetic profiles showed the inactivations followed pseudo-first-order kinetics for all reagents used. For activity with MCAD, maximum inactivation of ETF was accomplished by 2,3-butanedione (4% residual activity after 120 min) and it was shown that modification of one arginine residue was responsible for the inactivation. Almost 100% restoration of this ETF activity was achieved upon incubation with free arginine. However, the same 2,3-butanedione modified ETF only possessed decreased activity with dimethylglycine-(DMGDH, 44%) and sarcosine- (SDH, 27%) dehydrogenases unlike the abolition with MCAD. Full protection of ETF from arginine modification by 2,3-butanedione was achieved using substrate-protected DMGDH, MCAD and SDH respectively. Cross-protection studies of ETF with the three dehydrogenases implied use of the same single arginine residue in the binding of all three dehydrogenases. These results lead us to conclude that this single arginine residue is essential in the binding of the ETF to MCAD, but only contributes partially to the binding of ETF to SDH and DMGDH and thus, the determinants of the dehydrogenase binding sites overlap but are not identical.

Electron transfer reactions of metal complexes in solution

International Nuclear Information System (INIS)

Sutin, N.

1977-01-01

A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

Selectivity in heavy ion transfer reactions

International Nuclear Information System (INIS)

Boucenna, A.

1989-01-01

One-two-and three-nucleon stripping reactions induced by 480 MeV 12 C and by 793 MeV 16 O have been studied on 12 C, 16 O, 28 Si, 40 Ca, and 54 Fe targets. Discrete levels are fed with cross sections up to 1 mb/sr for d-transfer reactions and one and two orders of magnitude less for 2p- and 3 He-transfers, respectively. These reactions are governed by two selection rules contained in the semi-classical model of Brink: i) Large orbital final momentum states are selectively populated and ii) The most highly populated states correspond to no-flip transitions. Two-proton transfer reactions induced by 112 MeV 12 C on even Ni and Zn isotopes are found to be less selective than two-neutron transfer reactions induced by the same projectile on the same targets in a similar incident energy range. The additional collective aspects observed in the two-proton transfers are examined in view of a semiphenomenological model of two quasi-particles coupled to a triaxial asymmetric rotor. The energy of excited states is well reproduced by simple shell model calculations. Such estimates are useful in proposing spins of newly observed states, especially as the shapes of the measured angular distributions are independant of the final spin of the residual nucleus. The experimental results of two-proton and two-neutron stripping reactions and the simple shell model allow an estimate of two-body matrix elements describing the nucleon-nucleon interaction and of the Coulomb energy [fr

Electrocatalysis of anodic oxygen-transfer reactions at modified lead dioxide electrodes

Energy Technology Data Exchange (ETDEWEB)

Hsiao, Yun-Lin.

1990-09-21

The electrocatalytic activities were compared for pure and chloride-doped beta-PbO{sub 2} (Cl-PbO{sub 2}) films on gold and platinum substrates. Rate constants were increased significantly for oxidations of Mn{sup 2+}, toluene, benzyl alcohol, dimethylsulphoxide (DMSO) and benzaldehyde in acidic media by the incorporation of Cl{sup {minus}} into the oxide films. These reactions are concluded to occur by the electrocatalytic transfer of oxygen from H{sub 2}O to the reaction products. Results of x-ray diffraction studies indicate the Cl-PbO{sub 2} film continues to have the slightly distorted rutile structure of pure beta-PbO{sub 2}. The observed electrocatalytic phenomena are concluded to be the beneficial consequence of surface defects generated when Cl{sup {minus}} serves for charge compensation within the surface matrix and, thereby, increases the number of surface sites capable of adsorbing hydroxyl radicals which are transferred in the electrocatalytic O-transfer reactions. 91 refs., 44 figs., 10 tabs.

A ring polymer molecular dynamics study of the isotopologues of the H + H2 reaction.

Science.gov (United States)

Suleimanov, Yury V; de Tudela, Ricardo Pérez; Jambrina, Pablo G; Castillo, Jesús F; Sáez-Rábanos, Vicente; Manolopoulos, David E; Aoiz, F Javier

2013-03-14

The inclusion of Quantum Mechanical (QM) effects such as zero point energy (ZPE) and tunneling in simulations of chemical reactions, especially in the case of light atom transfer, is an important problem in computational chemistry. In this respect, the hydrogen exchange reaction and its isotopic variants constitute an excellent benchmark for the assessment of approximate QM methods. In particular, the recently developed ring polymer molecular dynamics (RPMD) technique has been demonstrated to give very good results for bimolecular chemical reactions in the gas phase. In this work, we have performed a detailed RPMD study of the H + H(2) reaction and its isotopologues Mu + H(2), D + H(2) and Heμ + H(2), at temperatures ranging from 200 to 1000 K. Thermal rate coefficients and kinetic isotope effects have been computed and compared with exact QM calculations as well as with quasiclassical trajectories and experiment. The agreement with the QM results is good for the heaviest isotopologues, with errors ranging from 15% to 45%, and excellent for Mu + H(2), with errors below 15%. We have seen that RPMD is able to capture the ZPE effect very accurately, a desirable feature of any method based on molecular dynamics. We have also verified Richardson and Althorpe's prediction [J. O. Richardson and S. C. Althorpe, J. Chem. Phys., 2009, 131, 214106] that RPMD will overestimate thermal rates for asymmetric reactions and underestimate them for symmetric reactions in the deep tunneling regime. The ZPE effect along the reaction coordinate must be taken into account when assigning the reaction symmetry in the multidimensional case.

A SIFT study of the reactions of H2ONO+ ions with several types of organic molecules

Science.gov (United States)

Smith, David; Wang, Tianshu; Spanel, Patrik

2003-11-01

A selected ion flow tube (SIFT) study has been carried out of the reactions of hydrated nitrosonium ions, NO+H2O, which theory has equated to protonated nitrous acid ions, H2ONO+. One objective of this study was to investigate if this ion exhibits the properties of both a cluster ion and a protonated acid in their reactions with a variety of organic molecules. The chosen reactant molecules comprise two each of the following types--amines, terpenes, aromatic hydrocarbons, esters, carboxylic acids, ketones, aldehydes and alcohols. The reactant H2ONO+ (NO+H2O) ions are formed in a discharge ion source and injected into helium carrier gas where they are partially vibrationally excited and partially dissociated to NO+ ions. Hence, the reactions of the H2ONO+ ions had to be studies simultaneously with NO+ ions, the reactions of the latter ions readily being studied by selectively injecting NO+ ions into the carrier gas. The results of this study indicate that the H2ONO+ ions undergo a wide variety of reaction processes that depend on the properties of the reactant molecules such as their ionisation energies and proton affinities. These processes include charge transfer with compounds, M, that have low ionisation energies (producing M+), proton transfer with compounds possessing large proton affinities (MH+), hydride ion transfer (M---H+), alkyl radical (M---R+), alkoxide radical transfer (M---OR+), ion-molecule association (NO+H2OM) and ligand switching (NO+M), producing the ions given in parentheses.

Electron transfer reactions, cyanide and O2 binding of truncated hemoglobin from Bacillus subtilis

International Nuclear Information System (INIS)

Fernandez, Esther; Larsson, Jonas T.; McLean, Kirsty J.; Munro, Andrew W.; Gorton, Lo; Wachenfeldt, Claes von; Ferapontova, Elena E.

2013-01-01

The truncated hemoglobin from Bacillus subtilis (trHb-Bs) possesses a surprisingly high affinity for oxygen and resistance to (auto)oxidation; its physiological role in the bacterium is not understood and may be connected with its very special redox and ligand binding reactions. Electron transfer reactions of trHb-Bs were electrochemically studied in solution and at graphite electrodes. Spectrophotometrical potentiometric titration and direct electrochemical measurements gave a heme iron redox potential of −103 ± 4 mV and −108 ± 2 mV vs. NHE, at pH 7, respectively. The redox potential of the heme in trHb-Bs shifted −59 mV per pH unit at pH higher than 7, consistently with a 1e − /1 H + – transfer reaction. The heterogeneous rate constant k s for a quasi-reversible 1e − – 1H + – transfer reaction between graphite and trHb-Bs was 10.1 ± 2.3 s −1 . Upon reversible cyanide binding the k s doubled, while the redox potential of heme shifted 21 mV negatively, presumably reflecting changes in redox activity and in vivo signaling functions of trHb-Bs associated with ligand binding. Bioelectrocatalytic reduction of O 2 catalyzed by trHb-Bs was one of the most efficient hitherto reported for Hbs, with an apparent catalytic rate constant, k cat , of 56 ± 6 s −1 . The results obtained are of particular interest for applications of trHb in environmental biosensing and toxicity screening

One-electron transfer reactions of the couple NAD./NADH

International Nuclear Information System (INIS)

Grodkowski, J.; Neta, P.; Carlson, B.W.; Miller, L.

1983-01-01

One-electron transfer reactions involving nicotinamide-adenine dinucleotide in its oxidized and reducd forms (NAD./NADH) were studied by pulse radiolysis in aqueous solutions. One-electron oxidation of NADH by various phenoxyl radicals and phenothiazine cation radicals was found to take place with rate constants in the range of 10 5 to 10 8 M -1 s -1 , depending on the redox potential of the oxidizing species. In all cases, NAD. is formed quantitatively with no indication for the existence of the protonated form (NADH + .). The spectrum of NAD., as well as the rates of oxidation of NADH by phenoxyl and by (chlorpromazine) + . were independent of pH between pH 4.5 and 13.5. Reaction of deuterated NADH indicated only a small kinetic isotope effect. All these findings point to an electron transfer mechanism. On the other hand, attempts to observe the reverse electron transfer, i.e., one-electron reduction of NAD. to NADH by radicals such as semiquinones, showed that k was less than 10 4 to 10 5 M -1 s -1 , so that it was unobservable. Consequently, it was not possible to achieve equilibrium conditions which would have permitted the direct measurement of the redox potential for NAD./NADH. One-electron reduction of NAD. appears to be an unlikely process. 1 table

Competitive roles of reagent vibration and translation in the exothermic proton transfer reaction H+2+Ar→HAr++H

International Nuclear Information System (INIS)

Bilotta, R.M.; Farrar, J.M.

1981-01-01

We present a crossed beam study of the title reaction at fixed collision energies of 1.2 and 2.3 eV with reagent H + 2 average vibrational energies of 0.44 and 0.89 eV; we also present data at fixed total energies with variable proportions of reagent vibrational and translational energy. At fixed collision energy, reagent vibrational excitation is found to have negligible effect on the total cross section for proton transfer. At fixed total energy, a decrease in reagent vibrational excitation with a corresponding increase in reagent translation leads to partial disposal of the incremental translation in product translation: At a total energy of 3.5 eV, 50% of this incremental reagent translation appears as product translation. At a total energy of 4.6 eV, 78% of the incremental translation appears in product translation. The experimental data are discussed in terms of induced attractive and repulsive energy release on an attractive potential surface. The role of noncollinear geometries and compressed reactant configurations is judged to be of substantial importance in assessing product rotational excitation and dissociation

A Commensal Gone Bad: Complete Genome Sequence of the Prototypical Enterotoxigenic Escherichia coli Strain H10407

Science.gov (United States)

2010-11-01

and Escherichia ferguso- . TABLE 2. General characteristics of the plasm ids from ETEC strains H10407 and E1392/75 Value in E. c·oli: Characteristic...0352). consetved proteins with unknown func- tions (CDSs 0673 to 0678), a flavoprotein electron transfer system (CDSs 1730 to 1734), the colanic...mediating diarrhea are not chromosomally encoded. indicating that the essential virulence factors are encoded on the plasm ids (61 ). Potentia l

Geometric phase and quantum interference in photosynthetic reaction center: Regulation of electron transfer

Energy Technology Data Exchange (ETDEWEB)

Sun, Yuming, E-mail: ymsun@ytu.edu.cn; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian

2016-10-20

Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C{sub 2}-symmetrically arranged into two branches. In view of quantum mechanism, both branches are possible pathways traversed by the transferred electron. Due to different evolution of spin state along two pathways in transmembrane electric potential (TEP), quantum state of the transferred electron at the bridged site acquires a geometric phase difference dependent on TEP, the most efficient electron transport takes place in a specific range of TEP beyond which electron transfer is dramatically suppressed. What’s more, reaction center acts like elaborately designed quantum device preparing polarized spin dependent on TEP for the transferred electron to regulate the reduction potential at bridged site. In brief, electron transfer generates the TEP, reversely, TEP modulates the efficiency of electron transfer. This may be an important approach to maintaining an appreciable pH environment in photosynthesis.

Proton-transfer reactions in ionized gases

International Nuclear Information System (INIS)

Stiller, W.; Schmidt, R.; Schuster, R.

1985-01-01

Ion-molecule reactions play an important role in various radiolytic processes, e.g. gas-pulse radiolysis, environmental research. For a discussion of mechanisms rate coefficients have to be assessed. Here gas-phase rate coefficients of ion-(polar) molecule reactions are calculated using the ideas of interaction potentials, reactive cross-sections and distribution functions of the translational energies of both the reactants (ions I, molecules M). The starting point of our approach, directed especially to gas-phase proton-transfer reactions, is the idea that the rate coefficient k can be calculated as an ion-molecule capture-rate coefficient multiplied by a 'steric factor' representing the probability for proton transfer. Mutual capture of the reaction partners within a possible reaction zone is caused by the physical interaction between an ion and a polar molecule. A model is discussed. Results are presented. (author)

One-nucleon transfer reactions and the optical potential

CERN Document Server

Nunes, F M; Ross, A; Titus, L J; Charity, R J; Dickhoff, W H; Mahzoon, M H; Sarich, J; Wild, S M

2015-01-01

We provide a summary of new developments in the area of direct reaction theory with a particular focus on one-nucleon transfer reactions. We provide a status of the methods available for describing (d,p) reactions. We discuss the effects of nonlocality in the optical potential in transfer reactions. The results of a purely phenomenological potential and the optical potential obtained from the dispersive optical model are compared; both point toward the importance of including nonlocality in transfer reactions explicitly. Given the large ambiguities associated with optical potentials, we discuss some new developments toward the quantification of this uncertainty. We conclude with some general comments and a brief account of new advances that are in the pipeline.

Measurement and calculation of polarization transfer coefficients in the reaction {sup 2}H(p,p){sup 2}H at E{sub p}=22.5 MeV

Energy Technology Data Exchange (ETDEWEB)

Clajus, M.; Albert, J.; Bruno, M.; Egun, P.M.; Glockle, W.; Glombik, A.; Gruebler, W.; Hautle, P.; Kretschmer, W.; Rauscher, A.; Schmelzbach, P.A.; Slaus, I.; Weidmann, R.; Witala, H. [Inst. fuer Mittelenergiephys., Eidgenoessische Tech. Hochschule, Zurich (Switzerland)

1995-10-01

The polarization transfer coefficients K{sub x}{sup x}', K{sub y}{sup y}' and K{sub z}{sup x}' in the reaction {sup 2}H(p,p){sup 2}H have been measured at an incident proton energy of 22.5 MeV. The results are compared to predictions from Faddeev calculations using various nucleon-nucleon potential models. The overall agreement is rather good. The comparison in more detail shows a pronounced sensitivity of the results, especially for K{sub y}{sup y}', to the {sup 3}S{sub 1}-{sup 3}D{sub 1} and {sup 1}P{sub 1} NN force components. As in nucleon-nucleon scattering, however, these two parameters are correlated, thus hampering definite conclusions. (author)

Photo- and radiation chemical studies of intermediates involved in excited-state electron-transfer reactions

International Nuclear Information System (INIS)

Hoffman, M.Z.

1985-01-01

Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H 2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV 2+ , the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV + ; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV 2+ with rate constants of 2.8 x 10 9 , 7.6 x 10 9 , and 8.5 x 10 6 M -1 s -1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV + to be severely diminished

Human METTL20 methylates lysine residues adjacent to the recognition loop of the electron transfer flavoprotein in mitochondria.

Science.gov (United States)

Rhein, Virginie F; Carroll, Joe; He, Jiuya; Ding, Shujing; Fearnley, Ian M; Walker, John E

2014-08-29

In mammalian mitochondria, protein methylation is a relatively uncommon post-transcriptional modification, and the extent of the mitochondrial protein methylome, the modifying methyltransferases, and their substrates have been little studied. As shown here, the β-subunit of the electron transfer flavoprotein (ETF) is one such methylated protein. The ETF is a heterodimer of α- and β-subunits. Lysine residues 199 and 202 of mature ETFβ are almost completely trimethylated in bovine heart mitochondria, whereas ETFα is not methylated. The enzyme responsible for the modifications was identified as methyltransferase-like protein 20 (METTL20). In human 143B cells, the methylation of ETFβ is less extensive and is diminished further by suppression of METTL20. Tagged METTL20 expressed in HEK293T cells specifically associates with the ETF and promotes the trimethylation of ETFβ lysine residues 199 and 202. ETF serves as a mobile electron carrier linking dehydrogenases involved in fatty acid oxidation and one-carbon metabolism to the membrane-associated ubiquinone pool. The methylated residues in ETFβ are immediately adjacent to a protein loop that recognizes and binds to the dehydrogenases. Suppression of trimethylation of ETFβ in mouse C2C12 cells oxidizing palmitate as an energy source reduced the consumption of oxygen by the cells. These experiments suggest that the oxidation of fatty acids in mitochondria and the passage of electrons via the ETF may be controlled by modulating the protein-protein interactions between the reduced dehydrogenases and the β-subunit of the ETF by trimethylation of lysine residues. METTL20 is the first lysine methyltransferase to be found to be associated with mitochondria. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Neutron transfer reactions in the fp-shell region

International Nuclear Information System (INIS)

Mahgoub, Mahmoud

2008-01-01

Neutron transfer reactions were used to study the stability of the magic number N=28 near 56 Ni. On one hand the one-neutron pickup (d,p) reaction was used for precision spectroscopy of single-particle levels in 55 Fe. On the other hand we investigated the two-neutron transfer mechanism into 56 Ni using the pickup reaction 58 Ni(vectorp,t) 56 Ni. In addition the reliability of inverse kinematics reactions at low energy to study exotic nuclei was tested by the neutron transfer reactions t( 40 Ar,p) 42 Ar and d( 54 Fe,p) 55 Fe using tritium and deuterium targets, respectively, and by comparing the results with those of the normal kinematics reactions. The experimental data, differential cross-section and analyzing powers, are compared to DWBA and coupled channel calculations utilizing the code CHUCK3. By performing the single-neutron stripping reaction (vectord,p) on 54 Fe the 1f 7/2 shell in the ground state configuration was found to be partly broken. The instability of the 1f 7/2 shell and the magic number N=28 was confirmed once by observing a number of levels with J π = 7/2 - at low excitation energies, which should not be populated if 54 Fe has a closed 1f 7/2 shell, and also by comparing our high precision experimental data with a large scale shell model calculation using the ANTOINE code [5]. Calculations including a partly broken 1f 7/2 shell show better agreement with the experiment. The instability of the 1f 7/2 shell was confirmed also by performing the two-neutron pick-up reaction (vectorp,t) on 58 Ni to study 56 Ni, where a considerable improvement in the DWBA calculation was observed after considering 1f 7/2 as a broken shell. To prove the reliability of inverse kinematics transfer reactions at low energies (∝ 2 AMeV), the aforementioned single-neutron transfer reaction (d,p) was repeated using a beam of 54 Fe ions and a deuteron target. From this inverse kinematics experiment we were able to reproduce the absolute cross-section and angular

Reaction mechanism and spectroscopy of transfer reactions induced by heavy ions

International Nuclear Information System (INIS)

Lemaire, M.-C.

1977-01-01

The specific features displayed by data on heavy ion elastic and inelastic angular distributions are discussed, and their physical origin is pointed out from semi-classical calculations in counterpart ambiguities in the phenomenological description of the optical potential appear. Two nucleon transfer reactions induced by heavy ions successfully point out important contributions of a two-step process where the transfer is proceeding via target and residual nucleus inelastic excitation. At incident energies not too high above the Coulomb barrier, such process produces clear shape changes between different final state angular distributions. At higher incident energy, the angular distributions are forward peaked and display oscillations for both mechanisms. As for four-nucleon transfer reactions, the existing data suggest that the nucleons are well transferred into a Os relative

Two-neutron transfer reactions with heavy-deformed nuclei

International Nuclear Information System (INIS)

Price, C.; Landowne, S.; Esbensen, H.

1988-01-01

In a recent communication we pointed out that one can combine the macroscopic model for two-particle transfer reactions on deformed nuclei with the sudden limit approximation for rotational excitation, and thereby obtain a practical method for calculating transfer reactions leading to high-spin states. As an example, we presented results for the reaction 162 Dy( 58 Ni, 60 Ni) 160 Dy populating the ground-state rotational band up to the spin I = 14 + state. We have also tested the validity of the sudden limit for the inelastic excitation of high spin states and we have noted how the macroscopic model may be modified to allow for more microscopic nuclear structure effects in an application to diabolic pair-transfer processes. This paper describes our subsequent work in which we investigated the systematic features of pair-transfer reactions within the macroscopic model by using heavier projectiles to generate higher spins and by decomposing the cross sections according to the multipolarity of the transfer interaction. Particular attention is paid to characteristic structures in the angular distributions for the lower spin states and how they depend on the angular momentum carried by the transferred particles. 11 refs., 3 figs

Complementary Strategies for Directed C(sp3 )-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer.

Science.gov (United States)

Chu, John C K; Rovis, Tomislav

2018-01-02

The functionalization of C(sp 3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp 3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Counter-transference reactions contributing to completed suicide.

Science.gov (United States)

Modestin, J

1987-12-01

Counter-transference reactions are frequently elicited while treating suicidal patients and they may contribute to the patient's committing suicide. Therapeutic constellations including the failure of the therapist to (1) cope with the patient's aggressiveness, (2) tolerate the patient's dependency, (3) handle the erotic transference adequately and (4) preserve loyalty towards the patient; they have all been identified as being responsible for a therapeutic impasse with fatal consequences. Knowledge of the therapeutic constellations especially prone to facilitate negative counter-transference reactions may help the therapist to master them effectively.

Probing cluster structures through sub-barrier transfer reactions

Directory of Open Access Journals (Sweden)

Rafferty D. C.

2016-01-01

Full Text Available Multinucleon transfer probabilities and excitation energy distributions have been measured in 16,18O, 19F + 208Pb at energies between 90% - 100% of the Coulomb barrier. A strong 2p2n enhancement is observed for all reactions, though most spectacularly in the 18O induced reaction. Results are interpreted in terms of the Semiclassical model, which seems to suggest α-cluster transfer in all studied systems. The relation to cluster-states in the projectile is discussed, with the experimental results consistent with previous structure studies. Dissipation of energy in the collisions of 18O is compared between different reaction modes, with cluster transfer associated with dissipation over a large number of internal states. Cluster transfer is shown to be a long range dissipation mechanism, which will inform the development of future models to treat these dynamic processes in reactions.

Imaging of Neuronal Activity in Awake Mice by Measurements of Flavoprotein Autofluorescence Corrected for Cerebral Blood Flow.

Science.gov (United States)

Takahashi, Manami; Urushihata, Takuya; Takuwa, Hiroyuki; Sakata, Kazumi; Takado, Yuhei; Shimizu, Eiji; Suhara, Tetsuya; Higuchi, Makoto; Ito, Hiroshi

2017-01-01

Green fluorescence imaging (e.g., flavoprotein autofluorescence imaging, FAI) can be used to measure neuronal activity and oxygen metabolism in living brains without expressing fluorescence proteins. It is useful for understanding the mechanism of various brain functions and their abnormalities in age-related brain diseases. However, hemoglobin in cerebral blood vessels absorbs green fluorescence, hampering accurate assessments of brain function in animal models with cerebral blood vessel dysfunctions and subsequent cerebral blood flow (CBF) alterations. In the present study, we developed a new method to correct FAI signals for hemoglobin-dependent green fluorescence reductions by simultaneous measurements of green fluorescence and intrinsic optical signals. Intrinsic optical imaging enabled evaluations of light absorption and scatters by hemoglobin, which could then be applied to corrections of green fluorescence intensities. Using this method, enhanced flavoprotein autofluorescence by sensory stimuli was successfully detected in the brains of awake mice, despite increases of CBF, and hemoglobin interference. Moreover, flavoprotein autofluorescence could be properly quantified in a resting state and during sensory stimulation by a CO 2 inhalation challenge, which modified vascular responses without overtly affecting neuronal activities. The flavoprotein autofluorescence signal data obtained here were in good agreement with the previous findings from a condition with drug-induced blockade of cerebral vasodilation, justifying the current assaying methodology. Application of this technology to studies on animal models of brain diseases with possible changes of CBF, including age-related neurological disorders, would provide better understanding of the mechanisms of neurovascular coupling in pathological circumstances.

Simultaneous mass transfer of H2S and CO2 with complex chemical reactions in an aqueous di-isopropanolamine solution = Gleichzeitige absorption von H2S und CO2 in Wässriger Di-isopropanolaminlösung

NARCIS (Netherlands)

Blauwhoff, P.M.M.; van Swaaij, Willibrordus Petrus Maria

1985-01-01

The absorption of H2S and CO2 into an aqueous di-isopropanolamine (DIPA) solution was studied experimentally and theoretically as an example of simultaneous mass transfer with complex reversible reactions. The absorption phenomena were classified into three regimes: (1) negligible mutual interaction

Neutron transfer reactions in the fp-shell region

Energy Technology Data Exchange (ETDEWEB)

Mahgoub, Mahmoud

2008-06-26

Neutron transfer reactions were used to study the stability of the magic number N=28 near {sup 56}Ni. On one hand the one-neutron pickup (d,p) reaction was used for precision spectroscopy of single-particle levels in {sup 55}Fe. On the other hand we investigated the two-neutron transfer mechanism into {sup 56}Ni using the pickup reaction {sup 58}Ni((vector)p,t){sup 56}Ni. In addition the reliability of inverse kinematics reactions at low energy to study exotic nuclei was tested by the neutron transfer reactions t({sup 40}Ar,p){sup 42}Ar and d({sup 54}Fe,p){sup 55}Fe using tritium and deuterium targets, respectively, and by comparing the results with those of the normal kinematics reactions. The experimental data, differential cross-section and analyzing powers, are compared to DWBA and coupled channel calculations utilizing the code CHUCK3. By performing the single-neutron stripping reaction ((vector)d,p) on {sup 54}Fe the 1f{sub 7/2} shell in the ground state configuration was found to be partly broken. The instability of the 1f{sub 7/2} shell and the magic number N=28 was confirmed once by observing a number of levels with J{sup {pi}} = 7/2{sup -} at low excitation energies, which should not be populated if {sup 54}Fe has a closed 1f{sub 7/2} shell, and also by comparing our high precision experimental data with a large scale shell model calculation using the ANTOINE code [5]. Calculations including a partly broken 1f{sub 7/2} shell show better agreement with the experiment. The instability of the 1f{sub 7/2} shell was confirmed also by performing the two-neutron pick-up reaction ((vector)p,t) on {sup 58}Ni to study {sup 56}Ni, where a considerable improvement in the DWBA calculation was observed after considering 1f{sub 7/2} as a broken shell. To prove the reliability of inverse kinematics transfer reactions at low energies ({proportional_to} 2 AMeV), the aforementioned single-neutron transfer reaction (d,p) was repeated using a beam of {sup 54}Fe ions and a

Nuclear structure effects in multi-nucleon transfer and sequential fission reactions

International Nuclear Information System (INIS)

Biswas, D.C.

2001-01-01

The role of the nuclear structure in multi-nucleon transfer and sequential fission reactions has been discussed. The recent results on multi-nucleon transfer and transfer induced fission reaction, have brought out many interesting features in understanding the reaction mechanism and collective dynamics of heavy ion reactions. The structure of the projectile nucleus has strong influence on the transfer of multi-nucleons and/or clusters from the projectile to the target. The mechanism of multi-nucleon transfer between two heavy nuclei is a complex process which has a strong dependence on the ground state Q-value of the reaction as well as on the number of transferred nucleons

Kinetic mechanism of molecular energy transfer and chemical reactions in low-temperature air-fuel plasmas.

Science.gov (United States)

Adamovich, Igor V; Li, Ting; Lempert, Walter R

2015-08-13

This work describes the kinetic mechanism of coupled molecular energy transfer and chemical reactions in low-temperature air, H2-air and hydrocarbon-air plasmas sustained by nanosecond pulse discharges (single-pulse or repetitive pulse burst). The model incorporates electron impact processes, state-specific N(2) vibrational energy transfer, reactions of excited electronic species of N(2), O(2), N and O, and 'conventional' chemical reactions (Konnov mechanism). Effects of diffusion and conduction heat transfer, energy coupled to the cathode layer and gasdynamic compression/expansion are incorporated as quasi-zero-dimensional corrections. The model is exercised using a combination of freeware (Bolsig+) and commercial software (ChemKin-Pro). The model predictions are validated using time-resolved measurements of temperature and N(2) vibrational level populations in nanosecond pulse discharges in air in plane-to-plane and sphere-to-sphere geometry; temperature and OH number density after nanosecond pulse burst discharges in lean H(2)-air, CH(4)-air and C(2)H(4)-air mixtures; and temperature after the nanosecond pulse discharge burst during plasma-assisted ignition of lean H2-mixtures, showing good agreement with the data. The model predictions for OH number density in lean C(3)H(8)-air mixtures differ from the experimental results, over-predicting its absolute value and failing to predict transient OH rise and decay after the discharge burst. The agreement with the data for C(3)H(8)-air is improved considerably if a different conventional hydrocarbon chemistry reaction set (LLNL methane-n-butane flame mechanism) is used. The results of mechanism validation demonstrate its applicability for analysis of plasma chemical oxidation and ignition of low-temperature H(2)-air, CH(4)-air and C(2)H(4)-air mixtures using nanosecond pulse discharges. Kinetic modelling of low-temperature plasma excited propane-air mixtures demonstrates the need for development of a more accurate

Coherent and semi-coherent neutron transfer reactions

International Nuclear Information System (INIS)

Hagelstein, P.L.

1992-01-01

Neutron transfer reactions are proposed to account for anomalies reported in Pons-Fleischmann experiments. The prototypical reaction involves the transfer of a neutron (mediated by low frequency electric or magnetic fields) from a donor nucleus to virtual continuum states, followed by the capture of the virtual neutron by an acceptor nucleus. In this work we summarize basic principles, recent results and the ultimate goals of the theoretical effort

Coherent and semi-coherent neutron transfer reactions

International Nuclear Information System (INIS)

Hagelstein, P.L.

1993-01-01

Neutron transfer reactions are proposed to account for anomalies reported in Pons-Fleischmann experiments. The prototypical reaction involves the transfer of a neutron (mediated by low frequency electric or magnetic fields) from a donor nucleus to virtual continuum states, followed by the capture of the virtual neutron by an acceptor nucleus. In this work we summarize basic principles, recent results and the ultimate goals of the theoretical effort. (author)

Single-collision studies of hot atom energy transfer and chemical reaction

International Nuclear Information System (INIS)

Valentini, J.J.

1991-01-01

This report discusses research in the collision dynamics of translationally hot atoms, with funding with DOE for the project ''Single-Collision Studies of Hot Atom Energy Transfer and Chemical Reaction,'' Grant Number DE-FG03-85ER13453. The work reported here was done during the period September 9, 1988 through October 31, 1991. During this period this DOE-funded work has been focused on several different efforts: (1) experimental studies of the state-to-state dynamics of the H + RH → H 2 R reactions where RH is CH 4 , C 2 H 6 , or C 3 H 8 , (2) theoretical (quasiclassical trajectory) studies of hot hydrogen atom collision dynamics, (3) the development of photochemical sources of translationally hot molecular free radicals and characterization of the high resolution CARS spectroscopy of molecular free radicals, (4) the implementation of stimulated Raman excitation (SRE) techniques for the preparation of vibrationally state-selected molecular reactants

The H2 + + He proton transfer reaction: quantum reactive differential cross sections to be linked with future velocity mapping experiments

Science.gov (United States)

Hernández Vera, Mario; Wester, Roland; Gianturco, Francesco Antonio

2018-01-01

We construct the velocity map images of the proton transfer reaction between helium and molecular hydrogen ion {{{H}}}2+. We perform simulations of imaging experiments at one representative total collision energy taking into account the inherent aberrations of the velocity mapping in order to explore the feasibility of direct comparisons between theory and future experiments planned in our laboratory. The asymptotic angular distributions of the fragments in a 3D velocity space is determined from the quantum state-to-state differential reactive cross sections and reaction probabilities which are computed by using the time-independent coupled channel hyperspherical coordinate method. The calculations employ an earlier ab initio potential energy surface computed at the FCI/cc-pVQZ level of theory. The present simulations indicate that the planned experiments would be selective enough to differentiate between product distributions resulting from different initial internal states of the reactants.

Reduced Flavin: NMR investigation of N(5-H exchange mechanism, estimation of ionisation constants and assessment of properties as biological catalyst

Directory of Open Access Journals (Sweden)

Rüterjans Heinz

2005-11-01

Full Text Available Abstract Background The flavin in its FMN and FAD forms is a versatile cofactor that is involved in catalysis of most disparate types of biological reactions. These include redox reactions such as dehydrogenations, activation of dioxygen, electron transfer, bioluminescence, blue light reception, photobiochemistry (as in photolyases, redox signaling etc. Recently, hitherto unrecognized types of biological reactions have been uncovered that do not involve redox shuffles, and might involve the reduced form of the flavin as a catalyst. The present work addresses properties of reduced flavin relevant in this context. Results N(5-H exchange reactions of the flavin reduced form and its pH dependence were studied using the 15N-NMR-signals of 15N-enriched, reduced flavin in the pH range from 5 to 12. The chemical shifts of the N(3 and N(5 resonances are not affected to a relevant extent in this pH range. This contrasts with the multiplicity of the N(5-resonance, which strongly depends on pH. It is a doublet between pH 8.45 and 10.25 that coalesces into a singlet at lower and higher pH values. From the line width of the 15N(5 signal the pH-dependent rate of hydrogen exchange was deduced. The multiplicity of the 15N(5 signal and the proton exchange rates are little dependent on the buffer system used. Conclusion The exchange rates allow an estimation of the pKa value of N(5-H deprotonation in reduced flavin to be ≥ 20. This value imposes specific constraints for mechanisms of flavoprotein catalysis based on this process. On the other hand the pK ≈ 4 for N(5-H protonation (to form N(5+-H2 would be consistent with a role of N(5-H as a base.

Imaging of Neuronal Activity in Awake Mice by Measurements of Flavoprotein Autofluorescence Corrected for Cerebral Blood Flow

Directory of Open Access Journals (Sweden)

Manami Takahashi

2018-01-01

Full Text Available Green fluorescence imaging (e.g., flavoprotein autofluorescence imaging, FAI can be used to measure neuronal activity and oxygen metabolism in living brains without expressing fluorescence proteins. It is useful for understanding the mechanism of various brain functions and their abnormalities in age-related brain diseases. However, hemoglobin in cerebral blood vessels absorbs green fluorescence, hampering accurate assessments of brain function in animal models with cerebral blood vessel dysfunctions and subsequent cerebral blood flow (CBF alterations. In the present study, we developed a new method to correct FAI signals for hemoglobin-dependent green fluorescence reductions by simultaneous measurements of green fluorescence and intrinsic optical signals. Intrinsic optical imaging enabled evaluations of light absorption and scatters by hemoglobin, which could then be applied to corrections of green fluorescence intensities. Using this method, enhanced flavoprotein autofluorescence by sensory stimuli was successfully detected in the brains of awake mice, despite increases of CBF, and hemoglobin interference. Moreover, flavoprotein autofluorescence could be properly quantified in a resting state and during sensory stimulation by a CO2 inhalation challenge, which modified vascular responses without overtly affecting neuronal activities. The flavoprotein autofluorescence signal data obtained here were in good agreement with the previous findings from a condition with drug-induced blockade of cerebral vasodilation, justifying the current assaying methodology. Application of this technology to studies on animal models of brain diseases with possible changes of CBF, including age-related neurological disorders, would provide better understanding of the mechanisms of neurovascular coupling in pathological circumstances.

Hydrogen atom transfer reactions in thiophenol: photogeneration of two new thione isomers.

Science.gov (United States)

Reva, Igor; Nowak, Maciej J; Lapinski, Leszek; Fausto, Rui

2015-02-21

Photoisomerization reactions of monomeric thiophenol have been investigated for the compound isolated in low-temperature argon matrices. The initial thiophenol population consists exclusively of the thermodynamically most stable thiol form. Phototransformations were induced by irradiation of the matrices with narrowband tunable UV light. Irradiation at λ > 290 nm did not induce any changes in isolated thiophenol molecules. Upon irradiation at 290-285 nm, the initial thiol form of thiophenol converted into its thione isomer, cyclohexa-2,4-diene-1-thione. This conversion occurs by transfer of an H atom from the SH group to a carbon atom at the ortho position of the ring. Subsequent irradiation at longer wavelengths (300-427 nm) demonstrated that this UV-induced hydrogen-atom transfer is photoreversible. Moreover, upon irradiation at 400-425 nm, the cyclohexa-2,4-diene-1-thione product converts, by transfer of a hydrogen atom from the ortho to para position, into another thione isomer, cyclohexa-2,5-diene-1-thione. The latter thione isomer is also photoreactive and is consumed if irradiated at λ atom-transfer isomerization reactions dominate the unimolecular photochemistry of thiophenol confined in a solid argon matrix. A set of low-intensity infrared bands, observed in the spectra of UV irradiated thiophenol, indicates the presence of a phenylthiyl radical with an H- atom detached from the SH group. Alongside the H-atom-transfer and H-atom-detachment processes, the ring-opening photoreaction occurred in cyclohexa-2,4-diene-1-thione by the cleavage of the C-C bond at the alpha position with respect to the thiocarbonyl C[double bond, length as m-dash]S group. The resulting open-ring conjugated thioketene adopts several isomeric forms, differing by orientations around single and double bonds. The species photogenerated upon UV irradiation of thiophenol were identified by comparison of their experimental infrared spectra with the spectra theoretically calculated for

Redox-neutral rhodium-catalyzed C-H functionalization of arylamine N-oxides with diazo compounds: primary C(sp(3))-H/C(sp(2))-H activation and oxygen-atom transfer.

Science.gov (United States)

Zhou, Bing; Chen, Zhaoqiang; Yang, Yaxi; Ai, Wen; Tang, Huanyu; Wu, Yunxiang; Zhu, Weiliang; Li, Yuanchao

2015-10-05

An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterization of the free energy dependence of an interprotein electron transfer reaction by variation of pH and site-directed mutagenesis.

Science.gov (United States)

Dow, Brian A; Davidson, Victor L

2015-10-01

The interprotein electron transfer (ET) reactions of the cupredoxin amicyanin, which mediates ET from the tryptophan tryptophylquinone (TTQ) cofactor of methylamine dehydrogenase to cytochrome c-551i have been extensively studied. However, it was not possible to perform certain key experiments in that native system. This study examines the ET reaction from reduced amicyanin to an alternative electron acceptor, the diheme protein MauG. It was possible to vary the ΔG° for this ET reaction by simply changing pH to determine the dependence of kET on ΔG°. A P94A mutation of amicyanin significantly altered its oxidation-reduction midpoint potential value. It was not possible to study the ET from reduced P94A amicyanin to cytochrome c-551i in the native system because that reaction was kinetically coupled. However, the reaction from reduced P94A amicyanin to MauG was a true ET reaction and it was possible to determine values of reorganization energy (λ) and electronic coupling for the reactions of this variant as well as native amicyanin. Comparison of the λ values associated with the ET reactions between amicyanin and the TTQ of methylamine dehydrogenase, the diheme center of MauG and the single heme of cytochrome c-551i, provides insight into the factors that dictate the λ values for the respective reactions. These results demonstrate how study of ET reactions with alternative redox partner proteins can complement and enhance our understanding of the reactions with the natural redox partners, and further our understanding of mechanisms of protein ET reactions. Copyright © 2015 Elsevier B.V. All rights reserved.

Tem holder for sample transfer under reaction conditions

DEFF Research Database (Denmark)

Damsgaard, Christian Danvad; Zandbergen, Henny W.; Wagner, Jakob Birkedal

Environmental transmission electron microscopy (ETEM) studies are usually performed using conventional sample holders in a dedicated ETEM [1] or in a traditional TEM by use of a dedicated high-pressure cell sample holder [2]. In both cases, the setup defines the conditions regarding gas, pressure......]. Furthermore, dedicated transfer holders have been used to transfer catalyst samples between reactor set-ups and TEM at room temperature in inert atmosphere [5]. To take the full advantage of complementary in situ techniques, transfer under reactions conditions is essential. This study introduces the in situ...... transfer concept by use of a dedicated TEM transfer holder capable of enclosing the sample in a gaseous environment at temperatures up to approx. 900C. By oxidation and reduction experiments of Cu nanoparticles it is shown possible to keep the reaction conditions during transfer outside the microscope...

Analysis of trace gases at ppb levels by proton transfer reaction mass spectrometry (PTR-MS)

International Nuclear Information System (INIS)

Lindinger, W.; Hansel, A.

1996-01-01

A proton transfer reaction mass spectrometry (PTR-MS) system has been developed which allows for on-line measurements of trace gas components with concentrations as low as 1 ppb. The method is based on reactions of H 3 O + ions, which perform non-dissociative proton transfer to most of the common organic trace constituents but do not react with any of the components present in clean air. Examples of medical information obtained by means of breath analysis, of environmental trace analysis, and examples in the field of food chemistry demonstrate the wide applicability of the method. (Authors)

Stereochemistry of 1,2-elimination and proton-transfer reactions: toward a unified understanding.

Science.gov (United States)

Mohrig, Jerry R

2013-07-16

Many mechanistic and stereochemical studies have focused on the breaking of the C-H bond through base-catalyzed elimination reactions. When we began our research, however, chemists knew almost nothing about the stereospecificity of addition-elimination reactions involving conjugated acyclic carbonyl compounds, even though the carbonyl group is a pivotal functional group in organic chemistry. Over the last 25 years, we have studied the addition-elimination reactions of β-substituted acyclic esters, thioesters, and ketones in order to reach a comprehensive understanding of how electronic effects influence their stereochemistry. This Account brings together our understanding of the stereochemistry of 1,2-elimination and proton-transfer reactions, describing how each study has built upon previous work and contributed to our understanding of this field. When we began, chemists thought that anti stereospecificity in base-catalyzed 1,2-elimination reactions occurred via concerted E2 mechanisms, which provide a smooth path for anti elimination. Unexpectedly, we discovered that some E1cBirrev reactions produce the same anti stereospecificity as E2 reactions even though they proceed through diffusionally equilibrated, "free" enolate-anion intermediates. This result calls into question the conventional wisdom that anti stereochemistry must result from a concerted mechanism. While carrying out our research, we developed insights ranging from the role of historical contingency in the evolution of hydratase-dehydratase enzymes to the influence of buffers on the stereochemistry of H/D exchange in D2O. Negative hyperconjugation is the most important concept for understanding our results. This idea provides a unifying view for the largely anti stereochemistry in E1cBirrev elimination reactions and a basis for understanding the stereoelectronic influence of electron-withdrawing β-substituents on proton-transfer reactions.

Scattering and transfer reactions with heavy ions

International Nuclear Information System (INIS)

Hussein, M.S.

From the elastic scattering analysis the input parameters are found for the inelastic scattering analysis and the transfer reactions of the heavy ion reactions. The main theme reported is the likeness and conection among these processes. (L.C.) [pt

Studies on the mechanism of electron bifurcation catalyzed by electron transferring flavoprotein (Etf) and butyryl-CoA dehydrogenase (Bcd) of Acidaminococcus fermentans.

Science.gov (United States)

Chowdhury, Nilanjan Pal; Mowafy, Amr M; Demmer, Julius K; Upadhyay, Vikrant; Koelzer, Sebastian; Jayamani, Elamparithi; Kahnt, Joerg; Hornung, Marco; Demmer, Ulrike; Ermler, Ulrich; Buckel, Wolfgang

2014-02-21

Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD(+) complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH(-) is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH(-) by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH(•), immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH(-) that converts crotonyl-CoA to butyryl-CoA.

B-side charge separation in bacterial photosynthetic reaction centers: nanosecond time scale electron transfer from HB- to QB.

Science.gov (United States)

Kirmaier, Christine; Laible, Philip D; Hanson, Deborah K; Holten, Dewey

2003-02-25

We report time-resolved optical measurements of the primary electron transfer reactions in Rhodobacter capsulatus reaction centers (RCs) having four mutations: Phe(L181) --> Tyr, Tyr(M208) --> Phe, Leu(M212) --> His, and Trp(M250) --> Val (denoted YFHV). Following direct excitation of the bacteriochlorophyll dimer (P) to its lowest excited singlet state P, electron transfer to the B-side bacteriopheophytin (H(B)) gives P(+)H(B)(-) in approximately 30% yield. When the secondary quinone (Q(B)) site is fully occupied, P(+)H(B)(-) decays with a time constant estimated to be in the range of 1.5-3 ns. In the presence of excess terbutryn, a competitive inhibitor of Q(B) binding, the observed lifetime of P(+)H(B)(-) is noticeably longer and is estimated to be in the range of 4-8 ns. On the basis of these values, the rate constant for P(+)H(B)(-) --> P(+)Q(B)(-) electron transfer is calculated to be between approximately (2 ns)(-)(1) and approximately (12 ns)(-)(1), making it at least an order of magnitude smaller than the rate constant of approximately (200 ps)(-)(1) for electron transfer between the corresponding A-side cofactors (P(+)H(A)(-) --> P(+)Q(A)(-)). Structural and energetic factors associated with electron transfer to Q(B) compared to Q(A) are discussed. Comparison of the P(+)H(B)(-) lifetimes in the presence and absence of terbutryn indicates that the ultimate (i.e., quantum) yield of P(+)Q(B)(-) formation relative to P is 10-25% in the YFHV RC.

Regio- and Stereospecific Conversion of 4-Alkylphenols by the Covalent Flavoprotein Vanillyl-Alcohol Oxidase

NARCIS (Netherlands)

Heuvel, Robert H.H. van den; Fraaije, Marco W.; Laane, Colja; Berkel, Willem J.H. van

1998-01-01

The regio- and stereospecific conversion of prochiral 4-alkylphenols by the covalent flavoprotein vanillyl-alcohol oxidase was investigated. The enzyme was active, with 4-alkylphenols bearing aliphatic side chains of up to seven carbon atoms. Optimal catalytic efficiency occurred with 4-ethylphenol

The nuclear reaction n + 3He -> 1H + 3H as proximity reaction

International Nuclear Information System (INIS)

Hilber, H.C.

1982-01-01

The present thesis tries to give by means of the nuclear reaction n + 3 He -> 1 H + 3 H as proximity reaction on the three-particle system 3 He + 9 Be -> 1 H + 3 H + 8 Be an experimental verification to the second term of a multiple scattering series. The study of these rescattering effects is of great interest for the present theory of the final-state interaction. At three incident energies (7.08 MeV, 8.98 MeV, and 6.37 MeV) to detector telescopes identify the exit channel of the three-particle system in list-mode coincidence experiments according to protons and tritons. Peaks on the kinematical curves occur. The detailed study of their kinematic behaviour allows to exclude the inconcurrence to the proximity reaction lying cascade decays via intermediate states in 4 He, 9 B, and 11 B. Regarding the Coulomb interaction the experimental results can be also explained in the sense of the classical kinematics by the proximity model. (orig.) [de

Anomalous H/D isotope effect in hydrogen bonded systems: H-bonded cyclic structures and transfers of protons

International Nuclear Information System (INIS)

Marechal, Y.

1993-01-01

The systematic H/D substitution is a precious tool to obtain information on the dynamics of H-bonds. It is particularly useful in IR spectroscopy where H-bonds are at the origin of particularly intense and specific bands and where the particularly great value for the m D /m H ratio ensures strongly marked effects. In most H-bonded systems the effects of these substitutions are normal, in the sense that they are at the origin of bands having intensities, centers (of intensity) and widths smaller in D-bonds by a factor close to √2 as compared to H-bonds. In some systems as carboxylic acid dimers, however, anomalous ratios of intensities are found upon such a substitution. Their origin is still obscure. Experimental results suggest that such anomalous ratios have much to do with the cyclic structure of these systems. It leads to stressing an important property of H-bonded cyclic structures which is that they seem necessary for having transfers of protons between molecules through H-bonds in a neutral aqueous medium (p H =7) at room temperature. The mechanism of such transfers of protons is still poorly known, but these transfers are now suspected to play a fundamental role in such widespread reactions as hydrolysis, peptide synthesis, etc... which may make them soon appear as being a crucial basic mechanism for reactivity of aqueous systems, particularly biological systems

Mass transfer with complex reversible chemical reactions. II: Parallel reversible chemical reactions

NARCIS (Netherlands)

Versteeg, Geert; van Beckum, F.P.H.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria

1990-01-01

An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and

Mass transfer with complex reversible chemical reactions. II: parallel reversible chemical reactions

NARCIS (Netherlands)

Versteeg, G.F.; Kuipers, J.A.M.; Beckum, van F.P.H.; van Swaaij, W.P.M.

1990-01-01

An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and

Tunable, Chemo- and Site-Selective Nitrene Transfer Reactions through the Rational Design of Silver(I) Catalysts.

Science.gov (United States)

Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

2017-09-19

Carbon-nitrogen (C-N) bonds are ubiquitous in pharmaceuticals, agrochemicals, diverse bioactive natural products, and ligands for transition metal catalysts. An effective strategy for introducing a new C-N bond into a molecule is through transition metal-catalyzed nitrene transfer chemistry. In these reactions, a metal-supported nitrene can either add across a C═C bond to form an aziridine or insert into a C-H bond to furnish the corresponding amine. Typical catalysts for nitrene transfer include Rh 2 L n and Ru 2 L n complexes supported by bridging carboxylate and related ligands, as well as complexes based on Cu, Co, Ir, Fe, and Mn supported by porphyrins and related ligands. A limitation of metal-catalyzed nitrene transfer is the ability to predictably select which specific site will undergo amination in the presence of multiple reactive groups; thus, many reactions rely primarily on substrate control. Achieving true catalyst-control over nitrene transfer would open up exciting possibilities for flexible installation of new C-N bonds into hydrocarbons, natural product-inspired scaffolds, existing pharmaceuticals or biorenewable building blocks. Silver-catalyzed nitrene transfer enables flexible control over the position at which a new C-N bond is introduced. Ag(I) supported by simple N-donor ligands accommodates a diverse range of coordination geometries, from linear to tetrahedral to seesaw, enabling the electronic and steric parameters of the catalyst to be tuned independently. In addition, the ligand, Ag salt counteranion, Ag/ligand ratio and the solvent all influence the fluxional and dynamic behavior of Ag(I) complexes in solution. Understanding the interplay of these parameters to manipulate the behavior of Ag-nitrenes in a predictable manner is a key design feature of our work. In this Account, we describe successful applications of a variety of design principles to tunable, Ag-catalyzed aminations, including (1) changing Ag/ligand ratios to influence

Computational Approach to Electron Charge Transfer Reactions

DEFF Research Database (Denmark)

Jónsson, Elvar Örn

-molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken...... in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems...... and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended...

Saponification reaction system: a detailed mass transfer coefficient determination.

Science.gov (United States)

Pečar, Darja; Goršek, Andreja

2015-01-01

The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate. This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures. The results indicated an important role of reliable kinetic model, as significant difference in k(L)a product was obtained with extended and simple approach.

Carboxylated, Fe-filled multiwalled carbon nanotubes as versatile catalysts for O2 reduction and H2 evolution reactions at physiological pH.

Science.gov (United States)

Bracamonte, M Victoria; Melchionna, Michele; Stopin, Antoine; Giulani, Angela; Tavagnacco, Claudio; Garcia, Yann; Fornasiero, Paolo; Bonifazi, Davide; Prato, Maurizio

2015-09-01

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl-functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O2 and H2 O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polarization transfer in (d-vector,n-vector) reactions

International Nuclear Information System (INIS)

Walter, R.L.; Tornow, W.

1986-01-01

The status of the measurements and the role of polarization transfer coefficients for (d/sup →/,n/sup →/) reactions is reviewed. Emphasis is given to reactions, involving light-nuclei systems. The importance of (d/sup →/,n/sup →/) reactions as sources of polarized neutrons is pointed out

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

Science.gov (United States)

Basilevsky, M. V.; Odinokov, A. V.; Titov, S. V.; Mitina, E. A.

2013-12-01

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/kBT where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the

Ab initio study of {sup 2}H(d,{gamma}){sup 4}He, {sup 2}H(d,p){sup 3}H, and {sup 2}H(d,n){sup 4}He reactions and the tensor force

Energy Technology Data Exchange (ETDEWEB)

Arai, K.; Aoyama, S.; Suzuki, Y.; Descouvemont, P.; Baye, D. [Division of General Education, Nagaoka National College of Technology, 888 Nishikatakai, Nagaoka, Niigata, 940-8532 (Japan); Center for Academic Information Service, Niigata University, Niigata 950-2181 (Japan); Department of Physics, Niigata University, Niigata 950-2181, Japan and RIKEN Nishina Center, Wako 351-0198 (Japan); Physique Nucleaire Theorique et Physique Mathematique, C.P.229, Universite Libre de Bruxelles, B 1050 Brussels (Belgium); Physique Quantique, CP165/82, Universite Libre de Bruxelles, B-1050 Brussels (Belgium)

2012-11-12

The {sup 2}H(d,p){sup 3}H, {sup 2}H(d,n){sup 3}He, and {sup 2}H(d,{gamma}){sup 4}He reactions at low energies are studied with realistic nucleon-nucleon interactions in an ab initio approach. The obtained astrophysical S-factors are all in very good agreement with experiment. The most important channels for both transfer and radiative capture are all found to dominate thanks to the tensor force.

Studies on the Mechanism of Electron Bifurcation Catalyzed by Electron Transferring Flavoprotein (Etf) and Butyryl-CoA Dehydrogenase (Bcd) of Acidaminococcus fermentans*

Science.gov (United States)

Chowdhury, Nilanjan Pal; Mowafy, Amr M.; Demmer, Julius K.; Upadhyay, Vikrant; Koelzer, Sebastian; Jayamani, Elamparithi; Kahnt, Joerg; Hornung, Marco; Demmer, Ulrike; Ermler, Ulrich; Buckel, Wolfgang

2014-01-01

Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD+ complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH− is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH− by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD⨪, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH•, immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH− that converts crotonyl-CoA to butyryl-CoA. PMID:24379410

Probing the reaction mechanism of IspH protein by x-ray structure analysis

KAUST Repository

Gräwert, Tobias

2009-12-28

Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) represent the two central intermediates in the biosynthesis of isoprenoids. The recently discovereddeoxyxylulose 5-phosphate pathway generates a mixture of IPP and DMAPP in its final step by reductive dehydroxylation of 1-hydroxy-2-methyl- 2-butenyl 4-diphosphate. This conversion is catalyzed by IspH protein comprising a central iron-sulfur cluster as electron transfer cofactor in the active site. The five crystal structures of IspH in complex with substrate, converted substrate, products and PPi reported in this article provide unique insights into the mechanism of this enzyme. While IspH protein crystallizes with substrate bound to a [4Fe-4S] cluster, crystals of IspH in complex with IPP, DMAPP or inorganic pyrophosphate feature [3Fe-4S] clusters. The IspH:substrate complex reveals a hairpin conformation of the ligand with the C(1) hydroxyl group coordinated to the unique site in a [4Fe-4S] cluster of aconitase type. The resulting alkoxide complex is coupled to a hydrogen-bonding network, which serves as proton reservoir via a Thr167 proton relay. Prolonged x-ray irradiation leads to cleavage of the C(1)-O bond (initiated by reducing photo electrons). The data suggest a reaction mechanism involving a combination of Lewis-acid activation and proton coupled electron transfer. The resulting allyl radical intermediate can acquire a second electron via the iron-sulfur cluster. The reaction may be terminated by the transfer of a proton from the β-phosphate of the substrate to C(1) (affording DMAPP) or C(3) (affording IPP).

Probing the reaction mechanism of IspH protein by x-ray structure analysis

KAUST Repository

Grä wert, Tobias; Span, Ingrid; Eisenreich, Wolfgang; Rohdich, Felix; Eppinger, Jö rg; Bacher, Adelbert; Groll, Michael

2009-01-01

Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) represent the two central intermediates in the biosynthesis of isoprenoids. The recently discovereddeoxyxylulose 5-phosphate pathway generates a mixture of IPP and DMAPP in its final step by reductive dehydroxylation of 1-hydroxy-2-methyl- 2-butenyl 4-diphosphate. This conversion is catalyzed by IspH protein comprising a central iron-sulfur cluster as electron transfer cofactor in the active site. The five crystal structures of IspH in complex with substrate, converted substrate, products and PPi reported in this article provide unique insights into the mechanism of this enzyme. While IspH protein crystallizes with substrate bound to a [4Fe-4S] cluster, crystals of IspH in complex with IPP, DMAPP or inorganic pyrophosphate feature [3Fe-4S] clusters. The IspH:substrate complex reveals a hairpin conformation of the ligand with the C(1) hydroxyl group coordinated to the unique site in a [4Fe-4S] cluster of aconitase type. The resulting alkoxide complex is coupled to a hydrogen-bonding network, which serves as proton reservoir via a Thr167 proton relay. Prolonged x-ray irradiation leads to cleavage of the C(1)-O bond (initiated by reducing photo electrons). The data suggest a reaction mechanism involving a combination of Lewis-acid activation and proton coupled electron transfer. The resulting allyl radical intermediate can acquire a second electron via the iron-sulfur cluster. The reaction may be terminated by the transfer of a proton from the β-phosphate of the substrate to C(1) (affording DMAPP) or C(3) (affording IPP).

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

International Nuclear Information System (INIS)

Basilevsky, M. V.; Mitina, E. A.; Odinokov, A. V.; Titov, S. V.

2013-01-01

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ 0 =ℏω 0 /k B T where ω 0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ 0 0 ≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the

Golden rule kinetics of transfer reactions in condensed phase: the microscopic model of electron transfer reactions in disordered solid matrices.

Science.gov (United States)

Basilevsky, M V; Odinokov, A V; Titov, S V; Mitina, E A

2013-12-21

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/k(B)T where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local

Mass transfer model for two-layer TBP oxidation reactions

International Nuclear Information System (INIS)

Laurinat, J.E.

1994-01-01

To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments. Three cases were investigated: (1) transfer of water into the TBP layer with sparging of both the aqueous and TBP layers, (2) transfer of water into the TBP layer with sparging of just the TBP layer, and (3) transfer of butanol into the aqueous layer with sparging of both layers. The TBP layer was comprised of 99% pure TBP (spiked with butanol for the butanol transfer experiments), and the aqueous layer was comprised of either water or an aluminum nitrate solution. The liquid layers were air sparged to simulate the mixing due to the evolution of gases generated by oxidation reactions. A plastic tube and a glass frit sparger were used to provide different size bubbles. Rates of mass transfer were measured using infrared spectrophotometers provided by SRTC/Analytical Development

Insights into the mechanisms on chemical reactions: reaction paths for chemical reactions

International Nuclear Information System (INIS)

Dunning, T.H. Jr.; Rosen, E.; Eades, R.A.

1987-01-01

We report reaction paths for two prototypical chemical reactions: Li + HF, an electron transfer reaction, and OH + H 2 , an abstraction reaction. In the first reaction we consider the connection between the energetic terms in the reaction path Hamiltonian and the electronic changes which occur upon reaction. In the second reaction we consider the treatment of vibrational effects in chemical reactions in the reaction path formalism. 30 refs., 9 figs

Experimental and numerical reaction analysis on sodium-water chemical reaction field

International Nuclear Information System (INIS)

Deguchi, Yoshihiro; Takata, Takashi; Yamaguchi, Akira; Kikuchi, Shin; Ohshima, Hiroyuki

2015-01-01

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. This process ends up damages on the heat transport equipment in the SFR. Therefore, the study on sodium-water chemical reactions is of paramount importance for security reasons. This study aims to clarify the sodium-water reaction mechanisms using an elementary reaction analysis. A quasi one-dimensional flame model is applied to a sodium-water counter-flow reaction field. The analysis contains 25 elementary reactions, which consist of 17 H_2-O_2 and 8 Na-H_2O reactions. Temperature and species concentrations in the counter-flow reaction field were measured using laser diagnostics such as LIF and CARS. The main reaction in the experimental conditions is Na+H_2O → NaOH+H and OH is produced by H_2O+H → H_2+OH. It is demonstrated that the reaction model in this study well explains the structure of the sodium-water counter-flow diffusion flame. (author)

Reaction kinetics in open reactors and serial transfers between closed reactors

Science.gov (United States)

Blokhuis, Alex; Lacoste, David; Gaspard, Pierre

2018-04-01

Kinetic theory and thermodynamics of reaction networks are extended to the out-of-equilibrium dynamics of continuous-flow stirred tank reactors (CSTR) and serial transfers. On the basis of their stoichiometry matrix, the conservation laws and the cycles of the network are determined for both dynamics. It is shown that the CSTR and serial transfer dynamics are equivalent in the limit where the time interval between the transfers tends to zero proportionally to the ratio of the fractions of fresh to transferred solutions. These results are illustrated with a finite cross-catalytic reaction network and an infinite reaction network describing mass exchange between polymers. Serial transfer dynamics is typically used in molecular evolution experiments in the context of research on the origins of life. The present study is shedding a new light on the role played by serial transfer parameters in these experiments.

Single-particle and collective states in transfer reactions

International Nuclear Information System (INIS)

Lhenry, I.; Suomijaervi, T.; Giai, N. van

1993-01-01

The possibility to excite collective states in transfer reactions induced by heavy ions is studied. Collective states are described within the Random Phase Approximation (RPA) and the collectivity is defined according to the number of configurations contributing to a given state. The particle transfer is described within the Distorted Wave Born Approximation (DWBA). Calculations are performed for two different stripping reactions: 207 Pb( 20 Ne, 19 Ne) 208 Pb and 59 Co( 20 Ne, 19 F) 60 Ni at 48 MeV/nucleon for which experimental data are available. The calculation shows that a sizeable fraction of collective strength can be excited in these reactions. The comparison with experiment shows that this parameter-free calculation qualitatively explains the data. (author) 19 refs.; 10 figs

Structure and Mechanism of Styrene Monooxygenase Reductase: New Insight into the FAD–Transfer Reaction†

Science.gov (United States)

Morrison, Eliot; Kantz, Auric; Gassner, George T.; Sazinsky, Matthew H.

2013-01-01

The two–component flavoprotein styrene monooxygenase (SMO) from Pseudomonas putida S12 catalyzes the NADH– and FAD–dependent epoxidation of styrene to styrene oxide. In this study we investigate the mechanism of flavin reduction and transfer from the reductase (SMOB) to epoxidase (NSMOA) component and report our findings in light of the 2.2–Å crystal structure of SMOB. Upon rapidly mixing with NADH, SMOB forms an NADH→FADox charge–transfer intermediate and catalyzes a hydride–transfer reaction from NADH to FAD, with a rate constant of 49.1 ± 1.4 s−1, in a step that is coupled to the rapid dissociation of NAD+. Electrochemical and equilibrium–binding studies indicate that NSMOA binds FADhq ~13–times more tightly than SMOB, which supports a vectoral transfer of FADhq from the reductase to the epoxidase. After binding to NSMOA, FADhq rapidly reacts with molecular oxygen to form a stable C(4a)–hydroperoxide intermediate. The half–life of apoSMOB generated in the FAD–transfer reaction is increased ~21–fold, supporting the model of a protein–protein interaction between apoSMOB and NSMOA with the peroxide intermediate. The mechanisms of FAD–dissociation and transport from SMOB to NSMOA were probed by monitoring the competitive reduction of cytochrome c in the presence and absence of pyridine nucleotides. Based on these studies, we propose a model in which reduced FAD binds to SMOB in equilibrium between an unreactive, sequestered state (S–state) and more reactive, transfer state (T–state). Dissociation of NAD+ after the hydride transfer–reaction transiently populates the T–state, promoting the transfer of FADhq to NSMOA. The binding of pyridine nucleotides to SMOB–FADhq shifts the FADhq–binding equilibrium from the T–state to the S–state. Additionally, the 2.2–Å crystal structure of SMOB–FADox reported in this work is discussed in light of the pyridine nucleotide–gated flavin–transfer and electron–transfer

Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer.

Science.gov (United States)

Choi, Gilbert J; Zhu, Qilei; Miller, David C; Gu, Carol J; Knowles, Robert R

2016-11-10

Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process-a subset of the classical Hofmann-Löffler-Freytag reaction-amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

Multi-nucleon transfer: a probe to investigate the reaction mechanism around the barrier

International Nuclear Information System (INIS)

Mandal, Samit K.

2014-01-01

The investigation of multi-nucleon transfer mechanism offers valuable information on the pairing interactions that enhance the transfer of nucleon pairs across heavy ions involved in the reaction. These reactions are also a useful tool to study exotic nuclei far from the stability line, which can be explored with the new generation radioactive beam facility. In this talk, multi-nucleon transfer reaction mechanisms between heavy ions and their effect on the reaction dynamics around the coulomb barrier energies have been discussed. Experimental results will be presented with a semi classical description of multi nucleon transfer reaction calculation. One and two nucleon transfer cross sections reproduced using a quantum mechanical coupled channel calculations will also be discussed. A feasibility of investigation of multi-nucleon transfer mechanism to explore the pairing correlation at moderate spin states with radioactive beams will be discussed. (author)

A Study on Catalysis and Electrolyte Engineering for H2/O2 Electrochemical Reactions

KAUST Repository

Shinagawa, Tatsuya

2016-09-27

Water electrolysis conjugated with renewable energy sources potentially realizes a sustainable society. Although the current electrolyzers operate at extreme pH to maximize the electrolysis efficiency, near-neutral pH conditions may optimize the overall system operation when conjugated with renewable energy sources. In this context, a study on the electrolysis in the mild conditions is essential. The dissertation investigates the water electrolysis in various conditions, with a particular focus placed on milder conditions, to rationalize and improve its performance. Microkinetic analysis was performed for the cathodic half-reaction in conjugation with mass transport evaluation using various electrode materials. The analysis revealed a significant universal influence of electrolyte properties on the reaction performances at near-neutral pH. Investigation of the associated electrolyte properties (ion size, viscosity and activity/fugacity) rationally optimized the reaction conditions. Together with the separately performed studies on the anodic half-reaction and system configurations, the finding was successfully transferred to electrocatalytic and solar-driven water splitting systems. The presented herein is a fundamental yet crucial aspect of water electrolysis, which can advance the water electrolysis for the future.

Mass Transfer and Chemical Reaction Approach of the Kinetics of the Acetylation of Gadung Flour using Glacial Acetic Acid

Directory of Open Access Journals (Sweden)

Andri Cahyo Kumoro

2015-03-01

Full Text Available Acetylation is one of the common methods of modifying starch properties by introducing acetil (CH3CO groups to starch molecules at low temperatures. While most acetylation is conducted using starch as anhidroglucose source and acetic anhydride or vinyl acetate as nucleophilic agents, this work employ reactants, namely flour and glacial acetic acid. The purpose of this work are to study the effect of pH reaction and GAA/GF mass ratio on the rate of acetylation reaction and to determine its rate constants. The acetylation of gadung flour with glacial acetic acid in the presence of sodium hydroxide as a homogenous catalyst was studied at ambient temperature with pH ranging from 8-10 and different mass ratio of acetic acid : gadung flour (1:3; 1:4; and 1:5. It was found that increasing pH, lead to increase the degree of substitution, while increasing GAA/GF mass ratio caused such decreases in the degree of substitution, due to the hydrolysis of the acetylated starch. The desired starch acetylation reaction is accompanied by undesirable hydrolysis reaction of the acetylated starch after 40-50 minutes reaction time. Investigation of kinetics of the reaction observed that the value of mass transfer rate constant (Kcs is smaller than the surface reaction rate constant (k. Thus, it can be concluded that rate controlling step is mass transfer.  © 2015 BCREC UNDIP. All rights reservedReceived: 7th August 2014; Revised: 8th September 2014; Accepted: 14th September 2014How to Cite: Kumoro, A.C., Amelia, R. (2015. Mass Transfer and Chemical Reaction Approach of the Kinetics of the Acetylation of Gadung Flour using Glacial Acetic Acid. Bulletin of Chemical Reaction Engineering & Catalysis, 10 (1: 30-37. (doi:10.9767/bcrec.10.1.7181.30-37Permalink/DOI: http://dx.doi.org/10.9767/bcrec.10.1.7181.30-37

Pre-steady-state kinetic studies of redox reactions catalysed by Bacillus subtilis ferredoxin-NADP(+) oxidoreductase with NADP(+)/NADPH and ferredoxin.

Science.gov (United States)

Seo, Daisuke; Soeta, Takahiro; Sakurai, Hidehiro; Sétif, Pierre; Sakurai, Takeshi

2016-06-01

Ferredoxin-NADP(+) oxidoreductase ([EC1.18.1.2], FNR) from Bacillus subtilis (BsFNR) is a homodimeric flavoprotein sharing structural homology with bacterial NADPH-thioredoxin reductase. Pre-steady-state kinetics of the reactions of BsFNR with NADP(+), NADPH, NADPD (deuterated form) and B. subtilis ferredoxin (BsFd) using stopped-flow spectrophotometry were studied. Mixing BsFNR with NADP(+) and NADPH yielded two types of charge-transfer (CT) complexes, oxidized FNR (FNR(ox))-NADPH and reduced FNR (FNR(red))-NADP(+), both having CT absorption bands centered at approximately 600n m. After mixing BsFNR(ox) with about a 10-fold molar excess of NADPH (forward reaction), BsFNR was almost completely reduced at equilibrium. When BsFNR(red) was mixed with NADP(+), the amount of BsFNR(ox) increased with increasing NADP(+) concentration, but BsFNR(red) remained as the major species at equilibrium even with about 50-fold molar excess NADP(+). In both directions, the hydride-transfer was the rate-determining step, where the forward direction rate constant (~500 s(-1)) was much higher than the reverse one (reaction. The characteristics of the BsFNR reactions with NADP(+)/NADPH were compared with those of other types of FNRs. Copyright © 2016 Elsevier B.V. All rights reserved.

Transfer reactions with very heavy ions. Quarterly report 3. quarter 1987

International Nuclear Information System (INIS)

Juutinen, Sakari.

1988-03-01

This thesis deals with the reaction mechanism of the few-nucleon transfer reactions between the 58 Ni projectiles and the Dy targets. A series of transfer experiments utilizing the particle-γ coincidence technique was performed. Particle detection was used to give the scattering angles of two reaction products and the reaction channel was selected by the discrete γ-rays in the Ge detectors. Total γ-ray energy and multiplicity distributions were measured by the Spin Spectrometer. Total γ-ray energy and multiplicity distributions, γ-ray spectra obtained by the Ge and NaI detectors and angular distributions of the projectile-like ions are discussed. For one- and two-neutron transfer the experimental results provide direct evidence of a cold mechanism populating high-spin states near the yrast line. A schematic model for the transfer mechanism is proposed. This model accounts for the prominent features of one- and two-neutron pickup

Two-proton transfer reactions on even Ni and Zn isotopes

International Nuclear Information System (INIS)

Boucenna, A.; Kraus, L.; Linck, I.; Tsan Ung Chan

1988-01-01

Two-proton transfer reactions induced by 112 MeV 12 C ions on even Ni and Zn isotopes are found to be less selective than the analogous two-neutron transfer reactions induced on the same targets in a similar incident energy range. The additional collective aspects observed in the proton transfer are examined in view of a semiphenomenological model of two quasi-particles coupled to a triaxial asymmetric rotor. Tentative spin and parity assignments emerge from this comparison, from crude shell model calculations and from systematic trends

Transfer and breakup reactions at intermediate energies

International Nuclear Information System (INIS)

Stokstad, R.G.

1986-04-01

The origin of the quasi-elastic peak in peripheral heavy-ion reactions is discussed in terms of inelastic scattering and transfer reactions to unbound states of the primary projectile-like fragment. The situation is analogous to the use of reverse kinematics in fusion reactions, a technique in which the object of study is moving with nearly the beam velocity. It appears that several important features of the quasi-elastic peak may be explained by this approach. Projectile-breakup reactions have attractive features for the study of nuclear structure. They may also be used to determine the partition of excitation energy in peripheral reactions. At intermediate energies, neutron-pickup reactions leading to four-body final states become important. Examples of experiments are presented that illustrate these points. 15 refs., 14 figs

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

Energy Technology Data Exchange (ETDEWEB)

Basilevsky, M. V.; Mitina, E. A. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); Odinokov, A. V. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow (Russian Federation); Titov, S. V. [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)

2013-12-21

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ{sub 0} < 1 − 3) and for low (ξ{sub 0}≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the

Stability and isomerization reactions of phenyl cation C{sub 6}H{sub 5}{sup +} isomers

Energy Technology Data Exchange (ETDEWEB)

Shi, Dandan [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Yang, Xue [College of Science, Jilin Institute of Chemical Technology, Jilin 132022 (China); Zhang, Xiaomei; Shan, Shimin [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Xu, Haifeng, E-mail: xuhf@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China); Yan, Bing, E-mail: yanbing@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012 (China)

2016-03-01

Highlights: • A total of 60 isomers of C{sub 6}H{sub 5}{sup +} cations were obtained at density functional theory. • The stability and isomerization reactions of C{sub 6}H{sub 5}{sup +} isomers were performed. • The structures, frequencies, thermodynamic properties of isomers were summarized. • Ring to ring or chain isomerization pathways were investigated using IRC method. • Result shows reactions contain hydrogen transfer, bond broken and reconstruction. - Abstract: As a key polyatomic molecular cation that plays a pivotal role in growth of the polycyclic aromatic hydrocarbons, phenyl cation C{sub 6}H{sub 5}{sup +} exhibits various isomers and isomerization reactions. Investigation on the structure and stability of the isomers as well as the isomerization is important for better understanding the chemical reactions involving C{sub 6}H{sub 5}{sup +} cations. In this work, we have performed a theoretical study on the stability and isomerization reactions of C{sub 6}H{sub 5}{sup +} isomers at density functional theory B3LYP/6-311G (d, p) level. We have obtained a total of 60 isomers of C{sub 6}H{sub 5}{sup +} cations, most of which are reported for the first time. The geometries, vibrational frequencies, thermodynamic properties and stability of 28 out of 60 isomers have been summarized in detail. Different ring-to-ring and ring-to-chain isomerization pathways, which are connected via 28 transition states, have been investigated using the intrinsic reaction coordinate method. The results show that the isomerization reactions occur via hydrogen migration followed by bond-breaking and reconstruction.

New Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

DEFF Research Database (Denmark)

Deville, Claire; Sundberg, Jonas; McKenzie, Christine Joy

Proton-coupled electron-transfer (PCET) is found in a range of oxidation-reduction reactions in biology.1 This mechanism is of interest for applications in energy conversion processes. The PCET reaction has been shown to be facilitated when the proton is transferred to an intramolecular basic sit...

Microbial flavoprotein monooxygenases as mimics of mammalian flavin-containing monooxygenases for the enantioselective preparation of drug metabolites

NARCIS (Netherlands)

Gul, Turan; Krzek, Marzena; Permentier, Hjalmar; Fraaije, Marco; Bischoff, Rainer

2016-01-01

Mammalian flavin-containing monooxygenases are difficult to obtain and study while they play a major role in detoxifying various xenobiotics. In order to provide alternative biocatalytic tools to generate FMO-derived drug metabolites, a collection of microbial flavoprotein monooxygenases,

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules.

Science.gov (United States)

Smith, Caleb A; Gillespie, Blanton R; Heard, George L; Setser, D W; Holmes, Bert E

2017-11-22

The recombination of CF 3 and CHF 2 radicals in a room-temperature bath gas was used to prepare vibrationally excited CF 3 CHF 2 * molecules with 101 kcal mol -1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF 3 , CF 3 (F)C: and C 2 F 4 product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF 3 (F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 10 4 , 4.7 × 10 4 , and 1.1 × 10 4 s -1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E 0 ) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol -1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with 1,1-HF elimination being more important than 1,2-HF elimination. The trend of increasing threshold energies for both 1,1-HF and 1,2-HF processes with the number of F atoms in the fluoroethane molecule is summarized and investigated with electronic-structure calculations. Examination of the intrinsic reaction coordinate associated with the 1,1-HF elimination reaction found an adduct between CF 3 (F)C: and HF in the exit channel with a dissociation energy of ∼5 kcal mol -1 . Hydrogen-bonded complexes between HF and the H atom migration transition state of CH 3 (F)C: and the F atom migration transition state of CF 3 (F)C: also were found by the calculations. The role that these carbene-HF complexes could play in 1,1-HF elimination reactions is discussed.

Observation of the one- to six-neutron transfer reactions at sub-barrier energies

Energy Technology Data Exchange (ETDEWEB)

Jiang, C.L.; Rehm, K.E.; Gehring, J. [and others

1995-08-01

It was suggested many years ago that when two heavy nuclei are in contact during a grazing collision, the transfer of several correlated neutron-pairs could occur. Despite considerable experimental effort, however, so far only cross sections for up to four-neutron transfers have been uniquely identified. The main difficulties in the study of multi-neutron transfer reactions are the small cross sections encountered at incident energies close to the barrier, and various experimental uncertainties which can complicate the analysis of these reactions. We have for the first time found evidence for multi-neutron transfer reactions covering the full sequence from one- to six-neutron transfer reactions at sub-barrier energies in the system {sup 58}Ni + {sup 100}Mo.

One-neutron transfer reaction: a toy model in one dimension

International Nuclear Information System (INIS)

G. Galilei, Padova, Italy INFN, Sezione di Padova, Padova (Italy))" data-affiliation=" (Dipartimento di Fisica e Astronomia G. Galilei, Padova, Italy INFN, Sezione di Padova, Padova (Italy))" >Moschini, L

2014-01-01

A simple 1D toy model to study one-neutron transfer reactions is developed. It is based on the solution of the time dependent Schroedinger equation for a particle initially bound by a fixed potential well, perturbed by a second moving potential, which accounts for the second partner of the reaction. At the end of the time evolution it is possible to evaluate the probability of the transfer of the particle from a potential to the other, as well as the transfer to continuum states in the case of weakly-bound systems. Although rather simple, the model accounts for most of the physical characteristics of these kind of reactions: such as the existence of an optimum Q-value and the dependence on the parameters defining the relative motion of the two potentials

Structuring Pd Nanoparticles on 2H-WS2 Nanosheets Induces Excellent Photocatalytic Activity for Cross-Coupling Reactions under Visible Light.

Science.gov (United States)

Raza, Faizan; Yim, DaBin; Park, Jung Hyun; Kim, Hye-In; Jeon, Su-Ji; Kim, Jong-Ho

2017-10-18

Effective photocatalysts and their surface engineering are essential for the efficient conversion of solar energy into chemical energy in photocatalyzed organic transformations. Herein, we report an effective approach for structuring Pd nanoparticles (NPs) on exfoliated 2H-WS 2 nanosheets (WS 2 /PdNPs), resulting in hybrids with extraordinary photocatalytic activity in Suzuki reactions under visible light. Pd NPs of different sizes and densities, which can modulate the photocatalytic activity of the as-prepared WS 2 /PdNPs, were effectively structured on the basal plane of 2H-WS 2 nanosheets via a sonic wave-assisted nucleation method without any reductants at room temperature. As the size of Pd NPs on WS 2 /PdNPs increased, their photocatalytic activity in Suzuki reactions at room temperature increased substantially. In addition, it was found that protic organic solvents play a crucial role in activating WS 2 /PdNPs catalysts in photocatalyzed Suzuki reactions, although these solvents are generally considered much less effective than polar aprotic ones in the conventional Suzuki reactions promoted by heterogeneous Pd catalysts. A mechanistic investigation suggested that photogenerated holes are transferred to protic organic solvents, whereas photogenerated electrons are transferred to Pd NPs. This transfer makes the Pd NPs electron-rich and accelerates the rate-determining step, i.e., the oxidative addition of aryl halides under visible light. WS 2 /PdNPs showed the highest turnover frequency (1244 h -1 ) for photocatalyzed Suzuki reactions among previously reported photocatalysts.

Proton transfer and unimolecular decay in the low-energy-reaction dynamics of H3O+ with acetone

International Nuclear Information System (INIS)

Creasy, W.R.; Farrar, J.M.

1983-01-01

The title reaction has been studied at collision energies of 0.83 and 2.41 eV. Direct reaction dynamics have been observed at both energies and an increasingly high fraction of the total energy appears in product translation as the collision energy increases. This result is consistent with the concept of induced repulsive energy release, which becomes more effective as trajectories sample the corner of the potential energy surface. At the higher collision energy, the protonated acetone cation undergoes two unimolecular decay channels: C-C bond cleavage to CH 3 CO + and CH 4 , and C-O bond cleavagto C 3 H 5 + (presumably to allyl cation) and H 2 O. The CH 3 CO + channel, endothermic relative to ground state protonated acetone cations by 0.74 eV, appears to liberate 0.4 eV in relative product translation while the C 3 H 5 + channel, endothermic by 2.17 eV, liberates only 0.07 eV in relative translation. These results are discussed in terms of the location on the reaction coordinate and magnitudes of potential energy barriers to 1,3-hydrogen atoms shifts which must precede the bond cleavage processes

Mass transfer with chemical reaction in multiphase systems

International Nuclear Information System (INIS)

Alper, E.

1983-01-01

These volumes deal with the phenomenon of 'mass transfer with chemical reaction' which is of industrial, biological and physiological importance. In process engineering, it is encountered both in separation processes and in reaction engineering and both aspects are covered here in four sections: introduction; gas-liquid system; liquid-liquid system; and gas-liquid-solid system

Selective population of high-j states via heavy-ion-induced transfer reactions

International Nuclear Information System (INIS)

Bond, P.D.

1982-01-01

One of the early hopes of heavy-ion-induced transfer reactions was to populate states not seen easily or at all by other means. To date, however, I believe it is fair to say that spectroscopic studies of previously unknown states have had, at best, limited success. Despite the early demonstration of selectivity with cluster transfer to high-lying states in light nuclei, the study of heavy-ion-induced transfer reactions has emphasized the reaction mechanism. The value of using two of these reactions for spectroscopy of high spin states is demonstrated: 143 Nd( 16 O, 15 O) 144 Nd and 170 Er( 16 O, 15 Oγ) 171 Er

Electron emission from transfer ionization reaction in 30 keV amu‑1 He 2+ on Ar collision

Science.gov (United States)

Amaya-Tapia, A.; Antillón, A.; Estrada, C. D.

2018-06-01

A model is presented that describes the transfer ionization process in H{e}2++Ar collision at a projectile energy of 30 keV amu‑1. It is based on a semiclassical independent-particle close-coupling method that yields a reasonable agreement between calculated and experimental values of the total single-ionization and single-capture cross sections. It is found that the transfer ionization reaction is predominantly carried out through simultaneous capture and ionization, rather than by sequential processes. The transfer-ionization differential cross section in energy that is obtained satisfactorily reproduces the global behavior of the experimental data. Additionally, the probabilities of capture and ionization as function of the impact parameter for H{e}2++A{r}+ and H{e}++A{r}+ collisions are calculated, as far as we know, for the first time. The results suggest that the model captures essential elements that describe the two-electron transfer ionization process and could be applied to systems and processes of two electrons.

A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solution based upon a mixed quantum-classical approximation. II. Proton transfer reaction in non-polar solvent

Science.gov (United States)

Kojima, H.; Yamada, A.; Okazaki, S.

2015-05-01

The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions.

Regge parametrization of angular distributions for heavy-ion transfer reactions

International Nuclear Information System (INIS)

Carlson, B.V.; McVoy, K.W.

1977-01-01

A two-pole one-zero Regge parametrization of the l-window for transfer reactions is employed in conjunction with a chi-squared search program to obtain high-quality fits to a wide variety of transfer data. The data employed include both direct and multi-step transfers. (Auth.)

Effect of electrostatic interactions on electron-transfer reactions

International Nuclear Information System (INIS)

Hickel, B.

1987-01-01

Fast reactions of electron transfer are studied by pulsed radiolysis. By this technique radicals and ionic radicals with high redox potentials are created homogeneously in the solution in about 10 -8 second. For solvated electron effect of electrostatic interaction on kinetics of reactions limited by diffusion is obtained with a good approximation by the Debye equation when ion mobility is known. Deviation from the theory occurs in ion pair formation, which is evidenced experimentally in reactions between anions when cations are complexed by a cryptate. Slow reactions k 8 M -1 s -1 are more sensitive to electrostatic interactions than reactions limited by diffusion. When there is no ion pair formation the velocity constant depends upon dielectric constant of the solvent and reaction distance. 17 refs

Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

Science.gov (United States)

Lennox, J Christian; Dempsey, Jillian L

2017-11-22

A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

Parallel proton transfer pathways in aqueous acid-base reactions

NARCIS (Netherlands)

Cox, M.J.; Bakker, H.J.

2008-01-01

We study the mechanism of proton transfer (PT) between the photoacid 8-hydroxy-1,3, 6-pyrenetrisulfonic acid (HPTS) and the base chloroacetate in aqueous solution. We investigate both proton and deuteron transfer reactions in solutions with base concentrations ranging from 0.25M to 4M. Using

Probing the dynamic interface between trimethylamine dehydrogenase (TMADH) and electron transferring flavoprotein (ETF) in the TMADH-2ETF complex: role of the Arg-alpha237 (ETF) and Tyr-442 (TMADH) residue pair.

Science.gov (United States)

Burgess, Selena G; Messiha, Hanan Latif; Katona, Gergely; Rigby, Stephen E J; Leys, David; Scrutton, Nigel S

2008-05-06

We have used multiple solution state techniques and crystallographic analysis to investigate the importance of a putative transient interaction formed between Arg-alpha237 in electron transferring flavoprotein (ETF) and Tyr-442 in trimethylamine dehydrogenase (TMADH) in complex assembly, electron transfer, and structural imprinting of ETF by TMADH. We have isolated four mutant forms of ETF altered in the identity of the residue at position 237 (alphaR237A, alphaR237K, alphaR237C, and alphaR237E) and with each form studied electron transfer from TMADH to ETF, investigated the reduction potentials of the bound ETF cofactor, and analyzed complex formation. We show that mutation of Arg-alpha237 substantially destabilizes the semiquinone couple of the bound FAD and impedes electron transfer from TMADH to ETF. Crystallographic structures of the mutant ETF proteins indicate that mutation does not perturb the overall structure of ETF, but leads to disruption of an electrostatic network at an ETF domain boundary that likely affects the dynamic properties of ETF in the crystal and in solution. We show that Arg-alpha237 is required for TMADH to structurally imprint the as-purified semiquinone form of wild-type ETF and that the ability of TMADH to facilitate this structural reorganization is lost following (i) redox cycling of ETF, or simple conversion to the oxidized form, and (ii) mutagenesis of Arg-alpha237. We discuss this result in light of recent apparent conflict in the literature relating to the structural imprinting of wild-type ETF. Our studies support a mechanism of electron transfer by conformational sampling as advanced from our previous analysis of the crystal structure of the TMADH-2ETF complex [Leys, D. , Basran, J. , Sutcliffe, M. J., and Scrutton, N. S. (2003) Nature Struct. Biol. 10, 219-225] and point to a key role for the Tyr-442 (TMADH) and Arg-alpha237 (ETF) residue pair in transiently stabilizing productive electron transfer configurations. Our work

An abnormally slow proton transfer reaction in a simple HBO derivative due to ultrafast intramolecular-charge transfer events.

Science.gov (United States)

Alarcos, Noemí; Gutierrez, Mario; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

2015-07-07

We report on the steady-state, picosecond and femtosecond time-resolved studies of a charge and proton transfer dye 6-amino-2-(2'-hydroxyphenyl)benzoxazole (6A-HBO) and its methylated derivative 6-amino-2-(2'-methoxyphenyl)benzoxazole (6A-MBO), in different solvents. With femtosecond resolution and comparison with the photobehaviour of 6A-MBO, we demonstrate for 6A-HBO in solution, the photoproduction of an intramolecular charge-transfer (ICT) process at S1 taking place in ∼140 fs or shorter, followed by solvent relaxation in the charge transferred species. The generated structure (syn-enol charge transfer conformer) experiences an excited-state intramolecular proton-transfer (ESIPT) reaction to produce a keto-type tautomer. This subsequent proton motion occurs in 1.2 ps (n-heptane), 14 ps (DCM) and 35 ps (MeOH). In MeOH, it is assisted by the solvent molecules and occurs through tunneling for which we got a large kinetic isotope effect (KIE) of about 13. For the 6A-DBO (deuterated sample in CD3OD) the global proton-transfer reaction takes place in 200 ps, showing a remarkable slow KIE regime. The slow ESIPT reaction in DCM (14 ps), not through tunnelling as it is not sensitive to OH/OD exchange, has however to overcome an energy barrier using intramolecular as well as solvent coordinates. The rich ESIPT dynamics of 6A-HBO in the used solutions is governed by an ICT reaction, triggered by the amino group, and it is solvent dependent. Thus, the charge injection to a 6A-HBO molecular frame makes the ICT species more stable, and the phenol group less acidic, slowing down the subsequent ESIPT reaction. Our findings bring new insights into the coupling between ICT and ESIPT reactions on the potential-energy surfaces of several barriers.

Effect of strain on bond-specific reaction kinetics during the oxidation of H-terminated (111) Si

International Nuclear Information System (INIS)

Gokce, Bilal; Aspnes, David E.; Gundogdu, Kenan

2011-01-01

Although strain is used in semiconductor technology for manipulating optical, electronic, and chemical properties of semiconductors, the understanding of the microscopic phenomena that are affected or influenced by strain is still incomplete. Second-harmonic generation data obtained during the air oxidation of H-terminated (111) Si reveal the effect of compressive strain on this chemical reaction. Even small amounts of strain manipulate the reaction kinetics of surface bonds significantly, with tensile strain enhancing oxidation and compressive strain retarding it. This dramatic change suggests a strain-driven charge transfer mechanism between Si-H up bonds and Si-Si back bonds in the outer layer of Si atoms.

Theory of nuclear heavy-ion direct transfer reactions

International Nuclear Information System (INIS)

Crowley, B.J.B.

1979-01-01

We review the distorted-wave approach to direct transfer reactions and draw attention to some of the shortcomings of current theories. We show that a reformulated form of the distorted-wave Born approximation (DWBA) for transfer can lead to important simplifications of the theory, which are valid for nuclear heavy-ion induced reactions at energies > or approx. =MeV/nucleon. In particular, in the semiclassical limit, it leads to a new and simple formula for the transfer t-matrix which includes all the essential physics while offering several important advantages over standard ''full-recoil finite-range'' DWBA. One such advantage is that the new formula is more transparent in that it is amendable to interpretation and analytical manipulation. At high-energy it is shown to reduce to one earlier deduced using eikonal-DWBA. The conditions for the validity of the new theory are discussed in detail. They are shown to be generally well satisfied for small-mass transfer between heavy-ions at energies at or above those particularly favour transfer (> or approx. =10 MeV/nucleon for transfer of valence nucleons). The restriction to small mass is not due to any recoil approximation; in fact, it is only a necessary restriction at certain energies. The theory treats recoil exactly. Consideration of the optimum dynamical conditions for transfer leads to a set of matching conditions. The presence of hitherto neglected absorption, arising from dynamical effects of poor matching, it suggested and qualitatively discussed. Condition under which such absorption may be neglected are derived. Results of numerical calculations are presented showing that the theory is capable of good agreement with standard full-recoil finite-range DWBA, and that it is capable of giving at least as good an account of experimental data for nucleon-transfer between heavy-ions at energies approx.10 MeV/nucleon

Positive photocatalysis of a Diels-Alder reaction by quenching of excited naphthalene-indole charge-transfer complex with cyclohexadiene.

Science.gov (United States)

Gonzalez-Béjar, María; Stiriba, Salah-Eddine; Miranda, Miguel A; Pérez-Prieto, Julia

2007-02-01

[reaction: see text] Naphthalene photo-catalyzes formation of cyclohexadiene-indole cycloadducts in a wavelength-dependent process. Steady-state irradiation and time-resolved fluorescence studies agree well with NP-InH ground-state charge transfer (CT) complexes as the key species responsible for the photo-catalyzed process.

Nuclear transfer in peripheral heavy ion reactions

International Nuclear Information System (INIS)

Werner, K.

1984-01-01

The aim of the whole thesis is to understand the experimental results of N. Frascaria et al. (1980), namely structures in the cross section as function of the excitation energy for the reaction 40 Ca + 40 Ca at 400 MeV incident energy. We present therefore in chapter 1 a simple model of two identical potentials with only two energy levels. On the base of statistically independent T-L excitations and by fitting a two parameters to the experiments it succeeds to reproduce sufficiently the experimental results. The next step is a microscopical treatment of these parameters for the understanding and the foundation of the fitted values. For this we develop in chapter 2 a theory of collective variables in the framework of TDHF which allows to perform in chapter 3 in a very transparent way microscopical calculations and especially to understand the transfer behaviour in peripheral heavy ion reactions. This transfer behaviour will also be the key for the understanding of the experimental structures. (orig.) [de

Synthesis and Reactions of Five-Membered Heterocycles Using Phase Transfer Catalyst (PTC Techniques

Directory of Open Access Journals (Sweden)

Ahmed M. El-Sayed

2014-01-01

Full Text Available Phase transfer catalysts (PTCs have been widely used for the synthesis of organic compounds particularly in both liquid-liquid and solid-liquid heterogeneous reaction mixtures. They are known to accelerate reaction rates by facilitating formation of interphase transfer of species and making reactions between reagents in two immiscible phases possible. Application of PTC instead of traditional technologies for industrial processes of organic synthesis provides substantial benefits for the environment. On the basis of numerous reports it is evident that phase-transfer catalysis is the most efficient way for generation and reactions of many active intermediates. In this review we report various uses of PTC in syntheses and reactions of five-membered heterocycles compounds and their multifused rings.

Mass transfer model for two-layer TBP oxidation reactions: Revision 1

International Nuclear Information System (INIS)

Laurinat, J.E.

1994-01-01

To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the Canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. Bubbles containing reaction products enhance the rate of transfer of water from the aqueous layer to the organic layer. These bubbles are generated by the oxidation of TBP and its reaction products in the organic layer and by the oxidation of butanol in the aqueous layer. Butanol is formed by the hydrolysis of TBP in the organic layer. For aqueous-layer bubbling to occur, butanol must transfer into the aqueous layer. Consequently, the rate of oxidation and bubble generation in the aqueous layer strongly depends on the rate of transfer of butanol from the organic to the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments

Sub-Coulomb heavy ion neutron transfer reactions and neutron orbit sizes

International Nuclear Information System (INIS)

Phillips, W.R.

1976-01-01

Direct transfer reactions below the Coulomb barrier offer the best means of determining neutron densities near the nuclear surface. This paper describes how heavy ion sub-Coulomb transfer can be used to determine the rms radii of neutron orbits in certain nuclei. The theoretical background is outlined and problems associated with the comparison of experiment and theory are discussed. Experiments performed to calibrate sub-Coulomb heavy ion transfer reactions are presented, and some comments are made on the relative roles of light and heavy ion reactions. Preliminary values for the rms radii of neutron orbits and neutron excesses extracted from recent experiments are given, and some remarks are made concerning the implications of these results for the triton wave function and for the Coulomb energy difference anomaly. (author)

Laser-induced charge transfer in the HeH2+ quasimolecule

International Nuclear Information System (INIS)

Errea, L.F.; Mendez, L.; Riera, A.

1983-01-01

In a recent publication, the charge transfer cross section for He 2+ +H(ls) collisions through photon-assisted 2psigma--3dsigma transitions was calculated; this calculation, however, contained several errors whose quantitative--even qualitative effect on the results is not obvious. We present a correct evaluation of this laser-induced cross section, which turns out to be larger, and present a maximum for longer wavelengths, than the values previously reported. In addition, we have checked the applicability of perturbation theory, of the stationary phase, uniform and Landau--Zener approximations, and the importance of potentially competitive photon-assisted reactions

High spin levels populated in multinucleon transfer reaction with 480 MeV 12C

International Nuclear Information System (INIS)

Kraus, L.; Boucenna, A.; Linck, I.

1988-01-01

Two- and three-nucleon stripping reactions induced by 480 MeV 12 C have been studied on 12 C, 16 O, 28 Si, 40 Ca and 54 Fe target nuclei. Discrete levels are fed with cross sections up to 1 mb/sr for d-transfer reactions and one order and two orders of magnitude less for 2p- and 3 He-transfer reactions, respectively. These reactions preferentially populate high spin states with stretched configurations. Several spin assignments were known from transfer reactions induced by lighter projectiles at incident energies well above the Coulomb barrier. In the case of two-nucleon transfer reactions, the energy of these states is well reproduced by crude shell model calculations. Such estimates are of use in proposing spins of newly observed states especially as the shapes of the measured angular distributions are independent of the final spin of the residual nucleus

Intermolecula transfer and elimination of molecular hydrogen in thermal reactions of unsaturated organic compounds

Energy Technology Data Exchange (ETDEWEB)

Suria, Sabartanty [Iowa State Univ., Ames, IA (United States)

1995-02-10

Two reactions which are important to coal liquefaction include intermolecular transfer and the elimination of two hydrogen atoms. We have designed several model reactions to probe the viability of several hydrogen transfer and elimination pathways. This report described studies on these reactions using organic model compounds.

Single proton transfer reactions on odd-even nuclei

International Nuclear Information System (INIS)

Blasi, N.

1984-01-01

This thesis is devoted to the study of one proton transfer reactions, performed with the use of the magnetic spectrograph QMG/2 of the KVI, in two regions of the mass table. Stripping and pickup reactions on the odd-A target nuclei 193 Ir and 197 Au are described in the first part. The experimental spectroscopic factors obtained are used to test several collective models that are based on coupling between bosons (phonons) and fermions. In the second part, the proton stripping reactions on 113 In and 115 In are studied. Shell model calculations are performed and applied to the experimental results. (Auth.)

Definition and determination of the triplet-triplet energy transfer reaction coordinate.

Science.gov (United States)

Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Acuña, A Ulises; Frutos, Luis Manuel

2014-01-21

A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

Mechanism and kinetics of LiX(X=H, D, T) + H2O reaction

International Nuclear Information System (INIS)

Lei Hongjie; Duan Hao; Xing Pifeng; Tang Yongjian

2011-01-01

The reaction mechanism of LiX(X=H, D, T) with H 2 O was investigated at MP2/6-311G (d) level using ab initio quantum chemistry in Gaussian 03 software. The equilibrium geometries, harmonic frequencies and energy of various stationary points on the potential energy surfaces were calculated in the lowest singlet states. Considering the quantum correction, the reaction rate constants were calculated using classical transition state theory. The results show the reaction of LiH (LiD, LiT) with H 2 O was considerably dependent on temperature that it is lower, the reaction rate constants are smaller. (authors)

1H(d,2p)n reaction at 2 GeV deuteron energy

International Nuclear Information System (INIS)

Erohuml, J.; Fodor, Z.; Koncz, P.; Seres, Z.; Perdrisat, C.F.; Punjabi, V.; Boudard, A.; Bonin, B.; Garcon, M.; Lombard, R.; Mayer, B.; Terrien, Y.; Tomasi, E.; Boivin, M.; Yonnet, J.; Bhang, H.C.; Youn, M.; Belostotsky, S.L.; Grebenuk, O.G.; Nikulin, V.N.; Kudin, L.G.

1994-01-01

The 1 H(d,2p)n deuteron breakup reaction was measured at 2 GeV deuteron energy in a kinematically complete experiment. Fivefold differential cross sections are given in a wide range of kinematical variables and analyzed in terms of impulse approximation and NN rescattering. The deuteron momentum density was determined and deviations were found depending on the value of the four-momentum transfer |t| in the scattering process. At low |t| the momentum densities are in good agreement with the impulse approximation whereas large discrepancies were found above q∼200 MeV/c when the four-momentum transfer was large. Various possible origins of the anomalous behavior at high q values are discussed

Double electron transfer in H- + H+ collisions

International Nuclear Information System (INIS)

Braeuning, H; Helm, H; Briggs, J S; Salzborn, E

2007-01-01

Absolute cross sections for double electron transfer in H - + H + collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations

Flat Graphene-Enhanced Electron Transfer Involved in Redox Reactions.

Science.gov (United States)

Pan, Meilan; Zhang, Yanyang; Shan, Chao; Zhang, Xiaolin; Gao, Guandao; Pan, Bingcai

2017-08-01

Graphene is easily warped in the out-of-plane direction because of its high in-plane Young's modulus, and exploring the influence of wrinkled graphene on its properties is essential for the design of graphene-based materials for environmental applications. Herein, we prepared wrinkled graphene (WGN-1 and WGN-2) by thermal treatment and compared their electrochemical properties with those of flat graphene nanosheets (FGN). FGN exhibit activities that are much better than those of wrinkled graphene nanosheets (WGN), not only in the electrochemical oxidation of methylene blue (MB) but also in the electrochemical reduction of nitrobenzene (NB). Transformation ratios of MB and NB in FGN, WGN-1, and WGN-2 were 97.5, 80.1, and 57.9% and 94.6, 92.1, and 81.2%, respectively. Electrochemical impedance spectroscopy and the surface resistance of the graphene samples increased in the following order: FGN reaction charges transfer faster across the reaction interfaces and along the surface of FGN than that of WGN, and wrinkles restrict reaction charge transfer and reduce the reaction rates. This study reveals that the morphology of the graphene (flat or wrinkle) greatly affects redox reaction activities and may have important implications for the design of novel graphene-based nanostructures and for our understanding of graphene wrinkle-dependent redox reactions in environmental processes.

Thermodynamic chemical energy transfer mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium chemical reactions

International Nuclear Information System (INIS)

Roh, Heui-Seol

2015-01-01

Chemical energy transfer mechanisms at finite temperature are explored by a chemical energy transfer theory which is capable of investigating various chemical mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium. Gibbs energy fluxes are obtained as a function of chemical potential, time, and displacement. Diffusion, convection, internal convection, and internal equilibrium chemical energy fluxes are demonstrated. The theory reveals that there are chemical energy flux gaps and broken discrete symmetries at the activation chemical potential, time, and displacement. The statistical, thermodynamic theory is the unification of diffusion and internal convection chemical reactions which reduces to the non-equilibrium generalization beyond the quasi-equilibrium theories of migration and diffusion processes. The relationship between kinetic theories of chemical and electrochemical reactions is also explored. The theory is applied to explore non-equilibrium chemical reactions as an illustration. Three variable separation constants indicate particle number constants and play key roles in describing the distinct chemical reaction mechanisms. The kinetics of chemical energy transfer accounts for the four control mechanisms of chemical reactions such as activation, concentration, transition, and film chemical reactions. - Highlights: • Chemical energy transfer theory is proposed for non-, quasi-, and equilibrium. • Gibbs energy fluxes are expressed by chemical potential, time, and displacement. • Relationship between chemical and electrochemical reactions is discussed. • Theory is applied to explore nonequilibrium energy transfer in chemical reactions. • Kinetics of non-equilibrium chemical reactions shows the four control mechanisms

Transfer reactions at the neutron dripline with triton target

CERN Multimedia

Two-neutron transfer to $^{9}$Li will populate the ground state of $^{11}$Li as well as low-lying resonances in a way that is complementary to studies of these states performed at higher beam energies. We aim at detecting the charged particles from the transfer reactions as well as neutrons coming from the decay of possible $^{11}$Li resonances.

Transfer reactions at the neutron dripline with triton target

CERN Document Server

Borge, M J G; Fynbo, H O U; Gomez Camacho, J; Johansen, J; Johansson, H T; Jonson, B; Krücken, R; Kurcewicz, J; Martel, I; Moro, A; Mücher, D; Nilsson, T; Nyman, G; Raabe, R; Randisi, G; Riisager, K; Sambi, S; Sanchez-Benitez, AM; Tengblad, O

2012-01-01

Two-neutron transfer to $^{9}$Li will populate the ground state of $^{11}$Li as well as low-lying resonances in a way that is complementary to studies of these states performed at higher beam energies. We aim at detecting the charged particles from the transfer reactions as well as neutrons coming from the decay of possible $^{11}$Li resonances.

Charged-particle transfer reactions and nuclear astrophysics problems

International Nuclear Information System (INIS)

Artemov, S.V.; Yarmukhamedov, R.; Yuldashev, B.S.; Burtebaev, N.; Duysebaev, A.; Kadyrzhanov, K.K.

2002-01-01

In the report a review of the recent results of calculation of the astrophysical S-factors S(E) for the D(α, γ) 6 Li, 3 He(α, γ) 7 Be, 7 Be(p, γ) 8 Be, 12,13 C(p, γ) 13, 14 N and 12 C(p,γ) 16 O* reactions at extremely low energies E, including value E=0 , performed within the framework of a new method taking into account the additional information about the nuclear vertex constant (Nc) (or the respective asymptotic normalization coefficient) are presented. The required values of Nc can be obtained from an analysis of measured differential cross-sections of proton and α-particle transfer reactions (for example A( 3 He,d)B, 6 Li(d, 6 Li)d, 6 Li(α, 6 Li)α, 12 C( 6 Li, d) 16 O* etc.). A comparative analysis between the results obtained by different authors is also done. Taking into account an important role of the NVC's values for the nuclear astrophysical A(p, γ)B and A(α, γ)B reactions, a possibility of obtaining the reliable NVC values for the virtual decay B→A+p and B→A+α from the analysis of differential cross sections both sub- and above-barrier A( 3 He, d) and A( 6,7 Li, 2,3 H)B reactions is discussed in detail. In this line the use the isochronous cyclotron U-150 M, the 'DC-60' heavy ion machine and electrostatic charge-exchanging accelerator UKP-2-1 of Institute of Nuclear Physics of National Nuclear Center of the Republic of Kazakhstan for carrying out the needed experiments is considered and the possibility of the obtained data application for the astrophysical interest is also discussed

On the length dependence of bridge-mediated electron transfer reactions

International Nuclear Information System (INIS)

Petrov, E.G.; Shevchenko, Ye.V.; May, V.

2003-01-01

Bridge-mediated nonadiabatic donor-acceptor (D-A) electron transfer (ET) is studied for the case of a regular molecular bridge of N identical units. It is shown that the multi-exponential ET kinetics reduces to a single-exponential transfer if, and only if, the integral population of the bridge remains small (less than 10 -2 ). An analytical expression for the overall D-A ET rate is derived and the necessary and sufficient conditions are formulated at which the rate is given as a sum of a superexchange and a sequential contribution. To describe experimental data on the N-dependence of ET reactions an approximate form of the overall transfer rate is derived. This expression is used to reproduce experimental data on distant ET through polyproline chains. Finally it is noted that the obtained analytical results can also be used for the description of more complex two-electron transfer reactions if the latter comprises separate single-electron pathways

The rate of second electron transfer to QB(-) in bacterial reaction center of impaired proton delivery shows hydrogen-isotope effect.

Science.gov (United States)

Maróti, Ágnes; Wraight, Colin A; Maróti, Péter

2015-02-01

The 2nd electron transfer in reaction center of photosynthetic bacterium Rhodobacter sphaeroides is a two step process in which protonation of QB(-) precedes interquinone electron transfer. The thermal activation and pH dependence of the overall rate constants of different RC variants were measured and compared in solvents of water (H2O) and heavy water (D2O). The electron transfer variants where the electron transfer is rate limiting (wild type and M17DN, L210DN and H173EQ mutants) do not show solvent isotope effect and the significant decrease of the rate constant of the second electron transfer in these mutants is due to lowering the operational pKa of QB(-)/QBH: 4.5 (native), 3.9 (L210DN), 3.7 (M17DN) and 3.1 (H173EQ) at pH7. On the other hand, the proton transfer variants where the proton transfer is rate limiting demonstrate solvent isotope effect of pH-independent moderate magnitude (2.11±0.26 (WT+Ni(2+)), 2.16±0.35 (WT+Cd(2+)) and 2.34±0.44 (L210DN/M17DN)) or pH-dependent large magnitude (5.7 at pH4 (L213DN)). Upon deuteration, the free energy and the enthalpy of activation increase in all proton transfer variants by about 1 kcal/mol and the entropy of activation becomes negligible in L210DN/M17DN mutant. The results are interpreted as manifestation of equilibrium and kinetic solvent isotope effects and the structural, energetic and kinetic possibility of alternate proton delivery pathways are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

Droplet heat transfer and chemical reactions during direct containment heating

International Nuclear Information System (INIS)

Baker, L. Jr.

1986-01-01

A simplified model of heat transfer and chemical reaction has been adapted to evaluate the expected behavior of droplets containing unreacted Zircaloy and stainless steel moving through the containment atmosphere during postulated accidents involving direct containment heating. The model includes internal and external diffusive resistances to reaction. The results indicate that reactions will be incomplete for many conditions characteristic of direct containment heating sequences

Cluster-transfer reactions with radioactive beams: a spectroscopic tool for neutron-rich nuclei

CERN Document Server

AUTHOR|(CDS)2086156; Raabe, Riccardo; Bracco, Angela

In this thesis work, an exploratory experiment to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier, as a possible mean to perform $\\gamma$ spectroscopy studies of exotic neutron-rich nuclei at medium-high energies and spins. The experiment was performed at ISOLDE (CERN), employing the heavy-ion reaction $^{98}$Rb + $^{7}$Li at 2.85 MeV/A. Cluster-transfer reaction channels were studied through particle-$\\gamma$ coincidence measurements, using the MINIBALL Ge array coupled to the charged particle Si detectors T-REX. Sr, Y and Zr neutron-rich nuclei with A $\\approx$ 100 were populated by either triton- or $\\alpha$ transfer from $^{7}$Li to the beam nuclei and the emitted complementary charged fragment was detected in coincidence with the $\\gamma$ cascade of the residues, after few neutrons evaporation. The measured $\\gamma$ spectra were studied in detail and t...

Many-nucleon transfer reactions at the coulomb barrier

International Nuclear Information System (INIS)

Wegmann, H.

1974-01-01

The aim of the present work was to investigate the many-nucleon transfer with heavy ion radiation near the coulomb barrier. The neutron-rich targets 76 Ge, sup(92,94,96)Zr and 100 Mo were thus irradiated with 32 S and 34 S radiation. By measuring the activity of the back-scattered light reaction products in the transfer, total cross sections were determined for the 3p, 4p, 3pn, 4pn, 3n, 4n and 6n transfer. Excitation functions for the 3p, 4p, 3pn and 4pn transfer were measured for the target-projectile combination 96 Zr- 32 S. Differential cross sections could be determined with 96 Zr and 100 Mo. The results were compared with various theoretical calculations. (orig./LH) [de

Arabidopsis CDS blastp result: AK098986 [KOME

Lifescience Database Archive (English)

Full Text Available AK098986 J013093P06 At1g50940.1 electron transfer flavoprotein alpha subunit family... protein contains Pfam profile: PF00766 electron transfer flavoprotein, alpha subunit 1e-105 ...

Arabidopsis CDS blastp result: AK063110 [KOME

Lifescience Database Archive (English)

Full Text Available AK063110 001-111-D06 At5g43430.1 electron transfer flavoprotein beta subunit family... protein contains Pfam profile: PF01012 electron transfer flavoprotein, beta subunit 1e-100 ...

Effect of vibrational excitation on the dynamics of ion-molecule reactions

International Nuclear Information System (INIS)

Anderson, S.L.

1981-11-01

A new experimental technique for the study of vibrational effects on ion-molecule reaction cross sections is described. Vibrational and collision energy dependent cross sections are presented for proton and H atom transfer, charge transfer and collision induced dissociation reactions in various isotopic H 2 + + H 2 systems. Charge and proton transfer cross sections are presented for the reactions of H 2 + and D 2 + with Ar, N 2 , CO, and O 2 . All the reactions are shown to be highly influenced by avoided crossings between the ground and first excited potential energy surfaces. Because of the nature of the crossings, vibrational motion of the systems can cause both adiabatic and non-adiabatic behavior of the system. This makes the vibrational dependences of the various cross sections a very sensitive probe of the dynamics of the collisions particularly, their behavior in the region of the crossings. Evidence is seen for charge transfer between reagents as they approach each other, transition to and in some cases reactions on excited potential energy surfaces, competition between different channels, and strong coupling of proton and charge transfer channels which occurs only for two of the systems studied (H 2 + + Ar, N 2 ). Oscillatory structure is observed in the collision energy dependence of the endoergic H 2 + (v = 0) + Ar charge transfer reaction for the first time, and a simple model which is commonly used for atom-atom charge transfer is used to fit the peaks. Finally a simple model is used to assess the importance of energy resonance and Franck-Condon effects on molecular charge transfer

Laboratory Measurements for H3+ Deuteration Reactions

Science.gov (United States)

Bowen, Kyle; Hillenbrand, Pierre-Michel; Urbain, Xavier; Savin, Daniel Wolf

2018-06-01

Deuterated molecules are important chemical tracers of protostellar cores. At the ~106 cm-3 particle densities and ~20 K temperatures typical for protostellar cores, most molecules freeze onto dust grains. A notable exception is H3+ and its isotopologues. These become important carriers of positive charge in the gas, can couple to any ambient magnetic field, and can thereby alter the cloud dynamics. Knowing the total abundance of H3+ and its isotopologues is important for studying the evolution of protostellar cores. However, H3+ and D3+ have no dipole moment. They lack a pure rotational spectrum and are not observable at protostellar core temperatures. Fortunately H2D+ and D2H+ have dipole moments and a pure rotational spectrum that can be excited in protostellar cores. Observations of these two molecules, combined with astrochemical models, provide information about the total abundance of H3+ and all its isotopologues. The inferred abundances, though, rely on accurate astrochemical data for the deuteration of H3+ and its isotopologues.Here we present laboratory measurements of the rate coefficients for three important deuterating reactions, namely D + H3+/H2D+/D2H+ → H + H2D+/ D2H+/D3+. Astrochemical models currently rely on rate coefficients from classical (Langevin) or semi-classical methods for these reactions, as fully quantum-mechanical calculations are beyond current computational capabilities. Laboratory studies are the most tractable means of providing the needed data. For our studies we used our novel dual-source, merged fast-beams apparatus, which enables us to study reactions of neutral atoms and molecular ions. Co-propagating beams allow us to measure experimental rate coefficients as a function of collision energy. We extract cross section data from these results, which we then convolve with a Maxwell-Boltzmann distribution to generate thermal rate coefficients. Here we present our results for these three reactions and discuss some implications.

High transfer cross sections from reactions with 254Es

International Nuclear Information System (INIS)

Schaedel, M.; Bruechle, W.; Bruegger, M.; Gaeggeler, H.; Moody, J.; Schardt, D.; Suemmerer, K.; Hulet, E.K.; Dougan, A.D.; Dougan, R.J.; Landrum, J.H.; Lougheed, R.W.; Wild, J.F.; O'Kelly, G.D.

1985-08-01

We report radiochemically determined cross sections for the heaviest known actinides produced in transfer reactions of 101 MeV 16 O, 98 MeV 18 O and 127 MeV 22 Ne with 254 Es as a target. A comparison with data for similar transfers from 248 Cm targets is made. Transfer cross sections are extrapolated for the production of unknown, neutron-rich isotopes of elements 101 through 105, and the unique potential of 254 Es as a target to make these exotic nuclei accessible is demonstrated. (orig.)

Nucleon transfer reactions to rotational states induced by 206,208PB projectiles

International Nuclear Information System (INIS)

Wollersheim, H.J.; DeBoer, F.W.N.; Emling, H.; Grein, H.; Grosse, E.; Spreng, W.; Eckert, G.; Elze, Th.W.; Stelzer, K.; Lauterbach, Ch.

1986-01-01

In a systematic study of nucleon transfer reactions accompanied by Coulomb excitation the authors bombarded 152 Sm, 160 Gd and 232 Th with 206, 208 Pb beams at incident energies close to the Coulomb barrier. Particle-gamma coincidence techniques were used to identify excited states of reaction products populated through inelastic scattering and in nucleon transfer reactions. Large cross sections were observed for one- and two-neutron pick-up from 232 Th at an incident energy of 6.4 MeV/μ. The results are analyzed in the framework of semiclassical models

Arabidopsis CDS blastp result: AK061773 [KOME

Lifescience Database Archive (English)

Full Text Available AK061773 001-039-D01 At1g50940.1 electron transfer flavoprotein alpha subunit famil...y protein contains Pfam profile: PF00766 electron transfer flavoprotein, alpha subunit 1e-105 ...

Arabidopsis CDS blastp result: AK105896 [KOME

Lifescience Database Archive (English)

Full Text Available AK105896 001-204-F02 At1g50940.1 electron transfer flavoprotein alpha subunit famil...y protein contains Pfam profile: PF00766 electron transfer flavoprotein, alpha subunit 1e-105 ...

GenBank blastx search result: AK061773 [KOME

Lifescience Database Archive (English)

Full Text Available AK061773 001-039-D01 U17242.1 Methylophilus methylotrophus electron transfer flavop...rotein small subunit and electron transfer flavoprotein large subunit genes, complete cds.|BCT BCT 1e-17 +3 ...

Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3 to CN under Extreme Conditions.

Science.gov (United States)

Zheng, Haiyan; Li, Kuo; Cody, George D; Tulk, Christopher A; Dong, Xiao; Gao, Guoying; Molaison, Jamie J; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; Ivanov, Ilia N; Basile, Leonardo; Idrobo, Juan-Carlos; Guthrie, Malcolm; Mao, Ho-Kwang

2016-09-19

Acetonitrile (CH3 CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. It is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH⋅⋅⋅N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp(2) and sp(3) bonded carbon. Finally, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mass transfer rate through liquid membranes: interfacial chemical reactions and diffusion as simultaneous permeability controlling factors

International Nuclear Information System (INIS)

Danesi, P.R.; Horwitz, E.P.; Vandegrift, G.F.; Chiarizia, R.

1981-01-01

Equations describing the permeability of a liquid membrane to metal cations have been derived taking into account aqueous diffusion, membrane diffusion, and interfacial chemical reactions as simultaneous permeability controlling factors. Diffusion and chemical reactions have been coupled by a simple model analogous to the one previously described by us to represent liquid-liquid extraction kinetics. The derived equations, which make use of experimentally determined interfacial reaction mechanisms, qualitatively fit unexplained literature data regarding Cu 2+ transfer through liquid membranes. Their use to predict and optimize membrane permeability in practical separation processes by setting the appropriate concentration of the membrane carrier [LIX 64 (General Mills), a commercial β-hydroxy-oxime] and the pH of the aqueous copper feed solution is briefly discussed. 4 figures

Eight-dimensional quantum reaction rate calculations for the H+CH4 and H2+CH3 reactions on recent potential energy surfaces.

Science.gov (United States)

Zhou, Yong; Zhang, Dong H

2014-11-21

Eight-dimensional (8D) transition-state wave packet simulations have been performed on two latest potential energy surfaces (PES), the Zhou-Fu-Wang-Collins-Zhang (ZFWCZ) PES [Y. Zhou, B. Fu, C. Wang, M. A. Collins, and D. H. Zhang, J. Chem. Phys. 134, 064323 (2011)] and the Xu-Chen-Zhang (XCZ)-neural networks (NN) PES [X. Xu, J. Chen, and D. H. Zhang, Chin. J. Chem. Phys. 27, 373 (2014)]. Reaction rate constants for both the H+CH4 reaction and the H2+CH3 reaction are calculated. Simulations of the H+CH4 reaction based on the XCZ-NN PES show that the ZFWCZ PES predicts rate constants with reasonable high accuracy for low temperatures while leads to slightly lower results for high temperatures, in line with the distribution of interpolation error associated with the ZFWCZ PES. The 8D H+CH4 rate constants derived on the ZFWCZ PES compare well with full-dimensional 12D results based on the equivalent m-ZFWCZ PES, with a maximum relative difference of no more than 20%. Additionally, very good agreement is shown by comparing the 8D XCZ-NN rate constants with the 12D results obtained on the ZFWCZ-WM PES, after considering the difference in static barrier height between these two PESs. The reaction rate constants calculated for the H2+CH3 reaction are found to be in good consistency with experimental observations.

Laser-induced charge transfer in the HeH/sup 2 +/ quasimolecule

Energy Technology Data Exchange (ETDEWEB)

Errea, L.F.; Mendez, L.; Riera, A.

1983-11-01

In a recent publication, the charge transfer cross section for He/sup 2 +/+H(ls) collisions through photon-assisted 2psigma--3dsigma transitions was calculated; this calculation, however, contained several errors whose quantitative--even qualitative effect on the results is not obvious. We present a correct evaluation of this laser-induced cross section, which turns out to be larger, and present a maximum for longer wavelengths, than the values previously reported. In addition, we have checked the applicability of perturbation theory, of the stationary phase, uniform and Landau--Zener approximations, and the importance of potentially competitive photon-assisted reactions.

7Li(d,p)8Li transfer reaction in the NCSM/RGM approach

Science.gov (United States)

Raimondi, F.; Hupin, G.; Navrátil, P.; Quaglioni, S.

2018-03-01

Recently, we applied an ab initio method, the no-core shell model combined with the resonating group method, to the transfer reactions with light p-shell nuclei as targets and deuteron as the projectile. In particular, we studied the elastic scattering of deuterium on 7Li and the 7Li(d,p)8Li transfer reaction starting from a realistic two-nucleon interaction. In this contribution, we review of our main results on the 7Li(d,p)8Li transfer reaction, and we extend the study of the relevant reaction channels, by showing the dominant resonant phase shifts of the scattering matrix. We assess also the impact of the polarization effects of the deuteron below the breakup on the positive-parity resonant states in the reaction. For this purpose, we perform an analysis of the convergence trend of the phase and eigenphase shifts, with respect to the number of deuteron pseudostates included in the model space.

Kinetic mechanism and nucleotide specificity of NADH peroxidase

International Nuclear Information System (INIS)

Stoll, V.S.; Blanchard, J.S.

1988-01-01

NADH peroxidase is a flavoprotein isolated from Streptococcus faecalis which catalyzes the pyridine nucleotide-dependent reduction of hydrogen peroxide to water. Initial velocity, product, and dead-end inhibition studies have been performed at pH 7.5 and support a ping-pong kinetic mechanism. In the absence of hydrogen peroxide, both transhydrogenation between NADH and thioNAD, and isotope exchange between [ 14 C]NADH and NAD, have been demonstrated, although in both these experiments, the maximal velocity of nucleotide exchange was less than 1.5% the maximal velocity of the peroxidatic reaction. We propose that NADH binds tightly to both oxidized and two-electron reduced enzyme. NADH oxidation proceeds stereospecifically with the transfer of the 4S hydrogen to enzyme, and then, via exchange, to water. No primary tritium kinetic isotope effect was observed, and no statistically significant primary deuterium kinetic isotope effects on V/K were determined, although primary deuterium kinetic isotope effects on V were observed in the presence and absence of sodium acetate. NADH peroxidase thus shares with other flavoprotein reductases striking kinetic, spectroscopic, and stereochemical similarities. On this basis, we propose a chemical mechanism for the peroxide cleaving reaction catalyzed by NADH peroxidase which involves the obligate formation of a flavinperoxide, and peroxo bond cleavage by nucleophilic attack by enzymatic dithiols

Search for low spin superdeformed states by transfer reactions

Energy Technology Data Exchange (ETDEWEB)

Blons, J; Goutte, D; Lepretre, A; Lucas, R; Meot, V; Paya, D; Phan, X H [DAPNIA SPhN CE Saclay 91191 Gif sur Yvette (France); Barreau, G; Doan, T P; Pedemay, G [CENBG, 33175 Gradignan (France); Becker, J A; Stoyer, M A [LLNL, Livermore, CA (United States)

1992-08-01

We present a specific experimental technique aiming to observe superdeformed isomeric states. Preliminary results on two proton transfer reaction on platinum targets leading to {sup 194}Hg are shown. (author). 6 refs., 5 figs.

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

International Nuclear Information System (INIS)

Nishimura, Akira; Kawahara, Nobuhiro; Takagi, Hiroshi

2013-01-01

Highlights: ► NO is produced from L-arginine in response to elevated temperature in yeast. ► Tah18 was first identified as the yeast protein involved in NO synthesis. ► Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe–S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

Nuclear rotational population patterns in heavy-ion scattering and transfer reactions

Energy Technology Data Exchange (ETDEWEB)

Rasmussen, J O; Stoyer, M A [Lawrence Berkeley Lab., CA (USA); Canto, L F; Donangelo, R [Universidade Federal do Rio de Janeiro, RJ (Brazil); Ring, P [Technische Univ. Muenchen, Garching (Germany, F.R.). Fakultaet fuer Physik

1991-05-01

A model of {sup 239}Pu with decoupled neutron is used for theoretical calculations of rotational population patterns in heavy ion inelastic scattering and one-neutron transfer reactions. The system treated in {sup 90}Zr on {sup 239}Pu at the near-barrier energy of 500 MeV and backscattering angles of 180deg and 140deg. The influence of the complex nuclear optical potential is seen to be very strong, and the Nilsson wave function of the odd neutron produces a distinctive pattern in the transfer reaction. (orig.).

Effects of electrostatic interactions on electron transfer reactions

International Nuclear Information System (INIS)

Hickel, B.

1987-01-01

The fast reactions of electron transfer are studied by pulse radiolysis. This technique allows the creation in about 10 -8 second radicals and radical ions with high redox potentials. For solvated electrons electrostatic interaction on the kinetics of reactions limited by diffusion is described by Debye's equation when ion mobility is known. Deviation from theory can occur in ion pairs formation. This is evidenced experimentally for anions by cation complexation with a cryptate. Relatively slow reactions are more sensitive to electrostatic interactions than limited by diffusion. If ion pairs are not formed kinetics constant depends on dielectric constant of solvent and reaction radius. Experimentally is studied the effect of electrostatic interaction on the rate constants of solvated electrons with anions and cations in water-ethanol mixtures where the dielectric constant change from 80 to 25 at room temperature. 17 refs

GenBank blastx search result: AK061773 [KOME

Lifescience Database Archive (English)

Full Text Available AK061773 001-039-D01 AF072475.1 Megasphaera elsdenii electron-transferring flavopro...tein b subunit (etfB) and electron-transferring flavoprotein a subunit (etfA) genes, complete cds.|BCT BCT 4e-27 +3 ...

Quantum-tunneling isotope-exchange reaction H2+D-→HD +H-

Science.gov (United States)

Yuen, Chi Hong; Ayouz, Mehdi; Endres, Eric S.; Lakhamanskaya, Olga; Wester, Roland; Kokoouline, Viatcheslav

2018-02-01

The tunneling reaction H2+D-→HD +H- was studied in a recent experimental work at low temperatures (10, 19, and 23 K) by Endres et al. [Phys. Rev. A 95, 022706 (2017), 10.1103/PhysRevA.95.022706]. An upper limit of the rate coefficient was found to be about 10-18cm3 /s. In the present study, reaction probabilities are determined using the ABC program developed by Skouteris et al. [Comput. Phys. Commun. 133, 128 (2000), 10.1016/S0010-4655(00)00167-3]. The probabilities for ortho-H2 and para-H2 in their ground rovibrational states are obtained numerically at collision energies above 50 meV with the total angular momentum J =0 -15 and extrapolated below 50 meV using a WKB approach. Thermally averaged rate coefficients for ortho- and para-H2 are obtained; the largest one, for ortho-H2, is about 3.1 ×10-20cm3 /s, which agrees with the experimental results.

In Situ Solid-State Reactions Monitored by X-ray Absorption Spectroscopy: Temperature-Induced Proton Transfer Leads to Chemical Shifts.

Science.gov (United States)

Stevens, Joanna S; Walczak, Monika; Jaye, Cherno; Fischer, Daniel A

2016-10-24

The dramatic colour and phase alteration with the solid-state, temperature-dependent reaction between squaric acid and 4,4'-bipyridine has been probed in situ with X-ray absorption spectroscopy. The electronic and chemical sensitivity to the local atomic environment through chemical shifts in the near-edge X-ray absorption fine structure (NEXAFS) revealed proton transfer from the acid to the bipyridine base through the change in nitrogen protonation state in the high-temperature form. Direct detection of proton transfer coupled with structural analysis elucidates the nature of the solid-state process, with intermolecular proton transfer occurring along an acid-base chain followed by a domino effect to the subsequent acid-base chains, leading to the rapid migration along the length of the crystal. NEXAFS thereby conveys the ability to monitor the nature of solid-state chemical reactions in situ, without the need for a priori information or long-range order. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational Study of Pincer Iridium Catalytic Systems: C-H, N-H, and C-C Bond Activation and C-C Coupling Reactions

Science.gov (United States)

Zhou, Tian

Computational chemistry has achieved vast progress in the last decades in the field, which was considered to be only experimental before. DFT (density functional theory) calculations have been proven to be able to be applied to large systems, while maintaining high accuracy. One of the most important achievements of DFT calculations is in exploring the mechanism of bond activation reactions catalyzed by organometallic complexes. In this dissertation, we discuss DFT studies of several catalytic systems explored in the lab of Professor Alan S. Goldman. Headlines in the work are: (1) (R4PCP)Ir alkane dehydrogenation catalysts are highly selective and different from ( R4POCOP)Ir catalysts, predicting different rate-/selectivity-determining steps; (2) The study of the mechanism for double C-H addition/cyclometalation of phenanthrene or biphenyl by (tBu4PCP)Ir(I) and ( iPr4PCP)Ir illustrates that neutral Ir(III) C-H addition products can undergo a very facile second C-H addition, particularly in the case of sterically less-crowded Ir(I) complexes; (3) (iPr4PCP)Ir pure solid phase catalyst is highly effective in producing high yields of alpha-olefin products, since the activation enthalpy for dehydrogenation is higher than that for isomerization via an allyl pathway; higher temperatures favor the dehydrogenation/isomerization ratio; (4) (PCP)Ir(H)2(N2H4) complex follows a hydrogen transfer mechanism to undergo both dehydrogenation to form N 2 and H2, as well as hydrogen transfer followed by N-N bond cleavage to form NH3, N2, and H2; (5) The key for the catalytic effect of solvent molecule in CO insertion reaction for RMn(CO)5 is hydrogen bond assisted interaction. The basicity of the solvent determines the strength of the hydrogen bond interaction during the catalytic path and determines the catalytic power of the solvent; and (6) Dehydrogenative coupling of unactivated C-H bonds (intermolecular vinyl-vinyl, intramolecular vinyl-benzyl) is catalyzed by precursors of the

Mass transfer and slag-metal reaction in ladle refining : a CFD approach

OpenAIRE

Ramström, Eva

2009-01-01

  In order to optimise the ladle treatment mass transfer modelling of aluminium addition and homogenisation time was carried out. It was stressed that incorporating slag-metal reactions into the mass transfer modelling strongly would enhance the reliability and amount of information to be analyzed from the CFD calculations.   In the present work, a thermodynamic model taking all the involved slag metal reactions into consideration was incorporated into a 2-D fluid flow model of an argon stirr...

Excitation functions for quasielastic transfer reactions induced with heavy ions in bismuth

International Nuclear Information System (INIS)

Gardes, D.; Bimbot, R.; Maison, J.; de Reilhac, L.; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

1978-01-01

The excitation functions for the production of 210 Bi, 210 Po, /sup 207-211/At, and 211 Rn through quasielastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two charges, and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ar, 40 Ca, 56 Fe, and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measuremnts of incident energies and cross sections were performed close to the reaction thresholds. All excitation functions exhibit the typical features of quasielastic transfer reactions: a sharp increase at low energy, and a constant value at high incident energy. The position of the thresholds are strongly influenced by the energetics of the reaction: High cross sections are observed under the strong interaction barrier if the energy balance at the minimum distance of approach is positive. This balance is equal to the difference between the interaction potentials in the entrance and exit channels, corrected for the mass balance. The constant cross sections observed for the high energy part of a given excitation function are consistent with the assumption that the curve P (R) which represents the transfer probability versus the distance between the nucleus centers does not vary with incident energy. This assumption implies the constancy of the optimum distance of approach R/sub opt/, of the R window ΔR for which P (R) is significant, and of the magnitude of P (R). Moreover the data show that the high energy cross sections for one-proton transfer are independent of the projectile, while odd-even effects of the projectile atomic number Z on the two-charge transfer cross sections are observed for the lightest incident ions 14 N to 20 Ne

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

Science.gov (United States)

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

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

Alpha-transfer reactions and the pairing-vibration model

International Nuclear Information System (INIS)

Betts, R.R.

1977-01-01

The pairing-vibration model with isospin is extended to include α-transfer reactions. Selection rules and expressions for transition strengths are derived and compared with experimental results for A = 40--66 nuclei. The selection rules are found to be followed quite well in the examples studied. The systematics of ground-state transition strengths are qualitatively quite well reproduced although the quantitative agreement is poor. When the changing nature of the pairing quanta is incorporated using two-particle transfer data the agreement becomes quantitatively good. Evidence is presented for clustering other than that due to pairing in 40 Ca and 44 Ti

Intramolecular kinetic isotope effect in gas-phase proton-transfer reactions

International Nuclear Information System (INIS)

Wellman, K.M.; Victoriano, M.E.; Isolani, P.C.; Riveros, J.M.

1979-01-01

The k/sub H//k/sub D/ isotope effects were determined by ICR for the reaction of substituted toluenes with several alkoxides. The results showed a definite trend for k/sub H//k/sub D/ starting as a normal isotope effect for appreciably exothermic reaction (> 3 kcal mol -1 ) and proceeding smoothly toward an inverse isotope effect as the reaction approached thermoneutrality or becomes endothermic. These observations were explained by a reaction which involved a double minima potential with a central energy barrier

Electron transfer reactions in microporous solids. Progress report, September 1990--January 1993

Energy Technology Data Exchange (ETDEWEB)

Mallouk, T.E.

1993-01-01

Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H{sub 2} and I{sub 3}{sup {minus}}, or H{sub 2} and O{sub 2)} from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

Dual level reaction-path dynamics calculations on the C2H6 + OH → C2H5 + H2O reaction

International Nuclear Information System (INIS)

Coitino, E.L.; Truhlar, D.G.

1996-01-01

Interpolated Variational Transition State Theory with Multidimensional Tunneling contributions (IVTST/MT) has been applied to the reaction of C 2 H 6 + OH, and it yields rate constants that agree well with the available experimental information. The main disadvantage of this method is the difficulty of interpolating all required information from a few points along the reaction path. A more recent alternative is Variational Transition State Theory with Multidimensional Tunneling and Interpolated Corrections (VTST/MT-IC, also called dual-level direct dynamics), in which the reaction-path properties are first determined at an economical (lower) level of theory and then open-quotes correctedclose quotes using more accurate information obtained at a higher level for a selected number of points on the reaction path. The VTST/MT-IC method also allows for interpolation through die wider reaction swath when large-curvature tunneling occurs. In the present work we examine the affordability/accuracy tradeoff for several combinations of higher and lower levels for VTST/MT-IC reaction rate calculations on the C 2 H 6 + OH process. Various levels of theory (including NDDO-SRP and ab initio ROMP2, UQCISD, UQCISD(T), and UCCSD) have been employed for the electronic structure calculations. We also compare several semiclassical approaches implemented in the POLYRATE and MORATE programs for taking tunneling effects into account

XPS study on the surface reaction of uranium metal in H2 and H2-CO atmospheres

International Nuclear Information System (INIS)

Wang Xiaolin; Fu Yibei; Xie Renshou

1996-04-01

The surface reactions of uranium metal in H 2 and H 2 -CO atmospheres and the effects of temperature and CO on the hydriding reaction have been studied by X-ray photoelectron spectroscopy (XPS). The reaction between commercial H 2 and uranium metal at 25 degree C leads mainly to the further oxidation of surface layer of metal due to traces of water vapour. At 200 degree C, it may lead to the hydriding reaction of uranium and the hydriding increases with increasing the exposure of H 2 . Investigation indicates CO inhibits both the hydriding reaction and oxidation on the condition of H 2 -CO atmospheres. (13 refs., 10 figs.)

Transfer reaction studies in the region of heavy and superheavy nuclei at SHIP

Energy Technology Data Exchange (ETDEWEB)

Heinz, S; Comas, V; Hofmann, S; Ackermann, D; Heredia, J; Hessberger, F P; Khuyagbaatar, J; Kindler, B; Lommel, B; Mann, R, E-mail: s.heinz@gsi.de [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, 64291 Darmstadt (Germany)

2011-02-01

We studied multi-nucleon transfer reactions in the region of heavy and superheavy nuclei. The goal was to investigate these reactions as possibility to create new superheavy neutron-rich isotopes, which cannot be produced in fusion reactions. The experiments have been performed at the velocity filter SHIP at GSI. At SHIP we can detect and identify the heavy, target-like, transfer products. Due to the low background at the focal plane detector and the isotope identification via radioactive decays, the setup allows to reach an upper cross-section limit of 10 pb/sr within one day of beamtime. We investigated the systems {sup 58,64}Ni + {sup 207}Pb and {sup 48}Ca + {sup 248}Cm at beam energies below and up to 20% above the Coulomb barrier. At all energies we observed a massive transfer of protons and neutrons, where transfer products with up to eight neutrons more than the target nucleus could be identified.

Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

Energy Technology Data Exchange (ETDEWEB)

Klobukowski, Erik [Iowa State Univ., Ames, IA (United States)

2011-01-01

This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallic complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly compared using the same reaction system and

Flavin-N5 Covalent Intermediate in a Nonredox Dehalogenation Reaction Catalyzed by an Atypical Flavoenzyme.

Science.gov (United States)

Dai, Yumin; Kizjakina, Karina; Campbell, Ashley C; Korasick, David A; Tanner, John J; Sobrado, Pablo

2018-01-04

The flavin-dependent enzyme 2-haloacrylate hydratase (2-HAH) catalyzes the conversion of 2-chloroacrylate, a major component in the manufacture of acrylic polymers, to pyruvate. The enzyme was expressed in Escherichia coli, purified, and characterized. 2-HAH was shown to be monomeric in solution and contained a non-covalent, yet tightly bound, flavin adenine dinucleotide (FAD). Although the catalyzed reaction was redox-neutral, 2-HAH was active only in the reduced state. A covalent flavin-substrate intermediate, consistent with the flavin-acrylate iminium ion, was trapped with cyanoborohydride and characterized by mass spectrometry. Small-angle X-ray scattering was consistent with 2-HAH belonging to the succinate dehydrogenase/fumarate reductase family of flavoproteins. These studies establish 2-HAH as a novel noncanonical flavoenzyme. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of transfer reactions in heavy-ion collisions at the Coulomb barrier

Directory of Open Access Journals (Sweden)

Pollarolo Giovanni

2011-10-01

Full Text Available One and two neutron transfer reactions are discussed in the semiclassical formalism. The twoneutrons transfer cross sections are calculated in the successive approximation. Comparisons with new experimental data below the Coulomb barrier are discussed in term of transfer probabilities as a function of the distance of closest approach for Coulomb scattering.

Light induced electron transfer reactions of metal complexes

International Nuclear Information System (INIS)

Sutin, N.; Creutz, C.

1980-01-01

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

Heavy-ion induced multinucleon transfer reactions in the 2s--1d shell

International Nuclear Information System (INIS)

Olmer, C.

1975-01-01

In order to investigate whether new nuclear structure information can be obtained from studying the direct transfer of more than two nucleons using heavy-ion projectiles, we have investigated the 28 Si( 16 O, 12 C) 32 S and 12 C( 14 N,d) 24 Mg reactions as candidates for the direct transfer of four- and twelve-nucleons, respectively. The counter telescope-position sensitive detector kinematic coincidence method--both angular distributions (22 0 less than theta/sub L/ less than 95 0 , E/sub L/ = 55.54 MeV) and excitation functions (theta/sub L/ = 26 0 , 50 less than E/sub L/ less than 63 MeV) were obtained for strongly excited states below 10 MeV in excitation in the first reaction. For the 12 C + 14 N interaction, a measurement of the angular distributions (25 0 less than theta/sub L/ less than 140 0 , E/sub L/ = 20,25 MeV) for proton, deuteron and alpha-particle emission to many low-lying states sufficed for the present purposes. Comparison of Hauser-Feshbach statistical model calculations with these data indicated that the light-particle production from the 12 C + 14 N interaction as investigated here is predominantly compound nuclear in nature. The selectively strong population of a few states in 32 S by the 28 Si-( 16 O, 12 C) 32 S reaction is primarily direct. The structure of these states was deduced from available light-ion-induced transfer reaction studies and shell model calculations; the importance of shell model configurations is indicated, and an alpha-particle transfer model can not account for the observed selectivity. Calculations of the 28 Si( 16 O, 12 C) 32 S reaction with a microscopic multinucleon transfer code indicate selectivities consistent with the present results. Moreover, the calculations suggest the presence of other, unexpected selectivities, all of which may be understood on a physical basis, and some of which appear as an extension of a similar effect seen in two-nucleon transfer reactions

Comparison of dynamical aspects of nonadiabatic electron, proton, and proton-coupled electron transfer reactions

International Nuclear Information System (INIS)

Hatcher, Elizabeth; Soudackov, Alexander; Hammes-Schiffer, Sharon

2005-01-01

The dynamical aspects of a model proton-coupled electron transfer (PCET) reaction in solution are analyzed with molecular dynamics simulations. The rate for nonadiabatic PCET is expressed in terms of a time-dependent probability flux correlation function. The impact of the proton donor-acceptor and solvent dynamics on the probability flux is examined. The dynamical behavior of the probability flux correlation function is dominated by a solvent damping term that depends on the energy gap correlation function. The proton donor-acceptor motion does not impact the dynamical behavior of the probability flux correlation function but does influence the magnitude of the rate. The approximations previously invoked for the calculation of PCET rates are tested. The effects of solvent damping on the proton donor-acceptor vibrational motion are found to be negligible, and the short-time solvent approximation, in which only equilibrium fluctuations of the solvent are considered, is determined to be valid for these types of reactions. The analysis of PCET reactions is compared to previous analyses of single electron and proton transfer reactions. The dynamical behavior is qualitatively similar for all three types of reactions, but the time scale of the decay of the probability flux correlation function is significantly longer for single proton transfer than for PCET and single electron transfer due to a smaller solvent reorganization energy for proton transfer

Impact of OH Radical-Initiated H2CO3 Degradation in the Earth's Atmosphere via Proton-Coupled Electron Transfer Mechanism.

Science.gov (United States)

Ghoshal, Sourav; Hazra, Montu K

2016-02-04

The decomposition of isolated carbonic acid (H2CO3) molecule into CO2 and H2O (H2CO3 → CO2 + H2O) is prevented by a large activation barrier (>35 kcal/mol). Nevertheless, it is surprising that the detection of the H2CO3 molecule has not been possible yet, and the hunt for the free H2CO3 molecule has become challenging not only in the Earth's atmosphere but also on Mars. In view of this fact, we report here the high levels of quantum chemistry calculations investigating both the energetics and kinetics of the OH radical-initiated H2CO3 degradation reaction to interpret the loss of the H2CO3 molecule in the Earth's atmosphere. It is seen from our study that proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) are the two mechanisms by which the OH radical initiates the degradation of the H2CO3 molecule. Moreover, the PCET mechanism is potentially the important one, as the effective barrier, defined as the difference between the zero point vibrational energy (ZPE) corrected energy of the transition state and the total energy of the isolated starting reactants in terms of bimolecular encounters, for the PCET mechanism at the CCSD(T)/6-311++G(3df,3pd) level of theory is ∼3 to 4 kcal/mol lower than the effective barrier height associated with the HAT mechanism. The CCSD(T)/6-311++G(3df,3pd) level predicted effective barrier heights for the degradations of the two most stable conformers of H2CO3 molecule via the PCET mechanism are only ∼2.7 and 4.3 kcal/mol. A comparative reaction rate analysis at the CCSD(T)/6-311++G(3df,3pd) level of theory has also been carried out to explore the potential impact of the OH radical-initiated H2CO3 degradation relative to that from water (H2O), formic acid (FA), acetic acid (AA) and sulfuric acid (SA) assisted H2CO3 → CO2 + H2O decomposition reactions in both the Earth's troposphere and stratosphere. The comparison of the reaction rates reveals that, although the atmospheric concentration of the OH radical is

The mechanism of electron gating in proton pumping cytochrome c oxidase: the effect of pH and temperature on internal electron transfer.

Science.gov (United States)

Brzezinski, P; Malmström, B G

1987-10-29

Electron-transfer reactions following flash photolysis of the mixed-valence cytochrome oxidase-CO complex have been measured at 445, 598 and 830 nm between pH 5.2 and 9.0 in the temperature range of 0-25 degrees C. There is a rapid electron transfer from the cytochrome a3-CuB pair to CuA (time constant: 14200 s-1), which is followed by a slower electron transfer to cytochrome a. Both the rate and the amplitude of the rapid phase are independent of pH, and the rate in the direction from CuA to cytochrome a3-CuB is practically independent of temperature. The second phase depends strongly on pH due to the titration of an acid-base group with pKa = 7.6. The equilibrium at pH 7.4 corresponds to reduction potentials of 225 and 345 mV for cytochrome a and a3, respectively, from which it is concluded that the enzyme is in a different conformation compared to the fully oxidized form. The results have been used to suggest a series of reaction steps in a cycle of the oxidase as a proton pump. Application of the electron-transfer theory to the temperature-dependence data suggests a mechanism for electron gating in the pump. Reduction of both cytochrome a and CuA leads to a conformational change, which changes the structure of cytochrome a3-CuB in such a way that the reorganizational barrier for electron transfer is removed and the driving force is increased.

Transfer reactions in inverse kinematics at REX-ISOLDE

CERN Document Server

Tengborn, E

Research on the structure of exotic nuclei is one of the most intriguing topics in present day nuclear physics. With the use of facilities for isotope separation on-line, such as ISOLDE at CERN, short-lived isotopes can be studied experimentally. Since 2002, the REX-ISOLDE facility enables radioactive ions produced by ISOLDE to be post-accelerated, increasing the energy of the ions enough to do nuclear transfer reactions in inverse kinematics. In this thesis, transfer reactions are used to study the structure of neutron-rich lithium isotopes through a series of experiments at REX-ISOLDE. The first experiment used a 9Li beam at 2.36 MeV/u impinging on a deuterated polyethylene target to study 10Li, 9Li and 8Li. For the (d,p)-channel the resonance ground state and a first excited state are observed and the results agree with theoretical calculations. The elastic channel agrees with Optical Model, OM, calculations. For the (d,t)-channel the shape of the angular distribution agrees with Distorted Wave Born Approx...

Spectroscopy of $^{46}$Ar by the $(t,p)$ two-neutron transfer reaction

CERN Document Server

Nowak, K.; Hellgartner, S.; Mücher, D.; Bildstein, V.; Diriken, J.; Elseviers, J.; Gaffney, L.P.; Gernhäuser, R.; Iwanicki, J.; Johansen, J.G.; Huyse, M.; Konki, J.; Kröll, T.; Krücken, T.; Lutter, R.; Orlandi, R.; Pakarinen, J.; Raabe, R.; Reiter, P.; Roger, T.; Schrieder, G.; Seidlitz, M.; Sorlin, O.; Van Duppen, P.; Warr, N.; De Witte, H.; Zielinska, M.

2016-04-27

States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^\\pi = 0^+$. The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell model calculations using state-of-the-art effective interactions.

Deep-inelastic multinucleon transfer processes in the 16O+27Al reaction

Science.gov (United States)

Roy, B. J.; Sawant, Y.; Patwari, P.; Santra, S.; Pal, A.; Kundu, A.; Chattopadhyay, D.; Jha, V.; Pandit, S. K.; Parkar, V. V.; Ramachandran, K.; Mahata, K.; Nayak, B. K.; Saxena, A.; Kailas, S.; Nag, T. N.; Sahoo, R. N.; Singh, P. P.; Sekizawa, K.

2018-03-01

The reaction mechanism of deep-inelastic multinucleon transfer processes in the 16O+27Al reaction at an incident 16O energy (Elab=134 MeV) substantially above the Coulomb barrier has been studied both experimentally and theoretically. Elastic-scattering angular distribution, total kinetic energy loss spectra, and angular distributions for various transfer channels have been measured. The Q -value- and angle-integrated isotope production cross sections have been deduced. To obtain deeper insight into the underlying reaction mechanism, we have carried out a detailed analysis based on the time-dependent Hartree-Fock (TDHF) theory. A recently developed method, TDHF+GEMINI, has been applied to evaluate production cross sections for secondary products. From a comparison between the experimental and theoretical cross sections, we find that the theory qualitatively reproduces the experimental data. Significant effects of secondary light-particle emissions are demonstrated. Possible interplay among fusion-fission, deep-inelastic, multinucleon transfer, and particle evaporation processes is discussed.

Identification of the human mitochondrial FAD transporter and its potential role in multiple acyl-CoA dehydrogenase deficiency

NARCIS (Netherlands)

Spaan, András N.; Ijlst, Lodewijk; van Roermund, Carlo W. T.; Wijburg, Frits A.; Wanders, Ronald J. A.; Waterham, Hans R.

2005-01-01

Multiple acyl-CoA dehydrogenase deficiency (MADD) or glutaric aciduria type II (GAII) is most often caused by mutations in the genes encoding the alpha- or beta-subunit of electron transfer flavoprotein (ETF) or electron transfer flavoprotein dehydrogenase (ETF-DH). Since not all patients have

H eat transfer betw een tw o surfaces usually in- creases w h en th e ...

Indian Academy of Sciences (India)

Srimath

H eat transfer betw een tw o surfaces usually in- creases w h en th e tem p eratu re d i® eren ce b etw een the tw o surfaces increases. H ere w e highlight an unusual situation in radiation heat transfer w herein the heat transfer decreases w hen the tem perature di®erence increases. In tro d u ctio n. In 1701,N ew ton ...

Determination of S17(0) from transfer reactions

International Nuclear Information System (INIS)

Tribble, R.E.; Azhari, A.; Clark, H.L.; Gagliardi, C.A.; Lui, Y.; Mukhamedzhanov, A.M.; Sattarov, A.; Trache, L.; Burjan, V.; Cejpek, J.; Kroha, V.; Piskor, S.; Vincour, J.

1998-01-01

The S-factor for the direct capture reaction 7 Be(p,γ) 8 B can be found at astrophysical energies from the asymptotic normalization coefficients which provide the normalization of the tails of the overlap functions for 8 B→ 7 Be+p. Peripheral transfer reactions offer a technique to determine these asymptotic normalization coefficients. As a test of the technique, the 16 O( 3 He,d) 17 F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of 17 F. The S-factors for 16 O(p,γ) 17 F calculated from these 17 F→ 16 O+p asymptotic normalization coefficients are found to be in very good agreement with recent measurements. Following the same technique, the 10 B( 7 Be, 8 B) 9 Be reaction has been used to measure the asymptotic normalization coefficient for 7 Be(p,γ) 8 B. This result provides an indirect determination of S 17 (0). copyright 1998 American Institute of Physics

Splendor and misery of the distorted wave method applied to heavy ions transfer reactions

International Nuclear Information System (INIS)

Mermaz, M.C.

1979-01-01

The success and failure of the Distorted Wave Method (DWM) applied to heavy ion transfer reactions are illustrated by few examples: one and multi-nucleon transfer reactions induced by 15 N and 18 O on 28 Si target nucleus performed on the vicinity of Coulomb barrier respectively at 44 and 56 MeV incident energy

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

International Nuclear Information System (INIS)

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

2013-01-01

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

Reactions of electronically excited molecular nitrogen with H2 and H2O molecules: theoretical study

Science.gov (United States)

Pelevkin, Alexey V.; Sharipov, Alexander S.

2018-05-01

Comprehensive quantum chemical analysis with the usage of the second-order perturbation multireference XMCQDPT2 approach was carried out to study the processes in the   +  H2 and   +  H2O systems. The energetically favorable reaction pathways have been revealed based on the exploration of potential energy surfaces. It has been shown that the reactions   +  H2 and   +  H2O occur with small activation barriers and, primarily, lead to the formation of N2H  +  H and N2H  +  OH products, respectively. Further, the interaction of these species could give rise to the ground state and H2 (or H2O) products, however, the estimations, based on RRKM theory and dynamic reaction coordinate calculations, exhibited that the   +  H2 and   +  H2O reactions lead to the dissociative quenching predominately. Appropriate rate constants for revealed reaction channels have been estimated by using a canonical variational theory and capture approximation. Corresponding three-parameter Arrhenius expressions for the temperature range T  =  300  ‑  3000 K were reported.

Ab initio chemical kinetics for SiH3 reactions with Si(x)H2x+2 (x = 1-4).

Science.gov (United States)

Raghunath, P; Lin, M C

2010-12-30

Gas-phase kinetics and mechanisms of SiH(3) reactions with SiH(4), Si(2)H(6), Si(3)H(8), and Si(4)H(10), processes of relevance to a-Si thin-film deposition, have been investigated by ab initio molecular orbital and transition-state theory (TST) calculations. Geometric parameters of all the species involved in the title reactions were optimized by density functional theory at the B3LYP and BH&HLYP levels with the 6-311++G(3df,2p) basis set. The potential energy surface of each reaction was refined at the CCSD(T)/6-311++G(3df,2p) level of theory. The results show that the most favorable low energy pathways in the SiH(3) reactions with these silanes occur by H abstraction, leading to the formation of SiH(4) + Si(x)H(2x+1) (silanyl) radicals. For both Si(3)H(8) and n-Si(4)H(10) reactions, the lowest energy barrier channels take place by secondary Si-H abstraction, yielding SiH(4) + s-Si(3)H(7) and SiH(4) + s-Si(4)H(9), respectively. In the i-Si(4)H(10) reaction, tertiary Si-H abstraction has the lowest barrier producing SiH(4) + t-Si(4)H(9). In addition, direct SiH(3)-for-X substitution reactions forming Si(2)H(6) + X (X = H or silanyls) can also occur, but with significantly higher reaction barriers. A comparison of the SiH(3) reactions with the analogous CH(3) reactions with alkanes has been made. The rate constants for low-energy product channels have been calculated for the temperature range 300-2500 K by TST with Eckart tunneling corrections. These results, together with predicted heats of formation of various silanyl radicals and Si(4)H(10) isomers, have been tabulated for modeling of a-Si:H film growth by chemical vapor deposition.

Electric form factor of the neutron from the 2H(e-->,e'n-->)1H reaction at Q2=0.255 (GeV/c)2

International Nuclear Information System (INIS)

T. Eden; R. Madey; W.-M. Zhang; B. D. Anderson; H. Arenhvel; A. R. Baldwin; D. Barkhuff; K. B. Beard; W. Bertozzi; J. M. Cameron; C. C. Chang; G. W. Dodson; K. Dow; M. Farkhondeh; J. M. Finn; B. S. Flanders; C. Hyde-Wright; W.-D. Jiang; D. Keane; J. J. Kelly; W. Korsch; S. Kowalski; R. Lourie; D. M. Manley; P. Markowitz; J. Mougey; B. Ni; T. Payerle; P. J. Pella; T. Reichelt; P. M. Rutt; M. Spraker; D. Tieger; W. Turchinetz; P. E. Ulmer; S. Van Verst; J. W. Watson; L. B. Weinstein; and R. R. Whitney

1994-01-01

We determined the electric form factor GnE of the neutron from the quasielastic 2H(e-->,e'n-->)1H reaction at a central squared four-momentum transfer Q2=0.255 (GeV/c)2 with a longitudinally polarized electron beam of 868 MeV and a low (∼0.8%) duty factor. A neutron polarimeter designed and constructed specifically for this experiment was used to measure the sideways polarization of the recoil neutron, which was detected in coincidence with the scattered electron. Theoretical calculations have established that this polarization-transfer technique for quasielastic scattering produces a value of GnE that shows little sensitivity to the influence of final-state interactions, meson-exchange currents, isobar configurations, and deuteron structure. The value for GnE from this measurement is 0.066 ± 0.036 ± 0.009

Manganese-Oxygen Intermediates in O-O Bond Activation and Hydrogen-Atom Transfer Reactions.

Science.gov (United States)

Rice, Derek B; Massie, Allyssa A; Jackson, Timothy A

2017-11-21

Biological systems capitalize on the redox versatility of manganese to perform reactions involving dioxygen and its derivatives superoxide, hydrogen peroxide, and water. The reactions of manganese enzymes influence both human health and the global energy cycle. Important examples include the detoxification of reactive oxygen species by manganese superoxide dismutase, biosynthesis by manganese ribonucleotide reductase and manganese lipoxygenase, and water splitting by the oxygen-evolving complex of photosystem II. Although these enzymes perform very different reactions and employ structurally distinct active sites, manganese intermediates with peroxo, hydroxo, and oxo ligation are commonly proposed in catalytic mechanisms. These intermediates are also postulated in mechanisms of synthetic manganese oxidation catalysts, which are of interest due to the earth abundance of manganese. In this Account, we describe our recent efforts toward understanding O-O bond activation pathways of Mn III -peroxo adducts and hydrogen-atom transfer reactivity of Mn IV -oxo and Mn III -hydroxo complexes. In biological and synthetic catalysts, peroxomanganese intermediates are commonly proposed to decay by either Mn-O or O-O cleavage pathways, although it is often unclear how the local coordination environment influences the decay mechanism. To address this matter, we generated a variety of Mn III -peroxo adducts with varied ligand environments. Using parallel-mode EPR and Mn K-edge X-ray absorption techniques, the decay pathway of one Mn III -peroxo complex bearing a bulky macrocylic ligand was investigated. Unlike many Mn III -peroxo model complexes that decay to oxo-bridged-Mn III Mn IV dimers, decay of this Mn III -peroxo adduct yielded mononuclear Mn III -hydroxo and Mn IV -oxo products, potentially resulting from O-O bond activation of the Mn III -peroxo unit. These results highlight the role of ligand sterics in promoting the formation of mononuclear products and mark an important

Near-field heat transfer between graphene/hBN multilayers

Science.gov (United States)

Zhao, Bo; Guizal, Brahim; Zhang, Zhuomin M.; Fan, Shanhui; Antezza, Mauro

2017-06-01

We study the radiative heat transfer between multilayer structures made by a periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN) slab. Surface plasmons in a monolayer graphene can couple with hyperbolic phonon polaritons in a single hBN film to form hybrid polaritons that can assist photon tunneling. For periodic multilayer graphene/hBN structures, the stacked metallic/dielectric array can give rise to a further effective hyperbolic behavior, in addition to the intrinsic natural hyperbolic behavior of hBN. The effective hyperbolicity can enable more hyperbolic polaritons that enhance the photon tunneling and hence the near-field heat transfer. However, the hybrid polaritons on the surface, i.e., surface plasmon-phonon polaritons, dominate the near-field heat transfer between multilayer structures when the topmost layer is graphene. The effective hyperbolic regions can be well predicted by the effective medium theory (EMT), thought EMT fails to capture the hybrid surface polaritons and results in a heat transfer rate much lower compared to the exact calculation. The chemical potential of the graphene sheets can be tuned through electrical gating and results in an additional modulation of the heat transfer. We found that the near-field heat transfer between multilayer structures does not increase monotonously with the number of layers in the stack, which provides a way to control the heat transfer rate by the number of graphene layers in the multilayer structure. The results may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in two-dimensional materials.

Mass transfer with complex reversible chemical reactions—II. parallel reversible chemical reactions

NARCIS (Netherlands)

Versteeg, G.F.; Kuipers, J.A.M.; Beckum, F.P.H. van; Swaaij, W.P.M. van

1990-01-01

An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

Energy Technology Data Exchange (ETDEWEB)

Nishimura, Akira; Kawahara, Nobuhiro [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); Takagi, Hiroshi, E-mail: hiro@bs.naist.jp [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

2013-01-04

Highlights: Black-Right-Pointing-Pointer NO is produced from L-arginine in response to elevated temperature in yeast. Black-Right-Pointing-Pointer Tah18 was first identified as the yeast protein involved in NO synthesis. Black-Right-Pointing-Pointer Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe-S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

Electron transfer reactions to probe the electrode/solution interface

Energy Technology Data Exchange (ETDEWEB)

Capitanio, F.; Guerrini, E.; Colombo, A.; Trasatti, S. [Milan Univ., Milan (Italy). Dept. of Physical Chemistry and Electrochemistry

2008-07-01

The reactions that occur at the interface between an electrode and an electrolyte were examined with particular reference to the interaction of different electrode surfaces with redox couples. A semi-integration or convolution technique was used to study the kinetics of electron transfer on different electrode materials with different hydrophilic behaviour, such as Boron-Doped-Diamond (BDD), Au and Pt. Standard reversible redox couples were also investigated, including (Fe3+/2+, Fe(CN)63-/4-, Ru(NH3)63+/2+, Co(NH3)63+/2+, Ir4+/3+, V4+/5+ and V3+/2+). The proposed method proved to be simple, straightforward and reliable since the obtained kinetic information was in good agreement with data in the literature. It was concluded that the kinetics of the electrode transfer reactions depend on the chemical nature of the redox couple and electrode material. The method should be further extended to irreversible couples and other electrode materials such as mixed oxide electrodes. 3 refs., 2 figs.

179Ta and 180Ta structure by transfer reactions

International Nuclear Information System (INIS)

Warde, Elias.

1979-01-01

Transfer reactions (α,t); ( 3 He,d); (p,t) and (p,d) have been used to study the nuclear spectroscopy of 179 Ta and 180 Ta. In 179 Ta, 5/2 - and 9/2 - states of the 1/2(541) configuration have been identified. The core-quasiproton interaction has to be taken into account in order to explain the two-nucleon transfer intensities in the 181 Ta(p,t) 179 Ta reaction. A level scheme has been proposed for 180 Ta for the first time. Especially the ground state is identified with the (1 + ,1) level of the [7/2 + (404)sub(p), 9/2 + (624)sub(n)] configuration and spin (9 - ,9) of the configuration [9/2 - (514)sub(p), 9/2 + (624)sub(n)] has been assigned to the long-lived isomer. From the observed configurations in 180 Ta, the matrix elements of the effective residual interaction vsub(np) have been deduced and compared to theoretical predictions [fr

Gamow-Teller transitions and neutron-proton-pair transfer reactions

Science.gov (United States)

Van Isacker, P.; Macchiavelli, A. O.

2018-05-01

We propose a schematic model of nucleons moving in spin-orbit partner levels, j = l ± 1/2, to explain Gamow-Teller and two-nucleon transfer data in N = Z nuclei above 40Ca. Use of the LS coupling scheme provides a more transparent approach to interpret the structure and reaction data. We apply the model to the analysis of charge-exchange, 42Ca(3He,t)42Sc, and np-transfer, 40Ca(3He,p)42Sc, reactions data to define the elementary modes of excitation in terms of both isovector and isoscalar pairs, whose properties can be determined by adjusting the parameters of the model (spin-orbit splitting, isovector pairing strength and quadrupole matrix element) to the available data. The overall agreement with experiment suggests that the approach captures the main physics ingredients and provides the basis for a boson approximation that can be extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry limit is not realized in 42Sc.

Squids, supercurrents, and slope anomalies: Nuclear structure from heavy-ion transfer reactions

International Nuclear Information System (INIS)

Guidry, M.W.

1989-01-01

Within the past five years we have developed experimental techniques to study heavy-ion transfer reactions to high spin states in deformed nuclei. These methods have been turned into a quantitative tool to assess the influence of collective excitation on single-particle and pairing structure. I discuss some of the nuclear structure questions which are being answered in these experiments: How strong is ground state pairing? How does pairing change with angular momentum? Why is two-neutron transfer much stronger than expected at large radial separation? What is the evidence for a nuclear Josephson Effect? What is the evidence for a nuclear Berry phase effect (nuclear SQUID)? Why does one-neutron transfer populate much higher spins than would be naively expected? Conversely, why does two-neutron transfer populate much lower spins than anyone expected? The answer to each of these questions involves the influence of detailed nuclear structure on transfer reactions, and represents quantitative new information about the effect of angular momentum and excitation energy on many-body systems with a finite number of particles. 8 refs., 6 figs

Analysis of transfer reactions: determination of spectroscopic factors

Energy Technology Data Exchange (ETDEWEB)

Keeley, N. [CEA Saclay, Dept. d' Astrophysique, de Physique des Particules de Physique Nucleaire et de l' Instrumentation Associee (DSM/DAPNIA/SPhN), 91- Gif sur Yvette (France); The Andrzej So an Institute for Nuclear Studies, Dept. of Nuclear Reactions, Warsaw (Poland)

2007-07-01

An overview of the most popular models used for the analysis of direct reaction data is given, concentrating on practical aspects. The 4 following models (in order of increasing sophistication): the distorted wave born approximation (DWBA), the adiabatic model, the coupled channels born approximation, and the coupled reaction channels are briefly described. As a concrete example, the C{sup 12}(d,p)C{sup 13} reaction at an incident deuteron energy of 30 MeV is analysed with progressively more physically sophisticated models. The effect of the choice of the reaction model on the spectroscopic information extracted from the data is investigated and other sources of uncertainty in the derived spectroscopic factors are discussed. We have showed that the choice of the reaction model can significantly influence the nuclear structure information, particularly the spectroscopic factors or amplitudes but occasionally also the spin-parity, that we wish to extract from direct reaction data. We have also demonstrated that the DWBA can fail to give a satisfactory description of transfer data but when the tenets of the theory are fulfilled DWBA can work very well and will yield the same results as most sophisticated models. The use of global rather than fitted optical potentials can also lead to important differences in the extracted spectroscopic factors.

Hydride Transfer versus Deprotonation Kinetics in the Isobutane–Propene Alkylation Reaction: A Computational Study

Science.gov (United States)

2017-01-01

The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane–propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation. Our calculations reveal that hydride transfer from isobutane to a carbenium ion occurs via a concerted C–C bond formation between a tert-butyl fragment and an additional olefin, or via deprotonation of the tert-butyl fragment to generate isobutene. A combination of high isobutane concentration and low propene concentration at the reaction center favor the selective alkylation. The key reaction step that has to be suppressed to increase the catalyst lifetime is the deprotonation of carbenium intermediates that are part of the hydride transfer reaction cycle. PMID:29226012

Hydride Transfer versus Deprotonation Kinetics in the Isobutane-Propene Alkylation Reaction: A Computational Study.

Science.gov (United States)

Liu, Chong; van Santen, Rutger A; Poursaeidesfahani, Ali; Vlugt, Thijs J H; Pidko, Evgeny A; Hensen, Emiel J M

2017-12-01

The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane-propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation. Our calculations reveal that hydride transfer from isobutane to a carbenium ion occurs via a concerted C-C bond formation between a tert -butyl fragment and an additional olefin, or via deprotonation of the tert -butyl fragment to generate isobutene. A combination of high isobutane concentration and low propene concentration at the reaction center favor the selective alkylation. The key reaction step that has to be suppressed to increase the catalyst lifetime is the deprotonation of carbenium intermediates that are part of the hydride transfer reaction cycle.

The proton transfer reaction in malonaldehyde derivatives: Substituent effects and quasi-aromaticity of the proton bridge

International Nuclear Information System (INIS)

Palusiak, Marcin; Simon, Silvia; Sola, Miquel

2007-01-01

The proton transfer in malonaldehyde and in some of its derivatives have been considered in order to study the interrelation between the reaction barrier and the π-delocalization in the quasi-ring. A set of simple and mostly common substituents having different properties in resonance effect according to values of substituents constants were chosen in order to simulate the influence of substitution in position 2 or in position 1 (or 3) of malonaldehyde on the quasi-aromaticity and H-bonding. The following substituents have been taken into consideration: NO, NO 2 , CN, CHO, F, H, CH 3 , OCH 3 , OH, and NH 2 . Our results show that when the substituent is attached at position 2 of the quasi-ring, the resonance effect predominates over the field/inductive effect which leads to changes in H-bonding and quasi-aromaticity of the ring motif, while in the case of 1(3) substitution the field/inductive effect is significantly more effective influencing the HB strength, and thus, the proton transfer barrier. Somehow counterintuitively, for the 1(3) substituted systems, the most stable isomer is the one having the weakest HB and lower aromaticity. The reason for this surprising behaviour is discussed

Kinetic isotope effects and tunnelling in the proton-transfer reaction between 4-nitrophenylnitromethane and tetramethylguanidine in various aprotic solvents

International Nuclear Information System (INIS)

Caldin, E.F.; Mateo, S.

1975-01-01

Rates and equilibrium constants have been determined for the proton-transfer reaction of 4-nitrophenylnitromethane, NO 2 C 6 H 4 CH 2 NO 2 , and its αα-deuterated analogue NO 2 C 6 H 4 CD 2 NO 2 , with the strong base tetramethylguanidine [HN=C(NMe 2 ) 2 ), at temperatures between -60 0 C and +65 0 in a range of aprotic solvents. Spectrophotometry and the stopped-flow technique were used. The reaction is a simple proton-transfer process leading to an ion-pair. The kinetic isotope effects are correlated with the polarity of the solvents, as measured by the dielectric constant or by the empirical parameter Esub(T). In the less polar solvents they are exceptionally large. In toluene, for example, at 25 0 C the rate ratio ksup(H)/ksup(D) = 45 +- 2, the activation energy difference Esub(a)sup(D) - Esub(a)sup(H) =4.3 +- 0.3 kcal molsup(-1) (16 kJ molsup(-1), and the ratio of the pre-exponential factors logsub(10) (Asup(D)/Asup(H)) = 1.5 +- 0.2+ and even larger values of logsub(10)(Asup(D)/Asup(H)) are found for mesitylene (1.94 +- 0.06) and cyclohexane (2.4 +- 0.2). Positive deviations from linear Arrhenius plots are found for these solvents. Tunnelling is the only interpretation that cannot account for these results. For the more polar solvents (dielectric constant 7 to 37), the isotope effects are closer to the range predicted by semi-classical theory. The isotope effects in all solvents have been fitted to Bell's equation for a parabolic barrier, and the barrier dimensions calculated for each solvent. The suggested interpretation of the results is that the solvent-solute interactions affect the height of the barrier and that motions of solvent molecules are coupled with the motion of the proton in the more polar solvents but not in the less polar ones; reorganization of solvent molecules accompanies the proton-transfer in the more polar solvents, but only electron-polarization in the less polar. Tunnelling has large effects in the less polar solvents, where the

Time-resolved FTIR emission studies of laser photofragmentation and radical reactions

Energy Technology Data Exchange (ETDEWEB)

Leone, S.R. [Univ. of Colorado, Boulder (United States)

1993-12-01

Recent studies have focused specifically on collision processes, such as single collision energy transfer, reaction dynamics, and radical reactions. The authors employ novel FTIR techniques in the study of single collision energy transfer processes using translationally fast H atom, as well as radical-radical reactions, e.g. CH{sub 3} + O, CF{sub 3} + H(D), and Cl + C{sub 2}H{sub 5}. The fast atoms permit unique high energy regions of certain transition states of combustion species to be probed for the first time.

Excitation functions for quasi-elastic transfer reactions induced with heavy ions in bismuth

International Nuclear Information System (INIS)

Gardes, D.; Bimbot, R.; Maison, J.; Reilhac, L. de; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

1977-01-01

The excitation functions for the production of 210 Bi, 210 Po, sup(207-211)At and 211 Rn through quasi-elastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ca, 56 Fe and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measurements of incident energies and cross sections were performed close to the reaction thresholds

Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions

Directory of Open Access Journals (Sweden)

Patrice Vanelle

2002-12-01

Full Text Available A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

Computational Replication of the Primary Isotope Dependence of Secondary Kinetic Isotope Effects in Solution Hydride-Transfer Reactions: Supporting the Isotopically Different Tunneling Ready State Conformations.

Science.gov (United States)

Derakhshani-Molayousefi, Mortaza; Kashefolgheta, Sadra; Eilers, James E; Lu, Yun

2016-06-30

We recently reported a study of the steric effect on the 1° isotope dependence of 2° KIEs for several hydride-transfer reactions in solution (J. Am. Chem. Soc. 2015, 137, 6653). The unusual 2° KIEs decrease as the 1° isotope changes from H to D, and more in the sterically hindered systems. These were explained in terms of a more crowded tunneling ready state (TRS) conformation in D-tunneling, which has a shorter donor-acceptor distance (DAD) than in H-tunneling. To examine the isotopic DAD difference explanation, in this paper, following an activated motion-assisted H-tunneling model that requires a shorter DAD in a heavier isotope transfer process, we computed the 2° KIEs at various H/D positions at different DADs (2.9 Å to 3.5 Å) for the hydride-transfer reactions from 2-propanol to the xanthylium and thioxanthylium ions (Xn(+) and TXn(+)) and their 9-phenyl substituted derivatives (Ph(T)Xn(+)). The calculated 2° KIEs match the experiments and the calculated DAD effect on the 2° KIEs fits the observed 1° isotope effect on the 2° KIEs. These support the motion-assisted H-tunneling model and the isotopically different TRS conformations. Furthermore, it was found that the TRS of the sterically hindered Ph(T)Xn(+) system does not possess a longer DAD than that of the (T)Xn(+) system. This predicts a no larger 1° KIE in the former system than in the latter. The observed 1° KIE order is, however, contrary to the prediction. This implicates the stronger DAD-compression vibrations coupled to the bulky Ph(T)Xn(+) reaction coordinate.

Quantifying Fenton reaction pathways driven by self-generated H2O2 on pyrite surfaces

Science.gov (United States)

Gil-Lozano, C.; Davila, A. F.; Losa-Adams, E.; Fairén, A. G.; Gago-Duport, L.

2017-03-01

Oxidation of pyrite (FeS2) plays a significant role in the redox cycling of iron and sulfur on Earth and is the primary cause of acid mine drainage (AMD). It has been established that this process involves multi-step electron-transfer reactions between surface defects and adsorbed O2 and H2O, releasing sulfoxy species (e.g., S2O32-, SO42-) and ferrous iron (Fe2+) to the solution and also producing intermediate by-products, such as hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), however, our understanding of the kinetics of these transient species is still limited. We investigated the kinetics of H2O2 formation in aqueous suspensions of FeS2 microparticles by monitoring, in real time, the H2O2 and dissolved O2 concentration under oxic and anoxic conditions using amperometric microsensors. Additional spectroscopic and structural analyses were done to track the dependencies between the process of FeS2 dissolution and the degradation of H2O2 through the Fenton reaction. Based on our experimental results, we built a kinetic model which explains the observed trend of H2O2, showing that FeS2 dissolution can act as a natural Fenton reagent, influencing the oxidation of third-party species during the long term evolution of geochemical systems, even in oxygen-limited environments.

Steric effects on the primary isotope dependence of secondary kinetic isotope effects in hydride transfer reactions in solution: caused by the isotopically different tunneling ready state conformations?

Science.gov (United States)

Maharjan, Binita; Raghibi Boroujeni, Mahdi; Lefton, Jonathan; White, Ormacinda R; Razzaghi, Mortezaali; Hammann, Blake A; Derakhshani-Molayousefi, Mortaza; Eilers, James E; Lu, Yun

2015-05-27

The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1°/2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations.

Theoretical investigation of elementary reaction of complexing LiH+BeH2 → LiBeH3

International Nuclear Information System (INIS)

Charkin, O.P.; Boldyrev, A.I.; Sukhanov, L.P.

1979-01-01

In the framework of non-empiric Hartree-Fock-Roothaan method on the basis of gauss functions of Roos and Siegbahn made are calculations of different sections of potential surface elementary reaction of complexing LiH+BeH 2 → LiBeH 3 . Charts of potential surface are presented. Questions of the elementary mechanism of elementary processes of complexing and effect of mutual orientation of the reagents upon the reaction mechanism are considered. Stability of LiBeH 3 molecule to different dissociation channels and different aspects of structural non-rigidity of the L[MXsub(k+1)] complexes at super barrier excitation are discussed

Asymmetric H-D exchange reactions of fluorinated aromatic ketones

KAUST Repository

Zhao, Yujun

2012-01-01

Chiral bicyclic guanidine catalyzes the asymmetric H-D exchange reactions. Up to 30% ee was achieved. DFT calculations were employed to elucidate and explain the origin of the reaction\\'s stereoselectivity. © 2012 The Royal Society of Chemistry.

Dynamically biased statistical model for the ortho/para conversion in the H2+H3+ --> H3++ H2 reaction

Science.gov (United States)

Gómez-Carrasco, Susana; González-Sánchez, Lola; Aguado, Alfredo; Sanz-Sanz, Cristina; Zanchet, Alexandre; Roncero, Octavio

2012-09-01

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007), 10.1063/1.2430711]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H_5^+ complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the H_5^+ complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice-Ramsperger-Kassel-Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011), 10.1063/1.3587246] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.

Probing the pairing interaction through two-neutron transfer reactions

Directory of Open Access Journals (Sweden)

Margueron J.

2012-12-01

Full Text Available The treatment of the pairing interaction in mean-field-based models is addressed. In particular, the possibility to use pair transfers as A tool to better constrain this interaction is discussed. First, pairing inter-actions with various density dependencies (surface/volume mixing are used in the microscopic Hartree-Fock-Bogoliubov + quasiparticle random-phase approximation model to generate the form factors to be used in reaction calculations. Cross sections for (p,t two-neutron transfer reactions are calculated in the one-step zero-range distorted-wave Born approximation for some Tin isotopes and for incident proton energies from 15 to 35 MeV. Three different surface/volume mixings of A zero-range density-dependent pairing interaction are employed in the microscopic calculations and the sensitivity of the cross sections to the different mixings is analyzed. Differences among the three different theoretical predictions are found espacially for the nucleus 136Sn and they are more important at the incident proton energy of 15 MeV. We thus indicate (p,t two-neutron transfer reactions with very neutron-rich Sn isotopes and at proton energies around 15 MeV as good experimental cases where the surface/volume mixing of the pairing interaction may be probed. In the second part of the manuscript, ground-state to ground-state transitions are investigated. Approximations made to estimate two-nucleon transfer probabilities in ground-state to ground-state transitions and the physical interpretation of these probabilities are discussed. Probabilities are often calculated by approximating both ground states of the initial nucleus A and of the final nucleus A±2 by the same quasiparticle vacuum. We analyze two improvements of this approach. First, the effect of using two different ground states with average numbers of particles A and A±2 is quantified. Second, by using projection techniques, the role of particle number restoration is analyzed. Our analysis

Low energy ion-molecule reactions

Energy Technology Data Exchange (ETDEWEB)

Farrar, J.M. [Univ. of Rochester, NY (United States)

1993-12-01

This project is concerned with elucidating the dynamics of elementary ion-molecule reactions at collision energies near and below 1 eV. From measurements of the angular and energy distributions of the reaction products, one can infer intimathe details about the nature of collisions leading to chemical reaction, the geometries and lifetimes of intermediate complexes that govern the reaction dynamics, and the collision energy dependence of these dynamical features. The author employs crossed-beam low energy mass spectrometry technology developed over the last several years, with the focus of current research on proton transfer and hydrogen atom transfer reactions of te O{sup {minus}} ion with species such as HF, H{sub 2}O, and NH{sub 3}.

H + H2 reaction barrier: A fixed-node quantum Monte Carlo study

International Nuclear Information System (INIS)

Barnett, R.N.; Reynolds, P.J.; Lester, W.A. Jr.

1985-01-01

The classical barrier height for the H+H 2 exchange reaction, as well as the energies at two other points along the reaction path, are calculated using fixed-node quantum Monte Carlo (FNQMC). Several single-determinant importance functions are used at the saddle point in order to relate the quality of the importance function to the accuracy and precision of the final result. The computed barrier is an upper bound since the energy of H and of H 2 is obtained exactly by FNQMC. Our best upper bound (9.70 +- 0.13 kcal/mol) has a mean within 0.1 kcal/mol of the presumed exact value. This best bound is obtained with a single determinant, double-zeta basis importance function. Contrary to experience with expansion methods, it is found that an importance function with a basis set of near Hartree--Fock quality, as well as one derived from a spin-unrestricted SCF calculation, are among the least efficient and least accurate of the importance functions used. Specifically, a nodal surface appearing in the lowest energy molecular orbital in these functions apparently increases the FNQMC energy. The FNQMC energy at the two other points along the reaction path is found to agree with the most accurate CI results of Liu to within statistical error

Transfer reactions in sup(32,36)S + sup(144,154)Sm

International Nuclear Information System (INIS)

Pacheco, A.J.; Tada, M. di; Fernandez Niello, J.; Testoni, J.E.

1990-01-01

The deformation of spherical nuclei in transfer reactions near to the coulomb barrier is studied. The sup(32,36)S + sup(144,154)Sm reactions were carried out using sup(32)S beams produced by TANDAR accelerator in Buenos Aires with energies of 148 MeV and 160 MeV and sup(36)S beams produced by tandem accelerator of Laboratorio Nazionale di Legnaro with energies of 142 MeV and 155 MeV. The angular distributions were measured for sup(32)S reaction using gas ionization chamber and position sensitive detector. The mass spectra of reaction products were obtained measuring time of flight between time detectors, in the sup(36)S reaction. (M.C.K.)

Coumarin or benzoxazinone bearing benzimidazolium and bis(benzimidazolium salts; involvement in transfer hydrogenation of acetophenone derivatives and hCA inhibition

Directory of Open Access Journals (Sweden)

Mert Olgun Karataş

2015-10-01

Full Text Available Four new salts of benzimidazolium and bis(benzimidazolium which include coumarin or benzoxazinone moieties were synthesized and the structures of the newly synthesized compounds were elucidated on the basis of spectral analyses such as 1H-NMR, 13C-NMR, HSQC, IR, LC-MS and elemental analysis. Benzimidazolium salts were used intensively as N-heterocyclic carbene (NHC precursors in the various catalytic reactions such as transfer hydrogenation (TH, C-H bond activation, Heck, Suzuki reaction etc. With the prospect of potential NHC precursor properties of the synthesized compounds, they were employed in the (TH reaction of p-substitute acetophenones (acetophenone, p-methyl acetophenone, p-chloro acetophenone and good yields were observed. Coumarin compounds are known as inhibitor of carbonic anhydrase and inhibition effects of the synthesized compounds on human carbonic anhydrases (hCA were investigated as in vitro. The in vitro results demonstrated that all compounds inhibited hCA I and hCA II activity. Among the synthesized compounds 1,4-bis(1-((6,8-dimethyl-2H-chromen-2-one-4-ylmethylbenzimidazolium-3-ylbutane dichloride was found to be the most active IC50= 5.55 mM and 6.06 mM for hCA I and hCA II, respectively.

Mass transfer with complex chemical reactions in gas–liquid systems : two-step reversible reactions with unit stoichiometric and kinetic orders

NARCIS (Netherlands)

Vas Bhat, R.D.; Kuipers, J.A.M.; Versteeg, G.F.

2000-01-01

An absorption model to study gas–liquid mass transfer accompanied by reversible two-step reactions in the liquid phase has been presented. This model has been used to determine mass transfer rates, enhancement factors and concentration profiles over a wide range of process conditions. Although

Quantum mechanics of electronic-rotational energy transfer in F(2P) + H2 collisions

International Nuclear Information System (INIS)

Wyatt, R.E.; Walker, R.B.

1977-01-01

A theoretical study is made of electronic-rotational energy transfer in F( 2 P) + H 2 three-dimensional collisions, with electronic matrix elements from DIM theory. The quantum close-coupled equations are integrated via the R-matrix propagation method. Inelastic quenching probabilities are emphasized, with and without simulated open reaction channels. Interweaving patterns in the transition probability for even and odd nuclear parity vs. J (total angular momentum quantum number) are analyzed in terms of avoided crossing structure in the electrotational energy correlation diagrams. Localized regions where electronic quenching is dominant are identified in the correlation diagrams, and are confirmed in separate calculations which neglect interchannel mixing in local regions of the atom-molecule separation. Open reaction channels are found to have little influence on the quenching probabilities in these low energy calculations

Interplay of break-up and transfer processes in reactions involving weakly-bound systems

Science.gov (United States)

Vitturi, Andrea; Moschini, Laura

2018-02-01

In this note we illustrate some applications of a simple model which has been devised to clarify the reaction mechanism and the interplay of different reaction channels (elastic, inelastic, transfer, break-up) in heavy-ion collisions. The model involves two potential wells moving in one dimension and few active particles; in spite of its simplicity, it is supposed to maintain the main features, the properties and the physics of the full three-dimensional case. Special attention is given to the role of continuum states in reactions involving weakly-bound systems, and different approximation schemes (as first-order or coupled-channels) as well as different continuum discretization procedures are tested. In the case of two active particles the reaction mechanism associated with two-particle transfer and the effect of pairing intearction are investigated. Work done in collaboration with Antonio Moro and Kouichi Hagino

Theoretical study of chain transfer to solvent reactions of alkyl acrylates.

Science.gov (United States)

Moghadam, Nazanin; Srinivasan, Sriraj; Grady, Michael C; Rappe, Andrew M; Soroush, Masoud

2014-07-24

This computational and theoretical study deals with chain transfer to solvent (CTS) reactions of methyl acrylate (MA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) self-initiated homopolymerization in solvents such as butanol (polar, protic), methyl ethyl ketone (MEK) (polar, aprotic), and p-xylene (nonpolar). The results indicate that abstraction of a hydrogen atom from the methylene group next to the oxygen atom in n-butanol, from the methylene group in MEK, and from a methyl group in p-xylene by a live polymer chain are the most likely mechanisms of CTS reactions in MA, EA, and n-BA. Energy barriers and molecular geometries of reactants, products, and transition states are predicted. The sensitivity of the predictions to three hybrid functionals (B3LYP, X3LYP, and M06-2X) and three different basis sets (6-31G(d,p), 6-311G(d), and 6-311G(d,p)) is investigated. Among n-butanol, sec-butanol, and tert-butanol, tert-butanol has the highest CTS energy barrier and the lowest rate constant. Although the application of the conductor-like screening model (COSMO) does not affect the predicted CTS kinetic parameter values, the application of the polarizable continuum model (PCM) results in higher CTS energy barriers. This increase in the predicted CTS energy barriers is larger for butanol and MEK than for p-xylene. The higher rate constants of chain transfer to n-butanol reactions compared to those of chain transfer to MEK and p-xylene reactions suggest the higher CTS reactivity of n-butanol.

The electrodisintegration of the deuteron reaction at high four-momentum transfer

Science.gov (United States)

Ibrahim, Hassan F.

This dissertation presents the highest four-momentum transfer, Q2, quasielastic (xBj = 1) results from Experiment E01-020 which systematically explored the 2H(e, e'p)n reaction ("Electro-disintegration" of the deuteron) at three different four-momentum transfers, Q 2 = 0.8, 2.1, and 3.5 GeV2 and missing momenta, pmiss = 0, 100, 200, 300, 400, and 500 GeV including separations of the longitudinal-transverse interference response function, RLT, and extraction of the longitudinal-transverse asymmetry, ALT. This systematic approach will help to understand the reaction mechanism and the deuteron structure down to the short range part of the nucleon-nucleon interaction which is one of the fundamental missions of nuclear physics. By studying the very short distance structure of the deuteron, one may also determine whether or to what extent the description of nuclei in terms of nucleon/meson degrees of freedom must be supplemented by inclusion of explicit quark effects. The unique combination of energy, current, duty factor, and control of systematics for Hall A at Jefferson Lab made Jefferson Lab the only facility in the world where these systematic studies of the deuteron can be undertaken. This is especially true when we want to understand the short range structure of the deuteron where high energies and high luminosity/duty factor are needed. All these features of Jefferson Lab allow us to examine large missing momenta (short range scales) at kinematics where the effects of final state interactions (FSI), meson exchange currents (MEC), and isobar currents (IC) are minimal, making the extraction of the deuteron structure less model-dependent. Jefferson Lab also provides the kinematical flexibility to perform the separation of RLT over a broad range of missing momenta and momentum transfers. Experiment E01-020 used the standard Hall A equipment in coincidence configuration in addition to the cryogenic target system. The low and middle Q2 kinematics were completed in June

The reaction of OH with H at elevated temperatures

DEFF Research Database (Denmark)

Lundström, T.; Christensen, H.; Sehested, K.

2002-01-01

The temperature dependence of the rate constant for the reaction between OH radicals and H atoms has been determined in Ar-saturated solutions at pH 2. The reaction was studied in the temperature range 5-233degreesC. The rate constants at 20degreesC and 200degreesC are 9.3 x 10(9) and 3.3 x 10...

Dissociation of protonated N-(3-phenyl-2H-chromen-2-ylidene)-benzenesulfonamide in the gas phase: cyclization via sulfonyl cation transfer.

Science.gov (United States)

Wang, Shanshan; Dong, Cheng; Yu, Lian; Guo, Cheng; Jiang, Kezhi

2016-01-15

In the tandem mass spectrometry of protonated N-(3-phenyl-2H-chromen-2-ylidene)benzenesulfonamides, the precursor ions have been observed to undergo gas-phase dissociation via two competing channels: (a) the predominant channel involves migration of the sulfonyl cation to the phenyl C atom and the subsequent loss of benzenesulfinic acid along with cyclization reaction, and (b) the minor one involves dissociation of the precursor ion to give an ion/neutral complex of [sulfonyl cation/imine], followed by decomposition to afford sulfonyl cation or the INC-mediated electron transfer to give an imine radical cation. The proposed reaction channels have been supported by theoretical calculations and D-labeling experiments. The gas-phase cyclization reaction originating from the N- to C-sulfonyl cation transfer has been first reported to the best of our knowledge. For the substituted sulfonamides, the presence of electron-donating groups (R(2) -) at the C-ring effectively facilitates the reaction channel of cyclization reaction, whereas that of electron-withdrawing groups inhibits this pathway. Copyright © 2015 John Wiley & Sons, Ltd.

Nobel Prize 1992: Rudolph A. Marcus: theory of electron transfer reactions in chemical systems

International Nuclear Information System (INIS)

Ulate Segura, Diego Guillermo

2011-01-01

A review of the theory developed by Rudolph A. Marcus is presented, who for his rating to the theory of electron transfer in chemical systems was awarded the Nobel Prize in Chemistry in 1992. Marcus theory has constituted not only a good extension of the use of a spectroscopic principle, but also has provided an energy balance and the application of energy conservation for electron transfer reactions. A better understanding of the reaction coordinate is exposed in terms energetic and establishing the principles that govern the transfer of electrons, protons and some labile small molecular groups as studied at present. Also, the postulates and equations described have established predictive models of reaction time, very useful for industrial environments, biological, metabolic, and others that involve redox processes. Marcus theory itself has also constituted a large contribution to the theory of complex transition [es

What's new in the proton transfer reaction from pyranine to water? A femtosecond study of the proton transfer dynamics

International Nuclear Information System (INIS)

Prayer, C.; Gustavsson, T.; Tran-Thi, T.-H.

1996-01-01

The proton transfer from excited pyranine to water is studied by the femtosecond fluorescence upconversion technique. It is shown for the first time that the proton transfer reaction in water proceeds by three successive steps: the solvent cage relaxation, the specific solute-solvent hydrogen-bond formation and finally the ion pair dissociation/diffusion

Mass transfer with complex chemical reactions in gas-liquid systems: two-step reversible reactions with unit stoichiometric and kinetic orders

NARCIS (Netherlands)

Vas bhat, R.D.; Kuipers, J.A.M.; Versteeg, Geert

2000-01-01

An absorption model to study gas¿liquid mass transfer accompanied by reversible two-step reactions in the liquid phase has been presented. This model has been used to determine mass transfer rates, enhancement factors and concentration profiles over a wide range of process conditions. Although

Reaction of ketene ions with ammonia

International Nuclear Information System (INIS)

Iraqi, M.; Lifshitz, C.; Reuben, B.G.

1991-01-01

Reactions of ketene ions with NH 3 , ND 3 , H 2 O, and CH 4 were investigated in a selected ion flow tube (SIFT). There were no observable products for H 2 O and CH 4 and no ion/neutral complex stabilization in any of the systems investigated. The ammonia system demonstrated two reaction channels, in agreement with previous FTICR data (1) distonic ion CH 2 NH 3 sm-bullet + formation, with a branching ratio of 0.2 and (2) proton transfer, with a branching ratio of 0.8. The overall second-order rate constant for NH 3 is (2.2 ± 0.15) x 10 -9 cm 3 molecule -1 s -1 , in agreement with the gas kinetic ion-dipole collision rate. Isotope scrambling was studied for primary (CH 2 CO + ) and for secondary (CH 2 NX 3 sm-bullet + and NX 4 + , X = H or D) proton-transfer reactions with ND 3 ; CH 2 NH 3 sm-bullet + appears to transfer an X + ion to ND 3 without any scrambling. CH 2 CO sm-bullet + undergoes reactions with partial scrambling and NX 4 + seems to react with almost complete scrambling. The results are compared with these of Adams, Smith, and Henchman on the NH 4 + /ND 3 system

Excited state intramolecular charge transfer reaction in 4-(1 ...

Indian Academy of Sciences (India)

Administrator

cal reactions to the determination of paleotempera- tures from isotopic ... ordered liquid than H2O due to stronger H-bond in- teractions in the deuterated water ... layer chromatography and monitoring the excitation wavelength dependence of ...

Highly efficient dual cocatalyst-modified TiO2 photocatalyst: RGO as electron-transfer mediator and MoSx as H2-evolution active site

Science.gov (United States)

Xu, Ying; Li, Yongan; Wang, Ping; Wang, Xuefei; Yu, Huogen

2018-02-01

The rapid interfacial charge transfer and interfacial catalytic reaction are highly desirable to improve the photocatalytic H2-evolution performance of semiconductor photocatalysts. To achieve the goal, in the paper, MoSx-rGO/TiO2 was synthesized by a facilely two-step photocatalytic reduction approach including reducing GO/TiO2 to rGO/TiO2 and then reducing ammonium tetrathiomolybdate ((NH4)2MoS4) to form amorphous MoSx on the rGO surface. In the case, the rGO nanosheets as an electron mediator caused rapid transportation of photogenerated electrons from the conduction band (CB) of TiO2, while amorphous MoSx served as an effective active site for the following interfacial reduction reaction for H2 evolution. The photocatalytic results indicated that the H2-evolution rate of synthesized MoSx-rGO/TiO2 was 206.6 μmol h-1, which was obviously higher than that of TiO2 (6.9 μmol h-1), rGO/TiO2 (31.8 μmol h-1) and MoSx/TiO2 (150.1 μmol h-1) due to the rapid interfacial charge transfer and interfacial catalytic reaction. Considering the present mild and green approach, the obtained MoSx-rGO/TiO2 could be regarded as a potential photocatalyst for the practical application. In addition, this work also could provide some new insights for the smart design and preparation of inexpensive and high-efficiency photocatalytic materials.

Theoretical investigation of elementary reaction of complexing LiH+BeH/sub 2/. -->. LiBeH/sub 3/

Energy Technology Data Exchange (ETDEWEB)

Charkin, O P; Boldyrev, A I; Sukhanov, L P [AN SSSR, Chernogolovka. Inst. Novykh Khimicheskikh Problem

1979-01-01

In the framework of non-empirical Hartree-Fock-Roothaan method on the basis of gauss functions of Roos and Siegbahn made are calculations of different sections of potential surface elementary reaction of complexing LiH+BeH/sub 2/ ..-->.. LiBeH/sub 3/. Charts of potential surface are presented. Questions of the elementary mechanism of elementary processes of complexing and effect of mutual orientation of the reagents upon the reaction mechanism are considered. Stability of LiBeH/sub 3/ molecule to different dissociation channels and different aspects of structural non-rigidity of the L(MXsub(k+1)) complexes at super barrier excitation are discussed.

Mass transfer with complex reversible chemical reactions—II. parallel reversible chemical reactions

OpenAIRE

Versteeg, G.F.; Kuipers, J.A.M.; Beckum, F.P.H. van; Swaaij, W.P.M. van

1990-01-01

An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and concentration profiles for a wide range of processes and conditions, for both film and penetration model. With the aid of this mass transfer model it is demonstrated that the absorption rates in syst...

Production of isomers in compound and transfer reactions with 4He ions

International Nuclear Information System (INIS)

Karamyan, S.A.; Aksenov, N.V.; Albin, Yu.A.; Bozhikov, G.A.; Dmitriev, S.N.; Starodub, G.Ya.; Vostokin, G.K.; Carroll, J.J.

2011-01-01

A well-known island of nuclear isomerism appears near A = 175-180 due to the deformation alignment of single-particle orbits at high angular momentum. This sometimes results in the formation of multi-quasiparticle states with record spin that are long-lived because of 'K-hindrance', i.e., symmetry rearrangement. Production methods and spectroscopic studies of these isomers remain a challenge for modern nuclear reaction and nuclear structure physics. Activities were produced by irradiation of 176 Yb(97.6%) enriched and nat Lu targets with 35-MeV 4 He ions from the internal beam of the U200 cyclotron. Induced activities were analyzed applying methods of radiochemistry and gamma spectroscopy. Yields of compound and nucleon-transfer reactions were measured and the isomer-to-ground state ratios were deduced. Calculated results were obtained using standard procedures to reproduce the (α, xn) cross sections, and the systematic behavior of the nucleon-transfer yields was established. The isomer-to-ground state ratios for direct reactions with 4 He ions were examined, resulting in a new characterization of the reaction mechanism

Dynamically biased statistical model for the ortho/para conversion in the H2 + H3+ → H3+ + H2 reaction.

Science.gov (United States)

Gómez-Carrasco, Susana; González-Sánchez, Lola; Aguado, Alfredo; Sanz-Sanz, Cristina; Zanchet, Alexandre; Roncero, Octavio

2012-09-07

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007)]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H(5)(+) complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the H(5)(+) complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice-Ramsperger-Kassel-Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011)] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.

Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

Science.gov (United States)

Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

2009-01-01

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

Vibrational state-resolved differential cross sections for the D + H2 → DH + H reaction

International Nuclear Information System (INIS)

Continetti, R.E.

1989-11-01

In this thesis, crossed-molecular-beams studies of the reaction D + H 2 → DH + H at collision energies of 0.53 and 1.01 eV are reported. Chapter 1 provides a survey of important experimental and theoretical studies on the dynamics of the hydrogen exchange reaction. Chapter 2 discusses the development of the excimer-laser photolysis D atom beam source that was used in these studies and preliminary experiments on the D + H 2 reaction. In Chapter 3, the differential cross section measurements are presented and compared to recent theoretical predictions. The measured differential cross sections for rotationally excited DH products showed significant deviations from recent quantum scattering calculations, in the first detailed comparison of experimental and theoretical differential cross sections. These results indicate that further work on the H 3 potential energy surface, particularly the bending potential, is in order

Elastic scattering and cluster-transfer reactions of 98Rb on 7Li at REX-ISOLDE

CERN Document Server

Bouma, Jake

Exotic nuclei are nuclei with unusual proton to neutron ratios that exist far away from stability. Due to their instability, these nuclei are only available for nuclear reactions as radioactive ion beams. Experiments must therefore be performed in inverse kinematics at advanced radioactive isotope separation and acceleration facilities. REX-ISOLDE at CERN is one such facility, capable of producing post-accelerated radioactive ion beams with energies up to 2.85 MeV/u. Cluster-transfer reactions in inverse kinematics with a $^{7}$Li target are proposed as a tool for the study of exotic nuclei at REX-ISOLDE. In these reactions, either the $\\alpha$ or triton clusters that make up the weakly bound $^{7}$Li nucleus can be transfered to the beam nucleus. The remaining cluster that is not transferred can be detected, and identifies the particular transfer channel. Through this mechanism it is possible to populate states of very high spin, which is useful for $\\gamma$-spectroscopy in poorly known exotic regions. Speci...

Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads

NARCIS (Netherlands)

Niemi, Marja; Tkachenko, Nikolai V.; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

2008-01-01

Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C-60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results

Communication: Transfer Ionization in a Thermal Reaction of a Cation and Anion: Ar+ with Br and I (Postprint)

Science.gov (United States)

2016-01-29

AFRL-RV-PS- AFRL-RV-PS- TP-2015-0016 TP-2015-0016 COMMUNICATION: TRANSFER IONIZATION IN A THERMAL REACTION OF A CATION AND ANION: AR+ WITH BR...DATES COVERED (From - To) 01 Jun 2013 – 23 Sep 2013 4. TITLE AND SUBTITLE Communication: Transfer Ionization in a Thermal Reaction of a Cation and Anion...Rights. Communication: Transfer ionization in a thermal reaction of a cation and anion: Ar+ with Br− and I− Nicholas S. Shuman, Thomas M. Miller

Temperature dependence on sodium-water chemical reaction

International Nuclear Information System (INIS)

Tamura, Kenta; Deguchi, Yoshihiro; Suzuki, Koichi; Takata, Takashi; Yamaguchi, Akira; Kikuchi, Shin; Ohshima, Hiroyuki

2012-01-01

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. This process ends up damages on the heat transport equipment in the SFR. Therefore, the study on sodium-water chemical reactions is of paramount importance for security reasons. This study aims to clarify the sodium-water reaction mechanisms using laser diagnostics. A quasi one-dimensional flame model is also applied to a sodium-water counter-flow reaction field. Temperature, H 2 , H 2 O, OH, Na and Particulate matter were measured using laser induced fluorescence and CARS in the counter-flow reaction field. The temperature of the reaction field was also modified to reduce the condensation of Na in the reaction zone. (author)

Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions.

Science.gov (United States)

Mitra, Mainak; Nimir, Hassan; Demeshko, Serhiy; Bhat, Satish S; Malinkin, Sergey O; Haukka, Matti; Lloret-Fillol, Julio; Lisensky, George C; Meyer, Franc; Shteinman, Albert A; Browne, Wesley R; Hrovat, David A; Richmond, Michael G; Costas, Miquel; Nordlander, Ebbe

2015-08-03

Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

Deuteron breakup in the 2H(e,e'p) reaction at low momentum transfer and close to threshold

International Nuclear Information System (INIS)

Neumann-Cosel, P. von; Richter, A.; Schrieder, G.; Shevchenko, A.; Stiller, A.; Arenhoevel, H.

2002-04-01

Deuteron breakup has been studied in a 2 H(e, e'p) coincidence experiment at low momentum transfer and for energies close to threshold. The longitudinal-plus-transverse (L + T) and longitudinal-transverse interference (LT) cross sections are deduced. Nonrelativistic calculations based on the Bonn potential and including leading order relativistic contributions, meson exchange currents and isobar configurations describe the (L + T) data well. Surprisingly large deviations of 30 to 45% are observed for the LT contribution. (orig.)

Pathways for the reaction of the butadiene radical cation, [C{sub 4}H{sub 6}]{sup {sm{underscore}bullet}+}, with ethylene

Energy Technology Data Exchange (ETDEWEB)

Hofmann, M.; Schaefer, H.F. III

1999-11-04

The Diels-Alder (DA) reaction, a [4+2] cycloaddition used to build six membered rings, is one of the most valuable cycloadditions in organic chemistry. In cases where the ene does not add to the diene (even with the help of Lewis acids which may reduce the electron density of one reactant by complexation) one electron oxidation (by an oxidizing agent or by photoinduced electron transfer (PET)) may accelerate the reaction. Reaction pathways for the addition of ethylene, 1, to butadiene radical cation, 2, involving H-shifts have been investigated at the coupled cluster UCCSD(T)/DZP//UMP2(fc)/DZP + ZPE level of theory. Activation energies are relatively low for [1,2]- (10.0 kcal mol{sup {minus}1}, TS-4/20) and [1,5]-hydrogen shifts (7.7 kcal mol{sup {minus}1}, TS-4/26) but are relatively high for [1,4]-(33.8 kcal mol{sup {minus}1}, TS-4/14) and [1,3]-H shifts (e.g., 42.2 kcal mol{sup {minus}1}, TS-12/13; 57.2 kcal mol{sup {minus}1}, TS-16/21). Several rearrangement reactions have been found to occur below the energy limit of separated 1 + 2. The cyclopentenyl cation, [C{sub 5}{sub 7}]{sup +}, 18, experimentally observed as reaction product of the butadiene radical cation, 2, and ethylene, 1, in the gas phase may origin from various reaction pathways. The following reaction sequence has been identified as the lowest in energy path from 1 + 2 to 18 with all relative energies ({Delta}E{degree}) of transition structures below that of 1 + 2: (a) ethylene adds to the butadiene radical cation to form an open-chain distonic intermediate, that undergoes a [1,5]-H shift to the 1,4-hexadiene radical cation; (b) intramolecular [2+1] cycloaddition to methyl-cyclopenta-1,3-diyl intermediates, which can interconvert through a bicyclo[2.1.0]pentane radical cation; (c) [1,2]-H shift to the 3-methyl cyclopentene radical cation; (d) methyl radical loss to give cyclopenten-3-yl cation. Along this reaction pathway, {Delta}H{sup 298} is below that of 1 + 2; max. ({Delta}G{sup 298} by

Single step synthesis of gold-amino acid composite, with the evidence of the catalytic hydrogen atom transfer (HAT) reaction, for the electrochemical recognition of Serotonin

Science.gov (United States)

Choudhary, Meenakshi; Siwal, Samarjeet; Nandi, Debkumar; Mallick, Kaushik

2016-03-01

A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of 'in-situ polymerization and composite formation (IPCF)' [1,2]. The formation mechanism of the composite has been supported by a model hydrogen atom (H•≡H++e-) transfer (HAT) type of reaction which belongs to the proton coupled electron transfer (PCET) mechanism. The 'gold-amino acid composite' was used as a catalyst for the electrochemical recognition of Serotonin.

Chemical Evolution of Groundwater Near a Sinkhole Lake, Northern Florida: 2. Chemical Patterns, Mass Transfer Modeling, and Rates of Mass Transfer Reactions

Science.gov (United States)

Katz, Brian G.; Plummer, L. Niel; Busenberg, Eurybiades; Revesz, Kinga M.; Jones, Blair F.; Lee, Terrie M.

1995-06-01

Chemical patterns along evolutionary groundwater flow paths in silicate and carbonate aquifers were interpreted using solute tracers, carbon and sulfur isotopes, and mass balance reaction modeling for a complex hydrologic system involving groundwater inflow to and outflow from a sinkhole lake in northern Florida. Rates of dominant reactions along defined flow paths were estimated from modeled mass transfer and ages obtained from CFC-modeled recharge dates. Groundwater upgradient from Lake Barco remains oxic as it moves downward, reacting with silicate minerals in a system open to carbon dioxide (CO2), producing only small increases in dissolved species. Beneath and downgradient of Lake Barco the oxic groundwater mixes with lake water leakage in a highly reducing, silicate-carbonate mineral environment. A mixing model, developed for anoxic groundwater downgradient from the lake, accounted for the observed chemical and isotopic composition by combining different proportions of lake water leakage and infiltrating meteoric water. The evolution of major ion chemistry and the 13C isotopic composition of dissolved carbon species in groundwater downgradient from the lake can be explained by the aerobic oxidation of organic matter in the lake, anaerobic microbial oxidation of organic carbon, and incongruent dissolution of smectite minerals to kaolinite. The dominant process for the generation of methane was by the CO2 reduction pathway based on the isotopic composition of hydrogen (δ2H(CH4) = -186 to -234‰) and carbon (δ13C(CH4) = -65.7 to -72.3‰). Rates of microbial metabolism of organic matter, estimated from the mass transfer reaction models, ranged from 0.0047 to 0.039 mmol L-1 yr-1 for groundwater downgradient from the lake.

Promotion of multi-electron transfer for enhanced photocatalysis: A review focused on oxygen reduction reaction

Energy Technology Data Exchange (ETDEWEB)

Wang, Changhua [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China); College of Chemistry and Biology, Beihua University, Jilin 132013 (China); Zhang, Xintong, E-mail: xtzhang@nenu.edu.cn [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China); Liu, Yichun [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China)

2015-12-15

Highlights: • Oxygen reduction reaction (ORR) in photocatalysis process is focused. • Multi-electron transfer ORR is reviewed. • This review provides a guide to access to enhanced photocatalysis via multi-electron transfer. - Abstract: Semiconductor photocatalysis has attracted significant interest for solar light induced environmental remediation and solar fuel generation. As is well known, photocatalytic performance is determined by three steps: photoexcitation, separation and transport of photogenerated charge carriers, and surface reactions. To achieve higher efficiency, significant efforts have been made on improvement of efficiency of above first two steps, which have been well documented in recent review articles. In contrast, this review intends to focus on strategies moving onto the third step of improvement for enhanced photocatalysis wherein active oxygen species including superoxide radical, hydrogen peroxide, hydroxyl radical are in situ detected. Particularly, surface electron-transfer reduction of oxygen over single component photocatalysts is reviewed and systems enabling multi-electron transfer induced oxygen reduction reaction (ORR) are highlighted. It is expected this review could provide a guideline for readers to better understand the critical role of ORR over photocatalyst in charge carrier separation and transfer and obtain reliable results for enhanced aerobic photocatalysis.

Asymmetric H-D exchange reactions of fluorinated aromatic ketones

KAUST Repository

Zhao, Yujun; Lim, XiaoZhi; Pan, Yuanhang; Zong, Lili; Feng, Wei; Tan, Choonhong; Huang, Kuo-Wei

2012-01-01

Chiral bicyclic guanidine catalyzes the asymmetric H-D exchange reactions. Up to 30% ee was achieved. DFT calculations were employed to elucidate and explain the origin of the reaction's stereoselectivity. © 2012 The Royal Society of Chemistry.

Cyclopentadiene-mediated hydride transfer from rhodium complexes.

Science.gov (United States)

Pitman, C L; Finster, O N L; Miller, A J M

2016-07-12

Attempts to generate a proposed rhodium hydride catalytic intermediate instead resulted in isolation of (Cp*H)Rh(bpy)Cl (1), a pentamethylcyclopentadiene complex, formed by C-H bond-forming reductive elimination from the fleeting rhodium hydride. The hydride transfer ability of diene 1 was explored through thermochemistry and hydride transfer reactions, including the reduction of NAD(+).

Catalytic biorefining of plant biomass to non-pyrolytic lignin bio-oil and carbohydrates through hydrogen transfer reactions.

Science.gov (United States)

Ferrini, Paola; Rinaldi, Roberto

2014-08-11

Through catalytic hydrogen transfer reactions, a new biorefining method results in the isolation of depolymerized lignin--a non-pyrolytic lignin bio-oil--in addition to pulps that are amenable to enzymatic hydrolysis. Compared with organosolv lignin, the lignin bio-oil is highly susceptible to further hydrodeoxygenation under low-severity conditions and therefore establishes a unique platform for lignin valorization by heterogeneous catalysis. Overall, the potential of a catalytic biorefining method designed from the perspective of lignin utilization is reported. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A nine-dimensional ab initio global potential energy surface for the H2O+ + H2 → H3O+ + H reaction

Science.gov (United States)

Li, Anyang; Guo, Hua

2014-06-01

An accurate full-dimensional global potential energy surface (PES) is developed for the title reaction. While the long-range interactions in the reactant asymptote are represented by an analytical expression, the interaction region of the PES is fit to more than 81 000 of ab initio points at the UCCSD(T)-F12b/AVTZ level using the permutation invariant polynomial neural network approach. Fully symmetric with respect to permutation of all four hydrogen atoms, the PES provides a faithful representation of the ab initio points, with a root mean square error of 1.8 meV or 15 cm-1. The reaction path for this exoergic reaction features an attractive and barrierless entrance channel, a submerged saddle point, a shallow H4O+ well, and a barrierless exit channel. The rate coefficients for the title reaction and kinetic isotope effect have been determined on this PES using quasi-classical trajectories, and they are in good agreement with available experimental data. It is further shown that the H2O+ rotational enhancement of reactivity observed experimentally can be traced to the submerged saddle point. Using our recently proposed Sudden Vector Projection model, we demonstrate that a rotational degree of freedom of the H2O+ reactant is strongly coupled with the reaction coordinate at this saddle point, thus unraveling the origin of the pronounced mode specificity in this reaction.

A nine-dimensional ab initio global potential energy surface for the H2O+ + H2 → H3O+ + H reaction

International Nuclear Information System (INIS)

Li, Anyang; Guo, Hua

2014-01-01

An accurate full-dimensional global potential energy surface (PES) is developed for the title reaction. While the long-range interactions in the reactant asymptote are represented by an analytical expression, the interaction region of the PES is fit to more than 81 000 of ab initio points at the UCCSD(T)-F12b/AVTZ level using the permutation invariant polynomial neural network approach. Fully symmetric with respect to permutation of all four hydrogen atoms, the PES provides a faithful representation of the ab initio points, with a root mean square error of 1.8 meV or 15 cm −1 . The reaction path for this exoergic reaction features an attractive and barrierless entrance channel, a submerged saddle point, a shallow H 4 O + well, and a barrierless exit channel. The rate coefficients for the title reaction and kinetic isotope effect have been determined on this PES using quasi-classical trajectories, and they are in good agreement with available experimental data. It is further shown that the H 2 O + rotational enhancement of reactivity observed experimentally can be traced to the submerged saddle point. Using our recently proposed Sudden Vector Projection model, we demonstrate that a rotational degree of freedom of the H 2 O + reactant is strongly coupled with the reaction coordinate at this saddle point, thus unraveling the origin of the pronounced mode specificity in this reaction

Influence of zeolite pore structure on product selectivities for protolysis and hydride transfer reactions in the cracking of n-pentane.

Science.gov (United States)

Miyaji, Akimitsu; Iwase, Yasuyoshi; Nishitoba, Toshiki; Long, Nguyen Quang; Motokura, Ken; Baba, Toshihide

2015-02-21

The conversion of n-pentane was carried out to examine the effects of reaction conditions on changes in product selectivities at 823 K, using zeolites with 10- and 12-membered rings. We also investigated the influence of the pore structure of these zeolites on their catalytic activities for both protolysis and hydride transfer reactions. In the first half of this work, we examined the influence of acidic proton concentration and n-pentane pressure on the reaction rates for protolysis and hydride transfer reactions using ZSM-5 zeolites. The rates of hydride transfer reactions were more influenced by pentane pressure compared to protolysis reactions, and were proportional to the square of n-pentane pressure and the concentration of acidic protons. In the second half of this work, the influence of the zeolite pore structure on changes in product selectivities with n-pentane conversion and that on the rates of protolysis and the hydride transfer reactions were revealed using various zeolites with 10- and 12-membered rings. The catalytic activities of zeolites for the protolysis and hydride transfer reactions were influenced more by the spatial volume of the zeolite cavity than the acid strength of protons on the zeolite.

Understanding the two neutron transfer reaction mechanism in {sup 206}Pb({sup 18}O,{sup 16}O){sup 208}Pb

Energy Technology Data Exchange (ETDEWEB)

Parmar, A.; Sonika [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai - 400 085 (India); Roy, B.J., E-mail: bjroy@barc.gov.in [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai - 400 085 (India); Jha, V.; Pal, U.K. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai - 400 085 (India); Sinha, T. [High Energy Nuclear and Particle Physics Division, Saha Institute of Nuclear Physics, Kolkata - 700 064 (India); Pandit, S.K.; Parkar, V.V.; Ramachandran, K.; Mahata, K.; Santra, S.; Mohanty, A.K. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai - 400 085 (India)

2015-08-15

The absolute cross sections for elastic scattering and two-neutron transfer reaction for {sup 18}O + {sup 206}Pb system have been measured at an incident energy near the Coulomb barrier. Detailed coupled reaction channel calculations have been carried out for description of the measured angular distributions for the elastic scattering and transfer reactions simultaneously. The two-neutron transfer reaction {sup 206}Pb({sup 18}O, {sup 16}O){sup 208}Pb in the g.s. → g.s. transition is analyzed in (i) extreme cluster model assuming a di-neutron transfer, (ii) two-step successive transfer, and (iii) microscopic approach (independent coordinate scheme) of simultaneous transfer of two neutrons. The relative importance of one step simultaneous transfer versus two-step successive transfer has been studied. Present analysis suggests dominance of cluster transfer of a di-neutron. The contribution from the two-step sequential processes is less significant, however, the combined “two-step plus simultaneous (microscopic)” calculations give a reasonably good agreement with the measurement. The possibility of multi-step route via projectile and target excitations and contribution from such indirect transfer paths to the present two-neutron transfer cross section has been investigated.

Kinetic Monte Carlo modeling of chemical reactions coupled with heat transfer.

Science.gov (United States)

Castonguay, Thomas C; Wang, Feng

2008-03-28

In this paper, we describe two types of effective events for describing heat transfer in a kinetic Monte Carlo (KMC) simulation that may involve stochastic chemical reactions. Simulations employing these events are referred to as KMC-TBT and KMC-PHE. In KMC-TBT, heat transfer is modeled as the stochastic transfer of "thermal bits" between adjacent grid points. In KMC-PHE, heat transfer is modeled by integrating the Poisson heat equation for a short time. Either approach is capable of capturing the time dependent system behavior exactly. Both KMC-PHE and KMC-TBT are validated by simulating pure heat transfer in a rod and a square and modeling a heated desorption problem where exact numerical results are available. KMC-PHE is much faster than KMC-TBT and is used to study the endothermic desorption of a lattice gas. Interesting findings from this study are reported.

Drift-tube studies of ion-molecule reactions at low collision energies

International Nuclear Information System (INIS)

Chatterjee, B.K.

1988-01-01

This thesis presents experimental studies of ion-molecule reactions at low collision energies using two drift tube mass spectrometer apparatus. The reactions studied are (i) proton transfer from HeH + to ArH + , (ii) charge and ion transfer reactions of O 2 2+ with NO, CO 2 , Ne and O 2 + ( 4 π u ) with CO 2 , (iii) oxidation reactions of Zr + and ZrO + with NO, CO 2 and O 2 , (iv) vibrational quenching reactions of H 3 + with He, (v) termolecular clustering reactions of H 2 CN + and H 2 CN + (HCN) (with He as the third body), (vi) three body association reactions of H + and D + with He (with He as the third body) and (vii) termolecular association reaction of NO + with NO (with Ne as third body). All the reactions were studied at thermal energies (at room temperature), reactions of O 2 2+ with NO and CO 2 , Zr + with NO/CO 2 /O 2 were also studied at center-of-mass energies higher than thermal and the association reactions of H 2 CN + /H 2 CN + (HCN) with HCN and H + /D + with He were studied at low temperatures. In addition, the thesis presents model calculations for the sweep-out effect which is an instrumental effect. A super Langevin rate constant is introduced which is a higher-order correction to the Langevin model. A theoretical model for the three-body ion-atom association rate constant is presented in the appendix of the thesis

Adoptive transfer of transplantation tolerance in the H-2 compatible mouse system CBA/C3H

International Nuclear Information System (INIS)

Siegl, E.; Brock, J.; Schulze, H.A.

1985-01-01

Transfer of neonatally induced tolerance in the H-2 compatible CBA/C3H strain combination is possible with different efficiency by injection of adherent and non-adherent spleen cells, unseparated spleen cells and lymph node cells from C3H-tolerant CBA mice into sublethal irradiated CBA mice. The most efficient cell populations are adherent spleen cells and lymph node cells. Successfull transfer of transplantation tolerance is not possible to non-irradiated mice. The adherent fraction of spleen cells and lymph node cells contains a suppressor cell population responsible for transplantation tolerance against non-H-2 antigens. The induced transplantation tolerance is not due to a chimeric state of C3H-tolerant CBA mice. (author)

A study of the accelerated zircaloy-4 oxidation reaction with H2O/H2 mixture gas

International Nuclear Information System (INIS)

Kim, Y. S.; Cho, I. J.

2001-01-01

A study of the Zircaloy-4 reaction with H 2 O/H 2 mixture gas is carried out by using TGA (Thermo Gravimetric Apparatus) to estimate the hydrogen embrittlement which can possibly cause catastrophic nuclear fuel rod failure. Reaction rates are measured as a function of H 2 /H 2 O. In the experiments reaction temperature is set at 500 .deg. C and total pressure of the mixture gas is maintained at 1 atm. Experimental results reveal that hydriding and oxidation reaction are competing. In early stage, hydriding kinetics is faster than oxidation, however, oxidant in H 2 O forms oxide on the surface as steam environment is maintained, thus, this growing oxide begins to protect the zirconium base metal against hydrogen permeation. In this second stage, the total kinetic rate follows enhanced oxidation kinetics. In the final stage, it is observed that the oxide is broken down and massive hydriding takes place through the mechanical defects in the oxide, whose kinetics is similar to pure hydriding kinetics. These results are confirmed by SEM and EDX analysis along with hydrogen concentration measurements

The effect of intramolecular quantum modes on free energy relationships for electron transfer reactions

DEFF Research Database (Denmark)

Ulstrup, Jens; Jortner, Joshua

1975-01-01

A general quantum mechanical description of exothermic electron transfer reactions is formulated by treating such reactions as the nonradiative decay of a ''supermolecule'' consisting of the electron donor, the electron acceptor, and the polar solvent. In particular, the role of the high-frequenc...

Reaction of O+, CO+, and CH+ ions with atomic hydrogen

International Nuclear Information System (INIS)

Federer, W.; Villinger, H.; Howorka, F.; Lindinger, W.; Tosis, P.; Bassi, D.; Ferguson, E.

1984-01-01

Rate coefficients for reactions of the ions O + , CO + , and CH + with atomic hydrogen have been measured for the first time at 300 K. This provides basic data for the ion chemistry of planetary atmospheres, cometary atmospheres, and interstellar molecular clouds. The O + +H measurement supports quantal calculations of this reaction. The CO + +H reaction provides an example of partial spin nonconservation in a charge-transfer reaction occurring in a deep potential well. Reactions of the same ions with H 2 that have been measured elsewhere are also reported

Mass of 11Li from the 1H(11Li,9Li)3H reaction

International Nuclear Information System (INIS)

Roger, T.; Savajols, H.; Mittig, W.; Caamano, M.; Roussel-Chomaz, P.; Tanihata, I.; Alcorta, M.; Bandyopadhyay, D.; Bieri, R.; Buchmann, L.; Davids, B.; Galinski, N.; Howell, D.; Mills, W.; Mythili, S.; Openshaw, R.; Padilla-Rodal, E.; Ruprecht, G.; Sheffer, G.; Shotter, A. C.

2009-01-01

The mass of 11 Li has been determined from Q-value measurements of the 1 H( 11 Li, 9 Li) 3 H reaction. The experiment was performed at TRIUMF laboratory with the GANIL active target MAYA. Energy-energy and angle-angle kinematics reconstruction give a Q value of 8.119(22) MeV for the reaction. The derived 11 Li two-neutron separation energy is S 2n =363(22) keV

Molecular treatment of the ion-pair formation reaction in H(1s) + H(1s) collisions

Energy Technology Data Exchange (ETDEWEB)

Borondo, F.; Martin, F.; Yaez, M.

1987-01-01

All the available theoretical calculations of the cross section for the ion-pair formation reaction H(1s)+H(1s)..-->..H/sup +/H/sup -/(1s/sup 2/) have been performed using methods that are only valid at high collision energies. They get good agreement with the experiments for impact energies greater than 25 keV, but fail completely at smaller energies. In this work we report the cross section for this reaction at impact energies less than 10 keV, calculated in the framework of the impact-parameter approximation and using the molecular method with a common translation factor.

Molecular treatment of the ion-pair formation reaction in H(1s) + H(1s) collisions

International Nuclear Information System (INIS)

Borondo, F.; Martin, F.; Yaez, M.

1987-01-01

All the available theoretical calculations of the cross section for the ion-pair formation reaction H(1s)+H(1s)→H + H - (1s 2 ) have been performed using methods that are only valid at high collision energies. They get good agreement with the experiments for impact energies greater than 25 keV, but fail completely at smaller energies. In this work we report the cross section for this reaction at impact energies less than 10 keV, calculated in the framework of the impact-parameter approximation and using the molecular method with a common translation factor

Energy transfer in reactive and non-reactive H2 + OH collisions

International Nuclear Information System (INIS)

Rashed, O.; Brown, N.J.

1985-04-01

We have used the methods of quasi-classical dynamics to compute energy transfer properties of non-reactive and reactive H 2 + OH collisions. Energy transfer has been investigated as function of translational temperature, reagent rotational energy, and reagent vibrational energy. The energy transfer mechanism is complex with ten types of energy transfer possible, and evidence was found for all types. There is much more exchange between the translational degree of freedom and the H 2 vibrational degree of freedom than there is between translation and OH vibration. Translational energy is transferred to the rotational degrees of freedom of each molecule. There is a greater propensity for the transfer of translation to OH rotation than H 2 rotation. In reactive collisions, increases in reagent translational temperature predominantly appear as vibrational energy in the water molecule. Energy transfer in non-reactive and reactive collisions does not depend strongly on the initial angular momentum in either molecule. In non-reactive collisions, vibrational energy is transferred to translation, to the rotational degree of freedom of the same molecule, and to the rotational and vibrational degrees of freedom of the other molecule. In reactive collisions, the major effect of increasing the vibrational energy in reagent molecules is that, on the average, the vibrational energy of the reagents appears as product vibrational energy. 18 refs., 16 figs., 6 tabs

New determination of the 2H(d,p)3H and 2H(d,n)3He reaction rates at astrophysical energies

International Nuclear Information System (INIS)

Tumino, A.; Spartà, R.; Spitaleri, C.; Pizzone, R. G.; La Cognata, M.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Mukhamedzhanov, A. M.; Typel, S.; Tognelli, E.; Degl'Innocenti, S.; Prada Moroni, P. G.; Burjan, V.; Kroha, V.; Hons, Z.; Mrazek, J.; Piskor, S.; Lamia, L.

2014-01-01

The cross sections of the 2 H(d,p) 3 H and 2 H(d,n) 3 He reactions have been measured via the Trojan Horse method applied to the quasi-free 2 H( 3 He,p 3 H) 1 H and 2 H( 3 He,n 3 He) 1 H processes at 18 MeV off the proton in 3 He. For the first time, the bare nucleus S(E) factors have been determined from 1.5 MeV, across the relevant region for standard Big Bang nucleosynthesis, down to the thermal energies of deuterium burning in the pre-main-sequence (PMS) phase of stellar evolution, as well as of future fusion reactors. Both the energy dependence and the absolute value of the S(E) factors deviate by more than 15% from the available direct data and existing fitting curves, with substantial variations in the electron screening by more than 50%. As a consequence, the reaction rates for astrophysics experience relevant changes, with a maximum increase of up to 20% at the temperatures of the PMS phase. From a recent primordial abundance sensitivity study, it turns out that the 2 H(d,n) 3 He reaction is quite influential on 7 Li, and the present change in the reaction rate leads to a decrease in its abundance by up to 10%. The present reaction rates have also been included in an updated version of the FRANEC evolutionary code to analyze their influence on the central deuterium abundance in PMS stars with different masses. The largest variation of about 10%-15% pertains to young stars (≤1 Myr) with masses ≥1 M ☉ .

The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

Science.gov (United States)

Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

2004-01-01

The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

Free radical transfer in polymers

International Nuclear Information System (INIS)

Sonntag, C. von; Bothe, E.; Ulanski, P.

1998-01-01

For the present study of free-radical transfer in polymers pulse radiolysis and product studies have been carried out in aqueous solutions using thus far only the water-soluble polymers polyacrylic acid, polymethacrylic acid and polyvinyl alcohol. When OH radicals, generated in the radiolysis of N 2 O-saturated aqueous solutions, react with polymers the lifetime of the polymer radical thus created very much depends on the number of radicals per polymer chain. When there are a large number of radicals per chain their bimolecular decay may be faster than the corresponding (diffusion controlled) decay of monomeric radicals, but when the macromolecule contains only few or even just one radical their lifetime is considerably prolonged. Highly charged polymers such as polyacrylic acid at high pH attain a rod-like conformation which again favors a long lifetime of the radicals. Under such conditions, radical transfer reactions can occur. For example, in polyacrylic acid OH radicals generate two kinds of radicals side by side. The radical in β-position to the carboxylate group converts into the thermodynamically more stable α-radicals by an H-transfer reaction as can be followed by spectrophotometry. Besides radical transfer reactions β-fragmentation reactions occur causing chain scission. Such reactions can be followed in a pulse radiolysis experiment by conductometry, because counter ions are released upon chain scission. Such a process is especially effective in the case of polymethacrylic acid, where it results in a chain depolymerization. An intramolecular H-abstraction is also observed in the γ-radiolysis of polyacrylic acid with the corresponding peroxyl radicals. This causes a chain reaction to occur. The resulting hydroperoxides are unstable and decarboxylate given rise to acetylacetone-like products. In polyvinyl alcohol the peroxyl radicals in α-position to the alcohol function undergo HO 2 -elimination. This prevents a scission of the polymer chain in the

Investigation of the unbound 21C nucleus via transfer reaction

Directory of Open Access Journals (Sweden)

Fukui Tokuro

2014-03-01

Full Text Available The cross section of the transfer reaction 20C(d,p21C at 30.0 MeV is investigated. The continuum-discretized coupled-channels method (CDCC is used in order to obtain the final state wave function. The smoothing procedure of the transition matrix and the channel-coupling effect on the cross section are discussed.

Vibrational state-resolved differential cross sections for the D + H sub 2 yields DH + H reaction

Energy Technology Data Exchange (ETDEWEB)

Continetti, R.E.

1989-11-01

In this thesis, crossed-molecular-beams studies of the reaction D + H{sub 2} {yields} DH + H at collision energies of 0.53 and 1.01 eV are reported. Chapter 1 provides a survey of important experimental and theoretical studies on the dynamics of the hydrogen exchange reaction. Chapter 2 discusses the development of the excimer-laser photolysis D atom beam source that was used in these studies and preliminary experiments on the D + H{sub 2} reaction. In Chapter 3, the differential cross section measurements are presented and compared to recent theoretical predictions. The measured differential cross sections for rotationally excited DH products showed significant deviations from recent quantum scattering calculations, in the first detailed comparison of experimental and theoretical differential cross sections. These results indicate that further work on the H{sub 3} potential energy surface, particularly the bending potential, is in order.

The rate of the reaction between C2H and C2H2 at interstellar temperatures

Science.gov (United States)

Herbst, E.; Woon, D. E.

1997-01-01

The reaction between the radical C2H and the stable hydrocarbon C2H2 is one of the simplest neutral-neutral hydrocarbon reactions in chemical models of dense interstellar clouds and carbon-rich circumstellar shells. Although known to be rapid at temperatures > or = 300 K, the reaction has yet to be studied at lower temperatures. We present here ab initio calculations of the potential surface for this reaction and dynamical calculations to determine its rate at low temperature. Despite a small potential barrier in the exit channel, the calculated rate is large, showing that this reaction and, most probably, more complex analogs contribute to the formation of complex organic molecules in low-temperature sources.

A Ring Polymer Molecular Dynamics Approach to Study the Transition between Statistical and Direct Mechanisms in the H2 + H3+ → H3+ + H2 Reaction.

Science.gov (United States)

Suleimanov, Yury V; Aguado, Alfredo; Gómez-Carrasco, Susana; Roncero, Octavio

2018-05-03

Because of its fundamental importance in astrochemistry, the H 2 + H 3 + → H 3 + + H 2 reaction has been studied experimentally in a wide temperature range. Theoretical studies of the title reaction significantly lag primarily because of the challenges associated with the proper treatment of the zero-point energy (ZPE). As a result, all previous theoretical estimates for the ratio between a direct proton-hop and indirect exchange (via the H 5 + complex) channels deviate from the experiment, in particular, at lower temperatures where the quantum effects dominate. In this work, the ring polymer molecular dynamics (RPMD) method is applied to study this reaction, providing very good agreement with the experiment. RPMD is immune to the shortcomings associated with the ZPE leakage and is able to describe the transition from direct to indirect mechanisms below room temperature. We argue that RPMD represents a useful tool for further studies of numerous ZPE-sensitive chemical reactions that are of high interest in astrochemistry.

Direct observation of forward-scattering oscillations in the H+HD→H2+D reaction

Science.gov (United States)

Yuan, Daofu; Yu, Shengrui; Chen, Wentao; Sang, Jiwei; Luo, Chang; Wang, Tao; Xu, Xin; Casavecchia, Piergiorgio; Wang, Xingan; Sun, Zhigang; Zhang, Dong H.; Yang, Xueming

2018-06-01

Accurate measurements of product state-resolved angular distributions are central to fundamental studies of chemical reaction dynamics. Yet, fine quantum-mechanical structures in product angular distributions of a reactive scattering process, such as the fast oscillations in the forward-scattering direction, have never been observed experimentally and the nature of these oscillations has not been fully explored. Here we report the crossed-molecular-beam experimental observation of these fast forward-scattering oscillations in the product angular distribution of the benchmark chemical reaction, H + HD → H2 + D. Clear oscillatory structures are observed for the H2(v' = 0, j' = 1, 3) product states at a collision energy of 1.35 eV, in excellent agreement with the quantum-mechanical dynamics calculations. Our analysis reveals that the oscillatory forward-scattering components are mainly contributed by the total angular momentum J around 28. The partial waves and impact parameters responsible for the forward scatterings are also determined from these observed oscillations, providing crucial dynamics information on the transient reaction process.

Oxidoreduction reactions involving the electrostatic and the covalent complex of cytochrome c and plastocyanin: Importance of the protein rearrangement for the intracomplex electron-transfer reaction

International Nuclear Information System (INIS)

Peerey, L.M.; Kostic, N.M.

1989-01-01

Horse heart cytochrome c and French bean plastocyanin are cross-linked one-to-one by a carbodiimide in the same general orientation in which they associate electrostatically. The reduction potentials of the Fe and Cu atoms in the covalent diprotein complex are respectively 245 and 385 mV vs NHE; the EPR spectra of the two metals are not perturbed by cross-linking. For isomers of the covalent diprotein complex, which probably differ slightly from one another in the manner of cross-linking, are separated efficiently by cation-exchange chromatography. Stopped-flow spectrophotometric experiments with the covalent diprotein complex show that the presence of plastocyanin somewhat inhibits oxidation of ferrocytochrome c by [Fe(CN) 6 ] 3- and somewhat promotes oxidation of this protein by [Fe(C 5 H 5 ) 2 ] + . These changes in reactivity are explained in terms of electrostatic and steric effects. Pulse-radiolysis experiments with the electrostatic diprotein complex yield association constants of ≥5 x 10 6 and 1 x 10 5 M -1 at ionic strengths of 1 and 40 mM, respectively, and the rate constant of 1.05 x 10 3 s -1 , regardless of the ionic strength, for the intracomplex electron-transfer reaction. Analogous pulse-radiolysis experiments with each of the four isomers of the covalent diprotein complex, at ionic strengths of both 2 and 200 mM, show an absence of the intracomplex electron-transfer reaction. A rearrangement of the proteins for this reaction seems to be possible (or unnecessary) in the electrostatic complex but impossible in the covalent complex

Using positive-ion electrospray ionization mass spectrometry and H/D exchange study phosphoryl group transfer reactions involved in amino acid ester isopropyl phosphoramidates of Brefeldin A

International Nuclear Information System (INIS)

Fang, Mei-Juan; Zhang, He; Liao, Chao; Qiu, Ying-Kun; Fang, Hua; Zheng, Zhen-Yu; Gao, Xiang; Zhao, Yu-Fen; Wu, Zhen

2015-01-01

Highlights: • ESI-MS n , HRMS and H/D exchange were used. • The fragmentation pathways of NPAAE-BFA in ESI-MS n were described. • Fragment ions involved in phosphorus group’s rearrangement reactions were observed. • Two rearrangement mechanisms about phosphorylation–dephosphorylation were proposed. - Abstract: As mini-chemical models, amino acid ester isopropyl phosphoramidates of Brefeldin A (compounds 2a–2d) were synthesized and investigated by electrospray ionization tandem mass spectrometry in combination with H/D exchange. To further confirm the fragments’s structures, off-line Fourier transform resonance tandem mass spectrometry (FT-ICR-MS/MS) was also performed. The fragmentation rules of compounds 2a–2d have been summarized and the plausible schemes for the fragmentation pathways were proposed. In this study, one dephosphorylated ion and two phosphorylated ions were observed in ESI-MS 2 spectra of [M + Na] + ions for compounds 2a–2d. The possible mechanisms about phosphorylation and dephosphorylation were proposed and confirmed by H/D exchange. For the “dephosphorylation” rearrangement, a nitrogen atom was migrated from the phosphoryl group to the carbon atom of Brefeldin A’s backbone with losing a molecule of C 3 H 7 PO 3 (122 Da). For the “phosphorylation” rearrangement, an oxygen atom of one phosphoryl group attacked the sideward phosphorus atom to form a nine-member ring intermediate, then two steps of C-H covalent bond cleavage with consecutive migration of hydrogen atom to lose a molecule of C 16 H 20 O 2 (244 Da). The two proposed rearrangement mechanisms about phosphoryl group transfer might be valuable for the structure analysis of other analogs and provide insights into elucidating the dynamic process of the phosphorylation–dephosphorylation of proteins

Using positive-ion electrospray ionization mass spectrometry and H/D exchange study phosphoryl group transfer reactions involved in amino acid ester isopropyl phosphoramidates of Brefeldin A

Energy Technology Data Exchange (ETDEWEB)

Fang, Mei-Juan; Zhang, He; Liao, Chao; Qiu, Ying-Kun [School of Pharmaceutical Sciences and the Key Laboratory for Chemical Biology of Fujian Province, Xiamen University, Xiang-An South Road, Xiamen 361102 (China); Fang, Hua [The Third Institute of Oceanography of the State Oceanic Administration, Xiamen 361005 (China); Zheng, Zhen-Yu [College of Chemistry and Chemical Engineering, Department of Chemistry, Xiamen University, Xiamen 361005 (China); Gao, Xiang [School of Pharmaceutical Sciences and the Key Laboratory for Chemical Biology of Fujian Province, Xiamen University, Xiang-An South Road, Xiamen 361102 (China); Zhao, Yu-Fen [School of Pharmaceutical Sciences and the Key Laboratory for Chemical Biology of Fujian Province, Xiamen University, Xiang-An South Road, Xiamen 361102 (China); College of Chemistry and Chemical Engineering, Department of Chemistry, Xiamen University, Xiamen 361005 (China); Wu, Zhen, E-mail: wuzhen@xmu.edu.cn [School of Pharmaceutical Sciences and the Key Laboratory for Chemical Biology of Fujian Province, Xiamen University, Xiang-An South Road, Xiamen 361102 (China)

2015-01-01

Highlights: • ESI-MS{sup n}, HRMS and H/D exchange were used. • The fragmentation pathways of NPAAE-BFA in ESI-MS{sup n} were described. • Fragment ions involved in phosphorus group’s rearrangement reactions were observed. • Two rearrangement mechanisms about phosphorylation–dephosphorylation were proposed. - Abstract: As mini-chemical models, amino acid ester isopropyl phosphoramidates of Brefeldin A (compounds 2a–2d) were synthesized and investigated by electrospray ionization tandem mass spectrometry in combination with H/D exchange. To further confirm the fragments’s structures, off-line Fourier transform resonance tandem mass spectrometry (FT-ICR-MS/MS) was also performed. The fragmentation rules of compounds 2a–2d have been summarized and the plausible schemes for the fragmentation pathways were proposed. In this study, one dephosphorylated ion and two phosphorylated ions were observed in ESI-MS{sup 2} spectra of [M + Na]{sup +} ions for compounds 2a–2d. The possible mechanisms about phosphorylation and dephosphorylation were proposed and confirmed by H/D exchange. For the “dephosphorylation” rearrangement, a nitrogen atom was migrated from the phosphoryl group to the carbon atom of Brefeldin A’s backbone with losing a molecule of C{sub 3}H{sub 7}PO{sub 3} (122 Da). For the “phosphorylation” rearrangement, an oxygen atom of one phosphoryl group attacked the sideward phosphorus atom to form a nine-member ring intermediate, then two steps of C-H covalent bond cleavage with consecutive migration of hydrogen atom to lose a molecule of C{sub 16}H{sub 20}O{sub 2} (244 Da). The two proposed rearrangement mechanisms about phosphoryl group transfer might be valuable for the structure analysis of other analogs and provide insights into elucidating the dynamic process of the phosphorylation–dephosphorylation of proteins.

Accurate quantum calculations of the reaction rates for H/D+ CH4

NARCIS (Netherlands)

Harrevelt, R. van; Nyman, G.; Manthe, U.

2007-01-01

In previous work [T. Wu, H. J. Werner, and U. Manthe, Science 306, 2227 (2004)], accurate quantum reaction rate calculations of the rate constant for the H+CH4 -> CH3+H-2 reaction have been presented. Both the electronic structure calculations and the nuclear dynamics calculations are converged with

Pentanidium-catalyzed enantioselective phase-transfer conjugate addition reactions

KAUST Repository

Ma, Ting

2011-03-09

A new chiral entity, pentanidium, has been shown to be an excellent chiral phase-transfer catalyst. The enantioselective Michael addition reactions of tert-butyl glycinate-benzophenone Schiff base with various α,β- unsaturated acceptors provide adducts with high enantioselectivities. A successful gram-scale experiment at a low catalyst loading of 0.05 mol % indicates the potential for practical applications of this methodology. Phosphoglycine ester analogues can also be utilized as the Michael donor, affording enantioenriched α-aminophosphonic acid derivatives and phosphonic analogues of (S)-proline. © 2011 American Chemical Society.

Origin of the Proton-transfer Step in the Cofactor-free (1H)-3-Hydroxy-4-oxoquinaldine 2,4-Dioxygenase

Science.gov (United States)

Hernandez-Ortega, Aitor; Quesne, Matthew G.; Bui, Soi; Heuts, Dominic P. H. M.; Steiner, Roberto A.; Heyes, Derren J.; de Visser, Sam P.; Scrutton, Nigel S.

2014-01-01

Dioxygenases catalyze a diverse range of chemical reactions that involve the incorporation of oxygen into a substrate and typically use a transition metal or organic cofactor for reaction. Bacterial (1H)-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (HOD) belongs to a class of oxygenases able to catalyze this energetically unfavorable reaction without any cofactor. In the quinaldine metabolic pathway, HOD breaks down its natural N-heteroaromatic substrate using a mechanism that is still incompletely understood. Experimental and computational approaches were combined to study the initial step of the catalytic cycle. We have investigated the role of the active site His-251/Asp-126 dyad, proposed to be involved in substrate hydroxyl group deprotonation, a critical requirement for subsequent oxygen reaction. The pH profiles obtained under steady-state conditions for the H251A and D126A variants show a strong pH effect on their kcat and kcat/Km constants, with a decrease in kcat/Km of 5500- and 9-fold at pH 10.5, respectively. Substrate deprotonation studies under transient-state conditions show that this step is not rate-limiting and yield a pKa value of ∼7.2 for WT HOD. A large solvent isotope effect was found, and the pKa value was shifted to ∼8.3 in D2O. Crystallographic and computational studies reveal that the mutations have a minor effect on substrate positioning. Computational work shows that both His-251 and Asp-126 are essential for the proton transfer driving force of the initial reaction. This multidisciplinary study offers unambiguous support to the view that substrate deprotonation, driven by the His/Asp dyad, is an essential requirement for its activation. PMID:24482238

Molecular dynamics simulation of the first electron transfer step in the oxygen reduction reaction

NARCIS (Netherlands)

Hartnig, C.B.; Koper, M.T.M.

2002-01-01

We present a molecular dynamics simulation of solvent reorganization in the first electron transfer step in the oxygen reduction reaction, i.e. O2+e-¿O2-, modeled as taking place in the outer Helmholtz plane. The first electron transfer step is usually considered the rate-determining step from many

Transfer and breakup reactions in 16O + CsI at 16.4 MeV/n

Directory of Open Access Journals (Sweden)

M.J. Murphy

1983-01-01

Full Text Available A streamer-chamber particle-telescope system has been used to observe ejectile charge, energy, and associated charged particle multiplicity in the reaction of 16O + CsI at 16.4 MeV/n. The measurement provides relative probabilities for transfer and projectile breakup as a function of ejectile charge, and spectra for the heavy ejectiles from transfer and breakup events. The results show that the interaction energy of 16.4 MeV/n is near the threshold for breakup reactions in heavy-ion collisions.

Study of nuclear isovector spin responses from polarization transfer in (p,n) reactions at intermediate energies

International Nuclear Information System (INIS)

Wakasa, Tomotsugu

1997-01-01

We have measured a complete set of polarization transfer observables has been measured for quasi-free (p vector, n vector) reactions on 2 H, 6 Li, 12 C, 40 Ca, and 208 Pb at a bombarding energy of 346MeV and a laboratory scattering angle of 22deg (q=1.7 fm -1 ). The polarization transfer observables for all five targets are remarkably similar. These polarization observables yield separated spin-longitudinal (σ·q) and spin-transverse (σxq) nuclear responses. These results are compared to the spin-transverse responses measured in deep-inelastic electron scattering as well as to nuclear responses based on the random phase approximation. Such a comparison reveals an enhancement in the (p vector, n vector) spin-transverse channel, which masks the effect of pionic correlations in the response ratio. Second, the double differential cross sections at θ lab between 0deg and 12.3deg and the polarization transfer D NN at 0deg for the 90 Zr(p,n) reaction are measured at a bombarding energy of 295MeV. The Gamow-Teller(GT) strength B(GT) in the continuum deduced from the L=0 cross section is compared both with the perturbative calculation by Bertsch and Hamamoto and with the second-order random phase approximation calculation by Drozdz et al. The sum of B(GT) values up to 50MeV excitation becomes S β- =28.0±1.6 after subtracting the contribution of the isovector spin-monopole strength. This S β- value of 28.0±1.6 corresponds to about (93±5)% of the minimum value of the sum-rule 3(N-Z)=30. Last, first measurements of D NN (0deg) for (p vector, n vector) reactions at 295MeV yield large negative values up to 50MeV excitation for the 6 Li, 11 B, 12 C, 13 C(p vector, n vector) reactions. DWIA calculations using the Franey and Love (FL) 270MeV interaction reproduce differential cross sections and D NN (0deg) values, while the FL 325MeV interaction yield D NN (0deg) values less negative than the experimental values. (J.P.N.)

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

DEFF Research Database (Denmark)

Christensen, H.; Sehested, K.; Løgager, T.

1994-01-01

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H2O2 has been determined. The reaction with H atoms, studied in the temperature range 20-250-degrees-C gives k(20-degrees-C) = 2.4 x 10(10) M-1 s-1 and the activation energy E......-1 and E(A) = 15.6 kJ mol-1 (3.7 kcal mol-1) measured from 5-150-degrees-C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction......(A) = 14.0 kJ mol-1 (3.3 kcal mol-1). For reaction with OH radicals the corresponding values are, k(20-degrees-C) = 3.1 x 10(10) M-1 s-1 and E(A) = 14.7 kJ mol-1 (3.5 kcal mol-1) determined in the temperature range 5-175-degrees-C. For reaction with H2O2 the values are, k(20-degrees-C) = 1.2 x 10(10) M-1 s...

Long-range versus short-range correlations in the two-neutron transfer reaction 64Ni(18O,16O)66Ni

Science.gov (United States)

Paes, B.; Santagati, G.; Vsevolodovna, R. Magana; Cappuzzello, F.; Carbone, D.; Cardozo, E. N.; Cavallaro, M.; García-Tecocoatzi, H.; Gargano, A.; Ferreira, J. L.; Lenzi, S. M.; Linares, R.; Santopinto, E.; Vitturi, A.; Lubian, J.

2017-10-01

Recently, various two-neutron transfer studies using the (18O,16O) reaction were performed with a large success. This was achieved because of a combined use of the microscopic quantum description of the reaction mechanism and of the nuclear structure. In the present work we use this methodology to study the two-neutron transfer reaction of the 18O+64Ni system at 84 MeV incident energy, to the ground and first 2+ excited state of the residual 66Ni nucleus. All the experimental data were measured by the large acceptance MAGNEX spectrometer at the Instituto Nazionale di Fisica Nucleare -Laboratori Nazionali del Sud (Italy). We have performed exact finite range cross section calculations using the coupled channel Born approximation (CCBA) and coupled reaction channel (CRC) method for the sequential and direct two-neutron transfers, respectively. Moreover, this is the first time that the formalism of the microscopic interaction boson model (IBM-2) was applied to a two-neutron transfer reaction. From our results we conclude that for two-neutron transfer to the ground state of 66Ni, the direct transfer is the dominant reaction mechanism, whereas for the transfer to the first excited state of 66Ni, the sequential process dominates. A competition between long-range and short-range correlations is discussed, in particular, how the use of two different models (Shell model and IBM's) help to disentangle long- and short-range correlations.

The improvement of the heat transfer model for sodium-water reaction jet code

International Nuclear Information System (INIS)

Hashiguchi, Yoshirou; Yamamoto, Hajime; Kamoshida, Norio; Murata, Shuuichi

2001-02-01

For confirming the reasonable DBL (Design Base Leak) on steam generator (SG), it is necessary to evaluate phenomena of sodium-water reaction (SWR) in an actual steam generator realistically. The improvement of a heat transfer model on sodium-water reaction (SWR) jet code (LEAP-JET ver.1.40) and application analysis to the water injection tests for confirmation of propriety for the code were performed. On the improvement of the code, the heat transfer model between a inside fluid and a tube wall was introduced instead of the prior model which was heat capacity model including both heat capacity of the tube wall and inside fluid. And it was considered that the fluid of inside the heat exchange tube was able to treat as water or sodium and typical heat transfer equations used in SG design were also introduced in the new heat transfer model. Further additional work was carried out in order to improve the stability of the calculation for long calculation time. The test calculation using the improved code (LEAP-JET ver.1.50) were carried out with conditions of the SWAT-IR·Run-HT-2 test. It was confirmed that the SWR jet behavior on the result and the influence to the result of the heat transfer model were reasonable. And also on the improved code (LEAP-JET ver.1.50), user's manual was revised with additional I/O manual and explanation of the heat transfer model and new variable name. (author)

On the pH dependence of electrochemical proton transfer barriers

DEFF Research Database (Denmark)

Rossmeisl, Jan; Chan, Karen; Skulason, Egill

2016-01-01

The pH dependence of rate of the hydrogen evolution/oxidation reaction HER/HOR is investigated. Based on thermodynamic considerations, a possible explanation to the low exchange current for hydrogen reactions in alkaline is put forward. We propose this effect to be a consequence of the change...... environment in the double layer region. The entropic barrier can be rate determining only when the surface catalysis is fast. Therefore the effect of pH is most pronounced on good catalysts and for fast reactions. This entropic barrier is also in a good agreement with the unusually low prefactor measured...

Spin transfer in reactions between heavy ions

International Nuclear Information System (INIS)

Dong Pil Min.

1980-06-01

The model presented affords a better understanding of the manner in which the orbital angular moment can be converted into an intrinsic spin in the collision between two heavy ions. After referring to the vector fields and the collective energy of a spheroidal nucleus, the calculation of the exchange of nucleons is described and the dissipation function is constructed. The spin transfer and the reorientation of the spin during the reaction are then examined (effect of friction and vibration). The estimated calculations are compared with the results of the 63 Cu+ 197 Au and 86 Kr+ 209 Bi experiments. The sensitivity of the calculation to the parameters of the model is discussed (nuclear potential, vibrational inertial parameter) [fr

Membrane introduction proton-transfer-reaction mass spectrometry

International Nuclear Information System (INIS)

Alexander, M.; Boscaini, E.; Maerk, T.; Lindinger, W.

2002-01-01

Proton-transfer-reaction mass spectrometry (PTR-MS) is a rapidly expanding field with multiple applications in ion physics, atmospheric chemistry, food chemistry, volatile organic compounds monitoring and biology. Initial studies that combine PTR-MS and membrane introduction mass spectrometry (MIMS) were researched and outlined. First using PTR-MS, certain fundamental physical properties of a poly-dimethylsiloxane (PDMS) membrane including solubilities and diffusion coefficients were measured. Second, it was shown how the chemical selectivity of the (PDMS) can be used to extend the capabilities of the PTR-MS instrument by eliminating certain isobaric interferences and excluding water from volatile organic compounds (VOCs). Experiments with mixtures of several VOCs (toluene, benzene, acetone, propanal, methanol) are presented. (nevyjel)

The Third Dimension of a More O'Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)(2)H(•) with X = O, NH, and CH(2).

Science.gov (United States)

Cembran, Alessandro; Provorse, Makenzie R; Wang, Changwei; Wu, Wei; Gao, Jiali

2012-11-13

A critical element in theoretical characterization of the mechanism of proton-coupled electron transfer (PCET) reactions, including hydrogen atom transfer (HAT), is the formulation of the electron and proton localized diabatic states, based on which a More O'Ferrall-Jencks diagram can be represented to determine the step-wise and concerted nature of the reaction. Although the More O'Ferrall-Jencks diabatic states have often been used empirically to develop theoretical models for PCET reactions, the potential energy surfaces for these states have never been determined directly based on first principles calculations using electronic structure theory. The difficulty is due to a lack of practical method to constrain electron and proton localized diabatic states in wave function or density functional theory calculations. Employing a multistate density functional theory (MSDFT), in which the electron and proton localized diabatic configurations are constructed through block-localization of Kohn-Sham orbitals, we show that distinction between concerted proton-electron transfer (CPET) and HAT, which are not distinguishable experimentally from phenomenological kinetic data, can be made by examining the third dimension of a More O'Ferrall-Jencks diagram that includes both the ground and excited state potential surfaces. In addition, we formulate a pair of effective two-state valence bond models to represent the CPET and HAT mechanisms. We found that the lower energy of the CPET and HAT effective diabatic states at the intersection point can be used as an energetic criterion to distinguish the two mechanisms. In the isoelectronic series of hydrogen exchange reaction in (PhX)(2)H(•), where X = O, NH, and CH(2), there is a continuous transition from a CPET mechanism for the phenoxy radical-phenol pair to a HAT process for benzyl radical and toluene, while the reaction between PhNH(2) and PhNH(•) has a mechanism intermediate of CPET and HAT. The electronically nonadiabatic

Momentum transfer in relativistic heavy ion charge-exchange reactions

Science.gov (United States)

Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

1991-01-01

Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

Studies of transfer reactions of photosensitized electrons involving complexes of transition metals in view of solar energy storage

International Nuclear Information System (INIS)

Takakubo, Masaaki

1984-01-01

This research thesis addresses electron transfer reactions occurring during photosynthesis, for example, photosensitized reaction in which chlorophyll is the sensitizer. More specifically, the author studied experimentally electron photo-transfers with type D sensitizers (riboflavin, phenoxazine and porphyrin), and various complexes of transition metals. After a presentation of these experiments, the author describes the photosensitisation process (photo-physics of riboflavin, oxygen deactivation, sensitized photo-oxidation and photo-reduction). The theoretical aspect of electron transfer is then addressed: generalities, deactivation of the riboflavin triplet, initial efficiency of electron transfer. Experimental results on three basic processes (non-radiative deactivation, energy transfer, electron transfer) are interpreted in a unified way by using the non-radiative transfer theory. Some applications are described: photo-electrochemical batteries, photo-oxidation and photo-reduction of the cobalt ion

Differential cross sections for transfer into the 2S state of hydrogen: H+ + H2, H+ + D2

International Nuclear Information System (INIS)

Williams, D.G.; Lee, A.R.; Butcher, E.C.

1986-01-01

Differential cross sections for electron capture into the 2S state of hydrogen are presented for the reactions H + + H 2 and H + + D 2 . The results are for laboratory collision energies between 3.3 and 24 keV and scattering angles between 30 and 90'. The measurements expand on the results previously presented. (author)

I + (H2O)2 → HI + (H2O)OH Forward and Reverse Reactions. CCSD(T) Studies Including Spin-Orbit Coupling.

Science.gov (United States)

Wang, Hui; Li, Guoliang; Li, Qian-Shu; Xie, Yaoming; Schaefer, Henry F

2016-03-03

The potential energy profile for the atomic iodine plus water dimer reaction I + (H2O)2 → HI + (H2O)OH has been explored using the "Gold Standard" CCSD(T) method with quadruple-ζ correlation-consistent basis sets. The corresponding information for the reverse reaction HI + (H2O)OH → I + (H2O)2 is also derived. Both zero-point vibrational energies (ZPVEs) and spin-orbit (SO) coupling are considered, and these notably alter the classical energetics. On the basis of the CCSD(T)/cc-pVQZ-PP results, including ZPVE and SO coupling, the forward reaction is found to be endothermic by 47.4 kcal/mol, implying a significant exothermicity for the reverse reaction. The entrance complex I···(H2O)2 is bound by 1.8 kcal/mol, and this dissociation energy is significantly affected by SO coupling. The reaction barrier lies 45.1 kcal/mol higher than the reactants. The exit complex HI···(H2O)OH is bound by 3.0 kcal/mol relative to the asymptotic limit. At every level of theory, the reverse reaction HI + (H2O)OH → I + (H2O)2 proceeds without a barrier. Compared with the analogous water monomer reaction I + H2O → HI + OH, the additional water molecule reduces the relative energies of the entrance stationary point, transition state, and exit complex by 3-5 kcal/mol. The I + (H2O)2 reaction is related to the valence isoelectronic bromine and chlorine reactions but is distinctly different from the F + (H2O)2 system.

Study of neutron-proton pairing in N=Z unstable nuclei through transfer reactions

International Nuclear Information System (INIS)

Le Crom, B.

2016-01-01

A nucleus is described as a set of independent neutrons and protons linked by a mean-field potential. However, in order to have a better description one needs to take into account some residual interactions such as pairing. Neutron-neutron and proton-proton pairings are well-studied but neutron-proton pairing is not well-known. np pairing can be isovector pairing such as nn and pp pairing or isoscalar which is yet unknown. Over-binding of N=Z nuclei could be a manifestation of np pairing. We have studied np pairing through transfer reactions. In this case, the cross-section of np pair transfer is expected to be enhanced in the presence of important np pairing. np pairing is expected to be important in N=Z nuclei with high J orbitals. Since the development of radioactive beam facilities, such beams are only available. The experiment was performed at GANIL with an efficient set-up so as to detect products from the (p, 3 He) transfer reaction. This reaction is affected by isovector and isoscalar np pairing. We used 56 Ni and 52 Fe beams so as to see the effect of the occupancy of 0f 7/2 shell on the np pairing. First, we analysed the data from the 56 Ni(p,d) 55 Ni reaction and we compared the results with the literature to validate analysis procedure. After analysing data from the 56 Ni(p, 3 He) 54 Co reaction and extracting the population of the various states of 54 Co, we obtained information about the relative intensity between isoscalar and isovector np pairing in 56 Ni showing the predominance of isovector np pairing in this nucleus. Moreover, in the framework of developing a new charged particle detector, research on the discrimination of light nuclei using pulse shape analysis was performed and is also presented. (author)

Communication: Rate coefficients from quasiclassical trajectory calculations from the reverse reaction: The Mu + H2 reaction re-visited

Science.gov (United States)

Homayoon, Zahra; Jambrina, Pablo G.; Aoiz, F. Javier; Bowman, Joel M.

2012-07-01

In a previous paper [P. G. Jambrina et al., J. Chem. Phys. 135, 034310 (2011), 10.1063/1.3611400] various calculations of the rate coefficient for the Mu + H2 → MuH + H reaction were presented and compared to experiment. The widely used standard quasiclassical trajectory (QCT) method was shown to overestimate the rate coefficients by several orders of magnitude over the temperature range 200-1000 K. This was attributed to a major failure of that method to describe the correct threshold for the reaction owing to the large difference in zero-point energies (ZPE) of the reactant H2 and product MuH (˜0.32 eV). In this Communication we show that by performing standard QCT calculations for the reverse reaction and then applying detailed balance, the resulting rate coefficient is in very good agreement with the other computational results that respect the ZPE, (as well as with the experiment) but which are more demanding computationally.

Separation of the longitudinal and transverse cross sections in the 1H(e,e(prime) K+)Λ and 1H(e,e(prime) K+)Σ0 reactions

International Nuclear Information System (INIS)

Mohring, R.M.; Abbott, David; Ahmidouch, Abdellah; Amatuni, Thomas; Pawel Ambrozewicz; Tatiana Angelescu; Christopher Armstrong; John Arrington; Ketevi Assamagan; Steven Avery; Kevin Bailey; Kevin Beard; S Beedoe; Elizabeth Beise; Herbert Breuer; Roger Carlini; Jinseok Cha; C. Chang; Nicholas Chant; Evaristo Cisbani; Glenn Collins; William Cummings; Samuel Danagoulian; Raffaele De Leo; Fraser Duncan; James Dunne; Dipangkar Dutta; T Eden; Rolf Ent; Laurent Eyraud; Lars Ewell; John Finn; H. Terry Fortune; Valera Frolov; Salvatore Frullani; Christophe Furget; Franco Garibaldi; David Gaskell; Donald Geesaman; Paul Gueye; Kenneth Gustafsson; Jens-Ole Hansen; Mark Harvey; Wendy Hinton; Ed Hungerford; Mauro Iodice; Ceasar Jackson; Cynthia Keppel; Wooyoung Kim; Kouichi Kino; Douglas Koltenuk; Serge Kox; Laird Kramer; Antonio Leone; Allison Lung; David Mack; Richard Madey; M Maeda; Stanislaw Majewski; Pete Markowitz; T Mart; C Martoff; David Meekins; A. Mihul; Joseph Mitchell; Hamlet Mkrtchyan; Sekazi Mtingwa; Maria-Ioana Niculescu; R. Perrino; David Potterveld; John Price; Brian Raue; Jean Sebastien Real; Joerg Reinhold; Philip Roos; Teijiro Saito; Geoff Savage; Reyad Sawafta; Ralph Segel; Stepan Stepanyan; Paul Stoler; Vardan Tadevosyan; Liguang Tang; Liliana Teodorescu; Tatsuo Terasawa; Hiroaki Tsubota; Guido Urciuoli; Jochen Volmer; William Vulcan; T. Welch; Robert Williams; Stephen Wood; Chen Yan; Benjamin Zeidman

2003-01-01

We report measurements of cross sections for the reaction 1 H(e,e(prime) K + )Y, for both the Λ and Σ 0 hyperon states, at an invariant mass of W = 1.84 GeV and four-momentum transfers 0.5 2 2 . Data were taken for three values of virtual photon polarization ε, allowing the decomposition of the cross sections into longitudinal and transverse components. The Λ data are a revised analysis of prior work, whereas the Σ 0 results have not been previously reported

Experimental and theoretical studies of the C{sub 6}H{sub 5} + C{sub 6}H{sub 6} reaction

Energy Technology Data Exchange (ETDEWEB)

Park, J.; Burova, S.; Rodgers, A.S.; Lin, M.C.

1999-11-11

The absolute rate constants for the C{sub 6}H{sub 5} + C{sub 6}H{sub 6} and C{sub 6}D{sub 6} reactions have been measured by cavity ringdown spectrometry at temperatures between 298 and 495 K at a constant 40 Torr Ar pressure. The new results, which reveal no detectable kinetic isotopic effect, can be represented by the Arrhenius equation, {kappa}{sub 1} = 10{sup (11.91{+-}0.13)} exp[{minus}(2,102 {+-} 106)/T] cm{sup 3}/(mol s). Low-temperature data for the addition/stabilization process, C{sub 6}H{sub 5} + C{sub 6}H{sub 6} {r{underscore}arrow} C{sub 12}H{sub 11}, can be correlated with those obtained in a low-pressure, high-temperature Knudsen cell study for the addition/displacement reaction, C{sub 6}H{sub 5} + C{sub 6}H{sub 6} {r{underscore}arrow} C{sub 12}H{sub 10} + H, by the RRKM theory using the molecular and transition-state parameters computed at the B3LYP/6-311G(d,p) level of theory. Combination of these two sets of data gives {kappa}{sub 1} = 10{sup (11.98{+-}0.03)} exp[{minus}(2168 {+-} 34)/T] cm{sup 3}/(mol s) covering the temperature range 298--1,330 K. The RRKM theory also correlates satisfactorily the forward reaction data with the high-temperature shock-tube result for the reverse H-for-C{sub 6}H{sub 5} substitution process with 2.7 and 4.7 kcal/mol barriers for the entrance (C{sub 6}H{sub 5} + C{sub 6}H{sub 6}) and reverse (H + C{sub 12}H{sub 10}) reactions, respectively. For modeling applications, the authors have calculated the forward reaction rate constants for the formation of the two competing products, H + C{sub 12}H{sub 10} and C{sub 12}H{sub 11}, at several pressures covering 300 K {lt} T {lt} 2,500 K.

Microporous hollow fibre membrane modules as gas-liquid contactors. Part 2. Mass transfer with chemical reaction

NARCIS (Netherlands)

Kreulen, H.; Versteeg, G.F.; Swaaij, W.P.M. van

1993-01-01

Absorption determined by mass transfer in the liquid is described well with the Graetz-Lévèque equation adapted from heat transfer. The influence of a chemical reaction on the mass transfer was simulated with a numerical model and tested on the absorption of CO2 in a hydroxide solution. Absorption

Electrochemical behaviours of Eu(III/E(II and Ce(IV/Ce(III in H3PO4-H2O media : solvation and complexation reactions

Directory of Open Access Journals (Sweden)

Belqat B.

2018-01-01

Full Text Available Many kinds of rare earth elements (REE such as europium and cerium have been make them essential elements in many high-tech components. The electrochemical studies can be presented as an interesting indication for europium and cerium extraction from phosphoric solutions, including solvation and complexation reactions. The normal redox potentials of Eu3+/Eu2+ and Ce4+/Ce3+ systems have been determined in H3PO4-H2O media with various phosphoric acid concentration. The solvation of these elements in phosphoric media is characterized by their transfer activity coefficients "f" calculated from the corresponding normal redox potentials. The corresponding solvation increases with increasing the H3PO4 concentration. For each REE, the electrochemical properties depend on its number of charges and on its basic properties. Results suggest that solvation and complexation of REE phosphates are important in controlling REE concentration.

Chemical reaction surface vibrational frequencies evaluated in curvilinear internal coordinates: Application to H + CH(4) H(2) + CH(3).

Science.gov (United States)

Banks, Simon T; Clary, David C

2009-01-14

We consider the general problem of vibrational analysis at nonglobally optimized points on a reduced dimensional reaction surface. We discuss the importance of the use of curvilinear internal coordinates to describe molecular motion and derive a curvilinear projection operator to remove the contribution of nonzero gradients from the Hessian matrix. Our projection scheme is tested in the context of a two-dimensional quantum scattering calculation for the reaction H + CH(4) --> H(2) + CH(3) and its reverse H(2) + CH(3) --> H + CH(4). Using zero-point energies calculated via rectilinear and curvilinear projections we construct two two-dimensional, adiabatically corrected, ab initio reaction surfaces for this system. It is shown that the use of curvilinear coordinates removes unphysical imaginary frequencies observed with rectilinear projection and leads to significantly improved thermal rate constants for both the forward and reverse reactions.

Tunneling in the CH{sub 3} + H{sub 2} {yields} CH{sub 4} + H reaction and its isotopic analog: an anomalous isotope effect

Energy Technology Data Exchange (ETDEWEB)

Kurosaki, Yuzuru; Takayanagi, Toshiyuki [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1998-10-01

Vibrationally adiabatic ground-state potential curves for the CH{sub 3} + H{sub 2} {yields} CH{sub 4} + H (I) and CD{sub 3} + H{sub 2} {yields} CD{sub 4}H + H (II) reactions were obtained by adding zero-point energies of harmonic vibrations orthogonal to intrinsic reaction coordinate (IRC) to bare potential curves along IRC. It was clarified that both the barrier height and barrier width of reaction II are smaller than those of reaction I. This computational result qualitatively explains the experimental observation of Momose et al. (J. Chem. Phys. 108 (1998) 7334) that reaction II occurs but reaction I does not occur in solid parahydrogen at 5 K. (author)

Hydrogen Transfer during Liquefaction of Elbistan Lignite to Biomass; Total Reaction Transformation Approach

Science.gov (United States)

Koyunoglu, Cemil; Karaca, Hüseyin

2017-12-01

Given the high cost of the tetraline solvent commonly used in liquefaction, the use of manure with EL is an important factor when considering the high cost of using tetraline as a hydrogen transfer source. In addition, due to the another cost factor which is the catalyst prices, red mud (commonly used, produced as a byproduct in the production of aluminium) is reduced cost in the work of liquefaction of coal, biomass, even coal combined biomass, corresponding that making the EL liquefaction an agenda for our country is another important factor. Conditions for liquefaction experiments conducted for hydrogen transfer from manure to coal; Catalyst concentration of 9%, liquid/solid ratio of 3/1, reaction time of 60 min, fertilizer/lignite ratio of 1/3, and the reaction temperature of 400 °C, the stirred speed of 400 rpm and the initial nitrogen pressure of 20 bar was fixed. In order to demonstrate the hydrogen, transfer from manure to coal, coal is used solely, by using tetraline (also known as a hydrogen carrier) and distilled water which is not hydrogen donor as a solvent in the co-liquefaction of experiments, and also the liquefaction conditions are carried out under an inert (N2) gas atmosphere. According to the results of the obtained liquefaction test; using tetraline solvent the total liquid product conversion percentage of the oil + gas conversion was 38.3 %, however, the results of oil+gas conversion obtained using distilled water and EL combined with manure the total liquid product conversion percentage was 7.4 %. According to the results of calorific value and elemental analysis, only the ratio of (H/C)atomic of coal obtained by using tetraline increased with the liquefaction of manure and distilled water. The reason of the increase in the amount of hydrogen due to hydrogen transfer from the manure on the solid surface of the coal, and also on the surface of the inner pore of the coal during the liquefaction, brings about the evaluation of the coal as a

Reaction of H2 with O2 in Excited Electronic States: Reaction Pathways and Rate Constants.

Science.gov (United States)

Pelevkin, Alexey V; Loukhovitski, Boris I; Sharipov, Alexander S

2017-12-21

Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H 2 with O 2 in a 1 Δ g , b 1 Σ g + , c 1 Σ u - , and A' 3 Δ u electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory. It has been shown that the interaction of O 2 (a 1 Δ g ) and O 2 (A' 3 Δ u ) with H 2 occurs through the H-abstraction process with relatively low activation barriers that resulted in the formation of the HO 2 molecule in A″ and A' electronic states, respectively. Meanwhile, molecular oxygen in singlet sigma states (b 1 Σ g + and c 1 Σ u - ) was proved to be nonreactive with respect to the molecular hydrogen. Appropriate rate constants for revealed reaction and quenching channels have been estimated using variational transition-state theory including corrections for the tunneling effect, possible nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. It was demonstrated that the calculated reaction rate constant for the H 2 + O 2 (a 1 Δ g ) process is in reasonable agreement with known experimental data. The Arrhenius approximations for these processes have been proposed for the temperature range T = 300-3000 K.

Proton transfer reaction time-of-flight mass spectrometry advancement in detection of hazardous substances

International Nuclear Information System (INIS)

Agarwal, B.

2012-01-01

Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a mass spectrometric technique based on chemical ionization, which provides very rapid measurements (within seconds) of volatile organic compounds in air, usually without special sample preparation, and with a very low detection limit. The detection and study of product ion patterns of threat agents such as explosives and drugs and some major environmental pollutants (isocyanates and polychlorinated biphenyls (PCBs)) is explored in detail here using PTR-MS, specifically Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). The proton transfer reaction (PTR) principle works on the detection of the compound in the vapor phase. For some compounds, which have extremely low vapor pressures, both sample and inlet line heating were needed. Generally, the protonated parent molecule (MH+) is found to be the dominant product ion, which therefore provides us with a higher level of confidence in the assignment of a trace compound. However, for several compounds, dissociative proton transfer can occur at various degrees resulting in other product ions. Analysis of other compounds, such as the presence of taggants and impurities were carried out, and in certain compounds unusual E/N anomalies were discovered (E/N is an instrumental set of parameters, where E is the electric field strength and N is the number density). Head space measurements above four different drinks (plain water, tea, red wine and white wine) spiked with four different 'date rape' drugs were also conducted. (author)

Organodioxygen complexes of some heavy metal ions and their oxygen transfer reactions

International Nuclear Information System (INIS)

Tarafder, M.T.H.; Mei Ling; Gino Mariotto

2003-09-01

Several novel organodioxygen complexes of lanthanide ions, viz., lanthanum(m) and cerium(IV) have been synthesized containing a number of organic co- ligands. The complexes characterized were, [La(0 2 )(det)(N0 3 ) 2 ] (1), [La(O 2 )(tet)(NO 3 ) 2 ] (2), [La(O 2 )(C 5 H 5 N)2NO 3 ] (3), [La(O 2 )(C 6 H 18 N 3 PO) 2 (NO 3 ) 2 ] (4), [La(0 2 )(OPPh 3 ) 2 (N0 3 ) 2 ] (5), [La(O 2 ) 2 (NH 2 CH 2 CH 2 NH 2 ) 2 NO 3 ] (6), [La(O 2 )(PPh 3 ) 2 (NO 3 ) 2 ] (7) and [Ce(O 2 )(C 6 H 18 N 3 PO) 2 (NO 3 ) 3 ] (8). IR and Raman spectra revealed that (3) was a peroxo complex while the others were, in particular, superoxo type. The IR spectrum of (3) gives V 1 (O-O) at 851 cm -1 while the Raman spectra of (4), (5), (7) and (8) give V 1 (O 2 ) bands at 1046 cm -1 , 1032 cm 1 , 1100 cm -1 and 1046 cm -1 , respectively. The oxygen transfer reactions of two selected complexes were carried out under stoichiometric conditions. The complex containing a bidentate ligand, (6), was found to oxidize triphenylphosphine and trans-stilbene to their oxides while the complex containing tridentate ligand (1) was stable and inert towards oxidation. (author)

Engineering of RuMb: Toward a Green Catalyst for Carbene Insertion Reactions.

Science.gov (United States)

Wolf, Matthew W; Vargas, David A; Lehnert, Nicolai

2017-05-15

The small, stable heme protein myoglobin (Mb) was modified through cofactor substitution and mutagenesis to develop a new catalyst for carbene transfer reactions. The native heme was removed from wild-type Mb and several Mb His64 mutants (H64D, H64A, H64V), and the resulting apoproteins were reconstituted with ruthenium mesoporphyrin IX (RuMpIX). The reconstituted proteins (RuMb) were characterized by UV-vis and circular dichroism spectroscopy and were used as catalysts for the N-H insertion of aniline derivatives and the cyclopropanation of styrene derivatives. The best catalysts for each reaction were able to achieve turnover numbers (TON) up to 520 for the N-H insertion of aniline, and 350 TON for the cyclopropanation of vinyl anisole. Our results show that RuMb is an effective catalyst for N-H insertion, with the potential to further increase the activity and stereoselectivity of the catalyst in future studies. Compared to native Mb ("FeMb"), RuMb is a more active catalyst for carbene transfer reactions, which leads to both heme and protein modification and degradation and, hence, to an overall much-reduced lifetime of the catalyst. This leads to lower TONs for RuMb compared to the iron-containing analogues. Strategies to overcome this limitation are discussed. Finally, comparison is also made to FeH64DMb and FeH64AMb, which have not been previously investigated for carbene transfer reactions.

Studies on the selectivity of the reaction of (CO){sub 5}W=C(aryl)H with enynes: transfer of the carbene ligand to the C=C Bond versus insertion of the C triple bond C into the W=C Bond

Energy Technology Data Exchange (ETDEWEB)

Fischer, H.; Volkland, H.P.; Stumpf, R.

1996-10-01

The strongly electrophilic monophenylcarbene complex [(CO){sub 5}W=C(Ph)H] (2a) reacts with the enynes H-C triple bond C-R(R=-C(Me)=CH{sub 2})(3), -C{sub 6}H{sub 4}-CH=CH{sub 2}-p (5) and subsequently with PMe{sub 3} to form the C{sub a}lpha-PMe{sub 3} adducts of the vinylidene complexes [(CO){sub 5}W-{l_brace}C(PMe{sub 3})=CH-C{sub 3}H{sub 3}(Me)Ph{r_brace}] (4) and [(CO){sub 5}W {l_brace}C(PMe{sub 3})=CH-C{sub 6}H{sub 4}-C{sub 3}H{sub 4}Ph{r_brace}] (6). The reaction very likely proceeds by transfer of the carbene ligand to the C=C bond of the enyne to form a cyclopropyl-substituted alkyne complex which is in equilibrium with its vinylidene isomer.

Electronic shift register memory based on molecular electron-transfer reactions

Science.gov (United States)

Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

1989-01-01

The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

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

KAUST Repository

He, Lipeng

2012-03-01

A dearomatized complex [RuH(PN 3P)(CO)] (PN 3PN, N′-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (3) was prepared by reaction of the aromatic complex [RuH(Cl)(PN 3P)(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 distorted square-pyramidal geometry around the ruthenium center was observed, with the CO ligand trans to the pyridinic nitrogen atom and the hydride located in the apical position. The dearomatized complex 3 displays efficient catalytic activity for hydrogen transfer of ketones in isopropanol. © 2011 Elsevier B.V. All rights reserved.

Gamma spectroscopy of multiple nucleon transfer reactions in Sn

International Nuclear Information System (INIS)

Grabowski, Z.W.; Mayer, R.H.; Fornal, B.; Nisius, D.T.; Bearden, I.G.; Daly, P.J.; Broda, R.; Carpenter, M.P.; Janssens, R.V.F.; Khoo, T.L.; Lauritsen, T.

1992-01-01

The decay of (πh 11/2 ) n yrast isomers was studied in a series of proton-rich N = 82 isotones culminating in determination of B(E2) values in 153 Lu and 154 Hf. In the N = 82 isotones however, it seems unlikely that the measurements could be extended beyond 154 Hf (n = 8). The opportunity to investigate the (h 11/2 ) n ) isomers across the whole h 11/2 subshell exists, at least in principle, in Sn isotopes where the counterpart νh 11/2 subshell is being filled with neutrons starting at 116 Sn. Before our measurements were initiated, the (νh 11/2 ) n 10 + isomers were known to exist in 116, 118, 120 Sn, where the νh 11/2 subshell begins to fill, and in 128,130 Sn at the other end. Important information, however, was missing about the 10 + isomers in 122,124,126 Sn where the long lifetimes are expected. The υ = 3 (h 11/2 ) isomers in odd tin isomers for A ≥ 119 were also not identified. A serious experimental difficulty in populating high spin states in heavier Sn isotopes is that they are not accessible by fusion-evaporation reactions. We decided to search for these missing tin isotopes among the products of heavy ion reactions on 122,124 Sn targets. Using this approach we were able to identify the isomeric decays and measure the lifetimes of the (νh 11/2 n ) υ = 2 isomeric states in 122,124 Sn. In odd tin isotopes we identified new I = 19/2 + yrast isomers in 119,121,123 Sn and measured their lifetimes. In addition (νh 11/2 ) n υ = 3, I = 27/2 - isomers in 119,121 Sn were observed for the first time

Study of actinides fission induced by multi-nucleon transfer reactions in inverse kinematics

International Nuclear Information System (INIS)

Derkx, X.

2010-10-01

The study of actinide fission encounters two major issues. On one hand, measurements of the fission fragment distributions and the fission probabilities allow a better understanding of the fission process itself and the discrimination among the models of nuclear structure and dynamics. On the other hand, new measurements are required to improve nuclear data bases, which are a key component for the design of new generation reactors and radio-toxic waste incinerators. This thesis is in line with different French and American experimental projects using the surrogate method, i.e. transfer reactions leading to the same compound nuclei as in neutron irradiation, allowing the study of fission of actinides which are inaccessible by conventional techniques, whereas they are important for applications. The experiment is based on multi-nucleon transfer reactions between a 238 U beam and a 12 C target, using the inverse kinematics technique to measure, for each transfer channel, the complete isotopic distributions of the fission fragments with the VAMOS spectrometer. The work presented in this dissertation is focused on the identification of the transfer channels and their properties, as their angular distributions and the distributions of the associated excitation energy, using the SPIDER telescope to identify the target recoil nuclei. This work of an exploratory nature aims to generalize the surrogate method to heavy transfers and to measure, for the first time, the fission probabilities in inverse kinematics. The obtained results are compared with available direct kinematics and neutron irradiation measurements. (author)

Application of laser diagnostics to sodium-water chemical reaction field

International Nuclear Information System (INIS)

Deguchi, Yoshihiro; Tamura, Kenta; Muranaka, Ryota; Kusano, Koji; Kikuchi, Shin; Kurihara, Akikazu

2013-01-01

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes in a steam generator. Therefore the study on sodium-water chemical reactions is of paramount importance for safety reasons. This study aims to clarify the sodium-water reaction mechanisms using laser diagnostics. The sodium-water counter-flow reactions were measured using laser diagnostics such as laser induced fluorescence, CARS, Raman scattering and photo-fragmentation. The measurement results show that the sodium-water reaction proceeds mainly by the reaction Na + H 2 O → NaOH + H and the main product is NaOH in this reaction. Its forward and backward reaction rates tend to balance with each other and the whole reaction rate reduces as temperature increases. (author)

Theoretical investigation of molecular hydrogen reactions with active centres in B6H5- and AlB6H5- clusters

International Nuclear Information System (INIS)

Mebel', A.M.; Charkin, O.P.

1991-01-01

Nonempirical calculations of sections of potential surface (PS) along the shortest way of reaction of hydrogen interaction with different active centres in AlB 5 H 5 - cluster were conducted. Mechanisms of reactions of valent-saturated hydrides (BH, AlH) and clusters (B 6 H 5 - , AlB 5 H 5 - ) with molecular hydrogen are correlated. Qualitative model enabling to form an opinion about the presence or the absence of barrier on PS of the shortest way of reactions of breaking σ-bond of H-H type on the active centre of cluster, is suggested. The model is based on analysis of the character of canonical MO reagents and products

Post-prior equivalence for transfer reactions with complex potentials

Science.gov (United States)

Lei, Jin; Moro, Antonio M.

2018-01-01

In this paper, we address the problem of the post-prior equivalence in the calculation of inclusive breakup and transfer cross sections. For that, we employ the model proposed by Ichimura et al. [Phys. Rev. C 32, 431 (1985), 10.1103/PhysRevC.32.431], conveniently generalized to include the part of the cross section corresponding the transfer to bound states. We pay particular attention to the case in which the unobserved particle is left in a bound state of the residual nucleus, in which case the theory prescribes the use of a complex potential, responsible for the spreading width of the populated single-particle states. We see that the introduction of this complex potential gives rise to an additional term in the prior cross-section formula, not present in the usual case of real binding potentials. The equivalence is numerically tested for the 58Ni(d ,p X ) reaction.

TD-DFT investigation of the potential energy surface for Excited-State Intramolecular Proton Transfer (ESIPT) reaction of 10-hydroxybenzo[h]quinoline: Topological (AIM) and population (NBO) analysis of the intramolecular hydrogen bonding interaction

International Nuclear Information System (INIS)

Paul, Bijan Kumar; Guchhait, Nikhil

2011-01-01

Here, we report a Density Functional Theoretical (DFT) study on the photophysics of a potent Excited-State Intramolecular Proton Transfer (ESIPT) molecular system, viz., 10-hydroxybenzo[h]quinoline (HBQ). Particular emphasis has been rendered on the assessment of the proton transfer reaction in HBQ in the ground and excited-states through elucidation and a careful perusal of the potential energy surfaces (PES). The non-viability of Ground-State Intramolecular Proton Transfer (GSIPT) process is dictated by a high-energy barrier coupled with no energy minimum for the proton transferred (K-form) form at the ground-state (S 0 ) PES. Remarkable reduction of the barrier along with thermodynamic stability inversion between the enol (E-form) and the keto forms (K-form) of HBQ upon photoexcitation from S 0 to the S 1 -state advocate for the operation of ESIPT process. These findings have been cross-validated on the lexicon of analysis of optimized geometry parameters, Mulliken's charge distribution on the heavy atoms, and molecular orbitals (MO) of the E- and the K-forms of HBQ. Our computational results also corroborate to experimental observations. From the modulations in optimized geometry parameters in course of the PT process a critical assessment has been endeavoured to delve into the movement of the proton during the process. Additional stress has been placed on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in HBQ. The IMHB interaction has been explored by calculation of electron density ρ(r) and the Laplacian ∇ 2 ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and by calculation of interaction between σ* of OH with the lone pair of the nitrogen atom using Natural Bond Orbital (NBO) analysis. - Highlights: → Theoretical modelling of the photophysics of an ESIPT probe 10-hydroxybenzo[h]quinoline (HBQ). → Calculation of intramolecular hydrogen bond (IMHB) energy. → Role of hyperconjugative charge transfer

Mass transfer with complex reversible chemical reactions—I. Single reversible chemical reaction

NARCIS (Netherlands)

Versteeg, G.F.; Kuipers, J.A.M.; Beckum, F.P.H. van; Swaaij, W.P.M. van

1989-01-01

An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass

Short range photoinduced electron transfer in proteins: QM-MM simulations of tryptophan and flavin fluorescence quenching in proteins

International Nuclear Information System (INIS)

Callis, Patrik R.; Liu Tiqing

2006-01-01

Hybrid quantum mechanical-molecular mechanics (dynamics) were performed on flavin reductase (Fre) and flavodoxin reductase (Fdr), both from Escherichia coli. Each was complexed with riboflavin (Rbf) or flavin mononucleotide (FMN). During 50 ps trajectories, the relative energies of the fluorescing state (S 1 ) of the isoalloxazine ring and the lowest charge transfer state (CT) were assessed to aid prediction of fluorescence lifetimes that are shortened due to quenching by electron transfer from tyrosine. The simulations for the four cases display a wide range in CT-S 1 energy gap caused by the presence of phosphate, other charged and polar residues, water, and by intermolecular separation between donor and acceptor. This suggests that the Gibbs energy change (ΔG 0 ) and reorganization energy (λ) for the electron transfer may differ in different flavoproteins

Fragmentation and direct transfer reactions for 40Ar incident beam on 27Al target at 1760 MeV

International Nuclear Information System (INIS)

Cisse, Ousmane

1985-01-01

Peripheral collision studies performed with 40 Ar projectiles at 44 MeV/A and 27 Al target show that both fragmentation and transfer reactions can be discerned in this type of interaction. The experimental observation of fragments with masses charges and velocities close to those of the incident beam are the signature of transfer reactions and a detailed analysis of the energy spectra of such fragments has been carried out and interpreted in terms of a direct diffraction transfer model. On the other hand, for large mass transfer reactions, abrasion is the suitable mechanism. Inclusive fragment measurement together with the appropriate residual nuclei-fragment coincidence results then provides experimental data in good agreement with the theoretical predictions obtained from a participant spectator model. These investigations also indicate that the separation energies of the participant from the spectator nucleus, at least within the framework of the above model, can be interpreted in terms of a friction force which becomes more efficient as the projectile energy decreases. (author) [fr

Radiolytic and electron-transfer reactions in supercritical CO2

International Nuclear Information System (INIS)

Bartels, D. M.; Dimitrijevic, N. M.; Jonah, C. D.; Takahashi, K.

2000-01-01

Using supercritical fluids as solvents is useful for both practical and theoretical reasons. It has been proposed to use supercritical CO 2 as a solvent for synthesis because it eliminates the air pollution arising from other solvents. The properties of supercritical fluids can be easily varied with only modest changes in temperature and density, so they provide a way of testing theories of chemical reactions. It has also been proposed to use supercritical fluids for the treatment of hazardous mixed waste. For these reasons the authors have studied the production of radiolytic species in supercritical CO 2 and have measured their reactivity as a function of density. They have shown that the C 2 O 4 + is formed. They also have shown that the electron transfer reactions of dimethylaniline to C 2 O 4 + and CO 2 (e - ) to benzoquinone are diffusion controlled over a considerable density range

Molecular-alignment dependence in the transfer excitation of H2

International Nuclear Information System (INIS)

Wang, Y.D.; McGuire, J.H.; Weaver, O.L.; Corchs, S.E.; Rivarola, R.D.

1993-01-01

Molecular-alignment effects in the transfer excitation of H 2 by high-velocity heavy ions are studied using a two-step mechanism with amplitudes evaluated from first-order perturbation theory. Two-electron transfer excitation is treated as a result of two independent collision processes (excitation and electron transfer). Cross sections for each one-electron subprocess as well as the combined two-electron process are calculated as functions of the molecular-alignment angle. Within the independent-electron approximation, the dynamic roles of electron excitation and transfer in conjunction with molecular alignment are explored. While both excitation and transfer cross sections may strongly depend on molecular alignment, it is electron transfer that is largely responsible for the molecular-alignment dependence in the transfer excitation process. Interpretation of some experimental observations based on this model will also be discussed

Structural and Functional Characterization of a Short-Chain Flavodoxin Associated with a Noncanonical 1,2-Propanediol Utilization Bacterial Microcompartment

Energy Technology Data Exchange (ETDEWEB)

Plegaria, Jefferson S. [MSU-DOE; Sutter, Markus [MSU-DOE; Molecular; Ferlez, Bryan [MSU-DOE; Aussignargues, Clément [MSU-DOE; Niklas, Jens [Solar; Poluektov, Oleg G. [Solar; Fromwiller, Ciara [MSU-DOE; TerAvest, Michaela [Department; amp, Molecular Biology, Michigan State University, East; Utschig, Lisa M. [Solar; Tiede, David M. [Solar; Kerfeld, Cheryl A. [MSU-DOE; Molecular; Department; amp, Molecular Biology, Michigan State University, East; Berkeley Synthetic Biology Institute, Berkeley, California 94720, United States

2017-09-21

Bacterial microcompartments (BMCs) are proteinaceous organelles that encapsulate enzymes involved in CO2 fixation (carboxysomes). or carbon catabolism (metabolosomes). Metabolosomes share a common core of enzymes and a distinct signature enzyme for substrate degradation that defines the function of the BMC (e,g., propanediol or ethanolamine utilization BMCs, or glycyl-radical enzyme microcompartments). Loci encoding metabolosomes also typically contain genes for proteins that support organelle function, such as regulation, transport of substrate, and cofactor (e.g., vitamin B-12) synthesis and recycling. Flavoproteins are frequently among these ancillary gene products, suggesting that these redox active proteins play an undetermined function in many metabolosomes. Here, we report the first characterization of a BMC-associated flavodoxin (Fld1C), a small flavoprotein, derived from the noncanonical 1,2-propanediol utilization BMC locus (PDU1C) of Lactobacillus reuteri. The 2.0 angstrom X-ray structure of Fld1C displays the alpha/beta flavodoxin fold, which noncovalently binds a single flavin mononucleotide molecule. Fld1C is a short-chain flavodoxin with redox potentials of -240 +/- 3 mV oxidized/semiquinone and -344 +/- 1 mV semiquinone/hydroquinone versus the standard hydrogen electrode at pH 7.5. It can participate in an electron transfer reaction with a photoreductant to form a stable semiquinone species. Collectively, our structural and functional results suggest that PDU1C BMCs encapsulate Fld1C to store and transfer electrons for the reactivation and/or recycling of the B-12 cofactor utilized by the signature enzyme.

Study of multi-nucleon transfer reactions in {sup 58,} {sup 64}Ni + {sup 207}Pb collisions at the velocity filter SHIP

Energy Technology Data Exchange (ETDEWEB)

Comas, V.F.; Heinz, S.; Ackermann, D.; Heredia, J.A.; Hessberger, F.P.; Khuyagbaatar, J.; Kindler, B.; Lommel, B.; Mann, R. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Hofmann, S. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Goethe-Universitaet Frankfurt, Institut fuer Physik, Frankfurt (Germany)

2013-09-15

We investigated multi-nucleon transfer reactions in collisions of {sup 58}Ni + {sup 207}Pb and {sup 64}Ni + {sup 207}Pb at Coulomb barrier energies. The new aspect is that we used a velocity filter (SHIP at GSI) for the separation of the heavy target-like transfer products from background events. The isotopic identification was performed via the {alpha} decay properties of the reaction products. The goal of the experiment was to study the characteristics of multi-nucleon transfer reactions in the region of heavy nuclei and the applicability of existing separation and detection techniques, which are usually used for identification of heavy fusion-evaporation residues, to heavy transfer products. This was motivated by recent theoretical results from macroscopic-microscopic models which suggest deep inelastic transfer reactions in heavy systems as a means to produce new neutron-rich isotopes in the region of N = 126 and in the region of superheavy nuclei. In this paper we present the isotopic yields, the excitation functions and the excitation energies of the heavy transfer products with Z > 82 as well as the influence of shell effects on the reaction products. The influence of the different neutron numbers of the projectiles is also discussed. (orig.)

Charge-transfer cross sections in collisions of ground-state Ca and H+

Science.gov (United States)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-03-01

We have investigated collisions of Ca(4s2) with H+ in the energy range of 200eV/u-10keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states ( 11Σ+1 and seven Π+1 states) to determine charge-transfer cross sections. Except for the incoming channel 6Σ+1 , the molecular states all correspond to charge-transfer channels. Inclusion of Ca2+-H- is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca2+-H- creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6Σ+1 and the energetically close charge-transfer channel 7Σ+1 the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4×10-15cm2 at 200eV/u to 4.5×10-15cm2 at 10keV/u . Charge transfer occurs mostly to the excited Ca+(5p) state in the entire energy range, which is the sum of the charge transfer to 7Σ+1 and 4Π+1 . It accounts for ˜47% of the total charge transfer cross sections at 200eV/u . However, as the energy increases, transfer to Ca+(4d) increases, and at 10keV/u the charge-transfer cross sections for Ca+(5p) and Ca+(4d) become comparable, each giving ˜38% of the total cross section.

Charge-transfer cross sections in collisions of ground-state Ca and H+

International Nuclear Information System (INIS)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-01-01

We have investigated collisions of Ca(4s 2 ) with H + in the energy range of 200 eV/u-10 keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states (11 1 Σ + and seven 1 Π + states) to determine charge-transfer cross sections. Except for the incoming channel 6 1 Σ + , the molecular states all correspond to charge-transfer channels. Inclusion of Ca 2+ -H - is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca 2+ -H - creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6 1 Σ + and the energetically close charge-transfer channel 7 1 Σ + the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4x10 -15 cm 2 at 200 eV/u to 4.5x10 -15 cm 2 at 10 keV/u. Charge transfer occurs mostly to the excited Ca + (5p) state in the entire energy range, which is the sum of the charge transfer to 7 1 Σ + and 4 1 Π + . It accounts for ∼47% of the total charge transfer cross sections at 200 eV/u. However, as the energy increases, transfer to Ca + (4d) increases, and at 10 keV/u the charge-transfer cross sections for Ca + (5p) and Ca + (4d) become comparable, each giving ∼38% of the total cross section

Digallane with redox-active diimine ligand: dualism of electron-transfer reactions.

Science.gov (United States)

Fedushkin, Igor L; Skatova, Alexandra A; Dodonov, Vladimir A; Chudakova, Valentina A; Bazyakina, Natalia L; Piskunov, Alexander V; Demeshko, Serhiy V; Fukin, Georgy K

2014-05-19

The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1), which consists of redox-active ligand 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian), has been studied. The reaction of 1 with I2 proceeds via one-electron oxidation of each of two dpp-Bian ligands to a radical-anionic state and affords complex (dpp-Bian)IGa-GaI(dpp-Bian) (2). Dissolution of complex 2 in pyridine (Py) gives monomeric compound (dpp-Bian)GaI(Py) (3) as a result of a solvent-induced intramolecular electron transfer from the metal-metal bond to the dpp-Bian ligands. Treatment of compound 3 with B(C6F5)3 leads to removal of pyridine and restores compound 2. The reaction of compound 1 with 3,6-di-tert-butyl-ortho-benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in 1 (the Ga-Ga bond and two dpp-Bian dianions) and results in mononuclear catecholate (dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q](2-)). Treatment of 4 with AgBF4 gives a mixture of [(dpp-Bian)2Ag][BF4] (5) and (dpp-Bian)GaF(Cat) (6), which both consist of neutral dpp-Bian ligands. The reduction of benzylideneacetone (BA) with 1 generates the BA radical-anions, which dimerize, affording (dpp-Bian)Ga-(BA-BA)-Ga(dpp-Bian) (7). In this case the Ga-Ga bond remains unchanged. Within 10 min at 95 °C in solution compound 7 undergoes transformation to paramagnetic complex (dpp-Bian)Ga(BA-BA) (8) and metal-free compound C36H40N2 (9). The latter is a product of intramolecular addition of the C-H bond of one of the iPr groups to the C═N bond in dpp-Bian. Diamagnetic compounds 3, 5, 6, and 9 have been characterized by NMR spectroscopy, and paramagnetic complexes 2, 4, 7, and 8 by ESR spectroscopy. Molecular structures of 2-7 and 9 have been established by single-crystal X-ray analysis.

Cross-Dehydrogenative Coupling Reactions Between P(O)-H and X-H (X = S, N, O, P) Bonds.

Science.gov (United States)

Hosseinian, Akram; Farshbaf, Sepideh; Fekri, Leila Zare; Nikpassand, Mohammad; Vessally, Esmail

2018-05-26

P(O)-X (X = S, N, O, P) bond-containing compounds have extensive application in medicinal chemistry, agrochemistry, and material chemistry. These useful organophosphorus compounds also have many applications in organic synthesis. In light of the importance of titled compounds, there is continuing interest in the development of synthetic methods for P(O)-X bonds construction. In the last 4 years, the direct coupling reaction of P(O)-H compounds with thiols, alcohols, and amines/amides has received much attention because of the atom-economic character. This review aims to give an overview of new developments in cross-dehydrogenative coupling reactions between P(O)-H and X-H (X = S, N, O, P) bonds, with special emphasis on the mechanistic aspects of the reactions.

Vibrational inelastic and charge transfer processes in H++H2 system: An ab initio study

Science.gov (United States)

Amaran, Saieswari; Kumar, Sanjay

2007-12-01

State-resolved differential cross sections, total and integral cross sections, average vibrational energy transfer, and the relative probabilities are computed for the H++H2 system using the newly obtained ab initio potential energy surfaces at the full CI/cc-pVQZ level of accuracy which allow for both the direct vibrational inelastic and the charge transfer processes. The quantum dynamics is treated within the vibrational close-coupling infinite-order-sudden approximation approach using the two ab initio quasidiabatic potential energy surfaces. The computed collision attributes for both the processes are compared with the available state-to-state scattering experiments at Ec.m.=20eV. The results are in overall good agreement with most of the observed scattering features such as rainbow positions, integral cross sections, and relative vibrational energy transfers. A comparison with the earlier theoretical study carried out on the semiempirical surfaces (diatomics in molecules) is also made to illustrate the reliability of the potential energy surfaces used in the present work.

Electron-transfer reactions of extremely small AgI colloids

International Nuclear Information System (INIS)

Vucemilovic, M.I.; Micic, O.I.

1988-01-01

Small colloidal AgI particles (particle diameter 20-50 A) have been prepared in water and acetonitrile, and optical effects due to size quantization have been observed. Electron transfer reactions involving electron donors and electron acceptors with AgI have been studied by pulse radiolysis techniques. Both reduction and oxidation of the colloids led to transient bleaching of semiconductor absorption. The recovery of the bleaching has been attributed to corrosion processes. Electrons injected into AgI colloids produce metallic silver and hydrogen. Hydrogen evolution is catalyzed by metallic silver formation. (author)

Four- and six-charge transfer reactions induced by 52Cr, 56Fe, 63Cu in rare-earths

International Nuclear Information System (INIS)

Mouchaty, G.

1977-01-01

The cross sections for transfer reactions in which 4 and 6 charges are gained by Sm and Nd targets have been measured, the projectiles being 52 Cr and 56 Fe at 343 and 377 MeV. These energies correspond to 1.5B, B being the interaction barrier. The results obtained indicate that the cross section increases when the number of charges transferred and the mass of the projectile are increased. The angular distributions and recoil ranges at each angle of 151 Dy produced through 52 Cr+ 148 Sm, 52 Cr+ 144 Nd, 56 Fe+ 144 Nd, 63 Cu+ 144 Nd reactions were determined for incident energies equivalent to 1.5B. After transformation into the c.m. system, the angular distributions exhibit a maximum close to 155 0 and a tail at small angles. The position of the maximum is independent of the incident ion and of the number of transferred charges. The analysis of the energy distributions indicate that the observed reactions can be explained by a two-step process: a transfer of nucleons followed by an evaporation step. The number of nucleons transferred in the 1st step and the associated excitation energies are higher for the events corresponding to the tail than for those corresponding to the maximum [fr

Beyond Born-Oppenheimer theory for ab initio constructed diabatic potential energy surfaces of singlet H3+ to study reaction dynamics using coupled 3D time-dependent wave-packet approach.

Science.gov (United States)

Ghosh, Sandip; Mukherjee, Saikat; Mukherjee, Bijit; Mandal, Souvik; Sharma, Rahul; Chaudhury, Pinaki; Adhikari, Satrajit

2017-08-21

The workability of beyond Born-Oppenheimer theory to construct diabatic potential energy surfaces (PESs) of a charge transfer atom-diatom collision process has been explored by performing scattering calculations to extract accurate integral cross sections (ICSs) and rate constants for comparison with most recent experimental quantities. We calculate non-adiabatic coupling terms among the lowest three singlet states of H 3 + system (1 1 A ' , 2 1 A ' , and 3 1 A ' ) using MRCI level of calculation and solve the adiabatic-diabatic transformation equation to formulate the diabatic Hamiltonian matrix of the same process [S. Mukherjee et al., J. Chem. Phys. 141, 204306 (2014)] for the entire region of nuclear configuration space. The nonadiabatic effects in the D + + H 2 reaction has been studied by implementing the coupled 3D time-dependent wave packet formalism in hyperspherical coordinates [S. Adhikari and A. J. C. Varandas, Comput. Phys. Commun. 184, 270 (2013)] with zero and non-zero total angular momentum (J) on such newly constructed accurate (ab initio) diabatic PESs of H 3 + . We have depicted the convergence profiles of reaction probabilities for the reactive non-charge transfer, non-reactive charge transfer, and reactive charge transfer processes for different collisional energies with respect to the helicity (K) and total angular momentum (J) quantum numbers. Finally, total and state-to-state ICSs are calculated as a function of collision energy for the initial rovibrational state (v = 0, j = 0) of the H 2 molecule, and consequently, those quantities are compared with previous theoretical and experimental results.

Reaction-transport simulations of non-oxidative methane conversion with continuous hydrogen removal: Homogeneous-heterogeneous methane reaction pathways

International Nuclear Information System (INIS)

Li, Lin; Borry, Richard W.; Iglesia, Enrique

2000-01-01

Detailed kinetic-transport models were used to explore thermodynamic and kinetic barriers in the non-oxidative conversion of CH4 via homogeneous and homogeneous-heterogeneous pathways and the effects of continuous hydrogen removal and of catalytic sites on attainable yields of useful C2-C10 products. The homogeneous kinetic model combines separately developed models for low-conversion pyrolysis and for chain growth to form large aromatics and carbon. The H2 formed in the reaction decreases CH4 pyrolysis rates and equilibrium conversions and it favors the formation of lighter products. The removal of H2 along tubular reactors with permeable walls increases reaction rates and equilibrium CH4 conversions. C2-C10 yields reach values greater than 90 percent at intermediate values of dimensionless transport rates (delta=1-10), defined as the ratio hydrogen transport and methane conversion rates. Homogeneous reactions require impractical residence times, even with H2 removal, because of slow initiation and chain transfer rates. The introduction of heterogeneous chain initiation pathways using surface sites that form methyl radicals eliminates the induction period without influencing the homogeneous product distribution. Methane conversion, however, occurs predominately in the chain transfer regime, within which individual transfer steps and the formation of C2 intermediates become limited by thermodynamic constraints. Catalytic sites alone cannot overcome these constraints. Catalytic membrane reactors with continuous H2 removal remove these thermodynamic obstacles and decrease the required residence time. Reaction rates become limited by homogeneous reactions of C2 products to form C6+ aromatics. Higher delta values lead to subsequent conversion of the desired C2-C10 products to larger polynuclear aromatics. We conclude that catalytic methane pyrolysis at the low temperatures required for restricted chain growth and the elimination of thermodynamics constraints via

Exchange reaction between hydrogen and deuterium. II - Proposal for an heterogeneous initiation mechanism of gaseous phase reactions

Energy Technology Data Exchange (ETDEWEB)

Marteau, Chantal; Gaillard-Cusin, Francoise; James, Henri [Centre National de la Recherche Scientifique, 45 - Orleans-la-Source (France). Centre de Recherches sur la Chimie de Combustion et des Hautes Temperatures

1978-05-01

Investigation of experimental data related to evolution period exhibited by H/sub 2/-D/sub 2/ exchange process requires to take into account the variation against time of every atomic species -adsorbed or not- implied in the reaction mechanism. The formation of first chain carriers involves: - chemisorption of either gaseous reactant on the surface active centres (..sigma..), e.g.: ..sigma.. + 1/2 H/sub 2/ reversible ..sigma..H; - consecutive generation of atomic species through hetero-homogeneous transfer between chemisorbed species (..sigma..H) and gaseous molecules: ..sigma..H+H/sub 2/..--> sigma..+H/sub 2/+H/sup 0/, ..sigma..H+D/sub 2/..--> sigma..+HD+D/sup 0/. Therefore, it can be shown that the heterogeneous initiation process of a gas phase reaction identifies to a chain linear mechanism. Such an heterogeneous sequence conditions the further proceeding of the homogeneous chain reaction; both evolutions being kinematically connected. Rate constant of hydrogen adsorption on silica glass: ksub(a1) approximately 10/sup 14/ exp(-47/RT)Isup(0,5).molesup(-0,5).S/sup -1/ has been evaluated.

Reaction of the H atom in gamma-irradiated ferrous sulphate solutions

International Nuclear Information System (INIS)

Mathews, R.W.

1977-10-01

The effect of sulphuric acid, ferrous and ferric ion, and oxygen concentrations on G(Fe 3+ ) values from cobalt-60 gamma-irradiated soltuions has been studied. Kinetic expressions were derived for reaction models involving reactions of various forms of the H atom and additional reactions postulated to be of importance at high solute concentration. Three models were assumed invoking the additional reactions: (1) an independent yield of an excited water species; (2) increasing contributions from interspur reactions of well established species at increasing solute concentration; (3) inhibition of charge pair recombination by acid and scavenger species. The calculated G(Fe 3+ ) values from the various models were compared by the least squares method with experimental G(Fe 3+ ) values from over 600 irradiations. Model 3 provided the best fit to the data for the least number of adjustable parameters. No evidence for more than one form of H atom was found with this model. (J.R.)

Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

Directory of Open Access Journals (Sweden)

Shinichi Yamabe

2014-01-01

Full Text Available Wolff–Kishner reduction reactions were investigated by DFT calculations for the first time. B3LYP/6-311+G(d,p SCRF=(PCM, solvent = 1,2-ethanediol optimizations were carried out. To investigate the role of the base catalyst, the base-free reaction was examined by the use of acetone, hydrazine (H2N–NH2 and (H2O8. A ready reaction channel of acetone → acetone hydrazine (Me2C=N–NH2 was obtained. The channel involves two likely proton-transfer routes. However, it was found that the base-free reaction was unlikely at the N2 extrusion step from the isopropyl diimine intermediate (Me2C(H–N=N–H. Two base-catalyzed reactions were investigated by models of the ketone, H2N–NH2 and OH−(H2O7. Here, ketones are acetone and acetophenone. While routes of the ketone → hydrazone → diimine are similar, those from the diimines are different. From the isopropyl diimine, the N2 extrusion and the C–H bond formation takes place concomitantly. The concomitance leads to the propane product concertedly. From the (1-phenylethyl substituted diimine, a carbanion intermediate is formed. The para carbon of the phenyl ring of the anion is subject to the protonation, which leads to a 3-ethylidene-1,4-cyclohexadiene intermediate. Its [1,5]-hydrogen migration gives the ethylbenzene product. For both ketone substrates, the diimines undergoing E2 reactions were found to be key intermediates.

2H(d,p)3H and 2H(d,n)3He reactions at sub-coulomb energies

International Nuclear Information System (INIS)

Tumino, A.; Spitaleri, C.; Mukhamedzhanov, A. M.; Typel, S.; Spartá, R.; Aliotta, M.; Kroha, V.; Hons, Z.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Mrazek, J.; Pizzone, R. G.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.

2012-01-01

The 2 H( 3 He,p 3 H) 1 H and 2 H( 3 He,n 3 He) 1 H processes have been measured in quasi free kinematics to investigate for the first time the 2 H(d,p) 3 H and 2 H(d,n) 3 He reactions by means of the Trojan Horse Method. The 3 He+d experiment was performed at 18 MeV, corresponding the a d-d energy range from 1.5 MeV down to 2 keV. This range overlaps with the relevant region for Standard Big Bang Nucleosynthesis as well as with the thermal energies of future fusion reactors and deuterium burning in the Pre Main Sequence phase of stellar evolution. This is the first pioneering experiment in quasi free regime where the charged spectator is detected. Both the energy dependence and the absolute value of the bare nucleus S(E) factors have been extracted for the first time. They deviate by more than 15% from available direct data with new S(0) values of 57.4±1.8 MeVb for 3 H+p and 60.1±1.9 MeVb for 3 He+n. None of the existing fitting curves is able to provide the correct slope of the new data in the full range, thus calling for a revision of the theoretical description. This has consequences in the calculation of the reaction rates with more than a 25% increase at the temperatures of future fusion reactors.

Electron transfer reactions induced by the triplet state of thiacarbocyanine dimers

International Nuclear Information System (INIS)

Chibisov, Alexander K.; Slavnova, Tatyana D.; Goerner, Helmut

2004-01-01

The photoinduced electron transfer between either cationic 5,5 ' -dichloro-3,3 ' ,9-triethylthiacarbocyanine (1) or a structurally similar anionic dye (2) and appropriate donors, e.g. ascorbic acid, and acceptors, e.g. methyl viologen, was studied by ns-laser photolysis. In aqueous solution the dyes in the ground state are present as an equilibrated mixture of dimers and monomers, whereas the triplet state is mainly populated from dimers. The triplet states of both dimers and monomers are quenched by electron donors or acceptors and the rate constant for quenching is generally 2-4 times higher for dimers than for monomers. The kinetics of triplet decay and radical formation and decay as a result of primary and secondary electron transfer were analyzed. While the one-electron reduced dimer decays due to back reactions, the one-electron oxidized dimer rapidly dissociates into the monomer and the monomeric dye radical. For the dimeric dye/donor/acceptor systems the primary photoinduced electron transfer occurs either from the donor or to the acceptor yielding the dimeric dye radicals. The one-electron reduced dimer can be efficiently oxidized by acceptors, e.g. the rate constant for reaction of the dimeric dye radical of 1 with methyl viologen (photoreductive pathway of sensitization) is 1.6x10 9 M -1 s -1 . The photooxidative pathway of sensitization is more complicated; after dissociation of the dimeric dye radical, the monomeric dye radical is reduced in a secondary electron transfer from ascorbic acid, e.g. with a rate constant of 1x10 9 M -1 s -1 for 2, yielding the monomer. On increasing the donor concentration the photooxidative pathway of sensitization is switched to a photoreductive one

Visible spectroscopy calibration transfer model in determining pH of Sala mangoes

International Nuclear Information System (INIS)

Yahaya, O.K.M.; MatJafri, M.Z.; Aziz, A.A.; Omar, A.F.

2015-01-01

The purpose of this study is to compare the efficiency of calibration transfer procedures between three spectrometers involving two Ocean Optics Inc. spectrometers, namely, QE65000 and Jaz, and also, ASD FieldSpec 3 in measuring the pH of Sala mango by visible reflectance spectroscopy. This study evaluates the ability of these spectrometers in measuring the pH of Sala mango by applying similar calibration algorithms through direct calibration transfer. This visible reflectance spectroscopy technique defines a spectrometer as a master instrument and another spectrometer as a slave. The multiple linear regression (MLR) of calibration model generated using the QE65000 spectrometer is transferred to the Jaz spectrometer and vice versa for Set 1. The same technique is applied for Set 2 with QE65000 spectrometer is transferred to the FieldSpec3 spectrometer and vice versa. For Set 1, the result showed that the QE65000 spectrometer established a calibration model with higher accuracy than that of the Jaz spectrometer. In addition, the calibration model developed on Jaz spectrometer successfully predicted the pH of Sala mango, which was measured using QE65000 spectrometer, with a root means square error of prediction RMSEP = 0.092 pH and coefficients of determination R 2  = 0.892. Moreover, the best prediction result is obtained for Set 2 when the calibration model developed on QE65000 spectrometer is successfully transferred to FieldSpec 3 with R 2  = 0.839 and RMSEP = 0.16 pH

Coupled-channels analyses for 9,11Li + 208Pb fusion reactions with multi-neutron transfer couplings

Science.gov (United States)

Choi, Ki-Seok; Cheoun, Myung-Ki; So, W. Y.; Hagino, K.; Kim, K. S.

2018-05-01

We discuss the role of two-neutron transfer processes in the fusion reaction of the 9,11Li + 208Pb systems. We first analyze the 9Li + 208Pb reaction by taking into account the coupling to the 7Li + 210Pb channel. To this end, we assume that two neutrons are directly transferred to a single effective channel in 210Pb and solve the coupled-channels equations with the two channels. By adjusting the coupling strength and the effective Q-value, we successfully reproduce the experimental fusion cross sections for this system. We then analyze the 11Li + 208Pb reaction in a similar manner, that is, by taking into account three effective channels with 11Li + 208Pb, 9Li + 210Pb, and 7Li + 212Pb partitions. In order to take into account the halo structure of the 11Li nucleus, we construct the potential between 11Li and 208Pb with a double folding procedure, while we employ a Woods-Saxon type potential with the global Akyüz-Winther parameters for the other channels. Our calculation indicates that the multiple two-neutron transfer process plays a crucial role in the 11Li + 208Pb fusion reaction at energies around the Coulomb barrier.

Calculation of rate coefficients of some proton-transfer ion-molecule reactions in weakly ionized gases

International Nuclear Information System (INIS)

Stiller, W.

1985-01-01

A classical collision theory is used to describe thermal bimolecular rate coefficeints for reaction between positive and negative ions and polar molecules in a carrier gas. Special attention is paid to ion-molecule reaction in which proton transfer occurs. These reactions play an important role in terrestrial plasma devices, in ionosphere, in planetary atmospheres and in interstellar matter. The equilibrium rate coefficients of the reactions are calculated based on a microscopic reactive cross section derived from a long distance polar molecule-ion potential. The results are compared with experimental values of afterglow measurements. (D.Gy.)

Near-field heat transfer between graphene/hBN multilayers

OpenAIRE

Zhao, Bo; Guizal, Brahim; Zhang, Zhuomin M.; Fan, Shanhui; Antezza, Mauro

2017-01-01

We study the radiative heat transfer between multilayer structures made by a periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN) slab. Surface plasmons in a monolayer graphene can couple with a hyperbolic phonon polaritons in a single hBN film to form hybrid polaritons that can assist photon tunneling. For periodic multilayer graphene/hBN structures, the stacked metallic/dielectric array can give rise to a further effective hyperbolic behavior, in addition to the intri...

Search for 4H, 5H and 6H nuclei in the 11B-induced reaction on 9Be

International Nuclear Information System (INIS)

Belozerov, A.V.; Borcea, C.; Dlouhy, Z.

1985-01-01

In the 11 B(88.0 MeV)+ 9 Be reaction the energy spectra of the 14 O, 15 O and 16 O nuclei have been measured to obtain some information about their partners in the exit channel - the neutron-rich hydrogen isotopes 4 H, 5 H and 6 H. The unbound levels in the 4 H and 6 H systems have been observed at excitation energies of 3.5 +- 0.5 MeV (GITA approximately 1 MeV) and 2.6 +- 0.5 MeV (GITA=1.5 +- 0.3 MeV), respectively

Capture and dissociation in the complex-forming CH + H2 → CH2 + H, CH + H2 reactions.

Science.gov (United States)

González, Miguel; Saracibar, Amaia; Garcia, Ernesto

2011-02-28

The rate coefficients for the capture process CH + H(2)→ CH(3) and the reactions CH + H(2)→ CH(2) + H (abstraction), CH + H(2) (exchange) have been calculated in the 200-800 K temperature range, using the quasiclassical trajectory (QCT) method and the most recent global potential energy surface. The reactions, which are of interest in combustion and in astrochemistry, proceed via the formation of long-lived CH(3) collision complexes, and the three H atoms become equivalent. QCT rate coefficients for capture are in quite good agreement with experiments. However, an important zero point energy (ZPE) leakage problem occurs in the QCT calculations for the abstraction, exchange and inelastic exit channels. To account for this issue, a pragmatic but accurate approach has been applied, leading to a good agreement with experimental abstraction rate coefficients. Exchange rate coefficients have also been calculated using this approach. Finally, calculations employing QCT capture/phase space theory (PST) models have been carried out, leading to similar values for the abstraction rate coefficients as the QCT and previous quantum mechanical capture/PST methods. This suggests that QCT capture/PST models are a good alternative to the QCT method for this and similar systems.

Evaporation rates and surface profiles on heterogeneous surfaces with mass transfer and surface reaction

Energy Technology Data Exchange (ETDEWEB)

Flytzani-Stephanopoulos, M; Schmidt, L D

1979-01-01

Simple models incorporating surface reaction and diffusion of volatile products through a boundary layer are developed to calculate effective rates of evaporation and local surface profiles on surfaces having active and inactive regions. The coupling between surface heterogeneities with respect to a particular reaction and external mass transfer may provide a mechanism for the surface rearrangement and metal loss encountered in several catalytic systems of practical interest. Calculated transport rates for the volatilization of platinum in oxidizing environments and the rearrangement of this metal during the ammonia oxidation reaction agree well with published experimental data.

Isotope exchange reaction in Li2ZrO3 packed bed

International Nuclear Information System (INIS)

Kawamura, Y.; Enoeda, M.; Okuno, K.

1998-01-01

To understand the release behavior of bred tritium in a solid breeder blanket, the tritium transfer rate and tritium inventory for various mass transfer processes should be investigated. The contribution of the surface reactions (adsorption, desorption and two kinds of isotope exchange reactions) to the release process cannot be ignored. It is believed that two kinds of isotope exchange reactions (gaseous hydrogen-tritiated water and water vapor-tritiated water) occur on the surface of the solid breeder materials when hydrogen is added to the sweep gas to enhance the tritium release rate. The isotope exchange reaction study in H-D systems was carried out using a Li 2 ZrO 3 packed bed. The exchange reaction between gaseous hydrogen and water was the rate controlling step among the two kinds of exchange reactions. The reaction rate constants were quantified, and experimental equations were proposed. The equilibrium constant of the isotope exchange reaction in the H-D system was obtained from experimental data and was found to be 1.17. (orig.)

Exploring possible reaction pathways for the o-atom transfer reactions to unsaturated substrates catalyzed by a [Ni-NO2 ] ↔ [Ni-NO] redox couple using DFT methods.

Science.gov (United States)

Tsipis, Athanassios C

2017-07-15

The (nitro)(N-methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex catalyses efficiently the O-atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] ↔ Ni(NO 2 )(S 2 CNHMe)(PMe 3 ) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five-member metallacycle intermediate, via a [3 + 2] cyclo-addition reaction of HC≡CH to the Ni-N = O moiety of the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex, followed by a β H-atom migration toward the C α carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( κN1-NO 2 )(S 2 CNHMe)(PMe 3 )] ⇌ [Ni( κO,O2-ONO)(S 2 CNHMe)(PMe 3 )] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Cell-secreted flavins bound to membrane cytochromes dictate electron transfer reactions to surfaces with diverse charge and pH.

Science.gov (United States)

Okamoto, Akihiro; Kalathil, Shafeer; Deng, Xiao; Hashimoto, Kazuhito; Nakamura, Ryuhei; Nealson, Kenneth H

2014-07-11

The variety of solid surfaces to and from which microbes can deliver electrons by extracellular electron transport (EET) processes via outer-membrane c-type cytochromes (OM c-Cyts) expands the importance of microbial respiration in natural environments and industrial applications. Here, we demonstrate that the bifurcated EET pathway of OM c-Cyts sustains the diversity of the EET surface in Shewanella oneidensis MR-1 via specific binding with cell-secreted flavin mononucleotide (FMN) and riboflavin (RF). Microbial current production and whole-cell differential pulse voltammetry revealed that RF and FMN enhance EET as bound cofactors in a similar manner. Conversely, FMN and RF were clearly differentiated in the EET enhancement by gene-deletion of OM c-Cyts and the dependency of the electrode potential and pH. These results indicate that RF and FMN have specific binding sites in OM c-Cyts and highlight the potential roles of these flavin-cytochrome complexes in controlling the rate of electron transfer to surfaces with diverse potential and pH.

The electrochemical transfer reactions and the structure of the iron|oxide layer|electrolyte interface

International Nuclear Information System (INIS)

Petrović, Željka; Metikoš-Huković, Mirjana; Babić, Ranko

2012-01-01

The thickness, barrier (protecting) and semiconducting properties of the potentiostatically formed oxide films on the pure iron electrode in an aqueous borate buffer solution were investigated by electrochemical quartz crystal nanobalance (EQCN), electrochemical impedance spectroscopy (EIS), and Mott–Schottky (MS) analysis. The thicknesses of the prepassive Fe(II)hydroxide layer (up to monolayer) nucleated on the bare iron surface and the passive Fe(II)/Fe(III) layer (up to 2 nm), deposited on the top of the first one, were determined using in situ gravimetry. Electronic properties of iron prepassive and passive films as well as ionic and electronic transfer reactions at the film|solution interface were discussed on the basis of a band structure model of the surface oxide film and the potential distribution at the interface. The anodic oxide film formation and cathodic decomposition are coupled processes and their reversible inter-conversion is mediated by the availability of free charge carriers on the electrode|solution interface. The structure of the reversible double layer at the iron oxide|solution interface was discussed based on the concept of the specific adsorption of the imidazolium cation on the negatively charged electrode surface at pH > pH pzc .

Ion cyclotron resonance study of reactions of ions with hydrogen atoms

International Nuclear Information System (INIS)

Karpas, Z.; Anicich, V.; Huntress, W.T. Jr.

1979-01-01

Reactions of H 2 + , HeH + , and CO 2 + ions with hydrogen atoms, and the reactions of D 2 + , CO 2 + , CO + , N 2 + and HCN + with deuterium atoms, were studied using ion cyclotron resonance techniques. These reactions proceed predominantly via a charge transfer mechanism. The rate constants measured are: 6.4, 9.1, 1.1, 5.0, 0.84, 0.90, 1.2, and 0.37 x 10 -10 cm 3 /sec, respectively. Hydrocarbon ions of the types CH/sub n/ + and C 2 H/sub n/ + , where n=2--4, do not react with H or D atoms

Mechanism of the Primary Charge Transfer Reaction in the Cytochrome bc1 Complex

DEFF Research Database (Denmark)

Barragan, Angela M; Schulten, Klaus; Solov'yov, Ilia A

2016-01-01

, the quinol-protein interaction, which initiates the Q-cycle, has not yet been completely described. Furthermore, the initial charge transfer reactions of the Q-cycle lack a physical description. The present investigation utilizes classical molecular dynamics simulations in tandem with quantum density...

An annular ionization detector for quasi-elastic and transfer reaction studies

CERN Document Server

Dinesh, B V; Nayak, B K; Biswas, D C; Saxena, A; Pant, L M; Sahu, P K; Choudhury, R K

2000-01-01

An annular ionization chamber detector has been developed to study quasi-elastic and transfer reactions in heavy-ion collisions at near-barrier and sub-barrier energies. The important feature of the detector is that it has a near 2 pi coverage in the azimuthal angle phi for the particles entering in the detector at a given theta direction. This feature makes the detector very useful for measurement of the differential cross-sections at backward angles with respect to the beam direction, involving low cross-section reaction channels. The split anode configuration of the detector makes it capable of both particle identification and energy measurement for heavy ions and fission fragments. The detector has been tested using heavy-ion beams from the 14 MV-pelletron accelerator at Mumbai. Results on quasi-elastic excitation function measurements and barrier distribution studies in many heavy-ion reactions using this detector setup are discussed.

One nucleon transfer reactions around $^{68}$Ni at REX-ISOLDE

CERN Multimedia

Blazhev, A A; Kruecken, R; Mertzimekis, T; Darby, I G; Lagogiannis, A; Habs, D; Diriken, J V J; Patronis, N

2008-01-01

We intend to investigate the single particle properties of the neutron-rich Ni isotopes in the mass region around $^{68}$Ni and at a later stage towards the doubly-magic $^{78}$Ni. As a first experiment we propose to study the single particle character of the ground and first excited states of $^{67}$Ni. This nucleus will be the projectile-like reaction product for the one-neutron transfer reaction. A $^{66}$Ni beam at 3A MeV delivered from REX-ISOLDE will be directed on a CD$_{2}$ target. Protons produced from the (d,p) reaction will be detected either in singles or in coincidence with ${\\gamma}$-rays recorded by the MINIBALL array. The particles will be detected by the newly-built Si position-sensitive barrel configuration. The objectives of this work are the unambiguous determination of the spins and parities of the first excited states of $^{67}$Ni and measurement of the relative spectroscopic factors of those states as well as of the ground state. The experimental results will be compared with those from...

Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads.

Science.gov (United States)

Niemi, Marja; Tkachenko, Nikolai V; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

2008-07-31

Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results in rapid ET from phthalocyanine to fullerene via an exciplex state in both polar and nonpolar solvents. Relaxation of the charge-separated (CS) state Pc(*+)-C60(*-) in a polar solvent occurs directly to the ground state in 30-70 ps. In a nonpolar solvent, roughly 20% of the molecules undergo transition from the CS state to phthalocyanine triplet state (3)Pc*-C60 before relaxation to the ground state. Formation of the CS state was confirmed with electron spin resonance measurements at low temperature in both polar and nonpolar solvent. Reaction schemes for the photoinduced ET reactions of the dyads were completed with rate constants obtained from the time-resolved absorption and emission measurements and with state energies obtained from the fluorescence, phosphorescence, and voltammetric measurements.

Factors affecting hydrogen-tunneling contribution in hydroxylation reactions promoted by oxoiron(IV) porphyrin π-cation radical complexes.

Science.gov (United States)

Cong, Zhiqi; Kinemuchi, Haruki; Kurahashi, Takuya; Fujii, Hiroshi

2014-10-06

Hydrogen atom transfer with a tunneling effect (H-tunneling) has been proposed to be involved in aliphatic hydroxylation reactions catalyzed by cytochrome P450 and synthetic heme complexes as a result of the observation of large hydrogen/deuterium kinetic isotope effects (KIEs). In the present work, we investigate the factors controlling the H-tunneling contribution to the H-transfer process in hydroxylation reaction by examining the kinetics of hydroxylation reactions at the benzylic positions of xanthene and 1,2,3,4-tetrahydronaphthalene by oxoiron(IV) 5,10,15,20-tetramesitylporphyrin π-cation radical complexes ((TMP(+•))Fe(IV)O(L)) under single-turnover conditions. The Arrhenius plots for these hydroxylation reactions of H-isotopomers have upwardly concave profiles. The Arrhenius plots of D-isotopomers, clear isosbestic points, and product analysis rule out the participation of thermally dependent other reaction processes in the concave profiles. These results provide evidence for the involvement of H-tunneling in the rate-limiting H-transfer process. These profiles are simulated using an equation derived from Bell's tunneling model. The temperature dependence of the KIE values (k(H)/k(D)) determined for these reactions indicates that the KIE value increases as the reaction temperature becomes lower, the bond dissociation energy (BDE) of the C-H bond of a substrate becomes higher, and the reactivity of (TMP(+•))Fe(IV)O(L) decreases. In addition, we found correlation of the slope of the ln(k(H)/k(D)) - 1/T plot and the bond strengths of the Fe═O bond of (TMP(+•))Fe(IV)O(L) estimated from resonance Raman spectroscopy. These observations indicate that these factors modulate the extent of the H-tunneling contribution by modulating the ratio of the height and thickness of the reaction barrier.

Reaction pathways of producing and losing particles in atmospheric pressure methane nanosecond pulsed needle-plane discharge plasma

Science.gov (United States)

Zhao, Yuefeng; Wang, Chao; Li, Li; Wang, Lijuan; Pan, Jie

2018-03-01

In this work, a two-dimensional fluid model is built up to numerically investigate the reaction pathways of producing and losing particles in atmospheric pressure methane nanosecond pulsed needle-plane discharge plasma. The calculation results indicate that the electron collisions with CH4 are the key pathways to produce the neutral particles CH2 and CH as well as the charged particles e and CH3+. CH3, H2, H, C2H2, and C2H4 primarily result from the reactions between the neutral particles and CH4. The charge transfer reactions are the significant pathways to produce CH4+, C2H2+, and C2H4+. As to the neutral species CH and H and the charged species CH3+, the reactions between themselves and CH4 contribute to substantial losses of these particles. The ways responsible for losing CH3, H2, C2H2, and C2H4 are CH3 + H → CH4, H2 + CH → CH2 + H, CH4+ + C2H2 → C2H2+ + CH4, and CH4+ + C2H4 → C2H4+ + CH4, respectively. Both electrons and C2H4+ are consumed by the dissociative electron-ion recombination reactions. The essential reaction pathways of losing CH4+ and C2H2+ are the charge transfer reactions.