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Sample records for atom transfer reactions

  1. Hydrogen atom transfer reactions of imido manganese(V) corrole: one reaction with two mechanistic pathways.

    Science.gov (United States)

    Zdilla, Michael J; Dexheimer, Jennifer L; Abu-Omar, Mahdi M

    2007-09-19

    Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,15-tris(pentafluorophenyl)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 +/- 0.03 and 0.17 +/- 0.01 M(-1) s(-1), respectively, at 22 degrees C. The products are the respective arenes, TsNH(2) and (tpfc)Mn(III). Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9',10,10'-tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a Mn(IV) intermediate. The imido complex (tpfc)Mn(V)NTs abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 +/- 0.02 M(-1) s(-1) at 22 degrees C. The other products from imido manganese(V) are TsNH(2) and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)Mn(IV)(NHTs) is confirmed by EPR spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on sigma, with electron-donating substituents exhibiting the expected negative rho while electron-withdrawing substituents fall above the linear fit (i.e., positive rho). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton-electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer.

  2. 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.

  3. 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

  4. 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. 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

  6. Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

    Directory of Open Access Journals (Sweden)

    Yannick Borguet

    2010-12-01

    Full Text Available The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium–indenylidene complex [(p-cymeneRu(μ-Cl3RuCl(3-phenyl-1-indenylidene(PCy3] (1 to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones from α,ω-diene substrates bearing trihaloacetamide or trichloroacetate functionalities. The individual steps were carefully monitored by 1H and 31P NMR spectroscopies in order to understand the intimate details of the catalytic cycles. Polyhalogenated substrates and the ethylene released upon metathesis induced the clean transformation of catalyst precursor 1 into the Ru(II–Ru(III mixed-valence compound [(p-cymeneRu(μ-Cl3RuCl2(PCy3], which was found to be an efficient promoter for atom transfer radical reactions under the adopted experimental conditions.

  7. New method for exploring deactivation kinetics in copper-catalyzed atom-transfer-radical reactions.

    Science.gov (United States)

    Zerk, Timothy J; Bernhardt, Paul V

    2014-11-03

    Copper polyamine complexes are among the most utilized catalysts for controlled radical polymerization reactions. Copper(I) complexes may react reversibly with an alkyl halide to form an alkyl radical, which promotes polymerization, and a copper(II) halido complex in a step known as activation. The kinetics of the reverse reaction between the alkyl radical and higher oxidation-state copper complex (deactivation) are less studied because these reactions approach diffusion-controlled rates, and it is difficult to isolate or quantify the concentration of the alkyl radical (R(•)) in situ. Herein we report a broadly applicable electrochemical technique for simultaneously measuring the kinetics of deactivation and kinetics of activation.

  8. Oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives by nitrous oxide via selective oxygen atom transfer reactions: insights from quantum chemistry calculations.

    Science.gov (United States)

    Xie, Hujun; Liu, Chengcheng; Yuan, Ying; Zhou, Tao; Fan, Ting; Lei, Qunfang; Fang, Wenjun

    2016-01-21

    The mechanisms for the oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives (Cp* = η(5)-C5Me5) by nitrous oxide via selective oxygen atom transfer reactions have been systematically studied by means of density functional theory (DFT) calculations. On the basis of the calculations, we investigated the original mechanism proposed by Hillhouse and co-workers for the activation of N2O. The calculations showed that the complex with an initial O-coordination of N2O to the coordinatively unsaturated Hf center is not a local minimum. Then we proposed a new reaction mechanism to investigate how N2O is activated and why N2O selectively oxidize phenyl and hydride ligands of . Frontier molecular orbital theory analysis indicates that N2O is activated by nucleophilic attack by the phenyl or hydride ligand. Present calculations provide new insights into the activation of N2O involving the direct oxygen atom transfer from nitrous oxide to metal-ligand bonds instead of the generally observed oxygen abstraction reaction to generate metal-oxo species.

  9. Development of atom-economical catalytic asymmetric reactions under proton transfer conditions: construction of tetrasubstituted stereogenic centers and their application to therapeutics.

    Science.gov (United States)

    Kumagai, Naoya

    2011-01-01

    The development of atom-economical catalytic asymmetric reactions based on two distinct sets of catalyst, a rare earth metal/amide-based ligand catalyst and a soft Lewis acid/hard Brønsted base catalyst, is reviewed. These catalytic systems exhibit high catalytic activity and stereoselectivity by harnessing a cooperative catalysis through hydrogen bond/metal coordination and soft-soft interactions/hard-hard interactions, respectively. The effectiveness of these cooperative catalysts is clearly delineated by the high stereoselectivity in reactions with highly coordinative substrates, and the specific activation of otherwise low-reactive pronucleophiles under proton transfer conditions. The rare earth metal/amide-based ligand catalyst was successfully applied to catalytic asymmetric aminations, nitroaldol (Henry) reactions, Mannich-type reactions, and conjugate addition reactions, generating stereogenic tetrasubstituted centers. Catalytic asymmetric amination and anti-selective catalytic asymmetric nitroaldol reactions were successfully applied to the efficient enantioselective synthesis of therapeutic candidates, such as AS-3201 and the β(3)-adrenoreceptor agonist, showcasing the practical utility of the present protocols. The soft Lewis acid/hard Brønsted base cooperative catalyst was specifically developed for the chemoselective activation of soft Lewis basic allylic cyanides and thioamides, which are otherwise low-reactive pronucleophiles. The cooperative action of the catalyst allowed for efficient catalytic generation of active carbon nucleophiles in situ, which were integrated into subsequent enantioselective additions to carbonyl-type electrophiles.

  10. Efficient transfer of francium atoms

    Science.gov (United States)

    Aubin, Seth; Behr, John; Gorelov, Alexander; Pearson, Matt; Tandecki, Michael; Collister, Robert; Gwinner, Gerald; Shiells, Kyle; Gomez, Eduardo; Orozco, Luis; Zhang, Jiehang; Zhao, Yanting; FrPNC Collaboration

    2016-05-01

    We report on the progress of the FrPNC collaboration towards Parity Non Conservation Measurements (PNC) using francium atoms at the TRIUMF accelerator. We demonstrate efficient transfer (higher than 40%) to the science vacuum chamber where the PNC measurements will be performed. The transfer uses a downward resonant push beam from the high-efficiency capture magneto optical trap (MOT) towards the science chamber where the atoms are recaptured in a second MOT. The transfer is very robust with respect to variations in the parameters (laser power, detuning, alignment, etc.). We accumulate a growing number of atoms at each transfer pulse (limited by the lifetime of the MOT) since the push beam does not eliminate the atoms already trapped in the science MOT. The number of atoms in the science MOT is on track to meet the requirements for competitive PNC measurements when high francium rates (previously demonstrated) are delivered to our apparatus. The catcher/neutralizer for the ion beam has been tested reliably to 100,000 heating/motion cycles. We present initial tests on the direct microwave excitation of the ground hyperfine transition at 45 GHz. Support from NSERC and NRC from Canada, NSF and Fulbright from USA, and CONACYT from Mexico.

  11. Transfer reactions with HELIOS

    Science.gov (United States)

    Wuosmaa, Alan H.

    2011-04-01

    Nucleon-transfer reactions have formed the backbone of nuclear-structure studies for several decades, providing a wealth of information about the energies, quantum numbers, and wave functions of single-particle states in nuclei throughout the nuclear chart. Current trends in nuclear-structure physics and the modern emphasis on properties of neutron-rich nuclei far from stability have renewed interest in such transfer reactions with radioactive beams. Here, the usual combination of light beam and heavy target cannot be used, and measurements must be performed in ``inverse kinematics,'' with a heavy, unstable beam incident on a light target. This arrangement introduces several technical difficulties, including the identification of the reaction products and the resolution of the states of interest in the residual nuclei. A new device, HELIOS (the HELIcal Orbit Spectrometer) at the ATLAS facility at Argonne National Laboratory, solves many of the problems encountered with inverse kinematics including particle identification and energy resolution in the center-of-mass frame. The device utilizes the uniform magnetic field of a large, superconducting solenoid to transport light reaction products from the target to a linear array of position-sensitive silicon detectors. The properties of HELIOS will be described, and examples from the initial research program that focuses on neutron transfer with the (d,p) reaction, using both stable and unstable beams with mass A = 11 to 136, will be presented. Work supported by the U. S. Department of Energy, Office of Nuclear Physics under contract numbers DE-FG02-04ER41320 (WMU) and DE-AC02-06CH11357 (ANL).

  12. Mass Transfer with Chemical Reaction.

    Science.gov (United States)

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  13. 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.

  14. Understanding the physics and chemistry of reaction mechanisms from atomic contributions: a reaction force perspective.

    Science.gov (United States)

    Vöhringer-Martinez, Esteban; Toro-Labbé, Alejandro

    2012-07-12

    Studying chemical reactions involves the knowledge of the reaction mechanism. Despite activation barriers describing the kinetics or reaction energies reflecting thermodynamic aspects, identifying the underlying physics and chemistry along the reaction path contributes essentially to the overall understanding of reaction mechanisms, especially for catalysis. In the past years the reaction force has evolved as a valuable tool to discern between structural changes and electrons' rearrangement in chemical reactions. It provides a framework to analyze chemical reactions and additionally a rational partition of activation and reaction energies. Here, we propose to separate these energies further in atomic contributions, which will shed new insights in the underlying reaction mechanism. As first case studies we analyze two intramolecular proton transfer reactions. Despite the atom based separation of activation barriers and reaction energies, we also assign the participation of each atom in structural changes or electrons' rearrangement along the intrinsic reaction coordinate. These participations allow us to identify the role of each atom in the two reactions and therfore the underlying chemistry. The knowledge of the reaction chemistry immediately leads us to suggest replacements with other atom types that would facilitate certain processes in the reaction. The characterization of the contribution of each atom to the reaction energetics, additionally, identifies the reactive center of a molecular system that unites the main atoms contributing to the potential energy change along the reaction path.

  15. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    Science.gov (United States)

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase.

  16. An environmental transfer hub for multimodal atom probe tomography.

    Science.gov (United States)

    Perea, Daniel E; Gerstl, Stephan S A; Chin, Jackson; Hirschi, Blake; Evans, James E

    2017-01-01

    Environmental control during transfer between instruments is required for samples sensitive to air or thermal exposure to prevent morphological or chemical changes prior to analysis. Atom probe tomography is a rapidly expanding technique for three-dimensional structural and chemical analysis, but commercial instruments remain limited to loading specimens under ambient conditions. In this study, we describe a multifunctional environmental transfer hub allowing controlled cryogenic or room-temperature transfer of specimens under atmospheric or vacuum pressure conditions between an atom probe and other instruments or reaction chambers. The utility of the environmental transfer hub is demonstrated through the acquisition of previously unavailable mass spectral analysis of an intact organic molecule made possible via controlled cryogenic transfer into the atom probe using the hub. The ability to prepare and transfer specimens in precise environments promises a means to access new science across many disciplines from untainted samples and allow downstream time-resolved in situ atom probe studies.

  17. The Unimolecular Reactions of CF3CHF2Studied 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.

  18. High-performance liquid chromatographic method to evaluate the hydrogen atom transfer during reaction between 1,1-diphenyl-2-picryl-hydrazyl radical and antioxidants

    Energy Technology Data Exchange (ETDEWEB)

    Boudier, Ariane; Tournebize, Juliana [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France); Bartosz, Grzegorz [Department of Molecular Biophysics, University of Lodz, Lodz (Poland); El Hani, Safae; Bengueddour, Rachid [Laboratoire de Nutrition et Sante, Biology Department, Faculty of Sciences, Ibn Tofail University, Kenitra (Morocco); Sapin-Minet, Anne [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France); Leroy, Pierre, E-mail: pierre.leroy@pharma.uhp-nancy.fr [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France)

    2012-01-20

    Highlights: Black-Right-Pointing-Pointer Both 1,1-diphenyl-2-picrylhydrazyl radical and its product measurement by HPLC. Black-Right-Pointing-Pointer Lowest limit of detection by monitoring 1,1-diphenyl-2-picryl-hydrazine. Black-Right-Pointing-Pointer Adsorption problem of the radical on HPLC parts have been pointed out. - Abstract: 1,1-Diphenyl-2-picrylhydrazyl (DPPH{center_dot}) is a stable nitrogen centred radical widely used to evaluate direct radical scavenging properties of various synthetic or natural antioxidants (AOs). The bleaching rate of DPPH{center_dot} absorbance at 515 nm is usually monitored for this purpose. In order to avoid the interference of complex coloured natural products used as antioxidant supplements or cosmetics, HPLC systems have been reported as alternative techniques to spectrophotometry. They also rely upon measurement of DPPH{center_dot} quenching rate and none of them permits to identify and measure 1,1-diphenyl-2-picryl-hydrazine (DPPH-H), the reduced product of DPPH{center_dot} resulting from hydrogen atom transfer (HAT), which is the main mechanism of the reaction between DPPH{center_dot} and AOs. We presently report an HPLC method devoted to the simultaneous measurement of DPPH{center_dot} and DPPH-H. Both were fully separated on a C18 column eluted with acetonitrile-10 mM ammonium citrate buffer pH 6.8 (70:30, v/v) and detected at 330 nm. Adsorption process of DPPH{center_dot} onto materials of the HPLC system was pointed out. Consequently, the linearity range observed for DPPH{center_dot} was restricted, thus a much lower limit of detection was obtained for DPPH-H than for DPPH{center_dot} using standards (0.02 and 14 {mu}M, respectively). The method was applied to three commonly used AOs, i.e. Trolox{sup Registered-Sign }, ascorbic acid and GSH, and compared with spectrophotometry. Further application to complex matrices (cell culture media, vegetal extracts) and nanomaterials demonstrated (i) its usefulness because of

  19. Transfer reactions in nuclear astrophysics

    Science.gov (United States)

    Bardayan, D. W.

    2016-08-01

    To a high degree many aspects of the large-scale behavior of objects in the Universe are governed by the underlying nuclear physics. In fact the shell structure of nuclear physics is directly imprinted into the chemical abundances of the elements. The tranquility of the night sky is a direct result of the relatively slow rate of nuclear reactions that control and determines a star’s fate. Understanding the nuclear structure and reaction rates between nuclei is vital to understanding our Universe. Nuclear-transfer reactions make accessible a wealth of knowledge from which we can extract much of the required nuclear physics information. A review of transfer reactions for nuclear astrophysics is presented with an emphasis on the experimental challenges and opportunities for future development.

  20. Hydride, hydrogen atom, proton, and electron transfer driving forces of various five-membered heterocyclic organic hydrides and their reaction intermediates in acetonitrile.

    Science.gov (United States)

    Zhu, Xiao-Qing; Zhang, Ming-Tian; Yu, Ao; Wang, Chun-Hua; Cheng, Jin-Pei

    2008-02-27

    weak one-electron oxidation agents. The energies of the intramolecular hydrogen bond in 3H, 3H+*, and 3* with a hydroxyl group at ortho-position on the 2-phenyl ring were estimated by using experimental method, the results disclose that the hydrogen bond energy is 3.2, 2.8-3.0, and 3.9-4.0 kcal/mol for 3H, 3H+*, and 3* in acetonitrile, respectively, which is favorable for hydrogen atom transfer but unfavorable for hydride transfer from 3H. The relative effective charges on the active center in ZH, ZH+*, Z*, and Z+, which is an efficient measurement of electrophilicity or nucleophilicity as well as dimerizing ability of a chemical species, were estimated by using experimental method; the results indicate that 1*-5* belong to electron-sufficient carbon-radicals, 6*-7* belong to electron-deficient carbon radicals, they are all difficult to dimerize, and that 1+-5+ belong to weak electrophilic agents, 6+-7+ belong to strong electrophilic agents. All these information disclosed in this work could not only supply a gap of the chemical thermodynamics of the five-membered heterocyclic compounds as organic hydride donors, but also strongly promote the fast development of the chemistry and applications of the five-membered heterocyclic organic hydrides.

  1. A New Global Potential Energy Surface for the Hydroperoxyl Radical, HO2: Reaction Coefficients for H + O2 and Vibrational Splittings for H Atom Transfer

    Science.gov (United States)

    Dateo, Christopher E.; Arnold, James O. (Technical Monitor)

    1994-01-01

    A new analytic global potential energy surface describing the hydroperoxyl radical system H((sup 2)S) + O2(X (sup 3)Sigma((sup -)(sub g))) (reversible reaction) HO2 ((X-tilde) (sup 2)A'') (reversible reaction) O((sup 3)P) + O H (X (sup 2)Pi) has been fitted using the ab initio complete active space SCF (self-consistent-field)/externally contracted configuration interaction (CASSCF/CCI) energy calculations of Walch and Duchovic. Results of quasiclassical trajectory studies to determine the rate coefficients of the forward and reverse reactions at combustion temperatures will be presented. In addition, vibrational energy levels were calculated using the quantum DVR-DGB (discrete variable representation-distributed Gaussian basis) method and the splitting due to H atom migration is investigated. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

  2. The coordination and atom transfer chemistry of titanium porphyrin complexes

    Energy Technology Data Exchange (ETDEWEB)

    Hays, James Allen [Iowa State Univ., Ames, IA (United States)

    1993-11-05

    Preparation, characterization, and reactivity of (η2- alkyne)(meso-tetratolylpoprphrinato)titanium(II) complexes are described, along with inetermetal oxygen atom transfer reactions involving Ti(IV) and Ti(III) porphyrin complexes. The η2- alkyne complexes are prepared by reaction of (TTP)TiCl2 with LiAlH4 in presence of alkyne. Structure of (OEP)Ti(η2-Ph-C≡C-Ph) (OEP=octaethylporphryin) was determined by XRD. The compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Structure of (TTP)Ti(4-picoline)2 was also determined by XRD. Reaction of (TTP)Ti=O with (OEP)Ti-Cl yields intermetal O/Cl exchange, which is a one-electron redox process mediated by O atom transfer. Also a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl2 is reacted with (OEP)Ti=O.

  3. Reactions of butadiyne. 1: The reaction with hydrogen atoms

    Science.gov (United States)

    Schwanebeck, W.; Warnatz, J.

    1984-01-01

    The reaction of hydrogen (H) atoms with butadiene (C4H2) was studied at room temperature in a pressure range between w mbar and 10 mbar. The primary step was an addition of H to C4H2 which is in its high pressure range at p 1 mbar. Under these conditions the following addition of a second H atom lies in the transition region between low and high pressure range. Vibrationally excited C4H4 can be deactivated to form buten-(1)-yne-(3)(C4H4) or decomposes into two C2H2 molecules. The rate constant at room temperature for primary step is given. The second order rate constant for the consumption of buten-(1)-yne-(3) is an H atom excess at room temperature is given.

  4. Recent Developments in Electron Transfer Reactions

    OpenAIRE

    Marcus, Rudolph A.

    1987-01-01

    Earlier results and more recent developments in electron transfer reactions are reviewed. The more recent results include inverted behavior, electronic orientation effects on reaction rates, solvent dynamics, early steps in photosynthesis, and light emission from metal electrodes.

  5. Thermally-generated reactive intermediates: Trapping of the parent ferrocene-based o-quinodimethane and reactions of diradicals generated by hydrogen-atom transfers

    Energy Technology Data Exchange (ETDEWEB)

    Ferguson, John Michael [Iowa State Univ., Ames, IA (United States)

    1993-09-01

    Ferrocenocyclobutene is prepared by flash vacuum pyrolysis (FVP) of the N-amino-2-phenylaziridine hydrazone of 2-methylferrocenealdehyde. In the second section of this dissertation, a series of hydrocarbon rearrangements were observed. FVP of o-allyltoluene at 0.1 Torr (700--900 C) gives 2-methylindan and indene, accompanied by o-propenyltoluene. FVP of 2-methyl-2`-vinylbiphenyl gives 9-methyl-9,10-dihydrophenanthrene, which fits the proposed mechanism. However, FVP of 2-(o-methylbenzyl)styrene gives mainly anthracene and 1-methylanthracene. This cyclization reaction was also successful with o-allylphenol and o-(2-methylallyl)phenol.

  6. Boron atom reactions with the halomethanes

    Science.gov (United States)

    Tabacco, M. B.; Stanton, C. T.; Sardella, D. J.; Davidovits, P.

    1985-12-01

    Rate constants have been measured for the reactions of boron atoms with a series of halomethanes. The experiments were performed in a linear flow tube apparatus at 300 K. The measured rate constants in units of cm3 molecule-1 s-1 are CCl4:9.5×10-11; CCl3H:4.8×10-11; CCl2H2:6.2×10-11; CClH3:1.4×10-11; CCl3F:3.1×10-11; CCl2F2:5.5×10-12; CClF3:1.7×10-13; CF4:explanations for the observed results.

  7. 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

  8. Structural and medium effects on the reactions of the cumyloxyl radical with intramolecular hydrogen bonded phenols. The interplay between hydrogen-bonding and acid-base interactions on the hydrogen atom transfer reactivity and selectivity.

    Science.gov (United States)

    Salamone, Michela; Amorati, Riccardo; Menichetti, Stefano; Viglianisi, Caterina; Bietti, Massimo

    2014-07-03

    A time-resolved kinetic study on the reactions of the cumyloxyl radical (CumO(•)) with intramolecularly hydrogen bonded 2-(1-piperidinylmethyl)phenol (1) and 4-methoxy-2-(1-piperidinylmethyl)phenol (2) and with 4-methoxy-3-(1-piperidinylmethyl)phenol (3) has been carried out. In acetonitrile, intramolecular hydrogen bonding protects the phenolic O-H of 1 and 2 from attack by CumO(•) and hydrogen atom transfer (HAT) exclusively occurs from the C-H bonds that are α to the piperidine nitrogen (α-C-H bonds). With 3 HAT from both the phenolic O-H and the α-C-H bonds is observed. In the presence of TFA or Mg(ClO4)2, protonation or Mg(2+) complexation of the piperidine nitrogen removes the intramolecular hydrogen bond in 1 and 2 and strongly deactivates the α-C-H bonds of the three substrates. Under these conditions, HAT to CumO(•) exclusively occurs from the phenolic O-H group of 1-3. These results clearly show that in these systems the interplay between intramolecular hydrogen bonding and Brønsted and Lewis acid-base interactions can drastically influence both the HAT reactivity and selectivity. The possible implications of these findings are discussed in the framework of the important role played by tyrosyl radicals in biological systems.

  9. Accurate atom-mapping computation for biochemical reactions.

    Science.gov (United States)

    Latendresse, Mario; Malerich, Jeremiah P; Travers, Mike; Karp, Peter D

    2012-11-26

    The complete atom mapping of a chemical reaction is a bijection of the reactant atoms to the product atoms that specifies the terminus of each reactant atom. Atom mapping of biochemical reactions is useful for many applications of systems biology, in particular for metabolic engineering where synthesizing new biochemical pathways has to take into account for the number of carbon atoms from a source compound that are conserved in the synthesis of a target compound. Rapid, accurate computation of the atom mapping(s) of a biochemical reaction remains elusive despite significant work on this topic. In particular, past researchers did not validate the accuracy of mapping algorithms. We introduce a new method for computing atom mappings called the minimum weighted edit-distance (MWED) metric. The metric is based on bond propensity to react and computes biochemically valid atom mappings for a large percentage of biochemical reactions. MWED models can be formulated efficiently as Mixed-Integer Linear Programs (MILPs). We have demonstrated this approach on 7501 reactions of the MetaCyc database for which 87% of the models could be solved in less than 10 s. For 2.1% of the reactions, we found multiple optimal atom mappings. We show that the error rate is 0.9% (22 reactions) by comparing these atom mappings to 2446 atom mappings of the manually curated Kyoto Encyclopedia of Genes and Genomes (KEGG) RPAIR database. To our knowledge, our computational atom-mapping approach is the most accurate and among the fastest published to date. The atom-mapping data will be available in the MetaCyc database later in 2012; the atom-mapping software will be available within the Pathway Tools software later in 2012.

  10. Hemoglobin and red blood cells catalyze atom transfer radical polymerization.

    Science.gov (United States)

    Silva, Tilana B; Spulber, Mariana; Kocik, Marzena K; Seidi, Farzad; Charan, Himanshu; Rother, Martin; Sigg, Severin J; Renggli, Kasper; Kali, Gergely; Bruns, Nico

    2013-08-12

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.

  11. Insights into the Hydrogen-Atom Transfer of the Blue Aroxyl.

    Science.gov (United States)

    Bächle, Josua; Marković, Marijana; Kelterer, Anne-Marie; Grampp, Günter

    2017-10-19

    An experimental and theoretical study on hydrogen-atom transfer dynamics in the hydrogen-bonded substituted phenol/phenoxyl complex of the blue aroxyl (2,4,6-tri-tert-butylphenoxyl) is presented. The experimental exchange dynamics is determined in different organic solvents from the temperature-dependent alternating line-width effect in the continuous-wave ESR spectrum. From bent Arrhenius plots, effective tunnelling contributions with parallel heavy-atom motion are concluded. To clarify the transfer mechanism, reaction paths for different conformers of the substituted phenol/phenoxyl complex are modelled theoretically. Various DFT and post-Hartree-Fock methods including multireference methods are applied. From the comparison of experimental and theoretical data it is concluded that the system favours concerted hydrogen-atom transfer along a parabolic reaction path caused by heavy-atom motion. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Understanding Hydrogen Atom Transfer: from Bond Strengths to Marcus Theory

    Science.gov (United States)

    MAYER, JAMES M.

    2010-01-01

    CONSPECTUS Hydrogen atom transfer (HAT) is one of the most fundamental chemical reactions: A–H + B → A + H–B. It is a key step in a wide range of chemical, environmental, and biological processes. Traditional HAT involves p-block radicals such as tBuO• abstracting H• from organic molecules. More recently, it has been recognized that many transition metal species undergo HAT. This has led to a broader perspective, with HAT viewed as one type of proton-coupled electron transfer (PCET). When transition metal complexes oxidize substrates by removing H• (≡ e– and H+), typically the electron transfers to the metal and the proton transfers to a ligand. Two examples are shown in the Figure: iron-imidazolinate and vanadium-oxo complexes. Although such reagents do not “look like” main group radicals, they have the same pattern of reactivity. For instance, their HAT rate constants parallel the A–H bond strengths within a series of similar reactions. Just like main group radicals, they abstract H• much faster from O–H bonds than from C–H bonds of the same strength. This shows that driving force is not the only determinant of reactivity. We have found that HAT reactivity is well described using a Marcus-theory approach. In the simplest model, the cross relation, kAH/B = (kAH/AkBH/BKeqf)½, predicts the rate constant for AH + B in terms of the self-exchange rate constants (kAH/A for AH + A) and the equilibrium constant. For a variety of transition metal oxidants, kAH/B is predicted within one or two orders of magnitude with only a few exceptions. For 36 organic reactions of oxyl radicals, kAH/B is predicted with an average deviation of a factor of 3.8, and within a factor of 5 for all but six of the reactions. These reactions involve both O–H or C–H bonds, occur either in water or organic solvents, and over a range of 1028 in Keq and 1013 in kAH/B. The treatment of organic reactions of O–H bonds includes the well-established kinetic solvent

  13. An environmental transfer hub for multimodal atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Perea, Daniel E.; Gerstl, Stephan S. A.; Chin, Jackson; Hirschi, Blake; Evans, James. E.

    2017-05-02

    Environmental control during transfer between instruments is required for specimens sensitive to air or thermal exposure to prevent morphological or chemical changes. Atom Probe Tomography is an expanding technique but commercial instruments remain limited to loading under ambient conditions. Here we describe a multifunctional environmental transfer hub allowing controlled cryogenic, atmospheric and vacuum transfer between an Atom Probe and other instruments containing separate chambers to allow downstream time-resolved in-situ studies.

  14. The pentafluorostyrene endeavours with atom transfer radical polymerization - quo vadis?

    DEFF Research Database (Denmark)

    Hvilsted, Søren

    2014-01-01

    The versatility of the atom transfer radical polymerization (ATRP) of pentafluorostyrene (FS) is comprehensively evaluated. The ATRP of a wide range of monomers derived from FS is likewise discussed with emphasis on the potential polymer applications. A large number of block and star copolymers...... centred around polypentafluorostyrene (PFS) and prepared primarily using the bromomacroinitiator concept is surveyed. Here the main emphasis is on the feasibility of the polymer design, but also the very many different applications are highlighted. The potential grafting onto PFS and PFS block copolymers...... by exploitation of the very labile para-fluorine demonstrates new material architecture possibilities through very mild reaction conditions. Finally the utility of PFS in various conducting materials is elaborated. The amphiphilic nature of PFS in triblock copolymers with polyethers has been exploited for Li+ ion...

  15. A crystalline singlet phosphinonitrene: a nitrogen atom-transfer agent.

    Science.gov (United States)

    Dielmann, Fabian; Back, Olivier; Henry-Ellinger, Martin; Jerabek, Paul; Frenking, Gernot; Bertrand, Guy

    2012-09-21

    A variety of transition metal-nitrido complexes (metallonitrenes) have been isolated and studied in the context of modeling intermediates in biological nitrogen fixation by the nitrogenase enzymes and the industrial Haber-Bosch hydrogenation of nitrogen gas into ammonia. In contrast, nonmetallic nitrenes have so far only been spectroscopically observed at low temperatures, despite their intermediacy in a range of organic reactions. Here, we report the synthesis of a bis(imidazolidin-2-iminato)phosphinonitrene, which is stable at room temperature in solution and can even be isolated in the solid state. The bonding between phosphorus and nitrogen is analogous to that observed for metallonitrenes. We also show that this nitrido phosphorus derivative can be used to transfer a nitrogen atom to organic fragments, a difficult task for transition metal-nitrido complexes.

  16. Hydrogen-atom transfer in reactions of organic radicals with [Co-II(por)](center dot) (por = porphyrinato) and in subsequent addition of [Co(H)(por)] to olefins

    NARCIS (Netherlands)

    de Bruin, B.; Dzik, W.I.; Li, S.; Wayland, B.B.

    2009-01-01

    The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical C-center dot(CH3)(2)CN to [Co-II(por)](center dot) (yielding [Co-III(H)(por)] and CH2=C(CH3)(CN); por = porphyrinato) and the insertion of vinyl acetate (CH2=CHOAc) into the Co-H bond of [Co(H)(por)] (giving

  17. Mechanism of electron transfer reaction of ternary ...

    Indian Academy of Sciences (India)

    The rate of the reaction increases with increasing pH due to the deprotonation equilibria of the complex. The experimental rate law is consistent with a mechanism in which the deprotonated form [CrIII(DPA)(OX)(OH)]2− is more reactive than the conjugated acid. It is proposed that electron transfer proceeds through an ...

  18. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    Science.gov (United States)

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  19. Molecular beam studies of hot atom chemical reactions: Reactive scattering of energetic deuterium atoms

    Energy Technology Data Exchange (ETDEWEB)

    Continetti, R.E.; Balko, B.A.; Lee, Y.T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H/sub 2/ /minus/> DH + H and the substitution reaction D + C/sub 2/H/sub 2/ /minus/> C/sub 2/HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs.

  20. Single-Atom Catalysts of Precious Metals for Electrochemical Reactions.

    Science.gov (United States)

    Kim, Jiwhan; Kim, Hee-Eun; Lee, Hyunjoo

    2018-01-10

    Single-atom catalysts (SACs), in which metal atoms are dispersed on the support without forming nanoparticles, have been used for various heterogeneous reactions and most recently for electrochemical reactions. In this Minireview, recent examples of single-atom electrocatalysts used for the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), hydrogen evolution reaction (HER), formic acid oxidation reaction (FAOR), and methanol oxidation reaction (MOR) are introduced. Many density functional theory (DFT) simulations have predicted that SACs may be effective for CO 2 reduction to methane or methanol production while suppressing H 2 evolution, and those cases are introduced here as well. Single atoms, mainly Pt single atoms, have been deposited on TiN or TiC nanoparticles, defective graphene nanosheets, N-doped covalent triazine frameworks, graphitic carbon nitride, S-doped zeolite-templated carbon, and Sb-doped SnO 2 surfaces. Scanning transmission electron microscopy, extended X-ray absorption fine structure measurement, and in situ infrared spectroscopy have been used to detect the single-atom structure and confirm the absence of nanoparticles. SACs have shown high mass activity, minimizing the use of precious metal, and unique selectivity distinct from nanoparticle catalysts owing to the absence of ensemble sites. Additional features that SACs should possess for effective electrochemical applications were also suggested. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Reactions the private life of atoms

    CERN Document Server

    Atkins, Peter

    2011-01-01

    Through an innovative, closely integrated design of images and text, and his characteristically clear, precise, and economical exposition, Peter Atkins explains the processes involved in chemical reactions. He begins by introducing a 'tool kit' of basic reactions, such as precipitation, corrosion, and catalysis, and concludes by showing how these building blocks are brought together in more complex processes such as photosynthesis.

  2. Signatures of a quantum diffusion limited hydrogen atom tunneling reaction.

    Science.gov (United States)

    Balabanoff, Morgan E; Ruzi, Mahmut; Anderson, David T

    2017-12-20

    We are studying the details of hydrogen atom (H atom) quantum diffusion in highly enriched parahydrogen (pH 2 ) quantum solids doped with chemical species in an effort to better understand H atom transport and reactivity under these conditions. In this work we present kinetic studies of the 193 nm photo-induced chemistry of methanol (CH 3 OH) isolated in solid pH 2 . Short-term irradiation of CH 3 OH at 1.8 K readily produces CH 2 O and CO which we detect using FTIR spectroscopy. The in situ photochemistry also produces CH 3 O and H atoms which we can infer from the post-photolysis reaction kinetics that display significant CH 2 OH growth. The CH 2 OH growth kinetics indicate at least three separate tunneling reactions contribute; (i) reactions of photoproduced CH 3 O with the pH 2 host, (ii) H atom reactions with the CH 2 O photofragment, and (iii) long-range migration of H atoms and reaction with CH 3 OH. We assign the rapid CH 2 OH growth to the following CH 3 O + H 2 → CH 3 OH + H → CH 2 OH + H 2 two-step sequential tunneling mechanism by conducting analogous kinetic measurements using deuterated methanol (CD 3 OD). By performing photolysis experiments at 1.8 and 4.3 K, we show the post-photolysis reaction kinetics change qualitatively over this small temperature range. We use this qualitative change in the reaction kinetics with temperature to identify reactions that are quantum diffusion limited. While these results are specific to the conditions that exist in pH 2 quantum solids, they have direct implications on the analogous low temperature H atom tunneling reactions that occur on metal surfaces and on interstellar grains.

  3. Theoretical studies on proton transfer reaction of 3(5)-substituted ...

    Indian Academy of Sciences (India)

    Abstract. The inter and intra molecular proton transfer reactions of a series of pyrazole derivatives have been studied by using density functional theory (DFT) and MP2 methods implementing 6-311++G(d,p) atomic basis set. The substituents have been selected to cover a wide range of electronic effects. Proton transfer ...

  4. Charge transfer for slow H atoms interacting with Al: Atomic levels and linewidths

    Science.gov (United States)

    Merino, J.; Lorente, N.; Pou, P.; Flores, F.

    1996-10-01

    The charge transfer of slow H atoms colliding with an Al(100) surface is studied by means of a linear combination of atomic orbitals method with local-density many-body contributions. The method is developed in order to calculate atomic levels and associated linewidths. Unlike previous theories, the present method is able to study the effect of the corrugation of the surface, together with the self-consistent potentials involved. This leads to a shift of atomic levels nonlinear on the external charge, contrary to the traditionally assumed image shift. The method works best at very short distances, where the strong coupling between atom and surface promotes molecular orbitals. Thus, the theory expounded in this work can describe the charge-transfer processes of systems in which the atomic levels are near the band edges, as protons scattered off aluminum.

  5. Atomic structure of clusters through chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Riley, S.J.

    1991-01-01

    Techniques for the probing of isolated metal cluster structure through adsorbate binding patterns will be described. The saturation of clusters with reagents such as ammonia and nitrogen provides information on the number of preferred binding sites for these reagents. The dependence of this number on cluster size can suggest particular structural themes. The equilibrium reaction with water can be used to identify cluster sizes having especially enhanced binding for the water molecule. Again, the sequence of cluster sizes showing such enhancement can point to specific cluster structure. The reaction with oxygen can identify cluster sizes having particularly high ionization potentials, and these can be compared to simple models for the electronic structure of metal clusters. Representative applications of these probes to iron, cobalt, nickel, and copper clusters will be discussed. 5 figs.

  6. Atom-Transfer Radical Addition to Unactivated Alkenes by using Heterogeneous Visible-Light Photocatalysis.

    Science.gov (United States)

    Mao, Liang-Liang; Cong, Huan

    2017-11-23

    Heterogeneous visible-light photocatalysis represents an important route toward the development of sustainable organic synthesis. In this study visible light-induced, heavy metal-free atom-transfer radical addition to unactivated terminal olefins is carried out by using the combination of heterogeneous titanium dioxide as photocatalyst and a hypervalent iodine(III) reagent as co-initiator. The reaction can be applied to a range of substrates with good functional-group tolerance under very mild conditions. In addition to a number of commonly used atom-transfer reagents, the relatively challenging chloroform is also suitable. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. The reactions of ground and excited state sodium atoms with hydrogen halide molecules

    Science.gov (United States)

    Weiss, P. S.; Mestdagh, J. M.; Covinsky, M. H.; Balko, B. A.; Lee, Y. T.

    1988-10-01

    The reactions of ground and excited state Na atoms with hydrogen halide (HX) molecules have been studied using the crossed molecular beams method. With both increasing translational and increasing electronic energy, the reactive cross sections increase in the reactions of HCl and HBr. From product angular and velocity distributions detailed center-of-mass information is derived. For the reactions of Na (3 2S 1/2, 3 2P 1/2, 4 2D 5/2, 5 2S 1/2) with HCl, the product NaCl is back-scattered with respect to the incoming Na atom in the center-of-mass frame of reference. The reaction of each Na state studied with HCl is direct and proceeds via collinear and near-collinear Na-Cl-H approach geometries. For the Na (3 2P 3/2) and Na (4 2D 5/2) reactions with HCl the predominant transition state symmetry is 2Σ in a collinear (C ∞ν) Na-Cl-H geometry. This is consistent with the reaction proceeding via electron transfer from the Na atom to the halide atom. Absolute reactive cross sections for each state of Na studied with HCl were determined by comparison with both small and large angle elastic scattering. We were unable to observe Na atoms with over 4 eV of electronic energy react with HF up to collision energies of 13 kcal/mole.

  8. Reactions of chlorine atoms with a series of aromatic hydrocarbons.

    Science.gov (United States)

    Wang, Lin; Arey, Janet; Atkinson, Roger

    2005-07-15

    Aromatic hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), are present in urban and rural atmospheres. Reactions of PAHs with Cl atoms may occur in the marine boundary layer and in coastal regions. To assess the importance of these reactions and to investigate whether any unique chlorine-containing products are formed from these reactions, we have measured the rate constants for the gas-phase reactions of Cl atoms with toluene-d8, 1,3,5-trimethylbenzene (1,3,5-TMB), naphthalene, 1-methylnaphthalene-d10 (1-MN-d10), 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the dimethylnaphthalenes (DMNs) at 296 +/- 2 K. A relative rate technique was used, and, using our measured rate constant forthe reaction of Cl atoms with 1,3,5-TMB of 2.42 x 10(-10) cm3 molecule(-1) s(-1), the rate constants (in units of 10(-10) cm3 molecule(-1) s(-1)) are as follows: naphthalene, isotope effects for the toluene-d8 and 1-MN-d10 reactions indicate that the reactions proceed by initial H- (or D-) atom abstraction. The products identified and quantified from the toluene and 1-MN reactions using gas chromatography and in situ direct air sampling atmospheric pressure ionization tandem mass spectrometry were benzaldehyde (84% +/- 7% yield) and benzyl alcohol (11% +/- 2% yield) from toluene and 1-naphthaldehyde (approximately 36%, lower limit to yield) and 1-naphthyl alcohol (approximately 12%, lower limit to yield) from 1-MN. These products confirm that H-atom abstraction is the dominant, if not sole, reaction pathway for the alkylbenzenes and alkylnaphthalenes, consistent with the 100-fold lower rate constant measured for naphthalene compared to the alkylnaphthalenes and with the measured deuterium isotope effects.

  9. Reactions of carbon atoms in pulsed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Reisler, H. [Univ. of Southern California, Los Angeles (United States)

    1993-12-01

    This research program consists of a broad scope of experiments designed to unravel the chemistry of atomic carbon in its two spin states, P and D, by using well-controlled initial conditions and state-resolved detection of products. Prerequisite to the proposed studies (and the reason why so little is known about carbon atom reactions), is the development of clean sources of carbon atoms. Therefore, in parallel with the studies of its chemistry and reaction dynamics, the authors continuously explore new, state-specific and efficient ways of producing atomic carbon. In the current program, C({sup 3}P) is produced via laser ablation of graphite, and three areas of study are being pursued: (i) exothermic reactions with small inorganic molecules (e.g., O{sub 2}, N{sub 2}O, NO{sub 2}) that can proceed via multiple pathways; (ii) the influence of vibrational and translational energy on endothermic reactions involving H-containing reactants that yield CH products (e.g., H{sub 2}O H{sub 2}CO); (iii) reactions of C({sup 3}P) with free radicals (e.g., HCO, CH{sub 3}O). In addition, the authors plan to develop a source of C({sup 1}D) atoms by exploiting the pyrolysis of diazotetrazole and its salts in the ablation source. Another important goal involves collaboration with theoreticians in order to obtain relevant potential energy surfaces, rationalize the experimental results and predict the roles of translational and vibrational energies.

  10. 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...... statistics and a simple post-sampling scheme used to generate free energy surfaces - which compare to full ab initio calculations. In the last part both the molecular dynamics and hybrid classical and quantum mechanics method are used to generate a vast data set for the accurate analysis of dynamical...... 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...

  11. Living atom transfer radical polymerization of 4-acetoxystyrene

    DEFF Research Database (Denmark)

    Gao, Bo; Chen, Xianyi; Ivan, Bela

    1997-01-01

    Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine(bpy) as initi......Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine...

  12. The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux

    Energy Technology Data Exchange (ETDEWEB)

    Cortés-Arriagada, Diego, E-mail: dcortesr@uc.cl; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro [Nucleus Millennium Chemical Processes and Catalysis, Laboratorio de Química Teórica Computacional (QTC), Departamento de Química-Física, Facultad de Química, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, Santiago (Chile)

    2014-10-07

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp{sup 3} hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state.

  13. International atomic time and time transfer

    Science.gov (United States)

    Lewandowski, Wlodzimierz

    Global Navigation Satellite Systems (GNSS) keep a central role in the international timekeeping. American Global Positioning System (GPS) is a navigation system that has proven itself to be a reliable source of positioning for both the military community and the civilian community. But, little known by many, is the fact that GPS has proven itself to be an important and valuabe utility to the timekeeping community (Lewandowski et al. 1999). GPS is a versatile and global tool which can be used to both distribute time to an arbitrary number of users and synchronise clocks over large distances with a high degree of precision and accuracy. Similar performance can be obtained with Russian Global Navigation Satellite System (GLONASS). It is expected in the near future satellites of a new European navigation system GALILEO might bring some important opportunities for international timekeeping. This paper after a brief introduction to international timekeeping focuses on the description of recent progress in time transfer techniques using GNSS satellites.

  14. ReactionMap: an efficient atom-mapping algorithm for chemical reactions.

    Science.gov (United States)

    Fooshee, David; Andronico, Alessio; Baldi, Pierre

    2013-11-25

    Large databases of chemical reactions provide new data-mining opportunities and challenges. Key challenges result from the imperfect quality of the data and the fact that many of these reactions are not properly balanced or atom-mapped. Here, we describe ReactionMap, an efficient atom-mapping algorithm. Our approach uses a combination of maximum common chemical subgraph search and minimization of an assignment cost function derived empirically from training data. We use a set of over 259,000 balanced atom-mapped reactions from the SPRESI commercial database to train the system, and we validate it on random sets of 1000 and 17,996 reactions sampled from this pool. These large test sets represent a broad range of chemical reaction types, and ReactionMap correctly maps about 99% of the atoms and about 96% of the reactions, with a mean time per mapping of 2 s. Most correctly mapped reactions are mapped with high confidence. Mapping accuracy compares favorably with ChemAxon's AutoMapper, versions 5 and 6.1, and the DREAM Web tool. These approaches correctly map 60.7%, 86.5%, and 90.3% of the reactions, respectively, on the same data set. A ReactionMap server is available on the ChemDB Web portal at http://cdb.ics.uci.edu .

  15. Nonradiative charge transfer in collisions of protons with rubidium atoms

    Science.gov (United States)

    Yan, Ling-Ling; Qu, Yi-Zhi; Liu, Chun-Hua; Zhang, Yu; Wang, Jian-Guo; Buenker, Robert J.

    2012-06-01

    The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV-10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

  16. Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer.

    Science.gov (United States)

    Anglada, Josep M; Crehuet, Ramon; Adhikari, Sarju; Francisco, Joseph S; Xia, Yu

    2018-02-14

    Hydropersulfides (RSSH) are highly reactive as nucleophiles and hydrogen atom transfer reagents. These chemical properties are believed to be key for them to act as antioxidants in cells. The reaction involving the radical species and the disulfide bond (S-S) in RSSH, a known redox-active group, however, has been scarcely studied, resulting in an incomplete understanding of the chemical nature of RSSH. We have performed a high-level theoretical investigation on the reactions of the hydroxyl radical (˙OH) toward a set of RSSH (R = -H, -CH 3 , -NH 2 , -C(O)OH, -CN, and -NO 2 ). The results show that S-S cleavage and H-atom abstraction are the two competing channels. The electron inductive effect of R induces selective ˙OH substitution at one sulfur atom upon S-S cleavage, forming RSOH and ˙SH for the electron donating groups (EDGs), whereas producing HSOH and ˙SR for the electron withdrawing groups (EWGs). The H-Atom abstraction by ˙OH follows a classical hydrogen atom transfer (hat) mechanism, producing RSS˙ and H 2 O. Surprisingly, a proton-coupled electron transfer (pcet) process also occurs for R being an EDG. Although for RSSH having EWGs hat is the leading channel, S-S cleavage can be competitive or even dominant for the EDGs. The overall reactivity of RSSH toward ˙OH attack is greatly enhanced with the presence of an EDG, with CH 3 SSH being the most reactive species found in this study (overall rate constant: 4.55 × 10 12 M -1 s -1 ). Our results highlight the complexity in RSSH reaction chemistry, the extent of which is closely modulated by the inductive effect of the substituents in the case of the oxidation by hydroxyl radicals.

  17. Concerted hydrogen atom and electron transfer mechanism for catalysis by lysine-specific demethylase.

    Science.gov (United States)

    Yu, Tao; Higashi, Masahiro; Cembran, Alessandro; Gao, Jiali; Truhlar, Donald G

    2013-07-18

    We calculate the free energy profile for the postulated hydride transfer reaction mechanism for the catalysis of lysine demethylation by lysine-specific demethylase LSD1. The potential energy surface is obtained by using combined electrostatically embedded multiconfiguration molecular mechanics (EE-MCMM) and single-configuration molecular mechanics (MM). We employ a constant valence bond coupling term to obtain analytical energies and gradients of the EE-MCMM subsystem, which contains 45 quantum mechanics (QM) atoms and which is parametrized with density functional calculations employing specific reaction parameters obtained by matching high-level wave function calculations. In the MM region, we employ the Amber ff03 and TIP3P force fields. The free energy of activation at 300 K is calculated by molecular dynamics (MD) umbrella sampling on a system with 102,090 atoms as the maximum of the free energy profile along the reaction coordinate as obtained by the weighted histogram analysis method with 17 umbrella sampling windows. This yields a free energy of activation of only 10 kcal/mol, showing that the previously postulated direct hydride transfer reaction mechanism is plausible, although we find that it is better interpreted as a concerted transfer of a hydrogen atom and an electron.

  18. High performance platinum single atom electrocatalyst for oxygen reduction reaction

    Science.gov (United States)

    Liu, Jing; Jiao, Menggai; Lu, Lanlu; Barkholtz, Heather M.; Li, Yuping; Wang, Ying; Jiang, Luhua; Wu, Zhijian; Liu, Di-Jia; Zhuang, Lin; Ma, Chao; Zeng, Jie; Zhang, Bingsen; Su, Dangsheng; Song, Ping; Xing, Wei; Xu, Weilin; Wang, Ying; Jiang, Zheng; Sun, Gongquan

    2017-07-01

    For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm-2 at 80 °C with a low platinum loading of 0.09 mgPt cm-2, corresponding to a platinum utilization of 0.13 gPt kW-1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.

  19. High performance platinum single atom electrocatalyst for oxygen reduction reaction

    Science.gov (United States)

    Liu, Jing; Jiao, Menggai; Lu, Lanlu; Barkholtz, Heather M.; Li, Yuping; Wang, Ying; Jiang, Luhua; Wu, Zhijian; Liu, Di-jia; Zhuang, Lin; Ma, Chao; Zeng, Jie; Zhang, Bingsen; Su, Dangsheng; Song, Ping; Xing, Wei; Xu, Weilin; Wang, Ying; Jiang, Zheng; Sun, Gongquan

    2017-01-01

    For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm−2 at 80 °C with a low platinum loading of 0.09 mgPt cm−2, corresponding to a platinum utilization of 0.13 gPt kW−1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction. PMID:28737170

  20. Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

    Directory of Open Access Journals (Sweden)

    Fabrice Chemla

    2013-02-01

    Full Text Available The formation of alkylidenezinc carbenoids by 1,4-addition/carbozincation of dialkylzincs or alkyl iodides based on zinc atom radical transfer, in the presence of dimethylzinc with β-(propargyloxyenoates having pendant iodo- and bromoalkynes, is disclosed. Formation of the carbenoid intermediate is fully stereoselective at −30 °C and arises from a formal anti-selective carbozincation reaction. Upon warming, the zinc carbenoid is stereochemically labile and isomerizes to its more stable form.

  1. Electron transfer processes of atomic and molecular doubly charged ions: information from beam experiments

    Science.gov (United States)

    Herman, Zdenek

    2013-07-01

    Single-electron transfer reactions in collisions of atomic and molecular doubly charged ions, with atoms and molecules, were investigated in a series of crossed-beam scattering, translational spectroscopy and product luminescence experiments. Investigation of a series of atomic dication-atom electron transfer at collision energies of 0.1-10 eV provided data on differential and relative total cross sections of state-to-state processes. Populations of electronic and vibrational states and rotational temperatures of molecular product ions were obtained from studies of non-dissociative electron transfer in systems containing simple molecular dications and/or molecular targets. The product electronic states populated with highest probability were those for which the translational energy release was 3-5 eV, indicating that the 'reaction window' concept, based on the Landau-Zener formalism, is applicable also to molecular systems. Population of the vibrational states of the molecular products could be described by Franck-Condon factors of the vertical transitions between the reactant and product states, especially at higher (keV) collision energies. Rotational temperature of the product molecular cations was found to be surprisingly low, mostly 400-500 K, practically the temperature of the ion source.

  2. Efficient inter-trap transfer of cold francium atoms

    Science.gov (United States)

    Zhang, J.; Collister, R.; Shiells, K.; Tandecki, M.; Aubin, S.; Behr, J. A.; Gomez, E.; Gorelov, A.; Gwinner, G.; Orozco, L. A.; Pearson, M. R.; Zhao, Y.

    2016-12-01

    We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

  3. Efficient inter-trap transfer of cold francium atoms

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J. [University of Maryland and National Institute of Standards and Technology, Department of Physics, Joint Quantum Institute (United States); Collister, R.; Shiells, K. [University of Manitoba, Department of Physics and Astronomy (Canada); Tandecki, M. [TRIUMF (Canada); Aubin, S., E-mail: saaubi@wm.edu [College of William and Mary, Department of Physics (United States); Behr, J. A. [TRIUMF (Canada); Gomez, E. [Universidad Autónoma de San Luis Potosí, Instituto de Física (Mexico); Gorelov, A. [TRIUMF (Canada); Gwinner, G. [University of Manitoba, Department of Physics and Astronomy (Canada); Orozco, L. A. [University of Maryland and National Institute of Standards and Technology, Department of Physics, Joint Quantum Institute (United States); Pearson, M. R. [TRIUMF (Canada); Zhao, Y. [Shanxi University, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy (China)

    2016-12-15

    We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

  4. Transfer reaction experiments with radioactive beams: from halos to the r-process

    CERN Document Server

    Jones, Kate L

    2013-01-01

    Transfer reactions are a powerful probe of the properties of atomic nuclei. When used in inverse kinematics with radioactive ion beams they can provide detailed information on the structure of exotic nuclei and can inform nucleosynthesis calculations. There are a number of groups around the world who use these reactions, usually with particle detection in large silicon arrays. Sometimes these arrays are coupled to gamma-ray detectors, and occasionally smaller arrays of silicon detectors are mounted within a solenoid magnet. Modern techniques using transfer reactions in inverse kinematics are covered, with specific examples, many from measurements made with beams from the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory.

  5. SSM atomic oxygen reactions on Kapton and silverized Teflon

    Science.gov (United States)

    Linton, R.; Whitaker, A.

    1985-01-01

    Surface morphology studies using scanning electron microscopy on Kapton and Inconel silver coated Teflon material samples retrieved from the Solar Maximum Mission spacecraft revealed significant changes attributed to orbital atomic oxygen induced reactions. The Kapton recession observed on the aluminized Kapton material samples appeared equivalent in nature with that observed on previous Space Shuttle LEO missions. SSM Teflon taped material samples, coated on the back side with films of Inconel protected silver were observed degraded on both sides. Visibly severe reactions on the back side produced total blackening, generally restricted to areas of tape with a narrow direct view-factor of the external orbital environment. High magnification scanning electron microscope views provided evidence of near total silver reaction, flaking, and subsequent erosion of the underlying Teflon itself. Only three of the extensive S.E.M. photographs illustrating the basic reactions observed are included pending further detailed investigations.

  6. Reaction dynamics of electronically excited alkali atoms with simple molecules

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, P.S.; Mestdagh, J.; Schmidt, H.; Vernon, M.F. Covinsky, M.H.; Balko, B.A.; Lee, Y.T.

    1985-09-01

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(3/sup 2/P/sub 3/2/,4/sup 2/D/sub 5/2/, and 5/sup 2/S/sub 1/2) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions.

  7. Reaction dynamics of electronically excited alkali atoms with simpler molecules

    Science.gov (United States)

    Weiss, P. S.; Mestdagh, J. M.; Schmidt, H.; Vernon, M. F.; Covinsky, M. H.; Balko, B. A.; Lee, Y. T.

    1985-05-01

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(3(2)P(sub 3/2), 4(2)D(sub 5/2), and 5(2)S(sub 1/2) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions.

  8. Investigating the role of atomic hydrogen on chloroethene reactions with iron using tafel analysis and electrochemical impedance spectroscopy.

    Science.gov (United States)

    Wang, Jiankang; Farrell, James

    2003-09-01

    Metallic iron filings are commonly employed as reducing agents in permeable barriers used for remediating groundwater contaminated by chlorinated solvents. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination. Experiments simultaneously measuring dechlorination and iron corrosion rates were performed to determine the fractions of the total current going toward dechlorination and hydrogen evolution. Corrosion rates were determined using Tafel analysis, and dechlorination rates were determined from rates of byproduct generation. Electrochemical impedance spectroscopy (EIS) was used to determine the number of reactions that controlled the observed rates of chlorocarbon disappearance, as well as the role of atomic hydrogen in TCE and PCE reduction. Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. At low pH values and micromolar concentrations, TCE reaction rates were faster than those for PCE due to more rapid reduction of TCE by atomic hydrogen. At neutral pH values and millimolar concentrations, PCE reaction rates were faster than those for TCE. This shift in relative reaction rates was attributed to a decreasing contribution of the atomic hydrogen reaction mechanism with increasing halocarbon concentrations and pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Results from this study show that differences in relative reaction rates of TCE and PCE with iron are dependent on the significance of the reduction pathway involving atomic hydrogen.

  9. Hemoglobin and Red Blood Cells Catalyze Atom Transfer Radical Polymerization

    OpenAIRE

    Silva Tilana B.; Spulber Mariana; Kocik Marzena K.; Seidi Farzad; Charan Himanshu; Rother Martin; Sigg Severin J.; Renggli Kasper; Kali Gergely; Bruns Nico

    2013-01-01

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity i.e. they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N isopropylacrylamide (NIPAAm) poly(ethylene glycol) methyl ether acrylate (PEGA) and poly(ethylene glycol) methyl eth...

  10. Single-collision studies of energy transfer and chemical reaction

    Energy Technology Data Exchange (ETDEWEB)

    Valentini, J.J. [Columbia Univ., New York, NY (United States)

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  11. Symmetric large momentum transfer for atom interferometry with BECs

    Science.gov (United States)

    Abend, Sven; Gebbe, Martina; Gersemann, Matthias; Rasel, Ernst M.; Quantus Collaboration

    2017-04-01

    We develop and demonstrate a novel scheme for a symmetric large momentum transfer beam splitter for interferometry with Bose-Einstein condensates. Large momentum transfer beam splitters are a key technique to enhance the scaling factor and sensitivity of an atom interferometer and to create largely delocalized superposition states. To realize the beam splitter, double Bragg diffraction is used to create a superposition of two symmetric momentum states. Afterwards both momentum states are loaded into a retro-reflected optical lattice and accelerated by Bloch oscillations on opposite directions, keeping the initial symmetry. The favorable scaling behavior of this symmetric acceleration, allows to transfer more than 1000 ℏk of total differential splitting in a single acceleration sequence of 6 ms duration while we still maintain a fraction of approx. 25% of the initial atom number. As a proof of the coherence of this beam splitter, contrast in a closed Mach-Zehnder atom interferometer has been observed with up to 208 ℏk of momentum separation, which equals a differential wave-packet velocity of approx. 1.1 m/s for 87Rb. The presented work is supported by the CRC 1128 geo-Q and the DLR with funds provided by the Federal Ministry of Economic Affairs and Energy (BMWi) due to an enactment of the German Bundestag under Grant No. DLR 50WM1552-1557 (QUANTUS-IV-Fallturm).

  12. The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Hongtao [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-12-01

    This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O2. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO2 + Na and NaO + NaO. NaO2 products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O2, which is likely a result of a charge transfer from Na2 to the excited state orbital of O2-. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH3 and Na(CH3OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

  13. Reaction of iodine atoms with submicrometer squalane and squalene droplets: mechanistic insights into heterogeneous reactions.

    Science.gov (United States)

    Popolan-Vaida, Denisia M; Wilson, Kevin R; Leone, Stephen R

    2014-11-13

    The gas-phase reaction of iodine atoms with hydrocarbon molecules is energetically unfavorable, and there is no direct evidence for iodinated product formation by either H abstraction or I addition reactions at ambient temperature. Here we consider the possible heterogeneous reaction of I atoms with submicrometer droplets composed of a saturated alkane, squalane (Sq), and an unsaturated alkene, squalene (Sqe). The investigations are performed in an atmospheric pressure photochemical flow tube reactor in conjunction with a vacuum ultraviolet photoionization aerosol mass spectrometer and a scanning mobility particle sizer. Squalane, a branched alkane, is unreactive toward I atoms within the signal-to-noise, and an upper limit of the effective reactive uptake coefficient is estimated to be γI(Sq) ≤ 8.58 × 10(–7). In contrast, the reaction of I atoms with unsaturated submicrometer squalene droplets results in observable iodinated squalene products. The effective reactive uptake coefficient of I atom with squalene particles is determined to be γI(Sqe) = (1.20 ± 0.52) × 10(–4) at an average I concentration of 1.5 × 10(14) molecules·cm(–3).

  14. Nitrogen Atom Transfer From High Valent Iron Nitrides

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Michael D. [New Mexico State Univ., Las Cruces, NM (United States); Smith, Jeremy M. [Indiana Univ., Bloomington, IN (United States)

    2015-10-14

    This report describes the synthesis and reactions of high valent iron nitrides. Organonitrogen compounds such as aziridines are useful species for organic synthesis, but there are few efficient methods for their synthesis. Using iron nitrides to catalytically access these species may allow for their synthesis in an energy-and atom-efficient manner. We have developed a new ligand framework to achieve these goals as well as providing a method for inducing previously unknown reactivity.

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

    Indian Academy of Sciences (India)

    [PVIVW11O40]5- and [PVIVVVW10O40]6-. Oxygraph measurements show that there is no uptake of molecular oxygen during the course of reaction. The reaction proceeds through multi-step electron-proton-electron transfer mechanism, with rate limiting initial one electron transfer from NADH to HPA by outer sphere ...

  16. Heavy ion transfer reactions: Status and perspectives

    Indian Academy of Sciences (India)

    2015-11-27

    array (CLARA), extensive investigations of nuclear structure and reaction dynamics have been carried out. In the present paper aspects of these studies will be presented, focussing more closely on the reaction mechanism, ...

  17. Excited state intramolecular charge transfer reaction in non-aqueous ...

    Indian Academy of Sciences (India)

    concentration dependent reaction rate constant of a. TICT reaction already measured in bulk electrolyte solutions.44–46 Here, we report such a study where photo-induced intramolecular charge transfer reaction has been investigated in AOT/heptane non-aqueous reverse micelles at different Ws values, and also in.

  18. Studies on electron transfer reactions: Reduction of heteropoly 10 ...

    Indian Academy of Sciences (India)

    Rates of electron transfer reaction of thioglycolic acid with vanadium(V) substituted Keggintype heteropolyanion, [PVVVVW10O40]5-, in acetate-acetic acid buffers have been measured spectrophotometrically at 25°C. The order of the reaction with respect to substrate and oxidant is unity. The reaction shows simple second ...

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

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several.

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

    Indian Academy of Sciences (India)

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other ...

  1. Intramolecular Halogen Atom Coordinated H Transfer via Ion-Neutral Complex in the Gas Phase Dissociation of Protonated Dichlorvos Derivatives

    Science.gov (United States)

    Zhang, Xiaoping; Cheng, Shuai

    2017-10-01

    Intramolecular halogen atom coordinated H transfer reaction in the gas phase dissociation of protonated dichlorvos derivatives has been explored by electrospray ionization tandem mass spectrometry. Upon collisional activation, protonated dichlorvos underwent dissociation reaction via cleavage of the P-O bond to give reactive ion-neutral complex (INC) intermediate, [dimethoxylphosphinoylium + dichloroacetaldehyde]. Besides direct dissociation of the complex, intramolecular chlorine atom coordinated H transfer reaction within the complex takes place, leading to the formation of protonated dimethyl chlorophosphate. To investigate the fragmentation mechanism, deuterium-labeled experiments and several other halogen-substituted (Br and F) analogs of dichlorvos were prepared and evaluated, which display a similar intramolecular halogen transfer. Density functional theory (DFT)-based calculations were performed and the computational results also support the mechanism. [Figure not available: see fulltext.

  2. Dynamics of competitive reactions: endothermic proton transfer and exothermic substitution.

    Science.gov (United States)

    Ren, Jianhua; Brauman, John I

    2004-03-03

    Dynamics of an endothermic proton-transfer reaction, F(-) with dimethyl sulfoxide, and an endothermic proton-transfer reaction with a competing exothermic substitution (S(N)2) channel, F(-) with borane-methyl sulfide complex, were investigated using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR) and kinetic modeling. The two proton-transfer reactions have slightly positive and a small negative overall free energy changes, respectively. Energy-dependent rate constants were measured as a function of F(-) ion translational energy, and the resulting kinetics were modeled with the RRKM (Rice-Ramsperger-Kassel-Marcus) theory. The observed rate constants for the proton-transfer reactions of F(-) with dimethyl sulfoxide and with borane-methyl sulfide complex are identical, with a value of 0.17 x 10(-9) cm(3) molecule(-1) s(-1); for the S(N)2 reaction, k = 0.90 x 10(-9) cm(3) molecule(-1) s(-1) at 350 K. Both proton-transfer reactions have positive entropy changes in the forward direction and show positive energy dependences. The competing S(N)2 reaction exhibits negative energy dependence and becomes less important at higher energies. The changes of the observed rate constants agree with RRKM theory predictions for a few kcal/mol of additional kinetic energy. The dynamic change of the branching ratio for the competing proton transfer and the substitution reactions results from the competition between the microscopic rate constants associated with each channel.

  3. Kinematical coincidence method in transfer reactions

    CERN Document Server

    Acosta, L; Auditore, L; Berceanu, I; Cardella, G; Chatterjiee, M B; De Filippo, E; FrancalanzA, L; Gianì, R; Grassi, L; Grzeszczuk, A; La Guidara, E; Lanzalone, G; Lombardo, I; Loria, D; Minniti, T; Pagano, E V; Papa, M; Pirrone, S; Politi, G; Pop, A; Porto, F; Rizzo, F; Rosato, E; Russotto, P; Santoro, S; Trifirò, A; Trimarchi, M; Verde, G; Vigilante, M

    2012-01-01

    A new method to extract high resolution angular distributions from kinematical coincidence measurements in binary reactions is presented. Kinematic is used to extract the center of mass angular distribution from the measured energy spectrum of light particles. Results obtained in the case of 10Be+p-->9Be+d reaction measured with the CHIMERA detector are shown. An angular resolution of few degrees in the center of mass is obtained.

  4. Rate Coefficient Determination in Charge Transfer Reactions

    OpenAIRE

    Nathalie Vaeck; Michèle Desouter-Lecomte; Ezinvi Baloïtcha; Marie-Christine Bacchus-Montabonel

    2002-01-01

    Abstract: The development of experimental ion-trap techniques provides the opportunity to compare directly theoretical rate coefficients to experimental data in the low-temperature regime. In the present work, we consider the ion-atom collisional systems, N2+, O2+, Si3+ and Si4+ on a He target, in order to examine the present status of the agreement between theory and experiment.

  5. Rate Coefficient Determination in Charge Transfer Reactions

    Directory of Open Access Journals (Sweden)

    Nathalie Vaeck

    2002-03-01

    Full Text Available Abstract: The development of experimental ion-trap techniques provides the opportunity to compare directly theoretical rate coefficients to experimental data in the low-temperature regime. In the present work, we consider the ion-atom collisional systems, N2+, O2+, Si3+ and Si4+ on a He target, in order to examine the present status of the agreement between theory and experiment.

  6. 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.

  7. 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.

  8. 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

  9. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    Administrator

    We will use the twisted intramolecular charge transfer (TICT) model to explain the photo-induced charge transfer ..... full width at half maxima (Γ) are expressed in 103 cm–1. –ΔGr are in kJ mol–1 units. PFH: per- ..... incorrect values of thermodynamic and kinetic parameters calculated using these reaction times, leading to ...

  10. Theory of reversible electron transfer reactions in a condensed phase.

    Science.gov (United States)

    Dhole, Kajal; Modak, Brindaban; Samanta, Alok; Ghosh, Swapan K

    2010-07-01

    We have derived an exact analytical expression for the average forward rate of a reversible electron transfer reaction, modeled through a reaction coordinate undergoing diffusive motion in arbitrary potential wells of the reactant and the product in presence of a localized sink of arbitrary location and strength. The dynamics of diffusive motion is described by employing two coupled generalized diffusion reaction (Smoluchowski) equations with coordinate dependent diffusivity and delta sink. The average forward electron transfer rate constant obtained here for the system, with equilibrium or nonequilibrium distributions as initial condition, is determined by the forward and backward rate constants calculated based on the transition state theory and the weighted average rate for the well dynamics. We also discuss various limiting cases for the rate of electron transfer reactions corresponding to the different experimental situations. As an illustrative example, we have considered back electron transfer (ET) reaction and shown that the present theory can explain the non-Marcus free energy gap dependence of the rate of ET reactions. More importantly, the approach presented here can easily be extended to systems describing the dynamics of diffusive motion in coupled multipotential surfaces associated with electron transfer reactions.

  11. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...... which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between...... quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment...

  12. Heavy ion transfer reactions: Status and perspectives

    Indian Academy of Sciences (India)

    respond to the transfer of two neutrons in the p3/2 orbital, and we remind that the single-particle form-factors for the p3/2 orbital is much larger than the one for the .... trajectory. The imaginary potential W(r), that describes the depopulation of the entrance channel, at very low energies is dominated by the single-nucleon ...

  13. Proton-transfer reactions in "super" photoacids and supramolecular assemblies

    NARCIS (Netherlands)

    Kumpulainen, T.S.

    2015-01-01

    Transfer of a proton is undoubtedly one of the most elementary and yet one of the most significant reactions in chemical and biological processes and have received great attention during the last 60 years. Surprisingly, the exact mechanism of this elementary reaction is still not fully understood

  14. 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 ...

  15. 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 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 existing theories of the ET. Our alternative dynamic ET model for

  16. Transfer reactions below the Coulomb barrier

    Energy Technology Data Exchange (ETDEWEB)

    Napoli, D.R.; Stefanini, A.M.; Million, B.; Narayanasamy, M.; Prete, G.; Spolaore, P.; Li Zichang (INFN, Legnaro (Italy) Lab. Nazionali, Legnaro (Italy)); Moreno Gonzalez, H. (INFN, Legnaro (Italy) Lab. Nazionali, Legnaro (Italy) Dept. de Fisica Atomica y Nuclear, Univ. Sevilla (Spain)); Pollarolo, G. (Univ. Turin (Italy) INFN, Turin (Italy)); Beghini, S.; Montagnoli, G.; Scarlassara, F.; Segato, G.F.; Signorini, C.; Soramel, F. (Univ. Padua (Italy) INFN, Padua (Italy)); Rapisarda, A. (INFN, Catania (Italy))

    1993-03-01

    We report here on the measurements of one-particle transfer cross sections and quasi-elastic scattering of [sup 32]Si+[sup 64]Ni at energies around and well below the Coulomb barrier. The experiment has been performed with the Legnaro Recoil Mass Spectrometer. We have measured the excitation function at [theta][sub cm]=170deg from E[sub lab]=68.3 to 92.4 MeV and the angular distribution at E[sub lab]=81.3 MeV from [theta][sub cm]=120deg to 170deg. The results have been analysed in the framework of the complex WKB theory and the semiclassical approach based on Coulomb trajectories. (orig.).

  17. Graphene Charge Transfer, Spectroscopy, and Photochemical Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Brus, Louis [Columbia Univ., New York, NY (United States)

    2017-01-31

    This project focused on the special electronic and optical properties of graphene and adsorbed molecular species. Graphene makes an excellent substrate for current collection in nanostructured photovoltaic designs. Graphene is almost transparent, and can be used as a solar cell window. It also has no surface states, and thus current is efficiently transported over long distances. Progress in graphene synthesis indicates that there will soon be practical methods for making large pieces of graphene for devices. We now need to understand exactly what happens to both ground state and electronically excited molecules and Qdots near graphene, if we are going to use them to absorb light in a nano-structured photovoltaic device using graphene to collect photocurrent. We also need to understand how to shift the graphene Fermi level, to optimize the kinetics of electron transfer to graphene. And we need to learn how to convert local graphene areas to semiconductor structure, to make useful spatially patterned graphenes. In this final report, we describe how we addressed these goals. We explored the question of possible Surface Enhanced Raman spectroscopy from molecular Charge Transfer onto Graphene substrates. We observed strong hole doping of graphene by adsorbed halogens as indicated by the shift of the graphene G Raman band. In the case of iodine adsorption, we also observed the anionic species made by hole doping. At low frequency in the Raman spectrum, we saw quite intense lines from I3- and I5- , suggesting possible SERS. We reported on Fresnel calculations on this thin film system, which did not show any net electromagnetic field enhancement.

  18. [Preparation of a novel polymer monolith using atom transfer radical polymerization method for solid phase extraction].

    Science.gov (United States)

    Shen, Ying; Qi, Li; Qiao, Juan; Mao, Lanqun; Chen, Yi

    2013-04-01

    In this study, a novel polymer monolith based solid phase extraction (SPE) material has been prepared by two-step atom transfer radical polymerization (ATRP) method. Firstly, employing ethylene glycol dimethacrylate (EDMA) as a cross-linker, a polymer monolith filled in a filter head has been in-situ prepared quickly under mild conditions. Then, the activators generated by electron transfer ATRP (ARGET ATRP) was used for the modification of poly(2-(dimethylamino)ethyl-methacrylate) (PDMAEMA) on the monolithic surface. Finally, this synthesized monolith for SPE was successfully applied in the extraction and enrichment of steroids. The results revealed that ATRP can be developed as a facile and effective method with mild reaction conditions for monolith construction and has the potential for preparing monolith in diverse devices.

  19. Effect of pairing on transfer and fusion reactions

    Directory of Open Access Journals (Sweden)

    Scamps Guillaume

    2015-01-01

    Full Text Available In the present contribution, the effect of pairing on nuclear transfer and fusion reactions close to the Coulomb barrier is discussed. A Time-Dependent Hartree-Fock + BCS (TDHF+BCS microscopic theory has been developed to incorporate pairing. One- and two-particle transfer probabilities can be obtained showing the importance of pairing. The calculated transfer probabilities are compared with the recent experimental results obtained for the 96Zr+40Ca. Reactions involving the 18O with lead isotopes are also presented, that are also of current experimental interest. Finally, a study of the fusion barrier height predicted with the TDHF+BCS theory is compared with the experimental values for the 40,44,48Ca+40Ca reactions

  20. Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3)-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

    Science.gov (United States)

    Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

    2018-03-01

    A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. 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.

  2. Organometallic Bonding in an Ullmann-Type On-Surface Chemical Reaction Studied by High-Resolution Atomic Force Microscopy.

    Science.gov (United States)

    Kawai, Shigeki; Sadeghi, Ali; Okamoto, Toshihiro; Mitsui, Chikahiko; Pawlak, Rémy; Meier, Tobias; Takeya, Jun; Goedecker, Stefan; Meyer, Ernst

    2016-10-01

    The on-surface Ullmann-type chemical reaction synthesizes polymers by linking carbons of adjacent molecules on solid surfaces. Although an organometallic compound is recently identified as the reaction intermediate, little is known about the detailed structure of the bonded organometallic species and its influence on the molecule and the reaction. Herein atomic force microscopy at low temperature is used to study the reaction with 3,9-diiododinaphtho[2,3-b:2',3'-d]thiophene (I-DNT-VW), which is polymerized on Ag(111) in vacuum. Thermally sublimated I-DNT-VW picks up a Ag surface atom, forming a CAg bond at one end after removing an iodine. The CAg bond is usually short-lived, and a CAgC organometallic bond immediately forms with an adjacent molecule. The existence of the bonded Ag atoms strongly affects the bending angle and adsorption height of the molecular unit. Density functional theory calculations reveal the bending mechanism, which reveals that charge from the terminus of the molecule is transferred via the Ag atom into the organometallic bond and strengths the local adsorption to the substrate. Such deformations vanish when the Ag atoms are removed by annealing and CC bonds are established. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Tape transfer atomization patterning of liquid alloys for microfluidic stretchable wireless power transfer.

    Science.gov (United States)

    Jeong, Seung Hee; Hjort, Klas; Wu, Zhigang

    2015-02-12

    Stretchable electronics offers unsurpassed mechanical compliance on complex or soft surfaces like the human skin and organs. To fully exploit this great advantage, an autonomous system with a self-powered energy source has been sought for. Here, we present a new technology to pattern liquid alloys on soft substrates, targeting at fabrication of a hybrid-integrated power source in microfluidic stretchable electronics. By atomized spraying of a liquid alloy onto a soft surface with a tape transferred adhesive mask, a universal fabrication process is provided for high quality patterns of liquid conductors in a meter scale. With the developed multilayer fabrication technique, a microfluidic stretchable wireless power transfer device with an integrated LED was demonstrated, which could survive cycling between 0% and 25% strain over 1,000 times.

  4. Tape Transfer Atomization Patterning of Liquid Alloys for Microfluidic Stretchable Wireless Power Transfer

    Science.gov (United States)

    Jeong, Seung Hee; Hjort, Klas; Wu, Zhigang

    2015-02-01

    Stretchable electronics offers unsurpassed mechanical compliance on complex or soft surfaces like the human skin and organs. To fully exploit this great advantage, an autonomous system with a self-powered energy source has been sought for. Here, we present a new technology to pattern liquid alloys on soft substrates, targeting at fabrication of a hybrid-integrated power source in microfluidic stretchable electronics. By atomized spraying of a liquid alloy onto a soft surface with a tape transferred adhesive mask, a universal fabrication process is provided for high quality patterns of liquid conductors in a meter scale. With the developed multilayer fabrication technique, a microfluidic stretchable wireless power transfer device with an integrated LED was demonstrated, which could survive cycling between 0% and 25% strain over 1,000 times.

  5. Performance of Frozen Density Embedding for Modeling Hole Transfer Reactions

    CERN Document Server

    Ramos, Pablo; Pavanello, Michele

    2015-01-01

    We have carried out a thorough benchmark of the FDE-ET method for calculating hole transfer couplings. We have considered 10 exchange-correlation functionals, 3 non-additive kinetic energy functionals and 3 basis sets. Overall, we conclude that with a 7% mean relative unsigned error, the PBE functional coupled with the PW91k non-additive Kinetic energy functional and a TZP basis set constitutes the most stable, and accurate level of theory for hole-transfer coupling calculations. The FDE-ET method is found to be an excellent tool for computing diabatic couplings for hole transfer reactions.

  6. 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

  7. Comparative evaluation of atom mapping algorithms for balanced metabolic reactions: application to Recon 3D.

    Science.gov (United States)

    Preciat Gonzalez, German A; El Assal, Lemmer R P; Noronha, Alberto; Thiele, Ines; Haraldsdóttir, Hulda S; Fleming, Ronan M T

    2017-06-14

    The mechanism of each chemical reaction in a metabolic network can be represented as a set of atom mappings, each of which relates an atom in a substrate metabolite to an atom of the same element in a product metabolite. Genome-scale metabolic network reconstructions typically represent biochemistry at the level of reaction stoichiometry. However, a more detailed representation at the underlying level of atom mappings opens the possibility for a broader range of biological, biomedical and biotechnological applications than with stoichiometry alone. Complete manual acquisition of atom mapping data for a genome-scale metabolic network is a laborious process. However, many algorithms exist to predict atom mappings. How do their predictions compare to each other and to manually curated atom mappings? For more than four thousand metabolic reactions in the latest human metabolic reconstruction, Recon 3D, we compared the atom mappings predicted by six atom mapping algorithms. We also compared these predictions to those obtained by manual curation of atom mappings for over five hundred reactions distributed among all top level Enzyme Commission number classes. Five of the evaluated algorithms had similarly high prediction accuracy of over 91% when compared to manually curated atom mapped reactions. On average, the accuracy of the prediction was highest for reactions catalysed by oxidoreductases and lowest for reactions catalysed by ligases. In addition to prediction accuracy, the algorithms were evaluated on their accessibility, their advanced features, such as the ability to identify equivalent atoms, and their ability to map hydrogen atoms. In addition to prediction accuracy, we found that software accessibility and advanced features were fundamental to the selection of an atom mapping algorithm in practice.

  8. An approach to quantum chemical consideration of "hydride" transfer reactions

    Directory of Open Access Journals (Sweden)

    BORIS I. DREVKO

    2004-06-01

    Full Text Available An approach to the quantum chemical study of "hydride ion" transfer has been proposed, according to which the sequences of changes in ionization potentials, enthalpies and free energies of the affinities to the hydride ion, to the hydrogen atom and to the proton of substrates molecules and their derivatives (cations, radicals, anions, are compared with the experimentally substantiated series of "hydride" mobility. It has been established that the experimental series of "hydride" mobility for six chalcogenopyrans based on "semicyclic" 1,5-diketones is in conformity with the computed ionization potentials of the molecules, and with the affinity of the corresponding radicals to the hydrogen atom involved in the transfer. The direct splitting-out of the hydride ion and the primary deprotonation of the substrates followed by the withdrawal of two electrons was elucidated to be unlikely. Feasible are the mechanisms of "hydride" mobility, the first step of which consists of electron or hydrogen atom transfer from the chalcogenopyrans molecules.

  9. 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.

  10. Transfer hydrogenation reactions catalyzed by chiral half-sandwich ...

    Indian Academy of Sciences (India)

    oxidoreductases catalyze transfer hydrogenation of car- ... ruthenium(II) complexes containing (S)-N-substituted- ... 2. Experimental. 2.1 Materials and methods. All reactions and manipulations were routinely per- formed under a nitrogen atmosphere using standard. Schlenk techniques in oven-dried glassware. L-Proline,.

  11. Photoinduced intramolecular charge-transfer reactions in 4-amino-3 ...

    Indian Academy of Sciences (India)

    Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase ...

  12. Hydrogen transfer reaction of cyclohexanone with 2-propanol ...

    Indian Academy of Sciences (India)

    Unknown

    Addition of ceria into zinc oxide was found to increase the catalytic activity for hydrogen transfer reaction. The catalytic activity also depended on the method of preparation. Citrate process results in uniformly dispersed mixed oxide with higher catalytic activity. Keywords. Cyclohexanone; ceria; ZnO; diffuse reflectance; EPR.

  13. Towards Neutron Drip Line via Transfer-Type Reactions

    CERN Document Server

    Penionzhkevich, Yu E; Antonenko, N V

    2005-01-01

    Possibilities of production of light neutron-rich isotopes $^{24,26}$O, $^{32}$Ne, $^{36,38}$Mg, $^{42}$Si and $^{56,58,60}$Ca in transfer-type reactions are analyzed. The optimal conditions for their production are suggested. The measurement of the excitation function can allow us to estimate the binding energy of exotic nuclei.

  14. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Variation of kinetic isotope effect in multiple proton transfer reactions. #. B SARITHA and M DURGA PRASAD. ∗. School of Chemistry, University of Hyderabad, Hyderabad 500 046, India e-mail: mdpsc@uohyd.ernet.in. Abstract. Recently, we had suggested that the motion along the promoter mode in the first part of the IRC.

  15. Mechanisms for control of biological electron transfer reactions.

    Science.gov (United States)

    Williamson, Heather R; Dow, Brian A; Davidson, Victor L

    2014-12-01

    Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions. Copyright © 2014 Elsevier Inc. All rights reserved.

  16. 16O-induced transfer reactions on 90Zr

    Science.gov (United States)

    Jha, V.; Roy, B. J.; Chatterjee, A.; Patel, H. S.; Srinivasan, B.; Betigeri, M. G.; Machner, H.

    Cross-section for transfer reactions 90Zr(16O, X) have been measured at an incident energy of 90 MeV. The angular distribution of the elastic scattering 90Zr(16O,16O)90Zr, the inelastic scattering to excited states of 90Zr, the one-nucleon transfer reactions 90Zr(16O,15N)91Nb (g.s., 0.104 and 3.37 MeV states), 90Zr(16O,15O)91Zr (g.s. and 2.17 MeV state) 90Zr(16O,17O)91Zr (g.s.) and the two-nucleon transfer reactions 90Zr(16O,14C)92Mo (ground and 1st excited states) are analyzed in the coupled-reaction-channel (CRC) formalism. Starting with a double-folded real potential, the elastic-scattering angular distribution is calculated using the CRC code FRESCO. The absorptive potential is then generated through the coupling of various inelastic and transfer processes that occur at the nuclear surface. Addition of a short-range imaginary potential in the coupling scheme, whose purpose was to take into account the effect due to loss of flux in fusion channel, reproduces the measured elastic-scattering angular distribution. A good description of all the quasi-elastic data has been achieved and the absolute magnitudes are reproduced without any arbitrary normalization. The relative importance of the one-step cluster transfer of two protons vs. the two-step successive transfer has been studied.

  17. Reaction Mechanism of Oxygen Atoms with Unsaturated Hydrocarbons by the Crossed-Molecular-Beams Method

    Science.gov (United States)

    Buss, R. J.; Baseman, R. J.; Guozhong, H.; Lee, Y. T.

    1982-04-01

    From a series of studies of the reaction of oxygen atoms with unsaturated hydrocarbons using the crossed molecular beam method, the dominant reaction mechanisms were found to be the simple substitution reactions with oxygen atoms replacing H, Cl, Br atom or alkyl groups. Complication due to secondary reaction was avoided by carrying out experiments under single collisions and observing primary products directly. Primary products were identified by measuring the angular and velocity distributions of products at all the mass numbers which could be detected by the mass spectrometer, and from comparison of these distributions, applying the requirement of energy and momentum conservation.

  18. Tem holder for sample transfer under reaction conditions

    DEFF Research Database (Denmark)

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

    and temperature, which usually are far from the operando conditions of e.g. heterogeneous catalysis. Our efforts focus on bridging these gaps by establishing in situ sample transfer between complementary measurement techniques. To fully exploit the capabilities of ETEM complementary experiments...... and characterization techniques are beneficial. Normally, the complementary measurements are done in parallel with experiments separated in time and space [3] or by mimicking a reactor bed by changing the feed gas composition according to reactivity and conversion measured in dedicated catalyst set-ups [4......]. 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...

  19. Crossed Molecular Beam Study of the Reactions of Oxygen and Fluorine Atoms.

    Science.gov (United States)

    1980-03-01

    products (i.e., benzaldehyde , cresol, anisole, and benzyl alcohol). Supersonic beams of O(3 P) atoms produced in a radiofrequency dis- charge I0 and toluene ...used to clarify the reaction mechanism. The reaction of O(3p) with another aromatic hydrocarbon toluene , results in competition between two...substitution channels, loss of H atom and loss of CH5. In contrast to the 0 + C6H6 reaction, no stabilized oxygen- toluene adduct was observed., The development

  20. Magnetic resonance studies of photo-induced electron transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    van Willigen, H.

    1992-11-01

    Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ([pi]/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C[sub 60] by electron donors.

  1. Surface Modification of Nanoporous 1,2-Polybutadiene by Atom Transfer Radical Polymerization or Click Chemistry

    DEFF Research Database (Denmark)

    Guo, Fengxiao; Jankova Atanasova, Katja; Schulte, Lars

    2010-01-01

    Surface-initiated atom transfer radical polymerization (ATRP) and click chemistry were used to obtain functional nanoporous polymers based oil nanoporous 1,2-polybutadiene (PB) with gyroid morphology. The ATRP monolith initiator was prepared by immobilizing bromoester initiators onto the pore walls...... through two different methodologies: (1) three-step chemical conversion of double bonds of PB into bromoisobutyrate, and (2) photochemical functionalization of PB with bromoisobutyrate groups. Azide functional groups were attached onto the pore walls before click reaction with alkynated MPEG. Following...... ATRP-grafting of hydrophilic polyacrylates and click of MPEG, the originally hydrophobic samples transformed into hydrophilic nanoporous materials. The successful modification was confirmed by infrared spectroscopy, contact angle measurements and measurements of spontaneous water uptake, while...

  2. On Surface-Initiated Atom Transfer Radical Polymerization Using Diazonium Chemistry To Introduce the Initiator Layer

    DEFF Research Database (Denmark)

    Iruthayaraj, Joseph; Chernyy, Sergey; Lillethorup, Mie

    2011-01-01

    of bromine shows a gradual transition from mushroom to brush-type conformation of the surface anchored chains in both polar and nonpolar reaction medium. Interestingly, it is revealed that very thick polymer brushes, on the order of 1 μm, can be obtained at high bromine content of the initiator layer......This work features the controllability of surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate, initiated by a multilayered 2-bromoisobutyryl moiety formed via diazonium chemistry. The thickness as a function of polymerization time has been studied by varying...... Cu(II)/Cu(I) complexes (L = Me(6)TREN, PMDETA, and BIPY). It is also observed that the ability of polymer brushes to reinitiate depends on the initial thickness and the solvent used for generating it....

  3. On the nuclear $(n;t)-$reaction in the three-electron ${}^{6}$Li atom

    CERN Document Server

    Frolov, Alexei M

    2012-01-01

    The nuclear $(n;t)-$reaction of the three-electron ${}^{6}$Li atom with thermal/slow neutrons is considered. An effective method has been developed for determining the probabilities of formation of various atoms and ions in different bound states. We discuss a number of fundamental questions directly related to numerical computations of the final state atomic probabilities. A few appropriate variational expansions for atomic wave functions of the incident lithium atom and final helium atom and/or tritium negatively charged ion are discussed. It appears that the final ${}^4$He atom arising during the nuclear $(n,{}^{6}$Li; ${}^4$He$,t)$-reaction in the three-electron Li atom can also be created in its triplet states. The formation of the quasi-stable three-electron $e^{-}_3$ during the nuclear $(n; t)-$reaction at the Li atom is briefly discussed. Bremsstrahlung emitted by atomic electrons accelerated by the rapidly moving fragments from this reaction is analyzed. The frequency spectrum of the emitted radiatio...

  4. Transfer reactions in the investigation of light-nuclei nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Guimaraes, V.; Camargo, O.; Lichtenthaler, R.; Scarduelli, V. [Instituto de Fisica, Universidade de Sao Paulo, P. O. Box 66318, 05389-970 Sao Paulo (Brazil); Kolata, J. J. [Department of Physics, University of Notre Dame, Notre Dame, 46556 Indiana (United States); Amro, H.; Becchetti, F. D.; Jiang, H. [Department of Physics, University of Michigan, Ann Arbor, 48109-1120 Michigan (United States); Aguilera, E. F.; Lizcano, D.; Martinez Q, E.; Garcia, H. [ININ, La Marquesa, 52750 Estado de Mexico (Mexico)

    2008-12-15

    Cross sections for the {sup 6}Li(p,{gamma}){sup 7}Be, {sup 7}Li(n,{gamma}){sup 8}Li{sup 8}Li(n,{gamma}){sup 9}Li and {sup 8}Li(p,{gamma}){sup 9}Be capture reactions have been investigated in the framework of the potential model. The main ingredients of the potential model are the potentials used to generate the continuum and bound-state wave functions and spectroscopic factors of the corresponding bound systems. The spectroscopic factors for the {sup 7}Lin={sup 8}Li{sub gs}, {sup 8}Lin={sup 9}Li{sub gs} bound systems were obtained from a FR-DWBA analysis of neutron transfer reactions induced by {sup 8}Li radioactive beam on a {sup 9}Be target, while spectroscopic factor for the {sup 8}Lip={sup 9}Be{sub gs} bound system were obtained from a proton transfer reaction. From the obtained capture reaction cross section, reaction rate for the {sup 8}Li(n,{gamma}){sup 9}Li and {sup 8}Li(p,{gamma}){sup 9}Be direct neutron and proton capture were determined and compared with other experimental and calculated values. (Author)

  5. Relative roles of H-atom transfer and electron transfer in the debromination of polybrominated diphenyl ethers by palladized nanoscale zerovalent iron.

    Science.gov (United States)

    Wang, Rui; Lu, Guining; Lin, Haozhong; Huang, Kaibo; Tang, Ting; Xue, Xiuling; Yang, Xingjian; Yin, Hua; Dang, Zhi

    2017-03-01

    The relative significance of H-atom transfer versus electron transfer in the dehalogenation of halogenated organic compounds (HOCs) in bimetallic systems has long been debated. In this study, we have investigated this question through the case study of the debromination of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47). The debromination rates of isomer products of BDE-47 by palladized nano zero-valent iron (n-ZVI/Pd) in the same reactor were compared. The results confirmed a shift in the debromination pathway of BDE-47 when treated with unpalladized nano zero-valent iron (n-ZVI) vs. treatment with n-ZVI/Pd. Study showed that BDEs could be rapidly debrominated in a palladium-H2 system, and the debromination pathway in this system is the same as that in the n-ZVI/Pd system. These results suggest that the H-atom species adsorbed on the surface of palladium are responsible for the enhanced reaction rates and the shift of the debromination pathway in the n-ZVI/Pd system. The Mulliken charges, calculated with density functional theory, on bromine atoms of PBDEs were directly correlated with the susceptibility to the e-transfer pathway in the n-ZVI system and inversely correlated with the susceptibility to the H-transfer pathway in n-ZVI/Pd system. These experimentally verified correlations in BDE-47 permit the prediction of the dominant debromination pathway in other BDEs. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Reactions of pulsed-laser evaporated lithium atoms with O 2 and N 2O

    Science.gov (United States)

    Andrews, Lester; Saffell, Wendy; Yustein, Jason T.

    1994-12-01

    Pulsed laser evaporated Li atoms were codeposited with O 2 in excess argon at 12 K. The same LiO 2 and LiO 2Li products were observed that were formed with thermal Li atoms. However, with N 2O the LiO product was observed in contrast to thermal Li atom reactions. Excess kinetic energy in the laser evaporated Li atoms provided activation energy for the abstraction reaction. In addition the extremely large yield of O 4- observed in O 2 experiments provides evidence for photoelectron emission from the lithium metal surface.

  7. The dynamics of chlorine-atom reactions with polyatomic organic molecules

    Science.gov (United States)

    Murray, Craig; Orr-Ewing, Andrew J.

    Chlorine atoms react with a variety of organic molecules by abstraction of an H atom, making HCl and a radical co-product, and investigations of these reactions provide a large and valuable body of data for improved fundamental understanding of the mechanisms of reactions involving polyatomic molecules. The kinetics and dynamics of reactions of Cl atoms with alkanes have been extensively studied both by experimental and computational methods, and the key outcomes and conclusions are reviewed. These reactions serve as benchmarks for the interpretation of recent experimental data on the dynamics of reactions of Cl atoms with heteroatom functionalized organic molecules such as alcohols, ethers, amines, alkyl halides and thiols. Although bearing many similarities to the dynamics of the alkane reactions, significant differences are found: in particular, the extent of HCl rotational excitation from reactions of Cl atoms with the functionalized molecules is much greater than the very cold rotational distributions obtained for H-atom abstraction from simple alkanes such as methane, ethane, propane and butane. These observations and the scattering dynamics are discussed in terms of reaction energetics, barriers and transition state geometries, and evidence is presented for post-transition-state interactions between the separating HCl and polar organic radical for which the HCl rotation appears to be a sensitive probe.

  8. Excited state charge transfer reaction in (mixed solvent + electrolyte ...

    Indian Academy of Sciences (India)

    charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in two sets of mixed solvents, (1-propanol + ethyl acetate) and (propylene ...... Harun Al Rasid Gazi and Ranjit Biswas. PrOH+EA. Normalized F.I.. 0. 1. Normalized F.I.. 0. 1. -3. 0. 3. 3000. 4000. 5000. 6000. Residual. -3. 0. 3. Residual. -3. 0. 3. Time(ps). 3000. 4000.

  9. Experimental and Computational Studies of the Reactions of N and O Atoms with Small Heterocyclic Anions.

    Science.gov (United States)

    Wang, Zhe-Chen; Bierbaum, Veronica M

    2017-05-18

    The existence of heterocyclic aromatic anions in extraterrestrial environments, such as the upper atmosphere of Titan, has been recently confirmed by data from the Cassini spacecraft. Nitrogen and oxygen atoms are also common species in the ionospheres of planets and moons and in the interstellar medium. In the current work, we extend previous studies to explore the reactivity of five-membered ring aromatic anions that contain nitrogen, oxygen, or sulfur (deprotonated pyrrole, furan, and thiophene) with N and O atoms both experimentally and computationally. Furanide and thiophenide anions react with the N atom by associative electron detachment (AED). All three anions react with the O atom both by AED and by processes that form ionic products. The reaction of pyrrolide anion with the O atom generates only one ionic product C4H3NO(-), corresponding to an O addition and H loss process. The corresponding process is observed as the major channel for the reaction of furanide anion with the O atom while other ionic products HCOO(-) and C2H(-) are also formed. The reaction of thiophenide with the O atom is more complex, and four ionic products are generated, of which three are sulfur-containing ions. The reaction mechanisms are studied theoretically by employing density functional theory calculations, and spin conversion is found to be critical for understanding some product distributions. This work provides insight into the rich gas-phase chemistry of aromatic ion-atom reactions, which are relevant to ionospheric and interstellar chemistry.

  10. Prediction of reacting atoms for the major biotransformation reactions of organic xenobiotics.

    Science.gov (United States)

    Rudik, Anastasia V; Dmitriev, Alexander V; Lagunin, Alexey A; Filimonov, Dmitry A; Poroikov, Vladimir V

    2016-01-01

    The knowledge of drug metabolite structures is essential at the early stage of drug discovery to understand the potential liabilities and risks connected with biotransformation. The determination of the site of a molecule at which a particular metabolic reaction occurs could be used as a starting point for metabolite identification. The prediction of the site of metabolism does not always correspond to the particular atom that is modified by the enzyme but rather is often associated with a group of atoms. To overcome this problem, we propose to operate with the term "reacting atom", corresponding to a single atom in the substrate that is modified during the biotransformation reaction. The prediction of the reacting atom(s) in a molecule for the major classes of biotransformation reactions is necessary to generate drug metabolites. Substrates of the major human cytochromes P450 and UDP-glucuronosyltransferases from the Biovia Metabolite database were divided into nine groups according to their reaction classes, which are aliphatic and aromatic hydroxylation, N- and O-glucuronidation, N-, S- and C-oxidation, and N- and O-dealkylation. Each training set consists of positive and negative examples of structures with one labelled atom. In the positive examples, the labelled atom is the reacting atom of a particular reaction that changed adjacency. Negative examples represent non-reacting atoms of a particular reaction. We used Labelled Multilevel Neighbourhoods of Atoms descriptors for the designation of reacting atoms. A Bayesian-like algorithm was applied to estimate the structure-activity relationships. The average invariant accuracy of prediction obtained in leave-one-out and 20-fold cross-validation procedures for five human isoforms of cytochrome P450 and all isoforms of UDP-glucuronosyltransferase varies from 0.86 to 0.99 (0.96 on average). We report that reacting atoms may be predicted with reasonable accuracy for the major classes of metabolic reactions

  11. Reaction mechanism of an intramolecular oxime transfer reaction: a computational study.

    Science.gov (United States)

    Moilanen, Jani; Neuvonen, Antti; Pihko, Petri

    2014-03-07

    Density functional theory (PBE0/def2-TZVPP) calculations in conjunction with a polarizable continuum model were used to assess the mechanism of the intramolecular oxime transfer reaction that leads to the formation of isoxazolines. Different diastereomers of the intermediates as well as different oximes (formaldehyde and acetone oxime) were considered. The computed reaction profile predicts the water-addition and -expulsion steps as the highest barriers along the pathway, a conclusion that is in line with the experimental evidence obtained previously for these reactions.

  12. Controlled state-to-state atom-exchange reaction in an ultracold atom-dimer mixture

    OpenAIRE

    Rui, Jun; Yang, Huan; Liu, Lan; Zhang, De-Chao; Liu, Ya-Xiong; Nan, Jue; Zhao, Bo; Pan, Jian-Wei

    2016-01-01

    Ultracold molecules offer remarkable opportunities to study chemical reactions at nearly zero temperature. Although significant progresses have been achieved in exploring ultracold bimolecular reactions, the investigations are usually limited to measurements of the overall loss rates of the reactants. Detection of the reaction products will shed new light on understanding the reaction mechanism and provide a unique opportunity to study the state-to-state reaction dynamics. Here we report on t...

  13. A Kinetico-Mechanistic Study on CuII Deactivators Employed in Atom Transfer Radical Polymerization.

    Science.gov (United States)

    Zerk, Timothy J; Martinez, Manuel; Bernhardt, Paul V

    2016-10-03

    Copper complexes of tertiary amine ligands have emerged as the catalysts of choice in the extensively employed atom transfer radical polymerization (ATRP) protocol. The halide ligand substitution reactions of five-coordinate copper(II) complexes of tris[2-(dimethylamino)ethyl]amine (Me6tren), one of the most active ATRP catalysts, has been studied in a range of organic solvents using stopped-flow techniques. The kinetic and activation parameters indicate that substitution reactions on [CuII(Me6tren)X]+ (X- = Cl- and Br-) and [CuII(Me6tren)(Solv)]2+ (Solv = MeCN, DMF, DMSO, MeOH, EtOH) are dissociatively activated; this behavior is independent of the solvent used. Adjusting the effective concentration of the solvent by addition of an olefinic monomer to the solution does not affect the kinetics of the halide binding (kon) but can alter the outer-sphere association equilibrium constant (KOS) between reactants prior to the formal ligand substitution. Halide (X-/Y-) exchange reactions (X = Br and Y = Cl) involving the complex [Cu(Me6tren)X]+ and Y- reveal that the substitution is thermodynamically favored. The influence of solvent on the substitution reactions of [Cu(Me6tren)X]+ is complex; the more polar DMF confers a greater entropic driving force but larger enthalpic demands than MeCN. These substitution reactions are compared with those for copper(II) complexes bearing the tris[2-(diethylamino)ethyl]amine (Et6tren) and tris[2-(pyridyl)methyl]amine (tpa) ligands, which have also been used as catalysts for ATRP. Changing the ligand has a significant impact on the kinetics of X-/Y- exchange. These correlations are discussed in relation to the ability of five-coordinate [CuLX]+ complexes to deactivate radicals in ATRP.

  14. Rate constant for reaction of atomic hydrogen with germane

    Science.gov (United States)

    Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

    1990-01-01

    Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

  15. Transferable Atomic Multipole Machine Learning Models for Small Organic Molecules.

    Science.gov (United States)

    Bereau, Tristan; Andrienko, Denis; von Lilienfeld, O Anatole

    2015-07-14

    Accurate representation of the molecular electrostatic potential, which is often expanded in distributed multipole moments, is crucial for an efficient evaluation of intermolecular interactions. Here we introduce a machine learning model for multipole coefficients of atom types H, C, O, N, S, F, and Cl in any molecular conformation. The model is trained on quantum-chemical results for atoms in varying chemical environments drawn from thousands of organic molecules. Multipoles in systems with neutral, cationic, and anionic molecular charge states are treated with individual models. The models' predictive accuracy and applicability are illustrated by evaluating intermolecular interaction energies of nearly 1,000 dimers and the cohesive energy of the benzene crystal.

  16. Creation, destruction, and transfer of atomic multipole moments by electron scattering: Quantum-mechanical treatment

    Science.gov (United States)

    Csanak, G.; Kilcrease, D. P.; Fursa, D. V.; Bray, I.

    2008-12-01

    Using the wave-packet propagation method of Rodberg and Thaler and the density matrix method of Fano and Blum, we have defined by completely quantum-mechanical methods the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets. All cross sections obtained quantum mechanically, except for the coherence transfer cross sections, agree in form with those obtained semiclassically by Fujimoto and co-workers. We also used the converged close-coupling (CCC) method to calculate numerically some of the above cross sections for selected transitions in electron scattering from hydrogen and barium atoms.

  17. Growth and Destruction of PAH Molecules in Reactions with Carbon Atoms

    Energy Technology Data Exchange (ETDEWEB)

    Krasnokutski, Serge A.; Huisken, Friedrich; Jäger, Cornelia; Henning, Thomas [Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Helmholtzweg 3, D-07743 Jena (Germany)

    2017-02-10

    A very high abundance of atomic carbon in the interstellar medium (ISM), and the high reactivity of these species toward different hydrocarbon molecules including benzene, raise questions regarding the stability of polycyclic aromatic hydrocarbon (PAH) molecules in space. To test the efficiency of destruction of PAH molecules via reactions with atomic carbon, we performed a set of laboratory and computational studies of the reactions of naphthalene, anthracene, and coronene molecules with carbon atoms in the ground state. The reactions were investigated in liquid helium droplets at T = 0.37 K and by quantum chemical computations. Our studies suggest that all small and all large catacondensed PAHs react barrierlessly with atomic carbon, and therefore should be efficiently destroyed by such reactions in a broad temperature range. At the same time, large compact pericondensed PAHs should be more inert toward such a reaction. In addition, taking into account their higher photostability, much higher abundances of pericondensed PAHs should be expected in various astrophysical environments. The barrierless reactions between carbon atoms and small PAHs also suggest that, in the ISM, these reactions could lead to the bottom-up formation of PAH molecules.

  18. Effect of Reactant Concentration Variations on the Kinetics of Atom Transfer Radical Polymerization of Acrylonitrile

    Directory of Open Access Journals (Sweden)

    H. Roghani-Mamaqani

    2013-01-01

    Full Text Available Polyacrylontrile synthesis, via atom transfer radical polymerization, is studied in various initiator concentrations, transitional metal catalyst and different concentrations of CuBr2. The variations of monomer conversion and the lin-earity of semi-logarithmic kinetic profile which is the evidence of living polymerization and constant radical concentration in the reaction medium, were revealed by gas chromatography technique (GC. Gel permeation chromatography (GPC studies revealed that, the number average molecular weight increases linearly against monomer conversion, an indicative of living nature of the polymerization process. Additionally, the conversion, apparent rate constant and number average molecular weight increased with increased initiator concentration as well as the transitional metal complex concentration. However, addition of CuBr2 lowered conversion, kapp, and the number average molecular weight of polyacrylonitrile. Molecular weight distribution of synthesized polymers broadened with increased initiator concentration and also transitional metal complex concentration. However, addition of CuBr2 has resulted in narrower molecular weight distribution polyacrylonitrile. Moreover, all the samples experienced a drop in PDI value from nearly 2 to almost 1.1 as the reaction progressed.

  19. 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.

  20. Quantum simulation of nuclear rearrangement in electron transfer reactions

    OpenAIRE

    Zheng, Chong; McCammon, J. Andrew; Wolynes, Peter G.

    1989-01-01

    A quantum simulation scheme based on the path integral molecular dynamics technique has been used to calculate the effective activation energies associated with nuclear rearrangement in the electron transfer reactions Co(NH3)62+ + Co(NH3)63+ → Co(NH3)63+ + Co(NH3)62+ and Ru(NH3)62+ + Ru(NH3)63+ → Ru(NH3)63+ + Ru(NH3)62+. Even with a simple Hamiltonian and short time dynamic simulations, the results are in satisfactory agreement with other theoretical calculations. This simulation approach can...

  1. Highly Durable Platinum Single-Atom Alloy Catalyst for Electrochemical Reactions

    DEFF Research Database (Denmark)

    Kim, Jiwhan; Roh, Chi-Woo; Sahoo, Suman Kalyan

    2018-01-01

    Single atomic Pt catalyst can offer efficient utilization of the expensive platinum and provide unique selectivity because it lacks ensemble sites. However, designing such a catalyst with high Pt loading and good durability is very challenging. Here, single atomic Pt catalyst supported on antimony...... functional theory calculations show that replacing Sb sites with Pt atoms in the bulk phase or at the surface of SbSn or ATO is energetically favorable. The Pt1/ATO shows superior activity and durability for formic acid oxidation reaction, compared to a commercial Pt/C catalyst. The single atomic Pt...

  2. Single-Atom Catalyst of Platinum Supported on Titanium Nitride for Selective Electrochemical Reactions.

    Science.gov (United States)

    Yang, Sungeun; Kim, Jiwhan; Tak, Young Joo; Soon, Aloysius; Lee, Hyunjoo

    2016-02-05

    As a catalyst, single-atom platinum may provide an ideal structure for platinum minimization. Herein, a single-atom catalyst of platinum supported on titanium nitride nanoparticles were successfully prepared with the aid of chlorine ligands. Unlike platinum nanoparticles, the single-atom active sites predominantly produced hydrogen peroxide in the electrochemical oxygen reduction with the highest mass activity reported so far. The electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, also exhibited unique selectivity on the single-atom platinum catalyst. A lack of platinum ensemble sites changed the reaction pathway for the oxygen-reduction reaction toward a two-electron pathway and formic acid oxidation toward direct dehydrogenation, and also induced no activity for the methanol oxidation. This work demonstrates that single-atom platinum can be an efficient electrocatalyst with high mass activity and unique selectivity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Rate of reaction of dimethylmercury with oxygen atoms in the gas phase

    DEFF Research Database (Denmark)

    Egsgaard, Helge

    1986-01-01

    The rate constant for the reaction of atomic oxygen (O(3P)) with dimethylmercury has been measured at room temperature at a pressure of about 1 Torr using a fast flow system with electron paramagnetic resonance and mass spectrometric detection. Some reaction products were identified. The rate...

  4. Electron transfer reactions in condensed phase: effect of reversibility.

    Science.gov (United States)

    Dhole, Kajal; Jena, Naresh K; Samanta, Alok; Ghosh, Swapan K

    2012-02-01

    We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well.

  5. Catalytic Transfer Hydogenation Reactions for Undergraduate Practical Programs

    Science.gov (United States)

    Hanson, R. W.

    1997-04-01

    A brief review of catalytic transfer hydrogenation (CTH) reactions is given. Attention is drawn, particularly, to the utility of ammonium formate as the hydrogen donor in this type of reaction. The reduction of aryl carbonyl compounds to the corresponding methylene derivatives by ammonium formate in the presence of 10% Pd/C at 110°C is compared to their reductive ammonation which occurs at higher temperatures in the absence of the catalyst (the Leuckart reaction). It is suggested that the low cost and simplicity of CTH reactions using ammonium formate as the hydrogen donor, together with the high yields obtained in many cases, make them excellent candidates for inclusion in undergraduate practical programmes. Laboratory instructions are given for the reduction of nitrobenzene to aniline (isolated as benzanilide), benzophenone to diphenylmethanol and fluorenone to fluorene, in all cases using ammonium formate as the hydrogen donor and 10% Pd/C as the catalyst. Thin layer chromatography shows that in each case the product is homogeneous; the yields are essentially quantitative.

  6. Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen.

    Science.gov (United States)

    Ruzi, Mahmut; Anderson, David T

    2015-12-17

    Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.8 to 4.3 K temperature range. Upon short-term in situ irradiation the NO readily undergoes photolysis to yield HNO, NOH, NH, NH3, H2O, and H atoms. We map the postphotolysis reactions of mobile H atoms with NO and document first-order growth in HNO and NOH reaction products for up to 5 h after photolysis. We perform three experiments at 4.3 K and one at 1.8 K to permit the temperature dependence of the reaction kinetics to be quantified. We observe Arrhenius-type behavior with a pre-exponential factor of A = 0.036(2) min(-1) and Ea = 2.39(1) cm(-1). This is in sharp contrast to previous H atom reactions we have studied in solid pH2 that display definitively non-Arrhenius behavior. The contrasting temperature dependence measured for the H + NO reaction is likely related to the details of H atom quantum diffusion in solid pH2 and deserves further study.

  7. Reaction and Protection of Electrical Wire Insulators in Atomic-oxygen Environments

    Science.gov (United States)

    Hung, Ching-Cheh; Cantrell, Gidget

    1994-01-01

    Atomic-oxygen erosion on spacecraft in low Earth orbit is an issue which is becoming increasingly important because of the growing number of spacecraft that will fly in the orbits which have high concentrations of atomic oxygen. In this investigation, the atomic-oxygen durability of three types of electrical wire insulation (carbon-based, fluoropolymer, and polysiloxane elastomer) were evaluated. These insulation materials were exposed to thermal-energy atomic oxygen, which was obtained by RF excitation of air at a pressure of 11-20 Pa. The effects of atomic-oxygen exposure on insulation materials indicate that all carbon-based materials erode at about the same rate as polyamide Kapton and, therefore, are not atomic-oxygen durable. However, the durability of fluoropolymers needs to be evaluated on a case by case basis because the erosion rates of fluoropolymers vary widely. For example, experimental data suggest the formation of atomic fluorine during atomic-oxygen amorphous-fluorocarbon reactions. Dimethyl polysiloxanes (silicone) do not lose mass during atomic-oxygen exposure, but develop silica surfaces which are under tension and frequently crack as a result of loss of methyl groups. However, if the silicone sample surfaces were properly pretreated to provide a certain roughness, atomic oxygen exposure resulted in a sturdy, non-cracked atomic-oxygen durable SiO2 layer. Since the surface does not crack during such silicone-atomic oxygen reaction, the crack-induced contamination by silicone can be reduced or completely stopped. Therefore, with proper pretreatment, silicone can be either a wire insulation material or a coating on wire insulation materials to provide atomic-oxygen durability.

  8. Transferable Pseudo-Classical Electrons for Aufbau of Atomic Ions

    Science.gov (United States)

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-01-01

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. PMID:24752384

  9. Transferable pseudoclassical electrons for aufbau of atomic ions.

    Science.gov (United States)

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-06-05

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. Copyright © 2014 Wiley Periodicals, Inc.

  10. Hot hydrogen atom reactions moderated by H2 and He

    Science.gov (United States)

    Aronowitz, S.; Scattergood, T.; Flores, J.; Chang, S.

    1986-01-01

    Photolysis experiments were performed on the H2-CD4-NH3 and He-CD4-NH3 systems. The photolysis (1849 A) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system resulted in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.

  11. Study of the Ne(^3P_2) + CH_3F Electron Transfer Reaction below 1 Kelvin

    CERN Document Server

    Jankunas, Justin; Osterwalder, Andreas

    2014-01-01

    Relatively little is known about the dynamics of electron transfer reactions at low collision energy. We present a study of Penning ionization of ground state methyl fluoride molecules by electronically excited neon atoms in the 13 $\\mu$eV--4.8 meV (150 mK--56 K) collision energy range, using a neutral-neutral merged beam setup. Relative cross sections have been measured for three Ne($^3P_2$)+ CH$_3$F reaction channels by counting the number of CH$_3$F$^+$, CH$_2$F$^+$, and CH$_3^+$ product ions, as a function of relative velocity between the neon and methyl fluoride molecular beams. Experimental cross sections markedly deviate from the Langevin capture model at collision energies above 20 K. The branching ratios are constant. In other words, the chemical shape of the CH$_3$F molecule, as seen by Ne($^3P_2$) atom, appears not to change as the collision energy is varied, in contrast to related Ne($^3P_J$) + CH$_3$X (X=Cl and Br) reactions at higher collision energies.

  12. Kinetics of the reaction of iodine atoms with HO sub 2 radicals

    Energy Technology Data Exchange (ETDEWEB)

    Jenkin, M.E.; Cox, R.A. (Harwell Laboratory, Oxfordshire (England)); Mellouki, A.; Le Bras, G.; Poulet, G. (CNRS, Orleans (France))

    1990-04-05

    The rate coefficient (k{sub 7}) for the reaction of iodine atoms with HO{sub 2} radicals, I + HO{sub 2} {yields} HI + O{sub 2}, has been measured directly with use of the discharge-flow/EPR technique, and the molecular-modulation/UV-absorption spectroscopy technique. Discharge-flow measurements were made under pseudo-first-order conditions with iodine atoms in large excess over HO{sub 2}. Molecular-modulation measurements were made with iodine atoms in excess over HO{sub 2}, but the I + HO{sub 2} reaction was occurring in competition with the self-reaction of HO{sub 2}. The potential significance of this reaction as a sink for iodine in the troposphere and other aspects of tropospheric iodine chemistry are considered with a simple model of the atmospheric boundary layer.

  13. Atom transfer radical polymerization preparation and photophysical properties of polypyridylruthenium derivatized polystyrenes.

    Science.gov (United States)

    Fang, Zhen; Ito, Akitaka; Keinan, Shahar; Chen, Zuofeng; Watson, Zoe; Rochette, Jason; Kanai, Yosuke; Taylor, Darlene; Schanze, Kirk S; Meyer, Thomas J

    2013-08-05

    A ruthenium containing polymer featuring a short carbonyl-amino-methylene linker has been prepared by atom transfer radical polymerization (ATRP). The polymer was derived from ATRP of the N-hydroxysuccinimide (NHS) derivative of p-vinylbenzoic acid, followed by an amide coupling reaction of the NHS-polystyrene with Ru(II) complexes derivatized with aminomethyl groups (i.e., [Ru(bpy)2(CH3-bpy-CH2NH2)](2+) where bpy is 2,2'-bipyridine, and CH3-bpy-CH2NH2 is 4-methyl-4'-aminomethyl-2,2'-bipyridine). The Ru-functionalized polymer structure was confirmed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that a high loading ratio of polypyridylruthenium chromophores on the polystyrene backbone was achieved. The photophysical properties of the polymer were characterized in solution and in rigid ethylene glycol glasses. In solution, emission quantum yield and lifetime studies reveal that the polymer's metal-to-ligand charge transfer (MLCT) excited states are quenched relative to a model Ru complex chromophore. In rigid media, the MLCT-ground state band gap and lifetime are both increased relative to solution with time-resolved emission measurements revealing fast energy transfer hopping within the polymer. Molecular dynamics studies of the polymer synthesized here as well as similar model systems with various spatial arrangements of the pendant Ru complex chromophores suggest that the carbonyl-amino-methylene linker probed in our target polymer provides shorter Ru-Ru nearest-neighbor distances leading to an increased Ru*-Ru energy hopping rate, compared to those with longer linkers in counterpart polymers.

  14. Atomic recombination rate determination through heat-transfer measurement.

    Science.gov (United States)

    Park, C.; Anderson, L. A.; Sheldahl, R. E.

    1973-01-01

    A theoretical and experimental demonstration is presented which shows that under suitable conditions the volume recombination coefficient can be determined by measuring the heat transfer rate into the wall of a cylinder through which a dissociated stream is passing. The experimental results obtained are in agreement with those of other investigators.

  15. 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...

  16. 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

  17. Measuring one nucleon transfer reaction 24Mg( p, d)23Mg for astrophysical reaction rates

    Science.gov (United States)

    Lee, E. J.; Chae, K. Y.

    2017-12-01

    The level structure of a radionuclide 23Mg has been studied by using the 24Mg( p, d)23Mg one nucleon transfer reaction measurement for the astrophysical 19Ne(α, γ)23Mg reaction rate. A 41 MeV proton beam was produced and accelerated at the 25 MV tandem accelerator of the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory in the United States. The beam particles impinged on an isotopically-enriched 24Mg solid target. Angular distributions of recoiling deuterons were extracted by using a large area silicon strip detector array. By comparing the experimentally-obtained angular distributions with zero range distorted wave Born approximation calculations, spins and parities of three energy levels of 23Mg could be constrained for the first time, which is very important information needed to understand the 19Ne(α, γ)23Mg reaction rate.

  18. Effect of mass transfer on the oxygen reduction reaction catalyzed by platinum dendrimer encapsulated nanoparticles

    Science.gov (United States)

    Dumitrescu, Ioana; Crooks, Richard M.

    2012-01-01

    Here we report on the effect of the mass transfer rate (kt) on the oxygen reduction reaction (ORR) catalyzed by Pt dendrimer-encapsulated nanoparticles (DENs) comprised of 147 and 55 atoms (Pt147 and Pt55). The experiments were carried out using a dual-electrode microelectrochemical device, which enables the study of the ORR under high kt conditions with simultaneous detection of H2O2. At low kt (0.02 to 0.12 cm s-1) the effective number of electrons involved in ORR, neff, is 3.7 for Pt147 and 3.4 for Pt55. As kt is increased, the mass-transfer-limited current for the ORR becomes significantly lower than the value predicted by the Levich equation for a 4-electron process regardless of catalyst size. However, the percentage of H2O2 detected remains constant, such that neff barely changes over the entire kt range explored (0.02 cm s-1). This suggests that mass transfer does not affect neff, which has implications for the mechanism of the ORR on Pt nanoparticles. Interestingly, there is a significant difference in neff for the two sizes of Pt DENs (neff = 3.7 and 3.5 for Pt147 and Pt55, respectively) that cannot be assigned to mass transfer effects and that we therefore attribute to a particle size effect. PMID:22665772

  19. Incremental Identification of Reaction and Mass-Transfer Kinetics Using the Concept of Extents

    OpenAIRE

    Bhatt, Nirav; Amrhein, Michael; Bonvin, Dominique

    2011-01-01

    This paper proposes a variation of the incremental approach to identify reaction and mass-transfer kinetics (rate expressions and the corresponding rate parameters) from concentration measurements for both homogeneous and gas-liquid reaction systems. This incremental approach proceeds in two steps: (i) computation of the extents of reaction and mass transfer from concentration measurements without explicit knowledge of the reaction and mass-transfer rate expressions, and (ii) estimation of ...

  20. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    Science.gov (United States)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  1. Mass transfer in porous media with heterogeneous chemical reaction

    Directory of Open Access Journals (Sweden)

    Souza S.M.A.G.Ulson de

    2003-01-01

    Full Text Available In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

  2. Is H Atom Abstraction Important in the Reaction of Cl with 1-Alkenes?

    Science.gov (United States)

    Walavalkar, M P; Vijayakumar, S; Sharma, A; Rajakumar, B; Dhanya, S

    2016-06-23

    The relative yields of products of the reaction of Cl atoms with 1-alkenes (C4-C9) were determined to see whether H atom abstraction is an important channel and if it is to identify the preferred position of abstraction. The presence of all the possible positional isomers of long chain alkenones and alkenols among the products, along with chloroketones and chloroalcohols, confirms the occurrence of H atom abstraction. A consistent pattern of distribution of abstraction products is observed with oxidation at C4 (next to allyl) being the lowest and that at CH2 groups away from the double bond being the highest. This contradicts with the higher stability of allyl (C3) radical. For a better understanding of the relative reactivity, ab initio calculations at MP2/6-311+G (d,p) level of theory are carried out in the case of 1-heptene. The total rate coefficient, calculated using conventional transition state theory, was found to be in good agreement with the experimental value at room temperature. The preferred position of Cl atom addition is predicted to be the terminal carbon atom, which matches with the experimental observation, whereas the rate coefficients calculated for individual channels of H atom abstraction do not explain the observed pattern of products. The distribution of abstraction products except at C4 is found to be better explained by reported structure activity relationship, developed from experimental rate coefficient data. This implies the reactions to be kinetically dictated and emphasizes the importance of secondary reactions.

  3. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084 (China)

    2016-12-30

    Highlights: • Surface modification of ND with water soluble and biocompatible polymers. • Functionalized ND through metal free surface initiated ATRP. • The metal free surface initiated ATRP is rather simple and effective. • The ND-poly(MPC) showed high dispersibility and desirable biocompatibility. - Abstract: Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by {sup 1}H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  4. Sustainable Electrochemically-Mediated Atom Transfer Radical Polymerization with Inexpensive Non-Platinum Electrodes.

    Science.gov (United States)

    Fantin, Marco; Lorandi, Francesca; Isse, Abdirisak A; Gennaro, Armando

    2016-08-01

    Electrochemically-mediated atom transfer radical polymerization (eATRP) of oligo(ethylene oxide) methyl ether methacrylate in water is investigated on glassy carbon, Au, Ti, Ni, NiCr and SS304. eATRPs are performed both in divided and undivided electrochemical cells operating under either potentiostatic or galvanostatic mode. The reaction is fast, reaching high conversions in ≈4 h, and yields polymers with dispersity <1.2 and molecular weights close to the theoretical values. Most importantly, eATRP in a highly simplified setup (undivided cell under galvanostatic mode) with inexpensive nonnoble metals, such as NiCr and SS304, as cathode is well-controlled. Additionally, these electrodes neither release harmful ions in solution nor react directly with the CX chain end and can be reused several times. It is demonstrated that Pt can be replaced with cheaper, and more readily available materials without negatively affecting eATRP performance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Synthesis of novel size exclusion chromatography support by surface initiated aqueous atom transfer radical polymerization.

    Science.gov (United States)

    Coad, Bryan R; Kizhakkedathu, Jayachandran N; Haynes, Charles A; Brooks, Donald E

    2007-11-06

    We report the use of aqueous surface-initiated atom transfer radical polymerization (SI-ATRP) to grow polymer brushes from a "gigaporous" polymeric chromatography support for use as a novel size exclusion chromatography medium. Poly(N,N-dimethylacrylamide) (PDMA) was grown from hydrolyzable surface initiators via SI-ATRP catalyzed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA)/CuCl. Grafted polymer was characterized semiquantitatively by ATR-FTIR and also cleaved and quantitatively characterized for mass, molecular weight, and polydispersity via analytical SEC/MALLS. The synthesis provides control over graft density and allows the creation of dense brushes. Incorporation of negative surface charge was found to be crucial for improving the initiation efficiency. As polymer molecular weight and density could be controlled through reaction conditions, the resulting low-polydispersity grafted polymer brush medium is shown to be suitable for use as a customizable size exclusion chromatography medium for investigating the principals of entropic interaction chromatography. All packed media investigated showed size-dependent partitioning of solutes, even for low graft density systems. Increasing the molecular weight of the grafts allowed solutes more access to the volume fraction in the column available for partitioning. Compared to low graft density media, increased graft density caused eluted solute probes to be retained less within the column and allowed for greater size discrimination of probes whose molecular weights were less than 10(4) kDa.

  6. Constructing Functional Ionic Membrane Surface by Electrochemically Mediated Atom Transfer Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Fen Ran

    2016-01-01

    Full Text Available The sodium polyacrylate (PAANa contained polyethersulfone membrane that was fabricated by preparation of PES-NH2 via nonsolvent phase separation method, the introduction of bromine groups as active sites by grafting α-Bromoisobutyryl bromide, and surface-initiated electrochemically atom transfer radical polymerization (SI-eATRP of sodium acrylate (AANa on the surface of PES membrane. The polymerization could be controlled by reaction condition, such as monomer concentration, electric potential, polymerization time, and modifier concentration. The membrane surface was uniform when the monomer concentration was 0.9 mol/L, the electric potential was −0.12 V, the polymerization time was 8 h, and the modifier concentration was 2 wt.%. The membrane showed excellent hydrophilicity and blood compatibility. The water contact angle decreased from 84° to 68° and activated partial thromboplastin increased from 51 s to 84 s after modification of the membranes.

  7. Fast adiabatic quantum state transfer and entanglement generation between two atoms via dressed states.

    Science.gov (United States)

    Wu, Jin-Lei; Ji, Xin; Zhang, Shou

    2017-04-11

    We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.

  8. Fast adiabatic quantum state transfer and entanglement generation between two atoms via dressed states

    Science.gov (United States)

    Wu, Jin-Lei; Ji, Xin; Zhang, Shou

    2017-04-01

    We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.

  9. Effect of energy transfer from atomic electron shell to an α particle emitted by decaying nucleus

    Energy Technology Data Exchange (ETDEWEB)

    Igashov, S. Yu., E-mail: igashov@theor.mephi.ru [All-Russian Research Institute of Automatics (Russian Federation); Tchuvil’sky, Yu. M. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation)

    2016-12-15

    The process of energy transfer from the electron shell of an atom to an α particle propagating through the shell is formulated mathematically. Using the decay of the {sup 226}Ra nucleus as an example, it is demonstrated that this phenomenon increases the α-decay intensity in contrast with other known effects of similar type. Moreover, the α decay of the nucleus is more strongly affected by the energy transfer than by all other effects taken together.

  10. Oxygen-atom transfer chemistry and thermolytic properties of a di-tert-butylphosphate-ligated Mn4O4 cubane.

    Science.gov (United States)

    Van Allsburg, Kurt M; Anzenberg, Eitan; Drisdell, Walter S; Yano, Junko; Tilley, T Don

    2015-03-16

    [Mn4O4{O2P(OtBu)2}6] (1), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen-evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen-atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O-atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X-ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to Mn(II) species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin = pinacolate) is described. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Kinetics and mechanism of the gas phase reaction of Cl atoms with iodobenzene

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Ponomarev, DA; Nielsen, OJ

    2001-01-01

    Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms with iodobenzene (C6H5I) in 20-700 Torr of N-2, air, or O-2 diluent at 296 K. The reaction proceeds with a rate constant k(Cl + QH(5)I) = (3.3 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1) to give...

  12. The reaction of hydrogen atoms with hydrogen peroxide as a function of temperature

    DEFF Research Database (Denmark)

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

    2001-01-01

    The temperature dependence for the reaction of H atoms with H2O2 at pH 1 has been determined using pulse radiolysis technique. The reaction was studied in the temperature range 10-120 degreesC. The rate constant at 25 degreesC was found to be 5.1 +/- 0.5 x 10(7) dm(3) mol(-1) s(-1) and the activa...

  13. Experimental and computational investigation on the gas phase reaction of p-cymene with Cl atoms.

    Science.gov (United States)

    Dash, Manas Ranjan; Srinivasulu, G; Rajakumar, B

    2015-01-29

    The rate coefficient for the gas-phase reaction of Cl atoms with p-cymene was determined as a function of temperature (288-350 K) and pressure (700-800 Torr) using the relative rate technique, with 1,3-butadiene and ethylene as reference compounds. Cl atoms were generated by UV photolysis of oxalyl chloride ((COCl)2) at 254 nm, and nitrogen was used as the diluent gas. The rate coefficient for the reaction of Cl atoms with p-cymene at 298 K was measured to be (2.58 ± 1.55) × 10(-10) cm(3) molecule(-1) s(-1). The kinetic data obtained over the temperature range 288-350 K were used to derive an Arrhenius expression: k(T) = (9.36 ± 2.90) × 10(-10) exp[-(488 ± 98)/T] cm(3) molecule(-1) s(-1). Theoretical kinetic calculations were also performed for the title reaction using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) between 250 and 400 K. The calculated rate coefficients obtained over the temperature range 250-400 K were used to derive an Arrhenius expression: k(T) = 5.41 × 10(-13) exp[1837/T] cm(3) molecule(-1) s(-1). Theoretical study indicated that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected. The atmospheric lifetime (τ) of p-cymene due to its reactions with various tropospheric oxidants was estimated, and it was concluded that the reactions of p-cymene with Cl atoms may compete with OH radicals in the marine boundary layer and in coastal urban areas where the concentration of Cl atoms is high.

  14. Palladium-atom catalyzed formic acid decomposition and the switch of reaction mechanism with temperature.

    Science.gov (United States)

    He, Nan; Li, Zhen Hua

    2016-04-21

    Formic acid decomposition (FAD) reaction has been an innovative way for hydrogen energy. Noble metal catalysts, especially palladium-containing nanoparticles, supported or unsupported, perform well in this reaction. Herein, we considered the simplest model, wherein one Pd atom is used as the FAD catalyst. With high-level theoretical calculations of CCSD(T)/CBS quality, we investigated all possible FAD pathways. The results show that FAD catalyzed by one Pd atom follows a different mechanism compared with that catalyzed by surfaces or larger clusters. At the initial stage of the reaction, FAD follows a dehydration route and is quickly poisoned by CO due to the formation of very stable PdCO. PdCO then becomes the actual catalyst for FAD at temperatures approximately below 1050 K. Beyond 1050 K, there is a switch of catalyst from PdCO to Pd atom. The results also show that dehydration is always favoured over dehydrogenation on either the Pd-atom or PdCO catalyst. On the Pd-atom catalyst, neither dehydrogenation nor dehydration follows the formate mechanism. In contrast, on the PdCO catalyst, dehydrogenation follows the formate mechanism, whereas dehydration does not. We also systematically investigated the performance of 24 density functional theory methods. We found that the performance of the double hybrid mPW2PLYP functional is the best, followed by the B3LYP, B3PW91, N12SX, M11, and B2PLYP functionals.

  15. Organic thin film transistors with polymer brush gate dielectrics synthesized by atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Pinto, J.C.; Whiting, G.L.; Khodabakhsh, S.

    2008-01-01

    , synthesized by atom transfer radical polymerization (ATRP), were used to fabricate low voltage OFETs with both evaporated pentacene and solution deposited poly(3-hexylthiophene). The semiconductor-dielectric interfaces in these systems were studied with a variety of methods including scanning force microscopy...

  16. Polymer coating comprising 2-methoxyethyl acrylate units synthesized by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    2011-01-01

    Source: US2012184029A The present invention relates to preparation of a polymer coating comprising or consisting of polymer chains comprising or consisting of units of 2-methoxyethyl acrylate synthesized by Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP) such as ARGET SI ATRP...

  17. Surface-initiated Atom Transfer Radical Polymerization - a Technique to Develop Biofunctional Coatings

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren

    2009-01-01

    The initial formation of initiating sites for atom transfer radical polymerization (ATRP) on various polymer surfaces and numerous inorganic and metallic surfaces is elaborated. The subsequent ATRP grafting of a multitude of monomers from such surfaces to generate thin covalently linked polymer...

  18. Acrylamide Homopolymers and Acrylamide-N-Isopropylacrylamide Block Copolymers by Atomic Transfer Radical Polymerization in Water

    NARCIS (Netherlands)

    Wever, D. A. Z.; Raffa, P.; Picchioni, F.; Broekhuis, A. A.

    2012-01-01

    Atomic transfer radical polymerization (ATRP) of acrylamide has been accomplished in aqueous media at room temperature. By using methyl 2-chloropropionate (MeClPr) as the initiator and tris[2-(dimethylamino)ethyl]-amine (Me6TREN)/copper halogenide (CuX) as the catalyst system, different linear

  19. Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

    Science.gov (United States)

    Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

    2002-01-01

    We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

  20. Novel fluorinated block copolymer architectures fuelled by atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Jankova, Katja; Hvilsted, Søren

    2005-01-01

    Block copolymers based on poly(pentafluorostyrene), PFS, in various numbers and of different lengths, and polystyrene are prepared by atom transfer radical polymerization (ATRP). Di- and triblock copolymers with varying amounts of PFS were synthesized employing either I phenylethylbromide or 1,4-...

  1. Surface-Initiated Atom Transfer Radical Polymerization from Electrospun Mats: An Alternative to Nafion

    DEFF Research Database (Denmark)

    Javakhishvili, Irakli; Dimitrov, Ivaylo; Tynelius, Oskar

    2017-01-01

    Proton exchange membranes for fuel cell applications are synthesized by surface-initiated(SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride-co-chlorotrifluoroethylene)is electrospun into 50 μm thick mat, which is then employed as multifunctionalinitiator for copper...

  2. Optimization of transfer of laser-cooled atom cloud to a quadrupole ...

    Indian Academy of Sciences (India)

    2014-02-08

    Feb 8, 2014 ... We present here our experimental results on transfer of laser-cooled atom cloud to a quadrupole magnetic trap. We show that by choosing appropriately the ratio of potential energy in magnetic trap to kinetic energy of cloud in molasses, we can obtain the maximum phase-space density in the magnetic trap.

  3. Intramolecular proton transfer and tunnelling reactions of hydroxyphenylbenzoxazole derivatives in Xenon at 15 K

    Energy Technology Data Exchange (ETDEWEB)

    Walla, Peter J. [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany) and Department for Biophysical Chemistry, Technical University of Brunswick, Institute for Physical and Theoretical Chemistry, Hans-Sommerstr. 10, D-38106 Braunschweig (Germany)]. E-mail: pwalla@gwdg.de; Nickel, Bernhard [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany)

    2005-06-06

    We investigated the site dependence and the tunnelling processes of the intramolecular proton and deuteron transfer in the triplet state of the compounds 2-(2'-hydroxy-4'-methylphenyl)benzoxazole (m-MeHBO) and 2-(2'-hydroxy-3'-methylphenyl)benzoxazoles (o-MeHBO) and their deuterio-oxy analogues in a solid xenon matrix. After singlet excitation there occurs an ultrafast intramolecular enol {yields} keto proton transfer and subsequent intersystem crossing mainly to the keto triplet state. In the triplet state of m-MeHBO, the proton transfer back to the lower enol triplet state is governed by tunnelling processes. In o-MeHBO, however, the enol triplet state is higher and therefore normally no tunnel reaction can be observed. Because of the external heavy atom-effect in a xenon matrix, we were able to investigate the reverse enol-keto-tunnelling after exciting directly the enol triplet state of deuterated o-MeHBO. The time constants of the reverse enol-keto tautomerization are similar to those of the normal keto-enol tautomerization. In a xenon matrix, the observed site-selective phosphorescence spectra are very well-resolved vibrationally. This allowed the study of the tunnel rates in different well-defined sites. The vibrational energies obtained in the spectra are in good agreement with vibrational energies found in resonant Raman and IR spectra of 2-(2'-hydroxyphenyl)benzoxazole (HBO)

  4. Learning about Regiochemistry from a Hydrogen-Atom Abstraction Reaction in Water

    Science.gov (United States)

    Sears-Dundes, Christopher; Huon, Yoeup; Hotz, Richard P.; Pinhas, Allan R.

    2011-01-01

    An experiment has been developed in which the hydrogen-atom abstraction and the coupling of propionitrile, using Fenton's reagent, are investigated. Students learn about the regiochemistry of radical formation, the stereochemistry of product formation, and the interpretation of GC-MS data, in a safe reaction that can be easily completed in one…

  5. The reaction of nitromethane with hydrogen and deuterium atoms in the gas phase. A mechanistic study

    DEFF Research Database (Denmark)

    Lund Thomsen, E.; Nielsen, O.J.; Egsgaard, H.

    1993-01-01

    The mechanism of the reaction between H and CH3NO2, has been studied in a discharge flow system using electron paramagnetic resonance and modulated molecular beam mass spectrometry for the detection of reactants and products. Deuterium atoms have, in addition to CD3NO2, been used to support...

  6. Conceptual DFT analysis of the fragility spectra of atoms along the minimum energy reaction coordinate

    Science.gov (United States)

    Ordon, Piotr; Komorowski, Ludwik; Jedrzejewski, Mateusz

    2017-10-01

    Theoretical justification has been provided to the method for monitoring the sequence of chemical bonds' rearrangement along a reaction path, by tracing the evolution of the diagonal elements of the Hessian matrix. Relations between the divergences of Hellman-Feynman forces and the energy and electron density derivatives have been demonstrated. By the proof presented on the grounds of the conceptual density functional theory formalism, the spectral amplitude observed on the atomic fragility spectra [L. Komorowski et al., Phys. Chem. Chem. Phys. 18, 32658 (2016)] reflects selectively the electron density modifications in bonds of an atom. In fact the spectral peaks for an atom reveal changes of the electron density occurring with bonds creation, breaking, or varying with the reaction progress.

  7. Effect of atom- and group-based truncations on biomolecules simulated with reaction-field electrostatics

    Science.gov (United States)

    Ni, Boris

    2011-01-01

    The performance of the reaction-field method of electrostatics is tested in molecular dynamics simulations of protein human interleukin-4 and a short DNA fragment in explicit solvent. Two truncation schemes are considered: one based on the position of atomic charges in water molecules and the other on the position of groups of charges. The group-based truncation leads to the melting of the DNA double helix. In contrast, the atom-based truncation maintains the helical structure intact. Similarly for the protein, the group-based truncation leads to an unfolding at pH 2 while the atom-based truncation produces stable trajectories at low and normal pH, in agreement with experiment. Artificial repulsion between charged residues associated with the group-based truncation is identified as the microscopic reason behind unfolding of the protein. Implications of different truncation schemes in reaction-field simulations of biomolecules are discussed. PMID:21311933

  8. Muon transfer from muonic hydrogen to heavier atoms; Transfert de charge muonique

    Energy Technology Data Exchange (ETDEWEB)

    Dupays, A

    2004-06-01

    This work concerns muon transfer from muonic hydrogen to heavier atoms. Recently, a method of measurement of the hyperfine structure of ground-state muonic hydrogen based on the collision energy dependence of the muon transfer rate to oxygen has been proposed. This proposal is based on measurements which where performed at the Paul Scherrer Institute in the early nineties which indicate that the muon transfer from muonic hydrogen to oxygen increases by a factor of 4 going from thermal to 0.12 eV energies. The motivation of our calculations was to confirm this behaviour. To study the collision energy dependence of the muon transfer rate, we have used a time-independent close-coupling method. We have set up an hyperspherical elliptic formalism valid for nonzero total angular momentum which allows accurate computations of state-to-state reactive and charge exchange processes. We have applied this formalism to muon-transfer process to oxygen and neon. The comparison with experimental results is in both cases excellent. Finally, the neon transfer rate dependence with energy suggests to use neon instead of oxygen to perform a measurement of the hyperfine structure of muonic hydrogen. The results of accurate calculations of the muon transfer rates from muonic protium and deuterium atoms to nitrogen, oxygen and neon are also reported. Very good agreement with measured rates is obtained and for the three systems, the isotopic effect is perfectly reproduced. (author)

  9. The effect of moderators on the reactions of hot hydrogen atoms with methane

    CERN Document Server

    Estrup, Peder J.

    1960-01-01

    The reaction of recoil tritium with methane has been examined in further detail. The previous hypothesis that this system involves a hot displacement reaction of high kinetic energy hydrogen to give CH$_{3}$T, CH$_{2}$T and HT is confirmed. The effect of moderator on this process is studied by the addition of noble gases. As predicted these gases inhibit the hot reaction action, their efficiency in this respect being He > Ne > A > Se. The data are quantitatively in accord with a theory of hot atom kinetics. The mechanism of the hot displacement process is briefly discussed.

  10. Probing resonant energy transfer in collisions of ammonia with Rydberg helium atoms by microwave spectroscopy

    Science.gov (United States)

    Zhelyazkova, V.; Hogan, S. D.

    2017-12-01

    We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH3 in the X1A1 ground electronic state to helium atoms in 1sns 3S1 Rydberg levels, where n = 37 and n = 40. For these values of n, the 1sns 3S1 → 1snp 3PJ transitions in helium lie close to resonance with the ground-state inversion transitions in NH3 and can be tuned through resonance using electric fields of less than 10 V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the 3S1 and 3PJ Rydberg levels and by monitoring the population of the 3DJ levels following pulsed microwave transfer from the 3PJ levels. Detection by microwave spectroscopic methods represents a highly state selective, low-background approach to probing the collisional energy transfer process and the environment in which the atom-molecule interactions occur. The experimentally observed electric-field dependence of the resonant energy transfer process, probed both by direct electric field ionization and by microwave transfer, agrees well with the results of calculations performed using a simple theoretical model of the energy transfer process. For measurements performed in zero electric field with atoms prepared in the 1s40s 3S1 level, the transition from a regime in which a single energy transfer channel can be isolated for detection to one in which multiple collision channels begin to play a role has been identified as the NH3 density was increased.

  11. 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.

  12. Reactions between cold methyl halide molecules and alkali-metal atoms

    CERN Document Server

    Lutz, Jesse J

    2013-01-01

    We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH$_{3}X$ ($X$ = F, Cl, Br, I) and alkali-metal atoms $A$ ($A$ = Li, Na, K, Rb) using high-level {\\it ab initio} calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, ${\\rm CH}_{3}X+A\\rightarrow{\\rm CH}_{3}+AX$. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

  13. Communication: Charge transfer dominates over proton transfer in the reaction of nitric acid with gas-phase hydrated electrons

    Science.gov (United States)

    Lengyel, Jozef; Med, Jakub; Slavíček, Petr; Beyer, Martin K.

    2017-09-01

    The reaction of HNO3 with hydrated electrons (H2O)n- (n = 35-65) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and ab initio molecular dynamics simulations. Kinetic analysis of the experimental data shows that OH-(H2O)m is formed primarily via a reaction of the hydrated electron with HNO3 inside the cluster, while proton transfer is not observed and NO3-(H2O)m is just a secondary product. The reaction enthalpy was determined using nanocalorimetry, revealing a quite exothermic charge transfer with -241 ± 69 kJ mol-1. Ab initio molecular dynamics simulations indicate that proton transfer is an allowed reaction pathway, but the overall thermochemistry favors charge transfer.

  14. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive ...

  15. Potential energy surfaces for atomic oxygen reactions: Formation of singlet and triplet biradicals as primary reaction products with unsaturated organic molecules

    Science.gov (United States)

    Jaffe, Richard L.

    1987-01-01

    The experimental study of the interaction of atomic oxygen with organic polymer films under LEO conditions has been hampered by the inability to conduct detailed experiments in situ. As a result, studies of the mechanism of oxygen atom reactions have relied on laboratory O-atom sources that do not fully reproduce the orbital environment. For example, it is well established that only ground electronic state O atoms are present at LEO, yet most ground-based sources are known to produce singlet O atoms and molecules and ions in addition to O(3P). Engineers should not rely on such facilities unless it can be demonstrated either that these different O species are inert or that they react in the same fashion as ground state atoms. Ab initio quantum chemical calculations have been aimed at elucidating the biradical intermediates formed during the electrophilic addition of ground and excited-state O atoms to carbon-carbon double bonds in small olefins and aromatic molecules. These biradicals are critical intermediates in any possible insertion, addition and elimination reaction mechanisms. Through these calculations, we will be able to comment on the relative importance of these pathways for O(3P) and O(1D) reactions. The reactions of O atoms with ethylene and benzene are used to illustrate the important features of the mechanisms of atomic oxygen reaction with unsaturated organic compounds and polymeric materials.

  16. Vibrational energy and bimolecular reactions: Enhancement of the electron transfer derived product channels for quenching of Xe(3P2) and Kr(3P2) atoms by CFnCl4 - n, C2FnCl6 - n, and CF3CFClCF2Cl

    Science.gov (United States)

    Sobczynski, R.; Setser, D. W.; Slagle, A. R.

    1990-01-01

    The yields of XeCl(B,C) and KrCl(B,C) from the reactions of Xe(3P2) and Kr(3P2) metastable atoms with chlorofluoromethanes and chlorofluoroethanes are enhanced by the addition of vibrational energy to the molecule. The reactions were studied in a fast flow reactor with He or Ar carrier gas; vibrational energy was added to the molecules by multiphoton absorption from a CO2 laser pulse at fluences of 0.2-1.0 J cm-2. The enhancement of the XeCl(B,C) or KrCl(B,C) product was observed by monitoring the B-X fluorescence intensity in real time following excitations by the CO2 laser. Enhancement factors are reported for reactions with CF2Cl2, CFCl3, CF3CFCl2, CF2ClCF2Cl, CF2ClCFCl2, and CF3CFClCF2Cl; survey experiments are presented to demonstrate enhancement of XeCl* and XeBr* from vibrationally excited CF2BrCl and CF3CH2Br. The decay times of the XeCl(B) and KrCl(B) signals provide information about the relaxation rates of the vibrationally excited CFnCl4-n and C2FnCl6-n molecules. In order to have a reliable reference, the total quenching rate constants and the branching fractions for XeCl(B,C) and KrCl(B,C) formation for 300 K conditions also were measured for most of the compounds; the branching fraction for XeCl* formation form CF3CCl3 is large for a polyatomic molecule.

  17. 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

  18. Direct Measurements of Half-Cycle Reaction Heats during Atomic Layer Deposition by Calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Lownsbury, James M. [Department; Gladden, James A. [Department; Campbell, Charles T. [Department; Department; Kim, In Soo [Materials; Martinson, Alex B. F. [Materials

    2017-10-05

    We introduce a new high-temperature adsorption calorimeter that approaches the ideal limit of a heat detector whereby the signal at any time is proportional to the heat power being delivered to the sample and prove its sensitivity for measuring pulse-to-pulse heats of half-reactions during atomic layer deposition (ALD) at 400 K. The heat dynamics of amorphous Al2O3 growth via sequential self-limiting surface reaction of trimethylaluminum (TMA) and H2O is clearly resolved. Calibration enables quantitation of the exothermic TMA and H2O half-reactions with high precision, -343 kJ/mol TMA and -251 kJ/mol H2O, respectively. A time resolution better than 1 ms is demonstrated, allowing for the deconvolution of at least two distinct surface reactions during TMA microdosing. It is further demonstrated that this method can provide the heat of reaction versus extent of reaction during each precursors half-reaction, thus providing even richer mechanistic information on the surface processes involved. The broad applicability of this novel calorimeter is demonstrated through excellent signal-to-noise ratios of less exothermic ALD half-reactions to produce TiO2 and MnO.

  19. Muonium reactions with chloroacetic acid in water: Contrasts with H atoms and hydrated electrons

    Science.gov (United States)

    Stadlbauer, John M.; Venkateswaran, Krishnan; Walker, David C.

    1997-09-01

    Muonium atoms react with chloroacetic acid and chloroacetate ions in dilute aqueous solution with rate constants of 2.3 × 10 6 and 9.1 × 10 5 dm 3 mol -1 s -1 respectively. These are compared with the reactions of 1H atoms (and e aq-) and discussed in terms of a pair of competing kinetic isotope effects. Muonium reacts at least eight times faster than H overall, and probably 28 times faster in forming Cl -. It behaves as a nucleophile, thus resembling e aq- more than H, in reacting faster with the acid than the anion. Muonium's reactions must be governed to a considerable extent by quantum-mechanical effects arising from its very small mass.

  20. Muonium reactions with chloroacetic acid in water: contrasts with H atoms and hydrated electrons

    Energy Technology Data Exchange (ETDEWEB)

    Stadlbauer, J.M.; Venkateswaran, Krishnan; Walker, D.C. [British Columbia Univ., Chemistry Dept., Vancouver, BC (Canada)]|[TRIUMF, Vancouver, BC (Canada)

    1997-09-01

    Muonium atoms react with chloroacetic acid and chloroacetate ions in dilute aqueous solution with rate constants of 2.3 x 10{sup 6} and 9.1 x 10{sup 5} dm{sup 3} mol{sup -1} s{sup -1} respectively. These are compared with the reactions of {sup 1}H atoms (and e{sub aq}{sup -}) and discussed in terms of a pair of competing kinetic isotope effects. Muonium reacts at least eight times faster than H overall, and probably 28 times faster in forming Cl{sup -}. It behaves as a nucleophilic, thus resembling e{sub aq}{sup -} more than H, in reacting faster with the acid than the anion. Muonium`s reactions must be governed to a considerable extent by quantum-mechanical effects arising from its very small mass. (author).

  1. Direct time-resolved spectroscopic investigation of intramolecular hydrogen atom transfer of deoxyblebbistatin

    Science.gov (United States)

    Li, Ming-De; Zhu, Ruixue; Lee Phillips, David

    2017-09-01

    The photophysics and photochemistry of deoxyblebbistatin was investigated using femtosecond time-resolved transient absorption spectroscopy. An ultrafast intramolecular hydrogen atom transfer (IHAT) appears to take place via the first singlet excited state of deoxyblebbistatin within 8 ps. Absorption and fluorescence photochemical results indicate the IHAT process leads to mainly conversion of deoxyblebbistatin into an enol form final product which was observed and characterized by resonance Raman spectroscopy.

  2. Bibliography on electron transfer processes in ion-ion/atom/molecule collisions. Updated 1997

    Energy Technology Data Exchange (ETDEWEB)

    Tawara, H.

    1997-04-01

    Following our previous compilations (IPPJ-AM-45 (1986), NIFS-DATA-7 (1990), NIFS-DATA-20 (1993)), bibliographic information on experimental and theoretical studies on electron transfer processes in ion-ion/atom/molecule collisions is up-dated. The references published through 1954-1996 are listed in the order of the publication year. For easy finding of the references for a combination of collision partners, a simple list is provided. (author)

  3. Seawater uranium sorbents: preparation from a mesoporous copolymer initiator by atom-transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yue, Yanfeng; Mayes, Richard T.; Fulvio, Pasquale F.; Sun, Xiao-Guang [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Kim, Jungseung; Tsouris, Costas [Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Chen, Jihua [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Brown, Suree [Department of Chemistry, University of Tennessee, Knoxville, TN (United States); Dai, Sheng [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Department of Chemistry, University of Tennessee, Knoxville, TN (United States)

    2013-12-09

    Nanoporous template-free initiators for atom-transfer radical polymerization (ATRP) were synthesized with surface and framework initiator sites and tailorable pore structures. Polyacrylonitrile grown on one initiator was converted into polyamidoxime to generate a uranium sorbent for seawater extraction with a high uptake rate and capacity relative to those of nonwoven irradiation-grafted polyethylene-fiber composites. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-oxyl Radical. A Kinetic and Theoretical Study.

    Science.gov (United States)

    DiLabio, Gino A; Franchi, Paola; Lanzalunga, Osvaldo; Lapi, Andrea; Lucarini, Fiorella; Lucarini, Marco; Mazzonna, Marco; Prasad, Viki Kumar; Ticconi, Barbara

    2017-06-16

    A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the quinolinimide-N-oxyl radical (QINO) was performed in CH3CN. The HAT rate constants are significantly higher than those observed with the phthalimide-N-oxyl radical (PINO) as a result of enthalpic and polar effects due to the presence of the N-heteroaromatic ring in QINO. The relevance of polar effects is supported by theoretical calculations conducted for the reactions of the two N-oxyl radicals with toluene, which indicate that the HAT process is characterized by a significant degree of charge transfer permitted by the π-stacking that occurs between the toluene and the N-oxyl aromatic rings in the transition state structures. An increase in the HAT reactivity of QINO was observed in the presence of 0.15 M HClO4 and 0.15 M Mg(ClO4)2 due to the protonation or complexation with the Lewis acid of the pyridine nitrogen that leads to a further decrease in the electron density in the N-oxyl radical. These results fully support the use of N-hydroxyquinolinimide as a convenient substitute for N-hydroxyphthalimide in the catalytic aerobic oxidations of aliphatic hydrocarbons characterized by relatively high C-H bond dissociation energies.

  5. Simulation of temperature effect on the structure control of polystyrene obtained by atom-transfer radical polymerization

    Directory of Open Access Journals (Sweden)

    Roniérik Pioli Vieira

    Full Text Available Abstract This paper uses a new kinetic modeling and simulations to analyse the effect of temperature on the polystyrene properties obtained by atom-transfer radical polymerization (ATRP. Differently from what has been traditionaly published in ATRP modeling works, it was considered “break” reactions in the mechanism aiming to reproduce the process at high temperatures. Results suggest that there is an upper limit temperature (130 °C, above which the polymer architecture loses the control. In addition, for the system considered in this work, the optimum operating temperature was 100 °C, because at this temperature polymer with very low polydispersity index is obtained, at considerable fast polymerization rate. Therefore, this present paper provides not only a tool to study ATRP processes by simulations, but also a tool for analysis and optimization, being a basis for future works dealing with this monomer and process.

  6. Phosphonium salts as chiral phase-transfer catalysts: asymmetric Michael and Mannich reactions of 3-aryloxindoles.

    Science.gov (United States)

    He, Rongjun; Ding, Changhua; Maruoka, Keiji

    2009-01-01

    It's a PTC: A highly efficient reaction of 3-aryloxindoles in an asymmetric Michael addition was achieved by using a quaternary tetraalkylphosphonium salt as a chiral phase-transfer catalyst (PTC). The products were obtained in quantitative yields high ee values. The reaction of 3-aryloxindoles in an asymmetric Mannich reaction using the same catalyst also proved to be feasible.

  7. Hydroperoxyl Radicals (HOO(.) ): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer.

    Science.gov (United States)

    Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo

    2016-11-07

    Hydroperoxyl (HOO(.) ) and alkylperoxyl (ROO(.) ) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analogue of α-tocopherol (TOH), but HOO(.) , unlike ROO(.) , is able to regenerate TOH by a fast H-atom transfer: TO(.) +HOO(.) →TOH+O2 . The kinetic solvent effect on the H-atom transfer from TOH to HOO(.) is much stronger than that observed for ROO(.) because noncovalent interactions with polar solvents (Solv⋅⋅⋅HOO(.) ) destabilize the transition state. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Theoretical investigation of hydrogen atom transfer in the cytosine-guanine base pair and its coupling with electronic rearrangement. Concerted vs stepwise mechanism.

    Science.gov (United States)

    Villani, Giovanni

    2010-07-29

    The transformation of the DNA base pairs from the Watson-Crick (WC) structures to its tautomers having imino-enol form can be achieved via two types of hydrogen atom transfer processes: (i) concerted, and/or (ii) stepwise (step by step). Here, we have studied and compared these two mechanisms in the cytosine-guanine (C-G) system. In the first mechanism there is the concerted movement of two hydrogen atoms along two of the three H-bridges that bond the bases, one from the cytosine to guanine and the other in the opposite direction. This movement must be coupled to an electronic reorganization, with some bond orders that pass from single to double and vice versa, in order to preserve the neutrality of these new structures. In the stepwise mechanism the movement of the hydrogen atoms and the electronic reorganization are not concerted, and it implicates the movement of a hydrogen atom at a time with the identification of two or more steps in this reaction. There are two possible neutral imino-enol structures in the C-G system, and both have been considered here. The principal result from this paper is that a different behavior is observed if the hydrogen transfer begins with a H of the guanine or of the cytosine and that a concerted (synchronic in the N-N and asynchronic in the N-O) double-hydrogen transfer can be activated only when the first H atom to move is that of the guanine, in particular. This is different from the A-T system(1) studied previously where the movement in a N-N bridge produces a zwitterionic structure and that in the N-O the concerted double-hydrogen transfer. In both cases a general conclusion can be given: the concerted double-hydrogen process begins with a hydrogen atom of a purinic base.

  9. Back-Influence of Molecular Motion on Energy Transfer in the Landau-Teller Model of Atom Molecule Scattering.

    Science.gov (United States)

    Pollak, Eli

    2016-07-21

    This year we celebrate the 80th anniversary of the Landau-Teller model for energy exchange in a collinear collision of an atom with a harmonic diatomic molecule. Even after 80 years though, the analytic theory to date has not included in it the back-influence of the oscillator's motion on the energy transfer between the approaching particle and the molecule. This is the topic of the present paper. The back-influence can be obtained by employing classical second-order perturbation theory. The second-order theory is used in both a classical and semiclassical context. Classically, analytic expressions are derived for the final phase and action of the diatom, after the collision. The energy loss of the atom is shown to decrease linearly with the increasing energy of the oscillator. The magnitude of this decrease is a direct consequence of the back-reaction of the oscillator on the translational motion. The qualitative result is universal, in the sense that it is not dependent on the details of the interaction of the atom with the oscillator. A numerical application to a model collision of an Ar atom with a Br2 diatom demonstrates the importance and accuracy of the second-order perturbation theory. The same results are then used to derive a second-order perturbation theory semiclassical expression for the quantum transition probability from initial vibrational state ni to final vibrational state nf of the oscillator. A comparison of the theory with exact quantum data is presented for a model collision of Br2 with a hydrogen molecule, where the hydrogen molecule is considered as a single approaching particle.

  10. From a network of computed reaction enthalpies to atom-based thermochemistry (NEAT).

    Science.gov (United States)

    Császár, Attila G; Furtenbacher, Tibor

    2010-04-26

    A simple and fast, weighted, linear least-squares refinement protocol and code is presented for inverting the information contained in a network of quantum chemically computed 0 K reaction enthalpies. This inversion yields internally consistent 0 K enthalpies of formation for the species of the network. The refinement takes advantage of the fact that the accuracy of computed enthalpies depends strongly on the quantum-chemical protocol employed for their determination. Different protocols suffer from different sources of error; thus, the reaction enthalpies computed by them have "random" residual errors. Since it is much more natural for quantum-chemical energy and enthalpy results, including reaction enthalpies, to be based on the electronic ground states of the atoms and not on the historically preferred elemental states, and since these two possible protocols can be converted into each other straightforwardly, it is proposed that first-principles thermochemistry should employ the ground electronic states of atoms. In this scheme, called atom-based thermochemistry (AT), the enthalpy of formation of a gaseous compound corresponds simply to the total atomization energy of the species; it is always positive, and it reflects the bonding strength within the molecule. The inversion protocol developed and based on AT is termed NEAT, which represents the fact that the protocol proceeds from a network of computed reaction enthalpies toward atom-based thermochemistry, most directly to atom-based enthalpies of formation. After assembling a database that consisted of 361 ab initio reactions and reaction enthalpies involving 188 species, collected from 31 literature sources, the following dependable 0 K atom-based enthalpies of formation, Delta(f)${H{{{\\rm AT}\\hfill \\atop 0\\hfill}}}$, all in kJ mol(-1), have been obtained by means of NEAT: H(2)=432.07(0), CH=334.61(15), NH=327.69(25), OH=425.93(21), HF=566.13(31), CO=1072.08(28), O(2)=493.51(34), CH(2)=752.40(21), H(2)O

  11. A model for energy transfer in collisions of atoms with highly excited molecules.

    Science.gov (United States)

    Houston, Paul L; Conte, Riccardo; Bowman, Joel M

    2015-05-21

    A model for energy transfer in the collision between an atom and a highly excited target molecule has been developed on the basis of classical mechanics and turning point analysis. The predictions of the model have been tested against the results of trajectory calculations for collisions of five different target molecules with argon or helium under a variety of temperatures, collision energies, and initial rotational levels. The model predicts selected moments of the joint probability distribution, P(Jf,ΔE) with an R(2) ≈ 0.90. The calculation is efficient, in most cases taking less than one CPU-hour. The model provides several insights into the energy transfer process. The joint probability distribution is strongly dependent on rotational energy transfer and conservation laws and less dependent on vibrational energy transfer. There are two mechanisms for rotational excitation, one due to motion normal to the intermolecular potential and one due to motion tangential to it and perpendicular to the line of centers. Energy transfer is found to depend strongly on the intermolecular potential and only weakly on the intramolecular potential. Highly efficient collisions are a natural consequence of the energy transfer and arise due to collisions at "sweet spots" in the space of impact parameter and molecular orientation.

  12. Atomic layer deposition by reaction of molecular oxygen with tetrakisdimethylamido-metal precursors

    Energy Technology Data Exchange (ETDEWEB)

    Provine, J, E-mail: jprovine@stanford.edu; Schindler, Peter; Torgersen, Jan; Kim, Hyo Jin [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Karnthaler, Hans-Peter [Physics of Nanostructured Materials, University of Vienna, 1090 Vienna (Austria); Prinz, Fritz B. [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 and Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)

    2016-01-15

    Tetrakisdimethylamido (TDMA) based precursors are commonly used to deposit metal oxides such as TiO{sub 2}, ZrO{sub 2}, and HfO{sub 2} by means of chemical vapor deposition and atomic layer deposition (ALD). Both thermal and plasma enhanced ALD (PEALD) have been demonstrated with TDMA-metal precursors. While the reactions of TDMA-type precursors with water and oxygen plasma have been studied in the past, their reactivity with pure O{sub 2} has been overlooked. This paper reports on experimental evaluation of the reaction of molecular oxygen (O{sub 2}) and several metal organic precursors based on TDMA ligands. The effect of O{sub 2} exposure duration and substrate temperature on deposition and film morphology is evaluated and compared to thermal reactions with H{sub 2}O and PEALD with O{sub 2} plasma.

  13. ARTICLE Crossed Beams Study on the Dynamics of F Atom Reaction with 1,2-Butadiene

    Science.gov (United States)

    Xiao, Chong-fa; Shen, Guan-lin; Wang, Xiu-yan; Yang, Xue-ming

    2010-12-01

    We have investigated the dynamics of the F+C4H6 reaction using the universal crossed molecular beam method. The C4H5F+H reaction channel was observed in this experiment. Angular resolved time-of-flight spectra have been measured for the C4H5F product. Product angular distributions as well as kinetic energy distributions were determined for this product channel. Experimental results show that the C4H5F product is largely backward scattered with considerable forward scattering signal, relative to the F atom beam direction. This suggests that the reaction channel mainly proceeds via a long-lived complex formation mechanism, with possible contribution from a direct SN2 type mechanism.

  14. Prediction of oxidoreductase-catalyzed reactions based on atomic properties of metabolites.

    Science.gov (United States)

    Mu, Fangping; Unkefer, Pat J; Unkefer, Clifford J; Hlavacek, William S

    2006-12-15

    Our knowledge of metabolism is far from complete, and the gaps in our knowledge are being revealed by metabolomic detection of small-molecules not previously known to exist in cells. An important challenge is to determine the reactions in which these compounds participate, which can lead to the identification of gene products responsible for novel metabolic pathways. To address this challenge, we investigate how machine learning can be used to predict potential substrates and products of oxidoreductase-catalyzed reactions. We examined 1956 oxidation/reduction reactions in the KEGG database. The vast majority of these reactions (1626) can be divided into 12 subclasses, each of which is marked by a particular type of functional group transformation. For a given transformation, the local structures of reaction centers in substrates and products can be characterized by patterns. These patterns are not unique to reactants but are widely distributed among KEGG metabolites. To distinguish reactants from non-reactants, we trained classifiers (linear-kernel Support Vector Machines) using negative and positive examples. The input to a classifier is a set of atomic features that can be determined from the 2D chemical structure of a compound. Depending on the subclass of reaction, the accuracy of prediction for positives (negatives) is 64 to 93% (44 to 92%) when asking if a compound is a substrate and 71 to 98% (50 to 92%) when asking if a compound is a product. Sensitivity analysis reveals that this performance is robust to variations of the training data. Our results suggest that metabolic connectivity can be predicted with reasonable accuracy from the presence or absence of local structural motifs in compounds and their readily calculated atomic features. Classifiers reported here can be used freely for noncommercial purposes via a Java program available upon request.

  15. Handshake electron transfer from hydrogen Rydberg atoms incident at a series of metallic thin films.

    Science.gov (United States)

    Gibbard, J A; Softley, T P

    2016-06-21

    Thin metallic films have a 1D quantum well along the surface normal direction, which yields particle-in-a-box style electronic quantum states. However the quantum well is not infinitely deep and the wavefunctions of these states penetrate outside the surface where the electron is bound by its own image-charge attraction. Therefore a series of discrete, vacant states reach out from the thin film into the vacuum increasing the probability of electron transfer from an external atom or molecule to the thin film, especially for the resonant case where the quantum well energy matches that of the atom. We show that "handshake" electron transfer from a highly excited Rydberg atom to these thin-film states is experimentally measurable. Thicker films have a wider 1D box, changing the energetic distribution and image-state contribution to the thin film wavefunctions, resulting in more resonances. Calculations successfully predict the number of resonances and the nature of the thin-film wavefunctions for a given film thickness.

  16. Photonic quantum state transfer between a cold atomic gas and a crystal.

    Science.gov (United States)

    Maring, Nicolas; Farrera, Pau; Kutluer, Kutlu; Mazzera, Margherita; Heinze, Georg; de Riedmatten, Hugues

    2017-11-22

    Interfacing fundamentally different quantum systems is key to building future hybrid quantum networks. Such heterogeneous networks offer capabilities superior to those of their homogeneous counterparts, as they merge the individual advantages of disparate quantum nodes in a single network architecture. However, few investigations of optical hybrid interconnections have been carried out, owing to fundamental and technological challenges such as wavelength and bandwidth matching of the interfacing photons. Here we report optical quantum interconnection of two disparate matter quantum systems with photon storage capabilities. We show that a quantum state can be transferred faithfully between a cold atomic ensemble and a rare-earth-doped crystal by means of a single photon at 1,552  nanometre telecommunication wavelength, using cascaded quantum frequency conversion. We demonstrate that quantum correlations between a photon and a single collective spin excitation in the cold atomic ensemble can be transferred to the solid-state system. We also show that single-photon time-bin qubits generated in the cold atomic ensemble can be converted, stored and retrieved from the crystal with a conditional qubit fidelity of more than 85 per cent. Our results open up the prospect of optically connecting quantum nodes with different capabilities and represent an important step towards the realization of large-scale hybrid quantum networks.

  17. 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.

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

    Science.gov (United States)

    Sun, Yuming; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian

    2016-10-01

    Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C2-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.

  19. Preparation of a novel polymer monolith with functional polymer brushes by two-step atom-transfer radical polymerization for trypsin immobilization.

    Science.gov (United States)

    Li, Nan; Zheng, Wei; Shen, Ying; Qi, Li; Li, Yaping; Qiao, Juan; Wang, Fuyi; Chen, Yi

    2014-12-01

    Novel porous polymer monoliths grafted with poly{oligo[(ethylene glycol) methacrylate]-co-glycidyl methacrylate} brushes were fabricated via two-step atom-transfer radical polymerization and used as a trypsin-based reactor in a continuous flow system. This is the first time that atom-transfer radical polymerization technique was utilized to design and construct polymer monolith bioreactor. The prepared monoliths possessed excellent permeability, providing fast mass transfer for enzymatic reaction. More importantly, surface properties, which were modulated via surface-initiated atom-transfer radical polymerization, were found to have a great effect on bioreactor activities based on Michaelis-Menten studies. Furthermore, three model proteins were digested by the monolith bioreactor to a larger degree within dramatically reduced time (50 s), about 900 times faster than that by free trypsin (12 h). The proposed method provided a platform to prepare porous monoliths with desired surface properties for immobilizing various enzymes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Tracking F plasmid TraI relaxase processing reactions provides insight into F plasmid transfer

    OpenAIRE

    Dostál, Lubomír; Shao, Sichen; Schildbach, Joel F.

    2010-01-01

    Early in F plasmid conjugative transfer, the F relaxase, TraI, cleaves one plasmid strand at a site within the origin of transfer called nic. The reaction covalently links TraI Tyr16 to the 5′-ssDNA phosphate. Ultimately, TraI reverses the cleavage reaction to circularize the plasmid strand. The joining reaction requires a ssDNA 3′-hydroxyl; a second cleavage reaction at nic, regenerated by extension from the plasmid cleavage site, may generate this hydroxyl. Here we confirm that TraI is tran...

  1. Measurement of Proton-Induced Transfer Reactions with JENSA

    Science.gov (United States)

    Chatterjee, Sidharth; Chipps, Kelly; Pain, Steven; Cizewski, Jolie; Jensa Collaboration

    2017-09-01

    Reaction measurements of radioactive nuclei on light targets are important to understanding the origin of and the trends in the structure of nuclei. To efficiently measure nuclear reactions, measurements require highly localized and pure light targets and need to accommodate arrays of light charged particles, gamma rays, and recoiling heavy ions. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) jet target system was designed to facilitate high resolution, low background nuclear reaction studies. To demonstrate the capability of the JENSA system, the 20Ne(p,3He)18F reaction was studied during the commissioning phase. The radioisotope 18F is one of the galactic gamma-ray sources targeted by next-generation space-based telescopes. In addition, the 20Ne(p,3He) reaction has not been previously used for the spectroscopic study of 18F. The JENSA system gives us the opportunity to study this reaction with high resolution and low background. The measurement was performed with a proton beam from the Holifield Radioactive Ion Beam Facility tandem on a neon jet of natural isotopic abundance from JENSA. The experimental setup of JENSA and preliminary results will be discussed. Oak Ridge National Laboratory; Rutgers University Department of Physics and Astronomy.

  2. Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer

    Science.gov (United States)

    Cabrero-Vilatela, A.; Alexander-Webber, J. A.; Sagade, A. A.; Aria, A. I.; Braeuninger-Weimer, P.; Martin, M.-B.; Weatherup, R. S.; Hofmann, S.

    2017-12-01

    The transfer of chemical vapour deposited graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to remove completely and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100 nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.

  3. Light-Mediated Atom Transfer Radical Polymerization of Semi-Fluorinated (Meth)acrylates: Facile Access to Functional Materials.

    Science.gov (United States)

    Discekici, Emre H; Anastasaki, Athina; Kaminker, Revital; Willenbacher, Johannes; Truong, Nghia P; Fleischmann, Carolin; Oschmann, Bernd; Lunn, David J; Read de Alaniz, Javier; Davis, Thomas P; Bates, Christopher M; Hawker, Craig J

    2017-04-26

    A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results disclosed herein should create opportunities across a variety of fields that exploit fluorine-containing polymers for tailored bulk, interfacial, and solution properties.

  4. Chemical reaction on MHD flow and heat transfer of a nanofluid ...

    African Journals Online (AJOL)

    DR OKE

    Keywords: Stagnation point flow; Chemical reaction; Heat transfer; Stretching ..... combined effects of the strength of the Brownian motion and thermophoresis .... J. and Hu W., 2005, Nanofluid coolants for advanced nuclear power plants”.

  5. Theoretical study on the excited-state intramolecular proton-transfer reaction of 10-hydroxybenzo[h]quinoline in methanol and cyclohexane

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Meng [Department of Chemistry, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Zhao, Jinfeng [Department of Physics, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Cui, Yanling; Wang, Qianyu [Department of Physics, Liaoning University, Shenyang 110036 (China); Dai, Yumei [Normal College, Shenyang University, Shenyang 110044 (China); Song, Peng, E-mail: songpeng@lnu.edu.cn [Department of Physics, Liaoning University, Shenyang 110036 (China); Xia, Lixin, E-mail: lixinxia@lnu.edu.cn [Department of Chemistry, Liaoning University, Shenyang 110036 (China)

    2015-05-15

    The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of 10-hydroxybenzoquinoline (HBQ) in different solvents, have been investigated based on the time-dependent density functional theory (TD-DFT) in detail. Upon excitation, the intramolecular hydrogen bond between the hydroxyl and phenanthrene functionality is significantly strengthened in the S{sub 1} state, which can be used as a reasonable tendency for facilitating the ESIPT process. In addition, the calculated vertical excitation energies in the S{sub 0} state and S{sub 1} state reproduce the experimental UV–vis absorbance and fluorescence emission spectra well. Through calculating the fluorescence spectra of the HBQ chromophore, two outcomes for this chromophore were found in the S{sub 1} state, which demonstrates that the ESIPT process occurs. The potential energy curves have been calculated to account for the mechanism of the proton-transfer process in the excited-state. As a result, the barrierless ESIPT process can occur in the S{sub 1} state with proton transfer from the O atom to the N atom. And maybe the ESIPT process is easier in methanol solvent due to the higher potential energy difference. - Highlights: • The hydrogen bond between the hydroxyl and phenanthrene is strengthened. • The hydrogen bond facilitates the proton transfer from the hydroxyl group to the N atom. • The spontaneous excited-state intramolecular proton transfer reaction can be observed.

  6. Efficient and Adaptive Methods for Computing Accurate Potential Surfaces for Quantum Nuclear Effects: Applications to Hydrogen-Transfer Reactions.

    Science.gov (United States)

    DeGregorio, Nicole; Iyengar, Srinivasan S

    2018-01-09

    We present two sampling measures to gauge critical regions of potential energy surfaces. These sampling measures employ (a) the instantaneous quantum wavepacket density, an approximation to the (b) potential surface, its (c) gradients, and (d) a Shannon information theory based expression that estimates the local entropy associated with the quantum wavepacket. These four criteria together enable a directed sampling of potential surfaces that appears to correctly describe the local oscillation frequencies, or the local Nyquist frequency, of a potential surface. The sampling functions are then utilized to derive a tessellation scheme that discretizes the multidimensional space to enable efficient sampling of potential surfaces. The sampled potential surface is then combined with four different interpolation procedures, namely, (a) local Hermite curve interpolation, (b) low-pass filtered Lagrange interpolation, (c) the monomial symmetrization approximation (MSA) developed by Bowman and co-workers, and (d) a modified Shepard algorithm. The sampling procedure and the fitting schemes are used to compute (a) potential surfaces in highly anharmonic hydrogen-bonded systems and (b) study hydrogen-transfer reactions in biogenic volatile organic compounds (isoprene) where the transferring hydrogen atom is found to demonstrate critical quantum nuclear effects. In the case of isoprene, the algorithm discussed here is used to derive multidimensional potential surfaces along a hydrogen-transfer reaction path to gauge the effect of quantum-nuclear degrees of freedom on the hydrogen-transfer process. Based on the decreased computational effort, facilitated by the optimal sampling of the potential surfaces through the use of sampling functions discussed here, and the accuracy of the associated potential surfaces, we believe the method will find great utility in the study of quantum nuclear dynamics problems, of which application to hydrogen-transfer reactions and hydrogen

  7. Atomic-Scale Modeling of Particle Size Effects for the Oxygen Reduction Reaction of Pt

    DEFF Research Database (Denmark)

    Tritsaris, Georgios; Greeley, Jeffrey Philip; Rossmeisl, Jan

    2011-01-01

    We estimate the activity of the oxygen reduction reaction on platinum nanoparticles of sizes of practical importance. The proposed model explicitly accounts for surface irregularities and their effect on the activity of neighboring sites. The model reproduces the experimentally observed trends...... in both the specific and mass activities for particle sizes in the range between 2 and 30 nm. The mass activity is calculated to be maximized for particles of a diameter between 2 and 4 nm. Our study demonstrates how an atomic-scale description of the surface microstructure is a key component...

  8. In situ AFM investigation of electrochemically induced surface-initiated atom-transfer radical polymerization.

    Science.gov (United States)

    Li, Bin; Yu, Bo; Zhou, Feng

    2013-02-12

    Electrochemically induced surface-initiated atom-transfer radical polymerization is traced by in situ AFM technology for the first time, which allows visualization of the polymer growth process. It affords a fundamental insight into the surface morphology and growth mechanism simultaneously. Using this technique, the polymerization kinetics of two model monomers were studied, namely the anionic 3-sulfopropyl methacrylate potassium salt (SPMA) and the cationic 2-(metharyloyloxy)ethyltrimethylammonium chloride (METAC). The growth of METAC is significantly improved by screening the ammonium cations by the addition of ionic liquid electrolyte in aqueous solution. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Hydrophilization of poly(ether ether ketone) films by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren

    2010-01-01

    Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) has been exploited to hydrophilize PEEK. The ketone groups on the PEEK surface were reduced to hydroxyl groups which were converted to bromoisobutyrate initiating sites for SI-ATRP. The modification steps were followed by contact...... angle measurements and XPS. Moreover, ATR FTIR has been used to confirm the formation of initiating groups. Grafting of PEGMA from PEEK was performed in aqueous solution. The presence of the PPEGMA grafts on PEEK was revealed by the thermograms from TGA whereas investigations with AFM rejected changes...

  10. Acrylamide Homopolymers and Acrylamide-N-Isopropylacrylamide Block Copolymers by Atomic Transfer Radical Polymerization in Water

    OpenAIRE

    Wever, D. A. Z.; Raffa, P.; Picchioni, F.; Broekhuis, A.A.

    2012-01-01

    Atomic transfer radical polymerization (ATRP) of acrylamide has been accomplished in aqueous media at room temperature. By using methyl 2-chloropropionate (MeClPr) as the initiator and tris[2-(dimethylamino)ethyl]-amine (Me6TREN)/copper halogenide (CuX) as the catalyst system, different linear polyacrylamides with apparent molecular weights up to >150 000 g/mol were synthesized with dispersities as low as 1.39. The molecular weights agreed well with the theoretical ones at relatively low-medi...

  11. 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.

  12. Proton transfer reaction-mass spectrometry applications in medical research.

    Science.gov (United States)

    Herbig, Jens; Amann, Anton

    2009-06-01

    Gathering information about a subject's physiological and pathophysiological condition from the `smell' of breath is an idea that dates back to antiquity. This intriguing concept of non-invasive diagnosis has been revitalized by `exhaled breath analysis' in recent decades. A main driving force was the development of sensitive and versatile gas-chromatographic and mass-spectrometric instruments for trace gas analysis. Ironically, only non-smelling constituents of breath, such as O(2), CO(2), H(2), and NO have so far been included in routine clinical breath analysis. The `smell' of human breath, on the other hand, arises through a combination of volatile organic compounds (VOCs) of which several hundred have been identified to date. Most of these volatiles are systemic and are released in the gas-exchange between blood and air in the alveoli. The concentration of these compounds in the alveolar breath is related to the respective concentrations in blood. Measuring VOCs in exhaled breath allows for screening of disease markers, studying the uptake and effect of medication (pharmacokinetics), or monitoring physiological processes. There is a range of requirements for instruments for the analysis of a complex matrix, such as human breath. Mass-spectrometric techniques are particularly well suited for this task since they offer the possibility of detecting a large variety of interesting compounds. A further requirement is the ability to measure accurately in the concentration range of breath VOCs, i.e. between parts-per-trillion (pptv) and parts-per-million (ppmv) range. In the mid 1990's proton transfer reaction-mass spectrometry (PTR-MS) was developed as a powerful and promising tool for the analysis of VOCs in gaseous media. Soon thereafter these instruments became commercially available to a still growing user community and have now become standard equipment in many fields including environmental research, food and flavour science, as well as life sciences. Their

  13. Mass transfer. Liquid-liquid extraction with chemical reaction; Transfert de matiere. Extraction liquide-liquide avec reaction chimique

    Energy Technology Data Exchange (ETDEWEB)

    Buch, A.; Rakib, M.; Stambouli, M. [Ecole Centrale de Paris, 75 (France)

    2009-06-15

    The coupling between the mass transfer and the chemical reaction is in the heart of the processes carried out in liquid-liquid extraction called reactive extraction. This coupling is in particular used in industrial applications such as nuclear industry (Purex process..). (O.M.)

  14. Tracking F plasmid TraI relaxase processing reactions provides insight into F plasmid transfer.

    Science.gov (United States)

    Dostál, Lubomír; Shao, Sichen; Schildbach, Joel F

    2011-04-01

    Early in F plasmid conjugative transfer, the F relaxase, TraI, cleaves one plasmid strand at a site within the origin of transfer called nic. The reaction covalently links TraI Tyr16 to the 5'-ssDNA phosphate. Ultimately, TraI reverses the cleavage reaction to circularize the plasmid strand. The joining reaction requires a ssDNA 3'-hydroxyl; a second cleavage reaction at nic, regenerated by extension from the plasmid cleavage site, may generate this hydroxyl. Here we confirm that TraI is transported to the recipient during transfer. We track the secondary cleavage reaction and provide evidence it occurs in the donor and F ssDNA is transferred to the recipient with a free 3'-hydroxyl. Phe substitutions for four Tyr within the TraI active site implicate only Tyr16 in the two cleavage reactions required for transfer. Therefore, two TraI molecules are required for F plasmid transfer. Analysis of TraI translocation on various linear and circular ssDNA substrates supports the assertion that TraI slowly dissociates from the 3'-end of cleaved F plasmid, likely a characteristic essential for plasmid re-circularization.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Frutos, Luis Manuel, E-mail: luisma.frutos@uah.es [Departamento de Química Física, Universidad de Alcalá, 28871 Alcalá de Henares, Madrid (Spain); Acuña, A. Ulises [Instituto de Química Física “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid (Spain)

    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.

  16. 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

    2014-01-01

    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.

  17. Reaction mechanism studies for platinum nanoparticle growth by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Liang Xinhua; Zhou Yun; Li Jianhua; Weimer, Alan W., E-mail: alan.weimer@colorado.edu [University of Colorado, Department of Chemical and Biological Engineering (United States)

    2011-09-15

    Mass spectrometry is used to study the reaction mechanism of platinum (Pt) atomic layer deposition (ALD) on large quantities of high surface area silica gel particles in a fluidized bed reactor. (Methylcyclopentadienyl)trimethylplatinum [(MeCp)PtMe{sub 3}] and oxygen are used as precursors. Studies are conducted at a substrate temperature of 320 Degree-Sign C. The self-limiting behavior of ALD appears to be disrupted with overexposure of Pt precursor. The amount of the deposited Pt and the size of the Pt nanoparticles increase with an increasing overdose time of Pt precursor. This can be explained by the thermal decomposition of Pt precursor at the reaction temperature of 320 Degree-Sign C and the in situ sintering of Pt nanoparticles forming larger particles. This finding is significant and its understanding is essential for better control of Pt deposition to achieve desirable morphological and structural properties for different application requirements.

  18. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Science.gov (United States)

    Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

    2018-01-01

    Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe2 )] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene /MoSe2 is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature MoSe2 exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe2 Raman modes, which reveals net photoinduced electron transfer from MoSe2 to graphene and hole accumulation in MoSe2 . Remarkably, the steady-state Fermi energy of graphene saturates at 290 ±15 meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene /MoSe2 . This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the

  19. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Guillaume Froehlicher

    2018-01-01

    Full Text Available Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe_{2}] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene/MoSe_{2} is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps room-temperature MoSe_{2} exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe_{2} Raman modes, which reveals net photoinduced electron transfer from MoSe_{2} to graphene and hole accumulation in MoSe_{2}. Remarkably, the steady-state Fermi energy of graphene saturates at 290±15  meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene/MoSe_{2}. This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron

  20. The 2H(e, e' p)n reaction at large energy transfers

    NARCIS (Netherlands)

    Willering, Hendrik Willem

    2003-01-01

    At the ELSA accelerator facillity in Bonn, Germany, we have measured the deutron "breakup" reaction 2H(e,e' p)n at four-momentum transfers around Q2 = -0 .20(GeV/c)2 with an electron beam energy of E0 = 1.6 GeV. The cross section has been determined for energy transfers extending from the

  1. Theoretical study of the reaction kinetics of atomic bromine with tetrahydropyran

    KAUST Repository

    Giri, Binod

    2015-02-12

    A detailed theoretical analysis of the reaction of atomic bromine with tetrahydropyran (THP, C5H10O) was performed using several ab initio methods and statistical rate theory calculations. Initial geometries of all species involved in the potential energy surface of the title reaction were obtained at the B3LYP/cc-pVTZ level of theory. These molecular geometries were reoptimized using three different meta-generalized gradient approximation (meta-GGA) functionals. Single-point energies of the stationary points were obtained by employing the coupled-cluster with single and double excitations (CCSD) and fourth-order Møller-Plesset (MP4 SDQ) levels of theory. The computed CCSD and MP4(SDQ) energies for optimized structures at various DFT functionals were found to be consistent within 2 kJ mol-1. For a more accurate energetic description, single-point calculations at the CCSD(T)/CBS level of theory were performed for the minimum structures and transition states optimized at the B3LYP/cc-pVTZ level of theory. Similar to other ether + Br reactions, it was found that the tetrahydropyran + Br reaction proceeds in an overall endothermic addition-elimination mechanism via a number of intermediates. However, the reactivity of various ethers with atomic bromine was found to vary substantially. In contrast with the 1,4-dioxane + Br reaction, the chair form of the addition complex (c-C5H10O-Br) for THP + Br does not need to undergo ring inversion to form a boat conformer (b-C4H8O2-Br) before the intramolecular H-shift can occur to eventually release HBr. Instead, a direct, yet more favorable route was mapped out on the potential energy surface of the THP + Br reaction. The rate coefficients for all relevant steps involved in the reaction mechanism were computed using the energetics of coupled cluster calculations. On the basis of the results of the CCSD(T)/CBS//B3LYP/cc-pVTZ level of theory, the calculated overall rate coefficients can be expressed as kov.,calc.(T) = 4.60 × 10

  2. Application of a BOSS-Gaussian interface for QM/MM simulations of Henry and methyl transfer reactions.

    Science.gov (United States)

    Vilseck, Jonah Z; Kostal, Jakub; Tirado-Rives, Julian; Jorgensen, William L

    2015-10-15

    Hybrid quantum mechanics and molecular mechanics (QM/MM) computer simulations have become an indispensable tool for studying chemical and biological phenomena for systems too large to treat with QM alone. For several decades, semiempirical QM methods have been used in QM/MM simulations. However, with increased computational resources, the introduction of ab initio and density function methods into on-the-fly QM/MM simulations is being increasingly preferred. This adaptation can be accomplished with a program interface that tethers independent QM and MM software packages. This report introduces such an interface for the BOSS and Gaussian programs, featuring modification of BOSS to request QM energies and partial atomic charges from Gaussian. A customizable C-shell linker script facilitates the interprogram communication. The BOSS-Gaussian interface also provides convenient access to Charge Model 5 (CM5) partial atomic charges for multiple purposes including QM/MM studies of reactions. In this report, the BOSS-Gaussian interface is applied to a nitroaldol (Henry) reaction and two methyl transfer reactions in aqueous solution. Improved agreement with experiment is found by determining free-energy surfaces with MP2/CM5 QM/MM simulations than previously reported investigations using semiempirical methods. © 2015 Wiley Periodicals, Inc.

  3. Charge transfer and association of Na+ with 87Rb atoms from extremely low to intermediate energies

    Science.gov (United States)

    Yan, L. L.; Liu, L.; Wu, Y.; Qu, Y. Z.; Wang, J. G.; Buenker, R. J.

    2013-07-01

    The nonradiative charge-transfer processes in Na++87Rb(5s) collisions have been investigated by using the quantum-mechanical molecular-orbital close-coupling method and the two-center atomic-orbital close-coupling method for the energy range of 10-4-5 and 0.3-100 keV/u, respectively. The radiative charge-transfer, radiative-decay, and radiative-association processes have been investigated by using the fully quantum, optical-potential, and semiclassical methods for the energy range of 10-18-0.2 eV/u. The nonradiative charge-transfer processes dominate the collisions for energies above 0.2 eV/u and radiative-decay processes dominate in the lower-energy region. At the very low collision energies of 10-18-10-3 eV/u, the radiative-association process is more important than the radiative charge-transfer process. Most importantly, it is found that the radiative cross sections exhibit Langevin behavior as E-1/2 for energies less than 10-2 eV/u.

  4. Modeling of mass transfer in combination with a homogeneously catalyzed reaction

    NARCIS (Netherlands)

    Hoorn, J.A.A.; Versteeg, G. F.

    The mass transfer rates of a gaseous reactant into a liquid where the reactions are catalyzed by homogeneous catalysts have been evaluated by the numerical solution of the diffusion-reaction equations according to Higbie's penetration theory. The concentration profiles as well as enhancement factors

  5. Excited states populated via nucleon transfer in the reaction [sup 32]S+[sup 208]Pb

    Energy Technology Data Exchange (ETDEWEB)

    Corradi, L.; Petrache, C.M.; Ackermann, D.; De Angelis, G.; Moreno, H.; Napoli, D.R.; Spolaore, P.; Stefanini, A.M. (INFN, Lab. Nazionali di Legnaro (Italy)); Beghini, S.; Montagnoli, G.; Scarlassara, F.; Segato, G.F.; Signorini, C. (Padua Univ. (Italy). Dipt. di Fisica INFN, Padua (Italy)); Pollarolo, G. (Turin Univ. (Italy). Dipt. di Fisica INFN, Turin (Italy))

    1993-01-01

    The population strengths of excited states in nuclei produced via transfer reactions in the 185 MeV[sup 32]S+[sup 208]Pb reaction have been investigated by heavy-ion-[gamma] coincidence techniques. The cross sections extracted from the [gamma] spectra, have been analyzed in the framework of the Complex WKB approximation theory. (orig.).

  6. Dynamics of the reaction of O(3P) atoms with alkylthiol self-assembled monolayers.

    Science.gov (United States)

    Waring, Carla; Bagot, Paul A J; Räisänen, Minna T; Costen, Matthew L; McKendrick, Kenneth G

    2009-04-23

    We have studied the dynamics of the reactions of O((3)P) atoms with alkylthiol self-assembled monolayers (SAMs). Superthermal O((3)P) atoms, with a fairly broad distribution of laboratory-frame kinetic energies (mean = 16 kJ mol(-1), fwhm = 26 kJ mol(-1)), were generated by 355 nm photolysis of NO(2) introduced at a low pressure above the SAM surface. Nascent OH v' = 0 products were detected by laser-induced fluorescence. SAMs of two different alkyl chain lengths, C(6) and C(18), were studied. The existence of SAM layers, and their robustness under our experimental conditions during the relevant measurement period, were confirmed by scanning-tunneling microscopy (STM). Reaction at the SAM surface was verified as the authentic source of the hydroxyl radicals using a perdeuterated C(6)D(13)-SAM sample. The OH appearance profiles as a function of photolysis-probe delay, and the rotational-state distributions at their peaks, were compared with those of liquid squalane (C(30)H(62), 2,6,10,15,19,23-hexamethyltetracosane). The reactivity of the SAMs and of squalane was found to be comparable. We conclude that the O((3)P) atoms must be able to access the more reactive secondary hydrogen atoms along the alkyl chains of the SAMs. We find no perceptible differences in reactivity or product energy disposal between the two SAM chain lengths. Both produce a substantial fraction of the OH with relatively high velocities, which must result from direct, impulsive reaction. There is also a slower component, with velocities consistent with a thermal, trapping-desorption mechanism. The proportion of this component appears to be lower for SAMs than for squalane. This would be compatible with the expected greater smoothness of the SAM surface at the molecular scale. We find little evidence for significant rotational excitation of the OH products, although the details of any correlation between translational and rotational energy release require further investigation. We compare our

  7. The thermodynamics of charge transfer in DNA photolyase: using thermodynamic integration calculations to analyse the kinetics of electron transfer reactions.

    Science.gov (United States)

    Krapf, Sebastian; Koslowski, Thorsten; Steinbrecher, Thomas

    2010-08-28

    DNA Photolyases are light sensitive oxidoreductases present in many organisms that participate in the repair of photodamaged DNA. They are capable of electron transfer between a bound cofactor and a chain of tryptophan amino acid residues. Due to their unique mechanism and important function, photolyases have been subject to intense study in recent times, with both experimental and computational efforts. In this work, we present a novel application of classical molecular dynamics based free energy calculations, combined with quantum mechanical computations, to biomolecular charge transfer. Our approach allows for the determination of all reaction parameters in Marcus' theory of charge transport. We were able to calculate the free energy profile for the movement of a positive charge along protein sidechains involved in the biomolecule's function as well as charge-transfer rates that are in good agreement with experimental results. Our approach to simulate charge-transfer reactions explicitly includes the influence of protein flexibility and solvent dynamics on charge-transfer energetics. As applied here to a biomolecular system of considerable scientific interest, we believe the method to be easily adaptable to the study of charge-transfer phenomena in biochemistry and other fields.

  8. Kinetic study of the gas-phase reaction of atomic chlorine with a series of aldehydes

    Directory of Open Access Journals (Sweden)

    D. Rodríguez

    2005-01-01

    Full Text Available The reactions of Cl atoms with a series of unsaturated aldehydes have been investigated for the first time using a relative method. In order to obtain additional information for a qualitative structure versus reactivity discussion, we have also determined the rate coefficients for the reactions of atomic chlorine with their respective saturated aldehydes. These relative measurements were performed at room temperature and atmospheric pressure of air and N2, by using ethane, propene and 1-butene as reference compounds. The weighted average relative rate constants obtained, kCl±2σ (in units of cm3 molecule−1 s−1 were: trans-2-pentenal (1.31±0.19×10−10; trans-2-hexenal (1.92±0.22×10−10; trans-2-heptenal (2.40±0.29×10−10; n-pentanal (2.56±0.27×10−10; n-hexanal (2.88±0.37×10−10; n-heptanal (3.00±0.34×10−10. Finally, results and atmospheric implications are discussed and compared with the reactivity with OH and NO3 radicals.

  9. Search for an explanation for neutralization rates of atomic ion-ion reactions

    Science.gov (United States)

    Miller, Thomas M.; Wiens, Justin P.; Shuman, Nicholas S.; Viggiano, Albert A.

    2016-09-01

    We have measured well over a hundred rate coefficients k for cation-anion mutual neutralization reactions at thermal energies. For molecular ions, the k at 300 K tend not to vary more than a factor of two or three, presumably because a great many neutral states cross the incoming Coulombic potential energy curve. Atomic-atomic systems, for which there are few favorable curve crossings between the neutral and Coulombic curves, show variation of at least a factor of 60 in the measured k values at 300 K. For reactions involving the noble-gas cations, we assume that the final state is the lowest excited state of the neutral, plus the ground state of the neutralized anion, because otherwise the crossing distance R is so small that the curve-crossing probability is nil. We plotted measured k values (in cm3/s) vs the distance R (in bohr) at which the neutral and Coulombic curves cross, the found that the data are fairly well fit by a power law for k, 10-4R - 2 . 8 . The question is, is there a physical explanation for the observed dependence on R? We will discuss the data and the expectations of Landau-Zener theory. Supported by Air Force Office of Scientific Research (AFOSR-2303EP).

  10. Functionalized polymer film surfaces via surface-initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Y. [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Li, J.S. [College of Polymer Science and Engineering, Sichuan University, Chengdu 610065 (China); Yang, W.T. [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Xu, F.J., E-mail: xufj@mail.buct.edu.cn [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China)

    2013-05-01

    The ability to manipulate and control the surface properties of polymer films, without altering the substrate properties, is crucial to their wide-spread applications. In this work, a simple one-step method for the direct immobilization of benzyl chloride groups (as the effective atom transfer radical polymerization (ATRP) initiators) on the polymer films was developed via benzophenone-induced coupling of 4-vinylbenzyl chloride (VBC). Polyethylene (PE) and nylon films were selected as examples of polymer films to illustrate the functionalization of film surfaces via surface-initiated ATRP. Functional polymer brushes of (2-dimethylamino)ethyl methacrylate, sodium 4-styrenesulfonate, 2-hydroxyethyl methacrylate and glycidyl methacrylate, as well as their block copolymer brushes, have been prepared via surface-initiated ATRP from the VBC-coupled PE or nylon film surfaces. With the development of a simple approach to the covalent immobilization of ATRP initiators on polymer film surfaces and the inherent versatility of surface-initiated ATRP, the surface functionality of polymer films can be precisely tailored. - Highlights: ► Atom transfer radical polymerization initiators were simply immobilized. ► Different functional polymer brushes were readily prepared. ► Their block copolymer brushes were also readily prepared.

  11. The Kinetics of Heterogeneous Electron Transfer Reactions in Polar Solvents

    Science.gov (United States)

    1994-04-20

    exp(-vei/ 2Vn )J (10) 2-exp(-vel/ 2Vn ) When Yel >> yn, jS is unity and the reaction is adiabatic. However, when ye, << yn, the expression for E becomes IC...approximation, IL is given by [31] TL - Em TD (13)Es where f, is the high frequency relative solvent permittivity and ID, the Debye relaxation time

  12. Neutron transfer reactions: Surrogates for neutron capture for basic and applied nuclear science

    Energy Technology Data Exchange (ETDEWEB)

    Cizewski, J. A. [Rutgers University; Jones, K. L. [University of Tennessee; Kozub, R. L. [Tennessee Technological University; Pain, Steven D [ORNL; Peters, W. A. [Rutgers University; Adekola, Aderemi S [ORNL; Allen, J. [Rutgers University; Bardayan, Daniel W [ORNL; Becker, J. [Lawrence Livermore National Laboratory (LLNL); Blackmon, Jeff C [ORNL; Chae, K. Y. [University of Tennessee; Chipps, K. [Colorado School of Mines, Golden; Erikson, Luke [Colorado School of Mines, Golden; Gaddis, A. L. [Furman University; Harlin, Christopher W [ORNL; Hatarik, Robert [Rutgers University; Howard, Joshua A [ORNL; Jandel, M. [Los Alamos National Laboratory (LANL); Johnson, Micah [ORNL; Kapler, R. [University of Tennessee; Krolas, W. [University of Warsaw; Liang, J Felix [ORNL; Livesay, Jake [ORNL; Ma, Zhanwen [ORNL; Matei, Catalin [Oak Ridge Associated Universities (ORAU); Matthews, C. [Rutgers University; Moazen, Brian [University of Tennessee; Nesaraja, Caroline D [ORNL; O' Malley, Patrick [Rutgers University; Patterson, N. P. [University of Surrey, UK; Paulauskas, Stanley [University of Tennessee; Pelham, T. [University of Surrey, UK; Pittman, S. T. [University of Tennessee, Knoxville (UTK); Radford, David C [ORNL; Rogers, J. [Tennessee Technological University; Schmitt, Kyle [University of Tennessee; Shapira, Dan [ORNL; ShrinerJr., J. F. [Tennessee Technological University; Sissom, D. J. [Tennessee Technological University; Smith, Michael Scott [ORNL; Swan, T. P. [University of Surrey, UK; Thomas, J. S. [Rutgers University; Vieira, D. J. [Los Alamos National Laboratory (LANL); Wilhelmy, J. B. [Los Alamos National Laboratory (LANL); Wilson, Gemma L [ORNL

    2009-04-01

    Neutron capture reactions on unstable nuclei are important for both basic and applied nuclear science. A program has been developed at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory to study single-neutron transfer (d,p) reactions with rare isotope beams to provide information on neutron-induced reactions on unstable nuclei. Results from (d,p) studies on {sup 130,132}Sn, {sup 134}Te and {sup 75}As are discussed.

  13. Proton transfer reactions and hydrogen-bond networks in protein environments.

    Science.gov (United States)

    Ishikita, Hiroshi; Saito, Keisuke

    2014-02-06

    In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pKa values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pKa values is opposite to that required for the formation of strong salt bridges, which play a key role in protein-protein interactions. To satisfy the pKa matching condition and allow for proton transfer reactions, proteins often adjust the pKa via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation.

  14. Chemical reaction of atomic oxygen with evaporated films of copper, part 4

    Science.gov (United States)

    Fromhold, A. T.; Williams, J. R.

    1990-01-01

    Evaporated copper films were exposed to an atomic oxygen flux of 1.4 x 10(exp 17) atoms/sq cm per sec at temperatures in the range 285 to 375 F (140 to 191 C) for time intervals between 2 and 50 minutes. Rutherford backscattering spectroscopy (RBS) was used to determine the thickness of the oxide layers formed and the ratio of the number of copper to oxygen atoms in the layers. Oxide film thicknesses ranged from 50 to 3000 A (0.005 to 0.3 microns, or equivalently, 5 x 10(exp -9) to 3 x 10(exp -7); it was determined that the primary oxide phase was Cu2O. The growth law was found to be parabolic (L(t) varies as t(exp 1/2)), in which the oxide thickness L(t) increases as the square root of the exposure time t. The analysis of the data is consistent with either of the two parabolic growth laws. (The thin-film parabolic growth law is based on the assumption that the process is diffusion controlled, with the space charge within the growing oxide layer being negligible. The thick-film parabolic growth law is also based on a diffusion controlled process, but space-charge neutrality prevails locally within very thick oxides.) In the absence of a voltage measurement across the growing oxide, a distinction between the two mechanisms cannot be made, nor can growth by the diffusion of neutral atomic oxygen be entirely ruled out. The activation energy for the reaction is on the order of 1.1 eV (1.76 x 10(exp -19) joule, or equivalently, 25.3 kcal/mole).

  15. Density Functional Reactivity Theory Characterizes Charge Separation Propensity in Proton-Coupled Electron Transfer Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shubin [Univ. of North Carolina, Chapel Hill, NC (United States); Ess, Daniel H. [Brigham Young Univ., Provo, UT (United States); Univ. of North Carolina, Chapel Hill, NC (United States); Schauer, Cynthia [Univ. of North Carolina, Chapel Hill, NC (United States)

    2011-04-20

    Proton-coupled electron transfer (PCET) reactions occur in many biological and artificial solar energy conversion processes. In these reactions the electron is often transferred to a site distant to the proton acceptor site. In this work, we employ the dual descriptor and the electrophilic Fukui function from density functional reactivity theory (DFRT) to characterize the propensity for an electron to be transferred to a site other than the proton acceptor site. The electrophilic regions of hydrogen bond or van der Waal reactant complexes were examined using these DFRT descriptors to determine the region of space to which the electron is most likely to be transferred. This analysis shows that in PCET reactions the electrophilic region of the reactant complex does not include the proton acceptor site.

  16. Synthesis of new transuranium isotopes in multinucleon transfer reactions using a velocity filter

    Energy Technology Data Exchange (ETDEWEB)

    Heinz, S.; Beliuskina, O. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Justus-Liebig-Universitaet Giessen, II. Physikalisches Institut, Giessen (Germany); Devaraja, H.M.; Gupta, M. [Manipal University, Manipal Centre for Natural Sciences, Manipal, Karnataka (India); Comas, V.; Hofmann, S.; Muenzenberg, G.; Ackermann, D.; Kindler, B.; Lommel, B.; Mann, R.; Maurer, J. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Hornung, C. [Justus-Liebig-Universitaet Giessen, II. Physikalisches Institut, Giessen (Germany); Henderson, R.A.; Moody, K.J.; Shaughnessy, D.A.; Stoyer, M.A. [Lawrence Livermore National Laboratory, Livermore, CA (United States); Hessberger, F.P. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Helmholtz-Institut Mainz, Mainz (Germany); Nishio, K. [Japan Atomic Energy Agency, Tokai Ibaraki (Japan); Popeko, A.G.; Yeremin, A.V. [Joint Institute for Nuclear Research, Dubna (Russian Federation)

    2016-09-15

    Recently, we reported the observation of several new isotopes with proton numbers Z ≥ 92 in low-energy collisions of {sup 48}Ca + {sup 248}Cm. The peculiarity is that the nuclei were produced in multinucleon transfer reactions, a method which is presently discussed as a possible new way to enter so far unknown regions in the upper part of the Chart of Nuclides. For separation of the transfer products we used a velocity filter, the Separator for Heavy Ion Reaction Products SHIP at GSI. The resulting strong background suppression allowed us to detect nuclei with cross-sections down to the sub-nanobarn scale. Beside the new isotopes we identified about 100 further target-like transfer products and determined their cross-sections. The results together with previous measurements strongly indicate that multinucleon transfer reactions are a viable pathway to the production of new transuranium isotopes. (orig.)

  17. Recent aspects of the proton transfer reaction in H-bonded complexes

    Science.gov (United States)

    Szafran, Mirosław

    1996-07-01

    Proton transfer processes cover a very wide range of situations and time scales and they are of great interest from the viewpoint of chemical reactions in solution. These processes can occur via thermally activated crossing or tunneling. This review considers various aspects of this many-faceted field. Spectroscopic, dielectric, colligative and energetic properties and structures of various species with H-bonds are examined. Proton transfer reactions in water and organic solvents, and the contribution of various H-bonded species and ions to these processes are discussed. Among other topics, this survey includes the effects of solvent, acid-base stoichiometry, concentration, temperature and impurity on proton transfer reactions in complexes of phenols and carboxylic acids with amines, pyridines and pyridine N-oxides. The contribution of the nonstoichiometric acid-base complexes and ionic species to the reversible proton transfer mechanism is discussed.

  18. Electronic state selectivity in dication-molecule single electron transfer reactions: NO(2+) + NO.

    Science.gov (United States)

    Parkes, Michael A; Lockyear, Jessica F; Schröder, Detlef; Roithová, Jana; Price, Stephen D

    2011-11-07

    The single-electron transfer reaction between NO(2+) and NO, which initially forms a pair of NO(+) ions, has been studied using a position-sensitive coincidence technique. The reactivity in this class of collision system, which involves the interaction of a dication with its neutral precursor, provides a sensitive test of recent ideas concerning electronic state selectivity in dicationic single-electron transfer reactions. In stark contrast to the recently observed single-electron transfer reactivity in the analogous CO(2)(2+)/CO(2) and O(2)(2+)/O(2) collision systems, electron transfer between NO(2+) and NO generates two product NO(+) ions which behave in an identical manner, whether the ions are formed from NO(2+) or NO. This observed behaviour is in excellent accord with the recently proposed rationalization of the state selectivity in dication-molecule SET reactions using simple propensity rules involving one-electron transitions. This journal is © the Owner Societies 2011

  19. The role of coherent excitation and collisional energy transfer in atomic vapor filters and photon detectors

    Science.gov (United States)

    Correll, Tiffany Lee

    Many optical techniques, including laser Doppler velocimetry, free space optical communications, and chemical imaging, require-or can be enhanced by-high spectral resolution photon detection. Such detection is characterized by spectral discrimination on the order of GHz or MHz i.e., approximately 10-4 nm in the near-infrared region. This spectral resolution has recently been achieved by exploiting the narrow absorption features of gas phase atoms. Absorption of light by alkali vapors is intrinsically selective and can be monitored by detecting the fluorescence resulting from laser excitation coupled to selectively excited atomic states. Imaging can be accomplished by spatially expanding the excitation lasers into two dimensions. Fluorescence photons are only created and detected when the interrogated object is forced to scatter radiation of an energy precisely matching one of the transitions of a pre-determined optimal excitation/fluorescence scheme. Devices based on resonance fluorescence photon detection have recently been described using cesium atoms. In this work, the sensitivity and spectral resolution of cesium-based photon detectors were evaluated and improved. To this end, initial experiments focused on laser induced fluorescence in room temperature cesium vapor. The fluorescence response of the detector was augmented by the use of cesium-induced collisional excitation energy transfer between states involved in the chosen excitation scheme. Additional studies focused on helium and argon-induced collisions in the vapor to increase the signal output while maintaining adequate spatial resolution in imaging mode. The probability or cross section of helium-cesium collisions at the operating temperature of the detector was determined by use of a simplified rate equation model. The spectral response of the detector was improved by the use of coherent optical effects resulting from the interaction of a multi-level atomic system with narrowband radiation. Superior

  20. One-dimensional description of multidimensional electron transfer reactions in condensed phase.

    Science.gov (United States)

    Dhole, Kajal; Samanta, Alok; Ghosh, Swapan K

    2008-06-05

    We derive a one-dimensional energy diffusion equation for describing the dynamics of multidimensional electron transfer reactions in condensed phase, which is conceptually simpler and computationally more economic than the conventional approaches. We also obtain an analytical expression for the rate of electron transfer reactions for a general one-dimensional effective potential as well as an energy dependent diffusitivity. As an illustrative example, we consider application to electron transfer in a contact ion pair system modeled through harmonic potentials consisting of two slow classical modes and a high frequency vibrational mode for which the numerical results calculated using the proposed one-dimensional approach are shown to be in good agreement with experimental results. The energy diffusion equation and the rate expression for electron transfer obtained from the present theory, therefore, open up the possibility of describing the dynamics of electron transfer in complex systems, through a simpler approach.

  1. Reactions of Azine Anions with Nitrogen and Oxygen Atoms: Implications for Titan's Upper Atmosphere and Interstellar Chemistry.

    Science.gov (United States)

    Wang, Zhe-Chen; Cole, Callie A; Demarais, Nicholas J; Snow, Theodore P; Bierbaum, Veronica M

    2015-08-26

    Azines are important in many extraterrestrial environments, from the atmosphere of Titan to the interstellar medium. They have been implicated as possible carriers of the diffuse interstellar bands in astronomy, indicating their persistence in interstellar space. Most importantly, they constitute the basic building blocks of DNA and RNA, so their chemical reactivity in these environments has significant astrobiological implications. In addition, N and O atoms are widely observed in the ISM and in the ionospheres of planets and moons. However, the chemical reactions of molecular anions with abundant interstellar and atmospheric atomic species are largely unexplored. In this paper, gas-phase reactions of deprotonated anions of benzene, pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine with N and O atoms are studied both experimentally and computationally. In all cases, the major reaction channel is associative electron detachment; these reactions are particularly important since they control the balance between negative ions and free electron densities. The reactions of the azine anions with N atoms exhibit larger rate constants than reactions of corresponding chain anions. The reactions of azine anions with O atoms are even more rapid, with complex product patterns for different reactants. The mechanisms are studied theoretically by employing density functional theory; spin conversion is found to be important in determining some product distributions. The rich gas-phase chemistry observed in this work provides a better understanding of ion-atom reactions and their contributions to ionospheric chemistry as well as the chemical processing that occurs in the boundary layers between diffuse and dense interstellar clouds.

  2. Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

    Science.gov (United States)

    Daly, G. M.; Meot-Ner, M.; Pithawalla, Y. B.; El-Shall, M. S.

    1996-05-01

    We present a new method that applies resonant-two-photon ionization to generate reactant ions selectively in the source of a high-pressure mass spectrometer (R2PI-HPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transfer reactions from C6H6+• to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3+• to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6+•)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogen-bonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C6H6+•)S+S→S2H++C6H5• and C6H6+•+2S→S2H++C6H5• reactions, respectively. The rate coefficients of these reactions are in the range 10-13-10-12 cm3 s-1 for the reaction through a bimolecular switching channel and in the range 10-26-10-28 cm6 s-1 for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined.

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

    Science.gov (United States)

    Dubey, Manvendra Krishna

    This thesis presents: (1) measurements of the kinetics of the reactions of the OH radical with several molecules by the discharge flow technique, (2) reactivity trend analysis, electronic structure, and transition state calculations, (3) molecular beam electric deflection experiments of hot polyatomics. A synthesis of these studies demonstrates that radical-molecule reactions frequently involve an indirect mechanism and are not necessarily direct, activated, bimolecular processes. Indirect mechanisms arise when the reactant frontier orbitals do not transform to the product configuration. Compact reactivity trends among homologous reaction sets are defined by the difference between the ionization potential of the electron donor and the electron affinity of the electron acceptor and show that charge-transfer stabilizations (rather than thermodynamics) govern radical-molecule reactivity. A multiple transition state model is developed to predict the mixed bimolecular/termolecular kinetics implicit in the indirect mechanism. The fundamental assumption of rapid intramolecular energy redistribution in the energized complex in the model is validated by our electric deflection studies. Model calculations for the rm OH + HNO_3to H_2O + NO_3 reaction reproduce the small A factor, negative activation energy, and pressure dependence of the rate. They elucidate the reaction mechanism in molecular detail. The OH first bonds to either the O or N atom of HNO_3 to form an energized complex, which subsequently suffers one of three fates: dissociation to reactants via a loose transition state, dissociation to products via a tight transition state with a negative threshold, or collisional stabilization. These processes compete to determine the overall kinetics. Isotopic scrambling rates are predicted. Our model predicts faster rates than the NASA recommendation at low temperatures with potential consequences for stratospheric photochemistry. The rate constants of the reactions of OH

  4. NI (II AND PB (II INHIBIT THE ENZYMATIC ACTIVITY OF DNA IN AN ELECTRON TRANSFER REACTION

    Directory of Open Access Journals (Sweden)

    B FARZAMI

    2002-03-01

    Full Text Available Introduction. Ni and Pb are metals with several suggested mechanisms for their toxicity on the biological systems. We have recently investigated involvement of DNA in an electron transfer reaction as an enzyme. In this reaction non- fluorescent dichlorofluorescin (LDCF is converted to the dichlorofluorescein (DCF in the presence of peroxides and hematin. Methods. The fluorometric technique was used in this study. The pH effect on the reaction rate was investigated. The results showed that DCF has the maximum emission on tris buffer 0.05 Mat pH 8.4. Results. DNA and carnosine catalyze the reaction, which proceeds by the electron transfer mechanism. The presence of carnosine is necessary for the catalytic action of DNA as a cofactor. Ni (II and Pb (11 are the potent inhibitors of the reaction. The kinetic parameters and determined in the presence and absence of the above ligands. Discussion. DNA, which has the electrical properties only in the double helical forms, acts as a catalyst in the conversion of LDCF to DCF. The existence of the carnosine, an endogenous dipeptide with antioxidant and free radical scavenging roles, is an important factor for the progress of the reaction. Both Ni (11 and Pb (II inhibit the reaction. These metals could act as the electron pool to cause inhibition in such electron transfer reaction. This phenomenon could be related to the carcinogenic effect of these metals.

  5. Solutions for a mass transfer process governed by fractional diffusion equations with reaction terms

    Science.gov (United States)

    Lenzi, E. K.; dos Santos, M. A. F.; Lenzi, M. K.; Menechini Neto, R.

    2017-07-01

    We investigate the behavior of a mass transfer process governed by a set of fractional diffusion equations coupled by appropriate reaction terms. The presence of memory effects in the diffusive term is also considered. For this set of equations, we obtain solutions and analyze the influence of the reaction terms on the spreading of these solutions. Particularly, we observe that for reversible reaction processes the reaction terms play an important role for intermediate times and for long times the processes are essentially governed by the bulk equations. These results show a rich class of behaviors which can be connected to sub- or superdiffusive regime.

  6. The nucleus 198Au investigated with neutron capture and transfer reactions. I. Experiments and evaluation.

    Science.gov (United States)

    Mayerhofer, Ulrich; von Egidy, Till; Klora, Jörg; Lindner, Helmut; Börner, Hans G.; Judge, Stephen; Krusche, Bernd; Robinson, Stephen; Schreckenbach, Klaus; Sukhovoj, Anatoly M.; Khitrov, Valery A.; Boneva, Stefka T.; Paar, Vladimir; Brant, Slobodan; Pezer, Robert

    The transfer reaction 197Au(d,p)198Au was measured at the Tandem Accelerator in Munich. The 197Au(n,g)198Au and 197Au(n,e)198Au reactions were performed at the High Flux Reactor of ILL, Grenoble. Up to 1560 keV a total of 111 levels were observed by the (d,p) reaction and 125 by the (n,g) reaction. For many of the levels, spins and parities were assigned. Additional information was obtained from summed (n,gg) coincidences measured in Dubna.

  7. Monolithic Laser Scribed Graphene Scaffold with Atomic Layer Deposited Platinum for Hydrogen Evolution Reaction

    KAUST Repository

    Nayak, Pranati

    2017-09-01

    The use of three-dimensional (3D) electrode architectures as scaffolds for conformal deposition of catalysts is an emerging research area with significant potential for electrocatalytic applications. In this study, we report the fabrication of monolithic, self-standing, 3D graphitic carbon scaffold with conformally deposited Pt by atomic layer deposition (ALD) as a hydrogen evolution reaction catalyst. Laser scribing is employed to transform polyimide into 3D porous graphitic carbon, which possesses good electronic conductivity and numerous edge plane sites. This laser scribed graphene (LSG) architecture makes it possible to fabricate monolithic electrocatalyst support without any binders or conductive additives. The synergistic effect between ALD of Pt on 3D network of LSG provides an avenue for minimal yet effective Pt usage, leading to an enhanced HER activity. This strategy establish a general approach for inexpensive and large scale HER device fabrication with minimum catalyst cost.

  8. Atomic-scale observation of lithiation reaction front in nanoscale SnO2 materials

    KAUST Repository

    Nie, Anmin

    2013-07-23

    In the present work, taking advantage of aberration-corrected scanning transmission electron microscopy, we show that the dynamic lithiation process of anode materials can be revealed in an unprecedented resolution. Atomically resolved imaging of the lithiation process in SnO2 nanowires illustrated that the movement, reaction, and generation of b = [1Ì...1Ì...1] mixed dislocations leading the lithiated stripes effectively facilitated lithium-ion insertion into the crystalline interior. The geometric phase analysis and density functional theory simulations indicated that lithium ions initial preference to diffuse along the [001] direction in the {200} planes of SnO2 nanowires introduced the lattice expansion and such dislocation behaviors. At the later stages of lithiation, the Li-induced amorphization of rutile SnO2 and the formation of crystalline Sn and LixSn particles in the Li2O matrix were observed. © 2013 American Chemical Society.

  9. Atomic-scale observation of lithiation reaction front in nanoscale SnO2 materials.

    Science.gov (United States)

    Nie, Anmin; Gan, Li-Yong; Cheng, Yingchun; Asayesh-Ardakani, Hasti; Li, Qianqian; Dong, Cezhou; Tao, Runzhe; Mashayek, Farzad; Wang, Hong-Tao; Schwingenschlögl, Udo; Klie, Robert F; Yassar, Reza S

    2013-07-23

    In the present work, taking advantage of aberration-corrected scanning transmission electron microscopy, we show that the dynamic lithiation process of anode materials can be revealed in an unprecedented resolution. Atomically resolved imaging of the lithiation process in SnO2 nanowires illustrated that the movement, reaction, and generation of b = [1[overline]1[overline]1] mixed dislocations leading the lithiated stripes effectively facilitated lithium-ion insertion into the crystalline interior. The geometric phase analysis and density functional theory simulations indicated that lithium ions initial preference to diffuse along the [001] direction in the {200} planes of SnO2 nanowires introduced the lattice expansion and such dislocation behaviors. At the later stages of lithiation, the Li-induced amorphization of rutile SnO2 and the formation of crystalline Sn and LixSn particles in the Li2O matrix were observed.

  10. Kinetics, mechanism, and thermochemistry of the gas-phase reaction of atomic chlorine with pyridine.

    Science.gov (United States)

    Zhao, Z; Huskey, D T; Olsen, K J; Nicovich, J M; McKee, M L; Wine, P H

    2007-08-21

    A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of atomic chlorine with pyridine (C(5)H(5)N) as a function of temperature (215-435 K) and pressure (25-250 Torr) in nitrogen bath gas. At T> or = 299 K, measured rate coefficients are pressure independent and a significant H/D kinetic isotope effect is observed, suggesting that hydrogen abstraction is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 299-435 K for C(5)H(5)N: k(1a) = (2.08 +/- 0.47) x 10(-11) exp[-(1410 +/- 80)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2sigma, precision only). At 216 K rate coefficients are pressure dependent and are much faster than computed from the above Arrhenius expression for the H-abstraction pathway, suggesting that the dominant reaction pathway at low temperature is formation of a stable adduct. Over the ranges of temperature, pressure, and pyridine concentration investigated, the adduct undergoes dissociation on the time scale of our experiments (10(-5)-10(-2) s) and establishes an equilibrium with Cl and pyridine. Equilibrium constants for adduct formation and dissociation are determined from the forward and reverse rate coefficients. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the addition reaction: Delta(r)H = -47.2 +/- 2.8 kJ mol(-1), Delta(r)H = -46.7 +/- 3.2 kJ mol(-1), and Delta(r)S = -98.7 +/- 6.5 J mol(-1) K(-1). The enthalpy changes derived from our data are in good agreement with ab initio calculations reported in the literature (which suggest that the adduct structure is planar and involves formation of an N-Cl sigma-bond). In conjunction with the well-known heats of formation of atomic chlorine and pyridine, the above Delta(r)H values lead to the following heats of formation for C(5)H(5)N-Cl at 298 K and 0 K: Delta(f)H = 216.0 +/- 4.1 kJ mol(-1), Delta(f)H = 233.4 +/- 4.6 k

  11. N2O + CO reaction over single Ga or Ge atom embedded graphene: A DFT study

    Science.gov (United States)

    Esrafili, Mehdi D.; Vessally, Esmail

    2018-01-01

    The possibility of using a single Ga or Ge atom embedded graphene as an efficient catalyst for the reduction of N2O molecule by CO is examined. We perform density functional theory calculations to calculate adsorption energies as well as analysis of the structural and electronic properties of different species involved in the N2O + CO reaction. The large activation energy for the diffusion of the single Ga or Ge atom on the C vacancy site of graphene shows the high stability of both Ga- and Ge-embedded graphene sheets in the N2O reduction. The activation energy needed for the decomposition of N2O is calculated to be 18.4 and 14.1 kcal/mol over Ga- and Ge-embedded graphene, respectively. The results indicate that the Ge-embedded graphene may serve as an effective catalyst for the N2O reduction. Moreover, the activation energy for the disproportionation of N2O molecules that generates N2 and O2 is relatively high; so, the generation of these side products may be hindered by decreasing the temperature.

  12. Wideband laser locking to an atomic reference with modulation transfer spectroscopy.

    Science.gov (United States)

    Negnevitsky, V; Turner, L D

    2013-02-11

    We demonstrate that conventional modulated spectroscopy apparatus, used for laser frequency stabilization in many atomic physics laboratories, can be enhanced to provide a wideband lock delivering deep suppression of frequency noise across the acoustic range. Using an acousto-optic modulator driven with an agile oscillator, we show that wideband frequency modulation of the pump laser in modulation transfer spectroscopy produces the unique single lock-point spectrum previously demonstrated with electro-optic phase modulation. We achieve a laser lock with 100 kHz feedback bandwidth, limited by our laser control electronics. This bandwidth is sufficient to reduce frequency noise by 30 dB across the acoustic range and narrows the imputed linewidth by a factor of five.

  13. Seawater uranium sorbents. Preparation from a mesoporous copolymer initiator by atom-transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yue, Yanfeng; Mayes, Richard T.; Fulvio, Pasquale F.; Sun, Xiao-Guang [Oak Ridge National Laboratory, TN (United States). Chemical Sciences Division; Kim, Jungseung; Tsouris, Costas [Oak Ridge National Laboratory, TN (United States). Energy and Transportation Science Division; Chen, Jihua [Oak Ridge National Laboratory, TN (United States). Center for Nanophase Materials Sciences; Brown, Suree [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Dai, Sheng [Oak Ridge National Laboratory, TN (United States). Chemical Sciences Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry

    2013-12-09

    From the sea to the reactor: Nanoporous template-free initiators for atom-transfer radical polymerization (ATRP) were synthesized with surface and framework initiator sites and tailorable pore structures. Polyacrylonitrile grown on one initiator was converted into polyamidoxime to generate a uranium sorbent for seawater extraction with a high uptake rate and capacity relative to those of nonwoven irradiation-grafted polyethylene-fiber composites. [German] Aus dem Meer in den Reaktor: Nanoporoese templatfreie Initiatoren fuer die radikalische Atomtransferpolymerisation (ATRP) mit einstellbarer Porenstruktur und Initiatorstellen an der Oberflaeche und im Geruestinneren wurden hergestellt. Auf einem Initiator erzeugtes Polyacrylnitril wurde in ein Polyamidoxim umgewandelt, um Uran aus Meerwasser zu extrahieren. Aufnahmerate und -kapazitaet waren hoch im Vergleich zu nichtverwobenen Kompositen aus Fasern und photochemisch aufgebrachtem Polyethylen.

  14. Modification of Jute Fibers with Polystyrene via Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Plackett, David; Jankova, Katja Atanassova; Egsgaard, Helge

    2005-01-01

    Atom transfer radical polymerization (ATRP) was investigated as a method of covalently bonding polystyrene to jute (Corchorus capsularis) and as a possible approach to fiber composites with enhanced properties. Jute fibers were modified with a brominated initiator and subsequently ATRP modified...... to attach polystyrene and then examined using SEM, DSC, TGA, FTIR, XPS, elemental analysis, and Py-GC-MS. These techniques confirmed that polystyrene had been covalently bound to the fibers and consequently ATRP-modified jute fiber mats were used to prepare hot-pressed polystyrene composites. Composite...... applications, we conclude that further optimization of the ATRP method is required, possibly targeting higher and more uniform loading of polystyrene on the fibers....

  15. High throughput engineering to revitalize a vestigial electron transfer pathway in bacterial photosynthetic reaction centers.

    Science.gov (United States)

    Faries, Kaitlyn M; Kressel, Lucas L; Wander, Marc J; Holten, Dewey; Laible, Philip D; Kirmaier, Christine; Hanson, Deborah K

    2012-03-09

    Photosynthetic reaction centers convert light energy into chemical energy in a series of transmembrane electron transfer reactions, each with near 100% yield. The structures of reaction centers reveal two symmetry-related branches of cofactors (denoted A and B) that are functionally asymmetric; purple bacterial reaction centers use the A pathway exclusively. Previously, site-specific mutagenesis has yielded reaction centers capable of transmembrane charge separation solely via the B branch cofactors, but the best overall electron transfer yields are still low. In an attempt to better realize the architectural and energetic factors that underlie the directionality and yields of electron transfer, sites within the protein-cofactor complex were targeted in a directed molecular evolution strategy that implements streamlined mutagenesis and high throughput spectroscopic screening. The polycistronic approach enables efficient construction and expression of a large number of variants of a heteroligomeric complex that has two intimately regulated subunits with high sequence similarity, common features of many prokaryotic and eukaryotic transmembrane protein assemblies. The strategy has succeeded in the discovery of several mutant reaction centers with increased efficiency of the B pathway; they carry multiple substitutions that have not been explored or linked using traditional approaches. This work expands our understanding of the structure-function relationships that dictate the efficiency of biological energy-conversion reactions, concepts that will aid the design of bio-inspired assemblies capable of both efficient charge separation and charge stabilization.

  16. Effect of current and atomized grain size distribution on the solidification of Plasma Transferred Arc coatings

    Directory of Open Access Journals (Sweden)

    Danielle Bond

    2012-10-01

    Full Text Available Plasma Transferred Arc (PTA is the only thermal spray process that results in a metallurgical bond, being frequently described as a hardfacing process. The superior properties of coatings have been related to the fine microstructures obtained, which are finer than those processed under similar heat input with welding techniques using wire feedstock. This observation suggests that the atomized feedstock plays a role on the solidification of coatings. In this study a model for the role of the powders grains in the solidification of PTA coatings is put forward and discussed. An experiment was setup to discuss the model which involved the deposition of an atomized Co-based alloy with different grain size distributions and deposition currents. X ray diffraction showed that there were no phase changes due to the processing parameters. Microstructure analysis by Laser Confocal Microscopy, dilution with the substrate steel and Vickers microhardness were used the characterized coatings and enriched the discussion confirming the role of the powdered feedstock on the solidification of coatings.

  17. Quantum Coherence as a Witness of Vibronically Hot Energy Transfer in Bacterial Reaction Centre

    CERN Document Server

    Paleček, David; Westenhoff, Sebastian; Zigmantas, Donatas

    2016-01-01

    Photosynthetic proteins have evolved over billions of years so as to undergo optimal energy transfer to the sites of charge separation. Based on spectroscopically detected quantum coherences, it has been suggested that this energy transfer is partially wavelike. This conclusion critically depends on assignment of the coherences to the evolution of excitonic superpositions. Here we demonstrate for a bacterial reaction centre protein that long-lived coherent spectroscopic oscillations, which bear canonical signatures of excitonic superpositions, are essentially vibrational excited state coherences shifted to the ground state of the chromophores . We show that appearance of these coherences is brought about by release of electronic energy during the energy transfer. Our results establish how energy migrates on vibrationally hot chromophores in the reaction centre and they call for a re-examination of claims of quantum energy transfer in photosynthesis.

  18. Deceleration of the electron transfer reaction in the photosynthetic reaction centre as a manifestation of its structure fluctuations

    Directory of Open Access Journals (Sweden)

    Knox P. P.

    2010-07-01

    Full Text Available Aim. To extract information on the nature of protein structural relaxation from the kinetics of electron transfer reaction in the photosynthetic reaction centre (RC. Methods. The kinetic curves obtained by absorption spectroscopy are processed by a maximum entropy method to get the spectrum of relaxation times. Results. A series of distinctive peaks of this spectrum in the interval from 0.1 s to hundreds of seconds is revealed. With the time of exposure of the sample to actinic light increasing, the positions of the peak maxima grow linearly. Conclusions. Theoretical analysis of these results reveals the formation of several structural states of the RC protein. Remarkably, in each of these states the slow reaction kinetics follow the same fractional power law that reflects the glass-like properties of the protein.

  19. Near-barrier transfer reactions in the sup 36 S+ sup 144,154 Sm systems

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez Niello, J.O.; Testoni, J.E.; di Tada, M.; Pacheco, A.J. (TANDAR, Departamento de Fisica, Comision Nacional de Energia Atomica, Avenida del Libertador 8250, 1429 Buenos Aires (Argentina)); Napoli, D.R.; Stefanini, A.M.; Corradi, L.; Million, B.; Narayanasamy, M.; Spolaore, P. (Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Padova (Italy)); Beghini, S.; Montagnoli, G.; Scarlassara, F.; Segato, G.F.; Signorini, C.; Soramel, F. (Dipartimento di Fisica, Universita e Istituto Nazionale di Fisica Nucleare, Padova (Italy))

    1992-02-01

    Angular distributions and {ital Q}-value spectra for transfer reactions in the systems {sup 36}S+{sup 144,154}Sm have been measured at two energies close to the Coulomb barrier. Mass and charge identification was achieved using a time-of-flight system followed by an ionization chamber. Transfer probabilities were analyzed considering direct and sequential barrier penetration mechanisms. The dependence of the cross sections on the static quadrupole deformation of the targets was compared with the predictions of a semiclassical approach. The relative yields of the different channels were analyzed in the light of a random-walk approach based on the reaction {ital Q} values.

  20. Surface modification of glycidyl-containing poly(methyl methacrylate) microchips using surface-initiated atom-transfer radical polymerization.

    Science.gov (United States)

    Sun, Xuefei; Liu, Jikun; Lee, Milton L

    2008-02-01

    Fabrication of microfluidic systems from polymeric materials is attractive because of simplicity and low cost. Unfortunately, the surfaces of many polymeric materials can adsorb biological samples. Therefore, it is necessary to modify their surfaces before these polymeric materials can be used for separation and analysis. Oftentimes it is difficult to modify polymeric surfaces because of their resistance to chemical reaction. Recently, we introduced a surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), which can be modified easily and is suitable for fabrication of microfluidic devices. Epoxy groups on the surface can be activated by air plasma treatment, hydrolysis, or aminolysis. In this work, the resulting hydroxyl or amino groups were reacted with 2-bromoisobutylryl bromide to introduce an initiator for surface-initiated atom-transfer radical polymerization (SI-ATRP). Polyethylene glycol (PEG) layers grown on the surface using this method were uniform, hydrophilic, stable, and resistant to protein adsorption. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize activated polymer surfaces, initiator-bound surfaces, and PEG-grafted surfaces. We obtained excellent capillary electrophoresis (CE) separations of proteins and peptides with the PEG-modified microchips. A separation efficiency of 4.4 x 10(4) plates for a 3.5 cm long separation channel was obtained.

  1. Control of interspecies electron transfer flow during anaerobic digestion: dynamic diffusion reaction models for hydrogen gas transfer in microbial flocs.

    Science.gov (United States)

    Ozturk, S S; Palsson, B O; Thiele, J H

    1989-02-05

    Dynamic reaction diffusion models were used to analyze the consequences of aggregation for syntrophic reactions in methanogenic ecosystems. Flocs from a whey digestor were used to measure all model parameters under the in situ conditions of a particular defined biological system. Fermentation simulations without adjustable parameters could precisely predict the kinetics of H(2) gas production of digestor flocs during syntrophic methanogenesis from ethanol. The results demonstrated a kinetic compartmentalization of H(2) metabolism inside the flocs. The interspecies electron transfer reaction was mildly diffusion controlled. The H(2) gas profiles across the flocs showed high H (2) concentrations inside the flocs at any time. Simulations of the syntrophic metabolism at low substrate concentrations such as in digestors or sediments showed that it is impossible to achieve high H(2) gas turnovers at simultaneously low steady-state H(2) concentrations. This showed a mechanistic contradiction in the concept of postulated low H(2) microenvironments for the anaerobic digestion process. The results of the computer experiments support the conclusion that syntrophic H(2) production may only be a side reaction of H(2) independent interspecies electron transfer in methanogenic ecosystems.

  2. Decoupling diffusion from the bimolecular photoinduced electron transfer reaction: a combined ultrafast spectroscopic and kinetic analysis.

    Science.gov (United States)

    Mukherjee, Puspal; Sen, Pratik

    2017-05-10

    We have studied the bimolecular photoinduced electron transfer (PET) reaction between benzophenone (Bp) and DABCO using femtosecond broadband transient absorption spectroscopy in different compositions of acetonitrile/1-butanol binary solvent mixtures. With the increase in the 1-butanol percentage in the mixture, we have observed an increase in the onset delay time of Bp˙(-), which is the product of the reaction. As 1-butanol is more viscous than acetonitrile, we related the onset time to the change in medium viscosity. Moreover, we undertook a complete kinetic analysis of the bimolecular PET reaction under different conditions to show that from transient absorption spectroscopy, we can get the exact rate of electron transfer. This kind of kinetic analysis along with the experimental data is the first of its kind to prove that transient absorption spectroscopy is probably the most useful tool in studying the PET reaction.

  3. Biomimetic surface modification of polypropylene by surface chain transfer reaction based on mussel-inspired adhesion technology and thiol chemistry

    Science.gov (United States)

    Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing; Gong, Yongkuan

    2016-11-01

    Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH2) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such zwitterion modified PP surface.

  4. Surface reaction of silicon chlorides during atomic layer deposition of silicon nitride

    Science.gov (United States)

    Yusup, Luchana L.; Park, Jae-Min; Mayangsari, Tirta R.; Kwon, Young-Kyun; Lee, Won-Jun

    2018-02-01

    The reaction of precursor with surface active site is the critical step in atomic layer deposition (ALD) process. We performed the density functional theory calculation with DFT-D correction to study the surface reaction of different silicon chloride precursors during the first half cycle of ALD process. SiCl4, SiH2Cl2, Si2Cl6 and Si3Cl8 were considered as the silicon precursors, and an NH/SiNH2*-terminated silicon nitride surface was constructed to model the thermal ALD processes using NH3 as well as the PEALD processes using NH3 plasma. The total energies of the system were calculated for the geometry-optimized structures of physisorption, chemisorption, and transition state. The order of silicon precursors in energy barrier, from lowest to highest, is Si3Cl8 (0.92 eV), Si2Cl6 (3.22 eV), SiH2Cl2 (3.93 eV) and SiCl4 (4.49 eV). Silicon precursor with lower energy barrier in DFT calculation showed lower saturation dose in literature for both thermal and plasma-enhanced ALD of silicon nitride. Therefore, DFT calculation is a promising tool in predicting the reactivity of precursor during ALD process.

  5. 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.

  6. Bis(pentamethylcyclopentadienyl) ytterbium: Electron-transfer reactions with organotransition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Matsunaga, Phillip Thomas [Univ. of California, Berkeley, CA (United States)

    1991-11-01

    The divalent lanthanide complex, (Me5C5)2Yb, reacts with methylcopper to produce the base-free, ytterbium-methyl complex, (Me5C5)2YbMe. This product forms a asymmetric, methyl-bridged dimer in the solid state. The bulky alkyl complex, (Me5C5)2YbCH(SiMe3)2, displays similar chemistry to (Me5C5)2YbMe, but at a reduced reaction rate due to the limited accessibility of the metal in (Me5C5)3YbCH(SiMe5)2. Copper and silver halide salts react with (Me5C5)2V to produce the trivalent halide derivatives, (Me5C5)2VX (X + F, Cl, Br, I). The chloride complex, (Me5C5)2VCl, reacts with lithium reagents to form the phenyl and borohydride species. Nitrous oxide transfers an oxygen atom to (Me5C5)2V producing the vanadium-oxo complex, (Me5Ce5)2VO. The trivalent titanium species, (Me5C5)2TiX (X = Cl, Br, Me, BH4), form bimetallic coordination complexes with (Me5C5)2Yb. The magnetic behavior of the products indicates that electron transfer has not occurred. The solid state structures of the chloride and bromide complexes show unusual bend angles for the halide bridges between ytterbium and titanium. A model based on frontier orbital theory has been proposed to account for the bending behavior in these species. The bimetallic methyl complex contains a linear methyl bridge between ytterbium and titanium.

  7. Bis(pentamethylcyclopentadienyl) ytterbium: Electron-transfer reactions with organotransition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Matsunaga, P.T.

    1991-11-01

    The divalent lanthanide complex, (Me{sub 5}C{sub 5}){sub 2}Yb, reacts with methylcopper to produce the base-free, ytterbium-methyl complex, (Me{sub 5}C{sub 5}){sub 2}YbMe. This product forms a asymmetric, methyl-bridged dimer in the solid state. The bulky alkyl complex, (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}, displays similar chemistry to (Me{sub 5}C{sub 5}){sub 2}YbMe, but at a reduced reaction rate due to the limited accessibility of the metal in (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}. Copper and silver halide salts react with (Me{sub 5}C{sub 5}){sub 2}V to produce the trivalent halide derivatives, (Me{sub 5}C{sub 5}){sub 2}VX (X + F, Cl, Br, I). The chloride complex, (Me{sub 5}C{sub 5}){sub 2}VCl, reacts with lithium reagents to form the phenyl and borohydride species. Nitrous oxide transfers an oxygen atom to (Me{sub 5}C{sub 5}){sub 2}V producing the vanadium-oxo complex, (Me{sub 5}Ce{sub 5}){sub 2}VO. The trivalent titanium species, (Me{sub 5}C{sub 5}){sub 2}TiX (X = Cl, Br, Me, BH{sub 4}), form bimetallic coordination complexes with (Me{sub 5}C{sub 5}){sub 2}Yb. The magnetic behavior of the products indicates that electron transfer has not occurred. The solid state structures of the chloride and bromide complexes show unusual bend angles for the halide bridges between ytterbium and titanium. A model based on frontier orbital theory has been proposed to account for the bending behavior in these species. The bimetallic methyl complex contains a linear methyl bridge between ytterbium and titanium.

  8. Electron transfer reaction of butane -1,3-diol and cr(vi) in aqueous ...

    African Journals Online (AJOL)

    Kinetic and mechanistic studies of electron transfer reaction of butane-1,3-diol and Cr(VI) ion in aqueous acidic medium have been carried out in aqueous medium at 271°C, I = 1.0 mol dm-3 (NaCl), [H +] = 0.5mol dm-3 (HCl). The reaction was inhibited by added anions and showed negative salt effect. Spectroscopic ...

  9. Atomic charge transfer-counter polarization effects determine infrared CH intensities of hydrocarbons: a quantum theory of atoms in molecules model.

    Science.gov (United States)

    Silva, Arnaldo F; Richter, Wagner E; Meneses, Helen G C; Bruns, Roy E

    2014-11-14

    Atomic charge transfer-counter polarization effects determine most of the infrared fundamental CH intensities of simple hydrocarbons, methane, ethylene, ethane, propyne, cyclopropane and allene. The quantum theory of atoms in molecules/charge-charge flux-dipole flux model predicted the values of 30 CH intensities ranging from 0 to 123 km mol(-1) with a root mean square (rms) error of only 4.2 km mol(-1) without including a specific equilibrium atomic charge term. Sums of the contributions from terms involving charge flux and/or dipole flux averaged 20.3 km mol(-1), about ten times larger than the average charge contribution of 2.0 km mol(-1). The only notable exceptions are the CH stretching and bending intensities of acetylene and two of the propyne vibrations for hydrogens bound to sp hybridized carbon atoms. Calculations were carried out at four quantum levels, MP2/6-311++G(3d,3p), MP2/cc-pVTZ, QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ. The results calculated at the QCISD level are the most accurate among the four with root mean square errors of 4.7 and 5.0 km mol(-1) for the 6-311++G(3d,3p) and cc-pVTZ basis sets. These values are close to the estimated aggregate experimental error of the hydrocarbon intensities, 4.0 km mol(-1). The atomic charge transfer-counter polarization effect is much larger than the charge effect for the results of all four quantum levels. Charge transfer-counter polarization effects are expected to also be important in vibrations of more polar molecules for which equilibrium charge contributions can be large.

  10. Heterogeneous Single-Atom Catalyst for Visible-Light-Driven High-Turnover CO2Reduction: The Role of Electron Transfer.

    Science.gov (United States)

    Gao, Chao; Chen, Shuangming; Wang, Ying; Wang, Jiawen; Zheng, Xusheng; Zhu, Junfa; Song, Li; Zhang, Wenkai; Xiong, Yujie

    2018-02-14

    Visible-light-driven conversion of CO 2 into chemical fuels is an intriguing approach to address the energy and environmental challenges. In principle, light harvesting and catalytic reactions can be both optimized by combining the merits of homogeneous and heterogeneous photocatalysts; however, the efficiency of charge transfer between light absorbers and catalytic sites is often too low to limit the overall photocatalytic performance. In this communication, it is reported that the single-atom Co sites coordinated on the partially oxidized graphene nanosheets can serve as a highly active and durable heterogeneous catalyst for CO 2 conversion, wherein the graphene bridges homogeneous light absorbers with single-atom catalytic sites for the efficient transfer of photoexcited electrons. As a result, the turnover number for CO production reaches a high value of 678 with an unprecedented turnover frequency of 3.77 min -1 , superior to those obtained with the state-of-the-art heterogeneous photocatalysts. This work provides fresh insights into the design of catalytic sites toward photocatalytic CO 2 conversion from the angle of single-atom catalysis and highlights the role of charge kinetics in bridging the gap between heterogeneous and homogeneous photocatalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Reactions of atomic hydrogen with formic acid and carbon monoxide in solid parahydrogen I: Anomalous effect of temperature.

    Science.gov (United States)

    Paulson, Leif O; Mutunga, Fredrick M; Follett, Shelby E; Anderson, David T

    2014-09-11

    Low-temperature condensed phase reactions of atomic hydrogen with closed-shell molecules have been studied in rare gas matrices as a way to generate unstable chemical intermediates and to study tunneling-driven chemistry. Although parahydrogen (pH2) matrix isolation spectroscopy allows these reactions to be studied equally well, little is known about the analogous reactions conducted in a pH2 matrix host. In this study, we present Fourier transform infrared (FTIR) spectroscopic studies of the 193 nm photoinduced chemistry of formic acid (HCOOH) isolated in a pH2 matrix over the 1.7 to 4.3 K temperature range. Upon short-term irradiation the HCOOH readily undergoes photolysis to yield CO, CO2, HOCO, HCO and H atoms. Furthermore, after photolysis at 1.9 K tunneling reactions between migrating H atoms and trapped HCOOH and CO continue to produce HOCO and HCO, respectively. A series of postphotolysis kinetic experiments at 1.9 K with varying photolysis conditions and initial HCOOH concentrations show the growth of HOCO consistently follows single exponential (k = 4.9(7)x10(-3) min(-1)) growth kinetics. The HCO growth kinetics is more complex displaying single exponential growth under certain conditions, but also biexponential growth at elevated CO concentrations and longer photolysis exposures. By varying the temperature after photolysis, we show the H atom reaction kinetics qualitatively change at ∼2.7 K; the reaction that produces HOCO stops at higher temperatures and is only observed at low temperature. We rationalize these results using a kinetic mechanism that involves formation of an H···HCOOH prereactive complex. This study clearly identifies anomalous temperature effects in the reaction kinetics of H atoms with HCOOH and CO in solid pH2 that deserve further study and await full quantitative theoretical modeling.

  12. Tunable self-assembled spin chains of strongly interacting cold atoms for demonstration of reliable quantum state transfer

    DEFF Research Database (Denmark)

    Loft, N. J. S.; Marchukov, O. V.; Petrosyan, D.

    2016-01-01

    We have developed an efficient computational method to treat long, one-dimensional systems of strongly-interacting atoms forming self-assembled spin chains. Such systems can be used to realize many spin chain model Hamiltonians tunable by the external confining potential. As a concrete demonstrat...... demonstration, we consider quantum state transfer in a Heisenberg spin chain and we show how to determine the confining potential in order to obtain nearly-perfect state transfer....

  13. The effect of defects on the catalytic activity of single Au atom supported carbon nanotubes and reaction mechanism for CO oxidation.

    Science.gov (United States)

    Ali, Sajjad; Fu Liu, Tian; Lian, Zan; Li, Bo; Sheng Su, Dang

    2017-08-23

    The mechanism of CO oxidation by O 2 on a single Au atom supported on pristine, mono atom vacancy (m), di atom vacancy (di) and the Stone Wales defect (SW) on single walled carbon nanotube (SWCNT) surface is systematically investigated theoretically using density functional theory. We determine that single Au atoms can be trapped effectively by the defects on SWCNTs. The defects on SWCNTs can enhance both the binding strength and catalytic activity of the supported single Au atom. Fundamental aspects such as adsorption energy and charge transfer are elucidated to analyze the adsorption properties of CO and O 2 and co-adsorption of CO and O 2 molecules. It is found that CO binds stronger than O 2 on Au supported SWCNT. We clearly demonstrate that the defected SWCNT surface promotes electron transfer from the supported single Au atom to O 2 molecules. On the other hand, this effect is weaker for pristine SWCNTs. It is observed that the high density of spin-polarized states are localized in the region of the Fermi level due to the strong interactions between Au (5d orbital) and the adjacent carbon (2p orbital) atoms, which influence the catalytic performance. In addition, we elucidate both the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms of CO oxidation by O 2 . For the LH pathway, the barriers of the rate-limiting step are calculated to be 0.02 eV and 0.05 eV for Au/m-SWCNT and Au/di-SWCNT, respectively. To regenerate the active sites, an ER-like reaction occurs to form a second CO 2 molecule. The ER pathway is observed on Au/m-SWCNT, Au/SW-SWCNT and Au/SWCNT in which the Au/m-SWCNT has a smaller barrier. The comparison with a previous study (Lu et al., J. Phys. Chem. C, 2009, 113, 20156-20160.) indicates that the curvature effect of SWCNTs is important for the catalytic property of the supported single Au. Overall, Au/m-SWCNT is identified as the most active catalyst for CO oxidation compared to pristine SWCNT, SW-SWCNT and di-SWCNT. Our findings give a

  14. Orientation dependence in the four-atom reaction of OH + HBr using the single-state oriented OH radical beam.

    Science.gov (United States)

    Tsai, Po-Yu; Che, Dock-Chil; Nakamura, Masaaki; Lin, King-Chuen; Kasai, Toshio

    2010-03-20

    The orientation dependence for the Br atom formation in the reaction of the oriented OH radicals with HBr molecules at 0.26 eV collision energy has been observed for the first time using the hexapole electric field, and we found that the reaction cross-section for O-end attack is more favorable than that for H-end attack by a factor of 3.4 +/- 2.3.

  15. Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

    Science.gov (United States)

    Payne, W. A.; Nava, D. F.; Brunning, J.; Stief, L. J.

    1986-01-01

    The first-order, diffusion, and bimolecular rate constants for the reaction Br + C2H2 yields C2H3Br are evaluated. The rate constants are measured at 210, 248, 298, and 393 K and at pressures between 15-100 torr Ar using flash photolysis combined with time-resolved detection of atomic bromine via Br resonance radiation. It is observed that the reaction is not affected by pressure or temperature and the bimolecular constant = (4.0 + or - 0.8) x 10 to the -15th cu cm/sec with an error of two standard deviations. The C2H2 + Br reaction rates are compared with reactions of C2H2 with Cl, OH, NH2, and H. The loss rates for atmospheric C2H2 for reactions with OH, Cl, O, and Br are calculated as a function of altitude.

  16. Single-drop reactive extraction/extractive reaction with forced convective diffusion and interphase mass transfer

    Science.gov (United States)

    Kleinman, Leonid S.; Red, X. B., Jr.

    1995-01-01

    An algorithm has been developed for time-dependent forced convective diffusion-reaction having convection by a recirculating flow field within the drop that is hydrodynamically coupled at the interface with a convective external flow field that at infinity becomes a uniform free-streaming flow. The concentration field inside the droplet is likewise coupled with that outside by boundary conditions at the interface. A chemical reaction can take place either inside or outside the droplet, or reactions can take place in both phases. The algorithm has been implemented, and for comparison results are shown here for the case of no reaction in either phase and for the case of an external first order reaction, both for unsteady behavior. For pure interphase mass transfer, concentration isocontours, local and average Sherwood numbers, and average droplet concentrations have been obtained as a function of the physical properties and external flow field. For mass transfer enhanced by an external reaction, in addition to the above forms of results, we present the enhancement factor, with the results now also depending upon the (dimensionless) rate of reaction.

  17. Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

    Science.gov (United States)

    Silverstein, Todd P.

    2012-01-01

    Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

  18. 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

  19. Production of Neutron-Rich Ca Isotopes in Transfer-Type Reactions

    CERN Document Server

    Penionzhkevich, Yu E; Antonenko, N V

    2005-01-01

    Possibilities of production of neutron-rich isotopes $^{56,58,60}$Ca in transfer-type reactions are analyzed. The optimal conditions for their production are suggested. The neutron separation energies in nuclei near the neutron drip line can be estimated by measuring the excitation functions.

  20. Analysis of coupled mass transfer and sol-gel reaction in a two-phase system

    NARCIS (Netherlands)

    Castelijns, H.J.; Huinink, H.P.; Pel, L.; Zitha, P.L.J.

    2006-01-01

    The coupled mass transfer and chemical reactions of a gel-forming compound in a two-phase system were studied in detail. Tetra-methyl-ortho-silicate (TMOS) is often used as a precursor in sol-gel chemistry to produce silica gels in aqueous systems. TMOS can also be mixed with many hydrocarbons

  1. 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...

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

    DEFF Research Database (Denmark)

    Fernandez, Esther; Larsson, Jonas T.; McLean, Kirsty J.

    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...

  3. 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.

  4. State-to-state chemiluminescence in reactions of Mn atoms with S2Cl2.

    Science.gov (United States)

    Khanniche, Sarah; Levy, Martin Richard

    2011-10-21

    A combined experimental and time-dependent density functional theory (TDDFT) investigation of the title reaction is presented. Both 'hot' and 'cold' laser-ablated Mn atom beams have been employed to determine the translational excitation functions for production of MnCl*(c(5)Σ(+), d(5)Π, e(5)Δ, e(5)Σ(+), A(7)Π). Analysis in terms of the multiple line-of-centres approach shows that the 'hot' results are dominated by reactions of the second metastable state of Mn, z(8)P(J), all with very low thresholds; while the first metastable state, a(6)D(J), and the ground state, a(6)S, are the precursors in the 'cold' results, all with significant excess barriers. The post-threshold behaviour of most z(8)P(J) and a(6)D(J) reaction channels implies that the transition states shift forward with increasing collision energy. The TDDFT calculations suggest that, while Mn*(z(8)P(J), a(6)D(J)) insertion into the S-Cl bond is facile, the observed chemiluminescence channels mostly derive from abstraction in a preferred linear Mn-Cl-S configuration, and that the low z(8)P(J) thresholds originate from attractive but excited reagent potentials which either reach a seam of interactions in the product valley or (in the c(5)Σ(+) case) lead to an octet potential very close in energy to the product sextet. The excess barriers in the Mn*(a(6)D(J)) and Mn(a(6)S) reactions appear for the most part to derive from exit channel mixing with lower-lying product potentials. The observed transition state shifts are consistent with the system being forced to ride up the repulsive wall of the entrance valley as collision energy increases, the location of that wall being different for the z(8)P(J) and a(6)D(J) cases. This journal is © the Owner Societies 2011

  5. ANISOTROPY EFFECTS IN SINGLE-ELECTRON TRANSFER BETWEEN LASER-EXCITED ATOMS AND HIGHLY-CHARGED IONS

    NARCIS (Netherlands)

    Recent collision experiments are reviewed in which one-electron transfer between laser excited target atoms and (highly charged) keV-ions has been studied. Especially results showing a dependence of the charge exchange on the initial target orbital alignment are discussed. The question to what

  6. Single crystal to single crystal transformation and hydrogen-atom transfer upon oxidation of a cerium coordination compound.

    Science.gov (United States)

    Williams, Ursula J; Mahoney, Brian D; Lewis, Andrew J; DeGregorio, Patrick T; Carroll, Patrick J; Schelter, Eric J

    2013-04-15

    Trivalent and tetravalent cerium compounds of the octamethyltetraazaannulene (H2omtaa) ligand have been synthesized. Electrochemical analysis shows a strong thermodynamic preference for the formal cerium(IV) oxidation state. Oxidation of the cerium(III) congener Ce(Homtaa)(omtaa) occurs by hydrogen-atom transfer that includes a single crystal to single crystal transformation upon exposure to an ambient atmosphere.

  7. Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization.

    Science.gov (United States)

    Lin, Ching Yeh; Coote, Michelle L; Gennaro, Armando; Matyjaszewski, Krzysztof

    2008-09-24

    High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R-X; R = CH 2CN, CH(CH 3)CN, C(CH 3) 2CN, CH 2COOC 2H 5, CH(CH 3)COOCH 3, C(CH 3) 2COOCH 3, C(CH 3) 2COOC 2H 5, CH 2Ph, CH(CH 3)Ph, CH(CH 3)Cl, CH(CH 3)OCOCH 3, CH(Ph)COOCH 3, SO 2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R (*), are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R-X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ATRP should occur via concerted dissociative electron transfer rather than a two-step process with radical anion intermediates. Both the homolytic and heterolytic reactions are favored by electron-withdrawing substituents and/or those that stabilize the product alkyl radical, which explains why monomers such as acrylonitrile and styrene require less active ATRP catalysts than vinyl chloride and vinyl acetate. The rate constant of the hypothetical OSET reaction between bromoacetonitrile and Cu (I)/TPMA complex was estimated using Marcus theory for the electron-transfer processes. The estimated rate constant k OSET = approximately 10 (-11) M (-1) s (-1) is significantly smaller than the experimentally measured activation rate constant ( k ISET = approximately 82 M (-1) s (-1) at 25 degrees C in acetonitrile) for the concerted atom transfer mechanism (inner-sphere electron transfer, ISET), implying that the ISET mechanism is preferred. For

  8. Transferable aspherical atom model refinement of protein and DNA structures against ultrahigh-resolution X-ray data.

    Science.gov (United States)

    Malinska, Maura; Dauter, Zbigniew

    2016-06-01

    In contrast to the independent-atom model (IAM), in which all atoms are assumed to be spherical and neutral, the transferable aspherical atom model (TAAM) takes into account the deformed valence charge density resulting from chemical bond formation and the presence of lone electron pairs. Both models can be used to refine small and large molecules, e.g. proteins and nucleic acids, against ultrahigh-resolution X-ray diffraction data. The University at Buffalo theoretical databank of aspherical pseudo-atoms has been used in the refinement of an oligopeptide, of Z-DNA hexamer and dodecamer duplexes, and of bovine trypsin. The application of the TAAM to these data improves the quality of the electron-density maps and the visibility of H atoms. It also lowers the conventional R factors and improves the atomic displacement parameters and the results of the Hirshfeld rigid-bond test. An additional advantage is that the transferred charge density allows the estimation of Coulombic interaction energy and electrostatic potential.

  9. A single residue controls electron transfer gating in photosynthetic reaction centers

    Czech Academy of Sciences Publication Activity Database

    Shlyk, O.; Samish, I.; Matěnová, M.; Dulebo, A.; Poláková, H.; Kaftan, David; Scherz, A.

    2017-01-01

    Roč. 7, MAR 16 (2017), s. 1-13, č. článku 44580. ISSN 2045-2322 R&D Projects: GA ČR GA15-00703S; GA MŠk(CZ) LO1416 Institutional support: RVO:61388971 Keywords : BACTERIA L REACTION CENTERS * INDUCED STRUCTURAL-CHANGES * ATOMIC-FORCE MICROSCOPE Subject RIV: EE - Microbiology, Virology Impact factor: 4.259, year: 2016

  10. Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides

    Science.gov (United States)

    An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production.

  11. Kinetics and mechanism of the gas-phase reaction of Cl atoms and OH radicals with fluorobenzene at 296 K

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Nielsen, Ole John; Hurley, MD

    2002-01-01

    with Cl atoms via a mechanism which, at least in part, leads neither to production of C6H5Cl nor to reformation of C6H5F. As the steady-state Cl atom concentration is increased, the fraction of the C6H5F-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate...... radical and adduct formation to give the C6H5F-Cl adduct. At 296 K the rate constant for the abstraction channel is k(5a)(Cl+C6H5F) = (1.1 +/- 0.1) x 10(-17) cm(3) molecule(-1) s(-1). The C6H5F-Cl adduct undergoes rapid (k similar to 10(8) s(-1)) decomposition to reform C6H5F and Cl atoms and reaction......) molecule(-1) s(-1) was, established for the reaction of the C6H5F-Cl adduct with O-2. The reaction of OH radicals with C6H5F was studied and a rate constant of k(OH + C6H5F) = (7.9 +/- 2.2) x 10(-13) cm(3) molecule(-1) s(-1) was determined. The results are discussed with respect to the available literature...

  12. Solvation dynamics and energetics of intramolecular hydride transfer reactions in biomass conversion.

    Science.gov (United States)

    Mushrif, Samir H; Varghese, Jithin J; Krishnamurthy, Chethana B

    2015-02-21

    Hydride transfer changes the charge structure of the reactant and thus, may induce reorientation/reorganization of solvent molecules. This solvent reorganization may in turn alter the energetics of the reaction. In the present work, we investigate the intramolecular hydride transfer by taking Lewis acid catalyzed glucose to fructose isomerization as an example. The C2-C1 hydride transfer is the rate limiting step in this reaction. Water and methanol are used as solvents and hydride transfer is simulated in the presence of explicit solvent molecules, treated quantum mechanically and at a finite temperature, using Car-Parrinello molecular dynamics (CPMD) and metadynamics. Activation free energy barrier for hydride transfer in methanol is found to be 50 kJ mol(-1) higher than that in water. In contrast, in density functional theory calculations, using an implicit solvent environment, the barriers are almost identical. Analysis of solvent dynamics and electronic polarization along the molecular dynamics trajectory and the results of CPMD-metadynamics simulation of the hydride transfer process in the absence of any solvent suggest that higher barrier in methanol is a result of non-equilibrium solvation. Methanol undergoes electronic polarization during the hydride transfer step. However, its molecular orientational relaxation is a much slower process that takes place after the hydride transfer, over an extended timescale. This results in non-equilibrium solvation. Water, on the other hand, does not undergo significant electronic polarization and thus, has to undergo minimal molecular reorientation to provide near equilibrium solvation to the transition state and an improved equilibrium solvation to the post hydride shift product state. Hence, the hydride transfer step is also observed to be exergonic in water and endergonic in methanol. The aforementioned explanation is juxtaposed to enzyme catalyzed charge transfer reactions, where the enhanced solvation of the

  13. Structural integrity of callosal midbody influences intermanual transfer in a motor reaction-time task.

    Science.gov (United States)

    Bonzano, Laura; Tacchino, Andrea; Roccatagliata, Luca; Mancardi, Giovanni Luigi; Abbruzzese, Giovanni; Bove, Marco

    2011-02-01

    Training one hand on a motor task results in performance improvements in the other hand, also when stimuli are randomly presented (nonspecific transfer). Corpus callosum (CC) is the main structure involved in interhemispheric information transfer; CC pathology occurs in patients with multiple sclerosis (PwMS) and is related to altered performance of tasks requiring interhemispheric transfer of sensorimotor information. To investigate the role of CC in nonspecific transfer during a pure motor reaction-time task, we combined motor behavior with diffusion tensor imaging analysis in PwMS. Twenty-two PwMS and 10 controls, all right-handed, were asked to respond to random stimuli with appropriate finger opposition movements with the right (learning) and then the left (transfer) hand. PwMS were able to improve motor performance reducing response times with practice with a trend similar to controls and preserved the ability to transfer the acquired motor information from the learning to the transfer hand. A higher variability in the transfer process, indicated by a significantly larger standard deviation of mean nonspecific transfer, was found in the PwMS group with respect to the control group, suggesting the presence of subtle impairments in interhemispheric communication in some patients. Then, we correlated the amount of nonspecific transfer with mean fractional anisotropy (FA) values, indicative of microstructural damage, obtained in five CC subregions identified on PwMS's FA maps. A significant correlation was found only in the subregion including posterior midbody (Pearson's r = 0.74, P = 0.003), which thus seems to be essential for the interhemispheric transfer of information related to pure sensorimotor tasks. Copyright © 2010 Wiley-Liss, Inc.

  14. Barrier heights of hydrogen-transfer reactions with diffusion quantum monte carlo method.

    Science.gov (United States)

    Zhou, Xiaojun; Wang, Fan

    2017-04-30

    Hydrogen-transfer reactions are an important class of reactions in many chemical and biological processes. Barrier heights of H-transfer reactions are underestimated significantly by popular exchange-correlation functional with density functional theory (DFT), while coupled-cluster (CC) method is quite expensive and can be applied only to rather small systems. Quantum Monte-Carlo method can usually provide reliable results for large systems. Performance of fixed-node diffusion quantum Monte-Carlo method (FN-DMC) on barrier heights of the 19 H-transfer reactions in the HTBH38/08 database is investigated in this study with the trial wavefunctions of the single-Slater-Jastrow form and orbitals from DFT using local density approximation. Our results show that barrier heights of these reactions can be calculated rather accurately using FN-DMC and the mean absolute error is 1.0 kcal/mol in all-electron calculations. Introduction of pseudopotentials (PP) in FN-DMC calculations improves efficiency pronouncedly. According to our results, error of the employed PPs is smaller than that of the present CCSD(T) and FN-DMC calculations. FN-DMC using PPs can thus be applied to investigate H-transfer reactions involving larger molecules reliably. In addition, bond dissociation energies of the involved molecules using FN-DMC are in excellent agreement with reference values and they are even better than results of the employed CCSD(T) calculations using the aug-cc-pVQZ basis set. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  15. Dynamic flexibility in the light reactions of photosynthesis governed by both electron and proton transfer reactions.

    Science.gov (United States)

    Kramer, David M; Avenson, Thomas J; Edwards, Gerald E

    2004-07-01

    Plant photosynthesis performs the remarkable feat of converting light energy into usable chemical forms, which involves taming highly reactive intermediates without harming plant cells. This requires an apparatus that is not only efficient and robust but also flexible in its responses to changing environmental conditions. It also requires that the output of the energy-storing reactions be matched with the demands of metabolism. This article addresses the mechanisms by which this flexibility is achieved for short-term environmental changes. We argue that chloroplasts need two types of flexible mechanisms: one for modulating the output ratio of ATP:NADPH, which involves cyclic electron flux around photosystem I; and another for changing the regulatory sensitivity of the light-harvesting antenna to electron (and proton) flow.

  16. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    Science.gov (United States)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

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

    Science.gov (United States)

    Cui, Qiang; Morokuma, Keiji

    1998-03-01

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

  18. Direct simulation of proton-coupled electron transfer reaction dynamics and mechanisms

    Science.gov (United States)

    Kretchmer, Joshua S.; Miller, Thomas F., III

    2014-03-01

    Proton-coupled electron transfer (PCET) reactions, in which both an electron and an associated proton undergo reactive transfer, play an important role in many chemical and biological systems. Due to the complexity of this class of reactions, a variety of different mechanisms fall under the umbrella of PCET. However, the physical driving forces that determine the preferred mechanism in a given system still remain poorly understood. Towards this end, we extend ring polymer molecular dynamics (RPMD), a path-integral quantum dynamics method, to enable the direct simulation and characterization of PCET reaction dynamics in both fully atomistic and system-bath models of organometallic catalysts. In addition to providing validation for the simulation method via extensive comparison with existing PCET rate theories, we analyze the RPMD trajectories to investigate the competition between the concerted and sequential reaction mechanisms for PCET, elucidating the large role of the solvent in controlling the preferred mechanism. We further employ RPMD to determine the kinetics and mechanistic features of concerted PCET reactions across different regimes of electronic and vibrational coupling, providing evidence for a new and distinct PCET reaction mechanism.

  19. Multinucleon transfer reactions of {sup 40}Ca+{sup 90,96}Zr

    Energy Technology Data Exchange (ETDEWEB)

    Montagnoli, G.; Beghini, S.; Scarlassara, F.; Segato, G.F. [Dipartimento di Fisica, Universita di Padova, and INFN, Padova, Via Marzolo 8, I-35135 (Italy); Corradi, L.; Lin, C.J.; Stefanini, A.M. [INFN, Laboratori Nazionali di Legnaro (Italy)

    1997-10-01

    The experimental investigation of multi-nucleon transfer channels of {sup 40}Ca+{sup 90,96}Zr has been triggered by the very different fusion excitation functions recently observed in these two systems. The cross sections of the transfer reactions in the two systems have been measured at two energies close to the Coulomb barrier. The time-of-flight spectrometer PISOLO allowed us to identify a multitude of transfer channels, even very weak ones, with high resolution and efficiency. Especially for the neutron pick-up channels, the cross sections are much larger for the target {sup 96}Zr than for {sup 90}Zr with evidence, in the Q-value spectra, of large energy losses (20-30 MeV) involved in the transfer mechanism at forward angles. (author)

  20. Atmospheric reactions of methylcyclohexanes with Cl atoms and OH radicals: determination of rate coefficients and degradation products.

    Science.gov (United States)

    Ballesteros, Bernabé; Ceacero-Vega, Antonio A; Jiménez, Elena; Albaladejo, José

    2015-04-01

    As the result of biogenic and anthropogenic activities, large quantities of chemical compounds are emitted into the troposphere. Alkanes, in general, and cycloalkanes are an important chemical class of hydrocarbons found in diesel, jet and gasoline, vehicle exhaust emissions, and ambient air in urban areas. In general, the primary atmospheric fate of organic compounds in the gas phase is the reaction with hydroxyl radicals (OH). The oxidation by Cl atoms has gained importance in the study of atmospheric reactions because they may exert some influence in the boundary layer, particularly in marine and coastal environments, and in the Arctic troposphere. The aim of this paper is to study of the atmospheric reactivity of methylcylohexanes with Cl atoms and OH radicals under atmospheric conditions (in air at room temperature and pressure). Relative kinetic techniques have been used to determine the rate coefficients for the reaction of Cl atoms and OH radicals with methylcyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, and 1,3,5-trimethylcyclohexane at 298 ± 2 K and 720 ± 5 Torr of air by Fourier transform infrared) spectroscopy and gas chromatography-mass spectrometry (GC-MS) in two atmospheric simulation chambers. The products formed in the reaction under atmospheric conditions were investigated using a 200-L Teflon bag and employing the technique of solid-phase microextraction coupled to a GC-MS. The rate coefficients obtained for the reaction of Cl atoms with the studied compounds are the following ones (in units of 10(-10) cm(3) molecule(-1) s(-1)): (3.11 ± 0.16), (2.89 ± 0.16), (2.89 ± 0.26), and (2.61 ± 0.42), respectively. For the reactions with OH radicals the determined rate coefficients are (in units of 10(-11) cm(3) molecule(-1) s(-1)): (1.18 ± 0.12), (1.49 ± 0.16), (1.41 ± 0.15), and (1.77 ± 0.23), respectively. The reported error is twice the standard deviation. A detailed

  1. Stereodynamical Origin of Anti-Arrhenius Kinetics: Negative Activation Energy and Roaming for a Four-Atom Reaction.

    Science.gov (United States)

    Coutinho, Nayara D; Silva, Valter H C; de Oliveira, Heibbe C B; Camargo, Ademir J; Mundim, Kleber C; Aquilanti, Vincenzo

    2015-05-07

    The OH + HBr → H2O + Br reaction, prototypical of halogen-atom liberating processes relevant to mechanisms for atmospheric ozone destruction, attracted frequent attention of experimental chemical kinetics: the nature of the unusual reactivity drop from low to high temperatures eluded a variety of theoretical efforts, ranking this one among the most studied four-atom reactions. Here, inspired by oriented molecular-beams experiments, we develop a first-principles stereodynamical approach. Thermalized sets of trajectories, evolving on a multidimensional potential energy surface quantum mechanically generated on-the-fly, provide a map of most visited regions at each temperature. Visualizations of rearrangements of bonds along trajectories and of the role of specific angles of reactants' mutual approach elucidate the mechanistic change from the low kinetic energy regime (where incident reactants reorient to find the propitious alignment leading to reaction) to high temperature (where speed hinders adjustment of directionality and roaming delays reactivity).

  2. Tests of stratospheric models - The reactions of atomic chlorine with O3 and CH4 at low temperature

    Science.gov (United States)

    Demore, W. B.

    1991-01-01

    The rate-constant ratio of the photochemical reactions of atomic chlorine with O3 and CH4 was determined using data from laboratory experiments on competitive chlorination of O3/CH4 mixtures at stratospheric temperatures (197-217 K). Two experimental approaches were used: (1) measuring the k1/k2 ratio for the reactions of atomic chlorine with ozone and methane and (2) testing for some of the ClO/CH3O2 chemistry. The chlorine and ozone concentrations were monitored by UV-Vis spectroscopy, and the CH3Cl concentration was measured by FTIR. The results on the k1/k2 ratio are in excellent agreement with the current NASA recommendation (DeMore et al., 1990), being only 12 percent higher. On the other hand, results on the ClO + CH3O2 reaction do not support the rate constant suggested by Simon et al. (1989).

  3. Ultralow fouling polyacrylamide on gold surfaces via surface-initiated atom transfer radical polymerization.

    Science.gov (United States)

    Liu, Qingsheng; Singh, Anuradha; Lalani, Reza; Liu, Lingyun

    2012-04-09

    In this work, polyacrylamide is investigated as an ultralow fouling surface coating to highly resist protein adsorption, cell adhesion, and bacterial attachment. Polyacrylamide was grafted on gold surfaces via surface-initiated atom transfer radical polymerization (ATRP). Protein adsorption from a wide range of biological media, including single protein solutions of fibrinogen, bovine serum albumin, and lysozyme, dilute and undiluted human blood serum, and dilute and undiluted human blood plasma, was studied by surface plasmon resonance (SPR). Dependence of the protein resistance on polyacrylamide film thickness was examined. With the optimal film thickness, the adsorption amount of all three single proteins on polyacrylamide-grafted surfaces was polyacrylamide-grafted surfaces were 5, 6.5, 17, and 28 pg/mm(2), respectively, comparable (if not better) than the adsorption levels on poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) surfaces, the best antifouling materials known to date. The polyacrylamide-grafted surfaces were also shown strongly resistant to adhesion from bovine aortic endothelial cells and two bacterial species, Gram-positive Staphylococcus epidermidis ( S. epidermidis ) and Gram-negative Pseudomonas aeruginosa ( P. aeruginosa ). Strong hydrogen bond with water is considered the key attribute for the ultralow fouling properties of polyacrylamide. This is the first work to graft gold surfaces with polyacrylamide brushes via ATRP to achieve ultralow fouling surfaces, demonstrating that polyacrylamide is a promising alternative to traditional PEG-based antifouling materials.

  4. Customized atomic force microscopy probe by focused-ion-beam-assisted tip transfer

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Andrew; Butte, Manish J., E-mail: manish.butte@stanford.edu [Department of Pediatrics, Division of Immunology, Allergy and Rheumatology, Stanford University, Stanford, California 94305 (United States)

    2014-08-04

    We present a technique for transferring separately fabricated tips onto tipless atomic force microscopy (AFM) cantilevers, performed using focused ion beam-assisted nanomanipulation. This method addresses the need in scanning probe microscopy for certain tip geometries that cannot be achieved by conventional lithography. For example, in probing complex layered materials or tall biological cells using AFM, a tall tip with a high-aspect-ratio is required to avoid artifacts caused by collisions of the tip's sides with the material being probed. We show experimentally that tall (18 μm) cantilever tips fabricated by this approach reduce squeeze-film damping, which fits predictions from hydrodynamic theory, and results in an increased quality factor (Q) of the fundamental flexural mode. We demonstrate that a customized tip's well-defined geometry, tall tip height, and aspect ratio enable improved measurement of elastic moduli by allowing access to low-laying portions of tall cells (T lymphocytes). This technique can be generally used to attach tips to any micromechanical device when conventional lithography of tips cannot be accomplished.

  5. Efficient Functionalization of Polyethylene Fibers for the Uranium Extraction from Seawater through Atom Transfer Radical Polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Neti, Venkata S. [Chemical; Das, Sadananda [Chemical; Brown, Suree [Department; Janke, Christopher J. [Materials; Kuo, Li-Jung [Marine; Gill, Gary A. [Marine; Dai, Sheng [Chemical; Department; Mayes, Richard T. [Chemical

    2017-09-14

    Brush-on-brush structures are proposed as one method to overcome support effects in grafted polymers. Utilizing glycidyl methacrylate (GMA) grafted on polyethylene (PE) fibers using radiation-induced graft polymerization (RIGP) provides a hydrophilic surface on the hydrophobic PE. When integrated with atom transfer radical polymerization (ATRP), the grafting of acrylonitrile (AN) and hydroxyethyl acrylate (HEA) can be controlled and manipulated more easily than with RIGP. Poly(acrylonitrile)-co-poly(hydroxyethyl acrylate) chains were grown via ATRP on PE-GMA fibers to generate an adsorbent for the extraction of uranium from seawater. The prepared adsorbents in this study demonstrated promise (159.9 g- U/kg of adsorbent) in laboratory screening tests using a high uranium concentration brine and 1.24 g-U/Kg of adsorbent in the filtered natural seawater in 21-days. The modest capacity in 21- days exceeds previous efforts to generate brush-on-brush adsorbents by ATRP while manipulating the apparent surface hydrophilicity of the trunk material (PE).

  6. Comparing the temperature dependence of photosynthetic electron transfer in Chloroflexus aurantiacus and Rhodobactor sphaeroides reaction centers.

    Science.gov (United States)

    Guo, Zhi; Lin, Su; Xin, Yueyong; Wang, Haiyu; Blankenship, Robert E; Woodbury, Neal W

    2011-09-29

    The process of electron transfer from the special pair, P, to the primary electron donor, H(A), in quinone-depleted reaction centers (RCs) of Chloroflexus (Cf.) aurantiacus has been investigated over the temperature range from 10 to 295 K using time-resolved pump-probe spectroscopic techniques. The kinetics of the electron transfer reaction, P* → P(+)H(A)(-), was found to be nonexponential, and the degree of nonexponentiality increased strongly as temperature decreased. The temperature-dependent behavior of electron transfer in Cf. aurantiacus RCs was compared with that of the purple bacterium Rhodobacter (Rb.) sphaeroides . Distinct transitions were found in the temperature-dependent kinetics of both Cf. aurantiacus and Rb. sphaeroides RCs, at around 220 and 160 K, respectively. Structural differences between these two RCs, which may be associated with those differences, are discussed. It is suggested that weaker protein-cofactor hydrogen bonding, stronger electrostatic interactions at the protein surface, and larger solvent interactions likely contribute to the higher transition temperature in Cf. aurantiacus RCs temperature-dependent kinetics compared with that of Rb. sphaeroides RCs. The reaction-diffusion model provides an accurate description for the room-temperature electron transfer kinetics in Cf. aurantiacus RCs with no free parameters, using coupling and reorganization energy values previously determined for Rb. sphaeroides , along with an experimental measure of protein conformational diffusion dynamics and an experimental literature value of the free energy gap between P* and P(+)H(A)(-). © 2011 American Chemical Society

  7. Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

    Science.gov (United States)

    Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

    2008-04-01

    Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

  8. Development of New Barrel Array Design for Transfer Reactions with Fast Beams

    Science.gov (United States)

    Corrado, F.; Walter, D.; Pain, S. D.; Cizewski, J. A.

    2017-09-01

    Single-nucleon transfer reactions allow for extraction of spectroscopic information on unstable and exotic nuclei, providing details for understanding the rapid neutron capture process (r-process). To study exotic, neutron-rich isotopes, inverse kinematics is needed with light targets and beams of heavy projectiles. Measurement of the 84Se(d,p)85Se reaction at 45 MeV/u will be conducted at the NSCL in December 2017 to extract spectroscopic information on the 85Se nucleus. Single-particle transfer reactions in inverse kinematics at high energy - such as that for the 84Se(d,p) - are uncommon and require new designs and techniques to be developed. A modification to the current ORRUBA barrel design is needed to accommodate such changes. Features of this design include: a modular barrel able to cover a large desired angular range and detector coverage at backward angles in the lab, as well as allow for easy access to detectors without affecting the rest of the configuration. Improvements to the current design will be presented, including discussion of use in future transfer reactions with fast beams. This work is supported in part by the National Science Foundation and U.S. D.O.E.

  9. Probing the critical residues for intramolecular fructosyl transfer reaction of a levan fructotransferase.

    Science.gov (United States)

    Moon, Keum-Ok; Choi, Kyoung-Hwa; Kang, Ho-Young; Oh, Jeong-Il; Jang, Se Bok; Park, Cheon-Seok; Lee, Jong-Hoon; Cha, Jaeho

    2008-06-01

    Levan fructotransferase (LFTase) preferentially catalyzes the transfructosylation reaction in addition to levan hydrolysis, whereas other levan-degrading enzymes hydrolyze levan into a levan-oligosaccharide and fructose. Based on sequence comparisons and enzymatic properties, the fructosyl transfer activity of LFTase is proposed to have evolved from levanase. In order to probe the residues that are critical to the intramolecular fructosyl transfer reaction of the Microbacterium sp. AL-210 LFTase, an error-prone PCR mutagenesis process was carried out, and the mutants that led to a shift in activity from transfructosylation towards hydrolysis of levan were screened by the DNS method. After two rounds of mutagenesis, TLC and HPLC analyses of the reaction products by the selected mutants revealed two major products; one is a di-D-fructose- 2,6':6,2'-dianhydride (DFAIV) and the other is a levanbiose. The newly detected levanbiose corresponds to the reaction product from LFTase lacking transferring activity. Two mutants (2-F8 and 2-G9) showed a high yield of levanbiose (38-40%) compared with the wild-type enzyme, and thus behaved as levanases. Sequence analysis of the individual mutants responsible for the enhanced hydrolytic activity indicated that Asn-85 was highly involved in the transfructosylation activity of LFTase.

  10. Study of breakup and transfer of weakly bound nucleus 6Li to explore the low energy reaction dynamics

    Science.gov (United States)

    Zhang, G. L.; Zhang, G. X.; Hu, S. P.; Zhang, H. Q.; Gomes, P. R. S.; Lubian, J.; Guo, C. L.; Wu, X. G.; Yang, J. C.; Zheng, Y.; Li, C. B.; He, C. Y.; Zhong, J.; Li, G. S.; Yao, Y. J.; Guo, M. F.; Sun, H. B.; Valiente-Dobòn, J. J.; Goasduff, A.; Siciliano, M.; Galtarosa, F.; Francesco, R.; Testov, D.; Mengoni, D.; Bazzacco, D.; John, P. R.; Qu, W. W.; Wang, F.; Zheng, L.; Yu, L.; Chen, Q. M.; Luo, P. W.; Li, H. W.; Wu, Y. H.; Zhou, W. K.; Zhu, B. J.; Li, E. T.; Hao, X.

    2017-11-01

    Investigation of the breakup and transfer effect of weakly bound nuclei on the fusion process has been an interesting research topic in the past several years. However, owing to the low intensities of the presently available radioactive ion beam (RIB), it is difficult to clearly explore the reaction mechanisms of nuclear systems with unstable nuclei. In comparison with RIB, the beam intensities of stable weakly bound nuclei such as 6,7Li and 9Be, which have significant breakup probability, are orders of magnitude higher. Precise fusion measurements have already been performed with those stable weakly bound nuclei, and the effect of breakup of those nuclei on the fusion process has been extensively studied. Those nuclei indicated large production cross sections for particles other than the α + x breakup. The particles are originated from non-capture breakup (NCBU), incomplete fusion (ICF) and transfer processes. However, the conclusion of reaction dynamics was not clear and has the contradiction. In our previous experiments we have performed 6Li+96Zr and 154Sm at HI-13 Tandem accelerator of China Institute of Atomic Energy (CIAE) by using HPGe array. It is shown that there is a small complete fusion (CF) suppression on medium-mass target nucleus 96Zr different from about 35% suppression on heavier target nucleus 154Sm at near-barrier energies. It seems that the CF suppression factor depends on the charge of target nuclei. We also observed one neutron transfer process. However, the experimental data are scarce for medium-mass target nuclei. In order to have a proper understanding of the influence of breakup and transfer of weakly bound projectiles on the fusion process, we performed the 6Li+89Y experiment with incident energies of 22 MeV and 34 MeV on Galileo array in cooperation with Si-ball EUCLIDES at Legnaro National Laboratory (LNL) in Italy. Using particle-particle and particle-γ coincidences, the different reaction mechanisms can be clearly explored.

  11. 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

    -frequency intramolecular degrees of feedom on the free energy relationship for series of closely related reactions was investigated for various model systems involving displacement of potential energy surfaces, frequency shift, and anharmonicity effects. The free energy plots are generally found to pass through a maximum...... and to be asymmetric with a slower decrease in the transition probability with increasing energy of reaction. For high-frequency intramolecular modes this provides a rationalization of the experimental observation of ''activationless'' regions. Isotope effects are discussed as also are the oscillatory free energy......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...

  12. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-12-22

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  13. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'Yov, Ilia A.

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  14. Minor actinide fission induced by multi-nucleon transfer reaction in inverse kinematics

    Directory of Open Access Journals (Sweden)

    Taieb J.

    2010-03-01

    Full Text Available In the framework of nuclear waste incineration and design of new generation nuclear reactors, experimental data on fission probabilities and on fission fragment yields of minor actinides are crucial to design prototypes. Transfer-induced fission has proven to be an efficient method to study fission probabilities of actinides which cannot be investigated with standard techniques due to their high radioactivity. We report on the preliminary results of an experiment performed at GANIL that investigates fission probabilities with multi-nucleon transfer reactions in inverse kinematics between a 238U beam on a 12C target. Actinides from U to Cm were produced with an excitation energy range from 0 to 30 MeV. In addition, inverse kinematics allowed to characterize the fission fragments in mass and charge. A key point of the analysis resides in the identification of the actinides produced in the different transfer channels. The new annular telescope SPIDER was used to tag the target-like recoil nucleus of the transfer reaction and to determine the excitation energy of the actinide. The fission probability for each transfer channel is accessible and the preliminary results for 238U are promising.

  15. Application of discrete solvent reaction field model with self-consistent atomic charges and atomic polarizabilities to calculate the χ(1) and χ(2) of organic molecular crystals

    Science.gov (United States)

    Lu, Shih-I.

    2018-01-01

    We use the discrete solvent reaction field model to evaluate the linear and second-order nonlinear optical susceptibilities of 3-methyl-4-nitropyridine-1-oxyde crystal. In this approach, crystal environment is created by supercell architecture. A self-consistent procedure is used to obtain charges and polarizabilities for environmental atoms. Impact of atomic polarizabilities on the properties of interest is highlighted. This approach is shown to give the second-order nonlinear optical susceptibilities within error bar of experiment as well as the linear optical susceptibilities in the same order as experiment. Similar quality of calculations are also applied to both 4-N,N-dimethylamino-3-acetamidonitrobenzene and 2-methyl-4-nitroaniline crystals.

  16. Heavy-ion transfer reactions at large internuclear distances using the PRISMA magnetic spectrometer

    Directory of Open Access Journals (Sweden)

    Montanari D. J.

    2013-12-01

    Full Text Available We measured excitation functions for the main transfer channels in the 116Sn+60Ni reaction at different bombarding energies from above to well below the Coulomb barrier. The experiment has been performed in inverse kinematics, detecting the lighter (target-like ions with the magnetic spectrometer PRISMA at very forward angles. Good mass, nuclear charge and kinetic energy resolutions have been achieved. The comparison between the data and microscopic calculations for the present case and for the previously measured 96Zr+40Ca system, namely superfluid and near closed shells nuclei, should significantly improve our understanding of nucleon-nucleon correlation properties in multinucleon transfer processes.

  17. Outer-sphere 2 e{sup -}/2 H{sup +} transfer reactions of ruthenium(II)-amine and ruthenium(IV)-amido complexes

    Energy Technology Data Exchange (ETDEWEB)

    Cattaneo, Mauricio [Department of Chemistry, University of Washington (United States); INQUINOA-CONICET, Universidad Nacional de Tucuman, San Miguel de Tucuman (Argentina); Ryken, Scott A. [Department of Chemistry, University of Washington (United States); Mayer, James M. [Department of Chemistry, University of Washington (United States); Department of Chemistry, Yale University, New Haven, CT, 06520 (United States)

    2017-03-20

    A diverse set of 2 e{sup -}/2 H{sup +} reactions are described that interconvert [Ru{sup II}(bpy)(en*){sub 2}]{sup 2+} and [Ru{sup IV}(bpy)(en-H*){sub 2}]{sup 2+} (bpy=2,2'-bipyridine, en*=H{sub 2}NCMe{sub 2}CMe{sub 2}NH{sub 2}, en*-H=H{sub 2}NCMe{sub 2}CMe{sub 2}NH{sup -}), forming or cleaving different O-H, N-H, S-H, and C-H bonds. The reactions involve quinones, hydrazines, thiols, and 1,3-cyclohexadiene. These proton-coupled electron transfer reactions occur without substrate binding to the ruthenium center, but instead with precursor complex formation by hydrogen bonding. The free energies of the reactions vary over more than 90 kcal mol{sup -1}, but the rates are more dependent on the type of X-H bond involved than the associated ΔG . There is a kinetic preference for substrates that have the transferring hydrogen atoms in close proximity, such as ortho-tetrachlorobenzoquinone over its para-isomer and 1,3-cyclohexadiene over its 1,4-isomer, perhaps hinting at the potential for concerted 2 e{sup -}/2 H{sup +} transfers. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Communication: H-atom reactivity as a function of temperature in solid parahydrogen: The H + N2O reaction

    Science.gov (United States)

    Mutunga, Fredrick M.; Follett, Shelby E.; Anderson, David T.

    2013-10-01

    We present low temperature kinetic measurements for the H + N2O association reaction in solid parahydrogen (pH2) at liquid helium temperatures (1-5 K). We synthesize 15N218O doped pH2 solids via rapid vapor deposition onto an optical substrate attached to the cold tip of a liquid helium bath cryostat. We then subject the solids to short duration 193 nm irradiations to generate H-atoms produced as byproducts of the in situ N2O photodissociation, and monitor the subsequent reaction kinetics using rapid scan FTIR. For reactions initiated in solid pH2 at 4.3 K we observe little to no reaction; however, if we then slowly reduce the temperature of the solid we observe an abrupt onset to the H + N2O → cis-HNNO reaction at temperatures below 2.4 K. This abrupt change in the reaction kinetics is fully reversible as the temperature of the solid pH2 is repeatedly cycled. We speculate that the observed non-Arrhenius behavior (negative activation energy) is related to the stability of the pre-reactive complex between the H-atom and 15N218O reagents.

  19. Water-assisted atom transfer radical polymerization of N-isopropylacrylamide: nature of solvent and temperature.

    Science.gov (United States)

    Ye, Jianding; Narain, Ravin

    2009-01-22

    We demonstrate here via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) at low temperature that the negative function of water in aqueous ATRP is significantly suppressed. By the addition of a small amount of water in a water-miscible organic solvent and maintaining low polymerization temperature, the ATRP of NIPAM is relatively fast and well controlled. We observed that the rate of the polymerization in pure organic solvent at a monomer concentration of 20 wt % is slow, and relatively low conversions were obtained. The low conversion of PNIPAM in pure alcoholic media (such as methanol, ethanol, and n-propanol) is attributed to the poor solubility of the resulting low molecular weight polymer in such solvents. The consequence is that the PNIPAM chains are aggregated, resulting in the inaccessibility of the embedded halide atom of the polymer chain ends by the copper catalyst. As expected, the ATRP of NIPAM in pure water was found to be fast and uncontrolled. These results have therefore prompted us to study the ATRP of NIPAM in aqueous-organic mixtures. Room temperature polymerization of NIPAM in mixed aqueous-organic solvent mixtures (organic:water = 4:1 or 3:1) revealed to be fast and uncontrolled. However, when the NIPAM polymerization was conducted at low temperature (0 degrees C) in such solvent systems, the polymerization turned out to be well-controlled as the molar masses progress linearly with conversion, and pseudo-first-order kinetic plots were obtained. Furthermore, monomodal GPC traces and narrow molecular weight distributions were obtained in all aqueous-organic solvent systems. Chain extension for aqueous ATRP of NIPAM revealed to proceed well at low temperature as compared to room temperature. Furthermore, we observe that the rates of the polymerization of NIPAM in different aqueous-organic mixtures follow the trend of polarity in the case of the polar aprotic solvents. However, in the case of polar protic solvent

  20. High spin levels populated in multinucleon-transfer reactions with 480 MeV /sup 12/C

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, L.; Boucenna, A.; Linck, I.; Lott, B.; Rebmeister, R.; Schulz, N.; Sens, J.C.; Mermaz, M.C.; Berthier, B.; Lucas, R.; and others

    1988-06-01

    Two- and three-nucleon stripping reactions induced by 480 MeV /sup 12/C have been studied on /sup 12/C, /sup 16/O, /sup 28/Si, /sup 40/Ca, and /sup 54/Fe target nuclei. Discrete levels are fed with cross sections up to 1 mbsr for d-transfer reactions and 1 order and 2 orders of magnitude less for 2p- and /sup 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.

  1. Kinetic of the gas-phase reactions of OH radicals and Cl atoms with Diethyl Ethylphosphonate and Triethyl Phosphate

    KAUST Repository

    Laversin, H.

    2015-11-30

    In this paper, the relative-rate technique has been used to obtain rate coefficients for the reaction of two organophosphorus compounds: Triethyl phosphate (TEP) and Diethyl ethylphosphonate (DEEP) with OH radicals and Cl atoms at atmospheric pressure and at different temperatures. The calculated rate constants were fitted to the Arrhenius expression over the temperature range 298 – 352 K. The following expressions (in cm3molecule-1s-1) were obtained for the reactions of OH and CL with DEEP and TEP: kOH+DEEP= (7.84±0.65)x10-14exp((1866±824)/T), kOH+TEP = (6.54±0.42)x10-14exp((1897±626)/T), kCl+DEEP = (5.27± 0.80)x10−11exp(765±140/T) and kCl+TEP = (5.23± 0.80)x10−11exp(736± 110/T). These results show that the reaction of the studied compounds with Cl atoms proceeds more rapidly than that with OH radicals. The related tropospheric lifetimes suggest that once emitted into the atmosphere, TEP and DEEP can be removed within a few hours in areas close to their emission sources. TEP and DEEP are principally removed by OH radicals. However, in coastal areas where the Cl atoms’ concentration is higher, TEP and DEEP removal by reaction with Cl atoms could be a competitive process.

  2. Dichotomous Hydrogen Atom Transfer vs. Proton Coupled Electron Transfer During Activation of X-H Bonds (X = C, N, O) by Nonheme Iron-Oxo Complexes of Variable Basicity

    Science.gov (United States)

    Usharani, Dandamudi; Lacy, David C.; Borovik, A. S.; Shaik, Sason

    2013-01-01

    We describe herein the hydrogen-atom transfer (HAT)/ proton-coupled electron-transfer (PCET) reactivity for FeIV-oxo and FeIII-oxo complexes (1–4) that activate C-H, N-H, and O-H bonds in 9,10 dihydroanthracene (S1), dimethylformamide (S2), 1,2 diphenylhydrazine (S3), p-methoxyphenol (S4), and 1,4-cyclohexadiene (S5). In 1–3, the iron is pentacoordinated by tris[N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) or its derivatives. These complexes are basic, in the order 3 >> 1 > 2. Oxidant 4, [FeIVN4Py(O)]2+ (N4Py: N,N-bis(2-pyridylmethyl)-bis(2-pyridyl) methylamine), is the least basic oxidant. The DFT results match experimental trends and exhibit a mechanistic spectrum ranging from concerted HAT and PCET reactions to concerted-asynchronous proton transfer (PT) / electron transfer (ET) mechanisms, all the way to PT. The singly occupied orbital along the O---H---X (X= C, N, O) moiety in the TS shows clearly that in the PCET cases, the electron is transferred separately from the proton. The Bell-Evans-Polanyi principle does not account for the observed reactivity pattern, as evidenced by the scatter in the plot of calculated barrier vs. reactions driving forces. However, a plot of the deformation energy in the TS vs. the respective barrier provides a clear signature of the HAT/PCET dichotomy. Thus, in all C-H bond activations, the barrier derives from the deformation energy required to create the TS, whereas in N-H/O-H bond activations, the deformation energy is much larger than the corresponding barrier, indicating the presence of stabilizing interaction between the TS fragments. A valence bond model is used to link the observed results with the basicity/acidity of the reactants. PMID:24124906

  3. Multinucleon transfer reactions in {sup 40}Ca+{sup 124}Sn

    Energy Technology Data Exchange (ETDEWEB)

    Corradi, L.; He, J.H.; Ackermann, D.; Stefanini, A.M.; Pisent, A. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Via Romea 4, I-35020 Legnaro, Padova (Italy); Beghini, S.; Montagnoli, G.; Scarlassara, F.; Segato, G.F. [Dipartimento di Fisica, Universita di Padova, and Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via Marzolo 8, I-35131 Padova (Italy); Pollarolo, G. [Dipartimento di Fisica Teorica, Universita di Torino, and Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Via Pietro Giuria 1, 10125 Torino (Italy); Dasso, C.H.; Winther, A. [The Niels Bohr Institute, Blegdamsvej 17,2100 Copenhagen O/ (Denmark)

    1996-07-01

    Angular and {ital Q}-value distributions for a large variety of charge and mass partitions populated in the reaction {sup 40}Ca + {sup 124}Sn have been measured at 170 MeV with a new time-of-flight magnetic spectrometer. Reaction channels involving the net transfer of up to six protons and six neutrons have been detected. Population patterns, cross sections, and energy-loss distributions are compared with results of theoretical calculations based on independent single-nucleon transfer modes. The overall agreement is good, but more complex mechanisms may be needed to account for the larger drift towards neutron stripping revealed by the experimental data. {copyright} {ital 1996 The American Physical Society.}

  4. Ruthenium(II) pincer complexes with oxazoline arms for efficient transfer hydrogenation reactions

    KAUST Repository

    Chen, Tao

    2012-08-01

    Well-defined P NN CN pincer ruthenium complexes bearing both strong phosphine and weak oxazoline donors were developed. These easily accessible complexes exhibit significantly better catalytic activity in transfer hydrogenation of ketones compared to their PN 3P analogs. These reactions proceed under mild and base-free conditions via protonation- deprotonation of the \\'NH\\' group in the aromatization-dearomatization process. © 2012 Elsevier Ltd. All rights reserved.

  5. Picosecond laser studies of the charge-transfer reaction of excited triplet diphenylcarbene with electron donors

    Science.gov (United States)

    Sitzmann, E. V.; Langan, J.; Eisenthal, K. B.

    1983-12-01

    Evidence of a one-electron transfer process in a carbene reaction has been observed for the first time. The example is the quenching of the photoexcited triplet state of diphenylcarbene ( 3*DPC) by electron donors. Measurement of the fluorescence lifetime as a function of donor concentration yielded the bimolecular rate constant, 3* k. An explanation is offered as to why 3* and 1DPC react efficiently with amines as well as alcohols, whereas the ground triplet, 3DPC, does not.

  6. Probing nucleon-nucleon correlations in heavy-ion transfer reactions

    Directory of Open Access Journals (Sweden)

    Szilner S.

    2016-01-01

    Full Text Available The γ-particle coincident measurements, performed by coupling of the PRISMA spectrometer to the large γ arrays (CLARA and AGATA, demonstrate a strong interplay between single-particle and collective degrees of freedom that is pertinent to the reaction dynamics. By using the unique PRISMA performance in terms of both resolution and efficiency, measurements at very low bombarding energies have been performed. Via transfer of nucleon pairs, valuable information on the component responsible for particle correlations has been derived.

  7. 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.

  8. 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.

  9. Stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder.

    Science.gov (United States)

    Najib, Najwa; Bachok, Norfifah; Arifin, Norihan Md; Ishak, Anuar

    2014-02-26

    This paper is about the stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder. The governing partial differential equations in cylindrical form are transformed into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using a shooting method. Results for the skin friction coefficient, Schmidt number, velocity profiles as well as concentration profiles are presented for different values of the governing parameters. Effects of the curvature parameter, stretching/shrinking parameter and Schmidt number on the flow and mass transfer characteristics are examined. The study indicates that dual solutions exist for the shrinking cylinder but for the stretching cylinder, the solution is unique. It is observed that the surface shear stress and the mass transfer rate at the surface increase as the curvature parameter increases.

  10. Stagnation Point Flow and Mass Transfer with Chemical Reaction past a Stretching/Shrinking Cylinder

    Science.gov (United States)

    Najib, Najwa; Bachok, Norfifah; Arifin, Norihan Md.; Ishak, Anuar

    2014-02-01

    This paper is about the stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder. The governing partial differential equations in cylindrical form are transformed into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using a shooting method. Results for the skin friction coefficient, Schmidt number, velocity profiles as well as concentration profiles are presented for different values of the governing parameters. Effects of the curvature parameter, stretching/shrinking parameter and Schmidt number on the flow and mass transfer characteristics are examined. The study indicates that dual solutions exist for the shrinking cylinder but for the stretching cylinder, the solution is unique. It is observed that the surface shear stress and the mass transfer rate at the surface increase as the curvature parameter increases.

  11. Biomimetic surface modification of polypropylene by surface chain transfer reaction based on mussel-inspired adhesion technology and thiol chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing, E-mail: shisq@nwu.edu.cn; Gong, Yongkuan

    2016-11-15

    Highlights: • Biomimetic surface modification of PP was successfully conducted by integrating mussel-inspired technology, thiol chemistry and cell outer membranes-like structures. • The resultant biomimetic surface exhibits good interface and surface stability. • The obvious suppression of protein adsorption and platelet adhesion is also achieved. • The residue thoil groups on the surface could be further functionalized. - Abstract: Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH{sub 2}) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such

  12. 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.

  13. Synthesis of triblock and random copolymers of 4- acetoxystyrene and styrene by living atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Gao, Bo; Chen, Xianyi; Ivan, Bela

    1997-01-01

    Triblock copolymers containing polystyrene (PSt) and poly(4-acetoxystyrene) (PAcOSt) segments have been prepared by atom transfer radical polymerization (ATRP). In the first step one of the two monomers was polymerized in bulk using the initiating system alpha,alpha'-dibromo-p-xylene/CuBr/2...... weights and narrow molecular weight distributions. Polymerization of a mixture of equal molar amounts of the two monomers yielded a random copolymer with narrow molecular weight distribution....

  14. Dinuclear Tetrapyrazolyl Palladium Complexes Exhibiting Facile Tandem Transfer Hydrogenation/Suzuki Coupling Reaction of Fluoroarylketone

    KAUST Repository

    Dehury, Niranjan

    2016-07-18

    Herein, we report an unprecedented example of dinuclear pyrazolyl-based Pd complexes exhibiting facile tandem catalysis for fluoroarylketone: Tetrapyrazolyl di-palladium complexes with varying Pd-Pd distances efficiently catalyze the tandem reaction involving transfer hydrogenation of fluoroarylketone to the corresponding alcohol and Suzuki-Miyaura cross coupling reaction of the resulting fluoroarylalcohol under moderate reaction conditions, to biaryl alcohol. The complex with the shortest Pd-Pd distance exhibits the highest tandem activity among its di-metallic analogues, and exceeds in terms of activity and selectivity the analogous mononuclear compound. The kinetics of the reaction indicates clearly that reductive transformation of haloarylketone into haloaryalcohol is the rate determining step in the tandem reaction. Interestingly while fluoroarylketone undergoes the multistep tandem catalysis, the chloro- and bromo-arylketones undergo only a single step C-C coupling reaction resulting in biarylketone as the final product. Unlike the pyrazole based Pd compounds, the precursor PdCl2 and the phosphine based relevant complexes (PPh3)2PdCl2 and (PPh3)4Pd are found to be unable to exhibit the tandem catalysis.

  15. 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.

  16. A charge transfer ionic-embedded atom method potential for the O-Al-Ni-Co-Fe system

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Xiaowang; Wadley, Haydn N G [Department of Materials Science and Engineering, 116 Engineer' s Way, University of Virginia, Charlottesville, VA 22904-4745 (United States)

    2005-06-15

    Magnetic tunnel junctions (MTJs) require the growth of a thin ({approx}20 A) dielectric metal oxide layer, such as Al{sub 2}O{sub 3}, on a ferromagnetic metal layer, such as Co, CoFe, or CoNiFe. The atomic assembly mechanisms that combine to form a uniformly thin metal oxide layer on these metal surfaces are not well understood. The application of molecular dynamics simulations to the growth of metal and metal oxide multilayers that involve more than one metal element has not been possible using the conventional interatomic potentials. A recently proposed modified charge transfer ionic-embedded atom method potential appears to correctly enable the charge transfer between oxygen and numerous metal elements to be modelled in a format amenable for molecular dynamics studies. Here we parametrize this charge transfer ionic-embedded atom method potential for the quinternary O-Al-Ni-Co-Fe system so that a direct molecular dynamics simulation of the growth of the tunnelling magnetoresistive multilayers can be realized.

  17. Theoretical investigation of the coupling between hydrogen-atom transfer and stacking interaction in adenine-thymine dimers.

    Science.gov (United States)

    Villani, Giovanni

    2013-04-15

    Three different dimers of the adenine-thymine (A-T) base pair are studied to point out the changes of important properties (structure, atomic charge, energy and so on) induced by coupling between the movement of the atoms in the hydrogen bonds and the stacking interaction. The comparison of these results with those for the A-T monomer system explains the role of the stacking interaction in the hydrogen-atom transfer in this biologically important base pair. The results support the idea that this coupling depends on the exact dimer considered and is different for the N-N and N-O hydrogen bonds. In particular, the correlation between the hydrogen transfer and the stacking interaction is more relevant for the N-N bridge than for the N-O one. Also, the two different mechanisms of two-hydrogen transfer (step by step and concerted) can be modified by the stacking interaction between the base pairs. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. A manganese(V)-oxo π-cation radical complex: influence of one-electron oxidation on oxygen-atom transfer.

    Science.gov (United States)

    Prokop, Katharine A; Neu, Heather M; de Visser, Sam P; Goldberg, David P

    2011-10-12

    One-electron oxidation of Mn(V)-oxo corrolazine 2 affords 2(+), the first example of a Mn(V)(O) π-cation radical porphyrinoid complex, which was characterized by UV-vis, EPR, LDI-MS, and DFT methods. Access to 2 and 2(+) allowed for a direct comparison of their reactivities in oxygen-atom transfer (OAT) reactions. Both complexes are capable of OAT to PPh(3) and RSR substrates, and 2(+) was found to be a more potent oxidant than 2. Analysis of rate constants and activation parameters, together with DFT calculations, points to a concerted OAT mechanism for 2(+) and 2 and indicates that the greater electrophilicity of 2(+) likely plays a dominant role in enhancing its reactivity. These results are relevant to comparisons between Compound I and Compound II in heme enzymes.

  19. Combining polymers with the functionality of proteins: new concepts for atom transfer radical polymerization, nanoreactors and damage self-reporting materials.

    Science.gov (United States)

    Bruns, Nico; Lörcher, Samuel; Makyła, Katarzyna; Pollarda, Jonas; Renggli, Kasper; Spulber, Mariana

    2013-01-01

    Proteins are macromolecules with a great diversity of functions. By combining these biomolecules with polymers, exciting opportunities for new concepts in polymer sciences arise. This highlight exemplifies the aforementioned with current research results of our group. We review our discovery that the proteins horseradish peroxidase and hemoglobin possess ATRPase activity, i.e. they catalyze atom transfer radical polymerizations. Moreover, a permeabilization method for polymersomes is presented, where the photo-reaction of an α-hydroxyalkylphenone with block copolymer vesicles yields enzyme-containing nanoreactors. A further intriguing possibility to obtain functional nanoreactors is to enclose a polymerization catalyst into the thermosome, a protein cage from the family of chaperonins. Last but not least, fluorescent proteins are discussed as mechanoresponsive molecular sensors that report microdamages within fiber-reinforced composite materials.

  20. Ultrafast Dynamics of Chemical Reactions in Condensed Phase ...

    Indian Academy of Sciences (India)

    Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond. Dipak K. Palit Radaition & Photochemistry Division Bhabha Atomic Research Centre Mumbai 400 085, India.

  1. Bimolecular electron transfer in ionic liquids: are reaction rates anomalously high?

    Science.gov (United States)

    Liang, Min; Kaintz, Anne; Baker, Gary A; Maroncelli, Mark

    2012-02-02

    Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecular electron transfer reaction between the electron acceptor 9,10-dicyanoanthracene in its S(1) state and the donor N,N-dimethylaniline in a variety of ionic liquids and several conventional solvents. Detailed study of this quenching reaction was undertaken in order to better understand why rates reported for similar diffusion-limited reactions in ionic liquids sometimes appear much higher than expected given the viscous nature of these liquids. Consistent with previous studies, Stern-Volmer analyses of steady-state and lifetime data provide effective quenching rate constants k(q), which are often 10-100-fold larger than simple predictions for diffusion-limited rate constants k(D) in ionic liquids. Similar departures from k(D) are also observed in conventional organic solvents having comparably high viscosities, indicating that this behavior is not unique to ionic liquids. A more complete analysis of the quenching data using a model combining approximate solution of the spherically symmetric diffusion equation with a Marcus-type description of electron transfer reveals the reasons for frequent observation of k(q) ≫ k(D). The primary cause is that the high viscosities typical of ionic liquids emphasize the transient component of diffusion-limited reactions, which renders the interpretation of rate constants derived from Stern-Volmer analyses ambiguous. Using a more appropriate description of the quenching process enables satisfactory fits of data in both ionic liquid and conventional solvents using a single set of physically reasonable electron transfer parameters. Doing so requires diffusion coefficients in ionic liquids to exceed hydrodynamic predictions by significant factors, typically in the range of 3-10. Direct, NMR measurements of solute diffusion confirm this enhanced diffusion in ionic liquids.

  2. Room temperature deintercalation of alkali metal atoms from epitaxial graphene by formation of charge-transfer complexes

    Energy Technology Data Exchange (ETDEWEB)

    Shin, H.-C.; Ahn, S. J.; Kim, H. W.; Moon, Y.; Rai, K. B. [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Woo, S. H. [College of Pharmacy, Chungnam National University, Daejeon 305–764 (Korea, Republic of); Ahn, J. R., E-mail: jrahn@skku.edu [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); SAINT, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2016-08-22

    Atom (or molecule) intercalations and deintercalations have been used to control the electronic properties of graphene. In general, finite energies above room temperature (RT) thermal energy are required for the intercalations and deintercalations. Here, we demonstrate that alkali metal atoms can be deintercalated from epitaxial graphene on a SiC substrate at RT, resulting in the reduction in density of states at the Fermi level. The change in density of states at the Fermi level at RT can be applied to a highly sensitive graphene sensor operating at RT. Na atoms, which were intercalated at a temperature of 80 °C, were deintercalated at a high temperature above 1000 °C when only a thermal treatment was used. In contrast to the thermal treatment, the intercalated Na atoms were deintercalated at RT when tetrafluorotetracyanoquinodimethane (F4-TCNQ) molecules were adsorbed on the surface. The RT deintercalation occurred via the formation of charge-transfer complexes between Na atoms and F4-TCNQ molecules.

  3. pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Kouta [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Matsumura, Hirotoshi; Ishida, Takuya [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Yoshida, Makoto [Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509 (Japan); Igarashi, Kiyohiko; Samejima, Masahiro [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Ohno, Hiroyuki [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Nakamura, Nobuhumi, E-mail: nobu1@cc.tuat.ac.jp [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of L-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. - Highlights: • pH dependencies of activity were different for the reduction of cyt c and DCPIP. • DET-based bioelectrocatalysis of CcPDH was observed. • The similar pH-dependent profile was found with cyt c and electrode. • The present results suggested that IET reaction of CcPDH shows pH dependence.

  4. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts.

    Science.gov (United States)

    Yin, Peiqun; Yao, Tao; Wu, Yuen; Zheng, Lirong; Lin, Yue; Liu, Wei; Ju, Huanxin; Zhu, Junfa; Hong, Xun; Deng, Zhaoxiang; Zhou, Gang; Wei, Shiqiang; Li, Yadong

    2016-08-26

    A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. (Multi-nucleon transfer in the reactions 16O, 32S+208Pb

    Directory of Open Access Journals (Sweden)

    Hinde D.J.

    2011-10-01

    Full Text Available A detailed analysis of the projectile-like fragments detected at backward angles in the reactions 16O,32 S+208Pb at energies below the fusion barrier is presented. Excitation functions corresponding to nucleon transfer with ∆Z = 1 and ∆Z = 2 were extracted, indicating surprisingly large absolute probabilities at subbarrier energies. A comparison of 2p transfer probabilities with time-dependent Hartree-Fock calculations suggests strong pairing correlations between the two protons. Excitation energies in the projectile-like fragments ~15 MeV and ~25 MeV for the 16O and 32S-induced reactions, respectively, indicate the population of highly excited states in the residual nuclei. A comparison with expected optimum Q-values suggests large losses in kinetic energy of the projectile-like fragments. These highly inelastic (large excitation energies and complex (correlated few-nucleon transfer processes may be closely related to the depletion of fusion through tunnelling at sub-barrier energies.

  6. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Schwartz, Benjamin Joel [Univ. of California, Berkeley, CA (United States)

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in ~240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH2I2 and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a ~350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  7. Theory of laser-induced ultrafast magneto-optic spin flip and transfer in charged two-magnetic-center molecular ions: Role of bridging atoms

    Science.gov (United States)

    Li, Chun; Jin, Wei; Xiang, Hongping; Lefkidis, Georgios; Hübner, Wolfgang

    2011-08-01

    Laser-induced ultrafast spin manipulations in positively charged two-magnetic-center molecular ions with a small number of bridging atoms are investigated to explore the role of bridging atoms in the spin switching process and spin transferability between the magnetic centers via the Λ process. Taking O and Mg as examples for bridging atoms, fully ab initio calculations demonstrate that spin flip can be readily achieved on subpicosecond time scales at both magnetic centers of the linear structures composed of two nonidentical magnetic atoms with a single bridging atom in between. Although these two nonmagnetic elements possess completely different chemical and electronic natures, both types of bridging atoms contribute to spin density redistribution at the magnetic atoms, especially for the low-lying triplet states that are suitable to act as initial and final states in the Λ-type process of spin flip or transfer. This also provides a rule of thumb that spins in the linear structures can be flipped more easily since symmetric structures exhibit weaker magnetocrystalline anisotropy. The spin transfer process achieved in the structure [Fe-O(Mg)-Co]+ demonstrates that if both bridging atoms are involved to further lower the symmetry of the linear structures, spin transferability between the Fe and Co atoms can be improved.

  8. In situ Regeneration of NADH via Lipoamide Dehydrogenase-catalyzed Electron Transfer Reaction Evidenced by Spectroelectrochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Tam, Tsz Kin; Chen, Baowei; Lei, Chenghong; Liu, Jun

    2012-08-01

    NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80 {+-} 0.15 mM and 1.91 {+-} 0.09 {micro}M s-1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

  9. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    Science.gov (United States)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  10. Experimental verification of orbital engineering at the atomic scale: Charge transfer and symmetry breaking in nickelate heterostructures

    Science.gov (United States)

    Phillips, Patrick J.; Rui, Xue; Georgescu, Alexandru B.; Disa, Ankit S.; Longo, Paolo; Okunishi, Eiji; Walker, Fred; Ahn, Charles H.; Ismail-Beigi, Sohrab; Klie, Robert F.

    2017-05-01

    Epitaxial strain, layer confinement, and inversion symmetry breaking have emerged as powerful new approaches to control the electronic and atomic-scale structural properties of complex metal oxides. Trivalent rare-earth (RE) nickelate R E NiO3 heterostructures have been shown to be exemplars since the orbital occupancy, degeneracy, and, consequently, electronic/magnetic properties can be altered as a function of epitaxial strain, layer thickness, and superlattice structure. One recent example is the tricomponent LaTiO3-LaNiO3-LaAlO3 superlattice which exhibits charge transfer and orbital polarization as the result of its interfacial dipole electric field. A crucial step towards control of these parameters for future electronic and magnetic device applications is to develop an understanding of both the magnitude and range of the octahedral network's response towards interfacial strain and electric fields. An approach that provides atomic-scale resolution and sensitivity towards the local octahedral distortions and orbital occupancy is therefore required. Here, we employ atomic-resolution imaging coupled with electron spectroscopies and first-principles theory to examine the role of interfacial charge transfer and symmetry breaking in a tricomponent nickelate superlattice system. We find that nearly complete charge transfer occurs between the LaTiO3 and LaNiO3 layers, resulting in a mixed Ni2 +/Ni3 + valence state. We further demonstrate that this charge transfer is highly localized with a range of about 1 unit cell within the LaNiO3 layers. We also show how Wannier-function-based electron counting provides a simple physical picture of the electron distribution that connects directly with formal valence charges. The results presented here provide important feedback to synthesis efforts aimed at stabilizing new electronic phases that are not accessible by conventional bulk or epitaxial film approaches.

  11. Chemically Induced Dynamic Nuclear Polarization during the Thermolysis of Alkoxyamines: A New Approach to Detect the Occurrence of H-Transfer Reactions

    Directory of Open Access Journals (Sweden)

    Elena Bagryanskaya

    2010-09-01

    Full Text Available Thermal decomposition of alkoxyamines in the presence of scavengers was found to proceed with the formation of chemically induced nuclear polarization detected by 1H NMR. The distinctive Chemically Induced Dynamic Nuclear Polarization (CIDNP features were studied using the example of three alkoxyamines: 4-nitrophenyl 2-(2,2,6,6-tetramethylpiperidin-1-yloxy-2-methylpropanoate (1a, 4-nitrophenyl 2-(2,2-diphenyl-3-phenylimino-2,3-dihydroindol-1-yloxy-2-methylpropanoate (2a and 4-nitrophenyl 2-(2,2,5,5-tetramethyl-4-phenyl-2H-imidazol-1-oxy-2-methylpropanoate (3a in the presence of PhSH. The analysis of CIDNP signs of methacrylate protons allows us to conclude on the occurrence of hydrogen atom transfer reaction in geminate radical pair formed in alkoxyamine thermolysis. Thus, CIDNP is a fast and sensitive method to detect the occurrence of intra/intermolecular hydrogen transfer in alkoxyamine thermolysis.

  12. On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. V. Comparison and Properties of Electrochemical and Chemical Rate Constants

    Science.gov (United States)

    Marcus, R. A.

    1962-01-01

    Using a theory of electron transfers which takes cognizance of reorganization of the medium outside the inner coordination shell and of changes of bond lengths inside it, relations between electrochemical and related chemical rate constants are deduced and compared with the experimental data. A correlation is found, without the use of arbitrary parameters. Effects of weak complexes with added electrolytes are included under specified conditions. The deductions offer a way of coordinating a variety of data in the two fields, internally as well as with each those in another. For example, the rate of oxidation or reduction of a series of related reactants by one reagent is correlated with that of another and with that of the corresponding electrochemical oxidation-reduction reaction, under certain specified conditions. These correlations may also provide a test for distinguishing an electron from an atom transfer mechanism. (auth)

  13. Matter, energy, and heat transfer in a classical ballistic atom pump.

    Science.gov (United States)

    Byrd, Tommy A; Das, Kunal K; Mitchell, Kevin A; Aubin, Seth; Delos, John B

    2014-11-01

    A ballistic atom pump is a system containing two reservoirs of neutral atoms or molecules and a junction connecting them containing a localized time-varying potential. Atoms move through the pump as independent particles. Under certain conditions, these pumps can create net transport of atoms from one reservoir to the other. While such systems are sometimes called "quantum pumps," they are also models of classical chaotic transport, and their quantum behavior cannot be understood without study of the corresponding classical behavior. Here we examine classically such a pump's effect on energy and temperature in the reservoirs, in addition to net particle transport. We show that the changes in particle number, of energy in each reservoir, and of temperature in each reservoir vary in unexpected ways as the incident particle energy is varied.

  14. Energetic efficiency of mass transfer accompanied by chemical reactions in liquid-liquid systems

    Directory of Open Access Journals (Sweden)

    Jasińska Magdalena

    2017-09-01

    Full Text Available Energetic efficiency depicting the fraction of energy dissipation rate used to perform processes of drop breakup and mass transfer in two-phase, liquid-liquid systems is considered. Results of experiments carried out earlier in two types of high-shear mixers: an in-line rotor-stator mixer and a batch rotor-stator mixer, have been applied to identify and compare the efficiency of drop breakage and mass transfer in both types of mixers. The applied method is based on experimental determination of both: the product distribution of chemical test reactions and the drop size distributions. Experimental data are interpreted using a multifractal model of turbulence for drop breakage and the model by Favelukis and Lavrenteva for mass transfer. Results show that the energetic efficiency of the in-line mixer is higher than that of the batch mixer; two stator geometries were considered in the case of the batch mixer and the energetic efficiency of the device equipped with a standard emulsor screen (SES was higher than the efficiency of the mixer equipped with a general purpose disintegrating head (GPDH for drop breakup but smaller for mass transfer.

  15. Mutations to R. sphaeroides Reaction Center Perturb Energy Levels and Vibronic Coupling but Not Observed Energy Transfer Rates.

    Science.gov (United States)

    Flanagan, Moira L; Long, Phillip D; Dahlberg, Peter D; Rolczynski, Brian S; Massey, Sara C; Engel, Gregory S

    2016-03-10

    The bacterial reaction center is capable of both efficiently collecting and quickly transferring energy within the complex; therefore, the reaction center serves as a convenient model for both energy transfer and charge separation. To spectroscopically probe the interactions between the electronic excited states on the chromophores and their intricate relationship with vibrational motions in their environment, we examine coherences between the excited states. Here, we investigate this question by introducing a series of point mutations within 12 Å of the special pair of bacteriochlorophylls in the Rhodobacter sphaeroides reaction center. Using two-dimensional spectroscopy, we find that the time scales of energy transfer dynamics remain unperturbed by these mutations. However, within these spectra, we detect changes in the mixed vibrational-electronic coherences in these reaction centers. Our results indicate that resonance between bacteriochlorophyll vibrational modes and excitonic energy gaps promote electronic coherences and support current vibronic models of photosynthetic energy transfer.

  16. Analysis of the non-Markovianity for electron transfer reactions in an oligothiophene-fullerene heterojunction

    Science.gov (United States)

    Mangaud, E.; Meier, C.; Desouter-Lecomte, M.

    2017-09-01

    The non-Markovianity of the electron transfer in an oligothiophene-fullerene heterojunction described by a spin-boson model is analyzed using the time dependent decoherence canonical rates and the volume of accessible states in the Bloch sphere. The dynamical map of the reduced electronic system is computed by the hierarchical equations of motion methodology (HEOM) providing an exact dynamics. Transitory witness of non-Markovianity is linked to the bath dynamics analyzed from the HEOM auxiliary matrices. The signature of the collective bath mode detected from HEOM in each electronic state is compared with predictions of the effective mode extracted from the spectral density. We show that including this main reaction coordinate in a one-dimensional vibronic system coupled to a residual bath satisfactorily describes the electron transfer by a simple Markovian Redfield equation. Non-Markovianity is computed for three inter fragment distances and compared with a priori criterion based on the system and bath characteristic timescales.

  17. Mixed convection heat and mass transfer in peristaltic flow with chemical reaction and inclined magnetic field

    Science.gov (United States)

    Noreen, S.; Hayat, T.; Alsaedi, A.; Qasim, M.

    2013-09-01

    A mathematical model is constructed to investigate the mixed convective heat and mass transfer effects on peristaltic flow of magnetohydrodynamic pseudoplastic fluid in a symmetric channel. An analysis has been carried out to examine the impact of an inclined magnetic field and chemical reaction in presence of heat sink/source. Mechanics of flow and heat/mass transfer described in terms of continuity, linear momentum, energy and concentration equations are predicted by using long wavelength and low Reynolds number. Expressions for stream function, temperature, concentration and pressure gradient are derived. Numerical simulation is performed for the rise in pressure per wave length. Effects of several physical parameters on the flow quantities are analyzed.

  18. On the ultrafast kinetics of the energy and electron transfer reactions in photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Slavov, Chavdar Lyubomirov

    2009-07-09

    The subject of the current work is one of the main participants in the light-dependent phase of oxygenic photosynthesis, Photosystem I (PS I). This complex carries an immense number of cofactors: chlorophylls (Chl), carotenoids, quinones, etc, which together with the protein entity exhibit several exceptional properties. First, PS I has an ultrafast light energy trapping kinetics with a nearly 100% quantum efficiency. Secondly, both of the electron transfer branches in the reaction center are suggested to be active. Thirdly, there are some so called 'red' Chls in the antenna system of PS I, absorbing light with longer wavelengths than the reaction center. These 'red' Chls significantly modify the trapping kinetics of PS I. The purpose of this thesis is to obtain better understanding of the above-mentioned, specific features of PS I. This will not merely cast more light on the mechanisms of energy and electron transfer in the complex, but also will contribute to the future developments of optimized artificial light-harvesting systems. In the current work, a number of PS I complexes isolated from different organisms (Thermosynechococcus elongatus, Chlamydomonas reinhardtii, Arabidopsis thaliana) and possessing distinctive features (different macroorganisation, monomers, trimers, monomers with a semibelt of peripheral antenna attached; presence of 'red' Chls) is investigated. The studies are primarily focused on the electron transfer kinetics in each of the cofactor branches in the PS I reaction center, as well as on the effect of the antenna size and the presence of 'red' Chls on the trapping kinetics of PS I. These aspects are explored with the help of several ultrafast optical spectroscopy methods: (i) time-resolved fluorescence ? single photon counting and synchroscan streak camera; and (ii) ultrafast transient absorption. Physically meaningful information about the molecular mechanisms of the energy trapping in PS I is

  19. PREPARATION OF BLOCK COPOLYMERS OF POLY(STYRENE) AND POLY(T-BUTYL ACRYLATE) OF VARIOUS MOLECULAR WEIGHTS AND ARCHITECTURES BY ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    Science.gov (United States)

    Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques. These polymers were synthesized with a CuBr/N,N,N,NNew Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

    DEFF Research Database (Denmark)

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

    .2 Metal complex of ligands possessing both H-donor and H-acceptor sites in the second coordination sphere should be interesting candidates for proton transfer reactions induced by photooxidation of the metal ion. We have prepared new oxime-containing ligands which coordinate to metal ions...... such that a pyridine group is sterically restricted so it does not coordinate. Instead it can act as proximal base for accepting the oxime proton. [1] M. H. V. Huynh, T. J. Meyer, Chem. Rev. 2007, 107, 5004-5064. [2] T. Irebo, O. Johansson, L. Hammarström, J. Am. Chem. Soc., 2008, 130, 9194-9195....

  1. Transfer reaction studies in inverse kinematics with the magnetic spectrometer PRISMA

    Directory of Open Access Journals (Sweden)

    Corradi L.

    2015-01-01

    Full Text Available The large solid angle magnetic spectrometers, in combination with large gamma arrays, allowed to perform reaction mechanism and nuclear structure studies in different regions of the nuclear chart, especially in the neutron-rich direction. By studying transfer of multiple pairs valuable information on nucleon-nucleon correlations can be derived, especially from measurements performed below the Coulomb barrier. There is growing interest in the study of the properties of the heavy binary partner, in the Pb and in the actinides regions, crucial also for astrophysics.

  2. 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 bc1 complex is a critical enzyme for the ATP production in photosynthesis and cellular respiration. Its biochemical function relies on the so-called Q-cycle, which is well established and operates via quinol substrates that bind inside the protein complex. Despite decades of research, the qui...... the conclusion. Finally, key structural elements of the bc1 complex that trigger the charge transfer reactions were established, manifesting the importance of the environment in the process, which is furthermore evidenced by free energy calculations....

  3. Numerical study for melting heat transfer and homogeneous-heterogeneous reactions in flow involving carbon nanotubes

    Science.gov (United States)

    Hayat, Tasawar; Muhammad, Khursheed; Alsaedi, Ahmed; Asghar, Saleem

    2018-03-01

    Present work concentrates on melting heat transfer in three-dimensional flow of nanofluid over an impermeable stretchable surface. Analysis is made in presence of porous medium and homogeneous-heterogeneous reactions. Single and multi-wall CNTs (carbon nanotubes) are considered. Water is chosen as basefluid. Adequate transformations yield the non-linear ordinary differential systems. Solution of emerging problems is obtained using shooting method. Impacts of influential variables on velocity and temperature are discussed graphically. Skin friction coefficient and Nusselt number are numerically discussed. The results for MWCNTs and SWCNTs are compared and examined.

  4. Studies of Nuclei Close to 132Sn Using Single-Neutron Transfer Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Jones, K. L. [University of Tennessee, Knoxville (UTK); Pain, S. D. [Rutgers University; Kozub, R. L. [Tennessee Technological University; Adekola, Aderemi S [ORNL; Bardayan, Daniel W [ORNL; Blackmon, Jeff C [ORNL; Catford, Wilton N [ORNL; Chae, K. Y. [University of Tennessee, Knoxville (UTK); Chipps, K. [Colorado School of Mines, Golden; Cizewski, J. A. [Rutgers University; Erikson, Luke [Colorado School of Mines, Golden; Gaddis, A. L. [Furman University; Greife, U. [Colorado School of Mines, Golden; Grzywacz, R. K. [University of Tennessee, Knoxville (UTK); Harlin, Christopher W [ORNL; Hatarik, Robert [Rutgers University; Howard, Joshua A [ORNL; James, J. [Colorado School of Mines, Golden; Kapler, R. [University of Tennessee, Knoxville (UTK); Krolas, W. [University of Warsaw; Liang, J Felix [ORNL; Ma, Zhanwen [ORNL; Matei, Catalin [Oak Ridge Associated Universities (ORAU); Moazen, Brian [University of Tennessee, Knoxville (UTK); Nesaraja, Caroline D [ORNL; O' Malley, Patrick [Rutgers University; Patterson, N. P. [University of Surrey, UK; Paulauskas, Stanley [University of Tennessee, Knoxville (UTK); Shapira, Dan [ORNL; ShrinerJr., J. F. [Tennessee Technological University; Sikora, M. [Rutgers University; Sissom, D. J. [Tennessee Technological University; Smith, Michael Scott [ORNL; Swan, T. P. [University of Surrey, UK; Thomas, J. S. [Rutgers University; Wilson, Gemma L [ORNL

    2009-01-01

    Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of 132Sn, 130Sn, and 134Te and deuterated polyethylene targets. Preliminary results are presented. The Q-value spectra for 133Sn, 131Sn and 135Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf7/2 nature of the ground state of 133Sn, and 2p3/2 for the 3.4 MeV state in 131Sn.

  5. Effects of mass transfer on MHD flow of casson fluid with chemical reaction and suction

    Directory of Open Access Journals (Sweden)

    S. A. Shehzad

    2013-03-01

    Full Text Available Effect of mass transfer in the magnetohydrodynamic flow of a Casson fluid over a porous stretching sheet is addressed in the presence of a chemical reaction. A series solution for the resulting nonlinear flow is computed. The skin friction coefficient and local Sherwood number are analyzed through numerical values for various parameters of interest. The velocity and concentration fields are illustrated for several pertinent flow parameters. We observed that the Casson parameter and Hartman number have similar effects on the velocity in a qualitative sense. We further analyzed that the concentration profile decreases rapidly in comparison to the fluid velocity when we increased the values of the suction parameter.

  6. Production of nuclear polarization of unstable nuclei via polarization transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Ishibashi, Y., E-mail: ishibashi@tac.tsukuba.ac.jp; Nagae, D.; Abe, Y. [University of Tsukuba, Institute of Physics (Japan); Nagatomo, T. [Institute of Materials Structure Science (Japan); Ozawa, A. [University of Tsukuba, Institute of Physics (Japan); Suzuki, H. [RIKEN Nishina Center (Japan); Fukuoka, S.; Nishikiori, R.; Niwa, T. [University of Tsukuba, Institute of Physics (Japan); Matsuta, K. [Osaka University, Department of Physics (Japan); Tagishi, Y. [University of Tsukuba, Institute of Physics (Japan)

    2013-05-15

    The polarized {sup 20}F(I{sup {pi}} = 2{sup + }, T{sub 1/2} = 11.163 s), {sup 24m}Al(I{sup {pi}} = 1{sup + }, T{sub 1/2} = 131.3 ms), {sup 29}P(I{sup {pi}} = 1/2{sup + }, T{sub 1/2} = 4.142 s) and {sup 41}Sc(I{sup {pi}} = 7/2{sup -}, T{sub 1/2} = 596.3 ms) isotopes were produced by nuclear-polarization transfer reactions with polarized proton or deuteron beams. In the case of {sup 29}P isotope, we have produced the polarization by two reactions; {sup 29}Si(p-vector,n){sup 29}P and {sup 28}Si(d-vector,n){sup 29}P. The degree of nuclear polarization of those nuclei have been measured using the {beta}-ray detected nuclear magnetic resonance method.

  7. Theoretical study on production cross sections of exotic actinide nuclei in multinucleon transfer reactions

    Science.gov (United States)

    Zhu, Long

    2017-12-01

    Within the dinuclear system (DNS) model, the multinucleon transfer reactions 129,136Xe + 248Cm, 112Sn + 238U, and 144Xe + 248Cm are investigated. The production cross sections of primary fragments are calculated with the DNS model. By using a statistical model, we investigate the influence of charged particle evaporation channels on production cross sections of exotic nuclei. It is found that for excited neutron-deficient nuclei the charged particle evaporation competes with neutron emission and plays an important role in the cooling process. The production cross sections of several exotic actinide nuclei are predicted in the reactions 112Sn + 238U and 136,144Xe + 248Cm. Considering the beam intensities, the collisions of 136,144Xe projectiles with a 248Cm target for producing neutron-rich nuclei with Z=92‑96 are investigated. Supported by National Natural Science Foundation of China (11605296) and Natural Science Foundation of Guangdong Province, China (2016A030310208)

  8. Transferable Potentials for Phase Equilibria. 4. United-Atom Description of Linear and Branched Alkenes and Alkylbenzenes

    Energy Technology Data Exchange (ETDEWEB)

    WICK,COLLIN D.; MARTIN,MARCUS G.; SIEPMANN,J. ILJA

    2000-07-12

    The Transferable Potentials for Phase Equilibria-United Atom (TraPPE-UA) force field for hydrocarbons is extended to alkenes and alkylbenzenes by introducing the following pseudo-atoms: CH{sub 2}(sp{sup 2}), CH(sp{sup 2}), CH(aro), R-C(aro) for the link to aliphatic side chains, and C(aro) for the link of two benzene rings. In this united-atom force field, the nonbonded interactions of the hydrocarbon pseudo-atoms are solely governed by Lennard-Jones 12-6 potentials, and the Lennard-Jones well depth and size parameters for the new pseudo-atoms were determined by fitting to the single-component vapor-liquid phase equilibria of a few selected model compounds. Configurational-bias Monte Carlo simulations in the NVT version of the Gibbs ensemble were carried out to calculate the single-component vapor-liquid coexistence curves for ethene, propene, 1-butene, trans- and cis-2-butene. 2-methylpropene, 1,5-hexadiene, 1-octene, benzene, toluene, ethylbenzene, propylbenzene, isopropylbenzene, o-, m-, and p-xylene, and naphthalene. The phase diagrams for the binary mixtures of (supercritical) ethene/n-heptane and benzene/n-pentane were determined from simulations in the NpT Gibbs ensemble. Although the TraPPE-UA force field is rather simple and makes use of relatively few different pseudo-atoms, its performance, as judged by comparisons to other popular force fields and available experimental data, is very satisfactory.

  9. Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium.

    Science.gov (United States)

    Zhang, Chenhao; Sha, Junwei; Fei, Huilong; Liu, Mingjie; Yazdi, Sadegh; Zhang, Jibo; Zhong, Qifeng; Zou, Xiaolong; Zhao, Naiqin; Yu, Haisheng; Jiang, Zheng; Ringe, Emilie; Yakobson, Boris I; Dong, Juncai; Chen, Dongliang; Tour, James M

    2017-07-25

    The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH3 atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO4, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N4 structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

  10. Gamma-ray spectroscopy of neutron-rich actinides after multi-nucleon transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, Andreas; Birkenbach, Benedikt; Reiter, Peter [IKP, Universitaet zu Koeln (Germany); Corradi, Lorenzo [INFN - LNL (Italy); Szilner, Suzana [IRB Zagreb (Croatia); Collaboration: LNL 11.22-Collaboration

    2015-07-01

    Excited states in neutron-rich actinide Th and U nuclei were investigated after multi-nucleon transfer reactions employing the AGATA demonstrator and PRISMA setup at LNL (INFN, Italy). A primary 1 GeV {sup 136}Xe beam hitting a {sup 238}U target was used to produce the nuclei of interest in the actinide region. Beam-like reaction products in the Xe-region were identified and selected by the magnetic spectrometer PRISMA. Hence, fission fragments can be discriminated against surviving nuclei, DANTE-MCPs were installed within the target chamber to exploit kinematic coincidences between the binary reaction products which allows for clean conditions for in-beam γ-ray spectroscopy. Coincident γ-rays from excited states in beam- and target-like particles were measured with the position-sensitive AGATA HPGe detectors. An improved Doppler correction for both beam- and target-like nuclei is based on the novel γ-ray tracking technique. An extension of the ground-state rotational band in {sup 240}U and insights into n-rich Th isotopes were achieved. Based on relative cross-section distributions for various reaction channels, perspectives and limitations for the production of the hard-to-reach neutron-rich isotopes with this experimental method will be presented.

  11. A Stefan model for mass transfer in a rotating disk reaction vessel

    KAUST Repository

    BOHUN, C. S.

    2015-05-04

    Copyright © Cambridge University Press 2015. In this paper, we focus on the process of mass transfer in the rotating disk apparatus formulated as a Stefan problem with consideration given to both the hydrodynamics of the process and the specific chemical reactions occurring in the bulk. The wide range in the reaction rates of the underlying chemistry allows for a natural decoupling of the problem into a simplified set of weakly coupled convective-reaction-diffusion equations for the slowly reacting chemical species and a set of algebraic relations for the species that react rapidly. An analysis of the chemical equilibrium conditions identifies an expansion parameter and a reduced model that remains valid for arbitrarily large times. Numerical solutions of the model are compared to an asymptotic analysis revealing three distinct time scales and chemical diffusion boundary layer that lies completely inside the hydrodynamic layer. Formulated as a Stefan problem, the model generalizes the work of Levich (Levich and Spalding (1962) Physicochemical hydrodynamics, vol. 689, Prentice-Hall Englewood Cliffs, NJ) and will help better understand the natural limitations of the rotating disk reaction vessel when consideration is made for the reacting chemical species.

  12. Chemical electron-transfer reactions in electrospray mass spectrometry: Effective oxidation potentials of electron-transfer reagents in methylene chloride

    Energy Technology Data Exchange (ETDEWEB)

    Van Berkel, G.J.; Zhou, F. (Oak Ridge National Lab., TN (United States))

    1994-10-15

    Cyclic voltammetry (CV), UV/visible absorption spectroscopy, and electrospray mass spectrometry (ES-MS) are used in conjunction to study the mono- and /or dications produced in solution from the reaction of three model compounds ([beta]-carotene, cobalt(II) octaethylporphyrin (Co[sup II]OEP), nickel(II) octaethylporphyrin (Ni[sup II]OEP), in three different solvent/electron-transfer reagent systems (methylene chloride/0.1% trifluoroacetic acid (TFA) (v/v), methylene chloride/0.1% TFA/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) v/v/200 [mu]M), methylene chloride/0.1% TFA/0.1% antimony pentafluoride (SbF[sub 5]) (v/v/v)). The reactions were carried out on-line with ES-MS by means of flow injection. Correlation of the CV data for these analytes with the ionic species determined to be in the solution on the basis of UV/visible absorption spectra and/or on the basis of the ionic species observed in the gas phase by ES-MS, along with our previously published data on these solvent/reagent systems, allowed an effective oxidation potential range, E, to be assigned to these solvent/reagent systems: methylene chloride/0.1% TFA (v/v), 0.6V [le] E[sub TFA] < 0.7 V; methylene chloride/0.1% TFA/DDQ (v/v/200 [mu]M), 0.8 [le] E[sub TFA/DDQ] < 1.0 V; methylene chloride/0.1% TFA/0.1% SbF[sub 5] (v/v/v), 1.3 [le] E[sub TFA/SbF(5)] < 1.5. 40 refs., 7 figs.

  13. Characterization of Porphyrin-Co(III)-'Nitrene Radical' Species Relevant in Catalytic Nitrene Transfer Reactions.

    Science.gov (United States)

    Goswami, Monalisa; Lyaskovskyy, Volodymyr; Domingos, Sérgio R; Buma, Wybren Jan; Woutersen, Sander; Troeppner, Oliver; Ivanović-Burmazović, Ivana; Lu, Hongjian; Cui, Xin; Zhang, X Peter; Reijerse, Edward J; DeBeer, Serena; van Schooneveld, Matti M; Pfaff, Florian Felix; Ray, Kallol; de Bruin, Bas

    2015-04-29

    To fully characterize the Co(III)-'nitrene radical' species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV-vis, IR, VCD, UHR-ESI-MS, and XANES/XAFS measurements. Reactions of cobalt(II) porphyrins 1(P1) (P1 = meso-tetraphenylporphyrin (TPP)) and 1(P2) (P2 = 3,5-Di(t)Bu-ChenPhyrin) with organic azides 2(Ns) (NsN3), 2(Ts) (TsN3), and 2(Troc) (TrocN3) led to the formation of mono-nitrene species 3(P1)(Ns), 3(P2)(Ts), and 3(P2)(Troc), respectively, which are best described as [Co(III)(por)(NR″(•-))] nitrene radicals (imidyl radicals) resulting from single electron transfer from the cobalt(II) porphyrin to the 'nitrene' moiety (Ns: R″ = -SO2-p-C6H5NO2; Ts: R″ = -SO2C6H6; Troc: R″ = -C(O)OCH2CCl3). Remarkably, the reaction of 1(P1) with N-nosyl iminoiodane (PhI═NNs) 4(Ns) led to the formation of a bis-nitrene species 5(P1)(Ns). This species is best described as a triple-radical complex [(por(•-))Co(III)(NR″(•-))2] containing three ligand-centered unpaired electrons: two nitrene radicals (NR″(•-)) and one oxidized porphyrin radical (por(•-)). Thus, the formation of the second nitrene radical involves another intramolecular one-electron transfer to the "nitrene" moiety, but now from the porphyrin ring instead of the metal center. Interestingly, this bis-nitrene species is observed only on reacting 4(Ns) with 1(P1). Reaction of the more bulky 1(P2) with 4(Ns) results again in formation of mainly mono-nitrene species 3(P2)(Ns) according to EPR and ESI-MS spectroscopic studies. The mono- and bis-nitrene species were initially expected to be five- and six-coordinate species, respectively, but XANES data revealed that both mono- and bis-nitrene species are six-coordinate O(h) species. The nature of the sixth ligand bound to cobalt(III) in the

  14. Prediction of Tetraoxygen Reaction Mechanism with Sulfur Atom on the Singlet Potential Energy Surface

    Directory of Open Access Journals (Sweden)

    Ashraf Khademzadeh

    2014-01-01

    Full Text Available The mechanism of S+O4 (D2h reaction has been investigated at the B3LYP/6-311+G(3df and CCSD levels on the singlet potential energy surface. One stable complex has been found for the S+O4 (D2h reaction, IN1, on the singlet potential energy surface. For the title reaction, we obtained four kinds of products at the B3LYP level, which have enough thermodynamic stability. The results reveal that the product P3 is spontaneous and exothermic with −188.042 and −179.147 kcal/mol in Gibbs free energy and enthalpy of reaction, respectively. Because P1 adduct is produced after passing two low energy level transition states, kinetically, it is the most favorable adduct in the 1S+1O4 (D2h atmospheric reactions.

  15. Path-integral calculations of heavy atom kinetic isotope effects in condensed phase reactions using higher-order Trotter factorizations.

    Science.gov (United States)

    Vardi-Kilshtain, Alexandra; Azuri, Asaf; Major, Dan Thomas

    2012-02-05

    A convenient approach to compute kinetic isotope effects (KIEs) in condensed phase chemical reactions is via path integrals (PIs). Usually, the primitive approximation is used in PI simulations, although such quantum simulations are computationally demanding. The efficiency of PI simulations may be greatly improved, if higher-order Trotter factorizations of the density matrix operator are used. In this study, we use a higher-order PI method, in conjunction with mass-perturbation, to compute heavy-atom KIE in the decarboxylation of orotic acid in explicit sulfolane solvent. The results are in good agreement with experiment and show that the mass-perturbation higher-order Trotter factorization provides a practical approach for computing condensed phase heavy-atom KIE. Copyright © 2011 Wiley Periodicals, Inc.

  16. Reaction of benzene with atomic carbon: pathways to fulvenallene and the fulvenallenyl radical in extraterrestrial atmospheres and the interstellar medium.

    Science.gov (United States)

    da Silva, Gabriel

    2014-06-05

    The reaction of benzene with ground-state atomic carbon, C((3)P), has been investigated using the G3X-K composite quantum chemical method. A suite of novel energetically favorable pathways that lead to previously unconsidered products are identified. Reaction is initiated by barrierless C atom cycloaddition to benzene on the triplet surface, producing a vibrationally excited [C7H6]* adduct that can dissociate to the cycloheptatrienyl radical (+ H) via a relatively loose transition state 4.4 kcal mol(-1) below the reactant energies. This study also identifies that this reaction adduct can isomerize to generate five-membered ring intermediates that can further dissociate to the global C7H5 minima, the fulvenallenyl radical (+ H), or to c-C5H4 and acetylene, with limiting barriers around 20 and 10 kcal mol(-1) below the reactants, respectively. If intersystem crossing to the singlet surface occurs, isomerization pathways that are lower-yet in energy are available leading to the C7H6 minima fulvenallene, with all barriers over 40 kcal mol(-1) below the reactants. From here further barrierless fragmentation to fulvenallenyl + H can proceed at ca. 25 kcal mol(-1) below the reactants. In the reducing atmospheres of planets like Jupiter and satellites like Titan, where benzene and C((3)P) are both expected, it is proposed that fulvenallene and the fulvenallenyl radical would be the dominant products of the C6H6 + C((3)P) reaction. Fulvenallenyl may also be a significant reaction product under collision-free conditions representative of the interstellar medium, although further work is required here to confirm the identity of the C7H5 radical product.

  17. Enhancing the quantum state transfer between two atoms in separate cavities via weak measurement and its reversal

    Science.gov (United States)

    Li, Yan-Ling; Huang, Jinsong; Xu, Zhonghui; Xiao, Xing

    2017-10-01

    Taking the advantage of weak measurement and quantum measurement reversal, we propose a scheme to enhance the fidelity of transferring quantum state from one atom trapped in cavity to another distant one trapped in another cavity which is coupled by an optical fiber. It is turned out that the fidelity can be greatly improved even when the system is under serious dissipation. Moreover, the scheme works in both the strong-coupling and weak-coupling regimes. It is also robust to the ratio of the coupling constant between the atoms and the cavity modes to the coupling constant between the fiber and cavity modes. The underlying mechanism can be attributed to the probabilistic nature of weak measurements.

  18. Porphyrin Cobalt(III “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH

    Directory of Open Access Journals (Sweden)

    Monalisa Goswami

    2016-02-01

    Full Text Available In the field of cobalt(II porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH aryl azides in Co(II porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O and phenylene diimine (Y = NH species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier.

  19. Atomic-Resolution Transmission Electron Microscopic Movies for Study of Organic Molecules, Assemblies, and Reactions: The First 10 Years of Development.

    Science.gov (United States)

    Nakamura, Eiichi

    2017-06-20

    A molecule is a quantum mechanical entity. "Watching motions and reactions of a molecule with our eyes" has therefore been a dream of chemists for a century. This dream has come true with the aid of the movies of atomic-resolution transmission electron microscopic (AR-TEM) molecular images through real-time observation of dynamic motions of single organic molecules (denoted hereafter as single-molecule atomic-resolution real-time (SMART) TEM imaging). Since 2007, we have reported movies of a variety of single organic molecules, organometallic molecules, and their assemblies, which are rotating, stretching, and reacting. Like movies in the theater, the atomic-resolution molecular movies provide us information on the 3-D structures of the molecules and also their time evolution. The success of the SMART-TEM imaging crucially depends on the development of "chemical fishhooks" with which fish (organic molecules) in solution can be captured on a single-walled carbon nanotube (CNT, serving as a "fishing rod"). The captured molecules are connected to a slowly vibrating CNT, and their motions are displayed on a monitor in real time. A "fishing line" connecting the fish and the rod may be a σ-bond, a van der Waals force, or other weak connections. Here, the molecule/CNT system behaves as a coupled oscillator, where the low-frequency anisotropic vibration of the CNT is transmitted to the molecules via the weak chemical connections that act as an energy filter. Interpretation of the observed motions of the molecules at atomic resolution needs us to consider the quantum mechanical nature of electrons as well as bond rotation, letting us deviate from the conventional statistical world of chemistry. What new horizons can we explore? We have so far carried out conformational studies of individual molecules, assigning anti or gauche conformations to each C-C bond in conformers that we saw. We can also determine the structures of van der Waals assemblies of organic molecules

  20. Effects of doping in 25-atom bimetallic nanocluster catalysts for carbon–carbon coupling reaction of iodoanisole and phenylacetylene

    Directory of Open Access Journals (Sweden)

    Zhimin Li

    2016-10-01

    Full Text Available We here report the catalytic effects of foreign atoms (Cu, Ag, and Pt doped into well-defined 25-gold-atom nanoclusters. Using the carbon-carbon coupling reaction of p-iodoanisole and phenylacetylene as a model reaction, the gold-based bimetallic MxAu25−x(SR18 (–SR=–SCH2CH2Ph nanoclusters (supported on titania were found to exhibit distinct effects on the conversion of p-iodoanisole as well as the selectivity for the Sonogashira cross-coupling product, 1-methoxy-4-(2-phenylethynylbenzene. Compared to Au25(SR18, the centrally doped Pt1Au24(SR18 causes a drop in catalytic activity but with the selectivity retained, while the AgxAu25−x(SR18 nanoclusters gave an overall performance comparable to Au25(SR18. Interestingly, CuxAu25−x(SR18 nanoclusters prefer the Ullmann homo-coupling pathway and give rise to product 4,4′-dimethoxy-1,1′-biphenyl, which is in opposite to the other three nanocluster catalysts. Our overall conclusion is that the conversion of p-iodoanisole is largely affected by the electronic effect in the bimetallic nanoclusters’ 13-atom core (i.e., Pt1Au12, CuxAu13−x, and Au13, with the exception of Ag doping, and that the selectivity is primarily determined by the type of atoms on the MxAu12−x shell (M=Ag, Cu, and Au in the nanocluster catalysts.

  1. Pathway of proton transfer in bacterial reaction centers: replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone.

    Science.gov (United States)

    Paddock, M L; McPherson, P H; Feher, G; Okamura, M Y

    1990-01-01

    The pathway of proton transfer in the reaction center (RC) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Ser-L223, a putative proton donor that forms a hydrogen bond with the secondary quinone acceptor QB, was replaced with Ala and Thr. RCs with Ala-L223 displayed reduced electron transfer and proton uptake rates in the reaction QA-QB- + 2H+----QAQBH2. The rate constant for this reaction, k(2)AB, was found to be reduced approximately 350-fold to 4.0 +/- 0.2 s-1. Proton uptake measurements using a pH indicator dye showed a rapid uptake of 1 H+ per RC followed by a slower uptake of 1 H+ per RC at a rate of 4.1 +/- 0.1 s-1; native RCs showed a rapid uptake of 2H+ per RC. Evidence is provided that these changes were not due to gross structural changes in the binding site of QB. RCs with Thr-L223 showed little reduction in the rates of electron and proton transfer. These results indicate that proton transfer from the hydroxyl group of Ser-L223 or Thr-L223 is required for fast electron and proton transfer associated with the formation of the dihydroquinone QH2. In contrast, previous work showed that replacing Glu-L212, another putative proton donor to QB, with Gln slowed proton uptake from solution without significantly altering electron transfer. We propose a model that involves two distinct proton transfer steps. The first step occurs prior to transfer of the second electron to QB and involves proton transfer from Ser-L223. The second step occurs after this electron transfer through a pathway involving Glu-L212. PMID:2168561

  2. Surprisingly Long-Lived Ascorbyl Radicals in Acetonitrile: Concerted Proton-Electron Transfer Reactions and Thermochemistry

    Science.gov (United States)

    Warren, Jeffrey J.; Mayer, James M.

    2008-01-01

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH−) have been examined in acetonitrile solvent.iAscH− is oxidized by 2,4,6-tBu3C6H2O• and by excess TEMPO• to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc•−), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc•− is surprising in light of the transience of the ascorbyl radical in aqueous solutions, and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH−. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O–H bond dissociation free energy (BDFE) for iAscH−of 65.4 ± 1.5 kcal mol−1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 ± 1.2 kcal mol−1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 ± 1.5 kcal mol−1 derived from reported data. PMID:18505256

  3. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions.

    Science.gov (United States)

    Oberhofer, Harald; Blumberger, Jochen

    2009-08-14

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following the earlier work of Wu and Van Voorhis [Phys. Rev. A 72, 024502 (2005)], the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

  4. Site-selective oxidation, amination and epimerization reactions of complex polyols enabled by transfer hydrogenation

    Science.gov (United States)

    Hill, Christopher K.; Hartwig, John F.

    2017-12-01

    Polyoxygenated hydrocarbons that bear one or more hydroxyl groups comprise a large set of natural and synthetic compounds, often with potent biological activity. In synthetic chemistry, alcohols are important precursors to carbonyl groups, which then can be converted into a wide range of oxygen- or nitrogen-based functionality. Therefore, the selective conversion of a single hydroxyl group in natural products into a ketone would enable the selective introduction of unnatural functionality. However, the methods known to convert a simple alcohol, or even an alcohol in a molecule that contains multiple protected functional groups, are not suitable for selective reactions of complex polyol structures. We present a new ruthenium catalyst with a unique efficacy for the selective oxidation of a single hydroxyl group among many in unprotected polyol natural products. This oxidation enables the introduction of nitrogen-based functional groups into such structures that lack nitrogen atoms and enables a selective alcohol epimerization by stepwise or reversible oxidation and reduction.

  5. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions.

    Science.gov (United States)

    Belal, Tarek S; El-Kafrawy, Dina S; Mahrous, Mohamed S; Abdel-Khalek, Magdi M; Abo-Gharam, Amira H

    2016-02-15

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415nm. The fourth method involves the formation of a yellow complex peaking at 361nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Expanded corn starch as a versatile material in atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate.

    Science.gov (United States)

    Bansal, Ankushi; Kumar, Arvind; Latha, Patnam Padma; Ray, Siddharth Sankar; Chatterjee, Alok Kumar

    2015-10-05

    Polymerization of styrene (St) and methyl methacrylate (MMA) was performed by surface initiated (SI) and activator generated by electron transfer (AGET) systems of atom transfer radical polymerization (ATRP) using renewable expanded corn starch (ECS) as a support. This prepared ECS is found to have V type crystallinity with 50 m(2)g(-1) surface area (<1m(2)g(-1) for corn starch (CS)) and average pore volume of 0.43 cm(3)g(-1) (<0.1cm(3)g(-1) for CS). In SI-ATRP, hydroxyl groups on ECS were converted into macro-initiator by replacing with 2-bromoisobutyryl bromide (BIBB) with a 0.06 degree of substitution determined from NMR. In AGET-ATRP, CuBr2/ligand complex get adsorbed on ECS (Cu(II)/ECS=10 wt.%) to catalyze the polymerization. Synthesized PS/PMMA was characterized by SEM, FT-IR, (1)H NMR. Copyright © 2015 Elsevier Ltd. All rights reserved.

  7. Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects.

    Science.gov (United States)

    Simándi, Tatiana M; May, Zoltán; Szigyártó, Imola Cs; Simándi, László I

    2005-01-21

    Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases.

  8. Role of solvent dynamics in ultrafast photoinduced proton-coupled electron transfer reactions in solution.

    Science.gov (United States)

    Hazra, Anirban; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2010-09-30

    A theoretical formulation for modeling photoinduced nonequilibrium proton-coupled electron transfer (PCET) reactions in solution is presented. In this formulation, the PCET system is described by donor and acceptor electron-proton vibronic free energy surfaces that depend on a single collective solvent coordinate. Dielectric continuum theory is used to obtain a generalized Langevin equation of motion for this collective solvent coordinate. The terms in this equation depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties characterizing the vibronic surfaces. The ultrafast dynamics following photoexcitation is simulated using a surface hopping method in conjunction with the Langevin equation of motion. This methodology is used to examine a series of model photoinduced PCET systems, where the initial nonequilibrium state is prepared by vertical photoexcitation from the ground electronic state to the donor electronic state. Analysis of the dynamical trajectories provides insight into the interplay between the solvent dynamics and the electron-proton transfer for these types of processes. In addition, these model studies illustrate how the coupling between the electron-proton transfer and the solvent dynamics can be tuned by altering the solute and solvent properties.

  9. Localization and Targeted Transfer of Atomic-Scale Nonlinear Excitations: Perspectives for Applications

    Science.gov (United States)

    Kopidakis, G.; Aubry, S.

    We review nonlinearity-induced localization in discrete systems with emphasis on theory and numerical calculations on models used in materials physics to describe interatomic interactions. We discuss how the concept of discrete breather or intrinsic localized mode could become an important tool for understanding nanoscale phenomena in molecules and solids. A particularly attractive field of application for nonlinear localized excitations is the controlled and directed transport of energy. We discuss the recently proposed targeted transfer of localized excitations based on the concept of nonlinear resonance and its potential applications. As an area for such applications, we present directional ultrafast electron transfer at low temperatures using this selective transfer mechanism and we give examples from biological electron transfer. We finally discuss possible applications in nanotechnology and biomolecules.

  10. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Hongying; Huang, Guangming, E-mail: gmhuang@ustc.edu.cn

    2015-03-31

    Graphical abstract: Direct and humidity independent mass spectrometry analysis of gas phase chemicals could be achieved via ambient proton transfer ionization, ion intensity was found to be stable with humidity ranged from ∼10% to ∼100%. - Highlights: • A humidity independent mass spectrometric method for gas phase samples analysis. • A universal and good sensitivity method. • The method can real time identify plant released raw chemicals. - Abstract: In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m{sup −3}, ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.

  11. Surface polyPEGylation of Eu3+ doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

    Science.gov (United States)

    Zeng, Guangjian; Liu, Meiying; Heng, Chunning; Huang, Qiang; Mao, Liucheng; Huang, Hongye; Hui, Junfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-01

    The Eu3+ doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu3+ doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface initiated ATRP. As compared with the traditional ATRP, the metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts such as copper ions. More importantly, the strategy described in this work should also be utilized for fabrications of many other luminescent polymer nanocomposites due to its good monomer adoptability.

  12. Hydrophilization of Poly(ether ether ketone) Films by Surface-initiated Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Eskimergen, Rüya; Burkrinsky, J.T.

    2008-01-01

    and confirmed by ATR FTIR, water contact ang;le, and Thermal Gravimetric Analysis (TGA). The surface topography was evaluated by "Atomic Force Microscopy (AFM). X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the degree of functionalization. The performed modification allowed for successful...

  13. Surface-Initiated Atom Transfer Radical Polymerization of Magnetite Nanoparticles with Statistical Poly(tert-butyl acrylate-poly(poly(ethylene glycol methyl ether methacrylate Copolymers

    Directory of Open Access Journals (Sweden)

    Patcharin Kanhakeaw

    2015-01-01

    Full Text Available This work presented the surface modification of magnetite nanoparticle (MNP with poly[(t-butyl acrylate-stat-(poly(ethylene glycol methyl ether methacrylate] copolymers (P[(t-BA-stat-PEGMA] via a surface-initiated “grafting from” atom transfer radical polymerization (ATRP. Loading molar ratio of t-BA to PEGMA was systematically varied (100 : 0, 75 : 25, 50 : 50, and 25 : 75, resp. such that the degree of hydrophilicity of the copolymers, affecting the particle dispersibility in water, can be fine-tuned. The reaction progress in each step of the synthesis was monitored via Fourier transform infrared spectroscopy (FTIR. The studies in the reaction kinetics indicated that PEGMA had higher reactivity than that of t-BA in the copolymerizations. Gel permeation chromatography (GPC indicated that the molecular weights of the copolymers increased with the increase of the monomer conversion. Transmission electron microscopy (TEM revealed that the particles were spherical with averaged size of 8.1 nm in diameter. Dispersibility of the particles in water was apparently improved when the copolymers were coated as compared to P(t-BA homopolymer coating. The percentages of MNP and the copolymer in the composites were determined via thermogravimetric analysis (TGA and their magnetic properties were investigated via vibrating sample magnetometry (VSM.

  14. 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...

  15. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    Science.gov (United States)

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages. Copyright © 2015 Elsevier B.V. All rights reserved.

  16. Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture.

    Science.gov (United States)

    Kasai, Yukako; Yoshida, Norio; Nakano, Haruyuki

    2015-05-28

    The co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water-acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is more stable than the neutral form. The reaction free energy is -10.6 kcal mol(-1). On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol(-1). The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.

  17. Metal Free Azide-Alkyne Click Reaction: Role of Substituents and Heavy Atom Tunneling.

    Science.gov (United States)

    Karmakar, Sharmistha; Datta, Ayan

    2015-09-03

    Metal free click reactions provide an excellent noninvasive tool to modify and understand the processes in biological systems. Release of ring strain in cyclooctynes on reaction with azides on the formation of triazoles results in small activation energies for various intermolecular Huisgen reactions (1-9). Substitution of difluoro groups at the α, α' position of the cyclooctyne ring enhances the rates of cycloadditions by 10 and 20 times for methyl azide and benzyl azide respectively at room temperature. The computed rate enhancement on difluoro substitution using direct dynamical calculations using the canonical variational transition state theory (CVT/CAG) with small curvature tunneling (SCT) corrections are in excellent agreement with the experimental results. For the intramolecular click reaction (10) notwithstanding its much higher activation energy, quantum mechanical tunneling (QMT) enhances the rate of cycloaddition significantly and increases the N(14)/N(15) primary kinetic isotope effect at 298 K. QMT is shown to be rather efficient in 10 due to a thin barrier of ∼2.4 Å. The present study shows that tunneling effects can be significant for intramolecular click reactions.

  18. Rational Design of Single Molybdenum Atoms Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction.

    Science.gov (United States)

    Chen, Wenxing; Pei, Jiajing; He, Chun-Ting; Wan, Jiawei; Ren, Hanlin; Zhu, Youqi; Wang, Yu; Dong, Juncai; Tian, Shubo; Cheong, Weng-Chon; Lu, Siqi; Zheng, Lirong; Zheng, Xusheng; Yan, Wensheng; Zhuang, Zhongbin; Chen, Chen; Peng, Qing; Wang, Dingsheng; Li, Yadong

    2017-12-11

    The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising pathway to resolve energy and environment problems. An electrocatalyst was designed with single Mo atoms (Mo-SAs) supported on N-doped carbon having outstanding HER performance. The structure of the catalyst was probed by aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, indicating the formation of Mo-SAs anchored with one nitrogen atom and two carbon atoms (Mo 1 N 1 C 2 ). Importantly, the Mo 1 N 1 C 2 catalyst displayed much more excellent activity compared with Mo 2 C and MoN, and better stability than commercial Pt/C. Density functional theory (DFT) calculation revealed that the unique structure of Mo 1 N 1 C 2 moiety played a crucial effect to improve the HER performance. This work opens up new opportunities for the preparation and application of highly active and stable Mo-based HER catalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Reactions of electronically excited boron atoms. Quenching rate constants and the radiative lifetime of the 4p 2P state

    Science.gov (United States)

    Yang, Xuefeng; Dagdigian, Paul J.

    1992-12-01

    Collisional quenching and radiative decay of the 4p 2P level of the boron atom has been studied in a cell experiment, in which B atoms are prepared by 266 nm multiphoton dissociation of BBr 3 and the 4p 2P level is prepared by sequential 2-photon absorption through the 3s 2S level. A radiative lifetime of 360 ± 50 ns is derived for B (4p 2P) by extrapolation of the measured decay rates versus BBr 3 partial pressure in several Torr helium buffer gas. Bimolecular quenching rate constants were also determined for a number of atomic and molecular species from the dependence of the B (4p 2P) decay rate on the quencher gas partial pressure. The quenching rate constants for the molecular species were quite large (≈(1-2)×10 -9 molecule -1 cm 3 s -1), presumably reflecting the small B (4p 2P) ionization potential and the rapid removal of the excited state by chemical reaction.

  20. A liquid metal reaction environment for the room-temperature synthesis of atomically thin metal oxides

    Science.gov (United States)

    Zavabeti, Ali; Ou, Jian Zhen; Carey, Benjamin J.; Syed, Nitu; Orrell-Trigg, Rebecca; Mayes, Edwin L. H.; Xu, Chenglong; Kavehei, Omid; O’Mullane, Anthony P.; Kaner, Richard B.; Kalantar-zadeh, Kourosh; Daeneke, Torben

    2017-10-01

    Two-dimensional (2D) oxides have a wide variety of applications in electronics and other technologies. However, many oxides are not easy to synthesize as 2D materials through conventional methods. We used nontoxic eutectic gallium-based alloys as a reaction solvent and co-alloyed desired metals into the melt. On the basis of thermodynamic considerations, we predicted the composition of the self-limiting interfacial oxide. We isolated the surface oxide as a 2D layer, either on substrates or in suspension. This enabled us to produce extremely thin subnanometer layers of HfO2, Al2O3, and Gd2O3. The liquid metal–based reaction route can be used to create 2D materials that were previously inaccessible with preexisting methods. The work introduces room-temperature liquid metals as a reaction environment for the synthesis of oxide nanomaterials with low dimensionality.

  1. Atomic layer deposition-Sequential self-limiting surface reactions for advanced catalyst "bottom-up" synthesis

    Science.gov (United States)

    Lu, Junling; Elam, Jeffrey W.; Stair, Peter C.

    2016-06-01

    Catalyst synthesis with precise control over the structure of catalytic active sites at the atomic level is of essential importance for the scientific understanding of reaction mechanisms and for rational design of advanced catalysts with high performance. Such precise control is achievable using atomic layer deposition (ALD). ALD is similar to chemical vapor deposition (CVD), except that the deposition is split into a sequence of two self-limiting surface reactions between gaseous precursor molecules and a substrate. The unique self-limiting feature of ALD allows conformal deposition of catalytic materials on a high surface area catalyst support at the atomic level. The deposited catalytic materials can be precisely constructed on the support by varying the number and type of ALD cycles. As an alternative to the wet-chemistry based conventional methods, ALD provides a cycle-by-cycle "bottom-up" approach for nanostructuring supported catalysts with near atomic precision. In this review, we summarize recent attempts to synthesize supported catalysts with ALD. Nucleation and growth of metals by ALD on oxides and carbon materials for precise synthesis of supported monometallic catalyst are reviewed. The capability of achieving precise control over the particle size of monometallic nanoparticles by ALD is emphasized. The resulting metal catalysts with high dispersions and uniformity often show comparable or remarkably higher activity than those prepared by conventional methods. For supported bimetallic catalyst synthesis, we summarize the strategies for controlling the deposition of the secondary metal selectively on the primary metal nanoparticle but not on the support to exclude monometallic formation. As a review of the surface chemistry and growth behavior of metal ALD on metal surfaces, we demonstrate the ways to precisely tune size, composition and structure of bimetallic metal nanoparticles. The cycle-by-cycle "bottom up" construction of bimetallic (or multiple

  2. Spin-unrestricted random-phase approximation with range separation: Benchmark on atomization energies and reaction barrier heights

    CERN Document Server

    Mussard, Bastien; Angyan, Janos; Toulouse, Julien

    2015-01-01

    We consider several spin-unrestricted random-phase approximation (RPA) variants for calculating correlation energies, with and without range separation, and test them on datasets of atomization energies and reaction barrier heights. We show that range separation greatly improves the accuracy of all RPA variants for these properties. Moreover, we show that a RPA variant with exchange, hereafter referred to as RPAx-SO2, first proposed by Sz-abo and Ostlund [A. Szabo and N. S. Ostlund, J. Chem. Phys. 67, 4351 (1977)] in a spin-restricted closed-shell formalism, and extended here to a spin-unrestricted formalism, provides on average the most accurate range-separated RPA variant for atomization energies and reaction barrier heights. Since this range-separated RPAx-SO2 method had already been shown to be among the most accurate range-separated RPA variants for weak intermolecular interactions [J. Toulouse, W. Zhu, A. Savin, G. Jansen, and J. G. {\\'A}ngy{\\'a}n, J. Chem. Phys. 135, 084119 (2011)], this works confirms...

  3. A combined experimental, theoretical, and Van't Hoff model study for identity methyl, proton, hydrogen atom, and hydride exchange reactions. Correlation with three-center four-, three-, and two-electron systems

    Science.gov (United States)

    Buck, Henk M.

    We have studied carbon transfer reactions following an SN2 reaction profile. With ab initio calculations and experimental geometries concerning the nature of the various complexes indicated as stable, intermediate, and transition state we were able to show the additional value of van't Hoff's tetrahedral configuration by changing its geometry via a trigonal pyramid into a trigonal bipyramid. The ratio of the apical bond and corresponding tetrahedral bond distances is then nearly 1.333. The relevance of this approach has also been shown for identity proton-(hydrogen atom-, and hydride-) in-line reactions. The use of this geometrical transmission will be demonstrated for the hydrogen bonding distances in e.g., DNA duplexes and other biological (supra) molecular systems.

  4. Hypochlorous acid-mediated protein oxidation: how important are chloramine transfer reactions and protein tertiary structure?

    Science.gov (United States)

    Pattison, David I; Hawkins, Clare L; Davies, Michael J

    2007-08-28

    Hypochlorous acid (HOCl) is a powerful oxidant generated from H2O2 and Cl- by the heme enzyme myeloperoxidase, which is released from activated leukocytes. HOCl possesses potent antibacterial properties, but excessive production can lead to host tissue damage that occurs in numerous human pathologies. As proteins and amino acids are highly abundant in vivo and react rapidly with HOCl, they are likely to be major targets for HOCl. In this study, two small globular proteins, lysozyme and insulin, have been oxidized with increasing excesses of HOCl to determine whether the pattern of HOCl-mediated amino acid consumption is consistent with reported kinetic data for isolated amino acids and model compounds. Identical experiments have been carried out with mixtures of N-acetyl amino acids (to prevent reaction at the alpha-amino groups) that mimic the protein composition to examine the role of protein structure on reactivity. The results indicate that tertiary structure facilitates secondary chlorine transfer reactions of chloramines formed on His and Lys side chains. In light of these data, second-order rate constants for reactions of Lys side chain and Gly chloramines with Trp side chains and disulfide bonds have been determined, together with those for further oxidation of Met sulfoxide by HOCl and His side chain chloramines. Computational kinetic models incorporating these additional rate constants closely predict the experimentally observed amino acid consumption. These studies provide insight into the roles of chloramine formation and three-dimensional structure on the reactions of HOCl with isolated proteins and demonstrate that kinetic models can predict the outcome of HOCl-mediated protein oxidation.

  5. Oxygen atom transfer from {mu}-Oxo-bis[1,4,8,11,15,18,22,25-octakis(trifluoromethyl)ph-thalocya ninato]diiron(III) : evidence for an Fe(IV)=O intermediate.

    Energy Technology Data Exchange (ETDEWEB)

    Chen, M. J.; Rathke, J. W.; Chemical Engineering

    1998-01-01

    The dimeric [(FPc)Fe]2({mu}-O) (1) (FPc is the dianion of 1,4,8,11,15,18,22,25-octakis(trifluoromethyl)phthalocyanine) has been shown to transfer its -oxo atom quantitatively to trimethylphosphine and triphenylphosphine. In the case of triphenylphosphine a base such as 1-methylimidazole (MeIm) or pyridine (py) is needed to induce the oxygen atom transfer. The reaction of 1 with MeIm at -40 C and below gives [(MeIm)(FPc)Fe]2({mu}-O) (4), which disproportionates to give (MeIm)2(FPc)Fe (5) and (FPc)Fe=O (6) at higher temperatures. The oxo atom of 6 has been shown to transfer to triphenylphosphine. Similarly, 6 is generated by the disproportionation of 1 with py. It has also been generated by the oxidation of 1 with t-butyl hydroperoxide. [(FPc)Fe]2({mu}-O) catalyzes the oxidation of hydrocarbons by iodosylbenzene. With stilbenes, styrenes, cyclohexenes and butenes as substrates, both epoxidations and alkyl C-H bond oxidations have been observed. The epoxidation of cis-stilbene leads to a mixture of cis- and trans-stilbene oxides, indicating that epoxidation of cis-stilbene, and possibly other olefins as well, proceeds through a non-concerted mechanism.

  6. Atomic platinum layer coated titanium copper nitride supported on carbon nanotubes for the methanol oxidation reaction

    CSIR Research Space (South Africa)

    Zheng, Y

    2017-09-01

    Full Text Available measurements. The results confirm the core-shell structure of the prepared TiN@Pt/CNTs catalyst. More importantly, the catalyst exhibits superb mass activity and durability for the methanol oxidation reaction (MOR) than that of the commercial JM Pt/C catalyst...

  7. Characterization of cement minerals, cements and their reaction products at the atomic and nano scale

    DEFF Research Database (Denmark)

    Skibsted, Jørgen; Hall, Christopher

    2008-01-01

    Recent advances and highlights in characterization methods are reviewed for cement minerals, cements and their reaction products. The emphasis is on X-ray and neutron diffraction, and on nuclear magnetic resonance methods, although X-ray absorption and Raman spectroscopies are discussed briefly...

  8. The measurement of cross sections of inelastic and transfer reactions with gamma-particle coincidence

    Energy Technology Data Exchange (ETDEWEB)

    Zagatto, V.A.B.; Oliveira, J.R.B.; Pereira, D.; Allegro, P.R.P.; Chamon, L.C.; Cybulska, E.W.; Medina, N.H.; Ribas, R.V.; Rossi Junior, E.S.; Seale, W.A.; Silva, C.P.; Gasques, L. [Universidade de Sao Paulo (USP), SP (Brazil); Toufen, D.L. [Instituto Federal de Educacao, Ciencia e Tecnologia de Sao Paulo (IFSP), Guarulhos, SP (Brazil); Silveira, M.A.G.; Zahn, G.S.; Genezini, F.A.; Shorto, J.M.B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Lubian, J.; Linares, R. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica; Nobre, G.P. [Lawrence Livermore National Laboratory, Livermore, CA (United States)

    2011-07-01

    Full text: The following work aims to obtain experimental reaction cross sections of inelastic excitation and transfer to excited states reactions (both measured by gamma-particle coincidences) and its comparison with theoretical predictions based in a new model based on the Sao Paulo Potential. The measurements were made at the Pelletron accelerator laboratory of the University of Sao Paulo with the Saci-Perere spectrometer, which consists of 4 a GeHP Compton suppressed gamma detectors and a 4 {pi} charged particle ancillary system with 11{Delta}{Epsilon} - {Epsilon} plastic phoswich scintillators (further details about the experimental procedure may be found in: J.R.B. Oliveira et al., XVIII International School on Nuclear Physics, Neutron Physics and Applications (2009). Theoretical angular distribution calculations (using code GOSIA) were performed with a new model based on the Sao Paulo Potential, specifically developed for the inclusion of dissipative processes like deep-inelastic collisions (DIC) considering the Coulomb plus nuclear potential (with the aid of code FRESCO). The experimental cross sections were obtained such as described in J.R.B. Oliveira et al however, in this work, the particle-gamma angular correlations and the vacuum de-alignment effects (caused by hyperfine interaction) were finally added for the {sup 110}Pd inelastic reaction and for the {sup 112}Pd transfer reaction. For these purposes a new code has been developed to assist in the data analysis. We take into account the particle-gamma angular correlations using the scattering amplitudes given by FRESCO, considering the vacuum de-alignment effects as proposed by A. Abragam and R. V. Pound, Phys. Rev. 92, 943 (1953). The theoretical predictions still consider 2 different types of Sao Paulo Potential, the first one has a multiplying factor equals to 1.0 in the real part of the potential and the second considers this factor equals to 0.6, as proposed in D. Pereira, J. Lubian, J

  9. Energetics of protein fluctuations: Ligand binding to myoglobin and electron transfer in reaction center

    Science.gov (United States)

    McMahon, Benjamin Hamilton

    We have measured the temperature dependent kinetics of two different protein reactions: Psp+Qsbsp{A}{-}-> PQsb{A} electron transfer (ET) in the photosynthetic reaction (RC), and recombination of carbonmonoxide (CO) to myoglobin (Mb) after flash photolysis. The ET reaction allows determination of the temperature dependence of energy dissipation as RC adapts to charge transfer on the 100 ms, 10sp3 and 10sp4 s time scales at temperatures from 5 to 300 K. The adaptation, or conformational relaxation, of RC is observed in four distinct tiers of conformational substrates, with average apparent Arrhenius activation enthalpies of 17, 50, 78, and 110 kJ/mol and pre-exponential factors of 10sp{13},\\ 10sp{15},\\ 10sp{21}, and 10sp{25}\\ ssp{-1}, respectively. This parameterization provides a prediction of the time course of relaxations at all temperatures. At 300 K, relaxations are expected to occur from 1 ps to 1 ms; at lower temperatures the distribution of relaxation times broaden. We extend this study to samples of different pH, viscosity, and salt composition. We observe kinetics of CO recombination to horse heart myoglobin between 10 ns and 100 s at temperatures from 80 to 320 K. Essentially all recombination is visible in this time window, allowing the effect of relaxations to be observed on the nanosecond time scale at high temperatures, as well as microsecond to second time scales at lower temperatures. Variation of the solvent pH from 5.1 to 8.0 changes the average low temperature enthalpy barrier to recombination from 6 to 13 kJ/mol, shifting the time scale probed by the recombination reaction by an order of magnitude. Addition of 500 mM KCl, KSCN, or (NHsb4)sb2SOsb4 significantly changes the probability of geminate recombination without affecting either the enthalpy barrier to recombination or the energetics of CO entry to and exit from the heme pocket of the protein. We present a model of recombination which emphasizes the role of protein fluctuations in

  10. Numerical simulation of ultrasonic enhancement on mass transfer in liquid-solid reaction by a new computational model.

    Science.gov (United States)

    Jiao, Qingbin; Bayanheshig; Tan, Xin; Zhu, Jiwei

    2014-03-01

    Mass transfer coefficient is an important parameter in the process of mass transfer. It can reflect the degree of enhancement of mass transfer process in liquid-solid reaction and in non-reactive systems like dissolution and leaching, and further verify the issues by experiments in the reaction process. In the present paper, a new computational model quantitatively solving ultrasonic enhancement on mass transfer coefficient in liquid-solid reaction is established, and the mass transfer coefficient on silicon surface with a transducer at frequencies of 40 kHz, 60 kHz, 80 kHz and 100 kHz has been numerically simulated. The simulation results indicate that mass transfer coefficient increases with the increasing of ultrasound power, and the maximum value of mass transfer coefficient is 1.467 × 10(-4) m/s at 60 kHz and the minimum is 1.310 × 10(-4) m/s at 80 kHz in the condition when ultrasound power is 50 W (the mass transfer coefficient is 2.384 × 10(-5) m/s without ultrasound). The extrinsic factors such as temperature and transducer diameter and distance between reactor and ultrasound source also influence the mass transfer coefficient on silicon surface. Mass transfer coefficient increases with the increasing temperature, with the decreasing distance between silicon and central position, with the decreasing of transducer diameter, and with the decreasing of distance between reactor and ultrasound source at the same ultrasonic power and frequency. The simulation results indicate that the computational model can quantitatively solve the ultrasonic enhancement on mass transfer coefficient. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Mass driver reaction engine characteristics and performance in earth orbital transfer missions

    Science.gov (United States)

    Snow, W. R.; Dunbar, R. S.

    1982-01-01

    Configurations of a typical mass driver reaction engine (MDRE) are presented and its use for delivery of payloads to geosynchronous orbit (GEO) from low earth orbit (LEO) is discussed. Basic rocket equations are developed for LEO to GEO round-trip missions using a single exhaust velocity. It is shown that exhaust velocities in the 5-10 km/sec range (specific impulse of 500-1000 sec) are well suited for mass drivers, minimizing the overall cost of missions. Payload delivery rate fractions show that there is little to be gained by stretching out LEO to GEO transfer times from 90 to 180 days. It therefore pays to use the shorter trip time, approximately doubling the amount of delivered payload during any fixed time of use of the MDRE.

  12. Neutron spectroscopic factors of 55Ni hole-states from (p,d transfer reactions

    Directory of Open Access Journals (Sweden)

    A. Sanetullaev

    2014-09-01

    Full Text Available Spectroscopic information has been extracted on the hole-states of 55Ni, the least known of the quartet of nuclei (55Ni, 57Ni, 55Co and 57Cu, one nucleon away from 56Ni, the N=Z=28 double magic nucleus. Using the H1(Ni56,dNi55 transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f7/2, p3/2 and the s1/2 hole-states of 55Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. State of the art calculations have been performed to describe the excitation energies and spectroscopic factors of the s1/2 hole-state below Fermi energy.

  13. Formaldehyde measurements by Proton transfer reaction – Mass Spectrometry (PTR-MS: correction for humidity effects

    Directory of Open Access Journals (Sweden)

    A. Vlasenko

    2010-08-01

    Full Text Available Formaldehyde measurements can provide useful information about photochemical activity in ambient air, given that HCHO is formed via numerous oxidation processes. Proton transfer reaction mass spectrometry (PTR-MS is an online technique that allows measurement of VOCs at the sub-ppbv level with good time resolution. PTR-MS quantification of HCHO is hampered by the humidity dependence of the instrument sensitivity, with higher humidity leading to loss of PTR-MS signal. In this study we present an analytical, first principles approach to correct the PTR-MS HCHO signal according to the concentration of water vapor in sampled air. The results of the correction are validated by comparison of the PTR-MS results to those from a Hantzsch fluorescence monitor which does not have the same humidity dependence. Results are presented for an intercomparison made during a field campaign in rural Ontario at Environment Canada's Centre for Atmospheric Research Experiments.

  14. Neutron spectroscopic factors of {sup 55}Ni hole-states from (p,d) transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Sanetullaev, A. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Tsang, M.B., E-mail: tsang@nscl.msu.edu [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Lynch, W.G.; Lee, Jenny; Bazin, D. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Chan, K.P. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Physics Department, Hong Kong Chinese University, Shatin, Hong Kong (China); Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Rogers, A.M. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Sun, Z.Y. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Institute of Modern Physics, CAS, Lanzhou 730000 (China); Youngs, M. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Charity, R.J.; Sobotka, L.G. [Department of Chemistry, Washington University, St. Louis, MO 63130 (United States); Famiano, M. [Department of Physics, Western Michigan University, Kalamazoo, MI 49008 (United States); Hudan, S. [Department of Chemistry, Indiana University, Bloomington, IN 47405 (United States); Shapira, D. [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Peters, W.A. [Rutgers University, Piscataway, NJ 08854 (United States); Barbieri, C. [Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); and others

    2014-09-07

    Spectroscopic information has been extracted on the hole-states of {sup 55}Ni, the least known of the quartet of nuclei ({sup 55}Ni, {sup 57}Ni, {sup 55}Co and {sup 57}Cu), one nucleon away from {sup 56}Ni, the N=Z=28 double magic nucleus. Using the {sup 1}H({sup 56}Ni,d){sup 55}Ni transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f{sub 7/2}, p{sub 3/2} and the s{sub 1/2} hole-states of {sup 55}Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. State of the art calculations have been performed to describe the excitation energies and spectroscopic factors of the s{sub 1/2} hole-state below Fermi energy.

  15. Reaction-Controlled Phase-Transfer Catalysis for Propylene Epoxidation to Propylene Oxide

    Science.gov (United States)

    Zuwei, Xi; Ning, Zhou; Yu, Sun; Kunlan, Li

    2001-05-01

    The epoxidation of olefins with H2O2 was performed with a tungsten-containing catalyst. This insoluble catalyst forms soluble active species by the action of H2O2, and when the H2O2 is used up, the catalyst precipitates for easy recycling. Thus, the advantages of both homogeneous and heterogeneous catalysts are combined in one system through reaction-controlled phase transfer of the catalyst. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H2O2 production, O2 can be used for the epoxidation of propylene to propylene oxide with 85% yield based on 2-ethylanthrahydroquinone without any co-products. This approach avoids the problematic co-products normally associated with the industrial production of propylene oxide.

  16. An interacting quantum atom study of model SN 2 reactions (X- ···CH3 X, X = F, Cl, Br, and I).

    Science.gov (United States)

    Alkorta, Ibon; Thacker, Joseph C R; Popelier, Paul L A

    2017-11-10

    The quantum chemical topology method has been used to analyze the energetic profiles in the X-  + CH3 X → XCH3  + X- SN 2 reactions, with X = F, Cl, Br, and I. The evolution of the electron density properties at the BCPs along the reaction coordinate has been analysed. The interacting quantum atoms (IQA) method has been used to evaluate the intra-atomic and interatomic energy variations along the reaction path. The different energetic terms have been examined by the relative energy gradient method and the ANANKE program, which enables automatic and unbiased IQA analysis. Four of the six most important IQA energy contributions were needed to reproduce the reaction barrier common to all reactions. The four reactions considered share many common characteristics but when X = F a number of particularities occur. © 2017 Wiley Periodicals, Inc. © 2017 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

  17. Modelling of the heat transfer during oxygen atoms recombination on metallic surfaces in a plasma reactor

    NARCIS (Netherlands)

    Cavadias, S; Cauquot, P; Amouroux, J

    1997-01-01

    Space shuttle overheating during the re-entry phase, due to catalytic oxygen recombination on the thermal protection system, is a problem of practical and theoretical interest. The energy transfer is characterised by the product of the accommodation and the recombination coefficients. Previous

  18. Reaction Coordinate, Free Energy and Rate of Intramolecular Proton Transfer in Human Carbonic Anhydrase II.

    Science.gov (United States)

    Paul, Sanjib; Paul, Tanmoy Kumar; Taraphder, Srabani

    2018-02-21

    The role of structure and dynamics of an enzyme has been investigated at three different stages of its function including the chemical event it catalyzes. A one-pot computational method has been designed for each of these stages based on classical and/or QM-MM molecular dynamics and transition path sampling simulations. For a pair of initial and final states A and B separated by a high free energy barrier, using a two-stage selection process, several collective variables (CVs) are identified that can delineate A and B. However, these CVs are found to exhibit strong cross-coupling over the transition paths. A set of mutually orthogonal order parameters is then derived from these CVs and an optimal reaction coordinate, r determined applying half trajectory likelihood maximization along with a Bayesian information criterion. The transition paths are also used to project the multi-dimensional free energy surface and barrier crossing dynamics along r. The proposed scheme has been applied to the rate determining intramolecular proton transfer reaction of the well known enzyme human carbonic anhydrase II (HCA II). The potential-of-mean force, F(r) in the absence of the chemical step is found to reproduce earlier results on the equilibrium population of two sidechain orientations of the key residue His-64. Estimation of rate constants, k from mean first passage times for the three different stages of catalysis shows that the rate determining step of intramolecular proton transfer occurs with k ≃ 1.0 X 10 6 sec -1 , in close agreement with known experimental results.

  19. Proton-transfer reaction dynamics and energetics in calcification and decalcification.

    Science.gov (United States)

    Suwa, Ryota; Hatta, Masayuki; Ichikawa, Kazuhiko

    2014-10-13

    CaCO3 -saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca(2+) +HCO3 (-) ⇌CaCO3 +H(+) ; and reversible static physical precipitation/dissolution, Ca(2+) +CO3 (2-) ⇌CaCO3 . The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/PCO2 -independent solubility product, [Ca(2+) ][CO3 (2-) ], may not be observed at pH below 8.5 because [Ca(2+) ][CO3 (2-) ]/([Ca(2+) ][HCO3 (-) ]) ≪1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and PCO2 . The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each PCO2 /pH-dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO3 saturation state Λ of 1.3 at PCO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at PCO2 ≈1000 ppm and pH ≈7.8. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Gas-phase ion-molecule reactions for resolution of atomic isobars: AMS and ICP-MS perspectives

    Science.gov (United States)

    Bandura, Dmitry R.; Baranov, Vladimir I.; Litherland, A. E.; Tanner, Scott D.

    2006-09-01

    Ion-molecule reactions that can be used for resolution of spectral overlaps of long-lived or stable (T1/2 > 100 years) atomic isobars on the long-lived radio-isotopes (100 < T1/2 < 1012 years) in mass spectrometry are considered. Results for the separations of isobaric overlaps via cation reactions with NO, N2O, O2, CO2, C2H2, CH3F studied with the Inductively Coupled Plasma Dynamic Reaction Cell(TM) Mass Spectrometer (ICP-DRC(TM)-MS) with use of stable isotopes are presented. Overview of potential and reported reactions for separation of 35 isobars is given. Potential for the following isobaric pairs separation is shown (reaction gas and the extent of separation achieved to date in parenthesis): 32Si+/32S+(NO, 5 x 104), 40K+/40Ar+(N2O, 1.9 x 103), 40K+/40Ca+(N2O, 50), 59Ni+/59Co+(N2O, 6), 79Se+/79Br+(O2, 7.2 x 103), 81Kr+/81Br+(C2H2, 1.5 x 104), 93Mo+/93Nb+(N2O, 100), 93Mo+/93Zr+(N2O, 150), 135Cs+/135Ba+(N2O, 8 x 104), 137,138La+/137,138Ba+(O2, 40), 146Sm+/146Nd+(CO2, 1.5 x 105), 176Lu+/176Hf+(NO, 2.8 x 103), 187Re+/187Os+(N2O, 2.8 x 104). Effect of instrumental parameters on reactivity is discussed. The relevance of this work to accelerator mass spectrometry is discussed briefly.

  1. All-Atom Multiscale Molecular Dynamics Theory and Simulation of Self-Assembly, Energy Transfer and Structural Transition in Nanosystems

    Science.gov (United States)

    Espinosa Duran, John Michael

    The study of nanosystems and their emergent properties requires the development of multiscale computational models, theories and methods that preserve atomic and femtosecond resolution, to reveal details that cannot be resolved experimentally today. Considering this, three long time scale phenomena were studied using molecular dynamics and multiscale methods: self-assembly of organic molecules on graphite, energy transfer in nanosystems, and structural transition in vault nanoparticles. Molecular dynamics simulations of the self-assembly of alkoxybenzonitriles with different tail lengths on graphite were performed to learn about intermolecular interactions and phases exhibited by self-organized materials. This is important for the design of ordered self-assembled organic photovoltaic materials with greater efficiency than the disordered blends. Simulations revealed surface dynamical behaviors that cannot be resolved experimentally today due to the lack of spatiotemporal resolution. Atom-resolved structures predicted by simulations agreed with scanning tunneling microscopy images and unit cell measurements. Then, a multiscale theory based on the energy density as a field variable is developed to study energy transfer in nanoscale systems. For applications like photothermal microscopy or cancer phototherapy is required to understand how the energy is transferred to/from nanosystems. This multiscale theory could be applied in this context and here is tested for cubic nanoparticles immersed in water for energy being transferred to/from the nanoparticle. The theory predicts the energy transfer dynamics and reveals phenomena that cannot be described by current phenomenological theories. Finally, temperature-triggered structural transitions were revealed for vault nanoparticles using molecular dynamics and multiscale simulations. Vault is a football-shaped supramolecular assembly very distinct from the commonly observed icosahedral viruses. It has very promising

  2. Electron-transfer reactions of the reductase component of soluble methane monooxygenase from Methylococcus capsulatus (Bath).

    Science.gov (United States)

    Kopp, D A; Gassner, G T; Blazyk, J L; Lippard, S J

    2001-12-11

    Soluble methane monooxygenase (sMMO) catalyzes the hydroxylation of methane by dioxygen to afford methanol and water, the first step of carbon assimilation in methanotrophic bacteria. This enzyme comprises three protein components: a hydroxylase (MMOH) that contains a dinuclear nonheme iron active site; a reductase (MMOR) that facilitates electron transfer from NADH to the diiron site of MMOH; and a coupling protein (MMOB). MMOR uses a noncovalently bound FAD cofactor and a [2Fe-2S] cluster to mediate electron transfer. The gene encoding MMOR was cloned from Methylococcus capsulatus (Bath) and expressed in Escherichia coli in high yield. Purified recombinant MMOR was indistinguishable from the native protein in all aspects examined, including activity, mass, cofactor content, and EPR spectrum of the [2Fe-2S] cluster. Redox potentials for the FAD and [2Fe-2S] cofactors, determined by reductive titrations in the presence of indicator dyes, are FAD(ox/sq), -176 +/- 7 mV; FAD(sq/hq), -266 +/- 15 mV; and [2Fe-2S](ox/red), -209 +/- 14 mV. The midpoint potentials of MMOR are not altered by the addition of MMOH, MMOB, or both MMOH and MMOB. The reaction of MMOR with NADH was investigated by stopped-flow UV-visible spectroscopy, and the kinetic and spectral properties of intermediates are described. The effects of pH on the redox properties of MMOR are described and exploited in pH jump kinetic studies to measure the rate constant of 130 +/- 17 s(-)(1) for electron transfer between the FAD and [2Fe-2S] cofactors in two-electron-reduced MMOR. The thermodynamic and kinetic parameters determined significantly extend our understanding of the sMMO system.

  3. Implementation of proton transfer reaction-mass spectrometry (PTR-MS) for advanced bioprocess monitoring.

    Science.gov (United States)

    Luchner, Markus; Gutmann, Rene; Bayer, Karl; Dunkl, Jürgen; Hansel, Armin; Herbig, Jens; Singer, Wolfgang; Strobl, Florian; Winkler, Klaus; Striedner, Gerald

    2012-12-01

    We report on the implementation of proton transfer reaction-mass spectrometry (PTR-MS) technology for on-line monitoring of volatile organic compounds (VOCs) in the off-gas of bioreactors. The main part of the work was focused on the development of an interface between the bioreactor and an analyzer suitable for continuous sampling of VOCs emanating from the bioprocess. The permanently heated sampling line with an inert surface avoids condensation and interaction of volatiles during transfer to the PTR-MS. The interface is equipped with a sterile sinter filter unit directly connected to the bioreactor headspace, a condensate trap, and a series of valves allowing for dilution of the headspace gas, in-process calibration, and multiport operation. To assess the aptitude of the entire system, a case study was conducted comprising three identical cultivations with a recombinant E. coli strain, and the volatiles produced in the course of the experiments were monitored with the PTR-MS. The high reproducibility of the measurements proved that the established sampling interface allows for reproducible transfer of volatiles from the headspace to the PTR-MS analyzer. The set of volatile compounds monitored comprises metabolites of different pathways with diverse functions in cell physiology but also volatiles from the process matrix. The trends of individual compounds showed diverse patterns. The recorded signal levels covered a dynamic range of more than five orders of magnitude. It was possible to assign specific volatile compounds to distinctive events in the bioprocess. The presented results clearly show that PTR-MS was successfully implemented as a powerful bioprocess-monitoring tool and that access to volatiles emitted by the cells opens promising perspectives in terms of advanced process control. Copyright © 2012 Wiley Periodicals, Inc.

  4. Chemiluminescent Reactions of Group VI Atoms (O(3P) and Se(3P)) with Azide Radicals

    Science.gov (United States)

    1990-03-01

    Ongstad, Thomas L. Henshaw, Robert I. Lawconnell, William G. Thorpe(D N N F. J. Seiler Research Laboratory FJSRL-JR-90-0015 USAF Academy CO 80840-6528...Frank J. Seller Research Laboratory, USAF Academy. Colorado 80840-6528 (Received: December 27, 1989; In Final Form: March 14, 1990) The O(3P) + N3(0115...features which make thici attractiv ,; laser candidates. Burrows reactions capable of producing specific electronic states of group and co-workers have

  5. Atomic force microscopy study of the adsorption of protein molecules on transferred Langmuir monolayer

    Energy Technology Data Exchange (ETDEWEB)

    Gainutdinov, R. V., E-mail: radmir@ns.crys.ras.ru; Tolstikhina, A. L.; Stepina, N. D. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Novikova, N. N. [Russian Research Center Kurchatov Institute (Russian Federation); Yur' eva, E. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Khripunov, A. K. [Russian Academy of Sciences, Institute of Macromolecular Compounds (Russian Federation)

    2010-09-15

    Ordered protein films have been obtained by the adsorption of protein molecules on a Langmuir monolayer, which had previously formed on a silicon substrate, using the Langmuir-Blodgett and molecular self-organization methods. A mixture of cholesterol with dipalmitoylphosphatidylcholine (DPPC) and a polymer-cellulose acetopivalinate-were used as immobilization materials. Protein molecules (catalase and alkaline phosphatase) immobilized on solid substrates have been investigated by atomic force micros-copy. It was shown that the developed combined technique provides a deposition of homogeneous ultrathin protein films with a high degree of filling.

  6. Tracking Unfolding and Refolding Reactions of Single Proteins using Atomic Force Microscopy Methods

    Science.gov (United States)

    Bujalowski, Paul J.; Oberhauser, Andres F.

    2013-01-01

    During the last two decades single-molecule manipulation techniques such as atomic force microscopy (AFM) has risen to prominence through their unique capacity to provide fundamental information on the structure and function of biomolecules. Here we describe the use of single-molecule AFM to track protein unfolding and refolding pathways, enzymatic catalysis and the effects of osmolytes and chaperones on protein stability and folding. We will outline the principles of operation for two different AFM pulling techniques: length clamp and force-clamp discuss prominent applications. We provide protocols for the construction of polyproteins which are amenable for AFM experiments, the preparation of different coverslips, choice and calibration of AFM cantilevers. We also discuss the selection criteria for AFM recordings, the calibration of AFM cantilevers, protein sample preparations and analysis of the obtained data. PMID:23523554

  7. Study of 11Be on 9Be one neutron transfer reactions at TRIUMF ISAC-II

    Science.gov (United States)

    Braid, Ryan; Sarazin, Fred; Tigress Collaboration; (PCB)2 Collaboration

    2017-09-01

    The structure of neutron-rich Beryllium isotopes displays interesting properties arising from the interplay of alpha clustering and valence neutrons, leading in some cases to halo states. In this presentation, we will present the results of the 11Be on 9Be reaction at 55 MeV and 30.14 MeV, leading to two interesting exit channels. The first channel allows for the study of 12Be, while the second enables the study of 10Be. The emphasis of this paper will be on the latter, namely the analysis of the 9Be(11Be, 10Be) 10Be channel. This transfer reaction using a heavier-than-usual target has advantages over the traditional (d , p) methods, since the reactants are both equal in mass, they both scatter in the Printed Circuit Board-Based Charged Particle (PCB2) detector setup. The addition of TIGRESS allows precise tagging of the 10Be excited states. Some challenges in analysis include the 10Be degeneracy, 11Be breakup, and multiple particle excitation. The data and ongoing analysis will be presented. This work is partially supported by the US Department of Energy through Grant/Contract No. DE-FG03-93ER40789 (Colorado School of Mines).

  8. OH clock determination by proton transfer reaction mass spectrometry at an environmental chamber

    Directory of Open Access Journals (Sweden)

    P. Barmet

    2012-03-01

    Full Text Available The hydroxyl free radical (OH is the major oxidizing species in the lower atmosphere. Measuring the OH concentration is generally difficult and involves elaborate, expensive, custom-made experimental setups. Thus other more economical techniques, capable of determining OH concentrations at environmental chambers, would be valuable. This work is based on an indirect method of OH concentration measurement, by monitoring an appropriate OH tracer by proton transfer reaction mass spectrometry (PTR-MS. 3-pentanol, 3-pentanone and pinonaldehyde (PA were used as OH tracers in α-pinene (AP secondary organic aerosol (SOA aging studies. In addition we tested butanol-d9 as a potential "universal" OH tracer and determined its reaction rate constant with OH: kbutanol-d9 = 3.4(±0.88 × 10−12 cm3 molecule−1 s−1. In order to make the chamber studies more comparable among each other as well as to atmospheric measurements we suggest the use of a chemical (time dimension: the OH clock, which corresponds to the integrated OH concentration over time.

  9. Pore to Core Scale Simulation of the Mass Transfer with Mineral Reaction in Porous Media

    Directory of Open Access Journals (Sweden)

    Bekri S.

    2015-04-01

    Full Text Available Pore Network Model (PNM is used to simulate mass transfer with mineral reaction in a single phase flow through porous medium which is here a sandstone sample from the reservoir formation of the Pakoslaw gas field. The void space of the porous medium is represented by an idealized geometry of pore-bodies joined by pore-throats. Parameters defining the pore-bodies and the pore-throats distribution are determined by an optimization process aiming to match the experimental Mercury Intrusion Capillary Pressure (MICP curve and petrophysical properties of the rock such as intrinsic permeability and formation factor. The generated network is used first to simulate the multiphase flow by solving Kirchhoff’s laws. The capillary pressure and relative permeability curves are derived. Then, reactive transport is addressed under asymptotic regime where the solute concentration undergoes an exponential evolution with time. The porosity/permeability relationship and the three phenomenological coefficients of transport, namely the solute velocity, the dispersion and the mean reaction rate are determined as functions of Peclet and Peclet-Damköhler dimensionless numbers. Finally, the role of the dimensionless numbers on the reactive flow properties is highlighted.

  10. Spectroscopy of Rn, Ra and Th isotopes using multi-nucleon transfer reactions

    CERN Document Server

    Cocks, J F C; Amzal, N; Butler, P A; Cann, K J; Greenlees, P T; Jones, G D; Asztalos, S; Clark, R M; Deleplanque, M A; Diamond, R M; Fallon, P; Lee, I Y; Macchiavelli, A O; MacLeod, R W; Stephens, F S; Jones, P; Julin, R; Broda, R; Fornal, B; Smith, J F; Lauritsen, T; Bhattacharya, P; Zhang, C T

    1999-01-01

    High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a sup 2 sup 3 sup 2 Th target and a sup 1 sup 3 sup 6 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin (approx 28(Planck constant/2 pi)) in sup 2 sup 1 sup 8 sup , sup 2 sup 2 sup 0 sup , sup 2 sup 2 sup 2 Rn, sup 2 sup 2 sup 2 sup , sup 2 sup 2 sup 4 sup , sup 2 sup 2 sup 6 sup , sup 2 sup 2 sup 8 Ra and sup 2 sup 2 sup 8 sup , sup 2 sup 3 sup 0 sup , sup 2 sup 3 sup 4 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational frequency. Measurement of the magnitude of the intrinsic electric dipole moment, D sub 0 , provides addi...

  11. Rapid hydrogen and oxygen atom transfer by a high-valent nickel-oxygen species

    NARCIS (Netherlands)

    Corona, Teresa; Draksharapu, Apparao; Padamati, Sandeep K; Gamba, Ilaria; Martin-Diaconescu, Vlad; Acuña-Parés, Ferran; Browne, Wesley R; Company, Anna

    2016-01-01

    Terminal high-valent metal-oxygen species are key reaction intermediates in the catalytic cycle of both enzymes (e.g., oxygenases) and synthetic oxidation catalysts. While tremendous efforts have been directed towards the characterization of the biologically relevant terminal manganese-oxygen and

  12. Tuning of electron transfer reactions in pluronic-surfactant supramolecular assemblies.

    Science.gov (United States)

    Verma, Poonam; Pal, Haridas

    2015-06-21

    Photoinduced electron transfer (ET) reaction between an anionic acceptor, coumarin-343 (C343), and a neutral donor, N,N-dimethylaniline (DMAN), has been investigated in composite supramolecular assemblies (mixed micelles) comprised of a pluronic copolymer (P123: EO20-PO70-EO20 or F88: EO103-PO39-EO103 where EO: ethylene oxide and PO: propylene oxide) and a cationic surfactant (CTAC: cetyltrimethylammonium chloride), following fluorescence quenching studies. Systematic increase in the quenching rates for the studied donor-acceptor system with the increasing CTAC to pluronic molar ratio in the mixed micelles demonstrates a large modulation in the ET rates. The mixed micellar systems in the present cases are formed through the incorporation of the hydrocarbon chains of CTAC into the poly-PO core of the pluronic micelles whereby the cationic head groups of CTAC are placed at the periphery of the micellar core, protruded into the hydrated poly-EO corona region, leading to the formation of a positively charged layer deep inside these mixed micelles. Thus, the anionic C343 dye, initially dissolved at the micelle-water interface, experiences a gradually increasing electrostatic attraction and is therefore systematically dragged deeper inside the micellar corona, as the CTAC composition is increased in the mixed micellar systems. Consequently, the ET rate of the C343-DMAN pair undergoes a large enhancement in the studied mixed micellar systems with the increasing CTAC to pluronic molar ratio. The present strategy of modulating ET reactions using such composite supramolecular assemblies can find applications in areas where bimolecular ET is an integral reaction step.

  13. Reactions of substituted benzene anions with N and O atoms: Chemistry in Titan’s upper atmosphere and the interstellar medium

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhe-Chen; Bierbaum, Veronica M. [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States)

    2016-06-07

    The likely existence of aromatic anions in many important extraterrestrial environments, from the atmosphere of Titan to the interstellar medium (ISM), is attracting increasing attention. Nitrogen and oxygen atoms are also widely observed in the ISM and in the ionospheres of planets and moons. In the current work, we extend previous studies to explore the reactivity of prototypical aromatic anions (deprotonated toluene, aniline, and phenol) with N and O atoms both experimentally and computationally. The benzyl and anilinide anions both exhibit slow associative electron detachment (AED) processes with N atom, and moderate reactivity with O atom in which AED dominates but ionic products are also formed. The reactivity of phenoxide is dramatically different; there is no measurable reaction with N atom, and the moderate reactivity with O atom produces almost exclusively ionic products. The reaction mechanisms are studied theoretically by employing density functional theory calculations, and spin conversion is found to be critical for understanding some product distributions. This work provides insight into the rich gas-phase chemistry of aromatic ion-atom reactions and their relevance to ionospheric and interstellar chemistry.

  14. The measurement of cross sections of inelastic and transfer reactions with gamma-particle coincidence

    Energy Technology Data Exchange (ETDEWEB)

    Zagatto, V.A.B.; Oliveira, J.R.B.; Pereira, D.; Allegro, P.R.P.; Chamon, L.C.; Cybulska, E.W.; Medina, N.H.; Ribas, R.V.; Rossi Junior, E.S.; Seale, W.A.; Silva, C.P.; Gasques, L. [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica; Toufen, D.L. [Instituto Federal de Educacao, Ciencia e Tecnologia, Guarulhos, SP (Brazil); Silveira, M.A.G. [Centro Universitario da FEI, Sao Bernardo do Campo, SP (Brazil); Zahn, G.S.; Genezini, F.A.; Shorto, J.M.B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Lubian, J.; Linares, R. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica; Nobre, G.P. [Lawrence Livermore National Laboratory, Livermore (United States)

    2012-07-01

    Full text: A new method was developed in Pelletron laboratory to measure gamma-particle coincidences and the chosen experiment to test this method was the {sup 18}O +{sup 110} Pd in the 46-60 MeV range. The following work aims to obtain experimental cross sections of inelastic excitation 0{sup +} {yields} 2{sup +} of {sup 110}Pd and transfer to excited states reactions (both measured by gamma-particle coincidences). The measurements were made at the Pelletron accelerator laboratory of the University of Sao Paulo with the Saci-Perere spectrometer [1], which consists of 4 GeHP Compton suppressed gamma detectors and a 4{pi} charged particle ancillary system with 11{Delta}E-E plastic phoswich scintillators (further details about the experimental procedure may be found in [2]). Calculations were performed with a new model based on the Sao Paulo Potential, specifically developed for the inclusion of dissipative processes like deep-inelastic collisions (DIC) [3,4] considering the Coulomb plus nuclear potential (with the aid of FRESCO code [5]). The experimental cross sections were obtained such as described in [6] including particle-gamma angular correlations, finite size of gamma and particle detectors as the vacuum de-alignment effects [7] (caused by hyperfine interaction) for the {sup 110}Pd inelastic reaction and for the {sup 110}Pd 2n transfer reaction. Also the effects of the beam spot size and energy loss in the target were included in these calculations. For these purposes a new code has been developed to assist in the data analysis. The gamma-particle angular correlations are calculated using the scattering amplitudes given by FRESCO. The theoretical predictions still consider 2 different types of normalization factors in its the real part: 1:0, and 0:6 as proposed in [3] for the weakly bound projectile cases. The analyses indicate that the 0:6 factor describes better the experimental data possible due to the large density of states in the transitional region. [1

  15. Colloidal polymer particles as catalyst carriers and phase transfer agents in multiphasic hydroformylation reactions.

    Science.gov (United States)

    Peral, D; Stehl, D; Bibouche, B; Yu, H; Mardoukh, J; Schomäcker, R; Klitzing, R von; Vogt, D

    2017-11-29

    Colloidal particles have been used to covalently bind ligands for the heterogenization of homogeneous catalysts. The replacement of the covalent bonds by electrostatic interactions between particles and the catalyst could preserve the selectivity of a truly homogeneous catalytic process. Functionalized polymer particles with trimethylammonium moieties, dispersed in water, with a hydrophobic core and a hydrophilic shell have been synthesized by emulsion polymerization and have been thoroughly characterized. The ability of the particles with different monomer compositions to act as catalyst carriers has been studied. Finally, the colloidal dispersions have been applied as phase transfer agents in the multiphasic rhodium-catalyzed hydroformylation of 1-octene. The hydrodynamic radius of the particles has been shown to be around 100 nm, and a core-shell structure could be observed by atomic force microscopy. The polymer particles were proven to act as carriers for the water-soluble hydroformylation catalyst, due to electrostatic interaction between the functionalized particles bearing ammonium groups and the sulfonated ligands of the catalyst. The particles were stable under the hydroformylation conditions and the aqueous catalyst phase could be recycled three times. Copyright © 2017 Elsevier Inc. All rights reserved.

  16. The Reaction between Sodium Hydroxide and Atomic Hydrogen in Atmospheric and Flame Chemistry.

    Science.gov (United States)

    Gómez Martín, J C; Seaton, C; de Miranda, M P; Plane, J M C

    2017-10-12

    We report the first direct kinetic study of the gas-phase reaction NaOH + H → Na + H2O, which is central to the chemistry of sodium in the upper atmosphere and in flames. The reaction was studied in a fast flow tube, where NaOH was observed by multiphoton ionization and time-of-flight mass spectrometry, yielding k(NaOH + H, 230-298 K) = (3.8 ± 0.8) × 10(-11) cm(3) molecule (-1) s(-1) (at 2σ confidence level), showing no significant temperature dependence over the indicated temperature range and essentially in agreement with previous estimates of the rate constant in hydrogen-rich flames. We show, using theoretical trajectory calculations, that the unexpectedly slow, yet T-independent, rate coefficient for NaOH + H is explained by severe constraints in the angle of attack that H can make on NaOH to produce H2O. This reaction is also central to explaining Na-catalyzed flame inhibition, which has been proposed to occur via the sequence Na + OH (+ M) → NaOH followed by NaOH + H → Na + H2O, thereby effectively recombinating H and OH to H2O. RRKM calculations for the recombination of Na and OH yield k(Na + OH + N2, 300-2400 K) = 2.7 × 10(-29) (300/T)(1.2) cm(6) molecule(-2) s(-1), in agreement with a previous flash photolysis measurement at 653 K and Na-seeded flame studies in the 1800-2200 K range. These results therefore provide strong evidence to support the mechanism of flame inhibition by Na.

  17. Influences of chemical reaction and wall properties on MHD Peristaltic transport of a Dusty fluid with Heat and Mass transfer

    Directory of Open Access Journals (Sweden)

    R. Muthuraj

    2016-03-01

    Full Text Available The influence of elasticity of flexible walls on peristaltic transport of a dusty fluid with heat and mass transfer in a horizontal channel in the presence of chemical reaction has been investigated under long wavelength approximation. Expressions have been constructed for stream function, temperature and concentration by using perturbation technique. The effects of various parameters on heat and mass transfer characteristics of the flow are discussed through graphs.

  18. Hetero-atom doped carbon nanotubes for dye degradation and oxygen reduction reaction

    Science.gov (United States)

    Nandan, Ravi; Nanda, Karuna Kar

    2015-06-01

    We report the synthesis of nitrogen doped vertically aligned multi-walled (MWNCNTs) carbon nanotubes by pyrolysis and its catalytic performance for degradation of methylene blue (MB) dye & oxygen reduction reaction (ORR). The degradation of MB was monitored spectrophotometrically with time. Kinetic studies show the degradation of MB follows a first order kinetic with rate constant k=0.0178 min-1. The present rate constant is better than that reported for various supported/non-supported semiconducting nanomaterials. Further ORR performance in alkaline media makes MWNCNTs a promising cost-effective, fuel crossover tolerance, metal-free, eco-friendly cathode catalyst for direct alcohol fuel cell.

  19. Hetero-atom doped carbon nanotubes for dye degradation and oxygen reduction reaction

    Energy Technology Data Exchange (ETDEWEB)

    Nandan, Ravi, E-mail: aerawat27@gmail.com; Nanda, Karuna Kar [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India)

    2015-06-24

    We report the synthesis of nitrogen doped vertically aligned multi-walled (MWNCNTs) carbon nanotubes by pyrolysis and its catalytic performance for degradation of methylene blue (MB) dye & oxygen reduction reaction (ORR). The degradation of MB was monitored spectrophotometrically with time. Kinetic studies show the degradation of MB follows a first order kinetic with rate constant k=0.0178 min{sup −1}. The present rate constant is better than that reported for various supported/non-supported semiconducting nanomaterials. Further ORR performance in alkaline media makes MWNCNTs a promising cost-effective, fuel crossover tolerance, metal-free, eco-friendly cathode catalyst for direct alcohol fuel cell.

  20. 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.

  1. Wave packet motions coupled to electron transfer in reaction centers of Chloroflexus aurantiacus.

    Science.gov (United States)

    Yakovlev, Andrei G; Shkuropatova, Tatiana A; Vasilieva, Lyudmila G; Shkuropatov, Anatoli Ya; Shuvalov, Vladimir A

    2008-08-01

    Transient absorption difference spectroscopy with approximately 20 femtosecond (fs) resolution was applied to study the time and spectral evolution of low-temperature (90 K) absorbance changes in isolated reaction centers (RCs) of Chloroflexus (C.) aurantiacus. In RCs, the composition of the B-branch chromophores is different with respect to that of purple bacterial RCs by occupying the B(B) binding site of accessory bacteriochlorophyll by bacteriopheophytin molecule (Phi(B)). It was found that the nuclear wave packet motion induced on the potential energy surface of the excited state of the primary electron donor P* by approximately 20 fs excitation leads to a coherent formation of the states P+Phi(B)(-) and P+B(A)(-) (B(A) is a bacteriochlorophyll monomer in the A-branch of cofactors). The processes were studied by measuring coherent oscillations in kinetics of the absorbance changes at 900 nm and 940 nm (P* stimulated emission), at 750 nm and 785 nm (Phi(B) absorption bands), and at 1,020-1028 nm (B(A)(-) absorption band). In RCs, the immediate bleaching of the P band at 880 nm and the appearance of the stimulated wave packet emission at 900 nm were accompanied (with a small delay of 10-20 fs) by electron transfer from P* to the B-branch with bleaching of the Phi(B) absorption band at 785 nm due to Phi(B)(-) formation. These data are consistent with recent measurements for the mutant HM182L Rb. sphaeroides RCs (Yakovlev et al., Biochim Biophys Acta 1757:369-379, 2006). Only at a delay of 120 fs was the electron transfer from P* to the A-branch observed with a development of the B(A)(-) absorption band at 1028 nm. This development was in phase with the appearance of the P* stimulated emission at 940 nm. The data on the A-branch electron transfer in C. aurantiacus RCs are consistent with those observed in native RCs of Rb. sphaeroides. The mechanism of charge separation in RCs with the modified B-branch pigment composition is discussed in terms of coupling between

  2. Local Structure of Electric Double Layer at Electrode/Electrolyte Interface∼For better understanding of electron transfer reaction at the interfaces∼

    Science.gov (United States)

    Fukui, Ken-Ichi

    For the electron transfer reaction of a molecule at the electrode/electrolyte interface, local distribution of ions, which determines the stability of the molecule at each moment, is much more important than the average electric double layer determined by the electrode potential. Recently we have developed electrochemical frequency-modulation atomic force microscopy (EC-FM-AFM), which is applicable to analyses of electrochemical systems by independent potential control of the sample and the tip with an advantage in high spatial resolution at low loading forces. We have applied this technique for the analyses of local structure of electric double layer at the electrode modified by redox-active molecules in HClO4 aqueous solution and found the redox-state dependent reversible change in topography and energy dissipation.

  3. Single-particle detection of products from atomic and molecular reactions in a cryogenic ion storage ring

    Science.gov (United States)

    Krantz, C.; Novotný, O.; Becker, A.; George, S.; Grieser, M.; Hahn, R. von; Meyer, C.; Schippers, S.; Spruck, K.; Vogel, S.; Wolf, A.

    2017-04-01

    We have used a single-particle detector system, based on secondary electron emission, for counting low-energetic (∼keV/u) massive products originating from atomic and molecular ion reactions in the electrostatic Cryogenic Storage Ring (CSR). The detector is movable within the cryogenic vacuum chamber of CSR, and was used to measure production rates of a variety of charged and neutral daughter particles. In operation at a temperature of ∼ 6 K , the detector is characterised by a high dynamic range, combining a low dark event rate with good high-rate particle counting capability. On-line measurement of the pulse height distributions proved to be an important monitor of the detector response at low temperature. Statistical pulse-height analysis allows to infer the particle detection efficiency of the detector, which has been found to be close to unity also in cryogenic operation at 6 K.

  4. Accelerated Oxygen Atom Transfer and C-H Bond Oxygenation by Remote Redox Changes in Fe3Mn-Iodosobenzene Adducts.

    Science.gov (United States)

    de Ruiter, Graham; Carsch, Kurtis M; Gul, Sheraz; Chatterjee, Ruchira; Thompson, Niklas B; Takase, Michael K; Yano, Junko; Agapie, Theodor

    2017-04-18

    We report the synthesis, characterization, and reactivity of [LFe 3 (PhPz) 3 OMn( s PhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene-metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57 Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2 Fe II Mn II vs. Fe III 3 Mn II ) influence oxygen atom transfer in tetranuclear Fe 3 Mn clusters. In particular, a one-electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Bottom-Up Fabrication of Nanopatterned Polymers on DNA Origami by In Situ Atom-Transfer Radical Polymerization.

    Science.gov (United States)

    Tokura, Yu; Jiang, Yanyan; Welle, Alexander; Stenzel, Martina H; Krzemien, Katarzyna M; Michaelis, Jens; Berger, Rüdiger; Barner-Kowollik, Christopher; Wu, Yuzhou; Weil, Tanja

    2016-05-04

    Bottom-up strategies to fabricate patterned polymers at the nanoscale represent an emerging field in the development of advanced nanodevices, such as biosensors, nanofluidics, and nanophotonics. DNA origami techniques provide access to distinct architectures of various sizes and shapes and present manifold opportunities for functionalization at the nanoscale with the highest precision. Herein, we conduct in situ atom-transfer radical polymerization (ATRP) on DNA origami, yielding differently nanopatterned polymers of various heights. After cross-linking, the grafted polymeric nanostructures can even stably exist in solution without the DNA origami template. This straightforward approach allows for the fabrication of patterned polymers with low nanometer resolution, which provides access to unique DNA-based functional hybrid materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Polymeric nanocapsules with controllable crosslinking degree via combination of surface-initiated atom transfer radical polymerisation and photocrosslinking techniques.

    Science.gov (United States)

    Liu, Peng; Mu, Bin; Du, Pengcheng; Hong, Zhilai

    2013-06-01

    The crosslinked polystyrene nanocapsules with controllable crosslinking degree have been prepared by the ultraviolet (UV)-induced photocrosslinking of the polystyrene grafted silica nanoparticles (SN-PS), which was obtained by the surface-initiated atom transfer radical polymerisation of styrene from the modified silica nanoparticle templates, after the silica templates were etched with hydrofluoric acid. The effect of the UV-irradiating time on the inner diameter of the nanocapsules, and the degree of crosslinking and the thickness of the shells was investigated. The dynamic light scattering results showed that the degree of crosslinking of the obtained nanocapsules increased with the prolongation of the UV-irradiation time, therefore the inner diameter of the nanocapsules increased. However, the percentage of grafting of the crosslinked polymer shells decreased with increasing the UV-irradiation time because of the photodecomposition of the polystyrene grafted during the UV-irradiated crosslinking process, according to the thermogravimetric analysis.

  7. Atomic scattering in the diffraction limit: electron transfer in keV Li+-Na(3s, 3p) collisions

    DEFF Research Database (Denmark)

    Poel, Mike van der; Nielsen, C.V.; Rybaltover, M.

    2002-01-01

    We measure angle differential cross sections (DCS) in Li+ + Na --> Li + Na+ electron transfer collisions in the 2.7-24 keV energy range. We do this with a newly constructed apparatus which combines the experimental technique of cold target recoil ion momentum spectroscopy with a laser-cooled target...... of the de Broglie wavelength lambda(dB) = 150 fm at a velocity v = 0.20 au and the effective atomic diameter for electron capture 2R = 20 au. Parallel AO and MO semiclassical coupled-channel calculations of the Na(3s, 3p) --> Li(2s, 2p) state-to-state collision amplitudes have been performed, and quantum...

  8. Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide.

    Science.gov (United States)

    Kumar, Mukesh; Chung, Jin Suk; Hur, Seung Hyun

    2014-01-01

    We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a 'grafting from' technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (T g) than those of pristine PMMA.

  9. Phenyl Benzo[b]phenothiazine as a Visible Light Photoredox Catalyst for Metal-Free Atom Transfer Radical Polymerization.

    Science.gov (United States)

    Dadashi-Silab, Sajjad; Pan, Xiangcheng; Matyjaszewski, Krzysztof

    2017-05-02

    This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Achieving highly effective nonfouling performance for surface-grafted poly(HPMA) via atom-transfer radical polymerization.

    Science.gov (United States)

    Zhao, Chao; Li, Lingyan; Zheng, Jie

    2010-11-16

    Human blood plasma and serum pose significant challenges to implanted devices because of highly unfavorable nonspecific protein adsorption on the surface. In this work, we introduce an improved two-step method to immobilize initiator thiols on a gold substrate for the surface-initiated atom-transfer radical polymerization (SI-ATRP) of hydroxypropyl methacrylate (HPMA). We investigate protein adsorption from a single-protein solution, diluted (10%) and undiluted (100%) human blood plasma, and serum on the poly(HPMA) brushes with different film thicknesses using surface plasmon resonance (SPR) sensors. SPR results show a correlation between antifouling properties and film thickness; that is, the poly(HPMA) brushes exhibit high protein resistance at medium film thicknesses of ∼25-40 nm (e.g. HPMA) brush also demonstrates its high resistance to fibroblast adhesion. This work provides an alternative surface polymerization approach to preparing effective antifouling poly(HPMA) materials for potential applications in blood-contacting medical devices.

  11. Synthesis of tri-block copolymers through reverse atom transfer radical polymerization of methyl methacrylate using polyurethane macroiniferter

    Directory of Open Access Journals (Sweden)

    2008-08-01

    Full Text Available Reverse atom transfer radical polymerization was successfully used for the first time to synthesis tri-block copolymers. Poly (methyl methacrylate-block-polyurethane-block-poly (methyl methacrylate tri-block copolymers were synthesized using tetraphenylethane-based polyurethane as a macroiniferter, copper(II halide as a catalyst and N, N, N′, N″, N″-pentamethyldiethylenetriamine as a ligand. Controlled nature of the polymerization was confirmed by the linear increase of number average molecular weight with increasing conversion. Mole contents of poly (methyl methacrylate present in the tri-block copolymers were calculated using proton nuclear magnetic resonance spectroscopy and the results were comparable with the gel permeation chromatography results. Differential scanning calorimetric results confirmed the presence of two different types of blocks in the tri-block copolymers.

  12. The electronic structure of the primary electron donor of reaction centers of purple bacteria at atomic resolution as observed by photo-CIDNP 13C NMR.

    Science.gov (United States)

    Daviso, Eugenio; Prakash, Shipra; Alia, A; Gast, Peter; Neugebauer, Johannes; Jeschke, Gunnar; Matysik, Jörg

    2009-12-29

    Composed of the two bacteriochlorophyll cofactors, P(L) and P(M), the special pair functions as the primary electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the electronic ground state, P(L) is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total electron spin densities between P(L) and P(M) is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of P(L). The significant difference in electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine.

  13. Reaction microscopes applied to study atomic and molecular fragmentation in intense laser fields: non-sequential double ionization of helium

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, V.L.B. de [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Rudenko, A. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Feuerstein, B. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Zrost, K. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Schroeter, C.D. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Moshammer, R. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Ullrich, J. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)]. E-mail: joachim.ullrich@mpi-hd.mpg.de

    2004-12-01

    'Reaction Microscopes' enable to detect the momentum vectors of several electrons and ions after the fragmentation of atoms or molecules. Thus, the investigation of pathways to single and multiple electron ejection in femtosecond PW/cm{sup 2} laser fields has become experimentally accessible in unprecedented detail. In this paper, a newly designed machine is described, resolutions achieved for electrons and ions are discussed and examples are given for many-particle fragmentation of atoms and molecules. Moreover, for helium, new results on single as well as first multiple differential data on double ionization are presented. Covering a wide intensity range within the 'non-sequential' (NS) double ionization regime, the importance of different NS double ionization mechanisms is explored as a function of the laser intensity. Contributions due to recollision-excitation plus subsequent field ionization (RESI) are identified and correlated electron emission spectra are discussed in the longitudinal as well as transverse directions. Whereas only weak indications of Coulomb-repulsion between the electrons in the final state are observed the emitted electrons are found to be strongly correlated with the ions.

  14. Experimental and theoretical studies of the reactions of ground-state sulfur atoms with hydrogen and deuterium

    Science.gov (United States)

    Thompson, Kristopher M.; Gao, Yide; Marshall, Paul; Wang, Han; Zhou, Linsen; Li, Yongle; Guo, Hua

    2017-10-01

    The gas-phase kinetics of S(3P) atoms with H2 and D2 have been studied via the laser flash photolysis—resonance fluorescence technique. S atoms were generated by pulsed photolysis of CS2 at 193 nm and monitored by time-resolved fluorescence at 181 nm. The rate coefficients for H2 (k1) and D2 (k2), respectively, are summarized as k1(600-1110 K) = 3.0 × 10-9 exp(-1.317/×105-2.703 ×107K /T 8.314 T /K ) cm3 molecule-1 s-1 and k2(770-1110 K) = 2.2 × 10-14 (T/298 K)3.55 exp(-5420 K/T) cm3 molecule-1 s-1. Error limits are discussed in the text. The rate coefficients for formation of SH(SD) + H(D) on a newly developed triplet potential energy surface were characterized via ring polymer molecular dynamics and canonical variational transition-state theory. There is excellent agreement above about 1000 K between theory and experiment. At lower temperatures, the experimental rate coefficient is substantially larger than the results computed for the adiabatic reaction, suggesting a significant role for intersystem crossing to the singlet potential energy surface at lower temperatures.

  15. Poly(vinyl acetate-Based Block Copolymer/Clay Nanocomposites Prepared by In Situ Atom Transfer Radical Polymerization

    Directory of Open Access Journals (Sweden)

    M.A. Semsarzadeh

    2009-12-01

    Full Text Available Atom transfer radical polymerization of styrene (St and methyl methacrylate (MMA was performed at 90oC in the absence and presence of nanoclay (Cloisite 30B. Trichloromethyl-terminated poly(vinyl acetate telomerand CuCl/ PMDETA were used as a macroinitiator and catalyst system, respectively. The experimental results showed that the atom transfer radical polymerization of St and MMA in the absence or presence of nanoclay proceeds via a controlled/living mode. It was observed that nanoclay significantly enhances the homopolymerization rate of MMA, which was attributed to the activated conjugated C=C bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (Al-O-H of nanoclay as well as the effect of nanoclay on the dynamic equilibrium between the active (macro radicals and dormant species.Homopolymerization rate of St (a non-coordinative monomer with nanoclay decreased slightly in the presence of nanoclay. This could be explained by insertion of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. The results obtained from XRD, TEM and TGA analyses were fully in agreement with the kinetic data. Structure of the poly(vinyl acetate-bpolystyrene nanocomposite was found to be a combination of stacking layers and exfoliated structures while poly(vinyl acetate-b-poly(methyl methacryale nanocomposite had an exfoliated structure. This difference in the structure of nanocomposites was attributed to the different capability of the monomers (styrene and methyl methacrylate to react with the hydroxyl moiety (Al-O-H of nanoclay.

  16. Surface polyPEGylation of Eu{sup 3+} doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Guangjian; Liu, Meiying [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Heng, Chunning [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Shaanxi Key Laboratory of Degradable Biomedical Materials, Shaanxi R& D Center of Biomaterials and Fermentation Engineering, School of Chemical and Engineering, Northwest University, Xi’an 710069 (China); Huang, Qiang; Mao, Liucheng; Huang, Hongye [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Hui, Junfeng [Shaanxi Key Laboratory of Degradable Biomedical Materials, Shaanxi R& D Center of Biomaterials and Fermentation Engineering, School of Chemical and Engineering, Northwest University, Xi’an 710069 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and The Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing 100084 (China)

    2017-03-31

    Highlights: • Surface modification of HAp nanorods through the combination of ligand exchange reaction and metal free SI-ATRP. • HAp-polyPEGMA displayed high water dispersibility, good biocompatibility and biological imaging capability. • Metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts of conventional ATRP. - Abstract: The Eu{sup 3+} doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu{sup 3+} doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface

  17. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jingjing, E-mail: jjwang1@hotmail.com; Wei, Jun

    2016-09-30

    Highlights: • Crosslinked hydrogel brushes were grafted from SS surfaces for marine antifouling. • All brush-coated SS surfaces could effectively reduce the adhesion of biofouling. • The antifouling efficacy increased with the crosslinking density of hydrogels. - Abstract: Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  18. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    Science.gov (United States)

    Wang, Jingjing; Wei, Jun

    2016-09-01

    Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  19. Study of gas-phase reactions of NO2+ with aromatic compounds using proton transfer reaction time-of-flight mass spectrometry.

    Science.gov (United States)

    Li, Jianquan; Du, Xubing; Guo, Teng; Peng, Zhen; Xu, Li; Dong, Junguo; Cheng, Ping; Zhou, Zhen

    2017-12-01

    The study of ion chemistry involving the NO2+ is currently the focus of considerable fundamental interest and is relevant in diverse fields ranging from mechanistic organic chemistry to atmospheric chemistry. A very intense source of NO2+ was generated by injecting the products from the dielectric barrier discharge of a nitrogen and oxygen mixture upstream into the drift tube of a proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) apparatus with H3 O+ as the reagent ion. The NO2+ intensity is controllable and related to the dielectric barrier discharge operation conditions and ratio of oxygen to nitrogen. The purity of NO2+ can reach more than 99% after optimization. Using NO2+ as the chemical reagent ion, the gas-phase reactions of NO2+ with 11 aromatic compounds were studied by PTR-TOF-MS. The reaction rate coefficients for these reactions were measured, and the product ions and their formation mechanisms were analyzed. All the samples reacted with NO2+ rapidly with reaction rate coefficients being close to the corresponding capture ones. In addition to electron transfer producing [M]+ , oxygen ion transfer forming [MO]+ , and 3-body association forming [M·NO2 ]+ , a new product ion [M-C]+ was also formed owing to the loss of C═O from [MO]+ .This work not only developed a new chemical reagent ion NO2+ based on PTR-MS but also provided significant interesting fundamental data on reactions involving aromatic compounds, which will probably broaden the applications of PTR-MS to measure these compounds in the atmosphere in real time. Copyright © 2017 John Wiley & Sons, Ltd.

  20. Enhancement of nucleate pool boiling heat transfer to dilute binary mixtures using endothermic chemical reactions around the smoothed horizontal cylinder

    Science.gov (United States)

    Sarafraz, M. M.; Peyghambarzadeh, S. M.; Alavifazel, S. A.

    2012-10-01

    Experimental studies on enhancing the pool boiling heat transfer coefficient of binary dilute mixtures of water/glycerol, water/MEG (Mono-ethylene glycol) and water/DEG (di-ethylene glycol) have been carried out. Some particular endothermic chemical reactions related to ammonium salts were used to enhance the pool boiling heat transfer coefficient, simultaneously with occurrence of pool boiling heat transfer. Accordingly, 100 g of Ammonium nitrate, ammonium perborate and Ammonium sulfate were selected to dissolve into mixtures. High and extreme solution enthalpies of each of these ammonium salt powders are employed to reduce the surface temperature around the horizontal cylinder locally. Results demonstrated that presence of ammonium salts into the mixtures deteriorates the surface temperature of cylinder and as the result, higher pool boiling heat transfer coefficient is reported for tested solutions. Results are also reported and compared for different ammonium salts to find the influence of inducing different enthalpies of solution on pool boiling heat transfer coefficient. Obtained results also indicated that presence of endothermic reaction besides the pool boiling heat transfer enhances the heat transfer coefficients in comparison with nucleate pool boiling phenomenon solely.

  1. Investigation of the Cleavage of the Ester Bond in Phosphate Monoesters: Enzymatic and Solution Studies of Phosphoryl Transfer Reactions and Comparison with Analogous Sulfuryl Transfer Reactions

    National Research Council Canada - National Science Library

    Hoff, Richard

    1999-01-01

    .... The role of solvation was explored by a series of experiments using the extrathermodynamic assumption, which allowed a detailed thermodynamic accounting for the effects of solvent on the reaction...

  2. 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

  3. Control and Automation of Fluid Flow, Mass Transfer and Chemical Reactions in Microscale Segmented Flow

    Science.gov (United States)

    Abolhasani, Milad

    Flowing trains of uniformly sized bubbles/droplets (i.e., segmented flows) and the associated mass transfer enhancement over their single-phase counterparts have been studied extensively during the past fifty years. Although the scaling behaviour of segmented flow formation is increasingly well understood, the predictive adjustment of the desired flow characteristics that influence the mixing and residence times, remains a challenge. Currently, a time consuming, slow and often inconsistent manual manipulation of experimental conditions is required to address this task. In my thesis, I have overcome the above-mentioned challenges and developed an experimental strategy that for the first time provided predictive control over segmented flows in a hands-off manner. A computer-controlled platform that consisted of a real-time image processing module within an integral controller, a silicon-based microreactor and automated fluid delivery technique was designed, implemented and validated. In a first part of my thesis I utilized this approach for the automated screening of physical mass transfer and solubility characteristics of carbon dioxide (CO2) in a physical solvent at a well-defined temperature and pressure and a throughput of 12 conditions per hour. Second, by applying the segmented flow approach to a recently discovered CO2 chemical absorbent, frustrated Lewis pairs (FLPs), I determined the thermodynamic characteristics of the CO2-FLP reaction. Finally, the segmented flow approach was employed for characterization and investigation of CO2-governed liquid-liquid phase separation process. The second part of my thesis utilized the segmented flow platform for the preparation and shape control of high quality colloidal nanomaterials (e.g., CdSe/CdS) via the automated control of residence times up to approximately 5 minutes. By introducing a novel oscillatory segmented flow concept, I was able to further extend the residence time limitation to 24 hours. A case study of a

  4. Poly(glycidyl methacrylate) grafted CdSe quantum dots by surface-initiated atom transfer radical polymerization: Novel synthesis, characterization, properties, and cytotoxicity studies

    Energy Technology Data Exchange (ETDEWEB)

    Bach, Long Giang; Islam, Md. Rafiqul [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of); Lee, Doh Chang [Department of Chemical and Biomolecular Engineering, KAIST Institute for the Nanocentury (KINC), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Lim, Kwon Taek, E-mail: ktlim@pknu.ac.kr [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of)

    2013-10-15

    A novel approach for the synthesis of poly(glycidyl methacrylate) grafted CdSe quantum dot (QDs) (PGMA-g-CdSe) was developed. The PGMA-g-CdSe nanohybrids were synthesized by the surface-initiated atom transfer radical polymerization of glycidyl methacrylate from the surface of the strategic initiator, CdSe-BrIB QDs prepared by the interaction of 2-bromoisobutyryl bromide (BrIB) and CdSe-OH QDs. The structure, morphology, and optical property of the PGMA-g-CdSe nanohybrids were analyzed by FT-IR, XPS, TGA, XRD, TEM, and PL. The as-synthesized PGMA-g-CdSe nanohybrids having multi-epoxide groups were employed for the direct coupling of biotin via ring-opening reaction of the epoxide groups to afford the Biotin-f-PGMA-g-CdSe nanobioconjugate. The covalent immobilization of biotin onto PGMA-g-CdSe was confirmed by FT-IR, XPS, and EDX. Biocompatibility and imaging properties of the Biotin-f-PGMA-g-CdSe were investigated by MTT bioassay and PL analysis, respectively. The cell viability study suggested that the biocompatibility was significantly enhanced by the functionalization of CdSe QDs by biotin and PGMA.

  5. A combination of "thiol-ene" click chemistry and surface initiated atom transfer radical polymerization: Fabrication of boronic acid functionalized magnetic graphene oxide composite for enrichment of glycoproteins.

    Science.gov (United States)

    Su, Jie; He, Xiwen; Chen, Langxing; Zhang, Yukui

    2018-04-01

    An efficient glycoproteins enrichment platform is one of vital preprocessing steps in biomarker research and in particular glycoproteomics. In this work, a well-defined boronic acid functionalized magnetic graphene oxide nanocomposite (Fe3O4-GO@PAAPBA) was synthesized for the selective enrichment of glycoproteins from complex biological samples via a novel strategy based on the "thiol-ene" click chemistry and surface initiated atom transfer radical polymerization (SI-ATRP). The initiator of ATRP was anchored to the surface of substrate through "thiol-ene" click reaction. The product Fe3O4-GO@PAAPBA was successfully synthesized in following SI-ATRP. The Fe3O4-GO@PAAPBA nanocomposite was characterized by transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and thermogravimetric analysis. The adsorption capacity of Fe3O4-GO@PAAPBA towards ovalbumin (OVA) and transferrin (Trf) is 471mgg-1 and 450mgg-1, respectively. The nanocomposite also featured good selectivity to glycoproteins in the mixture of glycoproteins and non-glycoproteins at alkaline (pH 9.0) and physiological conditions (pH 7.4). Furthermore, it can be applied to extract glycoproteins directly from egg white samples. These results have indicated that Fe3O4-GO@PAAPBA was a potential affinity material in glycoprotein analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Kinetics and energetics of electron transfer in reaction centers of the photosynthetic bacterium Roseiflexus castenholzii.

    Science.gov (United States)

    Collins, Aaron M; Kirmaier, Christine; Holten, Dewey; Blankenship, Robert E

    2011-03-01

    The kinetics and thermodynamics of the photochemical reactions of the purified reaction center (RC)-cytochrome (Cyt) complex from the chlorosome-lacking, filamentous anoxygenic phototroph, Roseiflexus castenholzii are presented. The RC consists of L- and M-polypeptides containing three bacteriochlorophyll (BChl), three bacteriopheophytin (BPh) and two quinones (Q(A) and Q(B)), and the Cyt is a tetraheme subunit. Two of the BChls form a dimer P that is the primary electron donor. At 285K, the lifetimes of the excited singlet state, P*, and the charge-separated state P(+)H(A)(-) (where H(A) is the photoactive BPh) were found to be 3.2±0.3 ps and 200±20 ps, respectively. Overall charge separation P*→→ P(+)Q(A)(-) occurred with ≥90% yield at 285K. At 77K, the P* lifetime was somewhat shorter and the P(+)H(A)(-) lifetime was essentially unchanged. Poteniometric titrations gave a P(865)/P(865)(+) midpoint potential of +390mV vs. SHE. For the tetraheme Cyt two distinct midpoint potentials of +85 and +265mV were measured, likely reflecting a pair of low-potential hemes and a pair of high-potential hemes, respectively. The time course of electron transfer from reduced Cyt to P(+) suggests an arrangement where the highest potential heme is not located immediately adjacent to P. Comparisons of these and other properties of isolated Roseiflexus castenholzii RCs to those from its close relative Chloroflexus aurantiacus and to RCs from the purple bacteria are made. Copyright © 2010 Elsevier B.V. All rights reserved.

  7. Three-dimensional effects in resonant charge transfer between atomic particles and nanosystems

    Science.gov (United States)

    Gainullin, I. K.; Sonkin, M. A.

    2015-08-01

    Resonant charge transfer (RCT) between negative ions and a metallic nanosystem was investigated by means of a high-performance ab initio three-dimensional (3D) numerical solver. During RCT, an electron was shown to occupy succesively nanosystem eigenstates along the z , ρ , and φ coordinates. Electron tunneling into a nanosystem is a reversible process, because after some time the electron propagates back to the ion. RCT efficiency in a nanosystem was found to exhibit quantum-size effects as well as lateral ion position dependence. This means that during ion-surface interaction, the nanosystem's size and the ion trajectory strongly influence the final charge state of the ion. In the case of real 3D systems (without cylindrical symmetry), the electron density currents form quantum vortices; this result is rather nontrivial for static systems. In addition, the limits of the adiabatic approximation (rate equation) for the RCT calculation with nanosystems are defined.

  8. Atomic layer deposition to prevent metal transfer from implants: An X-ray fluorescence study

    Energy Technology Data Exchange (ETDEWEB)

    Bilo, Fabjola [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Borgese, Laura, E-mail: laura.borgese@unibs.itl [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Prost, Josef; Rauwolf, Mirjam; Turyanskaya, Anna; Wobrauschek, Peter; Kregsamer, Peter; Streli, Christina [Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna (Austria); Pazzaglia, Ugo [Dipartimento Specialità Medico Chirurgiche Sc. Radiol. e Sanità Pubblica, University of Brescia, v.le Europa, 11, 25121 Brescia (Italy); Depero, Laura E. [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy)

    2015-12-30

    Highlights: • Co and Cr migrate from bare alloy implant to the surrounding tissue showing a cluster distribution. • Co and Cr migrate from the TiO{sub 2} coated implant to the surrounding tissue showing a decreasing gradient distribution from the alloy surface. • TiO{sub 2} coating layers obtained by ALD on Co–Cr alloy show a barrier effect for the migration of metals. • The thicker the TiO{sub 2} layer deposited by ALD, the lower the metal migration. • The migration of metals from bare alloy toward the surrounding tissue increases with time. This effect is not detected in the coated samples. - Abstract: We show that Atomic Layer Deposition is a suitable coating technique to prevent metal diffusion from medical implants. The metal distribution in animal bone tissue with inserted bare and coated Co–Cr alloys was evaluated by means of micro X-ray fluorescence mapping. In the uncoated implant, the migration of Co and Cr particles from the bare alloy in the biological tissues is observed just after one month and the number of particles significantly increases after two months. In contrast, no metal diffusion was detected in the implant coated with TiO{sub 2}. Instead, a gradient distribution of the metals was found, from the alloy surface going into the tissue. No significant change was detected after two months of aging. As expected, the thicker is the TiO{sub 2} layer, the lower is the metal migration.

  9. Nanosheet Array-Like Palladium-Catalysts Pdx/rGO@CoAl-LDH via Lattice Atomic-Confined in Situ Reduction for Highly Efficient Heck Coupling Reaction.

    Science.gov (United States)

    Wang, Yanna; Dou, Liguang; Zhang, Hui

    2017-11-08

    A series of novel nanosheet array-like catalysts Pdx/rGO@CoAl-LDH (x = 0.0098-1.9, refers to Pd loading in wt % on ICP, rGO: reduced graphene oxide, LDH: layered double hydroxide) were first prepared via a simple and green lattice atomic-confined in situ reduction of oxidative Pd precursors by the evenly atomic-dispersed reductive Co2+ sites on LDH layers of a nanohybrid rGO@CoAl-LDH with hexagonal LDH nanoplates (∼73 × 7 nm) interdigitated vertical to the surfaces of rGO layer in both sides, fabricated through a simple citric acid-assisted aqueous-phase coprecipitation method. The as-obtained Pd catalysts possess clean Pd nanoclusters (NCs) with tunable sizes in 1.3-1.8 nm on varied Pd loadings. All the Pdx/rGO@CoAl-LDH catalysts show excellent activities for the Heck reaction, and the Pd0.0098/rGO@CoAl-LDH with the ultrafine Pd NCs of 1.3 ± 0.2 nm yields a maximum turnover frequency of 160 000 h-1 over a heterogeneous catalyst so far. The excellent activities can be attributed to the ultrasmall Pd NCs with high dispersion and clean Pd surfaces, increased electron transfer capacity and surface area, and remarkable Pd-CoAl-LDH-rGO three-phase synergistic effect of the present unique nanosheet array-like Pd NCs catalysts. Moreover, the catalyst Pd0.33/rGO@CoAl-LDH shows a broad range of substrate applicability and can be reused more than five runs without obvious loss of activity, giving the present catalysts long-term stability. These findings make the rGO@CoAl-LDH hybrid prepared by a facile and scalable synthesis route a universal green platform to support other noble or nonprecious metal NCs via lattice atomic-confined in situ reduction strategy to construct more desired heterogeneous catalysts.

  10. 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

    The Journal of Chemical Physics : 17 October 2013. Government Purpose...Rainer Johnsen, and Albert A. Viggiano Citation: The Journal of Chemical Physics 139, 171102 (2013); doi: 10.1063/1.4828455 View online: http...release; distribution is unlimited. 1 THE JOURNAL OF CHEMICAL PHYSICS 139, 171102 (2013) Communication: Transfer ionization in a thermal reaction of

  11. A simple approach to the solvent reorganisation Gibbs free energy in electron transfer reactions of redox metalloproteins

    DEFF Research Database (Denmark)

    Ulstrup, Jens

    1999-01-01

    We discuss a simple model for the environmental reorganisation Gibbs free energy, E-r, in electron transfer between a metalloprotein and a small reaction partner. The protein is represented as a dielectric globule with low dielectric constant, the metal centres as conducting spheres, all embedded...

  12. Detection of trace gases from fermentation processes using photoacoustic spectroscopy and proton-transfer-reaction mass spectrometry

    NARCIS (Netherlands)

    Boamfă-Ivan, Elena Iuliana

    2005-01-01

    This thesis presents novel interdisciplinary Physics - Biology research work that employed Photoacoustic Spectroscopy and Proton-Transfer-Reaction Mass Spectrometry. Both techniques were used in biological studies of trace gasses emitted by crop plants and fruit under stress situations. The findings

  13. Modeling of mass transfer and chemical reactions in a bubble column reactor using a discrete bubble model

    NARCIS (Netherlands)

    Darmana, D.; Deen, N.G.; Kuipers, J.A.M.

    2004-01-01

    A 3D discrete bubble model is adopted to investigate complex behavior involving hydrodynamics, mass transfer and chemical reactions in a gas-liquid bubble column reactor. In this model a continuum description is adopted for the liquid phase and additionally each individual bubble is tracked in a

  14. Detailed modeling of hydrodynamics mass transfer and chemical reactions in a bubble column using a discrete bubble model

    NARCIS (Netherlands)

    Darmana, D.; Deen, N.G.; Kuipers, J.A.M.

    2005-01-01

    A 3D discrete bubble model is adopted to investigate complex behavior involving hydrodynamics, mass transfer and chemical reactions in a gas¿liquid bubble column reactor. In this model a continuum description is adopted for the liquid phase and additionally each individual bubble is tracked in a

  15. Geographical provenancing of purple grape juices from different farming systems by proton transfer reaction mass spectrometry using supervised statistical techniques

    NARCIS (Netherlands)

    Granato, Daniel; Koot, Alex; Ruth, van S.M.

    2015-01-01

    BACKGROUND: Organic, biodynamic and conventional purple grape juices (PGJ; n = 79) produced in Brazil and Europe were characterized by volatile organic compounds (m/z 20-160) measured by proton transfer reaction mass spectrometry (PTR-MS), and classification models were built using supervised

  16. Heterogeneous electron transfer and oxygen reduction reaction at nanostructured iron(II) phthalocyanine and its MWCNTs nanocomposites

    CSIR Research Space (South Africa)

    Mamuru, SA

    2010-05-01

    Full Text Available species within the porous layers of MWCNTs. Electron transfer process is much easier at the EPPGE-MWCNT and EPPGE-MWCNT-nanoFePc compared to the other electrodes. The best response for oxygen reduction reaction was at the EPPGE-MWCNTnanoFePc, yielding a 4...

  17. In vitro and in vivo volatile flavour analysis of red kidney beans by proton transfer reaction-mass spectrometry

    NARCIS (Netherlands)

    Ruth, van S.M.; Dings, L.; Buhr, K.; Posthumus, M.A.

    2004-01-01

    The volatile flavour released from red kidney beans was evaluated in vitro (in a model mouth system) and in vivo (in-nose). The dynamic release of the volatile flavour compounds was analysed by proton transfer reaction¿mass spectrometry. The flavour compounds were identified by gas

  18. Online monitoring of air quality at the postanesthetic care unit by proton-transfer-reaction mass spectrometry

    NARCIS (Netherlands)

    Rieder, J.; Prazeller, P.; Boehler, M.; Lirk, P.; Lindinger, W.; Amann, A.

    2001-01-01

    The subthreshold exposure to trace anesthetic gases is not associated with considerable risk of adverse health effects. Online control of ambient air exchange at the postoperative workplace may help in supervising air quality and lead to cost reduction. A proton-transfer-reaction mass spectrometer

  19. 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.

  20. Experimental study of the $^{66}$Ni$(d,p)^{67}$Ni one-neutron transfer reaction

    CERN Document Server

    Diriken, J.; Andreyev, A.N.; Antalic, S.; Bildstein, V.; Blazhev, A.; Darby, I.G.; De Witte, H.; Eberth, J.; Elseviers, J.; Fedosseev, V.N.; Flavigny, F.; Fransen, Ch.; Georgiev, G.; Gernhauser, R.; Hess, H.; Huyse, M.; Jolie, J.; Kröll, Th.; Krücken, R.; Lutter, R.; Marsh, B.A.; Mertzimekis, T.; Muecher, D.; Orlandi, R.; Pakou, A.; Raabe, R.; Randisi, G.; Reiter, P.; Roger, T.; Seidlitz, M.; Seliverstov, M.; Sotty, C.; Tornqvist, H.; Van De Walle, J.; Van Duppen, P.; Voulot, D.; Warr, N.; Wenander, F.; Wimmer, K.

    2015-01-01

    The quasi-SU(3) sequence of the positive parity $νg_{9/2}, d_{5/2}, s_{1/2}$ orbitals above the N=40 shell gap are assumed to induce strong quadrupole collectivity in the neutron-rich Fe (Z=26) and Cr (Z=24) isotopes below the nickel region. In this paper the position and strength of these single-particle orbitals are characterized in the neighborhood of $^{68}$Ni (Z=28,N=40) through the $^{66}$Ni($d,p$)$^{67}$Ni one-neutron transfer reaction at 2.95 MeV/nucleon in inverse kinematics, performed at the REX-ISOLDE facility in CERN. A combination of the Miniball $\\gamma$-array and T-REX particle-detection setup was used and a delayed coincidence technique was employed to investigate the 13.3-$\\mu$s isomer at 1007 keV in $^{67}$Ni. Excited states up to an excitation energy of 5.8 MeV have been populated. Feeding of the $νg_{9/2}$ (1007 keV) and $νd_{5/2}$ (2207 keV and 3277 keV) positive-parity neutron states and negative parity ($νpf$) states have been observed at low excitation energy. The extracted relativ...