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Sample records for hydrogen transfer reactions

  1. Hydrogen-Atom Transfer Reactions.

    PubMed

    Wang, Liang; Xiao, Jian

    2016-04-01

    The cascade [1,n]-hydrogen transfer/cyclization, recognized as the tert-amino effect one century ago, has received considerable interest in recent decades, and great achievements have been made. With the aid of this strategy, the inert C(sp(3))-H bonds can be directly functionalized into C-C, C-N, C-O bonds under catalysis of Lewis acids, Brønsted acids, as well as organocatalysts, and even merely under thermal conditions. Hydrogen can be transferred intramolecularly from hydrogen donor to acceptor in the form of hydride, or proton, followed by cyclization to furnish the cyclic products in processes featuring high atom economy. Methylene/methine adjacent to heteroatoms, e.g., nitrogen, oxygen, sulfur, can be exploited as hydride donor as well as methylene/methine without heteroatom assistance. Miscellaneous electrophilic subunits or intermediates, e.g., alkylidene malonate, carbophilic metal activated alkyne or allene, α,β-unsaturated aldehydes/ketone, saturated aldehydes/iminium, ketenimine/carbodiimide, metal carbenoid, electron-withdrawing groups activated allene/alkyne, in situ generated carbocation, can serve as hydride acceptors. This methodology has shown preeminent power to construct 5-, 6-, or 7-membered heterocyclic as well as carbon rings. In this chapter, various hydrogen donors and acceptors are adequately discussed. PMID:27573142

  2. Intramolecular hydrogen transfer reaction: menthon from isopulegol.

    PubMed

    Schaub, Thomas; Rüdenauer, Stefan; Weis, Martine

    2014-05-16

    The flavor menthon (isomeric mixture of (-)-menthon and (+)-isomenthon) was obtained in good yields and selectivities by a solventless ruthenium catalyzed isomerization of the homoallylic alcohol (-)-isopulegol. In contrast to most previous assumptions on such "isomerization" reactions, this reaction follows an intermolecular pathway, with menthol and pulegon being the central intermediates in this transformation. PMID:24779450

  3. Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry.

    PubMed

    Kumar, Manoj; Sinha, Amitabha; Francisco, Joseph S

    2016-05-17

    Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis

  4. Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry.

    PubMed

    Kumar, Manoj; Sinha, Amitabha; Francisco, Joseph S

    2016-05-17

    Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis

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

    SciTech Connect

    Suria, S.

    1995-02-10

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

  6. Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer

    NASA Astrophysics Data System (ADS)

    Herek, J. L.; Pedersen, S.; Bañares, L.; Zewail, A. H.

    1992-12-01

    The real-time dynamics of hydrogen-atom-transfer processes under collisionless conditions are studied using femtosecond depletion techniques. The experiments focus on the methyl salicylate system, which exhibits ultrafast hydrogen motion between two oxygen atoms due to molecular tautomerization, loosely referred to as intramolecular ``proton'' transfer. To test for tunneling and mass effects on the excited potential surface, we also studied deuterium and methyl-group substitutions. We observe that the motion of the hydrogen, under collisionless conditions, takes place within 60 fs. At longer times, on the picosecond time scale, the hydrogen-transferred form decays with a threshold of 15.5 kJ/mol; this decay behavior was observed up to a total vibrational energy of ˜7200 cm-1. The observed dynamics provide the global nature of the motion, which takes into account bonding before and after the motion, and the evolution of the wave packet from the initial nonequilibrium state to the transferred form along the O-H—O reaction coordinate. The vibrational periods (2π/ω) of the relevant modes range from 13 fs (the OH stretch) to 190 fs (the low-frequency distortion) and the motion involves (in part) these coordinates. The intramolecular vibrational-energy redistribution dynamics at longer times are important to the hydrogen-bond dissociation and to the nonradiative decay of the hydrogen-transferred form.

  7. Quantum-chemical ab initio investigation of the two-step charge transfer process of hydrogen reaction: approach of reaction pathways via hydrogen intermediate on Cu(100)

    NASA Astrophysics Data System (ADS)

    Kuznetsov, An. M.; Lorenz, W.

    1994-08-01

    Local reaction events in the course of the electrochemical two-step hydrogen evolution reaction have been investigated by means of quantum-chemical all-electron ab initio calculations on interfacial supermolecular cluster models including a hydrated hydrogen intermediate on Cu(100). Expanding on preceding study to larger hydration clusters, an approach to relevant reaction path characteristics has been pursued for two processes: (i) the transfer of hydrated hydronium ion into a chemisorbed hydrogen intermediate: (ii) the reaction of hydronium ion with the intermediate to molecular hydrogen. Computations were carried out on RHF level, using contracted (12,8,4)/[8,6,2,] and/or 6-31G * or G ** pol-O bases for the metal and adsorbate part, respectively. Destruction of the hydronium configuration in process (i) has been confirmed. Electronic partial charge transfer dut to chemical bond conversions in both steps (i) and (ii) has been displayed along relevant cuts of adiabatic potential surfaces, proving significantly different amounts of charge transfer in both steps, λ 1 > 1, λ 2≡(2-λ 1) < 1. In advance of consideration of macroscopic double layer effects, first insight has been gained into coupled nuclear motions and into the origin of reaction barriers

  8. Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

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

    DOE PAGES

    Zheng, Haiyan; Li, Kuo; Cody, George D.; Tulk, Christopher A.; Dong, Xiao; Gao, Guoying; Molaison, Jamie J.; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; et al

    2016-08-25

    Acetonitrile (CH3CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. In this study, it is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH···N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp2 and sp3more » bonded carbon. Lastly, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst.« less

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

    PubMed

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

    2016-09-19

    Acetonitrile (CH3 CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. It is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH⋅⋅⋅N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp(2) and sp(3) bonded carbon. Finally, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst. PMID:27561179

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

    PubMed

    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 < 332 nm. The obtained results clearly show that H-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

  12. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    SciTech Connect

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-03-10

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydro¬pyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)¬imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reactions of Co and Fe complexes with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer: ΔSºHAT = -30 ± 2 cal mol-1 K-1 for the two iron complexes and -41 ± 2 cal mol-1 K-1 for [CoII(H2bim)3]2+. The ΔSºHAT for TEMPO + RuII(acac)2(py-imH) is much closer to zero, 4.9 ± 1.1 cal mol-1 K-1. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSºHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHºHAT = 11.2 ± 0.5 kcal mol-1 which matches the enthalpy predicted from the difference in literature solution BDEs. An evaluation of the literature BDEs of both TEMPOH and tBu3PhOH is briefly presented and new estimates are included on the relative enthalpy of solvation for tBu3PhO• vs. tBu3PhOH. The primary contributor to the large magnitude of the ground-state entropy |ΔSºHAT| for the metal complexes is vibrational entropy, ΔSºvib. The common assumption that ΔSºHAT ≈ 0 for HAT reactions, developed for organic and small gas phase molecules, does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSºHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSºET, in aprotic solvents. ΔSºET and

  13. Ab initio studies of the reaction of hydrogen transfer from DNA to the calicheamicinone diradical.

    PubMed Central

    Sapse, A. M.; Rothchild, R.; Kumar, R.; Lown, J. W.

    2001-01-01

    BACKGROUND: The biological activity of enediyne chemotherapeutic (anti-cancer) agents is attributed to their ability to cleave duplex DNA. Part of the reaction of cleavage is the abstraction of hydrogens from the deoxyribose moiety of DNA by the biradical formed via a Bergman rearrangement. METHODS: The mechanism of the reaction of abstraction of two hydrogen atoms from two deoxyribophosphate molecules by the calicheamicinone biradical is studied with ab initio calculations at Hartree-Fock and post-Hartree-Fock level. The Titan program is used to perform the calculations. RESULTS: It is found that the reactions are exothermic and thus thermodynamically reasonable. CONCLUSIONS: The mechanism of DNA cleavage by the enediyne-containing drugs is likely to proceed by the abstraction of the hydrogens from deoxyribose by the biradical formed by the drug. Further studies should determine in which way the modification of the drug's structure would make this reaction even more exothermic and, thus, more likely to occur. PMID:11844867

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

    PubMed

    Ishikita, Hiroshi; Saito, Keisuke

    2014-02-01

    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.

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

    PubMed Central

    Ishikita, Hiroshi; Saito, Keisuke

    2014-01-01

    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. PMID:24284891

  16. N-Heterocyclic olefins as ancillary ligands in catalysis: a study of their behaviour in transfer hydrogenation reactions.

    PubMed

    Iturmendi, Amaia; García, Nestor; Jaseer, E A; Munárriz, Julen; Sanz Miguel, Pablo J; Polo, Victor; Iglesias, Manuel; Oro, Luis A

    2016-08-01

    The Ir(i) complexes [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 and [IrCl(cod)(κC-NHO(OMe))] (cod = 1,5-cyclooctadiene, NHO(PPh2) = 1,3-bis(2-(diphenylphosphanyl)ethyl)-2-methyleneimidazoline) and NHO(OMe) = 1,3-bis(2-(methoxyethyl)-2-methyleneimidazoline), both featuring an N-heterocyclic olefin ligand (NHO), have been tested in the transfer hydrogenation reaction; this representing the first example of the use of NHOs as ancillary ligands in catalysis. The pre-catalyst [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 has shown excellent activities in the transfer hydrogenation of aldehydes, ketones and imines using (i)PrOH as a hydrogen source, while [IrCl(cod)(κC-NHO(OMe))] decomposes throughout the reaction to give low yields of the hydrogenated product. Addition of one or two equivalents of a phosphine ligand to the latter avoids catalyst decomposition and significantly improves the reaction yields. The reaction mechanism has been investigated by means of stoichiometric studies and theoretical calculations. The formation of the active species ([Ir(κP,C,P'-NHO(PPh2))((i)PrO)]) has been proposed to occur via isopropoxide coordination and concomitant COD dissociation. Moreover, throughout the catalytic cycle the NHO moiety behaves as a hemilabile ligand, thus allowing the catalyst to adopt stable square planar geometries in the transition states, which reduces the energetic barrier of the process. PMID:27472896

  17. N-Heterocyclic olefins as ancillary ligands in catalysis: a study of their behaviour in transfer hydrogenation reactions.

    PubMed

    Iturmendi, Amaia; García, Nestor; Jaseer, E A; Munárriz, Julen; Sanz Miguel, Pablo J; Polo, Victor; Iglesias, Manuel; Oro, Luis A

    2016-08-01

    The Ir(i) complexes [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 and [IrCl(cod)(κC-NHO(OMe))] (cod = 1,5-cyclooctadiene, NHO(PPh2) = 1,3-bis(2-(diphenylphosphanyl)ethyl)-2-methyleneimidazoline) and NHO(OMe) = 1,3-bis(2-(methoxyethyl)-2-methyleneimidazoline), both featuring an N-heterocyclic olefin ligand (NHO), have been tested in the transfer hydrogenation reaction; this representing the first example of the use of NHOs as ancillary ligands in catalysis. The pre-catalyst [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 has shown excellent activities in the transfer hydrogenation of aldehydes, ketones and imines using (i)PrOH as a hydrogen source, while [IrCl(cod)(κC-NHO(OMe))] decomposes throughout the reaction to give low yields of the hydrogenated product. Addition of one or two equivalents of a phosphine ligand to the latter avoids catalyst decomposition and significantly improves the reaction yields. The reaction mechanism has been investigated by means of stoichiometric studies and theoretical calculations. The formation of the active species ([Ir(κP,C,P'-NHO(PPh2))((i)PrO)]) has been proposed to occur via isopropoxide coordination and concomitant COD dissociation. Moreover, throughout the catalytic cycle the NHO moiety behaves as a hemilabile ligand, thus allowing the catalyst to adopt stable square planar geometries in the transition states, which reduces the energetic barrier of the process.

  18. Imino Transfer Hydrogenation Reductions.

    PubMed

    Wills, Martin

    2016-04-01

    This review contains a summary of recent developments in the transfer hydrogenation of C=N bonds, with a particularly focus on reports from within the last 10 years and asymmetric transformations. However, earlier work in the area is also discussed in order to provide context for the more recent results described. I focus strongly on the Ru/TsDPEN class of asymmetric transfer hydrogenation reactions originally reported by Noyori et al., together with examples of their applications, particularly to medically valuable target molecules. The recent developments in the area of highly active imine-reduction catalysts, notably those based on iridium, are also described in some detail. I discuss diastereoselective reduction methods as a route to the synthesis of chiral amines using transfer hydrogenation. The recent development of a methodology for positioning reduction complexes within chiral proteins, permitting the generation of asymmetric reduction products through a directed modification of the protein environment in a controlled manner, is also discussed. PMID:27573139

  19. Photochemistry and proton transfer reaction chemistry of selected cinnamic acid derivatives in hydrogen bonded environments

    NASA Astrophysics Data System (ADS)

    Huang, Yong; Russell, David H.

    1998-05-01

    Proton transfer reactions between cinnamic acid derivatives (MH) and ammonia are studied using a time-of-flight mass spectrometer equipped with a supersonic nozzle to entrain neutral species formed by 337 nm laser desorption. The supersonic nozzle is used to form clusters of the type MH(NH3)n where n ranges to numbers greater than 20. Multimeric clusters of MH, e.g. MH2(NH3)n are not detected in this experiment or are of low abundance. Photoexcitation of MH(NH3)n clusters by using 355 nm photons yields ionic species that correspond to direct multiphoton ionization, e.g. MH+[middle dot](NH3)n, and proton transfer reactions, e.g. H+(NH3)n. Analogous product ions are formed by photoexcitation of the methylamine, MH(CH3NH2)n, and ammonia/methanol, MH(NH3)(CH3OH)n, clusters. Detailed analysis of energetics data suggests that proton transfer occurs through neutral excited stare species, and a mechanism analogous to one proposed previously is used to rationalize the data. The energetics of proton transfer via a radical cation form of the cinnarnic acid dimer is also consistent with the data. The relevance of this work to fundamental studies of matrix-assisted laser desorption ionization (MALDI) is discussed. In particular, the role of excited state proton transfer (ESPT) in MALDI is discussed.

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

    PubMed

    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.

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

    SciTech Connect

    Brett Kimball Simpson

    2002-08-27

    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 MnO{sub 2} films] revealed that MnO{sub 2} 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 MnO{sub 2} 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 RuO{sub 2} films showed that the Fe(III)-doped RuO{sub 2}-film electrodes are applicable for anodic detection of sulfur compounds. The Fe(III) sites in the Fe-RuO{sub 2} films are speculated to act as adsorption sites for the sulfur species while the Ru(IV) sites function for anodic discharge of H{sub 2}O 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 Sb{sub 10}Sn{sub 20}Ti{sub 70}, Cu{sub 63}Ni{sub 37} and Cu{sub 25}Ni{sub 75} alloy electrodes exhibited improved activity for nitrate reduction as compared to their pure component metals. The Cu{sub 63}Ni{sub 37} 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 NO{sub 3}{sup -} at the Cu-Ni alloy electrode is superior to the response at the pure Cu and Ni electrodes. This is explained on the basis of the

  2. Calculation of High Pressure Effects in Reactions of Hydrogen Transfer from Substituted Toluenes to Bromine Atom

    NASA Astrophysics Data System (ADS)

    Wiebe, Brandon; Spooner, Jacob; Weinberg, Noham

    2013-06-01

    A given reaction may proceed through several different mechanisms, each with its own transition state (TS). These TSs may have similar energies but different geometries and, as a result, different volumes. According to transition state theory, the activation volume (ΔV≠) is the difference between the volume of the TS and the reactants. Experimentally, activation volumes can be obtained from the pressure dependences of the rate constants: -RT(∂ln k/ ∂P)T = Δ V≠ = V≠ - VR By comparing the calculated and experimental activation volumes, one can pick a TS of the right ``size'' and thus elucidate the reaction mechanism by identifying the most likely reaction pathway. It has recently been shown by our research group that molecular dynamics simulations provide a suitable tool for theoretical calculations of activation volumes. In this project we focus on the calculation of the activation volumes for a series of reactions in which an alpha-hydrogen is abstracted from a substituted aromatic hydrocarbon by bromine radical.

  3. Hydrogen evolution reaction catalyst

    DOEpatents

    Subbaraman, Ram; Stamenkovic, Vojislav; Markovic, Nenad; Tripkovic, Dusan

    2016-02-09

    Systems and methods for a hydrogen evolution reaction catalyst are provided. Electrode material includes a plurality of clusters. The electrode exhibits bifunctionality with respect to the hydrogen evolution reaction. The electrode with clusters exhibits improved performance with respect to the intrinsic material of the electrode absent the clusters.

  4. Steric effect for proton, hydrogen-atom, and hydride transfer reactions with geometric isomers of NADH-model ruthenium complexes.

    PubMed

    Cohen, Brian W; Polyansky, Dmitry E; Achord, Patrick; Cabelli, Diane; Muckerman, James T; Tanaka, Koji; Thummel, Randolph P; Zong, Ruifa; Fujita, Etsuko

    2012-01-01

    Two isomers, [Ru(1)]2+ (Ru = Ru(bpy)2, bpy = 2,2'-bipyridine, 1 = 2-(pyrid-2'-yl)-1-azaacridine) and [Ru(2)]2+ (2 = 3-(pyrid-2'-yl)-4-azaacridine), are bioinspired model compounds containing the nicotinamide functionality and can serve as precursors for the photogeneration of C-H hydrides for studying reactions pertinent to the photochemical reduction of metal-C1 complexes and/or carbon dioxide. While it has been shown that the structural differences between the azaacridine ligands of [Ru(1)]2+ and [Ru(2)]2+ have a significant effect on the mechanism of formation of the hydride donors, [Ru(1HH)]2+ and [Ru(2HH)]2+, in aqueous solution, we describe the steric implications for proton, net-hydrogen-atom and net-hydride transfer reactions in this work. Protonation of [Ru(2*-)] in aprotic and even protic media is slow compared to that of [Ru(1*-)]+. The net hydrogen-atom transfer between *[Ru(1)]2+ and hydroquinone (H2Q) proceeds by one-step EPT, rather than stepwise electron-proton transfer. Such a reaction was not observed for *[Ru(2)]2+ because the non-coordinated N atom is not easily available for an interaction with H2Q. Finally, the rate of the net hydride ion transfer from [Ru(1HH)]2+ to [Ph3C]+ is significantly slower than that of [Ru (2HH)]2+ owing to steric congestion at the donor site. PMID:22470971

  5. Synthesis of new asymmetric substituted boron amidines - reactions with CO and transfer hydrogenations of phenylacetylene.

    PubMed

    Cabrera, Alan R; Rojas, Rene S; Valderrama, Mauricio; Plüss, Pascal; Berke, Heinz; Daniliuc, Constantin G; Kehr, Gerald; Erker, Gerhard

    2015-12-01

    The syntheses of the new asymmetric substituted boron amidines [N'-(2,6-diisopropylphenyl)-N-(pentafluorophenyl)acetimidamide]bis(pentafluorophenyl)borate () and [N'-(2,6-diisopropylphenyl)-N-(4-cyanophenyl)acetimidamide]bis(pentafluorophenyl)borate () were achieved by reaction of one equivalent of HB(C6F5)2 and the respective amidines and . These adducts, bearing electron withdrawing groups, showed thermally induced H2 elimination forming the four-membered cyclic diazaborate derivatives and . These new species were characterized by spectroscopic methods. X-ray diffraction studies have been carried out on , and . To prevent undesired reactions at the nitrile group, one equivalent of B(C6F5)3 was added to yielding the -B(C6F5)3 nitrile adduct . Compound underwent thermally induced dehydrogenation to give the four-membered cyclic diazaborate derivative . CO was inserted into the ring systems of and forming the five-membered diazaborolone derivatives and . Phenylacetylene reacted stoichiometrically with the asymmetric substituted boron amidines , and to give styrene by double H transfer.

  6. Switchover of the Mechanism between Electron Transfer and Hydrogen-Atom Transfer for a Protonated Manganese(IV)-Oxo Complex by Changing Only the Reaction Temperature.

    PubMed

    Jung, Jieun; Kim, Surin; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi

    2016-06-20

    Hydroxylation of mesitylene by a nonheme manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) (1), proceeds via one-step hydrogen-atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid-bound manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) -(HOTf)2 (2), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2, however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around -0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT. PMID:27191357

  7. Hybrid quantum/classical molecular dynamics simulations of the proton transfer reactions catalyzed by ketosteroid isomerase: analysis of hydrogen bonding, conformational motions, and electrostatics.

    PubMed

    Chakravorty, Dhruva K; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2009-11-10

    Hybrid quantum/classical molecular dynamics simulations of the two proton transfer reactions catalyzed by ketosteroid isomerase are presented. The potential energy surfaces for the proton transfer reactions are described with the empirical valence bond method. Nuclear quantum effects of the transferring hydrogen increase the rates by a factor of approximately 8, and dynamical barrier recrossings decrease the rates by a factor of 3-4. For both proton transfer reactions, the donor-acceptor distance decreases substantially at the transition state. The carboxylate group of the Asp38 side chain, which serves as the proton acceptor and donor in the first and second steps, respectively, rotates significantly between the two proton transfer reactions. The hydrogen-bonding interactions within the active site are consistent with the hydrogen bonding of both Asp99 and Tyr14 to the substrate. The simulations suggest that a hydrogen bond between Asp99 and the substrate is present from the beginning of the first proton transfer step, whereas the hydrogen bond between Tyr14 and the substrate is virtually absent in the first part of this step but forms nearly concurrently with the formation of the transition state. Both hydrogen bonds are present throughout the second proton transfer step until partial dissociation of the product. The hydrogen bond between Tyr14 and Tyr55 is present throughout both proton transfer steps. The active site residues are more mobile during the first step than during the second step. The van der Waals interaction energy between the substrate and the enzyme remains virtually constant along the reaction pathway, but the electrostatic interaction energy is significantly stronger for the dienolate intermediate than for the reactant and product. Mobile loop regions distal to the active site exhibit significant structural rearrangements and, in some cases, qualitative changes in the electrostatic potential during the catalytic reaction. These results suggest

  8. Hybrid Quantum/Classical Molecular Dynamics Simulations of the Proton Transfer Reactions Catalyzed by Ketosteroid Isomerase: Analysis of Hydrogen Bonding, Conformational Motions, and Electrostatics

    PubMed Central

    Chakravorty, Dhruva K.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2009-01-01

    Hybrid quantum/classical molecular dynamics simulations of the two proton transfer reactions catalyzed by ketosteroid isomerase are presented. The potential energy surfaces for the proton transfer reactions are described with the empirical valence bond method. Nuclear quantum effects of the transferring hydrogen increase the rates by a factor of ~8, and dynamical barrier recrossings decrease the rates by a factor of 3–4. For both proton transfer reactions, the donor-acceptor distance decreases substantially at the transition state. The carboxylate group of the Asp38 side chain, which serves as the proton acceptor and donor in the first and second steps, respectively, rotates significantly between the two proton transfer reactions. The hydrogen bonding interactions within the active site are consistent with the hydrogen bonding of both Asp99 and Tyr14 to the substrate. The simulations suggest that a hydrogen bond between Asp99 and the substrate is present from the beginning of the first proton transfer step, whereas the hydrogen bond between Tyr14 and the substrate is virtually absent in the first part of this step but forms nearly concurrently with the formation of the transition state. Both hydrogen bonds are present throughout the second proton transfer step until partial dissociation of the product. The hydrogen bond between Tyr14 and Tyr55 is present throughout both proton transfer steps. The active site residues are more mobile during the first step than during the second step. The van der Waals interaction energy between the substrate and the enzyme remains virtually constant along the reaction pathway, but the electrostatic interaction energy is significantly stronger for the dienolate intermediate than for the reactant and product. Mobile loop regions distal to the active site exhibit significant structural rearrangements and, in some cases, qualitative changes in the electrostatic potential during the catalytic reaction. These results suggest that

  9. B-Methylated Amine-Boranes: Substituent Redistribution, Catalytic Dehydrogenation, and Facile Metal-Free Hydrogen Transfer Reactions.

    PubMed

    Stubbs, Naomi E; Schäfer, André; Robertson, Alasdair P M; Leitao, Erin M; Jurca, Titel; Sparkes, Hazel A; Woodall, Christopher H; Haddow, Mairi F; Manners, Ian

    2015-11-16

    Although the dehydrogenation chemistry of amine-boranes substituted at nitrogen has attracted considerable attention, much less is known about the reactivity of their B-substituted analogues. When the B-methylated amine-borane adducts, RR'NH·BH2Me (1a: R = R' = H; 1b: R = Me, R' = H; 1c: R = R' = Me; 1d: R = R' = iPr), were heated to 70 °C in solution (THF or toluene), redistribution reactions were observed involving the apparent scrambling of the methyl and hydrogen substituents on boron to afford a mixture of the species RR'NH·BH3-xMex (x = 0-3). These reactions were postulated to arise via amine-borane dissociation followed by the reversible formation of diborane intermediates and adduct reformation. Dehydrocoupling of 1a-1d with Rh(I), Ir(III), and Ni(0) precatalysts in THF at 20 °C resulted in an array of products, including aminoborane RR'N═BHMe, cyclic diborazane [RR'N-BHMe]2, and borazine [RN-BMe]3 based on analysis by in situ (11)B NMR spectroscopy, with peak assignments further supported by density functional theory (DFT) calculations. Significantly, very rapid, metal-free hydrogen transfer between 1a and the monomeric aminoborane, iPr2N═BH2, to yield iPr2NH·BH3 (together with dehydrogenation products derived from 1a) was complete within only 10 min at 20 °C in THF, substantially faster than for the N-substituted analogue MeNH2·BH3. DFT calculations revealed that the hydrogen transfer proceeded via a concerted mechanism through a cyclic six-membered transition state analogous to that previously reported for the reaction of the N-dimethyl species Me2NH·BH3 and iPr2N═BH2. However, as a result of the presence of an electron donating methyl substituent on boron rather than on nitrogen, the process was more thermodynamically favorable and the activation energy barrier was reduced. PMID:26535961

  10. Mechanism of ruthenium-catalyzed hydrogen transfer reactions. Concerted transfer of OH and CH hydrogens from an alcohol to a (Cyclopentadienone)ruthenium complex.

    PubMed

    Johnson, Jeffrey B; Bäckvall, Jan-E

    2003-10-01

    Kinetic studies of the ruthenium-catalyzed dehydrogenation of 1-(4-fluorophenyl)ethanol (4) by tetrafluorobenzoquinone (7) using the Shvo catalyst 1 at 70 degrees C show that the dehydrogenation by catalytic intermediate 2 is rate-determining with the rate = k[4][1](1/2) and with deltaH++ = 17.7 kcal mol(-1) and deltaS++ = -13.0 eu. The use of specifically deuterated derivative 4-CHOD and 4-CDOH gave individual isotope effects of k(CHOH)/k(CHOD) = 1.87 +/- 0.17 and k(CHOH)/k(CDOH) = 2.57 +/- 0.26, respectively. Dideuterated derivative 4-CDOD gave a combined isotope effect of k(CHOH)/k(CDOD) = 4.61 +/- 0.37. These isotope effects are consistent with a concerted transfer of both hydrogens of the alcohol to ruthenium species 2. PMID:14510542

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  12. Hydrogen tunnelling in enzyme-catalysed H-transfer reactions: flavoprotein and quinoprotein systems

    PubMed Central

    Sutcliffe, Michael J; Masgrau, Laura; Roujeinikova, Anna; Johannissen, Linus O; Hothi, Parvinder; Basran, Jaswir; Ranaghan, Kara E; Mulholland, Adrian J; Leys, David; Scrutton, Nigel S

    2006-01-01

    It is now widely accepted that enzyme-catalysed C–H bond breakage occurs by quantum mechanical tunnelling. This paradigm shift in the conceptual framework for these reactions away from semi-classical transition state theory (TST, i.e. including zero-point energy, but with no tunnelling correction) has been driven over the recent years by experimental studies of the temperature dependence of kinetic isotope effects (KIEs) for these reactions in a range of enzymes, including the tryptophan tryptophylquinone-dependent enzymes such as methylamine dehydrogenase and aromatic amine dehydrogenase, and the flavoenzymes such as morphinone reductase and pentaerythritol tetranitrate reductase, which produced observations that are also inconsistent with the simple Bell-correction model of tunnelling. However, these data—especially, the strong temperature dependence of reaction rates and the variable temperature dependence of KIEs—are consistent with other tunnelling models (termed full tunnelling models), in which protein and/or substrate fluctuations generate a configuration compatible with tunnelling. These models accommodate substrate/protein (environment) fluctuations required to attain a configuration with degenerate nuclear quantum states and, when necessary, motion required to increase the probability of tunnelling in these states. Furthermore, tunnelling mechanisms in enzymes are supported by atomistic computational studies performed within the framework of modern TST, which incorporates quantum nuclear effects. PMID:16873125

  13. Isotope Effects as Probes for Enzyme Catalyzed Hydrogen-Transfer Reactions

    PubMed Central

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2015-01-01

    Kinetic Isotope effects (KIEs) have long served as a probe for the mechanisms of both enzymatic and solution reactions. Here, we discuss various models for the physical sources of KIEs, how experimentalists can use those models to interpret their data, and how the focus of traditional models has grown to a model that includes motion of the enzyme and quantum mechanical nuclear tunneling. We then present two case studies of enzymes, thymidylate synthase and alcohol dehydrogenase, and discuss how KIEs have shed light on the C-H bond cleavages those enzymes catalyze. We will show how the combination of both experimental and computational studieshas changed our notion of how these enzymes exert their catalytic powers. PMID:23673528

  14. Role of bonding mechanisms during transfer hydrogenation reaction on heterogeneous catalysts of platinum nanoparticles supported on zinc oxide nanorods

    NASA Astrophysics Data System (ADS)

    Al-Alawi, Reem A.; Laxman, Karthik; Dastgir, Sarim; Dutta, Joydeep

    2016-07-01

    For supported heterogeneous catalysis, the interface between a metal nanoparticle and the support plays an important role. In this work the dependency of the catalytic efficiency on the bonding chemistry of platinum nanoparticles supported on zinc oxide (ZnO) nanorods is studied. Platinum nanoparticles were deposited on ZnO nanorods (ZnO NR) using thermal and photochemical processes and the effects on the size, distribution, density and chemical state of the metal nanoparticles upon the catalytic activities are presented. The obtained results indicate that the bonding at Pt-ZnO interface depends on the deposition scheme which can be utilized to modulate the surface chemistry and thus the activity of the supported catalysts. Additionally, uniform distribution of metal on the catalyst support was observed to be more important than the loading density. It is also found that oxidized platinum Pt(IV) (platinum hydroxide) provided a more suitable surface for enhancing the transfer hydrogenation reaction of cyclohexanone with isopropanol compared to zero valent platinum. Photochemically synthesized ZnO supported nanocatalysts were efficient and potentially viable for upscaling to industrial applications.

  15. Hydrogen Bonds in Excited State Proton Transfer

    NASA Astrophysics Data System (ADS)

    Horke, D. A.; Watts, H. M.; Smith, A. D.; Jager, E.; Springate, E.; Alexander, O.; Cacho, C.; Chapman, R. T.; Minns, R. S.

    2016-10-01

    Hydrogen bonding interactions between biological chromophores and their surrounding protein and solvent environment significantly affect the photochemical pathways of the chromophore and its biological function. A common first step in the dynamics of these systems is excited state proton transfer between the noncovalently bound molecules, which stabilizes the system against dissociation and principally alters relaxation pathways. Despite such fundamental importance, studying excited state proton transfer across a hydrogen bond has proven difficult, leaving uncertainties about the mechanism. Through time-resolved photoelectron imaging measurements, we demonstrate how the addition of a single hydrogen bond and the opening of an excited state proton transfer channel dramatically changes the outcome of a photochemical reaction, from rapid dissociation in the isolated chromophore to efficient stabilization and ground state recovery in the hydrogen bonded case, and uncover the mechanism of excited state proton transfer at a hydrogen bond, which follows sequential hydrogen and charge transfer processes.

  16. 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.

    PubMed

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

    2014-07-01

    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.

  17. Hydrogen Tunneling in Enzyme Reactions

    NASA Astrophysics Data System (ADS)

    Cha, Yuan; Murray, Christopher J.; Klinman, Judith P.

    1989-03-01

    Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that kH/kT = (kD/kT)3.26, where kH, kD, and kT are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.

  18. Hydrogen tunneling in enzyme reactions.

    PubMed

    Cha, Y; Murray, C J; Klinman, J P

    1989-03-10

    Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that kH/kT = (kD/kT)3.26, where kH, kD, and kT are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.

  19. Interaction between Cytochrome c2 and Photosynthetic Reaction Center from Rhodobacter sphaeroides: Role of Inter- Protein Hydrogen Bonds in Binding and Electron Transfer

    PubMed Central

    Abresch, Edward C.; Paddock, Mark L.; Villalobos, Miguel; Chang, Charlene; Okamura, Melvin Y.

    2008-01-01

    The role of short-range hydrogen bond interactions at the interface between electron transfer proteins cytochrome c2 (cyt) and reaction center (RC) from Rb. sphaeroides was studied by mutation (to Ala) of RC residues Asn M187, Asn M188 and Gln L258 which form inter-protein hydrogen bonds to cyt in the cyt:RC complex. The largest decrease in binding constant KA (8-fold) for single mutation was observed for Asn M187, which forms an intra-protein hydrogen bond to the key residue Tyr L162 in the center of the contact region having low solvent accessibility. Interaction between Asn M187 and Tyr L162 was also implicated in binding by double mutation of the two residues. The hydrogen bond mutations did not significantly change the second order rate constant, k2 , indicating the mutations did not change the association rate for forming the cyt:RC complex, but increased the dissociation rate. The first order electron transfer rate, ke, for the cyt:RC complex was reduced by up to a factor of 4 (for Asn M187). The changes in ke were correlated with the changes in binding affinity but were not accompanied by increases in activation energy. We conclude that short-range hydrogen bond interactions contribute to the close packing of residues in the central contact region between the cyt and RC near Asn M187 and Tyr L162. The close packing contributes to fast electron transfer by increasing the electronic coupling and contributes to the binding energy holding the cyt in position for times long enough for electron transfer to occur. PMID:19053264

  20. Importance of π-stacking interactions in the hydrogen atom transfer reactions from activated phenols to short-lived N-oxyl radicals.

    PubMed

    Mazzonna, Marco; Bietti, Massimo; DiLabio, Gino A; Lanzalunga, Osvaldo; Salamone, Michela

    2014-06-01

    A kinetic study of the hydrogen atom transfer from activated phenols (2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols, 2,2,5,7,8-pentamethylchroman-6-ol, caffeic acid, and (+)-cathechin) to a series of N-oxyl radical (4-substituted phthalimide-N-oxyl radicals (4-X-PINO), 6-substituted benzotriazole-N-oxyl radicals (6-Y-BTNO), 3-quinazolin-4-one-N-oxyl radical (QONO), and 3-benzotriazin-4-one-N-oxyl radical (BONO)), was carried out by laser flash photolysis in CH3CN. A significant effect of the N-oxyl radical structure on the hydrogen transfer rate constants (kH) was observed with kH values that monotonically increase with increasing NO-H bond dissociation energy (BDENO-H) of the N-hydroxylamines. The analysis of the kinetic data coupled to the results of theoretical calculations indicates that these reactions proceed by a hydrogen atom transfer (HAT) mechanism where the N-oxyl radical and the phenolic aromatic rings adopt a π-stacked arrangement. Theoretical calculations also showed pronounced structural effects of the N-oxyl radicals on the charge transfer occurring in the π-stacked conformation. Comparison of the kH values measured in this study with those previously reported for hydrogen atom transfer to the cumylperoxyl radical indicates that 6-CH3-BTNO is the best N-oxyl radical to be used as a model for evaluating the radical scavenging ability of phenolic antioxidants.

  1. The Role of Vibrational Excitation on the Dynamics of the F(^2P) + HCl → FH + Cl(2P) Hydrogen-Transfer Reaction

    NASA Astrophysics Data System (ADS)

    Ray, Sara E.; Vissers, G. W. M.; McCoy, Anne B.

    2010-06-01

    Recently, open-shell systems have gained interest in experimental and theoretical science. What proves interesting about these open-shell systems is that the potential energy surfaces often contain a van der Waals well in the reactant or product channel that allows researchers to probe the pre-reactive species. Here we present the results of time-dependent quantum wave packet calculations on the asymmetric hydrogen-transfer reaction of F(^SUP>2P) + HCl. In these calculations, the reaction is initiated by vibrationally exciting the HCl stretching motion of the pre-reactive F\\cdotsHCl complex in the van der Waals well. The wave packet is propagated on a three-dimensional, fully coupled potential energy surface that has been constructed based on electronic energies calculated at the multi-reference configuration interation+Davidson correction (MRCI+Q) level of theory with an aug-cc-pVnZ (n=2,3,4) basis. Product state distributions were calculated for reactions initiated in the first three vibrationally excited states of HCl, v=1, 2, and 3. Specifically, we analyzed the final electronic, vibrational, and rotational distributions. Previous studies on the hydrogen-transfer reaction of the Cl(^2P) + HCl system focused on whether vibrational excitation of the HCl stretch would promote the reaction and if so, how the reaction dynamics reflect the coupling among the diabatic potential surfaces that describe this system. We also compare our F(^2P) + HCl results to those of this related system. M. P. Deskevich, M. Y. Hayes, K. Takahashi, R. T. Skodje, and D. J. Nesbitt J. Chem. Phys., 124(22) 224303 (2006) G. W. M. Vissers and A. B. McCoy J. Phys Chem. A, 110 5978 (2006)

  2. Charge Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Dennerl, Konrad

    2010-12-01

    Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

  3. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    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)

  4. Photoelectrochemical cells based on hydrogen-atom abstraction and electron-transfer reactions in solution: systems based on benzophenone, 2-propanol, trialkylamines, and methyl viologen

    SciTech Connect

    Chandrasekaran, K.; Whitten, D.G.

    1981-12-02

    This paper reports the linking of well-studied solution photoprocesses such as hydrogen-atom abstraction by triplet benzophenone from 2-propanol and electron transfer from triethylamine to triplet benzophenone to proton reduction in aqueous acid via a two-compartment photoelectrochemical cell. In each case the intermediate reduction of N,N'-dimethyl-4,4'-bipyridinium (methyl viologen, MV/sup 2 +/) provides a means for circumventing undesirable radical reactions and generating a stable carrier in high overall efficiency. The net result is reasonably efficient generation of a photocurrent concurrent with the occurrence of an endothermic reaction providing products that can in principle be recycled. An interesting aspect of this work is the finding that the overall efficiency of these cells is enhanced by the photochemical self-sensitization of MV/sup +/ in the presence of 2-propanol or triethylamine and MV/sup 2 +/.

  5. Mechanisms of some hydrogen-transfer reactions: temperature dependence of the kinetic isotope effect and intramolecular C-H insertion: synthesis of (+/-)-pentalenolactone E methyl ester

    SciTech Connect

    Schuchardt, J.L.

    1985-01-01

    The mechanisms of three familiar organic hydrogen transfer reactions have been investigated by a study of the temperature dependence of the kinetic isotope effect. The Oppenauer oxidation of benzhydrol to benzophenone resulted in relatively small isotope effects (k/sub H//k/sub D/ = 2.3 10/sup 0/C), which are consistent with either a linear, unsymmetrical or a nonlinear H-transfer. The temperature dependence of k/sub H//k/sub D/ is in doubt due to an unanticipated isotopic scrambling effect. The Grignard reduction of benzophenone by isobutylmagnesium bromide shows significant temperature dependence of the kinetic isotope effect. The less-than-maximum isotope effects and activation energy difference suggest an unsymmetrical linear H-transfer mechanism. There is no evidence of tunneling in either the Oppenauer oxidation of the Grignard reduction with the system investigated. The reduction of benzyl bromide by tri-n-butyltin hydride gives temperature-dependent isotope effects and activation parameters consistent with an unsymmetrical linear H-transfer. The results for cyclohexyl bromide were less illuminating. (+/-)-Pentalenolactone E methyl ester was synthesized in 12 steps from 4,4-dimethylcyclohexanone. Disconnection of the target molecule at a unveils substantial molecular symmetry. The key to the analysis is the synthetic step which allows bond formation to an unfunctionalized carbon atom. The key step, rhodium-mediated intramolecular C-H insertion successfully generated the tricyclic skeleton of pentalenolactone via a sterically congested transition state.

  6. Kinetics of catalytic transfer hydrogenation of soybean lecithin

    SciTech Connect

    Naglic, M.; Smidovnik, A.; Koloini, T.

    1997-12-01

    Catalytic transfer hydrogenation of soybean lecithin has been studied using aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined at intensive stirring. Hydrogenation reactions followed the first-order kinetics with respect to fatty acids. In addition to short reaction time, this method offers safe and easy handling. Hydrogenated soybean lecithin provides products with increased stability with respect to oxidation.

  7. Synthesis of 2,3-anti-3,4-anti and 2,3-anti-3,4-syn propionate motifs: a diastereoselective tandem sequence of Mukaiyama and free-radical-based hydrogen transfer reactions.

    PubMed

    Guindon, Yvan; Prévost, Michel; Mochirian, Philippe; Guérin, Brigitte

    2002-03-21

    [reaction: see text] Reported herein is a strategy employing a Mukaiyama reaction in tandem with a hydrogen transfer reaction for the elaboration of 2,3-anti-3,4-anti and 2,3-anti-3,4-syn propionate motifs. The mode of complexation is controlled through monodentate or chelate pathways for the Mukaiyama reaction to give access to either syn or anti aldol products, precursors of the free-radical reduction reaction. Boron Lewis acid is used to control the free-radical reaction through the exocyclic pathway.

  8. Spectroscopic investigation and computational analysis of charge transfer hydrogen bonded reaction between 3-aminoquinoline with chloranilic acid in 1:1 stoichiometric ratio

    NASA Astrophysics Data System (ADS)

    Al-Ahmary, Khairia M.; Alenezi, Maha S.; Habeeb, Moustafa M.

    2015-10-01

    Charge transfer hydrogen bonded reaction between the electron donor (proton acceptor) 3-aminoquinoline with the electron acceptor (proton donor) chloranilic acid (H2CA) has been investigated experimentally and theoretically. The experimental work included the application of UV-vis spectroscopy to identify the charge transfer band of the formed complex, its molecular composition as well as estimating its formation constants in different solvent included acetonitrile (AN), methanol (MeOH), ethanol (EtOH) and chloroform (CHL). It has been recorded the presence of new absorption bands in the range 500-550 nm attributing to the formed complex. The molecular composition of the HBCT complex was found to be 1:1 (donor:acceptor) in all studied solvents based on continuous variation and photometric titration methods. In addition, the calculated formation constants from Benesi-Hildebrand equation recorded high values, especially in chloroform referring to the formation of stable HBCT complex. Infrared spectroscopy has been applied for the solid complex where formation of charge and proton transfer was proven in it. Moreover, 1H and 13C NMR spectroscopies were used to characterize the formed complex where charge and proton transfers were reconfirmed. Computational analysis included the use of GAMESS computations as a package of ChemBio3D Ultr12 program were applied for energy minimization and estimation of the stabilization energy for the produced complex. Also, geometrical parameters (bond lengths and bond angles) of the formed HBCT complex were computed and analyzed. Furthermore, Mullikan atomic charges, molecular potential energy surface, HOMO and LUMO molecular orbitals as well as assignment of the electronic spectra of the formed complex were presented. A full agreement between experimental and computational analysis has been found especially in the existence of the charge and proton transfers and the assignment of HOMO and LUMO molecular orbitals in the formed complex as

  9. N-Alkylation by Hydrogen Autotransfer Reactions.

    PubMed

    Ma, Xiantao; Su, Chenliang; Xu, Qing

    2016-06-01

    Owing to the importance of amine/amide derivatives in all fields of chemistry, and also the green and environmentally benign features of using alcohols as alkylating reagents, the relatively high atom economic dehydrative N-alkylation reactions of amines/amides with alcohols through hydrogen autotransfer processes have received much attention and have developed rapidly in recent decades. Various efficient homogeneous and heterogeneous transition metal catalysts, nano materials, electrochemical methods, biomimetic methods, asymmetric N-alkylation reactions, aerobic oxidative methods, and even certain transition metal-free, catalyst-free, or autocatalyzed methods, have also been developed in recent years. With a brief introduction to the background and developments in this area of research, this chapter focuses mainly on recent progress and technical and conceptual advances contributing to the development of this research in the last decade. In addition to mainstream research on homogeneous and heterogeneous transition metal-catalyzed reactions, possible mechanistic routes for hydrogen transfer and alcohol activation, which are key processes in N-alkylation reactions but seldom discussed in the past, the recent reports on computational mechanistic studies of the N-alkylation reactions, and the newly emerged N-alkylation methods based on novel alcohol activation protocols such as air-promoted reactions and transition metal-free methods, are also reviewed in this chapter. Problems and bottlenecks that remained to be solved in the field, and promising new research that deserves greater future attention and effort, are also reviewed and discussed.

  10. N-Alkylation by Hydrogen Autotransfer Reactions.

    PubMed

    Ma, Xiantao; Su, Chenliang; Xu, Qing

    2016-06-01

    Owing to the importance of amine/amide derivatives in all fields of chemistry, and also the green and environmentally benign features of using alcohols as alkylating reagents, the relatively high atom economic dehydrative N-alkylation reactions of amines/amides with alcohols through hydrogen autotransfer processes have received much attention and have developed rapidly in recent decades. Various efficient homogeneous and heterogeneous transition metal catalysts, nano materials, electrochemical methods, biomimetic methods, asymmetric N-alkylation reactions, aerobic oxidative methods, and even certain transition metal-free, catalyst-free, or autocatalyzed methods, have also been developed in recent years. With a brief introduction to the background and developments in this area of research, this chapter focuses mainly on recent progress and technical and conceptual advances contributing to the development of this research in the last decade. In addition to mainstream research on homogeneous and heterogeneous transition metal-catalyzed reactions, possible mechanistic routes for hydrogen transfer and alcohol activation, which are key processes in N-alkylation reactions but seldom discussed in the past, the recent reports on computational mechanistic studies of the N-alkylation reactions, and the newly emerged N-alkylation methods based on novel alcohol activation protocols such as air-promoted reactions and transition metal-free methods, are also reviewed in this chapter. Problems and bottlenecks that remained to be solved in the field, and promising new research that deserves greater future attention and effort, are also reviewed and discussed. PMID:27573267

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

    PubMed

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

    2012-11-13

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

  12. Orbital-optimized coupled-electron pair theory and its analytic gradients: Accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions

    NASA Astrophysics Data System (ADS)

    Bozkaya, Uǧur; Sherrill, C. David

    2013-08-01

    Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N6) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the λ2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (ΔR is 0.0003 Å on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm-1) is fortuitously even better than that of CCSD(T) (50 cm-1), while the MAEs of CEPA(0) (184 cm-1) and CCSD (84 cm-1) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol-1, which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol-1), and comparing to MP2 (7.7 kcal mol-1) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal

  13. Orbital-optimized coupled-electron pair theory and its analytic gradients: accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions.

    PubMed

    Bozkaya, Uğur; Sherrill, C David

    2013-08-01

    Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N(6)) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the λ2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (ΔR is 0.0003 Å on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm(-1)) is fortuitously even better than that of CCSD(T) (50 cm(-1)), while the MAEs of CEPA(0) (184 cm(-1)) and CCSD (84 cm(-1)) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol(-1), which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol(-1)), and comparing to MP2 (7.7 kcal mol(-1)) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is

  14. A General Catalytic Enantioselective Transfer Hydrogenation Reaction of β,β-Disubstituted Nitroalkenes Promoted by a Simple Organocatalyst.

    PubMed

    Bernardi, Luca; Fochi, Mariafrancesca

    2016-01-01

    Given its synthetic relevance, the catalytic enantioselective reduction of β,β-disubstituted nitroalkenes has received a great deal of attention. Several bio-, metal-, and organo-catalytic methods have been developed, which however are usually applicable to single classes of nitroalkene substrates. In this paper, we present an account of our previous work on this transformation, which implemented with new disclosures and mechanistic insights results in a very general protocol for nitroalkene reductions. The proposed methodology is characterized by (i) a remarkably broad scope encompassing various nitroalkene classes; (ii) Hantzsch esters as convenient (on a preparative scale) hydrogen surrogates; (iii) a simple and commercially available thiourea as catalyst; (iv) user-friendly procedures. Overall, the proposed protocol gives a practical dimension to the catalytic enantioselective reduction of β,β-disubstituted nitroalkenes, offering a useful and general platform for the preparation of nitroalkanes bearing a stereogenic center at the β-position in a highly enantioenriched form. A transition state model derived from control kinetic experiments combined with literature data is proposed and discussed. This model accounts and justifies the observed experimental results. PMID:27483233

  15. Tandem ring-closing metathesis/transfer hydrogenation: practical chemoselective hydrogenation of alkenes.

    PubMed

    Connolly, Timothy; Wang, Zhongyu; Walker, Michael A; McDonald, Ivar M; Peese, Kevin M

    2014-09-01

    An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented. PMID:25140991

  16. Tandem ring-closing metathesis/transfer hydrogenation: practical chemoselective hydrogenation of alkenes.

    PubMed

    Connolly, Timothy; Wang, Zhongyu; Walker, Michael A; McDonald, Ivar M; Peese, Kevin M

    2014-09-01

    An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented.

  17. Transfer reactions in nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    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.

  18. A classical but new kinetic equation for hydride transfer reactions.

    PubMed

    Zhu, Xiao-Qing; Deng, Fei-Huang; Yang, Jin-Dong; Li, Xiu-Tao; Chen, Qiang; Lei, Nan-Ping; Meng, Fan-Kun; Zhao, Xiao-Peng; Han, Su-Hui; Hao, Er-Jun; Mu, Yuan-Yuan

    2013-09-28

    A classical but new kinetic equation to estimate activation energies of various hydride transfer reactions was developed according to transition state theory using the Morse-type free energy curves of hydride donors to release a hydride anion and hydride acceptors to capture a hydride anion and by which the activation energies of 187 typical hydride self-exchange reactions and more than thirty thousand hydride cross transfer reactions in acetonitrile were safely estimated in this work. Since the development of the kinetic equation is only on the basis of the related chemical bond changes of the hydride transfer reactants, the kinetic equation should be also suitable for proton transfer reactions, hydrogen atom transfer reactions and all the other chemical reactions involved with breaking and formation of chemical bonds. One of the most important contributions of this work is to have achieved the perfect unity of the kinetic equation and thermodynamic equation for hydride transfer reactions.

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

    PubMed

    Boudier, Ariane; Tournebize, Juliana; Bartosz, Grzegorz; El Hani, Safae; Bengueddour, Rachid; Sapin-Minet, Anne; Leroy, Pierre

    2012-01-20

    1,1-Diphenyl-2-picrylhydrazyl (DPPH·) 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· absorbance at 515nm 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· quenching rate and none of them permits to identify and measure 1,1-diphenyl-2-picryl-hydrazine (DPPH-H), the reduced product of DPPH· resulting from hydrogen atom transfer (HAT), which is the main mechanism of the reaction between DPPH· and AOs. We presently report an HPLC method devoted to the simultaneous measurement of DPPH· 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· onto materials of the HPLC system was pointed out. Consequently, the linearity range observed for DPPH· was restricted, thus a much lower limit of detection was obtained for DPPH-H than for DPPH· using standards (0.02 and 14 μM, respectively). The method was applied to three commonly used AOs, i.e. Trolox(®), 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 higher selectivity than colorimetry, and (ii) its help to investigate the mechanisms occurring with the free radical.

  20. Transfer reactions with heavy elements

    SciTech Connect

    Hoffman, D.C.

    1986-04-01

    Transfer reactions for several transuranium elements are studied. (/sup 248/Cm, /sup 249/Bk, /sup 249/CF, /sup 254/Es), /sup 16,18/O, /sup 20,22/Ne, and /sup 40,48/Ca projectiles are used. The production of neutron-rich heavy actinides is enhanced by the use of neutron-rich projectiles /sup 18/O and /sup 22/Ne. The maxima of the isotopic distributions occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions with /sup 248/Cm. The cross sections decrease rapidly with the number of nucleons transferred. The use of neutron-rich targets favors the production of neutron-rich isotopes. ''Cold'' heavy targets are produced. Comparisons with simple calculations of the product excitation energies assuming binary transfers indicate that the maxima of the isotopic distributions occur at the lightest product isotope for which the energy exceeds the reaction barrier. The cross sections for transfer of the same nucleon clusters appear to be comparable for a wide variety of systems. 23 refs., 4 figs., 4 tabs.

  1. C-Alkylation by Hydrogen Autotransfer Reactions.

    PubMed

    Obora, Yasushi

    2016-04-01

    The development of practical, efficient, and atom-economical methods for the formation of carbon-carbon bonds remains a topic of considerable interest in current synthetic organic chemistry. In this review, we have summarized selected topics from the recent literature with particular emphasis on C-alkylation processes involving hydrogen transfer using alcohols as alkylation reagents. This review includes selected highlights concerning recent progress towards the modification of catalytic systems for the α-alkylation of ketones, nitriles, and esters. Furthermore, we have devoted a significant portion of this review to the methylation of ketones, alcohols, and indoles using methanol. Lastly, we have also documented recent advances in β-alkylation methods involving the dimerization of alcohols (Guerbet reaction), as well as new developments in C-alkylation methods based on sp (3) C-H activation. PMID:27573136

  2. Nickel-catalyzed transfer hydrogenation of ketones using ethanol as a solvent and a hydrogen donor.

    PubMed

    Castellanos-Blanco, Nahury; Arévalo, Alma; García, Juventino J

    2016-09-14

    We report a nickel(0)-catalyzed direct transfer hydrogenation (TH) of a variety of alkyl-aryl, diaryl, and aliphatic ketones with ethanol. This protocol implies a reaction in which a primary alcohol serves as a hydrogen atom source and solvent in a one-pot reaction without any added base. The catalytic activity of the nickel complex [(dcype)Ni(COD)] (e) (dcype: 1,2-bis(dicyclohexyl-phosphine)ethane, COD: 1,5-cyclooctadiene), towards transfer hydrogenation (TH) of carbonyl compounds using ethanol as the hydrogen donor was assessed using a broad scope of ketones, giving excellent results (up to 99% yield) compared to other homogeneous phosphine-nickel catalysts. Control experiments and a mercury poisoning experiment support a homogeneous catalytic system; the yield of the secondary alcohols formed in the TH reaction was monitored by gas chromatography (GC) and NMR spectroscopy. PMID:27511528

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

    PubMed

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

    2015-02-01

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

  4. Mechanism of Pd(NHC)-catalyzed transfer hydrogenation of alkynes.

    PubMed

    Hauwert, Peter; Boerleider, Romilda; Warsink, Stefan; Weigand, Jan J; Elsevier, Cornelis J

    2010-12-01

    The transfer semihydrogenation of alkynes to (Z)-alkenes shows excellent chemo- and stereoselectivity when using a zerovalent palladium(NHC)(maleic anhydride)-complex as precatalyst and triethylammonium formate as hydrogen donor. Studies on the kinetics under reaction conditions showed a broken positive order in substrate and first order in catalyst and hydrogen donor. Deuterium-labeling studies on the hydrogen donor showed that both hydrogens of formic acid display a primary kinetic isotope effect, indicating that proton and hydride transfers are separate rate-determining steps. By monitoring the reaction with NMR, we observed the presence of a coordinated formate anion and found that part of the maleic anhydride remains coordinated during the reaction. From these observations, we propose a mechanism in which hydrogen transfer from coordinated formate anion to zerovalent palladium(NHC)(MA)(alkyne)-complex is followed by migratory insertion of hydride, after which the product alkene is liberated by proton transfer from the triethylammonium cation. The explanation for the high selectivity observed lies in the competition between strongly coordinating solvent and alkyne for a Pd(alkene)-intermediate.

  5. Part B: Heat Transfer to Slush Hydrogen

    NASA Technical Reports Server (NTRS)

    Sindt, C. F.

    1972-01-01

    Heat transfer to slush hydrogen was measured at one atmosphere and at triple-point pressure. The data were compared with those for heat transfer to liquid hydrogen, and to classical heat transfer correlations for nucleate boiling. The slush data fit convective heat transfer correlations quite well. In general, the data show that for a given heat flux, the temperature difference between the wall and the bulk liquid is not as highly influenced by pressure as predicted by the core correlation for nucleate boiling.

  6. Hydrogenation-dehydrogenation reactions of polycyclic aromatics

    SciTech Connect

    Dutta, R.P.; Schobert, H.H.

    1995-12-31

    An understanding of the hydrogenation/dehydrogenation of polycyclic aromatic compounds is an important step in producing cycloalkanes from coal. Coal fragments released during depolymerization of coal tend to be aromatic in nature and therefore they need to be hydrogenated to produce desirable compounds. If these compounds can be hydrogenated to some extent during the depolymerization stage, a more efficient liquefaction process can be achieved. Studies at Penn State and other laboratories have shown that coal can be converted to over 95% oils. If the reaction conditions can be fine-tuned, a better quality product can be obtained. To obtain an understanding of how coal fragments would behave under various conditions, model compounds have been used in this investigation. Naphthalene, phenanthrene, pyrene and chrysene were subjected to various catalytic hydrogenation conditions. These included three temperatures and reaction times varying from 1 minute to 2 hours. Trends in the product compositions were analyzed and kinetic/thermodynamic data were compared for the various compounds. Once hydrogenation of the compounds has been optimized, the next most important factor that needs to be addressed is how do we avoid dehydrogenation reactions taking place. To understand this, some of the products from each compound that were hydrogenated were subjected to dehydrogenation conditions. This was achieved by heating the compounds under nitrogen for various reaction times and temperatures. Trends in the product composition were followed and analyzed, along with comparisons of kinetic data for each of the hydroaromatic dehydrogenations.

  7. Reaction of atomic hydrogen with formic acid.

    PubMed

    Cao, Qian; Berski, Slawomir; Latajka, Zdzislaw; Räsänen, Markku; Khriachtchev, Leonid

    2014-04-01

    We study the reaction of atomic hydrogen with formic acid and characterize the radical products using IR spectroscopy in a Kr matrix and quantum chemical calculations. The reaction first leads to the formation of an intermediate radical trans-H2COOH, which converts to the more stable radical trans-cis-HC(OH)2via hydrogen atom tunneling on a timescale of hours at 4.3 K. These open-shell species are observed for the first time as well as a reaction between atomic hydrogen and formic acid. The structural assignment is aided by extensive deuteration experiments and ab initio calculations at the UMP2 and UCCSD(T) levels of theory. The simplest geminal diol radical trans-cis-HC(OH)2 identified in the present work as the final product of the reaction should be very reactive, and further reaction channels are of particular interest. These reactions and species may constitute new channels for the initiation and propagation of more complex organic species in the interstellar clouds.

  8. A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

    PubMed

    Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

    2015-10-14

    While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion.

  9. A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

    PubMed

    Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

    2015-10-14

    While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion. PMID:26193994

  10. The effective molarity (EM) puzzle in proton transfer reactions.

    PubMed

    Karaman, Rafik

    2009-08-01

    The DFT and HF calculation results for the proton transfer reactions of three different systems reveal that the reaction mechanism (transfer of a proton to a nucleophile) is largely determined by the distance between the two reactive centers (r). Systems with relatively large r values tend to abstract a proton from a molecule of water, whereas, these with a relatively small r values prefer to be engaged intramolecularly and their interaction with water is only via hydrogen bonding. Further, the results indicate that the effective molarity (logEM) for an intramolecular process is strongly correlated with the distance between the two reacting centers (r) in accordance with Menger's "spatiotemporal hypothesis".

  11. Metal-Catalysed Transfer Hydrogenation of Ketones.

    PubMed

    Štefane, Bogdan; Požgan, Franc

    2016-04-01

    We highlight recent developments of catalytic transfer hydrogenation of ketones promoted by transition metals, while placing it within its historical context. Since optically active secondary alcohols are important building blocks in fine chemicals synthesis, the focus of this review is devoted to chiral catalyst types which are capable of inducing high stereoselectivities. Ruthenium complexes still represent the largest part of the catalysts, but other metals (e.g. Fe) are rapidly penetrating this field. While homogeneous transfer hydrogenation catalysts in some cases approach enzymatic performance, the interest in heterogeneous catalysts is constantly growing because of their reusability. Despite excellent activity, selectivity and compatibility of metal complexes with a variety of functional groups, no universal catalysts exist. Development of future catalyst systems is directed towards reaching as high as possible activity with low catalyst loadings, using "greener" conditions, and being able to operate under mild conditions and in a highly selective manner for a broad range of substrates. PMID:27573143

  12. Alkane desaturation by concerted double hydrogen atom transfer to benzyne.

    PubMed

    Niu, Dawen; Willoughby, Patrick H; Woods, Brian P; Baire, Beeraiah; Hoye, Thomas R

    2013-09-26

    The removal of two vicinal hydrogen atoms from an alkane to produce an alkene is a challenge for synthetic chemists. In nature, desaturases and acetylenases are adept at achieving this essential oxidative functionalization reaction, for example during the biosynthesis of unsaturated fatty acids, eicosanoids, gibberellins and carotenoids. Alkane-to-alkene conversion almost always involves one or more chemical intermediates in a multistep reaction pathway; these may be either isolable species (such as alcohols or alkyl halides) or reactive intermediates (such as carbocations, alkyl radicals, or σ-alkyl-metal species). Here we report a desaturation reaction of simple, unactivated alkanes that is mechanistically unique. We show that benzynes are capable of the concerted removal of two vicinal hydrogen atoms from a hydrocarbon. The discovery of this exothermic, net redox process was enabled by the simple thermal generation of reactive benzyne intermediates through the hexadehydro-Diels-Alder cycloisomerization reaction of triyne substrates. We are not aware of any single-step, bimolecular reaction in which two hydrogen atoms are simultaneously transferred from a saturated alkane. Computational studies indicate a preferred geometry with eclipsed vicinal C-H bonds in the alkane donor.

  13. Muon transfer from muonic hydrogen to carbon

    SciTech Connect

    Dupays, Arnaud

    2005-11-15

    Exact three-dimensional quantum calculations of muon exchange between muonic hydrogen and carbon for collision energies in the range 10{sup -3}-100 eV, are presented. Muon transfer rates at thermal and epithermal energies are calculated including partial waves up to J=7. The relative populations of the final states are also given. The results show that above 1 eV, the relative population of ({mu}C){sub n=5}{sup 5+} can reach up to 30%.

  14. Boryl-mediated reversible H2 activation at cobalt: catalytic hydrogenation, dehydrogenation, and transfer hydrogenation.

    PubMed

    Lin, Tzu-Pin; Peters, Jonas C

    2013-10-16

    We describe the synthesis of a cobalt(I)-N2 complex (2) supported by a meridional bis-phosphino-boryl (PBP) ligand. Complex 2 undergoes a clean reaction with 2 equiv of dihydrogen to afford a dihydridoboratocobalt dihydride (3). The ability of boron to switch between a boryl and a dihydridoborate conformation makes possible the reversible conversion of 2 and 3. Complex 3 reacts with HMe2N-BH3 to give a hydridoborane cobalt tetrahydridoborate complex. We explore this boryl-cobalt system in the context of catalytic olefin hydrogenation as well as amine-borane dehydrogenation/transfer hydrogenation. PMID:24079337

  15. Kinetics of Hydrogen-Transfer Isomerizations of Butoxyl Radicals

    SciTech Connect

    Zheng, J.; Truhlar, D. G.

    2010-01-01

    Five isomerization reactions involving intramolecular hydrogen-transfer in butoxyl radicals have been studied using variational transition state theory with small curvature tunneling. A set of best estimates of barrier heights and reaction energies for these five reactions was obtained by using coupled cluster theory including single and double excitations with a quasiperturbative treatment of connected triple excitations and a basis set extrapolated to the complete basis set limit plus core–valence correlation contributions and scalar relativistic corrections. This work predicts high-pressure limiting rate constants of these five reactions over the temperature range 200–2500 K and clarifies the available experimental data from indirect measurements. This study shows the importance of performing rate calculations with proper accounting for tunneling and torsional anharmonicity. We also proposed two new models for use in fitting rate constants over wide ranges of temperature.

  16. Hydrogen atom scrambling in ion-molecule reactions of methane and ethylene.

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.

    1972-01-01

    The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5(+) + H2, is determined by examining the product distribution for the reactions CH3(+) + CD4 and CD3(+) + CH4 as a function of relative kinetic energy from thermal energies to 10 eV. It is found that the reaction of CH4(+) with the parent neutral proceeds both via proton transfer and hydrogen abstraction accompanied by approximately 10% hydrogen atom exchange during the reaction.

  17. Photoinduced Electron Transfer Reactions for Macromolecular Syntheses.

    PubMed

    Dadashi-Silab, Sajjad; Doran, Sean; Yagci, Yusuf

    2016-09-14

    Photochemical reactions, particularly those involving photoinduced electron transfer processes, establish a substantial contribution to the modern synthetic chemistry, and the polymer community has been increasingly interested in exploiting and developing novel photochemical strategies. These reactions are efficiently utilized in almost every aspect of macromolecular architecture synthesis, involving initiation, control of the reaction kinetics and molecular structures, functionalization, and decoration, etc. Merging with polymerization techniques, photochemistry has opened up new intriguing and powerful avenues for macromolecular synthesis. Construction of various polymers with incredibly complex structures and specific control over the chain topology, as well as providing the opportunity to manipulate the reaction course through spatiotemporal control, are one of the unique abilities of such photochemical reactions. This review paper provides a comprehensive account of the fundamentals and applications of photoinduced electron transfer reactions in polymer synthesis. Besides traditional photopolymerization methods, namely free radical and cationic polymerizations, step-growth polymerizations involving electron transfer processes are included. In addition, controlled radical polymerization and "Click Chemistry" methods have significantly evolved over the last few decades allowing access to narrow molecular weight distributions, efficient regulation of the molecular weight and the monomer sequence and incredibly complex architectures, and polymer modifications and surface patterning are covered. Potential applications including synthesis of block and graft copolymers, polymer-metal nanocomposites, various hybrid materials and bioconjugates, and sequence defined polymers through photoinduced electron transfer reactions are also investigated in detail.

  18. Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides.

    PubMed

    Belkova, Natalia V; Epstein, Lina M; Filippov, Oleg A; Shubina, Elena S

    2016-08-10

    The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed. PMID:27285818

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

    SciTech Connect

    Ferguson, J.M.

    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.

  20. Incomplete Combustion of Hydrogen: Trapping a Reaction Intermediate

    ERIC Educational Resources Information Center

    Mattson, Bruce; Hoette, Trisha

    2007-01-01

    The combustion of hydrogen in air is quite complex with at least 28 mechanistic steps and twelve reaction species. Most of the species involved are radicals (having unpaired electrons) in nature. Among the various species generated, a few are stable, including hydrogen peroxide. In a normal hydrogen flame, the hydrogen peroxide goes on to further…

  1. High-power CW laser using hydrogen-fluorine reaction

    NASA Technical Reports Server (NTRS)

    Moynihan, P. I.

    1975-01-01

    Continuous-wave laser has been proposed based on reaction of hydrogen and fluorine. Hydrogen is produced by dissociation of hydrazine, which can be stored as liquid in light containers at room temperature.

  2. Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

    PubMed Central

    Pérez, Manuel; Caputo, Christopher B.; Dobrovetsky, Roman; Stephan, Douglas W.

    2014-01-01

    A major advance in main-group chemistry in recent years has been the emergence of the reactivity of main-group species that mimics that of transition metal complexes. In this report, the Lewis acidic phosphonium salt [(C6F5)3PF][B(C6F5)4] 1 is shown to catalyze the dehydrocoupling of silanes with amines, thiols, phenols, and carboxylic acids to form the Si-E bond (E = N, S, O) with the liberation of H2 (21 examples). This catalysis, when performed in the presence of a series of olefins, yields the concurrent formation of the products of dehydrocoupling and transfer hydrogenation of the olefin (30 examples). This reactivity provides a strategy for metal-free catalysis of olefin hydrogenations. The mechanisms for both catalytic reactions are proposed and supported by experiment and density functional theory calculations. PMID:25002489

  3. Effects of nonlocality on transfer reactions

    NASA Astrophysics Data System (ADS)

    Titus, Luke

    Nuclear reactions play a key role in the study of nuclei away from stability. Single-nucleon transfer reactions involving deuterons provide an exceptional tool to study the single-particle structure of nuclei. Theoretically, these reactions are attractive as they can be cast into a three-body problem composed of a neutron, proton, and the target nucleus. Optical potentials are a common ingredient in reactions studies. Traditionally, nucleon-nucleus optical potentials are made local for convenience. The effects of nonlocal potentials have historically been included approximately by applying a correction factor to the solution of the corresponding equation for the local equivalent interaction. This is usually referred to as the Perey correction factor. In this thesis, we have systematically investigated the effects of nonlocality on (p,d) and (d,p) transfer reactions, and the validity of the Perey correction factor. We implemented a method to solve the single channel nonlocal equation for both bound and scattering states. We also developed an improved formalism for nonlocal interactions that includes deuteron breakup in transfer reactions. This new formalism, the nonlocal adiabatic distorted wave approximation, was used to study the effects of including nonlocality consistently in ( d,p) transfer reactions. For the (p,d) transfer reactions, we solved the nonlocal scattering and bound state equations using the Perey-Buck type interaction, and compared to local equivalent calculations. Using the distorted wave Born approximation we construct the T-matrix for (p,d) transfer on 17O, 41Ca, 49Ca, 127 Sn, 133Sn, and 209Pb at 20 and 50 MeV. Additionally we studied (p,d) reactions on 40Ca using the the nonlocal dispersive optical model. We have also included nonlocality consistently into the adiabatic distorted wave approximation and have investigated the effects of nonlocality on on (d,p) transfer reactions for deuterons impinged on 16O, 40Ca, 48Ca, 126Sn, 132Sn, 208Pb at 10

  4. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water

    PubMed Central

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-01-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed ‘green technique’. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of −20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of −0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production. PMID:26541371

  5. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water

    NASA Astrophysics Data System (ADS)

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-11-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed ‘green technique’. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production.

  6. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water.

    PubMed

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-01-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed 'green technique'. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production. PMID:26541371

  7. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water.

    PubMed

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-11-06

    Splitting water for hydrogen production using light, or electrical energy, is the most developed 'green technique'. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production.

  8. Transfer reaction code with nonlocal interactions

    NASA Astrophysics Data System (ADS)

    Titus, L. J.; Ross, A.; Nunes, F. M.

    2016-10-01

    We present a suite of codes (NLAT for nonlocal adiabatic transfer) to calculate the transfer cross section for single-nucleon transfer reactions, (d , N) or (N , d) , including nonlocal nucleon-target interactions, within the adiabatic distorted wave approximation. For this purpose, we implement an iterative method for solving the second order nonlocal differential equation, for both scattering and bound states. The final observables that can be obtained with NLAT are differential angular distributions for the cross sections of A(d , N) B or B(N , d) A. Details on the implementation of the T-matrix to obtain the final cross sections within the adiabatic distorted wave approximation method are also provided. This code is suitable to be applied for deuteron induced reactions in the range of Ed =10-70 MeV, and provides cross sections with 4% accuracy.

  9. Palladium-catalyzed one pot 2-arylquinazoline formation via hydrogen-transfer strategy.

    PubMed

    Wang, Huamin; Chen, Hui; Chen, Ya; Deng, Guo-Jun

    2014-10-21

    The palladium catalytic system was first applied to 2-arylquinazoline synthesis via hydrogen transfer methodology. Various (E)-2-nitrobenzaldehyde O-methyl oximes reacted easily with alcohols or benzyl amines to provide N-heterocyclic compounds in good to high yields. Similarly, the heterocyclic products could be prepared by the reaction of 1-(2-nitrophenyl)ethanone, urea and benzyl alcohols. In these reactions, the nitro group was reduced in situ by hydrogen generated from the alcohol dehydrogenation step. PMID:25156121

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Calculation of deuterium isotope effects in proton transfer reactions

    NASA Astrophysics Data System (ADS)

    Scheiner, Steve

    1994-05-01

    Various levels of theory are tested for the purpose of computing the rate constant for proton transfer reactions. Standard transition state theory is applied to a series of molecules with a progressively more bent intramolecular hydrogen bond. The systems all display similar deuterium isotope effects (DIEs); the larger DIE at low temperature is attributed to zero-point vibrational effects. However, when tunneling is incorporated via a microcanonical approach, a dramatically enhanced effect is observed for the most distorted H-bond. The energy barrier for proton transfer between carbon atoms involved in triple bonds is smaller than for carbons with lesser multiplicity. The DIE displays a sensitivity to temperature that is least for the carbon atoms with the greatest multiplicity of bonding. The tunneling obtained by following the minimum energy reaction path along the potential energy surface is similar to that when the potential is approximated by an Eckart barrier. However, significant discrepancies are observed at temperatures below about 250 K.

  12. Vibrationally Driven Hydrogen Abstraction Reaction by Bromine Radical in Solution

    NASA Astrophysics Data System (ADS)

    Shin, Jae Yoon; Shalowski, Michael A.; Crim, F. Fleming

    2013-06-01

    Previously, we have shown that preparing reactants in specific vibrational states can affect the product state distribution and branching ratios in gas phase reactions. In the solution phase, however, no vibrational mediation study has been reported to date. In this work, we present our first attempt of vibrationally mediated bimolecular reaction in solution. Hydrogen abstraction from a solvent by a bromine radical can be a good candidate to test the effect of vibrational excitation on reaction dynamics because this reaction is highly endothermic and thus we can suppress any thermally initiated reaction in our experiment. Br radical quickly forms CT (charge transfer) complex with solvent molecule once it is generated from photolysis of a bromine source. The CT complex strongly absorbs visible light, which allows us to use electronic transient absorption for tracking Br radical population. For this experiment, we photolyze bromoform solution in dimethyl sulfoxide (DMSO) solvent with 267 nm to generate Br radical and excite the C-H stretch overtone of DMSO with 1700 nm a few hundred femtoseconds after the photolysis. Then, we monitor the population of Br-DMSO complex with 400 nm as a function of delay time between two pump beams and probe beam. As a preliminary result, we observed the enhancement of loss of Br-DMSO complex population due to the vibrational excitation. We think that increased loss of Br-DMSO complex is attributed to more loss of Br radical that abstracts hydrogen from DMSO and it is the vibrational excitation that promotes the reaction. To make a clear conclusion, we will next utilize infrared probing to directly detect HBr product formation.

  13. Thermal hydrogen-atom transfer from methane: A mechanistic exercise

    NASA Astrophysics Data System (ADS)

    Schwarz, Helmut

    2015-06-01

    Hydrogen-atom transfer (HAT) constitutes a key process in a broad range of chemical transformations as it covers heterogeneous, homogeneous, and enzymatic reactions. While open-shell metal oxo species [MO]rad are no longer regarded as being involved in the heterogeneously catalyzed oxidative coupling of methane (2CH4 + → C2H6 + H2O), these reagents are rather versatile in bringing about (gas-phase) hydrogen-atom transfer, even from methane at ambient conditions. In this mini-review, various mechanistic scenarios will be presented, and it will be demonstrated how these are affected by the composition of the metal-oxide cluster ions. Examples will be discussed, how 'doping' the clusters permits the control of the charge and spin situation at the active site and, thus, the course of the reaction. Also, the interplay between supposedly inert support material and the active site - the so-called 'aristocratic atoms' - of the gas-phase catalyst will be addressed. Finally, gas-phase HAT from methane will be analyzed in the broader context of thermal activation of inert Csbnd H bonds by metal-oxo species.

  14. CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: experimental and computational studies.

    PubMed

    Baratta, Walter; Baldino, Salvatore; Calhorda, Maria José; Costa, Paulo J; Esposito, Gennaro; Herdtweck, Eberhardt; Magnolia, Santo; Mealli, Carlo; Messaoudi, Abdelatif; Mason, Sax A; Veiros, Luis F

    2014-10-13

    Reaction of [RuCl(CNN)(dppb)] (1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2 P(CH2 )4 PPh2 ) with NaOCH2 CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2 CF3 )(dppb)] (1-OCH2 CF3 ), whose neutron diffraction study reveals a short RuO⋅⋅⋅HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)]⋅(EtOH)n (1-OEt⋅n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] (1-H) and acetaldehyde. Compound 1-OEt⋅n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt⋅n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2 ) of ketones to alcohols (turnover frequency (TOF) up to 6.5×10(4) h(-1) , 40 °C). DFT calculations were performed on the reaction of [RuH(CNN')(dmpb)] (2-H) (HCNN'=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2 P(CH2 )4 PMe2 ) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key "amide" intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2 ; both pathways have low barriers and are alcohol assisted. PMID:25195979

  15. Vibrationally enhanced tunneling as a mechanism for enzymatic hydrogen transfer.

    PubMed Central

    Bruno, W J; Bialek, W

    1992-01-01

    We present a theory of enzymatic hydrogen transfer in which hydrogen tunneling is mediated by thermal fluctuations of the enzyme's active site. These fluctuations greatly increase the tunneling rate by shortening the distance the hydrogen must tunnel. The average tunneling distance is shown to decrease when heavier isotopes are substituted for the hydrogen or when the temperature is increased, leading to kinetic isotope effects (KIEs)--defined as the factor by which the reaction slows down when isotopically substituted substrates are used--that need be no larger than KIEs for nontunneling mechanisms. Within this theory we derive a simple KIE expression for vibrationally enhanced ground state tunneling that is able to fit the data for the bovine serum amine oxidase (BSAO) system, correctly predicting the large temperature dependence of the KIEs. Because the KIEs in this theory can resemble those for nontunneling dynamics, distinguishing the two possibilities requires careful measurements over a range of temperatures, as has been done for BSAO. PMID:1420907

  16. In tandem or alone: a remarkably selective transfer hydrogenation of alkenes catalyzed by ruthenium olefin metathesis catalysts.

    PubMed

    Zieliński, Grzegorz Krzysztof; Samojłowicz, Cezary; Wdowik, Tomasz; Grela, Karol

    2015-03-01

    A system for transfer hydrogenation of alkenes, composed of a ruthenium metathesis catalyst and HCOOH, is presented. This operationally simple system can be formed directly after a metathesis reaction to effect hydrogenation of the metathesis product in a single-pot. These hydrogenation conditions are applicable to a wide range of alkenes and offer remarkable selectivity. PMID:25586518

  17. In tandem or alone: a remarkably selective transfer hydrogenation of alkenes catalyzed by ruthenium olefin metathesis catalysts.

    PubMed

    Zieliński, Grzegorz Krzysztof; Samojłowicz, Cezary; Wdowik, Tomasz; Grela, Karol

    2015-03-01

    A system for transfer hydrogenation of alkenes, composed of a ruthenium metathesis catalyst and HCOOH, is presented. This operationally simple system can be formed directly after a metathesis reaction to effect hydrogenation of the metathesis product in a single-pot. These hydrogenation conditions are applicable to a wide range of alkenes and offer remarkable selectivity.

  18. Organocatalytic Transfer Hydrogenation and Hydrosilylation Reactions.

    PubMed

    Herrera, Raquel P

    2016-06-01

    The reduction of different carbon-carbon or carbon-heteroatom double bonds is a powerful tool that generates in many cases new stereogenic centers. In the last decade, the organocatalytic version of these transformations has attracted more attention, and remarkable progress has been made in this way. Organocatalysts such as chiral Brønsted acids, thioureas, chiral secondary amines or Lewis bases have been successfully used for this purpose. In this context, this chapter will cover pioneering and seminal examples using Hantzsch dihydropyridines 1 and trichlorosilane 2 as reducing agents. More recent examples will be also cited in order to cover as much as possible the complete research in this field. PMID:27573269

  19. Organocatalytic Transfer Hydrogenation and Hydrosilylation Reactions.

    PubMed

    Herrera, Raquel P

    2016-06-01

    The reduction of different carbon-carbon or carbon-heteroatom double bonds is a powerful tool that generates in many cases new stereogenic centers. In the last decade, the organocatalytic version of these transformations has attracted more attention, and remarkable progress has been made in this way. Organocatalysts such as chiral Brønsted acids, thioureas, chiral secondary amines or Lewis bases have been successfully used for this purpose. In this context, this chapter will cover pioneering and seminal examples using Hantzsch dihydropyridines 1 and trichlorosilane 2 as reducing agents. More recent examples will be also cited in order to cover as much as possible the complete research in this field.

  20. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    PubMed

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    CONSPECTUS: A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C═X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a

  1. The reactions of carbon in a hydrogen plasma

    SciTech Connect

    Li, M.; Fan, Y.; Bao, W.; Guan, Y.; Li, S.

    2006-07-01

    Acetylene can be directly produced by coal pyrolysis in hydrogen plasma. A key factor affecting acetylene yield is whether the residue solid carbon is able to react with hydrogen to form acetylene after volatile matters released from coal powders pyrolyzed in hydrogen plasma. Reactions of carbon in hydrogen plasma are studied in this article. The study showed that solid carbon could hardly react with hydrogen at temperatures below the sublimation point, while sublimated carbon could easily react with hydrogen at temperatures above sublimation point, and mainly acetylene and other hydrocarbons can be obtained after quenching process.

  2. Coordinating Chiral Ionic Liquids: Design, Synthesis, and Application in Asymmetric Transfer Hydrogenation under Aqueous Conditions

    PubMed Central

    Vasiloiu, Maria; Gaertner, Peter; Zirbs, Ronald; Bica, Katharina

    2015-01-01

    Hydrophilic coordinating chiral ionic liquids with an amino alcohol substructure were developed and efficiently applied to the asymmetric reduction of ketones. Their careful design and adaptability to the desired reaction conditions allow for these chiral ionic liquids to be used as the sole source of chirality in a ruthenium-catalyzed transfer hydrogenation reaction of aromatic ketones. When used in this reaction system, these chiral ionic liquids afforded excellent yields and high enantioselectivities. PMID:26279638

  3. Excited-state hydrogen-atom transfer along solvent wires: water molecules stop the transfer.

    PubMed

    Tanner, Christian; Thut, Markus; Steinlin, Andreas; Manca, Carine; Leutwyler, Samuel

    2006-02-01

    Excited-state hydrogen-atom transfer (ESHAT) along a hydrogen-bonded solvent wire occurs for the supersonically cooled n = 3 ammonia-wire cluster attached to the scaffold molecule 7-hydroxyquinoline (7HQ) [Tanner, C.; et al. Science 2003, 302, 1736]. Here, we study the analogous three-membered solvent-wire clusters 7HQ.(NH3)n.(H2O)m, n + m = 3, using resonant two-photon ionization (R2PI) and UV-UV hole-burning spectroscopies. Substitution of H2O for NH3 has a dramatic effect on the excited-state H-atom transfer: The threshold for the ESHAT reaction is approximately 200 cm(-1) for 7HQ.(NH3)3, approximately 350 cm(-1) for both isomers of the 7HQ.(NH3)2.H2O cluster, and approximately 600 cm(-1) for 7HQ.NH3.(H2O)2 but increases to approximately 2000 cm(-1) for the pure 7HQ.(H2O)3 water-wire cluster. To understand the effect of the chemical composition of the solvent wire on the H-atom transfer, the reaction profiles of the low-lying electronic excited states of the n = 3 pure and mixed solvent-wire clusters are calculated with the configuration interaction singles (CIS) method. For those solvent wires with an NH3 molecule at the first position, injection of the H atom into the wire can occur by tunneling. However, further H-atom transfer is blocked by a high barrier at the first (and second) H2O molecule along the solvent wire. H-atom transfer along the entire length of the solvent wire, leading to formation of the 7-ketoquinoline (7KQ) tautomer, cannot occur for any of the H2O-containing clusters, in agreement with experimentally observed absence of 7KQ fluorescence.

  4. Coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, December 27, 1991--March 27, 1992

    SciTech Connect

    Curtis, C.W.

    1992-12-31

    The research conducted this quarter evaluated hydrogen transfer from resids reduced using the Birch reduction method and their corresponding parent resid to an aromatic acceptor, anthracene (ANT). The reactions involved thermal and catalytic reactions using sulfur introduced as thiophenol. This catalyst has been shown by Rudnick to affect the hydrogen transfer from cycloalkane to aromatics/or coal. The purpose of this current study was to evaluate the efficacy of hydrogen transfer from the hydrogen-enriched reduced resid to an aromatic species and to compare that to the hydrogen transfer from the original resid. The analyses performed to evaluate hydrogen transfer were the determination of product slates from the hydrogenation of ANT and the fractionation of the resid into solubility fractions after reaction with ANT. The amount of coal conversion to THF solubles was higher in the coprocessing reactions with the reduced resids compared to the reactions with the corresponding untreated resid. The reduction of the resids by the Birch method increased the hydrogen donating ability of the resid to the same level as that obtained with the introduction of isotetralin (ISO) to the original resid. The ISO was introduced at a level of 0.5 wt % donable hydrogen. Both the original resids and the resids reduced by the Birch method were reacted in the presence of an aromatic species, anthracene (ANT). These reactions were performed under both nitrogen and hydrogen atmospheres at a pressure of 1250 psig introduced at ambient temperature. The reactions were performed both thermally and catalytically at 380{degree}C for 30 minutes. The catalyst used was thiophenol which is the same catalyst as has been used in the previously reported model compound studies involving hydrogen transfer from cycloalkanes to aromatics.

  5. Reaction of O/sup +/, CO/sup +/, and CH/sup +/ ions with atomic hydrogen

    SciTech Connect

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

    1984-06-04

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

  6. Charge transfer reactions in multiply charged ion-atom collisions. [in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

  7. Asymmetric catalytic hydrogenation reactions in supercritical carbon dioxide

    SciTech Connect

    Burk, M.J.; Gross, M.F.; Feng, S.; Tumas, W.

    1995-08-09

    We demonstrate that asymmetric catalytic hydrogenation reactions can be conducted in supercritical CO{sub 2} and that, in some cases, higher enantioselectivities can be achieved in this solvent relative to conventional solvents. These preliminary studies effectively demonstrate the feasibility of conducting highly enantioselective hydrogenation reactions in supercritical CO{sub 2}. Importantly, we have shown that higher enantioselectivities may be achieved in supercritical CO{sub 2} relative to conventional solvents. 16 refs., 2 tabs.

  8. Formation of C-C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation.

    PubMed

    Bower, John F; Krische, Michael J

    2011-01-01

    The formation of C-C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C-C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile-nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C-H bonds. PMID:21822399

  9. Formation of C–C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

    PubMed Central

    Bower, John F.; Krische, Michael J.

    2011-01-01

    The formation of C–C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C–C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile–nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C–H bonds. PMID:21822399

  10. Electron Transfer and Reaction Mechanism of Laccases

    PubMed Central

    Jones, Stephen M.; Solomon, Edward I.

    2015-01-01

    Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (TNC) where dioxygen reduction occurs. This review outlines the electron transfer (ET) process in laccases, and the mechanism of O2 reduction as elucidated through spectroscopic, kinetic, and computational data. Marcus theory is used to describe the relevant factors which impact ET rates including the driving force (ΔG°), reorganization energy (λ), and electronic coupling matrix element (HDA). Then the mechanism of O2 reaction is detailed with particular focus on the intermediates formed during the two 2e− reduction steps. The first 2e− step forms the peroxide intermediate (PI), followed by the second 2e− step to form the native intermediate (NI), which has been shown to be the catalytically relevant fully oxidized form of the enzyme. PMID:25572295

  11. Phosphoryl Transfer Reaction Snapshots in Crystals

    PubMed Central

    Gerlits, Oksana; Tian, Jianhui; Das, Amit; Langan, Paul; Heller, William T.; Kovalevsky, Andrey

    2015-01-01

    To study the catalytic mechanism of phosphorylation catalyzed by cAMP-dependent protein kinase (PKA) a structure of the enzyme-substrate complex representing the Michaelis complex is of specific interest as it can shed light on the structure of the transition state. However, all previous crystal structures of the Michaelis complex mimics of the PKA catalytic subunit (PKAc) were obtained with either peptide inhibitors or ATP analogs. Here we utilized Ca2+ ions and sulfur in place of the nucleophilic oxygen in a 20-residue pseudo-substrate peptide (CP20) and ATP to produce a close mimic of the Michaelis complex. In the ternary reactant complex, the thiol group of Cys-21 of the peptide is facing Asp-166 and the sulfur atom is positioned for an in-line phosphoryl transfer. Replacement of Ca2+ cations with Mg2+ ions resulted in a complex with trapped products of ATP hydrolysis: phosphate ion and ADP. The present structural results in combination with the previously reported structures of the transition state mimic and phosphorylated product complexes complete the snapshots of the phosphoryl transfer reaction by PKAc, providing us with the most thorough picture of the catalytic mechanism to date. PMID:25925954

  12. An Updated Synthesis of the Diazo-Transfer Reagent Imidazole-1-sulfonyl Azide Hydrogen Sulfate.

    PubMed

    Potter, Garrett T; Jayson, Gordon C; Miller, Gavin J; Gardiner, John M

    2016-04-15

    Imidazole-1-sulfonyl azide and salts thereof are valuable reagents for diazo-transfer reactions, most particularly conversion of primary amines to azides. The parent reagent and its HCl salt present stability and detonation risks, but the hydrogen sulfate salt is significantly more stable. An updated procedure for the large-scale synthesis of this salt avoids isolation or concentration of the parent compound or HCl salt and will facilitate the use of hydrogen sulfate salt as the reagent of choice for diazo transfer. PMID:26998999

  13. [Mechanistic examination of organometallic electron transfer reactions: Annual report, 1989

    SciTech Connect

    Not Available

    1989-12-31

    Our mechanistic examination of electron transfer reactions between organometallic complexes has required data from our stopped-flow infrared spectrophotometer that was constructed in the first year. Our research on organometallic electron transfer reaction mechanisms was recognized by an invitation to the Symposium on Organometallic Reaction Mechanisms at the National ACS meeting in Miami. We have obtained a reasonable understanding of the electron transfer reactions between metal cations and anions and between metal carbonyl anions and metal carbonyl dimers. In addition we have begun to obtain data on the outer sphere electron transfer between metal carbonyl anions and coordination complexes and on reactions involving cluster anions.

  14. Reaction of Aluminum with Water to Produce Hydrogen - 2010 Update

    SciTech Connect

    Petrovic, John; Thomas, George

    2011-06-01

    A Study of Issues Related to the Use of Aluminum for On-Board Vehicular Hydrogen Storage The purpose of this White Paper is to describe and evaluate the potential of aluminum-water reactions for the production of hydrogen for on-board hydrogen-powered vehicle applications. Although the concept of reacting aluminum metal with water to produce hydrogen is not new, there have been a number of recent claims that such aluminum-water reactions might be employed to power fuel cell devices for portable applications such as emergency generators and laptop computers, and might even be considered for possible use as the hydrogen source for fuel cell-powered vehicles.

  15. Transfer Hydrogenation Employing Ethylene Diamine Bisborane in Water and Pd- and Ru-Nanoparticles in Ionic Liquids.

    PubMed

    Sahler, Sebastian; Scott, Martin; Gedig, Christian; Prechtl, Martin H G

    2015-09-17

    Herein we demonstrate the use of ethylenediamine bisborane (EDAB) as a suitable hydrogen source for transfer hydrogenation reactions on C-C double bonds mediated by metal nanoparticles. Moreover, EDAB also acts as a reducing agent for carbonyl functionalities in water under metal-free conditions.

  16. Transfer-type products accompanying cold fusion reactions

    SciTech Connect

    Adamian, G.G.; Antonenko, N.V.

    2005-12-15

    Production of nuclei heavier than the target is treated for projectile-target combinations used in cold fusion reactions leading to superheavy nuclei. These products are related to transfer-type or to asymmetry-exit-channel quasifission reactions. The production of isotopes in the transfer-type reactions emitting of {alpha} particles with large energies is discussed.

  17. Production of dimethylfuran from hydroxymethylfurfural through catalytic transfer hydrogenation with ruthenium supported on carbon.

    PubMed

    Jae, Jungho; Zheng, Weiqing; Lobo, Raul F; Vlachos, Dionisios G

    2013-07-01

    RuC ees' transfer: Transfer hydrogenation using alcohols as hydrogen donors and supported ruthenium catalysts results in the selective conversion of hydroxymethylfurfural to dimethylfuran (>80% yield). During transfer hydrogenation, the hydrogen produced from alcohols is utilized in the hydrogenation of hydroxymethylfurfural. PMID:23754805

  18. Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

    ERIC Educational Resources Information Center

    Mirich, Anne; Miller, Trisha Hoette; Klotz, Elsbeth; Mattson, Bruce

    2015-01-01

    Two gas phase deuterium/hydrogen exchange reactions are described utilizing a simple inexpensive glass catalyst tube containing 0.5% Pd on alumina through which gas mixtures can be passed and products collected for analysis. The first of these exchange reactions involves H[subscript 2] + D[subscript 2], which proceeds at temperatures as low as 77…

  19. Applications of light-induced electron-transfer and hydrogen-abstraction processes: photoelectrochemical production of hydrogen from reducing radicals

    SciTech Connect

    Chandrasekaran, K.; Whitten, D.G.

    1980-07-16

    A study of several photoprocesses which generate reducing radicals in similar photoelectrochemical cells was reported. Coupling of a light-induced reaction to produce a photocurrent concurrent with hydrogen generation in a second compartment can occur for a number of electron transfers and hydrogen abstractions in what appears to be a fairly general process. Irradiation of the RuL/sub 3//sup +2//Et/sub 3/N: photoanode compartment leads to production of a photocurrent together with generation of hydrogen at the cathode. A rather different type of reaction that also results in formation of two reducing radicals as primary photoproducts if the photoreduction of ketones and H-heteroaromatics by alcohols and other hydrogen atom donors. Irradiation of benzophenone/2-propanol/MV/sup +2/ solutions in the photoanode compartment (intensity 1.4 x 10/sup -8/ einstein/s) leads to a buildup of moderate levels of MV/sup +/ and to a steady photocurrent of 320 ..mu..A. The MV/sup +/ is oxidized at the anode of the photolyzed compartment with concomitant reduction of H/sup +/ in the cathode compartment. There was no decrease in benzophenone concentration over moderate periods of irradiation, and a steady production of hydrogen in the cathode compartment was observed. The photocurrent produced was linear with the square of absorbed light intensity. The quantum efficiency at the above-indicated intensity is 22%; quantitative analysis of the hydrogen produced gives good agreement with this value. 1 figure, 1 table. (DP)

  20. Overview of Light Hydrogen-Based Low Energy Nuclear Reactions

    NASA Astrophysics Data System (ADS)

    Miley, George H.; Shrestha, Prajakti J.

    This paper reviews light water and hydrogen-based low-energy nuclear reactions (LENRs) including the different methodologies used to study these reactions and the results obtained. Reports of excess heat production, transmutation reactions, and nuclear radiation emission are cited. An aim of this review is to present a summary of the present status of light water LENR research and provide some insight into where this research is heading.

  1. Improved performance in coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, March 27, 1990--June 26, 1990

    SciTech Connect

    Curtis, C.W.

    1990-12-31

    To gain a fundamental understanding of the role and importance of hydrogen transfer reactions in thermal and catalytic coprocessing by examining possible hydrogen donation from cycloalkane/aromatic systems and by understanding the chemistry and enhanced reactivity of hydrotreated residuum, as well as by enriching petroleum solvent with potent new donors, nonaromatic hydroaromatics, thereby promoting hydrogen transfer reactions in coprocessing. The detailed results of experiments performed on several subtasks during the quarter are presented.

  2. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  3. Tension-Enhanced Hydrogen Evolution Reaction on Vanadium Disulfide Monolayer.

    PubMed

    Pan, Hui

    2016-12-01

    Water electrolysis is an efficient way for hydrogen production. Finding efficient, cheap, and eco-friendly electrocatalysts is essential to the development of this technology. In the work, we present a first-principles study on the effects of tension on the hydrogen evolution reaction of a novel electrocatalyst, vanadium disulfide (VS2) monolayer. Two electrocatalytic processes, individual and collective processes, are investigated. We show that the catalytic ability of VS2 monolayer at higher hydrogen coverage can be efficiently improved by escalating tension. We find that the individual process is easier to occur in a wide range of hydrogen coverage and the collective process is possible at a certain hydrogen coverage under the same tension. The best hydrogen evolution reaction with near-zero Gibbs free energy can be achieved by tuning tension. We further show that the change of catalytic activity with tension and hydrogen coverage is induced by the change of free carrier density around the Fermi level, that is, higher carrier density, better catalytic performance. It is expected that tension can be a simple way to improve the catalytic activity, leading to the design of novel electrocatalysts for efficient hydrogen production from water electrolysis.

  4. Magnetically Recoverable Supported Ruthenium Catalyst for Hydrogenation of Alkynes and Transfer Hydrogenation of Carbonyl Compounds

    EPA Science Inventory

    A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe2O4) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The cata...

  5. Hydrogen addition reactions of aliphatic hydrocarbons in comets

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hitomi; Watanabe, N.; Watanabe, Y.; Fukushima, T.; Kawakita, H.

    2013-10-01

    Comets are thought as remnants of early solar nebula. Their chemical compositions are precious clue to chemical and physical evolution of the proto-planetary disk. Some hydrocarbons such as C2H6, C2H2 and CH4 in comets have been observed by using near-infrared spectroscopy. Although the compositions of C2H6 were about 1% relative to the water in normal comets, there are few reports on the detection of C2H6 in ISM. Some formation mechanisms of C2H6 in ISM have been proposed, and there are two leading hypotheses; one is the dimerizations of CH3 and another is the hydrogen addition reactions of C2H2 on cold icy grains. To evaluate these formation mechanisms for cometary C2H6 quantitatively, it is important to search the C2H4 in comets, which is the intermediate product of the hydrogen addition reactions toward C2H6. However, it is very difficult to detect the C2H4 in comets in NIR (3 microns) regions because of observing circumstances. The hydrogen addition reactions of C2H2 at low temperature conditions are not well characterized both theoretically and experimentally. For example, there are no reports on the reaction rate coefficients of those reaction system. To determine the production rates of those hydrogen addition reactions, we performed the laboratory experiments of the hydrogenation of C2H2 and C2H4. We used four types of the initial composition of the ices: pure C2H4, pure C2H2, C2H2 on amorphous solid water (ASW) and C2H4 on ASW at three different temperatures of 10, 20, and 30K. We found 1) reactions are more efficient when there are ASW in the initial compositions of the ice; 2) hydrogenation of C2H4 occur more rapid than that of C2H2.

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

    SciTech Connect

    Valentini, J.J.

    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.

  7. A Note on the Reaction of Hydrogen and Plutonium

    SciTech Connect

    Noone, Bailey C

    2012-08-15

    Plutonium hydride has many practical and experimental purposes. The reaction of plutonium and hydrogen has interesting characteristics, which will be explored in the following analysis. Plutonium is a radioactive actinide metal that emits alpha particles. When plutonium metal is exposed to air, the plutonium oxides and hydrides, and the volume increases. PuH{sub 2} and Pu{sub 2}O{sub 3} are the products. Hydrogen is a catalyst for plutonium's corrosion in air. The reaction can take place at room temperature because it is fairly insensitive to temperature. Plutonium hydride, or PuH{sub 2}, is black and metallic. After PuH{sub 2} is formed, it quickly flakes off and burns. The reaction of hydrogen and plutonium is described as pyrophoric because the product will spontaneously ignite when oxygen is present. This tendency must be considered in the storage of metal plutonium. The reaction is characterized as reversible and nonstoichiometric. The reaction goes as such: Pu + H{sub 2} {yields} PuH{sub 2}. When PuH{sub 2} is formed, the hydrogen/plutonium ratio is between 2 and 2.75 (approximately). As more hydrogen is added to the system, the ratio increases. When the ratio exceeds 2.75, PuH{sub 3} begins to form along with PuH{sub 2}. Once the ratio surpasses 2.9, only PuH{sub 3} remains. The volume of the plutonium sample increases because of the added hydrogen and the change in crystal structure which the sample undergoes. As more hydrogen is added to a system of metal plutonium, the crystal structure evolves. Plutonium has a crystal structure classified as monoclinic. A monoclinic crystal structure appears to be a rectangular prism. When plutonium reacts with hydrogen, the product PuH{sub 2}, becomes a fluorite structure. It can also be described as a face centered cubic structure. PuH{sub 3} forms a hexagonal crystal structure. As plutonium evolves from metal plutonium to plutonium hydride to plutonium trihydride, the crystal structure evolves from monoclinic to

  8. Evidence for Coupled Motion and Hydrogen Tunneling the Reaction Catalyzed by Glutamate Mutase:†

    PubMed Central

    Cheng, Mou-Chi; Marsh, E. Neil G.

    2008-01-01

    Glutamate mutase is one of a group of adenosylcobalamin-dependent enzymes that catalyze unusual isomerizations that proceed through organic radical intermediates generated by homolytic fission of coenzyme's unique cobalt-carbon bond. These enzymes are part of a larger family of enzymes that catalyze radical chemistry in which a key step is the abstraction of a hydrogen atom from an otherwise inert substrate. To gain insight into the mechanism of hydrogen transfer we previously used pre-steady state, rapid quench techniques to measure the α-secondary tritium kinetic and equilibrium isotope effects associated with the formation of 5’-deoxyadenosine when glutamate mutase was reacted with [5’-3H]-adenosylcobalamin and L-glutamate. We showed that both the kinetic and equilibrium isotope effects are large and inverse, 0.76 and 0.72 respectively. We have now repeated these measurements using glutamate deuterated in the position of hydrogen abstraction. The effect of introducing a primary deuterium kinetic isotope effect on the hydrogen transfer step is to reduce the magnitude of the secondary kinetic isotope effect to a value close to unity, 1.05 ± 0.08, whereas the equilibrium isotope effect is unchanged. The significant reduction in the secondary kinetic isotope effect is consistent with motions of the 5’-hydrogen atoms being coupled in the transition state to the motion of the hydrogen undergoing transfer, in a reaction that involves a large degree of quantum tunneling. PMID:17223710

  9. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    NASA Technical Reports Server (NTRS)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  10. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R. . Inst. de Physique); Bailey, J.M. ); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A. ); Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M. ); Huber, T.M. ); Kammel, P.; Zmeskal, J.

    1992-01-01

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of [mu][sup [minus]p] atoms in each target. The rates [lambda][sub pp[mu

  11. Hydrogen transport membranes for dehydrogenation reactions

    DOEpatents

    Balachandran; Uthamalingam

    2008-02-12

    A method of converting C.sub.2 and/or higher alkanes to olefins by contacting a feedstock containing C.sub.2 and/or higher alkanes with a first surface of a metal composite membrane of a sintered homogenous mixture of an Al oxide or stabilized or partially stabilized Zr oxide ceramic powder and a metal powder of one or more of Pd, Nb, V, Zr, Ta and/or alloys or mixtures thereof. The alkanes dehydrogenate to olefins by contact with the first surface with substantially only atomic hydrogen from the dehydrogenation of the alkanes passing through the metal composite membrane. Apparatus for effecting the conversion and separation is also disclosed.

  12. Hydrogen release from irradiated elastomers measured by Nuclear Reaction Analysis

    NASA Astrophysics Data System (ADS)

    Jagielski, J.; Ostaszewska, U.; Bielinski, D. M.; Grambole, D.; Romaniec, M.; Jozwik, I.; Kozinski, R.; Kosinska, A.

    2016-03-01

    Ion irradiation appears as an interesting method of modification of elastomers, especially friction and wear properties. Main structural effect caused by heavy ions is a massive loss of hydrogen from the surface layer leading to its smoothening and shrinking. The paper presents the results of hydrogen release from various elastomers upon irradiation with H+, He+ and Ar+ studied by using Nuclear Reaction Analysis (NRA) method. The analysis of the experimental data indicates that the hydrogen release is controlled by inelastic collisions between ions and target electrons. The last part of the study was focused on preliminary analysis of mechanical properties of irradiated rubbers.

  13. MODELING OF SYNGAS REACTIONS AND HYDROGEN GENERATION OVER SULFIDES

    SciTech Connect

    Kamil Klier; Jeffery A. Spirko; Michael L. Neiman

    2004-10-01

    The objective of the research is to analyze pathways of reactions of hydrogen with oxides of carbon over sulfides, and to predict which characteristics of the sulfide catalyst (nature of metal, defect structure) give rise to the lowest barriers toward oxygenated hydrocarbon product. Reversal of these pathways entails the generation of hydrogen, which is also proposed for study. During this study, adsorption reactions of H atoms and H{sub 2} molecules with MoS{sub 2}, both in molecular and solid form, have been modeled using high-level density functional theory. The relative stabilities of pure MoS{sub 2} edges were calculated and small clusters exhibiting properties of the edges were modeled. The results were finalized and published in the journal ''Surface Science''. Hydrogen adsorption energies on both the edges and the clusters were calculated, and the thermodynamics of hydrogen adsorption on both systems were evaluated. The adsorption locations and vibrational frequencies were also determined. These additional results were published in a second paper in ''Surface Science''. Most recently, the bonding and effect of alkali and transition metal ions was investigated on the MoS{sub 2} clusters. Potassium atoms bind to the clusters and increase the binding of hydrogen to the clusters while reducing the activation barriers for hydrogen adsorption. Silver attaches to the Mo7S14 cluster and donates its odd electron to the nearby Mo atoms and should have a similar effect to hydrogen as potassium does.

  14. Triplet-Triplet Energy Transfer Study in Hydrogen Bonding Systems.

    PubMed

    Wang, Zhijia; Zhao, Jianzhang; Guo, Song

    2015-01-01

    The 2,6-diiodoBodipy-styrylBodipy hydrogen bonding system was prepared to study the effect of hydrogen bonding on the triplet-triplet-energy-transfer (TTET) process. 2,6-DiiodoBodipy linked with N-acetyl-2,6-diaminopyridine (D-2) was used as the triplet energy donor, and the styrylBodipy connected with thymine (A-1) was used as triplet energy acceptor, thus the TTET process was established upon photoexcitation. The photophysical processes of the hydrogen bonding system were studied with steady-state UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence lifetime measurement and nanosecond time-resolved transient absorption spectroscopies. The TTET of the intramolecular/hydrogen bonding/intermolecular systems were compared through nanosecond transient absorption spectroscopy. The TTET process of the hydrogen bonding system is faster and more efficient (kTTET = 6.9 × 10(4) s(-1), ΦTTET = 94.0%) than intermolecular triplet energy transfer (kTTET = 6.0 × 10(4) s(-1), ΦTTET = 90.9%), but slower and less efficient than intramolecular triplet energy transfer (kTTET > 10(8) s(-1)). These results are valuable for designing self-assembly triplet photosensitizers and for the study of the TTET process of hydrogen bonding systems.

  15. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones.

    PubMed

    Li, Yan-Yun; Yu, Shen-Luan; Shen, Wei-Yi; Gao, Jing-Xing

    2015-09-15

    Chiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention. As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the precious metals for catalysis and sustainable chemical manufacturing. However, iron catalysts have been undeveloped compared to other transition metals. Compared with the examples of iron-catalyzed asymmetric reduction, cobalt- and nickel-catalyzed ATH and AH of ketones are even seldom reported. In early 2004, we reported the first ATH of ketones with catalysts generated in situ from iron cluster complex and chiral PNNP ligand. Since then, we have devoted ourselves to the development of ATH and AH of ketones with iron, cobalt, and nickel catalysts containing novel chiral aminophosphine ligands. In our study, the iron catalyst containing chiral aminophosphine ligands, which are expected to control the stereochemistry at the metal atom, restrict the number of possible diastereoisomers, and effectively transfer chiral information, are successful catalysts for enantioselective reduction of ketones. Among these novel chiral aminophosphine ligands, 22-membered macrocycle P2N4

  16. Polynuclear aromatic hydrocarbons hydrogenation. 1: Experimental reaction pathways and kinetics

    SciTech Connect

    Korre, S.C.; Klein, M.T. . Dept. of Chemical Engineering); Quann, R.J. . Paulsboro Research Lab.)

    1995-01-01

    The relationship between molecular structure and hydrogenation reactivity in heavy oil hydroprocessing was sought via the elucidation of the controlling reaction pathways and kinetics of one-, two-, three-, and four-fused ring compounds. Hydrogenation reactions of o-xylene, tetralin, naphthalene, phenanthrene, anthracene, pyrene, and chrysene and their multicomponent mixtures were studied in cyclohexane solvent using a presulfided CoMo/Al[sub 2]O[sub 3] catalyst in a 1-liter batch autoclave at P[sub H[sub 2

  17. Impact of Mutation on Proton Transfer Reactions in Ketosteroid Isomerase: Insights from Molecular Dynamics Simulations

    PubMed Central

    Chakravorty, Dhruva K.; Hammes-Schiffer, Sharon

    2010-01-01

    The two proton transfer reactions catalyzed by ketosteroid isomerase (KSI) involve a dienolate intermediate stabilized by hydrogen bonds with Tyr14 and Asp99. Molecular dynamics simulations based on an empirical valence bond model are used to examine the impact of mutating these residues on the hydrogen-bonding patterns, conformational changes, and van der Waals and electrostatic interactions during the proton transfer reactions. While the rate constants for the two proton transfer steps are similar for wild-type (WT) KSI, the simulations suggest that the rate constant for the first proton transfer step is smaller in the mutants due to the significantly higher free energy of the dienolate intermediate relative to the reactant. The calculated rate constants for the mutants D99L, Y14F, and Y14F/D99L relative to WT KSI are qualitatively consistent with the kinetic experiments indicating a significant reduction in the catalytic rates along the series of mutants. In the simulations, WT KSI retained two hydrogen-bonding interactions between the substrate and the active site, while the mutants typically retained only one hydrogen-bonding interaction. A new hydrogen-bonding interaction between the substrate and Tyr55 was observed in the double mutant, leading to the prediction that mutation of Tyr55 will have a greater impact on the proton transfer rates for the double mutant than for WT KSI. The electrostatic stabilization of the dienolate intermediate relative to the reactant was greater for WT KSI than for the mutants, providing a qualitative explanation for the significantly reduced rates of the mutants. The active site exhibited highly restricted motion during the proton transfer reactions, but small conformational changes occurred to facilitate the proton transfer reactions by strengthening the hydrogen-bonding interactions and by bringing the proton donor and acceptor closer to each other with the proper orientation for proton transfer. Thus, these calculations

  18. Role of iron-based catalyst and hydrogen transfer in direct coal liquefaction

    SciTech Connect

    Xian Li; Shuxun Hu; Lijun Jin; Haoquan Hu

    2008-03-15

    The aim of this research is to understand the major function of iron-based catalysts on direct coal liquefaction (DCL). Pyrolysis and direct liquefaction of Shenhua bituminous coal were carried out to investigate the effect of three solvents (wash-oil from coal-tar, cycle-oil from coal liquefaction, and tetralin) in a N{sub 2} or a H{sub 2} atmosphere and with or without catalyst. The hydrogen content in the solvent and liquid product and the H{sub 2} consumption for every run were calculated to understand the hydrogen transfer approach in DCL. The results showed that the iron-based catalyst promotes the coal pyrolysis, and the dominating function of the catalyst in DCL is to promote the formation of activated hydrogen and to accelerate the secondary distribution of H in the reaction system including the gas, liquid, and solid phases. The major transfer approach of the activated hydrogen is from molecular hydrogen to solvent and then from solvent to coal, and the solvent takes on the role of a 'bridge' in the hydrogen transfer approach. 31 refs., 5 figs., 3 tabs.

  19. Dispersed Polaron Simulations of Electron Transfer in Photosynthetic Reaction Centers

    NASA Astrophysics Data System (ADS)

    Warshel, A.; Chu, Z. T.; Parson, W. W.

    1989-10-01

    A microscopic method for simulating quantum mechanical, nuclear tunneling effects in biological electron transfer reactions is presented and applied to several electron transfer steps in photosynthetic bacterial reaction centers. In this ``dispersed polaron'' method the fluctuations of the protein and the electron carriers are projected as effective normal modes onto an appropriate reaction coordinate and used to evaluate the quantum mechanical rate constant. The simulations, based on the crystallographic structure of the reaction center from Rhodopseudomonas viridis, focus on electron transfer from a bacteriopheophytin to a quinone and the subsequent back-reaction. The rates of both of these reactions are almost independent of temperature or even increase with decreasing temperature. The simulations reproduce this unusual temperature dependence in a qualitative way, without the use of adjustable parameters for the protein's Franck-Condon factors. The observed dependence of the back-reaction on the free energy of the reaction also is reproduced, including the special behavior in the ``inverted region.''

  20. The plutonium-hydrogen reaction: SEM characterization of product morphology

    NASA Astrophysics Data System (ADS)

    Dinh, L. N.; McCall, S. K.; Saw, C. K.; Haschke, J. M.; Allen, P. G.; McLean, W.

    2014-08-01

    The product morphology of the hydrogen reaction with plutonium near the visibly observable reaction front, which separates the hydrided zone from the unreacted metal zone, has been investigated by scanning electron microscopy (SEM). Results indicate the existence of a mixed phase of metal and metal hydride, located some 20-30 μm ahead of the visibly hydrided-zone. The mixed phase regions are often located next to a grain boundary network and exhibit rays of hydride advancing toward the unreacted metal regions. Analysis indicates that hydrogen transport and therefore the hydriding reaction are preferable along the grain boundary network and defects in the metal structure rather than through a homogeneous intragrain reaction. Product fracture and formation of small hydride particles during hydriding are likely results of such inhomogeneous growth.

  1. Sorption enhanced reaction process (SERP) for production of hydrogen

    SciTech Connect

    Sircar, S.; Anand, M.; Carvill, B.

    1995-09-01

    Sorption Enhanced Reaction (SER) is a novel process that is being developed for the production of lower cost hydrogen by steam-methane reforming (SMR). In this process, the reaction of methane with steam is carried out in the presence of an admixture of a catalyst and a selective adsorbent for carbon dioxide. The consequences of SER are: (1) reformation reaction at a significantly lower temperature (300-500{degrees}C) than conventional SMR (800-1100{degrees}C), while achieving the same conversion of methane to hydrogen, (2) the product hydrogen is obtained at reactor pressure (200-400 psig) and at 99+% purity directly from the reactor (compared to only 70-75% H{sub 2} from conventional SMR reactor), (3) downstream hydrogen purification step is either eliminated or significantly reduced in size. The early focus of the program will be on the identification of an adsorbent/chemisorbent for CO{sub 2} and on the demonstration of the SER concept for SMR in our state-of-the-art bench scale process. In the latter stages, a pilot plant will be built to scale-up the technology and to develop engineering data. The program has just been initiated and no significant results for SMR will be reported. However, results demonstrating the basic principles and process schemes of SER technology will be presented for reverse water gas shift reaction as the model reaction. If successful, this technology will be commercialized by Air Products and Chemicals, Inc. (APCI) and used in its existing hydrogen business. APCI is the world leader in merchant hydrogen production for a wide range of industrial applications.

  2. Investigating Inner Sphere Reorganization via Secondary Kinetic Isotope Effects in the C–H Cleavage Reaction Catalyzed by Soybean Lipoxygenase: Tunneling in the Substrate Backbone as well as the Transferred Hydrogen

    PubMed Central

    Meyer, Matthew P.; Klinman, Judith P.

    2011-01-01

    This work describes the application of NMR to the measurement of secondary deuterium (2° 2H) and carbon-13 (13C) kinetic isotope effects (KIES) at positions 9 to 13 within the substrate linoleic acid (LA) of soybean lipoxygenase-1. The KIEs have been measured using linoleic acid labeled with either protium (11,11-h2-LA) or deuterium (11,11-d2-LA) at the reactive C11 position, which has been previously shown to yield a primary deuterium isotope effect of ca. 80. The conditions of measurement yield the intrinsic 2° 2H and 13C KIEs on kcat/Km directly for 11,11-d2-LA, whereas the values for the 2° 2H KIEs for 11,11-h2-LA are obtained after correction for a kinetic commitment. The pattern of the resulting 2° 2H and 13C isotope effects reveals values that lie far above those predicted from changes in local force constants. Additionally, many of the experimental values cannot be modeled by electronic effects, torsional strain, or the simple inclusion of a tunneling correction to the rate. Although previous studies have shown the importance of extensive tunneling for cleavage of the primary hydrogen at C11 of LA, the present findings can only be interpreted by extending the conclusion of non-classical behavior to the secondary hydrogens and carbons that flank the position undergoing C-H bond cleavage. A quantum mechanical method introduced by Buhks et al. [J. Phys. Chem. 85, 3763 (1981)] to model the inner sphere reorganization that accompanies electron transfer has been shown to be able to reproduce the scale of the 2° 2H KIEs. PMID:21192631

  3. The effect of the environment on the methyl transfer reaction mechanism between trimethylsulfonium and phenolate.

    PubMed

    Saez, David Adrian; Vogt-Geisse, Stefan; Inostroza-Rivera, Ricardo; Kubař, Tomáš; Elstner, Marcus; Toro-Labbé, Alejandro; Vöhringer-Martinez, Esteban

    2016-09-14

    Methyl transfer reactions play an important role in biology and are catalyzed by various enzymes. Here, the influence of the molecular environment on the reaction mechanism was studied using advanced ab initio methods, implicit solvation models and QM/MM molecular dynamics simulations. Various conceptual DFT and electronic structure descriptors identified different processes along the reaction coordinate e.g. electron transfer. The results show that the polarity of the solvent increases the energy required for the electron transfer and that this spontaneous process is located in the transition state region identified by the (mean) reaction force analysis and takes place through the bonds which are broken and formed. The inclusion of entropic contributions and hydrogen bond interactions in QM/MM molecular dynamics simulations with a validated DFTB3 Hamiltonian yields activation barriers in good agreement with the experimental values in contrast to the values obtained using two implicit solvation models. PMID:27524496

  4. Hydrogen evolution from water through metal sulfide reactions

    NASA Astrophysics Data System (ADS)

    Saha, Arjun; Raghavachari, Krishnan

    2013-11-01

    Transition metal sulfides play an important catalytic role in many chemical reactions. In this work, we have conducted a careful computational study of the structures, electronic states, and reactivity of metal sulfide cluster anions M2SX- (M = Mo and W, X = 4-6) using density functional theory. Detailed structural analysis shows that these metal sulfide anions have ground state isomers with two bridging sulfide bonds, notably different in some cases from the corresponding oxides with the same stoichiometry. The chemical reactivity of these metal sulfide anions with water has also been carried out. After a thorough search on the reactive potential energy surface, we propose several competitive, energetically favorable, reaction pathways that lead to the evolution of hydrogen. Selectivity in the initial water addition and subsequent hydrogen migration are found to be the key steps in all the proposed reaction channels. Initial adsorption of water is most favored involving a terminal metal sulfur bond in Mo2S4- isomers whereas the most preferred orientation for water addition involves a bridging metal sulfur bond in the case of W2S4- and M2S5- isomers. In all the lowest energy H2 elimination steps, the interacting hydrogen atoms involve a metal hydride and a metal hydroxide (or thiol) group. We have also observed a higher energy reaction channel where the interacting hydrogen atoms in the H2 elimination step involve a thiol (-SH) and a hydroxyl (-OH) group. For all the reaction pathways, the Mo sulfide reactions involve a higher barrier than the corresponding W analogues. We observe for both metals that reactions of M2S4- and M2S5- clusters with water to liberate H2 are exothermic and involve modest free energy barriers. However, the reaction of water with M2S6- is highly endothermic with a considerable barrier due to saturation of the local bonding environment.

  5. Hydrogen evolution from water through metal sulfide reactions.

    PubMed

    Saha, Arjun; Raghavachari, Krishnan

    2013-11-28

    Transition metal sulfides play an important catalytic role in many chemical reactions. In this work, we have conducted a careful computational study of the structures, electronic states, and reactivity of metal sulfide cluster anions M2S(X)(-) (M = Mo and W, X = 4-6) using density functional theory. Detailed structural analysis shows that these metal sulfide anions have ground state isomers with two bridging sulfide bonds, notably different in some cases from the corresponding oxides with the same stoichiometry. The chemical reactivity of these metal sulfide anions with water has also been carried out. After a thorough search on the reactive potential energy surface, we propose several competitive, energetically favorable, reaction pathways that lead to the evolution of hydrogen. Selectivity in the initial water addition and subsequent hydrogen migration are found to be the key steps in all the proposed reaction channels. Initial adsorption of water is most favored involving a terminal metal sulfur bond in Mo2S4(-) isomers whereas the most preferred orientation for water addition involves a bridging metal sulfur bond in the case of W2S4(-) and M2S5(-) isomers. In all the lowest energy H2 elimination steps, the interacting hydrogen atoms involve a metal hydride and a metal hydroxide (or thiol) group. We have also observed a higher energy reaction channel where the interacting hydrogen atoms in the H2 elimination step involve a thiol (-SH) and a hydroxyl (-OH) group. For all the reaction pathways, the Mo sulfide reactions involve a higher barrier than the corresponding W analogues. We observe for both metals that reactions of M2S4(-) and M2S5(-) clusters with water to liberate H2 are exothermic and involve modest free energy barriers. However, the reaction of water with M2S6(-) is highly endothermic with a considerable barrier due to saturation of the local bonding environment.

  6. Hydrogen storage reactions on titanium decorated carbon nanocones theoretical study

    NASA Astrophysics Data System (ADS)

    Shalabi, A. S.; Taha, H. O.; Soliman, K. A.; Abeld Aal, S.

    2014-12-01

    Hydrogen storage reactions on Ti decorated carbon nanocones (CNC) are investigated by using the state of the art density functional theory calculations. The single Ti atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to 6 hydrogen molecules with average adsorption energies of -1.73, -0.74, -0.57, -0.45, -0.42, and -0.35 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances, and the hydrogen storage capacity is expected to be as large as 14.34 wt%. Two types of interactions are recognized. While the interaction of 2H2 with Ti-CNC is irreversible at 532 K, the interaction of 3H2 with Ti-CNC is reversible at 392 K. Further characterizations of the former two reactions are considered in terms of projected densities of states, simulated infrared and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability. The free energy of the highest hydrogen storage capacity reaction between 6H2 and Ti-CNC meets the ultimate targets of department of energy at (233.15 K) and (11.843 atm) with surface coverage (0.941) and (direct/inverse) rate constants ratio (1.35).

  7. Thermochemical hydrogen production via a cycle using barium and sulfur - Reaction between barium sulfide and water

    NASA Technical Reports Server (NTRS)

    Ota, K.; Conger, W. L.

    1977-01-01

    The reaction between barium sulfide and water, a reaction found in several sulfur based thermochemical cycles, was investigated kinetically at 653-866 C. Gaseous products were hydrogen and hydrogen sulfide. The rate determining step for hydrogen formation was a surface reaction between barium sulfide and water. An expression was derived for the rate of hydrogen formation.

  8. Microscale Synthesis of Chiral Alcohols via Asymmetric Catalytic Transfer Hydrogenation

    ERIC Educational Resources Information Center

    Peeters, Christine M.; Deliever, Rik; De Vos, Dirk

    2009-01-01

    Synthesis of pure enantiomers is a key issue in industry, especially in areas connected to life sciences. Catalytic asymmetric synthesis has emerged as a powerful and practical tool. Here we describe an experiment on racemic reduction and asymmetric reduction via a catalytic hydrogen transfer process. Acetophenone and substituted acetophenones are…

  9. Nickel phlorin intermediate formed by proton-coupled electron transfer in hydrogen evolution mechanism

    PubMed Central

    Solis, Brian H.; Maher, Andrew G.; Dogutan, Dilek K.; Nocera, Daniel G.; Hammes-Schiffer, Sharon

    2016-01-01

    The development of more effective energy conversion processes is critical for global energy sustainability. The design of molecular electrocatalysts for the hydrogen evolution reaction is an important component of these efforts. Proton-coupled electron transfer (PCET) reactions, in which electron transfer is coupled to proton transfer, play an important role in these processes and can be enhanced by incorporating proton relays into the molecular electrocatalysts. Herein nickel porphyrin electrocatalysts with and without an internal proton relay are investigated to elucidate the hydrogen evolution mechanisms and thereby enable the design of more effective catalysts. Density functional theory calculations indicate that electrochemical reduction leads to dearomatization of the porphyrin conjugated system, thereby favoring protonation at the meso carbon of the porphyrin ring to produce a phlorin intermediate. A key step in the proposed mechanisms is a thermodynamically favorable PCET reaction composed of intramolecular electron transfer from the nickel to the porphyrin and proton transfer from a carboxylic acid hanging group or an external acid to the meso carbon of the porphyrin. The C–H bond of the active phlorin acts similarly to the more traditional metal-hydride by reacting with acid to produce H2. Support for the theoretically predicted mechanism is provided by the agreement between simulated and experimental cyclic voltammograms in weak and strong acid and by the detection of a phlorin intermediate through spectroelectrochemical measurements. These results suggest that phlorin species have the potential to perform unique chemistry that could prove useful in designing more effective electrocatalysts. PMID:26655344

  10. Transient heat transfer characteristics of liquid hydrogen, including freezing

    NASA Astrophysics Data System (ADS)

    Waynert, J. A.; Jaeger, S.; Barclay, J. A.

    1990-10-01

    This paper discusses a novel technique for obtaining the transient heating, cooling, and freezing heat transfer characteristics of liquid hydrogen. The method is based on the magnetocaloric effect (MCE). The MCE refers to the reversible change in temperature exhibited by certain magnetic materials as they experience increasing or decreasing magnetic fields. A single crystal of paramagnetic gadolinium gallium garnet (GGG) was placed in a temperature regulated chamber which could be filled with liquid hydrogen. The temperature of the GGG was monitored as it experienced relatively rapid increasing or decreasing magnetic field strengths in vacuum or in the presence of liquid hydrogen. The results of a one dimensional finite difference model were compared to the data to yield the transient heat transfer characteristics.

  11. Replacing precious metals with carbide catalysts for hydrogenation reactions

    DOE PAGES

    Ruijun, Hou; Chen, Jingguang G.; Chang, Kuan; Wang, Tiefeng

    2015-03-03

    Molybdenum carbide (Mo₂C and Ni/Mo₂C) catalysts were compared with Pd/SiO₂ for the hydrogenation of several diene molecules, 1,3- butadiene, 1,3- and 1,4-cyclohexadiene (CHD). Compared to Pd/SiO₂, Mo₂C showed similar hydrogenation rate for 1,3-butadiene and 1,3-CHD and even higher rate for 1,4-CHD, but with significant deactivation rate for 1,3-CHD hydrogenation. However, the hydrogenation activity of Mo₂C could be completely regenerated by H₂ treatment at 723 K for the three molecules. The Ni modified Mo₂C catalysts retained similar activity for 1,3-butadiene hydrogenation with significantly enhanced selectivity for 1-butene production. The 1-butene selectivity increased with increasing Ni loading below 15%. Among the Nimore » modified Mo₂C catalysts, 8.6%Ni/Mo₂C showed the highest selectivity to 1-butene, which was even higher selectivity than that over Pd/SiO₂. Compared to Pd/SiO₂, both Mo₂C and Ni/Mo₂C showed combined advantages in hydrogenation activity and catalyst cost reduction, demonstrating the potential to use less expensive carbide catalysts to replace precious metals for hydrogenation reactions.« less

  12. Replacing precious metals with carbide catalysts for hydrogenation reactions

    SciTech Connect

    Ruijun, Hou; Chen, Jingguang G.; Chang, Kuan; Wang, Tiefeng

    2015-03-03

    Molybdenum carbide (Mo₂C and Ni/Mo₂C) catalysts were compared with Pd/SiO₂ for the hydrogenation of several diene molecules, 1,3- butadiene, 1,3- and 1,4-cyclohexadiene (CHD). Compared to Pd/SiO₂, Mo₂C showed similar hydrogenation rate for 1,3-butadiene and 1,3-CHD and even higher rate for 1,4-CHD, but with significant deactivation rate for 1,3-CHD hydrogenation. However, the hydrogenation activity of Mo₂C could be completely regenerated by H₂ treatment at 723 K for the three molecules. The Ni modified Mo₂C catalysts retained similar activity for 1,3-butadiene hydrogenation with significantly enhanced selectivity for 1-butene production. The 1-butene selectivity increased with increasing Ni loading below 15%. Among the Ni modified Mo₂C catalysts, 8.6%Ni/Mo₂C showed the highest selectivity to 1-butene, which was even higher selectivity than that over Pd/SiO₂. Compared to Pd/SiO₂, both Mo₂C and Ni/Mo₂C showed combined advantages in hydrogenation activity and catalyst cost reduction, demonstrating the potential to use less expensive carbide catalysts to replace precious metals for hydrogenation reactions.

  13. Kinetic Isotope Effects as a Probe of Hydrogen Transfers to and from Common Enzymatic Cofactors

    PubMed Central

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2013-01-01

    Enzymes use a number of common cofactors as sources of hydrogen to drive biological processes, but the physics of the hydrogen transfers to and from these cofactors is not fully understood. Researchers study the mechanistically important contributions from quantum tunneling and enzyme dynamics and connect those processes to the catalytic power of enzymes that use these cofactors. Here we describe some progress that has been made in studying these reactions, particularly through the use of kinetic isotope effects (KIEs). We first discuss the general theoretical framework necessary to interpret experimental KIEs, and then describe practical uses for KIEs in the context of two case studies. The first example is alcohol dehydrogenase, which uses a nicotinamide cofactor to catalyze a hydride transfer, and the second example is thymidylate synthase, which uses a folate cofactor to catalyze both a hydride and a proton transfer. PMID:24161942

  14. Kinetic isotope effects as a probe of hydrogen transfers to and from common enzymatic cofactors.

    PubMed

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2014-02-15

    Enzymes use a number of common cofactors as sources of hydrogen to drive biological processes, but the physics of the hydrogen transfers to and from these cofactors is not fully understood. Researchers study the mechanistically important contributions from quantum tunneling and enzyme dynamics and connect those processes to the catalytic power of enzymes that use these cofactors. Here we describe some progress that has been made in studying these reactions, particularly through the use of kinetic isotope effects (KIEs). We first discuss the general theoretical framework necessary to interpret experimental KIEs, and then describe practical uses for KIEs in the context of two case studies. The first example is alcohol dehydrogenase, which uses a nicotinamide cofactor to catalyze a hydride transfer, and the second example is thymidylate synthase, which uses a folate cofactor to catalyze both a hydride and a proton transfer.

  15. Sum Frequency Generation Studies of Hydrogenation Reactions on Platinum Nanoparticles

    SciTech Connect

    Krier, James M.

    2013-08-31

    Sum Frequency Generation (SFG) vibrational spectroscopy is used to characterize intermediate species of hydrogenation reactions on the surface of platinum nanoparticle catalysts. In contrast to other spectroscopy techniques which operate in ultra-high vacuum or probe surface species after reaction, SFG collects information under normal conditions as the reaction is taking place. Several systems have been studied previously using SFG on single crystals, notably alkene hydrogenation on Pt(111). In this thesis, many aspects of SFG experiments on colloidal nanoparticles are explored for the first time. To address spectral interference by the capping agent (PVP), three procedures are proposed: UV cleaning, H2 induced disordering and calcination (core-shell nanoparticles). UV cleaning and calcination physically destroy organic capping while disordering reduces SFG signal through a reversible structural change by PVP.

  16. Biological phosphoryl-transfer reactions: understanding mechanism and catalysis.

    PubMed

    Lassila, Jonathan K; Zalatan, Jesse G; Herschlag, Daniel

    2011-01-01

    Phosphoryl-transfer reactions are central to biology. These reactions also have some of the slowest nonenzymatic rates and thus require enormous rate accelerations from biological catalysts. Despite the central importance of phosphoryl transfer and the fascinating catalytic challenges it presents, substantial confusion persists about the properties of these reactions. This confusion exists despite decades of research on the chemical mechanisms underlying these reactions. Here we review phosphoryl-transfer reactions with the goal of providing the reader with the conceptual and experimental background to understand this body of work, to evaluate new results and proposals, and to apply this understanding to enzymes. We describe likely resolutions to some controversies, while emphasizing the limits of our current approaches and understanding. We apply this understanding to enzyme-catalyzed phosphoryl transfer and provide illustrative examples of how this mechanistic background can guide and deepen our understanding of enzymes and their mechanisms of action. Finally, we present important future challenges for this field. PMID:21513457

  17. KOtBu: A Privileged Reagent for Electron Transfer Reactions?

    PubMed

    Barham, Joshua P; Coulthard, Graeme; Emery, Katie J; Doni, Eswararao; Cumine, Florimond; Nocera, Giuseppe; John, Matthew P; Berlouis, Leonard E A; McGuire, Thomas; Tuttle, Tell; Murphy, John A

    2016-06-15

    Many recent studies have used KOtBu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and SRN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KOtBu; instead, it provides new mechanistic information that in each case supports the in situ formation of organic electron donors. We go on to show that direct electron transfer from KOtBu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KOtBu, and the example that we use is CBr4. In this case, computational results support electrochemical data in backing a direct electron transfer reaction. PMID:27183183

  18. Osmium pyme complexes for fast hydrogenation and asymmetric transfer hydrogenation of ketones.

    PubMed

    Baratta, Walter; Ballico, Maurizio; Del Zotto, Alessandro; Siega, Katia; Magnolia, Santo; Rigo, Pierluigi

    2008-01-01

    The osmium compound trans,cis-[OsCl2(PPh3)2(Pyme)] (1) (Pyme=1-(pyridin-2-yl)methanamine), obtained from [OsCl2(PPh3)3] and Pyme, thermally isomerizes to cis,cis-[OsCl2(PPh3)(2)(Pyme)] (2) in mesitylene at 150 degrees C. Reaction of [OsCl2(PPh3)3] with Ph2P(CH2)(4)PPh2 (dppb) and Pyme in mesitylene (150 degrees C, 4 h) leads to a mixture of trans-[OsCl2(dppb)(Pyme)] (3) and cis-[OsCl2(dppb)(Pyme)] (4) in about an 1:3 molar ratio. The complex trans-[OsCl2(dppb)(Pyet)] (5) (Pyet=2-(pyridin-2-yl)ethanamine) is formed by reaction of [OsCl2(PPh3)3] with dppb and Pyet in toluene at reflux. Compounds 1, 2, 5 and the mixture of isomers 3/4 efficiently catalyze the transfer hydrogenation (TH) of different ketones in refluxing 2-propanol and in the presence of NaOiPr (2.0 mol %). Interestingly, 3/4 has been proven to reduce different ketones (even bulky) by means of TH with a remarkably high turnover frequency (TOF up to 5.7 x 10(5) h(-1)) and at very low loading (0.05-0.001 mol %). The system 3/4 also efficiently catalyzes the hydrogenation of many ketones (H2, 5.0 atm) in ethanol with KOtBu (2.0 mol %) at 70 degrees C (TOF up to 1.5 x 10(4) h(-1)). The in-situ-generated catalysts prepared by the reaction of [OsCl2(PPh3)3] with Josiphos diphosphanes and (+/-)-1-alkyl-substituted Pyme ligands, promote the enantioselective TH of different ketones with 91-96 % ee (ee=enantiomeric excess) and with a TOF of up to 1.9 x 10(4) h(-1) at 60 degrees C.

  19. Substituent effects on the reaction rates of hydrogen abstraction in the pyrolysis of phenethyl phenyl ethers

    SciTech Connect

    Beste, Ariana; Buchanan III, A C

    2010-01-01

    We report reaction profiles and forward rate constants for hydrogen abstraction reactions occurring in the pyrolysis of methoxy-substituted derivatives of phenethyl phenyl ether (PhCH{sub 2}CH{sub 2}OPh, PPE), where the substituents are located on the aryl ether ring (PhCH{sub 2}CH{sub 2}OPh-X). We use density functional theory in combination with transition-state theory, and anharmonic corrections are included within the independent mode approximation. PPE is the simplest model of the abundant {beta}-O-4 linkage in lignin. The mechanism of PPE pyrolysis and overall product selectivities have been studied experimentally by one of us, which was followed by computational analysis of key individual hydrogen-transfer reaction steps. In the previous work, we have been able to use a simplified kinetic model based on quasi-steady-state conditions to reproduce experimental {alpha}/{beta} selectivities for PPE and PPEs with substituents on the phenethyl ring (X-PhCH{sub 2}CH{sub 2}OPh). This model is not applicable to PPE derivatives where methoxy substituents are located on the phenyl ring adjacent to the ether oxygen because of the strongly endothermic character of the hydrogen abstraction by substituted phenoxy radicals as well as the decreased kinetic chain lengths resulting from enhanced rates of the initial C?O homolysis step. Substituents decelerate the hydrogen abstraction by the phenoxy radical, while the influence on the benzyl abstraction is less homogeneous. The calculations provide insight into the contributions of steric and polar effects in these important hydrogen-transfer steps. We emphasize the importance of an exhaustive conformational space search to calculate rate constants and product selectivities. The computed rate constants will be used in future work to numerically simulate the pyrolysis mechanism, pending the calculation of the rate constants of all participating reactions.

  20. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R.; Bailey, J.M.; Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A.; Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M.; Huber, T.M.; Kammel, P.; Zmeskal, J.; Kunselman, A.R.; Petitjean, C.

    1992-12-31

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of {mu}{sup {minus}p} atoms in each target. The rates {lambda}{sub pp{mu}} and {lambda}{sub pd} can be extracted.

  1. Probing cluster structures through sub-barrier transfer reactions

    NASA Astrophysics Data System (ADS)

    Rafferty, D. C.; Dasgupta, M.; Hinde, D. J.; Simenel, C.; Simpson, E. C.; Williams, E.; Carter, I. P.; Cook, K. J.; Luong, D. H.; McNeil, S. D.; Ramachandran, K.; Vo-Phuoc, K.; Wakhle, A.

    2016-09-01

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

  2. Electron transfer, proton transfer and photoaddition reactions in isolated clusters

    NASA Astrophysics Data System (ADS)

    Bernstein, Elliot R.

    1993-02-01

    This report contains the abstracts of the published and to be published papers from this work. They include studies of the structure of nonrigid molecules, the formation of clusters and dimers, liquid cluster structure, chemical reaction studies, and studies of cluster dynamics.

  3. Study of transfer and breakup reactions with the plastic box

    SciTech Connect

    Stokstad, R.G.; Albiston, C.R.; Bantel, M.; Chan, Y.; Countryman, P.J.; Gazes, S.; Harvey, B.G.; Homeyer, H.; Murphy, M.J.; Tserruya, I.

    1984-12-01

    The study of transfer reactions with heavy-ion projectiles is complicated by the frequent presence of three or more nuclei in the final state. One prolific source of three-body reactions is the production of a primary ejectile in an excited state above a particle threshold. A subset of transfer reactions, viz., those producing ejectiles in bound states, can be identified experimentally. This has been accomplished with a 4..pi.. detector constructed of one-millimeter-thick scintillator paddles of dimension 20 cm x 20 cm. The paddles are arranged in the form of a cube centered around the target with small entrance and exit apertures for the beam and the projectile-like fragments, (PLF). The detection of a light particle (e.g., a proton or an alpha particle) in coincidence with a PLF indicates a breakup reaction. The absence of any such coincidence indicates a reaction in which all the charge lost by the projectile was transferred to the target. With this technique we have studied the transfer and breakup reactions induced by 220 and 341 MeV /sup 20/Ne ions on a gold target. Ejectiles from Li to Ne have been measured at several scattering angles. The absolute cross sections, angular distributions and energy spectra for the transfer and breakup reactions are presented. Relatively large cross sections are observed for the complete transfer of up to seven units of charge (i.e., a nitrogen nucleus). The relatively large probabilities for ejectiles to be produced in particle-bound states suggest that on the average, most of the excitation energy in a collision resides in the heavy fragment when mass is transferred from the lighter to the heavier fragment. The gross features and trends in the energy spectra for transfer and breakup reactions are similar. 20 references.

  4. Amine, Alcohol and Phosphine Catalysts for Acyl Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Spivey, Alan C.; Arseniyadis, Stellios

    An overview of the area of organocatalytic asymmetric acyl transfer processes is presented including O- and N-acylation. The material has been ordered according to the structural class of catalyst employed rather than reaction type with the intention to draw mechanistic parallels between the manner in which the various reactions are accelerated by the catalysts and the concepts employed to control transfer of chiral information from the catalyst to the substrates.

  5. Coherent and semi-coherent neutron transfer reactions

    SciTech Connect

    Hagelstein, P.L.

    1992-01-01

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

  6. Coherent and semi-coherent neutron transfer reactions

    SciTech Connect

    Hagelstein, P.L.

    1992-12-31

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

  7. Dynamic salt effect on intramolecular charge-transfer reactions

    SciTech Connect

    Zhu Jianjun; Ma Rong; Lu Yan; Stell, George

    2005-12-08

    The dynamic salt effect in charge-transfer reactions is investigated theoretically in this paper. Free-energy surfaces are derived based on a nonequilibrium free-energy functional. Reaction coordinates are clearly defined. The solution of the reaction-diffusion equation leads to a rate constant depending on the time correlation function of the reaction coordinates. The time correlation function of the ion-atmosphere coordinate is derived from the solution of the Debye-Falkenhagen equation. It is shown that the dynamic salt effect plays an important role in controlling the rate of charge-transfer reactions in the narrow-window limit but is balanced by the energetics and the dynamics of the polar-solvent coordinate. The simplest version of the theory is compared with an experiment, and the agreement is fairly good. The theory can also be extended to charge-transfer in the class of electrolytes that has come to be called 'ionic fluids'.

  8. Hydrogen evolution from water through metal sulfide reactions

    SciTech Connect

    Saha, Arjun; Raghavachari, Krishnan

    2013-11-28

    Transition metal sulfides play an important catalytic role in many chemical reactions. In this work, we have conducted a careful computational study of the structures, electronic states, and reactivity of metal sulfide cluster anions M{sub 2}S{sub X}{sup −} (M = Mo and W, X = 4–6) using density functional theory. Detailed structural analysis shows that these metal sulfide anions have ground state isomers with two bridging sulfide bonds, notably different in some cases from the corresponding oxides with the same stoichiometry. The chemical reactivity of these metal sulfide anions with water has also been carried out. After a thorough search on the reactive potential energy surface, we propose several competitive, energetically favorable, reaction pathways that lead to the evolution of hydrogen. Selectivity in the initial water addition and subsequent hydrogen migration are found to be the key steps in all the proposed reaction channels. Initial adsorption of water is most favored involving a terminal metal sulfur bond in Mo{sub 2}S{sub 4}{sup −} isomers whereas the most preferred orientation for water addition involves a bridging metal sulfur bond in the case of W{sub 2}S{sub 4}{sup −} and M{sub 2}S{sub 5}{sup −} isomers. In all the lowest energy H{sub 2} elimination steps, the interacting hydrogen atoms involve a metal hydride and a metal hydroxide (or thiol) group. We have also observed a higher energy reaction channel where the interacting hydrogen atoms in the H{sub 2} elimination step involve a thiol (–SH) and a hydroxyl (–OH) group. For all the reaction pathways, the Mo sulfide reactions involve a higher barrier than the corresponding W analogues. We observe for both metals that reactions of M{sub 2}S{sub 4}{sup −} and M{sub 2}S{sub 5}{sup −} clusters with water to liberate H{sub 2} are exothermic and involve modest free energy barriers. However, the reaction of water with M{sub 2}S{sub 6}{sup −} is highly endothermic with a considerable

  9. Development of invar joint for hydrogen transfer line in JSNS

    NASA Astrophysics Data System (ADS)

    Teshigawara, M.; Harada, M.; Ooi, M.; Kai, T.; Maekawa, F.; Futakawa, M.

    2012-12-01

    A plan of 2nd moderator fabrication in JSNS is under way. In terms of low thermal expansion, invar joints, such as Invar-Al and Invar-SS316L joints, were developed by friction welding method as a component of hydrogen transfer line. Mechanical tests such as tensile tests, were carried out at room and cold (77 K) temperature conditions. Especially, Invar-SS316L joint gave high tensile strength (yield strength: ca. 20% higher and ultimate strength: ca. 2.5 times higher) and large strain at 77 K, and fractured not at bonding interface but at base metal of invar. In case of Invar-Al joint, it also gave high yield strength, but fracture was occurred at bonding interface. However, these joints will be available for component of hydrogen transfer line.

  10. Catalytic Transfer Hydrogenation with a Methandiide-Based Carbene Complex: An Experimental and Computational Study.

    PubMed

    Weismann, Julia; Gessner, Viktoria H

    2015-11-01

    The transfer hydrogenation (TH) reaction of ketones with catalytic systems based on a methandiide-derived ruthenium carbene complex was investigated and optimised. The complex itself makes use of the noninnocent behaviour of the carbene ligand (M=CR2 →MH-C(H)R2 ), but showed only moderate activity, thus requiring long reaction times to achieve sufficient conversion. DFT studies on the reaction mechanism revealed high reaction barriers for both the dehydrogenation of iPrOH and the hydrogen transfer. A considerable improvement of the catalytic activity could be achieved by employing triphenylphosphine as additive. Mechanistic studies on the role of PPh3 in the catalytic cycle revealed the formation of a cyclometalated complex upon phosphine coordination. This ruthenacycle was revealed to be the active species under the reaction conditions. The use of the isolated complex resulted in high catalytic activities in the TH of aromatic as well as aliphatic ketones. The complex was also found to be active under base-free conditions, suggesting that the cyclometalation is crucial for the enhanced activity. PMID:26403918

  11. Analysis of Thermal and Reaction Times for Hydrogen Reduction of Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Hegde, U.; Balasubramaniam, R.; Gokoglu, S.

    2009-01-01

    System analysis of oxygen production by hydrogen reduction of lunar regolith has shown the importance of the relative time scales for regolith heating and chemical reaction to overall performance. These values determine the sizing and power requirements of the system and also impact the number and operational phasing of reaction chambers. In this paper, a Nusselt number correlation analysis is performed to determine the heat transfer rates and regolith heat up times in a fluidized bed reactor heated by a central heating element (e.g., a resistively heated rod, or a solar concentrator heat pipe). A coupled chemical and transport model has also been developed for the chemical reduction of regolith by a continuous flow of hydrogen. The regolith conversion occurs on the surfaces of and within the regolith particles. Several important quantities are identified as a result of the above analyses. Reactor scale parameters include the void fraction (i.e., the fraction of the reactor volume not occupied by the regolith particles) and the residence time of hydrogen in the reactor. Particle scale quantities include the particle Reynolds number, the Archimedes number, and the time needed for hydrogen to diffuse into the pores of the regolith particles. The analysis is used to determine the heat up and reaction times and its application to NASA s oxygen production system modeling tool is noted.

  12. Analysis of Thermal and Reaction Times for Hydrogen Reduction of Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Hegde, U.; Balasubramaniam, R.; Gokoglu, S.

    2008-01-01

    System analysis of oxygen production by hydrogen reduction of lunar regolith has shown the importance of the relative time scales for regolith heating and chemical reaction to overall performance. These values determine the sizing and power requirements of the system and also impact the number and operational phasing of reaction chambers. In this paper, a Nusselt number correlation analysis is performed to determine the heat transfer rates and regolith heat up times in a fluidized bed reactor heated by a central heating element (e.g., a resistively heated rod, or a solar concentrator heat pipe). A coupled chemical and transport model has also been developed for the chemical reduction of regolith by a continuous flow of hydrogen. The regolith conversion occurs on the surfaces of and within the regolith particles. Several important quantities are identified as a result of the above analyses. Reactor scale parameters include the void fraction (i.e., the fraction of the reactor volume not occupied by the regolith particles) and the residence time of hydrogen in the reactor. Particle scale quantities include the particle Reynolds number, the Archimedes number, and the time needed for hydrogen to diffuse into the pores of the regolith particles. The analysis is used to determine the heat up and reaction times and its application to NASA s oxygen production system modeling tool is noted.

  13. Amide-Substituted Titanocenes in Hydrogen-Atom Transfer Catalysis.

    PubMed

    Zhang, Yong-Qiang; Jakoby, Verena; Stainer, Katharina; Schmer, Alexander; Klare, Sven; Bauer, Mirko; Grimme, Stefan; Cuerva, Juan Manuel; Gansäuer, Andreas

    2016-01-22

    Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis. PMID:26636435

  14. Catalytic Asymmetric Transfer Hydrogenation of Imines: Recent Advances.

    PubMed

    Foubelo, Francisco; Yus, Miguel

    2015-10-01

    In this review article recent developments in the asymmetric transfer hydrogenation of imines from 2008 up to today are presented. The main methodology involves either metal-catalyzed procedures in the presence of a chiral ligand or organocatalyzed technologies using a Hantzsch ester and a chiral BINOL-derived phosphoric acid. The most important procedures are collected, paying special attention to the application of this methodology in synthetic organic chemistry.

  15. A continuous flow strategy for the coupled transfer hydrogenation and etherification of 5-(hydroxymethyl)furfural using Lewis acid zeolites.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Crisci, Anthony J; Gunther, William R; Michaelis, Vladimir K; Griffin, Robert G; Román-Leshkov, Yuriy

    2014-08-01

    Hf-, Zr- and Sn-Beta zeolites effectively catalyze the coupled transfer hydrogenation and etherification of 5-(hydroxymethyl)furfural with primary and secondary alcohols into 2,5-bis(alkoxymethyl)furans, thus making it possible to generate renewable fuel additives without the use of external hydrogen sources or precious metals. Continuous flow experiments reveal nonuniform changes in the relative deactivation rates of the transfer hydrogenation and etherification reactions, which impact the observed product distribution over time. We found that the catalysts undergo a drastic deactivation for the etherification step while maintaining catalytic activity for the transfer hydrogenation step. (119) Sn and (29) Si magic angle spinning (MAS) NMR studies show that this deactivation can be attributed to changes in the local environment of the metal sites. Additional insights were gained by studying effects of various alcohols and water concentration on the catalytic reactivity. PMID:25045144

  16. A continuous flow strategy for the coupled transfer hydrogenation and etherification of 5-(hydroxymethyl)furfural using Lewis acid zeolites.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Crisci, Anthony J; Gunther, William R; Michaelis, Vladimir K; Griffin, Robert G; Román-Leshkov, Yuriy

    2014-08-01

    Hf-, Zr- and Sn-Beta zeolites effectively catalyze the coupled transfer hydrogenation and etherification of 5-(hydroxymethyl)furfural with primary and secondary alcohols into 2,5-bis(alkoxymethyl)furans, thus making it possible to generate renewable fuel additives without the use of external hydrogen sources or precious metals. Continuous flow experiments reveal nonuniform changes in the relative deactivation rates of the transfer hydrogenation and etherification reactions, which impact the observed product distribution over time. We found that the catalysts undergo a drastic deactivation for the etherification step while maintaining catalytic activity for the transfer hydrogenation step. (119) Sn and (29) Si magic angle spinning (MAS) NMR studies show that this deactivation can be attributed to changes in the local environment of the metal sites. Additional insights were gained by studying effects of various alcohols and water concentration on the catalytic reactivity.

  17. Production of 199Ir via Exotic Nucleon Transfer Reaction

    NASA Astrophysics Data System (ADS)

    Zhao, Kui; J, S. Lilley; P, V. Drumm; D, D. Warner; R, A. Cunningham; J, N. Mo

    1993-05-01

    A new nucleus 199Ir has been produced using the exotic transfer reaction 198Pt(18O, 17F)199Ir at 140 MeV. The mass of 199Ir has been measured by the determination of the reaction Q value. Its mass excess is -24.424 ± 0.034 MeV.

  18. Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

    PubMed Central

    Warren, Jeffrey J.; Mayer, James M.

    2010-01-01

    Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold’s model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions. PMID:20215463

  19. Geometric phase effects in ultracold hydrogen exchange reaction

    NASA Astrophysics Data System (ADS)

    Hazra, Jisha; Kendrick, Brian K.; Balakrishnan, N.

    2016-10-01

    The role of the geometric phase effect on chemical reaction dynamics is explored by examining the hydrogen exchange process in the fundamental H+HD reaction. Results are presented for vibrationally excited HD molecules in the v = 4 vibrational level and for collision energies ranging from 1 μK to 100 K. It is found that, for collision energies below 3 K, inclusion of the geometric phase leads to dramatic enhancement or suppression of the reaction rates depending on the final quantum state of the HD molecule. The effect was found to be the most prominent for rotationally resolved integral and differential cross sections but it persists to a lesser extent in the vibrationally resolved and total reaction rate coefficients. However, no significant GP effect is present in the reactive channel leading to the D+H2 product or in the D+H2 (v=4,j=0) \\to HD+H reaction. A simple interference mechanism involving inelastic (nonreactive) and exchange scattering amplitudes is invoked to account for the observed GP effects. The computed results also reveal a shape resonance in the H+HD reaction near 1 K and the GP effect is found to influence the magnitude of the resonant part of the cross section. Experimental detection of the resonance may allow a sensitive probe of the GP effect in the H+HD reaction.

  20. Absolute rate calculations: atom and proton transfers in hydrogen-bonded systems.

    PubMed

    Barroso, Mónica; Arnaut, Luis G; Formosinho, Sebastião J

    2005-02-01

    We calculate energy barriers of atom- and proton-transfer reactions in hydrogen-bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond-dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high-level ab initio calculations. We relate the height of the barrier with the molecular properties of the reactants and complexes. The structure of complexes with strong hydrogen bonds approaches that of the transition state, and substantially reduces the barrier height. We calculate the hydrogen-abstraction rates in H-bonded systems using the transition-state theory with the semiclassical correction for tunneling, and show that they are in excellent agreement with the experimental data. H-bonding leads to an increase in tunneling corrections at room temperature. PMID:15751360

  1. Reactions of atomic hydrogen in water : solvent and isotope effects.

    SciTech Connect

    Bartels, D. M.

    1999-06-10

    It has been known for many years that hydrogen atoms can be easily created and studied in water using radiolytic techniques [1]. The use of CW EPR detection coupled with electron radiolysis proved extremely useful in estimating many reaction rates, and revealed the interesting phenomenon of chemically induced dynamic electron polarization (CIDEP) [2]. In recent years, we have made use of pulsed EPR detection to make precision reaction rate measurements which avoid the complications of CIDEP [3]. Activation energies and H/D isotope effects measured in these studies [4-14] will be described below. An interesting aspect of the hydrogen atom reactions is the effect of hydrophobic solvation. EPR evidence--an almost gas-phase hyperfine coupling and extremely narrow linewidth--is quite convincing to show that the H atom is just a minimally perturbed gas phase atom inside a small ''bubble''. In several systems we have found that the hydrophobic free energy of solvation dominates the solvent effect on reaction rates.

  2. Revisiting the Meerwein-Ponndorf-Verley Reduction: A Sustainable Protocol for Transfer Hydrogenation of Aldehydes and Ketones

    EPA Science Inventory

    The metal-catalyzed transfer hydrogenation of carbonyl compounds has received much interest because of the immense number of opportunities that exist to prepare high-value products. This reaction is featured in numerous multi-step organic syntheses and is arguably the most import...

  3. Synthetic and mechanistic studies of metal-free transfer hydrogenations applying polarized olefins as hydrogen acceptors and amine borane adducts as hydrogen donors.

    PubMed

    Yang, Xianghua; Fox, Thomas; Berke, Heinz

    2012-01-28

    Metal-free transfer hydrogenation of polarized olefins (RR'C=CEE': R, R' = H or organyl, E, E' = CN or CO(2)Me) using amine borane adducts RR'NH-BH(3) (R = R' = H, AB; R = Me, R' = H, MAB; R = (t)Bu, R' = H, tBAB; R = R' = Me, DMAB) as hydrogen donors, were studied by means of in situ NMR spectroscopy. Deuterium kinetic isotope effects and the traced hydroboration intermediate revealed that the double H transfer process occurred regio-specifically in two steps with hydride before proton transfer characteristics. Studies on substituent effects and Hammett correlation indicated that the rate determining step of the H(N) transfer is in agreement with a concerted transition state. The very reactive intermediate [NH(2)=BH(2)] generated from AB was trapped by addition of cyclohexene into the reaction mixture forming Cy(2)BNH(2). The final product borazine (BHNH)(3) is assumed to be formed by dehydrocoupling of [NH(2)=BH(2)] or its solvent stabilized derivative [NH(2)=BH(2)]-(solvent), rather than by dehydrogenation of cyclotriborazane (BH(2)NH(2))(3) which is the trimerization product of [NH(2)=BH(2)]. PMID:22124505

  4. Mobility mechanism of hydroxyl radicals in aqueous solution via hydrogen transfer.

    PubMed

    Codorniu-Hernández, Edelsys; Kusalik, Peter G

    2012-01-11

    The hydroxyl radical (OH*) is a highly reactive oxygen species that plays a salient role in aqueous solution. The influence of water molecules upon the mobility and reactivity of the OH* constitutes a crucial knowledge gap in our current understanding of many critical reactions that impact a broad range of scientific fields. Specifically, the relevant molecular mechanisms associated with OH* mobility and the possibility of diffusion in water via a H-transfer reaction remain open questions. Here we report insights into the local hydration and electronic structure of the OH* in aqueous solution from Car-Parrinello molecular dynamics and explore the mechanism of H-transfer between OH* and a water molecule. The relatively small free energy barrier observed (~4 kcal/mol) supports a conjecture that the H-transfer can be a very rapid process in water, in accord with very recent experimental results, and that this reaction can contribute significantly to OH* mobility in aqueous solution. Our findings reveal a novel H-transfer mechanism of hydrated OH*, resembling that of hydrated OH(-) and presenting hybrid characteristics of hydrogen-atom and electron-proton transfer processes, where local structural fluctuations play a pivotal role. PMID:22107057

  5. Vibrational control of electron-transfer reactions: a feasibility study for the fast coherent transfer regime.

    PubMed

    Antoniou, P; Ma, Z; Zhang, P; Beratan, D N; Skourtis, S S

    2015-12-14

    Molecular vibrations and electron-vibrational interactions are central to the control of biomolecular electron and energy-transfer rates. The vibrational control of molecular electron-transfer reactions by infrared pulses may enable the precise probing of electronic-vibrational interactions and of their roles in determining electron-transfer mechanisms. This type of electron-transfer rate control is advantageous because it does not alter the electronic state of the molecular electron-transfer system or irreversibly change its molecular structure. For bridge-mediated electron-transfer reactions, infrared (vibrational) excitation of the bridge linking the electron donor to the electron acceptor was suggested as being capable of influencing the electron-transfer rate by modulating the bridge-mediated donor-to-acceptor electronic coupling. This kind of electron-transfer experiment has been realized, demonstrating that bridge-mediated electron-transfer rates can be changed by exciting vibrational modes of the bridge. Here, we use simple models and ab initio computations to explore the physical constraints on one's ability to vibrationally perturb electron-transfer rates using infrared excitation. These constraints stem from the nature of molecular vibrational spectra, the strengths of the electron-vibrational coupling, and the interaction between molecular vibrations and infrared radiation. With these constraints in mind, we suggest parameter regimes and molecular architectures that may enhance the vibrational control of electron transfer for fast coherent electron-transfer reactions.

  6. Arrhenius curves of hydrogen transfers: tunnel effects, isotope effects and effects of pre-equilibria

    PubMed Central

    Limbach, Hans-Heinrich; Miguel Lopez, Juan; Kohen, Amnon

    2006-01-01

    In this paper, the Arrhenius curves of selected hydrogen-transfer reactions for which kinetic data are available in a large temperature range are reviewed. The curves are discussed in terms of the one-dimensional Bell–Limbach tunnelling model. The main parameters of this model are the barrier heights of the isotopic reactions, barrier width of the H-reaction, tunnelling masses, pre-exponential factor and minimum energy for tunnelling to occur. The model allows one to compare different reactions in a simple way and prepare the kinetic data for more-dimensional treatments. The first type of reactions is concerned with reactions where the geometries of the reacting molecules are well established and the kinetic data of the isotopic reactions are available in a large temperature range. Here, it is possible to study the relation between kinetic isotope effects (KIEs) and chemical structure. Examples are the tautomerism of porphyrin, the porphyrin anion and related compounds exhibiting intramolecular hydrogen bonds of medium strength. We observe pre-exponential factors of the order of kT/h≅1013 s−1 corresponding to vanishing activation entropies in terms of transition state theory. This result is important for the second type of reactions discussed in this paper, referring mostly to liquid solutions. Here, the reacting molecular configurations may be involved in equilibria with non- or less-reactive forms. Several cases are discussed, where the less-reactive forms dominate at low or at high temperature, leading to unusual Arrhenius curves. These cases include examples from small molecule solution chemistry like the base-catalysed intramolecular H-transfer in diaryltriazene, 2-(2′-hydroxyphenyl)-benzoxazole, 2-hydroxy-phenoxyl radicals, as well as in the case of an enzymatic system, thermophilic alcohol dehydrogenase. In the latter case, temperature-dependent KIEs are interpreted in terms of a transition between two regimes with different temperature

  7. A reaction-diffusion model of cytosolic hydrogen peroxide.

    PubMed

    Lim, Joseph B; Langford, Troy F; Huang, Beijing K; Deen, William M; Sikes, Hadley D

    2016-01-01

    As a signaling molecule in mammalian cells, hydrogen peroxide (H2O2) determines the thiol/disulfide oxidation state of several key proteins in the cytosol. Localization is a key concept in redox signaling; the concentrations of signaling molecules within the cell are expected to vary in time and in space in manner that is essential for function. However, as a simplification, all theoretical studies of intracellular hydrogen peroxide and many experimental studies to date have treated the cytosol as a well-mixed compartment. In this work, we incorporate our previously reported reduced kinetic model of the network of reactions that metabolize hydrogen peroxide in the cytosol into a model that explicitly treats diffusion along with reaction. We modeled a bolus addition experiment, solved the model analytically, and used the resulting equations to quantify the spatiotemporal variations in intracellular H2O2 that result from this kind of perturbation to the extracellular H2O2 concentration. We predict that micromolar bolus additions of H2O2 to suspensions of HeLa cells (0.8 × 10(9)cells/l) result in increases in the intracellular concentration that are localized near the membrane. These findings challenge the assumption that intracellular concentrations of H2O2 are increased uniformly throughout the cell during bolus addition experiments and provide a theoretical basis for differing phenotypic responses of cells to intracellular versus extracellular perturbations to H2O2 levels.

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

    NASA Astrophysics Data System (ADS)

    Wang, Changhua; Zhang, Xintong; Liu, Yichun

    2015-12-01

    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.

  9. Effect of thermal nonequilibrium on reactions in hydrogen combustion

    NASA Astrophysics Data System (ADS)

    Voelkel, S.; Raman, V.; Varghese, P. L.

    2016-09-01

    The presence of shocks in scramjet internal flows introduces nonequilibrium of internal energy modes of the molecules. Here, the effect of vibrational nonequilibrium on key reactions of hydrogen-air combustion is studied. A quasi-classical trajectory (QCT) approach is used to derive reaction probability for nonequilibrium conditions using ab initio-derived potential energy surfaces. The reaction rates under nonequilibrium are studied using a two-temperature description, where the vibrational modes are assumed to be distributed according to a Boltzmann distribution at a characteristic vibrational temperature, in addition to a translational temperature describing the translational and rotational population distribution. At scramjet-relevant conditions, it is found that the nonequilibrium reaction rate depends not only on the level of vibrational excitation, but also on the reactants involved. Conventional two-temperature models for reaction rates, often derived using empirical means, were found to be inaccurate under these conditions, and modified parameters are proposed based on the QCT calculations. It is also found that models that include details of the reaction process through dissociation energy, for instance, provide a better description of nonequilibrium effects.

  10. Slush hydrogen transfer studies at the NASA K-Site Test Facility

    NASA Technical Reports Server (NTRS)

    Hardy, Terry L.; Whalen, Margaret V.

    1992-01-01

    An experimental study was performed as part of the National Aerospace Plane (NASP) effort to determine slush hydrogen production and transfer characteristics. Flow rate and pressure drop characteristics were determined for slush hydrogen flow through a vacuum-jacketed transfer system. These characteristics were compared to similar tests using normal boiling point and triple point hydrogen. In addition, experimental flow characteristic data was compared with predictions from the FLUSH analytical model. Slush hydrogen density loss during the transfer process was also examined.

  11. Slush hydrogen transfer studies at the NASA K-Site Test Facility

    NASA Astrophysics Data System (ADS)

    Hardy, Terry L.; Whalen, Margaret V.

    1992-07-01

    An experimental study was performed as part of the National Aerospace Plane (NASP) effort to determine slush hydrogen production and transfer characteristics. Flow rate and pressure drop characteristics were determined for slush hydrogen flow through a vacuum-jacketed transfer system. These characteristics were compared to similar tests using normal boiling point and triple point hydrogen. In addition, experimental flow characteristic data was compared with predictions from the FLUSH analytical model. Slush hydrogen density loss during the transfer process was also examined.

  12. Two-neutron transfer reactions with heavy-deformed nuclei

    SciTech Connect

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

    1988-01-01

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

  13. Path Sampling Methods for Enzymatic Quantum Particle Transfer Reactions.

    PubMed

    Dzierlenga, M W; Varga, M J; Schwartz, S D

    2016-01-01

    The mechanisms of enzymatic reactions are studied via a host of computational techniques. While previous methods have been used successfully, many fail to incorporate the full dynamical properties of enzymatic systems. This can lead to misleading results in cases where enzyme motion plays a significant role in the reaction coordinate, which is especially relevant in particle transfer reactions where nuclear tunneling may occur. In this chapter, we outline previous methods, as well as discuss newly developed dynamical methods to interrogate mechanisms of enzymatic particle transfer reactions. These new methods allow for the calculation of free energy barriers and kinetic isotope effects (KIEs) with the incorporation of quantum effects through centroid molecular dynamics (CMD) and the full complement of enzyme dynamics through transition path sampling (TPS). Recent work, summarized in this chapter, applied the method for calculation of free energy barriers to reaction in lactate dehydrogenase (LDH) and yeast alcohol dehydrogenase (YADH). We found that tunneling plays an insignificant role in YADH but plays a more significant role in LDH, though not dominant over classical transfer. Additionally, we summarize the application of a TPS algorithm for the calculation of reaction rates in tandem with CMD to calculate the primary H/D KIE of YADH from first principles. We found that the computationally obtained KIE is within the margin of error of experimentally determined KIEs and corresponds to the KIE of particle transfer in the enzyme. These methods provide new ways to investigate enzyme mechanism with the inclusion of protein and quantum dynamics.

  14. Path Sampling Methods for Enzymatic Quantum Particle Transfer Reactions.

    PubMed

    Dzierlenga, M W; Varga, M J; Schwartz, S D

    2016-01-01

    The mechanisms of enzymatic reactions are studied via a host of computational techniques. While previous methods have been used successfully, many fail to incorporate the full dynamical properties of enzymatic systems. This can lead to misleading results in cases where enzyme motion plays a significant role in the reaction coordinate, which is especially relevant in particle transfer reactions where nuclear tunneling may occur. In this chapter, we outline previous methods, as well as discuss newly developed dynamical methods to interrogate mechanisms of enzymatic particle transfer reactions. These new methods allow for the calculation of free energy barriers and kinetic isotope effects (KIEs) with the incorporation of quantum effects through centroid molecular dynamics (CMD) and the full complement of enzyme dynamics through transition path sampling (TPS). Recent work, summarized in this chapter, applied the method for calculation of free energy barriers to reaction in lactate dehydrogenase (LDH) and yeast alcohol dehydrogenase (YADH). We found that tunneling plays an insignificant role in YADH but plays a more significant role in LDH, though not dominant over classical transfer. Additionally, we summarize the application of a TPS algorithm for the calculation of reaction rates in tandem with CMD to calculate the primary H/D KIE of YADH from first principles. We found that the computationally obtained KIE is within the margin of error of experimentally determined KIEs and corresponds to the KIE of particle transfer in the enzyme. These methods provide new ways to investigate enzyme mechanism with the inclusion of protein and quantum dynamics. PMID:27497161

  15. Hydrogen evolution reaction measurements of dealloyed porous NiCu

    PubMed Central

    2013-01-01

    Porous metals are of interest for their high surface area and potential for enhanced catalytic behavior. Electrodeposited NiCu thin films with a range of compositions were electrochemically dealloyed to selectively remove the Cu component. The film structure, composition, and reactivity of these samples were characterized both before and after the dealloying step using scanning electron microscopy, energy-dispersive spectroscopy, and electrochemical measurements. The catalytic behavior of the dealloyed porous Ni samples towards the hydrogen evolution reaction was measured and compared to that of the as-deposited samples. The dealloyed samples were generally more reactive than their as-deposited counterparts at low overpotentials, making the dealloying procedure a promising area of exploration for improved hydrogen evolution catalysts. PMID:24341569

  16. Hydrogen evolution reaction measurements of dealloyed porous NiCu

    NASA Astrophysics Data System (ADS)

    Koboski, Kyla R.; Nelsen, Evan F.; Hampton, Jennifer R.

    2013-12-01

    Porous metals are of interest for their high surface area and potential for enhanced catalytic behavior. Electrodeposited NiCu thin films with a range of compositions were electrochemically dealloyed to selectively remove the Cu component. The film structure, composition, and reactivity of these samples were characterized both before and after the dealloying step using scanning electron microscopy, energy-dispersive spectroscopy, and electrochemical measurements. The catalytic behavior of the dealloyed porous Ni samples towards the hydrogen evolution reaction was measured and compared to that of the as-deposited samples. The dealloyed samples were generally more reactive than their as-deposited counterparts at low overpotentials, making the dealloying procedure a promising area of exploration for improved hydrogen evolution catalysts.

  17. Heat transfer to a supercritical hydrocarbon fuel with endothermic reaction.

    SciTech Connect

    Yu, W.; France, D. M.; Wambsganss, M. W.; Energy Technology; Univ. of Illinois at Chicago

    2000-01-01

    Supercritical fuel reforming is being studied as a technology for reducing emissions of industrial gas turbine engines. In this study, experiments were performed in a 2.67-mm-inside-diameter stainless steel tube with a heated length of 0.610 m for the purpose of investigating the characteristics of supercritical heat transfer with endothermic fuel reforming. Thermocouples were positioned along the tube both in the fluid stream and on the heated wall for local heat transfer measurements. Both heat transfer coefficients and endotherms were calculated from the measured results. State-of-the-art correlations for heat transfer were evaluated, and a correlation for supercritical heat transfer to hydrocarbon fuel has been developed. The results provide a basis for supercritical fuel heat-exchanger/reactor design and its practical applications, in an area that has received relatively little attention in the engineering literature, viz., supercritical forced convection heat transfer with endothermic chemical reaction.

  18. Exclusive Reactions at High Momentum Transfer

    NASA Astrophysics Data System (ADS)

    Radyushkin, Anatoly; Stoler, Paul

    2008-03-01

    Hard exclusive scattering at JLab / P. Kroll -- AdS/CFT and exclusive processes in QCD / S. J. Brodsky and G. F. de Téramond -- Hadron structure matters in collisions at high energy and momentum / A. W. Thomas -- Inclusive perspectives / P. Hoyer -- Fitting DVCS at NLO and beyond / K. Kumericki, D. Müller and K. Passek-Kumericki -- Spin-orbit correlations and single-spin asymmetries / M. Burkardt -- Electroproduction of soft pions at large momentum transfers / V. M. Braun, D. Yu. Ivanov and A. Peters -- Color transparency: 33 years and still running / M. Strikman -- Meson clouds and nucleon electromagnetic form factors / G. A. Miller -- Covariance, dynamics and symmetries, and hadron form factors / M. S. Bhagwat, I. C. Cloët and C. D. Roberts -- N to [symbol] electromagnetic and axial form factors in full QCD / C. Alexandrou -- Real and virtual compton scattering in perturbative QCD / C.-R. Ji and R. Thomson -- Deeply virtual compton scattering at Jefferson Lab / F. Sabatie -- DVCS at HERMES: recent results / F. Ellinghaus -- Deeply virtual compton scattering with CLAS / F. X. Girod -- Deeply virtual compton scattering off the neutron at JLab Hall A / M. Mazouz -- The future DVCS experiments in Hall A at JLab / J. Roche -- Deeply virtual compton scattering with CLAS12 / L. Elouadrhiri -- Quark helicity flip and the transverse spin dependence of inclusive DIS / A. Afanasev, M. Strikman and C. Weiss -- Deeply virtual pseudoscalar meson production / V. Kubarovsky and P. Stoler -- Exclusive p[symbol] electroproduction on the proton: GPDs or not GPDs? / M. Guidal and S. Morrow -- p[symbol] transverse target spin asymmetry at HERMES / A. Airapetian -- Electroproduction of ø(1020) mesons / J. P. Santoro and E. S. Smith -- Generalized parton distributions from hadronic observables / S. Ahmad ... [et al.] -- Imaging the proton via hard exclusive production in diffractive pp scattering / G. E. Hyde ... [et al.] -- Regge contributions to exclusive electro-production / A

  19. Exclusive Reactions at High Momentum Transfer

    NASA Astrophysics Data System (ADS)

    Radyushkin, Anatoly; Stoler, Paul

    2008-03-01

    Hard exclusive scattering at JLab / P. Kroll -- AdS/CFT and exclusive processes in QCD / S. J. Brodsky and G. F. de Téramond -- Hadron structure matters in collisions at high energy and momentum / A. W. Thomas -- Inclusive perspectives / P. Hoyer -- Fitting DVCS at NLO and beyond / K. Kumericki, D. Müller and K. Passek-Kumericki -- Spin-orbit correlations and single-spin asymmetries / M. Burkardt -- Electroproduction of soft pions at large momentum transfers / V. M. Braun, D. Yu. Ivanov and A. Peters -- Color transparency: 33 years and still running / M. Strikman -- Meson clouds and nucleon electromagnetic form factors / G. A. Miller -- Covariance, dynamics and symmetries, and hadron form factors / M. S. Bhagwat, I. C. Cloët and C. D. Roberts -- N to [symbol] electromagnetic and axial form factors in full QCD / C. Alexandrou -- Real and virtual compton scattering in perturbative QCD / C.-R. Ji and R. Thomson -- Deeply virtual compton scattering at Jefferson Lab / F. Sabatie -- DVCS at HERMES: recent results / F. Ellinghaus -- Deeply virtual compton scattering with CLAS / F. X. Girod -- Deeply virtual compton scattering off the neutron at JLab Hall A / M. Mazouz -- The future DVCS experiments in Hall A at JLab / J. Roche -- Deeply virtual compton scattering with CLAS12 / L. Elouadrhiri -- Quark helicity flip and the transverse spin dependence of inclusive DIS / A. Afanasev, M. Strikman and C. Weiss -- Deeply virtual pseudoscalar meson production / V. Kubarovsky and P. Stoler -- Exclusive p[symbol] electroproduction on the proton: GPDs or not GPDs? / M. Guidal and S. Morrow -- p[symbol] transverse target spin asymmetry at HERMES / A. Airapetian -- Electroproduction of ø(1020) mesons / J. P. Santoro and E. S. Smith -- Generalized parton distributions from hadronic observables / S. Ahmad ... [et al.] -- Imaging the proton via hard exclusive production in diffractive pp scattering / G. E. Hyde ... [et al.] -- Regge contributions to exclusive electro-production / A

  20. Multidimensional modelling to investigate interspecies hydrogen transfer in anaerobic biofilms.

    PubMed

    Batstone, D J; Picioreanu, C; van Loosdrecht, M C M

    2006-09-01

    Anaerobic digestion is a multistep process, mediated by a functionally and phylogenetically diverse microbial population. One of the crucial steps is oxidation of organic acids, with electron transfer via hydrogen or formate from acetogenic bacteria to methanogens. This syntrophic microbiological process is strongly restricted by a thermodynamic limitation on the allowable hydrogen or formate concentration. In order to study this process in more detail, we developed an individual-based biofilm model which enables to describe the processes at a microbial resolution. The biochemical model is the ADM1, implemented in a multidimensional domain. With this model, we evaluated three important issues for the syntrophic relationship: (i) Is there a fundamental difference in using hydrogen or formate as electron carrier? (ii) Does a thermodynamic-based inhibition function produced substantially different results from an empirical function? and; (iii) Does the physical co-location of acetogens and methanogens follow directly from a general model. Hydrogen or formate as electron carrier had no substantial impact on model results. Standard inhibition functions or thermodynamic inhibition function gave similar results at larger substrate field grid sizes (> 10 microm), but at smaller grid sizes, the thermodynamic-based function reduced the number of cells with long interspecies distances (> 2.5 microm). Therefore, a very fine grid resolution is needed to reflect differences between the thermodynamic function, and a more generic inhibition form. The co-location of syntrophic bacteria was well predicted without a need to assume a microbiological based mechanism (e.g., through chemotaxis) of biofilm formation.

  1. Charge transfer in proton-hydrogen collisions under Debye plasma

    SciTech Connect

    Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

    2015-02-15

    The effect of plasma environment on the 1s → nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20–1000 keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature.

  2. Charge transfer in proton-hydrogen collisions under Debye plasma

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

    2015-02-01

    The effect of plasma environment on the 1s → nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20-1000 keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature.

  3. Homolytic N–H Activation of Ammonia: Hydrogen Transfer of Parent Iridium Ammine, Amide, Imide, and Nitride Species

    PubMed Central

    2015-01-01

    The redox series [Irn(NHx)(PNP)] (n = II–IV, x = 3–0; PNP = N(CHCHPtBu2)2) was examined with respect to electron, proton, and hydrogen atom transfer steps. The experimental and computational results suggest that the IrIII imido species [Ir(NH)(PNP)] is not stable but undergoes disproportionation to the respective IrII amido and IrIV nitrido species. N–H bond strengths are estimated upon reaction with hydrogen atom transfer reagents to rationalize this observation and are used to discuss the reactivity of these compounds toward E–H bond activation. PMID:26192601

  4. Hydrogen-transferring pyrolysis of long-chain alkanes and thermal stability improvement of jet fuels by hydrogen donors

    SciTech Connect

    Song, C.; Lai, W.C.; Schobert, H.H. . Fuel Science Program)

    1994-03-01

    Hydrogen-transferring pyrolysis refers to the thermal decomposition of hydrocarbons in the presence of hydrogen donors. Relative to the pyrolysis of pure n-tetradecane (C[sub 14]H[sub 28]) at 450 C, adding 10 vol % of H-donor tetralin suppressed n-C[sub 14] conversion by 68 % after 12 min of residence time, by about 66% after 21 min, and by 37% after 30 min. The presence of tetralin not only inhibited the n-C[sub 14] decomposition, but also altered the product distribution. The decomposition and isomerization of primary radicals are strongly suppressed, leading to a much higher ratio of the 1-alkene to n-alkane with 12 carbon atoms and slightly higher alkene/alkane ratio for the other product groups. The overall reaction mechanism for the initial stage of hydrogen-transferring pyrolysis is characterized by a one-step [beta]-scission of secondary radical followed by H-abstraction of the resulting primary radical. Moreover, desirable effects of the H-donor are also observed even after 240 min at 450 C, especially for inhibiting solid deposition. The authors also examined the effect of tetralin addition on the deposit formation from a paraffinic jet fuel JP-8 which is rich in C[sub 9]-C[sub 16] long-chain alkanes, and an aromatic compound, n-butylbenzene. Adding 10 vol % tetralin to a JP-8 jet fuel, n-C[sub 14], and n-butylbenzene reduced the formation of deposits by 90% (from 3.1 to 0.3 wt %), 77 % (from 3.0 to 0.7 wt %), and 54 % (from 5.6 to 2.6 wt %), respectively. These results suggest that, by taking advantage of H-transferring pyrolysis, hydrocarbon jet fuels may be used at high operating temperatures with little or no solid deposition.

  5. Dependence of Vibronic Coupling on Molecular Geometry and Environment: Bridging Hydrogen Atom Transfer and Electron–Proton Transfer

    PubMed Central

    2016-01-01

    The rate constants for typical concerted proton-coupled electron transfer (PCET) reactions depend on the vibronic coupling between the diabatic reactant and product states. The form of the vibronic coupling is different for electronically adiabatic and nonadiabatic reactions, which are associated with hydrogen atom transfer (HAT) and electron–proton transfer (EPT) mechanisms, respectively. Most PCET rate constant expressions rely on the Condon approximation, which assumes that the vibronic coupling is independent of the nuclear coordinates of the solute and the solvent or protein. Herein we test the Condon approximation for PCET vibronic couplings. The dependence of the vibronic coupling on molecular geometry is investigated for an open and a stacked transition state geometry of the phenoxyl-phenol self-exchange reaction. The calculations indicate that the open geometry is electronically nonadiabatic, corresponding to an EPT mechanism that involves significant electronic charge redistribution, while the stacked geometry is predominantly electronically adiabatic, corresponding primarily to an HAT mechanism. Consequently, a single molecular system can exhibit both HAT and EPT character. The dependence of the vibronic coupling on the solvent or protein configuration is examined for the soybean lipoxygenase enzyme. The calculations indicate that this PCET reaction is electronically nonadiabatic with a vibronic coupling that does not depend significantly on the protein environment. Thus, the Condon approximation is shown to be valid for the solvent and protein nuclear coordinates but invalid for the solute nuclear coordinates in certain PCET systems. These results have significant implications for the calculation of rate constants, as well as mechanistic interpretations, of PCET reactions. PMID:26412613

  6. The reaction of cobaloximes with hydrogen: Products and thermodynamics

    SciTech Connect

    Estes, Deven P.; Grills, David C.; Norton, Jack R.

    2014-11-26

    In this study, a cobalt hydride has been proposed as an intermediate in many reactions of the Co(dmgBF₂)₂L₂ system, but its observation has proven difficult. We have observed the UV–vis spectra of Co(dmgBF₂)₂L₂ (1) in CH₃CN under hydrogen pressures up to 70 atm. A Co(I) compound (6), with an exchangeable proton, is eventually formed. We have determined the bond dissociation free energy and pKa of the new O–H bond in 6 to be 50.5 kcal/mol and 13.4, respectively, in CH₃CN, matching previous reports.

  7. Charge transfer in collisions of doubly charged ions of iron and nickel with hydrogen atoms

    SciTech Connect

    Neufeld, D.A.; Dalgarno, A.

    1987-04-01

    The Landau-Zener approximation is used to compute the charge-transfer recombination rate coefficients of Fe/sup 2+/ and Ni/sup 2+/ in hydrogen at thermal energies. The energy separations of the adiabatic potential-energy curves of the quasimolecules FeH/sup 2+/ and NiH/sup 2+/ are obtained from one-electron calculations. The rate coefficients are of the order of 10/sup -9/ cm/sup 3/X sup -1: or greater. Charge transfer of Fe/sup 2+/ occurs preferentially into the ground state of Fe/sup +/ so that the reverse process of charge-transfer ionization of Fe/sup +/ in collision with H/sup +/ also occurs rapidly above the reaction threshold.

  8. Hydrogen-Borrowing and Interrupted-Hydrogen-Borrowing Reactions of Ketones and Methanol Catalyzed by Iridium**

    PubMed Central

    Shen, Di; Poole, Darren L; Shotton, Camilla C; Kornahrens, Anne F; Healy, Mark P; Donohoe, Timothy J

    2015-01-01

    Reported herein is the use of catalytic [{Ir(cod)Cl}2] to facilitate hydrogen-borrowing reactions of ketone enolates with methanol at 65 °C. An oxygen atmosphere accelerates the process, and when combined with the use of a bulky monodentate phosphine ligand, interrupts the catalytic cycle by preventing enone reduction. Subsequent addition of pro-nucleophiles to the reaction mixture allowed a one-pot methylenation/conjugate addition protocol to be developed, which greatly expands the range of products that can be made by this methodology. PMID:25491653

  9. Coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, March 28, 1992--June 30, 1992

    SciTech Connect

    Curtis, C.W.

    1992-12-31

    Hydrogen transfer from naphthenes to aromatics, coal, resid, and coal plus resid has been investigated at 430{degree}C in a N{sub 2} atmosphere. The reaction of perhydropyrene (PHP) with anthracene (ANT) resulted in the formation of pyrene (PYR) and dihydroanthracene. The weight percents of the products formed varied according to the initial ratio of ANT/PHP with a minimum appearing at a 2:1 weight ratio. Increased reaction times and high ANT/PHP ratios also yielded tetrahydroanthracene (THA). Reactions of Illinois No. 6 coal from the Argonne Premium Coal Sample Bank with PHP, ANT, and PYR resulted in higher coal conversion with PHP and lower with ANT and PYR. Reactions of PHP with resid resulted in less retrogressive reactions occurring in the resid than with either PYR or ANT. Apparent hydrogen transfer from coal or resid to ANT and PYR was observed. Combining PHP with ANT or PYR with coal, resid or coal plus resid yielded higher conversions and less retrogressive reactions. Hydrogen transfer occurred from PHP to ANT or PYR and to the coal and resid as evinced by the increased conversion.

  10. Femtochemistry of Intramolecular Charge and Proton Transfer Reactions in Solution

    SciTech Connect

    Douhal, Abderrazzak; Sanz, Mikel; Carranza, Maria Angeles; Organero, Juan Angel; Tormo, Laura

    2005-03-17

    We report on the first observation of ultrafast intramolecular charge- and proton-transfer reactions in 4'-dimethylaminoflavonol (DAMF) in solution. Upon femtosecond excitation of a non-planar structure of DMAF in apolar medium, the intramolecular charge transfer (ICT) does not occur, and a slow (2 ps) proton motion takes place. However, in polar solvents, the ICT is very fast (100-200 fs) and the produced structure is stabilized that proton motion takes place in few or tens of ps.

  11. Catalytic transfer hydrogenation for stabilization of bio-oil oxygenates: reduction of p-cresol and furfural over bimetallic Ni-Cu catalysts using isopropanol

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Transfer hydrogenation and hydrodeoxygenation of model bio-oil compounds (p-cresol and furfural) and bio-oils derived from biomass via traditional pyrolysis and tail-gas reactive pyrolysis (TGRP) were conducted. Mild batch reaction conditions were employed, using isopropanol as a hydrogen donor over...

  12. Intrinsic barriers for H-atom transfer reactions involving hydrocarbons

    SciTech Connect

    Camaioni, D.M.; Autrey, S.T.; Franz, J.A.

    1994-08-01

    Intrinsic barriers (formally the barrier in the absence of driving force) for H-atom transfer reactions are key parameters in Evans-Polyanyi and Marcus equations for estimating exothermic reaction barriers and are fundamentally significant for the insight they provide about bond reorganization energies for formation of transition state structures. Although knowable from experiment, relatively few of these barriers have been measured due to experimental difficulties in measuring rates for identity reactions. Thus, the authors have used semiempirical Molecular Orbital theoretical methods (MNDO/PM3) to calculate barriers for a series of H-atom transfer identity reactions involving alkyl, alkenyl, arylalkyl and hydroaryl radicals and donors. Briefly stated, they find that barriers decrease with the degree of alkyl substitution at the radical site whereas barriers increase with the degree of conjugation with the radical site. Details of the methodology and analyses of how these barrier heights correlate with reactant and transition state properties will be presented and discussed.

  13. Coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, September 26, 1991--December 26, 1991

    SciTech Connect

    Curtis, C.W.

    1991-12-31

    The research conducted during this quarter evaluated hydrogen transfer from hydroaromatics and cyclic olefins to aromatics under thermal and catalytic conditions. The reactions under study involved thermal reactions of a cyclic olefin, isotetralin (ISO), with aromatics, anthracene (ANT) and pyrene (PYR). These reactions completed a set of experiments with hydrogen-rich species and aromatics previously reported that included cycloalkanes of perhydropyrene (PHP) and perhydroanthracene (PHA), hydroaromatic donors, tetralin (TET) and dihydroanthracene (DHA), cyclic olefins, hexahydroanthracene (HHA) and ISO, and aromatics, PYR and ANT. Catalytic reactions performed this quarter used a sulfur catalyst that had been shown by Rudnick to affect the hydrogen transfer from cycloalkanes to aromatics and/or coal. Rudnick investigated the dehydrogenation of alicyclic compounds converting them to the corresponding aromatic compounds in a process in which the alicyclic compounds served as hydrogen donors. Thiophenol and thiol were effective catalysts and helped promote the conversion of alicyclic compounds to aromatic compounds. The research performed in our laboratory focused on evaluating the effect of a sulfur catalyst on the transfer of hydrogen from cycloalkanes like perhydropyrene (PHP) to aromatics like anthracene under catalytic conditions. The catalyst used in this study was sulfur generated from thiophenol present at a concentration level of 2000 ppm of sulfur. The reactions were performed under two temperature conditions, 380 and 440{degrees}C; both thermal and catalytic reactions were performed for comparison. In addition, the individual cycloalkane and aromatic compounds were reacted under these conditions so that a direct comparison of the effect of temperature and of catalyst on the reaction products formed could be made.

  14. Impact of Distal Mutation on Hydrogen Transfer Interface and Substrate Conformation in Soybean Lipoxygenase

    PubMed Central

    Edwards, Sarah J.; Soudackov, Alexander V.

    2010-01-01

    The impact of distal mutation on the hydrogen transfer interface properties and on the substrate mobility, conformation, and orientation in soybean lipoxygenase-1 (SLO) is examined. SLO catalyzes a hydrogen abstraction reaction that occurs by a proton-coupled electron transfer mechanism. Mutation of isoleucine 553 to less bulky residues has been found experimentally to increase the magnitude and temperature dependence of the kinetic isotope effect for this reaction. This residue borders the linoleic acid substrate but is ~15 Å from the active site iron. In the present study, we model these experimental data with a vibronically nonadiabatic theory and perform all-atom molecular dynamics simulations on the complete solvated wild-type and mutant enzymes. Our calculations indicate that the proton transfer equilibrium distance increases and the associated frequency decreases as residue 553 becomes less bulky. The molecular dynamics simulations illustrate that this mutation impacts the mobility, geometrical conformation, and orientation of the linoleic acid within the active site. In turn, these effects alter the proton donor-acceptor equilibrium distance and frequency, leading to the experimentally observed changes in the magnitude and temperature dependence of the kinetic isotope effect. This study provides insight into how the effects of distal mutations may be transmitted in enzymes to ultimately impact the catalytic rates. PMID:20423074

  15. Ruthenium-Catalyzed Transfer Hydrogenation for C-C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs.

    PubMed

    Perez, Felix; Oda, Susumu; Geary, Laina M; Krische, Michael J

    2016-06-01

    Merging the chemistry of transfer hydrogenation and carbonyl or imine addition, a broad new family of redox-neutral or reductive hydrohydroxyalkylations and hydroaminomethylations have been developed. In these processes, hydrogen redistribution between alcohols and π-unsaturated reactants is accompanied by C-C bond formation, enabling direct conversion of lower alcohols to higher alcohols. Similarly, hydrogen redistribution between amines to π-unsaturated reactants results in direct conversion of lower amines to higher amines. Alternatively, equivalent products of hydrohydroxyalkylation and hydroaminomethylation may be generated through the reaction of carbonyl compounds or imines with π-unsaturated reactants under the conditions of 2-propanol-mediated reductive coupling. Finally, using vicinally dioxygenated reactants, that is, diol, ketols, or diones, successive transfer hydrogenative coupling occurs to generate 2 C-C bonds, resulting in products of formal [4+2] cycloaddition. PMID:27573275

  16. Concerted Hydrogen Atom and Electron Transfer Mechanism for Catalysis by Lysine-Specific Demethylase

    PubMed Central

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

    2015-01-01

    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 multi-configuration 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 QM atoms and which is parametrized with a 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 102090 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. PMID:23725223

  17. Rydberg phases of Hydrogen and low energy nuclear reactions

    NASA Astrophysics Data System (ADS)

    Olafsson, Sveinn; Holmlid, Leif

    2016-03-01

    For over the last 26 years the science of cold fusion/LENR has been researched around the world with slow pace of progress. Modest quantity of excess heat and signatures of nuclear transmutation and helium production have been confirmed in experiments and theoretical work has only resulted in a large flora of inadequate theoretical scenarios. Here we review current state of research in Rydberg matter of Hydrogen that is showing strong signature of nuclear processes. In the presentation experimental behavior of Rydberg matter of hydrogen is described. An extensive collaboration effort of surface physics, catalysis, atomic physics, solid state physics, nuclear physics and quantum information is need to tackle the surprising experimental results that have so far been obtained. Rydberg matter of Hydrogen is the only known state of matter that is able to bring huge collection of protons to so short distances and for so long time that tunneling becomes a reasonable process for making low energy nuclear reactions. Nuclear quantum entanglement can also become realistic process at theses conditions.

  18. An annulative transfer hydrogenation strategy enables straightforward access to tetrahydro fused-pyrazine derivatives.

    PubMed

    Xiong, Biao; Zhang, Shu-Di; Chen, Lu; Li, Bin; Jiang, Huan-Feng; Zhang, Min

    2016-08-23

    A ruthenium-catalysed annulative transfer hydrogenation strategy, enabling straightforward access to tetrahydro fused-pyrazine derivatives from N-heteroaryl diamines and vicinal diols, has been demonstrated for the first time. Such a synthesis proceeds with unprecedented synthetic effectiveness including high step- and atom efficiency, generation of water as the sole by-product, short reaction time and no need for external high pressure H2 gas, offering an important basis for the transformation of vicinal diols, a class of bio-mass derived resources, into functionalized products. PMID:27499170

  19. Sorption Enhanced Reaction Process (SERP) for production of hydrogen

    SciTech Connect

    Anand, M.; Hufton, J.; Mayorga, S.

    1996-10-01

    Sorption Enhanced Reaction Process (SERP) is a novel process that is being developed for the production of lower cost hydrogen by steam-methane reforming (SMR). In this process the reaction of methane with steam is carried out in the presence of an admixture of a catalyst and a selective adsorbent for carbon dioxide. The key consequences of SERP are: (i) reformation reaction is carried out at a significantly lower temperature (300-500{degrees}C) than that in a conventional SMR reactor (800-1100{degrees}C), while achieving the same conversion of methane to hydrogen, (ii) the product hydrogen is obtained at reactor pressure (200-400 psig) and at 98+% purity directly from the reactor (compared to only 70-75% H{sub 2} from conventional SMR reactor), (iii) downstream hydrogen purification step is either eliminated or significantly reduced in size. The first phase of the program has focused on the development of a sorbent for CO{sub 2} which has (a) reversible CO{sub 2} capacity >0.3 mmol/g at low partial pressures of CO{sub 2} (0.1 - 1.0 atm) in the presence of excess steam (pH{sub 2}O/pCO{sub 2}>20) at 400-500{degrees}C and (b) fast sorption-desorption kinetics for CO{sub 2}, at 400-500{degrees}C. Several families of supported sorbents have been identified that meet the target CO{sub 2} capacity. A few of these sorbents have been tested under repeated sorption/desorption cycles and extended exposure to high pressure steam at 400-500{degrees}C. One sorbent has been scaled up to larger quantities (2-3 kg) and tested in the laboratory process equipment for sorption and desorption kinetics of CO{sub 2}. The CO{sub 2}, sorption and desorption kinetics are desirably fast. This was a critical path item for the first phase of the program and now has been successfully demonstrated. A reactor has been designed that will allow nearly isothermal operation for SERP-SMR. This reactor was integrated into an overall process flow diagram for the SERP-SMR process.

  20. Disulfide bond cleavage: a redox reaction without electron transfer.

    PubMed

    Hofbauer, Florian; Frank, Irmgard

    2010-05-01

    By using Car-Parrinello molecular dynamics (CPMD) simulations we have simulated a mechanically induced redox reaction. Previous single-molecule atomic force microscopy (AFM) experiments demonstrated that the reduction of disulfide bonds in proteins with the weak reducing agent dithiothreitol depends on a mechanical destabilization of the breaking bond. With reactive molecular dynamics simulations the single steps of the reaction mechanism can be elucidated and the motion of the electrons can be monitored. The simulations show that the redox reaction consists of the heterolytic cleavage of the S--S bond followed by a sequence of proton transfers. PMID:20349464

  1. Non-catalytic transfer hydrogenation in supercritical CO2 for coal liquefaction

    NASA Astrophysics Data System (ADS)

    Elhussien, Hussien

    This thesis presents the results of the investigation on developing and evaluating a low temperature (<150°C) non - catalytic process using a hydrogen transfer agent (instead of molecu-lar hydrogen) for coal dissolution in supercritical CO2. The main idea behind the thesis was that one hydrogen atom from water and one hydrogen atom from the hydrogen transfer agent (HTA) were used to hydrogenate the coal. The products of coal dissolution were non-polar and polar while the supercritical CO2, which enhanced the rates of hydrogenation and dissolution of the non-polar molecules and removal from the reaction site, was non-polar. The polar modifier (PM) for CO2 was added to the freed to aid in the dissolution and removal of the polar components. The addition of a phase transfer agent (PTA) allowed a seamless transport of the ions and by-product between the aqueous and organic phases. DDAB, used as the PTA, is an effective phase transfer catalyst and showed enhancement to the coal dissolution process. COAL + DH- +H 2O → COAL.H2 + DHO-- This process has a great feature due to the fact that the chemicals were obtained without requir-ing to first convert coal to CO and H2 units as in indirect coal liquefaction. The experiments were conducted in a unique reactor set up that can be connected through two lines. one line to feed the reactor with supercritical CO 2 and the other connected to gas chromatograph. The use of the supercritical CO2 enhanced the solvent option due to the chemical extraction, in addition to the low environmental impact and energy cost. In this thesis the experiment were conducted at five different temperatures from atmos-pheric to 140°C, 3000 - 6000 psi with five component of feed mixture, namely water, HTA, PTA, coal, and PM in semi batch vessels reactor system with a volume of 100 mL. The results show that the chemicals were obtained without requiring to first convert coal to CO and H2 units as in indirect coal liquefaction. The results show that

  2. Saponification reaction system: a detailed mass transfer coefficient determination.

    PubMed

    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.

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

    SciTech Connect

    van Willigen, H.

    1990-12-01

    During the period covered by this report research has been concerned with the application of Fourier Transform Electron Paramagnetic Resonance (FT EPR) in the study of photo-induced electron transfer reactions. Donor molecules used in this investigation have been various porphyrins, whereas quinones were used as acceptor molecules.

  4. Mechanisms for control of biological electron transfer reactions

    PubMed Central

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

    2014-01-01

    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. PMID:25085775

  5. Primary reactions in photosynthetic reaction centers of Rhodobacter sphaeroides - Time constants of the initial electron transfer

    NASA Astrophysics Data System (ADS)

    Dominguez, Pablo Nahuel; Himmelstoss, Matthias; Michelmann, Jeff; Lehner, Florian Thomas; Gardiner, Alastair T.; Cogdell, Richard J.; Zinth, Wolfgang

    2014-05-01

    The primary dynamics of reaction centers from Rhodobacter sphaeroides at room temperature are studied at low excitation intensities and low excitation rates. Analysis based on singular value decomposition yields three time constants in the picosecond range (ca. 1.2 ps, 3.5 ps and 220 ps). The spectral and temporal signatures are fully consistent with the step-wise electron transfer model published previously, with a first electron transfer to the bacteriochlorophyll with a time constant of 3.5 ps and a second 1.2 ps transfer to the bacteriopheophytin. No indications for adiabatic electron transfer are found in the time range >0.5 ps.

  6. Tetrahydroxydiboron-Mediated Palladium-Catalyzed Transfer Hydrogenation and Deuteriation of Alkenes and Alkynes Using Water as the Stoichiometric H or D Atom Donor.

    PubMed

    Cummings, Steven P; Le, Thanh-Ngoc; Fernandez, Gilberto E; Quiambao, Lorenzo G; Stokes, Benjamin J

    2016-05-18

    There are few examples of catalytic transfer hydrogenations of simple alkenes and alkynes that use water as a stoichiometric H or D atom donor. We have found that diboron reagents efficiently mediate the transfer of H or D atoms from water directly onto unsaturated C-C bonds using a palladium catalyst. This reaction is conducted on a broad variety of alkenes and alkynes at ambient temperature, and boric acid is the sole byproduct. Mechanistic experiments suggest that this reaction is made possible by a hydrogen atom transfer from water that generates a Pd-hydride intermediate. Importantly, complete deuterium incorporation from stoichiometric D2O has also been achieved. PMID:27135185

  7. Concerted or stepwise hydrogen transfer in the transfer hydrogenation of acetophenone catalyzed by ruthenium-acetamido complex: a theoretical mechanistic investigation.

    PubMed

    Guo, Xiaojia; Tang, Yanhui; Zhang, Xin; Lei, Ming

    2011-11-10

    In this paper, the mechanism of transfer hydrogenation of acetophenone catalyzed by ruthenium-acetamido complex was studied using density function theory (DFT) method. The catalytic cycle of transfer hydrogenation consists of hydrogen transfer (HT) step and dehydrogenation (DH) step of isopropanol (IPA). Inner sphere mechanism (paths 1 and 7) and outer sphere mechanism (paths 2-6) in HT step are fully investigated. Calculated results indicate that DH step of IPA (from (i)1 to (i)2) is the rate-determining step in the whole catalytic cycle, which has a potential energy barrier of 16.2 kcal/mol. On the other hand, the maximum potential energy barriers of paths 1-7 in the HT step are 5.9, 12.7, 24.4, 16.8, 23.7, 7.2, and 6.1 kcal/mol, respectively. The inner sphere pathways (paths 1 and 7) are favorable hydrogen transfer modes compared with outer sphere pathways, and the proton transferred to the oxygen atom of acetophenone comes from the hydroxyl group but not from amino group of acetamido ligand. Those theoretical results are in agreement with experimental report. However, in view of this DFT study in the inner sphere mechanism of HT step, hydride transfer and proton transfer are concerted and asynchronous hydrogen transfer but not a stepwise one, and hydride transfer precedes proton transfer in this case. PMID:21974747

  8. Kinetic study of the reactions between chloramine disinfectants and hydrogen peroxide: temperature dependence and reaction mechanism.

    PubMed

    McKay, Garrett; Sjelin, Brittney; Chagnon, Matthew; Ishida, Kenneth P; Mezyk, Stephen P

    2013-09-01

    The temperature-dependent kinetics for the reaction between hydrogen peroxide and chloramine water disinfectants (NH2Cl, NHCl2, and NCl3) have been determined using stopped flow-UV/Vis spectrophotometry. Rate constants for the mono- and dichloramine-peroxide reaction were on the order of 10(-2)M(-1)s(-1) and 10(-5)M(-1)s(-1), respectively. The reaction of trichloramine with peroxide was negligibly slow compared to its thermal and photolytically-induced decomposition. Arrhenius expressions of ln(kH2O2-NH2Cl)=(17.3±1.5)-(51500±3700)/RT and ln(kH2O2-NHCl2)=(18.2±1.9)-(75800±5100)/RT were obtained for the mono- and dichloramine peroxide reaction over the temperature ranges 11.4-37.9 and 35.0-55.0°C, respectively. Both monochloramine and hydrogen peroxide were first-order in the rate-limiting kinetic step and concomitant measurements made using a chloride ion selective electrode showed that the chloride was produced quantitatively. These data will aid water utilities in predicting chloramine concentrations (and thus disinfection potential) throughout the water distribution system.

  9. Hydrogen generation from alcohols catalyzed by ruthenium-triphenylphosphine complexes: multiple reaction pathways.

    PubMed

    Sieffert, Nicolas; Bühl, Michael

    2010-06-16

    We report a comprehensive density functional theory (DFT) study of the mechanism of the methanol dehydrogenation reaction catalyzed by [RuH(2)(H(2))(PPh(3))(3)]. Using the B97-D dispersion-corrected functional, four pathways have been fully characterized, which differ in the way the critical beta-hydrogen transfer step is brought about (e.g., by prior dissociation of one PPh(3) ligand). All these pathways are found to be competitive (DeltaG(++) = 27.0-32.1 kcal/mol at 150 degrees C) and strongly interlocked. The reaction can thus follow multiple reaction channels, a feature which is expected to be at the origin of the good kinetics of this system. Our results also point to the active role of PPh(3) ligands, which undergo significant conformational changes as the reaction occurs, and provide insights into the role of the base, which acts as a "co-catalyst" by facilitating proton transfers within active species. Activation barriers decrease on going from methanol to ethanol and 2-propanol substrates, in accord with experiment. PMID:20481632

  10. Kinetics of the reaction of nitric oxide with hydrogen

    NASA Technical Reports Server (NTRS)

    Flower, W. L.; Hanson, R. K.; Kruger, C. H.

    1975-01-01

    The reaction of nitric oxide with hydrogen has been studied in the temperature range 2400-4500 K using a shock-tube technique. Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principal result of the study was the determination of the rate constant k1 for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k1 were obtained for each test through comparisons of measured and numerically predicted NO profiles. The data are fit closely by the expression k1 = 1.34 times 10 to the fourteenth power exp(-49 200/RT) cu cm/mole-sec. These data appear to be the first available for this rate constant.

  11. Rationalizing the Hydrogen and Oxygen Evolution Reaction Activity of Two-Dimensional Hydrogenated Silicene and Germanene.

    PubMed

    Rupp, Caroline J; Chakraborty, Sudip; Anversa, Jonas; Baierle, Rogério J; Ahuja, Rajeev

    2016-01-20

    We have undertaken first-principles electronic structure calculations to show that the chemical functionalization of two-dimensional hydrogenated silicene (silicane) and germanene (germanane) can become a powerful tool to increase the photocatalytic water-splitting activity. Spin-polarized density functional theory within the GGA-PBE and HSE06 types of exchange correlation functionals has been used to obtain the structural, electronic, and optical properties of silicane and germanane functionalized with a series of nonmetals (N, P, and S), alkali metals (Li, Na, and K) and alkaline-earth metals (Mg and Ca). The surface-adsorbate interaction between the functionalized systems with H2 and O2 molecules that leads to envisaged hydrogen and oxygen evolution reaction activity has been determined.

  12. Enzymatic Catalysis of Proton Transfer and Decarboxylation Reactions.

    PubMed

    Richard, John P

    2011-07-01

    Deprotonation of carbon and decarboxylation at enzyme active sites proceed through the same carbanion intermediates as for the uncatalyzed reactions in water. The mechanism for the enzymatic reactions can be studied at the same level of detail as for nonenzymatic reactions, using the mechanistic tools developed by physical organic chemists. Triosephosphate isomerase (TIM) catalyzed interconversion of D-glyceraldehyde 3-phosphate and dihydroxyacetone phosphate is being studied as a prototype for enzyme catalyzed proton transfer, and orotidine monophosphate decarboxylase (OMPDC) catalyzed decarboxylation of orotidine 5'-monophosphate is being studied as a prototype for enzyme-catalyzed decarboxylation. (1)H NMR spectroscopy is an excellent analytical method to monitor proton transfer to and from carbon catalyzed by these enzymes in D2O. Studies of these partial enzyme-catalyzed exchange reactions provide novel insight into the stability of carbanion reaction intermediates, that is not accessible in studies of the full enzymatic reaction. The importance of flexible enzyme loops and the contribution of interactions between these loops and the substrate phosphodianion to the enzymatic rate acceleration are discussed. The similarity in the interactions of OMPDC and TIM with the phosphodianion of bound substrate is emphasized.

  13. Multi-neutron transfer reactions at sub-barrier energies.

    SciTech Connect

    Rehm, K. E.

    1998-01-20

    The optimum conditions for multi-neutron transfer have been studied in the system {sup 58}Ni + {sup 124}Sn at bombarding energies at and below the Coulomb barrier. The experiments were performed in inverse kinematics with a {sup 124}Sn beam bombarding a {sup 58}Ni target. The particles were identified with respect to mass and Z in the split-pole spectrograph with a hybrid focal plane detector with mass and Z-resolutions of A/{Delta}A = 150 and Z/{Delta}Z = 70. At all energies the transfer of up to 6 neutrons was observed. The yields for these transfer reactions are found to decrease by about a factor of four for each transferred neutron.

  14. Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer.

    PubMed

    Eisenhart, Thomas T; Howland, William C; Dempsey, Jillian L

    2016-08-18

    The proton-coupled electron transfer (PCET) oxidation of p-aminophenol in acetonitrile was initiated via stopped-flow rapid-mixing and spectroscopically monitored. For oxidation by ferrocenium in the presence of 7-(dimethylamino)quinoline proton acceptors, both the electron transfer and proton transfer components could be optically monitored in the visible region; the decay of the ferrocenium absorbance is readily monitored (λmax = 620 nm), and the absorbance of the 2,4-substituted 7-(dimethylamino)quinoline derivatives (λmax = 370-392 nm) red-shifts substantially (ca. 70 nm) upon protonation. Spectral analysis revealed the reaction proceeds via a stepwise electron transfer-proton transfer process, and modeling of the kinetics traces monitoring the ferrocenium and quinolinium signals provided rate constants for elementary proton and electron transfer steps. As the pKa values of the conjugate acids of the 2,4-R-7-(dimethylamino)quinoline derivatives employed were readily tuned by varying the substituents at the 2- and 4-positions of the quinoline backbone, the driving force for proton transfer was systematically varied. Proton transfer rate constants (kPT,2 = (1.5-7.5) × 10(8) M(-1) s(-1), kPT,4 = (0.55-3.0) × 10(7) M(-1) s(-1)) were found to correlate with the pKa of the conjugate acid of the proton acceptor, in agreement with anticipated free energy relationships for proton transfer processes in PCET reactions. PMID:27500804

  15. Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer.

    PubMed

    Eisenhart, Thomas T; Howland, William C; Dempsey, Jillian L

    2016-08-18

    The proton-coupled electron transfer (PCET) oxidation of p-aminophenol in acetonitrile was initiated via stopped-flow rapid-mixing and spectroscopically monitored. For oxidation by ferrocenium in the presence of 7-(dimethylamino)quinoline proton acceptors, both the electron transfer and proton transfer components could be optically monitored in the visible region; the decay of the ferrocenium absorbance is readily monitored (λmax = 620 nm), and the absorbance of the 2,4-substituted 7-(dimethylamino)quinoline derivatives (λmax = 370-392 nm) red-shifts substantially (ca. 70 nm) upon protonation. Spectral analysis revealed the reaction proceeds via a stepwise electron transfer-proton transfer process, and modeling of the kinetics traces monitoring the ferrocenium and quinolinium signals provided rate constants for elementary proton and electron transfer steps. As the pKa values of the conjugate acids of the 2,4-R-7-(dimethylamino)quinoline derivatives employed were readily tuned by varying the substituents at the 2- and 4-positions of the quinoline backbone, the driving force for proton transfer was systematically varied. Proton transfer rate constants (kPT,2 = (1.5-7.5) × 10(8) M(-1) s(-1), kPT,4 = (0.55-3.0) × 10(7) M(-1) s(-1)) were found to correlate with the pKa of the conjugate acid of the proton acceptor, in agreement with anticipated free energy relationships for proton transfer processes in PCET reactions.

  16. Structural tuning intra- versus inter-molecular proton transfer reaction in the excited state.

    PubMed

    Chung, Min-Wen; Liao, Jia-Ling; Tang, Kuo-Chun; Hsieh, Cheng-Chih; Lin, Tsung-Yi; Liu, Chun; Lee, Gene-Hsiang; Chi, Yun; Chou, Pi-Tai

    2012-07-01

    A series of 2-pyridyl-pyrazole derivatives 1-4 possessing five-membered ring hydrogen bonding configuration are synthesized, the structural flexibility of which is strategically tuned to be in the order of 1 > 2 > 3 > 4. This system then serves as an ideal chemical model to investigate the correlation between excited-state intramolecular proton transfer (ESIPT) reaction and molecular skeleton motion associated with hydrogen bonds. The resulting luminescence data reveal that the rate of ESIPT decreases upon increasing the structural constraint. At sufficiently low concentration where negligible dimerization is observed, ESIPT takes place in 1 and 2 but is prohibited in 3 and 4, for which high geometry constraint is imposed. The results imply that certain structural bending motions associated with hydrogen bonding angle/distance play a key role in ESIPT. This trend is also well supported by the DFT computational approach, in which the barrier associated with ESIPT is in the order of 1 < 2 < 3 < 4. Upon increasing the concentration in cyclohexane, except for 2, the rest of the title compounds undergo ground-state dimerization, from which the double proton transfer takes place in the excited state, resulting in a relatively blue shifted dimeric tautomer emission (cf. the monomer tautomer emission). The lack of dimerization in 2 is rationalized by substantial energy required to adjust the angle of hydrogen bond via twisting the propylene bridge prior to dimerization. PMID:22618273

  17. Coupling of protein motions and hydrogen transfer during catalysis by Escherichia coli dihydrofolate reductase

    PubMed Central

    Swanwick, Richard S.; Maglia, Giovanni; Tey, Lai-hock; Allemann, Rudolf K.

    2005-01-01

    The enzyme DHFR (dihydrofolate reductase) catalyses hydride transfer from NADPH to, and protonation of, dihydrofolate. The physical basis of the hydride transfer step catalysed by DHFR from Escherichia coli has been studied through the measurement of the temperature dependence of the reaction rates and the kinetic isotope effects. Single turnover experiments at pH 7.0 revealed a strong dependence of the reaction rates on temperature. The observed relatively large difference in the activation energies for hydrogen and deuterium transfer led to a temperature dependence of the primary kinetic isotope effects from 3.0±0.2 at 5 °C to 2.2±0.2 at 40 °C and an inverse ratio of the pre-exponential factors of 0.108±0.04. These results are consistent with theoretical models for hydrogen transfer that include contributions from quantum mechanical tunnelling coupled with protein motions that actively modulate the tunnelling distance. Previous work had suggested a coupling of a remote residue, Gly121, with the kinetic events at the active site. However, pre-steady-state experiments at pH 7.0 with the mutant G121V-DHFR, in which Gly121 was replaced with valine, revealed that the chemical mechanism of DHFR catalysis was robust to this replacement. The reduced catalytic efficiency of G121V-DHFR was mainly a consequence of the significantly reduced pre-exponential factors, indicating the requirement for significant molecular reorganization during G121V-DHFR catalysis. In contrast, steady-state measurements at pH 9.5, where hydride transfer is rate limiting, revealed temperature-independent kinetic isotope effects between 15 and 35 °C and a ratio of the pre-exponential factors above the semi-classical limit, suggesting a rigid active site configuration from which hydrogen tunnelling occurs. The mechanism by which hydrogen tunnelling in DHFR is coupled with the environment appears therefore to be sensitive to pH. PMID:16241906

  18. Reaction kinetics for the oxygen hydrogenation process on Pt(111) derived from temperature-programmed XPS

    NASA Astrophysics Data System (ADS)

    Näslund, Lars-Åke

    2013-12-01

    Oxygen hydrogenation under ultra high vacuum conditions at the platinum surface was explored using temperature-programmed X-ray photoelectron spectroscopy. Through modeling of the oxygen consumption, information on the reaction kinetics was obtained indicating that the reaction rate of the oxygen hydrogenation process depends on the hydrogen diffusion and on the lifetime of hydroxyl intermediates. The reaction rate is, however, enhanced when an autocatalytic process stabilizes the hydroxyl intermediates through hydrogen bonding to neighboring water molecules. The overall activation energy for the hydrogenation of atomic oxygen to form water was determined to be 0.20 eV with a frequency factor of only 103 s- 1.

  19. Intra- and interspecies transfer and expression of Rhizobium japonicum hydrogen uptake genes and autotrophic growth capability

    PubMed Central

    Lambert, Grant R.; Cantrell, Michael A.; Hanus, F. Joe; Russell, Sterling A.; Haddad, Karen R.; Evans, Harold J.

    1985-01-01

    Cosmids containing hydrogen uptake genes have previously been isolated in this laboratory. Four new cosmids that contain additional hup gene(s) have now been identified by conjugal transfer of a Rhizobium japonicum 122DES gene bank into a Tn5-generated Hup- mutant and screening for the acquisition of Hup activity. The newly isolated cosmids, pHU50-pHU53, contain part of the previously isolated pHU1 but extend as far as 20 kilobases beyond its border. pHU52 complements five of six Hup- mutants and confers activity on several Hup- wild-type R. japonicum strains in the free-living state and where tested in nodules. Transconjugants obtained from interspecies transfer of pHU52 to Rhizobium meliloti 102F28, 102F32, and 102F51 and Rhizobium leguminosarum 128C53 showed hydrogen-dependent methyleneblue reduction, performed the oxyhydrogen reaction, and showed hydrogen-dependent autotrophic growth by virtue of the introduced genes. The identity of the presumptive transconjugants was confirmed by antibiotic-resistance profiles and by plant nodulation tests. Images PMID:16578786

  20. The reaction of cobaloximes with hydrogen: products and thermodynamics.

    PubMed

    Estes, Deven P; Grills, David C; Norton, Jack R

    2014-12-17

    A cobalt hydride has been proposed as an intermediate in many reactions of the Co(dmgBF2)2L2 system, but its observation has proven difficult. We have observed the UV-vis spectra of Co(dmgBF2)2L2 (1) in CH3CN under hydrogen pressures of up to 70 atm. A Co(I) compound (6a) with an exchangeable proton is eventually formed. We have determined the bond dissociation free energy and pK(a) of the new O-H bond in 6a to be 50.5 kcal/mol and 13.4, respectively, in CH3CN, matching previous reports. PMID:25427140

  1. A Perovskite Electrocatalyst for Efficient Hydrogen Evolution Reaction.

    PubMed

    Xu, Xiaomin; Chen, Yubo; Zhou, Wei; Zhu, Zhonghua; Su, Chao; Liu, Meilin; Shao, Zongping

    2016-08-01

    Perovskite oxides are demonstrated for the first time as efficient electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solutions. A-site praseodymium-doped Pr0.5 (Ba0.5 Sr0.5 )0.5 Co0.8 Fe0.2 O3- δ (Pr0.5BSCF) exhibits dramatically enhanced HER activity and stability compared to Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF), superior to many well-developed bulk/nanosized nonprecious electrocatalysts. The improved HER performance originates from the modified surface electronic structures and properties of Pr0.5BSCF induced by the Pr-doping. PMID:27185219

  2. Mechanism of Action of Sulforaphane as a Superoxide Radical Anion and Hydrogen Peroxide Scavenger by Double Hydrogen Transfer: A Model for Iron Superoxide Dismutase.

    PubMed

    Prasad, Ajit Kumar; Mishra, P C

    2015-06-25

    The mechanism of action of sulforaphane as a scavenger of superoxide radical anion (O2(•-)) and hydrogen peroxide (H2O2) was investigated using density functional theory (DFT) in both gas phase and aqueous media. Iron superoxide dismutase (Fe-SOD) involved in scavenging superoxide radical anion from biological media was modeled by a complex consisting of the ferric ion (Fe(3+)) attached to three histidine rings. Reactions related to scavenging of superoxide radical anion by sulforaphane were studied using DFT in the presence and absence of Fe-SOD represented by this model in both gas phase and aqueous media. The scavenging action of sulforaphane toward both superoxide radical anion and hydrogen peroxide was found to involve the unusual mechanism of double hydrogen transfer. It was found that sulforaphane alone, without Fe-SOD, cannot scavenge superoxide radical anion in gas phase or aqueous media efficiently as the corresponding reaction barriers are very high. However, in the presence of Fe-SOD represented by the above-mentioned model, the scavenging reactions become barrierless, and so sulforaphane scavenges superoxide radical anion by converting it to hydrogen peroxide efficiently. Further, sulforaphane was found to scavenge hydrogen peroxide also very efficiently by converting it into water. Thus, the mechanism of action of sulforaphane as an excellent antioxidant has been unravelled. PMID:26020652

  3. Mechanism of Action of Sulforaphane as a Superoxide Radical Anion and Hydrogen Peroxide Scavenger by Double Hydrogen Transfer: A Model for Iron Superoxide Dismutase.

    PubMed

    Prasad, Ajit Kumar; Mishra, P C

    2015-06-25

    The mechanism of action of sulforaphane as a scavenger of superoxide radical anion (O2(•-)) and hydrogen peroxide (H2O2) was investigated using density functional theory (DFT) in both gas phase and aqueous media. Iron superoxide dismutase (Fe-SOD) involved in scavenging superoxide radical anion from biological media was modeled by a complex consisting of the ferric ion (Fe(3+)) attached to three histidine rings. Reactions related to scavenging of superoxide radical anion by sulforaphane were studied using DFT in the presence and absence of Fe-SOD represented by this model in both gas phase and aqueous media. The scavenging action of sulforaphane toward both superoxide radical anion and hydrogen peroxide was found to involve the unusual mechanism of double hydrogen transfer. It was found that sulforaphane alone, without Fe-SOD, cannot scavenge superoxide radical anion in gas phase or aqueous media efficiently as the corresponding reaction barriers are very high. However, in the presence of Fe-SOD represented by the above-mentioned model, the scavenging reactions become barrierless, and so sulforaphane scavenges superoxide radical anion by converting it to hydrogen peroxide efficiently. Further, sulforaphane was found to scavenge hydrogen peroxide also very efficiently by converting it into water. Thus, the mechanism of action of sulforaphane as an excellent antioxidant has been unravelled.

  4. Plastic foils as primary hydrogen standards for nuclear reaction analysis

    NASA Astrophysics Data System (ADS)

    Rudolph, W.; Bauer, C.; Brankoff, K.; Grambole, D.; Grötzschel, R.; Heiser, C.; Herrmann, F.

    1986-04-01

    Plastic materials like polypropylene, polyester (Mylar) and polycarbonate (Lexan or Makrofol E) contain large amounts of hydrogen and their compositions are well known. However, these materials are not stable during ion bombardment. Using the 1H( 15N,αγ) 12C and 1H( 19F, αγ) 16O nuclear resonance reaction at energies EN = 6.50 MeV and EF = 6.83 MeV, respectively, we have investigated the behaviour of plastic foils during 15N and 19F ion bombardment. By means of a rotating sample holder low current densities of 1-2 {nA}/{cm 2} and large irradiated foil areas of up to 10 cm 2 were realized. Under these measuring conditions the γ-ray yields change only slightly and the initial yields, which correspond to the known compositions of the foils, can be determined with good accuracy. In this way the plastic foils can be used as primary standards for hydrogen content calibration. The method was employed to calibrate an a-Si(H) reference target.

  5. Reaction of Aplysia limacina metmyoglobin with hydrogen peroxide.

    PubMed

    Svistunenko, Dimitri A; Reeder, Brandon J; Wankasi, Mieebi M; Silaghi-Dumitrescu, Radu-Lucian; Cooper, Chris E; Rinaldo, Serena; Cutruzzolà, Francesca; Wilson, Michael T

    2007-02-28

    Myoglobin (Mb) from gastropod mollusc Aplysia limacina shows only 20% sequence homology to the 'prototype' sperm whale Mb but exhibits a typical Mb fold and can reversibly bind oxygen. An intriguing feature of aplysia Mb is that it lacks the distal histidine and displays a ligand stabilisation based on an arginine. Here we report the reaction of aplysia metMb with hydrogen peroxide studied by optical and electron paramagnetic resonance (EPR) spectroscopies. Two electron oxidation of the protein by H2O2 results in formation of two intermediates typical for this class of reactions, the oxoferryl haem state and a globin-bound free radical. An unusual characteristic of the aplysia Mb reaction is formation, prior to haem oxidation, of an optically distinct compound with an EPR spectrum typical of the low spin Fe3+ haem state. This compound is interpreted as the complex between H2O2 and the ferric haem state (Compound), formed prior to cleavage of the dioxygen bond. We conclude that H2O2 is singly deprotonated in Compound which can thus be notated as [Fe3+--OOH]. A new low spin ferric haem state has been observed over the period of Compound decay, and hypotheses have been formulated as to its identity and role. The location of the protein bound radical observed in aplysia Mb is discussed in light of the fact that the protein does not have any tyrosine residues, the most common site of free radical formation in the haem protein/peroxide systems. All intermediates of the reaction are kinetically characterised.

  6. Study of multi-nucleon transfer reactions with light nuclei

    SciTech Connect

    Benzoni, G.; Montanari, D.; Bracco, A.; Blasi, N.; Camera, F.; Crespi, F. C. L.; Corsi, A.; Leoni, S.; Million, B.; Nicolini, R.; Wieland, O.; Zalite, A.; Zocca, F.; Azaiez, F.; Franchoo, S.; Stefan, I.; Ibrahim, F.; Verney, D.; Battacharyya, S.; De France, G.

    2008-05-12

    Multi-nucleon transfer reactions are useful tools to populate exotic nuclei, particularly the neutron-rich ones. In this view, two different experiments have been performed employing a stable ({sup 22}Ne) and a radioactive ({sup 24}Ne) beam, both impinging on a {sup 208}Pb target. The first reaction has been studied using the CLARA-PRISMA-DANTE set-up at Laboratori Nazionali di Legnaro (Legnaro-Italy), while the second reaction was performed at Ganil (Caen-France) employing a SPIRAL radioactive beam of {sup 24}Ne. In this case recoils and coincident {gamma} rays were detected with the VAMOS-EXOGAM set-up.The data show that MNT reactions can selectively populate states of different nature and, therefore, are a good tool to study nuclear structure further away from stability.

  7. Mass transfer model for two-layer TBP oxidation reactions

    SciTech Connect

    Laurinat, J.E.

    1994-09-28

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

  8. Highly Active Catalyst of Two-Dimensional CoS2/Graphene Nanocomposites for Hydrogen Evolution Reaction

    NASA Astrophysics Data System (ADS)

    Xing, Wei; Zhang, Yu; Xue, Qingzhong; Yan, Zifeng

    2015-12-01

    Hydrogen evolution reaction (HER) by electrochemical water splitting using new promising non-precious metal catalysts shows great potential for clean energy technology. The design and fabrication of a high-performance electrode material based on cobalt disulfide/reduced graphene oxide (CoS2/RGO) nanocomposites is reported by a one-step hydrothermal method. Benefiting from its structural advantages, namely, large amount of exposed surface, fast charge transfer, and synergistic effect between CoS2 and RGO, the as-prepared nanocomposites are exploited as a catalyst for the HER. The results indicate that CoS2/RGO-5 % exhibits the best performance of hydrogen evolution and the smallest overpotential of 159 mV to achieve a 15 mA cm-2 current density, possessing the easiest releasing of hydrogen gas and the highest charge transfer rate, as well as remarkable stability.

  9. Key Role of Active-Site Water Molecules in Bacteriorhodopsin Proton-Transfer Reactions

    SciTech Connect

    Bondar, A.N.; Baudry, Jerome Y; Suhai, Sandor; Fischer, S.; Smith, Jeremy C

    2008-10-01

    The functional mechanism of the light-driven proton pump protein bacteriorhodopsin depends on the location of water molecules in the active site at various stages of the photocycle and on their roles in the proton-transfer steps. Here, free energy computations indicate that electrostatic interactions favor the presence of a cytoplasmic-side water molecule hydrogen bonding to the retinal Schiff base in the state preceding proton transfer from the retinal Schiff base to Asp85. However, the nonequilibrium nature of the pumping process means that the probability of occupancy of a water molecule in a given site depends both on the free energies of insertion of the water molecule in this and other sites during the preceding photocycle steps and on the kinetic accessibility of these sites on the time scale of the reaction steps. The presence of the cytoplasmic-side water molecule has a dramatic effect on the mechanism of proton transfer: the proton is channeled on the Thr89 side of the retinal, whereas the transfer on the Asp212 side is hindered. Reaction-path simulations and molecular dynamics simulations indicate that the presence of the cytoplasmic-side water molecule permits a low-energy bacteriorhodopsin conformer in which the water molecule bridges the twisted retinal Schiff base and the proton acceptor Asp85. From this low-energy conformer, proton transfer occurs via a concerted mechanism in which the water molecule participates as an intermediate proton carrier.

  10. Interplay between aromaticity and strain in double group transfer reactions to 1,2-benzyne.

    PubMed

    Fernández, Israel; Cossío, Fernando P

    2016-05-30

    Density Functional Theory calculations are used to explore the double hydrogen atom transfer from different alkanes to 1,2-benzyne. State-of-the-art calculations including the Activation Strain Model of reactivity, Energy Decomposition Analysis, and Valence Bond methods, reveal the origins of the relatively low activation barriers computed for these processes compared to the analogous reaction involving acetylene. In addition, the interplay between the in-plane aromaticity of the corresponding transition states and the variation of the π-aromaticity associated with the benzyne moiety as well as their influence on the barrier heights of the transformations are analyzed in detail.

  11. Transfer hydrogenation catalysis in cells as a new approach to anticancer drug design

    PubMed Central

    Soldevila-Barreda, Joan J.; Romero-Canelón, Isolda; Habtemariam, Abraha; Sadler, Peter J.

    2015-01-01

    Organometallic complexes are effective hydrogenation catalysts for organic reactions. For example, Noyori-type ruthenium complexes catalyse reduction of ketones by transfer of hydride from formate. Here we show that such catalytic reactions can be achieved in cancer cells, offering a new strategy for the design of safe metal-based anticancer drugs. The activity of ruthenium(II) sulfonamido ethyleneamine complexes towards human ovarian cancer cells is enhanced by up to 50 × in the presence of low non-toxic doses of formate. The extent of conversion of coenzyme NAD+ to NADH in cells is dependent on formate concentration. This novel reductive stress mechanism of cell death does not involve apoptosis or perturbation of mitochondrial membrane potentials. In contrast, iridium cyclopentadienyl catalysts cause cancer cell death by oxidative stress. Organometallic complexes therefore have an extraordinary ability to modulate the redox status of cancer cells. PMID:25791197

  12. Hydrogen transfer between methanogens and fermentative heterotrophs in hyperthermophilic cocultures

    SciTech Connect

    Muralidharan, V.; Hirsh, I.S.; Bouwer, E.J.; Rinker, K.D.; Kelly, R.M.

    1997-11-05

    Interactions involving hydrogen transfer were studied in a coculture of two hyperthermophilic microorganisms: Thermotoga maritima, an anaerobic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic methanogen. Cell densities of T. maritima increased 10-fold when cocultured with M. jannaschii at 85 C, and the methanogen was able to grow in the absence of externally supplied H{sub 2} and CO{sub 2}. The coculture could not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximity. The significance of spatial proximity was also supported by cell cytometry, where the methanogen was only found in cell sorts at or above 4.5 {micro}m in samples of the coculture in exponential phase. An unstructured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophilic cocultures. Calculations suggest the increases in methanogenesis rates with temperature result from greater interactions between the methanogenic and fermentative organisms, as evidenced by the sharp decline in H{sub 2} concentration in the proximity of a hyperthermophilic methanogen. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations at elevated temperatures.

  13. Molecular modeling of the reaction pathway and hydride transfer reactions of HMG-CoA reductase.

    PubMed

    Haines, Brandon E; Steussy, C Nicklaus; Stauffacher, Cynthia V; Wiest, Olaf

    2012-10-01

    HMG-CoA reductase catalyzes the four-electron reduction of HMG-CoA to mevalonate and is an enzyme of considerable biomedical relevance because of the impact of its statin inhibitors on public health. Although the reaction has been studied extensively using X-ray crystallography, there are surprisingly no computational studies that test the mechanistic hypotheses suggested for this complex reaction. Theozyme and quantum mechanical (QM)/molecular mechanical (MM) calculations up to the B3LYP/6-31g(d,p)//B3LYP/6-311++g(2d,2p) level of theory were employed to generate an atomistic description of the enzymatic reaction process and its energy profile. The models generated here predict that the catalytically important Glu83 is protonated prior to hydride transfer and that it acts as the general acid or base in the reaction. With Glu83 protonated, the activation energies calculated for the sequential hydride transfer reactions, 21.8 and 19.3 kcal/mol, are in qualitative agreement with the experimentally determined rate constant for the entire reaction (1 s(-1) to 1 min(-1)). When Glu83 is not protonated, the first hydride transfer reaction is predicted to be disfavored by >20 kcal/mol, and the activation energy is predicted to be higher by >10 kcal/mol. While not involved in the reaction as an acid or base, Lys267 is critical for stabilization of the transition state in forming an oxyanion hole with the protonated Glu83. Molecular dynamics simulations and MM/Poisson-Boltzmann surface area free energy calculations predict that the enzyme active site stabilizes the hemithioacetal intermediate better than the aldehyde intermediate. This suggests a mechanism in which cofactor exchange occurs before the breakdown of the hemithioacetal. Slowing the conversion to aldehyde would provide the enzyme with a mechanism to protect it from solvent and explain why the free aldehyde is not observed experimentally. Our results support the hypothesis that the pK(a) of an active site acidic

  14. Test of Sum Rules in Nucleon Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Schiffer, J. P.; Hoffman, C. R.; Kay, B. P.; Clark, J. A.; Deibel, C. M.; Freeman, S. J.; Howard, A. M.; Mitchell, A. J.; Parker, P. D.; Sharp, D. K.; Thomas, J. S.

    2012-01-01

    The quantitative consistency of nucleon transfer reactions as a probe of the occupancy of valence orbits in nuclei is tested. Neutron-adding, neutron-removal, and proton-adding transfer reactions were measured on the four stable even Ni isotopes, with particular attention to the cross section determinations. The data were analyzed consistently in terms of the distorted wave Born approximation to yield spectroscopic factors. Valence-orbit occupancies were extracted, utilizing the Macfarlane-French sum rules. The deduced occupancies are consistent with the changing number of valence neutrons, as are the vacancies for protons, both at the level of <5%. While there has been some debate regarding the true “observability” of spectroscopic factors, the present results indicate that empirically they yield self-consistent results.

  15. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

  16. Modelling charge transfer reactions with the frozen density embedding formalism

    SciTech Connect

    Pavanello, Michele; Neugebauer, Johannes

    2011-12-21

    The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two {pi}-stacked nucleobase dimers of B-DNA: 5{sup '}-GG-3{sup '} and 5{sup '}-GT-3{sup '}. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionals are used the electronic couplings are grossly overestimated.

  17. Ruthenium supported on magnetic nanoparticles: An efficient and recoverable catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds

    EPA Science Inventory

    Ruthenium supported on surface modified magnetic nanoparticles (NiFe2O4) has been successfully synthesized and applied for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The ...

  18. Fission of actinide nuclei using multi-nucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Léguillon, Romain; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, Riccardo; Makii, Hiroyuki; Nishinaka, Ichiro; Ishii, Tetsuro; Tsukada, Kazuaki; Asai, Masato; Chiba, Satoshi; Ohtsuki, Tsutomu; Araki, Shohei; Watanabe, Yukinobu; Tatsuzawa, Ryotaro; Takaki, Naoyuki

    2014-09-01

    We are promoting a campaign to measure fission-fragment mass distributions for neutron-rich actinide nuclei populated by transfer reactions from their ground state up to an excitation energy of several tens MeV. We thus obtain the excitation energy dependence of the mass distribution. The experiment was carried out at the 20 MV JAEA tandem facility at Tokai. We report on the data obtained in the direct reaction 18 O + 232 Th . Transfer-channels and excitation energies of the fissioning nuclei were identified using silicon dE-E detectors located at forward angle. Two fission fragments were detected in coincidence using multi-wire proportional counters. Fission fragment masses were determined by kinematic consideration. We obtained the fission fragment mass distributions for 13 nuclei from actinium to uranium and some fission barrier heights. We are promoting a campaign to measure fission-fragment mass distributions for neutron-rich actinide nuclei populated by transfer reactions from their ground state up to an excitation energy of several tens MeV. We thus obtain the excitation energy dependence of the mass distribution. The experiment was carried out at the 20 MV JAEA tandem facility at Tokai. We report on the data obtained in the direct reaction 18 O + 232 Th . Transfer-channels and excitation energies of the fissioning nuclei were identified using silicon dE-E detectors located at forward angle. Two fission fragments were detected in coincidence using multi-wire proportional counters. Fission fragment masses were determined by kinematic consideration. We obtained the fission fragment mass distributions for 13 nuclei from actinium to uranium and some fission barrier heights. Present study is supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan.

  19. Momentum transfer in relativistic heavy ion charge-exchange reactions

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  20. Selective conversion of polyenes to monoenes by RuCl(3) -catalyzed transfer hydrogenation: the case of cashew nutshell liquid.

    PubMed

    Perdriau, Sébastien; Harder, Sjoerd; Heeres, Hero J; de Vries, Johannes G

    2012-12-01

    Cardanol, a constituent of cashew nutshell liquid (CNSL), was subjected to transfer hydrogenation catalyzed by RuCl(3) using isopropanol as a reductant. The side chain of cardanol, which is a mixture of a triene, a diene, and a monoene, was selectively reduced to the monoene. Surprisingly, it is the C8-C9 double bond that is retained with high selectivity. A similar transfer hydrogenation of linoleic acid derivatives succeeded only if the substrate contained an aromatic ring, such as a benzyl ester. TEM and a negative mercury test showed that the catalyst was homogeneous. By using ESI-MS, ruthenium complexes were identified that contained one, two, or even three molecules of substrate, most likely as allyl complexes. The interaction between ruthenium and the aromatic ring determines selectivity in the hydrogenation reaction.

  1. Efficient and limiting reactions in aqueous light-induced hydrogen evolution systems using molecular catalysts and quantum dots.

    PubMed

    Gimbert-Suriñach, Carolina; Albero, Josep; Stoll, Thibaut; Fortage, Jérôme; Collomb, Marie-Noëlle; Deronzier, Alain; Palomares, Emilio; Llobet, Antoni

    2014-05-28

    Hydrogen produced from water and solar energy holds much promise for decreasing the fossil fuel dependence. It has recently been proven that the use of quantum dots as light harvesters in combination with catalysts is a valuable strategy to obtain photogenerated hydrogen. However, the light to hydrogen conversion efficiency of these systems is reported to be lower than 40%. The low conversion efficiency is mainly due to losses occurring at the different interfacial charge-transfer reactions taking place in the multicomponent system during illumination. In this work we have analyzed all the involved reactions in the hydrogen evolution catalysis of a model system composed of CdTe quantum dots, a molecular cobalt catalyst and vitamin C as sacrificial electron donor. The results demonstrate that the electron transfer from the quantum dots to the catalyst occurs fast enough and efficiently (nanosecond time scale), while the back electron transfer and catalysis are much slower (millisecond and microsecond time scales). Further improvements of the photodriven proton reduction should focus on the catalytic rate enhancement, which should be at least in the hundreds of nanoseconds time scale.

  2. Shell effects in fission, quasifission and multinucleon transfer reaction

    NASA Astrophysics Data System (ADS)

    Kozulin, E. M.; Knyazheva, G. N.; Itkis, I. M.; Kozulina, N. I.; Loktev, T. A.; Novikov, K. V.; Harca, I.

    2014-05-01

    Results of the study of mass-energy distributions of binary fragments for a wide range of nuclei with Z= 82-122 produced in reactions of ions located between 22Ne and 136Xe at energies close and below the Coulomb barrier are reported. The role of the shell effects, the influence of the entrance channel asymmetry and the deformations of colliding nuclei on the mechanism of the fusion-fission, quasifission and multinucleon transfer reactions are discussed. The observed peculiarities of the mass and energy distributions of reaction fragments are determined by the shell structure of the formed fragments. Special attention is paid on the symmetric fragment features in order to clarify the origin of these fragments (fission or quasifission). The influence of shell effects on the fragment yield in quasifission and multinucleon transfer reactions is considered. It is noted that the major part of the asymmetric quasifission fragments peaks around the region of the Z=82 and N=126 (double magic lead) and Z=28 and N=50 shells; moreover the maximum of the yield of the quasifission component is a mixing between all these shells. Hence, shell effects are everywhere present and determine the basic characteristics of fragment mass distributions.

  3. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    NASA Astrophysics Data System (ADS)

    Esboui, Mounir

    2015-07-01

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH3)2 complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH3)2 cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″(1πσ∗) and A'(1nσ∗) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A'(1ππ∗) and A″(1nπ∗) potential energy surfaces. For the unconstrained complex, potential energy profiles show two 1ππ∗-1πσ∗ conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  4. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer.

    PubMed

    Esboui, Mounir

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH3)2 complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH3)2 cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″((1)πσ*) and A'((1)nσ*) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A'((1)ππ*) and A″((1)nπ*) potential energy surfaces. For the unconstrained complex, potential energy profiles show two (1)ππ*-(1)πσ* conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  5. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    SciTech Connect

    Esboui, Mounir

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH{sub 3}){sub 2} complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH{sub 3}){sub 2} cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″({sup 1}πσ{sup ∗}) and A′({sup 1}nσ{sup ∗}) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A′({sup 1}ππ{sup ∗}) and A″({sup 1}nπ{sup ∗}) potential energy surfaces. For the unconstrained complex, potential energy profiles show two {sup 1}ππ{sup ∗}-{sup 1}πσ{sup ∗} conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  6. Hydrogen bonding constrains free radical reaction dynamics at serine and threonine residues in peptides.

    PubMed

    Thomas, Daniel A; Sohn, Chang Ho; Gao, Jinshan; Beauchamp, J L

    2014-09-18

    Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal Cα-C or N-Cα bond rather than the typical Cα-C bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied π orbital on the β-carbon and the N-Cα bond, leading to low-barrier β-cleavage of the N-Cα bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and z(•) ions, whereas C-terminal interaction leads to effective cleavage of the Cα-C bond through rapid loss of isocyanic acid. Dissociation of the Cα-C bond may also occur via water loss followed by β-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes.

  7. Light and heavy transfer products in 136Xe+238U multinucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Vogt, A.; Birkenbach, B.; Reiter, P.; Corradi, L.; Mijatović, T.; Montanari, D.; Szilner, S.; Bazzacco, D.; Bowry, M.; Bracco, A.; Bruyneel, B.; Crespi, F. C. L.; de Angelis, G.; Désesquelles, P.; Eberth, J.; Farnea, E.; Fioretto, E.; Gadea, A.; Geibel, K.; Gengelbach, A.; Giaz, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Hess, H.; John, P. R.; Jolie, J.; Judson, D. S.; Jungclaus, A.; Korten, W.; Leoni, S.; Lunardi, S.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Montagnoli, G.; Napoli, D.; Pellegri, L.; Pollarolo, G.; Pullia, A.; Quintana, B.; Radeck, F.; Recchia, F.; Rosso, D.; Şahin, E.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Stefanini, A. M.; Steinbach, T.; Stezowski, O.; Szpak, B.; Theisen, Ch.; Ur, C.; Valiente-Dobón, J. J.; Vandone, V.; Wiens, A.

    2015-08-01

    Background: Multinucleon transfer reactions (MNT) are a competitive tool to populate exotic neutron-rich nuclei in a wide region of nuclei, where other production methods have severe limitations or cannot be used at all. Purpose: Experimental information on the yields of MNT reactions in comparison with theoretical calculations are necessary to make predictions for the production of neutron-rich heavy nuclei. It is crucial to determine the fraction of MNT reaction products which are surviving neutron emission or fission at the high excitation energy after the nucleon exchange. Method: Multinucleon transfer reactions in +238U 136Xe have been measured in a high-resolution γ -ray/particle coincidence experiment. The large solid-angle magnetic spectrometer PRISMA coupled to the high-resolution Advanced Gamma Tracking Array (AGATA) has been employed. Beamlike reaction products after multinucleon transfer in the Xe region were identified and selected with the PRISMA spectrometer. Coincident particles were tagged by multichannel plate detectors placed at the grazing angle of the targetlike recoils inside the scattering chamber. Results: Mass yields have been extracted and compared with calculations based on the grazing model for MNT reactions. Kinematic coincidences between the binary reaction products, i.e., beamlike and targetlike nuclei, were exploited to obtain population yields for nuclei in the actinide region and compared to x-ray yields measured by AGATA. Conclusions: No sizable yield of actinide nuclei beyond Z =93 is found to perform nuclear structure investigations. In-beam γ -ray spectroscopy is feasible for few-neutron transfer channels in U and the -2 p channel populating Th isotopes.

  8. Competition between Hydrogen Bonding and Proton Transfer during Specific Anion Recognition by Dihomooxacalix[4]arene Bidentate Ureas.

    PubMed

    Martínez-González, Eduardo; González, Felipe J; Ascenso, José R; Marcos, Paula M; Frontana, Carlos

    2016-08-01

    Competition between hydrogen bonding and proton transfer reactions was studied for systems composed of electrogenerated dianionic species from dinitrobenzene isomers and substituted dihomooxacalix[4]arene bidentate urea derivatives. To analyze this competition, a second-order ErCrCi mechanism was considered where the binding process is succeeded by proton transfer and the voltammetric responses depend on two dimensionless parameters: the first related to hydrogen bonding reactions, and the second one to proton transfer processes. Experimental results indicated that, upon an increase in the concentration of phenyl-substituted dihomooxacalix[4]arene bidentate urea, voltammetric responses evolve from diffusion-controlled waves (where the binding process is at chemical equilibrium) into irreversible kinetic responses associated with proton transfer. In particular, the 1,3-dinitrobenzene isomer showed a higher proton transfer rate constant (∼25 M(-1) s(-1)) compared to that of the 1,2-dinitrobenzene (∼5 M(-1) s(-1)), whereas the 1,4-dinitrobenzene did not show any proton transfer effect in the experimental conditions employed. PMID:27384148

  9. Sensitive non-radioactive determination of aminotransferase stereospecificity for C-4' hydrogen transfer on the coenzyme.

    PubMed

    Jomrit, Juntratip; Summpunn, Pijug; Meevootisom, Vithaya; Wiyakrutta, Suthep

    2011-02-25

    A sensitive non-radioactive method for determination of the stereospecificity of the C-4' hydrogen transfer on the coenzymes (pyridoxal phosphate, PLP; and pyridoxamine phosphate, PMP) of aminotransferases has been developed. Aminotransferase of unknown stereospecificity in its PLP form was incubated in (2)H(2)O with a substrate amino acid resulted in PMP labeled with deuterium at C-4' in the pro-S or pro-R configuration according to the stereospecificity of the aminotransferase tested. The [4'-(2)H]PMP was isolated from the enzyme protein and divided into two portions. The first portion was incubated in aqueous buffer with apo-aspartate aminotransferase (a reference si-face specific enzyme), and the other was incubated with apo-branched-chain amino acid aminotransferase (a reference re-face specific enzyme) in the presence of a substrate 2-oxo acid. The (2)H at C-4' is retained with the PLP if the aminotransferase in question transfers C-4' hydrogen on the opposite face of the coenzyme compared with the reference aminotransferase, but the (2)H is removed if the test and reference aminotransferases catalyze hydrogen transfer on the same face. PLP formed in the final reactions was analyzed by LC-MS/MS for the presence or absence of (2)H. The method was highly sensitive that for the aminotransferase with ca. 50 kDa subunit molecular weight, only 2mg of the enzyme was sufficient for the whole test. With this method, the use of radioactive substances could be avoided without compromising the sensitivity of the assay.

  10. Sensitive non-radioactive determination of aminotransferase stereospecificity for C-4' hydrogen transfer on the coenzyme

    SciTech Connect

    Jomrit, Juntratip; Summpunn, Pijug; Meevootisom, Vithaya; Wiyakrutta, Suthep

    2011-02-25

    Research highlights: {yields} Stereochemical mechanism of PLP enzymes is important but difficult to determine. {yields} This new method is significantly less complicated than the previous ones. {yields} This assay is as sensitive as the radioactive based method. {yields} LC-MS/MS positively identify the analyte coenzyme. {yields} The method can be used with enzyme whose apo form is unstable. -- Abstract: A sensitive non-radioactive method for determination of the stereospecificity of the C-4' hydrogen transfer on the coenzymes (pyridoxal phosphate, PLP; and pyridoxamine phosphate, PMP) of aminotransferases has been developed. Aminotransferase of unknown stereospecificity in its PLP form was incubated in {sup 2}H{sub 2}O with a substrate amino acid resulted in PMP labeled with deuterium at C-4' in the pro-S or pro-R configuration according to the stereospecificity of the aminotransferase tested. The [4'-{sup 2}H]PMP was isolated from the enzyme protein and divided into two portions. The first portion was incubated in aqueous buffer with apo-aspartate aminotransferase (a reference si-face specific enzyme), and the other was incubated with apo-branched-chain amino acid aminotransferase (a reference re-face specific enzyme) in the presence of a substrate 2-oxo acid. The {sup 2}H at C-4' is retained with the PLP if the aminotransferase in question transfers C-4' hydrogen on the opposite face of the coenzyme compared with the reference aminotransferase, but the {sup 2}H is removed if the test and reference aminotransferases catalyze hydrogen transfer on the same face. PLP formed in the final reactions was analyzed by LC-MS/MS for the presence or absence of {sup 2}H. The method was highly sensitive that for the aminotransferase with ca. 50 kDa subunit molecular weight, only 2 mg of the enzyme was sufficient for the whole test. With this method, the use of radioactive substances could be avoided without compromising the sensitivity of the assay.

  11. Defects Engineered Monolayer MoS2 for Improved Hydrogen Evolution Reaction

    DOE PAGES

    Ye, Gonglan; Gong, Yongji; Lin, Junhao; Li, Bo; He, Yongmin; Pantelides, Sokrates T.; Zhou, Wu; Vajtai, Robert; Ajayan, Pulickel M.

    2016-01-13

    MoS2 is a promising, low-cost material for electrochemical hydrogen production due to its high activity and stability during the reaction. Our work represents an easy method to increase the hydrogen production in electrochemical reaction of MoS2 via defect engineering, and helps to understand the catalytic properties of MoS2.

  12. Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

    SciTech Connect

    Westlake, Brittany C.; Brennaman, Kyle M.; Concepcion, Javier J.; Paul, Jared J.; Bettis, Stephanie E.; Hampton, Shaun D.; Miller, Stephen A.; Lebedeva, Natalia V.; Forbes, Malcolm D. E.; Moran, Andrew M.; Meyer, Thomas J.; Papanikolas, John M.

    2011-05-24

    The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H⁺ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated ⁺H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

  13. N-H-Type Excited-State Proton Transfer in Compounds Possessing a Seven-Membered-Ring Intramolecular Hydrogen Bond.

    PubMed

    Chen, Yi-An; Meng, Fan-Yi; Hsu, Yen-Hao; Hung, Cheng-Hsien; Chen, Chi-Lin; Chung, Kun-You; Tang, Wei-Feng; Hung, Wen-Yi; Chou, Pi-Tai

    2016-10-01

    A series of compounds containing 5-(2-aminobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one (o-ABDI) as the core chromophore with a seven-membered-ring N-H-type intramolecular hydrogen bond have been synthesized and characterized. The acidity of the N-H proton and thus the hydrogen-bond strength can be fine-tuned by replacing one of the amino hydrogen atoms by a substituent R, the acidity increasing with increasing electron-withdrawing strength of R, that is, in the order Htransfer (ESIPT) that results in proton-transfer emission solely in the red region. Reversible ESIPT, and hence dual emission, involving the normal and proton-transfer tautomers was resolved for the acetyl- and benzyl-substituted counterparts. For o-ABDI, which has the weakest acidity, ESIPT is prohibited due to its highly endergonic reaction. The results clearly demonstrate the harnessing of ESIPT by modifying the proton acidity and hydrogen-bonding strength in a seven-membered-ring intramolecular hydrogen-bonding system. For all the compounds studied, the emission quantum yields are weak (ca. 10(-3) ) in dichloromethane, but strong in the solid form, ranging from 3.2 to 47.4 %. PMID:27539818

  14. Reactions of hydrogen with V-Cr-Ti alloys

    SciTech Connect

    DiStefano, J.R.; DeVan, J.H.; Chitwood, L.D.; Roehrig, D.H.

    1998-09-01

    In the absence of increases in oxygen concentration, additions of up to 400 ppm hydrogen to V-4 Cr-4 Ti did not result in significant embrittlement as determined by room temperature tensile tests. However, when hydrogen approached 700 ppm after exposure at 325 C, rapid embrittlement occurred. In this latter case, hydride formation is the presumed embrittlement cause. When oxygen was added during or prior to hydrogen exposure, synergistic effects led to significant embrittlement by 100 ppm hydrogen.

  15. Reactions of Persistent Carbenes with Hydrogen-Terminated Silicon Surfaces.

    PubMed

    Zhukhovitskiy, Aleksandr V; Mavros, Michael G; Queeney, K T; Wu, Tony; Voorhis, Troy Van; Johnson, Jeremiah A

    2016-07-13

    Surface passivation has enabled the development of silicon-based solar cells and microelectronics. However, a number of emerging applications require a paradigm shift from passivation to functionalization, wherein surface functionality is installed proximal to the silicon surface. To address this need, we report here the use of persistent aminocarbenes to functionalize hydrogen-terminated silicon surfaces via Si-H insertion reactions. Through the use of model compounds (H-Si(TMS)3 and H-Si(OTMS)3), nanoparticles (H-SiNPs), and planar Si(111) wafers (H-Si(111)), we demonstrate that among different classes of persistent carbenes, the more electrophilic and nucleophilic ones, in particular, a cyclic (alkyl)(amino)carbene (CAAC) and an acyclic diaminocarbene (ADAC), are able to undergo insertion into Si-H bonds at the silicon surface, forming persistent C-Si linkages and simultaneously installing amine or aminal functionality in proximity to the surface. The CAAC (6) is particularly notable for its clean insertion reactivity under mild conditions that produces monolayers with 21 ± 3% coverage of Si(111) atop sites, commensurate with the expected maximum of ∼20%. Atomic force and transmission electron microscopy, nuclear magnetic resonance, X-ray photoelectron, and infrared spectroscopy, and time-of-flight secondary ion mass spectrometry provided evidence for the surface Si-H insertion process. Furthermore, computational studies shed light on the reaction energetics and indicated that CAAC 6 should be particularly effective at binding to silicon dihydride, trihydride, and coupled monohyride motifs, as well as oxidized surface sites. Our results pave the way for the further development of persistent carbenes as universal ligands for silicon and potentially other nonmetallic substrates. PMID:27366818

  16. Sorption enhanced reaction process (SERP) for the production of hydrogen

    SciTech Connect

    Hufton, J.; Mayorga, S.; Gaffney, T.; Nataraj, S.; Rao, M.; Sircar, S.

    1998-08-01

    The novel Sorption Enhanced Reaction Process has the potential to decrease the cost of hydrogen production by steam methane reforming. Current effort for development of this technology has focused on adsorbent development, experimental process concept testing, and process development and design. A preferred CO{sub 2} adsorbent, K{sub 2}CO{sub 3} promoted hydrotalcite, satisfies all of the performance targets and it has been scaled up for process testing. A separate class of adsorbents has been identified which could potentially improve the performance of the H{sub 2}-SER process. Although this material exhibits improved CO{sub 2} adsorption capacity compared to the HTC adsorbent, its hydrothermal stability must be improved. Single-step process experiments (not cyclic) indicate that the H{sub 2}-SER reactor performance during the reaction step improves with decreasing pressure and increasing temperature and steam to methane ratio in the feed. Methane conversion in the H{sub 2}-SER reactor is higher than for a conventional catalyst-only reactor operated at similar temperature and pressure. The reactor effluent gas consists of 90+% H{sub 2}, balance CH{sub 4}, with only trace levels (< 50 ppm) of carbon oxides. A best-case process design (2.5 MMSCFD of 99.9+% H{sub 2}) based on the HTC adsorbent properties and a revised SER process cycle has been generated. Economic analysis of this design indicates the process has the potential to reduce the H{sub 2} product cost by 25--31% compared to conventional steam methane reforming.

  17. Tryptophan as a probe of photosystem I electron transfer reactions: a UV resonance Raman study.

    PubMed

    Chen, Jun; Bender, Shana L; Keough, James M; Barry, Bridgette A

    2009-08-20

    Photosystem I (PSI) is one of the two membrane-associated reaction centers involved in oxygenic photosynthesis. In photosynthesis, solar energy is converted to chemical energy in the form of a transmembrane charge separation. PSI oxidizes cytochrome c(6) or plastocyanin and reduces ferredoxin. In cyanobacterial PSI, there are 10 tryptophan residues with indole side chains located less than 10 A from the electron transfer cofactors. In this study, we apply pump-probe difference UV resonance Raman (UVRR) spectroscopy to acquire the spectrum of aromatic amino acids in cyanobacterial PSI. This UVRR technique allows the use of the tryptophan vibrational spectrum as a reporter for structural changes, which are linked to PSI electron transfer reactions. Our results show that photo-oxidation of the chlorophyll a/a' heterodimer, P(700), causes shifts in the vibrational frequencies of two or more tryptophan residues. Similar perturbations of tryptophan are observed when P(700) is chemically oxidized. The observed spectral frequencies suggest that the perturbed tryptophan side chains are only weakly or not hydrogen bonded and are located in an environment in which there is steric repulsion. The direction of the spectral shifts is consistent with an oxidation-induced increase in dielectric constant or a change in hydrogen bonding. To explain our results, the perturbation of tryptophan residues must be linked to a PSI conformational change, which is, in turn, driven by P(700) oxidation.

  18. Calculated protein and proton motions coupled to electron transfer: electron transfer from QA- to QB in bacterial photosynthetic reaction centers.

    PubMed

    Alexov, E G; Gunner, M R

    1999-06-29

    Reaction centers from Rhodobacter sphaeroides were subjected to Monte Carlo sampling to determine the Boltzmann distribution of side-chain ionization states and positions and buried water orientation and site occupancy. Changing the oxidation states of the bacteriochlorophyll dimer electron donor (P) and primary (QA) and secondary (QB) quinone electron acceptors allows preparation of the ground (all neutral), P+QA-, P+QB-, P0QA-, and P0QB- states. The calculated proton binding going from ground to other oxidation states and the free energy of electron transfer from QA-QB to form QAQB- (DeltaGAB) compare well with experiment from pH 5 to pH 11. At pH 7 DeltaGAB is measured as -65 meV and calculated to be -80 meV. With fixed protein positions as in standard electrostatic calculations, DeltaGAB is +170 meV. At pH 7 approximately 0.2 H+/protein is bound on QA reduction. On electron transfer to QB there is little additional proton uptake, but shifts in side chain protonation and position occur throughout the protein. Waters in channels leading from QB to the surface change site occupancy and orientation. A cluster of acids (GluL212, AspL210, and L213) and SerL223 near QB play important roles. A simplified view shows this cluster with a single negative charge (on AspL213 with a hydrogen bond to SerL233) in the ground state. In the QB- state the cluster still has one negative charge, now on the more distant AspL210. AspL213 and SerL223 move so SerL223 can hydrogen bond to QB-. These rearrangements plus other changes throughout the protein make the reaction energetically favorable.

  19. Microscale Enhancement of Heat and Mass Transfer for Hydrogen Energy Storage

    SciTech Connect

    Drost, Kevin; Jovanovic, Goran; Paul, Brian

    2015-09-30

    The document summarized the technical progress associated with OSU’s involvement in the Hydrogen Storage Engineering Center of Excellence. OSU focused on the development of microscale enhancement technologies for improving heat and mass transfer in automotive hydrogen storage systems. OSU’s key contributions included the development of an extremely compact microchannel combustion system for discharging hydrogen storage systems and a thermal management system for adsorption based hydrogen storage using microchannel cooling (the Modular Adsorption Tank Insert or MATI).

  20. Liquid-phase hydrogenation of citral over Pt/SiO{sub 2} catalysts. 2. Hydrogenation of reaction intermediate compounds

    SciTech Connect

    Singh, U.K.; Sysak, M.N.; Vannice, M.A.

    2000-04-01

    Liquid-phase hydrogenation of the four principal reaction intermediates formed during citral hydrogenation, i.e., nerol, geraniol, citronellal, and citronellol, was studied at 298 and 373 K under 20 atm H{sub 2} at concentrations of 0.5 to 1.0 M in hexane. A decrease in the initial reaction rate as temperature increased from 298 to 373 K was exhibited during the hydrogenation of all four compounds, just as reported earlier for citral; however, the decrease in rate at 373 K was only one-half for citronellal whereas it was orders of magnitude greater for nerol and geraniol. Furthermore, simultaneous hydrogenation of citronellal and geraniol at 298 K resulted in a continuous decrease in the rate of citronellal disappearance in contrast to the nearly constant rate of disappearance observed during hydrogenation of citronellal alone. Competitive hydrogenation of citral with either geraniol or citronellal showed that geraniol hydrogenation to citronellol is kinetically insignificant during citral hydrogenation at 373 K. The initial activity for hydrogenation of the intermediates at 298 K follows the following trend: geraniol > nerol < citronellol < E-citral, citronellal > Z-citral. Based on the relative hydrogenation rates of the intermediate alone versus its hydrogenation in the presence of other reactants, the relative size of the adsorption equilibrium constants for the various organic compounds appears to be as follows: citral > citronellal > geraniol, nerol > citronellol > 3,7-dimethyloctanol. This study indicates that activation of the C{double_bond}O bond should be performed at higher reaction temperatures to maximize selectivity to the unsaturated alcohols.

  1. A RhxSy/C Catalyst for the Hydrogen Oxidation and Hydrogen Evolution Reactions in HBr

    SciTech Connect

    Masud, J; Nguyen, TV; Singh, N; McFarland, E; Ikenberry, M; Hohn, K; Pan, CJ; Hwang, BJ

    2015-01-13

    Rhodium sulfide (Rh2S3) on carbon support was synthesized by refluxing rhodium chloride with ammonium thiosulfate. Thermal treatment of Rh2S3 at high temperatures (600 degrees C to 850 degrees C) in presence of argon resulted in the transformation of Rh2S3 into Rh3S4, Rh17S15 and Rh which were characterized by TGA/DTA, XRD, EDX, and deconvolved XPS analyses. The catalyst particle size distribution ranged from 3 to 12 nm. Cyclic voltammetry and rotating disk electrode measurements were used to evaluate the catalytic activity for hydrogen oxidation and evolution reactions in H2SO4 and HBr solutions. The thermally treated catalysts show high activity for the hydrogen reactions. The exchange current densities (i(o)) of the synthesized RhxSy catalysts in H-2-saturated 1M H2SO4 and 1M HBr for HER and HOR were 0.9 mA/cm(2) to 1.0 mA/cm(2) and 0.8 to 0.9 mA/cm(2), respectively. The lower i(o) values obtained in 1M HBr solution compared to in H2SO4 might be due to the adsorption of Br- on the active surface. Stable electrochemical active surface area (ECSA) of RhxSy catalyst was obtained for CV scan limits between 0 V and 0.65 V vs. RHE. Scans with upper voltage limit beyond 0.65 V led to decreased and unreproducible ECSA measurements. (C) The Author(s) 2015. Published by ECS. All rights reserved.

  2. A RhxSy/C Catalyst for the Hydrogen Oxidation and Hydrogen Evolution Reactions in HBr

    DOE PAGES

    Masud, Jahangir; Nguyena, Trung V.; Singh, Nirala; McFarland, Eric; Ikenberry, Myles; Hohn, Keith; Pan, Chun-Jern; Hwang, Bing-Joe

    2015-02-01

    Rhodium sulfide (Rh2S3) on carbon support was synthesized by refluxing rhodium chloride with ammonium thiosulfate. Thermal treatment of Rh2S3 at high temperatures (600°C to 850°C) in presence of argon resulted in the transformation of Rh2S3 into Rh3S4, Rh17S15 and Rh which were characterized by TGA/DTA, XRD, EDX, and deconvolved XPS analyses. The catalyst particle size distribution ranged from 3 to 12 nm. Cyclic voltammetry and rotating disk electrode measurements were used to evaluate the catalytic activity for hydrogen oxidation and evolution reactions in H2SO4 and HBr solutions. The thermally treated catalysts show high activity for the hydrogen reactions. The exchangemore » current densities (io) of the synthesized RhxSy catalysts in H2-saturated 1M H2SO4 and 1M HBr for HER and HOR were 0.9 mA/cm2 to 1.0 mA/cm2 and 0.8 to 0.9 mA/cm2, respectively. The lower io values obtained in 1M HBr solution compared to in H2SO4 might be due to the adsorption of Br- on the active surface. Stable electrochemical active surface area (ECSA) of RhxSy catalyst was obtained for CV scan limits between 0 V and 0.65 V vs. RHE. Scans with upper voltage limit beyond 0.65 V led to decreased and unreproducible ECSA measurements.« less

  3. Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions

    PubMed Central

    Wang, Xue Lu; Liu, Wenqing; Yu, Yan-Yan; Song, Yanhong; Fang, Wen Qi; Wei, Daxiu; Gong, Xue-Qing; Yao, Ye-Feng; Yang, Hua Gui

    2016-01-01

    Proton transfer (PT) processes in solid–liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid–liquid phases. PMID:27311326

  4. Ruthenium(ii) complexes of hemilabile pincer ligands: synthesis and catalysing the transfer hydrogenation of ketones.

    PubMed

    Nair, Ashwin G; McBurney, Roy T; Walker, D Barney; Page, Michael J; Gatus, Mark R D; Bhadbhade, Mohan; Messerle, Barbara A

    2016-09-28

    A series of Ru(ii) complexes were synthesised based on a hemilabile pyrazole-N-heterocyclic carbene (NHC)-pyrazole (C3N2H3)CH2(C3N2H2)CH2(C3N2H3) NCN pincer ligand 1. All complexes were fully characterised using single crystal X-ray crystallography and multinuclear NMR spectroscopy. Hemilabile ligands provide flexible coordination modes for the coordinating metal ion which can play a significant effect on the efficiency and mechanism of catalysis by the resulting complex. Here we observed and isolated mono-, bi- and tri-dentate complexes of both Ag(i) and Ru(ii) with 1 in which the resultant coordination mode was controlled by careful reagent selection. The catalytic activity of the Ru(ii) complexes for the transfer hydrogenation reaction of acetophenone with isopropanol was investigated. The unexpected formation of the pentaborate anion, [B5O6(OH)4](-), during the synthesis of complex 6a was found to have an unexpected positive effect by enhancing the catalysis rate. This work provides insights into the roles that different coordination modes, counterions and ligand hemilability play on the catalytic activity in transfer hydrogenations. PMID:27539740

  5. Liquid-Phase Catalytic Transfer Hydrogenation of Furfural over Homogeneous Lewis Acid-Ru/C Catalysts.

    PubMed

    Panagiotopoulou, Paraskevi; Martin, Nickolas; Vlachos, Dionisios G

    2015-06-22

    The catalytic performance of homogeneous Lewis acid catalysts and their interaction with Ru/C catalyst are studied in the catalytic transfer hydrogenation of furfural by using 2-propanol as a solvent and hydrogen donor. We find that Lewis acid catalysts hydrogenate the furfural to furfuryl alcohol, which is then etherified with 2-propanol. The catalytic activity is correlated with an empirical scale of Lewis acid strength and exhibits a volcano behavior. Lanthanides are the most active, with DyCl3 giving complete furfural conversion and a 97 % yield of furfuryl alcohol at 180 °C after 3 h. The combination of Lewis acid and Ru/C catalysts results in synergy for the stronger Lewis acid catalysts, with a significant increase in the furfural conversion and methyl furan yield. Optimum results are obtained by using Ru/C combined with VCl3 , AlCl3 , SnCl4 , YbCl3 , and RuCl3 . Our results indicate that the combination of Lewis acid/metal catalysts is a general strategy for performing tandem reactions in the upgrade of furans.

  6. Effect of intermolecular hydrogen bonding and proton transfer on fluorescence of salicylic acid

    NASA Astrophysics Data System (ADS)

    Denisov, G. S.; Golubev, N. S.; Schreiber, V. M.; Shajakhmedov, Sh. S.; Shurukhina, A. V.

    1997-12-01

    Effects of intermolecular interactions, in particular the influence of intermolecular hydrogen bonds formed by salicylic acid (SA) as a proton donor with proton acceptors of different strength, on fluorescence spectra of SA in non-aqueous solutions have been investigated. Infrared spectra of studied systems have been analyzed in order to elucidate the ground state structure of the complexes formed. It has been found that at the room temperature in dilute solutions in non-polar or slightly polar aprotic solvents, where the SA molecule is not involved in intermolecular hydrogen bonding, the position of the main (blue) fluorescence component is determined by the excited state intramolecular proton transfer (ESIPT) in the lowest singlet excited state S 1. With increasing proton acceptor ability of the environment, when formation of weak or middle strength intermolecular H-bonds is possible, the emission band shifts gradually to lower frequency, the quantum yield falls and poorly resolved doublet structure becomes more pronounced, especially in the solvents containing heavy bromine atoms. As a possible reason for these effects, coupling between the S 1 and closely lying triplet term is considered. With the strongest proton acceptors like aliphatic amines, intermolecular proton transfer with ionic pair formation in the ground state and double (intra- and intermolecular) proton transfer in the excited state take place, resulting in a blue shift of the emission band. Similar emission is typical for the SA anion in aqueous solutions. The p Ka value of SA in S 1 state has been found to be 3.1. Such a small value can be explained taking into account the ESIPT reaction following the excitation. The SA complex with pyridine exhibits emission spectrum containing both molecular-like and anion-like bands with relative intensities strongly dependent on the temperature and solvent properties. The most probable origin of this dual emission is the molecular-ionic tautomerism caused by

  7. Transfer function between tibial acceleration and ground reaction force.

    PubMed

    Lafortune, M A; Lake, M J; Hennig, E

    1995-01-01

    The purpose of the present study was to capture the relationship between ground reaction force (GRF) and tibial axial acceleration. Tibia acceleration and GRF were simultaneously recorded from five subjects during running. The acceleration of the bone was measured with a transducer mounted onto an intracortical pin. The signals were analyzed in the frequency domain to characterize the relationship between GRF and tibial acceleration. The results confirmed that for each subject this relationship could be represented by a frequency transfer function. The existence of a more general relationship for all five subjects was also confirmed by the results. The transfer functions provided information about transient shock transmissibility for the entire impact phase of running.

  8. Effects of copper catalytic reactions on the development of supersonic hydrogen flames

    SciTech Connect

    Chang, S.L.; Lottes, S.A.; Berry, G.F.

    1992-10-01

    Copper species are present in hydrogen flames in arc heated supersonic ramjet testing facilities. Homogeneous and heterogeneous copper catalytic reactions may affect the flame development by enhancing the recombination of hydrogen atoms. Computer simulation is used to investigate the effects of the catalytic reactions on the reaction and ignition times of the flames. The simulation uses a modified general chemical kinetics computer program to simulate the development of copper-contaminated hydrogen flames under scramjet testing conditions. Reaction times of hydrogen flames are found to be reduced due to the copper catalytic effects, but ignition times are much less sensitive to such effects. The reduction of reaction time depends on copper concentration, particle size (if copper is in the condensed phase), and Mach number (or initial temperature and pressure). As copper concentration increases or the particle size decreases, reaction time decreases. As Mach number increases (or pressure and temperature decrease), the copper catalytic effects are greater.

  9. Advancing the electrochemistry of the hydrogen-evolution reaction through combining experiment and theory.

    PubMed

    Zheng, Yao; Jiao, Yan; Jaroniec, Mietek; Qiao, Shi Zhang

    2015-01-01

    The electrocatalytic hydrogen-evolution reaction (HER), as the main step of water splitting and the cornerstone of exploring the mechanism of other multi-electron transfer electrochemical processes, is the subject of extensive studies. A large number of high-performance electrocatalysts have been developed for HER accompanied by recent significant advances in exploring its electrochemical nature. Herein we present a critical appraisal of both theoretical and experimental studies of HER electrocatalysts with special emphasis on the electronic structure, surface (electro)chemistry, and molecular design. It addresses the importance of correlating theoretical calculations and electrochemical measurements toward better understanding of HER electrocatalysis at the atomic level. Fundamental concepts in the computational quantum chemistry and its relation to experimental electrochemistry are also presented along with some featured examples. PMID:25384712

  10. Role of aromatic structure in pathways of hydrogen transfer and bond cleavage in coal liquefaction: Theoretical studies

    SciTech Connect

    Franz, J.A.; Autrey, T.; Camaioni, D.M.; Watts, J.D.; Bartlett, R.J.

    1995-09-01

    The mechanisms by which strong carbon-carbon bonds between aromatic rings and side chains are cleaved under hydropyrolysis conditions remain a subject of wide interest to fuel science. Recently, the authors have studied in detail an alternate pathway for hydrogen atom transfer to {pi}-systems, radical hydrogen transfer (RHT). RHT is the direct, bimolecular transfer of hydrogen from the {beta}-position of an organic radical to the target {pi}-system. In the initial theoretical study, they examined the reaction ethyl radical + ethylene = ethylene + ethyl at the spin-projected UMP2/6-31G** level of theory. Recently, they have used a calibrated ROHF-MNDO-PM3 method to predict thermoneutral RHT barriers for hydrogen transfer between hydroaryl radicals and the corresponding arene. Because of the inherent limitations of semiempirical methods such as ROHF-MNDO-PM3, they have extended the initial work with the ethyl + ethylene study to examine this reaction at the ROHF-MBPT[2]-6-31G** and ROHF-CCSD[T]-6-31G** levels of ab initio theory. The primary objective was to determine how intrinsic RHT barriers change with conjugative stabilization of the radicals. The spin-restricted ROHF approach has been applied to study several RHT reactions, and they present completed ROHF results for the ethyl + ethylene system and preliminary results for the methallyl + butadiene system. The methallyl + butadiene system serves as a model for highly stabilized hydroaryl radicals: the methallyl radical exhibits a C-H bond strength of 46.5 kcal/mol compared to 9-hydroanthracenyl, 43.1 kcal/mol.

  11. A new setup for transfer reactions at REX-ISOLDE

    NASA Astrophysics Data System (ADS)

    Bildstein, V.; Gernhäuser, R.; Kröll, Th.; Krücken, R.; Raabe, R.; van Duppen, P.; Rex-Isolde; Miniball Collaborations

    2007-07-01

    A new setup is proposed aimed at the study of single particle structures of nuclei far from stability by nucleon transfer reactions in inverse kinematics using radioactive ion beams obtained from REX-ISOLDE. The setup combines particle and γ-ray detection using the MINIBALL array and was designed to achieve a high particle efficiency by covering a large angular range while retaining the high γ-ray efficiency of the MINIBALL setup. All particle detectors are segmented and/or position-sensitive silicon detectors, for forward angles built as ΔE-E telescopes for light particle identification. As a first experiment with this new setup, the d( 30Mg, 31Mg)p reaction at 3 MeV/u will be performed in 2007.

  12. Chemical reaction fouling model for single-phase heat transfer

    SciTech Connect

    Panchal, C.B.; Watkinson, A.P.

    1993-08-01

    A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

  13. Modeling charge transfer in the photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Pudlak, Michal; Pinčak, Richard

    2003-12-01

    In this work, we present a model to elucidate the unidirectionality of the primary charge-separation process in the bacterial reaction centers. We have used a model of three sites/molecules with electron transfer beginning at site 1 with an option to proceed to site 2 or site 3. We used a stochastic model with arbitrary correlation functions. We get the quantum yields of electron escape via the sites 2,3 in two limiting cases that correspond to a spectral density of underdamped and overdamped Brownian oscillator. In the fast modulation limit of an overdamped regime we get the effect, which was named “fear of death,” in which for strong enough sink parameters the electron has a tendency to avoid the place with greater sink. The presented model was used to provide a plausible explanation of the temperature dependence of the quantum yields of the Rhodobacter sphaeroides photosynthetic reaction center in the high-temperature regime.

  14. Slush hydrogen propellant production, transfer, and expulsion studies at the NASA K-Site Facility

    NASA Technical Reports Server (NTRS)

    Hardy, Terry L.; Whalen, Margaret V.

    1991-01-01

    Slush hydrogen is currently being considered as a fuel for the National AeroSpace Plane (NASP) because it offers the potential for decreased vehicle size and weight. However, no large scale data was available on the production, transfer, and tank pressure control characteristics required to use the fuel for the NASP. Therefore, experiments were conducted at NASA-Lewis K-Site Facility to improve the slush hydrogen data base. Slush hydrogen was produced using the evaporative cooling, or freeze-thaw, technique in batches for approx. 800 gallons. This slush hydrogen was pressure transferred to a 5 ft diameter spherical test tank following production, and flow characteristics were measured during this transfer process. The slush hydrogen in the test tank was pressurized and expelled using a pressurized expulsion technique to obtain information on tank pressure control for the NASP. Results from the production, transfer, pressurization, and pressurized expulsion tests are described.

  15. Slush hydrogen propellant production, transfer, and expulsion studies at the NASA K-Site Facility

    NASA Technical Reports Server (NTRS)

    Hardy, Terry L.; Whalen, Margaret V.

    1991-01-01

    Slush hydrogen is currently being considered as a fuel for the National Aero-Space Plane (NASP) because it offers the potential for decreased vehicle size and weight. However, no large-scale data was available on the production, transfer, and tank pressure control characteristics required to use the fuel for the NASP. Therefore, experiments were conducted at the NASA Lewis Research Center K-Site Facility to improve the slush hydrogen database. Slush hydrogen was produced using the evaporative cooling, or freeze-thaw, technique in batches of about 800 gallons. This slush hydrogen was pressure transferred to a 5 ft diameter spherical test tank following production, and flow characteristics were measured during this transfer process. The slush hydrogen in the test tank was pressurized and expelled using a pressurized expulsion technique to obtain information on tank pressure control for the NASP. Results from the production, transfer, pressurization, and pressurized expulsion tests are described.

  16. Ketyl Radical Formation via Proton-Coupled Electron Transfer in an Aqueous Solution versus Hydrogen Atom Transfer in Isopropanol after Photoexcitation of Aromatic Carbonyl Compounds.

    PubMed

    Zhang, Xiting; Ma, Jiani; Li, Songbo; Li, Ming-De; Guan, Xiangguo; Lan, Xin; Zhu, Ruixue; Phillips, David Lee

    2016-07-01

    The excited nπ* and ππ* triplets of two benzophenone (BP) and two anthraquinone (AQ) derivatives have been observed in acetonitrile, isopropanol, and mixed aqueous solutions using time-resolved resonance Raman spectroscopic and nanosecond transient absorption experiments. These experimental results, combined with results from density functional theory calculations, reveal the effects of solvent and substituents on the properties, relative energies, and chemical reactivities of the nπ* and ππ* triplets. The triplet nπ* configuration was found to act as the reactive species for a subsequent hydrogen atom transfer reaction to produce a ketyl radical intermediate in the isopropanol solvent, while the triplet ππ* undergoes a proton-coupled electron transfer (PCET) in aqueous solutions to produce a ketyl radical intermediate. This PCET reaction, which occurs via a concerted proton transfer (to the excited carbonyl group) and electron transfer (to the excited phenyl ring), can account for the experimental observation by several different research groups over the past 40 years of the formation of ketyl radicals after photolysis of a number of BP and AQ derivatives in aqueous solutions, although water is considered to be a relatively "inert" hydrogen-donor solvent. PMID:27266916

  17. Cu/MgAl(2)O(4) as bifunctional catalyst for aldol condensation of 5-hydroxymethylfurfural and selective transfer hydrogenation.

    PubMed

    Pupovac, Kristina; Palkovits, Regina

    2013-11-01

    Copper supported on mesoporous magnesium aluminate has been prepared as noble-metal-free solid catalyst for aldol condensation of 5-hydroxymethylfurfural with acetone, followed by hydrogenation of the aldol condensation products. The investigated mesoporous spinels possess high activity as solid-base catalysts. Magnesium aluminate exhibits superior activity compared to zinc and cobalt-based aluminates, reaching full conversion and up to 81 % yield of the 1:1 aldol product. The high activity can be correlated to a higher concentration of basic surface sites on magnesium aluminate. Applying continuous regeneration, the catalysts can be recycled without loss of activity. Focusing on the subsequent hydrogenation of aldol condensation products, Cu/MgAl2 O4 allows a selective hydrogenation and CO bond cleavage, delivering 3-hydroxybutyl-5-methylfuran as the main product with up to 84 % selectivity avoiding ring saturation. Analysis of the hydrogenation activity reveals that the reaction proceeds in the following order: CC>CO>CO cleavage>ring hydrogenation. Comparable activity and selectivity can be also achieved utilizing 2-propanol as solvent in the transfer hydrogenation, providing the possibility for partial recycling of acetone and optimization of the hydrogen management. PMID:24038987

  18. Kinetic and mechanistic studies of carbon-to-metal hydrogen atom transfer involving Os-centered radicals: evidence for tunneling.

    PubMed

    Lewandowska-Andralojc, Anna; Grills, David C; Zhang, Jie; Bullock, R Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-01

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene, and 1,4-cyclohexadiene to Cp(CO)2Os(•) and (η(5)-(i)Pr4C5H)(CO)2Os(•) radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons are in the range 1.5 × 10(5) M(-1) s(-1) to 1.7 × 10(7) M(-1) s(-1) at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary deuterium kinetic isotope effects of 13.4 ± 1.0 and 16.8 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (η(5)-(i)Pr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 °C temperature range were carried out to obtain the difference in activation energies (E(D) - E(H)) and the pre-exponential factor ratio (A(H)/A(D)). For hydrogen atom transfer from xanthene to (η(5)-(i)Pr4C5H)(CO)2Os(•), the (E(D) - E(H)) = 3.3 ± 0.2 kcal mol(-1) and A(H)/A(D) = 0.06 ± 0.02 values suggest a quantum mechanical tunneling mechanism.

  19. Catalytic enantioselective OFF ↔ ON activation processes initiated by hydrogen transfer: concepts and challenges.

    PubMed

    Quintard, Adrien; Rodriguez, Jean

    2016-08-18

    Hydrogen transfer initiated processes are eco-compatible transformations allowing the reversible OFF ↔ ON activation of otherwise unreactive substrates. The minimization of stoichiometric waste as well as the unique activation modes provided by these transformations make them key players for a greener future for organic synthesis. Long limited to catalytic reactions that form racemic products, considerable progress on the development of strategies for controlling diastereo- and enantioselectivity has been made in the last decade. The aim of this review is to present the different strategies that enable enantioselective transformations of this type and to highlight how they can be used to construct key synthetic building blocks in fewer operations with less waste generation. PMID:27381644

  20. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation

    SciTech Connect

    Schwartz, B.J.

    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 {approximately}240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH{sub 2}I{sub 2} and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a {approximately}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.

  1. Variation of reaction dynamics for OH hydrogen abstraction from glycine between ab initio levels of theory.

    PubMed

    Lin, Ren-Jie; Wu, Chen-Chang; Jang, Soonmin; Li, Feng-Yin

    2010-02-01

    The variation in reaction dynamics of OH hydrogen abstraction from glycine between HF, MP2, CCSD(T), M05-2X, BHandHLYP, and B3LYP levels was demonstrated. The abstraction mode shows distinct patterns between these five levels and determines the barrier height, and the spin density transfer between OH radical and glycine. These differences are mainly resulted from the spin density distribution and geometry of the alpha carbon during the abstraction. The captodative effect which is commonly believed as one of the major factors to stabilize the caron-centered radical can only be observed in DFT levels but not in HF and MP2 levels. Difference in the abstraction energy were found in these calculation levels, by using the result of CCSD(T) as reference, B3LYP, BHandHLYP, and M05-2X underestimated the reaction barrier about 5.1, 0.1, and 2.4 kcal mol(-1), while HF and MP2 overestimated 19.1 kcal mol(-1) and 1.6 kcal mol(-1), respectively. These differences can be characterized by the vibration mode of imaginary frequency of transition states, which indicates the topology around transition states and determines reaction barrier height. In this model system, BHandHLYP provides the best prediction of the energy barrier among those tested methods.

  2. Numerical Radiative Transfer and the Hydrogen Reionization of the Universe

    NASA Astrophysics Data System (ADS)

    Petkova, M.

    2011-03-01

    ) simulation code GADGET. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the "OTVET"-suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionization and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump, and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying reionization, our new method can be used on-the-fly during dynamical cosmological simulations, allowing simultaneous treatments of galaxy formation and the reionization process of the Universe. We carry out hydrodynamical simulations of galaxy formation that simultaneously follow radiative transfer of hydrogen-ionizing photons, based on the optically-thin variable Eddington tensor approximation as implemented in the GADGET code. We consider only star-forming galaxies as sources and examine to what extent they can yield a reasonable reionization history and thermal state of the intergalactic medium at redshifts

  3. Mechanistic analysis of the hydrogen evolution and absorption reactions on iron

    NASA Astrophysics Data System (ADS)

    Abd Elhamid, Mahmoud Hassan

    2000-10-01

    The work in this thesis investigates the effect of additives on the kinetics of the hydrogen evolution reaction (HER) and hydrogen absorption reaction (HAR) on iron. The electrochemical hydrogen permeation cell has been used to collect data on both reactions in the absence and presence of the additives. The effect of two additives on the kinetics of both the HER and HAR on iron in acidic solutions was quantified. These two compounds have different behaviors towards both reactions. While benzotriazole (BTA) inhibits both reactions, iodide enhances hydrogen absorption while inhibiting the HER. Analysis of the results using the IPZ (Iyer, Pickering, Zamanzadeh) model shows that both compounds inhibit the HER by decreasing its discharge rate constant and hence the exchange current density. On the other hand, while BTA decreases the rate of hydrogen absorption by decreasing both the hydrogen surface coverage and the kinetic-diffusion constant, k (see chapter 5), iodide ions decrease the rate of hydrogen absorption by increasing the kinetic-diffusion constant, k, while decreasing the hydrogen surface coverage (see chapter 6). A separate study was devoted to investigate the effect of thiosulfate on the kinetics of the HER and HAR on iron (chapter 7). It was shown that thiosulfate enhances both reactions in acidic solutions. The promoting effect was mainly due to its decomposition product H2SO3 with a small contribution from the colloidal sulfur and/or the undecomposed thiosulfate. In chapter 8 it was shown that the polarization data of the hydrogen evolution reaction (HER) can be analyzed to calculate the hydrogen surface coverage and the rate constants of the hydrogen discharge and recombination reactions for metals which have very low permeabilities of hydrogen, and on which the HER proceeds through a coupled Volmer discharge-Tafel recombination mechanism. The analysis is applied to the results of the HER on copper and iron and the rate constants obtained using the

  4. 40 CFR 721.10445 - 2-Propen-1-ol, reaction products with hydrogen sulfide, distn. residues.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false 2-Propen-1-ol, reaction products with... Significant New Uses for Specific Chemical Substances § 721.10445 2-Propen-1-ol, reaction products with...) The chemical substance identified as 2-propen-1-ol, reaction products with hydrogen sulfide,...

  5. 40 CFR 721.10445 - 2-Propen-1-ol, reaction products with hydrogen sulfide, distn. residues.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false 2-Propen-1-ol, reaction products with... Significant New Uses for Specific Chemical Substances § 721.10445 2-Propen-1-ol, reaction products with...) The chemical substance identified as 2-propen-1-ol, reaction products with hydrogen sulfide,...

  6. Double group transfer reactions: role of activation strain and aromaticity in reaction barriers.

    PubMed

    Fernández, Israel; Bickelhaupt, F Matthias; Cossío, Fernando P

    2009-12-01

    Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in-plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high-energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile DeltaE(zeta) and the height of the overall reaction barrier DeltaE( not equal)=DeltaE(zeta=zeta(TS)) is interpreted in terms of the strain energy DeltaE(strain)(zeta) associated with deforming the reactants along the reaction coordinate zeta plus the interaction energy DeltaE(int)(zeta) between these deformed reactants: DeltaE(zeta)=DeltaE(strain)(zeta)+DeltaE(int)(zeta). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states. PMID:19852009

  7. Novel mechanistic aspects on the reaction between low spin Fe(II) Schiff base amino acid complexes and hydrogen peroxide-spectrophotometric tracer of intraperoxo intermediate catalyzed reaction.

    PubMed

    Awad, Aida M; Shaker, Ali Mohamad; Zaki, Ahmad Borhan El-Din; Nassr, Lobna Abdel-Mohsen Ebaid

    2008-12-01

    The kinetics and mechanism of the reaction of hydrogen peroxide with some Fe(II) Schiff base complexes were investigated spectrophotometrically in aqueous solution at pH 8 and 35 degrees C under pseudo-first-order conditions. The used ligands were derived from salicylaldehyde or o-hydroxynaphthaldehyde and some amino acids (l-leucine, l-iso-leucine, l-serine, l-methionine and dl-tryptophan). It was found that the formation of the purple interaperoxo complex appears only above pH 7.5. The reaction consists of two steps. The first step involves reversible formation of the intraperoxo intermediate which renders irreversible at pH 8. The second step consists of inner-sphere electron transfer. The suggested scheme illustrated first-order kinetics at low [H(2)O(2)] and zero-order at high [H(2)O(2)]. Moreover, the activation parameters of the reaction were evaluated. PMID:18394952

  8. Hydrogen Photogeneration Promoted by Efficient Electron Transfer from Iridium Sensitizers to Colloidal MoS2 Catalysts

    NASA Astrophysics Data System (ADS)

    Yuan, Yong-Jun; Yu, Zhen-Tao; Liu, Xiao-Jie; Cai, Jian-Guang; Guan, Zhong-Jie; Zou, Zhi-Gang

    2014-02-01

    We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (λ = 400 nm).

  9. Hydrogen Photogeneration Promoted by Efficient Electron Transfer from Iridium Sensitizers to Colloidal MoS2 Catalysts

    PubMed Central

    Yuan, Yong-Jun; Yu, Zhen-Tao; Liu, Xiao-Jie; Cai, Jian-Guang; Guan, Zhong-Jie; Zou, Zhi-Gang

    2014-01-01

    We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (λ = 400 nm). PMID:24509729

  10. Electrocatalysis of anodic and cathodic oxygen-transfer reactions

    SciTech Connect

    Wels, B.R.

    1990-09-21

    The electrocatalysis of oxygen-transfer reactions is discussed in two parts. In Part I, the reduction of iodate (IO{sub 3}{sup {minus}}) is examined as an example of cathodic oxygen transfer. On oxide-covered Pt electrodes (PtO), a large cathodic current is observed in the presence of IO{sub 3}{sup {minus}} to coincide with the reduction of PtO. The total cathodic charge exceeds the amount required for reduction of PtO and IO{sub 3}{sup {minus}} to produce an adsorbed product. An electrocatalytic link between reduction of IO{sub 3}{sup {minus}} and reduction of PtO is indicated. In addition, on oxide-free Pt electrodes, the reduction of IO{sub 3}{sup {minus}} is determined to be sensitive to surface treatment. The electrocatalytic oxidation of CN{sup {minus}} is presented as an example of anodic oxygen transfer in Part II. The voltametric response of CN{sup {minus}} is virtually nonexistent at PbO{sub 2} electrodes. The response is significantly improved by doping PbO{sub 2} with Cu. Cyanide is also oxidized effectively at CuO-film electrodes. Copper is concluded to serve as an adsorption site for CN{sup {minus}}. It is proposed that an oxygen tunneling mechanism comparable to electron tunneling does not occur at the electrode-solution interface. The adsorption of CN{sup {minus}} is therefore considered to be a necessary prerequisite for oxygen transfer. 201 refs., 23 figs., 2 tabs.

  11. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

    NASA Astrophysics Data System (ADS)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-01

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  12. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    PubMed

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  13. Liquid-to-Gas Mass Transfer in Anaerobic Processes: Inevitable Transfer Limitations of Methane and Hydrogen in the Biomethanation Process

    PubMed Central

    Pauss, André; Andre, Gérald; Perrier, Michel; Guiot, Serge R.

    1990-01-01

    Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of kLa, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen. PMID:16348206

  14. Application of the electron nuclear dynamics method to hydrogen abstraction and exchange reactions of hydrogen + HOD and deuterium + ammonium ion

    NASA Astrophysics Data System (ADS)

    Coutinho Neto, Mauricio Domingues

    2001-07-01

    The field of quantum molecular dynamics have flourished in the last 20 years. Methods that propose the solution of the time dependent Schrodinger equation for a molecular reactive process abound in the literature. However the majority of these methods focus on solving the nuclear Schrodinger equation subject to a known electronic potential. The electron nuclear dynamics (END) method proposes a framework of a hierarchy of approximations to the Schrodinger equation based on the time dependent variational Principle (TDVP). A general approach is sought to solve the electronic and nuclear problem simultaneously without making use of the Born-Oppenheimer approximation. The purpose of this work is to apply the minimal END to areas where its unique qualities can give new insight into the relevant dynamics of a chemical or physical process. Minimal END is a method for direct non-adiabatic dynamics. It describes the electrons with a family of complex determinantal wave-functions in terms of non-orthogonal spin orbitals and treats the nuclei as classical particles. In the first two studies, we apply the END method to hydrogen abstraction and exchange reactions at hyper-thermal collision energies. We investigate the D2+ NH+3 reaction at collision energies ranging from 6 to 16 eV and the H + HOD reaction at a collision energy of 1.575 eV. Collision energies refer to center of mass energies. Emphasis is put on the details of the abstraction and exchange reaction mechanisms for ground state reactants. In a final application we use minimal END to study the interaction of a strong laser field with the diatomic molecules HF and LiH. Effects of the polarization of the electronic potential on the dynamics are investigated. Emphasis is also placed on the development of a general method for interpreting the final time dependent wave-function of the product fragments. The purpose is to analyze the final state wave-function in terms of charge transfer channels as well as individual

  15. Catalysts for initiating the hydrogen-oxygen reaction at 78 K.

    NASA Technical Reports Server (NTRS)

    Jennings, T. J.; Voge, H. H.; Armstrong, W. E.

    1972-01-01

    Catalysts for initiating reaction of hydrogen with oxygen in gas mixtures at temperatures down to 78 K (-195 C) were sought. A rising-temperature reactor was used for detecting onset of reaction. The platinum metals, especially iridium, platinum, and ruthenium, were the most active. With high concentrations of iridium on an alumina support, reaction initiation was observed at -195 C for a helium stream containing 3% hydrogen and 1% oxygen. Best results were obtained when the catalyst had been preheated in hydrogen and cooled in a hydrogen environment before being contacted with oxygen-containing gas. The initiation is interpreted to be the result of transient phenomena which occur when a hydrogen-oxygen mixture contacts an active catalyst. Chemisorption of oxygen and formation of some water, along with water adsorption on the support, serve to raise the temperature to a point where true catalysis can proceed.

  16. Revisited reaction-diffusion model of thermal desorption spectroscopy experiments on hydrogen retention in material

    SciTech Connect

    Guterl, Jerome Smirnov, R. D.; Krasheninnikov, S. I.

    2015-07-28

    Desorption phase of thermal desorption spectroscopy (TDS) experiments performed on tungsten samples exposed to flux of hydrogen isotopes in fusion relevant conditions is analyzed using a reaction-diffusion model describing hydrogen retention in material bulk. Two regimes of hydrogen desorption are identified depending on whether hydrogen trapping rate is faster than hydrogen diffusion rate in material during TDS experiments. In both regimes, a majority of hydrogen released from material defects is immediately outgassed instead of diffusing deeply in material bulk when the evolution of hydrogen concentration in material is quasi-static, which is the case during TDS experiments performed with tungsten samples exposed to flux of hydrogen isotopes in fusion related conditions. In this context, analytical expressions of the hydrogen outgassing flux as a function of the material temperature are obtained with sufficient accuracy to describe main features of thermal desorption spectra (TDSP). These expressions are then used to highlight how characteristic temperatures of TDSP depend on hydrogen retention parameters, such as trap concentration or activation energy of detrapping processes. The use of Arrhenius plots to characterize retention processes is then revisited when hydrogen trapping takes place during TDS experiments. Retention processes are also characterized using the shape of desorption peaks in TDSP, and it is shown that diffusion of hydrogen in material during TDS experiment can induce long desorption tails visible aside desorption peaks at high temperature in TDSP. These desorption tails can be used to estimate activation energy of diffusion of hydrogen in material.

  17. Liquid composition having ammonia borane and decomposing to form hydrogen and liquid reaction product

    DOEpatents

    Davis, Benjamin L; Rekken, Brian D

    2014-04-01

    Liquid compositions of ammonia borane and a suitably chosen amine borane material were prepared and subjected to conditions suitable for their thermal decomposition in a closed system that resulted in hydrogen and a liquid reaction product.

  18. Tetramethylallene and 2,4-dimethyl-1,3-pentadiene as hydrogen atom acceptors in reactions with HMn(CO)/sub 5/ and HCo(CO)/sub 4/

    SciTech Connect

    Garst, J.F.; Bockman, T.M.; Batlaw, R.

    1986-04-02

    The authors report evidence that reactions of tetramethylallene with HMn(CO)/sub 5/ or HCo(CO)/sub 4/ proceed by initial hydrogen atom transfer (Scheme I), providing the first examples of such reactions of nonconjugated alkenes. 2,4-Dimethyl-1,3-pentadiene also reacts with HCo(CO)/sub 4/, and probably HMn(CO)/sub 5/, through a similar mechanism.

  19. Hydrogenolysis of 5-carbon sugars, sugar alcohols, and other methods and compositions for reactions involving hydrogen

    DOEpatents

    Werpy, Todd A [West Richland, WA; Zacher, Alan H [Kennewick, WA

    2002-11-12

    Methods and compositions for reactions of hydrogen over a Re-containing catalyst with compositions containing a 5-carbon sugar, sugar alcohol, or lactic acid are described. It has been surprisingly discovered that reaction with hydrogen over a Re-containing multimetallic catalyst resulted in superior conversion and selectivity to desired products such as propylene glycol. A process for the synthesis of PG from lactate or lactic acid is also described.

  20. Hydrogenolysis Of 5-Carbon Sugars, Sugar Alcohols And Compositions For Reactions Involving Hydrogen

    DOEpatents

    Werpy, Todd A.; Frye, Jr., John G.; Zacher, Alan H.; Miller, Dennis J.

    2004-01-13

    Methods and compositions for reactions of hydrogen over a Re-containing catalyst with compositions containing a 5-carbon sugar, sugar alcohol, or lactic acid are described. It has been surprisingly discovered that reaction with hydrogen over a Re-containing multimetallic catalyst resulted in superior conversion and selectivity to desired products such as propylene glycol. A process for the synthesis of PG from lactate or lactic acid is also described.

  1. The reaction of hydrogen peroxide with nitrogen dioxide and nitric oxide.

    NASA Technical Reports Server (NTRS)

    Gray, D.; Lissi, E.; Heicklen, J.

    1972-01-01

    The reactions were studied with the aid of a mass spectrometer. A pinhole bleed system provided continuous sampling of the gas mixture in the cell during the reaction. It was found that the homogeneous reactions of nitric oxide and nitrogen dioxide with hydrogen peroxide are too slow to be of any significance in the upper atmosphere. However, the heterogeneous reactions may be important in the conversion of nitric oxide to nitrogen dioxide in the case of polluted urban atmospheres.

  2. Population of high spin states in very heavy ion transfer reactions. The experimental evidence

    SciTech Connect

    Guidry, M.W.

    1985-01-01

    Transfer reactions have been studied for some time with light heavy ions such as oxygen. Although states of spin I approx.10 h are sometimes populated in such reactions, it is assumed that collective excitation is small, and the transferred particles are responsible for the angular momentum transfer. In this paper we will discuss a qualitatively different kind of transfer reaction using very heavy ions (A greater than or equal to 40). In these reactions the collective excitation in both the entrance and exit channels is strong, and there may be appreciable angular momentum transfer associated with inelastic excitation. 12 refs., 13 figs.

  3. Plasmonic Properties of Bimetallic Nanostructures and Their Applications in Hydrogen Sensing and Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Jiang, Ruibin

    their photocatalytic performance for Suzuki coupling reactions. The results indicate that plasmonic Au/Pd bimetallic nanostructures can efficiently harvest light energy for chemical reactions. The intimate integration of plasmonic and catalytic components in one nanostructure enables the light energy absorbed by the plasmonic component to be directly transferred to the catalytic component. Both hot electron transfer and photothermal heating contribute to the plasmon-enhanced chemical reactions. The photothermal effect is a nonlocal heating and the contribution of the hot electron transfer effect is dependent on the environmental temperature. Therefore, the photothermal heating effect can promote the hot electron transfer effect. I believe that my research work will be very helpful for the design and application of plasmonic bimetallic nanostructures. My study on the plasmonic properties of Au/Ag bimetallic nanocrystals has deepened the understanding of the plasmons of Au/Ag nanorods and will be helpful for utilizing the different modes to achieve specific functions. The hydrogen sensing and photocatalysis of Au/Pd bimetallic nanostructures have shown that the integration of functional components with plasmonic nanostructures can achieve unconventional properties, which will flourish the applications of plasmons in life sciences, energy, and environmental areas.

  4. Analysis of surface, subsurface, and bulk hydrogen in ZnO using nuclear reaction analysis

    SciTech Connect

    Traeger, F.; Kauer, M.; Woell, Ch.; Rogalla, D.; Becker, H.-W.

    2011-08-15

    Hydrogen concentrations in ZnO single crystals exposing different surfaces have been determined to be in the range of (0.02-0.04) at.% with an error of {+-}0.01 at.% using nuclear reaction analysis. In the subsurface region, the hydrogen concentration has been determined to be higher by up to a factor of 10. In contrast to the hydrogen in the bulk, part of the subsurface hydrogen is less strongly bound, can be removed by heating to 550 deg. C, and reaccommodated by loading with atomic hydrogen. By exposing the ZnO(1010) surface to water above room temperature and to atomic hydrogen, respectively, hydroxylation with the same coverage of hydrogen is observed.

  5. The mechanism of electron transfer in laccase-catalysed reactions.

    PubMed

    Andréasson, L E; Reinhammar, B

    1979-05-10

    1. The reaction of the electron acceptors in Rhus vernicifera laccase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) have been studied with stopped-flow and rapid-freeze EPR techniques. The studies have been directed mainly towards elucidation of the role of the type 2Cu2+ as a possible pH-sensitve regulator of electron transfer. 2. Anaerobic reduction experiments with Rhus laccase indicate that the type 1 and 2 sites contribute one electron each to the reduction of the two-electron-accepting type 3 site. There is also evidence that the reduction of the type 1 Cu2+ triggers the reduction of the type 2 Cu2+. 3. Only at pH values at which the reduction of the two-electron acceptor is limited by a slow intramolecular reaction can an OH- be displaced from the type 2 Cu2+ by the inhibitor F-. 4. A model describing the role of the electron-accepting sites in catalysis is formulated. PMID:221027

  6. Multinucleon transfer in the 136Xe+208Pb reaction

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Zhang, Fan; Li, Jingjing; Zhu, Long; Tian, Junlong; Wang, Ning; Zhang, Feng-Shou

    2016-01-01

    The dynamic mechanics in the multinucleon transfer reaction 136Xe+208Pb at an incident energy of Ec .m .=450 MeV is investigated by using the improved quantum molecular dynamics model (ImQMD). The lifetime of the neck directly influences the nucleon exchange and energy dissipation between the projectile and the target. The total-kinetic-energy-mass distributions and excitation energy division of primary binary fragments and the mass distributions of primary fragments at different impact parameters are calculated. The thermal equilibrium between two reaction partners has been observed at the lifetime of a neck larger than 480 fm /c . By using the statistical decay code gemini to describe the de-excitation process of the primary fragments, the isotope production cross sections from Pt to At are compared with the prediction by the dinuclear system and GRAZING model. The calculations indicate that the GRAZING model is suitable for estimating the isotope production cross sections only for Δ Z =-1 to +2; the DNS + gemini calculations underestimate the cross sections in the neutron-rich and neutron-deficient regions; and the ImQMD + gemini calculations give reasonable predictions of the isotope production cross sections for Δ Z =-3 to 0.

  7. 40 CFR 721.10325 - Cyclosilazanes, di-Me, Me hydrogen, polymers with di-Me, Me hydrogen silazanes, reaction products...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine. 721..., reaction products with 3-(triethoxysilyl)-1-propanamine. (a) Chemical substance and significant new uses..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine (PMN...

  8. 40 CFR 721.10325 - Cyclosilazanes, di-Me, Me hydrogen, polymers with di-Me, Me hydrogen silazanes, reaction products...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine. 721..., reaction products with 3-(triethoxysilyl)-1-propanamine. (a) Chemical substance and significant new uses..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine (PMN...

  9. 40 CFR 721.10325 - Cyclosilazanes, di-Me, Me hydrogen, polymers with di-Me, Me hydrogen silazanes, reaction products...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine. 721..., reaction products with 3-(triethoxysilyl)-1-propanamine. (a) Chemical substance and significant new uses..., polymers with di-Me, Me hydrogen silazanes, reaction products with 3-(triethoxysilyl)-1-propanamine (PMN...

  10. Electrochemical Impedance Spectroscopy (bio)sensing through hydrogen evolution reaction induced by gold nanoparticles.

    PubMed

    Mayorga-Martinez, Carmen C; Chamorro-Garcia, Alejandro; Merkoçi, Arben

    2015-05-15

    A new gold nanoparticle (AuNP) based detection strategy using Electrochemical Impedance Spectroscopy (EIS) through hydrogen evolution reaction (HER) is proposed. This EIS-HER method is used as an alternative to the conventional EIS based on [Fe(CN)6](3-/4-) or [Ru(NH3)6](3+/2+) indicators. The proposed method is based on the HER induced by AuNPs. EIS measurements for different amounts of AuNP are registered and the charge transfer resistance (Rct) was found to correlate and be useful for their quantification. Moreover the effect of AuNP size on electrical properties of AuNPs for HER using this sensitive technique has been investigated. Different EIS-HER signals generated in the presence of AuNPs of different sizes (2, 5, 10, 15, 20, and 50 nm) are observed, being the corresponding phenomena extendible to other nanoparticles and related catalytic reactions. This EIS-HER sensing technology is applied to a magneto-immunosandwich assay for the detection of a model protein (IgG) achieving improvements of the analytical performance in terms of a wide linear range (2-500 ng mL(-1)) with a good limit of detection (LOD) of 0.31 ng mL(-1) and high sensitivity. Moreover, with this methodology a reduction of one order of magnitude in the LOD for IgG detection, compared with a chroamperometric technique normally used was achieved. PMID:24953452

  11. Transition-metal-catalyzed hydrogen-transfer annulations: access to heterocyclic scaffolds.

    PubMed

    Nandakumar, Avanashiappan; Midya, Siba Prasad; Landge, Vinod Gokulkrishna; Balaraman, Ekambaram

    2015-09-14

    The ability of hydrogen-transfer transition-metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research efforts on the construction of heterocyclic scaffolds. Transition-metal-catalyzed hydrogen-transfer annulations are environmentally benign and highly atom-economical as they release of water and hydrogen as by-product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein.

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

    PubMed

    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 < 1 - 3) and for low (ξ0 ≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually

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

    PubMed

    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 < 1 - 3) and for low (ξ0 ≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually

  14. Zeolite Membrane Reactor for Water Gas Shift Reaction for Hydrogen Production

    SciTech Connect

    Lin, Jerry Y.S.

    2013-01-29

    Gasification of biomass or heavy feedstock to produce hydrogen fuel gas using current technology is costly and energy-intensive. The technology includes water gas shift reaction in two or more reactor stages with inter-cooling to maximize conversion for a given catalyst volume. This project is focused on developing a membrane reactor for efficient conversion of water gas shift reaction to produce a hydrogen stream as a fuel and a carbon dioxide stream suitable for sequestration. The project was focused on synthesizing stable, hydrogen perm-selective MFI zeolite membranes for high temperature hydrogen separation; fabricating tubular MFI zeolite membrane reactor and stable water gas shift catalyst for membrane reactor applications, and identifying experimental conditions for water gas shift reaction in the zeolite membrane reactor that will produce a high purity hydrogen stream. The project has improved understanding of zeolite membrane synthesis, high temperature gas diffusion and separation mechanisms for zeolite membranes, synthesis and properties of sulfur resistant catalysts, fabrication and structure optimization of membrane supports, and fundamentals of coupling reaction with separation in zeolite membrane reactor for water gas shift reaction. Through the fundamental study, the research teams have developed MFI zeolite membranes with good perm-selectivity for hydrogen over carbon dioxide, carbon monoxide and water vapor, and high stability for operation in syngas mixture containing 500 part per million hydrogen sulfide at high temperatures around 500°C. The research teams also developed a sulfur resistant catalyst for water gas shift reaction. Modeling and experimental studies on the zeolite membrane reactor for water gas shift reaction have demonstrated the effective use of the zeolite membrane reactor for production of high purity hydrogen stream.

  15. Transition metal dichalcogenides as a catalyst for hydrogen-evolution reaction

    NASA Astrophysics Data System (ADS)

    Lee, Jun-Ho; Son, Young-Woo; Seok, Jinbong; Yang, Heejun

    Hydrogen evolution using electrochemical reaction of water with specific catalysts has been considered as next-generation energy resources. The best-well known and most productive electrochemical catalyst is platinum. However, there has been a continuous struggle to replace the precious Pt-based catalysts by inexpensive and earth-abundant materials such as transition metal dichalcogenides (TMDs). We investigated catalytic performances of various TMDs for hydrogen-evolution reaction (HER) by using first-principles density functional theory calculation. We calculate Gibbs free energy, most widely used descriptor of catalytic activity, of hydrogen atom on TMDs and analyze an origin of significant performance of HER.

  16. Variable photosynthetic units, energy transfer and light-induced evolution of hydrogen in algae and bacteria.

    NASA Technical Reports Server (NTRS)

    Gaffron, H.

    1971-01-01

    The present state of knowledge regarding the truly photochemical reactions in photosynthesis is considered. Nine-tenths of the available knowledge is of a biochemical nature. Questions regarding the activities of the chlorophyll system are examined. The simplest photochemical response observed in living hydrogen-adapted algal cells is the release of molecular hydrogen, which continues even after all other known natural reactions have been eliminated either by heating or the action of poisons.

  17. Can hydridic-to-protonic hydrogen bonds catalyze hydride transfers in biological systems?

    PubMed

    Marincean, Simona; Jackson, James E

    2010-12-30

    Catalysis of hydride transfer by hydridic-to-protonic hydrogen (HHH) bonding in α-hydroxy carbonyl isomerization reactions was examined computationally in the lithium salts of 7-substituted endo-3-hydroxybicyclo[2.2.1]hept-5-en-2-ones. The barrier for intramolecular hydride transfer in the parent system was calculated to be 17.2 kcal/mol. Traditional proton donors, such as OH and NH(3)(+), stabilized the metal cation-bridged transition state by 1.4 and 3.3 kcal/mol, respectively. Moreover, among the conformers of the OH systems, the one in which the proton donor is able to interact with the migrating hydride (H(m)) has an activation barrier lower by 1.3 and 1.7 kcal/mol than the other possible OH conformers. By contrast, the presence of an electronegative group such as F, which disfavors the migration electronically by opposing development of hydridic charge, destabilizes the hydride migration by 1.5 kcal/mol relative to the epimeric exo system. In both ground and transition states the H(m)···H distance decreased with increasing acidity of the proton donor, reaching a minimum of 1.58 Å at the transition state for NH(3)(+). Both Mulliken and NPA charges show enhancement of negative character of the migrating hydride in the cases in which HHH bonding is possible. PMID:21141894

  18. Proton-hydrogen reaction in an effectively two-body model

    SciTech Connect

    Pupyshev, V. V.

    2013-02-15

    A model of total interaction between a proton incident to a hydrogen atom and the proton that is the nucleus of this atom is proposed. This interaction is assumed to be the sum of the short-range nuclear Reid potential and the long-range Thomas-Fermi potential induced by the Coulomb interaction of the electron with the nucleus of the hydrogen atom. The explicit low-energy asymptotic behavior of the cross section for the proton-hydrogen reaction leading to deuteron production is found. It is shown that this cross section increases in inverse proportion to the collision energy for the proton and hydrogen atom in its zero limit.

  19. Ab Initio Vibrational Levels For HO2 and Vibrational Splittings for Hydrogen Atom Transfer

    NASA Technical Reports Server (NTRS)

    Barclay, V. J.; Dateo, Christopher E.; Hamilton, I. P.; Arnold, James O. (Technical Monitor)

    1994-01-01

    We calculate vibrational levels and wave functions for HO2 using the recently reported ab initio potential energy surface of Walch and Duchovic. There is intramolecular hydrogen atom transfer when the hydrogen atom tunnels through a T-shaped saddle point separating two equivalent equilibrium geometries, and correspondingly, the energy levels are split. We focus on vibrational levels and wave functions with significant splitting. The first three vibrational levels with splitting greater than 2/cm are (15 0), (0 7 1) and (0 8 0) where V(sub 2) is the O-O-H bend quantum number. We discuss the dynamics of hydrogen atom transfer; in particular, the O-O distances at which hydrogen atom transfer is most probable for these vibrational levels. 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.

  20. Bimetallic promotion of cooperative hydrogen transfer and heteroatom removal in coal liquefaction

    SciTech Connect

    Eisch, J.J.

    1991-10-01

    The ultimate objective of this research is to uncover new catalytic processes for the liquefaction of coal and for upgrading coal-derived fuels by removing undesirable organosulfur, organonitrogen and organooxygen constituents. Basic to both the liquefaction of coal and the purification of coal liquids is the transfer of hydrogen from such sources as dihydrogen, metal hydrides or partially reduced aromatic hydrocarbons to the extensive aromatic rings in coal itself or to aromatic sulfides, amines or ethers. Accordingly, this study is exploring how such crucial hydrogen-transfer processes might be catalyzed by soluble, low-valent transition metal complexes and/or Lewis acids under moderate conditions of temperature and pressure. By learning the mechanism whereby H{sub 2}, metal hydrides or partially hydrogenated aromatics do transfer hydrogen to model aromatic compounds, with the aid of homogeneous, bimetallic catalysts, we hope to identify new methods for producing superior fuels from coal.

  1. Rate of reaction between molecular hydrogen and molecular oxygen

    NASA Technical Reports Server (NTRS)

    Brokaw, R. S.

    1973-01-01

    The shock tube data of Jachimowski and Houghton were rigorously analyzed to obtain rate constants for the candidate initiation reactions H2 + O2 yields H + HO2, H2 + O2 yields H2O + O, and H2 + O2 yields OH + OH. Reaction (01) is probably not the initiation process because the activation energy obtained is less than the endothermicity and because the derived rates greatly exceed values inferred in the literature from the reverse of reaction (01). Reactions (02) and (03) remain as possibilities, with reaction (02) slightly favored on the basis of steric and statistical considerations. The solution of the differential equations is presented in detail to show how the kinetics of other ignition systems may be solved.

  2. CHROMATOGRAPHIC SEPARATION AND IDENTIFICATION OF PRODUCTS FROM THE REACTION OF DIMETHYLARSINIC ACID WITH HYDROGEN SULFIDE

    EPA Science Inventory

    The reaction of dimethylarsinic acid (DMAV) with hydrogen sulfide (H2S) is of biological significance and may be implicated in the overall toxicity and carcinogenicity of arsenic. The course of the reaction in aqueous phase was monitored and an initial product, dimethylthioarsin...

  3. Reaction of Hydrogen Sulfide with Oxygen in the Presence ofSulfite

    SciTech Connect

    Weres, Oleh; Tsao, Leon

    1983-01-01

    Commonly, abatement of hydrogen sulfide emissions from a geothermal powerplant requires that hydrogen sulfide dissolved in the cooling water be eliminated by chemical reaction. Oxidation by atmospheric oxygen is the preferred reaction, but requires a suitable catalyst. Nickel is the most potent and thereby cheapest catalyst for this purpose. One Mg/L nickel in the cooling water would allow 99% removal of hydrogen sulfide to be attained. A major drawback of catalytic air oxidation is that colloidal sulfur is a major reaction product; this causes rapid sludge accumulation and deposition of sulfur scale. The authors studied the kinetics and product distribution of the reaction of hydrogen sulfide with oxygen, catalyzed by nickel. Adding sodium sulfite to the solution completely suppresses formation of colloidal sulfur by converting it to thiosulfate. The oxidation reaction is an autocatalytic, free radical chain reaction. A rate expression for this reaction and a detailed reaction mechanism were developed. Nickel catalyzes the chain initiation step, and polysulfidoradical ions propagate the chains. Several complexes of iron and cobalt were also studied. Iron citrate and iron N-hydroxyEDT are the most effective iron based catalysts. Uncomplexed cobalt is as effective as nickel, but forms a precipitate of cobalt oxysulfide and is too expensive for practical use.

  4. Reaction of hydrogen sulfide with oxygen in the presence of sulfite

    SciTech Connect

    Weres, O.; Tsao, L.

    1983-01-14

    Commonly, abatement of hydrogen sulfide emission from a geothermal powerplant requires that hydrogen sulfide dissolved in the cooling water be eliminated by chemical reaction. Oxidation by atmospheric oxygen is the preferred reaction, but requires a suitable catalyst. Nickel is the most potent and thereby cheapest catalyst for this purpose. One mg/L nickel in the cooling water would allow 99% removal of hydrogen sulfide to be attained. A major drawback of catalytic air oxidation is that colloidal sulfur is a major reaction product; this causes rapid sludge accumulation and deposition of sulfur scale. We studied the kinetics and product distribution of the reaction of hydrogen sulfide with oxygen, catalyzed by nickel. Adding sodium sulfite to the solution completely suppresses formation of colloidal sulfur by converting it to thiosulfate. The oxidation reaction is an autocatalytic, free radical chain reaction. A rate expression for this reaction and a detailed reaction mechanism were developed. Nickel catalyzes the chain initiation step, and polysulfidoradical ions propagate the chains. Several complexes of iron and cobalt were also studied. Iron citrate and iron N-hydroxyEDTA are the most effective iron based catalysts. Uncomplexed cobalt is as effective as nickel, but forms a precipitate of cobalt oxysulfide and is too expensive for practical use. 33 figures, 9 tables.

  5. Hydrogenation Reactions during Pyrolysis-Gas Chromatography/Mass Spectrometry Analysis of Polymer Samples Using Hydrogen Carrier Gas.

    PubMed

    Watanabe, Atsushi; Watanabe, Chuichi; Freeman, Robert R; Teramae, Norio; Ohtani, Hajime

    2016-05-17

    Pyrolysis-gas chromatography/mass spectrometry of polymer samples is studied focusing on the effect of hydrogen (H2) carrier gas on chromatographic and spectral data. The pyrograms and the related mass spectra of high density polyethylene (HDPE), low density polyethylene, and polystyrene (PS) serve to illustrate the differences between the species formed in H2 and the helium environment. Differences in the pyrograms and the spectra are generally thought to be a result of the hydrogenation reaction of the pyrolyzates. From the peak intensity changes in the pyrograms of HDPE and PS, hydrogenation of unsaturated pyrolyzates is concluded to occur when the pyrolysis is done in H2. Moreover, additional hydrogenation of the pyrolyzates occurs in the electron ionization source of a MS detector when H2 is used as a carrier gas. Finally, the applicability of mass spectral libraries to characterize pyrograms obtained in H2 is illustrated using 24 polymers. The effect of the hydrogenation reaction on the library search results is found to be negligible for most polymer samples with polar and nonpolar monomer units. PMID:27125864

  6. Hydrogen-bonded proton transfer in the protonated guanine-cytosine (GC+H)+ base pair.

    PubMed

    Lin, Yuexia; Wang, Hongyan; Gao, Simin; Schaefer, Henry F

    2011-10-13

    The single proton transfer at the different sites of the Watson-Crick (WC) guanine-cytosine (GC) DNA base pair are studied here using density functional methods. The conventional protonated structures, transition state (TS) and proton-transferred product (PT) structures of every relevant species are optimized. Each transition state and proton-transferred product structure has been compared with the corresponding conventional protonated structure to demonstrate the process of proton transfer and the change of geometrical structures. The relative energies of the protonated tautomers and the proton-transfer energy profiles in gas and solvent are analyzed. The proton-transferred product structure G(+H(+))-H(+)C(N3)(-H(+))(PT) has the lowest relative energy for which only two hydrogen bonds exist. Almost all 14 isomers of the protonated GC base pair involve hydrogen-bonded proton transfer following the three pathways, with the exception of structure G-H(+)C(O2). When the positive charge is primarily "located" on the guanine moiety (H(+)G-C, G-H(+)C(C4), and G-H(+)C(C6)), the H(1) proton transfers from the N(1) site of guanine to the N(3) site of cytosine. The structures G-H(+)C(C5) and G-H(+)C(C4) involve H(4a) proton transfer from the N(4) of cytosine to the O(6) site of guanine. H(2a) proton transfer from the N(2) site of guanine to the O(2) site of cytosine is found only for the structure G-H(+)C(C4). The structures to which a proton is added on the six-centered sites adjoining the hydrogen bonds are more prone to proton transfer in the gas phase, whereas a proton added on the minor groove and the sites adjoining the hydrogen bonds is favorable to the proton transfer in energy in the aqueous phase.

  7. In-situ diagnostic tools for hydrogen transfer leak characterization in PEM fuel cell stacks part II: Operational applications

    NASA Astrophysics Data System (ADS)

    Niroumand, Amir M.; Homayouni, Hooman; DeVaal, Jake; Golnaraghi, Farid; Kjeang, Erik

    2016-08-01

    This paper describes a diagnostic tool for in-situ characterization of the rate and distribution of hydrogen transfer leaks in Polymer Electrolyte Membrane (PEM) fuel cell stacks. The method is based on reducing the air flow rate from a high to low value at a fixed current, while maintaining an anode overpressure. At high air flow rates, the reduction in air flow results in lower oxygen concentration in the cathode and therefore reduction in cell voltages. Once the air flow rate in each cell reaches a low value at which the cell oxygen-starves, the voltage of the corresponding cell drops to zero. However, oxygen starvation results from two processes: 1) the electrochemical oxygen reduction reaction which produces current; and 2) the chemical reaction between oxygen and the crossed over hydrogen. In this work, a diagnostic technique has been developed that accounts for the effect of the electrochemical reaction on cell voltage to identify the hydrogen leak rate and number of leaky cells in a fuel cell stack. This technique is suitable for leak characterization during fuel cell operation, as it only requires stack air flow and voltage measurements, which are readily available in an operational fuel cell system.

  8. Structure and Reactions of Carbon and Hydrogen on Ru(0001): A Scanning Tunneling Microscopy Study

    SciTech Connect

    Shimizu, Tomoko K.; Mugarza, Aitor; Cerda, Jorge; Salmeron, Miquel

    2008-09-09

    The interaction between carbon and hydrogen atoms on a Ru(0001) surface was studied using scanning tunneling microscopy (STM), Density Functional Theory (DFT) and STM image calculations. Formation of CH species by reaction between adsorbed H and C was observed to occur readily at 100 K. When the coverage of H increased new complexes of the form CH+nH (n = 1, 2 and 3) were observed. These complexes, never observed before, might be precursors for further hydrogenation reactions. DFT analysis reveals that a considerable energy barrier exists for the CH+H {yields} CH{sub 2} reaction.

  9. Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

    PubMed

    Barman, Prasenjit; Upadhyay, Pranav; Faponle, Abayomi S; Kumar, Jitendra; Nag, Sayanta Sekhar; Kumar, Devesh; Sastri, Chivukula V; de Visser, Sam P

    2016-09-01

    Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.

  10. Rate constant for reaction of atomic hydrogen with germane

    NASA Technical Reports Server (NTRS)

    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.

  11. Distribution of hydrogen peroxide-dependent reaction in a gelatin sample irradiated by carbon ion beam.

    PubMed

    Matsumoto, Ken-ichiro; Aoki, Ichio; Nakanishi, Ikuo; Matsumoto, Atsuko; Nyui, Minako; Endo, Kazutoyo; Anzai, Kazunori

    2010-01-01

    We investigated the amount and distribution of hydrogen peroxide (H(2)O(2)) generated in a solid gelatin sample irradiated by heavy ion (carbon) beam. We irradiated the gelatin sample, which contained a nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, TEMPOL), with a 290-MeV/nucleon carbon beam (~128 Gy). To verify the distribution of H(2)O(2) generation in the irradiated sample, we employed both electron paramagnetic resonance (EPR) spectroscopic and magnetic resonance (MR) imaging methods based on H(2)O(2)-dependent paramagnetic loss of TEMPOL. We obtained a distribution profile of the H(2)O(2)-dependent reaction in the gelatin sample when we irradiated gelatin samples with carbon beams with several different linear energy transfer (LET) values. Because the profiles of oxygen consumption in the gelatin sample measured by L-band EPR oxymetry and of the H(2)O(2)-dependent reaction have almost the same shape, the profile of the H(2)O(2)-dependent reaction can be used as an estimation of the profile of the generation of H(2)O(2). The H(2)O(2) profile in one intact gelatin sample scanned by 7-tesla MR imaging showed a similar shape as a result of the EPR experiment. We obtained several hundreds of micromolars of H(2)O(2) generated in a gelatin sample irradiated by carbon beam when 200 Gy was given at the surface of the sample. H(2)O(2) distribution was almost flat, with only a slight peak just before the end of the beam.

  12. The reaction of a titanium alloy with hydrogen gas at low temperatures.

    NASA Technical Reports Server (NTRS)

    Williams, D. N.; Wood, R. A.

    1973-01-01

    An investigation of the effect of temperature on the surface hydriding reaction of Ti-5Al-2.5Sn alloy exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultra-pure hydrogen atmosphere. Reaction times up to 1458 hr were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding was observed after exposure for 162 hr. The amount of hydriding was observed to decrease with decreasing temperature at 75, 36, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hr at -110 or -160 F.

  13. Hydrogen production from carbonaceous material

    DOEpatents

    Lackner, Klaus S.; Ziock, Hans J.; Harrison, Douglas P.

    2004-09-14

    Hydrogen is produced from solid or liquid carbon-containing fuels in a two-step process. The fuel is gasified with hydrogen in a hydrogenation reaction to produce a methane-rich gaseous reaction product, which is then reacted with water and calcium oxide in a hydrogen production and carbonation reaction to produce hydrogen and calcium carbonate. The calcium carbonate may be continuously removed from the hydrogen production and carbonation reaction zone and calcined to regenerate calcium oxide, which may be reintroduced into the hydrogen production and carbonation reaction zone. Hydrogen produced in the hydrogen production and carbonation reaction is more than sufficient both to provide the energy necessary for the calcination reaction and also to sustain the hydrogenation of the coal in the gasification reaction. The excess hydrogen is available for energy production or other purposes. Substantially all of the carbon introduced as fuel ultimately emerges from the invention process in a stream of substantially pure carbon dioxide. The water necessary for the hydrogen production and carbonation reaction may be introduced into both the gasification and hydrogen production and carbonation reactions, and allocated so as transfer the exothermic heat of reaction of the gasification reaction to the endothermic hydrogen production and carbonation reaction.

  14. Effect of odd hydrogen on ozone depletion by chlorine reactions

    NASA Technical Reports Server (NTRS)

    Donahue, T. M.; Cicerone, R. J.; Liu, S. C.; Chameides, W. L.

    1976-01-01

    The present paper discusses how the shape of the ozone layer changes under the influence of injected ClX for several choices of two key HOx reaction rates. The two HOx reactions are: OH + HO2 yields H2O + O2 and O + HO2 yields OH + O2. Results of calculations are presented which show that the two reaction rates determine the stratospheric concentrations of OH and HO2, and that these concentrations regulate the amount by which the stratospheric ozone column can be reduced due to injections of odd chlorine. It is concluded that the amount of ozone reduction by a given mixing ratio of ClX will remain very uncertain until the significance of several possible feedback effects involving HOx in a chlorine-polluted atmosphere are determined and measurements of the reaction rates and HOx concentrations are made at the relevant temperatures.

  15. Dark reaction of oxidation of iodine by hydrogen peroxide

    SciTech Connect

    Moskalev, P.N.; Sedov, V.P.; Isupov, V.K.

    1989-01-01

    The oxidation of iodine in darkness was studied in the system H/sub 2/O/sub 2/-I/sub 2/-HNO/sub 3/ by a potentiometric method using an ion-selective electrode and a spectrophotometric method. The concentration limits of the reaction was established. The reaction rate is satisfactorily described by the equation of a first-order reaction. It was established experimentally that the maximum of the reaction rate constant lies in the region of 0.2-0.6 M HNO/sub 3/ and 0.06 M H/sub 2/O/sub 2/ and reaches a value of 0.1 min/sup /minus/1/.

  16. Hydrogen-generating reactions in LWR severe accidents

    SciTech Connect

    Baker, L. Jr.

    1983-01-01

    The available data on the reactions of Zircaloys, stainless steels, uranium metal and uranium dioxide with steam at temperatures above about 1000/sup 0/C and the reactions of core melts during concrete penetration have been reviewed and assessed for the IDCOR Program. The uranium metal is included because small quantities can be formed from the high temperature interaction between Zircaloy and uranium dioxide and because the uranium data adds insight into the nature of the reactions of core materials with steam. Thermodynamic analyses and comparisons of reaction rate data have been made. One of the purposes of this assessment was to develop fully the information generated in the early studies of oxidation processes, particularly the extensive program carried out at ANL from about 1960 to 1968.

  17. Investigating the mechanism of the selective hydrogenation reaction of cinnamaldehyde catalyzed by Ptn clusters.

    PubMed

    Li, Laicai; Wang, Wei; Wang, Xiaolan; Zhang, Lin

    2016-08-01

    Cinnamaldehyde (CAL) belongs to the group of aromatic α,β-unsaturated aldehydes; the selective hydrogenation of CAL plays an important role in the fine chemical and pharmaceutical industries. Using Ptn clusters as catalytic models, we studied the selective hydrogenation reaction mechanism for CAL catalyzed by Ptn (n = 6, 10, 14, 18) clusters by means of B3LYP in density functional theory at the 6-31+ G(d) level (the LanL2DZ extra basis set was used for the Pt atom). The rationality of the transition state was proved by vibration frequency analysis and intrinsic reaction coordinate computation. Moreover, atoms in molecules theory and nature bond orbital theory were applied to discuss the interaction among orbitals and the bonding characteristics. The results indicate that three kinds of products, namely 3-phenylpropyl aldehyde, 3-phenyl allyl alcohol and cinnamyl alcohol, are produced in the selective hydrogenation reaction catalyzed by Ptn clusters; each pathway possesses two reaction channels. Ptn clusters are more likely to catalyze the activation and hydrogenation of the C = O bond in CAL molecules, eventually producing cinnamic alcohol, which proves that Ptn clusters have a strong reaction selectivity to catalyze CAL. The reaction selectivity of the catalyzer cluster is closely related to the size of the Ptn cluster, with Pt14 clusters having the greatest reaction selectivity. Graphical Abstract The reaction mechanism for the selective hydrogenation reaction ofcinnamaldehyde catalyzed by Ptn clusters was studied by densityfunctional theory. The reactionselectivity of cluster catalyzer was concluded to be closely related to the size of Ptn clusters, with Pt14 clusters having the greatest reaction selectivity. PMID:27444877

  18. Investigating the mechanism of the selective hydrogenation reaction of cinnamaldehyde catalyzed by Ptn clusters.

    PubMed

    Li, Laicai; Wang, Wei; Wang, Xiaolan; Zhang, Lin

    2016-08-01

    Cinnamaldehyde (CAL) belongs to the group of aromatic α,β-unsaturated aldehydes; the selective hydrogenation of CAL plays an important role in the fine chemical and pharmaceutical industries. Using Ptn clusters as catalytic models, we studied the selective hydrogenation reaction mechanism for CAL catalyzed by Ptn (n = 6, 10, 14, 18) clusters by means of B3LYP in density functional theory at the 6-31+ G(d) level (the LanL2DZ extra basis set was used for the Pt atom). The rationality of the transition state was proved by vibration frequency analysis and intrinsic reaction coordinate computation. Moreover, atoms in molecules theory and nature bond orbital theory were applied to discuss the interaction among orbitals and the bonding characteristics. The results indicate that three kinds of products, namely 3-phenylpropyl aldehyde, 3-phenyl allyl alcohol and cinnamyl alcohol, are produced in the selective hydrogenation reaction catalyzed by Ptn clusters; each pathway possesses two reaction channels. Ptn clusters are more likely to catalyze the activation and hydrogenation of the C = O bond in CAL molecules, eventually producing cinnamic alcohol, which proves that Ptn clusters have a strong reaction selectivity to catalyze CAL. The reaction selectivity of the catalyzer cluster is closely related to the size of the Ptn cluster, with Pt14 clusters having the greatest reaction selectivity. Graphical Abstract The reaction mechanism for the selective hydrogenation reaction ofcinnamaldehyde catalyzed by Ptn clusters was studied by densityfunctional theory. The reactionselectivity of cluster catalyzer was concluded to be closely related to the size of Ptn clusters, with Pt14 clusters having the greatest reaction selectivity.

  19. Oxidant-free dehydrogenative coupling reactions via hydrogen evolution.

    PubMed

    He, Ke-Han; Li, Yang

    2014-10-01

    Oxidant-free dehydrogenative coupling reactions: Recently, coupling reactions have followed a novel strategy for the construction of C==C, C==N, C==P, and S==S bonds by dehydrogenation without using any extra oxidant, via H2 evolution. These breakthroughs inspire a new direction in the construction of chemical bonds, towards more sustainable, highly atom-economical, and environmentally benign synthetic methods. PMID:25139249

  20. Ions interacting with planar aromatic molecules: Modeling electron transfer reactions

    SciTech Connect

    Forsberg, B. O.; Alexander, J. D.; Chen, T.; Pettersson, A. T.; Gatchell, M.; Cederquist, H.; Zettergren, H.

    2013-02-07

    We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C{sub 14}H{sub 10}, coronene C{sub 24}H{sub 12}, or circumcoronene C{sub 54}H{sub 18}. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

  1. Next-generation transfer reaction studies with JENSA

    NASA Astrophysics Data System (ADS)

    Chipps, K. A.

    2015-04-01

    Next generation radioactive ion beam facilities are being planned and built across the globe, and with them an incredible new array of exotic isotopes will be available for study. To keep pace with the state of nuclear physics research, both new detector systems and new target systems are needed. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target is one of these new target systems, designed to provide a target of light gas that is localized, dense, and pure. The JENSA gas jet target was originally constructed at Oak Ridge National Laboratory for testing and characterization, and has now moved to the ReA3 reaccelerated beam hall at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University for use with radioactive beams. The availability of a pure, localized target of light gases will enable exceptional scattering and transfer reaction studies with these exotic beams. Some examples will be given, and future plans will be discussed. This work is supported by the US DOE Office of Science (Office of Nuclear Physics) and the NSF.

  2. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

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

    PubMed

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

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

  4. Water formation at low temperatures by surface O2 hydrogenation II: The reaction network.

    PubMed

    Cuppen, H M; Ioppolo, S; Romanzin, C; Linnartz, H

    2010-10-14

    Water is abundantly present in the Universe. It is the main component of interstellar ice mantles and a key ingredient for life. Water in space is mainly formed through surface reactions. Three formation routes have been proposed in the past: hydrogenation of surface O, O(2), and O(3). In a previous paper [Ioppolo et al., Astrophys. J., 2008, 686, 1474] we discussed an unexpected non-standard zeroth-order H(2)O(2) production behaviour in O(2) hydrogenation experiments, which suggests that the proposed reaction network is not complete, and that the reaction channels are probably more interconnected than previously thought. In this paper we aim to derive the full reaction scheme for O(2) surface hydrogenation and to constrain the rates of the individual reactions. This is achieved through simultaneous H-atom and O(2) deposition under ultra-high vacuum conditions for astronomically relevant temperatures. Different H/O(2) ratios are used to trace different stages in the hydrogenation network. The chemical changes in the forming ice are followed by means of reflection absorption infrared spectroscopy (RAIRS). New reaction paths are revealed as compared to previous experiments. Several reaction steps prove to be much more efficient (H + O(2)) or less efficient (H + OH and H(2) + OH) than originally thought. These are the main conclusions of this work and the extended network concluded here will have profound implications for models that describe the formation of water in space.

  5. Dynamics of the reaction glucose-catalase-glucose oxidase-hydrogen peroxide

    NASA Astrophysics Data System (ADS)

    Číp, M.; Schreiberová, L.; Schreiber, I.

    2011-12-01

    Glucose-catalase-glucose oxidase-hydrogen peroxide reaction is one of the few known enzymatic systems studied in vitro in the field of nonlinear chemical dynamics. This reaction belongs to the family of oscillatory enzymatic reactions, which form a natural basis of oscillations in biological systems. A parametric study of dependence on mixing, temperature and initial concentrations of components in a batch stirred reactor was carried out. A newly proposed mathematical model of the reaction conforms to the obtained experimental data. Results of our experiments and simulations hint at further directions of research of non-linear dynamics in this reaction.

  6. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    SciTech Connect

    Bartram, Michael E.; Creighton, J. Randall

    1999-05-26

    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

  7. Photoinduced homogeneous proton-coupled electron transfer: model study of isotope effects on reaction dynamics.

    PubMed

    Venkataraman, Charulatha; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2009-10-21

    A model Hamiltonian for photoinduced homogeneous proton-coupled electron transfer reactions is presented, and the equations of motion for the reduced density matrix elements in an electron-proton vibronic basis are derived. This formalism enables a detailed analysis of the proton vibrational dynamics, as well as the dynamics of the electronic state populations, following photoexcitation. The application of this theory to model systems provides insight into the fundamental physical principles underlying these types of processes. The initial nonequilibrium state is prepared by vertical photoexcitation from the ground electronic state to a coherent vibrational mixture in the donor electronic state. This nonstationary state relaxes to the equilibrium distributions in the donor and acceptor electronic states via dynamical processes arising from nonadiabatic transitions between the donor and acceptor vibronic states concurrent with energy dissipation to the bath. During the initial stage, when the proton vibrational population in the donor state is distributed among higher vibrational states and the donor proton wavepacket is oscillating with large amplitude, the electronic state population dynamics exhibits virtually no hydrogen/deuterium isotope effect. After vibrational relaxation, when the proton vibrational population in the donor state becomes concentrated in the lower vibrational states and the donor proton wavepacket becomes more localized near the minimum of the donor potential, a significant hydrogen/deuterium isotope effect on the electronic state population dynamics is exhibited. These model system calculations lead to experimentally testable predictions about the qualitative behavior of these isotope effects. PMID:20568867

  8. A molecular mechanism of the energetic coupling of a sequence of electron transfer reactions to endergonic reactions.

    PubMed Central

    Cartling, B; Ehrenberg, A

    1978-01-01

    A molecular mechanism of the energetic coupling of a sequence of electron transfer reactions to endergonic reactions is proposed and discussed from a physical point of view. The scheme represents a synthesis of concepts of electron transfer by tunneling and the conformational and chemiosmotic aspects of energy coupling processes. Its relation to existing experimental information and theoretical models is discussed, and further experimental tests are suggested. PMID:698347

  9. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion.

    PubMed

    Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  10. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander; Hammes-Schiffer, Sharon

    2015-11-17

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approach in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy

  11. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  12. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion.

    PubMed

    Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  13. Kinetics of the reaction of nitric oxide with hydrogen

    NASA Technical Reports Server (NTRS)

    Flower, W. L.; Hanson, R. K.; Kruger, C. H.

    1974-01-01

    Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.

  14. Modeling the reaction kinetics of a hydrogen generator onboard a fuel cell -- Electric hybrid motorcycle

    NASA Astrophysics Data System (ADS)

    Ganesh, Karthik

    Owing to the perceived decline of the fossil fuel reserves in the world and environmental issues like pollution, conventional fuels may be replaced by cleaner alternative fuels. The potential of hydrogen as a fuel in vehicular applications is being explored. Hydrogen as an energy carrier potentially finds applications in internal combustion engines and fuel cells because it is considered a clean fuel and has high specific energy. However, at 6 to 8 per kilogram, not only is hydrogen produced from conventional methods like steam reforming expensive, but also there are storage and handling issues, safety concerns and lack of hydrogen refilling stations across the country. The purpose of this research is to suggest a cheap and viable system that generates hydrogen on demand through a chemical reaction between an aluminum-water slurry and an aqueous sodium hydroxide solution to power a 2 kW fuel cell on a fuel cell hybrid motorcycle. This reaction is essentially an aluminum-water reaction where sodium hydroxide acts as a reaction promoter or catalyst. The Horizon 2000 fuel cell used for this purpose has a maximum hydrogen intake rate of 28 lpm. The study focuses on studying the exothermic reaction between the reactants and proposes a rate law that best describes the rate of generation of hydrogen in connection to the surface area of aluminum available for the certain reaction and the concentration of the sodium hydroxide solution. Further, the proposed rate law is used in the simulation model of the chemical reactor onboard the hybrid motorcycle to determine the hydrogen flow rate to the fuel cell with time. Based on the simulated rate of production of hydrogen from the chemical system, its feasibility of use on different drive cycles is analyzed. The rate of production of hydrogen with a higher concentration of sodium hydroxide and smaller aluminum powder size was found to enable the installation of the chemical reactor on urban cycles with frequent stops and starts

  15. Ph(i-PrO)SiH2: An Exceptional Reductant for Metal-Catalyzed Hydrogen Atom Transfers.

    PubMed

    Obradors, Carla; Martinez, Ruben M; Shenvi, Ryan A

    2016-04-13

    We report the discovery of an outstanding reductant for metal-catalyzed radical hydrofunctionalization reactions. Observations of unexpected silane solvolysis distributions in the HAT-initiated hydrogenation of alkenes reveal that phenylsilane is not the kinetically preferred reductant in many of these transformations. Instead, isopropoxy(phenyl)silane forms under the reaction conditions, suggesting that alcohols function as important silane ligands to promote the formation of metal hydrides. Study of its reactivity showed that isopropoxy(phenyl)silane is an exceptionally efficient stoichiometric reductant, and it is now possible to significantly decrease catalyst loadings, lower reaction temperatures, broaden functional group tolerance, and use diverse, aprotic solvents in iron- and manganese-catalyzed hydrofunctionalizations. As representative examples, we have improved the yields and rates of alkene reduction, hydration, hydroamination, and conjugate addition. Discovery of this broadly applicable, chemoselective, and solvent-versatile reagent should allow an easier interface with existing radical reactions. Finally, isotope-labeling experiments rule out the alternative hypothesis of hydrogen atom transfer from a redox-active β-diketonate ligand in the HAT step. Instead, initial HAT from a metal hydride to directly generate a carbon-centered radical appears to be the most reasonable hypothesis. PMID:26984323

  16. Hot hydrogen atom reactions moderated by H2 and He

    NASA Technical Reports Server (NTRS)

    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.

  17. Gas-Phase Reaction Pathways and Rate Coefficients for the Dichlorosilane-Hydrogen and Trichlorosilane-Hydrogen Systems

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Walch, Stephen P.

    2002-01-01

    As part of NASA Ames Research Center's Integrated Process Team on Device/Process Modeling and Nanotechnology our goal is to create/contribute to a gas-phase chemical database for use in modeling microelectronics devices. In particular, we use ab initio methods to determine chemical reaction pathways and to evaluate reaction rate coefficients. Our initial studies concern reactions involved in the dichlorosilane-hydrogen (SiCl2H2--H2) and trichlorosilane-hydrogen (SiCl2H-H2) systems. Reactant, saddle point (transition state), and product geometries and their vibrational harmonic frequencies are determined using the complete-active-space self-consistent-field (CASSCF) electronic structure method with the correlation consistent polarized valence double-zeta basis set (cc-pVDZ). Reaction pathways are constructed by following the imaginary frequency mode of the saddle point to both the reactant and product. Accurate energetics are determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations (CCSD(T)) extrapolated to the complete basis set limit. Using the data from the electronic structure calculations, reaction rate coefficients are obtained using conventional and variational transition state and RRKM theories.

  18. Theoretical Investigation of Intramolecular Hydrogen Shift Reactions in 3-Methyltetrahydrofuran (3-MTHF) Oxidation.

    PubMed

    Parab, Prajakta R; Sakade, Naoki; Sakai, Yasuyuki; Fernandes, Ravi; Heufer, K Alexander

    2015-11-01

    3-Methyltetrahydrofuran (3-MTHF) is proposed to be a promising fuel component among the cyclic oxygenated species. To have detailed insight of its combustion kinetics, intramolecular hydrogen shift reactions for the ROO to QOOH reaction class are studied for eight ROO isomers of 3-MTHF. Rate constants of all possible reaction paths that involve formation of cyclic transition states are computed by employing the CBS-QB3 composite method. A Pitzer-Gwinn-like approximation has been applied for the internal rotations in reactants, products, and transition states for the accurate treatment of hindered rotors. Calculated relative barrier heights highlight that the most favorable reaction channel proceeds via a six membered transition state, which is consistent with the computed rate constants. Comparing total rate constants in ROO isomers of 3-MTHF with the corresponding isomers of methylcyclopentane depicts faster kinetics in 3-MTHF than methylcyclopentane reflecting the effect of ring oxygen on the intramolecular hydrogen shift reactions. PMID:26444499

  19. A Fluorescent Molecular Probe for the Detection of Hydrogen Based on Oxidative Addition Reactions with Crabtree-Type Hydrogenation Catalysts.

    PubMed

    Kos, Pavlo; Plenio, Herbert

    2015-11-01

    A Crabtree-type Ir(I) complex tagged with a fluorescent dye (bodipy) was synthesized. The oxidative addition of H2 converts the weakly fluorescent Ir(I) complex (Φ=0.038) into a highly fluorescent Ir(III) species (Φ=0.51). This fluorogenic reaction can be utilized for the detection of H2 and to probe the oxidative addition step in the catalytic hydrogenation of olefins.

  20. Improved performance in coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Final report, September 26, 1989--March 31, 1993

    SciTech Connect

    Curtis, C.W.

    1993-12-31

    The key results obtained from this research project are given: (1) Hydrogen transfer from naphthenes to aromatics, coal and resid occurred at coprocessing temperatures and in a N{sub 2} atmosphere; (2) Hydrogen donors ranked in reactivity as cyclic olefins (nonaromatic hydroaromatic compounds) > hydroaromatic compounds > naphthenes. This ranking held regardless of the type of atmosphere, hydrogen or nitrogen, used; (3) Resids reduced by the Birch method transferred substantially more hydrogen to the aromatic acceptor than did the parent resids under coprocessing conditions; (4) Hydropretreatment of resids resulted in enhanced coal conversion compared to the parent resid; (5) Addition of hydrogen donors such as cyclic olefins or hydroaromatic donors increased the amount of coal conversion during coprocessing. Cyclic olefins and the active hydroaromatic donor, dihydroanthracene, showed the highest level of hydrogen donability. Tetralin and octahydroanthracene showed low reactivity; (6) Reduced resids were more effective in coprocessing than the parent resids, in terms of enhanced coal conversion; (7) Thermal and catalytic reactivity of cyclic olefins under nitrogen and hydrogen atmospheres was much higher than conventional hydroaromatic donors when no aromatic acceptor was present; (8) Reactivity of hydrogen donors was dependent upon the reactivity of the acceptor as well as that of the donors; (9) Three-ring hydrogen donors, dihydroanthracene and hexahydroanthracene, were most effective for transferring hydrogen to the Argonne coals while octahydroanthracene was the least reactive; (10) The kinetics data obtained for thermal and catalytic reactions involving cyclic olefins and hydroaromatic donors were adequately modeled by pseudo-first order kinetics; and (11) {Delta}G values calculated for cyclic olefins and hydroaromatic donors based on kinetics data adequately represented the reactivity observed experimentally.

  1. Stability of noble metal catalysts for the hydrogen-oxygen reaction.

    NASA Technical Reports Server (NTRS)

    Armstrong, W. E.; Jennings, T. J.; Voge, H. H.

    1972-01-01

    Stability of various supported noble metal catalysts for initiation of the hydrogen-oxygen reaction was tested by means of steam-hydrogen treatment at 1000-1200 C followed by a simple activity test. Many catalysts were stable to 1100 C, but all lost some activity at 1200 C. The most active with very good stability was an iridium/alumina catalyst of high iridium content.

  2. Enhancing alkaline hydrogen evolution reaction activity through Ni-Mn3O4 nanocomposites.

    PubMed

    Li, Xu; Liu, Peng Fei; Zhang, Le; Zu, Meng Yang; Yang, Yun Xia; Yang, Hua Gui

    2016-08-18

    Developing efficient, stable and cost-effective electrocatalysts towards hydrogen production in alkaline environments is vital to improve energy efficiency for water splitting. In this work, we prepared Ni-Mn3O4 nanocomposites on Ni foam which exhibit an excellent hydrogen evolution reaction catalytic activity with a current density (j) of 10 mA cm(-2) at an overpotential (η) of 91 mV and show good stability in an alkaline medium. PMID:27500290

  3. Bioorthogonal tetrazine-mediated transfer reactions facilitate reaction turnover in nucleic acid-templated detection of microRNA.

    PubMed

    Wu, Haoxing; Cisneros, Brandon T; Cole, Christian M; Devaraj, Neal K

    2014-12-31

    Tetrazine ligations have proven to be a powerful bioorthogonal technique for the detection of many labeled biomolecules, but the ligating nature of these reactions can limit reaction turnover in templated chemistry. We have developed a transfer reaction between 7-azabenzonorbornadiene derivatives and fluorogenic tetrazines that facilitates turnover amplification of the fluorogenic response in nucleic acid-templated reactions. Fluorogenic tetrazine-mediated transfer (TMT) reaction probes can be used to detect DNA and microRNA (miRNA) templates to 0.5 and 5 pM concentrations, respectively. The endogenous oncogenic miRNA target mir-21 could be detected in crude cell lysates and detected by imaging in live cells. Remarkably, the technique is also able to differentiate between miRNA templates bearing a single mismatch with high signal to background. We imagine that TMT reactions could find wide application for amplified fluorescent detection of clinically relevant nucleic acid templates.

  4. Ab initio study of the kinetics of hydrogen abstraction reactions on toluene and tetralin

    SciTech Connect

    Beste, Ariana; Britt, Phillip F; Buchanan III, A C; Harrison, Robert J; Hathorn, Bryan C

    2008-01-01

    Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the reaction barriers and rate constants for the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are calculated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. Thermolysis of PPE occurs by a free radical chain mechanism in which the product selectivity arises from competitive hydrogen abstraction at the benzylic and nonbenzylic methylen sites by chain carrying benzyl and phenoxyl radicals. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE through comparison of the rate constants and the reaction enthalpies with reliable experimental values. In this study, we used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment. Absolute and relative rate constants were calculated using transition state theory. We found that the relative rate constant using the B3LYP functional agrees within a factor of 2.0 with experiment at the experimental temperature of 333 K, indicating that the B3LYP functional will be successful in predicting relative rate constants for hydrogen abstraction reactions participating in the pyrolysis of PPE.

  5. UV-light-induced hydrogen transfer in guanosine-guanosine aggregates.

    PubMed

    Hunger, Katharina; Buschhaus, Laura; Biemann, Lars; Braun, Michaela; Kovalenko, Sergey; Improta, Roberto; Kleinermanns, Karl

    2013-04-22

    Aggregates of a lipophilic guanine (G) derivative have been studied in n-hexane by femtosecond-to-microsecond UV-visible broadband transient absorption, stationary infrared and UV-visible spectroscopy and by quantum chemical calculations. We report the first time-resolved spectroscopic detection of hydrogen transfer in GG aggregates, which leads to (G-H)(·) radicals by means of G(+)G(-) charge transfer followed by proton transfer. These radicals show a characteristic electronic spectrum in the range 300-550 nm. The calculated superimposed spectrum of the species that result from NH⋅⋅⋅N proton transfer agrees best with the experimental spectrum.

  6. Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics.

    PubMed

    Daschakraborty, Snehasis; Kiefer, Philip M; Miller, Yifat; Motro, Yair; Pines, Dina; Pines, Ehud; Hynes, James T

    2016-03-10

    Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car-Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid-base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen's charge from approximately midway between that of a hydrogen atom and that of a proton. PMID:26879554

  7. Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics.

    PubMed

    Daschakraborty, Snehasis; Kiefer, Philip M; Miller, Yifat; Motro, Yair; Pines, Dina; Pines, Ehud; Hynes, James T

    2016-03-10

    Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car-Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid-base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen's charge from approximately midway between that of a hydrogen atom and that of a proton.

  8. Hydrogenation of O and OH on Pt(111): A comparison between the reaction rates of the first and the second hydrogen addition steps

    SciTech Connect

    Näslund, L.-Å.

    2014-03-14

    The formation of water through hydrogenation of oxygen on platinum occurs at a surprisingly low reaction rate. The reaction rate limited process for this catalytic reaction is, however, yet to be settled. In the present work, the reaction rates of the first and the second hydrogen addition steps are compared when hydrogen is obtained through intense synchrotron radiation that induces proton production in a water overlayer on top of the adsorbed oxygen species. A substantial amount of the produced hydrogen diffuses to the platinum surface and promotes water formation at the two starting conditions O/Pt(111) and (H{sub 2}O+OH)/Pt(111). The comparison shows no significant difference in the reaction rate between the first and the second hydrogen addition steps, which indicates that the rate determining process of the water formation from oxygen on Pt(111) is neither the first nor the second H addition step or, alternatively, that both H addition steps exert rate control.

  9. Kinetic and Mechanistic Studies of Carbon-to-Metal Hydrogen Atom Transfer Involving Os-Centered Radicals: Evidence for Tunneling

    SciTech Connect

    Lewandowska-Androlojc, Anna; Grills, David C.; Zhang, Jie; Bullock, R. Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-05

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Studies by means of time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene and 1,4-cyclohexadiene to Cp(CO)2Os• and (n5-iPr4C5H)(CO)2Os• radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons were found to be in the range 1.54 × 105 M 1 s 1 -1.73 × 107 M 1 s-1 at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary kinetic isotope effects of 13.4 ± 1.0 and 16.6 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (n5-iPr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 -C temperature range were carried out to obtain the difference in activation energies and the pre-exponential factor ratio. For hydrogen atom transfer from xanthene to (n5-iPr4C5H)(CO)2Os•, the (ED - EH) = 3.25 ± 0.20 kcal/mol and AH/AD = 0.056 ± 0.018 values are greater than the semi-classical limits and thus suggest a quantum mechanical tunneling mechanism. The work at BNL was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences & Biosciences, Office of Basic Energy Sciences. RMB also thanks the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for support. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

  10. Reaction of Molecular Hydrogen with Tetraaminecopper(II) Sulfate Monohydrate

    NASA Astrophysics Data System (ADS)

    Kanda, Seiichi; Kori, Toshinari; Kida, Sigeo

    1994-02-01

    The reaction of tetraammincopper(II) sulfate monohydrate in a solid state with H 2 (10 MPa) was studied. The Cu(II) ion in the complex was reduced to Cu(0). The final product was a mixture of (NH 4) 2SO 4 and colloidal black Cu(0) which showed a remarkable reactivity as follows. In thermogravimetric analysis up to 440°C under nitrogen atmosphere, the above product reacted between the components very much differently from a control sample with the same composition. The six intermediate samples, taken at successive reaction times, were examined by powder diffraction method. As one of the intermediates, the copper double salt, (NH 4) 2Cu(SO 4) 2, was identified.

  11. Reactions of Hydrogen with Si-SiO2 Interfaces

    NASA Astrophysics Data System (ADS)

    Rashkeev, Sergey N.

    2001-11-01

    Three different types of behavior have been observed for H in Si-SiO2 structures: a) Radiation experiments established that H^+ released in SiO2 migrates to the Si-SiO2 interface where it induces new defects; b) For oxides exposed first to high-temperature annealing and then to molecular hydrogen, mobile positive charge believed to be H^+ can be cycled to and from the interface by reversing the oxide electric field; c) Hydrogen is known to passivate Si dangling bonds at the Si-SiO2 interface, but the subsequent arrival of H^+ at the interface causes depassivation of Si-H bonds. We report first-principles calculations that identify atomic-scale mechanisms for the different types of behavior and the conditions that are necessary for each. We show that the Si-Si bonds on the oxide side, i.e., ``suboxide bonds'', can trap H^+ in deep wells with asymmetric barrier (1.5 eV on the Si side, 1 eV on the SiO2 side). In radiation experiments these centers can act as fixed positive charge. In the mobile-positive-charge experiments, the protons can be cycled between opposite Si-SiO2 interfaces if the density of suboxide bonds is high. Also, we establish that H^+ is the only stable charge state at the interface and that H^+ reacts directly (without being neutralized by a Si electron) with a Si-H bond, forming an H2 molecule and a positively charged dangling bond (Pb center). As a result, H-induced interface-trap formation does not depend on the availability of Si electrons. This work was supported in part by AFOSR Grant F-49620-99-1-0289.

  12. The maximum momentum transfer in proton-hydrogen collisions

    NASA Technical Reports Server (NTRS)

    Xu, Y. J.; Khandelwal, G. S.; Wilson, J. W.; Townsend, L. W. (Principal Investigator)

    1986-01-01

    The upper limit of momentum transfer by a proton to K-shell electrons is calculated in a restricted three-body classical model. The model shows that the infinite upper limit used in practice, is generally good except for low energy protons passing through an extremely rarefied gas.

  13. Direct Dynamics Study of Hydrogen-Transfer Isomerization of 1-Pentyl and 1-Hexyl Radicals

    NASA Astrophysics Data System (ADS)

    Zheng, Jingjing; Truhlar, Donald G.

    2009-07-01

    The rate constants of three intramolecular hydrogen-transfer isomerization reactions, namely, 1-4 isomerization of the 1-pentyl radical and 1-4 and 1-5 isomerizations of the 1-hexyl radical, are calculated using variational transition state theory with multidimensional tunneling, in particular by using canonical variational theory (CVT, which is the version of variational transition state theory in which the transition state dividing surface is optimized for a canonical ensemble) with small-curvature tunneling (SCT) for the transmission coefficient. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) and variational transition state theory with interpolated single-point energies (VTST-ISPE). Single-level direct dynamics calculations were performed for all of the reactions by IVTST-M using M06-2X/MG3S or M08-HX/cc-pVTZ+ potential energy surfaces or both. The stationary points of 1-4 isomerization of 1-pentyl and the stationary points for the forward reactions of 1-4 and 1-5 isomerizations of 1-hexyl were also optimized by BMC-CCSD, and for all three reactions we also performed dual-level direct dynamics calculations using VTST-ISPE in which MCG3-MPW single-point energies served as the higher level. The calculated MCG3-MPW//M06-2X/MG3S rate constants agree well with experimental values for 1-4 isomerization of the 1-pentyl radical at high temperature, and this validates the accuracy of this theoretical method for 1-4 isomerization. The MCG3-MPW//M06-2X/MG3S method was therefore used to make a reliable prediction for the rata constants of 1-4 isomerization of the 1-hexyl radical for which a direct experimental measurement is not available. The calculated CVT/SCT/M08-HX/cc-pVTZ+ rate constants agree well with experimental values for 1-5 isomerization of the 1-hexyl radical, and they show that the tunneling effect for these reactions was underestimated in

  14. Formation of C–C bonds via ruthenium-catalyzed transfer hydrogenation*

    PubMed Central

    Moran, Joseph; Krische, Michael J.

    2013-01-01

    Ruthenium-catalyzed transfer hydrogenation of diverse π-unsaturated reactants in the presence of aldehydes provides products of carbonyl addition. Dehydrogenation of primary alcohols in the presence of the same π-unsaturated reactants provides identical products of carbonyl addition. In this way, carbonyl addition is achieved from the alcohol or aldehyde oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. In this account, the discovery of ruthenium-catalyzed C–C bond-forming transfer hydrogenations and the recent development of diastereo- and enantioselective variants are discussed. PMID:23430602

  15. Formation of C-C bonds via ruthenium-catalyzed transfer hydrogenation().

    PubMed

    Moran, Joseph; Krische, Michael J

    2012-01-01

    Ruthenium-catalyzed transfer hydrogenation of diverse π-unsaturated reactants in the presence of aldehydes provides products of carbonyl addition. Dehydrogenation of primary alcohols in the presence of the same π-unsaturated reactants provides identical products of carbonyl addition. In this way, carbonyl addition is achieved from the alcohol or aldehyde oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. In this account, the discovery of ruthenium-catalyzed C-C bond-forming transfer hydrogenations and the recent development of diastereo- and enantioselective variants are discussed. PMID:23430602

  16. An analytical comparison of convective heat transfer correlations in supercritical hydrogen

    NASA Technical Reports Server (NTRS)

    Dziedzic, William M.; Jones, Stuart C.; Gould, Dana C.; Petley, Dennis H.

    1991-01-01

    Four correlations that cover the ranges of liquid to gas for turbulent flow convection of hydrogen are compared with CFD analysis over a range of expected design conditions for active cooling of hypersonic aircraft. Analysis of hydrogen cooling in a typical cooling panel shows how predicted design performance varies with the correlation utilized. The CFD heat transfer coefficient results for a heat spike differed significantly from all four correlations. An acceptable heat transfer coefficient can be calculated at the heat spike location by overlooking the coefficient at the spike and averaging the coefficient before and after the spike.

  17. To jump or not to jump? Cα hydrogen atom transfer in post-cleavage radical-cation complexes.

    PubMed

    Bythell, Benjamin J

    2013-02-14

    Conventionally, electron capture or transfer to a polyprotonated peptide ion produces an initial radical-cation intermediate which dissociates "directly" to generate complementary c(n)' and z(m)(•) sequence ions (or ions and neutrals). Alternatively, or in addition, the initial radical-cation intermediate can undergo H(•) migration to produce c(n)(•) (or c(n) - H(•)) and z(m)' (or z(m)(•) + H(•)) species prior to complex separation ("nondirect"). This reaction significantly complicates spectral interpretation, creates ambiguity in peak assignment, impairs effective algorithmic processing (reduction of the spectrum to solely (12)C m/z values), and reduces sequence ion signal-to-noise. Experimental evidence indicates that the products of hydrogen atom transfer reactions are substantially less prevalent for higher charge state precursors. This effect is generally rationalized on the basis of decreased complex lifetime. Here, we present a theoretical study of these reactions in post N-C(α) bond cleavage radical-cation complexes as a function of size and precursor charge state. This approach provides a computational estimate of the barriers associated with these processes for highly charged peptides with little charge solvation. The data indicate that the H(•) migration is an exothermic process and that the barrier governing this reaction rises steeply with precursor ion charge state. There is also some evidence for immediate product separation following N-C(α) bond cleavage at higher charge state. PMID:22809411

  18. Reactions of atomic hydrogen with formic acid and carbon monoxide in solid parahydrogen II: Deuterated reaction studies.

    PubMed

    Wonderly, William R; Anderson, David T

    2014-09-11

    It is difficult to determine whether the measured rate constant for reaction of atomic hydrogen with formic acid reported in Part 1 reflects the H atom quantum diffusion rate or the rate constant for the tunneling reaction step. In Part 2 of this series, we present kinetic studies of the postphotolysis H atom reactions with deuterated formic acid (DCOOD) to address this ambiguity. Short duration 193 nm in situ photolysis of DCOOD trapped in solid parahydrogen results in partial depletion of the DCOOD precursor and photoproduction of primarily CO, CO2, DOCO, HCO and mobile H atoms. At 1.9 K we observe post-irradiation growth in the concentrations of DOCO and HCO that can be explained by H atom tunneling reactions with DCOOD and CO, respectively. Conducting experiments with different deuterium isotopomers of formic acid (DCOOD, DCOOH, HCOOD and HCOOH) provides strong circumstantial evidence the reaction involves H atom abstraction from the alkyl group of formic acid. Further, the anomalous temperature dependence measured for the H + HCOOH reaction in Part 1 is also observed for the analogous reactions with deuterated formic acid. The rate constants extracted for H atom reactions with DCOOD and HCOOH are equivalent to within experimental uncertainty. This lack of a kinetic isotope effect in the measured rate constant is interpreted as evidence the reactions are diffusion limited; the measured rate constant reflects the H atom diffusion rate and not the tunneling reaction rate. Whether or not H atom reactions with chemical species in solid parahydrogen are diffusion limited is one of the outstanding questions in this field, and this work makes significant strides toward showing the reaction kinetics with formic acid are diffusion limited.

  19. Ab initio study of charge-transfer dynamics in collisions of C{sup 2+} ions with hydrogen chloride

    SciTech Connect

    Rozsalyi, E.; Vibok, A.; Bene, E.; Halasz, G. J.; Bacchus-Montabonel, M. C.

    2011-05-15

    Ab initio quantum chemistry molecular calculations followed by a semiclassical dynamical treatment in the keV collision energy range have been developed for the study of the charge-transfer process in collisions of C{sup 2+} ions with hydrogen chloride. The mechanism has been investigated in detail in connection with avoided crossings between states involved in the reaction. A simple mechanism driven by a strong nonadiabatic coupling matrix element has been pointed out for this process. A comparative analysis with the halogen fluoride target corresponding to a similar electronic configuration shows a quite different charge-transfer mechanism leading to a very different behavior of the cross sections. Such behavior may be correlated to specific nonadiabatic interactions observed in these collision systems.

  20. Experimental Studies of Hydrogenation and Other Reactions on Surfaces Under Astrophysically Relevant Conditions

    NASA Technical Reports Server (NTRS)

    Vidali, Gianfranco

    1998-01-01

    The goal of our project is to study hydrogen recombination reactions on solid surfaces under conditions that are relevant in astrophysics. Laboratory experiments were conducted using low-flux, cold atomic H and D beams impinging on a sample kept under ultra high vacuum conditions. Realistic analogues of interstellar dust grains were used. Our results show that current models for hydrogen recombination reactions have to be modified to take into account the role of activated diffusion of H on surfaces even at low temperature.

  1. Hydrogen Peroxide Promoted Mizoroki-Heck Reactions of Phenyldiazenes with Acrylates, Acrylamides, and Styrenes.

    PubMed

    Lasch, Roman; Fehler, Stefanie K; Heinrich, Markus R

    2016-04-01

    Mizoroki-Heck reactions, which are well-known for aryldiazonium salts and which have recently been described for arylhydrazines, have now been extended to phenyldiazenes. In situ generation of phenyldiazenes from azocarboxylates allowed clean and selective reactions with styrenes, acrylates, and acrylamides using palladium(II) acetate in the presence of silver(I) acetate or hydrogen peroxide as oxidant. Hydrogen peroxide was thereby shown to be a cheap and broadly applicable alternative for the established palladium-silver(I) system. PMID:26974469

  2. Comparison of the proton-transfer paths in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order III. O-H-O hydrogen bonds.

    PubMed

    Majerz, Irena; Olovsson, Ivar

    2010-01-01

    The quantum-mechanically derived reaction coordinates (QMRC) for the proton transfer in O-H-O hydrogen bonds have been derived from ab initio calculations of potential-energy surfaces. A comparison is made between the QMRC and the corresponding bond-order reaction coordinates (BORC) derived by applying the Pauling bond order concept together with the principle of conservation of bond order. In agreement with earlier results for N-H-N(+) hydrogen bonds there is virtually perfect agreement between the QMRC and BORC curves for intermolecular O-H-O hydrogen bonds. For intramolecular O-H-O hydrogen bonds, the donor and acceptor parts of the molecule impose strong constraints on the O···O distance and the QMRC does not follow the BORC relation in the whole range. The neutron-determined proton positions are located close to the theoretically calculated potential-energy minima, and where the QMRC and the BORC curves coincide with each other. The results confirm the universal character of intermolecular hydrogen bonds: BORC is identical with QMRC and the proton can be moved from donor to acceptor keeping its valency equal to 1. The shape of PES for intramolecular hydrogen bonds is more complex as it is sensitive to the geometry of the molecule as well as of the hydrogen bridge.

  3. Mass transfer of corrosion products and corrosion of steel in sodium at high hydrogen concentrations

    NASA Astrophysics Data System (ADS)

    Alekseev, V. V.; Kozlov, F. A.; Sorokin, A. P.; Varseev, E. V.; Orlova, E. A.; Torbenkova, I. Yu.

    2015-10-01

    Serviceability of steels in a loop having an increased content of hydrogen is estimated. The equilibrium pressure of hydrogen in a sodium loop saturated with hydrogen is around 10 MPa at a temperature of approximately 630°C and around 100 MPa at 800°C. At the hydrogen pressure equal to 10 MPa, steel with a chromium content of 5% is serviceable to a temperature of 840°C, and steel with a chromium content of 25% is serviceable in the entire considered range of temperatures (above 600°C). At a hydrogen pressure of 80 MPa, steel containing 5% of chromium is not serviceable in the entire considered range of temperatures, and steel containing 25% of chromium is serviceable to a temperature of 830°C. The article presents the results from experimental investigations of the effect of hydrogen on corrosion and mass transfer of corrosion products in a sodium loop at the hydrogen concentration in sodium equal to 6 ppm, which were carried out in the high-temperature section of the sodium test facility (the test facility and the investigation methodology were described in the previous publications of the authors). The distributions of chromium and nickel flows toward the walls over the channel length are obtained at increased hydrogen content (around 6 ppm) and at low oxygen content (less than 2 ppm) in sodium and at a temperature of up to 780°C. For the conditions with relatively low content of oxygen and hydrogen in sodium, the experimental values of chromium flow toward the channel wall are consistent with the calculated data. This fact confirms the possibility of using the previously obtained physicochemical constants for calculating the mass transfer of chromium in high-temperature sodium loops at an increased content of hydrogen in sodium.

  4. Charge-Transfer Induced High Efficient Hydrogen Evolution of MoS2/graphene Cocatalyst

    NASA Astrophysics Data System (ADS)

    Li, Honglin; Yu, Ke; Li, Chao; Tang, Zheng; Guo, Bangjun; Lei, Xiang; Fu, Hao; Zhu, Ziqiang

    2015-12-01

    The MoS2 and reduced graphite oxide (rGO) composite has attracted intensive attention due to its favorable performance as hydrogen evolution reaction (HER) catalyst, but still lacking is the theoretical understanding from a dynamic perspective regarding to the influence of electron transfer, as well as the connection between conductivity and the promoted HER performance. Based on the first-principles calculations, we here clearly reveal how an excess of negative charge density affects the variation of Gibbs free energy (ΔG) and the corresponding HER behavior. It is demonstrated that the electron plays a crucial role in the HER routine. To verify the theoretical analyses, the MoS2 and reduced graphite oxide (rGO) composite with well defined 3-dimensional configuration was synthesized via a facile one-step approach for the first time. The experimental data show that the HER performance have a direct link to the conductivity. These findings pave the way for a further developing of 2-dimension based composites for HER applications.

  5. Charge-Transfer Induced High Efficient Hydrogen Evolution of MoS2/graphene Cocatalyst

    PubMed Central

    Li, Honglin; Yu, Ke; Li, Chao; Tang, Zheng; Guo, Bangjun; Lei, Xiang; Fu, Hao; Zhu, Ziqiang

    2015-01-01

    The MoS2 and reduced graphite oxide (rGO) composite has attracted intensive attention due to its favorable performance as hydrogen evolution reaction (HER) catalyst, but still lacking is the theoretical understanding from a dynamic perspective regarding to the influence of electron transfer, as well as the connection between conductivity and the promoted HER performance. Based on the first-principles calculations, we here clearly reveal how an excess of negative charge density affects the variation of Gibbs free energy (ΔG) and the corresponding HER behavior. It is demonstrated that the electron plays a crucial role in the HER routine. To verify the theoretical analyses, the MoS2 and reduced graphite oxide (rGO) composite with well defined 3-dimensional configuration was synthesized via a facile one-step approach for the first time. The experimental data show that the HER performance have a direct link to the conductivity. These findings pave the way for a further developing of 2-dimension based composites for HER applications. PMID:26688209

  6. Charge-Transfer Induced High Efficient Hydrogen Evolution of MoS2/graphene Cocatalyst.

    PubMed

    Li, Honglin; Yu, Ke; Li, Chao; Tang, Zheng; Guo, Bangjun; Lei, Xiang; Fu, Hao; Zhu, Ziqiang

    2015-01-01

    The MoS2 and reduced graphite oxide (rGO) composite has attracted intensive attention due to its favorable performance as hydrogen evolution reaction (HER) catalyst, but still lacking is the theoretical understanding from a dynamic perspective regarding to the influence of electron transfer, as well as the connection between conductivity and the promoted HER performance. Based on the first-principles calculations, we here clearly reveal how an excess of negative charge density affects the variation of Gibbs free energy (ΔG) and the corresponding HER behavior. It is demonstrated that the electron plays a crucial role in the HER routine. To verify the theoretical analyses, the MoS2 and reduced graphite oxide (rGO) composite with well defined 3-dimensional configuration was synthesized via a facile one-step approach for the first time. The experimental data show that the HER performance have a direct link to the conductivity. These findings pave the way for a further developing of 2-dimension based composites for HER applications. PMID:26688209

  7. Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol over Nitrogen-Doped Carbon-Supported Iron Catalysts.

    PubMed

    Li, Jiang; Liu, Jun-Ling; Zhou, Hong-Jun; Fu, Yao

    2016-06-01

    Iron-based heterogeneous catalysts, which were generally prepared by pyrolysis of iron complexes on supports at elevated temperature, were found to be capable of catalyzing the transfer hydrogenation of furfural (FF) to furfuryl alcohol (FFA). The effects of metal precursor, nitrogen precursor, pyrolysis temperature, and support on catalytic performance were examined thoroughly, and a comprehensive study of the reaction parameters was also performed. The highest selectivity of FFA reached 83.0 % with a FF conversion of 91.6 % under the optimal reaction condition. Catalyst characterization suggested that iron cations coordinated by pyridinic nitrogen functionalities were responsible for the enhanced catalytic activity. The iron catalyst could be recycled without significant loss of catalytic activity for five runs, and the destruction of the nitrogen-iron species, the presence of crystallized Fe2 O3 phase, and the pore structure change were the main reasons for catalyst deactivation. PMID:27144965

  8. Enantiodivergent Atroposelective Synthesis of Chiral Biaryls by Asymmetric Transfer Hydrogenation: Chiral Phosphoric Acid Catalyzed Dynamic Kinetic Resolution.

    PubMed

    Mori, Keiji; Itakura, Tsubasa; Akiyama, Takahiko

    2016-09-12

    Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosphoric acid, dynamic kinetic resolution (DKR) involving a reductive amination reaction proceeded smoothly to furnish both R and S isomers of chiral biaryls with excellent enantioselectivities by proper choice of hydroxyaniline derivative. This trend was observed in wide variety of substrates, and various chiral biphenyl and phenyl naphthyl adducts were synthesized with satisfactory enantioselectivities in enantiodivergent fashion. The enantiodivergent synthesis of synthetically challenging, chiral o-tetrasubstituted biaryls were also accomplished, and suggests high synthetic potential of the present method. PMID:27491630

  9. Why are sec-alkylperoxyl bimolecular self-reactions orders of magnitude faster than the analogous reactions of tert-alkylperoxyls? The unanticipated role of CH hydrogen bond donation.

    PubMed

    Lee, Richmond; Gryn'ova, Ganna; Ingold, K U; Coote, Michelle L

    2016-08-24

    High-level ab initio calculations are used to identify the mechanism of secondary (and primary) alkylperoxyl radical termination and explain why their reactions are much faster than their tertiary counterparts. Contrary to existing literature, the decomposition of both tertiary and non-tertiary tetroxides follows the same asymmetric two-step bond cleavage pathway to form a caged intermediate of overall singlet multiplicity comprising triplet oxygen and two alkoxyl radicals. The alpha hydrogen atoms of non-tertiary species facilitate this process by forming unexpected CHO hydrogen bonds to the evolving O2. For non-tertiary peroxyls, subsequent alpha hydrogen atom transfer then yields the experimentally observed non-radical products, ketone, alcohol and O2, whereas for tertiary species, this reaction is precluded and cage escape of the (unpaired) alkoxyl radicals is a likely outcome with important consequences for autoxidation. PMID:27511438

  10. Reactions of Hydrogen with Si-SiO2 Interfaces

    NASA Astrophysics Data System (ADS)

    Rashkeev, S. N.; Pantelides, S. T.; Buczko, R.; Fleetwood, D. M.; Schrimpf, R. D.

    2001-03-01

    Two contrasting behaviors have been observed for H in Si-SiO2 structures: a) Radiation experiments established that H^+ released in SiO2 migrates to the Si-SiO2 interface where it induces new defects; b) For oxides exposed first to high-temperature annealing and then to molecular hydrogen, mobile positive charge believed to be H^+ can be cycled to and from the interface by reversing the oxide electric field. We report first-principles calculations that identify atomic-scale mechanisms for the two types of behavior and the conditions that are necessary for each. Si-Si bonds on the oxide side, i.e., ``suboxide bonds'', can trap H^+ in deep wells with asymmetric barrier (1.5 eV on the Si side, 1 eV on the SiO2 side). In radiation experiments these centers can act as fixed positive charge. In the mobile-positive-charge experiments, the protons can be cycled between opposite Si-SiO2 interfaces if the density of suboxide bonds is high. This work was supported in part by AFOSR Grant F-49620-99-1-0289.

  11. Middle atmosphere heating by exothermic chemical reactions involving odd-hydrogen species

    NASA Technical Reports Server (NTRS)

    Mlynczak, Martin G.; Solomon, Susan

    1991-01-01

    The rate of heating which occurs in the middle atmosphere due to four exothermic reactions involving members of the odd-hydrogen family is calculated. The following reactions are considered: O + OH yields O2 + H; H + O2 + M yields HO2 + M; H + O3 yields OH + O2; and O + HO2 yields OH + O2. It is shown that the heating rates due to these reactions rival the oxygen-related heating rates conventionally considered in middle-atmosphere models. The conversion of chemical potential energy into molecular translational energy (heat) by these odd-hydrogen reactions is shown to be a significant energy source in the middle atmosphere that has not been previously considered.

  12. Reaction electronic flux and its role in DNA intramolecular proton transfers.

    PubMed

    Durán, Rocío; Vöhringer-Martinez, Esteban; Toro-Labbé, Alejandro; Herrera, Bárbara

    2016-06-01

    Proton transfer reactions present a key step in many biological and chemical processes. Here, we focused on the electronic changes in the proton transfer reactions of the four DNA bases. In combination with the previous structural analysis the reaction electronic flux together with local descriptors as the Hirshfeld-I charges allow us to identify chemical events and rationalize the underlying reaction mechanism. Our results show that imine-enamine in adenine and citosyne, and keto-enol tautomerizations in thymine and guanine have different reaction mechanisms. The former involve net structural rearrangements driven by favoured electrostatic interactions between the proton and the acceptor atom whereas the keto-enol tautomerizations require electronic changes reflected in the reaction electronic flux and changes in the NBO bond orders which favour the proton transfer reaction.

  13. Methanosarcina spp. drive vinyl chloride dechlorination via interspecies hydrogen transfer.

    PubMed

    Heimann, Axel C; Batstone, Damien J; Jakobsen, Rasmus

    2006-04-01

    Two highly enriched cultures containing Dehalococcoides spp. were used to study the effect of aceticlastic methanogens on reductive vinyl chloride (VC) dechlorination. In terms of aceticlastic methanogens, one culture was dominated by Methanosaeta, while the other culture was dominated by Methanosarcina, as determined by fluorescence in situ hybridization. Cultures amended with 2-bromoethanesulfonate (BES), an efficient inhibitor of methanogens, exhibited slow VC dechlorination when grown on acetate and VC. Methanogenic cultures dominated by Methanosaeta had no impact on dechlorination rates, compared to BES-amended controls. In contrast, methanogenic cultures dominated by Methanosarcina displayed up to sevenfold-higher rates of VC dechlorination than their BES-amended counterparts. Methanosarcina-dominated cultures converted a higher percentage of [2-(14)C]acetate to (14)CO(2) when concomitant VC dechlorination took place, compared to nondechlorinating controls. Respiratory indices increased from 0.12 in nondechlorinating cultures to 0.51 in actively dechlorinating cultures. During VC dechlorination, aqueous hydrogen (H(2)) concentrations dropped to 0.3 to 0.5 nM. However, upon complete VC consumption, H(2) levels increased by a factor of 10 to 100, indicating active hydrogen production from acetate oxidation. This process was thermodynamically favorable by means of the extremely low H(2) levels during dechlorination. VC degradation in nonmethanogenic cultures was not inhibited by BES but was limited by the availability of H(2) as electron donor, in cultures both with and without BES. These findings all indicate that Methanosarcina (but not Methanosaeta), while cleaving acetate to methane, simultaneously oxidizes acetate to CO(2) plus H(2), driving hydrogenotrophic dehalorespiration of VC to ethene by Dehalococcoides.

  14. Correlating the hydrogen evolution reaction activity in alkaline electrolytes with the hydrogen binding energy on monometallic surfaces

    SciTech Connect

    Sheng, WC; Myint, M; Chen, JGG; Yan, YS

    2013-05-01

    The slow reaction kinetics of the hydrogen evolution and oxidation reactions (HER/HOR) on platinum in alkaline electrolytes hinders the development of alkaline electrolysers, solar hydrogen cells and alkaline fuel cells. A fundamental understanding of the exchange current density of the HER/HOR in alkaline media is critical for the search and design of highly active electrocatalysts. By studying the HER on a series of monometallic surfaces, we demonstrate that the HER exchange current density in alkaline solutions can be correlated with the calculated hydrogen binding energy (HBE) on the metal surfaces via a volcano type of relationship. The HER activity varies by several orders of magnitude from Pt at the peak of the plot to W and Au located on the bottom of each side of the plot, similar to the observation in acids. Such a correlation suggests that the HBE can be used as a descriptor for identifying electrocatalysts for HER/HOR in alkaline media, and that the HER exchange current density can be tuned by modifying the surface chemical properties.

  15. Regulating energy transfer of excited carriers and the case for excitation-induced hydrogen dissociation on hydrogenated graphene

    PubMed Central

    Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.

    2013-01-01

    Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations. PMID:23277576

  16. State-selective reaction dynamics of atomic oxygen with molecular hydrogen, methanethiol, and ethanethiol

    NASA Astrophysics Data System (ADS)

    Han, Jiande

    2000-11-01

    Reaction dynamics have been studied for the following four systems: (1)The rotational state distribution of the nascent NO fragment generated from the photodissociation of (i- C3H7) 3SiONO near 226 nm (S2 absorption band) has been obtained via 1+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy and with a time-of-flight mass spectrometer (TOFMS). The absence of vibrational excitation and relative cold rotational distribution suggest a direct dissociation mechanism upon photolysis of the parent molecule. (2)The reaction dynamics of O(3P) and H2(v = 1). The quantum state specific reactant H2(v = 1) was prepared effectively via Stimulated Raman Pumping (SRP). The internal quantum state distribution of the product OH (X 2Π1/2,3/2) was interrogated by laser-induced fluorescence (LIF) spectroscopy. The one-quantum vibrational excitation of hydrogen not only dramatically increases the reaction rate, but also may have slightly changed the reaction mechanism from the known ground-state hydrogen reaction. (3)Experimental and ab initio studies of the reaction dynamics of O(3P) + CH3SH. Experiments utilized LIF detection of OH, CH3S, SO, and also HSO. Theoretically, ab initio energy evaluations using Gaussian 94 software and G2MP2 theory, and ab initio molecular dynamics were carried out for the reaction. The combination of the experimental and theoretical works has resulted in great insight into the reaction mechanism. (4)Experimental study of the reaction dynamics of O(3P) + C2H 5SH by the similar experimental measurements to the reaction O( 3P) + CH3SH. The reaction O(3P) + C 2H5SD further eliminated the ambiguity in confirming the each other in suggesting the proper reaction mechanisms for the two reaction systems.

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

    SciTech Connect

    Jiang, C.L.; Rehm, K.E.; Gehring, J.

    1995-08-01

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

  18. A convenient and general ruthenium-catalyzed transfer hydrogenation of nitro- and azobenzenes.

    PubMed

    Jagadeesh, Rajenahally V; Wienhöfer, Gerrit; Westerhaus, Felix A; Surkus, Annette-Enrica; Junge, Henrik; Junge, Kathrin; Beller, Matthias

    2011-12-16

    An easily accessible in situ catalyst composed of [{RuCl(2)(p-cymene)}(2)] and terpyridine has been developed for the selective transfer hydrogenation of aromatic nitro and azo compounds. The procedure is general and the selectivity of the catalyst has been demonstrated by applying a series of structurally diverse nitro and azo compounds (see scheme).

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

    NASA Technical Reports Server (NTRS)

    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. Magnetic Silica-Supported Ruthenium Nanoparticles: An Efficient Catalyst for Transfer Hydrogenation of Carbonyl Compounds

    EPA Science Inventory

    One-pot synthesis of ruthenium nanoparticles on magnetic silica is described which involve the in situ generation of magnetic silica (Fe3O4@ SiO2) and ruthenium nano particles immobilization; the hydration of nitriles and transfer hydrogenation of carbonyl compounds occurs in hi...

  1. A 10,000-gpm liquid hydrogen transfer system for the Saturn/Apollo program.

    NASA Technical Reports Server (NTRS)

    Wybranowski, E., Jr.

    1972-01-01

    Brief description of the design and operation of the liquid hydrogen transfer system used to service the Saturn V launch vehicle. The cryogenic loading of the huge booster begins eight hours before the scheduled liftoff. The first three hours of fueling are spent in cold hydrogen gas conditioning of the fuel tank. The cold hydrogen gas is provided by vaporizing liquid hydrogen from the storage tank and routing the resultant gas through the fill system. Boil-off losses after loading are continuously replaced through control valves which are driven by a computer system. The liquid hydrogen transfer system is made up of a number of subsystems including the 850,000 gal storage tank whose boil-off losses amount to only 200 gal/day, the pressurization system, the burn pond for controlled disposal of hydrogen waste gas, the storage tank fill manifold, and the hazardous gas monitoring system. Some of the subsystems and components are redundant to provide a high degree of reliability.

  2. Modeling of hydrogen evolution reaction on the surface of GaInP2

    NASA Astrophysics Data System (ADS)

    Choi, Woon Ih; Wood, Brandon; Schwegler, Eric; Ogitsu, Tadashi

    2012-02-01

    GaInP2 is promising candidate material for hydrogen production using sunlight. It reduces solvated proton into hydrogen molecule using light-induced excited electrons in the photoelectrochemical cell. However, it is challenging to model hydrogen evolution reaction (HER) using first-principles molecular dynamics. Instead, we use Anderson-Newns model and generalized solvent coordinate in Marcus-Hush theory to describe adiabatic free energy surface of HER. Model parameters are fitted from the DFT calculations. We model Volmer-Heyrovsky reaction path on the surfaces of CuPt phase of GaInP2. We also discuss effects of surface oxide and catalyst atoms that exist on top of bare surfaces in experimental circumstances.

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

    ERIC Educational Resources Information Center

    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…

  4. Carboxylic Group Embedded Carbon Balls as a New Supported Catalyst for Hydrogen Economic Reactions.

    PubMed

    Bordoloi, Ankur

    2016-03-01

    Carboxylic group functionalized carbon balls have been successfully synthesized by using a facile synthesis method and well characterized with different characterization techniques such as XPS, MAS NMR, SEM, ICP and N2 physi-sorption analysis. The synthesized material has been effectively utilized as novel support to immobilized ruthenium catalyst for hydrogen economic reactions.

  5. Determination of the Molar Volume of Hydrogen from the Metal-Acid Reaction: An Experimental Alternative.

    ERIC Educational Resources Information Center

    de Berg, Kevin; Chapman, Ken

    1996-01-01

    Describes an alternative technique for determining the molar volume of hydrogen from the metal-acid reaction in which the metal sample is encased in a specially prepared cage and a pipette filler is used to fill an inverted burette with water. Eliminates some difficulties encountered with the conventional technique. (JRH)

  6. Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Bottoni, S.; Leoni, S.; Fornal, B.; Raabe, R.; Rusek, K.; Benzoni, G.; Bracco, A.; Crespi, F. C. L.; Morales, A. I.; Bednarczyk, P.; Cieplicka-Oryńczak, N.; Królas, W.; Maj, A.; Szpak, B.; Callens, M.; Bouma, J.; Elseviers, J.; De Witte, H.; Flavigny, F.; Orlandi, R.; Reiter, P.; Seidlitz, M.; Warr, N.; Siebeck, B.; Hellgartner, S.; Mücher, D.; Pakarinen, J.; Vermeulen, M.; Bauer, C.; Georgiev, G.; Janssens, R. V. F.; Balabanski, D.; Sferrazza, M.; Kowalska, M.; Rapisarda, E.; Voulot, D.; Lozano Benito, M.; Wenander, F.

    2015-08-01

    An exploratory experiment performed at REX-ISOLDE 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 mechanism to explore the structure of exotic neutron-rich nuclei. The reactions 7Li(98Rb,α xn ) and 7Li(98Rb,t xn ) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be described well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.

  7. Hydrogen isotope transfer in austenitic steels and high-nickel alloy during in-core irradiation

    SciTech Connect

    Polosukhin, B.G.; Sulimov, E.M.; Zyrianov, A.P.; Kalinin, G.M.

    1995-10-01

    The transfer of protium and deuterium in austenitic chromium-nickel steels and in a high-nickel alloy was studied in a specially designed facility. The transfer parameters of protium and deuterium were found to change greatly during in-core irradiation, and the effects of irradiation increased as the temperature decreased. Thus, at temperature T<673K, the relative increase in the permeability of hydrogen isotopes under irradiation can be orders of magnitude higher in these steels. Other radiation effects were also observed, in addition to the changes from the initial values in the effects of protium and deuterium isotopic transfer. 4 refs., 3 figs., 2 tabs.

  8. The Photochemical Oxidation of Siderite That Drove Hydrogen Based Microbial Redox Reactions in The Archean Biosphere

    NASA Astrophysics Data System (ADS)

    Kim, J. D.; Yee, N.; Falkowski, P. G.

    2012-12-01

    Hydrogen is the most abundant element in the universe and molecular hydrogen (H2) is a rich source of electron in a mildly reducing environment for microbial redox reactions, such as anoxygenic photosynthesis and methanogenesis. Subaerial volcanoes, ocean crust serpentinization and mid-ocean ridge volcanoes have been believed to be the major source of the hydrogen flux to the atmosphere. Although ferrous ion (Fe2+) photooxidation has been proposed as an alternative mechanism by which hydrogen gas was produced, ferruginous water in contact with a CO2-bearing atmosphere is supersaturated with respect to FeCO3 (siderite), thus the precipitation of siderite would have been thermodynamically favored in the Archean environment. Siderite is the critical mineral component of the oldest fossilized microbial mat. It has also been inferred as a component of chemical sedimentary protolith in the >3750 Ma Nuvvuagittuq supracrustal belt, Canada and the presence of siderite in the protolith suggests the occurrence of siderite extends to Hadean time. Analyses of photooxidation of siderite suggest a significant flux of hydrogen in the early atmosphere. Our estimate of the hydrogen production rate under Archean solar flux is approximately 50 times greater than the estimated hydrogen production rate by the volcanic activity based on a previous report (Tian et al. Science 2005). Our analyses on siderite photooxidation also suggest a mechanism by which banded iron formation (BIF) was formed. The photooxidation transforms siderite to magnetite/maghemite (spinnel iron oxide), while oxygenic oxidation of siderite leads to goethite, and subsequently to hematite (Fe3+2O3) upon dehydration. We will discuss the photochemical reaction, which was once one of the most ubiquitous photochemical reactions before the rise of oxygen in the atmosphere. Photooxidation of siderite over time by UV light From left to right: UV oxidized siderite, pristine siderite, oxidized siderite by oxygen

  9. Infrared Spectroscopy of OH··CH3OH: Hydrogen-Bonded Intermediate Along the Hydrogen Abstraction Reaction Path.

    PubMed

    Hernandez, Federico J; Brice, Joseph T; Leavitt, Christopher M; Pino, Gustavo A; Douberly, Gary E

    2015-07-23

    Substantial non-Arrhenius behavior has been previously observed in the low temperature reaction between the hydroxyl radical and methanol. This behavior can be rationalized assuming the stabilization of an association adduct in the entrance channel of the reaction, from which barrier penetration via quantum mechanical tunneling produces the CH3O radical and H2O. Helium nanodroplet isolation and a serial pick-up technique are used to stabilize the hydrogen bonded prereactive OH··CH3OH complex. Mass spectrometry and infrared spectroscopy are used to confirm its production and probe the OH stretch vibrations. Stark spectroscopy reveals the magnitude of the permanent electric dipole moment, which is compared to ab initio calculations that account for wide-amplitude motion in the complex. The vibrationally averaged structure has Cs symmetry with the OH moiety hydrogen bonded to the hydroxyl group of methanol. Nevertheless, the zero-point level of the complex exhibits a wave function significantly delocalized over a bending coordinate leading to the transition state of the CH3O producing reaction.

  10. Hydrogen detection near surfaces and shallow interfaces with resonant nuclear reaction analysis

    NASA Astrophysics Data System (ADS)

    Wilde, Markus; Fukutani, Katsuyuki

    2014-12-01

    This review introduces hydrogen depth profiling by nuclear reaction analysis (NRA) via the resonant 1H(15N,αγ)12C reaction as a versatile method for the highly depth-resolved observation of hydrogen (H) at solid surfaces and interfaces. The technique is quantitative, non-destructive, and readily applied to a large variety of materials. Its fundamentals, instrumental requirements, advantages and limitations are described in detail, and its main performance benchmarks in terms of depth resolution and sensitivity are compared to those of elastic recoil detection (ERD) as a competing method. The wide range of 1H(15N,αγ)12C NRA applications in research of hydrogen-related phenomena at surfaces and interfaces is reviewed. Special emphasis is placed on the powerful combination of 1H(15N,αγ)12C NRA with surface science techniques of in-situ target preparation and characterization, as the NRA technique is ideally suited to investigate hydrogen interactions with atomically controlled surfaces and intact interfaces. In conjunction with thermal desorption spectroscopy, 15N NRA can assess the thermal stability of absorbed hydrogen species in different depth locations against diffusion and desorption. Hydrogen diffusion dynamics in the near-surface region, including transitions of hydrogen between the surface and the bulk, and between shallow interfaces of nanostructured thin layer stacks can directly be visualized. As a unique feature of 15N NRA, the analysis of Doppler-broadened resonance excitation curves allows for the direct measurement of the zero-point vibrational energy of hydrogen atoms adsorbed on single crystal surfaces.

  11. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

    Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

  12. Bimetallic promotion of cooperative hydrogen transfer and heteroatom removal in coal liquefaction

    SciTech Connect

    Eisch, J.J.

    1992-04-07

    The ultimate objective of this research has been to uncover novel reagents and experimental conditions for heteroatom removal and hydrogen transfer processes, which would be applicable to the liquefaction of coal under low-severity conditions. To this end, one phase of this research has investigated the cleavage of carbon-heteroatom bonds involving sulfur, oxygen, nitrogen and halogen by subvalent transition-metal complexes. A second phase of the study has assessed the capability of the same transition-metal complexes or of organoaluminum Lewis acids to catalyze the cleavage of carbon-hydrogen bonds in aromatics and hence to promote hydrogen shuttling. Finally, a third phase of our work has uncovered a remarkable synergistic effect of combinations of transition metals with organoaluminum Lewis acids on hydrogen shuttling between aromatics and hydroaromatics. (VC)

  13. MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

    SciTech Connect

    Burt, Scott Russell

    2008-01-01

    The power of magnetic resonance imaging (MRI) is its ability to image the internal structure of optically opaque samples and provide detailed maps of a variety of important parameters, such as density, diffusion, velocity and temperature. However, one of the fundamental limitations of this technique is its inherent low sensitivity. For example, the low signal to noise ratio (SNR) is particularly problematic for imaging gases in porous materials due to the low density of the gas and the large volume occluded by the porous material. This is unfortunate, as many industrially relevant chemical reactions take place at gas-surface interfaces in porous media, such as packed catalyst beds. Because of this severe SNR problem, many techniques have been developed to directly increase the signal strength. These techniques work by manipulating the nuclear spin populations to produce polarized} (i.e., non-equilibrium) states with resulting signal strengths that are orders of magnitude larger than those available at thermal equilibrium. This dissertation is concerned with an extension of a polarization technique based on the properties of parahydrogen. Specifically, I report on the novel use of heterogeneous catalysis to produce parahydrogen induced polarization and applications of this new technique to gas phase MRI and the characterization of micro-reactors. First, I provide an overview of nuclear magnetic resonance (NMR) and how parahydrogen is used to improve the SNR of the NMR signal. I then present experimental results demonstrating that it is possible to use heterogeneous catalysis to produce parahydrogen-induced polarization. These results are extended to imaging void spaces using a parahydrogen polarized gas. In the second half of this dissertation, I demonstrate the use of parahydrogen-polarized gas-phase MRI for characterizing catalytic microreactors. Specifically, I show how the improved SNR allows one to map parameters important for characterizing the heat and mass

  14. Examining the effect of nonlocality in (d ,n ) transfer reactions

    NASA Astrophysics Data System (ADS)

    Ross, A.; Titus, L. J.; Nunes, F. M.

    2016-07-01

    Background: In the past year we have been exploring the effect of the explicit inclusion of nonlocality in (d ,p ) reactions. Purpose: The goal of this paper is to extend previous studies to (d ,n ) reactions, which, although similar to (d ,p ) reactions, have specific properties that merit inspection. Method: We apply our methods (both the distorted-wave Born approximation and the adiabatic wave approximation) to (d ,n ) reactions on 16O,40Ca,48Ca,126Sn,132Sn , and 208Pb at 20 and 50 MeV. Results: We look separately at the modifications introduced by nonlocality in the final bound and scattering states as well as the consequences reflected on the differential angular distributions. The cross sections obtained when using nonlocality explicitly are significantly different than those using the local approximation, just as in (d ,p ) reactions. Due to the particular role of the Coulomb force in the bound state, often we found the effects of nonlocality to be larger in (d ,n ) than in (d ,p ) reactions. Conclusions: Our results confirm the importance of including nonlocality explicitly in deuteron-induced reactions.

  15. A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solutions based upon mixed quantum-classical approximation. I. Proton transfer reaction in water

    SciTech Connect

    Yamada, Atsushi; Kojima, Hidekazu; Okazaki, Susumu

    2014-08-28

    In order to investigate proton transfer reaction in solution, mixed quantum-classical molecular dynamics calculations have been carried out based on our previously proposed quantum equation of motion for the reacting system [A. Yamada and S. Okazaki, J. Chem. Phys. 128, 044507 (2008)]. Surface hopping method was applied to describe forces acting on the solvent classical degrees of freedom. In a series of our studies, quantum and solvent effects on the reaction dynamics in solutions have been analysed in detail. Here, we report our mixed quantum-classical molecular dynamics calculations for intramolecular proton transfer of malonaldehyde in water. Thermally activated proton transfer process, i.e., vibrational excitation in the reactant state followed by transition to the product state and vibrational relaxation in the product state, as well as tunneling reaction can be described by solving the equation of motion. Zero point energy is, of course, included, too. The quantum simulation in water has been compared with the fully classical one and the wave packet calculation in vacuum. The calculated quantum reaction rate in water was 0.70 ps{sup −1}, which is about 2.5 times faster than that in vacuum, 0.27 ps{sup −1}. This indicates that the solvent water accelerates the reaction. Further, the quantum calculation resulted in the reaction rate about 2 times faster than the fully classical calculation, which indicates that quantum effect enhances the reaction rate, too. Contribution from three reaction mechanisms, i.e., tunneling, thermal activation, and barrier vanishing reactions, is 33:46:21 in the mixed quantum-classical calculations. This clearly shows that the tunneling effect is important in the reaction.

  16. Activation of Electron-Deficient Quinones through Hydrogen-Bond-Donor-Coupled Electron Transfer.

    PubMed

    Turek, Amanda K; Hardee, David J; Ullman, Andrew M; Nocera, Daniel G; Jacobsen, Eric N

    2016-01-11

    Quinones are important organic oxidants in a variety of synthetic and biological contexts, and they are susceptible to activation towards electron transfer through hydrogen bonding. Whereas this effect of hydrogen bond donors (HBDs) has been observed for Lewis basic, weakly oxidizing quinones, comparable activation is not readily achieved when more reactive and synthetically useful electron-deficient quinones are used. We have successfully employed HBD-coupled electron transfer as a strategy to activate electron-deficient quinones. A systematic investigation of HBDs has led to the discovery that certain dicationic HBDs have an exceptionally large effect on the rate and thermodynamics of electron transfer. We further demonstrate that these HBDs can be used as catalysts in a quinone-mediated model synthetic transformation.

  17. Why Nature Eschews the Concerted [2 + 2 + 2] Cycloaddition of a Nonconjugated Cyanodiyne. Computational Study of a Pyridine Synthesis Involving an Ene – Diels-Alder – Bimolecular Hydrogen Transfer Mechanism

    PubMed Central

    Lan, Yu; Danheiser, Rick L.; Houk, K. N.

    2012-01-01

    An intramolecular formal metal-free intramolecular [2 + 2 + 2] cycloaddition for the formation of pyridines has been investigated with M06-2X and B3LYP density functional theory, and compared to the experimentally established three-step mechanism that involves ene reaction - Diels-Alder reaction -hydrogen transfer. The ene reaction of two alkynes is the rate-determining step. This is considerably easier than other possible mechanisms, such as those involving an ene reaction of an alkyne with a nitrile, a concerted [2 + 2 + 2] cycloaddition, or a 1,4-diradical mechanism. The relative facilities of these processes are analyzed with the distortion-interaction model. A bimolecular hydrogen transfer mechanism involving a radical pair intermediate is proposed rather than a concerted intramolecular 1,5-hydrogen shift for the last step in the mechanism. PMID:22188179

  18. Ion-ion reactions in the gas phase: Proton transfer reactions of protonated pyridine with multiply charged oligonucleotide anions.

    PubMed

    Herron, W J; Goeringer, D E; McLuckey, S A

    1995-06-01

    Isolated triply and doubly charged anions of the single-stranded deoxynucleotide 5'-d(AAAA)-3' were allowed to undergo ion-ion proton transfer reactions with protonated pyridine cations within a quadrupole ion trap mass spectrometer. Sufficiently high ion number densities and spatial overlap of the oppositely charged ion clouds could be achieved to yield readily measurable rates. Three general observations were made: (1) the ion-ion reaction rate constants were estimated to be 10(- (7 - 8)) cm(3) ion(-1) s(-1); (2) the ion-ion reaction rates were found to be dependent on the reactant ion number density, which could be controlled by both the reactant ion number and the pseudopotential well depth, and (3) very little fragmentation, if any, was observed, as might normally be expected with highly exothermic proton transfer reactions.

  19. A kinetic study on the adsorption and reaction of hydrogen over silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide

    SciTech Connect

    VanderWiel, D.P.

    1999-02-12

    Although the catalytic hydrogenation of carbon monoxide has been a subject of considerable investigation for many years, its increasing economical attractiveness as an industrial source of hydrocarbons has recently led to a search for more active and selective catalysts. A fundamental problem in the development of such catalysts is an incomplete knowledge of the operative surface processes, due in large part to the inability to accurately measure surface concentrations of reactant species during reaction. Specifically, the concentration of surface hydrogen proves difficult to estimate using normally revealing techniques such as transient isotopic exchange due to kinetic isotope effects. Knowledge of such concentrations is essential to the determination of the mechanisms of adsorption and reaction, since many kinetic parameters are concentration dependent. It is the aim of this research to investigate the mechanism and kinetics of the adsorption and reaction of hydrogen on silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide. By preadsorbing carbon monoxide onto the surface of ruthenium and silver-ruthenium catalysts, the kinetics of hydrogen adsorption and reaction can be monitored upon exposure of this surface to ambient hydrogen gas. This is accomplished by conducting identical experiments on two separate systems. First, the formation of methane is monitored using mass spectroscopy, and specific reaction rates and apparent activation energies are measured. Next, in situ {sup 1}H-NMR is used to monitor the amount of hydrogen present on the catalyst surface during adsorption and reaction. The results for these two sets of experiments are then combined to show a correlation between the rate of reaction and the surface hydrogen concentration. Finally, transition state theory is applied to this system and is used to explain the observed change in the apparent activation energy. The structure sensitivity of hydrogen

  20. Formation Of Cometary Hydrocarbons By Hydrogen Addition Reactions On Cold Grains

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hitomi; Watanabe, N.; Kawakita, H.; Fukushima, T.

    2012-10-01

    Hydrogen addition reactions on cold grains are considered to play an important role to form many kinds of volatiles in low temperature conditions like molecular clouds or early solar nebula. We can investigate the physical conditions (e.g., temperature, gas density, and etc.) of the early solar nebula via chemical properties of the pristine bodies like comets. The hydrocarbons like C2H2 and C2H6 have been studied so far and C2H6 might be a product of successive hydrogen addition of C2H2 on the cold grain. To evaluate the efficiency of hydrogen addition reactions from C2H2 to C2H6 quantitatively, we conducted laboratory measurements of those reactions under multiple conditions of the samples (on H2O ice) at different temperatures (10, 20, 30 K) with the LASSIE apparatus at Hokkaido University. Our results provide more detailed information about those reactions than previous quantitative studies. We discuss about the reaction rates with different samples and conditions.

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

    PubMed

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

    2015-07-01

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

  2. Note: Charge transfer in a hydrated peptide group is determined mainly by its intrinsic hydrogen-bond energetics

    SciTech Connect

    Mirkin, Noemi G.; Krimm, Samuel

    2014-01-28

    Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ωB97X-D/6-31++G** and CHelpG atomic charge calculations of individual peptide-water interactions as well as that of the entire complex. In the latter, the electron transfer to water is 0.19 e, influenced primarily by the hydrogen bonds to the C=O group. The values of such charge transfer are paralleled by the corresponding intrinsic hydrogen-bond energies. These results support the desirability of incorporating charge transfer in molecular mechanics energy functions.

  3. Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions.

    PubMed

    Gao, Zhe; Dong, Mei; Wang, Guizhen; Sheng, Pei; Wu, Zhiwei; Yang, Huimin; Zhang, Bin; Wang, Guofu; Wang, Jianguo; Qin, Yong

    2015-07-27

    To design highly efficient catalysts, new concepts for optimizing the metal-support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni-based nanocatalyst. The Ni nanoparticles are not only confined in Al2 O3 nanotubes, but also embedded in the cavities of Al2 O3 interior wall. The cavities create more Ni-Al2 O3 interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni-based catalyst supported on the outer surface of Al2 O3 nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD-assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.

  4. Uranium metal reactions with hydrogen and water vapour and the reactivity of the uranium hydride produced

    SciTech Connect

    Godfrey, H.; Broan, C.; Goddard, D.; Hodge, N.; Woodhouse, G.; Diggle, A.; Orr, R.

    2013-07-01

    Within the nuclear industry, metallic uranium has been used as a fuel. If this metal is stored in a hydrogen rich environment then the uranium metal can react with the hydrogen to form uranium hydride which can be pyrophoric when exposed to air. The UK National Nuclear Laboratory has been carrying out a programme of research for Sellafield Limited to investigate the conditions required for the formation and persistence of uranium hydride and the reactivity of the material formed. The experimental results presented here have described new results characterising uranium hydride formed from bulk uranium at 50 and 160 C. degrees and measurements of the hydrolysis kinetics of these materials in liquid water. It has been shown that there is an increase in the proportion of alpha-uranium hydride in material formed at lower temperatures and that there is an increase in the rate of reaction with water of uranium hydride formed at lower temperatures. This may at least in part be attributable to a difference in the reaction rate between alpha and beta-uranium hydride. A striking observation is the strong dependence of the hydrolysis reaction rate on the temperature of preparation of the uranium hydride. For example, the reaction rate of uranium hydride prepared at 50 C. degrees was over ten times higher than that prepared at 160 C. degrees at 20% extent of reaction. The decrease in reaction rate with the extent of reaction also depended on the temperature of uranium hydride preparation.

  5. Controlling bimolecular reactions: Mode and bond selected reaction of water with hydrogen atoms

    SciTech Connect

    Sinha, A.; Hsiao, M.C.; Crim, F.F. )

    1991-04-01

    Vibrational overtone excitation prepares water molecules in the {vert bar}13{r angle}{sup {minus}}, {vert bar}04{r angle}{sup {minus}}, {vert bar}12{r angle}{sup {minus}}, {vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}, and {vert bar}03{r angle}{sup {minus}} local mode states for a study of the influence of reagent vibration on the endothermic bimolecular reaction H+H{sub 2}O{r arrow}OH+H{sub 2}. The reaction of water molecules excited to the {vert bar}04{r angle}{sup {minus}} vibrational state predominantly produces OH({ital v}=0) while reaction from the {vert bar}13{r angle}{sup {minus}} state forms mostly OH({ital v}=1). These results support a spectator model for reaction in which the vibrational excitation of the products directly reflects the nodal pattern of the vibrational wave function in the energized molecule. Relative rate measurements for the three vibrational states {vert bar}03{r angle}{sup {minus}}, {vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}, and {vert bar}12{r angle}{sup {minus}}, which have similar total energies but correspond to very different distributions of vibrational energy, demonstrate the control that initially selected vibrations exert on reaction rates. The local mode stretching state {vert bar}03{r angle}{sup {minus}} promotes the H+H{sub 2}O reaction much more efficiently than either the state having part of its energy in bending excitation ({vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}) or the stretching state with the excitation shared between the two O--H oscillators ({vert bar}12{r angle}{sup {minus}}). The localized character of the vibrational overtone excitation in water has permitted the first observation of a bond selected bimolecular reaction using this approach.

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

    SciTech Connect

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

    2011-12-05

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

  7. Reaction engineering for materials processing in space: Reduction of ilmenite by hydrogen and carbon monoxide

    NASA Technical Reports Server (NTRS)

    Zhao, Y.; Shadman, F.

    1991-01-01

    Oxygen is a consumable material which needs to be produced continuously in most space missions. Its use for propulsion as well as life support makes oxygen one of the largest volume chemicals to be produced in space. Production of oxygen from lunar materials is of particular interest and is very attractive possibility. The kinetics and mechanism of reduction of ilmenite by carbon monoxide and hydrogen at 800 to 1100 C were investigated. The temporal profiles of conversion for carbon monoxide have a sigmoidal shape and indicate the presence of three different stages (induction, acceleration, and deceleration) during the reduction reaction. The apparent activation energy decreases from 18 kcal/mole at 10 percent conversion to 10 kcal/mole at 50 percent conversion. The reaction is first order with respect to carbon monoxide under the experimental conditions studied. Both SEM and EDX analysis show that the diffusion of Fe product away from the reaction front and through the TiO2 phase, followed by the nucleation and growth of a separate Fe phase are important steps affecting the process kinetics. The results from hydrogen reduction show that the mechanism of ilmenite reduction by hydrogen is similar to that by carbon monoxide. However, the titanium dioxide can be further reduced by hydrogen at 800 to 1000 C. The detailed comparison and theoretical modeling of both reduction processes is presented.

  8. A microwave study of hydrogen-transfer-triggered methyl-group rotation in 5-methyltropolone.

    PubMed

    Ilyushin, Vadim V; Cloessner, Emily A; Chou, Yung-Ching; Picraux, Laura B; Hougen, Jon T; Lavrich, Richard

    2010-11-14

    We present here the first experimental and theoretical study of the microwave spectrum of 5-methyltropolone, which can be visualized as a seven-membered "aromatic" carbon ring with a five-membered hydrogen-bonded cyclic structure at the top and a methyl group at the bottom. The molecule is known from earlier studies in the literature to exhibit two large-amplitude motions, an intramolecular hydrogen transfer and a methyl torsion. The former motion is particularly interesting because transfer of the hydrogen atom from the hydroxyl to the carbonyl group induces a tautomerization in the molecule, which then triggers a 60° internal rotation of the methyl group. Measurements were carried out by Fourier-transform microwave spectroscopy in the 8-24 GHz frequency range. Theoretical analysis was carried out using a tunneling-rotational Hamiltonian based on a G(12)(m) extended-group-theory formalism. Our global fit of 1015 transitions to 20 molecular parameters gave a root-mean-square deviation of 1.5 kHz. The tunneling splitting of the two J=0 levels arising from a hypothetical pure hydrogen-transfer motion is calculated to be 1310 MHz. The tunneling splitting of the two J=0 levels arising from a hypothetical pure methyl top internal-rotation motion is calculated to be 885 MHz. We have also carried out ab initio calculations, which support the structural parameters determined from our spectroscopic analysis and give estimates of the barriers to the two large-amplitude motions.

  9. Liquid Transfer Cryogenic Test Facility: Initial hydrogen and nitrogen no-vent fill data

    NASA Technical Reports Server (NTRS)

    Moran, Matthew E.; Nyland, Ted W.; Papell, S. Stephen

    1990-01-01

    The Liquid Transfer Cryogenic Test Facility is a versatile testbed for ground-based cryogenic fluid storage, handling, and transfer experimentation. The test rig contains two well instrumented tanks, and a third interchangeable tank, designed to accommodate liquid nitrogen or liquid hydrogen testing. The internal tank volumes are approx. 18, 5, and 1.2 cu. ft. Tank pressures can be varied from 2 to 30 psia. Preliminary no vent fill tests with nitrogen and hydrogen were successfully completed with the test rig. Initial results indicate that no vent fills of nitrogen above 90 percent full are achievable using this test configuration, in a 1-g environment, and with inlet liquid temperatures as high as 143 R, and an average tank wall temperature of nearly 300 R. This inlet temperature corresponds to a saturation pressure of 19 psia for nitrogen. Hydrogen proved considerably more difficult to transfer between tanks without venting. The highest temperature conditions resulting in a fill level greater than 90 percent were with an inlet liquid temperature of 34 R, and an estimated tank wall temperature of slightly more than 100 R. Saturation pressure for hydrogen at this inlet temperature is 10 psia. All preliminary no vent fill tests were performed with a top mounted full cone nozzle for liquid injection. The nozzle produces a 120 degree conical droplet spray at a differential pressure of 10 psi. Pressure in the receiving tank was held to less than 30 psia for all tests.

  10. Microwave Study of a Hydrogen-Transfer Methyl-Group Internal Rotation in 5-METHYLTROPOLONE

    NASA Astrophysics Data System (ADS)

    Ilyushin, Vadim V.; Cloessner, Emily A.; Chou, Yung-Ching; Picraux, Laura B.; Hougen, Jon T.; Lavrich, Richard

    2010-06-01

    We present here the first experimental and theoretical study of the microwave spectrum of 5-methyltropolone, which can be visualized as a 7-membered "aromatic" carbon ring with a five-membered hydrogen-bonded cyclic structure at the top and a methyl group at the bottom. The molecule exhibits two large-amplitude motions, an intramolecular hydrogen transfer and a methyl torsion. The former motion is particularly interesting because transfer of the hydrogen atom from the hydroxyl to the carbonyl group induces a tautomerization in the molecule, which then triggers a 60° internal rotation of the methyl group. Measurements were carried out by Fourier-transform microwave spectroscopy in the 8 to 24 GHz frequency range. Theoretical analysis was carried out using a tunneling-rotational Hamiltonian based on a G12^m extended-group-theory formalism. Our global fit of 1015 transitions to 20 molecular parameters gave a root-mean-square deviation of 1.5 kHz. The tunneling splitting of the two J = 0 levels arising from a hypothetical pure hydrogen transfer motion is calculated to be 1310 MHz. The tunneling splitting of the two J = 0 levels arising from a hypothetical pure methyl-top internal rotation motion is calculated to be 885 MHz. Some theoretical difficulties in interpreting the low-order tunneling parameters in this and the related molecule 2-methylmalonaldehyde will be discussed.

  11. Reactions of heavier main-group compounds with hydrogen, ammonia, ethylene and related small molecules.

    PubMed

    Power, Philip P

    2012-04-01

    The first reaction between hydrogen and a main-group compound under ambient conditions was reported in 2005. This unexpected result has been followed by numerous others which show that such reactivity is widespread in unsaturated and multiple bonded main-group species. These may react spontaneously not only with hydrogen, but also with ethylene, ammonia and related molecules. This account focuses on results from the author's laboratory but also on parallel work by other groups. The link between HOMO-LUMO separations, symmetry considerations and reactivity of the main-group species is emphasized as is their similarity in reactivity to transition-metal organometallic compounds.

  12. Optical radiation and ionization of hydrogen atoms in heterogeneous exothermal reactions proceeding in an electric field

    NASA Astrophysics Data System (ADS)

    Blashenkov, N. M.; Lavrent'ev, G. Ya.

    2009-09-01

    Optical radiation related to the Balmer series (Hα, Hβ, Hγ) of hydrogen atoms is discovered when studying the isothermal reaction of trimeric acetone peroxide decomposition on the surface of oxidized tungsten in a static electric field with a strength of up to 4 × 106 V/cm at T = 300 K. The distance from the surface over which desorbing excited hydrogen atoms radiate is determined from the Stark splitting of the lines. Electronically excited atoms remaining on the surface ionize according to the surface ionization mechanism.

  13. Recyclable polystyrene-supported siloxane-transfer agent for palladium-catalyzed cross-coupling reactions.

    PubMed

    Nguyen, Minh H; Smith, Amos B

    2014-04-01

    The rational design, synthesis, and validation of a significantly improved insoluble polymer-supported siloxane-transfer agent has been achieved that permits efficient palladium-catalyzed cross-coupling reactions. The cross-linked polystyrene support facilitates product purification with excellent siloxane recycling. Drawbacks of a previous polymer-supported siloxane-transfer agent, relating to reaction efficiency and polymer stability after repeated cycles, have been addressed.

  14. Recyclable Polystyrene-Supported Siloxane-Transfer Agent for Palladium-Catalyzed Cross-Coupling Reactions

    PubMed Central

    2015-01-01

    The rational design, synthesis, and validation of a significantly improved insoluble polymer-supported siloxane-transfer agent has been achieved that permits efficient palladium-catalyzed cross-coupling reactions. The cross-linked polystyrene support facilitates product purification with excellent siloxane recycling. Drawbacks of a previous polymer-supported siloxane-transfer agent, relating to reaction efficiency and polymer stability after repeated cycles, have been addressed. PMID:24661113

  15. Structure of Light Neutron-rich Nuclei Studied with Transfer Reactions

    SciTech Connect

    Wuosmaa, A. H.

    2015-01-01

    Transfer reactions have been used for many years to understand the shell structure of nuclei. Recent studies with rare-isotope beams extend this work and make it possible to probe the evolution of shell structure far beyond the valley of stability, requiring measurements in inverse kinematics. We present a novel technical approach to measurements in inverse kinematics, and apply this method to different transfer reactions, each of which probes different properties of light, neutron-rich nuclei.

  16. Photoelectron Spectroscopy of Transition Metal Hydride Cluster Anions and Their Roles in Hydrogenation Reactions

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxing; Bowen, Kit

    The interaction between transition metals and hydrogen has been an intriguing research topic for such applications as hydrogen storage and catalysis of hydrogenation and dehydrogenation. Special bonding features between TM and hydrogen are interesting not only because they are scarcely reported but also because they could help to discover and understand the nature of chemical bonding. Very recently, we discovered a PtZnH5- cluster which possessed an unprecedented planar pentagonal coordination between the H5- moiety and Pt, and exhibited special σ-aromaticity. The H5-kernel as a whole can be viewed as a η5-H5 ligand for Pt. As the second example, an H2 molecule was found to act as a ligand in the PdH3-cluster, in which two H atoms form a η2-H2 type of ligation to Pd. These transition metal hydride clusters were considered to be good hydrogen sources for hydrogenation. The reactions between PtHn- and CO2 were investigated. We observed formate in the final product H2Pt(HCO2)- .

  17. Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects.

    PubMed

    Martínez-González, Eduardo; Frontana, Carlos

    2014-05-01

    In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, λi,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k. PMID:24653999

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

    PubMed

    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

  19. Interfacial engineering of MoS2/TiO2 hybrids for enhanced electrocatalytic hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Song, Xiaolin; Chen, Guifeng; Guan, Lixiu; Zhang, Hui; Tao, Junguang

    2016-09-01

    Herein, we show that the synergistic effect between MoS2 and TiO2 enhances the hydrogen evolution reaction (HER) performance of their hybrids, which is tunable via interface engineering. Among several interfaces, MoS2/TiO2–H complexes exhibit the best HER activity. The observed Tafel slope of 66.9 mV/dec is well in range of previous literature reports, suggesting a Volmer–Heyrovsky mechanism. Enhanced activities were attributed to abundant active sites at the interfaces, as well as improved charge transfer efficiency. Our results emphasize the roles that interfaces play in enhancing the HER activities of MoS2-based heterogeneous catalysts.

  20. Interfacial engineering of MoS2/TiO2 hybrids for enhanced electrocatalytic hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Song, Xiaolin; Chen, Guifeng; Guan, Lixiu; Zhang, Hui; Tao, Junguang

    2016-09-01

    Herein, we show that the synergistic effect between MoS2 and TiO2 enhances the hydrogen evolution reaction (HER) performance of their hybrids, which is tunable via interface engineering. Among several interfaces, MoS2/TiO2-H complexes exhibit the best HER activity. The observed Tafel slope of 66.9 mV/dec is well in range of previous literature reports, suggesting a Volmer-Heyrovsky mechanism. Enhanced activities were attributed to abundant active sites at the interfaces, as well as improved charge transfer efficiency. Our results emphasize the roles that interfaces play in enhancing the HER activities of MoS2-based heterogeneous catalysts.

  1. Novel molybdenum disulfide nanosheets-decorated polyaniline: Preparation, characterization and enhanced electrocatalytic activity for hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Ding, Shuangshuang; He, Ping; Feng, Wanru; Li, Lian; Zhang, Guangli; Chen, Jingchao; Dong, Faqin; He, Huichao

    2016-04-01

    Novel molybdenum disulfide nanosheets-decorated polyaniline (MoS2/PANI) was synthesized and investigated as an efficient catalyst for hydrogen evolution reaction (HER). Compared with MoS2, MoS2/PANI nanocomposites exhibited higher catalytic activity and lower Tafel slope for HER in H2SO4 solution. The amount of 19 wt% PANI for coupling with MoS2 resulted in a high current density of 80 mA cm-2 at 400 mV (vs. RHE). In addition, the optimal MoS2/PANI nanocomposite showed impressive long-term stability even after 500 cycles. The enhanced catalytic activity of MoS2/PANI nanocomposites was primarily ascribed to the effective electron transport channels of PANI and the increase of electrochemically accessible surface area in composite materials, which was advantageous to facilitate the charge transfer at catalyst/electrolyte interface.

  2. Metallic Iron-Nickel Sulfide Ultrathin Nanosheets As a Highly Active Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media.

    PubMed

    Long, Xia; Li, Guixia; Wang, Zilong; Zhu, HouYu; Zhang, Teng; Xiao, Shuang; Guo, Wenyue; Yang, Shihe

    2015-09-23

    We report on the synthesis of iron-nickel sulfide (INS) ultrathin nanosheets by topotactic conversion from a hydroxide precursor. The INS nanosheets exhibit excellent activity and stability in strong acidic solutions as a hydrogen evolution reaction (HER) catalyst, lending an attractive alternative to the Pt catalyst. The metallic α-INS nanosheets show an even lower overpotential of 105 mV at 10 mA/cm(2) and a smaller Tafel slope of 40 mV/dec. With the help of DFT calculations, the high specific surface area, facile ion transport and charge transfer, abundant electrochemical active sites, suitable H(+) adsorption, and H2 formation kinetics and energetics are proposed to contribute to the high activity of the INS ultrathin nanosheets toward HER.

  3. Metallic Iron-Nickel Sulfide Ultrathin Nanosheets As a Highly Active Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media.

    PubMed

    Long, Xia; Li, Guixia; Wang, Zilong; Zhu, HouYu; Zhang, Teng; Xiao, Shuang; Guo, Wenyue; Yang, Shihe

    2015-09-23

    We report on the synthesis of iron-nickel sulfide (INS) ultrathin nanosheets by topotactic conversion from a hydroxide precursor. The INS nanosheets exhibit excellent activity and stability in strong acidic solutions as a hydrogen evolution reaction (HER) catalyst, lending an attractive alternative to the Pt catalyst. The metallic α-INS nanosheets show an even lower overpotential of 105 mV at 10 mA/cm(2) and a smaller Tafel slope of 40 mV/dec. With the help of DFT calculations, the high specific surface area, facile ion transport and charge transfer, abundant electrochemical active sites, suitable H(+) adsorption, and H2 formation kinetics and energetics are proposed to contribute to the high activity of the INS ultrathin nanosheets toward HER. PMID:26338434

  4. Estimation of free energy barriers in the cytoplasmic and mitochondrial aspartate aminotransferase reactions probed by hydrogen-exchange kinetics of C alpha-labeled amino acids with solvent

    SciTech Connect

    Julin, D.A.; Wiesinger, H.; Toney, M.D.; Kirsch, J.F. )

    1989-05-02

    The existence of the postulated quinonoid intermediate in the cytoplasmic aspartate amino-transferase catalyzed transamination of aspartate to oxaloacetate was probed by determining the extent of transfer of tritium from the C alpha position of tritiated L-aspartate to pyridoxamine 5'-phosphate in single turnover experiments in which washout from the back-reaction was obviated by product trapping. The maximum amount of transferred tritium observed was 0.7%, consistent either with a mechanism in which a fraction of the net transamination reaction proceeds through a quinonoid intermediate or with a mechanism in which this intermediate is formed off the main reaction pathway. It is shown that transfer of labeled hydrogen from the amino acid to cofactor cannot be used to differentiate a stepwise from a concerted transamination mechanism. The amount of tritium transferred is a function of the rate constant for torsional equilibration about the epsilon-amino group of Lys-258, the presumptive abstractor of the C alpha proton; the relative rate constants for hydrogen exchange with solvent versus cofactor protonation; and the tritium isotope effect on this ratio. The free energy barriers facing the covalent intermediate between aldimine and keto acid product (i.e., ketimine and possibly quinonoid) were evaluated relatively by comparing the rates of C alpha-hydrogen exchange in starting amino acid with the rates of keto acid formation. The value of theta (= kexge/kprod) was found to be 2.6 for the reaction of cytoplasmic isozyme with aspartate and ca. 0.5 for that of the mitochondrial form with glutamate.

  5. Effect of photosensitizer and hydrogen peroxide on desulfurization of light oil by photochemical reaction and liquid-liquid extraction

    SciTech Connect

    Hirai, Takayuki; Shiraishi, Yasuhiro; Ogawa, Ken; Komasawa, Isao

    1997-03-01

    A desulfurization process for dibenzothiophene (DBT) by a combination of photochemical reaction and liquid-liquid extraction has been investigated. The DBT dissolved in tetradecane was photodecomposed by the use of a high-pressure mercury lamp and removed into the water phase at conditions of room temperature and atmospheric pressure. The addition of benzophenone (BZP), a triplet photosensitizer, enhanced the removal of DBT from tetradecane. This reaction, however, hardly proceeded in the presence of naphthalene (NP), probably because of triplet energy transfer from photoexcited DBT or BZP to ground-state NP. The addition of hydrogen peroxide enhanced the desulfurization of commercial light oil as well as the removal of DBT from tetradecane, since H{sub 2}O{sub 2} acted as a weak oxidizing agent for photoexcited DBT and interrupted the energy transfer from excited DBT to NP to some extent. In the case using a 30% H{sub 2}O{sub 2} solution, the desulfurization yield of commercial light oil was 75% following 24 h of photoirradiation and the sulfur content in the light oil was reduced from 0.2 wt % to less than 0.05 wt %.

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

    PubMed

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

    2014-01-21

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

  7. Catalytic conversion of polycyclic aromatic hydrocarbons: Mechanistic investigations of hydrogen transfer from an iron-based catalyst to alkylarenes

    SciTech Connect

    Autrey, T.; Linehan, J.C.; Camaioni, D.M.

    1995-12-31

    The mechanisms of hydrogen transfer from iron/sulfur-based catalysts to a series of coal model compounds have been investigated. The iron oxyhydroxides catalyst precursors are produced by the RTDS method with the actual catalytic species, an iron/sulfur catalyst, generated in situ by addition of sulfur and a hydrogen donor solvent. These catalysts promote the selective scission of thermally stable carbon-carbon bonds. Both the rate and the selectivity of catalytic induced bond scission are enhanced relative to the thermal hydrogen transfer pathways in 9,10-dihydrophenanthrene donor solvent. The reactivity of alkylated diphenylmethanes and derivatives of 1,2-diphenylethanol support a non-ionic free radical hydrogen transfer pathway. The selectivity of catalytic engendered bond scission is rationalized by an ipso displacement mechanism competing with a back-hydrogen transfer to the catalytic surface. This mechanism explains the scission of thermal stable coal linkages without the formation of light gases.

  8. Population of mixed-symmetry states via {alpha} transfer reactions

    SciTech Connect

    Alonso, C. E.; Arias, J. M.; Fortunato, L.; Vitturi, A.; Pietralla, N.

    2008-07-15

    Within the neutron-proton interacting boson model we study the population of mixed-symmetry states via {alpha} transfer processes. Closed expressions are deduced in the case of the limiting U{sub {pi}}{sub +{nu}}(5) and SU{sub {pi}}{sub +{nu}}(3). We find that the population of the lowest mixed-symmetry 2{sup +} state, vanishing along the N{sub {pi}}=N{sub {nu}} line, depends on the number of active bosons and is normally smaller than that of the lowest full symmetric 2{sup +} state. In particular, for deformed nuclei where the number of bosons is normally large, the relative population of the mixed-symmetry 2{sup +} state is of the order of a few percent. More favorable cases can be found near shell closures, as in the case of {alpha} transfer leading to {sup 140}Ba.

  9. Ab initio molecular dynamics simulations for the role of hydrogen in catalytic reactions of furfural on Pd(111)

    NASA Astrophysics Data System (ADS)

    Xue, Wenhua; Dang, Hongli; Liu, Yingdi; Jentoft, Friederike; Resasco, Daniel; Wang, Sanwu

    2014-03-01

    In the study of catalytic reactions of biomass, furfural conversion over metal catalysts with the presence of hydrogen has attracted wide attention. We report ab initio molecular dynamics simulations for furfural and hydrogen on the Pd(111) surface at finite temperatures. The simulations demonstrate that the presence of hydrogen is important in promoting furfural conversion. In particular, hydrogen molecules dissociate rapidly on the Pd(111) surface. As a result of such dissociation, atomic hydrogen participates in the reactions with furfural. The simulations also provide detailed information about the possible reactions of hydrogen with furfural. Supported by DOE (DE-SC0004600). This research used the supercomputer resources of the XSEDE, the NERSC Center, and the Tandy Supercomputing Center.

  10. Kinetic energy release in thermal ion--molecule reactions: The Nb sup 2+ --(benzene) single charge--transfer reaction

    SciTech Connect

    Gord, J.R.; Freiser, B.S. ); Buckner, S.W. )

    1991-03-15

    We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge--transfer reaction of Nb{sup 2+} with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism, in which the reactants approach on an ion-induced dipole attractive potential and cross to a repulsive potential at a critical separation of {similar to}7.5 A when electron transfer occurs. The reaction exothermicity, 5.08 eV, is partitioned to translation of Nb{sup +} , 0.81{plus minus}0.25 eV, translation of C{sub 6} H{sub 6}{sup +}, 1.22{plus minus}0.25 eV, and internal excitation of C{sub 6} H{sub 6}{sup +} to produce the la{sub 2{ital u}} electronic state, which is {similar to}3 eV above the ground state of the ion. We have also studied the kinetics of the reaction of Nb{sup 2+} with benzene and determined the rate constant, {ital k} = 1.4{times}10{sup {minus}9} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, and the efficiency, 0.60, of the process. These also support the proposed charge--transfer mechanism. In addition to the charge--transfer pathway, which accounts for 95% of the reaction products, Nb{sup 2+} is observed to dehydrogenate benzene to form Nb{sup 2+} (benzyne). This process implies {ital D}(Nb{sup 2+} --benzyne){ge}79 kcal/mol.

  11. Resonant charge transfer of hydrogen Rydberg atoms incident at a metallic sphere

    NASA Astrophysics Data System (ADS)

    Gibbard, J. A.; Softley, T. P.

    2016-06-01

    A wavepacket propagation study is reported for the charge transfer of low principal quantum number (n = 2) hydrogen Rydberg atoms incident at an isolated metallic sphere. Such a sphere acts as a model for a nanoparticle. The three-dimensional confinement of the sphere yields discrete surface-localized ‘well-image’ states, the energies of which vary with sphere radius. When the Rydberg atom energy is degenerate with one of the quantized nanoparticle states, charge transfer is enhanced, whereas for off-resonant cases little to no charge transfer is observed. Greater variation in charge-transfer probability is seen between the resonant and off-resonant examples in this system than for any other Rydberg-surface system theoretically investigated thus far. The results presented here indicate that it may be possible to use Rydberg-surface ionization as a probe of the surface electronic structure of a nanoparticle, and nanostructures in general.

  12. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation. [Spiropyrans

    SciTech Connect

    Schwartz, B.J.

    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 [approximately]240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH[sub 2]I[sub 2] and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a [approximately]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.

  13. A cobalt(ii) iminoiodane complex and its scandium adduct: mechanistic promiscuity in hydrogen atom abstraction reactions.

    PubMed

    Kundu, Subrata; Chernev, Petko; Engelmann, Xenia; Chung, Chan Siu; Dau, Holger; Bill, Eckhard; England, Jason; Nam, Wonwoo; Ray, Kallol

    2016-10-01

    In addition to oxometal [M(n+)[double bond, length as m-dash]O] and imidometal [M(n+)[double bond, length as m-dash]NR] units, transient metal-iodosylarene [M((n-2)+)-O[double bond, length as m-dash]IPh] and metal-iminoiodane [M((n-2)+)-N(R)[double bond, length as m-dash]IPh] adducts are often invoked as a possible "second oxidant" responsible for the oxo and imido group transfer reactivity. Although a few metal-iodosylarene adducts have been recently isolated and/or spectroscopically characterized, metal-iminoiodane adducts have remained elusive. Herein, we provide UV-Vis, EPR, NMR, XAS and DFT evidence supporting the formation of a metal-iminoiodane complex 2 and its scandium adduct 2-Sc. 2 and 2-Sc are reactive toward substrates in the hydrogen-atom and nitrene transfer reactions, which confirm their potential as active oxidants in metal-catalyzed oxidative transformations. Oxidation of para-substituted 2,6-di-tert-butylphenols by 2 and 2-Sc can occur by both coupled and uncoupled proton and electron transfer mechanisms; the exact mechanism depends on the nature of the para substituent.

  14. A cobalt(ii) iminoiodane complex and its scandium adduct: mechanistic promiscuity in hydrogen atom abstraction reactions.

    PubMed

    Kundu, Subrata; Chernev, Petko; Engelmann, Xenia; Chung, Chan Siu; Dau, Holger; Bill, Eckhard; England, Jason; Nam, Wonwoo; Ray, Kallol

    2016-10-01

    In addition to oxometal [M(n+)[double bond, length as m-dash]O] and imidometal [M(n+)[double bond, length as m-dash]NR] units, transient metal-iodosylarene [M((n-2)+)-O[double bond, length as m-dash]IPh] and metal-iminoiodane [M((n-2)+)-N(R)[double bond, length as m-dash]IPh] adducts are often invoked as a possible "second oxidant" responsible for the oxo and imido group transfer reactivity. Although a few metal-iodosylarene adducts have been recently isolated and/or spectroscopically characterized, metal-iminoiodane adducts have remained elusive. Herein, we provide UV-Vis, EPR, NMR, XAS and DFT evidence supporting the formation of a metal-iminoiodane complex 2 and its scandium adduct 2-Sc. 2 and 2-Sc are reactive toward substrates in the hydrogen-atom and nitrene transfer reactions, which confirm their potential as active oxidants in metal-catalyzed oxidative transformations. Oxidation of para-substituted 2,6-di-tert-butylphenols by 2 and 2-Sc can occur by both coupled and uncoupled proton and electron transfer mechanisms; the exact mechanism depends on the nature of the para substituent. PMID:27465222

  15. Unsupported Nanoporous Gold Catalyst for Chemoselective Hydrogenation Reactions under Low Pressure: Effect of Residual Silver on the Reaction.

    PubMed

    Takale, Balaram S; Feng, Xiujuan; Lu, Ye; Bao, Ming; Jin, Tienan; Minato, Taketoshi; Yamamoto, Yoshinori

    2016-08-17

    For the first time, H-H dissociation on an unsupported nanoporous gold (AuNPore) surface is reported for chemoselective hydrogenation of C≡C, C═C, C═N, and C═O bonds under mild conditions (8 atm H2 pressure, 90 °C). Silver doping in AuNPore, which was inevitable for its preparation through a process of dealloying of Au-Ag alloy, exhibited a remarkable difference in catalytic activity between two catalysts, Au>99Ag1NPore and Au90Ag10NPore.The former was more active and the latter less active in H2 hydrogenation, while the reverse tendency was observed for O2 oxidation. This marked contrast between H2 reduction and O2 oxidation is discussed. Further, Au>99Ag1NPore showed a high chemoselectivity toward reduction of terminal alkynes in the presence of internal alkynes which was not achieved using supported gold nanoparticle catalysts and other previously known methods. Reductive amination, which has great significance in synthesis of amines due to its atom-economical nature, was also realized using Au>99Ag1NPore, and the Au>99Ag1NPore/H2 system showed a preference for the reduction of aldehydes in the presence of imines. In addition to this high chemoselectivity, easy recovery and high reusability of AuNPore make it a promising heterogeneous catalyst for hydrogenation reactions. PMID:27430955

  16. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches

    SciTech Connect

    Wasielewski, M.R.

    1992-01-01

    Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

  17. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches

    SciTech Connect

    Wasielewski, M.R.

    1992-08-01

    Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

  18. Two-dimensional boron: Lightest catalyst for hydrogen and oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Mir, Showkat H.; Chakraborty, Sudip; Jha, Prakash C.; Wärnâ, John; Soni, Himadri; Jha, Prafulla K.; Ahuja, Rajeev

    2016-08-01

    The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) have been envisaged on a two-dimensional (2D) boron sheet through electronic structure calculations based on a density functional theory framework. To date, boron sheets are the lightest 2D material and, therefore, exploring the catalytic activity of such a monolayer system would be quite intuitive both from fundamental and application perspectives. We have functionalized the boron sheet (BS) with different elemental dopants like carbon, nitrogen, phosphorous, sulphur, and lithium and determined the adsorption energy for each case while hydrogen and oxygen are on top of the doping site of the boron sheet. The free energy calculated from the individual adsorption energy for each functionalized BS subsequently guides us to predict which case of functionalization serves better for the HER or the OER.

  19. A diabatic state model for double proton transfer in hydrogen bonded complexes

    SciTech Connect

    McKenzie, Ross H.

    2014-09-14

    Four diabatic states are used to construct a simple model for double proton transfer in hydrogen bonded complexes. Key parameters in the model are the proton donor-acceptor separation R and the ratio, D{sub 1}/D{sub 2}, between the proton affinity of a donor with one and two protons. Depending on the values of these two parameters the model describes four qualitatively different ground state potential energy surfaces, having zero, one, two, or four saddle points. Only for the latter are there four stable tautomers. In the limit D{sub 2} = D{sub 1} the model reduces to two decoupled hydrogen bonds. As R decreases a transition can occur from a synchronous concerted to an asynchronous concerted to a sequential mechanism for double proton transfer.

  20. Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid.

    PubMed

    Boatright, William L

    2016-04-01

    The effect of oxygen on the two separate one-electron reactions involved in the oxidation of ascorbic acid was investigated. The rate of ascorbate radical (Asc(-)) formation (and stability) was strongly dependent on the presence of oxygen. A product of ascorbic acid oxidation was measurable levels of hydrogen peroxide, as high as 32.5 μM from 100 μM ascorbic acid. Evidence for a feedback mechanism where hydrogen peroxide generated during the oxidation of ascorbic acid accelerates further oxidation of ascorbic acid is also presented. The second one-electron oxidation reaction of ascorbic acid leading to the disappearance of Asc(-) was also strongly inhibited in samples flushed with argon. In the range of 0.05-1.2 mM ascorbic acid, maximum levels of measurable hydrogen peroxide were achieved with an initial concentration of 0.2 mM ascorbic acid. Hydrogen peroxide generation was greatly diminished at ascorbic acid levels of 0.8 mM or above.

  1. Hydrodesulphurization of Light Gas Oil using hydrogen from the Water Gas Shift Reaction

    NASA Astrophysics Data System (ADS)

    Alghamdi, Abdulaziz

    2009-12-01

    The production of clean fuel faces the challenges of high production cost and complying with stricter environmental regulations. In this research, the ability of using a novel technology of upgrading heavy oil to treat Light Gas Oil (LGO) will be investigated. The target of this project is to produce cleaner transportation fuel with much lower cost of production. Recently, a novel process for upgrading of heavy oil has been developed at University of Waterloo. It is combining the two essential processes in bitumen upgrading; emulsion breaking and hydroprocessing into one process. The water in the emulsion is used to generate in situ hydrogen from the Water Gas Shift Reaction (WGSR). This hydrogen can be used for the hydrogenation and hydrotreating reaction which includes sulfur removal instead of the expensive molecular hydrogen. This process can be carried out for the upgrading of the bitumen emulsion which would improve its quality. In this study, the hydrodesulphurization (HDS) of LGO was conducted using in situ hydrogen produced via the Water Gas Shift Reaction (WGSR). The main objective of this experimental study is to evaluate the possibility of producing clean LGO over dispersed molybdenum sulphide catalyst and to evaluate the effect of different promoters and syn-gas on the activity of the dispersed Mo catalyst. Experiments were carried out in a 300 ml Autoclave batch reactor under 600 psi (initially) at 391°C for 1 to 3 hours and different amounts of water. After the hydrotreating reaction, the gas samples were collected and the conversion of carbon monoxide to hydrogen via WGSR was determined using a refinery gas analyzer. The sulphur content in liquid sample was analyzed via X-Ray Fluorescence. Experimental results showed that using more water will enhance WGSR but at the same time inhibits the HDS reaction. It was also shown that the amount of sulfur removed depends on the reaction time. The plan is to investigate the effect of synthesis gas (syngas

  2. Neutron Transfer Reactions: Surrogates for Neutron Capture for Basic and Applied Nuclear Science

    NASA Astrophysics Data System (ADS)

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, S. D.; Peters, W. A.; Adekola, A.; Allen, J.; Bardayan, D. W.; Becker, J. A.; Blackmon, J. C.; Chae, K. Y.; Chipps, K. A.; Erikson, L.; Gaddis, A.; Harlin, C.; Hatarik, R.; Howard, J.; Jandel, M.; Johnson, M. S.; Kapler, R.; Krolas, W.; Liang, F.; Livesay, R. J.; Ma, Z.; Matei, C.; Matthews, C.; Moazen, B.; Nesaraja, C. D.; O'Malley, P.; Patterson, N.; Paulauskas, S. V.; Pelham, T.; Pittman, S. T.; Radford, D.; Rogers, J.; Schmitt, K.; Shapira, D.; Shriner, J. F.; Sissom, D. J.; Smith, M. S.; Swan, T.; Thomas, J. S.; Vieira, D. J.; Wilhelmy, J. B.; Wilson, G. L.

    2009-03-01

    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 130,132Sn, 134Te and 75As are discussed.

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

    SciTech Connect

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, Steven D; Peters, W. A.; Adekola, Aderemi S; Allen, J.; Bardayan, Daniel W; Becker, J.; Blackmon, Jeff C; Chae, K. Y.; Chipps, K.; Erikson, Luke; Gaddis, A. L.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; Jandel, M.; Johnson, Micah; Kapler, R.; Krolas, W.; Liang, J Felix; Livesay, Jake; Ma, Zhanwen; Matei, Catalin; Matthews, C.; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Patterson, N. P.; Paulauskas, Stanley; Pelham, T.; Pittman, S. T.; Radford, David C; Rogers, J.; Schmitt, Kyle; Shapira, Dan; ShrinerJr., J. F.; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Thomas, J. S.; Vieira, D. J.; Wilhelmy, J. B.; Wilson, Gemma L

    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.

  4. Active Site Dynamical Effects in the Hydrogen Transfer Rate-limiting Step in the Catalysis of Linoleic Acid by Soybean Lipoxygenase-1 (SLO-1): Primary and Secondary Isotope Contributions.

    PubMed

    Phatak, Prasad; Venderley, Jordan; Debrota, John; Li, Junjie; Iyengar, Srinivasan S

    2015-07-30

    Using ab initio molecular dynamics (AIMD) simulations that facilitate the treatment of rare events, we probe the active site participation in the rate-determining hydrogen transfer step in the catalytic oxidation of linoleic acid by soybean lipoxygenase-1 (SLO-1). The role of two different active site components is probed. (a) On the hydrogen atom acceptor side of the active site, the hydrogen bonding propensity between the acceptor side hydroxyl group, which is bound to the iron cofactor, and the backbone carboxyl group of isoleucine (residue number 839) is studied toward its role in promoting the hydrogen transfer event. Primary and secondary (H/D) isotope effects are also probed and a definite correlation with subtle secondary H/D isotope effects is found. With increasing average nuclear kinetic energy, the increase in transfer probability is enhanced due to the presence of the hydrogen bond between the backbone carbonyl of I839 and the acceptor oxygen. Further increase in average nuclear kinetic energy reduces the strength of this secondary hydrogen bond which leads to a deterioration in hydrogen transfer rates and finally embrances an Arrhenius-like behavior. (b) On the hydrogen atom donor side, the coupling between vibrational modes predominantly localized on the donor-side linoleic acid group and the reactive mode is probed. There appears to be a qualitative difference in the coupling between modes that belong to linoleic acid and the hydrogen transfer mode, for hydrogen and deuterium transfer. For example, the donor side secondary hydrogen atom is much more labile (by nearly a factor of 5) during deuterium transfer as compared to the case for hydrogen transfer. This appears to indicate a greater coupling between the modes belonging to the linoleic acid scaffold and the deuterium transfer mode and also provides a new rationalization for the abnormal (nonclassical) secondary isotope effect results obtained by Knapp, Rickert, and Klinman in J. Am. Chem. Soc

  5. Role of Carbon-Addition and Hydrogen-Migration Reactions in Soot Surface Growth.

    PubMed

    Zhang, Hong-Bo; Hou, Dingyu; Law, Chung K; You, Xiaoqing

    2016-02-11

    Using density functional theory and master equation modeling, we have studied the kinetics of small unsaturated aliphatic molecules reacting with polycyclic aromatic hydrocarbon (PAH) molecules having a diradical character. We have found that these reactions follow the mechanism of carbon addition and hydrogen migration (CAHM) on both spin-triplet and open-shell singlet potential energy surfaces at a rate that is about ten times those of the hydrogen-abstraction-carbon-addition (HACA) reactions at 1500 K in the fuel-rich postflame region. The results also show that the most active reaction sites are in the center of the zigzag edges of the PAHs. Furthermore, the reaction products are more likely to form straight rather than branched aliphatic side chains in the case of reacting with diacetylene. The computed rate constants are also found to be independent of pressure at conditions of interest in soot formation, and the activation barriers of the CAHM reactions are linearly correlated with the diradical characters.

  6. Role of Carbon-Addition and Hydrogen-Migration Reactions in Soot Surface Growth.

    PubMed

    Zhang, Hong-Bo; Hou, Dingyu; Law, Chung K; You, Xiaoqing

    2016-02-11

    Using density functional theory and master equation modeling, we have studied the kinetics of small unsaturated aliphatic molecules reacting with polycyclic aromatic hydrocarbon (PAH) molecules having a diradical character. We have found that these reactions follow the mechanism of carbon addition and hydrogen migration (CAHM) on both spin-triplet and open-shell singlet potential energy surfaces at a rate that is about ten times those of the hydrogen-abstraction-carbon-addition (HACA) reactions at 1500 K in the fuel-rich postflame region. The results also show that the most active reaction sites are in the center of the zigzag edges of the PAHs. Furthermore, the reaction products are more likely to form straight rather than branched aliphatic side chains in the case of reacting with diacetylene. The computed rate constants are also found to be independent of pressure at conditions of interest in soot formation, and the activation barriers of the CAHM reactions are linearly correlated with the diradical characters. PMID:26799641

  7. Electron-transfer reaction of cinnamic acids and their methyl esters with the DPPH(*) radical in alcoholic solutions.

    PubMed

    Foti, Mario C; Daquino, Carmelo; Geraci, Corrada

    2004-04-01

    The kinetic behavior of cinnamic acids, their methyl esters, and two catechols 1-10 (ArOH) in the reaction with DPPH(*) in methanol and ethanol is not compatible with a reaction mechanism that involves hydrogen atom abstraction from the hydroxyl group of 1-10 by DPPH(*). The rate of this reaction at 25 degrees C is, in fact, comparatively fast despite that the phenolic OH group of ArOH is hydrogen bonded to solvent molecules. The observed rate constants (k(1)) relative to DPPH(*) + ArOH are 3-5 times larger for the methyl esters than for the corresponding free acids and, for the latter, decrease as their concentration is increased according to the relation k(1) = B/[ArOH](0)(m), where k(1) is given in units of M(-1) s(-1), m is ca. 0.5, and B ranges from 0.02 (p-coumaric acid) to ca. 3.48 (caffeic acid) in methanol and from 0.04 (p-coumaric acid) to ca. 13 (sinapic acid) in ethanol. Apparently, the reaction mechanism of DPPH(*) + ArOH involves a fast electron-transfer process from the phenoxide anion of 1-10 to DPPH(*). Kinetic analysis of the reaction sequence for the free acids leads to an expression for the observed rate constant, k(1), proportional to [ArOH](0)(-1/2) in excellent agreement with the experimental behavior of these phenols. The experimental results are also interpreted in terms of the influence that adventitious acids or bases present in the solvent may have. These impurities dramatically influence the ionization equilibrium of phenols and cause a reduction or an enhancement, respectively, of the measured rate constants. PMID:15049623

  8. Applications of nuclear reaction analysis for determining hydrogen and deuterium distribution in metals

    SciTech Connect

    Altstetter, C.J.

    1981-01-01

    The use of ion beams for materials analysis has made a successful transition from the domain of the particle physicist to that of the materials scientist. The subcategory of this field, nuclear reaction analysis, is just now undergoing the transition, particularly in applications to hydrogen in materials. The materials scientist must locate the nearest accelerator, because now he will find that using it can solve mysteries that do not yield to other techniques. 9 figures

  9. Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1978-01-01

    Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219-360 K by the flash photolysis-resonance fluorescence technique. The results can be expressed in Arrhenius form by K = (1.33 plus or minus 0.32)x10 to the minus 10 power exp (-449 plus or minus 58/T) cu cm/molecule/s (two standard deviations). The present work is compared to two previous determinations and is discussed theoretically.

  10. Theoretical study of piezoelectrochemical reactions in molecular compression chambers: In-situ generation of molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Pichierri, Fabio

    2016-09-01

    Nitrogen-containing molecular compression chambers (MCCs) undergo stepwise protonation followed by a 2-electron reduction step which affords molecular hydrogen in situ. This piezoelectrochemical reaction is favored by the high compression that characterizes the molecular skeleton of MCC and its fluorinated analogue. Besides H2, the MCCs are also capable of trapping molecular fluorine and the small monoatomic gases helium and neon. A topological analysis of the electronic charge density reveals the presence of closed-shell interactions between hosts and guests.

  11. Au25 Clusters as Electron-Transfer Catalysts Induced the Intramolecular Cascade Reaction of 2-nitrobenzonitrile

    PubMed Central

    Chong, Hanbao; Li, Peng; Wang, Shuxin; Fu, Fangyu; Xiang, Ji; Zhu, Manzhou; Li, Yadong

    2013-01-01

    Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z. PMID:24225495

  12. Fission Study of Actinide Nuclei Using Multi-nucleon Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Nishio, Katsuhisa; Hirose, Kentaro; Léguillon, R.; Makii, Hiroyuki; Nishinaka, Ichiro; Orlandi, Riccardo; Smallcombe, James; Tsukada, Kazuaki; Chiba, Satoshi; Ohtsuki, Tsutomu; Tatsuzawa, Ryotaro; Takaki, Naoyuki

    We have developed a set up to measure fission properties of excited compound nuclei populated by multi-nucleon transfer reactions. This approach has an advantage that we can study fission of neutron-rich nuclei which cannot be accessed by particle or charged-particle capture reactions. Unique feature in our setup is that we can produce fission data for many nuclei depending on different transfer channels. Also wide excitation energy range can be covered in this set up, allowing us to measure the excitation energy dependence of the fission properties. Preliminary data obtained in the 18O + 238U reaction will be presented.

  13. Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

    PubMed Central

    Driver, Tom G.

    2011-01-01

    Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Heinz, S.; Devaraja, H. M.; Beliuskina, O.; Comas, V.; Hofmann, S.; Hornung, C.; Münzenberg, G.; Ackermann, D.; Gupta, M.; Henderson, R. A.; Heßberger, F. P.; Kindler, B.; Lommel, B.; Mann, R.; Maurer, J.; Moody, K. J.; Nishio, K.; Popeko, A. G.; Shaughnessy, D. A.; Stoyer, M. A.; Yeremin, A. V.

    2016-09-01

    Recently, we reported the observation of several new isotopes with proton numbers Z ≥ 92 in low-energy collisions of 48Ca + 248Cm . 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.

  16. 9,10-Diphenylanthracene as a matrix for MALDI-MS electron transfer secondary reactions.

    PubMed

    Boutaghou, M Nazim; Cole, Richard B

    2012-08-01

    The most common secondary-ionization mechanism in positive ion matrix-assisted laser desorption/ionization (MALDI) involves a proton transfer reaction to ionize the analyte. Peptides and proteins are molecules that have basic (and acidic) sites that make them susceptible to proton transfer. However, non-polar, aprotic compounds that lack basic sites are more difficult to protonate, and creating charged forms of this type of analyte can pose a problem when conventional MALDI matrices are employed. In this case, forming a radical molecular ion through electron transfer is a viable alternative, and certain matrices may facilitate the process. In this work, we investigate the performance of a newly developed electron-transfer secondary reaction matrix: 9,10-diphenylanthracene (9,10-DPA). The use of 9,10-DPA as matrix for MALDI analysis has been tested using several model compounds. It appears to promote ionization through electron transfer in a highly efficient manner as compared to other potential matrices. Thermodynamic aspects of the observed electron transfers in secondary-ionization reactions were also considered, as was the possibility for kinetically controlled/endothermic, electron-transfer reactions in the MALDI plume.

  17. Reversible intramolecular hydrogen transfer between cysteine thiyl radicals and glycine and alanine in model peptides: absolute rate constants derived from pulse radiolysis and laser flash photolysis

    PubMed Central

    Nauser, Thomas; Casi, Giulio; Koppenol, Willem H.; Schöneich, Christian

    2008-01-01

    The intramolecular reaction of cysteine thiyl radicals with peptide and protein αC-H bonds represents a potential mechanism for irreversible protein oxidation. Here, we have measured absolute rate constants for these reversible hydrogen transfer reactions by means of pulse radiolysis and laser flash photolysis of model peptides. For N-Ac-CysGly6 and N-Ac-CysGly2AspGly3, Cys thiyl radicals abstract hydrogen atoms from Gly with kf = (1.0-1.1)×105 s-1, generating carbon-centered radicals, while the reverse reaction proceeds with kr = (8.0-8.9)×105 s-1. The forward reaction shows a normal kinetic isotope effect of kH/kD = 6.9, while the reverse reaction shows a significantly higher normal kinetic isotope effect of 17.6, suggesting a contribution of tunneling. For N-Ac-CysAla2AspAla3, cysteine thiyl radicals abstract hydrogen atoms from Ala with kf =(0.9-1.0)×104 s-1, while the reverse reaction proceeds with kr = 1.0×105 s-1. The order of reactivity, Gly > Ala, is in accord with previous studies on intermolecular reactions of thiyl radicals with these amino acids. The fact that kf < kr suggests some secondary structure of the model peptides, which prevents the adoption of extended conformations, for which calculations of homolytic bond dissociation energies would have predicted kf > kr. Despite kf < kr, model calculations show that intramolecular hydrogen abstraction by Cys thiyl radicals can lead to significant oxidation of other amino acids in the presence of physiologic oxygen concentrations. PMID:18973367

  18. Carboxyl group participation in sulfate and sulfamate group transfer reactions

    SciTech Connect

    Hopkins, A.; Williams, A.

    1982-04-23

    The pH dependence for the hydrolysis of N-(2-carboxyphenyl)sulfamic acid exhibits a plateau region corresponding to participation of the carboxyl function. A normal deuterium oxide solvent isotope effect indicates that proton transfer from the carboxylic acid is concerted with sulfamate group transfer to water. Hydrolysis of salicylic sulfate and N-(2-carboxyphenyl)sulfamate in /sup 18/O-enriched water yields salicylic acid and anthranilic acids with no enrichment, excluding catalysis by neighboring nucleophilic attack on sulfur by the carboxylate group. Intermolecular catalysis by carboxylic acids is demonstrated in the hydrolysis of N-(1-naphthyl)sulfamic acid; the mechanism is shown to involve preequilibrium protonation of the nitrogen followed by nucleophilic attack on sulfur by the carboxylate anion. Fast decomposition of the acyl sulfate completes the hydrolysis; this mechanism is considered to be the most efficient but is excluded in the intramolecular case which is constrained by the electronic requirements of displacement at the sulfur atom (6-ENDO-tet).

  19. SiC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION

    SciTech Connect

    Unknown

    2000-12-01

    A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. During Year I, we have successfully fabricated SiC macro porous membranes via extrusion of commercially available SiC powder, which were then deposited with thin, micro-porous (6 to 40{angstrom} in pore size) films via sol-gel technique as intermediate layers. Finally, an SiC hydrogen selective thin film was deposited on this substrate via our CVD/I technique. The composite membrane thus prepared demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers. Building upon the positive progress made in the Year I preliminary study, we will conduct an optimization study in Year II to develop an optimized H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment.

  20. Polyelectrolytes as interfaces for retarding back-reaction in photoinduced electron transfer

    SciTech Connect

    Otvos, J.W.; Casti, T.E.; Calvin, M.

    1984-08-01

    Flash photolysis experiments on the effect of the polyelectrolytes poly(styrene sulfonate) (PSS) and Poly(N,N-dimethyl-3, 5-dimethylene piperidinium chloride) (PolyP) on the photoinduced electron transfer reaction between zinc(II) tetrakis (4-N-methylpyridinium)porphyin (ZnP) and propyl viologen sulfonate (PVS/sup 0/) show that PSS decreases both the forward and back- electron transfer reaction rates significantly, by a factor of approx. 60. The effect of PSS is due to hydrophobic envelopment of ZnP by the polyelectrolyte, hindering approach of reactants to it and thus reducing all bimolecular reaction rates between ZnP and species in solution. The cationic polyelectrolyte, PolyP, decreases the back-electron transfer rate by a factor of approx. 2 without affecting other bimolecular reaction rates. This effect is probably due to binding of the PVS/sup -/ to the polyelectrolyte, which then repels the oxidized porphyrin electrostatically.