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Sample records for hydrogen transfer reactions

  1. Iridium-Catalyzed Hydrogen Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Saidi, Ourida; Williams, Jonathan M. J.

    This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst "borrows" hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C-C bonds where the only by-product is typically water.

  2. 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

  3. Nickel nanoparticles in hydrogen transfer reactions.

    PubMed

    Alonso, Francisco; Riente, Paola; Yus, Miguel

    2011-05-17

    The transfer hydrogenation of organic compounds is a much safer and more environmentally benign process than reduction reactions involving molecular hydrogen, metal hydrides, or dissolving metals. In transfer hydrogenation, 2-propanol is often preferred as the source of hydrogen because it is cheap, easy to remove, and environmentally friendly. This class of transformation has been mostly pursued through the use of expensive noble metals, such as Ru, Pd, and so forth; research involving cheaper catalytically active metals has been relatively neglected. On the other hand, alcohols have recently emerged as desirable alkylating agents, a useful alternative to organic halides, in reactions of hydrogen autotransfer, also known as the "borrowing of hydrogen" methodology. For instance, the α-alkylation of ketones with alcohols is an atom-efficient process that produces water as the only byproduct in the presence of a noble metal catalyst. Hydrogen autotransfer is also successful in the synthesis of amines through a reductive aza-Wittig reaction, which involves an iminophosphorane and primary alcohol under iridium catalysis. The in situ oxidation-Wittig olefination of primary alcohols with stabilized phosphorus ylides is a commonly practiced method in organic synthesis that precludes the necessity of handling aldehydes. These reactions are normally performed in one pot but sequentially; thus the course of the alcohol oxidation needs monitoring before the ylide addition. In this Account, we describe the development of our discovery that nickel(0), in the form of nanoparticles, can replace the more expensive noble metals in both transfer hydrogenation and hydrogen autotransfer reactions. These nanoparticles were found to catalyze the transfer hydrogenation of olefins and carbonyl compounds, as well as the reductive amination of aldehydes, with 2-propanol as the hydrogen donor. All reactions proceeded in the absence of base, and the catalyst could be easily and successfully

  4. Laser driven hydrogen transfer reactions in atmospheric chemistry

    NASA Astrophysics Data System (ADS)

    Lester, Marsha I.

    2015-03-01

    Ozonolysis of alkenes, an important non-photolytic source of OH radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. In this work, infrared laser activation of cold methyl-substituted Criegee intermediates is utilized to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of the Criegee intermediates in the CH stretch overtone region combined with sensitive OH detection reveals the infrared spectra of CH3CHOO and (CH3)2 COO, effective barrier heights for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the infrared overtone spectra as well as vibrational excitations, structural changes, and energy required to move from the minimum energy configuration of the Criegee intermediates to the transition state for the hydrogen transfer reaction. Research supported by the National Science Foundation.

  5. 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

  6. Hydrogen transfer in SAM-mediated enzymatic radical reactions.

    PubMed

    Hioe, Johnny; Zipse, Hendrik

    2012-12-14

    S-adenosylmethionine (SAM) plays an essential role in a variety of enzyme-mediated radical reactions. One-electron reduction of SAM is currently believed to generate the C5'-desoxyadenosyl radical, which subsequently abstracts a hydrogen atom from the actual substrate in a catalytic or a non-catalytic fashion. Using a combination of theoretical and experimental bond dissociation energy (BDE) data, the energetics of these radical processes have now been quantified. SAM-derived radicals are found to react with their respective substrates in an exothermic fashion in enzymes using SAM in a stoichiometric (non-catalytic) way. In contrast, the catalytic use of SAM appears to be linked to a sequence of moderately endothermic and exothermic reaction steps. The use of SAM in spore photoproduct lyase (SPL) appears to fit neither of these general categories and appears to constitute the first example of a SAM-initiated radical reaction propagated independently of the cofactor. PMID:23139189

  7. A theoretical and experimental study of unimolecular and biomolecular radical hydrogen transfer reactions

    SciTech Connect

    Franz, J.A.; Autrey, T.; Gleicher, G.J.; Camaioni, D.M; Ferris, K.F.

    1991-04-01

    We have examined the intramolecular radical hydrogen transfer (RHT) reaction of the 2-(2-phenylethyl)cyclohexadienyl radical. Intramolecular hydrogen shift from the cyclohexadienyl ring to the ipso position of the phenyl ring, followed by {beta}-scission would have given benzene and ethylbenzene as products. Competing with this reaction is {beta}-scission to give benzyl radical and isotoluene, or hydrogen loss to give bibenzyl. Studies to date suggest a barrier for thermoneutral hydrogen transfer in the RHT reaction between aromatic systems of ca. 18 kcal/mole. None of the studies of RHT or equivalent mechanisms have attempted to directly observe H{sub 2}, and direct determination of Arrhenius parameters and a detailed examination of the pathway of the hydrogen transfer process remains to be carried out. To better understand the structural and energetic aspects of RHT, we have carried out a semiempirical molecular orbital study of bimolecular and intramolecular RHT reactions for a variety of aromatic systems. We also examined in detail the energetics of hydrogen transfer between ethyl radical and ethylene via RHT, an addition/metathesis/scission pathway, and a hybrid concerted'' pathway. 11 refs., 1 fig., 4 tabs.

  8. Pincer-Type Complexes for Catalytic (De)Hydrogenation and Transfer (De)Hydrogenation Reactions: Recent Progress.

    PubMed

    Werkmeister, Svenja; Neumann, Jacob; Junge, Kathrin; Beller, Matthias

    2015-08-24

    Pincer complexes are becoming increasingly important for organometallic chemistry and organic synthesis. Since numerous applications for such catalysts have been developed in recent decades, this Minireview covers progress in their use as catalysts for (de)hydrogenation and transfer (de)hydrogenation reactions during the last four years. Aside from noble-metal-based pincer complexes, the corresponding base metal complexes are also highlighted and their applications summarized. PMID:26179375

  9. Ab initio studies on hydrogen-transfer tunneling for Cl + HCl abstraction hydrogen reaction

    SciTech Connect

    Yuxiang Bu; Zhaohua Cao; Xinyu Song

    1996-01-05

    This article presents a treatment scheme of the tunneling of hydrogen between two molecular centers (Cl...Cl). The purpose is to calculate the tunneling probabilities of hydrogen atom transfer from the initial (the proceeding complex) to the final-state energy minima (the succeeding complex) in two anharmonic vibrational states (0 {r_arrow} 0 and 1 {r_arrow} 1) in terms of the time-dependent perturbation theory expression and to see whether spectroscopic signatures of tunneling persist in the form of splittings of the vibrational modes. The analysis uses the realistic potential energy function calculated at the HF/6-31 + G** self-consistent-field basis-set level for the interaction between transferred hydrogen and its molecular skeleton (Cl ... H ... Cl). This potential energy surface is calibrated by comparing its properties with those from s POLO and the LEPS potential-energy surfaces. The anharmonic vibrational state is characterized by the corrected vibrational energy levels and a set of linear combination coefficients obtained via perturbation theory. The tunneling probabilities for two transitions (0 {r_arrow} 0 and 1 {r_arrow} 1) were calculated and compared with those from Gamow`s equation. Applicability of the time-dependent perturbation theory expression and Gamow`s equation to the [Cl-H ... Cl] system is discussed. The vibrational splitting energies are obtained, and a spectroscopic signature caused by tunneling is expected and should be observable. 28 refs., 1 fig., 4 tabs.

  10. Ionic hydrogenations of hindered olefins at low temperature. Hydride transfer reactions of transition metal hydrides

    SciTech Connect

    Bullock, R.M.; Song, J.S. )

    1994-09-21

    Sterically hindered olefins can be hydrogenated at -50[degree]C in dichloromethane using triflic acid (CF[sub 3]SO[sub 3]H) and a hydride donor. Mechanistic studies indicate that these reactions proceed by hydride transfer to the carbenium ion that is formed by protonation of the olefin. Olefins that form tertiary carbenium ions upon protonation are hydrogenated in high yields (90-100%). Styrenes generally produce lower yields of hydrogenated products (50-60%). Suitable hydride donors include HSiE[sub 3] and several transition metal carbonyl hydrides HW(CO)[sub 3]Cp, HW(CO)[sub 3]Cp[sup +], HMo-(CO)[sub 3]Cp, HMn(CO)[sub 5], HRe(CO)[sub 3], and HO[sub 3](CO)[sub 1]Cp*; Cp = [eta][sup 5]-C[sub 3]H[sub 5+], Cp* = [eta][sup 5]-C[sub 5]Me[sub 5]. A characteristic that is required for transition metal hydrides to be effective is that the cationic dihydrides (or dihydrogen complexes) that result from their protonation must have sufficient acidity to transfer a proton to the olefin, as well as sufficient thermal stability to avoid significant decomposition on the time scale of the hydrogenation reaction. Metal hydrides that fall due to insufficient stability of their protonated forms include HMo(CO)[sub 2](PPH[sub 3])Cp, HMo(CO)[sub 3]Cp*, and HFe(CO)[sub 2]Cp*. 62 refs., 2 tabs.

  11. 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.

  12. 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

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

    DOE PAGESBeta

    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

  14. Slow Hydrogen Transfer Reactions of Oxo— and Hydroxo— Vanadium Compounds: the Importance of Intrinsic Barriers

    PubMed Central

    Waidmann, Christopher R.; Zhou, Xin; Tsai, Erin A.; Kaminsky, Werner; Hrovat, David A.; Borden, Weston Thatcher; Mayer, James M.

    2009-01-01

    Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [VIVO(OH)(R2bpy)2]BF4 (1a-c) and vanadium(V) dioxo complexes [VVO2(R2bpy)2]BF4 (2a-c) [R2bpy = 4,4′-di-t-butyl-2,2′-bipyridine (tBu2bpy), a; 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), b; 2,2′-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H+ + e−). The VIV– tBu2bpy derivative 1a has a useful 1H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H• from organic substrates with weak O–H and C–H bonds, converting 2,6-tBu2-4-MeO-C6H2OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxy-piperidine (TEMPOH) to their corresponding radicals ArO• and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH ⇋ 1a + ArO• is (4 ± 2) × 10−3, implying that the VO–H bond dissociation free energy (BDFE) is 70.6 ± 1.2 kcal mol−1. Consistent with this value, 1a is oxidized by 2,4,6-tBu3C6H2O•. All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b ⇋ 2a + 1b, using the tBu- and Me-bpy substituents as labels, also occurs slowly, with kse = 1.3 × 10−2 M−1 s−1 at 298 K, ΔH‡ = 15 ± 2 kcal mol−1, and ΔS‡= 16 ± 5 cal mol−1 K. Using this kse and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 102 of the observed values. The vanadium self-exchange reaction is ca. 106 slower than that for the related RuIVO(py)(bpy)22+ / RuIIIOH(py)(bpy)22+ self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on mono-cationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in

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

    PubMed Central

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

    2009-01-01

    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-tetrahydropyrimidine, 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 reaction of [CoII(H2bim)3]2+ with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer, −41 ± 2 cal mol−1 K−1. This is even more negative than the ΔSoHAT = −30 ± 2 cal mol−1 K−1 for the two iron complexes and the ΔSoHAT for RuII(acac)2(py-imH) + TEMPO, 4.9 ± 1.1 cal mol−1 K−1, as reported earlier. 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. A brief evaluation of the literature thermochemistry of TEMPOH and tBu3PhOH supports the common assumption that ΔSoHAT ≈ 0 for HAT reactions of organic and small gas-phase molecules. However, this assumption 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. This is because both ΔSoET and ΔSoHAT have substantial contributions from vibrational entropy, which varies significantly with the metal center involved. The close connection between ΔSoHAT and ΔSoET provides an important

  16. 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

  17. Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

    PubMed Central

    Chen, Chao; Lu, Chunxin; Zheng, Qing; Zhang, Min

    2015-01-01

    Summary Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH3CN)4](PF6)2 with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh3)(CH3CN)3](PF6)2 (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones. PMID:26664598

  18. Rate-promoting vibrations and coupled hydrogen-electron transfer reactions in the condensed phase: A model for enzymatic catalysis

    NASA Astrophysics Data System (ADS)

    Mincer, Joshua S.; Schwartz, Steven D.

    2004-04-01

    A model is presented for coupled hydrogen-electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as the amine dehydrogenases and soybean lipoxygenase. Consistent with earlier results, turning off the promoting vibration results in an increased KIE. Increasing the barrier height increases the KIE, while increasing the rate of electron transfer decreases it. These results are discussed in light of other views of vibrationally enhanced tunneling in enzymes.

  19. 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. PMID:24284891

  20. 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

  1. 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

  2. Highly dispersed ruthenium hydroxide supported on titanium oxide effective for liquid-phase hydrogen-transfer reactions.

    PubMed

    Yamaguchi, Kazuya; Koike, Takeshi; Kim, Jung Won; Ogasawara, Yoshiyuki; Mizuno, Noritaka

    2008-01-01

    Supported ruthenium hydroxide catalysts (Ru(OH)(x)/support) were prepared with three different TiO(2) supports (anatase TiO(2) (TiO(2)(A), BET surface area: 316 m(2) g(-1)), anatase TiO(2) (TiO(2)(B), 73 m(2) g(-1)), and rutile TiO(2) (TiO(2)(C), 3.2 m(2) g(-1))), as well as an Al(2)O(3) support (160 m(2) g(-1)). Characterizations with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest-neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)(x)hydrogen-transfer reactions, such as racemization of chiral secondary alcohols and the reduction of carbonyl compounds and allylic alcohols. The catalytic activities of Ru(OH)(x)/TiO(2)(A) for these hydrogen-transfer reactions were at least one order of magnitude higher than those of previously reported heterogeneous catalysts, such as Ru(OH)(x)/Al(2)O(3). These catalyses were truly heterogeneous, and the catalysts recovered after the reactions could be reused several times without loss of catalytic performance. The reaction rates monotonically increased with an increase in the amount of monomeric ruthenium hydroxide species, which suggests that the monomeric species are effective for these hydrogen-transfer reactions. PMID:19021181

  3. 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

  4. 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

  5. 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.

  6. Role of pendant proton relays and proton-coupled electron transfer on the hydrogen evolution reaction by nickel hangman porphyrins

    PubMed Central

    Bediako, D. Kwabena; Solis, Brian H.; Dogutan, Dilek K.; Roubelakis, Manolis M.; Maher, Andrew G.; Lee, Chang Hoon; Chambers, Matthew B.; Hammes-Schiffer, Sharon; Nocera, Daniel G.

    2014-01-01

    The hangman motif provides mechanistic insights into the role of pendant proton relays in governing proton-coupled electron transfer (PCET) involved in the hydrogen evolution reaction (HER). We now show improved HER activity of Ni compared with Co hangman porphyrins. Cyclic voltammogram data and simulations, together with computational studies using density functional theory, implicate a shift in electrokinetic zone between Co and Ni hangman porphyrins due to a change in the PCET mechanism. Unlike the Co hangman porphyrin, the Ni hangman porphyrin does not require reduction to the formally metal(0) species before protonation by weak acids in acetonitrile. We conclude that protonation likely occurs at the Ni(I) state followed by reduction, in a stepwise proton transfer–electron transfer pathway. Spectroelectrochemical and computational studies reveal that upon reduction of the Ni(II) compound, the first electron is transferred to a metal-based orbital, whereas the second electron is transferred to a molecular orbital on the porphyrin ring. PMID:25298534

  7. 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

  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. Reactions of OOH radical with beta-carotene, lycopene, and torulene: hydrogen atom transfer and adduct formation mechanisms.

    PubMed

    Galano, Annia; Francisco-Marquez, Misaela

    2009-08-13

    The relative free radical scavenging activity of beta-carotene, lycopene, and torulene toward OOH radicals has been studied using density functional theory. Hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms have been considered. All the possible reaction sites have been included in the modeling, and detailed branching ratios are reported for the first time. The reactions of hydrocarbon carotenoids (Car) with peroxyl radicals, in both polar and nonpolar environments, are predicted to proceed via RAF mechanism, with contributions higher than 98% to the overall OOH + Car reactions. Lycopene and torulene were found to be more reactive than beta-carotene. In nonpolar environments the reactivity of the studied carotenoids toward peroxyl radical follows the trend LYC > TOR > BC, whereas in aqueous solutions it is TOR > LYC > BC. OOH adducts are predicted to be formed mainly at the terminal sites of the conjugated polyene chains. The main addition sites were found to be C5 for beta-carotene and lycopene and C30 for torulene. The general agreement between the calculated magnitudes and the available experimental data supports the predictions from this work. PMID:19627101

  11. A micellar model for investigating the chemical nature of hydrogen transfer in NAD(P)H-dependent enzymatic reactions.

    PubMed

    Rao, U M

    1989-03-31

    Aqueous micelles of Triton X-100 were shown to catalyse the redox reaction between NADH and 2-p-iodophenyl-3-p-nitrophenyl-5-phenyltetrazolium chloride (INT) at the neutral pH. The transfer of reducing equivalents between the reactants in the micellar system appeared to be direct and quantitative. N-tert-butylphenyl-alpha-nitrone, a lipophilic free-radical scavenger which can enter micelles, and superoxide dismutase did not alter the stoichiometry of the reaction. The oxidation product of NADH was found to be 100% enzymatically active. The IR spectrum of INT-formazan (i.e., the product of INT reduction) showed an absorbance at 3,100-3,700 cm- due to NH-stretching. The presence of NH proton, confirmed further by IH-NMR, together with the above observations suggests that INT, as part of the over-all redox process, abstracts a C(4) hydrogen of the dihydropyridine nucleus of NADH with a simultaneous cleavage at N(2-3) position of its 1,2,3,4-tetrazole ring system and that the redox events are confined to a microenvironment as in the case of NAD(P)H-dependent enzymatic reactions. PMID:2930563

  12. 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

  13. 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.

  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. C-Propargylation Overrides O-Propargylation in Reactions of Propargyl Chloride with Primary Alcohols: Rhodium-Catalyzed Transfer Hydrogenation.

    PubMed

    Liang, Tao; Woo, Sang Kook; Krische, Michael J

    2016-08-01

    The canonical SN 2 behavior displayed by alcohols and activated alkyl halides in basic media (O-alkylation) is superseded by a pathway leading to carbinol C-alkylation under the conditions of rhodium-catalyzed transfer hydrogenation. Racemic and asymmetric propargylations are described. PMID:27321353

  16. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Progress report, September 1, 1982-August 1, 1985

    SciTech Connect

    Whitten, D.G.

    1985-01-01

    The studies carried out have focused on photoinduced electron transfer and hydrogen atom abstraction processes. The main thrust over the past three years has been on a study of light induced electron transfer reactions and in particular on fates of the energy rich radical ions formed in electron transfer quenching of excited states. In particular we have studied these reactions under conditions - light absorbing substrates, quenchers, media - where net chemical conversion is favored over the usual back electron transfer to return to starting materials. The first part of the progress report focuses on our efforts to control reactivity by the use of specific substrates or quenchers which favor net chemical conversion. The second part describes our studies using reaction media - in this case amylose which preferentially complexes hydrophobic molecules in aqueous solution - to alter the rates of primary and secondary photophysical events associated with light induced electron transfer and other photoreactions. Our most extensive investigations of electron transfer reactions have involved the photoreduction of indigo dyes by electron donors. We have found that three representative indigo dyes, thioindigo, N,N'-diacetylindigo and oxalylindigo, all undergo photobleaching reactions with a variety of potential reductance ranging from alcohols to amines, such as triethylamine and N-benzyl-1, 4-dihydronicotinamide. 25 refs.

  17. Theoretical Studies of the Role of Vibrational Excitation on the Dynamics of the Hydrogen-Transfer Reaction of F(^2P) + HCl → FH + Cl({^2}P)

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

    Hydrogen-transfer reactions are probed through vibrational excitation of the HCl bond in the pre-reactive F\\cdotsHCl complex. Such open-shell species provide a challenge for quantum dynamical calculations due to the need to take into account multiple potential energy surfaces to accurately describe the system.A three-dimensional, fully-coupled potential energy surface has been constructed based on electronic energies calculated at the multireference configuration interaction+Davidson correction (MRCI+Q) level of theory with an aug-cc-pVnZ (n=2,3,4) basis. Spin orbit calculations have also been included. Here we present the results of time-dependent quantum wave packet calculations on the asymmetric hydrogen-transfer reaction of F(^2P) + HCl. In these calculations, the reaction is initiated by vibrationally exciting the HCl stretching motion in the pre-reactive F\\cdotsHCl complex. The wave packet is propagated on the coupled potential energy surfaces. Product state distributions were calculated for reactions initiated in the first three vibrationally excited states of HCl, v=1-3. M. P. Deskevich, M. Y. Hayes, K. Takahashi, R. T. Skodje, and D. J. Nesbitt J. Chem. Phys. 124 (22) 224303 (2006) M. P. Deskevich and D. J. Nesbitt private communication(2007)

  18. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Final report, March 1, 1981-February 28, 1984

    SciTech Connect

    Not Available

    1984-01-01

    Goal has been to study light-driven electron transfer and hydrogen atom abstraction processes with emphasis on reactions giving rise to net chemical or electrochemical conversion. The work focused on studies using substrates excitable with visible light - ranging from metal complexes, porphyrins and metalloporphyrins to dyes and ketones - and quencher-mediators capable of acting as electron donors or acceptors by virtue of having multiple closely spaced redox levels. The work can be conveniently divided into five major areas: Generation and Reaction of Reducing and Oxidizing Radicals and Radical Ions in Photoelectrochemical Cells; Studies of Weitz-type Quenchers Having Stable One-electron Redox Products; Two-electron Oxidative and Reductive Quenching Processes with Weitz-type Systems in Solution and Organized Media; Photoredox Reactions of Indigo Dyes; and Modification of Photochemical Reactivity by Formation of Amylose Inclusion Complexes in Aqueous and Partially Aqueous Solutions.

  19. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Progress report, March 1, 1981-September 1, 1982

    SciTech Connect

    Whitten, D.G.

    1982-01-01

    The major goal of this research as outlined in our proposal is to study light-driven electron transfer and hydrogen atom abstraction processes with a particular emphasis on reactions giving rise to net chemical or electrochemical conversion. During the past eighteen months we have obtained results of some significance in each of the five areas which are discussed individually in the report: (1) generation and reaction of reducing and oxidizing radicals and radical ions in photoelectrochemical cells; (2) studies of Weitz-type quenchers having stable one-electron redox products; (3) two-electron oxidative and reductive quenching processes with Weitz-type systems in solution and organized media; (4) photoredox reactions of indigo dyes; and (5) modification of photochemical reactivity by formation of amylose inclusion complexes in aqueous and partially aqueous solutions.

  20. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Part I. Progress report, March 1, 1981-July 1, 1983

    SciTech Connect

    Whitten, D.G.

    1983-01-01

    Goal is to study light-driven electron transfer and hydrogen atom abstraction processes with emphasis on reactions giving rise to net chemical or electrochemical conversion. The original proposal focused on studies using substrates excitable with visible light - ranging from metal complexes, porphyrins and metalloporphyrins to dyes and ketones - and quencher-mediators capable of acting as electron donors or acceptors by virtue of having multiple closely spaced redox levels. During the past eighteen months results were obtained in five areas: generation and reaction of reducing and oxidizing radicals and radical ions in photoelectrochemical cells; studies of Weitz-type quenchers having stable one-electron redox products; two-electron oxidative and reductive quenching processes with Weitz-type systems in solution and organized media; photoredox reactions of indigo dyes; and modification of photochemical reactivity by formation of amylose inclusion complexes in aqueous and partially aqueous solutions.

  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. 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)

  3. Steric Effect for Proton, Hydrogen-Atom, andHydride Transfer Reactions with Geometric Isomers of NADH-Model Ruthenium Complexes

    SciTech Connect

    Fujita E.; Cohen, B.W.; Polyansky, D.E.; Achord, P.; Cabelli, D.; Muckerman, J.T.; Tanaka, K.; Thummel, R.P.; Zong, R.

    2012-01-01

    Two isomers, [Ru(1)]{sup 2+} (Ru = Ru(bpy){sub 2}, bpy = 2,2{prime}-bipyridine, 1 = 2-(pyrid-2{prime}-yl)-1-azaacridine) and [Ru(2)]{sup 2+} (2 = 3-(pyrid-2{prime}-yl)-4-azaacridine), are bio-inspired 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-C{sub 1} complexes and/or carbon dioxide. While it has been shown that the structural differences between the azaacridine ligands of [Ru(1)]{sup 2+} and [Ru(2)]{sup 2+} have a significant effect on the mechanism of formation of the hydride donors, [Ru(1HH)]{sup 2+} and [Ru(2HH)]{sup 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{sup {sm_bullet}-})]{sup +} in aprotic and even protic media is slow compared to that of [Ru(1{sup {sm_bullet}-})]{sup +}. The net hydrogen-atom transfer between *[Ru(1)]{sup 2+} and hydroquinone (H{sub 2}Q) proceeds by one-step EPT, rather than stepwise electron-proton transfer. Such a reaction was not observed for *[Ru(2)]{sup 2+} because the non-coordinated N atom is not easily available for an interaction with H{sub 2}Q. Finally, the rate of the net hydride ion transfer from [Ru(1HH)]{sup 2+} to [Ph{sub 3}C]{sup +} is significantly slower than that of [Ru(2HH)]{sup 2+} owing to steric congestion at the donor site.

  4. Inequivalence of substitution pairs in hydroxynaphthaldehyde: A theoretical measurement by intramolecular hydrogen bond strength, aromaticity, and excited-state intramolecular proton transfer reaction.

    PubMed

    Mahanta, Subrata; Paul, Bijan Kumar; Balia Singh, Rupashree; Guchhait, Nikhil

    2011-01-15

    The inequivalence of substitution pair positions of naphthalene ring has been investigated by a theoretical measurement of hydrogen bond strength, aromaticity, and excited state intramolecular proton transfer (ESIPT) reaction as the tools in three substituted naphthalene compounds viz 1-hydroxy-2-naphthaldehyde (HN12), 2-hydroxy-1-naphthaldehyde (HN21), and 2-hydroxy-3-naphthaldehyde (HN23). The difference in intramolecular hydrogen bond (IMHB) strength clearly reflects the inequivalence of substitution pairs where the calculated IMHB strength is found to be greater for HN12 and HN21 than HN23. The H-bonding interactions have been explored by calculation of electron density ρ(r) and Laplacian ∇(2) ρ(r) at the bond critical point using atoms in molecule method and by calculation of interaction between σ* of OH with lone pair of carbonyl oxygen atom using NBO analysis. The ground and excited state potential energy surfaces (PESs) for the proton transfer reaction at HF (6-31G**) and DFT (B3LYP/6-31G**) levels are similar for HN12, HN21 and different for HN23. The computed aromaticity of the two rings of naphthalene moiety at B3LYP/6-31G** method also predicts similarity between HN12 and HN21, but different for HN23. PMID:20623648

  5. 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 +/.

  6. A ruthenium-grafted triazine functionalized mesoporous polymer: a highly efficient and multifunctional catalyst for transfer hydrogenation and the Suzuki-Miyaura cross-coupling reactions.

    PubMed

    Salam, Noor; Kundu, Sudipta K; Roy, Anupam Singha; Mondal, Paramita; Ghosh, Kajari; Bhaumik, Asim; Islam, S M

    2014-05-21

    A new ruthenium-grafted mesoporous organic polymer Ru-MPTAT-1 has been synthesized via simple and facile in situ radical polymerization of 2,4,6-triallyloxy-1,3,5-triazine (TAT) in aqueous medium in the presence of an anionic surfactant (sodium dodecyl sulfate) as a template, followed by grafting of Ru(II) onto its surface. Ru-MPTAT-1 has been characterized by elemental analysis, powder XRD, HRTEM, FT-IR, UV-vis DRS, TG-DTA, FESEM and XPS characterization tools. The Ru-MPTAT-1 material showed very good catalytic activity in the Suzuki-Miyaura cross-coupling reaction for aryl halides and transfer hydrogenation reaction for a series of carbonyl compounds. The catalyst is easily recoverable from the reaction mixture and can be reused several times without appreciable loss of catalytic activity in the above reactions. Highly dispersed and strongly bound Ru(II) sites at the mesoporous polymer surface could be responsible for the observed high activity of the Ru-MPTAT-1 catalyst in these reactions. PMID:24667768

  7. 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.

  8. 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.

  9. 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

  10. Reaction coordinates for electron transfer reactions

    SciTech Connect

    Rasaiah, Jayendran C.; Zhu Jianjun

    2008-12-07

    The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

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

    PubMed

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

    2015-08-01

    Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state. PMID:26198840

  12. 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

  13. 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

  14. The Third Dimension of a More O’Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)2H• with X = O, NH, and CH2

    PubMed Central

    Cembran, Alessandro; Provorse, Makenzie R.; Wang, Changwei

    2012-01-01

    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)2H•, where X = O, NH, and CH2, 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 PhNH2 and PhNH• has a mechanism intermediate of CPET and HAT. The electronically nonadiabatic

  15. 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

  16. Hydride transfer and dihydrogen elimination from osmium and ruthenium metalloporphyrin hydrides: Model processes for hydrogenase enzymes and the hydrogen electrode reaction

    SciTech Connect

    Collman, J.P.; Wagenknecht, P.S.; Lewis, N.S.

    1992-07-01

    A series of metalloporphyrin hydride complexes of the type K[M(Por)(L)(H)] (M - Ru, Os; Por - OEP, TMP; L = THF, *Im, PPh{sub 3}, pyridine) has been synthesized by stoichiometric protonation of the corresponding K{sub 2}[M(Por)], followed by addition of L. The addition of excess acids to these hydrides resulted in the elimination of dihydrogen. The kinetics showed no evidence for a bimolecular mechanism for this process and suggest simple protonation of the metal-hydride bond followed by dihydrogen loss. One-electron oxidation of the metal hydrides also resulted in dihydrogen formation. The kinetics of the oxidatively induced hydrogen evolution step from K[Ru(OEP)(THF)(H)] were examined and indicate a biomolecular mechanism in which two metal hydrides reductively eliminate one dihydrogen molecule. The rate constant was determined to be 88 {+-} 14 M{sup -1} s{sup -1}. These reaction mechanisms are discussed in the context of designing bimetallic proton reduction catalysts. The metal hydride K[Ru(OEP)(THF)(H)], was also synthesized by heterolytic activation of H{sub 2}. This hydride is a good one-electron reductant (-1.15 V vs FeCp{sub 2}) and is capable of reducing, by hydride transfer, the NAD{sup +} analogue, 1-benzyl-N,N-diethyl-nicotinamide. This nicotinamide reduction by a hydride formed from heterolytic dihydrogen activation is suggested as the mechanism for hydrogenase enzymes. 38 refs., 4 figs., 3 tabs.

  17. HYDROGEN-4 and HYDROGEN-5 from Transfer Reactions Induced by a 57.5-MEV Triton Beam on Deuterium and Tritium Targets

    NASA Astrophysics Data System (ADS)

    Oganessian, Yu. Ts.; Ter-Akopian, G. M.; Bogdanov, D. D.; Fomichev, A. S.; Golovkov, M. S.; Rodin, A. M.; Sidorchuk, S. I.; Slepnev, R. S.; Stepantsov, S. V.; Wolski, R.; Gorshkov, V. A.; Chelnokov, M. L.; Itkis, M. G.; Kozulin, E. M.; Bogatchev, A. A.; Kondratiev, N. A.; Korzyukov, I. V.; Yukhimchuk, A. A.; Perevozchikov, V. V.; Vinogradov, Yu. I.; Grishechkin, S. K.; Demin, A. M.; Zlatoustovsky, S. V.; Kuryakin, A. V.; Fil'Chagin, S. V.; Il'Kaev, R. I.; Hanappe, F.; Materna, T.; Stuttgé, L.; Ninane, A. H.; Korsheninnikov, A. A.; Nikolski, E. Yu.; Tanihata, I.; Roussel-Chomaz, P.; Mittig, W.; Alamanos, N.; Lapoux, V.; Pollacco, E. C.; Nalpas, L.

    2002-01-01

    A state of 4H with Eres=3.22± 0.15 MeV and Γobs=3.33 ± 0.25 MeV is obtained in t+d reaction. A valuable part of proton spectra observed in t+t reaction from ptn coincidence events is due to 5H. The 5H spectrum shows up a narrow maximum at about 2.5 MeV above the tnn decay threshold followed by a wide structure situated at 4-7 MeV.

  18. 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.

  19. 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.

  20. Intrinsic barriers for H-atom transfer reactions

    SciTech Connect

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

    1994-08-01

    Hydrogen transfer reactions play a well-recognized role in coal liquefaction. While H-abstraction reactions between radicals and H-donors have been well-studied, understanding of structure-reactivity relationships remains surprisingly incomplete. Another form of hydrogen transfer known as radical hydrogen transfer (radical donation of H to an unsaturated compound) is currently the subject of much speculation. The barriers for identity reactions are key parameters in the Evans-Polanyi equation for estimating 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 H-abstraction identity barriers and no barriers for hydrocarbon radical hydrogen transfer reactions have been measured. This paper seeks to supplement and extend existing experimental data with results obtained by calculation. The authors have used ab initio and semiempirical molecular orbital methods (MNDO-PM3) to calculate barriers for a series of H-atom abstraction and radical-hydrogen-transfer identity reactions for alkyl, alkenyl, arylalkyl and hydroaryl systems. Details of this methodology and analyses of how barrier heights correlate with reactant and transition state properties will be presented and discussed.

  1. Hydrogen atom transfer reactions of ferrate(VI) with phenols and hydroquinone. Correlation of rate constants with bond strengths and application of the Marcus cross relation.

    PubMed

    Xie, Jianhui; Ma, Li; Lam, William W Y; Lau, Kai-Chung; Lau, Tai-Chu

    2016-01-01

    The oxidation of phenols by HFeO4(-) proceeds via a hydrogen atom transfer (HAT) mechanism, as evidenced by a large deuterium isotope effect and a linear correlation between the log(rate constant) and bond dissociation free energy (BDFE) of phenols. The Marcus cross relation has been applied to predict the rate constant of HAT from hydroquinone to HFeO4(-). PMID:26610053

  2. 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

  3. Silicon layer transfer using plasma hydrogenation

    SciTech Connect

    Chen Peng; Lau, S.S.; Chu, Paul K.; Henttinen, K.; Suni, T.; Suni, I.; Theodore, N. David; Alford, T.L.; Mayer, J.W.; Shao Lin; Nastasi, M.

    2005-09-12

    In this work, we demonstrate a novel approach for the transfer of Si layers onto handle wafers, induced by plasma hydrogenation. In the conventional ion-cut process, hydrogen ion implantation is used to initiate layer delamination at a desired depth, which leads to ion damage in the transferred layer. In this study, we investigated the use of plasma hydrogenation to achieve high-quality layer transfer. To place hydrogen atoms introduced during plasma hydrogenation at a specific depth, a uniform trapping layer for H atoms must be prepared in the substrate before hydrogenation. The hydrogenated Si wafer was then bonded to another Si wafer coated with a thermal oxide, followed by thermal annealing to induce Si layer transfer. Cross-section transmission electron microscopy showed that the transferred Si layer was relatively free of lattice damage. The H trapping during plasma hydrogenation, and the subsequent layer delamination mechanism, are discussed. These results show direct evidence of the feasibility of using plasma hydrogenation to transfer relatively defect-free Si layers.

  4. Radiation-induced hydrogen transfer in metals

    NASA Astrophysics Data System (ADS)

    Tyurin, Yu I.; Vlasov, V. A.; Dolgov, A. S.

    2015-11-01

    The paper presents processes of hydrogen (deuterium) diffusion and release from hydrogen-saturated condensed matters in atomic, molecular and ionized states under the influence of the electron beam and X-ray radiation in the pre-threshold region. The dependence is described between the hydrogen isotope release intensity and the current density and the electron beam energy affecting sample, hydrogen concentration in the material volume and time of radiation exposure to the sample. The energy distribution of the emitted positive ions of hydrogen isotopes is investigated herein. Mechanisms of radiation-induced hydrogen transfer in condensed matters are suggested.

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

    PubMed

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

    2008-02-27

    weak one-electron oxidation agents. The energies of the intramolecular hydrogen bond in 3H, 3H+*, and 3* with a hydroxyl group at ortho-position on the 2-phenyl ring were estimated by using experimental method, the results disclose that the hydrogen bond energy is 3.2, 2.8-3.0, and 3.9-4.0 kcal/mol for 3H, 3H+*, and 3* in acetonitrile, respectively, which is favorable for hydrogen atom transfer but unfavorable for hydride transfer from 3H. The relative effective charges on the active center in ZH, ZH+*, Z*, and Z+, which is an efficient measurement of electrophilicity or nucleophilicity as well as dimerizing ability of a chemical species, were estimated by using experimental method; the results indicate that 1*-5* belong to electron-sufficient carbon-radicals, 6*-7* belong to electron-deficient carbon radicals, they are all difficult to dimerize, and that 1+-5+ belong to weak electrophilic agents, 6+-7+ belong to strong electrophilic agents. All these information disclosed in this work could not only supply a gap of the chemical thermodynamics of the five-membered heterocyclic compounds as organic hydride donors, but also strongly promote the fast development of the chemistry and applications of the five-membered heterocyclic organic hydrides. PMID:18254624

  6. 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

  7. Transfer Reaction Studies with JENSA

    NASA Astrophysics Data System (ADS)

    Thompson, P.; Bardayan, D. W.; Blackmon, J. C.; Chipps, K. A.; Greife, U.; Linhardt, L. E.; Kontos, A.; Kozub, R. L.; Matos, M.; Montes, F.; Pain, S. D.; Pittman, S. T.; Sachs, A.; Schatz, H.; Schmitt, K. T.; Smith, M. S.; Jensa Collaboration

    2015-10-01

    The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target system was designed to provide a gas target that was pure, localized, and dense. Several commissioning experiments with the JENSA target, performed at Oak Ridge National Laboratory (ORNL), were undertaken to demonstrate the unique capability of JENSA for transfer reaction studies. JENSA has since completed its move from ORNL to the ReA3 reaccelerated beam hall at the National Superconducting Cyclotron Laboratory (NSCL). An overview of the JENSA design and operation will be presented, as well as a brief discussion of the experiments performed at ORNL with JENSA, with a focus on preliminary results from the 20Ne(p,t)18Ne commissioning experiment.

  8. Ruthenium(II) carbonyl complexes bearing CCC-pincer bis-(carbene) ligands: synthesis, structures and activities toward recycle transfer hydrogenation reactions.

    PubMed

    Naziruddin, Abbas Raja; Huang, Zhao-Jiunn; Lai, Wei-Chih; Lin, Wan-Jung; Hwang, Wen-Shu

    2013-09-28

    A new series of ruthenium(II) carbonyl complexes with benzene-based CCC-pincer bis-(carbene) ligands, [((R)CCC(R))Ru(CO)2(X)](0/+) and [((R)CCC(R))Ru(CO)(NN)](+) ((R)CCC(R) = 2,6-bis-(1-alkylimidazolylidene)benzene, R = Me or (n)Bu; X = I, Br, CH3CN, or 6-(aminomethyl)pyridine (ampy); NN = 2·CH3CN, or chelating ampy or bipyridine), was synthesized and fully characterized. X-Ray structure determinations revealed that these eight complexes have pseudo-octahedral configurations around the ruthenium center with the pincer ligand occupying three meridional sites. These complexes prove to be efficient precatalysts demonstrating very good activity and reusability for the transfer hydrogenation of ketones. PMID:23880878

  9. Kinetic and geometrical isotope effects in hydrogen-atom transfer reaction, as calculated by the multi-component molecular orbital method

    NASA Astrophysics Data System (ADS)

    Ishimoto, Takayoshi; Tachikawa, Masanori; Tokiwa, Hiroaki; Nagashima, Umpei

    2005-07-01

    To estimate the kinetic isotope effect (KIE) for hydrogen (or deuterium) abstraction from H(D)OR (R = H, CH 3, and CN) by an OH radical, we have considered the geometrical isotope effect (GIE) induced by the difference of the protonic and deuteronic wavefunctions using the multi-component MO method. The difference by the GIE of hydrogen bond was about 0.005 Å. The ratio (kaH/kaD) of the rate constant of the reaction for R = H, HO + HOR → HOH + OR and HO + DOR → HOD + OR, is estimated as 4.4 by our calculation, which is reasonable agreement with experimental result of 6.0 ± 2.0. We have found that the difference of the nuclear wavefunction of the proton and deuteron affects the changes of geometry and electronic charge density, which plays an important role to theoretically determine the effective potential energy surfaces and the corresponding KIE between H and D compounds.

  10. Asymmetric Transfer Hydrogenation of Imines using Alcohol: Efficiency and Selectivity are Influenced by the Hydrogen Donor.

    PubMed

    Pan, Hui-Jie; Zhang, Yao; Shan, Chunhui; Yu, Zhaoyuan; Lan, Yu; Zhao, Yu

    2016-08-01

    The influence of the alcohol, as the hydrogen donor, on the efficiency and selectivity of the asymmetric transfer hydrogenation (ATH) of imines is reported for the first time. This discovery not only leads to a highly enantioselective access to N-aryl and N-alkyl amines, but also provides new insight into the mechanism of the ATH of imines. Both experimental and computational studies provide support for the reaction pathway involving an iridium alkoxide as the reducing species. PMID:27374880

  11. Polarization Transfer Coefficient Measurements in the Deuteron Breakup Reaction HYDROGEN-1(POLARIZED Deuteron, Polarized Proton)x at 2.1 GEV.

    NASA Astrophysics Data System (ADS)

    Cheung, Naipor Eric

    The polarization of the protons emerging at 0 ^circ from the inclusive deuteron breakup reaction ^1H(vec d,vec p)X was measured using a deuteron beam with kinetic energy of 2.1 GeV. The momentum of the protons was selected by the magnetic spectrometer SPES4 and the polarization was measured with the polarimeter POMME. This experiment was performed at eight different proton momenta. When those momenta are Lorentz transformed to the deuteron rest frame, they corresponded to values from 0.00 to 0.34 GeV/c. The result of the measurements is expressed in terms of polarization transfer coefficient which is defined as the ratio of the measured proton polarization P_{p} to the deuteron beam vector polarization P _{Z}:kappa_{o} = P_{p}/P_{Z}. The values of kappa_{o} decreased from 0.995 to -0.320 across the proton momentum range of this experiment. The trend of kappa_{o} is in general agreement with the expected behavior arising from the D state in the deuteron wave function. The impulse approximation predicts quite well the general shape of kappa_{o}. Multiple scattering and relativistic effect based on different models of reaction mechanism are discussed.

  12. 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

  13. A multilateral mechanistic study into asymmetric transfer hydrogenation in water.

    PubMed

    Wu, Xiaofeng; Liu, Jianke; Di Tommaso, Devis; Iggo, Jonathan A; Catlow, C Richard A; Bacsa, John; Xiao, Jianliang

    2008-01-01

    The mechanism of aqueous-phase asymmetric transfer hydrogenation (ATH) of acetophenone (acp) with HCOONa catalyzed by Ru-TsDPEN has been investigated by stoichiometric reactions, NMR probing, kinetic and isotope effect measurements, DFT modeling, and X-ray structure analysis. The chloride [RuCl(TsDPEN)(p-cymene)] (1), hydride [RuH(TsDPEN)(p-cymene)] (3), and the 16-electorn species [Ru(TsDPEN-H)(p-cymene)] (4) were shown to be involved in the aqueous ATH, with 1 being the precatalyst, and 3 as the active catalyst detectable by NMR in both stoichiometric and catalytic reactions. The formato complex [Ru(OCOH)(TsDPEN)(p-cymene)] (2) was not observed; its existence, however, was demonstrated by its reversible decarboxylation to form 3. Both 1 and 3 were protonated under acidic conditions, leading to ring opening of the TsDPEN ligand. 4 reacted with water, affording a hydroxyl species. In a homogeneous DMF/H(2)O solvent, the ATH was found to be first order in the concentration of catalyst and acp, and inhibited by CO(2). In conjunction with the NMR results, this suggests that hydrogen transfer to ketone is the rate-determining step. The addition of water stabilized the ruthenium catalyst and accelerated the ATH reaction; it does so by participating in the catalytic cycle. DFT calculations revealed that water hydrogen bonds to the ketone oxygen at the transition state of hydrogen transfer, lowering the energy barrier by about 4 kcal mol(-1). The calculations also suggested that the hydrogen transfer is more step-wise in nature rather than concerted. This is supported to some degree by the kinetic isotope effects, which were obscured by extensive H/D scrambling. PMID:18604853

  14. Neutron transfer reactions at large distances

    SciTech Connect

    Rehm, K.E.; Glagola, B.G.; Kutschera, W.; Wolfs, F.L.H.; Wuosmaa, A.H. )

    1993-06-01

    [sup 58]Ni-induced one- and two-neutron transfer reactions have been measured on [sup 232]Th at [ital E][sub lab]=500 MeV. The transfer probabilities at large internuclear distances measured for the deformed [sup 232]Th target are compared with similar data on spherical [sup 208]Pb. For one-neutron transfer reactions good agreement between experiment and the prediction from the tunneling model is observed in both cases. The transfer probabilities for two-neutron transfer reactions deviate from the semiclassical predictions. The disagreement increases at higher bombarding energies. These deviations can be explained by the influence of diffractive effects which become more important at higher bombarding energies.

  15. Muon transfer from hydrogen and deuterium atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R. )

    1995-03-01

    The muon exchange reactions from the ground state of muonic protium and deuterium atoms to neon are studied. Measurements have been performed in binary gas mixtures at room temperature. The transfer rate from thermalized muonic deuterium is found to exceed by about an order of magnitude the one from muonic protium. On the other hand, an energy dependence of the rate from [mu][ital d] is revealed, while none is observed from [mu][ital p]. The intensity patterns of the muonic Lyman series of neon resulting from the muon exchange differ from one hydrogen isotope to the other, the most obvious discrepancy being the presence of the muonic Ne(7-1) line after transfer from [mu][ital d], whereas this line is absent by transfer from [mu][ital p]. This indicates that the muon is transferred to the level [ital n][sub [ital p

  16. 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

  17. 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

  18. Hydrogen transfer in catalysis by adenosylcobalamin-dependent diol dehydratase.

    PubMed

    Moore, K W; Bachovchin, W W; Gunter, J B; Richards, J H

    1979-06-26

    Studies [bachovchin, W. W., et al. (1978) Biochemistry 17, 2218] of the mechanism of inactivation of adenosylcobalamin-dependent diol dehydratase have led to the development of a general method to describe the kinetics of a reaction pathway containing a reservoir of mobile hydrogen. Analysis by this method of catalytic rate measurements for mixtures of 1,2-propanediol and 1,1-dideuterio-1,2-propanediol supports a mechanism involving an intermediate with three equivalent hydrogens, in which hydrogen transfer from this intermediate to product is the major rate-contributing step. Other results using tritium as a trace label [essenberg, M. K., et al. (1971) J. Am. Chem. Soc. 93, 1242] are considered in light of these deuterium isotope studies. PMID:383139

  19. Chemical reactions and gas transfer in natural waters

    SciTech Connect

    O`Connor, D.J. |

    1998-02-01

    Many chemical reactions of environmental significance involve reactants or end products that exchange with the atmosphere. The transferable constituents are the atmospheric gases--oxygen, carbon dioxide, and, to a more limited degree, nitrogen--and volatile substances that are not usually present in the atmosphere, such as ammonia, sulfur dioxide, and hydrogen sulfide. Reactions of this type have many applications in natural water systems, as well as water and waste treatment processes. It is the general purpose of this paper to present a mathematical approach to the analysis of these reactions and to demonstrate the application to various environmental problems. Both variable and constant pH conditions are addressed. The latter frequently characterizes laboratory experiments in batch reactions, in which a constant pH is maintained. The former is commonly present in natural waters, in which the pH changes through the course of the chemical reaction.

  20. 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.

  1. Catalytic Transfer Hydogenation Reactions for Undergraduate Practical Programs

    NASA Astrophysics Data System (ADS)

    Hanson, R. W.

    1997-04-01

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

  2. Light induced electron transfer reactions of metal complexes

    SciTech Connect

    Sutin, N.; Creutz, C.

    1980-01-01

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

  3. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Progress report, March 1-December 15, 1984

    SciTech Connect

    Not Available

    1984-01-01

    Progress reports are presented for the following three projects: (1) light induced redox reactions of indigo dyes and related compounds; (2) rapid reactions of photogenerated radical cations; and (3) host-guest complex formation between amylose and photochemically reactive molecules. Recent studies have shown that the intrachain surfactant stilbene, 6S4A, has an extremely high binding constant for amylose such that in 1:1 DMSO-water complex formation is essentially complete. The amylose-complexed stilbene derivative shows rather dramatically modified intramolecular photoreactivity. The compound is almost completely resistant to photoisomerization and its fluorescence quantum yield approaches unity. The fluorescence lifetime increases to very near the radiative limit. Recently some bimolecular reactions of complexed stilbene in its excited state have been studied.

  4. Reaction of dimethyl hydrogen phosphite with acecyclone

    SciTech Connect

    Arbuzov, B.A.; Fuzhenkova, A.V.; Tyryshkin, N.I.

    1987-07-20

    In the presence of bases acecyclone reacts with dimethyl hydrogen phosphite with the formation of gamma-keto phosphonates with conjugated and unconjugated structures, and also an enol phosphate, a product containing a bond between oxygen of the cyclone and phosphorus. In the absence of bases, as well as the beta-keto phosphonate, gamma-keto phosphonates of cis and trans structure are formed; they are products of the 1,4 addition of dimethyl hydrogen phosphite to the conjugated fragment C=C-C=O of the cyclone. The compositions of the reaction mixture were determined by IR and NMR spectroscopy and TLC. Full-scale analysis of chemical shifts and spin-spin coupling constants was performed.

  5. 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

  6. 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.

  7. Radiative transfer effects in primordial hydrogen recombination

    SciTech Connect

    Ali-Haiemoud, Yacine; Hirata, Christopher M.; Grin, Daniel

    2010-12-15

    The calculation of a highly accurate cosmological recombination history has been the object of particular attention recently, as it constitutes the major theoretical uncertainty when predicting the angular power spectrum of cosmic microwave background anisotropies. Lyman transitions, in particular the Lyman-{alpha} line, have long been recognized as one of the bottlenecks of recombination, due to their very low escape probabilities. The Sobolev approximation does not describe radiative transfer in the vicinity of Lyman lines to a sufficient degree of accuracy, and several corrections have already been computed in other works. In this paper, we compute the impact of some radiative transfer effects that were previously ignored, or for which previous treatments were incomplete. First, the effect of Thomson scattering in the vicinity of the Lyman-{alpha} line is evaluated, using a full redistribution kernel incorporated into a radiative transfer code. The effect of feedback of distortions generated by the optically thick deuterium Lyman-{alpha} line blueward of the hydrogen line is investigated with an analytic approximation. It is shown that both effects are negligible during cosmological hydrogen recombination. Second, the importance of high-lying, nonoverlapping Lyman transitions is assessed. It is shown that escape from lines above Ly{gamma} and frequency diffusion in Ly{beta} and higher lines can be neglected without loss of accuracy. Third, a formalism generalizing the Sobolev approximation is developed to account for the overlap of the high-lying Lyman lines, which is shown to lead to negligible changes to the recombination history. Finally, the possibility of a cosmological hydrogen recombination maser is investigated. It is shown that there is no such maser in the purely radiative treatment presented here.

  8. 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

  9. Study of molybdenum electrodes for hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Padilha, Janine Carvalho; Martini, Emilse Maria Agostini; Brum, Cauã; de Souza, Michèle Oberson; de Souza, Roberto Fernando

    The molybdenum electrode, Mo, has been investigated for hydrogen production via water electrolysis in 10 vol.% aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF 4) using electrochemical impedance spectroscopy (EIS). The EIS measurements show that the Mo system has much higher interfacial capacitance, and correspondently the electrical double layer formed on this electrode is thicker than those formed on nickel or platinum. The positive displacement of potential of zero charge (PZC) values indicates the specific adsorption of the imidazolium cation on the Mo surface. This study provides an elegant explanation for the better performance of Mo electrodes in the hydrogen evolution reaction (HER): the BMI cation acts as an intermediate for the proton transfer from water to the electrode surface, thereby decreasing the overpotential of HER. This model explains the synergism between Mo and the BMI cation in the HER process.

  10. 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…

  11. Molecular polarizabilities in aqueous proton transfer reactions

    NASA Astrophysics Data System (ADS)

    Buin, Andrei; Iftimie, Radu

    2009-12-01

    Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree of advancement of the ionization reaction F-H+H2O⇄[Fδ -ṡHṡOδ+H2]⇄F-+H3O+. This observation explains the validity of the Lorentz-Lorenz formula for mixtures of acids and water and could have important practical consequences concerning the construction of empirical polarizable reactive force fields. Our results are consistent with the Mulliken charge-transfer picture of proton transfer reactions. The present results also suggest that the average isotropic polarizability of a chemical entity changes substantially only when that entity is involved in charge-transfer processes.

  12. Hydrogen transfer in excited pyrrole-ammonia clusters

    NASA Astrophysics Data System (ADS)

    David, O.; Dedonder-Lardeux, C.; Jouvet, C.; Kang, H.; Martrenchard, S.; Ebata, T.; Sobolewski, A. L.

    2004-06-01

    The excited state hydrogen atom transfer reaction (ESHT) has been studied in pyrrole-ammonia clusters [PyH-(NH3)n+hν→Py•+•NH4(NH3)n-1]. The reaction is clearly evidenced through two-color R2P1 experiments using delayed ionization and presents a threshold around 235 nm (5.3 eV). The cluster dynamics has also been explored by picosecond time scale experiments. The clusters decay in the 10-30 ps range with lifetimes increasing with the cluster size. The appearance times for the reaction products are similar to the decay times of the parent clusters. Evaporation processes are also observed in competition with the reaction, and the cluster lifetime after evaporation is estimated to be around 10 ns. The kinetic energy of the reaction products is fairly large and the energy distribution seems quasi mono kinetic. These experimental results rule out the hypothesis that the reaction proceeds through a direct N-H bond rupture but rather imply the existence of a fairly long-lived intermediate state. Calculations performed at the CASSCF/CASMP2 level confirm the experimental observations, and provide some hints regarding the reaction mechanism.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. Intramolecular energy transfer reactions in polymetallic

    SciTech Connect

    Petersen, J.

    1990-11-01

    This report is concerned with intramolecular, energy-transfer reactions. The concept of preparing synthetically a complex molecular species, capable of absorbing a photon at one metal center (antenna fragment), transferring that energy to a second metal center (reactive fragment) via a bridging ligand was first reported by our group in 1979. It is now apparent that a major emphasis in inorganic chemistry in the future will involve these types of molecular ensembles. Complexes discussed include Rh, Ru, and Cu complexes. 23 refs., 14 tabs.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. Organometallic derivatives of furan. LX. Reactions of di-2-furyldimethylgermane under catalytic-hydrogenation conditions

    SciTech Connect

    Lukevits, E.; Ignatovich, L.M.; Yuskovets, Zh.G.; Golender, L.O.; Shimanskaya, M.V.

    1987-11-20

    In the reaction of di-2-furyldimethylgermane with hydrogen in the presence of the homogeneous metal-complex catalyst RhH(CO)(PPh/sub 3/)/sub 3/ the selective hydrogenation of one of the furan rings occurs, but over heterogeneous catalysts (Raney Ni, Rh black, Pd/C) hydrogenation and hydrogenolysis reactions occur. Di-2-furyldimethylgermane is converted into (2-furyl)dimethyl(tetrahydro-2-furyl)-germane by the catalytic transfer of hydrogen from 2-propanol and cyclohexene. On the basis of the kinetic relations and quantum-chemical calculations of the electron structures of the original and partially hydrogenated furylgermanes a stagewise scheme is proposed of the hydrogenation of the furan ring and the further hydrogenolysis of the semihydrogenated germane molecule.

  7. 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

  8. Hydrogen bonding tunes the early stage of hydrogen-atom abstracting reaction.

    PubMed

    Yang, Yang; Liu, Lei; Chen, Junsheng; Han, Keli

    2014-09-01

    The spontaneous and collision-assisted hydrogen-atom abstracting reaction (HA) dynamics of triplet benzil are investigated through the combination of transient absorption spectroscopy with TD-DFT calculations. HA dynamics exhibit a remarkable dependence on the hydrogen donor properties. The effects of the triplet-state hydrogen bonding on the reaction dynamics are illustrated. In particular, it is experimentally observed that strengthened triplet-state hydrogen bonding could accelerate the HA, whereas weakened triplet-state hydrogen bonding would postpone the HA. The triplet-state hydrogen bonding has great influences on the early stage of the HA reaction, while the bond dissociation energy of the hydrogen donors determines the subsequent reaction pathways. Protic solvents could sustain longer lifetimes of the excited-state intermediate formed after HA than non-protic solvents by 10 μs. This investigation provides insights into the HA dynamics and guidance to improve the product efficiency of photochemical reactions. PMID:25036436

  9. Molecular polarizabilities in aqueous proton transfer reactions

    SciTech Connect

    Buin, Andrei; Iftimie, Radu

    2009-12-21

    Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree of advancement of the ionization reaction F-H+H{sub 2}O<-->[F{sup {delta}-}{center_dot}H{center_dot}{sup {delta}+}OH{sub 2}]<-->F{sup -}+H{sub 3}O{sup +}. This observation explains the validity of the Lorentz-Lorenz formula for mixtures of acids and water and could have important practical consequences concerning the construction of empirical polarizable reactive force fields. Our results are consistent with the Mulliken charge-transfer picture of proton transfer reactions. The present results also suggest that the average isotropic polarizability of a chemical entity changes substantially only when that entity is involved in charge-transfer processes.

  10. 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

  11. Electrochemical reaction mechanisms for hydrogen at highly disperse tungsten carbide

    SciTech Connect

    Boikova, G.V.; Zhutaeva, G.V.; Tarasevich, M.R.

    1988-01-01

    The kinetic parameters of the electrochemical reaction of hydrogen ionization and evolution of tungsten carbide were compared and these reactions were described in terms of a unified reaction scheme. Two types of electrodes were used, a rotating disk electrode with a thin catalyst layer of disperse tungsten carbide and the second model was a floating gas-diffusion electrode. Fluoropolymer lacquer was used as the binder. The kinetic parameters were determined by measuring steady-state polarization curves and potentiodynamic curves. A hypothesis for a hydrogen ionization reaction scheme was developed which may serve in future investigations and the authors suggest prior deprotonation of the hydrogen molecules.

  12. Electron-transfer reactions in polymer matrices

    NASA Astrophysics Data System (ADS)

    Vannikov, Anatolii V.; Grishina, Antonina D.

    1989-12-01

    This paper discusses the dark reactions and photoreactions that occur with transfer of an electron from a donor to an acceptor in polymer matrices under electron tunnelling conditions and when forming change-transfer complexes. The main emphasis is on an analysis of the factors that determine the rate of electron transfer, which, in accordance with the advanced theory of electron transfer, are the magnitude of the exchange interaction, the free energy of the process, and the reorganisation energies of the medium and the reacting donor and acceptor molecules. The existing models for the movement of charge carriers between single-type transport sites are discussed. The limits of applicability of the different models have been determined. The reorganisation energy of a polymer matrix is shown to have a considerable effect on the rate of movement of charge carriers on introduced transport molecules. The effect of the dielectric properties and free volume of polymer matrices on the characteristics of electron phototransfer in donor-acceptor complexes is discussed. The bibliography includes 126 references.

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

    PubMed

    Cortés-Arriagada, Diego; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro

    2014-10-01

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp(3) hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state. PMID:25296822

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

    SciTech Connect

    Cortés-Arriagada, Diego Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro

    2014-10-07

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

  15. 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.

  16. Hydrogen exchange in some coal-related reactions at 400C

    SciTech Connect

    Benjamin, B.M.; Michalczyk, M.J.; Woody, M.C.

    1980-01-01

    The source of hydrogen in cleavage reactions and the paths of internal hydrogen transfer reactions (''hydrogen shuttling'') during solvent refining of coal were studied with deuterium-labeled model compounds. The reactions of 1,2-diphenylethane (bibenzyl, BB) and diphenylmethane (DPM), in which the dimethylene and methylene linkages, respectively, were completely deuterated with tetralin showed that BB formed toluene by C-C cleavage and hydrogen abstraction from tetralin, that DPM was relatively stable to fragmentation, but that both underwent extensive hydrogen exchange at 400C. The kinetics and possible reaction paths were determined for the reactions BB and DPM with tetralin. Reactions of labeled DPM, which exchanged deuterium readily but was otherwise stable, with Illinois No. 6 coal and North Dakota lignite showed that deuterium exchange was much more rapid with coal than in the tetralin system, probably owing to the larger number of radicals present; and that the deuterium was mainly in the benzylic portions of the products. Separate tests with model compounds showed that some aromatic hydrogen, mainly from polynuclear compounds, also underwent exchange. Reaction paths are discussed.

  17. Decoupling interfacial reactions between plasmas and liquids: charge transfer vs plasma neutral reactions.

    PubMed

    Rumbach, Paul; Witzke, Megan; Sankaran, R Mohan; Go, David B

    2013-11-01

    Plasmas (gas discharges) formed at the surface of liquids can promote a complex mixture of reactions in solution. Here, we decouple two classes of reactions, those initiated by electrons (electrolysis) and those initiated by gaseous neutral species, by examining an atmospheric-pressure microplasma formed in different ambients at the surface of aqueous saline (NaCl) solutions. Electrolytic reactions between plasma electrons and aqueous ions yield an excess of hydroxide ions (OH(-)), making the solution more basic, while reactions between reactive neutral species formed in the plasma phase and the solution lead to nitrous acid (HNO2), nitric acid (HNO3), and hydrogen peroxide (H2O2), making the solution more acidic. The relative importance of either reaction path is quantified by pH measurements, and we find that it depends directly on the composition of the ambient background gas. With a background gas of oxygen or argon, electron transfer reactions yielding excess OH(-) dominate, while HNO2 and HNO3 formed in the plasma and by the dissolution of nitrogen oxide (NOx) species dominate in the case of air and nitrogen. For pure nitrogen (N2) gas, we observe a unique coupling between both reactions, where oxygen (O2) gas formed via water electrolysis reacts in the bulk of the plasma to form NOx, HNO2, and HNO3. PMID:24144120

  18. Proton Transfer Reaction Ion Trap Mass Spectrometer

    SciTech Connect

    Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom T.; Alexander, M. Lizabeth

    2003-06-11

    Proton transfer reaction mass spectrometry is a relatively new field that has attracted a great deal of interest in the last few years. This technique uses H₃Oþ as a chemical ionization (CI) reagent to measure volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) to parts per trillion by volume (pptv) range. Mass spectra acquired with a proton transfer reaction mass spectrometer (PTR-MS) are simple because proton transfer chemical ionization is ‘soft’ and results in little or no fragmentation. Unfortunately, peak identification can still be difficult due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). The use of an ITMS is appealing because of its ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates are possible that will allow for detection of multiple compounds. Here we present the first results from a proton transfer reaction ion trap mass spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype instrument in order to estimate possible detection limits of a second-generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated. Modifications are suggested that will enable further reduction in detection limits to the low-ppbv to high-pptv range. Furthermore, the applicability of MS/MS in differentiating between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making differentiation possible, even when a mixture of both species is present in the same sample. However, MS/MS spectra of acetone and propanal produce fragments with the same molecular masses but with different intensity ratios

  19. 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.

  20. Hydrogen atom reactions in coal liquefaction. [Demethylation of methylnaphthalene by hydrogen

    SciTech Connect

    Bockrath, B.C.; Schroeder, K.T.; Keldsen, G.L.

    1985-06-01

    Hydrogen atom reactions were investigated in the demethylation of methylnaphthalenes at 450/sup 0/C. Demethylation by the hydrogen atom at the 1-position was about 4 times faster than at the 2-position. The methylnaphthalenes were somewhat more reactive toward hydrocracking than was bibenzyl. The extent of hydrocracking was a function of hydrogen pressure and initiator concentration. 3 refs., 2 figs., 1 tab.

  1. Charge transfer reaction laser with preionization means

    NASA Technical Reports Server (NTRS)

    Lauderslager, J. B.; Pacala, T. J. (Inventor)

    1978-01-01

    A helium-nitrogen laser is described in which energy in the visible range is emitted as a result of charge transfer reaction between helium ions and nitrogen molecules. The helium and nitrogen are present in a gas mixture at several atmospheres pressure, with a nitrogen partial pressure on the order of a pair of main discharge electrodes, the gas mixture is preionized to prevent arcing when the discharge pulse is applied. The preionization is achieved by the application of a high voltage across a pair of secondary electrodes which are spaced apart in a direction perpendicular to the spacing direction of the main discharge electrodes and the longitudinal axis of the space in which the gas mixture is contained. Feedback, by means of a pair of appropriately spaced mirrors, is provided, to produce coherent energy pulses at a selected wavelength.

  2. Electron transfer reactions in microporous solids

    SciTech Connect

    Mallouk, T.E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

  3. Electron transfer reactions in microporous solids

    NASA Astrophysics Data System (ADS)

    Mallouk, T. E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru3(2+) in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows two remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently 'dry' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV(2+) ion in these zeolites, determined by this technique, is 10(exp -7) sq cm sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2 to 3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K(4-x)H(x)Nb6O17 - nH2O(x approx. = 2.5) yields photocatalysts for the production of H2 and I3(-) in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

  4. 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

  5. [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.

  6. (Mechanistic examination of organometallic electron transfer reactions: Annual report, 1989)

    SciTech Connect

    Not Available

    1989-01-01

    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.

  7. Activation entropy of electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.

    2006-05-01

    We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models.

  8. Proton Transfer Reaction Ion Trap Mass Spectrometer

    SciTech Connect

    Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom; Alexander, M. Lizabeth

    2003-07-07

    Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a relatively new field that has attracted a great deal of interest in the last several years. This technique uses H3O+ as a chemical ionization (CI) agent for measuring volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) - parts per trillion by volume (pptv) range. PTR-MS mass spectra are simple because the ionization method of proton transfer is “soft”, resulting in little or no fragmentation. Unfortunately, the simplicity of the mass spectra can cause problems in peak identification due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). ITMS is appealing because of the ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates can be realized for detection of multiple compounds. We present here the first results from a Proton Transfer Reaction Ion Trap Mass Spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype interface in order to estimate possible detection limits of a second generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated for the PTR-ITMS. Modifications are suggested that will enable further reduction in detection limits to the low ppbv to pptv range. Furthermore the applicability of MS/MS to differentiate between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making a differentiation possible even when a mixture of both species is present in the same sample. MS/MS spectra of acetone and propanal produce fragments with the same molecular weight but different ratios, allowing quantitative distinction only if one species

  9. 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.

  10. Improved performance in co-processing through fundamental and mechanistic studies in hydrogen transfer and catalysis: Quarterly report, December 27, 1988--March 27, 1989

    SciTech Connect

    Curtis, C.W.; Guin, J.A.; Tarrer, A.R.

    1989-01-01

    To gain fundamental understanding of the role and importance of hydrogen transfer reactions in thermal and catalytic coprocessing by examining possible donation from cycloalkane/aromatic systems and by understanding the chemistry and enhanced reactivity of hydrotreated residuum, by enriching petroleum solvent with potent new donors, nonaromatic hydroaromatics, thereby promoting hydrogen transfer reactions in coprocessing. This quarter, a complete literature search was performed on hydrogen donation in coprocessing and coal liquefaction. The objective of this search was to undercover the role of hydrogen transfer from different types of model molecules to one another as well as the role of hydrogen donation in coprocessing and coal liquefaction. 24 refs.

  11. 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

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

    NASA Astrophysics Data System (ADS)

    Bower, John F.; Krische, Michael J.

    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.

  13. 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

  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. 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…

  16. Investigation of plasma hydrogenation and trapping mechanism for layer transfer

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Chu, Paul K.; Höchbauer, T.; Lee, J.-K.; Nastasi, M.; Buca, D.; Mantl, S.; Loo, R.; Caymax, M.; Alford, T.; Mayer, J. W.; Theodore, N. David; Cai, M.; Schmidt, B.; Lau, S. S.

    2005-01-01

    Hydrogen ion implantation is conventionally used to initiate the transfer of Si thin layers onto Si wafers coated with thermal oxide. In this work, we studied the feasibility of using plasma hydrogenation to replace high dose H implantation for layer transfer. Boron ion implantation was used to introduce H-trapping centers into Si wafers to illustrate the idea. Instead of the widely recognized interactions between boron and hydrogen atoms, this study showed that lattice damage, i.e., dangling bonds, traps H atoms and can lead to surface blistering during hydrogenation or upon postannealing at higher temperature. The B implantation and subsequent processes control the uniformity of H trapping and the trap depths. While the trap centers were introduced by B implantation in this study, there are many other means to do the same without implantation. Our results suggest an innovative way to achieve high quality transfer of Si layers without H implantation at high energies and high doses.

  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. 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.

  19. Phenomenological manifestations of large-curvature tunneling in hydride-transfer reactions

    SciTech Connect

    Kreevoy, M.M.; Ostovic, D.; Truhlar, D.G.; Garrett, B.C.

    1986-01-01

    An important consequence of recent dynamical theories of tunneling is that, because of large curvature of the reaction path in a typical H(+), or H(-) transfer, light-isotope transfer occurs in more extended nuclear frameworks than heavy-isotope transfer. This is now incorporated into the Marcus phenomenological theory relating reaction rate constants to equilibrium constants. It leads to Bronsted slope parameters that depend on the isotope transferred. The new theoretical formulation is tested on experimental data for hydride and deuteride transfer between nicotinamide adenine dinucleotide analogs and on computational data for hydrogen-atom and deuterium atom transfer between pseudo-atoms. The experimental kinetic isotope effects (KIE's) are shown to vary with reaction equilibrium constant (K/sub ij/) in a way that is quantitatively consistent with the theory. The critical configurations generated by the calculations vary from the saddle point and from each other in the way anticipated by the theory. However, the calculated KIE values are a rather scattered function of K/sub ij/, because the tunneling corrections are large and somewhat system specific. Overall, we believe that this combination of experimental and calculated results provides considerable support for the idea that large-curvature results provides considerable support for the idea that large-curvature tunneling needs to be considered in hydrogen transfer reactions.

  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. 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)

  2. Improved performance in coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, September 27, 1990--December 26, 1990

    SciTech Connect

    Curtis, C.W.

    1990-12-31

    The objective is 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.

  3. Improved performance in coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, September 26, 1989--December 26, 1989

    SciTech Connect

    Curtis, C.W.

    1989-12-31

    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.

  4. Improved performance in coprocessing through fundamental and mechanistic studies in hydrogen transfer and catalysis. Quarterly report, March 27, 1991--June 26, 1991

    SciTech Connect

    Curtis, C.W.

    1991-12-31

    The objective is 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.

  5. 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.

  6. 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.

  7. 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. PMID:26924817

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

    NASA Astrophysics Data System (ADS)

    Pan, Hui

    2016-02-01

    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.

  9. 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.

  10. 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

  11. 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

  12. 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...

  13. Towards a zinc-catalyzed asymmetric hydrogenation/transfer hydrogenation of imines.

    PubMed

    Werkmeister, Svenja; Fleischer, Steffen; Junge, Kathrin; Beller, Matthias

    2012-11-01

    The first asymmetric hydrogenation/transfer hydrogenation of imines to amines using zinc(II) triflate in combination with chiral ligands is described. The monodentate binaphthophosphepine ligand (3 g) provided the highest enantioselectivities. Using different imines, the corresponding amines were obtained in moderate yields and enantioselectivities. PMID:22807402

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. Photoinduced Electron and H-atom Transfer Reactions of Xanthone by Laser Flash Photolysis

    NASA Astrophysics Data System (ADS)

    Wang, Jin-ting; Pan, Yang; Zhang, Li-min; Yu, Shu-qin

    2007-08-01

    The property of the lowest excited triplet states of xanthone in acetonitrile was investigated using time-resolved laser flash photolysis at 355 nm. The transient absorption spectra and the quenching rate constants (kq) of the excited xanthone with several amines were determined. Good correlation between lgkq and the driving force of the reactions suggests the electron transfer mechanism, except aniline and 3-nitroaniline (3-NO2-A) which showed energy transfer mechanism. With the appearance of ketyl radical, hydrogen atom transfer also happened between xanthone and dimethyl-p-toluidine, 3,5,N,N-tetramethylaniline, N,N-dimethylaniline, and triethylamine. Therefore, both electron transfer and H-atom transfer occured in these systems. Great discrepancies of kq values were discovered in H-atom abstraction reactions for alcohols and phenols, which can be explained by different abstraction mechanisms. The quenching rate constants between xanthone and alcohols correlate well with the α-C-H bonding energy of alcohols.

  20. 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

  1. 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.

  2. Droplet heat transfer and chemical reactions during direct containment heating

    SciTech Connect

    Baker, L. Jr.

    1986-01-01

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

  3. 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

  4. 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.

  5. Methanol oxidation and hydrogen reactions on NiZr in acid solution

    NASA Astrophysics Data System (ADS)

    Hays, C. C.; Manoharan, R.; Goodenough, J. B.

    The electrochemical properties of a Ni 50Zr 50 (at.%) alloy have been investigated by cyclic voltammetry and steady-state polarization measurements. The alloy forms a passivating oxyhydroxide film that makes it electrochemically stable in an acid solution. The oxyhydroxide film is shown to be an electrocatalyst for the methanol oxidation reaction (MOR). The reaction proceeds at surface O 2- ions neighboring a Ni 3+ ion of a thicker passivating film; electron transfer from the surface to the electrode occurs diffusively by the nickel atoms of the film. A reaction pathway is presented that accounts for the observation of an optimum thickness for the passivating film. The NiZr alloy was also found to catalyze both hydrogen-oxidation and proton-reduction reactions (HOR and PRR) if it has a thinner surface oxyhydroxide film. The alloy appears to form mixed NiZrH and NiZrH 3- x hydrides on cycling negative of the normal hydrogen potential. The activity of the hydrogen-oxidation reaction on a hydride surface was found to increase in the presence of streaming hydrogen gas and also with increasing negative initial potential. Although the hydride is unstable in acid, it may be an attractive candidate for use as a rechargeable negative electrode in an alkaline metal/air or nickel-metal hydride secondary battery.

  6. 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. PMID:24289348

  7. 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).

  8. Construction of the isocopalane skeleton: application of a desulfinylative 1,7-hydrogen atom transfer strategy.

    PubMed

    Xiao, Xiong; Xu, ZhongYu; Zeng, Qian-Ding; Chen, Xi-Bo; Ji, Wen-Hao; Han, Ying; Wu, PeiYing; Ren, Jiangmeng; Zeng, Bu-Bing

    2015-06-01

    Two attractive chirons, aldehyde 6 and chloride 7, exhibiting functionalized ent-spongiane-type tricyclic skeletons (ABC ring system), have been constructed and their absolute configurations have been studied by NMR spectroscopy and confirmed by single-crystal X-ray diffraction. Both of these chirons are derived from commercially available andrographolide in good yield. Aldehyde 6 is obtained through a novel K2 S2 O8 -catalyzed aquatic ring-closing reaction of allylic sodium sulfonate and intramolecular 1,7-hydrogen atom transfer process. Further mechanistic investigations demonstrate that the 1,7-hydrogen atom transfer is a free-radical process, whereby hydrogen migrates from C18 to C17, as evidenced by double-18- deuterium-labeled isotope experiments. Prospective applications of these two chiral sources are also discussed. PMID:25907201

  9. 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

  10. 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

  11. 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.

  12. 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

  13. Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage

    SciTech Connect

    Alapati, S.V.; Johnson, J.K.; Sholl, D.S.

    2007-02-01

    Reversible storage of hydrogen still remains one of the biggest challenges for widespread use of hydrogen as a fuel. Light metal hydrides have high hydrogen content but are typically too thermodynamically stable. Destabilization of metal hydrides is an effective way to improve their thermodynamics. First principles calculations have proven to be effective for screening potential destabilized reactions, but these calculations have previously been limited to examining approximations for reaction enthalpies. We have used density functional theory calculations to calculate the reaction free energy and van’t Hoff plots for a variety of potential destabilized metal hydride reactions. Our calculations suggest a multistage approach for efficiently screening new classes of metal hydrides prior to experimental studies.

  14. Iron-Catalyzed Regioselective Transfer Hydrogenative Couplings of Unactivated Aldehydes with Simple Alkenes.

    PubMed

    Zheng, Yan-Long; Liu, Yan-Yao; Wu, Yi-Mei; Wang, Yin-Xia; Lin, Yu-Tong; Ye, Mengchun

    2016-05-17

    An FeBr3 -catalyzed reductive coupling of various aldehydes with alkenes that proceeds through a direct hydride transfer pathway has been developed. With (i) PrOH as the hydrogen donor under mild conditions, previously challenging coupling reactions of unactivated alkyl and aryl aldehydes with simple alkenes, such as styrene derivatives and α-olefins, proceeded smoothly to furnish a diverse range of functionalized alcohols with complete linear regioselectivity. PMID:27072872

  15. 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…

  16. Hydrogen evolution from water by use of viologen polymers as electron transfer catalyst

    SciTech Connect

    Ageishi, K.; Endo, T.; Okawara, M.

    1981-05-01

    The behavior of viologen polymer (P-V/sup 2 +/) as an electron transfer catalyst in the reaction of hydrogen generation was studied. In the photoirradiation system, which contains triethanolamine (TEA), Ru(bpy)/sub 3//sup 3 +/, and P-V/sup 2 +/, the amount of hydrogen evolution was less than methyl viologen (MV/sup 2 +/); P-V/sup 2 +/, however, was more effective in sodium dithionite as the electron donor and showed higher initial rates than MV/sup 2 +/. 3 figures, 2 tables.

  17. 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.

  18. Replacing precious metals with carbide catalysts for hydrogenation reactions

    DOE PAGESBeta

    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

  19. Hydride transfer reaction dynamics of OD{sup +}+C{sub 3}H{sub 6}

    SciTech Connect

    Liu, Li; Richards, Elizabeth S.; Farrar, James M.

    2007-06-28

    The hydride transfer reaction between OD{sup +} and C{sub 3}H{sub 6} has been studied experimentally and theoretically over the center of mass collision energy range from 0.21 to 0.92 eV using the crossed beam technique and density functional theory calculations. The center of mass flux distributions of the product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor propylene beam, characteristic of direct reactions. In the hydride transfer process, the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the hydride ion is transferred with both the breaking and forming bonds extended. At higher collision energies, at least 85% of the incremental translational energy appears in product translation, providing a clear example of induced repulsive energy release. Compared to the related reaction of OD{sup +} with C{sub 2}H{sub 4}, reaction along the pathway initiated by addition of OD{sup +} to the C=C bond in propylene has a critical bottleneck caused by the torsional motion of the methyl substituent on the double bond. This bottleneck suppresses reaction through an intermediate complex in favor of direct hydride abstraction. Hydride abstraction appears to be a sequential process initiated by electron transfer in the triplet manifold, followed by rapid intersystem crossing and subsequent hydrogen atom transfer to form ground state allyl cation and HOD.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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'.

  6. Fission Study Using Multi-Nucleon Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Nishio, K.; Hirose, K.; Lėguillon, R.; Makii, H.; Nishinaka, I.; Orlandi, R.; Smallcombe, J.; Ishii, T.; Tsukada, K.; Asai, M.; Chiba, S.; Ohtsuki, T.; Tatsuzawa, R.; Takaki, N.

    2015-06-01

    Fission study using multi-nucleon transfer reaction will be discussed. 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 using many 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..

  7. Hydrogen exchange in some coal-related reactions at 400/sup 0/C

    SciTech Connect

    Benjamin, B.M.; Michalczyk, M.J.; Woody, M.C.

    1980-01-01

    Data are available for kinetics of the transfer of hydrogen from tetralin and other hydrogen-rich solvents, but not much is known about the detailed mechanism involving individual linkages or groups in coal. In order to obtain some of this information, we have chosen to work with the pure compounds, 1,2-diphenylethane (bibenzyl), and diphenylmethane as models for certain linkages in coal. Because the thermolysis of the compound gives some different products when heated alone or when heated in the presence of a good hydrogen donor, such as tetralin, it was of interest to know where the cleavage fragments derive their hydrogen to give the final product. While the source of hydrogen needed to cap off the thermolysis fragments is obvious when bibenzyl is heated alone, its origin is ambiguous when tetralin is present. In order to resolve this aspect of the reaction, we prepared bibenzyl completely deuterated (99.8%) in the dimethylene linkage, and pyrolyzed it in the presence of ordinary tetralin. The products were isolated and their hydrogen and deuterium content were determined. From the data we conclude that the benzyl radical, formed by cleavage of bibenzyl, gives toluene by abstracting hydrogen from tetralin. The product after 1 percent conversion was PhCD/sub 2/H. Further, it was observed that, upon heating the mixture for eight hours, deuterium appeared in all the compounds. A considerable amount of deuterium exchange had taken place. In fact, in this mixture, tetralin-bibenzyl-d/sub 4/ at 400/sup 0/C, deuterium is lost from bibenzyl by exchange 3 to 4 times faster than it undergoes carbon-carbon bond scission. Thus, the chemistry of bibenzyl at 400/sup 0/ is dominated by hydrogen exchange reactions.

  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. 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

  10. 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.

  11. 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.

  12. Selective ruthenium-catalyzed transfer hydrogenations of nitriles to amines with 2-butanol.

    PubMed

    Werkmeister, Svenja; Bornschein, Christoph; Junge, Kathrin; Beller, Matthias

    2013-04-01

    Transfer your hydrogen: Fast and general transfer hydrogenation of nitriles to form primary amines is possible with a homogeneous Ru/1,4-bis(diphenylphosphino)butane (DPPB) catalyst (see scheme). The use of 2-butanol as the hydrogen-transfer reagent is essential for the selective reduction of aromatic, heteroaromatic, and aliphatic nitriles with this system. PMID:23450803

  13. 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

  14. A new probe reaction for studying the hydrogen spillover phenomenon

    SciTech Connect

    Zhang, Aihua; Nakamura, Ikusei; Fujimoto, Kaoru

    1997-06-01

    It was found by FTIR measurement that pyridine strongly adsorbed on acid sites of ZSM-5 was hydrogenated over Pt/H-ZSM-5 (0.5 wt%) and a Pt-hybrid catalyst (a physically mixed catalyst with a weight ratio of Pt/SiO{sub 2} (2.5 wt%)/H-ZSM-5 = 1:4) to adsorbed piperidine in the presence of gaseous hydrogen at around 473 K, whereas no such phenomena were observed on either H-ZSM-5 or Pt/SiO{sub 2}. The phenomenon revealed the occurrence of hydrogen spillover from Pt sites to zeolite acid sites (Bronsted and Lewis). A quantitative description of this reaction was attained by calculating and measuring the amount of zeolite acid on the basis of pyridine chemisorption and hydrogen consumption. In connection with this finding, the dehydrogenation of adsorbed piperidine in correlation with reverse hydrogen spillover was also observed on Pt/H-ZSM-5 catalyst in the temperature range from 623 to 723 K. 29 refs., 9 figs., 1 tab.

  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. 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

  17. Proton transfer reactions for improved peptide characterisation.

    PubMed

    Rožman, Marko; Schneider, Andrea; Gaskell, Simon J

    2011-06-01

    The combination of deprotonation (via ion/molecule and ion/ion reactions) and low-energy collision-induced dissociation (CID) has been explored for the enhanced characterisation of tryptic peptides via access to different precursor charge states. This approach allows instant access to fragmentation properties of singly and doubly protonated precursors (arising from the availability of mobile protons) in a single experiment. Considering both charge states extended our base of structurally informative data (in comparison with considering just a single charge state) due to generation of additional sequence ions and by obtaining supplementary structural information derived from selective cleavages. Roughly 37% of combined data sets (CID spectra of doubly and singly charged precursor) showed a greater database identification confidence than each set alone. Moreover, comparison between a number of sequence ions of the singly charged precursor and the doubly charged precursor provided a mean of distinguishing the two classes of tryptic peptides (arginine or lysine containing). PMID:21630380

  18. 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.

  19. 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...

  20. 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.

  1. 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

  2. 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

  3. Effect of thermal nonequilibrium on reactions in hydrogen combustion

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

  4. Theoretical studies on shaking processes in nuclear transfer reactions

    NASA Astrophysics Data System (ADS)

    Sharma, Prashant; Nandi, Tapan

    2015-09-01

    The probabilities of shaking processes during nuclear transfer reactions have been studied using the Mukoyama formalism after the re-examination of formalism for β-decay processes. Electron shakeoff probabilities have been calculated for the α-transfer reaction in the range of Z = 10- 50. The Z-dependence on the shakeoff probabilities so obtained has been represented by an analytical equation with two parameters. The formalism has been applied on a typical nuclear transfer reaction Fe5626 +C126 →Ni6028 +Be84 and it is found that electron shakeup, shakedown and shakeoff probabilities dominate for low l quantum number of the respective shells of the projectile-like fragment ion. However, for a particular value of l these processes show high probabilities for low values of n quantum number.

  5. 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

  6. Forced flow heat transfer of supercritical hydrogen for superconductor cooling

    NASA Astrophysics Data System (ADS)

    Shiotsu, M.; Shirai, Y.; Tatsumoto, H.; Hata, K.; Kobayashi, H.; Naruo, Y.; Inatani, H.

    2014-01-01

    Heat transfer from inner side of a vertical tube to forced flow of hydrogen was measured at the pressure of 1.5 MPa. The test tubes were made of stainless steel 316L with the inner diameters from 3 mm to 9 mm and lengths from 100 mm to 250 mm. Heat transfer curves were obtained by gradually increasing the heating current to the test tube and raising the surface temperature up to around 200 K. Inlet fluid temperature and flow velocity were varied from 21 to 30 K and 0.5 to 12 m/s, respectively. Effects of inlet temperature, flow velocity and tube dimension were clearly observed. The heat transfer curve for each flow velocity consists of a lower temperature region with a higher gradient and higher temperature region with a lower gradient. The experimental results were compared with the authors' correlation presented formerly. It was confirmed that this correlation can describe the experimental results obtained here.

  7. Individual breathing reactions measured in hemoglobin by hydrogen exchange methods

    SciTech Connect

    Englander, S.W.; Calhoun, D.B.; Englander, J.J.; Kallenbach, N.R.; Liem, R.K.H.; Malin, E.L.; Mandal, C.; Rogero, J.R.

    1980-10-01

    Protein hydrogen exchange is generally believed to register some aspect of internal protein dynamics, but the kind of motion at work is not clear. Experiments are being done to identify the determinants of protein hydrogen exchange and to distinguish between local unfolding and accessibility-penetration mechanisms. Results with small molecules, polynucleotides, and proteins demonstrate that solvent accessibility is by no means sufficient for fast exchange. H-exchange slowing is quite generally connected with intramolecular H-bonding, and the exchange process depends pivotally on transient H-bond cleavage. At least in ..cap alpha..-helical structures, the cooperative aspect of H-bond cleavage mut be expressed in local unfolding reactions. Results obtained by use of a difference hydrogen exchange method appear to provide a direct measurement of transient, cooperative, local unfolding reactions in hemoglobin. The reality of these supposed coherent breathing units is being tested by using the difference H-exchange approach to tritium label the units one at a time and then attempting to locate the tritium by fragmenting the protein, separating the fragments, and testing them for label. Early results demonstrate the feasibility of this approach.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Probing active electron transfer branch in photosystem I reaction center.

    NASA Astrophysics Data System (ADS)

    Savikhin, Sergei; Dashdorj, Naranbaatar; Xu, Wu; Martinsson, Peter; Chitnis, Parag

    2003-03-01

    Complimentary point mutations were introduced at the primary electron acceptor sites in A and B branches of the photosystem I (PS I) reaction center (RC) from Synechocystis sp. PCC 6803 and their effect on the kinetics of the electron transfer process was studied by means of ultrafast pump-probe spectroscopy. The results indicate that in these species the electron transfer occurs primarily along the A-branch. Previous optical experiments on PS I complexes from Chlorella sorokiniana demonstrated that both branches of RC are equally active. That suggests that the directionality of electron transfer in PS I is species dependent.

  13. 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

  14. The effect of local substrate motion on quantum hydrogen transfer in soybean lipoxygenase-1 modeled with QTES-DFTB dynamics

    NASA Astrophysics Data System (ADS)

    Mazzuca, James W.; Garashchuk, Sophya; Jakowski, Jacek

    2014-10-01

    The motion of local substrate nuclei is incorporated into the quantum hydrogen transfer reaction which occurs in the active site of soybean lipoxygenase-1, modeled within a quantum trajectory (QT) framework. Interactions within the active site are obtained from on-the-fly electronic structure (ES) calculations at the density-functional tight-binding (DFTB) level. By selectively constraining substrate nuclei, changes in the rate constants and kinetic isotope effect are computed over a 100 K temperature range. Substrate motion, occurring on the time-scale of the hydrogen transfer, enhances both the rate constants and isotope effect, but does not change trends captured in a constrained substrate environment.

  15. 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.

  16. Facile Hydrogen Evolution Reaction on WO3Nanorods

    PubMed Central

    2007-01-01

    Tungsten trioxide nanorods have been generated by the thermal decomposition (450 °C) of tetrabutylammonium decatungstate. The synthesized tungsten trioxide (WO3) nanorods have been characterized by XRD, Raman, SEM, TEM, HRTEM and cyclic voltammetry. High resolution transmission electron microscopy and X-ray diffraction analysis showed that the synthesized WO3nanorods are crystalline in nature with monoclinic structure. The electrochemical experiments showed that they constitute a better electrocatalytic system for hydrogen evolution reaction in acid medium compared to their bulk counterpart.

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

    DOE PAGESBeta

    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.

  18. 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...

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. Electron Transfer versus Proton Transfer in Gas-Phase Ion/Ion Reactions of Polyprotonated Peptides

    PubMed Central

    Gunawardena, Harsha P.; He, Min; Chrisman, Paul A.; Pitteri, Sharon J.; Hogan, Jason M.; Hodges, Brittany D. M.; McLuckey, Scott A.

    2005-01-01

    The ion/ion reactions of several dozen reagent anions with triply protonated cations of the model peptide KGAILKGAILR have been examined to evaluate predictions of a Landau–Zener-based model for the likelihood for electron transfer. Evidence for electron transfer was provided by the appearance of fragment ions unique to electron transfer or electron capture dissociation. Proton transfer and electron transfer are competitive processes for any combination of anionic and cationic reactants. For reagent anions in reactions with protonated peptides, proton transfer is usually significantly more exothermic than electron transfer. If charge transfer occurs at relatively long distances, electron transfer should, therefore, be favored on kinetic grounds because the reactant and product channels cross at greater distances, provided conditions are favorable for electron transfer at the crossing point. The results are consistent with a model based on Landau–Zener theory that indicates both thermodynamic and geometric criteria apply for electron transfer involving polyatomic anions. Both the model and the data suggest that electron affinities associated with the anionic reagents greater than about 60–70 kcal/mol minimize the likelihood that electron transfer will be observed. Provided the electron affinity is not too high, the Franck–Condon factors associated with the anion and its corresponding neutral must not be too low. When one or the other of these criteria is not met, proton transfer tends to occur essentially exclusively. Experiments involving ion/ion attachment products also suggest that a significant barrier exists to the isomerization between chemical complexes that, if formed, lead to either proton transfer or electron transfer. PMID:16144411

  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. Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

    PubMed Central

    Perry, Richard H.; Brownell, Kristen R.; Chingin, Konstantin; Cahill, Thomas J.; Waymouth, Robert M.; Zare, Richard N.

    2012-01-01

    Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (β-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH3OH). By placing [(p-cymene)RuCl2]2 on a surface and spraying a solution of β-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH3). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O2 dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH3. These results represent an example that species generated from the (β-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH3OH to HCOOCH3. This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system. PMID:22315417

  6. 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

  7. 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

  8. Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols.

    PubMed

    Rhile, Ian J; Markle, Todd F; Nagao, Hirotaka; DiPasquale, Antonio G; Lam, Oanh P; Lockwood, Mark A; Rotter, Katrina; Mayer, James M

    2006-05-10

    Three phenols with pendant, hydrogen-bonded bases (HOAr-B) have been oxidized in MeCN with various one-electron oxidants. The bases are a primary amine (-CPh(2)NH(2)), an imidazole, and a pyridine. The product of chemical and quasi-reversible electrochemical oxidations in each case is the phenoxyl radical in which the phenolic proton has transferred to the base, (*)OAr-BH(+), a proton-coupled electron transfer (PCET) process. The redox potentials for these oxidations are lower than for other phenols, predominately from the driving force for proton movement. One-electron oxidation of the phenols occurs by a concerted proton-electron transfer (CPET) mechanism, based on thermochemical arguments, isotope effects, and DeltaDeltaG(++)/DeltaDeltaG degrees . The data rule out stepwise paths involving initial electron transfer to form the phenol radical cations [(*)(+)HOAr-B] or initial proton transfer to give the zwitterions [(-)OAr-BH(+)]. The rate constant for heterogeneous electron transfer from HOAr-NH(2) to a platinum electrode has been derived from electrochemical measurements. For oxidations of HOAr-NH(2), the dependence of the solution rate constants on driving force, on temperature, and on the nature of the oxidant, and the correspondence between the homogeneous and heterogeneous rate constants, are all consistent with the application of adiabatic Marcus theory. The CPET reorganization energies, lambda = 23-56 kcal mol(-)(1), are large in comparison with those for electron transfer reactions of aromatic compounds. The reactions are not highly non-adiabatic, based on minimum values of H(rp) derived from the temperature dependence of the rate constants. These are among the first detailed analyses of CPET reactions where the proton and electron move to different sites. PMID:16669677

  9. 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.

  10. Easy To Synthesize, Robust Organo‐osmium Asymmetric Transfer Hydrogenation Catalysts

    PubMed Central

    Coverdale, James P. C.; Sanchez‐Cano, Carlos; Clarkson, Guy J.; Soni, Rina

    2015-01-01

    Abstract Asymmetric transfer hydrogenation (ATH) is an important process in organic synthesis for which the Noyori‐type RuII catalysts [(arene)Ru(Tsdiamine)] are now well established and widely used. We now demonstrate for the first time the catalytic activity of the osmium analogues. X‐ray crystal structures of the 16‐electron OsII catalysts are almost identical to those of RuII. Intriguingly the precursor complex was isolated as a dichlorido complex with a monodentate amine ligand. The OsII catalysts are readily synthesised (within 1 h) and exhibit excellent enantioselectivity in ATH reactions of ketones. PMID:25853228

  11. 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

  12. 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.

  13. Modeling of Syngas Reactions and Hydrogen Generation Over Sulfides

    SciTech Connect

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

    2002-09-17

    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. In this first year of 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 geometries and strengths of the adsorption sites are described and the methods used in the study are described. An exposed MO{sup IV} species modeled as a bent MoS{sub 2} molecule is capable of homopolar dissociative chemisorption of H{sub 2} into a dihydride S{sub 2}MoH{sub 2}. Among the periodic edge structures of hexagonal MoS{sub 2}, the (1{bar 2}11) edge is most stable but still capable of dissociating H{sub 2}, while the basal plane (0001) is not. A challenging task of theoretically accounting for weak bonding of MoS{sub 2} sheets across the Van der Waals gap has been addressed, resulting in a weak attraction of 0.028 eV/MoS{sub 2} unit, compared to the experimental value of 0.013 eV/MoS{sub 2} unit.

  14. Calculation of muon transfer from muonic hydrogen to atomic oxygen

    SciTech Connect

    Dupays, Arnaud; Lepetit, Bruno; Beswick, J. Alberto; Rizzo, Carlo; Bakalov, Dimitar

    2003-06-01

    The muon-transfer probabilities between muonic hydrogen and an oxygen atom are calculated in a constrained geometry one-dimensional model for collision energies between 10{sup -6} and 10{sup 3} eV. For relative translational energies below 10{sup -1} eV, for which the de Broglie wavelength (>1 Aa) is much larger than the characteristic distance of the potential interaction ({approx}0.1 Aa), the problem corresponds to an ultracold collision. The close-coupling time-independent quantum equations are written in terms of hyperspherical coordinates and a diabatic-by-sectors basis set. The muon-transfer probabilities are qualitatively interpreted in terms of a model involving two Landau-Zener crossings together with the threshold energy dependence. Based on this analysis, a simple procedure to estimate the energy dependence of the muon-transfer rate in three dimensions is proposed. These estimated rates are discussed in the light of previous model calculations and available experimental data for this process. It is concluded that the high transfer rates at epithermal energies inferred from experiments are unlikely to be correct.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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

  1. Effects of nonlocal potentials on (p ,d ) transfer reactions

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    Background: Although local phenomenological optical potentials have been standardly used to interpret nuclear reactions, recent studies suggest the effects of nonlocality should not be neglected. Purpose: In this work we investigate the effects of nonlocality in (p ,d ) transfer reactions using nonlocal optical potentials. We compare results obtained with the dispersive optical model to those obtained using the Perey-Buck interaction. Method: We solve the scattering and bound-state equations for the nonlocal version of the dispersive optical model. Then, using the distorted-wave Born approximation, we calculate the transfer cross section for (p ,d ) on 40Ca at Ep=20 , 35, and 50 MeV. Results: The inclusion of nonlocality in the bound state has a larger effect than that in the scattering states. The overall effect on the transfer cross section is very significant. We found an increase due to nonlocality in the transfer cross section of ≈30 - 50 % when using the Perey-Buck interaction and of ≈15 - 50 % when using the dispersive optical potential. Conclusions: Although the details of the nonlocal interaction can change the magnitude of the effects, our study shows that qualitatively the results obtained using the dispersive optical potential and the Perey-Buck interaction are consistent, in both cases the transfer cross sections are significantly increased.

  2. Electron transfer pathways in photosystem I reaction centers

    NASA Astrophysics Data System (ADS)

    Ivashin, Nikolaj; Larsson, Sven

    2003-07-01

    Electron transfer following charge separation in the photosystem I (PSI) reaction center of Synechococcus elongatus is studied using theoretical methods. The difference in rate between two almost symmetrical A- and B-branches is caused by a difference in a single residue (Trp B673 versus Gly A693), close to the F X iron-sulfur cluster. Partly due to its polar environment, Trp B673 acts as an electron acceptor in its π-system. The rate increases on the B-side due to shortened distances for electron transfer.

  3. 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.

  4. 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

  5. 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.

  6. Cobalt-Boride: An efficient and robust electrocatalyst for Hydrogen Evolution Reaction

    NASA Astrophysics Data System (ADS)

    Gupta, Suraj; Patel, Nainesh; Miotello, Antonio; Kothari, D. C.

    2015-04-01

    This work presents Cobalt-Boride (Co-B) as a non-noble, efficient and robust electrocatalyst for Hydrogen Evolution Reaction (HER) active in aqueous solution of wide pH values. In neutral solution, amorphous Co-B nanoparticles (30-50 nm size) generate high current density (10 mA/cm2) at low overpotential (250 mV) with Tafel slope of 75 mV/dec following Volmer-Heyrovsky reaction mechanism. Highly active Co surface sites created by electronic transfer from B to Co (as inferred from XPS analysis and supported by theoretical calculations) are responsible for this significant HER activity in wide range of pH (4-9) values. Stability and reusability tests also demonstrate the robust nature of the catalyst.

  7. 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. © 2016 Wiley Periodicals, Inc. PMID:26864872

  8. 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. PMID:26704530

  9. 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.

  10. 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