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Sample records for c-c bond energy

  1. The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1989-01-01

    The bond dissociation energies (D sub e) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of D sub e with respect to the one particle basis is studied at the single reference modified coupled-pair functional (MCPF) level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration interaction (MRCI) D sub e values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size extensive averaged coupled pair functional (ACPF) method. It was found that the full valence complete active space self consistent field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds. To achieve chemical accuracy (1 kcal/mole) for the D sub e values of the doubly bonded species C2H4 and N2H2 requires one particle basis sets including up through h angular momentum functions (l = 5) and a multireference treatment of electron correlation: still higher levels of calculation are required to achieve chemical accuracy for the triply bonded species C2H2 and N2.

  2. The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1991-01-01

    The bond dissociation energies (De) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of De with respect to the one-particle basis is studied at the single-reference modified coupled-pair-functional (MCPF)level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration-interaction (MRCI) De values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size-extensive averaged-coupled-pair-functional (ACPF) method. The full-valence complete-active-space self-consistent-field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds.

  3. Understanding Rotation about a C=C Double Bond

    ERIC Educational Resources Information Center

    Barrows, Susan E.; Eberlein, Thomas H.

    2005-01-01

    The study focuses on the process and energetic cost of twisting around a C=C double bond and provides instructors with a simple vehicle for rectifying the common misrepresentation of C=C double bonds as rigid and inflexible. Discussions of cis and trans isomers of cycloalkenes are a good entry point for introducing students to the idea of a…

  4. Understanding Rotation about a C=C Double Bond

    ERIC Educational Resources Information Center

    Barrows, Susan E.; Eberlein, Thomas H.

    2005-01-01

    The study focuses on the process and energetic cost of twisting around a C=C double bond and provides instructors with a simple vehicle for rectifying the common misrepresentation of C=C double bonds as rigid and inflexible. Discussions of cis and trans isomers of cycloalkenes are a good entry point for introducing students to the idea of a

  5. Alkali metal mediated C-C bond coupling reaction

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2015-02-01

    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2]- was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results.

  6. C-C bond-forming desulfurizations of sulfoximines.

    PubMed

    Reggelin, M; Slavik, S; Bühle, P

    2008-09-18

    Highly substituted, enantiomerically pure azaheterocyclic ring systems play an important role in medicinal chemistry as potential peptide mimetics. Metalated 2-alkenyl sulfoximines offer an efficient entry to this class of compounds. In this paper, we describe a new means to remove the sulfonimidoyl auxiliary with concomitant formation of a C-C double bond. PMID:18712875

  7. S? Chalcogen Bonds between SF2 or SF4 and C-C Multiple Bonds.

    PubMed

    Nziko, Vincent de Paul N; Scheiner, Steve

    2015-06-01

    SF2 and SF4 were each paired with a series of unsaturated hydrocarbons including ethene, ethyne, 1,3-butadiene, and benzene, in each case forming a chalcogen bond between the S atom and the carbon ?-system. MP2 ab initio calculations reveal that the S atom is situated directly above one specific C?C bond, even when more than one are present. The binding energies range between 3.3 and 6.6 kcal/mol. SF2 engages in a stronger, and shorter, noncovalent bond than does SF4 for all systems with the exception of benzene, to which SF4 is more tightly bound. cis-Butadiene complexes contain the shortest chalcogen bond, even if not necessarily the strongest. The internal S-F covalent bonds elongate upon formation of each chalcogen bond. The molecules are held together largely by charge transfer forces, particularly from the C?C ?-bonds to the ?*(SF) antibonding orbitals. In the case of SF2, a sulfur lone pair can transfer charge into the ?* MOs of the alkene, a back-transfer which is more difficult for SF4. PMID:25970139

  8. Metal-Free Oxidative C-C Bond Formation through C-H Bond Functionalization.

    PubMed

    Narayan, Rishikesh; Matcha, Kiran; Antonchick, Andrey P

    2015-10-12

    The formation of C-C bonds embodies the core of organic chemistry because of its fundamental application in generation of molecular diversity and complexity. C-C bond-forming reactions are well-known challenges. To achieve this goal through direct functionalization of C-H bonds in both of the coupling partners represents the state-of-the-art in organic synthesis. Oxidative C-C bond formation obviates the need for prefunctionalization of both substrates. This Minireview is dedicated to the field of C-C bond-forming reactions through direct C-H bond functionalization under completely metal-free oxidative conditions. Selected important developments in this area have been summarized with representative examples and discussions on their reaction mechanisms. PMID:26239615

  9. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-01-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  10. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-12-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  11. Determination of effective potentials for the stretching of C? ? C? virtual bonds in polypeptide chains for coarse-grained simulations of proteins from ab initio energy surfaces of N-methylacetamide and N-acetylpyrrolidine

    PubMed Central

    Sieradzan, Adam K.; Scheraga, Harold A.; Liwo, Adam

    2012-01-01

    The potentials of mean force (PMFs) for the deformation of the C? ? C? virtual bonds in polypeptide chains were determined from the diabatic energy surfaces of N-methylacetamide (modeling regular peptide groups) and N-acetylpyrrolidine (modeling the peptide groups preceding proline), calculated at the Mller-Plesset (MP2) ab initio level of theory with the 6-31G(d,p) basis set. The energy surfaces were expressed in the C? ? C? virtual-bond length (d) and the H-N-C? ? C? improper dihedral angle (?) that describes the pyramidicity of the amide nitrogen, or in the C?-C?(O)-N-C? dihedral angle (?) and the angle ?. For each grid point, the potential energy was minimized with respect to all remaining degrees of freedom. The PMFs obtained from the (d, ?) energy surfaces produced realistic free-energy barriers to the trans-cis transition (10 kcal/mol and 13 kcal/mol for the regular and proline peptide groups, respectively, compared to 12.6 13.9 kcal/mol and 17.3 19.6 kcal/mol determined experimentally for glycylglycine and N-acylprolines, respectively), while those obtained from the (?, ?) energy maps produced either low-quality PMF curves when direct Boltzmann summation was implemented to compute the PMFs or too-flat curves with too-low free-energy barriers to the trans-cis transition if harmonic extrapolation was used to estimate the contributions to the partition function. An analytical bimodal logarithmic-Gaussian expression was fitted to the PMFs, and the potentials were implemented in the UNRES force field. Test Langevin-dynamics simulations were carried out for the Gly-Gly and Gly-Pro dipeptides, which showed a 106-fold increase of the simulated rate of the trans-cis isomerization with respect to that measured experimentally; effectively the same result was obtained with the analytical Kramers theory of reaction rate applied to the UNRES representation of the peptide groups. Application of Kramers theory to compute the rate constants from the all-atom ab initio energy surfaces of the model compounds studied resulted in isomerization rates close to the experimental values, which demonstrates that the increase of the isomerization rate in UNRES simulations results solely from averaging out the secondary degrees of freedom. PMID:23087598

  12. C-C bond formation: Rethinking cross-coupling

    NASA Astrophysics Data System (ADS)

    Sun, Ho-Yan; Hall, Dennis G.

    2014-07-01

    The palladium-catalysed cross-coupling of aryl- or alkenylboronates and aryl halides has proved phenomenally successful for the formation of Csp2-Csp2 bonds. Now, an alternative non-transition-metal-mediated coupling using similar reactants has been reported for the stereo-controlled formation of Csp2-Csp3 bonds.

  13. C-C and C-Heteroatom Bond Dissociation Energies in CH3R′C(OH)2: Energetics for Photocatalytic Processes of Organic Diolates on TiO2 Surfaces

    SciTech Connect

    Wang, Tsang-Hsiu; Dixon, David A.; Henderson, Michael A.

    2010-08-26

    The bond energies of a range of gem-diols, CH3R′C(OH)2 (R′ = H, F, Cl, Br, CN, NO2, CF3, CH3CH2, CH3CH2CH2, CH3CH2CH2CH2, ((CH3)2)CH, (CH3)3C, ((CH3)2CH)CH2, (CH3CH2)(CH3)CH, C6H5 (CH3CH2)(CH3)CH) which serve as models for binding to a surface have been studied with density functional theory (DFT) and the molecular orbital G3(MP2) methods to provide thermodynamic data for the analysis of the photochemistry of ketones on TiO2. The ultraviolet (UV) photon-induced photodecomposition of adsorbed acetone and 3,3-dimethylbutanone on the rutile TiO2 (110) surface have been investigated with photon stimulated desorption (PSD) and temperature programmed desorption (TPD). The C-CH3 and C-C(R′) bond dissociation energies in CH3R′C(OH)2 were predicted, and our calculated bond dissociation energies are in excellent agreement with the available experimental values. We used a series of isodemic reactions to provide small corrections to the various bond dissociation energies. The calculated bond dissociation energies are in agreement with the observed photodissociation processes except for R′ = CF3, suggesting that these processes are under thermodynamic control. For R′ = CF3, reaction dynamics also play a role in determining the photodissociation mechanism. The gas phase Brönsted acidities of the gem-diols were calculated. For three molecules, R′ = Cl, Br, and NO2, loss of a proton leads to the formation of a complex of acetic acid with the anion Cl-, Br-, and NO2-. The acidities of these three species are very high with the former two having acidities comparable to CF3SO3H. The ketones (R′RC(=O)) are weak Lewis acids except where addition of OH- leads to the dissociation of the complex to form an anion bonded to acetic acid, R' = NO2, Cl, and Br. The X-C bond dissociation energies for a number of X-CO2- species were calculated and these should be useful in correlating with photochemical reactivity studies.

  14. Building Giant Carbocycles by Reversible C-C Bond Formation.

    PubMed

    Beaudoin, Daniel; Levasseur-Grenon, Olivier; Maris, Thierry; Wuest, James D

    2016-01-01

    We describe a simple way to build giant macrocyclic hydrocarbons by the reversible formation of carbon-carbon bonds. Specifically, extended spirobifluorene-substituted derivatives of Wittig's hydrocarbon were synthesized and found to undergo oligomerization, giving the largest hydrocarbon that has been crystallized and characterized by X-ray diffraction to date. PMID:26597318

  15. Synthesis of Biaryls via Benzylic C-C Bond Cleavage of Styrenes and Benzyl Alcohols.

    PubMed

    Kumar, Arvind; Shah, Bhahwal Ali

    2015-11-01

    A metal-free oxidative coupling of styrenes and benzyl alcohols with arenes has been developed for the synthesis of biaryls. The reaction features a conspicuous benzylic C-C bond cleavage of styrenes and benzyl alcohols. The reaction with both substrates proceeds through a common aldehydic intermediate formed through oxidative C-C bond cleavage of alkene and oxidation of benzyl alcohols. The reaction proceeds efficiently over a broad range of substrates with excellent functional group tolerance. PMID:26479321

  16. Linear alkane C-C bond chemistry mediated by metal surfaces.

    PubMed

    Cai, Zeying; Liu, Meizhuang; She, Limin; Li, Xiaoli; Lee, Jason; Yao, Dao-Xin; Zhang, Haiming; Chi, Lifeng; Fuchs, Harald; Zhong, Dingyong

    2015-05-18

    Linear alkanes undergo different C-C bond chemistry (coupling or dissociation) thermally activated on anisotropic metal surfaces depending on the choice of the substrate material. Owing to the one-dimensional geometrical constraint, selective dehydrogenation and C-C coupling (polymerization) of linear alkanes take place on Au(110) surfaces with missing-row reconstruction. However, the case is dramatically different on Pt(110) surfaces, which exhibit similar reconstruction as Au(110). Instead of dehydrogenative polymerization, alkanes tend to dehydrogenative pyrolysis, resulting in hydrocarbon fragments. Density functional theory calculations reveal that dehydrogenation of alkanes on Au(110) surfaces is an endothermic process, but further C-C coupling between alkyl intermediates is exothermic. On the contrary, due to the much stronger C-Pt bonds, dehydrogenation on Pt(110) surfaces is energetically favorable, resulting in multiple hydrogen loss followed by C-C bond dissociation. PMID:25752674

  17. Structure sensitivity of hydrogenolytic cleavage of endocyclic and exocyclic C-C bonds in methylcyclohexane over supported iridium particles

    SciTech Connect

    Shi, Hui; Gutierrez, Oliver Y.; Haller, Gary L.; Mei, Donghai; Rousseau, Roger J.; Lercher, Johannes A.

    2013-01-02

    Structure sensitivities, H2 pressure effects and temperature dependencies for rates and selectivities of endo- and exocyclic CC bond cleavage in methylcyclohexane were studied over supported Ir catalysts. The rate of endocyclic CC bond cleavage first decreased and then increased with declining Ir dispersion from 0.65 to 0.035. The ring opening (RO) product distribution remained unchanged with varying H2 pressure on small Ir particles, while further shifting to methylhexanes with increasing H2 pressure on large particles. In contrast, the rate and selectivity of exocyclic CC bond cleavage decreased monotonically with increasing H2 pressure and decreasing Ir particle size. The distinct dependencies of endocyclic and exocyclic CC bond cleavage pathways on Ir dispersion and H2 pressure suggest that they are mediated by surface species with different ensemble size requirements. DFT calculations were performed on an Ir50 cluster and an Ir(111) surface, with or without pre-adsorbed hydrogen atoms, to provide insight into the observed effects of particle size and H2 pressure on RO pathways. On small Ir particles, the calculated dehydrogenation enthalpies for all endocyclic bonds were similar and affected to similar extents by H2 pressure; on large particles, the selectivity to n-heptane (via substituted C-C bond cleavage) was even lower than on small particles as a result of the least favorable adsorption and dehydrogenation energetics for hindered bonds. This work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences under Contract DE-AC05-76RL01830. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. The computing time is provided by the user project from EMSL, a national scientific user facility sponsored by the US Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

  18. Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

    PubMed Central

    Li, Fang-Ming; Yang, Hua-Qing; Ju, Ting-Yong; Li, Xiang-Yuan; Hu, Chang-Wei

    2012-01-01

    The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ?E?int, which is the actual interaction energy between the deformed reactants in the transition state. PMID:22942766

  19. Low temperature C?C bond scission during ethanol decomposition on Pt(331)

    NASA Astrophysics Data System (ADS)

    Cong, Y.; van Spaendonk, V.; Masel, R. I.

    1997-08-01

    The adsorption and decomposition of ethanol was studied on clean, and oxygen pre-covered Pt(331) surface by using mainly TPD, LEED and AES. It was found that ethanol adsorbed molecularly on the Pt(331) surface at low temperature. Upon heating, part of the ethanol desorbed molecularly from surface at 220 K, and part of the ethanol underwent C?C bond scission to form methane and a variety of other products. There are two distinct methane peaks at 240 K and 310 K in the desorption spectrum suggesting that there are two different pathways for ethanol decomposition on this surface; both pathways involve C?C bond scission since methane is a major desorption product. CO adsorption experiments as well as experiments with H (ad) and O (ad) suggest that the lower temperature pathway involves C?C bond scission at temperatures below that where the ethanol appreciably dehydrogenates, while the high temperature pathway involves dehydrogenation of the ethanol followed by C?C bond scission. O (ad) additions suppress the low temperature pathway and enhances the high temperature pathway presumably by speeding the dehydrogenation of the ethanol. H (ad) additions slightly enhance the low temperature pathway. We also observe hydrogenolysis of the ethanol to yield methanol at 180 K and methane at 240 K in the presence of excess hydrogen. These results show that the step sites on the Pt(331) surface have unusual activity for C?C bond scission in ethanol.

  20. Total synthesis of bryostatin 7 via C-C bond-forming hydrogenation.

    PubMed

    Lu, Yu; Woo, Sang Kook; Krische, Michael J

    2011-09-01

    The marine macrolide bryostatin 7 is prepared in 20 steps (longest linear sequence) and 36 total steps with five C-C bonds formed using hydrogenative methods. This approach represents the most concise synthesis of any bryostatin reported, to date. PMID:21780806

  1. Formation of CC Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

    PubMed Central

    Bower, John F.; Krische, Michael J.

    2011-01-01

    The formation of CC bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed CC 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 ?-unsaturated reactants generates electrophilenucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol CH bonds. PMID:21822399

  2. [Hydrogen induced C-C, C-N, and C-S bond activities on Pi and Ni surfaces]: Summary

    SciTech Connect

    Gland, J.L.

    1994-12-31

    This document summarizes research applied to chemical bond activation studies. Topics summarized include: Carbon nitrogen bonds experimentation with aniline on Ni(111), Mi(100), and Pt(111) surfaces; carbon sulfur bonds experimentation with methanethiol, phenylthiol, and dimethyl disulfide on Pt(111) and Ni(111) surfaces; carbon-carbon bonds experimentation on Ni(100), Ni(111) and Pt(111) surfaces; and in-situ fluorescence yield near edge spectroscopy.

  3. Conceptual Basis for Understanding C-C Bond Activation in Ethane by Second Row Transition Metal Carbides.

    PubMed

    Sahoo, Sanjubala; Reber, Arthur C; Khanna, Shiv N

    2015-12-24

    It has been suggested that the addition of carbon to Mo and W may improve their catalytic properties and even grant these metal carbides behaviors similar to those of late transition metals such as Pd and Pt. First-principles studies on the C-C bond activation of ethane by 4d transition metal (TM) atoms and TMC molecules have been carried out to develop a conceptual model underlying the changes. We find that the addition of carbon to TM atoms leads to large variations in the activation barrier depending on the metal, and that MoC indeed reveals a pronounced reduction in the C-C bond activation energy. A critical examination of molecular orbitals shows that the changes in reactivity are not linked to a dramatic increase in the filling of 4d states as implied by the analogy with Pd. The reactivity is governed by the location and filling of the 5s and 4d orbitals, with the different orbitals controlling different facets of reactivity. The 5s state controls the initial binding of ethane, with a strong anticorrelation between the ethane binding energy and the 5s occupation, while the location of the 4dz(2) orbital controls the reaction barrier that controls the activation energy for cleaving the C-C bond. PMID:26616749

  4. Iterative reactions of transient boronic acids enable sequential C-C bond formation.

    PubMed

    Battilocchio, Claudio; Feist, Florian; Hafner, Andreas; Simon, Meike; Tran, Duc N; Allwood, Daniel M; Blakemore, David C; Ley, Steven V

    2016-04-01

    The ability to form multiple carbon-carbon bonds in a controlled sequence and thus rapidly build molecular complexity in an iterative fashion is an important goal in modern chemical synthesis. In recent times, transition-metal-catalysed coupling reactions have dominated in the development of C-C bond forming processes. A desire to reduce the reliance on precious metals and a need to obtain products with very low levels of metal impurities has brought a renewed focus on metal-free coupling processes. Here, we report the in situ preparation of reactive allylic and benzylic boronic acids, obtained by reacting flow-generated diazo compounds with boronic acids, and their application in controlled iterative C-C bond forming reactions is described. Thus far we have shown the formation of up to three C-C bonds in a sequence including the final trapping of a reactive boronic acid species with an aldehyde to generate a range of new chemical structures. PMID:27001732

  5. Mechanisms of photoinduced C??C? bond breakage in protonated aromatic amino acids

    NASA Astrophysics Data System (ADS)

    Lucas, B.; Barat, M.; Fayeton, J. A.; Perot, M.; Jouvet, C.; Grgoire, G.; Brndsted Nielsen, S.

    2008-04-01

    Photoexcitation of protonated aromatic amino acids leads to C??C? bond breakage among other channels. There are two pathways for the C??C? bond breakage, one is a slow process (microseconds) that occurs after hydrogen loss from the electronically excited ion, whereas the other is a fast process (nanoseconds). In this paper, a comparative study of the fragmentation of four molecules shows that the presence of the carboxylic acid group is necessary for this fast fragmentation channel to occur. We suggest a mechanism based on light-induced electron transfer from the aromatic ring to the carboxylic acid, followed by a fast internal proton transfer from the ammonium group to the negatively charged carboxylic acid group. The ion formed is a biradical since the aromatic ring is ionized and the carbon of the COOH group has an unpaired electron. Breakage of the weak C??C? bond gives two even-electron fragments and is expected to quickly occur. The present experimental results together with the ab initio calculations support the interpretation previously proposed.

  6. Decomposition Pathways of Glycerol via CH, OH, and CC Bond Scission on Pt(111): A Density Functional Theory Study

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey

    2011-09-01

    Glycerol decomposition on Pt(111) via dehydrogenation or CC bond scission is examined with periodic density functional theory (DFT) calculations. The thermochemistry of dehydrogenation intermediates is first estimated using an empirical correlation scheme with parameters fit to selected DFT calculations; the resulting estimates for the more stable intermediates are refined with full DFT calculations. BrnstedEvansPolanyi (BEP) relationships for dehydrogenation and CC bond scission reactions are developed and used to estimate the kinetics of elementary dehydrogenation and CC bond scission steps in the reaction network. The combined thermochemical and kinetic analysis implies that glycerol dehydrogenation products at intermediate levels of dehydrogenation are the most thermochemically stable. Additionally, although CC bond scission transition state energies are high for glycerol and for intermediates at early stages of dehydrogenation, these energies decrease as the intermediates are successively dehydrogenated, reaching a minimum after the removal of several hydrogen atoms from glycerol. At these levels of dehydrogenation, the CC scission transition state energies become comparable to those of OH or CH scission. These results suggest that CC bonds are only broken after glycerol has been significantly dehydrogenated and demonstrate that DFT-based analyses, combined with simple correlation schemes, can be effective for elucidating general features of complex biomassic reaction networks.

  7. Decomposition Pathways of Glycerol via CH, OH, and CC Bond Scission on Pt(111): A Density Functional Theory Study

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey P.

    2011-10-13

    Glycerol decomposition on Pt(111) via dehydrogenation or CC bond scission is examined with periodic density functional theory (DFT) calculations. The thermochemistry of dehydrogenation intermediates is first estimated using an empirical correlation scheme with parameters fit to selected DFT calculations; the resulting estimates for the more stable intermediates are refined with full DFT calculations. BrnstedEvansPolanyi (BEP) relationships for dehydrogenation and CC bond scission reactions are developed and used to estimate the kinetics of elementary dehydrogenation and CC bond scission steps in the reaction network. The combined thermochemical and kinetic analysis implies that glycerol dehydrogenation products at intermediate levels of dehydrogenation are the most thermochemically stable. Additionally, although CC bond scission transition state energies are high for glycerol and for intermediates at early stages of dehydrogenation, these energies decrease as the intermediates are successively dehydrogenated, reaching a minimum after the removal of several hydrogen atoms from glycerol. At these levels of dehydrogenation, the CC scission transition state energies become comparable to those of OH or CH scission. These results suggest that CC bonds are only broken after glycerol has been significantly dehydrogenated and demonstrate that DFT-based analyses, combined with simple correlation schemes, can be effective for elucidating general features of complex biomassic reaction networks.

  8. Density Functional Theory Study of Selectivity Considerations for CC Versus CO Bond Scission in Glycerol Decomposition on Pt(111)

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey P.

    2012-05-01

    Glycerol decomposition via a combination of dehydrogenation, CC bond scission, and CO bond scission reactions is examined on Pt(111) with periodic Density Functional Theory (DFT) calculations. Building upon a previous study focused on CC bond scission in glycerol, the current work presents a ?rst analysis of the competition between CO and CC bond cleavage in this reaction network. The thermochemistry of various species produced from CO bond breaking in glycerol dehydrogenation intermediates is estimated using an extension of a previously introduced empirical correlation scheme, with parameters ?t to DFT calculations. BrnstedEvansPolanyi (BEP) relationships are then used to estimate the kinetics of CO bond breaking. When combined with the previous results, the thermochemical and kinetic analyses imply that, while CO bond scission may be competitive with CC bond scission during the early stages of glycerol dehydrogenation, the overall rates are likely to be very low. Later in the dehydrogenation process, where rates will be much higher, transition states for CC bond scission involving decarbonylation are much lower in energy than are the corresponding transition states for CO bond breaking, implying that the selectivity for CC scission will be high for glycerol decomposition on smooth platinum surfaces. It is anticipated that the correlation schemes described in this work will provide an ef?cient strategy for estimating thermochemical and kinetic energetics for a variety of elementary bond breaking processes on Pt(111) and may ultimately facilitate computational catalyst design for these and related catalytic processes.

  9. First principles study of the electronic and magnetic structures and bonding properties of UCoC2 ternary, characteristic of C-C units

    NASA Astrophysics Data System (ADS)

    Matar, Samir F.

    2013-03-01

    The electronic structure of UCoC2, a di-carbide with the C-C units is examined from ab initio with an assessment of the properties of chemical bonding. The energy-volume equation of state shows large anisotropy effects due to C-C alignment along tetragonal c-axis leading to high linear incompressibility. Relevant features of selective bonding of uranium and cobalt with carbon at two different Wyckoff sites and strong C-C interactions are remarkable. The vibrational frequencies for C⋯C stretching modes indicate closer behavior to aliphatic C-C rather than Cdbnd C double bond. A ferromagnetic ground state is proposed from the calculations.

  10. Metalloenzyme-Like Zeolites as Lewis Acid Catalysts for C-C Bond Formation.

    PubMed

    Van de Vyver, Stijn; Romn-Leshkov, Yuriy

    2015-10-19

    The use of metalloenzyme-like zeolites as Lewis acid catalysts for C-C bond formation reactions has received increasing attention over the past few years. In particular, the observation of direct aldol condensation reactions enabled by hydrophobic zeolites with isolated framework metal sites has encouraged the development of catalytic approaches for producing chemicals from biomass-derived compounds. The discovery of new Diels-Alder cycloaddition/dehydration routes and experimental and computational studies of Lewis acid catalyzed carbonyl-ene reactions have given a further boost to this rapidly evolving field. PMID:26465652

  11. Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

    SciTech Connect

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

  12. Ab initio calculations on a novel mode for storing and releasing electrons via C-C bond formation and cleavage

    SciTech Connect

    Cambi, R.; Nottoli, R.; Rosi, M.; Sgamellotti, A. ); Floriani, C. )

    1992-12-23

    Ab initio Hartree-Fock and second-order Moeller-Plesset calculations have been performed on systems which can be viewed as models for [Ni(salophen)] and its reductive product. The results indicate that the metal does not change its oxidation state in the reductive process because no orbitals, localized on nickel and at low energy, are available to accept electrons, except the in-plane d orbital, whose occupation would imply a large increase in the repulsion. The added electrons prefer to form a C-C bond, which can be cleaved restoring the original product. Ni[sup 2+] is electrostatically bonded to the ligand and acts as a shield among the negative charges of the ligand itself. Correlation effects influence the energetic balance of the reductive process but not as heavily as expected for transition metal systems because the electronic distribution at the transition metal ion does not change in the reaction. 17 refs., 2 figs., 2 tabs.

  13. A Homogeneous, Recyclable Polymer Support for Rh(I)-Catalyzed C-C Bond Formation

    PubMed Central

    Jana, Ranjan; Tunge, Jon A.

    2011-01-01

    A robust and practical polymer-supported, homogeneous, recyclable biphephos rhodium(I) catalyst has been developed for C-C bond formation reactions. Control of polymer molecular weight allowed tuning of the polymer solubility such that the polymer-supported catalyst is soluble in nonpolar solvents and insoluble in polar solvents. Using the supported rhodium catalysts, addition of aryl and vinylboronic acids to the electrophiles such as enones, aldehydes, N-sulfonyl aldimines, and alkynes occurs smoothly to provide products in high yields. Additions of terminal alkynes to enones and industrially relevant hydroformylation reactions have also been successfully carried out. Studies show that the leaching of Rh from the polymer support is low and catalyst recycle can be achieved by simple precipitation and filtration. PMID:21895010

  14. Silver(I) NHC mediated C-C bond activation of alkyl nitriles and catalytic efficiency in oxazoline synthesis.

    PubMed

    Heath, Rachael; Mller-Bunz, Helge; Albrecht, Martin

    2015-05-21

    Preparation of silver triazolylidene (trz) species from triazolium salts and Ag2O in refluxing MeCN leads to a selective C-C bond cleavage and the formation of complexes of general formula [(trz)Ag(CN)] from Calkyl-CN bond activation. Moreover, these silver carbene complexes are precursors of highly active catalysts for oxazoline formation via aldol condensation. PMID:25913007

  15. Bronsted-Evans-Polany relationships for C-C bond forming and C-C bond breaking reactions in thiamine-catalyzed decarboxylation of 2-keto acids using density functional theory.

    SciTech Connect

    Assary, R. S.; Broadbelt, L. J.; Curtiss, L. A.

    2012-01-01

    The concept of generalized enzyme reactions suggests that a wide variety of substrates can undergo enzymatic transformations, including those whose biotransformation has not yet been realized. The use of quantum chemistry to evaluate kinetic feasibility is an attractive approach to identify enzymes for the proposed transformation. However, the sheer number of novel transformations that can be generated makes this impractical as a screening approach. Therefore, it is essential to develop structure/activity relationships based on quantities that are more efficient to calculate. In this work, we propose a structure/activity relationship based on the free energy of binding or reaction of non-native substrates to evaluate the catalysis relative to that of native substrates. While Broensted-Evans-Polanyi (BEP) relationships such as that proposed here have found broad application in heterogeneous catalysis, their extension to enzymatic catalysis is limited. We report here on density functional theory (DFT) studies for C-C bond formation and C-C bond cleavage associated with the decarboxylation of six 2-keto acids by a thiamine-containing enzyme (EC 1.2.7.1) and demonstrate a linear relationship between the free energy of reaction and the activation barrier. We then applied this relationship to predict the activation barriers of 17 chemically similar novel reactions. These calculations reveal that there is a clear correlation between the free energy of formation of the transition state and the free energy of the reaction, suggesting that this method can be further extended to predict the kinetics of novel reactions through our computational framework for discovery of novel biochemical transformations.

  16. Application of a C-C Bond-Forming Conjugate Addition Reaction in Asymmetric Dearomatization of ?-Naphthols.

    PubMed

    Yang, Dongxu; Wang, Linqing; Kai, Ming; Li, Dan; Yao, Xiaojun; Wang, Rui

    2015-08-10

    A C-C bond-forming conjugate reaction was successfully applied to the enantioselective dearomatization of ?-naphthols. A C(sp2)-C(sp3) bond is formed by using propargylic ketones as reactive partners. Good to excellent Z/E?ratios and ee?values were obtained by employing an in?situ generated magnesium catalyst. Further transformations of the Z-configured C-C double bond in the products were achieved under mild reaction conditions. Moreover, the stereocontrolling element of this magnesium-catalyzed dearomatization reaction was explored by computational chemistry. PMID:26173841

  17. Aryl Nitriles from Alkynes Using tert-Butyl Nitrite: Metal-Free Approach to C?C Bond Cleavage.

    PubMed

    Dutta, Uttam; Lupton, David W; Maiti, Debabrata

    2016-02-19

    Alkyne C?C bond breaking, outside of alkyne metathesis, remains an underdeveloped area in reaction discovery. Recently, nitrogenation has been reported to allow nitrile formation from alkynes. A new protocol for the metal-free C?C bond cleavage of terminal alkynes to produce nitriles is reported. This method provides an opportunity to synthesize a vast range of nitriles containing aryl, heteroaryl, and natural product derivatives (38 examples). In addition, the potential of (t)BuONO to act as a powerful nitrogenating agent for terminal aryl alkynes is demonstrated. PMID:26849380

  18. Bond cleavage during isobutanol thermal decomposition and the breaking of C-C bonds in alcohols at high temperatures.

    PubMed

    Rosado-Reyes, Claudette; Tsang, Wing

    2013-10-10

    Isobutanol was thermally decomposed in a single pulse shock tube under conditions where chain processes were suppressed. The main reaction is the breaking of C-C bonds. Literature rate expressions, experimentally determined, are found in some cases to be in disagreement. The rate expressions for the decomposition processes at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm are k(isobutanol ? isopropyl + hydroxymethyl) + k(isobutanol ? methyl + 1-hydroxypropyl-2) = 10(16.70.3) exp(-41097 750) s(-1), where k(isobutanol ? isopropyl + hydroxymethyl) = 10(16.45 0.3) exp(-40910 750/T) s(-1) and k(isobutanol ? methyl + 1-hydroxypropyl-2) = 10(16.380.3) exp(-41560 750/T) s(-1). These values permit comparisons with recent estimates including those from ab initio calculations. A new procedure is presented that uses information on the kinetics of bond breaking reactions of alkanes and the effect of OH substitution to derive rate coefficients for similar reactions of alcohols. This leads to the following rate expression for the smaller alcohols, at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm, k(ethanol ? methyl + hydroxymethyl) = 10(16.420.3) exp(-43496 750 K/T) s(-1), k(isopropanol ? methyl + 1-hydroxyethyl) = 10(16.540.3) exp(-42495 750 K/T) s(-1), k(n-propanol ? ethyl + hydroxymethyl) = 10(16.430.3) exp(-41696 750 K/T) s(-1), and k(n-propanol ? methyl + 2-hydroxymethyl) = 10(16.530.3) exp(-42945 750 K/T) s(-1). Extension of this approach to other alcohols is straightforward. The resulting correlations along with the data on dehydration of alcohols provide novel information of the kinetic stability of alcohols. PMID:23968459

  19. Efficient synthesis of ?-tertiary ?-silylamines from aryl sulfonylimidates via one-pot, sequential C-Si/C-C bond formations.

    PubMed

    Han, Xiao-Jun; Yao, Ming; Lu, Chong-Dao

    2012-06-01

    An efficient and flexible route for the synthesis of ?-tertiary (?,?-dibranched) ?-silylamines via sequential reactions of sulfonylimidates using readily available phenyldimethylsilyllithium and Grignard reagents is described. The procedure allows successive formation of C-Si/C-C bonds in a single flask. PMID:22621235

  20. Regiospecific Synthesis of Benzoxepines through Pd-Catalyzed Carbene Migratory Insertion and C-C Bond Cleavage.

    PubMed

    Xie, Yang; Zhang, Ping; Zhou, Lei

    2016-03-01

    A new method for the synthesis of benzoxepines via migratory insertion into a Pd carbene followed by C-C bond cleavage was developed. Various benzoxepines were constructed by the regioselective ring expansion concomitant with the introduction of an aryl group at their 5-position. PMID:26841938

  1. Alkynylation of Tertiary Cycloalkanols via Radical C-C Bond Cleavage: A Route to Distal Alkynylated Ketones.

    PubMed

    Wang, Shun; Guo, Li-Na; Wang, Hua; Duan, Xin-Hua

    2015-10-01

    An efficient Na2S2O8-promoted radical coupling of tertiary cycloalkanols with alkynyl hypervalent iodide reagents via C-C bond cleavage was developed. This tandem ring-opening/alkynylation procedure showed some advantages, including mild conditions and wide substrate scope, thus providing a simple synthetic method for ?-, ?- and ?-alkynylated ketones. PMID:26378463

  2. Enantioselective Rh-Catalyzed Carboacylation of C?N Bonds via C-C Activation of Benzocyclobutenones.

    PubMed

    Deng, Lin; Xu, Tao; Li, Hongbo; Dong, Guangbin

    2016-01-13

    Herein we describe the first enantioselective Rh-catalyzed carboacylation of oximes (imines) via C-C activation. In this transformation, the benzocyclobutenone C1-C2 bond is selectively activated by a low valent rhodium catalyst and subsequently the resulting two Rh-C bonds add across a C?N bond, which provides a unique approach to access chiral lactams. A range of polycyclic nitrogen-containing scaffolds were obtained in good yields with excellent enantioselectivity. Further derivatization of the lactam products led to a rapid entry to various novel fused heterocycles. PMID:26674855

  3. Ruthenium-Catalyzed C-C Bond Cleavage of 2H-Azirines: A Formal [3+2+2] Cycloaddition to Fused Azepine Skeletons.

    PubMed

    Li, Tengfei; Xu, Fen; Li, Xincheng; Wang, Chunxiang; Wan, Boshun

    2016-02-01

    2H-azirines can serve as three-atom synthons by C-C bond cleavage, however, it involves a high energy barrier under thermal conditions (>50.0?kcal?mol(-1) ). Reported is a ruthenium-catalyzed [3+2+2] cycloaddition reaction of 2H-azirines with diynes, thus leading to the formation of fused azepine skeletons. This approach features an unprecedented metal-catalyzed C-C bond cleavage of 2H-azirines at room temperature, and the challenging construction of aza-seven-membered rings from diynes. The results of this study provide a new reaction pattern for constructing nitrogen-containing seven-membered rings and may find applications in the synthesis of other complex heterocycles. PMID:26800151

  4. Stereoselective total synthesis of (-)-nupharamine utilizing an ?-chlorosulfide and a sulfinimine for C-C bond formation.

    PubMed

    Raghavan, Sadagopan; Rajendar, Sheelamanthula

    2016-01-01

    An efficient stereoselective synthesis of the nuphar alkaloid, (-)-nupharamine, is reported. The key features include the Lewis acid catalyzed reaction of an ?-chlorosulfide with a silyl ketene acetal for C-C bond formation, creation of the stereocenter at C2 by a diastereoselective reaction of allyl indium with a sulfinimine and reductive amination for the introduction of the C6 stereocenter of the piperidine ring. PMID:26490750

  5. Phenyliodonium diacetate mediated direct synthesis of benzonitriles from styrenes through oxidative cleavage of C?C bonds.

    PubMed

    Xu, Jin-Hui; Jiang, Qing; Guo, Can-Cheng

    2013-12-01

    A metal-free PhI(OAc)2 mediated nitrogenation of alkenes through C?C bond cleavage using inorganic ammonia salt as nitrogen source under mild conditions was developed, affording nitriles in moderate to good yields. The advantages of this reaction are mild reaction conditions, operational simplicity, and use of an ammonium salt as nitrogen source. Based upon experimental observations, a plausible reaction mechanism is proposed. PMID:24171555

  6. Deamination, oxidation, and C-C bond cleavage reactivity of 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxycytosine.

    PubMed

    Schiesser, Stefan; Pfaffeneder, Toni; Sadeghian, Keyarash; Hackner, Benjamin; Steigenberger, Barbara; Schrder, Arne S; Steinbacher, Jessica; Kashiwazaki, Gengo; Hfner, Georg; Wanner, Klaus T; Ochsenfeld, Christian; Carell, Thomas

    2013-10-01

    Three new cytosine derived DNA modifications, 5-hydroxymethyl-2'-deoxycytidine (hmdC), 5-formyl-2'-deoxycytidine (fdC) and 5-carboxy-2'-deoxycytidine (cadC) were recently discovered in mammalian DNA, particularly in stem cell DNA. Their function is currently not clear, but it is assumed that in stem cells they might be intermediates of an active demethylation process. This process may involve base excision repair, C-C bond cleaving reactions or deamination of hmdC to 5-hydroxymethyl-2'-deoxyuridine (hmdU). Here we report chemical studies that enlighten the chemical reactivity of the new cytosine nucleobases. We investigated their sensitivity toward oxidation and deamination and we studied the C-C bond cleaving reactivity of hmdC, fdC, and cadC in the absence and presence of thiols as biologically relevant (organo)catalysts. We show that hmdC is in comparison to mdC rapidly oxidized to fdC already in the presence of air. In contrast, deamination reactions were found to occur only to a minor extent. The C-C bond cleavage reactions require the presence of high concentration of thiols and are acid catalyzed. While hmdC dehydroxymethylates very slowly, fdC and especially cadC react considerably faster to dC. Thiols are active site residues in many DNA modifiying enzymes indicating that such enzymes could play a role in an alternative active DNA demethylation mechanism via deformylation of fdC or decarboxylation of cadC. Quantum-chemical calculations support the catalytic influence of a thiol on the C-C bond cleavage. PMID:23980549

  7. Copper-catalyzed oxidative cyclization of 1,5-enynes with concomitant C-C bond cleavage: an unexpected access to 3-formyl-1-indenone derivatives.

    PubMed

    Zhang, Jian; Wu, Degui; Chen, Xiaoling; Liu, Yunkui; Xu, Zhenyuan

    2014-06-01

    A Cu(0)/Selectfluor system-mediated oxidative cyclization of 1,5-enynes with concomitant C-C bond cleavage to access 3-formyl-1-indenone derivatives is described. Preliminary mechanistic investigations disclosed that the C-C bond cleavage involved a novel water-participated oxygen-insertion ?-carbon elimination through double oxycuprations. PMID:24807823

  8. Metal-free oxidative cleavage of the C-C bond in ?-hydroxy-?-oxophosphonates.

    PubMed

    Battula, Satyanarayana; Kumar, Atul; Ahmed, Qazi Naveed

    2015-10-21

    The potential of TBHP to promote oxidative hydroxylation of ?-hydroxy-?-oxophosphonates (HOPs) through C(CO)-C bond cleavage is described. This cleavage, as depicted in the mechanism is expected through an isomer of HOP that reacts with TBHP to generate acids. PMID:26365809

  9. Matching plasmon resonances to the C=C and C-H bonds in estradiol

    NASA Astrophysics Data System (ADS)

    Mbomson, Ifeoma G.; McMeekin, Scott; De La Rue, Richard; Johnson, Nigel P.

    2015-03-01

    We tune nanoantennas to resonate within mid-infrared wavelengths to match the vibrational resonances of C=C and C-H of the hormone estradiol. Modelling and fabrication of the nanoantennas produce plasmon resonances between 2 μm to 7 μm. The hormone estradiol was dissolved in ethanol and evaporated, leaving thickness of a few hundreds of nanometres on top of gold asymmetric split H-like shaped on a fused silica substrate. The reflectance was measured and a red-shift is recorded from the resonators plasmonic peaks. Fourier transform infrared spectroscopy is use to observe enhanced spectra of the stretching modes for the analyte which belongs to alkenyl biochemical group.

  10. Synthesis of aromatic compounds by catalytic C-C bond activation of biphenylene or angular [3]phenylene.

    PubMed

    Korotvi?ka, Ale; Csa?ov, Ivana; Roithov, Jana; Kotora, Martin

    2012-04-01

    Substituted phenanthrenes and picenes were easily prepared by reaction of biphenylene or angular [3]phenylene with various alkynes in the presence of a catalytic amount of [IrCl(cod)](2) /dppe (cod=1,5-cyclooctadiene, dppe=1,2-bis(diphenylphosphino)ethane). The reaction is based on C-C bond activation of the cyclobutane ring. The reaction tolerates the presence of bulky groups on the alkyne, such as the ferrocene moiety. In addition, a catalytic system based on [RhCl(cod)](2)/dppe enabled the, hitherto unreported, reaction of biphenylene with nitriles to provide phenanthridines. PMID:22407483

  11. Energy pulse bonding

    NASA Technical Reports Server (NTRS)

    Smith, G. C.

    1972-01-01

    To eliminate many of the present termination problems a technique called energy pulse bonding (EPB) was developed. The process demonstrated the capability of: (1) joining conductors without prior removal of insulations, (2) joining conductors without danger of brittle intermetallics, (3) increased joint temperature capability, (4) simultaneous formation of several bonds, (5) capability of higher joint density, and (6) a production oriented process. The following metals were successfully bonded in the solid state: copper, beryllium copper, phosphor bronze, aluminum, brass, and Kovar.

  12. Cyanoalkylation: Alkylnitriles in Catalytic C-C Bond-Forming Reactions.

    PubMed

    Lpez, Rosa; Palomo, Claudio

    2015-11-01

    Alkylnitriles are one of the most ubiquitous nitrogen-containing chemicals and are widely employed in reactions which result in nitrile-group conversion into other functionalities. Nevertheless, their use as carbon pronucleophiles in carbon-carbon bond-forming reactions has been hampered by difficulties associated mainly with the catalytic generation of active species, that is, ?-cyano carbanions or metalated nitriles. Recent investigations have addressed this challenge and have resulted in different modes of alkylnitrile activation. This review illustrates these findings, which have set the foundation for the development of practical and conceptually new catalytic, direct cyanoalkylation methodologies. PMID:26387483

  13. The role of the steps in the cleavage of the C-C bond during ethanol oxidation on platinum electrodes.

    PubMed

    Colmati, Flavio; Tremiliosi-Filho, Germano; Gonzalez, Ernesto R; Bern, Antonio; Herrero, Enrique; Feliu, Juan M

    2009-10-28

    Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media using electrochemical and Fourier transform infrared (FTIR) techniques. The electrodes used belong to two different series of stepped surfaces: those having (111) terraces with (100) monoatomic steps and those with (111) terraces with (110) monoatomic steps. The behaviors of the two series of stepped surfaces for the oxidation of ethanol are very different. On the one hand, the presence of (100) steps on the (111) terraces provides no significant enhancement of the activity of the surfaces. On the other hand, (110) steps have a double effect on the ethanol oxidation reaction. At potentials below 0.7 V, the step catalyzes the C-C bond cleavage and also the oxidation of the adsorbed CO species formed. At higher potentials, the step is not only able to break the C-C bond, but also to catalyze the oxidation of ethanol to acetic acid and acetaldehyde. The highest catalytic activity from voltammetry for ethanol oxidation was obtained with the Pt(554) electrode. PMID:19812831

  14. Short Access to Belt Compounds with Spatially Close C=C Bonds and Their Transannular Reactions.

    PubMed

    Camps, Pelayo; Gmez, Tnia; Otermin, Ane; Font-Bardia, Merc; Estarellas, Carolina; Luque, Francisco Javier

    2015-09-28

    Two domino Diels-Alder adducts were obtained from 3,7-bis(cyclopenta-2,4-dien-1-ylidene)-cis-bicyclo[3.3.0]octane and dimethyl acetylenedicarboxylate or N-methylmaleimide under microwave irradiation. From the first adduct, a C20H24 diene with C2v symmetry was obtained by Zn/AcOH reduction, hydrolysis, oxidative decarboxylation, and selective hydrogenation. Photochemical [2+2] cycloaddition of this diene gave a thermally unstable cyclobutane derivative, which reverts to the diene. However, both the diene and the cyclobutane derivatives could be identified by X-ray diffraction analysis upon irradiation of the diene crystal. New six-membered rings are formed upon the transannular addition of bromine or iodine to the diene. The N-type selectivity of the addition was examined by theoretical calculations, which revealed the distinct susceptibility of the doubly bonded carbon atoms to the bromine attack. PMID:26376331

  15. Efficient C-C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects.

    PubMed

    Loukrakpam, Rameshwori; Yuan, Qiuyi; Petkov, Valeri; Gan, Lin; Rudi, Stefan; Yang, Ruizhi; Huang, Yunhui; Brankovic, Stanko R; Strasser, Peter

    2014-09-21

    Efficient catalytic C-C bond splitting coupled with complete 12-electron oxidation of the ethanol molecule to CO2 is reported on nanoscale electrocatalysts comprised of a Pt monolayer (ML) and sub-monolayer (sML) deposited on Au nanoparticles (Au@Pt ML/sML). The Au@Pt electrocatalysts were synthesized using surface limited redox replacement (SLRR) of an underpotentially deposited (UPD) Cu monolayer in an electrochemical cell reactor. Au@Pt ML showed improved catalytic activity for ethanol oxidation reaction (EOR) and, unlike their Pt bulk and Pt sML counterparts, was able to generate CO2 at very low electrode potentials owing to efficient C-C bond splitting. To explain this, we explore the hypothesis that competing strain effects due to the Pt layer coverage/morphology (compressive) and the Pt-Au lattice mismatch (tensile) control surface chemisorption and overall activity. Control experiments on well-defined model Pt monolayer systems are carried out involving a wide array of methods such as high-energy X-ray diffraction, pair-distribution function (PDF) analysis, in situ electrochemical FTIR spectroscopy, and in situ scanning tunneling microscopy. The vibrational fingerprints of adsorbed CO provide compelling evidence on the relation between surface bond strength, layer strain and morphology, and catalytic activity. PMID:25081353

  16. Chemistry of oxygenates on transition metal surfaces: Activation of C- H, C-C, and C-O bonds

    SciTech Connect

    Not Available

    1991-01-01

    Goal is to understand the requirements for and competition between activation of C-H, C-C, and C-O bonds in the synthesis and decomposition of oxygenates on transition metal surfaces. Efforts during the past year was devoted primarily to the role of activation of {beta}-CH bonds in decarbonylation of higher oxygenates on surfaces of metals such as Rh and Pd; studies were completed of more than a dozen C{sub 1}-C{sub 3} oxygenates on Rh(111), and progress was made with reagents for which {beta}-CH scission is blocked. It is shown that alcohols and aldehydes do not react via a common pathway on on Rh(111). Ethanol and acetaldehyde are formed from CO + H{sub 2} by parallel routes on Rh catalysts which do not contain interacting supports or oxide promoters; i.e., the two compounds result from CO insertion into different metal-hydrocarbon bonds. Aldehydes decarbonylate via {alpha}-CH scission to form acyl, followed by C-C scission to release an alkyl ligand; this ligand undergoes hydrogenation and dehydrogenation steps. Alcohols form surface alkoxides, but these do not dehydrogenate further to the aldehydes, they release CO + H{sub 2} but no volatile hydrocarbon. These results indicate that {beta}-CH scissors to form a surface oxametallacycle intermediate; supporting evidence is spresented for this intermediate. Chemistry of alcohols blocked to different extends at the {beta}-position was also studied; complete blocking (CF{sub 3}CH{sub 2}OH) forces the reaction to follow the aldehyde-acyl path, while partial substitution at the {beta} position (branched alcohols) favors the oxametallacycle pathway. (DLC)

  17. Transversely isotropic elastic properties of single-walled carbon nanotubes by a rectangular beam model for the C ?C bonds

    NASA Astrophysics Data System (ADS)

    Li, Haijun; Guo, Wanlin

    2008-05-01

    Continuum mechanics modeling of carbon nanotubes has long been an attractive issue, but how to reflect exactly the physics essential of the atomic bonds still remains to be a challenging problem. To capture the distinguishing in-plane ?-? and out-of-plane ?-? bond angle bending rigidities of C ?C bonds in carbon nanotubes, an equivalent beam element with rectangular section is proposed and a corresponding frame structure model for a single-walled carbon nanotube (SWNT) is developed. By using the model, the five independent elastic moduli of SWNTs with arbitrary chirality and diameter are evaluated systematically. It is found that the elastic properties of the SWNTs are transversely isotropic when the tube diameter is small. The smaller the tube diameter is, the stronger the dependence of the elastic properties on the tube size and chirality is, while when the tube diameter is large enough, the SWNTs degenerate from transversely isotropic to isotropic and the elastic moduli tend to that of a graphite sheet. The present model can be incorporated into any standard finite element software directly, providing an extremely versatile and powerful tool for the study of nanostructures that beyond the computational capability of current atomistic approaches.

  18. Intramolecular Interaction, Photoisomerization, and Mechanical C-C Bond Dissociation of 1,2-Di(9-anthryl)benzene and Its Photoisomer: A Fundamental Moiety of Anthracene-Based π-Cluster Molecules.

    PubMed

    Nishiuchi, Tomohiko; Uno, Shin-Ya; Hirao, Yasukazu; Kubo, Takashi

    2016-03-01

    We report variable and unique properties of 1,2-di(9-anthryl)benzene 1 as a fundamental moiety of anthracene-based π-cluster molecules. Due to a through-space π-conjugation between anthracene units, excimer emission at room temperature and charge delocalized state in radical cation state of 1 could be observed. Photoirradiation to 1 afforded an intramolecular [4 + 4] cyclized anthracene dimer 1' having a high strain energy with long C-C bond that exceeded 1.68 Å, resulting in C-C bond dissociation by simple mechanical grinding. PMID:26828776

  19. Bonding and Integration of C-C Composite to Cu-Clad-Molybdenum for Thermal Management Applications

    NASA Technical Reports Server (NTRS)

    Asthana, R.; Singh, M.; Shpargel, T.P.

    2008-01-01

    Two- and three-dimensional carbon-carbon composites with either resin-derived matrix or CVI matrix were joined to Cu-clad-Mo using active Ag-Cu braze alloys for thermal management applications. The joint microstructure and composition were examined using Field-Emission Scanning Electron Microscopy and Energy-Dispersive Spectroscopy, and the joint hardness was characterized using the Knoop microhardness testing. Observations on the infiltration of the composite with molten braze, dissolution of metal substrate, and solute segregation at the C-C surface have been discussed. The thermal response of the integrated assembly is also briefly discussed.

  20. Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, Tarah; Cerny, Jennifer

    2006-01-01

    Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed for the bonding of titanium to high conductivity Carbon-Carbon composite sub components in various shapes and sizes. Currently a number of different silver and copper based active metal brazes and adhesive compositions are being evaluated. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Several mechanical tests have been employed to ascertain the effectiveness of different brazing and adhesive approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these mechanical tests along with the fractographic analysis will be discussed. In addition, advantages, technical issues and concerns in using different bonding approaches will also be presented.

  1. Biosynthetic pathway toward carbohydrate-like moieties of alnumycins contains unusual steps for C-C bond formation and cleavage.

    PubMed

    Oja, Terhi; Klika, Karel D; Appassamy, Laura; Sinkkonen, Jari; Mntsl, Pekka; Niemi, Jarmo; Mets-Ketel, Mikko

    2012-04-17

    Carbohydrate moieties are important components of natural products, which are often imperative for the solubility and biological activity of the compounds. The aromatic polyketide alnumycin A contains an extraordinary sugar-like 4'-hydroxy-5'-hydroxymethyl-2',7'-dioxane moiety attached via a carbon-carbon bond to the aglycone. Here we have extensively investigated the biosynthesis of the dioxane unit through (13)C labeling studies, gene inactivation experiments and enzymatic synthesis. We show that AlnA and AlnB, members of the pseudouridine glycosidase and haloacid dehalogenase enzyme families, respectively, catalyze C-ribosylation conceivably through Michael-type addition of d-ribose-5-phosphate and dephosphorylation. The ribose moiety may be attached both in furanose (alnumycin C) and pyranose (alnumycin D) forms. The C(1')-C(2') bond of alnumycin C is subsequently cleaved and the ribose unit is rearranged into an unprecedented dioxolane (cis-bicyclo[3.3.0]-2',4',6'-trioxaoctan-3'?-ol) structure present in alnumycin B. The reaction is catalyzed by Aln6, which belongs to a previously uncharacterized enzyme family. The conversion was accompanied with consumption of O(2) and formation of H(2)O(2), which allowed us to propose that the reaction may proceed via hydroxylation of C1' followed by retro-aldol cleavage and acetal formation. Interestingly, no cofactors could be detected and the reaction was also conducted in the presence of metal chelating agents. The last step is the conversion of alnumycin B into the final end-product alnumycin A catalyzed by Aln4, an NADPH-dependent aldo-keto reductase. This characterization of the dioxane biosynthetic pathway sets the basis for the utilization of C-C bound ribose, dioxolane and dioxane moieties in the generation of improved biologically active compounds. PMID:22474343

  2. Unexpected activation of carbon-bromide bond promoted by palladium nanoparticles in Suzuki C-C couplings.

    PubMed

    Sanhes, Delphine; Raluy, Eva; Rétory, Stéphane; Saffon, Nathalie; Teuma, Emmanuelle; Gómez, Montserrat

    2010-10-28

    Dihydroanthracene derivatives (1-6) containing imide (1-3) and amine (4-6) functions have been used for the stabilization of palladium nanoparticles, starting from Pd(0) and Pd(ii) organometallic precursors. Well-dispersed nanoparticles of mean size in the range ca. 1.9 to 3.6 nm could be obtained using Pd(0) precursors (PdLc and PdLd, where L = 1-6 and c and d mean the organometallic precursor involved, [Pd(2)(dba)(3)] and [Pd(ma)(nbd)] respectively). With the aim to evaluate the behaviour of homogeneous species and nanoparticles used as catalytic precursors, palladium complex coordinated to the diamine 6, [Pd(OAc)(2)(κ(2)-N,N-6)], was prepared, reporting for the first time the X-ray diffraction structure of a metallic complex containing a ligand with a 9,10-dihydroanthracene backbone. Palladium systems were evaluated in Suzuki C-C coupling reactions and relevant differences were observed comparing the reactivity of the homogeneous systems in relation to that obtained using palladium nanoparticles as starting catalyst in relation to the activation of the C-Br bonds for deactivated substrates. PMID:20820601

  3. Intramolecular Cooperative C-C Bond Cleavage Reaction of 1,3-Dicarbonyl Compounds with 2-Iodoanilines to Give o-(N-Acylamino)aryl Ketones and Multisubstituted Indoles.

    PubMed

    Xing, Qi; Lv, Hui; Xia, Chungu; Li, Fuwei

    2015-06-01

    A copper-catalyzed C-C bond cleavage reaction of 1,3-dicarbonyl compounds with 2-iodoanilines was developed. In this process, the ortho effect played an important role in the reactivity and a new reaction pathway that involved a (2-aminophenyl)-bis-(1,3-dicarbonyl) copper species was clearly observed by a time-course HRMS analysis of the reaction mixture. Unlike the previous reports, both the nucleophilic and electrophilic parts of the 1,3-dicarbonyl compound were coupled with 2-iodoaniline by C-C bond cleavage to form o-(N-acylamino)aryl ketones, which could be efficiently converted into multisubstituted indoles. PMID:25940404

  4. Theoretical study of the bond dissociation energies of methanol

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Walch, Stephen P.

    1992-01-01

    A theoretical study of the bond dissociation energies for H2O and CH3OH is presented. The C-H and O-H bond energies are computed accurately with the modified coupled-pair functional method using a large basis set. For these bonds, an accuracy of +/- 2 kcal/mol is achieved, which is consistent with the C-H and C-C single bond energies of other molecules. The C-O bond is much more difficult to compute accurately because it requires higher levels of correlation treatment and more extensive one-particle basis sets.

  5. Stereoselective Halogenation of Integral Unsaturated C-C Bonds in Chemically and Mechanically Robust Zr and Hf MOFs.

    PubMed

    Marshall, Ross J; Griffin, Sarah L; Wilson, Claire; Forgan, Ross S

    2016-03-24

    Metal-organic frameworks (MOFs) containing Zr(IV) -based secondary building units (SBUs), as in the UiO-66 series, are receiving widespread research interest due to their enhanced chemical and mechanical stabilities. We report the synthesis and extensive characterisation, as both bulk microcrystalline and single crystal forms, of extended UiO-66 (Zr and Hf) series MOFs containing integral unsaturated alkene, alkyne and butadiyne units, which serve as reactive sites for postsynthetic modification (PSM) by halogenation. The water stability of a Zr-stilbene MOF allows the dual insertion of both -OH and -Br groups in a single, aqueous bromohydrination step. Quantitative bromination of alkyne- and butadiyne-containing MOFs is demonstrated to be stereoselective, as a consequence of the linker geometry when bound in the MOFs, while the inherent change in hybridisation and geometry of integral linker atoms is facilitated by the high mechanical stabilities of the MOFs, allowing bromination to be characterised in a single-crystal to single-crystal (SCSC) manner. The facile addition of bromine across the unsaturated C-C bonds in the MOFs in solution is extended to irreversible iodine sequestration in the vapour phase. A large-pore interpenetrated Zr MOF demonstrates an I2 storage capacity of 279 % w/w, through a combination of chemisorption and physisorption, which is comparable to the highest reported capacities of benchmark iodine storage materials for radioactive I2 sequestration. We expect this facile PSM process to not only allow trapping of toxic vapours, but also modulate the mechanical properties of the MOFs. PMID:26916707

  6. Synthesis of Multiply Substituted Polycyclic Aromatic Hydrocarbons by Iridium-Catalyzed Annulation of Ring-Fused Benzocyclobutenol with Alkyne through C-C Bond Cleavage.

    PubMed

    Yu, Jiajia; Yan, Hong; Zhu, Chen

    2016-01-01

    The first iridium-catalyzed intermolecular cyclization between alkynes and ring-fused benzocyclobutenols (RBCB) through C-C bond cleavage is described. A variety of elusive polycyclic aromatic hydrocarbons (PAHs) with multiple substituents are obtained in good yields under mild conditions. This procedure provides a unique and expeditious tool for the synthesis of PAHs. PMID:26633241

  7. Addition of C-C and C-H bonds by pincer-iridium complexes: a combined experimental and computational study.

    PubMed

    Laviska, David A; Guan, Changjian; Emge, Thomas J; Wilklow-Marnell, Miles; Brennessel, William W; Jones, William D; Krogh-Jespersen, Karsten; Goldman, Alan S

    2014-11-21

    We report that pincer-ligated iridium complexes undergo oxidative addition of the strained C-C bond of biphenylene. The sterically crowded species ((tBu)PCP)Ir ((R)PCP = ?(3)-1,3-C6H3(CH2PR2)2) initially reacts with biphenylene to selectively add the C(1)-H bond, to give a relatively stable aryl hydride complex. Upon heating at 125 C for 24 h, full conversion to the C-C addition product, ((tBu)PCP)Ir(2,2'-biphenyl), is observed. The much less crowded ((iPr)PCP)Ir undergoes relatively rapid C-C addition at room temperature. The large difference in the apparent barriers to C-C addition is notable in view of the fact that the addition products are not particularly crowded, since the planar biphenyl unit adopts an orientation perpendicular to the plane of the (R)PCP ligands. Based on DFT calculations the large difference in the barriers to C-C addition can be explained in terms of a "tilted" transition state. In the transition state the biphenylene cyclobutadiene core is calculated to be strongly tilted (ca. 50-60) relative to its orientation in the product in the plane perpendicular to that of the PCP ligand; this tilt results in very short, unfavorable, non-bonding contacts with the t-butyl groups in the case of the (tBu)PCP ligand. The conclusions of the biphenylene studies are applied to interpret computational results for cleavage of the unstrained C-C bond of biphenyl by ((R)PCP)Ir. PMID:25250874

  8. Dynamics of vibrational relaxation in the S 1 state of carotenoids having 11 conjugated C?C bonds

    NASA Astrophysics Data System (ADS)

    Hrvin Billsten, Helena; Zigmantas, Donatas; Sundstrm, Villy; Polvka, Tom

    2002-04-01

    Transient absorption spectra and kinetics in the 470-650 nm region were recorded for lycopene, ?-carotene and zeaxanthin, all carotenoids with 11 conjugated double bonds, in two solvents with different polarity. Analysis of the red wing of the carotenoid S 1-S n transition revealed presence of a pronounced shoulder at early delay times. The kinetics recorded at this low-energy shoulder of the S 1-S n transition yields an additional decay component of 500-800 fs in addition to the main S 1 decay. This dynamics is ascribed to a vibrational relaxation in the S 1 state of the carotenoids.

  9. Luminescent pincer platinum(II) complexes with emission quantum yields up to almost unity: photophysics, photoreductive C-C bond formation, and materials applications.

    PubMed

    Chow, Pui-Keong; Cheng, Gang; Tong, Glenna So Ming; To, Wai-Pong; Kwong, Wai-Lun; Low, Kam-Hung; Kwok, Chi-Chung; Ma, Chensheng; Che, Chi-Ming

    2015-02-01

    Luminescent pincer-type Pt(II) ?complexes supported by C-deprotonated ?-extended tridentate R?C^N^N?R' ligands and pentafluorophenylacetylide ligands show emission quantum yields up to almost unity. Femtosecond time-resolved fluorescence measurements and time-dependent DFT calculations together reveal the dependence of excited-state structural distortions of [Pt(R?C^N^N?R')(C?C-C6 F5 )] on the positional isomers of the tridentate ligand. Pt?complexes [Pt(R-C^N^N?R')(C?C-Ar)] are efficient photocatalysts for visible-light-induced reductive C?C bond formation. The [Pt(R-C^N^N?R')(C?C-C6 F5 )] complexes perform strongly as phosphorescent dopants for green- and red-emitting organic light-emitting diodes (OLEDs) with external quantum efficiency values over 22.1?%. These complexes are also applied in two-photon cellular imaging when incorporated into mesoporous silica nanoparticles (MSNs). PMID:25581564

  10. Intramolecular C-C Bond Coupling of Nitriles to a Diimine Ligand in Group 7 Metal Tricarbonyl Complexes.

    PubMed

    Yempally, Veeranna; Fan, Wai Yip; Arndtsen, Bruce A; Bengali, Ashfaq A

    2015-12-01

    Dissolution of M(CO)3(Br)(L(Ar)) [L(Ar) = (2,6-Cl2-C6H3-NCMe)2CH2] in either acetonitrile [M = Mn, Re] or benzonitrile (M = Re) results in C-C coupling of the nitrile to the diimine ligand. When reacted with acetonitrile, the intermediate adduct [M(CO)3(NCCH3)(L(Ar))]Br forms and undergoes an intramolecular C-C coupling reaction between the nitrile carbon and the methylene carbon of the ?-diimine ligand. PMID:26554575

  11. Gas-phase reaction of CeV2O7+ with C2H4: activation of C-C and C-H bonds.

    PubMed

    Ma, Jia-Bi; Yuan, Zhen; Meng, Jing-Heng; Liu, Qing-Yu; He, Sheng-Gui

    2014-12-15

    The reactivity of metal oxide clusters toward hydrocarbon molecules can be changed, tuned, or controlled by doping. Cerium-doped vanadium cluster cations CeV2O7(+) are generated by laser ablation, mass-selected by a quadrupole mass filter, and then reacted with C2H4 in a linear ion trap reactor. The reaction is characterized by a reflectron time-of-flight mass spectrometer. Three types of reaction channels are observed: 1) single oxygen-atom transfer , 2) double oxygen-atom transfer , and 3) C=C bond cleavage. This study provides the first bimetallic oxide cluster ion, CeV2O7(+), which gives rise to C=C bond cleavage of ethene. Neither Ce(x)O(y)(±) nor V(x)O(y)(±) alone possess the necessary topological and electronic properties to bring about such a reaction. PMID:25208512

  12. Catalytic constructive deoxygenation of lignin-derived phenols: new C-C bond formation processes from imidazole-sulfonates and ether cleavage reactions.

    PubMed

    Leckie, Stuart M; Harkness, Gavin J; Clarke, Matthew L

    2014-10-01

    As part of a programme aimed at exploiting lignin as a chemical feedstock for less oxygenated fine chemicals, several catalytic C-C bond forming reactions utilising guaiacol imidazole sulfonate are demonstrated. These include the cross-coupling of a Grignard, a non-toxic cyanide source, a benzoxazole, and nitromethane. A modified Meyers reaction is used to accomplish a second constructive deoxygenation on a benzoxazole functionalised anisole. PMID:25130565

  13. A metal-free tandem C-C/C-O bond formation approach to densely functionalized indolyl 4H-chromenes catalyzed by polystyrene-supported p-toluenesulfonic acid under solvent-free conditions.

    PubMed

    Shinde, Vijay Vilas; Jeong, Yong Seok; Jeong, Yeon Tae

    2015-05-01

    A new environmentally benign and highly convergent protocol for the synthesis of indolyl 4H-chromene derivatives has been developed. This one-pot three-component condensation reaction of salicylaldehyde, cyclic 1,3-diketones, and indole is promoted by PS-PTSA as a reusable heterogeneous acid catalyst under solvent-free conditions. This protocol demonstrates several notable advantages such as that the catalyst is readily available and can be recovered and reused for at least five runs without any significant impact on product yields, high atom economy, excellent yields, and efficiency of producing three new bonds (two C-C and one C-O) and one stereo center in a single operation. PMID:25802172

  14. Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic CC Bond Forming Reactions in Aqueous Solution

    PubMed Central

    Itoh, Susumu; Sonoike, Shotaro; Kitamura, Masanori; Aoki, Shin

    2014-01-01

    Extending carbon frameworks via a series of CC bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective CC bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective CC bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented. PMID:24481060

  15. Relationship between C=C Bonds and Mechanical Properties of Carbon Rich Low-k Films deposited by Plasma Enhanced Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Shim, Cheonman; Jung, Donggeun

    2004-03-01

    We have studied the relationship between C=C bonds and the mechanical properties of different low-k films deposited by plasma enhanced chemical vapor deposition (PECVD) using a p-xylene and/or hexamethyldisilane (HMDS) precursor. The three types of films were called plasma polymerized p-xylene (PPpX) using p-xylene only, plasma polymerized p-xylene:hexamethyldisilane (PPpX:HMDS) using a mixture of p-xylene and HMDS, and plasma polymerized hexamethyldisilane (PPHMDS) using HMDS only as precursors. The mechanical strengths such as Youngs modulus and hardness decreased as a function of annealing temperature, while C=C bonds increased in number. We suggest that the mechanical properties of low-k films containing a large amount of C and small amounts of Si and/or O are closely related to the generation of C=C bonds in the films after annealing, and not to the decrease in the film density. This was investigated by Fourier transform Raman (FT-Raman) spectroscopy.

  16. Aromaticity Changes along the Lowest-Triplet-State Path for C?C Bond Rotation of Annulenyl-Substituted Olefins Probed by the Electron Localization Function

    NASA Astrophysics Data System (ADS)

    Villaume, Sbastien; Ottosson, Henrik

    2009-10-01

    The ?-contribution to the electron localization function (ELF?) was used to analyze changes in the aromaticity of annulenyl-substituted olefins in their lowest triplet state (T1) when the structure around the olefin C?C bond is twisted from planar to a structure (3p*) at which the planes of the two RR'C units are perpendicular. The ring closure bifurcation value and the range in the bifurcation values of the ELF? basins serve as (anti)aromaticity indicators directly linked to the electronic structure. Both Hckel's 4n + 2 ?-electron rule for aromaticity in the singlet ground state (S0) and Baird's 4n ?-electron rule for aromaticity in the lowest ??* triplet state are applied. Three olefins with S0 aromatic (T1 antiaromatic) substituents and four olefins with T1 aromatic (S0 antiaromatic) substituents were studied using the ELF? topology at the OLYP/6-311G(d,p) density functional theory level. The changes in the substituent ELF? bifurcation values upon rotation about the olefin bond in the T1 state reveal that aromatic character is recovered for the first three olefins and that it is reduced for the latter ones. These changes in aromatic character are reflected in the shapes of the T1 potential energy surfaces as a twist away from planar structures in olefins with T1 antiaromatic substituents is energetically favorable, but that in olefins with T1 aromatic substituents is unfavorable. Hence, aromaticity change is a driver for a photochemical reaction as for many ground-state reactions.

  17. Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

    DOE PAGESBeta

    Welz, Oliver; Savee, John D.; Osborn, David L.; Taatjes, Craig A.

    2014-07-04

    The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH3)2CCHCH2OH) and isoprenol (3-methyl-3-buten-1-ol, CH2C(CH3)CH2CH2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant products arising from QOOH chemistry are observed. Thesemore » results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.« less

  18. Templated C-C and C-N Bond Formation Facilitated by a Molybdenum(VI) Metal Center.

    PubMed

    Zwettler, Niklas; Dup, Antoine; Schachner, Jrg A; Belaj, Ferdinand; Msch-Zanetti, Nadia C

    2015-12-21

    Preparation of molybdenum dioxido complexes with novel iminophenolate ligands bearing pendant secondary amide functionalities led to unprecedented C-C and C-N coupling reactions of two ?-iminoamides upon coordination. The diastereoselective cyclization to asymmetric imidazolidines occurs at the metal center in two consecutive steps via a monocoupled intermediate. A meaningful mechanism is proposed on the basis of full characterization of intermediate and final molybdenum-containing products by spectroscopic means and by single-crystal X-ray diffraction analyses. This process constitutes the first example of a diastereoselective self-cyclization of two ?-iminoamides. PMID:26646158

  19. Bond dissociation energies and bond orders for some astrophysical molecules

    NASA Astrophysics Data System (ADS)

    Reddy, R. R.; Viswanath, R.

    1989-06-01

    The bond dissociation energies for various astrophysically important diatomic molecules have been determined using a formula in which bond dissociation energies are the sum of the geometric average of the component bond energies and 32.058 times the Pauling electronegativity difference. Bond orders are estimated according to the formula of Reddy et al. (1985, 1987). The results confirm the definition of bond order given by Politzer (1969). The estimated bond energies are found to agree well with previous values and to give an error of 8 percent, as compared to the error of 26.8 percent found using Pauling's (1960) equation.

  20. Synthesis of Indolizines through Oxidative Linkage of C-C and C-N Bonds from 2-Pyridylacetates.

    PubMed

    Mohan, Darapaneni Chandra; Ravi, Chitrakar; Pappula, Venkatanarayana; Adimurthy, Subbarayappa

    2015-07-01

    Synthesis of indolizine-1-carboxylates through the Ortoleva-King reaction of 2-pyridylacetate followed by the Aldol condensation under mild reaction conditions has been described. This protocol is compatible with a broad range of functional groups, and it has been also successfully extended to unsaturated ketones, bringing about the regioselective formation of benzoyl-substituted indolizines through Michael addition followed by C-N bond formation, which are difficult to prepare by previous methods in a single step. PMID:26044904

  1. Catalytic asymmetric [3+2] cycloaddition of aromatic aldehydes with oxiranes by C-C bond cleavage of epoxides: highly efficient synthesis of chiral 1,3-dioxolanes.

    PubMed

    Chen, Weiliang; Lin, Lili; Cai, Yunfei; Xia, Yong; Cao, Weidi; Liu, Xiaohua; Feng, Xiaoming

    2014-02-28

    A novel and efficient N,N'-dioxide-Gd(III) complex was developed for the highly diastereo- and enantioselective [3+2] cycloaddition of aryl oxiranyl diketones and aldehydes via C-C bond cleavage of oxiranes. The corresponding chiral 1,3-dioxolanes were obtained in excellent yields (up to 99%) with high diastereoselectivities (>95 : 5 dr) and enantioselectivities (up to 91% ee). Moreover, a possible transition model was proposed to explain the origin of the asymmetric induction. PMID:24430105

  2. Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

    SciTech Connect

    Welz, Oliver; Savee, John D.; Osborn, David L.; Taatjes, Craig A.

    2014-07-04

    The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH3)2CCHCH2OH) and isoprenol (3-methyl-3-buten-1-ol, CH2C(CH3)CH2CH2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant products arising from QOOH chemistry are observed. These results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.

  3. Organolanthanide-induced C-C bond formation. Preparation and properties of monomeric lanthanide aldolates and enolates

    SciTech Connect

    Heeres, H.J.; Maters, M.; Teuben, J.H.

    1992-01-01

    The reactivity of early-lanthanide carbyls Cp* {sub 2}LnCH(SiMe{sub 3}){sub 2} (1, Ln = La; 2, Ln = Ce) toward ketones has been studied. No reaction was observed with the bulky di-tert-butyl ketone. The corresponding lanthanum hydride [Cp* {sub 2}LaH]{sub 2} (3) is more reactive and afforded the addition product Cp*{sub 2}LaOCH(t-Bu){sub 2}{sup center-dot}O=C(t-Bu){sub 2} (4). Hydrogen transfer and formation of lanthanide aldolates Cp* {sub 2}LnOCMe{sub 2}C(=O)Me (5, Ln = Ce; 6, Ln =La) together with the protonated carbyl CH{sub 2}(SiMe{sub 3}){sub 2} were observed when 1 or 2 was treated with acetone. The molecular structure of the cerium analogue 5 was determined by X-ray diffraction and was found to be a monomeric bent metallocene compound with a {eta}{sup 2}-coordinated aldol fragment. Addition of 3-pentanone to the carbyls 1 and 2 did not result in C-C coupling but provided enolate-ketone adducts Cp*{sub 2}LnOC(Et)=C(H)MeO=CEt{sub 2} (7, Ln = La; 8, Ln = Ce). Reactions of the carbyls 1 and 2 with 4-methyl-5-hydroxy-5ethyl-3-heptanone yielded the enolate-ketone adducts as well and suggest that the differences in reactivity between acetone and 3-pentanone are thermodynamic and not kinetic in origin. 32 refs., 2 figs., 5 tabs.

  4. Chemistry of oxygenates on transition metal surfaces: Activation of C- H, C-C, and C-O bonds. Progress report, December 15, 1991

    SciTech Connect

    Not Available

    1991-12-31

    Goal is to understand the requirements for and competition between activation of C-H, C-C, and C-O bonds in the synthesis and decomposition of oxygenates on transition metal surfaces. Efforts during the past year was devoted primarily to the role of activation of {beta}-CH bonds in decarbonylation of higher oxygenates on surfaces of metals such as Rh and Pd; studies were completed of more than a dozen C{sub 1}-C{sub 3} oxygenates on Rh(111), and progress was made with reagents for which {beta}-CH scission is blocked. It is shown that alcohols and aldehydes do not react via a common pathway on on Rh(111). Ethanol and acetaldehyde are formed from CO + H{sub 2} by parallel routes on Rh catalysts which do not contain interacting supports or oxide promoters; i.e., the two compounds result from CO insertion into different metal-hydrocarbon bonds. Aldehydes decarbonylate via {alpha}-CH scission to form acyl, followed by C-C scission to release an alkyl ligand; this ligand undergoes hydrogenation and dehydrogenation steps. Alcohols form surface alkoxides, but these do not dehydrogenate further to the aldehydes, they release CO + H{sub 2} but no volatile hydrocarbon. These results indicate that {beta}-CH scissors to form a surface oxametallacycle intermediate; supporting evidence is spresented for this intermediate. Chemistry of alcohols blocked to different extends at the {beta}-position was also studied; complete blocking (CF{sub 3}CH{sub 2}OH) forces the reaction to follow the aldehyde-acyl path, while partial substitution at the {beta} position (branched alcohols) favors the oxametallacycle pathway. (DLC)

  5. Understanding the mechanisms of unusually fast H-H, C-H, and C-C bond reductive eliminations from gold(III) complexes.

    PubMed

    Nijamudheen, A; Karmakar, Sharmistha; Datta, Ayan

    2014-11-01

    Carbon-carbon bond reductive elimination from gold(III) complexes are known to be very slow and require high temperatures. Recently, Toste and co-workers have demonstrated extremely rapid C?C reductive elimination from cis-[AuPPh3 (4-F-C6 H4 )2 Cl] even at low temperatures. We have performed DFT calculations to understand the mechanistic pathway for these novel reductive elimination reactions. Direct dynamics calculations inclusive of quantum mechanical tunneling showed significant contribution of heavy-atom tunneling (>25?%) at the experimental reaction temperatures. In the absence of any competing side reactions, such as phosphine exchange/dissociation, the complex cis-[Au(PPh3 )2 (4-F-C6 H4 )2 ](+) was shown to undergo ultrafast reductive elimination. Calculations also revealed very facile, concerted mechanisms for H?H, C?H, and C?C bond reductive elimination from a range of neutral and cationic gold(III) centers, except for the coupling of sp(3) carbon atoms. Metal-carbon bond strengths in the transition states that originate from attractive orbital interactions control the feasibility of a concerted reductive elimination mechanism. Calculations for the formation of methane from complex cis-[AuPPh3 (H)CH3 ](+) predict that at -52?C, about 82?% of the reaction occurs by hydrogen-atom tunneling. Tunneling leads to subtle effects on the reaction rates, such as large primary kinetic isotope effects (KIE) and a strong violation of the rule of the geometric mean of the primary and secondary KIEs. PMID:25224135

  6. Salt-Free Reduction of Nonprecious Transition-Metal Compounds: Generation of Amorphous Ni Nanoparticles for Catalytic C-C Bond Formation.

    PubMed

    Yurino, Taiga; Ueda, Yohei; Shimizu, Yoshiki; Tanaka, Shinji; Nishiyama, Haruka; Tsurugi, Hayato; Sato, Kazuhiko; Mashima, Kazushi

    2015-11-23

    A salt-free procedure for the generation of a wide variety of metal(0) particles, including Fe, Co, Ni, and Cu, was achieved using 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (1), which reduced the corresponding metal precursors under mild conditions. Notably, Ni?particles formed in?situ from the treatment of Ni(acac)2 (acac=acetylacetonate) with 1 in toluene exhibited significant catalytic activity for reductive C?C bond-forming reactions of aryl halides in the presence of excess amounts of 1. By examination of high-magnification transmission electron microscopy images and electron diffraction patterns, we concluded that amorphous Ni nanoparticles (Ni?aNPs) were essential for the high catalytic activity. PMID:26419693

  7. Formation of C?C bond via knoevenagel reaction between aromatic aldehyde and barbituric acid at liquid/HOPG and vapor/HOPG interfaces.

    PubMed

    Geng, Yanfang; Dai, Hongliang; Chang, Shaoqing; Hu, Fangyun; Zeng, Qingdao; Wang, Chen

    2015-03-01

    Controlling chemical reactions on surface is of great importance to constructing self-assembled covalent nanostructures. Herein, Knoevenagel reaction between aromatic aldehyde compound 2,5-di(5-aldehyde-2-thienyl)-1,4-dioctyloxybenzene (PT2) and barbituric acid (BA) has been successfully performed for the first time at liquid/HOPG interface and vapor/HOPG interface. The resulting surface nanostructures and the formation of C?C bond are recorded through scanning tunneling microscopy (STM), and confirmed by attenuated total reflectance Fourier-transform infrared (ATR/FT-IR) spectrometer and UV-vis absorption. The obtained results reveal that Knoevenagel condensation reaction can efficiently occur at both interfaces. This surface reaction would be an important step toward further reaction to produce innovative conjugated nanomaterial on the surface. PMID:25664650

  8. Unraveling the Fischer-Tropsch mechanism: a combined DFT and microkinetic investigation of C-C bond formation on Ru.

    PubMed

    Mirwald, Jens W; Inderwildi, Oliver R

    2012-05-21

    A combined modelling study on the Fischer-Tropsch Mechanism on Ru(0001). The DFT results presented herein approve the idea that the carbide mechanism is not the main reaction path in the synthesis of liquid hydrocarbons on Ru{0001}. The direct reaction of a CH(x)(s) species with a CO(s) species is kinetically and thermochemically preferred over CO dissociation and the hydrogenation of carbon monoxide can be seen as the initiation reaction of the hydrocarbon polymerisation process. Moreover, this study shows that CO dissociation is favoured over desorption on Ru{0001}, while on the analogue Co facet desorption is clearly favoured. This study therefore is an important further confirmation on new thinking in the Fischer-Tropsch synthesis. The fundamental insight gained in these studies will be of paramount importance for engineers optimising the FT process. Optimisation will not only lower the cost of FT fuels but simultaneously lower energy consumption and emissions. PMID:22482113

  9. Reversible Sigma C-C Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb

    SciTech Connect

    Nocton, Gré gory; Lukens, Wayne W.; Booth, Corwin H.; Rozenel, Sergio S.; Medling, Scott A.; Maron, Laurent; Andersen, Richard A.

    2014-06-26

    The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*2Yb are dramatically different from those of the 2,2?-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f13, and (phen ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009, 131, 6480; J. Am. Chem. Soc 2010, 132, 17537). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy has only one 1 orbital of b1 symmetry of accessible energy, but phen has two orbitals of b1 and a2 symmetry that are energetically accessible. The carbon p-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp 2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180190 C. When 3,8-Me2phenanthroline is used, the adduct Cp*2Yb(3,8-Me2phen) exists in the solution in a dimer monomer equilibrium in which G is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature 1H NMR spectroscopy.

  10. Three methods to measure RH bond energies

    SciTech Connect

    Berkowitz, J.; Ellison, G.B.; Gutman, D.

    1993-03-21

    In this paper the authors compare and contrast three powerful methods for experimentally measuring bond energies in polyatomic molecules. The methods are: radical kinetics; gas phase acidity cycles; and photoionization mass spectroscopy. The knowledge of the values of bond energies are a basic piece of information to a chemist. Chemical reactions involve the making and breaking of chemical bonds. It has been shown that comparable bonds in polyatomic molecules, compared to the same bonds in radicals, can be significantly different. These bond energies can be measured in terms of bond dissociation energies.

  11. DMSO/I2 mediated C-C bond cleavage of ?-ketoaldehydes followed by C-O bond formation: a metal-free approach for one-pot esterification.

    PubMed

    Venkateswarlu, Vunnam; Aravinda Kumar, K A; Gupta, Sorav; Singh, Deepika; Vishwakarma, Ram A; Sawant, Sanghapal D

    2015-08-01

    A novel and efficient I2/DMSO mediated metal-free strategy is presented for the direct C-C bond cleavage of aryl-/heteroaryl- or aliphatic ?-ketoaldehydes by C2-decarbonylation and C1-carbonyl oxidation to give the corresponding carboxylic acids followed by esterification in one pot, offering excellent yields in both the steps. Here, DMSO acts as the oxygen source/oxidant and this reaction works very well under both conventional heating and microwave irradiation. This is a very simple and convenient protocol. PMID:26110656

  12. Atomic force microscopy imaging of TiO{sub 2} surfaces active for C-C bond formation reactions in ultrahigh vacuum

    SciTech Connect

    Watson, B.A.; Barteau, M.A.

    1994-06-01

    TiO{sub 2}(001) single crystal surfaces active for a variety of different chemistries were examined using atomic force microscopy (AFM). C-C bond forming reactions previously identified on these surfaces include carboxylic acid ketonization, aldol condensation, reductive carbonyl coupling, and alkyne cyclotrimerization. The surfaces were prepared in ultrahigh vacuum (UHV) and examined by AFM in air. Surfaces examined included the (011)-faceted surface, (114)-faceted surface, and argon-ion-bombarded surfaces, as well as the mechanically polished single-crystal surface prior to treatment in UHV. The one unifying feature of all the images was their extreme flatness. Root-mean-square roughnesses were routinely less than 10 {Angstrom} in 500 x 500 nm scans. These same scans showed the surfaces to have surface areas exceeding that of an ideal flat surface by no more than 1.2%. Images of the polished surface revealed a variety of surface features, including polishing scratches and particle-like features. The argon-ion-bombarded surface and the faceted surfaces were composed of large flat plateaus ranging in size from 21 to 75 nm. The size of the plateaus was essentially the same for the ion bombarded surface and the (011)-faceted surface. The (114)-faceted surfaced exhibited slightly smaller plateau regions than the other surfaces. The images indicate that argon-ion bombardment, while disordering the surface and causing significant composition changes, does not lead to observable morphological changes on this scale. The relative uniformity of the surfaces examined is consistent with the selectivity of carbon-carbon bond-forming reactions that have been shown to take place on these surfaces. The images also reveal how the surface topography on the scale of the plateau structures observed is only slightly changed during the transformation of the surface unit cell structure from the (011)- to the (114)-faceted surface. 29 refs., 6 figs., 1 tab.

  13. Acetaldehyde partial oxidation on the Au(111) model catalyst surface: C-C bond activation and formation of methyl acetate as an oxidative coupling product

    NASA Astrophysics Data System (ADS)

    Karatok, Mustafa; Vovk, Evgeny I.; Shah, Asad A.; Turksoy, Abdurrahman; Ozensoy, Emrah

    2015-11-01

    Partial oxidation of acetaldehyde (CH3CHO) on the oxygen pre-covered Au(111) single crystal model catalyst was investigated via Temperature Programmed Desorption (TPD) and Temperature Programmed Reaction Spectroscopy (TPRS) techniques, where ozone (O3) was utilized as the oxygen delivery agent providing atomic oxygen to the reacting surface. We show that for low exposures of O3 and small surface oxygen coverages, two partial oxidation products namely, methyl acetate (CH3COOCH3) and acetic acid (CH3COOH) can be generated without the formation of significant quantities of carbon dioxide. The formation of methyl acetate as the oxidative coupling reaction product implies that oxygen pre-covered Au(111) single crystal model catalyst surface can activate C-C bonds. In addition to the generation of these products; indications of the polymerization of acetaldehyde on the gold surface were also observed as an additional reaction route competing with the partial and total oxidation pathways. The interplay between the partial oxidation, total oxidation and polymerization pathways reveals the complex catalytic chemistry associated with the interaction between the acetaldehyde and atomic oxygen on catalytic gold surfaces.

  14. Multinuclear silver(i) XPhos complexes with cyclooctatetraene: photochemical C-C bond cleavage of acetonitrile and cyanide bridged Ag cluster formation.

    PubMed

    Grirrane, A; Álvarez, E; Albero, J; García, H; Corma, A

    2016-04-01

    Cationic mono-, di-, tri- and tetra-nuclear silver complexes with Buchwald-type phosphane (XPhos) and cyclooctatetraene (COT) have been synthesized and characterized. Formation of [(XPhos-Ag)n(COT)][SbF6]n (n = 1 and 2) complexes was confirmed by single-crystal X-ray crystallography and multinuclear NMR spectroscopy. Variable-temperature NMR spectroscopy in CD2Cl2 solution shows the fluxionality of the COT ring in the mono-Ag(i) XPhos complex. Fluxionality of COT was also confirmed in the case of the di-Ag(i) XPhos complex by solid-state and solution (31)P NMR spectroscopy. The C-C bond cleavage of coordinated acetonitrile [XPhos-Ag(i)-NCCH3] resulting in cyanide bridged Ag cluster formation [(XPhos-Ag)2(μ-CN)n(μ-Ag)n-1] (n = 1, 2, 3 and 4) upon light excitation of [(XPhos-Ag)n(COT)] was confirmed by HRESI-MS, UV-Absorption and HR-TEM. PMID:26959701

  15. Iron-catalyzed aerobic oxidative cleavage of the C-C ?-bond using air as the oxidant: chemoselective synthesis of carbon chain-shortened aldehydes, ketones and 1,2-dicarbonyl compounds.

    PubMed

    Xing, Qi; Lv, Hui; Xia, Chungu; Li, Fuwei

    2016-01-11

    A simple iron-catalyzed aerobic oxidative C-C ?-bond cleavage of ketones has been developed. Readily available and environmentally benign air is used as the oxidant. This reaction avoids the use of noble metal catalysts or specialized oxidants, chemoselectively yielding carbon chain-shortened aldehydes, ketones and 1,2-dicarbonyl compounds without overoxidation. PMID:26529597

  16. Measurements of electron attachment lineshapes and cross sections at ultralow electron energies for c-C6F10, c-C6F12, C8F16 and 1,1,2-C2Cl3F3

    NASA Technical Reports Server (NTRS)

    Alajajian, S. H.; Chutjian, A.

    1986-01-01

    Electron attachment cross sections are reported in the electron energy range 0-160 meV and at energy resolutions of 4.5-7.5 meV (FWHM) for the molecules c-C6F10 (perfluorocyclohexene), c-C6F12 (perfluoro-1,2-dimethylcyclobutane), C8F16 (perfluoro-1,3-dimethylcyclohexane) and 1,1,2-C2Cl3F3 (1,1,2-trichlorotrifluoroethane). Use is made of the Kr photoionization technique, and measured attachment lineshapes are converted to cross sections by normalization through attachment rate constants. Comparisons are made with attachment cross sections derived from swarm-measured rate constants. Similar to previous results in eight other molecules, the present four molecules exhibit resolution-limited onsets at a threshold consistent with an s-wave attachment behavior and with a neutral-negative-ion curve crossing at zero energy.

  17. Degree of remaining C=C bonds, polymerization shrinkage and stresses of dual-cured core build-up resin composites.

    PubMed

    Stavridakis, Minos M; Kakaboura, Afrodite I; Krejci, Ivo

    2005-01-01

    This study measured the degree of remaining C=C bonds (RDB), linear polymerization shrinkage (LPS) and polymerization stresses (PS) of dual-cured resin composite build-up materials using a variety of light exposure scenarios. Four commercially available materials were used: Bis-Core, FluoroCore, Build-it! and Permalute. The RDB was measured using FTIR spectroscopy, and custom-made devices were used to measure LPS and PS values. Data were obtained using three different modes of photoactivation: NLC (No Light-Curing); ILC (Immediate Light-Curing, where 60 second light-curing was applied at the start of the observation period); and DLC (Delayed Light-Curing, where 60-second light-curing was applied 10 minutes from the start of the observation period). Statistical evaluation of the data at the end of the 13-minute observation period was performed with two-way analysis of variance (ANOVA), Tukey's Studentized Range (HSD) Test (p=0.05) and simple linear regression. Differences in the development of LPS and PS during the 13 minutes were studied using mathematical calculus. Bis-Core presented the highest RDB and Permalute the lowest when ILC was applied, while no differences were found between Build-it! and FluoroCore and NLC and DLC increased RDB for FluoroCore and Permalute compared to ILC; whereas, no differences were noted for Build-it! and Bis-Core. Using DLC, a decrease in RDB was found only for Build-it! FluoroCore and Permalute exhibited a reduction in LPS and PS using NLC relative to ILC. No differences in LPS and PS values were detected for the materials Bis-Core and Build-it! when subjected to NLC or DLC, compared to ILC. Simple linear regression showed that only the two polymerization shrinkage properties studied were highly correlated (LPS-PS r2=0.85). The RDB rate was not correlated with either polymerization shrinkage properties (RDB-LPS r2=0.40; RDB-PS r2=0.57). A study of the evolution of the real-time curves of percentage values of LPS and PS showed that these properties evolved in a similar exponential mode and that, most often, there was a delay in the development of PS. PMID:16130864

  18. A calculation of the diffusion energies for adatoms on surfaces of F.C.C. metals

    NASA Technical Reports Server (NTRS)

    Halicioglu, T.; Pound, G. M.

    1979-01-01

    The activation energies for diffusion were determined for gold, platinum and iridium adatoms on plane and plane PT surfaces and were found to be in good agreement with the measurements reported by Bassett and Webber. The Lennard-Jones pair potentials were used to model the interatomic forces, and relaxation of the substrate atoms in near proximity to the adatom was considered in detail. The present calculations clarify the mechanism of the observed two-dimensional diffusion of platinum and iridium atoms on a plane PT surface. The results are compared with those obtained using Morse potential functions and different relaxation techniques.

  19. Three methods to measure RH bond energies

    SciTech Connect

    Berkowitz, J. ); Ellison, G.B. ); Gutman, D. )

    1994-03-17

    We present a critical review of three different experimental methods used to measure bond energies: radical kinetics, gas-phase acidity cycles, and photoionization mass spectrometry. These experimental techniques are currently in use to measure the bond energies of a large number of molecules. We discuss the basic premises of each of these experiments and explicitly try to point out the strengths and weaknesses of each method. We directly compare each of these procedures using a set of about 30 important molecules. These three different techniques have only a few disagreements among them, the case of ethylene being the most serious. For the overwhelming number of studies, all measurements lead to bond energies within each other's error bars. We include tables of ionization potentials, electron affinities, and heats of formation for about 40 important organic and inorganic radicals. We also list bond energies for the parent molecules at 0 and 298 K. 273 refs., 10 figs., 5 tabs.

  20. Interaction of a pseudo-? C-C bond with cuprous and argentous chlorides: Cyclopropane?CuCl and cyclopropane?AgCl investigated by rotational spectroscopy and ab initio calculations.

    PubMed

    Zaleski, Daniel P; Mullaney, John C; Bittner, Dror M; Tew, David P; Walker, Nicholas R; Legon, Anthony C

    2015-10-28

    Strongly bound complexes (CH2)3?MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH2)3?CuCl and (CH2)3?AgCl. The geometry of each of these complexes was established unambiguously to have C2v symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH2)3?MCl. The M atom interacts with the pseudo-? bond linking the pair of equivalent carbon atoms (F)C (F = front) nearest to it, so that M forms a non-covalent bond to one C-C edge of the cyclopropane molecule. The (CH2)3?MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH2)3?HCl and (CH2)3?ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the (F)C-(F)C bond and the shrinkage of the two equivalent (B)C-(F)C (B = back) bonds relative to the C-C bond in cyclopropane itself. The expansions of the (F)C-(F)C bond are 0.1024(9) and 0.0727(17) in (CH2)3?CuCl and (CH2)3?AgCl, respectively, according to the determined r0 geometries. The C-C bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r(CC) in the pseudo-? complexes are discussed. PMID:26520520

  1. Interaction of a pseudo-? CC bond with cuprous and argentous chlorides: Cyclopropane⋯CuCl and cyclopropane⋯AgCl investigated by rotational spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Zaleski, Daniel P.; Mullaney, John C.; Bittner, Dror M.; Tew, David P.; Walker, Nicholas R.; Legon, Anthony C.

    2015-10-01

    Strongly bound complexes (CH2)3⋯MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH2)3⋯CuCl and (CH2)3⋯AgCl. The geometry of each of these complexes was established unambiguously to have C2v symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH2)3⋯MCl. The M atom interacts with the pseudo-? bond linking the pair of equivalent carbon atoms FC (F = front) nearest to it, so that M forms a non-covalent bond to one CC edge of the cyclopropane molecule. The (CH2)3⋯MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH2)3⋯HCl and (CH2)3⋯ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the FCFC bond and the shrinkage of the two equivalent BCFC (B = back) bonds relative to the CC bond in cyclopropane itself. The expansions of the FCFC bond are 0.1024(9) and 0.0727(17) in (CH2)3⋯CuCl and (CH2)3⋯AgCl, respectively, according to the determined r0 geometries. The CC bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r(CC) in the pseudo-? complexes are discussed.

  2. Primary photodissociation pathways of epichlorohydrin and analysis of the C-C bond fission channels from an O({sup 3}P)+allyl radical intermediate

    SciTech Connect

    FitzPatrick, Benjamin L.; Alligood, Bridget W.; Butler, Laurie J.; Lee, Shih-Huang; Lin, Jim Jr-Min

    2010-09-07

    This study initially characterizes the primary photodissociation processes of epichlorohydrin, c-(H{sub 2}COCH)CH{sub 2}Cl. The three dominant photoproduct channels analyzed are c-(H{sub 2}COCH)CH{sub 2}+Cl, c-(H{sub 2}COCH)+CH{sub 2}Cl, and C{sub 3}H{sub 4}O+HCl. In the second channel, the c-(H{sub 2}COCH) photofission product is a higher energy intermediate on C{sub 2}H{sub 3}O global potential energy surface and has a small isomerization barrier to vinoxy. The resulting highly vibrationally excited vinoxy radicals likely dissociate to give the observed signal at the mass corresponding to ketene, H{sub 2}CCO. The final primary photodissociation pathway HCl+C{sub 3}H{sub 4}O evidences a recoil kinetic energy distribution similar to that of four-center HCl elimination in chlorinated alkenes, so is assigned to production of c-(H{sub 2}COC)=CH{sub 2}; the epoxide product is formed with enough vibrational energy to isomerize to acrolein and dissociate. The paper then analyzes the dynamics of the C{sub 3}H{sub 5}O radical produced from C-Cl bond photofission. When the epoxide radical photoproduct undergoes facile ring opening, it is the radical intermediate formed in the O({sup 3}P)+allyl bimolecular reaction when the O atom adds to an end C atom. We focus on the HCO+C{sub 2}H{sub 4} and H{sub 2}CO+C{sub 2}H{sub 3} product channels from this radical intermediate in this report. Analysis of the velocity distribution of the momentum-matched signals from the HCO+C{sub 2}H{sub 4} products at m/e=29 and 28 shows that the dissociation of the radical intermediate imparts a high relative kinetic energy, peaking near 20 kcal/mol, between the products. Similarly, the energy imparted to relative kinetic energy in the H{sub 2}CO+C{sub 2}H{sub 3} product channel of the O({sup 3}P)+allyl radical intermediate also peaks at high-recoil kinetic energies, near 18 kcal/mol. The strongly forward-backward peaked angular distributions and the high kinetic energy release result from tangential recoil during the dissociation of highly rotationally excited nascent radicals formed photolytically in this experiment. The data also reveal substantial branching to an HCCH+H{sub 3}CO product channel. We present a detailed statistical prediction for the dissociation of the radical intermediate on the C{sub 3}H{sub 5}O potential energy surface calculated with coupled cluster theory, accounting for the rotational and vibrational energy imparted to the radical intermediate and the resulting competition between the H+acrolein, HCO+C{sub 2}H{sub 4}, and H{sub 2}CO+C{sub 2}H{sub 3} product channels. We compare the results of the theoretical prediction with our measured branching ratios. We also report photoionization efficiency (PIE) curves extending from 9.25 to 12.75 eV for the signal from the HCO+C{sub 2}H{sub 4} and H{sub 2}CO+C{sub 2}H{sub 3} product channels. Using the C{sub 2}H{sub 4} bandwidth-averaged absolute photoionization cross section at 11.27 eV and our measured relative photoion signals of C{sub 2}H{sub 4} and HCO yields a value of 11.6+1/-3 Mb for the photoionization cross section of HCO at 11.27 eV. This determination puts the PIE curve of HCO measured here on an absolute scale, allowing us to report the absolute photoionization efficiency of HCO over the entire range of photoionization energies.

  3. Ruthenium(0) Catalyzed Endiyne-?-Ketol [4 + 2] Cycloaddition: Convergent Assembly of Type II Polyketide Substructures via C-C Bond Forming Transfer Hydrogenation.

    PubMed

    Saxena, Aakarsh; Perez, Felix; Krische, Michael J

    2015-05-13

    Upon exposure of 3,4-benzannulated 1,5-diynes (benzo-endiynes) to ?-ketols (?-hydroxyketones) in the presence of Ru(0) catalysts derived from Ru3(CO)12 and RuPhos or CyJohnPhos, successive redox-triggered C-C coupling occurs to generate products of [4 + 2] cycloaddition. The proposed catalytic mechanism involves consecutive alkyne-carbonyl oxidative couplings to form transient oxaruthanacycles that suffer ?-ketol mediated transfer hydrogenolysis. This process provides a new, convergent means of assembling Type II polyketide substructures. PMID:25938947

  4. Rhodium(III)-Catalyzed Directed ortho-C-H Bond Functionalization of Aromatic Ketazines via C-S and C-C Coupling.

    PubMed

    Wen, Jing; Wu, An; Wang, Mingyang; Zhu, Jin

    2015-11-01

    Described herein is a convenient and efficient method for sulfuration and olefination of aromatic ketazines via rhodium-catalyzed oxidative C-H bond activation. A range of substituted substrates are supported, and a possible mechanism is proposed according to experimental results of kinetic isotopic effect, reversibility studies, and catalysis of rhodacycle intermediate c1. PMID:26417874

  5. All-carbon quaternary stereogenic centers in acyclic systems through the creation of several C-C bonds per chemical step.

    PubMed

    Marek, Ilan; Minko, Yury; Pasco, Morgane; Mejuch, Tom; Gilboa, Noga; Chechik, Helena; Das, Jaya P

    2014-02-19

    In the past few decades, it has become clear that asymmetric catalysis is one of the most powerful methods for the construction of carbon-carbon as well as carbon-heteroatom bonds in a stereoselective manner. However, when structural complexity increases (i.e., all-carbon quaternary stereogenic center), the difficulty in reaching the desired adducts through asymmetric catalytic reactions leads to a single carbon-carbon bond-forming event per chemical step between two components. Issues of efficiency and convergence should therefore be addressed to avoid extraneous chemical steps. In this Perspective, we present approaches that tackle the stimulating problem of efficiency while answering interesting synthetic challenges. Ideally, if one could create all-carbon quaternary stereogenic centers via the creation of several new carbon-carbon bonds in an acyclic system and in a single-pot operation from simple precursors, it would certainly open new horizons toward solving the synthetic problems. Even more important for any further design, the presence of polyreactive intermediates in synthesis (bismetalated, carbenoid, and oxenoids species) becomes now an indispensable tool, as it creates consecutively the same number of carbon-carbon bonds as in a multi-step process, but in a single-pot operation. PMID:24512113

  6. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, Robert J. (Oak Ridge, TN); McMillan, April D. (Knoxville, TN); Paulauskas, Felix L. (Oak Ridge, TN); Fathi, Zakaryae (Cary, NC); Wei, Jianghua (Raleigh, NC)

    1998-01-01

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy.

  7. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

    1998-08-25

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

  8. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

    1998-09-08

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

  9. CeCl37H2O catalyzed C-C and C-N bond-forming cascade cyclization with subsequent side-chain functionalization and rearrangement: a domino approach to pentasubstituted pyrrole analogues.

    PubMed

    Dhara, Dipankar; Gayen, Krishnanka S; Khamarui, Saikat; Pandit, Palash; Ghosh, Sukla; Maiti, Dilip K

    2012-11-16

    CeCl(3)7H(2)O is found as an efficient catalyst for new intermolecular domino reactions of three-, four- and seven-component assemblies of common precursors under benign reaction conditions. Generation of enaminioesters from ?-keto esters and primary amines, activation of their allylic sp(3) C-H, vinylic sp(2) C-H and N-H bonds, multi C-C and C-N bond-forming cascade cyclization with 1,2-diketones and subsequent side-chain alkylation have been developed to construct functionalized pentasubstituted pyrroles and their chiral analogues. The scope of the domino reaction is successfully explored toward synthesis of highly aryl-substituted pyrroles, pentasubstituted pyrroles bearing C2-olefinic side-chain and spiro-2-pyrrolinones and their chiral analogues via unusual side-chain amination, elimination and ring contraction. The new domino reaction is operationally simple, robust, substrate specific, selective and high yielding. PMID:23113545

  10. Hydrogenolysis and homologation of linear and branched pentenes on Ru/SiO/sub 2/ catalysts: implication in the mechanism of C-C bond formation and cleavage on metal surfaces

    SciTech Connect

    Rodriguez, E.; Leconte, M.; Basset, J.M.; Tanaka, K.; Tanaka, K.I.

    1988-01-06

    Hydrogenolysis and homologation of 1-pentene to butenes and hexenes take place simultaneously and at the same rate over a Ru/SiO/sub 2/ catalysts at 110/sup 0/C, suggesting that these two reactions are mechanistically related. /sup 13/C labeling experiments indicate that C-C cleavage occurs at the double bond of 1-pentene-1-/sup 13/C leading to unlabeled 1-butene and labeled hexenes. The product distribution in the hydrogenolysis of 1-pentene, 2-pentenes, 3-methyl-1-butene, 2-methyl-2-butene, and 2-methyl-1-butene is accounted for by a carbene-olefin mechanism, which can therefore be considered as a reasonable common path for the formation and cleavage of carbon-carbon bonds on metal surfaces.

  11. Theoretical study of the bond dissociation energies of propyne (C3H4)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1992-01-01

    The C-C and C-H bond dissociation energies (BDEs) of propyne have been computed using the modified coupled-pair functional method. Due to hyperconjugation, the C-C and methyl C-H single bonds are stronger and weaker, respectively than those in ethane. The acetylenic C-H and C triple bond C BDEs are larger and smaller, respectively, than in acetylene, also as a result of the hyperconjugation. Our best estimate of 92.5 +/- 2 kcal/mol for the methyl C-H BDE in propyne is slightly larger than the experimental value. For the acetylenic C-H BDE in propyne we predict 135.9 +/- 2 kcal/mol.

  12. Bond-Energy and Surface-Energy Calculations in Metals

    ERIC Educational Resources Information Center

    Eberhart, James G.; Horner, Steve

    2010-01-01

    A simple technique appropriate for introductory materials science courses is outlined for the calculation of bond energies in metals from lattice energies. The approach is applied to body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal-closest-packed (hcp) metals. The strength of these bonds is tabulated for a variety metals and is…

  13. Bond-Energy and Surface-Energy Calculations in Metals

    ERIC Educational Resources Information Center

    Eberhart, James G.; Horner, Steve

    2010-01-01

    A simple technique appropriate for introductory materials science courses is outlined for the calculation of bond energies in metals from lattice energies. The approach is applied to body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal-closest-packed (hcp) metals. The strength of these bonds is tabulated for a variety metals and is

  14. Methanol conversion to hydrocarbons over zeolite H-ZSM-5: Investigation of the role of CO and ketene in the formation of the initial C-C bond

    SciTech Connect

    Hutchings, G.J.; Johnston, P. ); Hunter, R. ); Van Rensburg, L.J. )

    1993-08-01

    Mechanistic studies concerning the formation of the initial carbon-carbon bond in the methanol conversion reaction over zeolite H-ZSM-5 are described and discussed. In particular, the possible roles of CO as a reaction intermediate or as a catalyst, via the formation of ketene, are evaluated. Experiments using [sup 13]CH[sub 3]OH/[sup 12]CO reactant mixtures demonstrate that no CO is incorporated into ethene, the primary product of this reaction. In addition, CO is found to have no significant effect on the induction period for this reaction. Model experiments for the methylation of ketene by reaction with Me[sub 2]SO[sub 4] and Me[sub 3]O[sup +]SbCl[sub 6][sup [minus

  15. Theoretical and structural analysis of long C-C bonds in the adducts of polycyanoethylene and anthracene derivatives and their connection to the reversibility of Diels-Alder reactions.

    PubMed

    Hirsch, Anna K H; Reutenauer, Philippe; Le Moignan, Marc; Ulrich, Sébastien; Boul, Peter J; Harrowfield, Jack M; Jarowski, Peter D; Lehn, Jean-Marie

    2014-01-20

    X-ray structure determinations on four Diels-Alder adducts derived from the reactions of cyano- and ester-substituted alkenes with anthracene and 9,10-dimethylanthracene have shown the bonds formed in the adduction to be particularly long. Their lengths range from 1.58 to 1.62 Å, some of the longest known for Diels-Alder adducts. Formation of the four adducts is detectably reversible at ambient temperature and is associated with free energies of reaction ranging from -2.5 to -40.6 kJ  mol(-1). The solution equilibria have been experimentally characterised by NMR spectroscopy. Density-functional-theory calculations at the MPW1K/6-31+G(d,p) level with PCM solvation agree with experiment with average errors of 6 kJ  mol(-1) in free energies of reaction and structural agreement in adduct bond lengths of 0.013 Å. To understand more fully the cause of the reversibility and its relationship to the long adduct bond lengths, natural-bond-orbital (NBO) analysis was applied to quantify donor-acceptor interactions within the molecules. Both electron donation into the σ*-anti-bonding orbital of the adduct bond and electron withdrawal from the σ-bonding orbital are found to be responsible for this bond elongation. PMID:24339005

  16. Kinetic and Structural Insight into the Mechanism of BphD, a C-C Bond Hydrolase from the Biphenyl Degradation Pathway

    PubMed Central

    Horsman, Geoff P.; Ke, Jiyuan; Dai, Shaodong; Seah, Stephen Y. K.; Bolin, Jeffrey T.; Eltis, Lindsay D.

    2008-01-01

    Kinetic and structural analyses of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) hydrolase from Burkholderia xenovorans LB400 (BphDLB400) provide insight into the catalytic mechanism of this unusual serine hydrolase. Single turnover stopped-flow analysis at 25 C showed that the enzyme rapidly (1/?1 ? 500 s?1) transforms HOPDA (?max = 434 nm) to a species with electronic absorption maxima at 473 and 492 nm. The absorbance of this enzyme-bound species (E:S) decayed in a biphasic manner (1/?2 = 54 s?1, 1/?3 = 6 s?1 ? kcat) with simultaneous biphasic appearance (48 and 8 s?1) of an absorbance band at 270 nm characteristic of one of the products, 2-hydroxypenta-2,4-dienoic acid (HPD). Increasing solution viscosity with glycerol slowed 1/?1 and 1/?2, but affected neither 1/?3 nor kcat, suggesting that 1/?2 may reflect diffusive HPD dissociation, while 1/?3 represents an intramolecular event. Product inhibition studies suggested that the other product, benzoate, is released after HPD. Contrary to studies in a related hydrolase, we found no evidence that ketonized HOPDA is partially released prior to hydrolysis, and therefore postulate that the biphasic kinetics reflect one of two mechanisms, pending assignment of E:S (?max = 492 nm). Crystal structures of wild type, the S112C variant, and S112C incubated with HOPDA were each determined to 1.6 resolution. The latter reveals interactions between conserved active site residues and the dienoate moiety of the substrate. Most notably, the catalytic residue His265 is hydrogen-bonded to the 2-hydroxy/oxo substituent of HOPDA, consistent with a role in catalyzing ketonization. The data are more consistent with an acyl-enzyme mechanism than with the formation of a gem-diol intermediate. PMID:16964968

  17. Molecular approach to the mechanisms of C-C bond formation and cleavage on metal surfaces: Hydrogenolysis, homologation, and dimerization of ethylene over Ru/SiO sub 2 catalysts

    SciTech Connect

    Rodriguez, E.; Leconte, M.; Basset, J.M.; Tanaka, K. )

    1989-09-01

    At temperatures above ca. 50 C, over Ru/SiO{sub 2} catalysts and in the presence of hydrogen, ethylene undergoes hydrogenation, hydrogenolysis, homologation, and dimerization reactions. The influence of contact times and reaction temperatures on conversions and selectivities has been examined. At low temperatures (C-C bond cleavage and formation; two mechanisms are proposed which involve either metallocarbene insertion-elimination reactions or formation and decomposition of dimetallacyclic intermediates. Several mechanisms are envisioned for dimerization of ethylene; experimental data seem to support a mechanism which involves formation and coupling of two ethylidene species.

  18. The Bond Dissociation Energies of 1-Butene

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    The bond dissociation energies of 1-butene and several calibration systems are computed using the G2(MP2) approach. The agreement between the calibration systems and experiment is very good. The computed values for 1-butene are compared with calibration systems and the agreement between the computed results for 1-butene and the "rule of thumb" values from the smaller systems is remarkably good.

  19. Synthesis of seco-B-ring bryostatin analogue WN-1 via C-C bond-forming hydrogenation: critical contribution of the B-ring in determining bryostatin-like and phorbol 12-myristate 13-acetate-like properties.

    PubMed

    Andrews, Ian P; Ketcham, John M; Blumberg, Peter M; Kedei, Noemi; Lewin, Nancy E; Peach, Megan L; Krische, Michael J

    2014-09-24

    The seco-B-ring bryostatin analogue, macrodiolide WN-1, was prepared in 17 steps (longest linear sequence) and 30 total steps with three bonds formed via hydrogen-mediated C-C coupling. This synthetic route features a palladium-catalyzed alkoxycarbonylation of a C2-symmetric diol to form the C9-deoxygenated bryostatin A-ring. WN-1 binds to PKCα (Ki = 16.1 nM) and inhibits the growth of multiple leukemia cell lines. Although structural features of the WN-1 A-ring and C-ring are shared by analogues that display bryostatin-like behavior, WN-1 displays PMA-like behavior in U937 cell attachment and proliferation assays, as well as in K562 and MV-4-11 proliferation assays. Molecular modeling studies suggest the pattern of internal hydrogen bonds evident in bryostatin 1 is preserved in WN-1, and that upon docking WN-1 into the crystal structure of the C1b domain of PKCδ, the binding mode of bryostatin 1 is reproduced. The collective data emphasize the critical contribution of the B-ring to the function of the upper portion of the molecule in conferring a bryostatin-like pattern of biological activity. PMID:25207655

  20. Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C-C?C(ads) on Ag(111) surface and their self-coupling reactions: Ab initio molecular dynamics approach

    NASA Astrophysics Data System (ADS)

    Lu, Shao-Yu; Lin, Jyh-Shing

    2014-01-01

    Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(?)?C(?) (ads)) and ethyl (H3C(?)-C(?)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(?)?C(?)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(?)?C(?)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(?)?C(?)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(?)-C(?)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(?)-C(?)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C-C(?)?C(?)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C-C(?)?C(?)(ads) due to the increasing s-character of C? leading to the stronger Ag-C? bond in comparison with that of H3C(?)-C(?)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C-C(?)?C(?)(ads) and H3C(?)-C(?)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C-C?C-C?C-CH3(g)) and butane (CH3-CH2-CH2-CH3(g)), respectively. The calculated reaction energy barriers for both H3C-C?C-C?C-CH3(g) (1.34 eV) and CH3-CH2-CH2-CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements.

  1. Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C-C?C(ads) on Ag(111) surface and their self-coupling reactions: ab initio molecular dynamics approach.

    PubMed

    Lu, Shao-Yu; Lin, Jyh-Shing

    2014-01-14

    Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(?)?C(?) (ads)) and ethyl (H3C(?)-C(?)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(?)?C(?)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(?)?C(?)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(?)?C(?)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(?)-C(?)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(?)-C(?)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C-C(?)?C(?)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C-C(?)?C(?)(ads) due to the increasing s-character of C? leading to the stronger Ag-C? bond in comparison with that of H3C(?)-C(?)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C-C(?)?C(?)(ads) and H3C(?)-C(?)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C-C?C-C?C-CH3(g)) and butane (CH3-CH2-CH2-CH3(g)), respectively. The calculated reaction energy barriers for both H3C-C?C-C?C-CH3(g) (1.34 eV) and CH3-CH2-CH2-CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements. PMID:24437901

  2. Accurate bond energies of biodiesel methyl esters from multireference averaged coupled-pair functional calculations.

    PubMed

    Oyeyemi, Victor B; Keith, John A; Carter, Emily A

    2014-09-01

    Accurate bond dissociation energies (BDEs) are important for characterizing combustion chemistry, particularly the initial stages of pyrolysis. Here we contribute to evaluating the thermochemistry of biodiesel methyl ester molecules using ab initio BDEs derived from a multireference averaged coupled-pair functional (MRACPF2)-based scheme. Having previously validated this approach for hydrocarbons and a variety of oxygenates, herein we provide further validation for bonds within carboxylic acids and methyl esters, finding our scheme predicts BDEs within chemical accuracy (i.e., within 1 kcal/mol) for these molecules. Insights into BDE trends with ester size are then analyzed for methyl formate through methyl crotonate. We find that the carbonyl group in the ester moiety has only a local effect on BDEs. C?C double bonds in ester alkyl chains are found to increase the strengths of bonds adjacent to the double bond. An important exception are bonds beta to C?C or C?O bonds, which produce allylic-like radicals upon dissociation. The observed trends arise from different degrees of geometric relaxation and resonance stabilization in the radicals produced. We also compute BDEs in various small alkanes and alkenes as models for the long hydrocarbon chain of actual biodiesel methyl esters. We again show that allylic bonds in the alkenes are much weaker than those in the small methyl esters, indicating that hydrogen abstractions are more likely at the allylic site and even more likely at bis-allylic sites of alkyl chains due to more electrons involved in ?-resonance in the latter. Lastly, we use the BDEs in small surrogates to estimate heretofore unknown BDEs in large methyl esters of biodiesel fuels. PMID:24621192

  3. Interaction geometries and energies of hydrogen bonds to C[double bond]O and C[double bond]S acceptors: a comparative study.

    PubMed

    Wood, Peter A; Pidcock, Elna; Allen, Frank H

    2008-08-01

    The occurrence, geometries and energies of hydrogen bonds from N-H and O-H donors to the S acceptors of thiourea derivatives, thioamides and thiones are compared with data for their O analogues - ureas, amides and ketones. Geometrical data derived from the Cambridge Structural Database indicate that hydrogen bonds to the C[double bond]S acceptors are much weaker than those to their C[double bond]O counterparts: van der Waals normalized hydrogen bonds to O are shorter than those to S by approximately 0.25 A. Further, the directionality of the approach of the hydrogen bond with respect to S, defined by the C[double bond]S...H angle, is in the range 102-109 degrees , much lower than the analogous C[double bond]O...H angle which lies in the range 127-140 degrees . Ab initio calculations using intermolecular perturbation theory show good agreement with the experimental results: the differences in hydrogen-bond directionality are closely reproduced, and the interaction energies of hydrogen bonds to S are consistently weaker than those to O, by approximately 12 kJ mol(-1), for each of the three compound classes. There are no CSD examples of hydrogen bonds to aliphatic thiones, (Csp(3))(2)C=S, consistent with the near-equality of the electronegativities of C and S. Thioureas and thioamides have electron-rich N substituents replacing the Csp(3) atoms. Electron delocalization involving C[double bond]S and the N lone pairs then induces a significant >C(delta+)[double bond]S(delta-) dipole, which enables the formation of the medium-strength C[double bond]S...H bonds observed in thioureas and thioamides. PMID:18641451

  4. On the differentiation of diffusion bond strength using the total acoustic energy reflected from the bond

    SciTech Connect

    Ojard, G.C.; Buck, O.; Rehbein, D.K.; Hughes, M.S.

    1992-12-31

    Single frequency reflection coefficients and reflected energy over a broad acoustic band (2-15 MHz), and the mechanical bond strength were evaluated on diffusion bonds in Cu/Cu, Cu/Ni, and Ti-6Al-4V/self. Results indicate that energy data are more sensitive to small bond strength changes as predicted by Parseval`s theorem. In all cases, the energy reflected mainly originates at voids still present at the original interface location. Other microstructural features caused by the interdiffusion appear to diminish the reflected energy. 7 refs., 4 figs.

  5. Direct-dynamics VTST study of hydrogen or deuterium abstraction and C-C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D

    NASA Astrophysics Data System (ADS)

    Ramazani, Shapour

    2013-05-01

    Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K/6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C-C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C-C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200-2200 K. The results of CVT/?OMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (-?E/RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200-2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures.

  6. Direct-dynamics VTST study of hydrogen or deuterium abstraction and C-C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D.

    PubMed

    Ramazani, Shapour

    2013-05-21

    Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K?6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C-C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C-C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200-2200 K. The results of CVT??OMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (-?E?RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200-2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures. PMID:23697416

  7. C-C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach

    SciTech Connect

    Boccia, A.; Lanzilotto, V.; Marrani, A. G.; Zanoni, R.; Stranges, S.; Alagia, M.; Fronzoni, G.; Decleva, P.

    2012-04-07

    We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the {sigma}/{pi} hyperconjugation in EtFC and the {pi}-conjugation in VFC and EFC.

  8. Comparison of bending, C-C stretching, and collision energy effects on the reaction of C2H + 2 with D2

    NASA Astrophysics Data System (ADS)

    Chiu, Yu-hui; Yang, Baorui; Fu, Hungshin; Anderson, Scott L.; Schweizer, Martin; Gerlich, Dieter

    1992-04-01

    We report the effects of vibrational excitation and collision energy on the cross sections and branching ratios for reaction of acetylene cations with D2, using two different guided-ion-beam instruments. Two major reaction channels are observed, both of which are nearly thermoneutral. Hydrogen atom exchange is slightly exoergic due to zero point energy, and is inhibited by both collision and vibrational energy. Formation of the two isotopic ``C2H+3 '' products is enhanced by collision energy and C-C stretching vibration, but not by bending vibration. The branching ratios at low collision energies are consistent with reaction via an intermediate complex, and Rice-Ramsberger-Kassel-Marcus (RRKM) analysis is used to extract further information. At collision energies above 1 eV, D-atom transfer by a direct mechanism is also observed as a route to C2H2D+ production. Comparison of our results using both the Stony Brook and Freiburg instruments is made with the state-selected experiments of Honma, Kato, Tanaka, and Koyano [J. Chem. Phys. 81, 5666 (1984)], who previously studied both the C2H+2+D2 and C2D+2+H2 isotopic reactants. Our results for C2H+2+D2 are consistent with their C2D+2+H2 data for all collision energies and with their C2H+2+D2 data at 0.2 eV collision energy. We do not reproduce the anomalous vibrational effects they reported for 1 and 2 eV collision energies.

  9. The Calculation of Accurate Metal-Ligand Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Partridge, Harry, III; Ricca, Alessandra; Arnold, James O. (Technical Monitor)

    1997-01-01

    The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.

  10. Do Bond Functions Help for the Calculation of Accurate Bond Energies?

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James (Technical Monitor)

    1998-01-01

    The bond energies of 8 chemically bound diatomics are computed using several basis sets with and without bond functions (BF). The bond energies obtained using the aug-pVnZ+BF basis sets (with a correction for basis set superposition error, BSSE) tend to be slightly smaller that the results obtained using the aug-pV(n+I)Z basis sets, but slightly larger than the BSSE corrected aug-pV(n+I)Z results. The aug-cc-pVDZ+BF and aug-cc-pVTZ+BF basis sets yield reasonable estimates of bond energies, but, in most cases, these results cannot be considered highly accurate. Extrapolation of the results obtained with basis sets including bond functions appears to be inferior to the results obtained by extrapolation using atom-centered basis sets. Therefore bond functions do not appear to offer a path for obtaining highly accurate results for chemically bound systems at a lower computational cost than atom centered basis sets.

  11. Calculation of bond dissociation energies of diatomic molecules using bond function basis sets with counterpoise corrections

    SciTech Connect

    Li, Z.; Pan, Y.K.; Tao, F.M.

    1996-01-15

    Bond function basis sets combined with the counterpoise procedure are used to calculate the molecular dissociation energies D{sub e} of 24 diatomic molecules and ions. The calculated values of D{sub e} are compared to those without bond functions and/or counterpoise corrections. The equilibrium bond lengths r{sub e}, and harmonic frequencies w{sub e} are also calculated for a few selected molecules. The calculations at the fourth-order-Moller-Plesset approximation (MP4) have consistently recovered about 95-99% of the experimental values for D{sub e}, compared to as low as 75% without use of bond functions. The calculated values of r{sub 3} are typically 0.01 {Angstrom} larger than the experimental values, and the calculated values of w{sub e} are over 95% of the experimental values. 37 refs., 2 tabs.

  12. Ubiquitous Transgenic Overexpression of C-C Chemokine Ligand 2: A Model to Assess the Combined Effect of High Energy Intake and Continuous Low-Grade Inflammation

    PubMed Central

    Rodríguez-Gallego, Esther; Hernández-Aguilera, Anna; Mariné-Casadó, Roger; Rull, Anna; Beltrán-Debón, Raúl; Menendez, Javier A.; Vazquez-Martin, Alejandro; Sirvent, Juan J.; Martín-Paredero, Vicente; Corbí, Angel L.; Sierra-Filardi, Elena; Aragonès, Gerard; García-Heredia, Anabel; Camps, Jordi; Alonso-Villaverde, Carlos; Joven, Jorge

    2013-01-01

    Excessive energy management leads to low-grade, chronic inflammation, which is a significant factor predicting noncommunicable diseases. In turn, inflammation, oxidation, and metabolism are associated with the course of these diseases; mitochondrial dysfunction seems to be at the crossroads of mutual relationships. The migration of immune cells during inflammation is governed by the interaction between chemokines and chemokine receptors. Chemokines, especially C-C-chemokine ligand 2 (CCL2), have a variety of additional functions that are involved in the maintenance of normal metabolism. It is our hypothesis that a ubiquitous and continuous secretion of CCL2 may represent an animal model of low-grade chronic inflammation that, in the presence of an energy surplus, could help to ascertain the afore-mentioned relationships and/or to search for specific therapeutic approaches. Here, we present preliminary data on a mouse model created by using targeted gene knock-in technology to integrate an additional copy of the CCl2 gene in the Gt(ROSA)26Sor locus of the mouse genome via homologous recombination in embryonic stem cells. Short-term dietary manipulations were assessed and the findings include metabolic disturbances, premature death, and the manipulation of macrophage plasticity and autophagy. These results raise a number of mechanistic questions for future study. PMID:24453432

  13. How resonance assists hydrogen bonding interactions: an energy decomposition analysis.

    PubMed

    Beck, John Frederick; Mo, Yirong

    2007-01-15

    Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between pi delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in beta-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of pi resonance, were decomposed into the Hitler-London energy (DeltaEHL), polarization energy (DeltaEpol), charge transfer energy (DeltaECT), and electron correlation energy (DeltaEcor) terms. This allows for the examination of the character of hydrogen bonds and the impact of pi conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole-dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. PMID:17143867

  14. The Chemical Bond in C2.

    PubMed

    Hermann, Markus; Frenking, Gernot

    2016-03-14

    Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for Hn CCHn (n=0-3) and N2 . The quadratic force constants and the stretching potentials of Hn CCHn have been calculated at the CASSCF/cc-pVTZ level. The bond dissociation energies of the C-C bonds of C2 and HC≡CH were computed using explicitly correlated CASPT2-F12/cc-pVTZ-F12 wave functions. The bond dissociation energies and the force constants suggest that C2 has a weaker C-C bond than acetylene. The analysis of the CASSCF wavefunctions in conjunction with the effective bond orders of the multiple bonds shows that there are four bonding components in C2 , while there are only three in acetylene and in N2 . The bonding components in C2 consist of two weakly bonding σ bonds and two electron-sharing π bonds. The bonding situation in C2 can be described with the σ bonds in Be2 that are enforced by two π bonds. There is no single Lewis structure that adequately depicts the bonding situation in C2 . The assignment of quadruple bonding in C2 is misleading, because the bond is weaker than the triple bond in HC≡CH. PMID:26756311

  15. Bond resonance energy and verification of the isolated pentagon rule

    SciTech Connect

    Aihara, Jun Ichi

    1995-04-12

    The isolated pentagon rule (IPR) states that fullerenes with isolated pentagons are kinetically much more stable than their fused pentagon counterparts. This rule can be verified in terms of a graph-theoretically defined bond resonance energy. In general, a {pi} bond shared by two pentagons has a large negative bond resonance energy, thus contributing significantly to the increase in kinetic instability or chemical reactivity of the molecule. The existence of such highly antiaromatic local structures sharply distinguishes IPR-violating fullerenes from isolated-pentagon isomers. {pi}bonds shared by two pentagons are shared by many antiaromatic conjugated circuits but not by relatively small aromatic conjugated circuits. 39 refs., 3 figs., 5 tabs.

  16. Bond energy decomposition analysis for subsystem density functional theory

    NASA Astrophysics Data System (ADS)

    Beyhan, S. Maya; Gtz, Andreas W.; Visscher, Lucas

    2013-03-01

    We employed an explicit expression for the dispersion (D) energy in conjunction with Kohn-Sham (KS) density functional theory and frozen-density embedding (FDE) to calculate interaction energies between DNA base pairs and a selected set of amino acid pairs in the hydrophobic core of a small protein Rubredoxin. We use this data to assess the accuracy of an FDE-D approach for the calculation of intermolecular interactions. To better analyze the calculated interaction energies we furthermore propose a new energy decomposition scheme that is similar to the well-known KS bond formation analysis [F. M. Bickelhaupt and E. J. Baerends, Rev. Comput. Chem. 15, 1 (2000), 10.1002/9780470125922.ch1], but differs in the electron densities used to define the bond energy. The individual subsystem electron densities of the FDE approach sum to the total electron density which makes it possible to define bond energies in terms of promotion energies and an explicit interaction energy. We show that for the systems considered only a few freeze-and-thaw cycles suffice to reach convergence in these individual bond energy components, illustrating the potential of FDE-D as an efficient method to calculate intermolecular interactions.

  17. Storing Renewable Energy in Chemical Bonds

    SciTech Connect

    Helm, Monte; Bullock, Morris

    2013-03-27

    With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

  18. Total energy calculations and bonding at interfaces

    SciTech Connect

    Louie, S.G.

    1984-08-01

    Some of the concepts and theoretical techniques employed in recent ab initio studies of the electronic and structural properties of surfaces and interfaces are discussed. Results of total energy calculations for the 2 x 1 reconstructed diamond (111) surface and for stacking faults in Si are reviewed. 30 refs., 8 figs.

  19. Storing Renewable Energy in Chemical Bonds

    ScienceCinema

    Helm, Monte; Bullock, Morris

    2014-06-13

    With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

  20. Bond dissociation energy of the phenol O sbnd H bond from ab initio calculations

    NASA Astrophysics Data System (ADS)

    da Silva, Gabriel; Chen, Chiung-Chu; Bozzelli, Joseph W.

    2006-06-01

    The phenol O sbnd H bond dissociation energy (BDE) is currently disputed, despite its importance in combustion chemistry and in the reactions of antioxidants such as vitamin E. We have studied this BDE using the computational methods G3, G3B3 and CBS-APNO, with bond-isodesmic work reactions. These calculations yield a BDE of 89.0 1.0 kcal mol -1, which supports other recent calculations [B.J. Costa Cabral, S. Canuto, Chem. Phys. Lett. 406 (2005) 300]. From our BDE we determine the enthalpy of formation of the phenoxy radical to be 13.9 1.0 kcal mol -1. Comparison of the phenol C sbnd H BDE with the vinyl alcohol H sbnd CH dbnd CHOH BDE reveals the bond in phenol to be around 3 kcal mol -1 stronger than that in vinyl alcohol. Replacement of a H atom with the OH group on benzene or ethylene strengthens the C sbnd H bonds on adjacent carbons by 3 to 4 kcal mol -1.

  1. Energy considerations show that low-barrier hydrogen bonds do not offer a catalytic advantage over ordinary hydrogen bonds.

    PubMed

    Warshel, A; Papazyan, A

    1996-11-26

    Low-barrier hydrogen bonds have recently been proposed as a major factor in enzyme catalysis. Here we evaluate the feasibility of transition state (TS) stabilization by low-barrier hydrogen bonds in enzymes. Our analysis focuses on the facts that (i) a low-barrier hydrogen bond is less stable than a regular hydrogen bond in water, (ii) TSs are more stable in the enzyme active sites than in water, and (iii) a nonpolar active site would destabilize the TS relative to its energy in water. Combining these points and other experimental and theoretical facts in a physically consistent frame-work shows that a low-barrier hydrogen bond cannot stabilize the TS more than an ordinary hydrogen bond. The reason for the large catalytic effect of active site hydrogen bonds is that their formation entails a lower reorganization energy than their solution counterparts, due to the preorganized enzyme environment. PMID:8942991

  2. Bonding energies of bitumen to tar sand mineral

    SciTech Connect

    Ensley, E.K.; Scott, M.A.

    1986-03-01

    The bonding energy of bitumen in a tar sand was found by algebraically adding the heat of dissolution of bitumen on tar sand, heat of dissolution of recovered bitumen and the heat of wetting of extracted tar sand mineral. The value for an Asphalt Ridge tar sand was found to be 270 cal/mole. 6 refs., 3 figs.

  3. Heats of Formation and Bond Energies in Group III Compounds

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Allendorf, Mark D.; Melius, Carl F.; Arnold, James O. (Technical Monitor)

    1999-01-01

    We present heats of formation and bond energies for Group-III compounds obtained from calculations of molecular ground-state I electronic energies. Data for compounds of the form MXn are presented, where M = B, Al, Ga, and In, X = He H, Cl, and CH3, and n = 1-3. Energies for the B, Al, and Ga compounds are obtained from G2 predictions, while those for the In compounds are obtained from CCSD(T)/CBS calculations; these are the most accurate calculations for indium-containing compounds published to date. In most cases, the calculated thermochemistry is in good agreement with published values derived from experiments for those species that have well-established heats of formation. Bond energies obtained from the heats of formation follow the expected trend (Cl much greater than CH3 approx. H). However, the CH3M-(CH3)2 bond energies obtained for trimethylgallium and trimethylindium are considerably stronger (greater than 15 kcal/mol) than currently accepted values.

  4. Bonding energies and long-range order in the trialuminides

    SciTech Connect

    Sparks, C.J.; Specht, E.D.; Ice, G.E.; Zschack, P.; Schneibel, J.

    1990-01-01

    The degree of long-range order in the trialuminides is determined by X-ray powder diffraction techniques. Long-range order exists to their melting points. For the binary trialuminides Al{sub 3}Ti, Al{sub 73}Ti{sub 27}, and Al{sub 3}Sc, the degree of long-range order is nearly perfect and is a measure of the lack of mixing of the aluminum atoms onto the sublattice occupied by either Ti or Sc. A calculation of the bond energy between neighboring pairs of atoms from the ordering (melting) temperature is made following the Bragg-Williams mean field theory approach. These bond energies compare favorably with more sophisticated calculations. Bond energies are found to be larger than the energy difference between the crystal structure forms DO{sub 22}, Ll{sub 2}, and DO{sub 23}, and therefore, more relevant to understanding the mechanical and chemical behavior of the trialuminides. Ordering or melting temperatures of these intermetallics reflect the strong Al-metal near-neighbor pair potentials and may provide insights to their brittle properties. 11 refs., 2 figs., 2 tabs.

  5. Argon hydrochloride, Ar.HCl, bond energy by infrared spectroscopy

    NASA Technical Reports Server (NTRS)

    Miziolek, A. W.; Pimentel, G. C.

    1976-01-01

    The infrared absorption of argon (200 to 760 torr) and hydrogen chloride (2 to 6 torr) mixtures is reexamined in the missing Q branch region (spectral region between 2860 and 3010 wavelength/cm) at temperatures ranging from 195 to 298 K. The temperature dependence of two absorption features of the argon hydrogen chloride complex, at 2887 and 2879 wavelength/cm, leads to a bond energy estimate that depends on the assumptions made about the internal degrees of freedom of the complex. It is shown that agreement with experiment can be reached for well depths near 1.2 kcal/mole. This result is relatively insensitive to the choice of the vibrational frequencies and anharmonicities, but does depend on the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. The bond energy is found to deviate from the commonly accepted value of 0.4 kcal/mole. Possible causes for the discrepancy are considered.

  6. Energy-based analysis of biochemical cycles using bond graphs

    PubMed Central

    Gawthrop, Peter J.; Crampin, Edmund J.

    2014-01-01

    Thermodynamic aspects of chemical reactions have a long history in the physical chemistry literature. In particular, biochemical cycles require a source of energy to function. However, although fundamental, the role of chemical potential and Gibb's free energy in the analysis of biochemical systems is often overlooked leading to models which are physically impossible. The bond graph approach was developed for modelling engineering systems, where energy generation, storage and transmission are fundamental. The method focuses on how power flows between components and how energy is stored, transmitted or dissipated within components. Based on the early ideas of network thermodynamics, we have applied this approach to biochemical systems to generate models which automatically obey the laws of thermodynamics. We illustrate the method with examples of biochemical cycles. We have found that thermodynamically compliant models of simple biochemical cycles can easily be developed using this approach. In particular, both stoichiometric information and simulation models can be developed directly from the bond graph. Furthermore, model reduction and approximation while retaining structural and thermodynamic properties is facilitated. Because the bond graph approach is also modular and scaleable, we believe that it provides a secure foundation for building thermodynamically compliant models of large biochemical networks. PMID:25383030

  7. Energy-based analysis of biochemical cycles using bond graphs.

    PubMed

    Gawthrop, Peter J; Crampin, Edmund J

    2014-11-01

    Thermodynamic aspects of chemical reactions have a long history in the physical chemistry literature. In particular, biochemical cycles require a source of energy to function. However, although fundamental, the role of chemical potential and Gibb's free energy in the analysis of biochemical systems is often overlooked leading to models which are physically impossible. The bond graph approach was developed for modelling engineering systems, where energy generation, storage and transmission are fundamental. The method focuses on how power flows between components and how energy is stored, transmitted or dissipated within components. Based on the early ideas of network thermodynamics, we have applied this approach to biochemical systems to generate models which automatically obey the laws of thermodynamics. We illustrate the method with examples of biochemical cycles. We have found that thermodynamically compliant models of simple biochemical cycles can easily be developed using this approach. In particular, both stoichiometric information and simulation models can be developed directly from the bond graph. Furthermore, model reduction and approximation while retaining structural and thermodynamic properties is facilitated. Because the bond graph approach is also modular and scaleable, we believe that it provides a secure foundation for building thermodynamically compliant models of large biochemical networks. PMID:25383030

  8. Bond Dissociation Energies for Substituted Polycyclic Aromatic Hydrocarbons and Their Cations

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

    1998-01-01

    The B3LYP/4-31G approach is used to compute bond energies for a series of substituted benzene, naphthalene, and anthracene molecules and their cations. The benzene bond energies are compared with experiment. The trends in the bond energies are discussed. The ionization energies are also reported and compared with available experiments.

  9. IR Spectra and Bond Energies Computed Using DFT

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles; Andrews, Lester; Arnold, James (Technical Monitor)

    2000-01-01

    The combination of density functional theory (DFT) frequencies and infrared (IR) intensities and experimental spectra is a very powerful tool in the identification of molecules and ions. The computed and measured isotopic ratios make the identification much more secure than frequencies and intensities alone. This will be illustrated using several examples, such as Mn(CO)n and Mn(CO)n-. The accuracy of DFT metal-ligand bond energies will also be discussed.

  10. Dissociation Energies of Sulfur-Centered Hydrogen-Bonded Complexes.

    PubMed

    Ghosh, Sanat; Bhattacharyya, Surjendu; Wategaonkar, Sanjay

    2015-11-01

    In this work we have determined dissociation energies of O-HS hydrogen bond in the H2S complexes of various phenol derivatives using 2-color-2-photon photofragmentation spectroscopy in combination with zero kinetic energy photoelectron (ZEKE-PE) spectroscopy. This is the first report of direct determination of dissociation energy of O-HS hydrogen bond. The ZEKE-PE spectra of the complexes revealed a long progression in the intermolecular stretching mode with significant anharmonicity. Using the anharmonicity information and experimentally determined dissociation energy, we also validated Birge-Sponer (B-S) extrapolation method, which is an approximate method to estimate dissociation energy. Experimentally determined dissociation energies were compared with a variety of ab initio calculations. One of the important findings is that ?B97X-D functional, which is a dispersion corrected DFT functional, was able to predict the dissociation energies in both the cationic as well as the ground electronic state very well for almost every case. PMID:26469685

  11. Analysis of liquid metal embrittlement from a bond energy viewpoint

    NASA Technical Reports Server (NTRS)

    Kelley, M. J.; Stoloff, N. S.

    1975-01-01

    Absorption induced embrittlement of solid metals by certain liquid metals is analyzed through an Engel-Brewer calculation of the solid-liquid interaction energy, and of the effect of the latter in reducing fracture surface energy. The reduction in fracture surface energy is estimated by comparison of the electronic contribution to the solid-liquid interaction energy with solid-solid bond energy for some 40 liquid-solid couples. Regular solution theory is used to estimate mutual solubility as the relative difference in parameter values. Embrittlement can be predicted by using reduction in fracture surface energy and solubility parameter difference as critical variables. The effect of solute additions to the liquid on the degree of embrittlement is interpreted via the same two variables; the principal effect of solutes is to modify solubility relationships at the solid-liquid interface.

  12. Bond length and local energy density property connections for non-transition-metal oxide-bonded interactions.

    PubMed

    Gibbs, G V; Spackman, M A; Jayatilaka, D; Rosso, K M; Cox, D F

    2006-11-01

    For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(r(c)), increases and the local potential energy density, V(r(c)), decreases as the M-O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, rho(r(c)), accumulates at the bond critical points, r(c). Despite the claim that the local kinetic energy density per electronic charge, G(r(c))/rho(r(c)), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(r(c)) = G(r(c)) + V(r(c)), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M-O bonded interaction, the greater the ratio, the larger the value of rho(r(c)), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(r(c))/rho(r(c)) versus G(r(c))/rho(r(c)) scatter diagrams categorize the M-O bonded interactions into domains with the local electronic energy density per electron charge, H(r(c))/rho(r(c)), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(r(c)) and V(r(c)), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C-O and N-O bonded interactions. PMID:17078623

  13. Modeling of inelastic deformation of f.c.c. single- and polycrystalline materials with low stacking fault energies[Face Centered Cubic

    SciTech Connect

    Staroselsky, A.; Anand, L.

    1999-07-01

    A new rate-independent constitutive model for plastic deformation of crystalline materials deforming by slip and twinning has been formulated, and implemented in a finite-element program. The authors have simulated three different structural levels by choosing representative volume elements (RVEs) as (1) a small part of a single crystal for the analysis of the heterogeneity of plastic deformation in single crystals, (2) a whole single crystal for polycrystal simulations, and (3) a group of crystals for a Taylor-type model of polycrystals. The authors show that the predictions for the texture and stress-strain response from the model are in reasonably good agreement with experiments in plane-strain compression for a different single crystal and polycrystalline f.c.c. materials.

  14. Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2004-01-01

    Since chemical reactions involve the breaking and making of bonds, understanding the relative strengths of bonds is of paramount importance in the study, teaching, and practice of chemistry. Further, it is showed that free atoms having p(super n) configuration with n = 2,3, or 4 are stabilized by exchange energy, and by spin-orbit coupling for n =…

  15. Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2004-01-01

    Since chemical reactions involve the breaking and making of bonds, understanding the relative strengths of bonds is of paramount importance in the study, teaching, and practice of chemistry. Further, it is showed that free atoms having p(super n) configuration with n = 2,3, or 4 are stabilized by exchange energy, and by spin-orbit coupling for n =

  16. Bond Energies in Models of the Schrock Metathesis Catalyst

    SciTech Connect

    Vasiliu, Monica; Li, Shenggang; Arduengo, Anthony J.; Dixon, David A.

    2011-06-02

    Heats of formation, adiabatic and diabatic bond dissociation energies (BDEs) of the model Schrock-type metal complexes M(NH)(CRŔ)(OH)₂ (M = Cr, Mo, W; CRŔ = CH₂, CHF, CF₂) and MO₂(OH)₂ compounds, and Brønsted acidities and fluoride affinities for the M(NH)(CH₂)(OH) ₂ transition metal complexes are predicted using high level CCSD(T) calculations. The metallacycle intermediates formed by reaction of C₂H4 with M(NH)-(CH₂)(OH)2 and MO₂(OH)₂ are investigated at the same level of theory. Additional corrections were added to the complete basis set limit to obtain near chemical accuracy ((1 kcal/mol). A comparison between adiabatic and diabatic BDEs is made and provides an explanation of trends in the BDEs. Electronegative groups bonded on the carbenic carbon lead to less stable Schrock-type complexes as the adiabatic BDEs ofMdCF₂ andMdCHF bonds are much lower than theMdCH₂ bonds. The Cr compounds have smaller BDEs than theWorMo complexes and should be less stable. Different M(NH)(OH)₂(C₃H₆) and MO(OH)₂(OC₂H4) metallacycle intermediates are investigated, and the lowest-energy metallacycles have a square pyramidal geometry. The results show that consideration of the singlet_triplet splitting in the carbene in the initial catalyst as well as in the metal product formed by the retro [2+2] cycloaddition is a critical component in the design of an effective olefin metathesis catalyst in terms of the parent catalyst and the groups being transferred.

  17. Controlling the bond scission sequence of oxygenates for energy applications

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan L.

    The so called "Holy Grail" of heterogeneous catalysis is a fundamental understanding of catalyzed chemical transformations which span multidimensional scales of both length and time, enabling rational catalyst design. Such an undertaking is realizable only with an atomic level understanding of bond formation and destruction with respect to intrinsic properties of the metal catalyst. In this study, we investigate the bond scission sequence of small oxygenates (methanol, ethanol, ethylene glycol) on bimetallic transition metal catalysts and transition metal carbide catalysts. Oxygenates are of interest both as hydrogen carriers for reforming to H2 and CO and as fuels in direct alcohol fuel cells (DAFC). To address the so-called "materials gap" and "pressure gap" this work adopted three parallel research approaches: (1) ultra high vacuum (UHV) studies including temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) on polycrystalline surfaces; (2) DFT studies including thermodynamic and kinetic calculations; (3) electrochemical studies including cyclic voltammetry (CV) and chronoamperometry (CA). Recent studies have suggested that tungsten monocarbide (WC) may behave similarly to Pt for the electrooxidation of oxygenates. TPD was used to quantify the activity and selectivity of oxygenate decomposition for WC and Pt-modifiedWC (Pt/WC) as compared to Pt. While decomposition activity was generally higher on WC than on Pt, scission of the C-O bond resulted in alkane/alkene formation on WC, an undesired product for DAFC. When Pt was added to WC by physical vapor deposition C-O bond scission was limited, suggesting that Pt synergistically modifies WC to improve the selectivity toward C-H bond scission to produce H2 and CO. Additionally, TPD confirmed WC and Pt/WC to be more CO tolerant than Pt. HREELS results verified that surface intermediates were different on Pt/WC as compared to Pt or WC and evidence of aldehyde intermediates was observed on the Pt and Pt/WC surfaces. For CH3OH decomposition, DFT calculations suggested that the bond scission sequence could be controlled using monolayer coverage of Pt on WC. The Ni/Pt bimetallic system was studied as an example for using oxygenates as a hydrogen source. There are two well characterized surface structures for the Ni/Pt system: the surface configuration, in which the Ni atoms reside primarily on the surface of the Pt bulk, and the subsurface configuration, in which the second atomic layer is enriched in Ni atoms and the surface is enriched in Pt atoms. These configurations are denoted NiPtPt and PtNiPt, respectively. DFT results revealed that trends established for the Ni/Pt(111) system extend to the Ni/Pt(100) analogue. TPD studies revealed that the NiPtPt surface was more active for oxygenate reforming than the Pt or PtNiPt surfaces. HREELS confirmed the presence of strongly bound reaction intermediates, including aldehyde-like species, and suggested that the first decomposition step was likely O-H bond scission. Thus, the binding energies of the deprotonated reaction intermediates are important parameters in controlling the decomposition pathways of oxygenates. These studies have demonstrated that the bond scission sequence of oxygenate decomposition can be controlled using bimetallic and transition metal carbide catalysts. While this study has focused on oxygenate decomposition for energy applications, the principles and methodology applied herein are universally applicable to the development of novel and marketable value-added products. The value in such a methodology is in the combination of both calculations to predict catalytic and chemical properties, and experiments to fine-tune theoretical predictions.

  18. Theoretical determination of the alkali-metal superoxide bond energies

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Sodupe, Mariona; Langhoff, Stephen R.

    1992-01-01

    The bond dissociation energies for the alkali-metal superoxides have been computed using extensive Gaussian basis sets and treating electron correlation at the modified coupled-pair functional level. Our computed D0 values are 61.4, 37.2, 40.6, and 38.4 kcal/mol for LiO2, NaO2, KO2, and RbO2, respectively. These values, which are expected to be lower bounds and accurate to 2 kcal/mol, agree well with some of the older flame data, but rule out several recent experimental measurements.

  19. The Trouble with Chemical Energy: Why Understanding Bond Energies Requires an Interdisciplinary Systems Approach

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

    Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk…

  20. The Trouble with Chemical Energy: Why Understanding Bond Energies Requires an Interdisciplinary Systems Approach

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

    Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk

  1. Mediatorless solar energy conversion by covalently bonded thylakoid monolayer on the glassy carbon electrode.

    PubMed

    Lee, Jinhwan; Im, Jaekyun; Kim, Sunghyun

    2016-04-01

    Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230nAcm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification. PMID:26625272

  2. Bond energy effects on strength, cooperativity and robustness of molecular structures

    PubMed Central

    Chou, Chia-Ching; Buehler, Markus J.

    2011-01-01

    A fundamental challenge in engineering biologically inspired materials and systems is the identification of molecular structures that define fundamental building blocks. Here, we report a systematic study of the effect of the energy of chemical bonds on the mechanical properties of molecular structures, specifically, their strength and robustness. By considering a simple model system of an assembly of bonds in a cluster, we demonstrate that weak bonding, as found for example in H-bonds, results in a highly cooperative behaviour where clusters of bonds operate synergistically to form relatively strong molecular clusters. The cooperative effect of bonding results in an enhanced robustness since the drop of strength owing to the loss of a bond in a larger cluster only results in a marginal reduction of the strength. Strong bonding, as found in covalent interactions such as disulphide bonds or in the backbone of proteins, results in a larger mechanical strength. However, the ability for bonds to interact cooperatively is lost, and, as a result, the overall robustness is lower since the mechanical strength hinges on individual bonds rather than a cluster of bonds. The systematic analysis presented here provides general insight into the interplay of bond energy, robustness and other geometric parameters such as bond spacing. We conclude our analysis with a correlation of structural data of natural protein structures, which confirms the conclusions derived from our study. PMID:23050078

  3. An Experimental and Theoretical Study on the Ionization Energies of Polyynes (H-(C = C)n-H; n = 1 - 9)

    SciTech Connect

    Kaiser, Ralf I.; Sun, Bian Jian; Lin, Hong Mao; Chang, Agnes H. H.; Mebel, Alexander M.; Kostko, Oleg; Ahmed, Musahid

    2010-05-17

    We present a combined experimental and theoretical work on the ionization energies of polyacetylene -- organic molecules considered as important building blocks to form polycyclic aromatic hydrocarbons (PAHs) in the proto planetary nebulae such as of CRL 618. This set of astrophysical data can be utilized with significant confidence in future astrochemical models of photon-dominated regions and also of the proto planetary nebulae CRL 618. We recommend ionization energies of polyacetylenes from diacetylene up to heptaacetylene with an experimental accuracy of +- 0.05 eV: 10.03 eV (diacetylene), 9.45 eV (triacetylene), 9.08 eV (tetraacetylene), 8.75 eV (pentaacetylene), 8.65 eV (hexaacetylene), and 8.50 eV (heptaacetylene); further, ionization energies and with an accuracy of +- 0.1 eV: 8.32 eV (octaacetylene) and 8.24 eV (nonaacetylene) were computed. Implications of these energies to the redox chemistry involved in the multiply charged metal-ion mediated chemistry of hydrocarbon-rich atmospheres of planets and their moons such as Titan are also discussed.

  4. Metallic bond effects on mean excitation energies for stopping powers

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Xu, Y. J.

    1982-01-01

    Mean excitation energies for first row metals are evaluated by means of the local plasma approximation. Particle corrections based on Pines' (1953) procedure and the Wigner Seitz (1934) model of the metallic state are included. The agreement with experimental values is remarkably good. In contrast to previous work, the calculations given here estimate shifts in the plasma frequency according to the theory for plane wave states in an extended plasma as calculated by Pines. It is demonstrated that the effects of the metallic bond in lithium and beryllium are quite large and that they appear mainly as a result of collective oscillations in the 'free' electron gas formed from the valence electrons. The usefulness of the plasma frequency shift derived for a degenerate electron gas in predicting the plasma frequency shift within the ion core is considered surprising.

  5. Bond dissociation energies from the topology of the charge density using gradient bundle analysis

    NASA Astrophysics Data System (ADS)

    Morgenstern, Amanda; Eberhart, Mark

    2016-02-01

    New and more robust models of chemical bonding are necessary to further our understanding of chemical phenomena. Among these are bond bundle and gradient bundle methods, which analyze bonding interactions in terms of property distributions over geometrically defined volumes. These methods have been shown to provide a systematic framework from which to search for structure–property relationships. In addition to providing a brief review of some of the relationships found using this framework, we present new findings that relate the lowering of kinetic energy in bonding regions to bond dissociation energy.

  6. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  7. Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities

    SciTech Connect

    Gibbs, Gerald V.; Cox, David; Crawford, T Daniel; Rosso, Kevin M.; Ross, Nancy; Downs, R. T.

    2006-02-28

    A classification of the HF bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio |V(rc)|/G(rc) where |V(rc)| is the magnitude of the local potential energy density and G(rc) is the local kinetic density evaluated at the bond critical points, rc. A calculation of the ratio for the MO bonded interactions comprising a relatively large number of molecules and earth materials, together with the constraints imposed by the values of 2?(rc) and the local electronic energy density H(rc) = G(rc) + V(rc) in the HF study, yielded the same classification for the oxides as found for the fluorides. This is true despite the different trends of the bond critical point and local energy properties with the bond length displayed by the HF and MO bonded interactions. LiO, NaO and MgO bonded interactions classify as closed shell ionic bonds, BeO, AlO, SiO, BO and PO bonded interactions classify as bonds of intermediate character and NO bonded interactions classify as shared covalent bonds. CO and SO bonded interactions classify as both intermediate and covalent bonded interactions. The CO triple bonded interaction classifies as a bond of intermediate character and the CO single bonded interaction classifies as a covalent bond whereas their H(rc) value indicates that they are both covalent bonds. The |V(rc)|/G(rc) ratios for the BeO, AlO and SiO bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between |V(rc)|/G(rc) and the character of the bonded interaction is consistent with trends expected from electronegativity considerations. The connection between the net charges and the experimental SiO bond length evaluated for the Si and O atoms comprising two orthosilicates are examined in terms of the |V(rc)|/G(rc) values.

  8. Interstellar Isomers: The Importance of Bonding Energy Differences

    NASA Technical Reports Server (NTRS)

    Remijan, Anthony J.; Hollis, J. M.; Lovas, F. J.; Plusquellic, D. F.; Jewell, P. R.

    2005-01-01

    We present strong detections of methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH3NC) for its J(sub K) = 1(sub 0) - 0(sub 0) transition, which is the first interstellar report of this line. To determine the spatial distribution of CH3NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(sub K) = 1(sub 0) - 0(sub 0) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is greater than 8500 per centimeter (greater than 12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH3NC emission with a single antenna (Gaussian beamsize(omega(sub B))=1723 arcsec(sup 2)) but not with an interferometer (omega(sub b)=192 arcsec(sup 2)), strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, largescale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH3CN can produce CH3NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

  9. Determination of the bond energy for copper and silver dimers on the Mo(011) face

    NASA Astrophysics Data System (ADS)

    Ko?aczkiewicz, J.

    1989-04-01

    A new method of the measurement of the bond energy for metallic dimers adsorbed on a metal surface is presented. The bond energies for Cu 2 and Ag 2 on the Mo(011) face have been found; the obtained values are of the same order as those calculated and measured for W(011).

  10. A revised set of values of single-bond radii derived from the observed interatomic distances in metals by correction for bond number and resonance energy

    PubMed Central

    Pauling, Linus; Kamb, Barclay

    1986-01-01

    An earlier discussion [Pauling, L. (1947) J. Am. Chem. Soc. 69, 542] of observed bond lengths in elemental metals with correction for bond number and resonance energy led to a set of single-bond metallic radii with values usually somewhat less than the corresponding values obtained from molecules and complex ions. A theory of resonating covalent bonds has now been developed that permits calculation of the number of resonance structures per atom and of the effective resonance energy per bond. With this refined method of correcting the observed bond lengths for the effect of resonance energy, a new set of single-bond covalent radii, in better agreement with values from molecules and complex ions, has been constructed. PMID:16593698

  11. Energy decomposition analysis of cation-?, metal ion-lone pair, hydrogen bonded, charge-assisted hydrogen bonded, and ?-? interactions.

    PubMed

    Sharma, Bhaskar; Srivastava, Hemant Kumar; Gayatri, Gaddamanugu; Sastry, Garikapati Narahari

    2015-03-30

    This study probes the nature of noncovalent interactions, such as cation-?, metal ion-lone pair (M-LP), hydrogen bonding (HB), charge-assisted hydrogen bonding (CAHB), and ?-? interactions, using energy decomposition schemes-density functional theory (DFT)-symmetry-adapted perturbation theory and reduced variational space. Among cation-? complexes, the polarization and electrostatic components are the major contributors to the interaction energy (IE) for metal ion-? complexes, while for onium ion-? complexes (NH4+, PH4+, OH3+, and SH3+) the dispersion component is prominent. For M-LP complexes, the electrostatic component contributes more to the IE except the dicationic metal ion complexes with H2 S and PH3 where the polarization component dominates. Although electrostatic component dominates for the HB and CAHB complexes, dispersion is predominant in ?-? complexes. PMID:25581071

  12. Facilitating room-temperature Suzuki coupling reaction with light: Mott-Schottky photocatalyst for C-C-coupling

    NASA Astrophysics Data System (ADS)

    Li, Xin-Hao; Baar, Moritz; Blechert, Siegfried; Antonietti, Markus

    2013-04-01

    The Suzuki coupling reaction is one of the most practiced classes of catalytic C-C bond formation. The development of new means of activating molecules and bonds over old catalysts for C-C bond formation is a fundamental objective for chemists. Here, we report the room-temperature C-C bond formation over heterogeneous Pd catalysts by light-mediated catalyst activation. We employ stimulated electron transfer at the metal-semiconductor interface from optically active mesoporous carbon nitride nanorods to Pd nanoparticles. This photocatalytic pathway is highly efficient for coupling aryl halides with various coupling partners with high activity and selectivity under photo irradiation and very mild conditions.

  13. Facilitating room-temperature Suzuki coupling reaction with light: Mott-Schottky photocatalyst for C-C-coupling

    PubMed Central

    Li, Xin-Hao; Baar, Moritz; Blechert, Siegfried; Antonietti, Markus

    2013-01-01

    The Suzuki coupling reaction is one of the most practiced classes of catalytic C-C bond formation. The development of new means of activating molecules and bonds over old catalysts for C-C bond formation is a fundamental objective for chemists. Here, we report the room-temperature C-C bond formation over heterogeneous Pd catalysts by light-mediated catalyst activation. We employ stimulated electron transfer at the metal-semiconductor interface from optically active mesoporous carbon nitride nanorods to Pd nanoparticles. This photocatalytic pathway is highly efficient for coupling aryl halides with various coupling partners with high activity and selectivity under photo irradiation and very mild conditions.

  14. 99. Catalog HHistory 1, C.C.C., 23 Guard Rail Construction, Negative ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    99. Catalog H-History 1, C.C.C., 23 Guard Rail Construction, Negative No. P455e (Photographer and date unknown) GUARD RAIL INSTALLATION. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  15. 100. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. P ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    100. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. P 733c (Photographer and date unknown) SLOPE MAINTENANCE WORK BY CCC. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  16. 98. Catalog HHistory 1, C.C.C., 19 Tree Planting, Negative No. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    98. Catalog H-History 1, C.C.C., 19 Tree Planting, Negative No. P 474c (Photographer and date unknown) TRANSPLANTING TREE. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  17. 101. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. 1340 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    101. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. 1340 (Photographer and date unknown) BANK BLENDING WORK BY CCC. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  18. The Trouble with Chemical Energy: Why Understanding Bond Energies Requires an Interdisciplinary Systems Approach

    PubMed Central

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

    Helping students understand chemical energy is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk about chemical energy (which is also the way we talk about energy in everyday life); 2) the macroscopic approach to energy concepts that is common in physics and physical sciences; and 3) the failure of chemistry courses to explicitly link molecular with macroscopic energy ideas. From a constructivist perspective, it is unlikely that students can, without a coherent understanding of such a central concept, attain a robust and accurate understanding of new concepts. However, changes are on the horizon, guided by the increasing understanding that difficult concepts require coherent, well-designed learning progressions and the new National Research Council Framework for K12 Science Education. We provide supporting evidence for our assertions and suggestions for an interdisciplinary learning progression designed to better approach the concept of bond energies, a first step in an understanding chemical energy and behavior of reaction systems that is central to biological systems. PMID:23737636

  19. Prediction of the bond lengths, vibrational frequencies, and bond dissociation energy of octahedral seaborgium hexacarbonyl, Sg(CO){sub 6}

    SciTech Connect

    Nash, C.S.; Bursten, B.E.

    1999-11-24

    The recent syntheses of several new elements (including the recent reports of elements 116 and 118), coupled with the controversy surrounding the naming of elements 104--109, have stimulated a great interest in the chemistry of the transactinide elements. This contribution addresses hypothetical hexacarbonyl complex of seaborgium (Sg, element 106), which is predicted to be a 6d-block transition element with six valence electrons, analogous to Cr, Mo, and W. The authors have previously predicted that, if it were to exist, Sg(CO){sub 6} would exhibit metal-carbonyl bonding that is very similar to that in Cr(CO){sub 6}, Mo(CO){sub 6}, and W(CO){sub 6}, and quite unlike that of the unknown valence isoelectronic actinide complex U(CO){sub 6}. This finding is in accord with the scant experimental data available for Sg. The relativistic DV-X{alpha} method used in the earlier paper facilitated the analysis of the molecular orbitals of Sg(CO){sub 6}, but did not allow for the calculation of total-energy properties, such as bond lengths and vibrational frequencies. Here the authors will use the superior methodology they have applied to other transactinide molecules to compare the bond lengths, vibrational frequencies, and CO dissociation energy of hypothetical Sg(CO){sub 6} to those of Mo(CO){sub 6} and W(CO){sub 6}.

  20. Measurements of ? (3686 )?K-? ? ++c .c . and ? (3686 )?? K-? ? ++c .c .

    NASA Astrophysics Data System (ADS)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; An, F. F.; An, Q.; Bai, J. Z.; Baldini Ferroli, R.; Ban, Y.; Bennett, D. W.; Bennett, J. V.; Bertani, M.; Bettoni, D.; Bian, J. M.; Bianchi, F.; Boger, E.; Bondarenko, O.; Boyko, I.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, H. Y.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Cibinetto, G.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dbeyssi, A.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; de Mori, F.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Duan, P. F.; Fan, J. Z.; Fang, J.; Fang, S. S.; Fang, X.; Fang, Y.; Fava, L.; Feldbauer, F.; Felici, G.; Feng, C. Q.; Fioravanti, E.; Fritsch, M.; Fu, C. D.; Gao, Q.; Gao, X. Y.; Gao, Y.; Gao, Z.; Garzia, I.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, Y.; Guo, Y. P.; Haddadi, Z.; Hafner, A.; Han, S.; Han, Y. L.; Hao, X. Q.; Harris, F. A.; He, K. L.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Hu, Y.; Huang, G. M.; Huang, G. S.; Huang, H. P.; Huang, J. S.; Huang, X. T.; Huang, Y.; Hussain, T.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, L. W.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Johansson, T.; Julin, A.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kang, X. S.; Kavatsyuk, M.; Ke, B. C.; Kliemt, R.; Kloss, B.; Kolcu, O. B.; Kopf, B.; Kornicer, M.; Khn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leng, C.; Li, C. H.; Li, Cheng; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, Jin; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. M.; Li, X. N.; Li, X. Q.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, J. Y.; Liu, K.; Liu, K. Y.; Liu, L. D.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, X. X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, H. J.; Lu, J. G.; Lu, R. Q.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Lyu, X. R.; Ma, F. C.; Ma, H. L.; Ma, L. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. N.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Marcello, S.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Mo, Y. J.; Morales Morales, C.; Moriya, K.; Muchnoi, N. Yu.; Muramatsu, H.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, S. L.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Patteri, P.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Pettersson, J.; Ping, J. L.; Ping, R. G.; Poling, R.; Pu, Y. N.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, N.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ren, H. L.; Ripka, M.; Rong, G.; Ruan, X. D.; Santoro, V.; Sarantsev, A.; Savri, M.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, P. X.; Shen, X. Y.; Sheng, H. Y.; Song, W. M.; Song, X. Y.; Sosio, S.; Spataro, S.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Tiemens, M.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, B. L.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Weber, T.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, L. H.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, L.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yin, J. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Yuncu, A.; Zafar, A. A.; Zallo, A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, K.; Zhang, L.; Zhang, S. H.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Y. T.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, H. S.; Zhao, J. W.; Zhao, J. Y.; Zhao, J. Z.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, W. J.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, S.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zotti, L.; Zou, B. S.; Zou, J. H.; Besiii Collaboration

    2015-05-01

    Using a sample of 1.06 1 08? (3686 ) events produced in e+e- collisions at ?{s }=3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays ? (3686 )?K-? ? ++c .c . and ? (3686 )?? K-? ? ++c .c . . We observe two hyperons, ? (1690 )- and ? (1820 )- , in the K-? invariant mass distribution in the decay ? (3686 )?K-? ? ++c .c . with significances of 4.9 ? and 6.2 ? , respectively. The branching fractions of ? (3686 )?K-? ? ++c .c . , ? (3686 )?K-?0? ++c .c . , ? (3686 )?? ?c J?? K-? ? ++c .c . (J =0 , 1, 2), and ? (3686 )?? (1690 /1820 )-? ++c .c . with subsequent decay ? (1690 /1820 )-?K-? are measured for the first time.

  1. The effect of bond functions on dissociation energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.

    1985-01-01

    The procedure employing bond functions recently suggested by Wright and Buenker has been applied to the N2 X 1 Sigma g + potential curve within the CAS SCF + MRSD CI treatment of electron correlation. The basis set used herein is identical to that employed by these authors in their SCF + CI calculations. The De and and the shape of the resulting potential curve, as judged by the computed vibrational levels, is not so accurate as would be expected from the results reported by Wright and Buenker (1984). The results indicate that using the CI superposition errors associated with bond functions to cancel basis set incompleteness depends on the treatment of the electron correlation.

  2. A Dynamic Pathway for Stone-Wales Bond Rotation on Carbon Nanotubes through Diamond-Like Bonds

    NASA Technical Reports Server (NTRS)

    Wei, Chen-Yu; Srivastava, Deepak; Cho, Kyeong-Jae; Menon, Madhu

    2003-01-01

    A new lower energy barrier with a two-step pathway of Stone-Wales (SW) ,ond rotation on carbon nanotubes (CNTs) is found through molecular dynamics (MD) simulations of CNTs under tension. The first step involves going over to a stable sp3-like metastable configuration with half rotated and partially tilted C-C bond. The second step involves going over to the fully rotated C-C bond with the formation of a SW defect in the nanotube. The energy barrier for this two-step dynamic pathway is significantly lower than the previously known static barrier for in-plane rotation of the C-C bond on a tensile strained (> 4%) CNT.

  3. On the differentiation of diffusion bond strength using the total acoustic energy reflected from the bond. [Ti-6Al-4V

    SciTech Connect

    Ojard, G.C. ); Buck, O.; Rehbein, D.K.; Hughes, M.S. . Center for NDE)

    1992-01-01

    Single frequency reflection coefficients and reflected energy over a broad acoustic band (2-15 MHz), and the mechanical bond strength were evaluated on diffusion bonds in Cu/Cu, Cu/Ni, and Ti-6Al-4V/self. Results indicate that energy data are more sensitive to small bond strength changes as predicted by Parseval's theorem. In all cases, the energy reflected mainly originates at voids still present at the original interface location. Other microstructural features caused by the interdiffusion appear to diminish the reflected energy. 7 refs., 4 figs.

  4. Estimation of the bond dissociation energies from the kinetic characteristics of liquid-phase radical reactions

    NASA Astrophysics Data System (ADS)

    Denisov, Evgenii T.; Tumanov, V. E.

    2005-09-01

    Three methods used in the kinetics of liquid-phase radical reactions for estimating the dissociation energies of individual bonds in polyatomic molecules are described. The first approach is based on the study of the equilibrium in radical abstraction reactions involving stable radicals and measurements of the equilibrium constants. The second method is based on the study of the kinetics of homolytic decomposition of molecules. Measuring the activation energy of these reactions makes it possible to estimate the dissociation energies of the weakest bonds, e.g., the O-O bonds in various peroxides. The essence of the third approach developed in the framework of the model of intersecting parabolas is calculations of the bond dissociation energy from the activation energy of a radical reaction involving the molecules under consideration. This method allowed the dissociation energies of the C-H, N-H, O-H and S-H bonds in a large number of organic compounds to be estimated. The scope and the specific features of application of each method are discussed and the bond dissociation energies determined by these methods are given.

  5. Equilibrium Acidities and Homolytic Bond Dissociation Energies of Acidic C H Bonds in Alpha-Arylacetophenones and Related Compounds

    SciTech Connect

    Alnajjar, Mikhail S.); Zhang, Xian-Man; Gleicher, Gerald J.; Truksa, Scott V.; Franz, James A.)

    2002-12-13

    The equilibrium acidities (pKAHs) and the oxidation potentials of the conjugate anions (Eox(A?{approx})s) were determined in dimethyl sulfoxide (DMSO) for eight ketones of the structure GCOCH3 and twenty of the structure RCOCH2G, (where R= alkyl, phenyl and G= alkyl, aryl). The homolytic bond dissociation energies (BDEs) for the acidic C H bonds of the ketones were estimated using the equation, BDEAH= 1.37pKAH+ 23.1Eox(A?{approx})+ 73.3. While the equilibrium acidities of GCOCH3 were found to be dependent on the remote substituent G, the BDE values for the C H bonds remained essentially invariant (93.5+ 0.5 kcal/mol). A linear correlation between pKAH values and (Eox(A?{approx})s) was found for the ketones. For RCOCH2G ketones, both pKAH and BDE values for the adjacent C-H bonds are sensitive to the nature of the substituent G. However, the steric bulk of the aryl group tends to exert a leveling effect on BDE's. The BDE of?p-9-anthracenylacetophenone is higher than that of??-2-anthracenylacetophenone by 3 kcal/mole, reflecting significant steric inhibition of resonance in the 9-substituted system. A range of 80.7 - 84.4 kcal/mole is observed for RCOCH2G ketones. The results are discussed in terms of solvation, steric, and resonance effects. Ab initio density functional theory (DFT) calculations are employed to illustrate the effect of steric interactions on radical and anion geometries. The DFT results parallel the trends in the experimental BDEs of??-arylacetophenones.

  6. Equilibrium acidities and homolytic bond dissociation energies of acidic C-H bonds in alpha-arylacetophenones and related compounds.

    PubMed

    Alnajjar, Mikhail S; Zhang, Xian-Man; Gleicher, Gerald J; Truksa, Scott V; Franz, James A

    2002-12-13

    The equilibrium acidities (pK(AH)s) and the oxidation potentials of the congugate anions [E(ox)(A(-))s] were determined in dimethyl sulfoxide (DMSO) for eight ketones of the structure GCOCH(3) and 20 of the structure RCOCH(2)G, (where R = alkyl, phenyl and G = alkyl, aryl). The homolytic bond dissociation energies (BDEs) for the acidic C-H bonds of the ketones were estimated using the equation BDE(AH) = 1.37pK(AH) + 23.1E(ox)(A(-)) + 73.3. While the equilibrium acidities of GCOCH(3) were found to be dependent on the remote substituent G, the BDE values for the C-H bonds remained essentially invariant (93.5 +/- 0.5 kcal/mol). A linear correlation between pK(AH) values and [E(ox)(A(-))s] was found for the ketones. For RCOCH(2)G ketones, both pK(AH) and BDE values for the adjacent C-H bonds are sensitive to the nature of the substituent G. However, the steric bulk of the aryl group tends to exert a leveling effect on BDEs. The BDE of alpha-9-anthracenylacetophenone is higher than that of alpha-2-anthracenylacetophenone by 3 kcal/mol, reflecting significant steric inhibition of resonance in the 9-substituted system. A range of 80.7-84.4 kcal/mol is observed for RCOCH(2)G ketones. The results are discussed in terms of solvation, steric, and resonance effects. Ab initio density functional theory (DFT) calculations are employed to illustrate the effect of steric interactions on radical and anion geometries. The DFT results parallel the trends in the experimental BDEs of alpha-arylacetophenones. PMID:12467424

  7. Mapping the Globe with C & C Technologies

    NASA Astrophysics Data System (ADS)

    Kleiner, A. A.

    2001-12-01

    C & C Technologies is an international survey and mapping company with an entrepreneurial spirit that is evident throughout. C & C was recently awarded the MTS (Marine Technology Society) ROV Committee Corporate Excellence Award in recognition of their pioneering spirit displayed by the introduction of the HUGIN 3000 Autonomous Underwater Vehicle (AUV) to the offshore industry. This presentation will outline the wide variety of global mapping projects that C & C has performed for government, private sector, and academia. These include high-resolution mapping of Cater Lake, the Panama Canal, Antarctica, Lake Tahoe, and the HUGIN 3000? discovery of the German submarine U-166 in 5000 feet of water in the Gulf of Mexico. Adacemic disciplines required to support these technical challenges will be characterized and job opportunities in this emerging field will be addressed.

  8. Hypovalency--a kinetic-energy density description of a 4c-2e bond.

    PubMed

    Jacobsen, Heiko

    2009-06-01

    A bond descriptor based on the kinetic energy density, the localized-orbital locator (LOL), is used to characterize the nature of the chemical bond in electron deficient multi-center bonds. The boranes B(2)H(6), B(4)H(4), B(4)H(10), [B(6)H(6)](2-), and [B(6)H(7)](-) serve as prototypical examples of hypovalent 3c-2e and 4c-2e bonding. The kinetic energy density is derived from a set of Kohn-Sham orbitals obtained from pure density functional calculations (PBE/TZVP), and the topology of LOL is analyzed in terms of (3,-3) attractors (Gamma). The B-B-B and B-H-B 3c-2e, and the B-B-H-B 4c-2e bonding situations are defined by their own characteristic LOL profiles. The presence of one attractor in relation to the three or four atoms that are engaged in electron deficient bonding provides sufficient indication of the type of 3c-2e or 4c-2e bond present. For the 4c-2e bond in [B(6)H(7)](-) the LOL analysis is compared to results from an experimental QTAIM study. PMID:19452076

  9. Different C-C coupling reactions of permethyltitanocene and permethylzirconocene with disubstituted 1,3-butadiynes

    PubMed

    Pellny; Kirchbauer; Burlakov; Baumann; Spannenberg; Rosenthal

    2000-01-01

    Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-

  10. Protein unfolding from free-energy calculations: Integration of the Gaussian network model with bond binding energies

    NASA Astrophysics Data System (ADS)

    Srivastava, Amit; Granek, Rony

    2015-02-01

    Motivated by single molecule experiments, we study thermal unfolding pathways of four proteins, chymotrypsin inhibitor, barnase, ubiquitin, and adenylate kinase, using bond network models that combine bond energies and elasticity. The protein elasticity is described by the Gaussian network model (GNM), to which we add prescribed bond binding energies that are assigned to all (nonbackbone) connecting bonds in the GNM of native state and assumed identical for simplicity. Using exact calculation of the Helmholtz free energy for this model, we consider bond rupture single events. The bond designated for rupture is chosen by minimizing the free-energy difference for the process, over all (nonbackbone) bonds in the network. Plotting the free-energy profile along this pathway at different temperatures, we observe a few major partial unfolding, metastable or stable, states, that are separated by free-energy barriers and change role as the temperature is raised. In particular, for adenylate kinase we find three major partial unfolding states, which is consistent with single molecule FRET experiments [Pirchi et al., Nat. Commun. 2, 493 (2011), 10.1038/ncomms1504] for which hidden Markov analysis reveals between three and five such states. Such states can play a major role in enzymatic activity.

  11. Protein unfolding from free-energy calculations: integration of the Gaussian network model with bond binding energies.

    PubMed

    Srivastava, Amit; Granek, Rony

    2015-02-01

    Motivated by single molecule experiments, we study thermal unfolding pathways of four proteins, chymotrypsin inhibitor, barnase, ubiquitin, and adenylate kinase, using bond network models that combine bond energies and elasticity. The protein elasticity is described by the Gaussian network model (GNM), to which we add prescribed bond binding energies that are assigned to all (nonbackbone) connecting bonds in the GNM of native state and assumed identical for simplicity. Using exact calculation of the Helmholtz free energy for this model, we consider bond rupture single events. The bond designated for rupture is chosen by minimizing the free-energy difference for the process, over all (nonbackbone) bonds in the network. Plotting the free-energy profile along this pathway at different temperatures, we observe a few major partial unfolding, metastable or stable, states, that are separated by free-energy barriers and change role as the temperature is raised. In particular, for adenylate kinase we find three major partial unfolding states, which is consistent with single molecule FRET experiments [Pirchi et al., Nat. Commun. 2, 493 (2011)] for which hidden Markov analysis reveals between three and five such states. Such states can play a major role in enzymatic activity. PMID:25768532

  12. Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

    PubMed

    Hudzik, Jason M; Castillo, lvaro; Bozzelli, Joseph W

    2015-09-24

    Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (?Hf298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ?B97X-D, and CCSD(T) methods are included in the analysis to determine ?Hf298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a similar range seen for loss of the second hydrogen to generate the diradical singlet species. A wider range for C-C BDEs is seen for the carbenes from about 77 to 100 kcal mol(-1) as compared to the diradicals. Results from the DFT methods for the parents, radicals, diradicals, and carbenes are in good agreement with results from the composite methods using our sets of work reactions. PMID:26295335

  13. Joining C/C composite to copper using active Cu-3.5Si braze

    NASA Astrophysics Data System (ADS)

    Shen, Yuanxun; Li, Zhenglin; Hao, Chuanyong; Zhang, Jinsong

    2012-02-01

    A simple technique was developed to join C/C composite to Cu using active Cu-3.5Si braze for nuclear thermal applications. The brazing alloy exhibited good wettability on C/C substrate due to the reaction layer formed at the interface. A strong interfacial bond of the brazing alloy on C/C with the formation of TiC + SiC + Ti 5Si 3 reaction layer was obtained. The produced CC/Cu/CuCrZr joint exhibited shear strength as high as 79 MPa and excellent thermal resistance during the thermal shock tests.

  14. Bond graph modeling and validation of an energy regenerative system for emulsion pump tests.

    PubMed

    Li, Yilei; Zhu, Zhencai; Chen, Guoan

    2014-01-01

    The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests. PMID:24967428

  15. Bond Graph Modeling and Validation of an Energy Regenerative System for Emulsion Pump Tests

    PubMed Central

    Li, Yilei; Zhu, Zhencai; Chen, Guoan

    2014-01-01

    The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests. PMID:24967428

  16. 102. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. 6040a ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    102. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. 6040a (Photographer and date unknown) BEAUTIFICATION PROGRAM STARTED AS SOON AS GRADING ALONG THE DRIVE WAS COMPLETED. CCC CAMP 3 SHOWN PLANTING LAUREL. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  17. 103. Catalog HHistory 1, C.C.C., 58 Landscaping, Negative No. 870 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    103. Catalog H-History 1, C.C.C., 58 Landscaping, Negative No. 870 10 ca. 1936 PROPAGATION AND PLANTING. ROOTED PLANTS TRANSPLANTED FROM HOT BEDS TO CANS TO SHADED BEDS IN PREPARATION FOR PLANTING ON ROAD SLOPES. NURSERY AT NORTH ENTRANCE. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  18. 104. Catalog HHistory 1, C.C.C., 73 Picnic Furniture Construction, Negative ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    104. Catalog H-History 1, C.C.C., 73 Picnic Furniture Construction, Negative No. 8821 ca. 1936 WOOD UTILIZATION. COMPLETED RUSTIC BENCH MADE BY CCC ENROLLEES AT CAMP NP-3 FOR USE AT PARKING OVERLOOKS AND PICNIC GROUNDS. NOTE SAW IN BACKGROUND USED FOR HALVING CHESTNUT. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  19. Hydrogen bond cooperativity in water hexamers: atomic energy perspective of local stabilities.

    PubMed

    Albrecht, Laura; Chowdhury, Saptarshi; Boyd, Russell J

    2013-10-17

    Atomic energies are used to describe local stability in eight low-lying water hexamers: prism, cage, boat 1, boat 2, bag, chair, book 1, and book 2. The energies are evaluated using the quantum theory of atoms in molecules (QTAIM) at MP2/aug-cc-pVTZ geometries. It is found that the simple, stabilizing cooperativity observed in linear hydrogen-bonded water systems is diminished as clusters move from nearly planar to three-dimensional structures. The prism, cage, and bag clusters can have local water stabilities differing up to 5 kcal mol(-1) as a result of mixed cooperative and anticooperative interactions. At the atomic level, in many cases a water may have a largely stabilized oxygen atom but the net water stability will be diminished due to strong destabilization of the water's hydrogen atoms. Analysis of bond critical point (BCP) electron densities shows that the reduced cooperativity results in a decrease in hydrogen bond strength and an increase in covalent bond strength, most evident in the prism. The chair, with the greatest cooperativity, has the largest average electron density at the BCP per hydrogen bond, whereas the cage has the largest total value for BCP density at all hydrogen bonds. The cage also has the second largest value (after the prism) for covalent bond critical point densities and an oxygen-oxygen BCP which may factor into the experimentally observed stability of the structure. PMID:24067198

  20. Understanding selenocysteine through conformational analysis, proton affinities, acidities and bond dissociation energies

    NASA Astrophysics Data System (ADS)

    Kaur, Damanjit; Sharma, Punita; Bharatam, Prasad V.; Kaur, Mondeep

    Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6-31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6-311++G*//B3LYP/6-31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine.0

  1. Renewable energy liberation by nonthermal intermolecular bond dissociation in water and ethanol

    NASA Astrophysics Data System (ADS)

    Graneau, N.; Verdoold, S.; Oudakker, G.; Yurteri, C. U.; Marijnissen, J. C. M.

    2011-02-01

    Prior indication that renewable energy can be extracted from hydrogen bonds in water has led to several investigations of the energy balance when bulk liquid is converted into micron scale droplets by directional (nonthermal) forces. The demonstration of this effect has previously involved pulsed high current arcs in water which produce large electrodynamic forces. Here, we show that renewable energy is also liberated during the creation of droplets by electrostatic forces in electrohydrodynamic atomization (electrospray) experiments. Using both ethanol and water, the energy outputs, primarily the droplet kinetic energy, were always greater than the energy inputs, implying that stored energy was liberated from the liquid. The energetics of generic chemical bonding are investigated to demonstrate that although this discovery was not publicly anticipated, it is consistent with conventional theory. This experimental breakthrough should have a major impact on the quest for renewable energy sources, capable of powering electricity generators.

  2. Addition, cycloaddition, and metathesis reactions of the cationic carbyne complexes [Cp(CO)[sub 2]Mn[triple bond]CCH[sub 2]R][sup +] and neutral vinylidene complexes Cp(CO)[sub 2]M=C=C(H)R (M = Mn, Re)

    SciTech Connect

    Terry, M.R.; Mercando, L.A.; Kelley, C.; Geoffroy, G.L. ); Nombel, P.; Lugan, N.; Mathieu, R. ); Ostrander, R.L.; Owens-Waltermire, B.E.; Rheingold, A.L. )

    1994-03-01

    The cationic alkylidyne complexes [Cp(CO)[sub 2]M=VCCH[sub 2]R][sup +] (M = Re, R = H; M = Mn, R = H, Me, Ph) undergo facile deprotonation to give the corresponding neutral vinylidene complexes Cp(CO)[sub 2]M=C=C(H)R. For [Cp(CO)[sub 2]Re=VCCH[sub 3

  3. Bond descriptors based on kinetic energy densities reveal regions of slow electrons - Another look at aromaticity

    NASA Astrophysics Data System (ADS)

    Jacobsen, Heiko

    2013-09-01

    An analysis of the kinetic energy density within a molecule identifies patterns within its electronic structure that are intuitively linked to familiar concepts of chemical bonding. Proposed are bond descriptors based on local kinetic energies in an extended mapping onto a finite range of values, so called RoSE-indicators. The usefulness and performance of RoSE-indicators is judged in applications on aromaticity. Results are presented for benzene, cyclobutadiene, borazine and the cyclic hydrogen fluoride trimer as examples for agreed-upon aromaticity and antiaromaticity, as well as for questionable aromaticity. All-metal aromaticity is discussed based on results obtained for tetra aluminum dianion.

  4. The Scalar Relativistic Contribution to Ga-Halide Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1998-01-01

    The one-electron Douglas Kroll (DK) and perturbation theory (+R) approaches are used to compute the scalar relativistic contribution to the atomization energies of GaFn. These results are compared with the previous GaCln results. While the +R and DK results agree well for the GaCln atom nation energies, they differ for GaFn. The present work suggests that the DK approach is more accurate than the +R approach. In addition, the DK approach is less sensitive to the choice of basis set. The computed atomization energies of GaF2 and GaF3 are smaller than the somewhat uncertain experiments. It is suggested that additional calibration calculations for the scalar relativistic effects in GaF2 and GaF3 would be valuable.

  5. Hydrogen Induced C-C, C-N, & C-S Bond Activation on Pt & Ni Surfaces

    SciTech Connect

    Gland, J. L.

    2004-07-29

    The primary reactions investigated were chosen based on their importance in fuel and chemical production as well as in environmental remediation, and include reactions for hydrodesulfurization (HDS), hydrodenitrogenation (HDN), carbon-carbon hydrogenolysis, and hydrocarbon oxidation.

  6. Hypervalent Activation as a Key Step for Dehydrogenative ortho C?C Coupling of Iodoarenes.

    PubMed

    Wu, Yichen; Arenas, Ismael; Broomfield, Lewis Marc; Martin, Eddy; Shafir, Alexandr

    2015-12-14

    Building on earlier results, a direct metal-free ?- arylation of substituted cyclic 1,3-diones using ArI(O2 CCF3 )2 reagents has been developed; unlike other arylative approaches, the arylated products retain the iodine substituent ortho to the newly formed C?C bond. The mechanism is explored by using DFT calculations, which show a vanishingly small activation barrier for the C?C bond-forming step. In fact, taking advantage of an efficient in situ hypervalent activation, the iodoarenes are shown to undergo a cross- dehydrogenative C?C coupling at the C?H ortho to the iodine. When Oxone is used as terminal oxidant, the process is found to benefit from a rapid initial formation of the hypervalent ArI(OR)2 species and the sulfate-accelerated final coupling with a ketone. This method complements the ipso selectivity obtained in the metal-catalyzed ?-arylation of carbonyl compounds. PMID:26559651

  7. Chemical bond as a test of density-gradient expansions for kinetic and exchange energies

    SciTech Connect

    Perdew, J.P.; Levy, M.; Painter, G.S.; Wei, S.; Lagowski, J.B.

    1988-01-15

    Errors in kinetic and exchange contributions to the molecular bonding energy are assessed for approximate density functionals by reference to near-exact Hartree-Fock values. From the molecular calculations of Allan et al. and of Lee and Ghosh, it is demonstrated that the density-gradient expansion does not accurately describe the noninteracting kinetic contribution to the bonding energy, even when this expansion is carried to fourth order and applied in its spin-density-functional form to accurate Hartree-Fock densities. In a related study, it is demonstrated that the overbinding of molecules such as N/sub 2/ and F/sub 2/, which occurs in the local-spin-density (LSD) approximation for the exchange-correlation energy, is not attributable to errors in the self-consistent LSD densities. Contrary to expectations based upon the Gunnarsson-Jones nodality argument, it is found that the LSD approximation for the exchange energy can seriously overbind a molecule even when bonding does not create additional nodes in the occupied valence orbitals. LSD and exact values for the exchange contribution to the bonding energy are displayed and discussed for several molecules.

  8. Electronic structure, molecular bonding and potential energy surfaces

    SciTech Connect

    Ruedenberg, K.

    1993-12-01

    By virtue of the universal validity of the generalized Born-Oppenheimer separation, potential energy surfaces (PES`) represent the central conceptual as well as quantitative entities of chemical physics and provide the basis for the understanding of most physicochemical phenomena in many diverse fields. The research in this group deals with the elucidation of general properties of PES` as well as with the quantitative determination of PES` for concrete systems, in particular pertaining to reactions involving carbon, oxygen, nitrogen and hydrogen molecules.

  9. Potential energy surfaces for CH bond cleavage reactions

    SciTech Connect

    Harding, L.B.

    1996-12-31

    Ab initio, multi-reference, configuration interaction calculations are reported for CH{sub 4}{leftrightarrow}CH{sub 3}+H, CH{sub 3}F{leftrightarrow}CH{sub 2}F+H, CH{sub 2}F{sub 2}{leftrightarrow}CHF{sub 2}+H, and CHF{sub 3}{leftrightarrow}CF{sub 3}+H. Two equivalent, barrier-less paths are found for the CH{sub 3}+H recombination, two inequivalent, barrier-less paths are found for the CH{sub 2}F+H and CHF{sub 2}+H recombinations (depending on which side of the radical the H atom approaches), and only one barrier-less path is found for the CF{sub 3}+H recombination. Minimum energy path for H atom approaching CF{sub 3} from the concave side is predicted to have a barrier of 27 kcal/mole. Both minimum energy path energies and transitional frequencies as function of R{sub CH} for all 4 reactions are predicted to be similar.

  10. A periodic energy decomposition analysis method for the investigation of chemical bonding in extended systems

    SciTech Connect

    Raupach, Marc; Tonner, Ralf

    2015-05-21

    The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the bonding energy between two fragments (e.g., the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic, Pauli repulsion, and orbital relaxation energies. This is complemented by consideration of dispersion interactions via a pairwise scheme. One major extension toward a previous implementation [Philipsen and Baerends, J. Phys. Chem. B 110, 12470 (2006)] lies in the separate discussion of electrostatic and Pauli and the addition of a dispersion term. The pEDA presented here for an implementation based on atomic orbitals can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy, and k-space sampling. Four typical bonding scenarios for surface-adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H{sub 2} on M(001), M = Pd, Cu), and semiconducting (CO and C{sub 2}H{sub 2} on Si(001)) substrates. These examples cover diverse substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence that the pEDA will be a powerful tool for the analysis of surface-adsorbate bonding in the future, enabling the transfer of concepts like ionic and covalent bonding, donor-acceptor interaction, steric repulsion, and others to extended systems.

  11. A periodic energy decomposition analysis method for the investigation of chemical bonding in extended systems

    NASA Astrophysics Data System (ADS)

    Raupach, Marc; Tonner, Ralf

    2015-05-01

    The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the bonding energy between two fragments (e.g., the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic, Pauli repulsion, and orbital relaxation energies. This is complemented by consideration of dispersion interactions via a pairwise scheme. One major extension toward a previous implementation [Philipsen and Baerends, J. Phys. Chem. B 110, 12470 (2006)] lies in the separate discussion of electrostatic and Pauli and the addition of a dispersion term. The pEDA presented here for an implementation based on atomic orbitals can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy, and k-space sampling. Four typical bonding scenarios for surface-adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H2 on M(001), M = Pd, Cu), and semiconducting (CO and C2H2 on Si(001)) substrates. These examples cover diverse substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence that the pEDA will be a powerful tool for the analysis of surface-adsorbate bonding in the future, enabling the transfer of concepts like ionic and covalent bonding, donor-acceptor interaction, steric repulsion, and others to extended systems.

  12. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    NASA Astrophysics Data System (ADS)

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-10-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2?-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4?-dimethyl-2,2?-bipyridine (Me2bpy), or dipyrido-[3,2-f:2?,3?-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the IrCNHC distances are 2.043(5)2.056(5) . The hydride chemical shifts for complexes bearing C1^C^C1 (?20.6 to ?20.3?ppm) are more upfield than those with C2^C^C2 (?19.5 and ?19.2?ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (??=?340530?nm (????103?dm3 mol?1 cm?1)) originate from a d?(IrIII)????*(N^N) metal-to-ligand charge transfer transition, where the d?(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553604?nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10?310?1.

  13. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    PubMed Central

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-01-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), or dipyrido-[3,2-f:2′,3′-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir–CNHC distances are 2.043(5)–2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (−20.6 to −20.3 ppm) are more upfield than those with C2^C^C2 (−19.5 and −19.2 ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340–530 nm (ε ≤ 103 dm3 mol−1 cm−1)) originate from a dπ(IrIII) → π*(N^N) metal-to-ligand charge transfer transition, where the dπ(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553–604 nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10−3–10−1. PMID:26487542

  14. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines.

    PubMed

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-01-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C(1)^C^C(1)) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C(2)^C^C(2)) and aromatic diimine (2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), or dipyrido-[3,2-f:2',3'-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)](+) have been prepared. Crystal structures for these complexes show that the Ir-CNHC distances are 2.043(5)-2.056(5) . The hydride chemical shifts for complexes bearing C(1)^C^C(1) (-20.6 to -20.3?ppm) are more upfield than those with C(2)^C^C(2) (-19.5 and -19.2?ppm), revealing that C(1)^C^C(1) is a better electron donor than C(2)^C^C(2). Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (??=?340-530?nm (????10(3)?dm(3) mol(-1) cm(-1))) originate from a d?(Ir(III))????*(N^N) metal-to-ligand charge transfer transition, where the d?(Ir(III)) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553-604?nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10(-3)-10(-1). PMID:26487542

  15. The Dissociation Energies of He2, HeH, and ArH; A Bond Function Study

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Arnold, James (Technical Monitor)

    1998-01-01

    The bond energies and bond lengths are determined for He2, HeH, and ArH at the CCSD(T) level using both atom-centered basis sets and those that include bond functions. The addition of bond functions dramatically improves the rate of convergence of the results with respect to the size of the atom-centered basis set; with bond functions, triple zeta atom-centered basis set, outperform quintuple zeta basis sets without bond functions. The addition of bond functions also reduces the number of diffuse functions that must be added to the atom-centered sets. Employing bond functions appear to offer a very cost effective method of computing the interaction between weakly bound systems, especially for He.

  16. Ionic bond effects on the mean excitation energy for stopping power

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Chang, C. K.; Kamaratos, E.; Xu, Y. J.

    1982-01-01

    Molecular mean excitation energies for ionic bonded molecules calculated according to the local plasma approximation are compared to the Bragg rule. Adjustments of 15% are calculated for LiF in agreement with experiments while 6% adjustments are predicted for HF and 3% for LiH.

  17. Total π-Electron Energy of Conjugated Molecules with Non-bonding Molecular Orbitals

    NASA Astrophysics Data System (ADS)

    Gutman, Ivan

    2016-02-01

    Lower and upper bounds for the total π-electron energy are obtained, which are applicable to conjugated π-electron systems with non-bonding molecular orbitals (NBMOs). These improve the earlier estimates, in which the number of NBMOs has not been taken into account.

  18. Covalent bonding effect on the mean excitation energy of H2 with the local plasma model

    NASA Technical Reports Server (NTRS)

    Kamaratos, E.

    1984-01-01

    Chemical bonding is taken into account explicitly in the determination of the mean excitation energy (I) for stopping power of H2 with the local plasma approximation by employing molecular electronic wave functions for H2 for the first time. This procedure leads to a new value for IH2 that is higher than all accepted experimental and theoretical values.

  19. Contributions of mass and bond energy difference and interface defects on thermal boundary conductance

    NASA Astrophysics Data System (ADS)

    Choi, ChangJin; Roberts, Nicholas

    2015-09-01

    The impact of mass and bond energy difference and interface defects on thermal boundary conductance (TBC) is investigated using non-equilibrium molecular dynamics (NEMD) with the Lennard-Jones (L-J) interatomic potential. Results show that the maximum TBC is achieved when the mass and bond energy of two dissimilar materials are matched, although the effective thermal conductivity is not necessarily a maximum due to the contributions of the thermal conductivity of the constituent materials. Mass and bond energy differences result in a mismatch between phonon dispersions, limiting high frequency phonon transport at the interface. This frequency mismatch is defined by a frequency ratio, which is a ratio of the characteristic frequencies of the two materials, presented in the discussion section, and is a reference of the level of phonon dispersion mismatch. Inelastic scattering may result at higher temperatures, especially when there exists a bond energy difference, resulting in strain in the lattice, which would allow phonons outside the allowable frequency range to contribute to transport. TBC decreases abruptly with small mass differences, but at which point larger differences in mass have no impact. In addition, interdiffusion across the interface further reduces the TBC between the frequency ratios of 0.79 and 1.26 while vacancies have negligible impact.

  20. Average bond energies between boron and elements of the fourth, fifth, sixth, and seventh groups of the periodic table

    NASA Technical Reports Server (NTRS)

    Altshuller, Aubrey P

    1955-01-01

    The average bond energies D(gm)(B-Z) for boron-containing molecules have been calculated by the Pauling geometric-mean equation. These calculated bond energies are compared with the average bond energies D(exp)(B-Z) obtained from experimental data. The higher values of D(exp)(B-Z) in comparison with D(gm)(B-Z) when Z is an element in the fifth, sixth, or seventh periodic group may be attributed to resonance stabilization or double-bond character.

  1. Bonding Motifs of Noble-Gas Compounds As Described by the Local Electron Energy Density.

    PubMed

    Borocci, Stefano; Giordani, Maria; Grandinetti, Felice

    2015-06-18

    The bonding situation of some exemplary noble-gas (Ng) compounds, including HNg(+), HNgF, FNgO(-), Ng-HF, and NgBeO (Ng = He-Xe) was assayed by examining their local electron energy density H(r). In general, this function partitions the space of atomic species (neutral and ionic) into inner regions of negative values and outer regions of positive values. In the formation of chemical bonds, these atomic regions combine so to form a molecular H(r), Hmol(r), whose plotted form naturally shows the "covalent" and "noncovalent" regions of the molecular species and allows also the recognition of different types of noncovalent interactions such van der Waals, hydrogen, and ionic or partially ionic bonds. The qualitative assignment of the various bonding motifs is corroborated by the topological analysis of Hmol(r), which typically includes several critical points of rank 3 and variable signature. These points are, in particular, characterized here in terms of their bond degree (BD). From a previous definition (Espinosa J. Chem. Phys. 2002, 117, 5529-5542), this quantity is taken as the ratio between the energy density calculated at the critical point of H(r), H(rc), and the corresponding electron density ?(rc): BD = -H(rc)/?(rc). Thus, the BD is positive for covalent interactions (H(rc) < 0) and negative for noncovalent interactions (H(rc) > 0). For structurally related species, the BD result, in general, positively correlated with the binding energies and is, therefore, a semiquantitative index of stability. The present study suggests the general validity of the Hmol(r) to effectively assay the bonding motifs of noble-gas compounds. PMID:25988571

  2. Trans-reflection thermal driven deformable mirror with flexible bonding in high energy laser system

    NASA Astrophysics Data System (ADS)

    Ma, Xingkun; Huang, Lei; Gong, Mali; Xue, Qiao

    2014-09-01

    Deformable mirrors used in high energy laser system suffer from problems like the stress from adhesive solidification or the relatively expensive unit price of piezoceramic actuator. The thermal driven deformable mirror (TDDM) investigated here provided a promising prospect to solve these problems. Four scenarios of TDDM were studied and compared. Results showed that the trans-reflection TDDM with flexible bonding best met the requirement in practical use. The flexible bonding excluded the stress problem in the solidification of adhesives, trans-reflection brought about enough correction range, and the choice of thermo-electric cooler as actuator could greatly bring down the cost of adaptive optics apparatus as well.

  3. An energetic scale for equilibrium H/D fractionation factors illuminates hydrogen bond free energies in proteins

    PubMed Central

    Cao, Zheng; Bowie, James U

    2014-01-01

    Equilibrium H/D fractionation factors have been extensively employed to qualitatively assess hydrogen bond strengths in protein structure, enzyme active sites, and DNA. It remains unclear how fractionation factors correlate with hydrogen bond free energies, however. Here we develop an empirical relationship between fractionation factors and free energy, allowing for the simple and quantitative measurement of hydrogen bond free energies. Applying our empirical relationship to prior fractionation factor studies in proteins, we find: [1] Within the folded state, backbone hydrogen bonds are only marginally stronger on average in ?-helices compared to ?-sheets by ?0.2 kcal/mol. [2] Charge-stabilized hydrogen bonds are stronger than neutral hydrogen bonds by ?2 kcal/mol on average, and can be as strong as 7 kcal/mol. [3] Changes in a few hydrogen bonds during an enzyme catalytic cycle can stabilize an intermediate state by 4.2 kcal/mol. [4] Backbone hydrogen bonds can make a large overall contribution to the energetics of conformational changes, possibly playing an important role in directing conformational changes. [5] Backbone hydrogen bonding becomes more uniform overall upon ligand binding, which may facilitate participation of the entire protein structure in events at the active site. Our energetic scale provides a simple method for further exploration of hydrogen bond free energies. PMID:24501090

  4. Quantum dynamics study of fulvene double bond photoisomerization: the role of intramolecular vibrational energy redistribution and excitation energy.

    PubMed

    Blancafort, Llus; Gatti, Fabien; Meyer, Hans-Dieter

    2011-10-01

    The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies. PMID:21992301

  5. Using Qualified Energy Conservation Bonds for Public Building Upgrades. Reducing Energy Bills in the City of Philadelphia

    SciTech Connect

    Zimring, Mark

    2012-07-18

    Qualified Energy Conservation Bonds (QECBs) are federally-subsidized bonds that enable state, tribal, and local government issuers to borrow money to fund a range of energy conservation projects, including public building upgrades that reduce energy use by at least 20 percent, at very attractive borrowing rates and long terms. As part of the American Recovery and Reinvestment Act (ARRA), the City of Philadelphia received a $15 million QECB award from the U.S. Department of the Treasury (Treasury). The city leveraged $6.25 million of its QECB allocation to finance half of a $12.6 million initiative to upgrade the energy efficiency of City buildings. The upgrades to four city facilities are expected to deliver over $10 million of net savings, and are a major step towards achieving the city’s goal of reducing government energy consumption by 30 percent by 2015.

  6. General formulation of the vibrational kinetic energy operator in internal bond-angle coordinates

    NASA Astrophysics Data System (ADS)

    Frederick, John H.; Woywod, Clemens

    1999-10-01

    A general formulation of the vibrational kinetic energy operator expressed in internal bond-angle coordinates is presented. This formulation is based on Podolsky's expression for the covariant form of the Laplace-Beltrami operator. When a valid set of internal bond-angle coordinates is employed, it is possible to adapt a systematic approach to solve for the Jacobian determinant governing the coordinate transformation from Cartesian coordinates. In the general case of an arbitrary N-atom system, this Jacobian always factorizes to a simple form. This allows one to evaluate all the terms that contribute to V̂', the effective potential that arises from transforming the kinetic energy operator to internal coordinates. We discuss restrictions on the choice of internal vibrational coordinates that may be included in a valid set. We then provide tabular information from which the vibrational kinetic energy operator for any molecular system can be constructed directly with no matrix inversion or chain rule manipulation required.

  7. Bond ionicity, lattice energy, bond energy and microwave dielectric properties of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Haitao, Wu

    2015-10-14

    The dependence of microwave dielectric properties on the structural characteristics of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) (0 ?x? 0.10) ceramics is investigated. All the compounds were prepared by a conventional solid-state reaction method and analyzed via multiphase structure refinement. The diffraction patterns of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) show the monoclinic wolframite structure of ZrZrNb2O8 which consists of an oxygen octahedron, with the Nb ion in the center of the oxygen octahedron. For the ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics, the dielectric constant (?r) decreased with the decrease in Nb-site bond ionicity. The quality factor (Qf) of ZnZr(Nb1-xSbx)2O8 ceramics was found to be the highest (89?400 GHz), which is explained in terms of the average of the Nb-site lattice energy. With the decrease in the bond energy of the Nb-site, the temperature coefficient of resonant frequency (|?f|) value increased. The substitution of A(5+) (A = Ta, Sb) for Nb(5+) effectively influences the microstructure and microwave dielectric properties of ZrZrNb2O8 ceramics. PMID:26348992

  8. Effect of ZnO on the interfacial bonding between Na 2O-B 2O 3-SiO 2 vitrified bond and diamond

    NASA Astrophysics Data System (ADS)

    Wang, P. F.; Li, Zh. H.; Li, J.; Zhu, Y. M.

    2009-08-01

    Diamond composites were prepared by sintering diamond grains with low melting Na 2O-B 2O 3-SiO 2 vitrified bonds in air. The influence of ZnO on the wettability and flowing ability of Na 2O-B 2O 3-SiO 2 vitrified bonds was characterized by wetting angle, the interfacial bonding states between diamond grains and the vitrified bonds were observed by scanning electron microscope (SEM), and the micro-scale bonding mechanism in the interfaces was investigated by means of energy-dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ZnO facilitated the dissociation of boron/silicon-oxygen polyhedra and the formation of larger amount of non-bridging oxygen in the glass network, which resulted in the increase of the vitrified bonds' wettability and the formation of -C dbnd O, -O-H and -C-H bonds on the surface of diamond grains. B and Si diffused from the vitrified bonds to the interface, and C-C, C-O, C dbnd O and C-B bond formed on the surface of sintered diamond grains during sintering process, by which the interfacial bonding between diamond grains and the vitrified bonds was strengthened.

  9. The role of structural ledges at phase boundaries; 2: F. c. c. -b. c. c. interfaces in Nishiyama-Wasserman orientation

    SciTech Connect

    Shiflet, G.J.; Merwe, J.H. van der . Dept. of Physics)

    1994-04-01

    The ledge mode of misfit accommodation was first postulated for boundaries between b.c.c. and f.c.c metal phases; the interfaces being [111] f.c.c.-[110] b.c.c. planes and relative orientations varying from Nishiyama-Wassermann (NW) to Kurdjumov-Sachs (KS). Here the geometrical quantities are uniquely related by the misfit ratio r of atomic diameters. They consider the so-called NW-x configuration in which the orientation is imposed by close matching along the <[bar 2]11> f.c.c. and <[bar 1]10> b.c.c. (taken as x-) directions. From the fact that no net shear pattern displacements are present with x-ledges (ledges normal to the x-direction) it is concluded that they are energetically preferable to y-ledges and justifies the approach of an energetic comparison between stepped interfaces with x-ledges and a planar interface containing conventional misfit dislocations (MDs). The NW-x stepped configuration is at first subjected to a rigid model analysis, i.e. a model with rigid crystals and periodic (truncated Fourier representation) interfacial interaction. This analysis provides (1) energetic justification for a relation between terrace periodicity and misfit cancellation, (2) values of upper and lower average energy bounds, (3) a method for estimating interfacial shear moduli, and (4) a motivation for the suggestion that a relative rigid translation of the crystals is needed for energy minimization.

  10. Densification Behavior and Performances of C/C Composites Derived from Various Carbon Matrix Precursors

    NASA Astrophysics Data System (ADS)

    Shao, H. C.; Xia, H. Y.; Liu, G. W.; Qiao, G. J.; Xiao, Z. C.; Su, J. M.; Zhang, X. H.; Li, Y. J.

    2014-01-01

    Three types of carbon/carbon (C/C) composites were manufactured by densifying the needled carbon fiber preform through resin and pitch impregnation/carbonization repeatedly, as well as propylene pyrolysis by chemical vapor infiltration plus carbonization after the resin impregnation/carbonization. The densification behavior and performances (involving electric, thermal, and mechanical properties, as well as impurity) of the C/C composites were investigated systematically. The results show that besides the processing and testing conditions, the electric resistivity, thermal conductivity (TC), coefficient of thermal expansion (CTE), strength, and fracture, as well as impurity content and composition of the C/C composites were closely related to the fiber orientation, interfacial bonding between carbon fiber and carbon matrix, material characteristics of the three precursors and the resulting matrix carbons. In particular, the resin-carbon matrix C/C (RC/C) composites had the highest electric resistivity, tensile, and flexural strength, as well as impurity content. Meanwhile, the pitch-carbon matrix C/C (PC/C) composites possessed the highest TC and CTE in the parallel and vertical direction. And most of the performances of pyro-carbon/resin carbon matrix C/C composites were between those of the RC/C and PC/C composites except the impurity content.

  11. Evaluation by Rocket Combustor of C/C Composite Cooled Structure Using Metallic Cooling Tubes

    NASA Astrophysics Data System (ADS)

    Takegoshi, Masao; Ono, Fumiei; Ueda, Shuichi; Saito, Toshihito; Hayasaka, Osamu

    In this study, the cooling performance of a C/C composite material structure with metallic cooling tubes fixed by elastic force without chemical bonding was evaluated experimentally using combustion gas in a rocket combustor. The C/C composite chamber was covered by a stainless steel outer shell to maintain its airtightness. Gaseous hydrogen as a fuel and gaseous oxygen as an oxidizer were used for the heating test. The surface of these C/C composites was maintained below 1500 K when the combustion gas temperature was about 2800 K and the heat flux to the combustion chamber wall was about 9 MW/m2. No thermal damage was observed on the stainless steel tubes that were in contact with the C/C composite materials. The results of the heating test showed that such a metallic tube-cooled C/C composite structure is able to control the surface temperature as a cooling structure (also as a heat exchanger) as well as indicated the possibility of reducing the amount of coolant even if the thermal load to the engine is high. Thus, application of this metallic tube-cooled C/C composite structure to reusable engines such as a rocket-ramjet combined-cycle engine is expected.

  12. Tubulin Bond Energies and Microtubule Biomechanics Determined from Nanoindentation in Silico

    PubMed Central

    2015-01-01

    Microtubules, the primary components of the chromosome segregation machinery, are stabilized by longitudinal and lateral noncovalent bonds between the tubulin subunits. However, the thermodynamics of these bonds and the microtubule physicochemical properties are poorly understood. Here, we explore the biomechanics of microtubule polymers using multiscale computational modeling and nanoindentations in silico of a contiguous microtubule fragment. A close match between the simulated and experimental force–deformation spectra enabled us to correlate the microtubule biomechanics with dynamic structural transitions at the nanoscale. Our mechanical testing revealed that the compressed MT behaves as a system of rigid elements interconnected through a network of lateral and longitudinal elastic bonds. The initial regime of continuous elastic deformation of the microtubule is followed by the transition regime, during which the microtubule lattice undergoes discrete structural changes, which include first the reversible dissociation of lateral bonds followed by irreversible dissociation of the longitudinal bonds. We have determined the free energies of dissociation of the lateral (6.9 ± 0.4 kcal/mol) and longitudinal (14.9 ± 1.5 kcal/mol) tubulin–tubulin bonds. These values in conjunction with the large flexural rigidity of tubulin protofilaments obtained (18,000–26,000 pN·nm2) support the idea that the disassembling microtubule is capable of generating a large mechanical force to move chromosomes during cell division. Our computational modeling offers a comprehensive quantitative platform to link molecular tubulin characteristics with the physiological behavior of microtubules. The developed in silico nanoindentation method provides a powerful tool for the exploration of biomechanical properties of other cytoskeletal and multiprotein assemblies. PMID:25389565

  13. Chemical Bonds II

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    The continuation of a paper discussing chemical bonding from a bond energy viewpoint, with a number of examples of single and multiple bonds. (Part I appeared in volume 1 number 3, pages 16-23, February 1972.) (AL)

  14. Theoretical study of the C-H bond dissociation energy of C2H

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    A theoretical study of the convergence of the C-H bond dissociation energy D(0) in C2H with respect to both the one- and n-particle spaces is presented. The calculated C-H bond energies of C2H2 and C2H4, which are in excellent agreement with experiment, are used for calibration. The best estimate for D(0) of 112.4 + or - 2.0 kcal/mol is slightly below the recent experimental value of 116.3 + or - 2.6 kcal/mol, but substantially above a previous theoretical estimate of 102 kcal/mol. The remaining discrepancy with experiment may reflect primarily the uncertainty in the experimental D(0) value of C2 required in the analysis.

  15. Sp2 bonding distributions in nanocrystalline diamond particles by electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Okada, Katsuyuki; Kimoto, Koji; Komatsu, Shojiro; Matsumoto, Seiichiro

    2003-03-01

    Nanocrystalline diamond particles with 200-500 nm in diameter have been prepared in a 13.56 MHz low pressure inductively coupled CH4/CO/H2 plasma. The chemical bonding map was investigated by electron energy loss spectroscopy (EELS). The EEL spectrum shows a peak at 290 eV due to ?* states and the energy loss near-edge structure is similar to that of diamond. A slight peak appears at 285 eV corresponding to ?* states. The mapping of sp2 states by ?* peak reveals that sp2-bonded carbons are identified around the 20-50 nm subgrains of nanocrystalline diamond particles at approximately 1 nm resolution.

  16. Autyomatic Differentiation of C/C++

    Energy Science and Technology Software Center (ESTSC)

    2005-11-14

    Automatic differentiation (AD) tools mechanize the process of developing code for the computation of derivatives. AD avoids the inaccuracies inherent in numerical approximations. Furthermore, sophisticated AD algoirthms can often produce c ode that is more reliable and more efficient than code written by an expert programmer. ADIC is the first and only AD tool for C and C++ based on compiler technology. This compiler foundation makes possible analyses and optimizations not available in toos basedmoreon operator overloading. The earliest implementations of ADIC included support for ANSI C applications, ADIC 2.0 lverages EDG, a commercial C/C++ parser, to provide robust C++ differentiation support. Modern AD tools, including ADIC are implemented in a modular way, aiming to isolate language-dependent program analyses and semantic transformations. The component design leads to much higher implementation quality because the different components can be implemented by experts in each of the different domains involved. For example, a compiler expert can focus on parsing, canonicalizing, and unparising C and C++, while an expert in graph theory and algorithms can produce new differentiation modules without having to worry about the complexity of parsing and generating C++ code. Thsi separation of concerns was achieved through the use of language-independent program analysis interfaces (in collaboration with researcgers at Rice University) and a language-independent XML representation of the computational portions of programs (XAIF). In addition to improved robustness and faster development times, this design naturally enables the reuse of program analysis algorithms and differentiation modules in compiler-based AD tools for other languages. In fact, the analysis and differention components are used in both ADIC and the Open AD Fortran front-end (based on Rice's Open64 compiler.less

  17. Autyomatic Differentiation of C/C++

    Energy Science and Technology Software Center (ESTSC)

    2005-11-14

    Automatic differentiation (AD) tools mechanize the process of developing code for the computation of derivatives. AD avoids the inaccuracies inherent in numerical approximations. Furthermore, sophisticated AD algoirthms can often produce c ode that is more reliable and more efficient than code written by an expert programmer. ADIC is the first and only AD tool for C and C++ based on compiler technology. This compiler foundation makes possible analyses and optimizations not available in toos basedmore » on operator overloading. The earliest implementations of ADIC included support for ANSI C applications, ADIC 2.0 lverages EDG, a commercial C/C++ parser, to provide robust C++ differentiation support. Modern AD tools, including ADIC are implemented in a modular way, aiming to isolate language-dependent program analyses and semantic transformations. The component design leads to much higher implementation quality because the different components can be implemented by experts in each of the different domains involved. For example, a compiler expert can focus on parsing, canonicalizing, and unparising C and C++, while an expert in graph theory and algorithms can produce new differentiation modules without having to worry about the complexity of parsing and generating C++ code. Thsi separation of concerns was achieved through the use of language-independent program analysis interfaces (in collaboration with researcgers at Rice University) and a language-independent XML representation of the computational portions of programs (XAIF). In addition to improved robustness and faster development times, this design naturally enables the reuse of program analysis algorithms and differentiation modules in compiler-based AD tools for other languages. In fact, the analysis and differention components are used in both ADIC and the Open AD Fortran front-end (based on Rice's Open64 compiler.« less

  18. Electronic structure, stacking energy, partial charge, and hydrogen bonding in four periodic B-DNA models

    NASA Astrophysics Data System (ADS)

    Poudel, Lokendra; Rulis, Paul; Liang, Lei; Ching, W. Y.

    2014-08-01

    We present a theoretical study of the electronic structure of four periodic B-DNA models labeled (AT)10,(GC)10, (AT)5(GC)5, and (AT-GC)5 where A denotes adenine, T denotes thymine, G denotes guanine, and C denotes cytosine. Each model has ten base pairs with Na counterions to neutralize the negative phosphate group in the backbone. The (AT)5(GC)5 and (AT-GC)5 models contain two and five AT-GC bilayers, respectively. When compared against the average of the two pure models, we estimate the AT-GC bilayer interaction energy to be 19.015 Kcal/mol, which is comparable to the hydrogen bonding energy between base pairs obtained from the literature. Our investigation shows that the stacking of base pairs plays a vital role in the electronic structure, relative stability, bonding, and distribution of partial charges in the DNA models. All four models show a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) gap ranging from 2.14 to 3.12 eV with HOMO states residing on the PO4 + Na functional group and LUMO states originating from the bases. Our calculation implies that the electrical conductance of a DNA molecule should increase with increased base-pair mixing. Interatomic bonding effects in these models are investigated in detail by analyzing the distributions of the calculated bond order values for every pair of atoms in the four models including hydrogen bonding. The counterions significantly affect the gap width, the conductivity, and the distribution of partial charge on the DNA backbone. We also evaluate quantitatively the surface partial charge density on each functional group of the DNA models.

  19. Observation of the decay ?(3686)?????+c.c.

    NASA Astrophysics Data System (ADS)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Ambrose, D. J.; An, F. F.; An, Q.; Bai, J. Z.; Baldini Ferroli, R.; Ban, Y.; Bennett, J. V.; Bertani, M.; Bian, J. M.; Boger, E.; Bondarenko, O.; Boyko, I.; Braun, S.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Chu, Y. P.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; Ding, W. M.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Fang, J.; Fang, S. S.; Fang, Y.; Fava, L.; Feng, C. Q.; Fu, C. D.; Fu, J. L.; Fuks, O.; Gao, Q.; Gao, Y.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, T.; Guo, Y. P.; Guo, Y. P.; Han, Y. L.; Harris, F. A.; He, K. L.; He, M.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Huang, G. M.; Huang, G. S.; Huang, J. S.; Huang, L.; Huang, X. T.; Hussain, T.; Ji, C. S.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Jing, F. F.; Johansson, T.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kavatsyuk, M.; Kloss, B.; Kopf, B.; Kornicer, M.; Kuehn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leyhe, M.; Li, C. H.; Li, Cheng; Li, Cui; Li, D.; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, Q. J.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. N.; Li, X. Q.; Li, X. R.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. L.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, K.; Liu, K. Y.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, G. R.; Lu, H. J.; Lu, H. L.; Lu, J. G.; Lu, X. R.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Ma, F. C.; Ma, H. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Moeini, H.; Morales Morales, C.; Moriya, K.; Muchnoi, N. Yu.; Nefedov, Y.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Ping, J. L.; Ping, R. G.; Poling, R.; Prencipe, E.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ripka, M.; Rong, G.; Ruan, X. D.; Sarantsev, A.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, X. Y.; Sheng, H. Y.; Shepherd, M. R.; Song, W. M.; Song, X. Y.; Spataro, S.; Spruck, B.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Werner, M.; Wiedner, U.; Wolke, M.; Wu, G. G.; Wu, L. H.; Wu, N.; Wu, W.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Xue, Z.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yu, S. P.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Zafar, A. A.; Zallo, A.; Zang, S. L.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. B.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, S. H.; Zhang, X. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, J. W.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, X. H.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zou, B. S.; Zou, J. H.

    2013-12-01

    Using a sample of 1.06108 ?(3686) events collected with the BESIII detector, we present the first observation of the decays of ?(3686)???+?-+c.c. and ?(3686)???-?++c.c. The branching fractions are measured to be B(?(3686)???+?-+c.c.)=(1.400.030.13)10-4 and B(?(3686)???-?++c.c.)=(1.540.040.13)10-4, where the first errors are statistical and the second ones systematic.

  20. Theoretical study of the C-H bond dissociation energy of acetylene

    NASA Technical Reports Server (NTRS)

    Taylor, Peter R.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    The authors present a theoretical study of the convergence of the C-H bond dissociation energy (D sub o) of acetylene with respect to both the one- and n-particle spaces. Their best estimate for D sub o of 130.1 plus or minus 1.0 kcal/mole is slightly below previous theoretical estimates, but substantially above the value determined using Stark anticrossing spectroscopy that is asserted to be an upper bound.

  1. Shock-induced initiation and energy release behavior of polymer bonded explosive materials

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Cai, Xuanming; Hypervelocity Impact Research Center Team

    2015-06-01

    In this paper, an initially sealed vented test chamber and a test projectile with a recessed hole were designed to complete the experiments. As the initiation takes place on the interior, great amounts of thermo-chemical energy gases were vented through a hole formed by the penetration process. The gas pressure inside the chamber was used to evaluate the energy release behavior of polymer bonded explosive materials. The impact pressure of the projectile was measured by the PVDF sensors. Based on the earlier work that the constitutive equation of polymer bonded explosive materials was established, the impact pressure of the projectile was obtained through the numerical simulation. The experimental results reveal that the impact pressure is significant to the energy release behavior, and in some extent the gas pressure improves with the velocity of the projectile. The impact pressure obtained by the experiments is comparing with which obtained through the numerical simulation, and the results of the comparing is that the value of them are closely relative. The experimental results also indicate that the constitutive equation of polymer bonded explosive materials used in the numerical simulation can correctly describe the mechanical behavior of PBX materials.

  2. Students' reasoning about "high-energy bonds" and ATP: A vision of interdisciplinary education

    NASA Astrophysics Data System (ADS)

    Dreyfus, Benjamin W.; Sawtelle, Vashti; Turpen, Chandra; Gouvea, Julia; Redish, Edward F.

    2014-06-01

    As interdisciplinary courses are developed, instructors and researchers have to grapple with questions of how students should make connections across disciplines. We explore the issue of interdisciplinary reconciliation (IDR): how students reconcile seemingly contradictory ideas from different disciplines. While IDR has elements in common with other frameworks for the reconciliation of ideas across contexts, it differs in that each disciplinary idea is considered canonically correct within its own discipline. The setting for the research is an introductory physics course for biology majors that seeks to build greater interdisciplinary coherence and therefore includes biologically relevant topics such as adenosine triphosphate (ATP) and chemical bond energy. In our case-study data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see students justifying context-dependent modeling choices, showing nuance in articulating how system choices may be related to disciplinary problems of interest. This represents a desired end point of IDR, in which students can build coherent connections between concepts from different disciplines while understanding each concept in its own disciplinary context. Our case study also illustrates elements of the instructional environment that play roles in the process of IDR.

  3. Influence of Cu+ on the RS-NO bond dissociation energy of S-nitrosothiols.

    PubMed

    Baciu, Cristina; Cho, Kyung-Bin; Gauld, James W

    2005-02-01

    Density functional theory methods have been used to investigate the role and effects of Cu+ binding to the S and N centers of the -SNO functional group within S-nitrosothiols (RSNOs), on the lability of the NO group. The binding of Cu+ to the S center is found to weaken the S-N bond, while the N-O bond is concomitantly strengthened, consistent with the notion that Cu+ binding catalyzes NO radical release. In contrast, however, the binding of Cu+ to the N center is found to dramatically shorten and strengthen the S-N bond with a concomitant lengthening of the N-O bond, suggesting stabilization of the RSNOs against NO release. Upon solvation, complexes with Cu+ bound to the N center are stabilized relative to the corresponding S-bound complexes, though remaining slightly higher in energy. The barriers to interconversion between corresponding isomers were also investigated. Implications for biochemical regulation of NO release from RSNOs are discussed. PMID:16851099

  4. Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)

    PubMed Central

    Netzel, Jeanette; van Smaalen, Sander

    2009-01-01

    Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ? 20?K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (l max = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent CC, CN and CO bonds, and for hydrogen bonds together with covalent CH and NH bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H?O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997) ?. An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds. PMID:19767685

  5. Prediction of Reliable Metal-PH? Bond Energies for Ni, Pd, and Pt in the 0 and +2 Oxidation States

    SciTech Connect

    Craciun, Raluca; Vincent, Andrew J.; Shaughnessy, Kevin H.; Dixon, David A.

    2010-06-21

    Phosphine-based catalysts play an important role in many metal-catalyzed carbon-carbon bond formation reactions yet reliable values of their bond energies are not available. We have been studying homogeneous catalysts consisting of a phosphine bonded to a Pt, Pd, or Ni. High level electronic structure calculations at the CCSD(T)/complete basis set level were used to predict the M-PH? bond energy (BE) for the 0 and +2 oxidation states for M=Ni, Pd, and Pt. The calculated bond energies can then be used, for example, in the design of new catalyst systems. A wide range of exchange-correlation functionals were also evaluated to assess the performance of density functional theory (DFT) for these important bond energies. None of the DFT functionals were able to predict all of the M-PH3 bond energies to within 5 kcal/mol, and the best functionals were generalized gradient approximation functionals in contrast to the usual hybrid functionals often employed for main group thermochemistry.

  6. Linear ketenimines. Variable structures of C,C-dicyanoketenimines and C,C-bis-sulfonylketenimines.

    PubMed

    Finnerty, Justin; Mitschke, Ullrich; Wentrup, Curt

    2002-02-22

    C,C-dicyanoketenimines 10a-c were generated by flash vacuum thermolysis of ketene N,S-acetals 9a-c or by thermal or photochemical decomposition of alpha-azido-beta-cyanocinnamonitrile 11. In the latter reaction, 3,3-dicyano-2-phenyl-1-azirine 12 is also formed. IR spectroscopy of the keteniminines isolated in Ar matrixes or as neat films, NMR spectroscopy of 10c, and theoretical calculations (B3LYP/6-31G) demonstrate that these ketenimines have variable geometry, being essentially linear along the CCN-R framework in polar media (neat films and solution), but in the gas phase or Ar matrix they are bent, as is usual for ketenimines. Experiments and calculations agree that a single CN substituent as in 13 is not enough to enforce linearity, and sulfonyl groups are less effective that cyano groups in causing linearity. C,C-bis(methylsulfonyl)ketenimines 4-5 and a C-cyano-C-(methylsulfonyl)ketenimine 15 are not linear. The compound p-O2NC6H4N=C=C(COOMe)2 previously reported in the literature is probably somewhat linearized along the CCNR moiety. A computational survey (B3LYP/6-31G) of the inversion barrier at nitrogen indicates that electronegative C-substituents dramatically lower the barrier; this is also true of N-acyl substituents. Increasing polarity causes lower barriers. Although N-alkylbis(methylsulfonyl)ketenimines are not calculated to be linear, the barriers are so low that crystal lattice forces can induce planarity in N-methylbis(methylsulfonyl)ketenimine 3. PMID:11846648

  7. Unusually long, multicenter, cation(?+)anion(?-) bonding observed for several polymorphs of [TTF][TCNE].

    PubMed

    Capdevila-Cortada, Maral; Novoa, Juan J; Bell, Joshua D; Moore, Curtis E; Rheingold, Arnold L; Miller, Joel S

    2011-08-16

    The ?, ?, and ? polymorphs of [TTF][TCNE] (TTF=tetrathiafulvalene; TCNE=tetracyanoethylene) exhibit a new type of long, multicenter bonding between the [TTF](?+) and [TCNE](?-) moieties, demonstrating the existence of long, hetero-multicenter bonding with a cationic(?+)anionic(?-) zwitterionic-like structure. These diamagnetic ?-[TTF](?+) [TCNE](?-) heterodimers exhibit a transfer of about 0.5 e(-) from the TTF to the TCNE fragments, as observed from experimental studies, in accord with theoretical predictions, that is, [TTF(?+)TCNE(?-)] (??0.5). They have several interfragment distances <3.4 , and a computed interaction energy of -21.2 kcal mol(-1), which is typical of long, multicenter bonds. The lower stability of [TTF](?+) [TCNE](?-) with respect to typical ionic bonds is due, in part, to the partial electron transfer that reduces the electrostatic bonding component. This reduced electrostatic interaction, and the large interfragment dispersion stabilize the long, heterocationic/anionic multicenter interaction, which in [TTF(?+)TCNE(?-)] always involves two electrons, but have ten, eight, and eight bond critical points (bcps) involving C-C, N-S, and sometimes C-S and C-N components for the ?, ?, and ? polymorphs, respectively. In contrast, ?-[TTF][TCNE] possesses [TTF](2)(2+) and [TCNE](2)(2-) dimers, each with long, homo-multicenter 2e(-)/12c (c=center, 2?C+4?S) [TTF](2)(2+) cationic(+)cationic(+) bonds, as well as long, homo-multicenter 2e(-)/4c [TCNE](2)(2-) anionic(-)anionic(-) bonding. The MO diagrams for the ?, ?, and ? polymorphs have all of the features found for conventional covalent C-C bonds, and for all of the previously studied multicenter long bonds, for example, ?-[TTF](2)(2+) and ?-[TCNE](2)(2-). The HOMOs for ?-, ?-, and ?-[TTF][TCNE] have 2c C-S and 3c C-C-C orbital-overlap contributions between the [TTF](?+-) and [TCNE](?-) moieties; these are the shortest intra [TTFTCNE] separations. Thus, from an orbital-overlap perspective, the bonding has 2c and 3c components residing over one S and four C atoms. PMID:21793061

  8. Time-resolved EPR study on reorganization energies for charge recombination reactions in the systems involving hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Yago, Tomoaki; Kobori, Yasuhiro; Akiyama, Kimio; Tero-Kubota, Shozo

    2003-02-01

    Hydrogen bonding effects on reorganization energies ( ?) in the photoinduced electron donor-acceptor system of duroquinone (DQ)-1,2,4-trimethoxybenzene (TMB) in benzonitrile have been investigated by time-resolved EPR and cyclic voltammetry measurements. The solvent reorganization energies ( ?S) determined for the radical ion pair systems involving the hydrogen-bonded complexes are larger by 0.2 eV than those calculated from the Marcus continuum dielectric model. The present results suggest that dissociation of the DQ anion-alcohol hydrogen-bonded complex results in the new component of ?S for the charge recombination reaction in polar solvents.

  9. Local bond length variations in boron-doped nanocrystalline diamond measured by spatially resolved electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Ying-Gang; Turner, Stuart; Verbeeck, Johan; Janssens, Stoffel D.; Haenen, Ken; Van Tendeloo, Gustaaf

    2013-07-01

    Variations in local bond length and coordination in boron-doped nanocrystalline diamond (NCD) films have been studied through changes in the fine structure of boron and carbon K-edges in electron energy-loss spectra, acquired in a scanning transmission electron microscope. The presence of high concentrations of B in pristine diamond regions and enrichment of B at defects in single NCD grains is demonstrated. Local bond length variations are evidenced through an energy shift of the carbon 1s ? ?* edge at B-rich defective regions within single diamond grains, indicating an expansion of the diamond bond length at sites with local high B content.

  10. Tailoring Bond Cleavage in Gas-Phase Biomolecules by Low Energy Electrons

    NASA Astrophysics Data System (ADS)

    Ptasinska, Sylwia

    2014-10-01

    The high energy quanta of impinging radiation can generate a large number (about 5x104) of secondary electrons per 1 MeV of energy deposited. When ejected in condensed phase water, the kinetic energy distribution of these free or quasi-free electrons is peaked below 10 eV. Low energy electrons also dominate in the secondary emission from biomolecular targets exposed to different energies of primary radiation. Due to the complexity of the radiation-induced processes in the condensed-phase environment, mechanisms of secondary electrons induced damage in biomolecules (BM) still need to be investigated. However, based on results from theory and different experiments accumulated within the last decade, it is now possible to determine the fundamental mechanisms that are involved in many chemical reactions induced in isolated gas-phase biomolecules by low energy electrons. The central finding of earlier research was the discovery of the bond- and site- selectivity in the dissociative electron attachment (DEA) process to biomolecules. It has been demonstrated that by tuning the energy of the incoming electron we can gain control over the location of the bond cleavage. These studies showed the selectivity in single bond cleavage reactions leading to the formation of the dehydrogenated closed shell anion (BM-H)- or the complementary reaction leading to H-. The loss of a hydrogen atom or an anion is fast compared with ring cleavage and the excision of heavier fragments and, hence, this reaction can compete efficiently with autodetachment. Moreover, site selectivity has been also observed in the metastable anion formation via the DEA process. Such delayed fragmentation was studied recently for the dehydrogenated closed-shell anion conversion into NCO- upon DEA proceeded a few ? sec after electron attachment, indicating a rather slow unimolecular decomposition. Interestingly, site selectivity was observed in the prompt as well as the metastable NCO- formation in DEA. The research described herein was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Basic Energy Sciences, Office of Science, United States Department of Energy through Grant Number DE-FC02-04ER15533.

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

    PubMed

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

    2014-09-18

    Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal C?-C or N-C? bond rather than the typical C?-C bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied ? orbital on the ?-carbon and the N-C? bond, leading to low-barrier ?-cleavage of the N-C? bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and z() ions, whereas C-terminal interaction leads to effective cleavage of the C?-C bond through rapid loss of isocyanic acid. Dissociation of the C?-C bond may also occur via water loss followed by ?-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes. PMID:24605822

  12. Distinguishing Bonds.

    PubMed

    Rahm, Martin; Hoffmann, Roald

    2016-03-23

    The energy change per electron in a chemical or physical transformation, ΔE/n, may be expressed as Δχ̅ + Δ(VNN + ω)/n, where Δχ̅ is the average electron binding energy, a generalized electronegativity, ΔVNN is the change in nuclear repulsions, and Δω is the change in multielectron interactions in the process considered. The last term can be obtained by the difference from experimental or theoretical estimates of the first terms. Previously obtained consequences of this energy partitioning are extended here to a different analysis of bonding in a great variety of diatomics, including more or less polar ones. Arguments are presented for associating the average change in electron binding energy with covalence, and the change in multielectron interactions with electron transfer, either to, out, or within a molecule. A new descriptor Q, essentially the scaled difference between the Δχ̅ and Δ(VNN + ω)/n terms, when plotted versus the bond energy, separates nicely a wide variety of bonding types, covalent, covalent but more correlated, polar and increasingly ionic, metallogenic, electrostatic, charge-shift bonds, and dispersion interactions. Also, Q itself shows a set of interesting relations with the correlation energy of a bond. PMID:26910496

  13. The Bond Order of C2 from a Strictly N-Representable Natural Orbital Energy Functional Perspective.

    PubMed

    Piris, Mario; Lopez, Xabier; Ugalde, Jesus M

    2016-03-14

    The bond order of the ground electronic state of the carbon dimer has been analyzed in the light of natural orbital functional theory calculations carried out with an approximate, albeit strictly N-representable, energy functional. Three distinct solutions have been found from the Euler equations of the minimization of the energy functional with respect to the natural orbitals and their occupation numbers, which expand upon increasing values of the internuclear coordinate. In the close vicinity of the minimum energy region, two of the solutions compete around a discontinuity point. The former, corresponding to the absolute minimum energy, features two valence natural orbitals of each of the following symmetries, σ, σ*, π and π*, and has three bonding interactions and one antibonding interaction, which is very suggestive of a bond order large than two but smaller than three. The latter, features one σ-σ* linked pair of natural orbitals and three degenerate pseudo-bonding like orbitals, paired each with one triply degenerate pseudo-antibonding orbital, which points to a bond order larger than three. When correlation effects, other than Hartree-Fock for example, between the paired natural orbitals are accounted for, this second solution vanishes yielding a smooth continuous dissociation curve. Comparison of the vibrational energies and electron ionization energies, calculated on this curve, with their corresponding experimental marks, lend further support to a bond order for C2 intermediate between acetylene and ethylene. PMID:26822104

  14. Fine-tuning the energy barrier for metal-mediated dinitrogen N?N bond cleavage.

    PubMed

    Keane, Andrew J; Yonke, Brendan L; Hirotsu, Masakazu; Zavalij, Peter Y; Sita, Lawrence R

    2014-07-16

    Experimental data support a mechanism for N?N bond cleavage within a series of group 5 bimetallic dinitrogen complexes of general formula, {Cp*M[N((i)Pr)C(R)N((i)Pr)]}2(?-N2) (Cp* = ?(5)-C5Me5) (M = Nb, Ta), that proceeds in solution through an intramolecular "end-on-bridged" (?-?(1):?(1)-N2) to "side-on-bridged" (?-?(2):?(2)-N2) isomerization process to quantitatively provide the corresponding bimetallic bis(?-nitrido) complexes, {Cp*M[N((i)Pr)C(R)N((i)Pr)](?-N)}2. It is further demonstrated that subtle changes in the steric and electronic features of the distal R-substituent, where R = Me, Ph and NMe2, can serve to modulate the magnitude of the free energy barrier height for N?N bond cleavage as assessed by kinetic studies and experimentally derived activation parameters. The origin of the contrasting kinetic stability of the first-row congener, {Cp*V[N((i)Pr)C(Me)N((i)Pr)]}2(?-?(1):?(1)-N2) toward N?N bond cleavage is rationalized in terms of a ground-state electronic structure that favors a significantly less-reduced ?-N2 fragment. PMID:24960112

  15. Accurate thermochemistry for larger molecules : gaussian-2 theory with bond separation energies.

    SciTech Connect

    Raghavachari, K.; Stefanov, B. B.; Curtiss, L. A.; Lucent Tech.

    1997-04-22

    Gaussian-2 (G2) theory is combined with isodesmic bond separation reaction energies to yield accurate thermochemistry for larger molecules. For a test set of 40 molecules composed of H, C, O, and N, our method yields enthalpies of formation, {Delta}H{sub f}{sup 0}(298 K), with a mean absolute deviation from experiment of only 0.5 kcal/mol. This is an improvement of a factor of three over the deviation of 1.5 kcal/mol seen in standard G2 theory.

  16. Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

    1997-01-01

    The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

  17. Incremental expansions for SCF interaction energies: A comparison for hydrogen-bonded clusters

    NASA Astrophysics Data System (ADS)

    Mata, R. A.; Stoll, H.

    2008-11-01

    We present an analysis of several types of embedding potentials for use within incremental expansions of SCF interaction energies. The test set comprises hydrogen-bonded clusters (water, ammonia, methanol). It is shown that an expansion up to two-body terms is sufficient for high accuracy, in all cases, as long as the environment is described by accurate embedded-monomer Coulomb and exchange potentials. A two-body expansion with atom-centered point charges for embedding leads to larger errors, but the relative differences are kept within bounds; inclusion of three-body terms often overcompensates the deviations at the two-body level, due to basis set superposition effects.

  18. Energy and critical ionic-bond parameter of a 3D large-radius bipolaron

    SciTech Connect

    Lakhno, V. D.

    2010-05-15

    A theory of a strong-coupling large-radius bipolaron has been developed. The possibility of the formation of 3D bipolarons in high-temperature superconductors is discussed. For the bipolaron energy, the lowest variational estimate has been obtained at {alpha} > 8, where {alpha} is the electron-phonon coupling constant. The critical ionic-bond parameter {eta}{sub c} = {epsilon}{sub {infinity}/{epsilon}0}, where {epsilon}{sub {infinity}} and {epsilon}{sub 0} are the high-frequency and static dielectric constants, has been found to be {eta}{sub c} = 0.2496.

  19. Controlling energy level offsets in organic/organic heterostructures using intramolecular polar bonds

    NASA Astrophysics Data System (ADS)

    Duhm, Steffen; Salzmann, Ingo; Heimel, Georg; Oehzelt, Martin; Haase, Anja; Johnson, Robert L.; Rabe, Jrgen P.; Koch, Norbert

    2009-01-01

    The impact of intramolecular polar bonds (IPBs) on the energy level alignment in layered systems of rodlike conjugated molecules standing on the substrate was investigated for pentacene (PEN) and perfluoropentacene (PFP) on SiO2 using ultraviolet photoelectron spectroscopy. A remarkably large energy offset of 1.75 eV was found between the highest occupied molecular orbital (HOMO) levels of PEN and PFP caused by IPBs at the surface of standing PFP layers. This large HOMO-level offset results in a narrow intermolecular energy gap of approximately 0.4 eV at the interface between PEN and PFP layers. However, the absence of significant spatial overlap of PEN and PFP electron wave functions across the layers suppresses interlayer optical transitions.

  20. Active Metal Brazing and Characterization of Brazed Joints in C-C and C-SiC Composites to Copper-Clad-Molybdenum System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon/carbon composites with CVI and resin-derived matrices, and C/SiC composites reinforced with T-300 carbon fibers in a CVI SiC matrix were joined to Cu-clad Mo using two Ag-Cu braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward delamination in resin-derived C/C composite. Extensive braze penetration of the inter-fiber channels in the CVI C/C composites was observed. The Knoop microhardness (HK) distribution across the C/C joints indicated sharp gradients at the interface, and a higher hardness in Ticusil than in Cusil-ABA. For the C/SiC composite to Cu-clad-Mo joints, the effect of composite surface preparation revealed that ground samples did not crack whereas unground samples cracked. Calculated strain energy in brazed joints in both systems is comparable to the strain energy in a number of other ceramic/metal systems. Theoretical predictions of the effective thermal resistance suggest that such joined systems may be promising for thermal management applications.

  1. Empirical valence bond models for reactive potential energy surfaces: A parallel multilevel genetic program approach

    NASA Astrophysics Data System (ADS)

    Bellucci, Michael A.; Coker, David F.

    2011-07-01

    We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent.

  2. Evaluating interaction energies of weakly bonded systems using the Buckingham-Hirshfeld method

    SciTech Connect

    Krishtal, A.; Van Alsenoy, C.; Geerlings, P.

    2014-05-14

    We present the finalized Buckingham-Hirshfeld method (BHD-DFT) for the evaluation of interaction energies of non-bonded dimers with Density Functional Theory (DFT). In the method, dispersion energies are evaluated from static multipole polarizabilities, obtained on-the-fly from Coupled Perturbed Kohn-Sham calculations and partitioned into diatomic contributions using the iterative Hirshfeld partitioning method. The dispersion energy expression is distributed over four atoms and has therefore a higher delocalized character compared to the standard pairwise expressions. Additionally, full multipolar polarizability tensors are used as opposed to effective polarizabilities, allowing to retain the anisotropic character at no additional computational cost. A density dependent damping function for the BLYP, PBE, BP86, B3LYP, and PBE0 functionals has been implemented, containing two global parameters which were fitted to interaction energies and geometries of a selected number of dimers using a bi-variate RMS fit. The method is benchmarked against the S22 and S66 data sets for equilibrium geometries and the S22x5 and S66x8 data sets for interaction energies around the equilibrium geometry. Best results are achieved using the B3LYP functional with mean average deviation values of 0.30 and 0.24 kcal/mol for the S22 and S66 data sets, respectively. This situates the BHD-DFT method among the best performing dispersion inclusive DFT methods. Effect of counterpoise correction on DFT energies is discussed.

  3. Electronic structure, charge transfer and bonding in intermetallics using EELS and density functional theory[Electron Energy Loss Spectroscopy

    SciTech Connect

    Humphreys, C.J.; Botton, G.A.; Pankhurst, D.A.; Keast, V.J.; Temmerman, W.M.

    1999-07-01

    Electron energy loss spectroscopy and density functional theory have been used to show that there is a covalent component to the bonding in NiAl, CoAl and FeAl, between the transition metal atom and Al. There is no charge transfer and no ionic component to the bonding in NiAl and probably not in CoAl and FeAl. The bonding is non-stoichiometric NiAl is studied. Preliminary results are given for a {Sigma}{sub 3} boundary in NiAl.

  4. Universal Bronsted-Evans-Polanyi Relations for C-C, C-O, C-N, N-O, N-N, and O-O Dissociation Reactions

    SciTech Connect

    Wang, Shengguang

    2010-10-27

    It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.

  5. Bridging the momentum distribution and the potential energy surface of protons in hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Morrone, Joseph; Lin, Lin; Car, Roberto; Parrinello, Michele

    2010-03-01

    Open path integral Car-Parrinello molecular dynamics studies have uncovered the proton momentum distribution in various phases of ice [1,2]. These systems exhibit a wide range of behavior, including symmetric hydrogen bonds and quantum tunneling. In this work, we provide an in-depth statistical analysis of the simulation results. This analysis reveals a direct relation between the open path formalism of quantum particles and their underlying potential energy surface. Application of this analysis to ice systems provides quantitative information about the principle axes of the potential energy surface that the proton experiences, and indicates that the oxygen-oxygen distance is a proper reaction coordinate for such systems. Our analysis also facilitates a direct observation of anharmonic effects along the principle axes. [1] J. A. Morrone and R. Car, Phys. Rev. Lett. 101, 17801, 2008. [2] J. A. Morrone, L. Lin and R. Car, J. Chem. Phys. 130, 204511, 2009.

  6. Gas-phase acidity and C H bond energy of diacetylene

    NASA Astrophysics Data System (ADS)

    Shi, Yang; Ervin, Kent M.

    2000-02-01

    Threshold energies for the proton transfer reaction C 4H -+C 2H 2 ? C 4H 2+C 2H - and for competitive collision-induced dissociation of the proton-bound complex of diacetylide and acetaldehyde, [HC 4HCH 2CHO] -, are measured using guided ion beam tandem mass spectrometry. From the bimolecular proton transfer threshold, the gas-phase acidity of diacetylene is ? acidH0(C 4H 2)?15008 kJ/mol as a lower limit. The competitive dissociation is modeled using RRKM theory, yielding ? acidH0(C 4H 2)=150812 kJ/mol. Using the literature electron affinity of C 4H, the derived bond dissociation energy of diacetylene is D0(HC 4-H)=53912 kJ/mol.

  7. The Pairwise Correlated Generalized Valence Bond Model of Electronic Structure I; The Estimation of Pair Energies from Orbital Overlaps

    PubMed Central

    Petersson, G. A.

    1974-01-01

    A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method. PMID:16592172

  8. Assessment of experimental bond dissociation energies using composite ab initio methods and evaluation of the performances of density functional methods in the calculation of bond dissociation energies.

    PubMed

    Feng, Yong; Liu, Lei; Wang, Jin-Ti; Huang, Hao; Guo, Qing-Xiang

    2003-01-01

    Composite ab initio CBS-Q and G3 methods were used to calculate the bond dissociation energies (BDEs) of over 200 compounds listed in CRC Handbook of Chemistry and Physics (2002 ed.). It was found that these two methods agree with each other excellently in the calculation of BDEs, and they can predict BDEs within 10 kJ/mol of the experimental values. Using these two methods, it was found that among the examined compounds 161 experimental BDEs are valid because the standard deviation between the experimental and theoretical values for them is only 8.6 kJ/mol. Nevertheless, 40 BDEs listed in the Handbook may be highly inaccurate as the experimental and theoretical values for them differ by over 20 kJ/mol. Furthermore, 11 BDEs listed in the Handbook may be seriously flawed as the experimental and theoretical values for them differ by over 40 kJ/mol. Using the 161 cautiously validated experimental BDEs, we then assessed the performances of the standard density functional (DFT) methods including B3LYP, B3P86, B3PW91, and BH&HLYP in the calculation of BDEs. It was found that the BH&HLYP method performed poorly for the BDE calculations. B3LYP, B3P86, and B3PW91, however, performed reasonably well for the calculation of BDEs with standard deviations of about 12.1-18.0 kJ/mol. Nonetheless, all the DFT methods underestimated the BDEs by 4-17 kJ/mol in average. Sometimes, the underestimation by the DFT methods could be as high as 40-60 kJ/mol. Therefore, the DFT methods were more reliable for relative BDE calculations than for absolute BDE calculations. Finally, it was observed that the basis set effects on the BDEs calculated by the DFT methods were usually small except for the heteroatom-hydrogen BDEs. PMID:14632451

  9. On the mean kinetic energy of the proton in strong hydrogen bonded systems

    NASA Astrophysics Data System (ADS)

    Finkelstein, Y.; Moreh, R.; Shang, S. L.; Shchur, Ya.; Wang, Y.; Liu, Z. K.

    2016-02-01

    The mean atomic kinetic energies of the proton, Ke(H), and of the deuteron, Ke(D), were calculated in moderate and strongly hydrogen bonded (HB) systems, such as the ferro-electric crystals of the KDP type (XH2PO4, X = K, Cs, Rb, Tl), the DKDP (XD2PO4, X = K, Cs, Rb) type, and the X3H(SO4)2 superprotonic conductors (X = K, Rb). All calculations utilized the simulated partial phonon density of states, deduced from density functional theory based first-principle calculations and from empirical lattice dynamics simulations in which the Coulomb, short range, covalent, and van der Waals interactions were accounted for. The presently calculated Ke(H) values for the two systems were found to be in excellent agreement with published values obtained by deep inelastic neutron scattering measurements carried out using the VESUVIO instrument of the Rutherford Laboratory, UK. The Ke(H) values of the M3H(SO4)2 compounds, in which the hydrogen bonds are centro-symmetric, are much lower than those of the KDP type crystals, in direct consistency with the oxygen-oxygen distance ROO, being a measure of the HB strength.

  10. Guiding Principle of Energy Level Controllability of Silicon Dangling Bonds in HfSiON

    NASA Astrophysics Data System (ADS)

    Umezawa, Naoto; Shiraishi, Kenji; Miyazaki, Seiichi; Uedono, Akira; Akasaka, Yasushi; Inumiya, Seiji; Hasunuma, Ryu; Yamabe, Kikuo; Momida, Hiroyoshi; Ohno, Takahisa; Ohmori, Kenji; Chikyow, Toyohiro; Nara, Yasuo; Yamada, Keisaku

    2007-04-01

    Silicon dangling bonds (Si-DBs) in HfSiOx have been studied using first-principles calculations. Interestingly, our computational result revealed that the Si-DB-related gap state in HfSiOx locates in a much lower energy region than that in SiOx. This is because Hf atoms enhance the ionic character of the HfSiOx film, which in turn induces a positive charge at the Si site. We consider that the low-lying Si-DB level, which is now very near the N 2p state, contributes to the formation of strong Si-N bonds in HfSiON. The lower shift of the Si-DB level upon cation metal inclusion can be useful information not only for improving the electric properties of high-k gate stacks but also for developing prominent silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memories where controllability of the charge trap level is a crucial issue.

  11. Protein collapse driven against solvation free energy without H-bonds.

    PubMed

    Karandur, Deepti; Harris, Robert C; Pettitt, B Montgomery

    2016-01-01

    Proteins collapse and fold because intramolecular interactions and solvent entropy, which favor collapse, outweigh solute-solvent interactions that favor expansion. Since the protein backbone actively participates in protein folding and some intrinsically disordered proteins are glycine rich, oligoglycines are good models to study the protein backbone as it collapses, both during conformational changes in disordered proteins and during folding. The solvation free energies of short glycine oligomers become increasingly favorable as chain length increases. In contrast, the solubility limits of glycine oligomers decrease with increasing chain length, indicating that peptide-peptide, and potentially solvent-solvent interactions, overcome peptide-solvent interactions to favor aggregation at finite concentrations of glycine oligomers. We have recently shown that hydrogen- (H-) bonds do not contribute significantly to the concentration-based aggregation of pentaglycines but that dipole-dipole (CO) interactions between the amide groups on the backbone do. Here we demonstrate for the collapse of oligoglycines ranging in length from 15 to 25 residues similarly that H-bonds do not contribute significantly to collapse but that CO dipole interactions do. These results illustrate that some intrapeptide interactions that determine the solubility limit of short glycine oligomers are similar to those that drive the collapse of longer glycine peptides. PMID:26174309

  12. On the mean kinetic energy of the proton in strong hydrogen bonded systems.

    PubMed

    Finkelstein, Y; Moreh, R; Shang, S L; Shchur, Ya; Wang, Y; Liu, Z K

    2016-02-01

    The mean atomic kinetic energies of the proton, Ke(H), and of the deuteron, Ke(D), were calculated in moderate and strongly hydrogen bonded (HB) systems, such as the ferro-electric crystals of the KDP type (XH2PO4, X = K, Cs, Rb, Tl), the DKDP (XD2PO4, X = K, Cs, Rb) type, and the X3H(SO4)2 superprotonic conductors (X = K, Rb). All calculations utilized the simulated partial phonon density of states, deduced from density functional theory based first-principle calculations and from empirical lattice dynamics simulations in which the Coulomb, short range, covalent, and van der Waals interactions were accounted for. The presently calculated Ke(H) values for the two systems were found to be in excellent agreement with published values obtained by deep inelastic neutron scattering measurements carried out using the VESUVIO instrument of the Rutherford Laboratory, UK. The Ke(H) values of the M3H(SO4)2 compounds, in which the hydrogen bonds are centro-symmetric, are much lower than those of the KDP type crystals, in direct consistency with the oxygen-oxygen distance ROO, being a measure of the HB strength. PMID:26851916

  13. Nano-Bonding of Silicon Oxides-based surfaces at Low Temperature: Bonding Interphase Modeling via Molecular Dynamics and Characterization of Bonding Surfaces Topography, Hydro-affinity and Free Energy

    NASA Astrophysics Data System (ADS)

    Whaley, Shawn D.

    In this work, a new method, "Nanobonding(TM)" [1,2] is conceived and researched to bond Si-based surfaces, via nucleation and growth of a 2 D silicon oxide SiOxHx interphase connecting the surfaces at the nanoscale across macroscopic domains. Nanobonding cross-bridges two smooth surfaces put into mechanical contact in an O2/H 2O mixed ambient below T ?200 C via arrays of SiOxH x molecules connecting into a continuous macroscopic bonding interphase. Nano-scale surface planarization via wet chemical processing and new spin technology are compared via Tapping Mode Atomic Force Microscopy (TMAFM) , before and after nano-bonding. Nanobonding uses precursor phases, 2D nano-films of beta-cristobalite (beta-c) SiO2, nucleated on Si(100) via the Herbots-Atluri (H-A) method [1]. beta-c SiO2 on Si(100) is ordered and flat with atomic terraces over 20 nm wide, well above 2 nm found in native oxides. When contacted with SiO2 this ultra-smooth nanophase can nucleate and grow domains with cross-bridging molecular strands of hydroxylated SiOx, instead of point contacts. The high density of molecular bonds across extended terraces forms a strong bond between Si-based substrates, nano- bonding [2] the Si and silica. A new model of beta-cristobalite SiO2 with its <110> axis aligned along Si[100] direction is simulated via ab-initio methods in a nano-bonded stack with beta-c SiO2 in contact with amorphous SiO2 (a-SiO2), modelling cross-bridging molecular bonds between beta-c SiO2 on Si(100) and a-SiO2 as during nanobonding. Computed total energies are compared with those found for Si(100) and a-SiO2 and show that the presence of two lattice cells of !-c SiO2 on Si(100) and a-SiO2 lowers energy when compared to Si(100)/ a-SiO 2 Shadow cone calculations on three models of beta-c SiO2 on Si(100) are compared with Ion Beam Analysis of H-A processed Si(100). Total surface energy measurements via 3 liquid contact angle analysis of Si(100) after H-A method processing are also compared. By combining nanobonding experiments, TMAFM results, surface energy data, and ab-initio calculations, an atomistic model is derived and nanobonding is optimized. [1] US Patent 6,613,677 (9/2/03), 7,851,365 (12/14/10), [2] Patent Filed: 4/30/09, 10/1/2011

  14. A big data approach to the ultra-fast prediction of DFT-calculated bond energies

    PubMed Central

    2013-01-01

    Background The rapid access to intrinsic physicochemical properties of molecules is highly desired for large scale chemical data mining explorations such as mass spectrum prediction in metabolomics, toxicity risk assessment and drug discovery. Large volumes of data are being produced by quantum chemistry calculations, which provide increasing accurate estimations of several properties, e.g. by Density Functional Theory (DFT), but are still too computationally expensive for those large scale uses. This work explores the possibility of using large amounts of data generated by DFT methods for thousands of molecular structures, extracting relevant molecular properties and applying machine learning (ML) algorithms to learn from the data. Once trained, these ML models can be applied to new structures to produce ultra-fast predictions. An approach is presented for homolytic bond dissociation energy (BDE). Results Machine learning models were trained with a data set of >12,000 BDEs calculated by B3LYP/6-311++G(d,p)//DFTB. Descriptors were designed to encode atom types and connectivity in the 2D topological environment of the bonds. The best model, an Associative Neural Network (ASNN) based on 85 bond descriptors, was able to predict the BDE of 887 bonds in an independent test set (covering a range of 17.67–202.30 kcal/mol) with RMSD of 5.29 kcal/mol, mean absolute deviation of 3.35 kcal/mol, and R2 = 0.953. The predictions were compared with semi-empirical PM6 calculations, and were found to be superior for all types of bonds in the data set, except for O-H, N-H, and N-N bonds. The B3LYP/6-311++G(d,p)//DFTB calculations can approach the higher-level calculations B3LYP/6-311++G(3df,2p)//B3LYP/6-31G(d,p) with an RMSD of 3.04 kcal/mol, which is less than the RMSD of ASNN (against both DFT methods). An experimental web service for on-line prediction of BDEs is available at http://joao.airesdesousa.com/bde. Conclusion Knowledge could be automatically extracted by machine learning techniques from a data set of calculated BDEs, providing ultra-fast access to accurate estimations of DFT-calculated BDEs. This demonstrates how to extract value from large volumes of data currently being produced by quantum chemistry calculations at an increasing speed mostly without human intervention. In this way, high-level theoretical quantum calculations can be used in large-scale applications that otherwise would not afford the intrinsic computational cost. PMID:23849655

  15. Bond dissociation energies in alcohols: kinetics and photochemical evidence regarding ion thermochemistry

    SciTech Connect

    Moylan, C.R.; Brauman, J.I.

    1984-07-19

    Gas-phase proton transfer from benzyl alcohol to fluoride ion is encounter controlled, whereas transfer from neopentyl alcohol to fluoride ion is slow. These observations suggest that the equilibrium gas-phase acidity of HF lies between those of the two alcohols, in contrast to the tabulated order. A small adjustment in the gas-phase acidities of alcohols not only makes the kinetics consistent but also resolves a long-standing discrepancy between RO-H bond energies measured by kinetic techniques and those determined by acidity/electron affinity data. It also accounts for the observed branching ratio in the IR laser photolysis of the neopentyl alcohol-fluoride ion complex. 21 references, 1 table.

  16. On deformation twinning in b. c. c. metals

    SciTech Connect

    Lagerloef, K.P.D. . Dept. of Materials Science and Engineering)

    1993-07-01

    A new model of deformation twinning in b.c.c. metals based on the dissociation of an a/2(111) screw dislocations into three co-linear a/6(111) partials on three adjacent (11[bar 2]) planes is proposed. A short screw segment of this zonal dislocation bows out under an applied stress in a fashion similar to a Frank-Read source, where each of the three partials glides on its individuals (11[bar 2]) plane. The correlated motion of the three partials on three adjacent (11[bar 2]) planes forms a three layered micro-twin. After one Frank-Read zonal dislocation loop forms, the screw segment undergoes cross-slip in a similar fashion as the model proposed by Pirouz for twinning in Si because the formation of a second Frank-Reid zonal dislocation loop would produce a stacking sequence of (11[bar 2]) planes associated with a high energy stacking fault. However, after cross-slip the screw-segment may again bow out on a new set of parallel (11[bar 2]) planes to form another three layered micro-twin bound by the zonal dislocation loop. The repeated cross-slip and bowing out of such zonal dislocation loops results in both lateral growth and thickening of the deformation twin.

  17. Communication: Towards the binding energy and vibrational red shift of the simplest organic hydrogen bond: Harmonic constraints for methanol dimer

    SciTech Connect

    Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A.

    2014-09-14

    The discrepancy between experimental and harmonically predicted shifts of the OH stretching fundamental of methanol upon hydrogen bonding to a second methanol unit is too large to be blamed mostly on diagonal and off-diagonal anharmonicity corrections. It is shown that a decisive contribution comes from post-MP2 electron correlation effects, which appear not to be captured by any of the popular density functionals. We also identify that the major deficiency is in the description of the donor OH bond. Together with estimates for the electronic and harmonically zero-point corrected dimer binding energies, this work provides essential constraints for a quantitative description of this simple hydrogen bond. The spectroscopic dissociation energy is predicted to be larger than 18 kJ/mol and the harmonic OH-stretching fundamental shifts by about ?121 cm{sup ?1} upon dimerization, somewhat more than in the anharmonic experiment (?111 cm{sup ?1})

  18. Transport pathways for mobile ions in disordered solids from the analysis of energy-scaled bond-valence mismatch landscapes.

    PubMed

    Adams, Stefan; Rao, R Prasada

    2009-05-01

    Structure-property relationships provide valuable guidelines for a systematic development of functional materials. Here an augmented bond-valence approach is worked out that is linked directly to the energy scale. This energy-scaled bond-valence approach is then used to identify ion-conduction pathways and to establish structure-property relationships in complex disordered solids using lithium silicate glasses as model systems. Representative local structure models of glassy solid electrolytes as a basis for the pathway analysis are derived from molecular dynamics simulations. Predictions of the bond-valence model from a static structure model are compared to a complete trajectory analysis, showing a high degree of agreement. The method yields consistent results when changing the simulation force field and is applicable to a wide range of glasses. PMID:19370216

  19. Microsolvation of methylmercury: structures, energies, bonding and NMR constants ((199)Hg, (13)C and (17)O).

    PubMed

    Flórez, Edison; Maldonado, Alejandro F; Aucar, Gustavo A; David, Jorge; Restrepo, Albeiro

    2016-01-21

    Hartree-Fock (HF) and second order perturbation theory (MP2) calculations within the scalar and full relativistic frames were carried out in order to determine the equilibrium geometries and interaction energies between cationic methylmercury (CH3Hg(+)) and up to three water molecules. A total of nine structures were obtained. Bonding properties were analyzed using the Quantum Theory of Atoms In Molecules (QTAIM). The analyses of the topology of electron densities reveal that all structures exhibit a partially covalent HgO interaction between methylmercury and one water molecule. Consideration of additional water molecules suggests that they solvate the (CH3HgOH2)(+) unit. Nuclear magnetic shielding constants σ((199)Hg), σ((13)C) and σ((17)O), as well as indirect spin-spin coupling constants J((199)Hg-(13)C), J((199)Hg-(17)O) and J((13)C-(17)O), were calculated for each one of the geometries. Thermodynamic stability and the values of NMR constants correlate with the ability of the system to directly coordinate oxygen atoms of water molecules to the mercury atom in methylmercury and with the formation of hydrogen bonds among solvating water molecules. Relativistic effects account for 11% on σ((13)C) and 14% on σ((17)O), which is due to the presence of Hg (heavy atom on light atom, HALA effect), while the relativistic effects on σ((199)Hg) are close to 50% (heavy atom on heavy atom itself, HAHA effect). J-coupling constants are highly influenced by relativity when mercury is involved as in J((199)Hg-(13)C) and J((199)Hg-(17)O). On the other hand, our results show that the values of NMR constants for carbon and oxygen, atoms which are connected through mercury (C-HgO), are highly correlated and are greatly influenced by the presence of water molecules. Water molecules introduce additional electronic effects to the relativistic effects due to the mercury atom. PMID:26670708

  20. Testing of DLR C/C-SiC and C/C for HIFiRE 8 Scramjet Combustor

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Capriotti, Diego P.; Reimer, Thomas; Kutemeyer, Marius; Smart, Michael K.

    2014-01-01

    Ceramic Matrix Composites (CMCs) have been proposed for use as lightweight hot structures in scramjet combustors. Previous studies have calculated significant weight savings by utilizing CMCs (active and passive) versus actively cooled metallic scramjet structures. Both a carbon/carbon (C/C) and a carbon/carbon-silicon carbide (C/C-SiC) material fabricated by DLR (Stuttgart, Germany) are being considered for use in a passively cooled combustor design for Hypersonic International Flight Research Experimentation (HIFiRE) 8, a joint Australia / Air Force Research Laboratory hypersonic flight program, expected to fly at Mach 7 for approximately 30 sec, at a dynamic pressure of 55 kilopascals. Flat panels of the DLR C/C and C/C-SiC materials were installed downstream of a hydrogen-fueled, dual-mode scramjet combustor and tested for several minutes at conditions simulating flight at Mach 5 and Mach 6. Gaseous hydrogen fuel was used to fuel the scramjet combustor. The test panels were instrumented with embedded Type K and Type S thermocouples. Zirconia felt insulation was used during some of the tests to reduce heat loss from the back surface and thus increase the heated surface temperature of the C/C-SiC panel approximately 177 C (350 F). The final C/C-SiC panel was tested for three cycles totaling over 135 sec at Mach 6 enthalpy. Slightly more erosion was observed on the C/C panel than the C/C-SiC panels, but both material systems demonstrated acceptable recession performance for the HIFiRE 8 flight.

  1. Nanoscale metals and semiconductors for the storage of solar energy in chemical bonds

    NASA Astrophysics Data System (ADS)

    Manthiram, Karthish

    The transduction of electrical energy into chemical bonds represents one potential strategy for storing energy derived from intermittent sources such as solar and wind. Driving the electrochemical reduction of carbon dioxide using light requires (1) developing light absorbers which convert photons into electron-hole pairs and (2) catalysts which utilize these electrons and holes to reduce carbon dioxide and oxidize water, respectively. For both the light absorbers and catalysts, the use of nanoscale particles is advantageous, as charge transport length scales are minimized in the case of nanoscale light absorbers and catalytic surface-area-to-volume ratio is maximized for nanoscale catalysts. In many cases, although semiconductors and metals in the form of thin films and foils are increasingly well-characterized as photoabsorbers and electrocatalysts for carbon dioxide reduction, respectively, the properties of their nanoscale counterparts remain poorly understood. This dissertation explores the nature of the light absorption mode of non-stoichiometric semiconductors which are utilized as light absorbers and the development of catalysts with enhanced stability, activity, and selectivity for carbon dioxide reduction. Chapter 1 provides an overview of the state of development of methods of transducing the energy of photons into chemical bonds. Chapters 2 and 3 investigate the development of stable, active, and selective catalysts for the electrochemical reduction of carbon dioxide. Chapter 2 examines how copper nanoparticles have enhanced activities and selectivities for methanation compared to copper foils. Chapter 3 focuses on the development of strategies to stabilize high-surface-area catalysts to prevent surface area loss during electrochemical carbon dioxide reduction. Chapters 4 and 5 entail a fundamental understanding of the light absorption mode of nanoscale photoabsorbers used in both photoelectrochemical cells and in photovoltaics. Chapter 4 focuses on the nature of the light absorption mode of non-stoichiometric tungsten oxide, a material which has been explored as a photoanode for the photon driven oxidation of water. Chapter 5 examines the tunability of the light absorption mode of nanoscale copper sulfide, a material which has been explored as a photoabsorber for photovoltaics. An understanding of the light absorption mode of non-stoichiometric oxides and sulfides at the nanoscale is critical for the use of these materials in redox active environments.

  2. C-H and C-C clumping in ethane by high-resolution mass spectrometry

    NASA Astrophysics Data System (ADS)

    Clog, M. D.; Eiler, J. M.

    2014-12-01

    Ethane (C2H6) is an important natural compound, and its geochemistry can be studied through 13C-13C, 13C-D and/or D-D clumping. Such measurements are potentially important both as a stepping stone towards the study of more complex organic molecules and, in its own regard, to understand processes controlling the generation, migration and destruction of natural gas. Isotopic clumping on C-C and C-H bonds could be influenced by thermodynamics, chemical kinetics, diffusion or gas mixing. Previous work showed that 13C-D clumping in methane generally reflects equilibrium and provides a measure of formation temperature (Stolper et al 2014a), whereas 13C-13C clumping in ethane is likely most controlled by chemical-kinetic processes and/or inheritance from the isotopic structure of source organic compounds (Clog et al 2014). 13C-D clumping in ethane has the potential to provide a thermometer for its synthesis, as it does for methane. However, the difference in C-H bond dissociation energy for these two compounds may suggest a lower 'blocking temperature' for this phenomenon in ethane (the blocking temperature for methane is ?~250 C in geological conditions). We present analytical techniques to measure both 13C-13C and 13C-D clumping in ethane, using a novel two-instrument technique, including both the Thermo 253-Ultra and the Thermo DFS. In this method, the Ultra is used to measure the relative abundances of combinations nearly isobaric isotopologues: (13C12CH6 + 12C2DH5)/12C2H6 and (13C2H6 + 12C13CDH5)/12C2H6, free of other isobaric interferences like O2. The DFS, a very high resolution single-collector instrument, is then used to measure the ratios of isotopologues of ethane at a single cardinal mass: 12C2DH5/13C12CH6, and 12C13CDH5/13C2H6, with precisions of ~1 permil. Those 4 measurements allow us to calculate the bulk isotopic composition (?D and ?13C) as well as the abundance of 13C2H6 and 13C12CDH5. We also present progress on the development of software tools to use the data measured with the DFS efficiently.

  3. Electronic excitation energies in dimers between radical ions presenting long, multicenter bonding.

    PubMed

    Fumanal, Maria; Capdevila-Cortada, Maral; Ribas-Arino, Jordi; Novoa, Juan J

    2015-06-01

    The formation of long, multicenter dimers between radical ions is usually monitored through UV-vis spectroscopy given the characteristic low-energy absorption band that they exhibit, not observed for the parent monomers. In this work, the performance of CASPT2, RASPT2, and TD-DFT methods for obtaining excitation energies of the long, multicenter bonded ?-[TCNE]2(2-) and ?-[TTF]2(2+) dimers has been addressed (TCNE = tetracyanoethylene; TTF = tetrathiafulvalene). The impact of the active space on the vertical electronic transitions computed at the RASPT2 and CASPT2 levels has been tested against experimentally observed absorption bands. Analogous tests have been carried out for a wide variety of density functionals within the TD-DFT formalism. Our calculations show that whereas CASPT2 predicts very accurate excitation energies for the ?-[TCNE]2(2-), the mean absolute error for ?-[TTF]2(2+) is higher for CASPT2 than for TD-DFT calculations, whenever pure density functionals or low % HF exchange hybrid functionals are used. Hybrid functionals with high % HF exchange (and thus RSH functionals) conduct to large errors on the excitation energies in both dimers. Furthermore, vertical electronic transitions are also obtained for 100 configurations extracted from a 45 ps molecular dynamics (CPMD) simulation aimed at providing an accurate description of the thermal fluctuation effects of a ?-[TCNE]2(2-) dimer in dichloromethane. These thermal effects explain the shape of the experimental UV-vis spectrum, where the lowest HOMO ? LUMO absorption presents a broad band and the following HOMO-1 ? LUMO absorption exhibits a narrower band. PMID:26575562

  4. Effect of ultrasonic energy on nanoscale interfacial structure in copper wire bonding on aluminium pads

    NASA Astrophysics Data System (ADS)

    Xu, H.; Liu, C.; Silberschmidt, V. V.; Chen, Z.; Acoff, V. L.

    2011-04-01

    The effect of ultrasonic vibration on nanoscale interfacial structure of thermosonic copper wire bonding on aluminium pads was investigated. It was found that bonding strength was determined by the extent of fragmentation of a native aluminium oxide overlayer (5-10 nm thick) on aluminium pads, forming paths for formation of intermetallic compound CuAl2 in areas of direct contact of bonded metal surfaces. The degree of fracture of the oxide layer was strongly affected by a level of ultrasonic power.

  5. Deoxygenative C-C Bond-Forming Processes via a Net Four-Electron Reductive Coupling.

    PubMed

    Todd, David P; Thompson, Benjamin B; Nett, Alex J; Montgomery, John

    2015-10-14

    The nickel-catalyzed coupling of enones or enals with alkynes in the presence of silane and titanium alkoxide reductants provides direct access to skipped diene products. The process involves a net four-electron reductive coupling and proceeds with deoxygenation of the starting enone or enal. A new class of well-defined nickel(0) precatalysts bearing an unhindered N-heterocyclic carbene ligand, which was developed in optimization of the process, is essential for the efficiency of the transformation. The strategy allows the high reactivity of ?,?-unsaturated carbonyl substrates to be utilized in couplings with simultaneous extrusion of the oxygen atom, thus enabling a traceless strategy for alkene installation. PMID:26436636

  6. Metal-catalyzed release of supported boronic acids for C-C bond formation.

    PubMed

    Pourbaix, C; Carreaux, F; Carboni, B

    2001-03-22

    The viability of solid-supported boronic acids as reagents for Suzuki couplings and nucleophilic additions to aldehydes and enones was successfully demonstrated. This metal-catalyzed cleavage strategy allows the synthesis of a series of functionalized biphenyl products, benzylic alcohols, and beta-substituted ketones. PMID:11263886

  7. Photochemically-induced C-C bond formation between tertiary amines and nitrones.

    PubMed

    Itoh, Kennosuke; Kato, Ryo; Kinugawa, Daito; Kamiya, Hideaki; Kudo, Ryuki; Hasegawa, Masayuki; Fujii, Hideaki; Suga, Hiroyuki

    2015-09-01

    Photoexcited nitrones serve as excellent electron acceptors as well as radical acceptors in the presence of tertiary amines to give ?-amino hydroxylamines via photochemically-induced direct sp(3) C-H functionalization of the tertiary amines. The combined use of an organophotosensitizer and photoirradiation was highly effective in accelerating addition reactions. Several nitrones and tertiary amines were successfully utilized to give ?-amino hydroxylamines in good yield. Highly regioselective generation of primary ?-aminoalkyl radicals based on Lewis's stereoelectronic rule and diastereoselective addition reactions of primary ?-aminoalkyl radicals with nitrones were successfully achieved. Furthermore, a highly diastereoselective reaction of an ?-aminoalkyl radical with a chiral (E)-geometry-fixed ?-alkoxycarbonylnitrone was performed. PMID:26205235

  8. Characterization of Brazed Joints of C-C Composite to Cu-clad-Molybdenum

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon-carbon composites with either pitch+CVI matrix or resin-derived matrix were joined to copper-clad molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C-C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the pitch+CVI C-C composites was observed. The relatively low brazing temperatures (<950 C) precluded melting of the clad layer and restricted the redistribution of alloying elements but led to metallurgically sound composite joints. The Knoop microhardness (HK) distribution across the joint interfaces revealed sharp gradients at the Cu-clad-Mo/braze interface and higher hardness in Ticusil (approx.85-250 HK) than in Cusil-ABA (approx.50-150 HK). These C-C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.

  9. Estimation of individual binding energies in some dimers involving multiple hydrogen bonds using topological properties of electron charge density

    NASA Astrophysics Data System (ADS)

    Ebrahimi, A.; Habibi Khorassani, S. M.; Delarami, H.

    2009-11-01

    Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine-thymine and guanine-cytosine using electron charge densities calculated at X⋯H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP/6-311++G ?? and MP2/6-311++G ?? levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between ?HBCP and individual EHB. Correlation coefficient between EHB and ?HBCP in the base of linear, quadratic, and exponential equations are acceptable and equal to 0.95. The estimated individual binding energies EHB are in good agreement with the results of atom-replacement approach and natural bond orbital analysis (NBO). The EHB values estimated from ? values at H⋯X BCP are in satisfactory agreement with the main geometrical parameter H⋯X. With respect to the obtained individual binding energies, the strength of a HB depends on the substituent and the cooperative effects of other HBs.

  10. Structure, energetics, and bonding of novel potential high energy density materials Rh2(N5)4: A DFT study

    NASA Astrophysics Data System (ADS)

    Tang, Lihong; Bao, Shuangyou; Peng, Jinhui; Li, Kai; Ning, Ping; Guo, Huibin; Zhu, Tingting; Gu, Junjie; Li, Qianshu

    2015-10-01

    Theoretical studies examining a series of binuclear transition metal pentazolides Rh2(N5)4 predict paddle wheel type structures with very short metal-metal distances. Natural bonding orbital analysis indicated that the bonding between the metal atom and the five-membered ring is predominantly ionic for Rh2(N5)4 species, and a high-order metal-metal multiple bonding exists between the two metal atoms. In addition, the presence of the delocalized ? orbital plays an important role in the stabilization of Rh2(N5)4. Nucleus independent chemical shift values confirm that the planar N5- exhibits aromaticity. The dissociation energies into mononuclear fragments are predicted for Rh2(N5)4.

  11. Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins

    SciTech Connect

    Bo, Maolin; Huang, Yongli; Zhang, Ting; Wang, Yan E-mail: ecqsun@ntu.edu.sg; Zhang, Xi; Li, Can; Sun, Chang Q. E-mail: ecqsun@ntu.edu.sg

    2014-04-14

    Consistency between x-ray photoelectron spectroscopy measurements and density-function theory calculations confirms our bond order-length-strength notation-incorporated tight-binding theory predictions on the quantum entrapment of Si solid skin and atomic clusters. It has been revealed that bond-order deficiency shortens and strengthens the Si-Si bond, which results in the local densification and quantum entrapment of the core and valence electrons. Unifying Si clusters and Si(001) and (111) skins, this mechanism has led to quantification of the 2p binding energy of 96.089 eV for an isolated Si atom, and their bulk shifts of 2.461 eV. Findings evidence the significance of atomic undercoordination that is of great importance to device performance.

  12. The interplay between interface structure, energy level alignment and chemical bonding strength at organic-metal interfaces.

    PubMed

    Willenbockel, M; Lftner, D; Stadtmller, B; Koller, G; Kumpf, C; Soubatch, S; Puschnig, P; Ramsey, M G; Tautz, F S

    2015-01-21

    What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of bonding strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on the three canonical low index Ag surfaces to provide exemplary answers to these questions. Specifically, we employ angular resolved photoemission spectroscopy for a systematic study of the energy level alignments of the two uppermost frontier states in ordered monolayer phases of PTCDA. Data are analysed using the orbital tomography approach. This allows the unambiguous identification of the orbital character of these states, and also the discrimination between inequivalent species. Combining this experimental information with DFT calculations and the generic Newns-Anderson chemisorption model, we analyse the alignments of highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) with respect to the vacuum levels of bare and molecule-covered surfaces. This reveals clear differences between the two frontier states. In particular, on all surfaces the LUMO is subject to considerable bond stabilization through the interaction between the molecular ?-electron system and the metal, as a consequence of which it also becomes occupied. Moreover, we observe a larger bond stabilization for the more open surfaces. Most importantly, our analysis shows that both the orbital binding energies of the LUMO and the overall adsorption heights of the molecule are linked to the strength of the chemical interaction between the molecular ?-electron system and the metal, in the sense that stronger bonding leads to shorter adsorption heights and larger orbital binding energies. PMID:25475998

  13. Novel carboncarbon bond formations for biocatalysis

    PubMed Central

    Resch, Verena; Schrittwieser, Joerg H; Siirola, Elina; Kroutil, Wolfgang

    2011-01-01

    Carboncarbon bond formation is the key transformation in organic synthesis to set up the carbon backbone of organic molecules. However, only a limited number of enzymatic CC bond forming reactions have been applied in biocatalytic organic synthesis. Recently, further name reactions have been accomplished for the first time employing enzymes on a preparative scale, for instance the Stetter and PictetSpengler reaction or oxidative CC bond formation. Furthermore, novel enzymatic CC bond forming reactions have been identified like benzylation of aromatics, intermolecular Diels-Alder or reductive coupling of carbon monoxide. PMID:21354781

  14. Adhesive-Bonded Composite Joint Analysis with Delaminated Surface Ply Using Strain-Energy Release Rate

    NASA Technical Reports Server (NTRS)

    Chadegani, Alireza; Yang, Chihdar; Smeltzer, Stanley S. III

    2012-01-01

    This paper presents an analytical model to determine the strain energy release rate due to an interlaminar crack of the surface ply in adhesively bonded composite joints subjected to axial tension. Single-lap shear-joint standard test specimen geometry with thick bondline is followed for model development. The field equations are formulated by using the first-order shear-deformation theory in laminated plates together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The system of second-order differential equations is solved to using the symbolic computation tool Maple 9.52 to provide displacements fields. The equivalent forces at the tip of the prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the crack closure method. Finite element analyses using the J integral as well as the crack closure method are performed to verify the developed analytical model. It has been shown that the results using the analytical method correlate well with the results from the finite element analyses. An attempt is made to predict the failure loads of the joints based on limited test data from the literature. The effectiveness of the inclusion of bondline thickness is justified when compared with the results obtained from the previous model in which a thin bondline and uniform adhesive stresses through the bondline thickness are assumed.

  15. Bonding silicones with epoxies

    SciTech Connect

    Tira, J.S.

    1980-01-01

    It is shown that silicones, both room temperature vulcanizing (RTV) and millable rubber (press cured) can be successfully bonded to other materials using plasma treatment and epoxy adhesives. The plasma treatment using dry air atmosphere increases the surface energy of the silicone and thus provides a lower water contact angle. This phenomenon allows the epoxy adhesive to wet the silicone surface and ultimately bond. Bond strengths are sufficiently high to result in failures in the silicone materials rather than the adhesive bond.

  16. Simple Bond Cleavage

    SciTech Connect

    Gary S. Groenewold

    2005-08-01

    Simple bond cleavage is a class of fragmentation reactions in which a single bond is broken, without formation of new bonds between previously unconnected atoms. Because no bond making is involved, simple bond cleavages are endothermic, and activation energies are generally higher than for rearrangement eliminations. The rate of simple bond cleavage reactions is a strong function of the internal energy of the molecular ion, which reflects a loose transition state that resembles reaction products, and has a high density of accessible states. For this reason, simple bond cleavages tend to dominate fragmentation reactions for highly energized molecular ions. Simple bond cleavages have negligible reverse activation energy, and hence they are used as valuable probes of ion thermochemistry, since the energy dependence of the reactions can be related to the bond energy. In organic mass spectrometry, simple bond cleavages of odd electron ions can be either homolytic or heterolytic, depending on whether the fragmentation is driven by the radical site or the charge site. Simple bond cleavages of even electron ions tend to be heterolytic, producing even electron product ions and neutrals.

  17. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

  18. Financing Public Sector Projects with Clean Renewable Energy Bonds; Fact Sheet Series on Financing Renewable Energy Projects, National Renewable Energy Laboratory (NREL)

    SciTech Connect

    Kreycik, C.; Couglin, J.

    2009-12-01

    Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest payments from the issuer. Because CREBs are theoretically interest free, they may be more attractive than traditional tax-exempt municipal bonds. In February 2009, Congress appropriated a total of $2.4 billion for the "New CREBs" program. No more than one-third of the budget may be allocated to each of the eligible entities: governmental bodies, electric cooperatives, and public power providers. Applications for this round of "New CREBs" were due to the Internal Revenue Service (IRS) on August 4, 2009. There is no indication Congress will extend the CREBs program; thus going forward, only projects that are approved under the 2009 round will be able to issue CREBs. This factsheet explains the CREBs mechanism and provides guidance on procedures related to issuing CREBs.

  19. Influence of functional groups on the C ?-C ? chain of L-phenylalanine and its derivatives

    NASA Astrophysics Data System (ADS)

    Ganesan, Aravindhan; Brunger, Michael; Wang, Feng

    2010-07-01

    L-phenylalanine ( L-phe) consists of three different functional groups, i.e., phenyl, carboxyl (-COOH) and amino (-NH 2), joining through the C ?-C ? bridge. Substitution of these groups produces 2-phenethylamine (PEA) and 3-phenylpropionic acid (PPA). Electronic structures of L-phe, PEA and PPA together with smaller "fragments" L-alanine and benzene were determined using density functional theory (DFT), from which core and valence shell ionization spectra were simulated. Comparison of the spectra reveals that core shell ionization energies clearly indicate that the carbon bridge is significantly affected by their functional group substitutions particularly at the C ? site. In the valence space, quite unexpectedly, the frontier orbitals are concentrated on the benzene group although some energy splitting is observed. The orbitals which significantly affect the C ?-C ? carbon backbone are from the inner valence shell in the ionization energy region of 20-26 eV of the molecules.

  20. Thermodynamic properties of carbon in b.c.c. and f.c.c. iron-silicon-carbon solid solutions.

    NASA Technical Reports Server (NTRS)

    Chraska, P.; Mclellan, R. B.

    1971-01-01

    The equilibrium between hydrogen-methane gas mixtures and Fe-Si-C solid solutions has been investigated both as a function of temperature and carburizing gas composition. The thermodynamic properties of the carbon atoms in both b.c.c. and f.c.c. solid solution have been derived from the equilibrium measurements. The results found have been compared with those of earlier investigations and with the predictions of recent theoretical models on ternary solid solutions containing both substitutional and interstitial solute atoms.

  1. Influence of oxygen inhibition on the surface free-energy and dentin bond strength of self-etch adhesives.

    PubMed

    Koga, Kensaku; Tsujimoto, Akimasa; Ishii, Ryo; Iino, Masayoshi; Kotaku, Mayumi; Takamizawa, Toshiki; Tsubota, Keishi; Miyazaki, Masashi

    2011-10-01

    We compared the surface free-energies and dentin bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The labial dentin surfaces of bovine mandibular incisors were wet ground with #600-grit silicon carbide paper. The adhesives were applied to the ground dentin, light-irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The dentin bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component was relatively constant at 35.5-39.8 mJ m(-2) . The value of the , Lewis acid component increased slightly when the oxygen-inhibited layer was removed, whereas that of the , Lewis base component decreased significantly. The bond strengths of the self-etch adhesives were significantly lower in specimens without an oxygen-inhibited layer (13.2-13.6 MPa) than in those with an oxygen-inhibited layer (17.5-18.4 MPa). These results indicate that the presence of an oxygen-inhibited layer in single-step self-etch adhesives with advanced photoinitiators promotes higher dentin bond strength. PMID:21896057

  2. Unraveling the interplay between hydrogen bonding and rotational energy barrier to fine-tune the properties of triazine molecular glasses.

    PubMed

    Laventure, Audrey; De Grandpr, Guillaume; Soldera, Armand; Lebel, Olivier; Pellerin, Christian

    2016-01-21

    Mexylaminotriazine derivatives form molecular glasses with outstanding glass-forming ability (GFA), high resistance to crystallization (glass kinetic stability, GS), and a glass transition temperature (Tg) above room temperature that can be conveniently modulated by selection of the headgroup and ancillary groups. A common feature of all these compounds is their secondary amino linkers, suggesting that they play a critical role in their GFA and GS for reasons that remain unclear because they can simultaneously form hydrogen (H) bonds and lead to a high interconversion energy barrier between different rotamers. To investigate independently and better control the influence of H bonding capability and rotational energy barrier on Tg, GFA and GS, a library of twelve analogous molecules was synthesized with different combinations of NH, NMe and O linkers. Differential scanning calorimetry (DSC) revealed that these compounds form, with a single exception, kinetically stable glasses with Tg values spanning a very broad range from -25 to 94 C. While variable temperature infrared spectroscopy combined to chemometrics reveals that, on average, around 60% of the NH groups are still H-bonded as high as 40 C above Tg, critical cooling rates obtained by DSC clearly show that molecules without H-bond donating linkers also present an outstanding GFA, meaning that H bonding plays a dominant role in controlling Tg but is not required to prevent crystallization. It is a high interconversion energy barrier, provoking a distribution of rotamers, that most efficiently promotes both GFA and resistance to crystallization. These new insights pave the way to more efficient glass engineering by extending the possible range of accessible Tg, allowing in particular the preparation of homologous glass-formers with high GS at ambient temperature in either the viscous or vitreous state. PMID:26675473

  3. High-energy, stable and recycled molecular solar thermal storage materials using AZO/graphene hybrids by optimizing hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Luo, Wen; Feng, Yiyu; Qin, Chengqun; Li, Man; Li, Shipei; Cao, Chen; Long, Peng; Liu, Enzuo; Hu, Wenping; Yoshino, Katsumi; Feng, Wei

    2015-10-01

    An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg-1 by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template.An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg-1 by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03558a

  4. A theoretical study on the strength of the C-NO2 bond and ring strain upon the formation of the intermolecular H-bonding interaction between HF and nitro group in nitrocyclopropane, nitrocyclobutane, nitrocyclopentane or nitrocyclohexane.

    PubMed

    Qiu, Wei; Ren, Fu-de; Shi, Wen-jing; Wang, Yan-hong

    2015-05-01

    As a follow-up to our investigation into the influence of H-bond on the C-NO2 trigger bond, a comparison of the effect of the H-bond on the ring strain energy with the C-NO2 bond dissociation energy was carried out in the HF complex with nitrocyclopropane, nitrocyclobutane, nitrocyclopentane, and nitrocyclohexane by using the DFT-B3LYP and MP2 (full) methods with the 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. The C-NO2 bond length decreases with strengthening of trigger-bond while the ring perimeter increases companied by weakening of ring strain upon the complex formation. The H-bonding energy correlates well with the increment of ring perimeter and the change of ring bond angle. For nitrocyclopropane???HF, the effect of H-bond on the ring strain energy is notable, while for the other complex, it is negligible. Therefore, for nitrocyclopropane???HF, the origin of the change of explosive sensitivity might be due to the increment of the C-NO2 bond dissociation energy and decrease of the ring strain energy, while for the other complex, it might be only due to the strengthening of C-NO2 bond. The analysis of electron density shifts shows that the C-C bond in ring loses density while the C-NO2 bond gains density, leading to the weakened ring strain and strengthened C-NO2 bond, and thus the possibly reduced explosive sensitivity. PMID:25863689

  5. Chemical bonding in view of electron charge density and kinetic energy density descriptors.

    PubMed

    Jacobsen, Heiko

    2009-05-01

    Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

  6. Quantification of the bond energy of bacteria attached to activated sludge floc surfaces.

    PubMed

    Mikkelsen, L H; Nielsen, P H

    2001-01-01

    The great majority of activated sludge bacteria exist incorporated in flocs. The increase in dispersed bacteria when exposed to increasing turbulent shear rates has been successfully modelled by a model assuming that the adhesion and erosion of cells may be considered in analogy to ordinary chemical phase transitions. By this adhesion-erosion model (AE-model), an "enthalpy" of cell adhesion can be estimated, and this value in turn determines the range of shear rates in which erosion of cells predominates. Application of the model has indicated that only a mass fraction less than ca. 6-17% may be released from activated sludge, even when exposed to a severe turbulent environment, i.e. only a small fraction of the flocs is dispersible by means of erosion by turbulence. The shear sensitivity and the dispersible floc fraction were found to depend on the floc composition. A net decrease in the floc EPS content during anaerobic sludge stabilisation causes a dramatic increase in the dispersed fraction, indicating the important role of EPS for the floc strength. It was found also that activated sludge cells do not reflocculate completely after exposure to high shear rates. This may be an indication that the cohesion energy of bacteria growing in colonies is greater than the energy of the more stochastic adhesion of dispersed cells to floc surfaces. It could also be another indicator of the importance of entanglement forces, which do not reform instantly, once broken. When the bond strength of cell attachment to sludge surfaces is altered by changes in the chemical environment, this may cause a change in the dispersible floc fraction as well as a change in the shear range of erosion. When the shear sensitivity constant kss is adopted for sludge characterisation, an increased degree of dispersion under standard test conditions will result in increased shear sensitivity estimates. The shear sensitivity may be used for the estimation of en equivalent change in the Gibb's energy of cell adhesion (delta (delta Gad/RT)). PMID:11381974

  7. On the Use of a Driven Wedge Test to Acquire Dynamic Fracture Energies of Bonded Beam Specimens

    SciTech Connect

    Dillard, David A.; Pohilt, David; Jacob, George Chennakattu; Starbuck, Michael; Rakesh, Kapania

    2011-01-01

    A driven wedge test is used to characterize the mode I fracture resistance of adhesively bonded composite beam specimens over a range of crosshead rates up to 1 m/s. The shorter moment arms (between wedge contact and crack tip) significantly reduce inertial effects and stored energy in the debonded adherends, when compared with conventional means of testing double cantilever beam (DCB) specimens. This permitted collecting an order of magnitude more crack initiation events per specimen than could be obtained with end-loaded DCB specimens bonded with an epoxy exhibiting significant stick-slip behavior. The localized contact of the wedge with the adherends limits the amount of both elastic and kinetic energy, significantly reduces crack advance during slip events, and facilitates higher resolution imaging of the fracture zone with high speed imaging. The method appears to work well under both quasi-static and high rate loading, consistently providing substantially more discrete fracture events for specimens exhibiting pronounced stick-slip failures. Deflections associated with beam transverse shear and root rotation for the shorter beams were not negligible, so simple beam theory was inadequate for obtaining qualitative fracture energies. Finite element analysis of the specimens, however, showed that fracture energies were in good agreement with values obtained from traditional DCB tests. The method holds promise for use in dynamic testing and for characterizing bonded or laminated materials exhibiting significant stick slip behavior, reducing the number of specimens required to characterize a sufficient number of fracture events.

  8. Bayesian Uncertainty Quantification for Bond Energies and Mobilities Using Path Integral Analysis.

    PubMed

    Chang, Joshua C; Fok, Pak-Wing; Chou, Tom

    2015-09-01

    Dynamic single-molecule force spectroscopy is often used to distort bonds. The resulting responses, in the form of rupture forces, work applied, and trajectories of displacements, are used to reconstruct bond potentials. Such approaches often rely on simple parameterizations of one-dimensional bond potentials, assumptions on equilibrium starting states, and/or large amounts of trajectory data. Parametric approaches typically fail at inferring complicated bond potentials with multiple minima, while piecewise estimation may not guarantee smooth results with the appropriate behavior at large distances. Existing techniques, particularly those based on work theorems, also do not address spatial variations in the diffusivity that may arise from spatially inhomogeneous coupling to other degrees of freedom in the macromolecule. To address these challenges, we develop a comprehensive empirical Bayesian approach that incorporates data and regularization terms directly into a path integral. All experimental and statistical parameters in our method are estimated directly from the data. Upon testing our method on simulated data, our regularized approach requires less data and allows simultaneous inference of both complex bond potentials and diffusivity profiles. Crucially, we show that the accuracy of the reconstructed bond potential is sensitive to the spatially varying diffusivity and accurate reconstruction can be expected only when both are simultaneously inferred. Moreover, after providing a means for self-consistently choosing regularization parameters from data, we derive posterior probability distributions, allowing for uncertainty quantification. PMID:26331254

  9. Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H +C2H6 reaction

    NASA Astrophysics Data System (ADS)

    Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G.

    2006-01-01

    This article presents a multifaceted study of the reaction H +C2H6?H2+C2H5 and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.80.5kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H +CH4 reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

  10. Carboncarbon bond activation of cyclobutenones enabled by the addition of chiral organocatalyst to ketone

    PubMed Central

    Li, Bao-Sheng; Wang, Yuhuang; Jin, Zhichao; Zheng, Pengcheng; Ganguly, Rakesh; Chi, Yonggui Robin

    2015-01-01

    The activation of carboncarbon (CC) bonds is an effective strategy in building functional molecules. The CC bond activation is typically accomplished via metal catalysis, with which high levels of enantioselectivity are difficult to achieve due to high reactivity of metal catalysts and the metal-bound intermediates. It remains largely unexplored to use organocatalysis for CC bond activation. Here we describe an organocatalytic activation of CC bonds through the addition of an NHC to a ketone moiety that initiates a CC single bond cleavage as a key step to generate an NHC-bound intermediate for chemo- and stereo-selective reactions. This reaction constitutes an asymmetric functionalization of cyclobutenones using organocatalysts via a CC bond activation process. Structurally diverse and multicyclic compounds could be obtained with high optical purities via an atom and redox economic process. PMID:25652912

  11. Benchmark Database for Ylidic Bond Dissociation Energies and Its Use for Assessments of Electronic Structure Methods.

    PubMed

    Zhao, Yan; Ng, Hou T; Peverati, Roberto; Truhlar, Donald G

    2012-08-14

    We report a database of 18 ylidic bond dissociation energies obtained by using highly accurate quantum mechanical methods, and we use it to test approximate electronic structure methods. The new benchmark database is called YBDE18 and is used to test a large number of electronic structure methods, including eight wave function methods and 98 density functional exchange-correlation functionals. Among them, we include some very recent density functionals, including the SOGGA11 GGA functional, the SOGGA11-X hybrid GGA functional, the M11-L local meta-GGA functional, and the M11 range-separated hybrid meta-GGA functional. We also consider other functionals of these classes plus a local spin density approximation, global-hybrid meta-GGAs, range-separated hybrid GGAs, doubly hybrid GGAs, and doubly hybrid meta-GGAs. We found M05-2X-D3, MPWB1K-D3, M05-2X, LC-BLYP, PBE0-D3, and MC3MPWB to be the best DFT methods for this database. Although they do not place in the top four overall, our new-generation functionals show overall competitive performances; each of the new functionals provides the smallest mean signed error within its class, while in terms of mean unsigned errors, SOGGA11 is the best GGA, and SOGGA11-X and M11-L are among the first three best functionals in their categories, global-hybrid GGA and local meta-GGA. The best local functionals are VSXC and M06-L, the best global-hybrids are M05-2X, M08-HX, M06-2X, and MPWB1K, and the best range-separated hybrids are LC-BLYP, ωB97, ωB97X, and M11. PMID:26592123

  12. Electrochemistry of Au(II) and Au(III) pincer complexes: determination of the Au(II)-Au(II) bond energy.

    PubMed

    Dann, Thomas; Roşca, Dragoş-Adrian; Wright, Joseph A; Wildgoose, Gregory G; Bochmann, Manfred

    2013-10-01

    The bond energy of the unsupported Au-Au bond in the Au(ii) dimer [(C(∧)N(∧)C)Au]2 and the difference between Au(III)-OH and Au(III)-H bond enthalpies have been determined experimentally by electrochemical methods, with Au-OH and Au-H complexes showing unexpected differences in their reduction pathways, supported by DFT modelling. PMID:24051607

  13. Infrared spectra of C(3)H(3)(+)-N(2) dimers: identification of proton-bound c-C(3)H(3)(+)-N(2) and H(2)CCCH(+)-N(2) isomers.

    PubMed

    Dopfer, Otto; Roth, Doris; Maier, John P

    2002-01-23

    Mid-infrared photodissociation spectra of mass selected C(3)H(3)(+)-N(2) ionic complexes are obtained in the vicinity of the C-H stretch fundamentals (2970-3370 cm(-1)). The C(3)H(3)(+)-N(2) dimers are produced in an electron impact cluster ion source by supersonically expanding a gas mixture of allene, N(2), and Ar. Rovibrational analysis of the spectra demonstrates that (at least) two C(3)H(3)(+) isomers are produced in the employed ion source, namely the cyclopropenyl (c-C(3)H(3)(+)) and the propargyl (H(2)CCCH(+)) cations. This observation is the first spectroscopic detection of the important c-C(3)H(3)(+) ion in the gas phase. Both C(3)H(3)(+) cations form intermolecular proton bonds to the N(2) ligand with a linear -C-H...N-N configuration, leading to planar C(3)H(3)(+)-N(2) structures with C(2v) symmetry. The strongest absorption of the H(2)CCCH(+)-N(2) dimer in the spectral range investigated corresponds to the acetylenic C-H stretch fundamental (v(1) = 3139 cm(-1)), which experiences a large red shift upon N(2) complexation (Delta(v1) approximately -180 cm(-1)). For c-C(3)H(3)(+)-N(2), the strongly IR active degenerate antisymmetric stretch vibration (v4)) of c-C(3)H(3)(+) is split into two components upon complexation with N(2): v4)(a(1)) = 3094 cm(-1) and v4)(b(2)) = 3129 cm(-1). These values bracket the yet unknown v4) frequency of free c-C(3)H(3)(+) in the gas phase, which is estimated as 3125 +/- 4 cm(-1) by comparison with theoretical data. Analysis of the nuclear spin statistical weights and A rotational constants of H(2)CCCH(+)-N(2) and c-C(3)H(3)(+)-N(2) provide for the first time high-resolution spectroscopic evidence that H(2)CCCH(+) and c-C(3)H(3)(+) are planar ions with C(2v) and D(3h) symmetry, respectively. Ab initio calculations at the MP2(full)/6-311G(2df,2pd) level confirm the given assignments and predict intermolecular separations of R(e) = 2.1772 and 2.0916 A and binding energies of D(e) = 1227 and 1373 cm(-1) for the H-bound c-C(3)H(3)(+)-N(2) and H(2)CCCH(+)-N(2) dimers, respectively. PMID:11792222

  14. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    PubMed Central

    Schmidt, Michael W.; Ivanic, Joseph; Ruedenberg, Klaus

    2014-01-01

    An analysis based on the variation principle shows that in the molecules H2+, H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation. PMID:24880263

  15. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    SciTech Connect

    Schmidt, Michael W; Ivanic, Joseph; Ruedenberg, Klaus

    2014-05-28

    An analysis based on the variation principle shows that in the molecules H2 +, H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation.

  16. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    SciTech Connect

    Schmidt, Michael W.; Ruedenberg, Klaus; Ivanic, Joseph

    2014-05-28

    An analysis based on the variation principle shows that in the molecules H{sub 2}{sup +}, H{sub 2}, B{sub 2}, C{sub 2}, N{sub 2}, O{sub 2}, F{sub 2}, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation.

  17. Is the decrease of the total electron energy density a covalence indicator in hydrogen and halogen bonds?

    PubMed

    Angelina, Emilio L; Duarte, Darío J R; Peruchena, Nélida M

    2013-05-01

    In this work, halogen bonding (XB) and hydrogen bonding (HB) complexes were studied with the aim of analyzing the variation of the total electronic energy density H(r b ) with the interaction strengthening. The calculations were performed at the MP2/6-311++G(2d,2p) level of approximation. To explain the nature of such interactions, the atoms in molecules theory (AIM) in conjunction with reduced variational space self-consistent field (RVS) energy decomposition analysis were carried out. Based on the local virial theorem, an equation to decompose the total electronic energy density H(r b ) in two energy densities, (-G(r b )) and 1/4∇(2)ρ(r b ), was derived. These energy densities were linked with the RVS interaction energy components. Through the connection between both decomposition schemes, it was possible to conclude that the decrease in H(r b ) with the interaction strengthening observed in the HB as well as the XB complexes, is mainly due to the increase in the attractive electrostatic part of the interaction energy and in lesser extent to the increase in its covalent character, as is commonly considered. PMID:23187685

  18. Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in small water and HCl clusters.

    PubMed

    Samanta, Amit K; Czak, Gbor; Wang, Yimin; Mancini, John S; Bowman, Joel M; Reisler, Hanna

    2014-08-19

    Water is one of the most pervasive molecules on earth and other planetary bodies; it is the molecule that is searched for as the presumptive precursor to extraterrestrial life. It is also the paradigm substance illustrating ubiquitous hydrogen bonding (H-bonding) in the gas phase, liquids, crystals, and amorphous solids. Moreover, H-bonding with other molecules and between different molecules is of the utmost importance in chemistry and biology. It is no wonder, then, that for nearly a century theoreticians and experimentalists have tried to understand all aspects of H-bonding and its influence on reactivity. It is somewhat surprising, therefore, that several fundamental aspects of H-bonding that are particularly important for benchmarking theoretical models have remained unexplored experimentally. For example, even the binding strength between two gas-phase water molecules has never been determined with sufficient accuracy for comparison with high-level electronic structure calculations. Likewise, the effect of cooperativity (nonadditivity) in small H-bonded networks is not known with sufficient accuracy. An even greater challenge for both theory and experiment is the description of the dissociation dynamics of H-bonded small clusters upon acquiring vibrational excitation. This is because of the long lifetimes of many clusters, which requires running classical trajectories for many nanoseconds to achieve dissociation. In this Account, we describe recent progress and ongoing research that demonstrates how the combined and complementary efforts of theory and experiment are enlisted to determine bond dissociation energies (D0) of small dimers and cyclic trimers of water and HCl with unprecedented accuracy, describe dissociation dynamics, and assess the effects of cooperativity. The experimental techniques rely on IR excitation of H-bonded X-H stretch vibrations, measuring velocity distributions of fragments in specific rovibrational states, and determining product state distributions at the pair-correlation level. The theoretical methods are based on high-level ab initio potential energy surfaces used in quantum and classical dynamical calculations. We achieve excellent agreement on D0 between theory and experiments for all of the clusters that we have compared, as well as for cooperativity in ring trimers of water and HCl. We also show that both the long-range and the repulsive parts of the potential must be involved in bond breaking. We explain why H-bonds are so resilient and hard to break, and we propose that a common motif in the breaking of cyclic trimers is the opening of the ring following transfer of one quantum of stretch excitation to form open-chain structures that are weakly bound. However, it still takes many vibrational periods to release one monomer fragment from the open-chain structures. Our success with water and HCl dimers and trimers led us to embark on a more ambitious project: studies of mixed water and HCl small clusters. These clusters eventually lead to ionization of HCl and serve as prototypes of acid dissociation in water. Measurements and calculations of such ionizations are yet to be achieved, and we are now characterizing these systems by adding monomers one at a time. We describe our completed work on the HCl-H2O dimer and mention our recent theoretical results on larger mixed clusters. PMID:25072730

  19. Phosphino imidazoles and imidazolium salts for Suzuki C-C coupling reactions.

    PubMed

    Milde, Bianca; Schaarschmidt, Dieter; Rüffer, Tobias; Lang, Heinrich

    2012-05-01

    The consecutive syntheses of imidazoles 1-(4-X-C(6)H(4))-4,5-R(2)-(c)C(3)HN(2) (3a, X = Br, R = H; 3b, X = I, R = Me; 3c, X = H, R = Me; 5, X = Fc, R = H; 7, X = C≡CFc, R = H; 9, X = C(6)H(5), R = Me; Fc = Fe(η(5)-C(5)H(4))(η(5)-C(5)H(5))), phosphino imidazoles 1-(4-X-C(6)H(4))-2-PR'(2)-4,5-R(2)-(c)C(3)N(2) (11a-k; X = Br, I, Fc, FcC≡C, Ph; R = H, Me; R' = Ph, (c)C(6)H(11), (c)C(4)H(3)O), imidazolium salts [1-(4-X-C(6)H(4))-3-R''-4,5-R(2)-(c)C(3)HN(2)]I (16a; X = Br, R = H, R'' = n-Bu; 16b, X = Br, R = H, R'' = n-C(8)H(17); 16c, X = I, R = Me, R'' = n-C(8)H(17), 16d, X = H, R = Me, R'' = n-C(8)H(17)) and phosphino imidazolium salts [1-C(6)H(5)-2-PR'(2)-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)N(2)]PF(6) (17a, R' = C(6)H(5); 17b, R' = (c)C(6)H(11)) or [1-(4-P(C(6)H(5))(2)-C(6)H(4))-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)HN(2)]PF(6), (20) and their selenium derivatives 1-(4-X-C(6)H(4))-2-P([double bond, length as m-dash]Se)R'(2)-4,5-R(2)-(c)C(3)N(2) (11a-Se-f-Se; X = Br, I; R = H, Me; R' = C(6)H(5), (c)C(6)H(11), (c)C(4)H(3)O) are reported. The structures of 11a-Se and [(1-(4-Br-C(6)H(4))-(c)C(3)H(2)N(2)-3-n-Bu)(2)PdI(2)] (19) in the solid state were determined. Cyclovoltammetric measurements were performed with the ferrocenyl-containing molecules 5 and 7 showing reversible redox events at E(0) = 0.108 V (ΔE(p) = 0.114 V) (5) and E(0) = 0.183 V (ΔE(p) = 0.102 V) (7) indicating that 7 is more difficult to oxidise. Imidazole oxidation does not occur up to 1.3 V in dichloromethane using [(n-Bu)(4)N][B(C(6)F(5))(4)] as supporting electrolyte, whereas an irreversible reduction is observed between -1.2 - -1.5 V. The phosphino imidazoles 11a-k and the imidazolium salts 17a,b and 20, respectively, were applied in the Suzuki C-C cross-coupling of 2-bromo toluene with phenylboronic acid applying [Pd(OAc)(2)] as palladium source. Depending on the electronic character of 11a-k, 17a,b and 20 the catalytic performance of the in situ generated catalytic active species can be predicted. As assumed, more electron-rich phosphines with their higher donor capability show higher activity and productivity. Additionally, 11e was applied in the coupling of 4-chloro toluene with phenylboronic acid showing an excellent catalytic performance when compared to catalysts used by Fu, Beller and Buchwald. Furthermore, 11e is eligible for the synthesis of sterically hindered biaryls under mild reaction conditions. C-C Coupling reactions with the phosphino imidazolium salts 17b and 20 in ionic liquids [BMIM][PF(6)] and [BDMIM][BF(4)] were performed, showing less activity than in common organic solvents. PMID:22450875

  20. Evaluation of Die-Attach Bonding Using High-Frequency Ultrasonic Energy for High-Temperature Application

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Bum; Aw, Jie-Li; Rhee, Min-Woo

    2014-09-01

    Room-temperature die-attach bonding using ultrasonic energy was evaluated on Cu/In and Cu/Sn-3Ag metal stacks. The In and Sn-3Ag layers have much lower melting temperatures than the base material (Cu) and can be melted through the heat generated during ultrasonic bonding, forming intermetallic compounds (IMCs). Samples were bonded using different ultrasonic powers, bonding times, and forces and subsequently aged at 300°C for 500 h. After aging, die shear testing was performed and the fracture surfaces were inspected by scanning electron microscopy. Results showed that the shear strength of Cu/In joints reached an upper plateau after 100 h of thermal aging and remained stable with aging time, whereas that of the Cu/Sn-3Ag joints decreased with increasing aging time. η-Cu7In4 and (Cu,Au)11In9 IMCs were observed at the Cu/In joint, while Cu3Sn and (Ag,Cu)3Sn IMCs were found at the Cu/Sn-3Ag joint after reliability testing. As Cu-based IMCs have high melting temperatures, they are highly suitable for use in high-temperature electronics, but can be formed at room temperature using an ultrasonic approach.

  1. Influence of an oxygen-inhibited layer on enamel bonding of dental adhesive systems: surface free-energy perspectives.

    PubMed

    Ueta, Hirofumi; Tsujimoto, Akimasa; Barkmeier, Wayne W; Oouchi, Hajime; Sai, Keiichi; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

    2016-02-01

    The influence of an oxygen-inhibited layer (OIL) on the shear bond strength (SBS) to enamel and surface free-energy (SFE) of adhesive systems was investigated. The adhesive systems tested were Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to bovine enamel surfaces to determine the SBS, with and without an OIL, of adhesives. The SFE of cured adhesives with and without an OIL were determined by measuring the contact angles of three test liquids. There were no significant differences in the mean SBS of SM and CS specimens with or without an OIL; however, the mean SBS of SU specimens with an OIL was significantly higher than that of SU specimens without an OIL. For all three systems, the mean total SFE (?S ), polarity force (?Sp), and hydrogen bonding force (?Sh) values of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The results of this study indicate that the presence of an OIL promotes higher SBS of a single-step self-etch adhesive system, but not of a three-step or a two-step self-etch primer system. The SFE values of cured adhesives with an OIL were significantly higher than those without an OIL. The SFE characteristics of the OIL of adhesives differed depending on the type of adhesive. PMID:26647775

  2. The influence of large-amplitude librational motion on the hydrogen bond energy for alcohol-water complexes.

    PubMed

    Andersen, J; Heimdal, J; Wugt Larsen, R

    2015-10-01

    The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with methanol and t-butanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic substitution of individual subunits enabled by a dual inlet deposition procedure provides for the first time unambiguous assignments of the intermolecular high-frequency out-of-plane and low-frequency in-plane donor OH librational modes for mixed alcohol-water complexes. The vibrational assignments confirm directly that water acts as the hydrogen bond donor in the most stable mixed complexes and the tertiary alcohol is a superior hydrogen bond acceptor. The class of large-amplitude donor OH librational motion is shown to account for up to 5.1 kJ mol(-1) of the destabilizing change of vibrational zero-point energy upon intermolecular OHO hydrogen bond formation. The experimental findings are supported by complementary electronic structure calculations at the CCSD(T)-F12/aug-cc-pVTZ level of theory. PMID:26304774

  3. High-energy, stable and recycled molecular solar thermal storage materials using AZO/graphene hybrids by optimizing hydrogen bonds.

    PubMed

    Luo, Wen; Feng, Yiyu; Qin, Chengqun; Li, Man; Li, Shipei; Cao, Chen; Long, Peng; Liu, Enzuo; Hu, Wenping; Yoshino, Katsumi; Feng, Wei

    2015-10-21

    An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg(-1) by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template. PMID:26289389

  4. Low-cost bump-bonding processes for high energy physics pixel detectors

    NASA Astrophysics Data System (ADS)

    Caselle, M.; Blank, T.; Colombo, F.; Dierlamm, A.; Husemann, U.; Kudella, S.; Weber, M.

    2016-01-01

    In the next generation of collider experiments detectors will be challenged by unprecedented particle fluxes. Thus large detector arrays of highly pixelated detectors with minimal dead area will be required at reasonable costs. Bump-bonding of pixel detectors has been shown to be a major cost-driver. KIT is one of five production centers of the CMS barrel pixel detector for the Phase I Upgrade. In this contribution the SnPb bump-bonding process and the production yield is reported. In parallel to the production of the new CMS pixel detector, several alternatives to the expensive photolithography electroplating/electroless metal deposition technologies are developing. Recent progress and challenges faced in the development of bump-bonding technology based on gold-stud bonding by thin (15 μm) gold wire is presented. This technique allows producing metal bumps with diameters down to 30 μm without using photolithography processes, which are typically required to provide suitable under bump metallization. The short setup time for the bumping process makes gold-stud bump-bonding highly attractive (and affordable) for the flip-chipping of single prototype ICs, which is the main limitation of the current photolithography processes.

  5. [Study on spectral emissivity of C/C composites].

    PubMed

    Zhu, Bo; Cao, Wei-Wei; Jing, Min; Dong, Xing-Guang; Wang, Cheng-Guo

    2009-11-01

    Different types of C/C composites were prepared by conventional molding, and the changes in normal spectral emissivity of samples were tested. The testing results show that spectral emissivity of C/C composite reinforced by short cut carbon fibers is generally higher than the sample reinforced by carbon cloth in the entire 2500-13000nm wavelength region. The structure of short cut carbon fibers is relatively loose and the number of material particles is less than other samples in unit volume, which increases the penetration depth of electromagnetic waves. This is the reason for higher normal spectral emissivity and better heat radiation property. Meanwhile, the test results of normal spectral emissivity for fiber perform and C/C composite samples show that the spectral emissivity of resin carbon is better than fiber carbon because of the difference in microstructure for the two kinds of carbon materials. Laser Raman spectroscopy was employed to analyze the microstructures of different carbon materials, and the results show that because sp3 and sp2 hybrid states of carbon atoms in resin carbon produced more vibration modes, the resin carbon also has higher normal spectral emissivity and better characteristics of heat radiation. PMID:20101951

  6. Metal cation dependence of interactions with amino acids: bond energies of Rb+ to Gly, Ser, Thr, and Pro.

    PubMed

    Bowman, Vanessa N; Heaton, Amy L; Armentrout, P B

    2010-03-25

    The interactions of rubidium cations with the four amino acids (AA), glycine (Gly), serine (Ser), threonine (Thr), and proline (Pro), are examined in detail. Experimentally, the bond energies are determined using threshold collision-induced dissociation of the Rb(+)(AA) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. 0 K bond energies of 108.9 +/- 7.0, 115.7 +/- 4.9, 122.1 +/- 4.6, and 125.2 +/- 4.5 kJ/mol are determined for complexes of Rb(+) with Gly, Ser, Thr, and Pro, respectively. Quantum chemical calculations are conducted at the B3LYP, B3P86, and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and Def2TZVP basis sets. Results obtained using the former basis sets are systematically low compared to the experimental bond energies, whereas the latter basis sets show good agreement. For Rb(+)(Gly), the ground state conformer has the rubidium ion binding to the carbonyl group of the carboxylic acid, and a similar geometry is found for Rb(+)(Pro) except the secondary nitrogen accepts the carboxylic acid hydrogen to form the zwitterionic structure. Both Rb(+)(Ser) and Rb(+)(Thr) are found to have tridentate binding at the B3LYP and MP2(full) levels, whereas the B3P86 slightly prefers binding Rb(+) at the carboxylic acid. Comparison of these results to those for the lighter alkali ions provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:20184306

  7. The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Wang, Xiuyu

    2015-06-28

    The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb(1-x)Sb(x))O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb(1-x)Sb(x))O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ?(r) had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Qf and |?(f)| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion. PMID:25997635

  8. Experimental determination of the HO-Br bond energy and its relevance to the stratospheric and tropospheric ozone cycles

    SciTech Connect

    Ruscic, B.; Berkowitz, J.

    1996-02-01

    The HO-Br bond energy (and consequently the heat of formation of HOBr) has been determined experimentally for the first time. HOBr can be photolyzed in the stratosphere to form Br and OH, both of which can react with ozone, and destroy it. Previous calculations modeling stratospheric reactions have assumed a lower stability than that found in the current research. The stability of HOBr was determined by measuring the threshold for formation of Br{sup +} from this molecule, using photoionization mass spectrometry. Their work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences.

  9. Using Qualified Energy Conservation Bonds (QECBs) to Fund a Residential Energy Efficiency Loan Program: Case Study on Saint Louis County, MO

    SciTech Connect

    Zimring, Mark

    2011-06-23

    Qualified Energy Conservation Bonds (QECBs) are federally-subsidized debt instruments that enable state, tribal, and local government issuers to borrow money to fund a range of qualified energy conservation projects. QECBs offer issuers very attractive borrowing rates and long terms, and can fund low-interest energy efficiency loans for home and commercial property owners. Saint Louis County, MO recently issued over $10 million of QECBs to finance the Saint Louis County SAVES residential energy efficiency loan program. The county's experience negotiating QECB regulations and restrictions can inform future issuers.

  10. Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Surface coating materials for application on transport type aircraft to reduce drag, were investigated. The investigation included two basic types of materials: spray on coatings and adhesively bonded films. A cost/benefits analysis was performed, and recommendations were made for future work toward the application of this technology.

  11. Performance and Reliability of Bonded Interfaces for High-Temperature Packaging; NREL (National Renewable Energy Laboratory)

    SciTech Connect

    DeVoto, Douglas

    2015-06-10

    This is a technical review of the DOE VTO EDT project EDT063, Performance and Reliability of Bonded Interfaces for High-Temperature Packaging. A procedure for analyzing the reliability of sintered-silver through experimental thermal cycling and crack propagation modeling has been outlined and results have been presented.

  12. Quantification of C?C and C?O Surface Carbons in Detonation Nanodiamond by NMR

    SciTech Connect

    Cui, J -F; Fang, X -W; Schmidt-Rohr, K

    2014-05-08

    The ability of solid-state 13C NMR to detect and quantify small amounts of sp2-hybridized carbon on the surface of ?5 nm diameter nanodiamond particles is demonstrated. The C?C carbon fraction is only 1.1 0.4% in pristine purified detonation nanodiamond, while a full single-layer graphitic or bucky diamond shell would contain ca. 25% of all C in a 5 nm diameter particle. Instead of large aromatic patches repeatedly proposed in the recent literature, sp3-hybridized CH and COH carbons cover most of the nanodiamond particle surface, accounting for ?5% each. C?O and COO groups also seen in X-ray absorption near-edge structure spectroscopy (XANES) but not detected in previous NMR studies make up ca. 1.5% of all C. They are removed by heat treatment at 800 C, which increases the aromatic fraction. 13C{1H} NMR demonstrates that the various sp2-hybridized carbons are mostly not protonated, but cross-polarization shows that they are separated from 1H by only a few bond lengths, which proves that they are near the protonated surface. Together, the observed CH, COH, C?O, and C?C groups account for 1214% of all C, which matches the surface fraction expected for bulk-terminated 5 nm diameter diamond particles.

  13. Catalysis of the Aza-Diels-Alder Reaction by Hydrogen and Halogen Bonds.

    PubMed

    Nziko, Vincent de Paul N; Scheiner, Steve

    2016-03-18

    The combination of H2C═NH and cis-1,3-butadiene to form a six-membered ring was examined by quantum calculations. The energy barrier for this reaction is substantially lowered by the introduction of an imidazolium catalyst with either a H or halogen (X) atom in the 2-position, which acts via a H or halogen bond to the N atom of the imine, respectively. X = I has the largest effect, and Cl the smallest; Br and H are roughly equivalent. The catalyst retards the formation of the incipient N-C bond from imine to diene while simultaneously accelerating the C-C bond formation. The energy of the π* LUMO of the imine is lowered by the catalyst, which thereby enhances charge transfer from the diene to the imine. Assessment of free energies suggests catalytic rate acceleration by as much as 4-6 orders of magnitude. PMID:26907727

  14. The influence of the energy density and other clinical parameters on bond strength of Er:YAG-conditioned dentin compared to conventional dentin adhesion.

    PubMed

    Gisler, Gottfried; Gutknecht, Norbert

    2014-01-01

    The aim of this in vitro study was to optimise clinical parameters and the energy density of Er:YAG laser-conditioned dentin for class V fillings. Shear tests in three test series were conducted with 24 freshly extracted human third molars as samples for each series. For every sample, two orofacial and two approximal dentin surfaces were prepared. The study design included different laser energies, a thin vs a thick bond layer, the influence of adhesives as well as one-time- vs two-time treatment. The best results with Er:YAG-conditioned dentin were obtained with fluences just above the ablation threshold (5.3 J/cm(2)) in combination with a self-etch adhesive, a thin bond layer and when bond and composite were two-time cured. Dentin conditioned this way reached an averaged bond strength of 23.32 MPa (SD 5.3) and 24.37 MPa (SD 6.06) for two independent test surfaces while showing no statistical significance to conventional dentin adhesion and two-time treatment with averaged bond strength of 24.93 MPa (SD 11.51). Significant reduction of bond strength with Er:YAG-conditioned dentin was obtained when using either a thick bond layer, twice the laser energy (fluence 10.6 J/cm(2)) or with no dentin adhesive. The discussion showed clearly that in altered (sclerotic) dentin, e.g. for class V fillings of elderly patients, bond strengths in conventional dentin adhesion are constantly reduced due to the change of the responsibles, bond giving dentin structures, whereas for Er:YAG-conditioned dentin, the only way to get an optimal microretentive bond pattern is a laser fluence just above the ablation threshold of sclerotic dentin. PMID:23224751

  15. Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of Etbnd UX3 (E = N, P, CH; X = H, F, Cl)

    NASA Astrophysics Data System (ADS)

    Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

    2014-12-01

    Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [Etbnd UX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of Utbnd N bond in [Ntbnd UF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate Utbnd N vibrational frequencies follows the order BLYP > revPBE > BP86 > PW91 > TPSS > PBE > M06-L. The BLYP functional gives accurate value of the Utbnd E bond distances. The uranium atom in the studied compounds [Etbnd UX3] is positively charged. Upon going from [Etbnd UF3] to [Etbnd UCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for Utbnd E bonds ranges from 2.90 to 3.29. The Utbnd E bond dissociation energies vary with different density functionals as M06-L < TPSS < BLYP < revPBE < BP86 < PBE ≈ PW91. The orbital interactions ΔEorb, in all studied compounds [Etbnd UX3] are larger than the electrostatic interaction ΔEelstat, which means the Utbnd N bonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The Usbnd E σ-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [Ptbnd UX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

  16. Thermal chemiluminescence from ?-irradiated polytetrafluoroethylene and its emission mechanism: Kinetic analysis and bond dissociation energy of fluoroperoxide group

    NASA Astrophysics Data System (ADS)

    Yamada, Emi; Noguchi, Tsuyoshi; Akai, Nobuyuki; Ishii, Hiroshi; Satoh, Chikahiro; Hironiwa, Takayuki; Millington, Keith R.; Nakata, Munetaka

    2014-11-01

    Temperature dependence of the time evolution of chemiluminescence intensity from ?-irradiated polytetrafluoroethylene was examined by heating isothermally in the range of 150 and 200 C. Kinetic analysis was carried out to estimate the rate constants, from which the dissociation energy of the Osbnd O bond in the fluoroperoxide group was determined to be 97 4 kJ mol-1, being consistent with the corresponding value for small fluorocarbon model systems obtained by quantum chemical calculations. This strongly supports the emission mechanism [sbnd CF(OOF)sbnd CF2sbnd ? sbnd COsbnd CF2sbnd + OF2 + h?] proposed in our previous paper to explain chemiluminescence from the ?-irradiated polytetrafluoroethylene.

  17. Energy transport mechanism in the form of proton soliton in a one-dimensional hydrogen-bonded polypeptide chain.

    PubMed

    Kavitha, L; Priya, R; Ayyappan, N; Gopi, D; Jayanthi, S

    2016-01-01

    The dynamics of protons in a one-dimensional hydrogen-bonded (HB) polypeptide chain (PC) is investigated theoretically. A new Hamiltonian is formulated with the inclusion of higher-order molecular interactions between peptide groups (PGs). The wave function of the excitation state of a single particle is replaced by a new wave function of a two-quanta quasi-coherent state. The dynamics is governed by a higher-order nonlinear Schrödinger equation and the energy transport is performed by the proton soliton. A nonlinear multiple-scale perturbation analysis has been performed and the evolution of soliton parameters such as velocity and amplitude is explored numerically. The proton soliton is thermally stable and very robust against these perturbations. The energy transport by the proton soliton is more appropriate to understand the mechanism of energy transfer in biological processes such as muscle contraction, DNA replication, and neuro-electric pulse transfer on biomembranes. PMID:26198375

  18. Accurate energies of hydrogen bonded nucleic acid base pairs and triplets in tRNA tertiary interactions

    PubMed Central

    2006-01-01

    Tertiary interactions are crucial in maintaining the tRNA structure and functionality. We used a combined sequence analysis and quantum mechanics approach to calculate accurate energies of the most frequent tRNA tertiary base pairing interactions. Our analysis indicates that six out of the nine classical tertiary interactions are held in place mainly by H-bonds between the bases. In the remaining three cases other effects have to be considered. Tertiary base pairing interaction energies range from ?8 to ?38 kcal/mol in yeast tRNAPhe and are estimated to contribute roughly 25% of the overall tRNA base pairing interaction energy. Six analyzed posttranslational chemical modifications were shown to have minor effect on the geometry of the tertiary interactions. Modifications that introduce a positive charge strongly stabilize the corresponding tertiary interactions. Non-additive effects contribute to the stability of base triplets. PMID:16461956

  19. Evidence of a long C-C attractive interaction in cerussite mineral: QTAIM and ELF analyses.

    PubMed

    Vidal, Isaac; Navas, Antonio Snchez

    2014-09-01

    Cerussite, an orthorhombic lead carbonate mineral, has a structure and physical properties that cannot be understood merely in terms of ionic anion-cation interactions. The nature of the chemical bonding in cerussite is analyzed by means of the quantum theory of atoms in molecules (QTAIM) and the analysis of the electron localization function (ELF). A long C-C attractive interaction (3.077 ) along the c axis of the cerussite structure is evidenced by the presence of bond critical points between the C atoms of the CO(3)(2-) molecular groups. It is proposed that the Pb-O interactions, which are mostly ionic in nature, disturb the structure of the CO(3)(2-) molecular groups and promote their interaction along the c axis. The importance of this long-range interaction in the high-pressure crystal chemistry of carbonate minerals and in the explanation of some crystal growth features observed for orthorhombic carbonates is also discussed in this work. PMID:25129662

  20. Chemical Bonds I

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

  1. Linear free energy relationships reveal structural changes in hydrogen-bonded host-guest interactions.

    PubMed

    McGrath, Jacqueline M; Pluth, Michael D

    2014-12-01

    Hydrogen bond strength in host-guest systems is modulated by many factors including preorganization, steric effects, and electronic effects. To investigate how electronic effects impact barbiturate binding in bifurcated Hamilton receptors, a library of receptors with differing electronic substituents was synthesized and (1)H NMR titrations were performed with diethyl barbital. The Hammett plot revealed a clear break between the different electronic substituents suggesting a change in binding conformation. The titration data were complimented with computational studies confirming the change in structure. PMID:25412431

  2. Linear Free Energy Relationships Reveal Structural Changes in Hydrogen-Bonded HostGuest Interactions

    PubMed Central

    2015-01-01

    Hydrogen bond strength in hostguest systems is modulated by many factors including preorganization, steric effects, and electronic effects. To investigate how electronic effects impact barbiturate binding in bifurcated Hamilton receptors, a library of receptors with differing electronic substituents was synthesized and 1H NMR titrations were performed with diethyl barbital. The Hammett plot revealed a clear break between the different electronic substituents suggesting a change in binding conformation. The titration data were complimented with computational studies confirming the change in structure. PMID:25412431

  3. Electrophilic, Ambiphilic, and Nucleophilic C-H bond Activation. Understanding the electronic continuum of C-H bond activation through transition-state and reaction pathway interaction energy decompositions

    SciTech Connect

    Ess, Daniel H.; Goddard, William A.; Periana, Roy A.

    2010-10-29

    The potential energy and interaction energy profiles for metal- and metal-ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d8, d6, d4, and d0), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal-ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, σ-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in metathesis reactions with W(II) and Sc(III) metal center complexes in reactions as well as late transition metal Ir(I) and Rh(I) pincer complexes that undergo C-H bond insertion. Comparison of pincer ligands shows that the PCP ligand imparts more nucleophilic character to an Ir metal center than a deprotonated PNP ligand. The PCP and POCOP ligands do not show a substantial difference in the electronics of C-H activation. It was also found that Rh(I) is substantially more nucleophilic than Ir(I). Lastly, as a qualitative approximation, investigation of transition-state fragment orbital energies showed that relative frontier orbital energy gaps correctly reflect electrophilic, ambiphilic, or nucleophilic charge-transfer stabilization patterns.

  4. C,C-diacetylenic phosphaalkenes as heavy diethynylethene analogues.

    PubMed

    Oberg, Elisabet; Schäfer, Bernhard; Geng, Xue-Li; Pettersson, Jenny; Hu, Qi; Kritikos, Mikael; Rasmussen, Torben; Ott, Sascha

    2009-12-18

    A series of C,C-diacetylenic phosphaalkenes 1b-e has been prepared from 1-chloropenta-1,2-dien-4-ynes 6b-e in a reaction with Mes*PCl(2) (Mes* = 2,4,6-((t)Bu)(3)Ph) in the presence of LDA. Under identical conditions, isomeric butadiyne-substituted phosphaalkenes 2c-f can be obtained from 3-chloropenta-1,4-diynes 5c-f. The title compounds represent rare examples of diethynylethenes in which a constituting methylene has been replaced by a phosphorus center. The formation of both isomers can be rationalized by a common pathway that involves isomeric allenyllithium species. Spectroscopic, electrochemical, and theoretical investigations show that the phosphorus heteroatoms are an intrinsic part of the compounds' pi-systems and lead to decreased HOMO-LUMO gaps compared to those in all-carbon-based reference compounds. PMID:19911774

  5. Defect structures in deformed F.C.C. metals

    SciTech Connect

    Dai, Y.; Victoria, M.

    1997-08-01

    A high density of small defect clusters, similar to those observed in irradiated or quenched metals, has been observed in the deformed f.c.c. metals Cu, Au and Ni. The preliminary results show that the defect clusters are predominantly stacking fault tetrahedral (SFT). The SFT number density, rather than the size distribution, is deformation dependent. The defect cluster density is greater in the vicinities of dislocation tangles and grain boundaries. Their size distribution is wider than that produced by irradiation with an important number of larger clusters being formed. It is argued that these deformation-produced clusters may play a role in determining the flow stress and work hardening at low deformations.

  6. Gas-phase structures of perfluorotetrahydrothiophene, c-C 4F 8S, tetrahydrothiophene-1-oxide, c-C 4F 8SO, and tetrahydrothiophene-1,1-dioxide, c-C 4F 8SO 2

    NASA Astrophysics Data System (ADS)

    Mack, Hans-Georg; Oberhammer, Heinz; Shreeve, Jean'ne M.; Xia, X.-B.

    1989-05-01

    The geometric structures of the three title compounds have been determined by gas-phase electron diffraction. In all cases the five-membered rings are strongly puckered and possess half chair conformations with the following geometric parameters ( ra values with 3? error limits). c-C 4F 8S: (C?C) mean=1.548(4), S?C=1.822(4) , CSC=94.5(3), SCC=107.4(3), CCC=106.4(4) and puckering amplitude q=0.411(8) . c-C 4F 8SO: (C?C) mean=1.553(5), S?C=1.903(4) , CSC=89.4(4), SCC=110.2(4), CCC=106.5(6), q=0.403(8) . c-C 4F 8SO 2: (C?C) mean=1.556(6), S?C=1.882(7) , CSC=93.2(10), SCC=107.7(10), CCC=107.9(12), q=0.382(10) . Comparison with the analogous protonated rings reveals that upon fluorination the degree of puckering decreases slightly in c-C 4F 8S and c-C 4F 8SO, whereas it increases strongly in c-C 4F 8SO 2.

  7. Sticker Bonding.

    ERIC Educational Resources Information Center

    Frazier, Laura Corbin

    2000-01-01

    Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

  8. Bond Issues.

    ERIC Educational Resources Information Center

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of

  9. Reactions of heteronuclear dimetalated olefin complexes. Reactions of CpFe-(CO){sub 2}[{mu}-(Z)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]Re -(CO){sub 4} with CO and p-tolyl isothiocyanate

    SciTech Connect

    Adams, R.D.; Huang, M.

    1995-10-01

    Addition of CO to the dimetalated olefin complex CpFe(CO){sub 2} [{mu}-(Z)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 4}, 1, at 25{degree}C/700 psi of CO resulted in the formation of the adduct CpFe(CO){sub 2}[{mu}-(E)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 5} , 2, in 52% yield by cleavage of the Re-O bond to the coordinated carboxylate group. In contrast the reaction of 1 with CO at 70{degree}C/ 900 psi of CO provided the new compound CpFe(CO){sub 2} [{mu}-(Z)-C=O(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 4}, 3, in 77% yield. Compounds 2 and 3 were characterized by single-crystal X-ray diffraction analyses. Compound 2 is a Z-dimetalated olefin formed by addition of CO to the Re(CO){sub 4} group in 1, C-C = 1. 35(1) Hi. Compound 3 is an isomer of 2 in which a CO was added to 1 and inserted into the iron-carbon bond to the alkyne. Compound 1 reacts with EtNH{sub 2} or H{sub 2}O to yield the new compound CpFe(CO){sub 2}[(MeO{sub 2}C)C=C(CO{sub 2}Me)(H)], 6, by the cleavage of the rhenium grouping from the molecule. The reaction with H{sub 2}O is catalyzed by silica gel. 22 refs., 3 figs., 6 tabs.

  10. Influence of Ti nanocrystallization on microstructure, interface bonding, surface energy and blood compatibility of surface TiO 2 films

    NASA Astrophysics Data System (ADS)

    Shao, Honghong; Yu, Chunhang; Xu, Xiaojing; Wang, Ji; Zhai, Rui; Wang, Xiaojing

    2010-12-01

    Recent progress in ultrafine-grained/nano-grained (UFG/NG) titanium permits a consideration for TiO 2 films deposited on nano-grained titanium for antithrombogenic application such as artificial valves and stents. For this paper, the microstructure, interface bonding, surface energy, and blood compatibility features of TiO 2 films deposited by direct current magnetron reactive sputtering technology on NG titanium and coarse-grained (CG) titanium were investigated. The results show that the nanocrystallization of titanium substrate has a significant influence on TiO 2 films. At the same deposition parameters, the content of rutile phase of TiO 2 film was increased from 47% (on the CG titanium substrate) to 72% (on the NG titanium substrate); the adhesion of TiO 2 film was improved from 5.8 N to 17 N; the surface energy was reduced from 6.37 dyn/cm to 3.01 dyn/cm; the clotting time was improved from 18 min to 28 min; the platelets accumulation and pseudopodium of adherent platelets on TiO 2 film on NG titanium were considerably reduced compared to that on CG titanium. The present results demonstrate the possibility of improving the blood compatibility of TiO 2 film through the approach of substrate nanocrystallization. Also it may provide an attractive idea to prepare stents with biological coatings of more outstanding blood compatibility and interface bonding.

  11. Describing the chemical bonding in C70 and C70O3 - A quantum chemical topology study

    NASA Astrophysics Data System (ADS)

    Bil, Andrzej; Latajka, Zdzis?aw; Hutter, Jrg; Morrison, Carole A.

    2014-03-01

    Cc-Cc and Ca-Cb bonds in C70 have dominant characteristics of double bonds, whereas the remaining six other types of bonds are single bonds with contributions from ?-electron density. 'Single' bonds can act as active sites in chemical reactions which would typically require a multiple bond, such as addition of an ozone molecule, due to the fact that all adjacent bonds can serve as an efficient source of ?-electron density. Thus any alteration in the electron density distribution following functionalization has far-reaching impact. We note that formation of the most stable ozonide isomer causes the smallest total perturbation in the electron density of the parent fullerene and C-C bond evolution correlates well with the shape of the minimum energy path for the ozone ring opening reaction on the fullerene surface. Finally, we observe that the O-O bond in C70O3 is protocovalent, and as such resembles the O-O bond in H2O2.

  12. Theoretical studies of pentene cracking on zeolites: C-C beta-scission processes

    SciTech Connect

    Hay, P.J.; Redondo, A.; Guo, Y.

    1997-04-01

    The nature of the molecular species involved in the cracking of hydrocarbons into smaller fragments over zeolite catalysts has been studied extensively, as the advent of zeolites such as faujasite to carry out these transformations more selectively has revolutionized the petroleum refining technology. While the nature of the acid-catalyzed process involving proposed carbocationic species has been proposed for nearly fifty years, there have been extensive studies involving heterogeneous processes and analogs with solution superacid chemistry to elucidate these mechanisms more clearly and to attempt to detect the intermediates involved in these reactions. Also in recent years there have been an increasing number of theoretical studies on the nature of the acid sites in zeolites, the interactions of these acid sites with adsorbates including hydrocarbons, and on simple reactions of hydrocarbon species using model systems to represent the zeolite. In this study the authors report the results of ab initio and density functional studies on one aspect--the beta-scission C-C bond-breaking step--that arises in the cracking process of alkanes and alkenes. The authors focus on the species arising from pentene adsorption on an acid site and the subsequent cracking of this C{sub 5} species as an illustration of the carbon-carbon bond-breaking step. In these studies they employ a simple three-T-site to represent the immediate vicinity of the acid site in faujasite comprised of the Si-O-Al-OH-O-Si skeleton with the unsatisfied bonds terminated by hydrogens. They study the reaction of the 2-pentyl cation undergoing beta-scission in the gas phase to form propene and the ethyl cation and the corresponding reaction on the zeolite cluster. The structures of the reactants, products and transition states are determined using ab initio electronic structure techniques.

  13. Evaluation of the hydrogen bond energy of base pairs formed between substituted 9-methyladenine derivatives and 1-methyluracil by use of molecular orbital theory.

    PubMed

    Kawahara, S; Taira, K; Sekine, M; Uchimaru, T

    2000-01-01

    Systematic substituent effects on the stability of the hydrogen bonding between substituted 9-methyladenine derivatives (Ax) and 1-methyluracil (U) were studied by ab initio molecular orbital theory. Predicted substituent effects on the hydrogen bond energies of Ax-U base pairs were in good agreement with those observed for experimental binding constants. Ab initio calculation is effective for evaluation of the stability of the hydrogen-bonding pairs of chemically modified nucleic acid base analogues. In contrast to the substitution effect of uracil on hydrogen bond energies of A-Ux base pairs, it is difficult to systematically interpret the substitution effect of adenine derivatives for Ax-U base pairs. PMID:12903356

  14. A DFT study of cyclopropane adsorption on Pt(1 1 1). Electronic structure and bonding

    NASA Astrophysics Data System (ADS)

    Germn, E.; Lpez-Corral, I.; Pirillo, S.; Juan, A.; Brizuela, G.

    2014-06-01

    We have studied the adsorption of cyclopropane (c-C3H6) on Pt(1 1 1) by means of the density functional theory (DFT). We have investigated the preferential adsorption geometry, considering different adsorption sites and bonding configurations for the molecular adsorbate. We have also computed the electronic structure and bonding interactions by means of density of states (DOS), crystal orbital overlap population (OPDOS), and overlap population (OP) analysis. Our results show a small preference for Bridge and Top adsorption sites with the cyclopropane ring parallel to the surface. Ptsbnd C equilibrium distance is 3.5 and a weak bond is formed during adsorption. The main bonding interaction comes from the Ptsbnd H overlap population. Pt 5pz orbitals play an important role in the bonding between c-C3H6 and the surface. We have found that Van der Waals (vdW) corrections to the energies improve the adsorption values without changing the preferential site geometries.

  15. Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Arnold, James (Technical Monitor)

    1999-01-01

    The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

  16. Amino Acid Mean Excitation Energies and Directional Dependencies from Core and Bond Calculations

    SciTech Connect

    Sabin, John R.; Oddershede, Jens; Sauer, Stephan P. A.

    2008-12-08

    We determine the mean excitation energies of several amino acids using a Bragg Rule developed for molecular fragments or functional groups. As the composition of the amino acids is very similar, we find that the amino acids have similar mean excitation energies (approximately 70 eV). Differences arise from variation of the side chains (-R); addition of-CH2-groups decreases the mean excitation energy. We also speculate concerning the directional dependence of the amino acid mean excitation energies.

  17. Unexpected interplay of bonding height and energy level alignment at heteromolecular hybrid interfaces.

    PubMed

    Stadtmller, Benjamin; Lftner, Daniel; Willenbockel, Martin; Reinisch, Eva M; Sueyoshi, Tomoki; Koller, Georg; Soubatch, Serguei; Ramsey, Michael G; Puschnig, Peter; Tautz, F Stefan; Kumpf, Christian

    2014-01-01

    Although geometric and electronic properties of any physical or chemical system are always mutually coupled by the rules of quantum mechanics, counterintuitive coincidences between the two are sometimes observed. The coadsorption of the organic molecules 3,4,9,10-perylene tetracarboxylic dianhydride and copper-II-phthalocyanine on Ag(111) represents such a case, since geometric and electronic structures appear to be decoupled: one molecule moves away from the substrate while its electronic structure indicates a stronger chemical interaction, and vice versa for the other. Our comprehensive experimental and ab-initio theoretical study reveals that, mediated by the metal surface, both species mutually amplify their charge-donating and -accepting characters, respectively. This resolves the apparent paradox, and demonstrates with exceptional clarity how geometric and electronic bonding parameters are intertwined at metal-organic interfaces. PMID:24739211

  18. Substituent Effects in CH Hydrogen Bond Interactions: Linear Free Energy Relationships and Influence of Anions.

    PubMed

    Tresca, Blakely W; Hansen, Ryan J; Chau, Calvin V; Hay, Benjamin P; Zakharov, Lev N; Haley, Michael M; Johnson, Darren W

    2015-12-01

    Aryl CH hydrogen bonds (HBs) are now commonly recognized as important factors in a number of fields, including molecular biology, stereoselective catalysis, and anion supramolecular chemistry. As the utility of CH HBs has grown, so to has the need to understand the structure-activity relationship for tuning both their strength and selectivity. Although there has been significant computational effort in this area, an experimental study of the substituent effects on CH HBs has not been previously undertaken. Herein we disclose a systematic study of a single CH HB by using traditional urea donors as directing groups in a supramolecular binding cavity. Experimentally determined association constants are examined by a combination of computational (electrostatic potential) and empirical (?m and ?p) values for substituent effects. The dominance of electrostatic parameters, as observed in a computational DFT study, is consistent with current CH HB theory; however, a novel anion dependence of the substituent effects is revealed in solution. PMID:26539974

  19. On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl

    SciTech Connect

    Ruscic, Branko; Wagner, Albert F.; Harding, Lawerence B.; Asher, Robert L.; Feller, David F. ); Dixon, David A. ); Peterson, Kirk A.; Song, Yang; Qian, Ximei; Ng, C Y.; Liu, Jianbo; Wenwu, Chen

    2001-12-01

    Several photoionization experiments utilizing the positive ion cycle to derive the O-H bond energy converge to a consensus value of AE0(OH+/H2O)= 146117? 24 cm-1 (18.1162? 0.0030 eV). With the most accurate currently available ZEKE value. IE(OH)= 104989? 2 cm-1, corroborated by a number of photoelectron measurements,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined. this leads to D0(H?OH)= 41128? 24 cm-1= 117.59? 0.07 kcal/mol. This corresponds to DHf 0(OH)= 8.85? 0.07 kcal/mol, and implies D0(OH)= 35593? 24 cm-1= 101.76? 0.07 kcal/mol. The most sophisticated theoretical calculations performed so far on the HxO system, CCSD(T)/aug-cc-pVnZ, n=Q, 5, 6, and 7, extrapolated to the CBS limit and including corrections for core-valence effects, scalar relativistic effects, incomplete correlation recovery, and diagonal Born-Oppenheimer corrections reproduce the experimental results to within 0.0 - 0.2 k cal/mol. The new values of the two successive bond dissociation energies of water supersede the previously accepted values,Error! Bookmark not defined.,Error! Bookmark not defined. which were based on spectroscopic determinationsError! Bookmark not defined.,Error! Bookmark not defined. of D0(OH) using a very short Birge-Sponer extrapolation on OH/OD A1S+. An exhaustive analysis of the latter approach, combined with the application of the same procedure on a calculated potential energy curve for the state in question, demonstrates that the Birge-Sponer extrapolation underestimates the bond dissociation energy, in spite of the fact that only the last vibrational level was not observed experimentally. The new values affect a large number of other thermochemical quantities which directly or indirectly rely on or refer to D0(H-OH), D0(OH), or DHf?(OH).

  20. A Simple Test to Determine the Effectiveness of Different Braze Compositions for Joining Ti-Tubes to C/C Composite Plates

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Singh, Mrityunjay; Shpargel, Tarah; Asthana, Rajiv

    2006-01-01

    A simple tube-plate joint tensile test was implemented to compare the effectiveness of commercial brazes, namely, TiCuNi, TiCuSil, and Cu-ABA, used for bonding Ti-tubes joined to C-C composite plates. The different braze systems yielded different; yet, repeatable results. The Cu-ABA system proved to have about twice the load-carrying ability of the other two systems due to the fact that the bonded area between the braze material and the C-C plate was largest for this system. The orientation of the surface fiber tows also had a significant effect on load-carrying ability with tows oriented perpendicular to the tube axis displaying the highest failure loads. Increasing the process load and modifying the surface of the C-C plate by grooving out channels for the Ti-Tube to nest in resulted in increased load-carrying ability for the TiCuSil and Cu-ABA systems due to increased bonded area and better penetration of the braze material into the C-C composite.

  1. Transition-metal catalysed C-N bond activation.

    PubMed

    Wang, Quanjun; Su, Yijin; Li, Lixin; Huang, Hanmin

    2016-02-29

    Transition-metal catalysed C-N bond activation has attracted much attention and become one of the most promising bond disconnection and formation strategies that encompass a broad spectrum of applications in many reactions. In this tutorial review, efficient strategies for catalytic cleavage of C(sp)-N, C(sp(2))-N and C(sp(3))-N bonds and their applications in new C-C and C-N bond formation reactions are summarized. PMID:26764537

  2. Surface-catalyzed C-C covalent coupling strategies toward the synthesis of low-dimensional carbon-based nanostructures.

    PubMed

    Fan, Qitang; Gottfried, J Michael; Zhu, Junfa

    2015-08-18

    Carbon-based nanostructures have attracted tremendous interest because of their versatile and tunable properties, which depend on the bonding type of the constituting carbon atoms. Graphene, as the most prominent representative of the π-conjugated carbon-based materials, consists entirely of sp(2)-hybridized carbon atoms and exhibits a zero band gap. Recently, countless efforts were made to open and tune the band gap of graphene for its applications in semiconductor devices. One promising method is periodic perforation, resulting in a graphene nanomesh (GNM), which opens the band gap while maintaining the exceptional transport properties. However, the typically employed lithographic approach for graphene perforation is difficult to control at the atomic level. The complementary bottom-up method using surface-assisted carbon-carbon (C-C) covalent coupling between organic molecules has opened up new possibilities for atomically precise fabrication of conjugated nanostructures like GNM and graphene nanoribbons (GNR), although with limited maturity. A general drawback of the bottom-up approach is that the desired structure usually does not represent the global thermodynamic minimum. It is therefore impossible to improve the long-range order by postannealing, because once the C-C bond formation becomes reversible, graphene as the thermodynamically most stable structure will be formed. This means that only carefully chosen precursors and reaction conditions can lead to the desired (non-graphene) material. One of the most popular and frequently used organic reactions for on-surface C-C coupling is the Ullmann reaction of aromatic halides. While experimentally simple to perform, the irreversibility of the C-C bond formation makes it a challenge to obtain long-range ordered nanostructures. With no postreaction structural improvement possible, the assembly process must be optimized to result in defect-free nanostructures during the initial reaction, requiring complete reaction of the precursors in the right positions. Incomplete connections typically result when mobile precursor monomers are blocked from reaching unsaturated reaction sites of the preformed nanostructures. For example, monomers may not be able to reach a randomly formed internal cavity of a two-dimensional (2D) nanostructure island due to steric hindrance in 2D confinement, leaving reaction sites in the internal cavity unsaturated. Wrong connections between precursor monomers, here defined as intermolecular C-C bonds forcing the monomer into a nonideal position within the structure, are usually irreversible and can induce further structural defects. The relative conformational flexibility of the monomer backbones permits connections between deformed monomers when they encounter strong steric hindrance. This, however, usually leads to heterogeneous structural motifs in the formed nanostructures. This Account reviews some of the latest developments regarding on-surface C-C coupling strategies toward the synthesis of carbon-based nanostructures by addressing the above-mentioned issues. The strategies include Ullmann coupling and other, "cleaner" alternative C-C coupling reactions like Glaser coupling, cyclo-dehydrogenation, and dehydrogenative coupling. The choice of substrate materials and precursor designs is crucial for optimizing substrate reactivity and precursor diffusion rates, and to reduce events of wrong linkage. Hierarchical polymerization is employed to steer the coupling route, which effectively improves the completeness of the reaction. Effects of byproducts on nanostructure formation is comprehended with both experimental and theoretical studies. PMID:26194462

  3. The Electronegativity Analysis of c-C4F8 as a Potential Insulation Substitute of SF6

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaoling; Jiao, Juntao; Li, Bing; Xiao, Dengming

    2016-03-01

    The density distributions related to gas electronegativity for c-C4F8 gas, including negative ion, electron number and electron energy densities in the discharge process, are derived theoretically in both plane-to-plane and point-to-plane electrode geometries. These calculations have been performed through the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment and a fluid model in the condition of both uniform and non-uniform electric fields. The electronegativity coefficients a = n‑/ne of c-C4F8 and SF6 are compared to further describe the electron affinity of c-C4F8. The result shows that c-C4F8 represents an obvious electron-attachment performance in the discharge process. However, c-C4F8 still has much weaker gas electronegativity than SF6, whose electronegativity coefficient is lower than that of SF6 by at least three orders of magnitude. supported by National Natural Science Foundation of China (No. 51337006)

  4. Bonding analyses, formation energies, and vibrational properties of M-R2dtc complexes (M=Ag(I), Ni(II), Cu(II), or Zn(II)).

    PubMed

    Georgieva, I; Trendafilova, N

    2007-12-20

    Detailed theoretical studies based on density functional theory (DFT)/B3LYP calculations of dimethyl- and diethyldithiocarbamate complexes of Ni(II), Cu(II), Zn(II), and Ag(I) are performed to characterize the metal-ligand bonding type as well as the metal-ligand bonding strength depending on the metal and the dialkyl substituent. The metal-ligand interactions in the studied complexes are investigated by means of charge decomposition analysis, energy partitioning analysis (EPA), and natural bond orbital analysis. According to the EPA calculations, the electrostatic attraction is the dominant contribution to the M-S2(R2dtc) (dtc=dithiocarbamate) bonding. The electrostatic and the orbital energies follow the order of the total binding energy, and hence both contributions are responsible for the binding energy order of M(R2dtc)2 complexes. The stability of the M(R2dtc)2 complexes is estimated by means of calculated formation reaction energies in the gas phase and solution, and it decreases in the order Ni(R2dtc)2>Cu(R2dtc)2>Zn(R2dtc)2. Larger formation reaction energies are found for M(Et2dtc)2 than for M(Me2dtc)2 complexes. The calculations predict stabilization of M(II)(R2dtc)2 complexes going from the gas phase to a polar solvent and destabilization of the bidentate AgR2dtc complex in a polar solvent. Gas-phase frequency calculations of all possible bonding types, symmetrical, asymmetrical, and uni- and bidentate, predict one band due to the nu(CS) IR absorption, and therefore the number of the bands in the 1060-920 cm(-1) region could not be used to discern the metal-ligand bonding type. Periodic DFT frequency calculations for Cu(Et2dtc)2 reveal that the splitting observed in the solid-state spectra of the complexes arises from the nonplanar MS4 fragment and intermolecular contacts but not from asymmetrical bonding. The calculations suggest that the important vibrational characteristic that can be used to discern uni- and bidentate bonding is the Raman activity of the nu(CS) band: It is very high for the unidentate dtc bonding (nu(C=S)) and low for the bidentate bonding (nuas(CS)). PMID:18034466

  5. JMS Proxy and C/C++ Client SDK

    NASA Technical Reports Server (NTRS)

    Wolgast, Paul; Pechkam, Paul

    2007-01-01

    JMS Proxy and C/C++ Client SDK (JMS signifies "Java messaging service" and "SDK" signifies "software development kit") is a software package for developing interfaces that enable legacy programs (here denoted "clients") written in the C and C++ languages to communicate with each other via a JMS broker. This package consists of two main components: the JMS proxy server component and the client C library SDK component. The JMS proxy server component implements a native Java process that receives and responds to requests from clients. This component can run on any computer that supports Java and a JMS client. The client C library SDK component is used to develop a JMS client program running in each affected C or C++ environment, without need for running a Java virtual machine in the affected computer. A C client program developed by use of this SDK has most of the quality-of-service characteristics of standard Java-based client programs, including the following: Durable subscriptions; Asynchronous message receipt; Such standard JMS message qualities as "TimeToLive," "Message Properties," and "DeliveryMode" (as the quoted terms are defined in previously published JMS documentation); and Automatic reconnection of a JMS proxy to a restarted JMS broker.

  6. Natural energy decomposition analysis: An energy partitioning procedure for molecular interactions with application to weak hydrogen bonding, strong ionic, and moderate donor-acceptor interactions

    NASA Astrophysics Data System (ADS)

    Glendening, Eric D.; Streitwieser, Andrew

    1994-02-01

    We present a procedure for partitioning the Hartree-Fock self-consistent-field (SCF) interaction energy into electrostatic, charge transfer, and deformation components. The natural bond orbital (NBO) approach of Weinhold and co-workers is employed to construct intermediate supermolecule and fragment wave functions that satisfy the Pauli exclusion principle, thereby avoiding the principal deficiency of the popular Kitaura-Morokuma energy decomposition scheme. The function counterpoise method of Boys and Bernardi enters the procedure naturally, providing an estimate of basis set superposition error (BSSE). We find that the energy components exhibit little basis set dependence when BSSE is small. Applications are presented for several representative molecular and ion complexes: the weak hydrogen bond of the water dimer, the strong ionic interaction of the alkali metal hydrides, and the moderate donor-acceptor interactions of BH3NH3 and BH3CO. Electrostatic interaction dominates the long-range region of the potential energy surface and charge transfer is strongly stabilizing for fragments within van der Waals contact. The repulsive interaction in the short range region of the potential arises from deformation as the fragment wave functions distort to avoid significant interpenetration.

  7. Atomistic bond relaxation, energy entrapment, and electron polarization of the RbN and CsN clusters (N ? 58).

    PubMed

    Guo, Yongling; Bo, Maolin; Wang, Yan; Liu, Yonghui; Huang, Yongli; Sun, Chang Q

    2015-11-11

    We systematically examined the effect of atomic undercoordination on the performance of bonds and electrons of Rb and Cs atomic clusters and their solid skins using a combination of photoelectron spectrometric analysis and density functional theory calculations. Results show that atomic coordination number reduction shortens the bonds by up to 30% for the Rb13 and Cs13 clusters, which densifies the local electrons and entraps their binding energies. Consistency between predictions and observations revealed that the Rb 4p level shifts from 13.654 eV for an isolated atom to a bulk value of 14.940 eV and the Cs 5p level shifts from 10.284 to 11.830 eV upon bulk formation. Such core-electron densification and entrapment polarize the valence charge from the inner to the outermost layer of skins, which perturbs the local Hamiltonian and hence dictates the unusual behavior of the Rb and Cs solid skins and nanocrystals. PMID:26507096

  8. Energy transfer pathways in dinuclear heteroleptic polypyridyl complexes: through-space vs through-bond interaction mechanisms.

    PubMed

    Weldon, Frances; Hammarstrm, Leif; Mukhtar, Emad; Hage, Ronald; Gunneweg, Eric; Haasnoot, Jaap G; Reedijk, Jan; Browne, Wesley R; Guckian, Adrian L; Vos, Johannes G

    2004-07-12

    A series of homo- and heteronuclear ruthenium and osmium polypyridyl complexes with the bridging ligands 1,3-bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H(2)mL) and 1,4-bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H(2)pL) are reported. The photophysical properties of these compounds are investigated, and particular attention is paid to the heteronuclear (RuOs) compounds, which exhibit dual emission. This is in contrast to phenyl-bridged polypyridine Ru-Os complexes with a similar metal-metal distance, in which the Ru emission is strongly quenched because the nature of the bridging ligand allows for an efficient through-bond coupling. The results obtained for the compounds reported here suggest that energy transfer is predominantly taking place via a dipole-dipole, Frster type, mechanism, that may dominate when through-bond coupling is weak. This is in stark contrast to ground state interaction, which is found to be critically dependent on the nature of the bridging unit employed. PMID:15236561

  9. Free Energy Landscapes for S-H Bonds in (Cp2Mo2S4)-Mo-star Complexes

    SciTech Connect

    Appel, Aaron M.; Lee, Suh-Jane; Franz, James A.; DuBois, Daniel L.; Rakowski DuBois, Mary

    2009-03-23

    Extensive thermochemical data have been determined for a series of complexes derived from Cp*Mo(? S)2(? SMe)(? SH)MoCp* and Cp*Mo(? S)2(? SH)2MoCp*. These data include electrochemical potentials, pKa values, homolytic solution bond dissociation free energies (SBDFEs), and hydride donor abilities in acetonitrile. Thermochemical data ranged from +0.6 to -2.0 V vs FeCp2+/o for electrochemical potentials, 5 to 31 for pKa values, 43 to 68 kcal/mol for homolytic SBDFEs, and 44 to 84 kcal/mol for hydride donor abilities. The observed values for these thermodynamic parameters are comparable to those of many transition metal hydrides, which is consistent with the many parallels in the chemistry of these two classes of compounds. The wealth of thermochemical data are presented in free energy landscapes as a useful approach to visualizing and understanding the relative stabilities of all of the species under specified conditions. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

  10. Adsorption of Water Monomer and Clusters on Platinum(111) Terrace and Related Steps and Kinks I. Configurations, Energies, and Hydrogen Bonding

    SciTech Connect

    Arnadottir, Liney; Stuve, Eric M.; Jonsson, Hannes

    2010-10-01

    Adsorption and rotation of water monomer, dimer, and trimer on the (111) terrace, (221) and (322) stepped, and (763) and (854) kinked surfaces of platinum were studied by density functional theory calculations using the PW91 approximation to the energy functional. On the (111) terrace, water monomer and the donor molecule of the dimer and trimer adsorb at atop sites. The permolecule adsorption energies of the monomer, dimer, and trimer are 0.30, 0.45, and 0.48 eV, respectively. Rotation of monomers, dimers, and trimers on the terrace is facile with energy barriers of 0.02 eV or less. Adsorption on steps and kinks is stronger than on the terrace, as evidenced by monomer adsorption energies of 0.46 to 0.55 eV. On the (221) stepped surface the zigzag extended configuration is most stable with a per-molecule adsorption energy of 0.57 eV. On the (322) stepped surface the dimer, two configurations of the trimer, and the zigzag configuration have similar adsorption energies of 0.55 ± 0.02 eV. Hydrogen bonding is strongest in the dimer and trimer adsorbed on the terrace, with respective energies of 0.30 and 0.27 eV, and accounts for their increased adsorption energies relative to the monomer. Hydrogen bonding is weak to moderate for adsorption at steps, with energies of 0.04 to 0.15 eV, as the much stronger water-metal interactions inhibit adsorption geometries favorable to hydrogen bonding. Correlations of hydrogen bond angles and energies with hydrogen bond lengths are presented. On the basis of these DFT/PW91 results, a model for water cluster formation on the Pt(111) surface can be formulated where kink sites nucleate chains along the top of step edges, consistent with the experimental findings of Morgenstern et al., Phys. Rev. Lett., 77 (1996) 703.

  11. Pressure-driven variations of hydrogen bonding energy in ammonium azide (NH4N3): IR absorption and Raman scattering studies

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoxin; Ma, Fengxian; Ma, Chunli; Cui, Hang; Liu, Zhenxian; Zhu, Hongyang; Wang, Xiaoli; Cui, Qiliang

    2014-07-01

    In this study, high pressure infrared (IR) absorption and Raman scattering studies for ammonium azide (NH4N3) were carried out at room temperature up to 20 GPa and 22 GPa, respectively. For comparison and further assignment, the vibrational spectra at ambient conditions were calculated using CASTEP code, particularly for the far- and mid-IR modes. The recorded vibrational data consistently indicated a pressure-induced phase transition at 2.9 GPa. All observed vibrational modes maintained their identities at the high pressure phase, indicating that NH4N3 was still presented in the form of ammonium cations and azide anions linked by the hydrogen bond (N-H⋯N). Above 2.9 GPa, the relative magnitude of the torsional mode weakened and the N-H symmetric stretch displayed a redshift, indicating strengthened hydrogen bonding energy. The opposite effects were observed above 12 GPa, where the relative magnitude of the torsional mode strengthened and the N-H symmetric stretch reverted to a blueshift, indicating weakened hydrogen bonding energy. It can be concluded that the hydrogen bonding energy exhibited a weakening (0-2.9 GPa), strengthening (2.9-12 GPa), and then again weakening (12-22 GPa) phenomena with the increasing of compression. The hydrogen bonding energy changing with the increase of pressure can be ascribed to a phase transition at 2.9 GPa and a rotational or bending behavior of azide ions at 12 GPa.

  12. The energy and geometric characteristics of the transition state in reactions of RO{2/} with carbonyl compound C-H bonds

    NASA Astrophysics Data System (ADS)

    Shestakov, A. F.; Denisov, E. T.; Emel'Yanova, N. S.; Denisova, T. G.

    2009-03-01

    The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its ? and ? C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO2/ + ethanol ? C-H bond), the CHO reaction center has an almost linear configuration (? = 176 2); polar interaction only influences the r ? (CO) interatomic bond. In the reaction of EtO2/ with the ethanol ? C-H bond, it is the O-HO H-bond formed in the transition state that determines the configuration of the reaction center with the angle ?(CHO) = 160. The results were used to estimate the r ? (CH) and r ? (OH) interatomic bonds in the transition state by the method of intersecting parabolas and the contribution of polar interaction to the activation energy of reactions between peroxyl radicals and aldehydes and ketones.

  13. Metastable innershell molecular state (MIMS) III: The universal binding energy and bond length of the homonucleus K-shell MIMS

    NASA Astrophysics Data System (ADS)

    Bae, Young K.

    2016-03-01

    This paper reports the discovery of a universal Z2-dependency of the binding energy of the homonucleus K-shell MIMS (K-MIMS: Metastable Innershell Molecular State bound by K-shell electrons), which has been established by analyzing extensive existing experimental data over several decades. An intuitive analytical theory on the K-MIMS has been developed for the homologous molecules to the He*2 excimer, which elucidates the universal Z-dependent behavior of the K-MIMS. The theory predicts a 1 / Z-dependency of the K-MIMS bond length, which is in agreement with the quasimolecule sizes estimated from the x-ray generation cross-sections in H-like Bi82+ and U91+ impact on Au solids.

  14. Ultrasonically bonded value assembly

    NASA Technical Reports Server (NTRS)

    Salvinski, R. J. (inventor)

    1975-01-01

    A valve apparatus capable of maintaining a fluid-tight seal over a relatively long period of time by releasably bonding a valve member to its seat is described. The valve member is bonded or welded to the seat and then released by the application of the same energy to the bond joint. The valve member is held in place during the bonding by a clamping device. An appropriate force device can activate the opening and closing of the valve member. Various combinations of material for the valve member and valve seat can be utilized to provide an adequate sealing bond. Aluminum oxide, stainless steel, inconel, tungsten carbide as hard materials and copper, aluminum, titanium, silver, and gold as soft materials are suggested.

  15. Low-energy physical properties of high- Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments

    NASA Astrophysics Data System (ADS)

    Yang, Kai-Yu; Shih, C. T.; Chou, C. P.; Huang, S. M.; Lee, T. K.; Xiang, T.; Zhang, F. C.

    2006-06-01

    In a recent review by Anderson and co-workers, it was pointed out that an early resonating valence bond (RVB) theory is able to explain a number of unusual properties of high-temperature superconducting (SC) Cu oxides. Here we extend previous calculations to study more systematically the low-energy physical properties of the plain vanilla d -wave RVB state, and to compare the results with the available experiments. We use a renormalized mean-field theory combined with variational Monte Carlo and power Lanczos methods to study the RVB state of an extended t-J model in a square lattice with parameters suitable for the hole-doped Cu oxides. The physical observable quantities we study include the specific heat, the linear residual thermal conductivity, the in-plane magnetic penetration depth, the quasiparticle energy at the antinode (?,0) , the superconducting energy gap, the quasiparticle spectra, and the Drude weights. The traits of nodes (including kF , the Fermi velocity vF , and the velocity along Fermi surface v2 ), and the SC order parameter are studied. Comparisons of the theory and the experiments in cuprates show an overall qualitative agreement, especially on their doping dependences.

  16. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons.

    PubMed

    Oyeyemi, Victor B; Krisiloff, David B; Keith, John A; Libisch, Florian; Pavone, Michele; Carter, Emily A

    2014-01-28

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs. PMID:25669533

  17. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons

    NASA Astrophysics Data System (ADS)

    Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.

    2014-01-01

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

  18. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons

    SciTech Connect

    Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.

    2014-01-28

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

  19. Institutional Bonding.

    ERIC Educational Resources Information Center

    Allard, M. June

    Institutional bonding was examined at a public, urban commuter college with exceptionally high attrition and visibly low morale. Changes in bonding and attrition were measured 6 years after a 2-year effort to develop school identity and student feelings of membership. It was found that a simple index of campus morale is provided by level of

  20. Demystifying Introductory Chemistry. Part 3: Ionization Energies, Electronegativity, Polar Bonds, and Partial Charges.

    ERIC Educational Resources Information Center

    Spencer, James; And Others

    1996-01-01

    Shows how ionization energies provide a convenient method for obtaining electronegativity values that is simpler than the conventional methods. Demonstrates how approximate atomic charges can be calculated for polar molecules and how this method of determining electronegativities may lead to deeper insights than are typically possible for the…

  1. Low energy electron induced cytosine base release in 2′-deoxycytidine-3′-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study

    SciTech Connect

    Bhaskaran, Renjith; Sarma, Manabendra

    2014-09-14

    Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2′-deoxycytidine-3′-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3′ C–O bond cleavage from the lowest π{sup *} shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the π{sup *} orbital of the base to the σ{sup *} orbital of the glycosidic N–C bond. In addition, the metastable state formed after impinging LEE (0–1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N–C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ∼35–55 fs. Comparison of salient features of the two dissociation events, i.e., 3′ C–O single strand break and glycosidic N–C bond cleavage in 3′-dCMPH molecule are also provided.

  2. Low energy electron induced cytosine base release in 2'-deoxycytidine-3'-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study

    NASA Astrophysics Data System (ADS)

    Bhaskaran, Renjith; Sarma, Manabendra

    2014-09-01

    Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2'-deoxycytidine-3'-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3' C-O bond cleavage from the lowest ?* shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?* orbital of the base to the ?* orbital of the glycosidic N-C bond. In addition, the metastable state formed after impinging LEE (0-1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N-C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of 35-55 fs. Comparison of salient features of the two dissociation events, i.e., 3' C-O single strand break and glycosidic N-C bond cleavage in 3'-dCMPH molecule are also provided.

  3. SnSb-TiC-C nanocomposite alloy anodes for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Leibowitz, Joshua; Allcorn, Eric; Manthiram, Arumugam

    2015-04-01

    SnSb-TiC-C nanocomposite alloy anodes for lithium-ion batteries have been synthesized by a mechanochemical process involving high-energy mechanical milling of Ti-Sn and Ti-Sb precursors with carbon black. Characterization of the formed nanocomposites using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals that these alloys are composed of crystalline nanoparticles of SnSb dispersed in a matrix of crystalline TiC and amorphous carbon. The SnSb-TiC-C alloy shows an initial gravimetric capacity of 769 mAh g-1 (1385 mAh cm-3), an initial coulombic efficiency of 84.9%, and a tap density of 1.8 g cm-3. The buffer matrix of TiC and carbon in the nanocomposite alloy anodes accommodates the large volume change occurring during the charge-discharge process and leads to enhanced cyclability compared to pure SnSb anodes as well as previously published SnSb composites.

  4. Surface structure, bonding, and dynamics: Universality of zinc blende (110) potential energy surfaces

    SciTech Connect

    Godin, T.J.; LaFemina, J.P. ); Duke, C.B. )

    1992-07-01

    Using a tight-binding, total energy (TBTE) model we examine the hypothesis that the potential energy surfaces (PES) describing the (110) cleavage faces of the tetrahedrally coordinated zinc blende structure compound semiconductors exhibit a common universal'' form if expressed in terms of suitably scaled parameters. TBTE calculations on both III--V and II--VI compounds reveal a linear scaling with bulk lattice constant of the geometric parameters of the reconstructed surfaces. This scaling is analogous to that found using low-energy, electron-diffraction surface-structure determination. The surface atomic force constants (found from a TBTE calculation) also scale monotonically with the lattice constant. Using TBTE models proposed previously for GaP, GaAs, GaSb, InP, InSb, and ZnSe, we find that the force constants scale as the inverse square of the bulk lattice constant. These results suggest that if distances are measured in units of the bulk lattice constant, the PES may be a universal function for the cleavage surfaces of zinc blende structure compound semiconductors, on average, with small fluctuations from this average occurring in individual materials.

  5. Effect of temperature on the electron attachment and detachment properties of c-C{sub 4}F{sub 6}

    SciTech Connect

    Datskos, P.G.; Christophorou, L.G. |; Carter, J.G.

    1994-06-01

    The temperature dependence of the low-energy electron attachment and autodetachment processes for c-C{sub 4}F{sub 6} in a N{sub 2} buffer gas has been studied in the temperature, T, range of 300 to 600 K and the mean electron energy, <{epsilon}>, range from 0.19 to 1.0 eV. The low-energy electron attachment rate constant for c-C{sub 4}F{sub 6} shows only a slight dependence on gas temperature. In contrast, the autodetachment frequency increases by more than four orders of magnitude when T is increased from 300 to 600 K. This increase in autodetachment is due to the increase in the internal energy content of the c-C{sub 4},F{sub 6}{sup {minus}} anion with increasing T. The autodetachment process under consideration is a heat-activated process and has an activation energy E* of 0.24 eV. Significance of these results to gaseous dielectrics is indicated.

  6. A quinone-assisted photoformation of energy-rich chemical bonds

    NASA Technical Reports Server (NTRS)

    Fox, S. W.; Adachi, T.; Stillwell, W.

    1980-01-01

    In a study of biochemical means of solar energy conversion, ADP and inorganic phosphates were converted to ATP by white light in the nonaqueous solvent dimethylformamide in the presence of tetrachloro-p-quinone or ubiquinone. Conversion of ADP to ATP has been accomplished in aqueous suspension by the use of cell-like structures aggregated from poly(aspartic acid, glutamic acid, tyrosine). This is believed to occur through the formation of dopaquinone in the peptide structure during illumination. The way in which the quantitative yield of ATP has been influenced by pH and by added substances, such as FeCl2, was studied.

  7. Hydrogen bonding in ionic liquids.

    PubMed

    Hunt, Patricia A; Ashworth, Claire R; Matthews, Richard P

    2015-03-01

    Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (?BCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X-H ?* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds. PMID:25582457

  8. Re-evaluation of the bond length-bond strength rule: The stronger bond is not always the shorter bond.

    PubMed

    Kraka, Elfi; Setiawan, Dani; Cremer, Dieter

    2016-01-01

    A set of 42 molecules with N-F, O-F, N-Cl, P-F, and As-F bonds has been investigated in the search for potential bond anomalies, which lead to reverse bond length-bond strength (BLBS) relationships. The intrinsic strength of each bond investigated has been determined by the local stretching force constant obtained at the CCSD(T)/aug-cc-pVTZ level of theory. N-F or O-F bond anomalies were found for fluoro amine radicals, fluoro amines, and fluoro oxides, respectively. A rationale for the deviation from the normal Badger-type inverse BLBS relation is given and it is shown that electron withdrawal accompanied by strong orbital contraction and bond shortening is one of the prerequisites for a bond anomaly. In the case of short electron-rich bonds such as N-F or O-F, anomeric delocalization of lone pair electrons in connection with lone pair repulsion are decisive whether a bond anomaly can be observed. This is quantitatively assessed with the help of the CCSD(T) local stretching force constants, CCSD(T) charge distributions, and G4 bond dissociation energies. Bond anomalies are not found for fluoro phosphines and fluoro arsines because the bond weakening effects are no longer decisive. 2015 Wiley Periodicals, Inc. PMID:26515027

  9. Energy localization in HMX-Estane polymer-bonded explosives during impact loading

    NASA Astrophysics Data System (ADS)

    Barua, A.; Horie, Y.; Zhou, M.

    2012-03-01

    We report the results of a mechanistic study of energy localization in aHMX (High Melting point eXplosive octahydro-1,3,5,7-tetranitro-1,2,3,5-tetrazocine)/Estane PBX system during dynamic loading. The focus is on the thermal-mechanical response over the strain rate range of 104 - 105 s-1 under different confinement conditions. A recently developed cohesive finite element method is used to track and analyze the contributions to heating from different constituents, interfaces, deformation and fracture mechanisms, and internal friction. In particular, energy dissipations due to viscoelastic deformation, grain fracture, interfacial debonding, and friction along crack faces are quantified as functions of time and overall deformation. The materials analyzed have HMX volume fractions between 0.69 and 0.82. Calculations show that variation in strain rate can significantly affect the spatial distribution but not the overall number of hot spots. Higher confining stresses lead to more intense heating in the binder and more uniform distribution of hot spots. The evolution of hot spots is quantified as a function of loading condition, deformation and microstructural attributes. The microstructure-response relations obtained can be used to assess the initiation sensitivity of energetic composites.

  10. Compositions and chemical bonding in ceramics by quantitative electron energy-loss spectrometry

    SciTech Connect

    Bentley, J.; Horton, L.L.; McHargue, C.J.; McKernan, S.; Carter, C.B.; Revcolevschi, A.; Tanaka, S.; Davis, R.F.

    1993-12-31

    Quantitative electron energy-loss spectrometry was applied to a range of ceramic materials at a spatial resolution of <5 nm. Analysis of Fe L{sub 23} white lines indicated a low-spin state with a charge transfer of {approximately}1.5 electrons/atom onto the Fe atoms implanted into (amorphized) silicon carbide. Gradients of 2 to 5% in the Co:O stoichiometry were measured across 100-nm-thick Co{sub 3}O{sub 4} layers in an oxidized directionally solidified CoO-ZrO{sub 2} eutectic, with the highest O levels near the ZrO{sub 2}. The energy-loss near-edge structures were dramatically different for the two cobalt oxides; those for CO{sub 3}O{sub 4} have been incorrectly ascribed to CoO in the published literature. Kinetically stabilized solid solubility occurred in an AlN-SiC film grown by low-temperature molecular beam epitaxy (MBE) on {alpha}(6H)-SiC, and no detectable interdiffusion occurred in couples of MBE-grown AlN on SiC following annealing at up to 1750C. In diffusion couples of polycrystalline AlN on SiC, interfacial 8H sialon (aluminum oxy-nitride) and pockets of Si{sub 3}N{sub 4}-rich {beta}{prime} sialon in the SiC were detected.

  11. C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes: synthesis, structures, photophysics and electrochemistry.

    PubMed

    Weber, Lothar; Kahlert, Jan; Brockhinke, Regina; Bhling, Lena; Halama, Johannes; Brockhinke, Andreas; Stammler, Hans-Georg; Neumann, Beate; Nervi, Carlo; Harder, Rachel A; Fox, Mark A

    2013-08-14

    Six new C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes, 1,A-R2-1,A-C2B10H10, where R represents the group 2-(1,3-Et2-1,3,2-N2BC6H4) or 2-(1,3-Ph2-1,3,2-N2BC6H4) and A is 2, 7 or 12, were synthesized from o-, m-, and p-dicarbadodecaboranes (carboranes) by lithiation and subsequent treatment with the respective 2-bromo-1,3,2-benzodiazaboroles. UV-visible and fluorescence spectra of all carboranes display low energy charge transfer emissions. While such emissions with Stokes shifts between 17,330 and 21,290 cm(-1) are typical for C,C'-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15,170 cm(-1) for the meta- and para-isomers are unusual as high-energy emissions are typical for meta- and para-dicarbadodecaboranes. Fluorescence quantum yields (?F) for the novel 1,7- and 1,12-bis(benzodiazaborolyl)-carboranes depend on the substituents at the nitrogen atoms of the heterocycle. Thus, the para-carborane with N-ethyl substituents 1,12-(1',3'-Et2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 has a ?F value of 41% in cyclohexane solution and only of 9% in the solid state, whereas the analogous 1,12-(1',3'-Ph2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 shows quantum yields of 3% in cyclohexane solution and 72% in the solid state. X-ray crystallographic, computational and cyclic voltammetry studies for these carboranes are also presented. PMID:23793134

  12. Ligand bond energies in cis- and trans-[L-Pd(PH3)2Cl]+ complexes from coupled cluster theory (CCSD(T)) and density functional theory.

    PubMed

    Chen, Mingyang; Craciun, Raluca; Hoffman, Norris; Dixon, David A

    2012-12-17

    The Pd-L ligand bond dissociation energies (BDEs) of cis- and trans-[L-Pd(PH(3))(2)Cl](+) were predicted using coupled cluster CCSD(T) theory and a variety of density functional theory (DFT) functionals at the B3LYP optimized geometries. trans-[L-Pd(PH(3))(2)Cl](+) is the more stable isomer when Pd forms a donor-acceptor bond with a C atom of the ligand, including the ?-bond in norbornene; for the remaining complexes, the cis-[L-Pd(PH(3))(2)Cl](+) isomer is substantially lower in energy. For cis-[L-Pd (PH(3))(2)Cl](+) complexes, the Pd-L bond energies are 28 kcal/mol for CO; ?40 kcal/mol for AH(3) (A = N, P, As, and Sb), norbornene, and CH(3)CN; and ?53 kcal/mol for CH(3)NC, pyrazole, pyridine, and tetrahydrothiophene at the CCSD(T) level. When Pd forms a donor-acceptor bond with the C atom in the ligand (i.e., CO, CH(3)NC, and the ?-bond in norbornene), the Pd-L bond energies for trans-[L-Pd(PH(3))(2)Cl](+) are generally ?10 kcal/mol greater than those for cis-[L-Pd(PH(3))(2)Cl](+) with the same L; for the remaining ligands, the ligand bond energy increases are ?3-5 kcal/mol from the cis-isomer to the trans-isomer. The benchmarks show that the dispersion-corrected hybrid, generalized gradient approximation, DFT functional ?-B97X-D is the best one to use for this system. Use of the ?-B97X-D/aD functional gives predicted BDEs within 1 kcal/mol of the CCSD(T)/aug-cc-pVTZ BDEs for cis-[L-Pd(PH(3))(2)Cl](+) and 1.5 kcal/mol for trans-[L-Pd(PH(3))(2)Cl](+). PMID:23194426

  13. Free Energy Diagram for the Heterogeneous Enzymatic Hydrolysis of Glycosidic Bonds in Cellulose.

    PubMed

    Srensen, Trine Holst; Cruys-Bagger, Nicolaj; Borch, Kim; Westh, Peter

    2015-09-01

    Kinetic and thermodynamic data have been analyzed according to transition state theory and a simplified reaction scheme for the enzymatic hydrolysis of insoluble cellulose. For the cellobiohydrolase Cel7A from Hypocrea jecorina (Trichoderma reesei), we were able to measure or collect relevant values for all stable and activated complexes defined by the reaction scheme and hence propose a free energy diagram for the full heterogeneous process. For other Cel7A enzymes, including variants with and without carbohydrate binding module (CBM), we obtained activation parameters for the association and dissociation of the enzyme-substrate complex. The results showed that the kinetics of enzyme-substrate association (i.e. formation of the Michaelis complex) was almost entirely entropy-controlled and that the activation entropy corresponded approximately to the loss of translational and rotational degrees of freedom of the dissolved enzyme. This implied that the transition state occurred early in the path where the enzyme has lost these degrees of freedom but not yet established extensive contact interactions in the binding tunnel. For dissociation, a similar analysis suggested that the transition state was late in the path where most enzyme-substrate contacts were broken. Activation enthalpies revealed that the rate of dissociation was far more temperature-sensitive than the rates of both association and the inner catalytic cycle. Comparisons of one- and two-domain variants showed that the CBM had no influence on the transition state for association but increased the free energy barrier for dissociation. Hence, the CBM appeared to promote the stability of the complex by delaying dissociation rather than accelerating association. PMID:26183776

  14. Theoretical Prediction of the Heats of Formation of C?H?O Radicals Derived from Ethanol and of the Kinetics of ?-C-C Scission in the Ethoxy Radical

    SciTech Connect

    Matus, Myrna H.; Nguyen, Minh T.; Dixon, David A.

    2006-12-15

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Thermochemical parameters of three C?H?O radicals derived from ethanol were reevaluated using coupledcluster theory CCSD(T) calculations, with the aug-cc-pVnZ (n = D, T, Q) basis sets, that allow the CC energies to be extrapolated at the CBS limit. Theoretical results obtained for methanol and two CH?O radicals were found to agree within 0.5 kcal/mol with the experiment values. A set of consistent values was determined for ethanol and its radicals: (a) heats of formation (298 K) ?Hf(C?H?OH) = -56.4 0.8 kcal/mol (exptl: -56.21 0.12 kcal/mol), ?Hf(CH?CHOH) = -13.1 0.8 kcal/mol, ?Hf(CH?CH?OH) = -6.2 0.8 kcal/mol, and ?Hf(CH?CH?O) = -2.7 0.8 kcal/mol; (b) bond dissociation energies (BDEs) of ethanol (0 K) BDE(CH?CHOH-H) = 93.9 0.8 kcal/mol, BDE(CH?CH?OH-H) = 100.6 0.8 kcal/mol, and BDE- (CH?CH?O-H) = 104.5 0.8 kcal/mol. The present results support the experimental ionization energies and electron affinities of the radicals, and appearance energy of (CH?CHOH+) cation. ?-C-C bond scission in the ethoxy radical, CH?CH?O, leading to the formation of CH? and CH?=O, is characterized by a C-C bond energy of 9.6 kcal/mol at 0 K, a zero-point-corrected energy barrier of E0 = 17.2 kcal/mol, an activation energy of Ea = 18.0 kcal/mol and a high-pressure thermal rate coefficient of k?(298 K) = 3.9 s-1, including a tunneling correction. The latter value is in excellent agreement with the value of 5.2 s-1 from the most recent experimental kinetic data. Using RRKM theory, we obtain a general rate expression of k(T,p) = 1.26 x 109p0.793 exp(-15.5/RT) s-1 in the temperature range (T) from 198 to 1998 K and pressure range (p) from 0.1 to 8360.1 Torr with N? as the collision partners, where k(298 K, 760 Torr) = 2.7 s-1, without tunneling and k = 3.2 s-1 with the tunneling correction. Evidence is provided that heavy atom tunneling can play a role in the rate constant for ?-C-C bond scission in alkoxy radicals.

  15. Determination of consecutive bond energies by photoionization of SbH[sub [ital n

    SciTech Connect

    Ruscic, B.; Berkowitz, J. )

    1993-10-15

    A photoionization mass spectrometric study of SbH[sub 3] is presented. The adiabatic ionization potential (IP) of SbH[sub 3] is [le]9.40[plus minus]0.02 eV. The lowest energy fragment ion, SbH[sup +] (+H[sub 2]), has an appearance potential (0 K) of 9.73[sub 0][plus minus]0.00[sub 8] eV, while SbH[sub 2][sup +] has an AP of 11.66[plus minus]0.02 eV. The transient species SbH[sub 2] and SbH are generated [ital in] [ital situ] by reacting F atoms with SbH[sub 3]. The IP of SbH[sub 2], forming SbH[sub 2][sup +] ([ital X] [sup 1][ital A][sub 1]), is 8.731[plus minus]0.012 eV. The IP of SbH ([ital X] [sup 3][Sigma][sup [minus

  16. Strength of Chemical Bonds

    NASA Technical Reports Server (NTRS)

    Christian, Jerry D.

    1973-01-01

    Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

  17. Chemical distribution and bonding of lithium in intercalated graphite: identification with optimized electron energy loss spectroscopy.

    PubMed

    Wang, Feng; Graetz, Jason; Moreno, M Sergio; Ma, Chao; Wu, Lijun; Volkov, Vyacheslav; Zhu, Yimei

    2011-02-22

    Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping of lithium in graphite revealed nanoscale inhomogeneities (nonstoichiometric regions), which are correlated with local phase separation and structural disorder (i.e., lattice distortion and dislocations) as observed by high-resolution transmission electron microscopy. The surface solid-electrolyte interphase (SEI) layer was also imaged and determined to have a thickness of 10-50 nm, covering both edge and basal planes with LiF as its primary inorganic component. The Li K-edge spectroscopy and mapping, combined with electron microscopy-based structural analysis provide a comprehensive view of the structure-correlated lithium intercalation in graphite and of the formation of the SEI layer. PMID:21218844

  18. Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy

    SciTech Connect

    Wang, Feng; Graetz, Jason; Moreno, M. Sergio; Ma, Chao; Wu, Lijun; Volkov, Vyacheslav; Zhu, Yimei

    2011-01-10

    Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping of lithium in graphite revealed nanoscale inhomogeneities (nonstoichiometric regions), which are correlated with local phase separation and structural disorder (i.e., lattice distortion and dislocations) as observed by high-resolution transmission electron microscopy. The surface solid-electrolyte interphase (SEI) layer was also imaged and determined to have a thickness of 10-50 nm, covering both edge and basal planes with LiF as its primary inorganic component. The Li K-edge spectroscopy and mapping, combined with electron microscopy-based structural analysis provide a comprehensive view of the structure-correlated lithium intercalation in graphite and of the formation of the SEI layer.

  19. Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy

    SciTech Connect

    Zhu, Y.; Wang, F.; Graetz, J.; Moreno, M.S.; Ma, C.; Wu, L.; Volkov, V.

    2011-02-01

    Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping of lithium in graphite revealed nanoscale inhomogeneities (nonstoichiometric regions), which are correlated with local phase separation and structural disorder (i.e., lattice distortion and dislocations) as observed by high-resolution transmission electron microscopy. The surface solid-electrolyte interphase (SEI) layer was also imaged and determined to have a thickness of 10-50 nm, covering both edge and basal planes with LiF as its primary inorganic component. The Li K-edge spectroscopy and mapping, combined with electron microscopy-based structural analysis provide a comprehensive view of the structure-correlated lithium intercalation in graphite and of the formation of the SEI layer.

  20. Effect of oxygen inhibition in two-step self-etch systems on surface free energy and dentin bond strength with a chemically cured resin composite.

    PubMed

    Yamaji, Ayumi; Tsujimoto, Akimasa; Asaoka, Tetsui; Matsuyoshi, Saki; Tsuchiya, Kenji; Takamizawa, Toshiki; Miyazaki, Masashi

    2014-09-01

    We compared the surface free energies and dentin bond strengths of two-step self-etch systems with and without an oxygen-inhibited layer. The adhesives were applied to self-etching primer-treated dentin surfaces of bovine incisors, after which the teeth were light-irradiated and the oxygen-inhibited layer was left intact or removed with ethanol. We determined surface free energies (?S) and their components by measuring the contact angles of three test liquids placed on the cured adhesives. We also measured the dentin bond strengths of chemically cured resin composite to the adhesives, with and without the oxygen-inhibited layer. For all surfaces, the estimated surface tension component, ?S(LW), was relatively constant. The Lewis base (?S(-)) component decreased significantly when the oxygen-inhibited layer was removed, whereas the Lewis acid (?S(+)) component slightly increased. The dentin bond strengths of the two-step self-etch systems did not significantly differ in relation to the presence of the oxygen-inhibited layer. Although the surface free energy of the adhesive was affected by the presence of the oxygen-inhibited layer, no changes in dentin bond strength were detected. PMID:25231146

  1. Carbon-carbon bond cleavage of 1,2-hydroxy ethers b7 vanadium(V) dipicolinate complexes

    SciTech Connect

    Hanson, Susan K; Gordon, John C; Thorn, David L; Scott, Brian L; Baker, R Tom

    2009-01-01

    The development of alternatives to current petroleum-based fuels and chemicals is becoming increasingly important due to concerns over climate change, growing world energy demand, and energy security issues. Using non-food derived biomass to produce renewable feedstocks for chemicals and fuels is a particularly attractive possibility. However, the majority of biomass is in the form of lignocellulose, which is often not fully utilized due to difficulties associated with breaking down both lignin and cellulose. Recently, a number of methods have been reported to transform cellulose directly into more valuable materials such as glucose, sorbitol, 5-(chloromethyl)furfural, and ethylene glycol. Less progress has been made with selective transformations of lignin, which is typically treated in paper and forest industries by kraft pulping (sodium hydroxide/sodium sulfide) or incineration. Our group has begun investigating aerobic oxidative C-C bond cleavage catalyzed by dipicolinate vanadium complexes, with the idea that a selective C-C cleavage reaction of this type could be used to produce valuable chemicals or intermediates from cellulose or lignin. Lignin is a randomized polymer containing methoxylated phenoxy propanol units. A number of different linkages occur naturally; one of the most prevalent is the {beta}-O-4 linkage shown in Figure 1, containing a C-C bond with 1,2-hydroxy ether substituents. While the oxidative C-C bond cleavage of 1,2-diols has been reported for a number of metals, including vanadium, iron, manganese, ruthenium, and polyoxometalate complexes, C-C bond cleavage of 1,2-hydroxy ethers is much less common. We report herein vanadium-mediated cleavage of C-C bonds between alcohol and ether functionalities in several lignin model complexes. In order to explore the scope and potential of vanadium complexes to effect oxidative C-C bond cleavage in 1,2-hydroxy ethers, we examined the reactivity of the lignin model complexes pinacol monomethyl ether (A), 2-phenoxyethanol (B), and 1,2-diphenyl-2-methoxyethanol (C) (Figure 1). Reaction of (dipic)V{sup V}(O)O{sup i}Pr (1a) or (dipic)V{sup v}(O)OEt (lb) with A, B, or C in acetonitrile yielded new vanadium(V) complexes where the alcohol-ether ligand was bound in a chelating fashion. From the reaction of 1b with pinacol monomethyl ether (A) in acetonitrile solution, (dipic)V{sup v}(O)(pinOMe) (2) (PinOMe = 2,3-dimethyl-3-methoxy-2-butanoxide) was isolated in 61 % yield. Reaction of 1b with 2-phenoxyethanol (B) in acetonitrile gave the new complex (dipic)V{sup v}(O)(OPE) (3) (OPE = 2-phenoxyethoxide), which was isolated in 76% yield. In a similar fashion, 1a reacted with 1,2-diphenyl-2-methoxyethanol (C) to give (dipic)V(O)(DPME) (4) (DPME = 1,2-diphenyl-2-methoxyethoxide), which was isolated in 39% yield. Complexes 2, 3, and 4 were characterized by {sup 1}H NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. Compared to the previously reported vanadium(V) pinacolate complex (dipic)V(O)(pinOH) the X-ray structure of complex 2 reveals a slightly shorter V = O bond, 1.573(2) {angstrom} vs 1.588(2) {angstrom} for the pinOH structure. Complexes 3 and 4 display similar vanadium oxo bond distances of 1.568(2) {angstrom} and 1.576(2) {angstrom}, respectively. All three complexes show longer bonds to the ether-oxygen trans to the oxo (2.388(2) {angstrom} for 2, 2.547(2) {angstrom} for 3, and 2.438(2) {angstrom} for 4) than to the hydroxy-oxygen in the pinOH structure (2.252(2) {angstrom}).

  2. Energy and structure of bonds in the interaction of organic anions with layered double hydroxide nanosheets: A molecular dynamics study.

    PubMed

    Tsukanov, A A; Psakhie, S G

    2016-01-01

    The application of hybrid and hierarchical nanomaterials based on layered hydroxides and oxyhydroxides of metals is a swiftly progressing field in biomedicine. Layered double hydroxides (LDH) possess a large specific surface area, significant surface electric charge and biocompatibility. Their physical and structural properties enable them to adsorb various kinds of anionic species and to transport them into cells. However, possible side effects resulting from the interaction of LDH with anions of the intercellular and intracellular medium need to be considered, since such interaction can potentially disrupt ion transport, signaling processes, apoptosis, nutrition and proliferation of living cells. In the present paper molecular dynamics is used to determine the energies of interaction of organic anions (aspartic acid, glutamic acid and bicarbonate) with a fragment of layered double hydroxide Mg/Al-LDH. The average number of hydrogen bonds between the anions and the hydroxide surface and characteristic binding configurations are determined. Possible effects of LDH on the cell resulting from binding of protein fragments and replacement of native intracellular anions with delivered anions are considered. PMID:26817816

  3. Energy and structure of bonds in the interaction of organic anions with layered double hydroxide nanosheets: A molecular dynamics study

    PubMed Central

    Tsukanov, A.A.; Psakhie, S.G.

    2016-01-01

    The application of hybrid and hierarchical nanomaterials based on layered hydroxides and oxyhydroxides of metals is a swiftly progressing field in biomedicine. Layered double hydroxides (LDH) possess a large specific surface area, significant surface electric charge and biocompatibility. Their physical and structural properties enable them to adsorb various kinds of anionic species and to transport them into cells. However, possible side effects resulting from the interaction of LDH with anions of the intercellular and intracellular medium need to be considered, since such interaction can potentially disrupt ion transport, signaling processes, apoptosis, nutrition and proliferation of living cells. In the present paper molecular dynamics is used to determine the energies of interaction of organic anions (aspartic acid, glutamic acid and bicarbonate) with a fragment of layered double hydroxide Mg/Al-LDH. The average number of hydrogen bonds between the anions and the hydroxide surface and characteristic binding configurations are determined. Possible effects of LDH on the cell resulting from binding of protein fragments and replacement of native intracellular anions with delivered anions are considered. PMID:26817816

  4. Copper Complexes with NH-Imidazolyl and NH-Pyrazolyl Units and Determination of Their Bond Dissociation Gibbs Energies.

    PubMed

    Wilting, Alexander; Kügler, Merle; Siewert, Inke

    2016-02-01

    We synthesized two dinuclear copper complexes, which have ionizable N imidazole and N pyrazole protons in the ligand, respectively, and determined the BDFE of the hypothetical H atom transfer reactions Cu(II)(LH-1) + H(•) ↔ Cu(I)(L) in MeOH/H2O (BDFE: bond dissociation Gibbs (free) energy). The ligands have two adjacent N,N',O-binding pockets, which differ in one N-heterocycle: L(a) has an imidazole unit and L(c), a pyrazole unit. The copper(II) complexes of L(a) and L(c) have been characterized, and the substitution pattern has only little influence on the structural properties. The BDFEs of the hypothetical PCET reactions have been determined by means of the species distribution and the redox potentials of the involved species in MeOH/H2O (80/20 by weight). The pyrazole copper complex 3 exhibits a lower BDFE than the isoelectronic imidazole copper complex 1 (1, 292(3) kJ mol(-1); 3, 279(1) kJ mol(-1)). The difference is mainly caused by the higher acidity of the N pyrazole proton of 3 compared to the N imidazole proton of 1. The redox potentials of 1 and 3 are very similar. PMID:26788812

  5. Energy and structure of bonds in the interaction of organic anions with layered double hydroxide nanosheets: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Tsukanov, A. A.; Psakhie, S. G.

    2016-01-01

    The application of hybrid and hierarchical nanomaterials based on layered hydroxides and oxyhydroxides of metals is a swiftly progressing field in biomedicine. Layered double hydroxides (LDH) possess a large specific surface area, significant surface electric charge and biocompatibility. Their physical and structural properties enable them to adsorb various kinds of anionic species and to transport them into cells. However, possible side effects resulting from the interaction of LDH with anions of the intercellular and intracellular medium need to be considered, since such interaction can potentially disrupt ion transport, signaling processes, apoptosis, nutrition and proliferation of living cells. In the present paper molecular dynamics is used to determine the energies of interaction of organic anions (aspartic acid, glutamic acid and bicarbonate) with a fragment of layered double hydroxide Mg/Al-LDH. The average number of hydrogen bonds between the anions and the hydroxide surface and characteristic binding configurations are determined. Possible effects of LDH on the cell resulting from binding of protein fragments and replacement of native intracellular anions with delivered anions are considered.

  6. A polarizable dipole-dipole interaction model for evaluation of the interaction energies for N-H···O=C and C-H···O=C hydrogen-bonded complexes.

    PubMed

    Li, Shu-Shi; Huang, Cui-Ying; Hao, Jiao-Jiao; Wang, Chang-Sheng

    2014-03-01

    In this article, a polarizable dipole-dipole interaction model is established to estimate the equilibrium hydrogen bond distances and the interaction energies for hydrogen-bonded complexes containing peptide amides and nucleic acid bases. We regard the chemical bonds N-H, C=O, and C-H as bond dipoles. The magnitude of the bond dipole moment varies according to its environment. We apply this polarizable dipole-dipole interaction model to a series of hydrogen-bonded complexes containing the N-H···O=C and C-H···O=C hydrogen bonds, such as simple amide-amide dimers, base-base dimers, peptide-base dimers, and β-sheet models. We find that a simple two-term function, only containing the permanent dipole-dipole interactions and the van der Waals interactions, can produce the equilibrium hydrogen bond distances compared favorably with those produced by the MP2/6-31G(d) method, whereas the high-quality counterpoise-corrected (CP-corrected) MP2/aug-cc-pVTZ interaction energies for the hydrogen-bonded complexes can be well-reproduced by a four-term function which involves the permanent dipole-dipole interactions, the van der Waals interactions, the polarization contributions, and a corrected term. Based on the calculation results obtained from this polarizable dipole-dipole interaction model, the natures of the hydrogen bonding interactions in these hydrogen-bonded complexes are further discussed. PMID:24497309

  7. Metallic Adhesion and Bonding

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Smith, J. R.; Rose, J. H.

    1984-01-01

    Although metallic adhesion has played a central part in much tribological speculation, few quantitative theoretical calculations are available. This is in part because of the difficulties involved in such calculations and in part because the theoretical physics community is not particularly involved with tribology. The calculations currently involved in metallic adhesion are summarized and shown that these can be generalized into a scaled universal relationship. Relationships exist to other types of covalent bonding, such as cohesive, chemisorptive, and molecular bonding. A simple relationship between surface energy and cohesive energy is offered.

  8. Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress.

    PubMed

    Bhattacharya, Somesh Kr; Tanaka, Shingo; Shiihara, Yoshinori; Kohyama, Masanori

    2013-04-01

    We present first-principle calculations on symmetric tilt grain boundaries (GBs) in bcc Fe. Using density functional theory (DFT), we studied the structural, electronic and magnetic properties of ?3(111) and ?11(332) GBs formed by rotation around the [110] axis. The optimized structures, GB energies and GB excess free volumes are consistent with previous DFT and classical simulation studies. The GB configurations can be interpreted by the structural unit model as given by Nakashima and Takeuchi (2000 ISIJ 86 357). Both the GBs are composed of similar structural units of three- and five-membered rings with different densities at the interface according to the rotation angle. The interface atoms with larger atomic volumes reveal higher magnetic moments than the bulk value, while the interface atoms with shorter bond lengths have reduced magnetic moments in each GB. The charge density and local density of states reveal that the interface bonds with short bond lengths have more covalent nature, where minority-spin electrons play a dominant role as the typical nature of ferromagnetic Fe. In order to understand the structural stability of these GBs, we calculated the local energy and local stress for each atomic region using the scheme of Shiihara et al (2010 Phys. Rev. B 81 075441). In each GB, the interface atoms with larger atomic volumes and enhanced magnetic moments reveal larger local energy increase and tensile stress. The interface atoms constituting more covalent-like bonds with reduced magnetic moments have lower local energy increase, contributing to the stabilization, while compressive stress is generated at these atoms. The relative stability between the two GBs can be understood by the local energies at the structural units. The local energy and local stress analysis is a powerful tool to investigate the structural properties of GBs based on the behavior of valence electrons. PMID:23478447

  9. Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Somesh Kr; Tanaka, Shingo; Shiihara, Yoshinori; Kohyama, Masanori

    2013-04-01

    We present first-principle calculations on symmetric tilt grain boundaries (GBs) in bcc Fe. Using density functional theory (DFT), we studied the structural, electronic and magnetic properties of ?3(111) and ?11(332) GBs formed by rotation around the [110] axis. The optimized structures, GB energies and GB excess free volumes are consistent with previous DFT and classical simulation studies. The GB configurations can be interpreted by the structural unit model as given by Nakashima and Takeuchi (2000 ISIJ 86 357). Both the GBs are composed of similar structural units of three- and five-membered rings with different densities at the interface according to the rotation angle. The interface atoms with larger atomic volumes reveal higher magnetic moments than the bulk value, while the interface atoms with shorter bond lengths have reduced magnetic moments in each GB. The charge density and local density of states reveal that the interface bonds with short bond lengths have more covalent nature, where minority-spin electrons play a dominant role as the typical nature of ferromagnetic Fe. In order to understand the structural stability of these GBs, we calculated the local energy and local stress for each atomic region using the scheme of Shiihara et al (2010 Phys. Rev. B 81 075441). In each GB, the interface atoms with larger atomic volumes and enhanced magnetic moments reveal larger local energy increase and tensile stress. The interface atoms constituting more covalent-like bonds with reduced magnetic moments have lower local energy increase, contributing to the stabilization, while compressive stress is generated at these atoms. The relative stability between the two GBs can be understood by the local energies at the structural units. The local energy and local stress analysis is a powerful tool to investigate the structural properties of GBs based on the behavior of valence electrons.

  10. Photodissociation dynamics of cyclopropenylidene, c-C3 H2.

    PubMed

    Schuurman, Michael S; Giegerich, Jens; Pachner, Kai; Lang, Daniel; Kiendl, Benjamin; MacDonell, Ryan J; Krueger, Anke; Fischer, Ingo

    2015-10-01

    In this joint experimental and theoretical study we characterize the complete dynamical "life cycle" associated with the photoexcitation of the singlet carbene cyclopropenylidene to the lowest lying optically bright excited electronic state: from the initial creation of an excited-state wavepacket to the ultimate fragmentation of the molecule on the vibrationally hot ground electronic state. Cyclopropenylidene is prepared in this work using an improved synthetic pathway for the preparation of the precursor quadricyclane, thereby greatly simplifying the assignment of the molecular origin of the measured photofragments. The excitation process and subsequent non-adiabatic dynamics have been previously investigated employing time-resolved photoelectron spectroscopy and are now complemented with high-level ab initio trajectory simulations that elucidate the specific vibronic relaxation pathways. Lastly, the fragmentation channels accessed by the molecule following internal conversion are probed using velocity map imaging (VMI) so that the identity of the fragmentation products and their corresponding energy distributions can be definitively assigned. PMID:26385048

  11. Overview of C/C-SiC Composite Development for the Orion Launch Abort System

    NASA Technical Reports Server (NTRS)

    Allen, Lee R.; Valentine, Peter G.; Schofield, Elizabeth S.; Beshears, Ronald D.; Coston, James E.

    2012-01-01

    Past and present efforts by the authors to further understanding of the ceramic matrix composite (CMC) material used in the valve components of the Orion Launch Abort System (LAS) Attitude Control Motor (ACM) will be presented. The LAS is designed to quickly lift the Orion Crew Exploration Vehicle (CEV) away from its launch vehicle in emergency abort scenarios. The ACM is a solid rocket motor which utilizes eight throttleable nozzles to maintain proper orientation of the CEV during abort operations. Launch abort systems have not been available for use by NASA on manned launches since the last Apollo ]Saturn launch in 1975. The CMC material, carbon-carbon/silicon-carbide (C/C-SiC), is manufactured by Fiber Materials, Inc. and consists of a rigid 4-directional carbon-fiber tow weave reinforced with a mixed carbon plus SiC matrix. Several valve and full system (8-valve) static motor tests have been conducted by the motor vendor. The culmination of these tests was the successful flight test of the Orion LAS Pad Abort One (PA ]1) vehicle on May 6, 2010. Due to the fast pace of the LAS development program, NASA Marshall Space Flight Center assisted the LAS community by performing a series of material and component evaluations using fired hardware from valve and full ]system development motor tests, and from the PA-1 flight ACM motor. Information will be presented on the structure of the C/C-SiC material, as well as the efficacy of various non ]destructive evaluation (NDE) techniques, including but not limited to: radiography, computed tomography, nanofocus computed tomography, and X-ray transmission microscopy. Examinations of the microstructure of the material via scanning electron microscopy and energy dispersive spectroscopy will also be discussed. The findings resulting from the subject effort are assisting the LAS Project in risk assessments and in possible modifications to the final ACM operational design.

  12. Efficient Access to Multifunctional Trifluoromethyl Alcohols through Base-Free Catalytic Asymmetric C-C Bond Formation with Terminal Ynamides.

    PubMed

    Cook, Andrea M; Wolf, Christian

    2016-02-01

    The asymmetric addition of terminal ynamides to trifluoromethyl ketones with a readily available chiral zinc catalyst gives CF3 -substituted tertiary propargylic alcohols in up to 99?% yield and 96?%?ee. The exclusion of organozinc additives and base as well as the general synthetic utility of the products are key features of this reaction. The value of the ?-hydroxy-?-trifluoromethyl ynamides is exemplified by selective transformations to chiral Z- and E-enamides, an amide, and N,O-ketene acetals. The highly regioselective hydration, stereoselective reduction, and hydroacyloxylation reactions proceed with high yields and without erosion of the ee?value of the parent ?-hydroxy ynamides. PMID:26806871

  13. Palladium-catalyzed enolate arylation as a key C-C bond-forming reaction for the synthesis of isoquinolines.

    PubMed

    Pilgrim, Ben S; Gatland, Alice E; Esteves, Carlos H A; McTernan, Charlie T; Jones, Geraint R; Tatton, Matthew R; Procopiou, Panayiotis A; Donohoe, Timothy J

    2016-01-21

    The palladium-catalyzed coupling of an enolate with an ortho-functionalized aryl halide (an ?-arylation) furnishes a protected 1,5-dicarbonyl moiety that can be cyclized to an isoquinoline with a source of ammonia. This fully regioselective synthetic route tolerates a wide range of substituents, including those that give rise to the traditionally difficult to access electron-deficient isoquinoline skeletons. These two synthetic operations can be combined to give a three-component, one-pot isoquinoline synthesis. Alternatively, cyclization of the intermediates with hydroxylamine hydrochloride engenders direct access to isoquinoline N-oxides; and cyclization with methylamine, gives isoquinolinium salts. Significant diversity is available in the substituents at the C4 position in four-component, one-pot couplings, by either trapping the in situ intermediate after ?-arylation with carbon or heteroatom-based electrophiles, or by performing an ?,?-heterodiarylation to install aryl groups at this position. The ?-arylation of nitrile and ester enolates gives access to 3-amino and 3-hydroxyisoquinolines and the ?-arylation of tert-butyl cyanoacetate followed by electrophile trapping, decarboxylation and cyclization, C4-functionalized 3-aminoisoquinolines. An oxime directing group can be used to direct a C-H functionalization/bromination, which allows monofunctionalized rather than difunctionalized aryl precursors to be brought through this synthetic route. PMID:26632484

  14. Acetylacetone-cleaving enzyme Dke1: a novel C-C-bond-cleaving enzyme from Acinetobacter johnsonii.

    PubMed Central

    Straganz, Grit D; Glieder, Anton; Brecker, Lothar; Ribbons, Douglas W; Steiner, Walter

    2003-01-01

    The toxicity of acetylacetone has been demonstrated in various studies. Little is known, however, about metabolic pathways for its detoxification or mineralization. Data presented here describe for the first time the microbial degradation of acetylacetone and the characterization of a novel enzyme that initiates the metabolic pathway. From an Acinetobacter johnsonii strain that grew with acetylacetone as the sole carbon source, an inducible acetylacetone-cleaving enzyme was purified to homogeneity. The corresponding gene, coding for a 153 amino acid sequence that does not show any significant relationship to other known protein sequences, was cloned and overexpressed in Escherichia coli and gave high yields of active enzyme. The enzyme cleaves acetylacetone to equimolar amounts of methylglyoxal and acetate, consuming one equivalent of molecular oxygen. No exogenous cofactor is required, but Fe(2+) is bound to the active protein and essential for its catalytic activity. The enzyme has a high affinity for acetylacetone with a K (m) of 9.1 microM and a k(cat) of 8.5 s(-1). A metabolic pathway for acetylacetone degradation and the putative relationship of this novel enzyme to previously described dioxygenases are discussed. PMID:12379146

  15. Hapalindole/Ambiguine Biogenesis Is Mediated by a Cope Rearrangement, C-C Bond-Forming Cascade.

    PubMed

    Li, Shasha; Lowell, Andrew N; Yu, Fengan; Raveh, Avi; Newmister, Sean A; Bair, Nathan; Schaub, Jeffrey M; Williams, Robert M; Sherman, David H

    2015-12-16

    Hapalindoles are bioactive indole alkaloids with fascinating polycyclic ring systems whose biosynthetic assembly mechanism has remained unknown since their initial discovery in the 1980s. In this study, we describe the fam gene cluster from the cyanobacterium Fischerella ambigua UTEX 1903 encoding hapalindole and ambiguine biosynthesis along with the characterization of two aromatic prenyltransferases, FamD1 and FamD2, and a previously undescribed cyclase, FamC1. These studies demonstrate that FamD2 and FamC1 act in concert to form the tetracyclic core ring system of the hapalindoles from cis-indole isonitrile and geranyl pyrophosphate through a presumed biosynthetic Cope rearrangement and subsequent 6-exo-trig cyclization/electrophilic aromatic substitution reaction. PMID:26629885

  16. Topotactic elimination of water across a C-C ligand bond in a dense 3-D metal-organic framework.

    PubMed

    Yeung, Hamish H-M; Kosa, Monica; Griffin, John M; Grey, Clare P; Major, Dan T; Cheetham, Anthony K

    2014-11-11

    Upon heating, lithium L-malate undergoes topotactic dehydration to form a phase containing the unsaturated fumarate ligand, in which the original 3-D framework remains intact. Insight into this unusual transformation has been obtained by single crystal X-ray diffraction, MAS-NMR, in situ powder X-ray diffraction and DFT calculations. PMID:25232700

  17. C-C Bond Formation via Copper-Catalyzed Conjugate Addition Reactions to Enones in Water at Room Temperature

    PubMed Central

    Lipshutz, Bruce H.; Huang, Shenlin; Leong, Wendy Wen Yi; Isley, Nicholas A.

    2013-01-01

    Conjugate addition reactions to enones can now be done in water at room temperature with in situ-generated organocopper reagents. Mixing an enone, zinc powder, TMEDA, and an alkyl halide in a micellar environemnt containing catalytic amounts of Cu(I), Ag(I), and Au(III), leads to 1,4-adducts in good isolated yields: no organometallic precursor is involved. PMID:23190029

  18. Chirality transfer based on reversible C-C bond formation/breaking in nickel(II) complexes.

    PubMed

    Kawamoto, Tatsuya; Suzuki, Narumi; Ono, Takeshi; Gong, Dafei; Konno, Takumi

    2013-01-25

    The reaction of (1R)-(-)-myrtenal-derived benzothiazoline with nickel(II) acetate in ethanol exclusively gave a Schiff base-type nickel(II) complex having M helical configurational myrtenyl arms, which is reversibly converted to a non-innocent-type complex having additional S,S configurational asymmetric carbon centres. PMID:23090291

  19. Insulation bonding test system

    NASA Technical Reports Server (NTRS)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (Inventor)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  20. Formation of tri- and tetranuclear titanacycles through decamethyltitanocene-mediated intermolecular C-C coupling of dinitriles.

    PubMed

    Becker, Lisanne; Arndt, Perdita; Spannenberg, Anke; Jiao, Haijun; Rosenthal, Uwe

    2015-04-27

    The reactions of [Cp*2 Ti(?(2) -Me3 SiC2 SiMe3 )] (Cp*=?(5) -pentamethylcyclopentadienyl) with various dicyano compounds were investigated. Nitrile-nitrile C?C couplings result in multinuclear complexes owing to the bifunctionality of the substrates. Applying 1,3- or 1,4-dicyanobenzene led to tri- and tetranuclear complexes of the rare 1-metalla-2,5-diaza-cyclopenta-2,4-dienes. These are potential catalysts and were tested in the ring-opening polymerization of ?-caprolactone. The reaction with adiponitrile as alkyl dinitrile afforded a trinuclear 1-metalla-2,5-diaza-cyclopent-3-ene through additional protonation of the nitrogen atoms. The structure and bonding of the products were investigated by X-ray crystallography and DFT analysis to understand the molecular organization in the macrocycles. PMID:25833142

  1. Pd loaded amphiphilic COF as catalyst for multi-fold Heck reactions, C-C couplings and CO oxidation

    PubMed Central

    Mullangi, Dinesh; Nandi, Shyamapada; Shalini, Sorout; Sreedhala, Sheshadri; Vinod, Chathakudath P.; Vaidhyanathan, Ramanathan

    2015-01-01

    COFs represent a class of polymers with designable crystalline structures capable of interacting with active metal nanoparticles to form excellent heterogeneous catalysts. Many valuable ligands/monomers employed in making coordination/organic polymers are prepared via Heck and C-C couplings. Here, we report an amphiphilic triazine COF and the facile single-step loading of Pd0 nanoparticles into it. An 1820% nano-Pd loading gives highly active composite working in open air at low concentrations (Conc. Pd(0) <0.05?mol%, average TON 1500) catalyzing simultaneous multiple site Heck couplings and C-C couplings using non-boronic acid substrates, and exhibits good recyclability with no sign of catalyst leaching. As an oxidation catalyst, it shows 100% conversion of CO to CO2 at 150?C with no loss of activity with time and between cycles. Both vapor sorptions and contact angle measurements confirm the amphiphilic character of the COF. DFT-TB studies showed the presence of Pd-triazine and Pd-Schiff bond interactions as being favorable. PMID:26057044

  2. Pd loaded amphiphilic COF as catalyst for multi-fold Heck reactions, C-C couplings and CO oxidation

    NASA Astrophysics Data System (ADS)

    Mullangi, Dinesh; Nandi, Shyamapada; Shalini, Sorout; Sreedhala, Sheshadri; Vinod, Chathakudath P.; Vaidhyanathan, Ramanathan

    2015-06-01

    COFs represent a class of polymers with designable crystalline structures capable of interacting with active metal nanoparticles to form excellent heterogeneous catalysts. Many valuable ligands/monomers employed in making coordination/organic polymers are prepared via Heck and C-C couplings. Here, we report an amphiphilic triazine COF and the facile single-step loading of Pd0 nanoparticles into it. An 18-20% nano-Pd loading gives highly active composite working in open air at low concentrations (Conc. Pd(0) <0.05 mol%, average TON 1500) catalyzing simultaneous multiple site Heck couplings and C-C couplings using ‘non-boronic acid’ substrates, and exhibits good recyclability with no sign of catalyst leaching. As an oxidation catalyst, it shows 100% conversion of CO to CO2 at 150 °C with no loss of activity with time and between cycles. Both vapor sorptions and contact angle measurements confirm the amphiphilic character of the COF. DFT-TB studies showed the presence of Pd-triazine and Pd-Schiff bond interactions as being favorable.

  3. A comparison of ab initio quantum-mechanical and experimental D0 binding energies of eleven H-bonded and eleven dispersion-bound complexes.

    PubMed

    Haldar, Susanta; Gnanasekaran, Ramachandran; Hobza, Pavel

    2015-10-28

    Dissociation energies (D0) of 11 H-bonded and 11 dispersion-bound complexes were calculated as the sum of interaction energies and the change of zero-point vibrational energies (?ZPVE). The structures of H-bonded complexes were optimized at the RI-MP2/cc-pVTZ level, at which deformation and harmonic ?ZPVE energies were also calculated. The structures of dispersion-bound complexes were optimized at the DFT-D3 level, and harmonic ?ZPVE energies were determined at the same level as well. For comparison, CCSD(T)/CBS D0 energies were also evaluated for both types of complexes. The CCSD(T)/CBS interaction energy was constructed as the sum of MP2/CBS interaction energy, extrapolated from aug-cc-pVTZ and aug-cc-pVQZ basis sets, and ?CCSD(T) correction, determined with the aug-cc-pVDZ basis set. The ?ZPVE energies were determined for all complexes at the harmonic level and for selected complexes, these energies were also calculated using second-order vibration perturbation (VPT2) theory. For H-bonded complexes, the harmonic CCSD(T)/CBS D0 energies were in better agreement with the experimental values (with a mean relative error (MRE) of 6.2%) than the RI-MP2/cc-pVTZ D0 (a MRE of 12.3%). The same trend was found for dispersion-bound complexes (6.2% (MRE) at CCSD(T)/CBS and 7.7% (MRE) at the DFT-D3 level). When the anharmonic ?ZPVE term was included instead of harmonic one, the agreement between theoretical and experimental D0 deteriorated for H-bonded as well as dispersion-bound complexes. Finally, the applicability of "diagonal approximation" for determining the anharmonic ?ZPVE was shown. For the phenolH2O complex, the ?ZPVE energy calculated at the VPT2 level and on the basis of "diagonal approximation" differed by less than 0.1 kcal mol(-1). PMID:26392236

  4. Determination and interrelation of bond heterolysis and homolysis energies in solution. Final report, January 1988-August 1991

    SciTech Connect

    Arnett, E.M.

    1993-01-01

    Solution phase heats of heterolysis Delta H(sub(het)) and homolysis Delta H(sub(homo)) were determined for covalent bonds that can be cleaved to produce resonance-stabilized carbenium ions, anions, and radicals. Simple and broadly applicable correlation equations were developed which relate Delta H(sub(het)) to ion stabilization properties pK(sub(R+5)) and pK(sub a) and relate Delta H(sub(homo)) to radical stabilization properties (AOPs and CRPs). Important conclusions from the study are: (1) there is no general correlation between Delta H(sub(het)) and Delta H(sub(homo)) which implies that heterolytic bond cleavage pathways in coal will be quite different than the homolytic bond cleavage pathways associated with coal thermolysis; (2) many covalent bonds in coal which require high temperature for homolytic cleavage may be susceptible to heterolytic cleavage under mild conditions; and (3) coal conversion process chemistry based upon heterolytic bond cleavage may be more selective and controllable than homolytic bond cleavage associated with coal thermolysis.

  5. Infrared spectroscopy and intramolecular vibrational relaxation of c-C 6F 12 excited above the dissociation threshold

    NASA Astrophysics Data System (ADS)

    Bagratashvili, V. N.; Burimov, V. N.; Ionov, S. I.; Sviridov, A. P.; Stuchebrukhov, A. A.; Turovetz, I. M.

    1987-05-01

    The IR spectrum of c-C 6F 12 at a vibrational energy of twice the dissociation threshold was investigated. Absorption of cw CO 2 laser radiation was measured at various frequencies. Our experimental conditions were chosen such that during absorption measurements all vibrational degrees of freedom were in equilibrium, the molecular rotation being at room temperature. The Boltzmann vibrational distribution allowed computer simulations of the spectrum to be made to determine the homogeneous contribution. The homogeneous half-width of the spectrum is ?=130.5 cm -1 and the homogeneous spectrum of c-C 6F 12 at E= 60000 cm -1 is non-Lorentzian. We attribute this to the influence of higher-order anharmonicities on the relaxation from the excited mode ( v27) to other modes in the molecule.

  6. Yankee bonds

    SciTech Connect

    Delaney, P. )

    1993-10-01

    Yankee and Euromarket bonds may soon find their way into the financing of power projects in Latin America. For developers seeking long-term commitments under build, own, operate, and transfer (BOOT) power projects in Latin America, the benefits are substantial.

  7. Testing of DLR C/C-SiC for HIFiRE 8 Scramjet Combustor

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Capriotti, Diego P.; Reimer, Thomas; Kutemeyer, Marius; Smart, Michael

    2013-01-01

    Ceramic Matrix Composites (CMCs) have been proposed for hot structures in scramjet combustors. Previous studies have calculated significant weight savings by utilizing CMCs (active and passive) versus actively cooled metallic scramjet structures. Both a C/C and a C/C-SiC material system fabricated by DLR (Stuttgart, Germany) are being considered for use in a passively cooled combustor design for HIFiRE 8, a joint Australia / AFRL hypersonic flight program, expected to fly at Mach 7 for approximately 30 sec, at a dynamic pressure of 55 kPa. Flat panels of the DLR C/C and the C/C-SiC were tested in the NASA Langley Direct Connect Rig (DCR) at Mach 5 and Mach 6 enthalpy for several minutes. Gaseous hydrogen fuel was used to fuel the scramjet combustor. The test panels were instrumented with embedded Type K and Type S thermocouples. Zirconia felt insulation was used in some of the tests to increase the surface temperature of the C/C-SiC panel for approximately 350degF. The final C/C-SiC panel was tested for 3 cycles totaling over 135 sec at Mach 6 enthalpy. Slightly more erosion was observed on the C/C panel than the C/C-SiC panels, but both material systems demonstrated acceptable recession performance for the HIFiRE 8 flight.

  8. 77 FR 10004 - C$ cMoney, Inc.; Order of Suspension of Trading

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-21

    ... From the Federal Register Online via the Government Publishing Office SECURITIES AND EXCHANGE COMMISSION C$ cMoney, Inc.; Order of Suspension of Trading February 16, 2012. It appears to the Securities... securities of C$ cMoney, Inc. (``cMoney'') because of questions regarding the accuracy of assertions by...

  9. A valence bond study of the Bergman cyclization: geometric features, resonance energy, and nucleus-independent chemical shift (NICS) values

    PubMed

    Galbraith; Schreiner; Harris; Wei; Wittkopp; Shaik

    2000-04-14

    The Bergman cyclization of (Z)-hex-3-ene-1,5-diynes (1, enediynes), which produces pharmacologically important DNA-cleaving biradicals (1,4-benzyne, 2), was studied by using Hartree-Fock (HF) and density-functional theory (DFT) based valence bond (VB) methods (VB-HF and VB-DFT, respectively). We found that only three VB configurations are needed to arrive at results not too far from complete active space [CASSCF(6 x 6)] computations, while the quality of VB-DTF utilizing the same three configurations improves upon CASSCF(6 x 6) analogous to CASPT2. The dominant VB configuration in 1 contributes little to 2, while the most important biradical configuration in 2 plays a negligible role in 1. The avoided crossing of the energy curves of these two configurations along the reaction coordinate leads to the transition state (TS). As a consequence of the shape and position of the crossing section, the changes in geometry and in the electronic wavefunction along the reaction coordinate are non-synchronous; the TS is geometrically approximately 80% product-like and electronically approximately 70% reactant-like. While the pi resonance in the TS is very small, it is large (64.4 kcal mol(-1)) for 2 (cf. benzene=61.5 kcal mol(-1)). As a consequence, substituents operating on the sigma electrons should be much more effective in changing the Bergman reaction cyclization barrier. Furthermore, additional sigma resonance in 2 results in unusually high values for the nucleus-independent chemical shift (NICS, a direct measure for aromaticity). Similarly, the high NICS value of the TS is due mostly to sigma resonance to which the NICS procedure is relatively sensitive. PMID:10840967

  10. Investigation of a self-sustained volume discharge in c-C4F8

    NASA Astrophysics Data System (ADS)

    Belevtsev, A. A.; Firsov, K. N.; Kazantsev, S. Yu; Kononov, I. G.; Podlesnykh, S. V.

    2015-11-01

    This paper reports the first experimental study of a self-sustained volume discharge (SSVD) in c-C4F8. The discharge voltage and current oscillograms are taken over a wide range of gas pressures. For the first time an SSVD in c-C4F8 preheated by CO2-laser radiation has been investigated. Some special features and temperature-dependent characteristics of this discharge are revealed. There is discussion on the peculiarities of an SSVD in a preirradiated c-C4F8. To refine the static limiting field in c-C4F8 the static dielectric strength of c-C4F8 is measured on changing the gas pressure by nearly two orders of magnitude.

  11. Photochemical tissue bonding

    SciTech Connect

    Redmond, Robert W.; Kochevar, Irene E.

    2012-01-10

    Photochemical tissue bonding methods include the application of a photosensitizer to a tissue and/or tissue graft, followed by irradiation with electromagnetic energy to produce a tissue seal. The methods are useful for tissue adhesion, such as in wound closure, tissue grafting, skin grafting, musculoskeletal tissue repair, ligament or tendon repair and corneal repair.

  12. Theoretical insights into the structures and mechanical properties of HMX/NQ cocrystal explosives and their complexes, and the influence of molecular ratios on their bonding energies.

    PubMed

    Li, Yong-Xiang; Chen, Shu-Sen; Ren, Fu-de

    2015-09-01

    Molecular dynamics (MD) methods were employed to study the binding energies and mechanical properties of selected crystal planes of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)/nitroguanidine (NQ) cocrystals at different molecular molar ratios. The densities and detonation velocities of the cocrystals at different molar ratios were estimated. The intermolecular interaction and bond dissociation energy (BDE) of the N-NO2 bond in the HMX:NQ (1:1) complex were calculated using the B3LYP, MP2(full) and M06-2X methods with the 6-311++G(d,p) and 6-311++G(2df,2p) basis sets. The results indicated that the HMX/NQ cocrystal prefers cocrystalizing in a 1:1 molar ratio, and the cocrystallization is dominated by the (0 2 0) and (1 0 0) facets. The K, G, and E values of the ratio of 1:1 are smaller than those of the other ratios, and the 1:1 cocrystal has the best ductility. The N-NO2 bond becomes stronger upon the formation of the intermolecular H-bonding interaction and the sensitivity of HMX decreases in the cocrystal. This sensitivity change in the HMX/NQ cocrystal originates not only from the formation of the intermolecular interaction but also from the increment of the BDE of N-NO2 bond in comparison with isolated HMX. The HMX/NQ (1:1) cocrystal exhibits good detonation performance. Reduced density gradient (RDG) reveals the nature of cocrystallization. Analysis of the surface electrostatic potential further confirmed that the sensitivity decreases in complex (or cocrystal) in comparison with that in isolated HMX. PMID:26318201

  13. Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry.

    PubMed

    Ruscic, Branko

    2015-07-16

    Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C-H, C-C, C-O, and O-H bond dissociation enthalpies at 298.15 K (BDE298) and bond dissociation energies at 0 K (D0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CHn, n = 4-0 species (methane, methyl, methylene, methylidyne, and carbon atom), C2Hn, n = 6-0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHn, n = 4-0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO2 and H2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species. PMID:25760799

  14. Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory

    SciTech Connect

    DiLabio, Gino A.; Koleini, Mohammad; Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4

    2014-05-14

    Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the S66 set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the D3 pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs.

  15. Visible-Light Photoredox Catalysis: Direct Synthesis of Sulfonated Oxindoles from N-Arylacrylamides and Arylsulfinic Acids by Means of a Cascade C-S/C-C Formation Process.

    PubMed

    Xia, Dong; Miao, Tao; Li, Pinhua; Wang, Lei

    2015-09-01

    A novel photocatalytic synthesis of sulfonated oxindoles from N-arylacrylamides and arylsulfinic acids was developed by means of a cascade C-S/C-C bond-formation process. This method provides mild, efficient, and atom-economical access to various sulfonated oxindoles in water. PMID:26097076

  16. Acid Gradient across Plasma Membrane Can Drive Phosphate Bond Synthesis in Cancer Cells: Acidic Tumor Milieu as a Potential Energy Source

    PubMed Central

    Dhar, Gautam; Sen, Suvajit; Chaudhuri, Gautam

    2015-01-01

    Aggressive cancers exhibit an efficient conversion of high amounts of glucose to lactate accompanied by acid secretion, a phenomenon popularly known as the Warburg effect. The acidic microenvironment and the alkaline cytosol create a proton-gradient (acid gradient) across the plasma membrane that represents proton-motive energy. Increasing experimental data from physiological relevant models suggest that acid gradient stimulates tumor proliferation, and can also support its energy needs. However, direct biochemical evidence linking extracellular acid gradient to generation of intracellular ATP are missing. In this work, we demonstrate that cancer cells can synthesize significant amounts of phosphate-bonds from phosphate in response to acid gradient across plasma membrane. The noted phenomenon exists in absence of glycolysis and mitochondrial ATP synthesis, and is unique to cancer. Biochemical assays using viable cancer cells, and purified plasma membrane vesicles utilizing radioactive phosphate, confirmed phosphate-bond synthesis from free phosphate (Pi), and also localization of this activity to the plasma membrane. In addition to ATP, predominant formation of pyrophosphate (PPi) from Pi was also observed when plasma membrane vesicles from cancer cells were subjected to trans-membrane acid gradient. Cancer cytosols were found capable of converting PPi to ATP, and also stimulate ATP synthesis from Pi from the vesicles. Acid gradient created through glucose metabolism by cancer cells, as observed in tumors, also proved critical for phosphate-bond synthesis. In brief, these observations reveal a role of acidic tumor milieu as a potential energy source and may offer a novel therapeutic target. PMID:25874623

  17. Acid gradient across plasma membrane can drive phosphate bond synthesis in cancer cells: acidic tumor milieu as a potential energy source.

    PubMed

    Dhar, Gautam; Sen, Suvajit; Chaudhuri, Gautam

    2015-01-01

    Aggressive cancers exhibit an efficient conversion of high amounts of glucose to lactate accompanied by acid secretion, a phenomenon popularly known as the Warburg effect. The acidic microenvironment and the alkaline cytosol create a proton-gradient (acid gradient) across the plasma membrane that represents proton-motive energy. Increasing experimental data from physiological relevant models suggest that acid gradient stimulates tumor proliferation, and can also support its energy needs. However, direct biochemical evidence linking extracellular acid gradient to generation of intracellular ATP are missing. In this work, we demonstrate that cancer cells can synthesize significant amounts of phosphate-bonds from phosphate in response to acid gradient across plasma membrane. The noted phenomenon exists in absence of glycolysis and mitochondrial ATP synthesis, and is unique to cancer. Biochemical assays using viable cancer cells, and purified plasma membrane vesicles utilizing radioactive phosphate, confirmed phosphate-bond synthesis from free phosphate (Pi), and also localization of this activity to the plasma membrane. In addition to ATP, predominant formation of pyrophosphate (PPi) from Pi was also observed when plasma membrane vesicles from cancer cells were subjected to trans-membrane acid gradient. Cancer cytosols were found capable of converting PPi to ATP, and also stimulate ATP synthesis from Pi from the vesicles. Acid gradient created through glucose metabolism by cancer cells, as observed in tumors, also proved critical for phosphate-bond synthesis. In brief, these observations reveal a role of acidic tumor milieu as a potential energy source and may offer a novel therapeutic target. PMID:25874623

  18. Reinterpretation of the Vibrational Spectroscopy of the Medicinal Bioinorganic Synthon c,c,t-[Pt(NH3)2Cl2(OH)2]†

    PubMed Central

    Johnstone, Timothy C.

    2014-01-01

    The Pt(IV) complex c,c,t-[Pt(NH3)2Cl2(OH)2] is an important intermediate in the synthesis of Pt(IV) anticancer prodrugs and has been investigated as an anticancer agent in its own right. An analysis of the vibrational spectroscopy of this molecule was previously reported [Faggiani et al., 1982, Can. J. Chem. 60, 529] in which crystallographic determination of the structure of the complex permitted a site group approach. The space group, however, was incorrectly assigned. In the present study we have redetermined at high resolution crystal structures of c,c,t-[Pt(NH3)2Cl2(OH)2] and c,c,t-[Pt(NH3)2Cl2(OH)2]·H2O2, which enable discussion of the effect of hydrogen bonding on the N–H and O–H vibrational bands. The correct crystallographic site symmetry of the platinum complex in the c,c,t-[Pt(NH3)2Cl2(OH)2] structure is employed to conduct a new vibrational analysis using both group theoretical and modern DFT methods. This analysis reveals the nature and symmetry of the “missing band” described in the original publication and suggests a possible explanation for its disappearance. PMID:24515615

  19. Coulombic Models in Chemical Bonding.

    ERIC Educational Resources Information Center

    Sacks, Lawrence J.

    1986-01-01

    Describes a bonding theory which provides a framework for the description of a wide range of substances and provides quantitative information of remarkable accuracy with far less computational effort than that required of other approaches. Includes applications, such as calculation of bond energies of two binary hydrides (methane and diborane).…

  20. Coulombic Models in Chemical Bonding.

    ERIC Educational Resources Information Center

    Sacks, Lawrence J.

    1986-01-01

    Describes a bonding theory which provides a framework for the description of a wide range of substances and provides quantitative information of remarkable accuracy with far less computational effort than that required of other approaches. Includes applications, such as calculation of bond energies of two binary hydrides (methane and diborane).

  1. Microwave bonding of MEMS component

    NASA Technical Reports Server (NTRS)

    Barmatz, Martin B. (Inventor); Mai, John D. (Inventor); Jackson, Henry W. (Inventor); Budraa, Nasser K. (Inventor); Pike, William T. (Inventor)

    2005-01-01

    Bonding of MEMs materials is carried out using microwave. High microwave absorbing films are placed within a microwave cavity, and excited to cause selective heating in the skin of the material. This causes heating in one place more than another. Thereby minimizing the effects of the bonding microwave energy.

  2. Clarifying Chemical Bonding. Overcoming Our Misconceptions.

    ERIC Educational Resources Information Center

    Hapkiewicz, Annis

    1991-01-01

    Demonstrations to help students change their misconceptions about chemical bond breaking are presented. Students' misconceptions about chemical bonds in both biological and chemical systems are discussed. A calculation for the release of energy from respiration is presented. (KR)

  3. High-Performance Zn-TiC-C Nanocomposite Alloy Anode with Exceptional Cycle Life for Lithium-Ion Batteries.

    PubMed

    Kim, Sang-Ok; Manthiram, Arumugam

    2015-07-15

    A Zn-based nanocomposite has been prepared through a facile, low-cost high-energy mechanochemical process and employed as an anode material for lithium-ion batteries. Structural characterization reveals that the micrometer-sized Zn-TiC-C nanocomposite is composed of Zn nanocrystals uniformly dispersed in a multifunctional TiC and conductive carbon matrix with a tap density of 1.3 g cm(-3). The Zn-TiC-C nanocomposite exhibits high reversible volumetric capacity (468 mA h cm(-3)), excellent cyclability over 800 cycles (79.2% retention), and good rate performance up to 12.5C (75% of its capacity at 0.25C rate). The enhanced electrochemical performance is mainly due to the presence of the well-mixed TiC+C matrix that plays an important role in providing high conductivity as well as mechanical buffer that mitigates the huge volume expansion and contraction during prolonged cycling. In addition, it prevents the particle growth by uniformly dispersing nanosized Zn within itself during cycling, maintaining high utilization (∼100%) and fast reaction kinetics of Zn anode. PMID:26098753

  4. Cu6Sn5-TiC-C nanocomposite anodes for high-performance sodium-ion batteries

    NASA Astrophysics Data System (ADS)

    Kim, Il Tae; Allcorn, Eric; Manthiram, Arumugam

    2015-05-01

    Cu6Sn5 alloy nanoparticles dispersed in a TiC and C conductive matrix have been developed via high energy mechanical milling (HEMM), and the resulting Cu6Sn5-TiC-C nanocomposite has been assessed as anodes for sodium-ion batteries. Composite anodes of Sn-C exhibit poor cyclic performance even with the introduction of 2 vol. % fluoroethylene carbonate (FEC) additive into the electrolyte. In contrast, Cu6Sn5-TiC-C nanocomposite anodes exhibit stable cycle life corresponding to a capacity retention of ?80% at 40 cycles and high-rate performance with a capacity retention of ?62% at 3000 mA g-1. These superior performance metrics is ascribed to the well-developed electrochemically active nanocrystalline material (Cu6Sn5) as well as a hybrid conductive matrix (TiC and C). The incorporation of 2 vol. % FEC additive into the electrolyte further improves the performance of Cu6Sn5-TiC-C nanocomposite to display a capacity retention of ?94% at 250 cycles and high-rate capacity retention of ?82% at 5000 mA g-1, which are attributed to the formation of a thin and stable SEI layer in presence of FEC.

  5. The antimony-group 11 chemical bond: Dissociation energies of the diatomic molecules CuSb, AgSb, and AuSb

    SciTech Connect

    Carta, V.; Ciccioli, A. E-mail: andrea.ciccioli@uniroma1.it; Gigli, G. E-mail: andrea.ciccioli@uniroma1.it

    2014-02-14

    The intermetallic molecules CuSb, AgSb, and AuSb were identified in the effusive molecular beam produced at high temperature under equilibrium conditions in a double-cell-like Knudsen source. Several gaseous equilibria involving these species were studied by mass spectrometry as a function of temperature in the overall range 1349–1822 K, and the strength of the chemical bond formed between antimony and the group 11 metals was for the first time measured deriving the following thermochemical dissociation energies (D{sub 0}{sup ∘}, kJ/mol): 186.7 ± 5.1 (CuSb), 156.3 ± 4.9 (AgSb), 241.3 ± 5.8 (AuSb). The three species were also investigated computationally at the coupled cluster level with single, double, and noniterative quasiperturbative triple excitations (CCSD(T)). The spectroscopic parameters were calculated from the potential energy curves and the dissociation energies were evaluated at the Complete Basis Set limit, resulting in an overall good agreement with experimental values. An approximate evaluation of the spin-orbit effect was also performed. CCSD(T) calculations were further extended to the corresponding group 11 arsenide species which are here studied for the first time and the following dissociation energies (D{sub 0}{sup ∘}, kJ/mol): 190 ± 10 (CuAs), 151 ± 10 (AgAs), 240 ± 15 (AuAs) are proposed. Taking advantage of the new experimental and computational information here presented, the bond energy trends along group 11 and 4th and 5th periods of the periodic table were analyzed and the bond energies of the diatomic species CuBi and AuBi, yet experimentally unobserved, were predicted on an empirical basis.

  6. The Dissociation Energies of CH4 and C2H2 Revisited

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    The bond dissociation energies of CH4 and C2H2 and their fragments are investigated using basis set extrapolations and high levels of correlation. The computed bond dissociation energies (D(sub e)) are accurate to within 0.2 kcal/mol. The agreement with the experimental (D(sub 0)) values is excellent if we assume that the zero-point energy of C2H is 9.18 kcal/mol. The effect of core (1s) correlation on the bond dissociation energies of C-H bonds is shown to vary from 0.2 to 0.7 kcal/mol and that for C-C bonds varies from 0.4 to 2.2 kcal/mol.

  7. The bond energy of ReO+: Guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2

    NASA Astrophysics Data System (ADS)

    Armentrout, P. B.

    2013-08-01

    The kinetic-energy dependence of the Re+ + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for ReO+ formation from ground state Re+ (7S) is unusual, exhibiting two endothermic features. The kinetic energy dependence for ReO+ formation is analyzed to determine D0(Re+-O) = 4.82 0.05 eV, with the higher energy feature having a threshold 1.35 0.28 eV higher in energy. This bond energy is consistent with much less precise values determined in the literature. Formation of ReO2+ is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of ReO+ with O2. The nature of the bonding for ReO+ and ReO2+ is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of ReO+ is identified as either 5? or 3?, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state ReO+ are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, although estimated spin-orbit corrections increase the latter close to experiment. Potential energy surfaces for the reaction of Re+ with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Re+ (7S) inserts into O2 by forming a Re+(O2) (5A?) complex which can then couple with additional surfaces to form ground state ReO2+ (3B1). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior.

  8. Investigations of electron attachment to the perfluorocarbon molecules c-C4F8, 2-C4F8, 1,3 C4F6, and c-C5F8

    NASA Astrophysics Data System (ADS)

    Feil, Stefan; Mrk, Tilmann D.; Mauracher, Andreas; Scheier, Paul; Mayhew, Chris A.

    2008-11-01

    Non-dissociative and dissociative electron attachment to a series of gas-phase perfluorocarbons (PFCs), namely octafluorocyclobutane, c-C4F8, octafluorobut-2-ene (perfluoro-2-butene), 2-C4F8, hexafluorobuta-1,3-diene (1,3 perfluorobutadiene), 1,3 C4F6, and octafluorocyclopentene (perfluorocyclopentene), c-C5F8, of importance to technological plasmas, have been investigated using two different, but complimentary, instruments available in Innsbruck over the electron energy range 0-20 eV. Anion yields as a function of electron energy have been recorded, with the positions and intensities of the electron attachment resonances being determined. One of these instruments is a double focusing sector field mass spectrometer (VG-ZAB-2SEQ), which has been used for measurements requiring high sensitivity and for obtaining accurate relative anion yields. It has also been used to determine the electron detachment lifetimes of the parent anions under various accelerating voltages, and these results are also presented. The second instrument (CELIA) is a trochoidal electron monochromator coupled to a quadrupole mass filter with a pulse counting system for detecting product anionic species. This provides a much higher energy resolution than the VG-ZAB, which makes it a better instrument to investigate narrow energy resonances close to 0 eV. The results of anion yields, peak positions and the relative intensities presented in this paper are compared with previous data of electron attachment to the above PFCs, including investigations by Professor Eugen Illenberger.

  9. Asymmetric bifurcated halogen bonds.

    PubMed

    Novk, Martin; Foroutan-Nejad, Cina; Marek, Radek

    2015-03-01

    Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as '?-hole - lone pair' or '?-hole - ?' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

  10. H-H, C-H, and C-C NMR spin-spin coupling constants calculated by the FP-INDO method for aromatic hydrocarbons

    NASA Technical Reports Server (NTRS)

    Long, S. A. T.; Memory, J. D.

    1978-01-01

    The FP-INDO (finite perturbation-intermediate neglect of differential overlap) method is used to calculate the H-H, C-H, and C-C coupling constants in hertz for molecules of six different benzenoid hydrocarbons: benzene, naphthalene, biphenyl, anthracene, phenanthrene, and pyrene. The calculations are based on both the actual and the average molecular geometries. It is found that only the actual molecular geometries can always yield the correct relative order of values for the H-H coupling constants. For the calculated C-C coupling constants, as for the calculated C-H coupling constants, the signs are positive (negative) for an odd (even) number of bonds connecting the two nuclei. Agreements between the calculated and experimental values of the coupling constants for all six molecules are comparable to those reported previously for other molecules.

  11. Pi Bond Orders and Bond Lengths

    ERIC Educational Resources Information Center

    Herndon, William C.; Parkanyi, Cyril

    1976-01-01

    Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

  12. 21. Historic American Buildings Survey Copyright C.C. Pierce Original: ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. Historic American Buildings Survey Copyright - C.C. Pierce Original: About 1902 Re-photo: April 1940 QUANDRANGLE (view from north) - Mission Nuestra Senora de la Soledad, Soledad, Monterey County, CA

  13. 5. Historic American Buildings Survey C.C. Woodburn, Photographer. January 12, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey C.C. Woodburn, Photographer. January 12, 1934 DETAIL OF ENTRANCE (WEST ELEVATION) - Ferdinand Daniel Pulver House, County Road F-70 Vicinity, Vandalia, Jasper County, IA

  14. Combustion Gas Heating Tests of C/C Composites Coated with SiC Layer

    NASA Astrophysics Data System (ADS)

    Sato, Masaki; Moriya, Shin-ichi; Sato, Masahiro; Tadano, Makoto; Kusaka, Kazuo; Hasegawa, Keiichi; Kumakawa, Akinaga; Yoshida, Makoto

    2008-02-01

    In order to examine the applicability of carbon fiber/carbon matrix composites coated with a silicon carbide layer (C/C-SiCs) to an advanced nozzle for the future reusable rocket engines, two series of combustion gas heating tests were conducted using a small rocket combustor. In the first series of heating tests, five different kinds of C/C-SiCs were tested with specimens in the shape of a square plate for material screening. In the second series of heating tests, two selected C/C-SiCs were tested with specimens in the shape of a small nozzle. The effectiveness of an interlayer between a C/C composite and a SiC layer, which was introduced to improve the durability based on the concept of functionally graded materials (FGMs), can be observed. The typical damage mode was also pointed out in the results of heating test using the small nozzle specimens.

  15. Brazing of C/C composites and Ni-based alloy using interlayer

    NASA Astrophysics Data System (ADS)

    Ikeshoji, Toshi-Taka; Tokunaga, Tatsuya; Suzumura, Akio; Yamazaki, Takahisa

    2014-08-01

    The brazing of C/C composites and Inconel-600 Ni-based heat resistant alloy was conducted using Fe-Ni-Cr-P-Si brazing filler alloy with inserting various thickness of Nb foil as stress relief interlayer. SEM observation of cross section of brazing interface revealed that Nb foil was resolved into the brazing filler layer on C/C composites side. Nb diffused to the surface of C/C composites and acted as the active metal element to enhance the wettability of molten metal on graphite matrix of C/C composites during the brazing process. The variation in shear strength values of the brazed joint with Nb layer thickness suggested that the Nb layer should be remained at least 100 ?m.

  16. Search for the weak decays J /? ?Ds(*)-e+?e+c .c .

    NASA Astrophysics Data System (ADS)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; An, F. F.; An, Q.; Bai, J. Z.; Ferroli, R. Baldini; Ban, Y.; Bennett, D. W.; Bennett, J. V.; Bertani, M.; Bettoni, D.; Bian, J. M.; Bianchi, F.; Boger, E.; Bondarenko, O.; Boyko, I.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, H. Y.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Chu, Y. P.; Cibinetto, G.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; de Mori, F.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Duan, P. F.; Fan, J. Z.; Fang, J.; Fang, S. S.; Fang, X.; Fang, Y.; Fava, L.; Feldbauer, F.; Felici, G.; Feng, C. Q.; Fioravanti, E.; Fu, C. D.; Gao, Q.; Gao, Y.; Garzia, I.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, T.; Guo, Y.; Guo, Y. P.; Haddadi, Z.; Hafner, A.; Han, S.; Han, Y. L.; Harris, F. A.; He, K. L.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Hu, Y.; Huang, G. M.; Huang, G. S.; Huang, H. P.; Huang, J. S.; Huang, X. T.; Huang, Y.; Hussain, T.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, L. W.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Johansson, T.; Julin, A.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kang, X. S.; Kavatsyuk, M.; Ke, B. C.; Kliemt, R.; Kloss, B.; Kolcu, O. B.; Kopf, B.; Kornicer, M.; Kuehn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Li, C. H.; Li, Cheng; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, Jin; Li, K.; Li, K.; Li, P. R.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. M.; Li, X. N.; Li, X. Q.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. L.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, J. Y.; Liu, K.; Liu, K. Y.; Liu, L. D.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, X. X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, H. J.; Lu, J. G.; Lu, R. Q.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Lyu, X. R.; Ma, F. C.; Ma, H. L.; Ma, L. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. N.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Marcello, S.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Mo, Y. J.; Moeini, H.; Morales, C. Morales; Moriya, K.; Muchnoi, N. Yu.; Muramatsu, H.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, S. L.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Patteri, P.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Ping, J. L.; Ping, R. G.; Poling, R.; Pu, Y. N.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, N.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ren, H. L.; Ripka, M.; Rong, G.; Ruan, X. D.; Santoro, V.; Sarantsev, A.; Savri, M.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, P. X.; Shen, X. Y.; Sheng, H. Y.; Shepherd, M. R.; Song, W. M.; Song, X. Y.; Sosio, S.; Spataro, S.; Spruck, B.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Tiemens, M.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, B. L.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, L. H.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, L.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yin, J. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Yuncu, A.; Zafar, A. A.; Zallo, A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, K.; Zhang, L.; Zhang, S. H.; Zhang, X. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, J. W.; Zhao, J. Y.; Zhao, J. Z.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, W. J.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, S.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.

    2014-12-01

    Using a sample of 2.25 1 08 J /? events collected with the BESIII detector at the BEPCII collider, we search for the J /? semileptonic weak decay J /? ?Ds-e+?e+c .c . with a much higher sensitivity than previous searches. We also perform the first search for J /? ?Ds*-e+?e+c .c . No significant excess of a signal above background is observed in either channel. At the 90% confidence level, the upper limits are determined to be B (J /? ?Ds-e+?e+c .c .)<1.3 1 0-6 and B (J /? ?Ds* -e+?e+c .c .)<1.8 1 0-6 , respectively. Both are consistent with Standard Model predictions.

  17. Qgui: A high-throughput interface for automated setup and analysis of free energy calculations and empirical valence bond simulations in biological systems.

    PubMed

    Isaksen, Geir Villy; Andberg, Tor Arne Heim; Åqvist, Johan; Brandsdal, Bjørn Olav

    2015-07-01

    Structural information and activity data has increased rapidly for many protein targets during the last decades. In this paper, we present a high-throughput interface (Qgui) for automated free energy and empirical valence bond (EVB) calculations that use molecular dynamics (MD) simulations for conformational sampling. Applications to ligand binding using both the linear interaction energy (LIE) method and the free energy perturbation (FEP) technique are given using the estrogen receptor (ERα) as a model system. Examples of free energy profiles obtained using the EVB method for the rate-limiting step of the enzymatic reaction catalyzed by trypsin are also shown. In addition, we present calculation of high-precision Arrhenius plots to obtain the thermodynamic activation enthalpy and entropy with Qgui from running a large number of EVB simulations. PMID:26080356

  18. Mechanical properties of oxidation-resistant SiC/C compositionally graded graphite materials

    SciTech Connect

    Nakano, Junichi; Fujii, Kimio; Yamada, Reiji

    1997-11-01

    Mechanical properties of oxidation-resistant SiC/C compositionally graded graphite materials composed of a CVD SiC coating layer, a SiC/C graded layer, and a graphite substrate were studied by bending, compressive, and hardness tests at room temperature. CVD SiC coated graphite and graphite with a SiC/C graded layer alone were also examined. The bending strengths of oxidation-resistant SiC/C compositionally graded graphite materials as well as CVD SiC coated graphite were about twice as much as that of graphite. The bending and compressive strengths of graphite with the SiC/C graded layer along were almost the same as those of graphite. The higher strengths of graphite with the CVD SiC layer can be mainly due to the CVD SiC strength itself, and partly due to the smooth CVD surface. No effect of the SiC/C layer on the strengths was discussed in terms of porosity, surface morphology, and the strength of SiC.

  19. Bonded Lubricants

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Another spinoff to the food processing industry involves a dry lubricant developed by General Magnaplate Corp. of Linden, N.J. Used in such spacecraft as Apollo, Skylab and Viking, the lubricant is a coating bonded to metal surfaces providing permanent lubrication and corrosion resistance. The coating lengthens equipment life and permits machinery to be operated at greater speed, thus increasing productivity and reducing costs. Bonded lubricants are used in scores of commercia1 applications. They have proved particularly valuable to food processing firms because, while increasing production efficiency, they also help meet the stringent USDA sanitation codes for food-handling equipment. For example, a cookie manufacturer plagued production interruptions because sticky batter was clogging the cookie molds had the brass molds coated to solve the problem. Similarly, a pasta producer faced USDA action on a sanitation violation because dough was clinging to an automatic ravioli-forming machine; use of the anti-stick coating on the steel forming plates solved the dual problem of sanitation deficiency and production line downtime.

  20. An ab initio study of structure, stability, and spectroscopic parameters of 5-atomic [C, C, H, N, S] isomers

    NASA Astrophysics Data System (ADS)

    Gronowski, Marcin; Kołos, Robert

    2015-06-01

    This theoretical study is focused on predicting structures, energetics, and selected spectroscopic constants for a range of 5-atomic chemical species sharing the [C, C, H, N, S] stoichiometry, including thioformyl cyanide and iminoethenethione. An in-depth study carried out on the four most stable isomers have yielded (i) structures and energy for the lowest singlet and triplet excited electronic states; (ii) anharmonic vibrational frequencies and IR absorption intensities for the fundamental, overtone and combination modes; (iii) molecular parameters of interest to microwave spectroscopy: rotational constants, electric dipole moments, and quadrupole coupling constants.

  1. LETTERS TO THE EDITORS: Lightning ball: experiments on creation and hypotheses(comment on "Energy density calculations for ball-lightning-like luminous silicon balls" by G S Paiva, J V Ferreira, C C Bastos, M V P dos Santos, A C Pavão)

    NASA Astrophysics Data System (ADS)

    Shabanov, Gennadii D.

    2010-05-01

    The problems addressed in this paper include estimating: the energy density of luminous silicon balls, the density range of a natural lightning ball, and whether and how the object created and described in the commented paper (Usp. Fiz. Nauk 180 218 (2010) [Phys. Usp. 53 (2) 209 (2010)]) corresponds to the natural phenomenon.

  2. Basics of Fidelity Bonding.

    ERIC Educational Resources Information Center

    Kahn, Steven P.

    Fidelity bonds are important for an agency to hold to protect itself against any financial loss that can result from dishonest acts by its employees. Three types of fidelity bonds are available to an agency: (1) public official bonds; (2) dishonesty bonds; and (3) faithful performance bonds. Public official bonds are required by state law to be

  3. Functional interactions in bacteriorhodopsin: a theoretical analysis of retinal hydrogen bonding with water.

    PubMed Central

    Nina, M; Roux, B; Smith, J C

    1995-01-01

    The light-driven proton pump, bacteriorhodopsin (bR) contains a retinal molecule with a Schiff base moiety that can participate in hydrogen-bonding interactions in an internal, water-containing channel. Here we combine quantum chemistry and molecular mechanics techniques to determine the geometries and energetics of retinal Schiff base-water interactions. Ab initio molecular orbital calculations are used to determine potential surfaces for water-Schiff base hydrogen-bonding and to characterize the energetics of rotation of the C-C single bond distal and adjacent to the Schiff base NH group. The ab initio results are combined with semiempirical quantum chemistry calculations to produce a data set used for the parameterization of a molecular mechanics energy function for retinal. Using the molecular mechanics force field the hydrated retinal and associated bR protein environment are energy-minimized and the resulting geometries examined. Two distinct sites are found in which water molecules can have hydrogen-bonding interactions with the Schiff base: one near the NH group of the Schiff base in a polar region directed towards the extracellular side, and the other near a retinal CH group in a relatively nonpolar region, directed towards the cytoplasmic side. Images FIGURE 1 FIGURE 2 FIGURE 6 FIGURE 8 PMID:7711248

  4. Structure-energy analysis of the role of metal ions in phosphodiester bond hydrolysis by DNA polymerase I

    SciTech Connect

    Fothergill, M.; Goodman, M.F.; Petruska, J.; Warsehl, A.

    1995-11-29

    The detailed mechanism of DNA hydrolysis by enzymes is of significant current interest. One of the most important questions in this respect is the catalytic role of metal ions such as Mg{sup 2+}. Experimental evaluation of the catalytic effects of the cations is problematic, since the cations are intimately involved in substrate binding. This problem is explored here by using a theoretical approach to analyze and interpret the key structural and biochemical experiments. Taking the X-ray structure of the exonuclease domain in the Klenow fragment of E. coli DNA polymerase I we use the empirical valence bond method to examine different feasible mechanisms for phosphodiester bond cleavage in the exonuclease site. This approach indicates that phosphodiester bond hydrolysis involves catalysis by an OH{sup -} ion from aqueous solution around the protein, rather than a general base catalysis by an active site residue. The catalytic effect of two divalent metal cations in the active site is found to be primarily electrostatic. The first cation provides a strong electrostatic stabilization to the OH{sup -} nucleophile, while the second cation provides a very large catalytic effect by its interaction with the negative charge being transferred to the transition state during the nucleophilic attack step. The calculations also demonstrate that the second metal ion is not likely to be involved in a previously proposed strain mechanism. 35 refs., 6 figs., 1 tab.

  5. Facile homolytic C?S bond breaking: the reaction of 2-propene-1-thiol on Mo(110)

    NASA Astrophysics Data System (ADS)

    Wiegand, B. C.; Friend, C. M.; Uvdal, P.; Napier, M. E.

    1996-06-01

    Investigations of 2-propene-1-thiol on Mo(110) show that the facility for thiol desulfurization correlates with the homolytic C?S bond strength of the thiol. A substantial amount of C?S bond scission occurs upon adsorption of 2-propene-1-thiol on Mo(110) at 120 K based on X-ray photoelectron data. 2-Propene-1-thiol has an extremely weak C?S bond because of the resonance stabilization of the allyl radical. Propene, the product of 2-propene-1-thiol hydrogenolysis, evolves into the gas phase in the range 160-250 K; the propene evolution being controlled by the rate of desorption. Vibrational (electron energy loss) spectra are consistent with formation of 2-propene-1-thiolate via S?H bond cleavage, as well as hydrocarbon fragments at low temperature. A large fraction of the thiolate desulfurizes at 120 K to afford propene. A second hydrocarbon species is formed in the range 160-200 K, characterized by a low-frequency C?H stretch mode at 2770 cm -1, which reacts further below 250 K. The C?C bond in the thiol and in the propene product leads to a greater degree of non-selective reaction than is anticipated from a comparison of saturated thiols. Only in the order of 50% of the thiol reacts to afford propene, despite the facility for C?S bond scission.

  6. A Model for the Chemical Bond

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2004-01-01

    Bond stereochemistry in polyatomic hydrides is explained in terms of the principle of bond energies maximization, which yields X-H straight bonds and suggests the formation of appropriate sp hybrids on the central atom. An introduction to the electron charge distribution in molecules is given, and atomic, overlap, gross and formal charges are…

  7. A Model for the Chemical Bond

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2004-01-01

    Bond stereochemistry in polyatomic hydrides is explained in terms of the principle of bond energies maximization, which yields X-H straight bonds and suggests the formation of appropriate sp hybrids on the central atom. An introduction to the electron charge distribution in molecules is given, and atomic, overlap, gross and formal charges are

  8. Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu/Al{sub 2}O{sub 3} interface

    SciTech Connect

    Mizoguchi, Teruyasu; Sasaki, Takeo; Matsunaga, Katsuyuki; Ikuhara, Yuichi; Tanaka, Shingo; Kohyama, Masanori; Yamamoto, Takahisa

    2006-12-15

    Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu/Al{sub 2}O{sub 3} heterointerfaces with hollow and on-top configurations were theoretically investigated by using a first principles orthogonalized linear combination of atomic orbitals method. From the chemical bonding analysis, it was found that the hollow configuration has stronger ionic and covalent bondings as compared with the on-top configuration, and the weakness of the on-top configuration originates from the strong antibonding interactions between an interfacial oxygen and the second near neighbor Cu. Detailed analysis using overlap population diagrams revealed the formation mechanism of the strong antibonding interactions in the on-top configuration. In the oxygen K ELNES calculation, a prepeak feature appears in both configurations and it was predicted that the prepeak for the on-top configuration is larger than that for the hollow configuration. The overlap population diagrams elucidated that the prepeak is mainly composed of the O-Cu antibonding interactions, and the larger prepeak of the on-top configuration originates from the larger O-Cu interactions. The dependence of O-K ELNES on the direction of the momentum transfer vector was also discussed. Knowledge of the responsible direction of the momentum transfer vector in relation to the interface orientation was concluded to be indispensable in order to discuss detailed profiles of the ELNES from metal/ceramic heterointerfaces. This study reveals the effect of the atomic configuration of the interface to the chemical bondings, interface strength, and ELNES.

  9. Highly Accurate CCSD(T) and DFTSAPT Stabilization Energies of H-Bonded and Stacked Structures of the Uracil Dimer

    SciTech Connect

    Pitonak, Michal; Riley, Kevin E.; Neogrady, Pavel; Hobza, Pavel

    2008-06-23

    The CCSD(T) interaction energies for the H-bonded and stacked structures of the uracil dimer are determined at the aug-cc-pVDZ and aug-cc-pVTZ levels. On the basis of these calculations we can construct the CCSD(T) interaction energies at the complete basis set (CBS) limit. The most accurate energies, based either on direct extrapolation of the CCSD(T) correlation energies obtained with the aug-cc-pVDZ and aug-cc-pVTZ basis sets or on the sum of extrapolated MP2 interaction energies (from aug-cc-pVTZ and aug-cc-pVQZ basis sets) and extrapolated ?CCSD(T) correction terms [difference between CCSD(T) and MP2 interaction energies] differ only slightly, which demonstrates the reliability and robustness of both techniques. The latter values, which represent new standards for the H-bonding and stacking structures of the uracil dimer, differ from the previously published data for the S22 set by a small amount. This suggests that interaction energies of the S22 set are generated with chemical accuracy. The most accurate CCSD(T)/CBS interaction energies are compared with interaction energies obtained from various computational procedures, namely the SCSMP2 (SCS: spin-component-scaled), SCS(MI)MP2 (MI: molecular interaction), MP3, dispersion-augmented DFT (DFTD), M062X, and DFTSAPT (SAPT: symmetry-adapted perturbation theory) methods. Among these techniques, the best results are obtained with the SCS(MI)MP2 method. Remarkably good binding energies are also obtained with the DFTSAPT method. Both DFT techniques tested yield similarly good interaction energies. The large magnitude of the stacking energy for the uracil dimer, compared to that of the benzene dimer, is explained by attractive electrostatic interactions present in the stacked uracil dimer. These interactions force both subsystems to approach each other and the dispersion energy benefits from a shorter intersystem separation.

  10. Oxidative addition of carbon-carbon bonds to gold.

    PubMed

    Joost, Maximilian; Estvez, Laura; Miqueu, Karinne; Amgoune, Abderrahmane; Bourissou, Didier

    2015-04-20

    The oxidative addition of strained C?C bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino-carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)?C(O) or C(alkyl)?C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation. PMID:25727203

  11. The use of exact Lamb waves modes for modeling the power and energy transduction of structurally bonded piezoelectric wafer active sensors

    NASA Astrophysics Data System (ADS)

    Lin, Bin; Giurgiutiu, Victor; Kamal, Ayman M.

    2012-04-01

    This paper presents a theoretical modeling of power and energy transduction of structurally-bonded piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM). After a literature review of the state of the art, we developed a model of power and energy transduction between the PWAS and a structure containing multimodal ultrasonic guided waves. The use of exact Lamb waves modes for power modeling is an extension of our previously presented simplified model that considered axial and flexural waves with low frequency approximation. The model assumptions include: (a) straight-crested multimodal ultrasonic guided wave propagation; (b) ideal bonding (pin-force) connection between PWAS and structure; (c) ideal excitation source at the transmitter PWAS and fully-resistive external load at the receiver PWAS. Frequency response functions are developed for voltage, current, complex power, active power, etc. Multimodal ultrasonic guided wave, normal mode expansion, electromechanical energy transformation of PWAS and structure were considered. The parametric study of PWAS size and impedance match gives the PWAS design guideline for PWAS sensing and power harvesting applications

  12. Understanding Excitation Energy Transfer in Metalloporphyrin Heterodimers with Different Linkers, Bonding Structures and Geometries through Stimulated X-Ray Raman Spectroscopy.

    PubMed

    Zhang, Yu; Biggs, Jason D; Mukamel, Shaul

    2014-01-01

    We present simulations of stimulated X-ray Raman (SXRS) signals from covalent porphyrin heterodimers with different linkers, chemical bonding structures and geometries. The signals are interpreted in terms of valence electron wavepacket motion. One- and two-color SXRS signals can jointly indicate excitation energy transfer (EET) between the porphyrin monomers. It is shown that the SXRS signals provide a novel window into EET dynamics in multiporphyrin systems, and can be used as a powerful tool to monitor the subtle chemical environment which affects EET. PMID:25045204

  13. Understanding Excitation Energy Transfer in Metalloporphyrin Heterodimers with Different Linkers, Bonding Structures and Geometries through Stimulated X-Ray Raman Spectroscopy

    PubMed Central

    Zhang, Yu; Biggs, Jason D.; Mukamel, Shaul

    2014-01-01

    We present simulations of stimulated X-ray Raman (SXRS) signals from covalent porphyrin heterodimers with different linkers, chemical bonding structures and geometries. The signals are interpreted in terms of valence electron wavepacket motion. One- and two-color SXRS signals can jointly indicate excitation energy transfer (EET) between the porphyrin monomers. It is shown that the SXRS signals provide a novel window into EET dynamics in multiporphyrin systems, and can be used as a powerful tool to monitor the subtle chemical environment which affects EET. PMID:25045204

  14. Nature of halogen bonding. A study based on the topological analysis of the Laplacian of the electron charge density and an energy decomposition analysis.

    PubMed

    Duarte, Darío J R; Sosa, Gladis L; Peruchena, Nélida M

    2013-05-01

    In this work we investigate the nature of the Cl···N interactions in complexes formed between substituted ammonium [NHn(X3-n) (with n = 0, 1, 2, 3 and X = -CH3, -F] as Lewis bases and F-Cl molecule as Lewis acid. They have been chosen as a study case due to the wide range of variation of their binding energies, BEs. Møller-Plesset [MP2/6-311++G(2d,2p)] calculations show that the BEs for this set of complexes lie in the range from 1.27 kcal/mol (in F-Cl···NF3) to 27.62 kcal/mol [in F-Cl···N(CH3)3]. The intermolecular distribution of the electronic charge density and their L(r) = -¼∇(2)ρ(r) function have been investigated within the framework of the atoms in molecules (AIM) theory. The intermolecular interaction energy decomposition has also been analyzed using the reduced variational space (RVS) method. The topological analysis of the L(r) function reveals that the local topological properties measured at the (3,+1) critical point [in L(r) topology] are good descriptors of the strength of the halogen bonding interactions. The results obtained from energy decomposition analysis indicate that electrostatic interactions play a key role in these halogen bonding interactions. These results allow us to establish that, when the halogen atom is bonded to a group with high electron-withdrawing capacity, the electrostatic interaction between the electron cloud of the Lewis base and the halogen atom unprotected nucleus of the Lewis acid produces the formation and determines the geometry of the halogen bonded complexes. In addition, a good linear relationship has been established between: the natural logarithm of the BEs and the electrostatic interaction energy between electron charge distribution of N atom and nucleus of Cl atom, denoted as V e-n(N,Cl) within the AIM theory. PMID:23076553

  15. Unconventional ionic hydrogen bonds: CH +⋯π (C tbnd C) binding energies and structures of benzene + rad (acetylene) 1-4 clusters

    NASA Astrophysics Data System (ADS)

    Soliman, Abdel-Rahman; Hamid, Ahmed M.; Abrash, Samuel A.; El-Shall, M. Samy

    2012-01-01

    Rapid condensation of acetylene onto the benzene cation with the addition of up to eight acetylene molecules is observed in the gas phase at 120-140 K forming the C6D6rad +(C2H2)n clusters. The binding energies and entropy changes of the stepwise condensation of the first four acetylene molecules onto the benzene cation have been measured and correlated with the calculated lowest energy isomers. The measured binding energies (3-4 kcal/mol) reflect weak charge-induced dipole and (benzene) Csbnd Hδ+⋯π Ctbnd C (acetylene) hydrogen bonding interactions. Associative charge transfer is suggested to activate the cyclization of three acetylene molecules to form a benzene molecule (C6H6).

  16. "Vibrational bonding": a new type of chemical bond is discovered.

    PubMed

    Rhodes, Christopher J; Macrae, Roderick M

    2015-01-01

    A long-sought but elusive new type of chemical bond, occurring on a minimum-free, purely repulsive potential energy surface, has recently been convincingly shown to be possible on the basis of high-level quantum-chemical calculations. This type of bond, termed a vibrational bond, forms because the total energy, including the dynamical energy of the nuclei, is lower than the total energy of the dissociated products, including their vibrational zero-point energy. For this to be the case, the ZPE of the product molecule must be very high, which is ensured by replacing a conventional hydrogen atom with its light isotope muonium (Mu, mass = 1/9 u) in the system Br-H-Br, a natural transition state in the reaction between Br and HBr. A paramagnetic species observed in the reaction Mu +Br2 has been proposed as a first experimental sighting of this species, but definitive identification remains challenging. PMID:25942773

  17. High-strength edge-bonded sapphire windows

    NASA Astrophysics Data System (ADS)

    Gentilman, Richard L.; McGuire, Patrick T.; Pazol, Brian G.; Askinazi, Joel; Steindl, Robert; Locher, John W.

    1999-07-01

    High strength edge bonds have been achieved between individual sapphire components, showing promise for fabricating window blanks up to 600 mm diameter or larger in size. Several bonding methods were investigated, with a directed-energy diffusion-bonding method yielding components with bond fracture strengths of 200 MPa. Bonded sapphire components 600 mm long and 3 mm thick with a 75 mm wide bond line have been produced. When polished, the bonded windows show no degradation in transmittance or transmitted wavefront quality. Process scale up to larger bonds lines is planned. Mechanical and optical characterizations of sub- scale edge-bonded sapphire windows are presented.

  18. C-H bond activation as the initial step in the Co sup + -mediated demethanation of propane: The critical role of angular momentum at the rate-limiting transition state

    SciTech Connect

    van Koppen, P.A.M.; Brodbelt-Lustig, J.; Bowers, M.T. ); Dearden, D.V.; Beauchamp, J.L. ); Fisher, E.R.; Armentrout, P.B. )

    1990-07-04

    Exothermic reactions of transition-metal ions with alkanes have in many instances been shown to be facile in the gas phase. Reactions mainly result in the loss of molecular hydrogen and small alkanes to yield metal ion-olefin complexes. A variety of experimental techniques have provided thermochemical, kinetic, dynamic, and mechanistic information for these reactions, with an important focus being the identification of the initial activation step. The question of C-H versus C-C bond activation as the initial step in the formation of C-C bond cleavage products has yet to be resolved. The authors have measured reaction cross sections and kinetic energy release distributions for the exothermic reactions of Co{sup +} with propane, propane-2-d{sub 1}, propane-2,2-d{sub 2}, propane-1,1,1-d{sub 3}, propane-1,1,1,3,3,3-d{sub 6}, and propane-d{sub 8}.

  19. Hexacoordinate bonding and aromaticity in silicon phthalocyanine.

    PubMed

    Yang, Yang

    2010-12-23

    Si-E bondings in hexacoordinate silicon phthalocyanine were analyzed using bond order (BO), energy partition, atoms in molecules (AIM), electron localization function (ELF), and localized orbital locator (LOL). Bond models were proposed to explain differences between hexacoordinate and tetracoordinate Si-E bondings. Aromaticity of silicon phthalocyanine was investigated using nucleus-independent chemical shift (NICS), harmonic oscillator model of aromaticity (HOMA), conceptual density functional theory (DFT), ring critical point (RCP) descriptors, and delocalization index (DI). Structure, energy, bonding, and aromaticity of tetracoordinate silicon phthalocyanine were studied and compared with hexacoordinate one. PMID:21105726

  20. Halogen bonding origin properties and applications

    NASA Astrophysics Data System (ADS)

    Hobza, Pavel

    2015-12-01

    ?-hole bonding represents an unusual and novel type of noncovalent interactions in which atom with ?- hole interacts with Lewis base such as an electronegative atom (oxygen, nitrogen, ) or aromatic systems. This bonding is of electrostatic nature since the ?-hole bears a positive charge. Dispersion energy forms equally important energy term what is due to the fact that two heavy atoms (e.g. halogen and oxygen) having high polarizability lie close together (the respective distance is typically shorter than the sum of van der Waals radii). Among different types of ?-hole bondings the halogen bonding is by far the most known but chalcogen and pnictogen bondings are important as well.

  1. A dense and strong bonding collagen film for carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Cao, Sheng; Li, Hejun; Li, Kezhi; Lu, Jinhua; Zhang, Leilei

    2015-08-01

    A strong bonding collagen film was successfully prepared on carbon/carbon (C/C) composites. The surface conditions of the modified C/C composites were detected by contact angle measurements, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectra. The roughness, optical morphology, bonding strength and biocompatibility of collagen films at different pH values were detected by confocal laser scanning microscope (CLSM), universal test machine and cytology tests in vitro. After a 4-h modification in 30% H2O2 solution at 100 °C, the contact angle on the surface of C/C composites was decreased from 92.3° to 65.3°. Large quantities of hydroxyl, carboxyl and carbonyl functional groups were formed on the surface of the modified C/C composites. Then a dense and continuous collagen film was prepared on the modified C/C substrate. Bonding strength between collagen film and C/C substrate was reached to 8 MPa level when the pH value of this collagen film was 2.5 after the preparing process. With 2-day dehydrathermal treatment (DHT) crosslinking at 105 °C, the bonding strength was increased to 12 MPa level. At last, the results of in vitro cytological test showed that this collagen film made a great improvement on the biocompatibility on C/C composites.

  2. Hydrogen Bonded Arrays: The Power of Multiple Hydrogen Bonds

    SciTech Connect

    Shokri, Alireza; Schmidt, Jacob C.; Wang, Xue B.; Kass, Steven R.

    2012-02-01

    Hydrogen bond interactions in small covalent model compounds (i.e. deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH2CH2)2CHO (2a), (HOCH2CH2) 3CO (3a) and (HOCH2CH2CH(OH)CH2)3CO (4a) reveal that hydrogen-bonded networks can provide enormous stabilizations, and that a single charge center not only can be stabilized by up to 3 hydrogen bonds but it can increase the interaction energy between non-charged OH groups by 5.8 kcal mol1 or more per hydrogen bond. This can lead to pKa values that are very different than in water, and provide some of the impetus for catalytic processes.

  3. Thermochemistry of C7H16 to C10H22 alkane isomers: primary, secondary, and tertiary C-H bond dissociation energies and effects of branching.

    PubMed

    Hudzik, Jason M; Bozzelli, Joseph W; Simmie, John M

    2014-10-01

    Standard enthalpies of formation (?Hf298) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S(T)), heat capacities (Cp(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ?Hf298 and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBS-QB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ?Hf298 values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered. PMID:25180943

  4. Effects of Anti-Oxidant Migration on Friction and Wear of C/C Aircraft Brakes

    NASA Astrophysics Data System (ADS)

    Don, Jarlen; Wang, Zhe

    2009-04-01

    The surfaces of carbon-carbon (C/C) aircraft brakes are usually coated with anti-oxidant to protect them from oxidation. These surfaces do not include the friction surfaces since it is known that when anti-oxidant get onto the friction surface, the friction coefficient decreases. The anti-oxidant migration (AOM), however, happens during processing, heat treatment and application. In this study, phosphorus based anti-oxidants inhibited 3-D C/C aircraft brake system was investigated. The effects of their migration on friction and wear in the 3-D C/C brakes were revealed by sub-scale dynamometer tests and microscopic analysis. Dynamometer results showed that when AOM occurred, both landing and taxi coefficients decreased in humid environment and the wear was slightly lowered. Microscopic study showed that under high humidity conditions there was no formation of the friction film.

  5. Effectiveness of Diffusion Barrier Coatings for Mo-Re Embedded in C/SiC and C/C

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Shenoy, Ravi N.; Wang, Zeng-Mei; Halbig, Michael C.

    2001-01-01

    Advanced high-temperature cooling applications may often require the elevated-temperature capability of carbon/silicon carbide or carbon/carbon composites in combination with the hermetic capability of metallic tubes. In this paper, the effects of C/SiC and C/C on tubes fabricated from several different refractory metals were evaluated. Though Mo, Nb, and Re were evaluated in the present study, the primary effort was directed toward two alloys of Mo-Re, namely, arc cast Mo-41Re and powder metallurgy Mo-47.5Re. Samples of these refractory metals were subjected to either the PyC/SiC deposition or embedding in C/C. MoSi2(Ge), R512E, and TiB2 coatings were included on several of the samples as potential diffusion barriers. The effects of the processing and thermal exposure on the samples were evaluated by conducting burst tests, microhardness surveys, and scanning electron microscopic examination (using either secondary electron or back scattered electron imaging and energy dispersive spectroscopy). The results showed that a layer of brittle Mo-carbide formed on the substrates of both the uncoated Mo-41Re and the uncoated Mo-47.5Re, subsequent to the C/C or the PyC/SiC processing. Both the R512E and the MoSi2(Ge) coatings were effective in preventing not only the diffusion of C into the Mo-Re substrate, but also the formation of the Mo-carbides. However, none of the coatings were effective at preventing both C and Si diffusion without some degradation of the substrate.

  6. The influence of hydrogen bonding on the dielectric constant and the piezoelectric energy harvesting performance of hydrated metal salt mediated PVDF films.

    PubMed

    Jana, Santanu; Garain, Samiran; Sen, Shrabanee; Mandal, Dipankar

    2015-07-14

    Polyvinylidene fluoride (PVDF) films are filled with various mass fractions (wt%) of hydrated metal salt (MgCl2·6H2O) (Mg-salt) to fabricate high performance piezoelectric energy harvesters (PEHs). They deliver up to 4 V of open circuit voltage by simply repeated human finger imparting (under a pressure of ∼4.45 kPa) and also generate sufficient power to turn on at least ten commercial blue light emitting diodes (LEDs) instantly. The enhanced piezo-response is attributed to the combined effect of the change in the inherent dipole moment of the electroactive phase containing PVDF itself and H-bonding arising between the Mg-salt filler and PVDF via electrostatic interactions. Furthermore, it also successfully charged the capacitors, signifying practical applicability as a piezoelectric based energy harvester power source. UV-visible optical absorption spectral analysis revealed the possibility to estimate a change in the optical band gap value at different concentrations of Mg-salt filler added PVDF films that possess a useful methodology where the Mg-salt can be used as an optical probe. In addition dielectric properties have been studied to understand the role of molecular kinetic and interfacial polarization occurs in H-bond PVDF films at different applied frequencies at room temperature. PMID:26077827

  7. Influence of chlorine substitution on intramolecular hydrogen bond energy and ESIPT barrier: Experimental and theoretical measurements on the photophysics of 3,5-dichlorosalicylic acid

    NASA Astrophysics Data System (ADS)

    Paul, Bijan Kumar; Samanta, Anuva; Guchhait, Nikhil

    2010-08-01

    The effect of chlorine atom on the intramolecular hydrogen bond strength and excited state proton transfer barrier in pharmaceutically important chloro-substituted derivative of salicylic acid viz., 3,5-dichlorosalicylic acid (3,5DCSA) has been explored through steady-state absorption, emission and time-resolved fluorescence spectroscopy. Stokes shifted emission band with negligible solvent polarity dependency corresponds to the spectroscopic signature of excited state intramolecular proton transfer (ESIPT) reaction. The spectral signature was compared with its parent molecule salicylic acid (SA) and 5-chlorosalicylic acid (5ClSA). Quantum chemical calculations by ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods have been fruitfully employed to correlate experimental findings. Calculated S0 and S1 states potential energy surfaces across the proton transfer co-ordinate substantiates the experimental evidence for the occurrence of ESIPT process and negates the ground state intramolecular proton transfer (GSIPT) reaction. Weakening of intramolecular hydrogen bond (IMHB) energy and subsequent enhancement of barrier to ESIPT reaction in 3,5DCSA as compared to SA and 5ClSA appears to be a reflection of conjugate impact of electron withdrawing inductive and electron donating resonance effects of chlorine substitutions depending on its location on the aromatic benzene nucleus.

  8. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems.

    PubMed

    van Meer, R; Gritsenko, O V; Baerends, E J

    2014-01-14

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Lo?wdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Lo?wdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Lo?wdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate. PMID:24437859

  9. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

    NASA Astrophysics Data System (ADS)

    van Meer, R.; Gritsenko, O. V.; Baerends, E. J.

    2014-01-01

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Lwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Lwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Lwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate.

  10. Molecular functionalization of silicene/Ag(111) by covalent bonds: a DFT study.

    PubMed

    Stephan, Rgis; Hanf, Marie-Christine; Sonnet, Philippe

    2015-06-14

    Among the 2D crystals, silicene, which forms sp(2)-sp(3) bonds, is expected to present a higher reactivity than graphene, characterized by sp(2) bonds only. However, silicene functionalization, in particular with organic molecules, remains an open question. By means of density functional theory, we study the adsorption of benzene, a model organic molecule, on (3 3) silicene on the (4 4) Ag(111) surface. Our calculations show that the dispersion interactions must be taken into account in order to describe this system properly. The adsorption energy is calculated by means of the semi-empirical dispersion-corrected density functional theory (DFT-D2) and the optB86b-vdW density functional. The charge density and electron localization function maps indicate that the molecule is chemisorbed on the silicene surface by means of two Si-C covalent bonds. In agreement with charge density difference calculations, two C-C double bonds are formed in the benzene molecule, which adopts a butterfly configuration. The silicene lattice is slightly deformed upon benzene adsorption, but the Si-Si distance remains the same as in bare silicene/Ag(111). Bader analysis shows a charge transfer from top Si atoms to both molecules and Ag substrates. Finally, we show that the covalent functionalization of silicene is possible. PMID:25845773

  11. AlkyneAldehyde Reductive CC Coupling through Ruthenium-Catalyzed Transfer Hydrogenation: Direct Regio- and Stereoselective Carbonyl Vinylation to Form Trisubstituted Allylic Alcohols in the Absence of Premetallated Reagents

    PubMed Central

    Leung, Joyce C.; Patman, Ryan L.; Sam, Brannon

    2011-01-01

    Nonsymmetric 1,2-disubstituted alkynes engage in reductive coupling to a variety of aldehydes under the conditions of ruthenium-catalyzed transfer hydrogenation by employing formic acid as the terminal reductant and delivering the products of carbonyl vinylation with good to excellent levels of regioselectivity and with complete control of olefin stereochemistry. As revealed in an assessment of the ruthenium counterion, iodide plays an essential role in directing the regioselectivity of CC bond formation. Isotopic labeling studies corroborate reversible catalytic propargyl CH oxidative addition in advance of the CC coupling, and demonstrate that the CC coupling products do not experience reversible dehydrogenation by way of enone intermediates. This transfer hydrogenation protocol enables carbonyl vinylation in the absence of stoichiometric metallic reagents. PMID:21953608

  12. Comprehensive analysis of individual pulp fiber bonds quantifies the mechanisms of fiber bonding in paper

    NASA Astrophysics Data System (ADS)

    Hirn, Ulrich; Schennach, Robert

    2015-05-01

    The process of papermaking requires substantial amounts of energy and wood consumption, which contributes to larger environmental costs. In order to optimize the production of papermaking to suit its many applications in material science and engineering, a quantitative understanding of bonding forces between the individual pulp fibers is of importance. Here we show the first approach to quantify the bonding energies contributed by the individual bonding mechanisms. We calculated the impact of the following mechanisms necessary for paper formation: mechanical interlocking, interdiffusion, capillary bridges, hydrogen bonding, Van der Waals forces, and Coulomb forces on the bonding energy. Experimental results quantify the area in molecular contact necessary for bonding. Atomic force microscopy experiments derive the impact of mechanical interlocking. Capillary bridges also contribute to the bond. A model based on the crystal structure of cellulose leads to values for the chemical bonds. In contrast to general believe which favors hydrogen bonding Van der Waals bonds play the most important role according to our model. Comparison with experimentally derived bond energies support the presented model. This study characterizes bond formation between pulp fibers leading to insight that could be potentially used to optimize the papermaking process, while reducing energy and wood consumption.

  13. Comprehensive analysis of individual pulp fiber bonds quantifies the mechanisms of fiber bonding in paper.

    PubMed

    Hirn, Ulrich; Schennach, Robert

    2015-01-01

    The process of papermaking requires substantial amounts of energy and wood consumption, which contributes to larger environmental costs. In order to optimize the production of papermaking to suit its many applications in material science and engineering, a quantitative understanding of bonding forces between the individual pulp fibers is of importance. Here we show the first approach to quantify the bonding energies contributed by the individual bonding mechanisms. We calculated the impact of the following mechanisms necessary for paper formation: mechanical interlocking, interdiffusion, capillary bridges, hydrogen bonding, Van der Waals forces, and Coulomb forces on the bonding energy. Experimental results quantify the area in molecular contact necessary for bonding. Atomic force microscopy experiments derive the impact of mechanical interlocking. Capillary bridges also contribute to the bond. A model based on the crystal structure of cellulose leads to values for the chemical bonds. In contrast to general believe which favors hydrogen bonding Van der Waals bonds play the most important role according to our model. Comparison with experimentally derived bond energies support the presented model. This study characterizes bond formation between pulp fibers leading to insight that could be potentially used to optimize the papermaking process, while reducing energy and wood consumption. PMID:26000898

  14. What Determines Bond Costs. Municipal Bonds Series.

    ERIC Educational Resources Information Center

    Young, Douglas; And Others

    Public officials in small towns who participate infrequently in the bond market need information about bond financing. This publication, one in a series of booklets published by the Western Rural Development Center using research gathered between 1967-77, discusses factors influencing the marketability and cost of bond financing for towns and

  15. Ordered mesoporous TiC-C composites as cathode materials for Li-O2 batteries.

    PubMed

    Qiu, Feilong; He, Ping; Jiang, Jie; Zhang, Xueping; Tong, Shengfu; Zhou, Haoshen

    2016-02-01

    Ordered mesoporous TiC-C (OMTC) composites were prepared and served as catalysts for nonaqueous Li-O2 batteries. The OMTC cathodes showed high specific capacity, low overpotential and good cyclability. Furthermore, the reaction mechanism of Li-O2 batteries during charge and discharge processes was investigated extensively by XRD, XPS and in situ GC-MS methods. PMID:26756043

  16. Reversible C-C coupling in phenanthroline complexes of divalent samarium and thulium.

    PubMed

    Nocton, Grgory; Ricard, Louis

    2015-02-28

    The reaction of a series of organolanthanide fragments of samarium and thulium with phenanthroline is reported. All adducts couple in the 4-position of the phenanthroline ligand to yield the 4-4' dimers when they crystallize. The analysis of the solution structure revealed a thermally reversible C-C coupling in all cases. PMID:25634655

  17. 76 FR 44800 - Election of Reduced Research Credit Under Section 280C(c)(3)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-27

    ... claiming the reduced research credit under section 280C(c)(3). On July 16, 2009, a notice of proposed rulemaking (REG-130200-08) was published in the Federal Register (74 FR 34523). No public hearing was...(c)(3) AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Final regulations. SUMMARY:...

  18. Ultralong carbon-carbon bonds in dispirobis(10-methylacridan) derivatives with an acenaphthene, pyracene, or dihydropyracylene skeleton.

    PubMed

    Kawai, Hidetoshi; Takeda, Takashi; Fujiwara, Kenshu; Wakeshima, Makoto; Hinatsu, Yukio; Suzuki, Takanori

    2008-01-01

    Acenapthalene, pyracene, and dihydropyracylene attached to two units of spiroacridan are a novel class of hexaphenylethane (HPE) derivatives that have an ultralong Csp3-Csp3 bond (1.77-1.70 A). These sterically challenged molecules were cleanly prepared by C-C bond formation through two-electron reduction from the less-hindered dications. These ultralong bonds were realized based on several molecular-design concepts including enhanced "front strain" through "multiclamping" by means of fusing or bridging aryl groups in the HPE molecule. The lengths of these ultralong bonds and their relation to the conformation (torsional angle) were also validated by means of theoretical calculations. Bond-fission experiments revealed that the bonds are more easily cleaved than standard covalent bonds to produce the corresponding dication upon oxidation with an increase in the length of the C-C bond. PMID:18478615

  19. Synthesis of Polyheteroaromatic Compounds via Rhodium-Catalyzed Multiple C-H Bond Activation and Oxidative Annulation.

    PubMed

    Peng, Shiyong; Liu, Suna; Zhang, Sai; Cao, Shengyu; Sun, Jiangtao

    2015-10-16

    Polyheteroaromatic compounds are potential optoelectronic conjugated materials due to their electro- and photochemical properties. Transition-metal-catalyzed multiple C-H activation and sequential oxidative annulation allows rapidly assembling of those compounds from readily available starting materials. A rhodium-catalyzed cascade oxidative annulation of ?-enamino esters or 4-aminocoumarins with internal alkynes is described to access those compounds, featuring multiple C-H/N-H bond cleavages and sequential C-C/C-N bond formations in one pot. PMID:26439472

  20. Predicting Trigger Bonds in Explosive Materials through Wiberg Bond Index Analysis.

    PubMed

    Harper, Lenora K; Shoaf, Ashley L; Bayse, Craig A

    2015-12-01

    Understanding the explosive decomposition pathways of high-energy-density materials (HEDMs) is important for developing compounds with improved properties. Rapid reaction rates make the detonation mechanisms of HEDMs difficult to understand, so computational tools are used to predict trigger bonds-weak bonds that break, leading to detonation. Wiberg bond indices (WBIs) have been used to compare bond densities in HEDMs to reference molecules to provide a relative scale for the bond strength to predict the activated bonds most likely to break to trigger an explosion. This analysis confirms that X-NO2 (X=N,C,O) bonds are trigger linkages in common HEDMs such as TNT, RDX and PETN, consistent with previous experimental and theoretical studies. Calculations on a small test set of substituted tetrazoles show that the assignment of the trigger bond depends upon the functionality of the material and that the relative weakening of the bond correlates with experimental impact sensitivities. PMID:26458868