Science.gov

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. Mechanistic studies of processes involving C-C bond cleavage in gas-phase organometallic reactions using product kinetic energy release distributions: Co sup + reacting with cyclopentane

    SciTech Connect

    van Koppen, P.A.M.; Bowers, M.T. ); Beauchamp, J.L. )

    1990-03-01

    A reverse-geometry mass spectrometer is used to obtain product ion kinetic energy release distributions to probe the energetics and mechanisms of several gas-phase organometallic reactions. In particular, we examine the mechanism for C{sub 2}H{sub 4} and C{sub 3}H{sub 6} elimination from Co(cyclopentane){sup +}. The kinetic energy release distribution associated with these processes can be modeled by using phase space calculations assuming, for the C{sub 3}H{sub 6} elimination process, propene rather than cyclopropane is being eliminated as the product neutral, and for the C{sub 2}H{sub 4} elimination process, Co(propene){sup +} rather than (cobaltacyclobutane){sup +} is being formed as the product ion. In addition, we obtain a heat of formation for the cobalt ethylene ion of 255 kcal/mol at 0 K, corresponding to a bond dissociation energy of 42 kcal/mol at 0 K, by fitting the theoretical results to the experimental distribution.

  8. 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

  9. 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.

  10. Theoretical thermochemistry of homolytic C-C and C-Cl bond dissociations in unbranched perchloroalkanes

    SciTech Connect

    Cioslowski, J.; Liu, G.; Moncrieff, D.

    1998-11-26

    Proper description of the dispersion interactions that attenuate the closed-shell repulsions among chlorine atoms in n-perchloroalkanes requires an accurate treatment of long-range electron correlation effects. The presently known density functionals, which do not correctly account for such effects, grossly underestimate thermodynamic stability of these molecules, yielding the standard enthalpy {Delta}H{degree}{sub C-C} of C-C bond dissociation in n-C{sub 4}Cl{sub 10} as low as 20 kcal/mol. In contrast, the predictions of the CBS-4 scheme fail to reproduce the weakening of the C-C bonds that is experimentally observed in the higher members of the C{sub n}Cl{sub 2n+2} homologous series. For the CCl{sub 4} and C{sub 2}Cl{sub 6} the most reliable estimates of {Delta}H{degree}{sub C-C} and {Delta}H{degree}{sub C-Cl} are provided by the G2 And G2MP2 methods. The MP2/6-311G{sup **} level of theory (without ZPEs and finite-temperature corrections) appears at present to be the only viable, though quite inaccurate, theoretical approach to theoretical thermochemistry of larger chlorocarbons. At that level of theory, {Delta}H{degree}{sub C-C} is predicted to decrease by ca. 10 kcal/mol upon the addition of each -CCl{sub 2}- unit, convincingly explaining the thermal lability of higher n-perchloroalkanes. Similar conclusions are reached by examining the estimates of {Delta}H{degree}{sub C-C} derived from the CBS-4 standard enthalpies with the E{sub CBS} energy term excluded.

  11. 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.

  12. Stereochemistry of enzymatic water addition to C=C bonds.

    PubMed

    Chen, Bi-Shuang; Otten, Linda G; Hanefeld, Ulf

    2015-01-01

    Water addition to carbon-carbon double bonds using hydratases is attracting great interest in biochemistry. Most of the known hydratases are involved in primary metabolism and to a lesser extent in secondary metabolism. New hydratases have recently been added to the toolbox, both from natural sources or artificial metalloenzymes. In order to comprehensively understand how the hydratases are able to catalyse the water addition to carbon-carbon double bonds, this review will highlight the mechanistic and stereochemical studies of the enzymatic water addition to carbon-carbon double bonds, focusing on the syn/anti-addition and stereochemistry of the reaction. PMID:25640045

  13. 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

  14. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Ruthenium-catalyzed conversion of sp3 C-O bonds in ethers to C-C bonds using triarylboroxines.

    PubMed

    Ogiwara, Yohei; Kochi, Takuya; Kakiuchi, Fumitoshi

    2011-06-17

    Catalytic conversion of unreactive sp(3) C-O bonds in alkyl ethers to C-C bonds is described. Alkyl ethers bearing 2- or 4-pyridyl groups were coupled with triarylboroxines in the presence of a ruthenium catalyst. Triarylboroxines bearing a variety of functional groups including electron-withdrawing and -donating groups can be used for the reaction. No additional base was required for the coupling with the organoboron reagents, and base-sensitive groups can be tolerated. The reaction is considered to proceed via dehydroalkoxylation followed by addition of triarylboroxines to form C-C bonds. PMID:21598994

  17. Synthesis of 2-Benzylphenyl Ketones by Aryne Insertion into Unactivated C-C Bonds.

    PubMed

    Rao, Bin; Tang, Jinghua; Zeng, Xiaoming

    2016-04-01

    A transition-metal-free procedure to access to functionalized 2-benzylphenyl ketones is described by direct insertion of arynes into benzylic C-C bonds. This reaction was promoted by cesium fluoride at room temperature, allowing the products to form in high selectivity and achieve good functional group tolerance. PMID:27004731

  18. 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

  19. [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.

  20. Organic chemistry. Rh-catalyzed C-C bond cleavage by transfer hydroformylation.

    PubMed

    Murphy, Stephen K; Park, Jung-Woo; Cruz, Faben A; Dong, Vy M

    2015-01-01

    The dehydroformylation of aldehydes to generate olefins occurs during the biosynthesis of various sterols, including cholesterol in humans. Here, we implement a synthetic version that features the transfer of a formyl group and hydride from an aldehyde substrate to a strained olefin acceptor. A Rhodium (Xantphos)(benzoate) catalyst activates aldehyde carbon-hydrogen (C-H) bonds with high chemoselectivity to trigger carbon-carbon (C-C) bond cleavage and generate olefins at low loadings (0.3 to 2 mole percent) and temperatures (22° to 80°C). This mild protocol can be applied to various natural products and was used to achieve a three-step synthesis of (+)-yohimbenone. A study of the mechanism reveals that the benzoate counterion acts as a proton shuttle to enable transfer hydroformylation. PMID:25554782

  1. 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.

  2. Palladium(II)-catalyzed dehydrogenative cross-coupling between two C(sp3)-H bonds: unexpected C=C bond formation.

    PubMed

    Li, Gaocan; Qian, Shengyou; Wang, Chunxia; You, Jingsong

    2013-07-22

    C=C bond construction: A palladium-catalyzed oxidative C(sp3)-H/C(sp3)-H cross-coupling is shown to forge C=C bonds rather than C(sp3)-C(sp3) bonds through reactions of indolin-2-ones or benzofuran-2-ones with O-benzoyl hydroxylamines in the absence of an added oxidant. PMID:23780778

  3. 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

  4. 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.

  5. Unusual formation of a N-heterocyclic germylene via homolytic cleavage of a C-C bond.

    PubMed

    Li, Yan; Mondal, Kartik Chandra; Stollberg, Peter; Zhu, Hongping; Roesky, Herbert W; Herbst-Irmer, Regine; Stalke, Dietmar; Fliegl, Heike

    2014-03-28

    Reaction of the monoanionic radical salt IP˙(-)K(+) (IP = (Py)CH(=NR); Py = C5H4N, R = 2,6-iPr2C6H3; α-iminopyridine) with GeCl2(dioxane) afforded compound (IPGeCl)2 (1) which produced red blocks of IPGe: (2), when treated with KC8 in toluene. 1 is a digermylene formed via C-C coupling between two carbon-centered radicals. 2 can be considered as an analogue of a N-heterocyclic carbene, which exhibits a five-membered GeC2N2 ring with one C=C double bond. 2 is formed by two-electron reduction of 1 with cleavage of the two Ge-Cl bonds and the central C-C single bond. PMID:24549122

  6. Central C-C Bonding Increases Optical and Chemical Stability of NIR Fluorophores

    PubMed Central

    Hyun, Hoon; Owens, Eric A.; Narayana, Lakshminarayana; Wada, Hideyuki; Gravier, Julien; Bao, Kai; Frangioni, John V.; Choi, Hak Soo; Henary, Maged

    2014-01-01

    Functional near-infrared (NIR) fluorophores have played a major role in the recent advances in bioimaging. However, the optical and physicochemical stabilities of NIR fluorophores in the biological and physiological environment are still a challenge. Especially, the ether linkage on the meso carbon of heptamethine core is fragile when exposed to serum proteins or other amine-rich biomolecules. To solve such a structural limitation, a rigid carbon-carbon bond was installed onto the framework of ether-linked NIR fluorophores through the Suzuki coupling. The robust fluorophores replaced as ZW800-1C and ZW800-3C displayed enhanced optical and chemical stability in various solvents and a 100% warm serum environment (> 99%, 24 h). The biodistribution and clearance of C-C coupled ZW800 compounds were almost identical to the previously developed oxygen-substituted ZW800 compounds. When conjugated with a small molecule ligand, ZW800-1C maintained the identical stable form in warm serum (>98%, 24 h), while ZW800-1A hydrolyzed quickly after 4 h incubation (34%, 24 h). PMID:25530846

  7. 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

  8. An alternative synthesis of the breast cancer drug fulvestrant (Faslodex®): catalyst control over C-C bond formation.

    PubMed

    Caprioglio, Diego; Fletcher, Stephen P

    2015-10-14

    Fulvestrant (Faslodex®) was synthesized in four steps (35% overall yield) from 6-dehydronandrolone acetate. Catalyst controlled, room temperature, diastereoselective 1,6-addition of the zirconocene derived from commercially available 9-bromonon-1-ene was used in the key C-C bond forming step. PMID:26300021

  9. 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

  10. 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

  11. Identification of Possible Pathways for C-C Bond Formation during Electrochemical Reduction of CO2: New Theoretical Insights from an Improved Electrochemical Model.

    PubMed

    Goodpaster, Jason D; Bell, Alexis T; Head-Gordon, Martin

    2016-04-21

    We have carried out a periodic Kohn-Sham density functional theory investigation of the pathways by which carbon-carbon bonds could be formed during the electrochemical reduction of CO2 on Cu(100) using a model that includes the effects of the electrochemical potential, solvent, and electrolyte. The electrochemical potential was set by relating the applied potential to the Fermi energy and then calculating the number of electrons required by the simulation cell for that specific Fermi energy. The solvent was included as a continuum dielectric, and the electrolyte was described using a linearized Poisson-Boltzmann model. The calculated potential of zero charge for a variety of surfaces agrees with experiment to within a mean average error of 0.09 V, thereby validating the assumptions of the model. Analysis of the mechanism for C-C bond formation revealed that at low-applied potential, C-C bond formation occurs through a CO dimer. However, at high applied potentials, a large activation barrier blocks this pathway; therefore, C-C bond formation occurs through reaction of adsorbed CHO and CO. Rate parameters determined from our calculations were used to simulate the kinetics of ethene formation during the electrochemical reduction of CO over a Cu(100) surface. An excellent match was observed between previously reported measurements of the partial current for ethene formation as a function of applied voltage and the variation in the partial current for C-C bond formation predicted by our microkinetic model. The electrochemical model reported here is simple, fairly easy to implement, and involves only a small increase in computational cost over calculations neglecting the effects of the electrolyte and the applied field. Therefore, it can be used to study the effects of applied potential and electrolyte composition on the energetics of surface reactions for a wide variety of electrochemical reactions. PMID:27045040

  12. Oxidative C(sp3)-H bond cleavage, C-C and C=C coupling at a boron center with O2 as the oxidant mediated by platinum(II).

    PubMed

    Pal, S; Zavalij, P Y; Vedernikov, A N

    2014-05-25

    Dimethyl- and diphenylplatinum(II) fragments Pt(II)R2 (R = Me, Ph) enable facile and efficient oxidative C(sp(3))-H bond cleavage and stepwise C-C and C=C coupling at the boron atom of a coordinated 1,5-cyclooctanediyldi(2-pyridyl)borato ligand with O2 as the sole oxidant. PMID:24287586

  13. 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

  14. Gold-Catalyzed Oxidation of Propargylic Ethers with Internal C-C Triple Bonds: Impressive Regioselectivity Enabled by Inductive Effect

    PubMed Central

    Ji, Kegong; D’Souza, Brendan; Nelson, Jon; Zhang, Liming

    2014-01-01

    Inductive perturbations of C-C triple bonds are shown to dictate the regiochemistry of gold-catalyzed oxidation of internal C-C triple bonds in the cases of propargylic ethers, resulting in highly regioselective formation of β-alkoxy-α,β-unsaturated ketones (up to >50/1 selectivity) via α-oxo gold carbene intermediates. Ethers derived from primary propargylic alcohols can be reliably transformed in good yields, and various functional groups are tolerated. With substrates derived from secondary propargylic alcohols, the development of a new P,N-bidentate ligand enables the minimization of competing alkyl group migration to the gold carbene center over the desired hydride migration; the preferred migration of a phenyl group, however, results in efficient formation of a α-phenyl-β-alkoxy-α,β-unsaturated ketone. These results further advance the surrogacy of a propargyl moiety to synthetically versatile enone function with reliable and readily predictable regioselectivity. PMID:25284890

  15. Highly Selective Cascade C-C Bond Formation via Palladium- Catalyzed Oxidative Carbonylation-Carbocyclization-Carbonylation-Alkynylation of Enallenes.

    PubMed

    Zhu, Can; Yang, Bin; Bäckvall, Jan-E

    2015-09-23

    A highly efficient palladium-catalyzed oxidative cascade reaction of enallenes undergoing overall four C-C bond formations has been developed. The insertion cascade proceeds via carbonylation-carbocyclization-carbonylation-alkynylation involving sequential insertion of carbon monoxide, olefin, and carbon monoxide. Furthermore, different types of terminal alkynes and functionalized enallenes have been investigated and found to undergo the cascade reaction under mild reaction conditions. PMID:26356201

  16. Ring Expansion via Cleavage of Benzylic C-C Bonds Enabling Direct Synthesis of Medium Ring-Fused Benzocarbocycles.

    PubMed

    Rao, Bin; Tang, Jinghua; Wei, Yu; Zeng, Xiaoming

    2016-04-01

    A fluoride-anion-induced, regioselective ring expansion of benzocyclic ketones and α-aryl cycloketones has been developed via insertion of arynes into unactivated benzylic C-C bonds. This reaction provides a straightforward, transition-metal-free avenue to prepare medium ring-fused benzocarbocycles by creating "noble" seven-, eight-, and nine-membered rings. Applications of this method in the creation of medium-sized exocyclic and inner benzocyclic olefins, nine-membered lactones, and lactams are described. PMID:26970443

  17. Stereoselective total synthesis of (-)-nupharamine utilizing an α-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 α-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

  18. Direct approaches to nitriles via highly efficient nitrogenation strategy through C-H or C-C bond cleavage.

    PubMed

    Wang, Teng; Jiao, Ning

    2014-04-15

    Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C-H or C-C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C-N bond formation via C-H or C-C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C-H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C-H or C-C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out C(sp(3))-H functionalization on benzylic, allylic, and propargylic C-H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of C═C double-bonds and C≡C triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our synthetic strategy more attractive. Our direct nitrile synthesis methodologies have potential applications in the synthesis of biologically active molecules and drug candidates. PMID:24684545

  19. Ceric ammonium nitrate (CAN) catalyzed modification of ketones via two C-C bond cleavages with the retention of the oxo-group.

    PubMed

    Feng, Peng; Sun, Xiang; Su, Yijin; Li, Xinyao; Zhang, Li He; Shi, Xiaodong; Jiao, Ning

    2014-06-20

    A simple ceric ammonium nitrate (CAN) catalyzed functionalization of ketones through double C-C bond cleavage strategy has been disclosed. This reaction provides a mild, practical method toward carbamoyl azides, which are versatile intermediates and building blocks in organic synthesis. Based on relevant mechanistic studies, a unique and plausible C-C bond and N-O bond cleavage process is proposed, where the oxyamination intermediate plays an important role in this reaction. PMID:24906031

  20. 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

  1. Ternary Electrocatalysts for Oxidizing Ethanol to Carbon Dioxide: Making Ir Capable of Splitting C-C bond

    SciTech Connect

    Li, Meng; Cullen, David A; Sasaki, Kotaro; Marinkovic, N.; More, Karren Leslie; Adzic, Radoslav R.

    2013-01-01

    Splitting the C-C bond is the main obstacle to electroxidation of ethanol (EOR) to CO2. We recently demonstrated that the ternary PtRhSnO2 electrocatalyst can accomplish that reaction at room temperature with Rh having a unique capability to split the C-C bond. In this article we report the finding that Ir can be induced to split the C-C bond as a component of the ternary catalyst. We synthesized, characterized and compared the properties of several ternary electrocatalysts. Carbon-supported nanoparticle (NP) electrocatalysts comprising a SnO2 NP core decorated with multi-metallic nanoislands (MM = PtIr, PtRh, IrRh, PtIrRh) were prepared using a seeded growth approach. An array of characterization techniques were employed to establish the composition and architecture of the synthesized MM /SnO2 NPs, while electrochemical and in situ infrared reflection absorption spectroscopy studies elucidated trends in activity and the nature of the reaction intermediates and products. Both EOR reactivity and selectivity towards CO2 formation of several of these MM /SnO2/C electrocatalysts are significantly higher compared to conventional Pt/C and Pt/SnO2/C catalysts. We demonstrate that the PtIr/SnO2/C catalyst with high Ir content shows outstanding catalytic property with the most negative EOR onset potential and reasonably good selectivity towards ethanol complete oxidation to CO2. PtRh/SnO2/C catalysts with a moderate Rh content exhibit the highest EOR selectivity, as deduced from infrared studies.

  2. 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.

  3. 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

  4. 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)

  5. 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.

  6. 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

  7. Recombinant Cyanobacteria for the Asymmetric Reduction of C=C Bonds Fueled by the Biocatalytic Oxidation of Water.

    PubMed

    Köninger, Katharina; Gómez Baraibar, Álvaro; Mügge, Carolin; Paul, Caroline E; Hollmann, Frank; Nowaczyk, Marc M; Kourist, Robert

    2016-04-25

    A recombinant enoate reductase was expressed in cyanobacteria and used for the light-catalyzed, enantioselective reduction of C=C bonds. The coupling of oxidoreductases to natural photosynthesis allows asymmetric syntheses fueled by the oxidation of water. Bypassing the addition of sacrificial cosubstrates as electron donors significantly improves the atom efficiency and avoids the formation of undesired side products. Crucial factors for product formation are the availability of NADPH and the amount of active enzyme in the cells. The efficiency of the reaction is comparable to typical whole-cell biotransformations in E. coli. Under optimized conditions, a solution of 100 mg prochiral 2-methylmaleimide was reduced to optically pure 2-methylsuccinimide (99 % ee, 80 % yield of isolated product). High product yields and excellent optical purities demonstrate the synthetic usefulness of light-catalyzed whole-cell biotransformations using recombinant cyanobacteria. PMID:27029020

  8. Rh(III)-Catalyzed Synthesis of N-Unprotected Indoles from Imidamides and Diazo Ketoesters via C-H Activation and C-C/C-N Bond Cleavage.

    PubMed

    Qi, Zisong; Yu, Songjie; Li, Xingwei

    2016-02-19

    The synthesis of N-unprotected indoles has been realized via Rh(III)-catalyzed C-H activation/annulation of imidamides with α-diazo β-ketoesters. The reaction occurs with the release of an amide coproduct, which originates from both the imidamide and the diazo as a result of C═N cleavage of the imidamide and C-C(acyl) cleavage of the diazo. A rhodacyclic intermediate has been isolated and a plausible mechanism has been proposed. PMID:26824751

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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

  15. Palladium-mediated C-C bond forming reactions: Cross-coupling reactions of organozinc and organotin reagents with purinones and triazines

    SciTech Connect

    Xia, Y.; Mirzai, B.; Chackalamannil, S.

    1995-12-31

    Palladium-mediated cross coupling reactions of organozinc and organotin reagents were used to form C-C bonds on heterocyclic substrates (8-bromopurin-6-ones and monochloro-1,3,5-triazines). These reactions represent the first examples of such coupling reactions on the above heterocyclic systems and they offer new ways to introduce a variety of carbon substituents into purinones and triazines.

  16. A facile C-C bond cleavage in the epoxides and its use for the synthesis of oxygenated heterocycles by a ring expansion strategy.

    PubMed

    Lakshmipathi, Pandarinathan; Grée, Danielle; Grée, René

    2002-02-01

    The bicyclic epoxy alcohols when treated with DAST gave a new class of rearranged organofluorine compounds, by a ring expansion via C-C bond cleavage of the oxirane ring. The outcome of this reaction with respect to ring size and stereochemical relation between the functionalities is presented here. PMID:11820902

  17. Factors That Control C-C Cleavage versus C-H Bond Hydroxylation in Copper-Catalyzed Oxidations of Ketones with O2.

    PubMed

    Tsang, Althea S-K; Kapat, Ajoy; Schoenebeck, Franziska

    2016-01-20

    The Cu-catalyzed oxidation of ketones with O2 has recently been extensively utilized to cleave the α-C-C bond. This report examines the selective aerobic hydroxylation of tertiary α-C-H bonds in ketones without C-C cleavage. We set out to understand the underlying mechanisms of these two possible reactivity modes. Using experimental, in situ IR spectroscopic, and computational studies, we investigated several mechanisms. Our data suggest that both C-C cleavage and C-H hydroxylation pathways proceed via a common key intermediate, i.e., an α-peroxo ketone. The fate of this peroxide dictates the ultimate product selectivity. Specifically, we uncovered the role of hppH [= 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine] to act not only as a base in the transformation but also as a reductant of the peroxide to the corresponding α-hydroxy ketone. This reduction may also be accomplished through exogenous phosphine additives, therefore allowing the tuning of reduction efficiency toward higher driving forces, if required (e.g., for more-activated substrates). The likely competitive pathway is the cleavage of peroxide to the α-oxy radical (likely catalyzed by Cu), which is computationally predicted to spontaneously trigger C-C bond cleavage. Increasing the susceptibility of this deperoxidation step via (i) the removal of reductant (use of different base, e.g., DBU) or the modulation of (ii) the substitution pattern toward greater activation (substrate control) and (iii) the nature of Cu catalyst (counterion and solvent dependence) will favor the C-C cleavage product. PMID:26675262

  18. 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

  19. Iridium-Catalyzed Formal [4 + 1] Cycloaddition of Biphenylenes with Alkenes Initiated by C-C Bond Cleavage for the Synthesis of 9,9-Disubstituted Fluorenes.

    PubMed

    Takano, Hideaki; Kanyiva, Kyalo Stephen; Shibata, Takanori

    2016-04-15

    An Ir-catalyzed intermolecular reaction of biphenylenes as a C4 unit with various alkenes as a C1 unit gave 9,9-disubstituted fluorenes in moderate to high yields. Preliminary mechanistic studies revealed that this formal [4 + 1] cycloaddition probably proceeds via C-C bond cleavage, alkene insertion, β-hydrogen elimination, intramolecular alkene insertion, and then reductive elimination. An example of enantioselective reaction was also disclosed. PMID:27031498

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. Formation of C-C Bonds via Ruthenium Catalyzed Transfer Hydrogenation: Carbonyl Addition from the Alcohol or Aldehyde Oxidation Level

    PubMed Central

    Shibahara, Fumitoshi; Krische, Michael J.

    2011-01-01

    Under the conditions of ruthenium catalyzed transfer hydrogenation employing isopropanol as terminal reductant, π-unsaturated compounds (1,3-dienes, allenes, 1,3-enynes and alkynes) reductively couple to aldehydes to furnish products of carbonyl addition. In the absence of isopropanol, π-unsaturated compounds couple directly from the alcohol oxidation level to form identical products of carbonyl addition. Such “alcohol-unsaturate C-C couplings” enable carbonyl allylation, propargylation and vinylation from the alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Thus, direct catalytic C-H functionalization of alcohols at the carbinol carbon is achieved. PMID:21927534

  5. Accurate In Bond Energies

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    InXn atomization energies are computed for n = 1-3 and X = H, Cl, and CH3. The geometries and frequencies are determined using density functional theory. The atomization energies are computed at the coupled cluster level of theory. The complete basis set limit is obtained by extrapolation. The scalar relativistic effect is computed using the Douglas-Kroll approach. While the heats of formation for InH, InCl and InCl3 are in good agreement with experiment, the current results show that the experimental value for In(CH3)3 must be wrong.

  6. 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

  7. Competitive intramolecular C-C vs. C-O bond coupling reactions toward C6 ring-fused 2-pyridone synthesis.

    PubMed

    Lepitre, T; Pintiala, C; Muru, K; Comesse, S; Rebbaa, A; Lawson, A M; Daïch, A

    2016-04-14

    An interesting competitive C-C vs. C-O bond coupling reaction on N,3,5-trisubstituted pyridones is reported. These coupling reactions provided selective access to C- or O-ring-fused pyridones, both at the challenging C6-pyridone position. 1,6-C-Annulated pyridones were generally achieved in good yields with excellent chemoselectivity under Pd(0) conditions. On the other hand, full C6-regioselective Csp(2) aryloxylation was achieved under oxidative coupling promoted by silver salts to access 5,6-O-annulated pyridones. Based on various experiments and observations, mechanistic evidence of these competitive reactions was provided and it was proposed that C-O bond formation proceeded through radical cyclization. These processes were performed under mild reaction conditions and offer an efficient and attractive methodology to selectively access a large scope of C-arylated and O-arylated pyridones of biological interest. PMID:26976735

  8. 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.

  9. 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.

  10. Cu-catalyzed cross-dehydrogenative coupling: A versatile strategy for C-C bond formations via the oxidative activation of sp3 C-H bonds

    NASA Astrophysics Data System (ADS)

    Li, Zhiping; Bohle, D. Scott; Li, Chao-Jun

    2006-06-01

    Cu-catalyzed cross-dehydrogenative coupling (CDC) methodologies were developed based on the oxidative activation of sp3 C-H bonds adjacent to a nitrogen atom. Various sp, sp2, and sp3 C-H bonds of pronucleophiles were used in the Cu-catalyzed CDC reactions. Based on these results, the mechanisms of the CDC reactions also are discussed. C-H activation | catalysis | Baylis-Hillman reaction | Mannich reaction | Friedel-Crafts reaction

  11. Selective scission of C-O and C-C bonds in ethanol using bimetal catalysts for the preferential growth of semiconducting SWNT arrays.

    PubMed

    Zhang, Shuchen; Hu, Yue; Wu, Juanxia; Liu, Dan; Kang, Lixing; Zhao, Qiuchen; Zhang, Jin

    2015-01-28

    For the application of single-walled carbon nanotubes (SWNTs) to electronic and optoelectronic devices, techniques to obtain semiconducting SWNT (s-SWNT) arrays are still in their infancy. We have developed herein a rational approach for the preferential growth of horizontally aligned s-SWNT arrays on a ST-cut quartz surface through the selective scission of C-O and C-C bonds of ethanol using bimetal catalysts, such as Cu/Ru, Cu/Pd, and Au/Pd. For a common carbon source, ethanol, a reforming reaction occurs on Cu or Au upon C-C bond breakage and produces C(ads) and CO, while a deoxygenating reaction occurs on Ru or Pd through C-O bond breaking resulting in the production of O(ads) and C2H4. The produced C2H4 by Ru or Pd can weaken the oxidative environment through decomposition and the neutralization of O(ads). When the bimetal catalysts with an appropriate ratio were used, the produced C(ads) and C2H4 can be used as carbon source for SWNT growth, and O(ads) promotes a suitable and durable oxidative environment to inhibit the formation of metallic SWNTs (m-SWNTs). Finally, we successfully obtained horizontally aligned SWNTs on a ST-cut quartz surface with a density of 4-8 tubes/μm and an s-SWNT ratio of about 93% using an Au/Pd (1:1) catalyst. The synergistic effects in bimetallic catalysts provide a new mechanism to control the growth of s-SWNTs. PMID:25585016

  12. 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)

  13. The cross-dehydrogenative coupling of C(sp3)-H bonds: a versatile strategy for C-C bond formations.

    PubMed

    Girard, Simon A; Knauber, Thomas; Li, Chao-Jun

    2014-01-01

    Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH bonds. This strategy was introduced by the group of Li as cross-dehydrogenative coupling (CDC) and discloses waste-minimized synthetic alternatives to classic coupling procedures which rely on the use of prefunctionalized starting materials. This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies. PMID:24214829

  14. The nature of solid-state N-H triplebondO/O-H triplebond N tautomeric competition in resonant systems. Intramolecular proton transfer in low-barrier hydrogen bonds formed by the triplebond O=C-C=N-NH triple bond --> <-- triplebond HO-C=C-N=N triplebond Ketohydrazone-Azoenol system. A variable-temperature X-ray crystallographic and DFT computational study.

    PubMed

    Gilli, Paola; Bertolasi, Valerio; Pretto, Loretta; Lycka, Antonín; Gilli, Gastone

    2002-11-13

    The tautomeric.O=C-C=N-NH triplebond --> <-- HO-C=C-N=N triplebond ketohydrazone-azoenol system may form strong N-H triplebond O/O-H triplebond N intramolecular resonance-assisted H-bonds (RAHBs) which are sometimes of the low-barrier H-bond type (LBHB) with dynamic exchange of the proton in the solid state. The problem of the N-H triplebond O/O-H triplebond N competition in these compounds is studied here through variable-temperature (100, 150, 200, and 295 K) crystal-structure determination of pF = 1-(4-F-phenylazo)2-naphthol and oF = 1-(2-F-phenylazo)2-naphthol, two molecules that, on the ground of previous studies (Gilli, P; Bertolasi, V.; Ferretti, V.; Gilli, G. J. Am. Chem. Soc. 2000, 122, 10405), were expected to represent an almost perfect balance of the two tautomers. According to predictions, the two molecules form remarkably strong bonds (d(N triplebond O) = 2.53-2.55 A) of double-minimum or LBHB type with dynamic N-H triplebond O/ O-H triplebond N exchange in the solid state. The enthalpy differences between the two minima, as measured by van't Hoff methods from the X-ray-determined proton populations, are very small and amount to DeltaH degrees = -0.120 and DeltaH degrees = -0.156 kcal mol(-)(1) in favor of the N-H triplebond O form for pF and oF, respectively. Successive emulation of pF by DFT methods at the B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d,p) level has shown that both energetic and geometric experimental aspects can be almost perfectly reproduced. Generalization of these results was sought by performing DFT calculations at the same level of theory along the complete proton-transfer (PT) pathway for five test molecules designed in such a way that the RAHB formed changes smoothly from weak N-H triplebond O to strong O-H.N through very strong N-H triplebond O/O-H triplebond N bond of LBHB type. A systematic correlation analysis of H-bond energies, H-bond and pi-conjugated fragment geometries, and H-bond Bader's AIM topological properties performed along the PT-pathways leads to the following conclusions: (a) any X-H triplebond Y H-bonded system is fully characterized by its intrinsic PT-barrier, that is, the symmetric barrier occurring when the proton affinities of X and Y are identical; (b) the intrinsic X-H triplebond Y bond associated with the symmetric barrier is the strongest possible bond in that system and will be single-minimum (single-well, no-barrier) or double-minimum (double-well, low-barrier) according to whether the intrinsic PT-barrier is lower or slightly higher than the zero-point vibrational level of the proton; (c) with reference to the intrinsic H-bond, the effect of chemical substitution can only be that of making more and more dissymmetric the PT-barrier, while the two H-bonds split in a higher-energy bond which is stronger because closer to the transition-state structure and in a lower-energy one (the stable form) which is weaker because farther from it; (d) complete dissymmetrization of the PT-barrier will increasingly weaken the more stable H-bond until the formation of an extreme dissymmetric single-minimum or dissymmetric single-well H-bond. PMID:12418911

  15. A Substrate-Assisted Mechanism of Nucleophile Activation in a Ser-His-Asp Containing C-C Bond Hydrolase

    SciTech Connect

    Ruzzini, Antonio C.; Bhowmik, Shiva; Ghosh, Subhangi; Yam, Katherine C.; Bolin, Jeffrey T.; Eltis, Lindsay D.

    2013-11-12

    The meta-cleavage product (MCP) hydrolases utilize a Ser–His–Asp triad to hydrolyze a carbon–carbon bond. Hydrolysis of the MCP substrate has been proposed to proceed via an enol-to-keto tautomerization followed by a nucleophilic mechanism of catalysis. Ketonization involves an intermediate, ESred, which possesses a remarkable bathochromically shifted absorption spectrum. We investigated the catalytic mechanism of the MCP hydrolases using DxnB2 from Sphingomonas wittichii RW1. Pre-steady-state kinetic and LC ESI/MS evaluation of the DxnB2-mediated hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid to 2-hydroxy-2,4-pentadienoic acid and benzoate support a nucleophilic mechanism catalysis. In DxnB2, the rate of ESred decay and product formation showed a solvent kinetic isotope effect of 2.5, indicating that a proton transfer reaction, assigned here to substrate ketonization, limits the rate of acylation. For a series of substituted MCPs, this rate was linearly dependent on MCP pKa2nuc ~ 1). Structural characterization of DxnB2 S105A:MCP complexes revealed that the catalytic histidine is displaced upon substrate-binding. The results provide evidence for enzyme-catalyzed ketonization in which the catalytic His–Asp pair does not play an essential role. The data further suggest that ESred represents a dianionic intermediate that acts as a general base to activate the serine nucleophile. This substrate-assisted mechanism of nucleophilic catalysis distinguishes MCP hydrolases from other serine hydrolases.

  16. Cyclopentadienyl nickel(ii) N,C-chelating benzothiazolyl NHC complexes: synthesis, characterization and application in catalytic C-C bond formation reactions.

    PubMed

    Teo, Wei Jie; Wang, Zhe; Xue, Fei; Andy Hor, T S; Zhao, Jin

    2016-04-25

    Cyclopentadienyl (Cp) Ni(ii) complexes [CpNiL][PF6] containing hybrid N,C chelating benzothiazolyl NHC ligands (L1 = 1-(2-benzothiazolyl)-3-methylimidazol-2-ylidene, ; L2 = 1-(2-benzothiazolyl)-3-allylimidazol-2-ylidene, ; L3 = 1-(2-benzothiazolyl)-3-benzylimidazol-2-ylidene, ) have been synthesized and fully characterized. The catalytic activity of in some C-C bond formation reactions has been examined. They are efficient catalysts for the homo-coupling of benzyl bromide in the presence of MeMgCl at r.t. with good functional group tolerance. Complex is active in the catalytic oxidative homo-coupling of Grignard reagents with 1,2-dichloroethane as an oxidant at r.t. PMID:27011227

  17. 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

  18. An Electron-Poor C64 Nanographene by Palladium-Catalyzed Cascade C-C Bond Formation: One-Pot Synthesis and Single-Crystal Structure Analysis.

    PubMed

    Seifert, Sabine; Shoyama, Kazutaka; Schmidt, David; Würthner, Frank

    2016-05-23

    Herein, we report the one-pot synthesis of an electron-poor nanographene containing dicarboximide groups at the corners. We efficiently combined palladium-catalyzed Suzuki-Miyaura cross-coupling and dehydrohalogenation to synthesize an extended two-dimensional π-scaffold of defined size in a single chemical operation starting from N-(2,6-diisopropylphenyl)-4,5-dibromo-1,8-naphthalimide and a tetrasubstituted pyrene boronic acid ester as readily accessible starting materials. The reaction of these precursors under the conditions commonly used for Suzuki-Miyaura cross-coupling afforded a C64 nanographene through the formation of ten C-C bonds in a one-pot process. Single-crystal X-ray analysis unequivocally confirmed the structure of this unique extended aromatic molecule with a planar geometry. The optical and electrochemical properties of this largest ever synthesized planar electron-poor nanographene skeleton were also analyzed. PMID:27058998

  19. 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

  20. 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.

  1. 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.

  2. Mild and Selective Catalytic Hydrogenation of the C=C Bond in α,β-Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles.

    PubMed

    Nagendiran, Anuja; Pascanu, Vlad; Bermejo Gómez, Antonio; González Miera, Greco; Tai, Cheuk-Wai; Verho, Oscar; Martín-Matute, Belén; Bäckvall, Jan-E

    2016-05-17

    Chemoselective reduction of the C=C bond in a variety of α,β-unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H2 : 1) nano-Pd on a metal-organic framework (MOF: Pd(0) -MIL-101-NH2 (Cr)), 2) nano-Pd on a siliceous mesocellular foam (MCF: Pd(0) -AmP-MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd(0) -MIL-101-NH2 (Cr) and Pd(0) -AmP-MCF were capable of delivering the desired products in very short reaction times (10-90 min) with low loadings of Pd (0.5-1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching. PMID:27111403

  3. 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

  4. 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

  5. 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.

  6. KO(t)Bu-mediated synthesis of dimethylisoindolin-1-ones and dimethyl-5-phenylisoindolin-1-ones: selective C-C coupling of an unreactive tertiary sp3 C-H bond.

    PubMed

    Bhakuni, Bhagat Singh; Yadav, Abhimanyu; Kumar, Shailesh; Patel, Saket; Sharma, Shubham; Kumar, Sangit

    2014-04-01

    A new reaction for the synthesis of dimethylisoindolinones has been presented from 2-halo-N-isopropyl-N-alkylbenzamide substrates and KO(t)Bu by the selective C-C coupling of an unreactive tertiary sp(3) C-H bond. The reaction manifested an excellent selectivity toward a tertiary sp(3) C-H bond over primary or sec C-H bond. Moreover, biaryl C-C coupling along with alkyl-aryl C-C coupling can be achieved in one pot using dihalobenzamides for the synthesis of biaryl 5-phenylisoindolin-1-ones. It seems that the reaction proceeds via a radical pathway in which the aryl radical translocates via 1,5-hydrogen atom transfer (HAT), forming a tertiary alkyl carbon-centered radical. The generated tertiary alkyl radical could attack the benzamide ring in a 5-exo/endo-trig manner followed by the release of an electron and a proton, leading to a five-membered isoindolinone ring. HAT seems to be responsible for the selective functionalization of the tertiary alkyl group over primary and secondary C-H bonds. PMID:24597670

  7. 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.

  8. 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.

  9. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, Robert J.; McMillan, April D.; Paulauskas, Felix L.; Fathi, Zakaryae; Wei, Jianghua

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

    This study initially characterizes the primary photodissociation processes of epichlorohydrin, c-(H2COCH)CH2Cl. The three dominant photoproduct channels analyzed are c-(H2COCH)CH2+Cl, c-(H2COCH)+CH2Cl, and C3H4O+HCl. In the second channel, the c-(H2COCH) photofission product is a higher energy intermediate on C2H3O 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, H2CCO. The final primary photodissociation pathway HCl+C3H4O evidences a recoil kinetic energy distribution similar to that of four-center HCl elimination in chlorinated alkenes, so is assigned to production of c-(H2COC)=CH2; the epoxide product is formed with enough vibrational energy to isomerize to acrolein and dissociate. The paper then analyzes the dynamics of the C3H5O 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(P3)+allyl bimolecular reaction when the O atom adds to an end C atom. We focus on the HCO+C2H4 and H2CO+C2H3 product channels from this radical intermediate in this report. Analysis of the velocity distribution of the momentum-matched signals from the HCO+C2H4 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 H2CO+C2H3 product channel of the O(P3)+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+H3CO product channel. We present a detailed statistical prediction for the dissociation of the radical intermediate on the C3H5O 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+C2H4, and H2CO+C2H3 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+C2H4 and H2CO+C2H3 product channels. Using the C2H4 bandwidth-averaged absolute photoionization cross section at 11.27 eV and our measured relative photoion signals of C2H4 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.

  11. Towards an understanding of the bonding in polyoxometalates through bond order and bond energy analysis.

    PubMed

    Bridgeman, Adam J; Cavigliasso, Germán

    2003-01-01

    The molecular and electronic structures of transition metal complexes, [MOCl5]n- (n = 2 for M = V,Nb,Ta and n = 1 for Mo,W) and mixed-metal polyoxometalates, [M'M5O19]3-V,Nb,Ta, M = Mo,W) containing a single terminal oxo group on each metal, and of complexes of the uranyl ion [UO2]2+, [UO2(H2O)5]2+ and [UO2Cl4]2-, have been calculated using density functional methods. The calculated structures of the complexes are in good agreement with available experimental parameters. For the mixed-metal hexametalates, for which no crystallographic data is available, the calculations predict a small tetragonal compression of the clusters with only minor structural changes compared to the parent molybdate and tungstate. The metal oxygen bonding in these anions has been probed using Mayer-Mulliken, bond energy and atoms in molecule analyses (AIM). These methods provide a consistent description of the bonding in polyoxometalates. The terminal bonds between transition metal or uranium and oxygen atoms have large sigma and pi components with the pi contributions exceeding the sigma bonding. The transition metals utilize their d orbitals almost exclusively to bond to oxygen whilst uranium uses both its 5f and 6d orbitals. Oxygen atom charges increase and covalency indexes decrease with coordination number, with a marked separation of these terms according to the oxygen atom type. The total valency and AIM energies of the oxygen atoms are predicted to be almost constant for all types of oxygen site. The constancy of the bonding power of the oxygen atoms appears to be an important factor in determining the gross structures and details of the bonding in polyoxometalates. The Mayer Mulliken approach provides direct characterization of the bonding power of atoms and the extent of the interaction between pairs of atoms that is consistent with the results of the considerably more computationally demanding bond energy and AIM approaches. PMID:14527219

  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. 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.

  15. 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.

  16. 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.

  17. Does C-C bonding proceed during exposure of adequate metal surfaces to CH{sub 4}? Reply to {open_quotes}Comment by Z. Hlavathy, Z. Paal, and P. Tetenyi{close_quotes}

    SciTech Connect

    Amaraiglio, A.; Pareja, P.; Amariglio, H.

    1997-02-01

    The comments, results, and reflections presented by Hlavathy and co-workers in their Letter aim at demonstrating that C-C bonding between CH{sub x} adspecies, formed upon exposure of Pt to CH{sub 4}, can proceed as well during the exposure itself as during further exposure to H{sub 2}. This possibility was implicitly put forward because they thought that a tight parallelism exists between the interactions of CH{sub 4} and CO with a metal surface, provided that the exposure to CH{sub 4} is carried out at a high enough temperature (450{degrees}C). In both cases these authors assumed that three kinds of carbon, C{sub {alpha}}, C{sub {beta}}, and C{sub {gamma}}, can be formed, C{sub {alpha}} being the main species responsible for the production of CH{sub 4} and of the C{sub 2}, alkanes obtained when the metal was further contacted with H{sub 2} at 100{degrees}C. As they argued that C{sub {alpha}} (also named carbidic carbon) has only metal atoms in its first coordination shell, they were implicitly led it that C-C bonding must take place during the hydrogenation step. The authors have not denied this possibility, but they have suggested that different situations can result from exposures to CH{sub 4} conducted at temperatures much lower than those used by Koerts et al.. 13 refs.

  18. 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

  19. 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

  20. 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/τ1 ∼ 500 s−1) transforms HOPDA (λmax = 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/τ2 = 54 s−1, 1/τ3 = 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/τ1 and 1/τ2, but affected neither 1/τ3 nor kcat, suggesting that 1/τ2 may reflect diffusive HPD dissociation, while 1/τ3 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 (λmax = 492 nm). Crystal structures of wild type, the S112C variant, and S112C incubated with HOPDA were each determined to 1.6 Å 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

  1. Ether complexes of tungsten with two different binding modes: An O-bound ether and an {eta}{sup 2}-(C=C) vinyl ether. Evidence for C-H...O hydrogen bonding of vinylic C-H groups

    SciTech Connect

    Song, J.S.; Szalda, D.J.; Bullock, R.M.

    1996-11-13

    The reaction of PhCH(OCH{sup 3}){sup 2} with Cp(CO){sup 3}WH and HOTf gives [Cp(CO){sup 3}W(PhCH{sup 2}OCH{sup 3})]{sup +}OTf{sup -}. The structure of this benzyl methyl ether complex was determined by single crystal X-ray diffraction and was shown to have the ether bonded to tungsten through the oxygen. This compound was isolated as a kinetic product of the reaction; it decomposes in solution by releasing free PhCH{sup 2}OCH{sup 3} and forming Cp(CO){sup 3}WOTf. An analog with the BAr`{sup 4}{sup -} counterion [Ar` = 3, 5-bis(trifluoromethyl)phenyl] is more stable. The reaction of the vinyl acetal CH{sup 2}=CHCH(OEt){sup 2} with Cp(CO){sup 3}WH and HOTf produces [Cp(CO){sup 3}W({eta}{sup 2}-EtOCH=CHCH{sup 3})]{sup +} OTf{sup -}, in which the ether is bonded to tungsten through the C=C bond of the vinyl ether. The crystal structure of this compound shows that the W-C(OEt) distance (2.69(3) A) is significantly longer than the W-C(CH{sup 3}) distance (2.37(3) A). There are weak C-H...O hydrogen bonds between both vinyl CH`s and oxygens of the triflate counterions. Evidence is presented that some of these weak hydrogen bonds are maintained in CD{sup 2}Cl{sup 2} solution but not in CD{sup 3}CN. 44 refs., 4 figs., 3 tabs.

  2. Effect of nanoscale surface roughness on the bonding energy of direct-bonded silicon wafers

    NASA Astrophysics Data System (ADS)

    Miki, N.; Spearing, S. M.

    2003-11-01

    Direct wafer bonding of silicon wafers is a promising technology for manufacturing three-dimensional complex microelectromechanical systems as well as silicon-on-insulator substrates. Previous work has reported that the bond quality declines with increasing surface roughness, however, this relationship has not been quantified. This article explicitly correlates the bond quality, which is quantified by the apparent bonding energy, and the surface morphology via the bearing ratio, which describes the area of surface lying above a given depth. The apparent bonding energy is considered to be proportional to the real area of contact. The effective area of contact is defined as the area sufficiently close to contribute to the attractive force between the two bonding wafers. Experiments were conducted with silicon wafers whose surfaces were roughened by a buffered oxide etch solution (BOE, HF:NH4F=1:7) and/or a potassium hydroxide solution. The surface roughness was measured by atomic force microscopy. The wafers were direct bonded to polished "monitor" wafers following a standard RCA cleaning and the resulting bonding energy was measured by the crack-opening method. The experimental results revealed a clear correlation between the bonding energy and the bearing ratio. A bearing depth of ˜1.4 nm was found to be appropriate for the characterization of direct-bonded silicon at room temperature, which is consistent with the thickness of the water layer at the interface responsible for the hydrogen bonds that link the mating wafers.

  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. 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

  5. A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Towards Catalyst Deactivation During Ketone Hydrogenation

    SciTech Connect

    Wu,F.; Dioumaev, V.; Szalda, D.; Hanson, J.; Bullock, R.

    2007-01-01

    The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

  6. Catalytic strategies for changing the energy content and achieving C--C coupling in biomass-derived oxygenated hydrocarbons.

    PubMed

    Simonetti, Dante A; Dumesic, James A

    2008-01-01

    This Concept examines the opportunities for the use of biomass feedstocks in the production of liquid fuels for the transportation sector of society. The cost-competitive conversion of biomass into liquid fuels involves the integration of processes that operate on lignocellulosic feeds with processes that convert specific fractions of lignocellulose. A brief description of current energy systems is given to indicate the potential contributions of biomass to replace fossil fuel feedstocks for energy production, followed by a description of current biomass-conversion technologies. Specific focus is given to promising reaction pathways and novel research opportunities for conversion of the carbohydrate fraction of lignocellulose into fuels with targeted structures. PMID:18683271

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. The Tautomeric Half-reaction of BphD, a C-C Bond Hydrolase Kinetic and Structural Evidence Supporting a Key Role for Histidine 265 of the Catalytic triad

    SciTech Connect

    Horsman, Geoff P.; Bhowmik, Shiva; Seah, Stephen Y.K.; Kumar, Pravindra; Bolin, Jeffrey T.; Eltis, Lindsay D.

    2010-01-07

    BphD of Burkholderia xenovorans LB400 catalyzes an unusual C-C bond hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) to afford benzoic acid and 2-hydroxy-2,4-pentadienoic acid (HPD). An enol-keto tautomerization has been proposed to precede hydrolysis via a gem-diol intermediate. The role of the canonical catalytic triad (Ser-112, His-265, Asp-237) in mediating these two half-reactions remains unclear. We previously reported that the BphD-catalyzed hydrolysis of HOPDA ({lambda}{sub max} is 434 nm for the free enolate) proceeds via an unidentified intermediate with a red-shifted absorption spectrum ({lambda}{sub max} is 492 nm) (Horsman, G. P., Ke, J., Dai, S., Seah, S. Y. K., Bolin, J. T., and Eltis, L. D. (2006) Biochemistry 45, 11071-11086). Here we demonstrate that the S112A variant generates and traps a similar intermediate ({lambda}{sub max} is 506 nm) with a similar rate, 1/{tau} {approx} 500 s{sup -1}. The crystal structure of the S112A:HOPDA complex at 1.8-{angstrom} resolution identified this intermediate as the keto tautomer, (E)-2,6-dioxo-6-phenyl-hex-3-enoate. This keto tautomer did not accumulate in either the H265A or the S112A/H265A double variants, indicating that His-265 catalyzes tautomerization. Consistent with this role, the wild type and S112A enzymes catalyzed tautomerization of the product HPD, whereas H265A variants did not. This study thus identifies a keto intermediate, and demonstrates that the catalytic triad histidine catalyzes the tautomerization half-reaction, expanding the role of this residue from its purely hydrolytic function in other serine hydrolases. Finally, the S112A:HOPDA crystal structure is more consistent with hydrolysis occurring via an acyl-enzyme intermediate than a gem-diol intermediate as solvent molecules have poor access to C6, and the closest ordered water is 7{angstrom} away.

  13. 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.

  14. 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

  15. 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

    Rodríguez-Gallego, Esther; Riera-Borrull, Marta; Hernández-Aguilera, Anna; Mariné-Casadó, Roger; Rull, Anna; Beltrán-Debón, Raúl; Luciano-Mateo, Fedra; 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

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. Sequential bond energies of water to sodium proline cation

    NASA Astrophysics Data System (ADS)

    Ye, S. J.; Moision, R. M.; Armentrout, P. B.

    2006-07-01

    Absolute bond dissociation energies of water to sodium proline cations and proline to hydrated sodium cations are determined experimentally by collision-induced dissociation of Na+Pro(H2O)x, where x = 1-4, complexes with xenon in a guided ion beam mass spectrometer. Experimental results show that the binding energies of water and proline to the complexes decrease monotonically with increasing number of water molecules. Ab initio calculations at three different levels show reasonable agreement with the experimental bond energies of water and proline for x = 1-4 except the theoretical values are higher for losing proline from x = 3 and 4. The primary binding site for Na+ is at the C terminus of proline for x = 0-4, i.e., the solvated sodiated proline complexes are in their zwitterionic forms. Calculations suggest that the first solvent shell of Na+Pro is essentially complete at four waters.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. Catalytic Carbonyl Allylation, Propargylation and Vinylation from the Alcohol or Aldehyde Oxidation Level via C-C Bond Forming Hydrogenation and Transfer Hydrogenation: A Departure from Preformed Organometallic Reagents**

    PubMed Central

    Bower, John F.; Kim, In Su; Patman, Ryan L.; Krische, Michael J.

    2009-01-01

    Classical protocols for carbonyl allylation, propargylation and vinylation typically rely upon the use of preformed allyl metal, allenyl metal and vinyl metal reagents, respectively, mandating stoichiometric generation of metallic byproducts. Through transfer hydrogenative C-C coupling, carbonyl addition may be achieved from the aldehyde or alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Here, we review transfer hydrogenative methods for carbonyl addition, which encompass the first cataltyic protocols enabling direct C–H functionalization of alcohols. PMID:19040235

  7. 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.

  8. 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.

  9. Structures, energies, and bonding in the water heptamer

    NASA Astrophysics Data System (ADS)

    Acelas, Nancy; Hincapié, Gina; Guerra, Doris; David, Jorge; Restrepo, Albeiro

    2013-07-01

    In this paper we report the geometries and properties of 38 distinct geometrical motifs located on the B3LYP/6-31+G(d), MP2/6-311++G(d, p) potential energy surfaces of the water heptamer. Binding energies of up to 45 kcal/mol are calculated. All motifs fall within 10 kcal/mol of the most stable conformation, with at least 13 structural patterns located no more than 3 kcal/mol above, leading to a very complex potential energy surface, populated by a multitude of motifs each one allowing large numbers of conformations. Cluster stability does not seem to be correlated with the number of hydrogen bonds. Compact structures are energetically favored by electronic energies with zero-point energy corrections, while more open structures are preferred when temperature and entropy are accounted for. The molecular interactions holding the clusters as discrete units lead to large binding energies but are not strong enough to cause significant changes in the geometries of the interacting monomers. Our results indicate that bonding in the water heptamers can be considered as largely non-shared interactions with contributions from intermediate character of increasing covalency.

  10. Samarium(III)-catalyzed C(sp3)-H bond activation: synthesis of indolizines via C-C and C-N coupling between 2-alkylazaarenes and propargylic alcohols.

    PubMed

    Wang, Xu; Li, Shen-yan; Pan, Ying-ming; Wang, Heng-shan; Liang, Hong; Chen, Zhen-feng; Qin, Xiao-huan

    2014-01-17

    A new rare earth metal and samarium-catalyzed C(sp(3))-H bond activation is reported in which 2-alkylazaarenes and propargylic alcohols were converted to indolizines. This process operates under mild conditions and solvent-free conditions. A broad scope of coupling partners has been established, and a likely mechanism has also been suggested. PMID:24359214

  11. 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 =…

  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. Sequential bond energies of water to sodium glycine cation

    NASA Astrophysics Data System (ADS)

    Ye, S. J.; Moision, R. M.; Armentrout, P. B.

    2005-02-01

    Absolute bond dissociation energies of water to sodium glycine cations and glycine to hydrated sodium cations are determined experimentally by competitive collision-induced dissociation (CID) of Na+Gly(H2O)x, x = 1-4, with xenon in a guided ion beam tandem mass spectrometer. The cross sections for CID are analyzed to account for unimolecular decay rates, internal energy of reactant ions, multiple ion-molecule collisions, and competition between reaction channels. Experimental results show that the binding energies of water and glycine to the complexes decrease monotonically with increasing number of water molecules. Ab initio calculations at four different levels show good agreement with the experimental bond energies of water to Na+Gly(H2O)x, x = 0-3, and glycine to Na+(H2O), whereas the bond energies of glycine to Na+(H2O)x, x = 2-4, are systematically higher than the experimental values. These discrepancies may provide some evidence that these Na+Gly(H2O)x complexes are trapped in excited state conformers. Both experimental and theoretical results indicate that the sodiated glycine complexes are in their nonzwitterionic forms when solvated by up to four water molecules. The primary binding site for Na+ changes from chelation at the amino nitrogen and carbonyl oxygen of glycine for x = 0 and 1 to binding at the C terminus of glycine for x = 2-4. The present characterization of the structures upon sequential hydration indicates that the stability of the zwitterionic form of amino acids in solution is a consequence of being able to solvate all charge centers.

  14. 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.

  15. 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.

  16. 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.

  17. 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…

  18. 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

  19. Synthesis and [2 + 2] cycloaddition of bimethyleneketene acetals. Reaction with C[sub 60] and facile hydrolysis of the C-C bond connected to C[sub 60

    SciTech Connect

    Yamago, Shigeru; Takeichi, Atsuo; Nakamura, Eiichi )

    1994-02-09

    We report here that the O-alkylated enolates of cyclopropanecarboxylates (dimethyleneketene acetals 3) can be prepared from readily available precursors, and that they are extemely reactive, serving as useful surrogates of the elusive parent enolates. Their utility is illustrated by the [2 + 2] cycloaddition to electron-deficient olefins, which, after hydrolytic workup, gives rise to the Michael addition products: a type of reaction product previously unavailable. We also found that 3 reacts smoothly with C[sub 60] to give the [2 + 2] adduct 5 and, most remarkably, that the asterisked C[minus]C [sigma] bond in 5 directly connected to the fullerene core is hydrolytically unstable and can be quantitatively cleaved with aqueous acid. 15 refs., 1 tab.

  20. 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.

  1. Formation energy of dangling bonds on hydrogenated diamond surfaces: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zilibotti, G.; Corni, S.; Righi, M. C.

    2012-01-01

    We calculate the energy cost to create dangling bonds on hydrogenated diamond (001) surfaces by means of spin-polarized first-principle calculations. We demonstrate that the dangling bond formation energy depends on both the density and the arrangement of the dangling bonds already present on the surface. In particular, at low dangling bond density, hydrogen removal is less energetically costly than at high dangling bond density. We also find that adjacent dangling bonds are more stable in the antiferromagnetic configuration than in the ferromagnetic one. We provide quantitative information and a physical rationale of these phenomena.

  2. Theoretical Electron Density Distributions for Fe- and Cu-Sulfide Earth Materials: A Connection between Bond Length, Bond Critical Point Properties, Local Energy Densities, and Bonded Interactions

    SciTech Connect

    Gibbs, Gerald V.; Cox, David F.; Rosso, Kevin M.; Ross, Nancy L.; Downs, R. T.; Spackman, M. A.

    2007-03-01

    Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, F(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, F(rc), the Laplacian, 32F(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of F(rc) and 32F(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of F(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the highspin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the F(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides.

  3. Bond Length and Local Energy Density Property Connections for Non-transition- Metal-Oxide-Bonded Interactions

    SciTech Connect

    Gibbs, Gerald V.; Spackman, M. A.; Jayatilaka, Dylan; Rosso, Kevin M.; Cox, David F.

    2006-11-09

    For a variety of molecules and Earth materials, the theoretical local kinetic energy density, G(rc), increases and the local potential energy density, V(rc), decreases as the MO bond lengths (M = first and second row metal atoms) decrease and electron density, ρ(rc), is localized at the bond critical points, rc. Despite claims that the ratio, G(rc)/ρ(rc), classifies bonded interactions as shared covalent when less than unity and closed shell ionic when greater than unity, the ratio was found to increase from 0.5 to 2.5 a.u. as the local electronic energy density H(rc) = G(rc) + V(rc) decreases and becomes progressively more negative. In any event, the ratio is indicated to be a measure of the character for a given M-O bond, the greater the ratio, the larger the value of ρ(rc), the smaller the coordination number of the M atom and the more covalent the bond. H(rc)/ρ(rc) vs. G(rc)/ρ(rc) scatter diagrams categorize the M-O bond data into domains with the H(rc)/ρ(rc) ratio tending to increase as the electronegativity of the M atoms increase. Estimated values of G(rc) and V(rc), using an expression based on gradient corrected electron gas theory, are in good agreement with theoretical values, particularly for bonded interactions involving second row M atoms. The agreement is poorer for the more covalent C-O and N-O bonds.

  4. 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 230 nA cm(-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

  5. 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.

  6. 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.

  7. 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.

  8. 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 Ñ2ρ(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.

  9. 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.

  10. 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.

  11. 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

  12. 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 K–12 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

  13. 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.

  14. The Bond Energy of CH3-H: A Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Dorain, Paul B.

    1979-01-01

    Describes an experiment, designed for use in the undergraduate laboratory, that measures the bond energies of molecules using a small commercial mass spectrometer and low-cost digital voltmeters. (BT)

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. SCAN: An Efficient Density Functional Yielding Accurate Structures and Energies of Diversely-Bonded Materials

    NASA Astrophysics Data System (ADS)

    Sun, Jianwei

    The accuracy and computational efficiency of the widely used Kohn-Sham density functional theory (DFT) are limited by the approximation to its exchange-correlation energy Exc. The earliest local density approximation (LDA) overestimates the strengths of all bonds near equilibrium (even the vdW bonds). By adding the electron density gradient to model Exc, generalized gradient approximations (GGAs) generally soften the bonds to give robust and overall more accurate descriptions, except for the vdW interaction which is largely lost. Further improvement for covalent, ionic, and hydrogen bonds can be obtained by the computationally more expensive hybrid GGAs, which mix GGAs with the nonlocal exact exchange. Meta-GGAs are still semilocal in computation and thus efficient. Compared to GGAs, they add the kinetic energy density that enables them to recognize and accordingly treat different bonds, which no LDA or GGA can. We show here that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-GGA improves significantly over LDA and the standard Perdew-Burke-Ernzerhof GGA for geometries and energies of diversely-bonded materials (including covalent, metallic, ionic, hydrogen, and vdW bonds) at comparable efficiency. Often SCAN matches or improves upon the accuracy of a hybrid functional, at almost-GGA cost. This work has been supported by NSF under DMR-1305135 and CNS-09-58854, and by DOE BES EFRC CCDM under DE-SC0012575.

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. Bond energies on the cesium halides determined by collision-induced dissociation

    SciTech Connect

    Parks, E.K.; Wexler, S.

    1984-09-27

    The bond energies of the four cesium halides are determined from the threshold for collision-induced dissociation to ion pairs by rare gas atoms. The bond energies (to neutral atoms) are 5.32 +/- 0.08, 4.58 +/- 0.08, 4.00 +/- 0.08, and 3.47 +/- 0.15 eV for CsF, CsCl, CsBr, and CsI, respectively. Except for CsI the ion thresholds are obtained from the sharply peaked cross section vs. energy curves for CsM/sup +/ + X/sup -/ formation (M = rare gas atom; X/sup -/ = halide ion) and for CsI the ion threshold is obtained from the onset of the channel M + Cs/sup +/ + I/sup -/. Comparison is made with bond energies determined by other techniques as well as that derived from the T-Rittner model potential.

  11. 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

  12. 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.

  13. Size, Kinetics, and Free Energy of Clusters Formed by Ultraweak Carbohydrate-Carbohydrate Bonds.

    PubMed

    Witt, Hannes; Savić, Filip; Oelkers, Marieelen; Awan, Shahid I; Werz, Daniel B; Geil, Burkhard; Janshoff, Andreas

    2016-04-12

    Weak noncovalent intermolecular interactions play a pivotal role in many biological processes such as cell adhesion or immunology, where the overall binding strength is controlled through bond association and dissociation dynamics as well as the cooperative action of many parallel bonds. Among the various molecules participating in weak bonds, carbohydrate-carbohydrate interactions are probably the most ancient ones allowing individual cells to reversibly enter the multicellular state and to tell apart self and nonself cells. Here, we scrutinized the kinetics and thermodynamics of small homomeric Lewis X-Lewis X ensembles formed in the contact zone of a membrane-coated colloidal probe and a solid supported membrane ensuring minimal nonspecific background interactions. We used an atomic force microscope to measure force distance curves at Piconewton resolution, which allowed us to measure the force due to unbinding of the colloidal probe and the planar membrane as a function of contact time. Applying a contact model, we could estimate the free binding energy of the formed adhesion cluster as a function of dwell time and thereby determine the precise size of the contact zone, the number of participating bonds, and the intrinsic rates of association and dissociation in the presence of calcium ions. The unbinding energy per bond was found to be on the order of 1 kBT. Approximately 30 bonds were opened simultaneously at an off-rate of koff = 7 ± 0.2 s(-1). PMID:27074683

  14. 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.

  15. 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.

  16. 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 3000ś 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.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

    Perdew, John P.; Levy, Mel; Painter, G. S.; Wei, Siqing; Lagowski, Jolanta B.

    1988-01-01

    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 N2 and F2, 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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.

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

    SciTech Connect

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

    2011-10-07

    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.

  12. 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 ρ(rc): BD = -H(rc)/ρ(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

  13. 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.

  14. Metal-cyclopentadienyl bond energies in metallocene cations measured using threshold collision-induced dissociation mass spectrometry.

    PubMed

    Rowland, Tyson G; Sztáray, Bálint; Armentrout, Peter B

    2013-02-14

    Metal-cyclopentadienyl bond dissociation energies (BDEs) were measured for seven metallocene ions (Cp(2)M(+), Cp = η(5)-cyclopentadienyl = c-C(5)H(5), M = Ti, V, Cr, Mn, Fe, Co, Ni) using threshold collision-induced dissociation (TCID) performed in a guided ion beam tandem mass spectrometer. For all seven room temperature metallocene ions, the dominant dissociation pathway is simple Cp loss from the metal. Traces of other fragment ions were also detected, such as C(10)H(10)(+), C(10)H(8)(+), C(8)H(8)(+), C(3)H(3)(+), H(2)M(+), C(3)H(3)M(+), C(6)H(6)M(+), and C(7)H(6)M(+), depending on the metal center. Statistical modeling of the Cp-loss TCID experimental data, including consideration of energy distributions, multiple collisions, and kinetic shifts, allow the extraction of 0 K [CpM(+)- Cp] BDEs. These are found to be 4.85 ± 0.15, 4.02 ± 0.14, 4.22 ± 0.13, 3.51 ± 0.12, 4.26 ± 0.15, 4.57 ± 0.15, and 3.37 ± 0.12 eV for Cp(2)Ti(+), Cp(2)V(+), Cp(2)Cr(+), Cp(2)Mn(+), Cp(2)Fe(+), Cp(2)Co(+), and Cp(2)Ni(+), respectively. The measured BDE trend is largely in line with arguments based on a simple molecular orbital picture, with the exception of the anomalous case of titanocene, most likely attributable to its bent structure. The new results presented here are compared to previous literature values and are found to provide a more complete and accurate set of thermochemistry. PMID:23215634

  15. Interlayer bonding energy of layered minerals: Implication for the relationship with friction coefficient

    NASA Astrophysics Data System (ADS)

    Sakuma, Hiroshi; Suehara, Shigeru

    2015-04-01

    The frictional strength of layered minerals is an important component of fault slip physics. A low-friction coefficient of these minerals has been attributed to the interlayer bonding energy (ILBE) of their weak interlayer bonding. The ILBE used for discussing the friction coefficient is based on a simple electrostatic calculation; however, the values should be revisited by precise calculations based on quantum mechanics. In this study, the ILBEs of layered minerals were calculated by using the density functional theory (DFT) method with van der Waals correction. The ILBEs calculated by the simple electrostatic method for hydrogen-bonding minerals such as kaolinite, lizardite, gibbsite, and brucite strongly overestimated the reliable energies calculated by the DFT method. This result should be ascribed to the inaccurate approximation of the point charges at the basal plane. A linear relationship between the experimentally measured friction coefficients of layered minerals and the ILBEs determined by the simple method was not confirmed by using the reliable ILBEs calculated by our DFT method. The results, however, do not remove the possibility of a relationship between interlayer bonding energy and the friction coefficient because the latter, used for comparing the former, was obtained through experiments conducted under various conditions.

  16. 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.

  17. Determination of bond dissociation energies via energy-resolved collision induced dissociation in a fourier transform ion cyclotron resonance spectrometer

    NASA Astrophysics Data System (ADS)

    Hop, C. E. C. A.; McMahon, T. B.; Willett, G. D.

    1990-12-01

    A Fourier transform ion cyclotron resonance (ICR) spectrometer has been used to determine bond dissociation energies via translation energy controlled collisions between mass-selected ions and a stationary target gas. The ions examined were the proton-bound dimers of diethyl ether, acetone and water, which were generated in a high pressure external ion source. A comparison between bond dissociation energies obtained with this technique and literature values showed that the r.f. excitation of ions in the ICR cell produced ions with a well-defined translation energy. Moreover, the translational energy distribution of the ions was narrow, as indicated by the fact that experimentally obtained threshold curves for dissociation were close to computed curves corrected for Doppler broadening.

  18. Controlling the subtle energy balance in protic ionic liquids: dispersion forces compete with hydrogen bonds.

    PubMed

    Fumino, Koichi; Fossog, Verlaine; Stange, Peter; Paschek, Dietmar; Hempelmann, Rolf; Ludwig, Ralf

    2015-02-23

    The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen-bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL [(C6 H13 )3 NH][CF3 SO3 ]. The characteristic vibrational features for both ion-pair species can be detected and assigned in the far-infrared spectra. Our approach gives direct access to the relative strength of hydrogen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol(-1) per additional methylene group in the alkyl chains of the ammonium cation. PMID:25639210

  19. Electron-energy-loss spectroscopy characterization of the sp2 bonding fraction within carbon thin films

    NASA Astrophysics Data System (ADS)

    Papworth, A. J.; Kiely, C. J.; Burden, A. P.; Silva, S. R. P.; Amaratunga, G. A. J.

    2000-11-01

    When using electron-energy-loss spectroscopy (EELS) to quantify the sp2/sp3 bonding fraction in thin film carbon, the spectrum taken from the film must be compared to that of a suitable known standard. In contrast to the work of Berger [S. D. Berger and D. R. McKenzie, Philos. Mag. Lett. 57, 285 (1988)], C60 fullerite is used in this work as the standard since highly oriented pyrolytic graphite (HOPG) is highly anisotropic, and can therefore lead to preferential orientation effects in EELS. It was found that C60 had a shoulder on the high-energy side of the 1s-->π* peak, which was centered at 287 eV. In theory, many Gaussian peaks can be fitted to the near edge structure (NES) of the energy-loss spectrum. In practice, we show that only three, centered at energies of 285, 287, and 293 eV, are necessary for semiquantitative analysis. The 285 eV peak is indicative of the sp2 bonding fraction; the second peak at 287 eV is attributed to molecular structure within the sample; the third at 293 eV is determined by sp3 bonding contributions in the sample. We show that by fitting these three peaks to C60 fullerite and evaporated amorphous carbon (a-C), that the a-C has a 0.99 sp2 bonding fraction compared with the C60 fullerite standard. The importance of considering the 287 eV peak in highly sp2 bonded amorphous carbon is further illustrated by analysis of a-C:H:N thin films.

  20. 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.

  1. Microscopic thermal characterization of C/C and C/C-SiC composites

    NASA Astrophysics Data System (ADS)

    Jumel, J.; Krapez, J. C.; Lepoutre, F.; Enguehard, F.; Rochais, D.; Neuer, G.; Cataldi, M.

    2002-05-01

    To measure the thermal properties of C/C and C/C-SiC composites constituents, photoreflectance microscopy is used. Specific methods are developed to cope with experimental artefacts (material semi-transparency, convolution effects), so as with fibers and matrix specificities (strong thermal anisotropy, geometric effects…). Experimental results are presented demonstrating the interest of photoreflectance microscopy for a quantitative determination of the microscopic thermal properties of these complex graphite materials.

  2. 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

  3. Effects of in-plane. pi. prime bonding on electronic transition energies for inorganic polymers

    SciTech Connect

    Ferris, K.F.; Risser, S.M.; Hanson, A.K.

    1990-03-01

    The electronic structure of organic and inorganic polymeric systems are well described in terms of their molecular symmetry, even with the large bond polarity shown by such systems as polyphosphazenes. We have performed calculations using the semi-empirical CNDO/1 method to determine the valence electronic structure for a series of model phosphonitrilic and organic compounds. The optical transition energies for phosphonitrilic compounds are greater than their organic counterparts as a result of in-plane {pi}{prime} bonding interactions. The extent of these interactions is modulated by the electronegativity of the substituent groups on the phosphorus atoms. We report values for the vertical ionization energy and electronic absorption wavelengths, and use molecular orbital contour analysis to show the effects of ligand electronegativity on the {pi}{prime} network. 15 refs., 3 tabs.

  4. 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.

  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. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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 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 (ɛ ≤ 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.

  11. 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)

  12. Prediction of Reliable Metal-PH₃ 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-PH₃ 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.

  13. 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 μ 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.

  14. 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

  15. 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.

  16. 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.

  17. Carbon K-shell electron energy loss spectra of 1- and 2-butenes, trans-1,3-butadiene, and perfluoro-2-butene. Carbon-carbon bond lengths from continuum shape resonances

    NASA Astrophysics Data System (ADS)

    Hitchcock, A. P.; Beaulieu, S.; Steel, T.; Stöhr, J.; Sette, F.

    1984-05-01

    Electron energy loss spectra of 1-butene, cis-2-butene, trans-2-butene, trans-1,3-butadiene, and perfluoro-2-butene in the region of carbon K-shell (C 1s) excitation and ionization have been recorded under dipole-dominated inelastic electron scattering conditions. The features observed below the C 1s I.P. in the spectra of the butenes and butadiene are assigned to promotions of C 1s electrons to unoccupied valence (π*) and Rydberg orbitals while broad features observed above the edge are assigned to σ(C-C) and σ(C-C) shape resonances. These spectra, along with carbon K-shell spectra of other hydrocarbons, are used to demonstrate that there is a quantitative relationship between carbon-carbon bond lengths and the location of σ shape resonances relative to the C 1s ionization threshold (I.P.). The C 1s spectrum of perfluoro-2-butene demonstrates dramatic potential barrier effects, namely suppression of Rydberg transitions and strong enhancement of σ(C-C) and σ(C-F) shape resonances in the region of the C 1s ionization threshold.

  18. 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.

  19. 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.

  20. 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.

  1. Synthesis, structure, and reductive elimination in the series Tp'Rh(PR3)(Ar(F))H; determination of rhodium-carbon bond energies of fluoroaryl substituents.

    PubMed

    Tanabe, Taro; Brennessel, William W; Clot, Eric; Eisenstein, Odile; Jones, William D

    2010-11-21

    A series of complexes of the type Tp'Rh(PR(3))(Ar(F))H, where PR(3) = PMe(3) (3) and PMe(2)Ph (9), Ar(F) = C(6)F(5) (a), 2,3,4,5-C(6)F(4)H (b), 2,3,5,6-C(6)F(4)H (c), 2,4,6-C(6)F(3)H(2) (d), 2,3-C(6)F(2)H(3) (e), 2,5-C(6)F(2)H(3) (g), and 2-C(6)FH(4) (h) and Tp' = tris(3,5-dimethylpyrazolyl)borate, has been synthesized as stable crystalline compounds by the reactions of the [Tp'Rh(PR(3))] fragment with the corresponding fluorinated aromatic hydrocarbons, and their structures were characterized by NMR spectroscopy and elemental analysis together with X-ray crystallography. The kinetics of the reductive eliminations of fluoroarenes from complexes 3a-h in benzene-d(6) solutions at 140 °C were investigated, but were complicated by the formation of the rhodium(I) bisphosphine complex, Tp'Rh(PMe(3))(2) (4). On the other hand, thermal reactions of (9) in THF-d(8) solutions at 120 °C resulted in the formation of an intramolecular C-H bond activated complex of the phenyl group on the phosphorus atom, Tp'Rh(κ(2)-C(6)H(4)-2-PMe(2))H (7), which prevents the formation of the corresponding bisphosphine complex. The experimentally determined rates of the reductive eliminations of fluoroarenes from the complexes 9a-h and their kinetic selectivities for formation in competition with the metallacycle have been used to determine relative Rh-CAr(F) bond energies. The Rh-CAr(F) bond energy is found to be dependent on the number of ortho fluorines. A plot of Rh-CAr(F) vs. C-H bond strengths resulted in a line with a slope R(M-C/C-H) of 2.15 that closely matches the DFT calculated value (slope = 2.05). PMID:20924525

  2. 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

  3. 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

  4. Free energy landscapes for S-H bonds in Cp*2Mo2S4 complexes.

    PubMed

    Appel, Aaron M; Lee, Suh-Jane; Franz, James A; DuBois, Daniel L; DuBois, M Rakowski

    2009-04-15

    An extensive family of thermochemical data is presented for a series of complexes derived from Cp*Mo(mu-S)(2)(mu-SMe)(mu-SH)MoCp* and Cp*Mo(mu-S)(2)(mu-SH)(2)MoCp*. These data include electrochemical potentials, pK(a) 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 FeCp(2)(+/o) for electrochemical potentials, 5 to 31 for pK(a) 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 extensive set of thermochemical data is presented in free energy landscapes as a useful approach to visualizing and understanding the relative stabilities of all of the species under varying conditions of pH and H(2) overpressure. In addition to the previously studied homogeneous reactivity and catalysis, Mo(2)S(4) complexes are also models for heterogeneous molybdenum sulfide catalysts, and therefore, the present results demonstrate the dramatic range of S-H bond strengths available in both homogeneous and heterogeneous reaction pathways. PMID:19309157

  5. 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.

  6. 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.

  7. Understanding bond formation in polar one-step reactions. Topological analyses of the reaction between nitrones and lithium ynolates.

    PubMed

    Roca-López, David; Polo, Victor; Tejero, Tomás; Merino, Pedro

    2015-04-17

    The mechanism of the reaction between nitrones and lithium ynolates has been studied using DFT methods at the M06-2X/cc-pVTZ/PCM=THF level. After the formation of a starting complex an without energy barrier, in which the lithium atom is coordinated to both nitrone and ynolate, the reaction takes place in one single kinetic step through a single transition structure. However, the formation of C-C and C-O bonds takes place sequentially through a typical two-stage, one-step process. A combined study of noncovalent interactions (NCIs) and electron localization function (ELFs) of selected points along the intrinsic reaction coordinate (IRC) of the reaction confirmed that, in the transition structure, only the C-C bond is being formed to some extent, whereas an electrostatic interaction is present between carbon and oxygen atoms previous to the formation of the C-O bond. Indeed, the formation of the second C-O bond only begins when the first C-C bond is completely formed without formation of any intermediate. Once the C-C bond is formed and before the C-O bond formation starts the RMS gradient norm dips, approaching but not reaching 0, giving rise to a hidden intermediate. PMID:25803829

  8. 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.

  9. 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

  10. 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

  11. Rhodium-catalyzed C-C coupling reactions via double C-H activation.

    PubMed

    Li, Shuai-Shuai; Qin, Liu; Dong, Lin

    2016-05-18

    Various rhodium-catalyzed double C-H activations are reviewed. These powerful strategies have been developed to construct C-C bonds, which might be widely embedded in complex aza-fused heterocycles, polycyclic skeletons and heterocyclic scaffolds. In particular, rhodium(iii) catalysis shows good selectivity and reactivity to functionalize the C-H bond, generating reactive organometallic intermediates in most of the coupling reactions. Generally, intermolecular, intramolecular and multi-component coupling reactions via double C-H activations with or without heteroatom-assisted chelation are discussed in this review. PMID:27099126

  12. Effect of aging on surface chemical bonds of PTFE irradiated by low energy Ti ion

    NASA Astrophysics Data System (ADS)

    Zhang, Jizhong; Zhang, Xiaoji; Zhou, Hongyu

    2003-01-01

    Polytetrafluoroethylene (PTFE) was irradiated by low energy titanium ion in a metal vapor vacuum arc (MEVVA) implanter. The samples were irradiated with 80 keV Ti ion with fluences from 5×10 15 to 5×10 17 Ti/cm 2, respectively. Transportation of Ion in Matters (TRIM) code was employed to simulate Ti ion irradiation. The as-irradiated samples were investigated by ESCA, SEM and wettability. As increasing ion fluence, various chemical bonds and irradiation-damaged surfaces were observed. The water droplet contact angel of PTFE samples increased gradually with ion fluence. All the as-irradiated PTFE samples were aged in air for 1 year. After aging the surface-restructuring behavior was observed on the surfaces of the samples irradiated with ion fluence equal to or less than 5×10 16 Ti/cm 2, which resulted in decrease of the droplet contact angle of these samples. The surface roughness change of the aged samples, which were measured by atomic force microscopy (AFM), was consistent with the droplet contact angle change. The experimental results revealed that Ti ion fluence closely affected the surface chemical bond, morphology and wettability, as well as the aging stability of the as-irradiated PTFE samples.

  13. 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

  14. Zero-kinetic-energy photoelectron spectroscopy of the hydrogen-bonded phenol-water complex

    NASA Astrophysics Data System (ADS)

    Dopfer, Otto; Reiser, Georg; Müller-Dethlefs, Klaus; Schlag, Edward W.; Colson, Steven D.

    1994-07-01

    Two-photon, two-color (1+1') zero-kinetic-energy (ZEKE) photoelectron spectra are presented for the 1:1 phenol-water complex, a prototype system for hydrogen bonding between an aromatic molecule and a simple solvent. ZEKE spectra via different (intermolecular) vibrational intermediate S1 levels of the fully protonated complex (C6H5OH-H2O, h3) as well as the ZEKE spectrum via the vibrationless S1 state of the threefold deuterated complex (C6H5OD-D2O, d3) have been recorded. The spectra are rich in structure, which is mainly attributable to intermolecular vibrations of the ionic complex. Progressions of the intermolecular stretch vibration (240 cm-1) in combination with different intermolecular and intramolecular vibrational levels are the dominant feature of all ZEKE spectra obtained and indicate a large change in the complex geometry along the hydrogen-bond coordinate on ionization. Comparison between the spectrum of the d3 complex and the spectra via different intermediate intermolecular levels of the h3 complex has allowed a more detailed analysis of the intermolecular features compared to previously reported results. Finally, the vibrational assignments obtained are compared with ab initio results for the phenol-water cation reported in the following paper in this issue.

  15. 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.

  16. 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

  17. 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

  18. A QSPR study of O-H bond dissociation energy in phenols.

    PubMed

    Bosque, Ramón; Sales, Joaquim

    2003-01-01

    A Quantitative Structure-Property Relationship (QSPR) is developed for the O-H bond dissociation energy (BDE) of a set of 78 phenols. The data set was composed of monosubstituted, disubstituted, and polysubstituted phenolic derivatives containing substituents with different steric and electronic effects in the ortho-, meta-, and para-positions of the aromatic ring. The proposed model, derived from multiple linear regression, contains seven descriptors calculated solely from the molecular structure of compounds. The average absolute relative errors are 1.37% (R(2) = 0.8978; SD: 6.67) and 1.13% (R(2) = 0.9076; SD: 4.26) for the working set (62 compounds) and the prediction set (16 compounds), respectively. These results are better than those obtained from DFT calculations, QSAR approach, and correlations with Hammet parameters. PMID:12653532

  19. Mass analyzed threshold ionization of phenolṡCO: Intermolecular binding energies of a hydrogen-bonded complex

    NASA Astrophysics Data System (ADS)

    Haines, Stephen R.; Dessent, Caroline E. H.; Müller-Dethlefs, Klaus

    1999-08-01

    [PhenolṡCO]+ was studied using a combination of two-color resonant zero kinetic energy (ZEKE) spectroscopy and mass analyzed threshold ionization (MATI) spectroscopy to investigate the interaction of the CO ligand with a hydrogen-bonding cation. Vibrational progressions were observed in three intermolecular modes, the in-plane bend (42 cm-1), stretch (130 cm-1), and in-plane wag (160 cm-1), and are consistent with a planar hydrogen-bonded structure where the CO bonds through the carbon atom to the phenol OH group. Dissociation energies for the S0, S1, and D0 states were determined as 659±20, 849±20, and 2425±10 cm-1, respectively. The cationic and neutral dissociation energies of the phenolṡCO complex are considerably stronger than those of phenolṡN2, demonstrating the extent to which the larger quadrupole of CO affects the strength of binding.

  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. Analysis of correlation consistent wavefunctions: H 3XH bond energies (X=C, Si and Ge)

    NASA Astrophysics Data System (ADS)

    Maître, Philippe; Ohanessian, Gilles

    1992-12-01

    We have analyzed the CCCI wavefunction for the calculation of bond dissociation energies. In the first part, CCCI is reexpressed as a non-orthogonal valence bond CI wavefunction which describes bond formation as the mixing of one covalent and two ionic parent configurations. Every other configuration is considered as an improvement of one of these three building blocks. They are grouped into different classes, the contribution of which are successively analyzed. We found the dynamical correlation of ionic structures (only one for a polar bond such as HSiH 3 or HGeH 3) to be of prime importance in obtaining accurate dissociation energies. In the second part, we improve CCCI by extending both the one- and N-electron bases, which lead to an increase and decrease of the computed bond energies, respectively. We thus conclude that the high accuracy of CCCI at the DZP level results from a cancellation of limited errors. The highest level used is uniformly accurate and yields De of 110.9, 96.3 and 92.5 kcal/mol for CH 4, SiH 4 and GeH 4 respectively.

  2. The formation of f.c.c. titanium in titanium-aluminum multilayers

    SciTech Connect

    Van Heerden, D.; Josell, D.; Shechtman, D.

    1996-01-01

    The Ti layers in Al/Ti multilayers are shown to transform from hexagonal close packed in the as-deposited multilayers to face centered cubic on ion milling in cross-section. By examining the change in free energy of the system on transformation it is demonstrated that interfacial, surface and strain free energies cannot overcome the theoretically predicted 0.08 eV/atom difference in bulk free energy between f.c.c. and h.c.p. Ti. Based on experimental observations of f.c.c. Ti in multilayers, it is argued that this value is too large.

  3. 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})

  4. 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

  5. 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.

  6. 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.

  7. Zener relaxation strength in B.C.C. and F.C.C. alloys under torsional and longitudinal excitations

    SciTech Connect

    Povolo, F.; Mosca, H.O.

    1994-01-01

    Calculations of the intensity of the Zener relaxation strength in b.c.c. and f.c.c. alloys are presented. Welch and Le Claire theory for the relaxation strength of shear modulus in f.c.c. alloys is extended to include the relaxation strength of Young`s and bulk modulus. A complete set of equations is given to be used for calculation of the relaxation strength of all the moduli in b.c.c. alloys. Finally, some applications to experimental data in both alloys systems are presented.

  8. Zero Steric Potential and bond order

    NASA Astrophysics Data System (ADS)

    Ghasemi, S.; Noorizadeh, S.

    2016-05-01

    The variation of Zero Steric Potential (ZSP) through a C-C bond shows two maximums, which their values depend on the bond order (BO). A good relationship (R2 = 1) is observed between the mean values of maximum ZSPs and the bond orders of C-C bonds in ethane, ethylene and acetylene, as reference molecules (Ln BO = 1.956ZSP‾max - 0.898). The obtained equation is used to predict the C-C bond orders of more than twenty aromatic and aliphatic hydrocarbons. The results show that the obtained bond orders from ZSP‾max are more reliable than those which are evaluated using NBO and Laplacian methods.

  9. Modelling of c-C2H4O formation on grain surfaces

    NASA Astrophysics Data System (ADS)

    Occhiogrosso, A.; Viti, S.; Ward, M. D.; Price, S. D.

    2012-12-01

    Despite its potential reactivity due to ring strain, ethylene oxide (c-C2H4O) is a complex molecule that seems to be stable under the physical conditions of an interstellar dense core; indeed, it has been detected towards several high-mass star-forming regions with a column density of the order of 1013 cm-2. To date, its observational abundances cannot be reproduced by chemical models and this may be due to the significant contribution played by its chemistry on grain surfaces. Recently, Ward & Price have performed experiments in order to investigate the surface formation of ethylene oxide starting with oxygen atoms and ethylene ice as reactants. We present a chemical model which includes the most recent experimental results from Ward & Price on the formation of c-C2H4O. We study the influence of the physical parameters of dense cores on the abundances of c-C2H4O. We verify that ethylene oxide can indeed be formed during the cold phase (when the interstellar medium dense cores are formed), via addition of an oxygen atom across the C=C double bond of the ethylene molecule, and released by thermal desorption during the hot core phase. A qualitative comparison between our theoretical results and those from the observations shows that we are able to reproduce the abundances of ethylene oxide towards high-mass star-forming regions.

  10. Isolation, Characterization of an Intermediate in an Oxygen Atom-Transfer Reaction, and the Determination of the Bond Dissociation Energy

    SciTech Connect

    Nemykin, Victor N.; Laskin, Julia; Basu, Partha

    2004-07-19

    Redox reactions coupled with the formal loss or gain of an oxygen atom are ubiquitous in chemical processes. Such reactions proceed through the reduction of the donor center (XO) and the oxidation of the acceptor (Y) molecule. Among many examples of the metal centered oxygen atom transfer (OAT) reactivity, those involving molybdenum complexes have been widely investigated due to their involvement in mononuclear molybdenum enzymes. The heat of reaction of the overall atom transfer process can be expressed as a difference between the bond dissociation energies (BDEs) of the oxygen-donor(X) and oxygen-acceptor(Y) bond, i.e., H=DX=o-DY=O.

  11. Accurate bond energies of hydrocarbons from complete basis set extrapolated multi-reference singles and doubles configuration interaction.

    PubMed

    Oyeyemi, Victor B; Pavone, Michele; Carter, Emily A

    2011-12-01

    Quantum chemistry has become one of the most reliable tools for characterizing the thermochemical underpinnings of reactions, such as bond dissociation energies (BDEs). The accurate prediction of these particular properties (BDEs) are challenging for ab initio methods based on perturbative corrections or coupled cluster expansions of the single-determinant Hartree-Fock wave function: the processes of bond breaking and forming are inherently multi-configurational and require an accurate description of non-dynamical electron correlation. To this end, we present a systematic ab initio approach for computing BDEs that is based on three components: 1) multi-reference single and double excitation configuration interaction (MRSDCI) for the electronic energies; 2) a two-parameter scheme for extrapolating MRSDCI energies to the complete basis set limit; and 3) DFT-B3LYP calculations of minimum-energy structures and vibrational frequencies to account for zero point energy and thermal corrections. We validated our methodology against a set of reliable experimental BDE values of CC and CH bonds of hydrocarbons. The goal of chemical accuracy is achieved, on average, without applying any empirical corrections to the MRSDCI electronic energies. We then use this composite scheme to make predictions of BDEs in a large number of hydrocarbon molecules for which there are no experimental data, so as to provide needed thermochemical estimates for fuel molecules. PMID:22052831

  12. 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.

  13. 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.

  14. 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 π 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.

  15. 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

  16. 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.

  17. Luminescent (N^C^C) Gold(III) Complexes: Stabilized Gold(III) Fluorides.

    PubMed

    Kumar, Roopender; Linden, Anthony; Nevado, Cristina

    2015-11-23

    We report the design, synthesis, and application of a (N^C^C)-ligand framework able to stabilize highly electron-deprived gold(III) species. This novel platform enabled the preparation of C(sp(2) )-gold(III) fluorides for the first time in monomeric, easy-to-handle, bench-stable form by a Cl/F ligand-exchange reaction. Devoid of oxidative conditions or stoichiometric use of toxic Hg salts, this method was applied to the preparation of multiple [C(sp(2) )-Au(III) -F] complexes, which were used as mechanistic probes for the study of the unique properties and intrinsic reactivity of AuF bonds. The improved photophysical properties of [(N^C^C)Au(III) ] complexes compared to classical pincer (C^N^C)-Au systems paves the way for the design of new late-transition-metal-based OLEDs. PMID:26439538

  18. 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

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

    PubMed

    Laventure, Audrey; De Grandpré, 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

  20. 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

  1. 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

  2. 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

  3. 7. Historic American Buildings Survey, C. C. Adams, Photographer August ...

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

    7. Historic American Buildings Survey, C. C. Adams, Photographer August 1931, SEED PACKING ROOM, Gift of New York State Department of Education. - Shaker North Family Washhouse (first), Shaker Road, New Lebanon, Columbia County, NY

  4. Valence-Bond Order (VBO): A New Approach to Modeling Reactive Potential Energy Surfaces for Complex Systems, Materials, and Nanoparticles.

    PubMed

    Zhao, Meiyu; Iron, Mark A; Staszewski, Przemysław; Schultz, Nathan E; Valero, Rosendo; Truhlar, Donald G

    2009-03-10

    The extension of molecular mechanics to reactive systems, metals, and covalently bonded clusters with variable coordination numbers requires new functional forms beyond those popular for organic chemistry and biomolecules. Here we present a new scheme for reactive molecular mechanics, which is denoted as the valence-bond order model, for approximating reactive potential energy surfaces in large molecules, clusters, nanoparticles, solids, and other condensed-phase materials, especially those containing metals. The model is motivated by a moment approximation to tight binding molecular orbital theory, and we test how well one can approximate potential energy surfaces with a very simple functional form involving only interatomic distances with no explicit dependence on bond angles or dihedral angles. For large systems the computational requirements scale linearly with system size, and no diagonalizations or iterations are required; thus the method is well suited to large-scale simulations. The method is illustrated here by developing a force field for particles and solids composed of aluminum and hydrogen. The parameters were optimized against both interaction energies and relative interaction energies. The method performs well for pure aluminum clusters, nanoparticles, and bulk lattices and reasonably well for pure hydrogen clusters; the mean unsigned error per atom for the aluminum-hydrogen clusters is 0.1 eV/atom. PMID:26610225

  5. Bonding aluminum beam leads

    NASA Technical Reports Server (NTRS)

    Burkett, F. S.

    1978-01-01

    Report makes it relatively easy for hybrid-circuit manufacturers to convert integrated circuit chips with aluminum bead leads. Report covers: techniques for handling tiny chips; proper geometries for ultrasonic bonding tips; best combinations of pressure, pulse time, and ultrasonic energy for bonding; and best thickness for metal films to which beam leads are bonded.

  6. 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

  7. Copper-catalyzed, C-C coupling-based one-pot tandem reactions for the synthesis of benzofurans using o-iodophenols, acyl chlorides, and phosphorus ylides.

    PubMed

    Liu, Yunyun; Wang, Hang; Wan, Jie-Ping

    2014-11-01

    One-pot reactions involving acyl chlorides, phosphorus ylides, and o-iodophenols with copper catalysis have been established for the rapid synthesis of functionalized benzofurans. With all of these easily available and stable reactants, the construction of the target products has been accomplished via tandem transformations involving a key C-C coupling, leading to the formation of one C(sp(2))-C bond, one C(sp(2))-O bond, and one C ═ C bond. PMID:25279735

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in small water and HCl clusters.

    PubMed

    Samanta, Amit K; Czakó, Gábor; 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

  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. 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.

  19. 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.

  20. 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 (γS), polarity force (γSp), and hydrogen bonding force (γSh) 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

  1. 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

  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. 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.

  4. Bismuth(iii)dichalcogenones as highly active catalysts in multiple C-C bond formation reactions.

    PubMed

    Srinivas, Katam; Sathyanarayana, Arruri; Naga Babu, Chatla; Prabusankar, Ganesan

    2016-03-15

    Thirteen new bismuth(iii) dichalcogenone derivatives of triflates and halides were synthesized and structurally characterized. The mono, di, tetra and heptanuclear complexes were isolated with different bismuth(iii) coordination environments. These newly isolated bismuth(iii)dichalcogenones were characterized by multinuclear NMR, FT-IR, UV-vis, TGA and single crystal X-ray diffraction techniques. These complexes were tested for the synthesis of symmetrical triaryl- or triheteroarylmethanes and the catalysts were found to be highly active. In particular, the selone complexes were relatively more active than thione complexes. Subsequently, the scope of the catalytic reactions was further explored with different substituents. PMID:26891252

  5. In Pursuit of an Ideal C-C Bond-Forming Reaction

    PubMed Central

    RajanBabu, T. V.

    2009-01-01

    Attempts to introduce the highly versatile vinyl group into other organic molecules in a chemo-, regio- and stereoselective fashion via catalytic activation of ethylene provided challenging opportunities to explore new ligand and salt effects in homogeneous catalysis. This review provides a personal account of the development of enantioselective reactions involving ethylene. PMID:19606231

  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. 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.

  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. Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

    PubMed Central

    Ye, Jianhuai; Fujiwara, Yoshihisa

    2013-01-01

    Summary Background: Localized singlet diradicals are in general quite short-lived intermediates in processes involving homolytic bond-cleavage and formation reactions. In the past decade, long-lived singlet diradicals have been reported in cyclic systems such as cyclobutane-1,3-diyls and cyclopentane-1,3-diyls. Experimental investigation of the chemistry of singlet diradicals has become possible. The present study explores the substituents and the effect of their substitution pattern at the C(1)–C(3) positions on the lifetime of singlet octahydropentalene-1,3-diyls to understand the role of the substituents on the reactivity of the localized singlet diradicals. Results: A series of singlet 2,2-dialkoxy-1,3-diaryloctahydropentalene-1,3-diyls DR were generated in the photochemical denitrogenation of the corresponding azoalkanes AZ. The ring-closed products CP, i.e., 3,3-dialkoxy-2,4-diphenyltricyclo[3.3.0.02,4]octanes, were quantitatively obtained in the denitrogenation reaction. The first-order decay process (k = 1/τ) was observed for the fate of the singlet diradicals DR (λmax ≈ 580–590 nm). The activation parameters, ΔH ‡ and ΔS ‡, for the ring-closing reaction (σ-bond formation process) were determined by the temperature-dependent change of the lifetime. The energy barrier was found to be largely dependent upon the substituents Ar and Ar’. The singlet diradical DRf (Ar = 3,5-dimethoxyphenyl, OCH2Ar’ = OCH2(3,5-dimethoxyphenyl)) was the longest-lived, τ293 = 5394 ± 59 ns, among the diradicals studied here. The lifetime of the parent diradical DR (Ar = Ph, OCH2Ar’ = OCH3) was 299 ± 2 ns at 293 K. Conclusion: The lifetimes of the singlet 1,3-diyls are found to be largely dependent on the substituent pattern of Ar and Ar’ at the C(1)–C(3) positions. Both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime. PMID:23766808

  10. 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.

  11. 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.

  12. Interstellar Detection of c-C3D2

    NASA Astrophysics Data System (ADS)

    Spezzano, S.; Brünken, S.; Schilke, P.; Caselli, P.; Menten, K. M.; McCarthy, M. C.; Bizzocchi, L.; Trevinõ-Morales, S. P.; Aikawa, Y.; Schlemmer, S.

    2013-06-01

    We report the first interstellar detection of c-C3D2. Doubly deuterated cyclopropenylidene, a carbene, has been detected toward the starless cores TMC-1C and L1544 using the IRAM 30 m telescope. The J_{K_a,K_c} = 3_{0,3} {--} 2_{1,2}, 31, 3-20, 2, and 22, 1-11, 0 transitions of this species have been observed at 3 mm in both sources. The expected 1:2 intensity ratio has been found in the 30, 3-21, 2 and 31, 3-20, 2 lines, belonging to the para and ortho species, respectively. We also observed lines of the main species, c-C3H2, singly deuterated c-C3HD, and the species with one 13C off of the principal axis of the molecule, c-H13CC2H. The lines of c-C3D2 have been observed with high signal-to-noise ratio, better than 7.5σ in TMC-1C and 9σ in L1544. The abundance of doubly deuterated cyclopropenylidene with respect to the normal species is found to be 0.4%-0.8% in TMC-1C and 1.2%-2.1% in L1544. The deuteration of this small hydrocarbon ring is analyzed with a comprehensive gas-grain model, the first including doubly deuterated species. The observed abundances of c-C3D2 can be explained solely by gas-phase processes, supporting the idea that c-C3H2 is a good indicator of gas-phase deuteration. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  13. Stretching the α-helix: a direct measure of the hydrogen-bond energy of a single-peptide molecule

    NASA Astrophysics Data System (ADS)

    Lantz, Mark A.; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Martynski, Tomasz; Kusumi, Toshinori; Nakamura, Chikashi; Miyake, Jun

    1999-12-01

    Atomic force microscopy was used to measure the force required to stretch individual molecules of the peptide cysteine 3-lysine 30-cysteine from the α-helical state into a linear chain (approximately 200 pN). The measured force versus peptide elongation was used to calculate the work done in breaking the hydrogen bonds which give rise to the helical structure. The average experimental value of the hydrogen-bond energy (20.2 kJ/mol) is in good agreement with reported theoretical calculations. In addition, the stiffness of individual peptides was measured directly using a force modulation technique and found to vary from approximately 0.005-0.012 N/m during elongation.

  14. Toward quantification of protein backbone–backbone hydrogen bonding energies: An energetic analysis of an amide-to-ester mutation in an α-helix within a protein

    PubMed Central

    Gao, Jianmin; Kelly, Jeffery W.

    2008-01-01

    Amide-to-ester backbone mutagenesis enables a specific backbone–backbone hydrogen bond (H-bond) in a protein to be eliminated in order to quantify its energetic contribution to protein folding. To extract a H-bonding free energy from an amide-to-ester perturbation free energy (ΔG folding,wt − ΔG folding,mut), it is necessary to correct for the putative introduction of a lone pair–lone pair electrostatic repulsion, as well as for the transfer free energy differences that may arise between the all amide sequence and the predominantly amide sequence harboring an ester bond. Mutation of the 9–10 amide bond within the V9F variant of the predominantly helical villin headpiece subdomain (HP35) to an ester or an E-olefin backbone bond results in a less stable but defined wild-type fold, an attribute required for this study. Comparing the folding free energies of the ester and E-olefin mutants, with correction for the desolvation free energy differences (ester and E-olefin) and the loss of an n-to-π* interaction (E-olefin), yields an experimentally based estimate of +0.4 kcal/mol for the O–O repulsion energy in an α-helical context, analogous to our previous experimentally based estimate of the O–O repulsion free energy in the context of a β-sheet. The small O–O repulsion energy indicates that amide-to-ester perturbation free energies can largely be attributed to the deletion of the backbone H-bonds after correction for desolvation differences. Quantitative evaluation of H-bonding in an α-helix should now be possible, an important step toward deciphering the balance of forces that enable spontaneous protein folding. PMID:18434500

  15. CO hydrogenation, deoxygenation, and C-C coupling promoted by ((silox)/sub 2/TaH/sub 2/)/sub 2/

    SciTech Connect

    Toreki, R.; LaPointe, R.E.; Wolczanski, P.T.

    1987-11-25

    The Fischer-Tropsch (F-T) reaction considered a potential solution to future energy concerns, has commanded the attention of researchers in both heterogeneous and homogeneous catalysis for the past 15 years. The most widely accepted mechanism for this conversion of synthesis gas (CO/H/sub 2/) to hydrocarbons and oxygenates incorporates three crucial steps: (1) CO is deoxygenated, presumably via dissociative adsorption; (2) H-transfer to surface carbides or CO/sub ads/ produces surface methylene groups, (3) C-C bond formation occurs through oligomerization of (CH/sub 2/)/sub ads/. Various organometallic species model the individual steps, yet fall short of corroborating the entire sequence. Reported herein is the carbonylation of ((silox)/sub 2/TaH/sub 2/)/sub 2/ (silox = t-Bu/sub 3/SiO/sup -/) and successive reactions which encompass the critical transformations of the F-T pathway.

  16. 30 CFR 281.33 - Bonds and bonding requirements.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 2 2011-07-01 2011-07-01 false Bonds and bonding requirements. 281.33 Section 281.33 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, REGULATION, AND ENFORCEMENT, DEPARTMENT OF... SHELF Financial Considerations § 281.33 Bonds and bonding requirements. (a) When the leasing...

  17. Effect of an external electric field on the dissociation energy and the electron density properties: The case of the hydrogen bonded dimer HF...HF.

    PubMed

    Mata, Ignasi; Molins, Elies; Alkorta, Ibon; Espinosa, Enrique

    2009-01-28

    The effect of a homogeneous external electric field parallel to the hydrogen bond in the FH...FH dimer has been studied by theoretical methods. The quantum theory of atoms in molecules methodology has been used for analyzing the electron distribution of the dimer, calculated with different hydrogen bond distances and external field magnitudes. It is shown that an electric field in the opposite direction to the dipole moment of the system strengthens the interaction due to a larger mutual polarization between both molecules and increases the covalent character of the hydrogen bond, while an external field in the opposite direction has the inverse effect. The properties of the complex at its equilibrium geometry with applied field have been calculated, showing that dependencies between hydrogen bond distance, dissociation energy, and properties derived from the topological analysis of the electron distribution are analogous to those observed in families of XDH...AY complexes. The application of an external field appears as a useful tool for studying the effect of the atomic environment on the hydrogen bond interaction. In the case of FH...FH, both the kinetic energy density and the curvature of the electron density along the hydrogen bond at the bond critical point present a surprisingly good linear dependence on the dissociation energy. The interaction energy can be modeled by the sum of two exponential terms that depend on both the hydrogen bond distance and the applied electric field. Moreover, as indicated by the resulting interaction energy observed upon application of different external fields, the equilibrium distance varies linearly with the external field, and the dependence of the dissociation energy on either the hydrogen bond distance or the external electric field is demonstrated to be exponential. PMID:19191374

  18. 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.

  19. 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

  20. Formation Mechanism of the First Carbon-Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons.

    PubMed

    Liu, Yue; Müller, Sebastian; Berger, Daniel; Jelic, Jelena; Reuter, Karsten; Tonigold, Markus; Sanchez-Sanchez, Maricruz; Lercher, Johannes A

    2016-05-01

    The elementary reactions leading to the formation of the first carbon-carbon bond during early stages of the zeolite-catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C-C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid-catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol(-1) for the formation of the first C-C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms. PMID:27037603

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Influence of surface treatment of contaminated lithium disilicate and leucite glass ceramics on surface free energy and bond strength of universal adhesives.

    PubMed

    Yoshida, Fumi; Tsujimoto, Akimasa; Ishii, Ryo; Nojiri, Kie; Takamizawa, Toshiki; Miyazaki, Masashi; Latta, Mark A

    2015-01-01

    This study investigates the influence of surface treatment of contaminated lithium disilicate and leucite glass ceramic restorations on the bonding efficacy of universal adhesives. Lithium disilicate and leucite glass ceramics were contaminated with saliva, and then cleaned using distilled water (SC), or 37% phosphoric acid (TE), or hydrofluoric acid (CE). Specimens without contamination served as controls. The surface free energy was determined by measuring the contact angles formed when the three test liquids were placed on the specimens. Bond strengths of the universal adhesives were also measured. Saliva contamination and surface treatment of ceramic surfaces significantly influenced the surface free energy. The bond strengths of universal adhesives were also affected by surface treatment and the choice of adhesive materials. Our data suggest that saliva contamination of lithum disilicate and leucite glass ceramics significantly impaired the bonding of the universal adhesives, and reduced the surface free energy of the ceramics. PMID:26632235

  6. Analytic bond-order potentials beyond Tersoff-Brenner. II. Application to the hydrocarbons

    NASA Astrophysics Data System (ADS)

    Oleinik, I. I.; Pettifor, D. G.

    1999-04-01

    The accuracy of the analytic bond-order potentials (BOP's) that were derived in the previous paper within the tight-binding (TB) formalism is studied for the case of diamond, graphite, and the hydrocarbon molecules. The simplified four-level variant, BOP4S, is found to reproduce the TB bond orders of the C-H and C-C σ bonds to better than 6% due partly to the inclusion of the shape parameter (b2/b1)2. The two-level matrix-derived expression BOP2M is shown to provide a good description of the saturated and conjugate π bonds, thereby overcoming the deficiencies of the Tersoff potential that are associated with overbinding of radicals and poor treatment of conjugacy. The analytic BOP's reproduce the C-H and C-C bond energies to better than 0.9 eV per bond. The errors would be reduced if the analytic potentials were fitted to experiment rather than predicted directly from known TB parameters.

  7. Analysis of hydrogen bond energies and hydrogen bonded networks in water clusters (H2O)20 and (H2O)25 using the charge-transfer and dispersion terms.

    PubMed

    Iwata, Suehiro

    2014-06-21

    The hydrogen bonds and their networks in the water clusters (H2O)20 and (H2O)25 are characterized using the charge-transfer (E(W(a),W(d))(CT)) and dispersion (E(W(a),W(d))(Disp)) terms for every pair of water molecules (Wa, Wd) in the clusters. The terms are evaluated by the perturbation theory based on the ab initio locally projected molecular orbitals (LPMO PT) developed by the present author. The relative binding energies among the isomers evaluated by the LPMO PT agree with those of the high level ab initio wave function based theories. A strong correlation between E(W(a),W(d))(CT) and E(W(a),W(d))(Disp) for the hydrogen bonded pairs is found. The pair-wise interaction energies are characterized by the types of hydrogen-donor (Wd) and hydrogen-acceptor (Wa) water molecules. The strongest pair is that of the D2A1 water molecule as a hydrogen-acceptor and the D1A2 water molecule as a hydrogen-donor, where the DnAm water molecule implies that the water molecule has n hydrogen bonding O-H and m accepting HO. The intra-molecular deformation as well as the O···O distance is also dependent on the types of hydrogen bonded pairs. The ring structures in the cluster are classified by the pattern of alignment of the hydrogen bonds. The lengthening of the hydrogen-bonding OH of Wd is strongly correlated with the charge-transfer (E(W(a),W(d))(CT)) energy. PMID:24800849

  8. 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

  9. Linear Free Energy Relationships Reveal Structural Changes in Hydrogen-Bonded Host–Guest Interactions

    PubMed Central

    2015-01-01

    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 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

  10. 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

  11. 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.

  12. 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.

  13. [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

  14. 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.

  15. 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

  16. Quantum-chemical calculations of bonding energy and the unit-cell parameters of crystalline magnesium difluoride

    SciTech Connect

    Iomin, L.M.; Buznik, V.M.

    1988-11-01

    Quantum-chemical calculations of the bonding energy of the crystal lattice, the unit-cell parameters, and the coordinates of the anions in crystalline magnesium difluoride have been performed in the framework of the Loewdin model. An expression for the energy of the three-particle interactions in rutile-like crystals has been obtained. The calculations were carried out in three successive approximations. A comparison with the experimental data shows that the best description of the interatomic interactions in rutile-like magnesium fluoride (in the framework of the Loewdin model) is achieved in an approximation which takes into account the non-Madelung interactions only in the first coordination sphere. Consideration of the short-range interactions with more distant ions worsens the agreement between theory and experiment.

  17. 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.

  18. 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

  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. 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. 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.

  2. 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 C–H, C–OH, C=O, and C=C groups account for 12–14% of all C, which matches the surface fraction expected for bulk-terminated 5 nm diameter diamond particles.

  3. A double-deletion method to quantifying incremental binding energies in proteins from experiment: example of a destabilizing hydrogen bonding pair.

    PubMed

    Campos, Luis A; Cuesta-López, Santiago; López-Llano, Jon; Falo, Fernando; Sancho, Javier

    2005-02-01

    The contribution of a specific hydrogen bond in apoflavodoxin to protein stability is investigated by combining theory, experiment and simulation. Although hydrogen bonds are major determinants of protein structure and function, their contribution to protein stability is still unclear and widely debated. The best method so far devised to estimate the contribution of side-chain interactions to protein stability is double mutant cycle analysis, but the interaction energies so derived are not identical to incremental binding energies (the energies quantifying net contributions of two interacting groups to protein stability). Here we introduce double-deletion analysis of 'isolated' residue pairs as a means to precisely quantify incremental binding. The method is exemplified by studying a surface-exposed hydrogen bond in a model protein (Asp96/Asn128 in apoflavodoxin). Combined substitution of these residues by alanines slightly destabilizes the protein due to a decrease in hydrophobic surface burial. Subtraction of this effect, however, clearly indicates that the hydrogen-bonded groups in fact destabilize the native conformation. In addition, molecular dynamics simulations and classic double mutant cycle analysis explain quantitatively that, due to frustration, the hydrogen bond must form in the native structure because when the two groups get approximated upon folding their binding becomes favorable. We would like to remark that 1), this is the first time the contribution of a specific hydrogen bond to protein stability has been measured by experiment; and 2), more hydrogen bonds need to be analyzed to draw general conclusions on protein hydrogen bond energetics. To that end, the double-deletion method should be of help. PMID:15556980

  4. 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…

  5. 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)

  6. 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.

  7. 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.

  8. 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.

  9. Phosphaannulation by palladium-catalyzed carbonylation of C-H bonds of phosphonic and phosphinic acids.

    PubMed

    Shin, Seohyun; Jeong, Yeonseok; Jeon, Woo Hyung; Lee, Phil Ho

    2014-06-01

    An efficient phosphaannulation by Pd-catalyzed carbonylation of C-H bonds of phosphonic and phosphinic acids for the synthesis of oxaphosphorinanone oxides is reported. These compounds are novel phosphorus heterocyclic scaffolds, thus opening a new avenue to sequential C-C/C-O bond formation in one pot. PMID:24856076

  10. Theoretical study of the C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The successive C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O (ketene) are determined using large-basis sets and a high level of correlation treatment. For CH4, C2H2, and C2H4 the computed values are in excellent agreement with experiment. Using these results, the values 107.9 + or - 2.0 and 96.7 + or - 2.0 kcal/mol are recommended for the C-H bond dissociation energies of H2C2O and HC2O, respectively.

  11. 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.

  12. 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

  13. 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 (π,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.

  14. 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.

  15. 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…

  16. Effects of bonding on the energy distribution of electrons scattered elastically at high momentum transfer

    SciTech Connect

    Vos, M.; Went, M. R.

    2006-11-15

    High-resolution measurements of 40-keV electrons scattered over 44.3 deg. from evaporated carbon films are presented. The observed width of the energy distribution of electrons scattered from carbon is significantly larger than the experimental energy resolution, and its position is shifted to lower energy. Measurements were done for transmission and reflection geometries for thin films with thicknesses varying from 90 A ring to 1400 A ring . The observed peak shape is largely independent of the thickness and measurement geometry. The peak shape deviates from Gaussian in all cases, in a way consistent with theories that describe these processes beyond the impulse approximation. The energy shift of the carbon peak is measured by evaporating a small amount of Au on these films. Separation of the Au and C peak is somewhat smaller than calculated assuming scattering from free C and Au atoms, but independent of measurement geometry. Finally spectra were measured from highly oriented pyrolytic graphite (HOPG) films. Now different widths are observed in reflection geometry and transmission geometry. This is attributed to the anisotropy of the motion of the C atoms in HOPG. Also the Au-C separation is slightly orientation dependent for HOPG. All observations agree at least semiquantitatively with neutron Compton scattering results, a related scattering experiment that studies neutron-atom collisions at similar momentum transfers.

  17. 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

  18. 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.

  19. 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

  20. 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 π* 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* orbital of the base to the σ* 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.

  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. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Free Energy Diagram for the Heterogeneous Enzymatic Hydrolysis of Glycosidic Bonds in Cellulose.

    PubMed

    Sørensen, 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

  8. Photodissociation measurements of bond dissociation energies: Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3

    SciTech Connect

    Russon, L.M.; Heidecke, S.A.; Birke, M.K.; Conceicao, J.; Morse, M.D.; Armentrout, P.B. )

    1994-04-01

    The bond dissociation energies of Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3] have been measured from the sudden onset of predissociation in the photodissociation spectra of these molecules, yielding values of [ital D][sup [circ

  9. 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

  10. 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)

  11. 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

  12. 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

  13. Molecular Structure and Bonding in Plutonium Carbides: A Theoretical Study of PuC3.

    PubMed

    Molpeceres, Germán; Rayón, Víctor M; Barrientos, Carmen; Largo, Antonio

    2016-04-14

    The most relevant species of plutonium tricarbide were characterized using theoretical methods. The global minimum is predicted to be a fan structure where the plutonium atom is bonded to a quasi-linear C3 unit. A rhombic isomer, shown to be a bicyclic species with transannular C-C bonding, lies about 39 kJ/mol above the fan isomer. A linear PuCCC isomer and a three-membered ring CPuC2 isomer were found to be higher in energy (150 and 195 kJ/mol, respectively, above the predicted global minimum). The possible processes for the formation of these species are discussed, and the IR spectra were predicted to help in possible experimental detection. The nature of the Pu-C interaction has been analyzed in terms of a topological analysis of the electronic density, showing that Pu-C bonding is essentially ionic with a certain degree of covalent character. PMID:27010701

  14. 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.

  15. Temperature dependence of internal motions of protein side-chain NH3(+) groups: insight into energy barriers for transient breakage of hydrogen bonds.

    PubMed

    Zandarashvili, Levani; Iwahara, Junji

    2015-01-20

    Although charged side chains play important roles in protein function, their dynamic properties are not well understood. Nuclear magnetic resonance methods for investigating the dynamics of lysine side-chain NH3(+) groups were established recently. Using this methodology, we have studied the temperature dependence of the internal motions of the lysine side-chain NH3(+) groups that form ion pairs with DNA phosphate groups in the HoxD9 homeodomain-DNA complex. For these NH3(+) groups, we determined order parameters and correlation times for bond rotations and reorientations at 15, 22, 28, and 35 °C. The order parameters were found to be virtually constant in this temperature range. In contrast, the bond-rotation correlation times of the NH3(+) groups were found to depend strongly on temperature. On the basis of transition state theory, the energy barriers for NH3(+) rotations were analyzed and compared to those for CH3 rotations. Enthalpies of activation for NH3(+) rotations were found to be significantly higher than those for CH3 rotations, which can be attributed to the requirement of hydrogen bond breakage. However, entropies of activation substantially reduce the overall free energies of activation for NH3(+) rotations to a level comparable to those for CH3 rotations. This entropic reduction in energy barriers may accelerate molecular processes requiring hydrogen bond breakage and play a kinetically important role in protein function. PMID:25489884

  16. 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.

  17. 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

  18. 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

  19. 3Drefine: Consistent Protein Structure Refinement by Optimizing Hydrogen Bonding Network and Atomic-Level Energy Minimization

    PubMed Central

    Bhattacharya, Debswapna; Cheng, Jianlin

    2013-01-01

    One of the major limitations of computational protein structure prediction is the deviation of predicted models from their experimentally derived true, native structures. The limitations often hinder the possibility of applying computational protein structure prediction methods in biochemical assignment and drug design that are very sensitive to structural details. Refinement of these low-resolution predicted models to high-resolution structures close to the native state, however, has proven to be extremely challenging. Thus, protein structure refinement remains a largely unsolved problem. Critical assessment of techniques for protein structure prediction (CASP) specifically indicated that most predictors participating in the refinement category still did not consistently improve model quality. Here, we propose a two-step refinement protocol, called 3Drefine, to consistently bring the initial model closer to the native structure. The first step is based on optimization of hydrogen bonding (HB) network and the second step applies atomic-level energy minimization on the optimized model using a composite physics and knowledge-based force fields. The approach has been evaluated on the CASP benchmark data and it exhibits consistent improvement over the initial structure in both global and local structural quality measures. 3Drefine method is also computationally inexpensive, consuming only few minutes of CPU time to refine a protein of typical length (300 residues). PMID:22927229

  20. 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

  1. 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

  2. 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 Σ3(111) and Σ11(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

  3. Chemo-regioselectivity in heterogeneous catalysis: competitive routes for C = O and C = C hydrogenations from a theoretical approach.

    PubMed

    Loffreda, David; Delbecq, Françoise; Vigné, Fabienne; Sautet, Philippe

    2006-02-01

    The usual empirical rule stating that the C=C bond is more reactive than the C=O group for catalytic hydrogenations of unsaturated aldehydes is invalidated from the present study. Density functional theory calculations of all the competitive hydrogenation routes of acrolein on Pt(111) reveals conversely that the attack at the C=O bond is systematically favored. The explanation of such catalytic behavior is the existence of metastable precursor states for the O-H bond formation showing that the attack at the oxygen atom follows a new preferential mechanism where the C=O moiety is not directly bonded with the Pt surface atoms, hence yielding an intermediate pathway between Langmuir-Hinshelwood and Rideal-Eley general types of mechanisms. When the whole catalytic cycle is considered, our results reconcile with experimental studies devoted to hydrogenation of acrolein on Pt, since the desorption step of the partially hydrogenated product (unsaturated alcohol versus saturated aldehyde) plays a key role for the selectivity. PMID:16433550

  4. 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.

  5. 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 (ΔZPVE). The structures of H-bonded complexes were optimized at the RI-MP2/cc-pVTZ level, at which deformation and harmonic ΔZPVE energies were also calculated. The structures of dispersion-bound complexes were optimized at the DFT-D3 level, and harmonic ΔZPVE 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 ΔCCSD(T) correction, determined with the aug-cc-pVDZ basis set. The ΔZPVE 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 ΔZPVE 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 ΔZPVE was shown. For the phenolH2O complex, the ΔZPVE energy calculated at the VPT2 level and on the basis of "diagonal approximation" differed by less than 0.1 kcal mol(-1). PMID:26392236

  6. 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.

  7. 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.

  8. 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.

  9. Impact of deformation energy on the hydrogen bonding interactions in gas phase 3-X catechol ⋯ H2O complexes (X = H, F, Cl, Br): The effect of approach of a water molecule

    NASA Astrophysics Data System (ADS)

    Deb, Debojit Kumar; Sarkar, Biplab

    2016-06-01

    The conformations and nature of hydrogen bonding interactions for 3-X catechol ⋯ H2O (X = H, F, Cl, Br) has been investigated by ab initio MP2, CCSD(T), and density functional B3LYP, wB97XD and M06-2X methods. The changes in interaction energies due to deformation of the structures has been studied in detail. The intra- and intermolecular hydrogen bonding interactions due to the different direction of approach of water molecule have been discussed. A detailed natural bond orbital (NBO) analysis and the symmetry-adapted perturbation theory (SAPT) based energy decomposition analysis has been carried out to elucidate interaction strength and properties in these hydrogen bonded systems. The charge transfer percentage (CTP) has been derived which will be universally useful for correlating binding energy, deformation energy and the geometrical parameters such as angles, bond lengths, etc. for other systems as well.

  10. Electron transfer characterization of iron and cobalt porphyrins and copper complexes, and of their metal-carbon and metal-oxygen bond energies

    SciTech Connect

    Qui, Aimin

    1992-12-31

    The electron-transfer and oxidation-reduction chemistry for the alkyl-iron and alkyl-cobalt porphyrins [(Por)M-R] and copper complexes has been investigated on the basis of cyclic voltammetric and controlled-potential-electrolysis measurements. Half-wave potentials for the oxidation and the reduction of (Por)M-R are directly influenced by the nature of the electron-donating or electron-withdrawing groups on the porphyrin ring and the structure of the alkyl groups. The redox potentials for a series of copper complexes are affected by the electron donating ability and the chelate effect of the ligands. Hydrolysis of the copper(II) cations (Cu{sup II}L{sub n}{sup 2+}) occurs in water. The reactivity of copper(I) complexes with dioxygen is directly related to the oxidation potential of the complexes in the solvent. The combination of Cu{sup I}(bpy)2{sup +} and tertiary-butyl hydroperoxide induces O{sub 2} activation to oxygenate methylenic carbon to ketones. Mechanistic schemes have been developed on the basis of electrochemical and spectrophotometric characteristics and reaction-product profiles for copper(II)-bis(bipyridine) [Cu{sup II}(bpy)2{sup 2+}]/base-induced activation of O{sub 2} to dehydrogenate primary alcohols to aldehydes. The free energies of bond formation (-{Delta}G{sub BF}) for the (Por)M-R and copper-ligand (oxygen or nitrogen) bonds have been determined from the redox potentials of the corresponding electrode reactions. The values of -{Delta}G{sub BF} are 14-35 kcal mol{sup {minus}1} for iron porphyrins and 20-38 kcal mol{sup {minus}1} for cobalt porphyrins which depend on the structures of the porphyrins and the alkyl groups. Apparent bond energies are 18-51 kcal mol{sup {minus}1} for the Cu{sup II}-L bonds are 46-78 kcal mol{sup {minus}1} for the Cu{sup I}-L bonds. The free energies of bond formation for the L{sub n}Cu{sup I}-OO bonds are 7-16 kcal mol{sup {minus}1}.

  11. 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

  12. 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}).

  13. 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.

  14. 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

  15. 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-ωPBE 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-ωPBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-ωPBE/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-ωPBE/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.

  16. 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

  17. 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

  18. Characteristic of structures and π-hydrogen bond of dimers C2H4-nFn-HF (n=0,1,2)

    NASA Astrophysics Data System (ADS)

    Li, Rui-Yan; Li, Zhi-Ru; Wu, Di; Li, Ying; Chen, Wei; Sun, Chia-Chung

    2004-11-01

    By the counterpoise-correlated potential energy surface method (interaction energy optimization), five structures of the C2H4-nFn-HF (n=0,1,2) dimers with all real frequencies have been obtained at MP2/aug-cc-pVDZ level. The influence of F substituent effect on the structure and π-hydrogen bond of dimer has been discussed. For C2H4-nFn-HF (n=1,2), the π-hydrogen bonds are elongated comparing with that for C2H4-HF. For C2H3F-HF, g-C2H2F2-HF, cis-C2H2F2-HF, the π-hydrogen bonds are further deformed. These changes (elongate, shift, and deformation) of π-hydrogen bond mainly come from deformation of π-electron cloud of C=C bond. The π-electron cloud is pushed towards the one C atom, the π H-bond shift also to the C direction. Since the two lobes of π-electron cloud have deviated slightly from the molecular vertical plane passing through C=C bond, the π-hydrogen bond is sloped. Intermolecular interaction energies of the dimers are calculated to be -3.9 for C2H4-HF, -2.8 for C2H3F-HF, -2.1 for g-C2H2F2-HF, -1.6 for cis-C2H2F2-HF, -1.3 kcal/mol for trans-C2H2F2-HF, at CCSD(T)/aug-cc-pVDZ level.

  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. 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.

  1. 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.

  2. Bonds Boom.

    ERIC Educational Resources Information Center

    Reynolds, Cathryn

    1989-01-01

    The combined effect of the "Serrano" decision and Proposition 13 left California school districts with aging, overcrowded facilities. Chico schools won a $18.5 million general obligation bond election for facilities construction. With $11 billion needed for new school construction, California will need to tap local sources. A sidebar outlines…

  3. Photochemical tissue bonding

    DOEpatents

    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.

  4. Application of C/C composites to the combustion chamber of rocket engines. Part 1: Heating tests of C/C composites with high temperature combustion gases

    NASA Astrophysics Data System (ADS)

    Tadano, Makoto; Sato, Masahiro; Kuroda, Yukio; Kusaka, Kazuo; Ueda, Shuichi; Suemitsu, Takeshi; Hasegawa, Satoshi; Kude, Yukinori

    1995-04-01

    Carbon fiber reinforced carbon composite (C/C composite) has various superior properties, such as high specific strength, specific modulus, and fracture strength at high temperatures of more than 1800 K. Therefore, C/C composite is expected to be useful for many structural applications, such as combustion chambers of rocket engines and nose-cones of space-planes, but C/C composite lacks oxidation resistivity in high temperature environments. To meet the lifespan requirement for thermal barrier coatings, a ceramic coating has been employed in the hot-gas side wall. However, the main drawback to the use of C/C composite is the tendency for delamination to occur between the coating layer on the hot-gas side and the base materials on the cooling side during repeated thermal heating loads. To improve the thermal properties of the thermal barrier coating, five different types of 30-mm diameter C/C composite specimens constructed with functionally gradient materials (FGM's) and a modified matrix coating layer were fabricated. In this test, these specimens were exposed to the combustion gases of the rocket engine using nitrogen tetroxide (NTO) / monomethyl hydrazine (MMH) to evaluate the properties of thermal and erosive resistance on the thermal barrier coating after the heating test. It was observed that modified matrix and coating with FGM's are effective in improving the thermal properties of C/C composite.

  5. 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.

  6. 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

  7. 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)

  8. 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).

  9. 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.

  10. 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).…

  11. 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

  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 α-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 α-arylation with carbon or heteroatom-based electrophiles, or by performing an α,α-heterodiarylation to install aryl groups at this position. The α-arylation of nitrile and ester enolates gives access to 3-amino and 3-hydroxyisoquinolines and the α-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. 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

  15. Catalytic tandem C-C bond formation/cleavage of cyclopropene for allylzincation of aldehydes or aldimine using organozinc reagents.

    PubMed

    Nakano, Takeo; Endo, Kohei; Ukaji, Yutaka

    2014-03-01

    The tandem allylation of aldehydes or an aldimine with allylzinc intermediates derived from organozinc reagents and cyclopropenes is described. The present three-component reaction involves carbozincation of cyclopropene and sequential cleavage of a cyclopropylzinc intermediate in situ without a transition-metal catalyst. The allylzinc intermediates generated in situ, which is an α,β-unsaturated acylanion equivalent, gave the corresponding homoallylic alcohols or amine in good yields. PMID:24564424

  16. 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

  17. 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

  18. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  19. 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.

  20. Modeling of the Reaction Mechanism of Enzymatic Radical C-C Coupling by Benzylsuccinate Synthase.

    PubMed

    Szaleniec, Maciej; Heider, Johann

    2016-01-01

    Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C-C coupling catalyzed by benzylsuccinate synthase (BSS). BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD) simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i) What mechanistic details of the BSS reaction yield the most probable molecular model? (ii) What is the molecular basis of enantiospecificity of BSS? (iii) Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R)-benzylsuccinate as a product and a kinetic isotope effect (KIE) ranging between 2 and 4? The quantum mechanics (QM) modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C-H activation and not C-C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R) orientation and reverse preference of benzyl radical attack on fumarate in pro(S) pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5) is still higher than the experimentally observed values (4.0) which suggests that both C-H activation and radical quenching may jointly be involved in the kinetic control of the reaction. PMID:27070573

  1. 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

  2. Design and Preparation of New Palladium Precatalysts for C-C and C-N Cross-Coupling Reactions

    PubMed Central

    Bruno, Nicholas C.

    2012-01-01

    A series of easily prepared, phosphine-ligated palladium precatalysts based on the 2-aminobiphenyl scaffold have been prepared. The role of the precatalyst-associated labile halide (or pseudohalide) in the formation and stability of the palladacycle has been examined. It was found that replacing the chloride in the previous version of the precatalyst with a mesylate leads to a new class of precatalysts with improved solution stability and that are readily prepared from a wider range of phosphine ligands. The differences between the previous version of precatalyst and that reported here are explored. In addition, the reactivity of the latter is examined in a range of C-C and C-N bond forming reactions. PMID:23667737

  3. 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.

  4. 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 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. PMID:26057044

  5. Electrolytes induce long-range orientational order and free energy changes in the H-bond network of bulk water

    PubMed Central

    Chen, Yixing; Okur, Halil I.; Gomopoulos, Nikolaos; Macias-Romero, Carlos; Cremer, Paul S.; Petersen, Poul B.; Tocci, Gabriele; Wilkins, David M.; Liang, Chungwen; Ceriotti, Michele; Roke, Sylvie

    2016-01-01

    Electrolytes interact with water in many ways: changing dipole orientation, inducing charge transfer, and distorting the hydrogen-bond network in the bulk and at interfaces. Numerous experiments and computations have detected short-range perturbations that extend up to three hydration shells around individual ions. We report a multiscale investigation of the bulk and surface of aqueous electrolyte solutions that extends from the atomic scale (using atomistic modeling) to nanoscopic length scales (using bulk and interfacial femtosecond second harmonic measurements) to the macroscopic scale (using surface tension experiments). Electrolytes induce orientational order at concentrations starting at 10 μM that causes nonspecific changes in the surface tension of dilute electrolyte solutions. Aside from ion-dipole interactions, collective hydrogen-bond interactions are crucial and explain the observed difference of a factor of 6 between light water and heavy water. PMID:27152357

  6. 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.

  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

    ... 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 c... in the securities of the above-listed company. Therefore, it is ordered, pursuant to Section 12(k)...

  9. Highly Accurate CCSD(T) and DFT–SAPT 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 ΔCCSD(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 SCS–MP2 (SCS: spin-component-scaled), SCS(MI)–MP2 (MI: molecular interaction), MP3, dispersion-augmented DFT (DFT–D), M06–2X, and DFT–SAPT (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 DFT–SAPT 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. 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)

  11. 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).

  12. 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

  13. 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

  14. 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

  15. 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

  16. Palladium-catalyzed oxidative insertion of carbon monoxide to N-sulfonyl-2-aminobiaryls through C-H bond activation: access to bioactive phenanthridinone derivatives in one pot.

    PubMed

    Rajeshkumar, Venkatachalam; Lee, Tai-Hua; Chuang, Shih-Ching

    2013-04-01

    Palladium-catalyzed oxidative carbonylation of N-sulfonyl-2-aminobiaryls through C-H bond activation and C-C, C-N bond formation under TFA-free and milder conditions has been developed. The reaction tolerates a variety of substrates and provides biologically important phenanthridinone derivatives in yields up to 94%. PMID:23477600

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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…

  2. 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…

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. Divalent metals can reside on bonds in fullerenes.

    PubMed

    Gao, Xuejiao; Sun, Baoyun; Zhao, Yuliang; Chen, Bo-Zhen; Gao, Xingfa

    2015-05-28

    DFT calculations consistently suggest that a lanthanide will sit on either the 6/6 bond inside C60 having a divalent state or the hexagonal center having a trivalent state. Some lanthanides can stay only above the 6/6 bond inside C60 to form stabilized structures, despite the greatly reduced metal-cage coordination numbers. The preference for C-C bonds by a divalent metal has been confirmed by revisiting the structures of Yb@C2v(3)-C80, Yb@Cs(6)-C82 and Yb@C2v(9)-C82, for which the calculations suggest that the Yb atoms are indeed situated above the C-C bonds, close to the reported structures obtained by single crystal XRD experiments. The result will guide the characterization of structures and electronic structures of endohedral metallofullerenes (EMFs), especially C60 mono-EMFs, in the future. PMID:25919542

  8. 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.

  9. 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

  10. Linear free energy relationships in C-N bond dissociations in molecular ions of 4-substituted N-(2-furylmethyl)anilines in the gas phase.

    PubMed

    Solano Espinoza, Eduardo A; Stashenko, Elena; Martínez, Jairo; Mora, Uriel; Kouznetsov, Vladimir

    2007-11-01

    The substituent effect on the reactivity of the C-N bond of molecular ions of 4-substituted N-(2-furylmethyl)anilines toward two dissociation pathways was studied. With this aim, six of these compounds were analyzed by mass spectrometry using electron ionization with energies between 7.8 and 69.9 eV. Also, the UB3LYP/6-31G (d,p) and UHF/6-31G (d, p) levels of theory were used to calculate the critical energies (reaction enthalpies at 0 K) of the processes that lead to the complementary ions [C(5)H(5)O](+) and [M - C(5)H(5)O](+), assuming structures that result from the heterolytic and homolytic C-N bond cleavages of the molecular ions, respectively. A kinetic approach proposed in the 1960s was applied to the mass spectral data to obtain the relative rate coefficients for both dissociation channels from ratios of the peak intensities of these ions. Linear relationships were obtained between the logarithms of the relative rate coefficients and the calculated critical energies and other thermochemical properties, whose slopes showed to be conditioned by the energy provided to the compounds within the ion source. Moreover, it was found that the dissociation that leads to [C(5)H(5)O](+) is a process strongly dependent upon the electron withdrawing or donating properties of the substituent, favored by those factors that destabilize the molecular ion. On the contrary, the dissociation that leads to [M - C(5)H(5)O](+) is indifferent to the polar electronic effects of the substituent. The abundance of both products was governed by the rule of Stevenson-Audier, according to which the major ion is the one of less negative electronic affinity. PMID:17687763

  11. 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}.

  12. High-performance FeSb-TiC-C nanocomposite anodes for sodium-ion batteries.

    PubMed

    Kim, Il Tae; Allcorn, Eric; Manthiram, Arumugam

    2014-07-01

    Antimony-based alloy anodes with a Fe metal support dispersed in a conductive matrix consisting of TiC and carbon have been developed by high energy mechanical milling (HEMM) for sodium-ion batteries. The samples have been characterized by X-ray diffraction before and after sodiation at different C rates and by high-resolution transmission electron microscopy before and after cycling for 100 cycles. Electrochemical charge-discharge cycling at various rates and electrochemical impedance spectroscopy measurements have been carried out with and without 2 vol% of the fluoroethylene carbonate (FEC) additive in the electrolyte. With well-defined crystalline FeSb and TiC structures, the FeSb-TiC-C nanocomposite anodes demonstrate superior rate capability with good capacity retention at 10,000 mA g(-1) for sodium-ion storage, which could be ascribed to the novel nanocomposite structure consisting of a good metal (Fe) framework and a combination of conductive TiC and carbon as a matrix. The FEC additive particularly leads to a longer cycle life with high rate capability due to the formation of a stable, thin SEI layer and a smaller charge-transfer resistance. PMID:24848297

  13. 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.

  14. C/C composite brake disk nondestructive evaluation by IR thermography

    NASA Astrophysics Data System (ADS)

    Chu, Tsuchin P.; Poudel, Anish; Filip, Peter

    2012-06-01

    This paper discusses the non-destructive evaluation of thick Carbon/Carbon (C/C) composite aircraft brake disks by using transient infrared thermography (IRT) approach. Thermal diffusivity measurement technique was applied to identify the subsurface anomalies in thick C/C brake disks. In addition, finite element analysis (FEA) modeling tool was used to determine the transient thermal response of the C/C disks that were subjected to flash heating. For this, series of finite element models were built and thermal responses with various thermal diffusivities subjected to different heating conditions were investigated. Experiments were conducted to verify the models by using custom built in-house IRT system and commercial turnkey system. The analysis and experimental results showed good correlation between thermal diffusivity value and anomalies within the disk. It was demonstrated that the step-heating transient thermal approach could be effectively applied to obtain the whole field thermal diffusivity value of C/C composites.

  15. 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.

  16. Sequential bond energies and barrier heights for the water loss and charge separation dissociation pathways of Cd2+(H2O)n, n = 3-11

    NASA Astrophysics Data System (ADS)

    Cooper, Theresa E.; Armentrout, P. B.

    2011-03-01

    The bond dissociation energies for losing one water from Cd2+(H2O)n complexes, n = 3-11, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with a thermal electrospray ionization source. Kinetic energy dependent cross sections are obtained for n = 4-11 complexes and analyzed to yield 0 K threshold measurements for loss of one, two, and three water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are converted from 0 to 298 K values to give the hydration enthalpies and free energies for sequentially losing one water from each complex. Theoretical geometry optimizations and single point energy calculations are performed on reactant and product complexes using several levels of theory and basis sets to obtain thermochemistry for comparison to experiment. The charge separation process, Cd2+(H2O)n → CdOH+(H2O)m + H+(H2O)n-m-1, is also observed for n = 4 and 5 and the competition between this process and water loss is analyzed. Rate-limiting transition states for the charge separation process at n = 3-6 are calculated and compared to experimental threshold measurements resulting in the conclusion that the critical size for this dissociation pathway of hydrated cadmium is ncrit = 4.

  17. 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.

  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. Detection and Formation of Interstellar c-C_3D_2

    NASA Astrophysics Data System (ADS)

    Spezzano, Silvia; Brunken, Sandra; Schilke, Peter; Menten, Karl M.; Caselli, Paola; McCarthy, Michael C.; Bizzocchi, Luca; Trevino, Sandra; Aikawa, Yuri; Schlemmer, Stephan

    2013-06-01

    Multiply deuterated molecules are unique observational probes for the earliest stages of star formation. Cyclopropenylidene, c-C_3H_2, is an ideal probe for deuterium chemistry. It is one of the most widespread molecules in our Galaxy and it has the possibility of double deuteration. Furthermore, since c-C_3H_2 is an "early-type" molecule, it is a particular useful tool to investigate early stages of a molecular cloud. This makes observations of its deuterated forms particularly important to test time-dependent chemical codes which include deuteration processes. The centimeter and millimeter wavelength spectra of doubly deuterated cyclopropenylidene have recently been measured in the laboratory, allowing for the first time a search for c-C_3D_2 in space. We report the detection of c-C_3D_2 in two starless cores, L1544 and TMC-1C. The deuteration of this small hydrocarbon ring is analysed with a comprehensive gas-grain model, the first including doubly deuterated species. The observed abundances of c-C_3D_2 can be explained solely by gas-phase processes, supporting the idea that c-C_3H_2 is a good indicator of gas-phase deuteration. S. Spezzano, F. Tamassia, S. Thorwirth, P. Thaddeus, C. A. Gottlieb, and M. C. McCarthy Astroph. J. Supp. Series {200}(1), 2012.

  20. Evaluation tests of C/C composites for RCS engine applications

    NASA Astrophysics Data System (ADS)

    Kuroda, Yukio; Sato, Masahiro; Ueda, Shuichi; Niino, Masayuki; Suemitsu, Takeshi; Kude, Yukinori

    Four kinds of carbon fiber reinforced carbon (C/C) composites were tested to evaluate the thermal fatigue resistance in the combustion gases of nitrogen tetroxide (NTO)/monomethyl Hydrazine (MMH) propellant. In the cyclic exposure test where surface temperature reached 2000 K, the SiC/C Functionally Gradient Materials (FGM) composite and the modified matrix C/C composite coated with SiC were not damaged and demonstrated greater resistance to thermal fatigue than the conventional C/C composite coated with SiC, indicating the potential of these materials to alleviate the thermal stress that occurs between the SiC and the base material in the coating process. Additionally, a combustion chamber constructed for a reaction control system (RCS) subscale engine made of conventional C/C composite coated with CVD center dot C on the inner wall and SiC on the outer wall underwent a firing test using NTO/MMH propellant to examine the gas-tight character of a C/C composite chamber at elevated temperatures.

  1. NON-THRESHOLD, THRESHOLD, AND NONADIABATIC BEHAVIOR OF THE KEY INTERSTELLAR C + C{sub 2}H{sub 2} REACTION

    SciTech Connect

    Costes, Michel; Halvick, Philippe; Hickson, Kevin M.; Daugey, Nicolas; Naulin, Christian

    2009-10-01

    The C + C{sub 2}H{sub 2} reaction is a key process in interstellar cloud chemistry. In a crossed-beam scattering experiment approaching the low-collision energies that characterize these environments, we determined relative differential cross sections by detecting the H-atom product. High-level ab initio calculations of the reaction energies of two competing pathways, leading to cyclic and linear C{sub 3}H, were also performed. Both channels are clearly distinguishable: the integral cross section of the c-C{sub 3}H + H channel monotonically decreases with increasing relative translational energy whilst the l-C{sub 3}H + H channel exhibits a translational energy threshold. Moreover, a comparison of the H-atom yields from the C + C{sub 2}H{sub 2} and C + C{sub 2}H{sub 4} reactions shows that the C{sub 3} + H{sub 2} nonadiabatic channel dominates. These results are consistent with the calculated enthalpies and corroborate earlier low-temperature kinetic experiments. Branching ratios of the three reaction pathways are given in the T = 15-300 K temperature domain for inclusion in astrochemical databases.

  2. Probing molecular interaction in ionic liquids by low frequency spectroscopy: Coulomb energy, hydrogen bonding and dispersion forces.

    PubMed

    Fumino, Koichi; Reimann, Sebastian; Ludwig, Ralf

    2014-10-28

    Ionic liquids are defined as salts composed solely of ions with melting points below 100 °C. These remarkable liquids have unique and fascinating properties and offer new opportunities for science and technology. New combinations of ions provide changing physical properties and thus novel potential applications for this class of liquid materials. To a large extent, the structure and properties of ionic liquids are determined by the intermolecular interaction between anions and cations. In this perspective we show that far infrared and terahertz spectroscopy are suitable methods for studying the cation-anion interaction in these Coulomb fluids. The interpretation of the measured low frequency spectra is supported by density functional theory calculations and molecular dynamics simulations. We present results for selected aprotic and protic ionic liquids and their mixtures with molecular solvents. In particular, we focus on the strength and type of intermolecular interaction and how both parameters are influenced by the character of the ions and their combinations. We show that the total interaction between cations and anions is a result of a subtle balance between Coulomb forces, hydrogen bonds and dispersion forces. For protic ionic liquids we could measure distinct vibrational modes in the low frequency spectra indicating clearly the cation-anion interaction characterized by linear and medium to strong hydrogen bonds. Using isotopic substitution we have been able to dissect frequency shifts related to pure interaction strength between cations and anions and to different reduced masses only. In this context we also show how these different types of interaction may influence the physical properties of ionic liquids such as the melting point, viscosity or enthalpy of vaporization. Furthermore we demonstrate that low frequency spectroscopy can also be used for studying ion speciation. Low vibrational features can be assigned to contact ion pairs and solvent separated ion pairs. In conclusion we showed how detailed knowledge of the low frequency spectra can be used to understand the change in interaction strength and structure by variation of temperature, solvent polarity and solvent concentration in ionic liquids and their mixtures with molecular solvents. In principle the used combination of methods is suitable for studying intermolecular interaction in pure molecular liquids and their solutions including additive materials such as nanoparticles. PMID:24898478

  3. Rearrangements of a Water Molecule in Both Directions between Two Hydrogen-Bonding Sites of 5-Hydroxyindole Cation: Experimental Determination of the Energy Threshold for the Rearrangement.

    PubMed

    Ikeda, Takamasa; Sakota, Kenji; Sekiya, Hiroshi

    2016-03-24

    Rearrangements of a water molecule in both directions between two hydrogen-bonding (H-bonding) sites of the 5-hydroxyindole (5HI) cation was investigated in the gas phase. IR-dip spectra of jet-cooled 5HI-(H2O)1 revealed that two structural isomers, 5HI(OH)-(H2O)1 and 5HI(NH)-(H2O)1, in which a water molecule is bound to either the OH group or the NH group of 5HI, were formed in the S0 state. The IR photodissociation spectrum of [5HI-(H2O)1](+) generated by two-color resonant two-photon ionization (2C-R2PI) via the S1-S0 origin of 5HI(NH)-(H2O)1 clearly showed that [5HI(OH)-(H2O)1](+) and [5HI(NH)-(H2O)1](+) coexist in the D0 state. The appearance of [5HI(OH)-(H2O)1](+) after R2PI via the S1-S0 origin of 5HI(NH)-(H2O)1 is explained by isomerization of [5HI(NH)-(H2O)1](+) to [5HI(OH)-(H2O)1](+), which corresponds to the rearrangement of the water. In addition, isomerization in the opposite direction was also observed when [5HI-(H2O)1](+) was generated via the S1-S0 origin of 5HI(OH)-(H2O)1. The upper limit of the energy threshold for the rearrangement of the water in [5HI(NH)-(H2O)1](+) was experimentally determined to be 2127 ± 30 cm(-1) from the adiabatic ionization energy of 5HI(NH)-(H2O)1. Above the energy threshold, the water molecule in [5HI-(H2O)1](+) may fluctuate between the two preferential H-bonding sites of 5HI(+). PMID:26950041

  4. 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

  5. How Bond Length Alternation and Thermal Disorder Affect the Optical Excitation Energies of π-Conjugated Chains: A Combined Density Functional Theory and Molecular Dynamics Study.

    PubMed

    Bois, Juliana; Körzdörfer, Thomas

    2016-04-12

    We dissect the sources of error leading to inaccuracies in the description of the geometry and optical excitation energies of π-conjugated polymers. While the ground-state bond length alternation is shown to be badly reproduced by standard functionals, the recently adapted functionals PBEh* and ωPBE* as well as the double hybrid functional XYGJ-OS manage to replicate results obtained at the CCSD(T) level. By analysis of the bond length alternation in the excited state, a sensitive dependence of the exciton localization on the long-range behavior of the functional and the amount of Hartree-Fock exchange present is shown. Introducing thermal disorder through molecular dynamics simulations allows the consideration of a range of thermally accessible configurations of each oligomer, including trans to cis rotations, which break the conjugation of the backbone. Thermal disorder has a considerable effect when combined with functionals that overestimate the delocalization of the excitation, such as B3LYP. For functionals with a larger amount of exact exchange such as our PBEh* and ωPBE*, however, the effect is small, as excitations are often localized enough to fit between twists in the chain. PMID:26960057

  6. 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(μ S)2(μ SMe)(μ SH)MoCp* and Cp*Mo(μ S)2(μ 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.

  7. Coherent Behavior and the Bound State of Water and K+ Imply Another Model of Bioenergetics: Negative Entropy Instead of High-energy Bonds

    PubMed Central

    Jaeken, Laurent; Vasilievich Matveev, Vladimir

    2012-01-01

    Observations of coherent cellular behavior cannot be integrated into widely accepted membrane (pump) theory (MT) and its steady state energetics because of the thermal noise of assumed ordinary cell water and freely soluble cytoplasmic K+. However, Ling disproved MT and proposed an alternative based on coherence, showing that rest (R) and action (A) are two different phases of protoplasm with different energy levels. The R-state is a coherent metastable low-entropy state as water and K+ are bound to unfolded proteins. The A-state is the higher-entropy state because water and K+ are free. The R-to-A phase transition is regarded as a mechanism to release energy for biological work, replacing the classical concept of high-energy bonds. Subsequent inactivation during the endergonic A-to-R phase transition needs an input of metabolic energy to restore the low entropy R-state. Matveev’s native aggregation hypothesis allows to integrate the energetic details of globular proteins into this view. PMID:23264833

  8. 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.

  9. 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

  10. Relativistic effects for the reaction Sg + 6 CO → Sg(CO){sub 6}: Prediction of the mean bond energy, atomization energy, and existence of the first organometallic transactinide superheavy hexacarbonyl Sg(CO){sub 6}

    SciTech Connect

    Malli, Gulzari L.

    2015-02-14

    Our ab initio all-electron fully relativistic Dirac–Fock (DF) and nonrelativistic (NR) Hartree-Fock calculations predict the DF relativistic and NR energies for the reaction: Sg + 6 CO → Sg(CO){sub 6} as −7.39 and −6.96 eV, respectively, i.e., our calculated ground state total DF relativistic and NR energies for the reaction product Sg(CO){sub 6} are lower by 7.39 and 6.96 eV than the total DF and NR ground state energies of the reactants, viz., one Sg atom plus six CO molecules, respectively. Our calculated DF relativistic and NR atomization energies (Ae) are 65.23 and 64.82 eV, respectively, and so the contribution of relativistic effects to the Ae of ∼0.40 eV is marginal. The Sg–C and C–O optimized bond distances for the octahedral geometry as calculated in our DF (NR) calculations are 2.151 (2.318 Å) and 1.119 (1.114 Å), respectively. The BSSE correction calculated using the DIRAC code ∼14 kcal/mol. The relativistic DF and NR mean energies predicted by us are 118.8 and 111.9 kJ/mol, respectively, and the contribution of ∼7 kJ/mol due to relativistic effects to the mean energy of Sg(CO){sub 6} is negligible. Ours are the first calculations of the relativistic effects for the atomization energy, mean bond energy, and energy of the reaction for possible formation of Sg(CO){sub 6}, and both our relativistic DF and the NR treatments clearly predict for the first time the existence of hexacarbonyl of the transactinide superheavy element seaborgium Sg. In conclusion, relativistic effects are not significant for Sg(CO){sub 6}.

  11. Epoxy-based nanocomposites for electrical energy storage. II: Nanocomposites with nanofillers of reactive montmorillonite covalently-bonded with barium titanate

    NASA Astrophysics Data System (ADS)

    Polizos, G.; Tomer, V.; Manias, E.; Randall, C. A.

    2010-10-01

    Barium titanate (BT) and montmorillonite (MMT) nanoparticles were covalently-bonded by organically modifying the particle surfaces and chemically reacting them in solution. These integrated two-material hybrid inorganic nanofillers were subsequently dispersed in epoxy resin and nanocomposites were obtained at several weight fractions. The inorganic component consisted of well dispersed BT spherical nanoparticles that are surrounded by attached layered MMT nanoplatelets, with the latter having the ability to react with the epoxy matrix. The thermodynamic properties of the glass transition process, the macroscopic mechanical properties of the nanocomposites, and the dynamics of the polymer segments at the inorganic interfaces, all indicate that this filler configuration enhances the polymer-ceramic interfaces. Polarization as a function of electric field and dielectric breakdown show improvements in the electrical properties of these composites, compared to the corresponding unfilled epoxy, despite the expected reduction in crosslinking density. The resulting nanocomposites have a property set which can be utilized in energy storage and power system applications.

  12. The heats of formation of some C2H5O + isomers, relevant bond energies in ethanol and PA(CH3CHO)

    NASA Astrophysics Data System (ADS)

    Ruscic, B.; Berkowitz, J.

    1994-12-01

    The ionization potentials of the transient species CH3CH2O, CH3CHOH, and CH2CH2OH (generated by the F+ethanol reactions) are measured by photoionization mass spectrometry: I.P.(CD3CD2O)=10.290.08 eV (tentative), I.P.(CH3CHOH)<6.85 eV, and I.P.(CD2CH2OH) ?8.350.06 eV. The latter results in a cation of uncertain structure. These reactions also generate vinyl alcohol (adiabatic I.P.=9.330.01 eV) and acetaldehyde. A redetermined appearance potential of CH3CHOH+ from ethanol enables one to infer the proton affinity of acetaldehyde to be ?183.80.2 kcal/mol and an ? (C-H) bond energy in ethanol ?91.1 kcal/mol (0 K). The appearance potential of m/e=45 ion from bromoethanol is interpreted as formation of a C2H5O+ isomer having the oxirane structure, with ?Hf00 of 173.9 kcal/mol, consistent with earlier alternative measurements. A second increase in the m/e=45 ion yield curve from ethanol is interpreted as formation of this same isomer. This interpretation, and an alternative cycle, lead to a ? (C-H) bond energy in ethanol of 982 kcal/mol. The implication of the current results to the dynamics of dissociation of ethanol cations is discussed.

  13. 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 (ΔH°f 298) 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. ΔH°f 298 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 ΔH°f 298 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

  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. Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys, and superlattices: Theoretical study of Cu/graphite bonding

    NASA Technical Reports Server (NTRS)

    Lambrecht, Walter R. L.

    1992-01-01

    The goals of the research were to provide a fundamental science basis for why the bonding of Cu to graphite is weak, to critically evaluate the previous analysis of the wetting studies with particular regard to the values used for the surface energies of Cu and graphite, and to make recommendations for future experiments or other studies which could advance the understanding and solution of this technological problem. First principles electronic structure calculations were used to study the problem. These are based on density functional theory in the local density approximation and the use of the linear muffin-tin orbital band structure method. Calculations were performed for graphite monolayers, single crystal graphite with the hexagonal AB stacking, bulk Cu, Cu(111) surface, and Cu/graphite superlattices. The study is limited to the basal plane of graphite because this is the graphite plane exposed to Cu and graphite surface energies and combined with the measured contact angles to evaluate the experimental adhesion energy.

  16. 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.

  17. Transformations of X (C, O, N)-CN Bonds: Cases of Selective X (C, O, N)-C Activation.

    PubMed

    Wang, Rui; Falck, John Russell

    2014-01-01

    Activation of C-C, C-N, and C-O bonds has in recent decades been recognized as a valuable strategic objective. While considerable progress has been achieved, many of the more challenging issues, e.g., regioselective activation of specific C-X (C, O, N) bonds, chemoselective cleavage of C(sp3)-X bonds, enantioselective activation and even the successful application of solid catalysts in such transformations remain elusive. The research disclosed herein summarize recent advances in C-X bond cleavages, including regioselective processes, although the carbon is activated in the form of a cyano group. PMID:24660056

  18. Transformations of X (C, O, N)-CN Bonds: Cases of Selective X (C, O, N)-C Activation**

    PubMed Central

    Wang, Rui; Falck, John Russell

    2014-01-01

    Activation of C-C, C-N, and C-O bonds has in recent decades been recognized as a valuable strategic objective. While considerable progress has been achieved, many of the more challenging issues, e.g., regioselective activation of specific C-X (C, O, N) bonds, chemoselective cleavage of C(sp3)-X bonds, enantioselective activation and even the successful application of solid catalysts in such transformations remain elusive. The research disclosed herein summarize recent advances in C-X bond cleavages, including regioselective processes, although the carbon is activated in the form of a cyano group. PMID:24660056

  19. 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.

  20. INTERSTELLAR DETECTION OF c-C{sub 3}D{sub 2}

    SciTech Connect

    Spezzano, S.; Bruenken, S.; Schilke, P.; Schlemmer, S.; Caselli, P.; Menten, K. M.; McCarthy, M. C.; Bizzocchi, L.; Trevino-Morales, S. P.; Aikawa, Y.

    2013-06-01

    We report the first interstellar detection of c-C{sub 3}D{sub 2}. Doubly deuterated cyclopropenylidene, a carbene, has been detected toward the starless cores TMC-1C and L1544 using the IRAM 30 m telescope. The J{sub K{sub a,K{sub c}}} = 3{sub 0,3}-2{sub 1,2}, 3{sub 1,3}-2{sub 0,2}, and 2{sub 2,1}-1{sub 1,0} transitions of this species have been observed at 3 mm in both sources. The expected 1:2 intensity ratio has been found in the 3{sub 0,3}-2{sub 1,2} and 3{sub 1,3}-2{sub 0,2} lines, belonging to the para and ortho species, respectively. We also observed lines of the main species, c-C{sub 3}H{sub 2}, singly deuterated c-C{sub 3}HD, and the species with one {sup 13}C off of the principal axis of the molecule, c-H{sup 13}CC{sub 2}H. The lines of c-C{sub 3}D{sub 2} have been observed with high signal-to-noise ratio, better than 7.5{sigma} in TMC-1C and 9{sigma} in L1544. The abundance of doubly deuterated cyclopropenylidene with respect to the normal species is found to be 0.4%-0.8% in TMC-1C and 1.2%-2.1% in L1544. The deuteration of this small hydrocarbon ring is analyzed with a comprehensive gas-grain model, the first including doubly deuterated species. The observed abundances of c-C{sub 3}D{sub 2} can be explained solely by gas-phase processes, supporting the idea that c-C{sub 3}H{sub 2} is a good indicator of gas-phase deuteration.

  1. On The Nature of the Halogen Bond.

    PubMed

    Wang, Changwei; Danovich, David; Mo, Yirong; Shaik, Sason

    2014-09-01

    The wide-ranging applications of the halogen bond (X-bond), notably in self-assembling materials and medicinal chemistry, have placed this weak intermolecular interaction in a center of great deal of attention. There is a need to elucidate the physical nature of the halogen bond for better understanding of its similarity and differences vis-à-vis other weak intermolecular interactions, for example, hydrogen bond, as well as for developing improved force-fields to simulate nano- and biomaterials involving X-bonds. This understanding is the focus of the present study that combines the insights of a bottom-up approach based on ab initio valence bond (VB) theory and the block-localized wave function (BLW) theory that uses monomers to reconstruct the wave function of a complex. To this end and with an aim of unification, we studied the nature of X-bonds in 55 complexes using the combination of VB and BLW theories. Our conclusion is clear-cut; most of the X-bonds are held by charge transfer interactions (i.e., intermolecular hyperconjugation) as envisioned more than 60 years ago by Mulliken. This is consistent with the experimental and computational findings that X-bonds are more directional than H-bonds. Furthermore, the good linear correlation between charge transfer energies and total interaction energies partially accounts for the success of simple force fields in the simulation of large systems involving X-bonds. PMID:26588518

  2. S-OO bond dissociation energies and enthalpies of formation of the thiomethyl peroxyl radicals CH{sub 3}S(O){sub n}OO (n=0,1,2)

    SciTech Connect

    Salta, Zoi; Kosmas, Agnie Mylona; Lesar, Antonija

    2014-10-06

    Optimized geometries, S-OO bond dissociation energies and enthalpies of formation for a series of thiomethyl peroxyl radicals are investigated using high level ab initio and density functional theory methods. The results show that the S-OO bond dissociation energy is largest in the methylsulfonyl peroxyl radical, CH{sub 3}S(O){sub 2}OO, which contains two sulfonic type oxygen atoms followed by the methylthiyl peroxyl radical, CH{sub 3}SOO. The methylsulfinyl peroxyl radical, CH{sub 3}S(O)OO, which contains only one sulfonic type oxygen shows the least stability with regard to dissociation to CH{sub 3}S(O)+O{sub 2}. This stabilization trend is nicely reflected in the variations of the S-OO bond distance which is found to be shortest in CH{sub 3}S(O){sub 2}OO and longest in CH{sub 3}S(O)OO.

  3. Competitive threshold collision-induced dissociation: Gas-phase acidities and bond dissociation energies for a series of alcohols

    SciTech Connect

    DeTuri, V.F.; Ervin, K.M.

    1999-09-02

    Energy-resolved competitive collision-induced dissociation methods are used to measure the gas-phase acidities of a series of alcohols (methanol, ethanol, 2-propanol, and 2-methyl-2-propanol). The competitive dissociation reactions of fluoride-alcohol, [F{sup {minus}}{center{underscore}dot}HOR], alkoxide-water, [RO{sup {minus}}{center{underscore}dot}HOH], and alkoxide-methanol [RO{+-}{center{underscore}dot}HOCH{sub 3}] proton-bound complexes are studied using a guided ion beam tandem mass spectrometer. The reaction cross sections and product branching fractions to the two proton transfer channels are measured as a function of collision energy. The enthalpy difference between the two product channels is found by modeling the reaction cross sections near threshold using RRKM theory to account for the energy-dependent product branching ratio and kinetic shift. From the enthalpy difference, the alcohol gas-phase acidities are determined relative to the well-known values of HF and H{sub 2}O. The measured gas-phase acidities are {Delta}{sub acid}H{sub 298}(CH{sub 3}OH) = 1599 {+-} 3 kJ/mol, {Delta}{sub acid}H{sub 298}(CH{sub 3}CH{sub 2}OH) = 1586 {+-} 5 kJ/mol, {Delta}{sub acid}H{sub 298}((CH{sub 3}){sub 2}CHOH) = 1576 {+-} 4 kJ/mol, and {Delta}{sub acid}H{sub 298}((CH{sub 3}){sub 3}COH) = 1573 {+-} 3 kJ/mol.

  4. Interfacial bond-breaking electron transfer in mixed water-ethylene glycol solutions: reorganization energy and interplay between different solvent modes.

    PubMed

    Ismailova, Oksana; Berezin, Alexander S; Probst, Michael; Nazmutdinov, Renat R

    2013-07-25

    We explore solvent dynamics effects in interfacial bond breaking electron transfer in terms of a multimode approach and make an attempt to interpret challenging recent experimental results (the nonmonotonous behavior of the rate constant of electroreduction of S2O8(2-) from mixed water-EG solutions when increasing the EG fraction; see Zagrebin, P.A. et al. J. Phys. Chem. B 2010, 114, 311). The exact expansion of the solvent correlation function (calculated using experimental dielectric spectra) in a series predicts the splitting of solvent coordinate in three independent modes characterized by different relaxation times. This makes it possible to construct a 5D free-energy surface along three solvent coordinates and one intramolecular degree of freedom describing first electron transfer at the reduction of a peroxodisulphate anion. Classical molecular dynamics simulations were performed to study the solvation of a peroxodisulphate anion (S2O8(2-)) in oxidized and reduced states in pure water and ethylene glycol (EG) as well as mixed H2O-EG solutions. The solvent reorganization energy of the first electron-transfer step at the reduction of S2O8(2-) was calculated for several compositions of the mixed solution. This quantity was found to be significantly asymmetric. (The reorganization energies of reduction and oxidation differ from each other.) The averaged reorganization energy slightly increases with increasing the EG content in solution. This finding clearly indicates that for the reaction under study the static solvent effect no longer competes with solvent dynamics. Brownian dynamics simulations were performed to calculate the electron-transfer rate constants as a function of the solvent composition. The results of the simulations explain the experimental data, at least qualitatively. PMID:23768162

  5. A Semi-Analytical Method for Determining the Energy Release Rate of Cracks in Adhesively-Bonded Single-Lap Composite Joints

    NASA Technical Reports Server (NTRS)

    Yang, Charles; Sun, Wenjun; Tomblin, John S.; Smeltzer, Stanley S., III

    2007-01-01

    A semi-analytical method for determining the strain energy release rate due to a prescribed interface crack in an adhesively-bonded, single-lap composite joint subjected to axial tension is presented. The field equations in terms of displacements within the joint are formulated by using first-order shear deformable, laminated plate theory together with kinematic 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. Based on the adhesive stress distributions, the forces at the crack tip are obtained and the strain energy release rate of the crack is determined by using the virtual crack closure technique (VCCT). Additionally, the test specimen geometry from both the ASTM D3165 and D1002 test standards are utilized during the derivation of the field equations in order to correlate analytical models with future test results. The system of second-order differential field equations is solved to provide the adherend and adhesive stress response using the symbolic computation tool, Maple 9. Finite element analyses using J-integral as well as VCCT were performed to verify the developed analytical model. The finite element analyses were conducted using the commercial finite element analysis software ABAQUS. The results determined using the analytical method correlated well with the results from the finite element analyses.

  6. Stacked and H-Bonded Cytosine Dimers. Analysis of the Intermolecular Interaction Energies by Parallel Quantum Chemistry and Polarizable Molecular Mechanics.

    PubMed

    Gresh, Nohad; Sponer, Judit E; Devereux, Mike; Gkionis, Konstantinos; de Courcy, Benoit; Piquemal, Jean-Philip; Sponer, Jiri

    2015-07-30

    Until now, atomistic simulations of DNA and RNA and their complexes have been executed using well calibrated but conceptually simple pair-additive empirical potentials (force fields). Although such simulations provided many valuable results, it is well established that simple force fields also introduce errors into the description, underlying the need for development of alternative anisotropic, polarizable molecular mechanics (APMM) potentials. One of the most abundant forces in all kinds of nucleic acids topologies is base stacking. Intra- and interstrand stacking is assumed to be the most essential factor affecting local conformational variations of B-DNA. However, stacking also contributes to formation of all kinds of noncanonical nucleic acids structures, such as quadruplexes or folded RNAs. The present study focuses on 14 stacked cytosine (Cyt) dimers and the doubly H-bonded dimer. We evaluate the extent to which an APMM procedure, SIBFA, could account quantitatively for the results of high-level quantum chemistry (QC) on the total interaction energies, and the individual energy contributions and their nonisotropic behaviors. Good agreements are found at both uncorrelated HF and correlated DFT and CCSD(T) levels. Resorting in SIBFA to distributed QC multipoles and to an explicit representation of the lone pairs is essential to respectively account for the anisotropies of the Coulomb and of the exchange-repulsion QC contributions. PMID:26119247

  7. TiCl, TiH and TiH+ Bond Energies, a Test of a Correlation Consistent Ti Basis Set

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    Correlation consistent basis sets are developed for Ti atom. The polarization functions are optimized for the average of the 3F and 5F states. One series of correlation consistent basis sets is for 3d and 4s correlation, while the second series includes 3s and 3p correlation as well as 3d and 4s correlation. These basis sets are tested using the Ti 3F-5F separation and the dissociation energies of TiCl X4Phi, TiH X4Phi, and TiH(+) X3Phi. The CCSD(T) complete basis set limit values are determined by extrapolation. The Douglas Kroll approach is used to compute the scalar relativistic effect. Spin-orbit effects are taken from experiment and/or computed at the CASSCF level. The Ti 3F-5F separation is in excellent agreement with experiment, while the TiCl, TiH, and TiH(+) bond energies are in good agreement with experiment. Extrapolation with the valence basis set is consistent with other atoms, while including 3s and 3p correlation appears to make extrapolation.

  8. Determination of the structure and bond energies of NiO2 and CuO2

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    On the basis of extensive ab initio calculations, we estimate the metal-O2 binding energies of NiO2 and CuO2 to be 48 +/- 7 and 18 +/- 4 kcal/mol, respectively. We feel that the experimental estimate of 57 +/- 10 kcal/mol for the binding energy of NiO2 is slightly too large, while we are in complete agreement with the experimental estimate of 15 +10/-5 kcal/mol for CuO2. While the 1A1 ground state of NiO2 definitely has a side-on C(2v) structure, matrix isolation studies suggest that CuO2 has an end-on C(s) structure. Calculations at the coupled-cluster singles plus doubles level with a perturbational estimate of triple excitations, CCSD(T), produce a 2A2 state with C(2v) as a global minimum. However, the entire 2A-double prime ground-state surface is exceedingly flat, precluding a reliable determination of the gas-phase equilibrium structure.

  9. Bonding PMMA microfluidics using commercial microwave ovens

    NASA Astrophysics Data System (ADS)

    Toossi, A.; Moghadas, H.; Daneshmand, M.; Sameoto, D.

    2015-08-01

    In this paper, a novel low-cost, rapid substrate-bonding technique is successfully applied to polymethyl methacrylate (PMMA) microfluidics bonding for the first time. This technique uses a thin intermediate metallic microwave susceptor layer at the interface of the bonding site (microchannels) which produces localized heating required for bonding during microwave irradiation. The metallic susceptor pattern is designed using a multiphysics simulation model developed in ANSYS Multiphysics software (high-frequency structural simulation (HFSS) coupled with ANSYS-Thermal). In our experiments, the required microwave energy for bonding is delivered using a relatively inexpensive, widely accessible commercial microwave oven. Using this technique, simple PMMA microfluidics prototypes are successfully bonded and sealed in less than 35 seconds with a minimum measured bond strength of 1.375 MPa.

  10. Theoretical in-Solution Conformational/Tautomeric Analyses for Chain Systems with Conjugated Double Bonds Involving Nitrogen(s).

    PubMed

    Nagy, Peter I

    2015-01-01

    Conformational/tautomeric transformations for X=CH-CH=Y structures (X = CH2, O, NH and Y = NH) have been studied in the gas phase, in dichloromethane and in aqueous solutions. The paper is a continuation of a former study where s-cis/s-trans conformational equilibria were predicted for analogues. The s-trans conformation is preferred for the present molecules in the gas phase on the basis of its lowest internal free energy as calculated at the B97D/aug-cc-pvqz and CCSD(T)CBS (coupled-cluster singles and doubles with non-iterative triples extrapolated to the complete basis set) levels. Transition state barriers are of 29-36 kJ/mol for rotations about the central C-C bonds. In solution, an s-trans form is still favored on the basis of its considerably lower internal free energy compared with the s-cis forms as calculated by IEF-PCM (integral-equation formalism of the polarizable continuum dielectric solvent model) at the theoretical levels indicated. A tetrahydrate model in the supermolecule/continuum approach helped explore the 2solute-solvent hydrogen bond pattern. The calculated transition state barrier for rotation about the C-C bond decreased to 27 kJ/mol for the tetrahydrate. Considering explicit solvent models, relative solvation free energies were calculated by means of the free energy perturbation method through Monte Carlo simulations. These calculated values differ remarkably from those by the PCM approach in aqueous solution, nonetheless the same prevalent conformation was predicted by the two methods. Aqueous solution structure-characteristics were determined by Monte Carlo. Equilibration of conformers/tautomers through water-assisted double proton-relay is discussed. This mechanism is not viable, however, in non-protic solvents where the calculated potential of mean force curve does not predict remarkable solute dimerization and subsequent favorable orientation. PMID:25984602

  11. Regulatory properties of araC(c) mutants in the L-arabinose operon of escherichia coliB/r.

    PubMed Central

    MacInnes, K R; Sheppard, D E; Falgout, B

    1978-01-01

    Merodiploids containing a high-constitutive and a low-constitutive araC(c) allele were assayed for constitutive expression of the ara operon. Low-constitutive araC(c) alleles either were unable to repress the constitutive rate of ara operon expression exhibited by by high-constitutive araC(c) alleles or achieved a partial repression of the high-constitutive rate of operon expression. Either mutation to a low-constitutive araC(c) mutant resulted in a partial or complete loss of repressor function, or subunit mixing between the two araC(c) mutant proteins resulted in a partial or complete dominance of the high-constitutive araC(c) allele. Five of the six araC(c) alleles tested allowed a partial induction of the ara operon in cya crp background. In general, a higher level of ara operon induction was achieved in the cya crp background by high araC(c) alleles than by low araC(c) alleles. Furthermore, several araC(c) mutants exhibited decreased sensitivity to catabolite repression, particularly in the presence of inducer. The results suggest a model in which certain araC(c) gene products can achieve ara operon induction in the presence of either arabinose (inducer) or catabolite activator protein-cyclic adenosine monophosphate, whereas the wild-type araC gene product requires the presence of both of these factors for operon expression. PMID:338579

  12. 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

  13. 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

  14. Effect of Pedestal Temperature on Bonding Strength and Deformation Characteristics for 5N Copper Wire Bonding

    NASA Astrophysics Data System (ADS)

    Singh, Gurbinder; Haseeb, A. S. M. A.

    2016-02-01

    In recent years, copper has increasingly been used to replace gold to create wire-bonded interconnections in microelectronics. While engineers and researchers in the semiconductor packaging field are continuously working on this transition from gold to copper wires to reduce costs, the challenge remains in producing robust and reliable joints for semiconductor devices. This research paper investigates the effect of pedestal temperature on bonding strength and deformation for 99.999% purity (5N) copper wire bonding on nickel-palladium-gold (NiPdAu) bond pads. With increasing pedestal temperature, significant thinning of the copper ball bond can be achieved, resulting in higher as-bonded ball shear strengths while producing no pad damage. This can be helpful for low-k devices with thin structures, so as to prevent the use of excessive bond force and ultrasonic energy during copper wire bonding.

  15. Effect of Pedestal Temperature on Bonding Strength and Deformation Characteristics for 5N Copper Wire Bonding

    NASA Astrophysics Data System (ADS)

    Singh, Gurbinder; Haseeb, A. S. M. A.

    2016-06-01

    In recent years, copper has increasingly been used to replace gold to create wire-bonded interconnections in microelectronics. While engineers and researchers in the semiconductor packaging field are continuously working on this transition from gold to copper wires to reduce costs, the challenge remains in producing robust and reliable joints for semiconductor devices. This research paper investigates the effect of pedestal temperature on bonding strength and deformation for 99.999% purity (5N) copper wire bonding on nickel-palladium-gold (NiPdAu) bond pads. With increasing pedestal temperature, significant thinning of the copper ball bond can be achieved, resulting in higher as-bonded ball shear strengths while producing no pad damage. This can be helpful for low-k devices with thin structures, so as to prevent the use of excessive bond force and ultrasonic energy during copper wire bonding.

  16. Sensor/ROIC Integration using Oxide Bonding

    SciTech Connect

    Ye, Zhenyu; /Fermilab

    2009-02-01

    We explore the Ziptronix Direct Bond Interconnect (DBI) technology [2] for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 {micro}m.

  17. Prompt J /? production in association with a c c pair within the framework of nonrelativistic QCD via photon-photon collisions at the International Linear Collider

    NASA Astrophysics Data System (ADS)

    Sun, Zhan; Wu, Xing-Gang; Zhang, Hong-Fei

    2015-10-01

    We present a systematical study on the prompt J /? production in association with a c c pair via the process, ? ? ?H (c c )+c +c , within the framework of nonrelativistic QCD at the future high-energy e+e- colliderInternational Linear Collider (ILC), including both direct and feed-down contributions. For direct J /? production, the states with color-octet channels, especially the P3 J[8] and S1 0[8] ones, provide a dominant contribution to the production cross section, which are about 52 times over that of the color-singlet one. This is clearly shown by the transverse momentum (pt) and rapidity distributions. The feed-down contribution from ?' and ?c J (J =0 , 1, 2) is sizable, which is about 20% to the total prompt cross section. Besides the yields, we also calculate the J /? polarization parameter ? . In the small pt region, the polarization of the prompt J /? is longitudinal due to large contributions through the P3 J[8] channel, and becomes transverse in the high pt region due to the S3 1[8] channel. Thus the J /? production via photon-photon collisions at the ILC shall provide a useful platform for testing the color-octet mechanism.

  18. Mechanistic Investigation of Phosphate Ester Bond Cleavages of Glycylphosphoserinyltryptophan Radical Cations under Low-Energy Collision-Induced Dissociation

    NASA Astrophysics Data System (ADS)

    Quan, Quan; Hao, Qiang; Song, Tao; Siu, Chi-Kit; Chu, Ivan K.

    2013-04-01

    Under the conditions of low-energy collision-induced dissociation (CID), the canonical glycylphosphoserinyltryptophan radical cation having its radical located on the side chain of the tryptophan residue ([G p SW]•+) fragments differently from its tautomer with the radical initially generated on the α-carbon atom of the glycine residue ([G• p SW]+). The dissociation of [G• p SW]+ is dominated by the neutral loss of H3PO4 (98 Da), with backbone cleavage forming the [b2 - H]•+/y1 + pair as the minor products. In contrast, for [G p SW]•+, competitive cleavages along the peptide backbone, such as the formation of [G p SW - CO2]•+ and the [c2 + 2H]+/[z1 - H]•+ pair, significantly suppress the loss of neutral H3PO4. In this study, we used density functional theory (DFT) to examine the mechanisms for the tautomerizations of [G• p SW]+ and [G p SW]•+ and their dissociation pathways. Our results suggest that the dissociation reactions of these two peptide radical cations are more efficient than their tautomerizations, as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. We also propose that the loss of H3PO4 from both of these two radical cationic tautomers is preferentially charge-driven, similar to the analogous dissociations of even-electron protonated peptides. The distonic radical cationic character of [G• p SW]+ results in its charge being more mobile, thereby favoring charge-driven loss of H3PO4; in contrast, radical-driven pathways are more competitive during the CID of [G p SW]•+.

  19. Influence of deposition time on the chemical bonding and composition of amorphous carbon nitride films

    NASA Astrophysics Data System (ADS)

    Azman, Nurul Izzati; Awang, Rozidawati; Kamal, Shafarina Azlinda Ahmad

    2014-09-01

    Amorphous carbon nitride (a-CNx) films have been deposited using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) under various deposition times. The effects on chemical bonding and composition of this film were characterized by using Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-Rays Spectroscopy (EDX) respectively. The spectrum shows several band that exist in this film such as CN (1020-1280 cm-1), CC (1300-1500 cm-1), CN (1500-1800 cm-1), CN (2000 - 2300 cm-1), CH (2800-3000 cm-1), and NH/OH (3300-3500 cm-1). The longer deposition time allows the increase in occurrences of breaking the CN bonds which results in the decrease in nitrogen content.

  20. Equilibrium positions of composite dislocations in the f.c.c. structure

    NASA Astrophysics Data System (ADS)

    Bonneville, J.; Douin, J.

    1992-10-01

    In the frame-work of the isotropic elastic theory, we have recently shown that it is possible to derive, from the total interaction energy between the partials, a simple analytic solution for the equilibrium configuration of the Lomer-Cottrell dislocation. We have established, contrary to what is generally believed, that it should be asymmetric. By using the same procedure, we reconsider in this paper the equilibrium configurations of the extended dislocations barriers (B2-B6) in the face centred cubic (f.c.c.) structure. As for the Lomer-Cottrell dislocation, the equilibrium configuration of the B2 barrier must be also asymmetric. The equilibrium shapes obtained for the other barriers (B3-B6) are found to be in good agreement with all previous predictions. Dans le cadre de la théorie élastique isotrope, nous avons récemment montré qu'il est possible d'obtenir, à partir de l'énergie totale d'interaction entre les différentes partielles, une détermination analytique simple de la configuration d'équilibre de la dislocation de Lomer-Cottrell. Nous avons ainsi établi que, contrairement à ce qui était généralement admis, celle-ci devait être asymétrique. En utilisant la même procédure, nous reconsidérons dans cet article les configurations d'équilibre de dissociation des différentes barrières de dislocations les plus probables dans la structure cubique à faces centrées (B2-B6). Nous montrons que, comme pour la dislocation de Lomer-Cottrell, la configuration d'équilibre de la barrière B2 doit également être asymétrique. Les formes d'équilibres obtenues pour les autres barrières (B3-B6) sont trouvées en bon accord avec l'ensemble des calculs antérieurs.

  1. Identification and H(D)-bond energies of C-H(D)Cl interactions in chloride-haloalkane clusters: a combined X-ray crystallographic, spectroscopic, and theoretical study.

    PubMed

    Serebryanskaya, Tatiyana V; Novikov, Alexander S; Gushchin, Pavel V; Haukka, Matti; Asfin, Ruslan E; Tolstoy, Peter M; Kukushkin, Vadim Yu

    2016-05-18

    The cationic (1,3,5-triazapentadiene)Pt(II) complex [Pt{NH[double bond, length as m-dash]C(N(CH2)5)N(Ph)C(NH2)[double bond, length as m-dash]NPh}2]Cl2 ([]Cl2) was crystallized from four haloalkane solvents giving [][Cl2(CDCl3)4], [][Cl2(CHBr3)4], [][Cl2(CH2Cl2)2], and [][Cl2(C2H4Cl2)2] solvates that were studied by X-ray diffraction. In the crystal structures of [][Cl2(CDCl3)4] and [][Cl2(CHBr3)4], the Cl(-) ion interacts with two haloform molecules via C-DCl(-) and C-HCl(-) contacts, thus forming the negatively charged isostructural clusters [Cl(CDCl3)2](-) and [Cl(CHBr3)2](-). In the structures of [][Cl2(CH2Cl2)2] and [][Cl2(C2H4Cl2)2], cations [](2+) are linked to a 3D-network by a system of H-bondings including one formed by each Cl(-) ion with CH2Cl2 or C2H4Cl2 molecules. The lengths and energies of these H-bonds in the chloride-haloalkane clusters were analyzed by DFT calculations (M06 functional) including AIM analysis. The crystal packing noticeably affected the geometry of the clusters, and energy of C-HCl(-) hydrogen bonds ranged from 1 to 6 kcal mol(-1). An exponential correlation (R(2) > 0.98) between the calculated Cl(-)H distances and the energies of the corresponding contacts was found and used to calculate hydrogen bond energies from the experimental Cl(-)H distances. Predicted energy values (3.3-3.9 kcal mol(-1) for the [Cl(CHCl3)2](-) cluster) are in a reasonable agreement with the energy of the Cl3C-HCl(-) bond estimated using ATRFTIR spectroscopy (2.7 kcal mol(-1)). PMID:27157359

  2. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

    A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

  3. Mechanical and Chemical Characterization of a TiC/C System Synthesized Using a Focus Plasma Arc

    PubMed Central

    Mahmoodian, Reza; Hamdi, M.; Hassan, M. A; Akbari, Abolghasem

    2015-01-01

    Titanium carbide-graphite (TiC/C) composite was successfully synthesized from Ti and C starting elemental powders using self-propagating high-temperature synthesis technique in an ultra-high plasma inert medium in a single stage. The TiC was exposed to a high-temperature inert medium to allow recrystallization. The product was then characterized using field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Rietveld refinement, nanoindentation, and micro-hardness to determine the product’s properties. The recorded micro-hardness of the product was 3660 HV, which is a 14% enhancement and makes is comparable to TiC materials. PMID:26111217

  4. Compression effects on electrons for chemical bonding

    NASA Astrophysics Data System (ADS)

    Hu, Anguang; Zhang, Fan

    2014-03-01

    How electrons move under compression as chemical bonds between atoms are broken and formed is central to a number of challenges on the performance of materials in extreme conditions. This is not only associated with the fundamental knowledge of material response to compressive loading but also would advance many aspects of material science towards future energy technologies. First-principles simulations of enthalpy minimization, in various target pressures on chemical transformation bonding pathways, reveal that high pressure can push electrons away from their denser regimes where the kinetic energy rises steeply on compression, causing a destabilization of intramolecular bonds. The high-pressure pushing of electrons from one regime to another thus leads to chemical bond destruction and formation with a cell volume collapse accompanied by a drop in stress components. Determination of such electron pathways following bonding conformations of molecular precursors would then result in a number of chemical transformations for novel materials, including high energy density materials.

  5. Guided ion beam studies of the reactions of Co{sub n}{sup +} (n=1-18) with N{sub 2}: Cobalt cluster mononitride and dinitride bond energies

    SciTech Connect

    Liu Fuyi; Li Ming; Tan Lin; Armentrout, P. B.

    2008-05-21

    The reactions of Co{sub n}{sup +} (n=1-18) with N{sub 2} are measured as a function of kinetic energy over a range of 0-15 eV in a guided ion beam tandem mass spectrometer. A variety of Co{sub m}{sup +}, Co{sub m}N{sup +}, and Co{sub m}N{sub 2}{sup +} (m{<=}n) product ions are observed, all in endothermic processes, with collision-induced dissociation dominating the products for all clusters. Bond dissociation energies for both cobalt cluster nitrides and dinitrides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different approaches. These values show only a mild dependence on cluster size over the range studied, although the Co{sub 13}{sup +}-N bond energy is relatively weak. The bond energies of Co{sub n}{sup +}-N for larger clusters suggest that a reasonable value for the desorption energy of atomic nitrogen from bulk phase cobalt is 6.3{+-}0.2 eV, which is somewhat lower than the only available value in the literature, an estimate based on the enthalpy of formation of bulk cobalt nitride. The trends in the cobalt nitride thermochemistry are also compared to previously determined metal-metal bond energies, D{sub 0}(Co{sub n}{sup +}-Co), and to D{sub 0}(Fe{sub n}{sup +}-N). Implications for catalytic ammonia production using cobalt versus iron are discussed.

  6. Bond dissociation mechanism of ethanol during carbon nanotube synthesis via alcohol catalytic CVD technique: Ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Oguri, Tomoya; Shimamura, Kohei; Shibuta, Yasushi; Shimojo, Fuyuki; Yamaguchi, Shu

    2014-03-01

    Dissociation of ethanol on a nickel cluster is investigated by ab initio molecular dynamics simulation to reveal the bond dissociation mechanism of carbon source molecules during carbon nanotube synthesis. C-C bonds in only CHxCO fragments are dissociated on the nickel cluster, whereas there is no preferential structure among the fragments for C-O bond dissociation. The dissociation preference is uncorrelated with the bond dissociation energy of corresponding bonds in freestanding molecules but is correlated with the energy difference between fragment molecules before and after dissociation on the nickel surface. Moreover, carbon-chain formation occurs after C-C bond dissociation in a continuous simulation. What determines the chirality of CNTs? What happens at the dissociation stage of carbon source molecules? Regarding the former question, many researchers have pointed out the good epitaxial relationship between a graphite network and a close-packed facet (i.e., fcc(1 1 1) or hcp(0 0 0 1)) of transition metals [17-19]. Therefore, the correlation between the chirality of CNTs and the angle of the step edge on metal (or metal carbide) surfaces has been closely investigated [20-22]. In association with this geometric matching, the epitaxial growth of graphene on Cu(1 1 1) and Ni(1 1 1) surfaces has recently been achieved via CCVD technique [23-25], which is a promising technique for the synthesis of large-area and monolayer graphene.Regarding the latter question, it is empirically known that the yield and quality of CNT products strongly depend on the choice of carbon source molecules and additives. For example, it is well known that the use of ethanol as carbon source molecules yields a large amount of SWNTs without amorphous carbons (called the alcohol CCVD (ACCVD) technique) compared with the CCVD process using hydrocarbons [4]. Moreover, the addition of a small amount of water dramatically enhances the activity and lifetime of the catalytic metal (called the supergrowth CVD technique) [26]. Recently, several experimental studies have been carried out in an attempt to understand these complicated dissociation processes. For example, Tomie et al. [27] performed in situ mass spectroscopic analysis during CNT synthesis by the ACCVD technique and revealed that ethylene molecules are formed by the dissociation of ethanol, which means that C-O bonds in the ethanol molecules are dissociated during CNT synthesis. Moreover, Xiang et al. [28] employed isotopically labeled ethanol (i.e., 12CH3-13CH2-OH, 13CH3-12CH2-OH, and so forth) to trace the carbon atoms during CNT synthesis and revealed that the carbon further away from the hydroxyl group in the ethanol is preferentially incorporated into the SNWT structure, which was confirmed from the different G band peaks of the Raman spectra. This experimental finding shows that the C-C bonds in ethanol molecules are dissociated during CNT synthesis. Although many experimental studies [29-32] have revealed part of the dissociation process during CNT growth, it is not yet well understood how the initial dissociation of carbon source molecules affects the subsequent formation process of CNTs.In parallel with the many experimental studies, there has been numerous computational works focusing on the formation process of CNTs. However, most of these studies [9-16] did not take the dissociation of carbon source molecules into account and examined the cap formation process starting from isolated carbon atoms. This is mainly due to the fact that a low-impact interatomic potential appropriately describing the dissociation of carbon source molecules has not been established for classical molecular dynamics (MD) simulation. Meanwhile, several classical MD simulations using the ReaxFF potential [33], which describes chemical reactions with a reasonable degree of accuracy but has a high computational cost, have demonstrated the dissociation of hydrocarbons on a nickel cluster [34] and a flat metal surface [35]. However, it is still challenging to treat the dissociation process of carbon source molecules in classical MD simulations in general.Under such circumstances, we have previously investigated the dissociation process of carbon source molecules at the initial stage of CNT [36,37] and graphene growth [38] by ab initio MD simulation, which simultaneously takes into account both chemical reactions with the accuracy of ab initio calculation and the dynamics of atoms. The current situation regarding the study of ethanol dissociation on Ni clusters as the initial stage of the ACCVD process [37] can be summarized as follows. Both C-C and C-O bonds in ethanol molecules are dissociated as well as C-H bonds, and subsequently various reaction products such as hydrogen atoms and molecules, carbon monoxide, oxygen atoms, water, ethylene, methane, and their fragments are formed. When dissociated hydrogen atoms cover the surface of the nickel cluster, they inhibit the additional adsorption and dissociation of ethanol molecules. Therefore, in a 10 ps simulation, C-C and C-O bond dissociation did not occur as often as C-H bond dissociation. Hence, it was not possible to clarify the preferential dissociation path of either C-C or C-O bonds in the previous study [37].On the basis of the above experience, here we investigate the energetic stability of fragment molecules before and after dissociation on a catalytic-metal surface to reveal the preferential dissociation path under CNT growth conditions via the ACCVD method. First, a subsequent ab initio MD simulation is performed starting from the atomic configuration extracted from the previous simulation [37] except for previously dissociated hydrogen atoms to enhance further C-C and C-O bond dissociations efficiently. Then, the bond dissociation energies of the C-C and C-O bonds in the fragment molecules obtained from the MD simulation are examined. Moreover, the energy difference between fragment molecules before and after dissociation on the Ni(1 1 1) surface is estimated on the basis of Hess's law. Then, the role of the metal catalyst in the dissociation process of carbon source molecules during CNT synthesis is discussed.

  7. Theoretical study of the bonding of Sc, Y, and La singly charged and dipositive ions to C2H2, C2H4, and C3H6

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The interaction of the Sc and Y singly-charged and dipositive ions with C2H2, C2H4, and C3H6 is studied using electronic structure calculations that include high levels of electron correlation. These results are compared with comparable calculations performed previously for La(+) and La(2+). For C2H2 and C2H4, all three metal ions insert into the C-C pi bond, making a three-membered ring. The optimal structures for the MC3H6(+) ions all involve rearrangement to make a four-membered ring. The strength of the metal-ligand bond for the singly charged ions follows the order La greater than Sc equal to about Y. In contrast, the bonds involving the dipositive ions are electrostatic, so that the binding energy increases as the size of the ion decreases, leading to the trend Sc greater than Y greater than La.

  8. 25 CFR 212.24 - Bonds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 false Bonds. 212.24 Section 212.24 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF ALLOTTED LANDS FOR MINERAL DEVELOPMENT How To Acquire Leases § 212.24 Bonds. The provisions of § 211.24 of this subchapter are applicable...

  9. 25 CFR 212.24 - Bonds.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 25 Indians 1 2012-04-01 2011-04-01 true Bonds. 212.24 Section 212.24 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF ALLOTTED LANDS FOR MINERAL DEVELOPMENT How To Acquire Leases § 212.24 Bonds. The provisions of § 211.24 of this subchapter are applicable...

  10. 25 CFR 212.24 - Bonds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 25 Indians 1 2011-04-01 2011-04-01 false Bonds. 212.24 Section 212.24 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF ALLOTTED LANDS FOR MINERAL DEVELOPMENT How To Acquire Leases § 212.24 Bonds. The provisions of § 211.24 of this subchapter are applicable...

  11. 25 CFR 212.24 - Bonds.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 25 Indians 1 2014-04-01 2014-04-01 false Bonds. 212.24 Section 212.24 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF ALLOTTED LANDS FOR MINERAL DEVELOPMENT How To Acquire Leases § 212.24 Bonds. The provisions of § 211.24 of this subchapter are applicable...

  12. 25 CFR 212.24 - Bonds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 25 Indians 1 2010-04-01 2010-04-01 false Bonds. 212.24 Section 212.24 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF ALLOTTED LANDS FOR MINERAL DEVELOPMENT How To Acquire Leases § 212.24 Bonds. The provisions of § 211.24 of this subchapter are applicable...

  13. 25 CFR 225.30 - Bonds.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS... Circular No. 570). (b) An operator may file a $75,000 bond for all geothermal, mining, or oil and gas... operator may file a $150,000 bond for full nationwide coverage to cover all geothermal or oil and...

  14. 25 CFR 225.30 - Bonds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS... Circular No. 570). (b) An operator may file a $75,000 bond for all geothermal, mining, or oil and gas... operator may file a $150,000 bond for full nationwide coverage to cover all geothermal or oil and...

  15. 25 CFR 211.24 - Bonds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF TRIBAL LANDS FOR MINERAL DEVELOPMENT...,000 bond for all geothermal, mining, or oil and gas leases, permits, or assignments in any one State...,000 bond for full nationwide coverage to cover all geothermal or oil and gas leases, permits,...

  16. 25 CFR 225.30 - Bonds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS... Circular No. 570). (b) An operator may file a $75,000 bond for all geothermal, mining, or oil and gas... operator may file a $150,000 bond for full nationwide coverage to cover all geothermal or oil and...

  17. 25 CFR 225.30 - Bonds.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS... Circular No. 570). (b) An operator may file a $75,000 bond for all geothermal, mining, or oil and gas... operator may file a $150,000 bond for full nationwide coverage to cover all geothermal or oil and...

  18. 25 CFR 225.30 - Bonds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS... Circular No. 570). (b) An operator may file a $75,000 bond for all geothermal, mining, or oil and gas... operator may file a $150,000 bond for full nationwide coverage to cover all geothermal or oil and...

  19. 25 CFR 216.8 - Performance bond.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS SURFACE EXPLORATION, MINING, AND... mining plan, the operator shall be required to file a suitable performance bond of not less than $2,000..., or contract, and the exploration or mining plan as approved, amended or supplemented. The bond...

  20. 25 CFR 227.8 - Bonds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 false Bonds. 227.8 Section 227.8 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING How to Acquire Leases § 227.8 Bonds. The provisions of § 211.6...