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1

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

2

Raman spectroscopic determination of the length, energy, Debye temperature, and compressibility of the C-C bond in carbon allotropes  

NASA Astrophysics Data System (ADS)

Raman phonon relaxation dynamics in carbon allotropes including graphene, carbon nanotube, C60, carbon nanobud, graphite, and diamond has been formulated in terms of the bond order-length-strength (BOLS) correlation. The length and energy responses of the representative bond to the change of coordination environment, pressure, and temperature determine intrinsically the Raman shifts. Reproduction of the measured results in quantitative information of the bond length, bond energy, mode cohesive energy, binding energy density, Debye temperature, and the compressibility of the C-C bond in each phase without needing involvement of the phonon scattering resonant processes or the mode Grüneisen constants.

Yang, X. X.; Zhou, Z. F.; Wang, Yan; Li, J. W.; Guo, N. G.; Zheng, W. T.; Peng, J. Z.; Sun, C. Q.

2013-06-01

3

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

4

The "excited state C-C bond cleavage-luminescence" phenomenon of a biphenyl-substituted methylenecyclopropane triggered by intermolecular energy transfer from triplet benzophenone.  

PubMed

Existence of the "excited state C-C bond cleavage-luminescence" phenomenon was demonstrated by utilizing intermolecular energy transfer from the excited-triplet benzophenone to 2,2-di(4-biphenylyl)-1-methylenecyclopropane (3). An excellent linear relationship between the intensity of the excitation laser light and that of luminescence clearly shows that formation of the corresponding excited trimethylenemethane biradical (3)4??* proceeds via a one-photon route. PMID:25267075

Matsui, Yasunori; Kido, Taiki; Ohta, Eisuke; Ikeda, Hiroshi

2014-11-21

5

Enantioselective C-C bond synthesis catalysed by enzymes.  

PubMed

The enantioselective synthesis of C-C bonds is often the pivotal step of a synthesis. Nature has made a variety of versatile enzymes available that catalyse this type of reaction very selectively under mild conditions. Cyanohydrins, acyloins (alpha-hydroxy ketones), alpha-hydroxy acids and aldols (beta-hydroxy ketones) are very efficiently synthesised enantioselectively with the aid of C-C bond forming enzymes, which we discuss in this tutorial review. In the case of the alpha-hydroxy acids the applications of nitrilases in a synthetic dkr even allows a disconnection that has no enantioselective chemical equivalent. PMID:16137165

Sukumaran, Joly; Hanefeld, Ulf

2005-06-01

6

Cerium-catalyzed oxidative C–C bond forming reactions  

Microsoft Academic Search

With respect to economical and ecological considerations, molecular oxygen is the oxidant of choice for functionalization of organic substrates. On the basis of our cerium-catalyzed ?-hydroxylation of ?-dicarbonyl compounds, we have developed an oxidative process for C–C bond formation in the presence of simple olefins like styrene. Products of these reactions, which are isolated as endoperoxidic 1,2-dioxane derivatives with potential

Jens Christoffers; Thomas Werner; Michael Rössle

2007-01-01

7

Novel C?-C? bond cleavages of tryptophan-containing peptide radical cations.  

PubMed

In this study, we observed unprecedented cleavages of the C(?)-C(?) bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M(•+)) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M - 116](+) ions. The formation of an ?-carbon radical intermediate at the tryptophan residue for the subsequent C(?)-C(?) bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH - 43](+) and [WGGGH - 116](+), obtained from the CID of [LGGGH](•+) and [WGGGH](•+), respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind](•)-2), in agreement with the CID data for [WGGGH](•+) and [W(1-CH3)GGGH](•+); replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C(?)-C(?) bond cleavage. Hydrogen atom transfer or proton transfer to the ?-carbon atom of the tryptophan residue weakens the C(?)-C(?) bond and, therefore, decreases the dissociation energy barrier dramatically. PMID:22135037

Song, Tao; Hao, Qiang; Law, Chun-Hin; Siu, Chi-Kit; Chu, Ivan K

2012-02-01

8

Spectroscopic and structural evidence for the hydrogen bond nature of C?C?H…C?C contacts in ethynyl steroids  

NASA Astrophysics Data System (ADS)

Structural and IR-spectroscopic evidence is given that directed contacts from terminal alkynes to C?C double bonds possess the essential characteristics of weak hydrogen bonds. The contacts are directed at the center of the ?-bond rather than at one of the individual C-atoms. The contact distances from H to the center of the C?C bond are typically 2.8 Å, with the shortest distances being ˜2.5 Å. The interaction is of pronounced long-range nature and can be detected in the infrared spectrum even with a long H…? distance of almost 3.0 Å. The sample used is mainly composed of ethynyl steroids belonging to the progestine family.

Lutz, Bert; Kanters, Jan A.; van der Maas, John; Kroon, Jan; Steiner, Thomas

1998-01-01

9

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

The potentials of mean force (PMF’s) 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 Møller-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 PMF’s 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 PMF’s 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 PMF’s, 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

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

2012-01-01

10

a Computational Investigation of c-C3H2...HX(X = F, Cl, Br) H-Bonded Complexes  

NASA Astrophysics Data System (ADS)

Cyclopropenylidene (c-C3H2) is of significant importance in interstellar chemistry and synthetic chemistry (e.g., transition metal and organic catalysis). Because of its peculiar structure, c-C3H2 can act as a hydrogen-bond donor or acceptor. In order to gain insight into this feature, the ground-state potential energy surfaces of singlet c-C3H2 complexed with hydrogen halides HX (X = F, Cl, Br) have been explored extensively by density-functional theory (B3LYP) and {ab initio} quantum chemistry (MP2) with a variety of basis sets, cc-pVxZ and aug-cc-pVxZ (x = D, T). The complexes characterized have the carbenic end of c-C3H2 H-bonded to HX, with some proton transfer occurring, the extent of which follows the order HF < HCl < HBr. Accompanying the complex formation are the dipole moment enhancement, the charge transfer, red shifts of the HX vibrational stretching frequencies together with the significant enhancement of band intensity and concomitant HX bond elongation. The nature of H-bonding in these complexes has been explored, based on energy decomposition schemes and the Bader's quantum theory of atoms-in-molecules, with the conclusion that c-C3H2 is a strong H-bond acceptor with respect to the hydrogen halides.

Varadwaj, Pradeep R.; Varadwaj, Arpita; Peslherbe, Gilles H.

2011-06-01

11

Borrowing hydrogen: a catalytic route to C-C bond formation from alcohols.  

PubMed

Ruthenium complexes have been shown to perform efficient transfer hydrogenation reactions between alcohols and alkenes; in combination with an in situ Wittig reaction, indirect formation of C-C bonds has been achieved from alcohols. PMID:14737346

Edwards, Michael G; Jazzar, Rodolphe F R; Paine, Belinda M; Shermer, Duncan J; Whittlesey, Michael K; Williams, Jonathan M J; Edney, Dean D

2004-01-01

12

Observation and X-ray analysis of the microstructures for a bonding material of C\\/C composite and copper  

Microsoft Academic Search

The purpose of this study is to examine the microstructure of a bonding material of C\\/C composite and copper before and after thermal shock tests. Optical and scanning electron microscopy, and energy dispersive X-ray analysis were used to study the microstructures before and after thermal shock tests. In this study, the specimen were given thermal shock without an active cooling,

A. Kurumada; B. McEnaney; T. Oku; K. Kawamata; O. Motojima; N. Noda

1996-01-01

13

Photochemical dynamics of Mg +-acetaldehyde: C-H vs. C-C bond activation pathways  

NASA Astrophysics Data System (ADS)

We have investigated the chemical dynamics of Mg +-acetaldehyde bimolecular complexes following Mg +-centered (3p?3s) excitation. Non-reactive dissociation to Mg + is the dominant decay channel. However, excitation in the 3p?(A ')?3s?(A ') band also results in reactive dissociation to MgH +, MgCHO +, and MgCH 3+ products, showing a clear ?-like electronic orbital alignment preference for chemical quenching. Isotope substitution shows reaction involves a direct attack on the aldehydic C-H or C-C bonds; the relative product branching indicates that the probabilities for C-H and C-C bond cleavage are comparable.

Lu, W.-Y.; Kleiber, P. D.

2001-04-01

14

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

PubMed Central

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

Bower, John F.; Krische, Michael J.

2011-01-01

15

The analysis and practical application about the effect of intra-vascular laser irradiation on C-C bond  

NASA Astrophysics Data System (ADS)

C-C bond is the most common kind of interactions in biological molecules. For example, the molecules of cholesterol and fibrinogen are connected with C-C bonds. We analysis the effect of Laser onto C-C bond in medical cure case by the method of Intra-vascular Laser Irradiation on blood (ILIB), and in theory a new model of "Laser-(C-C)" inharmonic oscillator is constructed on the base of quantum mechanics. Furthermore, we investigate the helpful influence of ILIB through sixty-two cases of brain-thrombus.

Zhang, Can-Bang; Dai, Zhi-Fu; Zhang, Li-Li; Tian, Jia-Jin; Zhou, Ling-Yun

2007-05-01

16

A quantum chemical topological analysis of the C-C bond formation in organic reactions involving cationic species.  

PubMed

ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P(k)(o) Parr functions of the iminium cation, and the nucleophilic P(k)(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible. PMID:24901220

Domingo, Luis R; Pérez, Patricia

2014-07-21

17

Formation of C–C bonds via ruthenium-catalyzed transfer hydrogenation*  

PubMed Central

Ruthenium-catalyzed transfer hydrogenation of diverse ?-unsaturated reactants in the presence of aldehydes provides products of carbonyl addition. Dehydrogenation of primary alcohols in the presence of the same ?-unsaturated reactants provides identical products of carbonyl addition. In this way, carbonyl addition is achieved from the alcohol or aldehyde oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. In this account, the discovery of ruthenium-catalyzed C–C bond-forming transfer hydrogenations and the recent development of diastereo- and enantioselective variants are discussed. PMID:23430602

Moran, Joseph; Krische, Michael J.

2013-01-01

18

An erbium-based bifuctional heterogeneous catalyst: a cooperative route towards C-C bond formation.  

PubMed

Heterogeneous bifuctional catalysts are multifunctional synthetic catalysts enabling efficient organic transformations by exploiting two opposite functionalities without mutual destruction. In this paper we report the first Er(III)-based metallorganic heterogeneous catalyst, synthesized by post-calcination MW-assisted grafting and modification of the natural aminoacid L-cysteine. The natural acid-base distance between sites was maintained to assure the cooperation. The applicability of this new bifunctional heterogeneous catalyst to C-C bond formation and the supposed mechanisms of action are discussed as well. PMID:25029070

Oliverio, Manuela; Costanzo, Paola; Macario, Anastasia; De Luca, Giuseppina; Nardi, Monica; Procopio, Antonio

2014-01-01

19

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

PubMed

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

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

2013-07-22

20

Transition-metal-free C-C bond forming reactions of aryl, alkenyl and alkynylboronic acids and their derivatives.  

PubMed

Investigation of new methods for the synthesis of C-C bonds is fundamental for the development of new organic drugs and materials. Aryl-, alkenyl- and alkynylboronic acids and their derivatives constitute attractive reagents towards this end, due to their stability, low toxicity and ease of handling. However, these compounds are only moderately nucleophilic. Consequently, the most popular C-C bond forming reactions of these boronic acids, such as the Suzuki-Miyaura, Heck, and Hayashi-Miyaura reactions, or additions to C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds, require catalysis by transition metals. However, due to the toxicity and cost of transition metals, some new methods for C-C bond formation using aryl-, alkenyl- and alkynylboronic acids under transition-metal-free conditions are beginning to emerge. In this tutorial review, the recent synthetic advances in this field are highlighted and discussed. PMID:25181967

Roscales, S; Csákÿ, A G

2014-12-21

21

The mechanism of hydrocarbon oxygenate reforming: C-C bond scission, carbon formation, and noble-metal-free oxide catalysts.  

PubMed

Towards a molecular understanding of the mechanism behind catalytic reforming of bioderived hydrocarbon oxygenates, we explore the C-C bond scission of C2 model compounds (acetic acid, ethanol, ethylene glycol) on ceria model catalysts of different complexity, with and without platinum. Synchrotron photoelectron spectroscopy reveals that the reaction pathway depends very specifically on both the reactant molecule and the catalyst surface. Whereas C-C bond scission on Pt sites and on oxygen vacancies involves intermittent surface carbon species, the reaction occurs without any carbon formation and deposition for ethylene glycol on CeO2(111). PMID:24203922

Lykhach, Yaroslava; Neitzel, Armin; Šev?íková, Klára; Johánek, Viktor; Tsud, Nataliya; Skála, Tomáš; Prince, Kevin C; Matolín, Vladimír; Libuda, Jörg

2014-01-01

22

A general synthesis of ynones from aldehydes via oxidative C-C bond cleavage under aerobic conditions.  

PubMed

We describe a direct synthesis of various ynones from readily available aldehydes and hypervalent alkynyl iodides. In this method, a gold catalyst and a secondary amine work synergistically to produce the trisubstituted allenyl aldehyde, which can be converted to the desired ynone through an in situ C-C bond oxidative cleavage using molecular oxygen. PMID:25133731

Wang, Zhaofeng; Li, Li; Huang, Yong

2014-09-01

23

Energy pulse bonding  

NASA Technical Reports Server (NTRS)

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

Smith, G. C.

1972-01-01

24

Theoretical study of the Diels-Alder reaction of C{sub 60}. Transition-state structures and reactivities of C-C bonds  

SciTech Connect

Chemical interactions between large species are not easy to look at by means of accurate MO calculations and by the usual orbital interaction scheme based on perturbation theory. By transforming the MO`s of the reagent and reactant parts into paired interacting orbitals, we have studied the Diels-Alder reaction of C{sub 60} with butadiene. The interaction involved in this system has been demonstrated to be almost completely localized on a C-C bond at the transition state, bearing a close resemblance to the orbital interactions between dienes and small dienophiles. The addition of butadiene to a C-C bond of C{sub 60} that is common to two annulated six-membered rings has been calculated to have a much lower activation energy than the addition to a C-C bond shared by a six-membered ring and a five-membered ring. The difference in reactivities has been shown to be related qualitatively to the local electron-donating potential and the electron-accepting capacitance of those bonds. The double addition of butadiene has been suggested to be not highly regioselective, both from these local reactivity scales and from the calculated heat of reactions. The possibility of C{sub 60} serving as a diene has also been studied. 98 refs., 6 figs., 9 tabs.

Chikama, Akirou; Fueno, Hiroyuki; Fujimoto, Hiroshi [Kyoto Univ. (Japan)

1995-05-25

25

The benzoyl peroxide promoted dual C-C bond formation via dual C-H bond cleavage: ?-phenanthridinylation of ether by isocyanide.  

PubMed

The benzoyl peroxide-promoted ?-phenanthridinylation of ether by isocyanide is developed, proceeding through dual C-H bond cleavage and dual C-C bond formation. The procedure tolerates a series of functional groups, such as methyl, fluoro, chloro, acetyl, methoxy carbonyl, cyano, and trifluoromethyl. Thus, it represents a facile pathway leading to 6-substituted phenanthridine derivatives. The addition of radical to the isonitrile followed by a radical aromatic cyclization is involved in this transformation. PMID:24684422

Wang, Lei; Sha, Wanxing; Dai, Qiang; Feng, Xiaomei; Wu, Wenting; Peng, Haibo; Chen, Bin; Cheng, Jiang

2014-04-18

26

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

PubMed

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

Wang, Teng; Jiao, Ning

2014-04-15

27

Raman spectroscopic determination of the length, strength, compressibility, Debye temperature, elasticity, and force constant of the C-C bond in graphene.  

PubMed

From the perspective of bond relaxation and bond vibration, we have formulated the Raman phonon relaxation of graphene, under the stimuli of the number-of-layers, the uni-axial strain, the pressure, and the temperature, in terms of the response of the length and strength of the representative bond of the entire specimen to the applied stimuli. Theoretical unification of the measurements clarifies that: (i) the opposite trends of the Raman shifts, which are due to the number-of-layers reduction, of the G-peak shift and arises from the vibration of a pair of atoms, while the D- and the 2D-peak shifts involve the z-neighbor of a specific atom; (ii) the tensile strain-induced phonon softening and phonon-band splitting arise from the asymmetric response of the C(3v) bond geometry to the C(2v) uni-axial bond elongation; (iii) the thermal softening of the phonons originates from bond expansion and weakening; and (iv) the pressure stiffening of the phonons results from bond compression and work hardening. Reproduction of the measurements has led to quantitative information about the referential frequencies from which the Raman frequencies shift as well as the length, energy, force constant, Debye temperature, compressibility and elastic modulus of the C-C bond in graphene, which is of instrumental importance in the understanding of the unusual behavior of graphene. PMID:22105904

Yang, X X; Li, J W; Zhou, Z F; Wang, Y; Yang, L W; Zheng, W T; Sun, Chang Q

2012-01-21

28

Metal-Free Tandem Oxidative Aryl Migration and C-C Bond Cleavage: Synthesis of ?-Ketoamides and Esters from Acrylic Derivatives.  

PubMed

A novel tandem metal-free oxidative aryl migration/C-C bond-cleavage reaction, mediated by hypervalent iodine reagent, has been discovered. The presented transformation provided straightforward access to important ?-ketoamide and ?-ketoester derivatives from readily available acrylic derivatives via a concerted process of 1,2-aryl shift concomitant with C-C bond cleavage. PMID:25343425

Liu, Le; Du, Liang; Zhang-Negrerie, Daisy; Du, Yunfei; Zhao, Kang

2014-11-01

29

Chiral BINOL-derived phosphoric acids: privileged Brønsted acid organocatalysts for C-C bond formation reactions.  

PubMed

BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene-type, Diels-Alder, as well as cascade and multi-component reactions. PMID:20820680

Zamfir, Alexandru; Schenker, Sebastian; Freund, Matthias; Tsogoeva, Svetlana B

2010-12-01

30

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

PubMed

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

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

2014-06-20

31

Unlocking Hydrogenation for C-C Bond Formation: A Brief Overview of Enantioselective Methods  

PubMed Central

Hydrogenation of ?-unsaturated reactants in the presence of carbonyl compounds or imines promotes reductive C-C coupling, providing a byproduct-free alternative to stoichiometric organometallic reagents in an ever-increasing range of C=X (X = O, NR) additions. Under transfer hydrogenation conditions, hydrogen exchange between alcohols and ?-unsaturated reactants triggers generation of electrophile-nucleophile pairs, enabling carbonyl addition directly from the alcohol oxidation level, bypassing discrete alcohol oxidation and generation of stoichiometric byproducts. PMID:22125398

Hassan, Abbas; Krische, Michael J.

2011-01-01

32

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

SciTech Connect

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.

Li, Meng [Brookhaven National Laboratory (BNL); Cullen, David A [ORNL; Sasaki, Kotaro [Brookhaven National Laboratory (BNL); Marinkovic, N. [University of Delaware; More, Karren Leslie [ORNL; Adzic, Radoslav R. [Brookhaven National Laboratory (BNL)

2013-01-01

33

Qualifying Energy Conservation Bonds  

E-print Network

1Qualified Energy Construction Bonds (QECB’s) CATEE Conference December 18, 2013 ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • Originally authorized by the Energy Improvement & Extension... are QECB’s ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • 70% of allocation must be for public use, 30% of allocation MAY be used for a private activity • Representative projects include school...

Briggs, J.

2013-01-01

34

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

PubMed

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

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

2014-09-21

35

Theoretical study of the bond dissociation energies of methanol  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

36

Oxidative addition of the C?-C? bond in ?-O-4 linkage of lignin to transition metals using a relativistic pseudopotential-based ccCA-ONIOM method.  

PubMed

A multi-level multi-layer QM/QM method, the relativistic pseudopotential correlation-consistent composite approach within an ONIOM framework (rp-ccCA-ONIOM), was applied to study the oxidative addition of the C(?)-C(?) bond in an archetypal arylglycerol ?-aryl ether (?-O-4 linkage) substructure of lignin to Ni, Cu, Pd and Pt transition metal atoms. The chemically active high-level layer is treated using the relativistic pseudopotential correlation-consistent composite approach (rp-ccCA), an efficient methodology designed to reproduce an accuracy that would be obtained using the more computationally demanding CCSD(T)/aug-cc-pCV?Z-PP, albeit at a significantly reduced computational cost, while the low-level layer is computed using B3LYP/cc-pVTZ. The thermodynamic and kinetic feasibilities of the model reactions are reported in terms of enthalpies of reactions at 298 K (?H°(298)) and activation energies (?H-act). The results obtained from the rp-ccCA:B3LYP hybrid method are compared to the corresponding values using CCSD(T) and several density functionals including B3LYP, M06, M06 L, B2PLYP, mPWPLYP and B2GP-PLYP. The energetics of the oxidative addition of C?C bond in ethane to Ni, Cu, Pd and Pt atoms are also reported to demonstrate that the rp-ccCA method effectively reproduces the accuracy of the CCSD(T)/aug-cc-pCV?Z method. Our results show that in the catalytic activation of the C(?)-C(?) bond of ?-O-4, the use of platinum metal catalysts will lead to the most thermodynamically favored reaction with the lowest activation barrier. PMID:22144374

Oyedepo, Gbenga A; Wilson, Angela K

2011-12-01

37

Low-oxidation state indium-catalyzed C-C bond formation.  

PubMed

The development of innovative metal catalysis for selective bond formation is an important task in organic chemistry. The group 13 metal indium is appealing for catalysis because indium-based reagents are minimally toxic, selective, and tolerant toward various functional groups. Among elements in this group, the most stable oxidation state is typically +3, but in molecules with larger group 13 atoms, the chemistry of the +1 oxidation state is also important. The use of indium(III) compounds in organic synthesis has been well-established as Lewis acid catalysts including asymmetric versions thereof. In contrast, only sporadic examples of the use of indium(I) as a stoichiometric reagent have been reported: to the best of our knowledge, our investigations represent the first synthetic method that uses a catalytic amount of indium(I). Depending on the nature of the ligand or the counteranion to which it is coordinated, indium(I) can act as both a Lewis acid and a Lewis base because it has both vacant p orbitals and a lone pair of electrons. This potential ambiphilicity may offer unique reactivity and unusual selectivity in synthesis and may have significant implications for catalysis, particularly for dual catalytic processes. We envisioned that indium(I) could be employed as a metallic Lewis base catalyst to activate Lewis acidic boron-based pronucleophiles for selective bond formation with suitable electrophiles. Alternatively, indium(I) could serve as an ambiphilic catalyst that activates both reagents at a single center. In this Account, we describe the development of low-oxidation state indium catalysts for carbon-carbon bond formation between boron-based pronucleophiles and various electrophiles. We discovered that indium(I) iodide was an excellent catalyst for ?-selective allylations of C(sp(2)) electrophiles such as ketones and hydrazones. Using a combination of this low-oxidation state indium compound and a chiral semicorrin ligand, we developed catalytic highly enantioselective allylation, crotylation, and ?-chloroallylation reactions of hydrazones. These transformations proceeded with rare constitutional selectivities and remarkable diastereoselectivities. Furthermore, indium(I) triflate served as the most effective catalyst for allylations and propargylations of C(sp(3)) electrophiles such as O,O-acetals, N,O-aminals, and ethers, and we applied this methodology to carbohydrate chemistry. In addition, a catalyst system composed of indium(I) chloride and a chiral silver BINOL-phosphate facilitated the highly enantioselective allylation and allenylation of N,O-aminals. Overall, these discoveries demonstrate the versatility, efficiency, and sensitivity of low-oxidation state indium catalysts in organic synthesis. PMID:22626010

Schneider, Uwe; Kobayashi, Shu

2012-08-21

38

Metal-catalyzed C-C bond cleavage in alkanes: effects of methyl substitution on transition-state structures and stability.  

PubMed

Methyl substituents at C-C bonds influence hydrogenolysis rates and selectivities of acyclic and cyclic C2-C8 alkanes on Ir, Rh, Ru, and Pt catalysts. C-C cleavage transition states form via equilibrated dehydrogenation steps that replace several C-H bonds with C-metal bonds, desorb H atoms (H*) from saturated surfaces, and form ? H2(g) molecules. Activation enthalpies (?H(‡)) and entropies (?S(‡)) and ? values for (3)C-(x)C cleavage are larger than for (2)C-(2)C or (2)C-(1)C bonds, irrespective of the composition of metal clusters or the cyclic/acyclic structure of the reactants. (3)C-(x)C bonds cleave through ?,?,?- or ?,?,?,?-bound transition states, as indicated by the agreement between measured activation entropies and those estimated for such structures using statistical mechanics. In contrast, less substituted C-C bonds involve ?,?-bound species with each C atom bound to several surface atoms. These ?,? configurations weaken C-C bonds through back-donation to antibonding orbitals, but such configurations cannot form with (3)C atoms, which have one C-H bond and thus can form only one C-M bond. (3)C-(x)C cleavage involves attachment of other C atoms, which requires endothermic C-H activation and H* desorption steps that lead to larger ?H(‡) values but also larger ?S(‡) values (by forming more H2(g)) than for (2)C-(2)C and (2)C-(1)C bonds, irrespective of alkane size (C2-C8) or cyclic/acyclic structure. These data and their mechanistic interpretation indicate that low temperatures and high H2 pressures favor cleavage of less substituted C-C bonds and form more highly branched products from cyclic and acyclic alkanes. Such interpretations and catalytic consequences of substitution seem also relevant to C-X cleavage (X = S, N, O) in desulfurization, denitrogenation, and deoxygenation reactions. PMID:24961991

Flaherty, David W; Hibbitts, David D; Iglesia, Enrique

2014-07-01

39

Transition-metal-catalyzed aminations and aziridinations of C-H and C=C bonds with iminoiodinanes.  

PubMed

Catalytic insertion or addition of a metal-imido/nitrene species, generated from reaction of a transition-metal catalyst with iminoiodanes, to C-H and C=C bonds offers a convenient and atom economical method for the synthesis of nitrogen-containing compounds. Following this groundbreaking discovery during the second half of the last century, the field has received an immense amount of attention with a myriad of impressive metal-mediated methods for the synthesis of amines and aziridines having been developed. This review will cover the significant progress made in improving the efficiency, versatility and stereocontrol of this important reaction. This will include the various iminoiodanes, their in situ formation, and metal catalysts that could be employed and new ligands, both chiral and non-chiral, which have been designed, as well as the application of this functional group transformation to natural product synthesis and the preparation of bioactive compounds of current therapeutic interest. PMID:22121122

Chang, Joyce Wei Wei; Ton, Thi My Uyen; Chan, Philip Wai Hong

2011-12-01

40

C?-C bond cleavage of the peptide backbone in MALDI in-source decay using salicylic acid derivative matrices.  

PubMed

The use of 5-formylsalicylic acid (5-FSA) and 5-nitrosalicylic acid (5-NSA) as novel matrices for in-source decay (ISD) of peptides in matrix-assisted laser desorption/ionization (MALDI) is described. The use of 5-FSA and 5-NSA generated a- and x-series ions accompanied by oxidized peptides [M - 2 H + H](+). The preferential formation of a- and x-series ions was found to be dependent on the hydrogen-accepting ability of matrix. The hydrogen-accepting ability estimated from the ratio of signal intensity of oxidized product [M - 2 H + H](+) to that of non-oxidized protonated molecule [M + H](+) of peptide was of the order 5-NSA > 5-FSA > 5-aminosalicylic acid (5-ASA) ? 2,5-dihydroxyl benzoic acid (2,5-DHB) ? 0. The results suggest that the hydrogen transfer reaction from peptide to 5-FSA and 5-NSA occurs during the MALDI-ISD processes. The hydrogen abstraction from peptides results in the formation of oxidized peptides containing a radical site on the amide nitrogen with subsequent radical-induced cleavage at the C?-C bond, leading to the formation of a- and x-series ions. The most significant feature of MALDI-ISD with 5-FSA and 5-NSA is the specific cleavage of the C?-C bond of the peptide backbone without degradation of side-chain and post-translational modifications (PTM). The matrix provides a useful complementary method to conventional MALDI-ISD for amino acid sequencing and site localization of PTMs in peptides. PMID:21953105

Asakawa, Daiki; Takayama, Mitsuo

2011-07-01

41

High chemoselectivity of an advanced iron catalyst for the hydrogenation of aldehydes with isolated c?c bond: a computational study.  

PubMed

Knölker's iron complex is a "green" catalyst that exhibits low toxicity and is abundant in nature. Density functional theory (DFT) was used to explore the highly chemoselective nature of the catalytic hydrogenation of CH2?CHCH2CHO. An outer-sphere concerted hydrogen transfer was found to be the most reasonable kinetic route for the hydrogenation of the olefin. However, the C?C hydrogenation reaction has a high free energy barrier of 28.1 kcal/mol, requiring a high temperature to overcome. By comparison, the CH?O bond concerted hydrogen-transfer reaction catalyzed using Knölker's iron catalyst has an energy barrier of only 14.0 kcal/mol. Therefore, only the CH?O of CH2?CHCH2CHO can be hydrogenated in the presence of Knölker's catalyst at room temperature, due to kinetic domination. All computational results were in good agreement with experimental results. PMID:25222376

Lu, Xi; Cheng, Runjiao; Turner, Nicholas; Liu, Qian; Zhang, Mingtao; Sun, Xiaomin

2014-10-01

42

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

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

43

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

44

Brønsted acid promoted addition-cyclization and C-C bond cleavage: a convenient synthesis of 2-amino-5-aroylmethylthiazoles derivatives.  

PubMed

A Brønsted acid promoted C-C bond cleavage method for the synthesis of novel 2-amino-5-aroylmethylthiazole derivatives has been directly developed from 1,4-enediones and thioureas through self-sequenced thio-Michael-addition, intramolecular selective cyclization, dehydration/aromatization, and C-C bond cleavage reactions. It is noteworthy that this reaction has significant advantages in simple reagents, under environmentally benign conditions and with excellent yields. This highly efficient method is also a highly attractive alternative for the preparation of PLTP, CETP inhibitors and novel biheterocycles. PMID:25327278

Ni, Fan; Yang, Yan; Shu, Wen-Ming; Ma, Jun-Rui; Wu, An-Xin

2014-12-14

45

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

PubMed Central

Carbohydrate moieties are important components of natural products, which are often imperative for the solubility and biological activity of the compounds. The aromatic polyketide alnumycin A contains an extraordinary sugar-like 4?-hydroxy-5?-hydroxymethyl-2?,7?-dioxane moiety attached via a carbon-carbon bond to the aglycone. Here we have extensively investigated the biosynthesis of the dioxane unit through 13C labeling studies, gene inactivation experiments and enzymatic synthesis. We show that AlnA and AlnB, members of the pseudouridine glycosidase and haloacid dehalogenase enzyme families, respectively, catalyze C-ribosylation conceivably through Michael-type addition of d-ribose-5-phosphate and dephosphorylation. The ribose moiety may be attached both in furanose (alnumycin C) and pyranose (alnumycin D) forms. The C1?-C2? bond of alnumycin C is subsequently cleaved and the ribose unit is rearranged into an unprecedented dioxolane (cis-bicyclo[3.3.0]-2?,4?,6?-trioxaoctan-3??-ol) structure present in alnumycin B. The reaction is catalyzed by Aln6, which belongs to a previously uncharacterized enzyme family. The conversion was accompanied with consumption of O2 and formation of H2O2, which allowed us to propose that the reaction may proceed via hydroxylation of C1? followed by retro-aldol cleavage and acetal formation. Interestingly, no cofactors could be detected and the reaction was also conducted in the presence of metal chelating agents. The last step is the conversion of alnumycin B into the final end-product alnumycin A catalyzed by Aln4, an NADPH-dependent aldo-keto reductase. This characterization of the dioxane biosynthetic pathway sets the basis for the utilization of C-C bound ribose, dioxolane and dioxane moieties in the generation of improved biologically active compounds. PMID:22474343

Oja, Terhi; Klika, Karel D.; Appassamy, Laura; Sinkkonen, Jari; Mantsala, Pekka; Niemi, Jarmo; Metsa-Ketela, Mikko

2012-01-01

46

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

PubMed

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)(?(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

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

2010-10-28

47

Significant evidence of C···O and C···C long-range contacts in several heterodimeric complexes of CO with CH3-X, should one refer to them as carbon and dicarbon bonds!  

PubMed

Noncovalent interactions in 18 weakly bound binary complexes formed between either of the two end-on orientations of the CO molecule and the methylated carbon positive ?-hole associated with the hydrophobic part of the CH3-X molecules are exploited using the density functional theory to examine the physical chemistry of the recently introduced 'carbon bonds' (Phys. Chem. Chem. Phys., 2013, 15, 14377), where X = -NO2, -CN, -F, -Cl, -Br, -OH, -CF3, -CCl3, and -NH2. The two important types of interactions are identified as C···O and C···C, the latter has probably never studied before, and are found to be stabilized by charge-transfer delocalizations between the electron-acceptor and -donor natural bond orbitals of the interacting partners involved, unveiled using natural bond orbital analysis. Application of atoms in molecular theory revealed preferable quantum mechanical exchange-correlation energy channels and (3, -1) bond critical points (bcps) between the atoms of noncovalently bonded pairs in these complexes, in excellent agreement with the results of the noncovalent-interaction reduced-density-gradient (NCI-RDG) theory that revealed expected isosurfaces and troughs in the low density region of the RDG vs. sign(?2)? plots. The dependencies of the C···O and C···C bcp charge densities on their corresponding local energy densities, as well as on their corresponding bond electron delocalization indices are found to exhibit nontrivial roles of these topological descriptors to explain the stabilities of the investigated binary complexes. Moreover, the vibrational red- and blue-shifts in the CO bond stretching frequencies, and concomitant elongations and contractions of the corresponding bond lengths, both with respect to the monomer values, are observed upon the formation of the C···O- and C···C-bonded complexes, respectively. The increase and decrease in the complex dipole moments, relative to the sum of their respective monomer values, are found to be a characteristic that separates the aforementioned red- and blue-shifted interactions. In analogy with dihydrogen bonding, as well as that with the charge and electrostatic surface potential model descriptions, we suggest the C···C interactions to be referred to as dicarbon bonds. PMID:25017184

Varadwaj, Pradeep R; Varadwaj, Arpita; Jin, Bih-Yaw

2014-08-28

48

Lewis acid mediated intramolecular C-C bond formation of alkyne-epoxide leading to six-membered nitrogen and oxygen heterocycles.  

PubMed

Intramolecular C-C bond formation of oxygen- and nitrogen-tethered alkynes and epoxide mediated by Lewis acid under ambient conditions is described. A simple procedure for the synthesis of 3,6- and 5,6-dihydropyrans and 3,4-dehydropiperidines from acyclic building blocks in good yields without using any transition metal is shown. PMID:24720735

Ghosh, Priya; Saha, Pipas; Bondalapati, Somasekhar; Indukuri, Kiran; Saikia, Anil K

2014-05-01

49

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

SciTech Connect

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.

Xia, Y.; Mirzai, B.; Chackalamannil, S. [Schering-Plough Research Institute, Kenilworth, NJ (United States)

1995-12-31

50

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

PubMed

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

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

2014-10-14

51

An asymmetric [3+2] cycloaddition of alkynes with oxiranes by selective C-C bond cleavage of epoxides: highly efficient synthesis of chiral furan derivatives.  

PubMed

An efficient enantioselective [3+2] cycloaddition of alkynes with oxiranes via selective C-C bond cleavage of epoxides was developed. A number of optically active 2,5-dihydrofurans were obtained in excellent yields (up to 99%) and enantioselectivities (up to 95% ee) under mild reaction conditions. Moreover, chiral tetrahydrofuran could also be obtained by cycloaddition of alkene and oxirane or hydrogenation of chiral 2,5-dihydrofuran. PMID:25133274

Chen, Weiliang; Fu, Xuan; Lin, Lili; Yuan, Xiao; Luo, Weiwei; Feng, Juhua; Liu, Xiaohua; Feng, Xiaoming

2014-10-01

52

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

PubMed

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

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

2014-10-01

53

Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic C-C Bond Forming Reactions in Aqueous Solution  

PubMed Central

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

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

2014-01-01

54

Design and synthesis of chiral Zn2+ complexes mimicking natural aldolases for catalytic C-C bond forming reactions in aqueous solution.  

PubMed

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

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

2014-01-01

55

Accurate In Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

56

Chemistry of Materials 1989, 1,83-101 How C-C Bonds Are Formed and How They Influence  

E-print Network

properties. In the UC2structure, both uranium-carbon bonding and carbon-carbon bonding are enhanced upon,has a substantialgap between the valence and conduction bands. The pairingof carbon atoms in Dy, with late transition-metal elements. Early transition-metal carbides of the same composition do not exist

Li, Jing

57

Long live vinylidene! A new view of the H(2)C=C: --> HC triple bond CH rearrangement from ab initio molecular dynamics.  

PubMed

We present complete active space self-consistent field (CASSCF) ab initio molecular dynamics (AIMD) simulations of the preparation of the metastable species vinylidene, and its subsequent, highly exothermic isomerization to acetylene, via electron removal from vinylidene anion (D(2)C=C(-) --> D(2)C=C: --> DC triple bond CD). After equilibrating vinylidene anion-d(2) at either 600 +/- 300 K (slightly below the isomerization barrier) or 1440 K +/- 720 K (just above the isomerization barrier), we remove an electron to form a vibrationally excited singlet vinylidene-d(2) and follow its dynamical evolution for 1.0 ps. Remarkably, we find that none of the vinylidenes equilibrated at 600 K and only 20% of the vinylidenes equilibrated at 1440 K isomerized, suggesting average lifetimes >1 ps for vibrationally excited vinylidene-d(2). Since the anion and neutral vinylidene are structurally similar, and yet extremely different geometrically from the isomerization transition state (TS), neutral vinylidene is not formed near the TS so that it must live until it has sufficient instantaneous kinetic energy in the correct vibrational mode(s). The origin of the delay is explained via both orbital rearrangement and intramolecular vibrational energy redistribution (IVR) effects. Unique signatures of the isomerization dynamics are revealed in the anharmonic vibrational frequencies extracted from the AIMD, which should be observable by ultrafast vibrational spectroscopy and in fact are consistent with currently available experimental spectra. Most interestingly, of those trajectories that did isomerize, every one of them violated conventional transition-state theory by recrossing back to vinylidene multiple times, against conventional notions that expect highly exothermic reactions to be irreversible. The dynamical motion responsible for the multiple barrier recrossings involves strong mode-coupling between the vinylidene CD(2) rock and a local acetylene DCC bend mode that has been recently observed experimentally. The multiple barrier recrossings can be used, via a generalized definition of lifetime, to reconcile extremely disparate experimental estimates of vinylidene's lifetime (differing by at least 6 orders of magnitude). Last, a caveat: These results are constrained by the approximations inherent in the simulation (classical nuclear motion, neglect of rotation-vibration coupling, and restriction to C(s) symmetry); refinement of these predictions may be necessary when more exact simulations someday become feasible. PMID:11456576

Hayes, R L; Fattal, E; Govind, N; Carter, E A

2001-01-31

58

Three methods to measure RH bond energies  

SciTech Connect

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.

Berkowitz, J. [Argonne National Lab., IL (United States); Ellison, G.B. [Univ. of Colorado, Boulder, CO (United States). Dept. of Chemistry and Biochemistry; Gutman, D. [Catholic Univ. of America, Washington, DC (United States). Dept. of Chemistry

1993-03-21

59

Iron-promoted C-C bond cleavage of 1,3-diketones: a route to 1,2-diketones under mild reaction conditions.  

PubMed

A conceptual method for the preparation of 1,2-diketones is reported. The selective C-C bond cleavage of 1,3-diketones affords the 1,2-diketones in high yields under mild reaction conditions in air by the use of FeCl(3) as the catalyst and tert-butyl nitrite (TBN) as the oxidant without the use of solvent. The possible reaction mechanism is discussed. This protocol provides an expeditious route to the useful 1,2-diketones. PMID:21627329

Huang, Lehao; Cheng, Kai; Yao, Bangben; Xie, Yongju; Zhang, Yuhong

2011-07-15

60

Computational Study of Low-Temperature Catalytic C-C Bond Activation of Alkanes for Portable Power.  

National Technical Information Service (NTIS)

The development of a room temperature (<50 C) fuel cell that would use a generally available fuel such as JP8 would be most valuable. However there are no known catalysts that can selectively activate the CC bonds of such fuels at such temperature. The go...

2013-01-01

61

Photodissociation Dynamics of 2-BROMOETHYLNITRITE at 351 NM and C-C Bond Fission in the ? - Radical Product  

NASA Astrophysics Data System (ADS)

We used a crossed laser-molecular beam scattering experiment to investigate the primary photodissociation channels of bromoethylnitrite at 351 nm. Only the O-NO bond fission channel forming the ? -bromoethoxy radical and NO, no HBr photoelimination, was detected upon 351 nm photoexcitation,. The subsequent decomposition of the highly vibrational excited ? -bromoethoxy radical to formaldehyde + CH{_2}Br was also investigated.

Wang, Lei; Chhantyal-Pun, Rabi; Brynteson, Matt D.; Miller, Terry A.; Butler, Laurie J.

2013-06-01

62

Acetate C-C bond formation and decomposition in the anaerobic world: the structure of a central enzyme and its key active-site metal cluster.  

PubMed

The structure of carbon monoxide dehydrogenase/acetyl-coenzyme A synthase (CODH/ACS), a central enzyme in the anaerobic metabolism of acetyl-coenzyme A (acetyl-CoA), has been solved to a resolution of 2.2A. The active-site metal cluster responsible for catalyzing acetyl C-C bond synthesis and cleavage, designated the A center, was identified as an Fe(4)S(4) iron sulfur cluster with one of its cysteine thiolates acting as a bridge to an adjacent binuclear metal site. Nickel was found at one position in the binuclear site and the other metal was indicated to be copper - a surprising result, implying a previously unrecognized role for copper. Details of the A center provided new insight into the unusual organometallic mechanism of acetyl C-C bond formation and cleavage, with substantial conformational changes indicated for binding of the large methylcorrinoid protein substrate, and a unique intramolecular channel acting to contain carbon monoxide within the protein and transfer it to the site needed for acetyl-CoA synthesis. PMID:12765830

Grahame, David A

2003-05-01

63

Reactivity of biomimetic iron(II)-2-aminophenolate complexes toward dioxygen: mechanistic investigations on the oxidative C-C bond cleavage of substituted 2-aminophenols.  

PubMed

The isolation and characterization of a series of iron(II)-2-aminophenolate complexes [(6-Me3-TPA)Fe(II)(X)](+) (X = 2-amino-4-nitrophenolate (4-NO2-HAP), 1; X = 2-aminophenolate (2-HAP), 2; X = 2-amino-3-methylphenolate (3-Me-HAP), 3; X = 2-amino-4-methylphenolate (4-Me-HAP), 4; X = 2-amino-5-methylphenolate (5-Me-HAP), 5; X = 2-amino-4-tert-butylphenolate (4-(t)Bu-HAP), 6 and X = 2-amino-4,6-di-tert-butylphenolate (4,6-di-(t)Bu-HAP), 7) and an iron(III)-2-amidophenolate complex [(6-Me3-TPA)Fe(III)(4,6-di-(t)Bu-AP)](+) (7(Ox)) supported by a tripodal nitrogen ligand (6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine) are reported. Substituted 2-aminophenols were used to prepare the biomimetic iron(II) complexes to understand the effect of electronic and structural properties of aminophenolate rings on the dioxygen reactivity and on the selectivity of C-C bond cleavage reactions. Crystal structures of the cationic parts of 5·ClO4 and 7·BPh4 show six-coordinate iron(II) centers ligated by a neutral tetradentate ligand and a monoanionic 2-aminophenolate in a bidentate fashion. While 1·BPh4 does not react with oxygen, other complexes undergo oxidative transformation in the presence of dioxygen. The reaction of 2·ClO4 with dioxygen affords 2-amino-3H-phenoxazin-3-one, an auto-oxidation product of 2-aminophenol, whereas complexes 3·BPh4, 4·BPh4, 5·ClO4 and 6·ClO4 react with O2 to exhibit C-C bond cleavage of the bound aminophenolates. Complexes 7·ClO4 and 7(Ox)·BPh4 produce a mixture of 4,6-di-tert-butyl-2H-pyran-2-imine and 4,6-di-tert-butyl-2-picolinic acid. Labeling experiments with (18)O2 show the incorporation of one oxygen atom from dioxygen into the cleavage products. The reactivity (and stability) of the intermediate, which directs the course of aromatic ring cleavage reaction, is found to be dependent on the nature of ring substituent. The presence of two tert-butyl groups on the aminophenolate ring in 7·ClO4 makes the complex slow to cleave the C-C bond of 4,6-di-(t)Bu-HAP, whereas 4·BPh4 containing 4-Me-HAP displays fastest reactivity. Density functional theory calculations were conducted on [(6-Me3-TPA)Fe(III)(4-(t)Bu-AP)](+) (6(Ox)) to gain a mechanistic insight into the regioselective C-C bond cleavage reaction. On the basis of the experimental and computational studies, an iron(II)-2-iminobenzosemiquinonate intermediate is proposed to react with dioxygen resulting in the oxidative C-C bond cleavage of the coordinated 2-aminophenolates. PMID:24787025

Chakraborty, Biswarup; Bhunya, Sourav; Paul, Ankan; Paine, Tapan Kanti

2014-05-19

64

Radical coupling for directed C-C/C-S bond formation in the reaction of Cp*IrS2C2B10H10 with 1-azido-3-nitrobenzene.  

PubMed

Reactions of half-sandwich complex Cp*IrS2C2B10H10 (1) with 1-azido-3-nitrobenzene (3-NO2C6H4N3, L) upon heating or under light led to new complexes 2-6. Complexes 2 and 3 contain a five-membered cyclometalated ligand arising from C(sp(2))-H activation of the azide ligand L. Complex 4 is a 16 electron species containing a new-generated C-C bond between the azide ligand L and the Cp* unit where C(sp(3))-H activation of the methyl unit occurred. Complexes 5 and 6 contain two types of the ligand which appear in complexes 2, 3 and 4. Further reactions of complexes 5 and 6 with L under more harsh conditions gave rise to the nucleophilic addition products 7 and 8, where ring expansion of the azide ligand at the imido site of complexes 5 and 6 happened. Complexes 2-8 were characterized by NMR, MS, IR, and elemental analysis, and X-ray structural analyses were performed for complexes 2-4 and 6-8. The radical mechanisms for the formation of complexes 2-6 were proposed on the basis of capture experiments by EPR and ESI-MS. And the formation mechanism of complexes 7 and 8 was also suggested. PMID:24108087

Zhong, Wei; Jiang, Qibai; Zhang, Qian; Shang, Yi; Yan, Hong; Bregadze, Vladimir

2014-04-01

65

Understanding the Mechanisms of Unusually Fast H?H, C?H, and C?C Bond Reductive Eliminations from Gold(III) Complexes.  

PubMed

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

Nijamudheen, A; Karmakar, Sharmistha; Datta, Ayan

2014-11-01

66

Facile O-atom insertion into C-C and C-H bonds by a trinuclear copper complex designed to harness a singlet oxene.  

PubMed

Two trinuclear copper [Cu(I)Cu(I)Cu(I)(L)](1+) complexes have been prepared with the multidentate ligands (L) 3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(dimethylamino)ethyl)(methyl)amino)propan-2-ol) (7-Me) and (3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(diethylamino) ethyl)(ethyl) amino)propan-2-ol) (7-Et) as models for the active site of the particulate methane monooxygenase (pMMO). The ligands were designed to form the proper spatial and electronic geometry to harness a "singlet oxene," according to the mechanism previously suggested by our laboratory. Consistent with the design strategy, both [Cu(I)Cu(I)Cu(I)(L)](1+) reacted with dioxygen to form a putative bis(mu(3)-oxo)Cu(II)Cu(II)Cu(III) species, capable of facile O-atom insertion across the central C-C bond of benzil and 2,3-butanedione at ambient temperature and pressure. These complexes also catalyze facile O-atom transfer to the C-H bond of CH(3)CN to form glycolonitrile. These results, together with our recent biochemical studies on pMMO, provide support for our hypothesis that the hydroxylation site of pMMO contains a trinuclear copper cluster that mediates C-H bond activation by a singlet oxene mechanism. PMID:17804786

Chen, Peter P-Y; Yang, Richard B-G; Lee, Jason C-M; Chan, Sunney I

2007-09-11

67

Bis(trifluoromethyl)methylene addition to vinyl-terminated SAMs: a gas-phase C-C bond-forming reaction on a surface.  

PubMed

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C-C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion. PMID:24806554

Adamkiewicz, Malgorzata; O'Hagan, David; Hähner, Georg

2014-05-20

68

Tailored synthesis of various nanomaterials by using a graphene-oxide-based gel as a nanoreactor and nanohybrid-catalyzed c?c bond formation.  

PubMed

New graphene oxide (GO)-based hydrogels that contain vitamin?B2 /B12 and vitamin?C (ascorbic acid) have been synthesized in water (at neutral pH value). These gel-based soft materials have been used to synthesize various metal nanoparticles, including Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing reduced graphene oxide (RGO)-based nanohybrid systems. This result indicates that GO-based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid systems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with Pd nanoparticles was used as an efficient catalyst for C?C bond-formation reactions with good yields and showed high recyclability in Suzuki-Miyaura coupling reactions. PMID:25224859

Biswas, Abhijit; Banerjee, Arindam

2014-12-01

69

Bis(trifluoromethyl)methylene Addition to Vinyl-Terminated SAMs: A Gas-Phase C-C Bond-Forming Reaction on a Surface  

PubMed Central

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C–C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion. PMID:24806554

2014-01-01

70

A substrate-assisted mechanism of nucleophile activation in a Ser-His-Asp containing C-C bond hydrolase  

PubMed Central

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, possessing 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 (HOPDA) to 2-hydroxy-2,4-pentadienoic acid (HPD) 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 pKa2 (?nuc ~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. PMID:24067021

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

2013-01-01

71

Electronic configuration and bond energy  

Microsoft Academic Search

Conclusions  The original interpretation of the method of molecular orbitals as a theory of valency, in which the single electron possesses\\u000a bonding power was based on the assumption that non-premoted electrons are bonding and premoted ones are anti-bonding or non-bonding.\\u000a This assumption is not the outcome of any requirements of theory but is an empirical postulate, which seeks justification\\u000a in experimental

R. K. Asundi; R. Samuel

1936-01-01

72

Trend in the C C and C O bond hydrogenation of acrolein on Pt–M (M = Ni, Co, Cu) bimetallic surfaces  

Microsoft Academic Search

Acrolein, the smallest ?,?-unsaturated aldehyde, is used as a probe molecule to study the effect on the hydrogenation activity toward the CC and CO bonds due to the presence of a 3d transition metal either on the surface or in the subsurface region of a Pt(111) substrate. Temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and density functional

Luis E. Murillo; Carl A. Menning; Jingguang G. Chen

2009-01-01

73

Measuring Bond Energy of an Ionic Compound  

NSDL National Science Digital Library

In this media-rich lesson, students investigate bond energy and the law of conservation of energy. They examine the chemistry behind instant cold packs by using a calorimeter to study the endothermic dissociation of ammonium chloride in water.

2007-08-09

74

Iron dicarbonyl complexes featuring bipyridine-based PNN pincer ligands with short interpyridine C-C bond lengths: innocent or non-innocent ligand?  

PubMed

A series of iron dicarbonyl complexes with bipyridine-based PNN pincer ligands were synthesized and characterized by multinuclear NMR spectroscopy ((1) H, (13) C, (15) N, (31) P), IR spectroscopy, cyclic voltammetry, (57) Fe Mössbauer spectroscopy, XPS spectroscopy, and single-crystal X-ray diffraction. The complexes with the general formula [(R-PNN)Fe(CO)2 ] (5: R-PNN=tBu-PNN=6-[(di-tert-butylphosphino)methyl]-2,2'-bipyridine, 6: R-PNN=iPr-PNN=6-[(diisopropylphosphino)methyl]-2,2'-bipyridine, and 7: R-PNN=Ph-PNN=6-[(diphenylphosphino)methyl]-2,2'-bipyridine) feature differently P-substituted PNN pincer ligands. Complexes 5 and 6 were obtained by reduction of the corresponding dihalide complexes [(R-PNN)Fe(X)2 ] (1: R=tBu, X=Cl; 2: R=tBu, X=Br; 3: R=iPr, X=Cl; 4: R=iPr, X=Br) in the presence of CO. The analogous Ph-substituted complex 7 was synthesized by a reaction of the free ligand with iron pentacarbonyl. The low-spin complexes 5-7 (S=0) are diamagnetic and have distorted trigonal bipyramidal structures in solution, whereas in the solid state the geometries around the iron are best described as distorted square pyramidal. Compared to other structurally characterized complexes with these PNN ligands, shortened interpyridine C?C bonds of about 1.43?Å were measured. A comparison with known examples, theoretically described as metal complexes bearing bipyridine ?-radical anions (bpy(.) (-) ), suggests that the complexes can be described as Fe(I) complexes with one electron antiferromagnetically coupled to the ligand-based radical anions. However, computational studies, at the NEVPT2/CASSCF level of theory, reveal that the shortening of the C?C bond is a result of extensive ?-backbonding of the iron center into the antibonding orbital of the bpy unit. Hence, the description of the complexes as Fe(0) complexes with neutral bipyridine units is the favorable one. PMID:24591249

Zell, Thomas; Milko, Petr; Fillman, Kathlyn L; Diskin-Posner, Yael; Bendikov, Tatyana; Iron, Mark A; Leitus, Gregory; Ben-David, Yehoshoa; Neidig, Michael L; Milstein, David

2014-04-01

75

Density Functional Theory Calculations on Oxidative C?C Bond Cleavage and N?O Bond Formation of [Ru(II) (bpy)2 (diamine)](2+) via Reactive Ruthenium Imide Intermediates.  

PubMed

DFT calculations are performed on [Ru(II) (bpy)2 (tmen)](2+) (M1, tmen=2,3-dimethyl-2,3-butanediamine) and [Ru(II) (bpy)2 (heda)](2+) (M2, heda=2,5-dimethyl-2,5-hexanediamine), and on the oxidation reactions of M1 to give the C?C bond cleavage product [Ru(II) (bpy)2 (NH=CMe2 )2 ](2+) (M3) and the N?O bond formation product [Ru(II) (bpy)2 (ONCMe2 CMe2 NO)](2+) (M4). The calculated geometrical parameters and oxidation potentials are in good agreement with the experimental data. As revealed by the DFT calculations, [Ru(II) (bpy)2 (tmen)](2+) (M1) can undergo oxidative deprotonation to generate Ru-bis(imide) [Ru(bpy)2 (tmen-4?H)](+) (A) or Ru-imide/amide [Ru(bpy)2 (tmen-3?H)](2+) (A') intermediates. Both A and A' are prone to C?C bond cleavage, with low reaction barriers (?G(?) ) of 6.8 and 2.9?kcal?mol(-1) for their doublet spin states (2) A and (2) A', respectively. The calculated reaction barrier for the nucleophilic attack of water molecules on (2) A' is relatively high (14.2?kcal?mol(-1) ). These calculation results are in agreement with the formation of the Ru(II) -bis(imine) complex M3 from the electrochemical oxidation of M1 in aqueous solution. The oxidation of M1 with Ce(IV) in aqueous solution to afford the Ru(II) -dinitrosoalkane complex M4 is proposed to proceed by attack of the cerium oxidant on the ruthenium imide intermediate. The findings of ESI-MS experiments are consistent with the generation of a ruthenium imide intermediate in the course of the oxidation. PMID:25267445

Guan, Xiangguo; Law, Siu-Man; Tse, Chun-Wai; Huang, Jie-Sheng; Che, Chi-Ming

2014-11-10

76

Regioselective functionalization of iminophosphoranes through Pd-mediated C-H bond activation: C-C and C-X bond formation.  

PubMed

The orthopalladation of iminophosphoranes [R(3)P=N-C(10)H(7)-1] (R(3) = Ph(3) 1, p-Tol(3) 2, PhMe(2) 3, Ph(2)Me 4, N-C(10)H(7)-1 = 1-naphthyl) has been studied. It occurs regioselectively at the aryl ring bonded to the P atom in 1 and 2, giving endo-[Pd(?-Cl)(C(6)H(4)-(PPh(2=N-1-C(10)H(7))-2)-?-C,N](2) (5) or endo-[Pd(?-Cl)(C(6)H(3)-(P(p-Tol)(2)=N-C(10)H(7)-1)-2-Me-5)-?-C,N](2) (6), while in 3 the 1-naphthyl group is metallated instead, giving exo-[Pd(?-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-?-C,N](2) (7). In the case of 4, orthopalladation at room temperature affords the kinetic exo isomer [Pd(?-Cl)(C(10)H(6)-(N=PPh(2)Me)-8)-?-C,N](2) (11exo), while a mixture of 11exo and the thermodynamic endo isomer [Pd(?-Cl)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-?-C,N](2) (11endo) is obtained in refluxing toluene. The heating in toluene of the acetate bridge dimer [Pd(?-OAc)(C(10)H(6)-(N=PPh(2)Me)-8)-?-C,N](2) (13exo) promotes the facile transformation of the exo isomer into the endo isomer [Pd(?-OAc)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-?-C,N](2) (13endo), confirming that the exo isomers are formed under kinetic control. Reactions of the orthometallated complexes have led to functionalized molecules. The stoichiometric reactions of the orthometallated complexes [Pd(?-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-?-C,N](2) (7), [Pd(?-Cl)(C(6)H(4)-(PPh(2)[=NPh)-2)](2) (17) and [Pd(?-Cl)(C(6)H(3)-(C(O)N=PPh(3))-2-OMe-4)](2) (18) with I(2) or with CO results in the synthesis of the ortho-halogenated compounds [PhMe(2)P=N-C(10)H(6)-I-8] (19), [I-C(6)H(4)-(PPh(2)=NPh)-2] (21) and [Ph(3)P=NC(O)C(6)H(3)-I-2-OMe-5] (23) or the heterocycles [C(10)H(6)-(N=PPhMe(2))-1-(C(O))-8]Cl (20), [C(6)H(5)-(N=PPh(2)-C(6)H(4)-C(O)-2]ClO(4) (22) and [C(6)H(3)-(C(O)-1,2-N-PPh(3))-OMe-4]Cl (24). PMID:20927428

Aguilar, David; Navarro, Rafael; Soler, Tatiana; Urriolabeitia, Esteban P

2010-11-21

77

Specific cleavage at peptide backbone C?-C and CO-N bonds during matrix-assisted laser desorption/ionization in-source decay mass spectrometry with 5-nitrosalicylic acid as the matrix.  

PubMed

The use of 5-nitrosalicylic acid (5-NSA) as a matrix for in-source decay (ISD) of peptides during matrix-assisted laser desorption/ionization (MALDI) is described herein. Mechanistically, the decay process is initiated by a hydrogen abstraction from a peptide backbone amide nitrogen by 5-NSA. Hydrogen abstraction results in formation of an oxidized peptide containing a radical amide nitrogen. Subsequently, the C(?)-C bond N-terminal to the peptide bond is cleaved to form an a·/x fragment pair. The C(?)-C bonds C-terminal to Gly residues were less susceptible to cleavage than were those of other residues. C(?)-C bonds N-terminal to Pro and Sar residues were not cleaved by the aforementioned mechanism; instead, after hydrogen abstraction from a Pro or Sar C(?)-H bond, the peptide bond N-terminal to the Pro was cleaved yielding b- and y-series ions. We also show that fragments produced by MALDI 5-NSA-induced ISD were formed independently of the ionization process. PMID:21793066

Asakawa, Daiki; Takayama, Mitsuo

2011-09-15

78

Adhesive bonding using variable frequency microwave energy  

SciTech Connect

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.

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

1998-01-01

79

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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.

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

1998-09-08

80

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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.

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

1998-08-25

81

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

82

Probing hydrogen bond energies by mass spectrometry.  

PubMed

Mass spectrometry with desorption electrospray ionization (DESI) is demonstrated to be useful for probing the strength of hydrogen bonding, exemplified by various complexes of benzothiazoles and carboxylic acids in the solid state. Efficiencies for fragmentation of the complexes, quantified by collision-induced dissociation (CID) technology, correspond well with energies of the hydrogen bonds of O-H···N and N-H···O bridging each pair of benzothiazole and carboxylic acid. Linear correlations (with correlation factors of 0.8953 and 0.9928) have been established for the calibration curves of normalized collision energy at 100% fragmentation rate vs the length between donor and acceptor (in the hydrogen bond of O-H···N) as well as the slope of the fragmentation efficiency curve vs the average length difference between O-H···N and N-H···O in the complex. The mechanism responsible for determination of the hydrogen bonds is proposed on the basis of the experiments starting from the mixtures of the complexes as well as labeling with deuterium. As a complement of previously available methods (e.g., X-ray diffraction analysis), expectably, the proposed mass spectrometric method seems to be versatile for probing hydrogen bond energies. PMID:23550909

Su, Hai-Feng; Xue, Lan; Li, Yun-Hua; Lin, Shui-Chao; Wen, Yi-Mei; Huang, Rong-Bin; Xie, Su-Yuan; Zheng, Lan-Sun

2013-04-24

83

Bond-Energy and Surface-Energy Calculations in Metals  

ERIC Educational Resources Information Center

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…

Eberhart, James G.; Horner, Steve

2010-01-01

84

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

NASA Technical Reports Server (NTRS)

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

Alajajian, S. H.; Chutjian, A.

1986-01-01

85

The Bond Dissociation Energies of 1-Butene  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

86

Bond Energies of Molecular Fragments to Metal Surfaces Track Their Bond Energies to H Atoms  

E-print Network

for the production of clean fuels, the combustion of fuels, and the production of chemicals with improved energy efficiency and less pollution, and in developing better fuel cells and batteries. Thus, one would like and H-C bond energies in the corresponding gaseous alkanes was predicted on the basis of density

Campbell, Charles T.

87

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

NASA Technical Reports Server (NTRS)

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.

Halicioglu, T.; Pound, G. M.

1979-01-01

88

Bond resonance energy and verification of the isolated pentagon rule  

Microsoft Academic Search

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 Ï bond shared by two pentagons has a large negative bond resonance energy, thus contributing significantly to the increase in kinetic instability

Jun-ichi Aihara; Jun Ichi

1995-01-01

89

Synthetic Approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) Reveal Redox Non-Innocence and C-C Bond-Formation  

PubMed Central

Attempted syntheses of (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiClnLm (n = 2–4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti]2(?-?3,?3-N,N(py)2-smif,smif) (2), (smif)Ti(?3-N,N(py)2-smif,(smif)H) (3), and (smif)Ti(dpma) (4). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox non-innnocent, such that d1 Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)2?}TiIII (1), [(smif2?)TiIII]2(?-?3,?3-N,N(py)2-smif,smif) (2), [(smif2?)TiIII](?3-N,N(py)2-smif,(smif)H) (3), and (smif2?)TiIII(dpma) (4). The instability of the (smif)2Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical anion ligands, which are also common to 3 and 4. Calculations support this contention. PMID:22830452

Frazier, Brenda A.; Wolczanski, Peter T.; Keresztes, Ivan; DeBeer, Serena; Lobkovsky, Emil B.; Pierpont, Aaron W.; Cundari, Thomas R.

2012-01-01

90

A comparative study of the bonding energy in adhesive wafer bonding  

NASA Astrophysics Data System (ADS)

Adhesion energies are determined for three different polymers currently used in adhesive wafer bonding of silicon wafers. The adhesion energies of the polymer off-stoichiometry thiol-ene-epoxy OSTE+ and the nano-imprint resist mr-I 9150XP are determined. The results are compared to the adhesion energies of wafers bonded with benzocyclobutene, both with and without adhesion promoter. The adhesion energies of the bonds are studied by blister tests, consisting of delaminating silicon lids bonded to silicon dies with etched circular cavities, using compressed nitrogen gas. The critical pressure needed for delamination is converted into an estimate of the bond adhesion energy. The fabrication of test dies and the evaluation method are described in detail. The mean bond energies of OSTE+ were determined to be 2.1 and 20 J m-2 depending on the choice of the epoxy used. A mean bond energy of 1.5 J m-2 was measured for mr-I 9150XP.

Forsberg, F.; Saharil, F.; Haraldsson, T.; Roxhed, N.; Stemme, G.; van der Wijngaart, W.; Niklaus, F.

2013-08-01

91

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

SciTech Connect

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

Rodriguez, E.; Leconte, M.; Basset, J.M.; Tanaka, K. (Institut de Recherches sur la Catalyse, Villeurbanne (France))

1989-09-01

92

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

PubMed Central

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

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

2008-01-01

93

Mechanisms of C-C bond formation and cleavage on metal surfaces: Formation of butenes and hexenes from linear and branched pentenes over Ru/SiO sub 2 catalysts  

SciTech Connect

Over Ru/SiO{sub 2} catalyst, at temperatures above 100-150C and in the presence of hydrogen, linear and branched pentenes (1-pentene, cis- and trans-2-pentene, 2-methyl-2-butene, 3-methyl-1-butene, and 2-methyl-1-butene) undergo isomerization, hydrogenation, hydrogenolysis, and homologation. The main primary products of these last two reactions of C-C bond cleavage and formation are methane, butenes, and hexanes. At low temperature (100-150C), the formation of methane is reduced and the major products are C{sub 4} and C{sub 6} olefinic hydrocarbons, which are obtained in roughly comparable amounts. The distribution of the butenes isomers and of the hexenes isomers strongly depends on the structure of the starting pentene (linear or branched, terminal or internal). The results confirm that hydrogenolysis and homologation of a C{sub 5} olefinic hydrocarbon occur at comparable rates and involve: (1) cleavage of mainly a terminal C-C bond of the pentene isomer leading to C{sup 4} and C{sup 1} fragments, (2) reaction of this C{sup 1} fragment with the starting C{sup 5} to give C{sup 6} hydrocarbons, and (or) (3) hydrogenation of the C{sup 1} fragment to methane. Two mechanisms, based on concepts of organometallic chemistry, can account for the results (especially for the distribution of the C{sup 4} and C{sup 6} olefinic isomers): (1) a methylene insertion-deinsertion mechanism or (2) a mechanism that involves formation and decomposition of dimetallacyclic intermediates. Several experimental results seem to be in favor of the last proposed mechanism.

Rodriguez, E.; Leconte, M.; Basset, J. (Conventionne a l'Universite Claude-Bernard, Lyon (France))

1991-12-01

94

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

NASA Astrophysics Data System (ADS)

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

Lu, Shao-Yu; Lin, Jyh-Shing

2014-01-01

95

Homolytic bond dissociation energies for C-H bonds adjacent to sulfur and aromatic moieties: The effects of substituents of C-H bond strengths of the benzylic positions in coal model compounds  

SciTech Connect

Sulfur-containing compounds are precursors for thiyl radicals at coal liquefaction temperatures due to the weakness of The and S-S bonds. Thiyl radicals play important roles in hydrogen atom shuttling between benzylic positions and catalyze the cleavage and the formation of strong C-C bonds. Although many reactions of thiyl and other sulfur-containing radicals are qualitatively understood, the homolytic bond dissociation energies (EDE`s) and the thermochemistry associated with many key high molecular weight hydrocarbon and sulfur-containing organic structures important to coal is lacking because they are inappropriate for gas-phase techniques. The measurement of BDE`s has been proven to be difficult even in the simplest of molecules.

Alnajjar, M.S.; Franz, J.A. [Pacific Northwest Lab., Richland, WA (United States); Gleicher, G.J.; Truksa, S. [Oregon State Univ., Corvallis, OR (United States). Dept. of Chemistry; Bordwell, F.; Zhang, Xian-Man [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

1993-09-01

96

The origin of exo-selectivity in methyl cyanoformate addition onto the C=C bond of norbornene in Pd-catalyzed cyanoesterification.  

PubMed

A computational investigation has been carried out to elucidate the origin of the exclusive exo-selectivity in the Pd-catalyzed cyanoesterification of strained cyclic olefins, norbornene and norbornadiene. A hybrid density functional was selected for the level of theory with a triple-? quality basis set, which was proposed in an earlier study to provide an experimentally sound ground state electronic structure description for palladium(ii) and palladium(iv) complexes from multi-edge X-ray absorption spectroscopic measurements. Given that the product of oxidative addition can be isolated, we focused on the olefin coordination as the earliest possible origin of exo-selectivity. The calculated geometric structure for the trans-Pd(CN)(COOR)(PPh3)2 complex at the BHandHLYP/def2TZVP/PCM(toluene) level is in an excellent agreement with its experimental structure from crystallographic measurements. Upon dissociation of one of its phosphane ligands, the coordinatively unsaturated trans-isomer is only 17 kJ mol(-1) away from the isomerization transition state, leading to the 14-electron cis-isomers that are 17 to 37 kJ mol(-1) lower in energy than the trans-isomers. Regardless of the initial complex for olefin coordination, the exo-isomer for the norbornene complex is at least 8 kJ mol(-1) lower than the corresponding endo-isomer. The origin of this considerable difference in Gibbs free energy can be attributed to the remarkably different steric and agostic hydrogen interactions between the methylene and the ethylene bridges of the norbornene and the adjacent cis-ligands at the Pd(II) center. PMID:24826897

Okuda, Yasuhiro; Szilagyi, Robert K; Mori, Seiji; Nishihara, Yasushi

2014-07-01

97

Bond Dissociation Energies of Organic Molecules  

E-print Network

to the enthalpy of reaction 1, rxnH298(1), which is by definition2 the bond dissociation enthalpy of the molecule.03 kcal mol-1, the forward reaction is determined to be exothermic since rxnH298(2) ) DH298(CH3CH2-H) - DH). By definition, it is the reaction enthalpy of the bond homolysis reaction 1, rxnH298(1), and thus depends

Ellison, Barney

98

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

99

The Calculation of Accurate Metal-Ligand Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

100

Tight coupling of partial reactions in the acetyl-CoA decarbonylase/synthase (ACDS) multienzyme complex from Methanosarcina thermophila: acetyl C-C bond fragmentation at the a cluster promoted by protein conformational changes.  

PubMed

Direct synthesis and cleavage of acetyl-CoA are carried out by the bifunctional CO dehydrogenase/acetyl-CoA synthase enzyme in anaerobic bacteria and by the acetyl-CoA decarbonylase/synthase (ACDS) multienzyme complex in Archaea. In both systems, a nickel- and Fe/S-containing active site metal center, the A cluster, catalyzes acetyl C-C bond formation/breakdown. Carbonyl group exchange of [1-(14)C]acetyl-CoA with unlabeled CO, a hallmark of CODH/ACS, is weakly active in ACDS, and exchange with CO(2) was up to 350 times faster, indicating tight coupling of CO release at the A cluster to CO oxidation to CO(2) at the C cluster in CO dehydrogenase. The basis for tight coupling was investigated by analysis of three recombinant A cluster proteins, ACDS beta subunit from Methanosarcina thermophila, acetyl-CoA synthase of Carboxydothermus hydrogenoformans (ACS(Ch)), and truncated ACS(Ch) lacking its 317-amino acid N-terminal domain. A comparison of acetyl-CoA synthesis kinetics, CO exchange, acetyltransferase, and A cluster Ni(+)-CO EPR characteristics demonstrated a direct role of the ACS N-terminal domain in promoting acetyl C-C bond fragmentation. Protein conformational changes, related to "open/closed" states previously identified crystallographically, were indicated to have direct effects on the coordination geometry and stability of the A cluster Ni(2+)-acetyl intermediate, controlling Ni(2+)-acetyl fragmentation and Ni(2+)(CO)(CH(3)) condensation. EPR spectral changes likely reflect variations in the Ni(+)-CO equatorial coordination environment in closed buried hydrophobic and open solvent-exposed states. The involvement of subunit-subunit interactions in ACDS, versus interdomain contacts in ACS, ensures that CO is not released from the ACDS beta subunit in the absence of appropriate interactions with the alpha(2)epsilon(2) CO dehydrogenase component. The resultant high efficiency CO transfer explains the low rate of CO exchange relative to CO(2). PMID:20202935

Gencic, Simonida; Duin, Evert C; Grahame, David A

2010-05-14

101

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

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.

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

2007-01-01

102

Synthesis and structure of cyclopropano-annelated homosesquinorbornene derivatives containing pyramidalized double bonds: evidence for the sterical effect of a cyclopropyl group on the degree of C=C double-bond pyramidalization.  

PubMed

[reaction: see text] endo- and exo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl esters have been synthesized, and their Diels-Alder cycloaddition reactions with maleic anhydride, dimethyl acetylenedicarboxylate and singlet oxygen have been investigated. The X-ray analysis of four adducts indicated the pyramidalization of the central double bond. Density functional theory calculations on the isolated products and model compounds showed excellent agreement between the experimental and theoretical determined butterfly angles. Furthermore, it has been shown that a cyclopropyl group fused to [2.2.2] system decreases significantly the degree of the pyramidalization which is attributed to the steric interactions between the cyclopropyl group and ethano bridge of the norbornene systems. Due to the instability of the bicyclic endoperoxides, their X-ray analysis could not be carried out. DFT calculations on model compounds showed increased bending in the case of the product obtained by the addition of singlet oxygen to endo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl ester. PMID:15989319

Saracoglu, Nurullah; Talaz, Oktay; Azizoglu, Akín; Watson, William H; Balci, Metin

2005-07-01

103

Various Carbon to Carbon Bond Lengths Inter-related via the Golden Ratio, and their Linear Dependence on Bond Energies  

E-print Network

This work presents the relations between the carbon to carbon bond lengths in the single, double and triple bonds and in graphite, butadiene and benzene. The Golden ratio, which was shown to divide the Bohr radius into two parts pertaining to the charged particles, the electron and proton, and to divide inter-atomic distances into their cationic and anionic radii, also plays a role in the carbon-carbon bonds and in the ionic/polar character of those in graphite, butadiene and benzene. Further, the bond energies of the various CC bonds are shown to vary linearly with the bond lengths.

Raji Heyrovska

2008-09-11

104

Bond resonance energy and verification of the isolated pentagon rule  

SciTech Connect

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.

Aihara, Jun Ichi [Shizuoka Univ. (Japan)

1995-04-12

105

Natural bond orbital study on the strain energy in cyclotrisilane  

Microsoft Academic Search

A comparative study between cyclotrisilane and cyclopropane by ab initio calculation and natural bond orbital analysis was carried out. A higher strain energy in the former can be attributed to a weaker rehybridization capbility of silicon relative to carbon in response to the angle strain such that SiH bond strengthening is less effective. Strained XH4 and X2H6 (X = C,

Ming-Chiu Ou; San-Yan Chu

1995-01-01

106

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.  

PubMed

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 ?/? hyperconjugation in EtFC and the ?-conjugation in VFC and EFC. PMID:22482553

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

2012-04-01

107

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  

NASA Astrophysics Data System (ADS)

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 ?/? hyperconjugation in EtFC and the ?-conjugation in VFC and EFC.

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

2012-04-01

108

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

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.

Boccia, A.; Lanzilotto, V.; Marrani, A. G.; Zanoni, R. [Dipartimento di Chimica, Universita degli Studi di Roma ''La Sapienza'', piazzale Aldo Moro 5, I-00185 Rome (Italy); Stranges, S. [Dipartimento di Chimica, Universita degli Studi di Roma ''La Sapienza'', piazzale Aldo Moro 5, I-00185 Rome (Italy); IOM-CNR, Laboratorio TASC, I-34149 Basovizza, Trieste (Italy); Alagia, M. [IOM-CNR, Laboratorio TASC, I-34149 Basovizza, Trieste (Italy); Fronzoni, G.; Decleva, P. [Dipartimento di Scienze Chimiche, Universita di Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy and IOM-CNR Democritos, Trieste (Italy)

2012-04-07

109

Three new phosphoric triamides with a [C(O)NH]P(O)[N(C)(C)]2 skeleton: a database analysis of C-N-C and P-N-C bond angles.  

PubMed

In N,N,N',N'-tetraethyl-N''-(4-fluorobenzoyl)phosphoric triamide, C15H25FN3O2P, (I), and N-(2,6-difluorobenzoyl)-N',N''-bis(4-methylpiperidin-1-yl)phosphoric triamide, C19H28F2N3O2P, (II), the C-N-C angle at each tertiary N atom is significantly smaller than the two P-N-C angles. For the other new structure, N,N'-dicyclohexyl-N''-(2-fluorobenzoyl)-N,N'-dimethylphosphoric triamide, C21H33FN3O2P, (III), one C-N-C angle [117.08?(12)°] has a greater value than the related P-N-C angle [115.59?(9)°] at the same N atom. Furthermore, for most of the analogous structures with a [C(=O)NH]P(=O)[N(C)(C)]2 skeleton deposited in the Cambridge Structural Database [CSD; Allen (2002). Acta Cryst. B58, 380-388], the C-N-C angle is significantly smaller than the two P-N-C angles; exceptions were found for four structures with the N-methylcyclohexylamide substituent, similar to (III), one structure with the seven-membered cyclic amide azepan-1-yl substituent and one structure with an N-methylbenzylamide substituent. The asymmetric units of (I), (II) and (III) contain one molecule, and in the crystal structures, adjacent molecules are linked via pairs of N-H...O=P hydrogen bonds to form dimers. PMID:25279604

Pourayoubi, Mehrdad; Tarahhomi, Atekeh; Rheingold, Arnold L; Golen, James A

2014-10-15

110

Students' interdisciplinary reasoning about "high-energy bonds" and ATP  

NSDL National Science Digital Library

Students' sometimes contradictory ideas about ATP (adenosine triphosphate) and the nature of chemical bonds have been studied in the biology and chemistry education literatures, but these topics are rarely part of the introductory physics curriculum. We present qualitative data from an introductory physics course for undergraduate biology majors that seeks to build greater interdisciplinary coherence and therefore includes these topics. In these data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see that students' perceptions of how each scientific discipline bounds the system of interest can influence how they justify their reasoning about a topic that crosses disciplines. This has consequences for a vision of interdisciplinary education that respects disciplinary perspectives while bringing them into interaction in ways that demonstrate consistency amongst the perspectives

Dreyfus, Benjamin W.; Geller, Benjamin D.; Sawtelle, Vashti; Svoboda, Julia; Turpen, Chandra; Redish, Edward F.

2013-09-07

111

Students' interdisciplinary reasoning about "high-energy bonds" and ATP  

NASA Astrophysics Data System (ADS)

Students' sometimes contradictory ideas about ATP (adenosine triphosphate) and the nature of chemical bonds have been studied in the biology and chemistry education literatures, but these topics are rarely part of the introductory physics curriculum. We present qualitative data from an introductory physics course for undergraduate biology majors that seeks to build greater interdisciplinary coherence and therefore includes these topics. In these data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see that students' perceptions of how each scientific discipline bounds the system of interest can influence how they justify their reasoning about a topic that crosses disciplines. This has consequences for a vision of interdisciplinary education that respects disciplinary perspectives while bringing them into interaction in ways that demonstrate consistency amongst the perspectives.

Dreyfus, Benjamin W.; Geller, Benjamin D.; Sawtelle, Vashti; Svoboda, Julia; Turpen, Chandra; Redish, Edward F.

2013-01-01

112

Storing Renewable Energy in Chemical Bonds  

SciTech Connect

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.

Helm, Monte; Bullock, Morris

2013-03-27

113

A micro energy harvester with 3D wire bonded microcoils  

Microsoft Academic Search

We developed the first micro energy harvester with optimized wire bonded microcoils. The coils were fabricated with a fully automated process on PCB. The 3D coils enable to effectively use the magnetic field and generate an output power of 0.62 !W at 1 ms -2 within a total harvester volume of 0.46 cm 3 . With the coil wire thickness

C. Cepnik; U. Wallrabe

2011-01-01

114

FRONTIERS ARTICLE Imaging bond breaking and vibrational energy transfer in small water  

E-print Network

FRONTIERS ARTICLE Imaging bond breaking and vibrational energy transfer in small water containing of state-to-state vibrational pre- dissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl­H2O and NH3

Reisler, Hanna

115

Heats of Formation and Bond Energies in Group III Compounds  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

116

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance  

E-print Network

bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing makes cash inter- est payments. The federal government exempts this interest income from federal taxes credit rating. ·Tax credit bonds. The federal government provides the investor with tax credits in lieu

117

Coulomb energy determination of a single Si dangling bond.  

PubMed

Determination of the Coulomb energy of single point defects is essential because changing their charge state critically affects the properties of materials. Based on a novel approach that allows us to simultaneously identify a point defect and to monitor the occupation probability of its electronic state, we unambiguously measure the charging energy of a single Si dangling bond with tunneling spectroscopy. Comparing the experimental result with tight-binding calculations highlights the importance of the particular surrounding of the localized state on the effective charging energy. PMID:21231404

Nguyen, T H; Mahieu, G; Berthe, M; Grandidier, B; Delerue, C; Stiévenard, D; Ebert, Ph

2010-11-26

118

IR Spectra and Bond Energies Computed Using DFT  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

119

Analysis of liquid metal embrittlement from a bond energy viewpoint  

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

120

Structures, energies, and bonding in the water heptamer  

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

121

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

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

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

122

Controlling the bond scission sequence of oxygenates for energy applications  

NASA Astrophysics Data System (ADS)

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.

Stottlemyer, Alan L.

123

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.  

PubMed

Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, rho(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, rho(rc), the Laplacian, triangle down2rho(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 rho(rc) and triangle down2rho(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of rho(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 high-spin 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 rho(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. PMID:17274642

Gibbs, G V; Cox, D F; Rosso, K M; Ross, N L; Downs, R T; Spackman, M A

2007-03-01

124

Theoretical determination of the alkali-metal superoxide bond energies  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

125

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

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

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

2009-01-01

126

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

E-print Network

as shared covalent bonds. C­O and S­O bonded interactions classify as both intermediate and covalent bonded with a substantial component of covalent character and the C­O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded

Crawford, T. Daniel

127

Free Energy Profiles for H + Conduction along Hydrogen-Bonded Chains of Water Molecules  

Microsoft Academic Search

The molecular mechanism for proton conduction along hydrogen-bonded chains, or “proton wires,” is studied with free energy simulations. The complete transport of a charge along a proton wire requires two complementary processes: 1) translocation of an excess proton (propagation of an ionic defect), and 2) reorientation of the hydrogen-bonded chain (propagation of a bonding defect). The potential of mean force

Régis Pomès; Benoît Roux

1998-01-01

128

Influence of confinement on hydrogen bond energy. The case of the FH···NCH dimer.  

PubMed

The influence of the external pressure on the energy of the intermolecular hydrogen bond is investigated by modeling the pressure effects with helium atoms located at fixed points in space around the hydrogen bonded dimer. Several methods of estimating the energy of the H···N hydrogen bond in the He···FH···NCH···He model system are proposed. They show that the energy of the H···N hydrogen bond in this confined dimer decreases continuously with the reduction of the He···He distance, thus with the increase of the pressure effect exerted on the confined dimer. PMID:20738112

Jab?o?ski, Miros?aw; Solà, Miquel

2010-09-23

129

Energy levels and charge distributions of nonideal dangling and floating bonds in amorphous Si  

NASA Astrophysics Data System (ADS)

Defect-state wave functions and energies are calculated for numerous configurations of nonideal dangling and floating bonds in a-Si with use of Bethe-lattice-terminated clusters and a tight-binding approach. The energy eigenvalue for the dangling bond is highly dependent on deviations from ideality while the wave-function amplitudes are much less so. Exactly the opposite holds for the floating bond. The experimental consequences of these calculations are discussed.

Fedders, P. A.; Carlsson, A. E.

1989-01-01

130

Interstellar Isomers: The Importance of Bonding Energy Differences  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

131

Construction of microbial platform for an energy-requiring bioprocess: practical 2?-deoxyribonucleoside production involving a C-C coupling reaction with high energy substrates  

PubMed Central

Background Reproduction and sustainability are important for future society, and bioprocesses are one technology that can be used to realize these concepts. However, there is still limited variation in bioprocesses and there are several challenges, especially in the operation of energy-requiring bioprocesses. As an example of a microbial platform for an energy-requiring bioprocess, we established a process that efficiently and enzymatically synthesizes 2?-deoxyribonucleoside from glucose, acetaldehyde, and a nucleobase. This method consists of the coupling reactions of the reversible nucleoside degradation pathway and energy generation through the yeast glycolytic pathway. Results Using E. coli that co-express deoxyriboaldolase and phosphopentomutase, a high amount of 2?-deoxyribonucleoside was produced with efficient energy transfer under phosphate-limiting reaction conditions. Keeping the nucleobase concentration low and the mixture at a low reaction temperature increased the yield of 2?-deoxyribonucleoside relative to the amount of added nucleobase, indicating that energy was efficiently generated from glucose via the yeast glycolytic pathway under these reaction conditions. Using a one-pot reaction in which small amounts of adenine, adenosine, and acetone-dried yeast were fed into the reaction, 75?mM of 2?-deoxyinosine, the deaminated product of 2?-deoxyadenosine, was produced from glucose (600?mM), acetaldehyde (250?mM), adenine (70?mM), and adenosine (20?mM) with a high yield relative to the total base moiety input (83%). Moreover, a variety of natural dNSs were further synthesized by introducing a base-exchange reaction into the process. Conclusion A critical common issue in energy-requiring bioprocess is fine control of phosphate concentration. We tried to resolve this problem, and provide the convenient recipe for establishment of energy-requiring bioprocesses. It is anticipated that the commercial demand for dNSs, which are primary metabolites that accumulate at very low levels in the metabolic pool, will grow. The development of an efficient production method for these compounds will have a great impact in both fields of applied microbiology and industry and will also serve as a good example of a microbial platform for energy-requiring bioprocesses. PMID:22709572

2012-01-01

132

Many-body energy decomposition of hydrogen-bonded glycine clusters in gas-phase  

Microsoft Academic Search

A detailed analysis of the many-body contribution to the interaction energies of the gas-phase hydrogen-bonded glycine clusters, (Gly)N, N=1–4 is presented. The energetics of the hydrogen-bonded dimer, trimer and tetramer complexes have been analyzed using density-functional theory. The magnitude of the two- through four-body energy terms have been calculated and compared. The relaxation energy and the two-body energy terms are

Puspitapallab Chaudhuri; Sylvio Canuto

2010-01-01

133

C. C. Jones: Scientific Photographs  

NSDL National Science Digital Library

This image gallery, by C. C. Jones of Union College, contains many examples of physical optics and also x-ray diffraction. Several images of diffraction show how the pattern changes when the wavelength, the distance between light sources, and the aperture is varied. Also included are pinhole photos and comparisons of emission spectra of various elements and the absorption spectrum of the sun. Captions provide background information.

2007-04-25

134

Palladium-catalyzed C-C, C-N and C-O bond formation  

E-print Network

New methods for Pd-catalyzed cross-coupling reactions of aryl halides or arenesulfonates are described. Key to the success of these transformations is the proper choice of ligand and reaction conditions. Palladium catalysts ...

Huang, Xiaohua, 1973-

2003-01-01

135

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

PubMed Central

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

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

136

A second-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons  

Microsoft Academic Search

A second-generation potential energy function for solid carbon and hydrocarbon molecules that is based on an empirical bond order formalism is presented. This potential allows for covalent bond breaking and forming with associated changes in atomic hybridization within a classical potential, producing a powerful method for modelling complex chemistry in large many-atom systems. This revised potential contains improved analytic functions

Donald W. Brenner; Olga A. Shenderova; Judith A. Harrison; Steven J. Stuart; Boris Ni; Susan B. Sinnott

2002-01-01

137

Sacrificial bonds and hidden length dissipate energy as mineralized fibrils separate during bone fracture  

Microsoft Academic Search

Properties of the organic matrix of bone as well as its function in the microstructure could be the key to the remarkable mechanical properties of bone. Previously, it was found that on the molecular level, calcium-mediated sacrificial bonds increased stiffness and enhanced energy dissipation in bone constituent molecules. Here we present evidence for how this sacrificial bond and hidden length

Georg E. Fantner; Tue Hassenkam; Johannes H. Kindt; James C. Weaver; Henrik Birkedal; Leonid Pechenik; Jacqueline A. Cutroni; Geraldo A. G. Cidade; Galen D. Stucky; Daniel E. Morse; Paul K. Hansma

2005-01-01

138

Bond Energy Sums in Benzene, Cyclohexatriene and Cyclohexane Prove Resonance Unnecessary  

E-print Network

The recent new structure of benzene shows that it consists of three C atoms of radii as in graphite alternating with three C atoms with double bond radii. This is different from the hypothetical cyclohexatriene (Kekule structure) involving alternate double and single bonds. It was shown that the difference in the bond energy sum of the atomic structure of benzene from that of the Kekule structure is the energy (erroneously) assumed to be due to resonance. Here it is shown that the present structure of benzene also explains the energy of hydrogenation into cyclohexane and its difference from that of cyclohexatriene.

Raji Heyrovska

2008-07-25

139

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

SciTech Connect

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.

Staroselsky, A.; Anand, L.

1999-07-01

140

Approaching the exact energy for H/sub 2/: Bond functions vs polarization functions  

SciTech Connect

Configuration interaction calculations are reported for hydrogen molecule. The relative efficiency of nuclear-centered polarization functions, verses mid-bond functions, in lowering the absolute energy of hydrogen molecule is examined.(AIP)

Wright, J.S.; Barclay, V.J.

1987-03-01

141

The bond energy of Rh2 Jon D. Langenberg and Michael D. Morse  

E-print Network

methodology and com- putational facilities, transition metal molecules remain diffi- cult systems for the electronic structure of the molecule is to be obtained. The bond energy is among the most diffi- cult

Morse, Michael D.

142

Fluorescein and Rosamine Derivatives as Donors/Acceptors for "Through-bond" Energy Transfer Cassettes  

E-print Network

A series of fluorescein and rosamine derivatives have been prepared and their spectroscopical properties analyzed to determine their usefulness as donor and/or acceptors in "through-bond" energy transfer systems. Such new systems have been tailored...

Castro, Juan C.

2010-07-14

143

Enzymatic enantioselective C-C-bond formation in microreactors.  

PubMed

We have demonstrated that multiple crude enzyme lysates containing a hydroxynitrile lyase can be used for the enantioselective synthesis of cyanohydrins from aldehydes in microchannels. Using a microreactor setup, two important parameters were efficiently screened consuming only minute amounts of reagents. More importantly, results from the continuous flow reaction were fully consistent with results obtained from larger batchwise processes in which a stable emulsion was formed. PMID:17879309

Koch, K; van den Berg, R J F; Nieuwland, P J; Wijtmans, R; Schoemaker, H E; van Hest, J C M; Rutjes, F P J T

2008-03-01

144

Correction: A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes BXY and BHX, where X and Y are halogen atoms.  

PubMed

Correction for 'A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes BXY and BHX, where X and Y are halogen atoms' by Anthony C. Legon, Phys. Chem. Chem. Phys., 2014, 16, 12415-12421. PMID:25325573

Legon, Anthony C

2014-12-01

145

Conformational changes of 1-4-glucopyranosyl residues of a sulfated C-C linked hexasaccharide.  

PubMed

This work describes the structure of a fully sulfated maltotriose alpha-beta C-C linked dimer, where a central glycosidic bond was substituted by a non natural, hydrolase-resistant C-C bond. Such compound shows anti-metastatic properties being an inhibitor of the heparanase enzymatic activity and of P-selectin-mediated cell-cell interactions. NMR spectroscopy was applied to investigate the structure and conformational properties of this C-C linked hexasaccharide. The presence of sulfate substituents and the internal C-C bond drives the two internal rings in an unusual (1)C(4) chair conformation, while the external rings linked by glycosidic bonds retain the typical (4)C(1) conformation. The NMR results were confirmed by molecular mechanics calculations using structure corresponding di- and tetrasaccharides as models. PMID:24680506

Coletti, Alessia; Elli, Stefano; Macchi, Eleonora; Galzerano, Patrizia; Zamani, Leila; Guerrini, Marco; Torri, Giangiacomo; Vismara, Elena

2014-05-01

146

Interlayer contraction in Mg B2 upon replacement of Mg by Al: Effect of the covalent bond energy  

NASA Astrophysics Data System (ADS)

The partitioning of the cohesive energy which we derived recently from the total energy expression of density functional theory [J. Phys.: Condens. Matter 13, 11541 (2001)] allows us to quantify the energy Ecov that describes the covalent and the metallic bond energy in a periodic solid. We apply this methodology to analyze various bonds in MgB2 and AlB2 . We find that the experimentally observed interlayer contraction when going from MgB2 to AlB2 is consistent with the calculated larger Ecov energy of the Al-B bond compared to the Mg-B bond. We further explain this result by the filling of bonding states in the boron- p-Al-p bonds as revealed by the energy resolved covalent bond energy Ecov(E) .

Bester, Gabriel; Fähnle, Manfred

2005-09-01

147

Dissociation Channels of c-C4F8 to CF2 Radical in Reactive Plasma  

NASA Astrophysics Data System (ADS)

It has been generally assumed that octafluorocyclobutane (c-C4F8) is mainly decomposed to CF2 via C2F4 in etching process plasma. However, the detailed mechanism for the dissociations is yet ambiguous. In this paper we have calculated the probable dissociation pathways by using ab initio molecular orbital method. The results show that c-C4F8 is dissociated via the first triplet excited state T1(3A2), the fourth triplet excited state T4(32E) and the fourth singlet excited state S4(12E). One of the degenerate excited states of T4 and S4 is constituted by antibonding combination of two ? bonding orbital of C2F4. T1 state is constituted by antibonding combination of b1u antibonding ? orbital of C2F4. Therefore, in the case of the dissociation via S4 and T4 excited states c-C4F8 may dissociate to two C2F4, and in the case of the dissociation via T1 excited state c-C4F8 may dissociate to four CF2 radicals. It is also found that C3F5+ ion observed as the main peak in c-C4F8 process plasma is produced by electron collision with the slightly larger energy than the ionization threshold value. The main dissociation path of C2F4 is a vertical electron attachment. However, it is also found that dissociation pathways via 1B2g, 3B1u, and 3B2g excited states are very important and should not be ignored.

Hayashi, Toshio; Ishikawa, Kenji; Sekine, Makoto; Hori, Masaru; Kono, Akihiro; Suu, Koukou

2011-03-01

148

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

PubMed

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

Li, Yilei; Zhu, Zhencai; Chen, Guoan

2014-01-01

149

Ab initio and natural bond orbital (NBO) study on the strain energy of chlorocyclotrisilane and chlorocyclopropane  

Microsoft Academic Search

A comparative study between hexachlorocyclotrisilane (1) and hexachlorocyclopropane (2) by ab initio method and natural bond orbital (NBO) analysis was carried out using 6-31G?? basis set, implemented in GAUSSIAN 03 program. The s and p character of SiCl and Si–Si bonds obtained for the compounds were then used to examine the rehybridization effect from the strain energy. A higher strain

M. S. Sadjadi; N. Farhadyar; K. Zare

2007-01-01

150

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

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

151

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

PubMed Central

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.

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

2013-01-01

152

Characterization of ground and excited electronic state deprotonation energies of systems containing double bonds using natural bond orbital analysis  

Microsoft Academic Search

Natural bond orbital analysis is applied to the ground and excited states of a set of neutral, cationic, and anionic doubly bonded species HnC=XHn (X=C, N, O) isoelectronic with ethylene. The character of the excitation is correlated with calculated charge shifts and geometry changes upon relaxation. For these planar molecules, depopulation of the ? bond or population of the ?*

Jay K. Badenhoop; Steve Scheiner

1996-01-01

153

Electronic excitation to singlet states of 1,3-C4F6, c-C4F6 and 2-C4F6 by electron impact--electron energy-loss spectroscopy and ab initio calculations.  

PubMed

We report on the first measurements of the electron impact electronic excitation cross sections for C(4)F(6) isomers, hexafluoro-1,3-butadiene (1,3-C(4)F(6)), hexafluorocyclobutene (c-C(4)F(6)), and hexafluoro-2-butyne (2-C(4)F(6)), measured at 100 eV, 3° scattering angle, while sweeping the energy loss over the range 2.0-15.0 eV. Under these experimental conditions, optically allowed transitions are favored. The electronic state spectroscopy has been investigated and the assignments supported by quantum chemical calculations. The n = 3 members of the Rydberg series have been assigned converging to the lowest ionization energy limits of the C(4)F(6) isomers and classified according to the magnitude of the quantum defects (?). PMID:23074974

Limão-Vieira, P; Anzai, K; Kato, H; Hoshino, M; Ferreira da Silva, F; Duflot, D; Mogi, D; Tanioka, T; Tanaka, H

2012-11-01

154

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

SciTech Connect

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.

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

2010-05-17

155

A Vision of Interdisciplinary Education: Students' Reasoning about "High-Energy Bonds" and ATP  

E-print Network

As interdisciplinary courses are developed, instructors and researchers have to grapple with questions of how students should make connections across disciplines. We explore the issue of interdisciplinary reconciliation (IDR): how students reconcile seemingly contradictory ideas from different disciplines. While IDR has elements in common with other frameworks for the reconciliation of ideas across contexts, it differs in that each disciplinary idea is considered canonically correct within its own discipline. The setting for the research is an introductory physics course for biology majors that seeks to build greater interdisciplinary coherence and therefore includes biologically relevant topics such as ATP and chemical bond energy. In our case-study data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see students justifying context-dependent modeling choices, showing nuanc...

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

2014-01-01

156

Co-C bond energies in adenosylcobinamide and methylcobinamide in the gas phase and in silico.  

PubMed

Essential to biological activity of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) is the Co-C bond cleavage step. Hence, we report an accurate determination of the homolytic gas-phase Co-C bond dissociation energies in the related adenosyl- and methylcobinamides (41.5 ± 1.2 and 44.6 ± 0.8 kcal/mol, respectively) utilizing an energy-resolved threshold collision-induced dissociation technique. This approach allows for benchmarking of electronic structure methods separate from (often ill-defined) solvent effects. Adequacy of various density functional theory methods has been tested with respect to the experimentally obtained values. PMID:24007238

Kobylianskii, Ilia J; Widner, Florian J; Kräutler, Bernhard; Chen, Peter

2013-09-18

157

Oxygen-oxygen bonds : catalytic redox pathways in energy storage  

E-print Network

Introduction: The present understanding of energy - its many forms, and its governing role in the time evolution of physical systems - underlies many of the most fundamental and unifying principles furnished by scientific ...

Fried, Stephen D. (Stephen David), 1987-

2009-01-01

158

The Scalar Relativistic Contribution to Ga-Halide Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

159

Energy transfer mediated by asymmetric hydrogen-bonded interfaces†  

PubMed Central

Amidine-appended ferrocene derivatives form a supramolecular assembly with Ru(ii)(bpy-COOH) (L)22+ complexes (bpy-COOH is 4-CO2H-4?-CH3-bpy and L = bpy, 2,2?-bipyridine or btfmbpy, 4,4?-bis (trifluoromethyl)-2,2?-bipyridine). Steady-state, time-resolved spectroscopy and kinetic isotope effects establish that the metal-to-ligand charge transfer excited states of the Ru(ii) complexes are quenched by proton-coupled energy transfer (PCEnT). These results show that proton motion can be effective in mediating not only electron transfer (ET) but energy transfer (EnT) as well. PMID:24363889

Young, Elizabeth R.; Rosenthal, Joel

2013-01-01

160

Coupling insertion reactions of diphenylbuta-1, 4-diyne into iron-carbene bonds of [Fe 2 (CO) 7 {?-C(Ph)C(NEt 2 }]. Syntheses and reactivities of the ferracyclopentadiene [Fe 2 (CO) 6 {C(Ph)C(NEt 2 )C(Ph)C(C 2 Ph)}] with [Fe 2 (CO) 9  

Microsoft Academic Search

The diiron ynamine complex [Fe2(CO)7{µ-C(Ph)C(NEt2)}] (1) reacts with the diphenylbuta-1, 4-diyne, PhC=C-C=CPh, in refluxing hexane to yield three isomer complexes [Fe2(CO)6{C(Ph)C(NEt2)C(Ph)C(C2Ph}] (2a), [Fe2(CO)6{C(Ph)C(NEt2)C(C2Ph)C(Ph)}] (2b), and [Fe2(CO)6{NEt2)C(Ph)C(C2)C(Ph)}] (2c) All three compounds were identified by their1H NMR spectra. Compounds2a and2c were characterized by single crystal X-ray diffraction analyses. Crystal data: for2a: space group = P21\\/n,a = 17.873(1) Å,ß = 18.388(6) Å,c =

J. C. Daran; E. Gilbert; M. Gouygou; S. Halut; B. Heim; Y. Jeannin

1994-01-01

161

Bonding and reactivity of cyclopentene on Pt(111)  

NASA Astrophysics Data System (ADS)

The adsorption and thermal reactivity of c-C 5H 8 on a Pt(111) surface has been studied by quantitative thermal desorption spectroscopy, high resolution electron energy loss spectroscopy and work function changes, and the bonding configurations and reactivity compared and contrasted with the linear olefins. At < 250 K, associative ?-donor-acceptor bonding in the Dewar-Chatt-Duncanson sense has been rejected. Instead, the vibrational data are more consistent with extensive sp 2 ? sp 3 rehybridization of the olefinic bond leading to a bonding configuration designated ?2(di- ?)- c-C 5H 8. Steric considerations suggest that there is a tilting of the C 5 ring which manifests itself in a soft CH stretch near 2750 cm -1 attributed to additional hydrogen-bonding interaction with the surface. At 250-300 K the partial dehydrogenation pathway of the linear olefins to an adsorbed alkylidyne is inhibited by the inherent stability of the C 5 ring. Instead, three hydrogen atoms from ?2(di- ?)- c-C 5H 8 are dissociated to produce a new adsorbed species identified as a pentahapto-cyclopentadienyl, ? 5-Cp, which is covalently ?-bonded to the surface in a manner analogous to the inorganic metallocenes like ferrocene, FeCp 5. Under these conditions, ? 5-Cp essentially saturates the surface with a coverage estimated at 1.5 ± 0.5×10 10 molecules cm -1. With the surface saturated with ?2(di- ?)- c-C 5H 8 the onset of hydrogen desorption at 250 K is accompanied by the desorption of excess parent c-C 5H 8. It is proposed that c-C 5H 8 is sterically displaced from the surface by the greater Van der Waals dimensions of the more strongly bound ? 5-Cp. c-C 5H 8 is not evolved from submonolayer coverages. Desorption of both hydrogen and c-C 5H 8 occurs with a common reaction-limited onset at 250 K. However, whereas c-C 5H 8 desorption occurs with a peak at 285 K, hydrogen may, with increasing conversion, be accommodated on the surface and subsequently desorbs in a ? 2 desorption-limited step at 305 K. ? 5-Cp is stable to 480 K when it dehydrogenates leaving, at 750 K, carbon on the surface. Decomposition is complex with the vibrational data suggesting a methylidyne stable to 600 K and a MCH?CHM species which is somewhat less stable.

Avery, Neu R.

1984-11-01

162

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

163

The energy of the intramolecular hydrogen bond in chloro-substituted N-methyl-salicylidene imines  

NASA Astrophysics Data System (ADS)

The energetic effects of the conformational rearrangement of eight Schiff bases, differently chloro-substituted, are discussed on the basis of the results of B3LYP/6-31+G(d,p) calculations. The proton transfer tautomers as well as "open"-non-hydrogen-bonded forms were considered. It was found, that the hydrogen-bonded forms have the lowest energy, but the second most stable were the proton transfer states with an O…H sbnd N intramolecular hydrogen bond. The proton transfer in Schiff bases dominates in comparison to other conformational rearrangements. This is important for the understanding of thermochromic and photochromic properties of these molecules. By using a thermodynamic cycle, the steric effects connected with chelate ring formation are estimated to be up to 5 kcal/mol, much higher than in related Mannich bases (˜1 kcal/mol) which do not form resonance assisted hydrogen bonds. Accounting these effects the "real" value of the energy of hydrogen bond formation was estimated to be 15 kcal/mol which increases with growing number of chlorine atoms up to 16.5 kcal/mol for 4,5,6-trichloro substitution.

Koll, A.; Karpfen, A.; Wolschann, P.

2007-11-01

164

Electronic structure, molecular bonding and potential energy surfaces  

SciTech Connect

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.

Ruedenberg, K. [Ames Laboratory, IA (United States)

1993-12-01

165

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

NASA Technical Reports Server (NTRS)

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.

Altshuller, Aubrey P

1955-01-01

166

Correlation energy estimates in periodic extended systems using the localized natural bond orbital coupled cluster approach  

Microsoft Academic Search

A new approach for the determination of correlation energies in periodic extended systems is proposed using the high transferability of amplitudes and integrals from natural bond orbital coupled cluster (NBO CC) calculations performed for small subunits. It is shown that the NBO CC calculations can in fact deliver detailed correlated wave function information for extended periodic systems. As an example

N. Flocke; R. J. Bartlett

2003-01-01

167

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

NASA Technical Reports Server (NTRS)

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.

Kamaratos, E.

1984-01-01

168

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

169

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

170

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

171

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

172

Anti-metastatic Semi-synthetic Sulfated Maltotriose C-C Linked Dimers. Synthesis and Characterisation  

PubMed Central

This manuscript describes the preparation and the spectroscopic characterisation of semi-synthetic sulfated maltotriose C-C linked dimers (SMTCs) where the natural C-O-C anomeric bond was substituted by one direct central C-C bond. This C-C bond induces conformation and flexibility changes with respect to the usual anomeric bond. SMTCs neutral precursors came from maltotriosyl bromide electroreduction through maltotriosyl radical intermediate dimerisation. The new C-C bond configuration, named for convenience ?,?, ?,? and ?,? as the natural anomeric bond, dictated the statistic ratio formation of three diastereoisomers. They were separated by silica gel flash chromatography followed by semi preparative HPLC chromatography. Each diastereoisomer was exhaustively sulfated to afford the corresponding SMTCs. SMTCs were huge characterised by NMR spectroscopy which provided the sulfation degree, too. ?,? and ?,? were found quite homogeneous samples with a high degree of sulfation (85–95%). ?,? appeared a non-homogeneous sample whose average sulfation degree was evaluated at around 78%. Mass spectroscopy experiments confirmed the sulfation degree range. Some considerations were proposed about SMTCs structure-biological properties. PMID:22902885

Vismara, Elena; Coletti, Alessia; Valerio, Antonio; Naggi, AnnaMaria; Urso, Elena; Torri, Giangiacomo

2013-01-01

173

The SIZE OF THINGS H-BOND = 2-5 kcal/mol  

E-print Network

C H 1.1 � C C 1.5 � C C 1.3 � C C 1.2 � The SIZE OF THINGS H-BOND = 2-5 kcal/mol FREE ENERGY AND Keq G = ­RT ln Keq Naphthalene: 6.1 x 5.1 � DNA helix: Protein: (300 aa) 50 � diameter Lipid bilayer: 50 � across (5 nm) Red blood cell: Thymus cell: Liver cell: Let's call an average cell 20 µm diam

Gates, Kent. S.

174

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

175

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

Microsoft Academic Search

Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine–thymine and guanine–cytosine using electron charge densities calculated at X?H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP\\/6-311++G?? and MP2\\/6-311++G?? levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between ?HBCP

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

2009-01-01

176

Computational study on the difference between the Co–C bond dissociation energy in methylcobalamin and adenosylcobalamin  

Microsoft Academic Search

The bond dissociation energies of the Co–C bonds in the cobalamin cofactors methylcobalamin and adenosylcobalamin were calculated using the hybrid quantum mechanics\\/molecular mechanics method IMOMM (integrated molecular orbital and molecular mechanics). Calculations were performed on models of differing complexities as well as on the full systems. We investigated the origin of the different experimental values for the Co–C bond dissociation

Nicole Dölker; Antonio Morreale; Feliu Maseras

2005-01-01

177

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

178

Relationships for the impact sensitivities of energetic C-nitro compounds based on bond dissociation energy.  

PubMed

The ZPE-corrected C-NO(2) bond dissociation energies (BDEs(ZPE)) of a series of model C-nitro compounds and 26 energetic C-nitro compounds have been calculated using density functional theory methods. Computed results show that for C-nitro compounds the UB3LYP calculated BDE(ZPE) is less than the UB3P86 using the 6-31G** basis set, and the UB3P86 BDE(ZPE) changes slightly with the basis set varying from 6-31G** to 6-31++G**. For the series of model C-nitro compounds with different chemical skeletons, it is drawn from NBO analysis that the order of BDE(ZPE) is not only in line with that of the NAO bond order but also with that of the energy gap between C-NO(2) bonding and antibonding orbitals. It is found that for the energetic C-nitro compounds whose drop energies (Es(dr)) are below 24.5 J a good linear correlation exists between E(dr) and BDE(ZPE), implying that these compounds ignite through the C-NO(2) dissociation mechanism. After excluding the so-called trinitrotoluene mechanism compounds, a polynomial correlation of ln(E(dr)) with the BDE(ZPE) calculated at density functional theory levels has been established successfully for the 18 C-NO(2) dissociation energetic C-nitro compounds. PMID:20092267

Li, Jinshan

2010-02-18

179

C-H and N-H bond dissociation energies of small aromatic hydrocarbons  

SciTech Connect

A survey of computational methods was undertaken to calculate the homolytic bond dissociation energies (BDEs) of the C-H and N-H bonds in monocyclic aromatic molecules that are representative of the functionalities present in coal. These include six-membered rings (benzene, pyridine, pyridazine, pyrimidine, pyrazine) and five-membered rings (furan, thiophene, pyrrole, oxazole). By comparison of the calculated C-H BDEs with the available experimental values for these aromatic molecules, the B3LYP/6-31G(d) level of theory was selected to calculate the BDEs of polycyclic aromatic hydrocarbons (PAHs), including carbonaceous PAHs (naphthalene, anthracene, pyrene, coronene) and heteroatomic PAHs (benzofuran, benzothiophene, indole, benzoxazole, quinoline, isoquinoline, dibenzofuran, carbazole). The cleavage of a C-H or a N-H bond generates a {sigma} radical that is, in general, localized at the site from which the hydrogen atom was removed. However, delocalization of the unpaired electron results in {approximately} 7 kcal {center{underscore}dot} mol{sup {minus}1} stabilization of the radical with respect to the formation of phenyl when the C-H bond is adjacent to a nitrogen atom in the azabenzenes. Radicals from five-membered rings are {approximately} 6 kcal {center{underscore}dot} mol{sup {minus}1} less stable than those formed from six-membered rings due to both localization of the spin density and geometric factors. The location of the heteroatoms in the aromatic ring affects the C-H bond strengths more significantly than does the size of the aromatic network. Therefore, in general, the monocyclic aromatic molecules can be used to predict the C-H BDE of the large PAHs within 1 kcal {center{underscore}dot} mol{sup {minus}1}.

Barckholtz, C.; Barckholtz, T.A.; Hadad, C.M.

1999-01-27

180

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

PubMed

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

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

2014-09-18

181

Mapping the Globe with C & C Technologies  

NASA Astrophysics Data System (ADS)

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

Kleiner, A. A.

2001-12-01

182

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  

SciTech Connect

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 (..pi..*) and Rydberg orbitals while broad features observed above the edge are assigned to sigma(C--C) and sigma(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 sigma 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 sigma(C--C) and sigma(C--F) shape resonances in the region of the C 1s ionization threshold.

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

1984-05-01

183

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

184

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

185

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

186

The Effect of Tensile Stress on the Conformational Free Energy Landscape of Disulfide Bonds  

PubMed Central

Disulfide bridges are no longer considered to merely stabilize protein structure, but are increasingly recognized to play a functional role in many regulatory biomolecular processes. Recent studies have uncovered that the redox activity of native disulfides depends on their C–C–S–S dihedrals, and . Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using force–clamp spectroscopy and computer simulation. The and angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, so–called closed states upon exerting tensile stress. In view of the growing evidence of the importance of C–C–S–S dihedrals in tuning the reactivity of disulfides, here we present a systematic study of the conformational diversity of disulfides as a function of tensile stress. With the help of force-clamp metadynamics simulations, we show that tensile stress brings about a large stabilization of the closed conformers, thereby giving rise to drastic changes in the conformational free energy landscape of disulfides. Statistical analysis shows that native TDi, DO and interchain Ig protein disulfides prefer open conformations, whereas the intrachain disulfide bridges in Ig proteins favor closed conformations. Correlating mechanical stress with the distance between the two –carbons of the disulfide moiety reveals that the strain of intrachain Ig protein disulfides corresponds to a mechanical activation of about 100 pN. Such mechanical activation leads to a severalfold increase of the rate of the elementary redox reaction step. All these findings constitute a step forward towards achieving a full understanding of functional disulfides. PMID:25286308

Anjukandi, Padmesh; Dopieralski, Przemyslaw; Ribas-Arino, Jordi; Marx, Dominik

2014-01-01

187

The effect of tensile stress on the conformational free energy landscape of disulfide bonds.  

PubMed

Disulfide bridges are no longer considered to merely stabilize protein structure, but are increasingly recognized to play a functional role in many regulatory biomolecular processes. Recent studies have uncovered that the redox activity of native disulfides depends on their C-C-S-S dihedrals, [Formula: see text] and [Formula: see text]. Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using force-clamp spectroscopy and computer simulation. The [Formula: see text] and [Formula: see text] angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, so-called closed states upon exerting tensile stress. In view of the growing evidence of the importance of C-C-S-S dihedrals in tuning the reactivity of disulfides, here we present a systematic study of the conformational diversity of disulfides as a function of tensile stress. With the help of force-clamp metadynamics simulations, we show that tensile stress brings about a large stabilization of the closed conformers, thereby giving rise to drastic changes in the conformational free energy landscape of disulfides. Statistical analysis shows that native TDi, DO and interchain Ig protein disulfides prefer open conformations, whereas the intrachain disulfide bridges in Ig proteins favor closed conformations. Correlating mechanical stress with the distance between the two [Formula: see text]-carbons of the disulfide moiety reveals that the strain of intrachain Ig protein disulfides corresponds to a mechanical activation of about 100 pN. Such mechanical activation leads to a severalfold increase of the rate of the elementary redox [Formula: see text] reaction step. All these findings constitute a step forward towards achieving a full understanding of functional disulfides. PMID:25286308

Anjukandi, Padmesh; Dopieralski, Przemyslaw; Ribas-Arino, Jordi; Marx, Dominik

2014-01-01

188

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

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

189

Energy of N-H-bond dissociation in phenothiazines and diphenylamines  

NASA Astrophysics Data System (ADS)

Energies of the dissociation of N-H-bonds ( D N-H) in 3 phenothiazines, phenoxazine, phenoselenoazine, and 9 diphenylamines (AmH) are determined. The D N-H values are calculated from kinetic data by means of intersecting parabolas. The rate constants of the following types of reaction are used in calculations: RO{2/·} + Am i H, R· + Am i H, Am{/i ·} + PhMe2CH, and Am{/i ·} + ROOH. As a rule, the results obtained for the reactions of different types are in good agreement with each other and with the results obtained using other methods.

Denisov, E. T.; Denisova, T. G.

2014-04-01

190

Role of bonding and coordination in the atomic structure and energy of diamond and silicon grain boundaries  

Microsoft Academic Search

The high-temperature equilibrated atomic structures and energies of large-unit-cell grain boundaries (GB{close_quote}s) in diamond and silicon are determined by means of Monte-Carlo simulations using Tersoff{close_quote}s potentials for the two materials. Silicon provides a relatively simple basis for understanding GB structural disorder in a purely sp³ bonded material against which the greater bond stiffness in diamond combined with its ability to

P. Keblinski; D. Wolf; S. R. Phillpot; H. Gleiter

1998-01-01

191

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

192

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

PubMed

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. PMID:24832251

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

2014-05-14

193

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

NASA Astrophysics Data System (ADS)

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

Whaley, Shawn D.

194

THE JOURNAL OF CHEMICAL PHYSICS 134, 211101 (2011) Communication: Determination of the bond dissociation energy (D0)  

E-print Network

dissociation energy (D0) of the water dimer, (H2O)2, by velocity map imaging Blithe E. Rocher-Casterline, Lee C online 1 June 2011) The bond dissociation energy (D0) of the water dimer is determined by using state. Phys. 130, 144314 (2009)]. © 2011 American Institute of Physics. [doi:10.1063/1.3598339] The water

Reisler, Hanna

195

Design Optimization of Energy-Efficient Hydrophobic Wafer-bonded III-V/Si Semiconductor Optical Amplifiers  

E-print Network

of Electrical and Computer Engineering, University of California, One Shields Ave., Davis, California 95616 USA) (b) energy band diagram of optimal In(1-x)GaxAsyP(1-y) composition bonding interface (c) current flow transport, optical gain computation, and optical wave-guiding are considered. The energy band diagram shows

Yoo, S. J. Ben

196

DEPARTMENT OF CELL BIOLOGY L V DJ C C C3 C1 C2b C2aC C  

E-print Network

biochemistry and genetics of chromatin. 7. Kitsis Lab: Micrograph of pancreatic islet from normal mouse blood cells (ESEP) and malignant erythroleukemia cells (MEL). 5. Birshtein/Scharff Labs: Mouse DEPARTMENT OF CELL BIOLOGY 2011-2012 3'5' L V DJ C C C3 C1 C2b C2aC C 3'EnhEnh intronic **** 1. 2

Jenny, Andreas

197

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

NASA Astrophysics Data System (ADS)

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

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

198

Influence of warm air-drying on enamel bond strength and surface free-energy of self-etch adhesives.  

PubMed

We examined the effect of warm air-drying on the enamel bond strengths and the surface free-energy of three single-step self-etch adhesives. Bovine mandibular incisors were mounted in self-curing resin and then wet ground with #600 silicon carbide (SiC) paper. The adhesives were applied according to the instructions of the respective manufacturers and then dried in a stream of normal (23°C) or warm (37°C) air for 5, 10, and 20 s. After visible-light irradiation of the adhesives, resin composites were condensed into a mold and polymerized. Ten samples per test group were stored in distilled water at 37°C for 24 h and then the bond strengths were measured. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths varied according to the air-drying time and ranged from 15.8 to 19.1 MPa. The trends for the bond strengths were different among the materials. The value of the ?S? component increased slightly when drying was performed with a stream of warm air, whereas that of the ?S? component decreased significantly. These data suggest that warm air-drying is essential to obtain adequate enamel bond strengths, although increasing the drying time did not significantly influence the bond strength. PMID:23841790

Shiratsuchi, Koji; Tsujimoto, Akimasa; Takamizawa, Toshiki; Furuichi, Tetsuya; Tsubota, Keishi; Kurokawa, Hiroyasu; Miyazaki, Masashi

2013-08-01

199

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

NASA Astrophysics Data System (ADS)

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-1 upon dimerization, somewhat more than in the anharmonic experiment (-111 cm-1).

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

2014-09-01

200

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

PubMed

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(-1) upon dimerization, somewhat more than in the anharmonic experiment (-111 cm(-1)). PMID:25217897

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

2014-09-14

201

Effects of hydrogen bonding on vibrational normal modes of pyrimidine.  

PubMed

The effects of weak intermolecular interactions on 10 vibrational normal modes of pyrimidine are investigated by Raman spectroscopy and electronic structure computations. Hydrogen-bonded networks of water induce a shift to higher energy in certain normal modes of pyrimidine with increasing water concentration, while other modes are relatively unaffected. Pyrimidine molecules also exhibit weak C-H...N interactions and shifted normal modes upon crystallization. The selective nature of the shifting of normal modes to higher energy allows for definitive assignments of the nearly degenerate nu(8a) and nu(8b) modes with polarized Raman spectroscopy. Natural bond orbital (NBO) analyses indicate that when water molecules donate hydrogen bonds to the nitrogen atoms of pyrimidine, there is significant charge transfer from pyrimidine to water, much of which can be accounted for by substantial decreases in the populations of the nitrogen lone pair orbitals. Despite the overall decrease of electron density in pyrimidine upon complexation with water, there are concomitant changes in NBO populations that polarize the pi-electron system toward the proton acceptor N atoms, as well as contractions of the bonds associated with the N-C-N and C-C-C regions of the pyrimidine ring. PMID:20527867

Howard, Austin A; Tschumper, Gregory S; Hammer, Nathan I

2010-07-01

202

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)

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.

Singh, M.; Asthana, R.

2008-01-01

203

Long time fluctuation of liquid water: l/f spectrum of energy fluctuation in hydrogen bond network rearrangement dynamics  

E-print Network

is comparably small, due to their cancellation through the flip-flop-type energy exchanges among water molecules the melting from ice to liquid, water absorbs the latent heat 80 Cal/g, about 1.4 kcal/mol, and hydrogen bonds in pica second time scale, sometimes reaching up to 20 kcal/mol, associated with these collec- tive

Ramaswamy, Ram

204

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster  

E-print Network

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infrared the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads

Iyengar, Srinivasan S.

205

A molecular orbital study of bonding and ionization energies in pentavalent uranium imide/amide complexes  

SciTech Connect

Discrete variational local density functional (X{alpha}) calculations on the model complexes ((RN)U(NR{sub 2}){sub 3}) (R = H (1), SiH{sub 3} (2)) have been performed in order to investigate the electronic structure of uranium amido/imido complexes. Special emphasis is placed on the energy ordering of the highest lying levels formed by U 5f orbitals and by out-of-plane N 2p{sub {pi}} orbitals. Orbital relaxations are also estimated by studying the fragments NR and NR{sub 2} with R = H and R = SiMe{sub 3} in order to allow a comparison of the model compounds 1 and 2 with the measured photoelectron spectrum of the complex ((Me{sub 3}SiN)U(N(SiMe{sub 3}){sub 2}){sub 3}). The ionization energies corresponding to the N 2p{sub {pi}} MOs are calculated in the order N 2p{sub {pi}} (amido) < N 2p{sub {pi}} (imido). The calculated level ordering is rationalized by comparing the order of the two types of U-N bonds and the charge distributions of the corresponding ligands. Taking the calculated ordering as well as the character of the molecular orbitals into account, a new assignment of the observed photoelectron spectra is given based on a comparison of He I and He II spectra.

Bowmaker, G.A.; Goerling, A.; Haeberlen, O.; Roesch, N. (Technische Univ. Muenchen, Garching (Germany)); Goodman, G.L. (Argonne National Lab., IL (United States)); Ellis, D.E. (Northwestern Univ., Evanston, IL (United States))

1992-02-19

206

Observation of the decay ?(3686)???¯±??+c.c.  

NASA Astrophysics Data System (ADS)

Using a sample of 1.06×108 ?(3686) events collected with the BESIII detector, we present the first observation of the decays of ?(3686)???¯+?-+c.c. and ?(3686)???¯-?++c.c. The branching fractions are measured to be B(?(3686)???¯+?-+c.c.)=(1.40±0.03±0.13)×10-4 and B(?(3686)???¯-?++c.c.)=(1.54±0.04±0.13)×10-4, where the first errors are statistical and the second ones systematic.

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

2013-12-01

207

Novel carbon-carbon bond formations for biocatalysis  

PubMed Central

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

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

2011-01-01

208

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

SciTech Connect

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.

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

2004-07-19

209

Energy barriers between H-bonded and stacked structures of 9-methyladenine...1-methylthymine and 9-methylguanine...1-methylcytosine complexes.  

PubMed

The transition structures (TS) between H-bonded (H) and stacked (S) structures of 9-methyladenine...1-methylthymine and 9-methylguanine...1-methylcytosine base pairs were localized at the DFT-D/TZVP potential energy surface. The energy barrier between the S and TS structures is considerably higher for the former pair than for the latter, which makes localization of the stacked structure of this pair possible. PMID:20066299

Cerný, Jirí; Hobza, Pavel

2010-01-21

210

Photoinduced C-C reactions on insulators toward photolithography of graphene nanoarchitectures.  

PubMed

On-surface chemistry for atomically precise sp(2) macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp(2)-carbon nanometer-thin films on insulators and under ultrahigh vacuum (UHV) conditions from photocoupled brominated precursors. We reveal that covalent coupling is initiated by C-Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C-Br scission and C-C coupling processes. Further, unreacted material can be sublimed and the coupled sp(2)-carbon precursors can be graphitized by e-beam treatment at 500 °C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp(2)-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology. PMID:24524804

Palma, Carlos-Andres; Diller, Katharina; Berger, Reinhard; Welle, Alexander; Björk, Jonas; Cabellos, Jose Luis; Mowbray, Duncan J; Papageorgiou, Anthoula C; Ivleva, Natalia P; Matich, Sonja; Margapoti, Emanuela; Niessner, Reinhard; Menges, Bernhard; Reichert, Joachim; Feng, Xinliang; Räder, Hans Joachim; Klappenberger, Florian; Rubio, Angel; Müllen, Klaus; Barth, Johannes V

2014-03-26

211

A DFT study on the interaction between adsorbed silver on C?? and disulfide bond.  

PubMed

Adsorption of a silver atom on the surface of Buckyball (C??) was investigated using density functional theory (DFT). The Ag atom tends to occupy the bridge site over C--C bond in pentagon-hexagon ring junction with the binding energy of -38.33 kcal mol?¹. The capability of destroying S--S bond by both a single silver atom and the silver atom adsorbed on C?? was also investigated by DFT calculations using dimethyl disulfide as the molecular model. The results of the natural bond orbital (NBO) and population analysis indicate that the cleavage of the S--S bond effectively occurs by the silver atom adsorbed on C??. Since denaturation of disulfide bonds of envelope glycoprotein (gp) 120 is a key step in the prevention of the spread of HIV-1, the development of the proposed study is promised to HIV-1 research field. PMID:23085174

Azizi, Khaled; Sohrabinia, Ali

2012-09-01

212

Unstrained carbon?carbon bond cleavage.  

PubMed

This Focus Review presents recent developments in the cleavage of C?C bonds in organic molecules. Significant progress in C?C activation, including the development of a variety of new synthetic strategies, has contributed to the development of this field over the past few decades. Transition-metal-mediated C?C bond cleavage has been shown to be a quite efficient process and several elegant metal-free methods have also recently been developed. Strained rings have been widely used in C?C cleavage transformations; however, unstrained C?C activation has increasingly caught the attention of organic researchers, which inspired us to clarify the developments in this field. PMID:25179561

Liu, Hui; Feng, Minghao; Jiang, Xuefeng

2014-12-01

213

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

NASA Astrophysics Data System (ADS)

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.

Bo, Maolin; Wang, Yan; Huang, Yongli; Zhang, Xi; Zhang, Ting; Li, Can; Sun, Chang Q.

2014-04-01

214

Intermolecular interactions in the N?C C?C H dimer  

NASA Astrophysics Data System (ADS)

Ab initio calculations on N?C-C?C-H and its anti-parallel dimer are reported, with a view to studying the intermolecular interactions present. Following initial optimisation of the monomer at the MP2/6-311+G(d,p) level, the PES of the dimer corresponding to variations in chain separation and overlap was explored. Two minima on this surface were found, varying in their degree of overlap, but both having C 2 h symmetry. Topological charge density analysis shows these two arrangements to have qualitatively different structures. Atoms in Molecules decomposition shows the origin of the dimer stabilisation to lie in an increase in nitrogen's population and self-stabilisation.

Platts, James A.; Howard, Sean T.; Fallis, Ian. A.

1998-03-01

215

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

PubMed Central

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/?) was observed for the fate of the singlet diradicals DR (?max ? 580–590 nm). The activation parameters, ?H ‡ and ?S ‡, for the ring-closing reaction (?-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, ?293 = 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

Ye, Jianhuai; Fujiwara, Yoshihisa

2013-01-01

216

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

217

Role of bonding and coordination in the atomic structure and energy of diamond and silicon grain boundaries  

SciTech Connect

The high-temperature equilibrated atomic structures and energies of large-unit-cell grain boundaries (GB{close_quote}s) in diamond and silicon are determined by means of Monte-Carlo simulations using Tersoff{close_quote}s potentials for the two materials. Silicon provides a relatively simple basis for understanding GB structural disorder in a purely sp{sup 3} bonded material against which the greater bond stiffness in diamond combined with its ability to change hybridization in a defected environment from sp{sup 3} to sp{sup 2} can be elucidated. We find that due to the purely sp{sup 3}-type bonding in Si, even in highly disordered, high-energy GB{close_quote}s at least 80{percent} of the atoms are fourfold coordinated in a rather dense confined amorphous structure. By contrast, in diamond even relatively small bond distortions exact a considerable price in energy that favors a change to sp{sup 2}-type local bonding; these competing effects translate into considerably more ordered diamond GB{close_quote}s; however, at the price of as many as 80{percent} of the atoms being only threefold coordinated. Structural disorder in the Si GB{close_quote}s is therefore partially replaced by coordination disorder in the diamond GB{close_quote}s. In spite of these large fractions of three-coordinated GB carbon atoms, however, the three-coordinated atoms are rather poorly connected amongst themselves, thus likely preventing any type of graphite-like electrical conduction through the GB{close_quote}s. {copyright} {ital 1998 Materials Research Society.}

Keblinski, P.; Wolf, D.; Phillpot, S.R. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Keblinski, P.; Gleiter, H. [Forschungszentrum Karlsruhe, 76021 Karlsruhe (Germany)

1998-08-01

218

Development of bonding methods and energy absorption of sandwich panels for thermoplastic advanced composites.  

E-print Network

??Given their high strength-to-weight and stiffness-to-weight ratios, sandwich composites continue to be considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased… (more)

Haslam, Erik Bravant

2012-01-01

219

Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.  

PubMed

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used. PMID:17257010

Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

2007-02-01

220

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

SciTech Connect

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.

Wang, Shengguang

2010-10-27

221

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

PubMed

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

Samanta, Amit K; Czakó, Gábor; Wang, Yimin; Mancini, John S; Bowman, Joel M; Reisler, Hanna

2014-08-19

222

Dissociative Low-Energy Electron Attachment to the C-S Bond of H3CSCH3 Influenced by Coulomb Stabilization  

NASA Astrophysics Data System (ADS)

In earlier works by our group, it was suggested that the presence of stabilizing Coulomb potentials can allow low-energy electrons (i.e., with kinetic energies <1 eV) to attach to [sigma]* orbitals of certain bonds and to thus cleave those bonds. In these earlier efforts, we focused on S-S bond cleavage and in breaking a variety of bonds that occur in typical peptides and proteins. In the present effort, we focus primarily on the stabilizing effects of nearby positive charges on the electron attachment process to dimethyl sulfide (DMS) to break one of the C-S bonds. Ab initio electronic structure calculations have been used to explore the influence of Coulomb potentials on the ability of low-energy electrons to directly attach to the [sigma]* orbital of the C-S bond and to effect bond cleavage, as well as to examine [sigma]* anion energy evolution as a function of C-S bond length.

Sobczyk, Monika; Skurski, Piotr; Simons, Jack

223

Modelling of c-C2H4O formation on grain surfaces  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

224

B r y n S a d o w n i k , M a r k J a c c a r d Shaping Sustainable Energy Use in Chinese Cities  

E-print Network

is predetermined when land-use and urban form are designated. Community Energy Management (CEM) is a sustainable- ergy consumption is predetermined when land-use and urban form are des- ignated. Patterns of urban form less energy for transportation, heating, cooking and other uses. Concerted ef- forts to promote urban

225

A multivariate relationship for the impact sensitivities of energetic N-nitrocompounds based on bond dissociation energy.  

PubMed

The ZPE-corrected N-NO(2) bond dissociation energies (BDEs(ZPE)) of a series of model N-nitrocompounds and typical energetic N-nitrocompounds have been calculated using density functional theory methods. Computed results show that using the 6-31G** basis set the UB3LYP calculated BDE(ZPE) is similar to the B3PW91 but is less than the UB3P86 and that for both UB3P86 and UB3PW91 methods the 6-31G(**) calculated BDE(ZPE) is close to the 6-31++G(**). For the series of model N-nitrocompounds it is drawn from the NBO analysis that at the UB3LYP/6-31G(**) level the order of BDE(ZPE) is not only in line with that of bond order but also with that of the energy gap between N-NO(2) bond and antibond orbitals. For the typical energetic N-nitrocompounds the impact sensitivity is strongly related to the BDE(ZPE) indeed, and based on the BDEs(ZPE) calculated at different density functional theory levels this work has established a good multivariate correlation of impact sensitivity with molecular parameters, which provides a method to address the sensitivity problem. PMID:19819622

Li, Jinshan

2010-02-15

226

Volume 4, number 9 CHEMICAL PHYSICSLETTERS 15 &uluary 1970 HYDROGEN-BOND ENERGY NONADDITIVITY IN WATER *  

E-print Network

. The value of accurate quantum-mechanic- al computation of electron cloud deformations in molecular clusters calculations based on point-charge and multipole- expansion models have been carried out to exam- ine which included only the four electrons di- rectly involved in the hydrogen-bonded system

Stillinger, Frank

227

Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction  

NASA Technical Reports Server (NTRS)

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.

1979-01-01

228

Theoretical Bond Dissociation Energies of Halo-Heterocycles: Trends and Relationships to Regioselectivity in Palladium-Catalyzed Cross-Coupling Reactions  

PubMed Central

Selectivity of the palladium-catalyzed cross-coupling reactions of heterocycles bearing multiple identical halogens is mainly determined by the relative ease of oxidative addition. This is related to both the energy to distort the carbon halogen bond to the transition-state geometry (related to the CX bond-dissociation energy) and to the interaction between the heterocycle ?* (LUMO) and PdL2 HOMO (J. Am. Chem. Soc. 2007, 129, 12664). The computed bond dissociation energies of a larger series of halo-heterocycles have been explored with B3LYP and higher accuracy G3B3 calculations. Quantitative trends in bond dissociation energies have been identified for five- and six-membered chloro and bromo substituted heterocycles with N, O, and S heteroatoms. PMID:19368385

Garcia, Yeimy; Schoenebeck, Franziska; Legault, Claude Y.; Merlic, Craig A.; Houk, K. N.

2009-01-01

229

Using Qualified Energy Conservation Bonds (QECBs) to Fund a Residential Energy Efficiency Loan Program: Case Study on Saint Louis County, MO  

SciTech Connect

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.

Zimring, Mark

2011-06-23

230

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

NASA Astrophysics Data System (ADS)

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.

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

2009-01-01

231

Natural bond orbital-based energy density analysis for correlated methods: Second-order Møller-Plesset perturbation and coupled-cluster singles and doubles  

Microsoft Academic Search

Natural bond orbital-based energy density analysis (NBO-EDA), which split energies into atomic and bonding contributions, is proposed for correlated methods such as coupled-cluster singles and doubles (CCSD) and second-order Møller-Plesset (MP2) perturbation. Applying NBO-EDA for CCSD and MP2 to ethylene and the Diels-Alder reaction, we are successful in obtaining useful knowledge regarding electron correlation of pi- and sigma-type orbitals, and

Yutaka Imamura; Takeshi Baba; Hiromi Nakai

2008-01-01

232

A novel salt bridge mechanism highlights the need for nonmobile proton conditions to promote disulfide bond cleavage in protonated peptides under low-energy collisional activation.  

PubMed

The gas-phase fragmentation mechanisms of small models for peptides containing intermolecular disulfide links have been studied using a combination of tandem mass spectrometry experiments, isotopic labeling, structural labeling, accurate mass measurements of product ions, and theoretical calculations (at the MP2/6-311 + G(2d,p)//B3LYP/3-21G(d) level of theory). Cystine and its C-terminal derivatives were observed to fragment via a range of pathways, including loss of neutral molecules, amide bond cleavage, and S-S and C-S bond cleavages. Various mechanisms were considered to rationalize S-S and C-S bond cleavage processes, including charge directed neighboring group processes and nonmobile proton salt bridge mechanism. Three low-energy fragmentation pathways were identified from theoretical calculations on cystine N-methyl amide: (1) S-S bond cleavage dominated by a neighboring group process involving the C-terminal amide N to form either a protonated cysteine derivative or protonated sulfenyl amide product ion (44.3 kcal mol(-1)); (2) C-S bond cleavage via a salt bridge mechanism, involving abstraction of the alpha-hydrogen by the N-terminal amino group to form a protonated thiocysteine derivative (35.0 kcal mol(-1)); and (3) C-S bond cleavage via a Grob-like fragmentation process in which the nucleophilic N-terminal amino group forms a protonated dithiazolidine (57.9 kcal mol(-1)). Interestingly, C-S bond cleavage by neighboring group processes have high activation barriers (63.1 kcal mol(-1)) and are thus not expected to be accessible during low-energy CID experiments. In comparison to the energetics of simple amide bond cleavage, these S-S and C-S bond cleavage reactions are higher in energy, which helps rationalize why bond cleavage processes involving the disulfide bond are rarely observed for low-energy CID of peptides with mobile proton(s) containing intermolecular disulfide bonds. On the other hand, the absence of a mobile proton appears to "switch on" disulfide bond cleavage reactions, which can be rationalized by the salt bridge mechanism. This potentially has important ramifications in explaining the prevalence of disulfide bond cleavage in singly protonated peptides under MALDI conditions. PMID:17462910

Lioe, Hadi; O'Hair, Richard A J

2007-06-01

233

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E=N, P, CH; X=H, F, Cl).  

PubMed

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] 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 UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-Lbonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The UE ?-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. 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. PMID:25014545

Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

2014-12-10

234

Promiscuous esterase activities of the C-C hydrolases from Dyella ginsengisoli.  

PubMed

A C-C hydrolase gene (bphD(LA-4)) from strain Dyella ginsengisoli LA-4 was cloned and expressed in Escherichia coli BL21 (DE3). BphD(LA-4) together with another hydrolase MfphA(LA-4), which derived from the same strain, possessed esterase activities. p-Nitrophenyl butyrate was the best substrate for both enzymes. BphD(LA-4) had high catalytic efficiency to p-nitrophenyl benzoate, whereas MfphA(LA-4) had no activity. Homology modeling and docking studies demonstrated that the proper hydrogen bond interaction was important for the reactivity of specific substrate. PMID:22361962

Zhou, Hao; Qu, Yuanyuan; Kong, Chunlei; Wu, Yingge; Zhu, Kang; Yang, Jie; Zhou, Jiti

2012-06-01

235

A Fracture Resisting Molecular Interaction in Trabecular Bone: Sacrificial Bonds and Hidden Length Dissipate Energy as Mineralized Fibrils Separate  

NASA Astrophysics Data System (ADS)

A molecular energy dissipation mechanism in the form of sacrificial bonds and hidden length was previously found in bone constituent molecules of which the efficiency increased with the presence of Ca^2+ ions in the experimental solution. Here we present evidence for how this sacrificial bond-hidden length mechanism contributes to the mechanical properties of the bone composite. From investigations into the nanoscale arrangement of the bone constituents in combination with pico-Newton adhesion force measurements between mineralized collagen fibrils, based on single molecule force spectroscopy, we find evidence that bone consists of mineralized collagen fibrils and a non fibrillar organic matrix which acts as a ``glue'' that holds the mineralized fibrils together. We propose that this ``glue'' resists the separation of mineralized collagen fibrils. Like in the case of the sacrificial bonds in single molecules, the effectiveness of this ``glue'' increases with the presence of Ca^2+ ions. We further investigate how this molecular scale strengthening mechanism increases the fracture toughness of the macroscopic material.

Fantner, Georg E.

2005-03-01

236

On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl  

Microsoft Academic Search

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

Branko Ruscic; Albert F. Wagner; Lawerence B. Harding; Robert L. Asher; David F. Feller; David A. Dixon; Kirk A. Peterson; Yang Song; Ximei Qian; C Y. Ng; Jianbo Liu; Chen Wenwu

2001-01-01

237

Accurate energies of hydrogen bonded nucleic acid base pairs and triplets in tRNA tertiary interactions.  

PubMed

Tertiary interactions are crucial in maintaining the tRNA structure and functionality. We used a combined sequence analysis and quantum mechanics approach to calculate accurate energies of the most frequent tRNA tertiary base pairing interactions. Our analysis indicates that six out of the nine classical tertiary interactions are held in place mainly by H-bonds between the bases. In the remaining three cases other effects have to be considered. Tertiary base pairing interaction energies range from -8 to -38 kcal/mol in yeast tRNA(Phe) and are estimated to contribute roughly 25% of the overall tRNA base pairing interaction energy. Six analyzed posttranslational chemical modifications were shown to have minor effect on the geometry of the tertiary interactions. Modifications that introduce a positive charge strongly stabilize the corresponding tertiary interactions. Non-additive effects contribute to the stability of base triplets. PMID:16461956

Oliva, Romina; Cavallo, Luigi; Tramontano, Anna

2006-01-01

238

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

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 (d{sup 8}, d{sup 6}, d{sup 4}, and d{sup 0}), 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, ?-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 d{sup 6} 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*(PMe{sub 3})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.

Ess, Daniel H; Goddard, William A; Periana, Roy A

2010-01-01

239

Synthesis of tertiary alkyl fluoride centers by asymmetric C?C(F) bond formation  

Microsoft Academic Search

Asymmetric alkylation of pseudoephedrine ?-fluoropropionamide (1) affords ?-alkylated products efficiently and with excellent stereocontrol at the newly formed tertiary alkyl fluoride center. Mild alkaline hydrolysis of the products provides the corresponding carboxylic acids with high enantiomeric excess.

Andrew G. Myers; Lydia McKinstry; James L. Gleason

1997-01-01

240

Total Synthesis of 6-Deoxyerythronolide B via C-C Bond-Forming Transfer Hydrogenation  

PubMed Central

The 14-membered macrolide 6-deoxyerythronolide B is prepared in 14 steps (longest linear sequence) and 20 total steps. Two different methods for alcohol CH-crotylation via transfer hydrogenation are deployed for the first time in target-oriented synthesis. Enyne metathesis is used to form the 14-membered ring. The present approach represents the most concise construction of any erythronolide reported, to date. PMID:23464668

Gao, Xin; Woo, Sang Kook; Krische, Michael J.

2013-01-01

241

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

PubMed Central

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

RajanBabu, T. V.

2009-01-01

242

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

PubMed

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

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

2014-06-01

243

New type polyamides containing disulfide bonds for positive active material of energy storage batteries  

Microsoft Academic Search

Various new types of polyamides [?NHCO?(CH2)2?S?S?(CH2)2?CONH?R?, I–IV: R = ? (CH2)n?, n = 4, 6, 8, 12, V : R = ?(CH2)2?S?S?(CH2)2?] containing disulfide bonds in the polymer backbone are prepared by condensation of 3,3?-dithiodipropionic acid and the corresponding diamine (I–IV: NH2?(CH2)n?NH2, n = 4, 6, 8, 12 and V: cystamine, NH2?(CH2)2?S?S?(CH2)2? NH2] with an interfacial polymerization technique. The polyamides

Hiromori Tsutsumi; Kazunari Fujita

1995-01-01

244

Infrared spectral investigation of steric effects on hydrogen-bond formation in esters of 3-benzoylamino-propionic acids. Part II. Empirical energy calculations  

NASA Astrophysics Data System (ADS)

The geometries and energies of the stable conformations of some t-butyl and ethyl esters of 2,3-disubstituted 3-benzoylaminopropionic acids have been obtained by means of empirical energy functions. Irrespective of the ? and ? substituents, the conformation with gauche NHCOC 6H 5, and COOR groups is of lowest energy. Substitution in the ? position diminishes the torsion angle between these groups but does not adversely affect the orientation of the COOR group necessary for hydrogen-bond formation. The conformational mobility around the C 3-N bond is determined by the steric interactions between the NHCOC 6H 5, group and the other groups at C 3. Hence, the ? substituents are responsible for the formation of the intramolecular hydrogen bond. The results of the empirical energy calculations are in accord with the IR spectral data for the esters.

Ivanovo, Petko M.; Arnaudov, Michail G.; Dobrev, Alexander A.

245

Ultrasonically bonded value assembly  

NASA Technical Reports Server (NTRS)

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.

Salvinski, R. J. (inventor)

1975-01-01

246

Interaction energies in hydrogen-bonded systems: A testing ground for subsystem formulation of density-functional theory  

NASA Astrophysics Data System (ADS)

The formalism based on the total energy bifunctional (E[?I,?II]) is used to derive interaction energies for several hydrogen-bonded complexes (water dimer, HCN-HF, H2CO-H2O, and MeOH-H2O). Benchmark ab initio data taken from the literature were used as a reference in the assessment of the performance of gradient-free [local density approximation (LDA)] and gradient-dependent [generalized gradient approximation (GGA)] approximations to the exchange-correlation and nonadditive kinetic-energy components of E[?I,?II]. On average, LDA performs better than GGA. The average absolute error of calculated LDA interaction energies amounts to 1.0 kJ/mol. For H2CO-H2O and H2O-H2O complexes, the potential-energy curves corresponding to the stretching of the intermolecular distance are also calculated. The positions of the minima are in a good agreement (less than 0.2 A?) with the reference ab initio data. Both variational and nonvariational calculations are performed to assess the energetic effects associated with complexation-induced deformations of molecular electron densities.

Kevorkyants, R.; Dulak, M.; Wesolowski, T. A.

2006-01-01

247

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

NASA Astrophysics Data System (ADS)

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

Ganesan, Aravindhan; Brunger, Michael; Wang, Feng

2010-07-01

248

Organohelium compounds: structures, stabilities and chemical bonding analyses.  

PubMed

This paper deals with the possibility of forming short and relatively strong carbon-helium bonds in small typical organic molecules through substitution of one or several H atoms by He(+). A structural and energetics study (based on high-level calculations) of this unusual bonding, as well as a topological characterization of the resulting cations, is undertaken. Stable species generally requires substitution of about half of the hydrogen atoms for formation. Under these conditions, the number of such species appears to be potentially unlimited. "True" C-He bonds exhibit equilibrium distances ranging from 1.327 (C2H2He2(2+)) to 1.129 Å (He2CO(2+)). The energies of neutral He releasing range from approximately 5 kcal?mol(-1) [He2CO(2+), (Z)-C2H2He2(2+)] to 25 kcal?mol(-1) (C2HHe3(3+)), but remain most frequently around 10 kcal?mol(-1). However, most of He(+)-substituted hydrocarbons are metastable with respect to C-C cleavage, except derivatives of ethene. Atoms in molecules (AIM) and electron localization function (ELF) topological descriptors classify the C-He bond as a weak charge-shift interaction [S. Shaik, D. Danovich, B. Silvi, D. L. Lauvergnat, P. C. Hiberty, Chem. Eur. J. 2005, 11, 6358-6371] in agreement with a recent publication by Rzepa [S. H. Rzepa, Nat. Chem. 2010, 2, 390-393]. He2CO(2+) is the only investigated compound that presents a C-He bonding ELF basin, which indicates a non-negligible covalent contribution to the bond. Other modifications in the electronic structure, such as the breaking of the triple bond in ethyne derivatives or the loss of aromaticity in C6H3He3(3+), are also nicely revealed by the ELF topology. PMID:24488791

Fourré, Isabelle; Alvarez, Elsa; Chaquin, Patrick

2014-02-24

249

VOLUME 77, NUMBER 21 P H Y S I C A L R E V I E W L E T T E R S 18 NOVEMBER 1996 Modeling of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves  

E-print Network

of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves Martin Z. Bazant and Efthimios Kaxiras a systematic test of empirical theories of covalent bonding in solids using an exact procedure to invert ab of a cluster expansion, and extract general features of covalent bonding. We test our methods on silicon

Bazant, Martin Z.

250

Adsorption of Water Monomer and Clusters on Platinum(111) Terrace and Related Steps and Kinks I. Configurations, Energies, and Hydrogen Bonding  

SciTech Connect

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.

Arnadottir, Liney; Stuve, Eric M.; Jonsson, Hannes

2010-10-01

251

Free Energy Landscapes for S-H Bonds in (Cp2Mo2S4)-Mo-star Complexes  

SciTech Connect

Extensive thermochemical data have been determined for a series of complexes derived from Cp*Mo(? S)2(? SMe)(? SH)MoCp* and Cp*Mo(? S)2(? SH)2MoCp*. These data include electrochemical potentials, pKa values, homolytic solution bond dissociation free energies (SBDFEs), and hydride donor abilities in acetonitrile. Thermochemical data ranged from +0.6 to -2.0 V vs FeCp2+/o for electrochemical potentials, 5 to 31 for pKa values, 43 to 68 kcal/mol for homolytic SBDFEs, and 44 to 84 kcal/mol for hydride donor abilities. The observed values for these thermodynamic parameters are comparable to those of many transition metal hydrides, which is consistent with the many parallels in the chemistry of these two classes of compounds. The wealth of thermochemical data are presented in free energy landscapes as a useful approach to visualizing and understanding the relative stabilities of all of the species under specified conditions. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

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

2009-03-23

252

Electronic structure and energies of interatomic bonds in the TiSi2 compound with a C49 crystal structure  

NASA Astrophysics Data System (ADS)

Full-electron calculations of the electronic structure of the TiSi2 compound in the structural modification C49 are performed using the augmented-plane-wave method. The total energy, the electronic band structure, and the density of states are calculated for an extended translational unit cell Ti4Si8, which is formed during the growth of a silicon nanowire on a p-Si substrate. Calculations are also carried out for two orthorhombic unit cells of the nonstoichiometric compositions Ti3Si9 and Ti5Si7. The energies of the interatomic bonds are determined to be E Si-Si = 1.8 eV, E Ti-Ti = 2.29 eV, and E Ti-Si = 4.47 eV. The dependence of the total energy of the unit cell E tot(V) on the unit cell volume V is obtained by optimizing the unit cell volume. The bulk modulus B 0 = 132 GPa is determined from the Murnaghan equation of state for solids and the dependence E tot (V). This value of the bulk modulus is used to estimate the activation energy for interstitial diffusion of silicon atoms Q i(Si) ? 0.8 eV.

Shanina, B. D.; Grigor'ev, N. N.; Klimovskaya, A. I.; Kamins, T. I.

2007-01-01

253

Hydrogen bonding, halogen bonding and lithium bonding: an atoms in molecules and natural bond orbital perspective towards conservation of total bond order, inter- and intra-molecular bonding.  

PubMed

One hundred complexes have been investigated exhibiting D-XA interactions, where X = H, Cl or Li and DX is the 'X bond' donor and A is the acceptor. The optimized structures of all these complexes have been used to propose a generalized 'Legon-Millen rule' for the angular geometry in all these interactions. A detailed Atoms in Molecules (AIM) theoretical analysis confirms an important conclusion, known in the literature: there is a strong correlation between the electron density at the XA bond critical point (BCP) and the interaction energy for all these interactions. In addition, we show that extrapolation of the fitted line leads to the ionic bond for Li-bonding (electrostatic) while for hydrogen and chlorine bonding, it leads to the covalent bond. Further, we observe a strong correlation between the change in electron density at the D-X BCP and that at the XA BCP, suggesting conservation of the bond order. The correlation found between penetration and electron density at BCP can be very useful for crystal structure analysis, which relies on arbitrary van der Waals radii for estimating penetration. Various criteria proposed for shared- and closed-shell interactions based on electron density topology have been tested for H/Cl/Li bonded complexes. Finally, using the natural bond orbital (NBO) analysis it is shown that the D-X bond weakens upon X bond formation, whether it is ionic (DLi) or covalent (DH/DCl) and the respective indices such as ionicity or covalent bond order decrease. Clearly, one can think of conservation of bond order that includes ionic and covalent contributions to both D-X and XA bonds, for not only X = H/Cl/Li investigated here but also any atom involved in intermolecular bonding. PMID:25127185

Shahi, Abhishek; Arunan, Elangannan

2014-10-01

254

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons.  

PubMed

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated. PMID:21303118

Alizadeh, Elahe; Gschliesser, David; Bartl, Peter; Hager, Michaela; Edtbauer, Achim; Vizcaino, Violaine; Mauracher, Andreas; Probst, Michael; Märk, Tilmann D; Ptasi?ska, Sylwia; Mason, Nigel J; Denifl, Stephan; Scheier, Paul

2011-02-01

255

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons  

NASA Astrophysics Data System (ADS)

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)- is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.

Alizadeh, Elahe; Gschliesser, David; Bartl, Peter; Hager, Michaela; Edtbauer, Achim; Vizcaino, Violaine; Mauracher, Andreas; Probst, Michael; Märk, Tilmann D.; Ptasi?ska, Sylwia; Mason, Nigel J.; Denifl, Stephan; Scheier, Paul

2011-02-01

256

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

NASA Technical Reports Server (NTRS)

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.

Chraska, P.; Mclellan, R. B.

1971-01-01

257

Photonics Integration for THz Generation , C.C. Renaud  

E-print Network

Photonics Integration for THz Generation F. Pozzi , C.C. Renaud , D.C. Rogers , I.F. Lealman. The concept of a photonic THz generator is introduced, focusing on the optical part of the phase locking section of the photonic system. Different approaches to the integration of this element of the THz source

Haddadi, Hamed

258

Enhancing Security Check in Visual Studio C\\/C++ Compiler  

Microsoft Academic Search

Buffer overflow exploitation is a major threat to software security. To reduce the threat, Visual studio C\\/C++compiler enables to randomize the addresses of the compiled program in initialization time, and to embed security stack guards by the compiled program in run time. The present paper upgrades the compiler by increasing the compiled program's capabilities in the following aspects: (1) protects

Yongdong Wu

2009-01-01

259

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)

Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2'-deoxycytidine-3'-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3' C-O bond cleavage from the lowest ?* shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?* orbital of the base to the ?* orbital of the glycosidic N-C bond. In addition, the metastable state formed after impinging LEE (0-1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N-C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ˜35-55 fs. Comparison of salient features of the two dissociation events, i.e., 3' C-O single strand break and glycosidic N-C bond cleavage in 3'-dCMPH molecule are also provided.

Bhaskaran, Renjith; Sarma, Manabendra

2014-09-01

260

S-OO bond dissociation energies and enthalpies of formation of the thiomethyl peroxyl radicals CH3S(O)nOO (n=0,1,2)  

NASA Astrophysics Data System (ADS)

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, CH3S(O)2OO, which contains two sulfonic type oxygen atoms followed by the methylthiyl peroxyl radical, CH3SOO. The methylsulfinyl peroxyl radical, CH3S(O)OO, which contains only one sulfonic type oxygen shows the least stability with regard to dissociation to CH3S(O)+O2. This stabilization trend is nicely reflected in the variations of the S-OO bond distance which is found to be shortest in CH3S(O)2OO and longest in CH3S(O)OO.

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

2014-10-01

261

Internal Energy, Specific Heat and Correlation Function of the Bond-Random Ising Model  

Microsoft Academic Search

Gauge transformations of the random Ising model are shown to be useful in obtaining rigorous results on thermodynamic quantities. In a restricted region of the phase diagram, we obtain the exact value of the internal energy, rigorous upper bound to the specific heat and a few rigorous relations concerning the correlation functions. In particular it is pointed out that the

Hidetoshi Nishimori

1981-01-01

262

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

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.

Christian, Jerry D.

1973-01-01

263

Production of charged pions, kaons and antikaons in relativistic C + C and C + Au collisions  

Microsoft Academic Search

:   Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies\\u000a of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann\\u000a distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating\\u000a nucleon M(?+)\\/A

F. Laue; I. Böttcher; M. Debowski; A. Förster; E. Grosse; P. Koczon; B. Kohlmeyer; M. Mang; M. Menzel; L. Naumann; H. Oeschler; F. Pühlhofer; E. Schwab; P. Senger; Y. Shin; J. Speer; H. Ströbele; C. Sturm; G. Surówka; F. Uhlig; A. Wagner; W. Walus

2000-01-01

264

Surface structure, bonding, and dynamics: The universality of zincblende (110) potential energy surfaces  

SciTech Connect

Using a tight-binding, total energy (TBTE) model we examine the hypothesis that the potential energy surfaces (PES) describing the (110) cleavage faces of the tetrahedrally coordinated, zincblende-structure compound semiconductors exhibit a common ``universal`` form if expressed in terms of suitably scaled parameters. TBTE calculations on both III-V and II-VI compounds reveal a linear scaling with bulk lattice constant of the geometric parameters of the reconstructed surfaces. This scaling is analogous to that found using low-energy, electron-diffraction surface-structure determination. The surface atomic force constants (found from a TBTE calculation) also scale monotonically with the lattice constant. Using TBTE models proposed previously for GaP, GaAs, GaSb, InP, and ZnSe, we find that the force constants scale as the inverse square of the bulk lattice constant. These results suggest that if distances are measured in units of the bulk lattice constant, the PES may be a universal function for the cleavage surface of zincblende-structure compound semiconductors, on average, with small fluctuations from this average occurring in individual materials. 22 refs., 5 figs., 1 tab.

Godin, T.J.; LaFemina, J.P.

1991-11-01

265

Energy-efficient green catalysis: supported gold nanoparticle-catalyzed aminolysis of esters with inert tertiary amines by C-O and C-N bond activations.  

PubMed

Catalyzed by supported gold nanoparticles, an aminolysis reaction between various aryl esters and inert tertiary amines by C-O and C-N bond activations has been developed for the selective synthesis of tertiary amides. Comparison studies indicated that the gold nanoparticles could perform energy-efficient green catalysis at room temperature, whereas Pd(OAc)2 could not. PMID:24935132

Bao, Yong-Sheng; Baiyin, Menghe; Agula, Bao; Jia, Meilin; Zhaorigetu, Bao

2014-07-18

266

Carbon-carbon bond cleavage of 1,2-hydroxy ethers b7 vanadium(V) dipicolinate complexes  

SciTech Connect

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}).

Hanson, Susan K [Los Alamos National Laboratory; Gordon, John C [Los Alamos National Laboratory; Thorn, David L [Los Alamos National Laboratory; Scott, Brian L [Los Alamos National Laboratory; Baker, R Tom [Los Alamos National Laboratory

2009-01-01

267

Compositions and chemical bonding in ceramics by quantitative electron energy-loss spectrometry  

SciTech Connect

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.

Bentley, J.; Horton, L.L. [Oak Ridge National Lab., TN (United States); McHargue, C.J. [Tennessee Univ., Knoxville, TN (United States); McKernan, S.; Carter, C.B. [Minnesota Univ., Minneapolis, MN (United States). Dept. of Chemical Engineering; Revcolevschi, A. [Univ. de Paris-Sud, Lab. de Chemie des Solides (France); Tanaka, S.; Davis, R.F. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering

1993-12-31

268

The Turbulent Alfvenic Aurora C. C. Chaston,1  

E-print Network

The Turbulent Alfve´nic Aurora C. C. Chaston,1 C. Salem,1 J. W. Bonnell,1 C. W. Carlson,1 R. E) It is demonstrated from observations that the Alfve´nic aurora may be powered by a turbulent cascade transverse acceleration of electrons from near-Earth space to form the aurora. We find that regions of Alfve´n wave

California at Berkeley, University of

269

Water's Hydrogen Bond Strength  

E-print Network

Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands, decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and chemical properties that evidence the particular uniqueness of liquid water. If aqueous hydrogen bonds were actually somewhat stronger then water would behave similar to a glass, whereas if they were weaker then water would be a gas and only exist as a liquid at sub-zero temperatures. The overall conclusion of this investigation is that water's hydrogen bond strength is poised centrally within a narrow window of its suitability for life.

Martin Chaplin

2007-06-10

270

Insulation bonding test system  

NASA Technical Reports Server (NTRS)

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.

Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (inventors)

1984-01-01

271

902 SULFAPYRIDINE Fig. 2. Packing diagram of SP IV, showing the hydrogen bonds. For  

E-print Network

902 SULFAPYRIDINE C C A Fig. 2. Packing diagram of SP IV, showing the hydrogen bonds. For clarity, thus leading to the proliferation of polymorphic structures. The hydrogen-bonding motifs of polymorphs distinguish the current structure is a pair of hydrogen bonds of the type N(3)-H(N3)...N(1) forming a cyclic

Paris-Sud XI, Université de

272

Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy  

SciTech Connect

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.

Zhu, Y.; Wang, F.; Graetz, J.; Moreno, M.S.; Ma, C.; Wu, L.; Volkov, V.

2011-02-01

273

Chemical distribution and bonding of lithium in intercalated graphite: identification with optimized electron energy loss spectroscopy.  

PubMed

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

Wang, Feng; Graetz, Jason; Moreno, M Sergio; Ma, Chao; Wu, Lijun; Volkov, Vyacheslav; Zhu, Yimei

2011-02-22

274

Photochemical tissue bonding  

DOEpatents

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.

Redmond, Robert W. (Brookline, MA); Kochevar, Irene E. (Charlestown, MA)

2012-01-10

275

Spectroscopic constants of diatomic molecules computed correcting Hartree-Fock or general-valence-bond potential-energy curves with correlation-energy functionals  

NASA Astrophysics Data System (ADS)

The Kohn-Sham energy with exact exchange [using the exact Hartree-Fock (HF) exchange but an approximate correlation-energy functional] may be computed very accurately by adding the correlation obtained from the HF density to the total HF energy. Three density functionals are used: local spin density (LSD), LSD with self-interaction correction, and LSD with generalized gradient correction. This scheme has been extended (Lie-Clementi, Colle-Salvetti, and Moscardo-San-Fabian) to be used with general-valence-bond (GVB) energies and wave functions, so that the extra correlation included in the GVB energy is not counted again. The effect of all these approximate correlations on HF or GVB spectroscopic constants (Re,?e, and De) is studied. Approximate relations showing how correlation affects them are derived, and may be summarized as follows: (1) the effect on Re and ?e depends only on the correlation derivative at Re, and (2) the effect on De depends mainly on the correlation difference between quasidissociated and equilibrium geometries. A consequence is that all the correlation corrections tested here give larger ?e and De and shorter Re than the uncorrected HF or GVB values. This trend is correct for De for both HF and GVB. For Re and ?e, it is correct in most cases for GVB, but it often fails for the HF cases. A comparison is made with Kohn-Sham calculations with both exchange and correlation approximated. As a final conclusion, it is found that, within the present scheme, a qualitatively correct HF or GVB potential-energy curve, together with a correlation-energy approximation with correct dissociation behavior, is crucial for obtaining good estimates of spectroscopic constants.

Pérez-Jordá, José M.; San-Fabián, Emilio; Moscardó, Federico

1992-04-01

276

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)

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.

Morscher, Gregory N.; Singh, Mrityunjay; Shpargel, Tarah; Asthana, Rajiv

2006-01-01

277

Ab initio study of symmetrical tilt grain boundaries in bcc Fe: structural units, magnetic moments, interfacial bonding, local energy and local stress  

NASA Astrophysics Data System (ADS)

We present first-principle calculations on symmetric tilt grain boundaries (GBs) in bcc Fe. Using density functional theory (DFT), we studied the structural, electronic and magnetic properties of ?3(111) and ?11(332) GBs formed by rotation around the [110] axis. The optimized structures, GB energies and GB excess free volumes are consistent with previous DFT and classical simulation studies. The GB configurations can be interpreted by the structural unit model as given by Nakashima and Takeuchi (2000 ISIJ 86 357). Both the GBs are composed of similar structural units of three- and five-membered rings with different densities at the interface according to the rotation angle. The interface atoms with larger atomic volumes reveal higher magnetic moments than the bulk value, while the interface atoms with shorter bond lengths have reduced magnetic moments in each GB. The charge density and local density of states reveal that the interface bonds with short bond lengths have more covalent nature, where minority-spin electrons play a dominant role as the typical nature of ferromagnetic Fe. In order to understand the structural stability of these GBs, we calculated the local energy and local stress for each atomic region using the scheme of Shiihara et al (2010 Phys. Rev. B 81 075441). In each GB, the interface atoms with larger atomic volumes and enhanced magnetic moments reveal larger local energy increase and tensile stress. The interface atoms constituting more covalent-like bonds with reduced magnetic moments have lower local energy increase, contributing to the stabilization, while compressive stress is generated at these atoms. The relative stability between the two GBs can be understood by the local energies at the structural units. The local energy and local stress analysis is a powerful tool to investigate the structural properties of GBs based on the behavior of valence electrons.

Bhattacharya, Somesh Kr; Tanaka, Shingo; Shiihara, Yoshinori; Kohyama, Masanori

2013-04-01

278

Aromaticity of simple hydrocarbons evaluated through computing isodesmic energies, rings bond order uniformity, and HOMO–LUMO energy gaps  

Microsoft Academic Search

The AM1 computational study of open-chain conjugated and cyclic chemical systems was performed with the aim of evaluating their aromatic character through frontier molecular orbital (FMO) change during the course of the ring formation. The change of the FMO energy difference was also used to determine the relative stability of fused unsaturated cyclic compounds. The relative change of the FMO

Branko S Jursic

1999-01-01

279

A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes B···XY and B···HX, where X and Y are halogen atoms.  

PubMed

It is shown by considering 76 halogen- and hydrogen-bonded complexes BXY and BHX (where B is a Lewis base N2, CO, C2H2, C2H4, H2S, HCN, H2O, PH3 or NH3 and X, Y are F, Cl, Br or I) that the intermolecular stretching force constants k? (determined from experimental centrifugal distortion constants via a simple model) and the intermolecular dissociation energies D? (calculated at the CCSD(T)(F12*)/cc-pVDZ-F12 level of theory) are related by D? = C?k?, where C? = 1.50(3) × 10(3) m(2) mol(-1). This suggests that one-dimensional functions implying direct proportionality of D? and k?, (e.g. a Morse or Rydberg function) might serve as reduced radial potential energy functions for such complexes. PMID:24827860

Legon, Anthony C

2014-06-28

280

Coulombic Models in Chemical Bonding.  

ERIC Educational Resources Information Center

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).…

Sacks, Lawrence J.

1986-01-01

281

Bonding and Energy Dissipation in a Nanohook Assembly Savas Berber, Young-Kyun Kwon,* and David Tomanek  

E-print Network

over conven- tional adhesives and welding, including thermal stability to 4000 K, and a self-repair surfaces, are a nanoscale counterpart of velcro fasteners, forming tough bonds with a capability of self-repair

282

Splitting rules for the electronic energy spectra of two-dimensional Thue Morse lattices with three kinds of atom and one bond length  

NASA Astrophysics Data System (ADS)

In this paper we study the splitting rules of the electronic energy spectra for two-dimensional Thue-Morse lattices with three kinds of atom and one bond length by means of a decomposition-decimation method. It is found that the symmetries of systems, boundary conditions, and then the branching types of energy spectra for the second and third hierarchies are all related to generations. For example, under the second-order approximation, the energy spectra of four-atom A molecules split in the proportion of one-to-five for even generations and one-to-three for odd ones. The analytical results are confirmed by numerical simulations.

Hu, Xubo; Yang, Xiangbo

2005-08-01

283

Strength of Hydrogen Bonds in NIDHI ARORA, B. JAYARAM  

E-print Network

-- --Hydrogen Bonds in Helices NIDHI ARORA, B. JAYARAM Department of Chemistry November 1996 > hydrogen Z .bonding energies with the experiment. 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 1245 1252, 1997 Keywords: hydrogen bonding

Jayaram, Bhyravabotla

284

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

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)?(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

Duarte, Darío J R; Sosa, Gladis L; Peruchena, Nélida M

2013-05-01

285

Charged pion production in C+C and Ar+KCl collisions measured with HADES  

E-print Network

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

The HADES Collaboration; P. Tlusty; G. Agakishiev; A. Balanda; G. Bellia; D. Belver; A. Belyaev; A. Blanco; M. Boehmer; J. L. Boyard; P. Braun-Munzinger; P. Cabanelas; E. Castro; S. Chernenko; T. Christ; M. Destefanis; J. Diaz; F. Dohrmann; A. Dybczak; L. Fabbietti; O. Fateev; P. Finocchiaro; P. Fonte; J. Friese; I. Froehlich; T. Galatyuk; J. A. Garzon; R. Gernhaeuser; A. Gil; C. Gilardi; M. Golubeva; D. Gonzalez-Diaz; E. Grosse; F. Guber; M. Heilmann; T. Hennino; R. Holzmann; A. Ierusalimov; I. Iori; A. Ivashkin; M. Jurkovic; B. Kaempfer; K. Kanaki; T. Karavicheva; D. Kirschner; I. Koenig; W. Koenig; B. W. Kolb; R. Kotte; A. Kozuch; A. Krasa; F. Krizek; R. Kruecken; W. Kuehn; A. Kugler; A. Kurepin; J. Lamas-Valverde; S. Lang; J. S. Lange; K. Lapidus; T. Liu; L. Lopes; M. Lorenz; L. Maier; A. Mangiarotti; J. Marin; J. Markert; V. Metag; B. Michalska; J. Michel; D. Mishra; E. Moriniere; J. Mousa; C. Muentz; L. Naumann; R. Novotny; J. Otwinowski; Y. C. Pachmayer; M. Palka; Y. Parpottas; V. Pechenov; O. Pechenova; T. Perez Cavalcanti; J. Pietraszko; W. Przygoda; B. Ramstein; A. Reshetin; A. Rustamov; A. Sadovsky; P. Salabura; A. Schmah; R. Simon; Yu. G. Sobolev; S. Spataro; B. Spruck; H. Stroebele; J. Stroth; C. Sturm; M. Sudol; A. Tarantola; K. Teilab; M. Traxler; R. Trebacz; H. Tsertos; I. Veretenkin; V. Wagner; M. Weber; M. Wisniowski; J. Wuestenfeld; S. Yurevich; Y. Zanevsky; P. Zhou; P. Zumbruch

2009-06-12

286

Improved bond-orbital calculations of rotation barriers and geometrical isomerism  

NASA Astrophysics Data System (ADS)

Rotational barriers in 19 molecules possessing a single internal rotation angle around a B-N, C-C, C-N, C-O, N-N, N-O, O-O central bond and geometrical isomerism in 3 molecules possessing a N=N double bond have been studied ab initio by the improved bond-orbital method. The first approximation, where the chemical groups occurring in these molecules are described in terms of non-orthogonal SCF bond-orbitals constructed from energy-optimized bond hybrids and polarities, is improved in second order of perturbation theory by admitting single excitations from bonding to antibonding orbitals and accounting for induction including exchange (polarization and delocalization). The molecules studied possess 16 to 34 electrons and a variety of functional groups differing in their chemical structure (CH3, NH2, OH, NO, CHO, CH=CH2, NH= and some of their F-derivatives). The overall results obtained using a STO-3G basis, rigid rotation and experimental geometries, are close to experiment and to the corresponding MO-SCF calculations in the same basis, but individual energy components allow us to establish a clear correlation between barriers and chemical structure, grouping the 22 molecules into 4 classes. In the first class (CH3-X molecules and 1,2-difluoroethane) barriers are dominated by steric interactions (Pauli repulsions) which are sufficiently well described in first order. In the second class (N2H4, NH2OH, NH=NH and its fluoroderivatives, molecules all possessing lone pairs adjacent to the central bond) barriers are due to competition between first-order Pauli repulsion and characteristic geminal ?-?* delocalization occurring in second order. In the third class (1,3-butadiene, glyoxal, formamide and formic acid, molecules possessing double bonds and/or ?-lone pairs at both ends of the rotation axis) barriers are dominated by large ?-?* vicinal delocalization. In the fourth class (HNO2, H2O2 and its fluoroderivatives, molecules presenting both previous structural features) barriers result from competition between all preceding effects.

Musso, Gian Franco; Magnasco, Valerio

287

Conversion of levulinate into succinate through catalytic oxidative carbon-carbon bond cleavage with dioxygen.  

PubMed

Grand Cleft Oxo: Levulinate, available from biomass, is oxidized into succinate through manganese(III)-catalyzed selective cleavage of C?C bonds with molecular oxygen. In addition to levulinate, a wide range of aliphatic methyl ketones also undergo oxidative C?C bond cleavage at the carbonyl group. This procedure offers a route to valuable dicarboxylic acids from biomass resources by nonfermentive approaches. PMID:23922234

Liu, Junxia; Du, Zhongtian; Lu, Tianliang; Xu, Jie

2013-12-01

288

The Dissociation Energies of CH4 and C2H2 Revisited  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

289

The antimony-group 11 chemical bond: dissociation energies of the diatomic molecules CuSb, AgSb, and AuSb.  

PubMed

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°(0), 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°(0), 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. PMID:24527913

Carta, V; Ciccioli, A; Gigli, G

2014-02-14

290

Theoretical study of bond distances and dissociation energies of actinide oxides AnO and AnO2.  

PubMed

In the present study we evaluated trends in the bond distances and dissociation enthalpies of actinide oxides AnO and AnO(2) (An = Th-Lr) on the basis of consistent computed data obtained by using density functional theory in conjunction with relativistic small-core pseudopotentials. Computations were carried out on AnO (An = Th-Lr) and AnO(2) (An = Np, Pu, Bk-Lr) species, while for the remaining AnO(2) species recent literature data (Theor. Chem. Acc. 2011, 129, 657) were utilized. The most important computed properties include the geometries, vibrational frequencies, dissociation enthalpies, and several excited electronic states. These molecular properties of the late actinide oxides (An = Bk-No) are reported here for the first time. We present detailed analyses of the bond distances, covalent bonding properties, and dissociation enthalpies. PMID:22471700

Kovács, Attila; Pogány, Peter; Konings, Rudy J M

2012-04-16

291

Bonded Lubricants  

NASA Technical Reports Server (NTRS)

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.

1977-01-01

292

Defect structures in deformed F.C.C. metals  

SciTech Connect

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.

Dai, Y.; Victoria, M. [Ecole Polytechnique Federale de Lausanne, Villigen PSI (Switzerland). CRPP-Fusion Technology Div.] [Ecole Polytechnique Federale de Lausanne, Villigen PSI (Switzerland). CRPP-Fusion Technology Div.

1997-08-01

293

The effect of CH3, F and NO2 substituents on the individual hydrogen bond energies in the adenine-thymine and guanine-cytosine base pairs  

Microsoft Academic Search

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as\\u000a X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The\\u000a electron withdrawing (EW) substituents (F and NO2) increase the total binding energy

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

2010-01-01

294

Basics of Fidelity Bonding.  

ERIC Educational Resources Information Center

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…

Kahn, Steven P.

295

High-accuracy coupled-cluster computations of bond dissociation energies in SH, H2S, and H2O  

NASA Astrophysics Data System (ADS)

The first and second bond dissociation enthalpies of H2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory. Corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D0)(S-H=349.9 and D0)(HS-H=375.8 kJ mol-1. Together these imply an atomization enthalpy for H2S about 1 kJ mol-1 larger than literature evaluations. Consideration of exchange of a second H atom from OH to SH yields D0)(HS-H=376.2 kJ mol-1. The two computations of D0)(HS-H lie within 0.5 kJ mol-1 of a recent spectroscopic measurement of D0)(HS-H=376.24plus-or-minus0.05 kJ mol-1 [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D2S are also considered. There is also accord to within 1.5 kJ mol-1 with D0)(S-H=348.4plus-or-minus0.8 kJ mol-1, which we derive from the experimental literature. We propose revised enthalpies of formation, Delta]fH0(2[Pi]3/2)SH=142.6[plus-or-minus0.8 kJ mol-1 and Delta]fH298.15)(SH=143.1[plus-or-minus0.8 kJ mol-1. The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol-1 uncertainty. We also obtain D0)(H-OH=492.6 kJ mol-1, which compares well with recent experiments.

Peebles, Lynda R.; Marshall, Paul

2002-08-01

296

Sensor/ROIC Integration using Oxide Bonding  

E-print Network

We explore the Ziptronix Direct Bond Interconnect technology 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 microns.

Zhenyu Ye; for the Fermilab Pixel R&D Group

2009-02-16

297

Excited state potential energy surfaces and their interactions in Fe(IV)[double bond, length as m-dash]O active sites.  

PubMed

The non-heme ferryl active sites are of significant interest for their application in biomedical and green catalysis. These sites have been shown to have an S = 1 or S = 2 ground spin state; the latter is functional in biology. Low-temperature magnetic circular dichroism (LT MCD) spectroscopy probes the nature of the excited states in these species including ligand-field (LF) states that are otherwise difficult to study by other spectroscopies. In particular, the temperature dependences of MCD features enable their unambiguous assignment and thus determination of the low-lying excited states in two prototypical S = 1 and S = 2 NHFe(IV)[double bond, length as m-dash]O complexes. Furthermore, some MCD bands exhibit vibronic structures that allow mapping of excited-state interactions and their effects on the potential energy surfaces (PESs). For the S = 2 species, there is also an unusual spectral feature in both near-infrared absorption and MCD spectra - Fano antiresonance (dip in Abs) and Fano resonance (sharp peak in MCD) that indicates the weak spin-orbit coupling of an S = 1 state with the S = 2 LF state. These experimental data are correlated with quantum-chemical calculations that are further extended to analyze the low-lying electronic states and the evolution of their multiconfigurational characters along the Fe-O PESs. These investigations show that the lowest-energy states develop oxyl Fe(III) character at distances that are relevant to the transition state (TS) for H-atom abstraction and define the frontier molecular orbitals that participate in the reactivity of S = 1 vs. S = 2 non-heme Fe(IV)[double bond, length as m-dash]O active sites. The S = 1 species has only one available channel that requires the C-H bond of a substrate to approach perpendicular to the Fe-oxo bond (the ? channel). In contrast, there are three channels (one ? and two ?) available for the S = 2 non-heme Fe(IV)[double bond, length as m-dash]O system allowing C-H substrate approach both along and perpendicular to the Fe-oxo bond that have important implications for enzymatic selectivity. PMID:24916844

Srnec, Martin; Wong, Shaun D; Solomon, Edward I

2014-11-12

298

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory  

E-print Network

that the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction. Note method is a reasonable model for VB simulations of condensed phase reactions. The results indicate

Minnesota, University of

299

Water-stabilized three- and four-atom palladium clusters as highly active catalytic species in ligand-free C-C cross-coupling reactions.  

PubMed

Elite cliques: Palladium clusters with three and four atoms were found to be the catalytically active species for ligand-free palladium-catalyzed C?C bond-forming reactions. These palladium cluster species could be stabilized in water and stored for long periods of time for use on demand with no loss of activity. High yields of products and turnover frequencies (TOFs) of up to 10(5) ?h(-1) were observed. PMID:24038914

Leyva-Pérez, Antonio; Oliver-Meseguer, Judit; Rubio-Marqués, Paula; Corma, Avelino

2013-10-25

300

Electron transfer in pnicogen bonds.  

PubMed

As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines XnPH3-n complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n ? ?*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO2 and CN, i.e., n ? d?*, which results from the interaction between the ? orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of ?-hole in pnicogen bonds. PMID:24588109

Guan, Liangyu; Mo, Yirong

2014-10-01

301

Selective activation of carbon-carbon bonds next to a carbonyl group  

NASA Astrophysics Data System (ADS)

ORGANOMETALLIC complexes are used to effect a wide range of catalytic transformations in organic synthesis, such as the activation of C-H bonds1,2. Carbon-carbon bonds, however, are generally unreactive towards transition metals under homogeneous conditions. C-C bond activation by a process of oxidative addition to soluble transition-metal complexes has been limited mostly to stoichiometric (not catalytic) reactions1,3-7,18, to highly strained substrates such as cyclopropane and cubane1,8-11 or to chelating ketones19. Here we present a synthetically useful process of selective C-C bond activation in which the C-C bond adjacent to a carbonyl group is opened by insertion of a soluble rhodium(I) complex. The resulting organometallic intermediate can be transformed to a variety of products in a way that regenerates the rhodium complex. We anticipate that this catalytic scheme will have considerable utility in organic synthesis.

Murakami, Masahiro; Amii, Hideki; Ito, Yoshihiko

1994-08-01

302

Methodology for hardware\\/software co-verification in C\\/C++ (short paper)  

Microsoft Academic Search

In this paper we present our C\\/C++-based design envi- ronment for hardware\\/software co-verification. Our approach is to use C\\/C++ to describe both hardware and software throughout the design flow. Our methodology supports the efficient mapping of C\\/ C++ functional descriptions directly into hardware and software. The advantages of a C\\/C++-based flow from the verification point of view are presented. The

Luc Séméria; Abhijit Ghosh

2000-01-01

303

Observations on the strength of hydrogen bonding  

Microsoft Academic Search

Both proton transfer and hydrogen bonding play important roles in biological systems. In order to measure hydrogen bond basicity,\\u000a we are building a new scale that differs significantly from the pKa scale of proton transfer basicity. The strength of hydrogen bond acceptors (HBAs) is measured from the Gibbs energy change\\u000a ?GHB for the formation of 1:1 hydrogen bonding complexes between

Christian Laurence; Michel Berthelot

2000-01-01

304

Effect of temperature on the electron attachment and detachment properties of c-C{sub 4}F{sub 6}  

SciTech Connect

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.

Datskos, P.G.; Christophorou, L.G. [Oak Ridge National Lab., TN (United States)]|[Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy; Carter, J.G. [Oak Ridge National Lab., TN (United States)

1994-06-01

305

Binding energies and 19F nuclear magnetic deshielding in paramagnetic halogen-bonded complexes of TEMPO with haloperfluorocarbons.  

PubMed

19F NMR measurements and theoretical calculations were performed to study paramagnetic complexes of iodoperfluorocarbons with stable nitroxide radicals. Contrary to what is usually measured for diamagnetic halogen-bonded complexes involving iodoperfluorocarbons, it was found that the formation of complexes with the 2,2,6,6-tetramethyl(piperidin-1-yloxyl) (TEMPO) radical determines downfield shifts in the 19F NMR spectra. The experimental finding was confirmed by calculating nuclear shielding using density functional theory and correcting the isotropic diamagnetic (19)F chemical shift with contact interactions evaluated from the hyperfine coupling tensor. The computational analysis of the interaction between CF3I and TEMPO, by using DFT and MP2 theories, showed that the occurrence of the halogen bond between the interacting partners is associated with a significant charge transfer to CF3I and that the measured downfield shift is due to the occurring spin transfer. PMID:18795762

Cavallotti, Carlo; Metrangolo, Pierangelo; Meyer, Franck; Recupero, Francesco; Resnati, Giuseppe

2008-10-01

306

Comparative study on the nonadditivity of methyl group in lithium bonding and hydrogen bonding  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations at the second-order Moeller-Plesset (MP2) level with 6-311++G(d,p) basis set have been performed on the lithium-bonded and hydrogen-bonded systems. The interaction energy, binding distance, bond length, and stretch frequency in these systems have been analyzed to study the nonadditivity of methyl group in the lithium bonding and hydrogen bonding. In the complexes involving with NH3, the introduction of one methyl group into NH3 molecule results in an increase of the strength of lithium bonding and hydrogen bonding. The insertion of two methyl groups into NH3 molecule also leads to an increase of the hydrogen bonding strength but a decrease of the lithium bonding strength relative to that of the first methyl group. The addition of three methyl groups into NH3 molecule causes the strongest hydrogen bonding and the weakest lithium bonding. Although the presence of methyl group has a different influence on the lithium bonding and hydrogen bonding, a negative nonadditivity of methyl group is found in both interactions. The effect of methyl group on the lithium bonding and hydrogen bonding has also been investigated with the natural bond orbital and atoms in molecule analyses.

Li, Qingzhong; Cheng, Jianbo; Li, Wenzuo; Gong, Baoan; Sun, Jiazhong

307

The enthalpy of formation of fullerene fluoride C60F18 and the C-F bond energy  

NASA Astrophysics Data System (ADS)

The enthalpy of combustion of crystalline fullerene fluoride C60F18 was determined in an isoperibolic calorimeter with a rotating platinized bomb, and the enthalpy of formation of the compound was calculated. The enthalpy of sublimation of C60F18 measured earlier was used to calculate the enthalpy of formation of fullerene fluoride in the gas phase and the mean enthalpy of dissociation of C-F bonds in this compound.

Papina, T. S.; Luk'yanova, V. A.; Goryunkov, A. A.; Ioffe, I. N.; Gol'Dt, I. V.; Buyanovskaya, A. G.; Kabaeva, N. M.; Sidorov, L. N.

2007-10-01

308

Simulation investigations in the binding energy and mechanical properties of HMX-based polymer-bonded explosives  

Microsoft Academic Search

The molecular simulations of the well-known high explosive ?-HMX (cyclotetramethylene tetranitramine) and its fluorine containing\\u000a polymer-bonded explosives (PBXs) were carried out with the combination method of quantum mechanics, molecular mechanics and\\u000a molecular dynamics. The atomic cluster model, containing the ?-HMX molecule and the polymer molecule whose chain dimension\\u000a was about the same as ?-HMX’s, was fully optimized by AM1 and

Jijun Xiao; Guoyong Fang; Guangfu Ji; Heming Xiao

2005-01-01

309

Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon  

Microsoft Academic Search

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si,Deltatheta, and the width of the transverse optical Raman peak, Gamma, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for Deltatheta and Gamma are used. This reduced dispersion in the predicted values of Deltatheta together with the broad agreement

P. Roura; J. Farjas; P. Roca I Cabarrocas

2008-01-01

310

The effect of CH3, F and NO2 substituents on the individual hydrogen bond energies in the adenine-thymine and guanine-cytosine base pairs.  

PubMed

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as X-adenine-thymine (X-A-T), X-thymine-adenine (X-T-A), X-guanine-cytosine (X-G-C), and X-cytosine-guanine (X-C-G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6-311++G(d,p) basis set. The electron withdrawing (EW) substituents (F and NO(2)) increase the total binding energy (DeltaE) of X-G-C derivatives and the electron donating (ED) substituent (CH(3)) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH(3) in the 1 position and F in the 5 position, which in both cases the DeltaE value decreases negligibly small. With minor exceptions (X=8-CH(3), 8-F, and 9-NO(2)), both ED and EW substituents increase slightly the DeltaE values of X-A-T derivatives. The individual HB energies (E (HB)s) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the role of atoms entered H-bonding. The remarkable change is observed for NO(2) substituted derivative in each case. PMID:20352295

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

2010-05-01

311

Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu/Al{sub 2}O{sub 3} interface  

SciTech Connect

Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu/Al{sub 2}O{sub 3} heterointerfaces with hollow and on-top configurations were theoretically investigated by using a first principles orthogonalized linear combination of atomic orbitals method. From the chemical bonding analysis, it was found that the hollow configuration has stronger ionic and covalent bondings as compared with the on-top configuration, and the weakness of the on-top configuration originates from the strong antibonding interactions between an interfacial oxygen and the second near neighbor Cu. Detailed analysis using overlap population diagrams revealed the formation mechanism of the strong antibonding interactions in the on-top configuration. In the oxygen K ELNES calculation, a prepeak feature appears in both configurations and it was predicted that the prepeak for the on-top configuration is larger than that for the hollow configuration. The overlap population diagrams elucidated that the prepeak is mainly composed of the O-Cu antibonding interactions, and the larger prepeak of the on-top configuration originates from the larger O-Cu interactions. The dependence of O-K ELNES on the direction of the momentum transfer vector was also discussed. Knowledge of the responsible direction of the momentum transfer vector in relation to the interface orientation was concluded to be indispensable in order to discuss detailed profiles of the ELNES from metal/ceramic heterointerfaces. This study reveals the effect of the atomic configuration of the interface to the chemical bondings, interface strength, and ELNES.

Mizoguchi, Teruyasu; Sasaki, Takeo; Matsunaga, Katsuyuki; Ikuhara, Yuichi [Institute of Engineering Innovation, The University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8656 (Japan); Tanaka, Shingo; Kohyama, Masanori [Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda 563-8577 (Japan); Yamamoto, Takahisa [Department of Advanced Materials Science, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)

2006-12-15

312

Effect of axial ligand, spin state, and hydrogen bonding on the inner-sphere reorganization energies of functional models of cytochrome p450.  

PubMed

Using a combination of self-assembly and synthesis, bioinspired electrodes having dilute iron porphyrin active sites bound to axial thiolate and imidazole axial ligands are created atop self-assembled monolayers (SAMs). Resonance Raman data indicate that a picket fence architecture results in a high-spin (HS) ground state (GS) in these complexes and a hydrogen-bonding triazole architecture results in a low-spin (LS) ground state. The reorganization energies (?) of these thiolate- and imidazole-bound iron porphyrin sites for both HS and LS states are experimentally determined. The ? of 5C HS imidazole and thiolate-bound iron porphyrin active sites are 10-16 kJ/mol, which are lower than their 6C LS counterparts. Density functional theory (DFT) calculations reproduce these data and indicate that the presence of significant electronic relaxation from the ligand system lowers the geometric relaxation and results in very low ? in these 5C HS active sites. These calculations indicate that loss of one-half a ? bond during redox in a LS thiolate bound active site is responsible for its higher ? relative to a ?-donor ligand-like imidazole. Hydrogen bonding to the axial ligand leads to a significant increase in ? irrespective of the spin state of the iron center. The results suggest that while the hydrogen bonding to the thiolate in the 5C HS thiolate bound active site of cytochrome P450 (cyp450) shifts the potential up, resulting in a negative ?G, it also increases ? resulting in an overall low barrier for the electron transfer process. PMID:25238648

Bandyopadhyay, Sabyasachi; Rana, Atanu; Mittra, Kaustuv; Samanta, Subhra; Sengupta, Kushal; Dey, Abhishek

2014-10-01

313

OH bond dissociation energies in hydroquinones and 4-hydroxyphenoxyl radicals and effect of solvation on the kinetics of reactions involving hydroquinones and semiquinone radicals  

Microsoft Academic Search

The O-H bond dissociation energies (D\\u000a OH) in the molecules of 2,5-dimethylhydroquinone (1) and 2,5-di-tert-butylhydroquinone (2) and in the corresponding semiquinone radicals (5 and 8, respectively) were estimated by the method of intersecting parabolas (IP) from experimental data on the rate constants for\\u000a the reactions of these compounds with N-phenyl-1,4-benzoquinonemonoimine (3) and using the density functional B3LYP\\/6-31+G* quantum chemical calculations.

V. T. Varlamov; B. E. Krisyuk; A. V. Antonov

2005-01-01

314

Halogen bonding (X-bonding): A biological perspective  

PubMed Central

The concept of the halogen bond (or X-bond) has become recognized as contributing significantly to the specificity in recognition of a large class of halogenated compounds. The interaction is most easily understood as primarily an electrostatically driven molecular interaction, where an electropositive crown, or ?-hole, serves as a Lewis acid to attract a variety of electron-rich Lewis bases, in analogous fashion to a classic hydrogen bonding (H-bond) interaction. We present here a broad overview of X-bonds from the perspective of a biologist who may not be familiar with this recently rediscovered class of interactions and, consequently, may be interested in how they can be applied as a highly directional and specific component of the molecular toolbox. This overview includes a discussion for where X-bonds are found in biomolecular structures, and how their structure–energy relationships are studied experimentally and modeled computationally. In total, our understanding of these basic concepts will allow X-bonds to be incorporated into strategies for the rational design of new halogenated inhibitors against biomolecular targets or toward molecular engineering of new biological-based materials. PMID:23225628

Scholfield, Matthew R; Zanden, Crystal M Vander; Carter, Megan; Ho, P Shing

2013-01-01

315

C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes: synthesis, structures, photophysics and electrochemistry.  

PubMed

Six new C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes, 1,A-R2-1,A-C2B10H10, where R represents the group 2-(1,3-Et2-1,3,2-N2BC6H4) or 2-(1,3-Ph2-1,3,2-N2BC6H4) and A is 2, 7 or 12, were synthesized from o-, m-, and p-dicarbadodecaboranes (carboranes) by lithiation and subsequent treatment with the respective 2-bromo-1,3,2-benzodiazaboroles. UV-visible and fluorescence spectra of all carboranes display low energy charge transfer emissions. While such emissions with Stokes shifts between 17,330 and 21,290 cm(-1) are typical for C,C'-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15,170 cm(-1) for the meta- and para-isomers are unusual as high-energy emissions are typical for meta- and para-dicarbadodecaboranes. Fluorescence quantum yields (?F) for the novel 1,7- and 1,12-bis(benzodiazaborolyl)-carboranes depend on the substituents at the nitrogen atoms of the heterocycle. Thus, the para-carborane with N-ethyl substituents 1,12-(1',3'-Et2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 has a ?F value of 41% in cyclohexane solution and only of 9% in the solid state, whereas the analogous 1,12-(1',3'-Ph2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 shows quantum yields of 3% in cyclohexane solution and 72% in the solid state. X-ray crystallographic, computational and cyclic voltammetry studies for these carboranes are also presented. PMID:23793134

Weber, Lothar; Kahlert, Jan; Brockhinke, Regina; Böhling, Lena; Halama, Johannes; Brockhinke, Andreas; Stammler, Hans-Georg; Neumann, Beate; Nervi, Carlo; Harder, Rachel A; Fox, Mark A

2013-08-14

316

Mechanistic Investigation of Catalytic Carbon-Carbon Bond Activation and Formation by Platinum and Palladium Phosphine  

E-print Network

Mechanistic Investigation of Catalytic Carbon-Carbon Bond Activation and Formation by Platinum). The breaking of C-C bonds is also crucial in coal liquefaction processes such as the Exxon Donor Solvent process or the Microcat Coal Liquefaction process. Presently cracking is achieved with heterogeneous

Jones, William D.

317

Diffusion Bonding of Metals.  

National Technical Information Service (NTIS)

The need to reduce the cost and weight of aerospace metallic structures has led to increased interest in solid state and liquid phase diffusion bonding processes, especially in combination with superplastic forming. The bonding mechanisms and bonding tech...

P. G. Partridge

1989-01-01

318

Low-energy (0.1 eV) electron attachment S?S bond cleavage assisted by Coulomb stabilization  

NASA Astrophysics Data System (ADS)

Electron capture by the ion H3C-S-S-CH2-CH2-NH +3 at either the -NH +3 site (to form the Rydberg radical H3C-S-S-CH2-CH2-NH3) or into the S-S antibonding ?* orbital is shown to be able to produce the same S-S bond fragmentation products H3C-S and HS-CH2-CH2-NH2, albeit by very different pathways. Capture into the S-S ?* orbital is, in the absence of the nearby positive site, endothermic by approximately 0.9 eV and leads to an electronically metastable anion that can undergo dissociation or autodetachment. In contrast, in the presence of the stabilizing Coulomb potential provided by the nearby NH +3 site, electron attachment into the S-S ?* orbital is rendered exothermic. As a result, as we have shown in this paper, the effective cross sections for forming the H3C-S and HS-CH2-CH2-NH2 products via attachment at the -NH +3 and S-S ?* sites are predicted to be comparable for our model compound. Moreover, we predict that the ?* site will become more amenable to electron attachment compared with the -NH +3 site for compounds in which the distance between the S-S bond and the protonated amine is larger than in our cation. These findings and insights should be of substantial value to workers studying bond cleavage rates and fragmentation patterns in gaseous positively charged samples of peptides and proteins.

Sawicka, Agnieszka; Berdys-Kocha?ska, Joanna; Skurski, Piotr; Simons, Jack

319

Thermochemistry of C7H16 to C10H22 Alkane Isomers: Primary, Secondary, and Tertiary C-H Bond Dissociation Energies and Effects of Branching.  

PubMed

Standard enthalpies of formation (?H°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. ?H°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 ?H°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

Hudzik, Jason M; Bozzelli, Joseph W; Simmie, John M

2014-10-01

320

A mild route to mesoporous Mo2C-C hybrid nanospheres for high performance lithium-ion batteries  

NASA Astrophysics Data System (ADS)

In this work, we have developed a mild route to fabricate typically mesoporous Mo2C-C hybrid nanospheres based on a solvothermal synthesis and reduction-carbonization process. This work opens a low-temperature route to synthesize valuable carbides. The resultant Mo2C-C hybrid, for the first time, is used as an anode material in lithium ion batteries (LIBs). Compared with bulk Mo2C, the Mo2C-C hybrid exhibits much better electrochemical performance. Remarkably, the hybrid electrode can deliver a specific capacity of over 670 mA h g-1 after 50 cycles at 100 mA g-1, which is much higher than that of the bulk material (113 mA h g-1). Even cycled at a high current density of 1000 mA g-1, high capacities of around 400-470 mA h g-1 can still be retained for the Mo2C-C hybrid. It might benefit from the synergistic effect of the nanohybridization, effectively relieving the volume change during the repeated lithium insertion-extraction reactions and maintaining the integrity of the electrical connections. It is expected that the present synthesis strategy for the Mo2C-C hybrid can be extended to other nanostructured carbides with good energy storage performance.In this work, we have developed a mild route to fabricate typically mesoporous Mo2C-C hybrid nanospheres based on a solvothermal synthesis and reduction-carbonization process. This work opens a low-temperature route to synthesize valuable carbides. The resultant Mo2C-C hybrid, for the first time, is used as an anode material in lithium ion batteries (LIBs). Compared with bulk Mo2C, the Mo2C-C hybrid exhibits much better electrochemical performance. Remarkably, the hybrid electrode can deliver a specific capacity of over 670 mA h g-1 after 50 cycles at 100 mA g-1, which is much higher than that of the bulk material (113 mA h g-1). Even cycled at a high current density of 1000 mA g-1, high capacities of around 400-470 mA h g-1 can still be retained for the Mo2C-C hybrid. It might benefit from the synergistic effect of the nanohybridization, effectively relieving the volume change during the repeated lithium insertion-extraction reactions and maintaining the integrity of the electrical connections. It is expected that the present synthesis strategy for the Mo2C-C hybrid can be extended to other nanostructured carbides with good energy storage performance. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06678a

Gao, Qing; Zhao, Xinyu; Xiao, Ying; Zhao, Di; Cao, Minhua

2014-05-01

321

Modular functionalized polyphosphines for supported materials: previously unobserved (31)P-NMR «through-space» ABCD spin systems and heterogeneous palladium-catalysed C-C and C-H arylation.  

PubMed

The modular design of polyphosphines, diversely functionalized for facile immobilization on virtually any kind of support, is reported. Previously unobserved ABCD (31)P NMR spin-spin systems evidence the control exercised on the polyphosphines conformation. We illustrate the catalytic performance at low Pd loading of the recyclable immobilized polyphosphines in C-C bond formation reactions. PMID:25008866

Beaupérin, Matthieu; Smaliy, Radomyr; Cattey, Hélène; Meunier, Philippe; Ou, Jun; Toy, Patrick H; Hierso, Jean-Cyrille

2014-08-28

322

Bond coordinates as an alternative: Low energy reactive collisions of He2+ with He; comparison of TD and TI quantum calculations  

NASA Astrophysics Data System (ADS)

``Reactive'' and ``inelastic'' processes in the ionic He3^+ system[1] have been separated and analyzed through the simulation of the ^3He + ^4He2 collision. The combined use of TD and TI techniques allowed the study for both high and very low kinetic energies; the agreement between the corresponding results in the medium energy range is very good. Influence of the internal excitation of the reagents and implications on the dynamics of evaporation in He clusters will be discussed[2,3]. Emphasis will be made on the TD wavepacket propagation methodology used for the calculation of state-to-state transition probabilies, based bond coordinates: This method[4] was suggested recently by one of the authors, and is applied for the first time to a process with three open channels. Bond coordinates can have several advantages over the use of standard Jacobi ones [1] E. Scifoni, E. Bodo and F. A. Gianturco, Eur. Phys. J. D, 30, 363 (2004) [2] E. Bodo, F. A. Gianturco, A. Dalgarno, J. Phys. B 35 (2002) 2391. [3] E. Bodo and F. A. Gianturco, Eur. Phys. J. D, 31 (2004) 423 [4] M. Lara, A. Aguado, O. Roncero,and M. Paniagua. J. Chem. Phys., 113, 1781 (2000)

Lara, Manuel; Bodo, Enrico; Gianturco, Franco A.

2005-05-01

323

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)

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.

Paul, Bijan Kumar; Samanta, Anuva; Guchhait, Nikhil

2010-08-01

324

Versatile low temperature wafer bonding and bond strength measurement by a blister test method  

Microsoft Academic Search

We present a low temperature plasma assisted bonding process that enables the bonding of silicon, silicon oxide and silicon nitride wafers among each other at annealing temperatures as low as room temperature. The process can be applied using standard clean room equipment. Surface energies of differently treated bonded samples are determined by a blister test method for square shaped cavities.

Alexander Doll; Martin Rabold; Frank Goldschmidtböing; Peter Woias

2006-01-01

325

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2013 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2013-07-01

326

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2010 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2010-07-01

327

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2011 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2011-07-01

328

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2012 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2012-07-01

329

Photodissociation of CS2 in the vacuum ultraviolet - Determination of bond dissociation energy from the lowest vibrational level of the ground state CS2.  

NASA Technical Reports Server (NTRS)

Photolysis in the vacuum ultraviolet results almost exclusively in the production of S(super-3)P atoms, which is in apparent violation of spin conservation. The threshold energy of incident photons required to produce fluorescence was used to calculate the bond dissociation energy (from the lowest vibrational level of the ground state), and the result agrees with the value previously derived from the photoionization of CS2. The fluorescence excitation spectrum shows peaks corresponding to Rydberg series I and II, indicating that the observed photodissociation of CS2 in the vacuum ultraviolet is mainly the result of predissociation from Rydberg states. The absorption coefficient of CS2 was measured in the region of 1200 to 1400 A.

Okabe, H.

1972-01-01

330

Total synthesis of (+)-trienomycins A and F via C-C bond-forming hydrogenation and transfer hydrogenation.  

PubMed

The triene-containing C17-benzene ansamycins trienomycins A and F were prepared in 16 steps (longest linear sequence, LLS) and 28 total steps. The C11-C13 stereotriad was generated via enantioselective Ru-catalyzed alcohol CH syn crotylation followed by chelation-controlled carbonyl dienylation. Enantioselective Rh-catalyzed acetylene-aldehyde reductive coupling mediated by gaseous H2 was used to form a diene that ultimately was subjected to diene-diene ring closing metathesis to form the macrocycle. The present approach is 14 steps shorter (LLS) than the prior syntheses of trienomycins A and F, and 8 steps shorter than any prior synthesis of a triene-containing C17-benzene ansamycin. PMID:23862627

Del Valle, David J; Krische, Michael J

2013-07-31

331

C-C Bond Formation via Copper-Catalyzed Conjugate Addition Reactions to Enones in Water at Room Temperature  

PubMed Central

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

Lipshutz, Bruce H.; Huang, Shenlin; Leong, Wendy Wen Yi; Isley, Nicholas A.

2013-01-01

332

Expanding the substrate scope in palladium-catalyzed C-N and C-C bond-forming reactions  

E-print Network

Chapter 1. The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of bulky electron-rich monophosphinobiaryl ligands or BINAP allow for the catalytic amination of electron-rich ...

Anderson, Kevin William

2006-01-01

333

Topotactic elimination of water across a C-C ligand bond in a dense 3-D metal-organic framework.  

PubMed

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

Yeung, Hamish H-M; Kosa, Monica; Griffin, John M; Grey, Clare P; Major, Dan T; Cheetham, Anthony K

2014-11-11

334

Cyanide-catalyzed C-C bond formation: synthesis of novel compounds, materials and ligands for homogeneous catalysis  

E-print Network

Cyanide-catalyzed aldimine coupling was employed to synthesize compounds with 1,2-ene-diamine and �±-imine-amine structural motifs: 1,2,N,N'- tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2- dihydroquinoxaline (17...

Reich, Blair Jesse Ellyn

2007-04-25

335

IBM XL C/C++ Advanced Edition V8.0 for Linux Programming Guide  

E-print Network

IBM XL C/C++ Advanced Edition V8.0 for Linux Programming Guide SC09-8014-00 #12;#12;IBM XL C/C++ Advanced Edition V8.0 for Linux Programming Guide SC09-8014-00 #12;Note! Before using this information) This edition applies to version 8.0 of IBM XL C/C++ Advanced Edition V8.0 for Linux (product number 5724-M16

Hickman, Mark

336

IBM XL C/C++ Advanced Edition V8.0 for Linux Compiler Reference  

E-print Network

IBM XL C/C++ Advanced Edition V8.0 for Linux Compiler Reference SC09-8013-00 #12;#12;IBM XL C/C++ Advanced Edition V8.0 for Linux Compiler Reference SC09-8013-00 #12;Note! Before using this information 2005 ) This edition applies to XL C/C++ Advanced Edition V8.0 for Linux (Program number 5724-M16

Hickman, Mark

337

IBM XL C/C++ Advanced Edition V8.0 for Linux Language Reference  

E-print Network

IBM XL C/C++ Advanced Edition V8.0 for Linux Language Reference SC09-8016-00 #12;#12;IBM XL C/C++ Advanced Edition V8.0 for Linux Language Reference SC09-8016-00 #12;Note! Before using this information (November, 2005) This edition applies to Version 8.0 of IBM XL C/C++ Advanced Edition for Linux (product

Hickman, Mark

338

Sequential bond energies and barrier heights for the water loss and charge separation dissociation pathways of Cd(2+)(H2O)n, n = 3-11.  

PubMed

The bond dissociation energies for losing one water from Cd(2+)(H(2)O)(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, Cd(2+)(H(2)O)(n) ? CdOH(+)(H(2)O)(m) + H(+)(H(2)O)(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 n(crit) = 4. PMID:21428620

Cooper, Theresa E; Armentrout, P B

2011-03-21

339

Formation of covalently bonded polycyclic hydrocarbon ions by intracluster polymerization of ionized ethynylbenzene clusters.  

PubMed

Here we report a detailed study aimed at elucidating the mechanism of intracluster ionic polymerization following the electron impact ionization of van der Waals clusters of ethynylbenzene (C8H6)n generated by a supersonic beam expansion. The structures of the C16H12, C24H18, C32H24, C40H30, and C48H36 radical cations resulting from the intracluster ion-molecule addition reactions have been investigated using a combination of mass-selected ion dissociation and ion mobility measurements coupled with theoretical calculations. Noncovalent structures can be totally excluded primarily because the measured fragmentations cannot result from noncovalent structures, and partially because of the large difference between the measured collision cross sections and the calculated values corresponding to noncovalent ion-neutral complexes. All the mass-selected cluster ions show characteristic fragmentations of covalently bonded molecular ions by the loss of stable neutral fragments such as CH3, C2H, C6H5, and C7H7. The population of the C16H12 dimer ions is dominated by structural isomers of the type (C6H5)-C?C-CH(•+)CH-(C6H5), which can grow by the sequential addition of ethynylbenzene molecules, in addition to some contributions from cyclic isomers such as the 1,3- or 1,4-diphenyl cyclobutadiene ions. Similarly, two major covalent isomers have been identified for the C24H18 trimer ions: one that has a blocked cyclic structure assigned to 1,2,4- or 1,3,5-triphenylbenzene cation, and a second isomer of the type (C6H5)-C?C-C(C6H5)?CH-CH(•+)CH-(C6H5) where the covalent addition of further ethynylbenzene molecules can occur. For the larger ions such as C32H24, C40H30, and C48H36, the major isomers present involve the growing oligomer sequence (C6H5)-C?C-[C(C6H5)?CH]n-CH(•+)CH-(C6H5) with different locations and orientations of the phenyl groups along the chain. In addition, the larger ions contain another family of structures consisting of neutral ethynylbenzene molecules associated with the blocked cyclic isomer ions such as the diphenylcyclobutadiene and triphenylbenzene cations. Low-energy dissociation channels corresponding to evaporation of ethynylbenzene molecules weakly associated with the covalent ions are observed in the large clusters in addition to the high-energy channels corresponding to fragmentation of the covalently bonded ions. However, in small clusters only high-energy dissociation channels are observed corresponding to the characteristic fragmentation of the molecular ions, thus providing structural signatures to identify the product ions and establish the mechanism of intracluster ionic polymerization. PMID:24689826

Momoh, Paul O; Attah, Isaac K; El-Shall, M Samy; Kanters, René P F; Pinski, John M; Abrash, Samuel A

2014-09-18

340

Understanding low-energy magnetic excitations and hydrogen bonding in VOHPO4 J. Cao,1 J. T. Haraldsen,2 S. Brown,1 J. L. Musfeldt,1 J. R. Thompson,2,3 S. Zvyagin,4 J. Krzystek,5 M.-H. Whangbo,6  

E-print Network

Understanding low-energy magnetic excitations and hydrogen bonding in VOHPO4· 1 2H2O J. Cao,1 J. T-temperature redshift of VuO and HuO related modes demonstrates enhanced low-temperature hydrogen bonding. The low are stacked along the c axis and held together by two types of interlayer hydrogen bonding interactions: 1

Cao, Jianming

341

Savings Bonds Value Calculator  

NSDL National Science Digital Library

From the Federal Reserve Bank of New York, this site computes the redemption value of users's US savings bonds. Easy-to-use pull-down menus allow visitors to enter information such as the date of issue and face value of their Series E bonds, Series EE bonds, and Series S bonds. After entering the information, the Calculator will then show a chart of issue dates and denominations and actual worth of the bonds, if cashed within a set period of time.

342

Overview of C/C-SiC Composite Development for the Orion Launch Abort System  

NASA Technical Reports Server (NTRS)

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.

Allen, Lee R.; Valentine, Peter G.; Schofield, Elizabeth S.; Beshears, Ronald D.; Coston, James E.

2012-01-01

343

LET'S BOND! A Chemical Bonding Webquest  

NSDL National Science Digital Library

Today we are going to use the internet to explore chemical bonding! Even though there are just a few questions for each website, you need to read the entire content. Don't worry about understanding all of it, but make sure that you are familiar with it! Stay on task and have fun! Let's start with some basics. Click on the link below and answer the questions on your worksheet under "Bonding Basics". Bonding Basics Good job! Lets move on and talk about ions. Ions are a big part of bonding, so make sure you get this section down pat! Click on the ...

Hicken, Mrs.

2009-04-08

344

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

PubMed Central

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

Jaeken, Laurent; Vasilievich Matveev, Vladimir

2012-01-01

345

Coatings that feature covalent-like fastness can be bonded non-covalently to low-surface-energy polymers: Evidence supporting the stepwise intercalation,  

E-print Network

adhesive bonding on polypropylene (PP) is its low surface tension, which is normally in the range of 29 PP is not wettable by adhesives and requires pretreatment to achieve bonding. Some common treatmentsCoatings that feature covalent-like fastness can be bonded non-covalently to low

Taralp, Alpay

346

Investing in Bonds.com  

NSDL National Science Digital Library

Investing in Bonds was created by the Bond Market Association to educate investors about the benefits of bonds investing. The Investor's Guide to Bond Basics educates investors about the types of bonds available, criteria for evaluating a bond, a guide to buying bonds, bond investment strategies and a glossary of bond market terms. The Bond Market section provides an overview of the U.S. bond market while the Investor's Checklist section takes the investor step-by-step through the bond investment decision process. Investors will also find sections with information on municipal bonds, corporate bonds, mortgage securities and U.S. Inflation-Indexed Securities.

347

Could the lithium bond be classified as the ?-hole bond? - QTAIM and NBO analysis  

NASA Astrophysics Data System (ADS)

The lithium bond is analyzed in complexes of ZH3Li and ZF3Li (ZC, Si and Ge) acting as the Lewis acids with HCN and N2 Lewis bases. There are the unique properties of the lithium bond if it is compared with the other non-covalent interactions. For the lithium bond the complexation leads to the decrease of the positive charge of the Li-atom and the increase of its volume while for the hydrogen bond usually the increase of the positive charge of H-atom and the decrease of its volume is observed. The lithium bond may be probably classified as the ?-hole bond. The other properties of the lithium bond are presented and analyzed based on MP2/aug-cc-pVTZ calculations, the quantum theory of atoms in molecules, natural bond orbitals method and the decomposition of the interaction energy.

Lipkowski, Pawe?; Grabowski, S?awomir J.

2014-01-01

348

Theoretical study on H2Y⋯Agsbnd X (X = F, Cl, Br, I; Y = O, S) complexes: Structures, energies and bonding  

NASA Astrophysics Data System (ADS)

The H2Y⋯Agsbnd X (X = F, Cl, Br, I; Y = O, S) complexes have been investigated by ab initio methods. All complexes are non-planar with Cs symmetry, and the Agsbnd X bond is strengthened during complexation processes. The binding energies of complexes were accurately calculated using the CCSD(T)/CBS by extrapolation method. The interaction between H2Y and AgX is weakened as X varies from F to I. The intermolecular interactions in these complexes show partial covalent character; moreover, the intermolecular interactions in H2S⋯Agsbnd X (X = F, Cl, Br, I) complexes are stronger than those in H2O⋯Agsbnd X complexes.

Wang, Qi; Zhang, Bohai; Huang, Zhengguo

2014-10-01

349

Evaluation of the bonding energy in donor-acceptor complexes formed upon the double doping of InSb by cadmium and selenium  

SciTech Connect

To ascertain the physio-chemical nature of the donor-acceptor complex formed in the double doping of InSb by cadmium and selenium, the authors prepared a series of alloys of InSb with Cd and Se. After experimental investigation of these alloys and mathematical analysis of the process, they conclude that the donor-acceptor interaction between the impurity atoms manifested itself in the form of special points on the compositionmicrohardness diagrams for isoconcentration sections of solutions based on InSb in the InSb-Cd-Se system. The special features of the variation in the microhardness made it possible to calculate the equilibrium constant for the donor-acceptor interaction and the bonding energy in the complex.

Glazov, V.M.; Smirnova, E.B.

1985-07-01

350

A quantitative relationship for the shock sensitivities of energetic compounds based on X-NO(2) (X=C, N, O) bond dissociation energy.  

PubMed

The ZPE-corrected X-NO(2) (X=C, N, O) bond dissociation energies (BDEs(ZPE)) of 11 energetic nitrocompounds of different types have been calculated employing density functional theory methods. Computed results show that using the 6-31G** basis set the UB3LYP calculated BDE(ZPE) is less than the UB3P86. For these typical energetic nitrocompounds the shock-initiated pressure (P(98)) is strongly related to the BDE(ZPE) indeed, and a polynomial correlation of ln(P(98)) with the BDE(ZPE) has been established successfully at different density functional theory levels, which provides a method to address the shock sensitivity problem. PMID:20447762

Li, Jinshan

2010-08-15

351

Sensor/ROIC Integration using Oxide Bonding  

SciTech Connect

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.

Ye, Zhenyu; /Fermilab

2009-02-01

352

INTERACTION BETWEEN GAS DIFFUSION AND MULTISTABLE HETEROGENEOUS CHEMICAL KINETICS IN C=C COMPOSITE  

E-print Network

brakes are frequently made of carbon/carbon (C=C) compos- ites. To deposit the composite interphaseINTERACTION BETWEEN GAS DIFFUSION AND MULTISTABLE HETEROGENEOUS CHEMICAL KINETICS IN C=C COMPOSITE PROCESSING G#19;erard L. VIGNOLES Universit#19;e Bordeaux 1, Laboratoire des Composites ThermoStructuraux 3

Recanati, Catherine

353

The University of Texas at Dallas Erik Jonsson School c C. D. Cantrell (06/1997)  

E-print Network

The University of Texas at Dallas Erik Jonsson School PhoTEC c C. D. Cantrell (06/1997) FRESNEL analytical solution Numerical solution #12;The University of Texas at Dallas Erik Jonsson School PhoTEC c C negligible except for very small aper- tures or obstacles · In a uniform dielectric and in Cartesian

Hart, Gus

354

Hydrogen-bonding-induced shifts of the excitation energies in nucleic acid bases: an interplay between electrostatic and electron density overlap effects.  

PubMed

The theoretically calculated dimerization-induced shifts of the lowest excitation energies in two model systems, adenine-thymine and guanine-cytosine base pairs, are analyzed. The applied formalism is based on first principles and allows one to study the influence of the microscopic environment of a given molecule on its ground- [Wesolowski, T. A.; Warshel, A. J. Phys. Chem. 1993, 97, 8050] and excited-state [Casida, M. E.; Wesolowski, T. A. Int. J. Quantum Chem. 2004, 96, 577] properties. The assessment of the relative importance of such effects as (a) Coulomb interactions, (b) orbital interactions, (c) electronic polarization of the environment, and (d) electron density overlap effects is straightforward in this formalism. In the applied formalism, electron density overlap effects can be further decomposed into the exchange-correlation component which provides a small attractive contribution and the repulsive kinetic energy-dependent component. It is shown that the shifts can be attributed to the electrostatic interactions and the repulsive overlap-dependent term in the embedding potential. The electronic polarization of the environment plays a significant role (up to 30% of the total shift) only in transitions involving the orbitals localized on hydrogen bond donor groups. For all analyzed shifts, the contribution of the intermolecular orbital interactions is negligible. The analysis of this work provides strong evidence supporting the use of the widely applied embedding-molecule strategy in computational studies of chromophores in a condensed phase even in such cases where only one end of the hydrogen bond is included in the quantum mechanical part. PMID:15366883

Wesolowski, Tomasz A

2004-09-22

355

Cleavage of NH bonds by active oxygen on Ag(110). II. Selective oxidation of ethylamine to acetonitrile  

NASA Astrophysics Data System (ADS)

The adsorption of ethylamine on Ag(110) and its reaction with adsorbed oxygen was studied with temperature programmed reaction spectroscopy (TPRS), X-ray photoelectron spectroscopy (XPS), and electron energy loss vibrational spectroscopy (EELS). Adsorption of ethylamine on the clean Ag(110) surface proceeds at 110 K without dissociation. Desorption from the multilayer occurs at 160 K, and a series of broader desorption peaks from monolayer states are observed from 150 to 400 K. The chemical shift of the N(1s) X-ray photoelectron spectrum indicates that ethylamine bonds through the nitrogen lone pair in the monolayer. The reaction of ethylamine with adsorbed oxygen starts with the formation of adsorbed CH 3CH 2NH and adsorbed hydroxyl groups upon adsorption at 110 K. These species undergo further reaction to yield water from 280 to 370 K, and hydrogen, acetonitrile, and regenerated ethylamine at 370 K. Acetonitrile is the only carbon-containing product observed (other than ethylamine), indicative of highly selective bond breaking processes. Deuterium labeling experiments showed that preadsorbed oxygen activates the N?H bonds, leading to water formation, while the hydrogen product evolved at higher temperatures originates from the carbon skeleton via C?H bond metallation by the silver surface. Disproportionation of CH 3CH 2NH groups was identified. Ethylamine is formed by rate-limiting C?H bond cleavage of adsorbed CH 3CH 2N. No evidence was found for the activation of either C?C or C?N bonds, and the surface metallation of N?H bonds does not occur.

Thornburg, D. M.; Madix, R. J.

1990-02-01

356

Investigations of electron attachment to the perfluorocarbon molecules c-C4F8, 2-C4F8, 1,3 C4F6, and c-C5F8  

NASA Astrophysics Data System (ADS)

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.

Feil, Stefan; Märk, Tilmann D.; Mauracher, Andreas; Scheier, Paul; Mayhew, Chris A.

2008-11-01

357

Substituent effects on cooperativity of pnicogen bonds.  

PubMed

Substituent effects on cooperativity of P···N pnicogen bonds are studied in XH2P···NCH(2)P···NCY (X=F, Cl; Y=H, F, CN, OH, NH(2)) complexes using high-level ab initio calculations. An increased attraction or a positive cooperativity is observed on introduction of a third molecule to the XH(2)P···NCH(2)P and NCH(2)P···NCY dyads. The shortening of the each pnicogen bond distance in the triads is dependent on the strength of the P···N bond and is increased in the order Y = NH(2) > OH > H > F > CN. The energy decomposition analysis indicates that the polarization energy is the important element in the interaction energy of P···N bond and may be regarded as being responsible for the stabilization in these systems. Natural bond orbital theory is used to characterize the interactions and analyze their enhancement with varying orbital interactions. PMID:25194434

Esrafili, Mehdi D; Ghanbari, Mojhgan; Mohammadian-Sabet, Fariba

2014-09-01

358

Electron and positron scattering from perfluorocyclobutane (c-C{sub 4}F{sub 8}) molecules  

SciTech Connect

Total cross sections (TCSs) are experimentally investigated for 0.8-600-eV electron and 0.7-600-eV positron scattering from c-C{sub 4}F{sub 8} molecules using a linear transmission time-of-flight method, and a comparative study of the results is carried out in this paper. Electron-scattering differential cross sections (DCS) measurements carried out for energies 1.5-100 eV are used for a combined TCS and DCS discussion. These DCS results help to offer a better understanding of some of the structures observed in the TCSs. Fingerprints of a low-energy resonance, consistent with large electron attachment cross sections near 0 eV, have been observed below 2 eV where TCSs show a continually rising trend. Another resonance peak at {approx}8.5 eV, attributed to dissociative electron attachment with the production of fragmented ions, and a broader one at 16-40 eV, have also been observed. Except for the pronounced shoulder at {approx}40 eV, there is good qualitative agreement between the TCS result and the integrated cross-section results. Although electron TCSs are found to be generally larger than positron TCSs in the 3-120-eV ranges, these two TCSs, however, show a tendency towards merging above 120 eV.

Makochekanwa, C. [Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Physics Department, Sofia University, Chiyoda-ku, Tokyo 102-8554 (Japan); Sueoka, O. [Department of Applied Science, Yamaguchi University, Ube 755-8611 (Japan); Kimura, M. [Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Kitajima, M.; Tanaka, H. [Physics Department, Sofia University, Chiyoda-ku, Tokyo 102-8554 (Japan)

2005-03-01

359

Direct measurements of chemical bonding at solid surfaces using a unique calorimetric method: Towards understanding surface chemistry in energy technologies  

NASA Astrophysics Data System (ADS)

Measuring the heat released when gas phase species adsorb onto surfaces provides essential information about the energies of surface species and the reactions they undergo. Here, heats of adsorption of technologically-interesting surface species were measured using a unique microcalorimetric technique in ultrahigh vacuum. Specifically, systems were studied which are relevant to understanding and improving transition metal catalysts and organic electronics. Metal adsorption energies were measured which elucidate metal-to-oxide and metal-to-polymer interfacial binding, and molecule adsorption energies were measured to understand how catalyst structure influences the energies of adsorbed reaction intermediates. Oxide-supported metal nanoparticles form the basis for many industrial catalysts. Nanoparticle activity, selectivity and resistance to sintering can depend strongly on particle size, oxide support, and defects on the oxide. To investigate the dependence of catalytic properties on oxide surface defects, defects were introduced on MgO(100) and CeO2(111), and their affect on the adsorption energy of metal atoms and the energy of supported nanoparticles was measured. These measurements help to explain why transition metal catalysts sinter more slowly and maintain smaller particles when supported on CeO 2 compared to other oxides, and how surface defects influence nanoparticle formation and film growth on oxides. The effect of nanoparticle size on the adsorption energy of CO on different-sized Pd nanoparticles on Fe3O 4(111) was measured, providing the first direct evidence that the heat of adsorption of CO decreases with decreasing Pd nanoparticle size. Knowledge of the direction and magnitude of particle size effects is necessary for improving existing catalysts and designing new ones. The metal/polymer interface is important because it impacts charge injection, extraction, and transport in organic electronics. Large-scale energy production using polymer photovoltaics is currently unfeasible due in part to their low efficiency and short lifetimes. Polymer degradation at the interface with the metal electrode is believed to impact device efficiency and lifetime. Calcium adsorption on poly(3-hexylthiophene) was investigated because it is one of the most efficient electrode/polymer combinations. The results were striking: calcium diffused nanometers into the polymer and reacted with the polymer backbone. A method to suppress diffusion was demonstrated, which may lead to improved devices.

Farmer, Jason A.

360

Dynamics, transition states, and timing of bond formation in Diels-Alder reactions.  

PubMed

The time-resolved mechanisms for eight Diels-Alder reactions have been studied by quasiclassical trajectories at 298 K, with energies and derivatives computed by UB3LYP/6-31G(d). Three of these reactions were also simulated at high temperature to compare with experimental results. The reaction trajectories require 50-150 fs on average to transverse the region near the saddle point where bonding changes occur. Even with symmetrical reactants, the trajectories invariably involve unequal bond formation in the transition state. Nevertheless, the time gap between formation of the two new bonds is shorter than a C ? C vibrational period. At 298 K, most Diels-Alder reactions are concerted and stereospecific, but at high temperatures (approximately 1,000 K) a small fraction of trajectories lead to diradicals. The simulations illustrate and affirm the bottleneck property of the transition state and the close connection between dynamics and the conventional analysis based on saddle point structure. PMID:22753502

Black, Kersey; Liu, Peng; Xu, Lai; Doubleday, Charles; Houk, Kendall N

2012-08-01

361

Design, Syntheses and Biological Applications of Through-bond Energy Transfer Cassettes and Novel Non-covalently Cell Penetrating Peptides  

E-print Network

A xanthene-BODIPY cassette is used as a ratiometric intracellular pH reporter for imaging protein-dye conjugates in living cells. A model was hypothesized to explain the pH-dependent energy transfer efficiencies from the donor to the acceptor based...

Han, Junyan

2012-02-14

362

Pressureless Bonding Using Sputtered Ag Thin Films  

NASA Astrophysics Data System (ADS)

To improve the performance and reliability of power electronic devices, particularly those built around next-generation wide-bandgap semiconductors such as SiC and GaN, the bonding method used for packaging must change from soldering to solderless technology. Because traditional solders are problematic in the harsh operating conditions expected for emerging high-temperature power devices, we propose a new bonding method in this paper, namely a pressureless, low-temperature bonding process in air, using abnormal grain growth on sputtered Ag thin films to realize extremely high temperature resistance. To investigate the mechanisms of this bonding process, we characterized the microstructural changes in the Ag films over various bonding temperatures and times. We measured the bonding properties of the specimens by a die-shear strength test, as well as by x-ray diffraction measurements of the residual stress in the Ag films to show how the microstructural developments were essential to the bonding technology. Sound bonds with high die strength can be achieved only with abnormal grain growth at optimum bonding temperature and time. Pressureless bonding allows for production of reliable high-temperature power devices for a wide variety of industrial, energy, and environmental applications.

Oh, Chulmin; Nagao, Shijo; Suganuma, Katsuaki

2014-08-01

363

Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy  

E-print Network

We investigated the electronic structures of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both bond type and the combination of the bonding partners affect the overall electronic structures. For singly bonded particles we observe a small impact of the bond type on the electronic structure, whereas for doubly bonded particles the connecting bond is the deciding factor, determining the electronic structure of the uppermost occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The strength of quantum confinement effects, i.e., the localization of electrons, depends on the bonding partner orbital energy difference. The experimental findings correspond well to density functional theory computations.

Zimmermann, Tobias; Knecht, Andre; Fokin, Andrey A; Koso, Tetyana V; Chernish, Lesya V; Gunchenko, Pavel A; Schreiner, Peter R; Möller, Thomas; Rander, Torbjörn

2013-01-01

364

A Common Eurozone Bond  

Microsoft Academic Search

Introduction\\u000aThe sovereign bond yields of the Eurozone, or more correctly the euro area, have since the introduction of the Euro undergone a bond yield compression. However, as can be seen in table 1, these bond yields started to diverge considerably around mid 2008 following the recent financial crisis and increased sovereign risk. Yields on Greek, Irish, and Portuguese bond

Erik Welin

2010-01-01

365

A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum-bis(dithione)  

PubMed Central

Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo4+O(i-Pr2Pipdt)2Cl][PF6] (where i-Pr2Pipdt is N,N’-piperazine-2,3-dithione), that possesses a piperazine ring as an integral part of the dithiolene ligand. The title complex displays unusual spectroscopic features for a formally reduced Mo(IV) dithiolene complex, namely a low energy metal-to-ligand charge transfer band with appreciable intensity and C-C and C-S stretching frequencies that are markedly different from those of oxomolydenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene contributing structures. PMID:23956683

Mtei, Regina P.; Perera, Eranda; Mogesa, Benjamin; Stein, Benjamin; Basu, Partha; Kirk, Martin L.

2013-01-01

366

Rapid adhesive bonding concepts  

NASA Technical Reports Server (NTRS)

Adhesive bonding in the aerospace industry typically utilizes autoclaves or presses which have considerable thermal mass. As a consequence, the rates of heatup and cooldown of the bonded parts are limited and the total time and cost of the bonding process is often relatively high. Many of the adhesives themselves do not inherently require long processing times. Bonding could be performed rapidly if the heat was concentrated in the bond lines or at least in the adherends. Rapid adhesive bonding concepts were developed to utilize induction heating techniques to provide heat directly to the bond line and/or adherends without heating the entire structure, supports, and fixtures of a bonding assembly. Bonding times for specimens are cut by a factor of 10 to 100 compared to standard press bonding. The development of rapid adhesive bonding for lap shear specimens (per ASTM D1003 and D3163), for aerospace panel bonding, and for field repair needs of metallic and advanced fiber reinforced polymeric matrix composite structures are reviewed.

Stein, B. A.; Tyeryar, J. R.; Hodges, W. T.

1984-01-01

367

Making and Breaking Bonds  

NSDL National Science Digital Library

Atoms collide and, under certain circumstances, react to form bonds with one another. The process of association is the bonding of atoms into a molecule while dissociation is the process by which a molecule breaks apart into simpler groups of atoms, individual atoms, or ions. Students interact with a molecular dynamics model to explore the making and breaking of bonds.

Consortium, The C.

2011-12-11

368

Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)  

NASA Astrophysics Data System (ADS)

The pure calcite surface was examined using techniques sensitive to the near-surface (XPS and LEED) immediately after fracture in ultra-high vacuum (10 -10 mbar) and then following exposure to various atmospheres and aqueous solutions that were free of trace metals. These spectroscopic techniques allow molecular-level observations that offer the possibility of gaining more insight into geochemical processes elucidated from macroscopic solution studies. Several absolute electron binding energies for the atoms in calcite were redetermined with XPS using the gold dot method. The results are 290.1 ± 0.1 eV for C 1 s, 347.7 and 351.2 ± 0.15 eV for Ca 2 psol3/2 and Ca 2 psol1/2, respectively, and 531.9 ± 0.15 eV for O 1 s. Photoelectron energy shifts from main peak positions suggest that immediately after fracture in ultra-high vacuum, bond reconfiguration leads to the formation of carbide-like bonds between Ca and C at the surface. Calcite that has been exposed to water, even as vapour from the atmosphere, shows binding energy shifts that indicate the presence of S · CO 3H and S · CaOH where S · represents the calcite surface. Surface hydration is also supported, independently, by the XPS peak intensity ratios and is consistent with adsorption theory derived from macroscopic solution studies. The modified oxygen Auger parameter, ?', (using O 1 s and O(KVV)), was found to be 1043.9 eV for all samples of calcite tested, whether powder or cleaved from Iceland Spar, clean or contaminated by adventitious carbon, freshly fractured, or exposed briefly to water, or in the process of dissolution or precipitation. LEED patterns of the {101} cleavage surface of samples that were freshly fractured in air and that were exposed to dissolving or precipitating solutions showed that the top few atomic layers exhibit long range order. Lattice spacings at the surface are statistically identical to those of bulk calcite, though some surface CO 3 groups may be rotated relative to the bulk structure. This work provides direct, molecular-level evidence for the processes of reconfiguration and hydration at the calcite surface. These results provide a basis for future spectroscopic studies of trace metal adsorption on calcite and subsequent solid-solution formation.

Stipp, Susan L.; Hochella, Michael F., Jr.

1991-06-01

369

Structures and energies in the simplest compounds with P?S bond: HPS, HPS, HSP and HSP  

NASA Astrophysics Data System (ADS)

A theoretical characterization has been performed for the molecular structure, rotational and vibrational constants of the simplest thioxophosphane HPS and its isomer thiohydroxyphosphinidene HSP in their lowest-lying singlet, triplet and ionized (HPS †, HSP † states. Geometries were optimized at both the HF and MP2/6-31G(d, p) leves, whereas harmonic vibrational frequencies were computed at HF/-31(d). Empirical corrections were made, when possible, on these calculated values in order to provide a more realistic prediction. HPS has a singlet ground state with a triplet-singlet separation of 24.4 kcal mol -1 and a first ionization energy (IE a) of 9.14 eV. HSP has a triplet ground state ( 3A?) with a rather small singlet-triplet gap (10.7 kcal mol -1) and a smaller IE a (8.14 eV). The radical cations present a reversed stability ordering as compared to their neutral counterparts. This results from a difference in proton affinities and binding energies of relevant species. Relative energies between stationary estimated at the MP4 SDQ/6-31+ +G(2d,p) level suggest that all equilibrium structures considered are relatively stable with respect to unimolecular rearrangement making them detectable in inert matrix at low temperature.

Nguyen, Minh Thou

1987-10-01

370

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

NASA Technical Reports Server (NTRS)

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.

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

2007-01-01

371

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

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

372

Metal cation dependence of interactions with amino acids: bond dissociation energies of Rb(+) and Cs(+) to the acidic amino acids and their amide derivatives.  

PubMed

Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu < Asn < Gln. PMID:24528155

Armentrout, P B; Yang, Bo; Rodgers, M T

2014-04-24

373

General Education Coursework: Credits General Education Coursework: Credits ENGL 110C (C or better) 3 ENGL 211C, 221C or 231C ( C or better) 3  

E-print Network

General Education Coursework: Credits General Education Coursework: Credits ENGL 110C (C or better: Credits General Education Coursework: Credits Information Literacy and Research 3 Human Creativity 3 BIOL SEMESTER (17 credits) SPRING SEMESTER (18 Major Coursework: Major Coursework: Major Coursework: Credits

374

Metal-thiolate bonds in bioinorganic chemistry.  

PubMed

Metal-thiolate active sites play major roles in bioinorganic chemistry. The M--S(thiolate) bonds can be very covalent, and involve different orbital interactions. Spectroscopic features of these active sites (intense, low-energy charge transfer transitions) reflect the high covalency of the M--S(thiolate) bonds. The energy of the metal-thiolate bond is fairly insensitive to its ionic/covalent and pi/sigma nature as increasing M--S covalency reduces the charge distribution, hence the ionic term, and these contributions can compensate. Thus, trends observed in stability constants (i.e., the Irving-Williams series) mostly reflect the dominantly ionic contribution to bonding of the innocent ligand being replaced by the thiolate. Due to high effective nuclear charges of the Cu(II) and Fe(III) ions, the cupric- and ferric-thiolate bonds are very covalent, with the former having strong pi and the latter having more sigma character. For the blue copper site, the high pi covalency couples the metal ion into the protein for rapid directional long range electron transfer. For rubredoxins, because the redox active molecular orbital is pi in nature, electron transfer tends to be more localized in the vicinity of the active site. Although the energy of hydrogen bonding of the protein environment to the thiolate ligands tends to be fairly small, H-bonding can significantly affect the covalency of the metal-thiolate bond and contribute to redox tuning by the protein environment. PMID:16807974

Solomon, Edward I; Gorelsky, Serge I; Dey, Abhishek

2006-09-01

375

Probing the bonding and electronic structure of single atom dopants in graphene with electron energy loss spectroscopy.  

PubMed

A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations reveal striking electronic structure differences between two distinct single substitutional Si defect geometries in graphene. Optimised acquisition conditions allow for exceptional signal-to-noise levels in the spectroscopic data. The near-edge fine structure can be compared with great accuracy to simulations and reveal either an sp(3)-like configuration for a trivalent Si or a more complicated hybridized structure for a tetravalent Si impurity. PMID:23259533

Ramasse, Quentin M; Seabourne, Che R; Kepaptsoglou, Despoina-Maria; Zan, Recep; Bangert, Ursel; Scott, Andrew J

2013-10-01

376

Charge-shift bonding--a class of electron-pair bonds that emerges from valence bond theory and is supported by the electron localization function approach.  

PubMed

This paper deals with a central paradigm of chemistry, the electron-pair bond. Valence bond (VB) theory and electron-localization function (ELF) calculations of 21 single bonds demonstrate that along the two classical bond families of covalent and ionic bonds, there exists a class of charge-shift bonds (CS bonds) in which the fluctuation of the electron pair density plays a dominant role. In VB theory, CS bonding manifests by way of a large covalent-ionic resonance energy, RE(CS), and in ELF by a depleted basin population with large variances (fluctuations). CS bonding is shown to be a fundamental mechanism that is necessary to satisfy the equilibrium condition, namely the virial ratio of the kinetic and potential energy contributions to the bond energy. The paper defines the atomic propensity and territory for CS bonding: Atoms (fragments) that are prone to CS bonding are compact electronegative and/or lone-pair-rich species. As such, the territory of CS bonding transcends considerations of static charge distribution, and involves: a) homopolar bonds of heteroatoms with zero static ionicity, b) heteropolar sigma and pi bonds of the electronegative and/or electron-pair-rich elements among themselves and to other atoms (e.g., the higher metalloids, Si, Ge, Sn, etc), c) all hypercoordinate molecules. Several experimental manifestations of charge-shift bonding are discussed, such as depleted bonding density, the rarity of ionic chemistry of silicon in condensed phases, and the high barriers of halogen-transfer reactions as compared to hydrogen-transfers. PMID:16086335

Shaik, Sason; Danovich, David; Silvi, Bernard; Lauvergnat, David L; Hiberty, Philippe C

2005-10-21

377

Prospective bonding applications  

NASA Astrophysics Data System (ADS)

Adhesive bonding in industry and in the laboratory is surveyed and prospects for its wider utilization are assessed. The economic impact of bonding technology on industry is discussed. Research is reviewed, centering on the development of nondestructive testing and inspection techniques. Traditional (wood) as well as new materials susceptible to bonding are considered. Applications in construction and civil engineering, in aeronautics, and in the automobile industry are covered. The use of glues in mechanical constructions, in assembling cylindrical parts, and in metal-metal bonding are examined. Hybrid assembling and bonding of composite materials are included.

Ancenay, H.; Benazet, D.

1981-07-01

378

Determination of the structure and bond energies of NiO2 and CuO2  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

379

Computational perspective on Pd-catalyzed C-C cross-coupling reaction mechanisms.  

PubMed

Palladium-catalyzed C-C cross-coupling reactions (Suzuki-Miyaura, Negishi, Stille, Sonogashira, etc.) are among the most useful reactions in modern organic synthesis because of their wide scope and selectivity under mild conditions. The many steps involved and the availability of competing pathways with similar energy barriers cause the mechanism to be quite complicated. In addition, the short-lived intermediates are difficult to detect, making it challenging to fully characterize the mechanism of these reactions using purely experimental techniques. Therefore, computational chemistry has proven crucial for elucidating the mechanism and shaping our current understanding of these processes. This mechanistic elucidation provides an opportunity to further expand these reactions to new substrates and to refine the selectivity of these reactions. During the past decade, we have applied computational chemistry, mostly using density functional theory (DFT), to the study of the mechanism of C-C cross-coupling reactions. This Account summarizes the results of our work, as well as significant contributions from others. Apart from a few studies on the general features of the catalytic cycles that have highlighted the existence of manifold competing pathways, most studies have focused on a specific reaction step, leading to the analysis of the oxidative addition, transmetalation, and reductive elimination steps of these processes. In oxidative addition, computational studies have clarified the connection between coordination number and selectivity. For transmetalation, computation has increased the understanding of different issues for the various named reactions: the role of the base in the Suzuki-Miyaura cross-coupling, the factors distinguishing the cyclic and open mechanisms in the Stille reaction, the identity of the active intermediates in the Negishi cross-coupling, and the different mechanistic alternatives in the Sonogashira reaction. We have also studied the closely related direct arylation process and highlighted the role of an external base as proton abstractor. Finally, we have also rationalized the effect of ligand substitution on the reductive elimination process. Computational chemistry has improved our understanding of palladium-catalyzed cross-coupling processes, allowing us to identify the mechanistic complexity of these reactions and, in a few selected cases, to fully clarify their mechanisms. Modern computational tools can deal with systems of the size and complexity involved in cross-coupling and have a continuing role in solving specific problems in this field. PMID:23848308

García-Melchor, Max; Braga, Ataualpa A C; Lledós, Agustí; Ujaque, Gregori; Maseras, Feliu

2013-11-19

380

Brazing of C/C composites and Ni-based alloy using interlayer  

NASA Astrophysics Data System (ADS)

The brazing of C/C composites and Inconel-600 Ni-based heat resistant alloy was conducted using Fe-Ni-Cr-P-Si brazing filler alloy with inserting various thickness of Nb foil as stress relief interlayer. SEM observation of cross section of brazing interface revealed that Nb foil was resolved into the brazing filler layer on C/C composites side. Nb diffused to the surface of C/C composites and acted as the active metal element to enhance the wettability of molten metal on graphite matrix of C/C composites during the brazing process. The variation in shear strength values of the brazed joint with Nb layer thickness suggested that the Nb layer should be remained at least 100 ?m.

Ikeshoji, Toshi-Taka; Tokunaga, Tatsuya; Suzumura, Akio; Yamazaki, Takahisa

2014-08-01

381

25 CFR 214.4 - Bonds.  

...DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF OSAGE RESERVATION LANDS, OKLAHOMA, FOR MINING, EXCEPT OIL AND GAS § 214.4 Bonds...Provided, That for leases for minerals other than oil and gas the Secretary...

2014-04-01

382

Accurate bond dissociation energy of water determined by triple-resonance vibrational spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

Triple-resonance vibrational spectroscopy is used to determine the lowest dissociation energy, D0, for the water isotopologue HD16O as 41 239.7 ± 0.2 cm-1 and to improve D0 for H216O to 41 145.92 ± 0.12 cm-1. Ab initio calculations including systematic basis set and electron correlation convergence studies, relativistic and Lamb shift effects as well as corrections beyond the Born-Oppenheimer approximation, agree with the measured values to 1 and 2 cm-1 respectively. The improved treatment of high-order correlation terms is key to this high theoretical accuracy. Predicted values for D0 for the other five major water isotopologues are expected to be correct within 1 cm-1.

Boyarkin, Oleg V.; Koshelev, Maxim A.; Aseev, Oleg; Maksyutenko, Pavel; Rizzo, Thomas R.; Zobov, Nikolay F.; Lodi, Lorenzo; Tennyson, Jonathan; Polyansky, Oleg L.

2013-05-01

383

Atomization energy and equilibrium geometry of fullerenes C60 and C70  

Microsoft Academic Search

The heat of formation of C60 crystals is determined experimentally. A semiempirical expression is proposed for calculating the heats of formation of fullerenes and fullerides C60(n-) and C70(n-) (where n varies from -2 to +6) from experimentally determined values of the equilibrium internuclear distances in chemical (valence) C-C bonds. The semiempirical approach makes it possible to determine the rupture energy

S. P. Ionov; A. C. Alikhanyan; N. G. Spitsyna; V. G. Yarzhemskij

1993-01-01

384

A Double-Deletion Method to Quantifying Incremental Binding Energies in Proteins from Experiment: Example of a Destabilizing Hydrogen Bonding Pair  

Microsoft Academic Search

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

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

2005-01-01

385

Effect of bond thickness on fracture and fatigue strength of adhesively bonded composite joints  

NASA Technical Reports Server (NTRS)

An experimental investigation of composite to composite bonded joints was undertaken to study the effect of bond thickness on debond growth rate under cyclic loading and critical strain energy release rate under static loading. Double cantilever beam specimens of graphite/epoxy adherends bonded with EC 3445 were tested under mode I loading. A different behavior of fracture and fatigue strength was observed with variation of bondline thickness.

Mall, S.; Ramamurthy, G.

1989-01-01

386

Carbon-carbon bond cleavage and rearrangement of benzene by a trinuclear titanium hydride  

NASA Astrophysics Data System (ADS)

The cleavage of carbon-carbon (C-C) bonds by transition metals is of great interest, especially as this transformation can be used to produce fuels and other industrially important chemicals from natural resources such as petroleum and biomass. Carbon-carbon bonds are quite stable and are consequently unreactive under many reaction conditions. In the industrial naphtha hydrocracking process, the aromatic carbon skeleton of benzene can be transformed to methylcyclopentane and acyclic saturated hydrocarbons through C-C bond cleavage and rearrangement on the surfaces of solid catalysts. However, these chemical transformations usually require high temperatures and are fairly non-selective. Microorganisms can degrade aromatic compounds under ambient conditions, but the mechanistic details are not known and are difficult to mimic. Several transition metal complexes have been reported to cleave C-C bonds in a selective fashion in special circumstances, such as relief of ring strain, formation of an aromatic system, chelation-assisted cyclometallation and ?-carbon elimination. However, the cleavage of benzene by a transition metal complex has not been reported. Here we report the C-C bond cleavage and rearrangement of benzene by a trinuclear titanium polyhydride complex. The benzene ring is transformed sequentially to a methylcyclopentenyl and a 2-methylpentenyl species through the cleavage of the aromatic carbon skeleton at the multi-titanium sites. Our results suggest that multinuclear titanium hydrides could serve as a unique platform for the activation of aromatic molecules, and may facilitate the design of new catalysts for the transformation of inactive aromatics.

Hu, Shaowei; Shima, Takanori; Hou, Zhaomin

2014-08-01

387

Correlated valence-bond states  

NASA Astrophysics Data System (ADS)

We study generalizations of the singlet-sector amplitude-product (AP) states in the valence-bond basis of S=1/2 quantum spin systems. In the standard AP states, the weight of a tiling of the system into valence bonds (singlets of two spins) is a product of amplitudes depending on the length of the bonds. We here introduce correlated AP (CAP) states, in which the AP is further multiplied by factors depending on two bonds connected to a pair of sites (here nearest neighbors). While the standard AP states can describe a phase transition between an antiferromagnetic (Néel) state and a valence-bond solid (VBS) in one dimension (which we also study here), in two dimensions it cannot describe VBS order. With the CAP states, Néel-VBS transitions are realized as a function of some parameter describing the bond correlations. We here study such phase transitions of CAP wave functions on the square lattice. We find examples of direct first-order Néel-VBS transitions, as well as cases where there is an extended U(1) spin liquid phase intervening between the Néel and VBS states. In the latter case the transitions are continuous and we extract critical exponents and address the issue of a possible emergent U(1) symmetry in the near-critical VBS. We also consider variationally optimized CAP states for the standard Heisenberg model in one and two dimensions and the J-Q model in two dimensions, with the latter including four-spin interactions (Q) in addition to the Heisenberg exchange (J) and harboring VBS order for large Q/J. The optimized CAP states lead to significantly lower variational energies than the simple AP states for these models.

Lin, Yu-Cheng; Tang, Ying; Lou, Jie; Sandvik, Anders W.

2012-10-01

388

The Role of Multiple, Reformable Parallel Bonds on the Self-healing Behavior of Dual Crosslinked Nanogel Materials  

NASA Astrophysics Data System (ADS)

Using computational modeling, we design novel self-healing materials composed of nanoscopic polymer gel particles, or nanogels. The particles are interconnected via both labile bonds (e.g., disulfide bonds) and stronger, less reactive bonds (e.g, C-C bonds) and therefore the nanogels form a "dual crosslinked" network. The stable bonds provide a rigid backbone while the labile bonds allow the material to undergo a dynamic reconfiguration in response to stress. We adapt the Hierarchical Bell Model (HBM) to describe the labile bonding interactions. The HBM effectively allows us to model cases where the ligands on neighboring nanogels interact through multiple sites. We show that the introduction of a small number of labile bonds that lie in parallel significantly increases the strength of the material relative to samples crosslinked solely by the stable bonds. We also isolate an optimal range of labile interconnections that provide high-strength, tough materials that are capable of self-repair.

Salib, Isaac G.; Kolmakov, German V.; Gnegy, Chet N.; Matyjaszewski, Krzysztof; Balazs, Anna C.

2011-03-01

389

Probing the nature of hydrogen bonds with x-rays  

Microsoft Academic Search

The smallish bond energy and the longish distance allows its formation and disruption under a wide range of physiologically interesting temperatures and conditions, i.e. it's crucial for life. In addition, hydrogen bonds are directional and therefore ideally suited to play a role in molecular recognition phenomena. Given the obvious importance and ubiquitous nature of hydrogen bonds it is remarkable that

P. M. Platzman

2000-01-01

390

Extreme metal carbonyl back bonding in cyclopentadienylthorium carbonyls generates bridging C2O2 ligands by carbonyl coupling.  

PubMed

Laboratory studies of the interaction of carbon monoxide with organoactinides result in the formation of isolable complexes such as Cp3UCO derivatives (Cp = cyclopentadienyl) as well as coupling reactions to give derivatives of the oligomeric anions C(n)O(n)(2-) (n = 2, 3, 4). To gain some insight into actinide carbonyl chemistry, binuclear cyclopentadienylthorium carbonyls Cp2Th2(CO)n (n = 2 to 5) as model compounds have been investigated using density functional theory. The most favorable such structures in terms of energy and thermochemistry are the tricarbonyl Cp2Th2(?(2)-?-CO)3 having three four-electron donor bridging carbonyl groups and the tetracarbonyl Cp2Th2(?(4)-?-C2O2)(?(2)-?-CO)2 having not only two four-electron donor bridging carbonyl groups but also a bridging ethynediolate ligand formed by coupling two CO groups through C-C bond formation. The bridging infrared ?(CO) frequencies ranging from 1140 to 1560 cm(-1) in these Cp2Th2(CO)n (n = 3, 4) derivatives indicate extremely strong Th?CO back bonding in these structures, corresponding to formally dianionic CO(2-) and C2O2(2-) ligands and the favorable +4 thorium oxidation state. A characteristic of the Cp2Th2(?(2)-?-CO)3 and Cp2Th2(?(4)-?-C2O2)(?(2)-?-CO)2 structures is their ability to add terminal CO groups, preferably to the thorium atom bonded to the fewest oxygen atoms. These terminal CO groups exhibit ?(CO) frequencies in a similar range as terminal CO groups in d-block metal carbonyls. However, these terminal CO groups are relatively weakly bonded to the thorium atoms as indicated by predicted CO dissociation energies of 14 kcal/mol for Cp2Th2(CO)5. Two low energy structures for the dicarbonyl Cp2Th2(CO)2 are found with two separate four-electron donor bridging CO groups and relatively short Th-Th distances of 3.3 to 3.4 Å suggesting formal single bonds and +3 thorium formal oxidation states. However, a QTAIM analysis of this formal Th-Th bond does not reveal a bond critical point thus suggesting a multicenter bonding model involving the bridging CO groups. PMID:23721544

Li, Huidong; Feng, Hao; Sun, Weiguo; King, R Bruce; Schaefer, Henry F

2013-06-17

391

Chemical bonding technology  

NASA Technical Reports Server (NTRS)

Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

Plueddemann, E.

1986-01-01

392

Stepwise cyclopalladation of 2-phenacylthiopyridine to give C,C,N-pincer complexes.  

PubMed

Orthopalladation of the phenyl ring in the cyclopalladated complex [Pd{C,N-pyl-SCHC(O)Ph}(?-X)]2 (pyl = 2-pyridyl, X = Cl; 1·Cl) occurs upon reacting it with AgOAc (1?:?2) in MeCN to give the pincer complex [Pd{C,C,N-pyl-SCHC(O)C6H4-2}(NCMe)] (2). The nature of the base and X plays a key role because palladation neither occurs with other bases nor when AgOAc is the base and X is Br, in which case 1·OAc is obtained. In addition, complex 2 is not obtained upon refluxing 1·OAc in MeCN. Complex 2 affords complexes [Pd{C,C,N,S-pyl-SCHC(O)C6H4-2}]n, [Pd{C,C,N-pyl-SCHC(O)C6H4-2}L] (L = PPh3, (t)BuNC, XyNC) or Me4N[Pd{C,C,N-pyl-SCHC(O)C6H4-2}Cl] upon acetonitrile loss, or its replacement by neutral or anionic ligands, respectively. Some such complexes act as metallaligands towards AgClO4 or [PdCl2(NCPh)2] giving rise to heterodinuclear [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(PPh3)}{Ag(PPh3)}]ClO4 or homodinuclear [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(Cl)}{Pd(?-Cl)}]2, [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(Cl)}{Pd(Cl)(PPh3}] complexes. Some derivatives of complexes 1 were also obtained. PMID:25182692

Chicote, María-Teresa; Rubio, Concepción; Bautista, Delia; Vicente, José

2014-10-28

393

Model for an inductively coupled Ar/c-C4F8 plasma discharge  

NASA Astrophysics Data System (ADS)

This article describes a two-dimensional model for an inductively coupled Ar/c-C4F8 plasma discharge, which is widely used in the microelectronics industry for dielectric etching and polymerization. The chemical mechanism for c-C4F8 incorporates known information about electron impact dissociation, ionization, and attachment processes. Unknown details such as neutral dissociation byproducts have been empirically inferred using energetics analysis or diagnostic experiments. The mechanism also considers electron impact processes for neutral radicals (e.g., CF, CF2, CF3) and stable molecules (e.g., C2F4) produced in a c-C4F8 plasma. It is demonstrated in the article that the resulting neutral species densities, ion flux to the wafer, and electron characteristics are in good agreement with experiments in the Gaseous Electronics Conference reference cell. The validated model is used to understand the dynamics of an inductively coupled Ar/c-C4F8 plasma discharge, and the impact of various control parameters on plasma characteristics. Results indicate that CF2 is the dominant CFx radical in the c-C4F8 discharge and the plasma is mildly electronegative. Enhanced ionization and dissociation of c-C4F8 with increasing inductive power deposition leads to an increase in electron and CFx radical densities, and total ion flux to the wafer. Enhanced dissociative attachment at higher gas pressure decreases the electron density and increases the negative ion density. The plasma becomes more electropositive with decreasing c-C4F8 concentration in the gas mixture, which increases the total positive ion flux to the wafer.

Rauf, Shahid; Ventzek, Peter L. G.

2002-01-01

394

Hydrogen Bonding Penalty upon Ligand Binding  

E-print Network

Ligand binding involves breakage of hydrogen bonds with water molecules and formation of new hydrogen bonds between protein and ligand. In this work, the change of hydrogen bonding energy in the binding process, namely hydrogen bonding penalty, is evaluated with a new method. The hydrogen bonding penalty can not only be used to filter unrealistic poses in docking, but also improve the accuracy of binding energy calculation. A new model integrated with hydrogen bonding penalty for free energy calculation gives a root mean square error of 0.7 kcal/mol on 74 inhibitors in the training set and of 1.1 kcal/mol on 64 inhibitors in the test set. Moreover, an application of hydrogen bonding penalty into a high throughput docking campaign for EphB4 inhibitors is presented, and remarkably, three novel scaffolds are discovered out of seven tested. The binding affinity and ligand efficiency of the most potent compound is about 300 nM and 0.35 kcal/mol per non-hydrogen atom, respectively.

Hongtao Zhao; Danzhi Huang

2011-01-01

395

Low temperature wafer direct bonding  

Microsoft Academic Search

A pronounced increase of interface energy of room temperature bonded hydrophilic Si\\/Si, Si\\/SiO2, and SiO2\\/SiO 2 wafers after storage in air at room temperature, 150°C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and\\/or silicon at the interface at temperatures below 110°C and the formation of

Qin-Yi Tong; Giho Cha; Roman Gafiteanu; Ulrich Gosele

1994-01-01

396

Natural bond orbital analysis of steric interactions  

Microsoft Academic Search

We describe an ab initio procedure for extracting the Pauli exchange antisymmetry (“steric”) contributions to molecular potential energy in the framework of self-consistent-field molecular orbital (SCFMO) theory. This “natural steric analysis” method is based on natural bond orbital (NBO) representation of the SCFMO wave function, which allows the steric exchange energy to be approximated as an energy difference between “preorthogonal”

J. K. Badenhoop; F. Weinhold

1997-01-01

397

Hydrogen bonding and anaesthesia  

NASA Astrophysics Data System (ADS)

General anaesthetics act by perturbing intermolecular associations without breaking or forming covalent bonds. These associations might be due to a variety of van der Waals interactions or hydrogen bonding. Neurotransmitters all contain OH or NH groups, which are prone to form hydrogen bonds with those of the neurotransmitter receptors. These could be perturbed by anaesthetics. Aromatic rings in amino acids can act as weak hydrogen bond acceptors. On the other hand the acidic hydrogen in halothane type anaesthetics are weak proton donors. These two facts together lead to a probable mechanism of action for all general anaesthetics.

Sándorfy, C.

2004-12-01

398

Effectiveness of Diffusion Barrier Coatings for Mo-Re Embedded in C/SiC and C/C  

NASA Technical Reports Server (NTRS)

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.

Glass, David E.; Shenoy, Ravi N.; Wang, Zeng-Mei; Halbig, Michael C.

2001-01-01

399

Criterion for mixed mode fracture in composite bonded joints  

NASA Technical Reports Server (NTRS)

A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite-epoxy composite adherends bonded with a toughened epoxy adhesive. The mode I, mode II and mixed mode I-II fracture energies of the tested adhesives were found to be equal to each other. The criterion for mixed mode fracture in composite bonded joints was found.

Mall, S.; Kochhar, N. K.

1986-01-01

400

Evaluation of shear bond strength of porcelain bonded to laser welded titanium surface and determination of mode of bond failure.  

PubMed

The aim of this study was to evaluate the shear bond strength of porcelain to laser welded titanium surface and to determine the mode of bond failure through scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS). Forty five cast rectangular titanium specimens with the dimension of 10 mm x 8 mm x 1 mm were tested. Thirty specimens had a perforation of 2 mm diameter in the centre. These were randomly divided into Group A and B. The perforations in the Group B specimens were repaired by laser welding using Cp Grade II titanium wire. The remaining 15 specimens were taken as control group. All the test specimens were layered with low fusing porcelain and tested for shear bond strength. The debonded specimens were subjected to SEM and EDS. Data were analysed with 1-way analysis of variance and Student's t-test for comparison among the different groups. One-way analysis of variance (ANOVA) showed no statistically significant difference in shear bond strength values at a 5% level of confidence. The mean shear bond strength values for control group, Group A and B was 8.4 +/- 0.5 Mpa, 8.1 +/- 0.4 Mpa and 8.3 +/- 0.3 Mpa respectively. SEM/EDS analysis of the specimens showed mixed and cohesive type of bond failure. Within the limitations of the study laser welding did not have any effect on the shear bond strength of porcelain bonded to titanium. PMID:21077419

Patil, Narendra P; Dandekar, Minal; Nadiger, Ramesh K; Guttal, Satyabodh S

2010-09-01

401

Reinterpretation of the bond-valence model with bond-order formalism: An improved bond-valence-based interatomic potential for PbTiO3  

NASA Astrophysics Data System (ADS)

We present a modified bond-valence model of PbTiO3 based on the principles of bond-valence and bond-valence vector conservation. The relationship between the bond-valence model and the bond-order potential is derived analytically in the framework of a tight-binding model. An energy term, bond-valence vector energy, is introduced into the atomistic model and the potential parameters are reoptimized. This model potential can be applied both to canonical-ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. This model reproduces the experimental phase transition in NVT MD simulations and also exhibits the experimental sequence of temperature-driven and pressure-driven phase transitions in NPT simulations. We expect that this improved bond-valence model can be applied to a broad range of inorganic materials.

Liu, Shi; Grinberg, Ilya; Takenaka, Hiroyuki; Rappe, Andrew M.

2013-09-01

402

Palladium-catalyzed cross-dehydrogenative functionalization of C(sp2)-H Bonds.  

PubMed

The catalytic cross-dehydrogenative coupling (CDC) reaction has received intense attention in recent years. The attractive feature of this coupling process is the formation of a C-C bond from two C-H moieties under oxidative conditions. In this Focus Review, recent advances in the palladium-catalyzed CDC reactions of C(sp(2) )-H bond are summarized, with a focus on the period from 2011 to early 2013. PMID:24123795

Wu, Yinuo; Wang, Jun; Mao, Fei; Kwong, Fuk Yee

2014-01-01

403

Homolytic substitution at phosphorus for C-P bond formation in organic synthesis  

PubMed Central

Summary Organophosphorus compounds are important in organic chemistry. This review article covers emerging, powerful synthetic approaches to organophosphorus compounds by homolytic substitution at phosphorus with a carbon-centered radical. Phosphination reagents include diphosphines, chalcogenophosphines and stannylphosphines, which bear a weak P–heteroatom bond for homolysis. This article deals with two transformations, radical phosphination by addition across unsaturated C–C bonds and substitution of organic halides. PMID:23843922

2013-01-01

404

Molecular-dynamics simulation of crystalline 18-crown-6: thermal shortening of covalent bonds  

Microsoft Academic Search

Molecular-dynamics simulations of crystalline 18-crown-6 have been performed in a study of the apparent thermal shortening of covalent bonds observed in crystal structures. At 100 K, a shortening of 0.006 _+ 0.001 A for C----C and C----O bonds was obtained. This result was found to be independent of details of the force field and the simulation. There was agreement between

J. van Eerden; S. Harkema; D. Feil

1990-01-01

405

Lead Screening for HIV of C-C Chemokine Receptor Type 5 Receptor Inhibited by Traditional Chinese Medicine  

PubMed Central

The acquired immunodeficiency syndrome (AIDS), caused by the human immunodeficiency virus (HIV), has become a serious world-wide problem because of this disease's rapid propagation and incurability. Recent research has pointed out that the C-C chemokine receptor type 5 (CCR5) is an important target for HIV infection. The traditional Chinese medicine (TCM) database (http://tcm.cmu.edu.tw/) has been screened for molecular compounds that, by simulating molecular docking and molecular dynamics, may protect CCR5 against HIV. Saussureamine C, 5-hydroxy-L-tryptophan, and abrine are selected based on the docking score being higher than Maraviroc and other TCM compounds. The molecular dynamics are helpful in the analysis and detection of protein-ligand interactions. According to the docking poses, hydrophobic interactions, and hydrogen bond variations, this research surmises TRP86, TYR108, GLN194, TYR251, and GLU283 are the main regions of important amino acids in CCR5. In addition to the detection of TCM compound efficacy, we suggest saussureamine C is better than the others for maintaining protein composition during protein-ligand interaction, based on the structural variation. PMID:24876870

Hung, Tzu-Chieh; Chen, Kuen-Bao; Huang, Hung-Jin; Chen, Calvin Yu-Chian

2014-01-01

406

Anodic bonded graphene  

Microsoft Academic Search

We show how to prepare graphene samples on a glass substrate with the anodic bonding method. In this method, a graphite precursor in flake form is bonded to a glass substrate with the help of an electrostatic field and then cleaved off to leave few layer graphene on the substrate. Now that several methods are available for producing graphene, the

Adrian Balan; Rakesh Kumar; Mohamed Boukhicha; Olivier Beyssac; Jean-Claude Bouillard; Dario Taverna; William Sacks; Massimiliano Marangolo; Emanuelle Lacaze; Roger Gohler; Walter Escoffier; Jean-Marie Poumirol; Abhay Shukla

2010-01-01

407

The Sibling Bond.  

ERIC Educational Resources Information Center

The relationships among brothers and sisters are infinitely varied, but whatever their characteristics, these bonds last throughout life. This book examines the sibling relationship as a distinctive emotional, passionate, painful, and solacing power. Chapter 1, "Unraveling the Sibling Bond," addresses research on siblings and development of the…

Bank, Stephen P.; Kahn, Michael D.

408

Measuring Abnormal Bond Performance  

Microsoft Academic Search

We analyze the empirical power and specification of test statistics designed to detect abnormal bond returns in corporate event studies, using monthly and daily data. We find that test statistics based on frequently used methods of calculating abnormal monthly bond returns are biased. Most methods implemented in monthly data also lack power to detect abnormal returns. We also consider unique

Hendrik Bessembinder; Kathleen M. Kahle; William F. Maxwell; Danielle Xu

2009-01-01

409

Water's Hydrogen Bond Strength  

Microsoft Academic Search

Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less

Martin Chaplin

2007-01-01

410

Interactive Pi Bonding Effects  

NSDL National Science Digital Library

This application demonstrates the effect of pi bonding on the one-electron ligand field splitting in an octahedral. By clicking on the appropriate buttons students can see how D changes when you move from ligands with no pi bonding capability to pi donor and pi acceptor ligands.

411

Wood Bond Testing  

NASA Astrophysics Data System (ADS)

A joint development program between Hartford Steam Boiler Inspection Technologies and The Weyerhaeuser Company resulted in an internal bond analyzer (IBA), a device which combines ultrasonics with acoustic emission testing techniques. It is actually a spinoff from a spinoff, stemming from a NASA Lewis invented acousto-ultrasonic technique that became a system for testing bond strength of composite materials. Hartford's parent company, Acoustic Emission Technology Corporation (AET) refined and commercialized the technology. The IBA builds on the original system and incorporates on-line process control systems. The IBA determines bond strength by measuring changes in pulsar ultrasonic waves injected into a board. Analysis of the wave determines the average internal bond strength for the panel. Results are displayed immediately. Using the system, a mill operator can adjust resin/wood proportion, reduce setup time and waste, produce internal bonds of a consistent quality and automatically mark deficient products.

1989-01-01

412

Metallic bonding in magnesium microclusters  

NASA Astrophysics Data System (ADS)

We investigate the size evolution of bonding in magnesium clusters Mgn, with n<=20. Computations are performed in the density-functional scheme with two prescriptions for the exchange-correlation energy: the local-density approximation (LDA), and an improved scheme including gradient corrections (GC). The LDA results show that Mg10 clusters already have acquired several of the characteristic features of metallic aggregates. GC significantly decrease the cohesive energies, and predict a slower convergence with n to the bulk, without changing, however, the qualitative picture given by LDA.

Delaly, P.; Ballone, P.; Buttet, J.

1992-02-01

413

The effect of intramolecular H-bonds on the aqueous solution continuum description of the N-protonated form of dopamine  

NASA Astrophysics Data System (ADS)

The conformational properties in vacuo and in solution of N-protonated dopamine have been studied making use of ab initio SCF calculations in vacuo and free energy calculations in aqueous solution, in the framework of the polarizable continuum model (PCM), on the STO-3G, 4-31G and 6-31G ? optimized geometries obtained in vacuo. The in vacuo energy profiles along a few sections of the potential energy surface turn out to be very close for the extended basis sets, while the STO-3G eresults are slightly dispalced. The largest difference between the minimal and the extended basis sets is found for the perpendicular arrangement, which is however the lowest energy profile with low barriers to the C?C?C?N rotation both invacuo and in solution. The solvent stabilizes the trans over the gauche rotamers. Teh conformers without intramolecular H-bond between the -OH side chains are favored by the solvent, which makes the planar i, anti conformers as stable as the corresponding conformers with an intramolecular H-bond in aqueous solution. The solvation free energy is considerably less basis set dependent than the potential energy in vacuo. The ab initio PCM results slightly favor the planar 1 form over the planar 2 form whereas the semiempirical AMSOL results of Urban, Cramer and Famini (J. Am. Chem. Soc. 114 (1992) 8226) do the opposite. The cavitation free energy is nearly independent of the basis set. The almost constant (about 4.4 kcal/mol) cavitation and dispersion-repulsion corrections do not affect the differential quantities.

Alagona, Giuliano; Ghio, Caterina

1996-04-01

414

Calorimetric and computational study of thiacyclohexane 1-oxide and thiacyclohexane 1,1-dioxide (thiane sulfoxide and thiane sulfone). Enthalpies of formation and the energy of the S=O bond.  

PubMed

A rotating-bomb combustion calorimeter specifically designed for the study of sulfur-containing compounds [J. Chem. Thermodyn. 1999, 31, 635] has been used for the determination of the enthalpy of formation of thiane sulfone, 4, Delta(f)H(o) m(g) = -394.8 +/- 1.5 kJ x mol(-1). This value stands in stark contrast with the enthalpy of formation reported for thiane itself, Delta(f)H(o) m(g) = -63.5 +/- 1.0 kJ x mol(-1), and gives evidence of the increased electronegativity of the sulfur atom in the sulfonyl group, which leads to significantly stronger C-SO2 bonds. Given the known enthalpy of formation of atomic oxygen in the gas phase, Delta(f)H(o) m(O,g) = +249.18 kJ x mol(-1), and the reported bond dissociation energy for the S=O bond in alkyl sulfones, BDE(S=O) = +470.0 kJ x mol(-1), it was possible to estimate the enthalpy of formation of thiane sulfoxide, 5, a hygroscopic compound not easy to use in experimental calorimetric measurements, Delta(f)H(o) m(5) = -174.0 kJ x mol(-1). The experimental enthalpy of formation of both 4 and 5 were closely reproduced by theoretical calculations at the G2(MP2)+ level, Delta(f)H(o) m(4) = -395.0 kJ x mol(-1) and Delta(f)H(o) m(5) = -178.0 kJ x mol(-1). Finally, calculated G2(MP2)+ values for the bond dissociation energy of the S=O bond in cyclic sulfoxide 5 and sulfone 4 are +363.7 and +466.2 kJ x mol(-1), respectively. PMID:12608789

Roux, María Victoria; Temprado, Manuel; Jiménez, Pilar; Dávalos, Juan Zenón; Notario, Rafael; Guzmán-Mejía, Ramón; Juaristi, Eusebio

2003-03-01

415

Generalized resonating valence bond description of cyclobutadiene  

SciTech Connect

The low-lying electronic states of square and rectangular cyclobutadiene (CBD) are calculated by using the generalized resonating valence bond (GRVB) method and compared with the results from Hartree-Fock and configuration interaction wavefunctions. We find that simple valence bond concepts correctly predict the sequence of excited states (including ground-state singlet) and the distortion to a rectangular geometry for the ground state. Contrary to common expectation, we find that the singlet ground state of square CBD has 22 kcal of resonance energy (relative to a single valence bond structure). Thus, CBD is not antiresonant, though it is much less stable than normal conjugated systems.

Voter, A.F.; Goddard, W.A. III

1986-05-28

416

Determination of ion-ligand bond energies and ion fragmentation energies of electrospray-produced ions by collision-induced dissociation threshold measurements  

Microsoft Academic Search

A triple quadrupole mass spectrometer adapted for the determination of collision-induced dissociation (CID) threshold energies of ions produced by electrospray (ES) is described. The ES-produced ions are transferred from 1 atm atm a low pressure source, 10 Torr, where they can be partially declustered and after that thermalized by gas collisions. The ions entering the vacuum of the triple quadrupole

Stephen G. Anderson; Arthur T. Blades; John Klassen; Paul Kebarle

1995-01-01

417

(N-heterocyclic-carbene)Copper(I)-catalyzed carbon-carbon bond formation using carbon dioxide  

E-print Network

This thesis presents work towards the development of a new catalytic C-C bond forming reaction. Alkynes and olefins insert into [(IPr)CuH]2 (IPr = N,N-bis-(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene) to give copper vinyl ...

Sirokman, Gergely

2007-01-01

418

Geometrical criteria versus quantum chemical criteria for assessment of intramolecular hydrogen bond (IMHB) interaction: A computational comparison into the effect of chlorine substitution on IMHB of salicylic acid in its lowest energy ground state conformer  

NASA Astrophysics Data System (ADS)

Density functional theory based computational study has been performed to characterize intramolecular hydrogen bonding (IMHB) interaction in a series of salicylic acid derivatives varying in chlorine substitution on the benzene ring. The molecular systems studied are salicylic acid, 5-chlorosalicylic acid, 3,5-dichlorosalicylic acid and 3,5,6-tricholorosalicylic acid. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ?(r) and Laplacian ?2?(r) at the bond critical point using atoms-in-molecule theory. Topological features, energy densities based on ?(r) through perturbing the intramolecular H-bond distances suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of covalent interaction. The interplay between aromaticity and resonance-assisted hydrogen bonding (RAHB) is discussed using both geometrical and magnetic criteria as the descriptors of aromaticity. The optimized geometry features, molecular electrostatic potential map analysis are also found to produce a consensus view in relation with the formation of RAHB in these systems.

Paul, Bijan Kumar; Guchhait, Nikhil

2013-02-01

419

Complexes between hypohalous acids and phosphine derivatives. Pnicogen bond versus halogen bond versus hydrogen bond  

NASA Astrophysics Data System (ADS)

The complexes of HOBr:PH2Y (Y = H, F, Cl, Br, CH3, NH2, OH, and NO2), HOCl:PH2F, and HOI:PH2F have been investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Four types of structures (1, 2, 3a, and 3b) were observed for these complexes. 1 is stabilized by an O⋯P pnicogen bond, 2 by a P⋯X halogen bond, 3a by a H⋯P hydrogen bond and a P⋯X pnicogen bond, and 3b by H⋯P and H⋯Br hydrogen bonds. Their relative stability is related to the halogen X of HOX and the substituent Y of PH2Y. These structures can compete with interaction energy of -10.22 ? -29.40 kJ/mol. The Hsbnd O stretch vibration shows a small red shift in 1, a small irregular shift in 2, but a prominent red shift in 3a and 3b. The Xsbnd O stretch vibration exhibits a smaller red shift in 1, a larger red shift in 2, but an insignificant blue shift in 3a and 3b. The Psbnd Y stretch vibration displays a red shift in 1 but a blue shift in 2, 3a, and 3b. The formation mechanism, stability, and properties of these structures have been analyzed with molecular electrostatic potentials, orbital interactions, and non-covalent interaction index.

Li, Qingzhong; Zhu, Hongjie; Zhuo, Hongying; Yang, Xin; Li, Wenzuo; Cheng, Jianbo

2014-11-01

420

Chemical Bonding, again ionic bonding (in salts): transfer of e-  

E-print Network

Chemical Bonding, again · ionic bonding (in salts): transfer of e- · covalent bonding (organicJ/mol Li+ (g) + F¯ (g) #12;The Covalent Bond H H HH+ HHH · + · H ! H : H Lewis electron-dot structures single bond, a shared pair of electrons The Covalent Bond H H HH+ HH #12;E N E R G Y kJ/mol distance 74

Zakarian, Armen

421

The pnicogen bond: its relation to hydrogen, halogen, and other noncovalent bonds.  

PubMed

Among a wide range of noncovalent interactions, hydrogen (H) bonds are well known for their specific roles in various chemical and biological phenomena. When describing conventional hydrogen bonding, researchers use the notation AH···D (where A refers to the electron acceptor and D to the donor). However, the AH molecule engaged in a AH···D H-bond can also be pivoted around by roughly 180°, resulting in a HA···D arrangement. Even without the H atom in a bridging position, this arrangement can be attractive, as explained in this Account. The electron density donated by D transfers into a AH ?* antibonding orbital in either case: the lobe of the ?* orbital near the H atom in the H-bonding AH···D geometry, or the lobe proximate to the A atom in the HA···D case. A favorable electrostatic interaction energy between the two molecules supplements this charge transfer. When A belongs to the pnictide family of elements, which include phosphorus, arsenic, antimony, and bismuth, this type of interaction is called a pnicogen bond. This bonding interaction is somewhat analogous to the chalcogen and halogen bonds that arise when A is an element in group 16 or 17, respectively, of the periodic table. Electronegative substitutions, such as a F for a H atom opposite the electron donor atom, strengthen the pnicogen bond. For example, the binding energy in FH(2)P···NH(3) greatly exceeds that of the paradigmatic H-bonding water dimer. Surprisingly, di- or tri-halogenation does not produce any additional stabilization, in marked contrast to H-bonds. Chalcogen and halogen bonds show similar strength to the pnicogen bond for a given electron-withdrawing substituent. This insensitivity to the electron-acceptor atom distinguishes these interactions from H-bonds, in which energy