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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

A rhodium(i)-catalysed formal intramolecular C-C/C-H bond metathesis.  

PubMed

Phenylcyclobutanes underwent skeletal reorganisation in the presence of Wilkinson's catalyst to afford indanes through a cascade process involving chelation-assisted C-C bond cleavage and intramolecular C-H bond cleavage. PMID:25823599

Matsuda, Takanori; Yuihara, Itaru

2015-04-14

3

Understanding Rotation about a C=C Double Bond  

ERIC Educational Resources Information Center

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

Barrows, Susan E.; Eberlein, Thomas H.

2005-01-01

4

Alkali metal mediated C-C bond coupling reaction  

NASA Astrophysics Data System (ADS)

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

Tachikawa, Hiroto

2015-02-01

5

Alkali metal mediated C-C bond coupling reaction.  

PubMed

Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2](-) was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results. PMID:25681900

Tachikawa, Hiroto

2015-02-14

6

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

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

2012-01-01

7

Catalyst-Free Approach to Construct C-C Bond Initiated by N-O Bond Cleavage under Thermal Conditions.  

PubMed

An unexpected and novel approach to construct the sp(2) C-sp(3) C bond has been developed via N-O bond cleavage without any external catalysts or additives. It is a very simple, efficient, and environmentally friendly method and will be a very attractive radical process toward new C-C bond formation. PMID:25423187

Li, Dan-Dan; Li, Zhong-Yuan; Wang, Guan-Wu

2014-12-01

8

Recent advances in the gold-catalyzed additions to CC multiple bonds  

PubMed Central

Summary CO, CN and CC bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of CC multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of XH (X = O, N, C) bonds to CC multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present. PMID:21804887

Huang, He; Zhou, Yu

2011-01-01

9

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

SciTech Connect

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

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

2013-01-02

10

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

PubMed Central

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

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

2012-01-01

11

Decarbonylative c?c bond-forming reactions of saccharins by nickel catalysis: homocoupling and cycloaddition.  

PubMed

Decarbonylation of saccharins by nickel catalysis enables two kinds of C?C bond-forming reactions; homocoupling of saccharins to form biaryls and cycloaddition with alkynes to form benzosultams. The former represents the first reported nickel-catalyzed decarbonylative C?C homocoupling reaction, whereas the latter constitutes a powerful method to pharmaceutically relevant benzosultams. The reactions proceed with good functional-group tolerance and excellent regioselectivity. PMID:25689489

Mi, Pengbing; Liao, Peiqiu; Tu, Tao; Bi, Xihe

2015-03-27

12

Aromaticity effects on the profiles of the lowest triplet-state potential-energy surfaces for rotation about the C=C bonds of olefins with five-membered ring substituents: an example of the impact of Baird's rule.  

PubMed

A density functional theory study on olefins with five-membered monocyclic 4n and 4n+2 ?-electron substituents (C4H3X; X=CH(+), SiH(+), BH, AlH, CH2, SiH2, O, S, NH, and CH(-)) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet-state (T1) potential-energy surface (PES) for twisting about olefinic C=C bonds. It exploited both Hckel's rule on aromaticity in the closed-shell singlet ground state (S0) and Baird's rule on aromaticity in the lowest ??* excited triplet state. The compounds CH2=CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0 -antiaromatic/T1 -aromatic (C5H4 (+)) to strongly S0 -aromatic/T1- antiaromatic (C5H4(-)). Our hypothesis is that the shapes of the T1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T1 [?E(T1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ?E(T1) and the (anti)aromaticity changes of the C4 H3 X groups, as measured by the zz-tensor component of the nucleus-independent chemical shift ?NICS(T1;1)zz , are found both for sets A and B separately (linear fits; r(2) =0.949 and 0.851, respectively) and for the two sets combined (linear fit; r(2) =0.851). For sets A and B combined, strong correlations are also found between ?E(T1) and the degree of S0 (anti)aromaticity as determined by NICS(S0,1)zz (sigmoidal fit; r(2) =0.963), as well as between the T1 energies of the planar olefins and NICS(S0,1)zz (linear fit; r(2) =0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T1 PESs suitable for adiabatic Z/E photoisomerization. PMID:23794153

Zhu, Jun; Fogarty, Heather A; Mllerstedt, Helene; Brink, Maria; Ottosson, Henrik

2013-08-01

13

Rhodium-Catalyzed Activation and Functionalization of the C-C Bond of Biphenylene  

E-print Network

Rhodium-Catalyzed Activation and Functionalization of the C-C Bond of Biphenylene Carl N. Iverson August 29, 2001 Biphenylene reacts with the rhodium(I) dimer [(dtbpm)RhCl]2 (1) (dtbpm ) bis have been stoichiometric, although catalytic reactions are known.2 Rhodium complexes in particular have

Jones, William D.

14

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

PubMed

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

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

2011-09-01

15

Palladium-catalyzed allylic esterification via C-C bond cleavage of a secondary homoallyl alcohol.  

PubMed

Palladium-catalyzed allylic esterifications of secondary homoallyl alcohols with acids via sequential retro-allylation and esterification are demonstrated, affording the corresponding allyl ester in up to 99% yield. The electron effect of the substituent of the secondary alcohol was found to be crucial to the selective C-C bond cleavage. PMID:25075757

Wang, Yong; Kang, Qiang

2014-08-15

16

Microbial aldolases as CC bonding enzymesunknown treasures and new developments  

Microsoft Academic Search

Aldolases are a specific group of lyases that catalyze the reversible stereoselective addition of a donor compound (nucleophile) onto an acceptor compound (electrophile). Whereas most aldolases are specific for their donor compound in the aldolization reaction, they often tolerate a wide range of aldehydes as acceptor compounds. CC bonding by aldolases creates stereocenters in the resulting aldol products. This makes

Anne K. Samland; Georg A. Sprenger

2006-01-01

17

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

PubMed Central

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

Bower, John F.; Krische, Michael J.

2011-01-01

18

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

SciTech Connect

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

Liu, Bin; Greeley, Jeffrey P.

2012-05-01

19

CC Bond formation catalyzed by natural gelatin and collagen proteins  

PubMed Central

Summary The activity of gelatin and collagen proteins towards CC bond formation via Henry (nitroaldol) reaction between aldehydes and nitroalkanes is demonstrated for the first time. Among other variables, protein source, physical state and chemical modification influence product yield and kinetics, affording the nitroaldol products in both aqueous and organic media under mild conditions. Significantly, the scale-up of the process between 4-nitrobenzaldehyde and nitromethane is successfully achieved at 1 g scale and in good yield. A comparative kinetic study with other biocatalysts shows an increase of the first-order rate constant in the order chitosan < gelatin < bovine serum albumin (BSA) < collagen. The results of this study indicate that simple edible gelatin can promote CC bond forming reactions under physiological conditions, which may have important implications from a metabolic perspective. PMID:23843902

Khbeck, Dennis; Bijayi Dhar, Basab; Schn, Eva-Maria; Cativiela, Carlos; Gotor-Fernndez, Vicente

2013-01-01

20

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

SciTech Connect

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

Colby, Denise; Bergman, Robert; Ellman, Jonathan

2010-05-13

21

Discovery and mechanistic studies of facile N-terminal C?-C bond cleavages in the dissociation of tyrosine-containing peptide radical cations.  

PubMed

Fascinating N-terminal C?-C bond cleavages in a series of nonbasic tyrosine-containing peptide radical cations have been observed under low-energy collision-induced dissociation (CID), leading to the generation of rarely observed x-type radical fragments, with significant abundances. CID experiments of the radical cations of the alanyltyrosylglycine tripeptide and its analogues suggested that the N-terminal C?-C bond cleavage, yielding its [x2 + H](+) radical cation, does not involve an N-terminal ?-carbon-centered radical. Theoretical examination of a prototypical radical cation of the alanyltyrosine dipeptide, using density functional theory calculations, suggested that direct N-terminal C?-C bond cleavage could produce an ion-molecule complex formed between the incipient a1(+) and x1() fragments. Subsequent proton transfer from the iminium nitrogen atom in a1(+) to the acyl carbon atom in x1() results in the observable [x1 + H](+). The barriers against this novel C?-C bond cleavage and the competitive N-C? bond cleavage, forming the complementary [c1 + 2H](+)/[z1 - H](+) ion pair, are similar (ca. 16 kcal mol(-1)). Rice-Ramsperger-Kassel-Marcus modeling revealed that [x1 + H](+) and [c1 + 2H](+) species are formed with comparable rates, in agreement with energy-resolved CID experiments for [AY](+). PMID:24678922

Mu, Xiaoyan; Song, Tao; Xu, Minjie; Lai, Cheuk-Kuen; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K

2014-04-24

22

Nickel-Catalyzed Enantioselective C?C Bond Formation through C?sp?2?O Cleavage in Aryl Esters.  

PubMed

We report the first enantioselective C?C bond formation through C?O bond cleavage using aryl ester counterparts. This method is characterized by its wide substrate scope and results in the formation of quaternary stereogenic centers with high yields and asymmetric induction. PMID:25650559

Cornella, Josep; Jackson, Evan P; Martin, Ruben

2015-03-23

23

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

SciTech Connect

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

Assary, R. S.; Broadbelt, L. J.; Curtiss, L. A. (Center for Nanoscale Materials); ( MSD); (Northwestern Univ.)

2012-01-01

24

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

PubMed Central

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

Jana, Ranjan; Tunge, Jon A.

2011-01-01

25

Reversible C-C bond activation enables stereocontrol in Rh-catalyzed carbonylative cycloadditions of aminocyclopropanes.  

PubMed

Upon exposure to neutral or cationic Rh(I)-catalyst systems, amino-substituted cyclopropanes undergo carbonylative cycloaddition with tethered alkenes to provide stereochemically complex N-heterocyclic scaffolds. These processes rely upon the generation and trapping of rhodacyclopentanone intermediates, which arise by regioselective, Cbz-directed insertion of Rh and CO into one of the two proximal aminocyclopropane C-C bonds. For cyclizations using cationic Rh(I)-systems, synthetic and mechanistic studies indicate that rhodacyclopentanone formation is reversible and that the alkene insertion step determines product diastereoselectivity. This regime facilitates high levels of stereocontrol with respect to substituents on the alkene tether. The option of generating rhodacyclopentanones dynamically provides a new facet to a growing area of catalysis and may find use as a (stereo)control strategy in other processes. PMID:25539136

Shaw, Megan H; McCreanor, Niall G; Whittingham, William G; Bower, John F

2015-01-14

26

New reactivity of oxaziridine: Pd(II)-catalyzed aromatic C-H ethoxycarbonylation via C-C bond cleavage.  

PubMed

A novel Pd(II)-catalyzed aromatic C-H ethoxycarbonylation with oxaziridine involving C-C bond cleavage is described. Various aromatic 2-phenylpyridines and related compounds as well as aryl ureas can be effectively ethoxycarbonylated. A catalytic cycle involving Pd(II) and Pd(IV) is proposed. PMID:21875037

Peng, Xingao; Zhu, Yingguang; Ramirez, Thomas A; Zhao, Baoguo; Shi, Yian

2011-10-01

27

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

PubMed Central

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

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

2014-01-01

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

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

30

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

PubMed

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

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

2013-10-01

31

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

32

Catalytic C-C Bond Activation in Biphenylene and Cyclotrimerization of Alkynes: Increased Reactivity of  

E-print Network

(iPr)2CH2CH2- NMe2 (PN).9 According to Pearson's concept of "hard" and "soft" Lewis acids and Lewis to its potential application in industrial petroleum refining and trans- formation processes. Because bases, the coordinated metal-nitrogen bond in (PN)Ni(2-alkyne) complexes is considered to be labile.10

Jones, William D.

33

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

34

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

PubMed

Knlker'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 Knlker'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 Knlker'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

35

Rh(I)-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes and CO by merging thermal and metal-catalyzed C-C bond cleavages.  

PubMed

A Rh-catalyzed benzo/[7+1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to benzocyclooctenones has been developed. In this reaction, CP-BCB acts as a benzo/7-C synthon and the reaction involves two C-C bond cleavages: a thermal electrocyclic ring-opening of the four-membered ring in CP-BCB and a Rh-catalyzed C-C cleavage of the cyclopropane ring. PMID:25612241

Fu, Xu-Fei; Xiang, Yu; Yu, Zhi-Xiang

2015-03-01

36

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

37

Significant evidence of CO and CC 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 CO and CC, 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 CO and CC 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 CO- and CC-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 CC interactions to be referred to as dicarbon bonds. PMID:25017184

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

2014-08-28

38

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

39

.c"'''''... '" ~:c c: '"o ':l  

E-print Network

.c"'''''... '" '".c '-'"c: .c: .D '" ~:c c: '"o ':l '" 0E ':l'" VI 0 '" "'0 '- '" · ·· '" ·· ··"'''' · .>c '""-'".c .c .c'"'".ca> V' '" C1'· - - - 0 0'" >'0 '" _.w 0 "'0 a>.c W:i:E· ' 0 :> '" "VI ~ 3:"" >,c: c: Vl __ 0 · -a. .D '"'" VI'" '"' '" · '" '" C >, c: · '"'- ..., C .c

40

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; Mntsl, Pekka; Niemi, Jarmo; Mets-Ketel, Mikko

2012-01-01

41

Kinetics, Thermodynamics, and Effect of BPh3 on Competitive C-C and C-H Bond Activation Reactions in the  

E-print Network

Kinetics, Thermodynamics, and Effect of BPh3 on Competitive C-C and C-H Bond Activation Reactions-H cleavage steps (larger Hq and positive Sq ). Addition of the Lewis acid BPh3 to 1 at low temperature yields exclusively the C-CN activation product (dippe)Ni(3 -allyl)(CNBPh3) (4). Independently prepared (dippe)Ni(crotononitrile-BPh

Jones, William D.

42

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

43

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

44

Atomic contributions to bond dissociation energies in aliphatic hydrocarbons  

NASA Astrophysics Data System (ADS)

This paper explores the atomic contributions to the electronic vibrationless bond dissociation enthalpy (BDE) at 0K of the central C-C bond in straight-chain alkanes (CnH2n+2) and trans-alkenes (CnH2n) with an even number of carbon atoms, where n =2, 4, 6, 8. This is achieved using the partitioning of the total molecular energy according to the quantum theory of atoms in molecules by comparing the atomic energies in the intact molecule and its dissociation products. The study is conducted at the MP2(full)/6-311++G(d,p) level of theory. It is found that the bulk of the electronic energy necessary to sever a single C-C bond is not supplied by these two carbon atoms (the ?-carbons) but instead by the atoms directly bonded to them. Thus, the burden of the electronic part of the BDE is primarily carried by the two hydrogens attached to each of the ?-carbons and by the ?-carbons. The effect drops off rapidly with distance along the hydrocarbon chain. The situation is more complex in the case of the double bond in alkenes, since here the burden is shared between the ?-carbons as well as the atoms directly bonded to them, namely, again the ?-hydrogens and the ?-carbons. These observations may lead to a better understanding of the bond dissociation process and should be taken into account when locally dense basis sets are introduced to improve the accuracy of BDE calculations.

Matta, Chrif F.; Castillo, Norberto; Boyd, Russell J.

2006-11-01

45

Copper-mediated synthesis of pyrazolo[1,5-a]pyridines through oxidative linkage of C-C/N-N bonds.  

PubMed

Copper-mediated synthesis of pyrazolo[1,5-a]pyridine-3-carboxylates through oxidative linkage of C-C and N-N bonds under mild reaction conditions is described. This protocol is applicable to a variety of pyridyl esters as well as various benzonitriles including nicotinonitrile, isonicotinonitrile and thiophene-2-carbonitrile. Better yields were observed with electron withdrawing substituted benzonitriles. PMID:25679457

Mohan, Darapaneni Chandra; Ravi, Chitrakar; Rao, Sadu Nageswara; Adimurthy, Subbarayappa

2015-03-11

46

C-H vs C-C Bond Activation of Acetonitrile and Benzonitrile via Oxidative Addition: Rhodium vs Nickel and Cp* vs Tp  

E-print Network

C-H vs C-C Bond Activation of Acetonitrile and Benzonitrile via Oxidative Addition: Rhodium vs@chem.rochester.edu Abstract: The photochemical reaction of (C5Me5)Rh(PMe3)H2 (1) in neat acetonitrile leads to formation of the C-H activation product, (C5Me5)Rh(PMe3)(CH2CN)H (2). Thermolysis of this product in acetonitrile

Jones, William D.

47

Silver-Mediated Radical Cyclization of Alkynoates and ?-Keto Acids Leading to Coumarins via Cascade Double C-C Bond Formation.  

PubMed

A novel and convenient silver-mediated radical cyclization method for the synthesis of coumarin derivatives via the direct difunctionalization of alkynoates with ?-keto acids through double C-C bond formation under mild conditions has been developed. This new method is highly efficient and practical, and the starting materials are readily prepared. The present method should provide a useful strategy for the construction of coumarin motifs. PMID:25562802

Yan, Kelu; Yang, Daoshan; Wei, Wei; Wang, Fen; Shuai, Yuanyuan; Li, Qiannan; Wang, Hua

2015-02-01

48

Hydroperoxide Oxidation of Difficult-to-Oxidize Substrates: An Unprecedented CC Bond Cleavage in Alkanes and the Oxidation of Molecular Nitrogen  

Microsoft Academic Search

In the V(V)H2O2\\/AcOH system, C5C20n-alkanes, isooctane, and neohexane undergo oxidation to ketones and alcohols; the oxidation products of branched alkanes are indicative of a CC bond cleavage in these substrates. A concept is developed, according to which the peroxo complexes of vanadium(V) are responsible for alkane oxidation. These complexes can transfer the oxygen atom or the O+ radical cation to

A. E. Gekhman; I. P. Stolyarov; N. V. Ershova; N. I. Moiseeva; I. I. Moiseev

2004-01-01

49

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

PubMed Central

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

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

2014-01-01

50

A metal-free tandem C-C/C-O bond formation approach to densely functionalized indolyl [Formula: see text]-chromenes catalyzed by polystyrene-supported [Formula: see text]-toluenesulfonic acid under solvent-free conditions.  

PubMed

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

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

2015-05-01

51

Energy decomposition analysis of covalent bonds and intermolecular interactions.  

PubMed

An energy decomposition analysis method is implemented for the analysis of both covalent bonds and intermolecular interactions on the basis of single-determinant Hartree-Fock (HF) (restricted closed shell HF, restricted open shell HF, and unrestricted open shell HF) wavefunctions and their density functional theory analogs. For HF methods, the total interaction energy from a supermolecule calculation is decomposed into electrostatic, exchange, repulsion, and polarization terms. Dispersion energy is obtained from second-order Mller-Plesset perturbation theory and coupled-cluster methods such as CCSD and CCSD(T). Similar to the HF methods, Kohn-Sham density functional interaction energy is decomposed into electrostatic, exchange, repulsion, polarization, and dispersion terms. Tests on various systems show that this algorithm is simple and robust. Insights are provided by the energy decomposition analysis into H(2), methane C-H, and ethane C-C covalent bond formation, CH(3)CH(3) internal rotation barrier, water, ammonia, ammonium, and hydrogen fluoride hydrogen bonding, van der Waals interaction, DNA base pair formation, BH(3)NH(3) and BH(3)CO coordinate bond formation, Cu-ligand interactions, as well as LiF, LiCl, NaF, and NaCl ionic interactions. PMID:19586091

Su, Peifeng; Li, Hui

2009-07-01

52

Energy decomposition analysis of covalent bonds and intermolecular interactions  

NASA Astrophysics Data System (ADS)

An energy decomposition analysis method is implemented for the analysis of both covalent bonds and intermolecular interactions on the basis of single-determinant Hartree-Fock (HF) (restricted closed shell HF, restricted open shell HF, and unrestricted open shell HF) wavefunctions and their density functional theory analogs. For HF methods, the total interaction energy from a supermolecule calculation is decomposed into electrostatic, exchange, repulsion, and polarization terms. Dispersion energy is obtained from second-order Mller-Plesset perturbation theory and coupled-cluster methods such as CCSD and CCSD(T). Similar to the HF methods, Kohn-Sham density functional interaction energy is decomposed into electrostatic, exchange, repulsion, polarization, and dispersion terms. Tests on various systems show that this algorithm is simple and robust. Insights are provided by the energy decomposition analysis into H2, methane C-H, and ethane C-C covalent bond formation, CH3CH3 internal rotation barrier, water, ammonia, ammonium, and hydrogen fluoride hydrogen bonding, van der Waals interaction, DNA base pair formation, BH3NH3 and BH3CO coordinate bond formation, Cu-ligand interactions, as well as LiF, LiCl, NaF, and NaCl ionic interactions.

Su, Peifeng; Li, Hui

2009-07-01

53

An easy access to ?-aryl substituted ?-ketophosphonates: Lewis acid mediated reactions of 1,3-diketones with ?-hydroxyphosphonates and tandem regioselective C-C bond cleavage.  

PubMed

A range of ?-aryl substituted ?-ketophosphonates is synthesised by Lewis acid mediated reactions of 1,3-diketones and easily accessible, inexpensive benzylic ?-hydroxyphosphonates in an operationally simple method under solvent-free conditions without exclusion of air/moisture. A regioselective C-C bond cleavage for 1,3-diketones in a tandem fashion has also been demonstrated. Synthesis of a ?-ketophosphonate with phenol functionality at the ?-position (structural analogue of raspberry ketone, a natural product) has also been presented. PMID:25098552

Pallikonda, Gangaram; Chakravarty, Manab; Sahoo, Manoj K

2014-09-28

54

C?-C? chromophore bond dissociation in protonated tyrosine-methionine, methionine-tyrosine, tryptophan-methionine, methionine-tryptophan and their sulfoxide analogs.  

PubMed

C(?)-C(?) chromophore bond dissociation in some selected methionine-containing dipeptides induced by UV photons is investigated. In methionine containing dipeptides with tryptophan as the UV chromophore, the tryptophan side chain is ejected either as an ion or as a neutral fragment while in dipeptides with tyrosine, the tyrosine side chain is lost only as a neutral fragment. Mechanisms responsible for these fragmentations are proposed based on measured branching ratios and fragmentation times, and on the results of DFT/B3-LYP calculations. It appears that the C(?)-C(?) bond cleavage is a non-statistical dissociation for the peptides containing tyrosine, and occurs after internal conversion for those with tryptophan. The proposed mechanisms are governed by the ionization potential of the aromatic side chain compared to that of the rest of the molecule, and by the proton affinity of the aromatic side chain compared to that of the methionine side chain. In tyrosine-containing peptides, the presence of oxygen on sulfur of methionine presumably reduces the ionization potential of the peptide backbone, facilitating the loss of the side chain as a neutral fragment. In tryptophan-containing peptides, the presence of oxygen on methionyl-sulfur expedites the transfer of the proton from the side chain to the sulfoxide, which facilitates the loss of the neutral side chain. PMID:22722478

Sunil Kumar, S; Lucas, B; Soorkia, S; Barat, M; Fayeton, J A

2012-08-01

55

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

56

Push-Pull Buta-1,2,3-trienes: Exceptionally Low Rotational Barriers of Cumulenic C?C Bonds and Proacetylenic Reactivity.  

PubMed

A variety of asymmetrically donor-acceptor-substituted [3]cumulenes (buta-1,2,3-trienes) were synthesized by developed procedures. The activation barriers to rotation ?G(?) were measured by variable temperature NMR spectroscopy and found to be as low as 11.8?kcal?mol(-1) , in the range of the barriers for rotation around sterically hindered single bonds. The central C?C bond of the push-pull-substituted [3]cumulene moiety is shortened down to 1.22? as measured by X-ray crystallography, leading to a substantial bond length alternation (BLA) of up to 0.17?. All the experimental results are supported by DFT calculations. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor-acceptor [3]cumulenes. Additional support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddition-retroelectrocyclization (CA-RE) cascade characteristic of donor-polarized acetylenes. PMID:25765373

Gawel, Przemyslaw; Wu, Yi-Lin; Finke, Aaron D; Trapp, Nils; Zalibera, Michal; Boudon, Corinne; Gisselbrecht, Jean-Paul; Schweizer, W Bernd; Gescheidt, Georg; Diederich, Franois

2015-04-13

57

Crystal structure of 2'-deoxycytidine hemidihydrogenphosphate reveals C+.C base pairs and tight, hydrogen-bonded (H2PO4-)infinity columns (1).  

PubMed

2'-Deoxycytidine hemidihydrogenphosphate has been crystallized in the hexagonal space group P6(2) with a = 25.839(3), c = 12.529(1) A. The structure has been solved using the Patterson search method. The asymmetric unit contains two protonated, base-paired 2'-deoxycytidine dimers and two H2PO4- anions. The C+.C base pairs are composed of a protonated and a neutral species each and are triple H-bonded, the central N(3) ... N(3) bonds being 2.850(7) and 2.884(5) A. The conformations of the four nucleosides fall in the same category (sugar puckers 2'-endo, glycosidic links anti) but in one of them the glycosidic torsion angle is quite low with consequences in other geometrical parameters. The H2PO4- anions are located on twofold axes and form two types of tight columns with P ... P separations about 4.18 A. The neighboring units along a column are linked via two very short O ... H ... O hydrogen bonds (O ... O about 2.49 A) leading to effective equalization of the P-O bonds. The base pairs of the two dC+.dC cations are coplanar and form layers perpendicular to the phosphate columns repeating every c/3. Within the layers, the dimers form a network through O(5') ... O(2) hydrogen bonds but their primary intermolecular interactions have the form of H-bond anchors [N(4)-H ... O-P and O(3')-H ... O-P] to the phosphate groups. PMID:7946075

Jasklski, M; Gdaniec, M; Gilski, M; Alejska, M; Bratek-Wiewirowska, M D

1994-06-01

58

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

PubMed

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

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

2015-01-28

59

Structure and bonding in a cyclobutyl tris(pyrazolyl)boratoniobium complex and the variation in agostic behaviour with ring size in the series Tp(Me2)NbCl(c-C(n)H(2n-1))(MeC[triple bond]CMe), n = 3-6.  

PubMed

The synthesis and characterisation of the cyclobutyl complex Tp(Me2)NbCl(c-C4H7)(MeC[triple bond]CMe) completes the family of cycloalkyl complexes Tp(Me2)NbCl(c-C(n)H(2n-1)), n = 3-6. The properties of the cyclobutyl complex are qualitatively similar to those of its cyclopentyl and cyclohexyl analogues, and dramatically different from those of the cyclopropyl derivative. Most conspicuously, the cyclobutyl system has an alpha-C-H agostic interaction in the dominant isomer, with no evidence for the alpha-C-C agostic character found for the smaller ring. C-C agostic character therefore seems to be unique to the cyclopropyl complex, where the acute C-C-C angles destabilise the C-C bonding orbitals. PMID:16688324

Besora, Maria; Maseras, Feliu; McGrady, John E; Ouli, Pascal; Dinh, Duy Hai; Duhayon, Carine; Etienne, Michel

2006-05-21

60

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

61

Bis(trifluoromethyl)methylene Addition to Vinyl-Terminated SAMs: A Gas-Phase CC 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 CC 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

62

Formation of C?C Bond via Knoevenagel Reaction between Aromatic Aldehyde and Barbituric Acid at Liquid/HOPG and Vapor/HOPG Interfaces.  

PubMed

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

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

2015-03-01

63

C-H activation and C=C double bond formation reactions in iridium ortho-methyl arylphosphane complexes.  

PubMed

The Vaska-type iridium(I) complex [IrCl(CO){PPh(2)(2-MeC(6)H(4))}(2)] (1), characterized by an X-ray diffraction study, was obtained from iridium(III) chloride hydrate and PPh(2)(2,6-MeRC(6)H(3)) with R=H in DMF, whereas for R=Me, activation of two ortho-methyl groups resulted in the biscyclometalated iridium(III) compound [IrCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)] (2). Conversely, for R=Me the iridium(I) compound [IrCl(CO){PPh(2)(2,6-Me(2)C(6)H(3))}(2)] (3) can be obtained by treatment of [IrCl(COE)(2)](2) (COE=cyclooctene) with carbon monoxide and the phosphane in acetonitrile. Compound 3 in CH(2)Cl(2) undergoes intramolecular C-H oxidative addition, affording the cyclometalated hydride iridium(III) species [IrHCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}] (4). Treatment of 2 with Na[BAr(f) (4)] (Ar(f)=3,5-C(6)H(3)(CF(3))(2)) gives the fluxional cationic 16-electron complex [Ir(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)][BAr(f) (4)] (5), which reversibly reacts with dihydrogen to afford the delta-agostic complex [IrH(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}][BAr(f)(4)] (6), through cleavage of an Ir-C bond. This species can also be formed by treatment of 4 with Na[BAr(f)(4)] or of 2 with Na[BAr(f)(4)] through C-H oxidative addition of one ortho-methyl group, via a transient 14-electron iridium(I) complex. Heating of the coordinatively unsaturated biscyclometalated species 5 in toluene gives the trans-dihydride iridium(III) complex [IrH(2)(CO){PPh(2)(2,6-MeC(6)H(3)CH=CHC(6)H(3)Me-2,6)PPh(2)}][BAr(f) (4)] (7), containing a trans-stilbene-type terdentate ligand, as result of a dehydrogenative carbon-carbon double bond coupling reaction, possibly through an iridium carbene species. PMID:17535000

Baratta, Walter; Ballico, Maurizio; Del Zotto, Alessandro; Zangrando, Ennio; Rigo, Pierluigi

2007-01-01

64

Characterization of a CC Bond Hydrolase from Sphingomonas wittichii RW1 with Novel Specificities towards Polychlorinated Biphenyl Metabolites?  

PubMed Central

Sphingomonas wittichii RW1 degrades chlorinated dibenzofurans and dibenzo-p-dioxins via meta cleavage. We used inverse PCR to amplify dxnB2, a gene encoding one of three meta-cleavage product (MCP) hydrolases identified in the organism that are homologues of BphD involved in biphenyl catabolism. Purified DxnB2 catalyzed the hydrolysis of 8-OH 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (HOPDA) approximately six times faster than for HOPDA at saturating substrate concentrations. Moreover, the specificity of DxnB2 for HOPDA (kcat/Km = 1.2 107 M?1 s?1) was about half that of the BphDs of Burkholderia xenovorans LB400 and Rhodococcus globerulus P6, two potent polychlorinated biphenyl (PCB)-degrading strains. Interestingly, DxnB2 transformed 3-Cl and 4-OH HOPDAs, compounds that inhibit the BphDs and limit PCB degradation. DxnB2 had a higher specificity for 9-Cl HOPDA than for HOPDA but a lower specificity for 8-Cl HOPDA (kcat/Km = 1.7 106 M?1 s?1), the chlorinated analog of 8-OH HOPDA produced during dibenzofuran catabolism. Phylogenetic analyses based on structure-guided sequence alignment revealed that DxnB2 belongs to a previously unrecognized class of MCP hydrolases, evolutionarily divergent from the BphDs although the physiological substrates of both enzyme types are HOPDAs. However, both classes of enzymes have mainly small hydrophobic residues lining the subsite that binds the C-6 phenyl of HOPDA, in contrast to the bulky hydrophobic residues (Phe106, Phe135, Trp150, and Phe197) found in the class II enzymes that prefer substrates possessing a C-6 alkyl. Thr196 and/or Asn203 appears to be an important determinant of specificity for DxnB2, potentially forming hydrogen bonds with the 8-OH substituent. This study demonstrates that the substrate specificities of evolutionarily divergent hydrolases may be useful for degrading mixtures of pollutants, such as PCBs. PMID:17416660

Seah, Stephen Y. K.; Ke, Jiyuan; Denis, Geoffroy; Horsman, Geoff P.; Fortin, Pascal D.; Whiting, Cheryl J.; Eltis, Lindsay D.

2007-01-01

65

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.

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

66

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

67

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

68

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

69

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

SciTech Connect

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

Nocton, Gr& #233; gory; Lukens, Wayne W.; Booth, Corwin H.; Rozenel, Sergio S.; Medling, Scott A.; Maron, Laurent; Andersen, Richard A.

2014-06-26

70

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

71

Direct construction of 2-alkylbenzo-1,3-azoles via C-H activation of alkanes for C-C and C-X (X = O, S) bond formation.  

PubMed

Copper catalyzed straightforward synthesis of 2-alkylbenzoxa(thia)azoles from aryl isocyanates/isothiocyanates and simple alkanes is reported. The protocol utilizes ditertiary butyl peroxide (DTBP) as a radical initiator and involves sequential formation of C-C and C-X (X = O, S) bonds followed by aromatization in a one-pot procedure. PMID:25578954

Yadav, Arvind K; Yadav, Lal Dhar S

2015-02-18

72

Ln[N(SiMe3 )2 ]3 -catalyzed cross-diinsertion of C?N/C?C into an N?H bond: facile synthesis of 1,2,4-trisubstituted imidazoles from propargylamines and nitriles.  

PubMed

A lanthanide-catalyzed sequential insertion of C?N and C?C into an N?H bond is presented. The convenient reaction, which proceeds under mild conditions, is an efficient method for preparing 1,2,4-trisubstituted imidazoles directly from readily available propargylamines and nitriles. PMID:24920226

Hong, Longcheng; Shao, Yinlin; Zhang, Lixin; Zhou, Xigeng

2014-07-01

73

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

74

Sulfur in coal: Model studies of the role of ArS radicals in C-C and C-S bond formation and structural evolution in coal liquefaction  

SciTech Connect

Experiments in this paper show the importance of thiyl radicals in sulfur containing coals during coal liquefaction processes. The presence of arylthiyl radicals enhances the cleavage of C-C, C=C, and C=C bonds in these otherwise refactory systems. Abstraction reactions, 1,2-phenyl migration from sulfur to carbon and displacement reactions at sulfur may be important mechanisms of structural evolution during liquefaction. In addition to cleavage of arylalkyl structures, the results also show that undesirable retrograde formation of inert diaryl- and triarylmethanes may be a consequence of the presence of sulfur and the attending aryl thiol structures. Thus, while a reaction medium including sulfur and hydrogen has been demonstrated to lead to the enhance cleavage of the bibenzyl model structure the present results suggest that retrograde reactions may be significant undesired pathways in coal liquefaction in the presence of sulfur. 17 refs.

Alnajjar, M.S.; Franz, J.A.

1987-06-01

75

Theoretical studies of the solvent effect on the conformation of the HO-C-C-X (X = F, NH2, NO2) moiety with competing intra- and intermolecular hydrogen bonds.  

PubMed

Theoretical calculations up to the ab initio IEF-PCM/CCSD(T)/CBS//IEF-PCM/B3LYP/6-311++G** and IEF-PCM/B97D/aug-cc-pvtz levels have been performed for 2X-ethanol and 2X-phenol systems with X = F, NH(2), NO(2) in chloroform and aqueous solution. The calculated relative free energies by means of the IEF-PCM continuum dielectric method do not differ very much at the DFT and ab initio levels. Application of explicit solvent models and the FEP/MC method for determining relative solvation free energies causes, however, large deviations in the predicted equilibrium compositions, although the predominant conformation for the solute is generally in agreement with that from the corresponding IEF-PCM calculations. Existence of an intramolecular hydrogen bond (HB structure) for species with the HO-C-C-X moiety is preferred compared with a conformation when the hydrogen bond is disrupted (NoHB) for the considered F- and NO(2)-substituted molecules both in chloroform and aqueous solution. For 2NH(2)-ethanol, the HB structure is predominant in chloroform, whereas the 93:7 ratio for the OCCN trans/gauche species was obtained in aqueous solution. 2NH(2)-phenol exhibits a subtle equilibrium of the HB and NoHB conformations in both solvents. Potential of mean force calculations predict about a 10% solute association for the trans 2NH(2)-ethanol solute even in the fairly dilute 0.22 molar solution, whereas direct MC simulations do not support the maintenance of a doubly hydrogen-bonded dimer. Aqueous solution characteristics, as coordination numbers and numbers of strongly bound water molecules to the solute at T = 298 K and p = 1 atm, correspond reasonably to the derived molecular structures. PMID:22731938

Nagy, Peter I

2012-07-26

76

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

NASA Astrophysics Data System (ADS)

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

Miki, N.; Spearing, S. M.

2003-11-01

77

An interpretation of organometalic bond dissociation energies  

SciTech Connect

Organometallic bond dissociation energies (BDE) are incorporated into the E and C model with excellent results. Since the data are consistent with gas-phase systems, the fit supports claims that the enthalpies are relatively free of solvation contributions. The organometallic catimers (fragments forming the positive end of the dipole) include (CO){sub 5}Mn{sup 1},({eta}{sup 5}-(CH{sub 3}){sub 3}SiC{sub 5}H{sub 4}){sub 3}U{sup IV}-,({eta}{sup 5}C{sub 5}H{sub 5})(CO){sub 3}Mo{sup II}{sub 5}-,({eta}C{sub 5}(CH{sub 3}){sub 5})(P(CH{sub 3}{sub 3}){sub 2}Ru{sup II}-, (PCH{sub 2})CH{sub 2}P(C{sub 6}H{sub 5}){sub 2})(CH{sub 3})Pt{sup II}-,({eta}{sup 5}-C{sub 5}(CH{sub 3}){sub 5}){sub 2}Zr-, and 1/2({eta}{sup 5}-(C{sub 5}(CH{sub 3}){sub 5}){sub 2}Sm){sub 2{minus}}. The animers (fragments forming the negative end of the dipole) include organics, halogens, and inorganics. In addition to predicting and interpreting enthalpies, the resulting parameters for the radicals provide reactivity scales that can be used to interpret reactivity and physicochemical properties. Significant chemical insight results from the fit of the data to the ECT model. The parameters are used to reinterpret {sup 19}F chemical shifts in (F-Ph)Pt(P{sub 2}R{sub 3}){sub 2}-X, in terms of a {sigma}-only Pt-X bond. The earlier interpretation is one of the classic examples used to support metal-ligand {pi}-bonding interactions, Predicted bond energies are analyzed to indicate the metal properties that facilitate the CO insertion reaction. The analysis provides insights into the relative importance of electrostatic and covalent interactions.

Drago, R.S.; Wong, N.M.; Ferris, D.C. [Univ. of Florida, Gainesvile, FL (United States)

1992-01-01

78

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

NASA Astrophysics Data System (ADS)

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.

1986-08-01

79

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

80

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

NASA Astrophysics Data System (ADS)

This study initially characterizes the primary photodissociation processes of epichlorohydrin, c-(H2COCH)CH2Cl. The three dominant photoproduct channels analyzed are c-(H2COCH)CH2+Cl, c-(H2COCH)+CH2Cl, and C3H4O+HCl. In the second channel, the c-(H2COCH) photofission product is a higher energy intermediate on C2H3O global potential energy surface and has a small isomerization barrier to vinoxy. The resulting highly vibrationally excited vinoxy radicals likely dissociate to give the observed signal at the mass corresponding to ketene, H2CCO. The final primary photodissociation pathway HCl+C3H4O evidences a recoil kinetic energy distribution similar to that of four-center HCl elimination in chlorinated alkenes, so is assigned to production of c-(H2COC)=CH2; the epoxide product is formed with enough vibrational energy to isomerize to acrolein and dissociate. The paper then analyzes the dynamics of the C3H5O radical produced from C-Cl bond photofission. When the epoxide radical photoproduct undergoes facile ring opening, it is the radical intermediate formed in the O(P3)+allyl bimolecular reaction when the O atom adds to an end C atom. We focus on the HCO+C2H4 and H2CO+C2H3 product channels from this radical intermediate in this report. Analysis of the velocity distribution of the momentum-matched signals from the HCO+C2H4 products at m/e=29 and 28 shows that the dissociation of the radical intermediate imparts a high relative kinetic energy, peaking near 20 kcal/mol, between the products. Similarly, the energy imparted to relative kinetic energy in the H2CO+C2H3 product channel of the O(P3)+allyl radical intermediate also peaks at high-recoil kinetic energies, near 18 kcal/mol. The strongly forward-backward peaked angular distributions and the high kinetic energy release result from tangential recoil during the dissociation of highly rotationally excited nascent radicals formed photolytically in this experiment. The data also reveal substantial branching to an HCCH+H3CO product channel. We present a detailed statistical prediction for the dissociation of the radical intermediate on the C3H5O potential energy surface calculated with coupled cluster theory, accounting for the rotational and vibrational energy imparted to the radical intermediate and the resulting competition between the H+acrolein, HCO+C2H4, and H2CO+C2H3 product channels. We compare the results of the theoretical prediction with our measured branching ratios. We also report photoionization efficiency (PIE) curves extending from 9.25 to 12.75 eV for the signal from the HCO+C2H4 and H2CO+C2H3 product channels. Using the C2H4 bandwidth-averaged absolute photoionization cross section at 11.27 eV and our measured relative photoion signals of C2H4 and HCO yields a value of 11.6+1/-3 Mb for the photoionization cross section of HCO at 11.27 eV. This determination puts the PIE curve of HCO measured here on an absolute scale, allowing us to report the absolute photoionization efficiency of HCO over the entire range of photoionization energies.

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

2010-09-01

81

Chords: Em 022000 Em Em Em Em C C C C  

E-print Network

Verse 1 Chorus Verse 2 Chorus Verse 3 Chords: Em 022000 C 035553 G 320002 F 133211 Intro: Em Em Em Em C C C C Em Em Em Em C C C C Em Em Em Em C C C C Em Em Em Em C C C C Verse: Em Em Em Em C C C C G G G G G G G G Em Em Em Em C C C C G G G G G G G G Em Em Em Em C C C C G G G G G G G G Em Em Em Em C C

Reiners, Peter W.

82

Enantioselective conversion of primary alcohols to ?-exo-methylene ?-butyrolactones via iridium-catalyzed C-C bond-forming transfer hydrogenation: 2-(alkoxycarbonyl)allylation.  

PubMed

Upon exposure of acrylic ester 1 to alcohols 2a-i in the presence of a cyclometalated iridium catalyst modified by (-)-TMBTP, catalytic C-C coupling occurs, providing enantiomerically enriched 5-substituted ?-exo-methylene ?-butyrolactones 3a-i. Bromination of the methylene butyrolactone products followed by zinc-mediated reductive aldehyde addition provides the disubstituted ?-exo-methylene ?-butyrolactones 6a and 6b with good to excellent levels of diastereoselectivity. PMID:22734694

Montgomery, T Patrick; Hassan, Abbas; Park, Boyoung Y; Krische, Michael J

2012-07-11

83

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

84

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

SciTech Connect

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

FitzPatrick, Benjamin L.; Alligood, Bridget W.; Butler, Laurie J. [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States); Lee, Shih-Huang [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Lin, Jim Jr-Min [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617 (China)

2010-09-07

85

Non-bonding potentials for the atom⋯atom interactions F⋯C?, F⋯N?, ?C⋯C?, ?C⋯N? and ?N⋯N? as derived from conformational data using molecular mechanics calculations  

NASA Astrophysics Data System (ADS)

Parameter values for the non-bonding interactions F⋯C?, F⋯N?, ?C⋯C?, ?C⋯N? and ?N⋯N? within the Morse potential formulation have been estimated from experimental data on HC?C?CH 2?CH 2?C?CH (BP), BrC?C?CH 2?CH 2?C?CH (BBP), Br BrC?C?CH 2?CH 2?C?CBr (DBBP), N?C?CH 2?CH 2?C?N, N?C?CF 2?CF 2?C?N, (N?C) 2?CH?CH?(C?N) 2, (N?C) 2?CCl?CCl? C?N) 2 and N? C?CH 2?CH 2?CH 2?C?N. Conformational energies, structures, torsional barrier heights and torsional force constants for BP, BBP and DBBP, for the eight cyanoethanes (C?H,F,Cl and Br) N?C?CX 2?CX 2?C?N and (N?C) 2?CX?CX?(C?N) 2, as well as for N?C?CH 2?CH 2?CH 2?C?N, have been estimated from molecular mechanics calculations.

Stavnebrekk, Per J.; Stlevik, Reidar

1989-10-01

86

A new mode of activation of CO2 by metal-ligand cooperation with reversible C-C and M-O bond formation at ambient temperature.  

PubMed

Team work: Although CO(2) binding to metal centers usually involves ? coordination to a C=O group or ? bonds to the carbon or oxygen atom of the CO(2) molecule, a new mode of metal-ligand cooperative activation of CO(2) to a ruthenium PNP pincer complex involving aromatization/dearomatization steps is presented in experimental and theoretical studies (see scheme). PMID:22736579

Vogt, Matthias; Gargir, Moti; Iron, Mark A; Diskin-Posner, Yael; Ben-David, Yehoshoa; Milstein, David

2012-07-23

87

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

88

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

89

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

PubMed

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

Lu, Shao-Yu; Lin, Jyh-Shing

2014-01-14

90

Hydrogen migration and CC bond breaking in 1,3-butadiene in intense laser fields studied by coincidence momentum imaging  

Microsoft Academic Search

Two-body dissociation processes of H2CCHCHCH22+ induced by an intense laser field were investigated by the coincidence momentum imaging method. Four dissociation pathways, C4H62+?CH2++C3H4+, C4H62+?CH3++C3H3+, C4H62+?C2H3++C2H3+ and C4H62+?C2H2++C2H4+, were identified. The existence of the second and fourth pathways can be regarded as evidences of the chemical bond rearrangement processes associated with hydrogen migration in the intense laser field. It was found

Huailiang Xu; Tomoya Okino; Katsunori Nakai; Kaoru Yamanouchi; Stefan Roither; Xinhua Xie; Daniil Kartashov; Markus Schffler; Andrius Baltuska; Markus Kitzler

2010-01-01

91

Synthetic approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) reveal redox non-innocence and C-C bond-formation.  

PubMed

Attempted syntheses of (smif)(2)Ti (smif =1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiCl(n)L(m) (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, dpma = di-2-pyridylmethyl-amide). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox noninnnocent, such that d(1) Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)(2-)}Ti(III) (1), [(smif(2-))Ti(III)](2)(?-?(3),?(3)-N,N(py)(2)-smif,smif) (2), [(smif(2-))Ti(III)](?(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif(2-))Ti(III)(dpma) (4). The instability of (smif)(2)Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical dianion 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

2012-08-01

92

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 = 24) 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

93

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

PubMed

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

Beck, John Frederick; Mo, Yirong

2007-01-15

94

Exclusive selectivity in the one-pot formation of C-C and C-Se bonds involving Ni-catalyzed alkyne hydroselenation: optimization of the synthetic procedure and a mechanistic study.  

PubMed

A unique Ni-catalyzed transformation is reported for the one-pot highly selective synthesis of previously unknown monoseleno-substituted 1,3-dienes starting from easily available terminal alkynes and benzeneselenol. The combination of a readily available catalyst precursor, Ni(acac)2, and an appropriately tuned phosphine ligand, PPh2Cy, resulted in the exclusive assembly of the s-gauche diene skeleton via the selective formation of C-C and C-Se bonds. The unusual diene products were stable under regular experimental conditions, and the products maintained the s-gauche geometry both in the solid state and in solution, as confirmed by X-ray analysis and NMR spectroscopy. Thorough mechanistic studies using ESI-MS revealed the key Ni-containing species involved in the reaction. PMID:25288369

Orlov, Nikolay V; Chistyakov, Igor V; Khemchyan, Levon L; Ananikov, Valentine P; Beletskaya, Irina P; Starikova, Zoya A

2014-12-19

95

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

SciTech Connect

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

Hutchings, G.J.; Johnston, P. (Univ. of Liverpool (United Kingdom)); Hunter, R. (Univ. of Cape Town, Rondesbosch (South Africa)); Van Rensburg, L.J. (Univ. of Witwatersrand (South Africa))

1993-08-01

96

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 Toward Catalyst Deactivation During Ketone Hydrogenation  

SciTech Connect

The initial reaction observed between N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]+[CpM(CO)2(PPh3)] . At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+B(C6F5)4- gives CpW(CO)2(IMes)+B(C6F5)4- 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 H2, THF, ketones or alcohols. Reaction of CpW(CO)2(IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H)2]+. Addition of Et2CHOH to CpW(CO)2(IMes)+B(C6F5)4- gives the alcohol complex [CpM(CO)2(IMes)(Et2CHOH)]+[B(C6F5)4] which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4] produces an equilibrium with the dihydride [CpW(CO)2(IMes)(H)2]+ (Keq = 1.1 ? 103 at 25 C). The tungsten ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4] serves as a modest catalyst for hydrogenation of Et2C=O to Et2CHOH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C6F5)4-, indicating that these catalysts with N-heterocyclic carbenes ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu, Fan; Dioumaev, Vladimir K.; Szalda, David J.; Hanson, Jonathan; Bullock, R. Morris

2007-09-24

97

July 18, 2012 Qualified Energy Conservation Bond (QECB) Update: New  

E-print Network

July 18, 2012 Qualified Energy Conservation Bond (QECB) Update: New Guidance from the U, and local governments be given wide discretion in methods to conserve energy that may be financed with QECBs governments by providing them with access to subsidized financing to help promote energy-efficient policies

98

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

99

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 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

100

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

101

Chemical and quantum mechanical studies of the free radical C-C bond formation in the lipoxygenase-catalyzed dimerisation of octodeca-9,12-diynoic acid.  

PubMed

Triple bond analogues of poly-unsaturated fatty acids are well-known inactivators of lipoxygenases. In an earlier study we proposed that, since 11-oxo-octadeca-9,12-diynoic acid (11-oxo-ODYA) is the only oxygenated product formed during the irreversible inactivation of soybean lipoxygenase-1, the inactivation should proceed via a C11 centered octadeca-9,12-diynoic acid radical (ODYA radical). In the present study we investigated the lipoxygenase-catalysed formation of the ODYA radical. In the reaction of lipoxygenase with ODYA in the absence of dioxygen and in the presence of 13(S)-hydroperoxy-octadeca-9Z, 11E-dienoic acid (13-HPOD), free ODYA radicals were formed which resulted in the formation of three dimeric ODYA products in which one ODYA moiety is linked via its C9 (12%), C11 (72%) or C13 (16%) to the C11 methylene of the other ODYA moiety. With the ab initio Hartree-Fock method, using the 2,5-heptadiynyl radical as a model compound, the electron spin in the ODYA radical was calculated to be located for 12.0, 75.0 and 12.0% on carbon atoms C9, C11 and C13 of the ODYA radical, respectively. The ODYA-ODYA dimer formation could thus be explained on the basis of the electron spin distribution in the ODYA radical. The dimer formation, i. e. reaction of an ODYA radical with an ODYA molecule was compared with the reaction of the ODYA radical with dioxygen. On the basis of this comparison it is concluded that a) the ODYA dimer formation occurs at the carbon atom with the highest electron spin population; b) ODYA dimer formation is predominantly a kinetically determined process; c) the electron spin distribution in the ODYA radical can be used to predict the composition of the dimer mixture; and d) the regiospecific oxygen addition in the formation of 11-oxo-ODYA is enzymatically controlled. PMID:9034248

Nieuwenhuizen, W F; van Lenthe, J H; Blomsma, E J; Van der Kerk-Van Hoof, A C; Veldink, G A; Vliegenthart, J F

1997-01-01

102

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

103

Bonding  

MedlinePLUS

... between teeth Make teeth look longer Change the shape or color of teeth Sometimes, bonding also is used to ... a color that will most closely match the color of the tooth. He or she will shape the tooth with a drill (handpiece) if necessary, ...

104

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

105

The kinetic energy change on covalent bond formation  

PubMed Central

Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change ?T, on nonpolar covalent bond formation in a diatomic molecule, of the form ?T(R) = ?F(R - r?)S(r?)dr?. Here F is a nonlinear response function which itself involves the overlap S. The kinetic change is known to satisfy the sum rule ?0??T(R)dR = Z?Z? exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ?0??T(R)R2dR, which is an important additional property of the kinetic energy change. Representation of ?T(R) as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form. PMID:16593098

March, Norman H.; Parr, Robert G.; Mucci, Joe F.

1981-01-01

106

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

107

Storing Renewable Energy in Chemical Bonds  

ScienceCinema

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

2014-06-13

108

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

109

Bond Dissociation Energies in Second-Row Compounds  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Heats of formation at 0 and 298 K are predicted for PF?, PF?, PF?O, SF?, SF?, SF?, SF?O, SF?O?, and SF?O as well as a number of radicals derived from these stable compounds on the basis of coupled cluster theory [CCSD(T)] calculations extrapolated to the complete basis set limit. In order to achieve near chemical accuracy (1 kcal/mol), additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and vibrational zero-point energies. The calculated values substantially reduce the error limits for these species. A detailed comparison of adiabatic and diabatic bond dissociation energies (BDEs) is made and used to explain trends in the BDEs. Because the adiabatic BDEs of polyatomic molecules represent not only the energy required for breaking a specific bond but also contain any reorganization energies of the bonds in the resulting products, these BDEs can be quite different for each step in the stepwise loss of ligands in binary compounds. For example, the adiabatic BDE for the removal of one fluorine ligand from the very stable closed-shell SF? molecule to give the unstable SF? radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF? radical to give the stable closed-shell SF? molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF?O molecule to give the unstable PF?O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF? molecule. The same principles govern the BDEs of the phosphorus fluorides and the sulfur oxofluorides. In polyatomic molecules, care must be exercised not to equate BDEs with the bond strengths of given bonds. The measurement of the bond strength or stiffness of a given bond represented by its force constant involves only a small displacement of the atoms near equilibrium and, therefore, does not involve any reorganization energies, i.e., it may be more appropriate to correlate with the diabatic product states.

Grant, Daniel J.; Matus, Myrna H.; Switzer, Jackson R.; Dixon, David A.; Francisco, Joseph S.; Christe, Karl O.

2008-04-10

110

Bonding energies of bitumen to tar sand mineral  

SciTech Connect

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

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

1986-03-01

111

Mixed mode energy release rates for adhesively bonded beam specimens  

Microsoft Academic Search

This paper presents closed-form solutions for the energy release rate and the mode ratio of an equal adherend adhesively bonded beam specimen subject to a mixed mode bending load. The developed expressions explicitly account for the thickness and the material properties of the adhesive layer using a beam on an elastic foundation model. The accuracy of the expressions is verified

G. Fernlund; J. K. Spelt; T Kevin O'Brien

1994-01-01

112

Hydrogen bond energy of the water dimer  

Microsoft Academic Search

Large scale ab initio molecular orbital calculations on the binding energy of the water dimer have been performed. These calculations extend the previous correlation consistent basis set work to include larger basis sets (up to 574 functions), and core\\/valence correlation effects have now been included. The present work confirms the earlier estimate of -4.9 kcal\\/mol as the MP2(FC) basis set

Martin W. Feyereisen; David Feller; David A. Dixon

1996-01-01

113

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

114

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

115

On the C?H bond dissociation energy of acetylene  

NASA Astrophysics Data System (ADS)

Ab initio calculations, including extrapolation to the complete basis set limit, are reported for the C?H bond dissociation energy of acetylene. These calculations, which have a rms error of 0.51 kcal/mol per bond for the atomization energies of 13 well-known molecules, give D0(H-CCH) = 131.54 kcal/mol, in good agreement with previous results, but about 5 kcal/mol above the recent measurement of Green, Kinsey and Field ( D0 ? 126.647 0.002 kcal/mol), and that of Segall, Lavi, Wen and Wittig ( D0 = 127 1.5 kcal/mol). The electron affinity of CCH is calculated to be within 0.18 kcal/mol of the recent measurement of Ervin et al. (2.969 0.010 eV)

Petersson, J. A. Montgomery G. A., Jr.

1990-04-01

116

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

PubMed

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

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

2006-11-01

117

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-HO=P hydrogen bonds to form dimers. PMID:25279604

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

2014-10-15

118

Accurate Bond Energies of Hydrocarbons from Complete Basis Set Extrapolated Multi-Reference Singles and Doubles Configuration Interaction  

SciTech Connect

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

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

2011-11-03

119

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

120

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

ERIC Educational Resources Information Center

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

Smith, Derek W.

2004-01-01

121

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.

122

Excitation energy transfer in covalently bonded porphyrin heterodimers  

NASA Astrophysics Data System (ADS)

We describe the photophysical properties of heterodimers that are formed by the free base 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphyrin and the zinc complex of 5-( p-aminophenyl)-10,15,20-triphenylporphyrin and that are covalently bonded by the amide link. These dimers differ in the configuration of the double bond in the spacer group. We determine fluorescence quantum yields of heterodimers and their porphyrin components. The energy transfer rate constants have been estimated from the measured fluorescence lifetimes and fluorescence excitation spectra and, also, they have been calculated from the steady-state absorption and fluorescence spectra according to the Frster theory. We have found that the efficiency of the intramolecular energy transfer in heterodimers is 0.97-0.99, and the energy migration rate constants have been found to be (1.82-4.49) 1010 s-1. The results of our investigation show that synthesized heterodimers can be used as efficient light-harvesting elements in solar energy conversion devices.

Paschenko, V. Z.; Konovalova, N. V.; Bagdashkin, A. L.; Gorokhov, V. V.; Tusov, V. B.; Yuzhakov, V. I.

2012-04-01

123

Cleavage of thymine N3H bonds by low-energy electrons attached Magali Theodore 1  

E-print Network

Cleavage of thymine N3H bonds by low-energy electrons attached to base p* orbitals Magali The the effects of base p-stacking on the rates of such bond cleavages. To date, our results suggest that sugarphosphate CO bonds have the lowest barriers to cleavage, that attach- ment of electrons with energies below 2

Simons, Jack

124

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

SciTech Connect

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

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

2010-01-07

125

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

ERIC Educational Resources Information Center

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

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

126

Direct evaluation of individual hydrogen bond energy in situ in intra- and intermolecular multiple hydrogen bonds system.  

PubMed

The results of evaluating the individual hydrogen bond (H-bond) strength are expected to be helpful for the rational design of new strategies for molecular recognition or supramolecular assemblies. Unfortunately, there is few obvious and unambiguous means of evaluating the energy of a single H-bond within a multiple H-bonds system. We present a local analytic model, ABEEM?? H-bond energy (HBE) model based on ab initio calculations (MP2) as benchmark, to directly and rapidly evaluate the individual HBE in situ in inter- and intramolecular multiple H-bonds system. This model describes the HBE as the sum of electrostatic and van der Waals (vdW) interactions which all depend upon the geometry and environment, and the ambient environment of H-bond in the model is accounted fairly. Thus, it can fairly consider the cooperative effect and secondary effect. The application range of ABEEM?? HBE model is rather wide. This work has discussed the individual H-bond in DNA base pair and protein peptide dimers. The results indicate that the interactions among donor H atom, acceptor atom as well as those atoms connected to them with 1,2 or 1,3 relationships are all important for evaluating the HBE, although the interaction between the donor H atom and the acceptor atom is large. Furthermore, our model quantitatively indicates the polarization ability of N, O, and S in a new style, and gives the percentage of the polarization effect in HBE, which can not be given by fixed partial charge force field. PMID:22170234

Liu, Cui; Zhao, Dong-Xia; Yang, Zhong-Zhi

2012-02-01

127

Low-Energy (0.1 eV) Electron Attachment SS Bond Cleavage  

E-print Network

Low-Energy (0.1 eV) Electron Attachment SS Bond Cleavage Assisted by Coulomb Stabilization and insights should be of substantial value to workers studying bond cleavage rates and fragmentation patterns Chem 102: 838846, 2005 Key words: electron attachment; bond cleavage; disulfide bridge Correspondence

Simons, Jack

128

CarbonCarbon Bond Cleavage and Dehydrogenation of Isobutane Over HZSM-5 at Low Pressures and Temperatures  

E-print Network

CarbonCarbon Bond Cleavage and Dehydrogenation of Isobutane Over HZSM-5 at Low Pressures 2012 Abstract Carboncarbon bond cleavage and dehydroge- nation are observed following low.4 kJ mol-1 (CC bond cleavage) and 62.8 1.0 kJ mol-1 (dehydrogenation). Such low energy barriers

Tesfatsion, Leigh

129

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

SciTech Connect

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

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

2006-02-28

130

Interstellar Isomers: The Importance of Bonding Energy Differences  

E-print Network

We present strong detections of methyl cyanide, vinyl cyanide, ethyl cyanide and cyanodiacetylene 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 for its J(K)=1(0)-0(0) transition, which is the first interstellar report of this line. To determine the spatial distribution of methyl isocyanide, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(K)=4(K)-3(K) (K=0-3) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is >8500 cm^-1 (>12,000 K). That we detect methyl isocyanide emission with a single antenna (Gaussian beamsize(Omega_B)=1723 arcsec^2) but not with an interferometer (Omega_B=192 arcsec^2), strongly suggests that methyl isocyanide has a widespread spatial distribution toward the Sgr B2(N) region. Thus, large-scale, non-thermal processes in the surrounding medium may account for the conversion of methyl cyanide to methyl isocyanide while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of methyl isocyanide. Ice analog experiments by other investigators have shown that radiation bombardment of methyl cyanide can produce methyl isocyanide, 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.

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

2005-06-21

131

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 it is possible to generate accurate potential energy surfaces (PESs) for small clusters, such as those of water (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl­H2O and NH3

Reisler, Hanna

132

Influence of confinement on hydrogen bond energy. The case of the FHNCH 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 HN hydrogen bond in the HeFHNCHHe model system are proposed. They show that the energy of the HN hydrogen bond in this confined dimer decreases continuously with the reduction of the HeHe distance, thus with the increase of the pressure effect exerted on the confined dimer. PMID:20738112

Jab?o?ski, Miros?aw; Sol, Miquel

2010-09-23

133

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

PubMed Central

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

Pauling, Linus; Kamb, Barclay

1986-01-01

134

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

135

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

PubMed Central

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

Rodrguez-Gallego, Esther; Hernndez-Aguilera, Anna; Marin-Casad, Roger; Rull, Anna; Beltrn-Debn, Ral; Menendez, Javier A.; Vazquez-Martin, Alejandro; Sirvent, Juan J.; Martn-Paredero, Vicente; Corb, Angel L.; Sierra-Filardi, Elena; Aragons, Gerard; Garca-Heredia, Anabel; Camps, Jordi; Alonso-Villaverde, Carlos; Joven, Jorge

2013-01-01

136

Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy  

E-print Network

stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond dissociation energies for the corresponding sensitive to deviations from planarity and give better linear correlations with RSE and BDE(C-H). The correlations cover a range of more than 20 kcal/mol and are reliable predictors of RSE and BDE(C-H

Brocks, Jochen J.

137

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

138

Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in the Water Dimer  

E-print Network

Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in the Water Dimer Lee C. Ch'ng, Amit K. Samanta, Gabor Czako,,§ Joel M. Bowman,*, and Hanna Reisler bonding in water is dominated by pairwise dimer interactions, and the predissociation of the water dimer

Reisler, Hanna

139

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

Microsoft Academic Search

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest payments from the issuer. Because CREBs are theoretically interest free, they may be more attractive than traditional tax-exempt municipal bonds.

C. Kreycik; J. Couglin

2009-01-01

140

Intrinsic affinities of alkali cations for 15-crown-5 and 18-crown-6: Bond dissociation energies of gas-phase M{sup +}-crown ether complexes  

SciTech Connect

Bond dissociation energies (BDEs) of M{sup +}[c-(C{sub 2}H{sub 4}O){sub 5}] and M{sup +}[c-(C{sub 2}H{sub 4}O){sub 6}] for M = Na, K, Rb, and Cs are reported. The BDEs are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-crown ether complexes by xenon measured by using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally in endothermic loss of the ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. For both 18-crown-6 and 15-crown-5, the BDEs decrease monotonically with increasing cation size. These results indicate that the intrinsic affinity of c-(C{sub 2}H{sub 4}O){sub 5} and c-(C{sub 2}H{sub 4}O){sub 6} for M{sup +} is determined principally by the charge density of the cation not by the ratio of the ionic radius to the cavity size. The BDEs reported here are in fair agreement with recent ab initio calculations at the MP2 level with 6-31+G* basis sets. The experimental values are systematically smaller than the computed values by 8 {+-} 2 kJ/mol per metal-oxygen interaction. The existence of less strongly bound isomers in the experimental apparatus for Rb{sup +}(15-crown-5) and Cs{sup +}(15-crown-5) appears likely, but their absence for Na{sup +} and K{sup +} complexes indicates interesting metal-dependent dynamics to the formation of such isomers.

More, M.B.; Ray, D.; Armentrout, P.B.

1999-01-20

141

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

2008-07-27

142

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.

Heyrovska, Raji

2008-01-01

143

Atomistic spectrometrics of local bond-electron-energy pertaining to Na and K clusters  

NASA Astrophysics Data System (ADS)

Consistency between density functional theory calculations and photoelectron spectroscopy measurements confirmed our predications on the undercoordination-induced local bond relaxation and core level shift of Na and K clusters. It is clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and local potential well depression and shift the electron binding-energy accordingly. Numerical consistency turns out the energy levels for an isolated Na (E2p = 31.167 eV) and K (E3p = 18.034 eV) atoms and their respective bulk shifts of 2.401 eV and 2.754 eV, which is beyond the scope of conventional approaches. This strategy has also resulted in quantification of the local bond length, bond energy, binding energy density, and atomic cohesive energy associated with the undercoordinated atoms.

Bo, Maolin; Wang, Yan; Huang, Yongli; Liu, Yonghui; Li, Can; Sun, Chang Q.

2015-01-01

144

Influence of nitrogen ion implantation energies on surface chemical bonding structure and mechanical properties of nitrogen-implanted silicon carbide ceramics  

NASA Astrophysics Data System (ADS)

Nitrogen ions were implanted into silicon carbide ceramics (N +-implanted SiC) at different ions energies. The surface chemical bonding structure of N +-implanted SiC ceramics were investigated by using X-ray photoelectron spectroscopy (XPS). The hardness of N +-implanted SiC ceramics was measured using nano-indenter, and the friction and wear properties of the N +-implanted SiC/SiC tribopairs were studied using ball-on-disk type tribo-meter in water lubrication. The wear tracks were observed using non-contact surface profilometer and scanning electron microscope (SEM). The results showed that the surface roughness of N +-implanted SiC ceramic was higher than that of SiC ceramic, and some chemical bonds such as Si-N, C-C, C dbnd N and C-N bonds were formed in N +-implanted layer besides Si-C bonds. In comparison of SiC ceramic's hardness, the hardness of N +-implanted SiC ceramics at 30 and 50 keV was higher while that at 65 keV was lower. Under water lubrication, the friction coefficient and the specific wear rates for the N +-implanted SiC/SiC tribopairs were all lower than those of the SiC/SiC tribopairs, and displayed the lowest values at 50 keV. According to XPS analysis, it was concluded that the high wear resistance and low friction coefficient for the N +-implanted SiC/SiC tribopairs were attributed to the formation of carbon rich composite on the surface of N +-implanted SiC ceramics.

Zhou, Fei; Yuan, Yingguang; Chen, Kangmin; Wang, Xiaolei

2009-09-01

145

PCM study of the solvent and substituent effects on bond dissociation energies of the C=NO bond  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are used to estimate the equilibrium C=NO bond dissociation energies (BDEs) for eight X=NO molecule (X = CCl3, C6F5, CH3, CH3CH2, iC3H7, tC4H9, CH2CHCH2, and C6H5CH2). These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 6-31G** and 6-311G** basis sets and the complete basis set (CBS-QB3) method. The obtained results are compared with the available experimental results. It is demonstrated that B3P86/6-31G** and CBS-QB3 methods are accurate for computing the reliable BDEs for the X=NO molecule. Considering the inevitably computational cost of CBS-QB3 method and the reliability of the B3P86 calculations, B3P86 method with 6-31G** basis set may be more suitable to calculate the BDEs of the C=NO bond. The solvent effects on the BDEs of the C=NO bond are analyzed and it is shown that the C=NO BDEs in a vacuum computed by using B3PW91/6-311G** method are the closest to the computed values in acetontrile and the average solvent effect is 1.48 kcal/mol. Subsequently, the substituent effects of the BDEs of the C=NO bond are further analyzed and it is found that electron denoting group stabilizes the radical and as a result BDE decreases; whereas electron withdrawing group stabilizes the group state of the molecule and thus increases the BDE from the parent molecule.

Li, Xiao-Hong; Tang, Zheng-Xin; Yang, Xiang-Dong

146

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

SciTech Connect

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

Alnajjar, Mikhail S.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Zhang, Xian-Man (Pacific Northwest National Laboratory) [Pacific Northwest National Laboratory; Gleicher, Gerald J.(VISITORS) [VISITORS; Truksa, Scott V.(VISITORS) [VISITORS; Franz, James A.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

2002-12-13

147

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

PubMed

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

Jacobsen, Heiko

2009-06-01

148

Toward accurate prediction of potential energy surfaces and the spectral density of hydrogen bonded systems  

NASA Astrophysics Data System (ADS)

Despite the considerable progress made in quantum theory and computational methods, detailed descriptions of the potential energy surfaces of hydrogen-bonded systems have not yet been achieved. In addition, the hydrogen bond (H-bond) itself is still so poorly understood at the fundamental level that it remains unclear exactly what geometry constitutes a real H-bond. Therefore, in order to investigate features essential for hydrogen bonded complexes, a simple, efficient, and general method for calculating matrix elements of vibrational operators capable of describing the stretching modes and the H-bond bridges of hydrogen-bonded systems is proposed. The derived matrix elements are simple and computationally easy to evaluate, which makes the method suitable for vibrational studies of multiple-well potentials. The method is illustrated by obtaining potential energy surfaces for a number of two-dimensional systems with repulsive potentials chosen to be in Gaussian form for the stretching mode and of the Morse-type for the H-bond bridge dynamics. The forms of potential energy surfaces of weak and strong hydrogen bonds are analyzed by varying the asymmetry of the Gaussian potential. Moreover, the choice and applicability of the selected potential for the stretching mode and comparison with other potentials used in the area of hydrogen bond research are discussed. The approach for the determination of spectral density has been constructed in the framework of the linear response theory for which spectral density is obtained by Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode. The approach involves anharmonic coupling between the high frequency stretching vibration (double well potential) and low-frequency donor-acceptor stretching mode (Morse potential) as well as the electrical anharmonicity of the dipole moment operator of the fast mode. A direct relaxation mechanism is incorporated through a time decaying exponential according to Rsch and Ratner theory.

Rekik, Najeh

2014-03-01

149

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

NASA Astrophysics Data System (ADS)

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

Srivastava, Amit; Granek, Rony

2015-02-01

150

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

PubMed Central

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

151

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

152

Rhodium-Carbon Bond Energies in TpRh(CNneopentyl)(CH2X)H: Quantifying Stabilization Effects in M-C Bonds  

E-print Network

Rhodium-Carbon Bond Energies in TpRh(CNneopentyl)(CH2X)H: Quantifying Stabilization Effects in M carbonyl shows preferential formation of linear over branched aldehydes (4:1), and use of a bulkier rhodium

Jones, William D.

153

Singlet-triplet energy separation in divalent seven-membered cyclic conjugated compounds C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb  

NASA Astrophysics Data System (ADS)

The electronic and thermal energy differences, ? E(t-s); enthalpy differences, ? H(t-s); and free energy differences between the singlet and triplet states, ? G(t-s), were calculated for C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb at the B3LYP/6-311++G (3 df, 2 p) level. The singlet-triplet splitting, G s-t, of C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb generally increased from C6H6C toward C6H6Pb. The most stable tautomers and conformers were suggested for the singlet and triplet states of C6H6M (M = C, Si, Ge, Sn and Pb). The geometrical parameters were calculated and discussed.

Vessally, E.; Chalyavi, N.; Rezaei, A.; Nikoorazm, M.

2007-11-01

154

Buried hydrophobic silicon bonding studied by high-energy x-ray reflectivity  

NASA Astrophysics Data System (ADS)

The non-conventional technique of high-energy x-ray reflectivity is used to investigate buried Si|Si interface obtained by hydrophobic wafer bonding. In this experiment the well-collimated beam is transmitted through the sample and is reflected by the bonding interface described by its density and width. Transmission x-ray reflectivity curves are fitted using this two-parameter model with a Gaussian or exponential profile to analyse the evolution of the bonding interface as a function of temperature from 250C to 1100C.

Buttard, D.; Rieutord, F.; Eymery, J.; Fournel, F.; Bataillou, B.

2003-05-01

155

Imaging bond breaking and vibrational energy transfer in small water containing clusters  

NASA Astrophysics Data System (ADS)

This letter presents a brief overview of our recent experimental studies of state-to-state vibrational predissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters following vibrational excitation. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl-H2O and NH3-H2O. Pair-correlated product energy distributions from the VP of these complexes are also presented and compared to theoretical models. Further insights into mechanisms are obtained from the recent quasi-classical trajectory (QCT) calculations of Bowman and coworkers. The D0 values for (H2O)2 and (H2O)3 are in very good agreement with recent calculated values, and the results are used to estimate the contributions of cooperative interactions to the H-bonding network.

Samanta, Amit K.; Ch'ng, Lee C.; Reisler, Hanna

2013-06-01

156

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 SiSi 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

157

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

158

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

159

Climate Change, Sustainable Energy, and Caron Finance: The Kyoto Bond  

Microsoft Academic Search

The Kyoto Protocol requires a 5.2% reduction of greenhouse gas emissions from developed countries. This is an important starting point both to prevent climate change and to start to implement new Sustainable Energy policy for a Sustainable Economy. At the local level (from regions to cities) lower cost\\/risk energy portfolios can be developed by adjusting the conventional mix of energy

Aldo Iacomellia; Emanuele Piccinno; Daniele Villoresi

160

Tuning the ionization energy of organic semiconductor films: the role of intramolecular polar bonds.  

PubMed

For the prototypical conjugated organic molecules pentacene and perfluoropentacene, we demonstrate that the surface termination of ordered organic thin films with intramolecular polar bonds (e.g., -H versus -F) can be used to tune the ionization energy. The collective electrostatics of these oriented bonds also explains the pronounced orientation dependence of the ionization energy. Furthermore, mixing of differently terminated molecules on a molecular length scale allows continuously tuning the ionization energy of thin organic films between the limiting values of the two pure materials. Our study shows that surface engineering of organic semiconductors via adjusting the polarity of intramolecular bonds represents a generally viable alternative to the surface modification of substrates to control the energetics at organic/(in)organic interfaces. PMID:18771262

Salzmann, Ingo; Duhm, Steffen; Heimel, Georg; Oehzelt, Martin; Kniprath, Rolf; Johnson, Robert L; Rabe, Jrgen P; Koch, Norbert

2008-10-01

161

Financing climate-friendly energy development through bonds  

Microsoft Academic Search

In this paper we review the various instruments that have been proposed and implemented for financing renewable energy and low-carbon technology projects, in both the developed and developing world, with a focus on private sector involvement. We consider their common features and compare their total impact so far with the scale of renewable energy funding likely to be needed over

John A Mathews; Sean Kidney

2012-01-01

162

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

163

A theory for calculating the surface-adsorbate bond dissociation energy from collision-induced desorption threshold measurements  

E-print Network

A theory for calculating the surface-adsorbate bond dissociation energy from collision is presented for determining the bond dissociation energy, Do, of a surface-adsorbate complex from collision-induced desorption measurements. D, is calculated from the minimum collision energy required for desorption

Levis, Robert J.

164

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

E-print Network

Long time fluctuation of liquid water: l/f spectrum of energy fluctuation in hydrogen bond network of the potential energy fluctuation of liquid water is examined and found to yield so-called l/f frequency bond network. `,* This rearrangement dynamics involves collective motion of water molecules and energy

Ramaswamy, Ram

165

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

166

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

167

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

SciTech Connect

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

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

1988-01-15

168

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

169

Bond Dissociation Energies in Second-Row Compounds  

Microsoft Academic Search

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Heats of formation at 0 and 298 K are predicted for PF, PF, PFO, SF, SF, SF, SFO, SFO, and

Daniel J. Grant; Myrna H. Matus; Jackson R. Switzer; David A. Dixon; Joseph S. Francisco; Karl O. Christe

2008-01-01

170

CH Bond Functionalization in Complex Organic Synthesis  

Microsoft Academic Search

Direct and selective replacement of carbon-hydrogen bonds with new bonds (such as C-C, C-O, and C-N) represents an important and long-standing goal in chemistry. These transformations have broad potential in synthesis because C-H bonds are ubiquitous in organic substances. At the same time, achieving selectivity among many different C-H bonds remains a challenge. Here, we focus on the functionalization of

Kamil Godula; Dalibor Sames

2006-01-01

171

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

172

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

173

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

174

An energy criterion for determining d orbital contribution to adsorbate bonding to a transition metal: CO\\/Fe 12  

Microsoft Academic Search

Summary A new criterion is presented for determining the contribution of a particular class or group of orbitals to a chemical bond. The new criterion is the diatomic energy contribution of particular orbitals to a bond. In neglect to differential overlap methods the total energy may be decomposed entirely into monoatomic and diatomic terms. The contribution of the electrons ind

George Blyholder; Michael Lawless

1990-01-01

175

Asymmetric hydrogen bonds in a centrosymmetric environment. III. Quantum mechanical calculations of the potential-energy surfaces for the very short hydrogen bonds in potassium hydrogen dichloromaleate.  

PubMed

In the crystal structure of potassium hydrogen dichloromaleate there are two short hydrogen bonds of 2.44 A. The 'heavy-atom' structure is centrosymmetric (space group P1) with centers of symmetry in the middle of the O-O bonds, suggesting centered hydrogen bonds. However, earlier unconventional types of refinements of the extensive neutron data taken at 30, 90, 135, 170 and 295 K demonstrated that the H atoms are actually non-centered in the hydrogen bonds, although the environment is centrosymmetric. Traditionally it has been assumed that the hydrogen distribution adopts the same symmetry as the environment. Reviewing these unusual results it was considered of great interest to verify that the non-centered locations of the H atoms are reasonable from an energy point of view. Quantum mechanical calculations have now been carried out for the potential-energy surfaces (PES) for both the centered and non-centered locations of the H atoms. In all cases the non-centered positions are closer to the energy minima in the PES than the centered positions, and this result confirms that the structure is best described with non-centered H atoms. There is virtually perfect agreement between the quantum-mechanically derived reaction coordinates (QMRC) and the bond-order reaction coordinates (BORC) derived using Pauling's bond-order concept together with the principle of conservation of bond order. [Part I: Olovsson et al. (2001). Acta Cryst. B57, 311-316; Part II: Olovsson et al. (2002). Acta Cryst. B58, 627-631.]. PMID:17873444

Majerz, I; Olovsson, I

2007-10-01

176

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

SciTech Connect

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

Blancafort, Lluis [Institut de Quimica Computacional, Department de Quimica, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Gatti, Fabien [CTMM, Institut Charles Gerhardt Montpellier (UMR 5253), CC 1501, Universite Montpellier 2, 34095 Montpellier Cedex 05 (France); Meyer, Hans-Dieter [Theoretische Chemie, Ruprecht-Karls-Universitaet, Im Neuenheimer Feld 229, 69120 Heidelberg (Germany)

2011-10-07

177

Bond dissociation energies and radical stabilization energies: an assessment of contemporary theoretical procedures.  

PubMed

Various contemporary theoretical procedures have been tested for their accuracy in predicting the bond dissociation energies (BDEs) and the radical stabilization energies (RSEs) for a test set of 22 monosubstituted methyl radicals. The procedures considered include the high-level W1, W1', CBS-QB3, ROCBS-QB3, G3(MP2)-RAD, and G3X(MP2)-RAD methods, unrestricted and restricted versions of the double-hybrid density functional theory (DFT) procedures B2-PLYP and MPW2-PLYP, and unrestricted and restricted versions of the hybrid DFT procedures BMK and MPWB1K, as well as the unrestricted DFT procedures UM05 and UM05-2X. The high-level composite procedures show very good agreement with experiment and are used to evaluate the performance of the comparatively less expensive DFT procedures. RMPWB1K and both RBMK and UBMK give very promising results for absolute BDEs, while additionally restricted and unrestricted X2-PLYP methods and UM05-2X give excellent RSE values. UM05, UB2-PLYP, UMPW2-PLYP, UM05-2X, and UMPWB1K are among the less well performing methods for BDEs, while UMPWB1K and UM05 perform less well for RSEs. The high-level theoretical results are used to recommend alternative experimental BDEs for propyne, acetaldehyde, and acetic acid. PMID:18047305

Menon, Ambili S; Wood, Geoffrey P F; Moran, Damian; Radom, Leo

2007-12-27

178

Aliphatic C-H to C-C conversion: synthesis of (-)-cameroonan-7?-ol.  

PubMed

In the course of a synthesis of the tricyclic sesquiterpene (-)-cameroonan-7?-ol from the acyclic (+)-citronellal, seven aliphatic C-H bonds were converted to C-C bonds, and three rings and four new stereogenic centers were established. PMID:21344897

Taber, Douglass F; Nelson, Christopher G

2011-03-18

179

Aliphatic C-H to C-C Conversion: Synthesis of (?)-Cameroonan-7?-ol  

PubMed Central

In the course of a synthesis of the tricyclic sesquiterpene (?)-cameroonan-7?-ol from the acyclic (+)-citronellal, seven aliphatic C-H bonds were converted to C-C bonds, and three rings and four new stereogenic centers were established. PMID:21344897

Taber, Douglass F.; Nelson, Christopher G.

2011-01-01

180

Photoionization spectroscopy of dichromium and dimolybdenum: Ionization potentials and bond energies  

NASA Astrophysics Data System (ADS)

Photoionization spectroscopy has been used to probe molecular beams of laser-vaporized chromium (Cr2) and molybdenum (Mo2) dimers. Two-color photoionization efficiency spectroscopy has been used to determine the adiabatic ionization potential (IP) of Cr2 and Mo2 to be 56 4498 cm-1 and 56 0428 cm-1, respectively. The IP of Cr2 is combined with the IP of Cr [54 575.60.3 cm-1, Huber et al., Proc. R. Soc. London, Ser. A 342, 431 (1975)] and the bond energy of Cr2+ [10 200500 cm-1, Su et al., Chem. Phys. Lett. 201, 199 (1993)] to yield a bond energy of 12 400500 cm-1 for Cr2. One-color resonant two-photon ionization (R2PI) spectroscopy has been employed to probe the molybdenum dimer molecule in the energy region where its dissociation should occur. The dissociation limit has been ascribed to the threshold observed at 36 10080 cm-1. This value is combined with the IP of Mo [57 204.30.3 cm-1, Rayner et al., J. Opt. Soc. Am. B 4, 900 (1987)] and Mo2 to yield a bond energy of 37 26080 cm-1 for Mo2+.

Simard, Benoit; Lebeault-Dorget, Marie-Ange; Marijnissen, Adrian; ter Meulen, J. J.

1998-06-01

181

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

PubMed Central

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

Netzel, Jeanette; van Smaalen, Sander

2009-01-01

182

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

PubMed

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 energies in methylcobalamin and adenosylcobalamin, and have provided an explanation for the difficulties encountered when we attempt to reproduce this difference in quantum chemistry. Additional calculations have been performed using the Miertus-Scrocco-Tomasi method in order to estimate the influence of solvent effects on the homolytic Co-C bond cleavage. Introduction of these solvation effects is shown to be necessary for the correct reproduction of experimental trends in bond dissociation energies in solution, which consequently have no direct correlation with dissociation processes in the enzyme. PMID:15986217

Dlker, Nicole; Morreale, Antonio; Maseras, Feliu

2005-08-01

183

Alfa and remote substituent effects on the homolytic dissociation energies of OH bonds  

Microsoft Academic Search

In the study we used a number of high level theoretical methods to calculate the OH bond dissociation energies (BDEs) as well as ? and remote para substituent effects on them. We found that only G3 and CBS-Q methods can be used to calculate the absolute OH BDEs. Other methods including B3LYP, MP2, and CCSD(T), either open-shelled or close-shelled, significantly

Yao Fu; Lei Liu; Yi Mou; Bo-Lin Lin; Qing-Xiang Guo

2004-01-01

184

Bond-specific dissociation following excitation energy transfer for distance constraint determination in the gas phase.  

PubMed

Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase. PMID:25174489

Hendricks, Nathan G; Lareau, Nichole M; Stow, Sarah M; McLean, John A; Julian, Ryan R

2014-09-24

185

2590 J. Am. Chem. SOC.1995,117, 2590-2599 The C-H Bond Energy of Benzene  

E-print Network

2590 J. Am. Chem. SOC.1995,117, 2590-2599 The C-H Bond Energy of Benzene Gustavo E. Davico ion with benzene and phenide ion with ammonia: c&6 +NH2- C6H5- +NH3. The ratio of these rate constants for derived. The enthalpy of deprotonationof benzene, the C-H bond dissociationenergy, and the electron

Ellison, Barney

186

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

E-print Network

/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infraredIsotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster Xiaohu Li,1 Jos Oomens,2 John R. Eyler,3 David T. Moore,4,a and Srinivasan S

Iyengar, Srinivasan S.

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

188

Understanding Bond Formation in Polar One-Step Reactions. Topological Analyses of the Reaction between Nitrones and Lithium Ynolates.  

PubMed

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

Roca-Lpez, David; Polo, Victor; Tejero, Toms; Merino, Pedro

2015-04-17

189

Influence of steric and intramolecular inductive effects on the variable trends in RX (R=Alkyl) bond dissociation energy  

Microsoft Academic Search

The question why are the variation trends of R-X bond dissociation energy different? is answered. The R-X bond dissociation\\u000a energy (BDE) may be influenced by three main factors: the C-X intrinsic bond energy, the 1,3 geminal repulsion, and the intramolecular\\u000a charge-induced dipole. In the presence of atom X, the variation trend of BDE in R-X (R= Me, Et, i-Pr, t-Bu)

ChenZhong Cao

2009-01-01

190

Progress on All Ends for Carbon-Carbon Bond Formation through Photoredox Catalysis.  

PubMed

Dual role for catalysts: Novel routes for the generation of asymmetric stereocenters using photoredox catalysis were recently developed. Different chiral catalytic systems allowed new C?C bonds to form in good yields and enantioselectivities using a mild methodology in which light is used as the energy source. PMID:25782707

Pea-Lpez, Miguel; Rosas-Hernndez, Alonso; Beller, Matthias

2015-04-20

191

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

192

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

193

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are performed to investigate the equilibrium CCOOH bond distances and the bond dissociation energies (BDEs) for 15 acids. These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3PW91, B3P86, PBE1PBE) and the complete basis set (CBSQ) method in conjunction with the 6-311G** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work. Comparisons between the computational results and the experimental values reveal that CBSQ method, which can produce reasonable BDEs for some systems in our previous work, seems unable to predict accurate BDEs here. However, the B3P86 calculated results accord very well with the experimental values, within an average absolute error of 2.3 kcal/mol. Thus, B3P86 method is suitable for computing the reliable BDEs of CCOOH bond for carboxylic acid compounds. In addition, the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated, based on which the relative thermal stabilities of the studied acids are also discussed.

Zeng, Hui; Zhao, Jun; Xiao, Xun

2013-02-01

194

Predicted bond energies in peroxides and disulfides by density functional methods  

SciTech Connect

We have performed self-consistent linear combination of Gaussian-type orbitals-density functional calculations for the molecules YY, RY, RYY, RYR{prime}, RYYR, and RYYR{prime} with Y=O,S and R,R{prime}=H,CH{sub 3}. The structures were optimized within the local spin density approximation while the Y--Y, Y--C, and Y--H bond dissociation energies (BDE) were calculated with both a local exchange-correlation energy functional and a gradient corrected functional. Comparison of results obtained with the local and gradient corrected exchange-correlation functionals provides more experience on the successes and failures of gradient corrections. Trends in BDEs and the nature of bonding in oxygen and sulfur containing analog molecules are analyzed on the basis of two observations: (1) the O atom is more electronegative than S, C, and H atoms; (2) a S atom can have a valency larger than two and has a greater ability for multiple bonding than oxygen. Finally, comparison with a number of experimental results suggest that the C--S BDE in CH{sub 3}S, the S--S BDE in CH{sub 3}SSCH{sub 3}, and the enthalpy of formation of CH{sub 3}S should be reexamined.

Fournier, R.; DePristo, A.E. (Ames Laboratory-USDOE, Iowa State University, Ames, Iowa (United States). Department of Chemistry)

1992-01-15

195

Bond dissociation energies and radical stabilization energies associated with model peptide-backbone radicals.  

PubMed

Bond dissociation energies (BDEs) and radical stabilization energies (RSEs) have been calculated for a series of models that represent a glycine-containing peptide-backbone. High-level methods that have been used include W1, CBS-QB3, U-CBS-QB3, and G3X(MP2)-RAD. Simpler methods used include MP2, B3-LYP, BMK, and MPWB1K in association with the 6-311+G(3df,2p) basis set. We find that the high-level methods produce BDEs and RSEs that are in good agreement with one another. Of the simpler methods, RBMK and RMPWB1K achieve good accuracy for BDEs and RSEs for all the species that were examined. For monosubstituted carbon-centered radicals, we find that the stabilizing effect (as measured by RSEs) of carbonyl substituents (CX=O) ranges from 24.7 to 36.9 kJ mol(-1), with the largest stabilization occurring for the CH=O group. Amino groups (NHY) also stabilize a monosubstituted alpha-carbon radical, with the calculated RSEs ranging from 44.5 to 49.5 kJ mol(-1), the largest stabilization occurring for the NH2 group. In combination, NHY and CX=O substituents on a disubstituted carbon-centered radical produce a large stabilizing effect ranging from 82.0 to 125.8 kJ mol(-1). This translates to a captodative (synergistic) stabilization of 12.8 to 39.4 kJ mol(-1). For monosubstituted nitrogen-centered radicals, we find that the stabilizing effect of methyl and related (CH2Z) substituents ranges from 25.9 to 31.7 kJ mol(-1), the largest stabilization occurring for the CH3 group. Carbonyl substituents (CX=O) destabilize a nitrogen-centered radical relative to the corresponding closed-shell molecule, with the calculated RSEs ranging from -30.8 to -22.3 kJ mol(-1), the largest destabilization occurring for the CH=O group. In combination, CH2Z and CX=O substituents at a nitrogen radical center produce a destabilizing effect ranging from -19.0 to -0.2 kJ mol(-1). This translates to an additional destabilization associated with disubstitution of -18.6 to -7.8 kJ mol(-1). PMID:16833974

Wood, Geoffrey P F; Moran, Damian; Jacob, Rebecca; Radom, Leo

2005-07-21

196

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

197

Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with periodic boundary conditions.  

PubMed

The hydrogen bond (H-bond) energies are evaluated for 18 molecular crystals with 28 moderate and strong O-HO bonds using the approaches based on the electron density properties, which are derived from the B3LYP/6-311G** calculations with periodic boundary conditions. The approaches considered explore linear relationships between the local electronic kinetic G(b) and potential V(b) densities at the HO bond critical point and the H-bond energy E(HB). Comparison of the computed E(HB) values with the experimental data and enthalpies evaluated using the empirical correlation of spectral and thermodynamic parameters (Iogansen, Spectrochim. Acta Part A 1999, 55, 1585) enables to estimate the accuracy and applicability limits of the approaches used. The V(b)-E(HB) approach overestimates the energy of moderate H-bonds (E(HB) < 60 kJ/mol) by ~20% and gives unreliably high energies for crystals with strong H-bonds. On the other hand, the G(b)-E(HB) approach affords reliable results for the crystals under consideration. The linear relationship between G(b) and E(HB) is basis set superposition error (BSSE) free and allows to estimate the H-bond energy without computing it by means of the supramolecular approach. Therefore, for the evaluation of H-bond energies in molecular crystals, the G(b) value can be recommended to be obtained from both density functional theory (DFT) computations with periodic boundary conditions and precise X-ray diffraction experiments. PMID:22786749

Vener, M V; Egorova, A N; Churakov, A V; Tsirelson, V G

2012-11-01

198

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

PubMed Central

Background The rapid access to intrinsic physicochemical properties of molecules is highly desired for large scale chemical data mining explorations such as mass spectrum prediction in metabolomics, toxicity risk assessment and drug discovery. Large volumes of data are being produced by quantum chemistry calculations, which provide increasing accurate estimations of several properties, e.g. by Density Functional Theory (DFT), but are still too computationally expensive for those large scale uses. This work explores the possibility of using large amounts of data generated by DFT methods for thousands of molecular structures, extracting relevant molecular properties and applying machine learning (ML) algorithms to learn from the data. Once trained, these ML models can be applied to new structures to produce ultra-fast predictions. An approach is presented for homolytic bond dissociation energy (BDE). Results Machine learning models were trained with a data set of >12,000 BDEs calculated by B3LYP/6-311++G(d,p)//DFTB. Descriptors were designed to encode atom types and connectivity in the 2D topological environment of the bonds. The best model, an Associative Neural Network (ASNN) based on 85 bond descriptors, was able to predict the BDE of 887 bonds in an independent test set (covering a range of 17.67202.30kcal/mol) with RMSD of 5.29kcal/mol, mean absolute deviation of 3.35kcal/mol, and R2?=?0.953. The predictions were compared with semi-empirical PM6 calculations, and were found to be superior for all types of bonds in the data set, except for O-H, N-H, and N-N bonds. The B3LYP/6-311++G(d,p)//DFTB calculations can approach the higher-level calculations B3LYP/6-311++G(3df,2p)//B3LYP/6-31G(d,p) with an RMSD of 3.04kcal/mol, which is less than the RMSD of ASNN (against both DFT methods). An experimental web service for on-line prediction of BDEs is available at http://joao.airesdesousa.com/bde. Conclusion Knowledge could be automatically extracted by machine learning techniques from a data set of calculated BDEs, providing ultra-fast access to accurate estimations of DFT-calculated BDEs. This demonstrates how to extract value from large volumes of data currently being produced by quantum chemistry calculations at an increasing speed mostly without human intervention. In this way, high-level theoretical quantum calculations can be used in large-scale applications that otherwise would not afford the intrinsic computational cost. PMID:23849655

2013-01-01

199

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 CCSS dihedrals, and . Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using forceclamp spectroscopy and computer simulation. The and angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, socalled closed states upon exerting tensile stress. In view of the growing evidence of the importance of CCSS 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; RibasArino, Jordi; Marx, Dominik

2014-01-01

200

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 (8595%). ?,? 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

201

Comment on "the origin of anomalous bond dissociation energies of V +(H 2) n clusters"  

NASA Astrophysics Data System (ADS)

In a recent study, we reported experimental determinations of bond dissociation energies and entropies for V +(H 2) n ( n = 1 to 6) and suggested that a spin change from quintet to triplet occurs upon addition of the sixth H 2 ligand. A very recent theoretical paper by Niu et al. disputes this and concludes that the experimental results are consistent with purely quintet clusters (J. Niu, B.K. Rao, S.N. Khanna and P. Jena, Chem. Phys. Letters 230 (1994) 299). In this Comment, we restate our reasons for the proposed spin charge and argue that important aspects of the results of Niu et al. are incorrect.

Kemper, P. R.; Bushnell, J. E.; Maitre, P.; Bowers, M. T.

1995-08-01

202

Metal-hydrogen bond energies in protonated transition-metal complexes  

SciTech Connect

Proton affinities of 20 organotransition-metal complexes in the gas phase are reported. For 16 of these complexes protonation occurs on the metal center. The corresponding metal-hydrogen homolytic bond dissociation energies were determined and these data summarized. All proton affinities were determined by the techniques of ion cyclotron resonance spectroscopy, by examining proton-transfer reactions in mixtures with compounds of known base strength. Ionization potentials are taken from a variety of sources and experimental procedures, as noted. The site of protonation in several of these compounds has been determined by either gas-phase or solution-phase studies. These results and their interpretations are presented. (AT)

Stevens, A.E.; Beauchamp, J.L.

1981-01-14

203

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

204

Rovibrational energy and spectroscopic constant calculations of complexes pairing via dihydrogen bonds.  

PubMed

In the present investigation, we performed a thorough study of potential energy curves, rovibrational spectra, and spectroscopic constants for complexes pairing via dihydrogen bonds. In particular, we dealt with LiH[Symbol: see text][Symbol: see text][Symbol: see text]HX (X = F, CN, CCH, CCF, CCCl) complexes by employing accurate electronic energy calculations at the MP2/aug-cc-pVDZ level of theory. Following this, the Numerov method was applied to solve the nuclear Schrdinger equation, thus obtaining spectroscopic constants and rovibrational spectra. Good linear correlation between the magnitudes of the interaction energies for interaction of HX with LiH, and the most positive electrostatic potentials of hydrogen in HX, was established. PMID:25877527

Solimannejad, Mohammad; Jouypazadeh, Hamidreza; Farrokhpour, Hossein

2015-05-01

205

Exotic c c-bar Mesons  

E-print Network

A surprising number of new c c-bar mesons with masses above the D D-bar threshold have been discovered at the B factories. Some of them are ordinary charmonium states, but others are definitely exotic mesons. The current theoretical status of the new c c-bar mesons is summarized.

Eric Braaten

2008-08-21

206

An alternative energysize relationship to that proposed by Bond for the design and optimisation of grinding circuits  

Microsoft Academic Search

Despite reservations of a number of researchers concerning the applicability of Bond's equation for relating specific energy to the size reduction of rocks, his approach has become an industry standard.Data from a large number of pilot and full-scale autogenous (AG), semi-autogenous (SAG) and ball mill circuits are used to show that Bond's equation does not hold over the particle size

Stephen Morrell

2004-01-01

207

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

PubMed Central

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

Petersson, G. A.

1974-01-01

208

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

209

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

210

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

211

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

212

Influence of surface treatment on adherence energy of alloys used in bonded prosthetics.  

PubMed

Usually, shear or tensile tests are used to assess bond strengths between resin and metal. In this study, a cleavage test, the Double Cantilever Beam test, was performed to measure the adherence energy in air and in water between a 4-META resin, and five alloys (palladium, palladium-silver, gold, cobalt-chromium and nickel-chromium alloys) whose surfaces have been treated by sandblasting only or by two methods of silica coating (Silicoater MD, Rocatec) or by painting with a primer (V-Primer). Results showed that, after storage in water, it is difficult to divide the studied alloys into a dental base alloys group and a noble alloys group. Therefore, the silica coating has significantly limited the propagation of fissures in water. Higher values of adherence energy were recorded with the Rocatec system except with the palladium alloy which must be treated with the Silicoater MD system. The treatment with V-Primer was sensitive to hydrolytic attack. PMID:10373089

Moulin, P; Degrange, M; Picard, B

1999-05-01

213

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

SciTech Connect

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. [Fachbereich Chemie, Technische Universitt Kaiserslautern, Erwin Schrdinger Strae 52, D-67663 Kaiserslautern (Germany)] [Fachbereich Chemie, Technische Universitt Kaiserslautern, Erwin Schrdinger Strae 52, D-67663 Kaiserslautern (Germany); Van Alsenoy, C. [Department of Chemistry, University of Antwerp, Universiteitsplein 1, B2610 Antwerp (Belgium)] [Department of Chemistry, University of Antwerp, Universiteitsplein 1, B2610 Antwerp (Belgium); Geerlings, P. [Algemene Chemie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels (Belgium)] [Algemene Chemie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels (Belgium)

2014-05-14

214

Enthalpies of formation, bond dissociation energies, and molecular structures of the n-aldehydes (acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal) and their radicals.  

PubMed

Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxidation processes, such as in low-temperature combustion, in the atmosphere, and in interstellar media. Despite their importance, the enthalpies of formation and bond dissociation energies (BDEs) for the aldehydes are not accurately known. We have determined enthalpies of formation for acetaldehyde, propanal, and butanal from thermodynamic cycles, using experimentally measured reaction and formation enthalpies. All enthalpy values used for reference molecules and reactions were first verified to be accurate to within around 1 kcal mol-1 using high-level ab initio calculations. Enthalpies of formation were found to be -39.72 +/- 0.16 kcal mol-1 for acetaldehyde, -45.18 +/- 1.1 kcal mol-1 for propanal, and -49.27 +/- 0.16 kcal mol-1 for butanal. Enthalpies of formation for these three aldehydes, as well as for pentanal, hexanal, and heptanal, were calculated using the G3, G3B3, and CBS-APNO theoretical methods, in conjunction with bond-isodesmic work reactions. On the basis of the results of our thermodynamic cycles, theoretical calculations using isodesmic work reactions, and existing experimental measurements, we suggest that the best available formation enthalpies for the aldehydes acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal are -39.72, -45.18, -50.0, -54.61, -59.37, and -64.2 kcal mol-1, respectively. Our calculations also identify that the literature enthalpy of formation of crotonaldehyde is in error by as much as 1 kcal mol-1, and we suggest a value of -25.1 kcal mol-1, which we calculate using isodesmic work reactions. Bond energies for each of the bonds in the aldehydes up to pentanal were calculated at the CBS-APNO level. Analysis of the BDEs reveals the R-CH(2)CH=O to be the weakest bond in all aldehydes larger than acetaldehyde, due to formation of the resonantly stabilized vinoxy radical (vinyloxy radical/formyl methyl radical). It is proposed that the vinoxy radical as well as the more commonly considered formyl and acetyl radicals are important products of aldehyde combustion and oxidation, and the reaction pathways of the vinoxy, formyl, and acetyl radicals are discussed. Group additivity values for the carbon-oxygen-hydrogen groups common to the aldehydes are also determined. Internal rotor profiles and electrostatic potential surfaces are used to study the dipole induced dipole-dipole interaction in the synperiplanar conformation of propanal. It is proposed that the loss of this dipole-dipole interaction in RC(.-)HCH(2)CH=O radicals causes a ca. 1-2 kcal mol-1 decrease in the aldehyde C-H and C-C bond energies corresponding to RC(.-)HCH(2)CH=O radical formation. PMID:17134166

da Silva, Gabriel; Bozzelli, Joseph W

2006-12-01

215

Energetic multifunctionalized nitraminopyrazoles and their ionic derivatives: ternary hydrogen-bond induced high energy density materials.  

PubMed

Diverse functionalization was introduced into the pyrazole framework giving rise to a new family of ternary hydrogen-bond induced high energy density materials. By incorporating extended cationic interactions, nitramine-based ionic derivatives exhibit good energetic performance and enhanced molecular stability. Performance parameters including heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. It is noteworthy to find that 5-nitramino-3,4-dinitropyrazole, 4, has a remarkable measured density of 1.97 g cm(-3) at 298 K, which is consistent with its crystal density (2.032 g cm(-3), 150 K), and ranks highest among azole-based CHNO compounds. Energetic evaluation indicates that, in addition to the molecular compound 4, some ionic derivatives, 9, 11, 12, 17, 19, and 22, also have high densities (1.83-1.97 g cm(-3)), excellent detonation pressures and velocities (P, 35.6-41.6 GPa; vD, 8880-9430 m s(-1)), as well as acceptable impact and friction sensitivities (IS, 4-30 J; FS, 40-240 N). These attractive features highlight the application potential of nitramino hydrogen-bonded interactions in the design of advanced energetic materials. PMID:25807076

Yin, Ping; Parrish, Damon A; Shreeve, Jean'ne M

2015-04-15

216

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 (23C) or warm (37C) 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 37C 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

217

Photodissociation measurements of bond dissociation energies: Tiz, Vi, Co,`, and Co;  

E-print Network

of predissociationthresholdsasbonddissociationenergiesandperiodictrendsin thebondingof the3d transition metal diatomic neutralsand monocationsare discussed. I. INTRODUCTION Investigationsinto the bonding of small transition metal clusters have beencarried out for many yearsnow. Part in these difficult elec- tronic systems.On one hand, d-orbital contributions to the bonding can strengthenthe bond

Morse, Michael D.

218

Hydrogen Bonding Induced Enhancement of Fermi Resonances: Ultrafast Vibrational Energy Flow Dynamics in Aniline-d5.  

PubMed

With hydrogen bonding of the amino group of aniline-d5 we can identify the roles of Fermi enhanced combination and overtone states in intramolecular vibrational re-distribution (IVR) pathways for N-H stretching excitations. Using linear Fourier transform infrared (FT-IR) spectroscopy, ultrafast one- and two-color IR-pump-IR-probe spectroscopy, and femtosecond two-dimensional IR spectroscopy, we can identify the primary accepting modes for N-H stretching excitations. In particular, a key role is played by the ?(NH2) bending degree of freedom, either via its ? = 2 overtone state or via a combination state with the ?(C?C) ring stretching mode. No significant transient population in these Fermi enhanced combination/overtone states can be observed, a consequence of similar decay rates of these Fermi enhanced combination/overtone states and of the N-H stretching states. A similar magnitude of the transient response of the two fingerprint modes regardless of direct excitation of the Fermi enhanced combination/overtone levels or of the N-H stretching states suggests an underlying coupling mechanism facilitating common IVR pathways. This mechanism is expected to be of general importance for other organic compounds with hydrogen-bonded amino groups, including DNA bases. PMID:25393885

Costard, Rene; Greve, Christian; Fidder, Henk; Nibbering, Erik T J

2015-02-12

219

Influence of Light Intensity on Surface Free Energy and Dentin Bond Strength of Core Build-up Resins.  

PubMed

SUMMARY Objective : We examined the influence of light intensity on surface free energy characteristics and dentin bond strength of dual-cure direct core build-up resin systems. Methods : Two commercially available dual-cure direct core build-up resin systems, Clearfil DC Core Automix with Clearfil Bond SE One and UniFil Core EM with Self-Etching Bond, were studied. Bovine mandibular incisors were mounted in acrylic resin and the facial dentin surfaces were wet ground on 600-grit silicon carbide paper. Adhesives were applied to dentin surfaces and cured with light intensities of 0 (no irradiation), 200, 400, and 600 mW/cm(2). The surface free energy of the adhesives (five samples per group) was determined by measuring the contact angles of three test liquids placed on the cured adhesives. To determine the strength of the dentin bond, the core build-up resin pastes were condensed into the mold on the adhesive-treated dentin surfaces according to the methods described for the surface free energy measurement. The resin pastes were cured with the same light intensities as those used for the adhesives. Ten specimens per group were stored in water maintained at 37C for 24 hours, after which they were shear tested at a crosshead speed of 1.0 mm/minute in a universal testing machine. Two-way analysis of variance (ANOVA) and a Tukey-Kramer test were performed, with the significance level set at 0.05. Results : The surface free energies of the adhesive-treated dentin surfaces decreased with an increase in the light intensity of the curing unit. Two-way ANOVA revealed that the type of core build-up system and the light intensity significantly influence the bond strength, although there was no significant interaction between the two factors. The highest bond strengths were achieved when the resin pastes were cured with the strongest light intensity for all the core build-up systems. When polymerized with a light intensity of 200 mW/cm(2) or less, significantly lower bond strengths were observed. Conclusions : The data suggest that the dentin bond strength of core build-up systems are still affected by the light intensity of the curing unit, which is based on the surface free energy of the adhesives. On the basis of the results and limitations of the test conditions used in this study, it appears that a light intensity of >400 mW/cm(2) may be required for achieving the optimal dentin bond strength. PMID:24809538

Shimizu, Y; Tsujimoto, A; Furuichi, T; Suzuki, T; Tsubota, K; Miyazaki, M; Platt, Ja

2015-01-01

220

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

SciTech Connect

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

Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A., E-mail: rmata@gwdg.de [Georg-August-Universitt Gttingen, Institut fr Physikalische Chemie, Tammannstr. 6, 37077 Gttingen (Germany)

2014-09-14

221

Relationship between rolling textures and shear textures in F. C. C. and B. C. C. metals  

SciTech Connect

The rolling and shear textures of aluminum (f.c.c.) and Fe-16%Cr (b.c.c.) have been compared. First a 90[degree] rotation relationship about the transverse direction was found experimentally between the stable orientation of the rolling textures and the shear textures. This was explained with the symmetry of the glide systems and the orientation relationship between both coordinate systems. Second for both kinds of deformation namely rolling and shear a 90[degree] rotation relationship about the transverse direction was also found between the stable b.c.c. and f.c.c. orientations. This was explained with the Taylor theory and the Sachs model making use of the orientation relationship between f.c.c. and b.c.c. glide systems.

Hoelscher, M.; Raabe, D.; Luecke, K. (Inst. fur Metallkunde und Metallphysik, Aachen (Germany))

1994-03-01

222

Synthesis of Through-bond Energy Transfer Cassettes and Their Encapsulation in Silica and Calcium Phosphate Nanoparticles  

E-print Network

have synthesized a set of six through-bond energy transfer cassettes which emit in the 600-800 nm region with Fluorescein or BODIPY as donor and benzophenoxazine dye Nile Red or cyanine dye Cy5 as acceptor. Their photophysical properties in organic...

Jose, Jiney

2011-02-22

223

Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in Small Water and HCl Clusters  

E-print Network

Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in Small Water and HCl Clusters Amit K. Samanta, Gabor Czako,§ Yimin Wang, John S. Mancini, Joel M. Bowman, Institute of Chemistry, Eotvos University, P.O. Box 32, H-1518 Budapest 112, Hungary CONSPECTUS: Water

Reisler, Hanna

224

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-strong hydrogen bonded cluster Xiaohu Li and Srinivasan S. Iyengar Department of Chemistry, Indiana University, Bloomington, IN 47405 Abstract We investigate and analyze the vibrational properties, including H/D isotope

Iyengar, Srinivasan S.

225

Bonding silicones with epoxies  

SciTech Connect

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

Tira, J.S.

1980-01-01

226

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

PubMed

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

Qiu, Wei; Ren, Fu-de; Shi, Wen-Jing; Wang, Yan-Hong

2015-05-01

227

Benchmark binding energies of ammonium and alkyl-ammonium ions interacting with water. Are ammonium-water hydrogen bonds strong?  

NASA Astrophysics Data System (ADS)

Alkyl-ammonium ion/water interactions are investigated using high level quantum computations, yielding thermodynamics data in good agreement with gas-phase experiments. Alkylation and hydration lead to weaken the NHsbnd O hydrogen bonds. Upon complete hydration by four water molecules, their main features are close to those of the OHsbnd O bond in the isolated water dimer. Energy decomposition analyses indicate that hydration of alkyl-ammonium ions are mainly due to electrostatic/polarization effects, as for hard monoatomic cations, but with a larger effect of dispersion.

Vallet, Valrie; Masella, Michel

2015-01-01

228

Bonding in silicates: Investigation of the Si L 2,3 edge by parallel electron energy-loss spectroscopy  

Microsoft Academic Search

The Si L2,3 core-loss edge can be used to probe the crystal chemistry around Si, providing information on the s- and d-like partial density of unoccupied states of the Si-O bonds. We present Si L 2,3 edges from 59 silicates, glasses, and amorphous materials acquired by parallel electron energy-loss spectroscopy (PEELS) with a transmission electron microscope (TEM) at an energy

LAURENCE A. J. GARVIE; PETER R. BUSECK

1999-01-01

229

Mutation Research 473 (2001) 211217 Total energy of deoxyguanosine bonded to  

E-print Network

, the bonding oc- curs between the carbon C8 of the guanosine and the nitrogen N2 of AAF. In the remaining instances the bond is formed between the nitrogen N2 of the guanosine and the carbon C3 of AAF. It has mechanics have been undertaken on AAF-modified guanosine and other modified base polymers [17

Besson, Morgan

230

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

SciTech Connect

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; Huang, Yongli; Zhang, Ting [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); Wang, Yan, E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Zhang, Xi [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li, Can [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China); Sun, Chang Q., E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China)

2014-04-14

231

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

PubMed Central

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

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

2015-01-01

232

Exceptional sensitivity of metal-aryl bond energies to ortho-fluorine substituents: influence of the metal, the coordination sphere, and the spectator ligands on M-C/H-C bond energy correlations.  

PubMed

DFT calculations are reported of the energetics of C-H oxidative addition of benzene and fluorinated benzenes, Ar(F)H (Ar(F) = C(6)F(n)H(5-n), n = 0-5) at ZrCp(2) (Cp = eta(5)-C(5)H(5)), TaCp(2)H, TaCp(2)Cl, WCp(2), ReCp(CO)(2), ReCp(CO)(PH(3)), ReCp(PH(3))(2), RhCp(PH(3)), RhCp(CO), IrCp(PH(3)), IrCp(CO), Ni(H(2)PCH(2)CH(2)PH(2)), Pt(H(2)PCH(2)CH(2)PH(2)). The change in M-C bond energy of the products fits a linear function of the number of fluorine substituents, with different coefficients corresponding to ortho-, meta-, and para-fluorine. The values of the ortho-coefficient range from 20 to 32 kJ mol(-1), greatly exceeding the values for the meta- and para-coefficients (2.0-4.5 kJ mol(-1)). Similarly, the H-C bond energies of Ar(F)H yield ortho- and para-coefficients of 10.4 and 3.4 kJ mol(-1), respectively, and a negligible meta-coefficient. These results indicate a large increase in the M-C bond energy with ortho-fluorine substitution on the aryl ring. Plots of D(M-C) vs D(H-C) yield slopes R(M-C/H-C) that vary from 1.93 to 3.05 with metal fragment, all in excess of values of 1.1-1.3 reported with other hydrocarbyl groups. Replacement of PH(3) by CO decreases R(M-C/H-C) significantly. For a given ligand set and metals in the same group of the periodic table, the value of R(M-C/H-C) does not increase with the strength of the M-C bond. Calculations of the charge on the aryl ring show that variations in ionicity of the M-C bonds correlate with variations in M-C bond energy. This strengthening of metal-aryl bonds accounts for numerous experimental results that indicate a preference for ortho-fluorine substituents. PMID:19453181

Clot, Eric; Mgret, Claire; Eisenstein, Odile; Perutz, Robin N

2009-06-10

233

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

234

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

235

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

236

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

PubMed

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

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

2015-01-21

237

Limitations for aggressively scaled CMOS Si devices due to bond coordination constraints and reduced band offset energies at Si-high- k dielectric interfaces  

NASA Astrophysics Data System (ADS)

The three chemical bonding effects at Si-dielectric interfaces that are important in substituting alternative gate dielectric materials for SiO 2 in aggressively scaled CMOS are (i) the character of the interface bonds, either isovalent with bond and nuclear charge balanced as in Si-SiO 2, or heterovalent, where there is an inherent mismatch between bond and nuclear charge, (ii) physical bonding constraints related to the average number of bonds/atom, Nav and (iii) reduced conduction band offset energies in transition metal (T-M) elemental and binary oxides that are derived from increased ionic bonding and d-state contributions to the lowest conduction bands. These effects are discussed with respect to several different emerging high- k materials including (i) nitrides, (ii) T-M oxides, (iii) alloys of SiO 2 and T-M oxides and (iv) Al 2O 3.

Lucovsky, Gerald; Phillips, James C.

2000-10-01

238

CUDA C/C++ BASICS NVIDIA Corporation  

E-print Network

in this session? ! Start from "Hello World!" ! Write and launch CUDA C/C++ kernels ! Manage GPU memory() Asynchronous operation Handling errors Managing devices CONCEPTS #12;HELLO WORLD! Heterogeneous Computing results from GPU memory to CPU memory PCI Bus #12;Hello World! int main(void) { printf("Hello World

Crawford, T. Daniel

239

CUDA C/C++ BASICS NVIDIA Corporation  

E-print Network

from "Hello World!" Write and launch CUDA C/C++ kernels Manage GPU memory Manage communication Managing devices CONCEPTS #12;HELLO WORLD! Heterogeneous Computing Blocks Threads Indexing Shared memory GPU memory to CPU memory PCI Bus #12;Hello World! int main(void) { printf("Hello World!\

McLaughlin, Richard M.

240

Hardware synthesis from C\\/C++ models  

Microsoft Academic Search

Software programming languages, such as C\\/C++, have been used as means for specifying hardware for quite a while. Different design methodologies have exploited the advantages of flexibility and fast simulation of models de- scribed with programming languages. At the same time, the mismatch (of software languages) in expressing power (for hardware systems) has caused several difficulties. In the recent past,

Giovanni De Micheli

1999-01-01

241

Bond energies and structures of ammonia-sulfuric acid positive cluster ions.  

PubMed

New particle formation in the atmosphere is initiated by nucleation of gas-phase species. The small molecular clusters that act as seeds for new particles are stabilized by the incorporation of an ion. Ion-induced nucleation of molecular cluster ions containing sulfuric acid generates new particles in the background troposphere. The addition of a proton-accepting species to sulfuric acid cluster ions can further stabilize them and may promote nucleation under a wider range of conditions. To understand and accurately predict atmospheric nucleation, the stabilities of each molecular cluster within a chemical family must be known. We present the first comprehensive measurements of the ammonia-sulfuric acid positive ion cluster system NH(4)(+)(NH(3))(n)(H(2)SO(4))(s). Enthalpies and entropies of individual growth steps within this system were measured using either an ion flow reactor-mass spectrometer system under equilibrium conditions or by thermal decomposition of clusters in an ion trap mass spectrometer. Low level ab initio structural calculations provided inputs to a master equation model to determine bond energies from thermal decomposition measurements. Optimized ab initio structures for clusters up through n = 3, s = 3 are reported. Upon addition of ammonia and sulfuric acid pairs, internal proton transfer generates multiple NH(4)(+) and HSO(4)(-) ions within the clusters. These multiple-ion structures are up to 50 kcal mol(-1) more stable than corresponding isomers that retain neutral NH(3) and H(2)SO(4) species. The lowest energy n = s clusters are composed entirely of ions. The addition of acid-base pairs to the core NH(4)(+) ion generates nanocrystals that begin to resemble the ammonium bisulfate bulk crystal starting with the smallest n = s cluster, NH(4)(+)(NH(3))(1)(H(2)SO(4))(1). In the absence of water, this cluster ion system nucleates spontaneously for conditions that encompass most of the free troposphere. PMID:22103290

Froyd, Karl D; Lovejoy, Edward R

2012-06-21

242

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

PubMed

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

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

2011-10-01

243

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

PubMed

We compared the surface free energies and enamel bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The adhesives were applied to the enamel surfaces of bovine incisors, light irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free energies and their components (?(S)(LW), ?(S)(+), and ?(S)(-)) were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component ?(S)(LW) was relatively constant. The value of the ?(S)(+) component increased slightly when the oxygen-inhibited layer was removed, whereas that of the ?(S)(-) component decreased significantly. The enamel bond strengths of the self-etch adhesives were significantly lower in the specimens without an oxygen-inhibited layer. The oxygen-inhibited layer therefore appeared to promote higher enamel bond strength. PMID:22277602

Oyama, Koji; Tsujimoto, Akimasa; Otsuka, Eiichiro; Shimizu, Yusuke; Shiratsuchi, Koji; Tsubota, Keishi; Takamizawa, Toshiki; Miyazaki, Masashi

2012-02-01

244

Hydrophobic silicon wafer bonding  

NASA Astrophysics Data System (ADS)

Wafers prepared by an HF dip without a subsequent water rinse were bonded at room temperature and annealed at temperatures up to 1100 C. Based on substantial differences between bonded hydrophilic and hydrophobic Si wafer pairs in the changes of the interface energy with respect to temperature, secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we suggest that hydrogen bonding between Si-F and H-Si across two mating wafers is responsible for room temperature bonding of hydrophobic Si wafers. The interface energy of the bonded hydrophobic Si wafer pairs does not change appreciably with time up to 150 C. This stability of the bonding interface makes reversible room-temperature hydrophobic wafer bonding attractive for the protection of silicon wafer surfaces.

Tong, Q.-Y.; Schmidt, E.; Gsele, U.; Reiche, M.

1994-01-01

245

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

SciTech Connect

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

Kreycik, C.; Couglin, J.

2009-12-01

246

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

247

Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu\\/Al2O3 interface  

Microsoft Academic Search

Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu\\/Al2O3 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

Teruyasu Mizoguchi; Takeo Sasaki; Shingo Tanaka; Katsuyuki Matsunaga; Takahisa Yamamoto; Masanori Kohyama; Yuichi Ikuhara

2006-01-01

248

Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu\\/AlO interface  

Microsoft Academic Search

Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu\\/AlO 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

Teruyasu Mizoguchi; Takeo Sasaki; Katsuyuki Matsunaga; Yuichi Ikuhara; Shingo Tanaka; Masanori Kohyama; Takahisa Yamamoto

2006-01-01

249

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

PubMed

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

Jacobsen, Heiko

2009-05-01

250

A Reassessment of the Bond Dissociation Energies of Peroxides. An ab Initio Study  

E-print Network

(BDE) have been used to derive O-O bond strengths. From these data it was concluded that the strength. The BDE of the O-O bond in diacyl peroxides was estimated by this method to be only 30 ( 1 kcal/mol.1b corresponds to 50.5 kcal/mol for the BDE at 298 K ((H°298 - H°0) ) 1.79 kcal/mol).8c It has been assumed

Schlegel, H. Bernhard

251

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

252

Evaluation of Die-Attach Bonding Using High-Frequency Ultrasonic Energy for High-Temperature Application  

NASA Astrophysics Data System (ADS)

Room-temperature die-attach bonding using ultrasonic energy was evaluated on Cu/In and Cu/Sn-3Ag metal stacks. The In and Sn-3Ag layers have much lower melting temperatures than the base material (Cu) and can be melted through the heat generated during ultrasonic bonding, forming intermetallic compounds (IMCs). Samples were bonded using different ultrasonic powers, bonding times, and forces and subsequently aged at 300C for 500 h. After aging, die shear testing was performed and the fracture surfaces were inspected by scanning electron microscopy. Results showed that the shear strength of Cu/In joints reached an upper plateau after 100 h of thermal aging and remained stable with aging time, whereas that of the Cu/Sn-3Ag joints decreased with increasing aging time. ?-Cu7In4 and (Cu,Au)11In9 IMCs were observed at the Cu/In joint, while Cu3Sn and (Ag,Cu)3Sn IMCs were found at the Cu/Sn-3Ag joint after reliability testing. As Cu-based IMCs have high melting temperatures, they are highly suitable for use in high-temperature electronics, but can be formed at room temperature using an ultrasonic approach.

Lee, Jong-Bum; Aw, Jie-Li; Rhee, Min-Woo

2014-09-01

253

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

SciTech Connect

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

Shiflet, G.J.; Merwe, J.H. van der (Univ. of South Africa, Pretoria (South Africa). Dept. of Physics)

1994-04-01

254

Is the decrease of the total electron energy density a covalence indicator in hydrogen and halogen bonds?  

PubMed

In this work, halogen bonding (XB) and hydrogen bonding (HB) complexes were studied with the aim of analyzing the variation of the total electronic energy density H(r b ) with the interaction strengthening. The calculations were performed at the MP2/6-311++G(2d,2p) level of approximation. To explain the nature of such interactions, the atoms in molecules theory (AIM) in conjunction with reduced variational space self-consistent field (RVS) energy decomposition analysis were carried out. Based on the local virial theorem, an equation to decompose the total electronic energy density H(r b ) in two energy densities, (-G(r b )) and 1/4?(2)?(r b ), was derived. These energy densities were linked with the RVS interaction energy components. Through the connection between both decomposition schemes, it was possible to conclude that the decrease in H(r b ) with the interaction strengthening observed in the HB as well as the XB complexes, is mainly due to the increase in the attractive electrostatic part of the interaction energy and in lesser extent to the increase in its covalent character, as is commonly considered. PMID:23187685

Angelina, Emilio L; Duarte, Daro J R; Peruchena, Nlida M

2013-05-01

255

Tubulin bond energies and microtubule biomechanics determined from nanoindentation in silico  

E-print Network

Microtubules, the primary components of the chromosome segregation machinery, are stabilized by longitudinal and lateral non-covalent bonds between the tubulin subunits. However, the thermodynamics of these bonds and the microtubule physico-chemical properties are poorly understood. Here, we explore the biomechanics of microtubule polymers using multiscale computational modeling and nanoindentations in silico of a contiguous microtubule fragment. A close match between the simulated and experimental force-deformation spectra enabled us to correlate the microtubule biomechanics with dynamic structural transitions at the nanoscale. Our mechanical testing revealed that the compressed MT behaves as a system of rigid elements interconnected through a network of lateral and longitudinal elastic bonds. The initial regime of continuous elastic deformation of the microtubule is followed by the transition regime, during which the microtubule lattice undergoes discrete structural changes, which include first the reversib...

Kononova, Olga; Theisen, Kelly E; Marx, Kenneth A; Dima, Ruxandra I; Ataullakhanov, Fazly I; Grishchuk, Ekaterina L; Barsegov, Valeri

2015-01-01

256

Structure and electronic spectra of the C C6- anion  

NASA Astrophysics Data System (ADS)

Ab initio calculations are employed for determining structures, spectroscopic parameters and transitions to the excited electronic states of the astrophysical relevant C C6- anion, which is a potential intermediate of chemical processes involving carbon chains and polycyclic aromatic hydrocarbons. Calculations confirm the prominent stability of linear carbon chain anions which guarantees their formation. The lowest doublet potential energy surface of C? displays six isomers, whereas in the lowest quartet potential energy surface, a unique minimum energy geometry is found. The most stable form is the linear anion l-C? (X2?u) followed by the c-C?(X2A1')at 9291 cm-1 above in energy, which presents a distorted D3h structure. The other isomers are also located at more than 9000 cm-1 above l-C? (X2?u). For each isomer, a set of spectroscopic parameters including their equilibrium structures, rotational constants at equilibrium, harmonic wavenumbers, dipole moments and electron affinities are predicted. For linear C?, eight electronic states lying below the electron detachment threshold, are computed. Four doublet electronic states, which play important roles in the C? reactivity, lie below 2 eV. Spin-orbit constants for the upper electronic states of l-C? are predicted.

Hammoutene, D.; Hochlaf, M.; Senent, M. L.

2012-08-01

257

Coordination-resolved local bond relaxation, electron binding-energy shift, and Debye temperature of Ir solid skins  

NASA Astrophysics Data System (ADS)

Numerical reproduction of the measured 4f7/2 energy shift of Ir(1 0 0), (1 1 1), and (2 1 0) solid skins turns out the following: (i) the 4f7/2 level of an isolated Ir atom shifts from 56.367 eV to 60.332 eV by 3.965 eV upon bulk formation; (ii) the local energy density increases by up to 130% and the atomic cohesive energy decreases by 70% in the skin region compared with the bulk values. Numerical match to observation of the temperature dependent energy shift derives the Debye temperature that varies from 285.2 K (Surface) to 315.2 K (Bulk). We clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and quantum entrapment of electron binding energy, which perturbs the Hamiltonian and the core shifts in the skin region.

Bo, Maolin; Wang, Yan; Huang, Yongli; Yang, Xuexian; Yang, Yezi; Li, Can; Sun, Chang Q.

2014-11-01

258

Pd(II)-Catalyzed CH Activation/CC Cross-Coupling Reactions: Versatility and Practicality  

PubMed Central

In the past decade, palladium-catalyzed CH activation/CC bond forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming CC bonds from CH bonds: Pd(II)/Pd(0), Pd(II)/Pd(IV), Pd(0)/Pd(II)/Pd(IV) and Pd(0)/Pd(II) catalysis. More detailed discussion is then directed towards the recent development of Pd(II)-catalyzed coupling of CH bonds with organometallic reagents through a Pd(II)/Pd(0) catalytic cycle. Despite much progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge. PMID:19557755

Chen, Xiao; Engle, Keary M.; Wang, Dong-Hui; Yu, Jin-Quan

2009-01-01

259

Fluorine hot atom oxidation of bismuth vapor. A comment on the evaluation of the BiF bond energy  

NASA Astrophysics Data System (ADS)

The energetics of the chemiluminescent reaction between bismuth dimers and fluorine atoms (T.C. Devore et al., Chem. Phys. 155 (1991) 423; 156 (1991) 156) has been evaluated to better refine a determination of the bismuth fluoride dissociation energy. By directly examining the spectrum of the SF 6 discharge used to generate the F atoms to establish the significant energy imparted to these dissociation products and by exploring F atom chemiluminescent reactions with known energetics, the F atom beam is established to have contributed a maximum of 0.8-0.9 eV to the chemiluminescent process. Based upon the observed population of the ?'=4 level of the BiF A0 + state resulting from the Bi 2 + F reaction, a BiF bond energy of 3.9 0.2 eV is established. This value is slightly higher than a very recent evaluation of the BiF bond energy (Yoo et al., Chem. Phys. 166 (1992) 215) but disagrees with previous determinations in the literature. Many of the previous evaluations of the group 15 halide dissociation energies have been based on BirgeSponer extrapolations. The data now available for BiF permits an evaluation of the nature of these extrapolations for this molecule. The limitations of these extrapolations and possible corrections for these shortcomings are presented.

Devore, T. C.; Gole, J. L.

1993-08-01

260

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

261

The C & C Companion Transitional Semantics  

E-print Network

The C & C Companion Transitional Semantics Act ff : E ff ! E. Sum j If E j ff ! E 0 j and j 2 I then P i2I E i ff ! E 0 j . Com 1 If E ff ! E 0 then EjF ff ! E 0 jF . Com 2 If F ff ! F 0 then EjF ff ! EjF 0 . Com 3 If E ` ! E 0 and F ` ! F 0 then EjF ø ! E 0 jF 0 . Res If E ff ! E 0 and ff; ff 62 L

Popeea, Corneliu - Chair for Foundations of Software Reliability and Theoretical Computer Science

262

Natural bond orbital-based energy density analysis for correlated methods: Second-order Mller-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 Mller-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

263

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

264

Chemical Bonds I  

ERIC Educational Resources Information Center

Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

Sanderson, R. T.

1972-01-01

265

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

266

R, Science Service Feature Released on r c c c i p t  

E-print Network

R, Science Service Feature Released on r c c c i p t but intended f o r use k y 2, 1928 Mailed t 8 of a clo.ud o r fog, under s u i t a b l e conditions of temperature4 C.G.Andrus, of t h e U*S'Weather Bureau, i n a r e c e n t discussion of such dcpOsit6, Points o u t t h a t t h e y a f f e c t t i e e f

267

Chemical Bonds  

NSDL National Science Digital Library

Electrons are key to forming the two broad categories of chemical bonds: covalent and ionic. Atoms, which have a nucleus surrounded by electrons, are represented in several different ways. In the Chemical Bonds activity, students explore the different kinds of chemical bonds that can form, ranging from non-polar covalent to ionic. In the model depicted above students adjust the electronegativity of two atoms and see the effect it has on electron distribution and bond type.

The Concord Consortium

2011-12-11

268

C.C. Berndt: Professional 1 Following your Passion while  

E-print Network

C.C. Berndt: Professional 1 4/20/12 1 Following your Passion while Navigating the Bumps in the Road Chris Berndt Swinburne University of Technology; Melbourne Stony Brook University (SBU); NY-USA #12;C.C. Berndt: Professional Sydney Melbourne Where am I? Brisbane 2 2 #12;C.C. Berndt: Professional 3 85 km #1

Alpay, S. Pamir

269

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

270

Linear free energy relationships reveal structural changes in hydrogen-bonded host-guest interactions.  

PubMed

Hydrogen bond strength in host-guest systems is modulated by many factors including preorganization, steric effects, and electronic effects. To investigate how electronic effects impact barbiturate binding in bifurcated Hamilton receptors, a library of receptors with differing electronic substituents was synthesized and (1)H NMR titrations were performed with diethyl barbital. The Hammett plot revealed a clear break between the different electronic substituents suggesting a change in binding conformation. The titration data were complimented with computational studies confirming the change in structure. PMID:25412431

McGrath, Jacqueline M; Pluth, Michael D

2014-12-01

271

Bonding with Your Baby  

MedlinePLUS

... baby feel the different textures of dad's face Building a Support System Of course, it's easier to ... can take nearly all of your attention and energy especially for a breastfeeding mom. Bonding will be ...

272

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

PubMed Central

A theoretical model is presented for deriving effective diabatic states based on ab initio self-consistent field valence bond (VBSCF) theory by reducing the multi-configurational VB Hamiltonian into an effective two-state model. We describe two computational approaches for the optimization of the effective diabatic configurations, resulting in two ways of interpreting such effective diabatic states. In the variational diabatic configuration (VDC) method, the energies of the individual diabatic states are variationally minimized. In the consistent diabatic configuration (CDC) method, both the configuration coefficients and orbital coefficients are simultaneously optimized to minimize the adiabatic ground-state energy in VBSCF calculations. In addition, we describe a mixed molecular orbital and valence bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction, whereas the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH3NH3+ as a test system, we found that the results from ab initio VBSCF and from MOVB calculations are in good agreement, suggesting that the computationally efficient MOVB method is a reasonable model for VB simulations of condensed phase reactions. The results indicate that CDC and VDC diabatic states converge, respectively, to covalent and ionic states as the molecular geometries are distorted from the minimum of the respective diabatic state along the reaction coordinate. Furthermore, the resonance energy that stabilizes the energy of crossing between the two diabatic states, resulting in the transition state of the adiabatic ground-state reaction, has a strong dependence on the overlap integral between the two diabatic states and is a function of both the exchange integral and the total diabatic ground-state energy. PMID:18828577

Song, Lingchun; Gao, Jiali

2009-01-01

273

Theoretical study of the OH addition to the endocyclic and exocyclic double bonds of the d-limonene  

NASA Astrophysics Data System (ADS)

The initial step of the d-limonene + OH gas-phase reaction mechanism was investigated by means of ab initio calculations. We have considered eight different possibilities for the OH addition, corresponding to the two C-C double bonds, the two C atoms of each double bond, and the syn or anti orientation, with respect to the isopropenyl group (endocyclic attack) or the ring cycle (exocyclic attack). Activation energies calculated at the QCISD(T)/6-31G(d)//UMP2/6-31G(d) level, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.

Ramrez-Ramrez, Vctor M.; Nebot-Gil, Ignacio

2005-06-01

274

The dehalogenation reaction of organic halides by tributyltin radical: The energy of activation vs. the BDE of the C?X bond  

Microsoft Academic Search

The energy of activation (Ea) of the dehalogenation reaction induced by Bu3Sn was measured for some aryl, alkyl and benzyl halides. BDE values of the C?X bond undergoing homolysis were obtained from thermochemical cycles, and correlated with the Ea values. No major effect due to the polarity of the C?X bond was found. Durene derivatives showed a buttressing effect. A

Carlo Galli; Tullia Pau

1998-01-01

275

Ion induced chemical bonding of carbon with Ta as studied by Auger electron spectroscopy and slow electron energy loss spectroscopy  

NASA Astrophysics Data System (ADS)

The chemical bonding of contaminants like carbon and oxygen on the surface of Ta and Ta2O5 films due to Ar+ ion bombardment during sputter etching, has been studied using Auger electron spectroscopy and slow electron energy loss spectroscopy. Finger printing of C KLL peak shows that the energy separation between the major positive-going and negative-going excursions, which is 23 eV in the pure graphitic form, reduces to 6 eV indicating the carbide formation after ion bombardment. It is assumed that the chemical reaction is initiated by an increase in ? electrons in the graphite due to ion bombardment. The carbide formation is found to be much less effected in Ta2O5 films which has been attributed to the absence of free d electrons of Ta in the oxide.

Sharma, J. K. N.; Bera, Santanu; Chakraborty, B. R.

1991-12-01

276

Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey  

NASA Technical Reports Server (NTRS)

The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

Dyall, Kenneth G.; Arnold, James (Technical Monitor)

1999-01-01

277

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

278

Rotational spectrum of ethyl cyanoacetylene (C2H5C?C-C?N), a compound of potential astrochemical interest  

NASA Astrophysics Data System (ADS)

Context. New radiotelescopes, such as the very sensitive ALMA, will enable the detection of interstellar molecules in much lower concentrations than previously possible. A successful identification of an interstellar molecule requires that laboratory microwave and millimeter-wave spectra are investigated. Several cyanopolyynes and alkynylcarbonitriles have already been detected in the interstellar medium (ISM). Cyanoacetylene (HC?C-C?N) is abundant in the ISM and its methyl derivative, 2-butynenitrile (CH3C?C-C?N), is also present. The next derivative, ethyl cyanoacetylene, (2-pentynenitrile C2H5C?C-C?N) may also be present in interstellar space. Aims: We report the rotational spectrum of the ethyl cyanoacetylene (C2H5C?C-C?N). This is hoped to facilitate identifying gaseous ethyl cyanoacetylene in the ISM. Methods: We studied the rotational spectrum of C2H5C?C-C?N between 13 and 116 GHz with the microwave spectrometer of the University of Oslo. The spectroscopic study was augmented by high-level quantum-chemical calculations at B3LYP/cc-pVTZ and CCSD/cc-pVTZ levels of theory. Results: We present for the first time the rotational spectrum of the ethyl cyanoacetylene (C2H5C?C-C?N). We assigned 342 transitions of the vibrational ground state, accurate values were obtained for rotational and centrifugal distortion constants, and the dipole moment was determined as well.

Carles, S.; Mllendal, H.; Guillemin, J.-C.

2013-10-01

279

Unexpected interplay of bonding height and energy level alignment at heteromolecular hybrid interfaces  

NASA Astrophysics Data System (ADS)

Although geometric and electronic properties of any physical or chemical system are always mutually coupled by the rules of quantum mechanics, counterintuitive coincidences between the two are sometimes observed. The coadsorption of the organic molecules 3,4,9,10-perylene tetracarboxylic dianhydride and copper-II-phthalocyanine on Ag(111) represents such a case, since geometric and electronic structures appear to be decoupled: one molecule moves away from the substrate while its electronic structure indicates a stronger chemical interaction, and vice versa for the other. Our comprehensive experimental and ab-initio theoretical study reveals that, mediated by the metal surface, both species mutually amplify their charge-donating and -accepting characters, respectively. This resolves the apparent paradox, and demonstrates with exceptional clarity how geometric and electronic bonding parameters are intertwined at metal-organic interfaces.

Stadtmller, Benjamin; Lftner, Daniel; Willenbockel, Martin; Reinisch, Eva M.; Sueyoshi, Tomoki; Koller, Georg; Soubatch, Serguei; Ramsey, Michael G.; Puschnig, Peter; Tautz, F. Stefan; Kumpf, Christian

2014-04-01

280

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

281

The contributions of through-bond interactions to the singlet-triplet energy difference in 1,3-dehydrobenzene.  

PubMed

Separation of the through-space (TS) from the through-bond (TB) interactions between the two atomic orbitals at C(1) and C(3) of 1,3-dehydrobenzene (1) has been achieved by carrying out ab initio, valence-bond, self-consistent-field (VBSCF) calculations. The results indicate that, at the CCSD(T)/cc-pVTZ optimized geometry of the singlet state of 1, the stabilization provided by TB interactions contributes 10% more than the stabilization provided by the TS interactions to the adiabatic singlet-triplet energy difference. The highest occupied MO of 1 contains a contribution from a hybrid AO at C(2), which has the same phase as the smaller lobes of the AOs at C(1) and C(3). Consequently, TB interactions in 1 increase with decreasing values of the C(1)-C(3) distance. The origin of this hybrid AO at C(2) and the contributions of hyperconjugation to TB and TS interactions in 1 are described and discussed. PMID:19711935

Wei, Haiyan; Hrovat, David A; Mo, Yirong; Hoffmann, Roald; Borden, Weston Thatcher

2009-09-24

282

The Contributions of Through-Bond Interactions to the Singlet-Triplet Energy Difference in 1,3-Dehydrobenzene  

NASA Astrophysics Data System (ADS)

Separation of the through-space (TS) from the through-bond (TB) interactions between the two atomic orbitals at C(1) and C(3) of 1,3-dehydrobenzene (1) has been achieved by carrying out ab initio, valence-bond, self-consistent-field (VBSCF) calculations. The results indicate that, at the CCSD(T)/cc-pVTZ optimized geometry of the singlet state of 1, the stabilization provided by TB interactions contributes 10% more than the stabilization provided by the TS interactions to the adiabatic singlet-triplet energy difference. The highest occupied MO of 1 contains a contribution from a hybrid AO at C(2), which has the same phase as the smaller lobes of the AOs at C(1) and C(3). Consequently, TB interactions in 1 increase with decreasing values of the C(1)-C(3) distance. The origin of this hybrid AO at C(2) and the contributions of hyperconjugation to TB and TS interactions in 1 are described and discussed.

Wei, Haiyan; Hrovat, David A.; Mo, Yirong; Hoffmann, Roald; Borden, Weston Thatcher

2009-08-01

283

C(sp(2))-C(aryl) Bond Rotation Barrier in N-Methylbenzamide  

SciTech Connect

The potential energy surfaces at different levels of ab initio electronic structure theory with correlation effects included are reported for rotation about the C(sp3)-C(aryl) bond in N-methylbenzamide. The results reveal a minimum at a C=C-C=O dihedral angle of? 28? with barrier heights (MP2/aug-cc-pVTZ// BLYP/DZVP2/A2) of 0.48 kcal/mol at 0? and 2.80 kcal/mol at 90?. Fully optimized geometries are in good agreement with crystal structure data and potential energy surfaces are consistent with the experimental dihedral angle distribution. The results are used to assign MM3 force field parameters to allow calculation on N-methyl benzamide and other benzamide derivatives.

Vargas-Fosada, Rubicelia V.(ASSOC WESTERN UNIVERSITY) [ASSOC WESTERN UNIVERSITY; Garza-Olguin, Jorge (ASSOC WESTERN UNIVERSITY) [ASSOC WESTERN UNIVERSITY; Dixon, David A.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Hay, Benjamin P.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

2001-02-01

284

Spontaneous direct bonding of thick silicon nitride  

NASA Astrophysics Data System (ADS)

Wafers with 0960-1317/7/3/007/img1 LPCVD silicon-rich nitride layers have been successfully direct bonded to silicon-rich nitride and boron-doped silicon surfaces. A chemical - mechanical polishing treatment was necessary to reduce the surface roughness of the nitride before bonding. The measured surface energies of the room-temperature bond were comparable to values found for Si - Si hydrophilic bonding. A mechanism similar to this bonding is suggested for silicon nitride bonding.

Snchez, S.; Gui, C.; Elwenspoek, M.

1997-09-01

285

Selective cleavage of the C?-C? linkage in lignin model compounds via Baeyer-Villiger oxidation.  

PubMed

Lignin is an amorphous aromatic polymer derived from plants and is a potential source of fuels and bulk chemicals. Herein, we present a survey of reagents for selective stepwise oxidation of lignin model compounds. Specifically, we have targeted the oxidative cleavage of C?-C? bonds as a means to depolymerize lignin and obtain useful aromatic compounds. In this work, we prepared several lignin model compounds that possess structures, characteristic reactivity, and linkages closely related to the parent lignin polymer. We observed that selective oxidation of benzylic hydroxyl groups, followed by Baeyer-Villiger oxidation of the resulting ketones, successfully cleaves the C?-C? linkage in these model compounds. PMID:25641654

Patil, Nikhil D; Yao, Soledad G; Meier, Mark S; Mobley, Justin K; Crocker, Mark

2015-03-01

286

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

287

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

2014-11-14

288

Hydrogen bonding in ionic liquids.  

PubMed

Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (?BCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X-H ?* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds. PMID:25582457

Hunt, Patricia A; Ashworth, Claire R; Matthews, Richard P

2015-02-23

289

Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons  

NASA Astrophysics Data System (ADS)

Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.

2014-01-01

290

Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons.  

PubMed

Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs. PMID:25669533

Oyeyemi, Victor B; Krisiloff, David B; Keith, John A; Libisch, Florian; Pavone, Michele; Carter, Emily A

2014-01-28

291

Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons  

SciTech Connect

Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

Oyeyemi, Victor B. [Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Krisiloff, David B. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Keith, John A.; Libisch, Florian [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Pavone, Michele [Department of Chemical Sciences, University of Napoli Federico II, Napoli 80120 (Italy)] [Department of Chemical Sciences, University of Napoli Federico II, Napoli 80120 (Italy); Carter, Emily A., E-mail: eac@princeton.edu [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544 (United States)

2014-01-28

292

Cleavage of Carbon-Carbon Bonds of Diphenylacetylene and Its Derivatives via Photolysis of Pt Complexes: Tuning the  

E-print Network

Cleavage of Carbon-Carbon Bonds of Diphenylacetylene and Its Derivatives via Photolysis of Pt analysis. While the C-C cleavage reaction occurs readily under photochemical conditions, thermal activation-withdrawing or electron-donating groups. Upon cleavage of the C-C bond in (dtbpe)Pt(2 -(p

Jones, William D.

293

Low energy electron induced cytosine base release in 2?-deoxycytidine-3?-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study  

SciTech Connect

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? CO bond cleavage from the lowest ?{sup *} shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?{sup *} orbital of the base to the ?{sup *} orbital of the glycosidic NC bond. In addition, the metastable state formed after impinging LEE (01 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 NC 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 ?3555 fs. Comparison of salient features of the two dissociation events, i.e., 3? CO single strand break and glycosidic NC bond cleavage in 3?-dCMPH molecule are also provided.

Bhaskaran, Renjith; Sarma, Manabendra, E-mail: msarma@iitg.ernet.in [Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039 (India)

2014-09-14

294

Low energy electron induced cytosine base release in 2'-deoxycytidine-3'-monophosphate via glycosidic bond cleavage: a time-dependent wavepacket study.  

PubMed

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. PMID:25217918

Bhaskaran, Renjith; Sarma, Manabendra

2014-09-14

295

The high temperature strength of C/C and C/C-SIC composites under shear loading  

SciTech Connect

In this paper the influence of the temperature on the shear strength of a C/C-SiC composite is studied and compared with that one of two C/C materials. The Interlaminar Shear Strengths (ILSS) were measured in the range from room temperature up to 2000{degrees}C under inert gas atmosphere using an unsymmetrical compression shear test. With increasing temperature the shear strengths of all materials increase. However, in each case the values of C/C-SiC were significantly higher than those of C/C.

Thielicke, B.; Soltesz, U. [Fraunhofer-Institut fuer Wekstoffmechanick, Freiburg (Germany)

1995-12-01

296

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

297

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

SciTech Connect

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

Vos, M.; Went, M. R. [Atomic and Molecular Physics Laboratories6, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia)

2006-11-15

298

Demystifying Introductory Chemistry. Part 3: Ionization Energies, Electronegativity, Polar Bonds, and Partial Charges.  

ERIC Educational Resources Information Center

Shows how ionization energies provide a convenient method for obtaining electronegativity values that is simpler than the conventional methods. Demonstrates how approximate atomic charges can be calculated for polar molecules and how this method of determining electronegativities may lead to deeper insights than are typically possible for the

Spencer, James; And Others

1996-01-01

299

Deprotonation of coordinated phosphanes in a rhenium complex: c?c coupling with diimine coligands.  

PubMed

The reaction of fac-[Re(bipy)(CO)3 (PMe3 )][OTf] (bipy=2,2'-bipyridine) with KN(SiMe3 )2 affords two neutral products: cis,trans-[Re(bipy)(CO)2 (CN)(PMe3 )], and a thermally unstable compound, which features a new C?C bond between a P-bonded methylene group (from methyl group deprotonation) and the C6 position of bipy. The solid-state structures of more stable 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene analogs, resulting from the deprotonation of PMe3 , PPhMe2 , and PPh2 Me ligands, are determined by X-ray diffraction. PMID:25604138

Arvalo, Rebeca; Prez, Julio; Riera, Luca

2015-02-23

300

Determination of S-O bond order in sulfur dioxide and dimethyl sulfite using a low-energy particle-accelerator technique  

NASA Astrophysics Data System (ADS)

Energy loss from a beam of He+ ions due to inelastic collisions with vaporous sulfur dioxide and dimethyl sulfite has been measured. Application of the Bragg rule to these results suggests minimal d-orbital involvement in the S-O bonds for these compounds.

Powers, D.; Olson, H. G.

1980-09-01

301

7978 J. Phys. Chem. 1993,97, 7978-7987 Sequential Bond Energies of Cr(CO)t, x = 1-6  

E-print Network

difficulttostudy. An importantelement in characterizing these species is the bond dissociation energy (BDE toobtainaccuratesequential BDEs for Fe(CO),+ species. In the present work, we apply this technique to obtain sequential BDEs theother fragments. This observation suggests that the BDEs for loss of CO from thesespeciesare smallerthan

Clemmer, David E.

302

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

303

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

Microsoft Academic Search

Polytetrafluoroethylene (PTFE) was irradiated by low energy titanium ion in a metal vapor vacuum arc (MEVVA) implanter. The samples were irradiated with 80keV Ti ion with fluences from 51015 to 51017 Ti\\/cm2, respectively. Transportation of Ion in Matters (TRIM) code was employed to simulate Ti ion irradiation. The as-irradiated samples were investigated by ESCA, SEM and wettability. As increasing ion

Jizhong Zhang; Xiaoji Zhang; Hongyu Zhou

2003-01-01

304

Bond dissociation energies of c10 and c18 methyl esters from local multireference averaged-coupled pair functional theory.  

PubMed

We previously developed a fast, local, reduced scaling Cholesky-decomposed multireference averaged-coupled pair functional (CD-LMRACPF2) method, which takes advantage of the locality of dynamic correlation and numerical approximations such as Cholesky decomposition and integral screening. Motivated by the desire to study large biodiesel methyl ester molecules, here we validate CD-LMRACPF2 for the computation of bond dissociation energies (BDEs) in a suite of oxygenated molecules, and show that the low-cost method is very accurate compared to the conventional variant. We then demonstrate the power of CD-LMRACPF2 for fast and accurate computation of energies of molecules containing up to 13 second-row atoms within a polarized triple-? (cc-pVTZ) basis set. We use biodiesel methyl esters as a chemically interesting model system and furnish BDEs of C10 and C18 methyl esters, with the latter performed within a cc-pVDZ basis set. We describe trends in the BDEs and explain how structural (isomeric) differences affect BDEs, as well as discuss implications of BDE trends for biodiesel physical and chemical properties. PMID:25775253

Oyeyemi, Victor B; Dieterich, Johannes M; Krisiloff, David B; Tan, Ting; Carter, Emily A

2015-04-01

305

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

306

A quinone-assisted photoformation of energy-rich chemical bonds  

NASA Technical Reports Server (NTRS)

In a study of biochemical means of solar energy conversion, ADP and inorganic phosphates were converted to ATP by white light in the nonaqueous solvent dimethylformamide in the presence of tetrachloro-p-quinone or ubiquinone. Conversion of ADP to ATP has been accomplished in aqueous suspension by the use of cell-like structures aggregated from poly(aspartic acid, glutamic acid, tyrosine). This is believed to occur through the formation of dopaquinone in the peptide structure during illumination. The way in which the quantitative yield of ATP has been influenced by pH and by added substances, such as FeCl2, was studied.

Fox, S. W.; Adachi, T.; Stillwell, W.

1980-01-01

307

C?C coupling of ketones with methanol catalyzed by a N-heterocyclic carbene-phosphine iridium complex.  

PubMed

An N-heterocyclic carbene-phosphine iridium complex system was found to be a very efficient catalyst for the methylation of ketone via a hydrogen transfer reaction. Mild conditions together with low catalyst loading (1?mol?%) were used for a tandem process which involves the dehydrogenation of methanol, C?C bond formation with a ketone, and hydrogenation of the new generated double bond by iridium hydride to give the alkylated product. Using this iridium catalyst system, a number of branched ketones were synthesized with good to excellent conversions and yields. PMID:25589169

Quan, Xu; Kerdphon, Sutthichat; Andersson, Pher G

2015-02-23

308

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

NASA Technical Reports Server (NTRS)

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

Singh, M.; Asthana, R.

2008-01-01

309

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

310

Homogeneous Gold Catalysis Highly Efficient Functionalization of CC Multiple Bonds and Electron-Rich CH Bonds  

E-print Network

Homogeneous Gold Catalysis Highly Efficient Functionalization of CC Multiple Bonds and Electron references: Puddephatt, R. The Chemistry of Gold; E. L. Sevier Scientific Publication Co., Amsterdam, 1978. Hashmi, A. S. K. Gold Bulletin 2004, 37, 51-65. Parish, R. V. Gold Bulletin 1997, 30, 3-12. Parish, R. V

Stoltz, Brian M.

311

Estimation of the Rh-Rh bond dissociation energy in the (octaethylporphyrinato)rhodium(II) dimer by /sup 1/H NMR line broadening  

SciTech Connect

The octaethylporphyrin dimer ((OEP)Rh)/sub 2/ has been reported to have an interesting range of organometallic reactivity. An estimation of the Rh-Rh bond dissociation energy (BDE) in the dimer from /sup 1/H NMR line broadening studies is reported herein. This value for the dissociation energy has been used in deriving the (R-H)BDE in (OEP)Rh-H and the (Rh-C)BDE in (OEP)Rh-CHO. 19 references, 2 figures.

Wayland, B.B.; Coffin, V.L.; Farnos, M.D.

1988-07-27

312

Unidirectional redox-stimulated movement around a C-C single bond.  

PubMed

A remarkable challenge for the design of molecular machines is the realization of a synchronized and unidirectional movement caused by an external stimulus. Such a movement can be achieved by a unidirectionally controlled change of the conformation or the configuration. Biphenol derivatives are one possibility to realize a redox-driven unidirectional molecular switch. For this reason, a 4,4'-biphenol derivative was fixed to a chiral cyclopeptidic scaffold and stimulated by chemical oxidants and reduction agents. The conformation of the switch was determined by DFT calculations by using B3LYP and the 6-31G* basis set. The switching process was observed by UV and circular dichroism (CD) spectroscopic measurements. Several oxidation agents and various conditions were tested, among which (diacetoxy)iodobenzene (DAIB) in methanol proved to be the best. In this way it was possible to synthesize a redox-stimulated molecular switch with a movement that is part of a rotation around a biaryl binding axis. PMID:21626582

Tepper, Christina; Haberhauer, Gebhard

2011-07-11

313

1 Reactivity Differences of Pt0 Phosphine Complexes in C-C Bond  

E-print Network

Acetylenes 3 Ahmet Gunay, Christian Muller, Rene J. Lachicotte, William W. Brennessel, and 4 William D. Joneseq 1. The syntheses all involve reaction of a 1:1:1 mixture of *Corresponding author. E-mail: jones. J. Mol. Catal. A 2002, 189, 145. (6) (a) Gunay, A.; Jones, W. D. J. Am. Chem. Soc. 2007, 129, 8729

Jones, William D.

314

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

315

Aminocatalytic cross-coupling approach via iminium ions to different C - C Bonds.  

PubMed

Given the attractive ability of iminium ions to functionalize molecules directly at ostensibly unreactive positions, the reactivity of iminium ions, in which an ? CH2 group is replaced by C?O was explored. Background studies on the ability of such iminium cations to promote reactions via an iminium-catalyzed or iminium-equivalent pathway are apparently unavailable. Previously, tandem cross-coupling reactions were reported, in which an iminium ion undergoes nucleophilic 1,2-addition to give a putative three-component intermediate that abstracts a proton in situ and undergoes self-deamination followed by unprecedented DMSO/aerobic oxidation to generate ?-ketoamides. However, later it was observed that iminium ions can generate valuable ?-ketoamides through simple aerobic oxidation. In all reactions, iminium ions were generated in situ by reaction of 2-oxoaldehydes with secondary amines. PMID:25524296

Mupparapu, Nagaraju; Battini, Narsaiah; Battula, Satyanarayana; Khan, Shahnawaz; Vishwakarma, Ram A; Ahmed, Qazi Naveed

2015-02-01

316

Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces  

PubMed Central

A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between KohnSham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized KohnSham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant KohnSham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the iondipole complex stabilization. PMID:20228960

Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

2010-01-01

317

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

318

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

SciTech Connect

We investigate and analyze the vibrational properties, including hydrogen/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental (infrared multiple photon dissociation and argon-tagged action spectroscopy) and computational techniques. We note a qualitative difference between the two experimental results discussed here and employ ab initio molecular dynamics simulations to explain these results. A deeper understanding of the differences between the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads to a system-bath coupling interpretation. Specifically, when a few active modes, involving the shared hydrogen/deuterium stretch, are identified and labeled as system, with all other molecular vibrational modes being identified as bath modes, we find critical differences in the coupling between the system modes for the shared proton and shared deuteron cases. These differences affect the energy repartitioning between these modes resulting in a complex spectral evolution as a function of temperature. Furthermore, intensity borrowing across modes that are widely distributed in the frequency domain plays an important role on the simulated spectra.

Li, Xiaohu [Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405 (United States); Oomens, Jos [FOM Institute for Plasma Physics Rijnhuizen, Edisonbaan 14, 3439 MN Nieuwegein (Netherlands); Eyler, John R. [Department of Chemistry, University of Florida, Gainesville, Florida 32611 (United States); Moore, David T., E-mail: iyengar@indiana.edu, E-mail: david.moore@lehigh.edu [Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 (United States); Iyengar, Srinivasan S., E-mail: iyengar@indiana.edu, E-mail: david.moore@lehigh.edu [Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405 (United States); Department of Physics, Indiana University, 727 E. Third St., Bloomington, Indiana 47405 (United States)

2010-06-28

319

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

320

Bonding mechanism in ultrasonic gold ball bonds on copper substrate  

NASA Astrophysics Data System (ADS)

The effects of process parameters on bond formation in thermosonic gold ball bonding on a copper substrate at ambient temperatures have been investigated with scanning electron microscopy (SEM). A model was developed based on classical microslip theory to explain the general phenomena observed in the evolution of bond footprints left on the substrate. The specific effects of ultrasonic energy and complex stress distributions arising from tool geometry must be taken into consideration and were incorporated into the model. It was shown that relative motion existed at the bonding interface as microslip at lower powers, transitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurred at higher ultrasonic bonding powers.

Lum, I.; Jung, J. P.; Zhou, Y.

2005-05-01

321

Bonding silicones with epoxies  

Microsoft Academic Search

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

Tira

1980-01-01

322

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

323

Facile displacement of ?5-cyclopentadienyl ligands from half-sandwich alkyl,NHC-nickel complexes: an original route to robust cis-C,C-nickel square planar complexes.  

PubMed

The ?(5)-cyclopentadienyl (Cp) ligands of 18-electron half-sandwich alkyl,NHC-nickel complexes are readily displaced under acidic conditions to afford a novel class of cis-C,C-nickel square planar complexes. Remarkably, the nickel-alkyl and nickel-carbene bonds are not ruptured in these unprecedented Cp acidolysis reactions. PMID:23752919

Henrion, Mickal; Oertel, Anna Magdalena; Ritleng, Vincent; Chetcuti, Michael J

2013-07-21

324

25 CFR 225.30 - Bonds.  

Code of Federal Regulations, 2010 CFR

...30 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS AGREEMENTS Minerals Agreements 225.30 Bonds. (a) Bonds required by provisions of a...

2010-04-01

325

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

326

High-Resolution Photoelectron Spectroscopic Study of Cyclopropene (c-C_3H_4)  

NASA Astrophysics Data System (ADS)

The spectroscopic information available on the cyclopropene radical cation is limited to that contained in low-resolution He I photoelectron spectra. To better characterize the structure of this cation, we have recently measured high-resolution PFI-ZEKE photoelectron spectra of c-C_3H_4 and several of its deuterated isotopomers in the vicinity of the adiabatic ionization threshold. Our new data include fully rotationally resolved spectra of the origin band of the widetilde{X}^+?widetilde{X} transition of c-C_3H_4 and spectra of the low-vibrational levels of c-C_3H_4 and the deuterated isotopomers recorded at lower resolution. Because our efforts at synthesizing the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, the analysis of the isotopic shifts turned out to be challenging. Combining the information contained in the rotational structure of the origin band of c-C_3H_4 with the ionization energies of the isotopomers measured by photoionization mass spectrometry and the vibrational structure observed in the PFI-ZEKE spectra of the mixtures of deuterated isotopomers, we were able to draw conclusions on the structure of the cyclopropene radical cation based solely on experimental data. The adiabatic ionization energy of c-C_3H_4 was determined to be 77931.8(5) {cm}-1. M. B. Robin, C. R. Brundle, N. A. Kuebler, G. B. Ellison and K. B. Wiberg, J. Chem. Phys. 57, 1758 (1972). P. Bischof and E. Heilbronner, Helv. Chim. Acta 53, 1677 (1970).

Vasilatou, Konstantina; Michaud, Julie M.; Grassi, Guido; Baykusheva, Denitsa; Merkt, Frederic

2012-06-01

327

Qualifying Energy Conservation Bonds  

E-print Network

$ 0 mm Georgia $100 mm $ 5 mm Illinois $134 mm $ 50 mm Kansas $ 29 mm $ 29 mm Louisiana $ 45 mm $ 30 mm Michigan $104 mm $ 11 mm Mississippi $ 30 mm $ 0 mm Oklahoma $ 38 mm $ 0 mm Washington $ 68 mm $ 40 mm TEXAS $252 mm $ 16...

Briggs, J.

2013-01-01

328

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

329

Diffusion Monte Carlo Study of Bond Dissociation Energies for BH2, B(OH)2, BCl2, and BCl  

NASA Astrophysics Data System (ADS)

On basis of bond dissociation energies (BDEs) for BH2, B(OH)2, BCl2, and BCl, the diffusion Monte Carlo (DMC) method is applied to explore the BDEs of HB-H, HOB-OH, ClB-Cl, and B-Cl. The effect of the choice of orbitals, as well as the backflow transformation, is studied. The Slater-Jastrow DMC algorithm gives BDEs of 359.10.12 kJ/mol for HB-H, 410.50.50 kJ/mol for HOB-OH, 357.81.46 kJ/mol for ClB-Cl, and 504.50.96 kJ/mol for B-Cl using B3PW91 orbitals and similar BDEs when B3LYP orbitals are used. DMC with backflow corrections (BF-DMC) gives a HB-H BDE of 369.90.12 kJ/mol which is close to one of the available experimental value (375.8 kJ/mol). In the case of HOB-OH BDE, the BF-DMC calculation is 446.01.84 kJ/mol that is closer to the experimental BDE. The BF-DMC BDE for ClB-Cl is 343.22.34 kJ/mol and the BF-DMC B-Cl BDE is 523.30.33 kJ/mol, which are close to the experimental BDEs, 341.9 and 530.0 kJ/mol, respectively.

Li, Hui-ran; Cheng, Xin-lu; Zhang, Hong

2012-02-01

330

Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory.  

PubMed

Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the "S66" set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the "D3" pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs. PMID:24832350

DiLabio, Gino A; Koleini, Mohammad

2014-05-14

331

Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory  

SciTech Connect

Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the S66 set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the D3 pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs.

DiLabio, Gino A., E-mail: Gino.DiLabio@nrc.ca [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada); Department of Chemistry, University of British Columbia, Okanagan, 3333 University Way, Kelowna, British Columbia V1V 1V7 (Canada); Koleini, Mohammad [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada) [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada); Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4 (Canada)

2014-05-14

332

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 ClN 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. Mller-Plesset [MP2/6-311++G(2d,2p)] calculations show that the BEs for this set of complexes lie in the range from 1.27kcal/mol (in F-ClNF3) to 27.62kcal/mol [in F-ClN(CH3)3]. The intermolecular distribution of the electronic charge density and their L(r)?=?-?(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, Daro J R; Sosa, Gladis L; Peruchena, Nlida M

2013-05-01

333

Biomolecular halogen bonds.  

PubMed

Halogens are atypical elements in biology, but are common as substituents in ligands, including thyroid hormones and inhibitors, which bind specifically to proteins and nucleic acids. The short-range, stabilizing interactions of halogens - now seen as relatively common in biology - conform generally to halogen bonds characterized in small molecule systems and as described by the ?-hole model. The unique properties of biomolecular halogen bonds (BXBs), particularly in their geometric and energetic relationship to classic hydrogen bonds, make them potentially powerful tools for inhibitor design and molecular engineering. This chapter reviews the current research on BXBs, focusing on experimental studies on their structure-energy relationships, how these studies inform the development of computational methods to model BXBs, and considers how BXBs can be applied to the rational design of more effective inhibitors against therapeutic targets and of new biological-based materials. PMID:25326832

Ho, P Shing

2015-01-01

334

Acid Gradient across Plasma Membrane Can Drive Phosphate Bond Synthesis in Cancer Cells: Acidic Tumor Milieu as a Potential Energy Source  

PubMed Central

Aggressive cancers exhibit an efficient conversion of high amounts of glucose to lactate accompanied by acid secretion, a phenomenon popularly known as the Warburg effect. The acidic microenvironment and the alkaline cytosol create a proton-gradient (acid gradient) across the plasma membrane that represents proton-motive energy. Increasing experimental data from physiological relevant models suggest that acid gradient stimulates tumor proliferation, and can also support its energy needs. However, direct biochemical evidence linking extracellular acid gradient to generation of intracellular ATP are missing. In this work, we demonstrate that cancer cells can synthesize significant amounts of phosphate-bonds from phosphate in response to acid gradient across plasma membrane. The noted phenomenon exists in absence of glycolysis and mitochondrial ATP synthesis, and is unique to cancer. Biochemical assays using viable cancer cells, and purified plasma membrane vesicles utilizing radioactive phosphate, confirmed phosphate-bond synthesis from free phosphate (Pi), and also localization of this activity to the plasma membrane. In addition to ATP, predominant formation of pyrophosphate (PPi) from Pi was also observed when plasma membrane vesicles from cancer cells were subjected to trans-membrane acid gradient. Cancer cytosols were found capable of converting PPi to ATP, and also stimulate ATP synthesis from Pi from the vesicles. Acid gradient created through glucose metabolism by cancer cells, as observed in tumors, also proved critical for phosphate-bond synthesis. In brief, these observations reveal a role of acidic tumor milieu as a potential energy source and may offer a novel therapeutic target. PMID:25874623

Dhar, Gautam; Sen, Suvajit; Chaudhuri, Gautam

2015-01-01

335

Asymmetric bifurcated halogen bonds.  

PubMed

Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as '?-hole - lone pair' or '?-hole - ?' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

Novk, Martin; Foroutan-Nejad, Cina; Marek, Radek

2015-03-01

336

Reactions of heteronuclear dimetalated olefin complexes. Reactions of CpFe-(CO){sub 2}[{mu}-(Z)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]Re -(CO){sub 4} with CO and p-tolyl isothiocyanate  

SciTech Connect

Addition of CO to the dimetalated olefin complex CpFe(CO){sub 2} [{mu}-(Z)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 4}, 1, at 25{degree}C/700 psi of CO resulted in the formation of the adduct CpFe(CO){sub 2}[{mu}-(E)-(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 5} , 2, in 52% yield by cleavage of the Re-O bond to the coordinated carboxylate group. In contrast the reaction of 1 with CO at 70{degree}C/ 900 psi of CO provided the new compound CpFe(CO){sub 2} [{mu}-(Z)-C=O(MeO{sub 2}C)C=C(CO{sub 2}Me)]-Re(CO){sub 4}, 3, in 77% yield. Compounds 2 and 3 were characterized by single-crystal X-ray diffraction analyses. Compound 2 is a Z-dimetalated olefin formed by addition of CO to the Re(CO){sub 4} group in 1, C-C = 1. 35(1) Hi. Compound 3 is an isomer of 2 in which a CO was added to 1 and inserted into the iron-carbon bond to the alkyne. Compound 1 reacts with EtNH{sub 2} or H{sub 2}O to yield the new compound CpFe(CO){sub 2}[(MeO{sub 2}C)C=C(CO{sub 2}Me)(H)], 6, by the cleavage of the rhenium grouping from the molecule. The reaction with H{sub 2}O is catalyzed by silica gel. 22 refs., 3 figs., 6 tabs.

Adams, R.D.; Huang, M. [Univ. of South Carolina, Columbia, SC (United States)

1995-10-01

337

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

SciTech Connect

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 13491822 K, and the strength of the chemical bond formed between antimony and the group 11 metals was for the first time measured deriving the following thermochemical dissociation energies (D{sub 0}{sup ?}, kJ/mol): 186.7 5.1 (CuSb), 156.3 4.9 (AgSb), 241.3 5.8 (AuSb). The three species were also investigated computationally at the coupled cluster level with single, double, and noniterative quasiperturbative triple excitations (CCSD(T)). The spectroscopic parameters were calculated from the potential energy curves and the dissociation energies were evaluated at the Complete Basis Set limit, resulting in an overall good agreement with experimental values. An approximate evaluation of the spin-orbit effect was also performed. CCSD(T) calculations were further extended to the corresponding group 11 arsenide species which are here studied for the first time and the following dissociation energies (D{sub 0}{sup ?}, kJ/mol): 190 10 (CuAs), 151 10 (AgAs), 240 15 (AuAs) are proposed. Taking advantage of the new experimental and computational information here presented, the bond energy trends along group 11 and 4th and 5th periods of the periodic table were analyzed and the bond energies of the diatomic species CuBi and AuBi, yet experimentally unobserved, were predicted on an empirical basis.

Carta, V.; Ciccioli, A., E-mail: guido.gigli@uniroma1.it, E-mail: andrea.ciccioli@uniroma1.it; Gigli, G., E-mail: guido.gigli@uniroma1.it, E-mail: andrea.ciccioli@uniroma1.it [Dipartimento di Chimica, Sapienza Universit di Roma, p.le A. Moro 5, 00185 Roma (Italy)

2014-02-14

338

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

339

Application of the PROTON(NITROGEN-15, Alpha Gamma)carbon -12 Nuclear Reaction to the Study of the Bond Energy and Direction of Bound Hydrogen.  

NASA Astrophysics Data System (ADS)

In 1983, two independent studies of the 6.4 MeV p(^{15}N, alpha gamma)^{12}C resonant nuclear reaction determined that the full width at half maximum of this reaction's cross section is 1.8 keV. Though it had long been suspected that this resonance was narrower than published values indicated, measurement of such an extremely narrow width was unexpected. It was soon recognized that such a narrow resonance would make a very sensitive tool for measuring the motion of hydrogen atoms. This work demonstrates that the width of this resonance, measured on an appropriate target, can yield valuable information about both the bond energy and bond direction of bound hydrogen atoms. For the purpose of clearly illustrating the sensitivity of this technique to differences in bond energy, excitation curves for the p(^{15}N, alpha gamma)^{12}C nuclear reaction have been measured on a number of hydrogen-bearing gases to investigate the bond-dependent Doppler broadening resulting from the motion of the target hydrogen atoms. Contributions to the resonance width due to the intrinsic width of the resonance, gas-induced beam energy loss and energy straggle, accelerator beam energy spread, and Doppler broadening are considered. Measurements of the excitation function of the p(^{15}N, alphagamma)^{12}C nuclear reaction on various hydrogen-bearing gases have shown distinct differences in the measured full width at half maximum of the resulting resonance curves. A theoretical model, based upon data extracted from the field of molecular spectroscopy, has been developed which predicts these resonance widths in very good agreement with the experimentally measured values. The theoretical model further indicates that the Doppler broadening technique can be used to resolve the different bond directions of bound hydrogen on a clean, homogeneous, hydrogen-saturated surface. Such a surface should show largely different Doppler broadening contributions between the stretching and bending mode vibrational directions. Preliminary measurements done on Si<100> surfaces along directions nominally off the stretching mode direction show Doppler broadening contributions which can only correspond to vibrational bending modes.

Horn, Kevin Michael

340

Investing in Bonds  

E-print Network

Bonds, which are issued by governments and corporations, can be an important part of one's investment portfolio. U.S. government bonds, municipal bonds, zero-coupon bonds and other types are described. Also learn strategies for coping with inflation...

Johnson, Jason; Polk, Wade

2002-08-12

341

The role of structural ledges at phase boundaries; 3: F. c. c. -b. c. c. interfaces in Kurdjumov-Sachs orientation  

SciTech Connect

The ledge mode of misfit accommodation is extended to [111] f.c.c. [parallel] [110] b.c.c. interfaces with the Kurdjumov-Sachs (KS) orientation relationship. As with the Nishiyama-Wassermann (NW) relationship the geometric quantities are uniquely related by the misfit ratio r of atomic diameters. A rigid lattice analysis shows that the driving forces for a KS orientation relationship are significantly larger than those for the NW-x and even more so than those for the NW-y relationships. The rigid analysis also predicts that the terrace width which satisfies the periodicity conditions for a stepped interface are well within the terrace widths which allow significant energy gains. The models developed for the NW analysis are modified for KS configurations and employed to sum energies for the terrace patches, tilt misfit dislocations and the riser interface energy. Comparing this energy with that of a planar interphase boundary comprised of only misfit compensating dislocations shows that a stepped interphase boundary is energetically favored at r values near and greater than r[sub KS] but less than r[sub NW[minus]y].

Merwe, J.H. van der; Shiflet, G.J. (Univ. of South Africa, Pretoria (South Africa). Dept. of Physics)

1994-04-01

342

Functional interactions in bacteriorhodopsin: a theoretical analysis of retinal hydrogen bonding with water.  

PubMed Central

The light-driven proton pump, bacteriorhodopsin (bR) contains a retinal molecule with a Schiff base moiety that can participate in hydrogen-bonding interactions in an internal, water-containing channel. Here we combine quantum chemistry and molecular mechanics techniques to determine the geometries and energetics of retinal Schiff base-water interactions. Ab initio molecular orbital calculations are used to determine potential surfaces for water-Schiff base hydrogen-bonding and to characterize the energetics of rotation of the C-C single bond distal and adjacent to the Schiff base NH group. The ab initio results are combined with semiempirical quantum chemistry calculations to produce a data set used for the parameterization of a molecular mechanics energy function for retinal. Using the molecular mechanics force field the hydrated retinal and associated bR protein environment are energy-minimized and the resulting geometries examined. Two distinct sites are found in which water molecules can have hydrogen-bonding interactions with the Schiff base: one near the NH group of the Schiff base in a polar region directed towards the extracellular side, and the other near a retinal CH group in a relatively nonpolar region, directed towards the cytoplasmic side. Images FIGURE 1 FIGURE 2 FIGURE 6 FIGURE 8 PMID:7711248

Nina, M; Roux, B; Smith, J C

1995-01-01

343

Co?C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry  

NASA Astrophysics Data System (ADS)

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B 12 analog 2',5'-dideoxyadenosylcobalamin, which lacks an ?OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield ? d (0.250.02), Co?C bond dissociation energy (BDE; 31.82.5 kcal mol -1) and reaction volume change ?V R (6.50.5 ml mol -1) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co?C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.

Chen, Hao; Li, Gang; Zhang, Fei Fei; Sun, Li; Chen, Hui Lan; Zhang, Shu Yi

2003-10-01

344

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

345

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

E-print Network

their structural integrity during the opening process. Arrays of hooks, which are permanently anchored in solid of graphite [8]. In single-wall nanotubes [9,10], substitution of hexa- gons by pentagon-heptagon pairs-repair mechanism under local shear. With a large density of hooks per area, strong bonding can be achieved

346

Effects of lead design on ultrasonic bond quality of wire bonds  

Microsoft Academic Search

Wire bonding is an important method of interconnection in microelectronics. The micro welding of the contact pad to the gold wire is achieved by a thermosonic wire bonding process. Ultrasonic energy is known to soften metallic materials and hence when used in the wire bond process to decrease the flow stress similar to thermal energy. But experimental results shows for

Narasimalu Srikanth; C. J. Vath

2005-01-01

347

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

348

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

349

Experimental bond critical point and local energy density properties determined for Mn-O, Fe-O and Co-O bonded interactions for tephroite, Mn2SiO4, fayalite, Fe2SiO4 and Co2SiO4 olivine and selected organic metal complexes: Comparison with properties calculated for non-transition and transition metal M-O bonded interactions for silicates and oxides  

SciTech Connect

Bond critical point, bcp, and local energy density properties for the electron density, ED, distributions, calculated with first principle quantum mechanical methods for divalent transition metal Mn-, Co- and Fe-containing silicates and oxides are compared with experimental model ED properties for tephroite, Mn2SiO4, fayalite, Fe2SiO4 and Co2SiO4 olivine, each determined with high energy synchrotron single crystal X-ray diffraction data. Trends observed between the experimental bond lengths, R(M-O), (M = Mn, Fe, Co), and the calculated bcp properties are comparable with those observed for non-transition M-O bonded interactions. The bcp, local total energy density, H(rc), and bond length trends determined for the Mn-O, Co-O and Fe-O interactions are virtually identical. A comparison is also made with model experimental bcp properties determined for several Mn-O, Fe-O and Co-O bonded interactions for organometallic complexes and several oxides. Despite the complexities of the structures of the organometallic complexes, the agreement between the calculated and the model experimental bcp properties is good in several cases. The G(rc)/p(rc) vs. R(M-O) trends established for non-transition metal M-O bonded interactions hold for the given transition metal M O bonded interactions with the G(rc)/p(rc) ratio increasing in value as H(rc) becomes progressively more negative in value and the shared character of the interaction increases. As observed for the non-transition metal M-O bonded interactions, the Laplacian, ?2p(rc), increases in value as p(rc) increases and as H(rc) decreases. The Mn-O, Fe-O, and Co-O bonded interactions are indicated to be of intermediate character with a substantial component of closed-shell character compared with Fe-S and Ni-S bonded interactions which show greater shared character based on the |V(rc)|/G(rc) bond character indicator. The atomic charges conferred on the transition metal atoms for the three olivines decrease with increasing atomic number from Mn to Fe to Co.

Gibbs, Gerald V.; Downs, R. T.; Cox, David F.; Rosso, Kevin M.; Ross, Nancy L.; Kirfel, Armin; Lippmann, Thomas; Morgenroth, W.; Crawford, T Daniel

2008-09-18

350

Quantification of C?C and C?O Surface Carbons in Detonation Nanodiamond by NMR  

SciTech Connect

The ability of solid-state 13C NMR to detect and quantify small amounts of sp2-hybridized carbon on the surface of ?5 nm diameter nanodiamond particles is demonstrated. The C?C carbon fraction is only 1.1 0.4% in pristine purified detonation nanodiamond, while a full single-layer graphitic or bucky diamond shell would contain ca. 25% of all C in a 5 nm diameter particle. Instead of large aromatic patches repeatedly proposed in the recent literature, sp3-hybridized CH and COH carbons cover most of the nanodiamond particle surface, accounting for ?5% each. C?O and COO groups also seen in X-ray absorption near-edge structure spectroscopy (XANES) but not detected in previous NMR studies make up ca. 1.5% of all C. They are removed by heat treatment at 800 C, which increases the aromatic fraction. 13C{1H} NMR demonstrates that the various sp2-hybridized carbons are mostly not protonated, but cross-polarization shows that they are separated from 1H by only a few bond lengths, which proves that they are near the protonated surface. Together, the observed CH, COH, C?O, and C?C groups account for 1214% of all C, which matches the surface fraction expected for bulk-terminated 5 nm diameter diamond particles.

Cui, J.-F.; Fang, X.-W.; Schmidt-Rohr, K.

2014-05-08

351

SUBJECT NAME 30033 1 Evolutionary Computation C C R  

E-print Network

SUBJECT NAME 30033 1 Evolutionary Computation C C R 30034 1 Model Driven Formal Software Design C 30041 1 Connectivity Models C 30042 1 Computational Neuroscience I: Theoretical Models and Applications in Neuronal Computing C 30044 1 New Technologies for Communications C 30046 1 Information Recovery and Storage

Autonoma de Madrid, Universidad

352

Mit Methanol iridiumkatalysiert C-C-Bindungen knpfen  

E-print Network

Mit Methanol iridiumkatalysiert C-C-Bindungen knüpfen i Die Reaktivität von Methanol (1) beruht meist auf dem nucleophilen Sauerstoffatom. Obwohl Methanol industriell im Monsanto-Prozess carbo, dass Methanol iridiumkatalysiert leicht an Allene (2) addiert. Damit entstehen 2,2-disub- stituierte

Meyer, Karsten

353

C/C++ Thread Safety Analysis DeLesley Hutchins  

E-print Network

C/C++ Thread Safety Analysis DeLesley Hutchins Google Inc. Email: delesley@google.com Aaron Ballman--Writing multithreaded programs is hard. Static analysis tools can help developers by allowing threading policies, and can detect potential race conditions and deadlocks. This paper describes Clang Thread Safety Analysis

Cortes, Corinna

354

FROM EUCLID TO ENTROPY C. C. Rodr'iguez  

E-print Network

FROM EUCLID TO ENTROPY C. C. Rodr'iguez Department of Mathematics and Statistics SUNY at Albany of geometry goes something like this... Once upon a time there was a greek man named Euclid who organized the mathematical knowledge in his time in six books known as The Elements. Euclid's work was so influential

Rodriguez, Carlos

355

Chris Jesshope (c) C R Jesshope 211/2/2004  

E-print Network

on this assignment backtracking problems: - Sudoku - Eight queens - Chess / Go clustered data parallelism - N-body simulation - Game of life (c) C R Jesshope 711/2/2004 compression / decompression: - bzip - wavelet Group 3 Game of Life Thorben Kruger, Martin Lohstroh, Vasco Visser Group 4 ? Arram Visser, Zhang

Jesshope, Chris

356

The Gas Leakage Analysis in C/C Composites  

NASA Astrophysics Data System (ADS)

Gas leakage through carbon fiber reinforcement carbon composites, C/Cs, was discussed so as to apply C/Cs to heat exchangers in an engine system for a future space-plane. Since C/Cs include many cracks and pores, gas easily leaks through C/Cs. To predict and to prevent the gas flow through a C/C, leakage rate was measured as a function of pressure and gas flow path was identified by micro-observation of the C/C. Then, several analytical models were examined to clarify principal mechanism yielding gas flow resistance. It was found that laminar flow models gave far small flow resistance compared with experimental results, but a model based on adiabatic expansion and compression flow, used for gas leak through labyrinth seals, resulted in reasonable agreement. Finally, Si impregnation in a C/C was examined to minimize the gas leakage. This treatment was shown to be an excellent measure to reduce the gas leakage through C/C.

Nishiyama, Yuichi; Hatta, Hiroshi; Bando, Takamasa; Sugibayashi, Toshio

357

Reactions of fourth-period metal ions (Ca sup + endash Zn sup + ) with O sub 2 : Metal-oxide ion bond energies  

SciTech Connect

Reactions of Ca{sup +}, Zn{sup +} and all first-row atomic transition metal ions with O{sub 2} are studied using guided ion beam techniques. While reactions of the ground states of Sc{sup +}, Ti{sup +}, and V{sup +} are exothermic, the remaining metal ions react with O{sub 2} in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M{sup +}--O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn{sup +}, Co{sup +}, Ni{sup +}, and Cu{sup +}. Results (in eV) at 0 K are {ital D}{sup 0}(Ca{sup +}--O)=3.57{plus minus}0.05, {ital D}{sup 0}(Cr{sup +}--O)=3.72{plus minus}0.12, {ital D}{sup 0}(Mn{sup +}--O)=2.95{plus minus}0.13, {ital D}{sup 0}(Fe{sup +}--O)=3.53{plus minus}0.06 (reported previously), {ital D}{sup 0}(Co{sup +}--O)=3.32{plus minus}0.06, {ital D}{sup 0}(Ni{sup +}--O)=2.74{plus minus}0.07, {ital D}{sup 0}(Cu{sup +}--O)=1.62{plus minus}0.15, and {ital D}{sup 0}(Zn{sup +}--O)=1.65{plus minus}0.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molecules.

Fisher, E.R.; Elkind, J.L.; Clemmer, D.E.; Georgiadis, R.; Loh, S.K.; Aristov, N.; Sunderlin, L.S.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (USA) Department of Chemistry, University of California, Berkeley, CA (USA))

1990-08-15

358

Hexacoordinate bonding and aromaticity in silicon phthalocyanine.  

PubMed

Si-E bondings in hexacoordinate silicon phthalocyanine were analyzed using bond order (BO), energy partition, atoms in molecules (AIM), electron localization function (ELF), and localized orbital locator (LOL). Bond models were proposed to explain differences between hexacoordinate and tetracoordinate Si-E bondings. Aromaticity of silicon phthalocyanine was investigated using nucleus-independent chemical shift (NICS), harmonic oscillator model of aromaticity (HOMA), conceptual density functional theory (DFT), ring critical point (RCP) descriptors, and delocalization index (DI). Structure, energy, bonding, and aromaticity of tetracoordinate silicon phthalocyanine were studied and compared with hexacoordinate one. PMID:21105726

Yang, Yang

2010-12-23

359

Quantum Confinement in Hydrogen Bond  

E-print Network

In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and non-confinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from Supersymmetric Quantum Mechanics (SQM) formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy.

Carlos da Silva dos Santos; Elso Drigo Filho; Regina Maria Ricotta

2015-02-09

360

Hydrogen Bonded Arrays: The Power of Multiple Hydrogen Bonds  

SciTech Connect

Hydrogen bond interactions in small covalent model compounds (i.e. deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH2CH2)2CHO (2a), (HOCH2CH2) 3CO (3a) and (HOCH2CH2CH(OH)CH2)3CO (4a) reveal that hydrogen-bonded networks can provide enormous stabilizations, and that a single charge center not only can be stabilized by up to 3 hydrogen bonds but it can increase the interaction energy between non-charged OH groups by 5.8 kcal mol1 or more per hydrogen bond. This can lead to pKa values that are very different than in water, and provide some of the impetus for catalytic processes.

Shokri, Alireza; Schmidt, Jacob C.; Wang, Xue B.; Kass, Steven R.

2012-02-01

361

Effect of alpha-irradiation of energy 0.5 MeV on the hydrogen bonding in a-Si : H thin films  

NASA Astrophysics Data System (ADS)

Hydrogenated amorphous silicon thin films (a-Si:H) have been prepared by the rf glow discharge technique. The configuration of bonded hydrogen was investigated by infrared absorption measurements of Si:H vibrational modes before and after bombardment with an alpha-particle beam energy of 125 keV/n. The results showed an increase in the absorption mode near 2100, 890 and 850 cm(-1) and a decrease in the absorption mode near 2000 cm(-1) after bombardment. These observations are interpreted in terms of changes of the oscillator strengths of vibrational modes.

Abo-Ghazala, M. S.; Al-Hazmi, S.; Awad, E. M.

2004-07-01

362

Bond dissociation energies of H{sub 2}NX compounds. Comparison with CH{sub 3}X, HOX, and FX compounds  

SciTech Connect

The bond dissociation energies (BDE) of H{sub 2}NNH{sub 2}, HONH{sub 2} and FNH{sub 2} have been calculated using Pople`s G1 procedure, and the known BDE for hydrazine is well reproduced. The BDE`s of MeX, H{sub 2}NX, HOX and FX derivatives where X = Me, H{sub 2}N, HO, and F, are compared, and the differences are related to changes in hybridization, internal Coulombic stabilization and lone pair-lone pair repulsion. 20 refs., 6 figs., 6 tabs.

Wiberg, K.B. [Yale Univ., New Haven CT (United States)

1992-07-09

363

Understanding Excitation Energy Transfer in Metalloporphyrin Heterodimers with Different Linkers, Bonding Structures and Geometries through Stimulated X-Ray Raman Spectroscopy  

PubMed Central

We present simulations of stimulated X-ray Raman (SXRS) signals from covalent porphyrin heterodimers with different linkers, chemical bonding structures and geometries. The signals are interpreted in terms of valence electron wavepacket motion. One- and two-color SXRS signals can jointly indicate excitation energy transfer (EET) between the porphyrin monomers. It is shown that the SXRS signals provide a novel window into EET dynamics in multiporphyrin systems, and can be used as a powerful tool to monitor the subtle chemical environment which affects EET. PMID:25045204

Zhang, Yu; Biggs, Jason D.; Mukamel, Shaul

2014-01-01

364

Evidence of a long C-C attractive interaction in cerussite mineral: QTAIM and ELF analyses.  

PubMed

Cerussite, an orthorhombic lead carbonate mineral, has a structure and physical properties that cannot be understood merely in terms of ionic anion-cation interactions. The nature of the chemical bonding in cerussite is analyzed by means of the quantum theory of atoms in molecules (QTAIM) and the analysis of the electron localization function (ELF). A long C-C attractive interaction (3.077 ) along the c axis of the cerussite structure is evidenced by the presence of bond critical points between the C atoms of the CO(3)(2-) molecular groups. It is proposed that the Pb-O interactions, which are mostly ionic in nature, disturb the structure of the CO(3)(2-) molecular groups and promote their interaction along the c axis. The importance of this long-range interaction in the high-pressure crystal chemistry of carbonate minerals and in the explanation of some crystal growth features observed for orthorhombic carbonates is also discussed in this work. PMID:25129662

Vidal, Isaac; Navas, Antonio Snchez

2014-09-01

365

Conformation and molecular structure of 1-bromo-1,5-hexadiyne, BrC?C?CH 2?CH 2?C?CH, by gas-phase electron diffraction. Molecular-mechanics calculations on HC?C?CH 2?CH 2?C?CH, BrC?C?CH 2?CH 2?C?CH and BrC?C?CH 2?CH 2?C?CBr  

NASA Astrophysics Data System (ADS)

Gaseous BrC?C?CH 2?CH 2?C?CH or 1-bromo-bipropargyl (BBP) has been studied by electron diffraction at 50C. The ED data are best explained in terms of a conformational mixture of 43% gauche and 57% anti. Normal values of the structural parameters were determined. The experimental results for the three molecules HC?C?CH 2?CH 2?C?H, BrC?C?CH 2?CH 2?C?CH and BrC?C?CH 2?CH 2?C?CBr were used in order to establish values for the parameters of the non-bonded interaction potentials (BrC( sp) and C( sp)C( sp) to be used in the molecular-mechanics calculations.

Gogstad, E.; Stlevik, R.; Traetteberg, M.

1984-05-01

366

Primary photodissociation pathways of epichlorohydrin and analysis of the CC bond fission channels from an O,,3  

E-print Network

Primary photodissociation pathways of epichlorohydrin and analysis of the CC bond fission channels This study initially characterizes the primary photodissociation processes of epichlorohydrin, c- H2COCH CH2

Butler, Laurie J.

367

An AB initio study of the geometry of the C?C(H)? group the fC?C 2 stretching force constant, and the fC?C,inC?C coupling constant in conjugated mono-substituted carbonyl compounds  

NASA Astrophysics Data System (ADS)

The geometry of the C?C(H)?O group, the stretching force constant fC?C 2, and the coupling constant fC?O,C?C, calculated using the unscaled 4-31G basis set with full geometry optimization, are reported for various planar mono-substituted carbonyl compounds. The trends in rC?C, rC?H, ?CCO and ?HCO as rC?O increases are investigated, and an inverse relationship established between rC?O and rC?C, i.e. rC?O X rC?C = 1.782 0.013. Linear relationships are found in the plot of In fC?C 2 versus In rC?C in accord with the general form of Clark's equation, and in the plot of fC?O,C?C versus the quotient rC?Oit/rinC?C.

Bock, Charles W.; Trachtman, Mendel; George, Philip

1982-06-01

368

Solar System planetary tests of \\dot c/c  

E-print Network

Analytical and numerical calculations show that a putative temporal variation of the speed of light c, with the meaning of space-time structure constant c_ST, assumed to be linear over timescales of about one century, would induce a secular precession of the longitude of the pericenter \\varpi of a test particle orbiting a spherically symmetric body. By comparing such a predicted effect to the corrections \\Delta\\dot\\varpi to the usual Newtonian/Einsteinian perihelion precessions of the inner planets of the Solar System, recently estimated by E.V. Pitjeva by fitting about one century of modern astronomical observations with the standard dynamical force models of the EPM epehemerides, we obtained \\dot c/c =(0.5 +/- 2)\\times 10^-7 yr^-1. Moreover, the possibility that \\dot c/c\

Lorenzo Iorio

2009-05-15

369

Determination of F.C.C. crystal orientation by indentation  

Microsoft Academic Search

A new method of determining the orientation of f.c.c. crystal by slip lines is presented. The angles between slip lines formed by hardness indentation were measured. Based on the angular relations, different (left brace) 111 (right brace) slip planes in accord with each set of slip lines could be defined unambiguously. Then, a system of non-linear equations representing the geometrical

S. C. Chang; H. C. Chen

1995-01-01

370

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

371

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 (?Hf298) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S(T)), heat capacities (Cp(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ?Hf298 and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBS-QB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ?Hf298 values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered. PMID:25180943

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

2014-10-01

372

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 structureenergy 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

373

Detection of Alpha Particles and Low Energy Gamma Rays by Thermo-Bonded Micromegas in Xenon Gas  

E-print Network

Micromegas is a type of micro-pattern gaseous detector currently under R&D for applications in rare event search experiments. Here we report the performance of a Micromegas structure constructed with a micromesh thermo-bonded to a readout plane, motivated by its potential application in two-phase xenon detectors for dark matter and neutrinoless double beta decay experiments. The study is carried out in pure xenon at room temperature. Measurements with alpha particles from the Americium-241 source showed that gas gains larger than 200 can be obtained at xenon pressure up to 3 atm. Gamma rays down to 8 keV were observed with such a device.

Yuehuan Wei; Liang Guan; Zhiyong Zhang; Qing Lin; Xiaolian Wang; Kaixuan Ni; Tianchi Zhao

2013-08-09

374

Chemistry in Laser-Induced Plasmas: Formation of M-C?C-Cl (M = Ag or Cu) and their Characterization by Rotational Spectroscopy.  

PubMed

The new linear molecule Ag-C?C-Cl has been detected and fully characterized by means of rotational spectroscopy. It was synthesized by laser ablation of a silver rod in the presence of a gaseous sample containing a low concentration of CCl4 in argon, cooled to a rotational temperature approaching ?1-3 K through supersonic expansion, and analyzed by chirped-pulse, Fourier transform microwave spectroscopy. Six isotopologues were investigated, and for each the spectroscopic constants B0, DJ and ?aa(Cl) were determined. The B0 values were interpreted to give the following bond lengths: r(Ag-C) = 2.015(14) and r(C-Cl) = 1.635(6) , with r(C?C) = 1.2219 assumed from an ab initio calculation at the CCSD(T)/aug-cc-pV5Z level of theory. The Cu analogue Cu-C?C-Cl was similarly identified and characterized. PMID:25732940

Zaleski, Daniel P; Tew, David P; Walker, Nicholas R; Legon, Anthony C

2015-03-26

375

Theoretical Prediction of the Heats of Formation of C?H?O? Radicals Derived from Ethanol and of the Kinetics of ?-C-C Scission in the Ethoxy Radical  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Thermochemical parameters of three C?H?O? radicals derived from ethanol were reevaluated using coupledcluster theory CCSD(T) calculations, with the aug-cc-pVnZ (n = D, T, Q) basis sets, that allow the CC energies to be extrapolated at the CBS limit. Theoretical results obtained for methanol and two CH?O? radicals were found to agree within 0.5 kcal/mol with the experiment values. A set of consistent values was determined for ethanol and its radicals: (a) heats of formation (298 K) ?Hf(C?H?OH) = -56.4 0.8 kcal/mol (exptl: -56.21 0.12 kcal/mol), ?Hf(CH?C?HOH) = -13.1 0.8 kcal/mol, ?Hf(C?H?CH?OH) = -6.2 0.8 kcal/mol, and ?Hf(CH?CH?O?) = -2.7 0.8 kcal/mol; (b) bond dissociation energies (BDEs) of ethanol (0 K) BDE(CH?CHOH-H) = 93.9 0.8 kcal/mol, BDE(CH?CH?OH-H) = 100.6 0.8 kcal/mol, and BDE- (CH?CH?O-H) = 104.5 0.8 kcal/mol. The present results support the experimental ionization energies and electron affinities of the radicals, and appearance energy of (CH?CHOH+) cation. ?-C-C bond scission in the ethoxy radical, CH?CH?O?, leading to the formation of C?H? and CH?=O, is characterized by a C-C bond energy of 9.6 kcal/mol at 0 K, a zero-point-corrected energy barrier of E0 = 17.2 kcal/mol, an activation energy of Ea = 18.0 kcal/mol and a high-pressure thermal rate coefficient of k?(298 K) = 3.9 s-1, including a tunneling correction. The latter value is in excellent agreement with the value of 5.2 s-1 from the most recent experimental kinetic data. Using RRKM theory, we obtain a general rate expression of k(T,p) = 1.26 x 109p0.793 exp(-15.5/RT) s-1 in the temperature range (T) from 198 to 1998 K and pressure range (p) from 0.1 to 8360.1 Torr with N? as the collision partners, where k(298 K, 760 Torr) = 2.7 s-1, without tunneling and k = 3.2 s-1 with the tunneling correction. Evidence is provided that heavy atom tunneling can play a role in the rate constant for ?-C-C bond scission in alkoxy radicals.

Matus, Myrna H.; Nguyen, Minh T.; Dixon, David A.

2007-01-11

376

Cleavage of Carbon-Carbon Bonds in Aromatic Nitriles Using Juventino J. Garcia, Nicole M. Brunkan, and William D. Jones*,  

E-print Network

Cleavage of Carbon-Carbon Bonds in Aromatic Nitriles Using Nickel(0) Juventino J. Garcia, Nicole M as dimetalated products. No C-C or C-N cleavage of the aromatic ring is seen with quinoline or acridine; only 2. Introduction The cleavage of a variety of strong C-X -bonds, including C-H, C-F, C-S, and C-C, has been

Jones, William D.

377

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

378

Characterization of chemical bonding in low-k dielectric materialsfor interconnect isolation: a xas and eels study  

SciTech Connect

The use of low dielectric constant materials in the on-chipinterconnect process reduces interconnect delay, power dissipation andcrosstalk noise. To achieve the requirements of the ITRS for 2007-2009minimal sidewall damage from etch, ash or cleans is required. In chemicalvapor deposited (CVD) organo-silicate glass (OSG) which are used asintermetal dielectric (IMD) materials the substitution of oxygen in SiO2by methyl groups (-CH3) reduces the permittivity significantly (from 4.0in SiO2 to 2.6-3.3 in the OSG), since the electronic polarizability islower for Si-C bonds than for Si-O bonds. However, plasma processing forresist stripping, trench etching and post-etch cleaning removes C and Hcontaining molecular groups from the near-surface layer of OSG.Therefore, compositional analysis and chemical bonding characterizationof structured IMD films with nanometer resolution is necessary forprocess optimization. OSG thin films as-deposited and after plasmatreatment are studied using X-ray absorption spectroscopy (XAS) andelectron energy loss spectroscopy (EELS). In both techniques, the finestructure near the C1s absorption or energy loss edge, respectively,allows to identify C-H, C-C, and C-O bonds. This gives the opportunity todifferentiate between individual low-k materials and their modifications.The O1s signal is less selective to individual bonds. XAS spectra havebeen recorded for non-patterned films and EELS spectra for patternedstructures. The chemical bonding is compared for as-deposited andplasma-treated low-k materials. The Fluorescence Yield (FY) and the TotalElectron Yield (TEY) recorded while XAS measurement are compared.Examination of the C 1s near-edge structures reveal a modified bonding ofthe remaining C atoms in the plasma-treated sample regions.

Hoffmann, P.; Schmeisser, D.; Engelmann, H.-J.; Zschech, E.; Stegmann, H.; Himpsel, F.; Denlinger, J.

2006-04-10

379

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

380

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

381

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

Code of Federal Regulations, 2014 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 ...

2014-07-01

382

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

383

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

384

Semiconductor wafer bonding  

NASA Astrophysics Data System (ADS)

When mirror-polished, flat, and clean wafers are brought into contact, they are locally attracted to each other and adhere or bond. This phenomenon is known as semiconductor wafer bonding. Different adhesion forces (van der Waals forces, hydrogen bonding) are the reason for the bonding effect at room temperature. The different bonding mechanisms acting in dependence on the surface conditions (hydrophilic, hydrophobic) are reviewed. Variations of the properties of bonded interfaces (structural, mechanical, electrical) during annealing are discussed. The focus is on low-temperature bonding techniques. Reasons for the formation of interface defects are presented. Applications of semiconductor wafer bonding for future developments are briefly summarized.

Reiche, M.

2006-03-01

385

Role of acid-base interfacial bonding in adhesion  

Microsoft Academic Search

The strength of macroscopic adhesive bonds of polymers is known to be directly proportional to the microscopic exothermic interfacial energy changes of bond formation, as measured by Dupre's 'work of adhesion'. Since the work of adhesion can be very appreciably increased by interfacial acid-base bonding with concomitant increases in adhesive bond strength, it is important to understand the acid-base character

Frederick M. Fowkes

1987-01-01

386

Rhodium-catalyzed alkylation of C-H bonds in aromatic amides with ?,?-unsaturated esters.  

PubMed

The alkylation of C-H bonds with ?,?-unsaturated carbonyl compounds by a rhodium-catalyzed reaction of aromatic amides containing an 8-aminoquinoline moiety is reported. The reaction is highly regioselective. The formation of C-C bonds occurs between the ortho C-H bonds in aromatic amides and the ?-position of the acyclic ?,?-unsaturated carbonyl compounds. The reaction is applicable to various acyclic ?,?-unsaturated carbonyl compounds, such as acrylic esters, acrylamide, fumarate, maleate, and phenyl vinyl sulfone. PMID:25226267

Shibata, Kaname; Chatani, Naoto

2014-10-01

387

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

PubMed

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

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

2007-11-01

388

Wafer bonding of gallium arsenide on sapphire  

NASA Astrophysics Data System (ADS)

Three-inch (100) gallium arsenide wafers were bonded to ( 1/line{1} 02) sapphire in a micro-cleanroom at room temperature under hydrophilic or hydrophobic surface conditions. Subsequent heating up to 500 C increased the bond energy of the GaAs-on-sapphire (GOS) wafer pair close to the fracture energy of the bulk material. The bond energy was measured as a function of the temperature. Since the thermal expansion coefficients of GaAs and sapphire are close to each other, the bonded wafer pair is stable against thermal treatment and quenching in liquid nitrogen. During heating in different gas atmospheres, macroscopic interface bubbles and microscopic imperfections were formed within the bonding interface, which were analysed by transmission electron microscopy (TEM). These interface bubbles can be prevented by hydrophobic bonding in a hydrogen atmosphere.

Kopperschmidt, P.; Kstner, G.; Senz, S.; Hesse, D.; Gsele, U.

389

Stable alkanes containing very long carbon-carbon bonds.  

PubMed

The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 C, which is not in line with common C-C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C-C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature (1)H- and (13)C NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C-C bond rotation barriers from 7 to 33 kcal mol(-1). We probe the ability of popular density functional theory (DFT) approaches (including BLYP, B3LYP, B98, B3LYP-Dn, B97D, B3PW91, BHandHLYP, B3P86, PBE1PBE, wB97XD, and M06-2X) with 6-31G(d,p) and cc-pVDZ basis sets to describe such an unusual bonding situation. Only functionals accounting for dispersion are able to reproduce the experimental geometries, while most DFT functionals are able to reproduce the experimental rotational barriers due to error cancellations. Computations on larger diamondoids reveal that the interplay between the shapes and the sizes of the CH surfaces may even allow the preparation of open-shell alkyl radical dimers (and possibly polymers) that are strongly held together exclusively by dispersion forces. PMID:22835264

Fokin, Andrey A; Chernish, Lesya V; Gunchenko, Pavel A; Tikhonchuk, Evgeniya Yu; Hausmann, Heike; Serafin, Michael; Dahl, Jeremy E P; Carlson, Robert M K; Schreiner, Peter R

2012-08-22

390

I 6 LA$:LTIGE I . 1 . l c K . A-I . Srm:lnllc ~ ~ O C C C C I ~ ?tn ~ I C ~ O I I C I~stenlnp*A re  

E-print Network

I 6 LA$:LTIGE I . 1 . l c K . A- I . Srm:lnllc ~ ~ O C C C C I ~ ?tn ~ I C ~ O I I C I~stenlnp*A re . I ! , l p , * . , L ,$ I ,~,,,,II,PPI. ItJ71. 2, 641 646. Voluntary versus Automatic I I I ~ ~ ~ I I ~ , ~ ~ ~ .\\ \\ I . S ~ k r k .>I . 8 Cicl:~tle. C; Selcc~~vcaltcntlnn and

Jonides, John

391

Strong bonding strength between HA and (NH4)2S2O8-treated carbon/carbon composite by hydrothermal treatment and induction heating.  

PubMed

Carbon/carbon composite with hydroxyapatite (HA) coating is an attractive material in the dental and orthopedic fields, but the reported bonding strength between them was very poor. In this study, a compact crystalline HA coating on (NH(4))(2)S(2)O(8)-treated C/C substrate about 10 microm in width was obtained by hydrothermal treatment and induction heating. The microstructure, composition and morphologies of the as-prepared coatings were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. A strong shear strength averaging 74.2 MPa between C/C substrate and HA was achieved and adhesion failures were observed more frequently than cohesion failures. The coating adhesion measured using a scratch test was 23 N and the reasons for this are discussed. PMID:19135422

Xiong, Xin-bo; Zeng, Xie-rong; Zou, Chun-li; Zhou, Ji-Zhao

2009-06-01

392

Ionic hydrogen-bond networks and ion solvation. 1. An efficient Monte Carlo/quantum mechanical method for structural search and energy computations: ammonium/water.  

PubMed

Hydrogen-bond networks about solvated ions can form many alternative structures, requiring extensive conformational searches with accurate but affordable energy computation. For this purpose we are combining Monte Carlo searches with a computationally efficient density-functional-based tight-binding (DFTB+) method. The approach is tested for the stepwise hydration energies of the ammonium ion in NH(4)(+)(H(2)O)(n) clusters (n = 1-8), for which experimental data are available. For each cluster size n, we perform Monte Carlo searches, where for each conformation we calculate the minimized energy using the DFTB+ method (and, for comparison, using MM3 or OPLS-AA force field). The Monte Carlo/DFTB+ search identifies the lowest energy structure that can be reoptimized with other quantum mechanical methods (here with HF, B3LYP, B3PW91, MP2, DFT, and CBS-Q, CBS-QB3, and CBS-APNO methods). Calculated geometries and charge densities for the clusters are also presented. The results show that the binding energies calculated by the DFTB+ method reproduce the values measured experimentally and predicted by highly correlated, but significantly more computationally intensive, ab initio quantum chemical methods. The encouraging results suggest that the Monte Carlo/DFTB+ approach is a computationally efficient quantum chemical method for relatively large solvated systems, as demonstrated here for cluster ions. PMID:19243164

Zhao, Yi-Lei; Meot-Ner Mautner, Michael; Gonzalez, Carlos

2009-03-26

393

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, Ren P F; Pinski, John M; Abrash, Samuel A

2014-09-18

394

Modified low-temperture direct bonding method for vacuum microelectronics application  

NASA Astrophysics Data System (ADS)

This paper presents the process and experimental results for the improved silicon-to-glass bonding using silicon direct bonding (SDB) followed by anodic bonding. The initial bonding between glass and silicon was caused by the hydrophilic surfaces of silicon-glass ensemble using SDB method. Then the initially bonded specimen had to be strongly bonded by anodic bonding process. The effects of the bonding process parameters on the interface energy were investigated as functions of the bonding temperature and voltage. We found that the specimen which was bonded using SDB process followed by anodic bonding process had higher interface energy than one using anodic bonding process only. The main factor contributing to the higher interface energy in the glass-to-silicon assemble bonded by SDB followed by anodic bonding was investigated by secondary ion mass spectroscopy analysis.

Ju, Byeong-Kwon; Lee, Duck-Jung; Choi, Woo-Beom; Lee, Yun-Hi; Jang, Jin; Lee, Kwang-Bae; Oh, Myung-Hwan

1997-06-01

395

Low-temperature hydrophobic silicon wafer bonding  

NASA Astrophysics Data System (ADS)

By introducing a nanometer-scale H trapping defective silicon layer on bonding surfaces, the bonding surface energy of bonded oxide-free, HF dipped, hydrophobic silicon wafers can reach a silicon fracture surface energy of 2500 mJ/m2 at 300 to 400 C compared with 700 C conventionally achieved. Adding boron atoms on bonding surfaces can reduce the surface hydrogen release temperature but would not increase the bonding energy unless a defective layer is also formed. This indicates that, in order to achieve high bonding energy, the released hydrogen must be removed from the bonding interface. Many prebonding treatments are available for low-temperature hydrophobic wafer bonding including the formation of an amorphous silicon layer by As+ implantation, by B2H6 or Ar plasma treatment, or by sputter deposition, followed by an HF dip and room temperature bonding in air. The interface amorphous layer may be recrystallized by annealing at elevated temperatures, e.g., at 450 C for As+-implanted samples.

Tong, Q.-Y.; Gan, Q.; Hudson, G.; Fountain, G.; Enquist, P.; Scholz, R.; Gsele, U.

2003-12-01

396

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.

397

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. Matveevs 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

398

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

PubMed

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

399

Preparation and characterization of SiC\\/C and C\\/SiC\\/C composites using pulse chemical vapor infiltration process  

Microsoft Academic Search

A porous carbon plate and carbon fiber\\/carbon composite (C\\/C) preforms were infiltrated with SiC using a pulse chemical vapor infiltration (Pulse-CVI) process, and the Pulse-CVI conditions for obtaining the densely infiltrated SiC\\/C or C\\/SiC\\/C composites were examined. The optimum reaction temperatures, at which the pores were uniformly filled with SiC deposits throughout the thickness, were 1173 K for the carbon

Akihito Sakai; Jun Gotoh; Seiji Motojima

1996-01-01

400

A theoretical study of the change in homolytic bond dissociation energy on conversion of A-B to A-B sup + H  

SciTech Connect

The bond dissociation energies (BDE) for the homolytic cleavage of a number of isoelectronic A-B dimers have been calculated to third order in Moeller-Plesset perturbation theory with the 6-31G** basis set. In particular, BDE's have been calculated for A-B {yields} A* + *B, with A = CH{sub 3}, NH{sub 2}, OH, and F and B = CH{sub 3}, NH{sub 2}, OH, F, N{sup +}H{sub 3}, O{sup +}H{sub 2}, and F{sup +}H. It is shown that a substantial increase in the BDE occurs upon protonation of A-B and that the more electronegative the element B, the greater the change in BDE that accompanies the protonation of B. These trends are rationalized by application of the earlier discussions of Pauling and Allred and shown to be consistent with known chemical transformations.

Boyd, R.J.; Glover, J.N.M.; Pincock, J.A. (Dalhousie Univ., Halifax, Nova Scotia (Canada))

1989-07-05

401

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

402

, 2006, . 47, 5, c. 557--567 http://www.izdatgeo.ru PP C C CX X  

E-print Network

, 2006, . 47, 5, c. 557--567 http://www.izdatgeo.ru 550.834 PP C C CX X P P CP . p Republic pp c px px cx x, pcpcpxc p p p cp, c c c. c cc p P- S-, pcpcpxc px x - p. pp c p SH-, pcpcpxc c- c cp p p cp. xppc p- p c p c c p cpc. p, cc c cc p pcpcp p c pc pccp c . p c c p

Cerveny, Vlastislav

403

Quantum mechanical calculations on the potential energy surface for the formation of xenon dichloride and the nature of the (n5-cyclopentadienyl) dicarbonyliron-arene bond  

E-print Network

orbital diagram of 1, 4-C6H4(BHz)z shows the acceptor nature of the tt bonding in BHz to the arene, as well as the a bonding. . . 60 This partial molecular orbital diagram of 1, 4-C6H4(NHz)z shows the donor nature of the tt bonding in NHz to the arene..., as well as the o bonding. . . 62 LIST OF FIGURES (Continued) Page 13 This partial molecular orbital diagram of 1, 4-C6H4(CH2)2 shows both the acceptor and donor nature of the x bonding in CH2 to the arene. . . . . . . . . . . . . . . . . . . . 63 14...

Richardson, Nancy Arline

1993-01-01

404

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

405

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 ...

Mrs. Hicken

2009-04-08

406

Methodology for hardware\\/software co-verification in C\\/C++  

Microsoft Academic Search

In this paper we present our C\\/C++-based design environment 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 use of

Luc Smria; Abhijit Ghosh

2000-01-01

407

Hydroxide-catalyzed bonding  

NASA Technical Reports Server (NTRS)

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

Gwo, Dz-Hung (Inventor)

2003-01-01

408

Silver- and gold-mediated nucleobase bonding.  

PubMed

We report the results of a density functional theory investigation of the bonding of nucleobases mediated by silver and gold atoms in the gas phase. Our calculations use the Becke exchange and Perdew-Wang correlation functional (BPW91) combined with the Stuttgart effective core potentials to represent the valence electrons of gold, silver, and platinum, and the all-electron DGTZVP basis set for C, H, N, and O. This combination was chosen based on tests on the metal atoms and tautomers of adenine, cytosine, and guanine. To establish a benchmark to understand the metal-mediated bonding, we calculated the binding energy of each of the base pairs in their canonical forms. Our calculations show rather strong bonds between the Watson-Crick base pairs when compared with typical values for N-H-N and N-H-O hydrogen bonds. The neutral metal atoms tend to bond near the nitrogen atoms. The effect of the metal atoms on the bonding of nucleobases differs depending on whether or not the metal atoms bond to one of the hydrogen-bonding sites. When the silver or gold atoms bond to a non-hydrogen-bonding site, the effect is a slight enhancement of the cytosine-guanine bonding, but there is almost no effect on the adenine-thymine pairing. The metal atoms can block one of the hydrogen-bonding sites, thus preventing the normal cytosine-guanine and adenine-thymine pairings. We also find that both silver and gold can bond to consecutive guanines in a similar fashion to platinum, albeit with a significantly lower binding energy. PMID:25107359

Acioli, Paulo H; Srinivas, Sudha

2014-08-01

409

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

NASA Technical Reports Server (NTRS)

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

Lambrecht, Walter R. L.

1992-01-01

410

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

411

Using beryllium bonds to change halogen bonds from traditional to chlorine-shared to ion-pair bonds.  

PubMed

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the structures, binding energies, and bonding characteristics of binary complexes HFBe:FCl, R2Be:FCl, and FCl:N-base, and of ternary complexes HFBe:FCl:N-base and R2Be:FCl:N-base for R = H, F, Cl; N-base = NH3, NHCH2, NCH. Dramatic synergistic cooperative effects have been found between the BeF beryllium bonds and the ClN halogen bonds in ternary complexes. The ClN traditional halogen bonds and the BeF beryllium bonds in binary complexes become significantly stronger in ternary complexes, while the F-Cl bond weakens. Charge-transfer from F to the empty p(?) orbital of Be leads to a bending of the XYBe molecule and a change in the hybridization of Be, which in the limit becomes sp(2). As a function of the intrinsic basicity of the nitrogen base and the intrinsic acidity of the Be derivative, the halogen-bond type evolves from traditional to chlorine-shared to ion-pair bonds. The mechanism by which an ion-pair complex is formed is similar to that involved in the dissociative proton attachment process. EOM-CCSD spin-spin coupling constants (1X)J(Cl-N) across the halogen bond in these complexes also provide evidence of the same evolution of the halogen-bond type. PMID:25486548

Alkorta, Ibon; Elguero, Jos; M, Otilia; Yez, Manuel; Del Bene, Janet E

2015-01-21

412

Functionalized olefin cross-coupling to construct carboncarbon bonds  

NASA Astrophysics Data System (ADS)

Carbon-carbon (C-C) bonds form the backbone of many important molecules, including polymers, dyes and pharmaceutical agents. The development of new methods to create these essential connections in a rapid and practical fashion has been the focus of numerous organic chemists. This endeavour relies heavily on the ability to form C-C bonds in the presence of sensitive functional groups and congested structural environments. Here we report a chemical transformation that allows the facile construction of highly substituted and uniquely functionalized C-C bonds. Using a simple iron catalyst, an inexpensive silane and a benign solvent under ambient atmosphere, heteroatom-substituted olefins are easily reacted with electron-deficient olefins to create molecular architectures that were previously difficult or impossible to access. More than 60 examples are presented with a wide array of substrates, demonstrating the chemoselectivity and mildness of this simple reaction.

Lo, Julian C.; Gui, Jinghan; Yabe, Yuki; Pan, Chung-Mao; Baran, Phil S.

2014-12-01

413

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

SciTech Connect

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

Salta, Zoi; Kosmas, Agnie Mylona [Department of Chemistry, University of Ioannina, Ioannina 45110 (Greece); Lesar, Antonija [Department of Physical and Organic Chemistry, Joef Stefan Institute, Jamova 39, SI-1000, Ljubljana (Slovenia)

2014-10-06

414

Experimental Bond Critical Point and Local Energy Density Properties Determined for Mn-O, Fe-O, and Co-O Bonded Interactions for Tephroite, Mn2SiO4, Fayalite, Fe2SiO4,  

E-print Network

Organic Metal Complexes: Comparison with Properties Calculated for Non-Transition and Transition Metal M are comparable with those observed for non-transition M-O bonded interactions. The bcp properties, local total the calculated and model experimental bcp properties is fair to good in several cases. The G(rc)/ F(rc) versus R

Downs, Robert T.

415

Competitive Carbon-Sulfur vs Carbon-Carbon Bond Activation of 2-Cyanothiophene with [Ni(dippe)H]2  

E-print Network

Competitive Carbon-Sulfur vs Carbon-Carbon Bond Activation of 2-Cyanothiophene with [Ni(dippe)H]2: The processes of C-C and C-S bond cleavage have been studied with the homogeneous organometallic compound [Ni(dippe)H]2 (1). When 1 is reacted with 2-cyanothiophene at room temperature, cleavage of the nitrile

Jones, William D.

416

Metal-organic frameworks catalyzed C-C and C-heteroatom coupling reactions.  

PubMed

Metal organic frameworks (MOFs) are porous crystalline solids whose structure is formed by metal ions or clusters of a few metal ions held in place by bi- or multipodal organic linkers. In some cases, the metal nodes in MOFs have exchangeable coordination positions that allow them to participate as active sites promoting organic reactions. There is much current interest in exploiting the advantages that MOFs offer as catalysts, including a large surface area, high metal content, flexibility in the design of the active sites in the framework, together with the easy synthesis of these materials. In the present review we describe the use of MOFs as catalysts to promote cross-coupling reactions involving organometallic reaction intermediates and catalysis by Lewis acid sites. These types of reactions are of large synthetic utility due to the high yields achieved, mild conditions and compatibility with other functional groups. The content includes C-C bond forming reactions, such as Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, Stille and Ullmann, but also C-O and C-N cross-couplings. The final section summarizes our views on future developments and targets in these types of reactions. The core of the review is references that have appeared in 2010 or after, which give an idea of the novelty and current interest in this area. PMID:25608717

Dhakshinamoorthy, Amarajothi; Asiri, Abdullah M; Garcia, Hermenegildo

2015-04-01

417

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.

418

Twisting of glycosidic bonds by hydrolases  

Technology Transfer Automated Retrieval System (TEKTRAN)

Patterns of scissile bond twisting have been found in crystal structures of glycoside hydrolases (GHs) that are complexed with substrates and inhibitors. To estimate the increased potential energy in the substrates that results from this twisting, we have plotted torsion angles for the scissile bond...

419

HYDROGEN BONDING IN THE METHANOL DIMER  

Technology Transfer Automated Retrieval System (TEKTRAN)

In this work, two methanol molecules are placed in different arrangements to study hydrogen bonding in carbohydrate materials such as cellulose. Energy was calculated as a function of both hydrogen bond length and angle over wide ranges, using quantum mechanics (QM). The QM wavefunctions are analyze...

420

Estimation of Impact Damage in C/C Composites by Drop Weight Tests  

NASA Astrophysics Data System (ADS)

The evaluation of impact damage properties and strength of C/C composites is becoming important, due to its low impact strength. In this study, the impact damage is evaluated by using the impact load-deflection diagrams and absorbed energy of specimens on a drop weight impact test. The measured impact load is decomposed in approximation components and detail components by multiple-resolution analysis based upon the wavelet transform. And then the possibility of wavelet analysis for estimating the impact damage is studied. The results are as follows: (1) The Daubechies' wavelet is useful for smoothing the impact load signals by multiple resolution analysis in wavelet transform. (2) In the low impact energy that most of the damage does not occur, the approximation component result demanded by wavelet analysis accords with the wave pattern of numerical one that is removed free vibration component.

Yoshioka, Takakazu; Takahashi, Ichiro

421

Electronic absorption spectra of binuclear rhodium (I) isocyanide complexes. Comparison of ground-state and d. sigma. * yields p. sigma. excited-state bond energies  

SciTech Connect

The polarized single-crystal absorption spectra of (Rh{sub 2}b{sub 4})(BPh{sub 4}){sub 2}{center dot}CH{sub 3}CN and (Rh{sub 2}(TMB){sub 4})(BPh{sub 4}){sub 2} have been measured and analyzed (b = 1,3-diisocyanopropane; TMB = 2,5-diisocyano-2,5-dimethylhexane). The results indicate that the fully allowed transitions near 550 and 310 nm in these d{sup 8}-d{sup 8} complexes are {sup 1}A{sub 1} {yields} {sup 1}A{sub 2} (d{sigma} {yields} p{sigma}) and {sup 1}A{sub 1} {yields} {sup 1}E (d{sub xz}, d{sub yz} {yields} p{sigma}), respectively (D{sub 4} point group designations). The weak singlet {yields} triplet systems associated with both excitations also have been identified. The vibronic structure of the {sup 1}A{sub 1g} {yields} {sup 3}A{sub 2u} system of Rh{sub 2}b{sub 4}{sup 2+} has been analysis in detail. The Rh-Rh bond length in the {sup 3}A{sub 2u} state of Rh{sub 2}b{sub 4}{sup 2+} is estimated from a Franck-Condon analysis to be 2.93 {angstrom} (the ground-state value is 3.24 {angstrom}). The ground-state and excited-state Rh-Rh bond energies are estimated to be 12 {plus minus} 6 and 36 {plus minus} 6 kcal/mol, respectively.

Rice, S.F.; Miskowski, V.M.; Gray, H.B. (California Institute of Technology, Pasadena (USA))

1988-12-28

422

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

PubMed

Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo(4+)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

2011-12-01

423

Diffusion bonding of superplastic aluminum alloys  

SciTech Connect

Ability to diffusion bond aluminum alloys, in particular superplastic aluminum alloys, will complete the technology-base that is strongly needed to enhance the use of superplastic forming (SPF) technology. Concurrent diffusion bonding (DB)-SPF is considered to be an energy-saving manufacturing process since it simplifies the production of complex components. Moreover, because of increased design flexibility, overall manufacturing cost and component weight are significantly reduced. Diffusion bonding is an attractive manufacturing option for applications where the preservation of the base metal microstructure and, in turn, mechanical properties is imperative in the bond area. The process utilizes either the solid state or transient liquid phase (TLP) bonding to produce a bond with microstructure continuity in the joint. In addition, there is no localized thermal gradient present to induce distortion or to create residual stresses in the component, thereby increasing structural integrity.

Sunwoo, A.J.

1993-12-01

424

Essays on corporate bonds  

E-print Network

This thesis consists of three empirical essays on corporate bonds, examining the role of both credit risk and liquidity. In the first chapter, I test the ability of structural models of default to price corporate bonds in ...

Bao, Jack (Jack C.)

2009-01-01

425

Direct bonding and beyond  

NASA Astrophysics Data System (ADS)

We present a number of recent evaluations of direct bonding, a glueless bonding technology, performed under ambient conditions. If combined with bond-strengthening, this geometry-conserving technology is well suited for an application in far ultraviolet immersion lithography. Our term beyond direct bonding refers to taking at least one additional technological step beyond direct bonding, involving chemical interface engineering, advanced silicon-on-insulator (SOI) technology, whereby the unwanted influence of dilatation mismatch is obviated. The combination of successive direct bonding, nanopillar lattice structures and silicon-technological engineering makes it possible for us to arrange quantum dots, wires, and planes in a transversal cascade. We also address the interrelationship between direct bonding and elasticity, as well as plasticity; the latter is in relation to direct bonded glass wafers that are thermally treated to create the geometric shape, e.g., required for specific lab-on-a-chip components with a three-dimensional overall configuration.

Haisma, Jan; Hattu, Nico; (Dook) Pulles, J. T. C. M.; Steding, Esther; Vervest, Jan C. G.

2007-09-01

426

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

427

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

428

Interfacial Bond-Breaking Electron Transfer in Mixed WaterEthylene Glycol Solutions: Reorganization Energy and Interplay between Different Solvent Modes  

PubMed Central

We explore solvent dynamics effects in interfacial bond breaking electron transfer in terms of a multimode approach and make an attempt to interpret challenging recent experimental results (the nonmonotonous behavior of the rate constant of electroreduction of S2O82 from mixed waterEG solutions when increasing the EG fraction; see Zagrebin, P.A. et al. J. Phys. Chem. B2010, 114, 311). The exact expansion of the solvent correlation function (calculated using experimental dielectric spectra) in a series predicts the splitting of solvent coordinate in three independent modes characterized by different relaxation times. This makes it possible to construct a 5D free-energy surface along three solvent coordinates and one intramolecular degree of freedom describing first electron transfer at the reduction of a peroxodisulphate anion. Classical molecular dynamics simulations were performed to study the solvation of a peroxodisulphate anion (S2O82) in oxidized and reduced states in pure water and ethylene glycol (EG) as well as mixed H2OEG solutions. The solvent reorganization energy of the first electron-transfer step at the reduction of S2O82 was calculated for several compositions of the mixed solution. This quantity was found to be significantly asymmetric. (The reorganization energies of reduction and oxidation differ from each other.) The averaged reorganization energy slightly increases with increasing the EG content in solution. This finding clearly indicates that for the reaction under study the static solvent effect no longer competes with solvent dynamics. Brownian dynamics simulations were performed to calculate the electron-transfer rate constants as a function of the solvent composition. The results of the simulations explain the experimental data, at least qualitatively. PMID:23768162

2013-01-01

429

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

430

IMPROVED BONDING METHOD  

Microsoft Academic Search

An improved process of bonding aluminum to aluminum without fusion by ; ultrasonic vibrations plus pressure is described. The surfaces to be bonded are ; coated with an aqueous solution of alkali metal stearate prior to assembling for ; bonding. (AEC) O H19504 Present information is reviewed on steady state ; proliferation, differentiation, and maturation of blood cells in mammals.

E. V. Jr. Padgett; D. H. Warf

1964-01-01

431

Friction behavior of sintered metallic brake pads on a C\\/CSiC composite brake disc  

Microsoft Academic Search

In this study we report on the frictional and wear properties of sintered metallic (MMC) brake linings in combination with a C\\/CSiC brake disc. The influence of additives, such as graphite, and abrasives in the metallic matrix on the formation of the friction layer was investigated using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and Auger

Zmago Stadler; Kristoffer Krnel; Tomaz Kosmac

2007-01-01

432

The direct arylation of allylic sp3 C-H bonds via organic and photoredox catalysis  

NASA Astrophysics Data System (ADS)

The direct functionalization of unactivated sp3 C-H bonds is still one of the most challenging problems facing synthetic organic chemists. The appeal of such transformations derives from their capacity to facilitate the construction of complex organic molecules via the coupling of simple and otherwise inert building blocks, without introducing extraneous functional groups. Despite notable recent efforts, the establishment of general and mild strategies for the engagement of sp3 C-H bonds in C-C bond forming reactions has proved difficult. Within this context, the discovery of chemical transformations that are able to directly functionalize allylic methyl, methylene and methine carbons in a catalytic manner is a priority. Although protocols for direct oxidation and amination of allylic C-H bonds (that is, C-H bonds where an adjacent carbon is involved in a C = C bond) have become widely established, the engagement of allylic substrates in C-C bond forming reactions has thus far required the use of pre-functionalized coupling partners. In particular, the direct arylation of non-functionalized allylic systems would enable access to a series of known pharmacophores (molecular features responsible for a drug's action), though a general solution to this long-standing challenge remains elusive. Here we report the use of both photoredox and organic catalysis to accomplish a mild, broadly effective direct allylic C-H arylation. This C-C bond forming reaction readily accommodates a broad range of alkene and electron-deficient arene reactants, and has been used in the direct arylation of benzylic C-H bonds.

Cuthbertson, James D.; MacMillan, David W. C.

2015-03-01

433

Reactions of a quintuply bonded chromium dimer with alkynes.  

PubMed

Quintuply bonded [(H)L(iPr)Cr](2) reacts with alkynes RC?CR (R = Me, Et, Ph, CF(3)) to form exclusively 1?:?1 adducts [(H)L(iPr)Cr](2)(RCCR). All products feature relatively short Cr-Cr distances (1.919-1.962 ) and elongated C-C bonds (1.315-1.436 ), consistent with [2+2] cycloaddition reactions. The hydrocarbon adducts are 4-membered metallacycles, the bridging alkynes of which are progressively skewed with respect to the Cr-Cr axis. In contrast, perfluoroalkyne adds across the metal ligand moiety. PMID:21986955

Shen, Jingmei; Yap, Glenn P A; Werner, Jan-Philipp; Theopold, Klaus H

2011-11-28