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Sample records for chemical bonding structure

  1. Valence-Bond Theory and Chemical Structure.

    Science.gov (United States)

    Klein, Douglas J.; Trinajstic, Nenad

    1990-01-01

    Discussed is the importance of valence bond theory on the quantum-mechanical theory of chemical structure and the nature of the chemical bond. Described briefly are early VB theory, development of VB theory, modern versions, solid-state applications, models, treatment in textbooks, and flaws in criticisms of valence bond theory. (KR)

  2. The chemical bond structure and dynamics

    CERN Document Server

    Zewail, Ahmed

    1992-01-01

    This inspired book by some of the most influential scientists of our time--including six Nobel laureates--chronicles our emerging understanding of the chemical bond through the last nine decades and into the future. From Pauling's early structural work using x-ray and electron diffraction to Zewail's femtosecond lasers that probe molecular dynamics in real time; from Crick's molecular biology to Rich's molecular recognition, this book explores a rich tradition of scientific heritage and accomplishment. The perspectives given by Pauling, Perutz, Rich, Crick, Porter, Polanyi, Herschbach, Zewail,

  3. The electronic structure and chemical bonding of vitamin B12

    Science.gov (United States)

    Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.

    2003-05-01

    The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.

  4. Structure of adsorbed monolayers. The surface chemical bond

    Energy Technology Data Exchange (ETDEWEB)

    Somorjai, G.A.; Bent, B.E.

    1984-06-01

    This paper attempts to provide a summary of what has been learned about the structure of adsorbed monolayers and about the surface chemical bond from molecular surface science. While the surface chemical bond is less well understood than bonding of molecules in the gas phase or in the solid state, our knowledge of its properties is rapidly accumulating. The information obtained also has great impact on many surface science based technologies, including heterogeneous catalysis and electronic devices. It is hoped that much of the information obtained from studies at solid-gas interfaces can be correlated with molecular behavior at solid-liquid interfaces. 31 references, 42 figures, 1 table.

  5. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

    This is the perfect complement to ""Chemical Bonding - Across the Periodic Table"" by the same editors, who are two of the top scientists working on this topic, each with extensive experience and important connections within the community. The resulting book is a unique overview of the different approaches used for describing a chemical bond, including molecular-orbital based, valence-bond based, ELF, AIM and density-functional based methods. It takes into account the many developments that have taken place in the field over the past few decades due to the rapid advances in quantum chemica

  6. Electronic structure and chemical bonding of Li4Pt3Si

    Science.gov (United States)

    Matar, S. F.; Pöttgen, R.; Al Alam, A. F.; Ouaini, N.

    2012-07-01

    The electronic structure of rhombohedral Li4Pt3Si (space group R32) is examined from ab initio with an assessment of the properties of chemical bonding relating to the presence of different Li and Pt Wyckoff sites. The structure with totally de-intercalated Li keeps the characteristics of the pristine compound with a reduction of the volume albeit with less cohesive energy. The binding energies of Li point to different bonding intensities according to their different Wyckoff sites and indicate the possibility of delithiation.

  7. YNi and its hydrides: Phase stabilities, electronic structures and chemical bonding properties from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Matar, S.F., E-mail: matar@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France); Nakhl, M. [Universite Libanaise, Laboratoire de Chimie-Physique des Materiaux LCPM, Fanar (Lebanon); Al Alam, A.F.; Ouaini, N. [Universite Saint-Esprit de Kaslik, Faculte des Sciences et de Genie Informatique, Jounieh (Lebanon); Chevalier, B. [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France)

    2010-11-25

    Graphical abstract: Base centered orthorhombic YNiH{sub X} structure. For x = 3, only H1 and H2 are present. Highest hydrogen content YNiH{sub 4} is obtained when H3 are added. - Abstract: Within density functional theory, establishing the equations of states of YNi in two different controversial structures in the literature, leads to determine the orthorhombic FeB-type as the ground state one with small energy difference. For YNiH{sub 3} and YNiH{sub 4} hydrides crystallizing in the orthorhombic CrB-type structure the geometry optimization and the ab initio determination of the H atomic positions show that the stability of hydrogen decreases from the tri- to the tetra- hydride. New states brought by hydrogen within the valence band lead to its broadening and to enhanced localization of metal density of states. The chemical bonding analysis shows a preferential Ni-H bonding versus Y-H.

  8. Electronic structure and chemical bonding in LaIrSi-type intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Matar, Samir F. [Bordeaux Univ., Pessac (France). CNRS; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Nakhl, Michel [Univ. Libanaise, Fanar (Lebanon). Ecole Doctorale Sciences et Technologies

    2017-05-01

    The cubic LaIrSi type has 23 representatives in aluminides, gallides, silicides, germanides, phosphides, and arsenides, all with a valence electron count of 16 or 17. The striking structural motif is a three-dimensional network of the transition metal (T) and p element (X) atoms with TX{sub 3/3} respectively XT{sub 3/3} coordination. Alkaline earth or rare earth atoms fill cavities within the polyanionic [TX]{sup δ-} networks. The present work presents a detailed theoretical study of chemical bonding in LaIrSi-type representatives, exemplarily for CaPtSi, BaIrP, BaAuGa, LaIrSi, CeRhSi, and CeIrSi. DFT-GGA-based electronic structure calculations show weakly metallic compounds with itinerant small magnitude DOSs at E{sub F} except for CeRhSi whose large Ce DOS at E{sub F} leads to a finite magnetization on Ce (0.73 μ{sub B}) and induced small moments of opposite sign on Rh and Si in a ferromagnetic ground state. The chemical bonding analyses show dominant bonding within the [TX]{sup δ-} polyanionic networks. Charge transfer magnitudes were found in accordance with the course of the electronegativites of the chemical constituents.

  9. Chemical Reasoning Based on an Invariance Property: Bond and Lone Pair Pictures in Quantum Structural Formulas

    Directory of Open Access Journals (Sweden)

    Joseph Alia

    2010-07-01

    Full Text Available Chemists use one set of orbitals when comparing to a structural formula, hybridized AOs or NBOs for example, and another for reasoning in terms of frontier orbitals, MOs usually. Chemical arguments can frequently be made in terms of energy and/or electron density without the consideration of orbitals at all. All orbital representations, orthogonal or not, within a given function space are related by linear transformation. Chemical arguments based on orbitals are really energy or electron density arguments; orbitals are linked to these observables through the use of operators. The Valency Interaction Formula, VIF, offers a system of chemical reasoning based on the invariance of observables from one orbital representation to another. VIF pictures have been defined as one-electron density and Hamiltonian operators. These pictures are classified in a chemically meaningful way by use of linear transformations applied to them in the form of two pictorial rules and the invariance of the number of doubly, singly, and unoccupied orbitals or bonding, nonbonding, and antibonding orbitals under these transformations. The compatibility of the VIF method with the bond pair – lone pair language of Lewis is demonstrated. Different electron lone pair representations are related by the pictorial rules and have stability understood in terms of Walsh’s rules. Symmetries of conjugated ring systems are related to their electronic state by simple mathematical formulas. Description of lone pairs in conjugated systems is based on the strength and sign of orbital interactions around the ring. Simple models for bonding in copper clusters are tested, and the bonding of O2 to Fe(II in hemoglobin is described. Arguments made are supported by HF, B3LYP, and MP2 computations.

  10. Heteromolecular metal–organic interfaces: Electronic and structural fingerprints of chemical bonding

    Energy Technology Data Exchange (ETDEWEB)

    Stadtmüller, Benjamin; Schröder, Sonja [Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich GmbH, D-52425 Jülich (Germany); Jülich-Aachen Research Alliance (JARA) – Fundamentals of Future Information Technology, 52425 Jülich (Germany); Kumpf, Christian, E-mail: c.kumpf@fz-juelich.de [Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich GmbH, D-52425 Jülich (Germany); Jülich-Aachen Research Alliance (JARA) – Fundamentals of Future Information Technology, 52425 Jülich (Germany)

    2015-10-01

    Highlights: • We present a study of molecular donor–acceptor blends adsorbed on Ag(1 1 1). • Geometric and electronic structure of blends and pristine phases are compared. • The surface bonding of the acceptor is strengthened, that of the donor weakened. • But counter intuitively, the acceptor (donor) bond length becomes larger (smaller). • This contradiction is resolved by a model based on charge transfer via the surface. - Abstract: Beside the fact that they attract highest interest in the field of organic electronics, heteromolecular structures adsorbed on metal surfaces, in particular donor–acceptor blends, became a popular field in fundamental science, possibly since some surprising and unexpected behaviors were found for such systems. One is the apparent breaking of a rather fundamental rule in chemistry, namely that stronger chemical bonds go along with shorter bond lengths, as it is, e.g., well-known for the sequence from single to triple bonds. In this review we summarize the results of heteromolecular monolayer structures adsorbed on Ag(1 1 1), which – regarding this rule – behave in a counterintuitive way. The charge acceptor moves away from the substrate while its electronic structure indicates a stronger chemical interaction, indicated by a shift of the formerly lowest unoccupied molecular orbital toward higher binding energies. The donor behaves in the opposite way, it gives away charge, hence, electronically the bonding to the surface becomes weaker, but at the same time it also approaches the surface. It looks as if the concordant link between electronic and geometric structure was broken. But both effects can be explained by a substrate-mediated charge transfer from the donor to the acceptor. The charge reorganization going along with this transfer is responsible for both, the lifting-up of the acceptor molecule and the filling of its LUMO, and also for the reversed effects at the donor molecules. In the end, both molecules

  11. Application of chemical structure and bonding of actinide oxide materials for forensic science

    Energy Technology Data Exchange (ETDEWEB)

    Wilkerson, Marianne Perry [Los Alamos National Laboratory

    2010-01-01

    We are interested in applying our understanding of actinide chemical structure and bonding to broaden the suite of analytical tools available for nuclear forensic analyses. Uranium- and plutonium-oxide systems form under a variety of conditions, and these chemical species exhibit some of the most complex behavior of metal oxide systems known. No less intriguing is the ability of AnO{sub 2} (An: U, Pu) to form non-stoichiometric species described as AnO{sub 2+x}. Environmental studies have shown the value of utilizing the chemical signatures of these actinide oxide materials to understand transport following release into the environment. Chemical speciation of actinide-oxide samples may also provide clues as to the age, source, or process history of the material. The scientific challenge is to identify, measure and understand those aspects of speciation of actinide analytes that carry information about material origin and history most relevant to forensics. Here, we will describe our efforts in material synthesis and analytical methods development that we will use to provide the fundamental science to characterize actinide oxide molecular structures for forensic science. Structural properties and initial results to measure structural variability of uranium oxide samples using synchrotron-based X-ray Absorption Fine Structure will be discussed.

  12. Structure and Chemical Bond of Thermoelectric Ce-Co-Sb Skutterudites

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The correlations among composition,structure,chemical bond and thermoelectric property of skutterudites CoSb3 and CeCo5Fe3Sb12 have been studied by using density function and discrete variation (DFT-DVM) method.Three models for this study were proposed and calculated by which the "rattling" pattern was described.Model 1 is with Ce in the center,model 2 is with Ce away the center and near to Sb,and model 3 is also with Ce away the center but near to Fe.The calculated results show that in model 3,the ionic bond is the strongest,but the covalent bond is the weakest.Due to the different changes between ionic and covalent bond,there is less difference in the stability among the models 1,2 and 3.Therefore,these different models can exist at the same time,or can translate from one to another more easily.In other words,the "rattling" pattern has taken place.Unfilled model of CoSb3,without Ce and Fe,is called model 4.The covalent bond of Co-Sb or Fe-Sb in models 1,2 and 3 is weaker than that of Co-Sb in model 4,as some electrical cloud of Sb takes part in the covalent bond of Ce-Sb in the filled models.The result is consistent with the experimental result that the thermal conductivity of CeCo5Fe3Sb12 is lower than that of CoSb3,and the thermoelectric property of CeCo5Fe3Sb12 is superior to that of CoSb3.

  13. Electronic Structures and Chemical Bonds of Cobaltite and Ni-Doped

    Institute of Scientific and Technical Information of China (English)

    MIN Xinmin; XING Xueling; ZHU Lei

    2005-01-01

    The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method(DFT-DVM). The results indicate that the highest valence band (HVB) and the lowest conduction band(LCB) are mainly attributed to Co3 d, Ni3 d and O2 p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6.

  14. Electronic Structure and Chemical Bond of Ti3SiC2 and Adding Al Element

    Institute of Scientific and Technical Information of China (English)

    MIN Xinmin; LU Ning; MEI Bingchu

    2006-01-01

    The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation (DFT-DVM) method. When Al element is added into Ti3SiC2, there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3SiC2, adding a proper quantity of Al can promote the formation of Ti3SiC2. The density of state shows that there is a mixed conductor character in both of Ti3SiC2 and adding Al element. Ti3SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.

  15. X-ray photoelectron spectra structure and chemical bonding in AmO2

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2015-01-01

    Full Text Available Quantitative analysis was done of the X-ray photoelectron spectra structure in the binding energy range of 0 eV to ~35 eV for americium dioxide (AmO2 valence electrons. The binding energies and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the Am63O216 and AmO8 (D4h cluster reflecting Am close environment in AmO2 were taken into account. The experimental data show that the many-body effects and the multiplet splitting contribute to the spectral structure much less than the effects of formation of the outer (0-~15 eV binding energy and the inner (~15 eV-~35 eV binding energy valence molecular orbitals. The filled Am 5f electronic states were shown to form in the AmO2 valence band. The Am 6p electrons participate in formation of both the inner and the outer valence molecular orbitals (bands. The filled Am 6p3/2 and the O 2s electronic shells were found to make the largest contributions to the formation of the inner valence molecular orbitals. Contributions of electrons from different molecular orbitals to the chemical bond in the AmO8 cluster were evaluated. Composition and sequence order of molecular orbitals in the binding energy range 0-~35 eV in AmO2 were established. The experimental and theoretical data allowed a quantitative scheme of molecular orbitals for AmO2, which is fundamental for both understanding the chemical bond nature in americium dioxide and the interpretation of other X-ray spectra of AmO2.

  16. Chemical bonding and electronic-structure in MAX phases as viewed by X-ray spectroscopy and density functional theory

    Science.gov (United States)

    Magnuson, Martin; Mattesini, Maurizio

    2017-01-01

    This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibit a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M-C bonds in high-density MC slabs, and relatively weak M-A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other materials properties makes it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.

  17. Valence XPS structure and chemical bond in Cs2UO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2016-01-01

    Full Text Available Quantitative analysis was done of the valence electrons X-ray photoelectron spectra structure in the binding energy (BE range of 0 eV to ~35 eV for crystalline dicaesium tetrachloro-dioxouranium (VI (Cs2UO2Cl4. This compound contains the uranyl group UO2. The BE and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the UO2Cl4(D4h cluster reflecting U close environment in Cs2UO2Cl4 were taken into account. The experimental data show that many-body effects due to the presence of cesium and chlorine contribute to the outer valence (0-~15 eV BE spectral structure much less than to the inner valence (~15 eV-~35 eV BE one. The filled U5f electronic states were theoretically calculated and experimentally confirmed to be present in the valence band of Cs2UO2Cl4. It corroborates the suggestion on the direct participation of the U5f electrons in the chemical bond. Electrons of the U6p atomic orbitals participate in formation of both the inner (IVMO and the outer (OVMO valence molecular orbitals (bands. The filled U6p and the O2s, Cl3s electronic shells were found to make the largest contributions to the IVMO formation. The molecular orbitals composition and the sequence order in the binding energy range 0 eV-~35 eV in the UO2Cl4 cluster were established. The experimental and theoretical data allowed a quantitative molecular orbitals scheme for the UO2Cl4 cluster in the BE range 0-~35 eV, which is fundamental for both understanding the chemical bond nature in Cs2UO2Cl4 and the interpretation of other X-ray spectra of Cs2UO2Cl4. The contributions to the chemical binding for the UO2Cl4 cluster were evaluated to be: the OVMO contribution - 76%, and the IVMO contribution - 24 %.

  18. Understanding boron through size-selected clusters: structure, chemical bonding, and fluxionality.

    Science.gov (United States)

    Sergeeva, Alina P; Popov, Ivan A; Piazza, Zachary A; Li, Wei-Li; Romanescu, Constantin; Wang, Lai-Sheng; Boldyrev, Alexander I

    2014-04-15

    Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar structures, stabilized by localized two-center-two-electron (2c-2e) σ bonds on the periphery and delocalized multicenter-two-electron (nc-2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron's electron deficiency and leads to fluxional behavior, which has been observed in B13(+) and B19(-). A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B(-), formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B(-)/C analogy. It is

  19. Understanding Boron through Size-Selected Clusters: Structure, Chemical Bonding, and Fluxionality

    Energy Technology Data Exchange (ETDEWEB)

    Sergeeva, Alina P.; Popov, Ivan A.; Piazza, Zachary A.; Li, Wei-Li; Romanescu, Constantin; Wang, Lai S.; Boldyrev, Alexander I.

    2014-04-15

    Conspectus Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar structures, stabilized by localized two-center–two-electron (2c–2e) σ bonds on the periphery and delocalized multicenter–two-electron (nc–2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron’s electron deficiency and leads to fluxional behavior, which has been observed in B13+ and B19–. A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B–, formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B

  20. Electronic structure and chemical bond nature in Cs2PuO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2015-01-01

    Full Text Available X-ray photoelectron spectral analysis of dicaesiumtetrachlorodioxoplutonate (Cs2PuO2Cl4 single crystal was done in the binding energy range 0-~35 eV on the basis of binding energies and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the PuO2Cl4 (D4h. This cluster reflects Pu close environment in Cs2PuO2Cl4 containing the plutonyl group PuO2. The many-body effects due to the presence of cesium and chlorine were shown to contribute to the outer valence (0-~15 eV binding energy spectral structure much less than to the inner valence (~15 eV- ~35 eV binding energy one. The filled Pu 5f electronic states were theoretically calculated and experimentally con- firmed to present in the valence band of Cs2PuO2Cl4. It corroborates the suggestion on the direct participation of the Pu 5f electrons in the chemical bond. The Pu 6p atomic orbitals were shown to participate in formation of both the inner and the outer valence molecular orbitals (bands, while the filled Pu 6p and O 2s, Cl 3s electronic shells were found to take the largest part in formation of the inner valence molecular orbitals. The composition of molecular orbitals and the sequence order in the binding energy range 0-~35 eV in Cs2PuO2Cl4 were established. The quantitative scheme of molecular orbitals for Cs2PuO2Cl4 in the binding energy range 0-~15 eV was built on the basis of the experimental and theoretical data. It is fundamental for both understanding the chemical bond nature in Cs2PuO2Cl4 and the interpretation of other X-ray spectra of Cs2PuO2Cl4. The contributions to the chemical binding for the PuO2Cl4 cluster were evaluated to be: the contribution of the outer valence molecular orbitals -66 %, the contribution of the inner valence molecular orbitals -34 %.

  1. The chemical bond in inorganic chemistry the bond valence model

    CERN Document Server

    Brown, I David

    2016-01-01

    The bond valence model is a version of the ionic model in which the chemical constraints are expressed in terms of localized chemical bonds formed by the valence charge of the atoms. Theorems derived from the properties of the electrostatic flux predict the rules obeyed by both ionic and covalent bonds. They make quantitative predictions of coordination number, crystal structure, bond lengths and bond angles. Bond stability depends on the matching of the bonding strengths of the atoms, while the conflicting requirements of chemistry and space lead to the structural instabilities responsible for the unusual physical properties displayed by some materials. The model has applications in many fields ranging from mineralogy to molecular biology.

  2. Density Functionals of Chemical Bonding

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz

    2008-06-01

    Full Text Available The behavior of electrons in general many-electronic systems throughout the density functionals of energy is reviewed. The basic physico-chemical concepts of density functional theory are employed to highlight the energy role in chemical structure while its extended influence in electronic localization function helps in chemical bonding understanding. In this context the energy functionals accompanied by electronic localization functions may provide a comprehensive description of the global-local levels electronic structures in general and of chemical bonds in special. Becke-Edgecombe and author’s Markovian electronic localization functions are discussed at atomic, molecular and solid state levels. Then, the analytical survey of the main workable kinetic, exchange, and correlation density functionals within local and gradient density approximations is undertaken. The hierarchy of various energy functionals is formulated by employing both the parabolic and statistical correlation degree of them with the electronegativity and chemical hardness indices by means of quantitative structure-property relationship (QSPR analysis for basic atomic and molecular systems.

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

    Institute of Scientific and Technical Information of China (English)

    Zeng Hui; Zhao Jun; Xiao Xun

    2013-01-01

    Quantum chemical calculations are performed to investigate the equilibrium C-COOH 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 (CBS-Q) method in conjunction with the 6-31 lG** 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 CBS-Q 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 C-COOH 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.

  4. What a difference a bond makes: the structural, chemical, and physical properties of methyl-terminated Si(111) surfaces.

    Science.gov (United States)

    Wong, Keith T; Lewis, Nathan S

    2014-10-21

    The chemical, electronic, and structural properties of surfaces are affected by the chemical termination of the surface. Two-step halogenation/alkylation of silicon provides a scalable, wet-chemical method for grafting molecules onto the silicon surface. Unlike other commonly studied wet-chemical methods of surface modification, such as self-assembly of monolayers on metals or hydrosilylation on silicon, the two-step method enables attachment of small alkyl chains, even methyl groups, to a silicon surface with high surface coverage and homogeneity. The methyl-terminated Si(111) surface, by comparison to hydrogen-terminated Si(111), offers a unique opportunity to study the effects of the first surface bond connecting the overlayer to the surface. This Account describes studies of methyl-terminated Si(111), which have shown that the H-Si(111) and CH3-Si(111) surfaces are structurally nearly identical, yet impart significantly different chemical and electronic properties to the resulting Si surface. The structure of methyl-terminated Si(111) formed by a two-step halogenation/methylation process has been studied by a variety of spectroscopic methods. A covalent Si-C bond is oriented normal to the surface, with the methyl group situated directly atop a surface Si atom. Multiple spectroscopic methods have shown that methyl groups achieve essentially complete coverage of the surface atoms while maintaining the atomically flat, terraced structure of the original H-Si(111) surface. Thus, the H-Si(111) and CH3-Si(111) surface share essentially identical structures aside from the replacement of a Si-H bond with a Si-C bond. Despite their structural similarity, hydrogen and methyl termination exhibit markedly different chemical passivation. Specifically, CH3-Si(111) exhibits significantly greater oxidation resistance than H-Si(111) in air and in aqueous electrolyte under photoanodic current flow. Both surfaces exhibit similar thermal stability in vacuum, and the Si-H and Si

  5. Using Concept Mapping to Uncover Students' Knowledge Structures of Chemical Bonding Concepts

    Science.gov (United States)

    Burrows, Nikita L.; Mooring, Suazette Reid

    2015-01-01

    General chemistry is the first undergraduate course in which students further develop their understanding of fundamental chemical concepts. Many of these fundamental topics highlight the numerous conceptual interconnections present in chemistry. However, many students possess incoherent knowledge structures regarding these topics. Therefore,…

  6. Crystal structure and chemical bonding of the high-temperature phase of AgN3.

    Science.gov (United States)

    Schmidt, Carsten L; Dinnebier, Robert; Wedig, Ulrich; Jansen, Martin

    2007-02-05

    The crystal structure of silver azide (AgN3) in its high-temperature (HT) modification was determined from X-ray powder diffraction data, recorded at T = 170 degrees C and was further refined by the Rietveld method. The structure is monoclinic (P21/c (No. 14), a = 6.0756(2) A, b = 6.1663(2) A, c = 6.5729(2) A, beta = 114.19(0) degrees, V = 224.62(14) A3, Z = 4) and consists of two-dimensional Ag and N containing layers in which the silver atoms are coordinated by four nitrogen atoms exhibiting a distorted square coordination environment. These sheets are linked together by weaker perpendicular Ag-N contacts, thus forming a 4 + 2 coordination geometry around the silver atoms. The phase transition has been characterized by DTA, DSC, and measurement of the density, as well as of the ionic conductivity. Both, the room-temperature and the HT phase are electrically insulating. This fact is getting support by DFT band structure calculations within the generalized gradient approximation, using the PBE functional. On the basis of the DFT band structure, the bonding characteristics of both phases are essentially the same. Finally, the implication of the existence of a low-symmetry HT-phase in a crystalline explosive concerning decomposition mechanisms is discussed.

  7. Crystal Structure and Chemical Bonding of the High-Temperature Phase of AgN3

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt,C.; Dinnebier, R.; Wedig, U.; Jansen, M.

    2007-01-01

    The crystal structure of silver azide (AgN{sub 3}) in its high-temperature (HT) modification was determined from X-ray powder diffraction data, recorded at T = 170 {sup o}C and was further refined by the Rietveld method. The structure is monoclinic (P2{sub 1}lc (No. 14), a = 6.0756(2) {angstrom}, b = 6.1663(2) {angstrom}, c = 6.5729(2) {angstrom}, {beta} = 114.19(0){sup o}, V = 224.62(14) {angstrom}{sup 3}, Z = 4) and consists of two-dimensional Ag and N containing layers in which the silver atoms are coordinated by four nitrogen atoms exhibiting a distorted square coordination environment. These sheets are linked together by weaker perpendicular Ag-N contacts, thus forming a 4 + 2 coordination geometry around the silver atoms. The phase transition has been characterized by DTA, DSC, and measurement of the density, as well as of the ionic conductivity. Both, the room-temperature and the HT phase are electrically insulating. This fact is getting support by DFT band structure calculations within the generalized gradient approximation, using the PBE functional. On the basis of the DFT band structure, the bonding characteristics of both phases are essentially the same. Finally, the implication of the existence of a low-symmetry HT-phase in a crystalline explosive concerning decomposition mechanisms is discussed.

  8. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties

    Science.gov (United States)

    Pishtshev, A.; Karazhanov, S. Zh.

    2017-02-01

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns—strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d10 closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  9. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties.

    Science.gov (United States)

    Pishtshev, A; Karazhanov, S Zh

    2017-02-14

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns-strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d(10) closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  10. The correlation theory of the chemical bond

    CERN Document Server

    Szalay, Szilárd; Szilvási, Tibor; Veis, Libor; Legeza, Örs

    2016-01-01

    The notion of chemical bond is a very useful concept in chemistry. It originated at the beginning of chemistry, it is expressive for the classically thinking mind, and the errors arising from the approximative nature of the concept can often be ignored. In the first half of the twentieth century, however, we learned that the proper description of the microworld is given by quantum mechanics. Quantum mechanics gives more accurate results for chemical systems than any preceding model, however, it is very inexpressive for the classically thinking mind. The quantum mechanical description of the chemical bond is given in terms of delocalized bonding orbitals, or, alternatively, in terms of correlations of occupations of localized orbitals. However, in the latter case, multiorbital correlations were treated only in terms of two-orbital correlations, although the structure of multiorbital correlations is far richer; and, in the case of bonds established by more than two electrons, multiorbital correlations represent...

  11. The Synthesis, Structures, and Chemical Properties of Macrocyclic Ligands Covalently Bonded into Layered Arrays

    Energy Technology Data Exchange (ETDEWEB)

    Clearfield, Abraham [Texas A & M Univ., College Station, TX (United States)

    2014-11-01

    In this part of the proposal we have concentrated on the surface functionalization of α-zirconium phosphate of composition Zr(O3POH)2•H2O. It is a layered compound that can be prepared as particles as small as 30 nm to single crystals in the range of cm. This compound is an ion exchanger with a capacity of 6.64 meq per gram. It finds use as a catalyst, proton conductor, sensors, biosensors, in kidney dialysis and drug delivery. By functionalizing the surface additional uses are contemplated as will be described. The layers consist of the metal, with 4+ charge, that is positioned slightly above and below the mean layer plane and bridged by three of the four phosphate oxygens. The remaining POH groups point into the interlayer space creating double rows of POH groups but single arrays on the surface layers. The surface groups are reactive and we were able to bond silanes, isocyanates, epoxides, acrylates ` and phosphates to the surface POH groups. The layers are easily exfoliated or filled with ions by ion exchange or molecules by intercalation reactions. Highlights of our work include, in addition to direct functionalization of the surfaces, replacement of the protons on the surface with ions of different charge. This allows us to bond phosphates, biophosphates, phosphonic acids and alcohols to the surface. By variation of the ion charge of the ions that replace the surface protons, different surface structures are obtained. We have already shown that polymer fillers, catalysts and Janus particles may be prepared. The combination of surface functionalization with the ability to insert molecules and ions between the layers allow for a rich development of numerous useful other applications as well as nano-surface chemistry.

  12. Electronic structure, chemical bond and thermal stability of hydrogen absorber Li2MgN2H2

    Institute of Scientific and Technical Information of China (English)

    WANG Qiang; CHEN YunGui; WU ChaoLing; TAO MingDa; GAI JingGang

    2009-01-01

    The lowest total energy crystal structure of Li2MgN2H2 was identified by the first principle calculation with RPBE exchange-correlation function. Furthermore, the fine structure parameters of this crystal structure were calculated with PBE and PW91 exchange-correlation function. In a further step, the density of states, electron density, charge density difference on (0 0 1) plane and heat of formation of Li2MgN2H2 hydrogenation were computed with PW91 exchange-correlation function. Consequently, the electronic structures and chemical bonds in this compound were analyzed and discussed, and then the thermodynamic character of Li2MgN2H2 for hydrogen storage was evacuated.

  13. Research Update: Mechanical properties of metal-organic frameworks – Influence of structure and chemical bonding

    Directory of Open Access Journals (Sweden)

    Wei Li

    2014-12-01

    Full Text Available Metal-organic frameworks (MOFs, a young family of functional materials, have been attracting considerable attention from the chemistry, materials science, and physics communities. In the light of their potential applications in industry and technology, the fundamental mechanical properties of MOFs, which are of critical importance for manufacturing, processing, and performance, need to be addressed and understood. It has been widely accepted that the framework topology, which describes the overall connectivity pattern of the MOF building units, is of vital importance for the mechanical properties. However, recent advances in the area of MOF mechanics reveal that chemistry plays a major role as well. From the viewpoint of materials science, a deep understanding of the influence of chemical effects on MOF mechanics is not only highly desirable for the development of novel functional materials with targeted mechanical response, but also for a better understanding of important properties such as structural flexibility and framework breathing. The present work discusses the intrinsic connection between chemical effects and the mechanical behavior of MOFs through a number of prototypical examples.

  14. The chemical bond of stibium. Technological aspects

    Directory of Open Access Journals (Sweden)

    Ashcheulov A. A.

    2011-08-01

    Full Text Available Thin structure of the chemical bond of the hexagonal and rhombohedral modifications of stibium was investigated. The boundaries of their polymorphism were identified, which opens new technological possibilities of creating optical, photoelectric, thermoelectric, and other materials for electronic equipment components.

  15. Bond-length analysis of the omega structure in Ti,Zr,Hf and their alloys: experimental data, new correlations and implications for chemical bonding models

    Energy Technology Data Exchange (ETDEWEB)

    Grad, G.B.; Benites, G.M. [Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche; Aurelio, G. [Departamento de Fisica, Universidad del Comahue, 8300, Neuquen (Argentina); Fernandez Guillermet, A. [Centro Atomico Bariloche, 8400, San Carlos de Bariloche (Argentina)

    1999-12-15

    An analysis is performed of the experimental information on the key interatomic distances (IDs) of the AlB{sub 2} type structure, the so-called omega ({omega}) phase in Ti and Zr, as well as in Ti-V and Zr-Nb alloys. Various remarkable correlations are found between these IDs and standard measures of the atomic size, and with Pauling's bond-lengths. These observations are discussed in the light of the phenomenological bonding pictures of the {omega} structure, and with our recent ab initio calculations of the electronic structure of this phase. (orig.)

  16. The adsorption of acrolein on a Pt (1 1 1): A study of chemical bonding and electronic structure

    Science.gov (United States)

    Pirillo, S.; López-Corral, I.; Germán, E.; Juan, A.

    2012-12-01

    The adsorption of acrolein on a Pt (1 1 1) surface was studied using ab-initio and semiempirical calculations. Geometry optimization and densities of states (DOS) curves were carried out using the Vienna Ab-initio Simulation Package (VASP) code. We started our study with the preferential geometries corresponding to the different acrolein/Pt (1 1 1) adsorption modes previously reported. Then, we examined the evolution of the chemical bonding in these geometries, using the crystal orbital overlap population (COOP) and overlap population (OP) analysis of selected pairs of atoms. We analyzed the acrolein intramolecular bonds, Pt (1 1 1) superficial bonds and new moleculesbnd surface formed bonds after adsorption. We found that Ptsbnd Pt bonds interacting with the molecule and acrolein Cdbnd O and Cdbnd C bonds are weakened after adsorption; this last bond is significantly linked to the surface. The obtained Csbnd Pt and Osbnd Pt OP values suggest that the most stable adsorption modes are η3-cis and η4-trans, while the η1-trans is the less favored configuration. We also found that C pz orbital and Pt pz and d orbitals participate strongly in the adsorption process.

  17. Rationalizing structure, stability, and chemical bonding of pure and doped clusters, isolated and solvated multiply charged anions, and solid-state materials

    Science.gov (United States)

    Sergeeva, Alina P.

    Chemistry is the study of materials and the changes that materials undergo. One can tune the properties of the known materials and design the novel materials with desired properties knowing what is responsible for the chemical reactivity, structure, and stability of those materials. The unified chemical bonding theory could address all these questions, but we do not have one available yet. The most accepted general theory of chemical bonding was proposed by Lewis in 1916, though Lewis's theory fails to explain the bonding in materials with delocalized electron density such as sub-nano and nanoclusters, as well as aromatic organic and organometallic molecules. The dissertation presents a set of projects that can be considered the steps towards the development of the unified chemical bonding theory by extending the ideas of Lewis. The dissertation also presents the studies of the properties of multiply charged anions, which tend to undergo Coulomb explosion in the isolated state and release the excess energy stored in them. It is shown how the properties of multiply charged anions can be tuned upon changing the chemical identity of the species or interaction with solvent molecules. Our findings led to the discovery of a new long-lived triply charged anionic species, whose metastability was explained by the existence of a repulsive Coulomb barrier. We also proposed two ways to restore high symmetry of compounds by suppression of the pseudo Jahn-Teller effect, which could lead to the design of new materials with the restored symmetry and therefore the novel properties.

  18. Coulombic Models in Chemical Bonding.

    Science.gov (United States)

    Sacks, Lawrence J.

    1986-01-01

    Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

  19. Structures and chemical bonding of B3O3 (-/0) and B3O3H(-/0): A combined photoelectron spectroscopy and first-principles theory study.

    Science.gov (United States)

    Zhao, Li-Juan; Tian, Wen-Juan; Ou, Ting; Xu, Hong-Guang; Feng, Gang; Xu, Xi-Ling; Zhai, Hua-Jin; Li, Si-Dian; Zheng, Wei-Jun

    2016-03-28

    We present a combined photoelectron spectroscopy and first-principles theory study on the structural and electronic properties and chemical bonding of B3O3 (-/0) and B3O3H(-/0) clusters. The concerted experimental and theoretical data show that the global-minimum structures of B3O3 and B3O3H neutrals are very different from those of their anionic counterparts. The B3O3 (-) anion is characterized to possess a V-shaped OB-B-BO chain with overall C2 v symmetry (1A), in which the central B atom interacts with two equivalent boronyl (B≡O) terminals via B-B single bonds as well as with one O atom via a B=O double bond. The B3O3H(-) anion has a Cs (2A) structure, containing an asymmetric OB-B-OBO zig-zag chain and a terminal H atom interacting with the central B atom. In contrast, the C2 v (1a) global minimum of B3O3 neutral contains a rhombic B2O2 ring with one B atom bonded to a BO terminal and that of neutral B3O3H (2a) is also of C2 v symmetry, which is readily constructed from C2 v (1a) by attaching a H atom to the opposite side of the BO group. The H atom in B3O3H(-/0) (2A and 2a) prefers to interact terminally with a B atom, rather than with O. Chemical bonding analyses reveal a three-center four-electron (3c-4e) π hyperbond in the B3O3H(-) (2A) cluster and a four-center four-electron (4c-4e) π bond (that is, the so-called o-bond) in B3O3 (1a) and B3O3H (2a) neutral clusters.

  20. Graphene composites containing chemically bonded metal oxides

    Indian Academy of Sciences (India)

    K Pramoda; S Suresh; H S S Ramakrishna Matte; A Govindaraj

    2013-08-01

    Composites of graphene involving chemically bonded nano films of metal oxides have been prepared by reacting graphene containing surface oxygen functionalities with metal halide vapours followed by exposure to water vapour. The composites have been characterized by electron microscopy, atomic force microscopy and other techniques. Magnetite particles chemically bonded to graphene dispersible in various solvents have been prepared and they exhibit fairly high magnetization.

  1. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    The paper examines the role of structured bonds in the optimal portfolio of a small retail investor. We consider the typical structured bond essentially repacking an exotic option and a zero coupon bond, i.e. an investment with portfolio insurance. The optimal portfolio is found when the investment...

  2. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    The paper examines the role of structured bonds in the optimal portfolio of a small retail investor. We consider the typical structured bond essentially repacking an exotic option and a zero coupon bond, i.e. an investment with portfolio insurance. The optimal portfolio is found when the investment...... opportunities consist of a risky reference fund, a risk-free asset and a structured bond. Key model elements are the trading strategy and utility function of the investor. Our numerical results indicate structured bonds do have basis for consideration in the optimal portfolio. The product holdings...

  3. Gradient Bundle Analysis: A Full Topological Approach to Chemical Bonding

    CERN Document Server

    Morgenstern, Amanda

    2016-01-01

    The "chemical bond" is a central concept in molecular sciences, but there is no consensus as to what a bond actually is. Therefore, a variety of bonding models have been developed, each defining the structure of molecules in a different manner with the goal of explaining and predicting chemical properties. This thesis describes the initial development of gradient bundle analysis (GBA), a chemical bonding model that creates a high resolution picture of chemical interactions within the charge density framework. GBA is based on concepts from the quantum theory of atoms in molecules (QTAIM), but uses a more complete picture of the topology and geometry of the electron charge density to understand and predict bonding interactions. Gradient bundles are defined as volumes bounded by zero-flux surfaces (ZFSs) in the gradient of the charge density with well-defined energies. The structure of gradient bundles provides an avenue for detecting the locations of valence electrons, which correspond to reactive regions in a ...

  4. Metallic bonding and cluster structure

    Energy Technology Data Exchange (ETDEWEB)

    Soler, Jose M. [Department of Physics, Lyman Laboratory, Harvard University, Cambridge, Massachusetts 02138 (United States); Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain); Beltran, Marcela R. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, Mexico Distrito Federal, 01000 Mexico (Mexico); Michaelian, Karo [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico Distrito Federal, 01000 Mexico (Mexico); Garzon, Ignacio L. [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain); Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico Distrito Federal, 01000 Mexico (Mexico); Ordejon, Pablo [Institut de Ciencia de Materials de Barcelona-CSIC, Campus de la U.A.B., 08193 Bellaterra, Barcelona, (Spain); Sanchez-Portal, Daniel [Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States); Artacho, Emilio [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain)

    2000-02-15

    Knowledge of the structure of clusters is essential to predict many of their physical and chemical properties. Using a many-body semiempirical Gupta potential (to perform global minimizations), and first-principles density functional calculations (to confirm the energy ordering of the local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are many intermediate-size disordered gold nanoclusters with energy near or below the lowest-energy ordered structure. This is especially surprising because we studied ''magic'' cluster sizes, for which very compact-ordered structures exist. Here, we show how the analysis of the local stress can be used to understand the physical origin of this amorphization. We find that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination. The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder in metals. Although these are very general properties of metallic bonding, we find that they are especially important in the case of gold, and we predict some general trends in the tendency of metallic clusters towards amorphous structures. (c) 2000 The American Physical Society.

  5. Density functional theory investigation of hydrogen bonding effects on the oxygen, nitrogen and hydrogen electric field gradient and chemical shielding tensors of anhydrous chitosan crystalline structure.

    Science.gov (United States)

    Esrafili, Mehdi D; Elmi, Fatemeh; Hadipour, Nasser L

    2007-02-08

    A systematic computational investigation was carried out to characterize the 17O, 14N and 2H electric field gradient, EFG, as well as 17O, 15N, 13C and 1H chemical shielding tensors in the anhydrous chitosan crystalline structure. To include the hydrogen-bonding effects in the calculations, the most probable interacting molecules with the target molecule in the crystalline phase were considered through a hexameric cluster. The computations were performed with the B3LYP method and 6-311++G(d,p) and 6-31++G(d,p) standard basis sets using the Gaussian 98 suite of programs. Calculated EFG and chemical shielding tensors were used to evaluate the 17O, 14N and 2H nuclear quadrupole resonance, NQR, and 17O, 15N, 13C and 1H nuclear magnetic resonance, NMR, parameters in the hexameric cluster, which are in good agreement with the available experimental data. The difference between the calculated NQR and NMR parameters of the monomer and hexamer cluster shows how much hydrogen bonding interactions affect the EFG and chemical shielding tensors of each nucleus. These results indicate that both O(3)-H(33)...O(5-3) and N-H(22)...O(6-4) hydrogen bonding have a major influence on NQR and NMR parameters. Also, the quantum chemical calculations indicate that the intra- and intermolecular hydrogen bonding interactions play an essential role in determining the relative orientation of EFG and chemical shielding principal components in the molecular frame axes.

  6. Chemical bonding structural analysis of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition

    Science.gov (United States)

    Gima, Hiroki; Zkria, Abdelrahman; Katamune, Yūki; Ohtani, Ryota; Koizumi, Satoshi; Yoshitake, Tsuyoshi

    2017-01-01

    Nitrogen-doped ultra-nanocrystalline diamond/hydrogenated amorphous carbon composite films prepared in hydrogen and nitrogen mixed-gas atmospheres by coaxial arc plasma deposition with graphite targets were studied electrically and chemical-bonding-structurally. The electrical conductivity was increased by nitrogen doping, accompanied by the production of n-type conduction. From X-ray photoemission, near-edge X-ray absorption fine-structure, hydrogen forward-scattering, and Fourier transform infrared spectral results, it is expected that hydrogen atoms that terminate diamond grain boundaries will be partially replaced by nitrogen atoms and, consequently, π C–N and C=N bonds that easily generate free electrons will be formed at grain boundaries.

  7. Structural, quantum chemical, vibrational and thermal studies of a hydrogen bonded zwitterionic co-crystal (nicotinic acid: pyrogallol)

    Science.gov (United States)

    Prabha, E. Arockia Jeya Yasmi; Kumar, S. Suresh; Athimoolam, S.; Sridhar, B.

    2017-02-01

    In the present work, a new co-crystal of nicotinic acid with pyrogallol (NICPY) has been grown in the zwitterionic form and the corresponding structural, vibrational, thermal, solubility and anti-cancer characteristics have been reported. The single crystal X-ray diffraction analysis confirms that the structural molecular packing of the crystal stabilized through N-H⋯O and O-H⋯O hydrogen bond. The stabilization energy of the hydrogen bond motifs were calculated in the solid state. Vibrational spectral studies such as Fourier transform-infrared (FT-IR) and FT-Raman were adopted to understand the zwitterionic co-crystalline nature of the compound, which has been compared with theoretically calculated vibrational frequencies. The thermal stability of the grown co-crystal was analyzed by TG/DTA study. The solubility of the NICPY co-crystal was investigated in water at different temperature and compared with that of the nicotinic acid, which is the parent compound of NICPY co-crystal. The grown crystals were treated with human cervical cancer cell line (HeLa) to analyze the cytotoxicity of NICPY crystals and compared with the parent compound, which shows that NICPY has moderate activity against human cervical cancer cell line.

  8. Chemical Bond Calculations of Crystal Growth of KDP and ADP

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel method was proposed to calculate the crystal morphology (or growth habit) on the basis of chemical bond analysis. All constituent chemical bonds were distinguished as relevant and independent bonds according to their variations during the crystallization process. By employing the current method, the influence of specific growth conditions on the crystal morphology can be considered in the structure analysis process. The ideal morphologies of both KDP (KH2PO4) and ADP (NH4H2PO4) crystals were calculated and compared with our obtained crystallites at room temperature, which validates the present calculation method very well.

  9. Facile Synthesis of Layer Structured GeP3/C with Stable Chemical Bonding for Enhanced Lithium-Ion Storage

    Science.gov (United States)

    Qi, Wen; Zhao, Haihua; Wu, Ying; Zeng, Hong; Tao, Tao; Chen, Chao; Kuang, Chunjiang; Zhou, Shaoxiong; Huang, Yunhui

    2017-01-01

    Recently, metal phosphides have been investigated as potential anode materials because of higher specific capacity compared with those of carbonaceous materials. However, the rapid capacity fade upon cycling leads to poor durability and short cycle life, which cannot meet the need of lithium-ion batteries with high energy density. Herein, we report a layer-structured GeP3/C nanocomposite anode material with high performance prepared by a facial and large-scale ball milling method via in-situ mechanical reaction. The P-O-C bonds are formed in the composite, leading to close contact between GeP3 and carbon. As a result, the GeP3/C anode displays excellent lithium storage performance with a high reversible capacity up to 1109 mA h g−1 after 130 cycles at a current density of 0.1 A g−1. Even at high current densities of 2 and 5 A g−1, the reversible capacities are still as high as 590 and 425 mA h g−1, respectively. This suggests that the GeP3/C composite is promising to achieve high-energy lithium-ion batteries and the mechanical milling is an efficient method to fabricate such composite electrode materials especially for large-scale application. PMID:28240247

  10. Facile Synthesis of Layer Structured GeP3/C with Stable Chemical Bonding for Enhanced Lithium-Ion Storage

    Science.gov (United States)

    Qi, Wen; Zhao, Haihua; Wu, Ying; Zeng, Hong; Tao, Tao; Chen, Chao; Kuang, Chunjiang; Zhou, Shaoxiong; Huang, Yunhui

    2017-02-01

    Recently, metal phosphides have been investigated as potential anode materials because of higher specific capacity compared with those of carbonaceous materials. However, the rapid capacity fade upon cycling leads to poor durability and short cycle life, which cannot meet the need of lithium-ion batteries with high energy density. Herein, we report a layer-structured GeP3/C nanocomposite anode material with high performance prepared by a facial and large-scale ball milling method via in-situ mechanical reaction. The P-O-C bonds are formed in the composite, leading to close contact between GeP3 and carbon. As a result, the GeP3/C anode displays excellent lithium storage performance with a high reversible capacity up to 1109 mA h g-1 after 130 cycles at a current density of 0.1 A g-1. Even at high current densities of 2 and 5 A g-1, the reversible capacities are still as high as 590 and 425 mA h g-1, respectively. This suggests that the GeP3/C composite is promising to achieve high-energy lithium-ion batteries and the mechanical milling is an efficient method to fabricate such composite electrode materials especially for large-scale application.

  11. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    2012-01-01

    and consider different utility functions and trading strategies. Our results show that investors should include structured bonds in their optimal portfolio only if they cannot access the index underlying the option directly and only if the products then provide sufficient diversification to compensate......Retail structured products regularly receive much criticism from financial experts but seem to remain popular with investors. This article considers a generic structured product: the principal-protected index-linked note (structured bond), which resembles a portfolio insurance contract. The purpose...

  12. Electronic structure and bonding in crystalline peroxides

    Science.gov (United States)

    Königstein, Markus; Sokol, Alexei A.; Catlow, C. Richard A.

    1999-08-01

    Hartree-Fock and density-functional PW91 theories as realized in the CRYSTAL95 code have been applied to investigate the structural and electronic properties of Ba, Sr, and Ca peroxide materials with the calcium carbide crystal structure, results for which are compared with those for the corresponding oxides. Special attention is paid to the stabilization of the peroxide molecular ion O2-2 in the ionic environment provided by the lattice, and to chemical bonding effects. In order to describe the covalent bonding within the O2-2 ion and the polarization of the O- ion in the crystal electrostatic field, it is essential to include an account of the effects of electron correlation. The PW91 density functional has allowed us to reproduce the crystallographic parameters within a 3% error. The chemical bonding within the peroxide molecular ion has a complex nature with a balance between the weak covalent bond of σz type and the strong electrostatic repulsion of the closed-shell electron groups occupying O 2s and O 2px and 2py states. Compression of the peroxide ion in the ionic crystals gives rise to an excessive overlap of the O 2s closed shells of the two O- ions of a peroxide molecular ion O2-2, which in turn determines the antibonding character of the interaction and chemical bonding in the O2-2 molecular ion.

  13. Probing the structures and chemical bonding of boron-boronyl clusters using photoelectron spectroscopy and computational chemistry: B4(BO)(n)- (n = 1-3).

    Science.gov (United States)

    Chen, Qiang; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng

    2012-07-28

    The electronic and structural properties of a series of boron oxide clusters, B(5)O(-), B(6)O(2)(-), and B(7)O(3)(-), are studied using photoelectron spectroscopy and density functional calculations. Vibrationally resolved photoelectron spectra are obtained, yielding electron affinities of 3.45, 3.54, and 4.94 eV for the corresponding neutrals, B(5)O, B(6)O(2), and B(7)O(3), respectively. Structural optimizations show that these oxide clusters can be formulated as B(4)(BO)(n)(-) (n = 1-3), which involve boronyls coordinated to a planar rhombic B(4) cluster. Chemical bonding analyses indicate that the B(4)(BO)(n)(-) clusters are all aromatic species with two π electrons.

  14. Probing the structures and chemical bonding of boron-boronyl clusters using photoelectron spectroscopy and computational chemistry: B4(BO)n- (n = 1-3)

    Science.gov (United States)

    Chen, Qiang; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng

    2012-07-01

    The electronic and structural properties of a series of boron oxide clusters, B5O-, B6O2-, and B7O3-, are studied using photoelectron spectroscopy and density functional calculations. Vibrationally resolved photoelectron spectra are obtained, yielding electron affinities of 3.45, 3.54, and 4.94 eV for the corresponding neutrals, B5O, B6O2, and B7O3, respectively. Structural optimizations show that these oxide clusters can be formulated as B4(BO)n- (n = 1-3), which involve boronyls coordinated to a planar rhombic B4 cluster. Chemical bonding analyses indicate that the B4(BO)n- clusters are all aromatic species with two π electrons.

  15. Exploring Conceptual Frameworks of Models of Atomic Structures and Periodic Variations, Chemical Bonding, and Molecular Shape and Polarity: A Comparison of Undergraduate General Chemistry Students with High and Low Levels of Content Knowledge

    Science.gov (United States)

    Wang, Chia-Yu; Barrow, Lloyd H.

    2013-01-01

    The purpose of the study was to explore students' conceptual frameworks of models of atomic structure and periodic variations, chemical bonding, and molecular shape and polarity, and how these conceptual frameworks influence their quality of explanations and ability to shift among chemical representations. This study employed a purposeful sampling…

  16. Nitrilotris(methylenephosphonato)potassium K[μ6-NH(CH2PO3)3H4]: Synthesis, structure, and the nature of the K-O chemical bond

    Science.gov (United States)

    Somov, N. V.; Chausov, F. F.; Zakirova, R. M.

    2016-07-01

    The crystal structure of nitrilotris(methylenephosphonato)potassium K[μ6-NH(CH2PO3)3H4]—a three-dimensional coordination polymer—was determined. The potassium atom is coordinated by seven oxygen atoms belonging to the six nearest ligand molecules, resulting in distorted monocapped octahedral coordination geometry. The complex contains the four-membered chelate ring K-O-P-O. The K-O chemical bond is predominantly ionic. Meanwhile, the bonds of the potassium atom with some oxygen atoms have a noticeable covalent component. In addition to coordination bonds, the molecules in the crystal packing are linked by hydrogen bonds.

  17. Upper Secondary Teachers' Knowledge for Teaching Chemical Bonding Models

    Science.gov (United States)

    Bergqvist, Anna; Drechsler, Michal; Rundgren, Shu-Nu Chang

    2016-01-01

    Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding science. However, many studies have determined that the use of models in science education can contribute to students' difficulties understanding the topic, and that students generally find chemical bonding a challenging topic. The aim of this study is to investigate teachers' knowledge of teaching chemical bonding. The study focuses on three essential components of pedagogical content knowledge (PCK): (1) the students' understanding, (2) representations, and (3) instructional strategies. We analyzed lesson plans about chemical bonding generated by 10 chemistry teachers with whom we also conducted semi-structured interviews about their teaching. Our results revealed that the teachers were generally unaware of how the representations of models they used affected student comprehension. The teachers had trouble specifying students' difficulties in understanding. Moreover, most of the instructional strategies described were generic and insufficient for promoting student understanding. Additionally, the teachers' rationale for choosing a specific representation or activity was seldom directed at addressing students' understanding. Our results indicate that both PCK components require improvement, and suggest that the two components should be connected. Implications for the professional development of pre-service and in-service teachers are discussed.

  18. Chemical Bonding: The Orthogonal Valence-Bond View

    Directory of Open Access Journals (Sweden)

    Alexander F. Sax

    2015-04-01

    Full Text Available Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO used to construct the wave functions. The transformation of such wave functions into valence bond (VB wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected.

  19. The effect of working pressure on the chemical bond structure and hydrophobic properties of PET surface treated by N ion beams bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Ding Wanyu, E-mail: dwysd_2000@163.com [Engineering Research Center of Optoelectronic Materials and Devices Education Department of Liaoning Province, Dalian, 116028 (China) and School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028 (China) and Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian, 116024 (China); Ju Dongying, E-mail: dyju@sit.ac.jp [Department of Material Science and Engineering, Saitama Institute of Technology Fukaya, 369-0293 (Japan); Chai Weiping, E-mail: wpchai@djtu.edu.cn [Engineering Research Center of Optoelectronic Materials and Devices Education Department of Liaoning Province, Dalian, 116028 (China); School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028 (China)

    2010-09-01

    Polyethylene terephthalate (PET) surface was bombarded by N ion beams at room temperature. Varying the working pressure of the ion beams, PET surfaces with different composition and properties were obtained. Characterization by X-ray photoelectron spectrometry showed that only on film surface, ester bonds, especially C-O bonds, were broken and N element chemical bonded with C. The influence depth was less than 5 nm because of the lower ion energy (about 10{sup 3} eV). Contact angle results revealed that with increasing the working pressure of ion beams, the contact angle of PET surface to pure water increased from 51 deg. to 130 deg.. With these results, one conclusion could be deduced that the hydrophilic and hydrophobic properties of PET surface could be influenced by N atom chemical bond with C, which in turn is controlled by the working pressure of N ion beams.

  20. Synthesis, structure, spectral properties and DFT quantum chemical calculations of 4-aminoazobenzene dyes. Effect of intramolecular hydrogen bonding on photoisomerization

    Science.gov (United States)

    Georgiev, Anton; Bubev, Emil; Dimov, Deyan; Yancheva, Denitsa; Zhivkov, Ivaylo; Krajčovič, Jozef; Vala, Martin; Weiter, Martin; Machkova, Maria

    2017-03-01

    In this paper three different "push-pull" 4-aminoazobenzene dyes have been synthesized in order to characterize their photochromic behavior in different solvents. The molecular geometry was optimized by DFT/B3LYP functional combined with the standard 6-31 + G(d,p) basis set for trans (E) and cis (Z) isomers and the energy levels of HOMO and LUMO frontier orbitals were computed using IEFPCM solvation in CHCl3 and DMF. The calculated results were compared to the experimental optical band gap and HOMO values of cyclic voltammetry. The intramolecular six-membered hydrogen bond was formed in both isomers of the synthesized dyes. The thermodynamic parameters such as total electronic energy E (RB3LYP), enthalpy H298 (sum of electronic and thermal enthalpies), free Gibbs energy G298 (sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed for trans (E) and cis (Z) isomers in order to estimate the ΔEtrans → cis, Δμtrans → cis, ΔHtrans → cis, ΔGtrans → cis and ΔStrans → cis values. The NBO analysis was performed in order to understand the intramolecular charge transfer and energy of resonance stabilization. The solvatochromic shift was evaluated by UV-VIS spectroscopy in CHCl3 (nonpolar), EtOH (polar protic) and DMF (polar aprotic) solvents to determine the electron withdrawing and donating properties of the substituents on electron transitions energy. Through the increasing solvent polarity a strong bathochromic shift is observed. The photoisomerization experiments have been performed in two solvents CHCl3 (nonpolar) and DMF (polar aprotic) by UV light irradiation with λ = 365 nm at equal concentrations and time of illuminations. The electronic spectra were computed by TD-DFT after geometry optimization using IEFPCM solvation in CHCl3 and DMF. The degree of photoisomerization was calculated for the three azo chromophores in both solvents. By using first derivative of the UV-VIS spectra it was possible to resolve the overlapped

  1. Chemical Bond Analysis of Single Crystal Growth of Magnesium Oxide

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Starting from the crystallographic structure of magnesium oxide (MgO), both the chemical bond model of solids and Pauling's third rule (polyhedral sharing rule) were employed to quantitatively analyze the chemical bonding structure of constituent atoms and single crystal growth. Our analytical results show that MgO single crystals prefer to grow along the direction and the growth rate of the {100} plane is the slowest one. Therefore, the results show that the {100} plane of MgO crystals can be the ultimate morphology face, which is in a good agreement with our previous experimental results. The study indicate that the structure analysis is an effective tool to control the single-crystal growth.

  2. A Corpuscular Picture of Electrons in Chemical Bond

    CERN Document Server

    Ando, Koji

    2015-01-01

    We introduce a theory of chemical bond with a corpuscular picture of electrons. It employs a minimal set of localized electron wave packets with 'floating and breathing' degrees of freedom and the spin-coupling of non-orthogonal valence-bond theory. It accurately describes chemical bonds in ground and excited states of spin singlet and triplet, in a distinct manner from conventional theories, indicating potential for establishing a dynamical theory of electrons in chemical bonds.

  3. Bonded and Stitched Composite Structure

    Science.gov (United States)

    Zalewski, Bart F. (Inventor); Dial, William B. (Inventor)

    2014-01-01

    A method of forming a composite structure can include providing a plurality of composite panels of material, each composite panel having a plurality of holes extending through the panel. An adhesive layer is applied to each composite panel and a adjoining layer is applied over the adhesive layer. The method also includes stitching the composite panels, adhesive layer, and adjoining layer together by passing a length of a flexible connecting element into the plurality of holes in the composite panels of material. At least the adhesive layer is cured to bond the composite panels together and thereby form the composite structure.

  4. Electronic structure and chemical bonding in La1-x Sr x MnO3 perovskite ceramics

    Science.gov (United States)

    Thenmozhi, N.; Sasikumar, S.; Sonai, S.; Saravanan, R.

    2017-04-01

    This study reports on the synthesis of La1-x Sr x MnO3 (x  =  0.3, 0.4 and 0.5) manganites by high temperature solid state reaction method using lanthanum oxide, strontium carbonate and manganese oxide as starting materials. The synthesized samples were characterized by XRD, UV-vis, SEM/EDS and VSM. Structural characterization shows that all the prepared samples have the perovskite rhombohedral structure. Influence of Sr doping on electron density distributions in the lattice structure of LaMnO3 were analyzed through maximum entropy method (MEM). Cell parameters are found to be decreasing with the addition of Sr content. The qualitative and quantitative analysis by MEM reveals that, incorporation of Sr into LaMnO3 lattice enhances the ionic nature between La and O ions and decreases the covalent nature between Mn and O ions. Optical band gap values are determined from the UV-visible absorption spectra. Particles with polygonal form are observed from the SEM micrographs. The elemental compositions of the synthesized samples are confirmed by EDS. The magnetic properties studied from the M-H plot taken at room temperature indicated that, the prepared samples are exhibited ferromagnetic behavior.

  5. Chemical Bonding and Structural Information of Black CarbonReference Materials and Individual Carbonaceous AtmosphericAerosols

    Energy Technology Data Exchange (ETDEWEB)

    Hopkins, Rebecca J.; Tivanski, Alexei V.; Marten, Bryan D.; Gilles, Mary K.

    2007-04-25

    The carbon-to-oxygen ratios and graphitic nature of a rangeof black carbon standard reference materials (BC SRMs), high molecularmass humic-like substances (HULIS) and atmospheric particles are examinedusing scanning transmission X-ray microscopy (STXM) coupled with nearedge X-ray absorption fine structure (NEXAFS) spectroscopy. UsingSTXM/NEXAFS, individual particles with diameter>100 nm are studied,thus the diversity of atmospheric particles collected during a variety offield missions is assessed. Applying a semi-quantitative peak fittingmethod to the NEXAFS spectra enables a comparison of BC SRMs and HULIS toparticles originating from anthropogenic combustion and biomass burns,thus allowing determination of the suitability of these materials forrepresenting atmospheric particles. Anthropogenic combustion and biomassburn particles can be distinguished from one another using both chemicalbonding and structural ordering information. While anthropogeniccombustion particles are characterized by a high proportion ofaromatic-C, the presence of benzoquinone and are highly structurallyordered, biomass burn particles exhibit lower structural ordering, asmaller proportion of aromatic-C and contain a much higher proportion ofoxygenated functional groups.

  6. Atomic Structure and Valence: Level II, Unit 10, Lesson 1; Chemical Bonding: Lesson 2; The Table of Elements: Lesson 3; Electrolysis: Lesson 4. Advanced General Education Program. A High School Self-Study Program.

    Science.gov (United States)

    Manpower Administration (DOL), Washington, DC. Job Corps.

    This self-study program for high-school level contains lessons on: Atomic Structure and Valence, Chemical Bonding, The Table of Elements, and Electrolysis. Each of the lessons concludes with a Mastery Test to be completed by the student. (DB)

  7. Emphasizing the Significance of Electrostatic Interactions in Chemical Bonding

    Science.gov (United States)

    Venkataraman, Bhawani

    2017-01-01

    This paper describes a pedagogical approach to help students understand chemical bonding by emphasizing the importance of electrostatic interactions between atoms. The approach draws on prior studies that have indicated many misconceptions among students in understanding the nature of the chemical bond and energetics associated with bond formation…

  8. Interrelationships among biological activity, disulfide bonds, secondary structure, and metal ion binding for a chemically synthesized 34-amino-acid peptide derived from alpha-fetoprotein.

    Science.gov (United States)

    MacColl, R; Eisele, L E; Stack, R F; Hauer, C; Vakharia, D D; Benno, A; Kelly, W C; Mizejewski, G J

    2001-10-01

    A 34-amino-acid peptide has been chemically synthesized based on a sequence from human alpha-fetoprotein. The purified peptide is active in anti-growth assays when freshly prepared in pH 7.4 buffer at 0.20 g/l, but this peptide slowly becomes inactive. This functional change is proven by mass spectrometry to be triggered by the formation of an intrapeptide disulfide bond between the two cysteine residues on the peptide. Interpeptide cross-linking does not occur. The active and inactive forms of the peptide have almost identical secondary structures as shown by circular dichroism (CD). Zinc ions bind to the active peptide and completely prevents formation of the inactive form. Cobalt(II) ions also bind to the peptide, and the UV-Vis absorption spectrum of the cobalt-peptide complex shows that: (1) a near-UV sulfur-to-metal-ion charge-transfer band had a molar extinction coefficient consistent with two thiolate bonds to Co(II); (2) the lowest-energy visible d-d transition maximum at 659 nm, also, demonstrated that the two cysteine residues are ligands for the metal ion; (3) the d-d molar extinction coefficient showed that the metal ion-ligand complex was in a distorted tetrahedral symmetry. The peptide has two cysteines, and it is speculated that the other two metal ion ligands might be the two histidines. The Zn(II)- and Co(II)-peptide complexes had similar peptide conformations as indicated by their ultraviolet CD spectra, which differed very slightly from that of the free peptide. Surprisingly, the cobalt ions acted in the reverse of the zinc ions in that, instead of stabilizing anti-growth form of the peptide, they catalyzed its loss. Metal ion control of peptide function is a saliently interesting concept. Calcium ions, in the conditions studied, apparently do not bind to the peptide. Trifluoroethanol and temperature (60 degrees C) affected the secondary structure of the peptide, and the peptide was found capable of assuming various conformations in solution

  9. Effect of Interface Bond Type on the Structure of InAs/GaSb Superlattices Grown by Metalorganic Chemical Vapor Deposition

    Institute of Scientific and Technical Information of China (English)

    LI Li-Gong; LIUShu-Man; LUO Shuai; YANG Tao; WANG Li-Jun; LIUFeng-Qi; YE Xiao-Ling; XU Bo; WANG Zhan-Guo

    2011-01-01

    InAs/GaSb type-II superlattices were grown on (100) GaSb substrates by meta.lorga.nic chemical vapor deposition. Raman scattering spectroscopy reveals that it is possible to grow superlattices with almost pure GaAs-like and mixed-like (plane of mixed As and Sb atoms that connect the GaSb and lnAs layers) interfaces. Introducing the InSb-like interface results in nanopipes and As contamination of the GaSb layers. X-ray diffraction and atomic force microscopy demonstrate that the superlattices with a mixed-like interface have better morphology and crystalline quality.%InAs/GaSb type-Ⅱ superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition.Raman scattering spectroscopy reveals that it is possible to grow superlattices with almost pure GaAs-like and mixed-like (plane of mixed As and Sb atoms that connect the GaSb and InAs layers) interfaces.Introducing the InSb-like interface results in nanopipes and As contamination of the GaSb layers.X-ray diffraction and atomic force microscopy demonstrate that the superlattices with a mixed-like interface have better morphology and crystalline quality.InAs/GaSb type-Ⅱ superlattices (SLs) have been shown to be a promising alternative to the existing HgCdTe and quantum well infrared detectors.[1,2]This material system can be tailored over a wide range of infrared wavelength from 3 to more than 30 μm by changing the thicknesses of the InAs and GaSb layers.Using the same technique,the Auger recombination rate can be significantly reduced in InAs/GaSb SLs,which is especially important for realizing high-performance infrared detectors at room temperature.[3,4] Furthermore,due to the large electron effective mass of the SL structures,the bandto-band tunneling current is intrinsically small compared to that of HgCdTe.[5] Since both the anion and the cation change across the interface (IF) of the InAs/GaSb SL,two types of interfaces are possible,InSb-like and GaAs-like.It has been shown that the

  10. Experimental charge density and neutron structural study of cis-HMn(CO){sub 4}PPh{sub 3}: Comprehensive analysis of chemical bonding and evidence for a C-H{hor_ellipsis}H-Mn hydrogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Abramov, Y.A.; Brammer, L. [Univ. of Missouri, St. Louis, MO (United States). Dept. of Chemistry; Klooster, W.T.; Bullock, R.M. [Brookhaven National Lab., Upton, NY (United States). Chemistry Dept.

    1998-11-30

    The structure and bonding in cis-HMn(CO){sub 4}PPh{sub 3} have been studied by low-temperature neutron and high-resolution X-ray diffraction, the latter study using a charge-coupled device (CCD) area detector. A charge density analysis, including the deformation density, a full topological analysis of {minus}{del}{sup 2}{rho}, has been conducted. The electrostatic component of the H{sup {delta}+}{hor_ellipsis}H{sup {delta}{minus}} interaction energy is calculated to be 5.7 kcal/mol from the experimental data. This electrostatic evidence coupled with the geometry C-H{hor_ellipsis}H 129.0(2){degree} and H{hor_ellipsis}H-Mn 126.5(1){degree} and the identification of an H{hor_ellipsis}H bond path in the charge density distribution strongly supports the characterization of this interaction as an intramolecular C-H{hor_ellipsis}H-Mn hydrogen bond. Both the deformation density and the topological study clearly illustrate the {sigma}-donor nature of both the H-Mn and Ph{sub 3}P-Mn interactions and the {sigma}-donor/{pi}-acceptor nature of the manganese-carbonyl bonds. The topological study further confirms the decrease in C-O bond order upon coordination to the metal and demonstrates for the first time by this method that the metal-ligand bonds, although showing characteristics of a closed-shell interaction, do have a significant dative covalent component to the bond. The latter is reinforced by a study of the derived Mn d-orbital populations, in which populations of the d{sub z{sup 2}} and d{sub x{sup 2}{minus}y{sup 2}} orbitals are significantly higher than would be predicted by a simple crystal field theory model of metal-ligand bonding.

  11. Chemical Bond Parameters in Sr3MRhO6 (M=Rare earth)

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Chemical bond parameters, that is, bond covalency, bond valence, macroscopic linear susceptibility, and oxidation states of elements in Sr3MRhO6 (M=Sm, Eu, Tb, Dy, Ho, Er, Yb) have been calculated. The results indicate that the bond covalency of M-O decreases sharply with the decrease of ionic radius of M3+ from Sm to Yb, while no obvious trend has been found for Rh-O and Sr-O bonds. The global instability index indicates that the crystal structures of Sr3MrhO6 (M = Sm, Eu, Tb, Dy, Ho) have strained bonds.

  12. Electronic structure, chemical bonding and elastic properties of the first thorium-containing nitride perovskite TaThN{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Bannikov, V.V.; Shein, I.R.; Ivanovskii, A.L. [Institute of Solid State Chemistry of the Ural Division of the Russian Academy of Sciences, GSP-145, 620041 Ekaterinburg (Russian Federation)

    2007-05-15

    The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange and correlation potential (LAPW-GGA) is used to understand the electronic and elastic properties of the first thorium-containing nitride perovskite TaThN{sub 3}. Total and partial density of states, charge distributions as well as the elastic constants, bulk modulus, compressibility, shear modulus, Young modulus and Poisson ratio are obtained for the first time and analyzed in comparison with cubic ThN. The chemical bonding in TaThN{sub 3} is a combination of ionic Th-N and of mixed covalent-ionic Ta-N bonds. The cubic TaThN{sub 3} is semiconducting with the direct gap at about 0.65 eV. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Structure and bonding in some organotitanium and related compounds

    NARCIS (Netherlands)

    Zeinstra, Jabik Dominicus

    1981-01-01

    In this thesis investigations on the structure and chemical bonding in some organometallic compounds of transition metals with few d electrons are described. Structural studies involve the X-ray diffraction analyses of two titanium compounds. Theoretical studies deal with the electronic structure of

  14. How do halogen bonds (S-O⋯I, N-O⋯I and C-O⋯I) and halogen-halogen contacts (C-I⋯I-C, C-F⋯F-C) subsist in crystal structures? A quantum chemical insight.

    Science.gov (United States)

    Pandiyan, B Vijaya; Deepa, P; Kolandaivel, P

    2017-01-01

    Thirteen X-ray crystal structures containing various non-covalent interactions such as halogen bonds, halogen-halogen contacts and hydrogen bonds (I⋯N, I⋯F, I⋯I, F⋯F, I⋯H and F⋯H) were considered and investigated using the DFT-D3 method (B97D/def2-QZVP). The interaction energies were calculated at MO62X/def2-QZVP and MP2/aug-cc-pvDZ level of theories. The higher interaction and dispersion energies (2nd crystal) of -9.58 kcal mol(-1) and -7.10 kcal mol(-1) observed for 1,4-di-iodotetrafluorobenzene bis [bis (2-phenylethyl) sulfoxide] structure indicates the most stable geometrical arrangement in the crystal packing. The electrostatic potential values calculated for all crystal structures have a positive σ-hole, which aids understanding of the nature of σ-hole bonds. The significance of the existence of halogen bonds in crystal packing environments was authenticated by replacing iodine atoms by bromine and chlorine atoms. Nucleus independent chemical shift analysis reported on the resonance contribution to the interaction energies of halogen bonds and halogen-halogen contacts. Hirshfeld surface analysis and topological analysis (atoms in molecules) were carried out to analyze the occurrence and strength of all non-covalent interactions. These analyses revealed that halogen bond interactions were more dominant than hydrogen bonding interactions in these crystal structures. Graphical Abstract Molecluar structure of 1,4-Di-iodotetrafluorobenzene bis(thianthrene 5-oxide) moelcule and its corresponding molecular electrostatic potential map for the view of σ-hole.

  15. Structural flexibility in magnetocaloric RE5T4 (RE=rare-earth; T=Si,Ge,Ga) materials: Effect of chemical substitution on structure, bonding and properties

    Energy Technology Data Exchange (ETDEWEB)

    Misra, Sumohan [Iowa State Univ., Ames, IA (United States)

    2008-01-01

    The binary, ternary and multicomponent intermetallic compounds of rare-earth metals (RE) with group 14 elements (Tt) at the RE5Tt4 stoichiometry have been known for over 30 years, but only in the past decade have these materials become a gold mine for solid-state chemistry, materials science and condensed matter physics. It all started with the discovery of a giant magnetocaloric effect in Gd5Si2Ge2, along with other extraordinary magnetic properties, such as a colossal magnetostriction and giant magnetoresistance. The distinctiveness of this series is in the remarkable flexibility of the chemical bonding between well-defined, subnanometer-thick slabs and the resultant magnetic, transport, and thermodynamic properties of these materials. This can be controlled by varying either or both RE and Tt elements, including mixed rare-earth elements on the RE sites and different group 14 (or T = group 13 or 15) elements occupying the Tt sites. In addition to chemical means, the interslab interactions are also tunable by temperature, pressure, and magnetic field. Thus, this system provides a splendid 'playground' to investigate the interrelationships among composition, structure, physical properties, and chemical bonding. The work presented in this dissertation involving RE5T4 materials has resulted in the successful synthesis, characterization, property measurements, and theoretical analyses of various new intermetallic compounds. The results provide significant insight into the fundamental magnetic and structural behavior of these materials and help us better understand the complex link between a compound's composition, its observed structure, and its properties.

  16. Upper Secondary Teachers' Knowledge for Teaching Chemical Bonding Models

    Science.gov (United States)

    Bergqvist, Anna; Drechsler, Michal; Chang Rundgren, Shu-Nu

    2016-01-01

    Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding…

  17. Ternary arsenides based on platinum–indium and palladium–indium fragments of the Cu{sub 3}Au-type: Crystal structures and chemical bonding

    Energy Technology Data Exchange (ETDEWEB)

    Zakharova, Elena Yu.; Andreeva, Natalia A.; Kazakov, Sergey M. [Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow (Russian Federation); Kuznetsov, Alexey N., E-mail: alexei@inorg.chem.msu.ru [Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow (Russian Federation); N.S. Kurnakov Institute of General and Inorganic Chemistry of Russian Academy of Sciences, Leninskii pr. 31, 119991 Moscow (Russian Federation)

    2015-02-05

    Highlights: • Three metal-rich platinum–indium and palladium–indium arsenides were synthesized. • Their crystal structures were determined from powder XRD. • Electronic structures and bonding were studied using DFT/FP-LAPW calculations. • Multi-centered Pt–In or Pd–In bonding was revealed using ELF and ELI-D analysis. • Extra pairwise Pt–Pt interactions are observed only for Pt-based compounds. - Abstract: Three metal-rich palladium–indium and platinum–indium arsenides, Pd{sub 5}InAs, Pt{sub 5}InAs, and Pt{sub 8}In{sub 2}As, were synthesized using a high-temperature ampoule technique. Their crystal structures were determined from Rietveld analysis of powder diffraction data. All the compounds crystallize in tetragonal system with P4/mmm space group (Pd{sub 5}InAs: a = 3.9874(1) Å, c = 6.9848(2) Å, Z = 1, R{sub p} = 0.053; R{sub b} = 0.013; Pt{sub 5}InAs: a = 3.9981(2) Å, c = 7.0597(4) Å, Z = 1, R{sub p} = 0.058, R{sub b} = 0.016; Pt{sub 8}In{sub 2}As: a = 3.9872(3) Å, c = 11.1129(7) Å, Z = 1, R{sub p} = 0.047; R{sub b} = 0.014). The first two compounds belong to the Pd{sub 5}TlAs structure type, while the third one is isotypic with the recently discovered Pd{sub 8}In{sub 2}Se. Main structural units in all arsenides are indium-centered [TM{sub 12}In] cuboctahedra (TM = Pd, Pt) of the Cu{sub 3}Au type, single- and double-stacked along the c axis in TM{sub 5}InAs and Pt{sub 8}In{sub 2}As, respectively, alternating with [TM{sub 8}As] rectangular prisms. DFT electronic structure calculations predict all three compounds to be 3D metallic conductors and Pauli-like paramagnets. According to the bonding analysis based on the electron localization function and electron localizability indicator topologies, all compounds feature multi-centered interactions between transition metal and indium in their heterometallic fragments. Additionally, pairwise interactions between platinum atoms are also observed, indicating a somewhat more localized bonding

  18. Closing in on chemical bonds by opening up relativity theory.

    Science.gov (United States)

    Whitney, Cynthia K

    2008-03-01

    This paper develops a connection between the phenomenology of chemical bonding and the theory of relativity. Empirical correlations between electron numbers in atoms and chemical bond stabilities in molecules are first reviewed and extended. Quantitative chemical bond strengths are then related to ionization potentials in elements. Striking patterns in ionization potentials are revealed when the data are viewed in an element-independent way, where element-specific details are removed via an appropriate scaling law. The scale factor involved is not explained by quantum mechanics; it is revealed only when one goes back further, to the development of Einstein's special relativity theory.

  19. Majorana, Pauling and the quantum theory of the chemical bond

    CERN Document Server

    Esposito, S

    2013-01-01

    We discuss in detail very little known results obtained by Majorana as early as 1931, regarding the quantum theory of the chemical bond in homopolar molecules, based on the key concept of exchange interaction. After a brief historical overview of the quantum homopolar valence theory, we address the intriguing issues of the formation of the helium molecular ion, He2+, and of the accurate description of the hydrogen molecule, H2. For the first case, the group theory-inspired approach used by Majorana is contrasted with that more known followed by Pauling (and published few months after that of Majorana), while for the second case we focus on his proposal concerning the possible existence of ionic structures in homopolar compounds, just as in the hydrogen molecule. The novelty and relevance of Majorana's results in the modern research on molecular and chemical physics is emphasized as well.

  20. DFT modeling of the electronic and magnetic structures and chemical bonding properties of intermetallic hydrides; Modelisation au sein de la DFT des proprietes des structures electronique et magnetique et de liaison chimique des Hydrures d'Intermetalliques

    Energy Technology Data Exchange (ETDEWEB)

    Al Alam, A.F.

    2009-06-15

    This thesis presents an ab initio study of several classes of intermetallics and their hydrides. These compounds are interesting from both a fundamental and an applied points of view. To achieve this aim two complementary methods, constructed within the DFT, were chosen: (i) pseudo potential based VASP for geometry optimization, structural investigations and electron localization mapping (ELF), and (ii) all-electrons ASW method for a detailed description of the electronic structure, chemical bonding properties following different schemes as well as quantities depending on core electrons such as the hyperfine field. A special interest is given with respect to the interplay between magneto-volume and chemical interactions (metal-H) effects within the following hydrided systems: binary Laves (e.g. ScFe{sub 2}) and Haucke (e.g. LaNi{sub 5}) phases on one hand, and ternary cerium based (e.g. CeRhSn) and uranium based (e.g. U{sub 2}Ni{sub 2}Sn) alloys on the other hand. (author)

  1. An investigation of hydrogen-bonding effects on the nitrogen and hydrogen electric field gradient and chemical shielding tensors in the 9-methyladenine real crystalline structure: a density functional theory study.

    Science.gov (United States)

    Mirzaei, Mahmoud; Hadipour, Nasser L

    2006-04-13

    Hydrogen-bonding effects in the real crystalline structure of 9-methyladenine, 9-MA, were studied using calculated electric field gradient, EFG, and chemical shielding, CS, tensors for nitrogen and hydrogen nuclei via density functional theory. The calculations were carried out at the B3LYP and B3PW91 levels with the 6-311++G basis set via the Gaussian 98 package. Nuclear quadrupole coupling constants, C(Q), and asymmetry parameters, eta(Q), are reported for (14)N and (2)H. The chemical shielding anisotropy, Deltasigma, and chemical shielding isotropy, sigma(iso), are also reported for (15)N and (1)H. The difference between the calculated parameters of the monomer and heptameric layer-like cluster 9-MA shows how much H-bonding interactions affect the EFG and CS tensors of each nucleus. This result indicates that N(10) (imino nitrogen) has a major role in H-bonding interactions, whereas that of N(9) is negligible. There is good agreement between the present calculated parameters and reported experimental data. Although some discrepancies were observed, this could be attributed to the different conditions which were applied for calculation and the experiments.

  2. Structure, chemical bonding states, and optical properties of the hetero-structured ZnO/CuO prepared by using the hydrothermal and the electrospinning methods

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Kyong-Soo; Kim, Jong Wook; Bae, Jong-Seong; Hong, Tae Eun; Jeong, Euh Duck; Jin, Jong Sung; Ha, Myoung Gyu; Kim, Jong-Pil, E-mail: jpkim@kbsi.re.kr

    2017-01-01

    ZnO-branched nanostructures have recently attracted considerable attention due to their rich architectures and promising applications in the field of optoelectronics. Contrary to n-type semiconducting metal oxides, cupric oxide is a p-type semiconductor which can be applied to high-critical-temperature superconductors, photovoltaic materials, field emission, and catalysis. We report the synthesis of the ZnO nanorods on the CuO nanofibers prepared by using the electrospinning method along with the hydrothermal method. As the growing time increases, emission spectra of the hetero-structured ZnO/CuO show that the observed band in the UV region is slightly increased, while the intensity of the green emission is highly enhanced. The hetero-structured ZnO/CuO is found to be a promising candidate for developing renewable devices with photoluminescent behavior and the increased surface to volume ratio.

  3. The structure, energetics, and nature of the chemical bonding of phenylthiol adsorbed on the Au(111) surface: implications for density-functional calculations of molecular-electronic conduction.

    Science.gov (United States)

    Bilić, Ante; Reimers, Jeffrey R; Hush, Noel S

    2005-03-01

    The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and

  4. Electronegativity, Bond Energy, and Chemical Reactivity.

    Science.gov (United States)

    Myers, R. Thomas

    1979-01-01

    Discusses the Pauling electronegativity concept which rationalizes several kinds of chemical reactions of covalent substances. Electronegativity differences applied to some reactions are demonstrated. (SA)

  5. The Bondons: The Quantum Particles of the Chemical Bond

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz

    2010-10-01

    Full Text Available By employing the combined Bohmian quantum formalism with the U(1 and SU(2 gauge transformations of the non-relativistic wave-function and the relativistic spinor, within the Schrödinger and Dirac quantum pictures of electron motions, the existence of the chemical field is revealed along the associate bondon particle  characterized by its mass (mΒ, velocity (vΒ, charge (eΒ, and life-time (tΒ. This is quantized either in ground or excited states of the chemical bond in terms of reduced Planck constant ħ, the bond energy Ebond and length Xbond, respectively. The mass-velocity-charge-time quaternion properties of bondons’ particles were used in discussing various paradigmatic types of chemical bond towards assessing their covalent, multiple bonding, metallic and ionic features. The bondonic picture was completed by discussing the relativistic charge and life-time (the actual zitterbewegung problem, i.e., showing that the bondon equals the benchmark electronic charge through moving with almost light velocity. It carries negligible, although non-zero, mass in special bonding conditions and towards observable femtosecond life-time as the bonding length increases in the nanosystems and bonding energy decreases according with the bonding length-energy relationship Ebond[kcal/mol]*Xbond[A]=182019, providing this way the predictive framework in which the particle may be observed. Finally, its role in establishing the virtual states in Raman scattering was also established.

  6. Handbook of adhesive bonded structural repair

    CERN Document Server

    Wegman, Raymond F

    1992-01-01

    Provides repair methods for adhesive bonded and composite structures; identifies suitable materials and equipment for repairs; describes damage evaluation criteria and techniques, and methods of inspection before and after repair.

  7. Benchmarking Density Functionals for Chemical Bonds of Gold

    DEFF Research Database (Denmark)

    Kepp, Kasper Planeta

    2017-01-01

    Gold plays a major role in nanochemistry, catalysis, and electrochemistry. Accordingly, hundreds of studies apply density functionals to study chemical bonding with gold, yet there is no systematic attempt to assess the accuracy of these methods applied to gold. This paper reports a benchmark...... against 51 experimental bond enthalpies of AuX systems and seven additional polyatomic and cationic molecules. Twelve density functionals were tested, covering meta functionals, hybrids with variable HF exchange, double-hybrid, dispersion-corrected, and nonhybrid GGA functionals. The defined benchmark...... bonds between gold and noble gases. Zero-point vibrational corrections are relatively small for Au-X bonds, ∼ 11-12 kJ/mol except for Au-H bonds. Dispersion typically provides ∼5 kJ/mol of the total bond enthalpy but grows with system size and is 10 kJ/mol for AuXe and AuKr. HF exchange and LYP...

  8. Diffusion-bonded beryllium aluminum optical structures

    Science.gov (United States)

    Grapes, Thomas F.

    2003-12-01

    Beryllium aluminum material can present significant advantages for optical support structures. A likely advantage of beryllium aluminum compared to aluminum or titanium for such structures is its higher specific stiffness. However, beryllium aluminum material is significantly more expensive than most competing materials. The cost problem with beryllium aluminum is exacerbated if fabrication methods that result in near net shape parts are not used. Near net shape methods result in the least amount of material "thrown away" in the fabrication process. Casting is a primary example of near net shape manufacturing that is appropriate for some optical support structures. Casting aluminum, and other materials as well, is common. Casting of beryllium aluminum is very difficult, however, and has not had significant success. Diffusion bonding - a different approach for achieving near net shape beryllium aluminum optical support structures, was pursued and accomplished. Diffusion bonding is a term used to describe the joining of solid metal pieces under high temperature and pressure, but without melting. Three different optical support structures were designed and built of beryllium aluminum using diffusion bonding. Relatively small solid beryllium aluminum pieces were arranged together and then joined under hot isostatic pressure conditions. The resulting relatively large pressure bonded part was then machined to achieve the final product. Significant cost savings as compared to machining the part from a solid block were realized. Difficulties achieving diffusion bonds in complex joints were experienced and addressed.

  9. Chemical cleaning agents and bonding to glass-fiber posts.

    Science.gov (United States)

    Gonçalves, Ana Paula Rodrigues; Ogliari, Aline de Oliveira; Jardim, Patrícia dos Santos; Moraes, Rafael Ratto de

    2013-01-01

    The influence of chemical cleaning agents on the bond strength between resin cement and glass-fiber posts was investigated. The treatments included 10% hydrofluoric acid, 35% phosphoric acid, 50% hydrogen peroxide, acetone, dichloromethane, ethanol, isopropanol, and tetrahydrofuran. Flat glass-fiber epoxy substrates were exposed to the cleaners for 60 s. Resin cement cylinders were formed on the surfaces and tested in shear. All treatments provided increased bond strength compared to untreated control specimens. All failures were interfacial. Although all agents improved the bond strength, dichloromethane and isopropanol were particularly effective.

  10. Chemical cleaning agents and bonding to glass-fiber posts

    Directory of Open Access Journals (Sweden)

    Ana Paula Rodrigues Gonçalves

    2013-02-01

    Full Text Available The influence of chemical cleaning agents on the bond strength between resin cement and glass-fiber posts was investigated. The treatments included 10% hydrofluoric acid, 35% phosphoric acid, 50% hydrogen peroxide, acetone, dichloromethane, ethanol, isopropanol, and tetrahydrofuran. Flat glass-fiber epoxy substrates were exposed to the cleaners for 60 s. Resin cement cylinders were formed on the surfaces and tested in shear. All treatments provided increased bond strength compared to untreated control specimens. All failures were interfacial. Although all agents improved the bond strength, dichloromethane and isopropanol were particularly effective.

  11. A qualitative study of high school students' pre- and post instructional conceptions in chemical bonding

    Science.gov (United States)

    Wang, Renhong

    This study investigated high school students' understanding of chemical bonding prior to and after formal chemistry instruction. Two sets of clinical interviews were conducted prior to and after formal instructions on the topic of chemical bonding using a teacher-as-researcher protocol. Twenty-two students enrolled in a New York Regents Chemistry course were interviewed. Six students participated in the pilot study and the other sixteen were involved in the full study. Oral and pictorial data from the interviews were collected and analyzed in two parts; first, the students' conceptual understanding of chemical bonding including common themes, ideas and misconceptions were identified; second, profiles of each student were made to determine conceptual changes due to formal instruction. The findings showed that students were not familiar with the basic components and structure of atoms, especially the electrostatic properties of the sub-atomic particles. Inter-particle distance, rather than the electrostatic forces between particles, was believed to be the determining cause of the state of matter of a substance. The role of repulsive and attractive electrostatic forces in chemical bonding was not recognized. Students were unable to accurately describe the underlying scientific concepts for all types of chemical bonding and revealed a number of misconceptions, which were resistant to change by instruction. Specific areas of difficulty included the accurate descriptions of ionic bonding, covalent bonding and hydrogen bonding. Further, almost all the students could not use electrostatic forces to explain three states of water and phase changes and most students were unable to describe the energy that was released or absorbed due to bond formation or breaking. Student difficulties stemmed from a lack of understanding of some of the underlying, fundamental chemistry, such as the basic atomic structure, the particulate nature of mater and the role of electrostatic forces in

  12. Nature of the chemical bond and origin of the inverted dipole moment in boron fluoride: a generalized valence bond approach.

    Science.gov (United States)

    Fantuzzi, Felipe; Cardozo, Thiago Messias; Nascimento, Marco Antonio Chaer

    2015-05-28

    The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)Σ(+) and a (3)Π states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that π back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation.

  13. Ab initio investigations of the electronic structures and chemical bonding in LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Matar, Samir F. [CNRS, ICMCB, UPR 9048, F‐33600 Pessac (France); Université de Bordeaux, ICMCB, UPR 9048, F‐33600 Pessac (France); Al-Alam, Adel; Ouaini, Naïm [Université Saint-Esprit de Kaslik (USEK), Groupe OCM (Optimization et Caractérisation des Matériaux), CSR-USEK, CNRS-L, Jounieh (Lebanon); Pöttgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstraße 30, D-48149 Münster (Germany)

    2013-06-15

    The electronic structures of the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7} were studied by DFT calculations. Both phosphides consist of three-dimensional [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] polyanionic networks which leave hexagonal channels for the lithium atoms. COOP data show strong Co–P and Co–Co bonding within the polyanions. The lithium atoms have trigonal prismatic phosphorus coordination. Total energy calculations indicate stability upon de-lithiation towards the Co{sub 6}P{sub 4} and Co{sub 12}P{sub 7} substructures - Graphical abstract: The cobalt–phosphorus networks in LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. - Highlights: • Chemical bonding resolved in the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. • Strong covalent Co–P bonding character in the [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] substructures. • Total energy calculations indicate stability of the de-lithiated substructures.

  14. Electronic parameters of Sr2Nb2O7 and chemical bonding

    DEFF Research Database (Denmark)

    Atuchin, V.V.; Grivel, Jean-Claude; Korotkov, A.S.

    2008-01-01

    /2)) and Delta(O-Sr) = BE(O 1s)-BE(Sr 3d(5/2)), were used to characterize the valence electron transfer on the formation of the Nb-O and Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr2Nb2O7 and earlier published structural and XPS data for other Sr- or Nb...

  15. The genesis of the quantum theory of the chemical bond

    CERN Document Server

    Esposito, S

    2013-01-01

    An historical overview is given of the relevant steps that allowed the genesis of the quantum theory of the chemical bond, starting from the appearance of the new quantum mechanics and following later developments till approximately 1931. General ideas and some important details are discussed concerning molecular spectroscopy, as well as quantum computations for simple molecular systems performed within perturbative and variational approaches, for which the Born-Oppenheimer method provided a quantitative theory accounting for rotational, vibrational and electronic states. The novel concepts introduced by the Heitler-London theory, complemented by those underlying the method of the molecular orbitals, are critically analyzed along with some of their relevant applications. Further improvements in the understanding of the nature of the chemical bond are also considered, including the ideas of one-electron and three-electron bonds introduced by Pauling, as well as the generalizations of the Heitler-London theory ...

  16. Chemical strategies for die/wafer submicron alignment and bonding.

    Energy Technology Data Exchange (ETDEWEB)

    Martin, James Ellis; Baca, Alicia I.; Chu, Dahwey; Rohwer, Lauren Elizabeth Shea

    2010-09-01

    This late-start LDRD explores chemical strategies that will enable sub-micron alignment accuracy of dies and wafers by exploiting the interfacial energies of chemical ligands. We have micropatterned commensurate features, such as 2-d arrays of micron-sized gold lines on the die to be bonded. Each gold line is functionalized with alkanethiol ligands before the die are brought into contact. The ligand interfacial energy is minimized when the lines on the die are brought into registration, due to favorable interactions between the complementary ligand tails. After registration is achieved, standard bonding techniques are used to create precision permanent bonds. We have computed the alignment forces and torque between two surfaces patterned with arrays of lines or square pads to illustrate how best to maximize the tendency to align. We also discuss complex, aperiodic patterns such as rectilinear pad assemblies, concentric circles, and spirals that point the way towards extremely precise alignment.

  17. Effects of Mechanical and Chemical Pretreatments of Zirconia or Fiber Posts on Resin Cement Bonding.

    Directory of Open Access Journals (Sweden)

    Rui Li

    Full Text Available The bonding strength between resin cement and posts is important for post and core restorations. An important method of improving the bonding strength is the use of various surface pretreatments of the post. In this study, the surfaces of zirconia (fiber posts were treated by mechanical and/or chemical methods such as sandblasting and silanization. The bonding strength between the zirconia (fiber post and the resin cement was measured by a push-out method after thermocycling based on the adhesion to Panavia F 2.0 resin cement. The zirconia and fiber posts exhibited different bonding strengths after sandblasting and/or silanization because of the different strengths and chemical structures. The zirconia post showed a high bonding strength of up to 17.1 MPa after a combined treatment of sandblasting and silanization because of the rough surface and covalent bonds at the interface. This effect was also enhanced by using 1,2-bis(trimethoxysilylethane for the formation of a flexible layer at the interface. In contrast, a high bonding strength of 13.9 MPa was obtained for the fiber post treated by silane agents because the sandblasting treatment resulted in damage to the fiber post, as observed by scanning electron microscopy. The results indicated that the improvement in the bonding strength between the post and the resin cement could be controlled by different chemical and/or mechanical treatments. Enhanced bonding strength depended on covalent bonding and the surface roughness. A zirconia post with high bonding strength could potentially be used for the restoration of teeth in the future.

  18. Structure-Induced Covalent Bonding in Al-Li Compounds

    Science.gov (United States)

    Nozawa, Kazuki; Ishii, Yasushi

    2010-06-01

    Formation mechanism of a deep pseudogap in the electronic density of states of the Al-Li Bergman and Zintl compounds is discussed with an emphasis on the differences among isostructural Al-Mg compounds. Since Li scatters electrons very weakly in comparison with Al and Mg, the potential landscape for electrons in Al-Li compounds is not that of the entire close-packed structure but that of the Al sublattice, which is a rather porous network like the diamond lattice. The porous network structure realized by the chemical decoration of close-packed structures enhances the covalent nature of electronic structures, hence the deep pseudogap in the electronic density of states. A concept of structure-induced covalent bonding in a network realized by the chemical decoration of close-packed structures may provide a novel picture in the electronic structures of complex intermetallic compounds.

  19. Characterizing and Representing Student's Conceptual Knowledge of Chemical Bonding

    Science.gov (United States)

    Yayon, Malka; Mamlok-Naaman, Rachel; Fortus, David

    2012-01-01

    Chemical bonding knowledge is fundamental and essential to the understanding of almost every topic in chemistry, but it is very difficult to learn. While many studies have characterized some of the central elements of knowledge of this topic, these elements of knowledge have not been systematically organized. We describe the development and…

  20. First-principles simulations on bonding pathways of chemical transformations under hydrostatic compression

    Science.gov (United States)

    Hu, Anguang; Zhang, Fan

    2012-02-01

    High pressure as a thermodynamic parameter provides a strong structural constraint to lead chemical transformations with selective ways. Thus, chemical transformations under pressure can create novel materials which may not be accessible by covalent synthesis. However, bonding evolution toward high pressure chemical transformations can be a complex process and may happen over widely different pressures. To understand bonding evolution pathways of high pressure chemical transformations, first-principles simulations were performed following hydrostatic compression enthalpy minimization paths to obtain experimentally and theoretically established phase transitions of carbon. The results showed that the chemical transformations from hydrostatic compression carbon to single-bonded phases were characterized by a sudden decrease in principal stress components, indicating the onset of chemical transformation. On this basis, a number of hydrostatic compression chemical transformations from molecular precursors to novel materials were predicted, such as hydrocarbon graphane, a hydrogenated carbon nitride sheet, and carbon nitrides. All predicted hydrostatic compression transformations are featured as a sudden change in principal stress components, representing chemical bonding destruction and formation reactions with a cell volume collapse.

  1. Bonding and structure of copper nitrenes.

    Science.gov (United States)

    Cundari, Thomas R; Dinescu, Adriana; Kazi, Abul B

    2008-11-03

    Copper nitrenes are of interest as intermediates in the catalytic aziridination of olefins and the amination of C-H bonds. However, despite advances in the isolation and study of late-transition-metal multiply bonded complexes, a bona fide structurally characterized example of a terminal copper nitrene has, to our knowledge, not been reported. In anticipation of such a report, terminal copper nitrenes are studied from a computational perspective. The nitrene complexes studied here are of the form (beta-diketiminate)Cu(NPh). Density functional theory (DFT), complete active space self-consistent-field (CASSCF) electronic structure techniques, and hybrid quantum mechanical/molecular mechanical (QM/MM) methods are employed to study such species. While DFT methods indicate that a triplet (S = 1) is the ground state, CASSCF calculations indicate that a singlet (S = 0) is the ground state, with only a small energy gap between the singlet and triplet. Moreover, the ground-state (open-shell) singlet copper nitrene is found to be highly multiconfigurational (i.e., biradical) and to possess a bent geometry about the nitrene nitrogen, contrasting with the linear nitrene geometry of the triplet copper nitrenes. CASSCF calculations also reveal the existence of a closed-shell singlet state with some degree of multiple bonding character for the copper-nitrene bond.

  2. AIScore chemically diverse empirical scoring function employing quantum chemical binding energies of hydrogen-bonded complexes.

    Science.gov (United States)

    Raub, Stephan; Steffen, Andreas; Kämper, Andreas; Marian, Christel M

    2008-07-01

    In this work we report on a novel scoring function that is based on the LUDI model and focuses on the prediction of binding affinities. AIScore extends the original FlexX scoring function using a chemically diverse set of hydrogen-bonded interactions derived from extensive quantum chemical ab initio calculations. Furthermore, we introduce an algorithmic extension for the treatment of multifurcated hydrogen bonds (XFurcate). Charged and resonance-assisted hydrogen bond energies and hydrophobic interactions as well as a scaling factor for implicit solvation were fitted to experimental data. To this end, we assembled a set of 101 protein-ligand complexes with known experimental binding affinities. Tightly bound water molecules in the active site were considered to be an integral part of the binding pocket. Compared to the original FlexX scoring function, AIScore significantly improves the prediction of the binding free energies of the complexes in their native crystal structures. In combination with XFurcate, AIScore yields a Pearson correlation coefficient of R P = 0.87 on the training set. In a validation run on the PDBbind test set we achieved an R P value of 0.46 for 799 attractively scored complexes, compared to a value of R P = 0.17 and 739 bound complexes obtained with the FlexX original scoring function. The redocking capability of AIScore, on the other hand, does not fully reach the good performance of the original FlexX scoring function. This finding suggests that AIScore should rather be used for postscoring in combination with the standard FlexX incremental ligand construction scheme.

  3. Electronic structure and bonding in hydroxocobalamin

    Science.gov (United States)

    Ouyang, Lizhi; Rulis, Paul; Ching, Wai-Y.; Slouf, Miroslav; Nardin, Giorgio; Randaccio, Lucio

    2005-05-01

    The electronic structure of hydroxocobalamin (OHCbl) has been calculated by a density functional method, using the orthogonalized linear combination of the atomic orbitals method (OLCAO). The X-ray crystal structure has been determined from synchrotron X-ray diffraction data and the geometry determined was used in the calculations. Comparison with the recently reported electronic structures of cyanocobalamin (CNCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) shows that Mulliken charges ( Q*) and bond orders (BO) vary only on the axial fragment.

  4. Halogen bonded supramolecular capsules: a challenging test case for quantum chemical methods.

    Science.gov (United States)

    Sure, Rebecca; Grimme, Stefan

    2016-08-02

    Recently, Diederich et al. synthesized the first supramolecular capsule with a well-defined four-point halogen bonding interaction [Angew. Chem., Int. Ed., 2015, 54, 12339]. This interesting system comprising about 400 atoms represents a challenging test case for accurate quantum chemical methods. We investigate it with our new density functional based composite method for structures and noncovalent interactions (PBEh-3c) as well as our standard protocol for supramolecular thermochemistry and give predictions for chemical modifications to improve the binding strength.

  5. Durability of Structural Adhesively Bonded System.

    Science.gov (United States)

    1981-06-01

    boundary zone at a time interval of At = 60 minutes (i.e. non-linear with strain rate effect solution). Fig. 8.1 Sequence of environmental history cycle...8.2 Sequence of environmental history cycle Nos. 11 and Il, for investigation of hygrothermal behavior of CFRP and adhesiv specimens, representing the... environmental history on the ’eformational behavior of an FRP adherend as part of a bonded structured more information is needed on the HEC and CTE

  6. Fast and accurate predictions of covalent bonds in chemical space

    Science.gov (United States)

    Chang, K. Y. Samuel; Fias, Stijn; Ramakrishnan, Raghunathan; von Lilienfeld, O. Anatole

    2016-05-01

    We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (˜1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H 2+ . Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

  7. The Chemical Bond and Solid-state Physics

    Science.gov (United States)

    Phillips, James C.

    1970-01-01

    Proposes a new scale of ionicity, with which the ionic character of bonding in crystals can be predicted and measured. This new scale of ionicity has led to improved understanding of such crystalline properties as lattice structure, heats of formation, elastic constants, and nonlinear optical properties. Bibliography. (LC)

  8. Synthesis of chemically bonded graphene/carbon nanotube composites and their application in large volumetric capacitance supercapacitors.

    Science.gov (United States)

    Jung, Naeyoung; Kwon, Soongeun; Lee, Dongwook; Yoon, Dong-Myung; Park, Young Min; Benayad, Anass; Choi, Jae-Young; Park, Jong Se

    2013-12-17

    Chemically bonded graphene/carbon nanotube composites as flexible supercapacitor electrode materials are synthesized by amide bonding. Carbon nanotubes attached along the edges and onto the surface of graphene act as spacers to increase the electrolyte-accessible surface area. Our lamellar structure electrodes demonstrate the largest volumetric capacitance (165 F cm(-3) ) ever shown by carbon-based electrodes.

  9. The structure and chemical bonding in the N(2)-CuX and N(2)...XCu (X = F, Cl, Br) systems studied by means of the molecular orbital and Quantum Chemical Topology methods.

    Science.gov (United States)

    Kisowska, Karolina; Berski, Slawomir; Latajka, Zdzislaw

    2008-12-01

    Ab initio studies carried out at the MP2(full)/6-311+G(2df) and MP2(full)/aug-cc-pVTZ-PP computational levels reveals that dinitrogen (N(2)) and cuprous halides (CuX, X = F, Cl, Br) form three types of systems with the side-on and end-on coordination of N(2): N[triple bond]N-CuX (C(infinity v)), N(2)-CuX (C(2v)) stabilized by the donor-acceptor bonds and weak van der Waals complexes N(2)...XCu (C(2v)) with dominant dispersive forces. An electron density transfer between the N(2) and CuX depends on type of the N(2) coordination and a comparison of the NPA charges yields the [N[triple bond]N](delta+)-[CuX](delta-) and [N(2)](delta-)-[CuX](delta+) formula. According to the NBO analysis, the Cu-N coordinate bonds are governed by predominant LP(N2)-->sigma*(Cu-X) "2e-delocalization" in the most stable N[triple bond]N-CuX systems, meanwhile back donation LP(Cu)-->pi*(N-N) prevails in less stable N(2)-CuX molecules. A topological analysis of the electron density (AIM) presents single BCP between the Cu and N nuclei in the N[triple bond]N-CuX, two BCPs corresponding to two donor-acceptor Cu-N bonds in the N(2)-CuX and single BCP between electron density maximum of the N[triple bond]N bond and halogen nucleus in the van der Waals complexes N(2)...XCu. In all systems values of the Laplacian nabla(2)rho(r)(r(BCP)) are positive and they decrease following a trend of the complex stability i.e. N[triple bond]N-CuX (C(infinity v)) > N(2)-CuX (C(2v)) > N(2)...XCu (C(2v)). A topological analysis of the electron localization function (ELF) reveals strongly ionic bond in isolated CuF and a contribution of covalent character in the Cu-Cl and Cu-Br bonds. The donor-acceptor bonds Cu-N are characterized by bonding disynaptic basins V(Cu,N) with attractors localized at positions corresponding to slightly distorted lone pairs V(N) in isolated N(2). In the N[triple bond]N-CuX systems, there were no creation of any new bonding attractors in regions where classically the donor-acceptor bonds

  10. Structure and bonding of second-row hydrides

    OpenAIRE

    Blinder, S. M.

    2014-01-01

    The atomic orbitals, hybridization and chemical bonding of the most common hydrides of boron, carbon, nitrogen and oxygen are described. This can be very instructive for beginning students in chemistry and chemical physics.

  11. The role of radial nodes of atomic orbitals for chemical bonding and the periodic table.

    Science.gov (United States)

    Kaupp, Martin

    2007-01-15

    The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding. Copyright (c) 2006 Wiley Periodicals, Inc.

  12. Structural, spectroscopic, and multiconfigurational quantum chemical investigations of the electron-rich metal-metal triple-bonded Tc(2)X(4)(PMe(3))(4) (X = Cl, Br) complexes.

    Science.gov (United States)

    Poineau, Frederic; Forster, Paul M; Todorova, Tanya K; Gagliardi, Laura; Sattelberger, Alfred P; Czerwinski, Kenneth R

    2010-07-19

    The compounds Tc(2)Cl(4)(PMe(3))(4) and Tc(2)Br(4)(PMe(3))(4) were formed from the reaction between (n-Bu(4)N)(2)Tc(2)X(8) (X = Cl, Br) and trimethylphosphine. The Tc(II) dinuclear species were characterized by single-crystal XRD, UV-visible spectroscopy, and cyclic voltammetry techniques, and the results are compared to those obtained from density functional theory and multiconfigurational (CASSCF/CASPT2) quantum chemical studies. The compound Tc(2)Cl(4)(PMe(3))(4) crystallizes in the monoclinic space group C2/c [a = 17.9995(9) A, b = 9.1821(5) A, c = 17.0090(9) A, beta = 115.4530(10) degrees ] and is isostructural to M(2)Cl(4)(PMe(3))(4) (M = Re, Mo, W) and to Tc(2)Br(4)(PMe(3))(4). The metal-metal distance (2.1318(2) A) is similar to the one found in Tc(2)Br(4)(PMe(3))(4) (2.1316(5) A). The calculated molecular structures of the ground states are in excellent agreement with the structures determined experimentally. Calculations of effective bond orders for Tc(2)X(8)(2-) and Tc(2)X(4)(PMe(3))(4) (X = Cl, Br) indicate stronger pi bonds in the Tc(2)(4+) core than in Tc(2)(6+) core. The electronic spectra were recorded in benzene and show a series of low intensity bands in the range 10 000-26 000 cm(-1). Assignment of the bands as well as computing their excitation energies and intensities were performed at both TD-DFT and CASSCF/CASPT2 levels of theory. Calculations predict that the lowest energy band corresponds to the delta* --> sigma* transition, the difference between calculated and experimental values being 228 cm(-1) for X = Cl and 866 cm(-1) for X = Br. The next bands are attributed to delta* --> pi*, delta --> sigma*, and delta --> pi* transitions. The cyclic voltammograms exhibit two reversible waves and indicate that Tc(2)Br(4)(PMe(3))(4) exhibits more positive oxidation potentials than Tc(2)Cl(4)(PMe(3))(4.) This phenomenon is discussed and ascribed to stronger metal (d) to halide (d) back bonding in the bromo complex. Further analysis indicates that Tc

  13. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba{sub 4}CuGa{sub 5}Q{sub 12} (Q=S, Se)

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H. [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba{sub 4}CuGa{sub 5}S{sub 12} and Ba{sub 4}CuGa{sub 5}Se{sub 12} compounds were calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to calculate the electronic structures, Fermi surface, thermoelectric, chemical bonding and dispersion of optical constants of these compounds. By investigating the influence of replacing S by Se, it has been found that the charge density around ‘Ga’ is greater in Ba{sub 4}CuGa{sub 5}Se{sub 12} than Ba{sub 4}CuGa{sub 5}S{sub 12}. Fermi surface of Ba{sub 4}CuGa{sub 5}S{sub 12} consists of an electronic sheet only because there is no empty region while Ba{sub 4}CuGa{sub 5}Se{sub 12} contains both holes and electronic sheets because this compound contains both empty and shaded region. As we replace S by Se the heights of the peaks decreases as a results the reflectivity also decreases. It is noticed that the reflectivity is over 68% (60%) for Ba{sub 4}CuGa{sub 5}S{sub 12} (Ba{sub 4}CuGa{sub 5}Se{sub 12}) compounds within the energy range studied. This implies that the material will serve as a good reflector. By replacing S by Se the figure of merit values increases from 0.97 to 1.0, which shows the good thermoelectric behavior of both compounds. - Highlights: • DFT-FPLAPW method used for calculating the properties. • For predicting the chemical bonding the charge density behavior is studied in 2D. • The optical properties were also calculated and analyzed. • The Fermi surface is composed of two bands crossing along the EF level. • The thermoelectric properties have also been calculated.

  14. Vitrified chemically bonded phosphate ceramics for immobilization of radioisotopes

    Science.gov (United States)

    Wagh, Arun S.

    2016-04-05

    A method of immobilizing a radioisotope and vitrified chemically bonded phosphate ceramic (CBPC) articles formed by the method are described. The method comprises combining a radioisotope-containing material, MgO, a source of phosphate, and optionally, a reducing agent, in water at a temperature of less than 100.degree. C. to form a slurry; curing the slurry to form a solid intermediate CBPC article comprising the radioisotope therefrom; comminuting the intermediate CBPC article, mixing the comminuted material with glass frits, and heating the mixture at a temperature in the range of about 900 to about 1500.degree. C. to form a vitrified CBPC article comprising the radioisotope immobilized therein.

  15. Effects of chemical bonding on heat transport across interfaces.

    Science.gov (United States)

    Losego, Mark D; Grady, Martha E; Sottos, Nancy R; Cahill, David G; Braun, Paul V

    2012-04-22

    Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump-probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold-SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.

  16. Chemical bonding in TiSb(2) and VSb(2): a quantum chemical and experimental study.

    Science.gov (United States)

    Armbrüster, Marc; Schnelle, Walter; Schwarz, Ulrich; Grin, Yuri

    2007-08-06

    The chemical bonding in the isostructural intermetallic compounds TiSb2 and VSb2, crystallizing in the CuAl2 type, was investigated by means of quantum chemical calculations, particularly the electron localization function (ELF), as well as by Raman spectroscopy, Hall effect and conductivity measurements on oriented single crystals, and high-pressure X-ray powder diffraction. The homogeneity ranges of the compounds were determined by powder X-ray diffraction, WDXS, and DSC measurements. TiSb2 exhibits no significant homogeneity range, while VSb2 shows a small homogeneity range of approximately 0.3 at. %. According to the ELF calculations, the Sb atoms form dumbbells via a two-center two-electron bond, while the T atoms (T = Ti, V) build up chains along the crystallographic c-axis. Both building units are connected by covalent T-Sb-T three-center bonds, thus forming a three-dimensional network. The strength of the bonds involving Sb was determined by fitting a force constant model to the vibrational mode frequencies observed by polarized Raman measurements on oriented single crystals. The resulting bond order of the Sb2 dumbbells is 1, while the strength of the three-center bonds resembles a bond order of 1.5. The weak pressure dependence of the c/a ratio confirms the slightly different bonding picture in TiSb2 compared to that in CuAl2. Electrical transport measurements show the presence of free charge carriers, as well as a metal-like temperature dependence of the electrical resistivity.

  17. Synthesis, molecular structure, hydrogen-bonding, NBO and chemical reactivity analysis of a novel 1,9-bis(2-cyano-2-ethoxycarbonylvinyl)-5-(4-hydroxyphenyl)-dipyrromethane: a combined experimental and theoretical (DFT and QTAIM) approach.

    Science.gov (United States)

    Singh, R N; Kumar, Amit; Tiwari, R K; Rawat, Poonam

    2013-09-01

    The spectroscopic analysis of a newly synthesized 1,9-bis(2-cyano-2-ethoxycarbonylvinyl)-5-(4-hydroxyphenyl)-dipyrromethane (3) has been carried out using (1)H NMR, UV-Visible, FT-IR and Mass spectroscopic techniques. All the quantum chemical calculations have been carried out using DFT level of theory, B3LYP functional and 6-31G(d,p) as basis set. Thermodynamic parameters (H, G, S) of all the reactants and products have been used to determine the nature of the chemical reaction. The chemical shift of pyrrolic NH in (1)H NMR spectrum appears at 9.4 ppm due to intramolecular hydrogen bonding. TD-DFT calculation shows the nature of electronic transitions as π→π(*) within the molecule. A combined experimental and theoretical vibrational analysis designates the existence of H-bonding between pyrrole N-H as proton donor and nitrogen of cyanide as proton acceptor, therefore, lowering in stretching vibration of NH and CN. To investigate the strength and nature of H-bonding, topological parameters at bond critical points (BCPs) are analyzed by 'Quantum theory of Atoms in molecules' (QTAIMs). Natural bond orbitals (NBOs) analysis has been carried out to investigate the intramolecular conjugative and hyperconjugative interactions within molecule and their second order stabilization energy (E((2))). Global electrophilicity index (ω=4.528 eV) shows that title molecule (3) is a strong electrophile. The maximum values of local electrophilic reactivity descriptors (fk(+),sk(+),ωk(+)) at vinyl carbon (C6/C22) of (3) indicate that these sites are more prone to nucleophilic attacks. Copyright © 2013 Elsevier B.V. All rights reserved.

  18. Optimisation of the shear stress transfer in structural bonded assemblies using a curved bonded joint geometry

    OpenAIRE

    Chataigner, Sylvain; CARON, Jean François

    2011-01-01

    Structural adhesive bonding is coming into increasing use in civil engineering either for strengthening operations involving the adhesive bonding of external reinforcements or to replace traditional assembly techniques in new structures. However adhesive bonding induces stress concentrations at the edges of the joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the assembly. These studies are all, th...

  19. Recognizing molecular patterns by machine learning: an agnostic structural definition of the hydrogen bond

    CERN Document Server

    Gasparotto, Piero

    2014-01-01

    The concept of chemical bonding can ultimately be seen as a rationalization of the recurring structural patterns observed in molecules and solids. Chemical intuition is nothing but the ability to recognize and predict such patterns, and how they transform into one another. Here we discuss how to use a computer to identify atomic patterns automatically, so as to provide an algorithmic definition of a bond based solely on structural information. We concentrate in particular on hydrogen bonding -- a central concept to our understanding of the physical chemistry of water, biological systems and many technologically important materials. Since the hydrogen bond is a somewhat fuzzy entity that covers a broad range of energies and distances, many different criteria have been proposed and used over the years, based either on sophisticate electronic structure calculations followed by an energy decomposition analysis, or on somewhat arbitrary choices of a range of structural parameters that is deemed to correspond to a ...

  20. Adhesive bonding of composite aircraft structures: Challenges and recent developments

    Science.gov (United States)

    Pantelakis, Sp.; Tserpes, K. I.

    2014-01-01

    In this review paper, the challenges and some recent developments of adhesive bonding technology in composite aircraft structures are discussed. The durability of bonded joints is defined and presented for parameters that may influence bonding quality. Presented is also, a numerical design approach for composite joining profiles used to realize adhesive bonding. It is shown that environmental ageing and pre-bond contamination of bonding surfaces may degrade significantly fracture toughness of bonded joints. Moreover, it is obvious that additional research is needed in order to design joining profiles that will enable load transfer through shearing of the bondline. These findings, together with the limited capabilities of existing non-destructive testing techniques, can partially explain the confined use of adhesive bonding in primary composite aircraft structural parts.

  1. Studies on Hydrogen Bonding Network Structures of Konjac Glucomannan

    Institute of Scientific and Technical Information of China (English)

    PANG Jie; SUN Yu-Jing; YANG You-Hui; CHEN Yuan-Yuan; CHEN Yi-Qing; SUN Yuan-Ming

    2008-01-01

    In this paper, the hydrogen bonding network models of konjac glucomannan (KGM) are predicted in the approach of molecular dynamics (MD). These models have been proved by experiments whose results are consistent with those from simulation.The results show that the hydrogen bonding network structures of KGM are stable and the key linking points of hydrogen bonding network are at the O(6) and O(2) positions on KGM ring. Moreover, acety1 has significant influence on hydrogen bonding network and hydrogen bonding network structures are more stable after deacetylation.

  2. Chemical bonding and charge density distribution analysis of undoped and lanthanum doped barium titanate ceramics

    Indian Academy of Sciences (India)

    J MANGAIYARKKARASI; R SARAVANAN; MUKHLIS M ISMAIL

    2016-12-01

    A-site deficient, Lanthanum substituted Ba1−xLa2x/3TiO3 (x=0.000, 0.005, 0.015, 0.020 and 0.025) ceramics have been synthesized by chemical route. The effects of lanthanum dopant on the BaTiO3 lattice and the electron density distributions in the unit cell of the samples were investigated. Structural studies suggested the reduction in cell parameters and shrinkage in cell volume with the increase in lanthanum content. Chemical bonding and electron density distributions were examined through high resolution maximum entropy method (MEM). The mid bond electron density values revealed the enhancement of covalent nature between titanium and oxygen ions and predominant ionic nature between barium and oxygen ions. Average grain sizes were estimated for the undoped and doped samples. SEM investigations showed the existence of smaller grains with large voids in between them.

  3. Chemical bonding and aromaticity in trinuclear transition-metal halide clusters.

    Science.gov (United States)

    Weck, Philippe F; Sergeeva, Alina P; Kim, Eunja; Boldyrev, Alexander I; Czerwinski, Kenneth R

    2011-02-07

    Trinuclear transition-metal complexes such as Re(3)X(9) (X = Cl, Br, I), with their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I), isomorphous with their rhenium congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that only [Tc(3)X(9)](2-) clusters exhibit aromatic character, stemming from a d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept incorrectly predict the neutral Tc(3)X(9) clusters to be aromatic.

  4. Gap measurement and bond strength of five selected adhesive systems bonded to tooth structure.

    Science.gov (United States)

    Arbabzadeh, F; Gage, J P; Young, W G; Shahabi, S; Swenson, S M

    1998-06-01

    The ability of a restorative material to bond and seal the interface with tooth structure is perhaps the most significant factor in determining resistance to marginal caries. Thus, the quality and durability of marginal seal and bond strength are major considerations in the selection of restorative materials. The purpose of this study was to compare the bond strength and marginal discrepancies of five adhesive systems: All-Bond 2, Clearfil Liner Bond, KB 200, ProBond and AELITE Bond. Twenty-five buccal and 25 lingual cavities were prepared in 25 caries-free extracted molar teeth, giving 10 cavities for each of the 5 adhesive systems. All teeth were restored with the resin composite Pertac Hybrid, or PRISMA Total Performance Hybrid with their appropriate adhesive systems. After restoration, the teeth were thermocycled, were stained with a 1.5% aqueous solution of a procion dye (reactive orange 14) and sectioned coronally with a saw microtome. Three sections of 200 microns thickness were prepared from each restoration which were then examined microscopically to measure marginal gap widths using a confocal tandem microscope. Shear bond strength measurements were carried out on the dentine bond using a universal testing machine. The All-Bond 2 adhesive system was found to have higher shear bond strength and to have the least gap width at the cementodentinal margin.

  5. Tetrel Bonds in Infinite Molecular Chains by Electronic Structure Theory and Their Role for Crystal Stabilization.

    Science.gov (United States)

    George, Janine; Dronskowski, Richard

    2017-02-16

    Intermolecular bonds play a crucial role in the rational design of crystal structures, dubbed crystal engineering. The relatively new term tetrel bonds (TBs) describes a long-known type of such interactions presently in the focus of quantum chemical cluster calculations. Here, we energetically explore the strengths and cooperativity of these interactions in infinite chains, a possible arrangement of such tetrel bonds in extended crystals, by periodic density functional theory. In the chains, the TBs are amplified due to cooperativity by up to 60%. Moreover, we computationally take apart crystals stabilized by infinite tetrel-bonded chains and assess the importance of the TBs for the crystal stabilization. Tetrel bonds can amount to 70% of the overall interaction energy within some crystals, and they can also be energetically decisive for the taken crystal structure; their individual strengths also compete with the collective packing within the crystal structures.

  6. The nature of resonance-assisted hydrogen bonds: a quantum chemical topology perspective.

    Science.gov (United States)

    Guevara-Vela, José Manuel; Romero-Montalvo, Eduardo; Costales, Aurora; Pendás, Ángel Martín; Rocha-Rinza, Tomás

    2016-10-14

    Resonance Assisted Hydrogen Bonds (RAHBs) are particularly strong H-Bonds (HBs) which are relevant in several fields of chemistry. The traditional explanation for the occurrence of these HBs is built on mesomeric structures evocative of electron delocalisation in the system. Nonetheless, there are several theoretical studies which have found no evidence of such electron delocalisation. We considered the origin of RAHBs by employing Quantum Chemical Topology tools, more specifically, the Quantum Theory of Atoms in Molecules (QTAIM) and the Interacting Quantum Atoms energy partition. Our results indicate that the π-conjugated bonds allow for a larger adjustment of electron density throughout the H-bonded system as compared with non-conjugated carbonyl molecules. This rearrangement of charge distribution is a response to the electric field due to the H atom involved in the hydrogen bonding of the considered compounds. As opposed to the usual description of RAHB interactions, these HBs lead to a larger electron localisation in the system, and concomitantly to larger QTAIM charges which in turn lead to stronger electrostatic, polarization and charge transfer components of the interaction. Overall, the results presented here offer a new perspective on the cause of strengthening of these important interactions.

  7. Electronic properties and chemical bonding in quaternary arsenide oxides LaZnAsO and YZnAsO

    Energy Technology Data Exchange (ETDEWEB)

    Bannikov, V.V.; Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Pervomaiskaya, 91, 620041, Ekaterinburg (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Pervomaiskaya, 91, 620041, Ekaterinburg (Russian Federation)

    2009-07-15

    First principles FLAPW-GGA band structure calculations are employed to obtain the structural, electronic properties and chemical bonding picture for two related phases, namely, quaternary arsenide oxides LaZnAsO and YZnAsO. These compounds are found to be direct-transition type semiconductors with the GGA gaps of about 0.65-1.30 eV. The peculiarities of chemical bonding in these phases are investigated and discussed in comparison with quaternary arsenide oxide LaFeAsO-a basic phase for the newly discovered 26-55 K superconductors.

  8. Studying Chemical Reactions, One Bond at a Time, with Single Molecule AFM Techniques

    Science.gov (United States)

    Fernandez, Julio M.

    2008-03-01

    atomic force microscopy (AFM) techniques, as shown here, can probe dynamic rearrangements within an enzyme's active site which cannot be resolved with any other current structural biological technique. Furthermore, our work at the single bond level directly demonstrates that thiol/disulfide exchange in proteins is a force-dependent chemical reaction. Our findings suggest that mechanical force plays a role in disulfide reduction in vivo, a property which has never been explored by traditional biochemistry. 1.-Wiita, A.P., Ainavarapu, S.R.K., Huang, H.H. and Julio M. Fernandez (2006) Force-dependent chemical kinetics of disulfide bond reduction observed with single molecule techniques. Proc Natl Acad Sci U S A. 103(19):7222-7 2.-Wiita, A.P., Perez-Jimenez, R., Walther, K.A., Gräter, F. Berne, B.J., Holmgren, A., Sanchez-Ruiz, J.M., and Fernandez, J.M. (2007) Probing the chemistry of thioredoxin catalysis with force. Nature, 450:124-7.

  9. Effect of raw material ratios on the compressive strength of magnesium potassium phosphate chemically bonded ceramics.

    Science.gov (United States)

    Wang, Ai-juan; Yuan, Zhi-long; Zhang, Jiao; Liu, Lin-tao; Li, Jun-ming; Liu, Zheng

    2013-12-01

    The compressive strength of magnesium potassium phosphate chemically bonded ceramics is important in biomedical field. In this work, the compressive strength of magnesium potassium phosphate chemically bonded ceramics was investigated with different liquid-to-solid and MgO-to-KH2PO4 ratios. X-ray diffractometer was applied to characterize its phase composition. The microstructure was imaged using a scanning electron microscope. The results showed that the compressive strength of the chemically bonded ceramics increased with the decrease of liquid-to-solid ratio due to the change of the packing density and the crystallinity of hydrated product. However, with the increase of MgO-to-KH2PO4 weight ratio, its compressive strength increased firstly and then decreased. The low compressive strength in lower MgO-to-KH2PO4 ratio might be explained by the existence of the weak phase KH2PO4. However, the low value of compressive strength with the higher MgO-to-KH2PO4 ratio might be caused by lack of the joined phase in the hydrated product. Besides, it has been found that the microstructures were different in these two cases by the scanning electron microscope. Colloidal structure appeared for the samples with lower liquid-to-solid and higher MgO-to-KH2PO4 ratios possibly because of the existence of amorphous hydrated products. The optimization of both liquid-to-solid and MgO-to-KH2PO4 ratios was important to improve the compressive strength of magnesium potassium phosphate chemically bonded ceramics.

  10. Hybrid density functional study on lattice vibration, thermodynamic properties, and chemical bonding of plutonium monocarbide

    Science.gov (United States)

    Rong, Yang; Bin, Tang; Tao, Gao; BingYun, Ao

    2016-06-01

    Hybrid density functional theory is employed to systematically investigate the structural, magnetic, vibrational, thermodynamic properties of plutonium monocarbide (PuC and PuC0.75). For comparison, the results obtained by DFT, DFT + U are also given. For PuC and PuC0.75, Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic (AFM) structure. The calculated phonon spectra suggest that PuC and PuC0.75 are dynamically stable. Values of the Helmholtz free energy ΔF, internal energy ΔE, entropy S, and constant-volume specific heat C v of PuC and PuC0.75 are given. The results are in good agreement with available experimental or theoretical data. As for the chemical bonding nature, the difference charge densities, the partial densities of states and the Bader charge analysis suggest that the Pu-C bonds of PuC and PuC0.75 have a mixture of covalent character and ionic character. The effect of carbon vacancy on the chemical bonding is also discussed in detail. We expect that our study can provide some useful reference for further experimental research on the phonon density of states, thermodynamic properties of the plutonium monocarbide. Project supported by the National Natural Science Foundation of China (Grant Nos. 21371160 and 21401173).

  11. Concept of chemical bond and aromaticity based on quantum information theory

    CERN Document Server

    Szilvási, T; Legeza, Ö

    2015-01-01

    Quantum information theory (QIT) emerged in physics as standard technique to extract relevant information from quantum systems. It has already contributed to the development of novel fields like quantum computing, quantum cryptography, and quantum complexity. This arises the question what information is stored according to QIT in molecules which are inherently quantum systems as well. Rigorous analysis of the central quantities of QIT on systematic series of molecules offered the introduction of the concept of chemical bond and aromaticity directly from physical principles and notions. We identify covalent bond, donor-acceptor dative bond, multiple bond, charge-shift bond, and aromaticity indicating unified picture of fundamental chemical models from ab initio.

  12. Structures, energies and bonding in neutral and charged Li microclusters.

    Science.gov (United States)

    Yepes, Diana; Kirk, Steven Robert; Jenkins, Samantha; Restrepo, Albeiro

    2012-09-01

    Structural and chemical properties of charged and neutral Lithium microclusters are investigated for [Formula: see text]. A total of 18 quantum conformational spaces are randomly walked to produce candidate structures for local minima. Very rich potential energy surfaces are produced, with the largest structural complexity predicted for anionic clusters. Analysis of the electron charge distributions using the quantum theory of atoms in molecules (QTAIM) predicts major stabilizing roles of Non-nuclear attractors (NNAs) via NNA···Li interactions with virtually no direct Li···Li interactions, except in the least stable configurations. A transition in behavior for clusters containing more than seven nuclei is observed by using the recently introduced quantum topology to determine in a quantum mechanically consistent fashion the number of spatial dimensions each cluster has. We experiment with a novel scheme for extracting persistent structural motifs with increase in cluster size. The new structural motifs correlate well with the energetic stability, particularly in highlighting the least stable structures. Quantifying the degree of covalent character in Lithium bonding independently agrees with the observation in the transition in cluster behavior for lithium clusters containing more than seven nuclei. Good correlation with available experimental data is obtained for all properties reported in this work.

  13. LETTER TO THE EDITOR: Electronic structure and bonding properties in layered ternary carbide Ti3SiC2

    Science.gov (United States)

    Zhou, Yanchun; Sun, Zhimei

    2000-07-01

    Ab initio calculations based on the density-functional pseudopotential approach have been used to study the electronic structure and chemical bonding in layered machinable Ti3SiC2 ceramic. The calculations reveal that all three types of bonding - metallic, covalent and ionic - contribute to the bonding in Ti3SiC2. The high electric conductivity is attributed to the metallic bonding parallel to the basal plane and the high modulus and high melting point are attributed to the strong Ti-C-Ti-C-Ti covalent bond chains in the structure.

  14. Mean bond-length variation in crystal structures: a bond-valence approach.

    Science.gov (United States)

    Bosi, Ferdinando

    2014-08-01

    The distortion theorem of the bond-valence theory predicts that the mean bond length 〈D〉 increases with increasing deviation of the individual bond lengths from their mean value according to the equation 〈D〉 = (D' + ΔD), where D' is the length found in a polyhedron having equivalent bonds and ΔD is the bond distortion. For a given atom, D' is expected to be similar from one structure to another, whereas 〈D〉 should vary as a function of ΔD. However, in several crystal structures 〈D〉 significantly varies without any relevant contribution from ΔD. In accordance with bond-valence theory, 〈D〉 variation is described here by a new equation: 〈D〉 = (DRU + ΔDtop + ΔDiso + ΔDaniso + ΔDelec), where DRU is a constant related to the type of cation and coordination environment, ΔDtop is the topological distortion related to the way the atoms are linked, ΔDiso is an isotropic effect of compression (or stretching) in the bonds produced by steric strain and represents the same increase (or decrease) in all the bond lengths in the coordination sphere, ΔDaniso is the distortion produced by compression and stretching of bonds in the same coordination sphere, ΔDelec is the distortion produced by electronic effects. If present, ΔDelec can be combined with ΔDaniso because they lead to the same kind of distortions in line with the distortion theorem. Each D-index, in the new equation, corresponds to an algebraic expression containing experimental and theoretical bond valences. On the basis of this study, the ΔD index defined in bond valence theory is a result of both the bond topology and the distortion theorem (ΔD = ΔDtop + ΔDaniso + ΔDelec), and D' is a result of the compression, or stretching, of bonds (D' = DRU + ΔDiso). The deficiencies present in the bond-valence theory in explaining mean bond-length variations can therefore be overcome, and the observed variations of 〈D〉 in crystal structures can be

  15. Laser Surface Preparation and Bonding of Aerospace Structural Composites

    Science.gov (United States)

    Belcher, M. A.; Wohl, C. J.; Hopkins, J. W.; Connell, J. W.

    2010-01-01

    Adhesive bonds are critical to the integrity of built-up structures. Disbonds can often be detected but the strength of adhesion between surfaces in contact is not obtainable without destructive testing. Typically the number one problem in a bonded structure is surface contamination, and by extension, surface preparation. Standard surface preparation techniques, including grit blasting, manual abrasion, and peel ply, are not ideal because of variations in their application. Etching of carbon fiber reinforced plastic (CFRP) panels using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser appears to be a highly precise and promising way to both clean a composite surface prior to bonding and provide a bond-promoting patterned surface akin to peel ply without the inherent drawbacks from the same (i.e., debris and curvature). CFRP surfaces prepared using laser patterns conducive to adhesive bonding were compared to typical prebonding surface treatments through optical microscopy, contact angle goniometry, and post-bonding mechanical testing.

  16. Method of waste stabilization with dewatered chemically bonded phosphate ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Wagh, Arun; Maloney, Martin D.

    2010-06-29

    A method of stabilizing a waste in a chemically bonded phosphate ceramic (CBPC). The method consists of preparing a slurry including the waste, water, an oxide binder, and a phosphate binder. The slurry is then allowed to cure to a solid, hydrated CBPC matrix. Next, bound water within the solid, hydrated CBPC matrix is removed. Typically, the bound water is removed by applying heat to the cured CBPC matrix. Preferably, the quantity of heat applied to the cured CBPC matrix is sufficient to drive off water bound within the hydrated CBPC matrix, but not to volatalize other non-water components of the matrix, such as metals and radioactive components. Typically, a temperature range of between 100.degree. C.-200.degree. C. will be sufficient. In another embodiment of the invention wherein the waste and water have been mixed prior to the preparation of the slurry, a select amount of water may be evaporated from the waste and water mixture prior to preparation of the slurry. Another aspect of the invention is a direct anyhydrous CBPC fabrication method wherein water is removed from the slurry by heating and mixing the slurry while allowing the slurry to cure. Additional aspects of the invention are ceramic matrix waste forms prepared by the methods disclosed above.

  17. Method of waste stabilization with dewatered chemically bonded phosphate ceramics

    Science.gov (United States)

    Wagh, Arun; Maloney, Martin D.

    2010-06-29

    A method of stabilizing a waste in a chemically bonded phosphate ceramic (CBPC). The method consists of preparing a slurry including the waste, water, an oxide binder, and a phosphate binder. The slurry is then allowed to cure to a solid, hydrated CBPC matrix. Next, bound water within the solid, hydrated CBPC matrix is removed. Typically, the bound water is removed by applying heat to the cured CBPC matrix. Preferably, the quantity of heat applied to the cured CBPC matrix is sufficient to drive off water bound within the hydrated CBPC matrix, but not to volatalize other non-water components of the matrix, such as metals and radioactive components. Typically, a temperature range of between 100.degree. C.-200.degree. C. will be sufficient. In another embodiment of the invention wherein the waste and water have been mixed prior to the preparation of the slurry, a select amount of water may be evaporated from the waste and water mixture prior to preparation of the slurry. Another aspect of the invention is a direct anyhydrous CBPC fabrication method wherein water is removed from the slurry by heating and mixing the slurry while allowing the slurry to cure. Additional aspects of the invention are ceramic matrix waste forms prepared by the methods disclosed above.

  18. First principles study of the alloying effect on chemical bonding characteristics of helium in La-Ni-M tritides

    Energy Technology Data Exchange (ETDEWEB)

    Hu, C.H. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Zhang, R.J. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Shi, L.Q. [Applied Ion Bean Physics Laboratory, Fudan University, Shanghai 200433 (China); Chen, D.M. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Wang, Y.M. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China)]. E-mail: ymwang@imr.ac.cn; Yang, K. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China)

    2005-11-15

    The alloying effect on the electronic structure of La-Ni-M tritides is investigated using the first principles discrete variational X{alpha}(DV-X{alpha}) method. The calculated results show that the covalent interaction between atoms will play a much more important role in studying the alloying effect on chemical bonding characteristics in La-Ni-M tritides than ionic interaction. It is also found that in La-Ni-M tritides helium forms stronger covalent bonds with the weaker hydride forming elements than La. By analyzing the relation between the binding energy difference and bond order, our study indicates that after some alloying elements substituting for Ni locating in 3g site in tritides, the helium retention capability becomes stronger, changes as the following sequence: Al > Cr > Mn > Fe > Co > Ni, and is also very distinct for Cu although the chemical bonding between Cu atom and Ni atom is degraded drastically.

  19. Recognizing molecular patterns by machine learning: An agnostic structural definition of the hydrogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Gasparotto, Piero; Ceriotti, Michele, E-mail: michele.ceriotti@epfl.ch [Laboratory of Computational Science and Modeling, and National Center for Computational Design and Discovery of Novel Materials MARVEL, IMX, École Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

    2014-11-07

    The concept of chemical bonding can ultimately be seen as a rationalization of the recurring structural patterns observed in molecules and solids. Chemical intuition is nothing but the ability to recognize and predict such patterns, and how they transform into one another. Here, we discuss how to use a computer to identify atomic patterns automatically, so as to provide an algorithmic definition of a bond based solely on structural information. We concentrate in particular on hydrogen bonding – a central concept to our understanding of the physical chemistry of water, biological systems, and many technologically important materials. Since the hydrogen bond is a somewhat fuzzy entity that covers a broad range of energies and distances, many different criteria have been proposed and used over the years, based either on sophisticate electronic structure calculations followed by an energy decomposition analysis, or on somewhat arbitrary choices of a range of structural parameters that is deemed to correspond to a hydrogen-bonded configuration. We introduce here a definition that is univocal, unbiased, and adaptive, based on our machine-learning analysis of an atomistic simulation. The strategy we propose could be easily adapted to similar scenarios, where one has to recognize or classify structural patterns in a material or chemical compound.

  20. Hydrogen bonding and multiphonon structure in copper pyrazine coordination polymers.

    Science.gov (United States)

    Brown, S; Cao, J; Musfeldt, J L; Conner, M M; McConnell, A C; Southerland, H I; Manson, J L; Schlueter, J A; Phillips, M D; Turnbull, M M; Landee, C P

    2007-10-15

    We report a systematic investigation of the temperature-dependent infrared vibrational spectra of a family of chemically related coordination polymer magnets based upon bridging bifluoride (HF(2)-) and terminal fluoride (F-) ligands in copper pyrazine complexes including Cu(HF(2))(pyz)(2)BF(4), Cu(HF(2))(pyz)(2)ClO(4), and CuF(2)(H(2)O)(2)(pyz). We compare our results with several one- and two-dimensional prototype materials including Cu(pyz)(NO(3))(2) and Cu(pyz)(2)(ClO(4))(2). Unusual low-temperature hydrogen bonding, local structural transitions associated with stronger low-temperature hydrogen bonding, and striking multiphonon effects that derive from coupling of an infrared-active fundamental with strong Raman-active modes of the pyrazine building-block molecule are observed. On the basis of the spectroscopic evidence, these interactions are ubiquitous to this family of coordination polymers and may work to stabilize long-range magnetic ordering at low temperature. Similar interactions are likely to be present in other molecule-based magnets.

  1. LOBSTER: A tool to extract chemical bonding from plane-wave based DFT.

    Science.gov (United States)

    Maintz, Stefan; Deringer, Volker L; Tchougréeff, Andrei L; Dronskowski, Richard

    2016-04-30

    The computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) enables chemical-bonding analysis based on periodic plane-wave (PAW) density-functional theory (DFT) output and is applicable to a wide range of first-principles simulations in solid-state and materials chemistry. LOBSTER incorporates analytic projection routines described previously in this very journal [J. Comput. Chem. 2013, 34, 2557] and offers improved functionality. It calculates, among others, atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the recently introduced bond-weighted distribution function (BWDF). The software is offered free-of-charge for non-commercial research. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

  2. Molecular structure and intramolecular hydrogen bonding in 2-hydroxybenzophenones: A theoretical study

    Indian Academy of Sciences (India)

    Mansoureh Zahedi-Tabrizi; Sayyed Faramarz Tayyari; Farideh Badalkhani-Khamseh; Reihaneh Ghomi; Fatemeh Afshar-Qahremani

    2014-07-01

    The intramolecular hydrogen bonding (IHB) in a series of 3-, 4- and 5-substituted 2-hydroxybenzophenone (HBP) is studied using density functional theory calculations. All calculations are performed at the B3LYP level, using 6-311++G∗∗ basis set. To understand the substitution effects on the nature of IHB and the electronic structure of the chelated ring system, the vibrational frequencies, 1H chemical shift, topological parameters, natural bond orders and natural charges over atoms involved in the chelated ring of HBP and its derivatives were calculated. TheWiberg bond indices and the natural charges over atoms involved in the chelated ring have been computed using the natural bond orbital (NBO) analysis. The computations were further complemented with an atoms-in-molecules (AIM) topological analysis to characterize the nature of the IHB in the considered molecules. Several correlations between geometrical parameters, 1H NMR chemical shift and topological parameters with the IHB strength are obtained.

  3. Intermolecular atom-atom bonds in crystals - a chemical perspective.

    Science.gov (United States)

    Thakur, Tejender S; Dubey, Ritesh; Desiraju, Gautam R

    2015-03-01

    Short atom-atom distances between molecules are almost always indicative of specific intermolecular bonding. These distances may be used to assess the significance of all hydrogen bonds, including the C-H⋯O and even weaker C-H⋯F varieties.

  4. An alternative empirical model for the relationship between the bond valence and the thermal expansion rate of chemical bonds.

    Science.gov (United States)

    Sidey, Vasyl

    2015-08-01

    The relationship between the bond valence s and the thermal expansion rate of chemical bonds (dr/dT) has been closely approximated by using the alternative three-parameter empirical model (dr/dT) = (u + vs)(-1/w), where u, v and w are the refinable parameters. Unlike the s-(dr/dT) model developed by Brown et al. [(1997), Acta Cryst. B53, 750-761], this alternative model can be optimized for particular s-(dr/dT) datasets in the least-squares refinement procedure. For routine calculations of the thermal expansion rates of chemical bonds, the alternative model with the parameters u = -63.9, v = 2581.0 and w = 0.647 can be recommended.

  5. Trigermanides AEGe{sub 3} (AE = Ca, Sr, Ba). Chemical bonding and superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Castillo, Rodrigo; Schnelle, Walter; Baranov, Alexey I.; Burkhardt, Ulrich; Bobnar, Matej; Cardoso-Gil, Raul; Schwarz, Ulrich; Grin, Yuri [Max-Planck-Institut fuer Chemische Physik Fester Stoffe, Dresden (Germany)

    2016-08-01

    The crystal structures of the trigermanides AEGe{sub 3}(tI32) (AE = Ca, Sr, Ba; space group I4/mmm, for SrGe{sub 3}: a = 7.7873(1), c = 12.0622(3) Aa) comprise Ge{sub 2} dumbbells forming layered Ge substructures which enclose embedded AE atoms. The chemical bonding analysis by application of the electron localizability approach reveals a substantial charge transfer from the AE atoms to the germanium substructure. The bonding within the dumbbells is of the covalent two-center type. A detailed analysis of SrGe{sub 3} reveals that the interaction on the bond-opposite side of the Ge{sub 2} groups is not lone pair-like - as it would be expected from the Zintl-like interpretation of the crystal structure with anionic Ge layers separated by alkaline-earth cations - but multi-center strongly polar between the Ge{sub 2} dumbbells and the adjacent metal atoms. Similar atomic interactions are present in CaGe{sub 3} and BaGe{sub 3}. The variation of the alkaline-earth metal has a merely insignificant influence on the superconducting transition temperatures in the s,p-electron compounds AEGe{sub 3}.

  6. Structure validation in chemical crystallography.

    Science.gov (United States)

    Spek, Anthony L

    2009-02-01

    Automated structure validation was introduced in chemical crystallography about 12 years ago as a tool to assist practitioners with the exponential growth in crystal structure analyses. Validation has since evolved into an easy-to-use checkCIF/PLATON web-based IUCr service. The result of a crystal structure determination has to be supplied as a CIF-formatted computer-readable file. The checking software tests the data in the CIF for completeness, quality and consistency. In addition, the reported structure is checked for incomplete analysis, errors in the analysis and relevant issues to be verified. A validation report is generated in the form of a list of ALERTS on the issues to be corrected, checked or commented on. Structure validation has largely eliminated obvious problems with structure reports published in IUCr journals, such as refinement in a space group of too low symmetry. This paper reports on the current status of structure validation and possible future extensions.

  7. A constitutive model for bonded geomaterials subject to mechanical and/or chemical degradation

    Science.gov (United States)

    Nova, R.; Castellanza, R.; Tamagnini, C.

    2003-08-01

    The mechanical behaviour of bonded geomaterials is described by means of an elastoplastic strain-hardening model. The internal variables, taking into account the history of the material, depend on the plastic strains experienced and on a conveniently defined scalar measure of damage induced by weathering and/or chemical degradation.For the sake of simplicity, it is assumed that only internal variables are affected by mechanical and chemical history of the material. Despite this simplifying assumption, it can be shown that many interesting phenomena exhibited by weathered bonded geomaterials can be successfully described. For instance, (i) the transition from brittle to ductile behaviour with increasing pressure of a calcarenite with collapsing internal structure, (ii) the complex behaviour of chalk and other calcareous materials in oedometric tests, (iii) the chemically induced variation of the stress and strain state of such kind of materials, are all phenomena that can be qualitatively reproduced. Several comparisons with experimental data show that the model can capture the observed behaviour also quantitatively.

  8. Unconventional N-H…N Hydrogen Bonds Involving Proline Backbone Nitrogen in Protein Structures.

    Science.gov (United States)

    Deepak, R N V Krishna; Sankararamakrishnan, Ramasubbu

    2016-05-10

    Contrary to DNA double-helical structures, hydrogen bonds (H-bonds) involving nitrogen as the acceptor are not common in protein structures. We systematically searched N-H…N H-bonds in two different sets of protein structures. Data set I consists of neutron diffraction and ultrahigh-resolution x-ray structures (0.9 Å resolution or better) and the hydrogen atom positions in these structures were determined experimentally. Data set II contains structures determined using x-ray diffraction (resolution ≤ 1.8 Å) and the positions of hydrogen atoms were generated using a computational method. We identified 114 and 14,347 potential N-H…N H-bonds from these two data sets, respectively, and 56-66% of these were of the Ni+1-Hi+1…Ni type, with Ni being the proline backbone nitrogen. To further understand the nature of such unusual contacts, we performed quantum chemical calculations on the model compound N-acetyl-L-proline-N-methylamide (Ace-Pro-NMe) with coordinates taken from the experimentally determined structures. A potential energy profile generated by varying the ψ dihedral angle in Ace-Pro-NMe indicates that the conformation with the N-H…N H-bond is the most stable. An analysis of H-bond-forming proline residues reveals that more than 30% of the proline carbonyl groups are also involved in n → π(∗) interactions with the carbonyl carbon of the preceding residue. Natural bond orbital analyses demonstrate that the strength of N-H…N H-bonds is less than half of that observed for a conventional H-bond. This study clearly establishes the H-bonding capability of proline nitrogen and its prevalence in protein structures. We found many proteins with multiple instances of H-bond-forming prolines. With more than 15% of all proline residues participating in N-H…N H-bonds, we suggest a new, to our knowledge, structural role for proline in providing stability to loops and capping regions of secondary structures in proteins.

  9. Glutamic Acid Selective Chemical Cleavage of Peptide Bonds.

    Science.gov (United States)

    Nalbone, Joseph M; Lahankar, Neelam; Buissereth, Lyssa; Raj, Monika

    2016-03-04

    Site-specific hydrolysis of peptide bonds at glutamic acid under neutral aqueous conditions is reported. The method relies on the activation of the backbone amide chain at glutamic acid by the formation of a pyroglutamyl (pGlu) imide moiety. This activation increases the susceptibility of a peptide bond toward hydrolysis. The method is highly specific and demonstrates broad substrate scope including cleavage of various bioactive peptides with unnatural amino acid residues, which are unsuitable substrates for enzymatic hydrolysis.

  10. The Term Structure of Credit Spreads on Euro Corporate Bonds

    NARCIS (Netherlands)

    van Landschoot, A.

    2003-01-01

    Although there is a broad literature on structural credit risk models, there has been little empirical testing of these models.In this paper we examine the term structure of credit spreads on euro corporate bonds and the empirical validation of structural credit risk models.The latter provide a fram

  11. The use of dialogic electronic journal writing to develop students' understanding of chemical bonding

    Science.gov (United States)

    English, Sarah Collard

    The intent of this study is to examine how the implementation of a dialogic electronic journal writing environment continues the development of students' understanding of chemistry, specifically chemical bonding, through written communication between the individual students and their chemistry teacher. This study is framed within a constructivist theoretical context where students' understanding is constructed through written discussions with the educator, the students' interaction with the classroom environment, and his/her interaction with the computer environment. The research design of collective case study was employed to allow multiple perspectives and processes conveyed by the participants to be examined in the context in which they occurred while considering multiple sources of information. Data sources included electronic journal entries, classroom artifacts, and semi-structured interviews. Data were analyzed using the constant comparative method, which involved coding, categorizing, and interpreting for patterns and relationships. Four cases were reported in detail. This study found that the dialogic electronic journal-writing environment was an effective venue in revealing previously undiscovered students' alternative conceptions of chemical bonding. Opportunities to actively confront and reconcile such conceptions were afforded through educator/student dialogic written interaction. The dialogic electronic journal-writing environment was also critical in the identification of gaps in students' conceptual understanding linked to improper sequencing of chemistry content. This study also found that the on-line environment provided the educator the opportunity to scaffold chemical bonding concepts to meet the needs of the students involved in the study. This study concluded that the dialogic electronic journal-writing environment positively contributed to the development of student understanding. These findings may have practical implications for teachers in

  12. Interface Fracture in Adhesively Bonded Shell Structures

    DEFF Research Database (Denmark)

    Jensen, Henrik Myhre

    2007-01-01

    Two methods for the prediction of crack propagation through the interface of adhesively bonded shells are discussed. One is based on a fracture mechanics approach; the other is based on a cohesive zone approach. Attention is focussed on predicting the shape of the crack front and the critical...... stress required to propagate the crack under quasi-static conditions. The fracture mechanical model is theoretically sound and it is accurate and numerically stable. The cohesive zone model has some advantages over the fracture mechanics based model. It is easier to generalise the cohesive zone model...... to take into account effects such as plastic deformation in the adhering shells, and to take into account effects of large local curvatures of the interface crack front. The comparison shows a convergence of the results based on the cohesive zone model towards the results based on a fracture mechanics...

  13. Bonding, structure and solid-state chemistry

    CERN Document Server

    Ladd, Mark

    2016-01-01

    This book is aimed at undergraduate students in both chemistry and those degree subjects in which chemistry forms a significant part. It does not reflect any particular academic year, and so finds a place during the normal span of degree studies in the physical sciences. An A-level standard in science and mathematics is presumed; additional mathematical treatments are discussed in Appendices. An introductory first chapter leads into the main subject matter, which is treated through four chapters in terms of the principle bonding forces of cohesion in the solid state; a further chapter discusses nanosize materials. Important applications of the study topics are interspersed at appropriate points within the text. Each chapter is provided with a set of problems of varying degrees of difficulty, so as to assist the reader in gaining a facility with the subject matter and its applications. The problems are supplemented by detailed tutorial solutions, some of which present additional relevant material that indicate...

  14. Innovations in bonding to zirconia-based materials. Part II: focusing on chemical interactions

    NARCIS (Netherlands)

    M.N. Aboushelib; H. Mirmohamadi; J.P. Matinlinna; E. Kukk; H.F. Ounsi; Z. Salameh

    2009-01-01

    Objectives: The zirconia-resin bond strength was enhanced using novel engineered zirconia primers in combination with selective infiltration etching as a surface pre-treatment. The aim of this study was to evaluate the effect of artificial aging on the chemical stability of the established bond and

  15. Laser Surface Preparation for Adhesive Bonding of Aerospace Structural Composites

    Science.gov (United States)

    Belcher, M. A.; Wohl, C. J.; Hopkins, J. W.; Connell, J. W.

    2010-01-01

    Adhesive bonds are critical to the integrity of built-up structures. Disbonds can often be detected but the strength of adhesion between surfaces in contact is not obtainable without destructive testing. Typically the number one problem in a bonded structure is surface contamination, and by extension, surface preparation. Standard surface preparation techniques, including grit blasting, manual abrasion, and peel ply, are not ideal because of variations in their application. Etching of carbon fiber reinforced plastic (CFRP) panels using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser appears to be a highly precise and promising way to both clean a composite surface prior to bonding and provide a bond-promoting patterned surface akin to peel ply without the inherent drawbacks from the same (i.e., debris and curvature). CFRP surfaces prepared using laser patterns conducive to adhesive bonding were compared to typical pre-bonding surface treatments through optical microscopy, contact angle goniometry, and post-bonding mechanical testing.

  16. EVALUATION OF CHEMICALLY BONDED PHOSPHATE CERAMICS FOR MERCURY STABILIZATION OF A MIXED SYNTHETIC WASTE

    Science.gov (United States)

    This experimental study was conducted to evaluate the stabilization and encapsulation technique developed by Argonne National Laboratory, called the Chemically Bonded Phosphate Ceramics technology for Hg- and HgCl2-contaminated synthetic waste materials. Leachability ...

  17. Adhesion to tooth structure mediated by contemporary bonding systems.

    Science.gov (United States)

    Stangel, Ivan; Ellis, Thomas H; Sacher, Edward

    2007-07-01

    Given the enormity of the field of adhesion and the number of commercial products available, the discipline of modern adhesive dentistry can be daunting with respect to materials and techniques. This article organizes contemporary bonding practice and materials around an understanding of the fundamentals of adhesion to tooth structure. In providing this context, adhesive development, bonding systems, and their appropriate use are better understood. The end result is the better practice of adhesive dentistry.

  18. sup 1 H NMR studies of a biosynthetic lacto-ganglio hybrid glycosphingolipid: Confirmation of structure, interpretation of anomalous' chemical shifts, and evidence for interresidue amide-amide hydrogen bonding

    Energy Technology Data Exchange (ETDEWEB)

    Levery, S.B.; Harris, D.D.; Hakomori, Senitiroh (Univ. of Washington, Seattle (United States)); Holmes, E.H. (Pacific Northwest Research Foundation, Seattle, WA (United States))

    1992-02-04

    Glycosphinogolipids bearing GlcNAc{beta}1 {yields} 3 and GalNAc{beta}1 {yields} 4 linked to {beta}-Gal of lactosylceramide first isolated from a murine myelogenous leukemia cell line have since been found as normal components of mullet roe and English sole liver. In order to clarify the biosynthetic pathways responsible for its occurrence both as a product of normal tissues and as a possible mammalian cancer-associated antigen, the lacto-ganglio hybrid core structure LcGg{sub 4}Cer was synthesized from Lc{sub 3}Cer using a GalNAc{beta}1 {yields} 4 transferase preparation from English sole liver. A preliminary characterization of the enzyme, which may be identical to the GalNAc T-1 responsible for synthesis of GM{sub 2} ganglioside, is presented. The enzymatically synthesized product was analyzed by 1- and 2-D {sup 1}H NMR spectroscopy, confirming its primary structure as GalNAc{beta}1 {yields} 4-(GlcNAc{beta}1 {yields} 3)Gal{beta}1 {yields} 4Glc{beta}1 {yields} 1Cer. An approximate three-dimensional structure for LcGg{sub 4}Cer is proposed, consistent with all data obtained, which should be useful in discussing the results of {sup 1}H NMR analysis of compounds containing this core tetrasaccharide. The structure is characterized by an unusual arrangement of terminal N-acetylhexosamine residues, resulting in a {pi}-H hydrogen-bonding interaction between their acetamido groups.

  19. Quantum-Mechanical Definition of Atoms and Chemical Bonds in Molecules

    Science.gov (United States)

    2015-01-01

    AFRL-RQ-ED-TR-2014-0025 Quantum-Mechanical Definition of Atoms and Chemical Bonds in Molecules P.W. Langhoff J.D. Mills J.A...manufacture, use, or sell any patented invention that may relate to them. Qualified requestors may obtain copies of this report from the Defense...DATES COVERED (From - To) 15 Oct 2013 - 15 Oct 2014 4. TITLE AND SUBTITLE Quantum-Mechanical Definition of Atoms and Chemical Bonds in Molecules

  20. Chemical bonding in aqueous hexacyano cobaltate from photon- and electron-detection perspectives

    Science.gov (United States)

    Lalithambika, Sreeju Sreekantan Nair; Atak, Kaan; Seidel, Robert; Neubauer, Antje; Brandenburg, Tim; Xiao, Jie; Winter, Bernd; Aziz, Emad F.

    2017-01-01

    The electronic structure of the [Co(CN)6]3- complex dissolved in water is studied using X-ray spectroscopy techniques. By combining electron and photon detection methods from the solutions ionized or excited by soft X-rays we experimentally identify chemical bonding between the metal center and the CN ligand. Non-resonant photoelectron spectroscopy provides solute electron binding energies, and nitrogen 1 s and cobalt 2p resonant core-level photoelectron spectroscopy identifies overlap between metal and ligand orbitals. By probing resonances we are able to qualitatively determine the ligand versus metal character of the respective occupied and non-occupied orbitals, purely by experiment. For the same excitations we also detect the emitted X-rays, yielding the complementary resonant inelastic X-ray scattering spectra. For a quantitative interpretation of the spectra, we perform theoretical electronic-structure calculations. The latter provide both orbital energies and orbital character which are found to be in good agreement with experimental energies and with experimentally inferred orbital mixing. We also report calculated X-ray absorption spectra, which in conjunction with our orbital-structure analysis, enables us to quantify various bonding interactions with a particular focus on the water-solvent - ligand interaction and the strength of π-backbonding between metal and ligand.

  1. A theoretical study of molecular structure, optical properties and bond activation of energetic compound FOX-7 under intense electric fields

    Science.gov (United States)

    Tao, Zhiqiang; Wang, Xin; Wei, Yuan; Lv, Li; Wu, Deyin; Yang, Mingli

    2017-02-01

    Molecular structure, vibrational and electronic absorption spectra, chemical reactivity of energetic compound FOX-7, one of the most widely used explosives, were studied computationally in presence of an electrostatic field of 0.01-0.05 a.u. The Csbnd N bond, which usually triggers the decomposition of FOX-7, is shortened/elongated under a parallel/antiparallel field. The Csbnd N bond activation energy varies with the external electric field, decreasing remarkably with the field strength in regardless of the field direction. This is attributed to two aspects: the bond weakening by the field parallel to the Csbnd N bond and the stabilization effect on the transition-state structure by the field antiparallel to the bond. The variations in the structure and property of FOX-7 under the electric fields were further analyzed with its distributional polarizability, which is dependent on the charge transfer characteristics through the Csbnd N bond.

  2. Bonded structure application for aircraft. Kokuki ni okeru secchaku gijutsu

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, O. (Japan Airlines Co. Ltd., Tokyo (Japan))

    1991-01-05

    Adhesives play an important role in a technology of the aircraft structure for which lightness and strength are required. The paper explains the present situation of bonding technology employed for aircraft, the honeycomb structure, production of composite materials and the related problems. Advantages and purposes of employing adhesives as substitutes for fasteners like screws, rivets, etc. are as follows: decreases in stress concentration, weight reduction, smoothing of surfaces, improvement of acoustic fatigue by adhesives flexibility, prevention of gas-liquid leakage. Epoxide adhesives are mainly used for aircraft. Together with tear straps, which are metal-metal bonded to the rear fuselage plate of aircraft, and waffle doublers, an aluminium honeycomb sandwich structure, whose weight is 1/7 of an aluminium plate same in rigidity, is used in such parts of aircraft as spoilers, outer plates of flaps, etc. The problem of the bonded structure is detachment. Therefore, how to prevent, discover and repair it is most important. 3 figs.

  3. Organometallic Bonding in an Ullmann-Type On-Surface Chemical Reaction Studied by High-Resolution Atomic Force Microscopy.

    Science.gov (United States)

    Kawai, Shigeki; Sadeghi, Ali; Okamoto, Toshihiro; Mitsui, Chikahiko; Pawlak, Rémy; Meier, Tobias; Takeya, Jun; Goedecker, Stefan; Meyer, Ernst

    2016-10-01

    The on-surface Ullmann-type chemical reaction synthesizes polymers by linking carbons of adjacent molecules on solid surfaces. Although an organometallic compound is recently identified as the reaction intermediate, little is known about the detailed structure of the bonded organometallic species and its influence on the molecule and the reaction. Herein atomic force microscopy at low temperature is used to study the reaction with 3,9-diiododinaphtho[2,3-b:2',3'-d]thiophene (I-DNT-VW), which is polymerized on Ag(111) in vacuum. Thermally sublimated I-DNT-VW picks up a Ag surface atom, forming a CAg bond at one end after removing an iodine. The CAg bond is usually short-lived, and a CAgC organometallic bond immediately forms with an adjacent molecule. The existence of the bonded Ag atoms strongly affects the bending angle and adsorption height of the molecular unit. Density functional theory calculations reveal the bending mechanism, which reveals that charge from the terminus of the molecule is transferred via the Ag atom into the organometallic bond and strengths the local adsorption to the substrate. Such deformations vanish when the Ag atoms are removed by annealing and CC bonds are established.

  4. Structure validation in chemical crystallography

    Science.gov (United States)

    Spek, Anthony L.

    2009-01-01

    Automated structure validation was introduced in chemical crystallography about 12 years ago as a tool to assist practitioners with the exponential growth in crystal structure analyses. Validation has since evolved into an easy-to-use checkCIF/PLATON web-based IUCr service. The result of a crystal structure determination has to be supplied as a CIF-formatted computer-readable file. The checking software tests the data in the CIF for completeness, quality and consistency. In addition, the reported structure is checked for incomplete analysis, errors in the analysis and relevant issues to be verified. A validation report is generated in the form of a list of ALERTS on the issues to be corrected, checked or commented on. Structure validation has largely eliminated obvious problems with structure reports published in IUCr journals, such as refinement in a space group of too low symmetry. This paper reports on the current status of structure validation and possible future extensions. PMID:19171970

  5. Developing and validating a chemical bonding instrument for Korean high school students

    Science.gov (United States)

    Jang, Nak Han

    The major purpose of this study was to develop a reliable and valid instrument designed to collect and investigate on Korean high school students' understanding about concepts regarding chemical bonding. The Chemical Bonding Diagnostic Test (CBDT) was developed by the procedure by previously relevant researches (Treagust, 1985; Peterson, 1986; Tan, 1994). The final instrument consisted of 15 two-tier items. The reliability coefficient (Cronbach alpha) for the whole test was 0.74. Also, the range of values for the discrimination index was from 0.38 to 0.90 and the overall average difficulty index was 0.38. The test was administered to 716 science declared students in Korean high school. The 37 common misconceptions on chemical bonding were identified through analysis of the items from the CBDT. The grade 11 students had slightly more misconceptions than the grade 12 students for ionic bonding, covalent bonding, and hydrogen bonding while the grade 12 students had more misconceptions about octet rule and hydrogen bonding than the grade 11 students. From the analysis of ANCOVA, there was no significant difference in grades, and between grade levels and gender on the mean score of CBDT. However, there was a significant difference in gender and a significant interaction between grade levels and chemistry preference. In conclusion, Korean high school students had the most common misconception about the electron configuration on ionic bonding and the water density on hydrogen bonding. Korean students' understanding about the chemical bonding was dependent on the interaction between grade levels and the chemistry preference. Consequently, grade 12 chemistry-preferred students had the highest mean scores among student groups concerned by this study.

  6. Structural and vibrational spectral studies on hydrogen bonded salts: 4-chloroanilinium maleate and nitrate

    Indian Academy of Sciences (India)

    R Anitha; M Gunasekaran; S Suresh Kumar; S Athimoolam

    2015-08-01

    In the present study, proton transfer from nitric and maleic acids to amine group (4-chloroaniline) led to hydrogen bonded crystals of 4-chloroanilinium maleate (4CAM) and 4-chloroanilinium nitrate (4CAN) which are investigated by the experimental and theoretical approaches. The molecular structures of these two compounds were optimized with the Density Functional Theory (DFT) using B3LYP function and the Hartree-Fock (HF) level with a6-311++G(d,p) basis set. Geometrical parameters of the molecules were also analyzed along with their intermolecular hydrogen bond, which tailors the ions. These analyses show that present molecules are stabilized through the N–H· · · O and O–H· · · O hydrogen bonds. The vibrational modes were computed by quantum chemical methods. Further, these modes are investigated by FT-IR and FT-Raman spectroscopy in the range of 4000–400 cm−1. The optimized molecular geometry and computed vibrational spectra are compared with experimental results, which show significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjucative interaction and intramolecular charge transfer (ICT). This analysis gives the precise insight into the nature of H-bond interactions. The chemical hardness, electronegativity and chemical potential of the molecules were determined by HOMO–LUMO plot. The frontier molecular orbitals have small band gap value, which signify the possible biological/pharmaceutical activity of the compounds.

  7. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Hansen, Poul Erik

    2015-01-01

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static......” and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N−. The paper will be deal with both secondary and primary...... isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles...

  8. Initiated chemical vapor deposited nanoadhesive for bonding National Ignition Facility's targets

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Tom [Univ. of California, Berkeley, CA (United States)

    2016-05-19

    Currently, the target fabrication scientists in National Ignition Facility Directorate at Lawrence Livermore National Laboratory (LLNL) is studying the propagation force resulted from laser impulses impacting a target. To best study this, they would like the adhesive used to glue the target substrates to be as thin as possible. The main objective of this research project is to create adhesive glue bonds for NIF’s targets that are ≤ 1 μm thick. Polyglycidylmethacrylate (PGMA) thin films were coated on various substrates using initiated chemical vapor deposition (iCVD). Film quality studies using white light interferometry reveal that the iCVD PGMA films were smooth. The coated substrates were bonded at 150 °C under vacuum, with low inflow of Nitrogen. Success in bonding most of NIF’s mock targets at thicknesses ≤ 1 μm indicates that our process is feasible in bonding the real targets. Key parameters that are required for successful bonding were concluded from the bonding results. They include inert bonding atmosphere, sufficient contact between the PGMA films, and smooth substrates. Average bond strength of 0.60 MPa was obtained from mechanical shearing tests. The bonding failure mode of the sheared interfaces was observed to be cohesive. Future work on this project will include reattempt to bond silica aerogel to iCVD PGMA coated substrates, stabilize carbon nanotube forests with iCVD PGMA coating, and kinetics study of PGMA thermal crosslinking.

  9. Understanding metallic bonding: Structure, process and interaction by Rasch analysis

    Science.gov (United States)

    Cheng, Maurice M. W.; Oon, Pey-Tee

    2016-08-01

    This paper reports the results of a survey of 3006 Year 10-12 students on their understandings of metallic bonding. The instrument was developed based on Chi's ontological categories of scientific concepts and students' understanding of metallic bonding as reported in the literature. The instrument has two parts. Part one probed into students' understanding of metallic bonding as (a) a submicro structure of metals, (b) a process in which individual metal atoms lose their outermost shell electrons to form a 'sea of electrons' and octet metal cations or (c) an all-directional electrostatic force between delocalized electrons and metal cations, that is, an interaction. Part two assessed students' explanation of malleability of metals, for example (a) as a submicro structural rearrangement of metal atoms/cations or (b) based on all-directional electrostatic force. The instrument was validated by the Rasch Model. Psychometric assessment showed that the instrument possessed reasonably good properties of measurement. Results revealed that it was reliable and valid for measuring students' understanding of metallic bonding. Analysis revealed that the structure, process and interaction understandings were unidimensional and in an increasing order of difficulty. Implications for the teaching of metallic bonding, particular through the use of diagrams, critiques and model-based learning, are discussed.

  10. Chemical reactivity of C-F bonds attached to graphene with diamines depending on their nature and location.

    Science.gov (United States)

    Li, Baoyin; He, Taijun; Wang, Zaoming; Cheng, Zheng; Liu, Yang; Chen, Teng; Lai, Wenchuan; Wang, Xu; Liu, Xiangyang

    2016-06-29

    The attachment of fluorine to graphene is a facile means to activate the carbon bonds for subsequent covalent bonding to other molecules for the preparation of desired graphene derivatives. Therefore, an insight into the chemical reactivity of fluorinated graphene (FG) is very essential to enable precise control of the composition and structure of the final products. In this study, FG has been treated with various mass amounts of poly(oxypropylene)diamine (PEA) ranging from starvation to saturation to explore the dependence of a substitution reaction of diamines on the nature and location (attached onto the basal planes or along defects or edges) of C-F bonds. X-ray photoelectron spectroscopy directly tracked the atomic percentage of fluorine present and the carbon 1s bonding state, showing that the grafting ratio of diamines gradually increases with increased diamine mass ratio. The varying of the types and orientation of C-F bonds characterized by polarized attenuated total reflectance Fourier transform infrared spectroscopy indicates that "covalent" C-F bonds are more sensitive to the substitution reaction of diamines than ''semi-ionic'' C-F bonds, and the C-F bonds attached onto basal planes more preferably participate in the functionalization reaction of diamines than that of C-F bonded on non-coplanar regions (edges or defects). The one-dimensional expansion along the graphene c-axis shown by wide angle X-ray diffraction provides further evidence on the preferred functionalization reaction of C-F attached on the basal planes, resulting in a change of the average intersheet distance by various magnitudes.

  11. Thermoplastic polymeric adhesive for structural bonding applications for orthopaedic devices

    Energy Technology Data Exchange (ETDEWEB)

    Devanathan, D.; King, R.; Swarts, D.; Lin, S. [Zimmer, Inc., Warsaw, IN (United States); Ramani, K.; Tagle, J. [Purdue Univ., West Lafayette, IN (United States). Dept. of Mechanical Engineering

    1994-12-31

    The orthopaedics industry has witnessed tremendous growth in recent years primarily due to the introduction of high performance, porous coated implants. These devices have eliminated the need for the use of bone cement for in vivo implant fixation, replacing it with the ingrowth of bone into the porous surfaces. The metallurgical bonding processes used for attaching the porous to the implant body introduce some undesirable effect i.e., the reduction of the fatigue strength of the implant due to the ``notches`` created and also due to the high temperature exposure during the sintering operations. This paper describes the development of a thermoplastic polymeric adhesive based structural bonding technique. The high performance polymeric adhesive is fully characterized with respect to its intended application. The design of the porous layer is optimized to achieve a reliable bond to the implant. A thermal heating/cooling process was developed to control the final polymer morphology. Static and fatigue tests were conducted to fully characterize the adhesive bond strength. A ring shear test method was developed to determine the shear strength of the bond interface. Besides the characterization of the adhesive bond, the joints will be analyzed using finite element models. The correlation between the analytical models and the

  12. Wollastonite based-Chemically Bonded Phosphate Ceramics with lead oxide contents under gamma irradiation

    Science.gov (United States)

    Colorado, H. A.; Pleitt, J.; Hiel, C.; Yang, J. M.; Hahn, H. T.; Castano, C. H.

    2012-06-01

    The shielding properties to gamma rays as well as the effect of lead concentration incorporated into Chemically Bonded Phosphate Ceramics (CBPCs) composites are presented. The Wollastonite-based CBPC was fabricated by mixing a patented aqueous phosphoric acid formulation with Wollastonite powder. CBPC has been proved to be good structural material, with excellent thermal resistant properties, and research already showed their potential for radiation shielding applications. Wollastonite-based CBPC is a composite material itself with several crystalline and amorphous phases. Irradiation experiments were conducted on different Wollastonite-based CBPCs with lead oxide. Radiation shielding potential, attenuation coefficients in a broad range of energies pertinent to engineering applications and density experiments showing the effect of the PbO additions (to improve gamma shielding capabilities) are also presented. Microstructure was identified by using scanning electron microscopy and X-ray diffraction.

  13. Intramolecular hydrogen bonding in myricetin and myricitrin. Quantum chemical calculations and vibrational spectroscopy

    Science.gov (United States)

    Vojta, Danijela; Dominković, Katarina; Miljanić, Snežana; Spanget-Larsen, Jens

    2017-03-01

    The molecular structures of myricetin (3,3‧,4‧,5,5‧,7-hexahydroxyflavone; MCE) and myricitrin (myricetin 3-O-rhamnoside; MCI) are investigated by quantum chemical calculations (B3LYP/6-311G**). Two preferred molecular rotamers of MCI are predicted, corresponding to different conformations of the O-rhamnoside subunit. The rotamers are characterized by different hydrogen bonded cross-links between the hydroxy groups of the rhamnoside substituent and the parent MCE moiety. The predicted OH stretching frequencies are compared with vibrational spectra of MCE and MCI recorded for the sake of this investigation (IR and Raman). In addition, a reassignment of the Cdbnd O stretching bands is suggested.

  14. Bonding characteristics, thermal expansibility, and compressibility of RXO(4) (R = rare earths, X = P, As) within monazite and zircon structures.

    Science.gov (United States)

    Li, Huaiyong; Zhang, Siyuan; Zhou, Shihong; Cao, Xueqiang

    2009-05-18

    Systematically theoretical research was performed on the monazite- and zircon-structure RXO(4) (R = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; X = P, As) series by using the chemical bond theory of dielectric description. The chemical bond properties of R-O and X-O bonds were presented. In the zircon phase, the covalency fractions of X-O bonds increased in the order of V-O < As-O < P-O, which was in accordance with the ionic radii and electronegative trends, and the covalency fractions of R-O bonds varied slightly due to the lanthanide contraction. While in the monazite phase, both R-O and X-O bonds were divided into two groups by their covalency fractions. The contributions from the bond to the lattice energy, linear thermal expansion coefficient (LTEC), and bulk modulus were explored. The X-O bonds with short bond lengths and high chemical valence made greater contributions to the lattice energy and performed nearly rigidly during the deformation. A regular variation of lattice energy, LTEC, and bulk modulus with the ionic radii of the lanthanides was observed in both monazite and zircon phases.

  15. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    Science.gov (United States)

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

  16. Representational Classroom Practices that Contribute to Students' Conceptual and Representational Understanding of Chemical Bonding

    Science.gov (United States)

    Hilton, Annette; Nichols, Kim

    2011-11-01

    Understanding bonding is fundamental to success in chemistry. A number of alternative conceptions related to chemical bonding have been reported in the literature. Research suggests that many alternative conceptions held by chemistry students result from previous teaching; if teachers are explicit in the use of representations and explain their content-specific forms and functions, this might be avoided. The development of an understanding of and ability to use multiple representations is crucial to students' understanding of chemical bonding. This paper draws on data from a larger study involving two Year 11 chemistry classes (n = 27, n = 22). It explores the contribution of explicit instruction about multiple representations to students' understanding and representation of chemical bonding. The instructional strategies were documented using audio-recordings and the teacher-researcher's reflection journal. Pre-test-post-test comparisons showed an improvement in conceptual understanding and representational competence. Analysis of the students' texts provided further evidence of the students' ability to use multiple representations to explain macroscopic phenomena on the molecular level. The findings suggest that explicit instruction about representational form and function contributes to the enhancement of representational competence and conceptual understanding of bonding in chemistry. However, the scaffolding strategies employed by the teacher play an important role in the learning process. This research has implications for professional development enhancing teachers' approaches to these aspects of instruction around chemical bonding.

  17. Determining Chemical Reactivity Driving Biological Activity from SMILES Transformations: The Bonding Mechanism of Anti-HIV Pyrimidines

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz

    2013-07-01

    Full Text Available Assessing the molecular mechanism of a chemical-biological interaction and bonding stands as the ultimate goal of any modern quantitative structure-activity relationship (QSAR study. To this end the present work employs the main chemical reactivity structural descriptors (electronegativity, chemical hardness, chemical power, electrophilicity to unfold the variational QSAR though their min-max correspondence principles as applied to the Simplified Molecular Input Line Entry System (SMILES transformation of selected uracil derivatives with anti-HIV potential with the aim of establishing the main stages whereby the given compounds may inhibit HIV infection. The bonding can be completely described by explicitly considering by means of basic indices and chemical reactivity principles two forms of SMILES structures of the pyrimidines, the Longest SMILES Molecular Chain (LoSMoC and the Branching SMILES (BraS, respectively, as the effective forms involved in the anti-HIV activity mechanism and according to the present work, also necessary intermediates in molecular pathways targeting/docking biological sites of interest.

  18. Determining chemical reactivity driving biological activity from SMILES transformations: the bonding mechanism of anti-HIV pyrimidines.

    Science.gov (United States)

    Putz, Mihai V; Dudaş, Nicoleta A

    2013-07-30

    Assessing the molecular mechanism of a chemical-biological interaction and bonding stands as the ultimate goal of any modern quantitative structure-activity relationship (QSAR) study. To this end the present work employs the main chemical reactivity structural descriptors (electronegativity, chemical hardness, chemical power, electrophilicity) to unfold the variational QSAR though their min-max correspondence principles as applied to the Simplified Molecular Input Line Entry System (SMILES) transformation of selected uracil derivatives with anti-HIV potential with the aim of establishing the main stages whereby the given compounds may inhibit HIV infection. The bonding can be completely described by explicitly considering by means of basic indices and chemical reactivity principles two forms of SMILES structures of the pyrimidines, the Longest SMILES Molecular Chain (LoSMoC) and the Branching SMILES (BraS), respectively, as the effective forms involved in the anti-HIV activity mechanism and according to the present work, also necessary intermediates in molecular pathways targeting/docking biological sites of interest.

  19. Automated extraction of chemical structure information from digital raster images

    Directory of Open Access Journals (Sweden)

    Shedden Kerby A

    2009-02-01

    Full Text Available Abstract Background To search for chemical structures in research articles, diagrams or text representing molecules need to be translated to a standard chemical file format compatible with cheminformatic search engines. Nevertheless, chemical information contained in research articles is often referenced as analog diagrams of chemical structures embedded in digital raster images. To automate analog-to-digital conversion of chemical structure diagrams in scientific research articles, several software systems have been developed. But their algorithmic performance and utility in cheminformatic research have not been investigated. Results This paper aims to provide critical reviews for these systems and also report our recent development of ChemReader – a fully automated tool for extracting chemical structure diagrams in research articles and converting them into standard, searchable chemical file formats. Basic algorithms for recognizing lines and letters representing bonds and atoms in chemical structure diagrams can be independently run in sequence from a graphical user interface-and the algorithm parameters can be readily changed-to facilitate additional development specifically tailored to a chemical database annotation scheme. Compared with existing software programs such as OSRA, Kekule, and CLiDE, our results indicate that ChemReader outperforms other software systems on several sets of sample images from diverse sources in terms of the rate of correct outputs and the accuracy on extracting molecular substructure patterns. Conclusion The availability of ChemReader as a cheminformatic tool for extracting chemical structure information from digital raster images allows research and development groups to enrich their chemical structure databases by annotating the entries with published research articles. Based on its stable performance and high accuracy, ChemReader may be sufficiently accurate for annotating the chemical database with links

  20. Change in hydrogen bonding structures of a hydrogel with dehydration

    Science.gov (United States)

    Naohara, Ryo; Narita, Kentaro; Ikeda-Fukazawa, Tomoko

    2017-02-01

    To investigate the mechanisms of structural changes in polymer network and water during dehydration, X-ray diffraction of poly-N,N-dimethylacrylamide (PDMAA) hydrogels was measured. The variation process in the individual structures of water and PDMAA were analyzed by decomposition of the diffraction patterns to separate the respective contributions. The results show that the short-range structures of PDMAA expand during dehydration, whereas the network structure as a whole shrinks. The average length of the hydrogen bonds between water molecules increases with the process. The present results provide a direct evidence of the structural changes of water and polymer in the hydrogel during dehydration.

  1. Relaxation of the chemical bond skin chemisorption size matter ZTP mechanics H2O myths

    CERN Document Server

    Sun, Chang Q

    2014-01-01

    The aim of this book is to explore the detectable properties of a material to the parameters of bond and non-bond involved and to clarify the interdependence of various properties. This book is composed of four parts; Part I deals with the formation and relaxation dynamics of bond and non-bond during chemisorptions with uncovering of the correlation among the chemical bond, energy band, and surface potential barrier (3B) during reactions; Part II is focused on the relaxation of bonds between atoms with fewer neighbors than the ideal in bulk with unraveling of the bond order-length-strength (BOLS) correlation mechanism, which clarifies the nature difference between nanostructures and bulk of the same substance; Part III deals with the relaxation dynamics of bond under heating and compressing with revealing of rules on the temperature-resolved elastic and plastic properties of low-dimensional materials; Part IV is focused on the asymmetric relaxation dynamics of the hydrogen bond (O:H-O) and the anomalous behav...

  2. Character and Structure of Hydrogen Bonding in Liquid Water

    Science.gov (United States)

    Guo, Jinghua; Luo, Yi; Augustsson, Andreas; Rubensson, Jan-Erik; Sathe, Conny; Agren, Hans; Siegbahn, Hans; Nordgren, Joseph

    2003-03-01

    Pauling stated in the 50s that electron sharing between water molecules results in a covalency in the hydrogen bond. Many attempts have been made in the past to verify PaulingÂ's prediction, but without much success due to the limitation of experimental access to the electronic structure of liquids. We reported the first X-ray emission spectra of liquid water. X-ray emission is a direct probe of the local electronic structure of complex systems. Our experimental and theoretical studies on liquid water provide clear evidence that an electron sharing takes place between water molecules. Such a sharing mainly involves the so-called 3a1 orbital, which is a mixing of oxygen 2p and hydrogen 2s atomic orbitals. The outermost "lone pair" orbital (1b_1), however, hardly shows any change upon solvation, which is in contradiction with the normal definition of so-called coordinate-covalent bonding (also called donor-acceptor or Lewis acid-base bonding). Moreover, the X-ray emission spectra of liquid water nicely show the origin for the increasing of dipole moment in liquid water, and they have also been used to separately determine a particular structure with broken hydrogen bonding.

  3. Interface Structure and Atomic Bonding Characteristics in Silicon Nitride Ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Ziegler, A; Idrobo, J C; Cinibulk, M K; Kisielowski, C; Browning, N D; Ritchie, R O

    2004-10-12

    This investigation examines the interface atomic structure and bonding characteristics in an advanced ceramic, obtaining new and unique experimental information that will help to understand and improve the properties of ceramics. Unique direct atomic resolution images have been obtained that illustrate how a range of rare-earth atoms bond to the interface between the intergranular phase and the matrix grains in an advanced silicon nitride ceramic. It has been found that each rare-earth atom bonds to the interface at a different location, depending on atom size, electronic configuration and the presence of oxygen at the interface. This is the key factor to understanding the origin of the mechanical properties in these ceramics and will enable precise tailoring in the future to critically improve the materials performance in wide-ranging applications.

  4. Methods for Using Durable Adhesively Bonded Joints for Sandwich Structures

    Science.gov (United States)

    Smeltzer, Stanley S., III (Inventor); Lundgren, Eric C. (Inventor)

    2016-01-01

    Systems, methods, and apparatus for increasing durability of adhesively bonded joints in a sandwich structure. Such systems, methods, and apparatus includes an first face sheet and an second face sheet as well as an insert structure, the insert structure having a first insert face sheet, a second insert face sheet, and an insert core material. In addition, sandwich core material is arranged between the first face sheet and the second face sheet. A primary bondline may be coupled to the face sheet(s) and the splice. Further, systems, methods, and apparatus of the present disclosure advantageously reduce the load, provide a redundant path, reduce structural fatigue, and/or increase fatigue life.

  5. Ionothermal Synthesis, Structure, and Bonding of the Catena -Heteropolycation 1 ∞ [Sb 2 Se 2 ] +

    KAUST Repository

    Groh, Matthias F.

    2015-01-26

    The reaction of antimony and selenium in the Lewis-acidic ionic liquid 1-butyl-3-methyl-imidazolium tetrachloridoaluminate, [BMIm]Cl•4.7AlCl3, yielded dark-red crystals of [Sb2Se2]AlCl4. The formation starts above 160 ° C; at about 190 ° C, irreversible decomposition takes place. The compound crystallizes in the triclinic space group P 1¯ with a = 919.39(2) pm, b = 1137.92(3) pm, c = 1152.30(3) pm, α = 68.047(1)° , β = 78.115(1)° , γ = 72.530(1)° , and Z = 4. The structure is similar to that of [Sb2Te2]AlCl4 but has only half the number of crystallographically independent atoms. Polycationic chains 1∞ [Sb2Se2]+ form a pseudo-hexagonal arrangement along [011¯] ], which is interlaced by tetrahedral AlCl4 - groups. The catena-heteropolycation 1∞ [Sb2Se2]+ is a sequence of three different four-membered [Sb2Se2 ] rings. The chemical bonding scheme, established from the topological analysis of the real-space bonding indicator ELI-D, includes significantly polar covalent bonding in four-member rings withinthepolycation.Theringsareconnectedintoaninfinitechainbyhomonuclear non-polar Sb-Sb bonds and highly polar Sb-Se bonds. Half of the selenium atoms are three-bonded.

  6. Classification of fossil fuels according to structural-chemical characteristics

    Energy Technology Data Exchange (ETDEWEB)

    A.M. Gyul' maliev; G.S. Golovin; S.G. Gagarin [Institute for Fossil Fuels, Moscow (Russian Federation)

    2007-10-15

    On the basis of a set of linear equations that relate the amount of major elements n{sub E} (E = C, H, O, N, S) in the organic matter of fossil fuels to structural characteristics, such as the number of cycles R, the number of atoms n{sub E}, the number of mutual chemical bonds, the degree of unsaturation of the structure {delta}, and the extent of its reduction B, a structural-chemical classification of fossil coals that is closely related to the parameters of the industrial-genetic classification (GOST 25543-88) is proposed. Structural-chemical classification diagrams are constructed for power-generating coals of Russia; coking coals; and coals designed for nonfuel purposes including the manufacture of adsorbents, synthetic liquid fuel, ion exchangers, thermal graphite, and carbon-graphite materials.

  7. Effective solidification/stabilisation of mercury-contaminated wastes using zeolites and chemically bonded phosphate ceramics.

    Science.gov (United States)

    Zhang, Shaoqing; Zhang, Xinyan; Xiong, Ya; Wang, Guoping; Zheng, Na

    2015-02-01

    In this study, two kinds of zeolites materials (natural zeolite and thiol-functionalised zeolite) were added to the chemically bonded phosphate ceramic processes to treat mercury-contaminated wastes. Strong promotion effects of zeolites (natural zeolite and thiol-functionalised zeolite) on the stability of mercury in the wastes were obtained and these technologies showed promising advantages toward the traditional Portland cement process, i.e. using Portland cement as a solidification agent and natural or thiol-functionalised zeolite as a stabilisation agent. Not only is a high stabilisation efficiency (lowered the Toxicity Characteristic Leaching Procedure Hg by above 10%) obtained, but also a lower dosage of solidification (for thiol-functionalised zeolite as stabilisation agent, 0.5 g g(-1) and 0.7 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) and stabilisation agents (for natural zeolite as stabilisation agent, 0.35 g g(-1) and 0.4 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) were used compared with the Portland cement process. Treated by thiol-functionalised zeolite and chemically bonded phosphate ceramic under optimum parameters, the waste containing 1500 mg Hg kg(-1) passed the Toxicity Characteristic Leaching Procedure test. Moreover, stabilisation/solidification technology using natural zeolite and chemically bonded phosphate ceramic also passed the Toxicity Characteristic Leaching Procedure test (the mercury waste containing 625 mg Hg kg(-1)). Moreover, the presence of chloride and phosphate did not have a negative effect on the chemically bonded phosphate ceramic/thiol-functionalised zeolite treatment process; thus, showing potential for future application in treatment of 'difficult-to-manage' mercury-contaminated wastes or landfill disposal with high phosphate and chloride content.

  8. Determining hydrogen-bond interactions in spider silk with 1H-13C HETCOR fast MAS solid-state NMR and DFT proton chemical shift calculations.

    Science.gov (United States)

    Holland, Gregory P; Mou, Qiushi; Yarger, Jeffery L

    2013-07-28

    Two-dimensional (2D) (1)H-(13)C heteronuclear correlation (HETCOR) solid-state NMR spectra collected with fast magic angle spinning (MAS) are used in conjunction with density functional theory (DFT) proton chemical shift calculations to determine the hydrogen-bonding strength for ordered β-sheet and disordered 310-helical structures in spider dragline silk. The hydrogen-bond strength is determined to be identical for both structures in spider silk with a 1.83-1.84 Å NH···OC hydrogen-bond distance.

  9. Chemical bonding in hydrogen and lithium under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Naumov, Ivan I.; Hemley, Russell J. [Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 (United States); Hoffmann, Roald [Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States); Ashcroft, N. W. [Laboratory of Atomic and Solid State Physics and Cornell Center for Materials Research, Cornell University, Clark Hall, Ithaca, New York 14853 (United States)

    2015-08-14

    Though hydrogen and lithium have been assigned a common column of the periodic table, their crystalline states under common conditions are drastically different: the former at temperatures where it is crystalline is a molecular insulator, whereas the latter is a metal that takes on simple structures. On compression, however, the two come to share some structural and other similarities associated with the insulator-to-metal and metal-to-insulator transitions, respectively. To gain a deeper understanding of differences and parallels in the behaviors of compressed hydrogen and lithium, we performed an ab initio comparative study of these systems in selected identical structures. Both elements undergo a continuous pressure-induced s-p electronic transition, though this is at a much earlier stage of development for H. The valence charge density accumulates in interstitial regions in Li but not in H in structures examined over the same range of compression. Moreover, the valence charge density distributions or electron localization functions for the same arrangement of atoms mirror each other as one proceeds from one element to the other. Application of the virial theorem shows that the kinetic and potential energies jump across the first-order phase transitions in H and Li are opposite in sign because of non-local effects in the Li pseudopotential. Finally, the common tendency of compressed H and Li to adopt three-fold coordinated structures as found is explained by the fact that such structures are capable of yielding a profound pseudogap in the electronic densities of states at the Fermi level, thereby reducing the kinetic energy. These results have implications for the phase diagrams of these elements and also for the search for new structures with novel properties.

  10. Chemical bonding in hydrogen and lithium under pressure.

    Science.gov (United States)

    Naumov, Ivan I; Hemley, Russell J; Hoffmann, Roald; Ashcroft, N W

    2015-08-14

    Though hydrogen and lithium have been assigned a common column of the periodic table, their crystalline states under common conditions are drastically different: the former at temperatures where it is crystalline is a molecular insulator, whereas the latter is a metal that takes on simple structures. On compression, however, the two come to share some structural and other similarities associated with the insulator-to-metal and metal-to-insulator transitions, respectively. To gain a deeper understanding of differences and parallels in the behaviors of compressed hydrogen and lithium, we performed an ab initio comparative study of these systems in selected identical structures. Both elements undergo a continuous pressure-induced s-p electronic transition, though this is at a much earlier stage of development for H. The valence charge density accumulates in interstitial regions in Li but not in H in structures examined over the same range of compression. Moreover, the valence charge density distributions or electron localization functions for the same arrangement of atoms mirror each other as one proceeds from one element to the other. Application of the virial theorem shows that the kinetic and potential energies jump across the first-order phase transitions in H and Li are opposite in sign because of non-local effects in the Li pseudopotential. Finally, the common tendency of compressed H and Li to adopt three-fold coordinated structures as found is explained by the fact that such structures are capable of yielding a profound pseudogap in the electronic densities of states at the Fermi level, thereby reducing the kinetic energy. These results have implications for the phase diagrams of these elements and also for the search for new structures with novel properties.

  11. Influence of the chemical structure of functional monomers on their adhesive performance.

    Science.gov (United States)

    Van Landuyt, K L; Yoshida, Y; Hirata, I; Snauwaert, J; De Munck, J; Okazaki, M; Suzuki, K; Lambrechts, P; Van Meerbeek, B

    2008-08-01

    Functional monomers in adhesive systems can improve bonding by enhancing wetting and demineralization, and by chemical bonding to calcium. This study tested the hypothesis that small changes in the chemical structure of functional monomers may improve their bonding effectiveness. Three experimental phosphonate monomers (HAEPA, EAEPA, and MAEPA), with slightly different chemical structures, and 10-MDP (control) were evaluated. Adhesive performance was determined in terms of microtensile bond strength of 4 cements that differed only for the functional monomer. Based on the Adhesion-Decalcification concept, the chemical bonding potential was assessed by atomic absorption spectrophotometry of the dissolution rate of the calcium salt of the functional monomers. High bond strength of the adhesive cement corresponded to low dissolution rate of the calcium salt of the respective functional monomer. The latter is according to the Adhesion-Decalcification concept, suggestive of a high chemical bonding capacity. We conclude that the adhesive performance of an adhesive material depends on the chemical structure of the functional monomer.

  12. CHEMICAL ACTIVATION OF MOLECULES BY METALS: EXPERIMENTAL STUDIES OF ELECTRON DISTRIBUTIONS AND BONDING

    Energy Technology Data Exchange (ETDEWEB)

    LICHTENBERGER, DENNIS L.

    2002-03-26

    This research program is directed at obtaining detailed experimental information on the electronic interactions between metals and organic molecules. These interactions provide low energy pathways for many important chemical and catalytic processes. A major feature of the program is the continued development and application of our special high-resolution valence photoelectron spectroscopy (UPS), and high-precision X-ray core photoelectron spectroscopy (XPS) instrumentation for study of organometallic molecules in the gas phase. The study involves a systematic approach towards understanding the interactions and activation of bound carbonyls, C-H bonds, methylenes, vinylidenes, acetylides, alkenes, alkynes, carbenes, carbynes, alkylidenes, alkylidynes, and others with various monometal, dimetal, and cluster metal species. Supporting ligands include -aryls, alkoxides, oxides, and phosphines. We are expanding our studies of both early and late transition metal species and electron-rich and electron-poor environments in order to more completely understand the electronic factors that serve to stabilize particular organic fragments and intermediates on metals. Additional new directions for this program are being taken in ultra-high vacuum surface UPS, XPS, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) experiments on both physisorbed and chemisorbed organometallic thin films. The combination of these methods provides additional electronic structure information on surface-molecule and molecule-molecule interactions. A very important general result emerging from this program is the identification of a close relationship between the ionization energies of the species and the thermodynamics of the chemical and catalytic reactions of these systems.

  13. Strengthening of Concrete Structures with cement based bonded composites

    DEFF Research Database (Denmark)

    Täljsten, Björn; Blanksvärd, Thomas

    2008-01-01

    Polymers). The method is very efficient and has achieved world wide attention. However, there are some drawbacks with the use of epoxy, e.g. working environment, compatibility and permeability. Substituting the epoxy adherent with a cement based bonding agent will render a strengthening system...... with improved working environment and better compatibility to the base concrete structure. This study gives an overview of different cement based systems, all with very promising results for structural upgrading. Studied parameters are structural retrofit for bending, shear and confinement. It is concluded...

  14. Characterization and intramolecular bonding patterns of busulfan: Experimental and quantum chemical approach

    Science.gov (United States)

    Karthick, T.; Tandon, Poonam; Singh, Swapnil; Agarwal, Parag; Srivastava, Anubha

    2017-02-01

    The investigations of structural conformers, molecular interactions and vibrational characterization of pharmaceutical drug are helpful to understand their behaviour. In the present work, the 2D potential energy surface (PES) scan has been performed on the dihedral angles C6sbnd O4sbnd S1sbnd C5 and C25sbnd S22sbnd O19sbnd C16 to find the stable conformers of busulfan. In order to show the effects of long range interactions, the structures on the global minima of PES scan have been further optimized by B3LYP/6-311 ++G(d,p) method with and without empirical dispersion functional in Gaussian 09W package. The presence of n → σ* and σ → σ* interactions which lead to stability of the molecule have been predicted by natural bond orbital analysis. The strong and weak hydrogen bonds between the functional groups of busulfan were analyzed using quantum topological atoms in molecules analysis. In order to study the long-range forces, such as van der Waals interactions, steric effect in busulfan, the reduced density gradient as well as isosurface defining these interactions has been plotted using Multiwfn software. The spectroscopic characterization on the solid phase of busulfan has been studied by experimental FT-IR and FT-Raman spectra. From the 13C and 1H NMR spectra, the chemical shifts of individual C and H atoms of busulfan have been predicted. The maximum absorption wavelengths corresponding to the electronic transitions between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of busulfan have been found by UV-vis spectrum.

  15. Diversity of Chemical Bonding and Oxidation States in MS4 Molecules of Group 8 Elements.

    Science.gov (United States)

    Huang, Wei; Jiang, Ning; Schwarz, W H Eugen; Yang, Ping; Li, Jun

    2017-08-04

    The geometric and electronic ground-state structures of 30 isomers of six MS4 molecules (M=Group 8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density functional theory and correlated wavefunction approaches. The MS4 species were compared to analogous MO4 species recently investigated (W. Huang, W.-H. Xu, W. H. E. Schwarz, J. Li, Inorg. Chem. 2016, 55, 4616). A metal oxidation state (MOS) with a high value of eight appeared in the low-spin singlet Td geometric species (Os,Hs)S4 and (Ru,Os,Hs)O4 , whereas a low MOS of two appeared in the high-spin septet D2d species Fe(S2 )2 and (slightly excited) metastable Fe(O2 )2 . The ground states of all other molecules had intermediate MOS values, with S(2-) , S2(2-) , S2(1-) (and O(2-) , O(1-) , O2(2-) , O2(1-) ) ligands bonded by ionic, covalent, and correlative contributions. The known tendencies toward lower MOS on going from oxides to sulfides, from Hs to Os to Ru, and from Pu to Sm, and the specific behavior of Fe, were found to arise from the different atomic orbital energies and radii of the (n-1)p core and (n-1)d and (n-2)f valence shells of the metal atoms in row n of the periodic table. The comparative results of the electronic and geometric structures of the MO4 and MS4 species provides insight into the periodicity of oxidation states and bonding. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Electronic parameters of Sr2M2O7 (M = V, Nb, Ta) and Sr-O chemical bonding

    DEFF Research Database (Denmark)

    Atuchin, Victor V.; Grivel, Jean-Claude; Zhang, Zhaoming

    2010-01-01

    on the formation of the Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr2Nb2O7 and Sr2Ta2O7 and the previously published structural and XPS data for other Sr-oxide compounds. A new empirical relationship between Δ(O-Sr) and L(Sr-O) was obtained. Possible applications...

  17. The Strength of Chemical Bonds in Solids and Liquids (Preprint)

    Science.gov (United States)

    2011-07-01

    2001). 23 Gu, X. J., Poon, S. J., Shiflet, G. J. & Widom , M. Ductility improvement of amorphous steels: Roles of shear modulus and electronic...structure. Acta mater. 56, 88-94 (2008). 24 Gu, X. J., Poon, S. J., Shiflet, G. J. & Widom , M. Mechanical properties, glass transition temperature, and...www.nature.com/nature. Approved for public release; distribution unlimited. 20 Acknowledgements We thank P. Harrowell, R. Busch, M. Widom , D. Nicholson

  18. Modification of Substrates for Improved Chemical Bonding at Epoxy Interfaces

    Science.gov (United States)

    Schoch, Andrew B.; Fischer, Daniel A.; Lenhart, Joseph L.

    2010-03-01

    Near-edge X-ray absorption fine structure (NEXAFS) is exploited to investigate the interface between epoxy resins and a solid substrate, which is critical for many industrial and defense related composite structures. The goal is to link the interfacial chemistry, structure and resulting properties to the adhesive properties, enabling the design of interfaces with tunable strength, energy dissipation, and impact performance. Silicon surfaces were chosen as a model substrate and were coated sequentially through reactions with glycidyl propyl trimethoxysilane (GPS), various polyoxyalkyleneamines (POAAs), and finally diglycidyl ether of bisphenol-A (DGEBA). By controlling the molecular ratios of the POAAs, which have varying functionality and molecular weight the reactivity of these surfaces toward epoxies can be controlled. In addition to NEXAFS which provides insight regarding the molecular organization and chemistry at the interface, mechanical testing will also be explored to determine the impact on interfacial properties. Asymmetric dual cantilever beam testing was chosen for these samples because it drives the crack to the interface and allows for ease of characterization with surface science techniques after failure. A combination of NEXAFS and XPS will be utilized to interrogate the fracture surfaces and provide insight into the adhesive failure mechanisms and location.

  19. Effect of Microwave Radiation on Enzymatic and Chemical Peptide Bond Synthesis on Solid Phase

    Directory of Open Access Journals (Sweden)

    Alessandra Basso

    2009-01-01

    Full Text Available Peptide bond synthesis was performed on PEGA beads under microwave radiations. Classical chemical coupling as well as thermolysin catalyzed synthesis was studied, and the effect of microwave radiations on reaction kinetics, beads' integrity, and enzyme activity was assessed. Results demonstrate that microwave radiations can be profitably exploited to improve reaction kinetics in solid phase peptide synthesis when both chemical and biocatalytic strategies are used.

  20. Estimating Structural Models of Corporate Bond Prices in Indonesian Corporations

    Directory of Open Access Journals (Sweden)

    Lenny Suardi

    2014-08-01

    Full Text Available This  paper  applies  the  maximum  likelihood  (ML  approaches  to  implementing  the structural  model  of  corporate  bond,  as  suggested  by  Li  and  Wong  (2008,  in  Indonesian corporations.  Two  structural  models,  extended  Merton  and  Longstaff  &  Schwartz  (LS models,  are  used  in  determining  these  prices,  yields,  yield  spreads  and  probabilities  of default. ML estimation is used to determine the volatility of irm value. Since irm value is unobserved variable, Duan (1994 suggested that the irst step of ML estimation is to derive the likelihood function for equity as the option on the irm value. The second step is to ind parameters such as the drift and volatility of irm value, that maximizing this function. The irm value itself is extracted by equating the pricing formula to the observed equity prices. Equity,  total  liabilities,  bond  prices  data  and  the  irm's  parameters  (irm  value,  volatility of irm value, and default barrier are substituted to extended Merton and LS bond pricing formula in order to valuate the corporate bond.These models are implemented to a sample of 24 bond prices in Indonesian corporation during  period  of  2001-2005,  based  on  criteria  of  Eom,  Helwege  and  Huang  (2004.  The equity  and  bond  prices  data  were  obtained  from  Indonesia  Stock  Exchange  for  irms  that issued equity and provided regular inancial statement within this period. The result shows that both models, in average, underestimate the bond prices and overestimate the yields and yield spread. ";} // -->activate javascript

  1. Generating giant and tunable nonlinearity in a macroscopic mechanical resonator from a single chemical bond

    Science.gov (United States)

    Huang, Pu; Zhou, Jingwei; Zhang, Liang; Hou, Dong; Lin, Shaochun; Deng, Wen; Meng, Chao; Duan, Changkui; Ju, Chenyong; Zheng, Xiao; Xue, Fei; Du, Jiangfeng

    2016-05-01

    Nonlinearity in macroscopic mechanical systems may lead to abundant phenomena for fundamental studies and potential applications. However, it is difficult to generate nonlinearity due to the fact that macroscopic mechanical systems follow Hooke's law and respond linearly to external force, unless strong drive is used. Here we propose and experimentally realize high cubic nonlinear response in a macroscopic mechanical system by exploring the anharmonicity in chemical bonding interactions. We demonstrate the high tunability of nonlinear response by precisely controlling the chemical bonding interaction, and realize, at the single-bond limit, a cubic elastic constant of 1 × 1020 N m-3. This enables us to observe the resonator's vibrational bi-states transitions driven by the weak Brownian thermal noise at 6 K. This method can be flexibly applied to a variety of mechanical systems to improve nonlinear responses, and can be used, with further improvements, to explore macroscopic quantum mechanics.

  2. The Collaboration of Cooperative Learning and Conceptual Change: Enhancing the Students' Understanding of Chemical Bonding Concepts

    Science.gov (United States)

    Eymur, Gülüzar; Geban, Ömer

    2017-01-01

    The main purpose of this study was to investigate the effects of cooperative learning based on conceptual change approach instruction on ninth-grade students' understanding in chemical bonding concepts compared to traditional instruction. Seventy-two ninth-grade students from two intact chemistry classes taught by the same teacher in a public high…

  3. Nuclear radiation as a probe of chemical bonding: the current interplay between theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Newton, M D

    1978-01-01

    After a survey of appropriate theoretical formalisms, recent confrontations of theory and experiment in the areas of neutron scattering, Moessbauer spectroscopy, and positron chemistry are discussed, with major emphasis on the degree to which simple concepts of chemical bonding can be refined by complementary use of the above experimental probes and the powerful techniques of computational quantum chemistry.

  4. Damage tolerance of bonded composite aircraft repairs for metallic structures

    Science.gov (United States)

    Clark, Randal John

    This thesis describes the development and validation of methods for damage tolerance substantiation of bonded composite repairs applied to cracked plates. This technology is used to repair metal aircraft structures, offering improvements in fatigue life, cost, manufacturability, and inspectability when compared to riveted repairs. The work focuses on the effects of plate thickness and bending on repair life, and covers fundamental aspects of fracture and fatigue of cracked plates and bonded joints. This project falls under the UBC Bonded Composite Repair Program, which has the goal of certification and widespread use of bonded repairs in civilian air transportation. This thesis analyses the plate thickness and transverse stress effects on fracture of repaired plates and the related problem of induced geometrically nonlinear bending in unbalanced (single-sided) repairs. The author begins by developing a classification scheme for assigning repair damage tolerance substantiation requirements based upon stress-based adhesive fracture/fatigue criteria and the residual strength of the original structure. The governing equations for bending of cracked plates are then reformulated and line-spring models are developed for linear and nonlinear coupled bending and extension of reinforced cracks. The line-spring models were used to correct the Wang and Rose energy method for the determination of the long-crack limit stress intensity, and to develop a new interpolation model for repaired cracks of arbitrary length. The analysis was validated using finite element models and data from mechanical tests performed on hybrid bonded joints and repair specimens that are representative of an in-service repair. This work will allow designers to evaluate the damage tolerance of the repaired plate, the adhesive, and the composite patch, which is an airworthiness requirement under FAR (Federal Aviation Regulations) 25.571. The thesis concludes by assessing the remaining barriers to

  5. Microstructure and chemical bond evolution of diamond-like carbon films machined by femtosecond laser

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing; Wang, Chunhui [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Liu, Yongsheng, E-mail: yongshengliu@nwpu.edu.cn [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Cheng, Laifei [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Li, Weinan [State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 10068 (China); Zhang, Qing [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Yang, Xiaojun [State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 10068 (China)

    2015-06-15

    Highlights: • The machining depth was essentially proportional to the laser power. • The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. And the number of nanoparticles increased with the processing power as well. • It revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. • It showed that a great decrease of sp{sup 3}/sp{sup 2} after laser treatment. - Abstract: Femtosecond laser is of great interest for machining high melting point and hardness materials such as diamond-like carbon, SiC ceramic, et al. In present work, the microstructural and chemical bond evolution of diamond-like carbon films were investigated using electron microscopy and spectroscopy techniques after machined by diverse femtosecond laser power in air. The results showed the machining depth was essentially proportional to the laser power. The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. Considering the D and G Raman band parameters on the laser irradiation, it revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. X-ray photoelectron spectroscopy analysis showed a great decrease of sp{sup 3}/sp{sup 2} after laser treatment.

  6. Chemical Bonding of Transition-Metal Co13 Clusters with Graphene.

    Science.gov (United States)

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2015-12-01

    We carried out density functional calculations to study the adsorption of Co13 clusters on graphene. Several free isomers were deposited at different positions with respect to the hexagonal lattice nodes, allowing us to study even the hcp 2d isomer, which was recently obtained as the most stable one. Surprisingly, the Co13 clusters attached to graphene prefer icosahedron-like structures in which the low-lying isomer is much distorted; in such structures, they are linked with more bonds than those reported in previous works. For any isomer, the most stable position binds to graphene by the Co atoms that can lose electrons. We find that the charge transfer between graphene and the clusters is small enough to conclude that the Co-graphene binding is not ionic-like but chemical. Besides, the same order of stability among the different isomers on doped graphene is kept. These findings could also be of interest for magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.

  7. Atomic Structures of Riboflavin (Vitamin B2) and its Reduced Form with Bond Lengths Based on Additivity of Atomic Radii

    CERN Document Server

    Heyrovska, Raji

    2008-01-01

    It has been shown recently that chemical bond lengths, in general, like those in the components of nucleic acids, caffeine related compounds, all essential amino acids, methane, benzene, graphene and fullerene are sums of the radii of adjacent atoms constituting the bond. Earlier, the crystal ionic distances in all alkali halides and lengths of many partially ionic bonds were also accounted for by the additivity of ionic as well as covalent radii. Here, the atomic structures of riboflavin and its reduced form are presented based on the additivity of the same set of atomic radii as for other biological molecules.

  8. The Pauling 3-Electron Bond: A Recommendation for the Use of the Linnett Structure.

    Science.gov (United States)

    Harcourt, Richard D.

    1985-01-01

    Recommends the Linnett structure IV (as in VIII for molecular oxygen) for future use when a valence-bond structure for a Pauling 3-electron bond is required. Examples are provided to illustrate why this recommendation is made. (JN)

  9. Interplay between Peptide Bond Geometrical Parameters in Nonglobular Structural Contexts

    Directory of Open Access Journals (Sweden)

    Luciana Esposito

    2013-01-01

    Full Text Available Several investigations performed in the last two decades have unveiled that geometrical parameters of protein backbone show a remarkable variability. Although these studies have provided interesting insights into one of the basic aspects of protein structure, they have been conducted on globular and water-soluble proteins. We report here a detailed analysis of backbone geometrical parameters in nonglobular proteins/peptides. We considered membrane proteins and two distinct fibrous systems (amyloid-forming and collagen-like peptides. Present data show that in these systems the local conformation plays a major role in dictating the amplitude of the bond angle N-Cα-C and the propensity of the peptide bond to adopt planar/nonplanar states. Since the trends detected here are in line with the concept of the mutual influence of local geometry and conformation previously established for globular and water-soluble proteins, our analysis demonstrates that the interplay of backbone geometrical parameters is an intrinsic and general property of protein/peptide structures that is preserved also in nonglobular contexts. For amyloid-forming peptides significant distortions of the N-Cα-C bond angle, indicative of sterical hidden strain, may occur in correspondence with side chain interdigitation. The correlation between the dihedral angles Δω/ψ in collagen-like models may have interesting implications for triple helix stability.

  10. Molecular structure, spectral investigation (1H NMR, 13C NMR, UV-Visible, FT-IR, FT-Raman), NBO, intramolecular hydrogen bonding, chemical reactivity and first hyperpolarizability analysis of formononetin [7-hydroxy-3(4-methoxyphenyl)chromone]: A quantum chemical study

    Science.gov (United States)

    Srivastava, Anubha; Mishra, Rashmi; Kumar, Sudhir; Dev, Kapil; Tandon, Poonam; Maurya, Rakesh

    2015-03-01

    Formononetin [7-hydroxy-3(4-methoxyphenyl)chromone or 4‧-methoxy daidzein] is a soy isoflavonoid that is found abundantly in traditional Chinese medicine Astragalus mongholicus (Bunge) and Trifolium pretense L. (red clover), and in an Indian medicinal plant, Butea (B.) monosperma. Crude extract of B.monosperma is used for rapid healing of fracture in Indian traditional medicine. In this study, a combined theoretical and experimental approach is used to study the properties of formononetin. The optimized geometry was calculated by B3LYP method using 6-311++G(d,p) as a large basis set. The FT-Raman and FT-IR spectra were recorded in the solid phase, and interpreted in terms of potential energy distribution (PED) analysis. Density functional theory (DFT) is applied to explore the nonlinear optical properties of the molecule. Good consistency is found between the calculated results and observed data for the electronic absorption, IR and Raman spectra. The solvent effects have been calculated using time-dependent density functional theory in combination with the integral equation formalism polarized continuum model, and the results are in good agreement with observed measurements. The double well potential energy curve of the molecule about the respective bonds, have been plotted, as obtained from DFT/6-31G basis set. The computational results diagnose the most stable conformer of formononetin. The HOMO-LUMO energy gap of possible conformers has been calculated for comparing their chemical activity. Chemical reactivity has been measured by reactivity descriptors and molecular electrostatic potential surface (MEP). The 1H and 13C NMR chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. Furthermore, the role of CHsbnd O intramolecular hydrogen bond in the stability of molecule is investigated on the basis of the results of topological properties of AIM theory and NBO analysis. The calculated first hyperpolarizability shows

  11. Can chemical structure predict reproductive toxicity?

    NARCIS (Netherlands)

    Maslankiewicz L; Hulzebos EM; Vermeire TG; Muller JJA; Piersma AH; SEC

    2005-01-01

    Structure-Activity Relationships (SARs), including Quantitative SARs, are applied to the hazard assessment of chemicals. This need is all the more urgent considering the proposed new EU policy on chemicals in REACH, which stresses the need for non-animal testing. DEREKfW and the TSCA Chemical

  12. Structure of cis-[Pt(NH3)(2-picoline)]2+ and DNA adduct and its bonding characteristics

    Institute of Scientific and Technical Information of China (English)

    JIA; Muxin; LIU; Kai; YANG; Zuoyin; CHEN; Guangju

    2004-01-01

    Several methods including molecular mechanics, molecular dynamics, ONIOM that combines quantum chemistry with molecular mechanics and standard quantum chemistry are used to study the configuration and electron structures of an adduct of the DNA segment d(ATACATG*G*TACATA)·d(TATGTACCATGTAT) with cis-[Pt(NH3)(2-Picoline)]2+. The investigation shows that the configuration optimized by ONIOM is similar to that determined by NMR. Strong chemical bonds between Pt of the complex and two N7s of neighboring guanines in the DNA duplex and hydrogen bond between the NH3 of the complex and O6 of a nearby guanine have a large impact on the configuration of the adduct. Chemical bonds, the aforementioned hydrogen bond, and the interaction between a methyl of the complex and a methyl of the base in close proximity are critical for the complex to specifically recognize DNA.

  13. Students' Reasoning about Basic Chemical Thermodynamics and Chemical Bonding: What Changes Occur during a Context-based Post-16 Chemistry Course?

    Science.gov (United States)

    Barker, Vanessa; Millar, Robin

    2000-01-01

    A longitudinal study of students (n=250) following the Salters Advanced Chemistry course probed a range of chemical ideas including the exothermicity of bond formation and the development of thinking about covalent, ionic, and intermolecular bonds. At the start, many students demonstrated misunderstandings about these chemical ideas, but their…

  14. Electron-electron interactions in the chemical bond: ``1/3” Effect in the bond length of hydrogen molecule

    Indian Academy of Sciences (India)

    P Ganguly

    2001-10-01

    The prominent ``1/3” effect observed in the Hall effect plateaus of twodimensional electron gas (2DEG) systems has been postulated to indicating 1/3 fractional charge quasiparticle excitations arising from electron-electron interactions. Tunneling shot-noise experiments on 2DEF exhibiting fractional quantum Hall effect (FQHE) shows evidence for tunnelling of particles with and /3 charges for a constant band mass. A ``1/3” effect in the hydrogen molecule is seen in as much as its internuclear distance, - = - + +, with |+/-| = 1/3. This is examined in terms of electron-electron interactions involving electron- and hole quasiparticles, (-) and (ℎ+), equivalent to those observed in FQHE shot-noise experiments. The (/) ratio of the (-) and (ℎ+) quasiparticles is kept at 1: -3. Instead of a 2DEG, these particles are treated as being in flat Bohr orbits. A treatment in the language of charge-flux tube composites for the hydrogen atom as well as the hydrogen molecule is attempted. Such treatment gives important insights into changes in chemical potential and bond energy on crossing a phase boundary during the atom-bond transition as well as on models for FQHE itself.

  15. [Influence of primers ' chemical composition on shear bond strength of resin cement to zirconia ceramic].

    Science.gov (United States)

    Łagodzińska, Paulina; Bociong, Kinga; Dejak, Beata

    2014-01-01

    Resin cements establish a strong durable bond between zirconia ceramic and hard tissues of teeth. It is essential to use primers with proper chemical composition before cementation. The aim of this study was to assess the influence of primer's chemical composition on the shear bond strength of zirconia ceramic to resin cements. 132 zirconia specimens were randomly assigned to four groups. There were four resin systems used. They included resin cement and respective primer, dedicated to zirconia: Clearfil Ceramic Primer/Panavia F2.0, Monobond Plus/Multilink Automix, AZ - Primer/ResiCem, Z - Prime Plus/Duo-Link. In each group the protocol of cementation was as follows: application of primer to the zirconia surface and application of the respective resin cement in cylindric mold (dimensions: 3.0 mm height and 3.0 mm diameter). Then, the shear bond strength was evaluated and the failure type was assessed in lupes (×2.5 magnification), also random specimens under SEM. The Wilcoxon test was used to analyze the data, the level of significance was α = 0.05. Finally, the known chemical composition of each primer was analysed in reference to probable chemical bonds, which may occure between primers and zirconia. The mean shear bond strength between resin cements and zirconia was the highest for Z-Prime Plus/Duo-Link (8.24 ± 3,21 MPa) and lowest for Clearfil Ceramic Primer/Panavia F 2.0 (4.60 ± 2.21 MPa). The analysis revealed significant difference between all groups, except pair Clearfil Ceramic Primer/Panavia F 2.0 and AZ-Primer/ResiCem. The failure type in groups of Clearfil Ceramic Primer/Panavia F 2.0 and AZ-Primer/ResiCem was mainly adhesive, in groups Monobond Plus/ /Multilink Automix and Z-Prime Plus/Duo-Link mainly mixed. The chemical composition of primers affects different bond mechanisms between resin cements and zirconia. The highest shear bond strength of resin cement to zirconia can be obtained for the primer composed of 10-Methacryloyloxydecyl dihydrogen

  16. The bonding picture in hypervalent XF3 (X = Cl, Br, I, At) fluorides revisited with quantum chemical topology.

    Science.gov (United States)

    Amaouch, Mohamed; Sergentu, Dumitru-Claudiu; Steinmetz, David; Maurice, Rémi; Galland, Nicolas; Pilmé, Julien

    2017-08-03

    Hypervalent XF3 (X = Cl, Br, I, At) fluorides exhibit T-shaped C2V equilibrium structures with the heavier of them, AtF3 , also revealing an almost isoenergetic planar D3h structure. Factors explaining this behavior based on simple "chemical intuition" are currently missing. In this work, we combine non-relativistic (ClF3 ), scalar-relativistic and two-component (X = Br - At) density functional theory calculations, and bonding analyses based on the electron localization function and the quantum theory of atoms in molecules. Typical signatures of charge-shift bonding have been identified at the bent T-shaped structures of ClF3 and BrF3 , while the bonds of the other structures exhibit a dominant ionic character. With the aim of explaining the D3h structure of AtF3 , we extend the multipole expansion analysis to the framework of two-component single-reference calculations. This methodological advance enables us to rationalize the relative stability of the T-shaped C2v and the planar D3h structures: the Coulomb repulsions between the two lone-pairs of the central atom and between each lone-pair and each fluorine ligand are found significantly larger at the D3h structures than at the C2v ones for X = Cl - I, but not with X = At. This comes with the increasing stabilization, along the XF3 series, of the planar D3h structure with respect to the global T-shaped C2v minima. Hence, we show that the careful use of principles that are at the heart of the valence shell electron pair repulsion model provides reasonable justifications for stable planar D3h structures in AX3 E2 systems. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  17. Rare-earth transition-metal intermetallics: Structure-bonding-property relationships

    Energy Technology Data Exchange (ETDEWEB)

    Han, M. K. [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    The explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding property relationships. The work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe13-xSix system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides Re2-xFe4Si14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi2: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb3Zn3.6Al7.4: Partially ordered structure of Tb3Zn3.6Al7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn39(CrxAl1-x)81

  18. Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships

    Energy Technology Data Exchange (ETDEWEB)

    Han, Mi-Kyung [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    Our explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding-property relationships. Our work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe13-xSix system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn13-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides RE2-xFe4Si14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi2: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb3Zn3.6Al7.4: Partially ordered structure of Tb3.6Zn13-xAl7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn39(CrxAl1-x

  19. Elastic constants for superplastically formed/diffusion-bonded sandwich structures

    Science.gov (United States)

    Ko, W. L.

    1979-01-01

    Formulae and the associated graphs are presented for contrasting the effective elastic constants for a superplastically formed/diffusion-bonded (SPF/DB) corrugated sandwich core and a honeycomb sandwich core. The results used in the comparison of the structural properties of the two types of sandwich cores are under conditions of equal sandwich density. It was found that the stiffness in the thickness direction of the optimum SPF/DB corrugated core (i.e., triangular truss core) was lower than that of the honeycomb core, and that the former had higher transverse shear stiffness than the latter.

  20. Mapping lipid and collagen by multispectral photoacoustic imaging of chemical bond vibration

    Science.gov (United States)

    Wang, Pu; Wang, Ping; Wang, Han-Wei; Cheng, Ji-Xin

    2012-09-01

    Photoacoustic microscopy using vibrational overtone absorption as a contrast mechanism allows bond-selective imaging of deep tissues. Due to the spectral similarity of molecules in the region of overtone vibration, it is difficult to interrogate chemical components using photoacoustic signal at single excitation wavelength. Here we demonstrate that lipids and collagen, two critical markers for many kinds of diseases, can be distinguished by multispectral photoacoustic imaging of the first overtone of C-H bond. A phantom consisting of rat-tail tendon and fat was constructed to demonstrate this technique. Wavelengths between 1650 and 1850 nm were scanned to excite both the first overtone and combination bands of C-H bonds. B-scan multispectral photoacoustic images, in which each pixel contains a spectrum, were analyzed by a multivariate curve resolution-alternating least squares algorithm to recover the spatial distribution of collagen and lipids in the phantom.

  1. Evidence for chemical bond formation at rubber-brass interface: Photoelectron spectroscopy study of bonding interaction between copper sulfide and model molecules of natural rubber

    Science.gov (United States)

    Ozawa, Kenichi; Mase, Kazuhiko

    2016-12-01

    Strong adhesion between rubber and brass has been considered to arise mainly from the mechanical interaction, which is characterized by dendritic interlocking at the interface. In order to examine a possible contribution of the chemical interaction, chemical state analysis was carried out for model molecules of natural rubber (2-methyl-2-butene and isoprene) adsorbed on Cu2S, a key chemical species for adhesion, by means of photoelectron spectroscopy (PES). Absence of a C 1s PES component associated with C=C bonds and the appearance of adsorption-induced components in the S 2p region indicate that the molecules interact with the Cu2S surface via the C=C bond to form C-S covalent bonds. This proves that the chemical interaction certainly plays a role in rubber-brass adhesion along with the mechanical interaction.

  2. Intramolecular hydrogen bond, molecular structure and vibrational assignment of tetra-acetylethane. A density functional study.

    Science.gov (United States)

    Raissi, Heidar; Nowroozi, Alireza; Mohammdi, Reza; Hakimi, Mohammad

    2006-11-01

    The intramolecular hydrogen bond, molecular structure and vibrational frequencies of tetra-acetylethane have been investigated by means of high-level density functional theory (DFT) methods with most popular basis sets. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were recorded in the regions 400-4000 cm(-1) and 40-4000 cm(-1), respectively. The calculated geometrical parameters of tetra-acetylethane were compared to the experimental results of this compound and its parent molecule (acetylacetone), obtained from X-ray diffraction. The O...O distance in tetra-acetylethane, about 2.424A, suggests that the hydrogen bond in this compound is stronger than acetylacetone. This conclusion is well supported by the NMR proton chemical shifts and O-H stretching mode at 2626 cm(-1). Furthermore, the calculated hydrogen bond energy in the title compound is 17.22 kcal/mol, which is greater than the acetylacetone value. On the other hand, the results of theoretical calculations show that the bulky substitution in alpha-position of acetylacetone results in an increase of the conjugation of pi electrons in the chelate ring. Finally, we applied the atoms in molecules (AIM) theory and natural bond orbital method (NBO) for detail analyzing the hydrogen bond in tetra-acetylethane and acetylacetone. These results are in agreement with the vibrational spectra interpretation and quantum chemical calculation results. Also, the conformations of methyl groups with respect to the plane of the molecule and with respect to each other were investigated.

  3. Surface Monitoring of CFRP Structures for Adhesive Bonding

    Science.gov (United States)

    Ledesma, Rodolfo; Palmieri, Frank L.; Yost, William T.; Connell, John W.; Fitz-Gerald, James M.

    2017-01-01

    Adhesive bonding of composite materials requires reliable monitoring and detection of surface contaminants to assure robust and durable bonded structures. Surface treatment and effective monitoring prior to bonding is essential in order to obtain a surface free from contaminants that may degrade structural performance. Two techniques which monitor the effectiveness of the laser surface treatment of carbon fiber reinforced polymer (CFRP) materials are being investigated: laser induced breakdown spectroscopy (LIBS) and optically stimulated electron emission (OSEE). The applicability of LIBS to detect silicone contaminants on CFRP composites is studied using 35 ns Nd:YAG laser pulses at 355 nm with a pulse energy of 45 mJ. The LIBS regime in which pulse energies are < 100 mJ is referred to as mLIBS. CFRP surfaces were contaminated with polydimethylsiloxane (PDMS), a major component of silicone based mold release agents. The presence of PDMS is found by inspecting the Si I emission line at 288.2 nm. Untreated CFRP samples and CFRP contaminated with PDMS were tested. The PDMS areal density ranged from 0.36 Â+/- 0.04 to 0.51 Â+/- 0.16 mg/cm2. The results demonstrate the successful detection of PDMS on CFRP using mLIBS. In addition, OSEE was used to measure CFRP surface cleanliness pre- and post-treatment by laser ablation on specimens contaminated with PDMS coatings from 8 nm to 1311 nm in thickness. The results showed a significant increase in the OSEE photocurrent after laser surface treatment.

  4. Investigation of Chemical Bond Properties and Mssbauer Spectroscopy in YBa2Cu3O7

    Institute of Scientific and Technical Information of China (English)

    高发明; 李东春; 张思远

    2003-01-01

    Chemical bond properties of YBa2Cu3O7 were studied by using the average band-gap model. The calculated results show that the covalency of Cu(1)-O bond is 0.406, and one of Cu(2)-O is 0.276. Mssbauer isomer shifts of 57Fe in Y-123 were calculated by the chemical surrounding factor hv defined by covalency and electronic polarizability. The charge-state and site of Fe were determined. The relation between the coupling constant of electron-phonon interaction and covalency is employed to explain that the Cu(2)-O plane is more important than the Cu(1)-O chain on the superconductivity in the Y-123 compounds.

  5. Detection of sub-GeV Dark Matter and Solar Neutrinos via Chemical-Bond Breaking

    CERN Document Server

    Essig, Rouven; Slone, Oren; Volansky, Tomer

    2016-01-01

    We explore a new low-threshold direct-detection concept for dark matter, based on the breaking of chemical bonds between atoms. This includes the dissociation of molecules and the creation of defects in a lattice. With thresholds of a few to 10's of eV, such an experiment could probe the nuclear couplings of dark matter particles as light as a few MeV. We calculate the expected rates for dark matter to break apart diatomic molecules, which we take as a case study for more general systems. We briefly mention ideas for how chemical-bond breaking might be detected in practice. We also discuss the possibility of detecting solar neutrinos, including pp neutrinos, with this experimental concept. With an event rate of $\\mathcal{O}$(0.1/kg-year), large exposures are required, but measuring low-energy solar neutrinos would provide a crucial test of the solar model.

  6. Developing density functional theory for Bose-Einstein condensates. The case of chemical bonding

    Energy Technology Data Exchange (ETDEWEB)

    Putz, Mihai V., E-mail: mvputz@cbg.uvt.ro [Laboratory of Physical and Computational Chemistry, Chemistry Department, West University of Timisoara, Str. Pestalozzi No. 16, 300115 Timisoara, Romania and Theoretical Physics Institute, Free University Berlin, Arnimallee 14, 14195 Berlin (Germany)

    2015-01-22

    Since the nowadays growing interest in Bose-Einstein condensates due to the expanded experimental evidence on various atomic systems within optical lattices in weak and strong coupling regimes, the connection with Density Functional Theory is firstly advanced within the mean field framework at three levels of comprehension: the many-body normalization condition, Thomas-Fermi limit, and the chemical hardness closure with the inter-bosonic strength and universal Hohenberg-Kohn functional. As an application the traditional Heitler-London quantum mechanical description of the chemical bonding for homopolar atomic systems is reloaded within the non-linear Schrödinger (Gross-Pitaevsky) Hamiltonian; the results show that a two-fold energetic solution is registered either for bonding and antibonding states, with the bosonic contribution being driven by the square of the order parameter for the Bose-Einstein condensate density in free (gas) motion, while the associate wave functions remain as in classical molecular orbital model.

  7. Structure and bonding in crystalline cesium uranyl tetrachloride under pressure.

    Science.gov (United States)

    Osman, Hussien H; Pertierra, Pilar; Salvadó, Miguel A; Izquierdo-Ruiz, F; Recio, J M

    2016-07-21

    A thorough investigation of pressure effects on the structural properties of crystalline cesium uranyl chloride was performed by means of first-principles calculations within the density functional theory framework. Total energies, equilibrium geometries and vibrational frequencies were computed at selected pressures up to 50 GPa. Zero pressure results present good agreement with available experimental and theoretical data. Our calculated equation of state parameters reveal that Cs2UO2Cl4 is a high compressible material, similar to other ionic compounds with cesium cations, and displays a structural anisotropic behavior guided by the uranyl moiety. An unexpected variation of the U-O bond length, dUO, is detected as pressure is applied. It leads to a dUO-stretching frequency relationship that cannot be described by the traditional Badger's rule. Interestingly enough, it can be explained in terms of a change in the main factor controlling dUO. At low pressure, the charge transferred to the uranyl cation induces an increase of the bond length and a red shift of the stretching frequencies, whereas it is the mechanical effect of the applied pressure above 10 GPa that is the dominant factor that leads to a shortening of dUO and a blue shift of the stretching frequencies.

  8. Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Wagh, A.S.; Cunnane, J.C.; Singh, D.; Reed, D.T.; Armstrong, S.; Subhan, W.; Chawla, N.

    1993-01-01

    Results of an initial investigation of low temperature setting chemically bonded magnesium ammonium phosphate (MAP) ceramics as waste form materials, for solidification and stabilization of radioactive and mixed waste, are reported. The suitability of MAP for solidifying and encapsulating waste materials was tested by encapsulating zeolites at loadings up to [approximately]50 wt%. The resulting composites exhibited very good compressive strength characteristics. Microstructure studies show that zeolite grains remain unreacted in the matrix. Potential uses for solidifying and stab wastes are discussed.

  9. Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Wagh, A.S.; Cunnane, J.C.; Singh, D.; Reed, D.T.; Armstrong, S.; Subhan, W.; Chawla, N.

    1993-01-01

    Results of an initial investigation of low temperature setting chemically bonded magnesium ammonium phosphate (MAP) ceramics as waste form materials, for solidification and stabilization of radioactive and mixed waste, are reported. The suitability of MAP for solidifying and encapsulating waste materials was tested by encapsulating zeolites at loadings up to {approximately}50 wt%. The resulting composites exhibited very good compressive strength characteristics. Microstructure studies show that zeolite grains remain unreacted in the matrix. Potential uses for solidifying and stab wastes are discussed.

  10. Multi-layered, chemically bonded lithium-ion and lithium/air batteries

    Energy Technology Data Exchange (ETDEWEB)

    Narula, Chaitanya Kumar; Nanda, Jagjit; Bischoff, Brian L; Bhave, Ramesh R

    2014-05-13

    Disclosed are multilayer, porous, thin-layered lithium-ion batteries that include an inorganic separator as a thin layer that is chemically bonded to surfaces of positive and negative electrode layers. Thus, in such disclosed lithium-ion batteries, the electrodes and separator are made to form non-discrete (i.e., integral) thin layers. Also disclosed are methods of fabricating integrally connected, thin, multilayer lithium batteries including lithium-ion and lithium/air batteries.

  11. Multi-layered, chemically bonded lithium-ion and lithium/air batteries

    Science.gov (United States)

    Narula, Chaitanya Kumar; Nanda, Jagjit; Bischoff, Brian L; Bhave, Ramesh R

    2014-05-13

    Disclosed are multilayer, porous, thin-layered lithium-ion batteries that include an inorganic separator as a thin layer that is chemically bonded to surfaces of positive and negative electrode layers. Thus, in such disclosed lithium-ion batteries, the electrodes and separator are made to form non-discrete (i.e., integral) thin layers. Also disclosed are methods of fabricating integrally connected, thin, multilayer lithium batteries including lithium-ion and lithium/air batteries.

  12. Chemical-assisted bonding of thermoplastics/elastomer for fabricating microfluidic valves.

    Science.gov (United States)

    Gu, Pan; Liu, Ke; Chen, Hong; Nishida, Toshikazu; Fan, Z Hugh

    2011-01-01

    Thermoplastics such as cyclic olefin copolymer (COC) and polymethylmethacrylate (PMMA) have been increasingly used in fabricating microfluidic devices. However, the state-of-the-art microvalve technology is a polydimethylsiloxane (PDMS)-based three-layer structure. In order to integrate such a valve with a thermoplastics-based microfluidic device, a bonding method for thermoplastics/PDMS must be developed. We report here a method to bond COC with PDMS through surface activation by corona discharge, surface modification using 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), and thermal annealing. The method is also applicable to PMMA. The bonding strength between thermoplastics and PDMS was represented by the peeling force, which was measured using a method established by the International Organization for Standardization (ISO). The bonding strength measurement offered an objective and quantitative indicator for protocol optimization, as well as comparison with other PDMS-associated bonding methods. Using optimized bonding conditions, two valve arrays were fabricated in a COC/PDMS/COC device and cyclic operations of valve closing/opening were successfully demonstrated. The valve-containing devices withstood 100 psi (∼689 KPa) without delamination. Further, we integrated such valve arrays in a device for protein separation and demonstrated isoelectric focusing in the presence of valves.

  13. Relationships among the structural topology, bond strength, and mechanical properties of single-walled aluminosilicate nanotubes.

    Science.gov (United States)

    Liou, Kai-Hsin; Tsou, Nien-Ti; Kang, Dun-Yen

    2015-10-21

    Carbon nanotubes (CNTs) are regarded as small but strong due to their nanoscale microstructure and high mechanical strength (Young's modulus exceeds 1000 GPa). A longstanding question has been whether there exist other nanotube materials with mechanical properties as good as those of CNTs. In this study, we investigated the mechanical properties of single-walled aluminosilicate nanotubes (AlSiNTs) using a multiscale computational method and then conducted a comparison with single-walled carbon nanotubes (SWCNTs). By comparing the potential energy estimated from molecular and macroscopic material mechanics, we were able to model the chemical bonds as beam elements for the nanoscale continuum modeling. This method allowed for simulated mechanical tests (tensile, bending, and torsion) with minimum computational resources for deducing their Young's modulus and shear modulus. The proposed approach also enabled the creation of hypothetical nanotubes to elucidate the relative contributions of bond strength and nanotube structural topology to overall nanotube mechanical strength. Our results indicated that it is the structural topology rather than bond strength that dominates the mechanical properties of the nanotubes. Finally, we investigated the relationship between the structural topology and the mechanical properties by analyzing the von Mises stress distribution in the nanotubes. The proposed methodology proved effective in rationalizing differences in the mechanical properties of AlSiNTs and SWCNTs. Furthermore, this approach could be applied to the exploration of new high-strength nanotube materials.

  14. First-Principles Calculations on Electronic, Chemical Bonding and Optical Properties of Cubic Hf3N4

    Institute of Scientific and Technical Information of China (English)

    FENG Li-Ping; WANG Zhi-Qiang; LIU Zheng-Tang

    2013-01-01

    Electronic,chemical bonding and optical properties of cubic Hf3N4(c-Hf3N4) are calculated using the firstprinciples based on the density functional theory (DFT).The optimized lattice parameter is in good agreement with the available experimental and calculational values.Band structure shows that c-Hf3N4 has direct band gap.Densities of states (DOS) and charge densities indicate that the bonding between Hf and N is ionic.The optical properties including complex dielectric function,refractive index,extinction coefficient,absorption coefficient,and reflectivity are predicted.From the theory of crystal-field and molecudar-orbital bonding,the optical transitions of c-Hf3N4 affected by the electronic structure and molecular orbital are studied.It is found that the absorptive transitions of c-Hf3N4 compound are predominantly composed of the transitions from N T22p valence bands to HfT2 (dxy,dxz,dyz) conduction bands.

  15. Chemical bonding and the incorporation of potassium into the Earth's core

    Energy Technology Data Exchange (ETDEWEB)

    Sherman, D.M. (Geological Survey, Denver, CO (USA))

    1990-05-01

    It has been argued that most of the Earth's potassium was segregated into the outer core and that the radioactive decay of {sup 40}K provided the heat source for the geodynamo. This idea rests on the assumption that the affinity of potassium for sulfur or metallic iron is enhanced at high pressure. In this paper, the high pressure electronic structures of K in sulfide, iron sulfide and metallic iron coordination environments were determined from molecular orbital (SCF-X{alpha}-SW) calculations on (KS{sub 8}){sup 15{minus}}, (KS{sub 8}Fe{sub 6}){sup 3{minus}} and KFe{sub 14} clusters. It is shown that, even at high pressure, potassium cannot alloy with metallic iron. Although a high-pressure electronic transition may enhance the potassium-sulfur chemical bond, the electronic structure of the KS{sub 8}Fe{sub 6} cluster shows that this electronic transition cannot happen in an iron sulfide melt. Consequently, potassium will not have an enhanced affinity for sulfur in planetary interiors. If the lower mantle were more reducing, potassium might be excluded from the silicate phases by more strongly lithophile elements and segregated into a metal sulfide phase in the outer core (cf. the phase assemblages in enstatite chondrites). Given the oxidation state of the Earth, however, it is unlikely that significant quantities of potassium have been incorporated into the outer core. The Earth, like the moon and the eucrite parent body, is depleted in potassium. An alternative heat source (e.g., the radioactive decay of U and Th) must be invoked to explain the geodynamo.

  16. On structural health monitoring of aircraft adhesively bonded repairs

    Science.gov (United States)

    Pavlopoulou, Sofia

    The recent interest in life extension of ageing aircraft and the need to address the repair challenges in the new age composite ones, led to the investigation of new repair methodologies such as adhesively bonded repair patches. The present thesis focuses on structural health monitoring aspects of the repairs, evaluating their performance with guided ultrasonic waves aiming to develop a monitoring strategy which would eliminate unscheduled maintenance and unnecessary inspection costs. To address the complex nature of the wave propagation phenomena, a finite element based model identified the existing challenges by exploring the interaction of the excitation waves with different levels of damage. The damage sensitivity of the first anti-symmetric mode was numerically investigated. An external bonded patch and a scarf repair, were further tested in static and dynamic loadings, and their performance was monitored with Lamb waves, excited by surface-bonded piezoelectric transducers.. The response was processed by means of advanced pattern recognition and data dimension reduction techniques such as novelty detection and principal component analysis. An optimisation of these tools enabled an accurate damage detection under complex conditions. The phenomena of mode isolation and precise arrival time determination under a noisy environment and the problem of inadequate training data were investigated and solved through appropriate transducer arrangements and advanced signal processing respectively. The applicability of the established techniques was demonstrated on an aluminium repaired helicopter tail stabilizer. Each case study utilised alternative non-destructive techniques for validation such as 3D digital image correlation, X-ray radiography and thermography. Finally a feature selection strategy was developed through the analysis of the instantaneous properties of guided waves for damage detection purposes..

  17. Single-crystal growth and size control of three novel polar intermetallics: Eu2.94(2)Ca6.06In8Ge8, Eu3.13(2)Ca5.87In8Ge8, and Sr3.23(3)Ca5.77In8Ge8 with crystal structure, chemical bonding, and magnetism studies.

    Science.gov (United States)

    Woo, Hyein; Nam, Gnu; Jang, Eunyoung; Kim, Jin; Lee, Yunho; Ahn, Kyunghan; You, Tae-Soo

    2014-05-05

    Three new quaternary polar intermetallic compounds of Eu2.94(2)Ca6.06In8Ge8, Eu3.13(2)Ca5.87In8Ge8, and Sr3.23(3)Ca5.77In8Ge8 have been synthesized by a metal-flux method using molten indium metal as a reactive flux, and the novel isotypic crystal structures have been characterized by both powder and single-crystal X-ray diffractions. All compounds crystallize in the orthorhombic space group Pmmn (Z = 2, Pearson symbol oP50) with 14 crystallographically unique atomic positions in the asymmetric unit. The lattice parameters are refined as follows: a = 36.928(2) Å, b = 4.511(1) Å, and c = 7.506(1) Å for Eu2.94(2)Ca6.06In8Ge8; a = 37.171(19) Å, b = 4.531(2) Å, and c = 7.560(4) Å for Eu3.13(2)Ca5.87In8Ge8; and a = 37.350(2) Å, b = 4.550(3) Å, and c = 7.593(4) Å for Sr3.23(3)Ca5.77In8Ge8. In particular, single crystals of two Eu-containing compounds are obtained as bundles of bar/needle-shaped crystals, and the thicknesses of those crystals can be controlled in the range between ca. 300 μm and ca. <10 μm by adjusting several reaction conditions, including the reaction cooling rate and the centrifugation temperature. The overall crystal structure is illustrated as an assembly of (1) the three-dimensional anionic framework, which is formed by the chains of edge-sharing InGe4 tetrahedra and the annulene-like "12-membered anionic rings" connected via Ge2 dimers, and (2) the cationic mixed sites embedded in the space between the anionic frameworks. Theoretical investigations based on tight-binding linear muffin-tin orbital (TB-LMTO) calculations provide a comprehesive understanding of the overall electronic structure and chemical bonding observed among anionic components and between anions and cations. Electron localization function (ELF) and electron density map present chemical bond strengths and polarization within the anionic framework. Magnetic susceptibility measurement proves an antiferromagnetic (AFM) ordering of Eu atoms below 4 K with a reduced effective

  18. Non-standard tests for process control in chemically bonded sands

    Directory of Open Access Journals (Sweden)

    S. Ramrattan

    2016-01-01

    Full Text Available Chemically bonded sand cores and molds are more commonly referred to as precision sand systems in the high production automotive powertrain sector. Their behavior in contact with molten metal can lead to casting defects. Consequently, the interaction is of great interest and an important part of metal casting technology. The American Foundry Society (AFS sand testing is based on physical, mechanical, thermal and chemical properties of the sand system. Foundry engineers have long known that certain AFS sand tests provide limited information regarding control of molding and casting quality. The inadequacy is due to the fact that sand casting processes are inherently thermo-mechanical, thermo-chemical and thermo-physical. Non-standard foundry sand testing has proven useful for laboratory measurement of these characteristics in foundry sand using a disc-shaped specimen. Similarly, the equivalent disc-shaped specimens are used for casting trials. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand both the properties of the sand system, as well as the interface of molten metal when different binders, additives and/or refractory coatings are used. The methodology for the following non-standard chemically bonded sand tests is described: (1 disc transverse; (2 impact; (3 modified permeability; (4 abrasion; (5 thermal distortion; (6 quick loss on ignition. The data related to the non-standard sand tests were analyzed and interpreted. The test results indicate that there is relatively lower test-to-test variability with the disc-shaped specimens. The non-standard tests were able to discriminate between the chemically bonded polyurethane cold box sand specimens. Further studies should be conducted on various other sand and binder systems as well as on different specimen thicknesses.

  19. Non-standard tests for process control in chemically bonded sands

    Directory of Open Access Journals (Sweden)

    S. Ramrattan

    2016-01-01

    Full Text Available Chemically bonded sand cores and molds are more commonly referred to as precision sand systems in the high production automotive powertrain sector. Their behavior in contact with molten metal can lead to casting defects. Consequently, the interaction is of great interest and an important part of metal casting technology. The American Foundry Society (AFS sand testing is based on physical, mechanical, thermal and chemical properties of the sand system. Foundry engineers have long known that certain AFS sand tests provide limited information regarding control of molding and casting quality. The inadequacy is due to the fact that sand casting processes are inherently thermo-mechanical, thermo-chemical and thermo-physical. Non-standard foundry sand testing has proven useful for laboratory measurement of these characteristics in foundry sand using a disc-shaped specimen. Similarly, the equivalent disc-shaped specimens are used for casting trials. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand both the properties of the sand system, as well as the interface of molten metal when different binders, additives and/or refractory coatings are used. The methodology for the following non-standard chemically bonded sand tests is described: (1 disc transverse; (2 impact; (3 modified permeability; (4 abrasion; (5 thermal distortion; (6 quick loss on ignition. The data related to the non-standard sand tests were analyzed and interpreted. The test results indicate that there is relatively lower test-to-test variability with the disc-shaped specimens. The non-standard tests were able to discriminate between the chemically bonded polyurethane cold box sand specimens. Further studies should be conducted on various other sand and binder systems as well as on different specimen thicknesses.

  20. In vitro comparison of the shear bond strength of amalgam to tooth structure using two bonding agents--lutting glass ionomer and 4-META.

    OpenAIRE

    Sheela K; Sudeep P; Hegde V; Francis R; Bhat K

    1998-01-01

    Bonding dental amalgam to tooth structure using 4-META has become an accepted clinical procedure. Glass ionomer cements possess the ability to bind to tooth structure as well as to the components of dental amalgam. The present in vitro study evaluates the shear bond strength of amalgam to tooth structure using luting glass ionomer as a bond mediating agent, and compares with that obtained using 4-META. Results indicate that it is possible to bond amalgam to tooth structure using a thin layer ...

  1. In vitro comparison of the shear bond strength of amalgam to tooth structure using two bonding agents--lutting glass ionomer and 4-META.

    Science.gov (United States)

    Sheela, K; Sudeep, P T; Hegde, V; Francis, R F; Bhat, K S; Sundeep, P T

    1998-01-01

    Bonding dental amalgam to tooth structure using 4-META has become an accepted clinical procedure. Glass ionomer cements possess the ability to bind to tooth structure as well as to the components of dental amalgam. The present in vitro study evaluates the shear bond strength of amalgam to tooth structure using luting glass ionomer as a bond mediating agent, and compares with that obtained using 4-META. Results indicate that it is possible to bond amalgam to tooth structure using a thin layer of glass ionomer cement. The shear bond strength of glass ionomer cement mediated bond is significant and may be adequate for clinical application.

  2. Four chemical methods of porcelain conditioning and their influence over bond strength and surface integrity

    Science.gov (United States)

    Stella, João Paulo Fragomeni; Oliveira, Andrea Becker; Nojima, Lincoln Issamu; Marquezan, Mariana

    2015-01-01

    OBJECTIVE: To assess four different chemical surface conditioning methods for ceramic material before bracket bonding, and their impact on shear bond strength and surface integrity at debonding. METHODS: Four experimental groups (n = 13) were set up according to the ceramic conditioning method: G1 = 37% phosphoric acid etching followed by silane application; G2 = 37% liquid phosphoric acid etching, no rinsing, followed by silane application; G3 = 10% hydrofluoric acid etching alone; and G4 = 10% hydrofluoric acid etching followed by silane application. After surface conditioning, metal brackets were bonded to porcelain by means of the Transbond XP system (3M Unitek). Samples were submitted to shear bond strength tests in a universal testing machine and the surfaces were later assessed with a microscope under 8 X magnification. ANOVA/Tukey tests were performed to establish the difference between groups (α= 5%). RESULTS: The highest shear bond strength values were found in groups G3 and G4 (22.01 ± 2.15 MPa and 22.83 ± 3.32 Mpa, respectively), followed by G1 (16.42 ± 3.61 MPa) and G2 (9.29 ± 1.95 MPa). As regards surface evaluation after bracket debonding, the use of liquid phosphoric acid followed by silane application (G2) produced the least damage to porcelain. When hydrofluoric acid and silane were applied, the risk of ceramic fracture increased. CONCLUSIONS: Acceptable levels of bond strength for clinical use were reached by all methods tested; however, liquid phosphoric acid etching followed by silane application (G2) resulted in the least damage to the ceramic surface. PMID:26352845

  3. Four chemical methods of porcelain conditioning and their influence over bond strength and surface integrity

    Directory of Open Access Journals (Sweden)

    João Paulo Fragomeni Stella

    2015-08-01

    Full Text Available OBJECTIVE: To assess four different chemical surface conditioning methods for ceramic material before bracket bonding, and their impact on shear bond strength and surface integrity at debonding.METHODS: Four experimental groups (n = 13 were set up according to the ceramic conditioning method: G1 = 37% phosphoric acid etching followed by silane application; G2 = 37% liquid phosphoric acid etching, no rinsing, followed by silane application; G3 = 10% hydrofluoric acid etching alone; and G4 = 10% hydrofluoric acid etching followed by silane application. After surface conditioning, metal brackets were bonded to porcelain by means of the Transbond XP system (3M Unitek. Samples were submitted to shear bond strength tests in a universal testing machine and the surfaces were later assessed with a microscope under 8 X magnification. ANOVA/Tukey tests were performed to establish the difference between groups (α= 5%.RESULTS: The highest shear bond strength values were found in groups G3 and G4 (22.01 ± 2.15 MPa and 22.83 ± 3.32 Mpa, respectively, followed by G1 (16.42 ± 3.61 MPa and G2 (9.29 ± 1.95 MPa. As regards surface evaluation after bracket debonding, the use of liquid phosphoric acid followed by silane application (G2 produced the least damage to porcelain. When hydrofluoric acid and silane were applied, the risk of ceramic fracture increased.CONCLUSIONS: Acceptable levels of bond strength for clinical use were reached by all methods tested; however, liquid phosphoric acid etching followed by silane application (G2 resulted in the least damage to the ceramic surface.

  4. Immobilization of TiO2 nanoparticles in polymeric substrates by chemical bonding for multi-cycle photodegradation of organic pollutants.

    Science.gov (United States)

    Lei, Ping; Wang, Feng; Gao, Xiaowei; Ding, Yanfen; Zhang, Shimin; Zhao, Jincai; Liu, Shaoren; Yang, Mingshu

    2012-08-15

    Nano titanium dioxide (TiO(2)) photocatalyst is generally immobilized onto the matrix through the physical absorption, hydrogen bonding or chemical bonding, which is utilized for the application of wastewater treatment. In this research, TiO(2) nanoparticles were immobilized in polyvinyl alcohol (PVA) matrix via solution-casting combined with heat-treatment method. Structure characterization indicated that Ti-O-C chemical bond formed via dehydration reaction between TiO(2) and PVA during the heat treatment process, and TiO(2) nanoparticles had been chemically immobilized in PVA matrix. Photodegradation results of methyl orange (MO) showed that the film with 10 wt% TiO(2) and treated at 140°C for 2h exhibited a remarkable ultraviolet (UV) photocatalytic activity, approximately close to the TiO(2) slurry system. This was mainly attributed to the fixation effect by Ti-O-C chemical bonds, which was indirectly confirmed by the slight loss of TiO(2) photocatalysts even after 25-cycle use. In addition, the good swelling ability of PVA matrix provided the MO molecules with more opportunities to fully contact with TiO(2), thus benefited the photocatalysis. This route to chemically immobilize TiO(2) nanoparticles is simple and cheap to prepare polymer/TiO(2) hybrid materials with high photocatalytic activity for multi-cycle use, which is of significance to the practical application of TiO(2) catalysts.

  5. Protein Structure Determination Using Chemical Shifts

    DEFF Research Database (Denmark)

    Christensen, Anders Steen

    In this thesis, a protein structure determination using chemical shifts is presented. The method is implemented in the open source PHAISTOS protein simulation framework. The method combines sampling from a generative model with a coarse-grained force field and an energy function that includes...... chemical shifts. The method is benchmarked on folding simulations of five small proteins. In four cases the resulting structures are in excellent agreement with experimental data, the fifth case fail likely due to inaccuracies in the energy function. For the Chymotrypsin Inhibitor protein, a structure...... is determined using only chemical shifts recorded and assigned through automated processes. The CARMSD to the experimental X-ray for this structure is 1.1. Å. Additionally, the method is combined with very sparse NOE-restraints and evolutionary distance restraints and tested on several protein structures >100...

  6. Ion Mobility-Mass Spectrometry as a Tool for the Structural Characterization of Peptides Bearing Intramolecular Disulfide Bond(s)

    Science.gov (United States)

    Massonnet, Philippe; Haler, Jean R. N.; Upert, Gregory; Degueldre, Michel; Morsa, Denis; Smargiasso, Nicolas; Mourier, Gilles; Gilles, Nicolas; Quinton, Loïc; De Pauw, Edwin

    2016-10-01

    Disulfide bonds are post-translationnal modifications that can be crucial for the stability and the biological activities of natural peptides. Considering the importance of these disulfide bond-containing peptides, the development of new techniques in order to characterize these modifications is of great interest. For this purpose, collision cross cections (CCS) of a large data set of 118 peptides (displaying various sequences) bearing zero, one, two, or three disulfide bond(s) have been measured in this study at different charge states using ion mobility-mass spectrometry. From an experimental point of view, CCS differences (ΔCCS) between peptides bearing various numbers of disulfide bonds and peptides having no disulfide bonds have been calculated. The ΔCCS calculations have also been applied to peptides bearing two disulfide bonds but different cysteine connectivities (Cys1-Cys2/Cys3-Cys4; Cys1-Cys3/Cys2-Cys4; Cys1-Cys4/Cys2-Cys3). The effect of the replacement of a proton by a potassium adduct on a peptidic structure has also been investigated.

  7. Weak Intermolecular Hydrogen Bonds with Fluorine: Detection and Implications for Enzymatic/Chemical Reactions, Chemical Properties, and Ligand/Protein Fluorine NMR Screening.

    Science.gov (United States)

    Dalvit, Claudio; Vulpetti, Anna

    2016-05-23

    It is known that strong hydrogen-bonding interactions play an important role in many chemical and biological systems. However, weak or very weak hydrogen bonds, which are often difficult to detect and characterize, may also be relevant in many recognition and reaction processes. Fluorine serving as a hydrogen-bond acceptor has been the subject of many controversial discussions and there are different opinions about it. It now appears that there is compelling experimental evidence for the involvement of fluorine in weak intramolecular or intermolecular hydrogen bonds. Using established NMR methods, we have previously characterized and measured the strengths of intermolecular hydrogen-bond complexes involving the fluorine moieties CH2 F, CHF2 , and CF3 , and have compared them with the well-known hydrogen-bond complex formed between acetophenone and the strong hydrogen-bond donor p-fluorophenol. We now report evidence for the formation of hydrogen bonds involving fluorine with significantly weaker donors, namely 5-fluoroindole and water. A simple NMR method is proposed for the simultaneous measurement of the strengths of hydrogen bonds between an acceptor and a donor or water. Important implications of these results for enzymatic/chemical reactions involving fluorine, for chemical and physical properties, and for ligand/protein (19) F NMR screening are analyzed through experiments and theoretical simulations.

  8. Structure and Bonding in Small Neutral Alkali-Halide Clusters

    CERN Document Server

    Aguado, A; López, J M; Alonso, J A

    1997-01-01

    The structural and bonding properties of small neutral alkali-halide clusters (AX)n, with n less than or equal to 10, A=Li, Na, K, Rb and X=F, Cl, Br, I, are studied using the ab initio Perturbed Ion (aiPI) model and a restricted structural relaxation criterion. A trend of competition between rock-salt and hexagonal ring-like isomers is found and discussed in terms of the relative ionic sizes. The main conclusion is that an approximate value of r_C/r_A=0.5 (where r_C and r_A are the cationic and anionic radii) separates the hexagonal from the rock-salt structures. The classical electrostatic part of the total energy at the equilibrium geometry is enough to explain these trends. The magic numbers in the size range studied are n= 4, 6 and 9, and these are universal since they occur for all alkali-halides and do not depend on the specific ground state geometry. Instead those numbers allow for the formation of compact clusters. Full geometrical relaxations are considered for (LiF)n (n=3-7) and (AX)_3 clusters, an...

  9. Diffusion phenomena in chemically stabilized multilayer structures

    NARCIS (Netherlands)

    Bruijn, Saskia

    2011-01-01

    Multilayered thin film structures are widely applied as reflective coatings for optical elements in the extreme ultraviolet wavelength regime. In this thesis we investigate the structural and chemical changes that occur in Mo/Si based multilayers as a result of radiation induced thermal loads and ot

  10. Protein Structure Determination Using Chemical Shifts

    DEFF Research Database (Denmark)

    Christensen, Anders Steen

    In this thesis, a protein structure determination using chemical shifts is presented. The method is implemented in the open source PHAISTOS protein simulation framework. The method combines sampling from a generative model with a coarse-grained force field and an energy function that includes...... chemical shifts. The method is benchmarked on folding simulations of five small proteins. In four cases the resulting structures are in excellent agreement with experimental data, the fifth case fail likely due to inaccuracies in the energy function. For the Chymotrypsin Inhibitor protein, a structure...

  11. Atom-specific look at the surface chemical bond using x-ray emission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Nilsson, A.; Wassdahl, N.; Weinelt, M. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    CO and N{sub 2} adsorbed on the late transition metals have become prototype systems regarding the general understanding of molecular adsorption. It is in general assumed that the bonding of molecules to transition metals can be explained in terms of the interaction of the frontier HOMO and LUMO molecular orbitals with the d-orbitals. In such a picture the other molecular orbitals should remain essentially the same as in the free molecule. For the adsorption of the isoelectronic molecules CO and N{sub 2} this has led to the so called Blyholder model i.e., a synergetic {sigma} (HOMO) donor and {pi} (LUMO) backdonation bond. The authors results at the ALS show that such a picture is oversimplified. The direct observation and identification of the states related to the surface chemical bond is an experimental challenge. For noble and transition metal surfaces, the adsorption induced states overlap with the metal d valence band. Their signature is therefore often obscured by bulk substrate states. This complication has made it difficult for techniques such as photoemission and inverse photoemission to provide reliable information on the energy of chemisorption induced states and has left questions unanswered regarding the validity of the frontier orbitals concept. Here the authors show how x-ray emission spectroscopy (XES), in spite of its inherent bulk sensitivity, can be used to investigate adsorbed molecules. Due to the localization of the core-excited intermediate state, XE spectroscopy allows an atomic specific separation of the valence electronic states. Thus the molecular contributions to the surface measurements make it possible to determine the symmetry of the molecular states, i.e., the separation of {pi} and {sigma} type states. In all the authors can obtain an atomic view of the electronic states involved in the formation of the chemical bond to the surface.

  12. Probing the electronic structure and Au–C chemical bonding in AuC{sub 2}{sup −} and AuC{sub 2} using high-resolution photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    León, Iker; Yang, Zheng; Wang, Lai-Sheng, E-mail: Lai-Sheng-Wang@brown.edu [Department of Chemistry, Brown University, Providence, Rhode Island 02912 (United States)

    2014-02-28

    We report photoelectron spectroscopy (PES) and high-resolution PE imaging of AuC{sub 2}{sup −} at a wide range of photon energies. The ground state of AuC{sub 2}{sup −} is found to be linear (C{sub ∞v}, {sup 1}Σ{sup +}) with a …8π{sup 4}4δ{sup 4}17σ{sup 2}9π{sup 4}18σ{sup 2} valence configuration. Detachments from all the five valence orbitals of the ground state of AuC{sub 2}{sup −} are observed at 193 nm. High-resolution PE images are obtained in the energy range from 830 to 330 nm, revealing complicated vibronic structures from electron detachment of the 18σ, 9π, and 17σ orbitals. Detachment from the 18σ orbital results in the {sup 2}Σ{sup +} ground state of neutral AuC{sub 2}, which, however, is bent due to strong vibronic coupling with the nearby {sup 2}Π state from detachment of a 9π electron. The {sup 2}Σ{sup +}–{sup 2}Π vibronic and spin-orbit coupling results in complicated vibronic structures for the {sup 2}Σ{sup +} and {sup 2}Π{sub 3/2} states with extensive bending excitations. The electron affinity of AuC{sub 2} is measured accurately to be 3.2192(7) eV with a ground state bending frequency of 195(6) cm{sup −1}. The first excited state ({sup 2}A′) of AuC{sub 2}, corresponding to the {sup 2}Π{sub 3/2} state at the linear geometry, is only 0.0021 eV above the ground state ({sup 2}A′) and has a bending frequency of 207(6) cm{sup −1}. The {sup 2}Π{sub 1/2} state, 0.2291 eV above the ground state, is linear with little geometry change relative to the anion ground state. The detachment of the 17σ orbital also results in complicated vibronic structures, suggesting again a bent state due to possible vibronic coupling with the lower {sup 2}Π state. The spectrum at 193 nm shows the presence of a minor species with less than 2% intensity relative to the ground state of AuC{sub 2}{sup −}. High-resolution data of the minor species reveal several vibrational progressions in the Au–C stretching mode, which are assigned to

  13. Effect of applied dc bias voltage on composition, chemical bonding and mechanical properties of carbon nitride films prepared by PECVD

    Institute of Scientific and Technical Information of China (English)

    LI Hong-xuan; XU Tao; HAO Jun-ying; CHEN Jian-min; ZHOU Hui-di; XUE Qun-ji; LIU Hui-wen

    2004-01-01

    Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.

  14. An unexpected bridge between chemical bonding indicators and electrical conductivity through the localization tensor.

    Science.gov (United States)

    Pendás, Ángel Martín; Guevara-Vela, José Manuel; Crespo, Daniel Menéndez; Costales, Aurora; Francisco, Evelio

    2017-01-18

    While the modern theory of the insulating state shows that the conducting or insulating properties of a system can be extracted solely from the ground state properties via the so-called localization tensor (LT), no chemical reading of this important quantity has ever been offered. Here, a remarkable link between the LT and the bond orders as described by the delocalization indices (DIs) of chemical bonding theory is reported. This is achieved through a real space partition of the LT into intra- and interatomic contributions. We show that the convergence or divergence of the LT in the thermodynamic limit, which signals the insulating or conducting nature of an extended system, respectively, can be nailed down to DIs. This allows for the exploitation of traditional chemical intuition to identify essential and spectator atomic groups in determining electrical conductivity. The thermodynamic limit of the LT is controlled by the spatial decay rate of the interatomic DIs, exponential in insulators and power-law in conductors. Computational data of a few selected toy systems corroborate our results.

  15. Chemical structure and dynamics: Annual report 1993

    Energy Technology Data Exchange (ETDEWEB)

    Colson, S.D.

    1994-07-01

    The Chemical Structure and Dynamics program responds to the need for a fundamental, molecular-level understanding of chemistry at the wide variety of environmentally-important interfaces. The research program is built around the established relationship between structure, thermodynamics, and kinetics. This research effort continues to evolve into a program of rigorous studies of fundamental molecular processes in model systems (e.g., well-characterized surfaces, single-component solutions, clusters, and biological molecules), and studies of complex systems found in the environment. Experimental studies of molecular and supramolecular structures and thermodynamics are key to understanding the nature of matter, and lead to direct comparison with computational results. Kinetic and mechanistic measurements, combined with real-time dynamics measurements of atomic and molecular motions during chemical reactions, provide for a molecular-level description of chemical reactions. The anticipated results of this work are the achievement of a quantitative understanding of chemical processes at complex interfaces, the development of new techniques for the detection and measurement of species at such interfaces, and the interpretation and extrapolation of the observations in terms of models of interfacial chemistry. The Chemical Structure and Dynamics research program includes five areas described in detail in this report: Reaction mechanisms at solid interfaces; Solution and solution interfaces; Structure and dynamics of biological systems; Analytical methods development; and atmospheric chemistry. Extended abstracts are presented for 23 studies.

  16. Chemical structure and dynamics. Annual report 1995

    Energy Technology Data Exchange (ETDEWEB)

    Colson, S.D.; McDowell, R.S.

    1996-05-01

    The Chemical Structure and Dynamics program is a major component of Pacific Northwest National Laboratory`s Environmental Molecular Sciences Laboratory (EMSL), providing a state-of-the-art collaborative facility for studies of chemical structure and dynamics. We respond to the need for a fundamental, molecular-level understanding of chemistry at a wide variety of environmentally important interfaces by (1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces; (2) developing a multidisciplinary capability for describing interfacial chemical processes within which the new knowledge generated can be brought to bear on complex phenomena in environmental chemistry and in nuclear waste processing and storage; and (3) developing state-of-the-art analytical methods for the characterization of waste tanks and pollutant distributions, and for detection and monitoring of trace atmospheric species.

  17. Chemical structure and dynamics: Annual report 1996

    Energy Technology Data Exchange (ETDEWEB)

    Colson, S.D.; McDowell, R.S.

    1997-03-01

    The Chemical Structure and Dynamics (CS&D) program is a major component of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) developed by Pacific Northwest National Laboratory (PNNL) to provide a state-of-the-art collaborative facility for studies of chemical structure and dynamics. We respond to the need for a fundamental, molecular-level understanding of chemistry at a wide variety of environmentally important interfaces by (1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces; (2) developing a multidisciplinary capability for describing interfacial chemical processes within which the new knowledge generated can be brought to bear on complex phenomena in environmental chemistry and in nuclear waste processing and storage; and (3) developing state-of-the-art analytical methods for characterizing waste tanks and pollutant distributions, and for detecting and monitoring trace atmospheric species.

  18. Annual Report 2000. Chemical Structure and Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Colson, Steven D.; McDowell, Robin S.

    2001-04-15

    This annual report describes the research and accomplishments of the Chemical Structure and Dynamics Program in the year 2000, one of six research programs at the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) - a multidisciplinary, national scientific user facility and research organization. The Chemical Structure and Dynamics (CS&D) program is meeting the need for a fundamental, molecular-level understanding by 1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces; 2) developing a multidisciplinary capability for describing interfacial chemical processes relevant to environmental chemistry; and 3) developing state-of-the-art research and analytical methods for characterizing complex materials of the types found in natural and contaminated systems.

  19. Peptide Bond Synthesis by a Mechanism Involving an Enzymatic Reaction and a Subsequent Chemical Reaction.

    Science.gov (United States)

    Abe, Tomoko; Hashimoto, Yoshiteru; Zhuang, Ye; Ge, Yin; Kumano, Takuto; Kobayashi, Michihiko

    2016-01-22

    We recently reported that an amide bond is unexpectedly formed by an acyl-CoA synthetase (which catalyzes the formation of a carbon-sulfur bond) when a suitable acid and l-cysteine are used as substrates. DltA, which is homologous to the adenylation domain of nonribosomal peptide synthetase, belongs to the same superfamily of adenylate-forming enzymes, which includes many kinds of enzymes, including the acyl-CoA synthetases. Here, we demonstrate that DltA synthesizes not only N-(d-alanyl)-l-cysteine (a dipeptide) but also various oligopeptides. We propose that this enzyme catalyzes peptide synthesis by the following unprecedented mechanism: (i) the formation of S-acyl-l-cysteine as an intermediate via its "enzymatic activity" and (ii) subsequent "chemical" S → N acyl transfer in the intermediate, resulting in peptide formation. Step ii is identical to the corresponding reaction in native chemical ligation, a method of chemical peptide synthesis, whereas step i is not. To the best of our knowledge, our discovery of this peptide synthesis mechanism involving an enzymatic reaction and a subsequent chemical reaction is the first such one to be reported. This new process yields peptides without the use of a thioesterified fragment, which is required in native chemical ligation. Together with these findings, the same mechanism-dependent formation of N-acyl compounds by other members of the above-mentioned superfamily demonstrated that all members most likely form peptide/amide compounds by using this novel mechanism. Each member enzyme acts on a specific substrate; thus, not only the corresponding peptides but also new types of amide compounds can be formed.

  20. ELECTRONIC AND CHEMICAL PROPERTIES OF PD IN BIMETALLIC SYSTEMS: HOW MUCH DO WE KNOW ABOUT HETERONUCLEAR METAL-METAL BONDING?

    Energy Technology Data Exchange (ETDEWEB)

    RODRIGUEZ,J.A.

    2001-09-27

    The experimental and theoretical studies described above illustrate the complex nature of the heteronuclear metal-metal bond. In many cases, bimetallic bonding induces a significant redistribution of charge around the bonded metals. This redistribution of charge is usually linked to the strength of the bimetallic bond, affects the position of the core and valence levels of the metals, and can determine the chemical reactivity of the system under study. New concepts are emerging [22,23,34,36] and eventually the coupling of experiment and theory can be useful for designing more efficient bimetallic catalysts [98,106,107].

  1. Hydrogen bonding in oxalic acid and its complexes: A database study of neutron structures

    Indian Academy of Sciences (India)

    R Chitra; Amit Das; R R Choudhury; M Ramanadham; R Chidambaram

    2004-08-01

    The basic result of carboxylic group that the oxygen atom of the –OH never seems to be a hydrogen bond acceptor is violated in the cases, namely urea oxalic acid and bis urea oxalic acid complexes, where the hydroxyl oxygen atom is an acceptor of a weak N–H... O hydrogen bond. The parameters of this hydrogen bond, respectively in these structures are: hydrogen acceptor distance 2.110 Å and 2.127 Å and the bending angle at hydrogen, 165.6° and 165.8°. The bond strength around the hydroxyl oxygen is close to 1.91 valence units, indicating that it has hardly any strength left to form hydrogen bonds. These two structures being highly planar, force the formation of this hydrogen bond. As oxalic acid is the common moiety, the structures of the two polymorphs, -oxalic acid and -oxalic acid, also were looked into in terms of hydrogen bonding and packing.

  2. Processing–structure–property relations of chemically bonded phosphate ceramic composites

    Indian Academy of Sciences (India)

    H A Colorado; C Hiel; H T Hahn

    2011-07-01

    Mechanical properties and microstructures of a chemically bonded phosphate ceramic (CBPC) and its composite with 1.0 wt% graphite nanoplatelets (GNPs) reinforcement have been investigated. Microstructure was identified by using optical and scanning electron microscopes, X-ray tomography, and X-ray diffraction. In addition, weight loss of the resin at room temperature was studied. The microstructure characterization shows that CBPC is itself a composite with several crystalline (wollastonite and brushite) and amorphous phases. SEM and micro tomography show a homogeneous distribution of crystalline phases. Bending and compression strength of the CBPC was improved by reducing bubbles via preparation in vacuum.

  3. Influence of chemical bonding on X-ray spectra of different aluminium compounds

    Energy Technology Data Exchange (ETDEWEB)

    Bonetto, Rita [Centro de Investigacion y Desarrollo en Ciencias Aplicadas Dr. Jorge Ronco, Calle 47 No. 257, CC 59, 1900 La Plata (Argentina) and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina (Argentina)]. E-mail: bonetto@quimica.unlp.edu.ar; Trincavelli, Jorge [Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000, Cordoba (Argentina) and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina (Argentina)]. E-mail: jorge@quechua.fis.uncor.edu; Vasconcellos, Marcos [Instituto de Fisica, Universidade Federal de Rio Grande do Sul, Campus do Vale, Av. Bento Goncalves 9500, CEP: 91501-970, Porto Alegre (Brazil)]. E-mail: marcos@if.ufrgs.br

    2005-11-15

    Five minerals containing aluminium in different crystal configurations are studied. The different kinds of chemical bonding between aluminium and oxygen originate molecular orbitals with energy levels and transition probabilities varying from one compound to another. This effect appears as shifts and changes in relative intensities of K{alpha} emission lines and as modifications of the K{beta} characteristic spectrum. In the present work, the aluminium K characteristic spectra obtained by means of an electron microprobe with a wavelength dispersive system are compared for topaz, albite, spodumene, biotite and corundum.

  4. A tutorial for understanding chemical reactivity through the valence bond approach.

    Science.gov (United States)

    Usharani, Dandamudi; Lai, Wenzhen; Li, Chunsen; Chen, Hui; Danovich, David; Shaik, Sason

    2014-07-21

    This is a tutorial on the usage of valence bond (VB) diagrams for understanding chemical reactivity in general, and hydrogen atom transfer (HAT) reactivity in particular. The tutorial instructs the reader how to construct the VB diagrams and how to estimate HAT barriers from raw data, starting with the simplest reaction H + H2 and going all the way to HAT in the enzyme cytochrome P450. Other reactions are treated as well, and some unifying principles are outlined. The tutorial projects the unity of reactivity treatments, following Coulson's dictum "give me insight, not numbers", albeit with its modern twist: giving numbers and insight.

  5. Adsorption structure and bonding of trimesic acid on Cu(100)

    Science.gov (United States)

    Kanninen, L.; Jokinen, N.; Ali-Löytty, H.; Jussila, P.; Lahtonen, K.; Hirsimäki, M.; Valden, M.; Kuzmin, M.; Pärna, R.; Nõmmiste, E.

    2011-12-01

    Combining scanning tunneling microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy using synchrotron radiation, we have studied the adsorption and growth of trimesic acid (TMA, 1,3,5-benzenetricarboxylic acid, C6H3(COOH)3) on Cu(100) in a wide range of coverages (from submonolayer to multilayer ones) at room temperature and after subsequent annealing. A series of coverage-dependent TMA structures, transitions between these structures, and their properties are characterized, demonstrating the interplay between the bonding, orientation, and deprotonation reaction of adsorbed species. In particular, it is shown that the degree of deprotonation in TMA overlayers depends on the amount of deposited molecules non-monotonously, and that such behavior is well consistent with the formation mechanism proposed for the TMA/Cu(100) system. The results provide a good platform for further understanding of non-covalent interactions and self-assembly phenomena underlying the growth of supramolecular nanoassemblies of aromatic carboxylic (benzenecarboxylic) acids on metallic substrates.

  6. Caul and method for bonding and curing intricate composite structures

    Science.gov (United States)

    Willden, Kurtis S. (Inventor); Goodno, Kenneth N. (Inventor)

    1993-01-01

    The invention disclosed here is a method for forming and curing an intricate structure of criss-crossing composite stringers and frames that are bonded to a skin panel. A structure constructed in accordance with the invention would be well-suited for use as a portion of an aircraft fuselage, a boat hull, or the like. The method is preferably practiced by applying uncured composite stringers to an uncured composite sheet panel. This is followed by placing cured frames crosswise over the stringers. The frames have openings at the locations where they intersect with the stringers which enables the frames to come into direct contact with the skin along most of their length. During the forming and curing process, the stringers are covered with a plurality of cauls, and the entire assembly of skin panel, stringers, frames and cauls is subjected to a vacuum bagging and curing process. The cauls serve to maintain both part shape and to control the flow of resin within the stringers as they are cured. Further, they probably eliminate the need for intermediate protective materials between the vacuum bag and the stringers.

  7. The electronic nature of the 1,4-β-glycosidic bond and its chemical environment: DFT insights into cellulose chemistry.

    Science.gov (United States)

    Loerbroks, Claudia; Rinaldi, Roberto; Thiel, Walter

    2013-11-25

    The molecular understanding of the chemistry of 1,4-β-glucans is essential for designing new approaches to the conversion of cellulose into platform chemicals and biofuels. In this endeavor, much attention has been paid to the role of hydrogen bonding occurring in the cellulose structure. So far, however, there has been little discussion about the implications of the electronic nature of the 1,4-β-glycosidic bond and its chemical environment for the activation of 1,4-β-glucans toward acid-catalyzed hydrolysis. This report sheds light on these central issues and addresses their influence on the acid hydrolysis of cellobiose and, by analogy, cellulose. The electronic structure of cellobiose was explored by DFT at the BB1 K/6-31++G(d,p) level. Natural bond orbital (NBO) analysis was performed to grasp the key bonding concepts. Conformations, protonation sites, and hydrolysis mechanisms were examined. The results for cellobiose indicate that cellulose is protected against hydrolysis not only by its supramolecular structure, as currently accepted, but also by its electronic structure, in which the anomeric effect plays a key role.

  8. Chemical structure and physical properties of radiation-induced crosslinking of polytetrafluoroethylene

    Energy Technology Data Exchange (ETDEWEB)

    Oshima, Akihiro E-mail: aks@taka.jaeri.go.jp; Ikeda, Shigetoshi; Katoh, Etsuko; Tabata, Yoneho

    2001-07-01

    The chemical structure and physical properties of polytetrafluoroethylene (PTFE) that has been crosslinked by radiation have been studied by various methods. It has been found that a Y-type crosslinking structure and a Y-type structure incorporating a double bond (modified Y-type) is formed in PTFE by radiation-crosslinking in the molten state. In addition, various types of double bond structures, excluding the crosslinking site, have been identified. The crosslinked PTFE has a good light transparency due to the loss of crystallites, whilst it retains the excellent properties of electrical insulation and heat resistance. The coefficient of abrasion and the permanent creep are also greatly improved by crosslinking.

  9. Improvement in reinforcing bond strength in reinforced concrete with self-repairing chemical adhesives

    Science.gov (United States)

    Dry, Carolyn M.

    1997-05-01

    Self-healing concretes have embedded adhesives which are released from hollow fibers inside the concrete when and where cracking of the matrix and the fibers occurs. It was found that the adhesive improves the strength of the cracked portions of the concrete and increases its ability to deflect under load. Structural materials subjected to dynamic events such as earthquakes and impacts can have improved response by the noise of adhesive type which can impart improved damping, lateral stiffness, or deflection. Testing also assessed the improvement of the bond strength in structures. In laboratory tests the internal adhesive repair system improved the bond between the reinforcing steel and the concrete to prevent pullout failure or debonding at the interface.

  10. Chemical bonding and magnetic properties of gadolinium (Gd) substituted cobalt ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Puli, Venkata Sreenivas, E-mail: vspuli@utep.edu [Department of Mechanical Engineering, University of Texas, El Paso, TX 79968 (United States); Adireddy, Shiva [Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118 (United States); Ramana, C.V. [Department of Mechanical Engineering, University of Texas, El Paso, TX 79968 (United States)

    2015-09-25

    Graphical abstract: Room temperature Raman spectra of CoFe{sub 2−x}Gd{sub x}O{sub 4} (CFGO, x = 0.0–0.3) compounds as a function of wavenumber (cm{sup −1}). - Highlights: • Gd substituted ferrites were synthesized under controlled concentration. • Gd ion induced lattice dynamical changes are significant. • Enhanced magnetization is observed upon Gd-incorporation in cobalt ferrite. • A correlation between lattice dynamics and magnetic properties is established. - Abstract: Polycrystalline gadolinium (Gd) substituted cobalt ferrites (CoFe{sub 2−x}Gd{sub x}O{sub 4}; x = 0–0.3, referred to CFGO) ceramics have been synthesized by solid state reaction method. Chemical bonding, crystal structure and magnetic properties of CFGO compounds have been evaluated as a function of Gd-content. X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure. However, a secondary ortho-ferrite phase (GdFeO{sub 3}) nucleates for higher values of Gd-content. A considerable increase in the saturation magnetization has been observed upon the initial substitution of Gd (x = 0.1). The saturation magnetization drastically decreases at higher Gd content (x ⩾ 0.3). No contribution from ortho-ferrite GdFeO{sub 3} phase is noted to the magnetic properties. The increase in the magnetic saturation magnetization is attributed to the higher magnetic moment of Gd{sup 3+} (4f{sup 7}) residing in octahedral sites is higher when compared to that of Fe{sup 3+} (3d{sup 5}) and as well due to the migration of Co{sup 2+} (3d{sup 7}) ions from the octahedral to the tetrahedral sites with a magnetic moment aligned anti-parallel to those of rare earth (RE{sup 3+}) ions in the spinel lattice. Increase in coercivity with increase in Gd{sup 3+} is content is attributed to magnetic anisotropy in the ceramics.

  11. Synthesis, solid-state structure, and bonding analysis of a homoleptic beryllium azide

    Energy Technology Data Exchange (ETDEWEB)

    Naglav, Dominik; Tobey, Briac; Lyhs, Benjamin; Roemer, Beate; Blaeser, Dieter; Woelper, Christoph; Jansen, Georg; Schulz, Stephan [Faculty of Chemistry and Center for Nanointegration Duisburg-Essen (Cenide), Duisburg-Essen Univ., Essen (Germany)

    2017-07-10

    [Ph{sub 4}P]{sub 2}[Be(N{sub 3}){sub 4}] (1) and [PNP]{sub 2}[Be(N{sub 3}){sub 4}] (2; PNP=Ph{sub 3}PNPPh{sub 3}) were synthesized by reacting Be(N{sub 3}){sub 2} with [Ph{sub 4}P]N{sub 3} and [PNP]N{sub 3}. Compound 1 represents the first structurally characterized homoleptic beryllium azide. The electronic structure and bonding situation in the tetraazidoberyllate dianion [Be(N{sub 3}){sub 4}]{sup 2-} were investigated by quantum-chemical calculations (NPA, ELF, LOL). (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. The PubChem chemical structure sketcher

    Directory of Open Access Journals (Sweden)

    Ihlenfeldt Wolf D

    2009-12-01

    Full Text Available Abstract PubChem is an important public, Web-based information source for chemical and bioactivity information. In order to provide convenient structure search methods on compounds stored in this database, one mandatory component is a Web-based drawing tool for interactive sketching of chemical query structures. Web-enabled chemical structure sketchers are not new, being in existence for years; however, solutions available rely on complex technology like Java applets or platform-dependent plug-ins. Due to general policy and support incident rate considerations, Java-based or platform-specific sketchers cannot be deployed as a part of public NCBI Web services. Our solution: a chemical structure sketching tool based exclusively on CGI server processing, client-side JavaScript functions, and image sequence streaming. The PubChem structure editor does not require the presence of any specific runtime support libraries or browser configurations on the client. It is completely platform-independent and verified to work on all major Web browsers, including older ones without support for Web2.0 JavaScript objects.

  13. Chemically bonded phosphorus/graphene hybrid as a high performance anode for sodium-ion batteries.

    Science.gov (United States)

    Song, Jiangxuan; Yu, Zhaoxin; Gordin, Mikhail L; Hu, Shi; Yi, Ran; Tang, Duihai; Walter, Timothy; Regula, Michael; Choi, Daiwon; Li, Xiaolin; Manivannan, Ayyakkannu; Wang, Donghai

    2014-11-12

    Room temperature sodium-ion batteries are of great interest for high-energy-density energy storage systems because of low-cost and natural abundance of sodium. Here, we report a novel phosphorus/graphene nanosheet hybrid as a high performance anode for sodium-ion batteries through facile ball milling of red phosphorus and graphene stacks. The graphene stacks are mechanically exfoliated to nanosheets that chemically bond with the surfaces of phosphorus particles. This chemical bonding can facilitate robust and intimate contact between phosphorus and graphene nanosheets, and the graphene at the particle surfaces can help maintain electrical contact and stabilize the solid electrolyte interphase upon the large volume change of phosphorus during cycling. As a result, the phosphorus/graphene nanosheet hybrid nanostructured anode delivers a high reversible capacity of 2077 mAh/g with excellent cycling stability (1700 mAh/g after 60 cycles) and high Coulombic efficiency (>98%). This simple synthesis approach and unique nanostructure can potentially be applied to other phosphorus-based alloy anode materials for sodium-ion batteries.

  14. Chemical bonding and humidity sensing properties of amorphous carbon nitride (a-CNx) by acetylene gas

    Science.gov (United States)

    Aziz, Siti Aisyah Abd; Purhanudin, Noorain; Awang, Rozidawati

    2017-05-01

    Amorphous carbon nitride (a-CNx) thin films were deposited by radio frequency plasma enhance chemical vapor deposition (RF-PECVD) using a fixed mixture of acetylene (C2H2) at 20 sccm and nitrogen (N2) gases at 50 sccm. The films were deposited at different RF power of 60, 70, 80, 90 and 100 W. The deposition pressure, deposition time and substrate temperature were kept constant at 0.8 mbar, 30 minutes and 100°C, respectively. The chemical bonding of the a-CNx thin films was characterized using Fourier transform infrared spectroscopy (FTIR) and its sensing properties was determined using a home built humidity sensor system. The increase of RF powers leads to an increment of formation of double (C=N) and triple (C≡N) bonds as compared to a-CNx deposited using methane (CH4) or ethane (C2H6) gas. This is due to a higher ratio of C to H atoms in C2H2. The humidity sensing performance show the sensitivity of the films is the highest at low deposition power in changes of relative humidity (%RH). The a-CNx thin film show good repeatability and high sensitivity as a humidity sensing materials which prepared at low RF power.

  15. Experimental evidence of chemical components in the bonding of helium and neon with neutral molecules.

    Science.gov (United States)

    Cappelletti, David; Bartocci, Alessio; Grandinetti, Felice; Falcinelli, Stefano; Belpassi, Leonardo; Tarantelli, Francesco; Pirani, Fernando

    2015-04-13

    The complexes of helium and neon with gaseous neutral molecules are generally perceived to be van der Waals adducts held together by physical (non-covalent) forces, owing to the combination of size (exchange) repulsion with dispersion/induction attraction. Molecular beam experiments confirm that this is the case for He-CF4 , Ne-CF4 adducts, but revealed that the interaction of He and Ne with CCl4 features an appreciable contribution of chemical components that arise from the anisotropy of the electron density of CCl4 that enhances a charge transfer from Ng (Ng=He, Ne). These findings furnish a novel assay of the bonding capabilities of helium and neon, and invite to revisit the neutral complexes of these elements as systems of chemical relevance. The CCl4 -Ng are also peculiar examples of halogen bonds, a group of interactions of major current concern. Finally, this investigation is a prelude to the development of semi-empirical models for force fields aimed to the unified description of static and dynamical properties of systems of comparable or higher complexity.

  16. Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale

    Science.gov (United States)

    Tian, Kaiwen; Gosvami, Nitya N.; Goldsby, David L.; Liu, Yun; Szlufarska, Izabela; Carpick, Robert W.

    2017-02-01

    Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds. The role of normal load (and, thus, normal stress) on this interfacial chemical bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.

  17. Effects of structural differences on the NMR chemical shifts in isostructural dipeptides.

    Science.gov (United States)

    Altheimer, Benjamin D; Mehta, Manish A

    2014-04-10

    Porous crystalline dipeptides have gained recent attention for their potential as gas-storage materials. Within this large class is a group of dipeptides containing alanine, valine, and isoleucine with very similar crystal structures. We report the (13)C (carbonyl and Cα) and (15)N (amine and amide) solid-state NMR isotropic chemical shifts in a series of seven such isostructural porous dipeptides as well as shift tensor data for the carbonyl and amide sites. Using their known crystal structures and aided by ab initio quantum chemical calculations for the resonance assignments, we elucidate trends relating local structure, hydrogen-bonding patterns, and chemical shift. We find good correlation between the backbone dihedral angles and the Cα1 and Cα2 shifts. For the C1 shift tensor, the δ11 value shifts downfield as the hydrogen-bond distance increases, δ22 shifts upfield, and δ33 shows little variation. The C2 shift tensor shows no appreciable correlation with structural parameters. For the N2 tensor, δ11 shows little dependence on the hydrogen-bond length, whereas δ22 and δ33 both show a decrease in shielding as the hydrogen bond shortens. Our analysis teases apart some, but not all, structural contributors to the observed differences the solid-state NMR chemical shifts.

  18. The hierarchical structure of chemical engineering

    Institute of Scientific and Technical Information of China (English)

    Mooson KWAUK

    2007-01-01

    Around the turn of the present century, scholars began to recognize chemical engineering as a complex system, and have been searching for a convenient point of entry for refreshing its knowledge base. From our study of the dynamic structures of dispersed particles in fluidization and the resulting multi-scale method, we have been attempting to extend our findings to structures prevailing in other multiphase systems as well as in the burgeoning industries producing functional materials. Chemical engineering itself is hierarchically structured. Besides structures based on space and time, such hierarchy could be built from ChE history scaled according to science content, or from ChE operation according to the expenditure of manpower and capital investment.

  19. Correlation between topological band character and chemical bonding in a Bi14Rh3I9-based family of insulators

    Science.gov (United States)

    Rasche, Bertold; Isaeva, Anna; Ruck, Michael; Koepernik, Klaus; Richter, Manuel; van den Brink, Jeroen

    2016-02-01

    Recently the presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Here, we present a density-functional-theory-based study on a family of TIs derived from the Bi14Rh3I9 parent structure via substitution of Ru, Pd, Os, Ir and Pt for Rh. Comparative analysis of the band-structures throughout the entire series is done by means of a unified minimalistic tight-binding model that evinces strong similarity between the quantum-spin-Hall (QSH) layer in Bi14Rh3I9 and graphene in terms of -molecular orbitals. Topologically non-trivial energy gaps are found for the Ir-, Rh-, Pt- and Pd-based systems, whereas the Os- and Ru-systems remain trivial. Furthermore, the energy position of the metal -band centre is identified as the parameter which governs the evolution of the topological character of the band structure through the whole family of TIs. The -band position is shown to correlate with the chemical bonding within the QSH layers, thus revealing how the chemical nature of the constituents affects the topological band character.

  20. The Use of Chemical-Chemical Interaction and Chemical Structure to Identify New Candidate Chemicals Related to Lung Cancer.

    Directory of Open Access Journals (Sweden)

    Lei Chen

    Full Text Available Lung cancer causes over one million deaths every year worldwide. However, prevention and treatment methods for this serious disease are limited. The identification of new chemicals related to lung cancer may aid in disease prevention and the design of more effective treatments. This study employed a weighted network, constructed using chemical-chemical interaction information, to identify new chemicals related to two types of lung cancer: non-small lung cancer and small-cell lung cancer. Then, a randomization test as well as chemical-chemical interaction and chemical structure information were utilized to make further selections. A final analysis of these new chemicals in the context of the current literature indicates that several chemicals are strongly linked to lung cancer.

  1. Synthesis, XRD crystal structure, spectroscopic characterization (FT-IR, 1H and 13C NMR), DFT studies, chemical reactivity and bond dissociation energy studies using molecular dynamics simulations and evaluation of antimicrobial and antioxidant activities of a novel chalcone derivative, (E)-1-(4-bromophenyl)-3-(4-iodophenyl)prop-2-en-1-one

    Science.gov (United States)

    Zainuri, D. Alwani; Arshad, Suhana; Khalib, N. Che; Razak, I. Abdul; Pillai, Renjith Raveendran; Sulaiman, S. Fariza; Hashim, N. Shafiqah; Ooi, K. Leong; Armaković, Stevan; Armaković, Sanja J.; Panicker, C. Yohannan; Van Alsenoy, C.

    2017-01-01

    In the present study, the title compound named as (E)-1-(4-bromophenyl)-3-(4-iodophenyl)prop-2-en-1-one was synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system with P21/c space group with the unit cell parameters of a = 16.147 (2) Å, b = 14.270 (2) Å, c = 5.9058 (9) Å, β = 92.577 (3)° and Z = 4. The molecular geometry obtained from X-Ray structure determination was optimized by Density Functional Theory (DFT) using B3LYP/6-31G+(d, p)/Lanl2dz(f) method in the ground state. The IR spectrum was recorded and interpreted in details with the aid of Density Functional Theory (DFT) calculations and Potential Energy Distribution (PED) analysis. In order to investigate local reactivity properties of the title molecule, we have conducted DFT calculations of average local ionization energy surface and Fukui functions which were mapped to the electron density surface. In order to predict the open air stability and possible degradation properties, within DFT approach, we have also calculated bond dissociation energies. 1H and 13C NMR spectra were recorded and chemical shifts were calculated theoretically and compared with the experimental values. In addition, in vitro antimicrobial results show that the title compound has great potential of antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis and Micrococcus luteus bacteria and antifungal activity against Candida albicans in comparison to some reported chalcone derivatives. Antioxidant studies revealed the highest metal chelating activity of this compound.

  2. β-Sheet 13C Structuring Shifts Appear only at the H-bonded Sites of Hairpins

    Science.gov (United States)

    Shu, Irene; Stewart, James M.; Scian, Michele; Kier, Brandon L.

    2011-01-01

    The 13C chemical shifts measured for designed β hairpins indicate that the structuring shifts (upfield for Cα and C′, downfield for Cβ) previously reported as diagnostic for β structuring in protein appear only at the H-bonded strand residues. The resulting periodicity of structuring shift magnitudes is not, however, a consequence of H-bonding status; rather, it reflects a previously unrecognized alternation in the backbone torsion angles of β strands. This feature of hairpins is also likely to be present in proteins. The study provides reference values for the expectation shifts for 13C sites in β structures that should prove useful in the characterization of the folding equilibria of β sheet models. PMID:21214243

  3. Sandwiched Thin-Film Anode of Chemically Bonded Black Phosphorus/Graphene Hybrid for Lithium-Ion Battery.

    Science.gov (United States)

    Liu, Hanwen; Zou, Yuqin; Tao, Li; Ma, Zhaoling; Liu, Dongdong; Zhou, Peng; Liu, Hongbo; Wang, Shuangyin

    2017-09-01

    A facile vacuum filtration method is applied for the first time to construct sandwich-structure anode. Two layers of graphene stacks sandwich a composite of black phosphorus (BP), which not only protect BP from quickly degenerating but also serve as current collector instead of copper foil. The BP composite, reduced graphene oxide coated on BP via chemical bonding, is simply synthesized by solvothermal reaction at 140 °C. The sandwiched film anode used for lithium-ion battery exhibits reversible capacities of 1401 mAh g(-1) during the 200th cycle at current density of 100 mA g(-1) indicating superior cycle performance. Besides, this facile vacuum filtration method may also be available for other anode material with well dispersion in N-methyl pyrrolidone (NMP). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Development of structural health monitoring systems for composite bonded repairs on aircraft structures

    Science.gov (United States)

    Galea, Stephen C.; Powlesland, Ian G.; Moss, Scott D.; Konak, Michael J.; van der Velden, Stephen P.; Stade, Bryan; Baker, Alan A.

    2001-08-01

    The application of bonded composite patches to repair or reinforce defective metallic structures is becoming recognized as a very effective versatile repair procedure for many types of problems. Immediate applications of bonded patches are in the fields of repair of cracking, localized reinforcement after removal of corrosion damage and for reduction of fatigue strain. However, bonded repairs to critical components are generally limited due to certification concerns. For certification and management of repairs to critical structure, the Smart Patch approach may be an acceptable solution from the airworthiness prospective and be cost effective for the operator and may even allow some relaxation of the certification requirements. In the most basic form of the Smart Patch in-situ sensors can be used as the nerve system to monitor in service the structural condition (health or well-being) of the patch system and the status of the remaining damage in the parent structure. This application would also allow the operator to move away from current costly time-based maintenance procedures toward real-time health condition monitoring of the bonded repair and the repaired structure. TO this end a stand-alone data logger device, for the real-time health monitoring of bonded repaired systems, which is in close proximity to sensors on a repair is being developed. The instrumentation will measure, process and store sensor measurements during flight and then allow this data to be up-loaded, after the flight, onto a PC, via remote (wireless) data access. This paper describes two in-situ health monitoring systems which will be used on a composite bonded patch applied to an F/A-18. The two systems being developed consists of a piezoelectric (PVDF) film-based and a conventional electrical-resistance foil strain gauge-based sensing system. The latter system uses a primary cell (Lithium- based battery) as the power source, which should enable an operating life of 1-2 years. The patch

  5. Chemical Structure and Dynamics annual report 1997

    Energy Technology Data Exchange (ETDEWEB)

    Colson, S.D.; McDowell, R.S.

    1998-03-01

    The Chemical Structure and Dynamics (CS and D) program is a major component of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), developed by Pacific Northwest National Laboratory (PNNL) to provide a state-of-the-art collaborative facility for studies of chemical structure and dynamics. The authors respond to the need for a fundamental, molecular level understanding of chemistry at a wide variety of environmentally important interfaces by: (1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces; (2) developing a multidisciplinary capability for describing interfacial chemical processes within which the new knowledge generated can be brought to bear on complex phenomena in environmental chemistry and in nuclear waste processing and storage; and (3) developing state-of-the-art analytical methods for characterizing complex materials of the types found in stored wastes and contaminated soils, and for detecting and monitoring trace atmospheric species. The focus of the research is defined primarily by DOE`s environmental problems: fate and transport of contaminants in the subsurface environment, processing and storage of waste materials, cellular effects of chemical and radiological insult, and atmospheric chemistry as it relates to air quality and global change. Twenty-seven projects are described under the following topical sections: Reaction mechanisms at interfaces; High-energy processes at environmental interfaces; Cluster models of the condensed phase; and Miscellaneous.

  6. Electronic Structure of Pi Systems: Part III--Applications in Spectroscopy and Chemical Reactivity.

    Science.gov (United States)

    Fox, Marye Anne; Matsen, F. A.

    1985-01-01

    Shows that electronic structure diagrams make more accurate predictions of spectral properties and chemical reactivity for simple pi systems than do either Huckel molecular orbital or valence bond theory alone. Topics addressed include absorption and photoelectron spectra, spin density distribution in radicals, and several problems regarding…

  7. Protein structure validation and refinement using amide proton chemical shifts derived from quantum mechanics

    DEFF Research Database (Denmark)

    Christensen, Anders Steen; Linnet, Troels Emtekær; Borg, Mikael;

    2013-01-01

    We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level...

  8. Magnetovolume and chemical bonding effects of Sn atom in the γ'-(Fe1-xSnx)4N compounds

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Combining x-ray diffraction and high pressure Mossbauer spectroscopy,the structure and the hyperfine parameters of Sn substituted for Fe in γ'-Fe4N were in-vestigated. The results of x-ray diffraction indicate that single phase γ'-(Fel-xSnx)4Ncompounds can be synthesized in the composition range 0≤ x ≤ 0.3, and the latticeparameter can be well fitted with two linear formulas α0(x) = 3.795 + 0.019 × x (0.0≤x ≤0.10) and α0(x) = 3.795+ 0.228 × (x- 0.1)(0.10 ≤ x ≤0.30) for different contentof Sn. Using high pressure Mossbauer spectra, the influences of the magnetovolunceffect and the chemical bonding effect of Sn atom on the hyperfine magnetic field andthe isomer shift were first distinguished. It is found that the magnetovolume and thechemical bonding have different influences on the properties of γ'-(Fe1-xSnx)4N, andthe latter plays a more important role.

  9. Triple oxygen isotope systematics of structurally bonded water in gypsum

    Science.gov (United States)

    Herwartz, Daniel; Surma, Jakub; Voigt, Claudia; Assonov, Sergey; Staubwasser, Michael

    2017-07-01

    The triple oxygen isotopic composition of gypsum mother water (gmw) is recorded in structurally bonded water in gypsum (gsbw). Respective fractionation factors have been determined experimentally for 18O/16O and 17O/16O. By taking previous experiments into account we suggest using 18αgsbw-gmw = 1.0037; 17αgsbw-gmw = 1.00195 and θgsbw-gmw = 0.5285 as fractionation factors in triple oxygen isotope space. Recent gypsum was sampled from a series of 10 ponds located in the Salar de Llamara in the Atacama Desert, Chile. Total dissolved solids (TDS) in these ponds show a gradual increase from 23 g/l to 182 g/l that is accompanied by an increase in pond water 18O/16O. Gsbw falls on a parallel curve to the ambient water from the saline ponds. The offset is mainly due to the equilibrium fractionation between gsbw and gmw. However, gsbw represents a time integrated signal biased towards times of strong evaporation, hence the estimated gmw comprises elevated 18O/16O compositions when compared to pond water samples taken on site. Gypsum precipitation is associated with algae mats in the ponds with lower salinity. No evidence for respective vital effects on the triple oxygen isotopic composition of gypsum hydration water is observed, nor are such effects expected. In principle, the array of δ18Ogsbw vs. 17Oexcess can be used to: (1) provide information on the degree of evaporation during gypsum formation; (2) estimate pristine meteoric water compositions; and (3) estimate local relative humidity which is the controlling parameter of the slope of the array for simple hydrological situations. In our case study, local mining activities may have decreased deep groundwater recharge, causing a recent change of the local hydrology.

  10. Protein structure validation and refinement using amide proton chemical shifts derived from quantum mechanics

    CERN Document Server

    Christensen, Anders S; Borg, Mikael; Boomsma, Wouter; Lindorff-Larsen, Kresten; Hamelryck, Thomas; Jensen, Jan H

    2013-01-01

    We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level QM results obtained for a small protein with an RMSD of 0.25 ppm (r = 0.94). ProCS is interfaced with the PHAISTOS protein simulation program and is used to infer statistical protein ensembles that reflect experimentally measured amide proton chemical shift values. Such chemical shift-based structural refinements, starting from high-resolution X-ray structures of Protein G, ubiquitin, and SMN Tudor Domain, result in average chemical shifts, hydrogen bond geometries, and trans-hydrogen bond (h3JNC') spin-spin coupling constants that are in excellent agreement with experiment. We show that the structural sensitivity of the QM-based amide proton chemical shift predictions is needed to refine protein structures to this...

  11. Physio-chemical Investigation and Natural Bond Orbital Analysis of the Most Actives Ingredient of Fennel Plant

    Directory of Open Access Journals (Sweden)

    Mansoureh Pishehabadi

    2016-10-01

    Full Text Available In this study, physio-chemical properties of effective compounds of fennel plant were investigated through using computational chemistry. To do this, trans-anethole, estragole, 3'- hydroxyanethole and 4- methoxycinnamyl alcohol compounds that the most active ingredient combinations make up the fennel plant have been carried out at three different levels of HF, BLYP and B3LYP theories using 6-31G*, 6-311G*, 6-311G**, 6-311+G and 6-311++G basis sets. Additionally, ab initio calculation in the gas phase have been studied and physio-chemical parameters including Gibbs free energy, thermal energy, enthalpy, entropy, and thermal capacity in constant volume (CV of these compounds have been computed as well as Gibbs free energy in polar solvents such as ethanol and methanol and water. Based on these obtained data the structural stabilities of these flavorful compounds have been discussed. However, in these herbal effective compounds presented here the natural bond orbital (NBO analysis has been performed which seemed quite informative to show some important atomic and structural features. The result lead to the issue that all those compounds in polar solvents, particularly alcoholic solvents solved and the compounds can be used sufficiently to extract the active ingredients of herb fennel.

  12. Influence of Copper Oxidation State on the Bonding and Electronic Structure of Cobalt-Copper Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Eisenhart, Reed J.; Carlson, Rebecca K.; Clouston, Laura J.; Young, Jr., Victor G.; Chen, Yu-Sheng; Bill, Eckhard; Gagliardi, Laura; Lu, Connie C. (UC); (UMM); (MXPL)

    2016-03-04

    Heterobimetallic complexes that pair cobalt and copper were synthesized and characterized by a suite of physical methods, including X-ray diffraction, X-ray anomalous scattering, cyclic voltammetry, magnetometry, electronic absorption spectroscopy, electron paramagnetic resonance, and quantum chemical methods. Both Cu(II) and Cu(I) reagents were independently added to a Co(II) metalloligand to provide (py3tren)CoCuCl (1-Cl) and (py3tren)CoCu(CH3CN) (2-CH3CN), respectively, where py3tren is the triply deprotonated form of N,N,N-tris(2-(2-pyridylamino)ethyl)amine. Complex 2-CH3CN can lose the acetonitrile ligand to generate a coordination polymer consistent with the formula “(py3tren)CoCu” (2). One-electron chemical oxidation of 2-CH3CN with AgOTf generated (py3tren)CoCuOTf (1-OTf). The Cu(II)/Cu(I) redox couple for 1-OTf and 2-CH3CN is reversible at -0.56 and -0.33 V vs Fc+/Fc, respectively. The copper oxidation state impacts the electronic structure of the heterobimetallic core, as well as the nature of the Co–Cu interaction. Quantum chemical calculations showed modest electron delocalization in the (CoCu)+4 state via a Co–Cu σ bond that is weakened by partial population of the Co–Cu σ antibonding orbital. By contrast, no covalent Co–Cu bonding is predicted for the (CoCu)+3 analogue, and the d-electrons are fully localized at individual metals.

  13. Time-dependent density functional theory study on the electronic excited-state geometric structure, infrared spectra, and hydrogen bonding of a doubly hydrogen-bonded complex.

    Science.gov (United States)

    Liu, Yufang; Ding, Junxia; Liu, Ruiqiong; Shi, Deheng; Sun, Jinfeng

    2009-12-01

    The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen-bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S(1) state of this doubly hydrogen-bonded FN-2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen-bonded FN-2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm(-1) observed in the IR spectra should be assigned as the doubly hydrogen-bonded FN-2MeOH complex from our calculated results. The electronic excited-state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S(1) state of the doubly hydrogen-bonded FN-2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen-bonded FN-MeOH complex and play important role on the photophysics of fluorenone in solutions.

  14. Influence of chemical bonding of chlorides with aluminates in cement hidratation process on corrosion steel bars in concrete

    OpenAIRE

    2010-01-01

    The presence of chlorides in concrete is a permanent subject of research because they cause corrosion of steel bars. Chlorides added to the concrete during preparation, as accelerators of the bonding of cement minerals process, enter into reaction with aluminates, creating a phase known as chloroaluminate hydrates. In everyday conditions the product of chemical bonding between chlorides and aluminates is usually monochloridealuminate C3A·CaCl2·Hx, better known as Friedel's salt. In this paper...

  15. Enhancement of POD for Structural Health Monitoring of Bonded Repaired Structures

    Science.gov (United States)

    2010-01-04

    wing structure. The work discussed in this paper shall address the issues relating to the detection of this type of sub-surface crack in an aluminium ...lower wing skin fatigue crack repair (DSTO Scientific Publications, 1997) [7] C. Harding, G. Hugo and S. Bowles, Model- assisted probability of...sensor durability, sensor bond durability and environmental effects on this stress wave based methodology. For example, the effects of operational

  16. Theoretical prediction of hydrogen-bond basicity pKBHX using quantum chemical topology descriptors.

    Science.gov (United States)

    Green, Anthony J; Popelier, Paul L A

    2014-02-24

    Hydrogen bonding plays an important role in the interaction of biological molecules and their local environment. Hydrogen-bond strengths have been described in terms of basicities by several different scales. The pKBHX scale has been developed with the interests of medicinal chemists in mind. The scale uses equilibrium constants of acid···base complexes to describe basicity and is therefore linked to Gibbs free energy. Site specific data for polyfunctional bases are also available. The pKBHX scale applies to all hydrogen-bond donors (HBDs) where the HBD functional group is either OH, NH, or NH+. It has been found that pKBHX can be described in terms of a descriptor defined by quantum chemical topology, ΔE(H), which is the change in atomic energy of the hydrogen atom upon complexation. Essentially the computed energy of the HBD hydrogen atom correlates with a set of 41 HBAs for five common HBDs, water (r2=0.96), methanol (r2=0.95), 4-fluorophenol (r2=0.91), serine (r2=0.93), and methylamine (r2=0.97). The connection between experiment and computation was strengthened with the finding that there is no relationship between ΔE(H) and pKBHX when hydrogen fluoride was used as the HBD. Using the methanol model, pKBHX predictions were made for an external set of bases yielding r2=0.90. Furthermore, the basicities of polyfunctional bases correlate with ΔE(H), giving r2=0.93. This model is promising for the future of computation in fragment-based drug design. Not only has a model been established that links computation to experiment, but the model may also be extrapolated to predict external experimental pKBHX values.

  17. Hydrogen Atomic Positions of O-H···O Hydrogen Bonds in Solution and in the Solid State: The Synergy of Quantum Chemical Calculations with ¹H-NMR Chemical Shifts and X-ray Diffraction Methods.

    Science.gov (United States)

    Siskos, Michael G; Choudhary, M Iqbal; Gerothanassis, Ioannis P

    2017-03-07

    The exact knowledge of hydrogen atomic positions of O-H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement of labile hydrogen positions with the use of: (i) density functional theory (DFT) calculations after a structure has been determined by X-ray from single crystals or from powders; (ii) ¹H-NMR chemical shifts as constraints in DFT calculations, and (iii) use of root-mean-square deviation between experimentally determined and DFT calculated ¹H-NMR chemical shifts considering the great sensitivity of ¹H-NMR shielding to hydrogen bonding properties.

  18. Chemical structure and dynamics. Annual report 1994

    Energy Technology Data Exchange (ETDEWEB)

    Colson, S.D.

    1995-07-01

    The Chemical Structure and Dynamics program was organized as a major component of Pacific Northwest Laboratory`s Environmental and Molecular Sciences Laboratory (EMSL), a state-of-the-art collaborative facility for studies of chemical structure and dynamics. Our program responds to the need for a fundamental, molecular-level understanding of chemistry at the wide variety of environmentally important interfaces by (1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces, and (2) developing a multidisciplinary capability for describing interfacial chemical processes within which the new knowledge generated can be brought to bear on complex phenomena in environmental chemistry and in nuclear waste processing and storage. This research effort was initiated in 1989 and will continue to evolve over the next few years into a program of rigorous studies of fundamental molecular processes in model systems, such as well-characterized surfaces, single-component solutions, clusters, and biological molecules; and studies of complex systems found in the environment (multispecies, multiphase solutions; solid/liquid, liquid/liquid, and gas/surface interfaces; colloidal dispersions; ultrafine aerosols; and functioning biological systems). The success of this program will result in the achievement of a quantitative understanding of chemical reactions at interfaces, and more generally in condensed media, that is comparable to that currently available for gas-phase reactions. This understanding will form the basis for the development of a priori theories for predictions of macroscopic chemical behavior in condensed and heterogeneous media, adding significantly to the value of field-scale environmental models, the prediction of short- and long-term nuclear waste storage stabilities, and other problems related to the primary missions of the DOE.

  19. Annual Report 1998: Chemical Structure and Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    SD Colson; RS McDowell

    1999-05-10

    The Chemical Structure and Dynamics (CS&D) program is a major component of the William R. Wiley Environmental Molecular Sciences Labo- ratory (EMSL), developed by Pacific Northwest National Laboratory (PNNL) to provide a state-of- the-art collaborative facility for studies of chemical structure and dynamics. We respond to the need for a fundamental, molecular-level understanding of chemistry at a wide variety of environmentally important interfaces by (1) extending the experimental characterization and theoretical description of chemical reactions to encompass the effects of condensed media and interfaces; (2) developing a multidisciplinary capability for describing interracial chemical processes within which the new knowledge generated can be brought to bear on complex phenomena in envi- ronmental chemistry and in nuclear waste proc- essing and storage; and (3) developing state-of- the-art analytical methods for characterizing com- plex materials of the types found in stored wastes and contaminated soils, and for detecting and monitoring trace atmospheric species. Our program aims at achieving a quantitative understanding of chemical reactions at interfaces and, more generally, in condensed media, compa- rable to that currently available for gas-phase reactions. This understanding will form the basis for the development of a priori theories for pre- dicting macroscopic chemical behavior in con- densed and heterogeneous media, which will add significantly to the value of field-scale envi- ronmental models, predictions of short- and long- term nuclear waste storage stabilities, and other areas related to the primary missions of the U.S. Department of Energy (DOE).

  20. Carbene→N⁺ Coordination Bonds in Drugs: A Quantum Chemical Study

    Indian Academy of Sciences (India)

    DEEPIKA KATHURIA; MINHAJUL ARFEEN; APOORVA A BANKAR; PRASAD V BHARATAM

    2016-10-01

    Coordination chemistry of bonds between main group elements and electron donating ligands as in L→E (where E is electron acceptor centre like C⁰, Si⁰, N¹, P¹, As¹, B¹ and L is an electron donating N-heterocyclic carbene) have been recently gaining attention. Many important drugs have nitrogen atom as an electron acceptor center and can be represented by two general formulae:(L→N←L)⊕ and L→N-R. Divalent N¹ compounds possess two lone pairs at central nitrogen and low nucleophilicity associated with them are found to be of importance. In this article, electronic structure analysis of drug molecules like picloxydine, chlorhexidine, and moroxydine were performed at B3LYP/6-311++G(d,p) level of theory. Evaluation of electron localization function (ELF), molecular orbitals, charge density, nucleophilicity, proton affinity and complexation energy estimation confirm the presence of coordination bonds (L→N←L)⊕ in the above mentioned drug molecules in their cationic state. Further, electronic structure analysis of drugs like clonidine, apraclonidine, brimonidine and xylazine indicated the presence of electronic structure similar to L→N-R systems.

  1. Interface structure of Be/DSCu diffusion bonding

    Energy Technology Data Exchange (ETDEWEB)

    Makino, T.; Iwadachi, T. [NGK Insulators Ltd., Nagoya (Japan)

    1998-01-01

    Beryllium is used as plasma facing components of the first wall on ITER. Dispersion-Strengthened Copper (DSCu) is used as heat sink material by joining to Be because DSCu has high thermal conductivity and strength. In this study, Be/DSCu diffusion bonding tests using the interlayer of Al, Ni, Nb, Ti, Zr and Be-Cu alloy have been conducted to choose the suitable interlayer materials. As a result of the shear strength tests, Be/DSCu joints by using Be-Cu alloy interlayer showed the strength of about 200 MPa. Diffusion bonding tests using Be-Cu alloy interlayer or no interlayer (direct bonding) at the range of temperature from 600degC to 850degC have been conducted to identify the effect of bonding temperature and time on interface formation and strength. The thickness of diffusion layer was proportional to a square root of bonding time by diffusion controlled process. The shear strength is controlled by the formation of intermetallic layer at Be side. (author)

  2. Fabrication of a molecular-level multilayer film on organic polymer surfaces via chemical bonding assembly.

    Science.gov (United States)

    Zhao, Hongchi; Yang, Peng; Deng, Jianping; Liu, Lianying; Zhu, Jianwu; Sui, Yuan; Lu, Jiaoming; Yang, Wantai

    2007-02-13

    A fresh multilayer film was fabricated on a molecular level and successfully tethered to the surface of a hydroxylated organic substrate via chemical bonding assembly (CBA). Sulfate anion groups (SO4-) were preintroduced onto the surface of biaxially oriented polypropylene (BOPP) films via a reference method. Upon hydrolysis of the SO4- groups, hydroxyl groups (--OH) were formed that subsequently acted as initial reagents for a series of alternate reactions with terephthalyl chloride (TPC) and bisphenol A (BPA). A stable and well-defined multilayer film was thus fabricated via the CBA method. As a result of the nanoscale multilayer fresh film being abundant with reactive groups, it is believed that the film and its fabrication method should provide a fundamental platform for further surface functionalization and direct the design of advanced materials with desired properties.

  3. Method for Producing Chemically Bonded Phosphate Ceramics and for Stabilizing Contaminants Encapsulated therein Utilizing Reducing Agents

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Dileep; Wagh, Arun S.; Jeong, Seung-Young

    1999-05-05

    Known phosphate ceramic formulations are improved and the ability to produce iron-based phosphate ceramic systems is enabled by the addition of an oxidizing or reducing step during the acid-base reactions that form the phosphate ceramic products. The additives allow control of the rate of the acid-base reactions and concomitant heat generation. In an alternate embodiment, waste containing metal anions is stabilized in phosphate ceramic products by the addition of a reducing agent to the phosphate ceramic mixture. The reduced metal ions are more stable and/or reactive with the phosphate ions, resulting in the formation of insoluble metal species within the phosphate ceramic matrix, such that the resulting chemically bonded phosphate ceramic product has greater leach resistance.

  4. Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical X-ray Spectroscopic Study

    CERN Document Server

    Engel, Nicholas; Suljoti, Edlira; Garcia-Diez, Raul; Lange, Kathrin M; Atak, Kaan; Golnak, Ronny; Kothe, Alexander; Dantz, Marcus; Kühn, Oliver; Aziz, Emad F

    2013-01-01

    Resonant inelastic X-ray scattering (RIXS) and X-ray absorption (XA) experiments at the iron L- and nitrogen K-edge are combined with high-level first principles restricted active space self-consistent field (RASSCF) calculations for a systematic investigation of the nature of the chemical bond in potassium ferrocyanide in aqueous solution. The atom- and site-specific RIXS excitations allow for direct observation of ligand-to-metal (Fe L-edge) and metal-to-ligand (N K-edge) charge transfer bands and thereby evidence for strong {\\sigma}-donation and {\\pi}-back-donation. The effects are identified by comparing experimental and simulated spectra related to both the unoccupied and occupied molecular orbitals in solution.

  5. Micro-chemical analysis of diffusion bonded W-SiC joint

    Energy Technology Data Exchange (ETDEWEB)

    Matsuo, Genichiro [Graduate Student, Graduate School of Engineering, Hokkaido University, Sapporo Hokkaido 060-8628 (Japan); Shibayama, Tamaki, E-mail: shiba@ufml.caret.hokudai.ac.jp [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo Hokkaido 060-8628 (Japan); Kishimoto, Hirotatsu [Department of Materials Science and Engineering, Muroran Institute of Technology, Muroran Hokkaido 050-8585 (Japan); Hamada, Kouichi; Watanabe, Seiichi [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo Hokkaido 060-8628 (Japan)

    2011-10-01

    W and SiC joining has an attractive feature for high-temperature energy conversion systems. However, it is unclear and that is necessary to study the microstructure of the reaction phase between W and SiC by using the thermal diffusion bonding method. This work demonstrates the strengthening mechanism of W and SiC joining through a microstructure analysis of the reaction phase by FE-TEM/EDS and the observation of the interface in W and SiC after the crack propagation in HVEM. The reaction phase was amorphous, with a gap from 500 to 600 nm between W and SiC. Fine precipitates with a diameter of several tens nanometer were formed in the reaction phase. The reaction phase and precipitates did not match the chemical composition of the equilibrium compound. It is conceivable that the reaction phase and precipitates exist as a non-equilibrium condition before they reach equilibrium condition.

  6. Novel Chemically-Bonded Phosphate Ceramic Borehole Sealants (Ceramicretes) for Arctic Environments

    Energy Technology Data Exchange (ETDEWEB)

    Shirish Patil; Godwin A. Chukwu; Gang Chen; Santanu Khataniar

    2008-12-31

    Novel chemically bonded phosphate ceramic borehole sealant, i.e. Ceramicrete, has many advantages over conventionally used permafrost cement at Alaska North Slope (ANS). However, in normal field practices when Ceramicrete is mixed with water in blenders, it has a chance of being contaminated with leftover Portland cement. In order to identify the effect of Portland cement contamination, recent tests have been conducted at BJ services in Tomball, TX as well as at the University of Alaska Fairbanks with Ceramicrete formulations proposed by the Argonne National Laboratory. The tests conducted at BJ Services with proposed Ceramicrete formulations and Portland cement contamination have shown significant drawbacks which has caused these formulations to be rejected. However, the newly developed Ceramicrete formulation at the University of Alaska Fairbanks has shown positive results with Portland cement contamination as well as without Portland cement contamination for its effective use in oil well cementing operations at ANS.

  7. Effect of cross-linking with riboflavin and ultraviolet A on the chemical bonds and ultrastructure of human sclera

    Science.gov (United States)

    Jung, Gyeong-Bok; Lee, Hui-Jae; Kim, Ji-Hye; Lim, Jin Ik; Choi, Samjin; Jin, Kyung-Hyun; Park, Hun-Kuk

    2011-12-01

    This study examined the effect of the cross-linking with riboflavin-ultraviolet A (UVA) irradiation on the chemical bonds and ultrastructural changes of human sclera tissues using Raman spectroscopy and atomic force microscopy (AFM). Raman spectroscopy of the normal and cross-linked human sclera tissue revealed different types of the riboflavin-UVA and collagen interactions, which could be identified from their unique peaks, intensity, and shape. Raman spectroscopy can prove to be a powerful tool for examining the chemical bond of collagenous tissues at the molecular level. After riboflavin-UVA treatment, unlike a regular parallel arrangement of normal collagen fibrils, the AFM image revealed interlocking arrangements of collagen fibrils. The observed changes in the surface topography of the collagen fibrils, as well as in their chemical bonds in the sclera tissue, support the formation of interfibrilar cross-links in sclera tissues.

  8. Mechanical properties of chemically bonded sand core materials dipped in sol-gel coating impregnated with filter

    DEFF Research Database (Denmark)

    Nwaogu, Ugochukwu Chibuzoh; Tiedje, Niels Skat

    2012-01-01

    -displacement curve from which the mechanical properties of the materials are deduced. The fracture surfaces were examined using a stereomicroscope and a scanning electron microscope. From the results, the strengths of the core materials were slightly reduced by the coating in tensile and flexural modes, while...... the strengths were increased under compression. The mode of fracture of the chemically bonded sand core materials was observed to be intergranular through the binder. The stiffness of the chemically bonded sand core materials was determined. For better understanding of the mechanical properties......A novel sol-gel coating impregnated with filter dust was applied on chemically bonded sand core materials by dipping. After curing, the strengths of the core materials were measured under uniaxial loading using a new strength testing machine (STM). The STM presents the loading history as a force...

  9. Layer-by-layer fabrication of chemical-bonded graphene coating for solid-phase microextraction.

    Science.gov (United States)

    Zhang, Suling; Du, Zhuo; Li, Gongke

    2011-10-01

    A new fabrication strategy of the graphene-coated solid-phase microextraction (SPME) fiber is developed. Graphite oxide was first used as starting coating material that covalently bonded to the fused-silica substrate using 3-aminopropyltriethoxysilane (APTES) as cross-linking agent and subsequently deoxidized by hydrazine to give the graphene coating in situ. The chemical bonding between graphene and the silica fiber improve its chemical stability, and the obtained fiber was stable enough for more than 150 replicate extraction cycles. The graphene coating was wrinkled and folded, like the morphology of the rough tree bark. Its performance is tested by headspace (HS) SPME of polycyclic aromatic hydrocarbons (PAHs) followed by GC/MS analysis. The results showed that the graphene-coated fiber exhibited higher enrichment factors (EFs) from 2-fold for naphthalene to 17-fold for B(b)FL as compared to the commercial polydimethylsioxane (PDMS) fiber, and the EFs increased with the number of condensed rings of PAHs. The strong adsorption affinity was believed to be mostly due to the dominant role of π-π stacking interaction and hydrophobic effect, according to the results of selectivity study for a variety of organic compounds including PAHs, the aromatic compounds with different substituent groups, and some aliphatic hydrocarbons. For PAHs analysis, the graphene-coated fiber showed good precision (<11%), low detection limits (1.52-2.72 ng/L), and wide linearity (5-500 ng/L) under the optimized conditions. The repeatability of fiber-to-fiber was 4.0-10.8%. The method was applied to simultaneous analysis of eight PAHs with satisfactory recoveries, which were 84-102% for water samples and 72-95% for soil samples, respectively.

  10. Changes in the chemical structure of polytetrafluoroethylene induced by electron beam irradiation in the molten state

    CERN Document Server

    Lappan, U; Lunkwitz, K

    2000-01-01

    Polytetrafluoroethylene (PTFE) was exposed to electron beam radiation at elevated temperature above the melting point under nitrogen atmosphere and in vacuum for comparison. Fourier-transform infrared (FTIR) spectroscopy was used to study the changes in the chemical structure. The irradiation under nitrogen atmosphere leads to the same structures as described recently for PTFE irradiated in vacuum. Trifluoromethyl branches and double bond structures were detected. The concentrations of terminal and internal double bonds are higher after irradiation under nitrogen than in vacuum. Annealing experiments have shown that the thermal oxidative stability of the radiation-modified PTFE is reduced compared to unirradiated PTFE. The reason are the formation of unstable structures such as double bonds.

  11. Anatomy of bond formation. Bond length dependence of the extent of electron sharing in chemical bonds from the analysis of domain-averaged Fermi holes.

    Science.gov (United States)

    Ponec, Robert; Cooper, David L

    2007-01-01

    We demonstrate that domain-average Fermi hole (DAFH) analysis, which has previously been used at the Hartree-Fock level, remains useful after the proper introduction of electron correlation. We perform a systematic investigation of the variation of the picture of bonding with increasing bond length in simple diatomic molecules such as N2 and LiH. Alongside values of a shared-electron distribution index (SEDI), this analysis provides further insight into the geometry dependence of the extent of electron sharing in polar and non-polar systems. We also use DAFH analysis, with correlated wave functions, to evaluate the (potential) multicentre bonding in the electron-deficient and electron-rich molecules CH2Li2 and CH2N2, respectively.

  12. The hierarchical structure of chemical engineering

    Institute of Scientific and Technical Information of China (English)

    Mooson; KWAUK

    2007-01-01

    Around the turn of the present century,scholars began to recognize chemical engineering as a com-plex system,and have been searching for a convenient point of entry for refreshing its knowledge base.From our study of the dynamic structures of dispersed particles in fluidization and the resultingmulti-scale method,we have been attempting to extend our findings to structures prevailing in othermultiphase systems as well as in the burgeoning industries producing functional materials.Chemicalengineering itself is hierarchically structured.Besides structures based on space and time,such hier-archy could be built from ChE history scaled according to science content,or from ChE operation ac-cording to the expenditure of manpower and capital investment.

  13. Hydrogen Bonding and Multiphonon Structure in One- and Two-Dimensional Polymeric Magnets

    Science.gov (United States)

    Musfeldt, J. L.; Brown, S.; Cao, J.; Conner, M. M.; McConnell, A. C.; Southerland, H. I.; Manson, J. L.; Schlueter, J. A.; Phillips, M. D.; Turnbull, M. M.; Landee, C. P.

    2007-03-01

    We report a systematic investigation of the temperature dependent infrared vibrational spectra of a family of chemically related coordination polymeric magnets based upon two different bridging anions, fluoride (F^-) and bifluoride (HF2^-), in copper-pyrazine complexes including Cu(HF2)(pyz)2BF4, Cu(HF2)(pyz)2ClO4, and CuF2(H2O)(pyz)). We compare our results with several one- and two-dimensional prototype materials including Cu(NO3)2(pyz) and Cu(ClO4)(pyz) 2. Unusual low temperature hydrogen bonding, local structural transitions associated with stronger low-temperature hydrogen bonding, and striking multiphonon effects that derive from coupling of an infrared-active fundamental with strong Raman-active modes of the pyrazine building-block molecule are observed. Based on the spectroscopic evidence, these interactions are common to this family of coordination polymers and work to stabilize the low temperature magnetic state. Similar interactions are likely to be present in other molecule-based magnets.

  14. Laser ablation assisted adhesive bonding of automotive structural composites

    Energy Technology Data Exchange (ETDEWEB)

    Boeman, R.G.; Paulauskas, F.L.; Warren, C.D.

    1999-07-03

    Laser ablation has been evaluated as a surface pretreatment prior to adhesive bonding. In prior experimental work, it was observed that when adhesively bonded, composite, single lap shear samples fail, the fracture often occurs at either the adhesive/adherend interface or in the resin rich surface layer of the composite. These two areas represent the weakest portion of the joint. Laser ablation pretreatment generates areas where the resin on the composite surface is selectively removed leaving behind exposed reinforcing fibers which are the major load bearing members of the composite. In a subsequent adhesive bonding operation, this allows portions of the fibers to be encapsulated in the adhesive while other portions of the fiber remain in the composite resin. This type of pretreatment permits fibers to bridge and reinforce the interface between adhesive and adherend. A secondary benefit is the removal of surface contaminantes by pyrolysis. Microscopic observation of laser ablated surfaces indicates a prominent, fiber rich area. Results of the mechanical evaluation indicated that the lap shear strength for laser ablated samples was significantly higher than specimens with no pretreatment or with solvent cleaning only, but were slightly lower than specimens that were mechanically roughened and cleaned with solvents prior to bonding.

  15. Study of hydrogen-bonding, vibrational dynamics and structure-activity relationship of genistein using spectroscopic techniques coupled with DFT

    Science.gov (United States)

    Singh, Harshita; Singh, Swapnil; Srivastava, Anubha; Tandon, Poonam; Bharti, Purnima; Kumar, Sudhir; Dev, Kapil; Maurya, Rakesh

    2017-02-01

    The conformational and hydrogen bonding studies of genistein have been performed by combined spectroscopic and quantum chemical approach. The vibrational spectra (FT-IR and FT-Raman), UV-visible and 1H and 13C NMR absorption spectra of genistein have been recorded and examined. The vibrational wavenumbers of optimized geometry and total energy for isolated molecule and hydrogen-bonded dimers of genistein have been determined using the quantum chemical calculation (DFT/B3LYP) with extended 6-311++G (d,p) basis set. The vibrational assignments for the observed FT-IR and FT-Raman spectra of genistein are provided by calculations on monomer and hydrogen-bonded dimer. The quantum theory of atoms in molecules (QTAIM) is used for investigating the nature and strength of hydrogen-bonds. UV-visible spectrum of the genistein was recorded in methanol solvent and the electronic properties were calculated by using time-dependent density functional theory (TD-DFT). The computed HOMO and LUMO energies predicted the type of transition as π → π*. The 1H and 13C NMR signals of the genistein were computed by the Gauge including atomic orbital (GIAO) approach. Natural bond orbital (NBO) analysis predicted the stability of molecules due to charge delocalization and hyper conjugative interactions. NBO analysis shows that there is an Osbnd H⋯O inter and intramolecular hydrogen bond, and π → π* transition in the monomer and dimer, which is consistent with the conclusion obtained by the investigation of molecular structure and assignment of UV-visible spectra.

  16. Pair copula constructions to determine the dependence structure of Treasury bond yields

    Directory of Open Access Journals (Sweden)

    Marcelo Brutti Righi

    2015-12-01

    Full Text Available We estimated the dependence structure of US Treasury bonds through a pair copula construction. As a result, we verified that the variability of the yields decreases with a longer time of maturity of the bond. The yields presented strong dependence with past values, strongly positive bivariate associations between the daily variations, and prevalence of the Student's t copula in the relationships between the bonds. Furthermore, in tail associations, we identified relevant values in most of the relationships, which highlights the importance of risk management in the context of bonds diversification.

  17. Photodiodes integration on a suspended ridge structure VOA using 2-step flip-chip bonding method

    Science.gov (United States)

    Kim, Seon Hoon; Kim, Tae Un; Ki, Hyun Chul; Kim, Doo Gun; Kim, Hwe Jong; Lim, Jung Woon; Lee, Dong Yeol; Park, Chul Hee

    2015-01-01

    In this works, we have demonstrated a VOA integrated with mPDs, based on silica-on-silicon PLC and flip-chip bonding technologies. The suspended ridge structure was applied to reduce the power consumption. It achieves the attenuation of 30dB in open loop operation with the power consumption of below 30W. We have applied two-step flipchip bonding method using passive alignment to perform high density multi-chip integration on a VOA with eutectic AuSn solder bumps. The average bonding strength of the two-step flip-chip bonding method was about 90gf.

  18. Investigation of Highly Designable Dented Structures in HP Model with Hydrogen Bond Energy

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wei; HUANG Shengyou; YU Tao; ZOU Xianwu

    2007-01-01

    Some highly designable protein structures have dented on the surface of their native structures, and are not full compactly folded. According to hydrophobic-polar (HP) model the most designable structures are full compactly folded. To investigate the designability of the dented structures, we introduce the hydrogen bond energy in the secondary structures by using the secondary-structure-favored HP model proposed by Ou-yang etc. The result shows that the average designability increases with the strength of the hydrogen bond. The designabilities of the structures with same dented shape increase exponentially with the number of secondary structure sites. The dented structures can have the highest designabilities for a certain value of hydrogen bond energy density.

  19. The coefficient of bond thermal expansion measured by extended x-ray absorption fine structure.

    Science.gov (United States)

    Fornasini, P; Grisenti, R

    2014-10-28

    The bond thermal expansion is in principle different from the lattice expansion and can be measured by correlation sensitive probes such as extended x-ray absorption fine structure (EXAFS) and diffuse scattering. The temperature dependence of the coefficient α(bond)(T) of bond thermal expansion has been obtained from EXAFS for CdTe and for Cu. A coefficient α(tens)(T) of negative expansion due to tension effects has been calculated from the comparison of bond and lattice expansions. Negative lattice expansion is present in temperature intervals where α(bond) prevails over α(tens); this real-space approach is complementary but not equivalent to the Grüneisen theory. The relevance of taking into account the asymmetry of the nearest-neighbours distribution of distances in order to get reliable bond expansion values and the physical meaning of the third cumulant are thoroughly discussed.

  20. Chemical adhesion rather than mechanical retention enhances resin bond durability of a dental glass-ceramic with leucite crystallites

    Energy Technology Data Exchange (ETDEWEB)

    Meng, X F [Department of Prosthodontics, The Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing 210008 (China); Yoshida, K [Division of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8588 (Japan); Gu, N, E-mail: mengsoar@nju.edu.c [Jiangsu Key Laboratory for Biomaterials and Devices, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096 (China)

    2010-08-01

    This study aims to evaluate the effect of chemical adhesion by a silane coupler and mechanical retention by hydrofluoric acid (HFA) etching on the bond durability of resin to a dental glass ceramic with leucite crystallites. Half of the ceramic plates were etched with 4.8% HFA (HFA group) for 60 s, and the other half were not treated (NoHFA group). The scale of their surface roughness and rough area was measured by a 3D laser scanning microscope. These plates then received one of the following two bond procedures to form four bond test groups: HFA/cement, NoHFA/cement, HFA/silane/cement and NoHFA/silane/cement. The associated micro-shear bond strength and bond failure modes were tested after 0 and 30 000 thermal water bath cycles. Four different silane/cement systems (Monobond S/Variolink II, GC Ceramic Primer/Linkmax HV, Clearfil Ceramic Primer/Clearfil Esthetic Cement and Porcelain Liner M/SuperBond C and B) were used. The data for each silane/cement system were analyzed by three-way ANOVA. HFA treatment significantly increased the surface R{sub a} and R{sub y} values and the rough area of the ceramic plates compared with NoHFA treatment. After 30 000 thermal water bath cycles, the bond strength of all the test groups except the HFA/Linkmax HV group was significantly reduced, while the HFA/Linkmax HV group showed only adhesive interface failure. The other HFA/cement groups and all NoHFA/cement groups lost bond strength completely, and all NoHFA/silane/cement groups with chemical adhesion had significantly higher bond strength and more ceramic cohesive failures than the respective HFA/cement groups with mechanical retention. The result of the HFA/silane/cement groups with both chemical adhesion and mechanical retention revealed that HFA treatment could enhance the bond durability of resin/silanized glass ceramics, which might result from the increase of the chemical adhesion area on the ceramic rough surface and subsequently reduced degradation speed of the silane

  1. Development of a Nonchromate Structural Adhesive Bond Primer

    Science.gov (United States)

    2014-11-01

    Prevent corrosion of base metal • Applied to porous anodized surface • Overcoated with non- inhibited epoxy adhesive • High adhesive bond strength...primers •Long-running surveillance of chromate-free alternatives by UTC companies shows weak corrosion inhibition • (A) strontium chromate... corrosion inhibiter achieved Electrokinetic Confirmation of Active Inhibition in Coatings 7 Schematic of defect production and samples for salt

  2. Structure, stability, and spectroscopic properties of H-bonded complexes of HOSO and CH3SO with H2O.

    Science.gov (United States)

    Lesar, Antonija; Tušar, Simona

    2014-09-11

    Quantum chemical calculations have been carried out to investigate the structure and stability of 1:1 and 1:2 HOSO-water and CH3SO-water complexes. All of the geometries have been optimized at the DFT and at the CCSD levels of theory using 6-311++G(2df,2pd) and aug-cc-pVDZ basis sets, respectively. The energetics of the hydrogen-bonded complexes are reported at G4 and CBS-QB3 levels of theory. A general characteristic future of the minimum-energy structure complexes is cyclic double H bonding for 1:1 complexes and cyclic triple H bonding for 1:2 complexes. Calculations predict relative large binding energies of 8.2 and 16.8 kcal mol(-1) for 1:1 and 1:2 HOSO-water complexes, respectively, at the CBS-QB3 level of theory. CH3SO-water complexes have somewhat lower stability; the binding energy of 3.8 kcal mol(-1) for the 1:1 CH3SO-water complex increases to 9.5 kcal mol(-1) for the 1:2 complex. The calculated shifts in vibrational frequencies due to complex formation show that the frequencies and intensities of H-bonded OH stretching regions are most affected by complex formation. The large frequency shift is mainly oriented to these OH bonds involved in H-bonding interactions. Vertical electronic excitation energies and the corresponding oscillator strengths have been calculated for the representative radical-water complexes using the TDDFT method and aug-cc-pVTZ basis set. No significant excitation energy difference was observed between the low-lying electronic states of either HOSO within the HOSO-water complexes or CH3SO within the CH3SO-water 1:1 complexes.

  3. Effects of designed sulfhydryl groups and disulfide bonds into soybean proglycinin on its structural stability and heat-induced gelation.

    Science.gov (United States)

    Adachi, Motoyasu; Chunying, Ho; Utsumi, Shigeru

    2004-09-08

    The gel-forming ability of glycinin is one of soybean's most important functional properties. The proglycinin A1aB1b homotrimer was engineered to introduce sulfhydryl groups and disulfide bonds, and their effects on the structural stability and the heat-induced gelation were evaluated. On the basis of the crystal structure, five mutants were designed and prepared: R161C and F163C forming an interprotomer disulfide bond with the inherent free cysteine residue of Cys377, N116C/P248C forming a new intraprotomer disulfide bond, and N116C and P248C introducing a new sulfhydryl group. Mutants of R161C, F163C, and N116C/P248C formed a new disulfide bond as expected. N116C/P248C was significantly more stable than the wild type against chemical and thermal denaturation and more resistant to alpha-chymotrypsin digestion, whereas F163C showed significantly increased thermal stability. All mutants exhibited greater hardness of heat-induced gels than wild type, and in particular, N116C/P248C gave the hardest gel. This result indicates that it is possible to increase hardness of glycinin gel by introduction of cysteine residues using protein engineering.

  4. Structures, bonding and reactivity of iron and manganese high-valent metal-oxo complexes: A computational investigation

    Indian Academy of Sciences (India)

    Bhawana Pandey; Azaj Ansari; Nidhi Vyas; Gopalan Rajaraman

    2015-02-01

    Iron and manganese ions with terminal oxo and hydroxo ligands are discovered as key intermediates in several synthetic and biochemical catalytic cycles. Since many of these species possess vigorous catalytic abilities, they are extremely transient in nature and experiments which probe the structure and bonding on such elusive species are still rare. We present here comprehensive computational studies on eight iron and manganese oxo and hydroxo (FeIII/IV/V-O, FeIII-OH and MnIII/IV/V-O, MnIII-OH) species using dispersion corrected (B3LYP-D2) density functional method. By computing all the possible spin states for these eight species, we set out to determine the ground state S value of these species; and later on employing MO analysis, we have analysed the bonding aspects which contribute to the high reactivity of these species. Direct structural comparison to iron and manganese-oxo species are made and the observed similarity and differences among them are attributed to the intricate metal–oxygen bonding. By thoroughly probing the bonding in all these species, their reactivity towards common chemical reactions such as C–H activation and oxygen atom transfer are discussed.

  5. Dimorphic HT- and LT-TbTiGe: Electronic and magnetic structures and bonding properties from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Matar, Samir F., E-mail: samir.matar@icmcb.cnrs.fr; Chevalier, Bernard; Etourneau, Jean

    2016-01-01

    TbTiGe intermetallic compound is characterized by temperature dimorphism with different but related crystal structures with ferromagnetic high temperature (HT) form versus antiferromagnetic low temperature (LT) form. Such different structure properties and magnetic behaviors have been addressed based on DFT computations of cohesive energies, charge transfers, mechanical and chemical properties of the two structures. This is particularly illustrated by harder and less ductile LT-form with stronger Ti–Ge bond and larger charge transfer from Tb and Ti on one hand and Ge on the other hand. - Highlights: • Temperature induced dimorphism in TbTiGe (LT – HT) leads to different magnetic orders. • Long range ferromagnetic SPF and antiferromagnetic SPAF orders addressed within DFT. • SPAF-LT results from differentiated mechanical and chemical behaviors versus SPF-HT.

  6. Double hydrogen bond mediating self-assembly structure of cyanides on metal surface

    Science.gov (United States)

    Wang, Zhongping; Xiang, Feifei; Lu, Yan; Wei, Sheng; Li, Chao; Liu, Xiaoqing; Liu, Lacheng; Wang, Li

    2016-10-01

    Cyanides with different numbers of -C≡N, 1,2,4,5-Tetracyanobenzene (TCNB) and 2,3-Dicyanonaphthalene (2,3-DCN) deposited on Ag(111) and Ag(110) surfaces, have been investigated by room temperature scanning tunneling microscopy (RTSTM), respectively. High resolution STM images show double hydrogen bond is the main driving force to form variety of self-assembly structures, indicating the double hydrogen bond affects the electron distribution of cyanides and leads to a more stable structure with lower energy. In addition, the difference between Ag(111) and Ag(110) surfaces in their lattice structure induces a bigger assembly structural change of 2,3-DCN than that of 1,2,4,5-TCNB, which confirms the fact that the opposite double hydrogen bond formation formed by 1,2,4,5-TCNB is more stable than the neighboring double hydrogen bond formation formed by molecule 2,3-DCN.

  7. Bond strength of self-adhesive resin cements to tooth structure

    Directory of Open Access Journals (Sweden)

    Susan Hattar

    2015-04-01

    Conclusions: Regardless of their clinical simplicity, the self-adhesive resin cements examined in this study exhibit limited bond performance to tooth structures; therefore, these cements must be used with caution.

  8. Structural Basis of Stereospecificity in the Bacterial Enzymatic Cleavage of β-Aryl Ether Bonds in Lignin*

    Science.gov (United States)

    Helmich, Kate E.; Pereira, Jose Henrique; Gall, Daniel L.; Heins, Richard A.; McAndrew, Ryan P.; Bingman, Craig; Deng, Kai; Holland, Keefe C.; Noguera, Daniel R.; Simmons, Blake A.; Sale, Kenneth L.; Ralph, John; Donohue, Timothy J.; Adams, Paul D.; Phillips, George N.

    2016-01-01

    Lignin is a combinatorial polymer comprising monoaromatic units that are linked via covalent bonds. Although lignin is a potential source of valuable aromatic chemicals, its recalcitrance to chemical or biological digestion presents major obstacles to both the production of second-generation biofuels and the generation of valuable coproducts from lignin's monoaromatic units. Degradation of lignin has been relatively well characterized in fungi, but it is less well understood in bacteria. A catabolic pathway for the enzymatic breakdown of aromatic oligomers linked via β-aryl ether bonds typically found in lignin has been reported in the bacterium Sphingobium sp. SYK-6. Here, we present x-ray crystal structures and biochemical characterization of the glutathione-dependent β-etherases, LigE and LigF, from this pathway. The crystal structures show that both enzymes belong to the canonical two-domain fold and glutathione binding site architecture of the glutathione S-transferase family. Mutagenesis of the conserved active site serine in both LigE and LigF shows that, whereas the enzymatic activity is reduced, this amino acid side chain is not absolutely essential for catalysis. The results include descriptions of cofactor binding sites, substrate binding sites, and catalytic mechanisms. Because β-aryl ether bonds account for 50–70% of all interunit linkages in lignin, understanding the mechanism of enzymatic β-aryl ether cleavage has significant potential for informing ongoing studies on the valorization of lignin. PMID:26637355

  9. Structural Basis of Stereospecificity in the Bacterial Enzymatic Cleavage of β-Aryl Ether Bonds in Lignin.

    Science.gov (United States)

    Helmich, Kate E; Pereira, Jose Henrique; Gall, Daniel L; Heins, Richard A; McAndrew, Ryan P; Bingman, Craig; Deng, Kai; Holland, Keefe C; Noguera, Daniel R; Simmons, Blake A; Sale, Kenneth L; Ralph, John; Donohue, Timothy J; Adams, Paul D; Phillips, George N

    2016-03-04

    Lignin is a combinatorial polymer comprising monoaromatic units that are linked via covalent bonds. Although lignin is a potential source of valuable aromatic chemicals, its recalcitrance to chemical or biological digestion presents major obstacles to both the production of second-generation biofuels and the generation of valuable coproducts from lignin's monoaromatic units. Degradation of lignin has been relatively well characterized in fungi, but it is less well understood in bacteria. A catabolic pathway for the enzymatic breakdown of aromatic oligomers linked via β-aryl ether bonds typically found in lignin has been reported in the bacterium Sphingobium sp. SYK-6. Here, we present x-ray crystal structures and biochemical characterization of the glutathione-dependent β-etherases, LigE and LigF, from this pathway. The crystal structures show that both enzymes belong to the canonical two-domain fold and glutathione binding site architecture of the glutathione S-transferase family. Mutagenesis of the conserved active site serine in both LigE and LigF shows that, whereas the enzymatic activity is reduced, this amino acid side chain is not absolutely essential for catalysis. The results include descriptions of cofactor binding sites, substrate binding sites, and catalytic mechanisms. Because β-aryl ether bonds account for 50-70% of all interunit linkages in lignin, understanding the mechanism of enzymatic β-aryl ether cleavage has significant potential for informing ongoing studies on the valorization of lignin.

  10. Molecular structure, heteronuclear resonance assisted hydrogen bond analysis, chemical reactivity and first hyperpolarizability of a novel ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate: a combined DFT and AIM approach.

    Science.gov (United States)

    Singh, R N; Kumar, Amit; Tiwari, R K; Rawat, Poonam; Baboo, Vikas; Verma, Divya

    2012-06-15

    A new ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate (EDPHEDPC) has been synthesized and characterized by FT-IR, (1)H NMR, UV-vis, DART-Mass spectroscopy and elemental analysis. Quantum chemical calculations have been performed by DFT level of theory using B3LYP functional and 6-31G(d,p) as basis set. The (1)H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO as solvent. The time dependent density functional theory (TD-DFT) is used to find the various electronic transitions and their nature within molecule. A combined theoretical and experimental wavenumber analysis confirms the existence of dimer. Topological parameters such as electron density (ρ(BCP)), Laplacian of electron density (nabla(2)ρ(BCP)), kinetic electron energy density (G(BCP)), potential electron density (V(BCP)) and the total electron energy density (H(BCP)) at bond critical points (BCP) have been analyzed by Bader's 'Atoms in molecules' AIM theory in detail. The intermolecular hydrogen bond energy of dimer is calculated as -12.51 kcal/mol using AIM calculations. AIM ellipticity analysis is carried out to confirm the presence of resonance assisted intra and intermolecular hydrogen bonds in dimer. The calculated thermodynamic parameters show that reaction is exothermic and non-spontaneous at room temperature. The local reactivity descriptors such as Fukui functions (f(k)(+), f(k)(-)), local softnesses (s(k)(-), s(k)(+)) and electrophilicity indices (ω(k)(+), ω(k)(-)) analyses are performed to determine the reactive sites within molecule. Nonlinear optical (NLO) behavior of title compound is investigated by the computed value of first hyperpolarizability (β(0)). Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Diffusion bonding and brazing of high purity copper for linear collider accelerator structures

    Directory of Open Access Journals (Sweden)

    J. W. Elmer

    2001-05-01

    -step joining method is proposed for fabricating the NLC structures. The structure would be assembled with pure silver braze inserts using a self-aligning step joint design, then the assembly would be vacuum diffusion bonded at 700 °C and 3.45 MPa pressure to seal the critical inner portion of the assembly. Finally, during the same furnace cycle, the temperature would be increased to 800 °C in order to react the silver with the copper to form a liquid braze alloy that would join and seal the outer portion of the cells together.

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

    Science.gov (United States)

    Manthiram, Karthish

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

  13. Detecting the bonding state of explosive welding structures based on EEMD and sensitive IMF time entropy

    Science.gov (United States)

    Si, Yue; Zhang, Zhousuo; Liu, Qiang; Cheng, Wei; Yuan, Feichen

    2014-07-01

    With the increasing application of explosive welding structures in many engineering fields, interface bonding state detection has become more and more significant to avoid catastrophic accidents. However, the complexity of the interface bonding state makes this task challenging. In this paper, a new method based on ensemble empirical mode decomposition (EEMD) and sensitive intrinsic mode function (IMF) time entropy is proposed for this task. As a self-adaptive non-stationary signal analysis method, EEMD can decompose a complicated signal into a set of IMFs with truly physical meaning, which is beneficial to allocate the structural vibration response signal containing a wealth of bonding state information to certain IMFs. Then, the time entropies of these IMFs are calculated to quantitatively assess the bonding state of the explosive welding structure. However, the IMF time entropies have different sensitivities to the bonding state. Therefore, the most sensitive IMF time entropy is selected based on a distance evaluation technique to detect the bonding state of explosive welding structures. The proposed method is applied to bonding state detection of explosive welding pipes in three cases, and the results demonstrate its effectiveness.

  14. Protein structure validation and refinement using amide proton chemical shifts derived from quantum mechanics

    DEFF Research Database (Denmark)

    Christensen, Anders Steen; Linnet, Troels Emtekær; Borg, Mikael;

    2013-01-01

    We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level...... QM results obtained for a small protein with an RMSD of 0.25 ppm (r = 0.94). ProCS is interfaced with the PHAISTOS protein simulation program and is used to infer statistical protein ensembles that reflect experimentally measured amide proton chemical shift values. Such chemical shift...

  15. Evidences for Cooperative Resonance-Assisted Hydrogen Bonds in Protein Secondary Structure Analogs

    Science.gov (United States)

    Zhou, Yu; Deng, Geng; Zheng, Yan-Zhen; Xu, Jing; Ashraf, Hamad; Yu, Zhi-Wu

    2016-11-01

    Cooperative behaviors of the hydrogen bonding networks in proteins have been discovered for a long time. The structural origin of this cooperativity, however, is still under debate. Here we report a new investigation combining excess infrared spectroscopy and density functional theory calculation on peptide analogs, represented by N-methylformamide (NMF) and N-methylacetamide (NMA). Interestingly, addition of the strong hydrogen bond acceptor, dimethyl sulfoxide, to the pure analogs caused opposite effects, namely red- and blue-shift of the N-H stretching infrared absorption in NMF and NMA, respectively. The contradiction can be reconciled by the marked lowering of the energy levels of the self-associates between NMA molecules due to a cooperative effect of the hydrogen bonds. On the contrary, NMF molecules cannot form long-chain cooperative hydrogen bonds because they tend to form dimers. Even more interestingly, we found excellent linear relationships between changes on bond orders of N-H/N-C/C = O and the hydrogen bond energy gains upon the formation of hydrogen bonding multimers in NMA, suggesting strongly that the cooperativity originates from resonance-assisted hydrogen bonds. Our findings provide insights on the structures of proteins and may also shed lights on the rational design of novel molecular recognition systems.

  16. Intermolecular CH···O/N H-bonds in the biologically important pairs of natural nucleobases: a thorough quantum-chemical study.

    Science.gov (United States)

    Brovarets', Ol'ha O; Yurenko, Yevgen P; Hovorun, Dmytro M

    2014-01-01

    ··O H-bonds and 1.45÷3.17/1.70÷3.43 kcal/mol for the CH···N H-bonds at the DFT/MP2 levels of theory, respectively. We revealed high linear mutual correlations between the H-bond energy and different physico-chemical parameters of the CH···O/N H-bonds. Based on these observations, the authors asserted that the most reliable descriptors of the H-bonding are the electron density ρ at the СН···О/N H-bond critical points and the NBO calculated stabilization energy E((2)). The linear dependence of the H-bond energy ECH···O/N (in kcal/mol) on the electron density ρ (in atomic units) was established (DFT/MP2): ECH···O = 248.501[Formula: see text]ρ-0.367/260.518[Formula: see text]ρ-0.373 and ECH···N = 218.125[Formula: see text]ρ-0.339/243.599[Formula: see text]ρ-0.441. Red-shifted and blue-shifted CH···O/N H-bonds behave in a similar way and can be described with the same fit parameters. It was found that the A-U HH2 and U-U3 nucleobase pairs are stabilized solely by the CH···O/N H-bonds. At the same time, in the A-U HH1, A-U HH2, A-Asyn 1, A-Asyn 2, A-Asyn 3, A-A4, A-G1, A-G2, G-U1, G-U2, G-U3, G-C HH1, U-U1, U-U2, U-U3 and A-C nucleobase pairs the CH···O/N H-bonds play a prominent role (>30%) in their stabilization. We suppose that unconventional CH···O/N H-bond plays the role of the third "fulcrum", ensuring structurally dynamic similarity of the isomorphic base pairs of different origin, which are incorporated equally well into the structure of the DNA double helix.

  17. Influence of chemical bonding of chlorides with aluminates in cement hidratation process on corrosion steel bars in concrete

    Directory of Open Access Journals (Sweden)

    Bikić Farzet H.

    2010-01-01

    Full Text Available The presence of chlorides in concrete is a permanent subject of research because they cause corrosion of steel bars. Chlorides added to the concrete during preparation, as accelerators of the bonding of cement minerals process, enter into reaction with aluminates, creating a phase known as chloroaluminate hydrates. In everyday conditions the product of chemical bonding between chlorides and aluminates is usually monochloridealuminate C3A·CaCl2·Hx, better known as Friedel's salt. In this paper, the influence of chemical bonding of chlorides with aluminates during the process of cement hydration on corrosion of steel bars in concrete was investigated. The process of chlorides bonding with aluminates yielding monochloride aluminate is monitored by XRD analyses. It was found that the amount of chlorides bonding with aluminates increases with an increase of temperature, and as a result, reduces the amount of 'free' chlorides in concrete. Potentiodynamic measurements have shown that increase in temperature of the heat treatment of working electrodes by chlorides leads to a reduction of steel bars corrosion as a result of either the increase of the monochloride-aluminate content or the decrease of free chlorides amount. Chlorides bound in chloroaluminate hydrates do not cause activation of steel bars corrosion in concrete. It was also proven that the increase of free chlorides concentration in the concrete leads to intensification of steel bars corrosion. This additionally approves that free chlorides are only the activators of process of steel bars corrosion in the concrete.

  18. Stabilization of Rocky Flats Pu-contaminated ash within chemically bonded phosphate ceramics

    Science.gov (United States)

    Wagh, A. S.; Strain, R.; Jeong, S. Y.; Reed, D.; Krause, T.; Singh, D.

    A feasibility study was conducted on the use of chemically bonded phosphate ceramics for stabilization of combustion residue of high transuranic (TRU) wastes. Using a matrix of magnesium potassium phosphate formed by the room-temperature reaction of MgO and KH 2PO 4 solution, we made waste forms that contained 5 wt% Pu to satisfy the requirements of the Waste Isolation Pilot Plant. The waste forms were ceramics whose compression strength was twice that of conventional cement grout and whose connected porosity was ≈50% that of cement grout. Both surrogate and actual waste forms displayed high leaching resistance for both hazardous metals and Pu. Hydrogen generation resulting from the radiolytic decomposition of water and organic compounds present in the waste form did not appear to be a significant issue. Pu was present as PuO 2 that was physically microencapsulated in the matrix. In the process, pyrophoricity was removed and leaching resistance was enhanced. The high leaching resistance was due to the very low solubility of PuO 2 coupled with superior microencapsulation. As a result, the waste forms satisfied the current Safeguard Termination Limit requirement for storage of TRU combustion residues.

  19. Chemical Bonding States of TiC Films before and after Hydrogen Ion Irradiation

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    TiC films deposited by rf magnetron sputtering followed by Ar+ ion bombardment were irradiated with a hydrogen ion beam. X-ray photoelectron spectroscopy (XPS) was used for characterization of the chemical bonding states of C and Ti elements of the TiC films before and after hydrogen ion irradiation, in order to understand the effect of hydrogen ion irradiation on the films and to study the mechanism of hydrogen resistance of TiC films. Conclusions can be drawn that ion bombardment at moderate energy can cause preferential physical sputtering of carbon atoms from the surface of low atomic number (Z) material. This means that ion beam bombardment leads to the formation of a non-stoichiometric composition of TiC on the surface.TiC films prepared by ion beam mixing have the more excellent characteristic of hydrogen resistance. One important cause, in addition to TiC itself, is that there are many vacant sites in TiC created by ion beam mixing.These defects can easily trap hydrogen and effectively enhance the effect of hydrogen resistance.

  20. Infrared spectral evidence and DFT calculations of hydrogen-bonding and molecular structures of acetogenins

    Science.gov (United States)

    Afonso, Sabrina; Silva, Fabiano B.; Silva, Arnaldo F.; Scarminio, Ieda S.; Bruns, Roy E.

    2017-02-01

    FTIR spectra have been measured for 31 different five component - simplex centroid design solvent mixture extracts of shaded and sun-exposed Annonaceous leaves harvested in all four seasons. The spectral frequencies are characteristic of anonnaceous acetogenins known to be a major component of these leaves. Osbnd H stretching spectral bands in the 3100-3600 cm-1 region provide evidence of notable intensity changes for the shaded and sun-exposed leaves. Chemometric principal component analysis involving 264 spectra show that shaded samples tend to have more intense Osbnd H stretching bands than those grown in the sun. B3LYP density functional calculations indicate significant Osbnd H stretching band changes in this region owing to hydrogen bond formation. Weak Osbnd H intensity enhancements, around 40 km mol-1, occur when an Osbnd H group forms a hydrogen bond with the oxygen atom of an adjacent tetrahydrofuran ring oxygen atom. Much more intense enhancements, 400-500 km mol-1, are predicted to occur for acetogenins with two tetrahydrofuran rings for which the Osbnd H group hydrogen bonds with its fartherest removed tetrahydrofuran ring oxygen. Whereas weak or moderate H-bond stretching intensities are obtained for acetogenins with slightly bent carbon chain structures the strongest hydrogen bond intensities are calculated for molecules with a 45° V-type backbone structure. These important structural modifications as well as significant changes in bond lengths and angles owing to hydrogen bonding are detailed.

  1. New sulfido antimonates of the heavy alkali metals. Synthesis, crystal structure and chemical bonding of (K/Rb/Cs){sub 3}SbS{sub 3} and Cs{sub 3}SbS{sub 4} . H{sub 2}O; Neue Sulfido-Antimonate der schweren Alkalimetalle. Synthese, Kristallstruktur und chemische Bindung von (K/Rb/Cs){sub 3}SbS{sub 3} und Cs{sub 3}SbS{sub 4} . H{sub 2}O

    Energy Technology Data Exchange (ETDEWEB)

    Schindler, Lisa V.; Schwarz, Michael; Roehr, Caroline [Freiburg Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie

    2013-12-15

    The new sulfido antimonates(III) (Rb/Cs){sub 3}SbS{sub 3} were prepared from the alkali metal sulfides Rb{sub 2}S/Cs{sub 2}S{sub 2} and elemental antimony and sulfur or Sb{sub 2}S{sub 3} at reaction temperatures of about 700 C. The known isotypic potassium compound was similarly synthesized from the elements. The structures of the light-yellow crystals were refined using single-crystal X-ray data. Both compounds are isotypic to the respective Na salt forming the Na{sub 3}AsS{sub 3} structure type (cubic, space group P2{sub 1}3, K/Rb/Cs: a = 947.21(7)/982.28(5)/1025.92(5) pm, Z = 4, R1 = 0.0159/0.0560/0.0582). The {psi}-tetrahedral SbS{sub 3}{sup 3-} anions with Sb-S bond lengths of 242 pm are arranged in a cubic face centered packing, in which the three crystallographically different A{sup +} cations occupy the tetrahedral and octahedral voids, overall exhibiting a distorted octahedral sulfur coordination. The chemical bonding and the characteristics of the stereochemically active lone electron pair have been investigated by means of FP-LAPW band structure calculations. Needle-shaped crystals of the monohydrate of the antimony(V) salt Cs{sub 3}SbS{sub 4} . H{sub 2}O were obtained from a suspension of Sb{sub 2}O{sub 3}, CsOH and elemental sulfur. Cs{sub 3}SbS{sub 4} . H{sub 2}O crystallizes in a new structure type (monoclinic, space group P2{sub 1}/c, a = 987.17(10), b = 994.83(7), c = 1600.46(14) pm, {beta} = 126.895(8) , Z = 4, R1 = 0.0234). As expected, the Sb-S distances (233.1-234.7 pm) in the nearly ideally tetrahedral anion SbS{sub 4}{sup 3-} are considerably shorter than in the antimonates(III) but match the bond lengths in the anhydrous sulfido antimonate(V) Cs{sub 3}SbS{sub 4}. Due to their similar fcc-like anion packing and the stereochemically active lone electron pair of Sb in the antimonates(III), the whole series of compounds A{sub 3}Sb{sup III,V}S{sub 3/4} shows a uniform structure relation, which is elucidated using crystallographic group

  2. Role of the chemical bonding for the time-dependent electron transport through an interacting quantum dot

    KAUST Repository

    Goker, Ali

    2011-06-01

    A combination of ab initio and many-body calculations is utilized to determine the effects of the bonding in Au electrodes on the time dependent current through a quantum dot suddenly shifted into the Kondo regime by a gate voltage. For an asymmetrically coupled system the instantaneous conductance exhibits fluctuations. The frequencies of the fluctuations turn out to be proportional to the energetic separation between the dominating peaks in the density of states and the Fermi level. The chemical bonding in the electrodes, thus, drastically alters the transient current, which can be accessed by ultrafast pump-probe techniques. © 2011 Elsevier B.V. All rights reserved.

  3. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    Science.gov (United States)

    Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

    2016-05-05

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  4. A STUDY OF TEMPERATURE-DEPENDENT VALENCE BOND STRUCTURE OF TITANIUM

    Institute of Scientific and Technical Information of China (English)

    X.B. Li; Y.Q. Xie; Y.Z. Nie; H.J. Peng; H.J. Tao; F.X. Yu

    2007-01-01

    On the basis of energy and shape method for the determination of the valence bond (VB) structures of crystal, the valence bond structure of titanium is redetermined at room temperature and calculated in the whole temperature range of 0-1943K. The outer shell electronic distribution of Ti is ec2.9907 .(sc0.4980 + dc2.4927) ef1.0093 in crystal. The temperature dependences of the VB structures of hcp and bcc phases are the same. The VB structures of hcp and bcc phases monotonically increase or decrease with the increase in temperature, but show discontinuous changes at the phase-transformation temperature 1155K.

  5. Chemical origin of blue- and redshifted hydrogen bonds: intramolecular hyperconjugation and its coupling with intermolecular hyperconjugation.

    Science.gov (United States)

    Li, An Yong

    2007-04-21

    Upon formation of a H bond Y...H-XZ, intramolecular hyperconjugation n(Z)-->sigma*(X-H) of the proton donor plays a key role in red- and blueshift characters of H bonds and must be introduced in the concepts of hyperconjugation and rehybridization. Intermolecular hyperconjugation transfers electron density from Y to sigma*(X-H) and causes elongation and stretch frequency redshift of the X-H bond; intramolecular hyperconjugation couples with intermolecular hyperconjugation and can adjust electron density in sigma*(X-H); rehybridization causes contraction and stretch frequency blueshift of the X-H bond on complexation. The three factors--intra- and intermolecular hyperconjugations and rehybridization--determine commonly red- or blueshift of the formed H bond. A proton donor that has strong intramolecular hyperconjugation often forms blueshifted H bonds.

  6. A dielectric barrier discharge terminally inactivates RNase A by oxidizing sulfur-containing amino acids and breaking structural disulfide bonds

    Science.gov (United States)

    Lackmann, J.-W.; Baldus, S.; Steinborn, E.; Edengeiser, E.; Kogelheide, F.; Langklotz, S.; Schneider, S.; Leichert, L. I. O.; Benedikt, J.; Awakowicz, P.; Bandow, J. E.

    2015-12-01

    RNases are among the most stable proteins in nature. They even refold spontaneously after heat inactivation, regaining full activity. Due to their stability and universal presence, they often pose a problem when experimenting with RNA. We investigated the capabilities of nonthermal atmospheric-pressure plasmas to inactivate RNase A and studied the inactivation mechanism on a molecular level. While prolonged heating above 90 °C is required for heat inactivating RNase A, direct plasma treatment with a dielectric barrier discharge (DBD) source caused permanent inactivation within minutes. Circular dichroism spectroscopy showed that DBD-treated RNase A unfolds rapidly. Raman spectroscopy indicated methionine modifications and formation of sulfonic acid. A mass spectrometry-based analysis of the protein modifications that occur during plasma treatment over time revealed that methionine sulfoxide formation coincides with protein inactivation. Chemical reduction of methionine sulfoxides partially restored RNase A activity confirming that sulfoxidation is causal and sufficient for RNase A inactivation. Continued plasma exposure led to over-oxidation of structural disulfide bonds. Using antibodies, disulfide bond over-oxidation was shown to be a general protein inactivation mechanism of the DBD. The antibody’s heavy and light chains linked by disulfide bonds dissociated after plasma exposure. Based on their ability to inactivate proteins by oxidation of sulfur-containing amino acids and over-oxidation of disulfide bonds, DBD devices present a viable option for inactivating undesired or hazardous proteins on heat or solvent-sensitive surfaces.

  7. Tertiary structure-based protein classification by virtual-bond-angles series

    Institute of Scientific and Technical Information of China (English)

    LI Bin; HE Hong-bo; LI Yi-bing; XIONG Gui-lin

    2005-01-01

    Structure-based protein classification can be based on the similarities in primary, second or tertiary structures of proteins. A method using virtual-bond-angles series that transformed the protein space configuration into a sequence was used for the classification of three-dimensional structures of proteins. By transforming the main chains formed by Cα atoms of proteins into sequences, the series of virtual-bond-angles corresponding to the tertiary structure of the proteins were constructed. Then a distance-based hierarchical clustering method similar to Ward method was introduced to classify these virtual-bond-angles series of proteins. 200 files of protein structures were selected from Brookheaven protein data bank, and 11 clusters were classified.

  8. Correlation of structural order, anomalous density, and hydrogen bonding network of liquid water.

    Science.gov (United States)

    Bandyopadhyay, Dibyendu; Mohan, S; Ghosh, S K; Choudhury, Niharendu

    2013-07-25

    We use extensive molecular dynamics simulations employing different state-of-the-art force fields to find a common framework for comparing structural orders and density anomalies as obtained from different water models. It is found that the average number of hydrogen bonds correlates well with various order parameters as well as the temperature of maximum densities across the different models, unifying apparently disparate results from different models and emphasizing the importance of hydrogen bonding in determining anomalous properties and the structure of water. A deeper insight into the hydrogen bond network of water reveals that the solvation shell of a water molecule can be defined by considering only those neighbors that are hydrogen-bonded to it. On the basis of this view, the origin of the appearance of a non-tetrahedral peak at a higher temperature in the distribution of tetrahedral order parameters has been explained. It is found that a neighbor that is hydrogen-bonded to the central molecule is tetrahedrally coordinated even at higher temperatures. The non-tetrahedral peak at a higher temperature arises due to the strained orientation of the neighbors that are non-hydrogen-bonded to the central molecule. With the new definition of the solvation shell, liquid water can be viewed as an instantaneously changing random hydrogen-bonded network consisting of differently coordinated hydrogen-bonded molecules with their distinct solvation shells. The variation of the composition of these hydrogen-bonded molecules against temperature accounts for the density anomaly without introducing the concept of large-scale structural polyamorphism in water.

  9. Influence of contamination on resin bond strength to nano-structured alumina-coated zirconia ceramic.

    Science.gov (United States)

    Zhang, Shanchuan; Kocjan, Andraz; Lehmann, Frank; Kosmac, Tomaz; Kern, Matthias

    2010-08-01

    The purpose of this study was to evaluate the influence of contamination and subsequent cleaning on the bond strength and durability of an adhesive resin to nano-structured alumina-coated zirconia ceramic. Zirconia ceramic disks were coated with nano-structured alumina, utilizing the hydrolysis of aluminum nitride powder. After immersion in saliva or the use of a silicone disclosing agent, specimens were cleaned with phosphoric acid etching or with tap water rinsing only. Uncontaminated specimens served as controls. Plexiglas tubes filled with composite resin were bonded with a phosphate monomer [10-methacryloxydecyl-dihydrogenphosphate (MDP)]-containing resin (Panavia 21). Subgroups of eight specimens each were stored in distilled water at 37 degrees C, either for 3 d without thermal cycling (TC) or for 150 d with 37,500 thermal cycles from 5 to 55 degrees C. The tensile bond strength (TBS) was determined using a universal testing machine at a crosshead speed of 2 mm min(-1). The topography of the debonded surface was scrutinized for fractographic features, utilizing both optical and scanning electron microscopy. The TBS to uncontaminated nano-structured alumina-coated zirconia ceramic was durable, while contamination significantly reduced the TBS. Phosphoric acid cleaning was effective in removal of saliva contamination from the coated bonding surface but was not effective in removal of the silicone disclosing agent. Nano-structured alumina coating improves resin bonding to zirconia ceramic and eliminates the need for air-abrasion before bonding.

  10. Trends in information theory-based chemical structure codification.

    Science.gov (United States)

    Barigye, Stephen J; Marrero-Ponce, Yovani; Pérez-Giménez, Facundo; Bonchev, Danail

    2014-08-01

    This report offers a chronological review of the most relevant applications of information theory in the codification of chemical structure information, through the so-called information indices. Basically, these are derived from the analysis of the statistical patterns of molecular structure representations, which include primitive global chemical formulae, chemical graphs, or matrix representations. Finally, new approaches that attempt to go "back to the roots" of information theory, in order to integrate other information-theoretic measures in chemical structure coding are discussed.

  11. A Study of Bond of Structural Timber and Carbon Fiber Reinforced Polymer Plate

    Directory of Open Access Journals (Sweden)

    Yongtaeg LEE

    2015-11-01

    Full Text Available The increase of well-being culture of problem related to environmental depletion of resource is not the growing interest in timber the natural material of construction markets. Also, the perception for historic preservation has been increased in respond to heightened interest. However, it is fairly difficult for architectural properties to maintain their durability because it was made by timber construction. Preventing traditional structure from damage and structural performance reduction is paramount in maintenance problem. A number of studies of reinforced method have been conducted in order to solve such a problem. In this paper, external bonded reinforcement and near-surface mounted was used as a way to reinforce timber structure’s durability. Bond strength for specimens with different bond length was investigated. As a result showed, maximum bond strength in bond length 300 mm from all method, was found to be not increased of bond strength over the certain bond length.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9702

  12. Electronic structure, bonding, spectra, and linear and nonlinear electric properties of Ti@C28.

    Science.gov (United States)

    Skwara, Bartłomiej; Góra, Robert W; Zaleśny, Robert; Lipkowski, Paweł; Bartkowiak, Wojciech; Reis, Heribert; Papadopoulos, Manthos G; Luis, Josep M; Kirtman, Bernard

    2011-09-22

    The potential energy surface (PES) of Ti@C(28) has been revisited, and the stationary points have been carefully characterized. In particular, the C(2v) symmetry structure considered previously turns out to be a transition state lying 2.3 kcal/mol above the ground state of C(3v) symmetry at the MP2/6-31G(d) level. A large binding energy of 181.3 kcal/mol is found at the ROMP2/6-31G(d) level. Topological analysis of the generalized Ti@C(28) density reveals four bond paths between Ti and carbon atoms of the host. The character of all four contacts corresponds to a partially covalent closed shell interaction. UV-vis, IR, and Raman spectra are calculated and compared with C(28)H(4). The dipole moment and the static electronic and double harmonic vibrational (hyper)polarizabilities have been obtained. Distortion of the fullerene cage due to encapsulation leads to nonzero diagonal components of the electronic first hyperpolarizability β, and to an increase in the diagonal components of the electronic polarizability α and second hyperpolarizability γ. However, introduction of the Ti atom causes a comparable or larger reduction in most cases due to localized bonding interactions. At the double harmonic level, the average vibrational β is much larger than its electronic counterpart, but the opposite is true for α and for the contribution to γ that has been calculated. There is also a very large anharmonic (nuclear relaxation) contribution to β which results from a shallow PES with four minima separated by very low barriers. Thus, the vibrational γ (and α) may, likewise, become much larger when anharmonicity is taken into account. © 2011 American Chemical Society

  13. Bond strength of self-adhesive resin cements to tooth structure

    OpenAIRE

    Susan Hattar; Hatamleh, Muhanad M.; Faleh Sawair; Mohammad Al-Rabab’ah

    2015-01-01

    Objectives: The aim of this study was to evaluate the strength of the bond between newly introduced self-adhesive resin cements and tooth structures (i.e., enamel and dentin). Methods: Three self-adhesive cements (SmartCem2, RelyX Unicem, seT SDI) were tested. Cylindrical-shaped cement specimens (diameter, 3 mm; height, 3 mm) were bonded to enamel and dentin. Test specimens were incubated at 37 °C for 24 h. The shear bond strength (SBS) was tested in a Zwick Roll testing machine. Results w...

  14. Bonding preference of carbon, nitrogen, and oxygen in niobium-based rock-salt structures.

    Science.gov (United States)

    Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro; Wada, Satoshi; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2013-09-03

    Carbon, nitrogen, and oxygen are essential components in solid-state materials. However, understanding their preference on the bonding to metals has not been straightforward. Here, niobium carbide, nitride, and oxide with simple rock-salt-based structures were analyzed by first-principles calculations and synchrotron X-ray diffraction. We found that an increase in the atomic number from carbon to oxygen formed fewer and shorter bonds to metals with better hybridization of atomic orbitals. This can provide a simple guiding principle for understanding the bonding and designing carbides, nitrides, oxides, and mixed-anion compounds.

  15. Structure and bonding properties of Y doped ∑37grain boundary in alumina

    Institute of Scientific and Technical Information of China (English)

    Wang Ya-Bin; Zhang Gang; Liu Ming-Jie; Chen Xiang-Long; Chen Jun

    2009-01-01

    The microscopic structures and the bonding properties of Y-doped and undoped (0118)/[0441]/180° (∑37) grain boundaries in alumina are investigated by using ab initio method. The formation energy of grain boundary and the segregation energy of Yto grain boundary are acquired. Electronic structures, potential distributions, bond orders and effective charges of Y-doped and undoped ∑37 GB systems are calculated. Our results reveal that the higher strength Y-O bond than Al-O bond is ascribed to the hybridization of Y(4p, 3d) with O(2s). Meanwhile, dopant Y also causes a change in potential distribution in the grain boundary region, thereby further affecting the transport property of ceramic alumina.

  16. Evaluation of the flocculation performance of carboxymethyl chitosan-graft-polyacrylamide, a novel amphoteric chemically bonded composite flocculant.

    Science.gov (United States)

    Yang, Zhen; Yuan, Bo; Huang, Xin; Zhou, Junyu; Cai, Jun; Yang, Hu; Li, Aimin; Cheng, Rongshi

    2012-01-01

    In the present work, a novel amphoteric chemically bonded composite flocculant (carboxymethyl chitosan-graft-polyacrylamide, denoted as CMC-g-PAM) was successfully prepared and used to flocculate the kaolin suspension. The flocculation performance of CMC-g-PAM in acidic, neutral, and alkaline conditions was systematically evaluated by light scattering in combination with fractal theory, as well as by traditional turbidity and zeta potential measurements. Based on the experimental facts from in situ size and fractal dimension measurements, different flocculation mechanisms play key roles at various pH levels, resulting in substantially varied flocculation kinetic processes under three pH conditions. In acidic condition, patching was the main mechanism involved in the opposite zeta potential between CMC-g-PAM and the kaolin suspension. A flat configuration was favored when the polymeric flocculant was adsorbed onto the particle surface, leading to a slower initial floc growth rate but larger and denser flocs. Bridging was the dominant mechanism in neutral and alkaline conditions. A faster initial rate of bridging resulted in smaller and more open floc structures. A rearrangement process in neutral pH subsequently led to more compact flocs, whereas no restructuration of flocs occurred in alkaline conditions because of the electrostatic repulsion of the same negative charges on the flocculant and particles.

  17. Diversity of Chemical Bonding and Oxidation States in MS 4 Molecules of Group 8 Elements

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Wei [Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084 P.R. China; Jiang, Ning [Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084 P.R. China; Schwarz, W. H. Eugen [Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084 P.R. China; Physical and Theoretical Chemistry, University of Siegen, Siegen 57068 Germany; Yang, Ping [Theoretical Division, Los Alamos National Laboratory, Los Alamos New Mexico 87545 USA; Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland Washington 953002 USA; Li, Jun [Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084 P.R. China; Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland Washington 953002 USA

    2017-07-11

    The geometric and electronic ground-state structures of six MS4 molecules (M = group-8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density-functional and correlated wave-function approaches. The MS4 species are compared to analogous MO4 species recently investi-gated (Inorg. Chem. 2016, 55: 4616). Metal oxidation state (MOS) of high value VIII appears in low- spin singlet Td geometric species (Os,Hs)S4 and (Ru,Os,Hs)O4, whereas low MOS=II appears in high- spin septet D2d species Fe(S2)2 and (slightly excited) metastable Fe(O2)2. The ground states of all other molecules have intermediate MOS values, containing S2-, S22-, S21- (and resp. O2--, O1-, O22-, O21-) ligands, bonded by ionic, covalent and correlative contributions.

  18. Fine Structure of Hydrogen Bond in Cholic Acid Revealed by 2DIR Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on cryogenic FT-IR spectroscopic studies of hydrogen bonds in cholic acid, two-dimensional FT-IR spectroscopy was applied to enhance our understanding of the hydrogen bonds of cholic acid. Fine spectral structures were revealed by asynchronous 2D FT-IR spectra. The co-relationship among various bands was discussed according to the synchronous 2D FT-IR spectrum.

  19. Electronic structure, molecular bonding and potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  20. [Intramolecular hygrogen bonds in conformers of 2'-deoxycytidine: results of quantum-chemical analysis of electron density topology].

    Science.gov (United States)

    Zhurakivs'kyĭ, R O; Hovorun, D M

    2006-01-01

    As many as 13 types of intramolecular hygrogen bonds are determined in 89 conformers of 2'-deoxycytidine nucleoside by means of quantum-chemical analysis (at DFT B3LYP/6-31G(d,p) theory level) of electron density topology with Atoms-in-Molecules (AIM) theory. The total number of H-bonds is 168 and their types are C1'H...O2, C2'H2...O5', C2'H2...O2, C3'H...O2, C5'H1...O2, C5'H2...O2, C6H...O4', C6H...O5', C3'H...HC6, O3'H...O5', O5'H...O3', O5'H...O4' and O5'H...O2. Conformational, geometric and electron-topological properties of H-bonds are presented.

  1. A Simple Visualization of Double Bond Properties: Chemical Reactivity and UV Fluorescence

    Science.gov (United States)

    Grayson, Scott M.

    2012-01-01

    A simple, easily visualized thin-layer chromatography (TLC) staining experiment is presented that highlights the difference in reactivity between aromatic double bonds and nonaromatic double bonds. Although the stability of aromatic systems is a major theme in organic chemistry, the concept is rarely reinforced "visually" in the undergraduate…

  2. A Simple Visualization of Double Bond Properties: Chemical Reactivity and UV Fluorescence

    Science.gov (United States)

    Grayson, Scott M.

    2012-01-01

    A simple, easily visualized thin-layer chromatography (TLC) staining experiment is presented that highlights the difference in reactivity between aromatic double bonds and nonaromatic double bonds. Although the stability of aromatic systems is a major theme in organic chemistry, the concept is rarely reinforced "visually" in the undergraduate…

  3. Principles and applications of halogen bonding in medicinal chemistry and chemical biology.

    Science.gov (United States)

    Wilcken, Rainer; Zimmermann, Markus O; Lange, Andreas; Joerger, Andreas C; Boeckler, Frank M

    2013-02-28

    Halogen bonding has been known in material science for decades, but until recently, halogen bonds in protein-ligand interactions were largely the result of serendipitous discovery rather than rational design. In this Perspective, we provide insights into the phenomenon of halogen bonding, with special focus on its role in drug discovery. We summarize the theoretical background defining its strength and directionality, provide a systematic analysis of its occurrence and interaction geometries in protein-ligand complexes, and give recent examples where halogen bonding has been successfully harnessed for lead identification and optimization. In light of these data, we discuss the potential and limitations of exploiting halogen bonds for molecular recognition and rational drug design.

  4. Estimating the Term Structure With a Semiparametric Bayesian Hierarchical Model: An Application to Corporate Bonds1

    Science.gov (United States)

    Cruz-Marcelo, Alejandro; Ensor, Katherine B.; Rosner, Gary L.

    2011-01-01

    The term structure of interest rates is used to price defaultable bonds and credit derivatives, as well as to infer the quality of bonds for risk management purposes. We introduce a model that jointly estimates term structures by means of a Bayesian hierarchical model with a prior probability model based on Dirichlet process mixtures. The modeling methodology borrows strength across term structures for purposes of estimation. The main advantage of our framework is its ability to produce reliable estimators at the company level even when there are only a few bonds per company. After describing the proposed model, we discuss an empirical application in which the term structure of 197 individual companies is estimated. The sample of 197 consists of 143 companies with only one or two bonds. In-sample and out-of-sample tests are used to quantify the improvement in accuracy that results from approximating the term structure of corporate bonds with estimators by company rather than by credit rating, the latter being a popular choice in the financial literature. A complete description of a Markov chain Monte Carlo (MCMC) scheme for the proposed model is available as Supplementary Material. PMID:21765566

  5. Research on the Interaction of Hydrogen-Bond Acidic Polymer Sensitive Sensor Materials with Chemical Warfare Agents Simulants by Inverse Gas Chromatography

    OpenAIRE

    Liu Yang; Qiang Han; Shuya Cao; Feng Huang; Molin Qin; Chenghai Guo; Mingyu Ding

    2015-01-01

    Hydrogen-bond acidic polymers are important high affinity materials sensitive to organophosphates in the chemical warfare agent sensor detection process. Interactions between the sensor sensitive materials and chemical warfare agent simulants were studied by inverse gas chromatography. Hydrogen bonded acidic polymers, i.e., BSP3, were prepared for micro-packed columns to examine the interaction. DMMP (a nerve gas simulant) and 2-CEES (a blister agent simulant) were used as probes. Chemical an...

  6. Hydrogen bonding properties and intermediate structure of N-(2-carboxyphenyl)salicylidenimine

    NARCIS (Netherlands)

    Ligtenbarg, Alette G.J.; Hage, Ronald; Meetsma, Auke; Feringa, Ben L.

    1999-01-01

    The hydrogen bonding properties, the nature of the tautomeric structure and dimerization of N-(2-carboxyphenyl)salicylidenimine 1 has been studied. The crystal and molecular structure of 1 has been determined by single-crystal X-ray diffraction analysis. This compound forms a dimer in the solid stat

  7. Confocal scanning laser microscopic study of the RDX defect structure in deformed polymer-bonded explosives

    NARCIS (Netherlands)

    Heijden, A.E.D.M. van der; Bouma, R.H.B.

    2016-01-01

    The influence of an explosion-driven deformation on the defect structure in RDX crystals embedded in a polymer-bonded explosive was investigated by means of confocal scanning laser microscopy. The images were compared to the defect structure in the as-received RDX grades, embedded

  8. Observed and predicted hydrogen bond motifs in crystal structures of hydantoins, dihydrouracils and uracils

    NARCIS (Netherlands)

    Cruz-Cabeza, A.J.; Schwalbe, C.H.

    2012-01-01

    A survey of crystal structures containing hydantoin, dihydrouracil and uracil derivatives in the Cambridge Structural Database revealed four main types of hydrogen bond motifs when derivatives with extra substituents able to interfere with the main motif are excluded. All these molecules contain two

  9. Bonded repair of composite aircraft structures: A review of scientific challenges and opportunities

    Science.gov (United States)

    Katnam, K. B.; Da Silva, L. F. M.; Young, T. M.

    2013-08-01

    Advanced composite materials have gained popularity in high-performance structural designs such as aerospace applications that require lightweight components with superior mechanical properties in order to perform in demanding service conditions as well as provide energy efficiency. However, one of the major challenges that the aerospace industry faces with advanced composites - because of their inherent complex damage behaviour - is structural repair. Composite materials are primarily damaged by mechanical loads and/or environmental conditions. If material damage is not extensive, structural repair is the only feasible solution as replacing the entire component is not cost-effective in many cases. Bonded composite repairs (e.g. scarf patches) are generally preferred as they provide enhanced stress transfer mechanisms, joint efficiencies and aerodynamic performance. With an increased usage of advanced composites in primary and secondary aerospace structural components, it is thus essential to have robust, reliable and repeatable structural bonded repair procedures to restore damaged composite components. But structural bonded repairs, especially with primary structures, pose several scientific challenges with the current existing repair technologies. In this regard, the area of structural bonded repair of composites is broadly reviewed - starting from damage assessment to automation - to identify current scientific challenges and future opportunities.

  10. Investigation of finite-size effects in chemical bonding of AuPd nanoalloys

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Beien [Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Oğuz, Ismail Can; Guesmi, Hazar, E-mail: hazar.guesmi@enscm.fr [CNRS-ICG UMR 5253, équipe MACS, 8 rue de l’Ecole Normale, 34296 Montpellier (France)

    2015-10-14

    In this paper, the size-dependent changes in energetic, vibrational, and electronic properties of C–O gas molecule interacting with surface Pd atom of a variety of AuPd nanoalloy structures are investigated by means of first principles calculations. The variation in C–O adsorption energies, C–O vibration frequencies (ν{sub C−O}), and Pd d-bond centers (ε{sub d}) on a series of non-supported Au{sub n−1}–Pd{sub 1} nanoparticles (with n varying from 13 to 147) and on two semi-finite surfaces are inspected with cluster size. We demonstrate for the first time that, with small AuPd bimetallic three-dimensional clusters as TOh{sub 38}, one can reach cluster size convergence even for such a sensitive observable as the adsorption energy on a metal surface. Indeed, the results show that the adsorbate-induced perturbation is extremely local and it only concerns the isolated Pd interacting with the reactive gas molecule. Except for 13 atom clusters, in which molecular behaviour is predominant, no finite-size effects are observed for surface Pd atom substituted in AuPd free nanoclusters above 38 atoms.

  11. Boron-Boron One-Electron Sigma Bonds versus B-X-B Bridged Structures.

    Science.gov (United States)

    Kusevska, Elena; Montero-Campillo, M Merced; Mó, Otilia; Yáñez, Manuel

    2016-09-12

    The existence of one-electron B-B σ bonds, for two different sets of compounds, was investigated by analyzing their electron density with different tools, namely QTAIM, ELF, NCIPLOT, and NBO approaches. Our results indicate that although the generic label "one-electron sigma bond" is often used in the literature, the nature of these bonds varies considerably, or they even do not exist. The [B2 X6 ](-) radical anions give place to true covalent one-electron σ bonds, the stronger the more electronegative is the X substituent. When both boron atoms are substituents in a rigid aromatic moiety, such as naphthalene, to yield 1,8-disubstituted derivatives, two kinds of equilibrium structures are found, those also stabilized through a one-electron σ bond (X=OH, F, Cl, CN) and those stabilized by the formation of B-X-B bridges (X=H, OMe). These 1,8-BX2 naphthalene derivatives can be considered as analogues of 1,8-NX2 naphthalene proton sponges. While the latter are able to stabilize a proton between the two basic sites, the former are able to stabilize an electron between the two electron-deficient B atoms. Interestingly, when all the H atoms attached to B are substituted by phenyl groups no one-electron σ bonds B-B bonds are formed, due to the dispersion of the unpaired electron in the aromatic substituents.

  12. Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile.

    Science.gov (United States)

    Agarwal, Parag; Bee, Saba; Gupta, Archana; Tandon, Poonam; Rastogi, V K; Mishra, Soni; Rawat, Poonam

    2014-01-01

    FT-IR (4000-400 cm(-1)) and FT-Raman (4000-200 cm(-1)) spectral measurements on solid 2,6-dichlorobenzonitrile (2,6-DCBN) have been done. The molecular geometry, harmonic vibrational frequencies and bonding features in the ground state have been calculated by density functional theory at the B3LYP/6-311++G (d,p) level. A comparison between the calculated and the experimental results covering the molecular structure has been made. The assignments of the fundamental vibrational modes have been done on the basis of the potential energy distribution (PED). To investigate the influence of intermolecular hydrogen bonding on the geometry, the charge distribution and the vibrational spectrum of 2,6-DCBN; calculations have been done for the monomer as well as the tetramer. The intermolecular interaction energies corrected for basis set superposition error (BSSE) have been calculated using counterpoise method. Based on these results, the correlations between the vibrational modes and the structure of the tetramer have been discussed. Molecular electrostatic potential (MEP) contour map has been plotted in order to predict how different geometries could interact. The Natural Bond Orbital (NBO) analysis has been done for the chemical interpretation of hyperconjugative interactions and electron density transfer between occupied (bonding or lone pair) orbitals to unoccupied (antibonding or Rydberg) orbitals. UV spectrum was measured in methanol solution. The energies and oscillator strengths were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. TD-DFT method has also been used for theoretically studying the hydrogen bonding dynamics by monitoring the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds in the ground and the first excited state. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge independent atomic orbital

  13. The Load and Time Dependence of Chemical Bonding-Induced Frictional Ageing of Silica at the Nanoscale

    Science.gov (United States)

    Tian, K.; Gosvami, N. N.; Goldsby, D. L.; Carpick, R. W.

    2015-12-01

    Rate and state friction (RSF) laws are empirical relationships that describe the frictional behavior of rocks and other materials in experiments, and reproduce a variety of observed natural behavior when employed in earthquake models. A pervasive observation from rock friction experiments is the linear increase of static friction with the log of contact time, or 'ageing'. Ageing is usually attributed to an increase in real area of contact associated with asperity creep. However, recent atomic force microscopy (AFM) experiments demonstrate that ageing of nanoscale silica-silica contacts is due to progressive formation of interfacial chemical bonds in the absence of plastic deformation, in a manner consistent with the multi-contact ageing behavior of rocks [Li et al., 2011]. To further investigate chemical bonding-induced ageing, we explored the influence of normal load (and thus contact normal stress) and contact time on ageing. Experiments that mimic slide-hold-slide rock friction experiments were conducted in the AFM for contact loads and hold times ranging from 23 to 393 nN and 0.1 to 100 s, respectively, all in humid air (~50% RH) at room temperature. Experiments were conducted by sequentially sliding the AFM tip on the sample at a velocity V of 0.5 μm/s, setting V to zero and holding the tip stationary for a given time, and finally resuming sliding at 0.5 μm/s to yield a peak value of friction followed by a drop to the sliding friction value. Chemical bonding-induced ageing, as measured by the peak friction minus the sliding friction, increases approximately linearly with the product of normal load and the log of the hold time. Theoretical studies of the roles of reaction energy barriers in nanoscale ageing indicate that frictional ageing depends on the total number of reaction sites and the hold time [Liu & Szlufarska, 2012]. We combine chemical kinetics analyses with contact mechanics models to explain our results, and develop a new approach for curve

  14. Accurate structure and dynamics of the metal-site of paramagnetic metalloproteins from NMR parameters using natural bond orbitals.

    Science.gov (United States)

    Hansen, D Flemming; Westler, William M; Kunze, Micha B A; Markley, John L; Weinhold, Frank; Led, Jens J

    2012-03-14

    A natural bond orbital (NBO) analysis of unpaired electron spin density in metalloproteins is presented, which allows a fast and robust calculation of paramagnetic NMR parameters. Approximately 90% of the unpaired electron spin density occupies metal-ligand NBOs, allowing the majority of the density to be modeled by only a few NBOs that reflect the chemical bonding environment. We show that the paramagnetic relaxation rate of protons can be calculated accurately using only the metal-ligand NBOs and that these rates are in good agreement with corresponding rates measured experimentally. This holds, in particular, for protons of ligand residues where the point-dipole approximation breaks down. To describe the paramagnetic relaxation of heavy nuclei, also the electron spin density in the local orbitals must be taken into account. Geometric distance restraints for (15)N can be derived from the paramagnetic relaxation enhancement and the Fermi contact shift when local NBOs are included in the analysis. Thus, the NBO approach allows us to include experimental paramagnetic NMR parameters of (15)N nuclei as restraints in a structure optimization protocol. We performed a molecular dynamics simulation and structure determination of oxidized rubredoxin using the experimentally obtained paramagnetic NMR parameters of (15)N. The corresponding structures obtained are in good agreement with the crystal structure of rubredoxin. Thus, the NBO approach allows an accurate description of the geometric structure and the dynamics of metalloproteins, when NMR parameters are available of nuclei in the immediate vicinity of the metal-site.

  15. Annealing-induced changes in chemical bonding and surface characteristics of chemical solution deposited Pb0.95La0.05Zr0.54Ti0.46O3 thin films

    Science.gov (United States)

    Batra, Vaishali; Ramana, C. V.; Kotru, Sushma

    2016-08-01

    We report the effect of post deposition annealing temperature (Ta = 550 and 750 °C) on the surface morphology, chemical bonding and structural development of lanthanum doped lead zirconate titanate (Pb0.95La0.05Zr0.54Ti0.46O3; referred to PLZT) thin films prepared using chemical solution deposition method. Atomic force microscopy demonstrates formation of nanocrystallites in the film annealed at Ta = 750 °C. X-ray photoelectron spectroscopy (XPS) analyses indicate that the binding energies (BE) of the Pb 4f, Zr 3d, and Ti 2p doublet experience a positive energy shift at Ta = 750 °C, whereas the BE of O 1s and La 3d doublet show a negative shift with respect to the BE of the films annealed at Ta = 750 °C. Thermal induced crystallization and chemical modification is evident from XPS results. The Ar+ sputtering of the films reveals change in oxidation state and chemical bonding between the constituent atoms, with respect to Ta. Raman spectroscopy used to study phonon-light interactions show shift in longitudinal and transverse optical modes with the change in Ta, confirming the change in phase and crystallinity of these films. The results suggest annealing at Ta = 750 °C yield crystalline perovskite PLZT films, which is essential to obtain photovoltaic response from devices based on such films.

  16. System integration and demonstration of adhesive bonded high temperature aluminum alloys for aerospace structure, phase 2

    Science.gov (United States)

    Falcone, Anthony; Laakso, John H.

    1993-01-01

    Adhesive bonding materials and processes were evaluated for assembly of future high-temperature aluminum alloy structural components such as may be used in high-speed civil transport aircraft and space launch vehicles. A number of candidate high-temperature adhesives were selected and screening tests were conducted using single lap shear specimens. The selected adhesives were then used to bond sandwich (titanium core) test specimens, adhesive toughness test specimens, and isothermally aged lap shear specimens. Moderate-to-high lap shear strengths were obtained from bonded high-temperature aluminum and silicon carbide particulate-reinforced (SiC(sub p)) aluminum specimens. Shear strengths typically exceeded 3500 to 4000 lb/in(sup 2) and flatwise tensile strengths exceeded 750 lb/in(sup 2) even at elevated temperatures (300 F) using a bismaleimide adhesive. All faceskin-to-core bonds displayed excellent tear strength. The existing production phosphoric acid anodize surface preparation process developed at Boeing was used, and gave good performance with all of the aluminum and silicon carbide particulate-reinforced aluminum alloys investigated. The results of this program support using bonded assemblies of high-temperature aluminum components in applications where bonding is often used (e.g., secondary structures and tear stoppers).

  17. Effects of Novel Structure Bonding Materials on Properties of Aeronautical Acrylic

    Directory of Open Access Journals (Sweden)

    LI Zhisheng

    2017-06-01

    Full Text Available Novel structure bonding materials, J-351 epoxy adhesive film with low curing temperature and liquid modified acrylate SY-50s adhesive were chosen and characterized. The effects of adhesives on the mechanical properties of acrylic were studied. The results reveal that both adhesives have excellent bonding properties to acrylic. The stress-solvent crazing value of J-351 is higher than that of SY-50s. With the application of adhesive on the surface, mechanical properties of acrylic are declined. Casting acrylic shows more drastic decline than that of oriented acrylic. Through the characterization of fracture surface, we find that fracture of tensile sample derives from the side with adhesive. Mechanical properties of acrylic are more sensitive to SY-50s, because the liquid adhesive presents integrate bonding interface with acrylic. The interface between J-351 and acrylic is clear, making acrylic insensitive to J-351 film. Edge attachment strength of samples bonded with J-351 are higher than that of samples bonded with SY-50s due to the effects of adhesives on acrylic. J-351 epoxy adhesive film presents preferable application performance in the structure bonding of aeronautical acrylic.

  18. After the electronic field: structure, bonding, and the first hyperpolarizability of HArF.

    Science.gov (United States)

    Wu, Heng-Qing; Zhong, Rong-Lin; Kan, Yu-He; Sun, Shi-Ling; Zhang, Min; Xu, Hong-Liang; Su, Zhong-Min

    2013-04-30

    In this work, we add different strength of external electric field (E(ext)) along molecule axis (Z-axis) to investigate the electric field induced effect on HArF structure. The H-Ar bond is the shortest at E(ext) = -189 × 10(-4) and the Ar-F bond show shortest value at E(ext) = 185 × 10(-4) au. Furthermore, the wiberg bond index analyses show that with the variation of HArF structure, the covalent bond H-Ar shows downtrend (ranging from 0.79 to 0.69) and ionic bond Ar-F shows uptrend (ranging from 0.04 to 0.17). Interestingly, the natural bond orbital analyses show that the charges of F atom range from -0.961 to -0.771 and the charges of H atoms range from 0.402 to 0.246. Due to weakened charge transfer, the first hyperpolarizability (β(tot)) can be modulated from 4078 to 1087 au. On the other hand, make our results more useful to experimentalists, the frequency-dependent first hyperpolarizabilities were investigated by the coupled perturbed Hartree-Fork method. We hope that this work may offer a new idea for application of noble-gas hydrides.

  19. Glass-silicon anodic bonding for the reduction of structural distortion; Yugami no sukunai yokyoku setsugo

    Energy Technology Data Exchange (ETDEWEB)

    Shoji, Y.; Minami, K.; Esashi, M. [Tohoku University, Sendai (Japan)

    1995-11-20

    Glass-silicon anodic bonding has been used for the fabrication of silicon micro sensors. A structural distortion during the anodic bonding process is sometimes observed and leads to the difficulty in fabricating the sensors with narrow gaps. It is considered that the distortion is mainly caused by not only the deference of thermal expansion coefficient between glass and silicon but also the structural change with the movement of ions in glass plate. This paper describes the experimental results which shows the effects of the bonding temperature and the movement of the positive ion in glass plate. It is also demonstrated that the structural distortion can be reduced by using a thick glass plate having high rigidity. 6 refs., 15 figs., 1 tab.

  20. Effect of hardening methods of moulding sands with water glass on structure of bonding bridges

    Directory of Open Access Journals (Sweden)

    M. Stachowicz

    2010-07-01

    Full Text Available Research on influence of hardening methods on structure of bonding bridges in moulding sands with sodium water glass is presented.Moulding sands with addition of 2.5 % of binder with molar module 2.0 were hardened with CO2 and dried in traditional way or hardenedwith microwaves. It was proved that the hardening method affects structure of bonding bridges, correlating with properties of the hardened moulding sands. It was found that strength of the moulding sands hardened with microwaves for 4 min is very close to that measured after traditional drying at 110 °C for 120 min. So, application of microwave hardening ensures significant shortening of the process time to the value comparable with CO2 hardening but guaranteeing over 10-fold increase of mechanical properties. Analysis of SEM images of hardened moulding sands permitted explaining differences in quality parameters of moulding sands by connecting them with structure of the created bonding bridges.

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

    Science.gov (United States)

    Froyd, Karl D; Lovejoy, Edward R

    2012-06-21

    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.

  2. Bond slip detection of concrete-encased composite structure using shear wave based active sensing approach

    Science.gov (United States)

    Zeng, Lei; Parvasi, Seyed Mohammad; Kong, Qingzhao; Huo, Linsheng; Lim, Ing; Li, Mo; Song, Gangbing

    2015-12-01

    Concrete-encased composite structure exhibits improved strength, ductility and fire resistance compared to traditional reinforced concrete, by incorporating the advantages of both steel and concrete materials. A major drawback of this type of structure is the bond slip introduced between steel and concrete, which directly reduces the load capacity of the structure. In this paper, an active sensing approach using shear waves to provide monitoring and early warning of the development of bond slip in the concrete-encased composite structure is proposed. A specimen of concrete-encased composite structure was investigated. In this active sensing approach, shear mode smart aggregates (SAs) embedded in the concrete act as actuators and generate desired shear stress waves. Distributed piezoceramic transducers installed in the cavities of steel plates act as sensors and detect the wave response from shear mode SAs. Bond slip acts as a form of stress relief and attenuates the wave propagation energy. Experimental results from the time domain analysis clearly indicate that the amplitudes of received signal by lead zirconate titanate sensors decreased when bond slip occurred. In addition, a wavelet packet-based analysis was developed to compute the received signal energy values, which can be used to determine the initiation and development of bond slip in concrete-encased composite structure. In order to establish the validity of the proposed method, a 3D finite element analysis of the concrete-steel bond model is further performed with the aid of the commercial finite element package, Abaqus, and the numerical results are compared with the results obtained in experimental study.

  3. Lightning Protection and Structural Bonding for the B2 Test Stand

    Science.gov (United States)

    Kinard, Brandon

    2015-01-01

    With the privatization of the space industry, NASA has entered a new era. To explore deeper parts of the solar system, NASA is developing a new spacecraft, the Space Launch System (SLS), capable of reaching these destinations, such as an asteroid or Mars. However, the test stand that is capable of testing the stage has been unused for many years. In addition to the updating/repair of the stand, more steel is being added to fully support the SLS. With all these modifications, the lightning protection system must be brought up to code to assure the protection of all personnel and assets. Structural bonding is a part of the lightning protection system. The focus of this project was to assure proper structural bonding. To begin, all relevant technical standards and the construction specifications were reviewed. This included both the specifications for the lightning protection and for general construction. The drawings were reviewed as well. From the drawings, bolted structural joints were reviewed to determine whether bonding was necessary. Several bolted joints were determined to need bonding according to the notes in the drawings. This exceeds the industry standards. The bolted joints are an electrically continuous joint. During tests, the stand experiences heavy vibration that may weaken the continuity of the bolted joint. Therefore, the secondary bonding is implemented to ensure that the structural joint has low resistance. If the structural joint has a high resistance because of corrosion, a potential gradient can occur that can cause a side flash. Damage, injury, or death can occur from a side flash so they are to be prevented. A list of the identified structural joints was compiled and sent to the contractor to be bonded. That covers the scope of this project.

  4. Ternary silicides ScIr{sub 4}Si{sub 2} and RERh{sub 4}Si{sub 2} (RE = Sc, Y, Tb-Lu) and quaternary derivatives RERh{sub 4}Si{sub 2-x}Sn{sub x} (RE = Y, Nd, Sm, Gd-Lu) - structure, chemical bonding, and solid state NMR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Vosswinkel, Daniel; Benndorf, Christopher; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Eckert, Hellmut [Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; Sao Paulo Univ., Sao Carlos (Brazil). Inst. of Physics; Matar, Samir F. [Bordeaux Univ., CNRS, ICMCB, UPR 9048, Pessac (France)

    2016-11-01

    The silicides ScIr{sub 4}Si{sub 2} and RERh{sub 4}Si{sub 2} (RE = Sc, Y, Tb-Lu) and silicide stannides RERh{sub 4}Si{sub 2-x}Sn{sub x}(RE = Y, Nd, Sm, Gd-Lu) were synthesized from the elements by arc-melting and subsequent annealing. The new compounds crystallize with the orthorhombic YRh{sub 4}Ge{sub 2} type structure, space group Pnma. They were characterized by X-ray powder patterns and several structures were refined from single crystal X-ray diffractometer data. The main structural motifs of this series of silicides are tricapped trigonal prisms formed by the transition metal and rare earth atoms. One of the two crystallographically independent silicon sites allows for formation of solid solutions with tin, exemplarily studied for ErRh{sub 4}Si{sub 2-x}Sn{sub x}. Electronic structure calculations reveal strong covalent Rh-Si bonding as the main stability factor. Multinuclear ({sup 29}Si, {sup 45}Sc, and {sup 89}Y) magic-angle spinning (MAS) NMR spectra of the structure representatives with diamagnetic rare-earth elements (Sc, Y, Lu) are found to be consistent with the crystallographic data and specifically confirm the selective substitution of Sn in the Si2 sites in the quaternary compounds YRh{sub 4}SiSn and LuRh{sub 4}SiSn.

  5. Surface chemical-bonds analysis of silicon particles from diamond-wire cutting of crystalline silicon

    Science.gov (United States)

    Benayad, Anass; Hajjaji, Hamza; Coustier, Fabrice; Benmansour, Malek; Chabli, Amal

    2016-12-01

    The recycling of the Si powder resulting from the kerf loss during silicon ingot cutting into wafers for photovoltaic application shows both significant and achievable economic and environmental benefits. A combined x-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR)-Fourier transform infrared (FTIR) and micro-Raman spectral analyses were applied to kerf-loss Si powders reclaimed from the diamond wire cutting using different cutting fluids. These spectroscopies performed in suitable configurations for the analysis of particles, yield detailed insights on the surface chemical properties of the powders demonstrating the key role of the cutting fluid nature. A combined XPS core peak, plasmon loss, and valence band study allow assessing a qualitative and quantitative chemical, structural change of the kerf-loss Si powders. The relative contribution of the LO and TO stretching modes to the Si-O-Si absorption band in the ATR-FTIR spectra provide a consistent estimation of the effective oxidation level of the Si powders. The change in the cutting media from deionized water to city water, induces a different silicon oxide layer thickness at the surface of the final kerf-loss Si, depending on the powder reactivity to the media. The surfactant addition induces an enhanced carbon contamination in the form of grafted carbonated species on the surface of the particles. The thickness of the modified surface, depending on the cutting media, was estimated based on a simple model derived from the combined XPS core level and plasmon peak intensities. The effective nature of these carbonated species, sensitive to the water quality, was evidenced based on coupled XPS core peak and valence band study. The present work paves the way to a controlled process to reclaim the kerf-loss Si powder without heavy chemical etching steps.

  6. Indications of chemical bond contrast in AFM images of a hydrogen-terminated silicon surface

    Science.gov (United States)

    Labidi, Hatem; Koleini, Mohammad; Huff, Taleana; Salomons, Mark; Cloutier, Martin; Pitters, Jason; Wolkow, Robert A.

    2017-02-01

    The origin of bond-resolved atomic force microscope images remains controversial. Moreover, most work to date has involved planar, conjugated hydrocarbon molecules on a metal substrate thereby limiting knowledge of the generality of findings made about the imaging mechanism. Here we report the study of a very different sample; a hydrogen-terminated silicon surface. A procedure to obtain a passivated hydrogen-functionalized tip is defined and evolution of atomic force microscopy images at different tip elevations are shown. At relatively large tip-sample distances, the topmost atoms appear as distinct protrusions. However, on decreasing the tip-sample distance, features consistent with the silicon covalent bonds of the surface emerge. Using a density functional tight-binding-based method to simulate atomic force microscopy images, we reproduce the experimental results. The role of the tip flexibility and the nature of bonds and false bond-like features are discussed.

  7. Bader’s Theory of Atoms in Molecules (AIM) and its Applications to Chemical Bonding

    Indian Academy of Sciences (India)

    P SHYAM VINOD KUMAR; V RAGHAVENDRA; V SUBRAMANIAN

    2016-10-01

    In this perspective article, the basic theory and applications of the “Quantum Theory of Atoms in Molecules” have been presented with examples from different categories of weak and hydrogen bonded molecular systems.

  8. Indications of chemical bond contrast in AFM images of a hydrogen-terminated silicon surface

    Science.gov (United States)

    Labidi, Hatem; Koleini, Mohammad; Huff, Taleana; Salomons, Mark; Cloutier, Martin; Pitters, Jason; Wolkow, Robert A.

    2017-01-01

    The origin of bond-resolved atomic force microscope images remains controversial. Moreover, most work to date has involved planar, conjugated hydrocarbon molecules on a metal substrate thereby limiting knowledge of the generality of findings made about the imaging mechanism. Here we report the study of a very different sample; a hydrogen-terminated silicon surface. A procedure to obtain a passivated hydrogen-functionalized tip is defined and evolution of atomic force microscopy images at different tip elevations are shown. At relatively large tip-sample distances, the topmost atoms appear as distinct protrusions. However, on decreasing the tip-sample distance, features consistent with the silicon covalent bonds of the surface emerge. Using a density functional tight-binding-based method to simulate atomic force microscopy images, we reproduce the experimental results. The role of the tip flexibility and the nature of bonds and false bond-like features are discussed. PMID:28194036

  9. Structures and Stabilization Mechanisms in Chemically Stabilized Ceramics

    Science.gov (United States)

    Gai-Boyes, Pratibha L.; Saltzberg, Michael A.; Vega, Alexander

    1993-09-01

    Structural complexities and disorder in chemically stabilized cristobalites (CSC), which are room temperature silica-based ceramics, prepared by a wet chemical route, are described. CSC displays many of the structural characteristics of the high temperature cristobalite, elucidated by HREM and X-ray diffraction. In-situ electron diffraction and NMR results suggest that the disorder is structural and is static.

  10. Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite

    Science.gov (United States)

    Arjunan, V.; Marchewka, Mariusz K.; Kalaivani, M.

    2012-10-01

    The molecular complex of betaine with selenious acid namely, betaine dihydrogen selenite (C5H13NO5Se, BDHSe) was synthesised by the reaction of betaine and SeO2 in a 1:1:1 solution of isopropanol, methanol and water. Crystals were grown from this solution by cooling to 253 K for few days. The complex was formed without accompanying proton transfer from selenious acid molecule to betaine. The complete vibrational assignments and analysis of BDHSe have been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G∗∗, 6-31G∗∗, cc-pVDZ and 3-21G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of BDHSe were determined by the DFT method. The 1H and 13C isotropic chemical shifts (δ ppm) of BDHSe with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. SHG experiment was carried out using Kurtz-Perry powder technique. The efficiency of second harmonic generation for BDHSe was estimated relatively to KDP: deff = 0.97 deff (KDP).

  11. Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite.

    Science.gov (United States)

    Arjunan, V; Marchewka, Mariusz K; Kalaivani, M

    2012-10-01

    The molecular complex of betaine with selenious acid namely, betaine dihydrogen selenite (C(5)H(13)NO(5)Se, BDHSe) was synthesised by the reaction of betaine and SeO(2) in a 1:1:1 solution of isopropanol, methanol and water. Crystals were grown from this solution by cooling to 253 K for few days. The complex was formed without accompanying proton transfer from selenious acid molecule to betaine. The complete vibrational assignments and analysis of BDHSe have been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G(**), 6-31G(**), cc-pVDZ and 3-21G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of BDHSe were determined by the DFT method. The (1)H and (13)C isotropic chemical shifts (δ ppm) of BDHSe with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. SHG experiment was carried out using Kurtz-Perry powder technique. The efficiency of second harmonic generation for BDHSe was estimated relatively to KDP: d(eff)=0.97 d(eff) (KDP).

  12. Finite Size Effects in Chemical Bonding: From Small Clusters to Solids

    DEFF Research Database (Denmark)

    Kleis, Jesper; Greeley, Jeffrey Philip; Romero, N. A.

    2011-01-01

    We address the fundamental question of which size a metallic nano-particle needs to have before its surface chemical properties can be considered to be those of a solid, rather than those of a large molecule. Calculations of adsorption energies for carbon monoxide and oxygen on a series of gold n......). Below that critical size, finite-size effects can be observed, and we show those to be related to variations in the local atomic structure augmented by quantum size effects for the smallest clusters.......We address the fundamental question of which size a metallic nano-particle needs to have before its surface chemical properties can be considered to be those of a solid, rather than those of a large molecule. Calculations of adsorption energies for carbon monoxide and oxygen on a series of gold...... nanoparticles ranging from 13 to 1,415 atoms, or 0.8–3.7 nm, have been made possible by exploiting massively parallel computing on up to 32,768 cores on the Blue Gene/P computer at Argonne National Laboratory. We show that bulk surface properties are obtained for clusters larger than ca. 560 atoms (2.7 nm...

  13. Effect of hardening methods of moulding sands with water glass on structure of bonding bridges

    OpenAIRE

    Stachowicz, M.; K. Granat; Nowak, D.

    2010-01-01

    Research on influence of hardening methods on structure of bonding bridges in moulding sands with sodium water glass is presented.Moulding sands with addition of 2.5 % of binder with molar module 2.0 were hardened with CO2 and dried in traditional way or hardenedwith microwaves. It was proved that the hardening method affects structure of bonding bridges, correlating with properties of the hardened moulding sands. It was found that strength of the moulding sands hardened with microwaves for 4...

  14. Green coloration of Co-doped ZnO explained from structural refinement and bond considerations.

    Science.gov (United States)

    Gaudon, M; Toulemonde, O; Demourgues, A

    2007-12-24

    ZnO doped with Co2+ has been prepared by a Pechini process and investigated in terms of crystallographic structure and UV-visible properties. We emphasize for the first time a splitting of the ZnO band gap in two "sub-band gaps" (never clearly mentioned until now) which is fully interpreted basing on the iono-covalent nature of the O-Zn bonds. An anticipative approach of the potential structure relaxations was discussed from exchanged effective charge per bond calculated with the purely ionic Brown and Altermatt model.

  15. Bond-slip detection of concrete-encased composite structure using electro-mechanical impedance technique

    Science.gov (United States)

    Liang, Yabin; Li, Dongsheng; Parvasi, Seyed Mohammad; Kong, Qingzhao; Lim, Ing; Song, Gangbing

    2016-09-01

    Concrete-encased composite structure is a type of structure that takes the advantages of both steel and concrete materials, showing improved strength, ductility, and fire resistance compared to traditional reinforced concrete structures. The interface between concrete and steel profiles governs the interaction between these two materials under loading, however, debonding damage between these two materials may lead to severe degradation of the load transferring capacity which will affect the structural performance significantly. In this paper, the electro-mechanical impedance (EMI) technique using piezoceramic transducers was experimentally investigated to detect the bond-slip occurrence of the concrete-encased composite structure. The root-mean-square deviation is used to quantify the variations of the impedance signatures due to the presence of the bond-slip damage. In order to verify the validity of the proposed method, finite element model analysis was performed to simulate the behavior of concrete-steel debonding based on a 3D finite element concrete-steel bond model. The computed impedance signatures from the numerical results are compared with the results obtained from the experimental study, and both the numerical and experimental studies verify the proposed EMI method to detect bond slip of a concrete-encased composite structure.

  16. Structure, bonding, and possible superhardness of CrB4

    Science.gov (United States)

    Niu, Haiyang; Wang, Jiaqi; Chen, Xing-Qiu; Li, Dianzhong; Li, Yiyi; Lazar, Petr; Podloucky, Raimund; Kolmogorov, Aleksey N.

    2012-04-01

    By electron and x-ray diffraction we establish that the CrB4 compound discovered over 40 years ago crystallizes in the oP10 (Pnnm) structure, in disagreement with previous experiments but in agreement with a recent first-principles prediction. The 3D boron network in this structure is a distorted version of the rigid carbon sp3 network proposed recently for the high-pressure C4 allotrope. Our systematic density functional theory analysis of the electronic, structural, and elastic properties in ten related transition metal TMB4 tetraborides (TM = Ti, V, Cr, Mn, Fe and Y, Zr, Nb, Mo, Tc) identifies CrB4 as the prime candidate to be a superhard material. In particular, the compound's calculated weakest shear and tensile stresses exceed 50 GPa, and its Vickers hardness is estimated to be 48 GPa. We compare the reported and estimated Vickers hardness for notable (super)hard materials and find that the CrB4 calculated value is exceptionally high for a material synthesizable under standard ambient-pressure conditions.

  17. Small cluster models of the surface electronic structure and bonding properties of titanium carbide, vanadium carbide, and titanium nitride.

    Science.gov (United States)

    Didziulis, Stephen V; Butcher, Kristine D; Perry, Scott S

    2003-12-01

    Density functional theory (DFT) calculations on stoichiometric, high-symmetry clusters have been performed to model the (100) and (111) surface electronic structure and bonding properties of titanium carbide (TiC), vanadium carbide (VC), and titanium nitride (TiN). The interactions of ideal surface sites on these clusters with three adsorbates, carbon monoxide, ammonia, and the oxygen atom, have been pursued theoretically to compare with experimental studies. New experimental results using valence band photoemission of the interaction of O(2) with TiC and VC are presented, and comparisons to previously published experimental studies of CO and NH(3) chemistry are provided. In general, we find that the electronic structure of the bare clusters is entirely consistent with published valence band photoemission work and with straightforward molecular orbital theory. Specifically, V(9)C(9) and Ti(9)N(9) clusters used to model the nonpolar (100) surface possess nine electrons in virtually pure metal 3d orbitals, while Ti(9)C(9) has no occupation of similar orbitals. The covalent mixing of the valence bonding levels for both VC and TiC is very high, containing virtually 50% carbon and 50% metal character. As expected, the predicted mixing for the Ti(9)N(9) cluster is somewhat less. The Ti(8)C(8) and Ti(13)C(13) clusters used to model the TiC(111) surface accurately predict the presence of Ti 3d-based surface states in the region of the highest occupied levels. The bonding of the adsorbate species depends critically on the unique electronic structure features present in the three different materials. CO bonds more strongly with the V(9)C(9) and Ti(9)N(9) clusters than with Ti(9)C(9) as the added metal electron density enables an important pi-back-bonding interaction, as has been observed experimentally. NH(3) bonding with Ti(9)N(9) is predicted to be somewhat enhanced relative to VC and TiC due to greater Coulombic interactions on the nitride. Finally, the interaction with

  18. Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Sweet, Lucas E.; Corbey, Jordan F.; Gendron, Frédéric; Autschbach, Jochen; McNamara, Bruce K.; Ziegelgruber, Kate L.; Arrigo, Leah M.; Peper, Shane M.; Schwantes, Jon M.

    2016-12-29

    Herein, we report the synthesis and structural characterization of K8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O. This is the second plutonium-containing addition to the previously studied alkali metal peroxo-carbonate series M8[(CO3)3A]2(µ-η2-η2-O2)2•xH2O (M = alkali metal; A = Ce or Pu; x = 8, 10, 12 or 18), for which only the M = Na analog has been previously reported when A = Pu. The previously reported crystal structure for Na8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M8[(CO3)3A]2(µ-η2-η2-O2)2•12H2O complexes, described below, has produced crystals of Na8[(CO3)3Ce]2(µ-η2-η2-O2)2•12H2O that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M8[(CO3)3Ce]2(µ-η2-η2-O2)2•xH2O have also been synthesized for systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy and density functional theory (DFT) calculations. The cerium salts in particular demonstrate subtle differences in the peroxide bond lengths which correlate to Raman shifts for the peroxide Op–Op stretch (Op = the oxygen atoms of the peroxide bridges) with each of the cations studied: Na+ (1.492(3) Å /847 cm-1), Rb+ (1.471(1) Å /854 cm-1), Cs+ (1.474(1) Å /859 cm-1), and K+ (1.468(6) Å, 870 cm-1). The trends observed in the M–Op and Op–Op bond distances appear to relate to supermolecular interactions between the neighboring cations.

  19. Ab initio calculations of the electronic structure and bonding characteristics of LaB6

    Science.gov (United States)

    Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.

    2005-12-01

    Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.

  20. On the reactivity of F(3)S[triple bond]NXeF(+): syntheses and structural characterizations of [F(4)S=N-Xe---N[triple bond]SF(3)][AsF(6)], a rare example of a N-Xe-N linkage, and [F(3)S(N[triple bond]SF(3))(2)][AsF(6)].

    Science.gov (United States)

    Smith, Gregory L; Schrobilgen, Gary J

    2009-08-17

    The F(4)S=N-Xe---N[triple bond]SF(3)(+) cation has been synthesized as the AsF(6)(-) salt by rearrangement of [F(3)S[triple bond]NXeF][AsF(6)] in N[triple bond]SF(3) solvent at 0 degrees C. Deep yellow [F(4)S=N-Xe---N[triple bond]SF(3)][AsF(6)], which crystallized from a N[triple bond]SF(3) solution at -10 degrees C, was characterized by Raman spectroscopy (-160 degrees C) and by single-crystal X-ray diffraction (-173 degrees C). The Xe-N bond length (2.079(3) A) of the F(4)S=N-Xe---N[triple bond]SF(3)(+) cation is among the shortest Xe-N bonds presently known. The F(4)S=NXe(+) cation interacts with N[triple bond]SF(3) by means of a Xe---N donor-acceptor bond (2.583(3) A) that is significantly longer than the primary Xe-N bond (2.079(3)A) but significantly shorter than the sum of the Xe and N van der Waals radii (3.71 A). The F(4)S=N-Xe---N[triple bond]SF(3)(+) cation undergoes a redox decomposition in N[triple bond]SF(3) at 0 degrees C, forming [F(3)S(N[triple bond]SF(3))(2)][AsF(6)], cis-N(2)F(2), and Xe, which were characterized by low-temperature Raman spectroscopy in the solid state and by (19)F NMR spectroscopy in N[triple bond]SF(3) solvent (0 degrees C). Colorless [F(3)S(N[triple bond]SF(3))(2)][AsF(6)] crystallized from N[triple bond]SF(3) at -10 degrees C and was characterized by low-temperature, single-crystal X-ray diffraction. The S(IV) atom of F(3)S(N[triple bond]SF(3))(2)(+) has long contacts with the N atoms of two N[triple bond]SF(3) molecules and a F ligand of a neighboring AsF(6)(-) anion. The arrangement of long contacts avoids, to the maximum extent, the F atoms of SF(3)(+) and the nonbonding electron pair situated on the pseudo-3-fold axis opposite the F ligands of SF(3)(+), providing distorted octahedral coordination about the S(IV) atom. Quantum-chemical calculations using MP2, B3LYP, and PBE1PBE methods were employed to arrive at the gas-phase geometries, charges, bond orders, valencies, and vibrational frequencies for F(4)S

  1. Theoretical study on Fe-Al clusters:geometric structure,bonding law and electronic structures

    Institute of Scientific and Technical Information of China (English)

    CHEN Shougang; YIN Yansheng; WANG Daoping; LU Yao

    2004-01-01

    Structures of the small Fe-Al clusters with different atom proportion are calculated using the B3LYP method in density functional theory (DFT). Calculated results show that the Al atoms lose electrons easily while the Fe atoms capture electrons easily. The most stable geometry is the bonding between Fe and Fe atoms and between Fe and Al atoms with the largest possibility, and the cluster stability law with the same atom proportion accords with the change of the highest occupied molecular orbital (HOMO) energy and the entropy of cluster system. Moreover, the electronic structure study of the ground-state Fe3Al and Fe2CrAl clusters shows that the substitution of Cr atom for the Fe atom located at the next neighboring site of Al atom reduces localized electrons not only between Al atom and the next neighboring Cr atom, but also between Al atom and the nearest neighboring Fe atom. Although the substitution increases the plasticity and the magnetism of intermetallic compound, the stability of the system slightly decreases. Our theoretical results agree well with the experimental results.

  2. Synthesis of 2,6-diaminopyridine substituted -oxoketene ,-acetals: Crystal structure and hydrogen bonding interactions

    Indian Academy of Sciences (India)

    Okram Mukherjee Singh; Laishram Ronibala Devi; Neeladri Das

    2013-09-01

    Polyaza -oxoketene ,-acetals can exist as either enamino or imino tautomeric forms. Based on the spectroscopic data and structural analysis of one of the ,-acetals, the stereochemistry was unambiguously assigned as an all--configuration. The crystal structure confirms the enamino structure and shows extensive use of C-H…X (X = N, O, and S) weak hydrogen bonding interactions, thereby generating a 3-dimensional network in solid state.

  3. CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE I REPORT AUGUST 1997 - JULY 1998

    Energy Technology Data Exchange (ETDEWEB)

    SUGAMA,T.; YAGER,K.A.

    2002-08-05

    In exploring methods to recycle boiler ash (BA) and waste water treatment sludge (WWTS), by-products generated from Keyspan's power plants, into commercially viable materials, we synthesized chemically bonded cements (CBC) offering the following three specific characteristics; (1) immobilization of hazardous heavy metals, such as Pb, Ni, and V, (2) rapid hardening and setting properties, and (3) development of high mechanical strength. The CBCs were prepared through an acid-base reaction between these by-products acting as the solid base reactants and the sodium polyphosphate solution as the cement-forming acid reactant, followed by a hydrating reaction. Furthermore, two additives, the calcium aluminate cements (CAC) and the calcium silicate cements (CSC) were incorporated into the CBC systems to improve their properties. Using a CBC formulation consisting of 53.8 wt% WWTS, 23.1 wt% CSC, and 23.1 wt% [40 wt% -(-NaPO{sub 3}-)-{sub n}]{sub 2} the Toxicity Characteristics Leaching Procedure (TCLP) tests showed that the concentrations of Pb, Ni, and V metals leached out from the specimens were minimal. This formulation originally contained {approx} 28800 mg/kg of Pb, {approx} 6300 mg/kg of Ni, and {approx} 11130 mg/kg of V; the amounts leaching into the acid extraction fluid were only 0.15 mg/L of Pb, 0.15 mg/L of Ni, and 4.63 mgiL of V. On the other hand, CBC specimens derived from a formulation consisting of 42 wt% BA, 18 wt% CAC and 40 wt% [40 wt% -(-NaPO{sub 3}-)-{sub n}] displayed an excellent compressive strength of 10.8 MPa at an early curing age of 2 hours after mixing at room temperature. The reason for its rapid hardening was due to a high exothermic energy evolved by the acid-base reaction. Furthermore, when these specimens were immersed for 28 days in water at 25 C, and exposed for 20 hours to steam at 80 C, a very high compressive strength of 3.32 MPa developed. Two physico-chemical factors played an important role in improving the mechanical strength

  4. From polymer to monomer: cleavage and rearrangement of Si-O-Si bonds after oxidation yielded an ordered cyclic crystallized structure.

    Science.gov (United States)

    Zuo, Yujing; Gou, Zhiming; Cao, Jinfeng; Yang, Zhou; Lu, Haifeng; Feng, Shengyu

    2015-07-27

    Polymerization reactions are very common in the chemical industry, however, the reaction in which monomers are obtained from polymers is rarely invesitgated. This work reveals for the first time that oxone can break the Si-O-Si bond and induce further rearrangement to yield an ordered cyclic structure. The oxidation of P1, which is obtained by reaction of 2,2'-1,2-ethanediylbis(oxy)bis(ethanethiol) (DBOET) with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (MM(Vi)), with oxone yielded cyclic crystallized sulfone-siloxane dimer (P1-ox) after unexpected cleavage and rearrangement of the Si-O-Si bond.

  5. Synthesis, Structure and Spectroscopy of Two Structurally Related Hydrogen Bonded Compounds in the dpma/HClO4 System; dpma (dimethylphosphorylmethanamine

    Directory of Open Access Journals (Sweden)

    Guido J. Reiss

    2013-06-01

    Full Text Available The new phosphine oxide compound, (dimethylphosphorylmethanaminium perchlorate, dpmaHClO4 (1, was synthesized by the reaction of (dimethylphosphoryl methanamine (dpma with concentrated perchloric acid. (Dimethylphosphorylmethanaminium perchlorate (dimethylphosphorylmethanamine solvate, dpmaHClO4•dpma (2 was obtained by the slow evaporation of an equimolar methanolic solution of 1 and dpma at room temperature. For both compounds, single-crystal X-ray structures, IR and Raman spectra are reported. The assignment of the spectroscopic data were supported by quantum chemical calculations at the B3LYP/6-311G(2d,p level of theory. In 1, the dpmaH cations form polymeric, polar double-strands along [010] by head to tail connections via N–H∙∙∙O hydrogen bonds. The perchlorate anions are located between these strands attached by one medium strong and two weaker un-bifurcated hydrogen bonds (monoclinic, centrosymmetric space group C2/c, a = 17.8796(5 Å, b = 5.66867(14 Å, c = 17.0106(5 Å, β = 104.788(3°, V = 1666.9(1 Å3, Z = 8, T = 293 K, R(F [I > 2σ(I] = 0.0391, wR(F2 [all] = 0.1113. In 2, besides the N–H∙∙∙O hydrogen bonds, medium strong N–H∙∙∙N hydrogen bonds are present. One dpmaH cation and the neutral dpma molecule are connected head to tail by two N–H∙∙∙O hydrogen bonds forming a monocationic cyclic unit. These cyclic units are further connected by N–H∙∙∙O and N–H∙∙∙N hydrogen bonds forming polymeric, polar double-strands along [001]. The perchlorate anions fill the gaps between these strands, and each [ClO4]− anion is weakly connected to the NH2 group by one N–H∙∙∙O hydrogen bond (orthorhombic, non-centrosymmetric space group Pca21 (No. 29, a = 18.5821(5 Å, b = 11.4320(3 Å, c = 6.89400(17 Å, V = 1464.50(6 Å3, Z = 4, T = 100 K, R(F [I > 2σ(I] = 0.0234, wR(F2 [all] = 0.0575. Both structures are structurally related, and their commonalities are discussed in terms of a graph

  6. Proton NMR Chemical Shift Behavior of Hydrogen-Bonded Amide Proton of Glycine-Containing Peptides and Polypeptides as Studied by ab initio MO Calculation

    Directory of Open Access Journals (Sweden)

    I. Ando

    2002-08-01

    Full Text Available Abstract: NMR chemical shifts of the amide proton of a supermolecule, an Nmethylacetamide hydrogen-bonded with a formamide, were calculated as functions of hydrogen-bond length RN…O and hydrogen-bond angles by FPT-GIAO method within the framework of HF/STO 6-31++G(d,p ab initio MO method. The calculations explained reasonably the experimental data reported previously that the isotropic proton chemical shifts move downfield with a decrease in RN…O. Further, the behavior of proton chemical shift tensor components depending on the hydrogen-bond length and hydrogen-bond angle was discussed.

  7. Quantum mechanical electronic structure calculation reveals orientation dependence of hydrogen bond energy in proteins.

    Science.gov (United States)

    Mondal, Abhisek; Datta, Saumen

    2017-06-01

    Hydrogen bond plays a unique role in governing macromolecular interactions with exquisite specificity. These interactions govern the fundamental biological processes like protein folding, enzymatic catalysis, molecular recognition. Despite extensive research work, till date there is no proper report available about the hydrogen bond's energy surface with respect to its geometric parameters, directly derived from proteins. Herein, we have deciphered the potential energy landscape of hydrogen bond directly from the macromolecular coordinates obtained from Protein Data Bank using quantum mechanical electronic structure calculations. The findings unravel the hydrogen bonding energies of proteins in parametric space. These data can be used to understand the energies of such directional interactions involved in biological molecules. Quantitative characterization has also been performed using Shannon entropic calculations for atoms participating in hydrogen bond. Collectively, our results constitute an improved way of understanding hydrogen bond energies in case of proteins and complement the knowledge-based potential. Proteins 2017; 85:1046-1055. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  8. Crystal structures and hydrogen bonding in the morpholinium salts of four phenoxyacetic acid analogues

    Directory of Open Access Journals (Sweden)

    Graham Smith

    2015-11-01

    Full Text Available The anhydrous salts morpholinium (tetrahydro-2-H-1,4-oxazin-4-ium phenoxyacetate, C4H10NO+·C8H7O3−, (I, morpholinium (4-fluorophenoxyacetate, C4H10NO+·C8H6 FO3−, (II, and isomeric morpholinium (3,5-dichlorophenoxyacetate (3,5-D, (III, and morpholinium (2,4-dichlorophenoxyacetic acid (2,4-D, C4H10NO+·C8H5Cl2O3−, (IV, have been determined and their hydrogen-bonded structures are described. In the crystals of (I, (III and (IV, one of the the aminium H atoms is involved in a three-centre asymmetric cation–anion N—H...O,O′ R12(4 hydrogen-bonding interaction with the two carboxyl O-atom acceptors of the anion. With the structure of (II, the primary N—H...O interaction is linear. In the structures of (I, (II and (III, the second N—H...Ocarboxyl hydrogen bond generates one-dimensional chain structures extending in all cases along [100]. With (IV, the ion pairs are linked though inversion-related N—H...O hydrogen bonds [graph set R42(8], giving a cyclic heterotetrameric structure.

  9. Rydberg and π-π* transitions in film surfaces of various kinds of nylons studied by attenuated total reflection far-ultraviolet spectroscopy and quantum chemical calculations: peak shifts in the spectra and their relation to nylon structure and hydrogen bondings.

    Science.gov (United States)

    Morisawa, Yusuke; Yasunaga, Manaka; Sato, Harumi; Fukuda, Ryoichi; Ehara, Masahiro; Ozaki, Yukihiro

    2014-10-09

    Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-260 nm region were measured for surfaces (thickness 50-200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations. Time-dependent density functional theory (TD-DFT/CAM-B3LYP) calculations were carried out using the model systems to provide the definitive assignments of their absorption spectra and to elucidate their peak shifts in several nylons, in particular, focusing on their crystal alignment structures and intermolecular hydrogen bondings. Two major bands of nylon films near 150 and 200 nm are characterized as σ-Rydberg 3p and π-π* transitions of nylons, respectively. These assignments are also coherent with those of liquid n-alkanes (n = 5-14) and liquid amides observed previously. The Rydberg transitions are delocalized over the hydrocarbon chains, while the π-π* transitions are relatively localized at the amide group. Differences in the peak positions and intensity were found in both ATR- and Tr-FUV spectra for different nylons. A red-shift of the π-π* amide band in the FUV spectra of nylon-6 and nylon-6/6 models in α-form is attributed to the crystal structure pattern and the intermolecular hydrogen bondings, which result in the different delocalization character of the π-π* transitions and transition dipole coupling.

  10. The potential utility of predicted one bond carbon-proton coupling constants in the structure elucidation of small organic molecules by NMR spectroscopy.

    Directory of Open Access Journals (Sweden)

    Chandrasekhar Venkata

    Full Text Available NMR spectroscopy is the most popular technique used for structure elucidation of small organic molecules in solution, but incorrect structures are regularly reported. One-bond proton-carbon J-couplings provide additional information about chemical structure because they are determined by different features of molecular structure than are proton and carbon chemical shifts. However, these couplings are not routinely used to validate proposed structures because few software tools exist to predict them. This study assesses the accuracy of Density Functional Theory for predicting them using 396 published experimental observations from a diverse range of small organic molecules. With the B3LYP functional and the TZVP basis set, Density Functional Theory calculations using the open-source software package NWChem can predict one-bond CH J-couplings with good accuracy for most classes of small organic molecule. The root-mean-square deviation after correction is 1.5 Hz for most sp3 CH pairs and 1.9 Hz for sp2 pairs; larger errors are observed for sp3 pairs with multiple electronegative substituents and for sp pairs. These results suggest that prediction of one-bond CH J-couplings by Density Functional Theory is sufficiently accurate for structure validation. This will be of particular use in strained ring systems and heterocycles which have characteristic couplings and which pose challenges for structure elucidation.

  11. The potential utility of predicted one bond carbon-proton coupling constants in the structure elucidation of small organic molecules by NMR spectroscopy.

    Science.gov (United States)

    Venkata, Chandrasekhar; Forster, Mark J; Howe, Peter W A; Steinbeck, Christoph

    2014-01-01

    NMR spectroscopy is the most popular technique used for structure elucidation of small organic molecules in solution, but incorrect structures are regularly reported. One-bond proton-carbon J-couplings provide additional information about chemical structure because they are determined by different features of molecular structure than are proton and carbon chemical shifts. However, these couplings are not routinely used to validate proposed structures because few software tools exist to predict them. This study assesses the accuracy of Density Functional Theory for predicting them using 396 published experimental observations from a diverse range of small organic molecules. With the B3LYP functional and the TZVP basis set, Density Functional Theory calculations using the open-source software package NWChem can predict one-bond CH J-couplings with good accuracy for most classes of small organic molecule. The root-mean-square deviation after correction is 1.5 Hz for most sp3 CH pairs and 1.9 Hz for sp2 pairs; larger errors are observed for sp3 pairs with multiple electronegative substituents and for sp pairs. These results suggest that prediction of one-bond CH J-couplings by Density Functional Theory is sufficiently accurate for structure validation. This will be of particular use in strained ring systems and heterocycles which have characteristic couplings and which pose challenges for structure elucidation.

  12. First-Principles Analysis on π-bonded Chain Structure on Several Polytypes of SiC Surfaces: Importance of Stacking Sequence on Energetics and Electronic Structures

    Science.gov (United States)

    Kaneko, Tomoaki; Tajima, Nobuo; Yamasaki, Takahiro; Ohno, Takahisa

    2017-09-01

    Using first principles calculations based on a density functional theory, the energetics and electronic properties of a (2 × 1) π-bonded chain structure in several polytypes of SiC surfaces are discussed with special attention to the stacking sequence of SiC bilayers. We found that the stacking sequence of the topmost two SiC bilayers plays a decisive role for the stability and electronic structures of the π-bonded chain structure. We showed that the homo-elemental bonds in π-bonded chain structures cause alterations in the electronic structures of both the Si- and C-faces. The energetics of π-bonded chain structures on other group IV and IV-IV compound semiconductors were also investigated. We also showed that the buckling structure in the monolayer honeycomb lattice reflects the buckling of the topmost two atoms in the π-bonded chain structure observed in Si(111) and Ge(111).

  13. Comparison of shear bond strength of resin reinforced chemical cure glass ionomer, conventional chemical cure glass ionomer and chemical cure composite resin in direct bonding systems: an in vitro study.

    Science.gov (United States)

    Rao, Kolasani Srinivasa; Reddy, T Praveen Kumar; Yugandhar, Garlapati; Kumar, B Sunil; Reddy, S N Chandrasekhar; Babu, Devatha Ashok

    2013-01-01

    The acid pretreatment and use of composite resins as the bonding medium has disadvantages like scratching and loss of surface enamel, decalcification, etc. To overcome disadvantages of composite resins, glass ionomers and its modifications are being used for bonding. The study was conducted to evaluate the efficiency of resin reinforced glass ionomer as a direct bonding system with conventional glass ionomer cement and composite resin. The study showed that shear bond strength of composite resin has the higher value than both resin reinforced glass ionomer and conventional glass ionomer cement in both 1 and 24 hours duration and it increased from 1 to 24 hours in all groups. The shear bond strength of resin reinforced glass ionomer cement was higher than the conventional glass ionomer cement in both 1 and 24 hours duration. Conditioning with polyacrylic acid improved the bond strength of resin reinforced glass ionomer cement significantly but not statistically significant in the case of conventional glass ionomer cement.

  14. Bond strength between stell-concrete and between concretes with different ages in structural rehabilitation

    Directory of Open Access Journals (Sweden)

    M. R. DORIA

    Full Text Available ABSTRACTIn inspections of buildings, it is common to find structures that, well before reaching its useful life longer require repairs and reinforcements. This study examined the bond strength between concrete of different ages and between steel and concrete, focusing on the recovery of reinforced concrete structures. To analyze the bond between concrete of different ages, trials with specimens receiving three different types of treatments at the interface between the concrete were performed: brushing; brushing and mortar equal to concrete of substrate and brushing and epoxy layer. Indirect tensile tests and oblique and vertical shear tests at the interface were made . The bond stress between steel and concrete was evaluated by pull out test under the conditions of the bar inserted in the still fresh concrete and when inserted in the hardened concrete with epoxy. Results showed increased bond strength by indirect tensile stress of 15% and 37%; 4% and 12% for the adherence test by oblique shear, and 108% and 178%, for the testing of vertical shear, respectively, for the specimens whose interfaces have received, in addition to brushing, layer of mortar and epoxy bridge, compared to those who received only brushing. Insignificant loss (about 0.52% of bond stress was noticed for pull out test of steel bar when compared with test results of the specimens that had steel bar inserted in the concrete in the hardened state with epoxy adhesion bridge, with those who had inserted steel bar in fresh concrete.

  15. A theoretical study of water clusters: the relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules.

    Science.gov (United States)

    Lenz, Annika; Ojamäe, Lars

    2005-05-07

    Quantum-chemical calculations of a variety of water clusters with eight, ten and twelve molecules were performed, as well as for selected clusters with up to 22 water molecules. Geometry optimizations were carried out at the B3LYP/cc-pVDZ level and single-point energies were calculated at the B3LYP/aug-cc-pVDZ level for selected clusters. The electronic energies were studied with respect to the geometry of the oxygen arrangement and six different characteristics of the hydrogen-bond arrangement in the cluster. Especially the effect of the placement of the non-hydrogen bonding hydrogens on the interaction energy was studied. Models for the interaction energy with respect to different characteristics of the hydrogen-bond arrangement were derived through least-square fits. The results from the study of the clusters with eight, ten and twelve molecules are used to predict possible low-energy structures for various shapes of clusters with up to 22 molecules.

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

    Energy Technology Data Exchange (ETDEWEB)

    Raupach, Marc; Tonner, Ralf, E-mail: tonner@chemie.uni-marburg.de [Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35032 Marburg (Germany)

    2015-05-21

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

  17. Reactivity of disulfide bonds is markedly affected by structure and environment

    DEFF Research Database (Denmark)

    Karimi, Maryam; Ignasiak, Marta T; Chan, Bun

    2016-01-01

    Disulfide bonds play a key role in stabilizing protein structures, with disruption strongly associated with loss of protein function and activity. Previous data have suggested that disulfides show only modest reactivity with oxidants. In the current study, we report kinetic data indicating...

  18. Phase transition in triglycine family of hydrogen bonded ferroelectrics: An interpretation based on structural studies

    Indian Academy of Sciences (India)

    R R Choudhury; R Chitra; P U Sastry; Amit Das; M Ramanadham

    2004-07-01

    Using the crystal structure, a comprehensive interpretation of the origin of ferroelectricity in the hydrogen bonded triglycine family of crystals is given. Our detailed analysis showed that the instability of nitrogen double well potential plays a driving role in the mechanism of the ferroelectric transitions in these crystals.

  19. The effect of RDX crystal defect structure on mechanical response of a polymer-bonded explosive

    NARCIS (Netherlands)

    Bouma, R.H.B.; Heijden, A.E.D.M. van der

    2016-01-01

    An explosive composition, derived from AFX-757, was systematically varied by using three different qualities of Class I RDX. The effect of internal defect structure of the RDX crystal on the shock sensitivity of a polymer bonded explosive is generally accepted (Doherty and Watt, 2008). Here the

  20. Magnetic structure and bonding of rare-earth diboride compounds RB{sub 2}: First-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kacimi, S.; Zazoua, F.; Djermouni, M.; Zaoui, A. [Modelling and Simulation in Materials Science Laboratory, Djillali Liabes University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria); Bekkouche, B. [Signals and Systems Laboratory, Abdelhamid Ibn Badis University of Mostaganem, Mostaganem 27000 (Algeria); Boukortt, A. [Elaboration Characterization Physico-Mechanics of Materials and Metallurgical Laboratory ECP3M, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University of Mostaganem, Mostaganem 27000 (Algeria)

    2012-07-15

    The electronic structure and magnetic behavior of hexagonal rare-earth diboride RB{sub 2} are studied using ab initio density-functional theory in the DFT + U approach. The effect of the spin-orbit coupling is also investigated and it is found to be a necessary requirement for the accurate description of the magnetic moment. In this paper, we study the magnetic phase stability of RB{sub 2} compounds; the band structure and the density of state (DOS) results prove that the coulomb potential and the spin-orbit interaction are keys factors to understand the magnetic properties of these series of materials. In addition, we also explain the behavior of a chemical bond of RB{sub 2} compounds through the analysis of the DOS and of the charge density. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Critical surface energy of composite cement containing MDP (10-methacryloyloxydecyl dihydrogen phosphate) and chemical bonding to hydroxyapatite.

    Science.gov (United States)

    Dabsie, Firas; Grégoire, Geneviève; Sharrock, Patrick

    2012-01-01

    Self-adhesive composite cements are increasingly used for cementing inlays/onlays, intraradicular posts, crowns and laminate veneers. Wider clinical acceptance is driven by simpler and faster handling procedures, much like observed for self-etching adhesives. 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) is a bi-functional monomer incorporated as the reactive ingredient in a contemporary self-adhesive cement. We have examined the surface free energy parameters of this cement and studied the mode of action of the cement on dentine substrate by contact angle measurements to determine the critical surface energy of the cement. Retention of the infrared absorption bands characteristic of the acrylate moieties on the surface of hydroxyapatite particles suggests that MDP contributes to the overall bonding to dentine by forming ionic chemical bonds with surface calcium ions in dentine crystalites.

  2. Structure, stability and electrochromic properties of polyaniline film covalently bonded to indium tin oxide substrate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wenzhi, E-mail: zhangwz@xatu.edu.cn [Key Laboratory for Photoelectric Functional Materials and Devices of Shaanxi Province, School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021 (China); Ju, Wenxing; Wu, Xinming; Wang, Yan; Wang, Qiguan; Zhou, Hongwei; Wang, Sumin [Key Laboratory for Photoelectric Functional Materials and Devices of Shaanxi Province, School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021 (China); Hu, Chenglong [Key Laboratory of Optoelectronic Chemical Materials and Devices of Ministry of Education, School of Chemistry and Environmental Engineering, Jianghan University, Wuhan 430056 (China)

    2016-03-30

    Graphical abstract: A chemical bonding approach was proposed to prepare the PANI film covalently bonded to ITO substrate and the film exhibited high electrochemical activities and stability compared with that obtained by conventional film-forming approach. - Highlights: • The PANI film covalently bonded to ITO substrate was prepared using ABPA as modifier. • The oxidative potentials of the obtained PANI film were decreased. • The obtained PANI film exhibits high electrochemical activities and stability. - Abstract: Indium tin oxide (ITO) substrate was modified with 4-aminobenzylphosphonic acid (ABPA), and then the polyaniline (PANI) film covalently bonded to ITO substrate was prepared by the chemical oxidation polymerization. X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR) spectroscopy, and atomic force microscopy (AFM) measurements demonstrated that chemical binding was formed between PANI and ABPA-modified ITO surface, and the maximum thickness of PANI layer is about 30 nm. The adhesive strength of PANI film on ITO substrate was tested by sonication. It was found that the film formed on the modified ITO exhibited a much better stability than that on bare one. Cyclic voltammetry (CV) and UV–vis spectroscopy measurements indicated that the oxidative potentials of PANI film on ABPA-modified ITO substrate were decreased and the film exhibited high electrochemical activities. Moreover, the optical contrast increased from 0.58 for PANI film (without ultrasound) to 1.06 for PANI film (after ultrasound for 60 min), which had an over 83% enhancement. The coloration time was 20.8 s, while the bleaching time was 19.5 s. The increase of electrochromic switching time was due to the lower ion diffusion coefficient of the large cation of (C{sub 4}H{sub 9}){sub 4}N{sup +} under the positive and negative potentials as comparison with the small Li{sup +} ion.

  3. Structural and Mechanistic Insights into C-P Bond Hydrolysis by Phosphonoacetate Hydrolase

    Energy Technology Data Exchange (ETDEWEB)

    Agarwal, Vinayak; Borisova, Svetlana A.; Metcalf, William W.; van der Donk, Wilfred A.; Nair, Satish K. (UIUC)

    2011-12-22

    Bacteria have evolved pathways to metabolize phosphonates as a nutrient source for phosphorus. In Sinorhizobium meliloti 1021, 2-aminoethylphosphonate is catabolized to phosphonoacetate, which is converted to acetate and inorganic phosphate by phosphonoacetate hydrolase (PhnA). Here we present detailed biochemical and structural characterization of PhnA that provides insights into the mechanism of C-P bond cleavage. The 1.35 {angstrom} resolution crystal structure reveals a catalytic core similar to those of alkaline phosphatases and nucleotide pyrophosphatases but with notable differences, such as a longer metal-metal distance. Detailed structure-guided analysis of active site residues and four additional cocrystal structures with phosphonoacetate substrate, acetate, phosphonoformate inhibitor, and a covalently bound transition state mimic provide insight into active site features that may facilitate cleavage of the C-P bond. These studies expand upon the array of reactions that can be catalyzed by enzymes of the alkaline phosphatase superfamily.

  4. ACToR Chemical Structure processing using Open Source ...

    Science.gov (United States)

    ACToR (Aggregated Computational Toxicology Resource) is a centralized database repository developed by the National Center for Computational Toxicology (NCCT) at the U.S. Environmental Protection Agency (EPA). Free and open source tools were used to compile toxicity data from over 1,950 public sources. ACToR contains chemical structure information and toxicological data for over 558,000 unique chemicals. The database primarily includes data from NCCT research programs, in vivo toxicity data from ToxRef, human exposure data from ExpoCast, high-throughput screening data from ToxCast and high quality chemical structure information from the EPA DSSTox program. The DSSTox database is a chemical structure inventory for the NCCT programs and currently has about 16,000 unique structures. Included are also data from PubChem, ChemSpider, USDA, FDA, NIH and several other public data sources. ACToR has been a resource to various international and national research groups. Most of our recent efforts on ACToR are focused on improving the structural identifiers and Physico-Chemical properties of the chemicals in the database. Organizing this huge collection of data and improving the chemical structure quality of the database has posed some major challenges. Workflows have been developed to process structures, calculate chemical properties and identify relationships between CAS numbers. The Structure processing workflow integrates web services (PubChem and NIH NCI Cactus) to d

  5. CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE II REPORT, SEPT.1998-JULY 1999.

    Energy Technology Data Exchange (ETDEWEB)

    SUGAMA,T.YAGER,K.A.BLANKENHORN,D.(KEYSPAN R AND D INITIATIVE)

    1999-08-01

    Based upon the previous Phase I research program aimed at looking for ways of recycling the KeySpan-generated wastes, such as waste water treatment sludge (WWTS) and bottom ash (BA), into the potentially useful cementitious materials called chemically bonded cement (CBC) materials, the emphasis of this Phase II program done at Brookhaven National Laboratory, in a period of September 1998 through July 1999, was directed towards the two major subjects: One was to assess the technical feasibility of WWTS-based CBC material for use as Pb-exchange adsorbent (PEA) which remediates Pb-contaminated soils in the field; and the other was related to the establishment of the optimum-packaging storage system of dry BA-based CBC components that make it a promising matrix material for the steam-cured concrete products containing sand and coarse aggregate. To achieve the goal of the first subject, a small-scale field demonstration test was carried out. Using the PEA material consisting of 30 wt% WWTS, 13 wt% Type I cement and 57 wt% water, the PES slurry was prepared using a rotary shear concrete mixer, and then poured on the Pb-contaminated soil. The PEA-to-soil ratio by weight was a factor of 2.0. The placed PEA slurry was blended with soil using hand mixing tools such as claws and shovels. The wettability of soils with the PEA was very good, thereby facilitating the soil-PEA mix procedures. A very promising result was obtained from this field test; in fact, the mount of Pb leached out from the 25-day-aged PEA-treated soil specimen was only 0.74 mg/l, meeting the requirement for EPA safe regulation of < 5 mg/l. In contrast, a large amount (26.4 mg/l) of Pb was detected from the untreated soil of the same age. Thus, this finding demonstrated that the WWTS-based CBC has a potential for use as PEA material. Regarding the second subject, the dry-packed storage system consisting of 68.7 wt% BA, 13.0 wt% calcium aluminate cement (CAC), 13.0 wt% Type I portland cement and 5.3 wt

  6. How to add chemical abstracts service registry numbers and structures to databases via chemical names comparison

    Science.gov (United States)

    Krebs; Jordis

    2000-03-01

    For the conversion of nonstructural chemical databases to structure databases, a series of algorithms to find the closest match between existing names to names in a reference database are described. On the basis of the best match, new fields such as the Chemical Abstracts Service Registry Number (CASRN) or structures were added to the database.

  7. The electron density distribution in the hydrogen bond. A quantum chemical and crystallographic study

    NARCIS (Netherlands)

    Feil, Dirk

    1990-01-01

    With the help of Hartree—Fock—Slater calculations in which very large basis sets are employed, the polarisation of the water molecule by an electric field is explored. The various features in the electron density distribution are encountered again in the long hydrogen bond in the water dimer, showin

  8. Physico-Chemical Factors Affecting Hydrothermal Resistance and Bonding of Polymeric Composites to Steel Surfaces

    Science.gov (United States)

    1985-11-01

    7 , I 71iil 7 7 771111011111111111171111 Type A consists of a strong ionic interaction associated with charge transfer bonding mechanisms which...the ionic interaction regions and the density of entangleicnt macromol- ecules at interfaces are not evident from the limited data. Nevertheless

  9. Solvent-dependent dynamics of hydrogen bonding structure 5-(methylthio)-1, 3, 4-thiadiazole-2(3H)-thione as determined by Raman spectroscopy and theoretical calculation

    Science.gov (United States)

    Pang, Sumei; Zhao, Yanying; Xin, Liu; Xue, Jiadan; Zheng, Xuming

    2017-01-01

    The vibration spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione (MTTN) in acetonitrile (CH3CN), methanol (CH3OH) and water (H2O) solvents were collected and evaluated via deuterium isotopic substitution Raman spectroscopic experiments. These experiments were combined with the quantum chemical theoretical calculations using the PCM solvent model and normal mode analysis. The results confirmed that the MTTN in CH3CN, CH3OH and H2O have hydrogen bonding (H-bonding) MTTN(solvent)n clusters that produce significantly different Raman intensity patterns in different solvents. Combined with the normal Raman assignment, most resonance Raman spectra were assigned to the vibration modes of the H-bonding MTTN(CH3CN), MTTN(CH3OH)3 and MTTN(H2O)3 clusters in CH3CN, CH3OH and H2O. The theoretically-predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands. The intermolecular > NH ⋯ O and > NH ⋯ N H-bonding interactions are key constituents of stable thione structures in MTTN. This underlines the significant structural differences of MTTN in CH3CN, CH3OH and H2O. H-bonding perturbation of MTTN reveal important insights about the intermolecular excited state proton transfer (ESPT) reaction mechanisms in the Franck-Condon region structural dynamics of the thione → thiol tautomer in CH3OH and H2O.

  10. Magnetovolume and chemical bonding effects of Ni atom in γ’-(Fe1-xNix)4N compounds

    Institute of Scientific and Technical Information of China (English)

    薛德胜; 李发伸

    1997-01-01

    By X-ray diffraction and high pressure Mossbauer spectroscopy, the structure and the hyperfine parameters of Ni substituted γ-Fe4N were investigated. The results of X-ray diffraction indicate that single phase γ’-(Fe1-xNix)4N compounds can be prepared in the composition range of 0≤x≤0.6, and with the increase of Ni content the lattice parameter is fit for the relationship a0(x) = 3.790 5-0.021 57x-0.031 67x2. By high pressure Mossbauer spectra, effects of magnetovolume and chemical bonding of Ni atom on hyperfine magnetic field and isomer shift of iron were distinguished for the first time, and their composition dependences for different lattice sites were studied simultaneously. It is found that the magnetovolume and chemical bonding have different influences on the properties of γ’-(Fe1-xNix)4N, and the latter one plays a key role in the property changes of γ-(Fe1-xNix)4N.

  11. The Effect of RDX Crystal Defect Structure on Mechanical Response of a Polymer-Bonded Explosive

    Science.gov (United States)

    2015-11-09

    deformation [a] R. H. B. Bouma Department Process Instrumentation and Design TNO, Organisation for Applied Scientific Research P.O. Box 6012 2600 JA, Delft, The...DOI: 10.1002/prep.201500222 The Effect of RDX Crystal Defect Structure on Mechanical Response of a Polymer-Bonded Explosive Richard H. B. Bouma[a...systematically varied by using three different qualities of Class I RDX. The effect of internal defect structure of the RDX crystal on the shock

  12. Electronic structure of alloxan and its dimers: QM/QD simulations and quantum chemical topology analysis.

    Science.gov (United States)

    Allehyani, Basmah H; Elroby, Shaaban A; Aziz, Saadalluh G; Hilal, Rifaat H

    2015-01-01

    This study aims to identify the origin of the extra stability of alloxan, a biologically active pyrimidine. To achieve this goal, detailed DFT computations and quantum dynamics simulations have been performed to establish the most stable conformation and the global minimum structure on the alloxan potential energy surface. The effects of the solvent, basis set, and DFT method have been examined to validate the theoretical model adopted throughout the work. Two non-covalent intermolecular dimers of alloxan, the H-bonded and dipolar dimers, have been investigated at the ωB97X-D and M06-2X levels of theory using the triple zeta 6-311++G** to establish their relative stability. Quantum chemical topology features and natural bond orbital analysis (NBO) have been performed to identify and characterize the forces that govern the structures and underlie the extra stability of alloxan.

  13. Catastrophe Bonds. From Structure to Strategy – A Cluster Analysis at European Level

    Directory of Open Access Journals (Sweden)

    Laura-Gabriela CONSTANTIN

    2014-12-01

    Full Text Available As a core activity and discipline of corporate management and corporate governance, risk management is, especially nowadays, a central part in pursuing the sustainable development desiderates, both from the perspective of the firm and of the society as a whole.Considering the negative impact natural catastrophes have on the companies’ and countries’ competitiveness, the development of sustainable financial products that make a contribution to transferring the risk and allocating the capital in case of disasters stands for a continual preoccupation, especially for the (reinsurance industry, while the study of catastrophe bonds – insurance-linked securities – is of interest in the specialized literature. In this context, the scope of the present research is to expand the empirical studies within this field while examining the link between the structure of the catastrophe bonds and the risk management approach employed while accessing the capital markets through this transactions.The methodology entailed clustering a selection of transactions developed by European cedents based on the size of each issue and correlating the results with an innovative score, developed to encompass several important catastrophe bonds structural components.The findings reflect that the general structural elements of the financial transactions reflect closely the corporate approach regarding the innovative risk intermediation instruments for the examined catastrophe bonds deals. The outcomes also emphasize, as expected, that companies with a stronger presence on this market seem to have a more sophisticated risk management approach.

  14. Intriguing structures and magic sizes of heavy noble metal nanoclusters around size 55 governed by relativistic effect and covalent bonding

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, X. J.; Xue, X. L.; Jia, Yu [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Guo, Z. X. [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Department of Chemistry and London Centre for Nanotechnology, University College London, London WC1H (United Kingdom); Li, S. F., E-mail: sflizzu@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China); ICQD, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zhang, Zhenyu, E-mail: zhangzy@ustc.edu.cn [ICQD, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Gao, Y. F., E-mail: ygao7@utk.edu [Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2015-11-07

    Nanoclusters usually display exotic physical and chemical properties due to their intriguing geometric structures in contrast to their bulk counterparts. By means of first-principles calculations within density functional theory, we find that heavy noble metal Pt{sub N} nanoclusters around the size N = 55 begin to prefer an open configuration, rather than previously reported close-packed icosahedron or core-shell structures. Particularly, for Pt{sub N}, the widely supposed icosahedronal magic cluster is changed to a three-atomic-layered structure with D{sub 6h} symmetry, which can be well addressed by our recently established generalized Wulff construction principle (GWCP). However, the magic number of Pt{sub N} clusters around 55 is shifted to a new odd number of 57. The high symmetric three-layered Pt{sub 57} motif is mainly stabilized by the enhanced covalent bonding contributed by both spin-orbital coupling effect and the open d orbital (5d{sup 9}6s{sup 1}) of Pt, which result in a delicate balance between the enhanced Pt–Pt covalent bonding of the interlayers and negligible d dangling bonds on the cluster edges. These findings about Pt{sub N} clusters are also applicable to Ir{sub N} clusters, but qualitatively different from their earlier neighboring element Os and their later neighboring element Au. The magic numbers for Os and Au are even, being 56 and 58, respectively. The findings of the new odd magic number 57 are the important supplementary of the recently established GWCP.

  15. Interfacial crystalline structures in injection over-molded polypropylene and bond strength.

    Science.gov (United States)

    Yan, Bowen; Wu, Hong; Jiang, Genjie; Guo, Shaoyun; Huang, Jian

    2010-11-01

    This paper describes interfacial crystalline structures found in injection overmolded polypropylene components and the relationship of these structures to bond strength between the components. The combined effects of the development of hierarchical gradient structures and the particular thermomechanical environment near the interface on the interfacial crystalline structures were investigated in detail by PLM, SEM, DSC, WAXD, and infrared dichroism spectroscopy. The experimental results showed that during molding there was competitive formation of interfacial crystalline structures consisted of "shish-kebab" layer (SKL) and a transcrystalline layers (TCL). Variation in shear stress (controlled by injection pressure and injection speed) plays an important role in the formation of the SKL. The formation of TCL is influenced by the thermal environment, namely melt temperature and mold temperature. Increasing within certain limits, interfacial temperature and the thermal gradient near the interface promotes β-iPP growth. The relationship between interfacial crystalline structures and interfacial bond strength was established by lap shear measurement. The interfacial bond strength is improved by enhancing the formation of TCL, but reduced if SKL predominates.

  16. First-principles study of structural and bonding properties of vanadium carbide and niobium carbide

    Science.gov (United States)

    Joshi, K. B.; Paliwal, U.

    2009-11-01

    An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes—P86 and PW92—are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.

  17. First-principles study of structural and bonding properties of vanadium carbide and niobium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, K B; Paliwal, U [Department of Physics, University College of Science, M L Sukhadia University, Udaipur - 313001 (India)], E-mail: k_joshi@yahoo.com

    2009-11-15

    An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes-P86 and PW92-are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.

  18. Effect of adhesive on molten pool structure and penetration in laser weld bonding of magnesium alloy

    Science.gov (United States)

    Liu, L. M.; Ren, D. X.

    2010-09-01

    Laser weld bonding (LWB) is a new hybrid technique that combines adhesive bonding with laser seam welding together, and can achieve higher joint strength than adhesive bonding or laser welding individually. Some new physical phenomena have been observed in this welding method, and the phenomena are different from the normal laser welding process, such as a remarkable deeper penetration in LWB than that in laser welding direct (LWD). The adhesive-induced gas can influence the molten pool structure in front of the keyhole, so that less energy is required for laser keyhole through the upper sheet; thus, higher laser power density can interact with the lower sheet, leading to deeper penetration. Simulation comparison experiments are set to indirectly verify these conclusions above.

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

    Science.gov (United States)

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

    2016-04-14

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

  20. Microstructure and hardness of HIP-bonded regions in F82H blanket structures

    Science.gov (United States)

    Furuya, K.; Wakai, E.; Ando, M.; Sawai, T.; Nakamura, K.; Takeuchi, H.; Iwabuchi, A.

    2002-12-01

    Metallurgical examinations and hardness measurements were performed at hot isostatic pressing (HIP)-bonded regions in blanket structures made from F82H alloy in order to investigate the HIP-bondability and the influence on the microstructure due to the HIP and heat treatments which would correspond to the fabrication of an actual blanket. The metallurgical examination showed that the HIP-bonded interfaces were sufficiently diffusion-bonded without significant defects, i.e. voids and/or exfoliations, although grain coarsening was observed at a part of the HIP interfaces. Hardness was nearly equal in the coarsening region and a region without coarsening, but about a 10 Hv increase was found in a boundary in between the regions with and without coarsening. Microcrystallized grains were observed in a region about ˜6 μm from HIP interfaces, and the hardness increased by about 0.2 GPa in the region.

  1. Love Waves in Layered Graded Composite Structures with Imperfectly Bonded Interface

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al layered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.

  2. Sequential bond energies and structures of the Cr+·(N2), n =1−4

    Indian Academy of Sciences (India)

    Jamal N Dawoud

    2014-11-01

    DFT calculations, with an effective core potential for the chromium ion and large polarized basis set functions have been used to calculate the sequential bond dissociation energies of the Cr+·(N2) (n = 1—4) complexes. A linear configuration was obtained for the Cr+·N2 and Cr+·(N2)2 complexes with sequential bond dissociation energies of 14.6 and 16.4 kcal mol-1, respectively. For the Cr+·(N2)3 and Cr+·(N2)4 complexes, distorted trigonal pyramidal and tetrahedral geometries were optimized with sequential bond dissociation energies of 6.5 and 5.5 kcal mol-1, respectively. - back-donation in side-on approach of the Cr+·N2 leads to the formation of a tilted structure with the Cr+ ion in central position. The di-ligated complex exhibits the strongest bond dissociation energy among these four Cr+·(N2) (n = 1—4) complexes since it has the largest Cr+—N bond order.

  3. Evolution in the structural and bonding properties of Aluminum-Lithium clusters

    CERN Document Server

    Chacko, S; Paranjape, V V

    2003-01-01

    We present a systematic study of the geometry, energetics, electronic structure and bonding in various Al-Li clusters viz. Al_nLi_n (n=1-11), Al_2^-, Al_2^{2-}, Al_2Li, Al_2Li^-, and Al_6Li_8 using Born-Oppenheimer molecular dynamics method within the framework of density functional theory. The growth patterns in these cluster are found to be divided in two broad categories: the first consisting of a quinted roof of Al_2Li_2 (n=2-4) and the second consisting of a pentagonal ring (n=7-9). A covalent bonding between Al-Li in Al_2Li_2 is seen, whereas, in larger clusters, it is ionic. A three dimensional growth of the Al cluster in Al_4^{2-}, Al_5Li_5, and Al_6Li_8 leads to a transition from localized to delocalized bonding. In clusters with more than six Al atoms, the eigenvalue spectrum is divided into two groups: a lower group of jellium-like states and a higher group of localized bonds arising out of p complex. Thus, a mixture of localized, delocalized, and ionic bonding is seen in these clusters. Finally, w...

  4. Mapping chemical performance on molecular structures using locally interpretable explanations

    CERN Document Server

    Whitmore, Leanne S; Hudson, Corey M

    2016-01-01

    In this work, we present an application of Locally Interpretable Machine-Agnostic Explanations to 2-D chemical structures. Using this framework we are able to provide a structural interpretation for an existing black-box model for classifying biologically produced fuel compounds with regard to Research Octane Number. This method of "painting" locally interpretable explanations onto 2-D chemical structures replicates the chemical intuition of synthetic chemists, allowing researchers in the field to directly accept, reject, inform and evaluate decisions underlying inscrutably complex quantitative structure-activity relationship models.

  5. Systems, Apparatuses, and Methods for Using Durable Adhesively Bonded Joints for Sandwich Structures

    Science.gov (United States)

    Smeltzer, III, Stanley S. (Inventor); Lundgren, Eric C. (Inventor)

    2014-01-01

    Systems, methods, and apparatus for increasing durability of adhesively bonded joints in a sandwich structure. Such systems, methods, and apparatus includes an first face sheet and an second face sheet as well as an insert structure, the insert structure having a first insert face sheet, a second insert face sheet, and an insert core material. In addition, sandwich core material is arranged between the first face sheet and the second face sheet. A primary bondline may be coupled to the face sheet(s) and the splice. Further, systems, methods, and apparatus of the present disclosure advantageously reduce the load, provide a redundant path, reduce structural fatigue, and/or increase fatigue life.

  6. Chemical synthesis of La1 isolated from the venom of the scorpion Liocheles australasiae and determination of its disulfide bonding pattern.

    Science.gov (United States)

    Nagao, Junya; Miyashita, Masahiro; Nakagawa, Yoshiaki; Miyagawa, Hisashi

    2015-08-01

    La1 is a 73-residue cysteine-rich peptide isolated from the scorpion Liocheles australasiae venom. Although La1 is the most abundant peptide in the venom, its biological function remains unknown. Here, we describe a method for efficient chemical synthesis of La1 using the native chemical ligation (NCL) strategy, in which three peptide components of less than 40 residues were sequentially ligated. The peptide thioester necessary for NCL was synthesized using an aromatic N-acylurea approach with Fmoc-SPPS. After completion of sequential NCL, disulfide bond formation was carried out using a dialysis method, in which the linear peptide dissolved in an acidic solution was dialyzed against a slightly alkaline buffer to obtain correctly folded La1. Next, we determined the disulfide bonding pattern of La1. Enzymatic and chemical digests of La1 without reduction of disulfide bonds were analyzed by liquid chromatography/mass spectrometry (LC/MS), which revealed two of four disulfide bond linkages. The remaining two linkages were assigned based on MS/MS analysis of a peptide fragment containing two disulfide bonds. Consequently, the disulfide bonding pattern of La1 was found to be similar to that of a von Willebrand factor type C (VWC) domain. To our knowledge, this is the first report of the experimental determination of the disulfide bonding pattern of peptides having a single VWC domain as well as their chemical synthesis. La1 synthesized in this study will be useful for investigation of its biological role in the venom.

  7. Chemical Probes Allow Structural Insight into the Condensation Reaction of Nonribosomal Peptide Synthetases.

    Science.gov (United States)

    Bloudoff, Kristjan; Alonzo, Diego A; Schmeing, T Martin

    2016-03-17

    Nonribosomal peptide synthetases (NRPSs) synthesize a vast variety of small molecules, including antibiotics, antitumors, and immunosuppressants. The NRPS condensation (C) domain catalyzes amide bond formation, the central chemical step in nonribosomal peptide synthesis. The catalytic mechanism and substrate determinants of the reaction are under debate. We developed chemical probes to structurally study the NRPS condensation reaction. These substrate analogs become covalently tethered to a cysteine introduced near the active site, to mimic covalent substrate delivery by carrier domains. They are competent substrates in the condensation reaction and behave similarly to native substrates. Co-crystal structures show C domain-substrate interactions, and suggest that the catalytic histidine's principle role is to position the α-amino group for nucleophilic attack. Structural insight provided by these co-complexes also allowed us to alter the substrate specificity profile of the reaction with a single point mutation.

  8. Socialization of didactic units for teaching-learning of chemical bond to students of basic course in high school

    National Research Council Canada - National Science Library

    Mercedes Cárdenas-Ojeda

    2016-01-01

    .... The test Covalent Bond and its structure was applied as a diagnostic tool to 42 students of Chemistry and Bachelor of Natural Science and Environmental Education of the Universidad Pedagógica y Tecnológica de Colombia, (UPTC) the perception of this topic becomes a field that allows to explain the natural phenomena and its accurate explanation allows, on one hand, to avoid the students adapt conceptual mistakes, and on the other, foster meaningful learning in them.

  9. Catastrophe Bonds Structures at European Level – A Cluster Analysis Approach

    Directory of Open Access Journals (Sweden)

    Nadotti Loris Lino Maria

    2014-12-01

    Full Text Available The present paper aims at examining several characteristics of the catastrophe bonds (CB market by focusing on emblematic transactions with the objective of stressing the choices of the European-based (reinsurance groups in terms of the CB tranches structure. For the purpose of highlighting the common individualities regarding the configuration of the catastrophe bonds, there are recognized homogenous groups in terms of covered perils and size of the each CB tranche, while emphasizing some stringent aspects linked to their trigger mechanism (like the basis risk, their rating, or tenor. The research identifies several profiles regarding the structural characteristics of the CB during the entire analysed period (1999-2014 and the main periods of development of the market. Accommodating categorical and continuous data, the structural patterns are determined and analysed by applying the two-step cluster methodology.

  10. Crystal structure and hydrogen-bonding patterns in 5-fluorocytosinium picrate

    Directory of Open Access Journals (Sweden)

    Marimuthu Mohana

    2017-03-01

    Full Text Available In the crystal structure of the title compound, 5-fluorocytosinium picrate, C4H5FN3O+·C6H2N3O7−, one N heteroatom of the 5-fluorocytosine (5FC ring is protonated. The 5FC ring forms a dihedral angle of 19.97 (11° with the ring of the picrate (PA− anion. In the crystal, the 5FC+ cation interacts with the PA− anion through three-centre N—H...O hydrogen bonds, forming two conjoined rings having R21(6 and R12(6 motifs, and is extended by N—H...O hydrogen bonds and C—H...O interactions into a two-dimensional sheet structure lying parallel to (001. Also present in the crystal structure are weak C—F...π interactions.

  11. Optimum metallic-bond scheme: Theoretical study ofgeometric structures for ground-state sodium clusters

    Institute of Scientific and Technical Information of China (English)

    苏长荣; 李家明

    2002-01-01

    We present an optimum metallic-bond scheme to study the geometric structures of sodium clusters Nan (n≤15) systematically by combining the characteristics of metallic bonds and the first principle molecular dynamics simulation. The scheme provides an optimum way to examine almost all stable structures of sodium clusters and to determine their ground state structures. It is interesting to note that for the larger sodium clusters (13≤n≤15), there are some plane-like substructures on their surfaces, which resemble the fragments of the (110) plane with the highest atomic area density in the bulk bcc sodium crystal. We also propose a possible way to understand the formation of large icosahedral sodium clusters (1500<n<22000).

  12. SOME QUANTUM CHEMICAL STUDY ON THE STRUCTURAL ...

    African Journals Online (AJOL)

    Preferred Customer

    Formula. Formula weight. (gmol-1) ... Quantum chemical calculations (Density Functional Theory, B3LYP/6-31G (d)) were used to purposed the ... correlation functional [B3LYP/6-31G(d)]) calculations were done by using Gaussian 03 program ...

  13. Extraordinarily Long 2-Electron - 4-Center (2e-/4c) 2.9-Å Carbon-Carbon Bonds - What is a Chemical Bond?

    OpenAIRE

    Miller, Joel S.

    2014-01-01

    Carbon-carbon (CC) bonding is a key essence of organic and biochemistry. The length of a CC bond, i.e. 1.54 Å found in the diamond allotrope of carbon and ethane, is among the essential information learned by all chemistry students. This is the length of a single bond () between sp3-hybridized carbons and is the longest of all common CC bonds. Our studies of the [TCNE]22- (TCNE = tetracyanoethylene) dimers reveal that 2.89 ± 0.05 Å 2 electron/4 center (2e-/4c) CC bonds are present. Struc...

  14. Solution structure and activity of the synthetic four-disulfide bond Mediterranean mussel defensin (MGD-1).

    Science.gov (United States)

    Yang, Y S; Mitta, G; Chavanieu, A; Calas, B; Sanchez, J F; Roch, P; Aumelas, A

    2000-11-28

    MGD-1 is a 39-residue defensin-like peptide isolated from the edible Mediterranean mussel, Mytilus galloprovincialis. This peptide is characterized by the presence of four disulfide bonds. We report here its solid-phase synthesis and an easy way to improve the yield of the four native disulfide bonds. Synthetic and native MGD-1 display similar antibacterial activity, suggesting that the hydroxylation of Trp28 observed in native MGD-1 is not involved in the antimicrobial effect. The three-dimensional solution structure of MGD-1 has been established using (1)H NMR and mainly consists of a helical part (Asn7-Ser16) and two antiparallel beta-strands (Arg20-Cys25 and Cys33-Arg37), together giving rise to the common cystine-stabilized alpha-beta motif frequently observed in scorpion toxins. In MGD-1, the cystine-stabilized alpha-beta motif is stabilized by four disulfide bonds (Cys4-Cys25, Cys10-Cys33, Cys14-Cys35, and Cys21-Cys38), instead of by the three disulfide bonds commonly found in arthropod defensins. Except for the Cys21-Cys38 disulfide bond which is solvent-exposed, the three others belong to the particularly hydrophobic core of the highly constrained structure. Moreover, the C4-P5 amide bond in the cis conformation characterizes the MGD-1 structure. MGD-1 and insect defensin A possess similar bactericidal anti-Gram-positive activity, suggesting that the fourth disulfide bond of MGD-1 is not essential for the biological activity. In agreement with the general features of antibacterial peptides, the MGD-1 and defensin A structures display a typical distribution of positively charged and hydrophobic side chains. The positively charged residues of MGD-1 are located in three clusters. For these two defensin peptides isolated from insects and mollusks, it appears that the rather well conserved location of certain positively charged residues and of the large hydrophobic cluster are enough to generate the bactericidal potency and the Gram-positive specificity.

  15. On the reactivity of sulfosalts in cyanide aqueous media: structural, bonding and electronic aspects.

    Science.gov (United States)

    Meléndez, Angel M; Arroyo, Rubén; González, Ignacio

    2010-09-10

    The reactivity of the ruby silver minerals proustite (3Ag(2)S⋅As(2)S(3)) and pyrargyrite (3Ag(2)S⋅Sb(2)S(3)) was studied with two types of electrodes: a carbon-paste electroactive electrode (CPEE) and a paraffin-impregnated graphite electrode (PIGE). Polycrystalline samples of α-Ag(2)S (acanthite), As(2)S(3) (orpiment), Sb(2)S(3) (stibnite), Ag(3)AsS(3) (proustite), Ag(3)SbS(3) (pyrargyrite), and three samples of the proustite-pyrargyrite solid solution series were synthesized from pure elements by a solid-state reaction method. Phase identification of samples was carried out by XRD and chemical homogeneity was checked by SEM-EDS. Besides, sulfosalts were characterized by diffuse reflectance spectroscopy (DRS). Flat-band and formal potentials of sulfosalts were determined by the Mott-Schottky method and differential pulse abrasive stripping voltammetry, respectively. Band structure, bonding and solid-state structure are considered to investigate the oxidation and reduction of the solids. A ligand-to-metal charge transfer (LMCT) transition from the AsS(3) (or SbS(3)) group to Ag is related to ease of reducing the pyrargyrite-proustite series. Despite the increase in the amount of As (Sb) in Ag(3)SbS(3) (Ag(3)AsS(3)), reactivity is similar due to the similarity of the solid-state structures, and the same oxidation states of S, As, Sb and Ag species in the lattice. However, the nature of the pnictogen (As or Sb) changes the position of the conduction and valence band edges and modulates the reactivity of the pyrargyrite-proustite series. Anodic dissolution occurs by hole transfer from the top of the valence band that is formed mainly by the states of the AsS(3) and SbS(3) groups. Meanwhile, silver reduction occurs by electron transfer from the Ag 5s orbitals located at the bottom of the conduction band. The difficulty in dissolving proustite and pyrargyrite in cyanide is related to the presence of pyramidal AsS(3) and SbS(3) groups in these sulfosalts.

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

    Science.gov (United States)

    Matar, Samir F.

    2013-03-01

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

  17. Evaluation of molecular assembly, spectroscopic interpretation, intra-/inter molecular hydrogen bonding and chemical reactivity of two pyrrole precursors

    Science.gov (United States)

    Rawat, Poonam; Singh, R. N.

    2014-10-01

    This paper describes the evaluation of conformational, spectroscopic, hydrogen bonding and chemical reactivity of pyrrole precursor: ethyl 3,5 dimethyl-1H-pyrrole-2-carboxylate (EDPC) and ethyl 3,4-dimethyl-4-acetyl-1H-pyrrole-2-carboxylate (EDAPC) for the convenient characterization, synthetic usefulness and comparative evaluations. All experimental spectral values of 1H NMR, UV-Vis and FT-IR spectra coincide well with calculated values by DFT. The orbital interactions in EDPC and EDAPC are found to lengthen their Nsbnd H and Cdbnd O bonds and lowers their vibrational frequencies (red shift) resulting to dimer formation. The QTAIM and NBO analyses provide the strength of interactions and charge transfer in the hydrogen bonding unit and stability of dimers. The binding energy of EDPC and EDPAC dimer are found to be 9.92, 10.22 kcal/mol, respectively. In EDPAC and EDPC dimer, hyperconjugative interactions between monomer units is due to n1(O) → σ*(Nsbnd H) that stabilize the molecule up to 9.7 and 9.3 kcal/mol, respectively. On evaluation of molecular electrostatic potential (MEP) and electronic descriptors for EDPC it has been found that it is a good precursor for synthesis of formyl and acetyl derivatives whereas EDAPC has been found to be a good precursor for synthesis of schiff base, hydrazones, hydrazide-hydrazones and chalcones.

  18. Bond-orientational analysis of hard-disk and hard-sphere structures.

    Science.gov (United States)

    Senthil Kumar, V; Kumaran, V

    2006-05-28

    We report the bond-orientational analysis results for the thermodynamic, random, and homogeneously sheared inelastic structures of hard-disks and hard-spheres. The thermodynamic structures show a sharp rise in the order across the freezing transition. The random structures show the absence of crystallization. The homogeneously sheared structures get ordered at a packing fraction higher than the thermodynamic freezing packing fraction, due to the suppression of crystal nucleation. On shear ordering, strings of close-packed hard-disks in two dimensions and close-packed layers of hard-spheres in three dimensions, oriented along the velocity direction, slide past each other. Such a flow creates a considerable amount of fourfold order in two dimensions and body-centered-tetragonal (bct) structure in three dimensions. These transitions are the flow analogs of the martensitic transformations occurring in metals due to the stresses induced by a rapid quench. In hard-disk structures, using the bond-orientational analysis we show the presence of fourfold order. In sheared inelastic hard-sphere structures, even though the global bond-orientational analysis shows that the system is highly ordered, a third-order rotational invariant analysis shows that only about 40% of the spheres have face-centered-cubic (fcc) order, even in the dense and near-elastic limits, clearly indicating the coexistence of multiple crystalline orders. When layers of close-packed spheres slide past each other, in addition to the bct structure, the hexagonal-close-packed (hcp) structure is formed due to the random stacking faults. Using the Honeycutt-Andersen pair analysis and an analysis based on the 14-faceted polyhedra having six quadrilateral and eight hexagonal faces, we show the presence of bct and hcp signatures in shear ordered inelastic hard-spheres. Thus, our analysis shows that the dense sheared inelastic hard-spheres have a mixture of fcc, bct, and hcp structures.

  19. Preparation of melanin from Catharsius molossus L. and preliminary study on its chemical structure.

    Science.gov (United States)

    Xin, Chao; Ma, Jia-hua; Tan, Cheng-jia; Yang, Zhou; Ye, Feng; Long, Chan; Ye, Shuang; Hou, Da-bin

    2015-04-01

    A great deal of melanin was found in the waste alkali liquor produced by extraction of chitin from Catharsius molossus L. Discarding the lye could harm the environment and cause waste of resources. In this paper, melanin from C. molossus L. was recovered through acid precipitation and purified by pepsin and so on. The purity, chemical composition and structure of the prepared melanin were explored by UV-visible absorption spectroscopy, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, high resolution (13)C Cross polarization magic angle spinning nuclear magnetic resonance spectroscopy pyrolysis gas chromatography mass spectrometry, X ray diffraction, X ray fluorescence, matrix-assisted laser desorption/ionization time of flight tandem mass spectrometry, thermal analysis, and so on. The results showed that the purity of the prepared melanin was higher than the commercial standard melanin and it was a kind of nanoaggregates composed of a large quantity of 5,6-dihydroxyindole eumelanin and a small amount of phaeomelanin. In addition, the prepared melanin was irregular in shape and its structure could be divided into three levels: advanced structure maintained by polypeptides, substructure maintained by the ferric ion and microstructure. In particular, the smallest structural unit showed the graphite-like layered structure containing five layers linked by non-covalent bonds and each layer mainly consisted of 5,6-dihydroxyindole and its derivatives, which might be connected to each other through various chemical bonds.

  20. Structural characterization of PTX3 disulfide bond network and its multimeric status in cumulus matrix organization.

    Science.gov (United States)

    Inforzato, Antonio; Rivieccio, Vincenzo; Morreale, Antonio P; Bastone, Antonio; Salustri, Antonietta; Scarchilli, Laura; Verdoliva, Antonio; Vincenti, Silvia; Gallo, Grazia; Chiapparino, Caterina; Pacello, Lucrezia; Nucera, Eleonora; Serlupi-Crescenzi, Ottaviano; Day, Anthony J; Bottazzi, Barbara; Mantovani, Alberto; De Santis, Rita; Salvatori, Giovanni

    2008-04-11

    PTX3 is an acute phase glycoprotein that plays key roles in resistance to certain pathogens and in female fertility. PTX3 exerts its functions by interacting with a number of structurally unrelated molecules, a capacity that is likely to rely on its complex multimeric structure stabilized by interchain disulfide bonds. In this study, PAGE analyses performed under both native and denaturing conditions indicated that human recombinant PTX3 is mainly composed of covalently linked octamers. The network of disulfide bonds supporting this octameric assembly was resolved by mass spectrometry and Cys to Ser site-directed mutagenesis. Here we report that cysteine residues at positions 47, 49, and 103 in the N-terminal domain form three symmetric interchain disulfide bonds stabilizing four protein subunits in a tetrameric arrangement. Additional interchain disulfide bonds formed by the C-terminal domain cysteines Cys(317) and Cys(318) are responsible for linking the PTX3 tetramers into octamers. We also identified three intrachain disulfide bonds within the C-terminal domain that we used as structural constraints to build a new three-dimensional model for this domain. Previously it has been shown that PTX3 is a key component of the cumulus oophorus extracellular matrix, which forms around the oocyte prior to ovulation, because cumuli from PTX3(-/-) mice show defective matrix organization. Recombinant PTX3 is able to restore the normal phenotype ex vivo in cumuli from PTX3(-/-) mice. Here we demonstrate that PTX3 Cys to Ser mutants, mainly assembled into tetramers, exhibited wild type rescue activity, whereas a mutant, predominantly composed of dimers, had impaired functionality. These findings indicate that protein oligomerization is essential for PTX3 activity within the cumulus matrix and implicate PTX3 tetramers as the functional molecular units required for cumulus matrix organization and stabilization.

  1. Quasi-Monolithic Structures for Spaceflight Using Hydroxide-Catalysis Bonding

    Science.gov (United States)

    Preston, Alix; Thorpe, J. Ira; Miner, Linda

    2012-01-01

    Future space-based missions will take measurements of the universe with unprecedented results. To do this, these missions will require materials and bonding techniques with ever-increasing stability in order to make their measurements. As an example, the Laser Interferometer Space Antenna (LISA) will detect and observe gravitational waves in the 0.1 mHz to 1 Hz frequency range with strain sensitivities on the order of 10(exp -21) at its most sensitive frequency. To make these measurements, critical components such as the optical bench or telescope support structure, will need to have path-length stabilities of better than 1 pm/(square root)Hz. The baseline construction method for the LISA optical bench is to affix fused silica optical components to a Zerodur baseplate using hydroxide-catalysis bonding (HCB). HCB is a recently developed technique that allows the bonding of glasses, some metals, and silicon carbide with significant strength and stability with a bond thickness of less than a few micrometers. In addition, a wide range of surface profiles can be bonded using only a small amount of hydroxide solution. These characteristics make HCB ideal for adhering optical components in complex optical systems. In addition to being used to construct the LISA optical bench, the HCB technique shows great promise for constructing other structures such as hollow retroreflectors to be used for lunar laser ranging, or a visible nulling coronograph to be used for exo-planet detection. Here we present construction techniques that could be used to make an optical bench, hollow retroreflector, nulling coronograph, or other quasi-monolithic structures using HCB. In addition, we present dimensional stability results of an optical bench that was made using HCB, as well as HCB strength measurements.

  2. Analytic projection from plane-wave and PAW wavefunctions and application to chemical-bonding analysis in solids.

    Science.gov (United States)

    Maintz, Stefan; Deringer, Volker L; Tchougréeff, Andrei L; Dronskowski, Richard

    2013-11-05

    Quantum-chemical computations of solids benefit enormously from numerically efficient plane-wave (PW) basis sets, and together with the projector augmented-wave (PAW) method, the latter have risen to one of the predominant standards in computational solid-state sciences. Despite their advantages, plane waves lack local information, which makes the interpretation of local densities-of-states (DOS) difficult and precludes the direct use of atom-resolved chemical bonding indicators such as the crystal orbital overlap population (COOP) and the crystal orbital Hamilton population (COHP) techniques. Recently, a number of methods have been proposed to overcome this fundamental issue, built around the concept of basis-set projection onto a local auxiliary basis. In this work, we propose a novel computational technique toward this goal by transferring the PW/PAW wavefunctions to a properly chosen local basis using analytically derived expressions. In particular, we describe a general approach to project both PW and PAW eigenstates onto given custom orbitals, which we then exemplify at the hand of contracted multiple-ζ Slater-type orbitals. The validity of the method presented here is illustrated by applications to chemical textbook examples-diamond, gallium arsenide, the transition-metal titanium-as well as nanoscale allotropes of carbon: a nanotube and the C60 fullerene. Remarkably, the analytical approach not only recovers the total and projected electronic DOS with a high degree of confidence, but it also yields a realistic chemical-bonding picture in the framework of the projected COHP method.

  3. Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution

    Institute of Scientific and Technical Information of China (English)

    Huiyong Wang; Miao Liu; Yuling Zhao; Xiaopeng Xuan; Yang Zhao; Jianji Wang

    2017-01-01

    Ion pair speciation of ionic liquids (ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential.It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them.Considering the fact that far-IR (FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding,in this work,this spectroscopic technique has been combined with molecular dynamic (MD) simulation and nuclear magnetic resonance hydrogen spectroscopy (1H NMR) to investigate ion pairs ofaprotic ILs [Bmim][NO3],[BuPy][NO3],[Pyr14][NO3],[PP14][NO3] and [Bu-choline][NO3] in aqueous IL mixtures.The FIR spectra have been assigned with the aid of density functional theory (DFT) calculations,and the results are used to understand the effect of cationic nature on the structure of ion pairs.It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion,were still maintained in aqueous solutions up to high water mole fraction (say 0.80 for [BuPy] [NO3]).When water content was increased to a critical mole fraction of water (say 0.83 for [BuPy] [NO3]),the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water.With the further dilution of the aqueous ILs solution,the solvent-separated ion pairs was finally turned into free cations and free anions (fully hydrated cations or anions).The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions (fully hydrated ion) were dependent on the cationic structures.These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous.solution.MD simulation and 1H NMR results support the conclusion

  4. Study on the covalence of Cu and chemical bonding in an inorganic fullerene-like molecule, [CuCl]20[Cp*FeP5]12[Cu-(CH3CN)2+Cl-]5, by a density functional approach

    Institute of Scientific and Technical Information of China (English)

    WANG Bingwu; XU Guangxian; CHEN Zhida

    2004-01-01

    The electronic structure and chemical bonding in a recently synthesized inorganic fullerene-like molecule, {[CuCl]20[Cp*FeP5]12 [Cu(CH3CN)+2Cl-]5}, has been studied by a density functional approach. Geometrical optimization of the three basic structural units of the molecule is performed with Amsterdam Density Functional Program. The results are in agreement with the experiment. Localized MO's obtained by Boys-Foster method give a clear picture of the chemical bonding in this molecule. The reason why CuCl can react with Cp*FeP5 in solvent CH3CN to form the fullerene-like molecule is explained in terms of the soft-hard Lewis acid base theory and a new concept of covalence.

  5. Structural modification of covalent-bonded networks: on some methodological resolutions for binary chalcogenide glasses

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, M; Shpotyuk, Ya; Shpotyuk, O, E-mail: shpotyukmy@yahoo.com [Lviv Scientific Research Institute of Materials of SRC ' Carat' , 212, Stryjska str., Lviv, 79031 (Ukraine)

    2011-04-01

    New methodology to estimate efficiency of externally-induced structural modification in chalcogenide glasses is developed. This approach is grounded on the assumption that externally-induced structural modification is fully associated with destruction-polymerization transformations, which reveal themselves as local misbalances in covalent bond distribution, normal atomic coordination and intrinsic electrical fields. The input of each of these components into the total value of structural modification efficiency was probed for quasibinary (As{sub 2}S{sub 3}){sub 100-x}(Sb{sub 2}S{sub 3}){sub x} ChG.

  6. Marine chemical ecology: chemical signals and cues structure marine populations, communities, and ecosystems.

    Science.gov (United States)

    Hay, Mark E

    2009-01-01

    Chemical cues constitute much of the language of life in the sea. Our understanding of biotic interactions and their effects on marine ecosystems will advance more rapidly if this language is studied and understood. Here, I review how chemical cues regulate critical aspects of the behavior of marine organisms from bacteria to phytoplankton to benthic invertebrates and water column fishes. These chemically mediated interactions strongly affect population structure, community organization, and ecosystem function. Chemical cues determine foraging strategies, feeding choices, commensal associations, selection of mates and habitats, competitive interactions, and transfer of energy and nutrients within and among ecosystems. In numerous cases, the indirect effects of chemical signals on behavior have as much or more effect on community structure and function as the direct effects of consumers and pathogens. Chemical cues are critical for understanding marine systems, but their omnipresence and impact are inadequately recognized.

  7. NDT evaluation of long-term bond durability of CFRP-structural systems applied to RC highway bridges

    Science.gov (United States)

    Crawford, Kenneth C.

    2016-06-01

    The long-term durability of CFRP structural systems applied to reinforced-concrete (RC) highway bridges is a function of the system bond behavior over time. The sustained structural load performance of strengthened bridges depends on the carbon fiber-reinforced polymer (CFRP) laminates remaining 100 % bonded to concrete bridge members. Periodic testing of the CFRP-concrete bond condition is necessary to sustain load performance. The objective of this paper is to present a non-destructive testing (NDT) method designed to evaluate the bond condition and long-term durability of CFRP laminate (plate) systems applied to RC highway bridges. Using the impact-echo principle, a mobile mechanical device using light impact hammers moving along the length of a bonded CFRP plate produces unique acoustic frequencies which are a function of existing CFRP plate-concrete bond conditions. The purpose of this method is to test and locate CFRP plates de-bonded from bridge structural members to identify associated deterioration in bridge load performance. Laboratory tests of this NDT device on a CFRP plate bonded to concrete with staged voids (de-laminations) produced different frequencies for bonded and de-bonded areas of the plate. The spectra (bands) of frequencies obtained in these tests show a correlation to the CFRP-concrete bond condition and identify bonded and de-bonded areas of the plate. The results of these tests indicate that this NDT impact machine, with design improvements, can potentially provide bridge engineers a means to rapidly evaluate long lengths of CFRP laminates applied to multiple highway bridges within a national transportation infrastructure.

  8. Structural and optical studies on hot wire chemical vapour deposited hydrogenated silicon films at low substrate temperature

    Energy Technology Data Exchange (ETDEWEB)

    Gogoi, Purabi; Agarwal, Pratima [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam (India)

    2009-02-15

    Thin films of hydrogenated silicon are deposited by hot wire chemical vapour deposition technique, as an alternative of plasma enhanced chemical vapour deposition technique. By varying the hydrogen and silane flow rate, we deposited the films ranging from pure amorphous to nanocrystallite-embedded amorphous in nature. In this paper we report extensively studied structural and optical properties of these films. It is observed that the rms bond angle deviation decreases with increase in hydrogen flow rate, which is an indication of improved order in the films. We discuss this under the light of breaking of weak Si-Si bonds and subsequent formation of strong Si-Si bonds and coverage of the growing surface by atomic hydrogen. (author)

  9. Frequent side chain methyl carbon-oxygen hydrogen bonding in proteins revealed by computational and stereochemical analysis of neutron structures.

    Science.gov (United States)

    Yesselman, Joseph D; Horowitz, Scott; Brooks, Charles L; Trievel, Raymond C

    2015-03-01

    The propensity of backbone Cα atoms to engage in carbon-oxygen (CH · · · O) hydrogen bonding is well-appreciated in protein structure, but side chain CH · · · O hydrogen bonding remains largely uncharacterized. The extent to which side chain methyl groups in proteins participate in CH · · · O hydrogen bonding is examined through a survey of neutron crystal structures, quantum chemistry calculations, and molecular dynamics simulations. Using these approaches, methyl groups were observed to form stabilizing CH · · · O hydrogen bonds within protein structure that are maintained through protein dynamics and participate in correlated motion. Collectively, these findings illustrate that side chain methyl CH · · · O hydrogen bonding contributes to the energetics of protein structure and folding.

  10. Ring Opening Reactions through C-O Bond Cleavage Uniquely Adding Chemical Functionality to Boron Subphthalocyanine

    Directory of Open Access Journals (Sweden)

    Catherine Bonnier

    2015-10-01

    Full Text Available We are reporting the unexpected reaction between bromo-boron subphthalocyanine (Br-BsubPc and THF, 1,4-dioxane or γ-butyrolactone that results in the ring opening of the solvent and its addition into the BsubPc moiety. Under heating, the endocyclic C-O bond of the solvent is cleaved and the corresponding bromoalkoxy-BsubPc derivative is obtained. These novel alkoxy-BsubPc derivatives have remaining alkyl-bromides suitable for further functionalization. The alkoxy-BsubPcs maintain the characteristic strongly absorption in visible spectrum and their fluorescence quantum yields.

  11. Electron emission degradation of nano-structured sp2-bonded amorphous carbon films

    Institute of Scientific and Technical Information of China (English)

    Lu Zhan-Ling; Wang Chang-Qing; Jia Yu; Zhang Bing-Lin; Yao Ning

    2007-01-01

    The initial field electron emission degradation behaviour of original nano-structured sp2-bonded amorphous carbon films has been observed.which can be attributed to the increase of the work function of the film in the field emission process analysed using a Fowler-Nordheim plot.The possible re.on for the change of work function is suggested to be the desorption of hydrogen from the original hydrogen termination film surface due to field emission current-induced local heating.For the explanation of the emission degradation behaviour of the nano-structured sp2-bonded amorphous carbon film,a cluster model with a series of graphite(0001) basal surfaces has been presented,and the theoretical calculations have been performed to investigate work functions of graphite(0001) surfaces with different hydrogen atom and ion chemisorption sites by using first principles method based on density functional theory-local density approximation.

  12. Research on the Interaction of Hydrogen-Bond Acidic Polymer Sensitive Sensor Materials with Chemical Warfare Agents Simulants by Inverse Gas Chromatography

    Directory of Open Access Journals (Sweden)

    Liu Yang

    2015-06-01

    Full Text Available Hydrogen-bond acidic polymers are important high affinity materials sensitive to organophosphates in the chemical warfare agent sensor detection process. Interactions between the sensor sensitive materials and chemical warfare agent simulants were studied by inverse gas chromatography. Hydrogen bonded acidic polymers, i.e., BSP3, were prepared for micro-packed columns to examine the interaction. DMMP (a nerve gas simulant and 2-CEES (a blister agent simulant were used as probes. Chemical and physical parameters such as heats of absorption and Henry constants of the polymers to DMMP and 2-CEES were determined by inverse gas chromatography. Details concerning absorption performance are also discussed in this paper.

  13. Research on the interaction of hydrogen-bond acidic polymer sensitive sensor materials with chemical warfare agents simulants by inverse gas chromatography.

    Science.gov (United States)

    Yang, Liu; Han, Qiang; Cao, Shuya; Huang, Feng; Qin, Molin; Guo, Chenghai; Ding, Mingyu

    2015-06-02

    Hydrogen-bond acidic polymers are important high affinity materials sensitive to organophosphates in the chemical warfare agent sensor detection process. Interactions between the sensor sensitive materials and chemical warfare agent simulants were studied by inverse gas chromatography. Hydrogen bonded acidic polymers, i.e., BSP3, were prepared for micro-packed columns to examine the interaction. DMMP (a nerve gas simulant) and 2-CEES (a blister agent simulant) were used as probes. Chemical and physical parameters such as heats of absorption and Henry constants of the polymers to DMMP and 2-CEES were determined by inverse gas chromatography. Details concerning absorption performance are also discussed in this paper.

  14. Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy

    Institute of Scientific and Technical Information of China (English)

    Wenbo HAN; Kaifeng ZHANG; Guofeng WANG; Xiaojun ZHANG

    2005-01-01

    Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6Al-4V sheet material. The sandwich structure of Ti-6Al-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.

  15. Ultra-stable Molecule-Surface Architectures at Metal Oxides: Structure, Bonding, and Electron-transfer Processes

    Energy Technology Data Exchange (ETDEWEB)

    Hamers, Robert John

    2013-12-07

    Research funded by this project focused on the development of improved strategies for functionalization of metal oxides to enhance charge-transfer processes relevant to solar energy conversion. Initial studies included Fe2O3, WO3, TiO2, SnO2, and ZnO as model oxide systems; these systems were chosen due to differences in metal oxidation state and chemical bonding types in these oxides. Later studies focused largely on SnO2 and ZnO, as these materials show particularly promising surface chemistry, have high electron mobility, and can be readily grown in both spherical nanoparticles and as elongated nanorods. New molecules were synthesized that allowed the direct chemical assembly of novel nanoparticle ?dyadic? structures in which two different oxide materials are chemically joined, leading to an interface that enhances the separation of of charge upon illumination. We demonstrated that such junctions enhance photocatalytic efficiency using model organic compounds. A separate effort focused on novel approaches to linking dye molecules to SnO2 and ZnO as a way to enhance solar conversion efficiency. A novel type of surface binding through

  16. Bayesian inference of protein structure from chemical shift data

    Science.gov (United States)

    Bratholm, Lars A.; Christensen, Anders S.; Hamelryck, Thomas

    2015-01-01

    Protein chemical shifts are routinely used to augment molecular mechanics force fields in protein structure simulations, with weights of the chemical shift restraints determined empirically. These weights, however, might not be an optimal descriptor of a given protein structure and predictive model, and a bias is introduced which might result in incorrect structures. In the inferential structure determination framework, both the unknown structure and the disagreement between experimental and back-calculated data are formulated as a joint probability distribution, thus utilizing the full information content of the data. Here, we present the formulation of such a probability distribution where the error in chemical shift prediction is described by either a Gaussian or Cauchy distribution. The methodology is demonstrated and compared to a set of empirically weighted potentials through Markov chain Monte Carlo simulations of three small proteins (ENHD, Protein G and the SMN Tudor Domain) using the PROFASI force field and the chemical shift predictor CamShift. Using a clustering-criterion for identifying the best structure, together with the addition of a solvent exposure scoring term, the simulations suggests that sampling both the structure and the uncertainties in chemical shift prediction leads more accurate structures compared to conventional methods using empirical determined weights. The Cauchy distribution, using either sampled uncertainties or predetermined weights, did, however, result in overall better convergence to the native fold, suggesting that both types of distribution might be useful in different aspects of the protein structure prediction. PMID:25825683

  17. Chemically bonded hybrid systems from functionalized hydroxypyridine molecular bridge: characterization and photophysical properties.

    Science.gov (United States)

    Yan, Bing; Qian, Kai

    2009-01-01

    A series of novel photoactive hybrid materials with organic parts covalently linked to inorganic parts via the acylamino group have been assembled by sol-gel process. The organic parts as molecular bridge derive from alpha-hydroxypyridine (HP) functionalized by 3-(triethoxysilyl)-propyl isocyanate (TESPIC). Finally homogeneous, molecular-based hybrid materials with different microstructure (uniform spherical or clubbed) are obtained, in which no phase separation is observed. This may be ascribed as the different coordination behavior of metal ions (Eu3+ (Tb3+) or Zn2+). Red emission of Eu-HP-Si, green emission of Tb-HP-Si and violet-blue luminescence of Zn-HP-Si hybrids can be achieved within these molecular-based hybrid materials. Besides, both Eu(Tb) and Zn are introduced into the same hybrid systems (Eu(Zn)-HP-Si or Tb(Zn)-HP-Si) through the covalent Si-O bond, whose sphere particle size can be modified. Especially the photoluminescence behavior can be enhanced, suggesting that intramolecular energy transfer takes place between inert Zn2+ and Eu3+ (Tb3+) in the covalently bonded hybrid systems.

  18. Torsion Property of the Structure Bonded Aluminum Foam Due to Impact

    Directory of Open Access Journals (Sweden)

    Hwang G.W.

    2017-06-01

    Full Text Available An aluminum foam added with foaming agent, is classified into an open-cell type for heat transfer and a closed-cell type for shock absorption. This study investigates the characteristic on the torsion of aluminum foam for a closed-cell type under impact. The fracture characteristics are investigated through the composite of five types of aluminum foam (the thicknesses of 25, 35, 45, 55 and 65 mm, when applying the torsional moment of impact energy on the junction of a porous structure attached by an adhesive. When applying the impact energy of 100, 200 and 300J, the aluminum foams with thicknesses of 25 mm and 35 mm broke off under all conditions. For the energy over 200J, aluminums thicker than 55 mm continued to be attached. Furthermore, the aluminum specimens with thicknesses of 55 mm and 65 mm that were attached with more than 30% of bonding interface remained, proving that they could maintain bonding interface against impact energy. By comparing the data based on the analysis and test result, an increase in the thickness of specimen leads to the plastic deformation as the stress at the top and bottom of bonding interface moves to the middle by spreading the stress horizontally. Based on this fracture characteristic, this study can provide the data on the destruction and separation of bonding interface and may contribute to the safety design.

  19. Influence of 5f electrons on structure and bonding in the actinide-hydrogen intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Ward, J.W.

    1984-01-01

    Complexa phases form for the Th + H and U + H systems that are found with no other metals. In the Pa + H system, simple bcc C15 Laves and A15 phases can form, dependent on temperature and composition. The phase transformations appear to b magnetically driven, as a resutl of the decoupling of the metallic 5f electron bonding that occurs during hydriding; the C15 phases contain two kinds of Pa atoms-the one sublattice being still fully f-bonded and the other magnetic. This is a unique situation in solid state physics which defies a valence description. A similar situation obtains for A15 ..beta.. - UH/sub 3/ structure. The parent metals themselves exhibit electronegativities not unlike those of the mid-3d transition metals (e.g., Fe) because the valence electrons re tied up in metallic bonding. However, under the driving force for hydriding, the lattices can open up, decoupling the f-bonding and inducing magnetism. The systems then aggressively form very stable hydrides typical of highly-electropositive metals. Beyond uranium the trivalent metallic state is favored and rare-earth-like hydrides are found for Np + H and Pu + H. Nevertheless, the solid-state and transport properties are markedly different than for the rare-earth hydrides, showing that the latent influence of the 5f electrons is still strong.

  20. Dinuclear Complexes Formed by Hydrogen Bonds: Synthesis, Structure and Magnetic and Electrochemical Properties.

    Science.gov (United States)

    Granelli, Matteo; Downward, Alan M; Huber, Robin; Guénée, Laure; Besnard, Céline; Krämer, Karl W; Decurtins, Silvio; Liu, Shi-Xia; Thompson, Laurence K; Williams, Alan F

    2017-05-23

    The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent M(II) M(II) , mixed-valent M(II) M(III) and heteronuclear M(II) M'(III) species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O⋅⋅⋅O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen-bonded structure. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Structure and Hydrogen Bonding of Water in Polyacrylate Gels: Effects of Polymer Hydrophilicity and Water Concentration.

    Science.gov (United States)

    Mani, Sriramvignesh; Khabaz, Fardin; Godbole, Rutvik V; Hedden, Ronald C; Khare, Rajesh

    2015-12-10

    The ability to tune the hydrophilicity of polyacrylate copolymers by altering their composition makes these materials attractive candidates for membranes used to separate alcohol-water mixtures. The separation behavior of these polyacrylate membranes is governed by a complex interplay of factors such as water and alcohol concentrations, water structure in the membrane, polymer hydrophilicity, and temperature. We use molecular dynamics simulations to investigate the effect of polymer hydrophilicity and water concentration on the structure and dynamics of water molecules in the polymer matrix. Samples of poly(n-butyl acrylate) (PBA), poly(2-hydroxyethyl acrylate) (PHEA), and a 50/50 copolymer of BA and HEA were synthesized in laboratory, and their properties were measured. Model structures of these systems were validated by comparing the simulated values of their volumetric properties with the experimental values. Molecular simulations of polyacrylate gels swollen in water and ethanol mixtures showed that water exhibits very different affinities toward the different (carbonyl, alkoxy, and hydroxyl) functional groups of the polymers. Water molecules are well dispersed in the system at low concentrations and predominantly form hydrogen bonds with the polymer. However, water forms large clusters at high concentrations along with the predominant formation of water-water hydrogen bonds and the acceleration of hydrogen bond dynamics.

  2. Bayesian inference of protein structure from chemical shift data

    DEFF Research Database (Denmark)

    Bratholm, Lars Andersen; Christensen, Anders Steen; Hamelryck, Thomas Wim

    2015-01-01

    content of the data. Here, we present the formulation of such a probability distribution where the error in chemical shift prediction is described by either a Gaussian or Cauchy distribution. The methodology is demonstrated and compared to a set of empirically weighted potentials through Markov chain......, the simulations suggests that sampling both the structure and the uncertainties in chemical shift prediction leads more accurate structures compared to conventional methods using empirical determined weights. The Cauchy distribution, using either sampled uncertainties or predetermined weights, did, however......Protein chemical shifts are routinely used to augment molecular mechanics force fields in protein structure simulations, with weights of the chemical shift restraints determined empirically. These weights, however, might not be an optimal descriptor of a given protein structure and predictive model...

  3. Chemical Structure of Carbon Nitride Films Prepared by MW-ECR Plasma Enhanced Magnetron Sputtering

    Institute of Scientific and Technical Information of China (English)

    XUJun,GAOPeng; DINGWan-yu; LIXin; DENGXin-lu; DONGChuang

    2004-01-01

    Amorphous carbon nitride thin films were prepared by plasma-enhanced DC magnetron sputtering using twinned microwave electron cyclotron resonance plasma sources. Chemical structure of deposited films was investigated using X-ray photoelectron spectroscopy and Fourier transtorm infrared spectroscopy. The results indicate that the deposition rate is strongly affected by direct current bias, and the films are mainly composed of a single amorphous carbon nitride phase with N/C ratio close to C3N4, and the bonding is predominantly of C-N type.

  4. Hydrogen-bonding structure and dynamics of aqueous carbonate species from car-parrinello molecular dynamics simulations.

    Science.gov (United States)

    Kumar, P Padma; Kalinichev, Andrey G; Kirkpatrick, R James

    2009-01-22

    A comprehensive Car-Parrinello molecular dynamics (CP-MD) study of aqueous solutions of carbonic acid (H(2)CO(3)), bicarbonate (HCO(3)(-)), carbonate (CO(3)(2-)), and carbon dioxide (CO(2)) provides new quantitative insight into the structural and dynamic aspects of the hydrogen-bonding environments for these important aqueous species and their effects on the structure, H-bonding, and dynamical behavior of the surrounding water molecules. The hydration structures of the different carbonate species depend on their ability to accept and donate H-bonds with H(2)O. The H-bonds donated by the C-O-H sites of the carbonate species to water molecules are generally stronger and longer-lived than those accepted by these sites from water molecules. The structural relaxation among the water molecules is dominated by diffusional (translational) motion of H(2)O, whereas the H-bond reorganization is dominated by the librational motion of the water molecules and the carbonate species. The rates of structural relaxation of the H(2)O molecules and the rates of H-bond reorganization among them are slower in systems containing carbonate species, consistent with previous studies of simple salt solutions. The strengths and lifetimes of H-bonds involving the carbonate species positively correlate with the total negative charge on the species. H-bond donation from H(2)O to CO(2) is weak, but the presence of CO(2) noticeably affects the structure and structural relaxation of the surrounding H-bonding network leading to generally stronger H-bonds and slower relaxation rates, the behavior typical of a hydrophobic solute.

  5. Crystal Structure, Chemical Bonding and Magnetism Studies for Three Quinary Polar Intermetallic Compounds in the (Eu1−xCax9In8(Ge1−ySny8 (x = 0.66, y = 0.03 and the (Eu1−xCax3In(Ge3−ySn1+y (x = 0.66, 0.68; y = 0.13, 0.27 Phases

    Directory of Open Access Journals (Sweden)

    Hyein Woo

    2015-04-01

    Full Text Available Three quinary polar intermetallic compounds in the (Eu1−xCax9In8(Ge1−ySny8 (x = 0.66, y = 0.03 and the (Eu1−xCax3In(Ge3-ySn1+y (x = 0.66, 0.68; y = 0.13, 0.27 phases have been synthesized using the molten In-metal flux method, and the crystal structures are characterized by powder and single-crystal X-ray diffractions. Two orthorhombic structural types can be viewed as an assembly of polyanionic frameworks consisting of the In(Ge/Sn4 tetrahedral chains, the bridging Ge2 dimers, either the annulene-like “12-membered rings” for the (Eu1−xCax9In8(Ge1−ySny8 series or the cis-trans Ge/Sn-chains for the (Eu1−xCax3In(Ge3−ySn1+y series, and several Eu/Ca-mixed cations. The most noticeable difference between two structural types is the amount and the location of the Sn-substitution for Ge: only a partial substitution (11% occurs at the In(Ge/Sn4 tetrahedron in the (Eu1−xCax9In8(Ge1−ySny8 series, whereas both a complete and a partial substitution (up to 27% are observed, respectively, at the cis-trans Ge/Sn-chain and at the In(Ge/Sn4 tetrahedron in the (Eu1−xCax3In(Ge3−ySn1+y series. A series of tight-binding linear muffin-tin orbital calculations is conducted to understand overall electronic structures and chemical bonding among components. Magnetic susceptibility measurement indicates a ferromagnetic ordering of Eu atoms below 5 K for Eu1.02(1Ca1.98InGe2.87(1Sn1.13.

  6. Nematic films at chemically structured surfaces

    Science.gov (United States)

    Silvestre, N. M.; Telo da Gama, M. M.; Tasinkevych, M.

    2017-02-01

    We investigate theoretically the morphology of a thin nematic film adsorbed at flat substrate patterned by stripes with alternating aligning properties, normal and tangential respectively. We construct a simple ‘exactly-solvable’ effective interfacial model where the liquid crystal distortions are accounted for via an effective interface potential. We find that chemically patterned substrates can strongly deform the nematic-air interface. The amplitude of this substrate-induced undulations increases with decreasing average film thickness and with increasing surface pattern pitch. We find a regime where the interfacial deformation may be described in terms of a material-independent universal scaling function. Surprisingly, the predictions of the effective interfacial model agree semi-quantitatively with the results of the numerical solution of a full model based on the Landau-de Gennes theory coupled to a square-gradient phase field free energy functional for a two phase system.

  7. The effect of composition on the bond structure and refractive index of silicon nitride deposited by HWCVD and PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Verlaan, V.; Verkerk, A.D.; Arnoldbik, W.M.; Van der Werf, C.H.M.; Bakker, R.; Houweling, Z.S.; Schropp, R.E.I. [Utrecht University, Faculty of Science, Debye Institute for Nanomaterials Science, Nanophotonics - Physics of Devices, P.O. Box 80.000, 3508 TA Utrecht (Netherlands); Romijn, I.G.; Borsa, D.M.; Weeber, A.W. [ECN Solar Energy, Petten (Netherlands); Luxembourg, S.L.; Zeman, M. [DIMES, Delft University of Technology, Delf (Netherlands); Dekkers, H.F.W. [IMEC, Leuven (Belgium)

    2009-04-15

    Silicon nitride (SiNx) is a material with many applications and can be deposited with various deposition techniques. Series of SiNx films were deposited with HWCVD, RF PECVD,MWPECVD and LF PECVD. The atomic densities are quantified using RBS and ERD. The influence of the atomic densities on the Si-N and Si-Si bond structure is studied. The density of N-N bonds is found to be negligible. New Si-N FTIR proportionality factors are determined which increase with increasing N/Si ratio from 1.2 x 10{sup 19} cm-1 for Si rich films (N/Si=0.2) to 2.4 x 10{sup 19}cm-1 for N rich films (N/Si=1.5). The peak position of the Si-H stretching mode in the FTIR spectrum is discussed using the chemical induction model. It is shown that especially for Si-rich films the hydrogen content affects the Si-H peak position. The influence of the composition on the refractive index of the films is discussed on the basis of the Lorentz-Lorenz equation and the Kramers-Kronig relation. The decreasing refractive index with increasing N/Si ratio is primarily caused by an increase of the band gap.

  8. Hybrid density functional study of the structural, bonding, and electronic properties of bismuth vanadate

    Science.gov (United States)

    Kweon, Kyoung E.; Hwang, Gyeong S.

    2012-10-01

    The structure and property prediction of metal oxides can significantly be improved by incorporating exact Hartree-Fock (HF) exchange into density functional theory (DFT), which is the so-called hybrid DFT. We explored the impact of HF exchange inclusion on the predicted structural, bonding, and electronic properties of bismuth vanadate (BiVO4), with particular attention to the difference between its monoclinic and tetragonal scheelite phases. The applied exchange-correlation (xc) functionals include the gradient corrected Perdew-Burke-Ernzerhof (PBE) and the PBE-HF hybrid functionals with HF exchange amounts of 10%, 25%, and 50%. We find that the PBE-HF25% yields a monoclinic structure in very close agreement with the experimentally determined structure, while the PBE-HF50% tends to overestimate the monoclinic distortion and the PBE/PBE-HF10% can hardly identify a distinct monoclinic configuration at ambient conditions. Electronic structure analysis reveals that the increasing monoclinic distortion with the amount of HF exchange is related to the enhancement of hybridization between Bi 6s-O 2p antibonding states and unoccupied Bi 6p states. The bonding mechanisms and band structures of the monoclinic and tetragonal phases of BiVO4 were also investigated, and we discuss how the predictions are sensitive to the xc functional choice.

  9. Effects of Jigsaw Cooperative Learning and Animation Techniques on Students' Understanding of Chemical Bonding and Their Conceptions of the Particulate Nature of Matter

    Science.gov (United States)

    Karacop, Ataman; Doymus, Kemal

    2013-04-01

    The aim of this study was to determine the effect of jigsaw cooperative learning and computer animation techniques on academic achievements of first year university students attending classes in which the unit of chemical bonding is taught within the general chemistry course and these students' learning of the particulate nature of matter of this unit. The sample of this study consisted of 115 first-year science education students who attended the classes in which the unit of chemical bonding was taught in a university faculty of education during the 2009-2010 academic year. The data collection instruments used were the Test of Scientific Reasoning, the Purdue Spatial Visualization Test: Rotations, the Chemical Bonding Academic Achievement Test, and the Particulate Nature of Matter Test in Chemical Bonding (CbPNMT). The study was carried out in three different groups. One of the groups was randomly assigned to the jigsaw group, the second was assigned to the animation group (AG), and the third was assigned to the control group, in which the traditional teaching method was applied. The data obtained with the instruments were evaluated using descriptive statistics, one-way ANOVA, and MANCOVA. The results indicate that the teaching of chemical bonding via the animation and jigsaw techniques was more effective than the traditional teaching method in increasing academic achievement. In addition, according to findings from the CbPNMT, the students from the AG were more successful in terms of correct understanding of the particulate nature of matter.

  10. Determination of Hydrogen Bond Structure in Water versus Aprotic Environments To Test the Relationship Between Length and Stability

    Energy Technology Data Exchange (ETDEWEB)

    Sigala, Paul A.; Ruben, Eliza A.; Liu, Corey W.; Piccoli, Paula M. B.; Hohenstein, Edward G.; Martinez, Todd J.; Schultz, Arthur J.; Herschiag, Daniel

    2015-05-06

    Hydrogen bonds profoundly influence the architecture and activity of biological macromolecules. Deep appreciation of hydrogen bond contributions to biomolecular function thus requires a detailed understanding of hydrogen bond structure and energetics and the relationship between these properties. Hydrogen bond formation energies (Delta G(f)) are enormously more favorable in aprotic solvents than in water, and two classes of contributing factors have been proposed to explain this energetic difference, focusing respectively on the isolated and hydrogen-bonded species: (I) water stabilizes the dissociated donor and acceptor groups much better than aprotic solvents, thereby reducing the driving force for hydrogen bond formation; and (II) water lengthens hydrogen bonds compared to aprotic environments, thereby decreasing the potential energy within the hydrogen bond. Each model has been proposed to provide a dominant contribution to Delta G(f), but incisive tests that distinguish the importance of these contributions are lacking. Here we directly test the structural basis of model II. Neutron crystallography, NMR spectroscopy, and quantum mechanical calculations demonstrate that O-H center dot center dot center dot O hydrogen bonds in crystals, chloroform, acetone, and water have nearly identical lengths and very similar potential energy surfaces despite Delta G(f) differences >8 kcal/mol across these solvents. These results rule out a substantial contribution from solvent-dependent differences in hydrogen bond structure and potential energy after association (model II) and thus support the conclusion that differences in hydrogen bond Delta G(f) are predominantly determined by solvent interactions with the dissociated groups (model I). These findings advance our understanding of universal hydrogen-bonding interactions and have important implications for biology and engineering.

  11. Na-induced bonding and bond-length changes for CO on Pt(111): A near-edge x-ray-absorption fine-structure study

    Energy Technology Data Exchange (ETDEWEB)

    Sette, F.; Stoehr, J.; Kollin, E.B.; Dwyer, D.J.; Gland, J.L.; Robbins, J.L.; Johnson, A.L.

    1985-03-04

    Near-edge x-ray absorption fine-structure studies above the C and O K edges for CO on Pt(111) reveal a 4-eV shift of the sigma shape resonance when Na(0.2 monolayer) is coabsorbed. This allows determination of a Na-induced (0.12 +- 0.03)-A expansion of the C-O bond. Na does not affect the vertical molecular orientation on the surface. Reduction and broadening of the 1s..-->..2..pi..( resonance and the CO bond lengthening in the presence of Na signifies substantially increased metal to CO backbonding.

  12. Catalytic C-C Bond Cleavage for the Production of Chemicals from Lignin

    NARCIS (Netherlands)

    Jastrzebski, R.

    2016-01-01

    Lignin is a major component of lignocellulosic biomass and could be an important renewable feedstock in industry for the production of (aromatic) bulk and fine chemicals. To this end, the development of new catalytic processes is required; both to depolymerise the biopolymer into small aromatic buil

  13. Catalytic C-C Bond Cleavage for the Production of Chemicals from Lignin

    NARCIS (Netherlands)

    Jastrzebski, R.|info:eu-repo/dai/nl/338017747

    2016-01-01

    Lignin is a major component of lignocellulosic biomass and could be an important renewable feedstock in industry for the production of (aromatic) bulk and fine chemicals. To this end, the development of new catalytic processes is required; both to depolymerise the biopolymer into small aromatic

  14. The mystery of gold's chemical activity: local bonding, morphology and reactivity of atomic oxygen.

    Science.gov (United States)

    Baker, Thomas A; Liu, Xiaoying; Friend, Cynthia M

    2011-01-07

    Recently, gold has been intensely studied as a catalyst for key synthetic reactions. Gold is an attractive catalyst because, surprisingly, it is highly active and very selective for partial oxidation processes suggesting promise for energy-efficient "green" chemistry. The underlying origin of the high activity of Au is a controversial subject since metallic gold is commonly thought to be inert. Herein, we establish that one origin of the high activity for gold catalysis is the extremely reactive nature of atomic oxygen bound in 3-fold coordination sites on metallic gold. This is the predominant form of O at low concentrations on the surface, which is a strong indication that it is most relevant to catalytic conditions. Atomic oxygen bound to metallic Au in 3-fold sites has high activity for CO oxidation, oxidation of olefins, and oxidative transformations of alcohols and amines. Among the factors identified as important in Au-O interaction are the morphology of the surface, the local binding site of oxygen, and the degree of order of the oxygen overlayer. In this Perspective, we present an overview of both theory and experiments that identify the reactive forms of O and their associated charge density distributions and bond strengths. We also analyze and model the release of Au atoms induced by O binding to the surface. This rough surface also has the potential for O(2) dissociation, which is a critical step if Au is to be activated catalytically. We further show the strong parallels between product distributions and reactivity for O-covered Au at low pressure (ultrahigh vacuum) and for nanoporous Au catalysts operating at atmospheric pressure as evidence that atomic O is the active species under working catalytic conditions when metallic Au is present. We briefly discuss the possible contributions of oxidants that may contain intact O-O bonds and of the Au-metal oxide support interface in Au catalysis. Finally, the challenges and future directions for fully

  15. Structure-based approach to the prediction of disulfide bonds in proteins.

    Science.gov (United States)

    Salam, Noeris K; Adzhigirey, Matvey; Sherman, Woody; Pearlman, David A

    2014-10-01

    Protein engineering remains an area of growing importance in pharmaceutical and biotechnology research. Stabilization of a folded protein conformation is a frequent goal in projects that deal with affinity optimization, enzyme design, protein construct design, and reducing the size of functional proteins. Indeed, it can be desirable to assess and improve protein stability in order to avoid liabilities such as aggregation, degradation, and immunogenic response that may arise during development. One way to stabilize a protein is through the introduction of disulfide bonds. Here, we describe a method to predict pairs of protein residues that can be mutated to form a disulfide bond. We combine a physics-based approach that incorporates implicit solvent molecular mechanics with a knowledge-based approach. We first assign relative weights to the terms that comprise our scoring function using a genetic algorithm applied to a set of 75 wild-type structures that each contains a disulfide bond. The method is then tested on a separate set of 13 engineered proteins comprising 15 artificial stabilizing disulfides introduced via site-directed mutagenesis. We find that the native disulfide in the wild-type proteins is scored well, on average (within the top 6% of the reasonable pairs of residues that could form a disulfide bond) while 6 out of the 15 artificial stabilizing disulfides scored within the top 13% of ranked predictions. Overall, this suggests that the physics-based approach presented here can be useful for triaging possible pairs of mutations for disulfide bond formation to improve protein stability.

  16. THE CRYSTAL STRUCTURE OF DIPHENYLTELLURIUM DIBROMIDE,

    Science.gov (United States)

    TELLURIUM COMPOUNDS, *ORGANOMETALLIC COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , BROMIDES, SYMMETRY(CRYSTALLOGRAPHY), X RAY DIFFRACTION, FOURIER ANALYSIS, LEAST SQUARES METHOD, MOLECULAR STRUCTURE, CHEMICAL BONDS.

  17. A quantum-chemical validation about the formation of hydrogen bonds and secondary interactions in intermolecular heterocyclic systems

    Directory of Open Access Journals (Sweden)

    Boaz Galdino Oliveira

    2009-08-01

    Full Text Available We have performed a detailed theoretical study in order to understand the charge density topology of the C2H4O···C2H2 and C2H4S···C2H2 heterocyclic hydrogen-bonded complexes. Through the calculations derived from Quantum Theory of Atoms in Molecules (QTAIM, it was observed the formation of hydrogen bonds and secondary interactions. Such analysis was performed through the determination of optimized geometries at B3LYP/6-31G(d,p level of theory, by which is that QTAIM topological operators were computed, such as the electronic density ρ(r, Laplacian Ñ2ρ(r, and ellipticity ε. The examination of the hydrogen bonds has been performed through the measurement of ρ(r, Ñ2ρ(r and ε between (O···H—C and (S···H—C, whereas the secondary interaction between axial hydrogen atoms Hα and carbon of acetylene. In this insight, it was verified the existence of secondary interaction only in C2H4S···C2H2 complex because its structure is propitious to form multiple interactions.

  18. On correlation between protein secondary structure, backbone bond angles, and side-chain orientations

    CERN Document Server

    Lundgren, Martin

    2012-01-01

    We investigate the fine structure of the sp3 hybridized covalent bond geometry that governs the tetrahedral architecture around the central C$_\\alpha$ carbon of a protein backbone, and for this we develop new visualization techniques to analyze high resolution X-ray structures in Protein Data Bank. We observe that there is a correlation between the deformations of the ideal tetrahedral symmetry and the local secondary structure of the protein. We propose a universal coarse grained energy function to describe the ensuing side-chain geometry in terms of the C$_\\beta$ carbon orientations. The energy function can model the side-chain geometry with a sub-atomic precision. As an example we construct the C$_\\alpha$-C$_\\beta$ structure of HP35 chicken villin headpiece. We obtain a configuration that deviates less than 0.4 \\.A in root-mean-square distance from the experimental X-ray structure.

  19. Sulfur bonding in MoS2 and Co-Mo-