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Sample records for chemical bond overlap

  1. Features of chemical bonds based on the overlap polarizabilities: diatomic and solid-state systems with the frozen-density embedding approach.

    PubMed

    Moura, Renaldo T; Duarte, Gian C S; da Silva, Thiago E; Malta, Oscar L; Longo, Ricardo L

    2015-03-28

    The chemical bond overlap properties were obtained for alkali halides NaY (Y = F, Cl, Br), alkaline-earth chalcogenides MX (M = Ca, Mg and X = O, S, Se) and alkali and alkali-earth metals (Li, Na, and Mg) in diatomic and solid-state systems using an embedding approach based on the frozen density functional theory to simulate the crystalline effects. The computational protocol established provides errors for bond distances smaller than 1%. The results indicate that larger chemical bond covalency leads to larger absorption or scattering by the overlap region. The ionic specific valence and overlap polarizability are closely related to the valence orbital compactness measured by the sum of Mulliken electronegativities. The embedding approach used in this work makes it possible to quantify the effects of the crystalline environment on the chemical bond overlap properties. In the solid-state, the bond overlap charges are less polarizable, in cases of well-known ionic systems (provided by electronegativity differences), leading to smaller chemical bond covalency in solids than in diatomics. The spectroscopic properties of the polarizability of the electron density in the overlap region of a chemical bond could be measured in the 1-20 eV spectral region and could be used to characterize some bands in several spectra whose assignments are ambiguous or not available.

  2. Chemical Bonds II

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

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

  3. Chemical bonding technology

    NASA Technical Reports Server (NTRS)

    Plueddemann, E.

    1986-01-01

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

  4. Chemical Bonds I

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

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

  5. Strength of Chemical Bonds

    NASA Technical Reports Server (NTRS)

    Christian, Jerry D.

    1973-01-01

    Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

  6. Clarifying Chemical Bonding. Overcoming Our Misconceptions.

    ERIC Educational Resources Information Center

    Hapkiewicz, Annis

    1991-01-01

    Demonstrations to help students change their misconceptions about chemical bond breaking are presented. Students' misconceptions about chemical bonds in both biological and chemical systems are discussed. A calculation for the release of energy from respiration is presented. (KR)

  7. A Model for the Chemical Bond

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2004-01-01

    Bond stereochemistry in polyatomic hydrides is explained in terms of the principle of bond energies maximization, which yields X-H straight bonds and suggests the formation of appropriate sp hybrids on the central atom. An introduction to the electron charge distribution in molecules is given, and atomic, overlap, gross and formal charges are…

  8. Heuristic overlap-exchange model of noble gas chemical shifts

    NASA Astrophysics Data System (ADS)

    Adrian, Frank J.

    2004-05-01

    It is now generally recognized that overlap-exchange interactions are the primary cause of the medium-dependent magnetic shielding (chemical shift) in all noble gases except helium, although the attractive electrostatic-dispersion (van der Waals) interactions play an indirect role in determining the penetration of the interacting species into the repulsive overlap-exchange region. The short-range nature of these overlap-exchange interactions, combined with the fact that they often can be approximated by simple functions of the overlap of the wave functions of the interacting species, suggests a useful semiempirical model of these chemical shifts. In it the total shielding is the sum of shieldings due to pairwise interactions of the noble gas atom with the individual atoms of the medium, with the "atomic" shielding terms either estimated by simple functions of the atomic overlap integrals averaged over their Boltzmann-weighted separations, or determined by fits to experimental data in systems whose complexity makes the former procedure impractical. Results for 129Xe chemical shifts in the noble gases and in a variety of molecular and condensed systems, including families of n-alkanes, straight-chain alcohols, and the endohedral compounds Xe@C60 and Xe@C70 are encouraging for the applicability of the model to systems of technical and biomedical interest.

  9. G. N. Lewis and the Chemical Bond.

    ERIC Educational Resources Information Center

    Pauling, Linus

    1984-01-01

    Discusses the contributions of G. N. Lewis to chemistry, focusing on his formulation of the basic principle of the chemical bond--the idea that the chemical bond consists of a pair of electrons held jointly by two atoms. (JN)

  10. Valence-Bond Theory and Chemical Structure.

    ERIC Educational Resources Information Center

    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)

  11. Coulombic Models in Chemical Bonding.

    ERIC Educational Resources Information Center

    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)

  12. Coulombic Models in Chemical Bonding.

    ERIC Educational Resources Information Center

    Sacks, Lawrence J.

    1986-01-01

    Describes a bonding theory which provides a framework for the description of a wide range of substances and provides quantitative information of remarkable accuracy with far less computational effort than that required of other approaches. Includes applications, such as calculation of bond energies of two binary hydrides (methane and diborane).…

  13. Analysis of Bonding between Conjugated Organic Molecules and Noble Metal Surfaces Using Orbital Overlap Populations.

    PubMed

    Rangger, Gerold M; Romaner, Lorenz; Hofmann, Oliver T; Heimel, Georg; Ramsey, Michael G; Zojer, Egbert

    2010-11-09

    The electronic structure of metal-organic interfaces is of paramount importance for the properties of organic electronic and single-molecule devices. Here, we use so-called orbital overlap populations derived from slab-type band-structure calculations to analyze the covalent contribution to the bonding between an adsorbate layer and a metal. Using two prototypical molecules, the strong acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on Ag(111) and the strong donor 1H,1'H-[4,4']bipyridinylidene (HV0) on Au(111), we present overlap populations as particularly versatile tools for describing the metal-organic interaction. Going beyond traditional approaches, in which overlap populations are represented in an atomic orbital basis, we also explore the use of a molecular orbital basis to gain significant additional insight. On the basis of the derived quantities, it is possible to identify the parts of the molecules responsible for the bonding and to analyze which of the molecular orbitals and metal bands most strongly contribute to the interaction and where on the energy scale they interact in bonding or antibonding fashion.

  14. Teaching Chemical Bonding: A Resource Book for Senior Chemistry.

    ERIC Educational Resources Information Center

    Lindsay, Margaret

    This document presents an instructional strategy for teaching chemical bonding using parables and music. Games, student interactions, and worksheets are included in the lesson plans. Topics include metallic bonding, covalent bonding including molecular and network structure, and ionic bonding. (JRH)

  15. Chemical Bonding Technology: Direct Investigation of Interfacial Bonds

    NASA Technical Reports Server (NTRS)

    Koenig, J. L.; Boerio, F. J.; Plueddemann, E. P.; Miller, J.; Willis, P. B.; Cuddihy, E. F.

    1986-01-01

    This is the third Flat-Plate Solar Array (FSA) Project document reporting on chemical bonding technology for terrestrial photovoltaic (PV) modules. The impetus for this work originated in the late 1970s when PV modules employing silicone encapsulation materials were undergoing delamination during outdoor exposure. At that time, manufacturers were not employing adhesion promoters and, hence, module interfaces in common with the silicone materials were only in physical contact and therefore easily prone to separation if, for example, water were to penetrate to the interfaces. Delamination with silicone materials virtually vanished when adhesion promoters, recommended by silicone manufacturers, were used. The activities related to the direct investigation of chemically bonded interfaces are described.

  16. Teaching Chemical Bonding through Jigsaw Cooperative Learning

    ERIC Educational Resources Information Center

    Doymus, Kemal

    2008-01-01

    This study examined the effectiveness of jigsaw cooperative learning in teaching chemical bonding at tertiary level. This study was carried out in two different classes in the Department of Primary Science Education of Ataturk University during the 2005-2006 academic year. One of the classes was the non-jigsaw group (control) and the other was the…

  17. The law of constant rejection. [chemical bonding in crystals

    NASA Technical Reports Server (NTRS)

    Philpotts, J. A.

    1978-01-01

    Improvements in analytical technique, study of multielement partitioning in natural systems, and improvements in ionic radius values have permitted construction of Onuma diagrams, in which the logarithm of partition coefficient is plotted versus ionic radius. The optimum radii, corresponding to crystallographic sites, do change in response to changes in major element composition for any particular mineral-type. In natural systems elements compete for sites rather than substituting for another element. It is proposed on empirical grounds, for equilibrium ionic bonding, that Onuma diagram curves for a particular lattice site are parabolic near optimum radius, linear elsewhere, parallel for different valences, and mirror images on opposite sides of optimum. Deviations may be due to overlapping peaks, liquid structure, polyvalence, bonding differences, contamination, kinetics, alteration, etc. However, dominant crystal-chemical control is indicated.

  18. Chemical Bonding: The Orthogonal Valence-Bond View

    PubMed Central

    Sax, Alexander F.

    2015-01-01

    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. PMID:25906476

  19. Chemically bonded phospho-silicate ceramics

    DOEpatents

    Wagh, Arun S.; Jeong, Seung Y.; Lohan, Dirk; Elizabeth, Anne

    2003-01-01

    A chemically bonded phospho-silicate ceramic formed by chemically reacting a monovalent alkali metal phosphate (or ammonium hydrogen phosphate) and a sparsely soluble oxide, with a sparsely soluble silicate in an aqueous solution. The monovalent alkali metal phosphate (or ammonium hydrogen phosphate) and sparsely soluble oxide are both in powder form and combined in a stochiometric molar ratio range of (0.5-1.5):1 to form a binder powder. Similarly, the sparsely soluble silicate is also in powder form and mixed with the binder powder to form a mixture. Water is added to the mixture to form a slurry. The water comprises 50% by weight of the powder mixture in said slurry. The slurry is allowed to harden. The resulting chemically bonded phospho-silicate ceramic exhibits high flexural strength, high compression strength, low porosity and permeability to water, has a definable and bio-compatible chemical composition, and is readily and easily colored to almost any desired shade or hue.

  20. Chemical bonding technology for terrestrial photovoltaic modules

    NASA Technical Reports Server (NTRS)

    Coulter, D. R.; Cuddihy, E. F.; Plueddeman, E. P.

    1983-01-01

    Encapsulated photovoltaic modules must hold together for 20 years, reliably resisting delamination and separation of any of the component materials. Delamination of encapsulation materials from each other, or from solar cells and interconnects, can create voids for accumulation of water, promoting corrosive failure. Delamination of silicone elastomers from unprimed surfaces was a common occurrence with early modules, but the incidences of silicone delamination with later modules decreased when adhesion promoters recommended by silicone manufacturers were used. An investigation of silicone delamination from unprimed surfaces successfully identified the mechanism, which was related to atmospheric oxygen and moisture. This early finding indicated that reliance on physical bonding of encapsulation interfaces for long life in an outdoor environment would be risky. For long outdoor life, the material components of a module must therefore be held together by weather-stable adhesion promoters that desirably form strong, interfacial chemical bonds.

  1. Spontaneous and specific activation of chemical bonds in macromolecular fluids.

    PubMed

    Park, Insun; Shirvanyants, David; Nese, Alper; Matyjaszewski, Krzysztof; Rubinstein, Michael; Sheiko, Sergei S

    2010-09-08

    Mechanical activation of chemical bonds typically involves the application of external forces, which implies a broad distribution of bond tensions. We demonstrate that controlling the flow profile of a macromolecular fluid generates and delineates mechanical force concentration, enabling a hierarchical activation of chemical bonds on different length scales from the macroscopic to the molecular. Bond tension is spontaneously generated within brushlike macromolecules as they spread on a solid substrate. The molecular architecture creates an uneven distribution of tension in the covalent bonds, leading to spatially controlled bond scission. By controlling the flow rate and the gradient of the film pressure, one can sever the flowing macromolecules with high precision. Specific chemical bonds are activated within distinct macromolecules located in a defined area of a thin film. Furthermore, the flow-controlled loading rate enables quantitative analysis of the bond activation parameters.

  2. Chemical Bonding of Polymer on Carbon Nanotube

    DTIC Science & Technology

    2001-04-01

    vetIcal displacement of CNT z dl:streched length of C-C bond in polymer .Z dLI: streching of C-C bond within polymer SdL2: streched length Of C-C...bond at interface - dL2: streching of C-C bond at intedace of B of polymer/CNT ’ n polymer-CNT at first bonding site E 1 1 I dL3: streching of C-C bond

  3. The electronic structure and chemical bonding of vitamin B12

    NASA Astrophysics Data System (ADS)

    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. Bioluminescence: from chemical bonds to photons.

    PubMed

    Hastings, J W

    1975-01-01

    The biological transformation of chemical to photic energy involves an enzyme-mediated chemiluminescent reaction, in which one of the products exists in an electronically excited state, emitting a photon as it returns to the ground state. The colour of bioluminescence differs in different organisms, ranging from the deep blue (460 nm) of certain crustacea, through the bluish green (490 nm) of some bacteria, the green (530 nm) of mushrooms to the red (about 600 nm) of the railroad worm. In one case, energy transfer has been demonstrated from the enzyme system to material that emits light with a longer wavelength. The energies involved range from about 165 to 250 kJ/einstein (40 to 60 kcal/einstein). Boyle first showed that air was involved in bioluminescence in 1668 in his experiments with an air pump. Over the past 100 years, it has become clear that most if not all bioluminescent systems require molecular oxygen. The recent isolation and characterization of an oxygen-containing (peroxide) enzyme intermediate from the bacterial system is described and a reaction mechanism is postulated. This scheme is compared with other hypothetical mechanisms, in particular those involving a four-membered ring intermediate, a dioxetane, in which the simultaneous cleavage of two bonds leaves one product in an excited state. I shall discuss the special role of luciferases in bioluminescence, especially in flashing mechanisms involving 'precharged' intermediates.

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

    ERIC Educational Resources Information Center

    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…

  6. Teaching and Learning the Concept of Chemical Bonding

    ERIC Educational Resources Information Center

    Levy Nahum, Tami; Mamlok-Naaman, Rachel; Hofstein, Avi; Taber, Keith S.

    2010-01-01

    Chemical bonding is one of the key and basic concepts in chemistry. The learning of many of the concepts taught in chemistry, in both secondary schools as well as in the colleges, is dependent upon understanding fundamental ideas related to chemical bonding. Nevertheless, the concept is perceived by teachers, as well as by learners, as difficult,…

  7. Teaching of Chemical Bonding: A Study of Swedish and South African Students' Conceptions of Bonding

    ERIC Educational Resources Information Center

    Nimmermark, Anders; Ohrstrom, Lars; Mårtensson, Jerker; Davidowitz, Bette

    2016-01-01

    Almost 700 Swedish and South African students from the upper secondary school and first-term chemistry university level responded to our survey on concepts of chemical bonding. The national secondary school curricula and most common textbooks for both countries were also surveyed and compared for their content on chemical bonding. Notable…

  8. Integrated defense system overlaps as a disease model: with examples for multiple chemical sensitivity.

    PubMed Central

    Rowat, S C

    1998-01-01

    The central nervous, immune, and endocrine systems communicate through multiple common messengers. Over evolutionary time, what may be termed integrated defense system(s) (IDS) have developed to coordinate these communications for specific contexts; these include the stress response, acute-phase response, nonspecific immune response, immune response to antigen, kindling, tolerance, time-dependent sensitization, neurogenic switching, and traumatic dissociation (TD). These IDSs are described and their overlap is examined. Three models of disease production are generated: damage, in which IDSs function incorrectly; inadequate/inappropriate, in which IDS response is outstripped by a changing context; and evolving/learning, in which the IDS learned response to a context is deemed pathologic. Mechanisms of multiple chemical sensitivity (MCS) are developed from several IDS disease models. Model 1A is pesticide damage to the central nervous system, overlapping with body chemical burdens, TD, and chronic zinc deficiency; model 1B is benzene disruption of interleukin-1, overlapping with childhood developmental windows and hapten-antigenic spreading; and model 1C is autoimmunity to immunoglobulin-G (IgG), overlapping with spreading to other IgG-inducers, sudden spreading of inciters, and food-contaminating chemicals. Model 2A is chemical and stress overload, including comparison with the susceptibility/sensitization/triggering/spreading model; model 2B is genetic mercury allergy, overlapping with: heavy metals/zinc displacement and childhood/gestational mercury exposures; and model 3 is MCS as evolution and learning. Remarks are offered on current MCS research. Problems with clinical measurement are suggested on the basis of IDS models. Large-sample patient self-report epidemiology is described as an alternative or addition to clinical biomarker and animal testing. Images Figure 1 Figure 2 Figure 3 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 PMID:9539008

  9. Closing in on Chemical Bonds by Opening up Relativity Theory

    PubMed Central

    Whitney, Cynthia Kolb

    2008-01-01

    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. PMID:19325749

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

    PubMed

    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.

  11. Overlap Dirac operator at nonzero chemical potential and random matrix theory.

    PubMed

    Bloch, Jacques; Wettig, Tilo

    2006-07-07

    We show how to introduce a quark chemical potential in the overlap Dirac operator. The resulting operator satisfies a Ginsparg-Wilson relation and has exact zero modes. It is no longer gamma5 Hermitian, but its nonreal eigenvalues still occur in pairs. We compute the spectral density of the operator on the lattice and show that, for small eigenvalues, the data agree with analytical predictions of non-Hermitian chiral random matrix theory for both trivial and nontrivial topology. We also explain an observed change in the number of zero modes as a function of chemical potential.

  12. Electronegativity, Bond Energy, and Chemical Reactivity.

    ERIC Educational Resources Information Center

    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)

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

    PubMed Central

    Putz, Mihai V.

    2010-01-01

    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 B̶ characterized by its mass (mB̶), velocity (vB̶), charge (eB̶), and life-time (tB̶). 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[A0]=182019, providing this way the predictive framework in which the B̶ particle may be observed. Finally, its role in establishing the virtual states in Raman scattering was also established. PMID:21151435

  14. In-silico bonding schemes to encode chemical bonds involving sharing of electrons in molecular structures.

    PubMed

    Punnaivanam, Sankar; Sathiadhas, Jerome Pastal Raj; Panneerselvam, Vinoth

    2016-05-01

    Encoding of covalent and coordinate covalent bonds in molecular structures using ground state valence electronic configuration is achieved. The bonding due to electron sharing in the molecular structures is described with five fundamental bonding categories viz. uPair-uPair, lPair-uPair, uPair-lPair, vPair-lPair, and lPair-lPair. The involvement of lone pair electrons and the vacant electron orbitals in chemical bonding are explained with bonding schemes namely "target vacant promotion", "source vacant promotion", "target pairing promotion", "source pairing promotion", "source cation promotion", "source pairing double bond", "target vacant occupation", and "double pairing promotion" schemes. The bonding schemes are verified with a chemical structure editor. The bonding in the structures like ylides, PCl5, SF6, IF7, N-Oxides, BF4(-), AlCl4(-) etc. are explained and encoded unambiguously. The encoding of bonding in the structures of various organic compounds, transition metals compounds, coordination complexes and metal carbonyls is accomplished.

  15. Stainless steel and silicon direct interface synthesis: Chemical bonding effects

    NASA Astrophysics Data System (ADS)

    Cox, Michael J.

    Planar stainless steel/stainless steel interfaces, with and without a titanium interlayer and silicon/silicon interfaces have been produced in an ultra high vacuum (UHV) diffusion bonding/deposition instrument. Interface synthesis was accomplished by diffusion bonding two substrates after subjecting the substrate surfaces to a variety of pre-bonding treatments including heat treating, ion-beam sputter cleaning and thin film deposition. Chemical characterization was performed in situ by Auger electron spectroscopy (AES) prior to deposition and/or bonding and ex situ by energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). Additionally, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study interfaces before and after bonding. Diffusion bonding behavior of stainless steel depends strongly on the chemistry of the surfaces to be bonded. Very smooth, mechanically polished and lapped substrates would bond completely in UHV in 1 hour at 1000°C under 3.5 MPa uniaxial pressure, if the native oxide on the substrates was removed by ion beam cleaning. No voids were observed in these bonded interfaces as studied by TEM and the strength was equal to the unbonded bare material. When an electron beam deposited, 200 A titanium interlayer was added to the stainless steel interface, while bonding under the same conditions, mechanical tensile testing resulted in very low strength when compared with that of chemically clean stainless steel interfaces. Analytical inspection of the interfaces, performed with EELS, EDS, and convergent beam electron diffraction (CBED) coupled with images from TEM and SEM, showed the reason for the significantly reduced strength is a result of limited contact area and delamination between titanium carbide particles precipitated in the interface. Silicon wafers bicrystals were synthesized by bonding two single-crystal substrates. Silicon wafers were

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Chemical Case Studies: Science-Society "Bonding."

    ERIC Educational Resources Information Center

    Hofstein, Avi; Nae, Nehemia

    1981-01-01

    Describes a unit designed to illustrate the "science-society-technology connection," in which three case studies of the chemical industry in Israel are presented to high school chemistry students. Chosen for the unit are case studies on copper production in Timna, on plastics, and on life from the Dead Sea. (CS)

  18. The nature of chemical bonds from PNOF5 calculations.

    PubMed

    Matxain, Jon M; Piris, Mario; Uranga, Jon; Lopez, Xabier; Merino, Gabriel; Ugalde, Jesus M

    2012-06-18

    Natural orbital functional theory (NOFT) is used for the first time in the analysis of different types of chemical bonds. Concretely, the Piris natural orbital functional PNOF5 is used. It provides a localization scheme that yields an orbital picture which agrees very well with the empirical valence shell electron pair repulsion theory (VSEPR) and Bent's rule, as well as with other theoretical pictures provided by valence bond (VB) or linear combination of atomic orbitals-molecular orbital (LCAO-MO) methods. In this context, PNOF5 provides a novel tool for chemical bond analysis. In this work, PNOF5 is applied to selected molecules that have ionic, polar covalent, covalent, multiple (σ and π), 3c-2e, and 3c-4e bonds.

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

    SciTech Connect

    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.

  20. Chemical bonds and vibrational properties of ordered (U, Np, Pu) mixed oxides

    NASA Astrophysics Data System (ADS)

    Yang, Yu; Zhang, Ping

    2013-01-01

    We use density functional theory +U to investigate the chemical bonding characters and vibrational properties of the ordered (U, Np, Pu) mixed oxides (MOXs), UNpO4,NpPuO4, and UPuO4. It is found that the 5f electronic states of different actinide elements keep their localized characters in all three MOXs. The occupied 5f electronic states of different actinide elements do not overlap with each other and tend to distribute over the energy band gap of the other actinide element's 5f states. As a result, the three ordered MOXs all show smaller band gaps than those of the component dioxides, with values of 0.91, 1.47, and 0.19 eV for UNpO4,NpPuO4, and UPuO4, respectively. Through careful charge density analysis, we further show that the U-O and Pu-O bonds in MOXs show more ionic character than in UO2 and PuO2, while the Np-O bonds show more covalent character than in NpO2. The change in covalencies in the chemical bonds leads to vibrational frequencies of oxygen atoms that are different in MOXs.

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

    ERIC Educational Resources Information Center

    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…

  2. Remediating Misconceptions Concerning Chemical Bonding through Conceptual Change Text

    ERIC Educational Resources Information Center

    Pabuccu, Aybuke; Geban, Omer

    2006-01-01

    The purpose of this study was to explore the effects of conceptual change texts oriented instruction on 9th grade students' understanding of chemical bonding concepts. In this study, the main aim of the preparation of conceptual change texts was to activate students' prior knowledge and misconceptions and to help them to understand the chemical…

  3. Is There a Need to Discuss Atomic Orbital Overlap When Teaching Hydrogen-Halide Bond Strength and Acidity Trends in Organic Chemistry?

    ERIC Educational Resources Information Center

    Devarajan, Deepa; Gustafson, Samantha J.; Bickelhaupt, F. Matthias; Ess, Daniel H.

    2015-01-01

    Undergraduate organic chemistry textbooks and Internet websites use a variety of approaches for presenting and explaining the impact of halogen atom size on trends in bond strengths and/or acidity of hydrogen halides. In particular, several textbooks and Internet websites explain these trends by invoking decreasing orbital overlap between the…

  4. Exploring Chemical Bonds through Variations in Magnetic Shielding.

    PubMed

    Karadakov, Peter B; Horner, Kate E

    2016-02-09

    Differences in nuclear isotropic magnetic shieldings give rise to the chemical shifts measured in NMR experiments. In contrast to existing NMR experimental techniques, quantum chemical methods are capable of calculating isotropic magnetic shieldings not just at nuclei, but also at any point in the space surrounding a molecule. Using s-trans-1,3-butadiene, ethane, ethene, and ethyne as examples, we show that the variations in isotropic magnetic shielding around a molecule, represented as isosurfaces and contour plots, provide an unexpectedly clear picture of chemical bonding, which is much more detailed than the traditional description in terms of the total electron density.

  5. Aspects of glycosidic bond formation in aqueous solution: chemical bonding and the role of water.

    PubMed

    Stubbs, John M; Marx, Dominik

    2005-04-22

    A model of the specific acid-catalyzed glycosidic bond formation in liquid water at ambient conditions is studied based on constrained Car-Parrinello ab initio molecular dynamics. Specifically the reaction of alpha-D-glucopyranose and methanol is found to proceed by a D(N)A(N) mechanism. The D(N) step consists of a concerted protonation of the O(1) hydroxyl leaving group; this process results in the breaking of the C(1)-O(1) bond, and oxocarbenium ion formation involving C(1)=O(5). The second step, A(N), is the formation of the C(1)-O(m) glycosidic bond, deprotonation of the methanol hydroxyl group O(m)H(m), and re-formation of the C(1)-O(5) single bond. A focus of this study is the analysis of the electronic structure during this condensed phase reaction relying on both Boys/Wannier localized orbitals and the electron localization function ELF. This analysis allows the clear elucidation of the chemical bonding features of the intermediate bracketed by the D(N) and A(N) steps, which is a non-solvent equilibrated oxocarbenium cation. Most interestingly, it is found that the oxygen in the pyranose ring becomes "desolvated" upon double bond/oxocarbenium formation, whereas it is engaged in the hydrogen-bonded water network before and after this period. This demonstrates that hydrogen bonding and thus the aqueous solvent play an active role in this reaction implying that microsolvation studies in the gas phase, both theoretical and experimental, might lead to qualitatively different reaction mechanisms compared to solution.

  6. Benchmarking Density Functionals for Chemical Bonds of Gold.

    PubMed

    Kepp, Kasper P

    2017-03-09

    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 data set probes all types of bonding to gold from very electronegative halides that force Au(+) electronic structure, via covalently bonded systems, hard and soft Lewis acids and bases that either work against or complement the softness of gold, the Au2 molecule probing gold's bond with itself, and weak 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 correlation produce weaker bonds to gold. Most functionals provide similar trend accuracy, though somewhat lower for M06 and M06L, but very different numerical accuracy. Notably, PBE and TPSS functionals with dispersion display the smallest numerical errors and very small mean signed errors (0-6 kJ/mol), i.e. no bias toward over- or under-binding. Errors are evenly distributed versus atomic number, suggesting that relativistic effects are treated fairly; the mean absolute error is almost halved from B3LYP (45 kJ/mol) to TPSS and PBE (23 kJ/mol, including difficult cases); 23 kJ/mol is quite respectable considering the diverse bonds to gold and the complication of relativistic effects. Thus, studies that use DFT with effective core potentials for gold chemistry, with no alternative due

  7. Variational Energy Decomposition Analysis of Chemical Bonding. 1. Spin-Pure Analysis of Single Bonds.

    PubMed

    Levine, Daniel S; Horn, Paul R; Mao, Yuezhi; Head-Gordon, Martin

    2016-10-11

    We have designed an energy decomposition analysis (EDA) to gain a deeper understanding of single chemical bonds, that is, those in which the interacting fragments are doublet open-shell systems but the supersystem is closed-shell. The method is a spin-pure extension of the absolutely localized molecular orbital (ALMO) EDA to the one-pair perfect pairing energy (equivalently to an active space of two electrons in two orbitals). The total interaction energy is broken up into four terms: frozen interactions, spin-coupling, polarization, and charge-transfer. A variety of single bonds are analyzed and, in addition, we use this method to show how solvation changes the nature of bonds, producing different results in the gas-phase and with explicit solvent molecules.

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

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

    2016-05-07

    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 H2 (+). 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

  10. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  11. Toward a consistent interpretation of the QTAIM: tortuous link between chemical bonds, interactions, and bond/line paths.

    PubMed

    Foroutan-Nejad, Cina; Shahbazian, Shant; Marek, Radek

    2014-08-04

    Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, "misinterpretations" of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM's topological analysis of the one-electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the "interaction" to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed "line paths" in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some "problematic" molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new "interpretation" of data is performed.

  12. Probing the nature of chemical bonding in uranyl(VI) complexes with quantum chemical methods.

    PubMed

    Vallet, Valérie; Wahlgren, Ulf; Grenthe, Ingmar

    2012-12-20

    To assess the nature of chemical bonds in uranyl(VI) complexes with Lewis base ligands, such as F(-), Cl(-), OH(-), CO(3)(2-), and O(2)(2-), we have used quantum chemical observables, such as the bond distances, the internal symmetric/asymmetric uranyl stretch frequencies, and the electron density with its topology analyzed using the quantum theory of atoms-in-molecules. This analysis confirms that complex formation induces a weakening of the uranium-axial oxygen bond, reflected by the longer U-O(yl) bond distance and reduced uranyl-stretching frequencies. The strength of the ligand-induced effect increases in the order H(2)O < Cl(-) < F(-) < OH(-) < CO(3)(2-) < O(2)(2-). In-depth analysis reveals that the trend across the series does not always reflect an increasing covalent character of the uranyl-ligand bond. By using a point-charge model for the uranyl tetra-fluoride and tetra-chloride complexes, we show that a significant part of the uranyl bond destabilization arises from purely electrostatic interactions, the remaining part corresponding either to charge-transfer from the negatively charged ligands to the uranyl unit or a covalent interaction. The charge-transfer and the covalent interaction are qualitatively different due to the absence of a charge build up in the uranyl-halide bond region in the latter case. In all the charged complexes, the uranyl-ligand bond is best described as an ionic interaction. However, there are covalent contributions in the very stable peroxide complex and, to some extent, also in the carbonate complex. This study demonstrates that it is possible to describe the nature of chemical bond by observables rather than by ad hoc quantities such as atomic populations or molecular orbitals.

  13. Investigation of the distinction between van der Waals interaction and chemical bonding based on the PAEM-MO diagram.

    PubMed

    Zhao, Dong-Xia; Yang, Zhong-Zhi

    2014-05-15

    In recent years, the basic problem of understanding chemical bonding, nonbonded, and/or van der Waals interactions has been intensively debated in terms of various theoretical methods. We propose and construct the potential acting on one electron in a molecule-molecular orbital (PAEM-MO) diagram, which draws the PAEM inserted the MO energy levels with their major atomic orbital components. PAEM-MO diagram is able to show clear distinction of chemical bonding from nonbonded and/or vdW interactions. The rule for this is as follows. Along the line connecting two atoms in a molecule or a complex, the existence of chemical bonding between these two atoms needs to satisfy two conditions: (a) a critical point of PAEM exists and (b) PAEM barrier between the two atoms is lower in energy than the occupied major valence-shell bonding MO which contains in-phase atomic components (positive overlap) of the two considered atoms. In contrast to the chemical bonding, for a nonbonded interaction or van der Waals interaction between two atoms, both conditions (a) and (b) do not be satisfied at the same time. This is demonstrated and discussed by various typical cases, particularly those related to helium atom and H-H bonding in phenanthrene. There are helium bonds in HHeF and HeBeO molecules, whereas no H-H bonding in phenanthrene. The validity and limitation for this rule is demonstrated through the investigations of the curves of the PAEM barrier top and MO energies versus the internuclear distances for He2 , H2 , and He2 (+) systems.

  14. Site-selective chemical cleavage of peptide bonds.

    PubMed

    Elashal, Hader E; Raj, Monika

    2016-05-07

    Site-selective cleavage of extremely unreactive peptide bonds is a very important chemical modification that provides invaluable information regarding protein sequence, and it acts as a modulator of protein structure and function for therapeutic applications. For controlled and selective cleavage, a daunting task, chemical reagents must selectively recognize or bind to one or more amino acid residues in the peptide chain and selectively cleave a peptide bond. Building on this principle, we have developed an approach that utilizes a chemical reagent to selectively modify the serine residue in a peptide chain and leads to the cleavage of a peptide backbone at the N-terminus of the serine residue. After cleavage, modified residues can be converted back to the original fragments. This method exhibits broad substrate scope and selectively cleaves various bioactive peptides with post-translational modifications (e.g. N-acetylation and -methylation) and mutations (d- and β-amino acids), which are a known cause of age related diseases.

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

    SciTech Connect

    Nilsson, A.; Wassdahl, N.; Weinelt, M.

    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.

  16. Vitrified chemically bonded phosphate ceramics for immobilization of radioisotopes

    DOEpatents

    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.

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

    PubMed

    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.

  18. A bond-topological approach to theoretical mineralogy: crystal structure, chemical composition and chemical reactions

    NASA Astrophysics Data System (ADS)

    Hawthorne, Frank C.

    2012-11-01

    Here, I describe a theoretical approach to the structure and chemical composition of minerals based on their bond topology. This approach allows consideration of many aspects of minerals and mineral behaviour that cannot be addressed by current theoretical methods. It consists of combining the bond topology of the structure with aspects of graph theory and bond-valence theory (both long range and short range), and using the moments approach to the electronic energy density-of-states to interpret topological aspects of crystal structures. The structure hierarchy hypothesis states that higher bond-valence polyhedra polymerize to form the (usually anionic) structural unit, the excess charge of which is balanced by the interstitial complex (usually consisting of large low-valence cations and (H2O) groups). This hypothesis may be justified within the framework of bond topology and bond-valence theory, and may be used to hierarchically classify oxysalt minerals. It is the weak interaction between the structural unit and the interstitial complex that controls the stability of the structural arrangement. The principle of correspondence of Lewis acidity-basicity states that stable structures will form when the Lewis-acid strength of the interstitial complex closely matches the Lewis-base strength of the structural unit, and allows us to examine the factors that control the chemical composition and aspects of the structural arrangements of minerals. It also provides a connection between a structure, the speciation of its constituents in aqueous solution and its mechanism of crystallization. The moments approach to the electronic energy density-of-states provides a link between the bond topology of a structure and its thermodynamic properties, as indicated by correlations between average anion coordination number and reduced enthalpy of formation from the oxides for [6]Mg{/m [4]}Si n O( m+2 n) and MgSO4(H2O) n .

  19. Topology of electron charge density for chemical bonds from valence bond theory: a probe of bonding types.

    PubMed

    Zhang, Lixian; Ying, Fuming; Wu, Wei; Hiberty, Philippe C; Shaik, Sason

    2009-01-01

    To characterize the nature of bonding we derive the topological properties of the electron charge density of a variety of bonds based on ab initio valence bond methods. The electron density and its associated Laplacian are partitioned into covalent, ionic, and resonance components in the valence bond spirit. The analysis provides a density-based signature of bonding types and reveals, along with the classical covalent and ionic bonds, the existence of two-electron bonds in which most of the bonding arises from the covalent-ionic resonance energy, so-called charge-shift bonds. As expected, the covalent component of the Laplacian at the bond critical point is found to be largely negative for classical covalent bonds. In contrast, for charge-shift bonds, the covalent part of the Laplacian is small or positive, in agreement with the weakly attractive or repulsive character of the covalent interaction in these bonds. On the other hand, the resonance component of the Laplacian is always negative or nearly zero, and it increases in absolute value with the charge-shift character of the bond, in agreement with the decrease of kinetic energy associated with covalent-ionic mixing. A new interpretation of the topology of the total density at the bond critical point is proposed to characterize covalent, ionic, and charge-shift bonding from the density point of view.

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

    NASA Astrophysics Data System (ADS)

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

    PubMed Central

    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. PMID:28098216

  2. Bond strengths of three chemical adhesive cements adhered to a nickel-chromium alloy for direct bonded retainers.

    PubMed

    Atta, M O; Smith, B G; Brown, D

    1990-02-01

    Sandblasted surfaces of a beryllium-free, nickel-chromium alloy were bonded with one of three chemical adhesives. After either immersion in water for up to 6 months or thermal cycling between 5 degrees and 60 degrees C for 500 cycles, the bonded specimens were tested for both shear and tensile strength. The highest values of tensile and shear bond strengths were found with Panavia Ex material, and these values showed no significant changes after thermal cycling. For ABC cement and for Super-Bond C & B material, the strength of the bond was significantly improved with thermal cycling. However, immersion in water for 6 months caused a significant decrease in the strength of the bond of specimens adhered with ABC cement.

  3. Chemical Bond Activation Observed with an X-ray Laser.

    PubMed

    Beye, Martin; Öberg, Henrik; Xin, Hongliang; Dakovski, Georgi L; Dell'Angela, Martina; Föhlisch, Alexander; Gladh, Jörgen; Hantschmann, Markus; Hieke, Florian; Kaya, Sarp; Kühn, Danilo; LaRue, Jerry; Mercurio, Giuseppe; Minitti, Michael P; Mitra, Ankush; Moeller, Stefan P; Ng, May Ling; Nilsson, Anders; Nordlund, Dennis; Nørskov, Jens; Öström, Henrik; Ogasawara, Hirohito; Persson, Mats; Schlotter, William F; Sellberg, Jonas A; Wolf, Martin; Abild-Pedersen, Frank; Pettersson, Lars G M; Wurth, Wilfried

    2016-09-15

    The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free-electron laser to directly observe the decreased bonding-antibonding splitting following bond-activation using an ultrashort optical laser pulse.

  4. Experimental Observation of the Nature of Weak Chemical Bonds in Labile Compounds.

    PubMed

    Hashizume, Daisuke

    2017-02-15

    Accurate single-crystal X-ray diffraction data afford a total electron density distribution for crystalline materials by employing an aspherical atomic model with comparable accuracy to that of theoretical calculations. Chemical bonds and intermolecular interactions in the crystalline state are characterized based on the electron density distribution of valence electrons, as well as structural parameters. Herein, the bonding nature of weak chemical bonds in labile compounds, such as hypervalent bonds and delocalized π-bonds, is explored on the basis of electronic structures derived from experimental electron density distribution analyses. In addition, the visualization of a radicalic orbital distribution on an sp(2) -hydridized carbon atom is demonstrated.

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

    DOEpatents

    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.

  6. Chemical Reactions and Mechanical Properties of the Directly Bonded Ge-Si Interface

    NASA Astrophysics Data System (ADS)

    Byun, Ki Yeol; Ferain, Isabelle; Yu, Ran; Colinge, Cindy

    2011-12-01

    In this study, chemical reactions and mechanical properties of directly bonded Ge-Si interfaces are investigated. The Ge-Si bonded interface has been systematically characterized as a function of the thermal budget (200 °C and 300 °C), which demonstrated that the formation of a thin GeO2 cap layer by radical pre-treatment can reduce the generation rate of voids at the bonded interface significantly. Patterning of one of the wafers prior to bonding can help to achieve high bonding quality thanks to enhanced out-diffusion of reaction by-products and stress reduction at the bonded interface. Both numerical modeling and structural analysis show that the presence of diffusion path (channels) at the bonded interfaces result in a maximum bond strength and minimum stress at the bonded interface.

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

    PubMed

    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.

  8. Exploring electron pair behaviour in chemical bonds using the extracule density.

    PubMed

    Proud, Adam J; Mackenzie, Dalton E C K; Pearson, Jason K

    2015-08-21

    We explore explicit electron pair behaviour within the chemical bond (and lone pairs) by calculating the probability distribution for the center-of-mass (extracule) of an electron pair described by single localized orbitals. Using Edmiston-Ruedenberg localized orbitals in a series of 61 chemical systems, we demonstrate the utility of the extracule density as an interpretive tool in chemistry. By accessing localized regions of chemical space we simplify the interpretation of the extracule density and afford a quantum mechanical interpretation of "chemically intuitive" features of electronic structure. Specifically, we describe the localized effects on chemical bonds due to changes in electronegativities of bonded neighbours, bond strain, and non-covalent interactions. We show that the extracule density offers unique insight into electronic structure and allows one to readily quantify the effects of changing the chemical environment.

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

    DTIC Science & Technology

    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...DATES COVERED (From - To) 15 Oct 2013 - 15 Oct 2014 4. TITLE AND SUBTITLE Quantum-Mechanical Definition of Atoms and Chemical Bonds in Molecules...indistinguishable electrons to particular atomic nuclei in a chemical aggregate has seemingly precluded quantum-mechanical definition of fragment atomic

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

    PubMed

    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.

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

    PubMed

    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.

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

    PubMed

    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.

  13. Natural Bond Critical Point analysis: quantitative relationships between natural bond orbital-based and QTAIM-based topological descriptors of chemical bonding.

    PubMed

    Weinhold, Frank

    2012-11-15

    We have developed a "Natural Bond Critical Point" (NBCP) module for the natural bond orbital (NBO) program that allows mutual analysis of NBO-based versus Bader-type quantum theory of atoms in molecules (QTAIM) topological descriptors of chemical bonding interactions. Conventional QTAIM bond path and bond critical point (BCP) descriptors deduced from total electron density ρ(r) can thereby be compared with analogous "natural" (NBCP) descriptors for idealized densities ρ(NAIM)(r) composed solely from NBO-based "natural atoms in molecules" (NAIM) at the terminal nuclei. Standard ρ(r(BCP)) and [nabla](2)ρ(r(BCP)) descriptors can also be decomposed into unique contributions from individual NBOs or other localized, semilocalized, or delocalized orbital components. These results allow one to recognize many relationships between QTAIM and NBO analyses, showing why close correlations are often found between NBO-based versus ρ(r(BCP))-based characterizations of chemical bonding interactions, despite strongly divergent conceptions of "the atom in the molecule."

  14. Glutamic Acid Selective Chemical Cleavage of Peptide Bonds.

    PubMed

    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.

  15. A combined deuterium NMR and quantum chemical investigation of inequivalent hydrogen bonds in organic solids.

    PubMed

    Webber, Renee; Penner, Glenn H

    2012-01-01

    Deuterium magic angle spinning (MAS) NMR spectroscopy and quantum chemical calculations are used to investigate organic solids in which inequivalent hydrogen bonds are present. The use of (2)H MAS allows one to measure the chemical shift, δ, quadrupolar coupling constant, C(Q), and asymmetry in the quadrupolar interaction, η(Q), for each type of hydrogen bond present in the system. Quantum chemical calculations of the magnetic shielding (σ, which can be related to δ) and the electric field gradient (EFG, which can be related to C(Q)) are compared to the experimental results and are discussed with respect to the relative strengths of the hydrogen bonds within each system.

  16. Electronic structure imperfections and chemical bonding at graphene interfaces

    NASA Astrophysics Data System (ADS)

    Schultz, Brian Joseph

    ) fabricate graphene/metal interfaces and metal/graphene/metal sandwich structures evidencing classical anisotropic umpolung chemistry from carbon pz-orbrital charge pinning, and (Chapter 5) engineer graphene/dielectric interfaces showing electron depletion from carbon atoms at the HfO2/graphene interface. The fabrication of graphene interfaces remains a critical gap for successful commercialization of graphene-based devices, yet we demonstrate that interfacial hybridization, anisotropic charge redistribution, local chemical bonding, and discrete electronic hybridization regimes play a critical role in the electronic structure at graphene interfaces.

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

    ERIC Educational Resources Information Center

    Hilton, Annette; Nichols, Kim

    2011-01-01

    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…

  18. Bond Order and Chemical Properties of BF, CO, and N[subscript 2

    ERIC Educational Resources Information Center

    Martinie, Ryan J.; Bultema, Jarred J.; Vander Wal, Mark N.; Burkhart, Brandon J.; Vander Griend, Douglas A.; DeKock, Roger L.

    2011-01-01

    The traditional chemical approaches, Lewis electron dot structures and molecular orbital theory, predict the relative bond orders of boron monofluoride, carbon monoxide, and dinitrogen to be BF less than CO less than N[subscript 2]. This is quantified by quantum mechanical, theoretical studies that show the bond orders to be approximately 1.4,…

  19. Cleavage enhancement of specific chemical bonds in DNA-Cisplatin complexes induced by X-rays

    NASA Astrophysics Data System (ADS)

    Zheng, Yi; Yao, Xiaobin; Luo, Xinglan; Fu, Xianzhi

    2014-04-01

    The chemical bond transformation of cisplatin-DNA complexes can be probed efficiently by XPS which provides a concomitant X-ray irradiation source as well. The presence to Pt could considerably increase formation of the SE induced by X-ray and that the further interaction of these LEE with DNA leads to the enhancement of bond cleavages.

  20. NEXAFS Chemical State and Bond Lengths of p-Aminobenzoic Acid in Solution and Solid State

    NASA Astrophysics Data System (ADS)

    Stevens, J. S.; Gainar, A.; Suljoti, E.; Xiao, J.; Golnak, R.; Aziz, E. F.; Schroeder, S. L. M.

    2016-05-01

    Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic state of para-aminobenzoic acid (PABA) as a function of its chemical environment, revealing the chemical state and bonding of the chemical species. Variations in the ionization potential (IP) and 1s→π* resonances unequivocally identify the chemical species (neutral, cationic, or anionic) present and the varying local environment. Shifts in σ* shape resonances relative to the IP in the NEXAFS spectra vary with C-N bond length, and the important effect of minor alterations in bond length is confirmed with nitrogen FEFF calculations, leading to the possibility of bond length determination in solution.

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

    EPA Science Inventory

    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 ...

  2. A Descriptive Analysis of the Chemical Bond Approach, the Chemical Education Material Study, and a Representative Traditional Chemistry Course.

    ERIC Educational Resources Information Center

    Crilly, Alice Roth

    This study compared three one-year courses in high school chemistry. One of these, entitled Modern Chemistry, represents the "traditional" precollegiate chemistry course. The others are the Chemical Bond Approach (CBA) and the Chemical Education Material Study (CHEM Study). These are the two major revisions in high school chemistry which emerged…

  3. A review on the chemical synthesis of pyrophosphate bonds in bioactive nucleoside diphosphate analogs.

    PubMed

    Xu, Zhihong

    2015-09-15

    Currently, there is an ongoing interest in the synthesis of nucleoside diphosphate analogs as important regulators in catabolism/anabolism, and their potential applications as mechanistic probes and chemical tools for bioassays. However, the pyrophosphate bond formation step remains as the bottleneck. In this Digest, the chemical synthesis of the pyrophosphate bonds of representative bioactive nucleoside diphosphate analogs, i.e. phosphorus-modified analogs, nucleoside cyclic diphosphates, and nucleoside diphosphate conjugates, will be described.

  4. The Chemical Bond and Solid-state Physics

    ERIC Educational Resources Information Center

    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)

  5. Chemical bonding of hydrogen molecules to transition metal complexes

    SciTech Connect

    Kubas, G.J.

    1990-01-01

    The complex W(CO){sub 3}(PR{sub 3}){sub 2}(H{sub 2}) (CO = carbonyl; PR{sub 3} = organophosphine) was prepared and was found to be a stable crystalline solid under ambient conditions from which the hydrogen can be reversibly removed in vacuum or under an inert atmosphere. The weakly bonded H{sub 2} exchanges easily with D{sub 2}. This complex represents the first stable compound containing intermolecular interaction of a sigma-bond (H-H) with a metal. The primary interaction is reported to be donation of electron density from the H{sub 2} bonding electron pair to a vacant metal d-orbital. A series of complexes of molybdenum of the type Mo(CO)(H{sub 2})(R{sub 2}PCH{sub 2}CH{sub 2}PR{sub 2}){sub 2} were prepared by varying the organophosphine substitutent to demonstrate that it is possible to bond either dihydrogen or dihydride by adjusting the electron-donating properties of the co-ligands. Results of infrared and NMR spectroscopic studies are reported. 20 refs., 5 fig.

  6. Scientists Get First Glimpse of a Chemical Bond Being Born

    ScienceCinema

    Nilsson, Anders

    2016-07-12

    Scientists have used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to get the first glimpse of the transition state where two atoms begin to form a weak bond on the way to becoming a molecule.

  7. Scientists Get First Glimpse of a Chemical Bond Being Born

    SciTech Connect

    Nilsson, Anders

    2015-02-12

    Scientists have used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to get the first glimpse of the transition state where two atoms begin to form a weak bond on the way to becoming a molecule.

  8. A New "Bottom-Up" Framework for Teaching Chemical Bonding

    ERIC Educational Resources Information Center

    Nahum, Tami Levy; Mamlok-Naaman, Rachel; Hofstein, Avi

    2008-01-01

    Traditional curriculum for teaching bonding often fosters the use of over-simplifications and over-generalizations. Therefore, there is a need for a presentation that is consistent with current scientific knowledge and that provides the student with the proper intellectual infrastructure for further studies. In this article, we present a general…

  9. Orbital Exponent Optimization in Elementary VB Calculations of the Chemical Bond in the Ground State of Simple Molecular Systems

    ERIC Educational Resources Information Center

    Magnasco, Valerio

    2008-01-01

    Orbital exponent optimization in the elementary ab-initio VB calculation of the ground states of H[subscript 2][superscript +], H[subscript 2], He[subscript 2][superscript +], He[subscript 2] gives a fair description of the exchange-overlap component of the interatomic interaction that is important in the bond region. Correct bond lengths and…

  10. Valence-bond description of chemical reactions on Born-Oppenheimer molecular dynamics trajectories

    NASA Astrophysics Data System (ADS)

    Noguchi, Nao; Nakano, Haruyuki

    2009-04-01

    The nature of chemical bonds on dynamic paths was investigated using the complete active space valence-bond (CASVB) method and the Born-Oppenheimer dynamics. To extract the chemical bond picture during reactions, a scheme to collect contributions from several VB (resonance) structures into a small numbers of indices was introduced. In this scheme, a tree diagram for the VB structures is constructed with the numbers of the ionic bonds treated as generation. A pair of VB structures is related to each other if one VB structure is transferred into the other by changing a covalent bond to an ionic bond. The former and latter VB structures are named parent and child structures, respectively. The weights of the bond pictures are computed as the sum of the CASVB occupation numbers running from the top generation to the bottom along the descent of the VB structures. Thus, a number of CASVB occupation numbers are collected into a small number of indices, and a clear bond picture may be obtained from the CASVB wave function. The scheme was applied to the hydrogen exchange reaction H2+F→H+HF and the Diels-Alder reaction C5H6(cyclopentadiene)+CH2=CH2(ethylene)→C7H10(norbornene). In both the reactions, the scheme gave a clear picture for the Born-Oppenheimer dynamics trajectories. The reconstruction of the bonds during reactions was well described by following the temporal changes in weight.

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

    DTIC Science & Technology

    2011-07-01

    for public release; distribution unlimited. 13. SUPPLEMENTARY NOTES PAO Case Number: 88ABW 2010- 2016 ; Clearance Date: 13 Apr 2010. Document contains...cubic (fcc) and hexagonal close-packed ( hcp ) structures, and breaks seven bonds in body-centred cubic (bcc) structures. This atom is placed on a free...in fcc structures, for (0001), (101�0), (112�0) and (112�1) planes in hcp structures, and on (100), (110) and (112) planes in bcc structures. The

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed Central

    Li, Rui; Zhou, Hui; Wei, Wei; Wang, Chen; Sun, Ying Chun; Gao, Ping

    2015-01-01

    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(trimethoxysilyl)ethane 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. PMID:26066349

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

    PubMed

    Hansen, Poul Erik

    2015-01-30

    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.

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

    SciTech Connect

    Lee, Tom

    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.

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

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Shear bond strength of ceramic brackets with chemical or mechanical retention.

    PubMed

    Forsberg, C M; Hagberg, C

    1992-08-01

    The study was undertaken to measure and compare the shear bond strengths of a ceramic bracket with chemical retention, a ceramic bracket with a new type of textured base providing mechanical retention, and a metal bracket with foil-mesh base. The tests were performed on 51 extracted human premolars which were randomly divided into three equally large groups (n = 17)--one group for each type of bracket. After debonding, the site of failure was noted and the enamel surface inspected with scanning electron microscopy. The ceramic bracket with chemical retention exhibited significantly higher bond strength than the corresponding bracket with textured base. In comparison with the metal bracket significantly higher bond strengths were recorded for both types of ceramic brackets. The ceramic bracket with mechanical retention and the metal bracket were comparable as regards the site of bond failure. In some cases the chemical bond provided very high values of bond strength. Enamel failure were recorded in three teeth which had been bonded with this type of ceramic bracket.

  19. Coulombic Interaction in Finnish Middle School Chemistry: A Systemic Perspective on Students' Conceptual Structure of Chemical Bonding

    ERIC Educational Resources Information Center

    Joki, Jarkko; Lavonen, Jari; Juuti, Kalle; Aksela, Maija

    2015-01-01

    The aim of this study was to design a novel and holistic way to teach chemical bonding at the middle school level according to research on the teaching and learning of bonding. A further aim was to investigate high achieving middle school students' conceptual structures concerning chemical bonding by using a systemic perspective. Students in one…

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Analytic projection from plane-wave and PAW wavefunctions and application to chemical-bonding analysis in solids.

    PubMed

    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.

  2. Effect of interfacial chemical bonding and surface topography on adhesion in carbon fiber/epoxy composites

    SciTech Connect

    Drzal, L.T.; Sugiura, N.; Hook, D. |

    1994-12-31

    A series of PAN-based IM6 carbon fibers having varying amounts of surface treatment were, pretreated with compounds representing the constituents encountered in epoxy composites to pre-react any groups on the fiber surface before composite fabrication in order to determine the effect of chemical bonding on fiber-matrix adhesion. Chemical bonding was quantified using XPS. Chemical bonding between reactive groups in amine cured epoxy matrices and the surface groups present on IN46 carbon fibers as a result of commercial surface treatments has been detected although the absolute amount of chemical bonding is low (1-3%). It was found that reaction with monofunctional epoxy groups having hydrocarbon functionalities blocked the surface from further reaction and reduced the adhesion that could be attained to its lowest value. Prereaction with difunctional amines had little effect on adhesion when compared to normal composite fabrication procedures. Prereaction with difunctional epoxy groups did enhance adhesion levels over the level attained in normal composite fabrication methods. These results showed that chemical bonding between epoxy and the carbon fiber surface could increases the adhesion between fiber and matrix about 25% while between the amino group and the carbon fiber surface about 15%. Quantitative measurements of the fiber surface microtopography were made with scanning tunneling microscopy. An increase in roughness was detected with increasing surface treatment. It was concluded that surface roughness also accounted for a significant increase in fiber-matrix adhesion.

  3. Covalent bond or noncovalent bond: a supramolecular strategy for the construction of chemically synthesized vaccines.

    PubMed

    Gao, Yue; Sun, Zhan-Yi; Huang, Zhi-Hua; Chen, Pu-Guang; Chen, Yong-Xiang; Zhao, Yu-Fen; Li, Yan-Mei

    2014-10-13

    A novel noncovalent strategy to construct chemically synthesized vaccines has been designed to trigger a robust immune response and to dramatically improve the efficiency of vaccine preparation. Glycosylated MUC1 tripartite vaccines were constructed through host-guest interactions with cucurbit[8]uril. These vaccines elicited high levels of IgG antibodies that were recognized by transformed cells and induced the secretion of cytokines. The antisera also mediated complement-dependent cytotoxicity. This noncovalent strategy with good suitability, scalability, and feasibility can be applied as a universal strategy for the construction of chemically synthesized vaccines.

  4. Relationship between chemical structure and supramolecular effective molarity for formation of intramolecular H-bonds.

    PubMed

    Sun, Hongmei; Hunter, Christopher A; Navarro, Cristina; Turega, Simon

    2013-09-04

    Effective molarity (EM) is a key parameter that determines the efficiency of a range of supramolecular phenomena from the folding of macromolecules to multivalent ligand binding. Coordination complexes formed between zinc porphyrins equipped H-bond donor sites and pyridine ligands equipped with H-bond acceptor sites have allowed systematic quantification of EM values for the formation of intramolecular H-bonds in 240 different systems. The results provide insights into the relationship of EM to supramolecular architecture, H-bond strength, and solvent. Previous studies on ligands equipped with phosphonate diester and ether H-bond acceptors were inconclusive, but the experiments described here on ligands equipped with phosphine oxide, amide, and ester H-bond acceptors resolve these ambiguities. Chemical double-mutant cycles were used to dissect the thermodynamic contributions of individual H-bond interactions to the overall stabilities of the complexes and hence determine the values of EM, which fall in the range 1-1000 mM. Solvent has little effect on EM, and the values measured in toluene and 1,1,2,2-tetrachloroethane are similar. For H-bond acceptors that have similar geometries but different H-bond strengths (amide and ester), the values of EM are very similar. For H-bond acceptors that have different geometries but similar H-bond strengths (amide and phosphonate diester), there is little correlation between the values of EM. These results imply that supramolecular EMs are independent of solvent and intrinsic H-bond strength but depend on supramolecular architecture and geometric complementarity.

  5. Analysis of Thermal and Chemical Effets on Negative Valve Overlap Period Energy Recovery for Low-Temperature Gasoline Combustion

    SciTech Connect

    Ekoto, Dr Isaac; Peterson, Dr. Brian; Szybist, James P; Northrop, Dr. William

    2015-01-01

    A central challenge for efficient auto-ignition controlled low-temperature gasoline combustion (LTGC) engines has been achieving the combustion phasing needed to reach stable performance over a wide operating regime. The negative valve overlap (NVO) strategy has been explored as a way to improve combustion stability through a combination of charge heating and altered reactivity via a recompression stroke with a pilot fuel injection. The study objective was to analyze the thermal and chemical effects on NVO-period energy recovery. The analysis leveraged experimental gas sampling results obtained from a single-cylinder LTGC engine along with cylinder pressure measurements and custom data reduction methods used to estimate period thermodynamic properties. The engine was fueled by either iso-octane or ethanol, and operated under sweeps of NVO-period oxygen concentration, injection timing, and fueling rate. Gas sampling at the end of the NVO period was performed via a custom dump-valve apparatus, with detailed sample speciation by in-house gas chromatography. The balance of NVO-period input and output energy flows was calculated in terms of fuel energy, work, heat loss, and change in sensible energy. Experiment results were complemented by detailed chemistry single-zone reactor simulations performed at relevant mixing and thermodynamic conditions, with results used to evaluate ignition behavior and expected energy recovery yields. For the intermediate bulk-gas temperatures present during the NVO period (900-1100 K), weak negative temperature coefficient behavior with iso-octane fueling significantly lengthened ignition delays relative to similar ethanol fueled conditions. Faster ethanol ignition chemistry led to lower recovered fuel intermediate yields relative to similar iso-octane fueled conditions due to more complete fuel oxidation. From the energy analysis it was found that increased NVO-period global equivalence ratio, either from lower NVOperiod oxygen

  6. Fundamental change in the nature of chemical bonding by isotopic substitution.

    PubMed

    Fleming, Donald G; Manz, Jörn; Sato, Kazuma; Takayanagi, Toshiyuki

    2014-12-08

    Isotope effects are important in the making and breaking of chemical bonds in chemical reactivity. Here we report on a new discovery, that isotopic substitution can fundamentally alter the nature of chemical bonding. This is established by systematic, rigorous quantum chemistry calculations of the isotopomers BrLBr, where L is an isotope of hydrogen. All the heavier isotopomers of BrHBr, BrDBr, BrTBr, and Br(4)HBr, the latter indicating the muonic He atom, the heaviest isotope of H, can only be stabilized as van der Waals bound states. In contrast, the lightest isotopomer, BrMuBr, with Mu the muonium atom, alone exhibits vibrational bonding, in accord with its possible observation in a recent experiment on the Mu+Br2 reaction. Accordingly, BrMuBr is stabilized at the saddle point of the potential energy surface due to a net decrease in vibrational zero point energy that overcompensates the increase in potential energy.

  7. The nature of chemical bonding in actinide and lanthanide ferrocyanides determined by X-ray absorption spectroscopy and density functional theory.

    PubMed

    Dumas, Thomas; Guillaumont, Dominique; Fillaux, Clara; Scheinost, Andreas; Moisy, Philippe; Petit, Sébastien; Shuh, David K; Tyliszczak, Tolek; Den Auwer, Christophe

    2016-01-28

    The electronic properties of actinide cations are of fundamental interest to describe intramolecular interactions and chemical bonding in the context of nuclear waste reprocessing or direct storage. The 5f and 6d orbitals are the first partially or totally vacant states in these elements, and the nature of the actinide ligand bonds is related to their ability to overlap with ligand orbitals. Because of its chemical and orbital selectivities, X-ray absorption spectroscopy (XAS) is an effective probe of actinide species frontier orbitals and for understanding actinide cation reactivity toward chelating ligands. The soft X-ray probes of the light elements provide better resolution than actinide L3-edges to obtain electronic information from the ligand. Thus coupling simulations to experimental soft X-ray spectral measurements and complementary quantum chemical calculations yields quantitative information on chemical bonding. In this study, soft X-ray XAS at the K-edges of C and N, and the L2,3-edges of Fe was used to investigate the electronic structures of the well-known ferrocyanide complexes K4Fe(II)(CN)6, thorium hexacyanoferrate Th(IV)Fe(II)(CN)6, and neodymium hexacyanoferrate KNd(III)Fe(II)(CN)6. The soft X-ray spectra were simulated based on quantum chemical calculations. Our results highlight the orbital overlapping effects and atomic effective charges in the Fe(II)(CN)6 building block. In addition to providing a detailed description of the electronic structure of the ferrocyanide complex (K4Fe(II)(CN)6), the results strongly contribute to confirming the actinide 5f and 6d orbital oddity in comparison to lanthanide 4f and 5d.

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

    PubMed

    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.

  9. Immobilization of RGD peptide on HA coating through a chemical bonding approach.

    PubMed

    Yang, Chunli; Cheng, Kui; Weng, Wenjian; Yang, Chunyu

    2009-11-01

    In this work, Arg-Gly-Asp (RGD) sequence containing peptide was immobilized on hydroxyapatite (HA) coatings through a chemical bonding approach in two steps, surface modification with 3-aminopropyltriethoxysilane (APTES) and RGD immobilization. The results indicate that RGD has been successfully immobilized on HA coatings. Comparing with physical adsorption coatings, the chemically bonded RGD on the coatings shows much better anti-wash-out ability. Since RGD is able to recognize cell-membrane integrins on biointerfaces, the present method will be an effective way to favor interaction of cells with HA coatings.

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

    SciTech Connect

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

    2006-12-15

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

  11. Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives

    PubMed Central

    Torres-Vega, Juan J; Vásquez-Espinal, Alejandro; Ruiz, Lina; Fernández-Herrera, María A; Alvarez-Thon, Luis; Merino, Gabriel; Tiznado, William

    2015-01-01

    The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R2>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6−n)Fn, where n=1–5). PMID:26246992

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

    PubMed

    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.

  13. Oscillations in the stability of consecutive chemical bonds revealed by ion-induced desorption.

    PubMed

    Ossowski, Jakub; Rysz, Jakub; Krawiec, Mariusz; Maciazek, Dawid; Postawa, Zbigniew; Terfort, Andreas; Cyganik, Piotr

    2015-01-19

    While it is a common concept in chemistry that strengthening of one bond results in weakening of the adjacent ones, no results have been published on if and how this effect protrudes further into the molecular backbone. By binding molecules to a surface in the form of a self-assembled monolayer, the strength of a primary bond can be selectively altered. Herein, we report that by using secondary-ion mass spectrometry, we are able to detect for the first time positional oscillations in the stability of consecutive bonds along the adsorbed molecule, with the amplitudes diminishing with increasing distance from the molecule-metal interface. To explain these observations, we have performed molecular dynamics simulations and DFT calculations. These show that the oscillation effects in chemical-bond stability have a very general nature and break the translational symmetry in molecules.

  14. Chemical bonding and electronic structures of microcline, orthoclase and the plagioclase series by X-ray photoelectron spectroscopy.

    PubMed

    Kloprogge, J Theo; Wood, Barry J

    2015-02-25

    A detailed analysis was undertaken of the X-ray photoelectron spectra obtained from microcline, orthoclase and several samples of plagioclase with varying Na/Ca ratio. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each specimen. The spectra for Si 2p and Al 2p vary with the change in symmetry between microcline and orthoclase, while in plagioclase an increase in Al-O-Si linkages results in a small but observable decrease in binding energy. The overall shapes of the O 1s peaks observed in all spectra are similar and show shifts similar to those observed for Si 2p and Al 2p. The lower-VB spectra for microcline and orthoclase are similar intermediate between α-SiO2 and α-Al2O3 in terms of binding energies. In the plagioclase series increasing coupled substitution of Na and Si for Ca and Al results in a change of the overall shape of the spectra, showing a distinct broadening associated with the presence of two separate but overlapping bands similar to the 21 eV band observed for quartz and the 23 eV band observed for corundum. The bonding character for microcline and orthoclase is more covalent than that of α-Al2O3, but less than that of α-SiO2. In contrast, the plagioclase samples show two distinct bonding characters that are comparable with those of α-SiO2 and α-Al2O3.

  15. Revealing the angular symmetry of chemical bonds by atomic force microscopy.

    PubMed

    Welker, Joachim; Giessibl, Franz J

    2012-04-27

    We have measured the angular dependence of chemical bonding forces between a carbon monoxide molecule that is adsorbed to a copper surface and the terminal atom of the metallic tip of a combined scanning tunneling microscope and atomic force microscope. We provide tomographic maps of force and current as a function of distance that revealed the emergence of strongly directional chemical bonds as tip and sample approach. The force maps show pronounced single, dual, or triple minima depending on the orientation of the tip atom, whereas tunneling current maps showed a single minimum for all three tip conditions. We introduce an angular dependent model for the bonding energy that maps the observed experimental data for all observed orientations and distances.

  16. Chemical methods for producing disulfide bonds in peptides and proteins to study folding regulation.

    PubMed

    Okumura, Masaki; Shimamoto, Shigeru; Hidaka, Yuji

    2014-04-01

    Disulfide bonds play a critical role in the folding of secretory and membrane proteins. Oxidative folding reactions of disulfide bond-containing proteins typically require several hours or days, and numerous misbridged disulfide isomers are often observed as intermediates. The rate-determining step in refolding is thought to be the disulfide-exchange reaction from nonnative to native disulfide bonds in folding intermediates, which often precipitate during the refolding process because of their hydrophobic properties. To overcome this, chemical additives or a disulfide catalyst, protein disulfide isomerase (PDI), are generally used in refolding experiments to regulate disulfide-coupled peptide and protein folding. This unit describes such methods in the context of the thermodynamic and kinetic control of peptide and protein folding, including (1) regulation of disulfide-coupled peptides and protein folding assisted by chemical additives, (2) reductive unfolding of disulfide-containing peptides and proteins, and (3) regulation of disulfide-coupled peptide and protein folding using PDI.

  17. Reflections on the Electron Theory of the Chemical Bond: 1900-1925.

    ERIC Educational Resources Information Center

    Stranges, Anthony N.

    1984-01-01

    Traces the history of the electron theory of the chemical bond. Nineteenth-century ideas on electrical combination, early twentieth-century theories of electrical attraction, and the contribution of G. N. Lewis's shared electron pair are among the topics considered. (JN)

  18. Bench-Scale Evaluation Of Chemically Bonded Phosphate Ceramic Technology To Stabilize Mercury Waste Mixtures

    EPA Science Inventory

    This bench-scale study was conducted to evaluate the stabilization of mercury (Hg) and mercuric chloride-containing surrogate test materials by the chemically bonded phosphate ceramics technology. This study was performed as part of a U.S. EPA program to evaluate treatment and d...

  19. Alternative Conceptions of Chemical Bonding Held by Upper Secondary and Tertiary Students.

    ERIC Educational Resources Information Center

    Coll, Richard K.; Taylor, Neil

    2001-01-01

    Examination of senior secondary and tertiary level chemistry students' descriptions of their mental models for chemical bonding revealed prevalent alternative conceptions. Some 20 alternative conceptions were revealed, the most common being belief that continuous ionic or metallic lattices were molecular in nature, and confusion over ionic size…

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

    ERIC Educational Resources Information Center

    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…

  1. An Investigation into the Relationship between Students' Conceptions of the Particulate Nature of Matter and Their Understanding of Chemical Bonding

    ERIC Educational Resources Information Center

    Othman, Jazilah; Treagust, David F.; Chandrasegaran, A. L.

    2008-01-01

    A thorough understanding of chemical bonding requires familiarity with the particulate nature of matter. In this study, a two-tier multiple-choice diagnostic instrument consisting of ten items (five items involving each of the two concepts) was developed to assess students' understanding of the particulate nature of matter and chemical bonding so…

  2. Developing a New Teaching Approach for the Chemical Bonding Concept Aligned with Current Scientific and Pedagogical Knowledge

    ERIC Educational Resources Information Center

    Nahum, Tami Levy; Mamlok-Naaman, Rachel; Hofstein, Avi; Krajcik, Joseph

    2007-01-01

    The traditional pedagogical approach for teaching chemical bonding is often overly simplistic and not aligned with the most up-to-date scientific models. As a result, high-school students around the world lack fundamental understanding of chemical bonding. In order to improve students' understanding of this concept, it was essential to propose a…

  3. Intramolecular hydrogen bonding in 5-nitrosalicylaldehyde: IR spectrum and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Moosavi-Tekyeh, Zainab; Taherian, Fatemeh; Tayyari, Sayyed Faramarz

    2016-05-01

    The structural parameters, and vibrational frequencies of 5-nitrosalicylaldehyde (5NSA) were studied by the FT-IR and Raman spectra and the quantum chemical calculations carried out at the B3LYP/6-311++G(d,p) level of theory in order to investigate the intramolecular hydrogen bonding (IHB) present in its structure. The strength and nature of IHB in the optimized structure of 5NSA were studied in detail by means of the atoms in molecules (AIM) and the natural bond orbital (NBO) approaches. The results obtained were then compared with the corresponding data for its parent molecule, salicylaldehyde (SA). Comparisons made between the geometrical structures for 5NSA and SA, their OH/OD stretching and out-of-plane bending modes, their enthalpies for the hydrogen bond, and their AIM parameters demonstrated a stronger H-bonding in 5NSA compared with that in SA. The calculated binding enthalpy (ΔHbind) for 5NSA was -10.92 kcal mol-1. The observed νOH and γOH appeared at about 3120 cm-1 and 786 cm-1 respectively. The stretching frequency shift of H-bond formation was 426 cm-1 which is consistent with ΔHbind and the strength of H-bond in 5NSA. The delocalization energies and electron delocalization indices derived by the NBO and AIM approaches indicate that the resonance effects were responsible for the stronger IHB in 5NSA than in SA.

  4. Duration of an intense laser pulse can determine the breakage of multiple chemical bonds

    NASA Astrophysics Data System (ADS)

    Xie, Xinhua; Lötstedt, Erik; Roither, Stefan; Schöffler, Markus; Kartashov, Daniil; Midorikawa, Katsumi; Baltuška, Andrius; Yamanouchi, Kaoru; Kitzler, Markus

    2015-08-01

    Control over the breakage of a certain chemical bond in a molecule by an ultrashort laser pulse has been considered for decades. With the availability of intense non-resonant laser fields it became possible to pre-determine femtosecond to picosecond molecular bond breakage dynamics by controlled distortions of the electronic molecular system on sub-femtosecond time scales using field-sensitive processes such as strong-field ionization or excitation. So far, all successful demonstrations in this area considered only fragmentation reactions, where only one bond is broken and the molecule is split into merely two moieties. Here, using ethylene (C2H4) as an example, we experimentally investigate whether complex fragmentation reactions that involve the breakage of more than one chemical bond can be influenced by parameters of an ultrashort intense laser pulse. We show that the dynamics of removing three electrons by strong-field ionization determines the ratio of fragmentation of the molecular trication into two respectively three moieties. We observe a relative increase of two-body fragmentations with the laser pulse duration by almost an order of magnitude. Supported by quantum chemical simulations we explain our experimental results by the interplay between the dynamics of electron removal and nuclear motion.

  5. Duration of an intense laser pulse can determine the breakage of multiple chemical bonds

    PubMed Central

    Xie, Xinhua; Lötstedt, Erik; Roither, Stefan; Schöffler, Markus; Kartashov, Daniil; Midorikawa, Katsumi; Baltuška, Andrius; Yamanouchi, Kaoru; Kitzler, Markus

    2015-01-01

    Control over the breakage of a certain chemical bond in a molecule by an ultrashort laser pulse has been considered for decades. With the availability of intense non-resonant laser fields it became possible to pre-determine femtosecond to picosecond molecular bond breakage dynamics by controlled distortions of the electronic molecular system on sub-femtosecond time scales using field-sensitive processes such as strong-field ionization or excitation. So far, all successful demonstrations in this area considered only fragmentation reactions, where only one bond is broken and the molecule is split into merely two moieties. Here, using ethylene (C2H4) as an example, we experimentally investigate whether complex fragmentation reactions that involve the breakage of more than one chemical bond can be influenced by parameters of an ultrashort intense laser pulse. We show that the dynamics of removing three electrons by strong-field ionization determines the ratio of fragmentation of the molecular trication into two respectively three moieties. We observe a relative increase of two-body fragmentations with the laser pulse duration by almost an order of magnitude. Supported by quantum chemical simulations we explain our experimental results by the interplay between the dynamics of electron removal and nuclear motion. PMID:26271602

  6. Duration of an intense laser pulse can determine the breakage of multiple chemical bonds.

    PubMed

    Xie, Xinhua; Lötstedt, Erik; Roither, Stefan; Schöffler, Markus; Kartashov, Daniil; Midorikawa, Katsumi; Baltuška, Andrius; Yamanouchi, Kaoru; Kitzler, Markus

    2015-08-14

    Control over the breakage of a certain chemical bond in a molecule by an ultrashort laser pulse has been considered for decades. With the availability of intense non-resonant laser fields it became possible to pre-determine femtosecond to picosecond molecular bond breakage dynamics by controlled distortions of the electronic molecular system on sub-femtosecond time scales using field-sensitive processes such as strong-field ionization or excitation. So far, all successful demonstrations in this area considered only fragmentation reactions, where only one bond is broken and the molecule is split into merely two moieties. Here, using ethylene (C2H4) as an example, we experimentally investigate whether complex fragmentation reactions that involve the breakage of more than one chemical bond can be influenced by parameters of an ultrashort intense laser pulse. We show that the dynamics of removing three electrons by strong-field ionization determines the ratio of fragmentation of the molecular trication into two respectively three moieties. We observe a relative increase of two-body fragmentations with the laser pulse duration by almost an order of magnitude. Supported by quantum chemical simulations we explain our experimental results by the interplay between the dynamics of electron removal and nuclear motion.

  7. Topological Properties of Chemical Bonds from Static and Dynamic Electron Densities.

    PubMed

    Jagannatha Prathapa, Siriyara; Held, Jeanette; van Smaalen, Sander

    2013-09-01

    Dynamic and static electron densities (EDs) based on the independent spherical atom model (IAM) and multipole (MP) models of crambin were successfully computed, holding no series-termination effects. The densities are compared to EDs of small biological molecules at diverse temperatures. It is outlined that proteins exhibit an intrinsic flexibility, present as frozen disorder at 100 K, in contrast to small molecules. The flexibility of the proteins is reflected by atomic displacement parameters (B-factors), which are considerably larger than for small molecules at 298 K. Thus, an optimal deconvolution of deformation density and thermal motion is not guaranteed, which prevents a free refinement of MP parameters but allows an application of transferable, fixed MP parameters. The analysis of the topological properties, such as the density at bond critical points (BCPs) and the Laplacian, reveals systematic differences between static and dynamic EDs. Zero-point-vibrations, yet present in dynamic EDs at low temperature, affect but marginally the EDs of small molecules. The zero-point-vibrations cause a smearing of the ED, which becomes more pronounced with increasing temperature. Topological properties, primarily the Laplacian, of covalent bonds appear to be more sensitive to effects by temperature and the polarity of the bonds. However, dynamic EDs at ca. 20 K based on MP models provide a good characterization of chemical bonding. Both the density at BCPs and the Laplacian of hydrogen bonds constitute similar values from static and dynamic EDs for all studied temperatures. Deformation densities demonstrate the necessity of the employment of MP parameters in order to comprise the nature of covalent bonds. The character of hydrogen bonds can be roughly pictured by IAM, whereas MP parameters are recommended for a classification of hydrogen bonds beyond a solely interpretation of topological properties.

  8. Nucleation-dependant chemical bonding paradigm: the effect of rare earth ions on the nucleation of urea in aqueous solution.

    PubMed

    Chen, Xiaoyan; Sun, Congting; Wu, Sixin; Xue, Dongfeng

    2017-03-29

    Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln(3+)) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH2, and CN vibration bands during the urea nucleation stage. Rare earth ions such as La(3+), Gd(3+), and Lu(3+) can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln(3+) and urea molecules have been confirmed, which are Ln(3+)O[double bond, length as m-dash]C-N and Ln(3+)NH2-C. Compared with Ln(3+)NH2-C, Ln(3+) prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln(3+) into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln(3+) concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln(3+), the different effects of La(3+), Gd(3+), and Lu(3+) on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

  9. Physical and chemical transformations of highly compressed carbon dioxide at bond energies.

    PubMed

    Yoo, Choong-Shik

    2013-06-07

    Carbon dioxide exhibits a richness of high-pressure polymorphs with a great diversity in intermolecular interaction, chemical bonding, and crystal structures. It ranges from typical molecular solids to fully extended covalent solids with crystal structures similar to those of SiO2. These extended solids of carbon dioxide are fundamentally new materials exhibiting interesting optical nonlinearity, low compressibility and high energy density. Furthermore, the large disparity in chemical bonding between the extended network and molecular structures results in a broad metastability domain for these phases to room temperature and almost to ambient pressure and thereby offers enhanced opportunities for novel materials developments. Broadly speaking, these molecular-to-non-molecular transitions occur due to electron delocalization manifested as a rapid increase in electron kinetic energy at high density. The detailed mechanisms, however, are more complex with phase metastabilities, path-dependent phases and phase boundaries, and large lattice strains and structural distortions - all of which are controlled by well beyond thermodynamic constraints to chemical kinetics associated with the governing phases and transitions. As a result, the equilibrium phase boundary is difficult to locate precisely (experimentally or theoretically) and is often obscured by the presence of metastable phases (ordered or disordered). This paper will review the pressure-induced transformations observed in highly compressed carbon dioxide and present chemistry perspectives on those molecular-to-non-molecular transformations that can be applied to other low-Z molecular solids at Mbar pressures where the compression energy rivals the chemical bond energies.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Fernandez, Julio M.

    2008-03-01

    The mechanisms by which mechanical forces regulate the kinetics of a chemical reaction are unknown. In my lecture I will demonstrate how we use single molecule force-clamp spectroscopy and protein engineering to study the effect of force on the kinetics of thiol/disulfide exchange. Reduction of disulfide bond via the thiol/disulfide exchange chemical reaction is crucial in regulating protein function and is of common occurrence in mechanically stressed proteins. While reduction is thought to proceed through a substitution nucleophilic bimolecular (SN2) reaction, the role of a mechanical force in modulating this chemical reaction is unknown. We apply a constant stretching force to single engineered disulfide bonds and measure their rate of reduction by dithiothreitol (DTT). We find that while the reduction rate is linearly dependent on the concentration of DTT, it is exponentially dependent on the applied force, increasing 10-fold over a 300 pN range. This result predicts that the disulfide bond lengthens by 0.34 å at the transition state of the thiol/disulfide exchange reaction. In addition to DTT, we also study the reduction of the engineered disulfide bond by the E. coli enzyme thioredoxin (Trx). Thioredoxins are enzymes that catalyze disulfide bond reduction in all organisms. As before, we apply a mechanical force in the range of 25-450 pN to the engineered disulfide bond substrate and monitor the reduction of these bonds by individual enzymes. In sharp contrast with the data obtained with DTT, we now observe two alternative forms of the catalytic reaction, the first requiring a reorientation of the substrate disulfide bond, causing a shortening of the substrate polypeptide by 0.76±0.07 å, and the second elongating the substrate disulfide bond by 0.21±0.01 å. These results support the view that the Trx active site regulates the geometry of the participating sulfur atoms, with sub-ångström precision, in order to achieve efficient catalysis. Single molecule

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Chemical role of oxygen plasma in wafer bonding using borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Hansen, D. M.; Albaugh, C. E.; Moran, P. D.; Kuech, T. F.

    2001-11-01

    Plasma-treated oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure chemical vapor deposition treated with an O2 plasma in reactive ion etching mode for 5 min at 0.6 W/cm2 and rinsed with DI H2O readily bond to GaAs and Si. The chemical role of this prebonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The peak intensities for both the Si-O and B-O absorbance bands decreased in intensity as a result of the plasma treatment is consistent with the uniform sputtering of 9.8 nm±0.8 nm of BSG. Polarization dependent ATR-FTIR revealed that the H2O/OH absorbance bands decreased in peak intensity with the OH groups being preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H2O rinse restores the water to the surface while removing B2O3 from the BSG layer. This prebonding treatment, therefore, results in a hydrophilic bond, but alters the composition of the BSG film at the bonded interface.

  14. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    SciTech Connect

    Lichtenberger, D.L.

    1991-10-01

    The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relationship has been used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. We have been able to obtain a direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal. The ionization energies have also been used to correlate the rates of carbonyl substitution reactions of ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2} complexes, and to reveal the electronic factors that control the stability of the transition state. The extent that the electronic features of these bonding interactions transfer to other chemical systems is being investigated in terms of the principle of additivity of ligand electronic effects. Specific examples under study include metal- phosphines, metal-halides, and metallocenes. Especially interesting has been the recent application of these techniques to the characterization of the soccer-ball shaped C{sub 60} molecule, buckminsterfullerene, and its interaction with a metal surface. The high-resolution valence ionizations in the gas phase reveal the high symmetry of the molecule, and studies of thin films of C{sub 60} reveal weak intermolecular interactions. Scanning tunneling and atomic force microscopy reveal the arrangement of spherical molecules on gold substrates, with significant delocalization of charge from the metal surface. 21 refs.

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

    SciTech Connect

    Putz, Mihai V.

    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.

  16. Aromatic thiol-mediated cleavage of N–O bonds enables chemical ubiquitylation of folded proteins

    PubMed Central

    Weller, Caroline E.; Dhall, Abhinav; Ding, Feizhi; Linares, Edlaine; Whedon, Samuel D.; Senger, Nicholas A.; Tyson, Elizabeth L.; Bagert, John D.; Li, Xiaosong; Augusto, Ohara; Chatterjee, Champak

    2016-01-01

    Access to protein substrates homogenously modified by ubiquitin (Ub) is critical for biophysical and biochemical investigations aimed at deconvoluting the myriad biological roles for Ub. Current chemical strategies for protein ubiquitylation, however, employ temporary ligation auxiliaries that are removed under harsh denaturing conditions and have limited applicability. We report an unprecedented aromatic thiol-mediated N–O bond cleavage and its application towards native chemical ubiquitylation with the ligation auxiliary 2-aminooxyethanethiol. Our interrogation of the reaction mechanism suggests a disulfide radical anion as the active species capable of cleaving the N–O bond. The successful semisynthesis of full-length histone H2B modified by the small ubiquitin-like modifier-3 (SUMO-3) protein further demonstrates the generalizability and compatibility of our strategy with folded proteins. PMID:27680493

  17. Detection of sub-GeV dark matter and solar neutrinos via chemical-bond breaking

    NASA Astrophysics Data System (ADS)

    Essig, Rouven; Mardon, Jeremy; Slone, Oren; Volansky, Tomer

    2017-03-01

    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 10s 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 O (0.1 /kg -year ) , large exposures are required, but measuring low-energy solar neutrinos would provide a crucial test of the solar model.

  18. Aromatic thiol-mediated cleavage of N-O bonds enables chemical ubiquitylation of folded proteins

    NASA Astrophysics Data System (ADS)

    Weller, Caroline E.; Dhall, Abhinav; Ding, Feizhi; Linares, Edlaine; Whedon, Samuel D.; Senger, Nicholas A.; Tyson, Elizabeth L.; Bagert, John D.; Li, Xiaosong; Augusto, Ohara; Chatterjee, Champak

    2016-09-01

    Access to protein substrates homogenously modified by ubiquitin (Ub) is critical for biophysical and biochemical investigations aimed at deconvoluting the myriad biological roles for Ub. Current chemical strategies for protein ubiquitylation, however, employ temporary ligation auxiliaries that are removed under harsh denaturing conditions and have limited applicability. We report an unprecedented aromatic thiol-mediated N-O bond cleavage and its application towards native chemical ubiquitylation with the ligation auxiliary 2-aminooxyethanethiol. Our interrogation of the reaction mechanism suggests a disulfide radical anion as the active species capable of cleaving the N-O bond. The successful semisynthesis of full-length histone H2B modified by the small ubiquitin-like modifier-3 (SUMO-3) protein further demonstrates the generalizability and compatibility of our strategy with folded proteins.

  19. Ultraviolet-curable polymers with chemically bonded carbon nanotubes for microelectromechanical system applications

    NASA Astrophysics Data System (ADS)

    Xie, Jining; Zhang, Nanyan; Guers, Manton; Varadan, Vijay K.

    2002-08-01

    Current UV-curable polymer techniques for microelectromechanical system fabrication pose certain challenges due to the electrical and mechanical properties of the polymer. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in situ polymerization. Purified multi-walled nanotubes, obtained by the microwave chemical vapor deposition method, were functionalized by oxidation. X-ray photoelectron spectroscopy was used to identify the -OH and -COOH groups attached to the nanotube surface. The UV-curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between the -NCO groups of TDI and the -OH, -COOH groups of functionalized nanotubes were confirmed by Fourier transform infrared spectra. This new UV-curable polymer is expected to be a cost-effective solution with a variety of applications in UV coating, phase shifters for telecommunications and global positioning systems, and polymer and BioMEMS devices.

  20. Aromatic thiol-mediated cleavage of N-O bonds enables chemical ubiquitylation of folded proteins.

    PubMed

    Weller, Caroline E; Dhall, Abhinav; Ding, Feizhi; Linares, Edlaine; Whedon, Samuel D; Senger, Nicholas A; Tyson, Elizabeth L; Bagert, John D; Li, Xiaosong; Augusto, Ohara; Chatterjee, Champak

    2016-09-29

    Access to protein substrates homogenously modified by ubiquitin (Ub) is critical for biophysical and biochemical investigations aimed at deconvoluting the myriad biological roles for Ub. Current chemical strategies for protein ubiquitylation, however, employ temporary ligation auxiliaries that are removed under harsh denaturing conditions and have limited applicability. We report an unprecedented aromatic thiol-mediated N-O bond cleavage and its application towards native chemical ubiquitylation with the ligation auxiliary 2-aminooxyethanethiol. Our interrogation of the reaction mechanism suggests a disulfide radical anion as the active species capable of cleaving the N-O bond. The successful semisynthesis of full-length histone H2B modified by the small ubiquitin-like modifier-3 (SUMO-3) protein further demonstrates the generalizability and compatibility of our strategy with folded proteins.

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

    PubMed

    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.

  2. Description of Polar Chemical Bonds from the Quantum Mechanical Interference Perspective.

    PubMed

    Fantuzzi, Felipe; Nascimento, Marco Antonio Chaer

    2014-06-10

    The Generalized Product Function Energy Partitioning (GPF-EP) method has been applied to a set of molecules, AH (A = Li, Be, B, C, N, O, F), CO and LiF with quite different dipole moments, in order to investigate the role played by the quantum interference effect in the formation of polar chemical bonds. The calculations were carried out with GPF wave functions treating all the core electrons as a single Hartree-Fock group and the bonding electrons at the Generalized Valence Bond Perfect-Pairing (GVB-PP) level, with the cc-pVTZ basis set. The results of the energy partitioning into interference and quasi-classical contributions along the respective Potential Energy Surfaces (PES) show that the main contribution to the depth of the potential wells comes from the interference term, which is an indication that all the molecules mentioned above form typical covalent bonds. In all cases, the stabilization promoted by the interference term comes from the kinetic contribution, in agreement with previous results. The analysis of the effect of quantum interference on the electron density reveals that while polarization effects (quasi-classical) tend to displace electronic density from the most polarizable atom toward the less polarizable one, interference (quantum effects) counteracts by displacing electronic density to the bond region, giving rise to the right electronic density and dipole moment.

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

    DOEpatents

    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.

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

    PubMed

    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.

  5. Chemically-bonded brick production based on burned clay by means of semidry pressing

    NASA Astrophysics Data System (ADS)

    Voroshilov, Ivan; Endzhievskaya, Irina; Vasilovskaya, Nina

    2016-01-01

    We presented a study on the possibility of using the burnt rocks of the Krasnoyarsk Territory for production of chemically-bonded materials in the form of bricks which are so widely used in multistory housing and private house construction. The radiographic analysis of the composition of burnt rock was conducted and a modifier to adjust the composition uniformity was identified. The mixing moisture content was identified and optimal amount at 13-15% was determined. The method of semidry pressing has been chosen. The process of obtaining moldings has been theoretically proved; the advantages of chemically-bonded wall materials compared to ceramic brick were shown. The production of efficient artificial stone based on material burnt rocks, which is comparable with conventionally effective ceramic materials or effective with cell tile was proved, the density of the burned clay-based cell tile makes up to 1630-1785 kg m3, with compressive strength of 13.6-20.0 MPa depending on the compression ratio and cement consumption, frost resistance index is F50, and the thermal conductivity in the masonry is λ = 0,459-0,546 W m * °C. The clear geometric dimensions of pressed products allow the use of the chemically-bonded brick based on burnt clay as a facing brick.

  6. Chemically-bonded brick production based on burned clay by means of semidry pressing

    SciTech Connect

    Voroshilov, Ivan Endzhievskaya, Irina Vasilovskaya, Nina

    2016-01-15

    We presented a study on the possibility of using the burnt rocks of the Krasnoyarsk Territory for production of chemically-bonded materials in the form of bricks which are so widely used in multistory housing and private house construction. The radiographic analysis of the composition of burnt rock was conducted and a modifier to adjust the composition uniformity was identified. The mixing moisture content was identified and optimal amount at 13-15% was determined. The method of semidry pressing has been chosen. The process of obtaining moldings has been theoretically proved; the advantages of chemically-bonded wall materials compared to ceramic brick were shown. The production of efficient artificial stone based on material burnt rocks, which is comparable with conventionally effective ceramic materials or effective with cell tile was proved, the density of the burned clay-based cell tile makes up to 1630-1785 kg \\ m{sup 3}, with compressive strength of 13.6-20.0 MPa depending on the compression ratio and cement consumption, frost resistance index is F50, and the thermal conductivity in the masonry is λ = 0,459-0,546 W \\ m {sup *} °C. The clear geometric dimensions of pressed products allow the use of the chemically-bonded brick based on burnt clay as a facing brick.

  7. Development of chemically bonded phosphate ceramics for stabilizing low-level mixed wastes

    NASA Astrophysics Data System (ADS)

    Jeong, Seung-Young

    1997-11-01

    Novel chemically bonded phosphate ceramics have been developed by acid-base reactions between magnesium oxide and an acid phosphate at room temperature for stabilizing U.S. Department of Energy's low-level mixed waste streams that include hazardous chemicals and radioactive elements. Newberyite (MgHPOsb4.3Hsb2O)-rich magnesium phosphate ceramic was formed by an acid-base reaction between phosphoric acid and magnesium oxide. The reaction slurry, formed at room-temperature, sets rapidly and forms stable mineral phases of newberyite, lunebergite, and residual MgO. Rapid setting also generates heat due to exothermic acid-base reaction. The reaction was retarded by partially neutralizing the phosphoric acid solution by adding sodium or potassium hydroxide. This reduced the rate of reaction and heat generation and led to a practical way of producing novel magnesium potassium phosphate ceramic. This ceramic was formed by reacting stoichiometric amount of monopotassium dihydrogen phosphate crystals, MgO, and water, forming pure-phase of MgKPOsb4.6Hsb2O (MKP) with moderate exothermic reaction. Using this chemically bonded phosphate ceramic matrix, low-level mixed waste streams were stabilized, and superior waste forms in a monolithic structure were developed. The final waste forms showed low open porosity and permeability, and higher compression strength than the Land Disposal Requirements (LDRs). The novel MKP ceramic technology allowed us to develop operational size waste forms of 55 gal with good physical integrity. In this improved waste form, the hazardous contaminants such as RCRA heavy metals (Hg, Pb, Cd, Cr, Ni, etc) were chemically fixed by their conversion into insoluble phosphate forms and physically encapsulated by the phosphate ceramic. In addition, chemically bonded phosphate ceramics stabilized radioactive elements such U and Pu. This was demonstrated with a detailed stabilization study on cerium used as a surrogate (chemically equivalent but nonradioactive

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

    PubMed Central

    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

  9. Revealing halogen bonding interactions with anomeric systems: an ab initio quantum chemical studies.

    PubMed

    Lo, Rabindranath; Ganguly, Bishwajit

    2015-02-01

    A computational study has been performed using MP2 and CCSD(T) methods on a series of O⋯X (X=Br, Cl and I) halogen bonds to evaluate the strength and characteristic of such highly directional noncovalent interactions. The study has been carried out on a series of dimeric complexes formed between interhalogen compounds (such as BrF, BrCl and BrI) and oxygen containing electron donor molecule. The existence and consequences of the anomeric effect of the electron donor molecule has also been investigated through an exploration of halogen bonding interactions in this halogen bonded complexes. The ab initio quantum chemical calculations have been employed to study both the nature and directionality of the halogen molecules toward the sp(3) oxygen atom in anomeric systems. The presence of anomeric nO→σ*CN interaction involves a dominant role for the availability of the axial and equatorial lone pairs of donor O atom to participate with interhalogen compounds in the halogen-bonded complexes. The energy difference between the axial and equatorial conformers with interhalogen compounds reaches up to 4.60 kJ/mol, which however depends upon the interacting halogen atoms and its attaching atoms. The energy decomposition analysis further suggests that the total halogen bond interaction energies are mainly contributed by the attractive electrostatic and dispersion components. The role of substituents attached with the halogen atoms has also been evaluated in this study. With the increase of halogen atom size and the positive nature of σ-hole, the halogen atom interacted more with the electron donor atom and the electrostatic contribution to the total interaction energy enhances appreciably. Further, noncovalent interaction (NCI) studies have been carried out to locate the noncovalent halogen bonding interactions in real space.

  10. Chemical bonding in electron-deficient boron oxide clusters: core boronyl groups, dual 3c-4e hypervalent bonds, and rhombic 4c-4e bonds.

    PubMed

    Chen, Qiang; Lu, Haigang; Zhai, Hua-Jin; Li, Si-Dian

    2014-04-28

    We explore the structural and bonding properties of the electron-deficient boron oxide clusters, using a series of B3On(-/0/+) (n = 2-4) clusters as examples. Global-minimum structures of these boron oxide clusters are identified via unbiased Coalescence Kick and Basin Hopping searches, which show a remarkable size and charge-state dependence. An array of new bonding elements are revealed: core boronyl groups, dual 3c-4e hypervalent bonds (ω-bonds), and rhombic 4c-4e bonds (o-bonds). In favorable cases, oxygen can exhaust all its 2s/2p electrons to facilitate the formation of B-O bonds. The current findings should help understand the bonding nature of low-dimensional boron oxide nanomaterials and bulk boron oxides.

  11. The trouble with chemical energy: why understanding bond energies requires an interdisciplinary systems approach.

    PubMed

    Cooper, Melanie M; Klymkowsky, Michael W

    2013-06-01

    Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk about chemical energy (which is also the way we talk about energy in everyday life); 2) the macroscopic approach to energy concepts that is common in physics and physical sciences; and 3) the failure of chemistry courses to explicitly link molecular with macroscopic energy ideas. From a constructivist perspective, it is unlikely that students can, without a coherent understanding of such a central concept, attain a robust and accurate understanding of new concepts. However, changes are on the horizon, guided by the increasing understanding that difficult concepts require coherent, well-designed learning progressions and the new National Research Council Framework for K-12 Science Education. We provide supporting evidence for our assertions and suggestions for an interdisciplinary learning progression designed to better approach the concept of bond energies, a first step in an understanding chemical energy and behavior of reaction systems that is central to biological systems.

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

    PubMed Central

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

    Helping students understand “chemical energy” is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk about chemical energy (which is also the way we talk about energy in everyday life); 2) the macroscopic approach to energy concepts that is common in physics and physical sciences; and 3) the failure of chemistry courses to explicitly link molecular with macroscopic energy ideas. From a constructivist perspective, it is unlikely that students can, without a coherent understanding of such a central concept, attain a robust and accurate understanding of new concepts. However, changes are on the horizon, guided by the increasing understanding that difficult concepts require coherent, well-designed learning progressions and the new National Research Council Framework for K–12 Science Education. We provide supporting evidence for our assertions and suggestions for an interdisciplinary learning progression designed to better approach the concept of bond energies, a first step in an understanding chemical energy and behavior of reaction systems that is central to biological systems. PMID:23737636

  13. Intermolecular and intramolecular hydrogen bonds involving fluorine atoms: implications for recognition, selectivity, and chemical properties.

    PubMed

    Dalvit, Claudio; Vulpetti, Anna

    2012-02-06

    A correlation between 19F NMR isotropic chemical shift and close intermolecular F⋅⋅⋅H-X contacts (with X=N or O) has been identified upon analysis of the X-ray crystal structures of fluorinated molecules listed in the Cambridge Structural Database (CSD). An optimal F⋅⋅⋅X distance involving primary and shielded secondary fluorine atoms in hydrogen-bond formation along with a correlation between F⋅⋅⋅H distance and F⋅⋅⋅H-X angle were also derived from the analysis. The hydrogen bonds involving fluorine are relevant, not only for the recognition mechanism and stabilization of a preferred conformation, but also for improvement in the permeability of the molecules, as shown with examples taken from a proprietary database. Results of an analysis of the small number of fluorine-containing natural products listed in the Protein Data Bank (PDB) appear to strengthen the derived correlation between 19F NMR isotropic chemical shift and interactions involving fluorine (also known as the "rule of shielding") and provides a hypothesis for the recognition mechanism and catalytic activity of specific enzymes. Novel chemical scaffolds, based on the rule of shielding, have been designed for recognizing distinct structural motifs present in proteins. It is envisaged that this approach could find useful applications in drug design for the efficient optimization of chemical fragments or promising compounds by increasing potency and selectivity against the desired biomolecular target.

  14. The active site of hen egg-white lysozyme: flexibility and chemical bonding

    SciTech Connect

    Held, Jeanette Smaalen, Sander van

    2014-04-01

    Chemical bonding at the active site of lysozyme is analyzed on the basis of a multipole model employing transferable multipole parameters from a database. Large B factors at low temperatures reflect frozen-in disorder, but therefore prevent a meaningful free refinement of multipole parameters. Chemical bonding at the active site of hen egg-white lysozyme (HEWL) is analyzed on the basis of Bader’s quantum theory of atoms in molecules [QTAIM; Bader (1994 ▶), Atoms in Molecules: A Quantum Theory. Oxford University Press] applied to electron-density maps derived from a multipole model. The observation is made that the atomic displacement parameters (ADPs) of HEWL at a temperature of 100 K are larger than ADPs in crystals of small biological molecules at 298 K. This feature shows that the ADPs in the cold crystals of HEWL reflect frozen-in disorder rather than thermal vibrations of the atoms. Directly generalizing the results of multipole studies on small-molecule crystals, the important consequence for electron-density analysis of protein crystals is that multipole parameters cannot be independently varied in a meaningful way in structure refinements. Instead, a multipole model for HEWL has been developed by refinement of atomic coordinates and ADPs against the X-ray diffraction data of Wang and coworkers [Wang et al. (2007), Acta Cryst. D63, 1254–1268], while multipole parameters were fixed to the values for transferable multipole parameters from the ELMAM2 database [Domagala et al. (2012), Acta Cryst. A68, 337–351] . Static and dynamic electron densities based on this multipole model are presented. Analysis of their topological properties according to the QTAIM shows that the covalent bonds possess similar properties to the covalent bonds of small molecules. Hydrogen bonds of intermediate strength are identified for the Glu35 and Asp52 residues, which are considered to be essential parts of the active site of HEWL. Furthermore, a series of weak C

  15. A theoretical study of the structures and chemical bonds of neptunium (III) molecules by a density functional method

    NASA Astrophysics Data System (ADS)

    Yin, Yao-Peng; Dong, Chen-Zhong; Du, Lei-Qiang; Wu, Fang-Xian; Ding, Xiao-Bin

    2014-10-01

    In this paper, equilibrium structures and chemical bond characteristics of neptunium trihalide molecules NpX3 (X = F, Cl, Br and I) have been investigated by using density functional theory (DFT). The influences of the size of the relativistic effective core potential (RECP) have been examined on the molecular structures. The chemical bond characteristics have also been systematically studied by calculating the density of states (DOS), bond length differences and electronic charge distributions. We have determined that the chemical bonds are mainly ionic in those molecules, and the covalency is enhancing while ionicity decreases from NpF3 to NpI3. The calculated bond energies show that the interaction strength in NpX3 molecules becomes weaker as the halogen atoms becoming heavier.

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

    NASA Astrophysics Data System (ADS)

    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).

  17. A two-step chemical mechanism for ribosome-catalysed peptide bond formation.

    PubMed

    Hiller, David A; Singh, Vipender; Zhong, Minghong; Strobel, Scott A

    2011-07-17

    The chemical step of natural protein synthesis, peptide bond formation, is catalysed by the large subunit of the ribosome. Crystal structures have shown that the active site for peptide bond formation is composed entirely of RNA. Recent work has focused on how an RNA active site is able to catalyse this fundamental biological reaction at a suitable rate for protein synthesis. On the basis of the absence of important ribosomal functional groups, lack of a dependence on pH, and the dominant contribution of entropy to catalysis, it has been suggested that the role of the ribosome is limited to bringing the substrates into close proximity. Alternatively, the importance of the 2'-hydroxyl of the peptidyl-transfer RNA and a Brønsted coefficient near zero have been taken as evidence that the ribosome coordinates a proton-transfer network. Here we report the transition state of peptide bond formation, based on analysis of the kinetic isotope effect at five positions within the reaction centre of a peptidyl-transfer RNA mimic. Our results indicate that in contrast to the uncatalysed reaction, formation of the tetrahedral intermediate and proton transfer from the nucleophilic nitrogen both occur in the rate-limiting step. Unlike in previous proposals, the reaction is not fully concerted; instead, breakdown of the tetrahedral intermediate occurs in a separate fast step. This suggests that in addition to substrate positioning, the ribosome is contributing to chemical catalysis by changing the rate-limiting transition state.

  18. Conceptual quantum chemical analysis of bonding and noncovalent interactions in the formation of frustrated Lewis pairs.

    PubMed

    Skara, Gabriella; Pinter, Balazs; Top, Jens; Geerlings, Paul; De Proft, Frank; De Vleeschouwer, Freija

    2015-03-27

    The contributions of covalent and noncovalent interactions to the formation of classical adducts of bulky Lewis acids and bases and frustrated Lewis pairs (FLPs) were scrutinized by using various conceptual quantum chemical techniques. Significantly negative complexation energies were calculated for fourteen investigated Lewis pairs containing bases and acids with substituents of various sizes. A Ziegler-Rauk-type energy decomposition analysis confirmed that two types of Lewis pairs can be distinguished on the basis of the nature of the primary interactions between reactants; dative-bond formation and concomitant charge transfer from the Lewis base to the acid is the dominant and most stabilizing factor in the formation of Lewis acid-base adducts, whereas weak interactions are the main thermodynamic driving force (>50 %) for FLPs. Moreover, the ease and extent of structural deformation of the monomers appears to be a key component in the formation of the former type of Lewis pairs. A Natural Orbital for Chemical Valence (NOCV) analysis, which was used to visualize and quantify the charge transfer between the base and the acid, clearly showed the importance and lack of this type of interaction for adducts and FLPs, respectively. The Noncovalent Interaction (NCI) method revealed several kinds of weak interactions between the acid and base components, such as dispersion, π-π stacking, C-H⋅⋅⋅π interaction, weak hydrogen bonding, halogen bonding, and weak acid-base interactions, whereas the Quantum Theory of Atoms in Molecules (QTAIM) provided further conceptual insight into strong acid-base interactions.

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

    PubMed

    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.

  20. Enhancement of chemical stability and crystallinity in porphyrin-containing covalent organic frameworks by intramolecular hydrogen bonds.

    PubMed

    Kandambeth, Sharath; Shinde, Digambar Balaji; Panda, Manas K; Lukose, Binit; Heine, Thomas; Banerjee, Rahul

    2013-12-02

    A strong bond: A strategy based on intramolecular hydrogen-binding interactions in 2D covalent organic frameworks (COFs) is shown to improve the crystallinity, porosity, and chemical stability of the material. The concept is validated by removing the hydrogen-bonding interaction in the methoxy analog which showed a lower stability and crystallinity.

  1. Biasing hydrogen bond donating host systems towards chemical warfare agent recognition.

    PubMed

    Hiscock, Jennifer R; Wells, Neil J; Ede, Jayne A; Gale, Philip A; Sambrook, Mark R

    2016-10-12

    A series of neutral ditopic and negatively charged, monotopic host molecules have been evaluated for their ability to bind chloride and dihydrogen phosphate anions, and neutral organophosphorus species dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PMP) and the chemical warfare agent (CWA) pinacolyl methylphosphonofluoridate (GD, soman) in organic solvent via hydrogen bonding. Urea, thiourea and boronic acid groups are shown to bind anions and neutral guests through the formation of hydrogen bonds, with the urea and thiourea groups typically exhibiting higher affinity interactions. The introduction of a negative charge on the host structure is shown to decrease anion affinity, whilst still allowing for high stability host-GD complex formation. Importantly, the affinity of the host for the neutral CWA GD is greater than for anionic guests, thus demonstrating the potential for selectivity reversal based on charge repulsion.

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

    PubMed

    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.

  3. Nitrogen implantation effects on the chemical bonding and hardness of boron and boron nitride coatings

    SciTech Connect

    Anders, S; Felter, T; Hayes, J; Jankowski, A F; Patterson, R; Poker, D; Stamler, T

    1999-02-08

    Boron nitride (BN) coatings are deposited by the reactive sputtering of fully dense, boron (B) targets utilizing an argon-nitrogen (Ar-N{sub 2}) reactive gas mixture. Near-edge x-ray absorption fine structure analysis reveals features of chemical bonding in the B 1s photoabsorption spectrum. Hardness is measured at the film surface using nanoindentation. The BN coatings prepared at low, sputter gas pressure with substrate heating are found to have bonding characteristic of a defected hexagonal phase. The coatings are subjected to post-deposition nitrogen (N{sup +} and N{sub 2}{sup +}) implantation at different energies and current densities. The changes in film hardness attributed to the implantation can be correlated to changes observed in the B 1s NEXAFS spectra.

  4. Chemical methods and approaches to the regioselective formation of multiple disulfide bonds.

    PubMed

    Shimamoto, Shigeru; Katayama, Hidekazu; Okumura, Masaki; Hidaka, Yuji

    2014-04-01

    Disulfide-bond formation plays an important role in the stabilization of the native conformation of peptides and proteins. In the case of multidisulfide-containing peptides and proteins, numerous folding intermediates are produced, including molecules that contain non-native and native disulfide bonds during in vitro folding. These intermediates can frequently be trapped covalently during folding and subsequently analyzed. The structural characterization of these kinetically trapped disulfide intermediates provides a clue to understanding the oxidative folding pathway. To investigate the folding of disulfide-containing peptides and proteins, in this unit, chemical methods are described for regulating regioselective disulfide formation (1) by using a combination of several types of thiol protecting groups, (2) by incorporating unique SeCys residues into a protein or peptide molecule, and (3) by combining with post-translational modification.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

  7. Bergman Clusters, Multiple Bonds, and Defect Planes: Synthetic Outcomes of Chemical Frustration in Ternary Intermetallic Systems

    NASA Astrophysics Data System (ADS)

    Hadler, Amelia Beth

    Intermetallics crystallize in a variety of complex structures, many of which show unusual bonding or intriguing properties. Understanding what factors drive this structural chemistry would be a valuable step towards designing new intermetallics with specific structures or properties. One pathway towards understanding and predicting the structures of complex intermetallics is chemical frustration, a design tool which harnesses competition between incompatible bonding or packing modes to induce complexity in ternary intermetallic systems. The research outlined in this thesis focuses on developing chemical frustration through exploratory synthesis in ternary systems designed to induce frustration between the tetrahedral close packing of many intermetallics and the simple cubic packing seen for ionic salts or elemental metals. Syntheses in three systems yielded six new ternary intermetallics, four of which crystallize in novel structure types. Three were discovered in the Ca-Cu-Cd system: Ca5Cu2Cd and Ca2Cu 2Cd9, which adopt ternary variants of binary structures, and Ca10Cu2Cd27, which crystallizes in a new structure built from Bergman clusters. All three structures can be traced to electronic packing frustration induced by the similar electronegativities but different metallic radii of Cu and Cd. The Gd-Fe-C system yielded the new carbometalate Gd13Fe 10C13 and an oxycarbide derivative. These phases crystallize in structures built from Gd tricapped trigonal prisms interpenetrated by an Fe-C network. Theoretical analyses reveal that Fe-Fe and Fe-C multiple bonding is found throughout this network. A theoretical investigation of similar carbides uncovers additional metal-metal, metal-carbon, and carbon-carbon multiple bonding. This unusual bonding stabilizes the carbides by satisfying preferred electron counts for their transition metal sites. One new phase, Mg4.5Pd5Ge1.5, was found in the Mg-Pd-Ge system. Its structure is closely related to the CsCl-type structure of

  8. An Effective Hamiltonian Molecular Orbital-Valence Bond (MOVB) Approach for Chemical Reactions Applied to the Nucleophilic Substitution Reaction of Hydrosulfide Ion and Chloromethane.

    PubMed

    Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-01-01

    An effective Hamiltonian mixed molecular orbital and valence bond (EH-MOVB) method is described to obtain an accurate potential energy surface for chemical reactions. Building upon previous results on the construction of diabatic and adiabatic potential surfaces using ab initio MOVB theory, we introduce a diabatic-coupling scaling factor to uniformly scale the ab initio off-diagonal matrix element H(12) such that the computed energy of reaction from the EH-MOVB method is in agreement with the target value. The scaling factor is very close to unity, resulting in minimal alteration of the potential energy surface of the original MOVB model. Furthermore, the relative energy between the reactant and product diabatic states in the EH-MOVB method can be improved to match the experimental energy of reaction. A key ingredient in the EH-MOVB theory is that the off-diagonal matrix elements are functions of all degrees of freedom of the system and the overlap matrix is explicitly evaluated. The EH-MOVB method has been applied to the nucleophilic substitution reaction between hydrosulfide and chloromethane to illustrate the methodology and the results were matched to reproduce the results from ab initio valence bond self-consistent valence bond (VBSCF) calculations. The diabatic coupling (the off-diagonal matrix element in the generalized secular equation) has small variations along the minimum energy reaction path in the EH-MOVB model, whereas it shows a maximum value at the transition state and has nearly zero values in the regions of the ion-dipole complexes from VBSCF calculations. The difference in the diabatic coupling stabilization is attributed to the large overlap integral in the computationally efficient MOVB method.

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

    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.

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

    SciTech Connect

    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].

  12. Chemical bonding in equiatomic cerium intermetallics - The case of CeMgSn, CePdSn, and CeMgPb

    NASA Astrophysics Data System (ADS)

    Matar, Samir F.; Pöttgen, Rainer

    2015-10-01

    The electronic and magnetic structures and the properties of chemical bonding in isopointal CeMgSn and CePdSn (both phases belong to the family of TiNiSi related intermetallics, space group Pnma) and CeMgPb belonging to the family of CeScSi intermetallics, space group I4/mmm, have been investigated within the density functional theory (DFT). The charge analyses indicate negatively charged tin and lead leading to assign the compounds as stannides and plumbides, as also illustrated by the mapping of the electron localization function ELF. Calculations within spin-degenerate non-magnetic spin-polarized ferro- (SP-F) and SP-antiferromagnetic configurations led to assign a major role of Ce 4f states in the onset of ordered moments within SP-AF ground states from energy differences. Chemical bonding analyses from crystal orbital overlap populations revealed the strongest interactions for Ce-Sn in CeMgSn, Ce-Pb in CeMgPb, and Ce-Pd in CePdSn.

  13. Effect of various chemicals on the bond strength of acrylic tooth and denture base -An Invitro comparative study

    PubMed Central

    Krishna, V Pridhvi; Premalatha, Averneni; Babu, P Jithendra; Raju, D Srinivasa; Kumar, M Praveen; Rao, D Bheemalingeswara

    2014-01-01

    Background: Debonding of acrylic teeth from the denture base is a common problem. Certain clinical conditions like ridge prominence leads to excess trimming of acrylic teeth and base, resulting in a weak interface. The denture base polymer debonds adhesively in the region of the highly cross –linked matrix of the teeth. To compare the effect of different chemical surface treatments on the bond between cross-linked acrylic teeth and different types of denture base material. Materials & Methods: A total of 180 wax specimens were fabricated and divided into 3 groups: Heat-cure, high impact heat-cure, flexible denture base material bonded to acrylic teeth. Each group was further subdivided into 6 subgroups with 10 specimens each according to the surface treatment ofthe ridge lap area: control, monomer, acetone 99%, chloroform 99%, acrylic adhesive cyanoacrylate, ethyl acetate 99%. After processing, specimens were tested for bond strength using a universal testing machine. The resulting bond strengths were recorded, statistically analyzed and compared. Results: Among all the 3types of denture base resins, highimpact heat-cure denture base resin gave highest bond strength. There was no bonding of teeth with flexible denture base material. Chemical surface treatment of acrylic teeth with ethyl acetate gave highest bond strength followed by control, chloroform, acetone and cyanoacrylate groups. Conclusion: Among all the 3types of denture base materials, high-impact heat-cure denture base resin gave highest bond strength with ethyl acetate surface treatment. Simple and quick tooth chemical surface treatment with ethylacetate could be an effective option in decreasing bonding failures and also avoid repeated denture repairs improving patient satisfaction. How to cite the article: Krishna VP, Premalatha A, Babu PJ, Raju DS, Kumar MP, Rao DB. Effect of various chemicals on the bond strength of acrylic tooth and denture base -An In-vitro comparative study. J Int Oral Health

  14. A numerical method to compute derivatives of functions of large complex matrices and its application to the overlap Dirac operator at finite chemical potential

    NASA Astrophysics Data System (ADS)

    Puhr, Matthias; Buividovich, Pavel

    2016-11-01

    We present a method for the numerical calculation of derivatives of functions of general complex matrices. The method can be used in combination with any algorithm that evaluates or approximates the desired matrix function, in particular with implicit Krylov-Ritz-type approximations. An important use case for the method is the evaluation of the overlap Dirac operator in lattice Quantum Chromodynamics (QCD) at finite chemical potential, which requires the application of the sign function of a non-Hermitian matrix to some source vector. While the sign function of non-Hermitian matrices in practice cannot be efficiently approximated with source-independent polynomials or rational functions, sufficiently good approximating polynomials can still be constructed for each particular source vector. Our method allows for an efficient calculation of the derivatives of such implicit approximations with respect to the gauge field or other external parameters, which is necessary for the calculation of conserved lattice currents or the fermionic force in Hybrid Monte-Carlo or Langevin simulations. We also give an explicit deflation prescription for the case when one knows several eigenvalues and eigenvectors of the matrix being the argument of the differentiated function. We test the method for the two-sided Lanczos approximation of the finite-density overlap Dirac operator on realistic SU(3) gauge field configurations on lattices with sizes as large as 14 ×143 and 6 ×183.

  15. Cleavage enhancement of specific chemical bonds in DNA by cisplatin radiosensitization.

    PubMed

    Xiao, Fangxing; Luo, Xinglan; Fu, Xianzhi; Zheng, Yi

    2013-05-02

    X-ray photoelectron spectroscopy (XPS) is harnessed as an in situ efficient characterization technique for monitoring chemical bond transformation in DNA and cisplatin-DNA complexes under synergic X-ray irradiation. By analyzing the variation of relative peak area of core elements of DNA as a function of irradiation time, we find that the most vulnerable scission sites in DNA are those containing phosphate and glycosidic bonds. Compared to DNA, the effective rate constants of the corresponding phosphodiester and glycosidic bond cleavages for cisplatin-DNA complexes are 1.8 and 1.9 folds larger. These damages and their enhancements are similar to those induced by low energy electrons (LEE). Consistently, the magnitude of the secondary electron distribution produced by the X-rays on the cisplatin-DNA complexes is considerably increased compared to that of pristine DNA. The data suggest that DNA radiosensization by cisplatin results not only from the sensitization of DNA to the action of LEE, but also from an increase the production of LEE at the site of binding of the cisplatin. The results provide new insights into the mechanisms of cisplatin-induced sensitization of DNA under X-ray irradiation, which could be helpful in the design of new cisplatin-based antitumor drugs.

  16. Development of a method to accurately calculate the Dpb and quickly predict the strength of a chemical bond

    NASA Astrophysics Data System (ADS)

    Du, Xia; Zhao, Dong-Xia; Yang, Zhong-Zhi

    2013-02-01

    A new approach to characterize and measure bond strength has been developed. First, we propose a method to accurately calculate the potential acting on an electron in a molecule (PAEM) at the saddle point along a chemical bond in situ, denoted by Dpb. Then, a direct method to quickly evaluate bond strength is established. We choose some familiar molecules as models for benchmarking this method. As a practical application, the Dpb of base pairs in DNA along C-H and N-H bonds are obtained for the first time. All results show that C7-H of A-T and C8-H of G-C are the relatively weak bonds that are the injured positions in DNA damage. The significance of this work is twofold: (i) A method is developed to calculate Dpb of various sizable molecules in situ quickly and accurately; (ii) This work demonstrates the feasibility to quickly predict the bond strength in macromolecules.

  17. Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)

    SciTech Connect

    Oshima, Yasuhiro; Sun, Yun; Kuzum, Duygu; Sugawara, Takuya; Saraswat, Krishna C.; Pianetta, Piero; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.

    2008-10-31

    Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.

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

    PubMed

    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.

  19. Effect of surface moisture on chemically bonded phosphor for thermographic phosphor thermometry

    NASA Astrophysics Data System (ADS)

    Cai, Tao; Kim, Dong; Kim, Mirae; Liu, Ying Zheng; Kim, Kyung Chun

    2016-09-01

    This study examined the effect of surface moisture on the calibration lifetime in chemically bonded phosphor paint preparation. Mg4FGeO6:Mn was used as a sensor material, which was excited by a pulsed UV LED. A high-speed camera with a frequency of 8000 Hz was used to conduct phosphor thermometry. Five samples with different degrees of surface moisture were selected during the preparation process, and each sample was calibrated 40 times at room temperature. A conventional post-processing method was used to acquire the phosphorescent lifetime for different samples with a 4  ×  4-pixel interrogation window. The measurement error and paint uniformity were also studied. The results showed that there was no obvious phosphorescence boundary between the wet parts and dry parts of phosphor paint. The lifetime increased by about 0.0345% per hour during the preparation process, showing the degree of surface moisture had almost no influence on the lifetime measurement. The lifetime changed only after annealing treatment. There was also no effect on the measurement error and uniformity. These results provide a reference for developing a real-time measurement method using thermographic phosphor thermometry. This study also provides a feasible basis for chemically bonded phosphor thermometry applications in humid and low-temperature environments.

  20. Chemical bonding and the equilibrium composition of Grignard reagents in ethereal solutions.

    PubMed

    Henriques, André M; Barbosa, André G H

    2011-11-10

    A thorough analysis of the electronic structure and thermodynamic aspects of Grignard reagents and its associated equilibrium composition in ethereal solutions is performed. Considering methylmagnesium halides containing fluorine, chlorine, and bromine, we studied the neutral, charged, and radical species associated with their chemical equilibrium in solution. The ethereal solvents considered, tetrahydrofuran (THF) and ethyl ether (Et(2)O), were modeled using the polarizable continuum model (PCM) and also by explicit coordination to the Mg atoms in a cluster. The chemical bonding of the species that constitute the Grignard reagent is analyzed in detail with generalized valence bond (GVB) wave functions. Equilibrium constants were calculated with the DFT/M06 functional and GVB wave functions, yielding similar results. According to our calculations and existing kinetic and electrochemical evidence, the species R(•), R(-), (•)MgX, and RMgX(2)(-) must be present in low concentration in the equilibrium. We conclude that depending on the halogen, a different route must be followed to produce the relevant equilibrium species in each case. Chloride and bromide must preferably follow a "radical-based" pathway, and fluoride must follow a "carbanionic-based" pathway. These different mechanisms are contrasted against the available experimental results and are proven to be consistent with the existing thermodynamic data on the Grignard reagent equilibria.

  1. Two functions of the density matrix and their relation to the chemical bond

    NASA Astrophysics Data System (ADS)

    Schmider, Hartmut L.; Becke, Axel D.

    2002-02-01

    We examine and compare two previously introduced functions of the one-particle density matrix that are suitable to represent its off-diagonal structure in a condensed form and that have illustrative connections to the nature of the chemical bond. One of them, the Localized-Orbital Locator (LOL) [J. Molec. Struct. (THEOCHEM) 527, 51 (2000)], is based only on the noninteracting kinetic-energy density τ and the charge density ρ at a point, and gives an intuitive measure of the relative speed of electrons in its vicinity. Alternatively, LOL focuses on regions that are dominated by single localized orbitals. The other one, the Parity Function P [J. Chem. Phys. 105, 11134 (1996)], is a section through the Wigner phase-space function at zero momentum, and contains information about the phase of the interference of atomiclike orbital contributions from bound centers. In this paper, we discuss the way in which these functions condense information in the density matrix, and illustrate on a variety of examples of unusual chemical bonds how they can help to understand the nature of "covalence."

  2. Stabilization of hazardous ash waste with newberyite-rich chemically bonded magnesium phosphate ceramic

    SciTech Connect

    Wagh, A.S.; Singh, D.; Jeong, S.Y.

    1995-11-01

    A novel newberyite-rich magnesium-phosphate ceramic, intended for the stabilization of the US Department of Energy`s low-level mixed-waste streams, has been developed by an acid-base reaction between magnesium oxide and a phosphoric acid solution. The reaction slurry, formed at room temperature, sets rapidly and forms a lightweight hard ceramic with low open porosity and a high compression strength of {approx} 6,200 psi. It is a composite of stable mineral phases of newberyite, luenebergite, and residual Mg oxide. Using this matrix, the authors developed superior waste forms for a surrogate ash waste stream. The final waste form is a low-permeability structural-quality ceramic, in which hazardous contaminants are chemically fixed and physically encapsulated. The compression strength of the waste form is an order of magnitude higher than the land disposal requirement, even at high waste loading. The high compression strength is attributed to stronger bonds in the waste form that result from participation of ash waste in the setting reactions. Long-term leaching studies show that the waste form is stable in an aqueous environment. The chemically bonded phosphate ceramic approach in this study may be a simple, inexpensive, and efficient method for fabricating high-performance waste forms either for stabilizing waste streams or for developing value-added construction materials from high-volume benign waste streams.

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

    PubMed

    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.

  4. Electronic structure and anisotropic chemical bonding in TiNF from ab initio study

    SciTech Connect

    Matar, Samir F.

    2012-01-15

    Accounting for disorder in anatase titanium nitride fluoride TiNF is done through atoms re-distributions based on geometry optimizations using ultra soft pseudo potentials within density functional theory DFT. The fully geometry relaxed structures are found to keep the body centering of anatase (I4{sub 1}/amd No. 141). The new structural setups are identified with space groups I-4m2 No. 119 and Imm2 No. 44 which obey the 'group to subgroup' relationships with respect to anatase. In the ground state Imm2 structure identified from energy differences, TiNF is found semi-conducting with similar density of states features to anatase TiO{sub 2} and a chemical bonding differentiated between covalent like Ti-N versus ionic like Ti-F. Inter-anion N-F bonding is also identified. - Graphical Abstract: The geometry optimized ground state anatase derived TiNF structure with arrangement of open faceted TiN3F3 distorted octahedra. The insert shows the arrangement of octahedra in anatase TiO{sub 2}. Highlights: Black-Right-Pointing-Pointer Original approach of TiNF structure for addressing the electronic band structure. Black-Right-Pointing-Pointer Based on anatase, two different ordering scheme models with geometry optimization. Black-Right-Pointing-Pointer New structures obeying the group{yields}subgroup relationships with Imm2 ground state from energy. Black-Right-Pointing-Pointer In the ground state TiNF is found semi-conducting with similar density of states to anatase TiO{sub 2}. Black-Right-Pointing-Pointer Chemical bonding differentiated between covalent like Ti-N and ionic Ti-F.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Wilkerson, Marianne Perry

    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.

  7. Effect of ultraviolet light irradiation and sandblasting treatment on bond strengths between polyamide and chemical-cured resin.

    PubMed

    Asakawa, Yuya; Takahashi, Hidekazu; Iwasaki, Naohiko; Kobayashi, Masahiro

    2014-01-01

    The aim of this study was to evaluate the effects of ultraviolet light (UV) irradiation and sandblasting treatment on the shear bond strength between polyamide and chemical-cured resin. Three types of commercial polyamides were treated using UV irradiation, sandblasting treatment, and a combining sandblasting and UV irradiation. The shear bond strength was measured and analyzed using the Kruskal-Wallis test (α=0.05). Comparing shear bond strengths without surface treatment, from 4.1 to 5.7 MPa, the UV irradiation significantly increased the shear bond strengths except for Valplast, whose shear bond strengths ranged from 5.2 to 9.3 MPa. The sandblasting treatment also significantly increased the shear bond strengths (8.0 to 11.4 MPa). The combining sandblasting and UV irradiation significantly increased the shear bond strengths (15.2 to 18.3 MPa) comparing without surface treatment. This combined treatment was considered the most effective at improving the shear bond strength between polyamide and chemical-cured resin.

  8. Simultaneous determination of interfacial molarities of amide bonds, carboxylate groups, and water by chemical trapping in micelles of amphiphiles containing peptide bond models.

    PubMed

    Zhang, Yongliang; Romsted, Laurence S; Zhuang, Lanzhen; de Jong, Sander

    2013-01-15

    Chemical trapping is a powerful approach for obtaining experimental estimates of interfacial molarities of weakly basic nucleophiles in the interfacial regions of amphiphile aggregates. Here, we demonstrate that the chemical probe 4-hexadecyl-2,6-dimethylbenzenediazonium ion (16-ArN(2)(+)) reacts competitively with interfacial water, with the amide carbonyl followed by cleavage of the headgroups from the tail at the amide oxygen, and with the terminal carboxylate groups in micelles of two N-acyl amino-acid amphiphiles, sodium N-lauroylsarcosinate (SLS) and sodium N-lauroylglycinate (SLG), simple peptide bond model amphiphiles. Interfacial molarities (in moles per liter of interfacial volume) of these three groups were obtained from product yields, assuming that selectivity toward a particular nucleophile compared to water is the same in an aqueous reference solution and in the interfacial region. Interfacial carboxylate group molarities are ~1.5 M in both SLS and SLG micelles, but the concentration of the amide carbonyl for SLS micelles is ~4.6-5 times less (ca. 0.7 M) than that of SLG micelles (~3 M). The proton on the secondary N of SLG helps solubilize the amide bond in the aqueous region, but the methyl on the tertiary N of SLS helps solubilize the amide bond in the micellar core, reducing its reaction with 16-ArN(2)(+). Application of chemical trapping to proteins in membrane mimetic interfaces should provide insight into the topology of the protein within the interface because trapping of the amide carbonyl and cleavage at the C-N bond occurs only within the interface, and fragment characterization marks those peptide bonds located within the interface.

  9. Theory of chemical bonds in metalloenzymes IV: Hybrid-DFT study of Rieske-type [2Fe bond 2S] clusters

    NASA Astrophysics Data System (ADS)

    Shoji, Mitsuo; Koizumi, Kenichi; Kitagawa, Yasutaka; Yamanaka, Shusuke; Okumura, Mitsutaka; Yamaguchi, Kizashi

    The Rieske-type [2Fe bond 2S] cores of electron-transfer (ET) proteins in the mitochondrial respiratory chain have unusual properties, such as redox potentials and spectroscopy. In this study, part IV of a series, the inherent molecular structures and characteristic electronic structures of the Rieske-type [2Fe bond 2S] clusters are investigated using broken-symmetry hybrid density functional theory (BS-HDFT). Geometry optimizations for the oxidized and reduced states were performed and their characteristic vibrational modes are assigned. Magnetic properties are investigated using model Hamiltonians to describe the electron delocalization and the unsymmetric property. The parameters of the model Hamiltonian, such as exchange coupling J, valence delocalization B, and potential energy difference ?, are evaluated from the BS-HDFT calculations. The valence localization and excitation energy (?E) of the Rieske-type [2Fe bond 2S] cluster are discussed. The chemical bond nature is characterized by chemical indices from natural orbital analysis. Our theoretical results are reasonably consistent with experimental results.

  10. Halogen-enriched fragment libraries as chemical probes for harnessing halogen bonding in fragment-based lead discovery.

    PubMed

    Zimmermann, Markus O; Lange, Andreas; Wilcken, Rainer; Cieslik, Markus B; Exner, Thomas E; Joerger, Andreas C; Koch, Pierre; Boeckler, Frank M

    2014-04-01

    Halogen bonding has recently experienced a renaissance, gaining increased recognition as a useful molecular interaction in the life sciences. Halogen bonds are favorable, fairly directional interactions between an electropositive region on the halogen (the σ-hole) and a number of different nucleophilic interaction partners. Some aspects of halogen bonding are not yet understood well enough to take full advantage of its potential in drug discovery. We describe and present the concept of halogen-enriched fragment libraries. These libraries consist of unique chemical probes, facilitating the identification of favorable halogen bonds by sharing the advantages of classical fragment-based screening. Besides providing insights into the nature and applicability of halogen bonding, halogen-enriched fragment libraries provide smart starting points for hit-to-lead evolution.

  11. Comparison of Marginal Gap and Microleakage in Copy-Milled and Cad-Milled Zirconia Copings Bonded Using Light Cure and Chemical Cure Resin Bonding Systems.

    PubMed

    Shetty, Manoj; Rajalakshmi, S; Krishna Prasad, D

    2014-12-01

    This in vitro study assessed the marginal gap and marginal microleakage in zirconia copings fabricated using two computer aided techniques- CAD milling and Copy milling and cemented to respective tooth preparations using two resin bonding systems, light cure and self-cure resin bonding systems. 32 extracted premolars were prepared to receive zirconia copings fabricated using CAD/CAM and Copy milling techniques. Once the copings were fabricated, the samples were evaluated for marginal fit prior to cementation through microscopic observation. Evaluation of marginal gap was done again after cementation, in order to incorporate the influence of the resin bonding system on the marginal microgap. The specimens were evaluated under the stereomicroscope for micro-leakage using commercial software. A comparative statistical analysis was done following data collection using Mann-Whitney U test, Wilcoxon test and chi-square test. The data collected regarding marginal gap was well within 120 µ, which is in accordance with previous studies. However, Copy milled specimens showed statistically lesser marginal gap when compared to CAD milled specimens. While comparing microleakage, it was observed that the microleakage in Copy milled specimens bonded with light cure resin bonded cement was statistically lesser than that of specimens cemented with chemical cure resin cement.(P = 0.003). This in vitro study concluded that Copy milling technique fabricated zirconia restorations with lesser marginal gap and microleakage score in comparison to CAD milled samples. Light cure resin bonding system also proved to be more effective option compared to self cure resin bonding systems. However, the limitations of this study should be taken into concern and further research should be aimed at a larger sample size to validate the results.

  12. Investigation of 1H NMR chemical shifts of organic dye with hydrogen bonds and ring currents.

    PubMed

    Park, Sung Soo; Won, Yong Sun; Lee, Woojin; Kim, Jae Hong

    2011-04-07

    The (1)H NMR chemical shifts were theoretically computed for the organic dyes 2-(2,6-dimethyl-4H-pyran-4-ylidene)-malononitrile (1), cyano-(2,6-dimethyl-4H-pyran-4-ylidene)-acetic acid methyl ester (2), 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-malononitrile (3), and methyl 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (4) at the GIAO/B3LYP/6-311++G(d,p)//B3LYP/6-311++G(d,p) level of theory. Moreover, the intramolecular rotational barriers of the molecules were calculated to evaluate the internal flexibility with respect to the torsional degrees of freedom, and the nuclear-independent chemical shifts (NICS) were employed to analyze the ring currents. The difference was explained in terms of intramolecular hydrogen bonds and ring currents of the molecules. The (1)H NMR spectra were reproduced by experiments for the comparison with computationally constructed data. Our results suggest a good guideline in interpreting (1)H NMR chemical shifts using computational methods and furthermore a reliable perspective for designing molecular structures.

  13. New chemical insights using weakly supported voltammetry: the reductive cleavage of Aryl-Br bonds is reversible.

    PubMed

    Wang, Yijun; Barnes, Edward O; Compton, Richard G

    2012-10-22

    Cyclic voltammetry carried out at a wide range of supporting electrolyte concentrations and compositions can elucidate additional kinetic and mechanistic details of the electrochemical reduction of aryl halides. The cleavage of the C-Br bond is reversible, driven by H abstraction and the second electron transfer. This is a new chemical insight, as the cleavage of such bonds has usually been regarded as irreversible.

  14. Theoretical Prediction of Hydrogen-Bond Basicity pKBHX Using Quantum Chemical Topology Descriptors

    PubMed Central

    2014-01-01

    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. PMID:24460383

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

    PubMed

    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.

  16. Effects of hydrogen bonding on amide-proton chemical shift anisotropy in a proline-containing model peptide

    NASA Astrophysics Data System (ADS)

    Pichumani, Kumar; George, Gijo; Hebbar, Sankeerth; Chatterjee, Bhaswati; Raghothama, Srinivasarao

    2015-05-01

    Longitudinal relaxation due to cross-correlation between dipolar (1HN-1Hα) and amide-proton chemical shift anisotropy (1HN CSA) has been measured in a model tripeptide Piv-LPro-LPro-LPhe-OMe. The peptide bond across diproline segment is known to undergo cis/trans isomerization and only in the cis form does the lone Phe amide-proton become involved in intramolecular hydrogen bonding. The strength of the cross correlated relaxation interference is found to be significantly different between cis and trans forms, and this difference is shown as an influence of intramolecular hydrogen bonding on the amide-proton CSA.

  17. Charge distribution and chemical bonding in B-O complexes in Cz-Si solar cells

    NASA Astrophysics Data System (ADS)

    Mao, Yuliang; Caliste, Damien; Pochet, Pascal

    2013-10-01

    Density functional calculations based on wavelet basis set are performed to investigate charge distribution and chemical bonding in possible BiOi (interstitial boron and interstitial oxygen), BsO2i (substitutional boron and interstitial oxygen dimer), and BiO2i (interstitial boron and interstitial oxygen dimer) complexes in Cz-Si solar cells. It is confirmed that the BsO2ist complex composed by Bs and staggered oxygen dimer (O2ist) at second nearest site to boron has the lowest formation energy, resulting in better agreement with experiment. This is resulted by Coulomb attraction between Si-Oi and Si-Bs and consequently a decreased Coulomb repulsion between Bs-Oi in BsO2ist complex. A more physical description of the localized nature on bonding has been analyzed by maximally localized Wannier functions. It is found through the predicted Wannier centers that a doubly negative charge state of interstitial oxygen exists, which is consistent with our Bader charge analysis.

  18. Precession technique and electron diffractometry as new tools for crystal structure analysis and chemical bonding determination.

    PubMed

    Avilov, A; Kuligin, K; Nicolopoulos, S; Nickolskiy, M; Boulahya, K; Portillo, J; Lepeshov, G; Sobolev, B; Collette, J P; Martin, N; Robins, A C; Fischione, P

    2007-01-01

    We have developed a new fast electron diffractometer working with high dynamic range and linearity for crystal structure determinations. Electron diffraction (ED) patterns can be scanned serially in front of a Faraday cage detector; the total measurement time for several hundred ED reflections can be tens of seconds having high statistical accuracy for all measured intensities (1-2%). This new tool can be installed to any type of TEM without any column modification and is linked to a specially developed electron beam precession "Spinning Star" system. Precession of the electron beam (Vincent-Midgley technique) reduces dynamical effects allowing also use of accurate intensities for crystal structure analysis. We describe the technical characteristics of this new tool together with the first experimental results. Accurate measurement of electron diffraction intensities by electron diffractometer opens new possibilities not only for revealing unknown structures, but also for electrostatic potential determination and chemical bonding investigation. As an example, we present detailed atomic bonding information of CaF(2) as revealed for the first time by precise electron diffractometry.

  19. Formation of chemical bonds and morphological studies of a-CNx : Effects of PECVD deposition pressure

    NASA Astrophysics Data System (ADS)

    Purhanudin, Noorain; Awang, Rozidawati

    2016-11-01

    We report the structural difference and film properties of amorphous carbon nitride (a-CNx) thin films as a function of PECVD deposition pressure using precursor gases of ethane (C2H6) and nitrogen (N2). The Fourier transform infra-red (FTIR) spectra reveal peaks of single C-N (1100 cm-1), double C=C (1500 cm-1), double C=N (1670 cm-1) and triple C≡N (2340 cm-1). A systematic change in the preferential peaks correspond to the C=N and C≡N triple bonds were found to increase as deposition pressure increased. Field emission scanning electron microscopy (FESEM) provides morphological structure of the film. From the samples prepare at low deposition pressure, the particles tend to agglomerate into clusters with non-homogenous grains distributed over the surface. Higher deposition pressure results in coalescence process of the film, reflecting the formation of grains evenly distributed on the film. The film morphology is increased in voids structure with increase in deposition pressure. Finally, the samples were successfully prepared by PECVD technique with deposition pressure in varied, and the effect of deposition pressure on the chemical bonding and the morphology of the films had been studied.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    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.

  3. Collision-free spatial hash functions for structural analysis of billion-vertex chemical bond networks

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Bansal, Bhupesh; Branicio, Paulo S.; Kalia, Rajiv K.; Nakano, Aiichiro; Sharma, Ashish; Vashishta, Priya

    2006-09-01

    State-of-the-art molecular dynamics (MD) simulations generate massive datasets involving billion-vertex chemical bond networks, which makes data mining based on graph algorithms such as K-ring analysis a challenge. This paper proposes an algorithm to improve the efficiency of ring analysis of large graphs, exploiting properties of K-rings and spatial correlations of vertices in the graph. The algorithm uses dual-tree expansion (DTE) and spatial hash-function tagging (SHAFT) to optimize computation and memory access. Numerical tests show nearly perfect linear scaling of the algorithm. Also a parallel implementation of the DTE + SHAFT algorithm achieves high scalability. The algorithm has been successfully employed to analyze large MD simulations involving up to 500 million atoms.

  4. Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3.

    PubMed

    Stashans, Arvids; Chamba, Gaston; Pinto, Henry

    2008-02-01

    The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures.

  5. Method for producing chemically bonded phosphate ceramics and for stabilizing contaminants encapsulated therein utilizing reducing agents

    DOEpatents

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

    2000-01-01

    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 are 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.

  6. Dynamics of chemical bonding mapped by energy-resolved 4D electron microscopy.

    PubMed

    Carbone, Fabrizio; Kwon, Oh-Hoon; Zewail, Ahmed H

    2009-07-10

    Chemical bonding dynamics are fundamental to the understanding of properties and behavior of materials and molecules. Here, we demonstrate the potential of time-resolved, femtosecond electron energy loss spectroscopy (EELS) for mapping electronic structural changes in the course of nuclear motions. For graphite, it is found that changes of milli-electron volts in the energy range of up to 50 electron volts reveal the compression and expansion of layers on the subpicometer scale (for surface and bulk atoms). These nonequilibrium structural features are correlated with the direction of change from sp2 [two-dimensional (2D) graphene] to sp3 (3D-diamond) electronic hybridization, and the results are compared with theoretical charge-density calculations. The reported femtosecond time resolution of four-dimensional (4D) electron microscopy represents an advance of 10 orders of magnitude over that of conventional EELS methods.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    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.

  9. The variational subspace valence bond method.

    PubMed

    Fletcher, Graham D

    2015-04-07

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented.

  10. The variational subspace valence bond method

    SciTech Connect

    Fletcher, Graham D.

    2015-04-07

    The variational subspace valence bond (VSVB) method based on overlapping orbitals is introduced. VSVB provides variational support against collapse for the optimization of overlapping linear combinations of atomic orbitals (OLCAOs) using modified orbital expansions, without recourse to orthogonalization. OLCAO have the advantage of being naturally localized, chemically intuitive (to individually model bonds and lone pairs, for example), and transferrable between different molecular systems. Such features are exploited to avoid key computational bottlenecks. Since the OLCAO can be doubly occupied, VSVB can access very large problems, and calculations on systems with several hundred atoms are presented.

  11. Shake for Sigma, Pray for Pi: Classroom Orbital Overlap Analogies

    ERIC Educational Resources Information Center

    Dicks, Andrew P.

    2011-01-01

    An introductory organic classroom demonstration is discussed where analogies are made between common societal hand contact and covalent bond formation. A handshake signifies creation of a [sigma] bond ("head-on" orbital overlap), whereas the action of praying illustrates "sideways" overlap and generation of a [pi] bond. The nature of orbital and…

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. On the chemical bonding effects in the Raman response: benzenethiol adsorbed on silver clusters.

    PubMed

    Saikin, Semion K; Olivares-Amaya, Roberto; Rappoport, Dmitrij; Stopa, Michael; Aspuru-Guzik, Alán

    2009-11-07

    We study the effects of chemical bonding on Raman scattering from benzenethiol chemisorbed on silver clusters using time-dependent density functional theory (TDDFT). Raman scattering cross sections are computed using a formalism that employs analytical derivatives of frequency-dependent electronic polarizabilities, which treats both off-resonant and resonant enhancement within the same scheme. In the off-resonant regime, Raman scattering into molecular vibrational modes is enhanced by one order of magnitude and shows pronounced dependence on the orientation and the local symmetry of the molecule. Additional strong enhancement of the order of 10(2) arises from resonant transitions to mixed metal-molecular electronic states. The Raman enhancement is analyzed using Raman excitation profiles (REPs) for the range of excitation energies 1.6-3.0 eV, in which isolated benzenethiol does not have electronic transitions. The computed vibrational frequency shifts and relative Raman scattering cross sections of the metal-molecular complexes are in good agreement with experimental data on surface enhanced Raman scattering (SERS) from benzenethiol adsorbed on silver surfaces. Characterization and understanding of these effects, associated with chemical enhancement mechanism, may be used to improve the detection sensitivity in molecular Raman scattering.

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

    SciTech Connect

    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.

  16. Atmospheric Black Carbon: Chemical Bonding and Structural Information of Individual Aerosol Particles

    NASA Astrophysics Data System (ADS)

    Gilles, M. K.; Tivanski, A. V.; Hopkins, R. J.; Marten, B. D.

    2006-12-01

    The formation of aerosols from both natural and anthropogenic sources affects the Earth's temperature and climate by altering the radiative properties of the atmosphere. Aerosols containing black carbon (BC) that are released into the atmosphere from the burning of biomass, natural fires and the combustion of coals, diesel and jet fuels, contribute a large positive component to this radiative forcing, thus causing a heating of the atmosphere. A distinct type of biomass burn aerosol referred to as "tar balls" has recently been reported in the literature and is characterized by a spherical morphology, high carbon content and ability to efficiently scatter and absorb light. At present, very little is known about the exact nature and variation of the range of BC aerosols in the atmosphere with regards to optical, chemical and physical properties. Additionally, the similarity of these aerosols to surrogates used in the laboratory as atmospheric mimics remains unclear. The local chemical bonding, structural ordering and carbon-to-oxygen ratios of a plethora of black carbon standard reference materials (BC SRMs), high molecular mass humic-like substances (HULIS) and atmospheric aerosols from a variety of sources are examined using scanning transmission X-ray microscopy (STXM) coupled with near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STXM/NEXAFS enables single aerosol particles of diameter upwards of 100 nm to be studied, which allows the diversity of atmospheric aerosol collected during a variety of field missions to be assessed. We apply a semi-quantitative peak fitting method to the recorded NEXAFS spectral fingerprints allowing comparison of BC SRMs and HULIS to BC aerosol originating from anthropogenic combustion and biomass burning events. This method allows us to distinguish between anthropogenic combustion and biomass burn aerosol using both chemical bonding and structural ordering information. The STXM/NEXAFS technique has also been utilized to

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

    PubMed

    Meng, X F; Yoshida, K; Gu, N

    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&B) were used. The data for each silane/cement system were analyzed by three-way ANOVA. HFA treatment significantly increased the surface R(a) and R(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 coupler

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

    SciTech Connect

    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

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

    PubMed

    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

  20. Energetics and chemical bonding of the 1,3,5-tridehydrobenzene triradical and its protonated form

    NASA Astrophysics Data System (ADS)

    Nguyen, Hue Minh Thi; Höltzl, Tibor; Gopakumar, G.; Veszprémi, Tamás; Peeters, Jozef; Nguyen, Minh Tho

    2005-09-01

    Quantum chemical calculations were applied to investigate the electronic structure of the parent 1,3,5-tridehydrobenzene triradical (C 6H 3, TDB) and its anion (C6H3-), cation (C6H3+) and protonated form (C6H4+). Our results obtained using the state-averaged complete active space self-consistent-field (CASSCF) followed by second-order multi-state multi-configuration perturbation theory, MS-CASPT2, and MRMP2 in conjunction with the large ANO-L and 6-311++G(3df,2p) basis set, confirm and reveal the followings: (i) TDB has a doublet 2A 1 ground state with a 4B 2- 2A 1 energy gap of 29 kcal/mol, (ii) the ground state of the C6H3- anion in the triplet 3B 2 being 4 kcal/mol below the 1A 1 state. (iii) the electron affinity (EA), ionization energy (IE) and proton affinity (PA) are computed to be: EA = 1.6 eV, IE = 7.2 eV, PA = 227 kcal/mol using UB3LYP/6-311++G(3df,2p) + ZPE; standard heat of formation Δ Hf(298 K, 1 atm) (TDB) = 179 ± 2 kcal/mol was calculated with CBS-QB3 method. An atoms-in-molecules (AIM) analysis of the structure reveals that the topology of the electron density is similar in all compounds: hydrogens connect to a six-membered ring, except for the case of the 2A 2 state of C6H4+ (MBZ +) which is bicyclic with fused five- and three-membered rings. Properties of the chemical bonds were characterized with Electron Localization Function (ELF) analysis, as well as Wiberg indices, Laplacian and spin density maps. We found that the radicals form separate monosynaptic basins on the ELF space, however its pair character remains high. In the 2A 1 state of TDB, the radical center is mainly localized on the C1 atom, while in the 2B 2 state it is equally distributed between the C3 and C5 atoms and, due to the symmetry, in the 4B 2 state the C1, C2 and C3 atoms have the same radical character. There is no C3-C5 bond in the 2A 1 state of TDB, but the interaction between these atoms is strong. The ground state of cation C6H3+ (DHP), 1A 1, is not a diradical and has

  1. Real-space imaging of molecular structure and chemical bonding by single-molecule inelastic tunneling probe.

    PubMed

    Chiang, Chi-lun; Xu, Chen; Han, Zhumin; Ho, W

    2014-05-23

    The arrangement of atoms and bonds in a molecule influences its physical and chemical properties. The scanning tunneling microscope can provide electronic and vibrational signatures of single molecules. However, these signatures do not relate simply to the molecular structure and bonding. We constructed an inelastic tunneling probe based on the scanning tunneling microscope to sense the local potential energy landscape of an adsorbed molecule with a carbon monoxide (CO)-terminated tip. The skeletal structure and bonding of the molecule are revealed from imaging the spatial variations of a CO vibration as the CO-terminated tip probes the core of the interactions between adjacent atoms. An application of the inelastic tunneling probe reveals the sharing of hydrogen atoms among multiple centers in intramolecular and extramolecular bonding.

  2. Prediction of the Intrinsic Hydrogen Bond Acceptor Strength of Chemical Substances from Molecular Structure

    NASA Astrophysics Data System (ADS)

    Schwöbel, Johannes; Ebert, Ralf-Uwe; Kühne, Ralph; Schüürmann, Gerrit

    2009-08-01

    Hydrogen bonding affects the partitioning of organic compounds between environmental and biological compartments as well as the three-dimensional shape of macromolecules. Using the semiempirical quantum chemical AM1 level of calculation, we have developed a model to predict the site-specific hydrogen bond (HB) acceptor strength from ground-state properties of the individual compounds. At present, the model parametrization is confined to compounds with one HB acceptor site of the following atom types: N, O, S, F, Cl, and Br that act as lone-pair HB acceptors, and π-electron (aromatic or conjugated) systems with the associated C atoms as particularly weak HB acceptors. The HB acceptor strength is expressed in terms of the Abraham parameter B and calculated from local molecular parameters, taking into account electrostatic, polarizability, and charge transfer contributions according to the Morokuma concept. For a data set of 383 compounds, the squared correlation coefficient r2 is 0.97 when electrostatic potential (ESP) derived net atomic charges are employed, and the root-mean-square (rms) error is 0.04 that is in the range of experimental uncertainty. The model is validated using an extended leave-50%-out approach, and its performance is comparatively analyzed with the ones of earlier introduced ab initio (HF/6-31G**) and density functional theory (B3LYP/6-31G**) models as well as of two increment methods with respect to the total compound set as well as HB acceptor type subsets. The discussion includes an explorative model application to amides and organophosphates that demonstrates the robustness of the approach, and further opportunities for model extensions.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

  5. Hydrolytic stability of the Si-O-Ti bonds in the chemical assembly of titania nanostructures on silica surfaces

    NASA Astrophysics Data System (ADS)

    Sosnov, Evgeni A.; Malkov, A. A.; Malygin, A. A.

    2010-12-01

    The hydrolytic stability of the Si-O-Ti bonds in titania nanostructures on the surface of silica materials of different genesis is analyzed. The mechanism of hydrolysis is considered and the decisive role of structural and chemical features of silicas in the stability of titania nanostructures on their surface is demonstrated.

  6. Enhancing Students' Understanding of the Concept of "Chemical Bonding" by Using Activities Provided on an Interactive Website

    ERIC Educational Resources Information Center

    Frailich, Marcel; Kesner, Miri; Hofstein, Avi

    2009-01-01

    This study investigated the effectiveness of a web-based learning environment in enhancing 10th grade high-school students' understanding of the concept of "chemical bonding". Two groups participated in this study: an experimental group (N = 161) and a comparison one (N = 93). The teachers in the experimental group were asked to implement four…

  7. Learning about Atoms, Molecules, and Chemical Bonds: A Case Study of Multiple-Model Use in Grade 11 Chemistry.

    ERIC Educational Resources Information Center

    Harrison, Allan G.; Treagust, David F.

    2000-01-01

    Reports in detail on a year-long case study of multiple-model use at grade 11. Suggests that students who socially negotiated the shared and unshared attributes of common analogical models for atoms, molecules, and chemical bonds used these models more consistently in their explanations. (Author/CCM)

  8. A Review of Chemical Bonding Studies: Needs, Aims, Methods of Exploring Students' Conceptions, General Knowledge Claims and Students' Alternative Conceptions

    ERIC Educational Resources Information Center

    Unal, Suat; Calik, Muammer; Ayas, Alipasa; Coll, Richard K.

    2006-01-01

    The present paper presents a detailed thematic review of chemical bonding studies. To achieve this, a matrix is developed to summarize and present the findings by focusing on insights derived from the related studies. The matrix incorporates the following themes: needs, aims, methods of exploring students' conceptions, general knowledge claims,…

  9. Chemical bonding, optical constants, and electrical resistivity of sputter-deposited gallium oxide thin films

    SciTech Connect

    Ramana, C. V. Rubio, E. J.; Barraza, C. D.; Miranda Gallardo, A.; McPeak, Samantha; Kotru, Sushma; Grant, J. T.

    2014-01-28

    Gallium oxide (Ga{sub 2}O{sub 3}) thin films were made by sputter deposition employing a Ga{sub 2}O{sub 3} ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (T{sub s}), from 25 to 600 °C. The effect of T{sub s} on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p{sub 3/2} and Ga 2p{sub 1/2} peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga{sup 3+}) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE ∼ 531 eV, which is also characteristic of Ga-O bonds in the Ga{sub 2}O{sub 3} phase. The granular morphology of the nanocrystalline Ga{sub 2}O{sub 3} films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5 nm to 3.0 nm with increasing T{sub s}. The SE analyses indicate that the index of refraction (n) of Ga{sub 2}O{sub 3} films increases with increasing T{sub s} due to improved structural quality and packing density of the films. The n(λ) of all the Ga{sub 2}O{sub 3} films follows the Cauchy's dispersion relation. The room temperature electrical resistivity was high (∼200 Ω-cm) for amorphous Ga{sub 2}O{sub 3} films grown at T{sub s} = RT-300 °C and decreased to ∼1 Ω-cm for nanocrystalline Ga{sub 2}O{sub 3} films grown at T{sub s} ≥ 500–600 °C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga{sub 2}O{sub 3} films is derived.

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

    PubMed

    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. On The Electronic Structure and Chemical Bonding in the Tantalum Trimer Cluster

    SciTech Connect

    Wang, Xue B.; Zhai, Hua Jin; Huang, Xin; Wang, Lai S.

    2008-10-03

    The electronic structure and chemical bonding in the Ta3- cluster are investigated using photoelectron spectroscopy and density functional theory calculations. Photoelectron spectra are obtained for Ta3- at four photon energies: 532, 355, 266 and 193 nm. While congested spectra are observed at high electron binding energies, several low-lying electronic transitions are well resolved and compared with the theoretical calculations. The electron affinity of Ta3 is determined to be 1.35±0.03 eV. Extensive density functional calculations are performed at the B3LYP/Stuttgart +2f1g level to locate the ground state and low-lying isomers for Ta3 and Ta3-. The ground state for the Ta3- anion is shown to be a quintet (5A1') with D3h symmetry, whereas two nearly isoenergetic states, C2v (4A1) and D3h (6A1'), are found to compete for the ground state for neutral Ta3. A detailed molecular orbital analysis is performed to elucidate the chemical boding in Ta3-, which is found to possess multiple d-orbital aromaticity, commensurate with its highly symmetric D3h structure.

  12. Development of a Fundamental Understanding of Chemical Bonding and Electronic Structure in Spinel Compounds

    SciTech Connect

    Sickafus, K.E.; Wills, J.M.; Chen, S.-P.; Terry, J.H., Jr.; Hartmann, T.; Sheldon, R.I.

    1999-05-14

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos national Laboratory (LANL). Hundreds of ceramic compounds possess the spinel crystal structure and exhibit a remarkable variety of properties, ranging from compounds that are electrical insulators to compounds that are superconducting, or from compounds with ferri- and antiferromagnetic behavior to materials with colossal magnetoresistive characteristics. The unique crystal structure of spinel compounds is in many ways responsible for the widely varying physical properties of spinels. The objective of this project is to investigate the nature of chemical bonding, point defects, and electronic structure in compounds with the spinel crystal structure. Our goal is to understand and predict the stability of the spinel structure as a function of chemical composition, stoichiometry, and cation disorder. The consequences of cation disorder in spinel materials can be profound . The ferromagnetic characteristics of magnesioferrite, for instance, are entirely attributable to disorder on the cation sublattices. Our studies provide insight into the mechanisms of point defect formation and cation disorder and their effects on the electronic band structure and crystal structure of spinel-structure materials. our ultimate objective is to develop a more substantive knowledge of the spinel crystal structure and to promote new and novel uses for spinel compounds. The technical approach to achieve our goals is to combine first-principles calculations with experimental measurements. The structural and electronic properties of spinel samples were experimentally determined primarily with X-ray and neutron scattering, optical and X-ray absorption, and electron energy-loss spectroscopy. Total energy electronic structure calculations were performed to determine structural stability, band structure, density of states, and electron distribution. We also used shell

  13. Development of a Fundamental Understanding of Chemical Bonding and Electronic Structure in Spinel Compounds

    SciTech Connect

    Sickafus, K.E.; Wills, J.M.; Chen, S.-P.; Terry, J.H., Jr.; Hartmann, T.; Sheldon, R.I.

    1999-06-03

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Hundreds of ceramic compounds possess the spinel crystal structure and exhibit a remarkable variety of properties, ranging from compounds that are electrical insulators to compounds that are superconducting, or from compounds with ferri- and antiferromagnetic behavior to materials with colossal magnetoresistive characteristics. The unique crystal structure of spinel compounds is in many ways responsible for the widely varying physical properties of spinels. The objective of this project is to investigate the nature of chemical bonding, point defects, and electronic structure in compounds with the spinel crystal structure. Our goal is to understand and predict the stability of the spinel structure as a function of chemical composition, stoichiometry, and cation disorder. The consequences of cation disorder in spinel materials can be profound . The ferromagnetic characteristics of magnesioferrite, for instance, are entirely attributable to disorder on the cation sublattices. Our studies provide insight into the mechanisms of point defect formation and cation disorder and their effects on the electronic band structure and crystal structure of spinel-structure materials. Our ultimate objective is to develop a more substantive knowledge of the spinel crystal structure and to promote new and novel uses for spinel compounds. The technical approach to achieve our goals is to combine first-principles calculations with experimental measurements. The structural and electronic properties of spinel samples were experimentally determined primarily with X-ray and neutron scattering, optical and X-ray absorption, and electron energy-loss spectroscopy. Total energy electronic structure calculations were performed to determine structural stability, band structure, density of states, and electron distribution. We also used shell

  14. Sticker Bonding.

    ERIC Educational Resources Information Center

    Frazier, Laura Corbin

    2000-01-01

    Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

  15. Principles of Chemical Bonding and Band Gap Engineering in Hybrid Organic–Inorganic Halide Perovskites

    PubMed Central

    2015-01-01

    The performance of solar cells based on hybrid halide perovskites has seen an unparalleled rate of progress, while our understanding of the underlying physical chemistry of these materials trails behind. Superficially, CH3NH3PbI3 is similar to other thin-film photovoltaic materials: a semiconductor with an optical band gap in the optimal region of the electromagnetic spectrum. Microscopically, the material is more unconventional. Progress in our understanding of the local and long-range chemical bonding of hybrid perovskites is discussed here, drawing from a series of computational studies involving electronic structure, molecular dynamics, and Monte Carlo simulation techniques. The orientational freedom of the dipolar methylammonium ion gives rise to temperature-dependent dielectric screening and the possibility for the formation of polar (ferroelectric) domains. The ability to independently substitute on the A, B, and X lattice sites provides the means to tune the optoelectronic properties. Finally, ten critical challenges and opportunities for physical chemists are highlighted. PMID:25838846

  16. Structural transformation with "negative volume expansion": chemical bonding and physical behavior of TiGePt.

    PubMed

    Ackerbauer, S-V; Senyshyn, A; Borrmann, H; Burkhardt, U; Ormeci, A; Rosner, H; Schnelle, W; Gamża, M; Gumeniuk, R; Ramlau, R; Bischoff, E; Schuster, J C; Weitzer, F; Leithe-Jasper, A; Tjeng, L H; Grin, Yu

    2012-05-14

    The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.

  17. Chemical bonding in excited states: Energy transfer and charge redistribution from a real space perspective.

    PubMed

    Jara-Cortés, Jesús; Guevara-Vela, José Manuel; Martín Pendás, Ángel; Hernández-Trujillo, Jesús

    2017-05-15

    This work provides a novel interpretation of elementary processes of photophysical relevance from the standpoint of the electron density using simple model reactions. These include excited states of H2 taken as a prototype for a covalent bond, excimer formation of He2 to analyze non-covalent interactions, charge transfer by an avoided crossing of electronic states in LiF and conical interesections involved in the intramolecular scrambling in C2 H4 . The changes of the atomic and interaction energy components along the potential energy profiles are described by the interacting quantum atoms approach and the quantum theory of atoms in molecules. Additionally, the topological analysis of one- and two-electron density functions is used to explore basic reaction mechanisms involving excited and degenerate states in connection with the virial theorem. This real space approach allows to describe these processes in a unified way, showing its versatility and utility in the study of chemical systems in excited states. © 2017 Wiley Periodicals, Inc.

  18. Coordination compounds of tetravalent silicon, germanium and tin: the structure, chemical bonding and intermolecular interactions in them

    NASA Astrophysics Data System (ADS)

    Korlyukov, A. A.

    2015-04-01

    The review is devoted to analysis and generalization of the results of (i) quantum chemical studies on the structure, chemical bonding and intermolecular interactions in coordination compounds of tetravalent silicon, germanium and tin in crystals, in solutions and in the gas phase and (ii) experimental investigations of the electron density distribution in these systems. The bibliography includes 147 references. In memoriam of Corresponding Member of the Russian Academy of Sciences M Yu Antipin (1951 - 2013), Academician of the Russian Academy of Sciences M G Voronkov (1921 - 2014) and Dr. S P Knyazev, Lomonosov Moscow University of Fine Chemical Technology (1949 - 2012).

  19. From Common Sense Concepts to Scientifically Conditioned Concepts of Chemical Bonding: An Historical and Textbook Approach Designed to Address Learning and Teaching Issues at the Secondary School Level

    ERIC Educational Resources Information Center

    Croft, Michael; de Berg, Kevin

    2014-01-01

    This paper selects six key alternative conceptions identified in the literature on student understandings of chemical bonding and illustrates how a historical analysis and a textbook analysis can inform these conceptions and lead to recommendations for improving the teaching and learning of chemical bonding at the secondary school level. The…

  20. Cutting a chemical bond with demon's scissors: Mode- and bond-selective reactivity of methane on metal surfaces

    NASA Astrophysics Data System (ADS)

    Lozano, A.; Shen, X. J.; Moiraghi, R.; Dong, W.; Busnengo, H. F.

    2015-10-01

    In this paper we discuss several aspects of methane reactive sticking on Pt(111) in the light of supersonic molecular beam experiments (including state-resolved measurements) and quasi-classical trajectory calculations based on an accurate reaction specific reactive force field constructed from Density Functional Theory (DFT) data. With the aim of understanding the origin of the full bond selectivity recently achieved experimentally and to predict how selectivity depends on the collision conditions, we discuss in detail, the role of initial translational and (mode-specific) vibrational energy of CH4 and all its deuterated isotopomers, as well as surface temperature effects. Last but not least, the systematic and detailed theoretical analysis presented here serves as an illustration of the possibilities and usefulness of accurate reaction specific reactive force fields built from DFT data. This approach allows investigating dynamical aspects of the interaction of polyatomic molecules on surfaces through quasi-classical trajectory calculations accounting for the full dimensionality of the system (including both molecular and surface degrees of freedom): something that a few years ago was just a dream for the gas-surface dynamics community.

  1. Proteolysis approach without chemical modification for a simple and rapid analysis of disulfide bonds using thermostable protease-immobilized microreactors.

    PubMed

    Yamaguchi, Hiroshi; Miyazaki, Masaya; Maeda, Hideaki

    2010-08-01

    Disulfide bonds in proteins are important not only for the conformational stability of the protein but also for the regulation of oxidation-reduction in signal transduction. The conventional method for the assignment of disulfide bond by chemical cleavage and/or proteolysis is a time-consuming multi-step procedure. In this study, we report a simple and rapid analysis of disulfide bond from protein digests that were prepared by the thermostable protease-immobilized microreactors. The feasibility and performance of this approach were evaluated by digesting lysozyme and BSA at several temperatures. The proteins which stabilize their conformations by disulfide bonds were thermally denatured during proteolysis and were efficiently digested by the immobilized protease but not by free protease. The digests were directly analyzed by ESI-TOF MS without any purification or concentration step. All four disulfide bonds on lysozyme and 10 of 17 on BSA were assigned from the digests by the trypsin-immobilized microreactor at 50 degrees C. The procedure for proteolysis and the assignment were achieved within 2 h without any reduction and alkylation procedure. From the present results, the proteolysis approach by the thermostable protease-immobilized microreactor provides a strategy for the high-throughput analysis of disulfide bond in proteomics.

  2. Insight into shock-induced chemical reaction from the perspective of ring strain and rotation of chemical bonds.

    PubMed

    Tan, Bisheng; Long, Xinping; Li, Jinshan; Nie, Fude; Huang, Jinglun

    2012-12-01

    Density functional theory BLYP/DNP and hyperhomodesmotic equations were employed to calculate ring strain energy, the bond dissociation energy of X-NO(2) (X=C, N) and the charges on the nitro groups of several four-membered and six-membered heterocycle compounds. BLYP/DNP and LST/QST + CG method were also applied to calculate bond rotational energy of X-NO(2) (X=C, N) of above mentioned compounds. It indicated that ring strain energy of four-membered heterocycle nitro compounds is apparently higher than that of six-membered heterocycle nitro compounds. Predictably, ring-opening reactions may preferentially occur for those compounds containing higher ring strain energy under shock. In addition, C-NO(2) bonds in these compounds may rotate easier than N-NO(2) bonds in response to the external shock. As for N-NO(2) bonds in these compounds, they also respond to the external shock by the rotation of N-NO(2) bonds, once to the saddle point of the rotational energy barrier, the whole molecule will become relaxed, N-NO(2) bond becomes weaker and eventually leads to the breakage. When one -C=O, -C=NH or -NH(2) group is introduced to the six-membered heterocycle, the charges on the nitro groups of the new compound decrease drastically, and ring strains increase remarkably. It can be predicted that the new compounds will be more sensitive to shock, and the viewpoint is confirmed by the experimental results of shock sensitivity (small scale gap test) of several explosives.

  3. A Simple Visualization of Double Bond Properties: Chemical Reactivity and UV Fluorescence

    ERIC Educational Resources Information Center

    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…

  4. X-ray photoelectron spectra structure and chemical bond nature in NpO2

    NASA Astrophysics Data System (ADS)

    Teterin, Yu. A.; Teterin, A. Yu.; Ivanov, K. E.; Ryzhkov, M. V.; Maslakov, K. I.; Kalmykov, St. N.; Petrov, V. G.; Enina, D. A.

    2014-01-01

    Quantitative analysis was done of the x-ray photoelectron spectra structure in the binding energy (BE) range of 0 to ˜35 eV for neptunium dioxide (NpO2) valence electrons. The BEs and structure of the core electronic shells (˜35-1250 eV) as well as the relativistic discrete variation calculation results for the finite fragment of the NpO2 lattice and the data of other authors 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) and the inner (˜15-˜35 eV) valence molecular orbitals (OVMO and IVMO, respectively). The filled Np 5f electronic states were shown to form in the NpO2 valence band. The Np 6p electrons participate in formation of both the IVMO and the OVMO (bands). The filled Np 6p3/2 and the O 2s electronic shells were found to take the maximum part in the IVMO formation. The MO composition and the sequence order in the BE range 0-˜35 eV in NpO2 were established. The experimental and theoretical data allowed a quantitative MO scheme for NpO2, which is fundamental for both understanding the chemical bond nature in neptunium dioxide and the interpretation of other x-ray spectra of NpO2.

  5. Iron-phosphate-based chemically bonded phosphate ceramics for mixed waste stabilization

    SciTech Connect

    Wagh, A.S.; Jeong, S.Y.; Singh, D.

    1997-01-01

    In an effort to develop chemically bonded phosphate ceramics for mixed waste stabilization, a collaborative project to develop iron-phosphate based ceramics has been initiated between Argonne National Laboratory and the V. G. Khlopin Radium Institute in St. Petersburg, Russia. The starter powders are oxides of iron that are generated as inexpensive byproduct materials in the iron and steel industry. They contain iron oxides as a mixture of magnetite (Fe{sub 3}O{sub 4}) and haematite (Fe{sub 2}O{sub 3}). In this initial phase of this project, both of these compounds were investigated independently. Each was reacted with phosphoric acid solution to form iron phosphate ceramics. In the case of magnetite, the reaction was rapid. Adding ash as the waste component containing hazardous contaminants resulted in a dense and hard ceramic rich in glassy phase. On the other hand, the reaction of phosphoric acid solution with a mixture of haematite and ash waste contaminated with cesium and americium was too slow. Samples had to be molded under pressure. They were cured for 2-3 weeks and then hardened by heating at 350{degrees}C for 3 h. The resulting ceramics in both cases were subjected to physical tests for measurement of density, open porosity, compression strength, phase analyses using X-ray diffraction and differential thermal analysis, and leaching tests using toxicity characteristic leaching procedure (TCLP) and ANS 16.1 with 7 days of leaching. Using the preliminary information obtained from these tests, we evaluated these materials for stabilization of Department of Energy`s mixed waste streams.

  6. Characteristics of hydrogen bond revealed from water clusters

    NASA Astrophysics Data System (ADS)

    Song, Yan; Chen, Hongshan; Zhang, Cairong; Zhang, Yan; Yin, Yuehong

    2014-09-01

    The hydrogen bond network is responsible for the exceptional physical and chemical properties of water, however, the description of hydrogen bond remains a challenge for the studies of condensed water. The investigation of structural and binding properties of water clusters provides a key for understanding the H-bonds in bulk water. In this paper, a new set of geometric parameters are defined to describe the extent of the overlap between the bonding orbital of the donor OH and the nonbonding orbital of the lone-pair of the acceptor molecule. This orbital overlap plays a dominant role for the strength of H-bonds. The dependences of the binding energy of the water dimer on these parameters are studied. The results show that these parameters properly describe the H-bond strength. The ring, book, cage and prism isomers of water hexamer form 6, 7, 8 and 9 H-bonds, and the strength of the bonding in these isomers changes markedly. The internally-solvated and the all-surface structures of (H2O) n for n = 17, 19 and 21 are nearly isoenergetic. The internally-solvated isomers form fewer but stronger H-bonds. The hydrogen bonding in the above clusters are investigated in detail. The geometric parameters can well describe the characters of the H-bonds, and they correlate well with the H-bond strength. For the structures forming stronger H-bonds, the H-bond lengths are shorter, the angle parameters are closer to the optimum values, and their rms deviations are smaller. The H-bonds emanating from DDAA and DDA molecules as H-donor are relatively weak. The vibrational spectra of (H2O) n ( n = 17, 19 and 21) are studied as well. The stretching vibration of the intramolecular OH bond is sensitive to its bonding environment. The H-bond strength judged from the geometric parameters is in good agreement with the bonding strength judged from the stretching frequencies.

  7. Temperature-dependent structures and chemical bonding states of the calcium chlorapatite powders doped with rare-earth-ions

    NASA Astrophysics Data System (ADS)

    Hong, Kyong-Soo; Yang, Ho-Soon

    2017-02-01

    Calcium chlorapatite powders doped with rare-earth-ions are synthesized by using the solid-state reaction method and sintering at 1,100 °C and 1,300 °C, respectively. This study focuses on the crystal structures and the chemical bonding states of calcium chlorapatite powders for different sintering temperatures, doping elements, and doping concentrations. The characterized physical properties show that the apatite powders exhibit two phases based on the sintering temperatures: the powders sintered at temperatures below 1,100 °C have a hexagonal structure while those sintered at 1,300 °C have a monoclinic structure. That is, the apatite compounds sintered at higher temperatures show a structure with a lower space symmetry. The chemical bonding states of the synthesized powders remain unchanged regardless of the amount of doped rare-earths and the sintering temperature.

  8. Anisotropy of chemical bonds in collagen molecules studied by X-ray absorption near-edge structure (XANES) spectroscopy.

    PubMed

    Lam, Raymond S K; Metzler, Rebecca A; Gilbert, Pupa U P A; Beniash, Elia

    2012-03-16

    Collagen type I fibrils are the major building blocks of connective tissues. Collagen fibrils are anisotropic supramolecular structures, and their orientation can be revealed by polarized light microscopy and vibrational microspectroscopy. We hypothesized that the anisotropy of chemical bonds in the collagen molecules, and hence their orientation, might also be detected by X-ray photoemission electron spectromicroscopy (X-PEEM) and X-ray absorption near-edge structure (XANES) spectroscopy, which use linearly polarized synchrotron light. To test this hypothesis, we analyzed sections of rat-tail tendon, composed of parallel arrays of collagen fibrils. The results clearly indicate that XANES-PEEM is sensitive to collagen fibril orientation and, more specifically, to the orientations of carbonyl and amide bonds in collagen molecules. These data suggest that XANES-PEEM is a promising technique for characterizing the chemical composition and structural organization at the nanoscale of collagen-based connective tissues, including tendons, cartilage, and bone.

  9. The Load and Time Dependence of Chemical Bonding-Induced Frictional Ageing of Silica at the Nanoscale

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

    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.

  11. Indications of chemical bond contrast in AFM images of a hydrogen-terminated silicon surface

    PubMed Central

    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

  12. Indications of chemical bond contrast in AFM images of a hydrogen-terminated silicon surface

    NASA Astrophysics Data System (ADS)

    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.

  13. Influence of the chemical bond on the K emission spectrum of oxygen and fluorine.

    NASA Technical Reports Server (NTRS)

    Koster, A. S.

    1971-01-01

    The K emission spectrum of oxygen and fluorine from a number of simple oxides and fluorides is divided into three to six sub-peaks. The spectra of many of these oxides and fluorides resemble one another owing to their basically ionic bonding. Certain sub-peaks, however, are ascribed to cross-over transitions and partially covalent energy levels. The different fluorine spectrum of Teflon is due to the hybrid nature of its covalent bonds.

  14. Accurate Dissociation of Chemical Bonds Using DFT-in-DFT Embedding Theory with External Orbital Orthogonality.

    PubMed

    Tamukong, Patrick K; Khait, Yuriy G; Hoffmann, Mark R

    2017-01-12

    Our recent density functional theory (DFT)-in-DFT embedding protocol, which enforces intersubsystem (or external orbital) orthogonality, is used for the first time to investigate covalent bond dissociation and is shown to do so accurately. Full potential energy curves for the dissociation of a H-O bond in H2O and the C-C bond in H3C-CH3 have been constructed using the new embedding method, as have the challenging ionic bonds in LiH and LiF, and were found to match the reference Kohn-Sham (KS)-DFT curves to at least one part in 10(6). The added constraint of external orbital orthogonality allows for the formulation of an embedding protocol that does not rely on approximate kinetic energy functionals for the evaluation of the so-called nonadditive kinetic potential, does not introduce compensatory potentials, and does not require a total system calculation at any stage. The present work extends the demonstrated applicability of the external orthogonality variant of embedding theory by more than a factor of 2 to the interaction strength range of strong single bonds. In particular, it is demonstrated that homolytic cleavage of both covalent and ionic bonds into radicals can be accomplished.

  15. The formation of new phase and chemical bonds in N-doped diamond films induced by swift heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Wang, Z. G.; Zhao, Z. M.; Song, Y.; Liu, J.; Sun, Y. M.; Zhang, C. H.; Duan, J. L.; Jin, Y. F.

    2004-06-01

    In this paper, the formation of the new phase and chemical bonds in N-doped diamond films after swift heavy ion irradiations was studied. The original samples were diamond films grown on (1 1 1) oriented p-Si by CVD deposition. These samples were implanted with 100 keV N-ions at room temperature to 5 × 10 17, 1 × 10 18 and 5 × 10 18 N/cm 2, irradiated with 345 MeV Xe or 2.64 GeV U ions, and then analyzed by means of RBS, micro-FTIR, micro-Raman and XRD spectroscopy. The obtained results suggested that N-sp 2C and N-sp 3C bonds formed in all N-doped diamond films, CN bond exists in all 5 × 10 18 N/cm 2 doped samples but could not form in the 5 × 10 17 N/cm 2 doped samples. In the 1 × 10 18 N/cm 2 doped sample, CN bond could form only after swift heavy ion irradiation. Intense energy deposition from the incident swift heavy ions induces the increase of sp 3/sp 2 bonding ratio and thus enhances the formation of N-sp 3C bonds in the samples. Furthermore, the X-ray diffraction analysis indicated that there existed new phases, α- and β-C 3N 4 in the N-doped diamond samples after irradiation by swift heavy ions.

  16. CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE I REPORT AUGUST 1997 - JULY 1998

    SciTech Connect

    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 of

  17. Geometries and tautomerism of OHN hydrogen bonds in aprotic solution probed by H/D isotope effects on (13)C NMR chemical shifts.

    PubMed

    Tolstoy, Peter M; Guo, Jing; Koeppe, Benjamin; Golubev, Nikolai S; Denisov, Gleb S; Smirnov, Sergei N; Limbach, Hans-Heinrich

    2010-10-14

    The (1)H and (13)C NMR spectra of 17 OHN hydrogen-bonded complexes formed by CH(3)(13)COOH(D) with 14 substituted pyridines, 2 amines, and N-methylimidazole have been measured in the temperature region between 110 and 150 K using CDF(3)/CDF(2)Cl mixture as solvent. The slow proton and hydrogen bond exchange regime was reached, and the H/D isotope effects on the (13)C chemical shifts of the carboxyl group were measured. In combination with the analysis of the corresponding (1)H chemical shifts, it was possible to distinguish between OHN hydrogen bonds exhibiting a single proton position and those exhibiting a fast proton tautomerism between molecular and zwitterionic forms. Using H-bond correlations, we relate the H/D isotope effects on the (13)C chemical shifts of the carboxyl group with the OHN hydrogen bond geometries.

  18. A theory of adhesion at a bimetallic interface - Overlap effects.

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Smith, J. R.

    1973-01-01

    A preliminary calculation of the chemical bonding adhesive interaction between metal surfaces is provided. In this first theory the Hohenberg and Kohn formalism is used to give the bimetallic adhesive binding energy versus separation. The close-packed planes of Al, Mg, and Zn are considered. The effect of simple overlap of the metal-vacuum distributions is determined. The importance of registry between contact surfaces is ascertained. A minimum in the binding energy curve is exhibited for all combinations. The theoretical predictions agree with trends in bond strengths taken from available experimental data. An insight into the mechanisms involved in metallic transfer is given. The relationship between adhesive energies, cohesive energies, and surface energies is discussed.

  19. Chemical Warfare Agent Surface Adsorption: Hydrogen Bonding of Sarin and Soman to Amorphous Silica.

    PubMed

    Davis, Erin Durke; Gordon, Wesley O; Wilmsmeyer, Amanda R; Troya, Diego; Morris, John R

    2014-04-17

    Sarin and soman are warfare nerve agents that represent some of the most toxic compounds ever synthesized. The extreme risk in handling such molecules has, until now, precluded detailed research into the surface chemistry of agents. We have developed a surface science approach to explore the fundamental nature of hydrogen bonding forces between these agents and a hydroxylated surface. Infrared spectroscopy revealed that both agents adsorb to amorphous silica through the formation of surprisingly strong hydrogen-bonding interactions with primarily isolated silanol groups (SiOH). Comparisons with previous theoretical results reveal that this bonding occurs almost exclusively through the phosphoryl oxygen (P═O) of the agent. Temperature-programmed desorption experiments determined that the activation energy for hydrogen bond rupture and desorption of sarin and soman was 50 ± 2 and 52 ± 2 kJ/mol, respectively. Together with results from previous studies involving other phosphoryl-containing molecules, we have constructed a detailed understanding of the structure-function relationship for nerve agent hydrogen bonding at the gas-surface interface.

  20. 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.

    PubMed

    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.

  1. Anisotropic chemical etching of semipolar [1011]/[101+1] ZnO crystallographic planes: polarity versus dangling bonds.

    PubMed

    Palacios-Lidón, E; Pérez-García, B; Vennéguès, P; Colchero, J; Muñoz-Sanjosé, V; Zúñiga-Pérez, J

    2009-02-11

    ZnO thin films grown by metal-organic vapor phase epitaxy along the nonpolar [formula: see text] direction and exhibiting semipolar [formula: see text] facets have been chemically etched with HCl. In order to get an insight into the influence of the ZnO wurtzite structure in the chemical reactivity of the material, Kelvin probe microscopy and convergent beam electron diffraction have been employed to unambiguously determine the absolute polarity of the facets, showing that [formula: see text] facets are unstable upon etching in an HCl solution and transform into [formula: see text] planes. In contrast, [formula: see text] facets undergo homogeneous chemical etching perpendicular to the initial crystallographic plane. The observed etching behavior has been explained in terms of surface oxygen dangling bond density, suggesting that the macroscopic polarity plays a secondary role in the etching process.

  2. Plasmon-driven dimerization via S-S chemical bond in an aqueous environment.

    PubMed

    Cui, Lin; Wang, Peijie; Chen, Xiaowei; Fang, Yurui; Zhang, Zhenglong; Sun, Mengtao

    2014-11-27

    The surface-enhanced Raman scattering (SERS) spectra of thioanisole are experimentally investigated in an electrochemical environment in this study. Two Raman peaks, which depend strongly not only on electric potential but also on the local surface plasmon resonances (LSPR), have been observed. Theoretical calculations reveal that thioanisole is first dissociated from thiophenol via the S-CH3 bond; plasmons then drive the dimerisation of thiophenol via the S-S bond, which is strongly potential dependent. One Raman peak corresponds to the S-S vibrational mode of the thiophenol dimer, and the other corresponds to the asymmetric C-C stretching modes of the benzenyl of the thiophenol dimer. The potential-dependent two Raman modes is the potential-dependent dimerisation dynamics of thiophenol via the S-S bond. Our experimental findings provide insight into the structural elucidation of adsorbed molecules and molecular surface reaction dynamics.

  3. Theoretical investigations on electronics structure and chemical bonding on iridathiabenzene and iridaoxabenzene

    NASA Astrophysics Data System (ADS)

    Ghiasi, Reza; Amini, Elaheh

    2013-10-01

    The electronic structure and properties of the iridathiabenzene and iridaoxabenzene isomers have been investigated using the hybrid density functional mpw1pw91 theory. The energetic aspect shows that trans- ortho-isomer is the most stable isomer. This is compatible with principles of minimum energy and minimum polarizability. Molecular orbital analysis shows a linear correlation between hardness and anisotropic polarizability values for Iridathiabenzene and iridaoxabenzene isomers. The structural and natural bond analysis (NBO) results illustrate electronic delocalization in these rings. Also, the study of non linear optical properties of these molecules indicate a good correlation between βtot and E(HOMO) for iridathiabenzene. The results from natural bond orbital (NBO) analysis have provided insights into Ir—ligand, P—Hapical and P—Hbasal bonding.

  4. Plasmon-driven dimerization via S-S chemical bond in an aqueous environment

    PubMed Central

    Cui, Lin; Wang, Peijie; Chen, Xiaowei; Fang, Yurui; Zhang, Zhenglong; Sun, Mengtao

    2014-01-01

    The surface-enhanced Raman scattering (SERS) spectra of thioanisole are experimentally investigated in an electrochemical environment in this study. Two Raman peaks, which depend strongly not only on electric potential but also on the local surface plasmon resonances (LSPR), have been observed. Theoretical calculations reveal that thioanisole is first dissociated from thiophenol via the S-CH3 bond; plasmons then drive the dimerisation of thiophenol via the S-S bond, which is strongly potential dependent. One Raman peak corresponds to the S-S vibrational mode of the thiophenol dimer, and the other corresponds to the asymmetric C-C stretching modes of the benzenyl of the thiophenol dimer. The potential-dependent two Raman modes is the potential-dependent dimerisation dynamics of thiophenol via the S-S bond. Our experimental findings provide insight into the structural elucidation of adsorbed molecules and molecular surface reaction dynamics. PMID:25427897

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

    SciTech Connect

    Raupach, Marc; Tonner, Ralf

    2015-05-21

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

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

    PubMed

    Raupach, Marc; Tonner, Ralf

    2015-05-21

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

  7. Marked influence of the nature of the chemical bond on CP-violating signature in molecular ions HBr(+) and HI(+).

    PubMed

    Ravaine, Boris; Porsev, Sergey G; Derevianko, Andrei

    2005-01-14

    Heavy polar molecules offer a great sensitivity to the electron electric dipole moment (EDM). To guide emerging searches for EDMs with molecular ions, we estimate the EDM-induced energy corrections for hydrogen halide ions HBr(+) and HI(+) in their respective ground X (2)Pi(3/2) states. We find that the energy corrections due to EDM for the two ions differ by an unexpectedly large factor of 15. We demonstrate that a major part of this enhancement is due to a dissimilarity in the nature of the chemical bond for the two ions: the bond that is nearly of ionic character in HBr(+) exhibits predominantly a covalent nature in HI(+). We conclude that because of this enhancement the HI(+) ion may be a potentially competitive candidate for the EDM search.

  8. Interfacial chemical bonding state and band alignment of CaF{sub 2}/hydrogen-terminated diamond heterojunction

    SciTech Connect

    Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M.; Koide, Y.

    2013-03-28

    CaF{sub 2} films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF{sub 2}/H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF{sub 2}/H-diamond heterointerface. Valence and conductance band offsets of the CaF{sub 2}/H-diamond heterojunciton are determined to be 3.7 {+-} 0.2 and 0.3 {+-} 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF{sub 2}/H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

  9. Critical surface energy of composite cement containing MDP (10-methacryloyloxydecyl dihydrogen phosphate) and chemical bonding to hydroxyapatite.

    PubMed

    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.

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

    PubMed

    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.

  11. CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE II REPORT, SEPT.1998-JULY 1999.

    SciTech Connect

    SUGAMA,T.YAGER,K.A.BLANKENHORN,D.

    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

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

    SciTech Connect

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

    1988-01-15

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

  13. Electronic Structure and Bonding in Co-Based Single and Mixed Valence Oxides: A Quantum Chemical Perspective.

    PubMed

    Singh, Vijay; Major, Dan Thomas

    2016-04-04

    The mixed valence cobalt oxide, Co3O4, is a potential candidate as a photovoltaic (PV) material, which also exhibits intriguing chemical and catalytic properties. Here, we present a comparative study of the electronic, magnetic, and chemical bonding properties of mixed valence Co3O4 (i.e., Co(2+/3+)) with the related single valence CoO (i.e., Co(2+)) and Co2O3 (i.e., Co(3+)) oxides using density functional theory (DFT). We have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06). We compare the electronic structure and band gap of the oxide materials, with available photoemission spectroscopy and optical band gaps. Our calculations suggest that the bonding between Co(3+) and O(2-) ions in Co2O3 and Co3O4 and Co(2+) and O(2-) ions in CoO and Co3O4 are rather different. We find that Co2O3 and Co3O4 are weakly correlated materials, whereas CoO is a strongly correlated material. Furthermore, our computed one-electron energy level diagrams reveal that strong Co-O antibonding states are present at the top of the valence band for all the cobalt oxides, hinting at a defect tolerant capacity in these materials. These results, which give a detailed picture of the chemical bonding in related single and mixed valence cobalt oxides, may serve as a guide to enhance the PV or photoelectrochemical activity of Co3O4, by reducing its internal defect states or changing its electronic structure by doping or alloying with suitable elements.

  14. Ab initio study of electron-ion structure factors in binary liquids with different types of chemical bonding

    SciTech Connect

    Klevets, Ivan; Bryk, Taras

    2014-12-07

    Electron-ion structure factors, calculated in ab initio molecular dynamics simulations, are reported for several binary liquids with different kinds of chemical bonding: metallic liquid alloy Bi–Pb, molten salt RbF, and liquid water. We derive analytical expressions for the long-wavelength asymptotes of the partial electron-ion structure factors of binary systems and show that the analytical results are in good agreement with the ab initio simulation data. The long-wavelength behaviour of the total charge structure factors for the three binary liquids is discussed.

  15. Formation of Lamellar Pores for Splats via Interfacial or Sub-interfacial Delamination at Chemically Bonded Region

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Yang, Guan-Jun; Li, Cheng-Xin

    2017-02-01

    To comprehensively understand the formation mechanism of lamellar pores in splats, the delamination morphologies and crack patterns of yttria-stabilized zirconia (YSZ) and lanthanum zirconia splats were examined. Results showed that both types of splats grew epitaxially on well-polished YSZ substrates, evidently confirming the formation of chemical bonding between splats and substrate. However, the interfacial or sub-interfacial delamination was observed in all kinds of splats in this study. Residual vertical cracks passing through delaminated domains (on bare substrate) were also observed, which clearly indicated that transverse delamination followed vertical cracking. Mechanical analysis about delamination was addressed, and the results were consistent with the experimental data.

  16. From Common Sense Concepts to Scientifically Conditioned Concepts of Chemical Bonding: An Historical and Textbook Approach Designed to Address Learning and Teaching Issues at the Secondary School Level

    NASA Astrophysics Data System (ADS)

    Croft, Michael; de Berg, Kevin

    2014-09-01

    This paper selects six key alternative conceptions identified in the literature on student understandings of chemical bonding and illustrates how a historical analysis and a textbook analysis can inform these conceptions and lead to recommendations for improving the teaching and learning of chemical bonding at the secondary school level. The historical analysis and the textbook analysis focus on the concepts of charge, octet, electron pair, ionic, covalent and metallic bonding. Finally, a table of recommendations is made for teacher and student in the light of four fundamental questions and the six alternative conceptions to enhance the quality of the curriculum resources available and the level of student engagement.

  17. Chemical synthesis of La1 isolated from the venom of the scorpion Liocheles australasiae and determination of its disulfide bonding pattern.

    PubMed

    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.

  18. Simple and surprisingly accurate approach to the chemical bond obtained from dimensional scaling.

    PubMed

    Svidzinsky, Anatoly A; Scully, Marlan O; Herschbach, Dudley R

    2005-08-19

    We present a new dimensional scaling transformation of the Schrödinger equation for the two electron bond. This yields, for the first time, a good description of the bond via D scaling. There also emerges, in the large-D limit, an intuitively appealing semiclassical picture, akin to a molecular model proposed by Bohr in 1913. In this limit, the electrons are confined to specific orbits in the scaled space, yet the uncertainty principle is maintained. A first-order perturbation correction, proportional to 1/D, substantially improves the agreement with the exact ground state potential energy curve. The present treatment is very simple mathematically, yet provides a strikingly accurate description of the potential curves for the lowest singlet, triplet, and excited states of H2. We find the modified D-scaling method also gives good results for other molecules. It can be combined advantageously with Hartree-Fock and other conventional methods.

  19. Controllable synthesis of silver and silver sulfide nanocrystals via selective cleavage of chemical bonds

    NASA Astrophysics Data System (ADS)

    Tang, Aiwei; Wang, Yu; Ye, Haihang; Zhou, Chao; Yang, Chunhe; Li, Xu; Peng, Hongshang; Zhang, Fujun; Hou, Yanbing; Teng, Feng

    2013-09-01

    A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag2S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S-C bonds or Ag-S bonds. Pure Ag2S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200 ° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190 ° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag2S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200 ° C. The formation mechanism has been discussed in detail in terms of selective S-C and Ag-S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag-S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals.

  20. Controllable synthesis of silver and silver sulfide nanocrystals via selective cleavage of chemical bonds.

    PubMed

    Tang, Aiwei; Wang, Yu; Ye, Haihang; Zhou, Chao; Yang, Chunhe; Li, Xu; Peng, Hongshang; Zhang, Fujun; Hou, Yanbing; Teng, Feng

    2013-09-06

    A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag₂S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S-C bonds or Ag-S bonds. Pure Ag₂S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200 ° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190 ° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag₂S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200 ° C. The formation mechanism has been discussed in detail in terms of selective S-C and Ag-S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag-S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals.

  1. Theory of chemical bonds in metalloenzymes V: Hybrid-DFT studies of the inorganic [8Fe-7S] core

    NASA Astrophysics Data System (ADS)

    Shoji, M.; Koizumi, K.; Kitagawa, Y.; Yamanaka, S.; Okumura, M.; Yamaguchi, K.; Ohki, Y.; Sunada, Y.; Honda, M.; Tatsumi, K.

    The electronic and spin structures of the [8Fe-7S] inorganic model complex (1) have been investigated using the density functional theory (DFT) UB3LYP and UBLYP methods. The experimental geometry of 1 was used to calculate the sets of exchange interactions (J values) between Fe-spin centers within spin Hamiltonian models. The experimental temperature-dependent paramagnetism is well reproduced on the basis of the calculated J values. The calculated low-lying energy levels are also consistent with those of the experiments. This indicates that the ground spin state of 1 is singlet (S = 0) for the weak antiferromagnetic coupling between two [4Fe-3S] cubane units, which take the Fe(III)Fe(II)3 formal charge and S = 7/2 spin states. The first-order density matrix of the most stable broken-symmetry (BS) solution has been diagonalized to elucidate the natural molecular orbitals (MOs) and their occupation number of 1, which are hardly obtained by the symmetry-adapted (SA) CASSCF approach. Several chemical indices such as the effective bond orders before and after spin projection are also calculated by using the occupation numbers to provide the SA MO picture of labile chemical bonds of 1. It is found that the BS MO calculation followed by spin-projected SA analysis is an effective and practical alternative to the CASSCF MO approach for the multinuclear transition metal clusters.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Textbook Errors: 137. Physical and Chemical Properties and Bonding of Metallic Elements.

    ERIC Educational Resources Information Center

    Myers, R. Thomas

    1979-01-01

    Focuses attention on the almost universal practice of discussing all metals as malleable. The author points out that some are brittle and then he presents the variation in chemical properties of metals. (SA)

  5. Bone bonding ability of a chemically and thermally treated low elastic modulus Ti alloy: gum metal.

    PubMed

    Tanaka, Masashi; Takemoto, Mitsuru; Fujibayashi, Shunsuke; Kawai, Toshiyuki; Yamaguchi, Seiji; Kizuki, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi; Nakamura, Takashi; Matsuda, Shuichi

    2014-03-01

    The gum metal with composition Ti-36Nb-2Ta-3Zr-0.3O, is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. We have previously demonstrated that this gum metal, once subjected to a series of surface treatments--immersion in 1 M NaOH (alkali treatment) and then 100 mM CaCl2, before heating at 700 °C (sample: ACaH-GM), with an optional final hot water immersion (sample: ACaHW-GM)--has apatite-forming ability in simulated body fluid. To confirm the in vivo bioactivity of these treated alloys, failure loads between implants and bone at 4, 8, 16, and 26 weeks after implantation in rabbits' tibiae were measured for untreated gum metal (UT-GM), ACaH-GM and ACaHW-GM, as well as pure titanium plates after alkali and heat treatment (AH-Ti). The ACaH-GM and UT-GM plates showed almost no bonding, whereas ACaHW-GM and AH-Ti plates showed successful bonding by 4 weeks, and their failure loads subsequently increased with time. The histological findings showed a large amount of new bone in contact with the surface of ACaHW-GM and AH-Ti plates, suggesting that the ACaHW treatment could impart bone-bonding bioactivity to a gum metal in vivo. Thus, with this improved bioactive treatment, these advantageous gum metals become useful candidates for orthopedic and dental devices.

  6. Chemical Reactions of Metal-Metal Bonded Compounds of the Transition Elements.

    DTIC Science & Technology

    1981-05-18

    M-M bonds. For example, PPh3 is lost by thermolysis of Pt(PPh3 )3 and ethylene is lost from Pt(PPh3 )2 (C2H4 ) to yield dinuclear and trinuclear...PPh3 )2, generates both 1- octene and octane, though the Ir-Ir dimer or cluster complex was nol ident-ified (46). 15 The reductive-coupling reaction...although Os 3 (CO) 1 2 reacts with ethylene at elevated temperatures, the product is not a simple substitution product, but H2 Os3 (CO)9 (C=CH2), in

  7. Carbosilane polymers with hydrogen bond acidic functionalization for chemical preconcentrator applications

    NASA Astrophysics Data System (ADS)

    Simonson, Duane L.; McGill, R. Andrew; Higgins, Bernadette A.

    2008-04-01

    Vapor collection systems, including solid phase microextraction (SPME), require the ability to selectively collect and concentrate a sample from a large volume of air. In the case of SPME, polymers are needed to adhere to the fiber for greater reproducibility and longer lasting fibers. The polymerization of carbosilanes was investigated and produced polymers with molecular weights over 500,000. This polymer class was then functionalized with hexafluoro-2-propanol (HFIP) end groups that will selectively sorb hydrogen bond basic vapors. The results of vapor testing with these polymers utilizing a variety of platforms such as preconcentrators, Surface Acoustic Wave (SAW) sensors, and microcantilevers will be discussed.

  8. Research on the interaction of hydrogen-bond acidic polymer sensitive sensor materials with chemical warfare agents simulants by inverse gas chromatography.

    PubMed

    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.

  9. Multi-walled carbon nanotubes covalently bonded cellulose composite for chemical vapor sensor

    NASA Astrophysics Data System (ADS)

    Yun, Sungryul; Yang, Sang Yeol; Kim, Jaehwan

    2010-04-01

    A cellulose solution was prepared by dissolving cotton pulp in LiCl/ N,N-Dimethylacetamide (DMAc) solution, and functionalized multi-walled carbon nanotubes (MWCNTs) were reacted with N, N-Carbonyldiimidazoles to obtain MWCNTs-imidazolides. By acylation of cellulose with MWCNTs-imidazolides, MWCNTs were covalently bonded with cellulose chains. Using the product, MWCNTs covalently bonded cellulose composite (M/C) composite was fabricated with mechanical stretching to align MWCNTs with cellulose. Finally, inter-digital comb electrode was formed on the composite via lift-off process. Chemo-electrical properties of the M/C composite in response of absorption of the volatile vapors corresponding to 1-propanol, 1-butanol, methanol and ethanol were investigated. Due to sensitive and reversible expansion/contraction of the M/C composite matrix in response to absorption of each analyte, the M/C composite showed fast and reversible change in chemo-electrical property. The ranking of relative resistance response of the composite was methanol < ethanol < 1-propanol < 1-butanol.

  10. Chemically bonded hybrid systems from functionalized hydroxypyridine molecular bridge: characterization and photophysical properties.

    PubMed

    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.

  11. Steganalysis of overlapping images

    NASA Astrophysics Data System (ADS)

    Whitaker, James M.; Ker, Andrew D.

    2015-03-01

    We examine whether steganographic images can be detected more reliably when there exist other images, taken with the same camera under the same conditions, of the same scene. We argue that such a circumstance is realistic and likely in practice. In `laboratory conditions' mimicking circumstances favourable to the analyst, and with a custom set of digital images which capture the same scenes with controlled amounts of overlap, we use an overlapping reference image to calibrate steganographic features of the image under analysis. Experimental results show that the analysed image can be classified as cover or stego with much greater reliability than traditional steganalysis not exploiting overlapping content, and the improvement in reliability depends on the amount of overlap. These results are curious because two different photographs of exactly the same scene, taken only a few seconds apart with a fixed camera and settings, typically have steganographic features that differ by considerably more than a cover and stego image.

  12. TECHNICAL NOTE: Chemical analysis of bonded and debonded silicon-glass interfaces

    NASA Astrophysics Data System (ADS)

    Visser, M. M.; Plaza, J. A.; Wang, D. T.; Hanneborg, A. B.

    2001-09-01

    We report on the nature of the interface of anodically bonded glass wafers (Pyrex 7740, Hoya SD-2) and silicon wafers, after having reversed the voltage across the wafer couples. The reaction products and defects discovered at the interface of the wafers are studied with scanning electron microscopy, electron dispersive x-ray spectroscopy and with an electron microprobe. An accumulation, especially of sodium, is found to be closely related to the presence of defects appearing as brown/yellow-brown spots and cracks. Gradients in potassium and zinc concentrations are also observed in regions containing defects. Some of the processes that are believed to take place in the interface region are discussed. ane{abstract

  13. LOBSTER: A tool to extract chemical bonding from plane‐wave based DFT

    PubMed Central

    Maintz, Stefan; Deringer, Volker L.; Tchougréeff, Andrei L.

    2016-01-01

    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. PMID:26914535

  14. Three-dimensional H-bonding and ferroelectric transition in KDP. Quantum-chemical study

    NASA Astrophysics Data System (ADS)

    Dolin, S. P.; Mikhailova, T. Yu; Solin, M. V.; Breslavskaya, N. N.; Levin, A. A.

    On basis of the nonempirical methods (SCF, B3LYP, MP2-MP4) and several cluster models, the ferroelectric KH2PO4 (KDP) and its deuteroanalogue are studied. The tunneling integralsΩ and the parameters of the effective coupling of protons/deuterons U,V (the Ising parameters) are calculated for these materials with the 3d network of H/D-bonds. Using the obtained U,V andΩ values in the frames of molecular field approximation, it is found that the structural phase (ferroelectric) transition occurs for both crystals within the lowering of temperature. Such low-temperature behavior differs the 3d KDP-family materials from 0d systems, where the low-temperature phase transition takes place only upon deuteration. It is demonstrated that this difference is associated with an abrupt Ising parameters growth for KDP if compared with the nondeuterated 0d materials.

  15. Electronic structure and chemical bonding in the lowest electronic states of TcN.

    PubMed

    Borin, Antonio Carlos; Gobbo, João Paulo

    2009-11-12

    Multiconfiguration second-order perturbation theory, with the inclusion of relativistic effects and spin-orbit coupling, was employed to investigate the nature of the ground and low-lying Lambda-S and Omega states of the TcN molecule. Spectroscopic constants, effective bond order, and potential energy curves for 13 low-lying Lambda-S states and 5 Omega states are given. The computed ground state of TcN is of Omega = 3 symmetry (R(e) = 1.605 A and omega(e) = 1085 cm(-1)), originating mainly from the (3)Delta Lambda-S ground state. This result is contrasted with the nature of the ground state for other VIIB transtion-metal mononitrides, including X(3)Sigma(-) symmetry for MnN and Omega = 0(+) symmetry for ReN, derived also from a X(3)Sigma(-) state.

  16. Effects of Jigsaw Cooperative Learning and Animation Techniques on Students' Understanding of Chemical Bonding and Their Conceptions of the Particulate Nature of Matter

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Clearfield, Abraham

    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.

  18. The mystery of gold's chemical activity: local bonding, morphology and reactivity of atomic oxygen.

    PubMed

    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

  19. All about that Amide Bond: The Sixth Chemical Protein Synthesis (CPS) Meeting.

    PubMed

    Weller, Caroline E; Chatterjee, Champak

    2015-11-01

    Endless potential: The sixth Chemical Protein Synthesis Meeting, held recently in St. Augustine, Florida, showed the potential of peptide and protein chemistry when applied toward understanding and controlling complex biological processes. This report highlights the diverse and cutting-edge protein chemistry presented at the meeting.

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

    ERIC Educational Resources Information Center

    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,…

  1. Construction of hybrid material with double chemical bond from functional bridge ligand: Molecular modification, lotus root-like micromorphology and strong luminescence

    NASA Astrophysics Data System (ADS)

    Yan, Bing; Sui, Yu-Long

    2006-07-01

    Modifying benzoic acid with a cross-linking molecule (3-aminopropyl)triethoxysilane (abbreviated as APES), a fictional molecular bridge with double reactivity was achieved by the amidation reaction between them. Then the modified functional molecule, which behaving as a bridge, both coordinate with terbium ion through amide's oxygen atom and form the Si-O chemical bond in an in situ sol-gel process with matrix precursor (tetraethoxysilane, TEOS). As a result, a novel molecular hybrid material (Tb-BA-APES) with double chemical bond (Tb-O coordination bond and Si-O covalent bond) was constructed. The strong luminescence of Tb 3+ substantiates optimum energy couple and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb 3+. Especially SEM of the molecular hybrid material exhibits unexpected microlotus root-like pore morphology.

  2. The electrical properties of low pressure chemical vapor deposition Ga doped ZnO thin films depending on chemical bonding configuration

    NASA Astrophysics Data System (ADS)

    Jung, Hanearl; Kim, Doyoung; Kim, Hyungjun

    2014-04-01

    The electrical and chemical properties of low pressure chemical vapor deposition (LP-CVD) Ga doped ZnO (ZnO:Ga) films were systematically investigated using Hall measurement and X-ray photoemission spectroscopy (XPS). Diethylzinc (DEZ) and O2 gas were used as precursor and reactant gas, respectively, and trimethyl gallium (TMGa) was used as a Ga doping source. Initially, the electrical properties of undoped LP-CVD ZnO films depending on the partial pressure of DEZ and O2 ratio were investigated using X-ray diffraction (XRD) by changing partial pressure of DEZ from 40 to 140 mTorr and that of O2 from 40 to 80 mTorr. The resistivity was reduced by Ga doping from 7.24 × 10-3 Ω cm for undoped ZnO to 2.05 × 10-3 Ω cm for Ga doped ZnO at the TMG pressure of 8 mTorr. The change of electric properties of Ga doped ZnO with varying the amount of Ga dopants was systematically discussed based on the structural crystallinity and chemical bonding configuration, analyzed by XRD and XPS, respectively.

  3. Thermal-mechanical-chemical responses of polymer-bonded explosives using a mesoscopic reactive model under impact loading.

    PubMed

    Wang, XinJie; Wu, YanQing; Huang, FengLei

    2017-01-05

    A mesoscopic framework is developed to quantify the thermal-mechanical-chemical responses of polymer-bonded explosive (PBX) samples under impact loading. A mesoscopic reactive model is developed for the cyclotetramethylenetetranitramine (HMX) crystal, which incorporates nonlinear elasticity, crystal plasticity, and temperature-dependent chemical reaction. The proposed model was implemented in the finite element code ABAQUS by the user subroutine VUMAT. A series of three-dimensional mesoscale models were constructed and calculated under low-strength impact loading scenarios from 100m/s to 600m/s where only the first wave transit is studied. Crystal anisotropy and microstructural heterogeneity are responsible for the nonuniform stress field and fluctuations of the stress wave front. At a critical impact velocity (≥300m/s), a chemical reaction is triggered because the temperature contributed by the volumetric and plastic works is sufficiently high. Physical quantities, including stress, temperature, and extent of reaction, are homogenized from those across the microstructure at the mesoscale to compare with macroscale measurements, which will advance the continuum-level models. The framework presented in this study has important implications in understanding hot spot ignition processes and improving predictive capabilities in energetic materials.

  4. Chemical shift changes provide evidence for overlapping single-stranded DNA and XPA binding sites on the 70 kDa subunit of human replication protein A

    SciTech Connect

    Daughdrill, Gary W.; Buchko, Garry W.; Botuyan, Maria V.; Arrowsmith, Cheryl H.; Wold, Marc S.; Kennedy, Michael A.; Lowry, David F.

    2003-07-15

    Replication protein A (RPA) is a heterotrimeric single-stranded DNA (ssDNA) binding protein that can form a complex with the xeroderma pigmentosum group A protein (XPA). This complex can preferentially recognize UV damaged DNA over undamaged DNA and has been implicated in the stabilization of open complex formation during nucleotide excision repair. In this report, NMR spectroscopy was used to investigate the interaction between a fragment of the 70 kDa subunit of human RPA, residues 1-326 (hRPA701-326), and a fragment of the human XPA protein, residues 98-219 (XPA-MBD). Intensity changes were observed for amide resonances in the 1H-15N correlation spectrum of uniformly 15N-labeled hRPA701-326 after the addition of unlabeled XPA-MBD. The intensity changes observed were restricted to an ssDNA binding domain that is between residues 183 and 296 of the hRPA701-326 fragment. The hRPA701-326 residues with the largest resonance intensity reductions were mapped onto the structure of the ssDNA binding domain to identify the binding surface with XPA-MBD. The XPA-MBD binding surface showed significant overlap with an ssDNA binding surface that was previously identified using NMR spectroscopy and X-ray crystallography.

  5. Stochastic flow shop scheduling of overlapping jobs on tandem machines in application to optimizing the US Army's deliberate nuclear, biological, and chemical decontamination process, (final report). Master's thesis

    SciTech Connect

    Novikov, V.

    1991-05-01

    The U.S. Army's detailed equipment decontamination process is a stochastic flow shop which has N independent non-identical jobs (vehicles) which have overlapping processing times. This flow shop consists of up to six non-identical machines (stations). With the exception of one station, the processing times of the jobs are random variables. Based on an analysis of the processing times, the jobs for the 56 Army heavy division companies were scheduled according to the best shortest expected processing time - longest expected processing time (SEPT-LEPT) sequence. To assist in this scheduling the Gap Comparison Heuristic was developed to select the best SEPT-LEPT schedule. This schedule was then used in balancing the detailed equipment decon line in order to find the best possible site configuration subject to several constraints. The detailed troop decon line, in which all jobs are independent and identically distributed, was then balanced. Lastly, an NBC decon optimization computer program was developed using the scheduling and line balancing results. This program serves as a prototype module for the ANBACIS automated NBC decision support system.... Decontamination, Stochastic flow shop, Scheduling, Stochastic scheduling, Minimization of the makespan, SEPT-LEPT Sequences, Flow shop line balancing, ANBACIS.

  6. Barrelane-like germanium clusters in Eu 3Ge 5: Crystal structure, chemical bonding and physical properties

    NASA Astrophysics Data System (ADS)

    Budnyk, Sergij; Weitzer, Franz; Kubata, Christof; Prots, Yurii; Akselrud, Lev G.; Schnelle, Walter; Hiebl, Kurt; Nesper, Reinhard; Wagner, Frank R.; Grin, Yuri

    2006-08-01

    Formation and crystal structure of the binary germanide Eu 3Ge 5 were investigated in detail. The compound forms peritectically at 1008 °C and does not undergo any phase transition down to room temperature. The crystal structure was determined first from X-ray powder diffraction data and was later confirmed by single-crystal X-ray diffraction: structure type Pu 3Pd 5, space group Cmcm (no. 63), a=9.7675(4) Å, b=7.9681(3) Å, c=9.8562(3) Å. The main building blocks are Ge 56- cluster anions surrounded by Eu 2+ cations. The nearly tetragonal-pyramidal shape is suggested by the interatomic distances. Contrary to that, the bonding analysis with the electron localization function (ELF) reveals only two- and three-bonded germanium atoms forming a strongly distorted [1.1.1]-barrelane-like cluster. Despite the formal electron deficiency, compared to the barrelane C 5H 8, the electron counting in the cluster anion and its conformation cannot be interpreted applying the Wade's rules. In accordance with the calculated electronic density of states, Eu 3Ge 5 shows a metal-like temperature dependence of the electrical resistivity with a sharp change of ρ(T) slope at the Néel point. Above the Néel point the inverse magnetic susceptibility reveals Curie-Weiss behavior with an effective moment of 8.11 μB (Eu 2+, 4 f7 configuration) in agreement with the analysis of the chemical bonding. The 4 f7 electronic configuration of europium is confirmed by Eu- LIII X-ray absorption spectroscopy.

  7. Mechanical control of the plasmon coupling with Au nanoparticle arrays fixed on the elastomeric film via chemical bond

    NASA Astrophysics Data System (ADS)

    Bedogni, Elena; Kaneko, Satoshi; Fujii, Shintaro; Kiguchi, Manabu

    2017-03-01

    We have fabricated Au nanoparticle arrays on the flexible poly(dimethylsiloxane) (PDMS) film. The nanoparticles were bound to the film via a covalent bond by a ligand exchange reaction. Thanks to the strong chemical bonding, highly stable and uniformly dispersed Au nanoparticle arrays were fixed on the PDMS film. The Au nanoparticle arrays were characterized by the UV–vis, scanning electron microscope (SEM) and surface enhanced Raman scattering (SERS). The UV–vis and SEM measurements showed the uniformity of the surface-dispersed Au nanoparticles, and SERS measurement confirmed the chemistry of the PDMS film. Reflecting the high stability and the uniformity of the Au nanoparticle arrays, the plasmon wavelength of the Au nanoparticles reversely changed with modulation of the interparticle distance, which was induced by the stretching of the PDMS film. The plasmon wavelength linearly decreased from 664 to 591 nm by stretching of 60%. The plasmon wavelength shift can be explained by the change in the strength of the plasmon coupling which is mechanically controlled by the mechanical strain.

  8. Structure, vibrations and quantum chemical investigations of hydrogen bonded complex of bis(1-hydroxy-2-methylpropan-2-aminium)selenate

    NASA Astrophysics Data System (ADS)

    Thirunarayanan, S.; Arjunan, V.; Marchewka, M. K.; Mohan, S.

    2017-04-01

    The hydrogen bonded molecular complex bis(1-hydroxy-2-methylpropan-2-aminium)selenate (C8H24N2O6Se) has been prepared by the reaction of 2-amino-2-methyl propanol and selenic acid. The X-ray diffraction analysis revealed that the intermolecular proton transfer from selenic acid (SeO4H2) to 2-amino-2-methylpropanol results in the formation of bis(1-hydroxy-2-methylpropan-2-aminium)selenate (HMPAS) salt and the fragments are connected through H-bonding and ion pairing. The N-H⋯O and O-H⋯O interactions between 2-amino-2-methylpropanol and selenic acid determine the supramolecular arrangement in three-dimensional space. The salt crystallises in the space group P121/n1 of monoclinic system. The complete vibrational assignments of HMPAS have been performed by FTIR and FT-Raman spectroscopy. The experimental data are correlated with the structural properties namely the energy, thermodynamic parameters, atomic charges, hybridization concepts and vibrational frequencies determined by quantum chemical studies performed with B3LYP method using 6-311++G*, 6-31+G* and 6-31G** basis sets.

  9. Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

    SciTech Connect

    Qiu, Wujie; Xi, Lili; Wei, Ping; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2014-10-06

    Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). Here, by analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemical-bond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. Lastly, the observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a “resonant” phonon scattering.

  10. Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy.

    PubMed

    Qiu, Wujie; Xi, Lili; Wei, Ping; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2014-10-21

    Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). By analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemical-bond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. The observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a "resonant" phonon scattering.

  11. Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

    DOE PAGES

    Qiu, Wujie; Xi, Lili; Wei, Ping; ...

    2014-10-06

    Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). Here, by analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemical-bond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flowmore » of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. Lastly, the observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a “resonant” phonon scattering.« less

  12. Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

    PubMed Central

    Xi, Lili; Wei, Ping; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2014-01-01

    Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). By analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemical-bond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. The observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a “resonant” phonon scattering. PMID:25288751

  13. A Comparative Evaluation of Effect of Different Chemical Solvents on the Shear Bond Strength of Glass Fiber reinforced Post to Core Material

    PubMed Central

    Samadi, Firoza; Jaiswal, JN; Saha, Sonali

    2014-01-01

    ABSTRACT% Aim: To compare the effect of different chemical solvents on glass fiber reinforced posts and to study the effect of these solvents on the shear bond strength of glass fiber reinforced post to core material. Materials and methods: This study was conducted to evaluate the effect of three chemical solvents, i.e. silane coupling agent, 6% H2O2 and 37% phosphoric acid on the shear bond strength of glass fiber post to a composite resin restorative material. The changes in post surface characteristics after different treatments were also observed, using scanning electron microscopy (SEM) and shear bond strength was analyzed using universal testing machine (UTM). Results: Surface treatment with hydrogen peroxide had greatest impact on the post surface followed by 37% phosphoric acid and silane. On evaluation of the shear bond strength, 6% H2O2 exhibited the maximum shear bond strength followed in descending order by 37% phosphoric acid and silane respectively. Conclusion: The surface treatment of glass fiber post enhances the adhesion between the post and composite resin which is used as core material. Failure of a fiber post and composite resin core often occurs at the junction between the two materials. This failure process requires better characterization. How to cite this article: Sharma A, Samadi F, Jaiswal JN, Saha S. A Comparative Evaluation of Effect of Different Chemical Solvents on the Shear Bond Strength of Glass Fiber Reinforced Post to Core Material. Int J Clin Pediatr Dent 2014;7(3):192-196. PMID:25709300

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

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

    2017-03-15

    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=365nm 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 electron

  16. Lattice dynamics and chemical bonding in Sb{sub 2}Te{sub 3} from first-principles calculations

    SciTech Connect

    Wang, Bao-Tian; Souvatzis, Petros; Eriksson, Olle; Zhang, Ping

    2015-05-07

    Pressure effects on the lattice dynamics and the chemical bonding of the three-dimensional topological insulator, Sb{sub 2}Te{sub 3}, have been studied from a first-principles perspective in its rhombohedral phase. Where it is possible to compare, theory agrees with most of the measured phonon dispersions. We find that the inclusion of relativistic effects, in terms of the spin-orbit interaction, affects the vibrational features to some extend and creates large fluctuations on phonon density of state in high frequency zone. By investigations of structure and electronic structure, we analyze in detail the semiconductor to metal transition at ∼2 GPa followed by an electronic topological transition at a pressure of ∼4.25 GPa.

  17. Evidence for porphyrins bound, via ester bonds, to the Messel oil shale kerogen by selective chemical degradation experiments

    NASA Astrophysics Data System (ADS)

    Huseby, B.; Ocampo, R.

    1997-09-01

    High amounts of nickel mono- and di-acid porphyrins were released from Messel oil shale kerogen (Eocene, Germany) by selective chemical degradation (acid and base hydrolysis). The released porphyrin fractions were quantified (UV-vis) and their constituents isolated and characterized at the molecular level (UV-vis, MS, NMR). The mono-acid porphyrin fraction released contained four compounds of similar abundance which arise from an obvious chlorophyll or bacteriochlorophyll precursor. The di-acid porphyrin fraction was, however, dominated by far by one compound, mesoporphyrin IX, which must have originated from heme-like precursors (heme, cytochromes, etc.). These results show unambigously that the released mono- and di-acid porphyrins were linked to the macromolecular kerogen network via ester bonds and suggest that precursor heme-like pigments could be selectively and/or more readily incorporated into the macromolecular kerogen network than precursor chlorophylls and bacteriochlorophylls.

  18. Robust C–C bonded porous networks with chemically designed functionalities for improved CO2 capture from flue gas

    PubMed Central

    Thirion, Damien; Lee, Joo S; Özdemir, Ercan

    2016-01-01

    Effective carbon dioxide (CO2) capture requires solid, porous sorbents with chemically and thermally stable frameworks. Herein, we report two new carbon–carbon bonded porous networks that were synthesized through metal-free Knoevenagel nitrile–aldol condensation, namely the covalent organic polymer, COP-156 and 157. COP-156, due to high specific surface area (650 m2/g) and easily interchangeable nitrile groups, was modified post-synthetically into free amine- or amidoxime-containing networks. The modified COP-156-amine showed fast and increased CO2 uptake under simulated moist flue gas conditions compared to the starting network and usual industrial CO2 solvents, reaching up to 7.8 wt % uptake at 40 °C. PMID:28144294

  19. Use of chemical auxiliaries to control p450 enzymes for predictable oxidations at unactivated C-h bonds of substrates.

    PubMed

    Auclair, Karine; Polic, Vanja

    2015-01-01

    Cytochrome P450 enzymes (P450s) have the ability to oxidize unactivated C-H bonds of substrates with remarkable regio- and stereoselectivity. Comparable selectivity for chemical oxidizing agents is typically difficult to achieve. Hence, there is an interest in exploiting P450s as potential biocatalysts. Despite their impressive attributes, the current use of P450s as biocatalysts is limited. While bacterial P450 enzymes typically show higher activity, they tend to be highly selective for one or a few substrates. On the other hand, mammalian P450s, especially the drug-metabolizing enzymes, display astonishing substrate promiscuity. However, product prediction continues to be challenging. This review discusses the use of small molecules for controlling P450 substrate specificity and product selectivity. The focus will be on two approaches in the area: (1) the use of decoy molecules, and (2) the application of substrate engineering to control oxidation by the enzyme.

  20. Robust C-C bonded porous networks with chemically designed functionalities for improved CO2 capture from flue gas.

    PubMed

    Thirion, Damien; Lee, Joo S; Özdemir, Ercan; Yavuz, Cafer T

    2016-01-01

    Effective carbon dioxide (CO2) capture requires solid, porous sorbents with chemically and thermally stable frameworks. Herein, we report two new carbon-carbon bonded porous networks that were synthesized through metal-free Knoevenagel nitrile-aldol condensation, namely the covalent organic polymer, COP-156 and 157. COP-156, due to high specific surface area (650 m(2)/g) and easily interchangeable nitrile groups, was modified post-synthetically into free amine- or amidoxime-containing networks. The modified COP-156-amine showed fast and increased CO2 uptake under simulated moist flue gas conditions compared to the starting network and usual industrial CO2 solvents, reaching up to 7.8 wt % uptake at 40 °C.

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

    SciTech Connect

    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.

  2. Investigation of finite-size effects in chemical bonding of AuPd nanoalloys

    SciTech Connect

    Zhu, Beien; Oğuz, Ismail Can; Guesmi, Hazar

    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.

  3. Investigation of finite-size effects in chemical bonding of AuPd nanoalloys.

    PubMed

    Zhu, Beien; Oğuz, Ismail Can; Guesmi, Hazar

    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 (νC-O), and Pd d-bond centers (εd) on a series of non-supported Aun-1-Pd1 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 TOh38, 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.

  4. Investigation of finite-size effects in chemical bonding of AuPd nanoalloys

    NASA Astrophysics Data System (ADS)

    Zhu, Beien; Oǧuz, Ismail Can; Guesmi, Hazar

    2015-10-01

    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 (νC-O), and Pd d-bond centers (ɛd) on a series of non-supported Aun-1-Pd1 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 TOh38, 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.

  5. Double bond localization in minor homoallylic fatty acid methyl esters using acetonitrile chemical ionization tandem mass spectrometry.

    PubMed

    Michaud, Anthony L; Diau, Guan-Yeu; Abril, Reuben; Brenna, J Thomas

    2002-08-15

    Double bond position in natural fatty acids is critical to biochemical properties, however, common instrument-based methods cannot locate double bonds in fatty acid methyl esters (FAME), the predominant analysis form of fatty acids. A recently described mass spectrometry (MS) method for locating double bonds in FAME is reported here for the analysis of minor (<1%) components of real FAME mixtures derived from three natural sources; golden algae (Schizochytrium sp.), primate brain white matter, and transgenic mouse liver. Acetonitrile chemical ionization tandem MS was used to determine double bond positions in 39 FAME, most at concentrations well below 1% of all fatty acid methyl esters. FAME identified in golden algae are 14:1n-6, 14:3n-3, 16:1n-7, 16:2n-6, 16:3n-6, 16:3n-3, 16:4n-3, 18:2n-7, 18:3n-7, 18:3n-8, 18:4n-3, 18:4n-5, 20:3n-7, 20:4n-3, 20:4n-5, 20:4n-7, 20:5n-3, and 22:4n-9. Additional FAME identified in primate brain white matter are 20:1n-7, 20:1n-9, 20:2n-7, 20:2n-9, 22:1n-7, 22:1n-9, 22:1n-13, 22:2n-6, 22:2n-7, 22:2n-9, 22:3n-6, 22:3n-7, 22:3n-9, 22:4n-6, 24:1n-7, 24:1n-9, and 24:4n-6. Additional FAME identified in mouse liver are 26:5n-6, 26:6n-3, 28:5n-6, and 28:6n-3. The primate brain 22:3n-7 and algae 18:4n-5 are novel fatty acids. These results demonstrate the usefulness of the technique for analysis of real samples. Tables are presented to aid in interpretation of acetonitrile CIMS/MS spectra.

  6. Surface chemical-bonds analysis of silicon particles from diamond-wire cutting of crystalline silicon

    NASA Astrophysics Data System (ADS)

    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.

  7. Illusion induced overlapped optics.

    PubMed

    Zang, XiaoFei; Shi, Cheng; Li, Zhou; Chen, Lin; Cai, Bin; Zhu, YiMing; Zhu, HaiBin

    2014-01-13

    The traditional transformation-based cloak seems like it can only hide objects by bending the incident electromagnetic waves around the hidden region. In this paper, we prove that invisible cloaks can be applied to realize the overlapped optics. No matter how many in-phase point sources are located in the hidden region, all of them can overlap each other (this can be considered as illusion effect), leading to the perfect optical interference effect. In addition, a singular parameter-independent cloak is also designed to obtain quasi-overlapped optics. Even more amazing of overlapped optics is that if N identical separated in-phase point sources covered with the illusion media, the total power outside the transformation region is N2I0 (not NI0) (I0 is the power of just one point source, and N is the number point sources), which seems violating the law of conservation of energy. A theoretical model based on interference effect is proposed to interpret the total power of these two kinds of overlapped optics effects. Our investigation may have wide applications in high power coherent laser beams, and multiple laser diodes, and so on.

  8. The Local Atomic Structure and Chemical Bonding in Sodium Tin Phases

    DOE PAGES

    Baggetto, Loic; Bridges, Craig A.; Jumas, Dr. Jean-Claude; ...

    2014-01-01

    To understand these electrochemically-derived materials we have reinvestigated the formation of Na-Sn alloys to identify all the phases which form when x ≥ 1 (NaxSn) and characterized the local bonding around the Sn atoms with X-ray diffraction, 119Sn M ssbauer spectroscopy, and X-ray absorption spectroscopies. The results from the well-defined crystallographic materials were compared to the spectroscopic measurements of the local Sn structures in the electrochemically prepared materials. The reinvestigation of the Na-Sn compounds yields a number of new results: (i) Na7Sn3 is a new thermodynamically-stable phase with a rhombohedral structure and R-3m space group; (ii) orthorhombic Na9Sn4 (Cmcm) hasmore » relatively slow formation kinetics suggesting why it does not form at room temperature during the electrochemical reaction; (iii) orthorhombic Na14.78Sn4 (Pnma), better described as Na16-xSn4, is Na-richer than cubic Na15Sn4 (I-43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, at the exception of Na7Sn3 and Na15Sn4, different crystal structures than similar Na-Sn compositions prepared via classic solid state reactions are formed. These phases are composed of disordered structures characteristic of kinetic-driven solid-state amorphization reactions. In these structures, Sn coordinates in asymmetric environments, which differ significantly from the environments present in Na-Sn model compounds.« less

  9. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3^rd order and now 5^th order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La0.7Sr0.3MnO3 layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below Tc in La0.7Sr0.3MnO3 thin films grown on SrTiO3.[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).

  10. The Local Atomic Structure and Chemical Bonding in Sodium Tin Phases

    SciTech Connect

    Baggetto, Loic; Bridges, Craig A.; Jumas, Dr. Jean-Claude; Mullins, David R.; Carroll, Kyler J.; Meisner, Roberta; Crumlin, Ethan; Liu, Xiason; Yang, Wanli; Veith, Gabriel M.

    2014-01-01

    To understand these electrochemically-derived materials we have reinvestigated the formation of Na-Sn alloys to identify all the phases which form when x ≥ 1 (NaxSn) and characterized the local bonding around the Sn atoms with X-ray diffraction, 119Sn M ssbauer spectroscopy, and X-ray absorption spectroscopies. The results from the well-defined crystallographic materials were compared to the spectroscopic measurements of the local Sn structures in the electrochemically prepared materials. The reinvestigation of the Na-Sn compounds yields a number of new results: (i) Na7Sn3 is a new thermodynamically-stable phase with a rhombohedral structure and R-3m space group; (ii) orthorhombic Na9Sn4 (Cmcm) has relatively slow formation kinetics suggesting why it does not form at room temperature during the electrochemical reaction; (iii) orthorhombic Na14.78Sn4 (Pnma), better described as Na16-xSn4, is Na-richer than cubic Na15Sn4 (I-43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, at the exception of Na7Sn3 and Na15Sn4, different crystal structures than similar Na-Sn compositions prepared via classic solid state reactions are formed. These phases are composed of disordered structures characteristic of kinetic-driven solid-state amorphization reactions. In these structures, Sn coordinates in asymmetric environments, which differ significantly from the environments present in Na-Sn model compounds.

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

    NASA Astrophysics Data System (ADS)

    Li, Wei; Henke, Sebastian; Cheetham, Anthony K.

    2014-12-01

    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.

  12. Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite

    NASA Astrophysics Data System (ADS)

    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).

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

    PubMed

    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.

  14. Interactions between free radicals and a graphene fragment: physical versus chemical bonding, charge transfer, and deformation.

    PubMed

    Wang, Fengting T; Chen, Lei; Tian, Chuanjin J; Meng, Yan; Wang, Zhigang G; Zhang, Ruiqin Q; Jin, Mingxing X; Zhang, Ping; Ding, Dajun J

    2011-11-30

    The adsorption of six free radicals (FRs) respectively on a graphene fragment was studied using a density functional tight-binding method with the inclusion of an empirical dispersion term in total energy. The results indicate that the different interaction paths between the FRs and the graphene lead to different forms of physical (PA) or chemical adsorptions (CA). The CA appears only in the condition where some of the nonhydrogen atoms are closer to the graphene, with the deformation occurring in the latter. The charge transfer increases with the increase in adsorption energy in every FR-graphene system. Although the deformation in the graphene is negligible in all PA cases, the FR is closer to the graphene and the graphene deformation is clearer in all CA cases, with all atomic displacements being larger than 0.1 Å. Our findings are useful not only for FR scavenging but also for studying the interaction between general molecules and material surfaces.

  15. Surfactant free synthesis of CdS nanospheres, microstructural analysis, chemical bonding, optical properties and photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Ganesh, R. Sankar; Sharma, Sanjeev K.; Durgadevi, E.; Navaneethan, M.; Binitha, H. S.; Ponnusamy, S.; Muthamizhchelvan, C.; Hayakawa, Y.; Kim, Deuk Young

    2017-04-01

    The surfactant free cadmium sulfide (CdS) nanospheres were synthesized by the chemical method in a single step. The uniform shape of CdS spheres was controlled by the variation of concentration of thioacetamide (C2H5NS). The cubic phase of CdS nanopowder was determined from XRD analysis, which closely matched to the standard card. The spherical grains of CdS powder were confirmed from the microstructural analysis. The concentration of thioacetamide (TAA) played a vital role in the formation of nanospheres. The bandgap of CdS nanospheres decreased from 2.44 to 2.22 eV as the mole concentration of C2H5NS increased from 0.05 M to 2.0 M. FTIR spectra confirmed the presence of the stretching bond of Cdsbnd S. The dominant PL peak of purely and uniformed CdS nanospheres was observed at 528 nm due to S vacancies or surface defects. The prepared photocatalyst demonstrated the superior visible light photocatalytic degradation of methylene blue (MB). The highest degradation (96%) of MB was achieved within 180 min. Therefore, CdS nanospheres grown in the single step by the chemical method has a remarkable enhancement in the degradation of pollutants under irradiation of visible light.

  16. Interplay among electrostatic, dispersion and steric interactions: Spectroscopy and quantum chemical calculations of π-hydrogen bonded complexes.

    PubMed

    Kumar, Sumit; Singh, Santosh Kumar; Vaishnav, Jamuna Kanaram; Hill, J Grant; Das, Aloke

    2017-01-26

    π-hydrogen bonding interactions are ubiquitous in both materials and biology. Despite their relatively weak nature great progress has been made in their investigation by experimental and theoretical methods, but this becomes significantly more complicated when secondary intermolecular interactions are present. In this study the effect of successive methyl substitution on the supramolecular structure and interaction energy of indole⋯methylated benzene (ind⋯n-mb, n = 1-6) complexes is probed through a combination of supersonic jet experiment and benchmark quality quantum chemical calculations. It is demonstrated that additional secondary interactions introduce a subtle interplay among electrostatic and dispersion forces, as well as steric repulsion, which fine-tunes the overall structural motif. Resonant Two-Photon Ionization (R2PI) and IR-UV double resonance spectroscopy techniques were used to probe jet-cooled ind⋯n-mb (n = 2, 3, 6) complexes, with red-shifting of the N-H IR stretching frequency showing that increasing the degree of methyl substitution increases the strength of the primary N-H⋯π interaction. Ab initio harmonic frequency and binding energy calculations confirm this trend for all six complexes. Electronic spectra of the three dimers are broad and structureless, with quantum chemical calculations revealing that this is likely due to multiple tilted conformations of each dimer possessing similar stabilization energies.

  17. Revealing unusual chemical bonding in planar hyper-coordinate Ni2Ge and quasi-planar Ni2Si two-dimensional crystals.

    PubMed

    Yang, Li-Ming; Popov, Ivan A; Frauenheim, Thomas; Boldyrev, Alexander I; Heine, Thomas; Bačić, Vladimir; Ganz, Eric

    2015-10-21

    We discover unusual chemical bonding in a novel planar hyper-coordinate Ni2Ge free-standing 2D monolayer, and also in a nearly planar slightly buckled Ni2Si monolayer. This unusual bonding is revealed by Solid State Adaptive Natural Density Partitioning analysis. This analysis shows that a new type of 2c-2e Ni-Si σ and 3c-2e Ni-Ge-Ni σ bonds stabilize these 2D crystals. This is completely different from any previously known 2D crystals. Both of these free-standing monolayers are global minima in two-dimensional space. Although their exotic structure has unprecedented chemical bonding, they show extraordinary stability as single layers. The stabilities of these frameworks are confirmed by phonon dispersion calculations and ab initio molecular dynamics calculations. For Ni2Si, the framework was maintained during short 10 ps molecular dynamics annealing up to 1500 K, while Ni2Ge survived 10 ps runs up to 900 K. Both systems are predicted to be non-magnetic and metallic. As these new 2D crystals contain hypercoordinated Group 14 atoms, they are examples of a new class of 2D crystals with unconventional chemical bonding and potentially exciting new properties. Interestingly, we find that the stabilities of Ni2Si and Ni2Ge are much higher than that of silicene and germanene. Thus, this work provides a novel way to stabilize 2D sheets of Group 14 elements.

  18. A Java chemical structure editor supporting the Modular Chemical Descriptor Language (MCDL).

    PubMed

    Trepalin, Sergei V; Yarkov, Alexander V; Pletnev, Igor V; Gakh, Andrei A

    2006-03-29

    A compact Modular Chemical Descriptor Language (MCDL) chemical structure editor (Java applet) is described. The small size (approximately 200 KB) of the applet allows its use to display and edit chemical structures in various Internet applications. The editor supports the MCDL format, in which structures are presented in compact canonical form and is capable of restoring bond orders as well as of managing atom and bond drawing overlap. A small database of cage and large cyclic fragment is used for optimal representation of difficult-to-draw molecules. The improved algorithm of the structure diagram generation can be used for other chemical notations that lack atomic coordinates (SMILES, InChI).

  19. Distal tibiofibular radiological overlap

    PubMed Central

    Sowman, B.; Radic, R.; Kuster, M.; Yates, P.; Breidiel, B.; Karamfilef, S.

    2012-01-01

    Objectives Overlap between the distal tibia and fibula has always been quoted to be positive. If the value is not positive then an injury to the syndesmosis is thought to exist. Our null hypothesis is that it is a normal variant in the adult population. Methods We looked at axial CT scans of the ankle in 325 patients for the presence of overlap between the distal tibia and fibula. Where we thought this was possible we reconstructed the images to represent a plain film radiograph which we were able to rotate and view in multiple planes to confirm the assessment. Results The scans were taken for reasons other than pathology of the ankle. We found there was no overlap in four patients. These patients were then questioned about previous injury, trauma, surgery or pain, in order to exclude underlying pathology. Conclusion We concluded that no overlap between the tibia and fibula may exist in the population, albeit in a very small proportion. PMID:23610666

  20. Overlap among Environmental Databases.

    ERIC Educational Resources Information Center

    Miller, Betty

    1981-01-01

    Describes the methodology and results of a study comparing the overlap of Enviroline, Pollution, and the Environmental Periodicals Bibliography files through searches on acid rain, asbestos and water, diesel, glass recycling, Lake Erie, Concorde, reverse osmosis wastewater treatment cost, and Calspan. Nine tables are provided. (RBF)

  1. A promising tool to achieve chemical accuracy for density functional theory calculations on Y-NO homolysis bond dissociation energies.

    PubMed

    Li, Hong Zhi; Hu, Li Hong; Tao, Wei; Gao, Ting; Li, Hui; Lu, Ying Hua; Su, Zhong Min

    2012-01-01

    A DFT-SOFM-RBFNN method is proposed to improve the accuracy of DFT calculations on Y-NO (Y = C, N, O, S) homolysis bond dissociation energies (BDE) by combining density functional theory (DFT) and artificial intelligence/machine learning methods, which consist of self-organizing feature mapping neural networks (SOFMNN) and radial basis function neural networks (RBFNN). A descriptor refinement step including SOFMNN clustering analysis and correlation analysis is implemented. The SOFMNN clustering analysis is applied to classify descriptors, and the representative descriptors in the groups are selected as neural network inputs according to their closeness to the experimental values through correlation analysis. Redundant descriptors and intuitively biased choices of descriptors can be avoided by this newly introduced step. Using RBFNN calculation with the selected descriptors, chemical accuracy (≤1 kcal·mol(-1)) is achieved for all 92 calculated organic Y-NO homolysis BDE calculated by DFT-B3LYP, and the mean absolute deviations (MADs) of the B3LYP/6-31G(d) and B3LYP/STO-3G methods are reduced from 4.45 and 10.53 kcal·mol(-1) to 0.15 and 0.18 kcal·mol(-1), respectively. The improved results for the minimal basis set STO-3G reach the same accuracy as those of 6-31G(d), and thus B3LYP calculation with the minimal basis set is recommended to be used for minimizing the computational cost and to expand the applications to large molecular systems. Further extrapolation tests are performed with six molecules (two containing Si-NO bonds and two containing fluorine), and the accuracy of the tests was within 1 kcal·mol(-1). This study shows that DFT-SOFM-RBFNN is an efficient and highly accurate method for Y-NO homolysis BDE. The method may be used as a tool to design new NO carrier molecules.

  2. Improvement in chemical and physical stability of fluvastatin drug through hydrogen bonding interactions with different polymer matrices.

    PubMed

    Papageorgiou, G Z; Papadimitriou, S; Karavas, E; Georgarakis, E; Docoslis, A; Bikiaris, D

    2009-01-01

    Solid dispersions of Fluvastatin with polyvinylpyrrolidone (PVP), eudragit RS100 (Eud), and chitosan (CS) as drug carrier matrices, were prepared using different techniques in order to evaluate their effect on Fluvastatin stability during storage. The characterization of the three different systems was performed with the use of differential scanning calorimetry (DSC) and wide angle X-ray diffractometry (WAXD). It was revealed that amorphization of the drug occurred in all of the solid dispersions of Fluvastatin as a result of drug dissolution into polymer matrices and due to physical interactions (hydrogen bonding) between the polymer matrix and Fluvastatin. This was established through the use of FTIR spectroscopy. SEM and micro-Raman spectroscopy showed that Fluvastatin was interspersed to the polymer matrices in the form of molecular dispersion and nanodispersion, too. The finding that completely different polymer matrices, used here as drug carriers, produce completely different dissolution profiles for each one of the solid dispersions, suggests that each matrix follows a different drug release mechanism. Hydrogen bonding interactions as in the case of CS/Fluva solid dispersions lead to controlled release profiles. All formulations were subjected to accelerated aging in order to evaluate Fluvastatin stability. From by-products analysis it was found that Fluvastatin is very unstable during storage and anti-isomer as well as lactones are the main formed by-products. On the other hand, solid dispersions due to the evolved interactions of their reactive groups with Fluvastatin provide a sufficient physical and chemical stability. The extent of interactions seems to play the most important role in the drug stabilization.

  3. Hydrogen bond geometries and proton tautomerism of homoconjugated anions of carboxylic acids studied via H/D isotope effects on 13C NMR chemical shifts.

    PubMed

    Guo, Jing; Tolstoy, Peter M; Koeppe, Benjamin; Golubev, Nikolai S; Denisov, Gleb S; Smirnov, Sergei N; Limbach, Hans-Heinrich

    2012-11-26

    Ten formally symmetric anionic OHO hydrogen bonded complexes, modeling Asp/Glu amino acid side chain interactions in nonaqueous environment (CDF(3)/CDF(2)Cl solution, 200-110 K) have been studied by (1)H, (2)H, and (13)C NMR spectroscopy, i.e. intermolecularly H-bonded homoconjugated anions of acetic, chloroacetic, dichloroacetic, trifluoroacetic, trimethylacetic, and isobutyric acids, and intramolecularly H-bonded hydrogen succinate, hydrogen rac-dimethylsuccinate, hydrogen maleate, and hydrogen phthalate. In particular, primary H/D isotope effects on the hydrogen bond proton signals as well as secondary H/D isotope effects on the (13)C signals of the carboxylic groups are reported and analyzed. We demonstrate that in most of the studied systems there is a degenerate proton tautomerism between O-H···O(-) and O(-)···H-O structures which is fast in the NMR time scale. The stronger is the proton donating ability of the acid, the shorter and more symmetric are the H-bonds in each tautomer of the homoconjugate. For the maleate and phthalate anions exhibiting intramolecular hydrogen bonds, evidence for symmetric single well potentials is obtained. We propose a correlation between H/D isotope effects on carboxylic carbon chemical shifts and the proton transfer coordinate, q(1) = ½(r(OH) - r(HO)), which allows us to estimate the desired OHO hydrogen bond geometries from the observed (13)C NMR parameters, taking into account the degenerate proton tautomerism.

  4. Localization of double bonds in triacylglycerols using high-performance liquid chromatography/atmospheric pressure chemical ionization ion-trap mass spectrometry.

    PubMed

    Háková, Eva; Vrkoslav, Vladimír; Míková, Radka; Schwarzová-Pecková, Karolina; Bosáková, Zuzana; Cvačka, Josef

    2015-07-01

    A method for localizing double bonds in triacylglycerols using high-performance liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization (APCI) was developed. The technique was based on collision-induced dissociation or pulsed Q collision-induced dissociation of the C3H5N(+•) adducts ([M + 55](+•)) formed in the presence of acetonitrile in the APCI source. The spectra were investigated using a large series of standards obtained from commercial sources and prepared by randomization. The fragmentation spectra made it possible to determine (i) the total number of carbons and double bonds in the molecule, (ii) the number of carbons and double bonds in acyls, (iii) the acyl in the sn-2 position on the glycerol backbone, and (iv) the double-bond positions in acyls. The double-bond positions were determined based on two types of fragments (alpha and omega ions) formed by cleavages of C-C bonds vinylic to the original double bond. The composition of the acyls and their positions on glycerol were established from the masses and intensities of the ions formed by the elimination of fatty acids from the [M + 55](+•) precursor. The method was applied for the analysis of triacylglycerols in olive oil and vernix caseosa.

  5. Evolution of chemical bonding and electron density rearrangements during D(3h) → D(3d) reaction in monolayered TiS2: a QTAIM and ELF study.

    PubMed

    Ryzhikov, Maxim R; Slepkov, Vladimir A; Kozlova, Svetlana G; Gabuda, Svyatoslav P

    2014-08-15

    Monolayered titanium disulfide TiS2, a prospective nanoelectronic material, was previously shown to be subject to an exothermic solid-state D3h -D3d reaction that proceeds via a newly discovered transition state. Here, we study the reaction in detail using topological methods of quantum chemistry (quantum theory of atoms in molecules and electron localization function analysis) and show how electron density and chemical bonding between the atoms change in the course of the reaction. The reaction is shown to undergo a series of topological catastrophes, associated with elementary chemical events such as break and formation of bonds (including the unexpected formation of S-S bonding between sulfur layers), and rearrangement of electron density of outer valence and core shells.

  6. L2 and L3 measurements of transition-metal 5d orbital occupancy, spin-orbit effects, and chemical bonding

    NASA Astrophysics Data System (ADS)

    Qi, Boyun; Perez, I.; Ansari, P. H.; Lu, F.; Croft, M.

    1987-08-01

    We present L2 and L3 x-ray absorption spectroscopy measurements on all of the 5d transition-metal (T) elements and selected TAl2 intermetallic compounds. For the 5d elements we discuss the general trends in the strength of the near-edge "white-line" (WL) feature, the manifestations of the spin-orbit effects, and the dearth of WL strength for Pt and Au. The changes in the intensity of the L-edge WL's in the intermetallic compounds TAl2 (T=Au and Pt) are discussed in terms of strong T-Al chemical bonding. Interestingly, our results for this bonding in AuAl2 are in good agreement with the arguments presented by Pauling [

    The Nature of the Chemical Bond (Cornell Univ. Press, Ithaca, NY, 1960), pp. 431-435
    ].

  7. Effects of Jigsaw Cooperative Learning and Animation Techniques on Students' Understanding of Chemical Bonding and Their Conceptions of the Particulate Nature of Matter

    ERIC Educational Resources Information Center

    Karacop, Ataman; Doymus, Kemal

    2013-01-01

    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…

  8. Effect of RF power and annealing on chemical bonding and morphology of a-CN{sub x} thin films as humidity sensor

    SciTech Connect

    Aziz, N. F. H; Hussain, N. S. Mohamed; Awang, R.; Ritikos, R.; Kamal, S. A. A.

    2013-11-27

    Amorphous carbon nitride (a-CN{sub x}) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique. A set of a-CN{sub x} thin films were prepared using pure methane (CH{sub 4}) gas diluted with nitrogen (N{sub 2}) gas. The rf power was varied at 50, 60, 70, 80, 90 and 100 W. These films were then annealed at 400 °C in a quartz tube furnace in argon (Ar) gas. The effects of rf power and thermal annealing on the chemical bonding and morphology of these samples were studied. Surface profilometer was used to measure film thickness. Fourier transform infra-red spectroscopy (FTIR) and Field emission scanning electron microscopy (FESEM) measurements were used to determine their chemical bonding and morphology respectively. The deposition rate of the films increased constantly with increasing rf power up to 80W, before decreasing with further increase in rf power. Fourier transform infra-red spectroscopy (FTIR) studies showed a systematic change in the spectra and revealed three main peaks included C-N, C=N, C=C and C≡N triple bond. C=N and C≡N bonds decreased with increased C-N bonds after thermal annealing process. The FESEM images showed that the structure is porous for as-deposited and covered by granule-like grain structure after thermal annealing process was done. The resistance of the a-CN{sub x} thin film changed from 23.765 kΩ to 5.845 kΩ in the relative humidity range of 5 to 92 % and the film shows a good response and repeatability as a humidity sensing materials. This work showed that rf power and thermal annealing has significant effects on the chemical bonding and surface morphology of the a-CN{sub x} films and but yield films which are potential candidate as humidity sensor device.

  9. Identifying Misconceptions Related to Chemical Bonding Concepts in the Slovak School System Using the Bonding Representations Inventory as a Diagnostic Tool

    ERIC Educational Resources Information Center

    Vrabec, Michal; Prokša, Miroslav

    2016-01-01

    In this article we present the results of a study in which we tested the use of the experimental inventory BRI (Bonding Representations Inventory), developed by Cynthia J. Luxford and Stacey Lowery Bretz. The aim of our study was to test the usability of the experimental instrument in the Slovak educational system and to identify concrete…

  10. Domain overlap matrices from plane-wave-based methods of electronic structure calculation

    NASA Astrophysics Data System (ADS)

    Golub, Pavlo; Baranov, Alexey I.

    2016-10-01

    Plane waves are one of the most popular and efficient basis sets for electronic structure calculations of solids; however, their delocalized nature makes it difficult to employ for them classical orbital-based methods of chemical bonding analysis. The quantum chemical topology approach, introducing chemical concepts via partitioning of real space into chemically meaningful domains, has no difficulties with plane-wave-based basis sets. Many popular tools employed within this approach, for instance delocalization indices, need overlap integrals over these domains—the elements of the so called domain overlap matrices. This article reports an efficient algorithm for evaluation of domain overlap matrix elements for plane-wave-based calculations as well as evaluation of its implementation for one of the most popular projector augmented wave (PAW) methods on the small set of simple and complex solids. The stability of the obtained results with respect to PAW calculation parameters has been investigated, and the comparison of the results with the results from other calculation methods has also been made.

  11. The Plate Overlap Technique.

    DTIC Science & Technology

    1978-07-31

    INTRODUCTION 1 II. NOTATION 2 III. THE GNOMONIC PROJECTION 4 IV . THE PLATE OVERLAP TECHNIQUE 6 A. MOTIVATION 6 B. FORNULATION 9 C. ON STATISTICAL RIGOR 14 D...and new hardware. Since this aim was clearly recognized long ago, wherever possible in earlier documents or software development flexibility was...reader should see 1, 2, and 3. The procedures one should use to update stellar positions are discussed in 4 with applica- tions to the SAOC in 5. Non

  12. Effects of lithium doping on microstructure, electrical properties, and chemical bonds of sol-gel derived NKN thin films

    SciTech Connect

    Lin, Chun-Cheng; Chen, Chan-Ching; Weng, Chung-Ming; Chu, Sheng-Yuan; Tsai, Cheng-Che

    2015-02-28

    Highly (100/110) oriented lead-free Li{sub x}(Na{sub 0.5}K{sub 0.5}){sub 1−x}NbO{sub 3} (LNKN, x = 0, 0.02, 0.04, and 0.06) thin films are fabricated on Pt/Ti/SiO{sub 2}/Si substrates via a sol-gel processing method. The lithium (Li) dopants modify the microstructure and chemical bonds of the LNKN films, and therefore improve their electrical properties. The optimal values of the remnant polarization (P{sub r} = 14.3 μC/cm{sup 2}), piezoelectric coefficient (d{sub 33} = 48.1 pm/V), and leakage current (<10{sup −5} A/cm{sup 2}) are obtained for a lithium addition of x = 0.04 (i.e., 4 at. %). The observation results suggest that the superior electrical properties are the result of an improved crystallization, a larger grain size, and a smoother surface morphology. It is shown that the ion transport mechanism is dominated by an Ohmic behavior under low electric fields and the Poole-Frenkel emission effect under high electric fields.

  13. Simple fabrication of hydrophilic nanochannels using the chemical bonding between activated ultrathin PDMS layer and cover glass by oxygen plasma.

    PubMed

    Kim, So Hyun; Cui, Yidan; Lee, Min Jung; Nam, Seong-Won; Oh, Doori; Kang, Seong Ho; Kim, Youn Sang; Park, Sungsu

    2011-01-21

    This study describes a simple and low cost method for fabricating enclosed transparent hydrophilic nanochannels by coating low-viscosity PDMS (monoglycidyl ether-terminated polydimethylsiloxane) as an adhesion layer onto the surface of the nanotrenches that are molded with a urethane-based UV-curable polymer, Norland Optical Adhesive (NOA 63). In detail, the nanotrenches made of NOA 63 were replicated from a Si master mold and coated with 6 nm thick layer of PDMS. These nanotrenches underwent an oxygen plasma treatment and finally were bound to a cover glass by chemical bonding between silanol and hydroxyl groups. Hydrophobic recovery that is observed in the bulk PDMS was not observed in the thin film of PDMS on the mold and the PDMS-coated nanochannel maintained its surface hydrophilicity for at least one month. The potentials of the nanochannels for bioapplications were demonstrated by stretching λ-DNA (48,502 bp) in the channels. Therefore, this fabrication approach provides a practical solution for the simple fabrication of the nanochannels for bioapplications.

  14. Evaluation of the flocculation performance of carboxymethyl chitosan-graft-polyacrylamide, a novel amphoteric chemically bonded composite flocculant.

    PubMed

    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.

  15. ``Additive'' cooperativity of hydrogen bonds in complexes of catechol with proton acceptors in the gas phase: FTIR spectroscopy and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Varfolomeev, Mikhail A.; Klimovitskii, Alexander E.; Abaidullina, Dilyara I.; Madzhidov, Timur I.; Solomonov, Boris N.

    2012-06-01

    Experimental study of hydrogen bond cooperativity in hetero-complexes in the gas phase was carried out by IR-spectroscopy method. Stretching vibration frequencies of Osbnd H groups in phenol and catechol molecules as well as of their complexes with nitriles and ethers were determined in the gas phase using a specially designed cell. Osbnd H groups experimental frequency shifts in the complexes of catechol induced by the formation of intermolecular hydrogen bonds are significantly higher than in the complexes of phenol due to the hydrogen bond cooperativity. It was shown that the cooperativity factors of hydrogen bonds in the complexes of catechol with nitriles and ethers in the gas phase are approximately the same. Quantum chemical calculations of the studied systems have been performed using density functional theory (DFT) methods. It was shown, that theoretically obtained cooperativity factors of hydrogen bonds in the complexes of catechol with proton acceptors are in good agreement with experimental values. Cooperative effects lead to a strengthening of intermolecular hydrogen bonds in the complexes of catechol on about 30%, despite the significant difference in the proton acceptor ability of the bases. The analysis within quantum theory of atoms in molecules was carried out for the explanation of this fact.

  16. "Additive" cooperativity of hydrogen bonds in complexes of catechol with proton acceptors in the gas phase: FTIR spectroscopy and quantum chemical calculations.

    PubMed

    Varfolomeev, Mikhail A; Klimovitskii, Alexander E; Abaidullina, Dilyara I; Madzhidov, Timur I; Solomonov, Boris N

    2012-06-01

    Experimental study of hydrogen bond cooperativity in hetero-complexes in the gas phase was carried out by IR-spectroscopy method. Stretching vibration frequencies of O-H groups in phenol and catechol molecules as well as of their complexes with nitriles and ethers were determined in the gas phase using a specially designed cell. O-H groups experimental frequency shifts in the complexes of catechol induced by the formation of intermolecular hydrogen bonds are significantly higher than in the complexes of phenol due to the hydrogen bond cooperativity. It was shown that the cooperativity factors of hydrogen bonds in the complexes of catechol with nitriles and ethers in the gas phase are approximately the same. Quantum chemical calculations of the studied systems have been performed using density functional theory (DFT) methods. It was shown, that theoretically obtained cooperativity factors of hydrogen bonds in the complexes of catechol with proton acceptors are in good agreement with experimental values. Cooperative effects lead to a strengthening of intermolecular hydrogen bonds in the complexes of catechol on about 30%, despite the significant difference in the proton acceptor ability of the bases. The analysis within quantum theory of atoms in molecules was carried out for the explanation of this fact.

  17. Chemical bonding and charge redistribution - Valence band and core level correlations for the Ni/Si, Pd/Si, and Pt/Si systems

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Grunthaner, F. J.; Madhukar, A.

    1982-01-01

    Via a systematic study of the correlation between the core and valence level X-ray photoemission spectra, the nature of the chemical bonding and charge redistribution for bulk transition metal silicides has been examined. Particular emphasis is placed on Pt2Si and PtSi. It is observed that the strength of the metal (d)-silicon (p) interaction increases in the order Ni2Si, Pd2Si, Pt2Si. It is also observed that both the metal and silicon core lines shift to higher binding energy as the silicides are formed. The notion of charge redistribution for metallic bonds is invoked to explain these data.

  18. Using Multiple Bonding Strategies.

    PubMed

    Larson, Thomas D

    2015-01-01

    There are many ways to bond to tooth structure, some micro-mechanical some chemical, some a combination. Different dentin bonding materials have different bonding strengths to differently prepared surfaces, and because of differences in their nature, different areas of tooth structure present peculiar bonding challenges. This paper will review a variety of material types, elucidating their particular bonding strengths and commenting on improved bonding strategies to increase durability, strength, and favorable pulpal response. In this discussion, resin dentin bonding systems, glass ionomers, Gluma, resin cements, and newer combined products will br reviewed.

  19. Characterization of metallic foil joints using diffusion bonding and diffusion soldering in micro-technology-based energy and chemical systems

    SciTech Connect

    Gabriel, Michael; Paul, B.K.; Wilson, R.D.

    2001-01-01

    The several 316 stainless steel mesoscopic devices were made using diffusing bonding and diffusion soldering. Tensile strength, pressure drop of the devices were measured, and metallurgical examinations were made of the joints. Continuous bonds were observed in both diffusion bonded and diffusion soldered samples. Strengths of the diffusion soldered samples were up to 80% of the strength of the Ag3Sn joint material or 125 MPa. The pressure drop in diffusion soldered samples was 0.76 psi at the highest flow rates of 2.08 L/min. Diffusion bonded joints had strengths of up to 700 MPa but the back pressures were higher at all flow rates.

  20. Characterization of metallic foil joints using diffusion bonding and diffusion soldering in micro-technology-based energy and chemical systems

    SciTech Connect

    Gabriel, Michael; Paul, Brian K.; Wilson, Rick D.; Alman, David E.

    2001-01-10

    The several 316 stainless steel mesoscopic devices were made using diffusing bonding and diffusion soldering. Tensile strength, pressure drop of the devices were measured, and metallurgical examinations were made of the joints. Continuous bonds were observed in both diffusion bonded and diffusion soldered samples. Strengths of the diffusion soldered samples were up to 80% of the strength of the Ag(sub3) Sn joint material or 125 MPa. The pressure drop in diffusion soldered samples was 0.76 psi at the highest flow rates of 2.08 L/min. Diffusion bonded joints had strengths of up to 700 MPa but the back pressures were higher at all flow rates.

  1. Effect of Mechanical and Chemical Root Surface Treatment on the Shear Bond Strength of Intracanal Post in Primary Anterior Teeth: An In vitro Study

    PubMed Central

    Karthikeyan, Shanmugaavel; Subramanian, EMG; Gurunathan, Deepa

    2017-01-01

    Abstract Introduction Aesthetic restoration of severely mutilated primary anterior teeth still remains as a special challenge to paediatric dentist. Due to increased parent’s concern for aesthetic rehabilitation for their children, paediatric dentist are in a state to improve technique sensitive restorative procedure to improve aesthetic rehabilitation in children. Aim The purpose of the study was to evaluate the effect of different root surface treatment on the shear bond strength of glass fibre reinforced post in primary anterior teeth using Universal Testing Machine (UTM). Materials and Methods Twenty single rooted primary anterior teeth were selected. Coronal portions of the teeth were sectioned transversally 2 mm above the Cemento-Enamel Junction (CEJ) and specimens were treated endodontically and obturated using metapex. Then the specimens were randomly divided into four groups. Group 1: Control group; Group 2: Chemical surface treatment of the root with 2% chlorhexidine; Group 3: Mechanical surface treatment with mushroom-shaped undercut; Group 4: Combination of mechanical and chemical surface treatments. Samples were tested for shear bond strength. ANOVA and Post-hoc Tukey test were used for statistical analysis using SPSS version 20.0. Results Combination of mechanical and chemical surface treatments exhibited higher mean shear bond strength (8.41 MPa), followed by mechanical surface treatment (4.68 MPa), chemical surface treatment (3.92 MPa) and control group (2.76 MPa). Conclusion Mechanical and chemical surface treatments together led to a improved shear bond strength and increased the retention of the post to the root surface. PMID:28274043

  2. 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.

    PubMed

    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.

  3. The Nature of the Chemical Bond in Linear Three-Body Systems: From I3− to Mixed Chalcogen/Halogen and Trichalcogen Moieties

    PubMed Central

    Aragoni, M. Carla; Arca, Massimiliano; Devillanova, Francesco A.; Garau, Alessandra; Isaia, Francesco; Lippolis, Vito; Mancini, Annalisa

    2007-01-01

    The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3− and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I3− anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom. PMID:18389065

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

    PubMed

    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.

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

    PubMed

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

    2014-02-19

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

  6. Solvent-free thermoplastic-poly(dimethylsiloxane) bonding mediated by UV irradiation followed by gas-phase chemical deposition of an adhesion linker

    NASA Astrophysics Data System (ADS)

    Ahn, S. Y.; Lee, N. Y.

    2015-07-01

    Here, we introduce a solvent-free strategy for bonding various thermoplastic substrates with poly(dimethylsiloxane) (PDMS) using ultraviolet (UV) irradiation followed by the gas-phase chemical deposition of aminosilane on the UV-irradiated thermoplastic substrates. The thermoplastic substrates were first irradiated with UV for surface hydrophilic treatment and were then grafted with vacuum-evaporated aminosilane, where the alkoxysilane side reacted with the oxidized surface of the thermoplastic substrate. Next, the amine-terminated thermoplastic substrates were treated with corona discharge to oxidize the surface and were bonded with PDMS, which was also oxidized via corona discharge. The two substrates were then hermetically sealed and pressed under atmospheric pressure for 30 min at 60 °C. This process enabled the formation of a robust siloxane bond (Si-O-Si) between the thermoplastic substrate and PDMS under relatively mild conditions using an inexpensive and commercially available UV lamp and Tesla coil. Various thermoplastic substrates were examined for bonding with PDMS, including poly(methylmethacrylate) (PMMA), polycarbonate (PC), poly(ethyleneterephthalate) (PET) and polystyrene (PS). Surface characterizations were performed by measuring the contact angle and performing x-ray photoelectron spectroscopy analysis, and the bond strength was analyzed by conducting various mechanical force measurements such as pull, delamination, leak and burst tests. The average bond strengths for the PMMA-PDMS, PC-PDMS, PET-PDMS and PS-PDMS assemblies were measured at 823.6, 379.3, 291.2 and 229.0 kPa, respectively, confirming the highly reliable performance of the introduced bonding strategy.

  7. Effect of different chemical bonds in pegylation of zinc protoporphyrin that affects drug release, intracellular uptake, and therapeutic effect in the tumor.

    PubMed

    Tsukigawa, Kenji; Nakamura, Hideaki; Fang, Jun; Otagiri, Masaki; Maeda, Hiroshi

    2015-01-01

    Pegylated zinc protoporphyrin (PEG-ZnPP) is a water-soluble inhibitor of heme oxygenase-1. In this study, we prepared two types of PEG-ZnPP conjugates with different chemical bonds between PEG and ZnPP, i.e., ester bonds and ether bonds, where both conjugates also contain amide bonds. Cleavability of these bonds in vitro and in vivo, especially cancer tissue, and upon intracellular uptake, was investigated in parallel with biological activities of the conjugates. Each conjugate showed different cleavability by plasma esterases and tumor proteases, as revealed by HPLC analyses. PEG-ZnPP with ester bond (esPEG-ZnPP) was more sensitive than PEG-ZnPP with ether bond (etPEG-ZnPP) for cleavage of PEG chains. etPEG-ZnPP showed no cleavage of PEG chains and had lower intracellular uptake and antitumor activity than did esPEG-ZnPP. The degradation of esPEG-ZnPP appeared to be facilitated by both serine and cysteine proteases in tumor tissues, whereas it was significantly slower in normal organs except the liver. Depegylated products such as free ZnPP had higher intracellular uptake than did intact PEG-ZnPP. We also studied hydrolytic cleavage by blood plasma of different animal species; mouse plasma showed the fastest cleavage whereas human plasma showed the slowest. These results suggest that ester-linked conjugates manifest more efficient cleavage of PEG, and greater yield of the active principle from the conjugates in tumor tissues than in normal tissues. More efficient intracellular uptake and thus an improved therapeutic effect with ester-linked conjugates are thus anticipated with fain stability, particularly in human blood.

  8. Chemical Bonding Analysis as a Guide for the Preparation of New Compounds: The Case of VIrGe and HfPtGe.

    PubMed

    Bende, David; Wagner, Frank R; Sichevych, Olga; Grin, Yuri

    2017-01-24

    The chemical bonding of transition metal compounds with a MgAgAs-type of crystal structure is analyzed with quantum chemical position-space techniques. The observed trends in QTAIM Madelung energy and nearest neighbor electron sharing explain the occurrence of recently synthesized MgAgAs-type compounds, TiPtGe and TaIrGe, at the boundary to the TiNiSi-type crystal structure. These bonding indicators are used to identify favorable element combinations for new MgAgAs-type compounds. The new phases-the high-temperature VIrGe and the low-temperature HfPtGe-showing this type of crystal structure are prepared and characterized by powder X-ray diffraction and differential thermal analysis.

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

    PubMed

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

    2014-01-01

    This study aims to cast light on the physico-chemical nature and energetic of the non-conventional CH···O/N H-bonds in the biologically important natural nucleobase pairs using a comprehensive quantum-chemical approach. As a whole, the 36 biologically important pairs, involving canonical and rare tautomers of nucleobases, were studied by means of all available up-to-date state-of-the-art quantum-chemical techniques along with quantum theory "Atoms in molecules" (QTAIM), Natural Bond Orbital (NBO) analysis, Grunenberg's compliance constants theory, geometrical and vibrational analyses to identify the CH···O/N interactions, reveal their physico-chemical nature and estimate their strengths as well as contribution to the overall base-pairs stability. It was shown that all the 38 CH···O/N contacts (25 CH···O and 13 CH···N H-bonds) completely satisfy all classical geometrical, electron-topological, in particular Bader's and "two-molecule" Koch and Popelier's, and vibrational criteria of H-bonding. The positive values of Grunenberg's compliance constants prove that the CH···O/N contacts in nucleobase pairs are stabilizing interactions unlike electrostatic repulsion and anti-H-bonds. NBO analysis indicates the electron density transfer from the lone electron pair of the acceptor atom (O/N) to the antibonding orbital corresponding to the donor group σ(∗)(CH). Moreover, significant increase in the frequency of the out-of-plane deformation modes γ (CH) under the formation of the CH···O (by 17.2÷81.3/10.8÷84.7 cm(-1)) and CH···N (by 32.7÷85.9/9.0÷77.9 cm(-1)) H-bonds at the density functional theory (DFT)/second-order Møller-Plesset (MP2) levels of theory, respectively, and concomitant changes of their intensities can be considered as reliable indicators of H-bonding. The strengths of the CH···O/N interactions, evaluated by means of Espinosa-Molins-Lecomte formula, lie within the range 0.45÷3.89/0.62÷4.10 kcal/mol for the CH

  10. Chemical Speciation and Bond Lengths of Organic Solutes by Core-Level Spectroscopy: pH and Solvent Influence on p -Aminobenzoic Acid

    SciTech Connect

    Stevens, Joanna S.; Gainar, Adrian; Suljoti, Edlira; Xiao, Jie; Golnak, Ronny; Aziz, Emad F.; Schroeder, Sven L. M.

    2015-03-18

    Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para-aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs and σ* shape resonances in the NEXAFS spectra. Finally, this provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions.

  11. Effects of Different Surface Treatments on the Tensile Bond Strength of Polymethyl Methacrylate Processed against Chemically Etched Ticonium 100

    DTIC Science & Technology

    1988-01-01

    Silanes have also been used to Spromote bonding between resins and ceramics and metals. A common silane used in dentistry is the ester of...surface active comonomers and coupling agents. The latter contain polar groups whereas the former do not. Historically, organofunctional silanes have been...leaving the vinyl group to react and form a bond with the resin. 23 Bowen’s resin was composed partly of %24 % silane treated glass particles.24

  12. A photoelectron spectroscopy and ab initio study of the structures and chemical bonding of the B{sub 25}{sup −} cluster

    SciTech Connect

    Piazza, Zachary A.; Li, Wei-Li; Wang, Lai-Sheng E-mail: lai-sheng-wang@brown.edu; Popov, Ivan A.; Boldyrev, Alexander I. E-mail: lai-sheng-wang@brown.edu; Pal, Rhitankar; Cheng Zeng, Xiao

    2014-07-21

    Photoelectron spectroscopy and ab initio calculations are used to investigate the structures and chemical bonding of the B{sub 25}{sup −} cluster. Global minimum searches reveal a dense potential energy landscape with 13 quasi-planar structures within 10 kcal/mol at the CCSD(T)/6-311+G(d) level of theory. Three quasi-planar isomers (I, II, and III) are lowest in energy and nearly degenerate at the CCSD(T) level of theory, with II and III being 0.8 and 0.9 kcal/mol higher, respectively, whereas at two density functional levels of theory isomer III is the lowest in energy (8.4 kcal/mol more stable than I at PBE0/6-311+G(2df) level). Comparison with experimental photoelectron spectroscopic data shows isomer II to be the major contributor while isomers I and III cannot be ruled out as minor contributors to the observed spectrum. Theoretical analyses reveal similar chemical bonding in I and II, both involving peripheral 2c-2e B−B σ-bonding and delocalized interior σ- and π-bonding. Isomer III has an interesting elongated ribbon-like structure with a π-bonding pattern analogous to those of dibenzopentalene. The high density of low-lying isomers indicates the complexity of the medium-sized boron clusters; the method dependency of predicting relative energies of the low-lying structures for B{sub 25}{sup −} suggests the importance of comparison with experiment in determining the global minima of boron clusters at this size range. The appearance of many low-lying quasi-planar structures containing a hexagonal hole in B{sub 25}{sup −} suggests the importance of this structural feature in maintaining planarity of larger boron clusters.

  13. Mechanical and Microstructure Study of Nickel-Based ODS Alloys Processed by Mechano-Chemical Bonding and Ball Milling

    NASA Astrophysics Data System (ADS)

    Amare, Belachew N.

    Due to the need to increase the efficiency of modern power plants, land-based gas turbines are designed to operate at high temperature creating harsh environments for structural materials. The elevated turbine inlet temperature directly affects the materials at the hottest sections, which includes combustion chamber, blades, and vanes. Therefore, the hottest sections should satisfy a number of material requirements such as high creep strength, ductility at low temperature, high temperature oxidation and corrosion resistance. Such requirements are nowadays satisfied by implementing superalloys coated by high temperature thermal barrier coating (TBC) systems to protect from high operating temperature required to obtain an increased efficiency. Oxide dispersive strengthened (ODS) alloys are being considered due to their high temperature creep strength, good oxidation and corrosion resistance for high temperature applications in advanced power plants. These alloys operating at high temperature are subjected to different loading systems such as thermal, mechanical, and thermo-mechanical combined loads at operation. Thus, it is critical to study the high temperature mechanical and microstructure properties of such alloys for their structural integrity. The primary objective of this research work is to investigate the mechanical and microstructure properties of nickel-based ODS alloys produced by combined mechano-chemical bonding (MCB) and ball milling subjected to high temperature oxidation, which are expected to be applied for high temperature turbine coating with micro-channel cooling system. Stiffness response and microstructure evaluation of such alloy systems was studied along with their oxidation mechanism and structural integrity through thermal cyclic exposure. Another objective is to analyze the heat transfer of ODS alloy coatings with micro-channel cooling system using finite element analysis (FEA) to determine their feasibility as a stand-alone structural

  14. Development of novel sol-gel coatings by chemically bonded ionic liquids for stir bar sorptive extraction--application for the determination of NSAIDS in real samples.

    PubMed

    Fan, Wenying; Mao, Xiangju; He, Man; Chen, Beibei; Hu, Bin

    2014-11-01

    In this work, a novel ionic liquid (IL) chemically bonded sol-gel coating was prepared for stir bar sorptive extraction (SBSE) of nonsteroidal anti-inflammatory drugs (NSAIDs) followed by high-performance liquid chromatography-ultraviolet detection (HPLC-UV). By using γ-(methacryloxypropyl)trimethoxysilane (KH-570) as a bridging agent, 1-allylimidazolium tetrafluoroborate ([AIM][BF4]) was chemically bonded onto the bare stir bar, and the prepared IL-bonded sol-gel stir bar coating showed higher extraction efficiency and better adsorption/desorption kinetics for target NSAIDs over other polydimethylsiloxane (PDMS)-based or monolithic stir bar coatings. The mechanical strength and durability (chemical/thermal stability) of the prepared IL-bonded sol-gel coating were excellent. The influencing factors of SBSE, such as sample pH, salt effect, stirring rate, extraction time, desorption solvent, and desorption time, were optimized, and the analytical performance of the developed SBSE-HPLC-UV method was evaluated under the optimized conditions. The limits of detection (LODs) of the proposed method for three NSAIDs were in the range of 0.23-0.31 μg L(-1), and the enrichment factors (EFs) were in the range of 51.6-56.3 (theoretical enrichment factor was 100). The reproducibility was also investigated at concentrations of 5, 20, and 100 μg L(-1), and the relative standard deviations (RSDs) were found to be less than 9.5, 7.5, and 7.6 %, respectively. The proposed method was successfully applied for the determination of NSAIDs in environmental water, urine, and milk samples.

  15. 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.

    PubMed

    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.

  16. P-H bonds in the surface unit cell of P-rich ordered InP(001) grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Letzig, T.; Schimper, H.-J.; Hannappel, T.; Willig, F.

    2005-01-01

    The Fourier transform infrared spectrum of the MOCVD-grown (metalorganic chemical vapor deposition) P-rich ordered InP(001) surface was measured in ultrahigh vacuum applying attenuated total reflection. The surface was measured without carrying out any post-transfer surface preparation. The low-energy electron defraction pattern showed the well-known (2×1) structure with streaks in the [-110] direction. After exposure to activated deuterium, the different infrared spectrum revealed a pronounced peak at 2308cm-1 , which was ascribed to P-H bonds. Polarization-dependent spectra showed the dipole moments of the P-H bonds oriented only in [001] and [-110] directions. A weak 0.8cm-1 splitting was measured between the symmetric and antisymmetric modes of two neighboring P-H bonds. These observations provide direct proof for two oriented P-H bonds as in the surface unit cell proposed by Hahn and Schmidt [Surf. Rev. Lett. 10, 163 (2003)]. Additional much smaller peaks with different polarization behavior varied greatly for different samples and were ascribed to defects or impurities.

  17. Evidence for excited-state intramolecular proton transfer in 4-chlorosalicylic acid from combined experimental and computational studies: Quantum chemical treatment of the intramolecular hydrogen bonding interaction

    NASA Astrophysics Data System (ADS)

    Paul, Bijan Kumar; Guchhait, Nikhil

    2012-07-01

    The photophysical study of a pharmaceutically important chlorine substituted derivative of salicylic acid viz., 4-chlorosalicylic acid (4ClSA) has been carried out by steady-state absorption, emission and time-resolved emission spectroscopy. A large Stokes shifted emission band with negligible solvent polarity dependence marks the spectroscopic signature of excited-state intramolecular proton transfer (ESIPT) reaction in 4ClSA. Theoretical calculation by ab initio and Density Functional Theory methods yields results consistent with experimental findings. Theoretical potential energy surfaces predict the occurrence of proton transfer in S1-state. Geometrical and energetic criteria, Atoms-In-Molecule topological parameters, Natural Bond Orbital population analysis have been exploited to evaluate the intramolecular hydrogen bond (IMHB) interaction and to explore its directional nature. The inter-correlation between aromaticity and resonance assisted H-bond is also discussed in this context. Our results unveil that the quantum chemical treatment is a more accurate tool to assess hydrogen bonding interaction in comparison to geometrical criteria.

  18. Bonding in diborane-metal complexes: a quantum-chemical and experimental study of complexes featuring early and late transition metals.

    PubMed

    Wagner, Arne; Kaifer, Elisabeth; Himmel, Hans-Jörg

    2013-06-03

    The coordination chemistry of the doubly base-stabilised diborane(4), [HB(hpp)]2 (hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido-[1,2-a]pyrimidinate), was extended by the synthesis of new late transition-metal complexes containing Cu(I) and Rh(I) fragments. A detailed experimental study was conducted and quantum-chemical calculations on the metal-ligand bonding interactions for [HB(hpp)]2 complexes of Group 6, 9, 11 and 12 metals revealed the dominant B-H-M interactions in the case of early transition-metal fragments, whereas the B-B-M bonding prevails in the case of the late d-block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]2 and model reactions between [B2H4⋅2NMe3] and [Rh(μ-Cl)(C2H4)2] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B-B bond. However, the formation of σ-complexes is thermodynamically favoured. The results point to the selective B-H or B-B bond-activation of diborane compounds by complexation, depending on the chosen transition-metal fragment.

  19. Energy and geometry of cooperative hydrogen bonds in p-substituted calix[n]- and thiacalix[n]arenes: a quantum-chemical approach.

    PubMed

    Novikov, Andrej N; Shapiro, Yury E

    2012-01-12

    (Thia)calix[n]arenes have been widely applied as molecular platforms and host molecules in supramolecular chemistry due to their high level of preorganization and well-detectable conformational preferences. Here we report on quantum-chemical calculations allowing the conformational analysis of p-substituted calix[4]-, calix[6]-, thiacalix[4]-, and thiacalix[6]arenes. To this effect, ab initio and density functional theory (DFT) calculations with the aid of RHF/3-21G, B3LYP/6-31G, B3LYP/6-31G(d,p), and B3LYP/6-311G(d,p) have been applied. The obtained structural data and the estimated energies of the intramolecular hydrogen bonds give clear evidence of the presence of cooperative effects of the hydrogen bonding. Multiple correlations between the pairs of Hammett constants of substituents and the calculated values of hydrogen bond energies in the corresponding p-substituted (thia)calix[n]arenes have been found. These energies can be considered as descriptors of a chemical reactivity of the p-substituted derivatives of (thia)calix[n]arenes. For example, the reaction of nucleophilic substitution, involving p-substituted calix[6]arenes in the presence of weak bases and in aprotic solvents or in the gas phase, under orbital control conditions should proceed through the diastereomeric transition states. Here, the achiral p-substituted calix[6]arene derivative mainly forms as an intermediate product of the reaction with a substrate without asymmetric centers.

  20. Theoretical description of halogen bonding - an insight based on the natural orbitals for chemical valence combined with the extended-transition-state method (ETS-NOCV).

    PubMed

    Mitoraj, Mariusz P; Michalak, Artur

    2013-11-01

    In the present study we have characterized the halogen bonding in selected molecules H3N-ICF3 (1-NH 3 ), (PH3)2C-ICF3 (1-CPH 3 ), C3H7Br-(IN2H2C3)2C6H4 (2-Br), H2-(IN2H2C3)2C6H4 (2-H 2 ) and Cl-(IC6F5)2C7H10N2O5 (3-Cl), containing from one halogen bond (1-NH 3 , 1-CPH 3 ) up to four connections in 3-Cl (the two Cl-HN and two Cl-I), based on recently proposed ETS-NOCV analysis. It was found based on the NOCV-deformation density components that the halogen bonding C-X (…) B (X-halogen atom, B-Lewis base), contains a large degree of covalent contribution (the charge transfer to X (…) B inter-atomic region) supported further by the electron donation from base atom B to the empty σ*(C-X) orbital. Such charge transfers can be of similar importance compared to the electrostatic stabilization. Further, the covalent part of halogen bonding is due to the presence of σ-hole at outer part of halogen atom (X). ETS-NOCV approach allowed to visualize formation of the σ-hole at iodine atom of CF3I molecule. It has also been demonstrated that strongly electrophilic halogen bond donor, [C6H4(C3H2N2I)2][OTf]2, can activate chemically inert isopropyl bromide (2-Br) moiety via formation of Br-I bonding and bind the hydrogen molecule (2-H 2 ). Finally, ETS-NOCV analysis performed for 3-Cl leads to the conclusion that, in terms of the orbital-interaction component, the strength of halogen (Cl-I) bond is roughly three times more important than the hydrogen bonding (Cl-HN).

  1. On the nature of chemical bonding in the all-metal aromatic [Sb3Au3Sb3](3-) sandwich complex.

    PubMed

    You, Xue-Rui; Tian, Wen-Juan; Li, Da-Zhi; Wang, Ying-Jin; Li, Rui; Feng, Lin-Yan; Zhai, Hua-Jin

    2016-05-21

    In a recent communication, an all-metal aromatic sandwich [Sb3Au3Sb3](3-) was synthesized and characterized. We report herein a density-functional theory (DFT) study on the chemical bonding of this unique cluster, which makes use of a number of computational tools, including the canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), Wiberg bond index, and orbital composition analyses. The 24-electron, triangular prismatic sandwich is intrinsically electron-deficient, being held together via six Sb-Sb, three Au-Au, and six Sb-Au links. A standard, qualitative bonding analysis suggests that all CMOs are primarily located on the three Sb3/Au3/Sb3 layers, three Au 6s based CMOs are fully occupied, and the three extra charges are equally shared by the two cyclo-Sb3 ligands. This bonding picture is referred to as the zeroth order model, in which the cluster can be formally formulated as [Sb3(1.5+)Au3(3-)Sb3(1.5+)](3-) or [Sb3(0)Au3(3-)Sb3(0)]. However, the system is far more complex and covalent than the above picture. Seventeen CMOs out of 33 in total involve remarkable Sb → Au electron donation and Sb ← Au back-donation, which are characteristic of covalent bonding and effectively redistribute electrons from the Sb3 and Au3 layers to the interlayer edges. This effect collectively leads to three Sb-Au-Sb three-center two-electron (3c-2e) σ bonds as revealed in the AdNDP analyses, despite the fact that not a single such bond can be identified from the CMOs. Orbital composition analyses for the 17 CMOs allow a quantitative understanding of how electron donation and back-donation redistribute the charges within the system from the formal Sb3(0)/Au3(3-) charge states in the zeroth order model to the effective Sb3(1.5-)/Au3(0) charge states, the latter being revealed from the natural bond orbital analysis.

  2. Evaluation of Questions in General Chemistry Textbooks According to the Form of the Questions and the Question-Answer Relationship (QAR): The Case of Intra-and Intermolecular Chemical Bonding

    ERIC Educational Resources Information Center

    Pappa, Eleni T.; Tsaparlis, Georgios

    2011-01-01

    One way of checking to what extent instructional textbooks achieve their aim is to evaluate the questions they contain. In this work, we analyze the questions that are included in the chapters on chemical bonding of ten general chemistry textbooks. We study separately the questions on intra- and on intermolecular bonding, with the former…

  3. First-principles calculations of the structural, elastic, electronic, chemical bonding and optical properties of zinc-blende and rocksalt GeC

    NASA Astrophysics Data System (ADS)

    Liu, Qi-Jun; Liu, Zheng-Tang; Che, Xing-Sen; Feng, Li-Ping; Tian, Hao

    2011-12-01

    Structural parameters, elastic, electronic, bonding and optical properties of zinc-blende and rocksalt GeC have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeC are found to be elastically stable and we have obtained the bulk, shear and Young's modulus, Poisson's coefficient and Lamé's constants for zinc-blende and rocksalt GeC. We estimated the Debye temperature of zinc-blende and rocksalt GeC from the acoustic velocity. Electronic and chemical bonding properties have been studied. Moreover, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated.

  4. Band alignment and chemical bonding at the GaAs/Al{sub 2}O{sub 3} interface: A hybrid functional study

    SciTech Connect

    Colleoni, Davide Miceli, Giacomo; Pasquarello, Alfredo

    2015-11-23

    The band alignment at the interface between GaAs and amorphous Al{sub 2}O{sub 3} is studied through the use of hybrid functionals. For the oxide component, a disordered model is generated through density-functional molecular dynamics. The achieved structure shows good agreement with the experimental characterization. The potential line-up across the interface is obtained for two atomistic GaAs/Al{sub 2}O{sub 3} interface models, which differ by the GaAs substrate termination. The calculated valence band offset amounts to 3.9 eV for an interface characterized by the occurrence of Ga–O bonds as dominant chemical bonding, favoring the high-energy side in the range of experimental values (2.6–3.8 eV). The effect of As antisite and As–As dimer defects on the band alignment is shown to be negligible.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Chemical bonding in the outer core: high-pressure electronic structures of oxygen and sulfur in metallic iron

    USGS Publications Warehouse

    Sherman, David M.

    1991-01-01

    The electronic structures of oxygen and sulfur impurities in metallic iron are investigated to determine if pressure, temperature, and composition-induced changes in bonding might affect phase equilibria along the Fe-FeS and Fe-FeO binaries. -from Authors

  7. Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile.

    PubMed

    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

  8. A quantum chemical insight to intermolecular hydrogen bonding interaction between cytosine and nitrosamine: Structural and energetic investigations

    NASA Astrophysics Data System (ADS)

    Khalili, Behzad

    2016-03-01

    Hydrogen bond interactions which are formed during complex formation between cytosine and nitrosamine have been fully investigated using B3LYP, B3PW91 and MP2 methods in conjunction with various basis sets including 6-311++G (d,p), 6-311++G (2d,2p), 6-311++G (df,pd) and AUG-cc-pVDZ. Three regions around the most stable conformer of cytosine in the gas phase with six possible double H-bonded interactions were considered. Two intermolecular hydrogen bonds of type NC-N-HNA and O-H(N-H)C-ONA were found on the potential energy surface in a cyclic system with 8-member in CN1, CN3, CN5 and 7-member in CN2, CN4, CN6 systems. Results of binding energy calculation at all applied methods reveal that the CN1 structure is the most stable one which is formed by interaction of nitrosamine with cytosine in S1 region. The BSSE-corrected binding energy for six complex system is ranging from -23.8 to -43.6 kJ/mol at MP2/6-311++G (df,pd) level and the stability order is as CN1 > CN2 > CN3 > CN4 > CN5 > CN6 in all studied levels of theories. The NBO results reveal that the charge transfer occurred from cytosine to nitrosamine in CN1, CN3, CN5 and CN6 whereas this matter in the case of CN2 and CN4 was reversed. The relationship between BEs with red shift of H-bond involved bonds vibrational frequencies, charge transfer energies during complex formation and electron densities at H-bond BCPs were discussed. In addition activation energetic properties related to the proton transfer process between cytosine and nitrosamine have been calculated at MP2/6-311++G (df,pd) level. AIM results imply that H-bond interactions are electrostatic with partially covalent characteristic in nature.

  9. Overlapping clusters for distributed computation.

    SciTech Connect

    Mirrokni, Vahab; Andersen, Reid; Gleich, David F.

    2010-11-01

    Scalable, distributed algorithms must address communication problems. We investigate overlapping clusters, or vertex partitions that intersect, for graph computations. This setup stores more of the graph than required but then affords the ease of implementation of vertex partitioned algorithms. Our hope is that this technique allows us to reduce communication in a computation on a distributed graph. The motivation above draws on recent work in communication avoiding algorithms. Mohiyuddin et al. (SC09) design a matrix-powers kernel that gives rise to an overlapping partition. Fritzsche et al. (CSC2009) develop an overlapping clustering for a Schwarz method. Both techniques extend an initial partitioning with overlap. Our procedure generates overlap directly. Indeed, Schwarz methods are commonly used to capitalize on overlap. Elsewhere, overlapping communities (Ahn et al, Nature 2009; Mishra et al. WAW2007) are now a popular model of structure in social networks. These have long been studied in statistics (Cole and Wishart, CompJ 1970). We present two types of results: (i) an estimated swapping probability {rho}{infinity}; and (ii) the communication volume of a parallel PageRank solution (link-following {alpha} = 0.85) using an additive Schwarz method. The volume ratio is the amount of extra storage for the overlap (2 means we store the graph twice). Below, as the ratio increases, the swapping probability and PageRank communication volume decreases.

  10. Chemical insight from density functional modeling of molecular adsorption: Tracking the bonding and diffusion of anthracene derivatives on Cu(111) with molecular orbitals

    SciTech Connect

    Wyrick, Jonathan; Bartels, Ludwig; Einstein, T. L.

    2015-03-14

    We present a method of analyzing the results of density functional modeling of molecular adsorption in terms of an analogue of molecular orbitals. This approach permits intuitive chemical insight into the adsorption process. Applied to a set of anthracene derivates (anthracene, 9,10-anthraquinone, 9,10-dithioanthracene, and 9,10-diselenonanthracene), we follow the electronic states of the molecules that are involved in the bonding process and correlate them to both the molecular adsorption geometry and the species’ diffusive behavior. We additionally provide computational code to easily repeat this analysis on any system.

  11. Prevalence of Bimolecular Routes in the Activation of Diatomic Molecules with Strong Chemical Bonds (O2, NO, CO, N2) on Catalytic Surfaces.

    PubMed

    Hibbitts, David; Iglesia, Enrique

    2015-05-19

    Dissociation of the strong bonds in O2, NO, CO, and N2 often involves large activation barriers on low-index planes of metal particles used as catalysts. These kinetic hurdles reflect the noble nature of some metals (O2 activation on Au), the high coverages of co-reactants (O2 activation during CO oxidation on Pt), or the strength of the chemical bonds (NO on Pt, CO and N2 on Ru). High barriers for direct dissociations from density functional theory (DFT) have led to a consensus that "defects", consisting of low-coordination exposed atoms, are required to cleave such bonds, as calculated by theory and experiments for model surfaces at low coverages. Such sites, however, bind intermediates strongly, rendering them unreactive at the high coverages prevalent during catalysis. Such site requirements are also at odds with turnover rates that often depend weakly on cluster size or are actually higher on larger clusters, even though defects, such as corners and edges, are most abundant on small clusters. This Account illustrates how these apparent inconsistencies are resolved through activations of strong bonds assisted by co-adsorbates on crowded low-index surfaces. Catalytic oxidations occur on Au clusters at low temperatures in spite of large activation barriers for O2 dissociation on Au(111) surfaces, leading to proposals that O2 activation requires low-coordination Au atoms or Au-support interfaces. When H2O is present, however, O2 dissociation proceeds with low barriers on Au(111) because chemisorbed peroxides (*OOH* and *HOOH*) form and weaken O-O bonds before cleavage, thus allowing activation on low-index planes. DFT-derived O2 dissociation barriers are much lower on bare Pt surfaces, but such surfaces are nearly saturated with CO* during CO oxidation. A dearth of vacant sites causes O2* to react with CO* to form *OOCO* intermediates that undergo O-O cleavage. NO-H2 reactions occur on Pt clusters saturated with NO* and H*; direct NO* dissociation requires vacant

  12. Chemically Bonding of Amantadine with Gardenamide A Enhances the Neuroprotective Effects against Corticosterone-Induced Insults in PC12 Cells.

    PubMed

    Zhao, Jiaqiang; Peng, Lizhi; Zheng, Wenhua; Wang, Rikang; Zhang, Lei; Yang, Jian; Chen, Heru

    2015-09-21

    Two amantadine (ATD)-gardenamide A (GA) ligands have been designed and synthesized. The bonding of ATD with GA through a methylene carbonyl brigde (L1) enhances the neuroprotective effect against corticosterone (CORT)-induced impairments in PC12 cells; while the bonding through a succinyl brigde (L2) does not. L1 reduces the level of reactive oxygen species (ROS) and cell apoptosis generated by CORT. It restores CORT-changed cell morphology to a state that is closed to normal PC12 cells. One mechanism of L1 to attenuate CORT-induced cell apoptosis is through the adjustment of both caspase-3 and Bcl-2 proteins. Like GA, both nNOS and eNOS might be involved in the neuroprotective mechanism of L1. All the evidences suggest that L1 may be a potential agent to treat depression.

  13. Phase diagram, chemical bonds, and gap bowing of cubic InxAl1-xN alloys: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Teles, L. K.; Scolfaro, L. M. R.; Leite, J. R.; Furthmüller, J.; Bechstedt, F.

    2002-12-01

    Thermodynamic, structural, and electronic properties of cubic InxAl1-xN alloys are studied by combining first-principles total energy calculations and the generalized quasichemical approach. Results for bond-lengths, second-nearest-neighbors distances, and bond angles in the alloy are presented. The calculated phase diagram of the alloy shows a broad and asymmetric miscibility gap. The gap fluctuations in the alloy allow for the definition of a minimum gap and an average gap with different bowing parameters, that can provide an explanation for the discrepancies found in the experimental values for the bowing parameter. It is also found that lattice matched In0.2Al0.8N with GaN is suitable to form a barrier material for electronic and optoelectronic nitride based devices.

  14. Direct probing of micromechanical properties of hydrogen-bonded layer-by-layer microcapsule shells with different chemical compositions.

    PubMed

    Lisunova, Milana O; Drachuk, Irina; Shchepelina, Olga A; Anderson, Kyle D; Tsukruk, Vladimir V

    2011-09-06

    The mechanical properties of hydrogen-bonded layer-by-layer (LbL) microcapsule shells constructed from tannic acid (TA) and poly(vinylpyrrolidone) (PVPON) components have been studied in both the dry and swollen states. In the dry state, the value of the elastic modulus was measured to be within 0.6-0.7 GPa, which is lower than the typical elastic modulus for electrostatically assembled LbL shells. Threefold swelling of the LbL shells in water results in a significant reduction of the elastic modulus to values well below 1 MPa, which is typical value seen for highly compliant gel materials. The increase of the molecular weight of the PVPON component from 55 to 1300 kDa promotes chain entanglements and causes a stiffening of the LbL shells with a more than 2-fold increase in elastic modulus value. Moreover, adding a polyethylenimine prime layer to the LbL shell affects the growth of hydrogen-bonded multilayers which consequently results in dramatically stiffer, thicker, and rougher LbL shells with the elastic modulus increasing by more than an order of magnitude, up to 4.3 MPa. An alternation of the elastic properties of very compliant hydrogen-bonded shells by variation of molecular weight is a characteristic feature of weakly bonded LbL shells. Such an ability to alter the elastic modulus in a wide range is critically important for the design of highly compliant microcapsules with tunable mechanical stability, loading ability, and permeability.

  15. Stable chemical bonding of porous membranes and poly(dimethylsiloxane) devices for long-term cell culture.

    PubMed

    Sip, Christopher G; Folch, A

    2014-05-01

    We have investigated the bonding stability of various silane treatments for the integration of track-etched membranes with poly(dimethylsiloxane) (PDMS) microfluidic devices. We compare various treatments using trialkoxysilanes or dipodal silanes to determine the effect of the organofunctional group, cross-link density, reaction solvent, and catalyst on the bond stability. We find that devices made using existing silane methods delaminated after one day when immersed in cell culture medium at 37 °C. In contrast, the dipodal silane, bis[3-(trimethoxysilyl)propyl]amine, is shown to yield stable and functional integration of membranes with PDMS that is suitable for long-term cell culture. To demonstrate application of the technique, we fabricated an open-surface device in which cells cultured on a track-etched membrane can be stimulated at their basal side via embedded microfluidic channels. C2C12 mouse myoblasts were differentiated into myotubes over the course of two weeks on these devices to demonstrate biocompatibility. Finally, devices were imaged during the basal-side delivery of a fluorescent stain to validate the membrane operation and long-term stability of the bonding technique.

  16. Stable chemical bonding of porous membranes and poly(dimethylsiloxane) devices for long-term cell culture

    PubMed Central

    Sip, Christopher G.; Folch, A.

    2014-01-01

    We have investigated the bonding stability of various silane treatments for the integration of track-etched membranes with poly(dimethylsiloxane) (PDMS) microfluidic devices. We compare various treatments using trialkoxysilanes or dipodal silanes to determine the effect of the organofunctional group, cross-link density, reaction solvent, and catalyst on the bond stability. We find that devices made using existing silane methods delaminated after one day when immersed in cell culture medium at 37 °C. In contrast, the dipodal silane, bis[3-(trimethoxysilyl)propyl]amine, is shown to yield stable and functional integration of membranes with PDMS that is suitable for long-term cell culture. To demonstrate application of the technique, we fabricated an open-surface device in which cells cultured on a track-etched membrane can be stimulated at their basal side via embedded microfluidic channels. C2C12 mouse myoblasts were differentiated into myotubes over the course of two weeks on these devices to demonstrate biocompatibility. Finally, devices were imaged during the basal-side delivery of a fluorescent stain to validate the membrane operation and long-term stability of the bonding technique. PMID:25379080

  17. Theory of chemical bonds in metalloenzymes XI: Full geometry optimization and vibration analysis of porphyrin iron-oxo species

    NASA Astrophysics Data System (ADS)

    Shoji, Mitsuo; Isobe, Hiroshi; Saito, Toru; Kitagawa, Yasutaka; Yamanaka, Shusuke; Kawakami, Takashi; Okumura, Mitsutaka; Yamaguchi, Kizashi

    Physiochemical properties of compound I and II intermediate states for heme enzymes (catalase, peroxidase, P450) and inorganic models are investigated by hybrid density functional theory. Used theoretical models are composed of an oxoferryl porphyrin and an axial ligand, which are cresol, methylimidazole, methylthiol, and chloride for catalase, peroxidase, P450, and inorganic models, respectively. The oxoferryl bonds are characterized in terms of bond lengths and vibration frequencies. It is found that the oxoferryl bond lengths (the stretching frequency) are shorter (higher) than those of the X-ray crystal structures of enzymes, on the other hand for inorganic models, they are comparable with the experimental values. Spin density distributions showed that radical state at the compound I can be classified into two types: (1) porphyrin radical state and (2) axial ligand radical state. Peroxidase and inorganic model are in the former case and Catalase and P450 are in the later case at the present calculation models. Magnetic interactions between oxoferryl and ligand radical moieties are analyzed by the natural orbital analysis and it is showed that the effective exchange integral (J) values are strongly related to the radical spin density distributions: axial ligand radical tends to increase the antiferromagnetic interaction. Mössbauer shift parameters are also evaluated and it is shown that iron charge states are similar for these models.

  18. The Different Sensitive Behaviors of a Hydrogen-Bond Acidic Polymer-Coated SAW Sensor for Chemical Warfare Agents and Their Simulants

    PubMed Central

    Long, Yin; Wang, Yang; Du, Xiaosong; Cheng, Luhua; Wu, Penglin; Jiang, Yadong

    2015-01-01

    A linear hydrogen-bond acidic (HBA) linear functionalized polymer (PLF), was deposited onto a bare surface acoustic wave (SAW) device to fabricate a chemical sensor. Real-time responses of the sensor to a series of compounds including sarin (GB), dimethyl methylphosphonate (DMMP), mustard gas (HD), chloroethyl ethyl sulphide (2-CEES), 1,5-dichloropentane (DCP) and some organic solvents were studied. The results show that the sensor is highly sensitive to GB and DMMP, and has low sensitivity to HD and DCP, as expected. However, the sensor possesses an unexpected high sensitivity toward 2-CEES. This good sensing performance can’t be solely or mainly attributed to the dipole-dipole interaction since the sensor is not sensitive to some high polarity solvents. We believe the lone pair electrons around the sulphur atom of 2-CEES provide an electron-rich site, which facilitates the formation of hydrogen bonding between PLF and 2-CEES. On the contrary, the electron cloud on the sulphur atom of the HD molecule is offset or depleted by its two neighbouring strong electron-withdrawing groups, hence, hydrogen bonding can hardly be formed. PMID:26225975

  19. The Different Sensitive Behaviors of a Hydrogen-Bond Acidic Polymer-Coated SAW Sensor for Chemical Warfare Agents and Their Simulants.

    PubMed

    Long, Yin; Wang, Yang; Du, Xiaosong; Cheng, Luhua; Wu, Penglin; Jiang, Yadong

    2015-07-28

    A linear hydrogen-bond acidic (HBA) linear functionalized polymer (PLF), was deposited onto a bare surface acoustic wave (SAW) device to fabricate a chemical sensor. Real-time responses of the sensor to a series of compounds including sarin (GB), dimethyl methylphosphonate (DMMP), mustard gas (HD), chloroethyl ethyl sulphide (2-CEES), 1,5-dichloropentane (DCP) and some organic solvents were studied. The results show that the sensor is highly sensitive to GB and DMMP, and has low sensitivity to HD and DCP, as expected. However, the sensor possesses an unexpected high sensitivity toward 2-CEES. This good sensing performance can't be solely or mainly attributed to the dipole-dipole interaction since the sensor is not sensitive to some high polarity solvents. We believe the lone pair electrons around the sulphur atom of 2-CEES provide an electron-rich site, which facilitates the formation of hydrogen bonding between PLF and 2-CEES. On the contrary, the electron cloud on the sulphur atom of the HD molecule is offset or depleted by its two neighbouring strong electron-withdrawing groups, hence, hydrogen bonding can hardly be formed.

  20. Impact of post-deposition annealing on interfacial chemical bonding states between AlGaN and ZrO{sub 2} grown by atomic layer deposition

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-03-02

    The effect of post-deposition annealing on chemical bonding states at interface between Al{sub 0.5}Ga{sub 0.5}N and ZrO{sub 2} grown by atomic layer deposition (ALD) is studied by angle-resolved x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that both of Al-O/Al 2p and Ga-O/Ga 3d area ratio decrease at annealing temperatures lower than 500 °C, which could be attributed to “clean up” effect of ALD-ZrO{sub 2} on AlGaN. Compared to Ga spectra, a much larger decrease in Al-O/Al 2p ratio at a smaller take-off angle θ is observed, which indicates higher effectiveness of the passivation of Al-O bond than Ga-O bond through “clean up” effect near the interface. However, degradation of ZrO{sub 2}/AlGaN interface quality due to re-oxidation at higher annealing temperature (>500 °C) is also found. The XPS spectra clearly reveal that Al atoms at ZrO{sub 2}/AlGaN interface are easier to get oxidized as compared with Ga atoms.

  1. Chemical bonding and defect states of LPCVD grown silicon-rich Si{sub 3}N{sub 4} for quantum dot applications

    SciTech Connect

    Mohammed, Shakil Hinkle, Christopher L.; Nimmo, Michael T.; Malko, Anton V.

    2014-03-15

    Si-rich Si{sub 3}N{sub 4} (SRN) thin films were investigated to understand the various defect states present within the SRN that can lead to reduced performance in quantum dot based devices made of these materials. The SRN films, deposited by low pressure chemical vapor deposition followed by furnace anneals over a range of temperatures, were determined to be comprised of two distinct phase separated SRN regions with different compositions (precipitates within a host matrix). Photoluminescence (PL) spectra showed multiple peaks convoluted together within the visible and near-visible range. Depending on deposition and annealing conditions, the films displayed changes in PL peak intensities which were correlated with chemical bonding utilizing x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and capacitance–voltage measurements. It is found that the PL originates from defect-state to defect-state and band edge to defect-state electronic transitions.

  2. Hydrogen multicentre bonds.

    PubMed

    Janotti, Anderson; Van de Walle, Chris G

    2007-01-01

    The concept of a chemical bond stands out as a major development in the process of understanding how atoms are held together in molecules and solids. Lewis' classical picture of chemical bonds as shared-electron pairs evolved to the quantum-mechanical valence-bond and molecular-orbital theories, and the classification of molecules and solids in terms of their bonding type: covalent, ionic, van der Waals and metallic. Along with the more complex hydrogen bonds and three-centre bonds, they form a paradigm within which the structure of almost all molecules and solids can be understood. Here, we present evidence for hydrogen multicentre bonds-a generalization of three-centre bonds-in which a hydrogen atom equally bonds to four or more other atoms. When substituting for oxygen in metal oxides, hydrogen bonds equally to all the surrounding metal atoms, becoming fourfold coordinated in ZnO, and sixfold coordinated in MgO. These multicentre bonds are remarkably strong despite their large hydrogen-metal distances. The calculated local vibration mode frequency in MgO agrees with infrared spectroscopy measurements. Multicoordinated hydrogen also explains the dependence of electrical conductivity on oxygen partial pressure, resolving a long-standing controversy on the role of point defects in unintentional n-type conductivity of ZnO (refs 8-10).

  3. Chemical bonding in the ternary transition metal bismuthides Ti{sub 4}TBi{sub 2} with T=Cr, Mn, Fe, Co, and Ni

    SciTech Connect

    Rytz, R.; Hoffman, R.

    1999-04-05

    The electronic structure and chemical bonding in the ternary transition metal bismuthides Ti{sub 4}TBi{sub 2} (T = Cr, Mn, Fe, Co, and Ni) is investigated by approximate MO calculations of the extended Hueckel tight-binding type. These intermetallic compounds crystallize in a layer structure, repeating sequence T-Ti/Bi-T-Ti/Bi, stacking along c; the late transition metals form linear chains with short T-T bonds. Other important structural elements are face-sharing chains of Ti{sub 4}Bi{sub 2} octahedra and Bi channels. The decrease of the T-T bond lengths from Cr to Ni is more pronounced than expected from the decrease of the metallic radii alone. The analysis of the electronic structure indicates that this behavior arises from the titanium-titanium and titanium-bismuth interlayer interactions. Diminution of the titanium-titanium interlayer distances as one goes from Ti{sub 4}CrBi{sub 2} to Ti{sub 4}NiBi{sub 2} is due to Ti(d)-Ti(d) bonding, which increases with increasing electron filling of the titanium d levels. The titanium-bismuth interactions remain strong along this series, as can also be seen by the constant intralayer/titanium-bismuth distances. A distinguishing feature of the title compounds is the channels formed by bismuth atoms. These channels are filled by Bi-centered, essentially unhybridized 6p orbitals forming a 2D net stacking along c and interacting with each other, stronger in the c direction than perpendicular to it. The possibility of intercalating electrophilic species into these electron-filled voids is also investigated.

  4. An XPS study on the chemical bond structure at the interface between SiO{sub x}N{sub y} and N doped polyethylene terephthalate

    SciTech Connect

    Ding Wanyu; Li Li; Zhang Lina; Chai Weiping; Ju Dongying; Peng Shou

    2013-03-14

    The super-thin silicon oxynitride (SiO{sub x}N{sub y}) films were deposited onto the N doped polyethylene terephthalate (PET) surface. Varying the N doping parameters, the different chemical bond structures were obtained at the interface between the SiO{sub x}N{sub y} film and the PET surface. X-ray photoelectron spectra results showed that at the initial stage of SiO{sub x}N{sub y} film growth, the C=N bonds could be broken and C-N-Si crosslink bonds could be formed at the interface of SiO{sub x}N{sub y}/PET, which C=N bonds could be formed onto the PET surface during the N doping process. At these positions, the SiO{sub x}N{sub y} film could be crosslinked well onto the PET surface. Meanwhile, the doped N could crosslink the [SiO{sub 4}] and [SiN{sub 4}] tetrahedrons, which could easily form the dense layer structure at the initial stage of SiO{sub x}N{sub y} film growth, instead of the ring and/or chain structures of [SiO{sub 4}] tetrahedrons crosslinked by O. Finally, from the point of applying SiO{sub x}N{sub y}/PET complex as the substrate, the present work reveals a simple way to crosslink them, as well as the crosslink model and physicochemical mechanism happened at the interface of complex.

  5. Tris(3,5-dimethylpyrazolyl)methane-based heterobimetallic complexes that contain Zn - and Cd - transition-metal bonds: synthesis, structures, and quantum chemical calculations.

    PubMed

    Meyer, Jens; González-Gallardo, Sandra; Hohnstein, Silvia; Garnier, Delphine; Armbruster, Markus K; Fink, Karin; Klopper, Wim; Breher, Frank

    2015-02-09

    Reactions of the tris(3,5-dimethylpyrazolyl)methanide amido complexes [M'{C(3,5-Me2 pz)3 }{N(SiMe3 )2 }] (M'=Mg (1 a), Zn (1 b), Cd (1 c); 3,5-Me2 pz=3,5-dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)3 H] (M=Cr (2 a), Mo (2 b)) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5-dimethylpyrazolyl)methanide ligand (Tpmd*) into the -methane derivative (Tpm*) and the reaction of the acidic hydride M = H bond with the M' = N(SiMe3 )2 moiety. The latter produces HN(SiMe3 )2 as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)3 }2 (thf)] (3 a/b) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal-metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)3 }](+) (4 a/b; [MCp(CO)3 ](-) as the counteranion) and [Cd(Tpm*){MCp(CO)3 }(thf)](+) (5 a/b; [Cd{MCp(CO)3 }3 ](-) as the counteranion). Complexes 4 a and 5 a/b are the first complexes that contain Zn - Cr, Cd - Cr, and Cd - Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4 a/b* (and also on 5 a/b*) provide evidence for an interaction between the metal atoms.

  6. The chemical bonding and electronic structure of RhC, RhN, and RhO by anion photoelectron spectroscopy

    SciTech Connect

    Li, X.; Wang, L. |

    1998-10-01

    The electronic structure and chemical bonding of RhC, RhN, and RhO were experimentally investigated using anion photoelectron spectroscopy. Vibrationally resolved photoelectron spectra of RhC{sup {minus}}, RhN{sup {minus}}, and RhO{sup {minus}} were obtained at two detachment photon energies, 532 (2.33 eV) and 355 nm (3.49 eV). Electron affinities, low-lying electronic states, and vibrational frequencies are reported for the neutral diatomic molecules. The adiabatic electron affinities are similar for the three molecules and increase slightly from RhC to RhO (RhC: 1.46; RhN: 1.51; RhO: 1.58 eV). The low-lying electronic states are rather simple for RhC, with its first electronic excited state occurring at 9400 cm{sup {minus}1} above the ground state, whereas those of RhN and RhO are more complicated, with numerous closely spaced low-lying electronic states. Excited states of the anions were also observed for RhC{sup {minus}} and RhN{sup {minus}}. The trend of the chemical bonding from RhC to RhO is discussed based on the experimental results. {copyright} {ital 1998 American Institute of Physics.}

  7. Thermal stability and chemical bonding states of AlO xN y/Si gate stacks revealed by synchrotron radiation photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    He, G.; Toyoda, S.; Shimogaki, Y.; Oshima, M.

    2010-12-01

    Annealing-temperature dependence of the thermal stability and chemical bonding states of AlO xN y/SiO 2/Si gate stacks grown by metalorganic chemical vapor deposition (MOCVD) using new chemistry was investigated by synchrotron radiation photoemission spectroscopy (SRPES). Results have confirmed the formation of the AlN and AlNO compounds in the as-deposited samples. Annealing the AlO xN y samples in N 2 ambient in 600-800 °C promotes the formation of SiO 2 component. Meanwhile, there is no formation of Al-O-Si and Al-Si binding states, suggesting no interdiffusion of Al with the Si substrate. A thermally induced reaction between Si and AlO xN y to form volatile SiO and Al 2O is suggested to be responsible for the full disappearance of the Al component that accompanies annealing at annealing temperature of 1000 °C. The released N due to the breakage of the Al-N bonding will react with the SiO 2 interfacial layer and lead to the formation of the Si 3-N-O/Si 2-N-O components at the top of Si substrate. These results indicate high temperature processing induced evolution of the interfacial chemistry and application range of AlO xN y/Si gate stacks in future CMOS devices.

  8. Hydrogen-bonding and the dissolution mechanism of uracil in an acetate ionic liquid: new insights from NMR spectroscopy and quantum chemical calculations.

    PubMed

    Araújo, João M M; Pereiro, Ana B; Canongia Lopes, José N; Rebelo, Luís P N; Marrucho, Isabel M

    2013-04-18

    The dissolution of uracil-a pyrimidine nucleic acid base-in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][CH3COO]) has been investigated by methods of (1)H and (13)C NMR spectroscopy, (1)H-(1)H NOESY NMR spectroscopy, and quantum chemical calculations. The uracil-[C2mim][CH3COO] interactions that define the dissolution mechanism comprise the hydrogen bonds between the oxygen atoms of the acetate anion and the hydrogen atoms of the N1-H and N3-H groups of uracil and also the hydrogen bonds between the most acidic aromatic hydrogen atom (H2) of the imidazolium cation and the oxygen atoms of the carbonyl groups of uracil. The bifunctional solvation nature of the ionic liquid can be inferred from the presence of interactions between both ions of the ionic liquid and the uracil molecule. The location of such interaction sites was revealed using NMR data ((1)H and (13)C chemical shifts both in the IL and in the uracil molecule), complemented by DFT calculations. NOESY experiments provided additional evidence concerning the cation-uracil interactions.

  9. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

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

  10. Influence of N-H...O and O-H...O hydrogen bonds on the (17)O, (15)N and (13)C chemical shielding tensors in crystalline acetaminophen: a density functional theory study.

    PubMed

    Esrafili, Mehdi D; Behzadi, Hadi; Hadipour, Nasser L

    2007-06-01

    A computational investigation was carried out to characterize the (17)O, (15)N and (13)C chemical shielding tensors in crystalline acetaminophen. We found that N-H...O and O-H...O hydrogen bonds around the acetaminophen molecule in the crystal lattice have different influences on the calculated (17)O, (15)N and (13)C chemical shielding eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the B3LYP method and 6-311++G(d, p) and 6-311+G(d) standard basis sets using the Gaussian 98 suite of programs. Calculated chemical shielding tensors were used to evaluate the (17)O, (15)N, and (13)C NMR chemical shift tensors in crystalline acetaminophen, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the chemical shielding tensors of each nucleus. The computed (17)O chemical shielding tensor on O(1), which is involved in two intermolecular hydrogen bonds, shows remarkable sensitivity toward the choice of the cluster model, whereas the (17)O chemical shielding tensor on O(2) involved in one N-H...O hydrogen bond, shows smaller improvement toward the hydrogen-bonding interactions. Also, a reasonably good agreement between the experimentally obtained solid-state (15)N and (13)C NMR chemical shifts and B3LYP/6-311++G(d, p) calculations is achievable only in molecular cluster model where a complete hydrogen-bonding network is considered. Moreover, at the B3LYP/6-311++G(d, p) level of theory, the calculated (17)O, (15)N and (13)C chemical shielding tensor orientations are able to reproduce the experimental values to a reasonably good degree of accuracy.

  11. Multiple boron-boron bonds in neutral molecules: an insight from the extended transition state method and the natural orbitals for chemical valence scheme.

    PubMed

    Mitoraj, Mariusz P; Michalak, Artur

    2011-03-21

    We have analyzed the character of B═B and B≡B bonds in the neutral molecules of general form: LHB═BHL (2-L) and LB≡BL (3-L), for various ancillary ligands L attached to the boron center, based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV). In the case of molecules with the B═B bond, 2-L, we have included L = PMe(3), PF(3), PCl(3), PH(3), C(3)H(4)N(2)═C(NHCH)(2), whereas for molecules containing the B≡B connection, 3-L, the following ligands were considered L = CO, PMe(3), PCl(3), (Me(2)NCH(2)CH(2)O)(2)Ge. The results led us to conclude that use of phosphorus ligands leads to strengthening of the B═B bond by 6.4 kcal/mol (for 2-PMe(3)), by 4.4 (for 2-PF(3)) and by 9.2 (for 2-PH(3)), when compared to a molecule developed on the experimental basis, 2-C(3)H(4)N(2) (ΔE(total) = -118.3 kcal/mol). The ETS scheme has shown that all contributions, that is, (i) orbital interaction ΔE(orb), (ii) Pauli repulsion ΔE(Pauli), and (iii) electrostatic stabilization ΔE(elstat), are important in determining the trend in the B═B bond energies, ΔE(total). ETS-NOCV results revealed that both σ(B═B) and π(B═B) contributions are responsible for the changes in ΔE(orb) values. All considered molecules of the type LB≡BL, 3-L, exhibit a stronger B≡B bond when compared to a double B═B connection in 2-L (|ΔE(total)| is lower by 11.8-42.5 kcal/mol, depending on the molecule). The main reason is a lower Pauli repulsion contribution noted for 3-CO, 3-PMe(3), and 3-PCl(3) molecules. In addition, in the case of 3-PMe(3) and 3-PCl(3), the orbital interaction term is more stabilizing; however, the effect is less pronounced compared to the drop in the Pauli repulsion term. In all of the systems with double and triple boron-boron bonds, the electronic factor (ΔE(orb)) dominates over the electrostatic contribution (ΔE(elstat)). Finally, the strongest B

  12. 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

    ERIC Educational Resources Information Center

    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…

  13. Chemically Non-Innocent Cyclic (Alkyl)(Amino)Carbenes: Ligand Rearrangement, C-H and C-F Bond Activation.

    PubMed

    Turner, Zoë R

    2016-08-01

    A cyclic (alkyl)(amino)carbene (CAAC) was found to undergo unprecedented rearrangements and transformations of its core structure in the presence of Group 1 and 2 metals. Although the carbene was also found to be prone to intramolecular C-H activation, it was competent for intermolecular activation of a variety of sp-, sp(2) -, and sp(3) -hybridized C-H bonds. Double C-F activation of hexafluorobenzene was also observed in this work. These processes all hold relevance to the role of these carbenes in catalysis, as well as to their use in the synthesis of new and unusual main group or transition metal complexes.

  14. Chemical Speciation and Bond Lengths of Organic Solutes by Core-Level Spectroscopy: pH and Solvent Influence on p -Aminobenzoic Acid

    DOE PAGES

    Stevens, Joanna S.; Gainar, Adrian; Suljoti, Edlira; ...

    2015-03-18

    Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para-aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs andmore » σ* shape resonances in the NEXAFS spectra. Finally, this provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions.« less

  15. The Solid Phase Extraction of Some Metal Ions Using Palladium Nanoparticles Attached to Silica Gel Chemically Bonded by Silica-Bonded N-Propylmorpholine as New Sorbent prior to Their Determination by Flame Atomic Absorption Spectroscopy

    PubMed Central

    Ghaedi, M.; Rezakhani, M.; Khodadoust, S.; Niknam, K.; Soylak, M.

    2012-01-01

    In this research at first palladium nanoparticle attached to a new chemically bonded silica gel has been synthesized and has been characterized with different techniques such as X-ray diffraction (XRD), fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Then, this new sorbent (chemically modified silica gel with N-propylmorpholine (PNP-SBNPM)) was efficiently used for preconcentration of some metal ions in various food samples. The influence of effective variables including mass of sorbent, flow rate, pH of sample solutions and condition of eluent such as volume, type and concentration on the recoveries of understudy metal ions were investigated. Following the optimization of variables, the interfering effects of some foreign ions on the preconcentration and determination of the investigated metal ions described. At optimum values of variables, all investigated metal ions were efficiently recovered with efficiency more than 95%, relative standard deviation (RSD) between 2.4 and 2.8, and detection limit in the range of 1.4–2.7 ng mL−1. The present method is simple and rapidly applicable for the determination of the understudied metal ions (ng mL−1) in different natural food samples. PMID:22666150

  16. The solid phase extraction of some metal ions using palladium nanoparticles attached to silica gel chemically bonded by silica-bonded N-propylmorpholine as new sorbent prior to their determination by flame atomic absorption spectroscopy.

    PubMed

    Ghaedi, M; Rezakhani, M; Khodadoust, S; Niknam, K; Soylak, M

    2012-01-01

    In this research at first palladium nanoparticle attached to a new chemically bonded silica gel has been synthesized and has been characterized with different techniques such as X-ray diffraction (XRD), fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Then, this new sorbent (chemically modified silica gel with N-propylmorpholine (PNP-SBNPM)) was efficiently used for preconcentration of some metal ions in various food samples. The influence of effective variables including mass of sorbent, flow rate, pH of sample solutions and condition of eluent such as volume, type and concentration on the recoveries of understudy metal ions were investigated. Following the optimization of variables, the interfering effects of some foreign ions on the preconcentration and determination of the investigated metal ions described. At optimum values of variables, all investigated metal ions were efficiently recovered with efficiency more than 95%, relative standard deviation (RSD) between 2.4 and 2.8, and detection limit in the range of 1.4-2.7 ng mL⁻¹. The present method is simple and rapidly applicable for the determination of the understudied metal ions (ng mL⁻¹) in different natural food samples.

  17. Effect of ester chemical structure and peptide bond conformation in fragmentation pathways of differently metal cationized cyclodepsipeptides.

    PubMed

    Banerjee, Raja; Sudarslal, S; Ranganayaki, R S; Raghothama, S

    2011-09-21

    Fragmentation behavior of two classes of cyclodepsipeptides, isariins and isaridins, obtained from the fungus Isaria, was investigated in the presence of different metal ions using multistage tandem mass spectrometry (MS(n)) with collision induced dissociation (CID) and validated by NMR spectroscopy. During MS(n) process, both protonated and metal-cationized isariins generated product ions belonging to the identical 'b-ion' series, exhibiting initial backbone cleavage explicitly at the β-ester bond. Fragmentation behavior for the protonated and metal-cationized acyclic methyl ester derivative of isariins was very similar. On the contrary, isaridins during fragmentation produced ions belonging to the 'b' or/and the 'y' ion series depending on the nature of interacting metal ions, due to initial backbone cleavages at the α-ester linkage or/and at a specific amide linkage. Interestingly, independent of the nature of the interacting metal ions, the product ions formed from the acyclic methyl ester derivative of isaridins belonged only to the 'y-type'. Complementary NMR data showed that, while all metal ions were located around the β-ester group of isariins, the metal ion interacting sites varied across the backbone for isaridins. Combined MS and NMR data suggest that the different behavior in sequence specific charge-driven fragmentation of isariins and isaridins is predetermined because of the constituent β-hydroxy acid residue in isariins and the cis peptide bond in isaridins.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Chemical bonding and dynamic fluxionality of a B15(+) cluster: a nanoscale double-axle tank tread.

    PubMed

    Wang, Ying-Jin; You, Xue-Rui; Chen, Qiang; Feng, Lin-Yan; Wang, Kang; Ou, Ting; Zhao, Xiao-Yun; Zhai, Hua-Jin; Li, Si-Dian

    2016-06-21

    A planar, elongated B15(+) cationic cluster is shown to be structurally fluxional and functions as a nanoscale tank tread on the basis of electronic structure calculations, bonding analyses, and molecular dynamics simulations. The outer B11 peripheral ring behaves like a flexible chain gliding around an inner B4 rhombus core, almost freely at the temperature of 500 K. The rotational energy barrier is only 1.37 kcal mol(-1) (0.06 eV) at the PBE0/6-311+G* level, further refined to 1.66 kcal mol(-1) (0.07 eV) at the single-point CCSD(T)/6-311G*//CCSD/6-311G* level. Two soft vibrational modes of 166.3 and 258.3 cm(-1) are associated with the rotation, serving as double engines for the system. Bonding analysis suggests that the "island" electron clouds, both σ and π, between the peripheral ring and inner core flow and shift continuously during the intramolecular rotation, facilitating the dynamic fluxionality of the system with a small rotational barrier. The B15(+) cluster, roughly 0.6 nm in dimension, is the first double-axle nanoscale tank tread equipped with two engines, which expands the concepts of molecular wheels, Wankel motors, and molecular tanks.

  20. Structural flexibility in magnetocaloric RE5T4 (RE = rare-earth; T = silicon, germanium, gallium) materials: Effect of chemical substitution on structure, bonding and properties

    NASA Astrophysics Data System (ADS)

    Misra, Sumohan

    The binary, ternary and multicomponent intermetallic compounds of rare-earth metals (RE) with group 14 elements (Tt) at the RE5 Tt4 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 Gd5Si 2Ge2, 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.

  1. Electronic structure and chemical bonding of {alpha}- and {beta}-CeIr{sub 2}Si{sub 2} intermediate valence compounds

    SciTech Connect

    Matar, Samir F.; Poettgen, Rainer; Chevalier, Bernard

    2012-02-15

    The dimorphism of the intermediate valence ternary cerium silicide CeIr{sub 2}Si{sub 2} in the ThCr{sub 2}Si{sub 2} ({alpha}) and CaBe{sub 2}Ge{sub 2} ({beta}) modifications is addressed in the framework of the density functional theory. The geometry optimization is in good agreement with the experiment and the subsequent establishment of the energy-volume equation of state (EOS) indicates a stabilization of the {beta}-type relative to the {alpha}-type concomitant with the trend of the cerium valence, changing to tetravalent in {beta}-CeIr{sub 2}Si{sub 2}. This is equally shown from the site projected DOS and from the large increase of the electronic contribution to the specific heat. The chemical bonding indicates the strongest bonding interactions within the Ir-Si substructure in both varieties. Stabilization of {beta}-CeIr{sub 2}Si{sub 2} with almost tetravalent cerium is in good agreement with Th{sup IV}Ir{sub 2}Si{sub 2} which exclusively crystallizes in the CaBe{sub 2}Ge{sub 2} type. The EOS behavior of different RIr{sub 2}Si{sub 2} (R=Th, Ce, La) is comparatively discussed. - Graphical abstract: The crystal structures of {alpha}- and {beta}-CeIr{sub 2}Si{sub 2}. Relevant interatomic distances (A), the three-dimensional [Ir{sub 2}Si{sub 2}] networks and the crystallographically independent iridium and silicon sites are indicated. Highlights: Black-Right-Pointing-Pointer Energy stabilization of (HT) {beta}-CeIr{sub 2}Si{sub 2} versus (LT) {alpha}-CeIr{sub 2}Si{sub 2} from DFT methods. Black-Right-Pointing-Pointer Concomitant with the change of Ce valence to tetravalent (HT)-enhanced specific heat. Black-Right-Pointing-Pointer Equations of states for La, Ce and Th members with CeIr{sub 2}Si{sub 2} resembling tetravalent-Th. Black-Right-Pointing-Pointer Chemical bonding shows changes on the {l_brace}Ir{sub 2}Si{sub 2}{r_brace} intralayer and Ce{sup IV}-Ir bonds.

  2. (1)H NMR spectra of alcohols in hydrogen bonding solvents: DFT/GIAO calculations of chemical shifts.

    PubMed

    Lomas, John S

    2016-01-01

    Proton nuclear magnetic resonance (NMR) shifts of aliphatic alcohols in hydrogen bonding solvents have been computed on the basis of density functional theory by applying the gauge-including atomic orbital method to geometry-optimized alcohol/solvent complexes. The OH proton shifts and hydrogen bond distances for methanol or ethanol complexed with pyridine depend very much on the functional employed and very little on the basis set, provided it is sufficiently large to give the correct quasi-linear hydrogen bond geometry. The CH proton shifts are insensitive to both the functional and the basis set. NMR shifts for all protons in several alcohol/pyridine complexes are calculated at the Perdew, Burke and Ernzerhof PBE0/cc-pVTZ//PBE0/6-311 + G(d,p) level in the gas phase. The results correlate with the shifts for the pyridine-complexed alcohols, determined by analysing data from the NMR titration of alcohols against pyridine. More pragmatically, computed shifts for a wider range of alcohols correlate with experimental shifts in neat pyridine. Shifts for alcohols in dimethylsulfoxide, based on the corresponding complexes in the gas phase, correlate well with the experimental values, but the overall root mean square difference is high (0.23 ppm), shifts for the OH, CHOH and other CH protons being systematically overestimated, by averages of 0.42, 0.21 and 0.06 ppm, respectively. If the computed shifts are corrected accordingly, a very good correlation is obtained with a gradient of 1.00 ± 0.01, an intercept of 0.00 ± 0.02 ppm and a root mean square difference of 0.09 ppm. This is a modest improvement on the result of applying the CHARGE programme to a slightly different set of alcohols. Some alcohol complexes with acetone and acetonitrile were investigated both in the gas phase and in a continuum of the relevant solvent.

  3. First-principles study of electronic structure, chemical bonding and elastic properties for new superconductor CaFeAs2

    NASA Astrophysics Data System (ADS)

    Yan, J. G.; Chen, Z. J.; Xu, G. B.; Kuang, Z.; Chen, T. H.; Li, D. H.

    2017-01-01

    Using first-principles calculation we investigated the structural, electronic and elastic properties of paramagnetic CaFeAs2. Our results indicated that the density of states (DOS) was dominated predominantly by Fe-3d states at Fermi levels, and stronger hybridization exists between As1 and As1 atoms. Three hole pockets are formed at Γ and Z points, and two electronic pockets are formed at A and E points. The Dirac cone-like bands appear near B and D points. For the first time we calculated the elastic properties and found that CaFeAs2 is a mechanically stable and moderately hard material, it has elastic anisotropy and brittleness, which agrees well with the bonding picture and the calculation of Debye temperature (ΘD).

  4. Stereocontrolled Synthesis of β-Lactams within [2]Rotaxanes: Showcasing the Chemical Consequences of the Mechanical Bond.

    PubMed

    Martinez-Cuezva, Alberto; Lopez-Leonardo, Carmen; Bautista, Delia; Alajarin, Mateo; Berna, Jose

    2016-07-20

    The intramolecular cyclization of N-benzylfumaramide [2]rotaxanes is described. The mechanical bond of these substrates activates this transformation to proceed in high yields and in a regio- and diastereoselective manner, giving interlocked 3,4-disubstituted trans-azetidin-2-ones. This activation effect markedly differs from the more common shielding protection of threaded functions by the macrocycle, in this case promoting an unusual and disfavored 4-exo-trig ring closure. Kinetic and synthetic studies allowed us to delineate an advantageous approach toward β-lactams based on a two-step, one-pot protocol: an intramolecular ring closure followed by a thermally induced dethreading step. The advantages of carrying out this cyclization in the confined space of a benzylic amide macrocycle are attributed to its anchimeric assistance.

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

    SciTech Connect

    Carta, V.; Ciccioli, A. E-mail: andrea.ciccioli@uniroma1.it; Gigli, G. E-mail: andrea.ciccioli@uniroma1.it

    2014-02-14

    The intermetallic molecules CuSb, AgSb, and AuSb were identified in the effusive molecular beam produced at high temperature under equilibrium conditions in a double-cell-like Knudsen source. Several gaseous equilibria involving these species were studied by mass spectrometry as a function of temperature in the overall range 1349–1822 K, and the strength of the chemical bond formed between antimony and the group 11 metals was for the first time measured deriving the following thermochemical dissociation energies (D{sub 0}{sup ∘}, kJ/mol): 186.7 ± 5.1 (CuSb), 156.3 ± 4.9 (AgSb), 241.3 ± 5.8 (AuSb). The three species were also investigated computationally at the coupled cluster level with single, double, and noniterative quasiperturbative triple excitations (CCSD(T)). The spectroscopic parameters were calculated from the potential energy curves and the dissociation energies were evaluated at the Complete Basis Set limit, resulting in an overall good agreement with experimental values. An approximate evaluation of the spin-orbit effect was also performed. CCSD(T) calculations were further extended to the corresponding group 11 arsenide species which are here studied for the first time and the following dissociation energies (D{sub 0}{sup ∘}, kJ/mol): 190 ± 10 (CuAs), 151 ± 10 (AgAs), 240 ± 15 (AuAs) are proposed. Taking advantage of the new experimental and computational information here presented, the bond energy trends along group 11 and 4th and 5th periods of the periodic table were analyzed and the bond energies of the diatomic species CuBi and AuBi, yet experimentally unobserved, were predicted on an empirical basis.

  6. Seeding for pervasively overlapping communities

    NASA Astrophysics Data System (ADS)

    Lee, Conrad; Reid, Fergal; McDaid, Aaron; Hurley, Neil

    2011-06-01

    In some social and biological networks, the majority of nodes belong to multiple communities. It has recently been shown that a number of the algorithms specifically designed to detect overlapping communities do not perform well in such highly overlapping settings. Here, we consider one class of these algorithms, those which optimize a local fitness measure, typically by using a greedy heuristic to expand a seed into a community. We perform synthetic benchmarks which indicate that an appropriate seeding strategy becomes more important as the extent of community overlap increases. We find that distinct cliques provide the best seeds. We find further support for this seeding strategy with benchmarks on a Facebook network and the yeast interactome.

  7. Effect of Si-H bond on the gas-phase chemistry of trimethylsilane in the hot wire chemical vapor deposition process.

    PubMed

    Shi, Y J; Li, X M; Toukabri, R; Tong, L

    2011-09-22

    The effect of the Si-H bond on the gas-phase reaction chemistry of trimethylsilane in the hot-wire chemical vapor deposition (HWCVD) process has been studied by examining its decomposition on a hot tungsten filament and the secondary gas-phase reactions in a reactor using a soft laser ionization source coupled with mass spectrometry. Trimethylsilane decomposes on the hot filament via Si-H and Si-CH(3) bond cleavages. A short-chain mechanism is found to dominate in the secondary reactions in the reactor. It has been shown that the hydrogen abstractions of both Si-H and C-H occur simultaneously, with the abstraction of Si-H being favored. Tetramethylsilane and hexamethyldisilane are the two major products formed from the radical recombination reactions in the termination steps. Three methyl-substituted disilacyclobutane molecules, i.e., 1,3-dimethyl-1,3-disilacyclobutane, 1,1,3-trimethyl-1,3-disilacyclobutane, and 1,1,3,3-tetramethyl-1,3-disilacyclobutane are also produced in reactor from the cycloaddition reactions of methyl-substituted silene species. Compared to tetramethylsilane and hexamethyldisilane, a common feature with trimethylsilane is that the short-chain mechanism still dominates. However, a more active involvement of the reactive silene intermediates has been found with trimethylsilane.

  8. Hydrogen bonding between acetate-based ionic liquids and water: Three types of IR absorption peaks and NMR chemical shifts change upon dilution

    NASA Astrophysics Data System (ADS)

    Chen, Yu; Cao, Yuanyuan; Zhang, Yuwei; Mu, Tiancheng

    2014-01-01

    The hydrogen-bonding interaction between acetate-based ionic liquids (AcIL) and water was investigated by attenuated total reflection infrared (ATR-IR) and 1H NMR. Interestingly, the relative change of chemical shift δ of 1H NMR upon dilution could be divided into three regions. All the H show an upfield shift in Regions 1 and 2 while a different tendency in Region 3 (upfield, no, and downfield shift classified as Types 1, 2, 3, respectively). For ATR-IR, the red, no, or blue shift of νOD (IR absorption peak of OD in D2O) and ν± (IR absorption peak of AcILs) also have three types, respectively. Two-Times Explosion Mechanism (TTEM) was proposed to interpret the dynamic processes of AcILs upon dilution macroscopically, meanwhile an Inferior Spring Model (ISM) was proposed to help to understand the TTEM microscopically, All those indicate that AcILs present the state of network, sub-network, cluster, sub-cluster, ion pairs and sub-ion pairs in sequence upon dilution by water and the elongation of hydrogen bonding between AcILs-water, between cation-anion of AcILs is plastic deformation rather than elastic deformation.

  9. Length Scale Discontinuities Between Non-Crystalline And Nano-Crystalline Thin Films: Chemical Bonding Self-Organization, Broken Constraints And Reductions of Macroscopic Strain

    SciTech Connect

    Lucovsky, G.; Phillips, J.C.

    2009-05-19

    This paper identifies different length scales, {lambda}{sub s}, for strain-reducing chemical bonding self-organizations in non-crystalline and nano-crystalline thin films. Length scales have been identified through spectroscopic studies, thermal heat flow measurements, and are analyzed by semi-empirical bond-constraint theory (SE-BCT) and symmetry adapted linear combinations (SALC) of atomic states. In both instances, strain-reducing self-organizations result in reduced defect densities that are minimized and enabling for device applications. The length scale for non-crystalline solids extends to at most 1 nm, and more generally to 0.5-0.8 nm; however, there are two different length scales for nano-crystalline films: one is <2.5 nm and is characterized by suppression of longer range ordering required for complex unit cells based on more than one primitive unit cell and the second is >3-3.5 nm and defines a regime where complex unit cells, comprised of two or more primitive unit cells are stabilized and the electronic structure is changed.

  10. Toughness governs the rupture of the interfacial H-bond assemblies at a critical length scale in hybrid materials.

    PubMed

    Sakhavand, Navid; Muthuramalingam, Prakash; Shahsavari, Rouzbeh

    2013-06-25

    The geometry and material property mismatch across the interface of hybrid materials with dissimilar building blocks make it extremely difficult to fully understand the lateral chemical bonding processes and design nanocomposites with optimal performance. Here, we report a combined first-principles study, molecular dynamics modeling, and theoretical derivations to unravel the detailed mechanisms of H-bonding, deformation, load transfer, and failure at the interface of polyvinyl alcohol (PVA) and silicates, as an example of hybrid materials with geometry and property mismatch across the interface. We identify contributing H-bonds that are key to adhesion and demonstrate a specific periodic pattern of interfacial H-bond network dictated by the interface mismatch and intramolecular H-bonding. We find that the maximum toughness, incorporating both intra- and interlayer strain energy contributions, govern the existence of optimum overlap length and thus the rupture of interfacial (interlayer) H-bond assemblies in natural and synthetic hybrid materials. This universally valid result is in contrast to the previous reports that correlate shear strength with rupture of H-bonds assemblies at a finite overlap length. Overall, this work establishes a unified understanding to explain the interplay between geometric constraints, interfacial H-bonding, materials characteristics, and optimal mechanical properties in hybrid organic-inorganic materials.

  11. [Chemical ribonucleases. 3. Synthesis of organic catalysts of hydrolysis of phosphodiester bonds based on quaternary salts of 1,4-diazabicyclo(2.2.2)octane].

    PubMed

    Konevets, D A; Bekk, I E; Sil'nikov, V N; Zenkova, M A; Shishkin, G V

    2000-11-01

    On the basis of imidazole and bisquaternary salts of 1,4-diazabicyclo[2.2.2]octane, a number of highly effective catalysts of the nDm series (here, n is the number of positive charges at neutral pH values and m is the digital code of the catalytically active fragment: 1, histamine, and 2, histidine methyl ester) were synthesized for the cleavage of the phosphodiester bonds in ribonucleic acids. A general method for the synthesis of chemical ribonucleases was suggested, which helps vary both the number of positive charges in their RNA-binding domain and the catalytic center. By the example of hydrolysis under physiological conditions of the in vitro transcript of tRNA(Lys) from human mitochondria, it was shown that the RNA cleavage rate with the nDm conjugates increases approximately 30-fold along with the increase in the number of positive charges from two to four.

  12. Enhanced Electrochemical Performances of Bi2O3/rGO Nanocomposite via Chemical Bonding as Anode Materials for Lithium Ion Batteries.

    PubMed

    Deng, Zhuo; Liu, Tingting; Chen, Tao; Jiang, Jiaxiang; Yang, Wanli; Guo, Jun; Zhao, Jianqing; Wang, Haibo; Gao, Lijun

    2017-03-31

    Bismuth oxide/reduced graphene oxide (termed Bi2O3@rGO) nanocomposite has been facilely prepared by a solvothermal method via introducing chemical bonding that has been demonstrated by Raman and X-ray photoelectron spectroscopy spectra. Tremendous single-crystal Bi2O3 nanoparticles with an average size of ∼5 nm are anchored and uniformly dispersed on rGO sheets. Such a nanostructure results in enhanced electrochemical reversibility and cycling stability of Bi2O3@rGO composite materials as anodes for lithium ion batteries in comparison with agglomerated bare Bi2O3 nanoparticles. The Bi2O3@rGO anode material can deliver a high initial capacity of ∼900 mAh/g at 0.1C and shows excellent rate capability of ∼270 mAh/g at 10C rates (1C = 600 mA/g). After 100 electrochemical cycles at 1C, the Bi2O3@rGO anode material retains a capacity of 347.3 mAh/g with corresponding capacity retention of 79%, which is significantly better than that of bare Bi2O3 material. The lithium ion diffusion coefficient during lithiation-delithiation of Bi2O3@rGO nanocomposite has been evaluated to be around ∼10(-15)-10(-16) cm(2)/S. This work demonstrates the effects of chemical bonding between Bi2O3 nanoparticles and rGO substrate on enhanced electrochemical performances of Bi2O3@rGO nanocomposite, which can be used as a promising anode alterative for superior lithium ion batteries.

  13. The effects of reasoning, use of models, sex type, and their interactions on posttest achievement in chemical bonding after constant instruction

    NASA Astrophysics Data System (ADS)

    Staver, John R.; Halsted, Douglas A.

    The purpose of the authors in this study was to determine the effects of reasoning, use of models during testing, and sex type on posttest achievement in chemical bonding under controlled instruction. Eighty-four high school students taking chemistry were randomly assigned within their classes to models and no models groups for the posttest. Reasoning capabilities were assessed by the Piagetian Logical Operations Test (PLOT) (Staver & Gabel, JRST, Vol. 16, No. 6, 1979), prior to instruction. All students then received the same instruction on chemical bonding which included teacher demonstrations of concepts with three-dimensional molecular models, interspersed teacher questions during the introduction and development of concepts, student manipulation of three-dimensional molecular models during laboratory experiments, and text reading assignments on concepts prior to their instruction in class. The posttest on molecular geometry and shape contained three sections requiring memory and application (Bloom, Taxonomy of educational objective, handbook I: Cognitive domain. New York: David McKay, 1956). Data were analyzed by regression (Nie et al., Statistical package for the social sciences, 2nd ed. New York: McGraw-Hill, 1975). Results indicate that reasoning accounted for a significant portion (p < 0.05) of the variance in the total score, memory score, and application score, but not on the synthesis score of the posttest. Use of models and sex type did not account for a significant (p > 0.05) portion of the variance on total scores or any section of posttest. The three-way interaction of reasoning, model usage, and sex type accounted for a significant portion (p < 0.05) of the variance in total scores, and in the memory and application sections of the posttest. Discussion focused on the results, conclusions, and implications for science teaching.

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

    NASA Astrophysics Data System (ADS)

    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.

  15. Chemically fixed p-n heterojunctions for polymer electronics by means of covalent B-F bond formation.

    PubMed

    Hoven, Corey V; Wang, Huiping; Elbing, Mark; Garner, Logan; Winkelhaus, Daniel; Bazan, Guillermo C

    2010-03-01

    Widely used solid-state devices fabricated with inorganic semiconductors, including light-emitting diodes and solar cells, derive much of their function from the p-n junction. Such junctions lead to diode characteristics and are attained when p-doped and n-doped materials come into contact with each other. Achieving bilayer p-n junctions with semiconducting polymers has been hindered by difficulties in the deposition of thin films with independent p-doped and n-doped layers. Here we report on how to achieve permanently fixed organic p-n heterojunctions by using a cationic conjugated polyelectrolyte with fluoride counteranions and an underlayer composed of a neutral conjugated polymer bearing anion-trapping functional groups. Application of a bias leads to charge injection and fluoride migration into the neutral layer, where irreversible covalent bond formation takes place. After the initial charging and doping, one obtains devices with no delay in the turn on of light-emitting electrochemical behaviour and excellent current rectification. Such devices highlight how mobile ions in organic media can open opportunities to realize device structures in ways that do not have analogies in the world of silicon and promise new opportunities for integrating organic materials within technologies now dominated by inorganic semiconductors.

  16. Invention of stimulus-responsive peptide-bond-cleaving residue (Spr) and its application to chemical biology tools.

    PubMed

    Shigenaga, Akira; Yamamoto, Jun; Kohiki, Taiki; Inokuma, Tsubasa; Otaka, Akira

    2017-01-19

    Elucidation of biological functions of peptides and proteins is essential for understanding peptide/protein-related biological events and developing drugs. Caged peptides and proteins that release a parent active peptide/protein by photo-irradiation have successfully been employed to elucidate the functions. Whereas the usual caged peptide/protein enables conversion of an inactive form to an active form (OFF-to-ON conversion) by photo-induced deprotection, photo-triggered main chain cleavage is reported to be applicable to ON-to-OFF conversion. These peptides and proteins are photo-responsive; however, if peptides and proteins could respond to other stimuli such as disease-related environment or enzymes, their range of application should be widened. To convert the photo-responsive peptide/protein into other stimulus-responsive peptide/protein, quite laborious de novo design and synthesis of the stimulus-responsive unit are required. In this context, we designed a stimulus-responsive peptide-bond-cleaving residue (Spr) in which the stimuli available for the main chain cleavage vary according to the choice of protecting groups on the residue. In this review, design and synthesis of Spr are introduced, and challenges to apply Spr to other fields to enable, for example, functional control, localization control, delivery of cargos, labeling of a protein of interest in living cells, and identification of target proteins of bioactive ligands are discussed. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

  17. First principle investigation of electronic structure, chemical bonding and optical properties of tetrabarium gallium trinitride oxide single crystal

    SciTech Connect

    Khan, Saleem Ayaz Azam, Sikander

    2015-10-15

    The electronic band structure, valence electron charge density and optical susceptibilities of tetrabarium gallium trinitride (TGT) were calculated via first principle study. The electronic band structure calculation describes TGT as semiconductor having direct band gap of 1.38 eV. The valence electronic charge density contour verified the non-polar covalent nature of the bond. The absorption edge and first peak of dielectric tensor components showed electrons transition from N-p state to Ba-d state. The calculated uniaxial anisotropy (0.4842) and birefringence (−0.0061) of present paper is prearranged as follow the spectral components of the dielectric tensor. The first peak in energy loss function (ELOS) shows the energy loss of fast traveling electrons in the material. The first sharp peak produced in ELOS around 10.5 eV show plasmon loss having plasma frequencies 0.1536, 0.004 and 0.066 of dielectric tensor components. This plasmon loss also cause decrease in reflectivity spectra.

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

    PubMed Central

    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

  19. Hydrogen bonding in ionic liquids.

    PubMed

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

    2015-03-07

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

  20. Internucleotide J-couplings and chemical shifts of the N-H···N hydrogen-bonds in the radiation-damaged guanine-cytosine base pairs.

    PubMed

    Li, Huifang; Zhang, Laibin; Han, Li; Sun, Wenming; Bu, Yuxiang

    2011-04-30

    Internucleotide (2h)J(NN) spin-spin couplings and chemical shifts (δ((1)H) and Δδ((15)N)) of N-H···N H-bond units in the natural and radiation-damaged G-C base pairs were predicted using the appropriate density functional theory calculations with a large basis set. Four possible series of the damaged G-C pairs (viz., dehydrogenated and deprotonated G-C pairs, GC(•-) and GC(•+) radicals) were discussed carefully in this work. Computational NMR results show that radicalization and anionization of the base pairs can yield strong effect on their (2h)J(NN) spin scalar coupling constants and the corresponding chemical shifts. Thus, variations of the NMR parameters associated with the N-H···N H-bonds may be taken as an important criterion for prejudging whether the natural G-C pair is radiation-damaged or not. Analysis shows that (2h)J(NN) couplings are strongly interrelated with the energy gaps (ΔE(LP→σ*)) and the second-order interaction energies (E(2)) between the donor N lone-pair (LP(N)) and the acceptor σ*(N-H) localized NBO orbitals, and also are sensitive to the electron density distributions over the σ*(N-H) orbital, indicating that (2h)J(NN) couplings across the N-H···N H-bonds are charge-transfer-controlled. This is well supported by variation of the electrostatic potential surfaces and corresponding charge transfer amount between G and C moieties. It should be noted that although the NMR spectra for the damaged G-C pair radicals are unavailable now and the states of the radicals are usually detected by the electron spin resonance, this study provides a correlation of the properties of the damaged DNA species with some of the electronic parameters associated with the NMR spectra for the understanding of the different state character of the damaged DNA bases.

  1. NbF5 and TaF5: Assignment of 19F NMR resonances and chemical bond analysis from GIPAW calculations

    NASA Astrophysics Data System (ADS)

    Biswal, Mamata; Body, Monique; Legein, Christophe; Sadoc, Aymeric; Boucher, Florent

    2013-11-01

    The 19F isotropic chemical shifts (δiso) of two isomorphic compounds, NbF5 and TaF5, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D 19F MAS NMR spectra. In parallel, the corresponding 19F chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M4F20] units of NbF5 and TaF5 being held together by van der Waals interactions, the relevance of Grimme corrections to the DFT optimization processes has been evaluated. However, the semi-empirical dispersion correction term introduced by such a method does not show any significant improvement. Nonetheless, a complete and convincing assignment of the 19F NMR lines of NbF5 and TaF5 is obtained, ensured by the linearity between experimental 19F δiso values and calculated 19F isotropic chemical shielding σiso values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF5. The relationships between the fluorine chemical shifts, the nature of the fluorine atoms (bridging or terminal), the position of the terminal ones (opposite or perpendicular to the bridging ones), the fluorine charges, the ionicity and the length of the M-F bonds have been established. Additionally, for three of the 19F NMR lines of NbF5, distorted multiplets, arising from 1J-coupling and residual dipolar coupling between the 19F and 93Nb nuclei, were simulated yielding to values of 93Nb-19F 1J-coupling for the corresponding fluorine sites.

  2. NbF{sub 5} and TaF{sub 5}: Assignment of {sup 19}F NMR resonances and chemical bond analysis from GIPAW calculations

    SciTech Connect

    Biswal, Mamata; Body, Monique; Legein, Christophe; Sadoc, Aymeric; Boucher, Florent

    2013-11-15

    The {sup 19}F isotropic chemical shifts (δ{sub iso}) of two isomorphic compounds, NbF{sub 5} and TaF{sub 5}, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D {sup 19}F MAS NMR spectra. In parallel, the corresponding {sup 19}F chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M{sub 4}F{sub 20}] units of NbF{sub 5} and TaF{sub 5} being held together by van der Waals interactions, the relevance of Grimme corrections to the DFT optimization processes has been evaluated. However, the semi-empirical dispersion correction term introduced by such a method does not show any significant improvement. Nonetheless, a complete and convincing assignment of the {sup 19}F NMR lines of NbF{sub 5} and TaF{sub 5} is obtained, ensured by the linearity between experimental {sup 19}F δ{sub iso} values and calculated {sup 19}F isotropic chemical shielding σ{sub iso} values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF{sub 5}. The relationships between the fluorine chemical shifts, the nature of the fluorine atoms (bridging or terminal), the position of the terminal ones (opposite or perpendicular to the bridging ones), the fluorine charges, the ionicity and the length of the M–F bonds have been established. Additionally, for three of the {sup 19}F NMR lines of NbF{sub 5}, distorted multiplets, arising from {sup 1}J-coupling and residual dipolar coupling between the {sup 19}F and {sup 93}Nb nuclei, were simulated yielding to values of {sup 93}Nb–{sup 19}F {sup 1}J-coupling for the corresponding fluorine sites. - Graphical abstract: The complete assignment of the {sup 19}F NMR lines of NbF{sub 5} and TaF{sub 5} allow establishing relationships between the {sup 19}F δ{sub iso} values, the nature of the fluorine atoms

  3. Surface morphology and bond characterization of nanocrystalline diamonds grown on tungsten carbide via hot filament chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hamzah, E.; Yong, T. M.; Mat Yajid, M. A.

    2013-06-01

    Nanocrystalline diamonds (NCDs) were deposited on chemically prepared tungsten carbide substrates via hot filament chemical vapor deposition. The surface morphology of the NCDs was examined using field emission scanning electron microscopy. The NCDs formed a ballas morphology evenly across the tungsten carbide surface. Overetching affected the diamond deposition by causing the ballas to form aggregations. Cross-sectional fragmentation using a diamond wafering blade caused the nanocrystalline diamond to fragment at overetched boundaries, and delamination only occurred 30-50 µm off the edge and revealed that the thickness of the diamond film was 6 µm. Grazing XRD is an effective method to identify diamonds even at the nanoscale. The crystallite size was calculated to be 18.4 nm by modeling. Cross-sectional TEM analysis indicated that the diamond grain size was approximately 10-30 nm near the interface. Amorphous carbon, an embedded diamond and voids were also observed. TEM also revealed that the tungsten carbide surface undulates. The nanocrystalline diamonds nucleated and grew on the tungsten carbide (100) planes in the <111> direction, forming (111) planes, as observed from HRTEM, d-spacing measurements, SAD and FFT analyses for a FIB-prepared sample.

  4. Effects of remote hydrogen plasma on chemical bonding features and electronic states of 4H-SiC(0001) surface

    NASA Astrophysics Data System (ADS)

    Truyen, Nguyen Xuan; Ohta, Akio; Makihara, Katsunori; Ikeda, Mitsuhisa; Miyazaki, Seiichi

    2017-01-01

    We have demonstrated a novel dry cleaning process for the 4H-SiC surface using remote hydrogen plasma (H2-RP). The effects of H2-RP exposure on the chemical structures and electronic states of the wet-cleaned 4H-SiC surface have been evaluated by X-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS). XPS shows that H2-RP exposure is effective in removing contaminants from the 4H-SiC surface. PYS indicates that the defect states at the surface are generated after the H2-RP exposure and such generated defect states are drastically decreased by annealing at 850 °C. The combination of H2-RP exposure with the subsequent annealing is found to be effective in 4H-SiC surface cleaning.

  5. Reaction dynamics. Extremely short-lived reaction resonances in Cl + HD (v = 1) → DCl + H due to chemical bond softening.

    PubMed

    Yang, Tiangang; Chen, Jun; Huang, Long; Wang, Tao; Xiao, Chunlei; Sun, Zhigang; Dai, Dongxu; Yang, Xueming; Zhang, Dong H

    2015-01-02

    The Cl + H2 reaction is an important benchmark system in the study of chemical reaction dynamics that has always appeared to proceed via a direct abstraction mechanism, with no clear signature of reaction resonances. Here we report a high-resolution crossed-molecular beam study on the Cl + HD (v = 1, j = 0) → DCl + H reaction (where v is the vibrational quantum number and j is the rotational quantum number). Very few forward scattered products were observed. However, two distinctive peaks at collision energies of 2.4 and 4.3 kilocalories per mole for the DCl (v' = 1) product were detected in the backward scattering direction. Detailed quantum dynamics calculations on a highly accurate potential energy surface suggested that these features originate from two very short-lived dynamical resonances trapped in the peculiar H-DCl (v' = 2) vibrational adiabatic potential wells that result from chemical bond softening. We anticipate that dynamical resonances trapped in such wells exist in many reactions involving vibrationally excited molecules.

  6. Ab initio thermodynamic study of the structure and chemical bonding of a β-Ni1-xAlx/α-Al2O3 interface

    NASA Astrophysics Data System (ADS)

    Li, Hongtao; Feng, Jiwei; Zhang, Wenqing; Jiang, Wan; Gu, Hui; Smith, John R.

    2009-11-01

    The properties of an interface between a metallic alloy and an oxide are computed by combining ab initio quantum mechanics with thermodynamics. Results for the stability, structures, and chemical compositions of the β-Ni1-xAlx/α-Al2O3 interface are presented. We found that there are two types of stable structures for the interface. Type I is characterized by joining an Al-rich Ni-Al alloy with an Al-rich Al2O3 surface (terminated by two Al atomic layers). Type II is a junction of a Ni-rich Ni-Al alloy with an Al2O3 surface terminated by an oxygen atomic layer and with atomic migrations and interchanges within the interfacial region. Both types of interfaces exhibit Al accumulation on top of the oxide scale while an adjacent Ni-rich layer is found at the type-II interfaces. The atomic geometries, electronic structures, and chemical bonds of the two types of interfacial systems were analyzed. The calculated interfacial works of separation Wsep agree reasonably well with experimental data and earlier calculations.

  7. Improvement of ground granulated blast furnace slag on stabilization/solidification of simulated mercury-doped wastes in chemically bonded phosphate ceramics.

    PubMed

    Liu, Zhongzhe; Qian, Guangren; Zhou, Jizhi; Li, Chuanhua; Xu, Yunfeng; Qin, Zhe

    2008-08-30

    This paper investigated the effectiveness of (ground granulated blast furnace slag) GGBFS-added chemically bonded phosphate ceramic (CBPC) matrix on the stabilization/solidification (S/S) of mercury chloride and simulated mercury-bearing light bulbs (SMLB). The results showed that the maximal compressive strength was achieved when 15% and 10% ground GGBFS was added for HgCl(2)-doped and SMLB-doped CBPC matrices, respectively. The S/S performances of GGBFS-added matrices were significantly better than non-additive matrices. As pore size was reduced, the leaching concentration of Hg(2+) from GGBFS-added CBPC matrix could be reduced from 697 microg/L to about 3 microg/L when treating HgCl(2). Meanwhile, the main hydrating product of GGBFS-added matrices was still MgKPO(4).6H(2)O. The improvement of S/S effectiveness was mainly due to physical filling of fine GGBFS particles and microencapsulation of chemical cementing gel.

  8. Synthesis of silica chemically bonded with poly(ethylene oxide) 4-arm, amine-terminated for copper cation removal.

    PubMed

    Kurczewska, Joanna; Schroeder, Grzegorz

    2010-12-01

    Chemically modified silica containing a poly(ethylene oxide) 4-arm, amine-terminated unit has been obtained in the multi-step synthesis. The synthesized material was characterized by elemental, thermogravimetric analysis and infrared spectroscopy. The surface morphology was analyzed by scanning electron microscopy. The support studied was applied for selective extraction of copper(II) [Cu(II)] from water solutions. The influence of different parameters (pH, amount of the support studied, and contact time) on the copper extraction was investigated. At the optimum conditions, the copper extraction was approximately 90%, significantly greater than that of the other coexisting ions--nickel(II) [Ni(II)], cobalt(II) [Co(II)], and manganese(II) [Mn(II)]. The exception was calcium(II) [Ca(II)], which reached 30% of the extraction percentage. The solid support retained its properties after treatment with different organic and inorganic solvents. The recovery of adsorbed Cu(II) ions was approximately 97%. The sorbent studied can be applied effectively for the pre-concentration of a low level of Cu(II) in the different water samples.

  9. Clique graphs and overlapping communities

    NASA Astrophysics Data System (ADS)

    Evans, T. S.

    2010-12-01

    It is shown how to construct a clique graph in which properties of cliques of a fixed order in a given graph are represented by vertices in a weighted graph. Various definitions and motivations for these weights are given. The detection of communities or clusters is used to illustrate how a clique graph may be exploited. In particular a benchmark network is shown where clique graphs find the overlapping communities accurately while vertex partition methods fail.

  10. 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.

    ERIC Educational Resources Information Center

    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)

  11. Tetrel Bonding Interactions.

    PubMed

    Bauzá, Antonio; Mooibroek, Tiddo J; Frontera, Antonio

    2016-02-01

    Tetrel (Tr) bonding is first placed into perspective as a σ-hole bonding interaction with atoms of the Tr family. An sp(3) R4Tr unit has four σ-holes with which a Lewis base can form a complex. We then highlight some inspiring crystal structures where Tr bonding is obvious, followed by an account of our own work. We have shown that Tr bonding is ubiquitous in the solid state and we have highlighted that Tr bonding with carbon is possible when C is placed in the appropriate chemical context. We hope that this account serves as an initial guide and source of inspiration for others wishing to exploit this vastly underexplored interaction.

  12. Direct Detection of a Chemical Equilibrium between a Localized Singlet Diradical and Its σ-Bonded Species by Time-Resolved UV/Vis and IR Spectroscopy.

    PubMed

    Yoshidomi, Shohei; Mishima, Megumi; Seyama, Shin; Abe, Manabu; Fujiwara, Yoshihisa; Ishibashi, Taka-Aki

    2017-03-06

    Localized singlet diradicals are key intermediates in bond homolyses. The singlet diradicals are energetically much less stable than the σ-bonded species. In general, only one-way reactions from diradicals to σ-bonded species are observed. In this study, a thermal equilibrium between a singlet 1,2-diazacyclopentane-3,5-diyl diradical and the corresponding σ-bonded species was directly observed. The singlet diradical was more stable than the σ-bonded species. The solvent effect clarified key features, such as the zwitterionic character of the singlet diradical. The effect of the nitrogen atoms is discussed in detail.

  13. Rapid adhesive bonding of advanced composites and titanium

    NASA Technical Reports Server (NTRS)

    Stein, B. A.; Tyeryart, J. R.; Hodgest, W. T.

    1985-01-01

    Rapid adhesive bonding (RAB) concepts utilize a toroid induction technique to heat the adhesive bond line directly. This technique was used to bond titanium overlap shear specimens with 3 advanced thermoplastic adhesives and APC-2 (graphite/PEEK) composites with PEEK film. Bond strengths equivalent to standard heated-platen press bonds were produced with large reductions in process time. RAB produced very strong bonds in APC-2 adherend specimens; the APC-2 adherends were highly resistant to delamination. Thermal cycling did not significantly affect the shear strengths of RAB titanium bonds with polyimide adhesives. A simple ultrasonic non-destructive evaluation process was found promising for evaluating bond quality.

  14. Three methods to measure RH bond energies

    NASA Astrophysics Data System (ADS)

    Berkowitz, Joseph; Ellison, G. Barney; Gutman, David

    1993-03-01

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

  15. Three methods to measure RH bond energies

    SciTech Connect

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

    1993-03-21

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

  16. Hospital mergers and market overlap.

    PubMed Central

    Brooks, G R; Jones, V G

    1997-01-01

    OBJECTIVE: To address two questions: What are the characteristics of hospitals that affect the likelihood of their being involved in a merger? What characteristics of particular pairs of hospitals affect the likelihood of the pair engaging in a merger? DATA SOURCES/STUDY SETTING: Hospitals in the 12 county region surrounding the San Francisco Bay during the period 1983 to 1992 were the focus of the study. Data were drawn from secondary sources, including the Lexis/Nexis database, the American Hospital Association, and the Office of Statewide Health Planning and Development of the State of California. STUDY DESIGN: Seventeen hospital mergers during the study period were identified. A random sample of pairs of hospitals that did not merge was drawn to establish a statistically efficient control set. Models constructed from hypotheses regarding hospital and market characteristics believed to be related to merger likelihood were tested using logistic regression analysis. DATA COLLECTION: See Data Sources/Study Setting. PRINCIPAL FINDINGS: The analysis shows that the likelihood of a merger between a particular pair of hospitals is positively related to the degree of market overlap that exists between them. Furthermore, market overlap and performance difference interact in their effect on merger likelihood. In an analysis of individual hospitals, conditions of rivalry, hospital market share, and hospital size were not found to influence the likelihood that a hospital will engage in a merger. CONCLUSIONS: Mergers between hospitals are not driven directly by considerations of market power or efficiency as much as by the existence of specific merger opportunities in the hospitals' local markets. Market overlap is a condition that enables a merger to occur, but other factors, such as the relative performance levels of the hospitals in question and their ownership and teaching status, also play a role in influencing the likelihood that a merger will in fact take place. PMID

  17. Comparison of the effect of shear bond strength with silane and other three chemical presurface treatments of a glass fiber-reinforced post on adhesion with a resin-based luting agent: An in vitro study

    PubMed Central

    Belwalkar, Vaibhavi Ramkrishna; Gade, Jaykumar; Mankar, Nikhil Purushottam

    2016-01-01

    Background: Loss of retention has been cited to be the most common cause of the failure of postretained restoration with irreversible consequences when materials with different compositions are in intimate contact at the post/adhesive interface. With this background, a study was conducted to improve the adhesion at the resin phase of fiber posts using silane and other chemical pretreatments. Materials and Methods: Hundred glass fiber-reinforced posts were tested with 4 different protocols (n = 25) using silane as a control (Group A) and other three experimental groups, namely, Group B-20% potassium permanganate, Group C-4% hydrofluoric acid, and Group D-10% hydrogen peroxide were pretreated on the postsurface followed by silanization. These specimens were bonded with dual-polymerizing resin-based luting agent, which were then loaded at the crosshead speed of 1 mm/min to record the shear bond strength at the post/adhesive interface. The data were analyzed using one-way ANOVA test for multiple group comparisons and the post hoc Bonferroni test for pairwise comparisons (P < 0.05). Results: Group B showed more influence on the shear bond strength when compared to other protocols, respectively (P < 0.001). Conclusion: Alone silanization as a surface treatment did not improve the bond strength. Combination of chemical presurface treatments followed by silanization significantly enhanced the bond strength at the post/adhesive interface. PMID:27307666

  18. A study of vibrational spectra and investigations of charge transfer and chemical bonding features of 2-chloro benzimidazole based on DFT computations

    NASA Astrophysics Data System (ADS)

    Muthunatesan, S.; Ragavendran, V.

    2015-01-01

    Benzimidazoles are bicyclic heteroatomic molecules. Polycyclic heteroatomic molecules have extensive coupling of different modes leading to strong coupling of force constants associated with the various chemical bonds of the molecules. To carry out a detailed vibrational spectroscopic analysis of such a bicyclic heteroatomic molecule, FT-IR and FT-Raman spectra of 2-chloro benzimidazole (CBZ) have been recorded in the condensed phase. Density Functional Theory calculations in the B3LYP/6-31G* level have been carried out to determine the optimized geometry and vibrational frequencies. In order to obtain a close agreement between theoretical and observed frequencies and hence to perform a reliable assignment, the theoretical DFT force field was transformed from Cartesian to local symmetry co-ordinates and then scaled empirically using SQM methodology. The SQM treatment resulted in a RMS deviation of 9.4 cm-1. For visual comparison, the observed and calculated spectra are presented on a common wavenumber scale. From the NBO analysis, the electron density (ED) charge transfers in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The calculated Homo and Lumo energies show that charge transfer occurs within the molecule. The results obtained from the vibrational, NBO and HOMO-LUMO analyses have been properly tabulated.

  19. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba4CuGa5Q12 (Q=S, Se)

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba4CuGa5S12 and Ba4CuGa5Se12 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 Ba4CuGa5Se12 than Ba4CuGa5S12. Fermi surface of Ba4CuGa5S12 consists of an electronic sheet only because there is no empty region while Ba4CuGa5Se12 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 Ba4CuGa5S12 (Ba4CuGa5Se12) 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.

  20. Advanced Fabrication of Chemically Bonded Graphene/TiO2 Continuous Fibers with Enhanced Broadband Photocatalytic Properties and Involved Mechanisms Exploration

    NASA Astrophysics Data System (ADS)

    Zhang, Qingzhe; Bao, Nan; Wang, Xinqiang; Hu, Xinde; Miao, Xinhan; Chaker, Mohamed; Ma, Dongling

    2016-12-01

    In this article, a novel route for the synthesis of graphene/TiO2 continuous fibers (GTF) using force-spinning combined with water vapor annealing method is reported for the first time. The morphology, structure and optical properties of the composite were fully characterized. With a single step of heat treatment process using steam at ambient conditions, we were able to initiate a series of chemical reactions, such as reduction of graphene oxide (GO), crystallization of TiO2, formation of C-Ti bond, and introduction of oxygen vacancies into TiO2. The incorporation of graphene in TiO2 fibers facilitated bandgap narrowing and improved photo-induced charge separation in the photocatalyst. As a result of synergistic effects, TiO2 fibers-2 wt% graphene (2%GTF) showed the highest photocatalytic activities in the degradation of X-3B under UV irradiation, superior to the benchmark photocatalyst P25. Under visible light irradiation, the same catalyst was about 4 times more efficient compared to pure TiO2 fibers (PTF). A detailed study of involved active species (in particular, ·, h+ and ·OH) unraveled the mechanism regarding photocatalysis.

  1. Advanced Fabrication of Chemically Bonded Graphene/TiO2 Continuous Fibers with Enhanced Broadband Photocatalytic Properties and Involved Mechanisms Exploration

    PubMed Central

    Zhang, Qingzhe; Bao, Nan; Wang, Xinqiang; Hu, Xinde; Miao, Xinhan; Chaker, Mohamed; Ma, Dongling

    2016-01-01

    In this article, a novel route for the synthesis of graphene/TiO2 continuous fibers (GTF) using force-spinning combined with water vapor annealing method is reported for the first time. The morphology, structure and optical properties of the composite were fully characterized. With a single step of heat treatment process using steam at ambient conditions, we were able to initiate a series of chemical reactions, such as reduction of graphene oxide (GO), crystallization of TiO2, formation of C-Ti bond, and introduction of oxygen vacancies into TiO2. The incorporation of graphene in TiO2 fibers facilitated bandgap narrowing and improved photo-induced charge separation in the photocatalyst. As a result of synergistic effects, TiO2 fibers-2 wt% graphene (2%GTF) showed the highest photocatalytic activities in the degradation of X-3B under UV irradiation, superior to the benchmark photocatalyst P25. Under visible light irradiation, the same catalyst was about 4 times more efficient compared to pure TiO2 fibers (PTF). A detailed study of involved active species (in particular, ·, h+ and ·OH) unraveled the mechanism regarding photocatalysis. PMID:27905488

  2. Advanced Fabrication of Chemically Bonded Graphene/TiO2 Continuous Fibers with Enhanced Broadband Photocatalytic Properties and Involved Mechanisms Exploration.

    PubMed

    Zhang, Qingzhe; Bao, Nan; Wang, Xinqiang; Hu, Xinde; Miao, Xinhan; Chaker, Mohamed; Ma, Dongling

    2016-12-01

    In this article, a novel route for the synthesis of graphene/TiO2 continuous fibers (GTF) using force-spinning combined with water vapor annealing method is reported for the first time. The morphology, structure and optical properties of the composite were fully characterized. With a single step of heat treatment process using steam at ambient conditions, we were able to initiate a series of chemical reactions, such as reduction of graphene oxide (GO), crystallization of TiO2, formation of C-Ti bond, and introduction of oxygen vacancies into TiO2. The incorporation of graphene in TiO2 fibers facilitated bandgap narrowing and improved photo-induced charge separation in the photocatalyst. As a result of synergistic effects, TiO2 fibers-2 wt% graphene (2%GTF) showed the highest photocatalytic activities in the degradation of X-3B under UV irradiation, superior to the benchmark photocatalyst P25. Under visible light irradiation, the same catalyst was about 4 times more efficient compared to pure TiO2 fibers (PTF). A detailed study of involved active species (in particular, ·, h(+) and ·OH) unraveled the mechanism regarding photocatalysis.

  3. Effect of surface pretreatment on interfacial chemical bonding states of atomic layer deposited ZrO{sub 2} on AlGaN

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-09-15

    Atomic layer deposition (ALD) of ZrO{sub 2} on native oxide covered (untreated) and buffered oxide etchant (BOE) treated AlGaN surface was analyzed by utilizing x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy. Evidenced by Ga–O and Al–O chemical bonds by XPS, parasitic oxidation during deposition is largely enhanced on BOE treated AlGaN surface. Due to the high reactivity of Al atoms, more prominent oxidation of Al atoms is observed, which leads to thicker interfacial layer formed on BOE treated surface. The results suggest that native oxide on AlGaN surface may serve as a protecting layer to inhibit the surface from further parasitic oxidation during ALD. The findings provide important process guidelines for the use of ALD ZrO{sub 2} and its pre-ALD surface treatments for high-k AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors and other related device applications.

  4. Silica chemically bonded N-propyl kriptofix 21 and 22 with immobilized palladium nanoparticles for solid phase extraction and preconcentration of some metal ions.

    PubMed

    Ghaedi, Mehrorang; Niknam, Khodabakhsh; Zamani, Saeed; Larki, Habib Abasi; Roosta, Mostafa; Soylak, Mustafa

    2013-08-01

    Silica gel chemically bonded N-propyl kriptofix 21 (SBNPK 21) and N-propyl kriptofix 22 (SBNPK 22) and subsequently immobilized with palladium nanoparticles (PNP-SBNPK 21 and PNP-SBNPK 22) to produce two new complexing lipophilic materials. Then these novel sorbents were applied for the enrichment of some metal ions and their subsequent determination by flame atomic absorption spectroscopy (FAAS). The influences of the variables including pH, amount of solid phase, sample flow rate, eluent conditions and sample volume on the metal ion recoveries were investigated. The detection limit of proposed method was in the interval 2.1-2.3 and 1.7-2.8 ng mL(-1) for PNP-SBNPK 21 and PNP-SBNPK 22 respectively, while the preconcentration factor was 80 for two sorbents. The relative standard deviations of recoveries were between 1.23-1.31 and 1.28-1.49 for PNP-SBNPK 21 and PNP-SBNPK 22 respectively. The method has high sorption-preconcentration efficiency even in the presence of various interfering ions. Due to the reasonable selectivity of proposed method, the relative standard deviation of recoveries of all understudied metal ions in some complicated matrices was less than 3.0%.

  5. Nitrogen Doping Enables Covalent-Like π–π Bonding between Graphenes

    DOE PAGES

    Tian, Yong-Hui; Huang, Jingsong; Sheng, Xiaolan; ...

    2015-07-07

    In neighboring layers of bilayer (and few-layer) graphenes, both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) pi-pi bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by upmore » to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the pi-pi overlap across the vdW gap while the individual layers maintain their in-plane pi-conjugation and are accordingly planar. Moreover, the existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.« less

  6. Nitrogen Doping Enables Covalent-Like π–π Bonding between Graphenes

    SciTech Connect

    Tian, Yong-Hui; Huang, Jingsong; Sheng, Xiaolan; Sumpter, Bobby G.; Yoon, Mina; Kertesz, Miklos

    2015-07-07

    In neighboring layers of bilayer (and few-layer) graphenes, both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) pi-pi bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the pi-pi overlap across the vdW gap while the individual layers maintain their in-plane pi-conjugation and are accordingly planar. Moreover, the existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.

  7. Nitrogen-Doping Enables Covalent-Like pi-pi Bonding between Graphenes

    SciTech Connect

    Tian, Yong-Hui; Huang, Jingsong; Sumpter, Bobby G; Kertesz, Prof. Miklos

    2015-01-01

    The neighboring layers in bi-layer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene molecules . Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) pi pi bonding in bi-layer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bi-layers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the pi pi overlap across the vdW gap while the individual layers maintain their in-plane pi-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.

  8. Nitrogen Doping Enables Covalent-Like π-π Bonding between Graphenes.

    PubMed

    Tian, Yong-Hui; Huang, Jingsong; Sheng, Xiaolan; Sumpter, Bobby G; Yoon, Mina; Kertesz, Miklos

    2015-08-12

    The neighboring layers in bilayer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) π-π bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the π-π overlap across the vdW gap while the individual layers maintain their in-plane π-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.

  9. A Series of Diamagnetic Pyridine Monoimine Rhenium Complexes with Different Degrees of Metal-to-Ligand Charge Transfer: Correlating (13) C NMR Chemical Shifts with Bond Lengths in Redox-Active Ligands.

    PubMed

    Sieh, Daniel; Kubiak, Clifford P

    2016-07-18

    A set of pyridine monoimine (PMI) rhenium(I) tricarbonyl chlorido complexes with substituents of different steric and electronic properties was synthesized and fully characterized. Spectroscopic (NMR and IR) and single-crystal X-ray diffraction analyses of these complexes showed that the redox-active PMI ligands are neutral and that the overall electronic structure is little affected by the choices of the substituent at the ligand backbone. One- and two-electron reduction products were prepared from selected starting compounds and could also be characterized by multiple spectroscopic methods and X-ray diffraction. The final product of a one-electron reduction in THF is a diamagnetic metal-metal-bonded dimer after loss of the chlorido ligand. Bond lengths in and NMR chemical shifts of the PMI ligand backbone indicate partial electron transfer to the ligand. Two-electron reduction in THF also leads to the loss of the chlorido ligand and a pentacoordinate complex is obtained. The comparison with reported bond lengths and (13) C NMR chemical shifts of doubly reduced free pyridine monoaldimine ligands indicates that both redox equivalents in the doubly reduced rhenium complex investigated here are located in the PMI ligand. With diamagnetic complexes varying over three formal reduction stages at the PMI ligand we were, for the first time, able to establish correlations of the (13) C NMR chemical shifts with the relevant bond lengths in redox-active ligands over a full redox series.

  10. Mechanisms of formation of chemical bonding and defect formation at the a-SiO 2 /BaTiO 3 interfaces

    SciTech Connect

    Kimmel, Anna V.; Sushko, Peter V.

    2015-10-28

    The structure and mechanisms of bonding and defect formation at the interfaces between amorphous silica (a-SiO2) and BaTiO3(0 0 1) were investigated using ab initio molecular dynamics. It was found that the nature of interfacial bonds crucially depends on the BaTiO3 surface termination. In particular, the interface between silica and TiO2-terminated BaTiO3 (BTO) slab is characterised by strong covalent Ti–O–Si bonds, while the interface between silica and BaO-terminated BTO demonstrates ionic character of interfacial bonds and exhibits bond instability. In both cases, the dynamics of oxygen species at oxide interfaces is a driving force of the formation of interfacial bonds and defects.

  11. Overlap in Facebook Profiles Reflects Relationship Closeness.

    PubMed

    Castañeda, Araceli M; Wendel, Markie L; Crockett, Erin E

    2015-01-01

    We assessed the association between self-reported Inclusion of Other in the Self (IOS) and Facebook overlap. Ninety-two participants completed online measures of IOS and investment model constructs. Researchers then recorded Facebook data from participants' profile pages. Results from multilevel models revealed that IOS predicted Facebook overlap. Furthermore, Facebook overlap was associated with commitment and investment in ways comparable to self-reported IOS. These findings suggest that overlap in Facebook profiles can be used to measure relationship closeness.

  12. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba4CuGa5Q12 (Q=S, Se)

    NASA Astrophysics Data System (ADS)

    Azam, Sikander; Reshak, A. H.

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba4CuGa5S12 and Ba4CuGa5Se12 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 Ba4CuGa5Se12 than Ba4CuGa5S12. Fermi surface of Ba4CuGa5S12 consists of an electronic sheet only because there is no empty region while Ba4CuGa5Se12 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 Ba4CuGa5S12 (Ba4CuGa5Se12) 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.

  13. 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.

    PubMed

    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.

  14. Overlapping structures in sensory-motor mappings.

    PubMed

    Earland, Kevin; Lee, Mark; Shaw, Patricia; Law, James

    2014-01-01

    This paper examines a biologically-inspired representation technique designed for the support of sensory-motor learning in developmental robotics. An interesting feature of the many topographic neural sheets in the brain is that closely packed receptive fields must overlap in order to fully cover a spatial region. This raises interesting scientific questions with engineering implications: e.g. is overlap detrimental? does it have any benefits? This paper examines the effects and properties of overlap between elements arranged in arrays or maps. In particular we investigate how overlap affects the representation and transmission of spatial location information on and between topographic maps. Through a series of experiments we determine the conditions under which overlap offers advantages and identify useful ranges of overlap for building mappings in cognitive robotic systems. Our motivation is to understand the phenomena of overlap in order to provide guidance for application in sensory-motor learning robots.

  15. Overlapping Structures in Sensory-Motor Mappings

    PubMed Central

    Earland, Kevin; Lee, Mark; Shaw, Patricia; Law, James

    2014-01-01

    This paper examines a biologically-inspired representation technique designed for the support of sensory-motor learning in developmental robotics. An interesting feature of the many topographic neural sheets in the brain is that closely packed receptive fields must overlap in order to fully cover a spatial region. This raises interesting scientific questions with engineering implications: e.g. is overlap detrimental? does it have any benefits? This paper examines the effects and properties of overlap between elements arranged in arrays or maps. In particular we investigate how overlap affects the representation and transmission of spatial location information on and between topographic maps. Through a series of experiments we determine the conditions under which overlap offers advantages and identify useful ranges of overlap for building mappings in cognitive robotic systems. Our motivation is to understand the phenomena of overlap in order to provide guidance for application in sensory-motor learning robots. PMID:24392118

  16. Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities.

    PubMed

    Keyvani, Zahra Alimohammadi; Shahbazian, Shant; Zahedi, Mansour

    2016-10-18

    The equivalence of the molecular graphs emerging from the comparative analysis of the optimized and the promolecule electron densities in two hundred and twenty five unsubstituted hydrocarbons was recently demonstrated [Keyvani et al. Chem. Eur. J. 2016, 22, 5003]. Thus, the molecular graph of an optimized molecular electron density is not shaped by the formation of the C-H and C-C bonds. In the present study, to trace the fingerprint of the C-H and C-C bonds in the electron densities of the same set of hydrocarbons, the amount of electron density and its Laplacian at the (3, -1) critical points associated with these bonds are derived from both optimized and promolecule densities, and compared in a newly proposed comparative analysis. The analysis not only conforms to the qualitative picture of the electron density build up between two atoms upon formation of a bond in between, but also quantifies the resulting accumulation of the electron density at the (3, -1) critical points. The comparative analysis also reveals a unified mode of density accumulation in the case of 2318 studied C-H bonds, but various modes of density accumulation are observed in the case of 1509 studied C-C bonds and they are classified into four groups. The four emerging groups do not always conform to the traditional classification based on the bond orders. Furthermore, four C-C bonds described as exotic bonds in previous studies, for example the inverted C-C bond in 1,1,1-propellane, are naturally distinguished from the analysis.

  17. 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.

    PubMed

    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.

  18. Computational Chemistry of Adhesive Bonds

    NASA Technical Reports Server (NTRS)

    Phillips, Donald H.

    1999-01-01

    This investigation is intended to determine the electrical mechanical, and chemical properties of adhesive bonds at the molecular level. The initial determinations will be followed by investigations of the effects of environmental effects on the chemistry and properties of the bond layer.

  19. 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.

    PubMed

    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.

  20. [A quantum chemical study of pi-back-donation bond and Raman intensity of 1 sigma + electronic state of Pt-CO molecule].

    PubMed

    Wu, D; Xu, X; Ren, B; Cao, Z; Shi, P; Tian, Z

    2000-12-01

    The Raman spectroscopic properties of Pt-CO molecule have been investigated based on the electronic state 1 sigma + determined by the HF and B3LYP methods. The result shows that the calculated stretching vibrational frequencies of the Pt-C and C-O bonds depend on the method and the basis sets used. It indicates that it is important to adopt an appropriate method to describe pi-donation and pi-back-donation bond. The result of the differential Raman scattering cross section for the stretching vibrations of the Pt-C and C-O bond shows that the latter is significantly larger value compared to the former.

  1. REACTION OF AMINO-ACIDS AND PEPTIDE BONDS WITH FORMALDEHYDE AS MEASURED BY CHANGES IN THE ULTRA-VIOLET SPECTRA,

    DTIC Science & Technology

    AMINO ACIDS , CHEMICAL REACTIONS), (*PEPTIDES, CHEMICAL REACTIONS), (*FORMALDEHYDE, CHEMICAL REACTIONS), (*ULTRAVIOLET SPECTROSCOPY, PROTEINS), ABSORPTION SPECTRA, CHEMICAL BONDS, AMIDES, CHEMICAL EQUILIBRIUM, REACTION KINETICS

  2. First-principle investigation of Jahn-Teller distortion and topological analysis of chemical bonds in LiNiO{sub 2}

    SciTech Connect

    Chen Zhenlian; Zou Huamin; Zhu Xiaopeng; Zou Jie; Cao Jiefeng

    2011-07-15

    First-principle GGA+U calculations were performed on the undistorted rhombohedral R3-bar m model, the collinear Jahn-Teller distorted monoclinic C2/m model, and six non-collinear Jahn-Teller distortion ordering models of LiNiO{sub 2}. The zigzag and C2/m models are found to be the most stable and the next most stable structural models, respectively. An energy gap appears for the C2/m and zigzag structures, whereas no energy gap appears for the R3-bar m structure. Topological analyses were performed on the R3-bar m, C2/m and zigzag models using the atoms-in-molecules theory and the electron localization function. The results show that the Ni-O interaction is the transit closed-shell interaction, in which the net electron transfer occurs from the Ni ion to the ligand O ions. The Ni-O bond possesses the {sigma} dative bond character and is polarized toward the O ions. In the distorted structures, the bonding electrons around the oxygen atom are strongly polarized toward the long Ni-O bond. - Graphical abstract: Isosurfaces of the difference charge density and the electron localization function for the zigzag structure of LiNiO{sub 2}. Highlights: > Using ELF and AIM, topological analyses were carried out on different structures. > The zigzag Jahn-Teller distortion ordering is the most stable structure. > Semiconductor gap emerges in the C2/m and zigzag structures. > The Ni-O bonds are dative bonds. > In the distorted structures, bond electrons accumulate in the long Ni-O bond basins.

  3. Solving Partial Differential Equations on Overlapping Grids

    SciTech Connect

    Henshaw, W D

    2008-09-22

    We discuss the solution of partial differential equations (PDEs) on overlapping grids. This is a powerful technique for efficiently solving problems in complex, possibly moving, geometry. An overlapping grid consists of a set of structured grids that overlap and cover the computational domain. By allowing the grids to overlap, grids for complex geometries can be more easily constructed. The overlapping grid approach can also be used to remove coordinate singularities by, for example, covering a sphere with two or more patches. We describe the application of the overlapping grid approach to a variety of different problems. These include the solution of incompressible fluid flows with moving and deforming geometry, the solution of high-speed compressible reactive flow with rigid bodies using adaptive mesh refinement (AMR), and the solution of the time-domain Maxwell's equations of electromagnetism.

  4. Intramolecular CH···O hydrogen bonds in the AI and BI DNA-like conformers of canonical nucleosides and their Watson-Crick pairs. Quantum chemical and AIM analysis.

    PubMed

    Yurenko, Yevgen P; Zhurakivsky, Roman O; Samijlenko, Svitlana P; Hovorun, Dmytro M

    2011-08-01

    The aim of this work is to cast some light on the H-bonds in double-stranded DNA in its AI and BI forms. For this purpose, we have performed the MP2 and DFT quantum chemical calculations of the canonical nucleoside conformers, relative to the AI and BI DNA forms, and their Watson-Crick pairs, which were regarded as the simplest models of the double-stranded DNA. Based on the atoms-in-molecules analysis (AIM), five types of the CH···O hydrogen bonds, involving bases and sugar, were detected numerically from 1 to 3 per a conformer: C2'H···O5', C1'H···O2, C6H···O5', C8H···O5', and C6H···O4'. The energy values of H-bonds occupy the range of 2.3-5.6 kcal/mol, surely exceeding the kT value (0.62 kcal/mol). The nucleoside CH···O hydrogen bonds appeared to "survive" turns of bases against the sugar, sometimes in rather large ranges of the angle values, pertinent to certain conformations, which points out to the source of the DNA lability, necessary for the conformational adaptation in processes of its functioning. The calculation of the interactions in the dA·T nucleoside pair gives evidence, that additionally to the N6H···O4 and N1···N3H canonical H-bonds, between the bases adenine and thymine the third one (C2H···O2) is formed, which, though being rather weak (about 1 kcal/mol), satisfies the AIM criteria of H-bonding and may be classified as a true H-bond. The total energy of all the CH···O nontraditional intramolecular H-bonds in DNA nucleoside pairs appeared to be commensurable with the energy of H-bonds between the bases in Watson-Crick pairs, which implies their possible important role in the DNA shaping.

  5. Finding overlapping communities using seed set

    NASA Astrophysics Data System (ADS)

    Yang, Jin-Xuan; Zhang, Xiao-Dong

    2017-02-01

    The local optimization algorithm using seed set to find overlapping communities has become more and more a significant method, but it is a great challenge how to choose a good seed set. In this paper, a new method is proposed to achieve the choice of candidate seed sets, and yields a new algorithm to find overlapping communities in complex networks. By testing in real world networks and synthetic networks, this method can successfully detect overlapping communities and outperform other state-of-the-art overlapping community detection methods.

  6. Overlap syndromes among autoimmune liver diseases.

    PubMed

    Rust, Christian; Beuers, Ulrich

    2008-06-07

    The three major immune disorders of the liver are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). Variant forms of these diseases are generally called overlap syndromes, although there has been no standardised definition. Patients with overlap syndromes present with both hepatitic and cholestatic serum liver tests and have histological features of AIH and PBC or PSC. The AIH-PBC overlap syndrome is the most common form, affecting almost 10% of adults with AIH or PBC. Single cases of AIH and autoimmune cholangitis (AMA-negative PBC) overlap syndrome have also been reported. The AIH-PSC overlap syndrome is predominantly found in children, adolescents and young adults with AIH or PSC. Interestingly, transitions from one autoimmune to another have also been reported in a minority of patients, especially transitions from PBC to AIH-PBC overlap syndrome. Overlap syndromes show a progressive course towards liver cirrhosis and liver failure without treatment. Therapy for overlap syndromes is empiric, since controlled trials are not available in these rare disorders. Anticholestatic therapy with ursodeoxycholic acid is usually combined with immunosuppressive therapy with corticosteroids and/or azathioprine in both AIH-PBC and AIH-PSC overlap syndromes. In end-stage disease, liver transplantation is the treatment of choice.

  7. Cast Aluminum Bonding Study

    DTIC Science & Technology

    1988-05-01

    fabricated using P?-’r;est11 bur)ld II19 te(hnll I Oly with 6 cIsL nqs. The cast a lumi num alloy used was A357 . The sur- face preparation was phosphoric acid...from a cast aluminum alloy designated A357 . The bonding surfaces of the adherends were prepared using PAA. One primer and two adhesives considered...System, Cast Aluminum Lap Shear 18 11 Bond Area of 350°F Adhesive System, Cast Aluminum Lap Shear 19 vi LIST OF TABLES TABLE PAGE 1 A357 Chemical

  8. Chemical bond properties and charge transfer bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) in Eu(3+)-doped garnet hosts Ln3M5O12 and ABO4 molybdate and tungstate phosphors.

    PubMed

    Liu, Xiaoguang; Li, Ling; Noh, Hyeon Mi; Moon, Byung Kee; Choi, Byung Chun; Jeong, Jung Hyun

    2014-06-21

    Charge transfer (CT) energy from the ligand to the central ions is an important factor in luminescence properties for rare earth doped inorganic phosphors. The dielectric theory of complex crystals was used to calculate chemical bond properties. Combining the photoluminescence and the dielectric theory of complex crystals, the CT bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) for Eu(3+)-doped inorganic phosphors have been investigated experimentally and theoretically. Taking Eu(3+)-doped Ln3M5O12 (Ln = Y, Lu and M = Al, Ga), Gd3Ga5O12, MMoO4 (M = Ca, Sr, Ba) and MWO4 (M = Ca, Sr, Ba) as typical phosphors, we investigated the effects of the cation size on the CT bands and chemical bond properties including the bond length (d), the covalency (fc), the bond polarizability (αb) and the environmental factor (he) of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+), respectively. For systematic isostructural Ln3M5O12 (Ln = Y, Lu and M = Al, Ga) phosphors, with the increasing M ion radius, the bond length of Ln-O decreases, but fc and αb increase, which is the main reason that the environmental factor increased. For the isostructural MMoO4:Eu, with the increasing M ion radius, the Mo-O bond length increases, but fc and αb decrease, and thus he decreases. However, in the compound system MWO4:Eu (M = Ca, Ba) with the increasing M ion radius, the O-W bond length increases, but fc and αb increase, and thus he increases and the O-W CT energy decreases. Their O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) CT bands as well as their full width at half maximum (FWHM) were directly influenced by he. And with the increasing he, CT bands of O-Eu or O-Mo or O-W decrease and their FWHM increases. These results indicate a promising approach for changing the material properties, searching for new Eu(3+) doped molybdate, tungstate or other oxide phosphors and analyzing the experimental result.

  9. Bone bonding bioactivity of Ti metal and Ti-Zr-Nb-Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments.

    PubMed

    Fukuda, A; Takemoto, M; Saito, T; Fujibayashi, S; Neo, M; Yamaguchi, S; Kizuki, T; Matsushita, T; Niinomi, M; Kokubo, T; Nakamura, T

    2011-03-01

    Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices.

  10. Chemical bond parameters and photoluminescence of a natural-white-light Ca9La(VO4)7:Tm3+,Eu3+ with one O2-→V5+ charge transfer and dual f-f transition emission centers

    NASA Astrophysics Data System (ADS)

    Li, Ling; Liu, Xiao Guang; Noh, Hyeon Mi; Jeong, Jung Hyun

    2015-01-01

    The relationship between the photoluminescence properties and the crystal structure of undoped, Eu3+ or/ and Tm3+ singly or codoped Ca9La(VO4)7 (CLaVO) samples was discussed. Under the excitation of UV light, CLaVO:Tm3+, CLaVO, and CLaVO:Eu3+ exhibit the characteristic emissions of Tm3+ (1G4→3H6, blue), O2-→V5+ charge transfer (CT), and Eu3+ (5D0→7F2, red), respectively. By adjusting the doping concentration of Tm3+ and Eu3+ ions in CLaVO, a natural white emission in a single composition with the color temperature at 6181 K was obtained. Based on the dielectric theory of complex crystal, the chemical bond parameters of La-O and V-O bonds were quantitatively calculated. The standard deviation of environmental factor of every bond (EFSD), which can be expressed as σ (hei) =√{ (1 / N) ∑ i = 1 N (hei - μ) 2 } (hei =(fciαbi) 1 / 2QBi and μ = (1 / N) ∑ i = 1 N hei), was proposed to quantitatively express the distortion degree of VO43- from that of an ideal tetrahedron. The maximum change of EFSD comes from the [VO4]- tetrahedra in CLaVO sample by comparison with that of EFSD of isostructural Ca9Gd(VO4)7. This is possible the key reason that the undoped CLaVO sample has self-activated emission while the self-activated emission of its isostructural Ca9Gd(VO4)7 sample cannot be found. The quantitative calculation also demonstrated that the broad excitation bands at 319 nm in CLaVO:Tm and at 335 nm in CLaVO:Eu were due to the O-V2 and O-V3 (overlap with O-V2) CT, not the CT energy of O2--Eu13+ (O2--Tm13+), O2--Eu23+ (O2--Tm23+), and O2--Eu33+ (O2--Tm33+). The environmental factors surrounding the atoms V1, V2 and V3 were calculated to be 1.577, 1.6379 and 1.7554, respectively. It can be demonstrated that the excitation spectra at 319 nm for CLaVO:Tm and 335 nm for CLaVO:Eu came from the O-V2 and O-V3 CT, respectively.

  11. Crystal Field Theory and the Angular Overlap Model Applied to Hydrides of Main Group Elements.

    ERIC Educational Resources Information Center

    Moore, E. A.

    1990-01-01

    Described is how crystal field theory and the angular overlap model can be applied to very simple molecules which can then be used to introduce such concepts as bonding orbitals, MO diagrams, and Walsh diagrams. The main-group compounds are used as examples and a switch to the transition metal complexes. (KR)

  12. Bond strength of direct and indirect bonded brackets after thermocycling.

    PubMed

    Daub, Jacob; Berzins, David W; Linn, Brandon James; Bradley, Thomas Gerard

    2006-03-01

    Thermocycling simulates the temperature dynamics in the oral environment. With direct bonding, thermocycling reduces the bond strength of orthodontic adhesives to tooth structure. The purpose of this study was to evaluate the shear bond strengths (SBS) of one direct and two indirect bonding methods/adhesives after thermocycling. Sixty human premolars were divided into three groups. Teeth in group 1 were bonded directly with Transbond XT. Teeth in group 2 were indirect bonded with Transbond XT/Sondhi Rapid Set, which is chemically cured. Teeth in group 3 were indirect bonded with Enlight LV/Orthosolo and light cured. Each sample was thermocycled between 5 degrees C and 55 degrees C for 500 cycles. Mean SBS in groups 1, 2, and 3 were not statistically significantly different (13.6 +/- 2.9, 12.3 +/- 3.0, and 11.6 +/- 3.2 MPa, respectively; P > .05). However, when these values were compared with the results of a previous study using the same protocol, but without thermocycling, the SBS was reduced significantly (P = .001). Weibull analysis further showed that group 3 had the lowest bonding survival rate at the minimum clinically acceptable bond-strength range. The Adhesive Remnant Index was also determined, and group 2 had a significantly (P < .05) higher percentage of bond failures at the resin/enamel interface.

  13. 47 CFR 73.509 - Prohibited overlap.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... operation would involve overlap of signal strength contours with any other station licensed by the... separation Contour of proposed station Contour of other station Co-channel 0.1mV/m (40 dBu)1 mV/m (60 dBu) 1... if the proposed operation would involve overlap of signal strength contours with any other station...

  14. 47 CFR 73.509 - Prohibited overlap.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... operation would involve overlap of signal strength contours with any other station licensed by the... separation Contour of proposed station Contour of other station Co-channel 0.1mV/m (40 dBu)1 mV/m (60 dBu) 1... if the proposed operation would involve overlap of signal strength contours with any other station...

  15. 47 CFR 73.509 - Prohibited overlap.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... operation would involve overlap of signal strength contours with any other station licensed by the... separation Contour of proposed station Contour of other station Co-channel 0.1mV/m (40 dBu)1 mV/m (60 dBu) 1... if the proposed operation would involve overlap of signal strength contours with any other station...

  16. Neural overlap in processing music and speech.

    PubMed

    Peretz, Isabelle; Vuvan, Dominique; Lagrois, Marie-Élaine; Armony, Jorge L

    2015-03-19

    Neural overlap in processing music and speech, as measured by the co-activation of brain regions in neuroimaging studies, may suggest that parts of the neural circuitries established for language may have been recycled during evolution for musicality, or vice versa that musicality served as a springboard for language emergence. Such a perspective has important implications for several topics of general interest besides evolutionary origins. For instance, neural overlap is an important premise for the possibility of music training to influence language acquisition and literacy. However, neural overlap in processing music and speech does not entail sharing neural circuitries. Neural separability between music and speech may occur in overlapping brain regions. In this paper, we review the evidence and outline the issues faced in interpreting such neural data, and argue that converging evidence from several methodologies is needed before neural overlap is taken as evidence of sharing.

  17. Genetic analysis of the Fourier-transform infrared spectra of bovine milk with emphasis on individual wavelengths related to specific chemical bonds.

    PubMed

    Bittante, G; Cecchinato, A

    2013-09-01

    transmittance, and the heritability estimates of individual waves were generally very low (with some exceptions). The 3 other identified regions contained many transmittance peaks that represented important chemical bonds; these showed much lower phenotypic and genetic variability in terms of individual waves, but relatively higher and less variable heritability estimates. Among them, the SWIR region (near-infrared) showed a peculiar cyclic pattern of the heritability coefficients of transmittance, the MWIR-1 region was particularly important for the estimation of fat, and the MWIR-LWIR region (also known also as the "fingerprint region") had 3 areas of relatively high heritability. In summary, we found that the transmittance data from the FTIR spectra of milk have genetic variability that may prove useful for the direct genetic improvement of dairy species, rather than only through indirect phenotypic predictions of individual milk quality and technological traits.

  18. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding. Technical progress report, March 1, 1992--February 28, 1995

    SciTech Connect

    Lichtenberger, D.L.

    1997-06-01

    During this period of the project we have (1) accomplished the high-resolution gas phase photoelectron spectra of C{sub 60} and C{sub 70}, (2) characterized the electronic features of imaging C{sub 60} on gold by STM, (3) evaluated the orbital distributions of C{sub 60} and the bonding interactions with metals, (4) revealed details of the bonding of phosphines to metals, including the subtleties of a geometrical twist in sterically crowded situations, (5) determined the formal electron distribution in the bonding of {eta}{sup 3} -cyclopropenyl with metals, (6) related gas-phase ionization energies to electron transfer kinetics and ion salvation thermochemistry of metallocenes, (7) correlated lone-pair ionization energies with proton affinities for a variety of amino acids and related compounds, (8) examined sigma-pi interactions in non-conjugated polyalkynes, (9) characterized extensive metal-ligand {pi} interactions in metal-acetylide compounds, and (10) continued to develop the experimental and theoretical methods for these studies. All of these studies have contributed significantly to expanding our understanding of the electronic structure and bonding of organic molecules and the ways this electronic structure is altered by interaction with metals. Further developments in the instrumentation and methods of gas phase and surface photoelectron spectroscopy are underway. Most notable is the progress on the new gas phase photoelectron spectrometer that combines improved capabilities for He I/He II UPS, XPS, and Auger investigations of organometallic molecules.

  19. Bond Strength of Two Resin Cements to Dentin After Disinfection Pretreatment: Effects of Er,Cr:YSGG Laser Compared with Chemical Antibacterial Agent

    PubMed Central

    Shafiei, Fereshteh; Fekrazad, Reza; Shafiei, Ehsan

    2013-01-01

    Abstract Objective: This study compared the effects of two disinfection procedures (2% chlorhexidine [CHX] solution versus Er,Cr:YSGG laser irradiation) on the shear bond strength of ED primer II/Panavia F2.0 (ED/P) and Excite DSC/Variolink N (Ex/V). Background data: Different methods are used for cavity disinfection prior to adhesive cementation, which may influence the bonding ability of resin cements. Methods: Flat dentin surfaces were prepared on 100 extracted premolars and randomly divided into 10 groups. In the eight experimental groups, indirect composite samples were cemented with either ED/P or Ex/V under three disinfecting conditions on the dentin surface as follows: (1) CHX application before ED primer II/ after etching, (2) wet laser irradiation (Er,Cr:YSGG laser, 20 Hz, 0.75 W, 15% water +15% air), (3) dry laser irradiation with no water and air cooling. The control groups had no disinfectant application. After 24 h water storage, bond strength test was performed. The data (MPa) were analyzed using two way ANOVA and Tukey tests. Results: The lowest and highest bond strengths were obtained by dry laser and wet laser (10.18±2.67 and 17.36±2.94 for ED/P, 9.64±2.66 and 20.07±3.36 for Ex/V, respectively). For each cement, two-by-two comparisons of four groups revealed significant differences only for dry laser with others (p<0.001). Conclusions: The use of CHX and Er,Cr:YSGG laser at the low fluences with water/air cooling as the antibacterial agents does not adversely influence the bonding ability of the etch-and-rinse and the self-etch cements. PMID:23600378

  20. Overlapping spectra resolution using non-negative matrix factorization.

    PubMed

    Gao, Hong-Tao; Li, Tong-Hua; Chen, Kai; Li, Wei-Guang; Bi, Xian

    2005-03-31

    Non-negative matrix factorization (NMF), with the constraints of non-negativity, has been recently proposed for multi-variate data analysis. Because it allows only additive, not subtractive, combinations of the original data, NMF is capable of producing region or parts-based representation of objects. It has been used for image analysis and text processing. Unlike PCA, the resolutions of NMF are non-negative and can be easily interpreted and understood directly. Due to multiple solutions, the original algorithm of NMF [D.D. Lee, H.S. Seung, Nature 401 (1999) 788] is not suitable for resolving chemical mixed signals. In reality, NMF has never been applied to resolving chemical mixed signals. It must be modified according to the characteristics of the chemical signals, such as smoothness of spectra, unimodality of chromatograms, sparseness of mass spectra, etc. We have used the modified NMF algorithm to narrow the feasible solution region for resolving chemical signals, and found that it could produce reasonable and acceptable results for certain experimental errors, especially for overlapping chromatograms and sparse mass spectra. Simulated two-dimensional (2-D) data and real GUJINGGONG alcohol liquor GC-MS data have been resolved soundly by NMF technique. Butyl caproate and its isomeric compound (butyric acid, hexyl ester) have been identified from the overlapping spectra. The result of NMF is preferable to that of Heuristic evolving latent projections (HELP). It shows that NMF is a promising chemometric resolution method for complex samples.