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Sample records for natural bond orbital

  1. Density functional theory, natural bond orbital and quantum theory of ...

    Indian Academy of Sciences (India)

    The nature of the H-bonds were characterized by the natural bond orbital (NBO) and the quantum theory of atoms in molecule (QTAIM) analyses as well. The intramolecular H-bond formed between the amino and carboxyl oxygen atom of tryptophan was retained in most of the complexes, and the cooperativity between the ...

  2. Introducing a new bond reactivity index: Philicities for natural bond orbitals.

    Science.gov (United States)

    Sánchez-Márquez, Jesús; Zorrilla, David; García, Víctor; Fernández, Manuel

    2017-12-22

    In the present work, a new methodology defined for obtaining reactivity indices (philicities) is proposed. This is based on reactivity functions such as the Fukui function or the dual descriptor, and makes it possible to project the information from reactivity functions onto molecular orbitals, instead of onto the atoms of the molecule (atomic reactivity indices). The methodology focuses on the molecules' natural bond orbitals (bond reactivity indices) because these orbitals have the advantage of being localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. This methodology provides a "philicity" index for every NBO, and a representative set of molecules has been used to test the new definition. A new methodology has also been developed to compare the "finite difference" and the "frontier molecular orbital" approximations. To facilitate their use, the proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, condensation schemes based on atomic populations of the "atoms in molecules" theory, the Hirshfeld population analysis, the approximation of Mulliken (with a minimal basis set) and electrostatic potential-derived charges have also been implemented, including the calculation of "bond reactivity indices" defined in previous studies. Graphical abstract A new methodology defined for obtaining bond reactivity indices (philicities) is proposed and makes it possible to project the information from reactivity functions onto molecular orbitals. The proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, this version can use new atomic condensation schemes and new "utilities" have also been included in this second version.

  3. DFT Study of the Structure, Reactivity, Natural Bond Orbital and Hyperpolarizability of Thiazole Azo Dyes

    Directory of Open Access Journals (Sweden)

    Osman I. Osman

    2017-02-01

    Full Text Available The structure, reactivity, natural bond orbital (NBO, linear and nonlinear optical (NLO properties of three thiazole azo dyes (A, B and C were monitored by applying B3LYP, CAM-B3LYP and ωB97XD functionals with 6-311++G** and aug-cc-pvdz basis sets. The geometrical parameters,dipolemoments,HOMO-LUMO(highest occupied molecular orbital,lowest unoccupied molecular orbital energy gaps, absorption wavelengths and total hyperpolarizabilities were investigated in carbon tetrachloride (CCl4 chloroform (CHCl3, dichloromethane (CH2Cl2 and dimethlysulphoxide (DMSO. The donor methoxyphenyl group deviates from planarity with the thiazole azo moiety by ca. 38◦; while the acceptor dicyanovinyl, indandione and dicyanovinylindanone groups diverge by ca. 6◦. The HOMOs for the three dyes are identical. They spread over the methoxyphenyl donor moiety, the thiazole and benzene rings as π-bonding orbitals. The LUMOs are shaped up by the nature of the acceptor moieties. The LUMOs of the A, B and C dyes extend over the indandione, malononitrile and dicyanovinylindanone acceptor moieties, respectively, as π-antibonding orbitals. The HOMO-LUMO splittings showed that Dye C is much more reactive than dyes A and B. Compared to dyes A and B, Dye C yielded a longer maximum absorption wavelength because of the stabilization of its LUMOs relative to those of the other two. The three dyes show solvatochromism accompanied by significant increases in hyperpolarizability. The enhancement of the total hyperpolarizability of C compared to those of A and B is due to the cumulative action of the long π-conjugation of the indanone ring and the stronger electron-withdrawing ability of the dicyanovinyl moiety that form the dicyanovinylindanone acceptor group. These findings are facilitated by a natural bond orbital (NBO technique. The very high total hyperpolarizabilities of the three dyes define their potent nonlinear optical (NLO behaviour.

  4. DFT Study of the Structure, Reactivity, Natural Bond Orbital and Hyperpolarizability of Thiazole Azo Dyes.

    Science.gov (United States)

    Osman, Osman I

    2017-02-01

    The structure, reactivity, natural bond orbital (NBO), linear and nonlinear optical (NLO) properties of three thiazole azo dyes (A, B and C) were monitored by applying B3LYP, CAM-B3LYP and ωB97XD functionals with 6-311++G** and aug-cc-pvdz basis sets. The geometrical parameters,dipolemoments,HOMO-LUMO(highest occupied molecular orbital,lowest unoccupied molecular orbital) energy gaps, absorption wavelengths and total hyperpolarizabilities were investigated in carbon tetrachloride (CCl4) chloroform (CHCl3), dichloromethane (CH2Cl2) and dimethlysulphoxide (DMSO). The donor methoxyphenyl group deviates from planarity with the thiazole azo moiety by ca. 38◦; while the acceptor dicyanovinyl, indandione and dicyanovinylindanone groups diverge by ca. 6◦. The HOMOs for the three dyes are identical. They spread over the methoxyphenyl donor moiety, the thiazole and benzene rings as π-bonding orbitals. The LUMOs are shaped up by the nature of the acceptor moieties. The LUMOs of the A, B and C dyes extend over the indandione, malononitrile and dicyanovinylindanone acceptor moieties, respectively, as π-antibonding orbitals. The HOMO-LUMO splittings showed that Dye C is much more reactive than dyes A and B. Compared to dyes A and B, Dye C yielded a longer maximum absorption wavelength because of the stabilization of its LUMOs relative to those of the other two. The three dyes show solvatochromism accompanied by significant increases in hyperpolarizability. The enhancement of the total hyperpolarizability of C compared to those of A and B is due to the cumulative action of the long π-conjugation of the indanone ring and the stronger electron-withdrawing ability of the dicyanovinyl moiety that form the dicyanovinylindanone acceptor group. These findings are facilitated by a natural bond orbital (NBO) technique. The very high total hyperpolarizabilities of the three dyes define their potent nonlinear optical (NLO) behaviour.

  5. Computational study of the vibrational spectroscopic studies, natural bond orbital, frontier molecular orbital and second-order non-linear optical properties of acetophenone thiosemicarbazone molecule

    Science.gov (United States)

    Li, Xiao-Hong; Mei, Zheng; Zhang, Xian-Zhou

    2014-01-01

    The vibrational frequencies of acetophenone thiosemicarbazone in the ground state have been calculated using density functional method (B3LYP) with 6-31G(d), 6-31G(d,p) and 6-311++G(d,p) basis sets. The analysis of natural bond orbital was also performed. The IR spectra were obtained and interpreted by means of potential energies distributions (PEDs) using MOLVIB program. In addition, the results show that there exist Nsbnd H…N and Nsbnd H…S hydrogen bonds in the title compound, which play a major role in stabilizing the molecule and are confirmed by the natural bond orbital analysis. The predicted NLO properties show that the title compound is a good candidate as second-order NLO material. In addition, the frontier molecular orbitals were analyzed and the crystal structure obtained by molecular mechanics belongs to the Pbca space group, with lattice parameters Z = 8, a = 16.0735 Å, b = 7.1719 Å, c = 7.8725 Å, ρ = 0.808 g/cm3.

  6. Natural bond orbital approach to the transmission of substituent effect through the fulvene and benzene ring systems.

    Science.gov (United States)

    Oziminski, Wojciech P; Krygowski, Tadeusz M

    2011-03-01

    Electronic structure of 22 monosubstituted derivatives of benzene and exocyclically substituted fulvene with substituents: B(OH)(2), BH(2), CCH, CF(3), CH(3), CHCH(2), CHO, Cl, CMe(3), CN, COCH(3), CONH(2), COOH, F, NH(2), NMe(2), NO, NO(2), OCH(3), OH, SiH(3), SiMe(3) were studied theoretically by means of Natural Bond Orbital analysis. It is shown, that sum of π-electron population of carbon atoms of the fulvene and benzene rings, pEDA(F) and pEDA(B), respectively correlate well with Hammett substituent constants [Formula in text] and aromaticity index NICS. The substituent effect acting on pi-electron occupation at carbon atoms of the fulvene ring is significantly stronger than in the case of benzene. Electron occupations of ring carbon atoms (except C1) in fulvene plotted against each other give linear regressions with high correlation coefficients. The same is true for ortho- and para-carbon atoms in benzene. Positive slopes of the regressions indicate similar for fulvene and benzene kind of substituent effect - mostly resonance in nature. Only the regressions of occupation at the carbon atom in meta- position of benzene against ortho- and para-positions gives negative slopes and low correlation coefficients.

  7. Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin

    Science.gov (United States)

    Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.

    2013-01-01

    In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the σ* and π* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis.

  8. Application of Time-Dependent Density Functional and Natural Bond Orbital Theories to the UV-vis Absorption Spectra of Some Phenolic Compounds.

    Science.gov (United States)

    Marković, Svetlana; Tošović, Jelena

    2015-09-03

    The UV-vis properties of 22 natural phenolic compounds, comprising anthraquinones, neoflavonoids, and flavonoids were systematically examined. The time-dependent density functional theory (TDDFT) approach in combination with the B3LYP, B3LYP-D2, B3P86, and M06-2X functionals was used to simulate the UV-vis spectra of the investigated compounds. It was shown that all methods exhibit very good (B3LYP slightly better) performance in reproducing the examined UV-vis spectra. However, the shapes of the Kohn-Sham molecular orbitals (MOs) involved in electronic transitions were misleading in constructing the MO correlation diagrams. To provide better understanding of redistribution of electron density upon excitation, the natural bond orbital (NBO) analysis was applied. Bearing in mind the spatial and energetic separations, as well as the character of the π bonding, lone pair, and π* antibonding natural localized molecular orbitals (NLMOs), the "NLMO clusters" were constructed. NLMO cluster should be understood as a part of a molecule characterized with distinguished electron density. It was shown that all absorption bands including all electronic transitions need to be inspected to fully understand the UV-vis spectrum of a certain compound, and, thus, to learn more about its UV-vis light absorption. Our investigation showed that the TDDFT and NBO theories are complementary, as the results from the two approaches can be combined to interpret the UV-vis spectra. Agreement between the predictions of the TDDFT approach and those based on the NLMO clusters is excellent in the case of major electronic transitions and long wavelengths. It should be emphasized that the approach for investigation of UV-vis light absorption based on the NLMO clusters is applied for the first time.

  9. Multiple boron-boron bonds in neutral molecules: an insight from the extended transition state method and the natural orbitals for chemical valence scheme.

    Science.gov (United States)

    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

  10. A natural orbital analysis of the long range behavior of chemical bonding and van der Waals interaction in singlet H2: the issue of zero natural orbital occupation numbers.

    Science.gov (United States)

    Sheng, X W; Mentel, Ł M; Gritsenko, O V; Baerends, E J

    2013-04-28

    This paper gives a natural orbital (NO) based analysis of the van der Waals interaction in (singlet) H2 at long distance. The van der Waals interaction, even if not leading to a distinct van der Waals well, affects the shape of the interaction potential in the van der Waals distance range of 5-9 bohrs and can be clearly distinguished from chemical bonding effects. In the NO basis the van der Waals interaction can be quantitatively covered with, apart from the ground state configurations (1σ(g))(2) and (1σ(u))(2), just the 4 configurations (2σ(g))(2) and (2σ(u))(2), and (1π(u))(2) and (1π(g))(2). The physics of the dispersion interaction requires and explains the peculiar relatively large positive CI coefficients of the doubly excited electron configurations (2σ(u))(2) and (1π(g))(2) (the occupancy amplitudes of the 2σ(u) and 1π(gx, y) NOs) in the distance range 5-9 bohrs, which have been observed before by Cioslowski and Pernal [Chem. Phys. Lett. 430, 188 (2006)]. We show that such positive occupancy amplitudes do not necessarily lead to the existence of zero occupation numbers at some H-H distances.

  11. Vibrational spectroscopic (FT-IR and FT-Raman) studies, natural bond orbital analysis and molecular electrostatic potential surface of Isoxanthopterin.

    Science.gov (United States)

    Prabavathi, N; Nilufer, A; Krishnakumar, V

    2013-10-01

    The FTIR and FT-Raman spectra of Isoxanthopterin have been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of Isoxanthopterin were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies are found to be in good agreement. The (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The UV-visible spectrum was also recorded and compared with the theoretical values. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β0), related properties (β, α0 and Δα) and the Mulliken charges of the molecule were also computed using DFT calculations. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. Information about the charge density distribution of the molecule and its chemical reactivity has been obtained by mapping molecular electrostatic potential surface. In addition, the non-linear optical properties were discussed from the dipole moment values and excitation wavelength in the UV-visible region. Copyright © 2013 Elsevier B.V. All rights reserved.

  12. The nature of chemical bonds from PNOF5 calculations.

    Science.gov (United States)

    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. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. On The Nature of the Halogen Bond.

    Science.gov (United States)

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

    2014-09-09

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

  14. Vibrational spectra (experimental and theoretical), molecular structure, natural bond orbital, HOMO-LUMO energy, Mulliken charge and thermodynamic analysis of N'-hydroxy-pyrimidine-2-carboximidamide by DFT approach.

    Science.gov (United States)

    Jasmine, N Jeeva; Muthiah, P Thomas; Arunagiri, C; Subashini, A

    2015-06-05

    The FT-IR, FT-Raman, (1)H, (13)C NMR and UV-Visible spectral measurements of N'-hydroxy-pyrimidine-2-carboximidamide (HPCI) and complete analysis of the observed spectra have been proposed. DFT calculation has been performed and the structural parameters of the compound was determined from the optimized geometry with 6-311+G(d,p) basis set and giving energies, harmonic vibrational frequencies and force constants. The results of the optimized molecular structure are presented and compared with the experimental. The geometric parameters, harmonic vibrational frequencies and chemical shifts were compared with the experimental data of the molecule. The title compound, C5H6N4O, is approximately planar, with an angle of 11.04 (15)°. The crystal structure is also stabilized by intermolecular N-H⋯O, N-H⋯N, O-H⋯N, C-H⋯O hydrogen bond and offset π-π stacking interactions. The influences of hydroxy and carboximidamide groups on the skeletal modes and proton chemical shifts have been investigated. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and band gap. The kinetic, thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intermolecular electronic interactions and their stabilization energy. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structure. Copyright © 2015 Elsevier B.V. All rights reserved.

  15. Analysis of the putative Cr-Cr quintuple bond in Ar'CrCrAr' (Ar' = C6H3-2,6(C6H3-2,6-Pr(i)2)2 based on the combined natural orbitals for chemical valence and extended transition state method.

    Science.gov (United States)

    Ndambuki, Sylvester; Ziegler, Tom

    2012-07-16

    The nature of the putative Cr-Cr quintuple bond in Ar'CrCrAr' (Ar' = C(6)H(3)-2,6(C(6)H(3)-2,6-Pr(i)(2))(2)) is investigated with the help of a newly developed energy and density decomposition scheme. The new approach combines the extended transition state (ETS) energy decomposition method with the natural orbitals for chemical valence (NOCV) density decomposition scheme within the same theoretical framework. The results show that in addition to the five bonding components (σ(2)π(2)π'(2)δ(2)δ'(2)) of the Cr-Cr bond, the quintuple bond is augmented by secondary Cr-C interactions involving the Cr-ipso-carbon of the flanking aryl rings. The presence of isopropyl groups (Pr(i)) is further shown to stabilize Ar'CrCrAr' by 20 kcal/mol compared to the two Ar'Cr monomers through stabilizing van der Waals dispersion interactions.

  16. The Nature of the Hydrogen Bond Outline of a Comprehensive Hydrogen Bond Theory

    CERN Document Server

    Gilli, Gastone

    2009-01-01

    Hydrogen bond (H-bond) effects are known: it makes sea water liquid, joins cellulose microfibrils in trees, shapes DNA into genes and polypeptide chains into wool, hair, muscles or enzymes. Its true nature is less known and we may still wonder why O-H...O bond energies range from less than 1 to more than 30 kcal/mol without apparent reason. This H-bond puzzle is re-examined here from its very beginning and presented as an inclusive compilation of experimental H-bond energies andgeometries.New concepts emerge from this analysis: new classes of systematically strong H-bonds (CAHBs and RAHBs: cha

  17. The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

    Energy Technology Data Exchange (ETDEWEB)

    Domin, D.; Braida, Benoit; Lester Jr., William A.

    2008-05-30

    This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

  18. The nature of Cu bonding to natural organic matter

    Science.gov (United States)

    Manceau, Alain; Matynia, Anthony

    2010-05-01

    Copper biogeochemistry is largely controlled by its bonding to natural organic matter (NOM) for reasons not well understood. Using XANES and EXAFS spectroscopy, along with supporting thermodynamic equilibrium calculations and structural and steric considerations, we show evidence at pH 4.5 and 5.5 for a five-membered Cu(malate) 2-like ring chelate at 100-300 ppm Cu concentration, and a six-membered Cu(malonate)) 1-2-like ring chelate at higher concentration. A "structure fingerprint" is defined for the 5.0-7.0 Å -1 EXAFS region which is indicative of the ring size and number (i.e., mono- vs. bis-chelate), and the distance and bonding of axial oxygens (O ax) perpendicular to the chelate plane formed by the four equatorial oxygens (O eq) at 1.94 Å. The stronger malate-type chelate is a C 4 dicarboxylate, and the weaker malonate-type chelate a C 3 dicarboxylate. The malate-type chelate owes its superior binding strength to an -OH for -H substitution on the α carbon, thus offering additional binding possibilities. The two new model structures are consistent with the majority of carboxyl groups being clustered and α-OH substitutions common in NOM, as shown by recent infrared and NMR studies. The high affinity of NOM for Cu(II) is explained by the abundance and geometrical fit of the two types of structures to the size of the equatorial plane of Cu(II). The weaker binding abilities of functionalized aromatic rings also is explained, as malate-type and malonate-type structures are present only on aliphatic chains. For example, salicylate is a monocarboxylate which forms an unfavorable six-membered chelate, because the OH substitution is in the β position. Similarly, phthalate is a dicarboxylate forming a highly strained seven-membered chelate. Five-membered Cu(II) chelates can be anchored by a thiol α-SH substituent instead of an alcohol α-OH, as in thio-carboxylic acids. This type of chelate is seldom present in NOM, but forms rapidly when Cu(II) is photoreduced

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

    Science.gov (United States)

    Hashizume, Daisuke

    2017-07-01

    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. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. The role of the 5f valence orbitals of early actinides in chemical bonding

    Science.gov (United States)

    Vitova, T.; Pidchenko, I.; Fellhauer, D.; Bagus, P. S.; Joly, Y.; Pruessmann, T.; Bahl, S.; Gonzalez-Robles, E.; Rothe, J.; Altmaier, M.; Denecke, M. A.; Geckeis, H.

    2017-07-01

    One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/φ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements.

  1. Estimation of bonding nature using diamagnetic susceptibility.

    Science.gov (United States)

    Tomiyasu, Keisuke; Sato, Toyoto; Orimo, Shin-ichi

    2015-05-21

    A chemical bond includes both covalent and ionic characteristics. We develop an experimental method to estimate the degree of each contribution based on magnetic susceptibility measurements, in which Pascal's scheme for Larmor diamagnetism is combined with electronegativity. The applicability to metal hydrides is also shown.

  2. On the nature of blueshifting hydrogen bonds.

    Science.gov (United States)

    Mo, Yirong; Wang, Changwei; Guan, Liangyu; Braïda, Benoît; Hiberty, Philippe C; Wu, Wei

    2014-07-01

    The block-localized wave function (BLW) method can derive the energetic, geometrical, and spectral changes with the deactivation of electron delocalization, and thus provide a unique way to elucidate the origin of improper, blueshifting hydrogen bonds versus proper, redshifting hydrogen bonds. A detailed analysis of the interactions of F(3)CH with NH(3) and OH(2) shows that blueshifting is a long-range phenomenon. Since among the various energy components contributing to hydrogen bonds, only the electrostatic interaction has long-range characteristics, we conclude that the contraction and blueshifting of a hydrogen bond is largely caused by electrostatic interactions. On the other hand, lengthening and redshifting is primarily due to the short-range n(Y)→σ*(X-H) hyperconjugation. The competition between these two opposing factors determines the final frequency change direction, for example, redshifting in F(3)CH⋅⋅⋅NH(3) and blueshifting in F(3)CH⋅⋅⋅OH(2). This mechanism works well in the series F(n)Cl(3)-n CH⋅⋅⋅Y (n=0-3, Y=NH(3), OH(2), SH(2)) and other systems. One exception is the complex of water and benzene. We observe the lengthening and redshifting of the O-H bond of water even with the electron transfer between benzene and water completely quenched. A distance-dependent analysis for this system reveals that the long-range electrostatic interaction is again responsible for the initial lengthening and redshifting. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Nature of bonding forces between two hydrogen-passivated silicon wafers

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Nielsen, E.; Hult, E.

    1998-01-01

    The nature and strength of the bonding forces between two II-passivated Si surfaces are studied with the density-functional theory, using an approach based on recent theoretical advances in understanding of van der Waals forces between two surfaces. Contrary to previous suggestions of van der Waals...... attraction between H overlayers, we find that the attraction is mainly due to long-range van der Waals interactions between the Si substrates, while the equilibrium separation is determined by short-range repulsion between occupied Si-H orbitals. Estimated bonding energies and Si-H frequency shifts...

  4. Role of s-p orbital mixing in the bonding and properties of second-period diatomic molecules

    NARCIS (Netherlands)

    Bickelhaupt, F.M.; Nagle, J.K.; Klemm, W.L.

    2008-01-01

    Qualitative molecular orbital theory is widely used as a conceptual tool to understand chemical bonding. Symmetry-allowed orbital mixing between atomic or fragment orbitais of different energies can greatly complicate such qualitative interpretations of chemical bonding. We use high-level Amsterdam

  5. The Role of s�p Orbital Mixing in the Bonding of Second-Period Diatomic Molecules

    NARCIS (Netherlands)

    Bickelhaupt, F.M.; Nagle, J.K.; Klemm, W.L.

    2008-01-01

    Qualitative molecular orbital theory is widely used as a conceptual tool to understand chemical bonding. Symmetry-allowed orbital mixing between atomic or fragment orbitais of different energies can greatly complicate such qualitative interpretations of chemical bonding. We use high-level Amsterdam

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

    Science.gov (United States)

    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 H 2 O and the C-C bond in H 3 C-CH 3 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.

  7. About the nature of halogen bond interaction under the spatial confinement

    Science.gov (United States)

    Roztoczyńska, Agnieszka; Lipkowski, Paweł; Kozłowska, Justyna; Bartkowiak, Wojciech

    2017-04-01

    Nowadays, much attention is put toward the description of noncovalent complexes exposed to the high pressure or embedded in confining environments. Such conditions may strongly modify the physical and chemical properties of molecular systems. This study focuses on the theoretical description of the confinement induced changes in geometry and energetic parameters of the halogen bonded FCl⋯CNF complex. A model analytical potential is applied to render the effect of orbital compression. In order to analyze the nature of halogen bond interaction, in the presence of spatial confinement, the supermolecular approach together with the symmetry-adapted perturbation theory is used. Furthermore, a thorough analysis of topological parameters, characterizing the halogen bond upon orbital compression, is performed within the quantum theory of atoms in molecules. The calculations are carried out using the ωB97x and CCSD(T) methods in connection with the aug-cc-pVTZ basis set. Among others, the obtained results indicate that the spatial confinement not only modifies the nature of halogen bond interaction but also induces the appearance of a completely new form of the studied FCl⋯CNF system.

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

    Science.gov (United States)

    Kaupp, Martin

    2007-01-15

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

  9. Electronic structure and chemical bond nature in Cs2NpO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2017-01-01

    Full Text Available On the basis of the X-ray photoelectron spectroscopy data and results of theoretical calculations for the NpO2Cl4 (D4h cluster, the electronic structure and the chemical bond nature in , was done in the binding Cs2NpO2Cl4 single crystal, containing the neptunyl group NpO2 energy range of 0 eV to ~35 eV. The filled Np 5f electronic states were established to form in the valence band of Cs2NpO2Cl4. This was attributed to the direct participation of the Np 5f electrons in the chemical bonding. The Np 6p electrons were shown to participate in formation of both the inner valence band (~15 eV-~35 eV and the outer valence band (0 eV-~15 eV. The filled Np 6p and the O 2s, Cl 3s electronic shells were found to make the largest contribution to the formation of the inner valence molecular orbitals. The molecular orbitals composition and the sequence order in the binding energy range 0 eV-~35 eV in Cs2NpO2Cl4, were established. For the first time the quantitative scheme of molecular orbitals for the NpO2Cl4 cluster in the binding energy range 0 eV-~35 eV, was built. This scheme reflects neptunium close environment in the studied compound and is fundamental for both understanding the chemical bond nature in Cs2NpO2Cl4 and the interpretation of other X-ray spectra of Cs2NpO2Cl4. The contributions to the chemical binding for the NpO2Cl4 cluster were evaluated to be: the outer valence molecular orbitals contribution - 73 %, and the inner valence molecular orbitals contribution - 27 %.

  10. The nature of electron correlation in a dissociating bond

    Science.gov (United States)

    Hollett, Joshua W.; McKemmish, Laura K.; Gill, Peter M. W.

    2011-06-01

    We have constructed the unrestricted Hartree-Fock (UHF), restricted Hartree-Fock (RHF), and full configuration interaction (FCI) position and momentum intracules and holes for HṡṡṡH at bond lengths R from 1 to 10 bohrs. We trace the recently discovered inversion of the UHF position hole at intermediate R to over-localization of the spin-orbitals, and support this by a correlation energy component analysis. The RHF and UHF momentum holes are found to be more complicated; however their features are explained through decomposition of electron correlation effects. The UHF momentum hole is also found to invert and exhibits interesting behavior at large R. The RHF (but not UHF) and FCI momentum intracules exhibit Young-type interference patterns related to recent double photoionization experiments. Our analyses yield the most comprehensive picture to date of the behavior of the electrons during homolytic bond fission.

  11. Density functional theory, natural bond orbital and quantum theory of ...

    Indian Academy of Sciences (India)

    O, Nakai H, Vreven T, Montgomery Jr. J A, Peralta. J E, Ogliaro F, Bearpark M, Heyd J J, Brothers E,. Kudin K N, Staroverov V N, Kobayashi R, Normand J,. Raghavachari K, Rendell A, Burant J C, Iyengar S S,. Tomasi J, Cossi M, Rega N, Millam J M, Klene M, Knox. J E, Cross J B, Bakken V, Adamo C, Jaramillo J,. Gomperts ...

  12. Estimating local bonding/antibonding character of canonical molecular orbitals from their energy derivatives. The case of coordinating lone pair orbitals

    OpenAIRE

    Chaquin, Patrick; Canac, Yves; Lepetit, Christine; Zargarian, D; Chauvin, Remi

    2016-01-01

    International audience; According to Koopmans theorem, the derivative of the energy of a canonical MO with respect to nuclear coordinates quantifies its bonding/antibonding character. This quantity allows predictions of bond length variation upon ionisation in a panel of 19 diatomic species. In polyatomic molecules, the derivative of a MO energy with respect to a given bond length reveals the nature and the degree of the bonding/antibonding contribution of this MO with respect to this bond. A...

  13. Probing the nature of hydrogen bonds in DNA base pairs.

    Science.gov (United States)

    Mo, Yirong

    2006-07-01

    Energy decomposition analyses based on the block-localized wave-function (BLW-ED) method are conducted to explore the nature of the hydrogen bonds in DNA base pairs in terms of deformation, Heitler-London, polarization, electron-transfer and dispersion-energy terms, where the Heitler-London energy term is composed of electrostatic and Pauli-exchange interactions. A modest electron-transfer effect is found in the Watson-Crick adenine-thymine (AT), guanine-cytosine (GC) and Hoogsteen adenine-thymine (H-AT) pairs, confirming the weak covalence in the hydrogen bonds. The electrostatic attraction and polarization effects account for most of the binding energies, particularly in the GC pair. Both theoretical and experimental data show that the GC pair has a binding energy (-25.4 kcal mol(-1) at the MP2/6-31G** level) twice that of the AT (-12.4 kcal mol(-1)) and H-AT (-12.8 kcal mol(-1)) pairs, compared with three conventional N-H...O(N) hydrogen bonds in the GC pair and two in the AT or H-AT pair. Although the remarkably strong binding between the guanine and cytosine bases benefits from the opposite orientations of the dipole moments in these two bases assisted by the pi-electron delocalization from the amine groups to the carbonyl groups, model calculations demonstrate that pi-resonance has very limited influence on the covalence of the hydrogen bonds. Thus, the often adopted terminology "resonance-assisted hydrogen bonding (RHAB)" may be replaced with "resonance-assisted binding" which highlights the electrostatic rather than electron-transfer nature of the enhanced stabilization, as hydrogen bonds are usually regarded as weak covalent bonds.

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

    Science.gov (United States)

    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…

  15. Bonding in Mercury-Alkali Molecules: Orbital-driven van der Waals Complexes

    Directory of Open Access Journals (Sweden)

    Dieter Cremer

    2008-06-01

    Full Text Available The bonding situation in mercury-alkali diatomics HgA (2Σ+ (A = Li, Na, K, Rb has been investigated employing the relativistic all-electron method Normalized Elimination of the Small Component (NESC, CCSD(T, and augmented VTZ basis sets. Although Hg,A interactions are typical of van der Waals complexes, trends in calculated De values can be explained on the basis of a 3-electron 2-orbital model utilizing calculated ionization potentials and the De values of HgA+(1Σ+ diatomics. HgA molecules are identified as orbital-driven van der Waals complexes. The relevance of results for the understanding of the properties of liquid alkali metal amalgams is discussed.

  16. Analysis of nondynamical correlation in the metal-ligand bond. Pauli repulsion and orbital localization in MnO - 4

    Science.gov (United States)

    Buijse, Marten A.; Baerends, Evert Jan

    1990-09-01

    The nondynamical correlation error in first row transition metal complexes is studied through calculations on the permanganate ion. The source of the error is the well-known Hartree-Fock failure in the weak-interaction limit, which is shown to exist for both the metal-ligand and the ligand-ligand bonds: the metal-ligand and the ligand-ligand distances are large compared to the size of the metal 3d and ligand 2p atomic orbitals (AO's). Pauli repulsion between ligand orbitals and 3s/3p orbitals prevent the metal-ligand and ligand-ligand distances to become small enough for efficient overlap and bonding. In multiply bonded systems the Hartree-Fock error does not show up in excessive electron repulsion, but leads to localization of the bonding orbitals (which sometimes requires symmetry breaking), resulting in a loss of covalent character. It is shown how, in the MnO-4 ion, the bonding electrons of E symmetry are localized on the oxygens while the T2 electrons are localized on the metal. The mechanism behind this (unphysical) localization is studied in detail, making use of a simple model system. The covalent character is reintroduced in configuration interaction or multiconfiguration self-consistent-field calculations: density is transferred from the ligand to the metal in the E bonds and vice versa in the T2 bonds. The total metal 3d occupation, however, remains unchanged. Several configuration selection schemes in the space of bonding, nonbonding, and antibonding orbitals are tested with the purpose to recover a large fraction of the nondynamical correlation error but still retain a manageable wave function. It is shown that the ``nonbonding'' O2p orbitals play an important role in the correlation process and cannot be excluded (kept closed) in a correlated calculation if quantatively correct results are required.

  17. Electronic structure and chemical bond nature in Cs2PuO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2015-01-01

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

  18. Molecular electric moments calculated by using natural orbital functional theory

    CERN Document Server

    Mitxelena, Ion

    2016-01-01

    The molecular electric dipole, quadrupole and octupole moments of a selected set of 21 spin-compensated molecules are determined employing the extended version of the Piris natural orbital functional 6 (PNOF6), using the triple-$\\zeta$ Gaussian basis set with polarization functions developed by Sadlej, at the experimental geometries. The performance of the PNOF6 is established by carrying out a statistical analysis of the mean absolute errors with respect to the experiment. The calculated PNOF6 electric moments agree satisfactorily with the corresponding experimental data, and are in good agreement with the values obtained by accurate ab initio methods, namely, the coupled-cluster single and doubles (CCSD) and multi-reference single and double excitation configuration interaction (MRSD-CI) methods.

  19. The Effective Fragment Molecular Orbital Method for Fragments Connected by Covalent Bonds

    Science.gov (United States)

    Steinmann, Casper; Fedorov, Dmitri G.; Jensen, Jan H.

    2012-01-01

    We extend the effective fragment molecular orbital method (EFMO) into treating fragments connected by covalent bonds. The accuracy of EFMO is compared to FMO and conventional ab initio electronic structure methods for polypeptides including proteins. Errors in energy for RHF and MP2 are within 2 kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides similar to FMO but obtained two to five times faster. For proteins, the errors are also within a few kcal/mol of the FMO results. We developed both the RHF and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures had an RMSD of 0.40 and 0.44 Å for RHF and MP2, respectively. PMID:22844433

  20. The effective fragment molecular orbital method for fragments connected by covalent bonds.

    Directory of Open Access Journals (Sweden)

    Casper Steinmann

    Full Text Available We extend the effective fragment molecular orbital method (EFMO into treating fragments connected by covalent bonds. The accuracy of EFMO is compared to FMO and conventional ab initio electronic structure methods for polypeptides including proteins. Errors in energy for RHF and MP2 are within 2 kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides similar to FMO but obtained two to five times faster. For proteins, the errors are also within a few kcal/mol of the FMO results. We developed both the RHF and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures had an RMSD of 0.40 and 0.44 Å for RHF and MP2, respectively.

  1. Exact equations of motion for natural orbitals of strongly driven two-electron systems

    CERN Document Server

    Rapp, J; Bauer, D

    2014-01-01

    Natural orbital theory is a computationally useful approach to the few and many-body quantum problem. While natural orbitals are known and applied since many years in electronic structure applications, their potential for time-dependent problems is being investigated only since recently. Correlated two-particle systems are of particular importance because the structure of the two-body reduced density matrix expanded in natural orbitals is known exactly in this case. However, in the time-dependent case the natural orbitals carry time-dependent phases that allow for certain time-dependent gauge transformations of the first kind. Different phase conventions will, in general, lead to different equations of motion for the natural orbitals. A particular phase choice allows us to derive the exact equations of motion for the natural orbitals of any (laser-) driven two-electron system explicitly, i.e., without any dependence on quantities that, in practice, require further approximations. For illustration, we solve th...

  2. EXPERIMENTAL INVESTIGATION ON THE EFFECT OF NATURAL TROPICAL WEATHER ON INTERFACIAL BONDING PERFORMANCE OF CFRP-CONCRETE BONDING SYSTEM

    Directory of Open Access Journals (Sweden)

    MOHD H. MOHD HASHIM

    2016-04-01

    Full Text Available The existing reinforced concrete structures may require rehabilitation and strengthening to overcome deficiencies due to defect and environmental deterioration. Fibre Reinforced Polymer (FRP-concrete bonding systems can provide solution for the deficiencies, but the durability of the bonded joint needs to be investigated for reliable structural performance. In this research the interfacial bonding behaviour of CFRP-concrete system under tropical climate exposure is main interest. A 300 mm concrete prism was bonded with CFRP plate on its two sides and exposed for 3, 6, and 9 months to laboratory environment, continuous natural weather, and wet-dry exposure in 3.5% saltwater solution at room and 40 °C temperature. The prisms were subjected to tension and compression load under bonding test to measure the strain and determine stress distribution and shear stress transfer behaviour. The results of the bonding test showed that load transfer was fairly linear and uniform at lower load level and changed to non-linear and non- uniform at higher load level. The force transfers causes the shear stress distribution being shifted along the bonded length. The combination of climate effects may have provided better curing of the bonded joints, but longer duration of exposure may be required to weaken the bond strength. Nevertheless, CFRP-concrete bonding system was only minimally affected under the tropical climate and salt solution.

  3. Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.

    Science.gov (United States)

    Pauling, Linus; Herman, Zelek S.

    1984-01-01

    Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)

  4. The nature of the bond between peptide and carrier molecule determines immunogenicity of the construct

    NARCIS (Netherlands)

    Beekman, N.L.C.M.; Schaaper, W.M.M.; Langeveld, J.P.M.; Boshuizen, R.S.; Meloen, R.H.

    2001-01-01

    The influence of the nature of the bond between a peptide and a (lipidic) carrier molecule on the immunogenicity of that construct was investigated. As types of bonds a thioester-, a disulfide-, an amide- and a thioether bond were investigated. As carrier molecules a peptide, an N-palmitoylated

  5. Orbits

    CERN Document Server

    Xu, Guochang

    2008-01-01

    This is the first book of the satellite era which describes orbit theory with analytical solutions of the second order with respect to all possible disturbances. Based on such theory, the algorithms of orbits determination are completely revolutionized.

  6. 7 CFR 1720.14 - Nature of guarantee; acceleration of guaranteed bonds.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 11 2010-01-01 2010-01-01 false Nature of guarantee; acceleration of guaranteed bonds. 1720.14 Section 1720.14 Agriculture Regulations of the Department of Agriculture (Continued) RURAL... TELEPHONE PURPOSES § 1720.14 Nature of guarantee; acceleration of guaranteed bonds. (a) Any guarantee...

  7. Ionic bonding of lanthanides, as influenced by d- and f-atomic orbitals, by core-shells and by relativity.

    Science.gov (United States)

    Ji, Wen-Xin; Xu, Wei; Schwarz, W H Eugen; Wang, Shu-Guang

    2015-03-15

    Lanthanide trihalide molecules LnX3 (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO-coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen-core approximations for Lu were compared: the (1s(2) -4d(10) ) [Pd] medium core, the [Pd+5s(2) 5p(6) = Xe] and [Pd+4f(14) ] large cores, and the [Pd+4f(14) +5s(2) 5p(6) ] very large core. The errors of LuX bonding are more serious on freezing the 5p(6) shell than the 4f(14) shell, more serious upon core-freezing than on the effective-core-potential approximation. The LnX distances correlate linearly with the AO radii of the ionic outer shells, Ln(3+) -5p(6) and X(-) -np(6) , characteristic for dominantly ionic Ln(3+) -X(-) binding. The heavier halogen atoms also bind covalently with the Ln-5d shell. Scalar relativistic effects contract and destabilize the LuX bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length Re , bond force k, and bond stretching frequency vs do not follow the simple rules of Badger and Gordy (Re ∼BE∼k∼vs ). The so-called degeneracy-driven covalence, meaning strong mixing of accidentally near-degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.

  8. A New Bond Albedo for Performing Orbital Debris Brightness to Size Transformations

    Science.gov (United States)

    Mulrooney, Mark K.; Matney, Mark J.

    2008-01-01

    We have developed a technique for estimating the intrinsic size distribution of orbital debris objects via optical measurements alone. The process is predicated on the empirically observed power-law size distribution of debris (as indicated by radar RCS measurements) and the log-normal probability distribution of optical albedos as ascertained from phase (Lambertian) and range-corrected telescopic brightness measurements. Since the observed distribution of optical brightness is the product integral of the size distribution of the parent [debris] population with the albedo probability distribution, it is a straightforward matter to transform a given distribution of optical brightness back to a size distribution by the appropriate choice of a single albedo value. This is true because the integration of a powerlaw with a log-normal distribution (Fredholm Integral of the First Kind) yields a Gaussian-blurred power-law distribution with identical power-law exponent. Application of a single albedo to this distribution recovers a simple power-law [in size] which is linearly offset from the original distribution by a constant whose value depends on the choice of the albedo. Significantly, there exists a unique Bond albedo which, when applied to an observed brightness distribution, yields zero offset and therefore recovers the original size distribution. For physically realistic powerlaws of negative slope, the proper choice of albedo recovers the parent size distribution by compensating for the observational bias caused by the large number of small objects that appear anomalously large (bright) - and thereby skew the small population upward by rising above the detection threshold - and the lower number of large objects that appear anomalously small (dim). Based on this comprehensive analysis, a value of 0.13 should be applied to all orbital debris albedo-based brightness-to-size transformations regardless of data source. Its prima fascia genesis, derived and constructed

  9. NATURAL DURABILITY AND PERFORMANCE OF HORNBEAM CEMENT BONDED PARTICLEBOARD

    National Research Council Canada - National Science Library

    Papadopoulos, Antonios N

    2008-01-01

    Cement bonded particleboards were manufactured from hornbeam (Carpinus betulus L.) wood particles. Hydration tests were carried out to determine the inhibitory index in order to characterise wood-cement compatibility...

  10. Orbital

    OpenAIRE

    Yourshaw, Matthew Stephen

    2017-01-01

    Orbital is a virtual reality gaming experience designed to explore the use of traditional narrative structure to enhance immersion in virtual reality. The story structure of Orbital was developed based on the developmental steps of 'The Hero's Journey,' a narrative pattern identified by Joseph Campbell. Using this standard narrative pattern, Orbital is capable of immersing the player quickly and completely for the entirety of play time. MFA

  11. Accurate ab initio calculations of O-HO and O-H(-)O proton chemical shifts: towards elucidation of the nature of the hydrogen bond and prediction of hydrogen bond distances.

    Science.gov (United States)

    Siskos, Michael G; Tzakos, Andreas G; Gerothanassis, Ioannis P

    2015-09-07

    The inability to determine precisely the location of labile protons in X-ray molecular structures has been a key barrier to progress in many areas of molecular sciences. We report an approach for predicting hydrogen bond distances beyond the limits of X-ray crystallography based on accurate ab initio calculations of O-HO proton chemical shifts, using a combination of DFT and contactor-like polarizable continuum model (PCM). Very good linear correlation between experimental and computed (at the GIAO/B3LYP/6-311++G(2d,p) level of theory) chemical shifts were obtained with a large set of 43 compounds in CHCl3 exhibiting intramolecular O-HO and intermolecular and intramolecular ionic O-H(-)O hydrogen bonds. The calculated OH chemical shifts exhibit a strong linear dependence on the computed (O)HO hydrogen bond length, in the region of 1.24 to 1.85 Å, of -19.8 ppm Å(-1) and -20.49 ppm Å(-1) with optimization of the structures at the M06-2X/6-31+G(d) and B3LYP/6-31+G(d) level of theory, respectively. A Natural Bond Orbitals (NBO) analysis demonstrates a very good linear correlation between the calculated (1)H chemical shifts and (i) the second-order perturbation stabilization energies, corresponding to charge transfer between the oxygen lone pairs and σ antibonding orbital and (ii) Wiberg bond order of the O-HO and O-H(-)O hydrogen bond. Accurate ab initio calculations of O-HO and O-H(-)O (1)H chemical shifts can provide improved structural and electronic description of hydrogen bonding and a highly accurate measure of distances of short and strong hydrogen bonds.

  12. Orbital

    Science.gov (United States)

    Hanson, Robert M.

    2003-06-01

    ORBITAL requires the following software, which is available for free download from the Internet: Netscape Navigator, version 4.75 or higher, or Microsoft Internet Explorer, version 5.0 or higher; Chime Plug-in, version compatible with your OS and browser (available from MDL).

  13. Correlated natural transition orbitals for core excitation energies in multilevel coupled cluster models

    Science.gov (United States)

    Høyvik, Ida-Marie; Myhre, Rolf Heilemann; Koch, Henrik

    2017-04-01

    In this article, we present a black-box approach for the selection of orbital spaces when computing core excitation energies in the multilevel coupled cluster (MLCC) framework. Information available from the lower level of theory is used to generate correlated natural transition orbitals (CNTOs) for the high-level calculation by including both singles and doubles information in the construction of the transition orbitals. The inclusion of the doubles excitation information is essential to obtain a set of orbitals that all contain physical information, in contrast to the natural transition orbitals where only a small subset of the virtual orbitals contains physical information. The CNTOs may be included in an active space based on a cutoff threshold for the eigenvalues corresponding to the orbitals. We present MLCC results for core excitation energies calculated using coupled cluster singles and doubles (CCSD) in the inactive space and CCSD with perturbative triples (CC3) in the active space. The use of CNTOs results in small errors compared to full CC3.

  14. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 9 2010-07-01 2010-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature of...

  15. The Fragment Molecular Orbital Method Reveals New Insight into the Chemical Nature of GPCR-Ligand Interactions.

    Science.gov (United States)

    Heifetz, Alexander; Chudyk, Ewa I; Gleave, Laura; Aldeghi, Matteo; Cherezov, Vadim; Fedorov, Dmitri G; Biggin, Philip C; Bodkin, Mike J

    2016-01-25

    Our interpretation of ligand-protein interactions is often informed by high-resolution structures, which represent the cornerstone of structure-based drug design. However, visual inspection and molecular mechanics approaches cannot explain the full complexity of molecular interactions. Quantum Mechanics approaches are often too computationally expensive, but one method, Fragment Molecular Orbital (FMO), offers an excellent compromise and has the potential to reveal key interactions that would otherwise be hard to detect. To illustrate this, we have applied the FMO method to 18 Class A GPCR-ligand crystal structures, representing different branches of the GPCR genome. Our work reveals key interactions that are often omitted from structure-based descriptions, including hydrophobic interactions, nonclassical hydrogen bonds, and the involvement of backbone atoms. This approach provides a more comprehensive picture of receptor-ligand interactions than is currently used and should prove useful for evaluation of the chemical nature of ligand binding and to support structure-based drug design.

  16. Primary extranodal Natural Killer/ T-cell lymphoma of the ethmoid sinus masquerading as orbital cellulitis

    Directory of Open Access Journals (Sweden)

    Ivana Mahovne

    2009-08-01

    Full Text Available This report presents a case of an exceptionallyrare primary Natural Killer/T cell (NK/T lymphomaof the right paranasal frontal and ethmoidsinuses in a patient treated previously for rightside chronic sinusitis. It highlighted the importanceof adequate tissue biopsy and patohistologicalexamination in patients with chronic sinusitisor orbital cellulitis that fail to respond totraditional management.

  17. Development of Monte Carlo configuration interaction: Natural orbitals and second-order perturbation theory

    CERN Document Server

    Coe, J P; 10.1063/1.4767436

    2013-01-01

    Approximate natural orbitals are investigated as a way to improve a Monte Carlo configuration interaction (MCCI) calculation. We introduce a way to approximate the natural orbitals in MCCI and test these and approximate natural orbitals from MP2 and QCISD in MCCI calculations of single-point energies. The efficiency and accuracy of approximate natural orbitals in MCCI potential curve calculations for the double hydrogen dissociation of water, the dissociation of carbon monoxide and the dissociation of the nitrogen molecule are then considered in comparison with standard MCCI when using full configuration interaction as a benchmark. We also use the method to produce a potential curve for water in an aug-cc-pVTZ basis. A new way to quantify the accuracy of a potential curve is put forward that takes into account all of the points and that the curve can be shifted by a constant. We adapt a second-order perturbation scheme to work with MCCI (MCCIPT2) and improve the efficiency of the removal of duplicate states i...

  18. Exploring the Nature of Silicon-Noble Gas Bonds in H3SiNgNSi and HSiNgNSi Compounds (Ng = Xe, Rn

    Directory of Open Access Journals (Sweden)

    Sudip Pan

    2015-03-01

    Full Text Available Ab initio and density functional theory-based computations are performed to investigate the structure and stability of H3SiNgNSi and HSiNgNSi compounds (Ng = Xe, Rn. They are thermochemically unstable with respect to the dissociation channel producing Ng and H3SiNSi or HSiNSi. However, they are kinetically stable with respect to this dissociation channel having activation free energy barriers of 19.3 and 23.3 kcal/mol for H3SiXeNSi and H3SiRnNSi, respectively, and 9.2 and 12.8 kcal/mol for HSiXeNSi and HSiRnNSi, respectively. The rest of the possible dissociation channels are endergonic in nature at room temperature for Rn analogues. However, one three-body dissociation channel for H3SiXeNSi and one two-body and one three-body dissociation channels for HSiXeNSi are slightly exergonic in nature at room temperature. They become endergonic at slightly lower temperature. The nature of bonding between Ng and Si/N is analyzed by natural bond order, electron density and energy decomposition analyses. Natural population analysis indicates that they could be best represented as (H3SiNg+(NSi− and (HSiNg+(NSi−. Energy decomposition analysis further reveals that the contribution from the orbital term (ΔEorb is dominant (ca. 67%–75% towards the total attraction energy associated with the Si-Ng bond, whereas the electrostatic term (ΔEelstat contributes the maximum (ca. 66%–68% for the same in the Ng–N bond, implying the covalent nature of the former bond and the ionic nature of the latter.

  19. Searching for some natural orbits to observe the double asteroid 2002CE26

    Science.gov (United States)

    Mescolotti, Bruna Yukiko Pinheiro Masago; Prado, Antonio Fernando Bertachini de Almeida; Chiaradia, Ana Paula Marins; Gomes, Vivian Martins

    2017-07-01

    Knowledge of the Solar System is increasing with data coming from space missions to small bodies. A mission to those bodies offers some problems, because they have several characteristics that are not well known, like their shapes, sizes and masses. The present research has the goal of searching for trajectories around the double asteroid 2002CE26, a system of Near-Earth Asteroids (NEAs) of the Apollo type. For every trajectory of the spacecraft, the evolution of the distances between the spacecraft and the two bodies that compose the system is crucial, due to its impact in the quality of the observations made from the spacecraft. Furthermore, this study has a first objective of searching for trajectories that make the spacecraft remain as long as possible near the two bodies that compose the asteroid system, without the use of orbital maneuvers. The model used here assumes elliptical orbits for the asteroids. The effect of the solar radiation pressure is also included, since it is a major perturbing force acting in spacecrafts traveling around small bodies. The natural orbits found here are useful for the mission. They can be used individually or combined in several pieces by orbital maneuvers. Another point considered here is the importance of the errors in the estimation of the physical parameters of the bodies. This task is very important, because there are great uncertainties in these values because the measurements are based on observations made from the Earth. It is shown that a variation of those parameters can make very large modifications in the times that the spacecraft remains close to the bodies of the system (called here "observational times"). Those modifications are large enough to make the best trajectories obtained under nominal conditions to be useless under some errors in the physical parameters. So, a search is made to find trajectories that have reasonable observation times for all the assumed error scenarios for the two bodies, because those

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

    Science.gov (United States)

    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…

  1. On the efficiency of VBSCF algorithms, a comment on "An efficient algorithm for energy gradients and orbital optimization in valence bond theory"

    NARCIS (Netherlands)

    van Lenthe, J. H.; Broer-Braam, H. B.; Rashid, Z.

    2012-01-01

    We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an

  2. Correlated natural transition orbital framework for low-scaling excitation energy calculations (CorNFLEx)

    Science.gov (United States)

    Baudin, Pablo; Kristensen, Kasper

    2017-06-01

    We present a new framework for calculating coupled cluster (CC) excitation energies at a reduced computational cost. It relies on correlated natural transition orbitals (NTOs), denoted CIS(D')-NTOs, which are obtained by diagonalizing generalized hole and particle density matrices determined from configuration interaction singles (CIS) information and additional terms that represent correlation effects. A transition-specific reduced orbital space is determined based on the eigenvalues of the CIS(D')-NTOs, and a standard CC excitation energy calculation is then performed in that reduced orbital space. The new method is denoted CorNFLEx (Correlated Natural transition orbital Framework for Low-scaling Excitation energy calculations). We calculate second-order approximate CC singles and doubles (CC2) excitation energies for a test set of organic molecules and demonstrate that CorNFLEx yields excitation energies of CC2 quality at a significantly reduced computational cost, even for relatively small systems and delocalized electronic transitions. In order to illustrate the potential of the method for large molecules, we also apply CorNFLEx to calculate CC2 excitation energies for a series of solvated formamide clusters (up to 4836 basis functions).

  3. The nature of chemical bond in trioxide Mi-UO3

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2002-01-01

    Full Text Available Low-energy X-ray photoelectron and conversion electron spectra from uranium trioxide were measured, and calculations were done for the [UO2O4]-6 (D4b cluster which reflects the structure of uranium close environment in MI-UO3 in the non-relativistic and relativistic Xa-DVM approximation. This enabled a satisfactory qualitative and in some cases quantitative agreement between the experimental and theoretical data, and interpretation of such spectra. Despite the traditional opinion that before participation in the chemical binding, the U5f electrons could be promoted to the higher (for example - U6d levels, it was theoretically proved and experimentally confirmed that the U5f electrons (about two U5f electrons are able to participate directly in the chemical bond formation in uranium trioxide. The filled U5f states proved to be localized in the outer valence molecular orbitals energy range 4-9 eV, while the vacant U5f states were generally localized in the low-energy range (0-6 eV above zero. It was experimentally shown that U6p electrons not only participate effectively in the inner valence molecular orbital formation but also participate strongly (more than 1 U6p electron in the formation of die filled outer valence molecular orbitals.

  4. Extranodal natural killer/T-cell lymphoma presenting as orbital cellulitis

    Directory of Open Access Journals (Sweden)

    Zuhaimy, Hanis

    2017-02-01

    Full Text Available Objective: To report an aggressive case of extranodal natural killer lymphoma (NKTCL of the ethmoid sinus presenting as orbital cellulitisMethod: Case reportResults: A 56-year-old male presented with right eye redness, reduced vision, and periorbital swelling for 5 weeks duration associated with a two-month history of blocked nose. The visual acuity of the right eye was 6/18. The eye was proptosed with periorbital oedema and conjunctival chemosis. The pupil was mid-dilated but there was no relative afferent pupillary defect. The fundus was normal. The extraocular movements were restricted in all directions of gaze. Nasal endoscopy revealed pansinusitis that corresponded with CT scan orbit and paranasal sinuses findings. Despite treatment, he showed no clinical improvement. Ethmoidal sinus biopsies performed revealed extranodal NKTCL. Further imaging showed involvement of the right orbital contents and its adnexa with intracranial extension into the right cavernous sinus and meninges over right temporal fossa. The patient underwent chemotherapy. However he succumbed to his illness two months after the diagnosis.Conclusion: Extranodal NKTCL is a great mimicker. This case demonstrated how an acute initial presentation of extranodal NKTCL can present as orbital cellulitis with pansinusitis.

  5. Extranodal natural killer/T-cell lymphoma presenting as orbital cellulitis.

    Science.gov (United States)

    Zuhaimy, Hanis; Aziz, Hayati Abdul; Vasudevan, Suresh; Hui Hui, Siah

    2017-01-01

    Objective: To report an aggressive case of extranodal natural killer/T-cell lymphoma (NKTCL) of the ethmoid sinus presenting as orbital cellulitis Method: Case report Results: A 56-year-old male presented with right eye redness, reduced vision, and periorbital swelling for 5 weeks duration associated with a two-month history of blocked nose. The visual acuity of the right eye was 6/18. The eye was proptosed with periorbital oedema and conjunctival chemosis. The pupil was mid-dilated but there was no relative afferent pupillary defect. The fundus was normal. The extraocular movements were restricted in all directions of gaze. Nasal endoscopy revealed pansinusitis that corresponded with CT scan orbit and paranasal sinuses findings. Despite treatment, he showed no clinical improvement. Ethmoidal sinus biopsies performed revealed extranodal NKTCL. Further imaging showed involvement of the right orbital contents and its adnexa with intracranial extension into the right cavernous sinus and meninges over right temporal fossa. The patient underwent chemotherapy. However he succumbed to his illness two months after the diagnosis. Conclusion: Extranodal NKTCL is a great mimicker. This case demonstrated how an acute initial presentation of extranodal NKTCL can present as orbital cellulitis with pansinusitis.

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

    Science.gov (United States)

    Loerbroks, Claudia; Rinaldi, Roberto; Thiel, Walter

    2013-11-25

    The molecular understanding of the chemistry of 1,4-β-glucans is essential for designing new approaches to the conversion of cellulose into platform chemicals and biofuels. In this endeavor, much attention has been paid to the role of hydrogen bonding occurring in the cellulose structure. So far, however, there has been little discussion about the implications of the electronic nature of the 1,4-β-glycosidic bond and its chemical environment for the activation of 1,4-β-glucans toward acid-catalyzed hydrolysis. This report sheds light on these central issues and addresses their influence on the acid hydrolysis of cellobiose and, by analogy, cellulose. The electronic structure of cellobiose was explored by DFT at the BB1 K/6-31++G(d,p) level. Natural bond orbital (NBO) analysis was performed to grasp the key bonding concepts. Conformations, protonation sites, and hydrolysis mechanisms were examined. The results for cellobiose indicate that cellulose is protected against hydrolysis not only by its supramolecular structure, as currently accepted, but also by its electronic structure, in which the anomeric effect plays a key role. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Electrostatic Potential Maps and Natural Bond Orbital Analysis: Visualization and Conceptualization of Reactivity in Sanger's Reagent

    Science.gov (United States)

    Mottishaw, Jeffery D.; Erck, Adam R.; Kramer, Jordan H.; Sun, Haoran; Koppang, Miles

    2015-01-01

    Frederick Sanger's early work on protein sequencing through the use of colorimetric labeling combined with liquid chromatography involves an important nucleophilic aromatic substitution (S[subscript N]Ar) reaction in which the N-terminus of a protein is tagged with Sanger's reagent. Understanding the inherent differences between this S[subscript…

  8. 29 CFR 453.11 - The nature of the “duties” to which the bonding requirement relates.

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 2 2010-07-01 2010-07-01 false The nature of the âdutiesâ to which the bonding requirement relates. 453.11 Section 453.11 Labor Regulations Relating to Labor OFFICE OF LABOR-MANAGEMENT STANDARDS... LABOR-MANAGEMENT REPORTING AND DISCLOSURE ACT OF 1959 Scope of the Bond § 453.11 The nature of the...

  9. Tractability gains in symmetry-adapted perturbation theory including coupled double excitations: CCD+ST(CCD) dispersion with natural orbital truncations

    Science.gov (United States)

    Parrish, Robert M.; Hohenstein, Edward G.; Sherrill, C. David

    2013-11-01

    This work focuses on efficient and accurate treatment of the intermolecular dispersion interaction using the CCD+ST(CCD) dispersion approach formulated by Williams et al. [J. Chem. Phys. 103, 4586 (1995)]. We apply natural orbital truncation techniques to the solution of the monomer coupled-cluster double (CCD) equations, yielding substantial accelerations in this computationally demanding portion of the SAPT2+(CCD), SAPT2+(3)(CCD), and SAPT2+3(CCD) analyses. It is shown that the wholly rate-limiting dimer-basis particle-particle ladder term can be computed in a reduced natural virtual space which is essentially the same size as the monomer-basis virtual space, with an error on the order of a few thousandths of 1 kcal mol-1. Coupled with our existing natural orbital techniques for the perturbative triple excitation contributions [E. G. Hohenstein and C. D. Sherrill, J. Chem. Phys. 133, 104107 (2010)], this technique provides speedups of greater than an order of magnitude for the evaluation of the complete SAPT2+3(CCD) decomposition, with a total error of a few hundredths of 1 kcal mol-1. The combined approach yields tractability gains of almost 2× in the system size, allowing for SAPT2+3(CCD)/aug-cc-pVTZ analysis to be performed for systems such as adenine-thymine for the first time. Natural orbital based SAPT2+3(CCD)/aug-cc-pVTZ results are presented for stacked and hydrogen-bonded configurations of uracil dimer and the adenine-thymine dimer.

  10. Optimising aesthetics and facilitating clinical application of free-hand bonding using the 'natural layering concept'.

    Science.gov (United States)

    Dietschi, D

    2008-02-23

    The use of composites in the smile frame has evolved and gained maturity. However, ceramics remain the preferred aesthetic option for many clinicians because bonding techniques are still considered intricate, sensitive and, to a certain extent, unpredictable. These drawbacks, essentially related to the complexity of many composite systems, can be overcome today by the application of the 'natural layering concept', which makes use of only two basics masses, dentine and enamel, perfectly mimicking natural tooth structure. There are plentiful indications for the use of such a simplified but aesthetically uncompromised treatment modality. Actually, this approach is highly suitable for young and post-orthodontic patients where conservation of tissue is a must and in general for all patients with rather healthy dentitions.

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

    Science.gov (United States)

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

    2014-01-01

    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

  12. Molecular structure, natural bond analysis, vibrational, and electronic spectra of aspartateguanidoacetatenickel(II), [Ni(Asp)(GAA)]·H2O: DFT quantum mechanical calculations

    Science.gov (United States)

    Ramos, J. M.; de M. Cruz, M. T.; Costa, A. C., Jr.; Ondar, G. F.; Ferreira, Glaucio B.; Raniero, L.; Martin, A. A.; Versiane, O.; Téllez Soto, C. A.

    2012-11-01

    The aspartateguanidoacetatenickel (II) complex, [Ni(Asp)(GAA)], was synthesized and structural analysis was performed by means of the experimental methods: determination of the C, H, N and O contents, thermogravimetry, infrared and Raman spectroscopy. DFT:B3LYP/6-311G(d, p) calculations have been performed giving optimized structure and harmonic vibrational wavenumbers. Second derivative of the FT-infrared, FT-Raman and Surface Raman Enhanced Scattering (SERS) spectra, and band deconvolution analysis were also performed. Features of the FT-infrared, FT-Raman and SERS confirmed theoretical structure prediction. Full assignment of the vibrational spectrum was also supported by a carefully analysis of the distorted geometries generated by the normal modes. The Natural Bond Orbital analysis (NBO) was also carried out as a way to study the Ni (II) hybridization leading to the pseudo planar geometry of the framework, and the extension of the atomic N and O hybrid orbital of the different amino acids in the bond formation. Bands of charge transfer and d-d transitions were assigned in the UV-Vis spectrum.

  13. On the performance of natural orbital functional approximations in the Hubbard model

    Science.gov (United States)

    Mitxelena, I.; Piris, M.; Rodríguez-Mayorga, M.

    2017-10-01

    Strongly correlated materials are now under intense development, and natural orbital functional (NOF) methods seem to be able to capture the physics of these systems. We present a benchmark based on the Hubbard model for a class of commonly used NOF approximations (also known as reduced density matrix functional approximations). Our findings highlight the importance of imposing ensemble N-representability conditions in order to obtain consistent results in systems with either weak or strong electronic correlation, such as the Hubbard system with a varying two-particle interaction parameter. Based on the accuracy of the results obtained using PNOF7, which retrieves a large amount of the total strong nondynamic correlation, the Hubbard model points out that N-representability gives solid foundations for NOF development.

  14. Orbit-Attitude Changes of Objects in Near Earth Space Induced by Natural Charging

    Science.gov (United States)

    2017-05-02

    Propagation; Magnetic Field; Geosynchronous Orbit ; Satellite Components; Electrons; Operational Anomalies 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF...charging in the near geosynchronous orbit have been done. DeForest [4] investigated charging of ATS-5 satellite in geosynchronous orbit . He found that...common, high-level charging can also be experienced in low Earth orbit . Defense Meteorological Satellite Program (DMSP) spacecraft in low Earth polar

  15. The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: implications for the enzyme mechanism.

    Science.gov (United States)

    Ogura, Hiroshi; Evans, John P; Peng, Dungeng; Satterlee, James D; Ortiz de Montellano, Paul R; La Mar, Gerd N

    2009-04-14

    The active site electronic structure of the azide complex of substrate-bound human heme oxygenase 1 (hHO) has been investigated by (1)H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. Two-dimensional (1)H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts that places the lone iron pi-spin in the d(xz) orbital, rather than the d(yz) orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy, and magnetic susceptibilities argues for a low-spin, (d(xy))(2)(d(yz),d(xz))(3), ground state in both azide and cyanide complexes. The switch from singly occupied d(yz) for the cyanide to d(xz) for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide pi-plane in the latter complex, which is approximately 90 degrees in-plane rotated from that of the imidazole pi-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicates that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 --> Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed.

  16. The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: Implications for the enzyme mechanism‡

    Science.gov (United States)

    Ogura, Hiroshi; Evans, John P.; Peng, Dungeng; Satterlee, James D.; de Montellano, Paul R. Ortiz; Mar, Gerd N. La

    2009-01-01

    The active site electronic structure of the azide complex of substrate-bound human heme oxygenase-1, (hHO) has been investigated by 1H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. 2D 1H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts, that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy and magnetic susceptibilities argues for a low-spin, (dxy)2(dyz,dxz)3, ground state in both azide and cyanide complexes. The switch from singly-occupied dyz for the cyanide to dxz for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide π-plane in the latter complex, which is ∼90° in-plane rotated from that of the imidazole π-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicate that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 → Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed. PMID:19243105

  17. Chemical insight from density functional modeling of molecular adsorption: Tracking the bonding and diffusion of anthracene derivatives on Cu(111) with molecular orbitals

    Energy Technology Data Exchange (ETDEWEB)

    Wyrick, Jonathan; Bartels, Ludwig, E-mail: ludwig.bartels@ucr.edu [Pierce Hall, University of California-Riverside, Riverside, California 92521 (United States); Einstein, T. L. [Department of Physics and Condensed Matter Theory Center, University of Maryland, College Park, Maryland 20742-4111 (United States)

    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.

  18. Chemical insight from density functional modeling of molecular adsorption: Tracking the bonding and diffusion of anthracene derivatives on Cu(111) with molecular orbitals

    Science.gov (United States)

    Wyrick, Jonathan; Einstein, T. L.; Bartels, Ludwig

    2015-03-01

    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.

  19. Spin-orbital nature of the high-field magnetic state in the Sr4Ru3O10

    Science.gov (United States)

    Granata, Veronica; Capogna, Lucia; Forte, Filomena; Lepetit, Marie-Bernadette; Fittipaldi, Rosalba; Stunault, Anne; Cuoco, Mario; Vecchione, Antonio

    2016-03-01

    We perform a spin-polarized neutron-diffraction study to investigate the nature of the high-field magnetic state of the trilayered Sr4Ru3O10 . The analysis indicates that a high field applied within the a b plane leads to an unbalance of the spin and orbital moments with a spatial profile that is strongly tied to the layers where the electrons are located in the unit cell. We provide evidence of a layer dependent magnetic anisotropy with the inner layers having larger spin and orbital magnetic moments than the outer ones and show that such behavior is robust to temperature variation being persistent above the Curie temperature. By means of an effective model that includes the coupling between the spin-orbital degrees of freedom at inequivalent Ru sites we ascribe the origin of the layer anisotropy to the cooperative effects between octahedral distortions, spin orbit, and Coulomb interactions.

  20. Influence of substituents on the nature of metal⋯π interaction and its cooperativity with halogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Meng; Cheng, Jianbo, E-mail: li70316@sohu.com, E-mail: liqingzhong1990@sina.com; Yang, Xin; Li, Wenzuo; Xiao, Bo; Li, Qingzhong, E-mail: li70316@sohu.com, E-mail: liqingzhong1990@sina.com [The Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Yantai University, Yantai 264005 (China)

    2015-08-07

    High-level quantum chemical calculations have been performed to investigate the influence of substituents on the metal—π interaction and its cooperative effect with halogen bond in C{sub 2}X{sub 4}⋯MCN⋯ClF (X = H, CN, CH{sub 3}; M = Cu, Ag, Au). The strong electron-withdrawing group CN weakens the metal—π covalent interaction, while the weak electron-withdrawing group CH{sub 3} strengthens it. The metal—π covalent interaction is dominated by electrostatic energy although the AuCN complex has approximately equal electrostatic and polarization contributions. However, the metal—π covalent interaction is governed by polarization energy due to the CN substitution. A cooperative effect is found for the halogen bond and metal—π interactions in C{sub 2}H{sub 4}⋯MCN⋯ClF, while a diminutive effect occurs in the triads by the CN substituent. Orbital interaction analysis indicates that the strong electron-withdrawing group CN causes the C=C group vary from a stronger donor orbital to a stronger acceptor orbital.

  1. Combining Accuracy and Efficiency: An Incremental Focal-Point Method Based on Pair Natural Orbitals.

    Science.gov (United States)

    Fiedler, Benjamin; Schmitz, Gunnar; Hättig, Christof; Friedrich, Joachim

    2017-12-12

    In this work, we present a new pair natural orbitals (PNO)-based incremental scheme to calculate CCSD(T) and CCSD(T0) reaction, interaction, and binding energies. We perform an extensive analysis, which shows small incremental errors similar to previous non-PNO calculations. Furthermore, slight PNO errors are obtained by using TPNO = TTNO with appropriate values of 10-7 to 10-8 for reactions and 10-8 for interaction or binding energies. The combination with the efficient MP2 focal-point approach yields chemical accuracy relative to the complete basis-set (CBS) limit. In this method, small basis sets (cc-pVDZ, def2-TZVP) for the CCSD(T) part are sufficient in case of reactions or interactions, while some larger ones (e.g., (aug)-cc-pVTZ) are necessary for molecular clusters. For these larger basis sets, we show the very high efficiency of our scheme. We obtain not only tremendous decreases of the wall times (i.e., factors >102) due to the parallelization of the increment calculations as well as of the total times due to the application of PNOs (i.e., compared to the normal incremental scheme) but also smaller total times with respect to the standard PNO method. That way, our new method features a perfect applicability by combining an excellent accuracy with a very high efficiency as well as the accessibility to larger systems due to the separation of the full computation into several small increments.

  2. Natural and orbital debris particles on LDEF's trailing and forward-facing surfaces

    Science.gov (United States)

    Hoerz, Friedrich; See, Thomas H.; Bernhard, Ronald P.; Brownlee, Donald E.

    1995-01-01

    Approximately 1000 impact craters on the Chemistry of Meteoroid Experiment (CME) have been analyzed by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDXA) to determine the compositional make-up of projectile residues. This report completes our systematic survey of gold and aluminum surfaces exposed at the trailing-edge (A03) and forward-facing (A11) LDEF sites, respectively. The major categories for the projectile residues were (1) natural, with diverse subgroups such as chondritic, monomineralic silicates, and sulfides, and (2) man made, that were classified into aluminum (metallic or oxide) and miscellaneous materials (such as stainless steel, paint flakes, etc). On CME gold collectors on LDEF's trailing edge approximately 11 percent of all craters greater than 100 micron in diameter were due to man-made debris, the majority (8.6 percent) caused by pure aluminum, approximately 31.4 percent were due to cosmic dust, while the remaining 58 percent were indeterminate via the analytical techniques utilized in this study. The aluminum surfaces located at the A11 forward-facing site did not permit analysis of aluminum impactors, but approximately 9.4 percent of all craters were demonstratably caused by miscellaneous debris materials and approximately 39.2 percent were the result of natural particles, leaving approximately 50 percent which were indeterminate. Model considerations and calculations are presented that focus on the crater-production rates for features greater than 100 micron in diameter, and on assigning the intermediate crater population to man-made or natural particles. An enhancement factor of 6 in the crater-production rate of natural impactors for the 'forward-facing' versus the 'trailing-edge' CME collectors was found to best explain all observations (i.e., total crater number(s), as well as their computational characteristics). Enhancement factors of 10 and 4 are either too high or too low. It is also suggested that

  3. Hydrogen bonding in ionic liquids.

    Science.gov (United States)

    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

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

    Science.gov (United States)

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

    2016-06-29

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

  5. Hydrogen- and Halogen-Bonds between Ions of like Charges: Are They Anti-Electrostatic in Nature?

    Science.gov (United States)

    Wang, Changwei; Fu, Yuzhuang; Zhang, Lina; Danovich, David; Shaik, Sason; Mo, Yirong

    2018-04-05

    Recent theoretical studies suggested that hydrogen bonds between ions of like charges are of a covalent nature due to the dominating n D →σ* H-A charge-transfer (CT) interaction. In this work, energy profiles of typical hydrogen (H) and halogen (X) bonding systems formed from ions of like charges are explored using the block-localized wavefunction (BLW) method, which can derive optimal geometries and wave functions with the CT interaction "turned off." The results demonstrate that the kinetic stability, albeit reduced, is maintained for most investigated systems even after the intermolecular CT interaction is quenched. Further energy decomposition analyses based on the BLW method reveal that, despite a net repulsive Coulomb repulsion, a stabilizing component exists due to the polarization effect that plays significant role in the kinetic stability of all systems. Moreover, the fingerprints of the augmented electrostatic interaction due to polarization are apparent in the variation patterns of the electron density. All in all, much like in standard H- and X-bonds, the stability of such bonds between ions of like charges is governed by the competition between the stabilizing electrostatic and charge transfer interactions and the destabilizing deformation energy and Pauli exchange repulsion. While in most cases of "anti-electrostatic" bonds the CT interaction is of a secondary importance, we also find cases where CT is decisive. As such, this work validates the existence of anti-electrostatic H- and X-bonds. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  6. Spectroscopic, electronic structure and natural bond analysis of 2-aminopyrimidine and 4-aminopyrazolo[3,4-d]pyrimidine: a comparative study.

    Science.gov (United States)

    Prabavathi, N; Nilufer, A; Krishnakumar, V; Akilandeswari, L

    2012-10-01

    The FTIR and FT-Raman spectra of 2-aminopyrimidine (2-AP) and 4-aminopyrazolo[3,4-d]pyrimidine (4-APP) has been recorded in the region 4000-400 and 3500-100 cm(-1), respectively. The tautomeric stability, optimized geometry, frequency and intensity of the vibrational bands of 2-AP and 4-APP were obtained by the DFT level using 6-31G(d) and 6-31G(d,p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. A detailed interpretation of the infrared and Raman spectra of 2-AP and 4-APP are also reported based on total energy distribution (TED). The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically simulated spectra. The (1)H and (13)C NMR spectra have been simulated using the gauge independent atomic orbital (GIAO) method. The theoretical UV-Vis spectrum of the compound using CIS method and the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β(0)) of these novel molecular system and related properties (β, α(0) and Δα) of 2-AP and 4-APP are calculated using DFT/6-31G(d) method on the finite-field approach. The Mulliken charges, the values of electric dipole moment (μ) of the molecule were computed using DFT calculations. The change in electron density (ED) in the σ(∗) antibonding orbitals and stabilization energies E(2) have been calculated by natural bond (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions. Copyright © 2012 Elsevier B.V. All rights reserved.

  7. Nature of bonding in group 13 dimetallenes: a delicate balance between singlet diradical character and closed shell interactions.

    Science.gov (United States)

    Moilanen, Jani; Power, Philip P; Tuononen, Heikki M

    2010-12-06

    The nature of metal-metal bonding in group 13 dimetallenes REER (E = Al, Ga, In, Tl; R = H, Me, (t)Bu, Ph) was investigated by use of quantum chemical methods that include HF, second order Møller-Plesset perturbation theory (MP2), coupled cluster (CCSD(T)), complete active space with (CASPT2) and without (CAS) second order perturbation theory, and two density functionals, namely, B3LYP and M06-2X. The results show that the metal-metal interaction in group 13 dimetallenes stems almost exclusively from static and dynamic electron correlation effects: both dialuminenes and digallenes have an important singlet diradical component in their wave function, whereas the bonding in the heavier diindenes and, in particular, dithallenes is dominated by closed shell metallophilic interactions. The reported calculations represent a systematic attempt to determine the metal and ligand dependent bonding changes in these systems.

  8. Local explicitly correlated second- and third-order Møller-Plesset perturbation theory with pair natural orbitals

    Science.gov (United States)

    Hättig, Christof; Tew, David P.; Helmich, Benjamin

    2012-05-01

    We present an algorithm for computing explicitly correlated second- and third-order Møller-Plesset energies near the basis set limit for large molecules with a cost that scales formally as N^4 with system size N. This is achieved through a hybrid approach where locality is exploited first through orbital specific virtuals (OSVs) and subsequently through pair natural orbitals (PNOs) and integrals are approximated using density fitting. Our method combines the low orbital transformation costs of the OSVs with the compactness of the PNO representation of the doubles amplitude vector. The N^4 scaling does not rely upon the a priori definition of domains, enforced truncation of pair lists, or even screening and the energies converge smoothly to the canonical values with decreasing occupation number thresholds, used in the selection of the PNO basis. For MP2.5 intermolecular interaction energies, we find that 99% of benchmark basis set limit correlation energy contributions are recovered using an aug-cc-pVTZ basis and that on average only 50 PNOs are required to correlate the significant orbital pairs.

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

    Science.gov (United States)

    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.

  10. A comparative study of the chalcogen bond, halogen bond and hydrogen bond S⋯O/Cl/H formed between SHX and HOCl.

    Science.gov (United States)

    Fang, Yi; Li, An Yong; Ma, Fei Yan

    2015-03-01

    Ab initio quantum chemistry methods were used to analyze the noncovalent interactions between HOCl and SHX (X = F, CN, NC, Cl, Br, NO2, CCH, CH3, H). Three energetic minimal configurations were characterized for each case, where the S center acts as a Lewis acid interacting with O to form a chalcogen bond, as well as a Lewis base interacting with Cl or H of HOCl to form halogen bond and hydrogen bond, respectively. An electronegative substituent such as F, CN, NC and NO2 tends to form a stronger chalcogen bond, while an electropositive substituent such as CCH, CH3 and H is inclined to form a more stable H-bonded complex. The chalcogen-bonded, halogen-bonded and H-bonded complexes are stabilized by charge transfers from Lp(O) to σ*(SX), from Lp(S) to σ*(ClO), and from Lp(S) to σ*(HO), respectively. As a result, the SHX unit becomes positively charged in halogen-bonded and hydrogen-bonded complexes but negatively charged in chalcogen-bonded complexes. Theory of atoms in molecules, natural bond orbital analysis, molecular electrostatic potential and localized molecular orbital energy decomposition analysis were applied to investigate these noncovalent bonds.

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

    Science.gov (United States)

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

    2016-10-14

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

  12. Orbital velocity

    OpenAIRE

    Modestino, Giuseppina

    2016-01-01

    The trajectory and the orbital velocity are determined for an object moving in a gravitational system, in terms of fundamental and independent variables. In particular, considering a path on equipotential line, the elliptical orbit is naturally traced, verifying evidently the keplerian laws. The case of the planets of the solar system is presented.

  13. Analysis of the half-projected Hartree--Fock function: density matrix, natural orbitals, and configuration interaction equivalence

    Energy Technology Data Exchange (ETDEWEB)

    Smeyers, Y.G.; Delgado-Barrio, G.

    1976-05-01

    The half-projected Hartree--Fock function for singlet states (HPHF) is analyzed in terms of natural electronic configurations. For this purpose the HPHF spinless density matrix and its natural orbitals are first deduced. It is found that the HPHF function does not contain any contribution from odd-times excited configurations. It is seen in addition, in the case of the singlet ground states, this function is approximately equivalent to two closed-shell configurations, although the nature of the excited one depends on the nuclear geometry. An example is given in the case of the LiH ground state. Finally, the application of this model for studying systems of more than two atoms is criticized.

  14. Involvement of 5f-orbitals in the bonding and reactivity of organoactinide compounds: thorium(IV) and uranium(IV) bis (hydrazonato) complexes

    Energy Technology Data Exchange (ETDEWEB)

    Cantat, Thibault [Los Alamos National Laboratory; Graves, Christopher R [Los Alamos National Laboratory; Morris, David E [Los Alamos National Laboratory; Kiplinger, Jaqueline L [Los Alamos National Laboratory

    2008-01-01

    Migratory insertion of diphenyldiazomethane into both metal-carbon bonds of the bis(alkyl) and bis(aryl) complexes (C5Me5)2AnR2 yields the first f-element bis(hydrazonato) complexes (C5Me5)2An[2-(N,N')-R-N-NCPh2]2 [An = Th, R = CH3 (18), PhCH2 (15), Ph (16); An = U, R = CH3 (17), PhCH2 (14)], which have been characterized by a combination of spectroscopy, electrochemistry, and X-ray crystallography. The two hydrazonato ligands adopt an 2-coordination mode leading to 20-electron (for Th) and 22-electron (for U) complexes that have no transition-metal analogues. In fact, reaction of (C5H5)2Zr(CH3)2 or (C5Me5)2Hf(CH3)2 with diphenyldiazomethane is limited to the formation of the corresponding mono(hydrazonato) complex (C5R5)2M[2-(N,N')-CH3-N-NCPh2](CH3) (M = Zr, R = H or M = Hf, R = CH3). The difference in the reactivities of the group 4 metal complexes and the actinides was used as a unique platform for investigating in depth the role of 5f orbitals on the reactivity and bonding in actinide organometallic complexes. The electronic structure of the (C5H5)2M[2-(N,N')-CH3-N-NCH2]2 (M = Zr, Th, U) model complexes was studied using density functional theory (DFT) calculations and compared to experimental structural, electrochemical, and spectroscopic results. Whereas transition-metal bis(cyclopentadienyl) complexes are known to stabilize three ligands in the metallocene girdle to form saturated (C5H5)2ML3 species, in a bis(hydrazonato) system, a fourth ligand is coordinated to the metal center to give (C5H5)2ML4. DFT calculations have shown that 5f orbitals in the actinide complexes play a crucial role in stabilizing this fourth ligand by stabilizing both the s and p electrons of the two 2-coordinated hydrazonato ligands. In contrast, the stabilization of the hydrazonato ligands was found to be significantly less effective for the putative bis(hydrazonato) zirconium(IV) complex, yielding a higher energy structure. However, the difference in the reactivities

  15. A theoretical perspective of the nature of hydrogen-bond types - the atoms in molecules approach

    Czech Academy of Sciences Publication Activity Database

    Pandiyan, B. V.; Kolandaivel, P.; Deepa, Palanisamy

    2014-01-01

    Roč. 112, č. 12 (2014), s. 1609-1623 ISSN 0026-8976 Institutional support: RVO:61388963 Keywords : hydrogen bond * proton affinity * deprotanation enthalpy * atoms in molecules * chemical shift Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.720, year: 2014

  16. C2H4 adsorption on Cu(210), revisited: bonding nature and coverage effects.

    Science.gov (United States)

    Amino, Shuichi; Arguelles, Elvis; Agerico Diño, Wilson; Okada, Michio; Kasai, Hideaki

    2016-08-24

    With the aid of density functional theory (DFT)-based calculations, we investigate the adsorption of C2H4 on Cu(210). We found two C2H4 adsorption sites, viz., the top of the step-edge atom (S) and the long bridge between two step-edge atoms (SS) of Cu(210). The step-edge atoms on Cu(210) block the otherwise active terrace sites found on copper surfaces with longer step sizes. This results in the preference for π-bonded over di-σ-bonded C2H4. We also found two stable C2H4 adsorption orientations on the S- and SS-sites, viz., with the C2H4 C[double bond, length as m-dash]C bond parallel (fit) and perpendicular (cross) to [001]. Furthermore, we found that the three peaks observed in previous temperature programmed desorption (TPD) experiment [Surf. Sci., 2011, 605, 934-940] could be attributed to C2H4 in the S-fit or S-cross, S-fit and S-cross-fit (S-cross and S-fit configurations that both exist in the same unit cell) configurations on Cu(210).

  17. Covalent and ionic nature of the dative bond and account of accurate ammonia borane binding enthalpies.

    Science.gov (United States)

    Plumley, Joshua A; Evanseck, Jeffrey D

    2007-12-27

    The inherent difficulty in modeling the energetic character of the B-N dative bond has been investigated utilizing density functional theory and ab initio methods. The underlying influence of basis set size and functions, thermal corrections, and basis set superposition error (BSSE) on the predicted binding enthalpy of ammonia borane (H3B-NH3) and four methyl-substituted ammonia trimethylboranes ((CH3)3B-N(CH3)nH3-n; n = 0-3) has been evaluated and compared with experiment. HF, B3LYP, MPW1K, MP2, QCISD, and QCISD(T) have been utilized with a wide range of Pople and correlation-consistent basis sets, totaling 336 levels of theory. MPW1K, B3LYP, and HF result in less BSSE and converge to binding enthalpies with fewer basis functions than post-SCF techniques; however, the methods fail to model experimental binding enthalpies and trends accurately, producing mean absolute deviations (MADs) of 5.1, 10.8, and 16.3 kcal/mol, respectively. Despite slow convergence, MP2, QCISD, and QCISD(T) using the 6-311++G(3df,2p) basis set reproduce the experimental binding enthalpy trend and result in lower MADs of 2.2, 2.6, and 0.5 kcal/mol, respectively, when corrected for BSSE and a residual convergence error of ca. 1.3-1.6 kcal/mol. Accuracy of the predicted binding enthalpy is linked to correct determination of the bond's dative character given by charge-transfer frustration, QCTF = -(Delta QN + Delta QB). Frustration gauges the incompleteness of charge transfer between the donor and the acceptor. The binding enthalpy across ammonia borane and methylated complexes is correlated to its dative character (R2 = 0.91), where a more dative bond (less charge-transfer frustration) results in a weaker binding enthalpy. However, a balance of electronic and steric factors must be considered to explain trends in experimentally reported binding enthalpies. Dative bond descriptors, such as bond ionicity and covalency are important in the accurate characterization of the dative bond. The B

  18. Electron transfer in pnicogen bonds.

    Science.gov (United States)

    Guan, Liangyu; Mo, Yirong

    2014-10-02

    As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines X(n)PH(3-n) complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n → σ*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO2 and CN, i.e., n → dπ*, which results from the interaction between the π orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of σ-hole in pnicogen bonds.

  19. Asymmetric bifurcated halogen bonds.

    Science.gov (United States)

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

    2015-03-07

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

  20. The Bond Between CO and Cp?3U in Cp?3U(CO) involves Backbondingfrom the Cp'3U Ligand-based Orbitals of ?pi-Symmetry, where Cp' Represents a Substituted Cyclopentadienyl Ligand.

    Energy Technology Data Exchange (ETDEWEB)

    Maron, Laurent; Eisenstein, Odile; Andersen, Richard

    2009-06-16

    The experimental CO stretching frequencies in the 1:1 adducts between (C5H5-nRn)3U and CO range from 1976 cm-1 in (C5H4SiMe3)3U(CO) to 1900 cm-1 in (C5HMe4)3U(CO). The origin of the large difference between the stretching frequencies in free (2143 cm-1) and coordinated CO and the large effect the substituents on the cyclopentadienyl ligands play in the difference is explored by DFT calculations with a small core effective core potential in which 32 electrons on uranium are explicitly treated. The results of these calculations, along with a NBO analysis, show that a sigma-bond is formed between CO and an empty sigma-orbital on the Cp'3U fragment composed of f sigma and d sigma parentage orbitals. The backbonding interaction, which results in lowering the CO stretching frequency, does not originate from non-bonding metal-based orbitals but from the filled ligand-based orbitals of pi-symmetry that are used for bonding in the Cp'3U fragment. This model, which is different from the backbonding model used in the d-transition metal complexes, rationalizes the large substituent effect in the 5f-metal complexes.

  1. C–C Bond formation catalyzed by natural gelatin and collagen proteins

    Directory of Open Access Journals (Sweden)

    Dennis Kühbeck

    2013-06-01

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

  2. Quasiparticle, natural, and mean-field orbitals in drops of liquid helium

    Energy Technology Data Exchange (ETDEWEB)

    Pieper, S.C.

    1987-01-01

    In the last few years we have used the variational Monte Carlo (VMC) technique to find accurate ground-state wave functions for drops of liquid helium containing 8 to 728 /sup 4/He atoms (Bose statistics) or 40 to 240 /sup 3/He atoms (Fermi statistics). The wave functions include both two- and three-particle correlations. From comparisons with GFMC results, we believe these wave functions to be among the most accurate for systems of approximately 100 strongly interacting particles. Having determined the wave functions, we can use them to investigate the properties of the quantum-mechanical ground states of large finite systems. In previous studies we have investigated the accuracy of local-density approximations (LDA) for the pair-correlation function and have studied the structure functions of the drops and their relationships to two-particle correlations. The present report is principally devoted to a recent study of single-particle orbitals in the drops.

  3. The Physical Nature and Orbital Behavior of the Eclipsing System DK Cygni

    Science.gov (United States)

    Lee, Jae Woo; Youn, Jae-Hyuck; Park, Jang-Ho; Wolf, Marek

    2015-06-01

    New CCD photometry is presented for the hot overcontact binary DK Cyg together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light that include 116 new timings and span more than 87 years, a period study reveals that the orbital period has varied due to a periodic oscillation superimposed on an upward parabola. The period and semi-amplitude of the modulation are about 78.1 years and 0.0037 days, respectively. This detail is interpreted as a light-travel-time effect due to a circumbinary companion with a minimum mass of M3 = 0.065 M⊙, within the theoretical limit of ˜0.07 M⊙ for a brown dwarf star. The observed period increase at a fractional rate of +2.74 × 10-10 is in excellent agreement with that calculated from our W-D synthesis. Mass transfer from the secondary to the primary component is mainly responsible for the secular period change. We examined the evolutionary status of the DK Cyg system from the absolute dimensions.

  4. Molecular Orbitals and the Atomistics of Fracture.

    Science.gov (United States)

    1982-02-10

    dominantly a N-N bonding orbital the N-Fe interaction is non- bonding. The b2 orbital in the Fe4 cluster is d-d w-bonding between nearest neig ;hbo and...distance. This is the distance which is realized when there is no electron density in a N-3 antibonding orbital. In this cluster son of the electron

  5. SparseMaps--A systematic infrastructure for reduced-scaling electronic structure methods. III. Linear-scaling multireference domain-based pair natural orbital N-electron valence perturbation theory.

    Science.gov (United States)

    Guo, Yang; Sivalingam, Kantharuban; Valeev, Edward F; Neese, Frank

    2016-03-07

    Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still two important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling "partially contracted" NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient "electron pair prescreening" that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed comparison

  6. Type of continuing bonds expression and its comforting versus distressing nature: implications for adjustment among bereaved mothers.

    Science.gov (United States)

    Field, Nigel P; Packman, Wendy; Ronen, Rama; Pries, Angeliki; Davies, Betty; Kramer, Robyn

    2013-01-01

    This study investigated type of continuing bonds (CB) expression and its comforting versus distressing nature in relation to psychosocial adjustment among bereaved mothers. Twenty-eight mothers whose child had died within the previous five years participated in a CB interview in which they rated the extent they used each of 11 different types of CB expression during the past month and the degree to which they experienced each of the CB expressions as comforting and distressing. CB expressions involving illusions and hallucinations of the deceased child were predictive of greater distress whereas those involving belief that the deceased child was aware of the mother or communicating with her through dreams were not associated with symptoms, but instead linked to greater spirituality. Furthermore, mothers who reported CB as more comforting than distressing had lower symptom ratings. The implications of the findings for the attachment theory perspective on unresolved loss are discussed.

  7. Environment-friendly adhesives for surface bonding of wood-based flooring using natural tannin to reduce formaldehyde and TVOC emission.

    Science.gov (United States)

    Kim, Sumin

    2009-01-01

    The objective of this research was to develop environment-friendly adhesives for face fancy veneer bonding of engineered flooring using the natural tannin form bark in the wood. The natural wattle tannin adhesive were used to replace UF resin in the formaldehyde-based resin system in order to reduce formaldehyde and volatile organic compound (VOC) emissions from the adhesives used between plywoods and fancy veneers. PVAc was added to the natural tannin adhesive to increase viscosity of tannin adhesive for surface bonding. For tannin/PVAc hybrid adhesives, 5%, 10%, 20% and 30% of PVAc to the natural tannin adhesives were added. tannin/PVAc hybrid adhesives showed better bonding than the commercial natural tannin adhesive with a higher level of wood penetration. The initial adhesion strength was sufficient to be maintained within the optimum initial tack range. The standard formaldehyde emission test (desiccator method), field and laboratory emission cell (FLEC) and VOC analyzer were used to determine the formaldehyde and VOC emissions from engineered flooring bonded with commercial the natural tannin adhesive and tannin/PVAc hybrid adhesives. By desiccator method and FLEC, the formaldehyde emission level of each adhesive showed the similar tendency. All adhesives satisfied the E(1) grade (below 1.5 mg/L) and E(0) grade (below 0.5 mg/L) with UV coating. VOC emission results by FLEC and VOC analyzer were different with the formaldehyde emission results. TVOC emission was slightly increased as adding PVAc.

  8. The Bonding Situation in Metalated Ylides.

    Science.gov (United States)

    Scharf, Lennart T; Andrada, Diego M; Frenking, Gernot; Gessner, Viktoria H

    2017-03-28

    Quantum chemical calculations have been carried out to study the electronic structure of metalated ylides particularly in comparison to their neutral analogues, the bisylides. A series of compounds of the general composition Ph3 P-C-L with L being either a neutral or an anionic ligand were analyzed and the impact of the nature of the substituent L and the total charge on the electronics and bonding situation was studied. The charge at the carbon atom as well as the dissociation energies, bond lengths, and Wiberg bond indices strongly depend on the nature of L. Here, not only the charge of the ligand but also the position of the charge within the ligand backbone plays an important role. Independent of the substitution pattern, the NBO analysis reveals the preference of unsymmetrical bonding situations (P=C-L or P-C=L) for almost all compounds. However, Lewis structures with two lone-pair orbitals at the central carbon atom are equally valid for the description of the bonding situation. This is confirmed by the pronounced lone-pair character of the frontier orbitals. Energy decomposition analysis mostly reveals the preference of several bonding situations, mostly with dative and ylidic electron-sharing bonds (e.g., P→C- -L). In general, the anionic systems show a higher preference of the ylidic bonding situations compared to the neutral analogues. However, in most of the cases different resonance structures have to be considered for the description of the "real" bonding situation. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  9. An LDEF 2 dust instrument for discrimination between orbital debris and natural particles in near-Earth space

    Science.gov (United States)

    Tuzzolino, A. J.; Simpson, J. A.; Mckibben, R. B.; Voss, H. D.; Gursky, H.

    1993-01-01

    The characteristics of a space dust instrument which would be ideally suited to carry out near-Earth dust measurements on a possible Long Duraction Exposure Facility reflight mission (LDEF 2) is discussed. As a model for the trajectory portion of the instrument proposed for LDEF 2, the characteristics of a SPAce DUSt instrument (SPADUS) currently under development for flight on the USA ARGOS mission to measure the flux, mass, velocity, and trajectory of near-Earth dust is summarized. Since natural (cosmic) dust and man-made dust particles (orbital debris) have different velocity and trajectory distributions, they are distinguished by means of the SPADUS velocity/trajectory information. The SPADUS measurements will cover the dust mass range approximately 5 x 10(exp -12) g (2 microns diameter) to approximately 1 x 10(exp -5) g (200 microns diameter), with an expected mean error in particle trajectory of approximately 7 deg (isotropic flux). Arrays of capture cell devices positioned behind the trajectory instrumentation would provide for Earth-based chemical and isotopic analysis of captured dust. The SPADUS measurement principles, characteristics, its role in the ARGOS mission, and its application to an LDEF 2 mission are summarized.

  10. The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: Implications for the enzyme mechanism‡

    OpenAIRE

    Ogura, Hiroshi; Evans, John P.; Peng, Dungeng; Satterlee, James D.; de Montellano, Paul R. Ortiz; Mar, Gerd N. La

    2009-01-01

    The active site electronic structure of the azide complex of substrate-bound human heme oxygenase-1, (hHO) has been investigated by 1H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. 2D 1H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts, that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in the cya...

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

    Science.gov (United States)

    Karacop, Ataman; Doymus, Kemal

    2013-04-01

    The aim of this study was to determine the effect of jigsaw cooperative learning and computer animation techniques on academic achievements of first year university students attending classes in which the unit of chemical bonding is taught within the general chemistry course and these students' learning of the particulate nature of matter of this unit. The sample of this study consisted of 115 first-year science education students who attended the classes in which the unit of chemical bonding was taught in a university faculty of education during the 2009-2010 academic year. The data collection instruments used were the Test of Scientific Reasoning, the Purdue Spatial Visualization Test: Rotations, the Chemical Bonding Academic Achievement Test, and the Particulate Nature of Matter Test in Chemical Bonding (CbPNMT). The study was carried out in three different groups. One of the groups was randomly assigned to the jigsaw group, the second was assigned to the animation group (AG), and the third was assigned to the control group, in which the traditional teaching method was applied. The data obtained with the instruments were evaluated using descriptive statistics, one-way ANOVA, and MANCOVA. The results indicate that the teaching of chemical bonding via the animation and jigsaw techniques was more effective than the traditional teaching method in increasing academic achievement. In addition, according to findings from the CbPNMT, the students from the AG were more successful in terms of correct understanding of the particulate nature of matter.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Karacop, Ataman; Doymus, Kemal

    2013-01-01

    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…

  14. Sigma-hole carbon-bonding interactions in carbon-carbon double bonds: an unnoticed contact.

    Science.gov (United States)

    Quiñonero, D

    2017-06-14

    In this manuscript, we combine high-level ab initio calculations on some small complexes and a CSD survey to analyze the existence of unprecedented noncovalent carbon bonds in X2C[double bond, length as m-dash]CH2Y systems (Y = electron-rich atom or group). The methylene group is usually seen as a weak hydrogen bond donor when interacting with an electron-rich atom. However, we demonstrate that when the electron-rich atom is located equidistant from the two H atoms and along the C[double bond, length as m-dash]C bond a σ-hole noncovalent carbon-bonding interaction is established, instead of a bifurcated hydrogen bond, as derived from Atoms-in-Molecules (AIM) and Natural bond orbital (NBO) analyses. The physical nature of the interaction has been analyzed using the Symmetry Adapted Perturbation Theory (SAPT) method. The results indicate that electrostatics is very important followed by either the induction or dispersion terms in anionic and neutral complexes, respectively. In addition the CSD analysis reveals the existence of such interactions, giving reliability to our calculations, which are much more numerous for neutral than for anionic Y systems.

  15. Neutron Crystallography, Molecular Dynamics, and Quantum Mechanics Studies of the Nature of Hydrogen Bonding in Cellulose I beta

    Science.gov (United States)

    In the crystal structure of cellulose Ibeta, disordered hydrogen (H) bonding can be represented by the average of two mutually exclusive H bonding schemes that have been designated A and B. An unanswered question is whether A and B interconvert dynamically, or whether they are static but present in ...

  16. Assessment of Orbital-Optimized MP2.5 for Thermochemistry and Kinetics: Dramatic Failures of Standard Perturbation Theory Approaches for Aromatic Bond Dissociation Energies and Barrier Heights of Radical Reactions.

    Science.gov (United States)

    Soydaş, Emine; Bozkaya, Uğur

    2015-04-14

    An assessment of orbital-optimized MP2.5 (OMP2.5) [ Bozkaya, U.; Sherrill, C. D. J. Chem. Phys. 2014, 141, 204105 ] for thermochemistry and kinetics is presented. The OMP2.5 method is applied to closed- and open-shell reaction energies, barrier heights, and aromatic bond dissociation energies. The performance of OMP2.5 is compared with that of the MP2, OMP2, MP2.5, MP3, OMP3, CCSD, and CCSD(T) methods. For most of the test sets, the OMP2.5 method performs better than MP2.5 and CCSD, and provides accurate results. For barrier heights of radical reactions and aromatic bond dissociation energies OMP2.5-MP2.5, OMP2-MP2, and OMP3-MP3 differences become obvious. Especially, for aromatic bond dissociation energies, standard perturbation theory (MP) approaches dramatically fail, providing mean absolute errors (MAEs) of 22.5 (MP2), 17.7 (MP2.5), and 12.8 (MP3) kcal mol(-1), while the MAE values of the orbital-optimized counterparts are 2.7, 2.4, and 2.4 kcal mol(-1), respectively. Hence, there are 5-8-folds reductions in errors when optimized orbitals are employed. Our results demonstrate that standard MP approaches dramatically fail when the reference wave function suffers from the spin-contamination problem. On the other hand, the OMP2.5 method can reduce spin-contamination in the unrestricted Hartree-Fock (UHF) initial guess orbitals. For overall evaluation, we conclude that the OMP2.5 method is very helpful not only for challenging open-shell systems and transition-states but also for closed-shell molecules. Hence, one may prefer OMP2.5 over MP2.5 and CCSD as an O(N(6)) method, where N is the number of basis functions, for thermochemistry and kinetics. The cost of the OMP2.5 method is comparable with that of CCSD for energy computations. However, for analytic gradient computations, the OMP2.5 method is only half as expensive as CCSD.

  17. Physical nature of interactions in Zn(II) complexes with 2,2'-bipyridyl: quantum theory of atoms in molecules (QTAIM), interacting quantum atoms (IQA), noncovalent interactions (NCI), and extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) comparative studies.

    Science.gov (United States)

    Cukrowski, Ignacy; de Lange, Jurgens H; Mitoraj, Mariusz

    2014-01-23

    In the present account factors determining the stability of ZnL, ZnL2, and ZnL3 complexes (L = bpy, 2,2′-bipyridyl) were characterized on the basis of various techniques: the quantum theory of atoms in molecules (QTAIM), energy decomposition schemes based on interacting quantum atoms (IQA), and extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV). Finally, the noncovalent interactions (NCI) index was also applied. All methods consistently indicated that the strength of the coordination bonds, Zn–O and Zn–N, decreases from ZnL to ZnL3. Importantly, it has been identified that the strength of secondary intramolecular heteropolar hydrogen bonding interactions, CH···O and CH···N, increases when going from ZnL to ZnL3. A similar trend appeared to be valid for the π-bonding as well as electrostatic stabilization. In addition to the above leading bonding contributions, all techniques suggested the existence of very subtle, but non-negligible additional stabilization from the CH···HC electronic exchange channel; these interactions are the weakest among all considered here. From IQA it was found that the local diatomic interaction energy, Eint(H,H), amounts at HF to −2.5, −2.7, and −2.9 kcal mol(–1) for ZnL, ZnL2, and ZnL3, respectively (−2.1 kcal mol(–1) for ZnL at MP2). NOCV-based deformation density channels showed that formation of CH--HC contacts in Zn complexes causes significant polarization of σ(C–H) bonds, which accordingly leads to charge accumulation in the CH···HC bay region. Charge depletion from σ(C–H) bonds was also reflected in the calculated spin–spin (1)J(C–H) coupling constants, which decrease from 177.06 Hz (ZnL) to 173.87 Hz (ZnL3). This last result supports our findings of an increase in the local electronic CH···HC stabilization from ZnL to ZnL3 found from QTAIM, IQA, and ETS-NOCV. Finally, this work unites for the first time the results from four methods that are widely

  18. Complete active space configuration interaction from state-averaged configuration interaction singles natural orbitals: Analytic first derivatives and derivative coupling vectors.

    Science.gov (United States)

    Fales, B Scott; Shu, Yinan; Levine, Benjamin G; Hohenstein, Edward G

    2017-09-07

    A new complete active space configuration interaction (CASCI) method was recently introduced that uses state-averaged natural orbitals from the configuration interaction singles method (configuration interaction singles natural orbital CASCI, CISNO-CASCI). This method has been shown to perform as well or better than state-averaged complete active space self-consistent field for a variety of systems. However, further development and testing of this method have been limited by the lack of available analytic first derivatives of the CISNO-CASCI energy as well as the derivative coupling between electronic states. In the present work, we present a Lagrangian-based formulation of these derivatives as well as a highly efficient implementation of the resulting equations accelerated with graphical processing units. We demonstrate that the CISNO-CASCI method is practical for dynamical simulations of photochemical processes in molecular systems containing hundreds of atoms.

  19. The nature of hydrogen-bonding interactions in nonsteroidal anti-inflammatory drugs revealed by polarized IR spectroscopy

    Science.gov (United States)

    Hachuła, Barbara

    2018-01-01

    The influence of hydrogen-bonding interactions in the solid phase on the IR spectroscopic pattern of the νOsbnd H band of nonsteroidal anti-inflammatory drugs (NSAIDs) was studied experimentally by IR spectroscopy with the use of polarized light at two temperatures (293 K and 77 K) and in isotopic dilution. The neat and deuterated crystals of (S)-naproxen ((S)-NPX), (R)-flurbiprofen ((R)-FBP), (RS)-flurbiprofen ((RS)-FBP) and (RS)-ketoprofen ((RS)-KTP) were obtained by melt crystallization between the two squeezed CaF2 plates. The vibrational spectra of selected α-aryl propionic acid derivatives (2APAs) reflected the characteristics of their hydrogen-bond networks, i.e., 2APAs were characterized by the chain ((S)-NPX, (R)-FBP) and by dimeric ((RS)-FBP, (RS)-KTP) arrangement of hydrogen bonds in the crystal lattice. Spectroscopic results showed that the interchain (through-space) exciton coupling, between two laterally-spaced hydrogen bonds, dominates in the crystals of four NSAIDs. The same exciton coupled hydrogen bonds were also responsible for the H/D isotopic recognition mechanism in the crystalline spectra of deuterated 2APAs. The presented spectral results may help to predict the hydrogen bond motifs in the crystalline NSAIDs, which structures are not yet known, based on their IR spectra of hydrogen bond in the crystals.

  20. "Pnicogen bonds" or "chalcogen bonds": exploiting the effect of substitution on the formation of PSe noncovalent bonds.

    Science.gov (United States)

    Shukla, Rahul; Chopra, Deepak

    2016-05-18

    In this article, we have analyzed the nature and characteristics of PSe noncovalent interactions by studying the effect of substitution on XH2PSeH2, H3PSeHX and XH2PSeHX (X= -H, -F, -CH3, -CF3, -Cl, -OH, -OCH3, -NH2, -NHCH3, and -CN) as our systems of interest at MP2/aug-cc-pVDZ level of theory. Binding energy calculations depict that binding energy increases in the order XH2PSeH2 bonds. NBO analysis helped in categorizing these interactions into pnicogen and chalcogen bonds, depending on the strength of P(lp) to σ*(Se-X) orbitals or Se(lp) to σ*(P-X) orbitals.

  1. The design of an optical sensor arrangement for the detection of oil contamination in an adhesively bonded structure of a liquefied natural gas (LNG) ship

    Science.gov (United States)

    Kim, Bu Gi; Lee, Dai Gil

    2009-06-01

    Liquefied natural gas (LNG) has been widely used as a substitute fuel for commercial purposes. It is transported mainly by LNG ships which have primary and secondary leakage barriers. The former is composed of welded thin stainless steel or invar plates, while the latter is composed of adhesively bonded glass composite or aluminum foil sheets. The role of the secondary barrier is to maintain fluid tightness when the primary barrier fails during the transport of LNG. The tightness of the secondary barrier is dependent on the wetting characteristics between the adhesive and adherend of the bonded structure during bonding operation, which depends much on the contamination on the adherend surface. Therefore, in this work, an optical measuring device of oil contamination on the aluminum surface for the secondary barrier was developed. A transparent oil was used as the contaminant and its effect on the bonding strength was investigated. From the experiments, it has been found that the developed measuring device for oil contamination can be used to detect oil contamination on a large bonding area of the secondary barrier in ship building yards.

  2. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

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

  3. Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

    Science.gov (United States)

    Chang, Xin; Zhang, Yang; Weng, Xinzhen; Su, Peifeng; Wu, Wei; Mo, Yirong

    2016-05-05

    Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes.

  4. Marked influence of the nature of chemical bond on CP-violating signature in molecular ions $\\mathrm{HBr}^{+}$ and $\\mathrm{HI}^{+}$

    CERN Document Server

    Ravaine, B; Derevianko, A; Ravaine, Boris; Porsev, Sergey G.; Derevianko, Andrei

    2004-01-01

    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 $\\mathrm{HBr}^{+}$ and $\\mathrm{HI}^{+}$ 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 fifteen. 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 $\\mathrm{HBr}^{+}$ exhibits predominantly covalent nature in $\\mathrm{HI}^{+}$. We conclude that because of this enhancement the HI$^+$ ion may be a potentially competitive candidate for the EDM search.

  5. Molecular Orbital and Density Functional Study of the Formation, Charge Transfer, Bonding and the Conformational Isomerism of the Boron Trifluoride (BF3 and Ammonia (NH3 Donor-Acceptor Complex

    Directory of Open Access Journals (Sweden)

    Dulal C. Ghosh

    2004-09-01

    Full Text Available The formation of the F3B–NH3 supermolecule by chemical interaction of its fragment parts, BF3 and NH3, and the dynamics of internal rotation about the ‘B–N’ bond have been studied in terms of parameters provided by the molecular orbital and density functional theories. It is found that the pairs of frontier orbitals of the interacting fragments have matching symmetry and are involved in the charge transfer interaction. The donation process stems from the HOMO of the donor into the LUMO of the acceptor and simultaneously, back donation stems from the HOMO of acceptor into the LUMO of the donor. The density functional computation of chemical activation in the donor and acceptor fragments, associated with the physical process of structural reorganization just prior to the event of chemical reaction, indicates that BF3 becomes more acidic and NH3 becomes more basic, compared to their separate equilibrium states. Theoretically it is observed that the chemical reaction event of the formation of the supermolecule from its fragment parts is in accordance with the chemical potential equalization principle of the density functional theory and the electronegativity equalization principle of Sanderson. The energetics of the chemical reaction, the magnitude of the net charge transfer and the energy of the newly formed bond are quite consistent, both internally and with the principle of maximum hardness, PMH. The dynamics of the internal rotation of one part with respect to the other part of the supermolecule about the ‘B–N’ bond mimics the pattern of the conformational isomerism of the isostructural ethane molecule. It is also observed that the dynamics and evolution of molecular conformations as a function of dihedral angles is also in accordance with the principle of maximum hardness, PMH. Quite consistent with spectroscopic predictions, the height of the molecule

  6. Crystal chemical study of a series of rare earth fluorinated compounds with formula LiNaLn/sub 2/F/sub 8/ and evidence for the participation of 4 f orbitals in bonding

    Energy Technology Data Exchange (ETDEWEB)

    Zambon, D.; Metin, J.; Picaud, B.; Avignant, D.

    1985-11-28

    A number of rare earth fluorides with formula LiNaLn/sub 2/F/sub 8/ (Ln=Ho, Er, Tm, Yb, Lu) have been synthesized. Their crystal chemical characteristics have been determined by analogy with the isostructural fluoride LiNaY/sub 2/F/sub 8/ which crystallizes in the monoclinic system with P2/sub 1//m space group and unit cell parameters: a=6.622 A, b=6.995 A, c=6.632 A and ..beta..=103/sup 0/14. The position of yttrium in comparison with the lanthanides family has been determined from the variation of the unit cell volume in the series. These results indicate that a certain degree of covalency due to the participation of 4f orbitals to bonding is present in these compounds with predominant ionic character.

  7. Pair natural orbital and canonical coupled cluster reaction enthalpies involving light to heavy alkali and alkaline earth metals: the importance of sub-valence correlation

    KAUST Repository

    Minenkov, Yury

    2017-03-07

    In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange and association/dissociation reaction enthalpies involving ionic complexes of Li, Be, Na, Mg, Ca, Sr, Ba and Pb(ii). Two strategies were investigated: in the former, only valence electrons were included in the correlation treatment, giving rise to the computationally very efficient FC (frozen core) approach; in the latter, all non-ECP electrons were included in the correlation treatment, giving rise to the AE (all electron) approach. Apart from reactions involving Li and Be, the FC approach resulted in non-homogeneous performance. The FC approach leads to very small errors (<2 kcal mol-1) for some reactions of Na, Mg, Ca, Sr, Ba and Pb, while for a few reactions of Ca and Ba deviations up to 40 kcal mol-1 have been obtained. Large errors are both due to artificial mixing of the core (sub-valence) orbitals of metals and the valence orbitals of oxygen and halogens in the molecular orbitals treated as core, and due to neglecting core-core and core-valence correlation effects. These large errors are reduced to a few kcal mol-1 if the AE approach is used or the sub-valence orbitals of metals are included in the correlation treatment. On the technical side, the CCSD(T) and DLPNO-CCSD(T) results differ by a fraction of kcal mol-1, indicating the latter method as the perfect choice when the CPU efficiency is essential. For completely black-box applications, as requested in catalysis or thermochemical calculations, we recommend the DLPNO-CCSD(T) method with all electrons that are not covered by effective core potentials included in the correlation treatment and correlation-consistent polarized core valence basis sets of cc-pwCVQZ(-PP) quality.

  8. Nature of non-nuclear (3, -3) π-attractor and π-bonding: Theoretical analysis on π-electron density

    Science.gov (United States)

    Lv, Jiao; Yang, Lihua; Sun, Zheng; Meng, Lingpeng; Li, Xiaoyan

    2018-01-01

    Understanding the nature of π-electron density is important to characterize the conjugate π molecular systems. In this work, the π-electron densities of some typical conjugated π molecular systems were separated from their total electron densities; the positions and natures of non-nuclear (3, -3) π-attractors and the π-bond critical points (π-BCPs) are investigated. The calculated results show that for the same element, the position of the π-attractor is constant, regardless of the chemical surroundings. The position of the π-BCP is closer to the atom with the larger electronegativity.

  9. Aufbau derived from a unified treatment of occupation numbers in Hartree-Fock, Kohn-Sham and Natural Orbital theories with the Karush-Kuhn-Tucker conditions for the inequality constraints ni≤1 and ni≥0

    NARCIS (Netherlands)

    Giesbertz, K.J.H.; Baerends, E.J.

    2010-01-01

    In the major independent particle models of electronic structure theory-Hartree-Fock, Kohn-Sham (KS), and natural orbital (NO) theories-occupations are constrained to 0 and 1 or to the interval [0,1]. We carry out a constrained optimization of the orbitals and occupation numbers with application of

  10. Electronic states and nature of bonding of the molecule NiGe by all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations and mass spectrometric equilibrium experiments

    DEFF Research Database (Denmark)

    Shim, Irene; Kingcade, Joseph E.; Gingerich, Karl A.

    1988-01-01

    All electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations have been applied to investigate the low-lying electronic states of the NiGe molecule. The ground state of the NiGe molecule is predicted to be 1Sigma+. The chemical bond in the 1Sigma+ ground state is a double...... bond composed of one sigma and one pi bond. The sigma bond is due to a delocalized molecular orbital formed by combining the Ni 4s and the Ge 4psigma orbitals. The pi bond is a partly delocalized valence bond, originating from the coupling of the 3dpi hole on Ni with the 4ppi electron on Ge. The low...... =286.8±10.9 kJ mol−1. The standard heat of formation of the NiGe molecule has been obtained as DeltaH [open circle] f,298 =514±12 kJ mol−1. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  11. The effects of endodontic substances and naturally reducing agents on the bond strength of epoxy resin-based sealer to root dentin

    Science.gov (United States)

    Cecchin, Doglas; Farina, Ana Paula; Bedran-Russo, Ana Karina

    2017-01-01

    Aim: To evaluate the effects of sodium hypochlorite (NaOCl), chlorhexidine (CHX), and two naturally derived reducing agents on the bond strength of epoxy resin-based sealer to root dentin. Materials and Methods: A total of 60 single-rooted human teeth were prepared using ProTaper (Dentsply Tulsa Dental Specialties, Johnson City, TN, USA) and an irrigation protocol including 5% NaOCl or 2% CHX gel, and ethylenediaminetetraacetic acid (EDTA), for smear layer removal. The following subgroups (n = 10) were also assessed according to the naturally derived reducing agent used: no agent (control group); grape seed extract (GSE); and green tea. Root canals were filled with gutta-percha and AH Plus (Dentsply DeTrey, Konstanz, Germany). Bond strength was measured using the push-out test, and statistical analyses were performed using ANOVA; failure patterns (modes) were classified as adhesive, cohesive, or mixed. The types of failure modes were evaluated using the Chi-squared test at α =0.05. Results: The irrigation protocols demonstrated similar bond strength values (P > 0.05). However, the Chi-squared test revealed significant differences in failure mode among the groups (P sealer to dentin; however, improvement was evident in the adhesion quality of AH Plus to NaOCl-treated root dentin, due to the prevalence of cohesive failure. PMID:29386775

  12. Structural properties and bonding nature of 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, Ali Hussain, E-mail: maalidph@yahoo.com [Institute of Physical Biology-South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Stys, Dalibor [Institute of Physical Biology-South Bohemia University, Nove Hrady 37333 (Czech Republic); Auluck, S. [National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110012 (India); Kityk, I.V. [Electrical Engineering Department, Technological University of Czestochowa, Al.Armii Krajowej 17/19, Czestochowa (Poland); Kamarudin, H. [School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia)

    2011-10-17

    Highlights: {yields} The atomic positions were optimized. {yields} The optimization done by minimization of the forces. {yields} The crystal possess direct gap. - Abstract: The atomic positions of 3-methyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole single crystal taken from the X-ray diffraction data obtained by Liu et al. were optimized by minimization of the forces acting on the atoms using a full potential linear augmented plane wave method within density-functional theory. The local density approximation (LDA) by Ceperley-Alder (CA) exchange-correlation potential was applied. The full potential calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at {Gamma} point of the Brillouin zone resulting in a direct energy gap of 3.4 eV for the original experimental structure and 3.2 eV for the optimized structure. The upper VB is formed mainly by C, H, and N atoms while the lower CB has mainly C and H atoms. We present an analysis of the partial densities of states which gives useful information on hybridization and the orbital character of the states. We have calculated the bond lengths and angles, a good agreement with the experimental data were found. The origin of the chemical bonding and the electronic charge density contour in the (1 0 0) and (1 1 0) planes were analyzed.

  13. Can there be a multi-bond between noble gas and metal? A theoretical study of F2XeMoF2.

    Science.gov (United States)

    Gao, Kunqi; Sheng, Li

    2017-04-05

    A new noble gas compound containing a Xe-Mo double bond, F 2 XeMoF 2 , was theoretically constructed and studied based on DFT and ab initio calculations. The CCSD(T)-calculated Xe-Mo bond length of 2.518 Å was comparable to the standard value of 2.56 Å. The bonding energy (32.3 kcal mol -1 ) was even higher than that of the Xe-Au bond in the well-known XeAuF complex (24.1 kcal mol -1 ). The result of natural bond orbital (NBO) analysis indicates that there is a σ-bond and a π-bond between the Xe and Mo atoms in F 2 XeMoF 2 . The properties of the Xe-Mo double bond were also analyzed with the atoms in molecules (AIM) approach and natural resonance theory (NRT).

  14. A crucial role of fractional occupation numbers of natural orbitals (NOs) in the description of double excitations in response time-dependent NO functional theory

    Science.gov (United States)

    Gritsenko, O. V.

    2017-09-01

    We demonstrate a crucial role of fractional occupation numbers (FONs) of natural orbitals (NOs) in the description of double excitations in time-dependent NO functional theory (TDNOFT). An analytical dependence of the double excitation energy ωα on the ratio of the FONs is derived in a model from the matrix diagonalization problem. In the large ratio Heitler-London limit the derived formula reproduces the correct asymptotics of ωα of the ionic state of double excitation character. In the small ratio Møller-Plesset, MP limit the reverse relation of static MP perturbation theory emerges in the dynamical response theory to provide ωα .

  15. A simultaneous estimation of the mass of Mars and its natural satellites, Phobos and Deimos, from the orbital perturbations on the Mariner 9, Viking 1, and Viking 2 orbiters

    Science.gov (United States)

    Lemoine, F. G.; Smith, D. E.; Fricke, S. K.; Mccarthy, J. J.

    1993-01-01

    The natural satellites of Mars, Phobos and Deimos, caused perturbations on the orbits of the Mariner 9, and the Viking spacecraft that were used to estimate the satellite masses. The Viking spacecraft were specifically targeted to make close flybys (within a few hundred kilometers) of Phobos in February 1977 and of Deimos in October 1977. These close encounters were used to estimate the moon's gravitational constant, GM (the universal constant of gravitation multiplied by the satellite mass). However, the Viking and Mariner 9 spacecraft made numerous flybys of Phobos and Deimos at distances of a few thousand kilometers. The tracking data from these more 'distant' encounters were processed to estimate the masses of Mars, Phobos, and Deimos.

  16. Are One-Electron Bonds Any Different from Standard Two-Electron Covalent Bonds?

    Science.gov (United States)

    Sousa, David Wilian Oliveira de; Nascimento, Marco Antonio Chaer

    2017-09-19

    The nature of the chemical bond is perhaps the central subject in theoretical chemistry. Our understanding of the behavior of molecules developed amazingly in the last century, mostly with the rise of quantum mechanics (QM) and QM-based theories such as valence bond theory and molecular orbital theory. Such theories are very successful in describing molecular properties, but they are not able to explain the origin of the chemical bond. This problem was first analyzed in the 1960s by Ruedenberg, who showed that covalent bonds are the direct result of quantum interference between one-electron states. The generality of this result and its quantification were made possible through the recent development of the generalized product function energy partitioning (GPF-EP) method by our group, which allows the partitioning of the electronic density and energy into their interference and quasi-classical (noninterference) contributions. Furthermore, with GPF wave functions these effects can be analyzed separately for each bond of a molecule. This interference energy analysis has been applied to a large variety of molecules, including diatomics and polyatomics, molecules with single, double, and triple bonds, molecules with different degrees of polarity, linear or branched molecules, cyclic or acyclic molecules, conjugated molecules, and aromatics, in order to verify the role played by quantum interference. In all cases the conclusion is exactly the same: for each bond in each of the molecules considered, the main contribution to its stability comes from the interference term. Two-center one-electron (2c1e) bonds are the simplest kind of chemical bonds. Yet they are often viewed as odd or unconventional cases of bonding. Are they any different from conventional (2c2e) bonds? If so, what differences can we expect in the nature of (2c1e) bonds relative to electron-pair bonds? In this Account, we extend the GPF-EP method to describe bonds involving N electrons in M orbitals (N

  17. Molecular structure, vibrational spectroscopic studies and natural ...

    Indian Academy of Sciences (India)

    pp. 845–860. Molecular structure, vibrational spectroscopic studies and natural bond orbital analysis of 7-amino-4-trifluoromethyl coumarin ..... [15] A Frisch, A B Nielsen and A J Holder, GAUSSIANVIEW Users Manual, Gaussian. Inc., Pittsburgh, PA (2000). [16] S Selladurai and K Subramanian, Acta Crystallogr. C48, 281 ...

  18. Molecular structure, vibrational spectroscopic studies and natural ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 74; Issue 5. Molecular structure ... The entropy of the title compound was also performed at HF using the hybrid functional BLYP and B3LYP with 6-31 G(d,p) as basis set levels of theory. Natural bond orbital (NBO) analysis of the title molecule is also carried out.

  19. Ground state isomerism in betacarboline hydrogen bond complexes: The charge transfer nature of its large Stokes shifted emission

    Science.gov (United States)

    Sánchez-Coronilla, Antonio; Balón, Manuel; Muñoz, María A.; Hidalgo, José; Carmona, Carmen

    2008-07-01

    The hydrogen bonding and excited state proton transfer reactions between betacarboline, 9 H-pyrido[3,4- b]indole, BC, and 1,1,1,3,3,3-hexafluoropropan-2-ol, HFIP, have been studied in the aprotic solvents cyclohexane and toluene by absorption, steady state and time resolved fluorescence measurements. On the basis of these results and those of previous works (Refs. [A. Sánchez-Coronilla, C. Carmona, M.A. Muñoz, M. Balón, Chem. Phys., 327 (2006) 70] and [A. Sánchez-Coronilla, M. Balón, M.A. Muñoz, C. Carmona, Chem. Phys. 344 (2008) 72]) two main fundamental conclusions can be drawn on the photophysical behaviour of BC. Thus, it is shown, for the first time, that the non-cyclic double hydrogen bond complexes formed through both nitrogen atoms of BC, DHB, can suffer, in their ground state, an isomerisation process. These adducts acquire a quinoid structure in cyclohexane, but maintain a dipolar zwitterionic structure in toluene. Moreover, it is concluded that the observed large Stokes shifted emission, around 520 nm, is not due, as it has been so far generally accepted, to the emission of a BC zwitterionic phototautomer, but to the intramolecular charge transfer, ICT, excited state emissions of the DHB hydrogen bond adducts.

  20. Theoretical study of the interaction between pyridine derivatives and atomic chlorine. Substituent effect and nature of the bonding

    Science.gov (United States)

    Sutradhar, Dipankar; Zeegers-Huyskens, Therese; Chandra, Asit K.

    2015-11-01

    The interaction of pyridine derivatives (H, 4-NH2, 4-CH3, 4-F, 4-CN, 4-NO2) with atomic chlorine is investigated theoretically by the density functional theory (DFT)-based LC-BLYP/aug-cc-pVDZ method. Pyridines and Cl° are held together by a (2c--3e) bond and the intermolecular distances range from 2.313 to 2.343 Å. The existence of a N…Cl bond is confirmed by the atom-in-molecule analysis of the systems. The binding energies of the adducts, ranging from -42.08 to -53.96 kJ mol-1, are linearly correlated to the proton affinity of the pyridines. The charge transfer from pyridine to Cl° varies between 0.222 and 0.277 e. The spin density analysis shows that the strongest complex has the highest (2c-3e) character. The CH bonds are contracted and the ν(CH) vibrations are blueshifted owing to the decrease in σ*(CH) occupation. This decrease results not only from the classical anomeric effect but also from the σ(CC) and σ(CN) → σ*(CH) delocalisation in the heteroaromatic ring.

  1. Structural and Energetic Impact of Non-Natural 7-Deaza-8-Azaadenine and its 7-Substituted Derivatives on H-Bonding Potential with Uracil in RNA Molecules

    KAUST Repository

    Chawla, Mohit

    2015-09-21

    Non-natural (synthetic) nucleobases, including 7-ethynyl- and 7-triazolyl-8-aza-7-deazaadenosine, have been introduced in RNA molecules for targeted applications, and have been characterized experimentally. However, no theoretical characterization of the impact of these modifications on the structure and energetics of the corresponding H-bonded base pair is available. To fill this gap, we performed quantum mechanics calculations, starting with the analysis of the impact of the 8-aza-7-deaza modification of the adenosine skeleton, and we moved then to analyze the impact of the specific substituents on the modified 8-aza-7-deazaadenosine. Our analysis indicates that, despite of these severe structural modifications, the H-bonding properties of the modified base pair gratifyingly replicate those of the unmodified base pair. Similar behavior is predicted when the same skeleton modifications are applied to guanosine when paired to cytosine. To stress further the H-bonding pairing in the modified adenosine-uracil base pair, we explored the impact of strong electron donor and electron withdrawing substituents on the C7 position. Also in this case we found minimal impact on the base pair geometry and energy, confirming the validity of this modification strategy to functionalize RNAs without perturbing its stability and biological functionality.

  2. Effect of Dentin Biomodification Using Naturally Derived Collagen Cross-Linkers: One-Year Bond Strength Study

    Directory of Open Access Journals (Sweden)

    Carina S. Castellan

    2013-01-01

    Full Text Available Purpose. This study investigated the long-term resin-dentin bond strength of dentin biomodified by proanthocyanidin-rich (PA agents. Materials and Methods. Forty molars had their coronal dentin exposed, etched, and treated for 10 minutes with 6.5% grape seed extract (GSE, 6.5% cocoa seed extract ethanol-water (CSE-ET, 6.5% cocoa seed extract acetone-water (CSE-AC, and distilled water (CO. Samples were restored either with One-Step Plus (OS or Adper Single-Bond Plus (SB. Bond strength test was performed immediately or after 3, 6, and 12 months. Results. Higher μTBS were observed for GSE immediately (SB- 62.9 MPa; OS- 51.9 MPa when compared to CSE-ET (SB- 56.95 MPa; OS- 60.28 MPa, CSE-AC (SB- 49.97 MPa; OS- 54.44 MPa, and CO (SB- 52.0 MPa; OS- 44.0 MPa (P<0.05. CSE outcomes were adhesive system and solvent dependant. After 12 months storage SB results showed no difference among treatment types (GSE- 57.15 MPa; CSE/ET- 54.04 MPa; CSE/AC- 48.22 MPa; CO- 51.68 MPa; P=0.347,while OS results where treatment dependent (GSE- 42.62 MPa; CSE/ET- 44.06 MPa; CSE/AC- 41.30 MPa; CO- 36.85 MPa; P=0.036. Conclusions. GSE and CSE-ET agents provided enhanced immediate adhesion and stabilization to demineralized dentin after long-term storage, depending on adhesive system.

  3. Predicting Bond Dissociation Energies of Transition-Metal Compounds by Multiconfiguration Pair-Density Functional Theory and Second-Order Perturbation Theory Based on Correlated Participating Orbitals and Separated Pairs.

    Science.gov (United States)

    Bao, Junwei Lucas; Odoh, Samuel O; Gagliardi, Laura; Truhlar, Donald G

    2017-02-14

    We study the performance of multiconfiguration pair-density functional theory (MC-PDFT) and multireference perturbation theory for the computation of the bond dissociation energies in 12 transition-metal-containing diatomic molecules and three small transition-metal-containing polyatomic molecules and in two transition-metal dimers. The first step is a multiconfiguration self-consistent-field calculation, for which two choices must be made: (i) the active space and (ii) its partition into subspaces, if the generalized active space formulation is used. In the present work, the active space is chosen systematically by using three correlated-participating-orbitals (CPO) schemes, and the partition is chosen by using the separated-pair (SP) approximation. Our calculations show that MC-PDFT generally has similar accuracy to CASPT2, and the active-space dependence of MC-PDFT is not very great for transition-metal-ligand bond dissociation energies. We also find that the SP approximation works very well, and in particular SP with the fully translated BLYP functional SP-ftBLYP is more accurate than CASPT2. SP greatly reduces the number of configuration state functions relative to CASSCF. For the cases of FeO and NiO with extended-CPO active space, for which complete active space calculations are unaffordable, SP calculations are not only affordable but also of satisfactory accuracy. All of the MC-PDFT results are significantly better than the corresponding results with broken-symmetry spin-unrestricted Kohn-Sham density functional theory. Finally we test a perturbation theory method based on the SP reference and find that it performs slightly worse than CASPT2 calculations, and for most cases of the nominal-CPO active space, the approximate SP perturbation theory calculations are less accurate than the much less expensive SP-PDFT calculations.

  4. Discrimination of hydrogen-bonded complexes with axial chirality

    Science.gov (United States)

    Alkorta, Ibon; Elguero, José

    2002-10-01

    The chiral self-discrimination of twelve molecules showing axial chirality has been studied. They included peroxides, hydrazines, carboxylic acids, amides, and allenes. The homo and heterochiral dimers of the selected compounds, that present two hydrogen bonds, have been studied by means of density functional theory (B3LYP/6-31+G**) and ab initio (MP2/6-31+G** and MP2/6-311++G**) methods. The energetic differences found for the complexes of each compound have been rationalized based on their electron density maps and the natural bond orbital analysis. In some cases, intermolecular oxygen-oxygen interactions have been found and interpreted as additional stabilizing contacts.

  5. Cesium's Off-the-Map Valence Orbital

    NARCIS (Netherlands)

    Goesten, Maarten G.; Rahm, Martin; Bickelhaupt, F. Matthias; Hensen, Emiel J.M.

    2017-01-01

    The Td-symmetric [CsO4]+ ion, featuring Cs in an oxidation state of 9, is computed to be a minimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms. The valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only. From a molecular orbital

  6. Treating sub-valence correlation effects in domain based pair natural orbital coupled cluster calculations: an out-of-the-box approach

    KAUST Repository

    Bistoni, Giovanni

    2017-06-12

    The validity of the main approximations used in canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) in standard chemical applications is discussed. In particular, we investigate the dependence of the results on the number of electrons included in the correlation treatment in frozen-core (FC) calculations and on the main threshold governing the accuracy of DLPNO all-electron (AE) calculations. Initially, scalar relativistic orbital energies for the ground state of the atoms from Li to Rn in the periodic table are calculated. An energy criterion is applied for determining the orbitals that can be excluded from the correlation treatment in FC coupled cluster calculations without significant loss of accuracy. The heterolytic dissociation energy (HDE) of a series of metal compounds (LiF, NaF, AlF3, CaF2, CuF, GaF3, YF3, AgF, InF3, HfF4 and AuF) is calculated at the canonical CCSD(T) level, and the dependence of the results on the number of correlated electrons is investigated. Although for many of the studied reactions sub-valence correlation effects contribute significantly to the HDE, the use of an energy criterion permits a conservative definition of the size of the core, allowing FC calculations to be performed in a black-box fashion while retaining chemical accuracy. A comparison of the CCSD and the DLPNO-CCSD methods in describing the core-core, core-valence and valence-valence components of the correlation energy is given. It is found that more conservative thresholds must be used for electron pairs containing at least one core electron in order to achieve high accuracy in AE DLPNO-CCSD calculations relative to FC calculations. With the new settings, the DLPNO-CCSD method reproduces canonical CCSD results in both AE and FC calculations with the same accuracy.

  7. Hydrogen bonding and coordination bonding in the electronically excited states of Cu2(L)2 (L = 5-(4-pyridyl)tetrazole)MeOH: A TDDFT study

    Science.gov (United States)

    Meng, Yanfang; Zhang, Chunqing; Ji, Min; Hao, Ce; Qiu, Jieshan

    2013-05-01

    The luminescent metal organic framework (MOF), Cu2(L)2·MeOH (L = 5-(4-pyridyl)tetrazole), was studied using time-dependent density functional theory (TDDFT). A combination of frontier molecular orbitals and electronic configuration analysis revealed that the emission mechanism was a ligand to metal charge transition (LMCT) rather than a metal to ligand charge transfer (MLCT). Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescence. Electronic transition energies predicted that the hydrogen bonding in excited state would become weaker with an electronic spectral blue-shift. The bond lengths, frequencies, and binding energies indicated weakening of the hydrogen bonding in the excited state, which can affect emissions in two ways, including: (i) a decrease in the electronic coupling between methanol and the motif and suppressing the occurrence of the photo-induced electron transfer (PET); and (ii) increasing the energy gap between S1 and S0, leading to radiative transition. Coordination bonding was also investigated in the excited state through bond lengths, frequencies, and bond orders. Coordination bonds were found to become stronger in the excited state leading to an enhancement of the luminescence.

  8. Linear M[triple bond]E-Me versus bent M-E-Me: bonding analysis in heavier metal-ylidyne complexes [(Cp)(CO)2M[triple bond]EMe] and metallo-ylidenes [(Cp)(CO)3M-EMe] (M = Cr, Mo, W; E = Si, Ge, Sn, Pb).

    Science.gov (United States)

    Pandey, Krishna K; Lledós, Agustí

    2009-04-06

    The electronic and molecular structures of the complexes [(eta(5)-C(5)H(5))(CO)(2)M[triple bond]EMe] and [(eta(5)-C(5)H(5))(CO)(3)M-EMe] (M = Cr, Mo, W; E = Si, Sn, Pb) are calculated at the density-functional theory (DFT) level using the exchange correlation functionals B3LYP and BP86. The theoretically predicted bond lengths and angles of the model compounds are in excellent agreement with experimental values. The calculations reveal the presence of a strong M[triple bond]E triple (sigma + 2pi) bond in [(eta(5)-C(5)H(5))(CO)(2)M[triple bond]EMe]. The M-E bond lengths in [(eta(5)-C(5)H(5))(CO)(3)M-EMe] are longer than those expected for a single bond. The nature of the M[triple bond]EMe and M-EMe interactions was analyzed with charge and energy decomposition methods. In the M[triple bond]EMe bond, the M-E sigma-bonding orbitals are always polarized toward the silicon, tin, and lead atoms, and the polarization increases from chromium to tungsten. In contrast, in the M-EMe bond, the M-E sigma-bonding orbitals are significantly polarized toward the metal atom. The hybridization at the metal atoms in the M[triple bond]E bonds has d character in the range 60.6-68.8%, while in the M-E bonds has large d character which is always >86% of the total atomic orbital contribution. In the complexes [(eta(5)-C(5)H(5))(CO)(2)M[triple bond]EMe], the contributions of the electrostatic interactions, DeltaE(elstat), and the covalent bonding, DeltaE(orb), have nearly the same values for silylidyne and germylidyne complexes, while for the stannylidyne and plumbylidyne complexes, the electrostatic interactions, DeltaE(elstat), are greater than the orbital interaction, DeltaE(orb). The covalent bonding has a high degree of pi-character. The total interaction energy DeltaE(int) in the compound [(eta(5)-C(5)H(5))(CO)(3)M-EMe] is less attractive than those in the complexes [(eta(5)-C(5)H(5))(CO)(2)M[triple bond]EMe]. The M-ER bonds have a slightly lower degree of covalent bonding (34

  9. Mother-Child Bonding.

    Science.gov (United States)

    Pearce, Joseph Chilton

    1994-01-01

    Examines the nature of mother-child bonding from the prenatal stage through early infancy, discussing how the mother's actions, even before birth, stimulate her child's senses. Explains the crucial role that physical contact, breastfeeding, and visual stimuli have on mother-child bonding in human and animal newborns. (MDM)

  10. Communication: An improved linear scaling perturbative triples correction for the domain based local pair-natural orbital based singles and doubles coupled cluster method [DLPNO-CCSD(T)].

    Science.gov (United States)

    Guo, Yang; Riplinger, Christoph; Becker, Ute; Liakos, Dimitrios G; Minenkov, Yury; Cavallo, Luigi; Neese, Frank

    2018-01-07

    In this communication, an improved perturbative triples correction (T) algorithm for domain based local pair-natural orbital singles and doubles coupled cluster (DLPNO-CCSD) theory is reported. In our previous implementation, the semi-canonical approximation was used and linear scaling was achieved for both the DLPNO-CCSD and (T) parts of the calculation. In this work, we refer to this previous method as DLPNO-CCSD(T0) to emphasize the semi-canonical approximation. It is well-established that the DLPNO-CCSD method can predict very accurate absolute and relative energies with respect to the parent canonical CCSD method. However, the (T0) approximation may introduce significant errors in absolute energies as the triples correction grows up in magnitude. In the majority of cases, the relative energies from (T0) are as accurate as the canonical (T) results of themselves. Unfortunately, in rare cases and in particular for small gap systems, the (T0) approximation breaks down and relative energies show large deviations from the parent canonical CCSD(T) results. To address this problem, an iterative (T) algorithm based on the previous DLPNO-CCSD(T0) algorithm has been implemented [abbreviated here as DLPNO-CCSD(T)]. Using triples natural orbitals to represent the virtual spaces for triples amplitudes, storage bottlenecks are avoided. Various carefully designed approximations ease the computational burden such that overall, the increase in the DLPNO-(T) calculation time over DLPNO-(T0) only amounts to a factor of about two (depending on the basis set). Benchmark calculations for the GMTKN30 database show that compared to DLPNO-CCSD(T0), the errors in absolute energies are greatly reduced and relative energies are moderately improved. The particularly problematic case of cumulene chains of increasing lengths is also successfully addressed by DLPNO-CCSD(T).

  11. Communication: An improved linear scaling perturbative triples correction for the domain based local pair-natural orbital based singles and doubles coupled cluster method [DLPNO-CCSD(T)

    KAUST Repository

    Guo, Yang

    2018-01-04

    In this communication, an improved perturbative triples correction (T) algorithm for domain based local pair-natural orbital singles and doubles coupled cluster (DLPNO-CCSD) theory is reported. In our previous implementation, the semi-canonical approximation was used and linear scaling was achieved for both the DLPNO-CCSD and (T) parts of the calculation. In this work, we refer to this previous method as DLPNO-CCSD(T0) to emphasize the semi-canonical approximation. It is well-established that the DLPNO-CCSD method can predict very accurate absolute and relative energies with respect to the parent canonical CCSD method. However, the (T0) approximation may introduce significant errors in absolute energies as the triples correction grows up in magnitude. In the majority of cases, the relative energies from (T0) are as accurate as the canonical (T) results of themselves. Unfortunately, in rare cases and in particular for small gap systems, the (T0) approximation breaks down and relative energies show large deviations from the parent canonical CCSD(T) results. To address this problem, an iterative (T) algorithm based on the previous DLPNO-CCSD(T0) algorithm has been implemented [abbreviated here as DLPNO-CCSD(T)]. Using triples natural orbitals to represent the virtual spaces for triples amplitudes, storage bottlenecks are avoided. Various carefully designed approximations ease the computational burden such that overall, the increase in the DLPNO-(T) calculation time over DLPNO-(T0) only amounts to a factor of about two (depending on the basis set). Benchmark calculations for the GMTKN30 database show that compared to DLPNO-CCSD(T0), the errors in absolute energies are greatly reduced and relative energies are moderately improved. The particularly problematic case of cumulene chains of increasing lengths is also successfully addressed by DLPNO-CCSD(T).

  12. Communication: An improved linear scaling perturbative triples correction for the domain based local pair-natural orbital based singles and doubles coupled cluster method [DLPNO-CCSD(T)

    Science.gov (United States)

    Guo, Yang; Riplinger, Christoph; Becker, Ute; Liakos, Dimitrios G.; Minenkov, Yury; Cavallo, Luigi; Neese, Frank

    2018-01-01

    In this communication, an improved perturbative triples correction (T) algorithm for domain based local pair-natural orbital singles and doubles coupled cluster (DLPNO-CCSD) theory is reported. In our previous implementation, the semi-canonical approximation was used and linear scaling was achieved for both the DLPNO-CCSD and (T) parts of the calculation. In this work, we refer to this previous method as DLPNO-CCSD(T0) to emphasize the semi-canonical approximation. It is well-established that the DLPNO-CCSD method can predict very accurate absolute and relative energies with respect to the parent canonical CCSD method. However, the (T0) approximation may introduce significant errors in absolute energies as the triples correction grows up in magnitude. In the majority of cases, the relative energies from (T0) are as accurate as the canonical (T) results of themselves. Unfortunately, in rare cases and in particular for small gap systems, the (T0) approximation breaks down and relative energies show large deviations from the parent canonical CCSD(T) results. To address this problem, an iterative (T) algorithm based on the previous DLPNO-CCSD(T0) algorithm has been implemented [abbreviated here as DLPNO-CCSD(T)]. Using triples natural orbitals to represent the virtual spaces for triples amplitudes, storage bottlenecks are avoided. Various carefully designed approximations ease the computational burden such that overall, the increase in the DLPNO-(T) calculation time over DLPNO-(T0) only amounts to a factor of about two (depending on the basis set). Benchmark calculations for the GMTKN30 database show that compared to DLPNO-CCSD(T0), the errors in absolute energies are greatly reduced and relative energies are moderately improved. The particularly problematic case of cumulene chains of increasing lengths is also successfully addressed by DLPNO-CCSD(T).

  13. Theoretical study of the S…Cl interaction between sulfides and atomic chlorine. Nature and strength of the two-center three-electron bond

    Science.gov (United States)

    Sutradhar, Dipankar; Zeegers-Huyskens, Thérèse; Chandra, Asit. K.

    2017-05-01

    The interaction between sulfides (H2S, CH3SH, CH3CH2SH, CH3SCH3 and CH3SCH2F) and atomic chlorine is investigated using DFT based LC-BLYP and CCSD(T) methods in conjugation with the aug-cc-pVTZ basis set. The intermolecular S…Cl distances in the complexes range between 2.5922 Å (H2S…Cl) and 2.5273 Å (CH3SCH3…Cl). The interaction energies ranging between -29.1 and -77.5 kJ mol-1 reveal the formation of relatively strong 2c-3e S…Cl bonds. The binding energies are linearly related to the proton affinity of the sulfides, to the charge transfer taking place from the sulfides to the Cl atom and inversely proportional to the difference between the ionization potential of the sulfides and the electron affinity of the Cl atom. The spin density analysis suggests that almost 48% of the spin is transferred from the Cl to the S atom in the strongest CH3SCH3…Cl complex. The AIM analysis shows that the S…Cl interaction possess a significant covalent character which decreases with decreasing binding strength of the complexes. All the data indicate that the S…Cl 2c-3e bonds are stronger than the O…Cl or N…Cl bonds and more covalent in nature. The variation of the CH distances and the blue shifts of the ν(CH) vibration resulting from the interaction with Cl are discussed.

  14. Bonding with Your Baby

    Science.gov (United States)

    ... in infant massage in your area. Breastfeeding and bottle-feeding are both natural times for bonding. Infants respond ... milk you've pumped, the staff, including a lactation consultant, can help you make the transition to ...

  15. Water's Hydrogen Bond Strength

    CERN Document Server

    Chaplin, Martin

    2007-01-01

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

  16. [Orbital cellulitis].

    Science.gov (United States)

    Mouriaux, F; Rysanek, B; Babin, E; Cattoir, V

    2012-01-01

    Orbital cellulitis is uncommon in ophthalmologic practice. The majority of cases arise from direct spread of sinus infection or eyelid infection. Clinically, orbital cellulitis is divided into two forms: the preseptal form, anterior to the orbital septum, and the retroseptal form, posterior to the orbital septum. Management and prognosis differ widely between the two types. The retroseptal form or "true" orbital cellulitis is a severe disease with potentially disastrous consequences for vision and survival. Clinical examination and urgent CT scanning are indispensable for correct diagnosis, evaluation of severity, surgical planning and antibiotic selection. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

  17. Bioinspired Nonheme Iron Catalysts for C-H and C═C Bond Oxidation: Insights into the Nature of the Metal-Based Oxidants.

    Science.gov (United States)

    Oloo, Williamson N; Que, Lawrence

    2015-09-15

    Recent efforts to design synthetic iron catalysts for the selective and efficient oxidation of C-H and C═C bonds have been inspired by a versatile family of nonheme iron oxygenases. These bioinspired nonheme (N4)Fe(II) catalysts use H2O2 to oxidize substrates with high regio- and stereoselectivity, unlike in Fenton chemistry where highly reactive but unselective hydroxyl radicals are produced. In this Account, we highlight our efforts to shed light on the nature of metastable peroxo intermediates, which we have trapped at -40 °C, in the reactions of the iron catalyst with H2O2 under various conditions and the high-valent species derived therefrom. Under the reaction conditions that originally led to the discovery of this family of catalysts, we have characterized spectroscopically an Fe(III)-OOH intermediate (EPR g(max) = 2.19) that leads to the hydroxylation of substrate C-H bonds or the epoxidation and cis-dihydroxylation of C═C bonds. Surprisingly, these organic products show incorporation of (18)O from H2(18)O, thereby excluding the possibility of a direct attack of the Fe(III)-OOH intermediate on the substrate. Instead, a water-assisted mechanism is implicated in which water binding to the iron(III) center at a site adjacent to the hydroperoxo ligand promotes heterolytic cleavage of the O-O bond to generate an Fe(V)(O)(OH) oxidant. This mechanism is supported by recent kinetic studies showing that the Fe(III)-OOH intermediate undergoes exponential decay at a rate enhanced by the addition of water and retarded by replacement of H2O with D2O, as well as mass spectral evidence for the Fe(V)(O)(OH) species obtained by the Costas group. The nature of the peroxo intermediate changes significantly when the reactions are carried out in the presence of carboxylic acids. Under these conditions, spectroscopic studies support the formation of a (κ(2)-acylperoxo)iron(III) species (EPR g(max) = 2.58) that decays at -40 °C in the absence of substrate to form an

  18. Gas phase detection of the NH-P hydrogen bond and importance of secondary interactions

    DEFF Research Database (Denmark)

    Møller, Kristian Holten; Hansen, Anne Schou; Kjærgaard, Henrik Grum

    2015-01-01

    We have observed the NH···P hydrogen bond in a gas phase complex. The bond is identified in the dimethylamine-trimethylphosphine complex by a red shift of the fundamental NH-stretching frequency observed using Fourier transform infrared spectroscopy (FT-IR). On the basis of the measured NH......-stretching frequency red shifts, we find that P is a hydrogen bond acceptor atom similar in strength to S. Both are stronger acceptors than O and significantly weaker acceptors than N. The hydrogen bond angle, ∠NHP, is found to be very sensitive to the functional employed in density functional theory (DFT......) optimizations of the complex and is a possible parameter to assess the quality of DFT functionals. Natural bonding orbital (NBO) energies and results from the topological methods atoms in molecules (AIM) and noncovalent interactions (NCI) indicate that the sensitivity is caused by the weakness of the hydrogen...

  19. Mie resonances and bonding in photonic crystals

    OpenAIRE

    Antonoyiannakis, M. I.; Pendry, J. B.

    1997-01-01

    Isolated dielectric spheres support resonant electromagnetic modes which are analogous to electronic orbitals and, like their electronic counterparts, can form bonding or anti-bonding interactions between neighbouring spheres. By irradiating the system with light at the bonding frequency an attractive interaction is induced between the spheres. We suggest that by judicious selection of bonding states we can drive a system towards a desired structure, rather than rely on the structure dictated...

  20. A novel tubular hydrogen-bond pattern in a new diazaphosphole oxide: a combination of X-ray crystallography and theoretical study of hydrogen bonds.

    Science.gov (United States)

    Sabbaghi, Fahimeh; Pourayoubi, Mehrdad; Farhadipour, Abolghasem; Ghorbanian, Nazila; Andreev, Pavel V

    2017-07-01

    In the structure of 2-(4-chloroanilino)-1,3,2λ 4 -diazaphosphol-2-one, C 12 H 11 ClN 3 OP, each molecule is connected with four neighbouring molecules through (N-H) 2 ...O hydrogen bonds. These hydrogen bonds form a tubular arrangement along the [001] direction built from R 3 3 (12) and R 4 3 (14) hydrogen-bond ring motifs, combined with a C(4) chain motif. The hole constructed in the tubular architecture includes a 12-atom arrangement (three P, three N, three O and three H atoms) belonging to three adjacent molecules hydrogen bonded to each other. One of the N-H groups of the diazaphosphole ring, not co-operating in classical hydrogen bonding, takes part in an N-H...π interaction. This interaction occurs within the tubular array and does not change the dimension of the hydrogen-bond pattern. The energies of the N-H...O and N-H...π hydrogen bonds were studied by NBO (natural bond orbital) analysis, using the experimental hydrogen-bonded cluster of molecules as the input file for the chemical calculations. In the 1 H NMR experiment, the nitrogen-bound proton of the diazaphosphole ring has a high value of 17.2 Hz for the 2 J H-P coupling constant.

  1. Orbital and spin ordering physics of the Mn3O4 spinel

    Science.gov (United States)

    Pal, Santanu; Lal, Siddhartha

    2017-08-01

    Motivated by recent experiments, we present a comprehensive theoretical study of the geometrically frustrated strongly correlated magnetic insulator Mn3O4 spinel oxide based on a microscopic Hamiltonian involving lattice, spin, and orbital degrees of freedom. Possessing the physics of degenerate eg orbitals, this system shows a strong Jahn-Teller effect at high temperatures. Further, careful attention is paid to the special nature of the superexchange physics arising from the 90∘ Mn-O-Mn bonding angle. The Jahn-Teller and superexchange-based orbital-spin Hamiltonians are then analyzed in order to track the dynamics of orbital and spin ordering. We find that a high-temperature structural transition results in orbital ordering the nature of which is mixed with respect to the two originally degenerate eg orbitals. This ordering of orbitals is shown to relieve the intrinsic geometric frustration of the spins on the spinel lattice, leading to ferrimagnetic Yafet-Kittel ordering at low temperatures. Finally, we develop a model for a magnetoelastic coupling in Mn3O4 , enabling a systematic understanding of the experimentally observed complexity in the low-temperature structural and magnetic phenomenology of this spinel. Our analysis predicts that a quantum fluctuation-driven orbital-spin liquid phase may be stabilized at low temperatures upon the application of pressure.

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

    OpenAIRE

    Beye, Martin; Öberg, Henrik; Kühn, Danilo; LaRue, Jerry; Mercurio, Giuseppe; Michael P. Minitti; Mitra, Ankush; Moeller, Stefan P.; Ng, May Ling; Nilsson, Anders; Nordlund, Dennis; Nørskov, Jens; Xin, Hongliang; Öström, Henrik; Ogasawara, Hirohito

    2016-01-01

    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–antibondin...

  3. ORBITAL, CELLULITIS

    African Journals Online (AJOL)

    Aim: The purpose of this study was to assess the prevalence of paranasal sinusitis as a cause of orbital cellulitis and to identify the commonest sinus(es) involved in our setting. Methods: A retrospective review of the case notes of 47 patients with orbital cellulitis admitted into the ophthalmic ward of the University College ...

  4. Effect of thermomechanical aging on bond strength and interface morphology of glass fiber and zirconia posts bonded with a self-etch adhesive and a self-adhesive resin cement to natural teeth.

    Science.gov (United States)

    Yaman, Batu Can; Ozer, Fusun; Takeichi, Takuro; Karabucak, Bekir; Koray, Fatma; Blatz, Markus B

    2014-09-01

    Information regarding the effect of thermomechanical aging (TMA) on the bond strength of luting cements to root canal dentin and endodontic posts is limited. The purpose of this study was to investigate the effect of TMA on the bond strength of fiber and zirconia posts bonded to root canal dentin with 2 different resin cements with microtensile and scanning electron microscopic evaluation. Eighty extracted single-rooted human premolars were endodontically treated and restored with either a glass fiber post (FP) or a zirconia post (ZP) with 2 commercially available resin luting cements. The teeth were divided into 2 main groups. In the first group, posts (n=40) were bonded with a self-etch adhesive cement (SEAC). In the second group (n=40), posts were bonded using a self-adhesive cement (SAC). During the first aging phase, all specimens in each group were stored in distilled water for 30 days at 37°C. During the second phase, half of the specimens in each group were subjected to the TMA. The test groups were as follows: FP/SEAC, FP/SEAC+TMA, ZP/SEAC, ZP/SEAC+TMA, FP/SAC, FP/SAC+TMA, ZP/SAC, and ZP/SAC+TMA. The bond strength was measured with a microtensile test. Data were analyzed by 3-way analysis of variance and the Tukey honest significant different test (α=.05). FP/SEAC at 30 days was higher than in the other groups. However, bond strength values were significantly reduced in this group after TMA (Pposts and the resin cements as well as between the resin cements and the root canal dentin. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  5. Exploring the nature of the H-bonds between the human class II MHC protein, HLA-DR1 (DRB*0101) and the influenza virus hemagglutinin peptide, HA306-318, using the quantum theory of atoms in molecules.

    Science.gov (United States)

    Aray, Yosslen; Aguilera-García, Ricardo; Izquierdo, Daniel R

    2018-01-02

    The nature of the H-bonds between the human protein HLA-DR1 (DRB*0101) and the hemagglutinin peptide HA306-318 has been studied using the Quantum Theory of Atoms in Molecules for the first time. We have found four H-bond groups: one conventional CO··HN bond group and three nonconventional CO··HC, π··HC involving aromatic rings and HN··HCaliphatic groups. The calculated electron density at the determined H-bond critical points suggests the follow protein pocket binding trend: P1 (2,311) > P9 (1.109) > P4 (0.950) > P6 (0.553) > P7 (0.213) which agrees and reveal the nature of experimental findings, showing that P1 produces by a long way the strongest binding of the HLA-DR1 human protein molecule with the peptide backbone as consequence of the vast number of H-bonds in the P1 area and at the same time the largest specific binding of the peptide Tyr308 residue with aromatic residues located at the binding groove floor. The present results suggest the topological analysis of the electronic density as a valuable tool that allows a non-arbitrary partition of the pockets binding energy via the calculated electron density at the determined critical points.

  6. The Hot Orbit: Orbital Cellulitis

    Science.gov (United States)

    Chaudhry, Imtiaz A.; Al-Rashed, Waleed; Arat, Yonca O.

    2012-01-01

    Orbital cellulitis is an uncommon condition previously associated with severe complications. If untreated, orbital cellulitis can be potentially sight and life threatening. It can affect both adults and children but has a greater tendency to occur in the pediatric age group. The infection most commonly originates from sinuses, eyelids or face, retained foreign bodies, or distant soources by hematogenous spread. It is characterized by eyelid edema, erythema, chemosis, proptosis, blurred vision, fever, headache, and double vision. A history of upper respiratory tract infection prior to the onset is very common especially in children. In the era prior to antibiotics, vision loss from orbital cellulitis was a dreaded complication. Currently, imaging studies for detection of orbital abcess, the use of antibiotics and early drainage have mitigated visual morbidity significantly. The purpose of this review is to describe current investigative strategies and management options in the treatment of orbital cellulitis, establish their effectiveness and possible complications due to late intervention. PMID:22346113

  7. Third-generation muffin–tin orbitals

    Indian Academy of Sciences (India)

    generation muffin–tin orbitals (MTOs) are. We demonstrate that they can be downfolded to smaller and smaller basis sets: s p 3 d 10 , s p 3 , and bond orbitals. For isolated bands, it is possible to generate Wannier functions a priori. Also for bands ...

  8. Covalency in the f-element-chalcogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Ingram, Kieran I.M. [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Kaltsoyannis, Nikolas [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)], E-mail: n.kaltsoyannis@ucl.ac.uk; Gaunt, Andrew J.; Neu, Mary P. [Inorganic, Isotope and Actinide Chemistry (C-IIAC), Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2007-10-11

    The geometric and electronic structures of the title complexes have been studied using gradient corrected density functional theory. Excellent agreement is observed between computed r(M-E) and experimental values in analogous {sup i}Pr complexes. Natural charge analysis indicates that the M-E bond becomes less ionic in the order O>S>S> Te, and that this decrease is largest for U and smallest for La. Natural and Mulliken overlap populations suggest increasing M-E covalency as group 16 is descended, and also in the order Labonding, while that from La to Pu and U stems from larger 5f orbital involvement compared with 4f.

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

    Science.gov (United States)

    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.

  10. Halogen bonding from a hard and soft acids and bases perspective: investigation by using density functional theory reactivity indices.

    Science.gov (United States)

    Pinter, Balazs; Nagels, Nick; Herrebout, Wouter A; De Proft, Frank

    2013-01-07

    Halogen bonds between the trifluoromethyl halides CF(3)Cl, CF(3)Br and CF(3)I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson's hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non-covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual-descriptor plots indicate an orbital σ hole on the halogen similar to the electrostatic σ hole manifested in the molecular electrostatic potential. The predicted high halogen-bond-acceptor affinity of N-heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF(3) I·NHC complex. The dominant NOCV orbital represents an electron-density deformation according to a n→σ*-type interaction. The characteristic signal found in the reduced density gradient versus electron-density diagram corresponds to the non-covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected C-X bond strengthening observed in several cases was rationalised within the molecular orbital framework. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Foreign body orbital cyst

    DEFF Research Database (Denmark)

    Yazdanfard, Younes; Heegard, Steffen; Fledelius, Hans C.

    2001-01-01

    Ophthalmology, penetrating orbital injury, orbital foreign body, ultrasound, computed tomography (CT), histology......Ophthalmology, penetrating orbital injury, orbital foreign body, ultrasound, computed tomography (CT), histology...

  12. A new kinematical definition of orbital eccentricity

    Directory of Open Access Journals (Sweden)

    Ninković S.

    2009-01-01

    Full Text Available A new concept of orbital eccentricity is given. The dimensionless quantities proposed in the present paper to serve as orbital eccentricities have a kinematical nature. The purpose is to use them in describing the motion for the case of three-dimensional orbits. A comparison done for nearly planar orbits shows that the values of the eccentricities proposed here do not differ significantly from those corresponding to the eccentricities of geometric nature usually applied.

  13. The enhancing effect of a cation-π interaction on the cooperativity of halogen bonds: A computational study.

    Science.gov (United States)

    Esrafili, Mehdi D; Asadollahi, Soheila

    2017-05-01

    In this work, we investigate the effect of a cation-π interaction on the cooperativity of X⋯N halogen bonds in PhX⋯NCX⋯NH3 complexes, where Ph=phenyl and X=Cl, Br, I. Molecular geometries and interaction energies of the resulting complexes are studied at the MP2/aug-cc-pVDZ(-PP) computational level. The mechanism of the cooperativity between halogen bonds is analyzed using parameters derived from the noncovalent index, quantum theory of atoms in molecules and natural bond orbital methodologies. It is found that the divalent cations (Be2+, Mg2+) have a larger influence on the cooperativity of halogen bonds than monovalent ones (Li+, Na+). The formation of a cation-π interaction leads to strengthening of the halogen bonds, hence increases their cooperativity. Copyright © 2017 Elsevier Inc. All rights reserved.

  14. Bonding in Heavier Group 14 Zero-Valent Complexes-A Combined Maximum Probability Domain and Valence Bond Theory Approach.

    Science.gov (United States)

    Turek, Jan; Braïda, Benoît; De Proft, Frank

    2017-10-17

    The bonding in heavier Group 14 zero-valent complexes of a general formula L2 E (E=Si-Pb; L=phosphine, N-heterocyclic and acyclic carbene, cyclic tetrylene and carbon monoxide) is probed by combining valence bond (VB) theory and maximum probability domain (MPD) approaches. All studied complexes are initially evaluated on the basis of the structural parameters and the shape of frontier orbitals revealing a bent structural motif and the presence of two lone pairs at the central E atom. For the VB calculations three resonance structures are suggested, representing the "ylidone", "ylidene" and "bent allene" structures, respectively. The influence of both ligands and central atoms on the bonding situation is clearly expressed in different weights of the resonance structures for the particular complexes. In general, the bonding in the studied E(0) compounds, the tetrylones, is best described as a resonating combination of "ylidone" and "ylidene" structures with a minor contribution of the "bent allene" structure. Moreover, the VB calculations allow for a straightforward assessment of the π-backbonding (E→L) stabilization energy. The validity of the suggested resonance model is further confirmed by the complementary MPD calculations focusing on the E lone pair region as well as the E-L bonding region. Likewise, the MPD method reveals a strong influence of the σ-donating and π-accepting properties of the ligand. In particular, either one single domain or two symmetrical domains are found in the lone pair region of the central atom, supporting the predominance of either the "ylidene" or "ylidone" structures having one or two lone pairs at the central atom, respectively. Furthermore, the calculated average populations in the lone pair MPDs correlate very well with the natural bond orbital (NBO) populations, and can be related to the average number of electrons that is backdonated to the ligands. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Aluminum-phosphorus triple bonds: Do substituents make Altbnd6 P synthetically accessible?

    Science.gov (United States)

    Lu, Jia-Syun; Yang, Ming-Chung; Su, Ming-Der

    2017-10-01

    The effect of substitution on the potential energy surfaces of triple-bonded RAltbnd6 PR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt (C6H2-2,4,6-{CH(SiMe3)2}3), and Ar∗ (C6H3-2,6-(C6H2-2,4,6-i-Pr3)2)) compounds was investigated by using the theoretical methods (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, B3LYP/LANL2DZ+dp, and CCSD(T)). The theoretical examinations reveal that all of the triple-bonded RAltbnd6 PR species prefer to adopt a bent form with a roughly perpendicular bond angle (∠ Al-P-R). In addition, the theoretical evidence demonstrates that only the bulkier substituents can efficiently stabilize the central Altbnd6 P triple bond. Moreover, the theoretical analyses (the natural bond orbital, the natural resonance theory, and the charge decomposition analysis) indicate that the bonding characters of the triply bonded RAltbnd6 PR molecules should be described as R‧Al

  16. Effect of double-hyperconjugation on the apparent donor ability of sigma-bonds: insights from the relative stability of delta-substituted cyclohexyl cations.

    Science.gov (United States)

    Alabugin, Igor V; Manoharan, Mariappan

    2004-12-24

    A combination of electronic, structural, and energetic analyses shows that a somewhat larger intrinsic donor ability of the C-H bonds compared to that of C-C bonds can be overshadowed by cooperative hyperconjugative interactions with participation of remote substituents (double hyperconjugation or through-bond interaction). The importance of double hyperconjugation was investigated computationally using two independent criteria: (a) relative total energies and geometries of two conformers ("hyperconjomers") of delta-substituted cyclohexyl cations (b) and natural bond orbital (NBO) analysis of electronic structure and orbital interactions in these molecules. Both criteria clearly show that the apparent donor ability of C-C bonds can vary over a wide range, and the relative order of donor ability of C-H and C-C bonds can be easily inverted depending on molecular connectivity and environment. In general, relative donor abilities of sigma bonds can be changed by their through-bond communication with remote substituents and by greater polarizability of C-X bonds toward heavier elements. These computational results can be confirmed by experimental studies of conformational equilibrium of delta-substituted cyclohexyl cations.

  17. Pediatric Orbital Fractures

    Science.gov (United States)

    Oppenheimer, Adam J.; Monson, Laura A.; Buchman, Steven R.

    2013-01-01

    It is wise to recall the dictum “children are not small adults” when managing pediatric orbital fractures. In a child, the craniofacial skeleton undergoes significant changes in size, shape, and proportion as it grows into maturity. Accordingly, the craniomaxillofacial surgeon must select an appropriate treatment strategy that considers both the nature of the injury and the child's stage of growth. The following review will discuss the management of pediatric orbital fractures, with an emphasis on clinically oriented anatomy and development. PMID:24436730

  18. Metal-ligand ``multiple`` bonding: Revelations in the electronic structure of complexes of high-valent f-elements

    Energy Technology Data Exchange (ETDEWEB)

    Burns, C.J.; Arney, D.S.J.; Schnabel, R.C.; Warner, B.P. [Los Alamos National Lab., NM (United States); Bursten, B.E. [Ohio State Univ., Columbus, OH (United States); Green, J.C. [Univ. of Oxford (United Kingdom); Marks, T.J. [Northwestern Univ., Boston, MA (United States)

    1997-07-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project has been to extend the understanding of the nature of interactions between f-metals and first row elements (important both in natural systems and in ceramics), as well as providing important new information regarding basic differences in the chemical nature of d- and f-metals. By developing preparative routes to novel classes of early actinide and lanthanide complexes in which metal-ligand bonding is formally unsaturated, this project has provided the means to study orbital interactions and charge distribution in these species by physical, chemical, and theoretical means. Evaluation of the physical and chemical characteristics of these species is providing dramatic evidence for the involvement of valence metal orbitals [nf and (n+1)d] in bonding, and is yielding new insights into the factors influencing stability of related species.

  19. The two faces of hydrogen-bond strength on triple AAA-DDD arrays.

    Science.gov (United States)

    Lopez, Alfredo Henrique Duarte; Caramori, Giovanni Finoto; Coimbra, Daniel Fernando; Parreira, Renato Luis Tame; da Silva, Éder Henrique

    2013-12-02

    Systems that are connected through multiple hydrogen bonds are the cornerstone of molecular recognition processes in biology, and they are increasingly being employed in supramolecular chemistry, specifically in molecular self-assembly processes. For this reason, the effects of different substituents (NO2, CN, F, Cl, Br, OCH3 and NH2) on the electronic structure, and consequently on the magnitude of hydrogen bonds in triple AAA-DDD arrays (A=acceptor, D=donor) were evaluated in the light of topological [electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM)], energetic [Su-Li energy-decomposition analysis (EDA) and natural bond orbital analysis (NBO)], and geometrical analysis. The results based on local H-bond descriptors (geometries, QTAIM, ELF, and NBO) indicate that substitutions with electron-withdrawing groups on the AAA module tend to strengthen, whereas electron-donating substituents tend to weaken the covalent character of the AAA-DDD intermolecular H-bonds, and also indicate that the magnitude of the effect is dependent on the position of substitution. In contrast, Su-Li EDA results show an opposite behavior when compared to local H-bond descriptors, indicating that electron-donating substituents tend to increase the magnitude of H-bonds in AAA-DDD arrays, and thus suggesting that the use of local H-bond descriptors describes the nature of H bonds only partially, not providing enough insight about the strength of such H bonds. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Electronic states and nature of bonding in the molecule YC by all electron ab initio multiconfiguration self-consistent-field calculations and mass spectrometric equilibrium experiments

    DEFF Research Database (Denmark)

    Shim, Irene; Pelino, Mario; Gingerich, Karl A.

    1992-01-01

    In the present work we present results of all electron ab initio multiconfiguration self-consistent-field calculations of eight electronic states of the molecule YC. Also reported are the calculated spectroscopic constants. The predicted electronic ground state is 4PI, but this state is found......, and they hardly contribute to the bonding. The chemical bond in the YC molecule is polar with charge transfer from Y to C giving rise to a dipole moment of 3.90 D at 3.9 a.u. in the 4PI ground state. Mass spectrometric equilibrium investigations in the temperature range 2365-2792 K have resulted...

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

    Science.gov (United States)

    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.

  2. Spying on the boron-boron triple bond using spin-spin coupling measured from 11B solid-state NMR spectroscopy.

    Science.gov (United States)

    Perras, Frédéric A; Ewing, William C; Dellermann, Theresa; Böhnke, Julian; Ullrich, Stefan; Schäfer, Thomas; Braunschweig, Holger; Bryce, David L

    2015-06-01

    There is currently tremendous interest in the previously documented example of a stable species exhibiting a boron-boron triple bond (Science, 2012, 336, 1420). Notably, it has recently been stated using arguments based on force constants that this diboryne may not, in reality, feature a boron-boron triple bond. Here, we use advanced solid-state NMR and computational methodology in order to directly probe the orbitals involved in multiple boron-boron bonds experimentally via analysis of 11B-11B spin-spin (J) coupling constants. Computationally, the mechanism responsible for the boron-boron spin-spin coupling in these species is found to be analogous to that for the case of multiply-bonded carbon atoms. The trend in reduced J coupling constants for diborenes and a diboryne, measured experimentally, is in agreement with that known for alkenes and alkynes. This experimental probe of the electronic structure of the boron-boron multiple bond provides strong evidence supporting the originally proposed nature of the bonds in the diboryne and diborenes, and demonstrates that the orbitals involved in boron-boron bonding are equivalent to those well known to construct the multiple bonds between other second-row elements such as carbon and nitrogen.

  3. natural

    Directory of Open Access Journals (Sweden)

    Elías Gómez Macías

    2006-01-01

    Full Text Available Partiendo de óxido de magnesio comercial se preparó una suspensión acuosa, la cual se secó y calcinó para conferirle estabilidad térmica. El material, tanto fresco como usado, se caracterizó mediante DRX, área superficial BET y SEM-EPMA. El catalizador mostró una matriz de MgO tipo periclasa con CaO en la superficie. Las pruebas de actividad catalítica se efectuaron en lecho fijo empacado con partículas obtenidas mediante prensado, trituración y clasificación del material. El flujo de reactivos consistió en mezclas gas natural-aire por debajo del límite inferior de inflamabilidad. Para diferentes flujos y temperaturas de entrada de la mezcla reactiva, se midieron las concentraciones de CH4, CO2 y CO en los gases de combustión con un analizador de gases tipo infrarrojo no dispersivo (NDIR. Para alcanzar conversión total de metano se requirió aumentar la temperatura de entrada al lecho a medida que se incrementó el flujo de gases reaccionantes. Los resultados obtenidos permiten desarrollar un sistema de combustión catalítica de bajo costo con un material térmicamente estable, que promueva la alta eficiencia en la combustión de gas natural y elimine los problemas de estabilidad, seguridad y de impacto ambiental negativo inherentes a los procesos de combustión térmica convencional.

  4. Characteristics of hydrogen bond revealed from water clusters

    Science.gov (United States)

    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.

  5. Chemical Bonding: The Orthogonal Valence-Bond View

    Directory of Open Access Journals (Sweden)

    Alexander F. Sax

    2015-04-01

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

  6. Valence-Bond Theory and Chemical Structure.

    Science.gov (United States)

    Klein, Douglas J.; Trinajstic, Nenad

    1990-01-01

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

  7. Measuring Scars of Periodic Orbits

    CERN Document Server

    Kaplan, L

    1999-01-01

    The phenomenon of periodic orbit scarring of eigenstates of classically chaotic systems is attracting increasing attention. Scarring is one of the most important ``corrections'' to the ideal random eigenstates suggested by random matrix theory. This paper discusses measures of scars and in so doing also tries to clarify the concepts and effects of eigenfunction scarring. We propose a new, universal scar measure which takes into account an entire periodic orbit and the linearized dynamics in its vicinity. This measure is tuned to pick out those structures which are induced in quantum eigenstates by unstable periodic orbits and their manifolds. It gives enhanced scarring strength as measured by eigenstate overlaps and inverse participation ratios, especially for longer orbits. We also discuss off-resonance scars which appear naturally on either side of an unstable periodic orbit.

  8. Inflammation of the Orbit

    Science.gov (United States)

    ... Glaucoma (Video) Macular Degeneration Additional Content Medical News Inflammation of the Orbit (Inflammatory Orbital Pseudotumor) By James ... Introduction to Eye Socket Disorders Cavernous Sinus Thrombosis Inflammation of the Orbit Orbital Cellulitis Preseptal Cellulitis Tumors ...

  9. Hydrogen-bonding Interactions between Apigenin and Ethanol/Water: A Theoretical Study

    Science.gov (United States)

    Zheng, Yan-Zhen; Zhou, Yu; Liang, Qin; Chen, Da-Fu; Guo, Rui; Lai, Rong-Cai

    2016-01-01

    In this work, hydrogen-bonding interactions between apigenin and water/ethanol were investigated from a theoretical perspective using quantum chemical calculations. Two conformations of apigenin molecule were considered in this work. The following results were found. (1) For apigenin monomer, the molecular structure is non-planar, and all of the hydrogen and oxygen atoms can be hydrogen-bonding sites. (2) Eight and seven optimized geometries are obtained for apigenin (I)–H2O/CH3CH2OH and apigenin (II)–H2O/CH3CH2OH complexes, respectively. In apigenin, excluding the aromatic hydrogen atoms in the phenyl substituent, all other hydrogen atoms and the oxygen atoms form hydrogen-bonds with H2O and CH3CH2OH. (3) In apigenin–H2O/CH3CH2OH complexes, the electron density and the E(2) in the related localized anti-bonding orbital are increased upon hydrogen-bond formation. These are the cause of the elongation and red-shift of the X−H bond. The sum of the charge change transfers from the hydrogen-bond acceptor to donor. The stronger interaction makes the charge change more intense than in the less stable structures. (4) Most of the hydrogen-bonds in the complexes are electrostatic in nature. However, the C4−O5···H, C9−O4···H and C13−O2···H hydrogen-bonds have some degree of covalent character. Furthermore, the hydroxyl groups of the apigenin molecule are the preferred hydrogen-bonding sites. PMID:27698481

  10. Quantum effects in a simple ring with hydrogen bonds.

    Science.gov (United States)

    Kariev, Alisher M; Green, Michael E

    2015-05-14

    Complexes containing multiple arginines are common in proteins. The arginines are typically salt-bridged or hydrogen-bonded, so that their charges do not repel. Here we present a quantum calculation of a ring in which the components of a salt bridge composed of a guanidinium, the arginine side chain, and a carboxylic acid are separated by water molecules. When one water molecule is displaced from the ring, atomic charges of the other water molecule, as well as other properties, are significantly affected. The exchange and correlation energy differences between optimized and displaced rings are larger than thermal energy at room temperature, and larger than the sum of other energy differences. This suggests that calculations on proteins and other systems where such a ring may occur must take quantum effects into account; charges on certain atoms shift as substituents are added to the system: another water molecule, an -OH, or -CN bonded to either moiety. Also, charge shifts accompany proton shifts from the acid to guanidinium to ionize the salt bridge. The consequences of moving one water out of the ring give evidence for electron delocalization. Bond order and atomic charges are determined using natural bond orbital calculations. The geometry of the complex changes with ionization as well as the -OH and -CN additions but not in a simple manner. These results help in understanding the role of groups of arginines in salt-bridged clusters in proteins.

  11. Generating realistic synthetic meteoroid orbits

    Science.gov (United States)

    Vida, Denis; Brown, Peter G.; Campbell-Brown, Margaret

    2017-11-01

    Context. Generating a synthetic dataset of meteoroid orbits is a crucial step in analysing the probabilities of random grouping of meteoroid orbits in automated meteor shower surveys. Recent works have shown the importance of choosing a low similarity threshold value of meteoroid orbits, some pointing out that the recent meteor shower surveys produced false positives due to similarity thresholds which were too high. On the other hand, the methods of synthetic meteoroid orbit generation introduce additional biases into the data, thus making the final decision on an appropriate threshold value uncertain. Aims. As a part of the ongoing effort to determine the nature of meteor showers and improve automated methods, it was decided to tackle the problem of synthetic meteoroid orbit generation, the main goal being to reproduce the underlying structure and the statistics of the observed data in the synthetic orbits. Methods. A new method of generating synthetic meteoroid orbits using the Kernel Density Estimation method is presented. Several types of approaches are recommended, depending on whether one strives to preserve the data structure, the data statistics or to have a compromise between the two. Results. The improvements over the existing methods of synthetic orbit generation are demonstrated. The comparison between the previous and newly developed methods are given, as well as the visualization tools one can use to estimate the influence of different input parameters on the final data.

  12. The Hydrogen bonding effects in structural analysis of phenilon C-2: the quantum-chemical interpretation

    Directory of Open Access Journals (Sweden)

    Andrey V. Tokar

    2017-11-01

    Full Text Available Using ab initio methods of quantum chemistry the structure and spectral properties for molecular complexes, which were formed by monomer of phenilon С-2 chain, including some intra- and intermolecular hydrogen bonding effects as well as electrostatic interactions with evaluation of their contributions in total stabilization energy, have been investigated at natural bond orbitals theory. It is shown, that the overlapping of n1,2(O→ σ*(NН type with energies 15.4 and 9.5 kJ/mol, which correspond to the strong hydrogen bonding between amide groups, is a main direction for co-operating of some area for structural fragments of macromolecules. The proposed theoretical models are validated in reflection of spectral and energetic parameters for investigating system.

  13. Gas Phase Detection of the NH-P Hydrogen Bond and Importance of Secondary Interactions.

    Science.gov (United States)

    Møller, Kristian H; Hansen, Anne S; Kjaergaard, Henrik G

    2015-11-05

    We have observed the NH···P hydrogen bond in a gas phase complex. The bond is identified in the dimethylamine-trimethylphosphine complex by a red shift of the fundamental NH-stretching frequency observed using Fourier transform infrared spectroscopy (FT-IR). On the basis of the measured NH-stretching frequency red shifts, we find that P is a hydrogen bond acceptor atom similar in strength to S. Both are stronger acceptors than O and significantly weaker acceptors than N. The hydrogen bond angle, ∠NHP, is found to be very sensitive to the functional employed in density functional theory (DFT) optimizations of the complex and is a possible parameter to assess the quality of DFT functionals. Natural bonding orbital (NBO) energies and results from the topological methods atoms in molecules (AIM) and noncovalent interactions (NCI) indicate that the sensitivity is caused by the weakness of the hydrogen bond compared to secondary interactions. We find that B3LYP favors the hydrogen bond and M06-2X favors the secondary interactions leading to under- and overestimation, respectively, of the hydrogen bond angle relative to a DF-LCCSD(T)-F12a calculated angle. The remaining functionals tested, B3LYP-D3, B3LYP-D3BJ, CAM-B3LYP, and ωB97X-D, as well as MP2, show comparable contributions from the hydrogen bond and the secondary interactions and are close to DF-LCCSD(T)-F12a results.

  14. Third-generation muffin–tin orbitals

    Indian Academy of Sciences (India)

    Unknown

    generation muffin–tin orbi- tals (MTOs) are. We demonstrate that they can be downfolded to smaller and smaller basis sets: sp3d10, sp3, and bond orbitals. For isolated bands, it is possible to generate Wannier functions a priori. Also for bands,.

  15. 21 CFR 177.2260 - Filters, resin-bonded.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Filters, resin-bonded. 177.2260 Section 177.2260... Components of Articles Intended for Repeated Use § 177.2260 Filters, resin-bonded. Resin-bonded filters may... of this section. (a) Resin-bonded filters are prepared from natural or synthetic fibers to which have...

  16. Orthogonal hydrogen/halogen bonding in 1-(2-methoxyphenyl)-1H-imidazole-2(3H)-thione-I2 adduct: An experimental and theoretical study

    Science.gov (United States)

    El-Sheshtawy, Hamdy S.; Ibrahim, Mohamed M.; El-Mehasseb, Ibrahim; El-Kemary, Maged

    2015-05-01

    The molecular complex between 1-(2-methoxyphenyl)-1H-imidazole-2(3H)-thione (HmimOMe) and iodine (I2) was investigated. Single crystal of [(HmimOMe)radI2] adduct was grown by slow evaporation technique from chloroform at room temperature. Spectroscopic techniques such as FT-IR and Raman techniques, as well as elemental and thermal analysis were used to characterize the complex. The crystal structure shows that the formed adduct stabilized by two noncovalent interactions, namely, hydrogen bond (HB) and halogen bond (XB). Orthogonal HB/XB associated with iodine atom (I) was observed and fully characterized. The ability of iodine to behave as hydrogen bond acceptor and halogen bond donor was held responsible for the orthogonal HB/XB presence. In addition, the structure of HmimOMeradI2 was investigated theoretically using MP2/aug-cc-pVDZ level of theory. Natural bond orbital analysis (NBO) was used to investigate the molecular orbitals interactions and orbitals stabilization energies.

  17. Cooperativity between the dihydrogen bond and the NHC hydrogen bond in LiH-(HCN)n Complexes.

    Science.gov (United States)

    Li, Qing-Zhong; Hu, Ting; An, Xiu-Lin; Gong, Bao-An; Cheng, Jian-Bo

    2008-09-15

    The cooperativity between the dihydrogen bond and the NHC hydrogen bond in LiH-(HCN)(n) (n=2 and 3) complexes is investigated at the MP2 level of theory. The bond lengths, dipole moments, and energies are analyzed. It is demonstrated that synergetic effects are present in the complexes. The cooperativity contribution of the dihydrogen bond is smaller than that of the NHC hydrogen bond. The three-body energy in systems involving different types of hydrogen bonds is larger than that in the same hydrogen-bonded systems. NBO analyses indicate that orbital interaction, charge transfer, and bond polarization are mainly responsible for the cooperativity between the two types of hydrogen bonds.

  18. Role of Negative Orbit Vector in Orbital Blow-Out Fractures.

    Science.gov (United States)

    Choi, Soo Youn; Lee, Hwa; Baek, Sehyun

    2017-11-01

    Negative orbit vector is defined as the most anterior globe portion protrudes past the malar eminence. The aim of the study was to evaluate the relationship between negative orbit vector and blow-out fracture location analyzing the distance between the anterior corneal surface and orbital bone with facial soft tissue in medial and orbital floor blow out fractures using orbital computed tomography (CT). Seventy-seven patients diagnosed with blow-out fractures involving the medial or orbital floor were included. Distances from the anterior cornea to lower lid fat, inferior orbital wall, inferior orbital rim, and anterior cheek mass were measured using orbital CT scans. The proportion of negative orbit vector and measured distanced were compared between medial wall fracture and orbital floor fracture. Medical records including age, sex, concomitant ophthalmic diagnosis, and nature of injury were retrospectively reviewed. Forty-three eyes from 43 patients diagnosed with medial wall fracture and 34 eyes from 34 patients diagnosed with orbital floor fracture were included. There was no significant difference in the distance from the anterior cornea to lower lid fat (P = 0.574), inferior orbital wall (P = 0.494), or orbital rim (P = 0.685). The distance from anterior cornea to anterior cheek mass was significantly different in medial wall fracture (-0.19 ± 3.49 mm) compared with orbital floor fracture (-1.69 ± 3.70 mm), P = 0.05. Negative orbit vector was significantly higher in orbital floor fracture patients (24 among 34 patients, 70.6%) compared with those with medial wall fractures (19 among 43 patients, 44.2%) (P = 0.04). Patients presenting with a negative orbit vector relationship when the most anterior portion of globe protruded past the anterior cheek mass and malar eminence were more likely to develop orbital floor fracture than medial wall fracture.

  19. A New Approach for Studying Bond Rupture/Closure of a Spiro Benzopyran Photochromic Material: Reactivity Descriptors Derived from Frontier Orbitals and DFT Computed Electrostatic Potential Energy Surface Maps

    Directory of Open Access Journals (Sweden)

    M. S. A. Abdel-Mottaleb

    2016-01-01

    Full Text Available This paper focuses on computations technique within the framework of the TD-DFT theory for studying the relationship between structure-properties of reversible conversion of photochromic materials. Specifically, we report on 1′,3′-dihydro-8-methoxy-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H-indole] (SP and its isomers. TD-DFT calculated UV-Vis electronic spectra of the closed and open isomers of this photochromic material are in excellent agreement with the experimental results. Moreover, this paper reports on the results of theoretical investigations of reactivity indices that may govern the conversion between spiropyrans and its isomers. In addition, the solvent and rigidity of the medium significantly control the thermal bleaching of the photogenerated colored isomers and hence the switch ability pattern of the photochromic material. The effect of molecular structure computed by DFT in gas-phase and solvents on Cspiro-O bond length has been shown to correlate with photochromic properties. For this compound, DFT optimized geometry could be used to predict photochromism. Furthermore, in an attempt to predict the driving force for MC → SP, this work explores, for the first time, profitable exploitation of the calculated and visualized mapped electrostatic potential energy surfaces (ESP map. Interestingly, it seems that the electrostatic potential forces over the molecular fragments govern spirobond rupture/closure reactions. Thermodynamically, all-trans-colored isomer (CTT is the most stable merocyanine-like form.

  20. Theoretical Study of H/D Isotope Effects on Nuclear Magnetic Shieldings Using an ab initio Multi-Component Molecular Orbital Method

    Directory of Open Access Journals (Sweden)

    Masanori Tachikawa

    2013-05-01

    Full Text Available We have theoretically analyzed the nuclear quantum effect on the nuclear magnetic shieldings for the intramolecular hydrogen-bonded systems of σ-hydroxy acyl aromatic species using the gauge-including atomic orbital technique combined with our multi-component density functional theory. The effect of H/D quantum nature for geometry and nuclear magnetic shielding changes are analyzed. Our study clearly demonstrated that the geometrical changes of hydrogen-bonds induced by H/D isotope effect (called geometrical isotope effect: GIE is the dominant factor of deuterium isotope effect on 13C chemical shift.

  1. Learning Organic Chemistry Through Natural Products -12 ...

    Indian Academy of Sciences (India)

    basic due to interaction between the orbital containing the lone pair and the n· orbital of the neighbouring double bond. This makes the non- bonding electron pair ... reactions, the trajectory of the attacking group is crucial. With the help of framework models, students should understand and appreciate this 'steric' aspect of ...

  2. A Unified Theory for the Blue- and Red-Shifting Phenomena in Hydrogen and Halogen Bonds.

    Science.gov (United States)

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

    2017-04-11

    Typical hydrogen and halogen bonds exhibit red-shifts of their vibrational frequencies upon the formation of hydrogen and halogen bonding complexes (denoted as D···Y-A, Y = H and X). The finding of blue-shifts in certain complexes is of significant interest, which has led to numerous studies of the origins of the phenomenon. Because charge transfer mixing (i.e., hyperconjugation in bonding systems) has been regarded as one of the key forces, it would be illuminating to compare the structures and vibrational frequencies in bonding complexes with the charge transfer effect "turned on" and "turned off". Turning off the charge transfer mixing can be achieved by employing the block-localized wave function (BLW) method, which is an ab initio valence bond (VB) method. Further, with the BLW method, the overall stability gained in the formation of a complex can be analyzed in terms of a few physically meaningful terms. Thus, the BLW method provides a unified and physically lucid way to explore the nature of red- and blue-shifting phenomena in both hydrogen and halogen bonding complexes. In this study, a direct correlation between the total stability and the variation of the Y-A bond length is established based on our BLW computations, and the consistent roles of all energy components are clarified. The n(D) → σ*(Y-A) electron transfer stretches the Y-A bond, while the polarization due to the approach of interacting moieties reduces the HOMO-LUMO gap and results in a stronger orbital mixing within the YA monomer. As a consequence, both the charge transfer and polarization stabilize bonding systems with the Y-A bond stretched and red-shift the vibrational frequency of the Y-A bond. Notably, the energy of the frozen wave function is the only energy component which prefers the shrinking of the Y-A bond and thus is responsible for the associated blue-shifting. The total variations of the Y-A bond length and the corresponding stretching vibrational frequency are thus

  3. Crystal structure, vibrational spectra and DFT studies of hydrogen bonded 1,2,4-triazolium hydrogenselenate

    Science.gov (United States)

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

    2017-10-01

    The new hydrogen bonded molecular complex 1,2,4-triazolium hydrogenselenate (THS) is prepared by the reaction of 1H-1,2,4-triazole and selenic acid. This complex is stabilised by N-H⋯O and C-H⋯O hydrogen bonding and electrostatic attractive forces between 1H and 1,2,4-triazolium cations and hydrogen selenate anions. The XRD studies revealed that intermolecular proton transfer occur from selenic acid to 1H-1,2,4-triazole molecule, results in the formation of 1,2,4-triazolium hydrogenselenate which contains 1,2,4-triazolium cations and hydrogenselenate anions. The molecular structure of THS crystal has also been optimised by using Density Functional Theory (DFT) using B3LYP/cc-pVTZ and B3LYP/6-311++G** methods in order to find the whole characteristics of the molecular complex. The theoretical structural parameters such as bond length, bond angle and dihedral angle determined by DFT methods are well agreed with the XRD parameters. The atomic charges and thermodynamic properties are also calculated and analysed. The energies of frontier molecular orbitals HOMO, LUMO, HOMO-1, LUMO+1 and LUMO-HUMO energy gap are calculated to understand the kinetic stability and chemical reactivity of the molecular complex. The natural bond orbital analysis (NBO) has been performed in order to study the intramolecular bonding interactions and delocalisation of electrons. These intra molecular charge transfer may induce biological activities such as antimicrobials, antiinflammatory, antifungal etc. The complete vibrational assignments of THS have been performed by using FT-IR and FT-Raman spectra.

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

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2015-01-01

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

  5. Control in the Rate-Determining Step Provides a Promising Strategy To Develop New Catalysts for CO2 Hydrogenation: A Local Pair Natural Orbital Coupled Cluster Theory Study.

    Science.gov (United States)

    Mondal, Bhaskar; Neese, Frank; Ye, Shengfa

    2015-08-03

    The development of efficient catalysts with base metals for CO2 hydrogenation has always been a major thrust of interest. A series of experimental and theoretical work has revealed that the catalytic cycle typically involves two key steps, namely, base-promoted heterolytic H2 splitting and hydride transfer to CO2, either of which can be the rate-determining step (RDS) of the entire reaction. To explore the determining factor for the nature of RDS, we present herein a comparative mechanistic investigation on CO2 hydrogenation mediated by [M(H)(η(2)-H2)(PP3(Ph))](n+) (M = Fe(II), Ru(II), and Co(III); PP3(Ph) = tris(2-(diphenylphosphino)phenyl)phosphine) type complexes. In order to construct reliable free energy profiles, we used highly correlated wave function based ab initio methods of the coupled cluster type alongside the standard density functional theory. Our calculations demonstrate that the hydricity of the metal-hydride intermediate generated by H2 splitting dictates the nature of the RDS for the Fe(II) and Co(III) systems, while the RDS for the Ru(II) catalyst appears to be ambiguous. CO2 hydrogenation catalyzed by the Fe(II) complex that possesses moderate hydricity traverses an H2-splitting RDS, whereas the RDS for the high-hydricity Co(III) species is found to be the hydride transfer. Thus, our findings suggest that hydricity can be used as a practical guide in future catalyst design. Enhancing the electron-accepting ability of low-hydricity catalysts is likely to improve their catalytic performance, while increasing the electron-donating ability of high-hydricity complexes may speed up CO2 conversion. Moreover, we also established the active roles of base NEt3 in directing the heterolytic H2 splitting and assisting product release through the formation of an acid-base complex.

  6. The nature of the U=C double bond: pushing the stability of high-oxidation-state uranium carbenes to the limit.

    Science.gov (United States)

    Cooper, Oliver J; Mills, David P; McMaster, Jonathan; Tuna, Floriana; McInnes, Eric J L; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2013-05-27

    Treatment of [K(BIPM(Mes)H)] (BIPM(Mes)={C(PPh2NMes)2}(2−); Mes=C6H2-2,4,6-Me3) with [UCl4(thf)3] (1 equiv) afforded [U(BIPM(Mes)H)(Cl)3(thf)] (1), which generated [U(BIPM(Mes))(Cl)2(thf)2] (2), following treatment with benzyl potassium. Attempts to oxidise 2 resulted in intractable mixtures, ligand scrambling to give [U(BIPM(Mes))2] or the formation of [U(BIPM(Mes)H)(O)2(Cl)(thf)] (3). The complex [U(BIPM(Dipp))(μ-Cl)4(Li)2(OEt2)(tmeda)] (4) (BIPM(Dipp)={C(PPh2NDipp)2}(2−); Dipp=C6H3-2,6-iPr2; tmeda=N,N,N′,N′-tetramethylethylenediamine) was prepared from [Li2(BIPM(Dipp))(tmeda)] and [UCl4(thf)3] and, following reflux in toluene, could be isolated as [U(BIPM(Dipp))(Cl)2(thf)2] (5). Treatment of 4 with iodine (0.5 equiv) afforded [U(BIPM(Dipp))(Cl)2(μ-Cl)2(Li)(thf)2] (6). Complex 6 resists oxidation, and treating 4 or 5 with N-oxides gives [{U(BIPM(Dipp)H)(O)2- (μ-Cl)2Li(tmeda)] (7) and [{U(BIPM(Dipp)H)(O)2(μ-Cl)}2] (8). Treatment of 4 with tBuOLi (3 equiv) and I2 (1 equiv) gives [U(BIPM(Dipp))(OtBu)3(I)] (9), which represents an exceptionally rare example of a crystallographically authenticated uranium(VI)–carbon σ bond. Although 9 appears sterically saturated, it decomposes over time to give [U(BIPM(Dipp))(OtBu)3]. Complex 4 reacts with PhCOtBu and Ph2CO to form [U(BIPM(Dipp))(μ-Cl)4(Li)2(tmeda)(OCPhtBu)] (10) and [U(BIPM(Dipp))(Cl)(μ-Cl)2(Li)(tmeda)(OCPh2)] (11). In contrast, complex 5 does not react with PhCOtBu and Ph2CO, which we attribute to steric blocking. However, complexes 5 and 6 react with PhCHO to afford (DippNPPh2)2C=C(H)Ph (12). Complex 9 does not react with PhCOtBu, Ph2CO or PhCHO; this is attributed to steric blocking. Theoretical calculations have enabled a qualitative bracketing of the extent of covalency in early-metal carbenes as a function of metal, oxidation state and the number of phosphanyl substituents, revealing modest covalent contributions to U=C double bonds. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Understanding Bonds - Denmark

    DEFF Research Database (Denmark)

    Rimmer, Nina Røhr

    2016-01-01

    a specified rate of interest during the life of the bond and to repay the face value of the bond (the principal) when it “matures,” or comes due. Among the types of bonds you can choose from are: Government securities, municipal bonds, corporate bonds, mortgage and asset-backed securities, federal agency...

  8. 3c/4e [small sigma, Greek, circumflex]-type long-bonding competes with ω-bonding in noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I): a NBO/NRT perspective.

    Science.gov (United States)

    Zhang, Guiqiu; Li, Hong; Weinhold, Frank; Chen, Dezhan

    2016-03-21

    Noble-gas hydrides HNgY are frequently described as a single ionic form (H-Ng)(+)Y(-). We apply natural bond orbital (NBO) and natural resonance theory (NRT) analyses to a series of noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I) to gain quantitative insight into the resonance bonding of these hypervalent molecules. We find that each of the studied species should be better represented as a resonance hybrid of three leading resonance structures, namely, H-Ng(+ -):Y (I), H:(- +)Ng-Y (II), and H^Y (III), in which the "ω-bonded" structures I and II arise from the complementary donor-acceptor interactions nY → σ*HNg and nH → σ*NgY, while the "long-bond" ([small sigma, Greek, circumflex]-type) structure III arises from the nNg → [small sigma, Greek, circumflex]*HY/[small sigma, Greek, circumflex]HY interaction. The bonding for all of the studied molecules can be well described in terms of the continuously variable resonance weightings of 3c/4e ω-bonding and [small sigma, Greek, circumflex]-type long-bonding motifs. Furthermore, we find that the calculated bond orders satisfy a generalized form of "conservation of bond order" that incorporates both ω-bonding and long-bonding contributions [viz., (bHNg + bNgY) + bHY = bω-bonding + blong-bonding = 1]. Such "conservation" throughout the title series implies a competitive relationship between ω-bonding and [small sigma, Greek, circumflex]-type long-bonding, whose variations are found to depend in a chemically reasonable manner on the electronegativity of Y and the outer valence-shell character of the central Ng atom. The calculated bond orders are also found to exhibit chemically reasonable correlations with bond lengths, vibrational frequencies, and bond dissociation energies, in accord with Badger's rule and related empirical relationships. Overall, the results provide electronic principles and chemical insight that may prove useful in the rational design of noble-gas hydrides of

  9. Imidazole Nitrogens of Two Histidine Residues Participating in N-H···N Hydrogen Bonds in Protein Structures: Structural Bioinformatics Approach Combined with Quantum Chemical Calculations.

    Science.gov (United States)

    Iyer, Abhishek Hariharan; Krishna Deepak, R N V; Sankararamakrishnan, Ramasubbu

    2018-01-25

    Protein structures are stabilized by different types of hydrogen bonds. However, unlike the DNA double helical structure, the N-H···N type of hydrogen bonds is relatively rare in proteins. N-H···N hydrogen bonds formed by imidazole groups of two histidine residues have not been investigated. We have systematically analyzed 5333 high-resolution protein structures with resolution 1.8 Å or better and identified 285 histidine pairs in which the nitrogen atoms of the imidazole side chains can potentially participate in N-H···N hydrogen bonds. The histidine pairs were further divided into two groups, neutral-neutral and protonated-neutral, depending on the protonation state of the donor histidine. Quantum chemical calculations were performed on imidazole groups adopting the same geometry observed in the protein structures. Average interaction energies between the interacting imidazole groups are -6.45 and -22.5 kcal/mol for neutral-neutral and protonated-neutral, respectively. Hydrogen bond interaction between the imidazole moieties is further confirmed by natural bond orbital analyses of the model compounds. Histidine residues involved in N-H···N hydrogen bonds are relatively more buried and have low B-factor values in the protein structures. N-H···N hydrogen bond formed by a pair of buried histidine residues can significantly contribute to the structural stability of proteins.

  10. Chemical Bonds II

    Science.gov (United States)

    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)

  11. S⋯N chalcogen bonded complexes of carbon disulfide with diazines. Theoretical study

    Science.gov (United States)

    Zierkiewicz, Wiktor; Fanfrlík, Jindřich; Michalczyk, Mariusz; Michalska, Danuta; Hobza, Pavel

    2018-01-01

    Carbon disulfide complexes with diazine (pyridazine, pyrimidine or pyrazine) have been studied by density functional BLYP-D3 and ab initio CCSD(T) methods. All possible conformers of these complexes have been found. In the chalcogen bonded complexes, the CCSD(T)/cc-pvtz calculated interaction energies (ΔE) range between -0.89 and -2.19 kcal mol-1. These complexes are more stable than those stabilized by hydrogen bond. The linear correlation between the ΔE and the most negative values of the electrostatic potential surfaces (Vs,min) on the nitrogen atom of the diazines has been found. According to the symmetry-adapted perturbation theory (SAPT) analysis, in the chalcogen bonded complexes among all of the attraction forces the electrostatic component is the most important one, while in the hydrogen bonded and stacking complexes the dispersion contribution is the leading term. Moreover, the Natural Bond Orbitals (NBO), AIM and Noncovalent Interaction Index (NCI) analyses have been performed.

  12. What Determines Bond Costs. Municipal Bonds Series.

    Science.gov (United States)

    Young, Douglas; And Others

    Public officials in small towns who participate infrequently in the bond market need information about bond financing. This publication, one in a series of booklets published by the Western Rural Development Center using research gathered between 1967-77, discusses factors influencing the marketability and cost of bond financing for towns and…

  13. A method of orbital analysis for large-scale first-principles simulations

    Energy Technology Data Exchange (ETDEWEB)

    Ohwaki, Tsukuru [Advanced Materials Laboratory, Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka, Kanagawa 237-8523 (Japan); Otani, Minoru [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ozaki, Taisuke [Research Center for Simulation Science (RCSS), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)

    2014-06-28

    An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF{sub 4})

  14. Unusual structure, bonding and properties in a californium borate

    Energy Technology Data Exchange (ETDEWEB)

    Polinski, Matthew J.; Garner, Edward B.; Maurice, Rémi; Planas, Nora; Stritzinger, Jared T.; Parker, T. Gannon; Cross, Justin N.; Green, Thomas D.; Alekseev, Evgeny V.; Van Cleve, Shelley M.; Depmeier, Wulf; Gagliardi, Laura; Shatruk, Michael; Knappenberger, Kenneth L.; Liu, Guokui; Skanthakumar, S.; Soderholm, Lynda; Dixon, David A.; Albrecht-Schmitt, Thomas E.

    2014-03-23

    The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. We demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations.

  15. Theoretical exploration of pnicogen bond noncovalent interactions ...

    Indian Academy of Sciences (India)

    block-localized wave function (BLW) based energy decomposition scheme, Guan and Mo39 investigated thoroughly the pnicogen bond nature and the corre- sponding electron transfer in a series of substituted phosphines complexed with ammonia. Moreover, some novel pnicogen bond with special electronic structures.

  16. Wire bonding in microelectronics

    CERN Document Server

    Harman, George G

    2010-01-01

    Wire Bonding in Microelectronics, Third Edition, has been thoroughly revised to help you meet the challenges of today's small-scale and fine-pitch microelectronics. This authoritative guide covers every aspect of designing, manufacturing, and evaluating wire bonds engineered with cutting-edge techniques. In addition to gaining a full grasp of bonding technology, you'll learn how to create reliable bonds at exceedingly high yields, test wire bonds, solve common bonding problems, implement molecular cleaning methods, and much more. Coverage includes: Ultrasonic bonding systems and technologies, including high-frequency systems Bonding wire metallurgy and characteristics, including copper wire Wire bond testing Gold-aluminum intermetallic compounds and other interface reactions Gold and nickel-based bond pad plating materials and problems Cleaning to improve bondability and reliability Mechanical problems in wire bonding High-yield, fine-pitch, specialized-looping, soft-substrate, and extreme-temperature wire bo...

  17. Halogen Bonds in Novel Polyhalogen Monoanions.

    Science.gov (United States)

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

    2017-06-27

    Polyhalogen monoanions [X 2n+1 ] - (X=Cl and Br; n=1, 2, 3, 4, and 5) have been systematically studied using the block-localized wave function (BLW) method, which offers a valence bond (VB) analysis. For each species, the most stable isomer can be described as a central halide anion X - non-classically bonded to a number of dihalogen molecules X 2 via "halogen bonds". VB analyses confirm the dominant role of the charge-transfer interaction between the lone pair on X - and the σ-anti-bonding orbital of X 2 molecule (n→σ*) in X 3 - and higher analogues. Thus, our study demonstrates that these halogen bonds are essentially dative covalent interactions. Importantly, the charge-transfer interaction between [X 2n-1 ] - and X 2 decreases with the increasing n, in accord with the weakening of the Lewis basicity as characterized by the corresponding HOMO energy. The reduction of the charge transfer interaction underscores the reduction of covalence in halogen bonds in [X 2n+1 ] - . This tendency highlights the anti-cooperative effect in polyhalogen monoanions. All in all, the halogen bond between X - and nX 2 molecules exhibits the same trends as in X - with a single X 2 molecule. In other words, halogen bonding in the larger clusters derives from the same bonding mechanism as the [X 3 ] - anion. As such, the X - ⋅⋅⋅X 2 halogen bond at different bond lengths forms a gauge of covalence for the entire [X 2n+1 ] - family. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Seniority Number in Valence Bond Theory.

    Science.gov (United States)

    Chen, Zhenhua; Zhou, Chen; Wu, Wei

    2015-09-08

    In this work, a hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, is proposed and applied to the studies of the potential energy curves (PECs) of H8, N2, and C2 molecules. It is found that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller nonparallelity errors than its molecular orbital (MO) theory-based analogue. Test results reveal that the nonorthogonal orbital-based VB theory provides a reverse but more efficient way to truncate the complete active Hilbert space by seniority numbers.

  19. Application of the Covalent Bond Classification Method for the Teaching of Inorganic Chemistry

    Science.gov (United States)

    Green, Malcolm L. H.; Parkin, Gerard

    2014-01-01

    The Covalent Bond Classification (CBC) method provides a means to classify covalent molecules according to the number and types of bonds that surround an atom of interest. This approach is based on an elementary molecular orbital analysis of the bonding involving the central atom (M), with the various interactions being classified according to the…

  20. Preseptal Cellulitis, Orbital Cellulitis, Orbital Abscess

    Directory of Open Access Journals (Sweden)

    Rana Altan Yaycıoğlu

    2012-12-01

    Full Text Available Patients with orbital infections present to our clinic usually with unilateral pain, hyperemia, and edema of the eyelids. The differentiation between preseptal and orbital cellulitis is utmost important in that the second requires hospitalization. Since in orbital cellulitis, the tissues posterior to the orbital septum are involved, signs such as conjunctival chemosis, limited eye movement, decreased vision, as well as afferent pupil defect secondary to optic nerve involvement may also be observed. Prompt intravenous antibiotic treatment should be started, and surgical drainage may be performed if patient shows failure to improve in 48 hours despite optimal management. Without treatment, the clinical course may progress to subperiosteal or orbital abscess, and even to cavernous sinus thrombosis. (Turk J Ophthalmol 2012; 42: Supplement 52-6

  1. Aryl-NHC-group 13 trimethyl complexes: structural, stability and bonding insights

    KAUST Repository

    Wu, Melissa M.

    2016-12-14

    Treatment of aromatic N-substituted N-heterocyclic carbenes (NHCs) with trimethyl-gallium and -indium yielded the new Lewis acid-base adducts, IMes·GaMe3 (1), SIMes·GaMe3 (2), IPr·GaMe3 (3), SIPr·GaMe3 (4), IMes·InMe3 (5), SIMes·InMe3 (6), IPr·InMe3 (7), and SIPr·InMe3 (8), with all complexes being identified by X-ray diffraction, IR, and multinuclear NMR analyses. Complex stability was found to be largely dependent on the nature of the constituent NHC ligands. Percent buried volume (%VBur) and topographic steric map analyses were employed to quantify and elucidate the observed trends. Additionally, a detailed bond snapping energy (BSE) decomposition analysis focusing on both steric and orbital interactions of the M-NHC bond (M = Al, Ga and In) has been performed.

  2. Transneptunian Orbit Computation

    Science.gov (United States)

    Virtanen, J.; Tancredi, G.; Bernstein, G. M.; Spahr, T.; Muinonen, K.

    We review the orbit computation problem for the transneptunian population. For these distant objects, the problem is characterized by their short observed orbital arcs, which are known to be coupled with large uncertainties in orbital elements. Currently, the observations of even the best observed objects, such as the first-ever transneptunian object (TNO), Pluto, cover only a fraction of their revolution. Furthermore, of the some 1200 objects discovered since 1992, roughly half have observations from only one opposition. To ensure realistic analyses of the population, e.g., in the derivation of unbiased orbital distributions or correlations between orbital and physical properties, realistic estimation of orbital uncertainties is important. We describe the inverse problem of orbit computation, emphasizing the short-arc problem and its statistical treatment. The complete solution to the problem can be given in terms of the orbital-element probability density function (p.d.f.), which then serves as a starting point for any further analysis, where knowledge of orbital uncertainties is required. We give an overview of the variety of computational techniques developed for TNO orbital uncertainty estimation in the recent years. After presenting the current orbital distribution, we demonstrate their application to several prediction problems, such as classification, ephemeris prediction, and dynamical analysis of objects. We conclude with some future prospects for TNO orbit computation concerning the forthcoming next-generation surveys, including the anticipated evolution of TNO orbital uncertainties over the coming decades.

  3. Quantifying the Sigma and Pi interactions between U(V) f orbitals and halide, alkyl, alkoxide, amide and ketimide ligands

    Energy Technology Data Exchange (ETDEWEB)

    University of California, Berkeley; Lukens, Wayne W.; Edelstein, Norman M.; Magnani, Nicola; Hayton, Trevor W.; Fortier, Skye; Seaman, Lani A.

    2013-06-20

    f Orbital bonding in actinide and lanthanide complexes is critical to their behavior in a variety of areas from separations to magnetic properties. Octahedral f1 hexahalide complexes have been extensively used to study f orbital bonding due to their simple electronic structure and extensive spectroscopic characterization. The recent expansion of this family to include alkyl, alkoxide, amide, and ketimide ligands presents the opportunity to extend this study to a wider variety of ligands. To better understand f orbital bonding in these complexes, the existing molecular orbital (MO) model was refined to include the effect of covalency on spin orbit coupling in addition to its effect on orbital angular momentum (orbital reduction). The new MO model as well as the existing MO model and the crystal field (CF) model were applied to the octahedral f1 complexes to determine the covalency and strengths of the ? and ? bonds formed by the f orbitals. When covalency is significant, MO models more precisely determined the strengths of the bonds derived from the f orbitals; however, when covalency was small, the CF model was better than either MO model. The covalency determined using the new MO model is in better agreement with both experiment and theory than that predicted by the existing MO model. The results emphasize the role played by the orbital energy in determining the strength and covalency of bonds formed by the f orbitals.

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

    Science.gov (United States)

    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. Copyright © 2016 Elsevier Inc. All rights reserved.

  5. A new noncovalent force: comparison of P···N interaction with hydrogen and halogen bonds.

    Science.gov (United States)

    Scheiner, Steve

    2011-03-07

    When PH(3) is paired with NH(3), the two molecules are oriented such that the P and N atoms face one another directly, without the intermediacy of a H atom. Quantum calculations indicate that this attraction is due in part to the transfer of electron density from the lone pair of the N atom to the σ(∗) antibond of a P-H covalent bond. Unlike a H-bond, the pertinent hydrogen is oriented about 180° away from, instead of toward, the N, and the N lone pair overlaps with the lobe of the P-H σ(∗) orbital that is closest to the P. In contrast to halogen bonds, there is no requirement of a σ-hole of positive electrostatic potential on the P atom, nor is it necessary for the two interacting atoms to be of differing potential. In fact, the two atoms can be identical, as the global minimum of the PH(3) homodimer has the same structure, characterized by a P···P attraction. Natural bond orbital analysis, energy decomposition, and visualization of total electron density shifts reveal other similarities and differences between the three sorts of molecular interaction. © 2011 American Institute of Physics.

  6. Exploring the Role of Substitution on the Formation of Se···O/N Noncovalent Bonds.

    Science.gov (United States)

    Shukla, Rahul; Chopra, Deepak

    2015-11-25

    In this article, we have examined the effect of substitution on the formation of neutral XHSe···O/N (X = -H, -F, -CH3, -CF3, -Cl, -OH, -OCH3, -NH2, -NHCH3, -CN) noncovalent bonds with the oxygen atom from H2O molecule and the nitrogen atom from NH3 being the electron donor atoms, respectively. In addition to this, analysis has also been performed on XMeSe···O/N complexes to study the effect of the role of hydrogen bonding with the hydrogen atoms of the methyl group on Se···O/N interactions. Binding energy calculations were performed to determine the strength of these contacts. The obtained results establish the fact that the presence of a methyl group influences the strength of the observed Se···O/N interactions. Also in some cases, the O-H···Se interaction was observed to be more preferable over the Se···O interaction. The major contribution for stabilization of such Se···O/N interactions is from an interplay among the electrostatics and the exchange energy. To obtain deeper insights and understanding of such Se···O/N contacts, a topological analysis, using the QTAIM approach were also performed. This analysis showed that although the presence of a Me group modifies the Se···O/N interaction, it does not necessitate the formation of hydrogen bonds. To obtain insights into the orbital contributions, a natural bond orbital (NBO) analysis were performed which depicts that the strength of such interactions were derived via charge transfer from the oxygen/nitrogen lone pair to the σ* orbital of the Se-X bond.

  7. "Vibrational bonding": a new type of chemical bond is discovered.

    Science.gov (United States)

    Rhodes, Christopher J; Macrae, Roderick M

    2015-01-01

    A long-sought but elusive new type of chemical bond, occurring on a minimum-free, purely repulsive potential energy surface, has recently been convincingly shown to be possible on the basis of high-level quantum-chemical calculations. This type of bond, termed a vibrational bond, forms because the total energy, including the dynamical energy of the nuclei, is lower than the total energy of the dissociated products, including their vibrational zero-point energy. For this to be the case, the ZPE of the product molecule must be very high, which is ensured by replacing a conventional hydrogen atom with its light isotope muonium (Mu, mass = 1/9 u) in the system Br-H-Br, a natural transition state in the reaction between Br and HBr. A paramagnetic species observed in the reaction Mu +Br2 has been proposed as a first experimental sighting of this species, but definitive identification remains challenging.

  8. Fe as hydrogen/halogen bond acceptor in square pyramidal Fe(CO)5.

    Science.gov (United States)

    Aiswaryalakshmi, P; Mani, Devendra; Arunan, E

    2013-08-05

    Hydrogen bonded complexes formed between the square pyramidal Fe(CO)5 with HX (X = F, Cl, Br), showing X-H···Fe interactions, have been investigated theoretically using density functional theory (DFT) including dispersion correction. Geometry, interaction energy, and large red shift of about 400 cm(-1) in the HX stretching frequency confirm X-H···Fe hydrogen bond formation. In the (CO)5Fe···HBr complex, following the significant red-shift, the HBr stretching mode is coupled with the carbonyl stretching modes. This clearly affects the correlation between frequency shift and binding energy, which is a hallmark of hydrogen bonds. Atoms in Molecule (AIM) theoretical analyses show the presence of a bond critical point between the iron and the hydrogen of HX and significant mutual penetration. These X-H···Fe hydrogen bonds follow most but not all of the eight criteria proposed by Koch and Popelier (J. Phys. Chem. 1995, 99, 9747) based on their investigations on C-H···O hydrogen bonds. Natural bond orbital (NBO) analysis indicates charge transfer from the organometallic system to the hydrogen bond donor. However, there is no correlation between the extent of charge transfer and interaction energy, contrary to what is proposed in the recent IUPAC recommendation (Pure Appl. Chem. 2011, 83, 1637). The "hydrogen bond radius" for iron has been determined to be 1.60 ± 0.02 Å, and not surprisingly it is between the covalent (1.27 Å) and van der Waals (2.0) radii of Fe. DFT and AIM theoretical studies reveal that Fe in square pyramidal Fe(CO)5 can also form halogen bond with ClF and ClH as "halogen bond donor". Both these complexes show mutual penetration as well, though the Fe---Cl distance is closer to the sum of van der Waals radii of Fe and Cl in (CO)5Fe···ClH, and it is about 1 Å less in (CO)5Fe···ClF.

  9. ASC Champ Orbit Model

    DEFF Research Database (Denmark)

    Riis, Troels; Jørgensen, John Leif

    1999-01-01

    This documents describes a test of the implementation of the ASC orbit model for the Champ satellite.......This documents describes a test of the implementation of the ASC orbit model for the Champ satellite....

  10. Lunar Orbiter Photo Gallery

    Data.gov (United States)

    National Aeronautics and Space Administration — The Lunar Orbiter Photo Gallery is an extensive collection of over 2,600 high- and moderate-resolution photographs produced by all five of the Lunar Orbiter...

  11. Natural Orbitals from Generalized Sturmian Calculations

    DEFF Research Database (Denmark)

    Avery, John Scales; Avery, James Emil

    2003-01-01

    The generalized Sturmian method is a direct configuration interaction method for solving the Schr\\"odinger equation of a many-electron system. The configurations in the basis set are solutions to an approximate Schr\\"odinger equation with a weighted potential $\\beta_\

  12. Spying on the boron–boron triple bond using spin–spin coupling measured from 11B solid-state NMR spectroscopy† †Electronic supplementary information (ESI) available: Experimental and computational details. See DOI: 10.1039/c5sc00644a Click here for additional data file.

    Science.gov (United States)

    Perras, Frédéric A.; Ewing, William C.; Dellermann, Theresa; Böhnke, Julian; Ullrich, Stefan; Schäfer, Thomas

    2015-01-01

    There is currently tremendous interest in the previously documented example of a stable species exhibiting a boron–boron triple bond (Science, 2012, 336, 1420). Notably, it has recently been stated using arguments based on force constants that this diboryne may not, in reality, feature a boron–boron triple bond. Here, we use advanced solid-state NMR and computational methodology in order to directly probe the orbitals involved in multiple boron–boron bonds experimentally via analysis of 11B–11B spin–spin (J) coupling constants. Computationally, the mechanism responsible for the boron–boron spin–spin coupling in these species is found to be analogous to that for the case of multiply-bonded carbon atoms. The trend in reduced J coupling constants for diborenes and a diboryne, measured experimentally, is in agreement with that known for alkenes and alkynes. This experimental probe of the electronic structure of the boron–boron multiple bond provides strong evidence supporting the originally proposed nature of the bonds in the diboryne and diborenes, and demonstrates that the orbitals involved in boron–boron bonding are equivalent to those well known to construct the multiple bonds between other second-row elements such as carbon and nitrogen. PMID:29142694

  13. On the theory of Killing orbits in spacetime

    Science.gov (United States)

    Hall, G. S.

    2003-09-01

    This paper gives a theoretical discussion of the orbits and isotropies which arise in a spacetime which admits a Lie algebra of Killing vector fields. The submanifold structure of the orbits is explored together with their induced Killing vector structure. A general decomposition of a spacetime in terms of the nature and dimension of its orbits is given and the concept of stability and instability for orbits introduced. A general relation is shown linking the dimensions of the Killing algebra, the orbits and the isotropies. The well-behaved nature of 'stable' orbits and the possible misbehaviour of the 'unstable' ones is pointed out and, in particular, the fact that independent Killing vector fields in spacetime may not induce independent Killing vector fields on unstable orbits. Several examples are presented to exhibit these features. Finally, an appendix is given which revisits and attempts to clarify the well-known theorem of Fubini on the dimension of Killing orbits.

  14. Introducing Earth's Orbital Eccentricity

    Science.gov (United States)

    Oostra, Benjamin

    2015-01-01

    Most students know that planetary orbits, including Earth's, are elliptical; that is Kepler's first law, and it is found in many science textbooks. But quite a few are mistaken about the details, thinking that the orbit is very eccentric, or that this effect is somehow responsible for the seasons. In fact, the Earth's orbital eccentricity is…

  15. Idiopathic granulomatous orbital inflammation

    NARCIS (Netherlands)

    Mombaerts, I.; Schlingemann, R. O.; Goldschmeding, R.; Koornneef, L.

    1996-01-01

    PURPOSE: Granulomatous orbital inflammation may occur as an isolated condition of unknown origin. These idiopathic granulomatous lesions are believed to belong to the orbital pseudotumor group by some authors, whereas others consider them sarcoidosis limited to the orbit. The aim of this study is to

  16. Artificial satellites orbiting planetary satellites: critical inclination and sun-synchronous orbits

    Science.gov (United States)

    da Costa, Maria Lívia G. T. X.; Vilhena de Moraes, Rodolpho; Carvalho, Jean Paulo S.; Prado, Antônio Fernando B. A.

    2017-10-01

    The behavior of critical inclinations and sun-synchronous orbits of artificial satellites orbiting planetary satellites are analyzed considering, simultaneously, the influence of the harmonics J 2 and C 22, both due to the non-uniform mass distribution of the natural satellite. In the present research, the central bodies of interest are the Moon and two of the Galilean moons: Io and Europa.

  17. Role of halogen and hydrogen bonds for stabilization of antithyroid drugs with hypohalous acids (HOX, X = I, Br, and Cl) adducts

    Science.gov (United States)

    El-Sheshtawy, Hamdy S.; El-Mehasseb, Ibrahim

    2017-11-01

    The mechanism for the inhibition of thyroid hormones by the thioamide-like antithyroid drug is a key process in the thyroid gland function. Therefore, in this study theoretical investigation of the molecular interaction between two antithyroid drugs, namely methimazol (MMI) and thiazoline-2-thione (T2T), with the hypohalous acids (HOX, X = I, Br, and Cl), which act as heme-linked halogenated species to tyrosine residue was discussed. The calculations were performed by M06-2X and MP2 using aug-cc-pVDZ level of theory. In addition, wB97xd/6-31G* level of theory was used in order to account for the dispersion forces. The results show the possible formation of three adducts, which is stabilized by halogen bond (I), both halogen and hydrogen bonds (II), two hydrogen bonds (III). The binding energies of the complexes reveals stabilization in the order III > II > I. The binding energies of the complexes was increased with increasing the electron affinity and polarizability of halogen atom, the dipole moment of the complexes (I and II), the electrostatic potential on halogen atom (Vmax:i.e σ-hole), and the charge-transfer process through the halogen bond in I. On the other hand, the binding energies of the complexes decreased with increasing the halogen atom electronegativity and the dipole moment of complex III. Natural bond orbital (NBO) analysis was used to investigate the molecular orbital interactions and the charge transfer process upon complexation.

  18. Complexes between hypohalous acids and phosphine derivatives. Pnicogen bond versus halogen bond versus hydrogen bond.

    Science.gov (United States)

    Li, Qingzhong; Zhu, Hongjie; Zhuo, Hongying; Yang, Xin; Li, Wenzuo; Cheng, Jianbo

    2014-11-11

    The complexes of HOBr:PH2Y (Y=H, F, Cl, Br, CH3, NH2, OH, and NO2), HOCl:PH2F, and HOI:PH2F have been investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Four types of structures (1, 2, 3a, and 3b) were observed for these complexes. 1 is stabilized by an O⋯P pnicogen bond, 2 by a P⋯X halogen bond, 3a by a H⋯P hydrogen bond and a P⋯X pnicogen bond, and 3b by H⋯P and H⋯Br hydrogen bonds. Their relative stability is related to the halogen X of HOX and the substituent Y of PH2Y. These structures can compete with interaction energy of -10.22∼-29.40 kJ/mol. The HO stretch vibration shows a small red shift in 1, a small irregular shift in 2, but a prominent red shift in 3a and 3b. The XO stretch vibration exhibits a smaller red shift in 1, a larger red shift in 2, but an insignificant blue shift in 3a and 3b. The PY stretch vibration displays a red shift in 1 but a blue shift in 2, 3a, and 3b. The formation mechanism, stability, and properties of these structures have been analyzed with molecular electrostatic potentials, orbital interactions, and non-covalent interaction index. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Symmetry in bonding and spectra an introduction

    CERN Document Server

    Douglas, Bodie E

    1985-01-01

    Many courses dealing with the material in this text are called ""Applications of Group Theory."" Emphasizing the central role and primary importance of symmetry in the applications, Symmetry in Bonding and Spectra enables students to handle applications, particularly applications to chemical bonding and spectroscopy. It contains the essential background in vectors and matrices for the applications, along with concise reviews of simple molecular orbital theory, ligand field theory, and treatments of molecular shapes, as well as some quantum mechanics. Solved examples in the text illustra

  20. Families of Keplerian orbits

    Energy Technology Data Exchange (ETDEWEB)

    Butikov, Eugene I [St Petersburg State University, St Petersburg (Russian Federation)

    2003-03-01

    Various properties of Keplerian orbits traced by satellites that are launched from one and the same spatial point with different initial velocities are discussed. Two families of elliptical orbits are investigated, namely the sets of orbits produced by a common direction but different magnitudes of the initial velocities, and by a common magnitude but various directions of the initial velocities. For the latter family, the envelope of all the orbits is found, which is the boundary of the spatial region occupied by the orbits.

  1. Families of Keplerian orbits

    CERN Document Server

    Butikov, E I

    2003-01-01

    Various properties of Keplerian orbits traced by satellites that are launched from one and the same spatial point with different initial velocities are discussed. Two families of elliptical orbits are investigated, namely the sets of orbits produced by a common direction but different magnitudes of the initial velocities, and by a common magnitude but various directions of the initial velocities. For the latter family, the envelope of all the orbits is found, which is the boundary of the spatial region occupied by the orbits.

  2. The pnicogen bond: its relation to hydrogen, halogen, and other noncovalent bonds.

    Science.gov (United States)

    Scheiner, Steve

    2013-02-19

    Among a wide range of noncovalent interactions, hydrogen (H) bonds are well known for their specific roles in various chemical and biological phenomena. When describing conventional hydrogen bonding, researchers use the notation AH···D (where A refers to the electron acceptor and D to the donor). However, the AH molecule engaged in a AH···D H-bond can also be pivoted around by roughly 180°, resulting in a HA···D arrangement. Even without the H atom in a bridging position, this arrangement can be attractive, as explained in this Account. The electron density donated by D transfers into a AH σ* antibonding orbital in either case: the lobe of the σ* orbital near the H atom in the H-bonding AH···D geometry, or the lobe proximate to the A atom in the HA···D case. A favorable electrostatic interaction energy between the two molecules supplements this charge transfer. When A belongs to the pnictide family of elements, which include phosphorus, arsenic, antimony, and bismuth, this type of interaction is called a pnicogen bond. This bonding interaction is somewhat analogous to the chalcogen and halogen bonds that arise when A is an element in group 16 or 17, respectively, of the periodic table. Electronegative substitutions, such as a F for a H atom opposite the electron donor atom, strengthen the pnicogen bond. For example, the binding energy in FH(2)P···NH(3) greatly exceeds that of the paradigmatic H-bonding water dimer. Surprisingly, di- or tri-halogenation does not produce any additional stabilization, in marked contrast to H-bonds. Chalcogen and halogen bonds show similar strength to the pnicogen bond for a given electron-withdrawing substituent. This insensitivity to the electron-acceptor atom distinguishes these interactions from H-bonds, in which energy depends strongly upon the identity of the proton-donor atom. As with H-bonds, pnicogen bonds can extract electron density from the lone pairs of atoms on the partner molecule, such as N, O, and

  3. Emphasizing the Significance of Electrostatic Interactions in Chemical Bonding

    Science.gov (United States)

    Venkataraman, Bhawani

    2017-01-01

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

  4. Orbital fractures: a review

    Directory of Open Access Journals (Sweden)

    Jeffrey M Joseph

    2011-01-01

    Full Text Available Jeffrey M Joseph, Ioannis P GlavasDivision of Ophthalmic Plastic and Reconstructive Surgery, Department of Ophthalmology, School of Medicine, New York University, New York, NY, USA; Manhattan Eye, Ear, and Throat Hospital, New York, NY, USAAbstract: This review of orbital fractures has three goals: 1 to understand the clinically relevant orbital anatomy with regard to periorbital trauma and orbital fractures, 2 to explain how to assess and examine a patient after periorbital trauma, and 3 to understand the medical and surgical management of orbital fractures. The article aims to summarize the evaluation and management of commonly encountered orbital fractures from the ophthalmologic perspective and to provide an overview for all practicing ophthalmologists and ophthalmologists in training.Keywords: orbit, trauma, fracture, orbital floor, medial wall, zygomatic, zygomatic complex, zmc fracture, zygomaticomaxillary complex fractures 

  5. The investigation of influence of adhesion promoters on adhesion bond between vulcanisate and zinc coated steel cord in products based on mixtures of natural and 1,4-cis-polybutadiene rubber

    Directory of Open Access Journals (Sweden)

    Gojić Mirko T.

    2007-01-01

    Full Text Available The mixtures of elastomer compounds based on natural and 1,4-cispolybutadiene rubber of 80:20 ratio, were used for the investigation of adhesion promoters influence on adhesion of vulcanisate to steel cord. Ni-stearate and resorsynol-formaldehyde resin combined with hexamethylenetetramine in various mass ratios were included as adhesion promoters. Elastomer mixtures were prepared using a laboratory double mill, and the rheological and vulcanization characteristics were examined on a vulcameter provided with an oscillating disc, a higher temperature of 145 °C. The crosslinking of the mixture was carried out by press, at a temperature of 145 °C and specific pressure of 40 bar, in period of 45 minutes. A wide number of standardized methods for physical mechanical characterization of vulcanization prior and after accelerated aging were used. The adhesion of vulcanizate bond with zinc coated steel cord was determined according to the so called H-test, by measuring the pulling-out force of the cord from the vulcanized block, and the degree of coverage of cord with vulcanizate after separation. The results of examinations show significant dependence of physico-mechanical characteristics and adhesion forces on the type and amount of used adhesion promoters in experimental elastomer mixtures.

  6. Spin-Orbital Order Modified by Orbital Dilution in Transition-Metal Oxides: From Spin Defects to Frustrated Spins Polarizing Host Orbitals

    Directory of Open Access Journals (Sweden)

    Wojciech Brzezicki

    2015-03-01

    Full Text Available We investigate the changes in spin and orbital patterns induced by magnetic transition-metal ions without an orbital degree of freedom doped in a strongly correlated insulator with spin-orbital order. In this context, we study the 3d ion substitution in 4d transition-metal oxides in the case of 3d^{3} doping at either 3d^{2} or 4d^{4} sites, which realizes orbital dilution in a Mott insulator. Although we concentrate on this doping case as it is known experimentally and more challenging than other oxides due to finite spin-orbit coupling, the conclusions are more general. We derive the effective 3d−4d (or 3d−3d superexchange in a Mott insulator with different ionic valencies, underlining the emerging structure of the spin-orbital coupling between the impurity and the host sites, and demonstrate that it is qualitatively different from that encountered in the host itself. This derivation shows that the interaction between the host and the impurity depends in a crucial way on the type of doubly occupied t_{2g} orbital. One finds that in some cases, due to the quench of the orbital degree of freedom at the 3d impurity, the spin and orbital order within the host is drastically modified by doping. The impurity either acts as a spin defect accompanied by an orbital vacancy in the spin-orbital structure when the host-impurity coupling is weak or favors doubly occupied active orbitals (orbital polarons along the 3d−4d bond leading to antiferromagnetic or ferromagnetic spin coupling. This competition between different magnetic couplings leads to quite different ground states. In particular, for the case of a finite and periodic 3d atom substitution, it leads to striped patterns either with alternating ferromagnetic or antiferromagnetic domains or with islands of saturated ferromagnetic order. We find that magnetic frustration and spin degeneracy can be lifted by the quantum orbital flips of the host, but they are robust in special regions of the

  7. THREE PLANETS ORBITING WOLF 1061

    Energy Technology Data Exchange (ETDEWEB)

    Wright, D. J.; Wittenmyer, R. A.; Tinney, C. G.; Bentley, J. S.; Zhao, Jinglin, E-mail: duncan.wright@unsw.edu.au [Department of Astronomy and Australian Centre for Astrobiology, School of Physics, University of New South Wales, NSW 2052 (Australia)

    2016-02-01

    We use archival HARPS spectra to detect three planets orbiting the M3 dwarf Wolf 1061 (GJ 628). We detect a 1.36 M{sub ⊕} minimum-mass planet with an orbital period P = 4.888 days (Wolf 1061b), a 4.25 M{sub ⊕} minimum-mass planet with orbital period P = 17.867 days (Wolf 1061c), and a likely 5.21 M{sub ⊕} minimum-mass planet with orbital period P = 67.274 days (Wolf 1061d). All of the planets are of sufficiently low mass that they may be rocky in nature. The 17.867 day planet falls within the habitable zone for Wolf 1061 and the 67.274 day planet falls just outside the outer boundary of the habitable zone. There are no signs of activity observed in the bisector spans, cross-correlation FWHMs, calcium H and K indices, NaD indices, or Hα indices near the planetary periods. We use custom methods to generate a cross-correlation template tailored to the star. The resulting velocities do not suffer the strong annual variation observed in the HARPS DRS velocities. This differential technique should deliver better exploitation of the archival HARPS data for the detection of planets at extremely low amplitudes.

  8. Hydrogen bond dynamics in bulk alcohols.

    Science.gov (United States)

    Shinokita, Keisuke; Cunha, Ana V; Jansen, Thomas L C; Pshenichnikov, Maxim S

    2015-06-07

    Hydrogen-bonded liquids play a significant role in numerous chemical and biological phenomena. In the past decade, impressive developments in multidimensional vibrational spectroscopy and combined molecular dynamics-quantum mechanical simulation have established many intriguing features of hydrogen bond dynamics in one of the fundamental solvents in nature, water. The next class of a hydrogen-bonded liquid--alcohols--has attracted much less attention. This is surprising given such important differences between water and alcohols as the imbalance between the number of hydrogen bonds, each molecule can accept (two) and donate (one) and the very presence of the hydrophobic group in alcohols. Here, we use polarization-resolved pump-probe and 2D infrared spectroscopy supported by extensive theoretical modeling to investigate hydrogen bond dynamics in methanol, ethanol, and isopropanol employing the OH stretching mode as a reporter. The sub-ps dynamics in alcohols are similar to those in water as they are determined by similar librational and hydrogen-bond stretch motions. However, lower density of hydrogen bond acceptors and donors in alcohols leads to the appearance of slow diffusion-controlled hydrogen bond exchange dynamics, which are essentially absent in water. We anticipate that the findings herein would have a potential impact on fundamental chemistry and biology as many processes in nature involve the interplay of hydrophobic and hydrophilic groups.

  9. Hydrogen bond dynamics in bulk alcohols

    Energy Technology Data Exchange (ETDEWEB)

    Shinokita, Keisuke; Cunha, Ana V.; Jansen, Thomas L. C.; Pshenichnikov, Maxim S., E-mail: Maxim.Pchenitchnikov@RuG.nl [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)

    2015-06-07

    Hydrogen-bonded liquids play a significant role in numerous chemical and biological phenomena. In the past decade, impressive developments in multidimensional vibrational spectroscopy and combined molecular dynamics–quantum mechanical simulation have established many intriguing features of hydrogen bond dynamics in one of the fundamental solvents in nature, water. The next class of a hydrogen-bonded liquid—alcohols—has attracted much less attention. This is surprising given such important differences between water and alcohols as the imbalance between the number of hydrogen bonds, each molecule can accept (two) and donate (one) and the very presence of the hydrophobic group in alcohols. Here, we use polarization-resolved pump-probe and 2D infrared spectroscopy supported by extensive theoretical modeling to investigate hydrogen bond dynamics in methanol, ethanol, and isopropanol employing the OH stretching mode as a reporter. The sub-ps dynamics in alcohols are similar to those in water as they are determined by similar librational and hydrogen-bond stretch motions. However, lower density of hydrogen bond acceptors and donors in alcohols leads to the appearance of slow diffusion-controlled hydrogen bond exchange dynamics, which are essentially absent in water. We anticipate that the findings herein would have a potential impact on fundamental chemistry and biology as many processes in nature involve the interplay of hydrophobic and hydrophilic groups.

  10. Hydrogen bond dynamics in bulk alcohols

    Science.gov (United States)

    Shinokita, Keisuke; Cunha, Ana V.; Jansen, Thomas L. C.; Pshenichnikov, Maxim S.

    2015-06-01

    Hydrogen-bonded liquids play a significant role in numerous chemical and biological phenomena. In the past decade, impressive developments in multidimensional vibrational spectroscopy and combined molecular dynamics-quantum mechanical simulation have established many intriguing features of hydrogen bond dynamics in one of the fundamental solvents in nature, water. The next class of a hydrogen-bonded liquid—alcohols—has attracted much less attention. This is surprising given such important differences between water and alcohols as the imbalance between the number of hydrogen bonds, each molecule can accept (two) and donate (one) and the very presence of the hydrophobic group in alcohols. Here, we use polarization-resolved pump-probe and 2D infrared spectroscopy supported by extensive theoretical modeling to investigate hydrogen bond dynamics in methanol, ethanol, and isopropanol employing the OH stretching mode as a reporter. The sub-ps dynamics in alcohols are similar to those in water as they are determined by similar librational and hydrogen-bond stretch motions. However, lower density of hydrogen bond acceptors and donors in alcohols leads to the appearance of slow diffusion-controlled hydrogen bond exchange dynamics, which are essentially absent in water. We anticipate that the findings herein would have a potential impact on fundamental chemistry and biology as many processes in nature involve the interplay of hydrophobic and hydrophilic groups.

  11. Intramolecular Hydrogen Bond in Biologically Active o-Carbonyl Hydroquinones

    Directory of Open Access Journals (Sweden)

    Maximiliano Martínez-Cifuentes

    2014-07-01

    Full Text Available Intramolecular hydrogen bonds (IHBs play a central role in the molecular structure, chemical reactivity and interactions of biologically active molecules. Here, we study the IHBs of seven related o-carbonyl hydroquinones and one structurally-related aromatic lactone, some of which have shown anticancer and antioxidant activity. Experimental NMR data were correlated with theoretical calculations at the DFT and ab initio levels. Natural bond orbital (NBO and molecular electrostatic potential (MEP calculations were used to study the electronic characteristics of these IHB. As expected, our results show that NBO calculations are better than MEP to describe the strength of the IHBs. NBO energies (∆Eij(2 show that the main contributions to energy stabilization correspond to LPàσ* interactions for IHBs, O1…O2-H2 and the delocalization LPàπ* for O2-C2 = Cα(β. For the O1…O2-H2 interaction, the values of ∆Eij(2 can be attributed to the difference in the overlap ability between orbitals i and j (Fij, instead of the energy difference between them. The large energy for the LP O2àπ* C2 = Cα(β interaction in the compounds 9-Hydroxy-5-oxo-4,8, 8-trimethyl-l,9(8H-anthracenecarbolactone (VIII and 9,10-dihydroxy-4,4-dimethylanthracen-1(4H-one (VII (55.49 and 60.70 kcal/mol, respectively when compared with the remaining molecules (all less than 50 kcal/mol, suggests that the IHBs in VIII and VII are strongly resonance assisted.

  12. Distant retrograde orbits and the asteroid hazard

    Science.gov (United States)

    Perozzi, Ettore; Ceccaroni, Marta; Valsecchi, Giovanni B.; Rossi, Alessandro

    2017-08-01

    Distant Retrograde Orbits (DROs) gained a novel wave of fame in space mission design because of their numerous advantages within the framework of the US plans for bringing a large asteroid sample in the vicinity of the Earth as the next target for human exploration. DROs are stable solutions of the three-body problem that can be used whenever an object, whether of natural or artificial nature, is required to remain in the neighborhood of a celestial body without being gravitationally captured by it. As such, they represent an alternative option to Halo orbits around the collinear Lagrangian points L1 and L2. Also known under other names ( e.g., quasi-satellite orbits, cis-lunar orbits, family- f orbits) these orbital configurations found interesting applications in several mission profiles, like that of a spacecraft orbiting around the small irregularly shaped satellite of Mars Phobos or the large Jovian moon Europa. In this paper a basic explanation of the DRO dynamics is presented in order to clarify some geometrical properties that characterize them. Their accessibility is then discussed from the point of view of mission analysis under different assumptions. Finally, their relevance within the framework of the present asteroid hazard protection programs is shown, stressing the significant increase in warning time they would provide in the prediction of impactors coming from the direction of the Sun.

  13. Orbital decomposition of CALIFA spiral galaxies

    Science.gov (United States)

    Zhu, Ling; van den Bosch, Remco; van de Ven, Glenn; Lyubenova, Mariya; Falcón-Barroso, Jesús; Meidt, Sharon E.; Martig, Marie; Shen, Juntai; Li, Zhao-Yu; Yildirim, Akin; Walcher, C. Jakob; Sanchez, Sebastian F.

    2018-01-01

    Schwarzschild orbit-based dynamical models are widely used to uncover the internal dynamics of early-type galaxies and globular clusters. Here we present for the first time the Schwarzschild models of late-type galaxies: an SBb galaxy NGC 4210 and an S0 galaxy NGC 6278 from the Calar Alto Legacy Integral Field Area (CALIFA) survey. The mass profiles within 2Re are constrained well with 1σ statistical error of ˜ 10 per cent. The luminous and dark mass can be disentangled with uncertainties of ˜20 and ˜ 50 per cent, respectively. From Re to 2Re, the dark matter fraction increases from 14 ± 10 to 18 ± 10 per cent for NGC 4210 and from 15 ± 10 to 30 ± 20 per cent for NGC 6278. The velocity anisotropy profiles of both σr/σt and σz/σR are well constrained. The inferred internal orbital distributions reveal clear substructures. The orbits are naturally separated into three components: a cold component with near circular orbits; a hot component with near radial orbits and a warm component in between. The photometrically identified exponential discs are predominantly made up of cold orbits only beyond ˜1Re, while they are constructed mainly with the warm orbits inside. Our dynamical hot components are concentrated in the inner regions, similar to the photometrically identified bulges. The reliability of the results, especially the orbit distribution, is verified by applying the model to mock data.

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

    Science.gov (United States)

    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.

  15. Acrylic mechanical bond tests

    Energy Technology Data Exchange (ETDEWEB)

    Wouters, J.M.; Doe, P.J.

    1991-02-01

    The tensile strength of bonded acrylic is tested as a function of bond joint thickness. 0.125 in. thick bond joints were found to posses the maximum strength while the acceptable range of joints varied from 0.063 in. to almost 0.25 in. Such joints are used in the Sudbury Neutrino Observatory.

  16. Phenylacetylene and H bond

    Indian Academy of Sciences (India)

    ... all resembling H bonds. Non-linear H bonds due to secondary interactions. C-H stretching frequency shows blue shift. Heavy atom distances are longer than the sum of van der Waals radii. Formed a task group through IUPAC to come up with a modern definition of H bond. 15 international experts including Desiraju.

  17. Neonatal orbital abscess

    Directory of Open Access Journals (Sweden)

    Khalil M Al-Salem

    2014-01-01

    Full Text Available Orbital complications due to ethmoiditis are rare in neonates. A case of orbital abscess due to acute ethmoiditis in a 28-day-old girl is presented. A Successful outcome was achieved following antimicrobial therapy alone; spontaneous drainage of the abscess occurred from the lower lid without the need for surgery. From this case report, we intend to emphasize on eyelid retraction as a sign of neonatal orbital abscess, and to review all the available literature of similar cases.

  18. Family of Orbiters

    Science.gov (United States)

    2008-01-01

    This image shows the paths of three spacecraft currently in orbit around Mars, as well as the path by which NASA's Phoenix Mars Lander will approach and land on the planet. The t-shaped crosses show where the orbiters will be when Phoenix enters the atmosphere, while the x-shaped crosses show their location at landing time. All three orbiters, NASA's Mars Reconnaissance Orbiter, NASA's Mars Odyssey and the European Space Agency's Mars Express, will be monitoring Phoenix during the final steps of its journey to the Red Planet. Phoenix will land just south of Mars's north polar ice cap.

  19. Chlorophylls - natural solar cells

    CERN Document Server

    Jantschi, Lorentz; Balan, Mugur C; Sestras, Radu E

    2011-01-01

    A molecular modeling study was conducted on a series of six natural occurring chlorophylls. Quantum chemistry calculated orbital energies were used to estimate frequency of transitions between occupied molecular orbital and unoccupied molecular orbital energy levels of chlorophyll molecules in vivo conditions in standard (ASTMG173) environmental conditions. Obtained results are in good agreement with energies necessary to fix the Magnesium atom by chlorophyll molecules and with occurrence of chlorophylls in living vegetal organisms.

  20. [Orbital mycetoma: a case report].

    Science.gov (United States)

    Gueye, N N; Seck, S M; Diop, Y; Ndiaye Sow, M N; Agboton, G; Diakhaté, M; Dieng, M; Dieng, M T

    2013-05-01

    Mycetomas are pathological processes through which exogenous fungal or actinomycotic etiological agents produce grains. These etiological agents live in the soil and plants of endemic areas. They are introduced traumatically, primarily into the foot. The orbital location is rare. We report the case of a 17-year-old student admitted for progressive left proptosis over 2 years, following penetrating trauma by a fork in a rural setting. Examination revealed a heterogenous orbital mass with multiple fistulae, producing pus and black grains, and suggested, due to the color of the grains, a diagnosis of fungal mycetoma. MRI revealed a destructive process at the level of the lamina papracea of the ethmoid and the orbital floor. Anatomopathological examination confirmed the fungal nature of the infection, while culture in Sabouraud's medium was inconclusive. The outcome was favorable after exenteration and debridementof the ipsilateral maxillary sinus and nasal cavities, along with 4 months of ketoconazole. No recurrence has been observed for 14 months after surgery. Mycetomas are endemic to northwest Africa. Most frequently located in the foot, they are seldom seen in the orbit. The color of the grains provides a clue as to the etiology. Black-grain mycetomas are always fungal and are treated surgically--essentially like cancer--as the persistence of a single grain will cause a recurrence. The orbital location of a mycetoma is rare. In the present case report, the concept of port of entry, the clinical appearance, and the color of the grains guided the diagnosis. The histological examination of the surgical specimen confirmed the diagnosis. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

  1. Halogen bonding origin properties and applications

    Science.gov (United States)

    Hobza, Pavel

    2015-12-01

    σ-hole bonding represents an unusual and novel type of noncovalent interactions in which atom with σ- hole interacts with Lewis base such as an electronegative atom (oxygen, nitrogen, …) or aromatic systems. This bonding is of electrostatic nature since the σ-hole bears a positive charge. Dispersion energy forms equally important energy term what is due to the fact that two heavy atoms (e.g. halogen and oxygen) having high polarizability lie close together (the respective distance is typically shorter than the sum of van der Waals radii). Among different types of σ-hole bondings the halogen bonding is by far the most known but chalcogen and pnictogen bondings are important as well.

  2. Halogen bonding origin properties and applications

    Energy Technology Data Exchange (ETDEWEB)

    Hobza, Pavel [Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 166 10 Prague (Czech Republic); Regional Center of Advanced Technologies and Materials, Department of Physical Chemistry, Palacky University, 77146 Olomouc (Czech Republic)

    2015-12-31

    σ-hole bonding represents an unusual and novel type of noncovalent interactions in which atom with σ- hole interacts with Lewis base such as an electronegative atom (oxygen, nitrogen, …) or aromatic systems. This bonding is of electrostatic nature since the σ-hole bears a positive charge. Dispersion energy forms equally important energy term what is due to the fact that two heavy atoms (e.g. halogen and oxygen) having high polarizability lie close together (the respective distance is typically shorter than the sum of van der Waals radii). Among different types of σ-hole bondings the halogen bonding is by far the most known but chalcogen and pnictogen bondings are important as well.

  3. Prospective bonding applications

    Science.gov (United States)

    Ancenay, H.; Benazet, D.

    1981-07-01

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

  4. Designation and Exploration of Halide-Anion Recognition Based on Cooperative Noncovalent Interactions Including Hydrogen Bonds and Anion-π.

    Science.gov (United States)

    Liu, Yan-Zhi; Yuan, Kun; Lv, Ling-Ling; Zhu, Yuan-Cheng; Yuan, Zhao

    2015-06-04

    A novel urea-based anion receptor with an electron-deficient aromatic structural unit, N-p-nitrophenyl-N-(4-vinyl-2-five-fluoro-benzoic acid benzyl ester)-phenyl-urea (FUR), was designed to probe the potential for halide-anion recognition through the cooperation of two distinct noncovalent interactions including hydrogen bonds and anion-π in this work. The nature of the recognition interactions between halide-anion and the designed receptor was theoretically investigated at the molecular level. The geometric features of the hydrogen bond and anion-π of the FUR@X(-) (X = F, Cl, Br, and I) systems were thoroughly investigated. The binding energies and thermodynamic information on the halide-anion recognitions show that the presently designed FUR might selectively recognize anion F(-) based on the cooperation of the N-H···F(-) hydrogen bond and anion-π interactions both in vacuum and in solvents. IR and UV-visible spectra of free FUR and FUR@F(-) have been simulated and discussed qualitatively, which may be helpful for further experimental investigations in the future. Additionally, the electronic properties and behaviors of the FUR@X(-) systems were discussed according to the calculations on the natural bond orbital (NBO) data, molecular electrostatic potential (MEP), and weak interaction regions.

  5. Recent advances in C-S bond formation via C-H bond functionalization and decarboxylation.

    Science.gov (United States)

    Shen, Chao; Zhang, Pengfei; Sun, Qiang; Bai, Shiqiang; Hor, T S Andy; Liu, Xiaogang

    2015-01-07

    The development of mild and general methods for C-S bond formation has received significant attention because the C-S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C-S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C-S bond formation, based upon direct C-H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C-S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C-S bond formation via C-H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

  6. Designing high-Performance layered thermoelectric materials through orbital engineering

    DEFF Research Database (Denmark)

    Zhang, Jiawei; Song, Lirong; Madsen, Georg K. H.

    2016-01-01

    Thermoelectric technology, which possesses potential application in recycling industrial waste heat as energy, calls for novel high-performance materials. The systematic exploration of novel thermoelectric materials with excellent electronic transport properties is severely hindered by limited...... insight into the underlying bonding orbitals of atomic structures. Here we propose a simple yet successful strategy to discover and design high-performance layered thermoelectric materials through minimizing the crystal field splitting energy of orbitals to realize high orbital degeneracy. The approach......-abundant elements. Moreover, the approach can be extended to several other non-cubic materials, thereby substantially accelerating the screening and design of new thermoelectric materials....

  7. Analysis of Hydrogen Bonds in Crystals

    Directory of Open Access Journals (Sweden)

    Sławomir J. Grabowski

    2016-05-01

    Full Text Available The determination of crystal structures provides important information on the geometry of species constituting crystals and on the symmetry relations between them. Additionally, the analysis of crystal structures is so conclusive that it allows us to understand the nature of various interactions. The hydrogen bond interaction plays a crucial role in crystal engineering and, in general, its important role in numerous chemical, physical and bio-chemical processes was the subject of various studies. That is why numerous important findings on the nature of hydrogen bonds concern crystal structures. This special issue presents studies on hydrogen bonds in crystals, and specific compounds and specific H-bonded patterns existing in crystals are analyzed. However, the characteristics of the H-bond interactions are not only analyzed theoretically; this interaction is compared with other ones that steer the arrangement of molecules in crystals, for example halogen, tetrel or pnicogen bonds. More general findings concerning the influence of the hydrogen bond on the physicochemical properties of matter are also presented.

  8. Orbital ordering and frustrations

    NARCIS (Netherlands)

    Khomskii, D.I.; Mostovoy, M.V.

    2003-01-01

    Orbital ordering occurs in many transition metal compounds with Jahn–Teller ions (Cu2+, Mn3+, low-spin Ni3+, Ti3+ etc). It plays an important role in these materials. At the same time, exchange interactions in orbitally degenerate systems are inherently frustrated, even in materials with simple

  9. CONGENITAL ORBITAL TERATOMA

    African Journals Online (AJOL)

    commenced on topical chloramphenicol therapy. The x-ray showed a left orbital soft tissue mass but no orbital enlargement and the swab showed no growth. ... proliferating neural bundles and some neural bundles lined by pigmented choroidal epithelium. Also seen are abundant fibrous tissues scattered within the.

  10. The Cost of Immediacy for Corporate Bonds

    DEFF Research Database (Denmark)

    Dick-Nielsen, Jens; Marco, Rossi

    Liquidity provision in the corporate bond market has become significantly more expensive after the 2008 credit crisis. Using index exclusions as a natural experiment during which uninformed index trackers request immediacy, we find that the price of immediacy has doubled for short-term investment...... grade bonds, and more than tripled for speculative-grade bonds. The increased cost of immediacy is a side-effect of a ban on proprietary trading (Volker Rule) and tighter post-crisis capital regulations, which have resulted in lower aggregate dealer inventories....

  11. The hydrogen bond in the solid state.

    Science.gov (United States)

    Steiner, Thomas

    2002-01-04

    The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

  12. Peripheral orbit model

    CERN Document Server

    Hara, Yasuo

    1975-01-01

    Peripheral orbit model, in which an incoming hadron is assumed to revolve in a peripheral orbit around a target hadron, is discussed. The non-diffractive parts of two-body reaction amplitudes of hadrons are expressed in terms of the radius, width an absorptivity of the orbit. The radius of the orbit is about 1 fm and the width of the orbit is determined by the range of the interaction between the hadrons. The model reproduces all available experimental data on differential cross-sections and polarizations of $K^{-}p\\to K^{-}p$ and $\\bar K^{\\circ}n$ reactions for all angles successfully. This contribution is not included in the proceedings since it will appear in Progress of Theoretical Physics Vol. 51 (1974) No 2. Any person interested in the subject may apply for reprints to the author.

  13. Weak bond screening system

    Science.gov (United States)

    Chuang, S. Y.; Chang, F. H.; Bell, J. R.

    Consideration is given to the development of a weak bond screening system which is based on the utilization of a high power ultrasonic (HPU) technique. The instrumentation of the prototype bond strength screening system is described, and the adhesively bonded specimens used in the system developmental effort are detailed. Test results obtained from these specimens are presented in terms of bond strength and level of high power ultrasound irradiation. The following observations were made: (1) for Al/Al specimens, 2.6 sec of HPU irradiation will screen weak bond conditions due to improper preparation of bonding surfaces; (2) for composite/composite specimens, 2.0 sec of HPU irradiation will disrupt weak bonds due to under-cured conditions; (3) for Al honeycomb core with composite skin structure, 3.5 sec of HPU irradiation will disrupt weak bonds due to bad adhesive or oils contamination of bonding surfaces; and (4) for Nomex honeycomb with Al skin structure, 1.3 sec of HPU irradiation will disrupt weak bonds due to bad adhesive.

  14. The Role of Divalent Alkaline Earth Cations in the Electrolyte-Promoted Hydrolysis of Si-O- Si Bonded Networks

    Science.gov (United States)

    Dove, P. M.; Wallace, A. F.; Gibbs, G. V.

    2006-12-01

    The dissolution of amorphous and crystalline varieties of SiO2 is an integral part of the global biogeochemical cycle of silicon. Nanoparticulate biogenic silica produced by marine phytoplankton and terrestrial plants are of particular interest because their enhanced reactivity and abundance make them important sources and sinks of dissolved silicon in natural environments. Low concentrations of major solutes [e.g. Na+, K+, Mg2+, Ca2+] have been shown to enhance the rate of silica dissolution by up to a hundred times; however, the underlying reaction mechanism remains poorly understood. Ab initio molecular orbital calculations were completed at the B3LYP / 6-31G(d) level to establish a mechanistic understanding of electrolyte-promoted Si-O bond hydrolysis at the atomic level. Local minima corresponding to the adsorption of metal aquo complexes [Me(H2O)62+] near a bridging oxygen on the surface of a neutral silica cluster [H8Si6O16] were determined through a series of constrained geometry optimizations at discrete metal ion and bridging oxygen separations. Bond critical point properties calculated from the theoretical electron density distribution are used to assess the strength and reactivity of the bonded interactions at different points along the reaction path. Adsorption of the Me2+ aquo complex to the silica surface weakens one of the Si-O bonds adjacent to the bridging oxygen, but does not induce bond hydrolysis; rather, complete bond cleavage is accomplished by concomitant attack of the weakened Si-O bond by water, resulting in a penta-coordinated Si transition state.

  15. Evidence for orbital ordering in LaCoO3

    NARCIS (Netherlands)

    Maris, G; Ren, Y; Volotchaev, [No Value; Zobel, C; Lorenz, T; Palstra, TTM

    2003-01-01

    We present powder and single-crystal x-ray diffraction data as evidence for a monoclinic distortion in the low-spin (S=0) and intermediate spin states (S=1) of LaCoO3. The alternation of short and long bonds in the ab plane indicates the presence of e(g) orbital ordering induced by a cooperative

  16. Theoretical Characterization of Sulfur-to-Selenium Substitution in an Emissive RNA Alphabet: Impact on H-bonding Potential and Photophysical Properties

    KAUST Repository

    Chawla, Mohit

    2018-02-23

    We employ density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to investigate the structural, energetic and optical properties of a new computationally designed RNA alphabet, where the nucleobases,tsA, tsG, tsC, and tsU (ts-bases), have been derived by replacing sulfur with selenium in the previously reported tz-bases, based on the isothiazolo[4.3-d]pyrimidine heterocycle core. We find out that the modeled non-natural bases have minimal impact on the geometry and energetics of the classical Watson-Crick base pairs, thus potentially mimicking the natural bases in a RNA duplex in terms of H-bonding. In contrast, our calculations indicate that H-bonded base pairs involving the Hoogsteen edge of purines are destabilized as compared to their natural counterparts. We also focus on the photophysical properties of the non-natural bases and correlate their absorption/emission peaks to the strong impact of the modification on the energy of the lowest unoccupied molecular orbital. It is indeed stabilized by roughly 1.1-1.6 eV as compared to the natural analogues, resulting in a reduction of the gap between the highest occupied and the lowest unoccupied molecular orbital from 5.3-5.5 eV in the natural bases to 3.9-4.2 eV in the modified ones, with a consequent bathochromic shift in the absorption and emission spectra. Overall, our analysis clearly indicates that the newly modelled ts-bases are expected to exhibit better fluorescent properties as compared to the previously reported tz-bases, while retaining similar H-bonding properties. In addition, we show that a new RNA alphabet based on size-extended benzo-homologated ts-bases can also form stable Watson-Crick base pairs with the natural complementary nucleobases.

  17. Orbit Stabilization of Nanosat

    Energy Technology Data Exchange (ETDEWEB)

    JOHNSON,DAVID J.

    1999-12-01

    An algorithm is developed to control a pulsed {Delta}V thruster on a small satellite to allow it to fly in formation with a host satellite undergoing time dependent atmospheric drag deceleration. The algorithm uses four short thrusts per orbit to correct for differences in the average radii of the satellites due to differences in drag and one thrust to symmetrize the orbits. The radial difference between the orbits is the only input to the algorithm. The algorithm automatically stabilizes the orbits after ejection and includes provisions to allow azimuthal positional changes by modifying the drag compensation pulses. The algorithm gives radial and azimuthal deadbands of 50 cm and 3 m for a radial measurement accuracy of {+-} 5 cm and {+-} 60% period variation in the drag coefficient of the host. Approaches to further reduce the deadbands are described. The methodology of establishing a stable orbit after ejection is illustrated in an appendix. The results show the optimum ejection angle to minimize stabilization thrust is upward at 86{sup o} from the orbital velocity. At this angle the stabilization velocity that must be supplied by the thruster is half the ejection velocity. An ejection velocity of 0.02 m/sat 86{sup o} gives an azimuthal separation after ejection and orbit stabilization of 187 m. A description of liquid based gas thrusters suitable for the satellite control is included in an appendix.

  18. Orbital cellulitis in children.

    Science.gov (United States)

    Nageswaran, Savithri; Woods, Charles R; Benjamin, Daniel K; Givner, Laurence B; Shetty, Avinash K

    2006-08-01

    To review the epidemiology and management of orbital cellulitis in children. The medical records of children orbital cellulitis and confirmed by computed tomography scan were reviewed. A literature search for additional studies for systematic review was also conducted. Forty-one children with orbital cellulitis were identified. The mean age was 7.5 years (range, 10 months to 16 years), and 30 (73%) were male (male:female ratio = 2.7). All cases of orbital cellulitis were associated with sinusitis; ethmoid sinusitis was present in 40 (98%) patients. Proptosis and/or ophthalmoplegia was documented in 30 (73%), and 34 (83%) had subperiosteal and/or orbital abscesses. Twenty-nine (71%) had surgical drainage and 12 (29%) received antibiotic therapy only. The mean duration of hospitalization was 5.8 days. The mean duration of antibiotic therapy was 21 days. Orbital cellulitis occurs throughout childhood and in similar frequency among younger and older children. It is twice as common among males as females. Selected cases of orbital cellulitis, including many with subperiosteal abscess, can be treated successfully without surgical drainage.

  19. Chemical bonding technology

    Science.gov (United States)

    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.

  20. Orbital cystic neurinoma.

    Science.gov (United States)

    Tokugawa, J; Nakao, Y; Mori, K; Maeda, M

    2003-07-01

    A 64-year-old woman presented with a 6-month history of exophthalmus of her right eye. She had no neurological deficit except for the exophthalmus and numbness in the right side of her forehead (frontal nerve territory). Neuro-imaging demonstrated a cystic mass in the right orbit. The tumour was totally removed by microsurgical transcranial surgery. The histological diagnosis was neurinoma. The origin of the tumour was considered to be the frontal nerve. Only two other cases of orbital cystic neurinoma have been reported. This rare clinical entity should be included in the differential diagnosis of a cystic mass in the orbit.

  1. Quark Orbital Angular Momentum

    Directory of Open Access Journals (Sweden)

    Burkardt Matthias

    2015-01-01

    Full Text Available Definitions of orbital angular momentum based on Wigner distributions are used as a framework to discuss the connection between the Ji definition of the quark orbital angular momentum and that of Jaffe and Manohar. We find that the difference between these two definitions can be interpreted as the change in the quark orbital angular momentum as it leaves the target in a DIS experiment. The mechanism responsible for that change is similar to the mechanism that causes transverse single-spin asymmetries in semi-inclusive deep-inelastic scattering.

  2. Copper wire bonding

    CERN Document Server

    Chauhan, Preeti S; Zhong, ZhaoWei; Pecht, Michael G

    2014-01-01

    This critical volume provides an in-depth presentation of copper wire bonding technologies, processes and equipment, along with the economic benefits and risks.  Due to the increasing cost of materials used to make electronic components, the electronics industry has been rapidly moving from high cost gold to significantly lower cost copper as a wire bonding material.  However, copper wire bonding has several process and reliability concerns due to its material properties.  Copper Wire Bonding book lays out the challenges involved in replacing gold with copper as a wire bond material, and includes the bonding process changes—bond force, electric flame off, current and ultrasonic energy optimization, and bonding tools and equipment changes for first and second bond formation.  In addition, the bond–pad metallurgies and the use of bare and palladium-coated copper wires on aluminum are presented, and gold, nickel and palladium surface finishes are discussed.  The book also discusses best practices and re...

  3. Using Atomic Orbitals and Kinesthetic Learning to Authentically Derive Molecular Stretching Vibrations

    Science.gov (United States)

    Bridgeman, Adam J.; Schmidt, Timothy W.; Young, Nigel A.

    2013-01-01

    The stretching modes of ML[subscript "x"] complexes have the same symmetry as the atomic orbitals on M that are used to form its s bonds. In the exercise suggested here, the atomic orbitals are used to derive the form of the stretching modes without the need for formal group theory. The analogy allows students to help understand many…

  4. Ab Initio Molecular Orbital Studies on the Active Site of Papain

    NARCIS (Netherlands)

    Broer, Ria; Duijnen, P.Th. van; Nieuwpoort, W.C.

    1976-01-01

    Ab initio molecular orbital calcuiations using a contracted basis of gaussian orbitals on the system methanethiol/imidazole are reported. For the hydrogen bond S---H---N in this system, which was chosen as a model for the active site of papain, a double-well potential was found at a S-N separation

  5. Two-component relativistic coupled-cluster methods using mean-field spin-orbit integrals

    Science.gov (United States)

    Liu, Junzi; Shen, Yue; Asthana, Ayush; Cheng, Lan

    2018-01-01

    A novel implementation of the two-component spin-orbit (SO) coupled-cluster singles and doubles (CCSD) method and the CCSD augmented with the perturbative inclusion of triple excitations [CCSD(T)] method using mean-field SO integrals is reported. The new formulation of SO-CCSD(T) features an atomic-orbital-based algorithm for the particle-particle ladder term in the CCSD equation, which not only removes the computational bottleneck associated with the large molecular-orbital integral file but also accelerates the evaluation of the particle-particle ladder term by around a factor of 4 by taking advantage of the spin-free nature of the instantaneous electron-electron Coulomb interaction. Benchmark calculations of the SO splittings for the thallium atom and a set of diatomic 2Π radicals as well as of the bond lengths and harmonic frequencies for a set of closed-shell diatomic molecules are presented. The basis-set and core-correlation effects in the calculations of these properties have been carefully analyzed.

  6. Modern ab initio valence bond theory calculations reveal charge shift bonding in protic ionic liquids.

    Science.gov (United States)

    Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo

    2016-06-21

    The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties.

  7. Orbital Models and Electronic Structure Theory

    DEFF Research Database (Denmark)

    Linderberg, Jan

    2012-01-01

    This tribute to the work by Carl Johan Ballhausen focuses on the emergence of quantitative means for the study of the electronic properties of complexes and molecules. Development, refinement and application of the orbital picture elucidated electric and magnetic features of ranges of molecules w...... when used for the interpretation of electronic transitions, electron spin resonance parameters, rotatory dispersion, nuclear quadrupole couplings as well as geometric bonding patterns. Ballhausen's profound impact on the field cannot be overestimated.......This tribute to the work by Carl Johan Ballhausen focuses on the emergence of quantitative means for the study of the electronic properties of complexes and molecules. Development, refinement and application of the orbital picture elucidated electric and magnetic features of ranges of molecules...

  8. Congenital orbital teratoma

    Directory of Open Access Journals (Sweden)

    Shereen Aiyub

    2013-01-01

    Full Text Available We present a case of mature congenital orbital teratoma managed with lid-sparing exenteration and dermis fat graft. This is a case report on the management of congenital orbital teratoma. A full-term baby was born in Fiji with prolapsed right globe which was surrounded by a nonpulsatile, cystic mass. Clinical and imaging features were consistent with congenital orbital teratoma. Due to limited surgical expertise, the patient was transferred to Adelaide, Australia for further management. The patient underwent a lid-sparing exenteration with frozen section control of the apical margin. A dermis fat graft from the groin was placed beneath the lid skin to provide volume. Histopathology revealed mature tissues from each of the three germ cell layers which confirmed the diagnosis of mature teratoma. We describe the successful use of demis fat graft in socket reconstruction following lid-sparing exenteration for congenital orbital teratoma.

  9. Orbital heat rate package

    Science.gov (United States)

    Lovin, J. K.; Spradley, L. W.

    1979-01-01

    Package consisting of three separate programs used to accurately predict temperature distribution of spacecraft in planetary orbit is invaluable tool for design and analysis of other structures that must function in complex thermal environment.

  10. Neonatal orbital abscess

    Directory of Open Access Journals (Sweden)

    Pratik Y Gogri

    2015-01-01

    Full Text Available Orbital abscess generally occurs in older children but it can rarely affect infants and neonates too. We report a case of community acquired methicillin resistant staphylococcus aureus (CA-MRSA neonatal orbital abscess in a 12-day-old term female neonate with no significant past medical history or risk factor for developing the infection. The case highlights the importance of consideration of CA-MRSA as a causative agent of neonatal orbital cellulitis even in a neonate without any obvious predisposing condition. Prompt initiation of appropriate medical therapy against MRSA and surgical drainage of the abscess prevents life threatening complications of orbital cellulitis which more often tend to be fatal in neonates.

  11. Dynamics of the chemical bond: inter- and intra-molecular hydrogen bond.

    Science.gov (United States)

    Arunan, Elangannan; Mani, Devendra

    2015-01-01

    In this discussion, we show that a static definition of a 'bond' is not viable by looking at a few examples for both inter- and intra-molecular hydrogen bonding. This follows from our earlier work (Goswami and Arunan, Phys. Chem. Chem. Phys. 2009, 11, 8974) which showed a practical way to differentiate 'hydrogen bonding' from 'van der Waals interaction'. We report results from ab initio and atoms in molecules theoretical calculations for a series of Rg∙∙∙HX complexes (Rg=He/Ne/Ar and X=F/Cl/Br) and ethane-1,2-diol. Results for the Rg∙∙∙HX/DX complexes show that Rg∙∙∙DX could have a 'deuterium bond' even when Rg∙∙∙HX is not 'hydrogen bonded', according to the practical criterion given by Goswami and Arunan. Results for ethane-1,2-diol show that an 'intra-molecular hydrogen bond' can appear during a normal mode vibration which is dominated by the OO stretching, though a 'bond' is not found in the equilibrium structure. This dynamical 'bond' formation may nevertheless be important in ensuring the continuity of electron density across a molecule. In the former case, a vibration 'breaks' an existing bond and in the later case, a vibration leads to 'bond' formation. In both cases, the molecule/complex stays bound irrespective of what happens to this 'hydrogen bond'. Both these cases push the borders on the recent IUPAC recommendation on hydrogen bonding (Arunan et al. Pure. Appl. Chem. 2011, 83 1637) and justify the inclusive nature of the definition.

  12. 27 CFR 24.147 - Operations bond or unit bond.

    Science.gov (United States)

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Operations bond or unit... § 24.147 Operations bond or unit bond. Notwithstanding the provisions of § 24.146, each person... amended, give an operations bond or unit bond in accordance with the applicable provisions of 27 CFR part...

  13. Orbital interactions in chemistry

    CERN Document Server

    Albright, Thomas A; Whangbo, Myung-Hwan

    2013-01-01

    Explains the underlying structure that unites all disciplines in chemistry Now in its second edition, this book explores organic, organometallic, inorganic, solid state, and materials chemistry, demonstrating how common molecular orbital situations arise throughout the whole chemical spectrum. The authors explore the relationships that enable readers to grasp the theory that underlies and connects traditional fields of study within chemistry, thereby providing a conceptual framework with which to think about chemical structure and reactivity problems. Orbital Interactions

  14. Molecular degrees of freedom: resonances and orbiting

    Energy Technology Data Exchange (ETDEWEB)

    Shapira, D.; Erb, K.A.

    1983-01-01

    Studies of orbiting and other gross features of heavy ion induced reactions show that molecular degrees of freedom play a significant role. The formation of a rotating dinuclear molecule appears as a general feature, and the radii derived for these dinuclear systems are larger than the radii of the conventional nucleus-nucleus potential. These large radii for the molecular bonding potential are similar to those derived from systematic studies performed recently on resonances in the /sup 12/C + /sup 12/C + /sup 16/O systems.

  15. The Lunar Orbital Prospector

    Science.gov (United States)

    Redd, Frank J.; Cantrell, James N.; McCurdy, Greg

    1992-09-01

    The establishment of lunar bases will not end the need for remote sensing of the lunar surface by orbiting platforms. Human and robotic surface exploration will necessarily be limited to some proximate distance from the support base. Near real-time, high-resolution, global characterization of the lunar surface by orbiting sensing systems will continue to be essential to the understanding of the Moon's geophysical structure and the location of exploitable minerals and deposits of raw materials. The Lunar Orbital Prospector (LOP) is an orbiting sensing platform capable of supporting a variety of modular sensing packages. Serviced by a lunar-based shuttle, the LOP will permit the exchange of instrument packages to meet evolving mission needs. The ability to recover, modify, and rotate sensing packages allows their reuse in varying combinations. Combining this flexibility with robust orbit modification capabilities and near real-time telemetry links provides considerable system responsiveness. Maintenance and modification of the LOP orbit are accomplished through use of an onboard propulsion system that burns lunar-supplied oxygen and aluminum. The relatively low performance of such a system is more than compensated for by the elimination of the need for Earth-supplied propellants. The LOP concept envisions a continuous expansion of capability through the incorporation of new instrument technologies and the addition of platforms.

  16. Resonance and Aromaticity : An Ab Initio Valence Bond Approach

    NARCIS (Netherlands)

    Rashid, Zahid; van Lenthe, Joop H.; Havenith, Remco W. A.

    2012-01-01

    Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB

  17. Destination bonding: Hybrid cognition using Instagram

    Directory of Open Access Journals (Sweden)

    Arup Kumar Baksi

    2015-01-01

    Full Text Available Empirical research has identified the phenomenon of destination bonding as a result of summated physical and emotional values associated with the destination. Physical values, namely natural landscape & other physical settings and emotional values, namely the enculturation processes, have a significant role to play in portraying visitors’ cognitive framework for destination preference. The physical values seemed to be the stimulator for bonding that embodies action or behavior tendencies in imagery. The emotional values were the conditions that lead to affective bonding and are reflected in attitudes for a place which were evident in text narratives. Social networking on virtual platforms offers the scope for hybrid cognitive expression using imagery and text to the visitors. Instagram has emerged as an application-window to capture these hybrid cognitions of visitors. This study focuses on assessing the relationship between hybrid cognition of visitors expressed via Instagram and their bond with the destination. Further to this, the study attempts to examine the impact of hybrid cognition of visitors on the behavioral pattern of prospective visitors to the destination. The study revealed that sharing of visual imageries and related text by the visitors is an expression of the physico-emotional bonding with the destination. It was further established that hybrid cognition strongly asserts destination bonding and has been also found to have moderating impact on the link between destination bonding and electronic-word-of-mouth.

  18. Half-metallic and insulating natures in Ru-based ordered double perovskite oxides Ba{sub 2}X{sup III}Ru{sup V}O{sub 6} (X = V, Cr) induced by 3d-t{sub 2g}{sup n} orbital filling

    Energy Technology Data Exchange (ETDEWEB)

    Saad, H.-E.M. Musa, E-mail: musa.1964@gmail.com; Althoyaib, S.S.

    2017-04-01

    In this paper, we present results of a comprehensive systemic study of the crystal, electronic and magnetic structures on two members of Ru-based ordered double perovskite oxides Ba{sub 2}XRuO{sub 6} (X = V, Cr). For the corporate compound, the analysis of density of states (DOS) results suggests that the 3d-t{sub 2g} orbital filling plays a major role in governing the conduction mechanism in these systems. The DOS and magnetic results show that Ba{sub 2}XRuO{sub 6} exhibits half-metallic (HM) nature as X = V, where the electronic structure of Ba{sub 2}V{sup III}Ru{sup V}O{sub 6} with 3d-t{sub 2g}{sup 2} behaves like that of HM ferrimagnetic (FI), switches to compensate FI insulating behavior as X = Cr, with an extra electron filled 3d-t{sub 2g}{sup 3} in Ba{sub 2}Cr{sup III}Ru{sup V}O{sub 6}. We find, on consideration of electron correlation (LSDA+U) and spin-orbital coupling (SOC) effects that the electronic structure of Ba{sub 2}XRuO{sub 6} takes a HM nature, whereas it is completely transformed to insulating nature once an extra electron filled the 3d-t{sub 2g} orbitals in X = Cr case. Such tuning is accompanied by spin-state hopping of one electron from half-filled spin-state in Ru{sup V} (t{sub 2g}{sup 3} e{sub g}{sup 0}) to two and three occupied spin-state in V{sup III} (t{sub 2g}{sup 2} e{sub g}{sup 0}) and Cr{sup III} (t{sub 2g}{sup 3} e{sub g}{sup 0}), respectively. The charge distribution results show that this extra electron occupies chiefly the spin-down of conduction orbitals and plays a major role in determining the electronic and magnetic structures of Ba{sub 2}XRuO{sub 6} system. - Highlights: • Half-metallic and insulating natures are observed in Ba{sub 2}XRuO{sub 6} (X = V, Cr). • 3d-t{sub 2g}{sup n} orbitals filling plays a major role in governing the conduction mechanism. • LSDA+U method under density functional theory (DFT) is considered. • HM ferrimagnetic (FI) (X = V) switch to compensate FI insulating (X = Cr).

  19. Comparison of Gold Bonding with Mercury Bonding

    NARCIS (Netherlands)

    Kraka, Elfi; Filatov, Michael; Cremer, Dieter

    2009-01-01

    Nine AuX molecules (X = H, O, S, Se, Te, F, Cl, Br, I), their isoelectronic HgX(+) analogues, and the corresponding neutral HgX diatomics have been investigated using NESC (Normalized Elimination of the Small Component) and B3LYP theory to determine relativistic effects for bond dissociation

  20. Chemical Bonds I

    Science.gov (United States)

    Sanderson, R. T.

    1972-01-01

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

  1. Corporate Bonds in Denmark

    DEFF Research Database (Denmark)

    Tell, Michael

    2015-01-01

    to think in alternative ways such as issuing corporate bonds. A market for corporate bonds exists in countries such as Norway, Germany, France, the United Kingdom and the United States, while Denmark is still behind in this trend. Some large Danish corporations have instead used foreign corporate bonds...... markets. However, NASDAQ OMX has introduced the First North Bond Market in December 2012 and new regulatory framework came into place in 2014, which may contribute to a Danish based corporate bond market. The purpose of this article is to present the regulatory changes in Denmark in relation to corporate......Corporate financing is the choice between capital generated by the corporation and capital from external investors. However, since the financial crisis shook the markets in 2007–2008, financing opportunities through the classical means of financing have decreased. As a result, corporations have...

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

    Science.gov (United States)

    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,…

  3. Substituent Effects in Multivalent Halogen Bonding Complexes: A Combined Theoretical and Crystallographic Study

    Directory of Open Access Journals (Sweden)

    Antonio Bauzá

    2017-12-01

    Full Text Available In this manuscript, we combined ab initio calculations (RI-MP2/def2-TZVPD level of theory and a search in the CSD (Cambridge Structural Database to analyze the influence of aromatic substitution in charge-assisted multivalent halogen bonding complexes. We used a series of benzene substituted iodine derivatives C6H4(IF4Y (Y = H, NH2, OCH3, F, CN, and CF3 as Lewis acids and used Cl− as electron rich interacting atoms. We have represented the Hammett’s plot and observed a good regression coefficient (interaction energies vs. Hammett’s σ parameter. Additionally, we demonstrated the direct correlation between the Hammett’s σ parameter and the value of molecular electrostatic potential measured at the I atom on the extension of the C–I bond. Furthermore, we have carried out AIM (atoms in molecules and NBO (natural bonding orbital analyses to further describe and characterize the interactions described herein. Finally, we have carried out a search in the CSD (Cambridge Structural Database and found several X-ray structures where these interactions are present, thus giving reliability to the results derived from the calculations.

  4. Influence of atomic bonds on the properties of the laxative drug sodium picosulphate

    Directory of Open Access Journals (Sweden)

    Davide Romani

    2016-11-01

    Full Text Available In this work, the influence of the different S═O, S−O, N⋯H, O⋯H, Na⋯O bonds present in the structures of the powerful laxative drug, sodium picosulphate in gas and aqueous solution phases were studied combining the density functional theory (DFT calculations with the experimental available infrared, 1H NMR and UV-visible spectra. The structural, topological, electronic and vibrational properties were investigated in both media by using the hybrid B3LYP/6-31G* method and the integral equation formalism variant polarised continuum model (IEFPCM. Here, the characteristics of the S═O, S−O, N⋯H, O⋯H, Na⋯O bonds were completely revealed by using atomic charges, natural bond orbital (NBO and atoms in molecules (AIM studies. The infrared, 1H NMR, 13C NMR and UV-visible spectra are in reasonable concordance with those experimental available in the literature. The vibrational analysis of sodium picosulphate was performed considering C3V symmetries for both SO42− groups and the complete assignments of the 126 vibration modes were reported in gas phase and aqueous solution together with their corresponding force fields. In addition, the reactivities of sodium picosulfate increase in solution due to their ionic characteristic which probably justifies their behaviour as a stimulant cathartic and their easy metabolic conversion, as reported in the literature.

  5. On the photostability of the disulfide bond

    DEFF Research Database (Denmark)

    Stephansen, Anne Boutrup; Larsen, Martin Alex Bjørn; Klein, Liv Bærenholdt

    2014-01-01

    Photostability is an essential property of molecular building blocks of nature. Disulfides are central in the structure determination of proteins, which is in striking contradiction to the result that the S-S bond is a photochemically labile structural entity that cleaves to form free radicals upon...... on a sub 50 fs timescale without further ado. In a cyclic motif resembling the cysteine-disulfide bond in proteins, light can perturb the S-S bond to generate short-lived diradicaloid species, but the sulfur atoms are conformationally restricted by the ring that prevents the sulfur atoms from flying apart...... the photostability of disulfide-bonds must be ascribed a cyclic structural arrangement....

  6. [Orbital complications of sinusitis].

    Science.gov (United States)

    Šuchaň, M; Horňák, M; Kaliarik, L; Krempaská, S; Koštialová, T; Kovaľ, J

    2014-12-01

    Orbital complications categorised by Chandler are emergency. They need early diagnosis and agresive treatment. Stage and origin of orbital complications are identified by rhinoendoscopy, ophtalmologic examination and CT of orbite and paranasal sinuses. Periorbital cellulitis and early stage of orbital cellulitis can be treated conservatively with i. v. antibiotics. Monitoring of laboratory parameters and ophtalmologic symptoms is mandatory. Lack of improvement or worsening of symptoms within 24-48 hours and advanced stages of orbital complications are indicated for surgery. The purpose of the study is to evaluate epidemiology, clinical features and management of sinogenic orbital complications. Retrospective data of 8 patients with suspicion of orbital complication admited to hospital from 2008 to 2013 were evaluated. Patients were analyzed in terms of gender, age, CT findings, microbiology, clinical features, stage and treatment. Male and female were afected in rate 1,66:1. Most of patients were young adult in 3rd. and 4th. decade of life (62,5 %). Acute and chronic sinusitis were cause of orbital complication in the same rate. The most common origin of orbital complication was ethmoiditis (62,5 %), than maxillary (25 %) and frontal (12,5 %) sinusitis. Polysinusitis with affection of ethmoidal, maxillary and frontal sinuses (75 %) was usual CT finding. Staphylococcus epidermidis and Staphylococcus aureus were etiological agens in half of cases. Periorbital oedema (100 %), proptosis, chemosis (50 %), diplopia and glaucoma (12,5 %) were observed. Based on examinations, diagnosis of periorbital oedema/preseptal cellulitis was made in 3 (37,5 %), orbital cellulitis in 3 (37,5 %) and subperiosteal abscess in 2 cases (25 %). All patients underwent combined therapy - i. v. antibiotics and surgery within 24 hours. Eradication of disease from ostiomeatal complex (OMC), drainage of affected sinuses and drainage of subperiosteal abscess were done via fuctional endonasal

  7. Orbital complications of rhinosinusitis.

    Science.gov (United States)

    Sijuwola, Oo; Adeyemo, Aa; Adeosun, Aa

    2007-06-01

    Suppurative extension of rhinosinusitis to the orbit is a complication that often results from delay in diagnosis and, or inadequate treatment. These complications may range from preseptal cellulitis, orbital cellulitis, orbital abscesses, and subperiosteal abscesses to intracranial extension with a threat to both vision and life. This study aims to review the clinical profile, treatment modalities and outcome of orbital complications of rhinosinusitis in Ibadan, Nigeria. A retrospective review of the charts of patients with orbital complications of rhinosinusitis managed in the departments of Otorhinolaryngology and Ophthalmology, University College Hospital, Ibadan over a five year period (Feb 2002- Jan 2007) was carried out .The diagnosis of rhinosinusitis was based on history, physical examination, plain x ray and CT scan findings and antral puncture. Demographic data, clinical presentation and treatment were evaluated. A total of 24 patients were reviewed in the study. There were 13males and 11females (M/F, 1:1). The age range was 8months to 75years, 14 (58.3%) patients were children and while 10 (41.7%) patients were adults. 75% of the patients were seen during the dry season (November to February). The duration of symptoms ranged from one day to three weeks. Involvement of one eye occurred in 14 patients (58.3%); right eye (4), left eye (10). Both eyes were involved in 10 patients (41.7%). Non-axial proptosis was seen in 8 patients (33.3%). It was infero-lateral in 6 patients (25%) and infero-nasal in two (8.3%) patients. Orbital cellulitis was seen in 10 (41.7%) patients, 6 (25%) patients had preseptal cellulitis while 8 (33%) patients had orbital abscess. Cavernous sinus thrombosis was seen in 3 (12.5%) patients. The cases with preseptal and orbital cellulitis were effectively managed by intravenous antibiotics. Orbital abscesses were drained surgically with complete resolution. Sinus surgical procedures were done in 10(41.7%) patients. This group of

  8. Effect of moist bonding on composite/enamel bond strength.

    Science.gov (United States)

    Moll, Karlheinz; Gärtner, Thomas; Haller, Bernd

    2002-04-01

    To evaluate the effect of moist bonding on shear bond strength of resin-based composite to enamel using different adhesive systems. Six restorative systems were selected for this study: OptiBond FL/Prodigy, Solid Bond/Charisma F, Syntac Single Component/Tetric, Prime&Bond 2.1/Spectrum TPH, Single Bond/Z100, Etch&Prime 3.0/Degufill Mineral. Flat enamel surfaces were ground on the buccal and lingual aspects of 80 extracted human molars. OptiBond FL and Solid Bond were tested with and without primer application. Prior to application of the adhesives, the enamel was either carefully dried with compressed air (dry bonding) or blot dried with a cotton pellet (moist bonding). Shear bond strength was determined with a universal testing machine after 24-hour storage in 0.9% NaCl at 37 degrees C. Moist bonding did not significantly affect shear bond strength to enamel of the adhesives tested except for Solid Bond without primer application. Primer contamination of the etched enamel did not significantly influence bond strength, neither in the dry bonding nor in the moist bonding group. Of all adhesives tested in both groups, the highest mean bond strength was observed with Prime&Bond 2.1 and the lowest with Etch&Prime 3.0.

  9. Actor bonds after relationship dissolution

    DEFF Research Database (Denmark)

    Skaates, Maria Anne

    2000-01-01

    Most of the presented papers at the 1st NoRD Workshop can be classified as belonging to the business marketing approach to relationship dissolution. Two papers were conceptual, and the remaining six were empirical studies. The first conceptual study by Skaates (2000) focuses on the nature...... of the actor bonds that remain after a business relationship has ended. The study suggests that an interdisciplinary approach would provide a richer understanding of the phenomenon; this could be achieved by using e.g. Bourdieu's sociological concepts in dissolution research....

  10. Looking Inside the Intramolecular C-H∙∙∙O Hydrogen Bond in Lactams Derived from α-Methylbenzylamine.

    Science.gov (United States)

    Mejía, Sandra; Hernández-Pérez, Julio M; Sandoval-Lira, Jacinto; Sartillo-Piscil, Fernando

    2017-02-28

    Recently, strong evidence that supports the presence of an intramolecular C-H···O hydrogen bond in amides derived from the chiral auxiliary α-methylbenzylamine was disclosed. Due to the high importance of this chiral auxiliary in asymmetric synthesis, the inadvertent presence of this C-H···O interaction may lead to new interpretations upon stereochemical models in which this chiral auxiliary is present. Therefore, a series of lactams containing the chiral auxiliary α-methylbenzylamine (from three to eight-membered ring) were theoretically studied at the MP2/cc-pVDZ level of theory with the purpose of studying the origin and nature of the C-Hα···O interaction. NBO analysis revealed that rehybridization at C atom of the C-Hα bond (s-character at C is ~23%) and the subsequent bond polarization are the dominant effect over the orbital interaction energy n(O)→σ*C-Hα (E(2) C-Hα bond distance and an increment in the positive charge in the Hα atom.

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

    Science.gov (United States)

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

    2009-11-01

    Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine-thymine and guanine-cytosine using electron charge densities calculated at X⋯H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP/6-311++G ∗∗ and MP2/6-311++G ∗∗ levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between ρHBCP and individual EHB. Correlation coefficient between EHB and ρHBCP in the base of linear, quadratic, and exponential equations are acceptable and equal to 0.95. The estimated individual binding energies EHB are in good agreement with the results of atom-replacement approach and natural bond orbital analysis (NBO). The EHB values estimated from ρ values at H⋯X BCP are in satisfactory agreement with the main geometrical parameter H⋯X. With respect to the obtained individual binding energies, the strength of a HB depends on the substituent and the cooperative effects of other HBs.

  12. The orbital record in stratigraphy

    Science.gov (United States)

    Fischer, Alfred G.

    1992-01-01

    Orbital signals are being discovered in pre-Pleistocene sediments. Due to their hierarchical nature these cycle patterns are complex, and the imprecision of geochronology generally makes the assignment of stratigraphic cycles to specific orbital cycles uncertain, but in sequences such as the limnic Newark Group under study by Olsen and pelagic Cretaceous sequence worked on by our Italo-American group the relative frequencies yield a definitive match to the Milankovitch hierarchy. Due to the multiple ways in which climate impinges on depositional systems, the orbital signals are recorded in a multiplicity of parameters, and affect different sedimentary facies in different ways. In platform carbonates, for example, the chief effect is via sea-level variations (possibly tied to fluctuating ice volume), resulting in cycles of emergence and submergence. In limnic systems it finds its most dramatic expression in alternations of lake and playa conditions. Biogenic pelagic oozes such as chalks and the limestones derived from them display variations in the carbonate supplied by planktonic organisms such as coccolithophores and foraminifera, and also record variations in the aeration of bottom waters. Whereas early studies of stratigraphic cyclicity relied mainly on bedding variations visible in the field, present studies are supplementing these with instrumental scans of geochemical, paleontological, and geophysical parameters which yield quantitative curves amenable to time-series analysis; such analysis is, however, limited by problems of distorted time-scales. My own work has been largely concentrated on pelagic systems. In these, the sensitivity of pelagic organisms to climatic-oceanic changes, combined with the sensitivity of botton life to changes in oxygen availability (commonly much more restricted in the Past than now) has left cyclic patterns related to orbital forcing. These systems are further attractive because (1) they tend to offer depositional continuity

  13. Orbit-attitude coupled motion around small bodies: Sun-synchronous orbits with Sun-tracking attitude motion

    Science.gov (United States)

    Kikuchi, Shota; Howell, Kathleen C.; Tsuda, Yuichi; Kawaguchi, Jun'ichiro

    2017-11-01

    The motion of a spacecraft in proximity to a small body is significantly perturbed due to its irregular gravity field and solar radiation pressure. In such a strongly perturbed environment, the coupling effect of the orbital and attitude motions exerts a large influence that cannot be neglected. However, natural orbit-attitude coupled dynamics around small bodies that are stationary in both orbital and attitude motions have yet to be observed. The present study therefore investigates natural coupled motion that involves both a Sun-synchronous orbit and Sun-tracking attitude motion. This orbit-attitude coupled motion enables a spacecraft to maintain its orbital geometry and attitude state with respect to the Sun without requiring active control. Therefore, the proposed method can reduce the use of an orbit and attitude control system. This paper first presents analytical conditions to achieve Sun-synchronous orbits and Sun-tracking attitude motion. These analytical solutions are then numerically propagated based on non-linear coupled orbit-attitude equations of motion. Consequently, the possibility of implementing Sun-synchronous orbits with Sun-tracking attitude motion is demonstrated.

  14. International Space Station: Meteoroid/Orbital Debris Survivability and Vulnerability

    Science.gov (United States)

    Graves, Russell

    2000-01-01

    This slide presentation reviews the surviability and vulnerability of the International Space Station (ISS) from the threat posed by meteoroid and orbital debris. The topics include: (1) Space station natural and induced environments (2) Meteoroid and orbital debris threat definition (3) Requirement definition (4) Assessment methods (5) Shield development and (6) Component vulnerability

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

    Science.gov (United States)

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

    2017-02-01

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

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

    Science.gov (United States)

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

    2017-02-15

    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 C6O4S1C5 and C25S22O19C16 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 (13)C and (1)H 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. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Molecular Energy Decompositions in the Hilbert-Space of Atomic Orbitals at Correlated Level

    Science.gov (United States)

    Alcoba, Diego R.; Bochicchio, Roberto C.; Lain, Luis; Torre, Alicia

    This work describes a new model to partition the molecular energy into one- and two-center contributions in the Hilbert-space of atomic orbitals at correlated level. Our proposal makes explicit use of the pairing nature of chemical bonding phenomena to accommodate appropriately the correlation effects within these contributions. The model is based on the treatment of the kinetic energy as contributing to both one- and two-atom terms, according to the pairing or unpairing character of the electron cloud, and on the appropriate assignment of the density cumulant dependent contributions. Numerical results for selected systems are reported and compared with those arising from other models, showing the reliability of our predictions.

  18. A Tapestry of Orbits

    Science.gov (United States)

    King-Hele, D. G.

    2005-07-01

    Satellites as they cross the night sky look like moving stars, which can be accurately tracked by an observer with binoculars as well as by giant radars and large cameras. These observations help to determine the satellite's orbit, which is sensitive to the drag of the upper atmosphere and to any irregularities in the gravity field of the Earth. Analysis of the orbit can be used to evaluate the density of the upper atmosphere and to define the shape of the Earth. Desmond King-Hele was the pioneer of this technique of orbit analysis, and this book tells us how the research began, before the launch of Sputnik in 1957. For thirty years King-Hele and his colleagues at the Royal Aircraft Establishment, Farnborough, developed and applied the technique to reveal much about the Earth and air at a very modest cost. In the 1960s the upper-atmosphere density was thoroughly mapped out for 100 to 2000 km, revealing immense variation of density with solar activity and between day and night. In the 1970s and 1980s a picture of the upper-atmosphere winds emerged, and the profile of the pear-shaped Earth was accurately charted. The number of satellites now orbiting the earth is over 5000. This book is the story of how this inexpensive research of their orbits developed to yield a rich harvest of knowledge about the Earth and its atmosphere, in a scientific narrative that is enlivened with many personal experiences.

  19. Extended duration orbiter (EDO) insignia

    Science.gov (United States)

    1990-01-01

    Extended duration orbiter (EDO) insignia incorporates a space shuttle orbiter with payload bay doors (PLBDs) open and a spacelab module inside. Trailing the orbiter are the initials EDO. The EDO-modified Columbia, Orbiter Vehicle (OV) 102, will be flown for the first EDO mission, STS-50.

  20. Relative motion of orbiting bodies

    Science.gov (United States)

    Butikov, Eugene I.

    2001-01-01

    A problem of relative motion of orbiting bodies is investigated on the example of the free motion of any body ejected from the orbital station that stays in a circular orbit around the earth. An elementary approach is illustrated by a simulation computer program and supported by a mathematical treatment based on approximate differential equations of the relative orbital motion.

  1. Elliptical Orbit Performance Computer Program

    Science.gov (United States)

    Myler, T.

    1984-01-01

    Elliptical Orbit Performance (ELOPE) computer program for analyzing orbital performance of space boosters uses orbit insertion data obtained from trajectory simulation to generate parametric data on apogee and perigee altitudes as function of payload data. Data used to generate presentation plots that display elliptical orbit performance capability of space booster.

  2. Indirect bonding technique in orthodontics

    National Research Council Canada - National Science Library

    Kübra Yıldırım; Banu Sağlam Aydınatay

    2016-01-01

    ‘Direct Bonding Technique’ which allows the fixed orthodontic appliances to be directly bonded to teeth without using bands decreased the clinic time for bracket bonding and increased esthetics and oral hygiene during orthodontic treatment...

  3. Total energy global optimizations using non orthogonal localized orbitals

    CERN Document Server

    Kim, J; Galli, G; Kim, Jeongnim; Mauri, Francesco; Galli, Giulia

    1994-01-01

    An energy functional for orbital based $O(N)$ calculations is proposed, which depends on a number of non orthogonal, localized orbitals larger than the number of occupied states in the system, and on a parameter, the electronic chemical potential, determining the number of electrons. We show that the minimization of the functional with respect to overlapping localized orbitals can be performed so as to attain directly the ground state energy, without being trapped at local minima. The present approach overcomes the multiple minima problem present within the original formulation of orbital based $O(N)$ methods; it therefore makes it possible to perform $O(N)$ calculations for an arbitrary system, without including any information about the system bonding properties in the construction of the input wavefunctions. Furthermore, while retaining the same computational cost as the original approach, our formulation allows one to improve the variational estimate of the ground state energy, and the energy conservation...

  4. Transversely Compressed Bonded Joints

    DEFF Research Database (Denmark)

    Hansen, Christian Skodborg; Schmidt, Jacob Wittrup; Stang, Henrik

    2012-01-01

    The load capacity of bonded joints can be increased if transverse pressure is applied at the interface. The transverse pressure is assumed to introduce a Coulomb-friction contribution to the cohesive law for the interface. Response and load capacity for a bonded single-lap joint was derived using...... non-linear fracture mechanics. The results indicated a good correlation between theory and tests. Furthermore, the model is suggested as theoretical base for determining load capacity of bonded anchorages with transverse pressure, in externally reinforced concrete structures....

  5. Intra- and intermolecular hydrogen bonding and conformation in 1-acyl thioureas: An experimental and theoretical approach on 1-(2-chlorobenzoyl)thiourea

    Science.gov (United States)

    Saeed, Aamer; Khurshid, Asma; Bolte, Michael; Fantoni, Adolfo C.; Erben, Mauricio F.

    2015-05-01

    The vibrational analysis (FT-IR and FT-Raman) for the new 1-(2-chlorobenzoyl)thiourea species suggests that strong intramolecular interactions affect the conformational properties. The X-ray structure determination corroborates that an intramolecular N-H⋯Odbnd C hydrogen bond occurs between the carbonyl (-Cdbnd O) and thioamide (-NH2) groups. Moreover, periodic system electron density and topological analysis have been applied to characterize the intermolecular interactions in the crystal. Extended N-H⋯Sdbnd C hydrogen-bonding networks between both the thioamide (N-H) and carbamide (NH2) groups and the thiocarbonyl bond (Cdbnd S) determine the crystal packing. The Natural Bond Orbital (NBO) population analysis demonstrates that strong hyperconjugative remote interactions are responsible for both, intra and intermolecular interactions. The Atom in Molecule (AIM) results also show that the N-H⋯Cl intramolecular hydrogen bond between the 2-Cl-phenyl ring and the amide group characterized in the free molecule changes to an N⋯Cl interaction as a consequence of crystal packing.

  6. Sinonasal disease and orbital cellulitis in children.

    Science.gov (United States)

    Meara, Daniel J

    2012-08-01

    Sinonasal disease is common in the pediatric population because of anatomic, environmental, and physiologic factors. Once paranasal sinusitis develops, orbital cellulitis is a concerning sequela that can result in loss of visual acuity and even intracranial disease. Thus, a clear history and physical examination in conjunction with radiographic studies are critical to a correct diagnosis and timely institution of treatment that may include hospitalization, serial ophthalmologic examinations, intravenous antibiotics, and surgery. The serious nature of orbital cellulitis in children cannot be overestimated; but, if prompt and appropriate treatment is initiated, the prognosis is excellent and long-term sequelae should be limited. Copyright © 2012 Elsevier Inc. All rights reserved.

  7. [Secondary orbital lymphoma].

    Science.gov (United States)

    Basanta, I; Sevillano, C; Álvarez, M D

    2015-09-01

    A case is presented of an 85 year-old Caucasian female with lymphoma that recurred in the orbit (secondary ocular adnexal lymphoma). The orbital tumour was a diffuse large B-cell lymphoma according to the REAL classification (Revised European-American Lymphoma Classification). Orbital lymphomas are predominantly B-cell proliferations of a variety of histological types, and most are low-grade tumours. Patients are usually middle-aged or elderly, and it is slightly more common in women. A palpable mass, proptosis and blepharoptosis are the most common signs of presentation. Copyright © 2011 Sociedad Española de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.

  8. Preseptal Cellulitis Or Orbital Cellulitis?

    Science.gov (United States)

    Lim, L T; Miller, D; Ah-Kee, E Y; Ferguson, A

    2015-06-29

    Preseptal cellulitis and orbital cellulitis can both present with increasing swelling, tenderness and redness around the eye, but their management differs. Preseptal cellulitis is more common and much less aggressive than orbital cellulitis. In contrast, orbital cellulitis is a medical emergency requiring urgent management. In this article, we provide a systematic approach to distinguish between preseptal cellulitis and orbital cellulitis at presentation, as the distinction between the two entities and the prompt recognition of orbital cellulitis can be potentially life-saving.

  9. Safe and Liquid Mortgage Bonds

    DEFF Research Database (Denmark)

    Dick-Nielsen, Jens; Gyntelberg, Jacob; Lund, Jesper

    eliminates credit risk from the investor's perspective. Similar to other safe bonds, funding liquidity becomes the main driver of mortgage bond liquidity and this creates commonality in liquidity across markets and countries. These findings have implications for how to design a robust mortgage bond system......This paper shows that strict match pass-through funding of covered bonds provides safe and liquid mortgage bonds. Despite a 30% drop in house prices during the 2008 global crisis Danish mortgage bonds remained as liquid as most European government bonds. The Danish pass-through system effectively...... and for the treatment of covered bonds in capital regulation....

  10. Preliminary orbit determination

    Science.gov (United States)

    Taff, L. G.; Belkin, B.; Schweiter, G.; Sommar, K.

    The problem of intercontinental ballistic missile reentry vehicle orbit determination from incomplete passive (i.e., angles-only) or active (i.e., distance plus angles) information is presented. Launch location and time and impact location and time to complete the computation of an orbital element set are utilized. In addition, it is possible to construct a good estimate of the variance of the key quantity in the angles only case; namely the computed topocentric distance. This type of observation/information situation is enlarged to include a complete discussion of single-point differential correction.

  11. [Orbital complications of rhinosinusitis].

    Science.gov (United States)

    Stojanović, J; Ilić, N; Belić, B; Zivić, L; Stanković, P; Erdevicki, L; Jovanović, S

    2009-01-01

    Orbital complications were observed in 53 patients (1.35%, n=53/3912 of all treated patients; 11.04%, n= 53/480 of hospitalized patients). Complications in the orbit can occur in 3-5% of adults with the inflammatory condition of sinuses, while the percentage in children ranges from 0.5-8%. The objective of our work was to determine the frequency of the occurence of orbital complications of the rhinosinal inflammatory origin in a group of adults and children. The retrospective analysis of patients treated of rhinosinusitis in the period 1992 to 2007, in the Clinical Center in Kragujevac. In the period of 15 years, a total number of 3912 patients were treated for inflamatory conditions of paranasal cavities. Orbital complications were found in 53 patients (1.35%, n=53/3912 of all treated patients). The number of children showing orbital complications caused by rhinosinusitis was 0.79%, while the number of adults was 1,88%. Acute rhinosinusitis in children was manifested as orbital complication in 14 patients (n=14/15, 93.33%), while 33 adults (n=33/38, 86.84%) had the exarcerbation of the chronic rhinosinusitis at the time of diagnosis of orbital complication. 80% of examined children had the maxillary and ethmoid sinus infected (n=12/15), while the adults most often had polysinusitis (n=22/38, 57.89%). In the juvenile age the most frequent complication was the cellulitis of the orbite (n=7/15, 46.66%), while in the adults it was the subperiostal absces (n=14/38, 36.84%). The adults were mostly treated surgically (n=31/38, 81.58%), while the children were treated by using conservative treatment (n=13/15, 86.67%). There were no cases of mortality. The prevention of complications is based on the adequate and timely treatment of acute sinusitis in children, as well as the curative treatment of chronical processes in adults.

  12. Satellite orbit predictor

    Science.gov (United States)

    Friedman, Morton l.; Garrett, James, Major

    An analog aid to determine satellite coverage of Emergency Locator Transmitters Emergency Position Indicating Radio Beacon (ELT/EPIRB) distress incidence is discussed. The satellite orbit predictor is a graphical aid for determining the relationship between the satellite orbit, antenna coverage of the spacecraft and coverage of the Local User Terminal. The predictor allows the user to quickly visualize if a selected position will probably be detected and is composed of a base map and a satellite track overlay for each satellite.A table of equator crossings for each satellite is included.

  13. Quintuple super bonding between the superatoms of metallic clusters.

    Science.gov (United States)

    Wang, Haiyan; Cheng, Longjiu

    2017-09-14

    The synthesis of a stable compound with Cr-Cr quintuple bonding (σ, 2π, 2δ) opened the door to a new field of chemistry (T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long and P. P. Power, Science, 2005, 310, 844). Looking back to the mass experiments on sodium clusters (W. D. Knight, K. Clemenger, W. A. de Heer, W. A. Saunders, M. Y. Chou and M. L. Cohen, Phys. Rev. Lett., 1984, 52, 2141), this work tells some new stories about the experimentally viewed magic numbers 26e and 30e. By unbiased global search, the 26e Li 20 Mg 3 cluster has a perfect double-icosahedral motif with a large HOMO-LUMO energy gap (1.44 eV). We theoretically found that each icosahedron is an independent superatom and molecule-like electronic shell-closure is achieved via quintuple super bonding between two superatoms: [8e](1D2S) 5 -(1D2S) 5 [8e]. Similar quintuple bonding also exists in the 30e double-icosahedral Li 18 Mg 3 Al 2 cluster: [8e](1D2S) 7 -(1D2S) 7 [8e]. The 26e/30e quintuple bonding was verified by the beautiful analogies in molecular orbital diagrams and chemical bonding patterns with V 2 /Re 2 molecules. Such a quintuple super bonding makes a bridge between the jellium model and chemical bonding, which further expands the community of chemical bonds.

  14. Frozen orbits at high eccentricity and inclination: application to Mercury orbiter

    Science.gov (United States)

    Delsate, N.; Robutel, P.; Lemaître, A.; Carletti, T.

    2010-11-01

    We hereby study the stability of a massless probe orbiting around an oblate central body (planet or planetary satellite) perturbed by a third body, assumed to lay in the equatorial plane (Sun or Jupiter for example) using a Hamiltonian formalism. We are able to determine, in the parameters space, the location of the frozen orbits, namely orbits whose orbital elements remain constant on average, to characterize their stability/unstability and to compute the periods of the equilibria. The proposed theory is general enough, to be applied to a wide range of probes around planet or natural planetary satellites. The BepiColombo mission is used to motivate our analysis and to provide specific numerical data to check our analytical results. Finally, we also bring to the light that the coefficient J 2 is able to protect against the increasing of the eccentricity due to the Kozai-Lidov effect and the coefficient J 3 determines a shift of the equilibria.

  15. Transfer and capture into distant retrograde orbits

    Science.gov (United States)

    Scott, Christopher J.

    collision orbits within the highly chaotic region commonly recognized as a saddle point on the energy manifold. The pragmatic techniques derived from this analysis solve a number of complications apparent in the literature. Notably a reliable methodology for the construction of an arbitrary number of transfer orbits circumvents the requirement of computing specialized periodic orbits or extensive numerical sampling of the phase space. The procedure provides a complete description of the design space accessing a wide range of distant retrograde orbits sizes, insertion points, and parking orbit altitudes in an automated manner. The transfers are studied in a similar fashion to periodic orbits unveiling the intimate relationship among design parameters and phase space structure. An arbitrary number of Earth return periodic orbits can be generated as a by-product. These orbits may be useful for spacecraft that must make a number of passes near the second primary without a reduction in energy. Further analysis of the lobe dynamics and a modification of the transfers to the center of the stable region yields sets of single impulse transfers to sticky distant retrograde orbits. It is shown that the evolution of the phase space structures with energy corresponds to the variation of capture time and target size. Capture phenomenon is related to the stability characteristics of the unstable periodic orbit and the geometry of the corresponding homoclinic tangle at various energies. Future spacecraft with little or no propulsive means may take advantage of these natural trajectories for operations in the region. Temporary capture along a sticky orbit may come before incremental stabilization of the spacecraft by way of a series of small impulsive or a low continuous thrust maneuvers. The requirements of small stabilization maneuver are calculated and compared to a direct transfer to the center of stable region. This mission design may be desirable as any failure in the classic set of

  16. Handbook of wafer bonding

    CERN Document Server

    Ramm, Peter; Taklo, Maaike M V

    2011-01-01

    Written by an author and editor team from microsystems companies and industry-near research organizations, this handbook and reference presents dependable, first-hand information on bonding technologies.In the first part, researchers from companies and institutions around the world discuss the most reliable and reproducible technologies for the production of bonded wafers. The second part is devoted to current and emerging applications, including microresonators, biosensors and precise measuring devices.

  17. Dioxines, furans and other pollutants emissions bond to the combustion of natural and additive woods; Facteurs d'emission. Emissions de dioxines, de furanes et d'autres polluants liees a la combustion de bois naturels et adjuvantes

    Energy Technology Data Exchange (ETDEWEB)

    Collet, S

    2000-02-15

    This report deals especially on the dioxines and furans bond to the combustion of wood in industrial furnaces and domestic furnaces. It aims to define the environmental strategy which would allow the combustion of wood residues to produce energy. The first part recalls general aspects concerning the wood. The six other parts presents the wood resources and wastes, the additive used, the combustion and the different factors of combustion and finally the pollutants emissions. (A.L.B.)

  18. 31 CFR 316.6 - Purchase of bonds.

    Science.gov (United States)

    2010-07-01

    ...) Bonds registered in names of natural persons in their own right only. At such incorporated banks, trust companies, and other agencies as had been duly qualified as issuing agents. (2) Bonds registered in names of trustees of employee savings plans. At such incorporated bank, trust company, or other agency, duly...

  19. The Lunar orbit paradox

    Directory of Open Access Journals (Sweden)

    Tomić Aleksandar S.

    2013-01-01

    Full Text Available Newton's formula for gravity force gives greather force intensity for atraction of the Moon by the Sun than atraction by the Earth. However, central body in lunar (primary orbit is the Earth. So appeared paradox which were ignored from competent specialist, because the most important problem, determination of lunar orbit, was inmediately solved sufficiently by mathematical ingeniosity - introducing the Sun as dominant body in the three body system by Delaunay, 1860. On this way the lunar orbit paradox were not canceled. Vujičić made a owerview of principles of mechanics in year 1998, in critical consideration. As an example for application of corrected procedure he was obtained gravity law in some different form, which gave possibility to cancel paradox of lunar orbit. The formula of Vujičić, with our small adaptation, content two type of acceleration - related to inertial mass and related to gravity mass. So appears carried information on the origin of the Moon, and paradox cancels.

  20. Myxoma of the orbit.

    Directory of Open Access Journals (Sweden)

    Rambhatla Saptagirish

    2003-01-01

    Full Text Available Myxomas are rare, benign neoplasms of mesenchymal origin that usually develop in soft tissues. As the clinical manifestations are non-specific, it is difficult to diagnose the tumour without biopsy and histopathological examination. We report a case of orbital myxoma with histopathological correlation.

  1. A Neptune Orbiter Mission

    Science.gov (United States)

    Wallace, R. A.; Spilker, T. R.

    1998-01-01

    This paper describes the results of new analyses and mission/system designs for a low cost Neptune Orbiter mission. Science and measurement objectives, instrumentation, and mission/system design options are described and reflect an aggressive approach to the application of new advanced technologies expected to be available and developed over the next five to ten years.

  2. Fingerprints of spin-orbital entanglement in transition metal oxides.

    Science.gov (United States)

    Oleś, Andrzej M

    2012-08-08

    The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the RV O(3) perovskites, with R = La,Pr,…,Y b,Lu, where the finite temperature properties of these compounds can be understood only using entangled states: (i) the thermal evolution of the optical spectral weights, (ii) the dependence of the transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the RV O(3) perovskites, and (iii) the dimerization observed in the magnon spectra for the C-type antiferromagnetic phase of Y V O(3). Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

  3. Theoretical investigation on hydrogen bond interaction of diketo/keto-enol form uracil and thymine tautomers with intercalators.

    Science.gov (United States)

    Anithaa, V S; Vijayakumar, S; Sudha, M; Shankar, R

    2017-11-06

    The interaction of diketo and keto-enol form of thymine and uracil tautomers with acridine (Acr), phenazine (Phen), benzo[c]cinnoline (Ben), 1,10-phenanthroline (1,10-Phe), and 4,7-phenenthroline (4,7-Phe) intercalating drug molecules was studied using density functional theory at B3LYP/6-311++G** and M05-2×/6-311++G** levels of theory. From the interaction energy, it is found that keto-enol form tautomers have stronger interaction with intercalators than diketone form tautomers. On complex formation of thymine and uracil tautomers with benzo[c]cinnoline the drug molecules have high interaction energy values of -20.14 (BenT3) and -20.55 (BenU3) kcal mol-1, while phenazine has the least interaction energy values of -6.52 (PhenT2) and -6.67 (PhenU2) kcal mol-1. The closed shell intermolecular type interaction between the molecules with minimum elliptical value of 0.018 and 0.019 a.u at both levels of theory has been found from topological analysis. The benzo[c]cinnoline drug molecule with thymine and uracil tautomers has short range intermolecular N-H…N, C-H…O, and O-H...N hydrogen bonds (H-bonds) resulting in higher stability than other drug molecules. The proper hydrogen bonds N-H..N and O-H..N have the frequency shifted toward the lower side (red shifted) with the elongation in their bond length while the improper hydrogen bond C-H...O has the frequency shifted toward the higher side (blue shifted) of the spectral region with the contraction in their bond length. Further, the charge transfer between proton acceptor and donor along with stability of the bond is studied using natural bond orbital (NBO) analysis. Graphical abstract Hydrogen bond interaction of diketo/keto-enol form uracil and thymine tautomers with intercalators.

  4. The chemical bond as an emergent phenomenon.

    Science.gov (United States)

    Golden, Jon C; Ho, Vinh; Lubchenko, Vassiliy

    2017-05-07

    We first argue that the covalent bond and the various closed-shell interactions can be thought of as symmetry broken versions of one and the same interaction, viz., the multi-center bond. We use specially chosen molecular units to show that the symmetry breaking is controlled by density and electronegativity variation. We show that the bond order changes with bond deformation but in a step-like fashion, regions of near constancy separated by electronic localization transitions. These will often cause displacive transitions as well so that the bond strength, order, and length are established self-consistently. We further argue on the inherent relation of the covalent, closed-shell, and multi-center interactions with ionic and metallic bonding. All of these interactions can be viewed as distinct sectors on a phase diagram with density and electronegativity variation as control variables; the ionic and covalent/secondary sectors are associated with on-site and bond-order charge density wave, respectively, the metallic sector with an electronic fluid. While displaying a contiguity at low densities, the metallic and ionic interactions represent distinct phases separated by discontinuous transitions at sufficiently high densities. Multi-center interactions emerge as a hybrid of the metallic and ionic bond that results from spatial coexistence of delocalized and localized electrons. In the present description, the issue of the stability of a compound is that of the mutual miscibility of electronic fluids with distinct degrees of electron localization, supra-atomic ordering in complex inorganic compounds coming about naturally. The notions of electronic localization advanced hereby suggest a high throughput, automated procedure for screening candidate compounds and structures with regard to stability, without the need for computationally costly geometric optimization.

  5. Electronic structure and bonding in the RhC molecule by all-electron ab initio HF–Cl calculations and mass spectrometric measurements

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, K. A.

    1984-01-01

    in a singly occupied, nonbonding orbital. The chemical bond in RhC is polar with a charge transfer from Rh to C giving rise to a dipole moment of 2.82 D at the experimental equilibrium distance. Mass spectrometric equilibrium measurements over the temperature range 1970–2806 K have resulted in the selected...... with the experimental data. The chemical bond in the electronic ground state is mainly due to interaction of the 4d orbitals of Rh with the 2s and 2p orbitals of C. The bond is a triple bond composed of two pi bonds and one sigma bond. The 5s electron of Rh hardly participates in the bond formation. It is located...

  6. Halogen-bond and hydrogen-bond interactions between three benzene derivatives and dimethyl sulphoxide.

    Science.gov (United States)

    Zheng, Yan-Zhen; Wang, Nan-Nan; Zhou, Yu; Yu, Zhi-Wu

    2014-04-21

    Halogen-bonds, like hydrogen-bonds, are a kind of noncovalent interaction and play an important role in diverse fields including chemistry, biology and crystal engineering. In this work, a comparative study was carried out to examine the halogen/hydrogen-bonding interactions between three fluoro-benzene derivatives and dimethyl sulphoxide (DMSO). A number of conclusions were obtained by using attenuated total reflection infrared spectroscopy (ATR-IR), nuclear magnetic resonance (NMR) and ab initio calculations. Electrostatic surface potential, geometry, energy, vibrational frequency, intensity and the natural population analysis (NPA) of the monomers and complexes are studied at the MP2 level of theory with the aug-cc-pVDZ basis set. First, the interaction strength decreases in the order C6F5H-DMSO ∼ ClC6F4H-DMSO > C6F5Cl-DMSO, implying that the hydrogen-bond is stronger than the halogen-bond in the systems and, when interacting with ClC6F4H, DMSO favors the formation of a hydrogen-bond rather than a halogen-bond. Second, attractive energy dependences on 1/r(3.3) and 1/r(3.1) were established for the hydrogen-bond and halogen-bond, respectively. Third, upon the formation of a hydrogen-bond and halogen-bond, there is charge transfer from DMSO to the hydrogen-bond and halogen-bond donor. The back-group CH3 was found to contribute positively to the stabilization of the complexes. Fourth, an isosbestic point was detected in the ν(C-Cl) absorption band in the C6F5Cl-DMSO-d6 system, indicating that there exist only two dominating forms of C6F5Cl in binary mixtures; the non-complexed and halogen-bond-complexed forms. The presence of stable complexes in C6F5H-DMSO and ClC6F4H-DMSO systems are evidenced by the appearance of new peaks with fixed positions.

  7. Fundamentals of fiber bonding in thermally point-bonded nonwovens

    Science.gov (United States)

    Chidambaram, Aparna

    Thermal point bonding (TPB) uses heat and pressure to bond a web of fibers at discrete points imparting strength to the manufactured fabric. This process significantly reduces the strength and elongation of the bridging fibers between bond points while strengthening the web. Single fiber experiments were performed with four structurally different polypropylene fibers to analyze the inter-relationships between fiber structure, fiber properties and bonding process. Two fiber types had a low birefringence sheath or surface layer while the remaining had uniform birefringence profiles through their thickness. Bonds were formed between isolated pairs of fibers by subjecting the fibers to a calendering process and simulating TPB process conditions. The dependence of bond strength on bonding temperature and on the type of fiber used was evaluated. Fiber strengths before and after bonding were measured and compared to understand the effect of bonding on fiber strength. Additionally, bonded fiber strength was compared to the strength of single fibers which had experienced the same process conditions as the bonded pairs. This comparison estimated the effect of mechanical damage from pressing fibers together with steel rolls while creating bonds in TPB. Interfiber bond strength increased with bonding temperature for all fiber types. Fiber strength decreased with increasing bonding temperature for all fiber types except for one type of low birefringent sheath fibers. Fiber strength degradation was unavoidable at temperatures required for successful bonding. Mechanical damage from compression of fibers between rolls was an insignificant factor in this strength loss. Thermal damage during bonding was the sole significant contributor to fiber strength degradation. Fibers with low birefringence skins formed strong bonds with minimal fiber strength loss and were superior to fibers without such surface layers in TPB performance. A simple model to predict the behavior of a two-bond

  8. Comparative study of Green's function matrix elements and charge transfers obtained from different partitioning schemes of molecular charge in hydrogen-bonded complexes

    Directory of Open Access Journals (Sweden)

    Parnaíba-da Silva Antenor J.

    2006-01-01

    Full Text Available RHF and MP2 ab initio molecular orbital calculations using the 4-31G**, 6-311G** and cc-pVTZ basis sets have revealed that the Green's function matrix element (G D,A values show a good correlation with the amount of intermolecular transferred charges obtained from different charge partitioning schemes for the CNH?CNH, NCH?CNH, CNH?NCH and NCH?NCH hydrogen bonded complexes. This is evident specially when the hydrogen bond distance is progressively increased from the equilibrium position until 4.5 Å. However, G D,A values show a better linear correlation with deltaQ values using corrected Mülliken charges, which are obtained from the charge-charge flux-overlap (CCFO model for infrared intensities. In this case, both G D,A and deltaQcorr form two practically superposed exponential curves. On the other hand, G D,A values show a smaller agreement with deltaQ values obtained from atomic charges derived from natural bonding orbitals. This is clearly verified when considering the first order exponential decay rate of G D,A versus deltaQ obtained from different charge partitioning schemes.

  9. Clustering of periodic orbits in chaotic systems

    Science.gov (United States)

    Gutkin, Boris; Osipov, Vladimir Al

    2013-01-01

    In the framework of the semiclassical approach, the universal spectral correlations in Hamiltonian systems with classical chaotic dynamics can be attributed to the systematic correlations between the actions of periodic orbits which (up to the switch in the momentum direction) pass through approximately the same points of the phase space. By considering symbolic dynamics of the system one can introduce a natural ultrametric distance between periodic orbits and organize them into clusters of orbits approaching each other in the phase space. We study the distribution of cluster sizes for the baker's map in the asymptotic limit of long trajectories. This problem is equivalent to the one of counting degeneracies in the length spectrum of the de Bruijn graphs. Based on this fact, we derive the probability P_k that k randomly chosen periodic orbits belong to the same cluster. Furthermore, we find asymptotic behaviour of the largest cluster size |C_{\\max}| and derive the probability P(t) that a random periodic orbit belongs to a cluster smaller than t|C_{\\max}| , t ∈ [0, 1].

  10. A retrograde object near Jupiter's orbit

    Science.gov (United States)

    Connors, M.; Wiegert, P.

    2018-02-01

    Asteroid 2007 VW266 is among the rare objects with a heliocentric retrograde orbit, and its semimajor axis is within a Hill sphere radius of that of Jupiter. This raised the interesting possibility that it could be in co-orbital retrograde resonance with Jupiter, a second "counter-orbital" object in addition to recently discovered 2015 BZ509. We find instead that the object is in 13/14 retrograde mean motion resonance (also referred to as 13/-14). The object is shown to have entered its present orbit about 1700 years ago, and it will leave it in about 8000 years, both through close approach to Jupiter. Entry and exit states both avoid 1:1 retrograde resonance, but the retrograde nature is preserved. The temporary stable state is due to an elliptic orbit with high inclination keeping nodal passages far from the associated planet. We discuss the motion of this unusual object based on modeling and theory, and its observational prospects.

  11. Unusual Sclerosing Orbital Pseudotumor Infiltrating Orbits and Maxillofacial Regions

    Directory of Open Access Journals (Sweden)

    Huseyin Toprak

    2014-01-01

    Full Text Available Idiopathic orbital pseudotumor (IOP is a benign inflammatory condition of the orbit without identifiable local or systemic causes. Bilateral massive orbital involvement and extraorbital extension of the IOP is very rare. We present an unusual case of IOP with bilateral massive orbital infiltration extending into maxillofacial regions and discuss its distinctive magnetic resonance imaging (MRI features that help to exclude other entities during differential diagnoses.

  12. Hemi bonds and noncovalent interactions in the cational systems (XH2P: SHY)+

    Science.gov (United States)

    Li, Xiang; Li, An Yong

    2016-08-01

    Quantum chemistry ab initio MP2 and CCSD calculations were performed to investigate the P⋯S hemi bonds and noncovalent interactions in the radical cational systems (H3P:SH2)+, (FH2P:SH2)+ and (H3P:SHF)+. The hydride dimer (H3P:SH2)+ has a P⋯S hemi bonding structure and a H-bonding structure, (FH2P:SH2)+ has two hemi bonding structures and a proton-transferred H-bonding structure, (H3P:SHF)+ has two hemi bonding structures and three noncovalent structures. It is remarkable that these hemi bonds also have characters of pnicogen and chalcogen bonds. The binding energy, stability and bonding nature of the hemi bonds were presented.

  13. Intrinsic Bond Energies from a Bonds-in-Molecules Neural Network.

    Science.gov (United States)

    Yao, Kun; Herr, John E; Brown, Seth N; Parkhill, John

    2017-06-15

    Neural networks are being used to make new types of empirical chemical models as inexpensive as force fields, but with accuracy similar to the ab initio methods used to build them. In this work, we present a neural network that predicts the energies of molecules as a sum of intrinsic bond energies. The network learns the total energies of the popular GDB9 database to a competitive MAE of 0.94 kcal/mol on molecules outside of its training set, is naturally linearly scaling, and applicable to molecules consisting of thousands of bonds. More importantly, it gives chemical insight into the relative strengths of bonds as a function of their molecular environment, despite only being trained on total energy information. We show that the network makes predictions of relative bond strengths in good agreement with measured trends and human predictions. A Bonds-in-Molecules Neural Network (BIM-NN) learns heuristic relative bond strengths like expert synthetic chemists, and compares well with ab initio bond order measures such as NBO analysis.

  14. Romanian government bond market

    Directory of Open Access Journals (Sweden)

    Cornelia POP

    2012-12-01

    Full Text Available The present paper aims to present the level of development reached by Romanian government bond market segment, as part of the country financial market. The analysis will be descriptive (the data series available for Romania are short, based on the secondary data offered by the official bodies involved in the process of issuing and trading the Romanian government bonds (Romanian Ministry of Public Finance, Romanian National Bank and Bucharest Stock Exchange, and also on secondary data provided by the Federation of European Stock Exchanges.To enhance the market credibility as a benchmark, a various combination of measures is necessary; among these measures are mentioned: the extension of the yield curve; the issuance calendars in order to improve transparency; increasing the disclosure of information on public debt issuance and statistics; holding regular meetings with dealers, institutional investors and rating agencies; introducing a system of primary dealers; establishing a repurchase (repo market in the government bond market. These measures will be discussed based on the evolution presented inside the paper.The paper conclude with the fact that, until now, the Romanian government bond market did not provide a benchmark for the domestic financial market and that further efforts are needed in order to increase the government bond market transparency and liquidity.

  15. Strength of Chemical Bonds

    Science.gov (United States)

    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.

  16. Quantum Mechanical Earth: Where Orbitals Become Orbits

    Science.gov (United States)

    Keeports, David

    2012-01-01

    Macroscopic objects, although quantum mechanical by nature, conform to Newtonian mechanics under normal observation. According to the quantum mechanical correspondence principle, quantum behavior is indistinguishable from classical behavior in the limit of very large quantum numbers. The purpose of this paper is to provide an example of the…

  17. Low Earth Orbit Satellite’s Orbit Propagation and Determination

    Science.gov (United States)

    2014-01-01

    Institute of Technology Email: honien.shou@xuite.net Abstract This paper represents orbit propagation and determination of Low Eearth Orbit(LEO...Arichandran, S. H. Tan, T. Bretschneider, High – Presicion Onboard Orbit Determination for Small Satellites - the GPS-Based XNS on X-SAT. 6th Symposium on

  18. Local orbitals by minimizing powers of the orbital variance

    DEFF Research Database (Denmark)

    Jansik, Branislav; Høst, Stinne; Kristensen, Kasper

    2011-01-01

    is obtained. For increasing power exponents, the penalty for delocalized orbitals is increased and smaller maximum orbital spreads are encountered. Calculations on superbenzene, C60, and a fragment of the titin protein show that for a power exponent equal to one, delocalized outlier orbitals may...

  19. Comparison of shear bond strength between unfilled resin to dry enamel and dentin bonding to moist and dry enamel

    Directory of Open Access Journals (Sweden)

    Yasini E.

    2005-05-01

    Full Text Available Statement of Problem: The use of dentine bondings on enamel and dentin in total etch protocols has recently become popular. Unfilled resin is hydrophobic and dentin bonding is hydrophilic in nature. This chemical difference could be effective in enamel bonding process. Purpose: The aim of this study was to compare the shear bond strength of unfilled resin to dry enamel and dentin bonding to dry and moist enamel. Materials and Methods: In this experimental study, a total of 30 incisor teeth were used. The specimens were randomly assigned to three groups of 10. 37% phosphoric acid etchant was applied to the enamel surfaces in each group for 15 seconds, rinsed with water for 20 seconds and dried for 20 seconds with compressed air in groups one and two. After conditioning, group 1 received unfilled resin (Margin Bond, Colten and group 2 received dentin bonding (Single Bond, 3M and in group 3 after conditioning and rinsing with water, a layer of dentin bonding (Single Bond was applied on wet enamel. The enamel and dentin bonding were light cured for 20 seconds. A ring mold 3.5 mm in diameter and 2 mm height was placed over the specimens to receive the composite filling material (Z100, 3M. The composite was cured for 40 seconds. The specimens were thermocycled and shear bond strengths were determined using an Instron Universal Testing Machine. The findings were analyzed by ANOVA One-Way and Tukey HSD tests. Results: Shear bond strength of dentin bonding to dry enamel was significantly less than unfilled resin to dry enamel (P<0.05. There was no significant difference between the bond strength of dentin bonding to moist and dry enamel. In addition bond strength of dentin bonding to wet enamel was not significantly different from unfilled resin to dry enamel. Conclusion: Based on the findings of this study, it is suggested that enamel surface should remain slightly moist after etching before bonding with single bond but when using unfilled resin, the

  20. Hydrogen Bond Basicity Prediction for Medicinal Chemistry Design.

    Science.gov (United States)

    Kenny, Peter W; Montanari, Carlos A; Prokopczyk, Igor M; Ribeiro, Jean F R; Sartori, Geraldo Rodrigues

    2016-05-12

    Hydrogen bonding is discussed in the context of medicinal chemistry design. Minimized molecular electrostatic potential (Vmin) is shown to be an effective predictor of hydrogen bond basicity (pKBHX), and predictive models are presented for a number of hydrogen bond acceptor types relevant to medicinal chemistry. The problems posed by the presence of nonequivalent hydrogen bond acceptor sites in molecular structures are addressed by using nonlinear regression to fit measured pKBHX to calculated Vmin. Predictions are made for hydrogen bond basicity of fluorine in situations where relevant experimental measurements are not available. It is shown how predicted pKBHX can be used to provide insight into the nature of bioisosterism and to profile heterocycles. Examples of pKBHX prediction for molecular structures with multiple, nonequivalent hydrogen bond acceptors are presented.

  1. Octahedral engineering of orbital polarizations in charge transfer oxides

    Science.gov (United States)

    Cammarata, Antonio; Rondinelli, James M.

    2013-04-01

    Negative charge transfer ABO3 oxides may undergo electronic metal-insulator transitions (MIT) concomitant with a dilation and contraction of nearly rigid octahedra. On both sides of the MIT are in-phase or out-of-phase (or both) rotations of adjacent octahedra that buckle the B-O-B bond angle away from 180∘. Using density functional theory with the PBEsol +U approach, we describe an octahedral engineering avenue to control the B 3d and O 2p orbital polarization through enhancement of the BO6 rotation “sense” rather than solely through conventional changes to the B-O bond lengths, i.e., crystal field distortions. Using CaFeO3 as a prototypical material, we show the flavor of the octahedral rotation pattern when combined with strain-rotation coupling and thin film engineering strategies offers a promising avenue to fine tune orbital polarizations near electronic phase boundaries.

  2. Plotting Orbital Trajectories For Maneuvers

    Science.gov (United States)

    Brody, Adam R.

    1991-01-01

    Interactive Orbital Trajectory Planning Tool (EIVAN) computer program is forward-looking interactive orbit-trajectory-plotting software tool for use with proximity operations (operations occurring within 1-km sphere of space station) and other maneuvers. Developed to plot resulting trajectories, to provide better comprehension of effects of orbital mechanics, and to help user develop heuristics for planning missions on orbit. Program runs with Microsoft's Excel for execution on MacIntosh computer running MacIntosh OS.

  3. Preseptal and orbital cellulitis

    Directory of Open Access Journals (Sweden)

    Emine Akçay

    2014-09-01

    Full Text Available Preseptal cellulitis (PC is defined as an inflammation of the eyelid and surrounding skin, whereas orbital cellulitis (OC is an inflammation of the posterior septum of the eyelid affecting the orbit and its contents. Periorbital tissues may become infected as a result of trauma (including insect bites or primary bacteremia. Orbital cellulitis generally occurs as a complication of sinusitis. The most commonly isolated organisms are Staphylococcus aureus, Streptococcus pneumoniae, S. epidermidis, Haempphilus influenzae, Moraxella catarrhalis and S. pyogenes. The method for the diagnosis of OS and PS is computed tomography. Using effective antibiotics is a mainstay for the treatment of PC and OC. There is an agreement that surgical drainage should be performed in cases of complete ophthalmoplegia or significant visual impairment or large abscesses formation. This infections are also at a greater risk of acute visual loss, cavernous sinus thrombosis, meningitis, cerebritis, endophthalmitis, and brain abscess in children. Early diagnosis and appropriate treatment are crucial to control the infection. Diagnosis, treatment, management and complications of PC and OC are summarized in this manuscript. J MicrobiolInfect Dis 2014; 4(3: 123-127

  4. On the theory of Killing orbits in spacetime

    Energy Technology Data Exchange (ETDEWEB)

    Hall, G S [Department of Mathematical Sciences, University of Aberdeen, Aberdeen AB24 3UE, Scotland (United Kingdom)

    2003-09-21

    This paper gives a theoretical discussion of the orbits and isotropies which arise in a spacetime which admits a Lie algebra of Killing vector fields. The submanifold structure of the orbits is explored together with their induced Killing vector structure. A general decomposition of a spacetime in terms of the nature and dimension of its orbits is given and the concept of stability and instability for orbits introduced. A general relation is shown linking the dimensions of the Killing algebra, the orbits and the isotropies. The well-behaved nature of 'stable' orbits and the possible misbehaviour of the 'unstable' ones is pointed out and, in particular, the fact that independent Killing vector fields in spacetime may not induce independent Killing vector fields on unstable orbits. Several examples are presented to exhibit these features. Finally, an appendix is given which revisits and attempts to clarify the well-known theorem of Fubini on the dimension of Killing orbits.

  5. Hydrogen bonded supramolecular materials

    CERN Document Server

    Li, Zhan-Ting

    2015-01-01

    This book is an up-to-date text covering topics in utilizing hydrogen bonding for constructing functional architectures and supramolecular materials. The first chapter addresses the control of photo-induced electron and energy transfer. The second chapter summarizes the formation of nano-porous materials. The following two chapters introduce self-assembled gels, many of which exhibit unique functions. Other chapters cover the advances in supramolecular liquid crystals and the versatility of hydrogen bonding in tuning/improving the properties and performance of materials. This book is designed

  6. Comment on "Rabbit-Ears Hybrids, VSEPR Sterics, and Other Orbital Anachronisms": A Reply to a Criticism

    Science.gov (United States)

    Hiberty, Philippe C.; Danovich, David; Shaik, Sason

    2015-01-01

    This commentary summarizes the authors' basic disagreements with the paper, "Rabbit-Ears, VSEPR Sterics, and Other Orbital Anachronisms," which criticizes the authors' usage of the hybrid orbitals for H[subscript 2]O in their book, "A Chemist's Guide to Valence Bond Theory" (Shaik and Hiberty, 2008). The current article shows…

  7. Quantitative classification of covalent and noncovalent H-bonds.

    Science.gov (United States)

    Grabowski, Sławomir J; Sokalski, W Andrzej; Dyguda, Edyta; Leszczyński, Jerzy

    2006-04-06

    The covalent nature of interactions within various hydrogen bonded molecular aggregates has been characterized by the two entirely different computational methods: Bader analysis of the electron density and variation-perturbation partitioning of the intermolecular interaction energy. Analysis of 34 complexes representing different types of hydrogen bonds indicates that the proton-acceptor distance approximately 1.8 A and the ratio of delocalization and electrostatic terms approximately 0.45 constitutes approximately a borderline between covalent and noncovalent hydrogen bonds. The latter ratio could be used to characterize quantitatively the degree of the covalent nature of transition state interactions with active site residues, a quantity essential for an enzyme catalytic activity.

  8. Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

    Energy Technology Data Exchange (ETDEWEB)

    Small, David W.; Sundstrom, Eric J.; Head-Gordon, Martin [Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2015-01-14

    Restricted Hartree Fock using complex-valued orbitals (cRHF) is studied. We introduce an orbital pairing theorem, with which we obtain a concise connection between cRHF and real-valued RHF, and use it to uncover the close relationship between cRHF, unrestricted Hartree Fock, and generalized valence bond perfect pairing. This enables an intuition for cRHF, contrasting with the generally unintuitive nature of complex orbitals. We also describe an efficient computer implementation of cRHF and its corresponding stability analysis. By applying cRHF to the Be + H{sub 2} insertion reaction, a Woodward-Hoffmann violating reaction, and a symmetry-driven conical intersection, we demonstrate in genuine molecular systems that cRHF is capable of removing certain potential energy surface singularities that plague real-valued RHF and related methods. This complements earlier work that showed this capability in a model system. We also describe how cRHF is the preferred RHF method for certain radicaloid systems like singlet oxygen and antiaromatic molecules. For singlet O{sub 2}, we show that standard methods fail even at the equilibrium geometry. An implication of this work is that, regardless of their individual efficacies, cRHF solutions to the HF equations are fairly commonplace.

  9. Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

    Science.gov (United States)

    Small, David W.; Sundstrom, Eric J.; Head-Gordon, Martin

    2015-01-01

    Restricted Hartree Fock using complex-valued orbitals (cRHF) is studied. We introduce an orbital pairing theorem, with which we obtain a concise connection between cRHF and real-valued RHF, and use it to uncover the close relationship between cRHF, unrestricted Hartree Fock, and generalized valence bond perfect pairing. This enables an intuition for cRHF, contrasting with the generally unintuitive nature of complex orbitals. We also describe an efficient computer implementation of cRHF and its corresponding stability analysis. By applying cRHF to the Be + H2 insertion reaction, a Woodward-Hoffmann violating reaction, and a symmetry-driven conical intersection, we demonstrate in genuine molecular systems that cRHF is capable of removing certain potential energy surface singularities that plague real-valued RHF and related methods. This complements earlier work that showed this capability in a model system. We also describe how cRHF is the preferred RHF method for certain radicaloid systems like singlet oxygen and antiaromatic molecules. For singlet O2, we show that standard methods fail even at the equilibrium geometry. An implication of this work is that, regardless of their individual efficacies, cRHF solutions to the HF equations are fairly commonplace.

  10. Orbits of four double stars

    Directory of Open Access Journals (Sweden)

    Novaković B.

    2006-01-01

    Full Text Available We present orbits of four double stars. Orbits of stars WDS 23516+4205 = ADS 17050 and WDS 18239+5848 = ADS 11336 were calculated for the first time. Orbits of double stars WDS 02022+3643 = ADS 1613 and WDS 18443+3940 = ADS 11635 were revised. We have also determined their masses, dynamical parallaxes and ephemerides.

  11. Orbital Cellulitis of Odontogenic Origin.

    Science.gov (United States)

    Yan, William; Chakrabarti, Rahul; Choong, Jessica; Hardy, Thomas

    2015-01-01

    Odontogenic orbital cellulitis, although uncommon, has the potential to cause severe vision loss if unsuspected and untreated. Compared to non-odontogenic bacteriology, odontogenic orbital abscesses typically feature a heavy mixed growth with anaerobic organisms. We review the literature and discuss the case of a 26-year-old male who presented with anaerobic orbital cellulitis for treatment.

  12. Influence of porphyrin radical type on V double bond O bond strength in vanadyl porphyrin cation radicals: Implications for heme protein intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Macor, K.A. (Univ. of Notre Dame, IN (USA)); Czernuszewicz, R.S.; Spiro, T.G. (Princeton Univ., NJ (USA))

    1990-05-16

    Resonance Raman spectra have been analyzed for vanadyl porphyrin cation radicals of octaethylporphyrin (OEP), meso-tetra-phenylporphyrin (TPP), and meso-tetrametisylporphyrin (TMP). The strength of the metal-oxo bond in these cation radicals is demonstrated to be a function of radical type, a{sub 1u} or a{sub 2u}. Porphyrin ring mode {nu}{sub 2}, which has previously been shown to be a marker for the radical type was used to identify the radicals. The a{sub 1u} OV(OEP) radical exhibited an upshift in the V{double bond}O stretching frequency resulting from the increased positive charge on the porphyrin, which reduces the porphyrin {yields} vanadium electron donation and increases the O {yields} vanadium donation. {nu}(V{double bond}O) frequency decreases were observed for the a{sub 2u} OV(TPP) and OV(TMP) radicals. These can be explained on the basis of mixing of the porphyrin {pi} a{sub 2u} orbital with the vanadium d{sub z{sup 2}} and oxygen p{sub z} orbitals, which is allowed in C{sub 4v} symmetry. This interaction decreases the bond strength in a {sub 2u} cation radicals, since an electron is removed from an orbital with partial V-O {sigma}-bonding character. Mixing of the porphyrin a{sub 1u} {pi} orbital with metal or oxygen orbitals is forbidden. These results imply that porphyrin radical type is an important determinant of the Fe{double bond}O bond strength in heme protein cation-radical intermediates. 34 refs., 5 figs.

  13. Retinoblastoma associated orbital cellulitis

    Science.gov (United States)

    Mullaney, P.; Karcioglu, Z.; Huaman, A.; Al-Mesfer, S.

    1998-01-01

    AIM—Preseptal and orbital cellulitis are rare presenting features of intraocular retinoblastoma. The objectives of this study were to determine the frequency of retinoblastoma associated cellulitis, as well as to review its clinical and histopathological features.
METHODS—The medical records of 292 retinoblastoma patients in the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia were reviewed. Those indicating a history of, or presenting with, cellulitis were retrieved and their clinical, radiological, and histopathological variables were assessed. Patients with definite extraocular tumour extension on clinical or radiological examination were excluded.
RESULTS—14 patients were found to have retinoblastoma associated cellulitis (4.8%); nine had bilateral and five had unilateral retinoblastoma. Conjunctival and blood cultures were performed in 10 cases and were negative. 10 children were treated with intravenous steroids, often in conjunction with antibiotics, resulting in a prompt decrease in inflammation. Three other children were treated with antibiotics alone and one received no treatment. Computed tomographic scanning depicted large intraocular tumours occupying between 80% and 100% of the globe in each case. In eight patients, periocular inflammation was radiologically interpreted as possible extraocular extension. In one patient serial computed tomographic scanning showed a reduction in intraocular calcification over time which occurred in the presence of cellulitis. 12 patients underwent enucleation and histopathological examination revealed large necrotic, poorly differentiated tumours associated with uveal involvement and early optic nerve invasion. Focal perilimbal destruction was seen in one patient, and in another peripapillary extrascleral extension was present. 12 patients are alive with a mean follow up of 56.4 months.
CONCLUSIONS—Radiological evaluation of scleral integrity may be hindered by periocular inflammatory

  14. Orbital Cellulitis Following Orbital Blow-out Fracture.

    Science.gov (United States)

    Byeon, Je Yeon; Choi, Hwan Jun

    2017-10-01

    Orbital cellulitis and abscess have been described in the literature as complication that usually occur secondary to infection in the maxillary, ethmoidal, and frontal sinuses. If left untreated, it can lead to blindness, cavernous sinus thrombosis, meningitis, or cerebral abscess. Orbital fractures are a common sequela of blunt orbital trauma, but are only rarely associated with orbital cellulitis. So, the authors present rare orbital cellulitis after orbital blow-out fracture. A 55-year-old Asian complains of severe orbital swelling and pain on the left side. These symptoms had started 2 days earlier and worsened within the 24 hours before hospital admission resulting in visual disturbances such as diplopia and photophobia. Contrast-enhanced computed tomography scan showed considerable soft tissue swelling and abscess formation on the left side. Patient was subjected to surgical drainage under general anesthesia in the operation room. In this case, the postoperative period was uneventful and the rapid improvement of symptoms was remarkable. In conclusion, the abscess of the orbit is a surgical emergency in patients whose impairment of vision or ocular symptoms cannot be controlled with medical therapy using antibiotics. In our case, orbital cellulitis can occur after blunt orbital trauma without predisposing sinusitis. Early and prompt diagnosis and surgical drainage before severe loss of visual acuity rescue or recover the vision in case of orbital cellulitis.

  15. QM AND AB INITIO INVESTIGATION ON THE HYDROGEN BONDING, NMR CHEMICAL SHIFTS AND SOLVENT EFFECTS ON THE DPPE

    Directory of Open Access Journals (Sweden)

    M. Monajjemi

    2010-06-01

    Full Text Available The hydrogen bonding effects that were produced from interaction of membrane lipid dipalmitoylphosphatidyl-ethanolamine (DPPE with 1-5 water molecules, has been theoretically  investigated through the quantum mechanical calculations at the Hartree-Fock level of theory and the 3-21G, 6-31G and 6-31G* basis sets with the computational package of Gaussian 98. According to the obtained results of the structural optimization of the isolated DPPE in the gas phase, we can see the evidences of interactions in the head group of this macromolecule (from the molecular point of view we have a proton transfer from the ammonium group to the phosphate oxygen of zwitterionic form. As we know that the hydrogen bonding of DPPE with water molecules which have surrounded its head group plays an important role in the permeability of DPPE. So, in order to understand the microscopic physico-chemical nature of this subject we have analyzed bond and torsion angles of DPPE before and after added water molecules.  In this paper we have theoretically studied the complexes DPPE with water molecules which have surrounded its head group. As mentioned before, this theoretically study has been done through Hartree-Fock level of theory by using simple basis sets. Theoretical data shows that the interaction of head group of DPPE with water molecules causes some changes in the geometry of DPPE which were explained by the contribution of zwitterionic form of DPPE macromolecule, and finally hydrated DPPE becomes stable complex. Comparison between theoretical and experimental geometry data of DPPE macromolecule shows that the calculation at the HF/3-21 level of theory produces results which they are in better agreement with the experimental data. Moreover the hydrogen bonding effects on the NMR shielding tensor of selected atoms in the hydrated complexes of DPPE were reported. The ";Gauge Including Atomic Orbitals"; (GIAO approaches within the SCF-Hartree-Fock approximation have

  16. Effective lattice model for the collective modes in a Fermi liquid with spin-orbit coupling

    Science.gov (United States)

    Kumar, Abhishek; Maslov, Dmitrii L.

    2017-04-01

    A Fermi liquid (FL) with spin-orbit coupling (SOC) supports a special type of collective modes—chiral spin waves—which are oscillations of magnetization that occur even in the absence of the external magnetic field. We study the chiral spin waves of a two-dimensional FL in the presence of both the Rashba and Dresselhaus types of SOC and also subject to the in-plane magnetic field. We map the system of coupled kinetic equations for the angular harmonics of the occupation number onto an effective one-dimensional tight-binding model, in which the lattice sites correspond to angular-momentum channels. Linear-in-momentum SOC ensures that the effective tight-binding model has only nearest-neighbor hopping on a bipartite lattice. In this language, the continuum of spin-flip particle-hole excitations becomes a conduction band of the lattice model, whereas electron-electron interaction, parametrized by harmonics of the Landau function, is mapped onto lattice defects of both on-site and bond type. The collective modes correspond to bound states formed by such defects. All the features of the collective-mode spectrum receive natural explanation in the lattice picture as resulting from the competition between on-site and bond defects.

  17. Amino Acid Patterns around Disulfide Bonds

    Science.gov (United States)

    Marques, José R. F.; da Fonseca, Rute R.; Drury, Brett; Melo, André

    2010-01-01

    Disulfide bonds provide an inexhaustible source of information on molecular evolution and biological specificity. In this work, we described the amino acid composition around disulfide bonds in a set of disulfide-rich proteins using appropriate descriptors, based on ANOVA (for all twenty natural amino acids or classes of amino acids clustered according to their chemical similarities) and Scheffé (for the disulfide-rich proteins superfamilies) statistics. We found that weakly hydrophilic and aromatic amino acids are quite abundant in the regions around disulfide bonds, contrary to aliphatic and hydrophobic amino acids. The density distributions (as a function of the distance to the center of the disulfide bonds) for all defined entities presented an overall unimodal behavior: the densities are null at short distances, have maxima at intermediate distances and decrease for long distances. In the end, the amino acid environment around the disulfide bonds was found to be different for different superfamilies, allowing the clustering of proteins in a biologically relevant way, suggesting that this type of chemical information might be used as a tool to assess the relationship between very divergent sets of disulfide-rich proteins. PMID:21151463

  18. Amino acid patterns around disulfide bonds.

    Science.gov (United States)

    Marques, José R F; da Fonseca, Rute R; Drury, Brett; Melo, André

    2010-11-18

    Disulfide bonds provide an inexhaustible source of information on molecular evolution and biological specificity. In this work, we described the amino acid composition around disulfide bonds in a set of disulfide-rich proteins using appropriate descriptors, based on ANOVA (for all twenty natural amino acids or classes of amino acids clustered according to their chemical similarities) and Scheffé (for the disulfide-rich proteins superfamilies) statistics. We found that weakly hydrophilic and aromatic amino acids are quite abundant in the regions around disulfide bonds, contrary to aliphatic and hydrophobic amino acids. The density distributions (as a function of the distance to the center of the disulfide bonds) for all defined entities presented an overall unimodal behavior: the densities are null at short distances, have maxima at intermediate distances and decrease for long distances. In the end, the amino acid environment around the disulfide bonds was found to be different for different superfamilies, allowing the clustering of proteins in a biologically relevant way, suggesting that this type of chemical information might be used as a tool to assess the relationship between very divergent sets of disulfide-rich proteins.

  19. Bond strength comparison of color change adhesives for orthodontic bonding.

    Science.gov (United States)

    Duers, Michael W; English, Jeryl D; Ontiveros, Joe C; Powers, John M; Bussa, Harry I; Frey, Gary N; Gallerano, Ronald L; Paige, Sebastian Z

    2011-03-01

    This study investigated whether three different color change light-cured orthodontic bonding adhesives have comparable shear bond strengths to a conventional light-cured orthodontic bonding adhesive. The sample of 240 bovine incisors was divided into four groups of 60 each. Each group tested one of four orthodontic bonding adhesives: 3M Unitek Transbond PLUS, Ormco Gréngloo, Ormco Blúgloo, and 3M Unitek Transbond XT (control). The four groups were further divided into two subgroups of 30 with shear bond strength tested at two different times (15 minutes and 24 hours) post-bond. The shear bond strength was measured on a universal testing machine. The data were analyzed by two-way analysis of variance and post-hoc comparisons (Fisher's PLSD) at the 0.05 level of significance. The average shear bond strength was greater at 24 hours than at 15 minutes for Transbond PLUS, Blúgloo, and Transbond XT. For Gréngloo, the average shear bond strength was greater at 15 minutes than at 24 hours. Gréngloo tested at 15 minutes had the highest average shear bond strength. Gréngloo tested at 24 hours had the lowest average shear bond strength. All four orthodontic bonding adhesives demonstrated bond strengths considered to be clinically acceptable for orthodontic purposes.

  20. Analysis of an unusual hetero-halogen bonded trimer using charge ...

    Indian Academy of Sciences (India)

    Halogen bond; electron density analysis; multipole refinement; intermolecular interaction. 1. Introduction. Hydrogen bonding is among the most widely studied noncovalent interactions in literature.1 3 Close on its heels comes the halogen bonding owing to its strength and directionality.4,5 In this context, the nature of halo-.

  1. [Direct bonding in orthodontics].

    Science.gov (United States)

    Hablützel, W

    1976-03-01

    Composite materials have been used to attach orthodontic brackets on the conditioned enamel surface. A method of direct bonding with Enamelite of metal brackets with a mechanical retention on the basis is described. Clinical experience with the adhesive technique, its range of indication and possible failures are discussed in several case reports.

  2. Orbital maneuvers and space rendezvous

    Science.gov (United States)

    Butikov, Eugene I.

    2015-12-01

    Several possibilities of launching a space vehicle from the orbital station are considered and compared. Orbital maneuvers discussed in the paper can be useful in designing a trajectory for a specific space mission. The relative motion of orbiting bodies is investigated on examples of spacecraft rendezvous with the space station that stays in a circular orbit around the Earth. An elementary approach is illustrated by an accompanying simulation computer program and supported by a mathematical treatment based on fundamental laws of physics and conservation laws. Material is appropriate for engineers and other personnel involved in space exploration, undergraduate and graduate students studying classical physics and orbital mechanics.

  3. Orbital Debris: A Policy Perspective

    Science.gov (United States)

    Johnson, Nicholas L.

    2007-01-01

    A viewgraph presentation describing orbital debris from a policy perspective is shown. The contents include: 1) Voyage through near-Earth Space-animation; 2) What is Orbital Debris?; 3) Orbital Debris Detectors and Damage Potential; 4) Hubble Space Telescope; 5) Mir Space Station Solar Array; 6) International Space Station; 7) Space Shuttle; 8) Satellite Explosions; 9) Satellite Collisions; 10) NASA Orbital Debris Mitigation Guidelines; 11) International Space Station Jettison Policy; 12) Controlled/Uncontrolled Satellite Reentries; 13) Return of Space Objects; 14) Orbital Debris and U.S. National Space Policy; 15) U.S Government Policy Strategy; 16) Bankruptcy of the Iridium Satellite System; 17) Inter-Agency Space Debris Coordination Committee (IADC); 18) Orbital Debris at the United Nations; 19) Chinese Anti-satellite System; 20) Future Evolution of Satellite Population; and 21) Challenge of Orbital Debris

  4. Bond-strengthening π backdonation in a transition-metal π-diborene complex.

    Science.gov (United States)

    Braunschweig, Holger; Damme, Alexander; Dewhurst, Rian D; Vargas, Alfredo

    2013-02-01

    Transition-metal catalysis is founded on the principle that electron donation from a metal to a ligand is accepted by an antibonding orbital of the ligand, thereby weakening one of the bonds in the ligand. Without this, the initial step of bond activation in many catalytic processes would simply not occur. This concept is enshrined in the well-accepted Dewar-Chatt-Duncanson model of transition-metal bonding. We present herein experimental and computational evidence for the first true violation of the Dewar-Chatt-Duncanson bonding model, found in a π-diborene complex in which an electron-rich group 10 metal donates electrons into an empty bonding π orbital on the ligand, and thereby strengthens the bond. The complex is also the first transition-metal complex to contain a bound diborene, a species not isolated before, either in its free form or bound to a metal.

  5. Orbit Propagation and Determination of Low Earth Orbit Satellites

    Directory of Open Access Journals (Sweden)

    Ho-Nien Shou

    2014-01-01

    Full Text Available This paper represents orbit propagation and determination of low Earth orbit (LEO satellites. Satellite global positioning system (GPS configured receiver provides position and velocity measures by navigating filter to get the coordinates of the orbit propagation (OP. The main contradictions in real-time orbit which is determined by the problem are orbit positioning accuracy and the amount of calculating two indicators. This paper is dedicated to solving the problem of tradeoffs. To plan to use a nonlinear filtering method for immediate orbit tasks requires more precise satellite orbit state parameters in a short time. Although the traditional extended Kalman filter (EKF method is widely used, its linear approximation of the drawbacks in dealing with nonlinear problems was especially evident, without compromising Kalman filter (unscented Kalman Filter, UKF. As a new nonlinear estimation method, it is measured at the estimated measurements on more and more applications. This paper will be the first study on UKF microsatellites in LEO orbit in real time, trying to explore the real-time precision orbit determination techniques. Through the preliminary simulation results, they show that, based on orbit mission requirements and conditions using UKF, they can satisfy the positioning accuracy and compute two indicators.

  6. Valence XPS structure and chemical bond in Cs2UO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2016-01-01

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

  7. Indirect bonding technique in orthodontics

    Directory of Open Access Journals (Sweden)

    Kübra Yıldırım

    2016-08-01

    Full Text Available ‘Direct Bonding Technique’ which allows the fixed orthodontic appliances to be directly bonded to teeth without using bands decreased the clinic time for bracket bonding and increased esthetics and oral hygiene during orthodontic treatment. However, mistakes in bracket positioning were observed due to decreased direct visual sight and access to posterior teeth. ‘Indirect Bonding Technique’ was developed for eliminating these problems. Initially, decreased bond strength, higher bond failure rate, periodontal tissue irritation, compromised oral hygiene and increased laboratory time were the main disadvantages of this technique when compared to direct bonding. The newly developed materials and modified techniques help to eliminate these negative consequences. Today, the brackets bonded with indirect technique have similar bond strength with brackets bonded directly. Moreover, indirect and direct bonding techniques have similar effects on periodontal tissues. However, indirect bonding technique requires more attention and precision in laboratory and clinical stage, and has higher cost. Orthodontist's preference between these two bonding techniques may differ according to time spent in laboratory and clinic, cost, patient comfort and personal opinion.

  8. Triel Bonds, π-Hole-π-Electrons Interactions in Complexes of Boron and Aluminium Trihalides and Trihydrides with Acetylene and Ethylene

    Directory of Open Access Journals (Sweden)

    Sławomir J. Grabowski

    2015-06-01

    Full Text Available MP2/aug-cc-pVTZ calculations were performed on complexes of aluminium and boron trihydrides and trihalides with acetylene and ethylene. These complexes are linked through triel bonds where the triel center (B or Al is characterized by the Lewis acid properties through its π-hole region while π-electrons of C2H2 or C2H4 molecule play the role of the Lewis base. Some of these interactions possess characteristics of covalent bonds, i.e., the Al-π-electrons links as well as the interaction in the BH3-C2H2 complex. The triel-π-electrons interactions are classified sometimes as the 3c-2e bonds. In the case of boron trihydrides, these interactions are often the preliminary stages of the hydroboration reaction. The Quantum Theory of “Atoms in Molecules” as well as the Natural Bond Orbitals approach are applied here to characterize the π-hole-π-electrons interactions.

  9. An Inverted-Sandwich Diuranium μ-η5:η5-Cyclo-P5 Complex Supported by U-P5 δ-Bonding.

    Science.gov (United States)

    Gardner, Benedict M; Tuna, Floriana; McInnes, Eric J L; McMaster, Jonathan; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2015-06-08

    Reaction of [U(TrenTIPS)] [1, TrenTIPS=N(CH2CH2NSiiPr3)3] with 0.25 equivalents of P4 reproducibly affords the unprecedented actinide inverted sandwich cyclo-P5 complex [{U(TrenTIPS)}2(μ-η5:η5-cyclo-P5)] (2). All prior examples of cyclo-P5 are stabilized by d-block metals, so 2 shows that cyclo-P5 does not require d-block ions to be prepared. Although cyclo-P5 is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P5)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo-P5 charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P5 compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals.

  10. Triel Bonds, π-Hole-π-Electrons Interactions in Complexes of Boron and Aluminium Trihalides and Trihydrides with Acetylene and Ethylene.

    Science.gov (United States)

    Grabowski, Sławomir J

    2015-06-19

    MP2/aug-cc-pVTZ calculations were performed on complexes of aluminium and boron trihydrides and trihalides with acetylene and ethylene. These complexes are linked through triel bonds where the triel center (B or Al) is characterized by the Lewis acid properties through its π-hole region while π-electrons of C2H2 or C2H4 molecule play the role of the Lewis base. Some of these interactions possess characteristics of covalent bonds, i.e., the Al-π-electrons links as well as the interaction in the BH3-C2H2 complex. The triel-π-electrons interactions are classified sometimes as the 3c-2e bonds. In the case of boron trihydrides, these interactions are often the preliminary stages of the hydroboration reaction. The Quantum Theory of "Atoms in Molecules" as well as the Natural Bond Orbitals approach are applied here to characterize the π-hole-π-electrons interactions.

  11. The effect of furcated hydrogen bond and coordination bond on luminescent behavior of metal-organic framework [CuCN·EIN]: a TDDFT study.

    Science.gov (United States)

    Wu, Danyang; Mi, Weihong; Ji, Min; Hao, Ce; Qiu, Jieshan

    2012-11-01

    The hydrogen bonding in electronically excited-state of the metal-organic framework [CuCN·EIN] was studied using time-dependent density functional theory (TDDFT). The representative fragment of [CuCN·EIN] was employed for the computation. The geometric structures, binding energies and IR spectra in both ground state and electronically excited state S(1) of the complex were computed using DFT and TDDFT methods to investigate excited-state hydrogen-bonding and coordination bonding, respectively. Based on the analysis of the frontier molecular orbitals and the electronic configuration of the complex, the ligand-to-metal charge transfer (LMCT) luminescence was confirmed. Furthermore, furcated hydrogen bonds are both strengthened in the S(1) state slightly. And then, the strengthening of the hydrogen bonds in the S(1) state goes against the charge transfer from ligand to metal and then should be in favor of the luminescence. In particular, we also discuss strengthening or weakening behavior of the coordination bonds in the S(1) state for the first time. Based on the results of the bond lengths and vibration frequency of the coordination bond, we can conclude that the coordination bond Cu(7)-N(8) is strengthened in the S(1) state. And the strengthening of the coordination bond Cu(7)-N(8) should also be in favor of the luminescence. Copyright © 2012 Elsevier B.V. All rights reserved.

  12. Comparison of shear bond strength of the stainless steel metallic brackets bonded by three bonding systems

    Directory of Open Access Journals (Sweden)

    Mehdi Ravadgar

    2013-09-01

    Full Text Available Introduction: In orthodontic treatment, it is essential to establish a satisfactory bond between enamel and bracket. After the self-etch primers (SEPs were introduced for the facilitation of bracket bonding in comparison to the conventional etch-and-bond system, multiple studies have been carried out on their shear bond strengths which have yielded different results. This study was aimed at comparing shear bond strengths of the stainless steel metallic brackets bonded by three bonding systems. Methods: In this experimental in vitro study, 60 extracted human maxillary premolar teeth were randomly divided into three equal groups: in the first group, Transbond XT (TBXT light cured composite was bonded with Transbond plus self-etching primer (TPSEP; in the second group, TBXT composite was bonded with the conventional method of acid etching; and in the third group, the self cured composite Unite TM bonding adhesive was bonded with the conventional method of acid etching. In all the groups, Standard edgewise-022 metallic brackets (American Orthodontics, Sheboygan, USA were used. Twenty-four hours after the completion of thermocycling, shear bond strength of brackets was measured by Universal Testing Machine (Zwick. In order to compare the shear bond strengths of the groups, the variance analysis test (ANOVA was adopted and p≤0.05 was considered as a significant level. Results: Based on megapascal, the average shear bond strength for the first, second, and third groups was 8.27±1.9, 9.78±2, and 8.92±2.5, respectively. There was no significant difference in the shear bond strength of the groups. Conclusions: Since TPSEP shear bond strength is approximately at the level of the conventional method of acid etching and within the desirable range for orthodontic brackets shear bond strength, applying TPSEP can serve as a substitute for the conventional method of etch and bond, particularly in orthodontic operations.

  13. Wafer bonding using Cu-Sn intermetallic bonding layers

    NARCIS (Netherlands)

    Flötgen, C.; Pawlak, M.; Pabo, E.; Wiel, H.J. van de; Hayes, G.R.; Dragoi, V.

    2014-01-01

    Wafer-level Cu-Sn intermetallic bonding is an interesting process for advanced applications in the area of MEMS and 3D interconnects. The existence of two intermetallic phases for Cu-Sn system makes the wafer bonding process challenging. The impact of process parameters on final bonding layer

  14. Making Weak Bonds (cooling) and Breaking Strong Bonds (heating ...

    Indian Academy of Sciences (India)

    Making Weak Bonds (cooling) and Breaking Strong Bonds (heating) with Supersonic Techniques · Acknowledgements · Outline · Slide 4 · A comparison of the two techniques · What is a hydrogen bond? Phenylacetylene and its complexes · Slide 8 · Phenylacetylene and PAH · phenylacetylene · Complexes in the interstellar ...

  15. Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

    2017-02-28

    Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

  16. Supramolecular spectral studies on metal-ligand bonding of novel quinoline azodyes

    Science.gov (United States)

    Diab, M. A.; El-Sonbati, A. Z.; El-Bindary, A. A.; Barakat, A. M.

    2013-12-01

    A series of novel bidentate azodye quinoline ligands were synthesized with various p-aromatic amines like p-(OCH3, CH3, H, Cl and NO2). All ligands and their complexes have been characterized on the basis of elemental analysis, IR, 1H and 13C NMR data and spectroscopic studies. IR and 1H NMR studies reveal that the ligands (HLn) exists in the tautomeric azo/hydrazo form in both states with intramolecular hydrogen bonding. The ligands obtained contain Ndbnd N and phenolic functional groups in different positions with respect to the quinoline group. IR spectra show that the azo compounds (HLn) act as monobasic bidentate ligand by coordinating via the azodye (sbnd Ndbnd Nsbnd ) and oxygen atom of the phenolic group. The ESR (g|| and g⊥) and bonding α2 parameters of the copper ion were greatly affected by substituting several groups position of ring of quinoline and p-aromatic ring. The ESR spectra of copper complexes in powder form show a broad signal with values in order g|| > g⊥ > ge > 2.0023. The value of covalency factor β and orbital reduction factor K accounts for the covalent nature of the complexes. All complexes possessed an octahedral and square planar geometry. The thermal properties of the complexes were investigated using TGA and DSC. It is found that the change of substituent affects the thermal properties of complexes.

  17. Analysis of tensile bond strengths using Weibull statistics.

    Science.gov (United States)

    Burrow, Michael F; Thomas, David; Swain, Mike V; Tyas, Martin J

    2004-09-01

    Tensile strength tests of restorative resins bonded to dentin, and the resultant strengths of interfaces between the two, exhibit wide variability. Many variables can affect test results, including specimen preparation and storage, test rig design and experimental technique. However, the more fundamental source of variability, that associated with the brittle nature of the materials, has received little attention. This paper analyzes results from micro-tensile tests on unfilled resins and adhesive bonds between restorative resin composite and dentin in terms of reliability using the Weibull probability of failure method. Results for the tensile strengths of Scotchbond Multipurpose Adhesive (3M) and Clearfil LB Bond (Kuraray) bonding resins showed Weibull moduli (m) of 6.17 (95% confidence interval, 5.25-7.19) and 5.01 (95% confidence interval, 4.23-5.8). Analysis of results for micro-tensile tests on bond strengths to dentin gave moduli between 1.81 (Clearfil Liner Bond 2V) and 4.99 (Gluma One Bond, Kulzer). Material systems with m in this range do not have a well-defined strength. The Weibull approach also enables the size dependence of the strength to be estimated. An example where the bonding area was changed from 3.1 to 1.1 mm diameter is shown. Weibull analysis provides a method for determining the reliability of strength measurements in the analysis of data from bond strength and tensile tests on dental restorative materials.

  18. Visualizing Chemical Bonds in Synthetic Molecules

    Science.gov (United States)

    Collins, Laura C.; Ruth, Anthony; Green, David B.; Janko, Boldizsar; Gomes, Kenjiro K.

    The use of synthetic quantum systems makes it possible to study phenomena that cannot be probed by conventional experiments. We created synthetic molecules using atomic manipulation and directly imaged the chemical bonds using tunneling spectroscopy. These synthetic systems allow us to probe the structure and electronic properties of chemical bonds in molecules, including those that would be unstable in nature, with unprecedented detail. The experimental images of electronic states in our synthetic molecules show a remarkable match to the charge distribution predicted by density functional theory calculations. The statistical analysis of the spectroscopy of these molecules can be adapted in the future to quantify aromaticity, which has been difficult to quantify universally thus far due to vague definitions. We can also study anti-aromatic molecules which are unstable naturally, to illuminate the electronic consequences of antiaromaticity.

  19. Geo satellite attitude and orbit control: fixed orbit control thrasters

    OpenAIRE

    Ermoshkin, Yu; V. Raevsky; Urusov, V.

    2009-01-01

    The paper describes the enhanced application ofhigh-economical electro-jet orbit control thrusters for geostationary satellites; in particular, generation of controlling moments to the benefit of satellite attitude determination and control subsystems in the course of orbit control maneuvers ongoing. The scheme with thrusters fixed on a satellite body is analyzed. Possible orbit control session procedures are proposed on the basis of controlling moments generation. Advantages and disadvantage...

  20. Bonds and bridges : social and poverty

    OpenAIRE

    Narayan, Deepa

    1999-01-01

    Using the lens of social capital-especially bridging or cross-cutting ties that cut across social groups and between social groups and government-provides new insights into policy design. Solidarity within social groups creates ties (bonding social capital) that bring people and resources together. In unequal societies, ties that cut across groups (bridging social capital) are essential for social cohesion and for poverty reduction. The nature of interaction between state and society is chara...

  1. Bond yield curve construction

    Directory of Open Access Journals (Sweden)

    Kožul Nataša

    2014-01-01

    Full Text Available In the broadest sense, yield curve indicates the market's view of the evolution of interest rates over time. However, given that cost of borrowing it closely linked to creditworthiness (ability to repay, different yield curves will apply to different currencies, market sectors, or even individual issuers. As government borrowing is indicative of interest rate levels available to other market players in a particular country, and considering that bond issuance still remains the dominant form of sovereign debt, this paper describes yield curve construction using bonds. The relationship between zero-coupon yield, par yield and yield to maturity is given and their usage in determining curve discount factors is described. Their usage in deriving forward rates and pricing related derivative instruments is also discussed.

  2. A Typical Presentation of Orbital Pseudotumor Mimicking Orbital Cellulitis

    Directory of Open Access Journals (Sweden)

    J. Ayatollahi

    2013-10-01

    Full Text Available Introduction: Orbital pseudotumor, also known as idiopathic orbital inflammatory syndrome (IOIS, is a benign, non- infective inflammatory condition of the orbit without identifiable local or systemic causes. The disease may mimics a variety of pathologic conditions. We pre-sent a case of pseudotumor observed in a patient admitted under the name of orbital celluli-ties. Case Report: A 26-year-old woman reffered to our hospital with the history of left ocular pain and headache 2 days before her visit.. Ophthalmological examination of the patient was normal except for the redness and lid edema, mild chemosis and conjunctival injection. Gen-eral assessment was normal but a low grade fever was observed. She was hospitalized as an orbital cellulitis patient. She was treated with intravenous antibiotics. On the third day , sud-denly diplopia, proptosis in her left eye and ocular pain in her right side appeared. MRI re-vealed bilateral enlargement of extraocular muscles. Diagnosis of orbital pseudotumor was made and the patient was treated with oral steroid.She responded promptly to the treatment. Antibiotics were discontinued and steroid was tapered in one month period under close fol-low up. Conclusion: The clinical features of orbital pseudotumor vary widely . Orbital pseudotumor and orbital cellulitis can occasionally demonstrate overlapping features.. Despite complete physical examination and appropriate imaging, sometimes correct diagnosis of the disease would be difficult (Sci J Hamadan Univ Med Sci 2013; 20 (3:256-259

  3. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

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

  4. Integration of European Bond Markets

    DEFF Research Database (Denmark)

    Christiansen, Charlotte

    2014-01-01

    I investigate the time variation in the integration of EU government bond markets. The integration is measured by the explanatory power of European factor portfolios for the individual bond markets for each year. The integration of the government bond markets is stronger for EMU than non...

  5. 46 CFR Sec. 10 - Bonds.

    Science.gov (United States)

    2010-10-01

    ...) shall be used. (b) In compliance with the perform- ance bond and payment bond requirements of Article 14... November 1950) respectively, shall be used. Such bonds (in the respective penal sums of 50 percent of the... penal sum of 40 percent of such job order contract price) shall guarantee the Contractor's performance...

  6. GEODYN Orbit Determination of Dawn at Vesta using Image Constraints

    Science.gov (United States)

    Centinello, F. J., III; Mazarico, E.; Zuber, M. T.

    2012-12-01

    The Dawn spacecraft has completed the orbital phase of its mapping mission of the asteroid 4 Vesta. We utilized radiometric measurements and image constraints to compute the spacecraft orbit using the GEODYN II orbit determination software. Image constraints are computed control point vectors which point from the spacecraft to landmarks observed in two images of the same region of Vesta, and are a newly developed measurement type for GEODYN. This capability was added because image constraints can provide supplemental information on the spacecraft trajectory especially in a weak gravity environment. Due to the geometric nature of image constraints, they can reduce the orbital errors in the along- and cross-track directions, which have typically carried higher uncertainty in previous interplanetary missions. Image constraints are also useful during times of absence of radiometric tracking data. Improvements to orbit determination can provide improved gravity field estimation and knowledge of the interior structure of Vesta. The NASA Deep Space Network (DSN) provides X-band tracking measurements for Dawn. Radiometric and image constraints were processed for the High Altitude Mapping Orbit (HAMO) I and II, and the Low Altitude Mapping Orbit (LAMO), from 23 Sept 2011 to 26 July 2012. The spacecraft altitude was roughly 685 km during HAMO and 200 km during LAMO. Doppler and range residual RMS were under 1 mm/s and 10 m, respectively. Improvement in orbital knowledge from image constraints is typically greatest in the cross-track direction and in our analysis these residuals were typically better than 500 m.

  7. Modelling of Shaft Orbiting with 3-D Solid Finite Elements

    Directory of Open Access Journals (Sweden)

    J. Yu

    1999-01-01

    Full Text Available A 3-D solid finite element model which can include bending, torsional, axial and other motions is proposed to analyse dynamic responses of shafts. For uniform shafts, this model shows consistency with beam theories when bending vibration is examined. For non-uniform shafts such as tapered ones, however, this model gives much more reliable and accurate results than beam theories which use an assumption that plane sections remain plane. Reduction procedures can be applied which involve only small matrix operations for such a system with a large number of degrees of freedom. The equations of motion have been consistently derived in a rotating frame. Shaft orbiting motion is then defined in this frame, giving a clear view of its trajectories. Forced responses due to excitation in the rotating frame have been examined to find some characteristics of the orbiting shaft. Resonant orbiting frequencies, i.e., natural frequencies of rotating shafts, can be determined in terms of the rotating or fixed frame. Trajectories of transverse displacements have been found to be varying with the forcing frequencies. At resonance, a uniform shaft will only have forward or backward orbiting motion with circular orbits. For other forcing frequencies, however, even a uniform shaft could present both forward and backward orbiting motions with non-circular orbits at different locations along its length. It is anticipated that modelling of shaft orbiting in the rotating frame with the proposed 3-D solid finite elements will lead to accurate dynamic stress evaluation.

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

    CERN Document Server

    Brown, I David

    2016-01-01

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

  9. Real-space mapping of electronic orbitals

    Energy Technology Data Exchange (ETDEWEB)

    Löffler, Stefan, E-mail: stefan.loeffler@tuwien.ac.at [Department for Materials Science and Engineering, McMaster University, 1280 Main Street West, L8S 4M1 Hamilton, Ontario (Canada); University Service Centre for Transmission Electron Microscopy, TU Vienna, Wiedner Hauptstraße 8-10/E057B, 1040 Wien (Austria); Institute for Solid State Physics, TU Vienna, Wiedner Hauptstraße 8-10/E138, 1040 Wien (Austria); Bugnet, Matthieu; Gauquelin, Nicolas [Department for Materials Science and Engineering, McMaster University, 1280 Main Street West, L8S 4M1 Hamilton, Ontario (Canada); Lazar, Sorin [FEI Electron Optics, Achtseweg Noord 5, 5651 GG Eindhoven (Netherlands); Assmann, Elias; Held, Karsten [Institute for Solid State Physics, TU Vienna, Wiedner Hauptstraße 8-10/E138, 1040 Wien (Austria); Botton, Gianluigi A. [Department for Materials Science and Engineering, McMaster University, 1280 Main Street West, L8S 4M1 Hamilton, Ontario (Canada); Schattschneider, Peter [University Service Centre for Transmission Electron Microscopy, TU Vienna, Wiedner Hauptstraße 8-10/E057B, 1040 Wien (Austria); Institute for Solid State Physics, TU Vienna, Wiedner Hauptstraße 8-10/E138, 1040 Wien (Austria)

    2017-06-15

    Highlights: • Electronic orbitals in Rutile are mapped using STEM-EELS. • Inelastic scattering simulations are performed for the experimental conditions. • The experiments and the simulations are found to be in excellent agreement. - Abstract: Electronic states are responsible for most material properties, including chemical bonds, electrical and thermal conductivity, as well as optical and magnetic properties. Experimentally, however, they remain mostly elusive. Here, we report the real-space mapping of selected transitions between p and d states on the Ångström scale in bulk rutile (TiO{sub 2}) using electron energy-loss spectrometry (EELS), revealing information on individual bonds between atoms. On the one hand, this enables the experimental verification of theoretical predictions about electronic states. On the other hand, it paves the way for directly investigating electronic states under conditions that are at the limit of the current capabilities of numerical simulations such as, e.g., the electronic states at defects, interfaces, and quantum dots.

  10. New Orbits for 18 Binaries

    Science.gov (United States)

    Cvetković, Z.; Pavlović, R.

    2017-12-01

    Orbital elements of 18 visual binaries are computed using the measurements collected in the Fourth Catalog of Interferometric Measurements of Binary Stars; 15 orbits are determined for the first time and three orbits are revised. Eleven of the binaries, denoted as HDS, were discovered during the Hipparcos mission. The remaining binaries were discovered a few years earlier or later than 1991. All studied pairs are close, and all measured separations are less than 0\\buildrel{\\prime\\prime}\\over{.} 46. The shortest orbital period is 10 years and the longest orbital period is 127 years. Dynamical parallaxes and total masses of systems are derived from the orbital elements. We also give absolute magnitudes, spectral types, and (O-C) residuals in θ and ρ.

  11. Gigantic blue shift of the H-Ar stretch vibration in pi hydrogen-bonded C(2)H(2)...HArCCF complex.

    Science.gov (United States)

    Cheng, Jianbo; Wang, Yilei; Li, Qingzhong; Liu, Zhenbo; Li, Wenzuo; Gong, Baoan

    2009-04-30

    Quantum chemical calculations have been performed to study the structure and properties of the pi hydrogen-bonded complex formed between acetylene and HArCCF at the MP2/6-311++G(2d,2p) level. The C(2)H(2)...HCCF and C(2)H(2)...HCCArF complexes were also studied for comparison with the C(2)H(2)...HArCCF complex. The basis set superposition errors (BSSE)-counterpoise corrected potential-energy surface (PES) has a larger influence on the structure and properties of the C(2)H(2)...HArCCF complex than those of the C(2)H(2)...HCCF and C(2)H(2)...HCCArF complexes. The C(2)H(2)...HArCCF complex exhibits a very large harmonic vibrational frequency blue shift of 574 cm(-1) for the H-Ar stretch, whereas the C(2)H(2)...HCCF and C(2)H(2)...HCCArF complexes exhibit a small red shift of 35 and 47 cm(-1) for the H-C stretch, respectively; upon complexation the IR intensity decreases in the former, whereas it increases in the latter. The origin of the frequency shift and nature of the hydrogen bond in these complexes have been unveiled with the natural bond orbital analysis and energy decomposition.

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

    Science.gov (United States)

    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.

  13. Elucidating bonding preferences in tetrakis(imido)uranate(VI) dianions

    Science.gov (United States)

    Anderson, Nickolas H.; Xie, Jing; Ray, Debmalya; Zeller, Matthias; Gagliardi, Laura; Bart, Suzanne C.

    2017-09-01

    Actinyl species, [AnO2]2+, are well-known derivatives of the f-block because of their natural occurrence and essential roles in the nuclear fuel cycle. Along with their nitrogen analogues, [An(NR)2]2+, actinyls are characterized by their two strong trans-An-element multiple bonds, a consequence of the inverse trans influence. We report that these robust bonds can be weakened significantly by increasing the number of multiple bonds to uranium, as demonstrated by a family of uranium(VI) dianions bearing four U-N multiple bonds, [M]2[U(NR)4] (M = Li, Na, K, Rb, Cs). Their geometry is dictated by cation coordination and sterics rather than by electronic factors. Multiple bond weakening by the addition of strong π donors has the potential for applications in the processing of high-valent actinyls, commonly found in environmental pollutants and spent nuclear fuels.

  14. Orbital science's 'Bermuda Triangle'

    Science.gov (United States)

    Sherrill, Thomas J.

    1991-02-01

    The effects of a part of the inner Van Allen belt lying closest to the earth, known as the South Atlantic Anomaly (SAA) upon spacecraft including the Hubble Space Telescope (HST), are discussed. The area consists of positively charged ions and electrons from the Van Allen Belt which become trapped in the earth's dipole field. Contor maps representing the number of protons per square centimeter per second having energies greater than 10 million electron volts are presented. It is noted that the HST orbit causes it to spend about 15 percent of its time in the SAA, but that, unlike the experience with earlier spacecraft, the satellite's skin, internal structure, and normal electronic's packaging provides sufficient protection against eletrons, although some higher energy protons still get through. Various charged particle effects which can arise within scientific instruments including fluorescence, Cerenkov radiation, and induced radioactivity are described.

  15. Orbital Eccrine Hidrocystoma

    Directory of Open Access Journals (Sweden)

    Deniz Marangoz

    2016-10-01

    Full Text Available A 29-year-old female patient presented with a painless mass on her upper eyelid medially. She noticed the mass 4 years earlier and it had increased in size over time. She had no diplopia, eyelid swelling, skin lesion overlying the mass, or visual disturbances. On ocular examination, eye movements and funduscopy were normal. The mass was movable and painless with palpation. Magnetic resonance imaging with contrast showed a 12x8x7 mm well-circumscribed cystic lesion with no contrast dye appearance. Surgical removal was performed delicately and no capsular rupture occured. Pathological examination revealed an eccrine hidrocystoma. Our aim is to underline that eccrine hidrocystoma should be included in differential diagnosis of orbital masses.

  16. The conservation of orbital symmetry

    CERN Document Server

    Woodward, R B

    2013-01-01

    The Conservation of Orbital Symmetry examines the principle of conservation of orbital symmetry and its use. The central content of the principle was that reactions occur readily when there is congruence between orbital symmetry characteristics of reactants and products, and only with difficulty when that congruence does not obtain-or to put it more succinctly, orbital symmetry is conserved in concerted reaction. This principle is expected to endure, whatever the language in which it may be couched, or whatever greater precision may be developed in its application and extension. The book ope

  17. CDDIS_DORIS_products_orbit

    Data.gov (United States)

    National Aeronautics and Space Administration — Precise satellite orbits derived from analysis of Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) data. These products are the generated by...

  18. The significant role of the intermolecular CH⋯O/N hydrogen bonds in governing the biologically important pairs of the DNA and RNA modified bases: a comprehensive theoretical investigation.

    Science.gov (United States)

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

    2015-01-01

    This paper is a logical continuation of the theoretical survey of the CH⋯O/N specific contacts in the nucleobase pairs using a wide arsenal of the modern methods, which was initiated in our previous study [J. Biomol. Struct. & Dynam., 2014, 32, 993-1022]. It was established that 34 CH⋯O and 7 CH⋯N interactions, that were detected by quantum-chemical calculations in the 39 biologically important pairs involving modified nucleobases, completely satisfy all geometrical, vibrational, electron-topological, in particular Bader's and "two-molecule" Koch and Popelier's, Grunenberg's compliance constants theory and natural bond orbital criteria indicating that they can be identified as true H-bonds. The geometrical criteria of the H-bond formation are fulfilled for all considered CH⋯O/N H-bonds without any exception. It was shown that the classical rule of the stretching vibration shifts does not work in the ~95% cases of the CH⋯O/N H-bonds. Furthermore, significant increase in the frequency of the out-of-plane deformation modes γ(CH) under the formation of CH⋯O/N H-bonds and corresponding changes of their intensities can be also considered as reliable indicators of the H-bonding. We revealed high linear mutual correlations between the electron density, Laplacian of the electron density, H-bond energy at the (3, -1) bond critical points of the CH⋯O/N H-bonds, and different physico-chemical parameters of the CH⋯O/N H-bonds. We suggested that the electron density ρ and the interaction energy E((2)) of the lone orbital pairs are the most reliable descriptors of the H-bonding. The linear dependence of the H-bond energy ECH⋯O/N on the electron density ρ was established: ECH⋯O = 250.263∙ρ - .380/258.255∙ρ - .396 and ECH⋯N = 196.800∙ρ - .172/268.559∙ρ - .703 obtained at the density functional theory (DFT)/Møller-Plesset (MP2) levels of theory, respectively. The studies of the interaction energies show that the

  19. On the physical origin of the cation-anion intermediate bond in ionic liquids Part I. Placing a (weak) hydrogen bond between two charges.

    Science.gov (United States)

    Lehmann, Sebastian B C; Roatsch, Martin; Schöppke, Matthias; Kirchner, Barbara

    2010-07-21

    The intermediate bond forces in ionic liquids are investigated from static quantum chemical calculations at various methods and two basis sets. The experimentally observed red-shift of the donor-proton bond stretching frequency due to a bond elongation is confirmed by all methods. Comparing Hartree-Fock to second-order Møller-Plesset perturbation theory, the Hartree-Fock method gives in many cases an erroneous description of the geometries. Furthermore, the Hartree-Fock interaction energies can deviate up to 60 kJ mol(-1) from Møller-Plesset perturbation theory indicating the importance of dispersion interaction. While the usual trends of decreasing stability or interaction energies with increasing ion sizes are found, the geometries involving hydrogen atoms do not change this order of total interaction energies. Therefore, the hydrogen bond is not the most important interaction for ion pairs with regard to the total interaction energy. On the other hand, the different established analysis methods give rise to hydrogen bonding in several ion pairs. Charge analysis reveals the hydrogen-bonding character of the ion pair and shows, depending on the type of ions combined and further on the type of conformers considered, that a hydrogen bond can be present. The possibility of hydrogen bonding is also shown by an analysis of the frontier orbitals. Calculating potential energy surfaces and observing from this the change in the donor proton bond indicates that regular hydrogen bonds are possible in ion pairs of ionic liquids. Thereby, the maximum of bond elongation exceeds the one of a usual hydrogen bond by far. The more salt-like hydrogen-bonded ion pair [NH(4)][BF(4)] exhibits a steeper maximum than the more ionic liquid like ion pair [EtNH(3)][BF(4)]. The fact that imidazolium-based ionic liquids as [Emim][Cl] can display two faces, hydrogen bonding and purely ionic bonding, points to a disturbing rather than stabilizing role of hydrogen bonding on the interaction of

  20. Additional disulfide bonds in insulin

    DEFF Research Database (Denmark)

    Vinther, Tine N; Pettersson, Ingrid; Huus, Kasper

    2015-01-01

    The structure of insulin, a glucose homeostasis-controlling hormone, is highly conserved in all vertebrates and stabilized by three disulfide bonds. Recently, we designed a novel insulin analogue containing a fourth disulfide bond located between positions A10-B4. The N-terminus of insulin's B......-chain is flexible and can adapt multiple conformations. We examined how well disulfide bond predictions algorithms could identify disulfide bonds in this region of insulin. In order to identify stable insulin analogues with additional disulfide bonds, which could be expressed, the Cβ cut-off distance had...... in comparison to analogues with additional disulfide bonds that were more difficult to predict. In contrast, addition of the fourth disulfide bond rendered all analogues resistant to fibrillation under stress conditions and all stable analogues bound to the insulin receptor with picomolar affinities. Thus...

  1. Orbital Evolution and Orbital Phase Resolved Spectroscopy of the ...

    Indian Academy of Sciences (India)

    tra in the 3–20 keV energy range were fitted with a power law and a high ... acceleration method and also depends on any anisotropy in the stellar wind structure. .... Orbital Evolution and Orbital Phase Resolved Spectroscopy. 415. Figure 3. (a) Pulse arrival time delays measured from the RXTE-PCA observation in 2003,.

  2. Quantum chemical exploration of the intramolecular hydrogen bond interaction in 2-thiazol-2-yl-phenol and 2-benzothiazol-2-yl-phenol in the context of excited-state intramolecular proton transfer: a focus on the covalency in hydrogen bond.

    Science.gov (United States)

    Paul, Bijan Kumar; Ganguly, Aniruddha; Guchhait, Nikhil

    2014-10-15

    The present work demonstrates a computational exploration of the intramolecular H-bond (IMHB) interaction in two model heterocyclic compounds - 2-thiazol-2-yl-phenol (2T2YP) and 2-benzothiazol-2-yl-phenol (2B2YP) by meticulous application of various quantum chemical tools. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ρ(r) and Laplacian ∇(2)ρ(r) at the bond critical point using the Atoms-In-Molecule methodology. Topological features based on ρ(r) suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of a covalent interaction. The interplay between aromaticity and Resonance-Assisted H-Bond (RAHB) has also been discussed using both geometrical and magnetic criteria. The occurrence of IMHB interaction in 2T2YP and 2B2YP has also been criticized under the provision of the Natural Bond Orbital (NBO) analysis. The ESIPT phenomenon in the molecular systems is also critically addressed on the lexicon of potential energy surface (PES) analysis. Copyright © 2014 Elsevier B.V. All rights reserved.

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

    Science.gov (United States)

    Beck, John Frederick; Mo, Yirong

    2007-01-15

    Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between pi delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in beta-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of pi resonance, were decomposed into the Hitler-London energy (DeltaEHL), polarization energy (DeltaEpol), charge transfer energy (DeltaECT), and electron correlation energy (DeltaEcor) terms. This allows for the examination of the character of hydrogen bonds and the impact of pi conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole-dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. Copyright (c) 2006 Wiley Periodicals, Inc.

  4. Spin Orbit Torque in Ferromagnetic Semiconductors

    KAUST Repository

    Li, Hang

    2016-06-21

    Electrons not only have charges but also have spin. By utilizing the electron spin, the energy consumption of electronic devices can be reduced, their size can be scaled down and the efficiency of `read\\' and `write\\' in memory devices can be significantly improved. Hence, the manipulation of electron spin in electronic devices becomes more and more appealing for the advancement of microelectronics. In spin-based devices, the manipulation of ferromagnetic order parameter using electrical currents is a very useful means for current-driven operation. Nowadays, most of magnetic memory devices are based on the so-called spin transfer torque, which stems from the spin angular momentum transfer between a spin-polarized current and the magnetic order parameter. Recently, a novel spin torque effect, exploiting spin-orbit coupling in non-centrosymmetric magnets, has attracted a massive amount of attention. This thesis addresses the nature of spin-orbit coupled transport and torques in non-centrosymmetric magnetic semiconductors. We start with the theoretical study of spin orbit torque in three dimensional ferromagnetic GaMnAs. Using the Kubo formula, we calculate both the current-driven field-like torque and anti-damping-like torque. We compare the numerical results with the analytical expressions in the model case of a magnetic Rashba two-dimensional electron gas. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described. Subsequently we study spin-orbit torques in two dimensional hexagonal crystals such as graphene, silicene, germanene and stanene. In the presence of staggered potential and exchange field, the valley degeneracy can be lifted and we obtain a valley-dependent Berry curvature, leading to a tunable antidamping torque by controlling the valley degree of freedom. This thesis then addresses the influence of the quantum spin Hall

  5. Covalent bonding in heavy metal oxides

    Energy Technology Data Exchange (ETDEWEB)

    Bagus, Paul S.; Nelin, Connie J.; Hrovat, Dave A.; Ilton, Eugene S.

    2017-04-07

    Novel theoretical methods were used to quantify the magnitude and the energetic contributions of 4f/5f-O2p and 5d/6d-O2p interactions to covalent bonding in lanthanide and actinide oxides. Although many analyses have neglected the involvement of the frontier d orbitals, the present study shows that f and d covalency are of comparable importance. Two trends are identified. As is expected, the covalent mixing is larger when the nominal oxidation state is higher. More subtly, the importance of the nf covalent mixing decreases sharply relative to (n+1)d as the nf occupation increases. Atomic properties of the metal cations that drive these trends are identified.

  6. Orbital Chondroma: A rare mesenchymal tumor of orbit

    Directory of Open Access Journals (Sweden)

    Ruchi S Kabra

    2015-01-01

    Full Text Available While relatively common in the skeletal system, cartilaginous tumors are rarely seen originating from the orbit. Here, we report a rare case of an orbital chondroma. A 27-year-old male patient presented with a painless hard mass in the superonasal quadrant (SNQ of left orbit since 3 months. On examination, best-corrected visual acuity of both eyes was 20/20, with normal anterior and posterior segment with full movements of eyeballs and normal intraocular pressure. Computerized tomography scan revealed well defined soft tissue density lesion in SNQ of left orbit. Patient was operated for anteromedial orbitotomy under general anesthesia. Mass was excised intact and sent for histopathological examination (HPE. HPE report showed lobular aggregates of benign cartilaginous cells with mild atypia suggesting of benign cartilaginous tumor - chondroma. Very few cases of orbital chondroma have been reported in literature so far.

  7. Unexpected climatic impacts of orbital forcing out of the Quaternary

    Science.gov (United States)

    Ramstein, G.; Zhang, Z.; Le Hir, G.; Contoux, C.; Donnadieu, Y.; Dumas, C.; Schuster, M.; Li, C.

    2016-12-01

    For Quaternary, the impact of orbital variations on climate is huge and well documented. Especially, during the last million years, drastic climate changes occurred, consisting in transitions from glacial to interglacial periods driven by changes in 65°N summer insolation with 100 kyrs periodicity. Nevertheless, the imprint of so-called Milankovic forcings has also been found for Tertiary and Secondary. For both periods, the climatic imprints of orbital forcings are recorded in a warm world without ice sheet. Here, we show through simulation studies the large impact of orbital forcing in very different geological contexts. The first and most striking result depicts the role of insolation changes during the melting of the Marinoan snowball [635 Ma] (Benn et al, Nature Geoscience 2015). This is one of the oldest imprints of orbital forcing on climate. Our result solved a long lasting controversy concerning the melting of the last snowball episode between a huge deglaciation at very high CO2 level and data showing glacial/interglacial cycles occurring during that melting. Our modelling studies focusing on Svalbard high resolution records demonstrate that the glacial/fluvial oscillation was related to orbital forcing in a context of very high CO2 level. Much more recently, during the Tortonian period [11-7 Ma], the orbital cycles shaped the environment and drove the hominin dispersal in Africa. During Tortonian, the ultimate shrinkage of a huge epicontinental sea, that extended from Eastern Europe to Western Asia, has been shown to produce major changes on Asian monsoon (Ramstein et al, Nature, 1997) and triggered the onset of Sahara desert (Zhang et al, Nature 2014). Moreover, this shrinkage drastically enhanced the climate response to orbital changes at the emergence of early hominins in North Africa. Through these two illustrations,we pointed out very different climatic impacts of orbital forcing out of Quaternary.

  8. Weak hydrogen bonding motifs of ethylamino neurotransmitter radical cations in a hydrophobic environment: infrared spectra of tryptamine(+)-(N2)n clusters (n ≤ 6).

    Science.gov (United States)

    Sakota, Kenji; Schütz, Markus; Schmies, Matthias; Moritz, Raphael; Bouchet, Aude; Ikeda, Takamasa; Kouno, Yuuki; Sekiya, Hiroshi; Dopfer, Otto

    2014-02-28

    Size-selected clusters of the tryptamine cation with N2 ligands, TRA(+)-(N2)n with n = 1-6, are investigated by infrared photodissociation (IRPD) spectroscopy in the hydride stretch range and quantum chemical calculations at the ωB97X-D/cc-pVTZ level to characterize the microsolvation of this prototypical aromatic ethylamino neurotransmitter radical cation in a nonpolar solvent. Two types of structural isomers exhibiting different interaction motifs are identified for the TRA(+)-N2 dimer, namely the TRA(+)-N2(H) global minimum, in which N2 forms a linear hydrogen bond (H-bond) to the indolic NH group, and the less stable TRA(+)-N2(π) local minima, in which N2 binds to the aromatic π electron system of the indolic pyrrole ring. The IRPD spectrum of TRA(+)-(N2)2 is consistent with contributions from two structural H-bound isomers with similar calculated stabilization energies. The first isomer, denoted as TRA(+)-(N2)2(2H), exhibits an asymmetric bifurcated planar H-bonding motif, in which both N2 ligands are attached to the indolic NH group in the aromatic plane via H-bonding and charge-quadrupole interactions. The second isomer, denoted as TRA(+)-(N2)2(H/π), has a single and nearly linear H-bond of the first N2 ligand to the indolic NH group, whereas the second ligand is π-bonded to the pyrrole ring. The natural bond orbital analysis of TRA(+)-(N2)2 reveals that the total stability of these types of clusters is not only controlled by the local H-bond strengths between the indolic NH group and the N2 ligands but also by a subtle balance between various contributing intermolecular interactions, including local H-bonds, charge-quadrupole and induction interactions, dispersion, and exchange repulsion. The systematic spectral shifts as a function of cluster size suggest that the larger TRA(+)-(N2)n clusters with n = 3-6 are composed of the strongly bound TRA(+)-(N2)2(2H) core ion to which further N2 ligands are weakly attached to either the π electron system or the

  9. Bonding of adhesive resin luting agents to metal and amalgam.

    Science.gov (United States)

    Osman, Saad A; McCabe, John F; Walls, Angus W G

    2008-12-01

    The shear bond strength of three adhesives, Panavia 21, Superbond, All Bond C&B Cement, and a dual cure resin (Variolink), to Ni-Cr-Be (Rexillium III), Midigold (Type III gold) and Amalgam (Sybraloy) were determined. Fifteen samples were prepared using 800 grit abrasive papers for Ni-Cr and Midi-Gold, and 100 grit papers for amalgam. Ni-Cr-Be and Midi-Gold samples were sandblasted for 30 s and steam cleaned for 10 s. The adhesives were bonded to the samples using gelatine capsules and were matured for 24 h in water at 37 degrees C. The samples were debonded in shear using an Instron at a cross-head speed of 1 mm/min. The data was analysed using ANOVA and a Tukey test. The bond strength of Superbond to both metal alloys was significantly higher (Pcement had shown to be not significant difference from those of Panavia 21 and Variolink, when bonded to Rexillium and Midi-Gold, respectively. The bond strength of All Bond C&B Cement to amalgam was significantly greater (Padhesives when compared with Rexillium (PPanavia 21>All Bond C&B>Variolink. The nature of substrate to be used for bonding and the adhesive material itself are important factors in bonding which can be achieved between cast metals and prepared teeth with amalgam filling. Superbond should be successful as an adhesive for the attachment of all substrates tested, with the possible exception of amalgam, for which All Bond C&B Cement gives the best result.

  10. Revisiting the beryllium bonding interactions from energetic and wavefunction perspectives

    Science.gov (United States)

    Zhong, Aiguo; Chen, Dan; Li, Rongrong

    2015-07-01

    Not too much is known about the beryllium bonding interactions. Here, the total energy partition schemes as well as DFT-SAPT are used to explore the origin and nature of the beryllium bonds from an energetic point of view. In addition, Shannon entropy and Fisher information, which are based upon the electron probability density, rather than the shape function, are adopted to dissect the impact resulted from a wavefunction perspective. Results reveal that the electrostatic potential largely causes the formation of beryllium bonds. Moreover, there are strong linear relationships between atomic Shannon entropy and Fisher information of Be atoms, which can aid to distinguish the different sources of noncovalent weak interactions.

  11. Quantum Mechanical Studies of Charge Assisted Hydrogen and Halogen Bonds

    OpenAIRE

    Nepal, Binod

    2016-01-01

    This dissertation is mainly focused on charge assisted noncovalent interactions specially hydrogen and halogen bonds. Generally, noncovalent interactions are only weak forces of interaction but an introduction of suitable charge on binding units increases the strength of the noncovalent bonds by a several orders of magnitude. These charge assisted noncovalent interactions have wide ranges of applications from crystal engineering to drug design. Not only that, nature accomplishes a number of i...

  12. Plasmablastic lymphoma mimicking orbital cellulitis.

    NARCIS (Netherlands)

    Barkhuysen, R.; Merkx, M.A.W.; Weijs, W.L.J.; Gerlach, N.L.; Berge, S.J.

    2008-01-01

    INTRODUCTION: Orbital cellulitis is an uncommon, potentially devastating condition that, when not promptly and adequately treated, can lead to serious sequelae. The presenting clinical signs are proptosis, swelling, ophthalmoplegia, pain and redness of the peri-orbital tissues. A number of cases

  13. Diffractive molecular-orbital tomography

    Science.gov (United States)

    Zhai, Chunyang; Zhu, Xiaosong; Lan, Pengfei; Wang, Feng; He, Lixin; Shi, Wenjing; Li, Yang; Li, Min; Zhang, Qingbin; Lu, Peixiang

    2017-03-01

    High-order-harmonic generation in the interaction of femtosecond lasers with atoms and molecules opens the path to molecular-orbital tomography and to probe the electronic dynamics with attosecond-Ångström resolutions. Molecular-orbital tomography requires both the amplitude and phase of the high-order harmonics. Yet the measurement of phases requires sophisticated techniques and represents formidable challenges at present. Here we report a scheme, called diffractive molecular-orbital tomography, to retrieve the molecular orbital solely from the amplitude of high-order harmonics without measuring any phase information. We have applied this method to image the molecular orbitals of N2, CO2, and C2H2 . The retrieved orbital is further improved by taking account the correction of Coulomb potential. The diffractive molecular-orbital tomography scheme, removing the roadblock of phase measurement, significantly simplifies the molecular-orbital tomography procedure and paves an efficient and robust way to the imaging of more complex molecules.

  14. Orbit Modeller - Virtual Astronomical Laboratory

    Science.gov (United States)

    Avdyushev, V. A.; Banshchikova, M. A.; Bordovitsyna, T. V.; Chuvashov, I. N.; Ryabova, G. O.

    2017-09-01

    We present a virtual astronomical laboratory project - "Orbit Modeller" (OM). This should be an interactive web-tool enabling one to simulate numerically the orbital motion of any celestial body within or beyond the solar system. Another function of OM is a repository of old observations and documents.

  15. Endoscopic treatment of orbital tumors.

    Science.gov (United States)

    Signorelli, Francesco; Anile, Carmelo; Rigante, Mario; Paludetti, Gaetano; Pompucci, Angelo; Mangiola, Annunziato

    2015-03-16

    Different orbital and transcranial approaches are performed in order to manage orbital tumors, depending on the location and size of the lesion within the orbit. These approaches provide a satisfactory view of the superior and lateral aspects of the orbit and the optic canal but involve risks associated with their invasiveness because they require significant displacement of orbital structures. In addition, external approaches to intraconal lesions may also require deinsertion of extraocular muscles, with subsequent impact on extraocular mobility. Recently, minimally invasive techniques have been proposed as valid alternative to external approaches for selected orbital lesions. Among them, transnasal endoscopic approaches, "pure" or combined with external approaches, have been reported, especially for intraconal lesions located inferiorly and medially to the optic nerve. The avoidance of muscle detachment and the shortness of the surgical intraorbital trajectory makes endoscopic approach less invasive, thus minimizing tissue damage. Endoscopic surgery decreases the recovery time and improves the cosmetic outcome not requiring skin incisions. The purpose of this study is to review and discuss the current surgical techniques for orbital tumors removal, focusing on endoscopic approaches to the orbit and outlining the key anatomic principles to follow for safe tumor resection.

  16. Density-orbital embedding theory

    NARCIS (Netherlands)

    Visscher, L.; Gritsenko, O.

    2010-01-01

    In the article density-orbital embedding (DOE) theory is proposed. DOE is based on the concept of density orbital (DO), which is a generalization of the square root of the density for real functions and fractional electron numbers. The basic feature of DOE is the representation of the total

  17. Developing Foreign Bond Markets: The Arirang Bond Experience in Korea

    OpenAIRE

    Jonathan A. Batten; Peter G. Szilagyi

    2006-01-01

    This study investigates the development of Korea’s foreign bond (Arirang) market for won-denominated foreign bonds. We provide an institutional perspective and discuss the problems, concerns and key issues related to the development of this market. We find no evidence that Arirang issuance either crowded out local debt or had exchange rate implications. Overall, the Korean experience provides valuable lessons for other emerging nations seeking to build bond markets for local and foreign issue...

  18. Economical and geopolitical aspects bond to the foreseen development of the natural gas in an open market; Aspects economiques et geopolitiques lies au developpement prevu du gaz naturel dans un marche ouvert

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-12-15

    For the first time in 2000, the part of natural gas is equal to those of coal in the world energy accounting. The economy and the geo-policy of this developing energy is analyzed, showing an economy dominated by the transport costs, the specificity of the european sector and the opening market since 1980. The european market opening incertitudes and opportunities are detailed. In conclusion the Gaz De France role in the european energy pole and the new regulations are discussed. (A.L.B.)

  19. Plasmablastic lymphoma mimicking orbital cellulitis

    Science.gov (United States)

    Merkx, Matthias A. W.; Weijs, Willem L. J.; Gerlach, Niek L.; Bergé, Stefaan J.

    2008-01-01

    Introduction Orbital cellulitis is an uncommon, potentially devastating condition that, when not promptly and adequately treated, can lead to serious sequelae. The presenting clinical signs are proptosis, swelling, ophthalmoplegia, pain and redness of the peri-orbital tissues. A number of cases have been reported in which these symptoms have been mistakenly interpreted as being secondary to an orbital infection whilst, in fact, other pathology was present. Discussion We add another case in which, on clinical grounds and after radiological assessment and laboratory tests, a working diagnosis of orbital cellulitis of the left eye was made. It was only after histopathological analysis of a soft tissue specimen from the maxillary sinus that a diagnosis of an AIDS-related plasmablastic lymphoma was made. The patient was referred to the department of haematology where chemotherapeutic treatment for the lymphoma and the HIV infection was started. This case report adds another differential diagnosis of orbital cellulitis to the existing literature. PMID:18597126

  20. Is there any fundamental difference between ionic, covalent, and others types of bond? A canonical perspective on the question.

    Science.gov (United States)

    Walton, Jay R; Rivera-Rivera, Luis A; Lucchese, Robert R; Bevan, John W

    2017-06-21

    The concept of chemical bonding is normally presented and simplified through two models: the covalent bond and the ionic bond. Expansion of the ideal covalent and ionic models leads chemists to the concepts of electronegativity and polarizability, and thus to the classification of polar and non-polar bonds. In addition, the intermolecular interactions are normally viewed as physical phenomena without direct correlation to the chemical bond in any simplistic model. Contrary to these traditional concepts of chemical bonding, recently developed canonical approaches demonstrate a unified perspective on the nature of binding in pairwise interatomic interactions. This new canonical model, which is a force-based approach with a basis in fundamental molecular quantum mechanics, confirms much earlier assertions that in fact there are no fundamental distinctions among covalent bonds, ionic bonds, and intermolecular interactions including the hydrogen bond, the halogen bond, and van der Waals interactions.

  1. Ultrafast dynamics of hydrogen bond exchange in aqueous ionic solutions.

    Science.gov (United States)

    Park, Sungnam; Odelius, Michael; Gaffney, Kelly J

    2009-06-04

    The structural and dynamical properties of aqueous ionic solutions influence a wide range of natural and biological processes. In these solutions, water has the opportunity to form hydrogen bonds with other water molecules and anions. Knowing the time scale with which these configurations interconvert represents a key factor to understanding the influence of molecular scale heterogeneity on chemical events in aqueous ionic solutions. We have used ultrafast IR spectroscopy and Car-Parrinello molecular dynamics (CPMD) simulations to investigate the hydrogen bond (H-bond) structural dynamics in aqueous 6 M sodium perchlorate (NaClO4) solution. We have measured the H-bond exchange dynamics between spectrally distinct water-water and water-anion H-bond configurations with 2DIR spectroscopy and the orientational relaxation dynamics of water molecules in different H-bond configurations with polarization-selective IR pump-probe experiments. The experimental H-bond exchange time correlates strongly with the experimental orientational relaxation time of water molecules. This agrees with prior observations in water and aqueous halide solutions, and has been interpreted within the context of an orientational jump model for the H-bond exchange. The CPMD simulations performed on aqueous 6 M NaClO4 solution clearly demonstrate that water molecules organize into two radially and angularly distinct structural subshells within the first solvation shell of the perchlorate anion, with one subshell possessing the majority of the water molecules that donate H-bonds to perchlorate anions and the other subshell possessing predominantly water molecules that donate two H-bonds to other water molecules. Due to the high ionic concentration used in the simulations, essentially all water molecules reside in the first ionic solvation shells. The CPMD simulations also demonstrate that the molecular exchange between these two structurally distinct subshells proceeds more slowly than the H-bond

  2. Combined Spectroscopic and Electrochemical Detection of a NiI•••H–N Bonding Interaction with Relevance to Electrocatalytic H2 Production

    Energy Technology Data Exchange (ETDEWEB)

    Kochem, Amelie; O' Hagan, Molly J.; Wiedner, Eric S.; van Gastel, Maurice

    2015-07-13

    The [Ni(PR2NR’2)2]2+ family of complexes are exceptionally active catalysts for proton reduction to H2. In this manuscript, we explore the first protonation step of the proposed catalytic cycle by using a catalytically inactive NiI complex possessing a sterically demanding variation of the ligand. Due to the paramagnetic nature of the NiI oxidation state, the protonated NiI intermediate has been characterized through a combination of cyclic voltammetry, ENDOR, and HYSCORE spectroscopy. Both the electrochemical and spectroscopic studies indicate that the NiI complex is protonated at a pendant amine that is endo to Ni, which suggests the presence of an intramolecular NiI•••HN bonding interaction. Using density functional theory, the proton was found to hydrogen bond to three doubly-occupied, localized molecular orbitals: the 3dxz, 3dz2, and 3dyz orbitals of nickel. These studies provide the first direct experimental evidence for this critical catalytic intermediate, and implications for catalytic H2 production are discussed. Research was supported by the Max Planck Society (EPR, ENDOR, and HYSCORE spectroscopy, computational studies), and as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (electrochemistry, NMR spectroscopy). Pacific Northwest National Laboratory is operated by Battelle for DOE.

  3. Better Bonded Ethernet Load Balancing

    Energy Technology Data Exchange (ETDEWEB)

    Gabler, Jason

    2006-09-29

    When a High Performance Storage System's mover shuttles large amounts of data to storage over a single Ethernet device that single channel can rapidly become saturated. Using Linux Ethernet channel bonding to address this and similar situations was not, until now, a viable solution. The various modes in which channel bonding could be configured always offered some benefit but only under strict conditions or at a system resource cost that was greater than the benefit gained by using channel bonding. Newer bonding modes designed by various networking hardware companies, helpful in such networking scenarios, were already present in their own switches. However, Linux-based systems were unable to take advantage of those new modes as they had not yet been implemented in the Linux kernel bonding driver. So, except for basic fault tolerance, Linux channel bonding could not positively combine separate Ethernet devices to provide the necessary bandwidth.

  4. Electronic bond tuning with heterocyclic carbenes

    KAUST Repository

    Falivene, Laura

    2013-01-01

    We discuss the impact of the nature of the heterocyclic carbene ring, when used as a complex forming ligand, on the relative stability of key intermediates in three typical Ru, Pd and Au promoted reactions. Results show that P-heterocyclic carbenes have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions, dissociation of a P-heterocyclic carbene is easier than dissociation of the N-heterocyclic analogue. In the case of the Au-OH synthon, the Au-OH bond is weakened with the P-heterocyclic carbene ligands. A detailed energy decomposition analysis is performed to rationalize these results. © 2013 The Royal Society of Chemistry.

  5. Circular revisit orbits design for responsive mission over a single target

    Science.gov (United States)

    Li, Taibo; Xiang, Junhua; Wang, Zhaokui; Zhang, Yulin

    2016-10-01

    The responsive orbits play a key role in addressing the mission of Operationally Responsive Space (ORS) because of their capabilities. These capabilities are usually focused on supporting specific targets as opposed to providing global coverage. One subtype of responsive orbits is repeat coverage orbit which is nearly circular in most remote sensing applications. This paper deals with a special kind of repeating ground track orbit, referred to as circular revisit orbit. Different from traditional repeat coverage orbits, a satellite on circular revisit orbit can visit a target site at both the ascending and descending stages in one revisit cycle. This typology of trajectory allows a halving of the traditional revisit time and does a favor to get useful information for responsive applications. However the previous reported numerical methods in some references often cost lots of computation or fail to obtain such orbits. To overcome this difficulty, an analytical method to determine the existence conditions of the solutions to revisit orbits is presented in this paper. To this end, the mathematical model of circular revisit orbit is established under the central gravity model and the J2 perturbation. A constraint function of the circular revisit orbit is introduced, and the monotonicity of that function has been studied. The existent conditions and the number of such orbits are naturally worked out. Taking the launch cost into consideration, optimal design model of circular revisit orbit is established to achieve a best orbit which visits a target twice a day in the morning and in the afternoon respectively for several days. The result shows that it is effective to apply circular revisit orbits in responsive application such as reconnoiter of natural disaster.

  6. Why Should Governments Issue Bonds?

    OpenAIRE

    Romer, David

    1993-01-01

    This paper has three purposes. First, it shows that several recent arguments that the optimal nominal interest rate on government bonds is zero even when second best considerations are accounted for rest on perfect substitutes assumptions. Second, it characterizes the conditions under which the issue of interest-bearing bonds is desirable once these assumptions are relaxed. And third, it shows that these potential microeconomic benefits of bond issue are closely related to traditional macroec...

  7. Adhesives for orthodontic bracket bonding

    OpenAIRE

    Déborah Daniella Diniz Fonseca; Daene Patrícia Tenório Salvador da Costa; Renata Cimões; Lúcia Carneiro de Souza Beatrice; Ana Cláudia da Silva Araújo

    2010-01-01

    The advent of acid etching, introduced by Buonocore in 1955, brought the possibility of bonding between the bracket base and enamel, contributing to more esthetic and conservative orthodontics. This direct bracket bonding technique has brought benefits such as reduced cost and time in performing the treatment, as well as making it easier to perform oral hygiene. The aim of this study was to conduct a survey of published studies on orthodontic bracket bonding to dental enamel. It was verified ...

  8. Orbital Debris-Debris Collision Avoidance

    CERN Document Server

    Mason, James; Marshall, William; Levit, Creon

    2011-01-01

    We investigate the feasibility of using a medium-powered (5kW) ground-based laser combined with a ground-based telescope to prevent collisions between debris objects in low-Earth orbit (LEO), for which there is no current, effective mitigation strategy. The scheme utilizes photon pressure alone as a means to perturb the orbit of a debris object. Applied over multiple engagements, this alters the debris orbit sufficiently to reduce the risk of an upcoming conjunction. We employ standard assumptions for atmospheric conditions and the resulting beam propagation. Using case studies designed to represent the properties (e.g. area and mass) of the current debris population, we show that one could significantly reduce the risk of more than half of all debris-debris collisions using only one such laser/telescope facility. We speculate on whether this could mitigate the debris fragmentation rate such that it falls below the natural debris re-entry rate due to atmospheric drag, and thus whether continuous long-term ope...

  9. Rehabilitation of orbital cavity after orbital exenteration using polymethyl methacrylate orbital prosthesis

    Directory of Open Access Journals (Sweden)

    Sumeet Jain

    2016-01-01

    Full Text Available Squamous cell carcinoma of the eyelid is the second most common malignant neoplasm of the eye with the incidence of 0.09 and 2.42 cases/100 000 people. Orbital invasion is a rare complication but, if recognized early, can be treated effectively with exenteration. Although with advancements in technology such as computer-aided design and computer-aided manufacturing, material science, and retentive methods like implants, orbital prosthesis with stock ocular prosthesis made of methyl methacrylate retained by anatomic undercuts is quiet effective and should not be overlooked and forgotten. This clinical report describes prosthetic rehabilitation of two male patients with polymethyl methacrylate resin orbital prosthesis after orbital exenteration, for squamous cell carcinoma of the upper eyelid. The orbital prosthesis was sufficiently retained by hard and soft tissue undercuts without any complications. The patients using the prosthesis are quite satisfied with the cosmetic results and felt comfortable attending the social events.

  10. Roll bonding of strained aluminium

    DEFF Research Database (Denmark)

    Staun, Jakob M.

    2003-01-01

    This report investigates roll bonding of pre-strained (å ~ 4) aluminium sheets to produce high strain material from high purity aluminium (99.996%) and commercial pure aluminium (99.6%). The degree of bonding is investigated by optical microscopy and ultrasonic scanning. Under the right...... circumstances both materials show good bonding, but the high purity material is excluded because of recrystallisation and the resulting loss of mechanical properties. The effect of cross stacking and roll bonding pre-strained sheets of the commercial purity material is investigated and some dependence...

  11. Wafer bonding applications and technology

    CERN Document Server

    Gösele, Ulrich

    2004-01-01

    During the past decade direct wafer bonding has developed into a mature materials integration technology. This book presents state-of-the-art reviews of the most important applications of wafer bonding written by experts from industry and academia. The topics include bonding-based fabrication methods of silicon-on-insulator, photonic crystals, VCSELs, SiGe-based FETs, MEMS together with hybrid integration and laser lift-off. The non-specialist will learn about the basics of wafer bonding and its various application areas, while the researcher in the field will find up-to-date information about this fast-moving area, including relevant patent information.

  12. A simplified indirect bonding technique

    Directory of Open Access Journals (Sweden)

    Radha Katiyar

    2014-01-01

    Full Text Available With the advent of lingual orthodontics, indirect bonding technique has become an integral part of practice. It involves placement of brackets initially on the models and then their transfer to teeth with the help of transfer trays. Problems encountered with current indirect bonding techniques used are (1 the possibility of adhesive flash remaining around the base of the brackets which requires removal (2 longer time required for the adhesive to gain enough bond strength for secure tray removal. The new simplified indirect bonding technique presented here overcomes both these problems.

  13. Hydrogen-bonded complexes of acetylene and acetonitrile: A matrix isolation infrared and computational study

    Science.gov (United States)

    Gopi, R.; Ramanathan, N.; Sundararajan, K.

    2015-03-01

    Hydrogen-bonded complexes of acetylene (C2H2) and acetonitrile (CH3CN) have been investigated using matrix isolation infrared spectroscopy and ab initio computations. The complexes were trapped in both solid argon and N2 matrices. The structure of the complexes and the energies were computed at the B3LYP and MP2 levels of theory using a 6-311++G(d,p) basis set and also at B3LYP/aug-cc-pVDZ level. Our computations indicated one minimum corresponding to the 1:1 C2H2sbnd CH3CN complex, with Csbnd H⋯N interaction, where C2H2 is the proton donor. Experimentally, we observed the 1:1 C2H2sbnd CH3CN complex in Ar and N2 matrices, which was evidenced by the shifts in the vibrational wavenumbers of the modes involving the C2H2 and CH3CN sub-molecules. Computations were also performed to study the higher complexes of C2H2 and CH3CN. One minimum was found for the 1:2 C2H2sbnd CH3CN complex and two minima for the 2:1 C2H2sbnd CH3CN complexes, at all levels of theory. Experimentally we observed features corresponding to the 1:2 C2H2sbnd CH3CN complexes in an Ar and N2 matrices. The computed vibrational wavenumbers of C2H2sbnd CH3CN complexes at B3LYP/6-311++G(d,p) level correlate well with the experimental wavenumbers. Atoms in Molecules (AIM) analysis was performed to understand the nature of interaction in the complexes. Natural Bond Orbital (NBO) analysis was performed to understand the effect of charge-transfer hyperconjugative interactions towards the stability of different C2H2sbnd CH3CN complexes.

  14. Study of the structural characteristics of a group of natural silicates by means of their K{beta} emission spectra

    Energy Technology Data Exchange (ETDEWEB)

    Torres Deluigi, Maria Torres [Departamento de Fisica, Facultad de Ciencias Fisico, Matematicas y Naturales, Universidad Nacional de San Luis, Chacabuco 917, CP 5700 San Luis (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Rivadavia 1917, CP C1033 AAJ, Buenos Aires (Argentina)], E-mail: charo@unsl.edu.ar; Strasser, Edgardo N. [Departamento de Geologia, Facultad de Ciencias Fisico, Matematicas y Naturales, Universidad Nacional de San Luis, Chacabuco 917, CP 5700 San Luis (Argentina); Vasconcellos, Marcos A.Z. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, CP 15051, 91501-970 Porto Alegre, RS (Brazil); Riveros, Jose A. [Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, Medina Allende y Haya de la Torre, CP 5000 Cordoba (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Rivadavia 1917, CP C1033 AAJ, Buenos Aires (Argentina)

    2006-04-21

    In this work, the Si K{beta} and Al K{beta} emission spectra of a group of natural silicates typical of a region in San Luis (Argentina) are described qualitatively within the frame of the Molecular Orbital (MO) theory. Since these spectra come from electron transitions from valence orbitals, they offer information on the chemical bonds that are present and on the molecular orbitals involved. The spectra were obtained by means of an electron microprobe. The energies, intensities and full-width at half-maximum (FWHM) of the lines that conform the silicon and aluminium K{beta} spectra were quantified. It was observed that an increase in the number of oxygen ions shared by the tetrahedra (SiO{sub 4}){sup 4-} caused a lineal increase in the FWHM of the Si K{beta}{sub 1,3} and Al K{beta}{sub 1,3} lines. This behavior is caused by the increase of the covalent character of the Si-O and Al-O bonds with the quantity of oxygen ions shared by the adjacent tetrahedra.

  15. Spin-orbit-coupled quantum gases

    Science.gov (United States)

    Radic, Juraj

    contact interactions. We show that strong inter-spin interactions can lead to the appearance of magnetically ordered phases at temperatures above the superfluid transition. For the case of inter-spin attraction, we also discuss the possibility of a bosonic analogue of the Cooper-paired phase, however this state is not energetically favourable. We extend our calculations to a spin-orbit-coupled Bose gas to investigate the possibility of stripe ordering in the normal phase. However, within our approximations, we do not find an instability towards stripe formation. Finally, we consider a two-dimensional Bose gas at zero temperature with an underlying quartic single-particle dispersion in one spatial direction. This Hamiltonian can be realized using the NIST scheme of spin-orbit coupling [Y.-J. Lin, K. Jimenez-Garcia, and I. B. Spielman, Nature 471 , 83 (2011)], or using the shaken lattice scheme of Parker et al. [C. V. Parker, L.-C. Ha and C. Chin, Nature Physics 9, 769 (2013)]. By numerically comparing energies of various trial wave-functions, we show that, at low densities, the ground state is strongly correlated, in contrast to a typical mean-field BEC. The trial wave-function with the lowest energy is of Jastrow-type and it describes a state with finite, but strongly reduced, condensate fraction.

  16. Orbital Infarction due to Sickle Cell Disease without Orbital Pain

    Directory of Open Access Journals (Sweden)

    Cameron L. McBride

    2016-01-01

    Full Text Available Sickle cell disease is a hemoglobinopathy that results in paroxysmal arteriolar occlusion and tissue infarction that can manifest in a plurality of tissues. Rarely, these infarcted crises manifest in the bony orbit. Orbital infarction usually presents with acute onset of periorbital tenderness, swelling, erythema, and pain. Soft tissue swelling can result in proptosis and attenuation of extraocular movements. Expedient diagnosis of sickle cell orbital infarction is crucial because this is a potentially sight-threatening entity. Diagnosis can be delayed since the presentation has physical and radiographic findings mimicking various infectious and traumatic processes. We describe a patient who presented with sickle cell orbital crisis without pain. This case highlights the importance of maintaining a high index of suspicion in patients with known sickle cell disease or of African descent born outside the United States in a region where screening for hemoglobinopathy is not routine, even when the presentation is not classic.

  17. SPHERES Mars Orbiting Sample Return External Orbiting Capture Project

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA's Mars Sample Return (MSR) mission scenario utilizes a small Orbiting Sample (OS) satellite, launched from the surface of Mars, which will rendezvous with an...

  18. Structural determinant of chemical reactivity and potential health effects of quinones from natural products.

    Science.gov (United States)

    Tu, Tingting; Giblin, Daryl; Gross, Michael L

    2011-09-19

    Although many phenols and catechols found as polyphenol natural products are antioxidants and have putative disease-preventive properties, others have deleterious health effects. One possible route to toxicity is the bioactivation of the phenolic function to quinones that are electrophilic, redox-agents capable of modifying DNA and proteins. The structure-property relationships of biologically important quinones and their precursors may help understand the balance between their health benefits and risks. We describe a mass-spectrometry-based study of four quinones produced by oxidizing flavanones and flavones. Those with a C2-C3 double bond on ring C of the flavonoid stabilize by delocalization of an incipient positive charge from protonation and render the protonated quinone particularly susceptible to nucleophilic attack. We hypothesize that the absence of this double bond is one specific structural determinant that is responsible for the ability of quinones to modify biological macromolecules. Those quinones containing a C2-C3 single bond have relatively higher aqueous stability and longer half-lives than those with a double bond at the same position; the latter have short half-lives at or below ∼1 s. Quinones with a C2-C3 double bond show little ability to depurinate DNA because they are rapidly hydrated to unreactive species. Molecular-orbital calculations support that quinone hydration by a highly structure-dependent mechanism accounts for their chemical properties. The evidence taken together support a hypothesis that those flavonoids and related natural products that undergo oxidation to quinones and are then rapidly hydrated are unlikely to damage important biological macromolecules.

  19. A Structural Determinant of Chemical Reactivity and Potential Health Effects of Quinones from Natural Products

    Science.gov (United States)

    Tu, Tingting; Giblin, Daryl; Gross, Michael L.

    2011-01-01

    Although many phenols and catechols found as polyphenol natural products are antioxidants and have putative disease-preventive properties, others have deleterious health effects. One possible route to toxicity is the bioactivation of the phenolic function to quinones that are electrophilic, redox-agents capable of modifying DNA and proteins. The structure-property relationships of biologically important quinones and their precursors may help understand the balance between their health benefits and risks. We describe a mass-spectrometry-based study of four quinones produced by oxidizing flavanones and flavones. Those with a C2-C3 double bond on ring C of the flavonoid stabilize by delocalization an incipient positive charge from protonation and render the protonated quinone particularly susceptible to nucleophilic attack. We hypothesize that the absence of this double bond is one specific structural determinant that is responsible for the ability of quinones to modify biological macromolecules. Those quinones containing a C2-C3 single bond have relative higher aqueous stability and longer half-lives than those with a double bond at the same position; the latter have short half-lives at or below ~ 1 s. Quinones with a C2-C3 double bond show little ability to depurinate DNA because they are rapidly hydrated to unreactive species. Molecular-orbital calculations support that quinone hydration by a highly structure-dependent mechanism accounts for their chemical properties. The evidence taken together support a hypothesis that those flavonoids and related natural products that undergo oxidation to quinones and are then rapidly hydrated are unlikely to damage important biological macromolecules. PMID:21721570

  20. Human Bond Communication

    DEFF Research Database (Denmark)

    Prasad, Ramjee

    2016-01-01

    Modern dexterous communication technology is progressively enabling humans to communicate their information through them with speech (aural) and media (optical) as underpinning essence. Humans realize this kind of aural and optical information by their optical and auditory senses. However, due...... to certain constraints, the ability to incorporate the other three sensory features namely, olfactory, gustatory, and tactile are still far from reality. Human bond communication is a novel concept that incorporates olfactory, gustatory, and tactile that will allow more expressive and holistic sensory...... information exchange through communication techniques for more human sentiment centric communication. This concept endorses the need of inclusion of other three senses and proposes an innovative approach of holistic communication for future communication network....

  1. Atomically Bonded Transparent Superhydrophobic Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Aytug, Tolga [ORNL

    2015-08-01

    Maintaining clarity and avoiding the accumulation of water and dirt on optically transparent surfaces such as US military vehicle windshields, viewports, periscope optical head windows, and electronic equipment cover glasses are critical to providing a high level of visibility, improved survivability, and much-needed safety for warfighters in the field. Through a combination of physical vapor deposition techniques and the exploitation of metastable phase separation in low-alkali borosilicate, a novel technology was developed for the fabrication of optically transparent, porous nanostructured silica thin film coatings that are strongly bonded to glass platforms. The nanotextured films, initially structurally superhydrophilic, exhibit superior superhydrophobicity, hence antisoiling ability, following a simple but robust modification in surface chemistry. The surfaces yield water droplet contact angles as high as 172°. Moreover, the nanostructured nature of these coatings provides increased light scattering in the UV regime and reduced reflectivity (i.e., enhanced transmission) over a broad range of the visible spectrum. In addition to these functionalities, the coatings exhibit superior mechanical resistance to abrasion and are thermally stable to temperatures approaching 500°C. The overall process technology relies on industry standard equipment and inherently scalable manufacturing processes and demands only nontoxic, naturally abundant, and inexpensive base materials. Such coatings, applied to the optical components of current and future combat equipment and military vehicles will provide a significant strategic advantage for warfighters. The inherent self-cleaning properties of such superhydrophobic coatings will also mitigate biofouling of optical windows exposed to high-humidity conditions and can help decrease repair/replacement costs, reduce maintenance, and increase readiness by limiting equipment downtime.

  2. Molecular orbital studies (hardness, chemical potential, electrophilicity, and first electron excitation), vibrational investigation and theoretical NBO analysis of 2-hydroxy-5-bromobenzaldehyde by density functional method

    Science.gov (United States)

    Nataraj, A.; Balachandran, V.; Karthick, T.

    2013-01-01

    In this work, the vibrational spectral analysis was carried out using Raman and infrared spectroscopy in the range 4000-400 cm-1 and 3500-100 cm-1, respectively, for the 2-hydroxy-5-bromobenzaldehyde (HBB). The experimental spectra were recorded in the solid phase. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311G++(d,p) method and basis set. Normal co-ordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of related compound. The stability of the molecule arising from hyper conjugative interactions and the charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η), chemical potential (μ), and first electron excitation (τ) are all correlated with the HOMO and LUMO energies with their molecular properties. These show that charge transfer occurs within the molecule. Furthermore, molecular electrostatic potential maps (MESP) of the molecule have been calculated.

  3. Comparison of shear bond strength of orthodontic brackets bonded using two different hydrophilic primers: An in vitro study

    Directory of Open Access Journals (Sweden)

    M Kumaraswamy Anand

    2014-01-01

    Full Text Available Context: Salivary control and maintenance of a dry operating field is a prime requisite of orthodontic bonding. Moisture insensitive primer (MIP with a clinical significant bond strength values have a better edge over the conventional hydrophobic bonding systems. Aim: The aim of this study is to investigate the effectiveness of two hydrophilic primers with respect to conventional hydrophobic primer by comparing their shear bond strength (SBS and adhesive-failure locations after contamination with saliva and saliva substitute. Materials and Methods: A total of 150 extracted human premolars were randomly divided into five group s ; Group A (Transbond MIP/saliva substitute, Group B (Opal Primo/saliva substitute, Group C (Transbond MIP/natural saliva, Group D (Opal Primo/natural saliva, control group - Group E (Transbond XT/dry, adhesive-Transbond XT used for all five groups and bonded using stainless steel brackets. Shear forces were applied to the samples with a universal testing machine. SBSs was measured in megapascals. The mode of bond failure was determined using the adhesive remnant index (ARI. Results: The mean SBS produced by Transbond MIP was higher than Opal Primo, which was statistically significant according to one-way analysis of variance. Both the tested groups showed lesser bond strength values than Transbond XT (the control. ARI scores revealed that there was no statistically significant difference in the site of bond failure between study groups. ARI scores were found to be lower for study groups suggesting adhesive failure, compared to higher ARI scores for the control group suggesting cohesive failure. Conclusion: Transbond XT adhesive with Transbond MIP or Opal Primo have clinically acceptable bond strength in wet fields. Opal Primo is a viable option to use as a hydrophilic primer clinically.

  4. JSC Orbital Debris Website Description

    Science.gov (United States)

    Johnson, Nicholas L.

    2006-01-01

    Purpose: The website provides information about the NASA Orbital Debris Program Office at JSC, which is the lead NASA center for orbital debris research. It is recognized world-wide for its leadership in addressing orbital debris issues. The NASA Orbital Debris Program Office has taken the international lead in conducting measurements of the environment and in developing the technical consensus for adopting mitigation measures to protect users of the orbital environment. Work at the center continues with developing an improved understanding of the orbital debris environment and measures that can be taken to control its growth. Major Contents: Orbital Debris research is divided into the following five broad efforts. Each area of research contains specific information as follows: 1) Modeling - NASA scientists continue to develop and upgrade orbital debris models to describe and characterize the current and future debris environment. Evolutionary and engineering models are described in detail. Downloadable items include a document in PDF format and executable software. 2) Measurements - Measurements of near-Earth orbital debris are accomplished by conducting ground-based and space-based observations of the orbital debris environment. The data from these sources provide validation of the environment models and identify the presence of new sources. Radar, optical and surface examinations are described. External links to related topics are provided. 3) Protection - Orbital debris protection involves conducting hypervelocity impact measurements to assess the risk presented by orbital debris to operating spacecraft and developing new materials and new designs to provide better protection from the environment with less weight penalty. The data from this work provides the link between the environment defined by the models and the risk presented by that environment to operating spacecraft and provides recommendations on design and operations procedures to reduce the risk as

  5. LAMMPS framework for dynamic bonding and an application modeling DNA

    Science.gov (United States)

    Svaneborg, Carsten

    2012-08-01

    We have extended the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to support directional bonds and dynamic bonding. The framework supports stochastic formation of new bonds, breakage of existing bonds, and conversion between bond types. Bond formation can be controlled to limit the maximal functionality of a bead with respect to various bond types. Concomitant with the bond dynamics, angular and dihedral interactions are dynamically introduced between newly connected triplets and quartets of beads, where the interaction type is determined from the local pattern of bead and bond types. When breaking bonds, all angular and dihedral interactions involving broken bonds are removed. The framework allows chemical reactions to be modeled, and use it to simulate a simplistic, coarse-grained DNA model. The resulting DNA dynamics illustrates the power of the present framework. Catalogue identifier: AEME_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEME_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence No. of lines in distributed program, including test data, etc.: 2 243 491 No. of bytes in distributed program, including test data, etc.: 771 Distribution format: tar.gz Programming language: C++ Computer: Single and multiple core servers Operating system: Linux/Unix/Windows Has the code been vectorized or parallelized?: Yes. The code has been parallelized by the use of MPI directives. RAM: 1 Gb Classification: 16.11, 16.12 Nature of problem: Simulating coarse-grain models capable of chemistry e.g. DNA hybridization dynamics. Solution method: Extending LAMMPS to handle dynamic bonding and directional bonds. Unusual features: Allows bonds to be created and broken while angular and dihedral interactions are kept consistent. Additional comments: The distribution file for this program is approximately 36 Mbytes and therefore is not delivered directly

  6. Push-out bond strengths of two fiber post types bonded with different dentin bonding agents.

    Science.gov (United States)

    Topcu, Fulya Toksoy; Erdemir, Ugur; Sahinkesen, Gunes; Mumcu, Emre; Yildiz, Esra; Uslan, Ibrahim

    2010-05-01

    The aim of this study was to evaluate the regional push-out bond strengths for two fiber-reinforced post types using three different dentin bonding agents. Sixty single-rooted extracted human first premolar teeth were sectioned below the cemento-enamel junction, and the roots were endodontically treated. Following standardized post space preparations, the roots were divided into two fiber-post groups (Glassix and Carbopost), and further divided into three subgroups of 10 specimens each for the bonding systems self-etching dentin bonding agents (Clearfil SE Bond and Optibond all-in-one), and total-etching dentin bonding agent (XP Bond). A dual-cure resin luting cement (Maxcem) was then placed in the post spaces and posts were then seated into the root canals polymerized through the cervical portion. The roots were then cut into 3-mm thick sections. Push-out tests were performed at a crosshead speed of 0.5 mm/min. The data were analyzed with multivariate ANOVA (alpha = 0.05). The morphology of interface between different dentin bonding agents from the cervical sections were analyzed with SEM. Glass fiber-reinforced posts demonstrated significantly higher push-out bond strengths than carbon fiber-reinforced posts (p dentin adhesive Clearfil SE Bond and total-etching dentin adhesive XP Bond demonstrated similar bond strengths values and this was significantly higher compared with the Optibond all-in-one in cervical root canal region. In conclusion, in all root segments, the glass fiber-reinforced posts provided significantly increased post retention than the carbon fiber-reinforced posts, regardless of the adhesive used. (c) 2010 Wiley Periodicals, Inc.

  7. Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3-(A=As, Sb, Bi) Complexes.

    Science.gov (United States)

    Wang, Jia-Qi; Chi, Chaoxian; Hu, Han-Shi; Meng, Luyan; Luo, Mingbiao; Li, Jun; Zhou, Mingfei

    2018-01-08

    Heteronuclear transition-metal-main-group-element carbonyl complexes of AsFe(CO) 3 - , SbFe(CO) 3 - , and BiFe(CO) 3 - were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C 3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO) 3 - . Chemical bonding analyses on the whole series of AFe(CO) 3 - (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp-p) type of transition-metal-main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO) 3 - (A=As, Sb, Bi) complexes. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Adapting ASPEN for Orbital Express

    Science.gov (United States)

    Chouinard, Caroline; Tran, Daniel; Jones, Grailing; Dang, Van; Knight, Russell

    2010-01-01

    By studying the Orbital Express mission, modeling the spacecraft and scenarios, and testing the system, a technique has been developed that uses recursive decomposition to represent procedural actions declaratively, schema-level uncertainty reasoning to make uncertainty reasoning tractable, and lightweight, natural language processing to automatically parse procedures to produce declarative models. Schema-level uncertainty reasoning has, at its core, the basic assumption that certain variables are uncertain, but not independent. Once any are known, then the others become known. This is important where a variable is uncertain for an action and many actions of the same type exist in the plan. For example, if the number of retries to purge pump lines was unknown (but bounded), and each attempt required a sub-plan, then, once the correct number of attempts required for a purge was known, it would likely be the same for all subsequent purges. This greatly reduces the space of plans that needs to be searched to ensure that all executions are feasible. To accommodate changing scenario procedures, each is ingested into a tabular format in temporal order, and a simple natural-language parser is used to read each step and to derive the impact of that step on memory, power, and communications. Then an ASPEN (Activity Scheduling and Planning Environment) model is produced based on this analysis. The model is tested and further changed by hand, if necessary, to reflect the actual procedure. This results in a great savings of time used for modeling procedures. Many processes that need to be modeled in ASPEN (a declarative system) are, in fact, procedural. ASPEN includes the ability to model activities in a hierarchical fashion, but this representation breaks down if there is a practically unbounded number of sub-activities and decomposition topologies. However, if recursive decomposition is allowed, HTN-like encodings are enabled to represent most procedural phenomena. For

  9. High Power Orbit Transfer Vehicle

    National Research Council Canada - National Science Library

    Gulczinski, Frank

    2003-01-01

    ... from Virginia Tech University and Aerophysics, Inc. to examine propulsion requirements for a high-power orbit transfer vehicle using thin-film voltaic solar array technologies under development by the Space Vehicles Directorate (dubbed PowerSail...

  10. Management of odontogenic orbital cellulitis.

    Science.gov (United States)

    DeCroos, F C; Liao, J C; Ramey, N A; Li, I

    2011-08-15

    This work describes a series of patients with odontogenic orbital cellulitis (OOC), focusing on rate of abscess formation, need for surgical intervention, and imaging findings helpful for rapid diagnosis. Review of a current case and 22 patients with OOC from the scientific literature demonstrated periapical lucency as the most commonly (36.4%) reported finding on facial and orbital computerized tomography (CT) scan. Orbital abscess occurred in 72.7% of cases, and tooth extraction and/or abscess drainage was required in 95.5% of cases reviewed for control of infection. The current case presented with periapical lucency on CT scan, developed orbital abscess despite broad spectrum antibiotic therapy, and required multiple surgical interventions for disease resolution. Though our patient regained excellent vision, OOC often can result in severe vision loss. Periapical lucency on CT can help identify this atypical origin of cellulitis that is strongly associated with abscess formation and need for surgical intervention.

  11. Size-extensive wave functions for quantum Monte Carlo: A linear scaling generalized valence bond approach

    NARCIS (Netherlands)

    Fracchia, F.; Filippi, Claudia; Amovilli, C.

    2012-01-01

    We propose a new class of multideterminantal Jastrow–Slater wave functions constructed with localized orbitals and designed to describe complex potential energy surfaces of molecular systems for use in quantum Monte Carlo (QMC). Inspired by the generalized valence bond formalism, we elaborate a

  12. Optimal Investment in Structured Bonds

    DEFF Research Database (Denmark)

    Jessen, Pernille; Jørgensen, Peter Løchte

    2012-01-01

    of the article is to provide possible explanations for the puzzle of why small retail investors hold structured bonds. The investment universe consists of a stock index, a risk-free bank account, and a structured bond containing an option written on another index. We apply expected utility maximization...

  13. Distance criterion for hydrogen bond

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Distance criterion for hydrogen bond. In a D-H ...A contact, the D...A distance must be less than the sum of van der Waals Radii of the D and A atoms, for it to be a hydrogen bond.

  14. Fusion-bonded fluidic interconnects

    NARCIS (Netherlands)

    Fazal, I.; Elwenspoek, Michael Curt

    2008-01-01

    A new approach to realize fluidic interconnects based on the fusion bonding of glass tubes with silicon is presented. Fusion bond strength analyses have been carried out. Experiments with plain silicon wafers and coated with silicon oxide and silicon nitride are performed. The obtained results are

  15. Why are Hydrogen Bonds Directional?

    Indian Academy of Sciences (India)

    for an interaction to be characterized as a hydro- gen bond but does not provide any rationale for the same. This article reports a rationale for limiting the angle, based on the electron density topology using the quantum theory of atoms in molecules. Electron density topol- ogy for common hydrogen bond donors HF, HCl, ...

  16. Orbital operations study. Executive summary

    Science.gov (United States)

    Hogan, L. R.

    1972-01-01

    A summary of the analyses of the orbital operations study is presented. Objectives, scope of study, and technical documentation format are discussed. A summary of the mission analyses including generic mission models, element pair interactions, and interfacing activities are presented. The analyses associated with each interfacing activity are also summarized. Significant implications derived during the course of the study on the EOS orbiter, space tug, RAM, and MSS are indicated.

  17. Materials resistance to low earth orbit environmental effects

    Science.gov (United States)

    Pippin, H. G.; Torre, L. P.; Linton, R. G.; Whitaker, A. F.

    1989-01-01

    A number of flexible polymeric materials have been considered as condidates for protective coatings on Kapton film. These coatings have been tested under a variety of environments, each of which simulates one or more aspects of the low earth orbit space environment. Mass loss rates vs fluence and temperatue, optical properties, and surface characteristics under exposure to the various environments will be presented. Kinetics data on Kapton and other materials is interpreted in terms of bond strengths and relative thermodynamic stabilities of potential products. Activation energy for degradation of Kapton by oxygen atoms was determined to be 30 + or - 5 kJ/mol. Materials tested include silicones, fluorosilicones, fluorophosphazenes, fluorocarbons, and hydrocarbons.

  18. The first row anomaly and recoupled pair bonding in the halides of the late p-block elements.

    Science.gov (United States)

    Dunning, Thom H; Woon, David E; Leiding, Jeff; Chen, Lina

    2013-02-19

    The dramatic differences between the properties of molecules formed from the late p-block elements of the first row of the periodic table (N-F) and those of the corresponding elements in subsequent rows is well recognized as the first row anomaly. Certain properties of the atoms, such as the relative energies and spatial extents of the ns and np orbitals, can explain some of these differences, but not others. In this Account, we summarize the results of our recent computational studies of the halides of the late p-block elements. Our studies point to a single underlying cause for many of these differences: the ability of the late p-block elements in the second and subsequent rows of the periodic table to form recoupled pair bonds and recoupled pair bond dyads with very electronegative ligands. Recoupled pair bonds form when an electron in a singly occupied ligand orbital recouples the pair of electrons in a doubly occupied lone pair orbital on the central atom, leading to a central atom-ligand bond. Recoupled pair bond dyads occur when a second ligand forms a bond with the orbital left over from the initial recoupled pair bond. Recoupled pair bonds and recoupled pair bond dyads enable the late p-block elements to form remarkably stable hypervalent compounds such as PF(5) and SF(6) and lead to unexpected excited states in smaller halides of the late p-block elements such as SF and SF(2). Recoupled pair bonding also causes the F(n-1)X-F bond energies to oscillate dramatically once the normal valences of the central atoms have been satisfied. In addition, recoupled pair bonding provides a lower-energy pathway for inversion in heavily fluorinated compounds (PF(3) and PF(2)H, but not PH(2)F and PH(3)) and leads to unusual intermediates and products in reactions involving halogens and late p-block element compounds, such as (CH(3))(2)S + F(2). Although this Account focuses on the halides of the second row, late p-block elements, recoupled pair bonds and recoupled pair

  19. Microbiological profile of orbital abscess

    Directory of Open Access Journals (Sweden)

    N Suneetha

    2012-01-01

    Full Text Available Background: Knowledge of the culture and sensitivity pattern is necessary, for the institution of appropriate empirical antibiotic therapy in orbital abscess. Objective: The objective of this study is to describe culture and sensitivity patterns of specimens from the orbit and surrounding structures. Materials and Methods: Retrospectively the medical records of 56 cases of orbital abscess were reviewed. Results: Cultures were positive in 38/56 (68.8% orbital specimens and the organisms included Staphylococcus aureus 18, Streptococci 7, Pseudomonas aeruginosa 3, 2 each of Enterobactersp, Escherichia coli, Proteus mirabilis, Acinetobacter sp. and 1 each of Actinomyces israelii, Diptheroids, Coagulase negative Staphylococcus, Citrobacter freundii, Methicillin-resistant S. aureus and Enterococcus faecalis. Four had polymicrobial infection. Culture of purulent nasal discharge, swabs taken from foci of infection on the face, and blood cultures were done in 26/56, and positive cultures were obtained in 16/26 (61.5% specimens. In 12 patients, there was a concurrence in the organism cultured from the orbit and from cultures from other sites. Gram-negative organisms were associated with increased ocular morbidity. Conclusion: Gram-positive cocci, especially S. aureus are the most common organisms isolated from orbital abscesses. Infections by Gram-negative organisms were associated with more complications. Empirical intravenous antibiotic therapy should have a broad spectrum of activity effective against a wide range of Staphylococcal organisms and Gram-negative bacilli.

  20. SOCIAL BONDING: REGULATION BY NEUROPEPTIDES

    Directory of Open Access Journals (Sweden)

    Claudia eLieberwirth

    2014-06-01

    Full Text Available Affiliative social relationships (e.g., among spouses, family members, and friends play an essential role in human society. These relationships affect psychological, physiological, and behavioral functions. As positive and enduring bonds are critical for the overall well-being of humans, it is not surprising that considerable effort has been made to study the neurobiological mechanisms that underlie social bonding behaviors. The present review details the involvement of the nonapeptides, oxytocin (OT and arginine vasopressin (AVP, in the regulation of social bonding in mammals including humans. In particular, we will discuss the role of OT and AVP in the formation of social bonds between partners of a mating pair as well as between parents and their offspring. Furthermore, the role of OT and AVP in the formation of interpersonal bonding involving trust is also discussed.

  1. Interplay of Electronic Cooperativity and Exchange Coupling in Regulating the Reactivity of Diiron(IV)-oxo Complexes towards C-H and O-H Bond Activation.

    Science.gov (United States)

    Ansari, Azaj; Ansari, Mursaleem; Singha, Asmita; Rajaraman, Gopalan

    2017-07-26

    Activation of inert C-H bonds such as those of methane are extremely challenging for chemists but in nature, the soluble methane monooxygenase (sMMO) enzyme readily oxidizes methane to methanol by using a diiron(IV) species. This has prompted chemists to look for similar model systems. Recently, a (μ-oxo)bis(μ-carboxamido)diiron(IV) ([Fe(IV)2 O(L)2 ](2+) L=N,N-bis-(3',5'-dimethyl-4'-methoxypyridyl-2'-methyl)-N'-acetyl-1,2-diaminoethane) complex has been generated by bulk electrolysis and this species activates inert C-H bonds almost 1000 times faster than mononuclear Fe(IV) =O species and at the same time selectively activates O-H bonds of alcohols. The very high reactivity and selectivity of this species is puzzling and herein we use extensive DFT calculations to shed light on this aspect. We have studied the electronic and spectral features of diiron {Fe(III) -μ(O)-Fe(III) }(+2) (complex I), {Fe(III) -μ(O)-Fe(IV) }(+3) (II), and {Fe(IV) -μ(O)-Fe(IV) }(+4) (III) complexes. Strong antiferromagnetic coupling between the Fe centers leads to spin-coupled S=0, S=3/2, and S=0 ground state for species I-III respectively. The mechanistic study of the C-H and O-H bond activation reveals a multistate reactivity scenario where C-H bond activation is found to occur through the S=4 spin-coupled state corresponding to the high-spin state of individual Fe(IV) centers. The O-H bond activation on the other hand, occurs through the S=2 spin-coupled state corresponding to an intermediate state of individual Fe(IV) centers. Molecular orbital analysis reveals σ-π/π-π channels for the reactivity. The nature of the magnetic exchange interaction is found to be switched during the course of the reaction and this offers lower energy pathways. Significant electronic cooperativity between two metal centers during the course of the reaction has been witnessed and this uncovers the reason behind the efficiency and selectivity observed. The catalyst is found to prudently choose the

  2. Bond Alternation, Polarizability and Resonance Detuning in Methine Dyes

    CERN Document Server

    Olsen, Seth

    2010-01-01

    Many organic molecules with a high nonlinear polarizability have a "Brooker dye" structure, featuring electron accepting or donating groups separated by an unsaturated (methine or polyene) hydrocarbon bridge. These systems have been the topic of much discussion with regard to their structure-property relationships - particularly relationships linking nonlinear response to bond-length alternation. Here, we show that these relationships can be subsumed within the conceptual framework of a Brooker dye color proposed by Platt [J.R. Platt, J. Chem. Phys. 25 80 (1956)]. The key quantities of Platt's model are the Brooker basicity difference and the isoexcitation energy. These concepts provide a spectroscopic definition of the resonant (cyanine) limit, which is independent of other descriptors commonly used (e.g. bond length alternation). We establish a relation ship between the bond length and the Brooker basicity difference, with which we establish a natural origin for bond length alternation coordinates in asymme...

  3. Classical Orbital Paramagnetism in Non-equilibrium Steady State

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Very significantly, the sign of the orbital magnetic moment turns out to be paramagnetic for our choice of parameters, varied over a wide range. This is shown specifically for the case of classical dynamics driven by a Kubo–Anderson type non-Markovian noise. Natural spatial boundary condition was ...

  4. Polymer complexes. XLXI. Supramolecular spectral studies on metal-ligand bonding of novel rhodanine sulphadrugs hydrazone

    Energy Technology Data Exchange (ETDEWEB)

    El-Sonbati, Adel Z., E-mail: elsonbatisch@yahoo.com [Chemistry Department, Faculty of Science, Mansoura University, Demiatta (Egypt); Diab, Mostafa A. [Chemistry Department, Faculty of Science, Mansoura University, Demiatta (Egypt); El-Halawany, Mohamed M.; Salam, Naglaa E. [Department of Mathematical and Physical Sciences, Faculty of Engineering, Mansoura University, Mansoura (Egypt)

    2010-10-01

    Graphical abstract: The ESR spectra of copper complexes in powder form show a broad signal with values in order g{sub ||} > g{sub (} > g{sub e} (2.0023). The value of covalency factor {beta} and orbital reduction factor K accounts for the covalent nature of the complexes. -- Abstract: Novel polymeric complexes with 5-sulphadiazineazo-3-phenyl-2-thioxo-4-thiazolidine (HL{sub 1}), 5-sulphamethazineazo-3-phenyl-2-thioxo-4-thiazolidine (HL{sub 2}) and 5-sulphamethoxazoleazo-3-phenyl-2-thioxo-4-thiazolidine (HL{sub 3}) and various anions were prepared. Structural and spectroscopic properties have been studied on the basis of elemental analyses, infrared spectra, {sup 1}HNMR spectra, electronic spectra, magnetic measurements and ESR. IR and {sup 1}H NMR studies reveal that the ligands (HL{sub n}) exists in the tautomeric enol/hydrazo form in both states with intramolecular hydrogen bonding. The analytical data and the molar conductance measurements of the polymeric complexes reveal that three molecules of the ligand and four/two(Cl/SO{sub 4}) of the anions are coordinated to the two metal atoms in all complexes. The infrared spectra of the ligands and their polymeric complexes, confirmed that the ligands coordinate to Cu(II) as a neutral and tetradentate via NH(hydrazone), oxygen of the carbonyl group (CO), nitrogen of the NH(3-phenylamine) and thion sulphur (CS) group. All the polymer complexes were found to have magnetic moments corresponding to one unpaired electrons. The ESR (g{sub ||} and g{sub perpendicular}) and bonding {alpha}{sup 2} parameters of the copper ion were greatly affected by substituting several groups position of ring of sulphadrug. The ESR spectra of copper complexes in powder form show a broad signal with values in order g{sub ||} > g{sub perpendicular} > g{sub e} (2.0023). The value of covalency factor {beta} and orbital reduction factor K accounts for the covalent nature of the complexes.

  5. Ping-pong protons: how hydrogen-bonding networks facilitate heterolytic bond cleavage in peptide radical cations.

    Science.gov (United States)

    Zhurov, Konstantin O; Wodrich, Matthew D; Corminboeuf, Clémence; Tsybin, Yury O

    2014-03-13

    Electron capture and electron transfer dissociation (ECD/ETD) tandem mass spectrometry (MS/MS) are commonly employed techniques for biomolecular analysis. The ECD/ETD process predominately cleaves N-Cα peptide backbone bonds, leading to primary sequence information complementary to other mass spectrometry techniques. Despite frequent laboratory use, the mechanistic underpinnings surrounding N-Cα bond cleavage remain debated. While the majority of mechanisms assume a homolytic bond rupture, we recently showed that heterolytic cleavage is also thermodynamically viable. For a cleavage of this type to be feasible, the charge separation created upon breaking of the N-Cα backbone bond must be quickly annihilated. In this work, we show, using density functional computations, that specific hydrogen-bonding motifs and structural rearrangements involving proton transfers stabilize the transition state associated with heterolytic cleavage and eliminate the ensuing charge separation from the final product fragments. The movement of protons can occur either directly from the z- to c-fragment or in a more complex manner including a ping-pong-type mechanism. The nature of these diverse hydrogen-bonding motifs reveals that not only those functional groups proximate to the bond rupture site, but also the entire global chemical environment, play important roles in backbone cleavage characteristic of ECD/ETD MS/MS. For doubly charged systems, both conformation and electron localization site dictate which of the two fragments retains the final positive charge.

  6. Space Tourism: Orbital Debris Considerations

    Science.gov (United States)

    Mahmoudian, N.; Shajiee, S.; Moghani, T.; Bahrami, M.

    2002-01-01

    Space activities after a phase of research and development, political competition and national prestige have entered an era of real commercialization. Remote sensing, earth observation, and communication are among the areas in which this growing industry is facing competition and declining government money. A project like International Space Station, which draws from public money, has not only opened a window of real multinational cooperation, but also changed space travel from a mere fantasy into a real world activity. Besides research activities for sending man to moon and Mars and other outer planets, space travel has attracted a considerable attention in recent years in the form of space tourism. Four countries from space fairing nations are actively involved in the development of space tourism. Even, nations which are either in early stages of space technology development or just beginning their space activities, have high ambitions in this area. This is worth noting considering their limited resources. At present, trips to space are available, but limited and expensive. To move beyond this point to generally available trips to orbit and week long stays in LEO, in orbital hotels, some of the required basic transportations, living requirements, and technological developments required for long stay in orbit are already underway. For tourism to develop to a real everyday business, not only the price has to come down to meaningful levels, but also safety considerations should be fully developed to attract travelers' trust. A serious hazard to space activities in general and space tourism in particular is space debris in earth orbit. Orbiting debris are man-made objects left over by space operations, hazardous to space missions. Since the higher density of debris population occurs in low earth orbit, which is also the same orbit of interest to space tourism, a careful attention should be paid to the effect of debris on tourism activities. In this study, after a

  7. Dentin-bonding agents

    Directory of Open Access Journals (Sweden)

    João Carlos Gomes

    2008-01-01

    Full Text Available New dental restorative materials have been developed to meet not only the functional demands, but esthetics as well, and in the last few years an enormous range of new materials has appeared for use in dentistry. Among them, several adhesive systems, and different operative techniques for each group materials. Therefore, is indispensable for the professional to know about the properties, characteristics, and association of these materials with the dental structures, in order to select and use them correctly. Should conventional self-etching adhesive systems be used? This question encouraged this literature review to be conducted, with the aim of comparing the conventional adhesive systems with the self-etching systems and to look for scientific data that would help professionals to choose which adhesive system to use. When compared to conventional systems, it was noted that the self-etching systems show less sensitivity to technique, especially as regards errors the operator could commit. The self-etching systems, particularly the 2-step type, have shown equivalent values of bond strength, marginal microleakage and performance, therefore, will be an option for direct composite resin restorations in posterior teeth.

  8. Triple Difference Approach to Low Earth Orbiter Precision Orbit Determination

    Science.gov (United States)

    Kwon, Jay-Hyoun; Grejner-Brzezinska, Dorota A.; Yom, Jae-Hong; Cheon, Lee-Dong

    2003-03-01

    A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. P-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy of P-KOD applied to CHAMP (CHAllenging Minisatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.

  9. Orbital, subconjunctival, and subcutaneous emphysema after an orbital floor fracture

    Directory of Open Access Journals (Sweden)

    Ababneh OH

    2013-06-01

    Full Text Available Osama H Ababneh Department of Ophthalmology, The University of Jordan and Jordan University Hospital, Amman, Jordan Abstract: A 16-year-old boy presented to the emergency department with the complaint of a sudden, painful left eye and proptosis after an episode of sneezing. A few hours earlier, he had sustained a blunt trauma to the left orbit as the result of a fistfight. The initial examination showed subcutaneous and subconjunctival emphysema. Visual acuity in the left eye was 20/30 (0.67, the pupils were reactive with no relative afferent pupillary defect, and there were mild limitations in levoduction and supraduction. A slit-lamp examination showed normal anterior and posterior segments with an intraocular pressure of 26 mmHg. An orbital computed tomography scan showed orbital, subconjunctival, and subcutaneous emphysema associated with a small fracture of the orbital floor. Following conservative management with broad-spectrum oral antibiotics, a topical antiglaucoma drug, and lubricating eye drops, the patient improved dramatically within one week. Keywords: emphysema, orbital fracture, trauma

  10. Covalency of hydrogen bonds in liquid water can be probed by proton nuclear magnetic resonance experiments.

    Science.gov (United States)

    Elgabarty, Hossam; Khaliullin, Rustam Z; Kühne, Thomas D

    2015-09-15

    The concept of covalency is widely used to describe the nature of intermolecular bonds, to explain their spectroscopic features and to rationalize their chemical behaviour. Unfortunately, the degree of covalency of an intermolecular bond cannot be directly measured in an experiment. Here we established a simple quantitative relationship between the calculated covalency of hydrogen bonds in liquid water and the anisotropy of the proton magnetic shielding tensor that can be measured experimentally. This relationship enabled us to quantify the degree of covalency of hydrogen bonds in liquid water using the experimentally measured anisotropy. We estimated that the amount of electron density transferred between molecules is on the order of 10  m while the stabilization energy due to this charge transfer is ∼15 kJ mol(-1). The physical insight into the fundamental nature of hydrogen bonding provided in this work will facilitate new studies of intermolecular bonding in a variety of molecular systems.

  11. Quantum entanglement in the one-dimensional spin-orbital SU (2 )⊗XXZ model

    Science.gov (United States)

    You, Wen-Long; Horsch, Peter; Oleś, Andrzej M.

    2015-08-01

    We investigate the phase diagram and the spin-orbital entanglement of a one-dimensional SU (2 )⊗XXZ model with SU(2) spin exchange and anisotropic XXZ orbital exchange interactions and negative exchange coupling constant. As a unique feature, the spin-orbital entanglement entropy in the entangled ground states increases here linearly with system size. In the case of Ising orbital interactions, we identify an emergent phase with long-range spin-singlet dimer correlations triggered by a quadrupling of correlations in the orbital sector. The peculiar translational-invariant spin-singlet dimer phase has finite von Neumann entanglement entropy and survives when orbital quantum fluctuations are included. It even persists in the isotropic SU (2 )⊗SU (2) limit. Surprisingly, for finite transverse orbital coupling, the long-range spin-singlet correlations also coexist in the antiferromagnetic spin and alternating orbital phase making this phase also unconventional. Moreover, we also find a complementary orbital singlet phase that exists in the isotropic case but does not extend to the Ising limit. The nature of entanglement appears essentially different from that found in the frequently discussed model with positive coupling. Furthermore, we investigate the collective spin and orbital wave excitations of the disentangled ferromagnetic-spin/ferro-orbital ground state and explore the continuum of spin-orbital excitations. Interestingly, one finds among the latter excitations two modes of exciton bound states. Their spin-orbital correlations differ from the remaining continuum states and exhibit logarithmic scaling of the von Neumann entropy with increasing system size. We demonstrate that spin-orbital excitons can be experimentally explored using resonant inelastic x-ray scattering, where the strongly entangled exciton states can be easily distinguished from the spin-orbital continuum.

  12. Hydrogen bonding motifs, spectral characterization, theoretical computations and anticancer studies on chloride salt of 6-mercaptopurine: An assembly of corrugated lamina shows enhanced solubility

    Science.gov (United States)

    Suresh Kumar, S.; Athimoolam, S.; Sridhar, B.

    2015-10-01

    6-Mercaptopurine (an anti cancer drug), is coming under the class II Biopharmaceutics Classification System (BCS). In order to enhance the solubility with retained physiochemical/pharmaceutical properties, the present work was attempted with its salt form. The single crystals of 6-mercaptopurinium chloride (6MPCl) were successfully grown by slow evaporation technique under ambient temperature. The X-ray diffraction study shows that the crystal packing is dominated by N-H⋯Cl classical hydrogen bonds leading to corrugated laminar network. The hydrogen bonds present in the lamina can be dismantled as three chain C21(6), C21(7) and C21(8) motifs running along ab-diagonal of the unit cell. These primary chain motifs are interlinked to each other forming ring R63(21) motifs. These chain and ring motifs are aggregated like a dendrimer structure leading to the above said corrugated lamina. This low dimensional molecular architecture differs from the ladder like arrays in pure drug though it possess lattice water molecule in lieu of the chloride anion in the present compound. Geometrical optimizations of 6MPCl were done by Density Functional Theory (DFT) using B3LYP function with two different basis sets. The optimized molecular geometries and computed vibrational spectra are compared with their experimental counterparts. The Natural Bond Orbital (NBO) analysis was carried out to interpret hyperconjugative interaction and Intramolecular Charge Transfer (ICT). The chemical hardness, electronegativity, chemical potential and electrophilicity index of 6MPCl were found along with the HOMO-LUMO plot. The lower band gap value obtained from the Frontier Molecular Orbital (FMO) analysis reiterates the pharmaceutical activity of the compound. The anticancer studies show that 6MPCl retains its activity against human cervical cancer cell line (HeLa). Hence, this anticancer efficacy and improved solubility demands 6MPCl towards the further pharmaceutical applications.

  13. Photometric Studies of GEO Orbital Debris

    Science.gov (United States)

    Seitzer, Patrick; Rodriquez-Cowardin, Heather M.; Barker, Ed; Abercromby, Kira J.; Foreman, Gary; Horstman, Matt

    2009-01-01

    The photometric signature of a debris object can be useful in determining what the physical characteristics of a piece of debris are. We report on optical observations in multiple filters of debris at geosynchronous Earth orbit (GEO). Our sample is taken from GEO objects discovered in a survey with the University of Michigan's 0.6-m aperture Schmidt telescope MODEST (for Michigan Orbital DEbris Survey Telescope), and then followed up in real-time with the Cerro Tololo Inter- American Observatory (CTIO) 0.9-m for orbits and photometry. Our goal is to determine 6 parameter orbits and measure colors for all objects fainter than R=15th magnitude that are discovered in the MODEST survey. At this magnitude the distribution of observed angular rates changes significantly from that of brighter objects. There are two objectives: 1. Estimate the orbital distribution of objects selected on the basis of two observational criteria: brightness (magnitude) and angular rates. 2. Obtain magnitudes and colors in standard astronomical filters (BVRI) for comparison with reflectance spectra of likely spacecraft materials. What is the faint debris likely to be? More than 90 calibrated sequences of R-B-V-I-R magnitudes for a sample of 50 objects have been obtained with the CTIO 0.9-m. For objects that do not show large brightness variations, the colors are largely redder than solar in both B-R and R-I. The width of the color distribution may be intrinsic to the nature of the surfaces, but also could be that we are seeing irregularly shaped objects and measuring the colors at different times with just one telescope. For a smaller sample of objects we have observed with synchronized CCD cameras on the two telescopes. The CTIO 0.9-m observes in B, and MODEST in R. The CCD cameras are electronically linked together so that the start time and duration of observations are the same to better than 50 milliseconds. Thus the B-R color is a true measure of the surface of the debris piece facing the

  14. Microbiology of pediatric orbital cellulitis.

    Science.gov (United States)

    McKinley, Steven H; Yen, Michael T; Miller, Aaron M; Yen, Kimberly G

    2007-10-01

    To evaluate the microbiology of pediatric orbital cellulitis associated with sinusitis. Retrospective review of medical records of pediatric patients treated for orbital cellulitis. All pediatric patients treated for orbital cellulitis associated with sinusitis at Texas Children's Hospital between December 1, 2001 and September 30, 2005 were reviewed. Data collected included patient age, history, microbiology results, and surgical intervention. Thirty-eight cases were identified. Fifteen cases required medical management, whereas 23 patients received a combination of medical and surgical intervention. Three patients had multiple surgical procedures performed. Of the procedures performed, four were sinus irrigation, 12 were sinusotomy and drainage, nine were orbitotomy with drainage of abscess, and one was craniotomy with drainage of abscess. Surgical aspirate specimens yielded a higher positive culture result rate with 9/9 of orbital abscesses and 13/16 of sinus aspirates demonstrating a positive yield. Two of the 27 blood cultures had a positive yield. Staphylococcus species was the most common organism isolated. Methicillin-resistant S. aureus (MRSA) represented 73% of S. aureus isolates. Streptococcus species was the next most common pathogen. Three cultures yielded Haemophilus species with one being positive for H. influenzae. Organisms responsible for causing pediatric orbital cellulitis are evolving, with Staphylococcus followed by Streptococcus species being the most common pathogens. The occurrence of MRSA in pediatric orbital cellulitis is increasing, and empiric antimicrobial therapy should be directed against these organisms if they are prevalent in the community. Sinus and orbital abscess aspirates yielded the greatest number of positive cultures, though these invasive surgical procedures should be performed only when clinically indicated.

  15. Bonding over Dentin Replacement Materials.

    Science.gov (United States)

    Meraji, Naghmeh; Camilleri, Josette

    2017-08-01

    Dentin replacement materials are necessary in large cavities to protect the pulp and reduce the bulk of filling material. These materials are layered with a composite resin restorative material. Microleakage caused by poor bonding of composite resin to underlying dentin replacement material will result in pulp damage. The aim of this study was to characterize the interface between dentin replacement materials and composite resin and to measure the shear bond strength after dynamic aging. Biodentine (Septodont, Saint Maur-des-Fosses, France), Theracal LC (Bisco, Schaumburg, IL), and Fuji IX (GC, Tokyo, Japan) were used as dentin replacement materials. They were then overlaid with a total-etch and bonding agent or a self-etch primer and composite resin or a glass ionomer cement. All combinations were thermocycled for 3000 cycles. The interface was characterized using scanning electron microscopy and elemental mapping. Furthermore, the shear bond strength was assessed. The Biodentine surface was modified by etching. The Theracal LC and Fuji IX microstructure was unchanged upon the application of acid etch. The Biodentine and glass ionomer interface showed an evident wide open space, and glass particles from the glass ionomer adhered to the Biodentine surface. Elemental migration was shown with aluminum, barium, fluorine, and ytterbium present in Biodentine from the overlying composite resin. Calcium was more stable. The bond strength between Theracal LC and composite using a total-etch technique followed by self-etch primer achieved the best bond strength values. Biodentine exhibited the weakest bond with complete failure of bonding shown after demolding and thermocycling. Dynamic aging is necessary to have clinically valid data. Bonding composite resin to water-based dentin replacement materials is still challenging, and further alternatives for restoration of teeth using such materials need to be developed. Copyright © 2017 American Association of Endodontists

  16. Competing intramolecular N-H⋯O=C hydrogen bonds and extended intermolecular network in 1-(4-chlorobenzoyl)-3-(2-methyl-4-oxopentan-2-yl) thiourea analyzed by experimental and theoretical methods

    Energy Technology Data Exchange (ETDEWEB)

    Saeed, Aamer, E-mail: aamersaeed@yahoo.com [Department of Chemistry, Quaid-I-Azam University, Islamabad 45320 (Pakistan); Khurshid, Asma [Department of Chemistry, Quaid-I-Azam University, Islamabad 45320 (Pakistan); Jasinski, Jerry P. [Department of Chemistry, Keene State College, 229 Main Street Keene, NH 03435-2001 (United States); Pozzi, C. Gustavo; Fantoni, Adolfo C. [Instituto de Física La Plata, Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 49 y 115, La Plata, Buenos Aires (Argentina); Erben, Mauricio F., E-mail: erben@quimica.unlp.edu.ar [CEQUINOR (UNLP, CONICET-CCT La Plata), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 962, (1900) La Plata, Buenos Aires (Argentina)

    2014-03-18

    Highlights: • Two distinct N-H⋯O=C intramolecular competing hydrogen bonds are feasible in the title molecule. • Crystal structures and vibrational properties were determined. • The C=O and C=S double bonds of the acyl-thiourea group are mutually oriented in opposite directions. • A strong hyperconjugative lpO1 → σ{sup ∗}(N2-H) remote interaction was detected. • Topological analysis reveals a Cl⋯N interaction playing a relevant role in crystal packing. - Abstract: The synthesis of a novel 1-acyl-thiourea species (C{sub 14}H{sub 17}N{sub 2}O{sub 2}SCl), has been tailored in such a way that two distinct N-H⋯O=C intramolecular competing hydrogen bonds are feasible. The X-ray structure analysis as well as the vibrational (FT-IR and FT-Raman) data reveal that the S conformation is preferred, with the C=O and C=S bonds of the acyl-thiourea group pointing in opposite directions. The preference for the intramolecular N-H⋯O=C hydrogen bond within the -C(O)NHC(S)NH- core is confirmed. The Natural Bond Orbital and the Atom in Molecule approaches demonstrate that a strong hyperconjugative lpO → σ{sup ∗}(N-H) remote interaction between the acyl and the thioamide N-H groups is responsible for the stabilization of the S conformation. Intermolecular interactions have been characterized in the periodic system electron density and the topological analysis reveals the presence of an extended intermolecular network in the crystal, including a Cl⋯N interaction playing a relevant role in crystal packing.

  17. Hydrogen bond docking site competition in methyl esters.

    Science.gov (United States)

    Zhao, Hailiang; Tang, Shanshan; Du, Lin

    2017-06-15

    The OH⋯O hydrogen bonds in the 2,2,2-trifluoroethanol (TFE)-methyl ester complexes in the gas phase have been investigated by FTIR spectroscopy and DFT calculations. Methyl formate (MF), methyl acetate (MA), and methyl trifluoroacetate (MTFA) were chosen as the hydrogen bond acceptors. A dominant inter-molecular hydrogen bond was formed between the OH group of TFE and different docking sites in the methyl esters (carbonyl oxygen or ester oxygen). The competition of the two docking sites decides the structure and spectral properties of the complexes. On the basis of the observed red shifts of the OH-stretching transition with respect to the TFE monomer, the order of the hydrogen bond strength can be sorted as TFE-MA (119cm-1)>TFE-MF (93cm-1)>TFE-MTFA (44cm-1). Combining the experimental infrared spectra with the DFT calculations, the Gibbs free energies of formation were determined to be 1.5, 4.5 and 8.6kJmol-1 for TFE-MA, TFE-MF and TFE-MTFA, respectively. The hydrogen bonding in the MTFA complex is much weaker than those of the TFE-MA and TFE-MF complexes due to the effect of the CF3 substitution on MTFA, while the replacement of an H atom with a CH3 group in methyl ester only slightly increases the hydrogen bond strength. Topological analysis and localized molecular orbital energy decomposition analysis was also applied to compare the interactions in the complexes. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Hydrogen bond docking site competition in methyl esters

    Science.gov (United States)

    Zhao, Hailiang; Tang, Shanshan; Du, Lin

    2017-06-01

    The Osbnd H ⋯ O hydrogen bonds in the 2,2,2-trifluoroethanol (TFE)-methyl ester complexes in the gas phase have been investigated by FTIR spectroscopy and DFT calculations. Methyl formate (MF), methyl acetate (MA), and methyl trifluoroacetate (MTFA) were chosen as the hydrogen bond acceptors. A dominant inter-molecular hydrogen bond was formed between the OH group of TFE and different docking sites in the methyl esters (carbonyl oxygen or ester oxygen). The competition of the two docking sites decides the structure and spectral properties of the complexes. On the basis of the observed red shifts of the OH-stretching transition with respect to the TFE monomer, the order of the hydrogen bond strength can be sorted as TFE-MA (119 cm- 1) > TFE-MF (93 cm- 1) > TFE-MTFA (44 cm- 1). Combining the experimental infrared spectra with the DFT calculations, the Gibbs free energies of formation were determined to be 1.5, 4.5 and 8.6 kJ mol- 1 for TFE-MA, TFE-MF and TFE-MTFA, respectively. The hydrogen bonding in the MTFA complex is much weaker than those of the TFE-MA and TFE-MF complexes due to the effect of the CF3 substitution on MTFA, while the replacement of an H atom with a CH3 group in methyl ester only slightly increases the hydrogen bond strength. Topological analysis and localized molecular orbital energy decomposition analysis was also applied to compare the interactions in the complexes.

  19. Direct Bonded Pontic (Laporan Kasus

    Directory of Open Access Journals (Sweden)

    Suhandi Sidjaja

    2015-10-01

    Full Text Available Advanced science and technology in dentistry enable dental practitioners to modified she bonding techniques in tooth replacement. A pontic made of composite resin bonded to etched enamel of the adjacent teeth can be used in the replacement of one missing anterior tooth with a virgin or sowed adpicent tooth. The advantages of this technique include a one visit treatment, cow cost, good esthetics, less side effects and easy repair or rebounding. Clinical evaluation showed a high success rate therefore with a proper diagnosis and a perfect skill of the direct bonded technique this treatment can be used as an alternative restoration.

  20. The chemisorptive bond basic concepts

    CERN Document Server

    Clark, Alfred

    1974-01-01

    The Chemisorptive Bond: Basic Concepts describes the basic concepts of the chemisorptive bond on solid surfaces from the simple analogies with ordinary chemical bonds to the quantum-mechanical approaches.This book is composed of 10 chapters and begins with discussions of simple formulas for correlating measurable quantities in chemisorptions and catalysis. The succeeding chapters deal with theories based on quantum-mechanical principles that describe the mutual interactions of atoms of the solid and foreign atoms on the surface. The remaining chapters consider the possible arrangements