Semiflexible macromolecules in quasi-one-dimensional confinement: Discrete versus continuous bond angles.

PubMed

Huang, Aiqun; Hsu, Hsiao-Ping; Bhattacharya, Aniket; Binder, Kurt

2015-12-28

The conformations of semiflexible polymers in two dimensions confined in a strip of width D are studied by computer simulations, investigating two different models for the mechanism by which chain stiffness is realized. One model (studied by molecular dynamics) is a bead-spring model in the continuum, where stiffness is controlled by a bond angle potential allowing for arbitrary bond angles. The other model (studied by Monte Carlo) is a self-avoiding walk chain on the square lattice, where only discrete bond angles (0° and ±90°) are possible, and the bond angle potential then controls the density of kinks along the chain contour. The first model is a crude description of DNA-like biopolymers, while the second model (roughly) describes synthetic polymers like alkane chains. It is first demonstrated that in the bulk the crossover from rods to self-avoiding walks for both models is very similar, when one studies average chain linear dimensions, transverse fluctuations, etc., despite their differences in local conformations. However, in quasi-one-dimensional confinement two significant differences between both models occur: (i) The persistence length (extracted from the average cosine of the bond angle) gets renormalized for the lattice model when D gets less than the bulk persistence length, while in the continuum model it stays unchanged. (ii) The monomer density near the repulsive walls for semiflexible polymers is compatible with a power law predicted for the Kratky-Porod model in the case of the bead-spring model, while for the lattice case it tends to a nonzero constant across the strip. However, for the density of chain ends, such a constant behavior seems to occur for both models, unlike the power law observed for flexible polymers. In the regime where the bulk persistence length ℓp is comparable to D, hairpin conformations are detected, and the chain linear dimensions are discussed in terms of a crossover from the Daoud/De Gennes "string of blobs"-picture to the flexible rod picture when D decreases and/or the chain stiffness increases. Introducing a suitable further coarse-graining of the chain contours of the continuum model, direct estimates for the deflection length and its distribution could be obtained.

Concentration effect on inter-mineral equilibrium isotope fractionation: insights from Mg and Ca isotopic systems

NASA Astrophysics Data System (ADS)

Huang, F.; Wang, W.; Zhou, C.; Kang, J.; Wu, Z.

2017-12-01

Many naturally occurring minerals, such as carbonate, garnet, pyroxene, and feldspar, are solid solutions with large variations in chemical compositions. Such variations may affect mineral structures and modify the chemical bonding environment around atoms, which further impacts the equilibrium isotope fractionation factors among minerals. Here we investigated the effects of Mg content on equilibrium Mg and Ca isotope fractionation among carbonates and Ca content on equilibrium Ca isotope fractionation between orthopyroxene (opx) and clinopyroxene (cpx) using first-principles calculations. Our results show that the average Mg-O bond length increases with decreasing Mg/(Mg+Ca) in calcite when it is greater than 1/48[1] and the average Ca-O bond length significantly decreases with decreasing Ca/(Ca+Mg+Fe) in opx when it ranges from 2/16 to 1/48[2]. Equilibrium isotope fractionation is mainly controlled by bond strengths, which could be measured by bond lengths. Thus, 103lnα26Mg/24Mg between dolomite and calcite dramatically increases with decreasing Mg/(Mg+Ca) in calcite [1] and it reaches a constant value when it is lower than 1/48. 103lnα44Ca/40Ca between opx and cpx significantly increases with decreasing Ca content in opx when Ca/(Ca+Mg+Fe) ranges from 2/16 to 1/48 [2]. If Ca/(Ca+Mg+Fe) is below 1/48, 103lnα44Ca/40Ca is not sensitive to Ca content. Based on our results, we conclude that the concentration effect on equilibrium isotope fractionation could be significant within a certain range of chemical composition of minerals, which should be a ubiquitous phenomenon in solid solution systems. [1] Wang, W., Qin, T., Zhou, C., Huang, S., Wu, Z., Huang, F., 2017. GCA 208, 185-197. [2] Feng, C., Qin, T., Huang, S., Wu, Z., Huang, F., 2014. GCA 143, 132-142.

Mean bond-length variations in crystals for ions bonded to oxygen

PubMed Central

2017-01-01

Variations in mean bond length are examined in oxide and oxysalt crystals for 55 cation configurations bonded to O2−. Stepwise multiple regression analysis shows that mean bond length is correlated to bond-length distortion in 42 ion configurations at the 95% confidence level, with a mean coefficient of determination (〈R 2〉) of 0.35. Previously published correlations between mean bond length and mean coordination number of the bonded anions are found not to be of general applicability to inorganic oxide and oxysalt structures. For two of 11 ions tested for the 95% confidence level, mean bond lengths predicted using a fixed radius for O2− are significantly more accurate as those predicted using an O2− radius dependent on coordination number, and are statistically identical otherwise. As a result, the currently accepted ionic radii for O2− in different coordinations are not justified by experimental data. Previously reported correlation between mean bond length and the mean electronegativity of the cations bonded to the oxygen atoms of the coordination polyhedron is shown to be statistically insignificant; similar results are obtained with regard to ionization energy. It is shown that a priori bond lengths calculated for many ion configurations in a single structure-type leads to a high correlation between a priori and observed mean bond lengths, but a priori bond lengths calculated for a single ion configuration in many different structure-types leads to negligible correlation between a priori and observed mean bond lengths. This indicates that structure type has a major effect on mean bond length, the magnitude of which goes beyond that of the other variables analyzed here.

Dipropyl 3,6-diphenyl-1,2-dihydro-1,2,4,5-tetrazine-1,2-dicarboxylate.

PubMed

Rao, Guo-Wu; Hu, Wei-Xiao

2003-05-01

The title compound, C(22)H(24)N(4)O(4), was prepared from propyl chloroformate and 3,6-diphenyl-1,2-dihydro-s-tetrazine. This reaction yields the title compound rather than dipropyl 3,6-diphenyl-1,4-dihydro-s-tetrazine-1,4-dicarboxylate. The 2,3-diazabutadiene group in the central six-membered ring is not planar; the C=N double-bond length is 1.285 (2) A, and the average N-N single-bond length is 1.401 (3) A, indicating a lack of conjugation. The ring has a twist conformation, in which adjacent N atoms lie +/- 0.3268 (17) A from the plane of the ring. The molecule has twofold crystallographic symmetry.

Highly Conductive One-Dimensional Manganese Oxide Wires by Coating with Graphene Oxides

NASA Astrophysics Data System (ADS)

Tojo, Tomohiro; Shinohara, Masaki; Fujisawa, Kazunori; Muramatsu, Hiroyuki; Hayashi, Takuya; Ahm Kim, Yoong; Endo, Morinobu

2012-10-01

Through coating with graphene oxides, we have developed a chemical route to the bulk production of long, thin manganese oxide (MnO2) nanowires that have high electrical conductivity. The average diameter of these hybrid nanowires is about 25 nm, and their average length is about 800 nm. The high electrical conductivity of these nanowires (ca. 189.51+/-4.51 µS) is ascribed to the homogeneous coating with conductive graphene oxides as well as the presence of non-bonding manganese atoms. The growth mechanism of the nanowires is theoretically supported by the initiation of morphological conversion from graphene oxide to wrapped structures through the formation of covalent bonds between manganese and oxygen atoms at the graphene oxide edge.

The Strength of Hydrogen Bonds between Fluoro-Organics and Alcohols, a Theoretical Study.

PubMed

Rosenberg, Robert E

2018-05-10

Fluorinated organic compounds are ubiquitous in the pharmaceutical and agricultural industries. To better discern the mode of action of these compounds, it is critical to understand the strengths of hydrogen bonds involving fluorine. There are only a few published examples of the strengths of these bonds. This study provides a high level ab initio study of inter- and intramolecular hydrogen bonds between RF and R'OH, where R and R' are aryl, vinyl, alkyl, and cycloalkyl. Intermolecular binding energies average near 5 kcal/mol, while intramolecular binding energies average about 3 kcal/mol. Inclusion of zero-point energies and applying a counterpoise correction lessen the difference. In both series, modest increases in binding energies are seen with increased acidity of R'OH and increased electron donation of R in RF. In the intramolecular compounds, binding energy increases with the rigidity of the F-(C) n -OH ring. Inclusion of free energy corrections at 298 K results in exoergic binding energies for the intramolecular compounds and endoergic binding energies for the intermolecular compounds. Parameters such as bond lengths, vibrational frequencies, and atomic populations are consistent with formation of a hydrogen bond and with slightly stronger binding in the intermolecular cases over the intramolecular cases. However, these parameters correlated poorly with binding energies.

Microwave structure for the propiolic acid-formic acid complex.

PubMed

Kukolich, Stephen G; Mitchell, Erik G; Carey, Spencer J; Sun, Ming; Sargus, Bryan A

2013-10-03

New microwave spectra were measured to obtain rotational constants and centrifugal distortion constants for the DCCCOOH···HOOCH and HCCCOOD···DOOCH isotopologues. Rotational transitions were measured in the frequency range of 4.9-15.4 GHz, providing accurate rotational constants, which, combined with previous rotational constants, allowed an improved structural fit for the propiolic acid-formic acid complex. The new structural fit yields reasonably accurate orientations for both the propiolic and formic acid monomers in the complex and more accurate structural parameters describing the hydrogen bonding. The structure is planar, with a positive inertial defect of Δ = 1.33 amu Å(2). The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations. The best-fit hydrogen bond lengths have an r(O1-H1···O4) of 1.64 Å and an r(O3-H2···O2) of 1.87 Å. The average of the two hydrogen bond lengths is r(av)(exp) = 1.76 Å, in good agreement with r(av)(theory) = 1.72 Å. The center of mass separation of the monomers is R(CM) = 3.864 Å. Other structural parameters from the least-squares fit using the experimental rotational constants are compared with theoretical values. The spectra were obtained using two different pulsed beam Fourier transform microwave spectrometers.

Electronegativity effects and single covalent bond lengths of molecules in the gas phase.

PubMed

Lang, Peter F; Smith, Barry C

2014-06-07

This paper discusses in detail the calculation of internuclear distances of heteronuclear single bond covalent molecules in the gaseous state. It reviews briefly the effect of electronegativity in covalent bond length. A set of single bond covalent radii and electronegativity values are proposed. Covalent bond lengths calculated by an adapted form of a simple expression (which calculated internuclear separation of different Group 1 and Group 2 crystalline salts to a remarkable degree of accuracy) show very good agreement with observed values. A small number of bond lengths with double bonds as well as bond lengths in the crystalline state are calculated using the same expression and when compared with observed values also give good agreement. This work shows that covalent radii are not additive and that radii in the crystalline state are different from those in the gaseous state. The results also show that electronegativity is a major influence on covalent bond lengths and the set of electronegativity scale and covalent radii proposed in this work can be used to calculate covalent bond lengths in different environments that have not yet been experimentally measured.

Analytic Energy Gradients for Variational Two-Electron Reduced-Density-Matrix-Driven Complete Active Space Self-Consistent Field Theory.

PubMed

Maradzike, Elvis; Gidofalvi, Gergely; Turney, Justin M; Schaefer, Henry F; DePrince, A Eugene

2017-09-12

Analytic energy gradients are presented for a variational two-electron reduced-density-matrix (2-RDM)-driven complete active space self-consistent field (CASSCF) method. The active-space 2-RDM is determined using a semidefinite programing (SDP) algorithm built upon an augmented Lagrangian formalism. Expressions for analytic gradients are simplified by the fact that the Lagrangian is stationary with respect to variations in both the primal and the dual solutions to the SDP problem. Orbital response contributions to the gradient are identical to those that arise in conventional CASSCF methods in which the electronic structure of the active space is described by a full configuration interaction (CI) wave function. We explore the relative performance of variational 2-RDM (v2RDM)- and CI-driven CASSCF for the equilibrium geometries of 20 small molecules. When enforcing two-particle N-representability conditions, full-valence v2RDM-CASSCF-optimized bond lengths display a mean unsigned error of 0.0060 Å and a maximum unsigned error of 0.0265 Å, relative to those obtained from full-valence CI-CASSCF. When enforcing partial three-particle N-representability conditions, the mean and maximum unsigned errors are reduced to only 0.0006 and 0.0054 Å, respectively. For these same molecules, full-valence v2RDM-CASSCF bond lengths computed in the cc-pVQZ basis set deviate from experimentally determined ones on average by 0.017 and 0.011 Å when enforcing two- and three-particle conditions, respectively, whereas CI-CASSCF displays an average deviation of 0.010 Å. The v2RDM-CASSCF approach with two-particle conditions is also applied to the equilibrium geometry of pentacene; optimized bond lengths deviate from those derived from experiment, on average, by 0.015 Å when using a cc-pVDZ basis set and a (22e,22o) active space.

Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges.

PubMed

Li, Yan; Blacque, Olivier; Fox, Thomas; Luber, Sandra; Polit, Walther; Winter, Rainer F; Venkatesan, Koushik; Berke, Heinz

2016-04-07

The mononuclear rhenium carbyne complex trans-[Re(C[triple bond, length as m-dash]CSiMe3)([triple bond, length as m-dash]C-Me)(PMe3)4][PF6] (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N2)(PMe3)4] (1), TlPF6, and an excess of HC[triple bond, length as m-dash]CSiMe3. 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(C[triple bond, length as m-dash]CSiMe3)([double bond, length as m-dash]C[double bond, length as m-dash]CH2)(PMe3)4] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp2Fe][PF6] at -78 °C gave the Cβ-C'β coupled dinuclear rhenium biscarbyne complex trans-[(Me3SiC[triple bond, length as m-dash]C)(PMe3)4Re[triple bond, length as m-dash]C-CH2-CH2-C[triple bond, length as m-dash]Re(PMe3)4(C[triple bond, length as m-dash]CSiMe3)][PF6]2 (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me3SiC[triple bond, length as m-dash]C)(PMe3)4Re[double bond, length as m-dash]C[double bond, length as m-dash]CH-CH[double bond, length as m-dash]C[double bond, length as m-dash]Re(PMe3)4(C[triple bond, length as m-dash]CSiMe3)] complex (E-6(S)) in 87% yield with an E-butadienediylidene bridge. Density functional theory (DFT) calculations of E-6(S) confirmed its singlet ground state. The Z-form of 6 (Z-6(S)) could not be observed, which is in accord with its DFT calculated 17.8 kJ mol(-1) higher energy. Oxidation of E-6 with 2 equiv. of [Cp2Fe][PF6] resulted in the stable diamagnetic dicationic trans-[(Me3SiC[triple bond, length as m-dash]C)(PMe3)4Re[triple bond, length as m-dash]C-CH[double bond, length as m-dash]CH-C[triple bond, length as m-dash]Re(PMe3)4(C[triple bond, length as m-dash]CSiMe3)][PF6]2 complex (E-6[PF6]2) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF6] was obtained by comproportionation of E-6(S) and E-6[PF6]2 or by oxidation of E-6(S) with 1 equiv. of [Cp2Fe][PF6]. The dicationic trans-[(Me3SiC[triple bond, length as m-dash]C)(PMe3)4Re[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]Re(PMe3)4(C[triple bond, length as m-dash]CSiMe3)][PF6]2 (7[PF6]2) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF6]2 with KOtBu followed by oxidation with 2 equiv. of [Cp2Fe][PF6]. The neutral complex 7 could be accessed best by reduction of 7[PF6]2 with KH in the presence of 18-crown-6. According to DFT calculations 7 possesses two equilibrating electronic states: diamagnetic 7(S) and triplet 7(F) with ferromagnetically coupled spins. The latter is calculated to be 5.2 kcal mol(-1) lower in energy than 7(S). There is experimental evidence that 7(S) prevails in solution. 7 could not be isolated in the crystalline state and is unstable transforming mainly by H-abstraction to give E-6(S). UV-Vis-NIR spectroscopy for the dinuclear rhenium complexes E-6(S), E-6[PF6] and E-6[PF6]2, as well as EPR spectroscopic and variable-temperature magnetization measurements for the MV complex E-6[PF6] were also conducted. Spectro-electrochemical reduction studies on 7[PF6]2 allowed the characterization of the mono- and direduced forms of 7(+) and 7 by means of IR- and UV-Vis-NIR-spectroscopy and revealed the chemical fate of the higher reduced form.

Prediction of boiling points of organic compounds by QSPR tools.

PubMed

Dai, Yi-min; Zhu, Zhi-ping; Cao, Zhong; Zhang, Yue-fei; Zeng, Ju-lan; Li, Xun

2013-07-01

The novel electro-negativity topological descriptors of YC, WC were derived from molecular structure by equilibrium electro-negativity of atom and relative bond length of molecule. The quantitative structure-property relationships (QSPR) between descriptors of YC, WC as well as path number parameter P3 and the normal boiling points of 80 alkanes, 65 unsaturated hydrocarbons and 70 alcohols were obtained separately. The high-quality prediction models were evidenced by coefficient of determination (R(2)), the standard error (S), average absolute errors (AAE) and predictive parameters (Qext(2),RCV(2),Rm(2)). According to the regression equations, the influences of the length of carbon backbone, the size, the degree of branching of a molecule and the role of functional groups on the normal boiling point were analyzed. Comparison results with reference models demonstrated that novel topological descriptors based on the equilibrium electro-negativity of atom and the relative bond length were useful molecular descriptors for predicting the normal boiling points of organic compounds. Copyright © 2013 Elsevier Inc. All rights reserved.

Metal-metal bond lengths in complexes of transition metals.

PubMed

Pauling, L

1976-12-01

In complexes of the transition metals containing clusters of metal atoms the cobalt-cobalt bond lengths are almost always within 1 pm of the single-bond value 246 pm given by the enneacovalent radius of cobalt, whereas most of the observed iron-iron bond lengths are significantly larger than the single-bond value 248 pm, the mean being 264 pm, which corresponds to a half-bond. A simple discussion of the structures of these complexes based on spd hybrid orbitals, the electroneutrality principle, and the partial ionic character of bonds between unlike atoms leads to the conclusion that resonance between single bonds and no-bonds would occur for iron and its congeners but not for cobalt and its congeners, explaining the difference in the bond lengths.

On the correlation between bond-length change and vibrational frequency shift in halogen-bonded complexes

NASA Astrophysics Data System (ADS)

Wang, Weizhou; Zhang, Yu; Ji, Baoming; Tian, Anmin

2011-06-01

The C-Hal (Hal = Cl, Br, or I) bond-length change and the corresponding vibrational frequency shift of the C-Hal stretch upon the C-Hal ⋯Y (Y is the electron donor) halogen bond formation have been determined by using density functional theory computations. Plots of the C-Hal bond-length change versus the corresponding vibrational frequency shift of the C-Hal stretch all give straight lines. The coefficients of determination range from 0.94366 to 0.99219, showing that the correlation between the C-Hal bond-length change and the corresponding frequency shift is very good in the halogen-bonded complexes. The possible effects of vibrational coupling, computational method, and anharmonicity on the bond-length change-frequency shift correlation are discussed in detail.

A P-H functionalized Al/P-based frustrated Lewis pair - hydrophosphination of nitriles, ring opening with cyclopropenones and evidence of P[double bond, length as m-dash]C double bond formation.

PubMed

Keweloh, Lukas; Aders, Niklas; Hepp, Alexander; Pleschka, Damian; Würthwein, Ernst-Ulrich; Uhl, Werner

2018-06-12

Hydroalumination of R-P(H)-C[triple bond, length as m-dash]C-tBu with bulky H-Al[CH(SiMe3)2]2 afforded the new P-H functionalized Al/P-based frustrated Lewis pair R-P(H)-C[[double bond, length as m-dash]C(H)-tBu]-AlR2 [R = CH(SiMe3)2; FLP 7]. A weak adduct of 7 with benzonitrile (8) was detected by NMR spectroscopy, but could not be isolated. tert-Butyl isocyanide afforded a similar, but isolable adduct (9), in which the isocyanide C atom was coordinated to aluminium. The unique reactivity of 7 became evident from its reactions with the heteroatom substituted nitriles PhO-C[triple bond, length as m-dash]N, PhCH2S-C[triple bond, length as m-dash]N and H8C4N-C[triple bond, length as m-dash]N. Hydrophosphination of the C[triple bond, length as m-dash]N triple bonds afforded imines at room temperature which were coordinated to the FLP by Al-N and P-C bonds to yield AlCPCN heterocycles (10 to 12). These processes depend on substrate activation by the FLP. Diphenylcyclopropenone and its sulphur derivative reacted with 7 by addition of the P-H bond to a C-C bond of the strained C3 ring and ring opening to afford the fragment (Z)-Ph-C(H)[double bond, length as m-dash]C(Ph)-C-X-Al (X = O, S). The C-O or C-S groups were coordinated to the FLP to yield AlCPCX heterocycles (13 and 14). The thiocarbonyl derived compound 14 contains an internally stabilized phosphenium cation with a localized P[double bond, length as m-dash]C bond, a trigonal planar coordinated P atom and a short P[double bond, length as m-dash]C distance (168.9 pm). Insight into formation mechanisms, the structural and energetic properties of FLP 7 and compounds 13 and 14 was gained by quantum chemical DFT calculations.

Investigation of the crystallization features, atomic structure, and microstructure of chromium-doped monticellite

NASA Astrophysics Data System (ADS)

Subbotin, K. A.; Iskhakova, L. D.; Zharikov, E. V.; Lavrishchev, S. V.

2008-12-01

A series of Cr4+:CaMgSiO4 single crystals is grown using floating zone melting, and their microstructure, composition, and crystal structure are investigated. It is shown that regions with inclusions of second phases, such as forsterite, akermanite, MgO, and Ca4Mg2Si3O12, can form over the length of the sample. The composition of the single-phase regions of the single crystals varies from the stoichiometric monticellite CaMgSiO4 to the solid solution Ca(1 - x)Mg(1 + x)SiO4( x = 0.22). The Cr:(Ca0.88Mg0.12)MgSiO4 crystal is studied using X-ray diffraction. It is revealed that, in this case, the olivine-like orthorhombic crystal lattice is distorted to the monoclinic lattice with the parameters a = 6.3574(5) Å, b = 4.8164(4) Å, c = 11.0387(8) Å, β = 90.30(1)o, Z = 4, V = 337.98 Å3, and space group P21/ c. In the monoclinic lattice, the M(1) position of the initial olivine structure is split into two nonequivalent positions with the center of symmetry, which are occupied only by Mg2+ cations with the average length of the Mg-O bond R av = 2.128 Å. The overstoichiometric Mg2+ cations partially replace Ca2+ cations (in the M(2) position of the orthorhombic prastructure) with the average bond length of 2.347 Å in the [(Ca,Mg)-O6] octahedron. The average distance in SiO4 distorted tetrahedra is 1.541 Å.

Metal-metal bond lengths in complexes of transition metals*

PubMed Central

Pauling, Linus

1976-01-01

In complexes of the transition metals containing clusters of metal atoms the cobalt-cobalt bond lengths are almost always within 1 pm of the single-bond value 246 pm given by the enneacovalent radius of cobalt, whereas most of the observed iron-iron bond lengths are significantly larger than the single-bond value 248 pm, the mean being 264 pm, which corresponds to a half-bond. A simple discussion of the structures of these complexes based on spd hybrid orbitals, the electroneutrality principle, and the partial ionic character of bonds between unlike atoms leads to the conclusion that resonance between single bonds and no-bonds would occur for iron and its congeners but not for cobalt and its congeners, explaining the difference in the bond lengths. PMID:16592368

Bent Bonds and Multiple Bonds.

ERIC Educational Resources Information Center

Robinson, Edward A.; Gillespie, Ronald J.

1980-01-01

Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

Bond length (Ti-O) dependence of nano ATO3-based (A = Pb, Ba, Sr) perovskite structures: Optical investigation in IR range

NASA Astrophysics Data System (ADS)

Ghasemifard, Mahdi; Ghamari, Misagh; Okay, Cengiz

2018-01-01

In the current study, ABO3 (A = Pb, Ba, Sr and B = Ti) perovskite structures are produced by the auto-combustion route by using citric acid (CA) and nitric acid (NA) as fuel and oxidizer. The X-ray diffraction (XRD) patterns confirmed the perovskite nanostructure with cubic, tetragonal, and rhombohedral for SrTiO3, PbTiO3, and BaTiO3, respectively. Using Scherrer’s equation and XRD pattern, the average crystallite size of the samples were acquired. The effect of Ti-O bond length on the structure of the samples was evaluated. The type of structures obtained depends on Ti-O bond length which is in turn influenced by A2+ substitutions. Microstructural studies of nanostructures calcined at 850∘C confirmed the formation of polyhedral particles with a narrow size distribution. The values of optical band gaps were measured and the impact of A2+ was discussed. The optical properties such as the complex refractive index and dielectric function were calculated by IR spectroscopy and Kramers-Kronig (K-K) relations. Lead, as the element with the highest density as compared to other elements, changes the optical constants, remarkably due to altering titanium and oxygen distance in TO6 groups.

Crystal structure of fac-tri-chlorido-[tris-(pyridin-2-yl-N)amine]-chromium(III).

PubMed

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol-ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris-(pyridin-2-yl)amine; C15H12N4], the Cr(III) ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa-hedral coordination sphere. The average Cr-N and Cr-Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol-ecule is located on a mirror plane. In the crystal, a combination of C-H⋯N and C-H⋯Cl hydrogen-bonding inter-actions connect the mol-ecules into a three-dimensional network.

Some transition metal complexes derived from mono- and di-ethynyl perfluorobenzenes.

PubMed

Armitt, David J; Bruce, Michael I; Gaudio, Maryka; Zaitseva, Natasha N; Skelton, Brian W; White, Allan H; Le Guennic, Boris; Halet, Jean-François; Fox, Mark A; Roberts, Rachel L; Hartl, Frantisek; Low, Paul J

2008-12-21

Transition metal alkynyl complexes containing perfluoroaryl groups have been prepared directly from trimethylsilyl-protected mono- and di-ethynyl perfluoroarenes by simple desilylation/metallation reaction sequences. Reactions between Me(3)SiC[triple bond, length as m-dash]CC(6)F(5) and RuCl(dppe)Cp' [Cp' = Cp, Cp*] in the presence of KF in MeOH give the monoruthenium complexes Ru(C[triple bond, length as m-dash]CC(6)F(5))(dppe)Cp' [Cp' = Cp (); Cp* ()], which are related to the known compound Ru(C[triple bond, length as m-dash]CC(6)F(5))(PPh(3))(2)Cp (). Treatment of Me(3)SiC[triple bond, length as m-dash]CC(6)F(5) with Pt(2)(mu-dppm)(2)Cl(2) in the presence of NaOMe in MeOH gave the bis(alkynyl) complex Pt(2)(mu-dppm)(2)(C[triple bond, length as m-dash]CC(6)F(5))(2) (). The Pd(0)/Cu(i)-catalysed reactions between Au(C[triple bond, length as m-dash]CC(6)F(5))(PPh(3)) and Mo( identical withCBr)(CO)(2)Tp* [Tp* = hydridotris(3.5-dimethylpyrazoyl)borate], Co(3)(mu(3)-CBr)(mu-dppm)(CO)(7) or IC[triple bond, length as m-dash]CFc [Fc = (eta(5)-C(5)H(4))FeCp] afford Mo( identical withCC[triple bond, length as m-dash]CC(6)F(5))(CO)(2)Tp* (), Co(3)(mu(3)-CC[triple bond, length as m-dash]CC(6)F(5))(mu-dppm)(CO)(7) () and FcC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC(6)F(5) (), respectively. The diruthenium complexes 1,4-{Cp'(PP)RuC[triple bond, length as m-dash]C}(2)C(6)F(4) [(PP)Cp' = (PPh(3))(2)Cp (); (dppe)Cp (); (dppe)Cp* ()] are prepared from 1,4-(Me(3)SiC[triple bond, length as m-dash]C)(2)C(6)F(4) in a manner similar to that described for the monoruthenium complexes -. The non-fluorinated complexes 1,4-{Cp'(PP)RuC[triple bond, length as m-dash]C}(2)C(6)H(4) [(PP)Cp' = (PPh(3))(2)Cp (); (dppe)Cp (); (dppe)Cp* ()], prepared for comparison, are obtained from 1,4-(Me(3)SiC[triple bond, length as m-dash]C)(2)C(6)H(4). Spectro-electrochemical studies of the ruthenium aryl and arylene alkynyl complexes - and -, together with DFT-based computational studies on suitable model systems, indicate that perfluorination of the aromatic ring has little effect on the electronic structures of these compounds, and that the frontier orbitals have appreciable diethynylphenylene character. Molecular structure determinations are reported for the fluoroaromatic complexes , , , and .

Sulfide bonded atomic radii

NASA Astrophysics Data System (ADS)

Gibbs, G. V.; Ross, N. L.; Cox, D. F.

2017-09-01

The bonded radius, r b(S), of the S atom, calculated for first- and second-row non-transition metal sulfide crystals and third-row transition metal sulfide molecules and crystals indicates that the radius of the sulfur atom is not fixed as traditionally assumed, but that it decreases systematically along the bond paths of the bonded atoms with decreasing bond length as observed in an earlier study of the bonded radius of the oxygen atom. When bonded to non-transition metal atoms, r b(S) decreases systematically with decreasing bond length from 1.68 Å when the S atom is bonded to the electropositive VINa atom to 1.25 Å when bonded to the more electronegative IVP atom. In the case of transition metal atoms, rb(S) likewise decreases with decreasing bond length from 1.82 Å when bonded to Cu and to 1.12 Å when bonded to Fe. As r b(S) is not fixed at a given value but varies substantially depending on the bond length and the field strength of the bonded atoms, it is apparent that sets of crystal and atomic sulfide atomic radii based on an assumed fixed radius for the sulfur atom are satisfactory in that they reproduce bond lengths, on the one hand, whereas on the other, they are unsatisfactory in that they fail to define the actual sizes of the bonded atoms determined in terms of the minima in the electron density between the atoms. As such, we urge that the crystal chemistry and the properties of sulfides be studied in terms of the bond lengths determined by adding the radii of either the atomic and crystal radii of the atoms but not in terms of existing sets of crystal and atomic radii. After all, the bond lengths were used to determine the radii that were experimentally determined, whereas the individual radii were determined on the basis of an assumed radius for the sulfur atom.

Origin of the X-Hal (Hal = Cl, Br) bond-length change in the halogen-bonded complexes.

PubMed

Wang, Weizhou; Hobza, Pavel

2008-05-01

The origin of the X-Hal bond-length change in the halogen bond of the X-Hal...Y type has been investigated at the MP2(full)/6-311++G(d,p) level of theory using a natural bond orbital analysis, atoms in molecules procedure, and electrostatic potential fitting methods. Our results have clearly shown that various theories explaining the nature of the hydrogen bond cannot be applied to explain the origin of the X-Hal bond-length change in the halogen bond. We provide a new explanation for this change. The elongation of the X-Hal bond length is caused by the electron-density transfer to the X-Hal sigma* antibonding orbital. For the blue-shifting halogen bond, the electron-density transfer to the X-Hal sigma* antibonding orbital is only of minor importance; it is the electrostatic attractive interaction that causes the X-Hal bond contraction.

Pi Bond Orders and Bond Lengths

ERIC Educational Resources Information Center

Herndon, William C.; Parkanyi, Cyril

1976-01-01

Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

[1,3-Bis(diphenyl-phosphino)pentane-κP,P']tetra-carbonyl-chromium(0).

PubMed

Shawkataly, Omar Bin; Thangadurai, Daniel T; Pankhi, Mohd Aslam A; Shahinoor Dulal Islam, S M; Fun, Hoong-Kun

2009-02-04

In the title compound, [Cr(C(29)H(30)P(2))(CO)(4)], the Cr atom is octa-hedrally coordinated by four carbonyl ligands and one bidentate phosphine ligand, which is bounded as a chelate in a cis position. The average Cr-P and Cr-C bond lengths are 2.377 and 1.865 Å, respectively.

Development of a QSAR model for predicting aqueous reaction rate constants of organic chemicals with hydroxyl radicals.

PubMed

Luo, Xiang; Yang, Xianhai; Qiao, Xianliang; Wang, Ya; Chen, Jingwen; Wei, Xiaoxuan; Peijnenburg, Willie J G M

2017-03-22

Reaction with hydroxyl radicals (˙OH) is an important removal pathway for organic pollutants in the aquatic environment. The aqueous reaction rate constant (k OH ) is therefore an important parameter for fate assessment of aquatic pollutants. Since experimental determination fails to meet the requirement of being able to efficiently handle numerous organic chemicals at limited cost and within a relatively short period of time, in silico methods such as quantitative structure-activity relationship (QSAR) models are needed to predict k OH . In this study, a QSAR model with a larger and wider applicability domain as compared with existing models was developed. Following the guidelines for the development and validation of QSAR models proposed by the Organization for Economic Co-operation and Development (OECD), the model shows satisfactory performance. The applicability domain of the model has been extended and contained chemicals that have rarely been covered in most previous studies. The chemicals covered in the current model contain functional groups including [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right], -C[triple bond, length as m-dash]C-, -C 6 H 5 , -OH, -CHO, -O-, [double bond splayed left]C[double bond, length as m-dash]O, -C[double bond, length as m-dash]O(O)-, -COOH, -C[triple bond, length as m-dash]N, [double bond splayed left]N-, -NH 2 , -NH-C(O)-, -NO 2 , -N[double bond, length as m-dash]C-N[double bond splayed right], [double bond splayed left]N-N[double bond splayed right], -N[double bond, length as m-dash]N-, -S-, -S-S-, -SH, -SO 3 , -SO 4 , -PO 4 , and -X (F, Cl, Br, and I).

Bis[μ-N-(tert-butyl­dimethyl­silyl)-N-(pyridin-2-ylmeth­yl)amido]­bis­[methyl­cobalt(II)

PubMed Central

Malassa, Astrid; Agthe, Christine; Görls, Helmar; Westerhausen, Matthias

2012-01-01

The green title complex, [Co2(CH3)2(C12H21N2Si)2], was obtained from bis­{[μ-N-tert-butyl­dimethyl­silyl-N-(pyridin-2-ylmeth­yl)amido]­chloridocobalt(II)} and methyl­lithium in diethyl ether at 195 K via a metathesis reaction. The dimeric cobalt(II) complex exhibits a crystallographic center of inversion in the middle of the Co2N2 ring (average Co—N = 2.050 Å). The CoII atom shows a distorted tetra­hedral coordination sphere. The exocyclic Co—N bond length to the pyridyl group shows a similar value of 2.045 (4) Å. The exocyclic methyl group has a rather long Co—C bond length of 2.019 (5) Å. PMID:22969464

The influence of plain bar on bond strength of geopolymer concrete

NASA Astrophysics Data System (ADS)

Dewi, Evrianti Syntia; Ekaputri, Januarti Jaya

2017-06-01

This paper presents some results of experimental study of bond strength of plain bar embedded in geopolymer concrete. Fly ash class F was used as a raw material activated with alkali solutions. The combination of 8 Molar of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as alkali activators was examined in the mixture with ratio of 2.5 by weight. Nine cubical specimens with a size of 150 × 150 × 150 mm were prepared to measure bond strength and slip between reinforcement and concrete. The influential factors studied for the experimental investigation were the diameter of reinforcement bar, bond area, and concrete cover to diameter (c/d) of reinforcement. The result showed that the average bond strength decreased as the diameter of plain bar and bonded length were increased from 16 mm to 19 mm. However, the 12 mm showed the different result allegedly caused by the effect of bond area and the passive confined provided by the concrete. Based on several equations used to compare the bond strength, it is clear that deformed bar of 12 mm in diameter is potential to increase the bond strength.

Test and analysis of Celion 3000/PMR-15, graphite/polyimide bonded composite joints: Data report

NASA Technical Reports Server (NTRS)

Cushman, J. B.; Mccleskey, S. F.; Ward, S. H.

1982-01-01

Standard single lap, double lap and symmetric step lap bonded joints of Celion 3000/PMR-15 graphite/polyimide composite were evaluated. Composite to composite and composite to titanium joints were tested at 116 K (-250 F), 294 K (70 F) and 561 K (550 F). Joint parameters evaluated are lap length, adherend thickness, adherend axial stiffness, lamina stacking sequence and adherend tapering. Advanced joint concepts were examined to establish the change in performance of preformed adherends, scalloped adherends and hybrid systems. The material properties of the high temperature adhesive, designated A7F, used for bonding were established. The bonded joint tests resulted in interlaminar shear or peel failures of the composite and there were very few adhesive failures. Average test results agree with expected performance trends for the various test parameters. Results of finite element analyses and of test/analysis correlations are also presented.

Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals.

PubMed

Gagné, Olivier Charles; Hawthorne, Frank Christopher

2016-08-01

Bond-length distributions have been examined for 55 configurations of alkali-metal ions and 29 configurations of alkaline-earth-metal ions bonded to oxygen, for 4859 coordination polyhedra and 38 594 bond distances (alkali metals), and for 3038 coordination polyhedra and 24 487 bond distances (alkaline-earth metals). Bond lengths generally show a positively skewed Gaussian distribution that originates from the variation in Born repulsion and Coulomb attraction as a function of interatomic distance. The skewness and kurtosis of these distributions generally decrease with increasing coordination number of the central cation, a result of decreasing Born repulsion with increasing coordination number. We confirm the following minimum coordination numbers: ([3])Li(+), ([3])Na(+), ([4])K(+), ([4])Rb(+), ([6])Cs(+), ([3])Be(2+), ([4])Mg(2+), ([6])Ca(2+), ([6])Sr(2+) and ([6])Ba(2+), but note that some reported examples are the result of extensive dynamic and/or positional short-range disorder and are not ordered arrangements. Some distributions of bond lengths are distinctly multi-modal. This is commonly due to the occurrence of large numbers of structure refinements of a particular structure type in which a particular cation is always present, leading to an over-representation of a specific range of bond lengths. Outliers in the distributions of mean bond lengths are often associated with anomalous values of atomic displacement of the constituent cations and/or anions. For a sample of ([6])Na(+), the ratio Ueq(Na)/Ueq(bonded anions) is partially correlated with 〈([6])Na(+)-O(2-)〉 (R(2) = 0.57), suggesting that the mean bond length is correlated with vibrational/displacement characteristics of the constituent ions for a fixed coordination number. Mean bond lengths also show a weak correlation with bond-length distortion from the mean value in general, although some coordination numbers show the widest variation in mean bond length for zero distortion, e.g. Li(+) in [4]- and [6]-coordination, Na(+) in [4]- and [6]-coordination. For alkali-metal and alkaline-earth-metal ions, there is a positive correlation between cation coordination number and the grand mean incident bond-valence sum at the central cation, the values varying from 0.84 v.u. for ([5])K(+) to 1.06 v.u. for ([8])Li(+), and from 1.76 v.u. for ([7])Ba(2+) to 2.10 v.u. for ([12])Sr(2+). Bond-valence arguments suggest coordination numbers higher than [12] for K(+), Rb(+), Cs(+) and Ba(2+).

Role of Hydrogen Bonding on Nonlinear Mechano-Optical Behavior of L-Phenylalanine-based Poly(ester urea)s.

NASA Astrophysics Data System (ADS)

Chen, Keke; Yu, Jiayi; Guzman, Gustavo; Es-Haghi, S. Shams; Becker, Matthew L.; Cakmak, Miko

The uniaxial mechano-optical behavior of a series of amorphous L-phenylalanine-based poly(ester urea) (PEU) films was studied in the rubbery state using a custom real-time measurement system. When the materials were subjected to deformation at temperatures near the glass transition temperature (Tg) , the photoelastic behavior was manifested by a small increase in birefringence with a significant increase in true stress. At temperatures above Tg, PEUs with a shorter diol chain length exhibited a liquid-liquid (Tll) transition at about 1.06 Tg (K), above which the material transforms from a heterogeneous ``liquid of fixed-structure'' to a ``true liquid'' state. The initial photoelastic behavior disappears with increasing temperature, as the initial slope of the stress optical curves becomes temperature independent. Fourier transform infrared spectra of PEUs revealed that the average strength of hydrogen bonding diminishes with increasing temperature. For PEUs with the longest diol chain length, the area associated with N-H stretching region exhibits a linear temperature dependence. The presence of hydrogen bonding enhances the ``stiff'' segmental correlations between adjacent chains in the PEU structure. As a result, the photoelastic constant decreases with increasing hydrogen bonding strength. This work was supported by the Ohio Department of Development's Innovation Platform Program and The National Science Foundation.

Cholesterol oxidase: ultrahigh-resolution crystal structure and multipolar atom model-based analysis.

PubMed

Zarychta, Bartosz; Lyubimov, Artem; Ahmed, Maqsood; Munshi, Parthapratim; Guillot, Benoît; Vrielink, Alice; Jelsch, Christian

2015-04-01

Examination of protein structure at the subatomic level is required to improve the understanding of enzymatic function. For this purpose, X-ray diffraction data have been collected at 100 K from cholesterol oxidase crystals using synchrotron radiation to an optical resolution of 0.94 Å. After refinement using the spherical atom model, nonmodelled bonding peaks were detected in the Fourier residual electron density on some of the individual bonds. Well defined bond density was observed in the peptide plane after averaging maps on the residues with the lowest thermal motion. The multipolar electron density of the protein-cofactor complex was modelled by transfer of the ELMAM2 charge-density database, and the topology of the intermolecular interactions between the protein and the flavin adenine dinucleotide (FAD) cofactor was subsequently investigated. Taking advantage of the high resolution of the structure, the stereochemistry of main-chain bond lengths and of C=O···H-N hydrogen bonds was analyzed with respect to the different secondary-structure elements.

Correlation of the bond-length change and vibrational frequency shift in model hydrogen-bonded complexes of pyrrole

NASA Astrophysics Data System (ADS)

McDowell, Sean A. C.

2017-04-01

An MP2 computational study of model hydrogen-bonded pyrrole⋯YZ (YZ = NH3, NCH, BF, CO, N2, OC, FB) complexes was undertaken in order to examine the variation of the Nsbnd H bond length change and its associated vibrational frequency shift. The chemical hardness of Y, as well as the YZ dipole moment, were found to be important parameters in modifying the bond length change/frequency shift. The basis set effect on the computed properties was also assessed. A perturbative model, which accurately reproduced the ab initio Nsbnd H bond length changes and frequency shifts, was useful in rationalizing the observed trends.

Zn Coordination Chemistry:  Development of Benchmark Suites for Geometries, Dipole Moments, and Bond Dissociation Energies and Their Use To Test and Validate Density Functionals and Molecular Orbital Theory.

PubMed

Amin, Elizabeth A; Truhlar, Donald G

2008-01-01

We present nonrelativistic and relativistic benchmark databases (obtained by coupled cluster calculations) of 10 Zn-ligand bond distances, 8 dipole moments, and 12 bond dissociation energies in Zn coordination compounds with O, S, NH3, H2O, OH, SCH3, and H ligands. These are used to test the predictions of 39 density functionals, Hartree-Fock theory, and seven more approximate molecular orbital theories. In the nonrelativisitic case, the M05-2X, B97-2, and mPW1PW functionals emerge as the most accurate ones for this test data, with unitless balanced mean unsigned errors (BMUEs) of 0.33, 0.38, and 0.43, respectively. The best local functionals (i.e., functionals with no Hartree-Fock exchange) are M06-L and τ-HCTH with BMUEs of 0.54 and 0.60, respectively. The popular B3LYP functional has a BMUE of 0.51, only slightly better than the value of 0.54 for the best local functional, which is less expensive. Hartree-Fock theory itself has a BMUE of 1.22. The M05-2X functional has a mean unsigned error of 0.008 Å for bond lengths, 0.19 D for dipole moments, and 4.30 kcal/mol for bond energies. The X3LYP functional has a smaller mean unsigned error (0.007 Å) for bond lengths but has mean unsigned errors of 0.43 D for dipole moments and 5.6 kcal/mol for bond energies. The M06-2X functional has a smaller mean unsigned error (3.3 kcal/mol) for bond energies but has mean unsigned errors of 0.017 Å for bond lengths and 0.37 D for dipole moments. The best of the semiempirical molecular orbital theories are PM3 and PM6, with BMUEs of 1.96 and 2.02, respectively. The ten most accurate functionals from the nonrelativistic benchmark analysis are then tested in relativistic calculations against new benchmarks obtained with coupled-cluster calculations and a relativistic effective core potential, resulting in M05-2X (BMUE = 0.895), PW6B95 (BMUE = 0.90), and B97-2 (BMUE = 0.93) as the top three functionals. We find significant relativistic effects (∼0.01 Å in bond lengths, ∼0.2 D in dipole moments, and ∼4 kcal/mol in Zn-ligand bond energies) that cannot be neglected for accurate modeling, but the same density functionals that do well in all-electron nonrelativistic calculations do well with relativistic effective core potentials. Although most tests are carried out with augmented polarized triple-ζ basis sets, we also carried out some tests with an augmented polarized double-ζ basis set, and we found, on average, that with the smaller basis set DFT has no loss in accuracy for dipole moments and only ∼10% less accurate bond lengths.

Bond Strength of Composite CFRP Reinforcing Bars in Timber

PubMed Central

Corradi, Marco; Righetti, Luca; Borri, Antonio

2015-01-01

The use of near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars is an interesting method for increasing the shear and flexural strength of existing timber members. This article examines the behaviour of carbon FRP (CFRP) bars in timber under direct pull-out conditions. The objective of this experimental program is to investigate the bond strength between composite bars and timber: bars were epoxied into small notches made into chestnut and fir wood members using a commercially-available epoxy system. Bonded lengths varied from 150 to 300 mm. Failure modes, stress and strain distributions and the bond strength of CFRP bars have been evaluated and discussed. The pull-out capacity in NSM CFRP bars at the onset of debonding increased with bonded length up to a length of 250 mm. While CFRP bar’s pull-out was achieved only for specimens with bonded lengths of 150 and 200 mm, bar tensile failure was mainly recorded for bonded lengths of 250 and 300 mm. PMID:28793423

Identification of the formation of metal-vinylidene interfacial bonds of alkyne-capped platinum nanoparticles by isotopic labeling.

PubMed

Hu, Peiguang; Chen, Limei; Deming, Christopher P; Bonny, Lewis W; Lee, Hsiau-Wei; Chen, Shaowei

2016-10-07

Stable platinum nanoparticles were prepared by the self-assembly of 1-dodecyne and dodec-1-deuteroyne onto bare platinum colloid surfaces. The nanoparticles exhibited consistent core size and optical properties. FTIR and NMR measurements confirmed the formation of Pt-vinylidene (Pt[double bond, length as m-dash]C[double bond, length as m-dash]CH-) interfacial linkages rather than Pt-acetylide (Pt-C[triple bond, length as m-dash]C-) and platinum-hydride (Pt-H) bonds.

The series of carbon-chain complexes {Ru(dppe)Cp*}₂{μ-(C≡C )x} (x = 4–8, 11): Synthesis, structures, properties and some reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruce, Michael I.; Cole, Marcus L.; Ellis, Benjamin G.

The construction of a series of compounds {Ru(dppe)Cp*} 2(μ-C 2x) (Ru*-C2x-Ru*, x = 4–8, 11)) is described. A direct reaction between RuCl(dppe)Cp* and Me 3Si(Ctriple bond; length of mdashC) 4SiMe 3 afforded Ru*-C8-Ru* in 89% yield. The Pd(0)/Cu(I)-catalysed coupling of Ru{Ctriple bond; length of mdashCCtriple bond; length of mdashCAu(PPh 3)}(dppe)Cp*Ru*-C4-Au (2 equiv.) with diiodoethyne gave Ru*-C10-Ru* (64%), or of 1 equiv. with I(Ctriple bond; length of mdashC) 3I gave Ru*-C14-Ru* (36%); similarly, Ru{(Ctriple bond; length of mdashC) 4Au(PPh 3)}(dppe)Cp*Ru*-C8-Au and I(Ctriple bond; length of mdashC) 3I gave Ru*-C22-Ru* (12%). Desilylation (TBAF) of Ru{(Ctriple bond; length of mdashC)xSiMe 3}(dppe)Cp*Ru*-C2x-Si (x =more » 3, 4) followed by oxidative coupling [Cu(OAc) 2/py] gave Ru*-C12-Ru* (82%) and Ru*-C16-Ru* (58%), respectively. Similar oxidative coupling of Ru(Ctriple bond; length of mdashCCtriple bond; length of mdashCH)(dppe)Cp* was a second route to Ru*-C8-Ru* (82%). Appropriate precursors are already known, or obtained by coupling of Ru*-C2x-Si (x = 2, 4) with AuCl(PPh 3)/NaOMe [Ru*-C4-Au, 95%; Ru*-C8-Au, 74%] or from Pd(0)/Cu(I) catalysed coupling of Ru*-C2x-Au (x = 2, 3) with I(Ctriple bond; length of mdashC) 2SiMe 3 (Ru*-C8-Si, 64%; Ru*-C10-Si, 2%). Reactions between Ru*-C2x-Ru* (x = 3, 4) and Fe 2(CO) 9 gave {Fe 3(CO) 9}{μ 3-CCtriple bond; length of mdashC[Ru(dppe)Cp*]} 2Fe(C 3-Ru*) 2 and {Fe 3(CO) 9}{μ 3-CCtriple bond; length of mdashC[Ru(dppe)Cp*]}{μ 3-C(Ctriple bond; length of mdashC) 2[Ru(dppe)Cp*]} Fe(C 3-Ru*)(C 5-Ru*), respectively. The redox properties of the series of complexes with 2x = 2–16 were measured and showed a diminution of the separation of the first two oxidation potentials, ΔE = E 2 - E 1, with increasing carbon chain length. The X-ray-determined molecular structures of Ru*-C8-Si, Ru*-C8-Ru*, Ru*-C14-Ru* (two C 6H 6 solvates), {Ru(PPh 3) 2Cp} 2{μ-(Ctriple bond; length of mdashC) 4}·4CHCl 3Ru-C 8-Ru·4CHCl 3 and of Fe(C 3-Ru*) 2 and Fe(C 3-Ru*)(C 5-Ru*) are reported.« less

A molecular scale perspective: Monte Carlo simulation for rupturing of ultra thin polymer film melts

NASA Astrophysics Data System (ADS)

Singh, Satya Pal

2017-04-01

Monte Carlo simulation has been performed to study the rupturing process of thin polymer film under strong confinement. The change in mean square displacement; pair correlation function; density distribution; average bond length and microscopic viscosity are sampled by varying the molecular interaction parameters such as the strength and the equilibrium positions of the bonding, non-bonding potentials and the sizes of the beads. The variation in mean square angular displacement χθ = [ < Δθ2 > - < Δθ>2 ] fits very well to a function of type y (t) = A + B *e-t/τ. This may help to study the viscous properties of the films and its dependence on different parameters. The ultra thin film annealed at high temperature gets ruptured and holes are created in the film mimicking spinodal dewetting. The pair correlation function and density profile reveal rich information about the equilibrium structure of the film. The strength and equilibrium bond length of finite extensible non-linear elastic potential (FENE) and non-bonding Morse potential have clear impact on microscopic rupturing of the film. The beads show Rouse or repetition motion forming rim like structures near the holes created inside the film. The higher order interaction as dipole-quadrupole may get prominence under strong confinement. The enhanced excluded volume interaction under strong confinement may overlap with the molecular dispersion forces. It can work to reorganize the molecules at the bottom of the scale and can imprint its signature in complex patterns evolved.

Formation of unexpected silicon- and disiloxane-bridged multiferrocenyl derivatives bearing Si-O-CH[double bond, length as m-dash]CH2 and Si-(CH2)2C(CH3)3 substituents via cleavage of tetrahydrofuran and trapping of its ring fragments.

PubMed

Bruña, Sonia; González-Vadillo, Ana Mª; Ferrández, Marta; Perles, Josefina; Montero-Campillo, M Merced; Mó, Otilia; Cuadrado, Isabel

2017-09-12

The formation of a family of silicon- and siloxane-bridged multiferrocenyl derivatives carrying different functional groups attached to silicon, including Fc 2 (CH 3 ) 3 C(CH 2 ) 2 SiCH[double bond, length as m-dash]CH 2 (5), Fc 2 (CH 2 [double bond, length as m-dash]CH-O)SiCH[double bond, length as m-dash]CH 2 (6), Fc 2 (OH)SiCH[double bond, length as m-dash]CH 2 (7), Fc 2 (CH 2 [double bond, length as m-dash]CH-O)Si-O-Si(O-CH[double bond, length as m-dash]CH 2 )Fc 2 (8) and Fc 2 (CH 2 [double bond, length as m-dash]CH-O)Si-O-SiFc 3 (9) is described. Silyl vinyl ether molecules 6, 8 and 9 and the heteroleptic vinylsilane 5 resulted from the competing metathesis reaction of lithioferrocene (FcLi), CH 2 [double bond, length as m-dash]CH-OLi or (CH 3 ) 3 C(CH 2 ) 2 Li with the corresponding multifunctional chlorosilane, Cl 3 SiCH[double bond, length as m-dash]CH 2 or Cl 3 Si-O-SiCl 3 . The last two organolithium species have been likely formed in situ by fragmentation of the tetrahydrofuran solvent. Diferrocenylvinyloxyvinylsilane 6 is noteworthy since it represents a rare example of a redox-active silyl mononomer in which two different C[double bond, length as m-dash]C polymerisable groups are directly connected to silicon. The molecular structures of the silicon-containing multiferrocenyl species 5, 6, 8 and 9 have been investigated by single-crystal X-ray diffraction studies, demonstrating the capture and storage processes of two ring fragments resulting from the cleavage of cyclic THF in redox-active and stable crystalline organometallic compounds. From electrochemical studies we found that by changing the anion of the supporting electrolyte from [PF 6 ] - to [B(C 6 F 5 ) 4 ] - , the redox behaviour of tetrametallic disiloxane 8 can be switched from a poorly resolved multistep redox process to four consecutive well-separated one-electron oxidations, corresponding to the sequential oxidation of the four ferrocenyl moieties.

Cis Effects in the Cobalt Corrins. 1. Crystal Structures of 10-Chloroaquacobalamin Perchlorate, 10-Chlorocyanocobalamin, and 10-Chloromethylcobalamin.

PubMed

Brown, Kenneth L.; Cheng, Shifa; Zou, Xiang; Zubkowski, Jeffrey D.; Valente, Edward J.; Knapton, Leanne; Marques, Helder M.

1997-08-13

The crystal structures of 10-chloroaquacobalamin perchlorate hydrate (10-Cl-H(2)OCbl.ClO(4)) (Mo Kalpha, 0.710 73 Å, monoclinic system, P2(1), a = 11.922(4) Å, b = 26.592(10) Å, c = 13.511(5) Å, beta = 93.05(3) degrees, 10 535 independent reflections, R(1) = 0.0426), 10-chlorocyanocobalamin-acetone hydrate (10-Cl-CNCbl) (Mo Kalpha, 0.710 73 Å, orthorhombic system, P2(1)2(1)2(1), a = 16.24(3) Å, b = 21.85(5) Å, c = 26.75(8) Å, 7699 independent reflections, R(1) = 0.0698), and 10-chloromethylcobalamin-acetone hydrate (10-Cl-MeCbl) (Mo Kalpha, 0.71073 Å, orthorhombic system, P2(1)2(1)2(1), a = 16.041(14) Å, b = 22.13(2) Å, c = 26.75(4) Å, 6792 independent reflections, R(1) = 0.0554), in which the C10 meso H is substituted by Cl, are reported. An unusual feature of the structures is disorder in the C ring, consistent with a two-site occupancy in which the major conformation has the C46 methyl group in the usual position, "upwardly" axial, and the C47 methyl group equatorial, while in the minor conformation both are pseudoequatorial, above and below the corrin ring. (13)C NMR chemical shifts of C46, C47, C12, and C13 suggest that the C ring disorder may persist in solution as a ring flip. Since molecular dynamics simulations fail to reveal any population of the minor conformation, the effect is likely to be electronic rather than steric. The axial bond lengths in 10-Cl-MeCbl are very similar to those in MeCbl (d(Co)(-)(C) = 1.979(7) vs 1.99(2); to 5,6-dimethylbenzimidazole, d(Co)(-)(NB3) = 2.200(7) vs 2.19(2)), but the bonds to the four equatorial N donors, d(Co)(-)(N(eq)), are on average 0.05 Å shorter. In 10-Cl-CNCbl, d(Co)(-)(C) and d(Co)(-)(NB3) are longer (by 0.10(2) and 0.03(1) Å, respectively) than the bond lengths observed in CNCbl itself, while conversely, the C-N bond length is shorter by 0.06(2) Å, but there is little difference in d(Co)(-)(N(eq)). The Co-O bond length to coordinated water in 10-Cl-H(2)OCbl(+) is very similar to that found in H(2)OCbl(+) itself, but the d(Co)(-)(NB3) bond is longer (1.967 vs1.925(2) Å), while the average d(Co)(-)(N(eq)) is very similar. The coordinated water molecule in 10-Cl-H(2)OCbl(+) is hydrogen bonded to the c side chain carbonyl oxygen, as in H(2)OCbl(+). NMR observations indicate that the H bond between coordinated H(2)O and the c side chain amide persists in solution. The equilibrium constant, K(Co), for coordination of bzm to Co(III) is smaller in 10-Cl-MeCbl and 10-Cl-CNCbl than in their C10-unsubstituted analogs (181 vs 452; 4.57 x 10(3) vs 3.35 x 10(5)), but could not be determined for 10-Cl-H(2)OCbl because hydrolysis of the phosphodiester is competitive with the establishment of the base-off equilibrium. Substitution of H by Cl at C10 causes the bands in the electronic spectrum of 10-Cl-XCbl complexes to move to lower energy, which is consistent with an increase in electron density in the corrin pi-conjugated system. This increased electron density is not due to greater electron donation from the axial ligand as bonds between these and the metal are either longer (not shorter) or unchanged, and it most probably arises from pi-donation to the corrin by Cl at C10. As the donor power of X increases (H(2)O < CN(-) < Me), the corrin ring becomes more flexible to deformation, and the number of bond lengths and bond angles that are significantly different in XCbl and 10-Cl-XCbl increases; importantly, the C10-Cl bond length, d(C10)(-)(Cl), increases as well. Thus, despite the fact that chlorine is an inductively electron withdrawing substituent, its resonance electron donation is the more important effect on electron distribution in the corrin ring. Mulliken charges obtained from semiempirical RHF-SCF MO calculations using the ZINDO/1 model on XCbl and their 10-Cl analogs at the crystal structure geometry are shown to correlate reasonably well with (13)C NMR shifts and may be used to determine the pattern of electron distribution in these complexes. Substitution by Cl at C10 causes an increase in charge density at Co when X = H(2)O and CN(-), while the charge density on the four equatorial N donors remains virtually unchanged, but a decrease when X = Me, while the charge density on the equatorial N donors also decreases. In response, d(Co)(-)(NB3) increases in the first two complexes but the equatorial bond lengths remain virtually unchanged, while d(Co)(-)(NB3) remains unchanged and the average d(Co)(-)(N(eq)) decreases in 10-Cl-MeCbl. Furthermore, the partial charge on chlorine increases as the donor power of X increases. The small decrease in the pK(a) of coordinated H(2)O in 10-Cl-H(2)OCbl(+) compared to H(2)OCbl(+) itself (7.65 vs 8.09) is due to a decreased charge density on oxygen in 10-Cl-OHCbl compared to OHCbl. The picture that emerges, therefore, is of competitive electron donation by X and Cl toward the corrin system. In 10-Cl-CNCbl, the decrease in the C&tbd1;N bond length as Co-C increases compared to CNCbl suggests that dpi-ppi bonding between cobalt and cyanide is important. (13)C and (15)N NMR observations on 10-Cl-(13)C(15)NCbl are consistent with these effects.

[1,3-Bis(diphenyl­phosphino)pentane-κ2 P,P′]tetra­carbonyl­chromium(0)

PubMed Central

Shawkataly, Omar bin; Thangadurai, Daniel T.; Pankhi, Mohd. Aslam A.; Shahinoor Dulal Islam, S. M.; Fun, Hoong-Kun

2009-01-01

In the title compound, [Cr(C29H30P2)(CO)4], the Cr atom is octa­hedrally coordinated by four carbonyl ligands and one bidentate phosphine ligand, which is bounded as a chelate in a cis position. The average Cr—P and Cr—C bond lengths are 2.377 and 1.865 Å, respectively. PMID:21582044

Crystal structure of fac-tri­chlorido­[tris­(pyridin-2-yl-N)amine]­chromium(III)

PubMed Central

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol­ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris­(pyridin-2-yl)amine; C15H12N4], the CrIII ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa­hedral coordination sphere. The average Cr—N and Cr—Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol­ecule is located on a mirror plane. In the crystal, a combination of C—H⋯N and C—H⋯Cl hydrogen-bonding inter­actions connect the mol­ecules into a three-dimensional network. PMID:25705455

Sensitivity of hydrogen bonds of DNA and RNA to hydration, as gauged by 1JNH measurements in ethanol-water mixtures.

PubMed

Manalo, Marlon N; Kong, Xiangming; LiWang, Andy

2007-04-01

Hydrogen-bond lengths of nucleic acids are (1) longer in DNA than in RNA, and (2) sequence dependent. The physicochemical basis for these variations in hydrogen-bond lengths is unknown, however. Here, the notion that hydration plays a significant role in nucleic acid hydrogen-bond lengths is tested. Watson-Crick N1...N3 hydrogen-bond lengths of several DNA and RNA duplexes are gauged using imino 1J(NH) measurements, and ethanol is used as a cosolvent to lower water activity. We find that 1J(NH) values of DNA and RNA become less negative with added ethanol, which suggests that mild dehydration reduces hydrogen-bond lengths even as the overall thermal stabilities of these duplexes decrease. The 1J(NH) of DNA are increased in 8 mol% ethanol to those of RNA in water, which suggests that the greater hydration of DNA plays a significant role in its longer hydrogen bonds. The data also suggest that ethanol-induced dehydration is greater for the more hydrated G:C base pairs and thereby results in greater hydrogen-bond shortening than for the less hydrated A:T/U base pairs of DNA and RNA.

Sacrificial bonds and hidden length in biomaterials -- a kinetic description of strength and toughness in bone

NASA Astrophysics Data System (ADS)

Lieou, Charles K. C.; Elbanna, Ahmed E.; Carlson, Jean M.

2013-03-01

Sacrificial bonds and hidden length in structural molecules account for the greatly increased fracture toughness of biological materials compared to synthetic materials without such structural features, by providing a molecular-scale mechanism of energy dissipation. One example of occurrence of sacrificial bonds and hidden length is in the polymeric glue connection between collagen fibrils in animal bone. In this talk, we propose a simple kinetic model that describes the breakage of sacrificial bonds and the revelation of hidden length, based on Bell's theory. We postulate a master equation governing the rates of bond breakage and formation, at the mean-field level, allowing for the number of bonds and hidden lengths to take up non-integer values between successive, discrete bond-breakage events. This enables us to predict the mechanical behavior of a quasi-one-dimensional ensemble of polymers at different stretching rates. We find that both the rupture peak heights and maximum stretching distance increase with the stretching rate. In addition, our theory naturally permits the possibility of self-healing in such biological structures.

The effect of redox-active cyanomanganese(I) ligands on intramolecular electron transfer to, and alkyne alignment in, M(CO)(RC[triple bond, length as m-dash]CR)Tp' (M = Mo or W) units.

PubMed

Adams, Christopher J; Connelly, Neil G; Onganusorn, Sriwipha

2009-04-28

The complexes [(eta-C(5)Me(5))(ON)LMn(micro-CN)M(CO)(RC[triple bond, length as m-dash]CR)Tp'](+) (L = CNXyl, M = Mo; L = CNBu(t), M = Mo or W, R = Ph or Me) and trans- or cis-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-CN)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+), and their linkage isomers [(eta-C(5)Me(5))(ON)LMn(micro-NC)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+) and trans- or cis-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+), undergo two one-electron oxidations. The complexes [(eta-C(5)Me(5))(ON)LMn(micro-XY)M(CO)(RC[triple bond, length as m-dash]CR)Tp'](+) (XY = CN or NC) are oxidised first at the N-bound metal centre and then at the C-bound centre. For [(dppm){(EtO)(3)P}(OC)(2)Mn(micro-XY)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+), the trans isomers are first oxidised at manganese whereas the cis isomers are first oxidised at M. Thus, the order of one-electron oxidation of the two series of binuclear monocations is influenced by linkage isomerisation of the cyanide bridge and cis-trans isomerisation of the Mn(CO)(2) group. IR spectroscopic changes on reaction of Ag(+) with [(eta-C(5)Me(5))(ON)(Bu(t)NC)Mn(micro-CN)W(CO)(MeC[triple bond, length as m-dash]CMe)Tp'](+) are consistent with one-electron at the N-bound tungsten centre. Likewise, trans-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+) (M = Mo or W) give the stable dications [(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)M(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](2+). Significantly longer Mn-P bond distances in trans-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)Mo(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](2+) than in trans-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)Mo(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+) are consistent with one-electron oxidation first at Mn(I); the alignment of the (CN)Mn(CO)(2){P(OEt)(3)}(dppm) fragment relative to the alkyne in trans-[(dppm){(EtO)(3)P}(OC)(2)Mn(micro-NC)Mo(CO)(PhC[triple bond, length as m-dash]CPh)Tp'](+) suggests it acts as a pi-acceptor, in contrast to related species such as trans-(NC)Mn(CO)(2){P(OEt)(3)}(dppm) and (NC)Mn(NO){P(OPh)(3)}(pi-C(5)H(4)Me) which behave as simple N-donors.

Driving force for hydrophobic interaction at different length scales.

PubMed

Zangi, Ronen

2011-03-17

We study by molecular dynamics simulations the driving force for the hydrophobic interaction between graphene sheets of different sizes down to the atomic scale. Similar to the prediction by Lum, Chandler, and Weeks for hard-sphere solvation [J. Phys. Chem. B 1999, 103, 4570-4577], we find the driving force to be length-scale dependent, despite the fact that our model systems do not exhibit dewetting. For small hydrophobic solutes, the association is purely entropic, while enthalpy favors dissociation. The latter is demonstrated to arise from the enhancement of hydrogen bonding between the water molecules around small hydrophobes. On the other hand, the attraction between large graphene sheets is dominated by enthalpy which mainly originates from direct solute-solute interactions. The crossover length is found to be inside the range of 0.3-1.5 nm(2) of the surface area of the hydrophobe that is eliminated in the association process. In the large-scale regime, different thermodynamic properties are scalable with this change of surface area. In particular, upon dimerization, a total and a water-induced stabilization of approximately 65 and 12 kJ/mol/nm(2) are obtained, respectively, and on average around one hydrogen bond is gained per 1 nm(2) of graphene sheet association. Furthermore, the potential of mean force between the sheets is also scalable except for interplate distances smaller than 0.64 nm which corresponds to the region around the barrier for removing the last layer of water. It turns out that, as the surface area increases, the relative height of the barrier for association decreases and the range of attraction increases. It is also shown that, around small hydrophobic solutes, the lifetime of the hydrogen bonds is longer than in the bulk, while around large hydrophobes it is the same. Nevertheless, the rearrangement of the hydrogen-bond network for both length-scale regimes is slower than in bulk water. © 2011 American Chemical Society

Monte Carlo Simulation of Endlinking Oligomers

NASA Technical Reports Server (NTRS)

Hinkley, Jeffrey A.; Young, Jennifer A.

1998-01-01

This report describes initial efforts to model the endlinking reaction of phenylethynyl-terminated oligomers. Several different molecular weights were simulated using the Bond Fluctuation Monte Carlo technique on a 20 x 20 x 20 unit lattice with periodic boundary conditions. After a monodisperse "melt" was equilibrated, chain ends were linked whenever they came within the allowed bond distance. Ends remained reactive throughout, so that multiple links were permitted. Even under these very liberal crosslinking assumptions, geometrical factors limited the degree of crosslinking. Average crosslink functionalities were 2.3 to 2.6; surprisingly, they did not depend strongly on the chain length. These results agreed well with the degrees of crosslinking inferred from experiment in a cured phenylethynyl-terminated polyimide oligomer.

Bond length variation in Zn substituted NiO studied from extended X-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Singh, S. D.; Poswal, A. K.; Kamal, C.; Rajput, Parasmani; Chakrabarti, Aparna; Jha, S. N.; Ganguli, Tapas

2017-06-01

Bond length behavior for Zn substituted NiO is determined through extended x-ray absorption fine structure (EXAFS) measurements performed at ambient conditions. We report bond length value of 2.11±0.01 Å for Zn-O of rock salt (RS) symmetry, when Zn is doped in RS NiO. Bond length for Zn substituted NiO RS ternary solid solutions shows relaxed behavior for Zn-O bond, while it shows un-relaxed behavior for Ni-O bond. These observations are further supported by first-principles calculations. It is also inferred that Zn sublattice remains nearly unchanged with increase in lattice parameter. On the other hand, Ni sublattice dilates for Zn compositions up to 20% to accommodate increase in the lattice parameter. However, for Zn compositions more than 20%, it does not further dilate. It has been attributed to the large disorder that is incorporated in the system at and beyond 20% of Zn incorporation in the cubic RS lattice of ternary solid solutions. For these large percentages of Zn incorporation, the Ni and the Zn atoms re-arrange themselves microscopically about the same nominal bond length rather than systematically increase in magnitude to minimize the energy of the system. This results in an increase in the Debye-Waller factor with increase in the Zn concentration rather than a systematic increase in the bond lengths.

A vector-based representation of the chemical bond for the substituted torsion of biphenyl

NASA Astrophysics Data System (ADS)

Li, Jiahui; Huang, Weijie; Xu, Tianlv; Kirk, Steven R.; Jenkins, Samantha

2018-06-01

We use a new interpretation of the chemical bond within QTAIM, the bond-path framework set B = {p, q, r} with associated linkages with lengths H∗, H and the familiar bond-path length is used to describe a torsion θ, 0.0° ≤ θ < 22.0° of para-substituted biphenyl, C12H9-x, x = N(CH3)2, NH2, CH3, CHO, CN, NO2. We include consideration of the H--H bonding interactions and find that the lengths H > H∗ that we explain in terms of the most and least preferred directions of charge density accumulation. We also consider the fractional eigenvector-following path with lengths Hf and Hfθmin.

Bond-length distributions for ions bonded to oxygen: results for the non-metals and discussion of lone-pair stereoactivity and the polymerization of PO4

PubMed Central

Gagné, Olivier Charles

2018-01-01

Bond-length distributions are examined for three configurations of the H+ ion, 16 configurations of the group 14–16 non-metal ions and seven configurations of the group 17 ions bonded to oxygen, for 223 coordination polyhedra and 452 bond distances for the H+ ion, 5957 coordination polyhedra and 22 784 bond distances for the group 14–16 non-metal ions, and 248 coordination polyhedra and 1394 bond distances for the group 17 non-metal ions. H⋯O and O—H + H⋯O distances correlate with O⋯O distance (R 2 = 0.94 and 0.96): H⋯O = 1.273 × O⋯O – 1.717 Å; O—H + H⋯O = 1.068 × O⋯O – 0.170 Å. These equations may be used to locate the hydrogen atom more accurately in a structure refined by X-ray diffraction. For non-metal elements that occur with lone-pair electrons, the most observed state between the n versus n+2 oxidation state is that of highest oxidation state for period 3 cations, and lowest oxidation state for period 4 and 5 cations when bonded to O2−. Observed O—X—O bond angles indicate that the period 3 non-metal ions P3+, S4+, Cl3+ and Cl5+ are lone-pair seteroactive when bonded to O2−, even though they do not form secondary bonds. There is no strong correlation between the degree of lone-pair stereoactivity and coordination number when including secondary bonds. There is no correlation between lone-pair stereoactivity and bond-valence sum at the central cation. In synthetic compounds, PO4 polymerizes via one or two bridging oxygen atoms, but not by three. Partitioning our PO4 dataset shows that multi-modality in the distribution of bond lengths is caused by the different bond-valence constraints that arise for Obr = 0, 1 and 2. For strongly bonded cations, i.e. oxyanions, the most probable cause of mean bond length variation is the effect of structure type, i.e. stress induced by the inability of a structure to follow its a priori bond lengths. For ions with stereoactive lone-pair electrons, the most probable cause of variation is bond-length distortion.

3-(2-Biphenyl)sydnone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riddle, Gordon B.; Grossie, David A.; Turnbull, Kenneth

2010-11-16

The title compound, C{sub 14}H{sub 10}N{sub 2}O{sub 2}, is one of many sydnones which have been synthesized in order to investigate the influence of substituents and sydnone-ring stability. There is medicinal interest in the sydnone if the ring can predictably release NO. Bond lengths and angles of the sydnone ring were compared with those of other published sydnone compounds and were found to fit the average of the published data.

Extreme oxatriquinanes and a record C-O bond length

NASA Astrophysics Data System (ADS)

Gunbas, Gorkem; Hafezi, Nema; Sheppard, William L.; Olmstead, Marilyn M.; Stoyanova, Irini V.; Tham, Fook S.; Meyer, Matthew P.; Mascal, Mark

2012-12-01

Oxatriquinanes are fused, tricyclic oxonium ions that are known to have exceptional stability compared to simple alkyl oxonium salts. C-O bonds in ethers are generally ˜1.43 Å in length, but oxatriquinane has been found to have C-O bond lengths of 1.54 Å. A search of the Cambridge Structural Database turned up no bona fide C-O bond length exceeding this value. Computational modelling of oxatriquinane alongside other alkyl oxonium ions indicated that the electronic consequences of molecular strain were primarily responsible for the observed bond elongation. We also show that substitution of the oxatriquinane ring system with alkyl groups of increasing steric demand pushes the C-O bond to unheard of distances, culminating in a tert-butyl derivative at a predicted 1.60 Å. Chemical synthesis and an X-ray crystallographic study of these compounds validated the results of the modelling work and, finally, an extraordinary 1.622 Å C-O bond was observed in 1,4,7-tri-tert-butyloxatriquinane.

1 mil gold bond wire study.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huff, Johnathon; McLean, Michael B.; Jenkins, Mark W.

2013-05-01

In microcircuit fabrication, the diameter and length of a bond wire have been shown to both affect the current versus fusing time ratio of a bond wire as well as the gap length of the fused wire. This study investigated the impact of current level on the time-to-open and gap length of 1 mil by 60 mil gold bond wires. During the experiments, constant current was provided for a control set of bond wires for 250ms, 410ms and until the wire fused; non-destructively pull-tested wires for 250ms; and notched wires. The key findings were that as the current increases, themore » gap length increases and 73% of the bond wires will fuse at 1.8A, and 100% of the wires fuse at 1.9A within 60ms. Due to the limited scope of experiments and limited data analyzed, further investigation is encouraged to confirm these observations.« less

An unusual alkylidyne homologation.

PubMed

Han, Yong-Shen; Hill, Anthony F; Kong, Richard Y

2018-02-27

The reaction of [W([triple bond, length as m-dash]CH)Br(CO) 2 (dcpe)] (dcpe = 1,2-bis(dicyclohexylphosphino)ethane) with t BuLi and SiCl 4 affords the trichlorosilyl ligated neopentylidyne complex [W([triple bond, length as m-dash]C t Bu)(SiCl 3 )(CO) 2 (dcpe)]. This slowly reacts with H 2 O to afford [W([triple bond, length as m-dash]CCH 2 t Bu)Cl 3 (dcpe)] and ultimately H 2 C[double bond, length as m-dash]CH t Bu via an unprecedented alkylidyne homologation in which coordinated CO is the source of the additional carbon atom with potential relevance to the Fischer-Tropsch process.

Vibrational overtone spectra of metallocenes: effect of the coordinating metal on the CH bond lengths

NASA Astrophysics Data System (ADS)

Billinghurst, Brant E.; Gough, Kathleen M.

2003-03-01

The first through third overtone spectra of ferrocene, ruthenocene, nickelocene, cobaltocene, dicyclopentadienyl magnesium and sodium cyclopentadienyl are examined with particular attention to the CH stretching of the cyclopentadienyl. Using semi-empirical correlations between CH bond length and CH stretching frequencies in each overtone region, we have determined that the type of metal atom within a metallocene complex has little effect on the CH bond length in the cyclopentadienyl. The only exception is cobaltocene where there is evidence that the Jahn-Teller effect results in several different CH bond lengths. Evidence that bis(cyclopentadienyl) magnesium is not ionic has been observed.

Adsorbate-induced reconstruction in the phase 1 × 2-3H/Rh(110)

NASA Astrophysics Data System (ADS)

Michl, M.; Nichtl-Pecher, W.; Oed, W.; Landskron, H.; Heinz, K.; Müller, K.

1989-10-01

The 1 × 2-3H superstructure of hydrogen on Rh(110) at coverage θ = {3}/{2} is analysed by low energy electron diffraction at 90 K. The spectra of eight beams are recorded with a computer-controlled TV measurement technique which yields low noise data even for weak superstructure spots by multiple averaging. Comparison to full dynamical calculations shows that a kinematic treatment of the hydrogen layer diffraction coupled to the full dynamical diffraction of the substrate is a very good approximation. Spectra computed in this way are compared with experimental data by R-factor evaluation. The three non-equivalent hydrogen atoms are found to adsorb in quasi-three-fold coordinated adsorption sites with slightly different local configurations and with H-Rh bond lengths between 1.87 and 1.93 Å to the first-layer rhodium atoms. Interaction between the adatoms seems to weaken the bonding to the adjacent atom in the second layer, so that H-Rh bond lengths larger than 2.17 Å result. A slight reconstruction of the substrate is necessary to bring superstructure spot intensities near the experimentally observed level. Rhodium atoms bonded to two hydrogen atoms are moved out of the surface by 0.03 ± 0.02 Å relative to Rh atoms bonded to only a single H atom. The relaxation of the first Rh layer spacing is determined to be {d 12}/{d 0} = -3.8 ± 1% and {d 22}/{d 0} = 0 ± 1% . The best fit Pendry R-factor is 0.33.

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

PubMed

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

2017-03-29

Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln 3+ ) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH 2 , and CN vibration bands during the urea nucleation stage. Rare earth ions such as La 3+ , Gd 3+ , and Lu 3+ can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln 3+ and urea molecules have been confirmed, which are Ln 3+ O[double bond, length as m-dash]C-N and Ln 3+ NH 2 -C. Compared with Ln 3+ NH 2 -C, Ln 3+ prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln 3+ into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln 3+ concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln 3+ , the different effects of La 3+ , Gd 3+ , and Lu 3+ on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

Principles determining the structure of high-pressure forms of metals: The structures of cesium(IV) and cesium(V)

PubMed Central

Pauling, Linus

1989-01-01

Consideration of the relation between bond length and bond number and the average atomic volume for different ways of packing atoms leads to the conclusion that the average ligancy of atoms in a metal should increase when a phase change occurs on increasing the pressure. Minimum volume for each value of the ligancy results from triangular coordination polyhedra (with triangular faces), such as the icosahedron and the Friauf polyhedron. Electron transfer may permit atoms of an element to assume different ligancies. Application of these principles to Cs(IV) and Cs(V), which were previously assigned structures with ligancy 8 and 6, respectively, has led to the assignment to Cs(IV) of a primitive cubic unit cell with a = 16.11 Å and with about 122 atoms in the cube and to Cs(V) of a primitive cubic unit cell resembling that of Mg32(Al,Zn)49, with a = 16.97 Å and with 162 atoms in the cube. PMID:16578839

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

PubMed

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Can HN[double bond, length as m-dash]NH, FN[double bond, length as m-dash]NH, or HN[double bond, length as m-dash]CHOH bridge the σ-hole and the lone pair at P in binary complexes with H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H?

PubMed

Del Bene, Janet E; Alkorta, Ibon; Elguero, José

2015-11-11

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the properties of complexes formed between H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H, and the possible bridging molecules HN[double bond, length as m-dash]NH, FN[double bond, length as m-dash]NH, and HN[double bond, length as m-dash]CHOH. H2XP:HNNH and H2XP:FNNH complexes are stabilized by PN pnicogen bonds, except for H2(CH3)P:FNNH and H3P:FNNH which are stabilized by N-HP hydrogen bonds. H2XP:HNCHOH complexes are stabilized by PN pnicogen bonds and nonlinear O-HP hydrogen bonds. For a fixed H2XP molecule, binding energies decrease in the order HNCHOH > HNNH > FNNH, except for the binding energies of H2(CH3)P and H3P with HNNH and FNNH. Binding energies of complexes with HNCHOH and HNNH increase as the P-N1 distance decreases, but binding energies of complexes with FNNH show little dependence on this distance. The large binding energies of H2XP:HNCHOH complexes arise from a cooperative effect involving electron-pair acceptance by P to form a pnicogen bond, and electron-pair donation by P to form a hydrogen bond. The dominant charge-transfer interaction in these complexes involves electron-pair donation by N across the pnicogen bond, except for complexes in which X is one of the more electropositive substituents, CCH, CH3, and H. For these, lone-pair donation by P across the hydrogen bond dominates. AIM and NBO data for these complexes are consistent with their bonding characteristics, showing molecular graphs with bond critical points and charge-transfer interactions associated with hydrogen and pnicogen bonds. EOM-CCSD spin-spin coupling constants (1p)J(P-N) across the pnicogen bond for each series of complexes correlate with the P-N distance. In contrast, (2h)J(O-P) values for complexes H2XP:HNCHOH do not correlate with the O-P distance, a consequence of the nonlinearity of these hydrogen bonds.

The selective activation of a C-F bond with an auxiliary strong Lewis acid: a method to change the activation preference of C-F and C-H bonds.

PubMed

Wang, Lin; Sun, Hongjian; Li, Xiaoyan; Fuhr, Olaf; Fenske, Dieter

2016-11-15

The selective activation of the C-F bonds in substituted (2,6-difluorophenyl)phenylimines (2,6-F 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-n'-R-C 6 H 4 (n' = 2, R = H (1); n' = 2, R = Me (2); n' = 4, R = tBu (3))) by Fe(PMe 3 ) 4 with an auxiliary strong Lewis acid (LiBr, LiI, or ZnCl 2 ) was explored. As a result, iron(ii) halides ((H 5 C 6 -(C[double bond, length as m-dash]NH)-2-FH 3 C 6 )FeX(PMe 3 ) 3 (X = Br (8); Cl (9)) and (n-RH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-FH 3 C 6 )FeX(PMe 3 ) 3 (n = 2, R = Me, X = Br (11); n = 4, R = tBu, X = I (12))) were obtained. Under similar reaction conditions, using LiBF 4 instead of LiBr or ZnCl 2 , the reaction of (2,6-difluorophenyl)phenylimine with Fe(PMe 3 ) 4 afforded an ionic complex [(2,6-F 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-H 4 C 6 )Fe(PMe 3 ) 4 ](BF 4 ) (10) via the activation of a C-H bond. The method of C-F bond activation with an auxiliary strong Lewis acid is appropriate for monofluoroarylmethanimines. Without the Lewis acid, iron(ii) hydrides ((2-RH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-FH 3 C 6 )FeH(PMe 3 ) 3 (R = H (13); Me (14))) were generated from the reactions of Fe(PMe 3 ) 4 with the monofluoroarylmethanimines (2-FH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-RC 6 H 4 (R = H (4); Me (5))); however, in the presence of ZnCl 2 or LiBr, iron(ii) halides ((2-RH 4 C 6 -(C[double bond, length as m-dash]NH)-H 4 C 6 )FeX(PMe 3 ) 3 (R = H, X = Cl (15); R = Me, X = Br (16))) could be obtained through the activation of a C-F bond. Furthermore, a C-F bond activation with good regioselectivity in (pentafluorophenyl)arylmethanimines (F 5 C 6 -(C[double bond, length as m-dash]NH)-2,6-Y 2 C 6 H 3 (Y = F (6); H (7))) could be realized in the presence of ZnCl 2 to produce iron(ii) chlorides ((2,6-Y 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-F 4 C 6 )FeCl(PMe 3 ) 3 (Y = F (17); H (18))). This series of iron(ii) halides could be used to catalyze the hydrosilylation reaction of aldehydes. Due to the stability of iron(ii) halides to high temperature, the reaction mixture was allowed to be heated to 100 °C and the reaction could finish within 0.5 h.

Equatorial and Apical Solvent Shells of the UO₂²⁺ Ion.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nichols, Pat; Bylaska, Eric J.; Schenter, Gregory K.

2008-03-08

First principles molecular dynamics simulations of the hydration shells surrounding UO₂²⁺ ions are reported for temperatures near 300 K. Most of the simulations were done with 64 solvating water molecules (22 ps). Simulations with 122 water molecules (9 ps) were also carried out. The hydration structure predicted from the simulations was found to agree very well known results from X-ray data. The average U=O bond length was found to be 1.77Å . The first hydration shell contained five trigonally coordinated water molecules that were equatorially oriented about the O-U-O axis with the hydrogen atoms oriented away from the uranium atom.more » The five waters in the first shell were located at an average distance of 2.44Å (2.46Å - 122 water simulation). The second hydration shell was composed of distinct equatorial and apical regions resulting in a peak in the U-O radial distribution function at 4.59Å. The equatorial second shell contained 10 water molecules hydrogen-bonded to the five first shell molecules. Above and below the UO₂²⁺ ion, the water molecules were found to be significantly less structured. In these apical regions, water molecules were found to sporadically hydrogen bond to the oxygen atoms of the UO₂²⁺; oriented in such way as to have their protons pointed towards the cation. While the number of apical waters varied greatly, an average of 5-6 waters was found in this region. Many water transfers into and out of the equatorial and apical second solvation shells were observed to occur on a picosecond (ps) time scale via dissociative mechanisms. Beyond these shells, the bonding pattern substantially returned to the tetrahedral structure of bulk water.« less

Modeling of hyaluronic acid containing anti-cancer drugs-loaded polylactic-co-glycolic acid bioconjugates for targeted delivery to cancer cells

NASA Astrophysics Data System (ADS)

Gul-e-Saba, Adulphakdee, A.; Madthing, A.; Zafar, M. N.; Abdullah, M. A.

2012-09-01

Molecular modeling of hyaluronan (HA), polylactic-co-glycolic acid (PLGA), polyethylene glycol-bis-amine (PEG-bis-amine), Curcumin, Cisplatin and the conjugate HA-PEG-PLGA containing Curcumin/Cisplatin were performed using Discovery Studio 2.5 to better understand issues and constraints related to targeted delivery of potent anticancer drugs to cancer cells. HA, a versatile biopolymer is a ligand of cancer cell receptor, CD44 that can be particularly useful in a receptor-mediated cellular uptake of drug-incorporated nanoparticles. Biocompatible and biodegradable polymers, PLGA and PEG, serve as polymeric micelles for controlled-release of drug. Curcumin as a natural anticancer agent has poor solubility that limits its use in drug therapeutics, while platinum-based Cisplatin exhibits systemic cytotoxicity. These can be overcome via drug delivery in polymeric biocompatible vehicles. The PLGA-PEG-HA conjugate shows the total measurement of 105 bond length with average bond length of 1.274163 Å. The conjugation between PEG and HA occurs at C8-O1 atoms and can be manipulated to improve properties.

A Computational Study on the Ground and Excited States of Nickel Silicide.

PubMed

Schoendorff, George; Morris, Alexis R; Hu, Emily D; Wilson, Angela K

2015-09-17

Nickel silicide has been studied with a range of computational methods to determine the nature of the Ni-Si bond. Additionally, the physical effects that need to be addressed within calculations to predict the equilibrium bond length and bond dissociation energy within experimental error have been determined. The ground state is predicted to be a (1)Σ(+) state with a bond order of 2.41 corresponding to a triple bond with weak π bonds. It is shown that calculation of the ground state equilibrium geometry requires a polarized basis set and treatment of dynamic correlation including up to triple excitations with CR-CCSD(T)L resulting in an equilibrium bond length of only 0.012 Å shorter than the experimental bond length. Previous calculations of the bond dissociation energy resulted in energies that were only 34.8% to 76.5% of the experimental bond dissociation energy. It is shown here that use of polarized basis sets, treatment of triple excitations, correlation of the valence and subvalence electrons, and a Λ coupled cluster approach is required to obtain a bond dissociation energy that deviates as little as 1% from experiment.

Estimating the hydraulic conductivity of two-dimensional fracture networks

NASA Astrophysics Data System (ADS)

Leung, C. T.; Zimmerman, R. W.

2010-12-01

Most oil and gas reservoirs, as well as most potential sites for nuclear waste disposal, are naturally fractured. In these sites, the network of fractures will provide the main path for fluid to flow through the rock mass. In many cases, the fracture density is so high as to make it impractical to model it with a discrete fracture network (DFN) approach. For such rock masses, it would be useful to have recourse to analytical, or semi-analytical, methods to estimate the macroscopic hydraulic conductivity of the fracture network. We have investigated single-phase fluid flow through stochastically generated two-dimensional fracture networks. The centres and orientations of the fractures are uniformly distributed, whereas their lengths follow either a lognormal distribution or a power law distribution. We have considered the case where the fractures in the network each have the same aperture, as well as the case where the aperture of each fracture is directly proportional to the fracture length. The discrete fracture network flow and transport simulator NAPSAC, developed by Serco (Didcot, UK), is used to establish the “true” macroscopic hydraulic conductivity of the network. We then attempt to match this conductivity using a simple estimation method that does not require extensive computation. For our calculations, fracture networks are represented as networks composed of conducting segments (bonds) between nodes. Each bond represents the region of a single fracture between two adjacent intersections with other fractures. We assume that the bonds are arranged on a kagome lattice, with some fraction of the bonds randomly missing. The conductance of each bond is then replaced with some effective conductance, Ceff, which we take to be the arithmetic mean of the individual conductances, averaged over each bond, rather than over each fracture. This is in contrast to the usual approximation used in effective medium theories, wherein the geometric mean is used. Our explanation is that the conductivities of the bonds that meet at a given node in a fracture network do not satisfy the usual assumption of being uncorrelated; rather, the conductances of at least two of these bonds are highly correlated, as they represent the incoming and outgoing branches of the same fracture. The effective conductance of our idealized “equivalent network” is then trivial to calculate. We find that this estimate of the hydraulic conductivity agrees very closely with the numerically computed value, essentially for all fracture densities that are not too close to the percolation threshold. Moreover, the same methodology applies regardless of whether the fracture lengths are distributed lognormally, or according to a power law.

Numerical analysis of interface debonding detection in bonded repair with Rayleigh waves

NASA Astrophysics Data System (ADS)

Xu, Ying; Li, BingCheng; Lu, Miaomiao

2017-01-01

This paper studied how to use the variation of the dispersion curves of Rayleigh wave group velocity to detect interfacial debonding damage between FRP plate and steel beam. Since FRP strengthened steel beam is two layers medium, Rayleigh wave velocity dispersion phenomenon will happen. The interface debonding damage of FRP strengthened steel beam have an obvious effect on the Rayleigh wave velocity dispersion curve. The paper first put forward average Euclidean distance and Angle separation degree to describe the relationship between the different dispersion curves. Numerical results indicate that there is a approximate linear mapping relationship between the average Euclidean distance of dispersion curves and the length of interfacial debonding damage.

Facile synthesis of -C[double bond, length as m-dash]N- linked covalent organic frameworks under ambient conditions.

PubMed

Ding, San-Yuan; Cui, Xiao-Hui; Feng, Jie; Lu, Gongxuan; Wang, Wei

2017-10-31

We reported herein a facile approach for the synthesis of -C[double bond, length as m-dash]N- linked covalent organic frameworks under ambient conditions. Three known (COF-42, COF-43, and COF-LZU1) and one new (Pr-COF-42) COF materials were successfully synthesized using this method. Furthermore, this simple synthetic approach makes the large-scale synthesis of -C[double bond, length as m-dash]N- linked COFs feasible.

Syntheses of monomeric (. eta. sup 5 -pentamethylcyclopentadienyl)platinum(IV) methyl and bromo complexes and of (hydrotris(3,5-dimethyl-1-pyrazolyl)borato)trimethylplatinum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roth, S.; Ramamoorthy, V.; Sharp, P.R.

1990-09-05

The reaction of Cp*MgCl{center dot}THF (Cp* = C{sub 5}Me{sub 5}) with 1 equiv of PtMe{sub 3}I and PtMe{sub 2}Br{sub 2} produces Cp*PtMe{sub 3} (1) and Cp*PtMe{sub 2}Br (2), respectively. Reaction of 2 with Br{sub 2} produces Cp*PtMeBr{sub 2} (3) in good yield. The structures of 2 and 3 have been determined by x-ray crystallography, and the crystal structure data are reported. Complex 2 crystallizes in the monoclinic space group, P2{sub 1}/m, and complex 3 crystallizes in the monoclinic space group, P2{sub 1}/m. The molecules reside on mirror planes and are monomeric pseudotetrahedral Pt(IV) complexes with piano stool type geometries andmore » {eta}{sup 5}-Cp* groups. Both molecules have Br atoms on the mirror. This leads to a disorder of the Me and the second Br positions in complex 3. The average Pt-C(Cp*) bond length is 2.25 (7) {angstrom} in 2 and 2.22 (4) {angstrom} in 3. The Pt-C(Me) and Pt-Br bond lengths in 2 are 2.07 (2) and 2.498 (2) {angstrom}, respectively. The ordered Pt-Br bond length in 3 is 2.496 (2) {angstrom}. Treatment of 1 with halogens results in the cleavage of the Pt-Cp* bond. The reaction of PtMe{sub 3}I with KTp* (Tp* = (HB(3,5-dimethylpyrazolyl){sub 3}){sup {minus}}) in thf gives Tp*PtMe{sub 3} (4) in almost quantitative yield. The reaction of 4 with Br{sub 2} brominates the 4-position of the pyrazolyl ring only. 28 refs., 2 figs., 5 tabs.« less

Analisis parametrico de las variables que influyen en el comportamiento adherente de las armaduras pretesas en el hormigon

NASA Astrophysics Data System (ADS)

Arbelaez Jaramillo, Cesar Augusto

Prestressed concrete technique through the use of prestressed reinforcement is extended in the precast concrete industry. This technique consists on casting a concrete element over a previously prestressed reinforcement, proceeding to release once the concrete has reached a determined strength so the prestressed stress introduced to the reinforcement be transmitted, by bond, to concrete. The bond behaviour of prestressed reinforcement includes two phenomena: prestress transmission from the reinforcement to concrete and anchorage of the reinforcement. This bond behaviour is characterized by mean of two lengths: transmission length and anchorage length. The good design of these lengths is a basic and fundamental aspect in the project of precast prestressed concrete elements to guaranty the appropriate transmission of prestress and to allow the anchorage of the reinforcement along the structural element service life. The influence of the parameters related to the concrete dosage on the transmission and anchorage lengths of prestressing strands have been analyzed. The ECADA test method has been applied. With this method the operations of transmission of prestress and anchorage of the reinforcement are sequentially done. The transmission and anchorage lengths are determined from the force control supported by the reinforcement testing series of specimens with different embedment lengths. The differentiation of the concepts of anchorage length without slips and with slips has been proposed. The relationship of the parameters of dosage with the bond stress and the registered slips during the processes of transmission and anchorage has been studied. Expressions to value the slips distribution of the reinforcement in the transmission zone and in the anchorage zone have been proposed. A study on the determination of the transmission length from the free reinforcement slip end has been done and the viability to experimentally determine the transmission length from the slips sequence in the pull-out end as a function of the embedment length has been verified. The experimental results have been compared with results and predictions from other authors and standards, and an expression to calculate the transmission length have been proposed. Finally, the bond behaviour of self-compacting concretes has been compared with the bond behaviour of traditional concretes.

Communication: Creation of molecular vibrational motions via the rotation-vibration coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shu, Chuan-Cun; School of Engineering and Information Technology, University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600; Henriksen, Niels E., E-mail: neh@kemi.dtu.dk

2015-06-14

Building on recent advances in the rotational excitation of molecules, we show how the effect of rotation-vibration coupling can be switched on in a controlled manner and how this coupling unfolds in real time after a pure rotational excitation. We present the first examination of the vibrational motions which can be induced via the rotation-vibration coupling after a pulsed rotational excitation. A time-dependent quantum wave packet calculation for the HF molecule shows how a slow (compared to the vibrational period) rotational excitation leads to a smooth increase in the average bond length whereas a fast rotational excitation leads to amore » non-stationary vibrational motion. As a result, under field-free postpulse conditions, either a stretched stationary bond or a vibrating bond can be created due to the coupling between the rotational and vibrational degrees of freedom. The latter corresponds to a laser-induced breakdown of the adiabatic approximation for rotation-vibration coupling.« less

Identification of phases, symmetries and defects through local crystallography

DOE PAGES

Belianinov, Alex; He, Qian; Kravchenko, Mikhail; ...

2015-07-20

Here we report that advances in electron and probe microscopies allow 10 pm or higher precision in measurements of atomic positions. This level of fidelity is sufficient to correlate the length (and hence energy) of bonds, as well as bond angles to functional properties of materials. Traditionally, this relied on mapping locally measured parameters to macroscopic variables, for example, average unit cell. This description effectively ignores the information contained in the microscopic degrees of freedom available in a high-resolution image. Here we introduce an approach for local analysis of material structure based on statistical analysis of individual atomic neighbourhoods. Clusteringmore » and multivariate algorithms such as principal component analysis explore the connectivity of lattice and bond structure, as well as identify minute structural distortions, thus allowing for chemical description and identification of phases. This analysis lays the framework for building image genomes and structure–property libraries, based on conjoining structural and spectral realms through local atomic behaviour.« less

Difference in the stable isotopic fractionations of Ce, Nd, and Sm during adsorption on iron and manganese oxides and its interpretation based on their local structures

NASA Astrophysics Data System (ADS)

Nakada, Ryoichi; Tanimizu, Masaharu; Takahashi, Yoshio

2013-11-01

Many elements have become targets for studies of stable isotopic fractionation with the development of various analytical techniques. Although several chemical factors that control the isotopic fractionation of heavy elements have been proposed, it remains controversial which properties are most important for the isotopic fractionation of elements. In this study, the stable isotopic fractionation of neodymium (Nd) and samarium (Sm) during adsorption on ferrihydrite and δ-MnO2 was examined. This examination was combined with speciation analyses of these ions adsorbed on the solid phases by extended X-ray absorption fine structure (EXAFS) spectroscopy. Neodymium isotope ratios for Nd on ferrihydrite and δ-MnO2 systems were, on average, 0.166‰ and 0.410‰ heavier than those of the liquid phase, which correspond to mean isotopic fractionation factors between the liquid and solid phases (αLq-So) of Nd on ferrihydrite and δ-MnO2 of 0.999834 (2σ = ±0.000048) and 0.999590 (2σ = ±0.000106), respectively. Similarly, averaged Sm isotope ratios on ferrihydrite and δ-MnO2 were 0.206‰ and 0.424‰ heavier than those of the liquid phase and the corresponding αLq-So values were 0.999794 (±0.000041) and 0.999576 (±0.000134), respectively. These results indicate that the directions of isotopic fractionation in the Nd and Sm systems are in contrast with that recently found for Ce(III) systems despite the similar chemical characteristics of rare earth elements. EXAFS analyses suggest that the bond length of the first coordination sphere (REE-O bond) of Nd and Sm adsorbed on δ-MnO2 is shorter than that of their aqua ions, although this was not clear for the ferrihydrite systems. The shorter bond length relative to the aqua ion is indicative of a stronger bond, suggesting that the equilibrium isotopic fractionation for the Nd and Sm systems can be governed by bond strength as has often been discussed for isotopic fractionation in solid-water adsorption systems. Meanwhile, EXAFS analyses of the Ce/ferrihydrite system showed a distorted structure for the first coordination sphere that was not observed for Ce3+ aqua ions. Such distortion was also observed for La adsorption on ferrihydrite and δ-MnO2. In addition, previous studies have suggested a high stability of the hydrated state for La and Ce in terms of Gibbs free energy change. Thus, we suggest here that the difference in the stable isotopic fractionation for Ce (and predicted for La) vs. Nd and Sm can be explained by (i) the shorter bond lengths of adsorbed relative to dissolved species for Nd and Sm and (ii) the distorted structure of adsorbed Ce (and La) species and high stability of the aqua Ce ion.

How Is the Enamel Affected by Different Orthodontic Bonding Agents and Polishing Techniques?

PubMed

Heravi, Farzin; Shafaee, Hooman; Abdollahi, Mojtaba; Rashed, Roozbeh

2015-03-01

The objective of this study was to assess the effect of new bonding techniques on enamel surface. Sixty upper central incisors were randomly divided into two equal groups. In the first group, metal brackets were bonded using TransbondXT and, in the second group, the same brackets were bonded with Maxcem Elite. The shear bond strength (SBS) of both agents to enamel was measured and the number and length of enamel cracks before bonding, after debonding and after polishing were compared. The number of visible cracks and the adhesive remnant index (ARI) scores in each group were also measured. There were significantly more enamel cracks in the Transbond XT group after debonding and polishing compared to the Maxcem Elite group. There was no significant difference in the length of enamel cracks between the two groups; but, in each group, a significant increase in the length of enamel cracks was noticeable after debonding. Polishing did not cause any statistically significant change in crack length. The SBS of Maxcem Elite was significantly lower than that of Transbond XT (95% confidence interval). Maxcem Elite offers clinically acceptable bond strength and can thus be used as a routine adhesive for orthodontic purposes since it is less likely to damage the enamel.

Utilisation of an eta(3)-allyl hydride complex, formed by UV irradiation, as a controlled source of 16-electron (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

PubMed

Sexton, Catherine J; López-Serrano, Joaquín; Lledós, Agustí; Duckett, Simon B

2008-10-21

Low temperature UV irradiation of solutions of (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe)(2) yields (eta(5)-C(5)Me(5))Rh(eta(3)-CH(2)CHCH(2))(H), which provides controlled access to the 16-electron fragment (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

Relationship between x-ray emission and absorption spectroscopy and the local H-bond environment in water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhovtobriukh, Iurii; Besley, Nicholas A.; Fransson, Thomas

Here, the connection between specific features in the water X-ray absorption spectrum and X-ray emission spectrum (XES) and the local H-bond coordination is studied based on structures obtained from path-integral molecular dynamics simulations using either the opt-PBE-vdW density functional or the MB-pol force field. Computing the XES spectrum using all molecules in a snapshot results in only one peak in the lone-pair (1b 1) region, while the experiment shows two peaks separated by 0.8-0.9 eV. Different H-bond configurations were classified based on the local structure index (LSI) and a geometrical H-bond cone criterion. We find that tetrahedrally coordinated molecules characterizedmore » by high LSI values and two strong donated and two strong accepted H-bonds contribute to the low energy 1b 1 emission peak and to the post-edge region in absorption. Molecules with the asymmetric H-bond environment with one strong accepted H-bond and one strong donated H-bond and low LSI values give rise to the high energy 1b 1 peak in the emission spectrum and mainly contribute to the pre-edge and main-edge in the absorption spectrum. The 1b 1 peak splitting can be increased to 0.62 eV by imposing constraints on the H-bond length, i.e., for very tetrahedral structures short H-bonds (less than 2.68 Å) and for very asymmetric structures elongated H-bonds (longer than 2.8 Å). Such structures are present, but underrepresented, in the simulations which give more of an average of the two extremes.« less

Relationship between x-ray emission and absorption spectroscopy and the local H-bond environment in water

DOE PAGES

Zhovtobriukh, Iurii; Besley, Nicholas A.; Fransson, Thomas; ...

2018-04-14

Here, the connection between specific features in the water X-ray absorption spectrum and X-ray emission spectrum (XES) and the local H-bond coordination is studied based on structures obtained from path-integral molecular dynamics simulations using either the opt-PBE-vdW density functional or the MB-pol force field. Computing the XES spectrum using all molecules in a snapshot results in only one peak in the lone-pair (1b 1) region, while the experiment shows two peaks separated by 0.8-0.9 eV. Different H-bond configurations were classified based on the local structure index (LSI) and a geometrical H-bond cone criterion. We find that tetrahedrally coordinated molecules characterizedmore » by high LSI values and two strong donated and two strong accepted H-bonds contribute to the low energy 1b 1 emission peak and to the post-edge region in absorption. Molecules with the asymmetric H-bond environment with one strong accepted H-bond and one strong donated H-bond and low LSI values give rise to the high energy 1b 1 peak in the emission spectrum and mainly contribute to the pre-edge and main-edge in the absorption spectrum. The 1b 1 peak splitting can be increased to 0.62 eV by imposing constraints on the H-bond length, i.e., for very tetrahedral structures short H-bonds (less than 2.68 Å) and for very asymmetric structures elongated H-bonds (longer than 2.8 Å). Such structures are present, but underrepresented, in the simulations which give more of an average of the two extremes.« less

Capture of SO3 isomers in the oxidation of sulfur monoxide with molecular oxygen.

PubMed

Wu, Zhuang; Lu, Bo; Feng, Ruijuan; Xu, Jian; Lu, Yan; Wan, Huabin; Eckhardt, André K; Schreiner, Peter R; Xie, Changjian; Guo, Hua; Zeng, Xiaoqing

2018-02-13

When mixing SO with O 2 in N 2 , Ne, or Ar, an end-on complex OS-OO forms in the gas phase and can subsequently be trapped at cryogenic temperatures (2.8-15.0 K). Upon infrared light irradiation, OS-OO converts to SO 3 and SO 2 + O with the concomitant formation of a rare 1,2,3-dioxathiirane 2-oxide, i.e., cyclic OS([double bond, length as m-dash]O)O. Unexpectedly, the ring-closure of 16 OS- 18 O 18 O yields a ca. 2 : 1 mixture of cyclic 18 OS([double bond, length as m-dash] 16 O) 18 O and 16 OS([double bond, length as m-dash] 18 O) 18 O. The characterization of OS-OO and OS([double bond, length as m-dash]O)O with IR and UV/Vis spectroscopy is supported by high-level ab initio computations.

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

PubMed Central

Pauling, Linus; Kamb, Barclay

1986-01-01

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

The Changing Nature of the Chemical Bond

NASA Astrophysics Data System (ADS)

Angel, R. J.; Ross, N. L.; Zhao, J.

2006-12-01

It is commonly assumed that the relationship between bond strength and bond length for a particular pair of atoms is a simple and single-valued one for a given coordination environment; longer bonds are weaker. This is the basis of the concept of bond valence, for example. Indeed, in strongly-bonded oxide minerals, the range of bond lengths found for a given cation-anion polyhedron is so small that it was long thought that the polyhedral bulk moduli were essentially independent of structure type and thus the environment of the polyhedron. This view is incompatible with the discovery that the response of the perovskite structure to high pressures is controlled by the equipartition of bond-valence strain between the A and B cation sites within the structure [1]. The same appears to be true, within experimental uncertainties, for all framework structures with rigid-unit modes. In perovskites, this explicitly implies that the octahedral compressibility depends not only upon the octahedral cation, but also upon the compressibility of the cation-oxygen bonds of the extra-framework (nominally dodecahedral) site. Thus the octahedral compressibility of a B cation site must change as the A- site cation is changed, whether or not the B-O bond lengths change as a result of the substitution on the A site. The strength of bonds is thus dependent upon the crystal environment and not solely upon the bond length. The observation of a plateau effect in the variation of octahedral compressibilities in perovskite solid solutions suggests that the bond-valence matching principle is followed not just globally, but on a local scale as well. Such observations should allow the change with pressure of the excess thermodynamic properties of solid solutions to be directly related to the microscopic (atomic scale) evolution of the structure. [1] Zhao, Ross, & Angel (2004). Acta Cryst. B60:263

Bond-length relaxation in crystalline Si1-xGex alloys: An extended x-ray-absorption fine-structure study

NASA Astrophysics Data System (ADS)

Kajiyama, Hiroshi; Muramatsu, Shin-Ichi; Shimada, Toshikazu; Nishino, Yoichi

1992-06-01

Extended x-ray-absorption fine-structure spectra for crystalline Si1-xGex alloys, measured at the K edge of Ge at room temperature, are analyzed with a curve-fitting method based on the spherical-wave approximation. The Ge-Ge and Ge-Si bond lengths, coordination numbers of Ge and Si atoms around a Ge atom, and Debye-Waller factors of Ge and Si atoms are obtained. It is shown that Ge-Ge and Ge-Si bonds relax completely, for all Ge concentrations of their study, while the lattice constant varies monotonically, following Vegard's law. As noted by Bragg and later by Pauling and Huggins, the Ge-Ge and Ge-Si bond lengths are close to the sum of their constituent-element atomic radii: nearly 2.45 Å for Ge-Ge bonds and 2.40 Å for Ge-Si bonds. A study on the coordination around a Ge atom in the alloys revealed that Ge and Si atoms mix randomly throughout the compositional range studied.

Hydridosilylamido complexes of Ta and Mo isolobal with Berry's zirconocenes: syntheses, β-Si-H agostic interactions, catalytic hydrosilylation, and insight into mechanism.

PubMed

McLeod, Nicolas A; Kuzmina, Lyudmila G; Korobkov, Ilia; Howard, Judith A K; Nikonov, Georgii I

2016-02-14

The syntheses of novel Group 5 and Group 6 hydrosilylamido complexes of the type R(ArN[double bond, length as m-dash])M{N((t)Bu)SiMe2-H}X (M = Ta, R = Cp; M = Mo, R = ArN; X = Cl, H, OBn, Me) are described. The various substituents in the X position seem to play the key role in determining the extent of β-agostic interaction with the Si-H bond. The Mo agostic hydrido complex (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H is a pre-catalyst for the hydrosilylation of carbonyls. The stoichiometric reaction between benzaldehyde and (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H gives the benzoxy complex (ArN[double bond, length as m-dash])2Mo{N((t)Bu)SiMe2-H}(OBn), which showed a similar catalytic reactivity compared to the parent hydride. Mechanistic studies suggest that a non-hydride mechanism is operative.

Local environment effects in the magnetic properties and electronic structure of disordered FePt

NASA Astrophysics Data System (ADS)

Khan, Saleem Ayaz; Minár, Ján; Ebert, Hubert; Blaha, Peter; Šipr, Ondřej

2017-01-01

Local aspects of magnetism of disordered FePt are investigated by ab initio fully relativistic full-potential calculations, employing the supercell approach and the coherent potential approximation (CPA). The focus is on trends of the spin and orbital magnetic moments with chemical composition and with bond lengths around the Fe and Pt atoms. A small but distinct difference between average magnetic moments obtained when using the supercells and when relying on the CPA is identified and linked to the neglect of the Madelung potential in the CPA.

3-Axis Fully-Integrated Capacitive Tactile Sensor with Flip-Bonded CMOS on LTCC Interposer.

PubMed

Asano, Sho; Muroyama, Masanori; Nakayama, Takahiro; Hata, Yoshiyuki; Nonomura, Yutaka; Tanaka, Shuji

2017-10-25

This paper reports a 3-axis fully integrated differential capacitive tactile sensor surface-mountable on a bus line. The sensor integrates a flip-bonded complementary metal-oxide semiconductor (CMOS) with capacitive sensing circuits on a low temperature cofired ceramic (LTCC) interposer with Au through vias by Au-Au thermo-compression bonding. The CMOS circuit and bonding pads on the sensor backside were electrically connected through Au bumps and the LTCC interposer, and the differential capacitive gap was formed by an Au sealing frame. A diaphragm for sensing 3-axis force was formed in the CMOS substrate. The dimensions of the completed sensor are 2.5 mm in width, 2.5 mm in length, and 0.66 mm in thickness. The fabricated sensor output coded 3-axis capacitive sensing data according to applied 3-axis force by three-dimensional (3D)-printed pins. The measured sensitivity was as high as over 34 Count/mN for normal force and 14 to 15 Count/mN for shear force with small noise, which corresponds to less than 1 mN. The hysteresis and the average cross-sensitivity were also found to be less than 2% full scale and 11%, respectively.

3-Axis Fully-Integrated Capacitive Tactile Sensor with Flip-Bonded CMOS on LTCC Interposer †

PubMed Central

Asano, Sho; Nakayama, Takahiro; Hata, Yoshiyuki; Tanaka, Shuji

2017-01-01

This paper reports a 3-axis fully integrated differential capacitive tactile sensor surface-mountable on a bus line. The sensor integrates a flip-bonded complementary metal-oxide semiconductor (CMOS) with capacitive sensing circuits on a low temperature cofired ceramic (LTCC) interposer with Au through vias by Au-Au thermo-compression bonding. The CMOS circuit and bonding pads on the sensor backside were electrically connected through Au bumps and the LTCC interposer, and the differential capacitive gap was formed by an Au sealing frame. A diaphragm for sensing 3-axis force was formed in the CMOS substrate. The dimensions of the completed sensor are 2.5 mm in width, 2.5 mm in length, and 0.66 mm in thickness. The fabricated sensor output coded 3-axis capacitive sensing data according to applied 3-axis force by three-dimensional (3D)-printed pins. The measured sensitivity was as high as over 34 Count/mN for normal force and 14 to 15 Count/mN for shear force with small noise, which corresponds to less than 1 mN. The hysteresis and the average cross-sensitivity were also found to be less than 2% full scale and 11%, respectively. PMID:29068429

Ammonolysis of ketene as a potential source of acetamide in the troposphere: a quantum chemical investigation.

PubMed

Sarkar, Saptarshi; Mallick, Subhasish; Kumar, Pradeep; Bandyopadhyay, Biman

2018-05-16

Quantum chemical calculations at the CCSD(T)/CBS//MP2/aug-cc-pVTZ levels of theory have been carried out to investigate a potential new source of acetamide in Earth's atmosphere through the ammonolysis of the simplest ketene. It was found that the reaction can occur via the addition of ammonia at either the C[double bond, length as m-dash]C or C[double bond, length as m-dash]O bond of ketene. The potential energy surface as well as calculated rate coefficients indicate that under tropospheric conditions, ammonolysis would occur almost exclusively via ammonia addition at the C[double bond, length as m-dash]O bond with negligible contribution from addition at the C[double bond, length as m-dash]C bond. The reaction of ketene with water has also been investigated in order to compare between hydrolysis and ammonolysis, as the former is known to be responsible for the formation of acetic acid. The rate coefficient for the formation of acetamide was found to be ∼106 to 109 times higher than that for the formation of acetic acid from the same ketene source in the troposphere. By means of the relative rate of ammonolysis with respect to hydrolysis, it was shown that acetamide formation would dominate over acetic acid formation at various altitudes in the troposphere.

Thermionic refrigeration at CNT-CNT junctions

NASA Astrophysics Data System (ADS)

Li, C.; Pipe, K. P.

2016-10-01

Monte Carlo (MC) simulation is used to study carrier energy relaxation following thermionic emission at the junction of two van der Waals bonded single-walled carbon nanotubes (SWCNTs). An energy-dependent transmission probability gives rise to energy filtering at the junction, which is predicted to increase the average electron transport energy by as much as 0.115 eV, leading to an effective Seebeck coefficient of 386 μV/K. MC results predict a long energy relaxation length (˜8 μm) for hot electrons crossing the junction into the barrier SWCNT. For SWCNTs of optimal length, an analytical transport model is used to show that thermionic cooling can outweigh parasitic heat conduction due to high SWCNT thermal conductivity, leading to a significant cooling capacity (2.4 × 106 W/cm2).

Full empirical potential curves for the X{sup 1}Σ{sup +} and A{sup 1}Π states of CH{sup +} from a direct-potential-fit analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Young-Sang; Le Roy, Robert J.

2016-01-14

All available “conventional” absorption/emission spectroscopic data have been combined with photodissociation data and translational spectroscopy data in a global analysis that yields analytic potential energy and Born-Oppenheimer breakdown functions for the X{sup 1}Σ{sup +} and A{sup 1}Π states of CH{sup +} and its isotopologues that reproduce all of the data (on average) within their assigned uncertainties. For the ground X{sup 1}Σ{sup +} state, this fully quantum mechanical “Direct-Potential-Fit” analysis yielded an improved empirical well depth of D{sub e} = 34 362.8(3) cm{sup −1} and equilibrium bond length of r{sub e} = 1.128 462 5 (58) Å. For the A{sup 1}Π state, the resulting wellmore » depth and equilibrium bond length are D{sub e} = 10 303.7(3) cm{sup −1} and r{sub e} = 1.235 896 (14) Å, while the electronic isotope shift from the hydride to the deuteride is ΔT{sub e} = − 5.99(±0.08) cm{sup −1}.« less

Short Carboxylic Acid–Carboxylate Hydrogen Bonds Can Have Fully Localized Protons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Jiusheng; Pozharski, Edwin; Wilson, Mark A.

Short hydrogen bonds (H-bonds) have been proposed to play key functional roles in several proteins. The location of the proton in short H-bonds is of central importance, as proton delocalization is a defining feature of low-barrier hydrogen bonds (LBHBs). Experimentally determining proton location in H-bonds is challenging. Here, bond length analysis of atomic (1.15–0.98 Å) resolution X-ray crystal structures of the human protein DJ-1 and its bacterial homologue, YajL, was used to determine the protonation states of H-bonded carboxylic acids. DJ-1 contains a buried, dimer-spanning 2.49 Å H-bond between Glu15 and Asp24 that satisfies standard donor–acceptor distance criteria for amore » LBHB. Bond length analysis indicates that the proton is localized on Asp24, excluding a LBHB at this location. However, similar analysis of the Escherichia coli homologue YajL shows both residues may be protonated at the H-bonded oxygen atoms, potentially consistent with a LBHB. A Protein Data Bank-wide screen identifies candidate carboxylic acid H-bonds in approximately 14% of proteins, which are typically short [O–O> = 2.542(2) Å]. Chemically similar H-bonds between hydroxylated residues (Ser/Thr/Tyr) and carboxylates show a trend of lengthening O–O distance with increasing H-bond donor pK a. This trend suggests that conventional electronic effects provide an adequate explanation for short, charge-assisted carboxylic acid–carboxylate H-bonds in proteins, without the need to invoke LBHBs in general. This study demonstrates that bond length analysis of atomic resolution X-ray crystal structures provides a useful experimental test of certain candidate LBHBs.« less

Evaluation of enamel damages following orthodontic bracket debonding in fluorosed teeth bonded with adhesion promoter.

PubMed

Baherimoghadam, Tahreh; Akbarian, Sahar; Rasouli, Reza; Naseri, Navid

2016-01-01

To evaluate shear bond strength (SBS) of the orthodontic brackets bonded to fluorosed and nonfluorosed teeth using Light Bond with and without adhesion promoters and compare their enamel damages following debonding. In this study, 30 fluorosed (Thylstrup and Fejerskov Index = 4-5) and 30 nonfluorosed teeth were randomly distributed between two subgroups according to the bonding materials: Group 1, fluorosed teeth bonded with Light Bond; Group 2, fluorosed teeth bonded with adhesion promoters and Light Bond; Group 3, nonfluorosed teeth bonded with Light Bond; Group 4, nonfluorosed bonded with adhesion promoters and Light Bond. After bonding, the SBS of the brackets was tested with a universal testing machine. Stereomicroscopic evaluation was performed by unbiased stereology in all teeth to determine the amount of adhesive remnants and the number and length of enamel cracks before bonding and after debonding. The data were analyzed using two-way analysis of variance, Kruskal-Wallis, Wilcoxon Signed Rank, and Mann-Whitney test. While fluorosis reduced the SBS of orthodontic bracket (P = 0.017), Enhance Locus Ceruleus LC significantly increased the SBS of the orthodontic bracket in fluorosed and nonfluorosed teeth (P = 0.039). Significant increasing in the number and length of enamel crack after debonding was found in all four groups. There were no significant differences in the length of enamel crack increased after debonding among four groups (P = 0.768) while increasing in the number of enamel cracks after debonding was significantly different among the four groups (P = 0.023). Teeth in Group 2 showed the highest enamel damages among four groups following debonding. Adhesion promoters could improve the bond strength of orthodontic brackets, but conservative debonding methods for decreasing enamel damages would be necessary.

Short Carboxylic Acid-Carboxylate Hydrogen Bonds Can Have Fully Localized Protons.

PubMed

Lin, Jiusheng; Pozharski, Edwin; Wilson, Mark A

2017-01-17

Short hydrogen bonds (H-bonds) have been proposed to play key functional roles in several proteins. The location of the proton in short H-bonds is of central importance, as proton delocalization is a defining feature of low-barrier hydrogen bonds (LBHBs). Experimentally determining proton location in H-bonds is challenging. Here, bond length analysis of atomic (1.15-0.98 Å) resolution X-ray crystal structures of the human protein DJ-1 and its bacterial homologue, YajL, was used to determine the protonation states of H-bonded carboxylic acids. DJ-1 contains a buried, dimer-spanning 2.49 Å H-bond between Glu15 and Asp24 that satisfies standard donor-acceptor distance criteria for a LBHB. Bond length analysis indicates that the proton is localized on Asp24, excluding a LBHB at this location. However, similar analysis of the Escherichia coli homologue YajL shows both residues may be protonated at the H-bonded oxygen atoms, potentially consistent with a LBHB. A Protein Data Bank-wide screen identifies candidate carboxylic acid H-bonds in approximately 14% of proteins, which are typically short [⟨d O-O ⟩ = 2.542(2) Å]. Chemically similar H-bonds between hydroxylated residues (Ser/Thr/Tyr) and carboxylates show a trend of lengthening O-O distance with increasing H-bond donor pK a . This trend suggests that conventional electronic effects provide an adequate explanation for short, charge-assisted carboxylic acid-carboxylate H-bonds in proteins, without the need to invoke LBHBs in general. This study demonstrates that bond length analysis of atomic resolution X-ray crystal structures provides a useful experimental test of certain candidate LBHBs.

Anomalous perovskite PbRuO3 stabilized under high pressure

PubMed Central

Cheng, J.-G.; Kweon, K. E.; Zhou, J.-S.; Alonso, J. A.; Kong, P.-P.; Liu, Y.; Jin, Changqing; Wu, Junjie; Lin, Jung-Fu; Larregola, S. A.; Yang, Wenge; Shen, Guoyin; MacDonald, A. H.; Manthiram, Arumugam; Hwang, G. S.; Goodenough, John B.

2013-01-01

Perovskite oxides ABO3 are important materials used as components in electronic devices. The highly compact crystal structure consists of a framework of corner-shared BO6 octahedra enclosing the A-site cations. Because of these structural features, forming a strong bond between A and B cations is highly unlikely and has not been reported in the literature. Here we report a pressure-induced first-order transition in PbRuO3 from a common orthorhombic phase (Pbnm) to an orthorhombic phase (Pbn21) at 32 GPa by using synchrotron X-ray diffraction. This transition has been further verified with resistivity measurements and Raman spectra under high pressure. In contrast to most well-studied perovskites under high pressure, the Pbn21 phase of PbRuO3 stabilized at high pressure is a polar perovskite. More interestingly, the Pbn21 phase has the most distorted octahedra and a shortest Pb—Ru bond length relative to the average Pb—Ru bond length that has ever been reported in a perovskite structure. We have also simulated the behavior of the PbRuO3 perovskite under high pressure by first principles calculations. The calculated critical pressure for the phase transition and evolution of lattice parameters under pressure match the experimental results quantitatively. Our calculations also reveal that the hybridization between a Ru:t2g orbital and an sp hybrid on Pb increases dramatically in the Pbnm phase under pressure. This pressure-induced change destabilizes the Pbnm phase to give a phase transition to the Pbn21 phase where electrons in the overlapping orbitals form bonding and antibonding states along the shortest Ru—Pb direction at P > Pc. PMID:24277807

Conformation-dependent backbone geometry restraints set a new standard for protein crystallographic refinement

DOE PAGES

Moriarty, Nigel W.; Tronrud, Dale E.; Adams, Paul D.; ...

2014-06-17

Ideal values of bond angles and lengths used as external restraints are crucial for the successful refinement of protein crystal structures at all but the highest of resolutions. The restraints in common usage today have been designed based on the assumption that each type of bond or angle has a single ideal value independent of context. However, recent work has shown that the ideal values are, in fact, sensitive to local conformation, and as a first step toward using such information to build more accurate models, ultra-high resolution protein crystal structures have been used to derive a conformation-dependent library (CDL)more » of restraints for the protein backbone (Berkholz et al. 2009. Structure. 17, 1316). Here, we report the introduction of this CDL into the Phenix package and the results of test refinements of thousands of structures across a wide range of resolutions. These tests show that use of the conformation dependent library yields models that have substantially better agreement with ideal main-chain bond angles and lengths and, on average, a slightly enhanced fit to the X-ray data. No disadvantages of using the backbone CDL are apparent. In Phenix usage of the CDL can be selected by simply specifying the cdl=True option. This successful implementation paves the way for further aspects of the context-dependence of ideal geometry to be characterized and applied to improve experimental and predictive modelling accuracy.« less

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

NASA Technical Reports Server (NTRS)

Altshuller, Aubrey P

1955-01-01

The average bond energies D(gm)(B-Z) for boron-containing molecules have been calculated by the Pauling geometric-mean equation. These calculated bond energies are compared with the average bond energies D(exp)(B-Z) obtained from experimental data. The higher values of D(exp)(B-Z) in comparison with D(gm)(B-Z) when Z is an element in the fifth, sixth, or seventh periodic group may be attributed to resonance stabilization or double-bond character.

Negative hyperconjugation and red-, blue- or zero-shift in X-Z∙∙∙Y complexes.

PubMed

Joy, Jyothish; Jemmis, Eluvathingal D; Vidya, Kaipanchery

2015-01-01

A generalized explanation is provided for the existence of the red- and blue-shifting nature of X-Z bonds (Z=H, halogens, chalcogens, pnicogens, etc.) in X-Z∙∙∙Y complexes based on computational studies on a selected set of weakly bonded complexes and analysis of existing literature data. The additional electrons and orbitals available on Z in comparison to H make for dramatic differences between the H-bond and the rest of the Z-bonds. The nature of the X-group and its influence on the X-Z bond length in the parent X-Z molecule largely controls the change in the X-Z bond length on X-Z∙∙∙Y bond formation; the Y-group usually influences only the magnitude of the effects controlled by X. The major factors which control the X-Z bond length change are: (a) negative hyperconjugative donation of electron density from X-group to X-Z σ* antibonding molecular orbital (ABMO) in the parent X-Z, (b) induced negative hyperconjugation from the lone pair of electrons on Z to the antibonding orbitals of the X-group, and (c) charge transfer (CT) from the Y-group to the X-Z σ* orbital. The exchange repulsion from the Y-group that shifts partial electron density at the X-Z σ* ABMO back to X leads to blue-shifting and the CT from the Y-group to the σ* ABMO of X-Z leads to red-shifting. The balance between these two opposing forces decides red-, zero- or blue-shifting. A continuum of behaviour of X-Z bond length variation is inevitable in X-Z∙∙∙Y complexes.

Bond between smooth prestressing wires and concrete : finite element model and transfer length analysis for pretensioned concrete crossties.

DOT National Transportation Integrated Search

2014-04-03

Pretensioned concrete ties are increasingly employed in railroad high speed : and heavy haul applications. The bond between prestressing wires or strands and : concrete plays an important role in determining the transfer length of pretensioned : conc...

Rhenium(V)-oxo complexes of neutral and monoanionic tetraazamacrocycles. X-ray structures of trans-oxohydroxo(1,4,8,11-tetraazacyclotetradecane)rhenium(V) bis(perchlorate)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsang, B.W.; Reibenspies, J.; Martell, A.E.

1993-03-17

The complexes of ReO[sub 2][sup +] and ReO(OH)[sup 2+] with 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,8,11-tetraazacyclotetradecan-2-one (O[sub 1]cyclam) have been synthesized and characterized. The complexes were prepared by ligand exchange reactions of the macrocycles with a variety of starting compounds including ReOCl[sub 3](PPh[sub 3])[sub 2] and ReO[sub 2](en)[sub 2]Cl. The ReO(OH)[sup 2+] complexes have been structurally characterized. ReO(OH)(H[sub [minus]1]O[sub 1]cyclam)ReO[sub 4] crystallizes in the monoclinic P2[sub 1]/n space group with a = 10.308(3) [Angstrom], b = 9.527(2) [Angstrom], c = 17.808(3) [Angstrom], and [beta] = 106.57(2)[degrees]. ReO(OH)(cyclam)(ClO[sub 4])[sub 2] crystallizes in the monoclinic C2/c space group with a = 9.734(4) [Angstrom], bmore » = 16.999(5) [Angstrom], c = 12.187(5) [Angstrom], and [beta] = 106.36[degrees]. The complex ReO(OH)(H[sub [minus]1]O[sub 1]cyclam)ReO[sub 4] has a distorted octahedral structure with one short ReO(oxo) bond and one long ReO(hydroxo) bond (1.685(8) vs 1.970(8) [Angstrom]). The deprotonated amide ReN(sp[sup 2]) bond is shorter than the other three ReN(sp[sup 3]) bond lengths (1.98(1) vs 2.13(3) [Angstrom] (average)). The structure of the ReO(OH)(cyclam)(ClO[sub 4])[sub 2] complex shows no distinction between the lengths of the two ReO(oxo and hydroxo) bonds (1.766(5) [Angstrom]) due to disorder of the oxo and hydroxo groups. Spectroscopic evidence is reported to confirm the presence of both oxo and hydroxo groups coordinated to rhenium. 38 refs., 7 figs., 6 tabs.« less

Charge disproportionation in tetragonal La2MoO5, a small band gap semiconductor influenced by direct Mo-Mo bonding.

PubMed

Colabello, Diane M; Camino, Fernando E; Huq, Ashfia; Hybertsen, Mark; Khalifah, Peter G

2015-01-28

The structure of the novel compound La2MoO5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.0568(2) Å and with Z = 8. It consists of equal proportions of bioctahedral (Mo2O10) and square prismatic (Mo2O8) dimers, both of which contain direct Mo-Mo bonds and are arranged in 1D chains. The Mo-Mo bond length in the Mo2O10 dimers is 2.684(8) Å, while there are two types of Mo2O8 dimers with Mo-Mo bonds lengths of 2.22(2) and 2.28(2) Å. Although the average Mo oxidation state in La2MoO5 is 4+, the very different Mo-Mo distances reflect the fact that the Mo2O10 dimers contain only Mo(5+) (d(1)), while the prismatic Mo2O8 dimers only contain Mo(3+) (d(3)), a result directly confirmed by density function theory calculations. This is due to the complete disproportionation of Mo(4+), a phenomenon which has not previously been observed in solid-state compounds. La2MoO5 is diamagnetic, behavior which is not expected for a nonmetallic transition-metal oxide whose cation sites have an odd number of d-electrons. The resistivity displays the Arrhenius-type activated behavior expected for a semiconductor with a band gap of 0.5 eV, exhibiting an unusually small transport gap relative to other diamagnetic oxides. Diffuse reflectance studies indicate that La2MoO5 is a rare example of a stable oxide semiconductor with strong infrared absorbance. It is shown that the d-orbital splitting associated with the Mo2O8 and Mo2O10 dimeric units can be rationalized using simple molecular orbital bonding concepts.

Electronic structure and bonding of intergranular glassy films in polycrystalline Si3 N4 : Ab initio studies and classical molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Rulis, P.; Chen, J.; Ouyang, L.; Ching, W.-Y.; Su, X.; Garofalini, S. H.

2005-06-01

The electronic structure and bonding of a realistic model of an intergranular glassy film (IGF) was studied with multiple computational methods. The model has a Si-O-N glassy region sandwiched between crystalline basal planes of β-Si3N4 and contains a total of 798 atoms. It was constructed with periodic boundary conditions via classical molecular dynamics (MD) techniques using an accurate multibody atomic potential. The model was then further relaxed by the VASP (Vienna ab initio simulation package) program. It is shown that the VASP-relaxed structure reduces the total energy from the MD-relaxed structure by only 47.38eV , validating the accuracy of the multiatom potential used. The calculated electronic structure shows the IGF model to be an insulator with a sizable gap of almost 3eV . Quasidefectlike states can be identified near the band edges arising from the more strained Si-N and Si-O bonds at the interface. Calculation of the Mulliken effective charge and bond order values indicates that the bonds in the glassy region and at the interface can be enhanced and weakened by distortions in the bond length and bond angle. The states at the top of the valence band are derived mostly from the crystalline part of the Si-N bonding while the states at the bottom of the conduction band are dominated by the Si-O bonding in the glassy region. Calculation of the electrostatic potential across the interface shows an average band offset of about 1.5eV between the crystalline β-Si3N4 and the glassy Si-O-N region which could be related to the space charge model for IGF.

Continuum in the X-Z---Y weak bonds: Z= main group elements.

PubMed

Joy, Jyothish; Jose, Anex; Jemmis, Eluvathingal D

2016-01-15

The Continuum in the variation of the X-Z bond length change from blue-shifting to red-shifting through zero- shifting in the X-Z---Y complex is inevitable. This has been analyzed by ab-initio molecular orbital calculations using Z= Hydrogen, Halogens, Chalcogens, and Pnicogens as prototypical examples. Our analysis revealed that, the competition between negative hyperconjugation within the donor (X-Z) molecule and Charge Transfer (CT) from the acceptor (Y) molecule is the primary reason for the X-Z bond length change. Here, we report that, the proper tuning of X- and Y-group for a particular Z- can change the blue-shifting nature of X-Z bond to zero-shifting and further to red-shifting. This observation led to the proposal of a continuum in the variation of the X-Z bond length during the formation of X-Z---Y complex. The varying number of orbitals and electrons available around the Z-atom differentiates various classes of weak interactions and leads to interactions dramatically different from the H-Bond. Our explanations based on the model of anti-bonding orbitals can be transferred from one class of weak interactions to another. We further take the idea of continuum to the nature of chemical bonding in general. © 2015 Wiley Periodicals, Inc.

Effect of metal surface topography on mechanical bonding at simulated total hip stem-cement interfaces.

PubMed

Chen, C Q; Scott, W; Barker, T M

1999-01-01

Bonding and loosening mechanisms between bone cement and joint prostheses have not been well identified. In this study, the effects of simulated hip stem surface topography on the interfacial shear strength were examined. Six different surface topographies were used. They were described by several surface characterization parameters that may directly relate to the interfacial bonding strength: average surface roughness R(a), root mean square slope R(Deltaq), correlation length beta, and fluid retention index R(ri). The shear strengths between Palacos E bone cement and stainless steel rods were measured using an Instron materials testing machine. We found that cement can "flow" into the surface microtopography and establish good contact with the metal surface. The results show that the interfacial strength increases monotonically with the increase of R(Deltaq) instead of with R(a). The relationship between interfacial strength and surface parameters shows that a metal stem with an isotropic surface texture, higher R(Deltaq), and greater R(ri) gives a higher interfacial strength. Copyright 1999 John Wiley & Sons, Inc.

Crystal structure of (eth­oxy­ethyl­idene)di­methyl­aza­nium ethyl sulfate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2015-01-01

In the title salt, C6H14NO+·C2H5SO4 −, the C—N bond lengths in the cation are 1.2981 (14), 1.4658 (14) and 1.4707 (15) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.3157 (13) Å shows double-bond character, indicating charge delocalization within the NCO plane of the iminium ion. In the crystal, C—H⋯O hydrogen bonds between H atoms of the cations and O atoms of neighbouring ethyl sulfate anions are present, generating a three-dimensional network. PMID:26870525

The Effect of Limited Diffusion and Wet-Dry Cycling on Reversible Polymerization Reactions: Implications for Prebiotic Synthesis of Nucleic Acids.

PubMed

Higgs, Paul G

2016-06-08

A long-standing problem for the origins of life is that polymerization of many biopolymers, including nucleic acids and peptides, is thermodynamically unfavourable in aqueous solution. If bond making and breaking is reversible, monomers and very short oligomers predominate. Recent experiments have shown that wetting and drying cycles can overcome this problem and drive the formation of longer polymers. In the dry phase, bond formation is favourable, but diffusion is restricted, and bonds only form between monomers that are initially close together. In the wet phase, some of the bonds are hydrolyzed. However, repositioning of the molecules allows new bonds to form in the next dry phase, leading to an increase in mean polymer length. Here, we consider a simple theoretical model that explains the effect of cycling. There is an equilibrium length distribution with a high mean length that could be achieved if diffusion occurred freely in the dry phase. This equilibrium is inaccessible without diffusion. A single dry cycle without diffusion leads to mean lengths much shorter than this. Repeated cycling leads to a significant increase in polymerization relative to a single cycle. In the most favourable case, cycling leads to the same equilibrium length distribution as would be achieved if free diffusion were possible in the dry phase. These results support the RNA World scenario by explaining a potential route to synthesis of long RNAs; however, they also imply that cycling would be beneficial to the synthesis of other kinds of polymers, including peptides, where bond formation involves a condensation reaction.

The Effect of Limited Diffusion and Wet–Dry Cycling on Reversible Polymerization Reactions: Implications for Prebiotic Synthesis of Nucleic Acids

PubMed Central

Higgs, Paul G.

2016-01-01

A long-standing problem for the origins of life is that polymerization of many biopolymers, including nucleic acids and peptides, is thermodynamically unfavourable in aqueous solution. If bond making and breaking is reversible, monomers and very short oligomers predominate. Recent experiments have shown that wetting and drying cycles can overcome this problem and drive the formation of longer polymers. In the dry phase, bond formation is favourable, but diffusion is restricted, and bonds only form between monomers that are initially close together. In the wet phase, some of the bonds are hydrolyzed. However, repositioning of the molecules allows new bonds to form in the next dry phase, leading to an increase in mean polymer length. Here, we consider a simple theoretical model that explains the effect of cycling. There is an equilibrium length distribution with a high mean length that could be achieved if diffusion occurred freely in the dry phase. This equilibrium is inaccessible without diffusion. A single dry cycle without diffusion leads to mean lengths much shorter than this. Repeated cycling leads to a significant increase in polymerization relative to a single cycle. In the most favourable case, cycling leads to the same equilibrium length distribution as would be achieved if free diffusion were possible in the dry phase. These results support the RNA World scenario by explaining a potential route to synthesis of long RNAs; however, they also imply that cycling would be beneficial to the synthesis of other kinds of polymers, including peptides, where bond formation involves a condensation reaction. PMID:27338479

Theoretical electrical conductivity of hydrogen-bonded benzamide-derived molecules and single DNA bases.

PubMed

Chen, Xiang

2013-09-01

A benzamide molecule is used as a "reader" molecule to form hydrogen bonds with five single DNA bases, i.e., four normal single DNA bases A,T,C,G and one for 5methylC. The whole molecule is then attached to the gold surface so that a meta-molecule junction is formed. We calculate the transmission function and conductance for the five metal-molecule systems, with the implementation of density functional theory-based non-equilibrium Green function method. Our results show that each DNA base exhibits a unique conductance and most of them are on the pS level. The distinguishable conductance of each DNA base provides a way for the fast sequencing of DNA. We also investigate the dependence of conductivity of such a metal-molecule system on the hydrogen bond length between the "reader" molecule and DNA base, which shows that conductance follows an exponential decay as the hydrogen bond length increases, i.e., the conductivity is highly sensitive to the change in hydrogen bond length.

Symmetry and novelty in the electronic and geometric structure of nanoalloys:. the case of Ag27Cu7

NASA Astrophysics Data System (ADS)

Ortigoza, M. Alcántara; Rahman, T. S.

2008-04-01

Nanoparticles of bimetallic alloys have been shown to possess composition dependent characteristics which distinguish themselves from the corresponding bulk alloys. Taking the 34-atom nanoalloy of Ag and Cu (Ag27Cu7), we show using first principles electronic structure calculations that this core-shell alloy indeed has perfect D5h symmetry and consists of only 6 non-equivalent (2 Cu and 4 Ag) atoms. Analysis of the interatomic bond lengths and detailed electronic structure further reveal that the Cu atoms play a major role in controlling the characteristics of the nanoalloy. The higher cohesive energy, together with shorter bond length for Cu, compared to Ag, conspire to produce a hierarchy in the relative strengths of the Ag - Cu, Ag - Ag, and Cu - Cu bonds and corresponding interatomic bond lengths, point to the uniqueness in the characteristics of this nanoalloy. Charge density plots of Ag27Cu7 provide further insights into the relative strengths of the various interatomic bonds.

Evidence from bond lengths and bond angles for enneacovalence of cobalt, rhodium, iridium, iron, ruthenium, and osmium in compounds with elements of medium electronegativity.

PubMed

Pauling, L

1984-03-01

Enneacovalence of neutral atoms can be achieved for Co, Rh, and Ir by promoting some electrons from the nd orbital to the (n + 1)s and (n + 1)p orbitals and for Fe, Ru, and Os by a similar promotion together with the addition of an electron, which may be provided by an electron pair from a singly bonded carbonyl group or other group. The bond lengths and bond angles are predicted by the theory of enneacovalence to be significantly different for the different transition metals. Recently reported experimental values are shown to be in good agreement with the predicted values, providing support for the theory of enneacovalence and the theory of hybrid sp(3)d(5) bond orbitals.

Computation of deuterium isotope perturbation of 13C NMR chemical shifts of alkanes: a local mode zero-point level approach.

PubMed

Yang, Kin S; Hudson, Bruce

2010-11-25

Replacement of H by D perturbs the (13)C NMR chemical shifts of an alkane molecule. This effect is largest for the carbon to which the D is attached, diminishing rapidly with intervening bonds. The effect is sensitive to stereochemistry and is large enough to be measured reliably. A simple model based on the ground (zero point) vibrational level and treating only the C-H(D) degrees of freedom (local mode approach) is presented. The change in CH bond length with H/D substitution as well as the reduction in the range of the zero-point level probability distribution for the stretch and both bend degrees of freedom are computed. The (13)C NMR chemical shifts are computed with variation in these three degrees of freedom, and the results are averaged with respect to the H and D distribution functions. The resulting differences in the zero-point averaged chemical shifts are compared with experimental values of the H/D shifts for a series of cycloalkanes, norbornane, adamantane, and protoadamantane. Agreement is generally very good. The remaining differences are discussed. The proton spectrum of cyclohexane- is revisited and updated with improved agreement with experiment.

Experimental and theoretical studies of the crystal structures of bis-isoxazole-bis-methylene dinitrate (BIDN) and bis-isoxazole tetramethylene tetranitrate (BITN) by x-ray crystallography and density functional theory

NASA Astrophysics Data System (ADS)

Taylor, Decarlos E.; Sausa, Rosario C.

2018-06-01

The determination of crystal structures plays an important role for model testing and validation, and understanding intra and intermolecular interactions that influence crystal packing. Here, we report the molecular structure of two recently synthesized energetic molecules, 3,3-bis-isoxazole-5,5‧-bis-methylene dinitrate (C8H6N4O8, BIDN) and bis-isoxazole tetramethylene tetranitrate (C10H8N6O14, BITN) determined by single crystal x-ray diffraction and solid state density functional theory (DFT). BIDN is composed of two planar alkyl nitrate groups (r.m.s deviation = 0.0004 (1) Å) bonded to two planar azole rings (r.m.s deviation = 0.001 (1) Å, whereas BITN is composed of four planar alkyl nitrate groups (average r.m.s deviation = 0.002 (1) Å) bonded to two planar azole rings (average r.m.s deviation = 0.002 (1) Å). The theoretical calculations predict very well the planarity of both the alkyl nitrate groups and rings for both compounds. Furthermore, they predict well the bond lengths and angles of both molecules with mean deviation values of 0.018 Å (BIDN) and 0.017 Å (BITN) and 0.481° (BIDN) and 0.747° (BITN). Overall, the DFT determined torsion angles agree well with those determined experimentally for both BIDN (average deviation = 1.139°) and BITN (average deviation = 0.604°). The theoretical cell constant values are in excellent agreement with those determined experimentally for both molecules, with the BIDN a cell value and β angle showing the largest deviation, 2.1% and -1.3%, respectively. Contacts between the atoms N and H dominate the intermolecular interactions of BIDN, whereas contacts involving the atoms O and H dominate the BITN intermolecular interactions. Electrostatic potential calculations at the B3LYP/6-31G* level reveal BIDN exhibits a lower sensitivity to impact compared to BITN.

Atomic and molecular analysis highlights the biophysics of unprotonated and protonated retinal in UV and scotopic vision.

PubMed

Kubli-Garfias, Carlos; Vázquez-Ramírez, Ricardo; Cabrera-Vivas, Blanca M; Gómez-Reyes, Baldomero; Ramírez, Juan Carlos

2015-09-26

During the photoreaction of rhodopsin, retinal isomerizes, rotating the C11[double bond, length as m-dash]C12 π-bond from cis to an all-trans configuration. Unprotonated (UR) or protonated (PR) retinal in the Schiff's base (SB) is related to UV and light vision. Because the UR and PR have important differences in their physicochemical reactivities, we compared the atomic and molecular properties of these molecules using DFT calculations. The C10-C11[double bond, length as m-dash]C12-C13 dihedral angle was rotated from 0° to 180° in 45° steps, giving five conformers, and the following were calculated from them: atomic orbital (AO) contributions to the HOMO and LUMO, atomic charges, bond length, bond order, HOMO, LUMO, hardness, electronegativity, polarizability, electrostatic potential, UV-vis spectra and dipole moment (DM). Similarly, the following were analyzed: the energy profile, hybridization, pyramidalization and the hydrogen-out-of-plane (HOOP) wagging from the H11-C11[double bond, length as m-dash]C12-H12 dihedral angle. In addition, retinal with a water H-bond (HR) in the SB was included for comparison. Interestingly, in the PR, C11 and C12 are totally the LUMO and the HOMO, respectively, and have a large electronegativity difference, which predicts an electron jump in these atoms during photoexcitation. At the same time, the PR showed a longer bond length and lower bond order, with a larger DM, lower HOMO-LUMO gap, lower hardness and higher electronegativity. In addition, the AOs of -45° and -90° conformers changed significantly, from pz to py, during the rotation concomitantly with marked hybridization, smooth pyramidalization and lower HOOP activity. Clearly, the atomic and molecular differences between the UR and PR are overwhelming, including the rotational energy profile and light absorption spectra, which indicates that light absorption of UR and PR is already determined by the retinal characteristics of the SB protonation. The HR-model compared with UR shows a lower energy barrier and a discreet bathochromic effect in the UV region.

Red shift of the SF6 vibration spectrum induced by the electron absorption: An ab initio study

NASA Astrophysics Data System (ADS)

Tang, Bin; Zhang, Long-Fei; Han, Fang-Yuan; Luo, Zong-Chang; Liang, Qin-Qin; Liu, Chen-Yao; Zhu, Li-Ping; Zhang, Jie-Ming

2018-01-01

As a widely used gas insulator, sulfur hexafluoride (SF6) has a large cross section for electron absorption, which may make the molecule ionized to the -1 charge state in the high-voltage environment. Using ab initio calculations, we show that the absorbed electron is located averagely on the six F atoms, occupying the antibonding level of the s-p σ bonds and increasing the S-F bond length. The ionized SF6- molecule decreases its decomposition energy to only 1.5 eV, much lower than that of the neutral molecule (4.8 eV), which can be understood according to the occupying of the antibonding orbital and thus weakening of the s-p σ bonds. The weakening of the bonds results in an obvious red shift in the vibrational modes of the ionized SF6- molecule by 120-270 cm-1, compared to those of the neutral molecule. The detailed origin of these vibrational modes is analyzed. Since the appearance of the ionized SF6- molecules is before the decomposition reaction of the SF6- molecule into low-fluoride sulfides, this method may improve the sensitivity of the defection of the partial discharge and save more time for the prevention of the insulation failure in advance.

All-atomic Molecular Dynamic Studies of Human CDK8: Insight into the A-loop, Point Mutations and Binding with Its Partner CycC

PubMed Central

Xu, Wu; Amire-Brahimi, Benjamin; Xie, Xiao-Jun; Huang, Liying; Ji, Jun-Yuan

2014-01-01

The Mediator, a conserved multisubunit protein complex in eukaryotic organisms, regulates gene expression by bridging sequence-specific DNA-binding transcription factors to the general RNA polymerase II machinery. In yeast, Mediator complex is organized in three core modules (head, middle and tail) and a separable ‘CDK8 submodule’ consisting of four subunits including Cyclin-dependent kinase CDK8 (CDK8), Cyclin C (CycC), MED12, and MED13. The 3-D structure of human CDK8-CycC complex has been recently experimentally determined. To take advantage of this structure and the improved theoretical calculation methods, we have performed molecular dynamic simulations to study dynamics of CDK8 and two CDK8 point mutations (D173A and D189N), which have been identified in human cancers, with and without full length of the A-loop as well as the binding between CDK8 and CycC. We found that CDK8 structure gradually loses two helical structures during the 50-ns molecular dynamic simulation, likely due to the presence of the full-length A-loop. In addition, our studies showed the hydrogen bond occupation of the CDK8 A-loop increases during the first 20-ns MD simulation and stays stable during the later 30-ns MD simulation. Four residues in the A-loop of CDK8 have high hydrogen bond occupation, while the rest residues have low or no hydrogen bond occupation. The hydrogen bond dynamic study of the A-loop residues exhibits three types of changes: increasing, decreasing, and stable. Furthermore, the 3-D structures of CDK8 point mutations D173A, D189N, T196A and T196D have been built by molecular modeling and further investigated by 50-ns molecular dynamic simulations. D173A has the highest average potential energy, while T196D has the lowest average potential energy, indicating that T196D is the most stable structure. Finally, we calculated theoretical binding energy of CDK8 and CycC by MM/PBSA and MM/GBSA methods, and the negative values obtained from both methods demonstrate stability of CDK8-CycC complex. Taken together, these analyses will improve our understanding of the exact functions of CDK8 and the interaction with its partner CycC. PMID:24754906

Sacrificial bonds and hidden length in biomaterials: A kinetic constitutive description of strength and toughness in bone

NASA Astrophysics Data System (ADS)

Lieou, Charles K. C.; Elbanna, Ahmed E.; Carlson, Jean M.

2013-07-01

Sacrificial bonds and hidden length in structural molecules account for the greatly increased fracture toughness of biological materials compared to synthetic materials without such structural features by providing a molecular-scale mechanism for energy dissipation. One example is in the polymeric glue connection between collagen fibrils in animal bone. In this paper we propose a simple kinetic model that describes the breakage of sacrificial bonds and the release of hidden length, based on Bell's theory. We postulate a master equation governing the rates of bond breakage and formation. This enables us to predict the mechanical behavior of a quasi-one-dimensional ensemble of polymers at different stretching rates. We find that both the rupture peak heights and maximum stretching distance increase with the stretching rate. In addition, our theory naturally permits the possibility of self-healing in such biological structures.

Studies of EXAFSSpectra using Copper (II) Schiff Base complexes and Determination of Bond lengths Using Synchrotron Radiation

NASA Astrophysics Data System (ADS)

Mishra, A.; Vibhute, V.; Ninama, S.; Parsai, N.; Jha, S. N.; Sharma, P.

2016-10-01

X-ray absorption fine structure (XAFS) at the K-edge of copper has been studied in some copper (II) complexes with substituted anilines like (2Cl, 4Br, 2NO2, 4NO2 and pure aniline) with o-PDA (orthophenylenediamine) as ligand. The X-ray absorption measurements have been performed at the recently developed BL-8 dispersive EXAFS beam line at 2.5 GeV Indus-2 Synchrotron Source at RRCAT, Indore, India. The data obtained has been processed using EXAFS data analysis program Athena.The graphical method gives the useful information about bond length and also the environment of the absorbing atom. The theoretical bond lengths of the complexes were calculated by using interactive fitting of EXAFS using fast Fourier inverse transformation (IFEFFIT) method. This method is also called as Fourier transform method. The Lytle, Sayers and Stern method and Levy's method have been used for determination of bond lengths experimentally of the studied complexes. The results of both methods have been compared with theoretical IFEFFIT method.

Evidence from bond lengths and bond angles for enneacovalence of cobalt, rhodium, iridium, iron, ruthenium, and osmium in compounds with elements of medium electronegativity

PubMed Central

Pauling, Linus

1984-01-01

Enneacovalence of neutral atoms can be achieved for Co, Rh, and Ir by promoting some electrons from the nd orbital to the (n + 1)s and (n + 1)p orbitals and for Fe, Ru, and Os by a similar promotion together with the addition of an electron, which may be provided by an electron pair from a singly bonded carbonyl group or other group. The bond lengths and bond angles are predicted by the theory of enneacovalence to be significantly different for the different transition metals. Recently reported experimental values are shown to be in good agreement with the predicted values, providing support for the theory of enneacovalence and the theory of hybrid sp3d5 bond orbitals. PMID:16593439

Theoretical verification and extension of the McKean relationship between bond lengths and stretching frequencies

NASA Astrophysics Data System (ADS)

Larsson, J. A.; Cremer, D.

1999-08-01

Vibrational spectra contain explicit information on the electronic structure and the bonding situation of a molecule, which can be obtained by transforming the vibrational normal modes of a molecule into appropriate internal coordinate modes, which are localized in a fragment of the molecule and which are associated to that internal coordinate that describes the molecular fragment in question. It is shown that the adiabatic internal modes derived recently (Int. J. Quant. Chem., 67 (1998) 1) are the theoretical counterparts of McKean's isolated CH stretching modes (Chem. Soc. Rev., 7 (1978) 399). Adiabatic CH stretching frequencies obtained from experimental vibrational spectra can be used to determine CH bond lengths with high accuracy. Contrary to the concept of isolated stretching frequencies a generalization to any bond of a molecule is possible as is demonstrated for the CC stretching frequencies. While normal mode frequencies do not provide a basis to determine CC bond lengths and CC bond strengths, this is possible with the help of the adiabatic CC stretching frequencies. Measured vibrational spectra are used to describe different types of CC bonds in a quantitative way. For CH bonds, it is also shown that adiabatic stretching frequency leads to the definition of an ideal dissociation energy, which contrary to the experimentally determined dissociation energy is a direct measure of the bond strength. The difference between measured and ideal dissociation energies gives information on stabilization or destabilization of the radicals formed in a dissociation process.

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

PubMed

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

2012-01-21

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

Introducing Quantum Mechanics into General Chemistry

NASA Astrophysics Data System (ADS)

Popkowski, Iwona; Bascal, Hafed

2008-10-01

Periodicity has long been recognized as the tool that chemists can use to bring some order to investigating the chemistry of more than one hundred elements. Such studies provide useful tools for understanding a wide array of chemical principles. The advances in computational chemistry make it possible to study and teach such trends with hands on approach. In this study we utilize recently acquired software Spartan Pro to illustrate theoretical measurements of bond length, bond angle and dipole as compared to experimental data. We constructed a matrix of values obtained from the theoretical calculations and obtained trends in bond length, bond angle and dipoles for the several periodic groups.

X-ray absorption spectral studies of copper (II) mixed ligand complexes

NASA Astrophysics Data System (ADS)

Soni, B.; Dar, Davood Ah; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2014-09-01

X-ray absorption spectra at the K-edge of copper have been studied in two copper mixed ligand complexes, one having tetramethyethylenediamine (tmen) and the other having tetraethyethylenediamine (teen) as one of the ligands. The spectra have been recorded at BL-8 dispersive extended X-ray absorption fine structure (EXAFS) beamline at the 2.5 GeV INDUS- 2 synchrotron, RRCAT, Indore, India. The data obtained has been processed using the data analysis program Athena. The energy of the K-absorption edge, chemical shift, edge-width and shift of the principal absorption maximum in the complexes have been determined and discussed. The values of these parameters have been found to be approximately the same in both the complexes indicating that the two complexes possess similar chemical environment around the copper metal atom. The chemical shift has been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length because of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase- uncorrected bond length. Bond length has also been determined by Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The results obtained from LSS and the Fourier transformation methods are comparable with each other, since both are phase uncorrected bond lengths.

Structural and Computational Studies of Cp(CO)2(PCy3)MoFBF3, a Complex with a Bound BF4- Ligand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Tan-Yun; Szalda, David J.; Franz, James A.

2010-02-15

Hydride transfer from Cp(CO)2(PCy3)MoH to Ph3C+BF4 gives Cp(CO)2(PCy3)MoFBF3, and the crystal structure of this complex was determined. In the weakly bound FBF3 ligand, the B-F(bridging) bond length is 1.475(8) Å, which is 0.15 Å longer than the average length of the three B-F(terminal) bonds. The PCy3 and FBF3 ligands are cis to each other in the four-legged piano stool structure. Electronic structure (DFT) calculations predict the trans isomer of Cp(CO)2(PCy3)MoFBF3 to be 9.5 kcal/mol (in ΔGog,298)) less stable than the cis isomer that was crystallographically characterized. Hydride transfer from Cp(CO)2(PCy3)MoH to Ph3C+BAr'4 [Ar' = 3,5-bis(trifluoromethyl)phenyl] in CH2Cl2 solvent produces [Cp(CO)2(PCy3)Mo(ClCH2Cl)]+[BAr'4]more » , in which CH2Cl2 is coordinated to the metal. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less

Finite Element Bond Modeling for Indented Wires in Pretensioned Concrete Crossties

DOT National Transportation Integrated Search

2016-04-12

Indented wires have been increasingly employed by : concrete crosstie manufacturers to improve the bond between : prestressing steel reinforcements and concrete, as bond can : affect several critical performance measures, including transfer : length,...

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

PubMed Central

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Crystal structure of catena-poly[[aquadi-n-propyl­tin(IV)]-μ-oxalato

PubMed Central

Reichelt, Martin; Reuter, Hans

2014-01-01

The title compound, [Sn(C3H7)2(H2O)(C2O4)]n, represents the first diorganotin(IV) oxalate hydrate to be structurally characterized. The tin(IV) atom of the one-dimensional coordination polymer is located on a twofold rotation axis and is coordinated by two chelating oxalate ligands with two slightly different Sn—O bond lengths of 2.290 (2) and 2.365 (2) Å, two symmetry-related n-propyl groups with a Sn—C bond lengths of 2.127 (3) Å, and a water mol­ecule with a Sn—O bond length of 2.262 (2) Å. The coordination polyhedron around the SnIV atom is a slightly distorted penta­gonal bipyramid with a nearly linear axis between the trans-oriented n-propyl groups [C—Sn—C = 176.8 (1)°]. The bond angles between the oxygen atoms of the equatorial plane range from 70.48 (6)° to 76.12 (8)°. A one-dimensional coordination polymer results from the less asymmetric bilateral coordination of the centrosymmetric oxalate anion, inter­nally reflected by two slightly different C—O bond lengths of 1.248 (3) and 1.254 (3) Å. The chains of the polymer propagate parallel to [001] and are held together by hydrogen bonds between water mol­ecules and oxalate anions of neighboring chains, leading to a two-dimensional network parallel to (100). PMID:25249862

Compositional effects on Si–OH bond length in hydrous silicates with implications for trends in the SiOH acidity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarubin, Dmitri P., E-mail: dmitri.zarubin@mtu-net.ru

2014-04-01

Theoretical calculations of the structure and Brønsted acidity of SiOH groups in silica clusters have never addressed the question if these vary with the degree of SiOH deprotonation. In this connection, a statistical analysis is presented of Si–OH bond lengths in crystalline hydrogen silicates with well-determined structures with a special emphasis placed on effects of the silicate composition. It is found that among hydrogen silicates of large cations with low charges the Si–OH bonds are always longer than terminal Si–O bonds in the same anion and correlate in length with the anionic charge per tetrahedron. The findings are explained bymore » steric limitations on charge balancing at oxygen atoms by hydrogen bonds and/or cations. It is suggested that similar limitations and imbalances may underlie the well-known trends in the Brønsted acidity of silicic acids and silicas in aqueous media: decreased acidity with increased SiOH deprotonation and increased acidity with increased tetrahedra connectivity. - Graphical abstract: Si–OH bonds in crystalline silicates lengthen with the anionic charge per tetrahedron, which is in parallel with the well-known trend of decreased acidity of silicic acids and silicas in solution with increased degree of deprotonation. - Highlights: • Si–OH bonds in alkali hydrogen silicates are always longer than terminal Si–O bonds. • Si–OH bonds in silicates lengthen with the anionic charge per tetrahedron. • The Si–OH bond elongation results from inherent underbonding of terminal O atoms. • The longer the Si–OH bond, the less acidic the OH group is.« less

Variations in enamel damage after debonding of two different bracket base designs: An in vitro study.

PubMed

Ahangar Atashi, Mohammad Hossein; Sadr Haghighi, Amir Hooman; Nastarin, Parastou; Ahangar Atashi, Sina

2018-01-01

Background. Bracket base design is a factor influencing shear bond strength. High shear bond strength leads to enamel crack formation during debonding. The aim of this study was to compare enamel damage variations, including the number and length of enamel cracks after debonding of two different base designs. Methods. Eighty-eight extracted human premolars were randomly divided into2 groups (n=44). The teeth in each group were bonded by two types of brackets with different base designs: 80-gauge mesh design versus anchor pylon design with pylons for adhesive retention. The number and length of enamel cracks before bonding and after debonding were evaluated under an optical stereomicroscope ×40 in both groups. Mann-Whitney U test was used to compare the number of cracks between the two groups. ANCOVA was used for comparison of crack lengths after and before debonding in each group and between the two groups. Results. There was a significant increase in enamel crack length and numbers in each group after debonding. There was no significant difference in enamel crack numbers after debonding between the two groups, whereas the length of enamel cracks was significantly greater in anchor pylon base design after debonding. Conclusion. Bracket bases with pylon design for adhesive retention caused more iatrogenic debonding damage to enamel surface.

Shock response of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX): The C-N bond scission studied by molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Yuan, Jiao-Nan; Wei, Yong-Kai; Zhang, Xiu-Qing; Chen, Xiang-Rong; Ji, Guang-Fu; Kotni, Meena Kumari; Wei, Dong-Qing

2017-10-01

The shock response has a great influence on the design, synthesis, and application of energetic materials in both industrial and military areas. Therefore, the initial decomposition mechanism of bond scission at the atomistic level of condensed-phase α-RDX under shock loading has been studied based on quantum molecular dynamics simulations in combination with a multi-scale shock technique. First, based on the frontier molecular orbital theory, our calculated result shows that the N-NO2 bond is the weakest bond in the α-RDX molecule in the ground state, which may be the initial bond for pyrolysis. Second, the changes of bonds under shock loading are investigated by the changes of structures, kinetic bond lengths, and Laplacian bond orders during the simulation. Also, the variation of thermodynamic properties with time in shocked α-RDX at 10 km/s along the lattice vector a for a timescale of up to 3.5 ps is presented. By analyzing the detailed structural changes of RDX under shock loading, we find that the shocked RDX crystal undergoes a process of compression and rotation, which leads to the C-N bond initial rupture. The time variation of dynamic bond lengths in a shocked RDX crystal is calculated, and the result indicates that the C-N bond is easier to rupture than other bonds. The Laplacian bond orders are used to predict the molecular reactivity and stability. The values of the calculated bond orders show that the C-N bonds are more sensitive than other bonds under shock loading. In a word, the C-N bond scission has been validated as the initial decomposition in a RDX crystal shocked at 10 km/s. Finally, the bond-length criterion has been used to identify individual molecules in the simulation. The distance thresholds up to which two particles are considered direct neighbors and assigned to the same cluster have been tested. The species and density numbers of the initial decomposition products are collected according to the trajectory.

Thinking Like a Chemist: Intuition in Thermoelectric Materials.

PubMed

Zeier, Wolfgang G; Zevalkink, Alex; Gibbs, Zachary M; Hautier, Geoffroy; Kanatzidis, Mercouri G; Snyder, G Jeffrey

2016-06-06

The coupled transport properties required to create an efficient thermoelectric material necessitates a thorough understanding of the relationship between the chemistry and physics in a solid. We approach thermoelectric material design using the chemical intuition provided by molecular orbital diagrams, tight binding theory, and a classic understanding of bond strength. Concepts such as electronegativity, band width, orbital overlap, bond energy, and bond length are used to explain trends in electronic properties such as the magnitude and temperature dependence of band gap, carrier effective mass, and band degeneracy and convergence. The lattice thermal conductivity is discussed in relation to the crystal structure and bond strength, with emphasis on the importance of bond length. We provide an overview of how symmetry and bonding strength affect electron and phonon transport in solids, and how altering these properties may be used in strategies to improve thermoelectric performance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pullout Performances of Grouted Rockbolt Systems with Bond Defects

NASA Astrophysics Data System (ADS)

Xu, Chang; Li, Zihan; Wang, Shanyong; Wang, Shuren; Fu, Lei; Tang, Chunan

2018-03-01

This paper presents a numerical study on the pullout behaviour of fully grouted rockbolts with bond defects. The cohesive zone model (CZM) is adopted to model the bond-slip behaviour between the rockbolt and grout material. Tensile tests were also conducted to validate the numerical model. The results indicate that the defect length can obviously influence the load and stress distributions along the rockbolt as well as the load-displacement response of the grouted system. Moreover, a plateau in the stress distribution forms due to the bond defect. The linear limit and peak load of the load-displacement response decrease as the defect length increases. A bond defect located closer to the loaded end leads to a longer nonlinear stage in the load-displacement response. However, the peak loads measured from the specimens made with various defect locations are almost approximately the same. The peak load for a specimen with the defects equally spaced along the bolt is higher than that for a specimen with defects concentrated in a certain zone, even with the same total defect length. Therefore, the dispersed pattern of bond defects would be much safer than the concentrated pattern. For the specimen with dispersed defects, the peak load increases with an increase in the defect spacing, even if the total defect length is the same. The peak load for a grouted rockbolt system with defects increases with an increases in the bolt diameter. This work leads to a better understanding of the load transfer mechanism for grouted rockbolt systems with bond defects, and paves the way towards developing a general evaluation method for damaged rockbolt grouted systems.

Anisotropy of atomic bonds formed by p-type dopants in bulk GaN crystals

NASA Astrophysics Data System (ADS)

Lawniczak-Jablonska, K.; Suski, T.; Gorczyca, I.; Christensen, N. E.; Libera, J.; Kachniarz, J.; Lagarde, P.; Cortes, R.; Grzegory, I.

The anisotropy of atomic bonds formed by acceptor dopants with nitrogen in bulk wurtzite GaN crystals was studied by means of linearly polarized synchrotron radiation used in measurements of X-ray-absorption spectra for the K-edgeof Mg and Zn dopants. These spectra correspond to i) a single acceptor N bond along the c-axis and ii) three bonds realized with N atoms occupying the ab-plane perpendicular to the c-axis. The Zn dopant formed resonant spectra similar to that characteristic for Ga cations. In the case of the Mg dopant, similarity to Ga cations was observed for triple bonds in the ab-plane, only. Practically no resonant structure for spectra detected along the c-axis was observed. The absorption spectra were compared with ab initio calculations using the full-potential linear muffin-tin-orbital method. These calculations were also used for determination of the bond length for Mg-N and Zn-N in wurtzite GaN crystals and show that introducing dopants causes an increase of the lengths of the bonds formed by both dopants. Extended X-ray-absorption fine-structure measurements performed for bulk GaN:Zn confirmed the prediction of the theory in the case of the Zn-N bond. Finally, it is suggested that the anisotropy in the length of the Mg-N bonds, related to their larger strength in the case of bonds in the ab-plane, can explain preferential formation of a superlattice consisting of Mg-rich layers arranged in ab-planes of several bulk GaN:Mg crystals observed by transmission electron microscopy. Within the sensitivity of the method used, no parasitic metallic clusters or oxide compounds formed by the considered acceptors in GaN crystals were found.

Investigation of non-corrin cobalt(II)-containing sites in protein structures of the Protein Data Bank.

PubMed

Abriata, Luciano Andres

2013-04-01

Protein X-ray structures with non-corrin cobalt(II)-containing sites, either natural or substituting another native ion, were downloaded from the Protein Data Bank and explored to (i) describe which amino acids are involved in their first ligand shells and (ii) analyze cobalt(II)-donor bond lengths in comparison with previously reported target distances, CSD data and EXAFS data. The set of amino acids involved in Co(II) binding is similar to that observed for catalytic Zn(II) sites, i.e. with a large fraction of carboxylate O atoms from aspartate and glutamate and aromatic N atoms from histidine. The computed Co(II)-donor bond lengths were found to depend strongly on structure resolution, an artifact previously detected for other metal-donor distances. Small corrections are suggested for the target bond lengths to the aromatic N atoms of histidines and the O atoms of water and hydroxide. The available target distance for cysteine (Scys) is confirmed; those for backbone O and other donors remain uncertain and should be handled with caution in refinement and modeling protocols. Finally, a relationship between both Co(II)-O bond lengths in bidentate carboxylates is quantified.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, L. H.; Wang, X. D.; Yu, Q.

Temperature-dependent atomistic structure evolution of liquid gallium (Ga) has been investigated by using in situ high energy X-ray diffraction experiment and ab initio molecular dynamics simulation. Both experimental and theoretical results reveal the existence of a liquid structural change around 1000 K in liquid Ga. Below and above this temperature the liquid exhibits differences in activation energy for selfdiffusion, temperature-dependent heat capacity, coordination numbers, density, viscosity, electric resistivity and thermoelectric power, which are reflected from structural changes of the bond-orientational order parameter Q6, fraction of covalent dimers, averaged string length and local atomic packing. This finding will trigger more studiesmore » on the liquid-to-liquid crossover in metallic melts.« less

From statistics of regular tree-like graphs to distribution function and gyration radius of branched polymers

NASA Astrophysics Data System (ADS)

Grosberg, Alexander Y.; Nechaev, Sergei K.

2015-08-01

We consider flexible branched polymer, with quenched branch structure, and show that its conformational entropy as a function of its gyration radius R, at large R, obeys, in the scaling sense, Δ S˜ {R}2/({a}2L), with a bond length (or Kuhn segment) and L defined as an average spanning distance. We show that this estimate is valid up to at most the logarithmic correction for any tree. We do so by explicitly computing the largest eigenvalues of Kramers matrices for both regular and ‘sparse’ three-branched trees, uncovering on the way their peculiar mathematical properties.

Vector-based model of elastic bonds for simulation of granular solids.

PubMed

Kuzkin, Vitaly A; Asonov, Igor E

2012-11-01

A model (further referred to as the V model) for the simulation of granular solids, such as rocks, ceramics, concrete, nanocomposites, and agglomerates, composed of bonded particles (rigid bodies), is proposed. It is assumed that the bonds, usually representing some additional gluelike material connecting particles, cause both forces and torques acting on the particles. Vectors rigidly connected with the particles are used to describe the deformation of a single bond. The expression for potential energy of the bond and corresponding expressions for forces and torques are derived. Formulas connecting parameters of the model with longitudinal, shear, bending, and torsional stiffnesses of the bond are obtained. It is shown that the model makes it possible to describe any values of the bond stiffnesses exactly; that is, the model is applicable for the bonds with arbitrary length/thickness ratio. Two different calibration procedures depending on bond length/thickness ratio are proposed. It is shown that parameters of the model can be chosen so that under small deformations the bond is equivalent to either a Bernoulli-Euler beam or a Timoshenko beam or short cylinder connecting particles. Simple analytical expressions, relating parameters of the V model with geometrical and mechanical characteristics of the bond, are derived. Two simple examples of computer simulation of thin granular structures using the V model are given.

Validation of nuclear magnetic resonance structures of proteins and nucleic acids: hydrogen geometry and nomenclature.

PubMed

Doreleijers, J F; Vriend, G; Raves, M L; Kaptein, R

1999-11-15

A statistical analysis is reported of 1,200 of the 1,404 nuclear magnetic resonance (NMR)-derived protein and nucleic acid structures deposited in the Protein Data Bank (PDB) before 1999. Excluded from this analysis were the entries not yet fully validated by the PDB and the more than 100 entries that contained < 95% of the expected hydrogens. The aim was to assess the geometry of the hydrogens in the remaining structures and to provide a check on their nomenclature. Deviations in bond lengths, bond angles, improper dihedral angles, and planarity with respect to estimated values were checked. More than 100 entries showed anomalous protonation states for some of their amino acids. Approximately 250,000 (1.7%) atom names differed from the consensus PDB nomenclature. Most of the inconsistencies are due to swapped prochiral labeling. Large deviations from the expected geometry exist for a considerable number of entries, many of which are average structures. The most common causes for these deviations seem to be poor minimization of average structures and an improper balance between force-field constraints for experimental and holonomic data. Some specific geometric outliers are related to the refinement programs used. A number of recommendations for biomolecular databases, modeling programs, and authors submitting biomolecular structures are given.

IR spectroscopy as a source of data on bond strengths

NASA Astrophysics Data System (ADS)

Finkelshtein, E. I.; Shamsiev, R. S.

2018-02-01

The aim of this work is the estimation of double bond strength, namely Cdbnd O bonds in ketones and aldehydes and Cdbnd C bonds in various compounds. By the breaking of these bonds one or both fragments formed are carbenes, for which experimental data on the enthalpies of formation (ΔHf298) are scarce. Thus for the estimation of ΔHf298 of the corresponding carbenes, the empirical equations were proposed based on different approximations. In addition, a quantum chemical calculations of the ΔHf298 values of carbenes were performed, and the data obtained were compared with experimental values and the results of earlier calculations. Equations for the calculation of Cdbnd O bond strengths of different ketones and aldehydes from the corresponding stretching frequencies ν(Cdbnd O) were derived. Using the proposed equations, the strengths of Cdbnd O bonds of 25 ketones and 12 conjugated aldehydes, as well as Cdbnd C bonds of 13 hydrocarbons and 7 conjugated aldehydes were estimated for the first time. Linear correlations of Cdbnd C and Cdbnd O bond strengths with the bond lengths were established, and the equations permitting the estimation of the double bond strengths and lengths with acceptable accuracy were obtained. Also, the strength of central Cdbnd C bond of stilbene was calculated for the first time. The uncertainty of the strengths of double bonds obtained may be regarded as accurate ±10-15 kJ/mol.

Bonding properties and bond activation of ylides: recent findings and outlook.

PubMed

Urriolabeitia, Esteban P

2008-11-14

The interaction of phosphorus and nitrogen ylides with metallic precursors has been examined from different points of view. The first one is related to the bonding properties of the ylides. Ylides with a unique stabilizing group bond through different atoms (the Calpha or the heteroatoms); while ylides with two stabilizing groups never coordinate through the Calpha atom. In the second section we examine the cause of the stereoselective coordination of bisylides of phosphorus, nitrogen and arsenic, and of mixed bisylides. We describe here the very interesting conformational preferences found in these systems, which have been determined and characterized. The DFT study of these bisylides has allowed for the characterization of strong intramolecular PO and AsO interactions, as well as moderate CHO[double bond, length as m-dash]C hydrogen bonds as the source of these conformational preferences. The third topic is related to the amazing reactivity of phosphorus ylides in bond activation processes. Depending on the nature of the metallic precursors, ylides can behave as sources of carbenes, of phosphine derivatives, of other ylides or of orthometallated complexes through P[double bond, length as m-dash]C, P-C or C-H bond activation reactions.

Synergistic oxygen atom transfer by ruthenium complexes with non-redox metal ions.

PubMed

Lv, Zhanao; Zheng, Wenrui; Chen, Zhuqi; Tang, Zhiming; Mo, Wanling; Yin, Guochuan

2016-07-28

Non-redox metal ions can affect the reactivity of active redox metal ions in versatile biological and heterogeneous oxidation processes; however, the intrinsic roles of these non-redox ions still remain elusive. This work demonstrates the first example of the use of non-redox metal ions as Lewis acids to sharply improve the catalytic oxygen atom transfer efficiency of a ruthenium complex bearing the classic 2,2'-bipyridine ligand. In the absence of Lewis acid, the oxidation of ruthenium(ii) complex by PhI(OAc)2 generates the Ru(iv)[double bond, length as m-dash]O species, which is very sluggish for olefin epoxidation. When Ru(bpy)2Cl2 was tested as a catalyst alone, only 21.2% of cyclooctene was converted, and the yield of 1,2-epoxycyclooctane was only 6.7%. As evidenced by electronic absorption spectra and EPR studies, both the oxidation of Ru(ii) by PhI(OAc)2 and the reduction of Ru(iv)[double bond, length as m-dash]O by olefin are kinetically slow. However, adding non-redox metal ions such as Al(iii) can sharply improve the oxygen transfer efficiency of the catalyst to 100% conversion with 89.9% yield of epoxide under identical conditions. Through various spectroscopic characterizations, an adduct of Ru(iv)[double bond, length as m-dash]O with Al(iii), Ru(iv)[double bond, length as m-dash]O/Al(iii), was proposed to serve as the active species for epoxidation, which in turn generated a Ru(iii)-O-Ru(iii) dimer as the reduced form. In particular, both the oxygen transfer from Ru(iv)[double bond, length as m-dash]O/Al(iii) to olefin and the oxidation of Ru(iii)-O-Ru(iii) back to the active Ru(iv)[double bond, length as m-dash]O/Al(iii) species in the catalytic cycle can be remarkably accelerated by adding a non-redox metal, such as Al(iii). These results have important implications for the role played by non-redox metal ions in catalytic oxidation at redox metal centers as well as for the understanding of the redox mechanism of ruthenium catalysts in the oxygen atom transfer reaction.

Research on Anchorage Performance of Grouting Anchor Connection of Precast Concrete Structure

NASA Astrophysics Data System (ADS)

Wang, Donghui; Liu, Xudong; Wang, Sheng; Cao, Xixi

2018-03-01

The bonding of grouted anchor bars is one of the vertical connection forms of steel bars in fabricated concrete structures. The performance of grouted connection is mainly affected by the anchorage length and lap length of steel bars. The mechanisms of bond and anchorage between steel bar and concrete are analyzed, and the factors that influence the anchorage performance of steel bar are systematically summarized. Results show that the bond and anchorage performance of steel and concrete have been studied widely, but there are still shortcomings, and the connection forms need to be further improved.

Evaluation of Internal Brushing on Pinch Weld Quality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korinko, P

2005-12-01

Post machining operations such as borescope inspection can cause linear indications down the length of the bore of fill stems. Often these indications are removed or obscured using rotary wire brushing. This study evaluated the effect this mechanical operation may have on pinch weld quality when relatively cold welds were made. A total of four stems with two levels of brushing of both Type 304L and 21-6-9 stainless steels were tested. In addition, two each of the Type 304L stems were Nitradd cleaned and the other two were aqueously cleaned; all four 21-6-9 stems were aqueously cleaned. All of themore » brushed stem areas exhibited more surface anomalies based on borescope evaluation. On average, the bond rating was a higher value (worse) for the brushed areas than the unadulterated areas for both Type 304L and 21-6-9 stems. The test method used may have biased the results towards a lesser quality bond for the brushed areas so additional testing is recommended.« less

XRD- and infrared-probed anisotropic thermal expansion properties of an organic semiconducting single crystal.

PubMed

Mohanraj, J; Capria, E; Benevoli, L; Perucchi, A; Demitri, N; Fraleoni-Morgera, A

2018-01-17

The anisotropic thermal expansion properties of an organic semiconducting single crystal constituted by 4-hydroxycyanobenzene (4HCB) have been probed by XRD in the range 120-300 K. The anisotropic thermal expansion coefficients for the three crystallographic axes and for the crystal volume have been determined. A careful analysis of the crystal structure revealed that the two different H-bonds stemming from the two independent, differently oriented 4HCB molecules composing the unit cell have different rearrangement patterns upon temperature variations, in terms of both bond length and bond angle. Linearly Polarized Mid InfraRed (LP-MIR) measurements carried out in the same temperature range, focused on the O-H bond spectral region, confirm this finding. The same LP-MIR measurements, on the basis of a semi-empirical relation and of geometrical considerations and assumptions, allowed calculation of the -CNH-O- hydrogen bond length along the a and b axes of the crystal. In turn, the so-calculated -CNH-O- bond lengths were used to derive the thermal expansion coefficients along the corresponding crystal axes, as well as the volumetric one, using just the LP-MIR data. Reasonable to good agreement with the same values obtained from XRD measurements was obtained. This proof-of-principle opens interesting perspectives about the possible development of a rapid, low cost and industry-friendly assessment of the thermal expansion properties of organic semiconducting single crystals (OSSCs) involving hydrogen bonds.

Investigation of field corrosion performance and bond/development length of galvanized reinforcing steel : [tech transfer summary].

DOT National Transportation Integrated Search

2014-12-01

In reinforced concrete systems, ensuring that a good bond between the : concrete and the embedded reinforcing steel is critical to long-term structural : performance. Without good bond between the two, the system simply cannot : behave as intended. :...

Investigation of field corrosion performance and bond/development length of galvanized reinforcing steel.

DOT National Transportation Integrated Search

2014-12-01

In reinforced concrete systems, ensuring that a good bond between the concrete and the embedded reinforcing steel is critical to : long-term structural performance. Without good bond between the two, the system simply cannot behave as intended. The b...

HYDROGEN BONDING IN THE METHANOL DIMER

USDA-ARS?s Scientific Manuscript database

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

Stability and electronic structure of the low- Σ grain boundaries in CdTe: a density functional study

DOE PAGES

Park, Ji-Sang; Kang, Joongoo; Yang, Ji-Hui; ...

2015-01-15

Using first-principles density functional calculations, we investigate the relative stability and electronic structure of the grain boundaries (GBs) in zinc-blende CdTe. Among the low-Σ-value symmetric tilt Σ3 (111), Σ3 (112), Σ5 (120), and Σ5 (130) GBs, we show that the Σ3 (111)GB is always the most stable due to the absence of dangling bonds and wrong bonds. The Σ5 (120) GBs, however, are shown to be more stable than the Σ3 (112) GBs, even though the former has a higher Σ value, and the latter is often used as a model system to study GB effects in zinc-blende semiconductors. Furthermore,more » we find that although containing wrong bonds, the Σ5 (120) GBs are electrically benign due to the short wrong bond lengths, and thus are not as harmful as the Σ3 (112) GBs also having wrong bonds but with longer bond lengths.« less

Electronic, elastic and optical properties of divalent (R+2X) and trivalent (R+3X) rare earth monochalcogenides

NASA Astrophysics Data System (ADS)

Kumar, V.; Chandra, S.; Singh, J. K.

2017-08-01

Based on plasma oscillations theory of solids, simple relations have been proposed for the calculation of bond length, specific gravity, homopolar energy gap, heteropolar energy gap, average energy gap, crystal ionicity, bulk modulus, electronic polarizability and dielectric constant of rare earth divalent R+2X and trivalent R+3X monochalcogenides. The specific gravity of nine R+2X, twenty R+3X, and bulk modulus of twenty R+3X monochalcogenides have been calculated for the first time. The calculated values of all parameters are compared with the available experimental and the reported values. A fairly good agreement has been obtained between them. The average percentage deviation of two parameters: bulk modulus and electronic polarizability for which experimental data are known, have also been calculated and found to be better than the earlier correlations.

Crystal structure of bis­[cis-(1,4,8,11-tetra­aza­cyclo­tetra­deca­ne-κ4 N)bis(thio­cyanato-κN)chrom­ium(III)] dichromate monohydrate from synchrotron X-ray diffraction data

PubMed Central

Moon, Dohyun; Takase, Masahiro; Akitsu, Takashiro; Choi, Jong-Ha

2017-01-01

The structure of the complex salt, cis-[Cr(NCS)2(cyclam)]2[Cr2O7]·H2O (cyclam = 1,4,8,11-tetra­aza­cyclo­tetra­decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit comprises of one [Cr(NCS)2(cyclam)]+ cation, one half of a Cr2O7 2− anion (completed by inversion symmetry) and one half of a water mol­ecule (completed by twofold rotation symmetry). The CrIII ion is coordinated by the four cyclam N atoms and by two N atoms of cis-arranged thio­cyanate anions, displaying a distorted octa­hedral coordination sphere. The Cr—N(cyclam) bond lengths are in the range 2.080 (2) to 2.097 (2) Å while the average Cr—N(NCS) bond length is 1.985 (4) Å. The macrocyclic cyclam moiety adopts the cis-V conformation. The bridging O atom of the dichromate anion is disordered around an inversion centre, leading to a bending of the Cr—O—Cr bridging angle [157.7 (3)°]; the anion has a staggered conformation. The crystal structure is stabilized by inter­molecular hydrogen bonds involving the cyclam N—H groups and water O—H groups as donor groups, and the O atoms of the Cr2O7 2− anion and water mol­ecules as acceptor groups, giving rise to a three-dimensional network. PMID:28083140

Crystal structure of bis­[(oxalato-κ2 O 1,O 2)(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ4 N)chromium(III)] dichromate octa­hydrate from synchrotron X-ray data

PubMed Central

Moon, Dohyun; Choi, Jong-Ha

2017-01-01

The asymmetric unit of the title compound, [Cr(C2O4)(C10H24N4)]2[Cr2O7]·8H2O (C10H24N4 = 1,4,8,11-tetra­aza­cyclo­tetra­decane, cyclam; C2O4 = oxalate, ox) contains one [Cr(ox)(cyclam)]+ cation, one half of a dichromate anion that lies about an inversion centre so that the bridging O atom is equally disordered over two positions, and four water mol­ecules. The terminal O atoms of the dichromate anion are also disordered over two positions with a refined occupancy ratio 0.586 (6):0.414 (6). The CrIII ion is coordinated by the four N atoms of the cyclam ligand and one bidentate oxalato ligand in a cis arrangement, resulting in a distorted octa­hedral geometry. The Cr—N(cyclam) bond lengths are in the range 2.069 (2)–2.086 (2) Å, while the average Cr—O(ox) bond length is 1.936 Å. The macrocyclic cyclam moiety adopts the cis-V conformation. The dichromate anion has a staggered conformation. The crystal structure is stabilized by inter­molecular hydrogen bonds involving the cyclam N—H groups and water O—H groups as donors, and the O atoms of oxalate ligand, water mol­ecules and the Cr2O7 2− anion as acceptors, giving rise to a three-dimensional network. PMID:28316819

N,N,N′,N′-Tetra­methyl­guanidinium tetra­phenyl­borate

PubMed Central

Tiritiris, Ioannis

2012-01-01

In the title salt, C5H14N3 +·C24H20B−, the C—N bond lengths in the central CN3 unit are 1.3322 (11), 1.3385 (12) and 1.3422 (12) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal-planar geometry [N—C—N angles = 119.51 (8), 119.81 (9) and 120.69 (8)°] and the positive charge is delocalized in the CN3 plane. The bond lengths between the N atoms and the terminal methyl groups all have values close to a typical single bond [1.4597 (12)–1.4695 (13) Å]. The crystal packing is caused by electrostatic inter­actions between cations and anions. PMID:23476307

Using Excel To Study The Relation Between Protein Dihedral Angle Omega And Backbone Length

NASA Astrophysics Data System (ADS)

Shew, Christopher; Evans, Samari; Tao, Xiuping

How to involve the uninitiated undergraduate students in computational biophysics research? We made use of Microsoft Excel to carry out calculations of bond lengths, bond angles and dihedral angles of proteins. Specifically, we studied protein backbone dihedral angle omega by examining how its distribution varies with the length of the backbone length. It turns out Excel is a respectable tool for this task. An ordinary current-day desktop or laptop can handle the calculations for midsized proteins in just seconds. Care has to be taken to enter the formulas for the spreadsheet column after column to minimize the computing load. Supported in part by NSF Grant #1238795.

Polymer brushes in explicit poor solvents studied using a new variant of the bond fluctuation model

NASA Astrophysics Data System (ADS)

Jentzsch, Christoph; Sommer, Jens-Uwe

2014-09-01

Using a variant of the Bond Fluctuation Model which improves its parallel efficiency in particular running on graphic cards we perform large scale simulations of polymer brushes in poor explicit solvent. Grafting density, solvent quality, and chain length are varied. Different morphological structures in particular octopus micelles are observed for low grafting densities. We reconsider the theoretical model for octopus micelles proposed by Williams using scaling arguments with the relevant scaling variable being σ/σc, and with the characteristic grafting density given by σc ˜ N-4/3. We find that octopus micelles only grow laterally, but not in height and we propose an extension of the model by assuming a cylindrical shape instead of a spherical geometry for the micelle-core. We show that the scaling variable σ/σc can be applied to master plots for the averaged height of the brush, the size of the micelles, and the number of chains per micelle. The exponents in the corresponding power law relations for the grafting density and chain length are in agreement with the model for flat cylindrical micelles. We also investigate the surface roughness and find that polymer brushes in explicit poor solvent at grafting densities higher than the stretching transition are flat and surface rippling can only be observed close to the stretching transition.

Dental plaque microcosm response to bonding agents containing quaternary ammonium methacrylates with different chain lengths and charge densities

PubMed Central

Zhou, Han; Li, Fang; Weir, Michael D.; Xu, Hockin H.K.

2013-01-01

Objectives Antibacterial bonding agents are promising to combat bacteria and caries at tooth-restoration margins. The objectives of this study were to incorporate new quaternary ammonium methacrylates (QAMs) to bonding agent and determine the effects of alkyl chain length (CL) and quaternary amine charge density on dental plaque microcosm bacteria response for the first time. Methods Six QAMs were synthesized with CL = 3, 6, 9, 12, 16, 18. Each QAM was incorporated into Scotchbond Multi-purpose (SBMP). To determine the charge density effect, dimethylaminododecyl methacrylate (DMAHDM, CL = 16) was mixed into SBMP at mass fraction = 0%, 2.5%, 5%, 7.5%, 10%. Charge density was measured using a fluorescein dye method. Dental plaque microcosm using saliva from ten donors was tested. Bacteria were inoculated on resins. Early-attachment was tested at 4 hours. Biofilm colony-forming units (CFU) were measured at 2 days. Results Incorporating QAMs into SBMP reduced bacteria early-attachment. Microcosm biofilm CFU for CL = 16 was 4 log lower than SBMP control. Charge density of bonding agent increased with DMAHDM content. Bacteria early-attachment decreased with increasing charge density. Biofilm CFU at 10% DMAHDM was reduced by 4 log. The killing effect was similarly-strong against total microorganisms, total streptococci, and mutans streptococci. Conclusions Increasing alkyl chain length and charge density of bonding agent was shown for the first time to decrease microcosm bacteria attachment and reduce biofilm CFU by 4 orders of magnitude. Novel antibacterial resins with tailored chain length and charge density are promising for wide applications in bonding, cements, sealants and composites to inhibit biofilms and caries. PMID:23948394

A QM/MM study of the initial excited state dynamics of green-absorbing proteorhodopsin.

PubMed

Borin, Veniamin A; Wiebeler, Christian; Schapiro, Igor

2018-04-17

The primary photochemical reaction of the green-absorbing proteorhodopsin is studied by means of a hybrid quantum mechanics/molecular mechanics (QM/MM) approach. The simulations are based on a homology model derived from the blue-absorbing proteorhodopsin crystal structure. The geometry of retinal and the surrounding sidechains in the protein binding pocket were optimized using the QM/MM method. Starting from this geometry the isomerization was studied with a relaxed scan along the C13[double bond, length as m-dash]C14 dihedral. It revealed an "aborted bicycle pedal" mechanism of isomerization that was originally proposed by Warshel for bovine rhodopsin and bacteriorhodopsin. However, the isomerization involved the concerted rotation about C13[double bond, length as m-dash]C14 and C15[double bond, length as m-dash]N, with the latter being highly twisted but not isomerized. Further, the simulation showed an increased steric interaction between the hydrogen at the C14 of the isomerizing bond and the hydroxyl group at the neighbouring tyrosine 200. In addition, we have simulated a nonadiabatic trajectory which showed the timing of the isomerization. In the first 20 fs upon excitation the order of the conjugated double and single bonds is inverted, consecutively the C13[double bond, length as m-dash]C14 rotation is activated for 200 fs until the S1-S0 transition is detected. However, the isomerization is reverted due to the specific interaction with the tyrosine as observed along the relaxed scan calculation. Our simulations indicate that the retinal - tyrosine 200 interaction plays an important role in the outcome of the photoisomerization.

Dental plaque microcosm response to bonding agents containing quaternary ammonium methacrylates with different chain lengths and charge densities.

PubMed

Zhou, Han; Li, Fang; Weir, Michael D; Xu, Hockin H K

2013-11-01

Antibacterial bonding agents are promising to combat bacteria and caries at tooth-restoration margins. The objectives of this study were to incorporate new quaternary ammonium methacrylates (QAMs) to bonding agent and determine the effects of alkyl chain length (CL) and quaternary amine charge density on dental plaque microcosm bacteria response for the first time. Six QAMs were synthesized with CL=3, 6, 9, 12, 16, 18. Each QAM was incorporated into Scotchbond multi-purpose (SBMP). To determine the charge density effect, dimethylaminododecyl methacrylate (DMAHDM, CL=16) was mixed into SBMP at mass fraction=0%, 2.5%, 5%, 7.5%, 10%. Charge density was measured using a fluorescein dye method. Dental plaque microcosm using saliva from ten donors was tested. Bacteria were inoculated on resins. Early-attachment was tested at 4h. Biofilm colony-forming units (CFU) were measured at 2 days. Incorporating QAMs into SBMP reduced bacteria early-attachment. Microcosm biofilm CFU for CL=16 was 4 log lower than SBMP control. Charge density of bonding agent increased with DMAHDM content. Bacteria early-attachment decreased with increasing charge density. Biofilm CFU at 10% DMAHDM was reduced by 4 log. The killing effect was similarly-strong against total microorganisms, total streptococci, and mutans streptococci. Increasing alkyl chain length and charge density of bonding agent was shown for the first time to decrease microcosm bacteria attachment and reduce biofilm CFU by 4 orders of magnitude. Novel antibacterial resins with tailored chain length and charge density are promising for wide applications in bonding, cements, sealants and composites to inhibit biofilms and caries. Copyright © 2013 Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2014-06-01

Hydrogen bonds and their strength were analysed based on their X-H proton-donor bond properties and the parameters of the H-Y distance (Y proton acceptor). Strong, moderate and weak interactions in hydrogen-bond types were verified through the proton affinities of bases (PA), deprotanation enthalpies of acids (DPE) and the chemical shift (σ). The aromaticity and anti-aromaticity were analysed by means of the NICS (0) (nucleus-independent chemical shift), NICS (1) and ΔNICS (0), ΔNICS (1) of hydrogen-bonded molecules. The strength of a hydrogen bond depends on the capacity of hydrogen atom engrossing into the electronegative acceptor atom. The correlation between the above parameters and their relations were discussed through curve fitting. Bader's theory of atoms in molecules has been applied to estimate the occurrence of hydrogen bonds through eight criteria reported by Popelier et al. The lengths and potential energy shifts have been found to have a strong negative linear correlation, whereas the lengths and Laplacian shifts have a strong positive linear correlation. This study illustrates the common factors responsible for strong, moderate and weak interactions in hydrogen-bond types.

Relativistic Corrections to the Properties of the Alkali Fluorides

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Partridge, Harry

1993-01-01

Relativistic corrections to the bond lengths, dissociation energies and harmonic frequencies of KF, RbF and CsF have been obtained at the self-consistent field level by dissociating to ions. The relativistic corrections to the bond lengths, harmonic frequencies and dissociation energies to the ions are very small, due to the ionic nature of these molecules and the similarity of the relativistic and nonrelativistic ionic radii.

Optoelectronic tuning of organoborylazadipyrromethenes via effective electronegativity at the metalloid center.

PubMed

Berhe, Seare A; Rodriguez, Marco T; Park, Eunsol; Nesterov, Vladimir N; Pan, Hongjun; Youngblood, W Justin

2014-03-03

Organoborylazadipyrromethenes were synthesized from free base and fluoroborylazadipyrromethenes and characterized with regard to their structural and electronic properties. B-N bond lengths, along with photophysical and redox behavior, appear dependent on the effective electronegativity at the boron atom as tuned by its substituents, with stronger electronegativity correlating to a shorter B-N bond length, red-shifted absorbance, enhanced fluorescence lifetime and yield, and positively shifted redox potentials.

Molecular mechanism of gelation upon the addition of water to a solution of poly(acrylonitrile) in dimethylsulfoxide

NASA Astrophysics Data System (ADS)

Vettegren, V. I.; Kulik, V. B.; Savitskii, A. V.; Fetisov, O. I.; Usov, V. V.

2010-05-01

The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005 and 1015 cm-1 appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously, water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN molecule. Accordingly, a band at 2250 cm-1 arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide limits and the band at 2250 cm-1 is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases (the band at 2250 cm-1 narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally strong” hydrogen bonds.

3-Methyl-4,5-di­hydro­oxazolium tetra­phenyl­borate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2014-01-01

In the cation of the title salt, C4H8NO+·C24H20B−, the C—N bond lengths are 1.272 (2), 1.4557 (19) and 1.4638 (19) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.3098 (19) Å shows that double-bond character and charge delocalization occurs within the NCO plane of the cation. In the crystal, a C—H⋯π inter­action is present between the methyl­ene H atom of the cation and one phenyl ring of the tetra­phenyl­borate ion. The latter forms an aromatic pocket in which the cation is embedded. PMID:24765023

Crystal structure of (1-eth­oxy­ethyl­idene)di­methyl­aza­nium tetra­phenyl­borate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2015-01-01

In the cation of the title salt, C6H14NO+·C24H20B−, the C—N bond lengths are 1.297 (2), 1.464 (2) and 1.468 (2) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.309 (2) Å shows double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. In the crystal, C—H⋯π inter­actions between the iminium H atoms and the phenyl C atoms of the anion are present. The phenyl rings form aromatic pockets, in which the iminium ions are embedded. PMID:26870564

A method of coupling the Paternò-Büchi reaction with direct infusion ESI-MS/MS for locating the C[double bond, length as m-dash]C bond in glycerophospholipids.

PubMed

Stinson, Craig A; Xia, Yu

2016-06-21

Tandem mass spectrometry (MS/MS) coupled with soft ionization is established as an essential platform for lipid analysis; however, determining high order structural information, such as the carbon-carbon double bond (C[double bond, length as m-dash]C) location, remains challenging. Recently, our group demonstrated a method for sensitive and confident lipid C[double bond, length as m-dash]C location determination by coupling online the Paternò-Büchi (PB) reaction with nanoelectrospray ionization (nanoESI) and MS/MS. Herein, we aimed to expand the scope of the PB reaction for lipid analysis by enabling the reaction with infusion ESI-MS/MS at much higher flow rates than demonstrated in the nanoESI setup (∼20 nL min(-1)). In the new design, the PB reaction was effected in a fused silica capillary solution transfer line, which also served as a microflow UV reactor, prior to ESI. This setup allowed PB reaction optimization and kinetics studies. Under optimized conditions, a maximum of 50% PB reaction yield could be achieved for a standard glycerophosphocholine (PC) within 6 s of UV exposure over a wide flow rate range (0.1-10 μL min(-1)). A solvent composition of 7 : 3 acetone : H2O (with 1% acid or base modifier) allowed the highest PB yields and good lipid ionization, while lower yields were obtained with an addition of a variety of organic solvents. Radical induced lipid peroxidation was identified to induce undesirable side reactions, which could be effectively suppressed by eliminating trace oxygen in the solution via N2 purge. Finally, the utility of coupling the PB reaction with infusion ESI-MS/MS was demonstrated by analyzing a yeast polar lipid extract where C[double bond, length as m-dash]C bond locations were revealed for 35 glycerophospholipids (GPs).

Maximum-valence radii of transition metals

PubMed Central

Pauling, Linus

1975-01-01

In many of their compounds the transition metals have covalence 9, forming nine bonds with use of nine hybrid spd bond orbitals. A set of maximum-valence single-bond radii is formulated for use in these compounds. These radii are in reasonably good agreement with observed bond lengths. Quadruple bonds between two transition metal atoms are about 50 pm (iron-group atoms) or 55 pm (palladium and platinum-group atoms) shorter than single bonds. This amount of shortening corresponds to four bent single bonds with the best set of bond angles, 79.24° and 128.8°. PMID:16578730

Local Bond Elections in California: Some Vital Statistics. EdSource Factsheet.

ERIC Educational Resources Information Center

EdSource, Inc., Palo Alto, CA.

This report examines the fate of general obligation (G.O.) bond measures in California from 1986 to 1999. For the entire 13-year period, the passage rate for local G.O. bonds averaged 54 percent. However, this average masks some dramatic variations depending on when the election was held, the district holding the election, and the area of…

Short and medium range structures of 80GeSe2–20Ga2Se3 chalcogenide glasses

NASA Astrophysics Data System (ADS)

Petracovschi, Elena; Calvez, Laurent; Cormier, Laurent; Le Coq, David; Du, Jincheng

2018-05-01

The short and medium range structures of 80GeSe2–20Ga2Se3 (or Ge23.5Ga11.8Se64.7) chalcogenide glasses have been studied by combining ab initio molecular dynamics (AIMD) simulations and experimental neutron diffraction studies. The structure factor and total correlation function were calculated from glass structures generated from AIMD simulations and compared with neutron diffraction experiments showing reasonable agreement. The atomic structures of ternary chalcogenide glasses were analyzed in detail, and it was found that gallium atoms are four-fold coordinated by selenium (Se) and form [GaSe4] tetrahedra. Germanium atoms on average also have four-fold coordination, among which Se is 3.5 with the remaining being Ge–Ge homo-nuclear bonds. Ga and Ge tetrahedra link together mainly through corner-sharing and some edge-sharing of Se. No homo-nuclear bonds were observed among Ga atoms or between Ge and Ga. In addition, Se–Se homo-nuclear bonds and Se chains with various lengths were observed. A small fraction of Se atom triclusters that bond to three cations of Ge and Ga were also observed, confirming earlier proposals from 77Se solid state nuclear magnetic resonance studies. Furthermore, the electronic structures of ternary chalcogenide glasses were studied in terms of atomic charge and electronic density of states in order to gain insights into the chemical bonding and electronic properties, as well as to provide an explanation of the observed atomic structures in these ternary chalcogenide glasses.

NDT evaluation of long-term bond durability of CFRP-structural systems applied to RC highway bridges

NASA Astrophysics Data System (ADS)

Crawford, Kenneth C.

2016-06-01

The long-term durability of CFRP structural systems applied to reinforced-concrete (RC) highway bridges is a function of the system bond behavior over time. The sustained structural load performance of strengthened bridges depends on the carbon fiber-reinforced polymer (CFRP) laminates remaining 100 % bonded to concrete bridge members. Periodic testing of the CFRP-concrete bond condition is necessary to sustain load performance. The objective of this paper is to present a non-destructive testing (NDT) method designed to evaluate the bond condition and long-term durability of CFRP laminate (plate) systems applied to RC highway bridges. Using the impact-echo principle, a mobile mechanical device using light impact hammers moving along the length of a bonded CFRP plate produces unique acoustic frequencies which are a function of existing CFRP plate-concrete bond conditions. The purpose of this method is to test and locate CFRP plates de-bonded from bridge structural members to identify associated deterioration in bridge load performance. Laboratory tests of this NDT device on a CFRP plate bonded to concrete with staged voids (de-laminations) produced different frequencies for bonded and de-bonded areas of the plate. The spectra (bands) of frequencies obtained in these tests show a correlation to the CFRP-concrete bond condition and identify bonded and de-bonded areas of the plate. The results of these tests indicate that this NDT impact machine, with design improvements, can potentially provide bridge engineers a means to rapidly evaluate long lengths of CFRP laminates applied to multiple highway bridges within a national transportation infrastructure.

Analytical energy gradient for the two-component normalized elimination of the small component method

NASA Astrophysics Data System (ADS)

Zou, Wenli; Filatov, Michael; Cremer, Dieter

2015-06-01

The analytical gradient for the two-component Normalized Elimination of the Small Component (2c-NESC) method is presented. The 2c-NESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac spin-orbit (SO) splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [Phys. Rev. B 62, 7809 (2000)]. The effect of spin-orbit coupling (SOC) on molecular geometries is analyzed utilizing the properties of the frontier orbitals and calculated SO couplings. It is shown that bond lengths can either be lengthened or shortened under the impact of SOC where in the first case the influence of low lying excited states with occupied antibonding orbitals plays a role and in the second case the jj-coupling between occupied antibonding and unoccupied bonding orbitals dominates. In general, the effect of SOC on bond lengths is relatively small (≤5% of the scalar relativistic changes in the bond length). However, large effects are found for van der Waals complexes Hg2 and Cn2, which are due to the admixture of more bonding character to the highest occupied spinors.

Influence of anatomical, physical, and mechanical properties of diffuse-porous hardwoods on moisture durability of bonded assemblies

Treesearch

Daniel J. Yelle; Ashley M. Stirgus

2016-01-01

Studying wood adhesive bond durability is challenging because wood is highly variable and heterogeneous at all length scales. In this study, three North American diffuse-porous hardwoods (hard maple, soft maple, and basswood) and their adhesively bonded as-semblies were exposed to wet and dry cyclic tests. Then, their den-sity differences were related to bond...

Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.

2013-02-21

The bonded radii for more than 550 bonded pairs of atoms, comprising more than 50 crystals, determined from experimental and theoretical electron density distributions, are compared with the effective ionic, ri(M), and crystal radii, rc(M), for metal atoms, M, bonded to O atoms. At odds with the fixed ionic radius of 1.40 Å, assumed for the O atom in the compilation of the ionic radii, the bonded radius for the atom, rb(O), is not fixed but displays a relatively wide range of values as the O atom is progressively polarized by the M-O bonded interactions: as such, rb(O) decreases systematicallymore » from 1.40 Å (the Pauling radius of the oxide anion) as bond lengths decrease when bonded to an electropositive atom like sodium, to 0.64 Å (Bragg’s atomic radius of the O atom) when bonded to an electronegative atom like nitrogen. Both rb(M) and rb(O) increase in tandum with the increasing coordination number of the M atom. The bonded radii of the M atoms are highly correlated with both ri(M) and rc(M), but they both depart systematically from rb(M) and become smaller as the electronegativity of the M atom increases and the M-O bond length decreases. The well-developed correlations between both sets of radii and rb(M) testifies to the relative precision of both sets of radii and the fact that both sets are highly correlated the M-O bond 1 lengths. On the other hand, the progressive departure of rb(O) from the fixed ionic radius of the O atom with the increasing electronegativity of the bonded M atom indicates that any compilation of sets of ionic radii, assuming that the radius for the oxygen atom is fixed in value, is problematical and impacts on the accuracy of the resulting sets of ionic and crystal radii thus compiled. The assumption of a fixed O atom radius not only results in a negative ionic radii for several atoms, but it also results in values of rb(M) that are much as ~ 0.6 Å larger than the ri(M) and rc(M) values, respectively, particularly for the more electronegative M atoms. On the other hand, the ionic radii are in closer agreement with rb(M) for the more electropositive atoms. Notwithstanding that ionic radii are typically smaller than bonded radii, particularly for the more electronegative atoms, they have been used with considerable success in understanding and rationalizing problems and properties in crystal chemistry primarily because both ionic and crystal radii are highly correlated on a one-to-one basis with both the bonded radii and the associated M-O bond lengths. The lack of agreement between the effective ionic and crystal radii and the bonded radii for the more shared bonded interactions is ascribed to the progressive increase in the polarization of the O atom by the bonded atoms with a concomitant decrease in its radius, a factor that was neglected in the compilation of ionic and crystal radii for fluorides, oxides, sulfides and nitrides. This accounts for ionic radii for these materials being smaller than the bonded radii for the more electronegative atoms.« less

Quantitative structure activity relationships from optimised ab initio bond lengths: steroid binding affinity and antibacterial activity of nitrofuran derivatives

NASA Astrophysics Data System (ADS)

Smith, P. J.; Popelier, P. L. A.

2004-02-01

The present day abundance of cheap computing power enables the use of quantum chemical ab initio data in Quantitative Structure-Activity Relationships (QSARs). Optimised bond lengths are a new such class of descriptors, which we have successfully used previously in representing electronic effects in medicinal and ecological QSARs (enzyme inhibitory activity, hydrolysis rate constants and pKas). Here we use AM1 and HF/3-21G* bond lengths in conjunction with Partial Least Squares (PLS) and a Genetic Algorithm (GA) to predict the Corticosteroid-Binding Globulin (CBG) binding activity of the classic steroid data set, and the antibacterial activity of nitrofuran derivatives. The current procedure, which does not require molecular alignment, produces good r2 and q2 values. Moreover, it highlights regions in the common steroid skeleton deemed relevant to the active regions of the steroids and nitrofuran derivatives.

Investigation of heat transfer and material flow of P-FSSW: Experimental and numerical study

NASA Astrophysics Data System (ADS)

Rezazadeh, Niki; Mosavizadeh, Seyed Mostafa; Azizi, Hamed

2018-02-01

Friction stir spot welding (FSSW) is the joining process which utilizes a rotating tool consisting of a shoulder and/or a probe. In this study, the novel method of FSSW, which is called protrusion friction stir spot welding (P-FSSW), has been presented and effect of shoulder diameter parameter has been studied numerically and experimentally on the weld quality including temperature field, velocity contour, material flow, bonding length, and the depth of the stirred area. The results show that the numerical findings are in good agreement with experimental measurements. The present model could well predict the temperature distribution, velocity contour, depth of the stirred area, and the bonding length. As the shoulder diameter increases, the amount of temperature rises which leads to a rise in stirred area depth, bonding length and temperatures and velocities. Therefore, a weld of higher quality will be performed.

Reductive transformation of V(iii) precursors into vanadium(ii) oxide nanowires.

PubMed

Ojelere, Olusola; Graf, David; Ludwig, Tim; Vogt, Nicholas; Klein, Axel; Mathur, Sanjay

2018-05-15

Vanadium(ii) oxide nanostructures are promising materials for supercapacitors and electrocatalysis because of their excellent electrochemical properties and high surface area. In this study, new homoleptic vanadium(iii) complexes with bi-dentate O,N-chelating heteroarylalkenol ligands (DmoxCH[double bond, length as m-dash]COCF3, PyCH[double bond, length as m-dash]COCF3 and PyN[double bond, length as m-dash]COCF3) were synthesized and successfully transformed by reductive conversion into VO nanowires. The chemical identity of V(iii) complexes and their redox behaviour were unambiguously established by single crystal X-ray diffraction studies, cyclic voltammetry, spectrometric studies and DFT calculations. Transformation into the metastable VO phase was verified by powder X-ray diffraction and thermo-gravimetry. Transmission electron microscopy and X-ray photoelectron spectroscopy data confirmed the morphology and chemical composition of VO nanostructures, respectively.

Linear free-energy relationships between a single gas-phase ab initio equilibrium bond length and experimental pKa values in aqueous solution.

PubMed

Alkorta, Ibon; Popelier, Paul L A

2015-02-02

Remarkably simple yet effective linear free energy relationships were discovered between a single ab initio computed bond length in the gas phase and experimental pKa values in aqueous solution. The formation of these relationships is driven by chemical features such as functional groups, meta/para substitution and tautomerism. The high structural content of the ab initio bond length makes a given data set essentially divide itself into high correlation subsets (HCSs). Surprisingly, all molecules in a given high correlation subset share the same conformation in the gas phase. Here we show that accurate pKa values can be predicted from such HCSs. This is achieved within an accuracy of 0.2 pKa units for 5 drug molecules. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vibrational studies of phosphoryl transfer enzymes: ras- p21(*)magnesium-GTP and Myosin S1(*)magnesium-ADP- vanadate

NASA Astrophysics Data System (ADS)

Wang, Jianghua

1999-07-01

We have measured the Raman spectra of monophosphate compounds in aqueous solution. The measured frequencies were correlated with P••O valence bond order by using a modification of the Hardcastle- Wachs procedure. The P••O bond order and bond length in phosphates can be determined from vibrational spectra by using the derived bond order/stretching frequency correlation and the bond length/bond order correlation of Brown and Wu. The Raman and infrared spectra of guanosine 5'-diphosphate (GDP) and guanosine 5'-triphosphate (GTP) in aqueous solution were also examined. Frequency shifts were observed as Mg2+ complexes with GDP and GTP in aqueous solution. These results suggested that Mg2+ binds to GDP in a bidentate manner to the α,β P••O bonds and in a tridentate manner to the α,β and γ P••O bonds of Mg•GTP . We have analyzed the previously obtained isotope edited Raman difference spectra of 1:1 complexes of Mg•GDP and Mg•GTP in ras-p21. Frequency changes of the phosphate groups were observed when Mg•GDP , Mg•GTP bind to the protein. Employing both the previous empirical relationships between bond orders/lengths and frequencies as well as vibrational analysis from ab initio calculations, the spectral changes can be explained by the change of the Mg2+ binding sites and hydrogen-bonding. Implications of these structural results for the reaction mechanism of GTP hydrolysis catalyzed by the GTPase are discussed. We have analyzed previously obtained isotope edited Raman difference spectra of the non-bridging V••O bonds of vanadates, both in solution, and when bound to the myosin S1•MgADP complex. By use of ab initio calculations on a model of the vanadate binding site in myosin, the angles between the non-bridging V••O bonds and between these bonds and the apical bonds in the myosin S1•MgADP -Vi complex were determined. The summed bond order of the two apical bonds between the attacking and leaving group oxygens with the central vanadium ion in the S1•MgADP -Vi complex was found to increase only slightly compared with the bond order of the ester V-O bond of a monoester vanadate model compound in solution, suggesting an SN2 like mechanism for the phosphoryl transfer reaction catalyzed by myosin.

(5-n-Butyl-10,20-diiso­butyl­porphyrin­ato)nickel(II)

PubMed Central

Senge, Mathias O.; Dahms, Katja

2014-01-01

The asymmetric unit of the title compound, [Ni(C32H36N4)], contains two independent mol­ecules exhibiting an overall ruffled conformation of the porphyrin macrocycle and differing mainly in the positions of the methyl groups. The average Ni—N bond lengths are 1.912 (2) and 1.910 (2) Å in the two mol­ecules. The mol­ecules form a closely spaced lattice structure in which neighbouring porphyrins are oriented in a nearly perpendicular fashion to each other. The compound was prepared via nucleophilic substitution of (5,15-diiso­butyl­porphyrinato)nickel(II) with n-butyl­lithium. PMID:25161518

Insertion of terminal alkyne into Pt-N bond of the square planar [PtI2(Me2phen)] complex.

PubMed

Benedetti, Michele; De Castro, Federica; Lamacchia, Vincenza; Pacifico, Concetta; Natile, Giovanni; Fanizzi, Francesco P

2017-11-21

The reactivity of [PtX 2 (Me 2 phen)] complexes (X = Cl, Br, I; Me 2 phen = 2,9-dimethyl-1,10-phenanthroline) with terminal alkynes has been investigated. Although the dichlorido species [PtCl 2 (Me 2 phen)] exhibits negligible reactivity, the bromido and iodido derivatives lead in short time to the formation of five-coordinate Pt(ii) complexes of the type [PtX 2 (Me 2 phen)(η 2 -CH[triple bond, length as m-dash]CR)] (X = Br, I; R = Ph, n-Bu), in equilibrium with the starting reagents. Similar to analogous complexes with simple acetylene, the five coordinate species can also undergo dissociation of an halido ligand and formation of the transient square-planar cationic species [PtX(Me 2 phen)(η 2 -CH[triple bond, length as m-dash]CR)] + . This latter can further evolve to give an unusual, sparingly soluble square planar product where the former terminal alkyne is converted into a :C[double bond, length as m-dash]C(H)(R) moiety with the α-carbon bridging the Pt(ii) core with one of the two N-donors of coordinated Me 2 phen. The final product [PtX 2 {κ 2 -N,C-(Z)-N[combining low line]1-N10-C[combining low line][double bond, length as m-dash]C(H)(R)}] (N1-N10 = 2,9-dimethyl-1,10-phenanthroline; X = Br, I) contains a Pt-N-C-C-N-C six-membered chelate ring in a square planar Pt(ii) coordination environment.

Computational Study of Quasi-2D Liquid State in Free Standing Platinum, Silver, Gold, and Copper Monolayers.

PubMed

Yang, Li-Ming; Ganz, Ariel B; Dornfeld, Matthew; Ganz, Eric

2016-12-01

Recently, freestanding atomically thick Fe metal patches up to 10 atoms wide have been fabricated experimentally in tiny pores in graphene. This concept can be extended conceptually to extended freestanding monolayers. We have therefore performed ab initio molecular dynamics simulations to evaluate the early melting stages of platinum, silver, gold, and copper freestanding metal monolayers. Our calculations show that all four freestanding monolayers will form quasi-2D liquid layers with significant out-of-plane motion and diffusion in the plane. Remarkably, we observe a 4% reduction in the Pt most likely bond length as the system enters the liquid state at 2400 K (and a lower effective spring constant), compared to the system at 1200 and 1800 K. We attribute this to the reduced average number of bonds per atom in the Pt liquid state. We used the highly accurate and reliable Density Functional Theory (DFT-D) method that includes dispersion corrections. These liquid states are found at temperatures of 2400 K, 1050 K, 1600 K, and 1400 K for platinum, silver, gold, and copper respectively. The pair correlation function drops in the liquid state, while the bond orientation order parameter is reduced to a lesser degree. Movies of the simulations can be viewed online (see Supplementary Material).

Two-Photon Absorption Properties of Gold Fluorescent Protein: A Combined Molecular Dynamics and Quantum Chemistry Study.

PubMed

Şimşek, Yusuf; Brown, Alex

2018-06-07

Molecular dynamics (MD) simulations were carried out to obtain the conformational changes of the chromophore in the gold fluorescent protein (PDB ID: 1OXF ). To obtain two-photon absorption (TPA) cross-sections, time dependent density functional theory (TD-DFT) computations were performed for chromophore geometries sampled along the trajectory. The TD-DFT computations used the CAM-B3LYP functional and 6-31+G(d) basis set. Results showed that two dihedral angles change remarkably over the simulation time. TPA cross-sections were found to average 13.82 GM for the excitation to S 1 computed from the equilibrium geometries; however, extending the structures with a water molecule and GLU residue, which make H bonds with the chromophore molecule, increased excitation energies and TPA cross-sections significantly. Besides the effects of the surrounding residues and the dihedrals on the spectroscopic properties, some bond lengths affected the excitation energies and the TPA cross-sections significantly (up to ±25-30%), while the effects of the bond angles were smaller (±5%). Overall the present results provide insight into the effects of the conformational flexibility on TPA (with gold fluorescent protein as a specific example) and suggest that further experimental measurements of TPA for the gold fluorescent protein should be undertaken.

Comparison of the structural basis for thermal stability between archaeal and bacterial proteins.

PubMed

Ding, Yanrui; Cai, Yujie; Han, Yonggang; Zhao, Bingqiang

2012-01-01

In this study, the structural basis for thermal stability in archaeal and bacterial proteins was investigated. There were many common factors that confer resistance to high temperature in both archaeal and bacterial proteins. These factors include increases in the Lys content, the bends and blanks of secondary structure, the Glu content of salt bridge; decreases in the number of main-side chain hydrogen bond and exposed surface area, and changes in the bends and blanks of amino acids. Certainly, the utilization of charged amino acids to form salt bridges is a primary factor. In both heat-resistant archaeal and bacterial proteins, most Glu and Asp participate in the formation of salt bridges. Other factors may influence either archaeal or bacterial protein thermostability, which includes the more frequent occurrence of shorter 3(10)-helices and increased hydrophobicity in heat-resistant archaeal proteins. However, there were increases in average helix length, the Glu content in salt bridges, temperature factors and decreases in the number of main-side chain hydrogen bonds, uncharged-uncharged hydrogen bonds, hydrophobicity, and buried and exposed polar surface area in heat-resistant bacterial proteins. Evidently, there are few similarities and many disparities between the heat-resistant mechanisms of archaeal and bacterial proteins.

Bonding thermoplastic polymers

DOEpatents

Wallow, Thomas I [Fremont, CA; Hunter, Marion C [Livermore, CA; Krafcik, Karen Lee [Livermore, CA; Morales, Alfredo M [Livermore, CA; Simmons, Blake A [San Francisco, CA; Domeier, Linda A [Danville, CA

2008-06-24

We demonstrate a new method for joining patterned thermoplastic parts into layered structures. The method takes advantage of case-II permeant diffusion to generate dimensionally controlled, activated bonding layers at the surfaces being joined. It is capable of producing bonds characterized by cohesive failure while preserving the fidelity of patterned features in the bonding surfaces. This approach is uniquely suited to production of microfluidic multilayer structures, as it allows the bond-forming interface between plastic parts to be precisely manipulated at micrometer length scales. The bond enhancing procedure is easily integrated in standard process flows and requires no specialized equipment.

Quadratic elongation: A quantitative measure of distortion in coordination polyhedra

USGS Publications Warehouse

Robinson, Kelly F.; Gibbs, G.V.; Ribbe, P.H.

1971-01-01

Quadratic elongation and the variance of bond angles are linearly correlated for distorted octahedral and tetrahedral coordination complexes, both of which show variations in bond length and bond angle. The quadratic elonga tion is dimensionless, giving a quantitative measure of polyhedral distortion which is independent of the effective size of the polyhedron.

Vibrational states and optical transitions in hydrogen bonds

NASA Astrophysics Data System (ADS)

Johannsen, P. G.

1998-03-01

Proton energies in hydrogen bonds are mostly calculated using a double Morse potential (the DMP model). This form, however, does not reproduce the experimentally observed correlation between the proton stretching frequency and the bond length in an extended bond-length region sufficiently well. An alternative potential is proposed in the present paper. The quantum states of this non-symmetric double-well potential are calculated numerically using the Numerov (Fox-Goodwin) algorithm. It is shown that the optical spectra of hydrogen bonds in various substances can be well approximated on the basis of the transition frequencies and intensities predicted by the present model. For weakly interacting OH impurities in 0953-8984/10/10/008/img1, the overtone spectrum and line intensities are well reproduced, whereas the line broadenings and the decrease of the fundamental stretching frequencies in intermediate and strong hydrogen bonds are traced back to the influence of the reduced height of the central barrier. The model is also extrapolated to the range of symmetric hydrogen bonds, and the calculated transition frequencies are discussed with respect to most recent infra-red experiments on ice under strong compression. A possible artificial infra-red signal from strained diamond anvils is thereby noted.

pKa prediction from an ab initio bond length: part 3--benzoic acids and anilines.

PubMed

Harding, A P; Popelier, P L A

2011-06-21

The prediction of pK(a) from a single ab initio bond length has been extended to provide equations for benzoic acids and anilines. The HF/6-31G(d) level of theory is used for all geometry optimisations. Similarly to phenols (Part 2 of this series of publications), the meta-/para-substituted benzoic acids can be predicted from a single model constructed from one bond length. This model had an impressive RMSEP of 0.13 pK(a) units. The prediction of ortho-substituted benzoic acids required the identification of high-correlation subsets, where the compounds in the same subset have at least one of the same (e.g. halogens, hydroxy) ortho substituent. Two pK(a) equations are provided for o-halogen benzoic acids and o-hydroxybenzoic acids, where the RMSEP values are 0.19 and 0.15 pK(a) units, respectively. Interestingly, the bond length that provided the best model differed between these two high-correlation subsets. This demonstrates the importance of investigating the most predictive bond length, which is not necessarily the bond involving the acid hydrogen. Three high-correlation subsets were identified for the ortho-substituted anilines. These were o-halogen, o-nitro and o-alkyl-substituted aniline high-correlation subsets, where the RMSEP ranged from 0.23 to 0.44 pK(a) units. The RMSEP for the meta-/para-substituted aniline model was 0.54 pK(a) units. This value exceeded our threshold of 0.50 pK(a) units and was higher than both the m-/p-benzoic acids in this work and the m-/p-phenols (RMSEP = 0.43) of Part 2. Constructing two separate models for the meta- and para- substituted anilines, where RMSEP values of 0.63 and 0.33 pK(a) units were obtained respectively, revealed it was the meta-substituted anilines that caused the large RMSEP value. For unknown reasons the RMSEP value increased with the addition of a further twenty meta-substituted anilines to this model. The C-N bond always produced the best correlations with pK(a) for all the high-correlation subsets. A higher level of theory and an ammonia probe improved the statistics only marginally for the hydroxybenzoic acid high-correlation subsets.

Computations and estimates of rate coefficients for hydrocarbon reactions of interest to the atmospheres of outer solar system

NASA Technical Reports Server (NTRS)

Laufer, A. H.; Gardner, E. P.; Kwok, T. L.; Yung, Y. L.

1983-01-01

The rate coefficients, including Arrhenius parameters, have been computed for a number of chemical reactions involving hydrocarbon species for which experimental data are not available and which are important in planetary atmospheric models. The techniques used to calculate the kinetic parameters include the Troe and semiempirical bond energy-bond order (BEBO) or bond strength-bond length (BSBL) methods.

Correlation of bond strength with surface roughness using a new roughness measurement technique.

PubMed

Winkler, M M; Moore, B K

1994-07-01

The correlation between shear bond strength and surface roughness was investigated using new surface measurement methods. Bonding agents and associated resin composites were applied to set amalgam after mechanically roughening its surface. Surface treatments were noe (as set against glass), 80 grit, and 600 grit abrasive paper. Surface roughness (R(a) as measured parallel and perpendicular (+) to the direction of the polishing scratches and true profile length were measured. A knife-edge was applied (rate = 2.54 mm/min) at the bonding agent/amalgam interface of each sample until failure. Coefficients of determination for mean bond strength vs either roughness (R(a), of profile length were significantly higher for measurements in parallel directions than for those measurements in (+) directions. The shear bond strength to set amalgam for a PENTA-containing adhesives system (L.D. Caulk Division) was not significantly different from that of a PENTA-free adhesive (3M Dental Products Division), even though PENTA has been reported to increase bond strength to nonprecious metals. The shear bond strength of resin composite to amalgam is correlated to surface roughness when it is measured parallel to the polishing scratches. This correlation is significantly lower when surface roughness is measured in the typical manner, perpendicular to the polishing scratches.

Bond breaking in epoxy systems: A combined QM/MM approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barr, Stephen A.; Ecker, Allison M.; Berry, Rajiv J., E-mail: Rajiv.Berry@us.af.mil

2016-06-28

A novel method to combine quantum mechanics (QM) and molecular mechanics has been developed to accurately and efficiently account for covalent bond breaking in polymer systems under high strain without the use of predetermined break locations. Use of this method will provide a better fundamental understanding of the mechano-chemical origins of fracture in thermosets. Since classical force fields cannot accurately account for bond breaking, and QM is too demanding to simulate large systems, a hybrid approach is required. In the method presented here, strain is applied to the system using a classical force field, and all bond lengths are monitored.more » When a bond is stretched past a threshold value, a zone surrounding the bond is used in a QM energy minimization to determine which, if any, bonds break. The QM results are then used to reconstitute the system to continue the classical simulation at progressively larger strain until another QM calculation is triggered. In this way, a QM calculation is only computed when and where needed, allowing for efficient simulations. A robust QM method for energy minimization has been determined, as well as appropriate values for the QM zone size and the threshold bond length. Compute times do not differ dramatically from classical molecular mechanical simulations.« less

Correlation of nonorthogonality of best hybrid bond orbitals with bond strength of orthogonal orbitals

PubMed Central

Pauling, Linus

1976-01-01

An expression is derived for the bond length of two spd orbitals with maximum values in two directions forming a given bond angle by consideration of the nonorthogonality integral of two best orbitals in these directions. This equation is equivalent to the expression derived by formulating the pair of orthogonal orbitals. Similar expressions are derived for spdf orbitals. Applications are made to icosahedral and cuboctahedral bonds and to the packing of nucleons in atomic nuclei. PMID:16578736

Correlation of nonorthogonality of best hybrid bond orbitals with bond strength of orthogonal orbitals.

PubMed

Pauling, L

1976-02-01

An expression is derived for the bond length of two spd orbitals with maximum values in two directions forming a given bond angle by consideration of the nonorthogonality integral of two best orbitals in these directions. This equation is equivalent to the expression derived by formulating the pair of orthogonal orbitals. Similar expressions are derived for spdf orbitals. Applications are made to icosahedral and cuboctahedral bonds and to the packing of nucleons in atomic nuclei.

Differential segregation in a cell-cell contact interface: the dynamics of the immunological synapse.

PubMed Central

Burroughs, Nigel John; Wülfing, Christoph

2002-01-01

Receptor-ligand couples in the cell-cell contact interface between a T cell and an antigen-presenting cell form distinct geometric patterns and undergo spatial rearrangement within the contact interface. Spatial segregation of the antigen and adhesion receptors occurs within seconds of contact, central aggregation of the antigen receptor then occurring over 1-5 min. This structure, called the immunological synapse, is becoming a paradigm for localized signaling. However, the mechanisms driving its formation, in particular spatial segregation, are currently not understood. With a reaction diffusion model incorporating thermodynamics, elasticity, and reaction kinetics, we examine the hypothesis that differing bond lengths (extracellular domain size) is the driving force behind molecular segregation. We derive two key conditions necessary for segregation: a thermodynamic criterion on the effective bond elasticity and a requirement for the seeding/nucleation of domains. Domains have a minimum length scale and will only spontaneously coalesce/aggregate if the contact area is small or the membrane relaxation distance large. Otherwise, differential attachment of receptors to the cytoskeleton is required for central aggregation. Our analysis indicates that differential bond lengths have a significant effect on synapse dynamics, i.e., there is a significant contribution to the free energy of the interaction, suggesting that segregation by differential bond length is important in cell-cell contact interfaces and the immunological synapse. PMID:12324401

Pressure-induced emission band separation of the hybridized local and charge transfer excited state in a TPE-based crystal.

PubMed

Liu, Xuedan; Li, Aisen; Xu, Weiqing; Ma, Zhiyong; Jia, Xinru

2018-05-08

We herein report a newly synthesized simple molecule, named TPE[double bond, length as m-dash]C4, with twisted D-A structure. TPE[double bond, length as m-dash]C4 showed two intrinsic emission bands ascribed to the locally excited (LE) state and the intramolecular charge transfer (ICT) state, respectively. In the crystal state, the LE emission band is usually observed. However, by applying hydrostatic pressure to the powder sample and the single crystal sample of TPE[double bond, length as m-dash]C4, dual-fluorescence (445 nm and 532 nm) was emerged under high pressure, owing to the pressure-induced emission band separation of the hybridized local and charge transfer excited state (HLCT). It is found that the emission of TPE[double bond, length as m-dash]C4 is generally determined by the ratio of the LE state to the ICT state. The ICT emission band is much more sensitive to the external pressure than the LE emission band. The HLCT state leads to a sample with different responsiveness to grinding and hydrostatic pressure. This study is of significance in the molecular design of such D-A type molecules and in the control of photoluminescence features by molecular structure. Such results are expected to pave a new way to further understand the relationship between the D-A molecular structure and stimuli-responsive properties.

(Meth­oxy­methyl­idene)di­methyl­aza­nium tetra­phenyl­borate aceto­nitrile monosolvate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2014-01-01

In the cation of the title salt, C4H10NO+·C24H20B−·C2H3N, the C—N bond lengths are 1.2864 (16), 1.4651 (17) and 1.4686 (16) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.2978 (15) Å shows double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. C—H⋯π inter­actions are present between the methine H atom and two of the phenyl rings of the tetra­phenyl­borate ion. The latter forms an aromatic pocket in which the cation is embedded. The iminium ion is further connected through a C—H⋯N hydrogen bond to the aceto­nitrile mol­ecule. This leads to the formation of a two-dimensional supramolecular pattern along the bc plane. PMID:24765028

Measurement accuracy of FBG used as a surface-bonded strain sensor installed by adhesive.

PubMed

Xue, Guangzhe; Fang, Xinqiu; Hu, Xiukun; Gong, Libin

2018-04-10

Material and dimensional properties of surface-bonded fiber Bragg gratings (FBGs) can distort strain measurement, thereby lowering the measurement accuracy. To accurately assess measurement precision and correct obtained strain, a new model, considering reinforcement effects on adhesive and measured object, is proposed in this study, which is verified to be accurate enough by the numerical method. Meanwhile, a theoretical strain correction factor is obtained, which is demonstrated to be significantly sensitive to recoating material and bonding length, as suggested by numerical and experimental results. It is also concluded that a short grating length as well as a thin but large-area (preferably covering the whole FBG) adhesive can enhance the correction precision.

Infrared Spectroscopic Investigation on CH Bond Acidity in Cationic Alkanes

NASA Astrophysics Data System (ADS)

Matsuda, Yoshiyuki; Xie, Min; Fujii, Asuka

2016-06-01

We have demonstrated large enhancements of CH bond acidities in alcohol, ether, and amine cations through infrared predissociation spectroscopy based on the vacuum ultraviolet photoionization detection. In this study, we investigate for the cationic alkanes (pentane, hexane, and heptane) with different alkyl chain lengths. The σ electrons are ejected in the ionization of alkanes, while nonbonding electrons are ejected in ionization of alcohols, ethers, and amines. Nevertheless, the acidity enhancements of CH in these cationic alkanes have also been demonstrated by infrared spectroscopy. The correlations of their CH bond acidities with the alkyl chain lengths as well as the mechanisms of their acidity enhancements will be discussed by comparison of infrared spectra and theoretical calculations.

The effect of the length of macro synthetic fibres on their performance in concrete

NASA Astrophysics Data System (ADS)

Juhász, K. P.; Kis, V.

2017-09-01

Nowadays macro synthetic fibres are able to compete with steel fibres despite their low Youngs Modulus. This is due to their different pull-out mechanism and a larger number of individual fibres per kilo compared to steel fibres. Macro synthetic fibres bond to the concrete along their full length, usually with an embossed surface, while steel fibres are mostly anchored by their hooked ends. If the bond is defined by the length of the embossed surface, logically the longer the synthetic fibre the higher post-crack capacity. In this paper the same type of macro synthetic fibre was researched with different lengths but at the same dosage. The consistency of the fresh concrete together with the quality of the distribution of the fibres have been analysed and compared with the residual strength. After analysing these data the optimum fibre length was able to be determined.

Structural relaxation processes in polyethylene glycol/CCl4 solutions by Brillouin scattering.

PubMed

Pochylski, M; Aliotta, F; Błaszczak, Z; Gapiński, J

2005-03-10

We present results of a Brillouin scattering experiment on solutions of poly(ethylene glycol) of mean molecular mass 600 g/mol (PEG600) in CCl4. The relaxation process detected has been assigned to conformational rearrangements of the polymeric chains, triggered by reorientation of the side groups. The concentration dependencies of the hypersound velocity and normalized absorption are compared against the indications from several models proposed in the literature. The concentration evolution of the system is described in terms of two distinct regimes. At high polymer content, the system is dominated by the structure of the dense polymer, where polymer-polymer interactions, together with excluded volume effects, induce the existence of a preferred local arrangement resulting in a narrow distribution of the relaxation times, with the average value of the relaxation time following a simple Arrhenius temperature dependence. As the concentration decreases, the original structure of the hydrogen bonded polymer network is destroyed, and a number of different local configuration coexist, giving rise to a wider distribution of relaxation times or to a multiple relaxation. At low concentrations, the experimental data are well fitted assuming a Vogel-Fulker-Tammon behavior for the average relaxation time. In addition, the observed deviation from the ideal behavior for the refractive index and the density suggests that CCl4 does not behave as an inert solvent, and due to polarization effects, it can develop local hetero-associated structures via electrostatic interaction with the O-H end groups of the polymeric chains. The hypothesis has been successfully tested by fitting the concentration behavior of the hypersonic velocity to a recent three-component model, suitable to describe the concentration dependence of sound velocity in moderately interacting fluids. The indication of the model furnishes a very high value for the association constant of the PEG600, confirming the literature indication that, in polymeric systems capable of developing long liner aggregates via hydrogen bonding interaction, the Brillouin probe is insensitive to the true length of the polymeric chains. The Brillouin scattering experiment just sees an effective hydrogen bonded aggregate that is huge relative to the length of the single polymeric chain and becomes sensitive only to the density fluctuations of the local segmental motions.

Local structure and polarization resistance of Ce doped SrMnO{sub 3} using extended x-ray fine structure analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Jiseung; Lee, Heesoo, E-mail: heesoo@pusan.ac.kr

2014-09-15

Changes to the local structure of Sr and Mn atoms in Sr{sub 1−x}Ce{sub x}MnO{sub 3} (SCM) according to increasing Ce content and the effect of the structural change on the polarization resistance of SCM were investigated. The reduction of manganese was confirmed by the absorption edge shift of the Mn K-edge toward lower energies. The noise of oscillation in extended X-ray absorption fine structure k{sup 3}χ data at Mn K-edge reveals the distortion of the local structure of Mn atoms, and the peak that indicates the bonding length of Mn-O, Sr/Ce, and -Mn decreased with the addition of Ce contentmore » in Fourier transformations of the Mn K-edge. The distortion of the local structure at Mn atoms was affected by the reduced manganese ions having larger ionic radii than Mn{sup 4+}. Meanwhile, few distortions of local atomic structures of Sr atoms occurred, and the average nearest neighboring distances of Sr-O and Sr-Mn are ∼2.13 Å and ∼2.95 Å, respectively. The average bonding lengths of the Ce-O and Ce-Mn increased because the ionic radius of substituted Ce ion with 12 coordination number is smaller than that of Sr ion, which leads the reduction of Mn ions and the distortion of local structure at the substituted A-site. Therefore, we reasoned that the distortion of the local atomic structure at Mn atoms in MnO{sub 6} and Ce atoms in A-site is one of the causes for interrupting oxygen ion transfers as a geometric factor, which results in an increase in the polarization resistance of SCM within the Ce composition range from 10 mol. % to 30 mol. %.« less

Anisotropy of the monomer random walk in a polymer melt: local-order and connectivity effects

NASA Astrophysics Data System (ADS)

Bernini, S.; Leporini, D.

2016-05-01

The random walk of a bonded monomer in a polymer melt is anisotropic due to local order and bond connectivity. We investigate both effects by molecular-dynamics simulations on melts of fully-flexible linear chains ranging from dimers (M  =  2) up to entangled polymers (M  =  200). The corresponding atomic liquid is also considered a reference system. To disentangle the influence of the local geometry and the bond arrangements, and to reveal their interplay, we define suitable measures of the anisotropy emphasising either the former or the latter aspect. Connectivity anisotropy, as measured by the correlation between the initial bond orientation and the direction of the subsequent monomer displacement, shows a slight enhancement due to the local order at times shorter than the structural relaxation time. At intermediate times—when the monomer displacement is comparable to the bond length—a pronounced peak and then decays slowly as t -1/2, becoming negligible when the displacement is as large as about five bond lengths, i.e. about four monomer diameters or three Kuhn lengths. Local-geometry anisotropy, as measured by the correlation between the initial orientation of a characteristic axis of the Voronoi cell and the subsequent monomer dynamics, is affected at shorter times than the structural relaxation time by the cage shape with antagonistic disturbance by the connectivity. Differently, at longer times, the connectivity favours the persistence of the local-geometry anisotropy, which vanishes when the monomer displacement exceeds the bond length. Our results strongly suggest that the sole consideration of the local order is not enough to understand the microscopic origin of the rattling amplitude of the trapped monomer in the cage of the neighbours.

77 FR 5728 - Airworthiness Directives; Airbus Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-06

... between bonding lead and the harness, due to over length of the bonding lead. As the affected wire is not... chafing of the wires, and corrective actions, if necessary. We are proposing this AD to detect and correct contact or chafing of wires and bonding leads which, if not detected could be a source of sparks in the...

Analytical energy gradient for the two-component normalized elimination of the small component method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Wenli; Filatov, Michael; Cremer, Dieter, E-mail: dcremer@smu.edu

2015-06-07

The analytical gradient for the two-component Normalized Elimination of the Small Component (2c-NESC) method is presented. The 2c-NESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac spin-orbit (SO) splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [Phys. Rev. B 62, 7809 (2000)]. The effect of spin-orbit coupling (SOC) on molecular geometries is analyzed utilizing the properties of the frontier orbitals and calculated SO couplings. It is shown thatmore » bond lengths can either be lengthened or shortened under the impact of SOC where in the first case the influence of low lying excited states with occupied antibonding orbitals plays a role and in the second case the jj-coupling between occupied antibonding and unoccupied bonding orbitals dominates. In general, the effect of SOC on bond lengths is relatively small (≤5% of the scalar relativistic changes in the bond length). However, large effects are found for van der Waals complexes Hg{sub 2} and Cn{sub 2}, which are due to the admixture of more bonding character to the highest occupied spinors.« less

Synthesis and SMM behaviour of trinuclear versus dinuclear 3d-5f uranyl(v)-cobalt(ii) cation-cation complexes.

PubMed

Chatelain, Lucile; Tuna, Floriana; Pécaut, Jacques; Mazzanti, Marinella

2017-05-02

Trinuclear versus dinuclear heterodimetallic U V O 2 + Co 2+ complexes were selectively assembled via a cation-cation interaction by tuning the ligand. The trimeric complex 2, with a linear [Co-O[double bond, length as m-dash]U[double bond, length as m-dash]O-Co] core, exhibits magnetic exchange and slow relaxation with a reversal barrier of 30.5 ± 0.9 K providing the first example of a U-Co exchange-coupled SMM.

Charging and geometric effects on conduction through Anthracene molecular junctions

NASA Astrophysics Data System (ADS)

Kaur, Rupan Preet; Sawhney, Ravinder Singh; Engles, Derick

We studied the geometric effects on the charge transfer through the anthracenedithiol (ADT) molecular junction using density functional theory combined with the non-equilibrium Green’s function approach. Two major geometric aspects, bond length and bond angle, were moderated to optimize the electrical conduction. From the results established in this paper, we found that the electrical conduction can be tuned from 0.2 G0 to 0.9 G0 by varying the Au-S bond length, whereas the moderation of bonding angle assayed a minor change from 0.37 G0 to 0.47 G0. We attributed this escalating zero bias conductance to the increasing charge on the terminal sulfur atom of the ADT molecule, which increased the energy of the HOMO orbital towards Fermi level and exhibited a semi-metallic behaviour. Therefore, geometry plays a critical role in deciding the charge transport through the metal/molecule interface.

Nanoscopic length scale dependence of hydrogen bonded molecular associates’ dynamics in methanol

PubMed Central

Bertrand, C. E.; Self, J. L.; Copley, J. R. D.; Faraone, A.

2017-01-01

In a recent paper [C. E. Bertrand et al., J. Chem. Phys. 145, 014502 (2016)], we have shown that the collective dynamics of methanol shows a fast relaxation process related to the standard density-fluctuation heat mode and a slow non-Fickian mode originating from the hydrogen bonded molecular associates. Here we report on the length scale dependence of this slow relaxation process. Using quasielastic neutron scattering and molecular dynamics simulations, we show that the dynamics of the slow process is affected by the structuring of the associates, which is accessible through polarized neutron diffraction experiments. Using a series of partially deuterated samples, the dynamics of the associates is investigated and is found to have a similar time scale to the lifetime of hydrogen bonding in the system. Both the structural relaxation and the dynamics of the associates are thermally activated by the breaking of hydrogen bonding. PMID:28527447

Ligand-to-ligand charge-transfer transitions of platinum(II) complexes with arylacetylide ligands with different chain lengths: spectroscopic characterization, effect of molecular conformations, and density functional theory calculations.

PubMed

Tong, Glenna So Ming; Law, Yuen-Chi; Kui, Steven C F; Zhu, Nianyong; Leung, King Hong; Phillips, David Lee; Che, Chi-Ming

2010-06-11

The complexes [Pt(tBu(3)tpy){C[triple bond]C(C(6)H(4)C[triple bond]C)(n-1)R}](+) (n = 1: R = alkyl and aryl (Ar); n = 1-3: R = phenyl (Ph) or Ph-N(CH(3))(2)-4; n = 1 and 2, R = Ph-NH(2)-4; tBu(3)tpy = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine) and [Pt(Cl(3)tpy)(C[triple bond]CR)](+) (R = tert-butyl (tBu), Ph, 9,9'-dibutylfluorene, 9,9'-dibutyl-7-dimethyl-amine-fluorene; Cl(3)tpy = 4,4',4''-trichloro-2,2':6',2''-terpyridine) were prepared. The effects of substituent(s) on the terpyridine (tpy) and acetylide ligands and chain length of arylacetylide ligands on the absorption and emission spectra were examined. Resonance Raman (RR) spectra of [Pt(tBu(3)tpy)(C[triple bond]CR)](+) (R = n-butyl, Ph, and C(6)H(4)-OCH(3)-4) obtained in acetonitrile at 298 K reveal that the structural distortion of the C[triple bond]C bond in the electronic excited state obtained by 502.9 nm excitation is substantially larger than that obtained by 416 nm excitation. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations on [Pt(H(3)tpy)(C[triple bond]CR)](+) (R = n-propyl (nPr), 2-pyridyl (Py)), [Pt(H(3)tpy){C[triple bond]C(C(6)H(4)C[triple bond]C)(n-1)Ph}](+) (n = 1-3), and [Pt(H(3)tpy){C[triple bond]C(C(6)H(4)C[triple bond]C)(n-1)C(6)H(4)-N(CH(3))(2)-4}](+)/+H(+) (n = 1-3; H(3)tpy = nonsubstituted terpyridine) at two different conformations were performed, namely, with the phenyl rings of the arylacetylide ligands coplanar ("cop") with and perpendicular ("per") to the H(3)tpy ligand. Combining the experimental data and calculated results, the two lowest energy absorption peak maxima, lambda(1) and lambda(2), of [Pt(Y(3)tpy)(C[triple bond]CR)](+) (Y = tBu or Cl, R = aryl) are attributed to (1)[pi(C[triple bond]CR)-->pi*(Y(3)tpy)] in the "cop" conformation and mixed (1)[d(pi)(Pt)-->pi*(Y(3)tpy)]/(1)[pi(C[triple bond]CR)-->pi*(Y(3)tpy)] transitions in the "per" conformation. The lowest energy absorption peak lambda(1) for [Pt(tBu(3)tpy){C[triple bond]C(C(6)H(4)C[triple bond]C)(n-1)C(6)H(4)-H-4}](+) (n = 1-3) shows a redshift with increasing chain length. However, for [Pt(tBu(3)tpy){C[triple bond]C(C6H4C[triple bond]C)(n-1)C(6)H(4)-N(CH(3))(2)-4}](+) (n = 1-3), lambda(1) shows a blueshift with increasing chain length n, but shows a redshift after the addition of acid. The emissions of [Pt(Y(3)tpy)(C[triple bond]CR)](+) (Y = tBu or Cl) at 524-642 nm measured in dichloromethane at 298 K are assigned to the (3)[pi(C[triple bond]CAr)-->pi*(Y(3)tpy)] excited states and mixed (3)[d(pi)(Pt)-->pi*(Y(3)tpy)]/(3)[pi(C[triple bond]C)-->pi*(Y(3)tpy)] excited states for R = aryl and alkyl groups, respectively. [Pt(tBu(3)tpy){C[triple bond]C(C(6)H(4)C[triple bond]C)(n-1)C(6)H(4)-N(CH(3))(2)-4}](+) (n = 1 and 2) are nonemissive, and this is attributed to the small energy gap between the singlet ground state (S(0)) and the lowest triplet excited state (T(1)).

Structural basis for new pattern of conserved amino acid residues related to chitin-binding in the antifungal peptide from the coconut rhinoceros beetle Oryctes rhinoceros.

PubMed

Hemmi, Hikaru; Ishibashi, Jun; Tomie, Tetsuya; Yamakawa, Minoru

2003-06-20

Scarabaecin isolated from hemolymph of the coconut rhinoceros beetle Oryctes rhinoceros is a 36-residue polypeptide that has antifungal activity. The solution structure of scarabaecin has been determined from twodimensional 1H NMR spectroscopic data and hybrid distance geometry-simulated annealing protocol calculation. Based on 492 interproton and 10 hydrogen-bonding distance restraints and 36 dihedral angle restraints, we obtained 20 structures. The average backbone root-mean-square deviation for residues 4-35 is 0.728 +/- 0.217 A from the mean structure. The solution structure consists of a two-stranded antiparallel beta-sheet connected by a type-I beta-turn after a short helical turn. All secondary structures and a conserved disulfide bond are located in the C-terminal half of the peptide, residues 18-36. Overall folding is stabilized by a combination of a disulfide bond, seven hydrogen bonds, and numerous hydrophobic interactions. The structural motif of the C-terminal half shares a significant tertiary structural similarity with chitin-binding domains of plant and invertebrate chitin-binding proteins, even though scarabaecin has no overall sequence similarity to other peptide/polypeptides including chitin-binding proteins. The length of its primary structure, the number of disulfide bonds, and the pattern of conserved functional residues binding to chitin in scarabaecin differ from those of chitin-binding proteins in other invertebrates and plants, suggesting that scarabaecin does not share a common ancestor with them. These results are thought to provide further strong experimental evidence to the hypothesis that chitin-binding proteins of invertebrates and plants are correlated by a convergent evolution process.

Role of composition, bond covalency, and short-range order in the disordering of stannate pyrochlores by swift heavy ion irradiation

NASA Astrophysics Data System (ADS)

Tracy, Cameron L.; Shamblin, Jacob; Park, Sulgiye; Zhang, Fuxiang; Trautmann, Christina; Lang, Maik; Ewing, Rodney C.

2016-08-01

A2S n2O7 (A =Nd ,Sm,Gd,Er,Yb,and Y) materials with the pyrochlore structure were irradiated with 2.2 GeV Au ions to systematically investigate disordering of this system in response to dense electronic excitation. Structural modifications were characterized, over multiple length scales, by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. Transformations to amorphous and disordered phases were observed, with disordering dominating the structural response of materials with small A -site cation ionic radii. Both the disordered and amorphous phases were found to possess weberite-type local ordering, differing only in that the disordered phase exhibits a long-range, modulated arrangement of weberite-type structural units into an average defect-fluorite structure, while the amorphous phase remains fully aperiodic. Comparison with the behavior of titanate and zirconate pyrochlores showed minimal influence of the high covalency of the Sn-O bond on this phase behavior. An analytical model of damage accumulation was developed to account for simultaneous amorphization and recrystallization of the disordered phase during irradiation.

Atomic structure of unligated laccase from Cerrena maxima at 1.76 A with molecular oxygen and hydrogen peroxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhukova, Yu. N., E-mail: amm@ns.crys.ras.ru; Lyashenko, A. V.; Lashkov, A. A.

2010-05-15

The three-dimensional structure of unligated laccase from Cerrena maxima was established by X-ray diffraction at 1.76-A resolution; R{sub work} = 18.07%, R{sub free} = 21.71%, rmsd of bond lengths, bond angles, and chiral angles are 0.008 A, 1.19{sup o}, and 0.077{sup o}, respectively. The coordinate error for the refined structure estimated from the Luzzati plot is 0.195 A. The maximum average error in the atomic coordinates is 0.047 A. A total of 99.4% of amino-acid residues of the polypeptide chain are in the most favorable, allowable, and accessible regions of the Ramachandran plot. The three-dimensional structures of the complexes ofmore » laccase from C. maxima with molecular oxygen and hydrogen peroxide were determined by the molecular simulation. These data provide insight into the structural aspect of the mechanism of the enzymatic cycle. The structure factors and the refined atomic coordinates were deposited in the Protein Data Bank (PDB-ID code is 3DIV).« less

Molecular dynamics simulations of AP/HMX composite with a modified force field.

PubMed

Zhu, Wei; Wang, Xijun; Xiao, Jijun; Zhu, Weihua; Sun, Huai; Xiao, Heming

2009-08-15

An all-atom force field for ammonium perchlorate (AP) is developed with the framework of pcff force field. The structural parameters of AP obtained with the modified force field are in good agreement with experimental values. Molecular dynamics (MD) simulations have been performed to investigate AP/HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) composite at different temperatures. The binding energies, thermal expansion coefficient, and the trigger bond lengths of HMX in the AP/HMX composite have been obtained. The binding energies of the system increase slightly with temperature increasing, peak at 245K, and then gradually decrease. The volume thermal expansion coefficient of the AP/HMX composite has been derived from the volume variation with temperature. As the temperature rises, the maximal lengths of the trigger bond N-NO(2) of HMX increase gradually. The simulated results indicate that the maximal length of trigger bond can be used as a criterion for judging the sensitivity of energetic composite.

Repeated bonding of fixed retainer increases the risk of enamel fracture.

PubMed

Chinvipas, Netrporn; Hasegawa, Yuh; Terada, Kazuto

2014-01-01

The aim of this study was to investigate the influences of repeated bonding, using 2 different orthodontic adhesive systems, on the shear bond strength (SBS) and the enamel surface morphology. Sixty premolars were divided into 2 groups (n = 30), and either Transbond XT (T group) or Fuji Ortho LC (F group) adhesives were used. SBS was measured 24 h after bonding, using a universal testing machine. Then, the enamel surfaces were investigated and the mode of failure was described using adhesive remnant index (ARI) scores. After each debonding, 10 teeth from each group were examined by scanning electron microscopy to determine the penetration of adhesives, the length of resin tags, and the state of the enamel surface. The other teeth were subjected to two more bonding/debonding procedures. In T group, the second debonding sequences had significantly higher bond strengths than the other sequences. The length of resin tags was greatest in the second debonding sequence, although there was no significant difference. In F group, the SBS increased with further rebonding and the failure mode tended towards cohesive failure. In both groups, the ARI scores increased with rebonding. Enamel loss could have occurred with both adhesives, although the surfaces appeared unchanged to the naked eye. From this study, we suggest that enamel damage caused by repeated bonding is of concern. To prevent bond failure, we should pay attention to the adhesion method used for bondable retainers.

Quantitative assessment of intermolecular interactions by atomic force microscopy imaging using copper oxide tips

NASA Astrophysics Data System (ADS)

Mönig, Harry; Amirjalayer, Saeed; Timmer, Alexander; Hu, Zhixin; Liu, Lacheng; Díaz Arado, Oscar; Cnudde, Marvin; Strassert, Cristian Alejandro; Ji, Wei; Rohlfing, Michael; Fuchs, Harald

2018-05-01

Atomic force microscopy is an impressive tool with which to directly resolve the bonding structure of organic compounds1-5. The methodology usually involves chemical passivation of the probe-tip termination by attaching single molecules or atoms such as CO or Xe (refs 1,6-9). However, these probe particles are only weakly connected to the metallic apex, which results in considerable dynamic deflection. This probe particle deflection leads to pronounced image distortions, systematic overestimation of bond lengths, and in some cases even spurious bond-like contrast features, thus inhibiting reliable data interpretation8-12. Recently, an alternative approach to tip passivation has been used in which slightly indenting a tip into oxidized copper substrates and subsequent contrast analysis allows for the verification of an oxygen-terminated Cu tip13-15. Here we show that, due to the covalently bound configuration of the terminal oxygen atom, this copper oxide tip (CuOx tip) has a high structural stability, allowing not only a quantitative determination of individual bond lengths and access to bond order effects, but also reliable intermolecular bond characterization. In particular, by removing the previous limitations of flexible probe particles, we are able to provide conclusive experimental evidence for an unusual intermolecular N-Au-N three-centre bond. Furthermore, we demonstrate that CuOx tips allow the characterization of the strength and configuration of individual hydrogen bonds within a molecular assembly.

Length-dependence of intramolecular electron transfer in σ-bonded rigid molecular rods: an ab initio molecular orbital study

NASA Astrophysics Data System (ADS)

Pati, Ranjit; Karna, Shashi P.

2002-01-01

The dependence of electron transfer (ET) coupling element, VAB, on the length of rigid-rod-like systems consisting of bicyclo[1.1.1]pentane (BCP), cubane (CUB), and bicyclo[2.2.2]octane (BCO) monomers, has been investigated with the use of ab initio Hartree-Fock (HF) method employing Marcus-Hush two-state (TS) model. The value of VAB decreases exponentially with increase in the number of the cage units of the σ-bonded molecules. The calculated decay constant, β, shows good agreement with previously reported data. For molecular length⩾15 Å, the value of VAB becomes negligibly small, suggesting complete suppression of the through bond direct tunneling contribution to ET process.

Dimensional Stability of Hexoloy SA® Silicon Carbide and Zerodur™ Materials for the LISA Mission

NASA Astrophysics Data System (ADS)

Preston, Alix; Cruz, Rachel J.; Thorpe, J. Ira; Mueller, Guido; Boothe, G. Trask; Delgadillo, Rodrigo; Guntaka, Sridhar R.

2006-11-01

In the LISA mission, incoming gravitational waves will modulate the distance between proof masses while laser beams monitor the optical path length changes with 20 pm/√Hz accuracy. Optical path length changes between bench components or the relative motion between the primary and secondary mirrors of the telescope need to be well below this level to result in a successful operation of LISA. The reference cavity for frequency stabilization must have a dimensional stability of a few fm/√Hz. While the effects of temperature fluctuations are well characterized in most materials at the macroscopic level (i.e. coefficients of thermal expansion), microscopic material internal processes and long term processes in the bonds between different components can dominate the dimensional stability at the pm or fm levels. Zerodur and ULE have been well studied, but the ultimate stabilities of other materials like silicon carbide or CFRP are virtually unknown. Chemical bonding techniques, like hydroxide bonding, provide significantly stronger bonds than the standard optical contacts. However, the noise levels of these bonds are also unknown. In this paper we present our latest results on the stability of silicon carbide and hydroxide bonds on Zerodur.

Crystal structure of cis-aqua­chlorido­bis­(1,10-phenanthroline-κ2 N,N′)chromium(III) tetra­chlorido­zincate monohydrate from synchrotron data

PubMed Central

Moon, Dohyun; Choi, Jong-Ha

2015-01-01

The structure of the title compound, [CrCl(C12H8N2)2(H2O)][ZnCl4]·H2O, has been determined from synchrotron data. The CrIII ion is bonded to four N atoms from two 1,10-phenanthroline (phen) ligands, one water mol­ecule and a Cl atom in a cis arrangement, displaying an overall distorted octa­hedral coordination environment. The Cr—N(phen) bond lengths are in the range of 2.0495 (18) to 2.0831 (18) Å, while the Cr—Cl and Cr—(OH2) bond lengths are 2.2734 (7) and 1.9986 (17) Å, respectively. The tetra­hedral [ZnCl4]2− anion is slightly distorted owing to its involvement in O—H⋯Cl hydrogen bonding with coordinating and non-coordinating water mol­ecules. The two types of water mol­ecules also inter­act through O—H⋯O hydrogen bonds. The observed hydrogen-bonding pattern leads to the formation of a three-dimensional network structure. PMID:25844190

Theoretical Studies of Oxygen Reduction and Proton Transfer in SOFCs and Nerve Agents on Selected Surfaces

DTIC Science & Technology

2015-11-19

hand, the energy change for CO3 2- +O2→CO5 2- is calculated to be - 105.5 kJ/mol and -87.3 kJ/mol by B3LYP and CCSD(T), respectively. Similarly, the...formation energy of CO4 2- ( CO3 2- +1/2O2→CO4 2- ) is -9.8 kJ/mol and -5.4 kJ/mol by B3LYP and CCSD(T), respectively. All testing results have...This configuration is same as those in their crystal structures of bulk Li2CO3, Na2CO3, and K2CO3. In addition, the average bond length between alkali

First principles prediction of amorphous phases using evolutionary algorithms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nahas, Suhas, E-mail: shsnhs@iitk.ac.in; Gaur, Anshu, E-mail: agaur@iitk.ac.in; Bhowmick, Somnath, E-mail: bsomnath@iitk.ac.in

2016-07-07

We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures. Applying this method, in conjunction with density functional theory based electronic, ionic and cell relaxation, we re-investigate two well known amorphous semiconductors, namely silicon and indium gallium zinc oxide. We find that characteristic structural parameters like average bond length and bondmore » angle are within ∼2% of those reported by ab initio MD calculations and experimental studies.« less

Syntheses, Raman spectroscopy and crystal structures of alkali hexa­fluorido­rhenates(IV) revisited

PubMed Central

Louis-Jean, James; Salamat, Ashkan; Pham, Chien Thang; Poineau, Frederic

2018-01-01

The A 2[ReF6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type P m1, adopting the K2[GeF6] structure type. Common to all A 2[ReF6] structures are slightly distorted octa­hedral [ReF6]2− anions with an average Re—F bond length of 1.951 (8) Å. In those salts, symmetry lowering on the local [ReF6]2− anions from Oh (free anion) to D 3d (solid-state structure) occur. The distortions of the [ReF6]2− anions, as observed in their Raman spectra, are correlated to the size of the counter-cations.

Syntheses, Raman spectroscopy and crystal structures of alkali hexafluoridorhenates(IV) revisited

DOE PAGES

Louis-Jean, James; Mariappan Balasekaran, Samundeeswari; Smith, Dean; ...

2018-04-06

The A 2[ReF 6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type Pmore » $$\\bar{3}$$m1, adopting the K 2[GeF 6] structure type. Common to all A 2[ReF 6] structures are slightly distorted octa­hedral [ReF 6] 2- anions with an average Re—F bond length of 1.951 (8) Å. In these salts, symmetry lowering on the local [ReF 6] 2- anions from O h (free anion) to D 3d (solid-state structure) occur. The distortions of the [ReF 6] 2- anions, as observed in their Raman spectra, are correlated to the size of the counter-cations.« less

A novel disulfide bond in the SH2 Domain of the C-terminal Src kinase controls catalytic activity.

PubMed

Mills, Jamie E; Whitford, Paul C; Shaffer, Jennifer; Onuchic, Jose N; Adams, Joseph A; Jennings, Patricia A

2007-02-02

The SH2 domain of the C-terminal Src kinase [Csk] contains a unique disulfide bond that is not present in other known SH2 domains. To investigate whether this unusual disulfide bond serves a novel function, the effects of disulfide bond formation on catalytic activity of the full-length protein and on the structure of the SH2 domain were investigated. The kinase activity of full-length Csk decreases by an order of magnitude upon formation of the disulfide bond in the distal SH2 domain. NMR spectra of the fully oxidized and fully reduced SH2 domains exhibit similar chemical shift patterns and are indicative of similar, well-defined tertiary structures. The solvent-accessible disulfide bond in the isolated SH2 domain is highly stable and far from the small lobe of the kinase domain. However, reduction of this bond results in chemical shift changes of resonances that map to a cluster of residues that extend from the disulfide bond across the molecule to a surface that is in direct contact with the small lobe of the kinase domain in the intact molecule. Normal mode analyses and molecular dynamics calculations suggest that disulfide bond formation has large effects on residues within the kinase domain, most notably within the active-site cleft. Overall, the data indicate that reversible cross-linking of two cysteine residues in the SH2 domain greatly impacts catalytic function and interdomain communication in Csk.

Bond angles in transition-metal tricarbonyl compounds: A test of the theory of hybrid bond orbitals*

PubMed Central

Pauling, Linus

1978-01-01

The theory of hybrid bond orbitals is used to calculate equations giving the value of the bond angle OC—M—CO in relation to the bond number of the metal—carbonyl bond for tricarbonyl groups in which the transition-metal atom is enneacovalent or octacovalent and the group has approximate trigonal symmetry. For cobalt and iron and their congeners the average experimental values lie within about 1° of the theoretical values for enneacovalence, which are 101.9° for Co(CO)3 and 94.5° for Fe(CO)3. This agreement provides strong support for the theory. For Mn(CO)3 and Cr(CO)3 the experimental values indicate the average covalence to be about 8.4 and 7.7, respectively, in agreement with considerations based on the electroneutrality principle. PMID:16592477

Bonding durability of dual-curing composite core material with different self-etching adhesive systems in a model complete vertical root fracture reconstruction.

PubMed

Waidyasekera, Kanchana; Nikaido, Toru; Weerasinghe, Dinesh; Nurrohman, Hamid; Tagami, Junji

2012-04-01

This study evaluated a dual-curing composite along with different dentin adhesive systems for 1 year under water storage, as a new bonding method of root fragments in complete vertical root fracture. Bovine root fragments were bonded with the dual-curing resin composite Clearfil DC Core Automix (DCA) and one of three adhesive systems: two-step self-etching adhesive Clearfil SE Bond (SE), one-step self-etching adhesive Tokuyama Bond Force (BF), one-step dual-curing self-etching adhesive Clearfil DC Bond (DC). Microtensile bond strength (µTBS)/ultimate tensile bond strength (UTS), FE-SEM ultramorphology of fracture modes, and adhesive dentin interface were observed after water storage for periods of up to one year. The data were analyzed with two-way ANOVA. µTBS was influenced by "dentin adhesive system" (F = 324.455, p < 0.001) and "length of water storage" (F = 8.470, p < 0.001). SE yielded significantly higher µTBS, regardless of storage period (p < 0.05) and maintained the initial µTBS without a significant change after 1 year of water storage (p > 0.05). From 24 h to 1 month, BF showed significantly higher bond strength than DC. UTS of DCA was influenced only by the curing mode of the material (F = 5.051, p = 0.027), but not by the length of water storage (F = 0.053, p > 0.05). Two-step self-etching adhesive systems and dual-curing composite core material can be considered as a suitable bonding method for complete root fractures.

Application of the bond valence method in the non-isovalent semiconductor alloy (GaN) 1–x (ZnO) x

DOE PAGES

Liu, Jian

2016-09-29

This paper studies the bond valence method (BVM) and its application in the non-isovalent semiconductor alloy (GaN) 1-x(ZnO) x. Particular attention is paid to the role of short-range order (SRO). A physical interpretation based on atomic orbital interaction is proposed and examined by density-functional theory (DFT) calculations. Combining BVM with Monte-Carlo simulations and a DFT-based cluster expansion model, bond-length distributions and bond-angle variations are predicted. The correlation between bond valence and bond stiffness is also revealed. Lastly the concept of bond valence is extended into the modelling of an atomistic potential.

Hydrogen bonding between nitriles and hydrogen halides and the topological properties of molecular charge distributions

NASA Astrophysics Data System (ADS)

Boyd, Russell J.; Choi, Sai Cheng

1986-08-01

The topological properties of the charge density of the hydrogen-bonded complexes between nitrites and hydrogen chloride correlate linearly with theoretical estimates of the hydrogen-bond energy. At the 6-31G ** level, the hydrogenbond energies range from a low of 10 kJ/mol m NCCN—HC1 to a high of 38 kJ/mol in LiCN—HCl. A linear relationship between the charge density at the hydrogen-bond critical point and the NH internuclear distance of the RCN—HC1 complexes indicates that the generalization of the bond-length-bond-order relationship of CC bonds due to Bader, Tang, Tal and Biegler-König can be extended to intermolecular hydrogen bonding.

Alkyl Chain Length Dependent Structural and Orientational Transformations of Water at Alcohol-Water Interfaces and Its Relevance to Atmospheric Aerosols.

PubMed

Mondal, Jahur A; Namboodiri, V; Mathi, P; Singh, Ajay K

2017-04-06

Although the hydrophobic size of an amphiphile plays a key role in various chemical, biological, and atmospheric processes, its effect at macroscopic aqueous interfaces (e.g., air-water, oil-water, cell membrane-water, etc.), which are ubiquitous in nature, is not well understood. Here we report the hydrophobic alkyl chain length dependent structural and orientational transformations of water at alcohol (C n H 2n+1 OH, n = 1-12)-water interfaces using interface-selective heterodyne-detected vibrational sum frequency generation (HD-VSFG) and Raman multivariate curve resolution (Raman-MCR) spectroscopic techniques. The HD-VSFG results reveal that short-chain alcohols (C n H 2n+1 OH, n < 4, i.e., up to 1-propanol) do not affect the structure (H-bonding) and orientation of water at the air-water interface; the OH stretch band maximum appears at ∼3470 cm -1 , and the water H atoms are pointed toward the bulk water, that is, "H-down" oriented. In contrast, long-chain alcohols (C n H 2n+1 OH, n > 4, i.e., beyond 1-butanol) make the interfacial water more strongly H-bonded and reversely orientated; the OH stretch band maximum appears at ∼3200 cm -1 , and the H atoms are pointed away from the bulk water, that is, "H-up" oriented. Interestingly, for the alcohol of intermediate chain length (C n H 2n+1 OH, n = 4, i.e, 1-butanol), the interface is quite unstable even after hours of its formation and the time-averaged result is qualitatively similar to that of the long-chain alcohols, indicating a structural/orientational crossover of interfacial water at the 1-butanol-water interface. pH-dependent HD-VSFG measurements (with H 2 O as well as isotopically diluted water, HOD) suggest that the structural/orientational transformation of water at the long-chain alcohol-water interface is associated with the adsorption of OH - anion at the interface. Vibrational mapping of the water structure in the hydration shell of OH - anion (obtained by Raman-MCR spectroscopy of NaOH in HOD) clearly shows that the water becomes strongly H-bonded (OH stretch max. ≈ 3200 cm -1 ) while hydrating the OH - anion. Altogether, it is conceivable that alcohols of different hydrophobic chain lengths that are present in the troposphere will differently affect the interfacial electrostatics and associated chemical processes of aerosol droplets, which are critical for cloud formation, global radiation budget, and climate change.

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

ERIC Educational Resources Information Center

Magnasco, Valerio

2008-01-01

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

The effects of chain length, embedded polar groups, pressure, and pore shape on structure and retention in reversed-phase liquid chromatography: molecular-level insights from Monte Carlo simulations.

PubMed

Rafferty, Jake L; Siepmann, J Ilja; Schure, Mark R

2009-03-20

Particle-based simulations using the configurational-bias and Gibbs ensemble Monte Carlo techniques are carried out to probe the effects of various chromatographic parameters on bonded-phase chain conformation, solvent penetration, and retention in reversed-phase liquid chromatography (RPLC). Specifically, we investigate the effects due to the length of the bonded-phase chains (C(18), C(8), and C(1)), the inclusion of embedded polar groups (amide and ether) near the base of the bonded-phase chains, the column pressure (1, 400, and 1000 atm), and the pore shape (planar slit pore versus cylindrical pore with a 60A diameter). These simulations utilize a bonded-phase coverage of 2.9 micromol/m(2)and a mobile phase containing methanol at a molfraction of 33% (about 50% by volume). The simulations show that chain length, embedded polar groups, and pore shape significantly alter structural and retentive properties of the model RPLC system, whereas the column pressure has a relatively small effect. The simulation results are extensively compared to retention measurements. A molecular view of the RPLC retention mechanism emerges that is more complex than can be inferred from thermodynamic measurements.

On the complexity of Engh and Huber refinement restraints: the angle τ as example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Touw, Wouter G.; Vriend, Gert, E-mail: vriend@cmbi.ru.nl

2010-12-01

The angle τ (backbone N—C{sup α}—C) is the most contested Engh and Huber refinement target parameter. It is shown that this parameter is ‘correct’ as a PDB-wide average, but can be improved by taking into account residue types, secondary structures and many other aspects of our knowledge of the biophysical relations between residue type and protein structure. The Engh and Huber parameters for bond lengths and bond angles have been used uncontested in macromolecular structure refinement from 1991 until very recently, despite critical discussion of their ubiquitous validity by many authors. An extensive analysis of the backbone angle τ (N—C{supmore » α}—C) illustrates that the Engh and Huber parameters can indeed be improved and a recent study [Tronrud et al. (2010 ▶), Acta Cryst. D66, 834–842] confirms these ideas. However, the present study of τ shows that improving the Engh and Huber parameters will be considerably more complex than simply making the parameters a function of the backbone ϕ, ψ angles. Many other aspects, such as the cooperativity of hydrogen bonds, the bending of secondary-structure elements and a series of biophysical aspects of the 20 amino-acid types, will also need to be taken into account. Different sets of Engh and Huber parameters will be needed for conceptually different refinement programs.« less

High-Resolution Coarse-Grained Modeling Using Oriented Coarse-Grained Sites.

PubMed

Haxton, Thomas K

2015-03-10

We introduce a method to bring nearly atomistic resolution to coarse-grained models, and we apply the method to proteins. Using a small number of coarse-grained sites (about one per eight atoms) but assigning an independent three-dimensional orientation to each site, we preferentially integrate out stiff degrees of freedom (bond lengths and angles, as well as dihedral angles in rings) that are accurately approximated by their average values, while retaining soft degrees of freedom (unconstrained dihedral angles) mostly responsible for conformational variability. We demonstrate that our scheme retains nearly atomistic resolution by mapping all experimental protein configurations in the Protein Data Bank onto coarse-grained configurations and then analytically backmapping those configurations back to all-atom configurations. This roundtrip mapping throws away all information associated with the eliminated (stiff) degrees of freedom except for their average values, which we use to construct optimal backmapping functions. Despite the 4:1 reduction in the number of degrees of freedom, we find that heavy atoms move only 0.051 Å on average during the roundtrip mapping, while hydrogens move 0.179 Å on average, an unprecedented combination of efficiency and accuracy among coarse-grained protein models. We discuss the advantages of such a high-resolution model for parametrizing effective interactions and accurately calculating observables through direct or multiscale simulations.

26 CFR 1.141-15 - Effective dates.

Code of Federal Regulations, 2010 CFR

2010-04-01

... that increases the amount of requirements covered by the contract by reason of a change in the method... section 1301 of the Tax Reform Act of 1986 (100 Stat. 2602); and (2)(i) The weighted average maturity of the refunding bonds is longer than— (A) The weighted average maturity of the refunded bonds; or (B) In...

Contact and Length Dependent Effects in Single-Molecule Electronics

NASA Astrophysics Data System (ADS)

Hines, Thomas

Understanding charge transport in single molecules covalently bonded to electrodes is a fundamental goal in the field of molecular electronics. In the past decade, it has become possible to measure charge transport on the single-molecule level using the STM break junction method. Measurements on the single-molecule level shed light on charge transport phenomena which would otherwise be obfuscated by ensemble measurements of groups of molecules. This thesis will discuss three projects carried out using STM break junction. In the first project, the transition between two different charge transport mechanisms is reported in a set of molecular wires. The shortest wires show highly length dependent and temperature invariant conductance behavior, whereas the longer wires show weakly length dependent and temperature dependent behavior. This trend is consistent with a model whereby conduction occurs by coherent tunneling in the shortest wires and by incoherent hopping in the longer wires. Measurements are supported with calculations and the evolution of the molecular junction during the pulling process is investigated. The second project reports controlling the formation of single-molecule junctions by means of electrochemically reducing two axial-diazonium terminal groups on a molecule, thereby producing direct Au-C covalent bonds in-situ between the molecule and gold electrodes. Step length analysis shows that the molecular junction is significantly more stable, and can be pulled over a longer distance than a comparable junction created with amine anchoring bonds. The stability of the junction is explained by the calculated lower binding energy associated with the direct Au-C bond compared with the Au-N bond. Finally, the third project investigates the role that molecular conformation plays in the conductance of oligothiophene single-molecule junctions. Ethyl substituted oligothiophenes were measured and found to exhibit temperature dependent conductance and transition voltage for molecules with between two and six repeat units. While the molecule with only one repeat unit shows temperature invariant behavior. Density functional theory calculations show that at higher temperatures the oligomers with multiple repeat units assume a more planar conformation, which increases the conjugation length and decreases the effective energy barrier of the junction.

Programmable Assembly of Peptide Amphiphile via Noncovalent-to-Covalent Bond Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Kohei; Ji, Wei; Palmer, Liam C.

Controlling the number of monomers in a supramolecular polymer has been a great challenge in programmable self-assembly of organic molecules. One approach has been to make use of frustrated growth of the supramolecular assembly by tuning the balance of attractive and repulsive intermolecular forces. We report here on the use of covalent bond formation among monomers, compensating for intermolecular electrostatic repulsion, as a mechanism to control the length of a supramolecular nanofiber formed by self-assembly of peptide amphiphiles. Circular dichroism spectroscopy in combination with dynamic light scattering, size-exclusion chromatography, and transmittance electron microscope analyses revealed that hydrogen bonds between peptidesmore » were reinforced by covalent bond formation, enabling the fiber elongation. To examine these materials for their potential biomedical applications, cytotoxicity of nanofibers against C2C12 premyoblast cells was tested. We demonstrated that cell viability increased with an increase in fiber length, presumably because of the suppressed disruption of cell membranes by the fiber end-caps.« less

Crystal structure of 2-bromo-3-di­methyl­amino-N,N,N′,N′,4-penta­methyl-4-(tri­methyl­sil­yloxy)pent-2-eneamidinium bromide

PubMed Central

Tiritiris, Ioannis; Kress, Ralf; Kantlehner, Willi

2015-01-01

The reaction of the ortho­amide 1,1,1-tris­(di­methyl­amino)-4-methyl-4-(tri­methyl­sil­yloxy)pent-2-yne with bromine in benzene, yields the title salt, C15H33BrN3OSi+·Br−. The C—N bond lengths in the amidinium unit are 1.319 (6) and 1.333 (6) Å, indicating double-bond character, pointing towards charge delocalization within the NCN plane. The C—Br bond length of 1.926 (5) Å is characteristic for a C—Br single bond. Additionally, there is a bromine–bromine inter­action [3.229 (3) Å] present involving the anion and cation. In the crystal, weak C—H⋯Br inter­actions between the methyl H atoms of the cation and the bromide ions are present. PMID:26870498

First principles study of the electronic properties and band gap modulation of two-dimensional phosphorene monolayer: Effect of strain engineering

NASA Astrophysics Data System (ADS)

Phuc, Huynh V.; Hieu, Nguyen N.; Ilyasov, Victor V.; Phuong, Le T. T.; Nguyen, Chuong V.

2018-06-01

The effect of strain on the structural and electronic properties of monolayer phosphorene is studied by using first-principle calculations based on the density functional theory. The intra- and inter-bond length and bond angle for monolayer phosphorene is also evaluated. The intra- and inter-bond length and the bond angle for phosphorene show an opposite tendency under different directions of the applied strain. At the equilibrium state, monolayer phosphorene is a semiconductor with a direct band gap at the Γ-point of 0.91 eV. A direct-indirect band gap transition is found in monolayer phosphorene when both the compression and tensile strain are simultaneously applied along both zigzag and armchair directions. Under the applied compression strain, a semiconductor-metal transition for monolayer phosphorene is observed at -13% and -10% along armchair and zigzag direction, respectively. The direct-indirect and phase transition will largely constrain application of monolayer phosphorene to electronic and optical devices.

Programmable Assembly of Peptide Amphiphile via Noncovalent-to-Covalent Bond Conversion

DOE PAGES

Sato, Kohei; Ji, Wei; Palmer, Liam C.; ...

2017-06-22

Controlling the number of monomers in a supramolecular polymer has been a great challenge in programmable self-assembly of organic molecules. One approach has been to make use of frustrated growth of the supramolecular assembly by tuning the balance of attractive and repulsive intermolecular forces. We report here on the use of covalent bond formation among monomers, compensating for intermolecular electrostatic repulsion, as a mechanism to control the length of a supramolecular nanofiber formed by self-assembly of peptide amphiphiles. Circular dichroism spectroscopy in combination with dynamic light scattering, size-exclusion chromatography, and transmittance electron microscope analyses revealed that hydrogen bonds between peptidesmore » were reinforced by covalent bond formation, enabling the fiber elongation. To examine these materials for their potential biomedical applications, cytotoxicity of nanofibers against C2C12 premyoblast cells was tested. We demonstrated that cell viability increased with an increase in fiber length, presumably because of the suppressed disruption of cell membranes by the fiber end-caps.« less

Spectroscopic and theoretical investigations of alkali metal linoleates and oleinates

NASA Astrophysics Data System (ADS)

Świsłocka, Renata; Regulska, Ewa; Jarońko, Paweł; Lewandowski, Włodzimierz

2017-11-01

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of the linoleic (cis-9,cis-12-octadecadienoic) and oleic (cis-9-octadecenoic) acids was investigated. The complementary analytical methods: vibrational (IR, Raman) and electronic (UV) molecular absorption spectroscopy as well as DFT quantum mechanical calculations (charge distribution, angles between bonds, bond lengths, theoretical IR and NMR spectra) were carried out. The regular shifts of bands connected with carboxylate anion in the spectra of studied salts were observed. Some bonds and angles reduced or elongated in the series: acid→Li→Na→K linoleates/oleinates. The highest changes were noted for bond lengths and angles concerning COO- ion. The electronic charge distribution in studied molecules was also discussed. Total atomic charges of carboxylate anion decrease as a result of the replacement of hydrogen atom with alkali metal cation. The increasing values of dipole moment and decreasing values of total energy in the order: linoleic/oleic acid→lithium→sodium→potassium linoleates/oleinates indicate an increase in stability of the compounds.

Real-space identification of intermolecular bonding with atomic force microscopy.

PubMed

Zhang, Jun; Chen, Pengcheng; Yuan, Bingkai; Ji, Wei; Cheng, Zhihai; Qiu, Xiaohui

2013-11-01

We report a real-space visualization of the formation of hydrogen bonding in 8-hydroxyquinoline (8-hq) molecular assemblies on a Cu(111) substrate, using noncontact atomic force microscopy (NC-AFM). The atomically resolved molecular structures enable a precise determination of the characteristics of hydrogen bonding networks, including the bonding sites, orientations, and lengths. The observation of bond contrast was interpreted by ab initio density functional calculations, which indicated the electron density contribution from the hybridized electronic state of the hydrogen bond. Intermolecular coordination between the dehydrogenated 8-hq and Cu adatoms was also revealed by the submolecular resolution AFM characterization. The direct identification of local bonding configurations by NC-AFM would facilitate detailed investigations of intermolecular interactions in complex molecules with multiple active sites.

Reaction of the thermo-labile triazenide Na[tBu3SiNNNSiMe3] with CO2: formation of the imido carbonate (tBu3SiO)(Me3SiO)C[double bond, length as m-dash]N-SitBu3 and carbamine acid (tBu3SiO)CONH2.

PubMed

Lerner, H-W; Bolte, M; Wagner, M

2017-07-11

The thermo-labile triazenide Na[tBu 3 SiNNNSiMe 3 ] was prepared by the reaction of Me 3 SiN 3 with Na(thf) 2 [SitBu 3 ] in pentane at -78 °C. Treatment of Na[tBu 3 SiNNNSiMe 3 ] with an excess of carbon dioxide in pentane at -78 °C yielded the imido carbonate (tBu 3 SiO)(Me 3 SiO)C[double bond, length as m-dash]N-SitBu 3 and the carbamine acid (tBu 3 SiO)CONH 2 along with other products. From the reaction solution we could isolate the imido carbonate (tBu 3 SiO)(Me 3 SiO)C[double bond, length as m-dash]N-SitBu 3 and carbamine acid (tBu 3 SiO)CONH 2 . At first single crystals of the carbamine acid (tBu 3 SiO)CONH 2 (triclinic, space group P1[combining macron]) were grown from this solution at room temperature. A second crop of crystals were obtained by concentrating the solution. The second charge consisted of the imido carbonate (tBu 3 SiO)(Me 3 SiO)C[double bond, length as m-dash]N-SitBu 3 (monoclinic, space group P2 1 /n).

Origin of anisotropic negative Poisson's ratio in graphene.

PubMed

Qin, Zhenzhen; Qin, Guangzhao; Hu, Ming

2018-06-07

Negative Poisson's ratio (NPR) in auxetic materials is of great interest due to the typically enhanced toughness, shear resistance, and sound and vibration absorption, which enables plenty of novel applications such as aerospace and defense. Insight into the mechanism underlying NPR is significant to the design of auxetic nanomaterials and nanostructures. However, the analysis of NPR in previous studies mainly remains on the level of the evolution of geometry parameters, such as bond length and bond angle, while a thorough and fundamental understanding is lacking. In this paper, we report anisotropic differential NPR in graphene for uniaxial strains applied along both zigzag and armchair directions based on first-principles calculations. The mechanism underlying the emergence of NPR in graphene (evolution of bond length and bond angle) is found to be different from the conclusions from previous classical molecular dynamics simulations with empirical potential. We propose that the decentralized electron localization function (ELF) driven by strain leads to ELF coupling between different types of bonds, which results in the counter-intuitive anomalous increase of the bond angle and thus the emergence of NPR in graphene. Moreover, the NPR phenomenon can be anticipated to emerge in other nanomaterials or nanostructures with a similar honeycomb structure as that of graphene, where the ELF coupling would also be possible.

Monte Carlo simulations of lattice models for single polymer systems

NASA Astrophysics Data System (ADS)

Hsu, Hsiao-Ping

2014-10-01

Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N ˜ O(10^4). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and sqrt{10}, we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior.

Electric Field Effects on the Intermolecular Interactions in Water Whiskers: Insight from Structures, Energetics, and Properties

DOE PAGES

Bai, Yang; He, Hui-Min; Li, Ying; ...

2015-02-19

Modulation of intermolecular interactions in response to external electric fields could be fundamental to the formation of unusual forms of water, such as water whiskers. However, a detailed understanding of the nature of intermolecular interactions in such systems is lacking. In this study, we present novel theoretical results based on electron correlation calculations regarding the nature of H-bonds in water whiskers, which is revealed by studying their evolution under external electric fields with various field strengths. We find that the water whiskers consisting of 2-7 water molecules all have a chain-length dependent critical electric field. Under the critical electric field,more » the most compact chain structures are obtained, featuring very strong H-bonds, herein referred to as covalent H-bonds. In the case of a water dimer whisker, the bond length of the novel covalent H-bond shortens by 25%, the covalent bond order increases by 9 times, and accordingly the H-bond energy is strengthened by 5 times compared to the normal H-bond in a (H 2O) 2 cluster. Below the critical electric field, it is observed that with increasing field strength, H-bonding orbitals display gradual evolutions in the orbital energy, orbital ordering, and orbital nature (i.e., from typical -style orbital to unusual -style double H-bonding orbital). We also show that beyond the critical electric field, a single water whisker may disintegrate to form a loosely bound zwitterionic chain due to a relay-style proton transfer, whereas two water whiskers may undergo intermolecular cross-linking to form a quasi-two-dimensional water network. In conclusion, these results help shed new insight on the effects of electric fields on water whisker formation.« less

Density functional theory and chromium: Insights from the dimers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Würdemann, Rolf; Kristoffersen, Henrik H.; Moseler, Michael

2015-03-28

The binding in small Cr clusters is re-investigated, where the correct description of the dimer in three charge states is used as criterion to assign the most suitable density functional theory approximation. The difficulty in chromium arises from the subtle interplay between energy gain from hybridization and energetic cost due to exchange between s and d based molecular orbitals. Variations in published bond lengths and binding energies are shown to arise from insufficient numerical representation of electron density and Kohn-Sham wave-functions. The best functional performance is found for gradient corrected (GGA) functionals and meta-GGAs, where we find severe differences betweenmore » functionals from the same family due to the importance of exchange. Only the “best fit” from Bayesian error estimation is able to predict the correct energetics for all three charge states unambiguously. With this knowledge, we predict small bond-lengths to be exclusively present in Cr{sub 2} and Cr{sub 2}{sup −}. Already for the dimer cation, solely long bond-lengths appear, similar to what is found in the trimer and in chromium bulk.« less

Efficient Organometallic Spin Filter between Single-Wall Carbon Nanotube or Graphene Electrodes

NASA Astrophysics Data System (ADS)

Koleini, Mohammad; Paulsson, Magnus; Brandbyge, Mads

2007-05-01

We present a theoretical study of spin transport in a class of molecular systems consisting of an organometallic benzene-vanadium cluster placed in between graphene or single-wall carbon-nanotube-model contacts. Ab initio modeling is performed by combining spin density functional theory and nonequilibrium Green’s function techniques. We consider weak and strong cluster-contact bonds. Depending on the bonding we find from 73% (strong bonds) up to 99% (weak bonds) spin polarization of the electron transmission, and enhanced polarization with increased cluster length.

Hydrogen-Bond Driven Loop-Closure Kinetics in Unfolded Polypeptide Chains

PubMed Central

Daidone, Isabella; Neuweiler, Hannes; Doose, Sören; Sauer, Markus; Smith, Jeremy C.

2010-01-01

Characterization of the length dependence of end-to-end loop-closure kinetics in unfolded polypeptide chains provides an understanding of early steps in protein folding. Here, loop-closure in poly-glycine-serine peptides is investigated by combining single-molecule fluorescence spectroscopy with molecular dynamics simulation. For chains containing more than 10 peptide bonds loop-closing rate constants on the 20–100 nanosecond time range exhibit a power-law length dependence. However, this scaling breaks down for shorter peptides, which exhibit slower kinetics arising from a perturbation induced by the dye reporter system used in the experimental setup. The loop-closure kinetics in the longer peptides is found to be determined by the formation of intra-peptide hydrogen bonds and transient β-sheet structure, that accelerate the search for contacts among residues distant in sequence relative to the case of a polypeptide chain in which hydrogen bonds cannot form. Hydrogen-bond-driven polypeptide-chain collapse in unfolded peptides under physiological conditions found here is not only consistent with hierarchical models of protein folding, that highlights the importance of secondary structure formation early in the folding process, but is also shown to speed up the search for productive folding events. PMID:20098498

Noble gas bond and the behaviour of XeO3 under pressure.

PubMed

Hou, Chunju; Wang, Xianlong; Botana, Jorge; Miao, Maosheng

2017-10-18

Over the past few decades, the concept of hydrogen bonds, in which hydrogen is electrophilic, has been extended to halogen bonds, chalcogen bonds and pnicogen bonds. Herein, we show that such a non-covalent bonding also exists in noble gas compounds. Using first principles calculations, we illustrate the OXe-O bond in molecular crystal XeO 3 and its effect on the behavior of this compound under pressure. Our calculations show that the covalent Xe-O bond lengths were elongated with increasing pressure and correspondingly the Xe-O stretching vibration frequencies were red shifted, which is similar to the change of H-bonds under pressure. The OXe-O bond and related hopping of O between neighboring Xe sites also correspond to the structural changes in the XeO 3 compounds at about 2 GPa. Our study extends the concept of hydrogen bonding to include all p-block elements and show a new bonding type for Noble gas elements in which it acts as an electrophilic species.

Tri-μ-oxido-bis­[(5,10,15,20-tetra­phenyl­porphyrinato-κ4 N)niobium(V)

PubMed Central

Soury, Raoudha; Belkhiria, Mohamed Salah; Daran, Jean-Claude; Nasri, Habib

2011-01-01

In the title dinuclear NbV compound, [Nb2(C44H28N4)2O3], each Nb atom is seven-coordinated with three bridging O atoms and four N atoms from a chelating tetra­phenyl­porphyrinate anion. The Nb—O bond lengths range from 1.757 (6) to 2.331 (6) Å, and the average (niobium–pyrrole N atom) distance is 2.239 Å. In the dinuclear mol­ecule, the Nb⋯Nb separation is 2.8200 (8) Å, and the dihedral angle between the two porphyrinate mean planes is 5.4 (1)°. Weak inter­molecular C—H⋯π inter­actions are present in the crystal structure. PMID:21836860

In Situ Neutron Diffraction of Rare-Earth Phosphate Proton Conductors Sr/Ca-doped LaPO4 at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Al-Wahish, Amal; Al-Binni, Usama; Bridges, C. A.; Huq, A.; Bi, Z.; Paranthaman, M. P.; Tang, S.; Kaiser, H.; Mandrus, D.

Acceptor-doped lanthanum orthophosphates are potential candidate electrolytes for proton ceramic fuel cells. We combined neutron powder diffraction (NPD) at elevated temperatures up to 800° C , X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) to investigate the crystal structure, defect structure, thermal stability and surface topography. NPD shows an average bond length distortion in the hydrated samples. We employed Quasi-Elastic Neutron Scattering (QENS) and electrochemical impedance spectroscopy (EIS) to study the proton dynamics of the rare-earth phosphate proton conductors 4.2% Sr/Ca-doped LaPO4. We determined the bulk diffusion and the self-diffusion coefficients. Our results show that QENS and EIS are probing fundamentally different proton diffusion processes. Supported by the U.S. Department of Energy.

Anisotropic pyrochemical microetching of poly(tetrafluoroethylene) initiated by synchrotron radiation-induced scission of molecule bonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamaguchi, Akinobu, E-mail: yamaguti@lasti.u-hyogo.ac.jp, E-mail: utsumi@lasti.u-hyogo.ac.jp; Kido, Hideki; Utsumi, Yuichi, E-mail: yamaguti@lasti.u-hyogo.ac.jp, E-mail: utsumi@lasti.u-hyogo.ac.jp

2016-02-01

We developed a process for micromachining polytetrafluoroethylene (PTFE): anisotropic pyrochemical microetching induced by synchrotron X-ray irradiation. X-ray irradiation was performed at room temperature. Upon heating, the irradiated PTFE substrates exhibited high-precision features. Both the X-ray diffraction peak and Raman signal from the irradiated areas of the substrate decreased with increasing irradiation dose. The etching mechanism is speculated as follows: X-ray irradiation caused chain scission, which decreased the number-average degree of polymerization. The melting temperature of irradiated PTFE decreased as the polymer chain length decreased, enabling the treated regions to melt at a lower temperature. The anisotropic pyrochemical etching process enabledmore » the fabrication of PTFE microstructures with higher precision than simultaneously heating and irradiating the sample.« less

Bond-strength inversion in (In,Ga)As semiconductor alloys

NASA Astrophysics Data System (ADS)

Eckner, Stefanie; Ritter, Konrad; Schöppe, Philipp; Haubold, Erik; Eckner, Erich; Rensberg, Jura; Röder, Robert; Ridgway, Mark C.; Schnohr, Claudia S.

2018-05-01

The atomic-scale structure and vibrational properties of semiconductor alloys are determined by the energy required for stretching and bending the individual bonds. Using temperature-dependent extended x-ray absorption fine-structure spectroscopy, we have determined the element-specific In-As and Ga-As effective bond-stretching force constants in (In,Ga)As as a function of the alloy composition. The results reveal a striking inversion of the bond strength where the originally stiffer bond in the parent materials becomes the softer bond in the alloy and vice versa. Our findings clearly demonstrate that changes of both the individual bond length and the surrounding matrix affect the bond-stretching force constants. We thus show that the previously used common assumptions about the element-specific force constants in semiconductor alloys do not reproduce the composition dependence determined experimentally for (In,Ga)As.

Vibrational spectral investigation and natural bond orbital analysis of pharmaceutical compound 7-Amino-2,4-dimethylquinolinium formate - DFT approach

NASA Astrophysics Data System (ADS)

Suresh, D. M.; Amalanathan, M.; Sebastian, S.; Sajan, D.; Hubert Joe, I.; Bena Jothy, V.; Nemec, Ivan

2013-11-01

The molecular geometry, the normal mode frequencies and corresponding vibrational assignments, natural bond orbital analysis and the HOMO-LUMO analysis of 7-Amino-2,4-dimethylquinolinium formate in the ground state were performed by B3LYP levels of theory using the 6-31G(d) basis set. The optimised bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of the title compound which is calculated by DFT method, reproduces vibrational wave numbers and intensities with an accuracy which allows reliable vibrational assignments. The possibility of N-H⋯O hydrogen bonding was identified using NBO analysis. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction.

An energetic scale for equilibrium H/D fractionation factors illuminates hydrogen bond free energies in proteins

PubMed Central

Cao, Zheng; Bowie, James U

2014-01-01

Equilibrium H/D fractionation factors have been extensively employed to qualitatively assess hydrogen bond strengths in protein structure, enzyme active sites, and DNA. It remains unclear how fractionation factors correlate with hydrogen bond free energies, however. Here we develop an empirical relationship between fractionation factors and free energy, allowing for the simple and quantitative measurement of hydrogen bond free energies. Applying our empirical relationship to prior fractionation factor studies in proteins, we find: [1] Within the folded state, backbone hydrogen bonds are only marginally stronger on average in α-helices compared to β-sheets by ∼0.2 kcal/mol. [2] Charge-stabilized hydrogen bonds are stronger than neutral hydrogen bonds by ∼2 kcal/mol on average, and can be as strong as –7 kcal/mol. [3] Changes in a few hydrogen bonds during an enzyme catalytic cycle can stabilize an intermediate state by –4.2 kcal/mol. [4] Backbone hydrogen bonds can make a large overall contribution to the energetics of conformational changes, possibly playing an important role in directing conformational changes. [5] Backbone hydrogen bonding becomes more uniform overall upon ligand binding, which may facilitate participation of the entire protein structure in events at the active site. Our energetic scale provides a simple method for further exploration of hydrogen bond free energies. PMID:24501090

Single-crystal X-ray diffraction study of Fe 2SiO 4 fayalite up to 31 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jin S.; Hu, Yi; Shelton, Hannah

2016-10-03

Olivine is widely believed to be the most abundant mineral in the Earth’s upper mantle. Here, we report structural refinement results for the Fe-end-member olivine, Fe 2SiO 4 fayalite, up to 31 GPa in diamond-anvil cell, using single-crystal synchrotron X-ray diffraction. Unit-cell parameters a, b, c and V, average Si–O Fe–O bond lengths, as well as Si–O Fe–O polyhedral volumes continuously decrease with increasing pressure. The pressure derivative of isothermal bulk modulus K' T0 is determined to be 4.0 (2) using third-order Birch–Murnaghan equation of state with ambient isothermal bulk modulus fixed to 135 GPa on the basis of previousmore » Brillouin measurements. The Si–O tetrahedron is stiffer than the Fe–O octahedra, and the compression mechanism is dominated by Fe–O bond and Fe–O octahedral compression. Densities of olivine along 1600 and 900 K adiabats are calculated based on this study. The existence of metastable olivine inside the cold subduction slab could cause large positive buoyancy force against subduction, slow down the subduction and possibly affect the slab geometry.« less

Improving proton conduction pathways in di- and triblock copolymer membranes: Branched versus linear side chains

NASA Astrophysics Data System (ADS)

Dorenbos, G.

2017-06-01

Phase separation within a series of polymer membranes in the presence of water is studied by dissipative particle dynamics. Each polymer contains hydrophobic A beads and hydrophilic C beads. Three parent architectures are constructed from a backbone composed of connected hydrophobic A beads to which short ([C]), long ([A3C]), or symmetrically branched A5[AC][AC] side chains spring off. Three di-block copolymer derivatives are constructed by covalently bonding an A30 block to each parent architecture. Also three tri-blocks with A15 blocks attached to both ends of each parent architecture are modeled. Monte Carlo tracer diffusion calculations through the water containing pores for 1226 morphologies reveal that water diffusion for parent architectures is slowest and diffusion through the di-blocks is fastest. Furthermore, diffusion increases with side chain length and is highest for branched side chains. This is explained by the increase of water pore size with , which is the average number of bonds that A beads are separated from a nearest C bead. Optimization of within the amphiphilic parent architecture is expected to be essential in improving proton conduction in polymer electrolyte membranes.

Crystal structure of bis-(benzyl-amine-κN)[5,10,15,20-tetra-kis-(4-chloro-phen-yl)porphyrinato-κ(4) N]iron(II) n-hexane monosolvate.

PubMed

Dhifaoui, Selma; Harhouri, Wafa; Bujacz, Anna; Nasri, Habib

2016-01-01

In the title compound, [Fe(II)(C44H24Cl4N4)(C6H5CH2NH2)2]·C6H14 or [Fe(II)(TPP-Cl)(BzNH2)2]·n-hexane [where TPP-Cl and BzNH2 are 5,10,15,20-tetra-kis-(4-chloro-phen-yl)porphyrinate and benzyl-amine ligands, respectively], the Fe(II) cation lies on an inversion centre and is octa-hedrally coordinated by the four pyrrole N atoms of the porphyrin ligand in the equatorial plane and by two amine N atoms of the benzyl-amine ligand in the axial sites. The crystal structure also contains one inversion-symmetric n-hexane solvent mol-ecule per complex mol-ecule. The average Fe-Npyrrole bond length [1.994 (3) Å] indicates a low-spin complex. The crystal packing is sustained by N-H⋯Cl and C-H⋯Cl hydrogen-bonding inter-actions and by C-H⋯π inter-molecular inter-actions, leading to a three-dimensional network structure.

Synthesis and characterization of (cryptand-222)potassium (2-methylimidazolato)(meso-tetraphenylporphinato)ferrate(II)-2-methylimidazole-tetrahydrofuran (1/1/2).

PubMed

Wu, Qi; Yao, Zhen; Li, Jianfeng

2017-09-01

Metalloporphyrin complexes containing an additional imidazole ligand can provide information about the effect of deprotonation or hydrogen bonding on the axial histidine unit in heme proteins. The title high-spin five-coordinate imidazolate-ligated iron(II) porphyrinate, [K(C 18 H 36 N 2 O 6 )][Fe(C 4 H 5 N 2 )(C 44 H 28 N 4 )]·C 4 H 6 N 2 ·2C 4 H 8 O, has been synthesized and investigated. The solvated salt crystallizes with one 2-methylimidazole molecule, two tetrahydrofuran solvent molecules and a potassium cation chelated inside a cryptand-222 (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) molecule. The imidazolate ligand is ordered. The average Fe-Np (Np is a porphyrin N atom) bond length is 2.113 (11) Å and the axial Fe-N Im (N Im is an imidazolate N atom) is 2.0739 (13) Å. The out-of-plane displacement of the Fe II atom from the 24-atom mean plane is 0.6098 (5) Å, indicating an apparent doming of the porphyrin core.

Bond, transfer length, and development length of prestressing strand in self-consolidating concrete.

DOT National Transportation Integrated Search

2014-07-01

Due to its economic advantages, the use of self-consolidating concrete (SCC) has increased rapidly in recent years. However, because : SCC mixes typically have decreased amounts of coarse aggregate and high amounts of admixtures, industry members hav...

The Hydrogen Bonded Structures of Two 5-Bromobarbituric Acids and Analysis of Unequal C5–X and C5–X′ Bond Lengths (X = X′ = F, Cl, Br or Me) in 5,5-Disubstituted Barbituric Acids

PubMed Central

Gelbrich, Thomas; Braun, Doris E.; Oberparleiter, Stefan; Schottenberger, Herwig; Griesser, Ulrich J.

2017-01-01

The crystal structure of the methanol hemisolvate of 5,5-dibromobarbituric acid (1MH) displays an H-bonded layer structure which is based on N–H⋯O=C, N–H⋯O(MeOH) and (MeOH)O–H⋯O interactions. The barbiturate molecules form an H-bonded substructure which has the fes topology. 5,5′-Methanediylbis(5-bromobarbituric acid) 2, obtained from a solution of 5,5-dibromobarbituric acid in nitromethane, displays a N–H⋯O=C bonded framework of the sxd type. The conformation of the pyridmidine ring and the lengths of the ring substituent bonds C5–X and C5–X′ in crystal forms of 5,5-dibromobarbituric acid and three closely related analogues (X = X′ = Br, Cl, F, Me) have been investigated. In each case, a conformation close to a C5-endo envelope is correlated with a significant lengthening of the axial C5–X′ in comparison to the equatorial C5–X bond. Isolated molecule geometry optimizations at different levels of theory confirm that the C5-endo envelope is the global conformational energy minimum of 5,5-dihalogenbarbituric acids. The relative lengthening of the axial bond is therefore interpreted as an inherent feature of the preferred envelope conformation of the pyrimidine ring, which minimizes repulsive interactions between the axial substituent and pyrimidine ring atoms. PMID:28670485

Site-specific binding of a water molecule to the sulfa drugs sulfamethoxazole and sulfisoxazole: a laser-desorption isomer-specific UV and IR study.

PubMed

Uhlemann, Thomas; Seidel, Sebastian; Müller, Christian W

2018-03-07

To determine the preferred water molecule binding sites of the polybasic sulfa drugs sulfamethoxazole (SMX) and sulfisoxazole (SIX), we have studied their monomers and monohydrated complexes through laser-desorption conformer-specific UV and IR spectroscopy. Both the SMX and SIX monomer adopt a single conformer in the molecular beam. On the basis of their conformer-specific IR spectra in the NH stretch region, these conformers were assigned to the SMX and SIX global minimum structures, both exhibiting a staggered sulfonamide group and an intramolecular C-HO[double bond, length as m-dash]S hydrogen bond. The SMX-H 2 O and SIX-H 2 O complexes each adopt a single isomer in the molecular beam. Their isomeric structures were determined based on their isomer-specific IR spectra in the NH/OH stretch region. Quantum Theory of Atoms in Molecules analysis of the calculated electron densities revealed that in the SMX-H 2 O complex the water molecule donates an O-HN hydrogen bond to the heterocycle nitrogen atom and accepts an N-HO hydrogen bond from the sulfonamide NH group. In the SIX-H 2 O complex, however, the water molecule does not bind to the heterocycle but instead donates an O-HO[double bond, length as m-dash]S hydrogen bond to the sulfonamide group and accepts an N-HO hydrogen bond from the sulfonamide NH group. Both water complexes are additionally stabilized by a C ph -HOH 2 hydrogen bond. Interacting Quantum Atoms analysis suggests that all intermolecular hydrogen bonds are dominated by the short-range exchange-correlation contribution.

Laser desorption single-conformation UV and IR spectroscopy of the sulfonamide drug sulfanilamide, the sulfanilamide-water complex, and the sulfanilamide dimer.

PubMed

Uhlemann, Thomas; Seidel, Sebastian; Müller, Christian W

2017-06-07

We have studied the conformational preferences of the sulfonamide drug sulfanilamide, its dimer, and its monohydrated complex through laser desorption single-conformation UV and IR spectroscopy in a molecular beam. Based on potential energy curves for the inversion of the anilinic and the sulfonamide NH 2 groups calculated at DFT level, we suggest that the zero-point level wave function of the sulfanilamide monomer is appreciably delocalized over all four conformer wells. The sulfanilamide dimer, and the monohydrated complex each exhibit a single isomer in the molecular beam. The isomeric structures of the sulfanilamide dimer and the monohydrated sulfanilamide complex were assigned based on their conformer-specific IR spectra in the NH and OH stretch region. Quantum Theory of Atoms in Molecules (QTAIM) analysis of the calculated electron density in the water complex suggests that the water molecule is bound side-on in a hydrogen bonding pocket, donating one O-HO[double bond, length as m-dash]S hydrogen bond and accepting two hydrogen bonds, a NHO and a CHO hydrogen bond. QTAIM analysis of the dimer electron density suggests that the C i symmetry dimer structure exhibits two dominating N-HO[double bond, length as m-dash]S hydrogen bonds, and three weaker types of interactions: two CHO bonds, two CHN bonds, and a chalcogen OO interaction. Most interestingly, the molecular beam dimer structure closely resembles the R dimer unit - the dimer unit with the greatest interaction energy - of the α, γ, and δ crystal polymorphs. Interacting Quantum Atoms analysis provides evidence that the total intermolecular interaction in the dimer is dominated by the short-range exchange-correlation contribution.

Conciliatory Inductive Model Explaining the Origin of Changes in the η(2)-SiH Bond Length Caused by Presence of Strongly Electronegative Atoms X (X = F, Cl) in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] (n = 0-3) Complexes.

PubMed

Jabłoński, Mirosław

2016-06-23

Using three theoretical methods, QTAIM, IQA, and NCI, we analyze an influence of halogen atoms X (X = F, Cl) substituted at various positions in the -SiH3-nXn group on the charge density distribution within the η(2)-SiH bond and on the SiH bond energies in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes and isolated HSiH3-nXn molecules. It is shown that shortening of the η(2)-SiH bond in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes should be considered as a normal inductive result of halogenation. This η(2)-SiH bond's compression may, however, be overcome by a predominant elongation resulting from a contingent presence of a halogen atom at position trans to the η(2)-SiH bond. This trans effect is particularly large for bulky and highly polarizable chlorine. Moreover, peculiar properties of the trans chlorine atom are manifested in several ways. To explain the origin of all the observed changes in both the length and the electron charge distribution of the η(2)-SiH bond in investigated Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes a new model, called the Conciliatory Inductive Model, is being proposed.

On the nature of the {SO2-4}/{Ag(111) } and {SO2-4}/{Au(111) } surface bonding

NASA Astrophysics Data System (ADS)

Patrito, E. M.; Olivera, P. Paredes; Sellers, Harrell

1997-05-01

The nature of sulfate-Ag(111) and sulfate-Au(111) surface bonding has been investigated at the SCF + MP2 level of theory. Convergence of binding energy with cluster size is investigated and, unlike neutral adsorbates, large clusters are required in order to obtain reliable binding energies. In the most stable adsorption mode, sulfate binds to the surface via three oxygen atoms (C 3v symmetry) with a binding energy of 159.3 kcal/mol on Ag(111) and 143.9 kcal/mol on Au(111). The geometry of adsorbed sulfate was optimized at the SCF level. While the bond length between sulfur and the oxygens coordinated to the surface increases, the sulfur-uncoordinated oxygen bond length decreases. This weakening and strengthening of the bonds, respectively, is consistent with bond order conservation in adsorbates on metal surfaces. Although a charge transfer of 0.4 electrons towards the metal is observed, the adsorbate remains very much sulfate-like. The molecular orbital analysis indicates that there is also some charge back-donation towards unoccupied orbitals of sulfate. This results in an increased electron density around sulfur as revealed in the electron density difference maps. Analysis of the Laplacian of the charge density of free sulfate provides a suitable framework to understand the nature of the different charge transfer processes and allows us to establish some similarities with the CO- and SO 2-metal bondings.

Synthesis, structure and reactivity of rare-earth metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2.

PubMed

Yang, Jingying; Xie, Zuowei

2015-04-14

Rare-earth metallacarborane alkyls can be stabilized by the incorporation of a functional sidearm into both π and σ ligands. Reaction of [Me3NH][7,8-O(CH2)2-7,8-C2B9H10] with one equiv. of Ln(CH2C6H4-o-NMe2)3 gave metallacarborane alkyls [η(1):η(5)-O(CH2)2C2B9H9]Ln(σ:η(1)-CH2C6H4-o-NMe2)(THF)2 (Ln = Y (), Gd (), Er ()) via alkane elimination. They represent the first examples of rare-earth metallacarborane alkyls. Treatment of with RN[double bond, length as m-dash]C[double bond, length as m-dash]NR (R = Cy, (i)Pr) or 2-benzoylpyridine afforded the corresponding mono-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[η(2)-(RN)2C(CH2C6H4-o-NMe2)](DME) (R = Cy (), (i)Pr ()) or [η(1):η(5)-O(CH2)2C2B9H9]Y[C5H4NC(Ph)(CH2C6H4-o-NMe2)O](THF)2 (), respectively. Complex also reacted with ArNCO or ArNC (Ar = 2,6-diisopropylphenyl, 2,6-dimethylphenyl) to give di-insertion products [η(1):η(5)-O(CH2)2C2B9H9]Y[OC([double bond, length as m-dash]NC6H3Me2)N(C6H3Me2)C(CH2C6H4-o-NMe2)O](THF)2 () or [η(1):η(5)-O(CH2)2C2B9H9]Y[C([double bond, length as m-dash]NC6H3(i)Pr2)C([double bond, length as m-dash]NC6H3(i)Pr2)(CH2C6H4-o-NMe2)](DME) (). These results showed that the reactivity pattern of the Ln-C σ bond in rare-earth metallacarborane alkyls was dependent on the nature of the unsaturated organic molecules. New complexes were characterized by various spectroscopic techniques and elemental analysis. Some were further confirmed by single-crystal X-ray analysis.

Local Bonding Influence on the Band Edge and Band Gap Formation in Quaternary Chalcopyrites.

PubMed

Miglio, Anna; Heinrich, Christophe P; Tremel, Wolfgang; Hautier, Geoffroy; Zeier, Wolfgang G

2017-09-01

Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu 2 ZnGeS 4- x Se x , the anion bond alteration parameter changes, showing larger bond lengths for metal-selenium than for metal-sulfur bonds. The changing bonding interaction directly influences the valence and conduction band edges, which result from antibonding Cu-anion and Ge-anion interactions, respectively. The knowledge of the underlying bonding interactions at the band edges can help design properties of these quaternary chalcopyrites for photovoltaic and thermoelectric applications.

Structure and dynamics of the hydration shells of the Al3+ ion

NASA Astrophysics Data System (ADS)

Bylaska, Eric J.; Valiev, Marat; Rustad, James R.; Weare, John H.

2007-03-01

First principles simulations of the hydration shells surrounding Al3+ ions are reported for temperatures near 300°C. The predicted six water molecules in the octahedral first hydration shell were found to be trigonally coordinated via hydrogen bonds to 12s shell water molecules in agreement with the putative structure used to analyze the x-ray data, but in disagreement with the results reported from conventional molecular dynamics using two-and three-body potentials. Bond lengths and angles of the water molecules in the first and second hydration shells and the average radii of these shells also agreed very well with the results of the x-ray analysis. Water transfers into and out of the second solvation shell were observed to occur on a picosecond time scale via a dissociative mechanism. Beyond the second shell the bonding pattern substantially returned to the tetrahedral structure of bulk water. Most of the simulations were done with 64 solvating water molecules (20ps). Limited simulations with 128 water molecules (7ps) were also carried out. Results agreed as to the general structure of the solvation region and were essentially the same for the first and second shell. However, there were differences in hydrogen bonding and Al-O radial distribution function in the region just beyond the second shell. At the end of the second shell a nearly zero minimum in the Al-O radial distribution was found for the 128 water system. This minimum is less pronounced minimum found for the 64 water system, which may indicate that sizes larger than 64 may be required to reliably predict behavior in this region.

Longer biopsy cores do not increase prostate cancer detection rate: A large-scale cohort study refuting cut-off values indicated in the literature

PubMed Central

Yılmaz, Hasan; Yavuz, Ufuk; Üstüner, Murat; Çiftçi, Seyfettin; Yaşar, Hikmet; Müezzinoğlu, Bahar; Uslubaş, Ali Kemal; Dillioğlugil, Özdal

2017-01-01

Objective Only a few papers in the literature aimed to evaluate biopsy core lengths. Additionally, studies evaluated the core length with different approaches. We aimed to determine whether prostate cancer (PCa) detection is affected from core lengths according to three different approaches in a large standard cohort and compare our cut-off values with the published cut-offs. Material and methods We retrospectively analyzed 1,523 initial consecutive transrectal ultrasound-guided 12-core prostate biopsies. Biopsies were evaluated with respect to total core length (total length of each patients’ core) average core length (total core length divided by total number of cores in each patient), and mean core length (mean length of all cores pooled), and compared our cut-off values with the published cut-offs. The prostate volumes were categorized into four groups (<30, 30–59.99, 60–119.99, ≥120 cm3) and PCa detection rates in these categories were examined. Results PCa was found in 41.5% patients. There was no difference between benign and malignant mean core lengths of the pooled cores (p>0.05). Total core length and average core length were not significantly associated with PCa in multivariate logistic regression analyses (p>0.05). The core lengths (mean, average and total core lengths) increased (p<0.001) and PCa rates decreased (p<0.001) steadily with increasing prostate volume categories. PCa percentages decreased in all categories above the utilized cut-offs for mean (p>0.05), average (p<0.05), and total core lengths (p>0.05). Conclusion There was no difference between mean core lengths of benign and malignant cores. Total core length and average core length were not significantly associated with PCa. Contrary to the cut-offs used for mean and average core lengths in the published studies, PCa rates decrease as these core lengths increase. Larger studies are necessary for the determination and acceptance of accurate cut-offs. PMID:28861301

Driven translocation of Polymer through a nanopore: effect of heterogeneous flexibility

NASA Astrophysics Data System (ADS)

Adhikari, Ramesh; Bhattacharya, Aniket

2014-03-01

We have studied translocation of a model bead-spring polymer through a nanopore whose building blocks consist of alternate stiff and flexible segments and variable elastic bond potentials. For the case of uniform spring potential translocation of a symmetric periodic stiff-flexible chain of contour length N and segment length m (mod(N,2m)=0), we find that the end-to-end distance and the mean first passage time (MFPT) have weak dependence on the length m. The characteristic periodic pattern of the waiting time distribution captures the stiff and flexible segments of the chain with stiff segments taking longer time to translocate. But when we vary both the elastic bond energy, and the bending energy, as well as the length of stiff/flexible segments, we discover novel patterns in the waiting time distribution which brings out structural information of the building blocks of the translocating chain. Partially supported by UCF Office of Research and Commercialization & College of Science SEED grant.

31 CFR 321.12 - Redemption value of securities.

Code of Federal Regulations, 2014 CFR

2014-07-01

... value of each savings security is determined by the terms of its offering and the length of time it has been outstanding. The Bureau of the Fiscal Service determines redemption values for Series A-E bonds, eligible Series EE and I bonds, and savings notes, that should be used in redeeming savings securities. [63...

Effect of Sb content on the physical properties of Ge-Se-Te chalcogenide glasses

NASA Astrophysics Data System (ADS)

Vashist, Priyanka; Anjali, Patial, Balbir Singh; Thakur, Nagesh

2018-05-01

In the present study, the bulk as-(Se80Te20)94-xGe6Sbx (x = 0, 1, 2, 4, 6, 8) glasses were synthesized using melt quenching technique. The physical properties viz coordination number, lone pair of electrons, number of constraints, glass transition temperature, mean bond energy, cohesive energy, electro-negativity and average heat of atomization of the investigated composition are reported and discussed. It is inferred that on increasing Sb content; average coordination number, average number of constraints, mean bond energy, cohesive energy and glass transition temperature increases but lone pair of electrons, average heat of atomization and deviation of stoichiometry decreases.

Efficient Transition State Optimization of Periodic Structures through Automated Relaxed Potential Energy Surface Scans.

PubMed

Plessow, Philipp N

2018-02-13

This work explores how constrained linear combinations of bond lengths can be used to optimize transition states in periodic structures. Scanning of constrained coordinates is a standard approach for molecular codes with localized basis functions, where a full set of internal coordinates is used for optimization. Common plane wave-codes for periodic boundary conditions almost exlusively rely on Cartesian coordinates. An implementation of constrained linear combinations of bond lengths with Cartesian coordinates is described. Along with an optimization of the value of the constrained coordinate toward the transition states, this allows transition optimization within a single calculation. The approach is suitable for transition states that can be well described in terms of broken and formed bonds. In particular, the implementation is shown to be effective and efficient in the optimization of transition states in zeolite-catalyzed reactions, which have high relevance in industrial processes.

Impact of hydrogen bonding on dynamics of hydroxyl-terminated polydimethylsiloxane

DOE PAGES

Xing, Kunyue; Chatterjee, Sabornie; Saito, Tomonori; ...

2016-04-06

Dielectric spectroscopy, rheology, and differential scanning calorimetry were employed to study the effect of chain-end hydrogen bonding on the dynamics of hydroxylterminated polydimethylsiloxane. We demonstrate that hydrogen bonding has a strong influence on both segmental and slower dynamics in the systems with low molecular weights. In particular, the decrease in the chain length leads to an increase of the glass transition temperature, viscosity, and fragility index, at variance with the usual behavior of nonassociating polymers. The supramolecular association of hydroxylterminated chains leads to the emergence in dielectric and mechanical relaxation spectra of the so-called Debye process traditionally observed in monohydroxymore » alcohols. Our analysis suggests that the hydroxyl-terminated PDMS oligomers may associate in brush-like or chain-like structures, depending on the size of their covalent chains. Finally, the effective length of the linear-associated chains was estimated from the rheological measurements.« less

Electronic structure and chemical bonding of the electron-poor II-V semiconductors ZnSb and ZnAs

NASA Astrophysics Data System (ADS)

Benson, Daryn; Sankey, Otto F.; Häussermann, Ulrich

2011-09-01

The binary compounds ZnSb and ZnAs with the CdSb structure are semiconductors (II-V), although the average electron concentration (3.5 per atom) is lower than that of the tetrahedrally bonded III-V and II-VI archetype systems (four per atom). We report a detailed electronic structure and chemical bonding analysis for ZnSb and ZnAs based on first-principles calculations. ZnSb and ZnAs are compared to the zinc blende-type semiconductors GaSb, ZnTe, GaAs, and ZnSe, as well as the more ionic, hypothetical, II-V systems MgSb and MgAs. We establish a clearly covalent bonding scenario for ZnSb and ZnAs where multicenter bonded structural entities (rhomboid rings Zn2Sb2 and Zn2As2) are connected to each other by classical two-center, two-electron bonds. This bonding scenario is only compatible with a weak ionicity in II-V semiconductor systems, and weak ionicity appears as a necessary condition for the stability of the CdSb structure type. It is argued that a chemical bonding scenario with mixed multicenter and two-center bonding resembles that of boron and boron-rich compounds and is typical of electron-poor sp-bonded semiconductors with average valence electron concentrations below four per atom.

Hydrogen bonds in concreto and in computro: the sequel

NASA Astrophysics Data System (ADS)

Stouten, Pieter F. W.; Van Eijck, Bouke P.; Kroon, Jan

1991-02-01

In the framework of our comparative research concerning hydrogen bonding in the crystalline and liquid phases we have carried out molecular dynamics (MD) simulations of liquid methanol. Six different rigid three site models are compared. Five of them had been reported in the literature and one (OM2) we developed by a fit to the experimental molar volume, heat of vaporization and neutron weighted radial distribution function. In general the agreement with experiment is satisfactory for the different models. None of the models has an explicit hydrogen bond potential, but five of the six models show a degree of hydrogen bonding comparable to experiments on liquid methanol. The analysis of the simulation hydrogen bonds indicates that there is a distinct preference of the O⋯O axis to lie in the acceptor lone pairs plane, but hardly any for the lone pair directions. Ab initio calculations and crystal structure statistics of OH⋯O hydrogen bonds agree with this observation. The O⋯O hydrogen bond length distributions are similar for most models. The crystal structures show a sharper O⋯O distribution. Explicit introduction of harmonic motion with a quite realistic root mean square amplitude of 0.08 Å to the thermally averaged crystal distribution results in a distribution comparable to OM2 although the maximum of the former is found at shorter distance. On the basis of the analysis of the static properties of all models we conclude that our OM2, Jorgenson's OPLS and Haughney, Ferrario and McDonald's HFM1 models are good candidates for simulations of liquid methanol under isothermal, isochoric conditions. Partly flexible and completely rigid OM2 are simulated at constant pressure and with fixed volume. The flexible simulations give essentially the same (correct) results under both conditions, which is not surprising because the flexible form was fitted under both conditions. Rigid OM2 has a similar potential energy but larger pressure in the isochoric case and larger energy and far larger volume in the isobaric case. Radial distribution functions and hydrogen bond geometries are very similar for all four cases. Only in the case of the osobaric rigid methanol does the volume expansion seem to be accompanied by a slight preference for tetrahedrality around the oxygen atom.

Formation of {Co(dppe)}2{μ2-η(2):η(2)-η(2):η(2)-[(C60)2]} Dimers Bonded by Single C-C Bonds and Bridging η(2)-Coordinated Cobalt Atoms.

PubMed

Konarev, Dmitri V; Troyanov, Sergey I; Ustimenko, Kseniya A; Nakano, Yoshiaki; Shestakov, Alexander F; Otsuka, Akihiro; Yamochi, Hideki; Saito, Gunzi; Lyubovskaya, Rimma N

2015-05-18

Coordination of two bridging cobalt atoms to fullerenes by the η(2) type in {Co(dppe)}2{μ2-η(2):η(2)-η(2):η(2)-[(C60)2]}·3C6H4Cl2 [1; dppe = 1,2-bis(diphenylphosphino)ethane] triggers fullerene dimerization with the formation of two intercage C-C bonds of 1.571(4) Å length. Coordination-induced fullerene dimerization opens a path to the design of fullerene structures bonded by both covalent C-C bonds and η(2)-coordination-bridged metal atoms.

The effect of elastomer chain length on properties of silicone-modified polyimide adhesives

NASA Technical Reports Server (NTRS)

St.clair, A. K.; St.clair, T. L.; Ezzell, S.

1981-01-01

A series of polyimides containing silicone elastomers was synthesized in order to study the effects of the elastomer chain length on polymer properties. The elastomer with repeat units varying from n=10 to 105 was chemically reacted into the backbone of an addition polyimide oligomer via reactive aromatic amine groups. Glass transition temperatures of the elastomer and polyimide phases were observed by torsional braid analysis. The elastomer-modified polyimides were tested as adhesives for bonding titanium in order to determine their potential for aerospace applications. Adhesive lap shear tests were performed before and after aging bonded specimens at elevated temperatures.

Bio-inspired passive actuator simulating an abalone shell mechanism for structural control

NASA Astrophysics Data System (ADS)

Yang, Henry T. Y.; Lin, Chun-Hung; Bridges, Daniel; Randall, Connor J.; Hansma, Paul K.

2010-10-01

An energy dispersion mechanism called 'sacrificial bonds and hidden length', which is found in some biological systems, such as abalone shells and bones, is the inspiration for new strategies for structural control. Sacrificial bonds and hidden length can substantially increase the stiffness and enhance energy dissipation in the constituent molecules of abalone shells and bone. Having been inspired by the usefulness and effectiveness of such a mechanism, which has evolved over millions of years and countless cycles of evolutions, the authors employ the conceptual underpinnings of this mechanism to develop a bio-inspired passive actuator. This paper presents a fundamental method for optimally designing such bio-inspired passive actuators for structural control. To optimize the bio-inspired passive actuator, a simple method utilizing the force-displacement-velocity (FDV) plots based on LQR control is proposed. A linear regression approach is adopted in this research to find the initial values of the desired parameters for the bio-inspired passive actuator. The illustrative examples, conducted by numerical simulation with experimental validation, suggest that the bio-inspired passive actuator based on sacrificial bonds and hidden length may be comparable in performance to state-of-the-art semi-active actuators.

Study of the physical properties of Ge-S-Ga glassy alloy

NASA Astrophysics Data System (ADS)

Rana, Anjli; Sharma, Raman

2018-05-01

In the present work, we have studied the effect of Ga doping on the physical properties of Ge20S80-xGax glassy alloy. The basic physical parameters which have important role in determining the structure and strength of the material viz. average coordination number, lone-pair electrons, mean bond energy, glass transition temperature, electro negativity, probabilities for bond distribution and cohesive energy have been computed theoretically for Ge-S-Ga glassy alloy. Here, the glass transition temperature and mean bond energy have been investigated using the Tichy-Ticha approach. The cohesive energy has been calculated by using chemical bond approach (CBA) method. It has been found that while average coordination number increases, all the other parameters decrease with the increase in Ga content in Ge-S-Ga system.

The Quest for Greater Chemical Energy Storage II: On the Relationship between Bond Length and Bond Energy

NASA Astrophysics Data System (ADS)

Lindsay, Michael; Buszek, Robert; Boatz, Jerry; Fajardo, Mario

2017-06-01

This is the second in a series of papers aimed at exploring the fundamental limitations to chemical energy storage. In the previous work, we summarized the lessons learned in various high energy density materials (HEDM) programs, the different degrees of freedom in which to store energy in materials, and the fundamental limitations and orders of magnitude of the energies involved.1 That discussion focused almost exclusively on the topic of molar energy density (J/mol) from the perspective of the energy of oxidation of the elements and Fritz Zwicky's ``free atom limit.''2 In this talk, we extend the analysis by considering a different, though equally important, aspect of the energy density calculation: the volumetric density of the energetic material. Specifically, we examine how the distances between individual atoms (i.e. intra- and inter-molecular bond lengths) are coupled to (in fact, approximately inversely proportional to) the energy stored in the bonds of the molecule. This relationship further limits the chemical energy that theoretically can be stored in a material below that predicted by the ``free atom limit.'' This talk will give specific examples of the trends with different bonding motifs and the implications to the fundamental limitations of chemical energy storage.

4-Bromo-N-(di-n-propyl-carbamothioyl)-benzamide.

PubMed

Binzet, Gün; Flörke, Ulrich; Külcü, Nevzat; Arslan, Hakan

2009-02-04

The synthesis of the title compound, C(14)H(19)BrN(2)OS, involves the reaction of 4-bromo-benzoyl chloride with potassium thio-cyanate in acetone followed by condensation of the resulting 4-bromo-benzoyl isothio-cyanate with di-n-propyl-amine. Typical thio-urea carbonyl and thio-carbonyl double bonds, as well as shortened C-N bonds, are observed in the title compound. The short C-N bond lengths in the centre of the mol-ecule reveal the effects of resonance in this part of the mol-ecule. The asymmetric unit of the title compound contains two crystallographically independent mol-ecules, A and B. There is very little difference between the bond lengths and angles of these mol-ecules. In mol-ecule B, one di-n-propyl group is twisted in a -anti-periplanar conformation with C-C-C-H = -179.1 (3)° and the other adopts a -synclinal conformation with C-C-C-H = -56.7 (4)°; in mol-ecule A the two di-n-propyl groups are twisted in + and -anti-periplanar conformations, with C-C-C-H = -179.9 (3) and 178.2 (3)°, respectively. In the crystal, the mol-ecules are linked into dimeric pairs via pairs of N-H⋯S hydrogen bonds.

Theoretical investigations on the structure and properties of p-n-alkoxy benzoic acid based liquid crystals

NASA Astrophysics Data System (ADS)

Subhapriya, P.; Dhanapal, V.; Sadasivam, K.; Vijayanand, P. S.

2016-05-01

The present study focused on the structural conformations, alkoxy chain lengths and mesogenic properties of two mole of alkoxy benzoic acid(nOBA) and one mole of suberic acid (SA) hydrogen bonded (nOBASA) complexes (n=8 to 10) by density functional theory (DFT) calculations and the Fourier Transform Infrared (FT-IR) spectrum. The intermolecular hydrogen bond formation was confirmed by the optimized geometric bond lengths and bond angles obtained by computation. Using the natural bond orbital (NBO) analysis, the stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed. Results obtained shows that the charge in electron density (ED) in σ*and π* antibonding orbital and second order delocalization energies E(2) authorizes the occurrence of intermolecular charge transfer. The molecular electrostatic potential (MEP) surface map is plotted over the optimized geometry of the molecule to obtain the chemical reactivity of the molecule. From the local charge distributions, the mesomorphic behavior and the nematic phase stabilities for each of the molecule have been predicted. Finally the calculated result is applied to simulated infrared spectra of 8OBASA mesogens which shows good agreement with the observed spectra. The comparison of the theoretical results obtained with the experimental ones shows the reliability of this DFT method.

Does time after pair bond disruption affect subsequent reproduction in the socially monogamous woodland vole (Microtus pinetorum)?

PubMed Central

Renfro, Caroline A.; Pesek, Daniel W.; Bobeck, Kelly; Solomon, Nancy G.

2010-01-01

Disruption of the pair bond between socially monogamous animals leads to changes in behavior, which may have reproductive consequences. There are two alternative hypotheses to explain the effect of the length of time since pair bond disruption on subsequent reproduction. One hypothesis predicts that voles housed immediately with a new opposite-sex conspecific will be as likely to produce litters and will produce them as quickly as voles separated from their initial mate for longer. Alternatively, if attachment between mates is enduring, we expect that more voles separated longer from their previous mates will produce litters and produce them sooner than voles re-paired immediately after separation from their initial mates. Woodland voles, paired with opposite-sex conspecifics, remained together until parturition. Mates were then separated for zero, seven, or fourteen days until re-pairing with an opposite-sex conspecific. Pair bond disruption did not prevent males and females from mating subsequently, which was consistent with data from our breeding colony. In addition, the length of time an individual remained alone after pair bond disruption did not affect the latency to produce a litter. Our results show that having been paired previously does not affect subsequent reproduction in this socially monogamous vole. PMID:19429197

Transient sheath overvoltages in armored power cables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gustavsen, B.; Sletbak, J.

1996-07-01

This paper is concerned with methods of limiting the build-up of transient voltages between sheath and armor in long armored power cables. Calculations by a frequency dependent cable model demonstrate that this voltage can be efficiently limited to an acceptable level by introducing sheath-armor bondings at regular intervals, or by using a semiconductive sheath-armor interlayer. The paper investigates the required minimum length between bondings, as well as the required conductivity of the sheath-armor interlayer if the use of bondings is to be avoided.

Stable Chloro- and Bromoxenate Cage Anions; [X3(XeO3)3]3- and [X4(XeO3)4]4- (X = Cl or Br).

PubMed

Goettel, James T; Haensch, Veit G; Schrobilgen, Gary J

2017-06-28

The number of isolable compounds which contain different noble-gas-element bonds is limited for xenon and even more so for krypton. Examples of Xe-Cl bonds are rare, and prior to this work, no Xe-Br bonded compound had been isolated in macroscopic quantities. The syntheses, isolation, and characterization of the first compounds to contain Xe-Br bonds and their chlorine analogues are described in the present work. The reactions of XeO 3 with [N(CH 3 ) 4 ]Br and [N(C 2 H 5 ) 4 ]Br have provided two bromoxenate salts, [N(C 2 H 5 ) 4 ] 3 [Br 3 (XeO 3 ) 3 ] and [N(CH 3 ) 4 ] 4 [Br 4 (XeO 3 ) 4 ], in which the cage anions have Xe-Br bond lengths that range from 3.0838(3) to 3.3181(8) Å. The isostructural chloroxenate anions (Xe-Cl bond lengths, 2.9316(2) to 3.101(4) Å) were synthesized by analogy with their bromine analogues. The bromo- and chloroxenate salts are stable in the atmosphere at room temperature and were characterized in the solid state by Raman spectroscopy and low-temperature single-crystal X-ray diffraction, and in the gas phase by quantum-chemical calculations. They are the only known examples of cage anions that contain a noble-gas element. The Xe-Br and Xe-Cl bonds are very weakly covalent and can be viewed as σ-hole interactions, similar to those encountered in halogen bonding. However, the halogen atoms in these cases are valence electron lone pair donors, and the σ* Xe-O orbitals are lone pair acceptors.

AceDRG: a stereochemical description generator for ligands

PubMed Central

Emsley, Paul; Gražulis, Saulius; Merkys, Andrius; Vaitkus, Antanas

2017-01-01

The program AceDRG is designed for the derivation of stereochemical information about small molecules. It uses local chemical and topological environment-based atom typing to derive and organize bond lengths and angles from a small-molecule database: the Crystallography Open Database (COD). Information about the hybridization states of atoms, whether they belong to small rings (up to seven-membered rings), ring aromaticity and nearest-neighbour information is encoded in the atom types. All atoms from the COD have been classified according to the generated atom types. All bonds and angles have also been classified according to the atom types and, in a certain sense, bond types. Derived data are tabulated in a machine-readable form that is freely available from CCP4. AceDRG can also generate stereochemical information, provided that the basic bonding pattern of a ligand is known. The basic bonding pattern is perceived from one of the computational chemistry file formats, including SMILES, mmCIF, SDF MOL and SYBYL MOL2 files. Using the bonding chemistry, atom types, and bond and angle tables generated from the COD, AceDRG derives the ‘ideal’ bond lengths, angles, plane groups, aromatic rings and chirality information, and writes them to an mmCIF file that can be used by the refinement program REFMAC5 and the model-building program Coot. Other refinement and model-building programs such as PHENIX and BUSTER can also use these files. AceDRG also generates one or more coordinate sets corresponding to the most favourable conformation(s) of a given ligand. AceDRG employs RDKit for chemistry perception and for initial conformation generation, as well as for the interpretation of SMILES strings, SDF MOL and SYBYL MOL2 files. PMID:28177307

Structure determination from XAFS using high-accuracy measurements of x-ray mass attenuation coefficients of silver, 11 keV-28 keV, and development of an all-energies approach to local dynamical analysis of bond length, revealing variation of effective thermal contributions across the XAFS spectrum.

PubMed

Tantau, L J; Chantler, C T; Bourke, J D; Islam, M T; Payne, A T; Rae, N A; Tran, C Q

2015-07-08

We use the x-ray extended range technique (XERT) to experimentally determine the mass attenuation coefficient of silver in the x-ray energy range 11 kev-28 kev including the silver K absorption edge. The results are accurate to better than 0.1%, permitting critical tests of atomic and solid state theory. This is one of the most accurate demonstrations of cross-platform accuracy in synchrotron studies thus far. We derive the mass absorption coefficients and the imaginary component of the form factor over this range. We apply conventional XAFS analytic techniques, extended to include error propagation and uncertainty, yielding bond lengths accurate to approximately 0.24% and thermal Debye-Waller parameters accurate to 30%. We then introduce the FDMX technique for accurate analysis of such data across the full XAFS spectrum, built on full-potential theory, yielding a bond length accuracy of order 0.1% and the demonstration that a single Debye parameter is inadequate and inconsistent across the XAFS range. Two effective Debye-Waller parameters are determined: a high-energy value based on the highly-correlated motion of bonded atoms (σ(DW) = 0.1413(21) Å), and an uncorrelated bulk value (σ(DW) = 0.1766(9) Å) in good agreement with that derived from (room-temperature) crystallography.

Report B : self-consolidating concrete (SCC) for infrastructure elements - bond, transfer length, and development length of prestressing strand in SCC.

DOT National Transportation Integrated Search

2012-08-01

Due to its economic advantages, the use of self-consolidating concrete (SCC) has : increased rapidly in recent years. However, because SCC mixes typically have decreased : amounts of coarse aggregate and high amounts of admixtures, industry members h...

Pressure dependence of effective Coulomb interaction parameters in BaFe2As2 by first-principle calculation

NASA Astrophysics Data System (ADS)

Aghajani, M.; Hadipour, H.; Akhavan, M.

2018-05-01

Pressure dependence of the onsite Coulomb interactions of the BaFe2As2 has been studied by employing the constrained random phase approximation within first-principle calculations. Analyzing total and projected density of states, a pseudogap is found for dxy band at the energy roughly 0.25 eV higher than the Fermi level. Also, by applying pressure the spectral weight of the dxy orbital vanishes while other orbitals remain metallic. The different screening channels, as discussed in four different models, affect significantly on the Hubbard U while the Hund J remains almost unchanged. The average onsite bare and partially and fully screened Coulomb interactions increase with different rates upon compression. These different rates can be explained by competition between the electronic screening and reduction of bond lengths.

A physical basis for remote rock mapping of igneous rocks using spectral variations in thermal infrared emittance

NASA Technical Reports Server (NTRS)

Walter, L. S.; Labovitz, M. L.

1980-01-01

Results of a theoretical investigation of the relation between spectral features in the 8-12 micrometer region and rock type are presented. Data on compositions of a suite of rocks and measurements of their spectral intensities in 8.2-10.9 and 9.4-12.1 micrometer bands published by Vincent (1973) were subjected to various quantitative procedures. There was no consistent direct relationship between rock group names and the relative spectral intensities. However, there is such a relationship between the Thornton-Tuttle (1960) Differentiation Index and the relative spectral intensities. This relationship is explicable on the basis of the change in average Si-O bond length which is a function of the degree of polymerization of the SiO4 tetrahedra of the silicate minerals in the igneous rocks.

Insights into the crystal chemistry of Earth materials rendered by electron density distributions: Pauling's rules revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.

2014-05-20

Pauling's first two rules are examined in terms of the accumulation of the electron density between bonded pairs of atoms for a relatively large number of oxide and silicate crystals and siloxane molecules. The distribution of the electron density shows that the radius of the oxygen atom is not fixed, but that it actually decreases systematically from ~1.40 Å to ~ 0.65 Å as the polarizing power and the electronegativity of the bonded metal atoms increase and the distribution of the O atom is progressively polarized and contracted along the bond vectors by the impact of the bonded interactions. Themore » contractions result in an aspherical oxygen atom that displays as many different bonded “radii” as it has bonded interactions. The bonded radii for the metal atoms match the Shannon and Prewitt ionic radii for the more electropositive atoms like potassium and sodium, but they are systematically larger for the more electronegative atoms like aluminum, silicon and phosphorous. Pauling's first rule is based on the assumption that the radius of the oxide anion is fixed and that the radii of the cations are such that radius sum of the spherical oxide anion and a cation necessarily equals the separation between the cation-anion bonded pair with the coordination number of the cation being determined by the ratio of the radii of the cation and anion. In the case of the bonded radii, the sum of the bonded radii for the metal atoms and the oxide anion necessarily equals the bond lengths by virtue of the way that the bonded radii were determined in the partitioning of the electron density along the bond path into metal and O atom parts. But, the radius ratio for the O and M atoms is an unsatisfactory rule for determining the coordination number of the metal atom inasmuch as a bonded O atom is not, in general, spherical, and its size varies substantially along its bonded directions. But by counting the number of bond paths that radiate from a bonded atom, the coordination number of the atom is determined uniquely independent of the asphericity and sizes of the atom. A power law connection established between the bond lengths and bond strengths for crystals and molecules is mirrored by a comparable power law connection between bond length and the accumulation of the electron density between bonded pairs of atoms, a connection that is consistent with Pauling's electroneutrality postulate that the charges of the atoms in an oxide are negligibly small. The connection indicates that a one-to-one correspondence exists between the accumulation between a pair of bonded atoms and the Pauling bond strength for M-O bonded interaction for all atoms of the periodic table. The connection provides a common basis for understanding the success of the manifold applications that have been made with the bond valence theory model together with the modeling of crystal structures, chemical zoning, leaching and cation transport in batteries and the like. We believe that the wide spread applications of the model in mineralogy and material science owes much of its success to the direct connection between bond strength and the quantum mechanical observable, the electron density distribution. Comparable power law expressions established for the bonded interactions for both crystals and molecules support Pauling's assertion that his second rule has significance for molecules as well as for crystals. A simple expression is found that provides a one to one connection between the accumulation of the electron density between bonded M and O atoms and the Pauling bond strength for all M atoms of the periodic table with ~ 95 % of the variation of the bond strength being explained in terms of a linear dependence on the accumulated electron density. Compelling evidence is presented that supports the argument that the Si-O bonded interactions for tiny siloxane molecules and silicate crystals are chemically equivalent.« less

Nanoindentation methods for wood-adhesive bond lines

Treesearch

Joseph E. Jakes; Donald S. Stone; Charles R. Frihart

2008-01-01

As an adherend, wood is structurally, chemically, and mechanically more complex than metals or plastics, and the largest source of this complexity is wood’s chemical and mechanical inhomogeneities. Understanding and predicting the performance of adhesively bonded wood requires knowledge of the interactions occurring at length scales ranging from the macro down to the...

Crystal structure of (4-cyano­pyridine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ4 N}zinc–4-cyano­pyridine (1/1)

PubMed Central

Nasri, Soumaya; Amiri, Nesrine; Turowska-Tyrk, Ilona; Daran, Jean-Claude; Nasri, Habib

2016-01-01

In the title compound, [Zn(C72H44N4O8)(C6H4N2)]·C6H4N2 or [Zn(TPBP)(4-CNpy]·(4-CNpy) [where TPBP and 4-CNpy are 5,10,15,20-(tetra­phenyl­benzoate)porphyrinate and 4-cyano­pyridine, respectively], the ZnII cation is chelated by four pyrrole-N atoms of the porphyrinate anion and coordinated by a pyridyl-N atom of the 4-CNpy axial ligand in a distorted square-pyramidal geometry. The average Zn—N(pyrrole) bond length is 2.060 (6) Å and the Zn—N(4-CNpy) bond length is 2.159 (2) Å. The zinc cation is displaced by 0.319 (1) Å from the N4C20 mean plane of the porphyrinate anion toward the 4-cyano­pyridine axial ligand. This porphyrinate macrocycle exhibits major saddle and moderate ruffling and doming deformations. In the crystal, the [Zn(TPBP)(4-CNpy)] complex mol­ecules are linked together via weak C—H⋯N, C—H⋯O and C—H⋯π inter­actions, forming supra­molecular channels parallel to the c axis. The non-coordinating 4-cyano­pyridine mol­ecules are located in the channels and linked with the complex mol­ecules, via weak C—H⋯N inter­actions and π-π stacking or via weak C—H⋯O and C—H⋯π inter­actions. The non-coordinating 4-cyano­pyridine mol­ecule is disordered over two positions with an occupancy ratio of 0.666 (4):0.334 (4). PMID:26958379

Induction of strand breaks by low-energy electrons (8-68 eV) in a self-assembled monolayer of oligonucleotides: Effective cross sections and attenuation lengths

NASA Astrophysics Data System (ADS)

Cai, Zhongli; Dextraze, Marie-Eve; Cloutier, Pierre; Hunting, Darel; Sanche, Léon

2006-01-01

Self-assembled monolayers of 5'-P32-labeled 3'-thiolated oligonucleotides chemisorbed on gold were bombarded by low-energy electrons (LEE) of 8-68eV. Shorter 5'-P32-oligonucleotides produced by LEE-induced strand breaks were separated with denaturing polyacrylamide gel electrophoresis and quantified by phosphor imaging. The yields of short oligonucleotides (y) decrease exponentially with their length (n), following the equation y =ae-bn, where a and b are constants, which are related to the average effective cross section per nucleotide for DNA strand break (σeff) and the attenuation length (AL=1/b) of LEE, respectively. The AL decreases with LEE energies from 2.5±0.6nm at 8eVto0.8±0.1nm at 68eV, whereas σeff increases from (3±1)×10-18to(5.1±1.6)×10-17cm2 within the same energy range. The energy dependence of σeff shows a resonance peak of (2.8±0.9)×10-17cm2 at 18eV superimposed on a monotonically rising curve. Transient electron attachment to a σ* anion state of the deoxyribose group, followed by dipolar dissociation into H- and the corresponding positive-ion radical, leading to C-O bond cleavage, is proposed to account for this maximum.

Improving consensus structure by eliminating averaging artifacts

PubMed Central

KC, Dukka B

2009-01-01

Background Common structural biology methods (i.e., NMR and molecular dynamics) often produce ensembles of molecular structures. Consequently, averaging of 3D coordinates of molecular structures (proteins and RNA) is a frequent approach to obtain a consensus structure that is representative of the ensemble. However, when the structures are averaged, artifacts can result in unrealistic local geometries, including unphysical bond lengths and angles. Results Herein, we describe a method to derive representative structures while limiting the number of artifacts. Our approach is based on a Monte Carlo simulation technique that drives a starting structure (an extended or a 'close-by' structure) towards the 'averaged structure' using a harmonic pseudo energy function. To assess the performance of the algorithm, we applied our approach to Cα models of 1364 proteins generated by the TASSER structure prediction algorithm. The average RMSD of the refined model from the native structure for the set becomes worse by a mere 0.08 Å compared to the average RMSD of the averaged structures from the native structure (3.28 Å for refined structures and 3.36 A for the averaged structures). However, the percentage of atoms involved in clashes is greatly reduced (from 63% to 1%); in fact, the majority of the refined proteins had zero clashes. Moreover, a small number (38) of refined structures resulted in lower RMSD to the native protein versus the averaged structure. Finally, compared to PULCHRA [1], our approach produces representative structure of similar RMSD quality, but with much fewer clashes. Conclusion The benchmarking results demonstrate that our approach for removing averaging artifacts can be very beneficial for the structural biology community. Furthermore, the same approach can be applied to almost any problem where averaging of 3D coordinates is performed. Namely, structure averaging is also commonly performed in RNA secondary prediction [2], which could also benefit from our approach. PMID:19267905

Vibrational spectral investigation and natural bond orbital analysis of pharmaceutical compound 7-Amino-2,4-dimethylquinolinium formate - DFT approach.

PubMed

Suresh, D M; Amalanathan, M; Sebastian, S; Sajan, D; Hubert Joe, I; Bena Jothy, V; Nemec, Ivan

2013-11-01

The molecular geometry, the normal mode frequencies and corresponding vibrational assignments, natural bond orbital analysis and the HOMO-LUMO analysis of 7-Amino-2,4-dimethylquinolinium formate in the ground state were performed by B3LYP levels of theory using the 6-31G(d) basis set. The optimised bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of the title compound which is calculated by DFT method, reproduces vibrational wave numbers and intensities with an accuracy which allows reliable vibrational assignments. The possibility of N-H⋯O hydrogen bonding was identified using NBO analysis. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Weak hydrogen bonds in complexes pairing monohalomethanes with neutral formic acid

NASA Astrophysics Data System (ADS)

Solimannejad, Mohammad; Scheiner, Steve

2006-06-01

Ab initio calculations are used to analyze the interaction between formic acid and CH 3X, for X equal to each of F, Cl, and Br. All minima are cyclic in that they contain more than one H-bond. The most strongly bound contain a OH⋯X bond, along with CH⋯O, and the others contain CH⋯X and CH⋯O interactions. Alterations of the covalent bond lengths within each subunit, and vibrational frequency shifts, coupled with electronic charge shifts, reveal fundamental features of these complexes, and the nature of the interactions. The OH⋯X bond is the strongest of those examined here, followed by CH⋯X and CH⋯O.

Average focal length and power of a section of any defined surface.

PubMed

Kaye, Stephen B

2010-04-01

To provide a method to allow calculation of the average focal length and power of a lens through a specified meridian of any defined surface, not limited to the paraxial approximations. University of Liverpool, Liverpool, United Kingdom. Functions were derived to model back-vertex focal length and representative power through a meridian containing any defined surface. Average back-vertex focal length was based on the definition of the average of a function, using the angle of incidence as an independent variable. Univariate functions allowed determination of average focal length and power through a section of any defined or topographically measured surface of a known refractive index. These functions incorporated aberrations confined to the section. The proposed method closely approximates the average focal length, and by inference power, of a section (meridian) of a surface to a single or scalar value. It is not dependent on the paraxial and other nonconstant approximations and includes aberrations confined to that meridian. A generalization of this method to include all orthogonal and oblique meridians is needed before a comparison with measured wavefront values can be made. Copyright (c) 2010 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

TiO(2) doping by hydroxyurea at the nucleation stage: towards a new photocatalyst in the visible spectral range.

PubMed

Azouani, R; Tieng, S; Chhor, K; Bocquet, J-F; Eloy, P; Gaigneaux, E M; Klementiev, K; Kanaev, A V

2010-10-07

We report an original method of preparation of OCN-doped TiO(2) for photocatalysis in the visible spectral range. The preparation is achieved by a sol-gel route using titanium tetraisopropoxide precursor. Special attention was paid to fluid micromixing, which enables homogeneous reaction conditions in the reactor bulk and monodispersity of the produced clusters/nanoparticles. The dopant hydroxyurea (HyU, CH(4)N(2)O(2)) is injected into the reactive fluid at the nucleation stage, which lasts tens of milliseconds. The doping results in a strong yellow coloration of the nanocolloids due to the absorption band in the spectral range 380-550 nm and accelerates the aggregation kinetics of both nuclei at the induction stage and sub-nuclei units (clusters) at the nucleation stage. FTIR, Raman and UV-visible absorption analyses show the formation of a stable HyU-TiO(2) complex. EXAFS spectra indicate no appreciable changes of the first-shell Ti atom environment. The doping agent takes available surface sites of TiO(2) clusters/nanoparticles attaining ∼10% molar loading. The reaction kinetics then accelerates due to a longer collisional lifetime between nanoparticles induced by the formation of a weak [double bond, length as m-dash]OTi bond. The OCN-group bonding to titanium atoms produces a weakening of the C[double bond, length as m-dash]O double bond and a strengthening of the C-N and N-O bonds.

Molecular structures of carotenoids as predicted by MNDO-AM1 molecular orbital calculations

NASA Astrophysics Data System (ADS)

Hashimoto, Hideki; Yoda, Takeshi; Kobayashi, Takayoshi; Young, Andrew J.

2002-02-01

Semi-empirical molecular orbital calculations using AM1 Hamiltonian (MNDO-AM1 method) were performed for a number of biologically important carotenoid molecules, namely all- trans-β-carotene, all- trans-zeaxanthin, and all- trans-violaxanthin (found in higher plants and algae) together with all- trans-canthaxanthin, all- trans-astaxanthin, and all- trans-tunaxanthin in order to predict their stable structures. The molecular structures of all- trans-β-carotene, all- trans-canthaxanthin, and all- trans-astaxanthin predicted based on molecular orbital calculations were compared with those determined by X-ray crystallography. Predicted bond lengths, bond angles, and dihedral angles showed an excellent agreement with those determined experimentally, a fact that validated the present theoretical calculations. Comparison of the bond lengths, bond angles and dihedral angles of the most stable conformer among all the carotenoid molecules showed that the displacements are localized around the substituent groups and hence around the cyclohexene rings. The most stable conformers of all- trans-zeaxanthin and all- trans-violaxanthin gave rise to a torsion angle around the C6-C7 bond to be ±48.7 and -84.8°, respectively. This difference is a key factor in relation to the biological function of these two carotenoids in plants and algae (the xanthophyll cycle). Further analyses by calculating the atomic charges and using enpartment calculations (division of bond energies between component atoms) were performed to ascribe the cause of the different observed torsion angles.

Morphology of the Dentin-resin Interface yielded by Two-step Etch-and-rinse Adhesives with Different Solvents.

PubMed

Ferreira, João C; Pires, Patrícia T; de Azevedo, Álvaro F; Arantes-Oliveira, Sofia; Silva, Mário J; de Melo, Paulo R

2017-10-01

The study aimed to analyze the morphology of the dentin-resin interface yielded by two-step etch-and-rinse adhesive systems with different solvents and compositions. A total of 32 dentine disks were prepared and randomly assigned to four groups of one-bottle etch-and-rinse adhesive systems containing different solvents: group I, Adper Scotchbond-IXT™ (ethanol/water); group II, XP-Bond™ (tertiary butanol); group III, Prime and Bond NT ® (acetone); and group IV, One Coat bond® (5% water). Adhesive systems were applied onto dentin disks, which were then thermal cycled, divided into two hemi-disks (n = 16), and prepared for field-emission scanning electron microscopy to examine the dentin-resin interdiffusion zone. Microphotographs were scanned and data were processed. Data were compared with analysis of variance multivariant test after Kolmogorov-Smirnov and Shapiro-Wilk tests using Statistic Package for the Social Sciences. The adhesive layer thickness average found was group I: 45.9 ± 13.41 urn, group II: 20.6 ± 16.32 urn, group III: 17.7 ± 11.75 urn, and group IV: 50.7 ± 27.81 urn. Significant differences were found between groups I and IV and groups II and III (p < 0.000). Groups I (3.23 ± 0.53 μm) and II (3.13 ± 0.73 μm) yielded significantly thicker hybrid layers than groups III (2.53 ± 0.50 μm) and IV (1.84 ± 0.27 μm) (p < 0.003). Group III presented a less homogeneous hybrid layer, with some gaps. Tag length average was greater in groups II (111.0 ± 36.92 μm) and IV (128.9 ± 78.38 μm) than in groups I (61.5 ± 18.10 μm) and III (68.6 ± 15.84 μm) (p < 0.008). Adhesives systems with different solvents led to significant differences in the dentin-resin interface morphology. Solvents role in adhesives bond strength should be considered together with the other adhesive system components. The adhesive containing tertiary butanol, in addition, seems to originate a good-quality hybrid layer and long, entangled tags and also appears to have greater ability to originate microtags, which may indicate higher bond strength.

Structure and elasticity of serpentine at high-pressure

NASA Astrophysics Data System (ADS)

Mookherjee, Mainak; Stixrude, Lars

2009-03-01

Serpentines occur in the subduction zone settings, both along the slab and within the mantle wedge, they are candidates for transporting water in to the deep earth. Their presence is manifested by serpentine mud volcanoes, high electrical conductivities, magnetic and seismic anomalies. Using theoretical methods, we predict a pressure induced structural transformations in serpentine. The transformations are related to the behavior of the silicate framework and misfit between octahedral and tetrahedral layers. As the structure is compressed, the octahedral layer and tetrahedral layers are compressed at different rates. At 7 GPa, the misfit between the layers vanishes. This causes non-linear pressure dependence of tetrahedral rotational angle. This is also manifested by the onset of anomalous pressure dependence of the elastic constants c11, c33, c12, c13. Beyond 7 GPa, the misfit between the layers grows again reaching extremum at 22 GPa. This is also manifested by discontinuity in average Si-O bond length, volume of tetrahedron and re-orientation of hydroxyl vector. The symmetry of the crystal-structure however, remains unaffected. Evidence of pressure-induced hydrogen bonding is absent in serpentine, as evident from reduction of O-H bond length upon compression. Results of compression for the low-pressure regime ( P < 7 GPa) is well represented by a fourth order Birch-Murnaghan finite strain expression with K0 = 79 GPa, K0' = 12 and K0″ = - 2, where K is the bulk modulus, prime indicates pressure derivatives, and O refers to zero pressure. Our best estimates of K0, K0' and the Grüneisen parameter, γ at 300 K and zero pressure based on our results are: 61 GPa, 17, and 0.77, respectively. At low pressures, serpentine structure is anisotropic with c11 ~ 2.4 × c33. The pressure derivative of elastic constants ( ∂cij/ ∂P) are such, that around 22 GPa c11~ c33. An elastic instability ( c66 < 0) at somewhat higher pressures (> 50 GPa) is also noted. The elastic constant tensor reveals large acoustic anisotropy (41% in VP) and seismic wave velocities that are significantly higher than those inferred from experiments on serpentinites.

Modeling single molecule junction mechanics as a probe of interface bonding

NASA Astrophysics Data System (ADS)

Hybertsen, Mark S.

2017-03-01

Using the atomic force microscope based break junction approach, applicable to metal point contacts and single molecule junctions, measurements can be repeated thousands of times resulting in rich data sets characterizing the properties of an ensemble of nanoscale junction structures. This paper focuses on the relationship between the measured force extension characteristics including bond rupture and the properties of the interface bonds in the junction. A set of exemplary model junction structures has been analyzed using density functional theory based calculations to simulate the adiabatic potential surface that governs the junction elongation. The junction structures include representative molecules that bond to the electrodes through amine, methylsulfide, and pyridine links. The force extension characteristics are shown to be most effectively analyzed in a scaled form with maximum sustainable force and the distance between the force zero and force maximum as scale factors. Widely used, two parameter models for chemical bond potential energy versus bond length are found to be nearly identical in scaled form. Furthermore, they fit well to the present calculations of N-Au and S-Au donor-acceptor bonds, provided no other degrees of freedom are allowed to relax. Examination of the reduced problem of a single interface, but including relaxation of atoms proximal to the interface bond, shows that a single-bond potential form renormalized by an effective harmonic potential in series fits well to the calculated results. This allows relatively accurate extraction of the interface bond energy. Analysis of full junction models shows cooperative effects that go beyond the mechanical series inclusion of the second bond in the junction, the spectator bond that does not rupture. Calculations for a series of diaminoalkanes as a function of molecule length indicate that the most important cooperative effect is due to the interactions between the dipoles induced by the donor-acceptor bond formation at the junction interfaces. The force extension characteristic of longer molecules such as diaminooctane, where the dipole interaction effects drop to a negligible level, accurately fit to the renormalized single-bond potential form. The results suggest that measured force extension characteristics for single molecule junctions could be analyzed with a modified potential form that accounts for the energy stored in deformable mechanical components in series.

Modeling single molecule junction mechanics as a probe of interface bonding

DOE PAGES

Hybertsen, Mark S.

2017-03-07

Using the atomic force microscope based break junction approach, applicable to metal point contacts and single molecule junctions, measurements can be repeated thousands of times resulting in rich data sets characterizing the properties of an ensemble of nanoscale junction structures. This paper focuses on the relationship between the measured force extension characteristics including bond rupture and the properties of the interface bonds in the junction. We analyzed a set of exemplary model junction structures using density functional theory based calculations to simulate the adiabatic potential surface that governs the junction elongation. The junction structures include representative molecules that bond tomore » the electrodes through amine, methylsulfide, and pyridine links. The force extension characteristics are shown to be most effectively analyzed in a scaled form with maximum sustainable force and the distance between the force zero and force maximum as scale factors. Widely used, two parameter models for chemical bond potential energy versus bond length are found to be nearly identical in scaled form. Furthermore, they fit well to the present calculations of N–Au and S–Au donor-acceptor bonds, provided no other degrees of freedom are allowed to relax. Examination of the reduced problem of a single interface, but including relaxation of atoms proximal to the interface bond, shows that a single-bond potential form renormalized by an effective harmonic potential in series fits well to the calculated results. This, then, allows relatively accurate extraction of the interface bond energy. Analysis of full junction models shows cooperative effects that go beyond the mechanical series inclusion of the second bond in the junction, the spectator bond that does not rupture. Calculations for a series of diaminoalkanes as a function of molecule length indicate that the most important cooperative effect is due to the interactions between the dipoles induced by the donor-acceptor bond formation at the junction interfaces. The force extension characteristic of longer molecules such as diaminooctane, where the dipole interaction effects drop to a negligible level, accurately fit to the renormalized single-bond potential form. Our results suggest that measured force extension characteristics for single molecule junctions could be analyzed with a modified potential form that accounts for the energy stored in deformable mechanical components in series.« less

Modeling single molecule junction mechanics as a probe of interface bonding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hybertsen, Mark S.

Using the atomic force microscope based break junction approach, applicable to metal point contacts and single molecule junctions, measurements can be repeated thousands of times resulting in rich data sets characterizing the properties of an ensemble of nanoscale junction structures. This paper focuses on the relationship between the measured force extension characteristics including bond rupture and the properties of the interface bonds in the junction. We analyzed a set of exemplary model junction structures using density functional theory based calculations to simulate the adiabatic potential surface that governs the junction elongation. The junction structures include representative molecules that bond tomore » the electrodes through amine, methylsulfide, and pyridine links. The force extension characteristics are shown to be most effectively analyzed in a scaled form with maximum sustainable force and the distance between the force zero and force maximum as scale factors. Widely used, two parameter models for chemical bond potential energy versus bond length are found to be nearly identical in scaled form. Furthermore, they fit well to the present calculations of N–Au and S–Au donor-acceptor bonds, provided no other degrees of freedom are allowed to relax. Examination of the reduced problem of a single interface, but including relaxation of atoms proximal to the interface bond, shows that a single-bond potential form renormalized by an effective harmonic potential in series fits well to the calculated results. This, then, allows relatively accurate extraction of the interface bond energy. Analysis of full junction models shows cooperative effects that go beyond the mechanical series inclusion of the second bond in the junction, the spectator bond that does not rupture. Calculations for a series of diaminoalkanes as a function of molecule length indicate that the most important cooperative effect is due to the interactions between the dipoles induced by the donor-acceptor bond formation at the junction interfaces. The force extension characteristic of longer molecules such as diaminooctane, where the dipole interaction effects drop to a negligible level, accurately fit to the renormalized single-bond potential form. Our results suggest that measured force extension characteristics for single molecule junctions could be analyzed with a modified potential form that accounts for the energy stored in deformable mechanical components in series.« less

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

PubMed

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 determined by the competition between the frozen-energy term and the sum of polarization and charge transfer energy terms. Because the frozen energy is composed of electrostatic and Pauli exchange interactions and frequency shifting is a long-range phenomenon, we conclude that long-range electrostatic interaction is the driving force behind the frozen energy term.

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

USDA-ARS?s Scientific Manuscript database

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 ...

Nonmetallic electronegativity equalization and point-dipole interaction model including exchange interactions for molecular dipole moments and polarizabilities.

PubMed

Smalø, Hans S; Astrand, Per-Olof; Jensen, Lasse

2009-07-28

The electronegativity equalization model (EEM) has been combined with a point-dipole interaction model to obtain a molecular mechanics model consisting of atomic charges, atomic dipole moments, and two-atom relay tensors to describe molecular dipole moments and molecular dipole-dipole polarizabilities. The EEM has been phrased as an atom-atom charge-transfer model allowing for a modification of the charge-transfer terms to avoid that the polarizability approaches infinity for two particles at infinite distance and for long chains. In the present work, these shortcomings have been resolved by adding an energy term for transporting charges through individual atoms. A Gaussian distribution is adopted for the atomic charge distributions, resulting in a damping of the electrostatic interactions at short distances. Assuming that an interatomic exchange term may be described as the overlap between two electronic charge distributions, the EEM has also been extended by a short-range exchange term. The result is a molecular mechanics model where the difference of charge transfer in insulating and metallic systems is modeled regarding the difference in bond length between different types of system. For example, the model is capable of modeling charge transfer in both alkanes and alkenes with alternating double bonds with the same set of carbon parameters only relying on the difference in bond length between carbon sigma- and pi-bonds. Analytical results have been obtained for the polarizability of a long linear chain. These results show that the model is capable of describing the polarizability scaling both linearly and nonlinearly with the size of the system. Similarly, a linear chain with an end atom with a high electronegativity has been analyzed analytically. The dipole moment of this model system can either be independent of the length or increase linearly with the length of the chain. In addition, the model has been parametrized for alkane and alkene chains with data from density functional theory calculations, where the polarizability behaves differently with the chain length. For the molecular dipole moment, the same two systems have been studied with an aldehyde end group. Both the molecular polarizability and the dipole moment are well described as a function of the chain length for both alkane and alkene chains demonstrating the power of the presented model.

Double bonds? Studies on the barrier to rotation about the cumulenic C=C bonds of tetraaryl[n]cumulenes (n = 3, 5, 7, 9).

PubMed

Buehringer, Martina U; Padberg, Kevin; Phleps, Martin; Maid, Harald; Placht, Christian; Neiss, Christian; Ferguson, Michael; Goerling, Andreas; Tykwinski, Rik R

2018-03-31

Bonding is the fundamental aspect of organic chemistry, yet the magnitude of C=C bonding in [n]cumulenes as a function of increasing chain length has yet to be experimentally verified for derivatives longer than n = 5. The synthesis of a series of apolar and unsymmetrically substituted tetraaryl[n]cumulenes (n = 3, 5, 7, 9) has been developed and rotational barriers for Z-/E-isomerization have been measured using dynamic VT-NMR spectroscopy. Both experiment and theory confirm a dramatic reduction of the rotational barrier (through estimation of G≠rot for the isomerization) from >24 to 19 to 15 to 11 kcal-1 in [n]cumulenes with n = 3, 5, 7, 9, respectively. Thus, the reduction of cumulenic bonding in longer cumulenes affords bond rotational barriers that are more characteristic of a sterically hindered single bond than that of a double bond. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of ligand electronegativity on recoupled pair bonds with application to sulfurane precursors.

PubMed

Lindquist, Beth A; Woon, David E; Dunning, Thom H

2014-07-31

Recoupled pair bonds (RPBs) are conditional bonds-they only form for selected central atoms and ligands. A complete theoretical description of RPBs requires an understanding of the properties of the central atom and ligands that enable such bonds to be formed. In this work, we show that ligand electronegativity is positively correlated with recoupled pair bond strength for a variety of ligands interacting with the 3p(2) pair of sulfur. We also describe substituent (X) effects on the SF(a(4)Σ(-)) state by investigating X2SF species. These effects generally mirror those observed for covalently bound analogues, but we found that recoupled pair bonding can lead to breakdowns in the expected relationships among bond length, strength, and force constant for some of these species. Finally, we compare the properties of two molecules of practical interest that are bound by recoupled pair bonds: the dimethyl sulfur fluoride and hydroxide radicals (DMS-F and DMS-OH).

Kinetics of the Multistep Rupture of Fibrin ‘A-a’ Polymerization Interactions Measured Using Atomic Force Microscopy

PubMed Central

Averett, Laurel E.; Schoenfisch, Mark H.; Akhremitchev, Boris B.; Gorkun, Oleg V.

2009-01-01

Abstract Fibrin, the structural scaffold of blood clots, spontaneously polymerizes through the formation of ‘A-a’ knob-hole bonds. When subjected to external force, the dissociation of this bond is accompanied by two to four abrupt changes in molecular dimension observable as rupture events in a force curve. Herein, the configuration, molecular extension, and kinetic parameters of each rupture event are examined. The increases in contour length indicate that the D region of fibrinogen can lengthen by ∼50% of the length of a fibrin monomer before rupture of the ‘A-a’ interaction. The dependence of the dissociation rate on applied force was obtained using probability distributions of rupture forces collected at different pull-off velocities. These distributions were fit using a model in which the effects of the shape of the binding potential are used to quantify the kinetic parameters of forced dissociation. We found that the weak initial rupture (i.e., event 1) was not well approximated by these models. The ruptured bonds comprising the strongest ruptures, events 2 and 3, had kinetic parameters similar to those commonly found for the mechanical unfolding of globular proteins. The bonds ruptured in event 4 were well described by these analyses, but were more loosely bound than the bonds in events 2 and 3. We propose that the first event represents the rupture of an unknown interaction parallel to the ‘A-a’ bond, events 2 and 3 represent unfolding of structures in the D region of fibrinogen, and event 4 is the rupture of the ‘A-a’ knob-hole bond weakened by prior structural unfolding. Comparison of the activation energy obtained via force spectroscopy measurements with the thermodynamic free energy of ‘A-a’ bond dissociation indicates that the ‘A-a’ bond may be more resistant to rupture by applied force than to rupture by thermal dissociation. PMID:19917237

Validating a Mentoring Relationship Quality Scale: Does Match Strength Predict Match Length?

ERIC Educational Resources Information Center

Rhodes, Jean E.; Schwartz, Sarah E. O.; Willis, Margaret M.; Wu, Max B.

2017-01-01

Youth mentoring relationships have significant potential for promoting positive youth development. Nonetheless, the benefits derived from such relationships depend considerably on the length and quality of the bonds that are created between mentors and youth. Although some attention has been paid to youth's experience of relationship quality, few…

A DFT-D Study on Structural, Electronic, Thermodynamic, and Mechanical Properties of HMX/MPNO Cocrystal under High Pressure

NASA Astrophysics Data System (ADS)

Lin, He; Chen, Jian-Fu; Cui, Yu-Ming; Zhang, Zhen-Jiang; Yang, Dong-Dong; Zhu, Shun-Guan; Li, Hong-Zhen

2017-04-01

An investigation on the structural, electronic, thermodynamic, and mechanical properties of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)/2-methylpyridine-N-oxide (MPNO) cocrystal was carried out from 0 to 100 GPa by using a dispersion-corrected density functional theory (DFT-D) method. Our calculated crystal structure is in excellent agreement with experimental results at ambient pressure. Based on the analysis of lattice parameters, lattice angles, bond lengths, bond angles, and dihedral angles under high pressure, we observe that HMX molecules in the cocrystal bulk are seriously distorted but MPNO molecules remain relatively unchanged. Hydrogen bond lengths are greatly shortened under high pressure. In addition, with the increase in pressure, the bandgap decreases gradually. However, it increases suddenly at 70 GPa. Some important hydrogen bonds between HMX and MPNO are also observed in the density of states spectrum. According to the thermodynamic analysis, this cocrystal is more easily prepared under low pressure. Finally, we characterized its mechanical properties and the results show that this cocrystal is malleable in nature. We expect that this research can provide a fundamental basis for further HMX cocrystal design and preparation.

Molecular structure, vibrational spectra, NBO analysis and molecular packing prediction of 3-nitroacetanilide by ab initio HF and density functional theory.

PubMed

Li, Xiao-Hong; Li, Tong-Wei; Ju, Wei-Wei; Yong, Yong-Liang; Zhang, Xian-Zhou

2014-01-24

Quantum chemical calculations of geometries and vibrational wavenumbers of 3-nitroacetanilide (C8H8N2O3) in the ground state were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6-31+G(*) basis set. The -311++G(**) basis set is also used for B3LYP level. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energies distributions (PEDs) using MOLVIB program. The theoretical spectrograms for IR spectra of the title compound have been constructed. The shortening of C-H bond length and the elongation of N-H bond length suggest the existence of weak C-H⋯O and N-H⋯O hydrogen bonds, which is confirmed by the natural bond orbital analysis. In addition, the crystal structure obtained by molecular mechanics belongs to the P2(1) space group, with lattice parameters Z=4, a=14.9989 Å, b=4.0367 Å, c=12.9913 Å, ρ=0.998 g cm(-3). Copyright © 2013 Elsevier B.V. All rights reserved.

Molecular structure, vibrational spectra, NBO analysis and molecular packing prediction of 3-nitroacetanilide by ab initio HF and density functional theory

NASA Astrophysics Data System (ADS)

Li, Xiao-Hong; Li, Tong-Wei; Ju, Wei-Wei; Yong, Yong-Liang; Zhang, Xian-Zhou

2014-01-01

Quantum chemical calculations of geometries and vibrational wavenumbers of 3-nitroacetanilide (C8H8N2O3) in the ground state were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6-31+G* basis set. The -311++G** basis set is also used for B3LYP level. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energies distributions (PEDs) using MOLVIB program. The theoretical spectrograms for IR spectra of the title compound have been constructed. The shortening of Csbnd H bond length and the elongation of Nsbnd H bond length suggest the existence of weak Csbnd H⋯O and Nsbnd H⋯O hydrogen bonds, which is confirmed by the natural bond orbital analysis. In addition, the crystal structure obtained by molecular mechanics belongs to the P21 space group, with lattice parameters Z = 4, a = 14.9989 Å, b = 4.0367 Å, c = 12.9913 Å, ρ = 0.998 g cm-3.

Persistent homology analysis of ion aggregations and hydrogen-bonding networks.

PubMed

Xia, Kelin

2018-05-16

Despite the great advancement of experimental tools and theoretical models, a quantitative characterization of the microscopic structures of ion aggregates and their associated water hydrogen-bonding networks still remains a challenging problem. In this paper, a newly-invented mathematical method called persistent homology is introduced, for the first time, to quantitatively analyze the intrinsic topological properties of ion aggregation systems and hydrogen-bonding networks. The two most distinguishable properties of persistent homology analysis of assembly systems are as follows. First, it does not require a predefined bond length to construct the ion or hydrogen-bonding network. Persistent homology results are determined by the morphological structure of the data only. Second, it can directly measure the size of circles or holes in ion aggregates and hydrogen-bonding networks. To validate our model, we consider two well-studied systems, i.e., NaCl and KSCN solutions, generated from molecular dynamics simulations. They are believed to represent two morphological types of aggregation, i.e., local clusters and extended ion networks. It has been found that the two aggregation types have distinguishable topological features and can be characterized by our topological model very well. Further, we construct two types of networks, i.e., O-networks and H2O-networks, for analyzing the topological properties of hydrogen-bonding networks. It is found that for both models, KSCN systems demonstrate much more dramatic variations in their local circle structures with a concentration increase. A consistent increase of large-sized local circle structures is observed and the sizes of these circles become more and more diverse. In contrast, NaCl systems show no obvious increase of large-sized circles. Instead a consistent decline of the average size of the circle structures is observed and the sizes of these circles become more and more uniform with a concentration increase. As far as we know, these unique intrinsic topological features in ion aggregation systems have never been pointed out before. More importantly, our models can be directly used to quantitatively analyze the intrinsic topological invariants, including circles, loops, holes, and cavities, of any network-like structures, such as nanomaterials, colloidal systems, biomolecular assemblies, among others. These topological invariants cannot be described by traditional graph and network models.

Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen

PubMed Central

Gagné, Olivier Charles; Hawthorne, Frank Christopher

2015-01-01

Published two-body bond-valence parameters for cation–oxygen bonds have been evaluated via the root mean-square deviation (RMSD) from the valence-sum rule for 128 cations, using 180 194 filtered bond lengths from 31 489 coordination polyhedra. Values of the RMSD range from 0.033–2.451 v.u. (1.1–40.9% per unit of charge) with a weighted mean of 0.174 v.u. (7.34% per unit of charge). The set of best published parameters has been determined for 128 ions and used as a benchmark for the determination of new bond-valence parameters in this paper. Two common methods for the derivation of bond-valence parameters have been evaluated: (1) fixing B and solving for R o; (2) the graphical method. On a subset of 90 ions observed in more than one coordination, fixing B at 0.37 Å leads to a mean weighted-RMSD of 0.139 v.u. (6.7% per unit of charge), while graphical derivation gives 0.161 v.u. (8.0% per unit of charge). The advantages and disadvantages of these (and other) methods of derivation have been considered, leading to the conclusion that current methods of derivation of bond-valence parameters are not satisfactory. A new method of derivation is introduced, the GRG (generalized reduced gradient) method, which leads to a mean weighted-RMSD of 0.128 v.u. (6.1% per unit of charge) over the same sample of 90 multiple-coordination ions. The evaluation of 19 two-parameter equations and 7 three-parameter equations to model the bond-valence–bond-length relation indicates that: (1) many equations can adequately describe the relation; (2) a plateau has been reached in the fit for two-parameter equations; (3) the equation of Brown & Altermatt (1985 ▸) is sufficiently good that use of any of the other equations tested is not warranted. Improved bond-valence parameters have been derived for 135 ions for the equation of Brown & Altermatt (1985 ▸) in terms of both the cation and anion bond-valence sums using the GRG method and our complete data set. PMID:26428406

Psychodynamic group psychotherapy: impact of group length and therapist professional characteristics on development of therapeutic alliance.

PubMed

Lorentzen, Steinar; Bakali, Jan Vegard; Hersoug, Anne Grete; Hagtvet, Knut A; Ruud, Torleif; Høglend, Per

2012-09-01

Little research has been done on therapeutic alliance in group psychotherapy, especially the impact of treatment duration and therapist professional characteristics. Therapeutic alliance was rated by patients on the Working Alliance Inventory-Short Form at three time points (sessions 3, 10 and 17) in a randomized controlled trial of short-term and long-term psychodynamic group psychotherapy. As predictors we selected therapist clinical experience and length of didactic training, which have demonstrated ambiguous results in previous research. Linear latent variable growth curve models (structural equation modeling) were developed for the three Working Alliance Inventory-Short Form subscales bond, task and goal. We found a significant variance in individual growth curves (intercepts and slopes) but no differential development due to group length. Longer therapist formal training had a negative impact on early values of subscale task in both treatments. There was an interaction between length of the therapists' clinical experience and group length on early bond, task and goal: therapists with longer clinical experience were rated lower on initial bond in the long-term group but less so in the short-term group. Longer clinical experience influenced initial task and goal positively in the short-term group but was unimportant for task or significantly negative for goal in the long-term group. There was no mean development of alliance, and group length did not differentially impact the alliance during 6 months. Early ratings of the three Working Alliance Inventory-Short Form subscales partly reflected different preparations of patients in the two group formats, partly therapist characteristics, but more research is needed to see how these aspects impact alliance development and outcome. Therapists should pay attention to all three aspects of the alliance, when they prepare patients for group therapy. In psychodynamic groups, length of therapy does not differentiate the overall level or the development of member-leader alliance. Within psychodynamic groups, each individual appear to have their unique perception of the member-leader alliance. Therapists with longer formal psychotherapy training may be less successful in establishing early agreement with patients on the tasks of psychodynamic group psychotherapy. Patients perceive a somewhat lower degree of early emotional bonding with the more clinically experienced therapists in long-term psychodynamics groups. Therapists with more clinical experience may contribute to a stronger degree of initial agreement with patients on the tasks and goals of short-term group psychotherapy. Copyright © 2011 John Wiley & Sons, Ltd.

Blood lead: Its effect on trace element levels and iron structure in hemoglobin

NASA Astrophysics Data System (ADS)

Jin, C.; Li, Y.; Li, Y. L.; Zou, Y.; Zhang, G. L.; Normura, M.; Zhu, G. Y.

2008-08-01

Lead is a ubiquitous environmental pollutant that induce a broad range of physiological and biochemical dysfunctions. The purpose of this study was to investigate its effects on trace elements and the iron structure in hemoglobin. Blood samples were collected from rats that had been exposed to lead. The concentration of trace elements in whole blood and blood plasma was determined by ICP-MS and the results indicate that lead exists mainly in the red blood cells and only about 1-3% in the blood plasma. Following lead exposure, the concentrations of zinc and iron in blood decrease, as does the hemoglobin level. This indicates that the heme biosynthetic pathway is inhibited by lead toxicity and that lead poisoning-associated anemia occurs. The selenium concentration also decreases after lead exposure, which may lead to an increased rate of free radical production. The effect of lead in the blood on iron structure in hemoglobin was determined by EXAFS. After lead exposure, the Fe-O bond length increases by about 0.07 Å and the Fe-Np bond length slightly increases, but the Fe-N ɛ bond length remains unchanged. This indicates that the blood content of Hb increases, but that the content of HbO 2 decreases.

Infrared study of matrix-isolated ethyl cyanide: simulation of the photochemistry in the atmosphere of Titan.

PubMed

Toumi, A; Piétri, N; Couturier-Tamburelli, I

2015-11-11

Low-temperature Ar matrix isolation has been carried out to investigate the infrared spectrum of ethyl cyanide (CH3CH2CN), a molecule present in the atmosphere of Titan. The λ > 120 nm and λ > 230 nm photolysis reactions of ethyl cyanide in an Ar matrix were also performed in order to compare the behaviour of this compound when it is submitted to high and low energetic radiations. These different wavelengths have been used with the aim to reproduce the radiation reaching the various parts of the atmosphere. Several photoproducts have been identified during photolysis such as vinyl cyanide (CH2[double bond, length as m-dash]CHCN), cyanoacetylene (HC3N), and ethylene/hydrogen cyanide (C2H4/HCN), ethylene/hydrogen isocyanide (C2H4/HNC), acetylene/hydrogen cyanide (C2H2/HCN), acetylene/hydrogen isocyanide (C2H2/HNC), and acetylene:methylenimine (C2H2:HNCH2) complexes. Ethyl isocyanide (CH3CH2NC) and a ketenimine form (CH3CH[double bond, length as m-dash]C[double bond, length as m-dash]NH) have been identified as well. Photoproduct identification and spectral assignments were done using previous studies and density functional theory (DFT) calculations with the B3LYP/cc-pVTZ basis set.

The atomic geometries of GaP(110) and ZnS(110) revisited - A structural ambiguity and its resolution

NASA Technical Reports Server (NTRS)

Duke, C. B.; Paton, A.; Kahn, A.

1984-01-01

The atomic geometries of GaP(110) and ZnS(110) are reexamined using the R-factor minimization procedure, developed for GaAs(110) and previously applied to GaSb(110), ZnTe(110), InAs(110), and AlP(110), to analyze experimental elastic low-energy electron diffraction intensities. Unlike most of the earlier cases, both GaP(110) and ZnS(110) exhibit two distinct minimum-Rx structures which cannot be distinguished by analysis of the shapes of the intensity profiles alone. One region of best-fit structures exhibits top-layer displacements normal to the surface characterized by a small bond-length-conserving, top-layer rotation (omega aproximately 2-3 deg), a small relaxation of the top layer away from the surface, and a 10 percent expansion of the top-layer bond length. The other region of best-fit structures is the conventional one: nearly bond-length-conserving rotations of omega = 26-28 deg in the top layer and a small (approximately 0.1 A) contraction of the uppermost layer spacing. This ambiguity may be removed, however, by consideration of the integrated beam intensities. The conventional region of structural parameters provides a decisively better description of the relative magnitudes of the integrated beam intensities and hence is the preferred structure.

Both the stroma and thylakoid lumen of tobacco chloroplasts are competent for the formation of disulphide bonds in recombinant proteins.

PubMed

Bally, Julia; Paget, Eric; Droux, Michel; Job, Claudette; Job, Dominique; Dubald, Manuel

2008-01-01

Plant chloroplasts are promising vehicles for recombinant protein production, but the process of protein folding in these organelles is not well understood in comparison with that in prokaryotic systems, such as Escherichia coli. This is particularly true for disulphide bond formation which is crucial for the biological activity of many therapeutic proteins. We have investigated the capacity of tobacco (Nicotiana tabacum) chloroplasts to efficiently form disulphide bonds in proteins by expressing in this plant cell organelle a well-known bacterial enzyme, alkaline phosphatase, whose activity and stability strictly depend on the correct formation of two intramolecular disulphide bonds. Plastid transformants have been generated that express either the mature enzyme, localized in the stroma, or the full-length coding region, including its signal peptide. The latter has the potential to direct the recombinant alkaline phosphatase into the lumen of thylakoids, giving access to this even less well-characterized organellar compartment. We show that the chloroplast stroma supports the formation of an active enzyme, unlike a normal bacterial cytosol. Sorting of alkaline phosphatase to the thylakoid lumen occurs in the plastid transformants translating the full-length coding region, and leads to larger amounts and more active enzyme. These results are compared with those obtained in bacteria. The implications of these findings on protein folding properties and competency of chloroplasts for disulphide bond formation are discussed.

A computational study of hydrogen-bonded X3CH⋯YZ (X = Cl, F, NC; YZ = FLi, BF, CO, N2) complexes

NASA Astrophysics Data System (ADS)

McDowell, Sean A. C.

2018-03-01

An MP2/6-311++G(3df,3pd) computational study of a series of hydrogen-bonded complexes X3CH⋯YZ (X = Cl, F, NC; YZ = FLi, BF, CO, N2) was undertaken to assess the trends in the relative stability and other molecular properties with variation of both the X group and the chemical hardness of the Y atom of YZ. The red- and blue-shifting propensities of the proton donor X3CH were investigated by considering the Csbnd H bond length change and its associated vibrational frequency shift. The proton donor Cl3CH, which has a positive dipole moment derivative with respect to Csbnd H bond extension, tends to form red-shifted complexes, this tendency being modified by the hardness (and dipole moment) associated with the proton acceptor. On the other hand, F3CH has a negative dipole moment derivative and tends to form blue-shifted complexes, suggesting that as X becomes more electron-withdrawing, the proton donor should have a negative dipole moment derivative and form blue-shifted complexes. Surprisingly, the most polar proton donor (NC)3CH was found to have a positive dipole moment derivative and produces red-shifted complexes. A perturbative model was found useful in rationalizing the trends for the Csbnd H bond length change and associated frequency shift.

Molecular dynamics modeling of PPTA crystallite mechanical properties in the presence of defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mercer, Brian; Zywicz, Edward; Papadopoulos, Panayiotis

Here, the mechanical properties of PPTA crystallites, the fundamental building blocks of aramid polymer fibers such as Kevlar® and Twaron®, are studied here using molecular dynamics simulations. The ReaxFF interatomic potential is employed to study crystallite failure via covalent and hydrogen bond rupture in constant strain-rate tensile loading simulations. Emphasis is placed on analyzing how chain-end defects in the crystallite influence its mechanical response and fracture strength. Chain-end defects are found to affect the behavior of nearby chains in a region of the PPTA crystallite that is small relative to the typical crystallite size in manufactured aramid fibers. The centralmore » Csingle bondN bond along the backbone chain is identified as the weakest in the PPTA polymer chain backbone in dynamic strain-to-failure simulations of the crystallite. It is found that clustering of chain-ends leads to reduced crystallite strength and crystallite failure via hydrogen bond rupture and chain sliding, whereas randomly scattered defects impact the strength less and failure is by covalent bond rupture and chain scission. The axial crystallite modulus increases with increasing chain length and is independent of chain-end defect locations. On the basis of these findings, a theoretical model is proposed to predict the axial modulus as a function of chain length.« less

Molecular dynamics modeling of PPTA crystallite mechanical properties in the presence of defects

DOE PAGES

Mercer, Brian; Zywicz, Edward; Papadopoulos, Panayiotis

2017-03-11

Here, the mechanical properties of PPTA crystallites, the fundamental building blocks of aramid polymer fibers such as Kevlar® and Twaron®, are studied here using molecular dynamics simulations. The ReaxFF interatomic potential is employed to study crystallite failure via covalent and hydrogen bond rupture in constant strain-rate tensile loading simulations. Emphasis is placed on analyzing how chain-end defects in the crystallite influence its mechanical response and fracture strength. Chain-end defects are found to affect the behavior of nearby chains in a region of the PPTA crystallite that is small relative to the typical crystallite size in manufactured aramid fibers. The centralmore » Csingle bondN bond along the backbone chain is identified as the weakest in the PPTA polymer chain backbone in dynamic strain-to-failure simulations of the crystallite. It is found that clustering of chain-ends leads to reduced crystallite strength and crystallite failure via hydrogen bond rupture and chain sliding, whereas randomly scattered defects impact the strength less and failure is by covalent bond rupture and chain scission. The axial crystallite modulus increases with increasing chain length and is independent of chain-end defect locations. On the basis of these findings, a theoretical model is proposed to predict the axial modulus as a function of chain length.« less

Some general aspects of torsional sensitivity and the GG-effect

NASA Astrophysics Data System (ADS)

Yu, C.-H.; Schäfer, L.; Ramek, M.; Miller, D. M.; Teppen, B. J.

1999-08-01

The geometries of 28 compounds of type X-C1-C2-C3-Y, with X,Y=CH 3, F, Cl, OH, NH 2, COH, and COOH, were fully optimized by ab initio HF/4-21G calculations at 30° grid points in their respective φ(X-C1-C2-C3), ψ(C1-C2-C3-Y)-torsional spaces. The results make it possible to construct parameter surfaces and their gradients in φ, ψ-space. The magnitude of the gradient, |∇ P|=[( ∂P/ ∂φ) 2+( ∂P/ ∂ψ) 2] 1/2, of a structural parameter P (a bond length, bond angle, or non-bonded distance) in φ, ψ-torsional space is a measure of torsional sensitivity (TS); i.e. a measure of the extent to which bond lengths, bond angles, and non-bonded distances change at a point in φ, ψ-space with backbone torsional angles. It is found that TS is not constant throughout the conformational space of a molecule, but varies in a characteristic way. It seems that, regardless of the nature of X or Y, extended forms are typically in regions of low TS; puckered conformations, of high TS. Conformations with two sequential gauche torsional angles (GG sequences) are characterized by high TS of 1,5-non-bonded distances concomitant with relatively low TS of other internal coordinates. This property of GG sequences is the source of a stabilizing and cooperative energy increment that is not afforded by other torsional sequences, such as trans- trans or trans- gauche. A structural data base, consisting of thousands of HF/4-21G structures of X-C-C-Y and X-C-C-C-Y systems has been assembled and is available on a CD.

Impact of Pb content on the physical parameters of Se-Te-Pb system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anjali,; Sharma, Raman; Thakur, Nagesh

2015-05-15

In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and meanmore » bond energy are found to decrease with Pb atomic percentage.« less

Laminate armor and related methods

DOEpatents

Chu, Henry S; Lillo, Thomas M; Zagula, Thomas M

2013-02-26

Laminate armor and methods of manufacturing laminate armor. Specifically, laminate armor plates comprising a commercially pure titanium layer and a titanium alloy layer bonded to the commercially pure titanium outer layer are disclosed, wherein an average thickness of the titanium alloy inner layer is about four times an average thickness of the commercially pure titanium outer layer. In use, the titanium alloy layer is positioned facing an area to be protected. Additionally, roll-bonding methods for manufacturing laminate armor plates are disclosed.

Fracture Behavior in Nylon 6 Fibers. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Lloyd, B. A.

1972-01-01

Electron paramagnetic resonance (EPR) techniques are used to determine the number of free radicals produced during deformation leading to fracture of nylon 6 fibers. A reaction rate molecular model is proposed to explain some of the deformation and bond rupture behavior leading to fracture. High-strength polymer fibers are assumed to consist of a sandwich structure of disordered and ordered regions along the fiber axis. In the disordered or critical flaw regions, tie chains connecting the ordered or crystalline block regions are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The effective length distribution was determined by EPR. The probability of bond rupture was assumed to be controlled by reaction-rate theory with a stress-aided activation energy and behavior of various loadings determined by numerical techniques. The model is successfully correlated with experimental stress, strain, and bond rupture results for creep, constant rate loadings, cyclic stress, stress relaxation and step strain tests at room temperature.

Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds

NASA Astrophysics Data System (ADS)

Jafri, S. Hassan M.; Löfås, Henrik; Blom, Tobias; Wallner, Andreas; Grigoriev, Anton; Ahuja, Rajeev; Ottosson, Henrik; Leifer, Klaus

2015-09-01

Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with ω-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

Discrete-to-continuum simulation approach to polymer chain systems: Subdiffusion, segregation, and chain folding

NASA Astrophysics Data System (ADS)

Foo, Grace M.; Pandey, R. B.

1998-05-01

A discrete-to-continuum approach is introduced to study the static and dynamic properties of polymer chain systems with a bead-spring chain model in two dimensions. A finitely extensible nonlinear elastic potential is used for the bond between the consecutive beads with the Lennard-Jones (LJ) potential with smaller (Rc=21/6σ=0.95) and larger (Rc=2.5σ=2.1) values of the upper cutoff for the nonbonding interaction among the neighboring beads. We find that chains segregate at temperature T=1.0 with Rc=2.1 and remain desegregated with Rc=0.95. At low temperature (T=0.2), chains become folded, in a ribbonlike conformation, unlike random and self-avoiding walk conformations at T=1.0. The power-law dependence of the rms displacements of the center of mass (Rc.m.) of the chains and their center node (Rcn) with time are nonuniversal, with the range of exponents ν1~=0.45-0.25 and ν2~=0.30-0.10, respectively. Both radius of gyration (Rg) and average bond length () decrease on increasing the range of interaction (Rc), consistent with the extended state in good solvent to collapsed state in poor solvent description of the polymer chains. Analysis of the radial distribution function supports these observations.

Structure, bonding nature, and binding energy of alkanethiolate on As-rich GaAs (001) surface: a density functional theory study.

PubMed

Voznyy, Oleksandr; Dubowski, Jan J

2006-11-30

Chemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied using first principles density functional calculations in a periodic supercell approach. The thiolate adsorption site, tilt angle and its direction are dictated by the high directionality of As dangling bond and sulfur 3p orbital participating in bonding and steric repulsion of the first three CH2 units from the surface. Small charge transfer between thiolate and surface, strong dependence of total energy on tilt angle, and a relatively short length of 2.28 A of the S-As bond indicate the highly covalent nature of the bonding. Calculated binding energy of 2.1 eV is consistent with the available experimental data.

Two-order-parameter description of liquid Al under five different pressures

NASA Astrophysics Data System (ADS)

Li, Y. D.; Hao, Qing-Hai; Cao, Qi-Long; Liu, C. S.

2008-11-01

In the present work, using the glue potential, the constant pressure molecular-dynamics simulations of liquid Al under five various pressures and a systematic analysis of the local atomic structures have been performed in order to test the two-order-parameter model proposed by Tanaka [Phys. Rev. Lett. 80, 5750 (1998)] originally for explaining the unusual behaviors of liquid water. The temperature dependence of the bond order parameter Q6 in liquid Al under five different pressures can be well fitted by the functional expression (Q6)/(1-Q6)=Q60exp((ΔE-PΔV)/(kBT)) which produces the energy gain ΔE and the volume change upon the formation of a locally favored structure: ΔE=0.025eV and ΔV=-0.27(Å)3 . ΔE is nearly equal to the difference between the average bond energy of the other type I bonds and the average bond energy of 1551 bonds (characterizing the icosahedronlike local structure); ΔV could be explained as the average volume occupied by one atom in icosahedra minus that occupied by one atom in other structures. With the obtained ΔE and ΔV , it is satisfactorily explained that the density of liquid Al displays a much weaker nonlinear dependence on temperature under lower pressures. So it is demonstrated that the behavior of liquid Al can be well described by the two-order-parameter model.

Batman-cracks. Observations and numerical simulations

NASA Astrophysics Data System (ADS)

Selvadurai, A. P. S.; Busschen, A. Ten; Ernst, L. J.

1991-05-01

To ensure mechanical strength of fiber reinforced plastics (FRP), good adhesion between fibers and the matrix is considered to be an essential requirement. An efficient test of fiber-matrix interface characterization is the fragmentation test which provides information about the interface slip mechanism. This test consists of the longitudinal loading of a single fiber which is embedded in a matrix specimen. At critical loads the fiber experiences fragmentation. This fragmentation will terminate depending upon the shear-slip strength of the fiber-matrix adhesion, which is inversely proportional to average fragment lengths. Depending upon interface strength characteristics either bond or slip matrix fracture can occur at the onset of fiber fracture. Certain particular features of matrix fracture are observed at the locations of fiber fracture in situations where there is sufficient interface bond strength. These refer to the development of fractures with a complex surface topography. The experimental procedure involved in the fragmentation tests is discussed and the boundary element technique to examine the development of multiple matrix fractures at the fiber fracture locations is examined. The mechanics of matrix fracture is examined. When bond integrity is maintained, a fiber fracture results in a matrix fracture. The matrix fracture topography in a fragmentation test is complex; however, simplified conoidal fracture patterns can be used to investigate the crack extension phenomena. Via a mixed-mode fracture criterion, the generation of a conoidal fracture pattern in the matrix is investigated. The numerical results compare favorably with observed experimental data derived from tests conducted on fragmentation test specimens consisting of a single glass fiber which is embedded in a polyester matrix.

Home Runs and Humbugs: Comment on Bond and DePaulo (2008)

ERIC Educational Resources Information Center

O'Sullivan, Maureen

2008-01-01

In 2006, C. F. Bond Jr. and B. M. DePaulo provided a meta-analysis of means and concluded that average lie detection accuracy was significantly greater than chance for most people. Now, they have presented an analysis of standard deviations (C. F. Bond Jr. & B. M. DePaulo, 2008), claiming that there are no reliable individual differences in lie…

The changing value of the `green' label on the US municipal bond market

NASA Astrophysics Data System (ADS)

Karpf, Andreas; Mandel, Antoine

2018-01-01

Green bonds are seen as a key instrument to unlock climate finance. While their volume has grown steadily in recent years, the impact of the `green' label on the bond market is poorly understood. Here, we investigate the differences between the yield term structures of green and conventional bonds in the US municipal bond market. We show that, although returns on conventional bonds are on average higher than for green bonds, the differences can largely be explained by the fundamental properties of the bonds. Historically, green bonds have been penalized on the municipal market, being traded at lower prices and higher yields than expected by their credit profiles. In recent years, however, the credit quality of municipal green bonds has increased and the premium turned positive. Green bonds are thus becoming an increasingly attractive investment, with scope to bridge the climate finance gap for mitigation and adaptation.

Thermoplastic Ribbon-Ply Bonding Model

NASA Technical Reports Server (NTRS)

Hinkley, Jeffrey A.; Marchello, Joseph M.; Messier, Bernadette C.

1996-01-01

The aim of the present work was to identify key variables in rapid weldbonding of thermoplastic tow (ribbon) and their relationship to matrix polymer properties and to ribbon microstructure. Theoretical models for viscosity, establishment of ply-ply contact, instantaneous (Velcro) bonding, molecular interdiffusion (healing), void growth suppression, and gap filling were reviewed and synthesized. Consideration of the theoretical bonding mechanisms and length scales and of the experimental weld/peel data allow the prediction of such quantities as the time and pressure required to achieve good contact between a ribbon and a flat substrate, the time dependence of bond strength, pressures needed to prevent void growth from dissolved moisture and conditions for filling gaps and smoothing overlaps.

2-Acetyl-1,1,3,3-tetra­methyl­guanidine

PubMed Central

Tiritiris, Ioannis

2012-01-01

In the mol­ecule of the title compound, C7H15N3O, the central C atom is surrounded in a nearly ideal trigonal–planar geometry by three N atoms. The C—N bond lengths in the CN3 unit are 1.3353 (13), 1.3463 (12) and 1.3541 (13) Å, indicating an inter­mediate character between a single and a double bond for each C—N bond. The bonds between the N atoms and the terminal C-methyl groups all have values close to that of a typical single bond [1.4526 (13)–1.4614 (14) Å]. In the crystal, the guanidine mol­ecules are connected by weak C—H⋯O and C—H⋯N hydrogen bonds, generating layers parallel to the ab plane. PMID:23125768

Hydrogen bond asymmetric local potentials in compressed ice.

PubMed

Huang, Yongli; Ma, Zengsheng; Zhang, Xi; Zhou, Guanghui; Zhou, Yichun; Sun, Chang Q

2013-10-31

A combination of the Lagrangian mechanics of oscillators vibration, molecular dynamics decomposition of volume evolution, and Raman spectroscopy of phonon relaxation has enabled us to resolve the asymmetric, local, and short-range potentials pertaining to the hydrogen bond (O:H-O) in compressed ice. Results show that both oxygen atoms in the O:H-O bond shift initially outwardly with respect to the coordination origin (H), lengthening the O-O distance by 0.0136 nm from 0.2597 to 0.2733 nm by Coulomb repulsion between electron pairs on adjacent oxygen atoms. Both oxygen atoms then move toward right along the O:H-O bond by different amounts upon being compressed, approaching identical length of 0.11 nm. The van der Waals potential VL(r) for the O:H noncovalent bond reaches a valley at -0.25 eV, and the lowest exchange VH(r) for the H-O polar-covalent bond is valued at -3.97 eV.

Modeling the IR spectra of aqueous metal carboxylate complexes: correlation between bonding geometry and stretching mode wavenumber shifts.

PubMed

Sutton, Catherine C R; da Silva, Gabriel; Franks, George V

2015-04-27

A widely used principle is that shifts in the wavenumber of carboxylate stretching modes upon bonding with a metal center can be used to infer if the geometry of the bonding is monodentate or bidentate. We have tested this principle with ab initio modeling for aqueous metal carboxylate complexes and have shown that it does indeed hold. Modeling of the bonding of acetate and formate in aqueous solution to a range of cations was used to predict the infrared spectra of the metal-carboxylate complexes, and the wavenumbers of the symmetric and antisymmetric vibrational modes are reported. Furthermore, we have shown that these shifts in wavenumber occur primarily due to how bonding with the metal changes the carboxylate C-O bond lengths and O-C-O angle. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wen; Zhou, Zhaofeng, E-mail: zfzhou@xtu.edu.cn; Zhong, Yuan

2015-11-15

Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (T{sub N}) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the T{sub N} by adjusting the atomic cohesive energy. The T{sub N} is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numericalmore » match between predictions and measurements reveals that the T{sub N} of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.« less

Bond characteristics of reinforcing steel embedded in geopolymer concrete

NASA Astrophysics Data System (ADS)

Kathirvel, Parthiban; Thangavelu, Manju; Gopalan, Rashmi; Raja Mohan Kaliyaperumal, Saravana

2017-07-01

The force transferring between reinforcing steel and the surrounding concrete in reinforced concrete is influenced by several factors. Whereas, the study on bond behaviour of geopolymer concrete (GPC) is lagging. In this paper, an experimental attempt has been made to evaluate the geopolymer concrete bond with reinforcing steel of different diameter and embedded length using standard pull out test. The geopolymer concrete is made of ground granulated blast furnace slag (GGBFS) as geopolymer source material (GSM). The tests were conducted to evaluate the development of bond between steel and concrete of grade M40 and M50 with 12 and 16 mm diameter reinforcing steel for geopolymer and cement concrete mixes and to develop a relation between bond strength and compressive strength. From the experimental results, it has been observed that the bond strength of the geopolymer concrete mixes was more compared to the cement concrete mixes and increases with the reduction in the diameter of the bar.

Possible steric control of the relative strength of chelation enhanced fluorescence for zinc(II) compared to cadmium(II): metal ion complexing properties of tris(2-quinolylmethyl)amine, a crystallographic, UV-visible, and fluorometric study.

PubMed

Williams, Neil J; Gan, Wei; Reibenspies, Joseph H; Hancock, Robert D

2009-02-16

The idea is examined that steric crowding in ligands can lead to diminution of the chelation enhanced fluorescence (CHEF) effect in complexes of the small Zn(II) ion as compared to the larger Cd(II) ion. Steric crowding is less severe for the larger ion and for the smaller Zn(II) ion leads to Zn-N bond length distortion, which allows some quenching of fluorescence by the photoinduced electron transfer (PET) mechanism. Some metal ion complexing properties of the ligand tris(2-quinolylmethyl)amine (TQA) are presented in support of the idea that more sterically efficient ligands, which lead to less M-N bond length distortion with the small Zn(II) ion, will lead to a greater CHEF effect with Zn(II) than Cd(II). The structures of [Zn(TQA)H(2)O](ClO(4))(2).1.5 H(2)O (1), ([Pb(TQA)(NO(3))(2)].C(2)H(5)OH) (2), ([Ag(TQA)(ClO(4))]) (3), and (TQA).C(2)H(5)OH (4) are reported. In 1, the Zn(II) is 5-coordinate, with four N-donors from the ligand and a water molecule making up the coordination sphere. The Zn-N bonds are all of normal length, showing that the level of steric crowding in 1 is not sufficient to cause significant Zn-N bond length distortion. This leads to the observation that, as expected, the CHEF effect in the Zn(II)/TQA complex is much stronger than that in the Cd(II)/TQA complex, in contrast to similar but more sterically crowded ligands, where the CHEF effect is stronger in the Cd(II) complex. The CHEF effect for TQA with the metal ions examined varies as Zn(II) > Cd(II) > Ni(II) > Pb(II) > Hg(II) > Cu(II). The structure of 2 shows an 8-coordinate Pb(II), with evidence of a stereochemically active lone pair, and normal Pb-N bond lengths. In 3, the Ag(I) is 5-coordinate, with four N-donors from the TQA and an oxygen from the perchlorate. The Ag(I) shows no distortion toward linear 2-coordinate geometry, and the Ag-N bonds fall slightly into the upper range for Ag-N bonds in 5-coordinate complexes. The structure of 4 shows the TQA ligand to be involved in pi-stacking between quinolyl groups from adjacent TQA molecules. Formation constants determined by UV-visible spectroscopy are reported in 0.1 M NaClO(4) at 25 degrees C for TQA with Zn(II), Cd(II), and Pb(II). When compared with other similar ligands, one sees that, as the level of steric crowding increases, the stability decreases most with the small Zn(II) ion and least with the large Pb(II) ion. This is in accordance with the idea that TQA has a moderate level of steric crowding and that steric crowding increases for TQA analogs tris(2-pyridylmethyl)amine (TPyA) < TQA < tris(6-methyl-2-pyridyl)amine (TMPyA).

The influence of the energy density and other clinical parameters on bond strength of Er:YAG-conditioned dentin compared to conventional dentin adhesion.

PubMed

Gisler, Gottfried; Gutknecht, Norbert

2014-01-01

The aim of this in vitro study was to optimise clinical parameters and the energy density of Er:YAG laser-conditioned dentin for class V fillings. Shear tests in three test series were conducted with 24 freshly extracted human third molars as samples for each series. For every sample, two orofacial and two approximal dentin surfaces were prepared. The study design included different laser energies, a thin vs a thick bond layer, the influence of adhesives as well as one-time- vs two-time treatment. The best results with Er:YAG-conditioned dentin were obtained with fluences just above the ablation threshold (5.3 J/cm(2)) in combination with a self-etch adhesive, a thin bond layer and when bond and composite were two-time cured. Dentin conditioned this way reached an averaged bond strength of 23.32 MPa (SD 5.3) and 24.37 MPa (SD 6.06) for two independent test surfaces while showing no statistical significance to conventional dentin adhesion and two-time treatment with averaged bond strength of 24.93 MPa (SD 11.51). Significant reduction of bond strength with Er:YAG-conditioned dentin was obtained when using either a thick bond layer, twice the laser energy (fluence 10.6 J/cm(2)) or with no dentin adhesive. The discussion showed clearly that in altered (sclerotic) dentin, e.g. for class V fillings of elderly patients, bond strengths in conventional dentin adhesion are constantly reduced due to the change of the responsibles, bond giving dentin structures, whereas for Er:YAG-conditioned dentin, the only way to get an optimal microretentive bond pattern is a laser fluence just above the ablation threshold of sclerotic dentin.

Nature's Mechanisms for Tough, Self-healing Polymers and Polymer Adhesives

NASA Astrophysics Data System (ADS)

Hansma, Paul

2007-03-01

Spider silk^2 and the natural polymer adhesives in abalone shells^3 and bone^4,5 can give us insights into nature's mechanisms for tough, self-healing polymers and polymer adhesives. The natural polymer adhesives in biomaterials have been optimized by evolution. An optimized polymer adhesive has five characteristics. 1) It holds together the strong elements of the composite. 2) It yields just before the strong elements would otherwise break. 3) It dissipates large amounts of energy as it yields. 4) It self heals after it yields. 5) It takes just a few percent by weight. Both natural polymer adhesives and silk rely on sacrificial bonds and hidden length for toughness and self-healing.^6 A relatively large energy, of order 100eV, is required to stretch a polymer molecule after a weak bond, a sacrificial bond, breaks and liberates hidden length, which was previously hidden, typically in a loop or folded domain, from whatever was stretching the polymer. The bond is called sacrificial if it breaks at forces well below the forces that could otherwise break the polymer backbone, typically greater than 1nN. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby also providing a ``self-healing'' property to the material.^2-4 Individual polymer adhesive molecules based on sacrificial bonds and hidden length can supply forces of order 300pN over distances of 100s of nanometers. Model calculations show that a few percent by weight of adhesives based on these principles could be optimized adhesives for high performance composite materials including nanotube and graphene sheet composites. ^2N. Becker, E. Oroudjev, S. Mutz et al., Nature Materials 2 (4), 278 (2003). ^3B. L. Smith, T. E. Schaffer, M. Viani et al., Nature 399 (6738), 761 (1999). ^4J. B. Thompson, J. H. Kindt, B. Drake et al., Nature 414 (6865), 773 (2001). ^5G. E. Fantner, T. Hassenkam, J. H. Kindt et al., Nature Materials 4, 612 (2005). ^6G. E. Fantner, E. Oroudjev, G. Schitter et al., Biophysical Journal 90 (4), 1411 (2006).

Time-of-flight neutron powder diffraction study on the third row transition metal hexafluorides WF6, OsF6, and PtF6

NASA Astrophysics Data System (ADS)

Marx, R.; Seppelt, K.; Ibberson, R. M.

1996-05-01

A neutron diffraction study on the third-row transition metal hexafluorides MF6 (M≡W, Os, Pt) has been performed using the high resolution neutron powder diffractometer (HRPD) at the spallation source ISIS, England. The previously unknown structures of the low-temperature phases of OsF6 and PtF6 are reported. WF6, OsF6, and PtF6, which exhibit a (5dt2g)0, (5dt2g)2, and (5dt2g)4 electronic configuration, respectively, are found to be isostructural and crystallize in the UF6 structure, space group Pmnb, (No. 62). The geometry of the MF6 molecules is to good approximation octahedral for each compound, the mean M-F bond length increasing only slightly from 182.5 (W) to 185.0 (Pt). For WF6 deviations from ideal octahedral geometry are only marginally significant [181.8(2) to 183.2(2) pm] and may be interpreted on the basis of packing effects. Deviations for the d2 complex OsF6 are somewhat larger [181.5(2) to 184.4(3) pm] and may be assumed to be caused by packing effects essentially the same as for WF6, in addition to a first-order Jahn-Teller effect arising from the (5dt2g)2 electronic configuration. While eliminating the effects of packing by a comparison of individual M-F bond lengths for WF6 and OsF6, the OsF6 molecule shows to have D4h symmetry with two apical M-F bonds about 1.8 pm longer than the four equatorial bonds as a result of the Jahn-Teller distortion. Only small deviations from ideal octahedral geometry [184.4(3) to 185.8(3) pm] are found for the d4 complex PtF6. Within the series W to Pt a substantial shortening of the F...F van der Waals contact distances is observed. This shortening more than compensates for the increase in the M-F bond lengths and leads to unit cell volumes and cell parameters decreasing continuously from W to Pt. The variation of F...F contact distances and M-F bond lengths may be rationalized in terms of polarization of the F-ligands in the field of the highly charged nuclei of the central atoms which are only incompletely shielded by the 5d electrons.

Mathematical analysis of compressive/tensile molecular and nuclear structures

NASA Astrophysics Data System (ADS)

Wang, Dayu

Mathematical analysis in chemistry is a fascinating and critical tool to explain experimental observations. In this dissertation, mathematical methods to present chemical bonding and other structures for many-particle systems are discussed at different levels (molecular, atomic, and nuclear). First, the tetrahedral geometry of single, double, or triple carbon-carbon bonds gives an unsatisfying demonstration of bond lengths, compared to experimental trends. To correct this, Platonic solids and Archimedean solids were evaluated as atoms in covalent carbon or nitrogen bond systems in order to find the best solids for geometric fitting. Pentagonal solids, e.g. the dodecahedron and icosidodecahedron, give the best fit with experimental bond lengths; an ideal pyramidal solid which models covalent bonds was also generated. Second, the macroscopic compression/tension architectural approach was applied to forces at the molecular level, considering atomic interactions as compressive (repulsive) and tensile (attractive) forces. Two particle interactions were considered, followed by a model of the dihydrogen molecule (H2; two protons and two electrons). Dihydrogen was evaluated as two different types of compression/tension structures: a coaxial spring model and a ring model. Using similar methods, covalent diatomic molecules (made up of C, N, O, or F) were evaluated. Finally, the compression/tension model was extended to the nuclear level, based on the observation that nuclei with certain numbers of protons/neutrons (magic numbers) have extra stability compared to other nucleon ratios. A hollow spherical model was developed that combines elements of the classic nuclear shell model and liquid drop model. Nuclear structure and the trend of the "island of stability" for the current and extended periodic table were studied.

The effect of Ga vacancies on the defect and magnetic properties of Mn-doped GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Joongoo; Chang, K. J.; Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea and Korea Institute for Advanced Study, Seoul 130-722

2007-10-15

We perform first-principles theoretical calculations to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (V{sub Ga}) is introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurs from the Mn d band to the acceptor levels of V{sub Ga}, and strong Mn-N bonds are formed between the Mn ion and the N atoms in the neighborhood of V{sub Ga}. The charge transfer and chemical bonding effects significantly affect the defect and magnetic properties of Mn-doped GaN. In a Mn-V{sub Ga} complex, whichmore » consists of a Ga vacancy and one Mn ion, the dangling bond orbital of the N atom involved in the Mn-N bond is electrically deactivated, and the remaining dangling bond orbitals of V{sub Ga} lead to the shallowness of the defect level. When a Ga vacancy forms a complex with two Mn ions located at a distance of about 6 A, which corresponds to the percolation length in determining the Curie temperature in diluted Mn-doped GaN, the Mn d band is broadened and the density of states at the Fermi level is reduced due to two strong Mn-N bonds. Although the broadening and depopulation of the Mn d band weaken the ferromagnetic stability between the Mn ions, the ferromagnetism is still maintained because of the lack of antiferromagnetic superexchange interactions at the percolation length.« less

Effect of phosphate activating group on oligonucleotide formation on montmorillonite: the regioselective formation of 3',5'-linked oligoadenylates

NASA Technical Reports Server (NTRS)

Prabahar, K. J.; Cole, T. D.; Ferris, J. P.

1994-01-01

The effects of amine structure on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidates of adenosine are investigated. 4-Aminopyridine derivatives yielded oligoadenylates as long as dodecamers with a regioselectivity for 3',5'-phosphodiester bond formation averaging 88%. Linear and cyclic oligomers are obtained and no A5'ppA-containing products are detected. Oligomers as long as the hexanucleotide are obtained using 2-aminobenzimidazole as the activating group. A predominance of pA2'pA is detected in the dimer fraction along with cyclic 3',5'-trimer; no A5'ppA-containing oligomers were detected. Little or no oligomer formation was observed when morpholine, piperidine, pyrazole, 1,2,4-triazole, and 2-pyridone are used as phosphate-activating groups. The effects of the structure of the phosphate activating group on the oligomer structure and chain lengths are discussed.

(Cryptand-222)potassium(+) (hydrogensulfido)[5,10,15,20-tetra-kis(2-pival-amido-phen-yl)porphyrinato]ferrate(II).

PubMed

Dhifet, Mondher; Belkhiria, Mohamed Salah; Daran, Jean-Claude; Nasri, Habib

2009-07-22

As part of a systematic investigation for a number of Fe(II) porphyrin complexes used as biomimetic models for cytochrome P450, crystals of the title compound, [K(C(18)H(36)N(2)O(6))][Fe(II)(C(64)H(64)N(8)O(4))(HS)], were prepared. The compound exhibits a non-planar conformation with major ruffling and saddling distortions. The average equatorial iron-pyrrole N atom [Fe-N(p) = 2.102 (2) Å] bond length and the distance between the Fe(II) atom and the 24-atom core of the porphyrin ring (Fe-P(C)= 0.558 Å) are typical for high-spin iron(II) penta-coordinate porphyrinates. One of the tert-butyl groups in the structure is disordered over two sets with occupancies of 0.84 and 0.16.

(Cryptand-222)potassium(+) (hydrogensulfido)[5,10,15,20-tetra­kis(2-pival­amido­phen­yl)porphyrinato]ferrate(II)

PubMed Central

Dhifet, Mondher; Belkhiria, Mohamed Salah; Daran, Jean-Claude; Nasri, Habib

2009-01-01

As part of a systematic investigation for a number of FeII porphyrin complexes used as biomimetic models for cytochrome P450, crystals of the title compound, [K(C18H36N2O6)][FeII(C64H64N8O4)(HS)], were prepared. The compound exhibits a non-planar conformation with major ruffling and saddling distortions. The average equatorial iron–pyrrole N atom [Fe—Np = 2.102 (2) Å] bond length and the distance between the FeII atom and the 24-atom core of the porphyrin ring (Fe—PC= 0.558 Å) are typical for high-spin iron(II) penta­coordinate porphyrinates. One of the tert-butyl groups in the structure is disordered over two sets with occupancies of 0.84 and 0.16. PMID:21583412

An Examination of United States Navy Leasing: Lessons from the MPS/T-5 Experience

DTIC Science & Technology

2004-12-01

issued by the FFB to the Deal’s special purpose entities. These bonds were not callable -- the FFB required that if the bonds were redeemed early, they...year) bonds purchased by the FFB. All debt funds flowed directly to the FFB, which held a mortgage on the vessel to secure the debt. • Delivery...debt/Owner-Participant equity ratio applied. Used 6% based on the average yield on 20-year Treasury bonds . Discount Rate Used 10% based on DoD

Effect of buoyancy on the motion of long bubbles in horizontal tubes

NASA Astrophysics Data System (ADS)

Atasi, Omer; Khodaparast, Sepideh; Scheid, Benoit; Stone, Howard A.

2017-09-01

As a confined long bubble translates along a horizontal liquid-filled tube, a thin film of liquid is formed on the tube wall. For negligible inertial and buoyancy effects, respectively, small Reynolds (Re) and Bond (Bo) numbers, the thickness of the liquid film depends only on the flow capillary number (Ca). However, buoyancy effects are no longer negligible as the diameter of the tube reaches millimeter length scales, which corresponds to finite values of Bo. We perform experiments and theoretical analysis for a long bubble in a horizontal tube to investigate the effect of Bond number (0.05

Microstructural characteristics of HIP-bonded monolithic nuclear fuels with a diffusion barrier

NASA Astrophysics Data System (ADS)

Jue, Jan-Fong; Keiser, Dennis D.; Breckenridge, Cynthia R.; Moore, Glenn A.; Meyer, Mitchell K.

2014-05-01

Due to the limitation of maximum uranium load achievable by dispersion fuel type, the Global Threat Reduction Initiative is developing an advanced monolithic fuel to convert US high-performance research reactors to low-enriched uranium. Hot-isostatic-press (HIP) bonding was the single process down-selected to bond monolithic U-Mo fuel meat to aluminum alloy cladding. A diffusion barrier was applied to the U-Mo fuel meat by roll-bonding process to prevent extensive interaction between fuel meat and aluminum-alloy cladding. Microstructural characterization was performed on fresh fuel plates fabricated at Idaho National Laboratory. Interfaces between the fuel meat, the cladding, and the diffusion barrier, as well as between the U-10Mo fuel meat and the Al-6061 cladding, were characterized by scanning electron microscopy. Preliminary results indicate that the interfaces contain many different phases while decomposition, second phases, and chemical banding were also observed in the fuel meat. The important attributes of the HIP-bonded monolithic fuel are:

Microstructural Characteristics of HIP-bonded Monolithic Nuclear Fuels with a Diffusion Barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jan-Fong Jue; Dennis D. Keiser, Jr.; Cynthia R. Breckenridge

Due to the limitation of maximum uranium load achievable by dispersion fuel type, the Global Threat Reduction Initiative (GTRI) is developing an advanced monolithic fuel to convert US high performance research reactors to low-enriched uranium. Hot-isostatic-press bonding was the single process down-selected to bond monolithic U-Mo fuel meat to aluminum alloy cladding. A diffusion barrier was applied to the U–Mo fuel meat by roll-bonding process to prevent extensive interaction between fuel meat and aluminum-alloy cladding. Microstructural characterization was performed on fresh fuel plates fabricated at Idaho National Laboratory. Interfaces between fuel meat, cladding, and diffusion barrier, as well as U–10Momore » fuel meat and Al–6061 cladding were characterized by scanning electron microscopy. Preliminary results indicate that the interfaces contain many different phases while decomposition, second phases, and chemical banding were also observed in the fuel meat. The important attributes of the HIP-bonded monolithic fuel are • A typical Zr diffusion barrier of thickness 25 µm • Transverse cross section that exhibits relatively equiaxed grains with an average grain diameter of 10 µm • Chemical banding, in some areas more than 100 µm in length, that is very pronounced in longitudinal (i.e., rolling) direction with Mo concentration varying from 7–13 wt% • Decomposed areas containing plate-shaped low-Mo phase • A typical Zr/cladding interaction layer of thickness 1-2 µm • A visible UZr2 bearing layer of thickness 1-2 µm • Mo-rich precipitates (mainly Mo2Zr, forming a layer in some areas) followed by a Mo-depleted sub-layer between the visible UZr2-bearing layer and the U–Mo matrix • No excessive interaction between cladding and the uncoated fuel edge • Cladding-to-cladding bonding that exhibits no cracks or porosity with second phases high in Mg, Si, and O decorating the bond line. • Some of these attributes might be critical to the irradiation performance of monolithic U-10Mo nuclear fuel. There are several issues or concerns that warrant more detailed study, such as precipitation along cladding-to-cladding bond line, chemical banding, uncovered fuel-zone edge, and interaction layer between U–Mo fuel meat and zirconium. Future post-irradiation examination results will focus, among other things, on identifying in-reactor failure mechanisms and, eventually, directing further fresh fuel characterization efforts.« less

A quantum chemistry study of Qinghaosu

NASA Astrophysics Data System (ADS)

Gu, Jian-De; Chen, Kai-Xian; Jiang, Hua-Liang; Zhu, Wei-Liang; Chen, Jian-Zhong; Ji, Ru-Yun

1997-10-01

The powerful anti-malarial drug, Qinghaosu (Artemisinin), has been studied using ab initio methods. The DFT B3LYP method with the 6-31G ∗ basis set gives an excellent geometry compared to experiments, especially for the OO bond length and the 1,2,4-Trioxane ring subsystem. The R(OO) bond length predicted at this level is 1.460 Å, only 0.018 Å shorter than the experimental measurement. The vibrational analysis shows that the OO stretching mode is combined with the OC vibration mode, having the character of an OOC entity. The OO vibrational band at 722 cm -1 suggested in the experimental studies has been assigned as 1,2,4-trioxane ring breathing.

All-electron molecular Dirac-Hartree-Fock calculations - The group IV tetrahydrides CH4, SiH4, GeH4, SnH4, and PbH4

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Taylor, Peter R.; Faegri, Knut, Jr.; Partridge, Harry

1991-01-01

A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but none of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

All-electron molecular Dirac-Hartree-Fock calculations: The group 4 tetrahydrides CH4, SiH4, GeH4, SnH4 and PbH4

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Taylor, Peter R.; Faegri, Knut, Jr.; Partridge, Harry

1990-01-01

A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but non of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

Quasiparticle and excitonic gaps of one-dimensional carbon chains.

PubMed

Mostaani, E; Monserrat, B; Drummond, N D; Lambert, C J

2016-06-01

We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm(-1), which is consistent with Raman spectroscopic measurements for large oligoynes.

High temperature extended x-ray absorption fine structure study of multiferroic BiFeO3

NASA Astrophysics Data System (ADS)

Raghavendra Reddy, V.; Meneghini, Carlo; Kothari, Deepti; Gupta, Ajay; Aquilanti, Giuliana

2012-08-01

Local atomic structure modifications around Fe atoms in polycrystalline multiferroic BiFeO3 are studied by Fe K edge x-ray absorption spectroscopy as a function of temperature across the Néel temperature (TN = 643 K) in order to reveal local structure modifications related to the magnetic transition. This work demonstrates that on crossing TN the local structure around Fe shows peculiar changes: the Fe-O bond lengths get shorter, the ligand symmetry increases and the Fe-O bond length disorder (σ2) deviates from Debye behaviour. These results suggest that the structural transition at the ferroelectric Curie temperature (TC = 1103 K) is anticipated by early local rearrangement of the structure starting already at TN.

Analysis of the vibronic structure of the trans-stilbene fluorescence and excitation spectra: the S0 and S1 PES along the Ce[double bond, length as m-dash]Ce and Ce-Cph torsions.

PubMed

Orlandi, Giorgio; Garavelli, Marco; Zerbetto, Francesco

2017-09-20

We analyze the highly resolved vibronic structure of the low energy (≤200 cm -1 ) region of the fluorescence and fluorescence excitation spectra of trans-stilbene in supersonic beams. In this spectral region the vibronic structure is associated mainly with vibrational levels of the C e -C e torsion (τ) and the a u combination of the two C e -C ph bond twisting (ϕ). We base this analysis on the well-established S 0 (τ, ϕ) two-dimensional potential energy surface (PES) and on a newly refined S 1 (τ, ϕ) PES. We obtain vibrational eigenvalues and eigenvectors of the anharmonic S 0 (τ, ϕ) and S 1 (τ, ϕ) PES using a numerical procedure based on the Meyer's flexible model [R. Meyer, J. Mol. Spectrosc., 1979, 76, 266]. Then we derive Franck-Condon factors and therefore intensities of the relevant vibronic bands for the S 0 → S 1 excitation and S 1 → S 0 fluorescence spectra. Furthermore, we assess the role of the b g combination of the two C e -C ph bond twisting (ν 48 ) in the structure of the S 1 → S 0 fluorescence spectra. By the use of these results we are able to assign most of the low energy vibrational levels of the S 0 → S 1 excitation spectra and of the fluorescence spectra of the emission from several low energy S 1 vibronic levels. The good agreement between the observed and the computed vibrational structure of the S 0 → S 1 and S 1 → S 0 spectra suggests that the proposed picture of the E 1 (τ, ϕ) and E 0 (τ, ϕ) PES, in particular along the coordinate τ governing trans-cis photo-isomerization in S 1 , is accurate. In S 0 , the barriers for the C e [double bond, length as m-dash]C e torsion and for the a u type C e -C ph bond twisting are 16 080 cm -1 and 3125 cm -1 , respectively, while in S 1 , where the bond orders of the C e [double bond, length as m-dash]C e and C e -C ph bonds are reversed, the two barriers become 1350 cm -1 and 8780 cm -1 , respectively.

The Molecular Structure of cis-FONO

NASA Technical Reports Server (NTRS)

Lee, Timothy J.; Dateo, Christopher E.; Rice, Julia E.; Langhoff, Stephen R. (Technical Monitor)

1994-01-01

The molecular structure of cis-FONO has been determined with the CCSD(T) correlation method using an spdf quality basis set. In agreement with previous coupled-cluster calculations but in disagreement with density functional theory, cis-FONO is found to exhibit normal bond distances. The quadratic and cubic force fields of cis-FONO have also been determined in order to evaluate the effect of vibrational averaging on the molecular geometry. Vibrational averaging is found to increase bond distances, as expected, but it does not affect the qualitative nature of the bonding. The CCSD(T)/spdf harmonic frequencies of cis-FONO support our previous assertion that a band observed at 1200 /cm is a combination band (upsilon(sub 3) + upsilon(sub 4)), and not a fundamental.

All-Dimensional H2–CO Potential: Validation with Fully Quantum Second Virial Coefficients

PubMed Central

Garberoglio, Giovanni; Jankowski, Piotr; Szalewicz, Krzysztof; Harvey, Allan H.

2017-01-01

We use a new high-accuracy all-dimensional potential to compute the cross second virial coefficient B12(T) between molecular hydrogen and carbon monoxide. The path-integral method is used to fully account for quantum effects. Values are calculated from 10 K to 2000 K and the uncertainty of the potential is propagated into uncertainties of B12. Our calculated B12(T) are in excellent agreement with most of the limited experimental data available, but cover a much wider range of temperatures and have lower uncertainties. Similar to recently reported findings from scattering calculations, we find that the reduced-dimensionality potential obtained by averaging over the rovibrational motion of the monomers gives results that are a good approximation to those obtained when flexibility is fully taken into account. Also, the four-dimensional approximation with monomers taken at their vibrationally averaged bond lengths works well. This finding is important, since full-dimensional potentials are difficult to develop even for triatomic monomers and are not currently possible to obtain for larger molecules. Likewise, most types of accurate quantum mechanical calculations, e.g., spectral or scattering, are severely limited in the number of dimensions that can be handled. PMID:28178790

All-dimensional H2-CO potential: Validation with fully quantum second virial coefficients.

PubMed

Garberoglio, Giovanni; Jankowski, Piotr; Szalewicz, Krzysztof; Harvey, Allan H

2017-02-07

We use a new high-accuracy all-dimensional potential to compute the cross second virial coefficient B 12 (T) between molecular hydrogen and carbon monoxide. The path-integral method is used to fully account for quantum effects. Values are calculated from 10 K to 2000 K and the uncertainty of the potential is propagated into uncertainties of B 12 . Our calculated B 12 (T) are in excellent agreement with most of the limited experimental data available, but cover a much wider range of temperatures and have lower uncertainties. Similar to recently reported findings from scattering calculations, we find that the reduced-dimensionality potential obtained by averaging over the rovibrational motion of the monomers gives results that are a good approximation to those obtained when flexibility is fully taken into account. Also, the four-dimensional approximation with monomers taken at their vibrationally averaged bond lengths works well. This finding is important, since full-dimensional potentials are difficult to develop even for triatomic monomers and are not currently possible to obtain for larger molecules. Likewise, most types of accurate quantum mechanical calculations, e.g., spectral or scattering, are severely limited in the number of dimensions that can be handled.

Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

DOE PAGES

Krogel, Jaron T.; Santana Palacio, Juan A.; Reboredo, Fernando A.

2016-02-22

Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentialsmore » to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.« less

Recent Advances in Insect Olfaction, Specifically Regarding the Morphology and Sensory Physiology of Antennal Sensilla of the Female Sphinx Moth Manduca sexta

PubMed Central

SHIELDS, VONNIE D.C.; HILDEBRAND, JOHN G.

2008-01-01

The antennal flagellum of female Manduca sexta bears eight sensillum types: two trichoid, two basiconic, one auriculate, two coeloconic, and one styliform complex sensilla. The first type of trichoid sensillum averages 34 μm in length and is innervated by two sensory cells. The second type averages 26 μm in length and is innervated by either one or three sensory cells. The first type of basiconic sensillum averages 22 μm in length, while the second type averages 15 μm in length. Both types are innervated by three bipolar sensory cells. The auriculate sensillum averages 4 μm in length and is innervated by two bipolar sensory cells. The coeloconic type-A and type-B both average 2 μm in length. The former type is innervated by five bipolar sensory cells, while the latter type, by three bipolar sensory cells. The styliform complex sensillum occurs singly on each annulus and averages 38-40 μm in length. It is formed by several contiguous sensilla. Each unit is innervated by three bipolar sensory cells. A total of 2,216 sensilla were found on a single annulus (annulus 21) of the flagellum. Electrophysiological responses from type-A trichoid sensilla to a large panel of volatile odorants revealed three different subsets of olfactory receptor cells (ORCs). Two subsets responded strongly to only a narrow range of odorants, while the third responded strongly to a broad range of odorants. Anterograde labeling of ORCs from type-A trichoid sensilla revealed that their axons projected mainly to two large female glomeruli of the antennal lobe. PMID:11754510

Tunnel current across linear homocatenated germanium chains

NASA Astrophysics Data System (ADS)

Matsuura, Yukihito

2014-01-01

The electronic transport properties of germanium oligomers catenating into linear chains (linear Ge chains) have been theoretically studied using first principle methods. The conduction mechanism of a Ge chain sandwiched between gold electrodes was analyzed based on the density of states and the eigenstates of the molecule in a two-probe environment. Like that of silicon chains (Si chains), the highest occupied molecular orbital of Ge chains contains the extended σ-conjugation of Ge 4p orbitals at energy levels close to the Fermi level; this is in contrast to the electronic properties of linear carbon chains. Furthermore, the conductance of a Ge chain is expected to decrease exponentially with molecular length L. The decay constant β, which is defined as e-βL, of a Ge chain is similar to that of a Si chain, whereas the conductance of the Ge chains is higher than that of Si chains even though the Ge-Ge bond length is longer than the Si-Si bond length.

New members of the A{sub 2}M′M{sub 2}{sup ″} structure family (A=Ca, Sr, Yb, La; M′=In,Sn,Pb; M″=Si,Ge)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jehle, Michael; Dürr, Ines; Fink, Saskia

The new mixed tetrelides Sr{sub 2}PbGe{sub 2} and Yb{sub 2}SnGe{sub 2}, several mixed Ca/Sr (A{sup II}) germanides A{sub 2}{sup II}(Sn,Pb)Ge{sub 2} and two polymorphs of La{sub 2}InSi{sub 2} represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A{sub 2}M′M{sub 2}{sup ″}(M′=In,Sn,Pb;M″=Si,Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr{sub 2}PbGe{sub 2} (Cmmm, a=402.36(11), b=1542.3(4), c=463.27(10) pm) crystallizes with the Mn{sub 2}AlB{sub 2}-type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. Themore » other borderline case, where only [Ge{sub 2}] dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca{sub 2}SnGe{sub 2} and Yb{sub 2}SnGe{sub 2} (Mo{sub 2}FeB{sub 2}-type; P4/mbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the A{sup II} cations: Ca{sub 0.45}Sr{sub 1.55}PbGe{sub 2} (new structure type; Pbam, a=791.64(5), b=2311.2(2), c=458.53(3) pm) contains planar six-membered chain segments [Ge{sub 6}]. Tetrameric pieces [Ge{sub 4}] are the conspicuous structure elements in Ca{sub 1.16}Sr{sub 0.84}SnGe{sub 2} and La{sub 2}InSi{sub 2} (La{sub 2}InNi{sub 2}-type; Pbam, a=781.01(2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of ’La{sub 2}InSi{sub 2}{sup ′} (exact composition: La{sub 2}In{sub 1.07}Si{sub 1.93}, P4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Si{sub 3}] trimers as cutouts of the planar chains. In all structures the Si/Ge zig-zag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band structure calculations within the FP-LAPW DFT approach together with the Zintl formalism, extended by the presence of hypervalent bonding of the heavier M′ elements, give insight into the chemical bonding of this series of p-block metallides. An analysis of the band structure for the border phases Sr{sub 2}PbGe{sub 2} and Ca{sub 2}SnGe{sub 2} shows the considerable π bonding contributions within the Ge building units, which also become apparent from the short Ge–Ge bond lengths. - Graphical abstract: Example of one of the mixed metallides A{sub 2}(In/Sn/Pb)(Si/Ge){sub 2} with planar Si/Ge zig-zag chain segments of variable lengths. - Highlights: • Mixed metallides A{sub 2}(In/Sn/Pb)(Si/Ge){sub 2} were prepared for A=Ca, Sr, Yb, La. • The structures exhibit planar Si/Ge zig-zag chain segments of variable lengths. • In, Sn and Pb atoms are connecting the Si/Ge anions to planar nets. • Atomic size effects are investigated by the synthesis of mixed Ca/Sr germanides. • Bandstructure calculations indicate Si/Ge–Si/Ge π bonding contributions.« less

Molecular geometry as a source of chemical information. 5. Substituent effect on proton transfer in para-substituted phenol complexes with fluoride--a B3LYP/6-311+G study.

PubMed

Krygowski, Tadeusz M; Szatyłowicz, Halina; Zachara, Joanna E

2005-01-01

The simplified model system [p-X-PhO...H...F](-), where -X are -NO, -NO(2), -CHO, -H, -CH(3), -OCH(3), and -OH, with various O...F distance was used to simulate the wide range of the H-bond strength. Structural changes due to variation of the substituent as well as the H-bond strength are well monitored by the changes in the aromaticity index HOMA and by two empirical measures of the H-bond strength-the (1)H NMR chemical shift of proton involved and the C-O bond length. Changes in H-bonding strengths and the position of proton transfer while shortening the O...F distance are well described by the Hammett equation.

The Distribution of Lightning Channel Lengths in Northern Alabama Thunderstorms

NASA Technical Reports Server (NTRS)

Peterson, H. S.; Koshak, W. J.

2010-01-01

Lightning is well known to be a major source of tropospheric NOx, and in most cases is the dominant natural source (Huntreiser et al 1998, Jourdain and Hauglustaine 2001). Production of NOx by a segment of a lightning channel is a function of channel segment energy density and channel segment altitude. A first estimate of NOx production by a lightning flash can be found by multiplying production per segment [typically 104 J/m; Hill (1979)] by the total length of the flash s channel. The purpose of this study is to determine average channel length for lightning flashes near NALMA in 2008, and to compare average channel length of ground flashes to the average channel length of cloud flashes.

Influence of electric field on the hydrogen bond network of methanol.

PubMed

Suresh, S J; Prabhu, Arun Laxman; Arora, Abhinav

2007-04-07

The understanding of the structure of hydrogen (H) bonding liquids in electric (E) fields is important in the context of several areas of research, such as electrochemistry, surface science, and thermodynamics of electrolyte solutions. We had earlier presented a general thermodynamic framework for this purpose, and had shown that the application of E field enhances H-bond interactions among water molecules. The present investigation with methanol suggests a different result-the H-bond structure, as indicated by the average number of H bonds per molecule, goes through a maxima with increasing field strength. This result is explained based on the symmetry in the location of the H-bonding sites in the two types of molecules.

Electrochemical reduction of carbon fluorine bond in 4-fluorobenzonitrile Mechanistic analysis employing Marcus Hush quadratic activation-driving force relation

NASA Astrophysics Data System (ADS)

Muthukrishnan, A.; Sangaranarayanan, M. V.

2007-10-01

The reduction of carbon-fluorine bond in 4-fluorobenzonitrile in acetonitrile as the solvent, is analyzed using convolution potential sweep voltammetry and the dependence of the transfer coefficient on potential is investigated within the framework of Marcus-Hush quadratic activation-driving force theory. The validity of stepwise mechanism is inferred from solvent reorganization energy estimates as well as bond length calculations using B3LYP/6-31g(d) method. A novel method of estimating the standard reduction potential of the 4-fluorobenzonitrile in acetonitrile is proposed.

Stereoselective heterocycle synthesis through oxidative carbon-hydrogen bond activation.

PubMed

Liu, Lei; Floreancig, Paul E

2010-01-01

Heterocycles are ubiquitous structures in both drugs and natural products, and efficient methods for their construction are being pursued constantly. Carbon-hydrogen bond activation offers numerous advantages for the synthesis of heterocycles with respect to minimizing the length of synthetic routes and reducing waste. As interest in chiral medicinal leads increases, stereoselective methods for heterocycle synthesis must be developed. The use of carbon-hydrogen bond activation reactions for stereoselective heterocycle synthesis has produced a range of creative transformations that provide a wide array of structural motifs, selected examples of which are described in this review.

Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the potts model.

PubMed

Jacobsen, J L; Saleur, H

2008-02-29

We determine exactly the probability distribution of the number N_(c) of valence bonds connecting a subsystem of length L>1 to the rest of the system in the ground state of the XXX antiferromagnetic spin chain. This provides, in particular, the asymptotic behavior of the valence-bond entanglement entropy S_(VB)=N_(c)ln2=4ln2/pi(2)lnL disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/3lnL. Our results generalize to the Q-state Potts model.

Zero-point corrections for isotropic coupling constants for cyclohexadienyl radical, C₆H₇ and C₆H₆Mu: beyond the bond length change approximation.

PubMed

Hudson, Bruce S; Chafetz, Suzanne K

2013-04-25

Zero-point vibrational level averaging for electron spin resonance (ESR) and muon spin resonance (µSR) hyperfine coupling constants (HFCCs) are computed for H and Mu isotopomers of the cyclohexadienyl radical. A local mode approximation previously developed for computation of the effect of replacement of H by D on ¹³C-NMR chemical shifts is used. DFT methods are used to compute the change in energy and HFCCs when the geometry is changed from the equilibrium values for the stretch and both bend degrees of freedom. This variation is then averaged over the probability distribution for each degree of freedom. The method is tested using data for the methylene group of C₆H₇, cyclohexadienyl radical and its Mu analog. Good agreement is found for the difference between the HFCCs for Mu and H of CHMu and that for H of CHMu and CH₂ of the parent radical methylene group. All three of these HFCCs are the same in the absence of the zero point average, a one-parameter fit of the static HFCC, a(0), can be computed. That value, 45.2 Gauss, is compared to the results of several fixed geometry electronic structure computations. The HFCC values for the ortho, meta and para H atoms are then discussed.

A unified bond theory, probabilistic meso-scale modeling, and experimental validation of deformed steel rebar in normal strength concrete

NASA Astrophysics Data System (ADS)

Wu, Chenglin

Bond between deformed rebar and concrete is affected by rebar deformation pattern, concrete properties, concrete confinement, and rebar-concrete interfacial properties. Two distinct groups of bond models were traditionally developed based on the dominant effects of concrete splitting and near-interface shear-off failures. Their accuracy highly depended upon the test data sets selected in analysis and calibration. In this study, a unified bond model is proposed and developed based on an analogy to the indentation problem around the rib front of deformed rebar. This mechanics-based model can take into account the combined effect of concrete splitting and interface shear-off failures, resulting in average bond strengths for all practical scenarios. To understand the fracture process associated with bond failure, a probabilistic meso-scale model of concrete is proposed and its sensitivity to interface and confinement strengths are investigated. Both the mechanical and finite element models are validated with the available test data sets and are superior to existing models in prediction of average bond strength (< 6% error) and crack spacing (< 6% error). The validated bond model is applied to derive various interrelations among concrete crushing, concrete splitting, interfacial behavior, and the rib spacing-to-height ratio of deformed rebar. It can accurately predict the transition of failure modes from concrete splitting to rebar pullout and predict the effect of rebar surface characteristics as the rib spacing-to-height ratio increases. Based on the unified theory, a global bond model is proposed and developed by introducing bond-slip laws, and validated with testing of concrete beams with spliced reinforcement, achieving a load capacity prediction error of less than 26%. The optimal rebar parameters and concrete cover in structural designs can be derived from this study.

A modification in the technique of computing average lengths from the scales of fishes

USGS Publications Warehouse

Van Oosten, John

1953-01-01

In virtually all the studies that employ scales, otollths, or bony structures to obtain the growth history of fishes, it has been the custom to compute lengths for each individual fish and from these data obtain the average growth rates for any particular group. This method involves a considerable amount of mathematical manipulation, time, and effort. Theoretically it should be possible to obtain the same information simply by averaging the scale measurements for each year of life and the length of the fish employed and computing the average lengths from these data. This method would eliminate all calculations for individual fish. Although Van Oosten (1929: 338) pointed out many years ago the validity of this method of computation, his statements apparently have been overlooked by subsequent investigators.

Bioremediation Using Dehaloperoxidase

DTIC Science & Technology

2011-02-01

distal pocket. The Fe—O bond length of 2.2 Å in the wild-type structure presented here is consistent with a chemical bond, while the longer distance in...130, 2128-2129 10.1021/ja0772952 CCC: $40.75 © 2008 American Chemical Society determination of the deuteron nuclei coupling constant. The assignment of...published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Article Characterization of Dehaloperoxidase Compound ES and

(But­oxy­methyl­idene)di­methyl­aza­nium tetra­phenyl­borate aceto­nitrile monosolvate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2014-01-01

In the title solvated salt, C7H16NO+·C24H20B−·C2H3N, the C—N bond lengths in the cation are 1.2831 (19), 1.467 (2) and 1.465 (2) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.2950 (18) Å shows a double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. The two C atoms of the n-butyl group are disordered over the two sites, with refined occupancy ratios of 0.890 (5):0.110 (5) and 0.888 (4):0.112 (4). In the crystal, C—H⋯π inter­actions occur between the methine H atom, H atoms of the –N(CH3)2 and –CH2 groups of the cation, and two of the phenyl rings of the tetra­phenyl­borate anion. The latter inter­action forms an aromatic pocket in which the cation is embedded. Thus, a two-dimensional pattern is created in the ac plane. PMID:24826158

Crystal structure of tetra­aqua­[2-(pyridin-2-yl)-1H-imidazole-κ2 N 2,N 3]iron(II) sulfate

PubMed Central

Setifi, Zouaoui; Setifi, Fatima; Francuski, Bojana M.; Novaković, Sladjana B.; Merazig, Hocine

2015-01-01

In the title compound, [Fe(C8H7N3)(H2O)4]SO4, the central FeII ion is octa­hedrally coordinated by two N atoms from the bidentate 2-(pyridin-2-yl)-1H-imidazole ligand and by four O atoms of the aqua ligands. The largest deviation from the ideal octa­hedral geometry is reflected by the small N—Fe—N bite angle of 76.0 (1)°. The Fe—N coordination bonds have markedly different lengths [2.1361 (17) and 2.243 (2) Å], with the shorter one to the pyrimidine N atom. The four Fe—O coordination bond lengths vary from 2.1191 (18) to 2.1340 (17) Å. In the crystal, the cations and anions are arranged by means of medium-strength O—H⋯O hydrogen bonds into layers parallel to the ab plane. Neighbouring layers further inter­connect by N—H⋯O hydrogen bonds involving the imidazole fragment as donor group to one sulfate O atom as an acceptor. The resulting three-dimensional network is consolidated by C—H⋯O, C—H⋯π and π–π inter­actions. PMID:26029386

Uranyl interaction with the hydrated (001) basal face of gibbsite: a combined theoretical and spectroscopic study.

PubMed

Veilly, Edouard; Roques, Jérôme; Jodin-Caumon, Marie-Camille; Humbert, Bernard; Drot, Romuald; Simoni, Eric

2008-12-28

The sorption of uranyl cations and water molecules on the basal (001) face of gibbsite was studied by combining vibrational and fluorescence spectroscopies together with density functional theory (DFT) computations. Both the calculated and experimental values of O-H bond lengths for the gibbsite bulk are in good agreement. In the second part, water sorption with this surface was studied to take into account the influence of hydration with respect to the uranyl adsorption. The computed water configurations agreed with previously published molecular dynamics studies. The uranyl adsorption in acidic media was followed by time-resolved laser-induced fluorescence spectroscopy and Raman spectrometry measurements. The existence of only one kind of adsorption site for the uranyl cation was then indicated in good agreement with the DFT calculations. The computation of the uranyl adsorption has been performed by means of a bidentate interaction with two surface oxygen atoms. The optimized structures displayed strong hydrogen bonds between the surface and the -yl oxygen of uranyl. The uranium-surface bond strength depends on the protonation state of the surface oxygen atoms. The calculated U-O(surface) bond lengths range between 2.1-2.2 and 2.6-2.7 A for the nonprotonated and protonated surface O atoms, respectively.

Size-induced changes of structural and ferromagnetic properties in La1-xSrxMnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Hintze, Cornelia E.; Fuchs, Dirk; Merz, Michael; Amari, Houari; Kübel, Christian; Huang, Meng-Jie; Powell, Annie; v. Löhneysen, Hilbert

2017-06-01

La1-xSrxMnO3 nanocrystals were grown using a microemulsion approach with different water-to-surfactant ratios Rw resulting in diameters between 20 and 40 nm. The variation of Rw entails a variation in the Sr concentrations between x = 0.35 and 0.50. This technique allows the controlled growth of structurally well-defined nanoparticles using the same calcination conditions. With decreasing particle size, the unit-cell volume increases together with the Mn-O bond length, while the Mn-O-Mn bond angle was found to decrease. The size-dependent change of structural properties is possibly related to surface effects or disorder. With the decrease in particle size, the ferromagnetic ordering temperature TC decreases significantly by up to 20%. The reduction of TC can be well understood with respect to the structural changes: the increase of Mn-O bond length and the decrease of Mn-O-Mn bond angle weaken the double-exchange coupling and hence reduce T C . In addition the intrinsic finite-size effect reduces T C . The observed size-induced change of magnetic properties may allow for a controlled manipulation of magnetism in La1-xSrxMnO3 nanoparticles by varying the particle size.

Does the 4f-shell contribute to bonding in tetravalent lanthanide halides?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Wen-Xin; School of Chemistry and Chemical Engineering, Ningxia University, 750015 Yinchuan; Xu, Wei

2014-12-28

Lanthanide tetrahalide molecules LnX{sub 4} (Ln = Ce, Pr, Tb; X = F, Cl, Br, I) have been investigated by density functional theory at the levels of the relativistic Zero Order Regular Approximation and the relativistic energy-consistent pseudopotentials, using frozen small- and medium-cores. The calculated bond lengths and vibrational frequencies are close to the experimental data. Our calculations indicate 4f shell contributions to bonding in LnX{sub 4}, in particular for the early lanthanides, which show significant overlap between the Ln 4f-shell and the halogen np-shells. The 4f shells contribute to Ln-X bonding in LnX{sub 4} about one third more thanmore » in LnX{sub 3}.« less

Anharmonic Potential Constants and Their Dependence Upon Bond Length

DOE R&D Accomplishments Database

Herschbach, D. R.; Laurie, V. W.

1961-01-01

Empirical study of cubic and quartic vibrational force constants for diatomic molecules shows them to be approximately exponential functions of internuclear distance. A family of curves is obtained, determined by the location of the bonded atoms in rows of the periodic table. Displacements between successive curves correspond closely to those in Badger's rule for quadratic force constants (for which the parameters are redetermined to accord with all data now available). Constants for excited electronic and ionic states appear on practically the same curves as those for the ground states. Predictions based on the diatomic correlations agree with the available cubic constants for bond stretching in polyatomic molecules, regardless of the type of bonding involved. Implications of these regularities are discussed. (auth)

Controlling formation of single-molecule junctions by electrochemical reduction of diazonium terminal groups.

PubMed

Hines, Thomas; Díez-Pérez, Ismael; Nakamura, Hisao; Shimazaki, Tomomi; Asai, Yoshihiro; Tao, Nongjian

2013-03-06

We report controlling the formation of single-molecule junctions by means of electrochemically reducing two axialdiazonium terminal groups on a molecule, thereby producing direct Au-C covalent bonds in situ between the molecule and gold electrodes. We report a yield enhancement in molecular junction formation as the electrochemical potential of both junction electrodes approach the reduction potential of the diazonium terminal groups. Step length analysis shows that the molecular junction is significantly more stable, and can be pulled over a longer distance than a comparable junction created with amine anchoring bonds. The stability of the junction is explained by the calculated lower binding energy associated with the direct Au-C bond compared with the Au-N bond.

Observation of Vacancies, Faults, and Superstructures in Ln5Mo2O12 (Ln = La, Y, and Lu) Compounds with Direct Mo-Mo Bonding.

PubMed

Colabello, Diane M; Sobalvarro, Elizabeth M; Sheckelton, John P; Neuefeind, Joerg C; McQueen, Tyrel M; Khalifah, Peter G

2017-11-06

Among oxide compounds with direct metal-metal bonding, the Y 5 Mo 2 O 12 (A 5 B 2 O 12 ) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B 2 O 10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal-metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal-metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal-metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln 5 Mo 2 O 12 (Ln = La-Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo 2 O 10 and LaO 6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1-2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La 5 Mo 2 O 11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. This represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.

Molecular structural property and potential energy dependence on nonequilibrium-thermodynamic state point of liquid n-hexadecane under shear.

PubMed

Tseng, Huan-Chang; Chang, Rong-Yeu; Wu, Jiann-Shing

2011-01-28

Extensive computer experiments have been conducted in order to shed light on the macroscopic shear flow behavior of liquid n-hexadecane fluid under isobaric-isothermal conditions through the nonequilibrium molecular dynamic methodology. With respect to shear rates, the accompanying variations in structural properties of the fluid span the microscopic range of understanding from the intrinsic to extrinsic characteristics. As drawn from the average value of bond length and bond angle, the distribution of dihedral angle, and the radius distribution function of intramolecular and intermolecular van der Waals distances, these intrinsic structures change with hardness, except in the situation of extreme shear rates. The shear-induced variation of thermodynamic state curve along with the shear rate studied is shown to consist of both the quasiequilibrium state plateau and the nonequilibrium-thermodynamic state slope. Significantly, the occurrence of nonequilibrium-thermodynamic state behavior is attributed to variations in molecular potential energies, which include bond stretching, bond bending, bond torsion, and intra- and intermolecular van der Waals interactions. To unfold the physical representation of extrinsic structural deformation, under the aggressive influence of a shear flow field, the molecular dimension and appearance can be directly described via the squared radius of gyration and the sphericity angle, R(g)(2) and ϕ, respectively. In addition, a specific orientational order S(x) defines the alignment of the molecules with the flow direction of the x-axis. As a result, at low shear rates, the overall molecules are slightly stretched and shaped in a manner that is increasingly ellipsoidal. Simultaneously, there is an obvious enhancement in the order. In contrast to high shear rates, the molecules spontaneously shrink themselves with a decreased value of R(g)(2), while their shape and order barely vary with an infinite value of ϕ and S(x). It is important to note that under different temperatures and pressures, these three parameters are integrated within a molecular description in response to thermodynamic state variable of density and rheological material function of shear viscosity.

Observation of Vacancies, Faults, and Superstructures in Ln 5Mo 2O 12 (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

DOE PAGES

Colabello, Diane M.; Sobalvarro, Elizabeth M.; Sheckelton, John P.; ...

2017-10-26

Among oxide compounds with direct metal–metal bonding, the Y 5Mo 2O 12 (A 5B 2O 12) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B 2O 10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal–metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal–metal bonding have integer oxidation states resulting from the lifting of orbital degeneracymore » typically induced by the metal–metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln 5Mo 2O 12 (Ln = La–Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown in this paper that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo 2O 10 and LaO 6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1–2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La 5Mo 2O 11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. Finally, this represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.« less

Observation of Vacancies, Faults, and Superstructures in Ln 5Mo 2O 12 (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colabello, Diane M.; Sobalvarro, Elizabeth M.; Sheckelton, John P.

Among oxide compounds with direct metal–metal bonding, the Y 5Mo 2O 12 (A 5B 2O 12) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B 2O 10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal–metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal–metal bonding have integer oxidation states resulting from the lifting of orbital degeneracymore » typically induced by the metal–metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln 5Mo 2O 12 (Ln = La–Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown in this paper that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo 2O 10 and LaO 6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1–2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La 5Mo 2O 11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. Finally, this represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.« less

Charge Disproportionation in Tetragonal La 2MoO 5 , a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

DOE PAGES

Colabello, Diane M.; Camino, Fernando E.; Huq, Ashfia; ...

2014-12-31

The structure of the novel compound La 2MoO 5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.0568(2) Å and with Z = 8. It consists of equal proportions of bioctahedral (Mo 2O 10) and square prismatic (Mo 2O 8) dimers, both of which contain direct Mo-Mo bonds and are arranged in 1D chains. The Mo-Mo bond length in the Mo 2O 10dimers is 2.684(8) Å, while there are two types of Mo 2O 8 dimers with Mo-Mo bonds lengthsmore » of 2.22(2) and 2.28(2) Å. Although the average Mo oxidation state in La 2MoO 5 is 4+, the very different Mo-Mo distances reflect the fact that the Mo 2O 10 dimers contain only Mo5+ (d(1)), while the prismatic Mo2O8 dimers only contain Mo 3+ (d 3), a result directly confirmed by density function theory calculations. This is due to the complete disproportionation of Mo 4+, a phenomenon which has not previously been observed in solid-state compounds. La 2MoO 5 is diamagnetic, behavior which is not expected for a nonmetallic transition-metal oxide whose cation sites have an odd number of d-electrons. The resistivity displays the Arrhenius-type activated behavior expected for a semiconductor with a band gap of 0.5 eV, exhibiting an unusually small transport gap relative to other diamagnetic oxides. Diffuse reflectance studies indicate that La 2MoO 5 is a rare example of a stable oxide semiconductor with strong infrared absorbance. Lastly, we show that the d-orbital splitting associated with the Mo 2O 8 and Mo 2O 10 dimeric units can be rationalized using simple molecular orbital bonding concepts.« less

Critical effects of alkyl chain length on fibril structures in benzene-trans(RR)- or (SS)-N,N'-alkanoyl-1,2-diaminocyclohexane gels.

PubMed

Sato, Hisako; Nakae, Takahiro; Morimoto, Kazuya; Tamura, Kenji

2012-02-28

Vibrational circular dichroism (VCD) spectra were recorded on benzene-d(6) gels formed by chiral low molecular mass gelators (LMGs), trans(RR)- or trans(SS)-N,N'-alkanoyl-1,2-diaminocyclohexane (denoted by RR-C(n) or SS-C(n), respectively; n = the number of carbon atoms in an introduced alkanoyl group). Attention was focused on the effects of alkyl chain length on the structures of the gels. When n was changed from 6 to 12, the signs of the coupled peaks around 1550 cm(-1) in the VCD spectra, which were assigned to the symmetric and asymmetric C=O stretching vibrations from the higher to lower wavenumber, respectively, critically depended on the alkyl chain length. In the case of RR-C(n), for example, the signs of the couplet were plus and minus for n = 8, 9, 10 and 12, while the signs of the same couplet were reversed for n = 6 and 7. The conformations of LMGs in fibrils were determined by comparing the observed IR and VCD spectra with those calculated for a monomeric molecule. The observed reversal of signs in the C=O couplet was rationalized in terms of the different modes of hydrogen bonding. In the case of C(8), C(9), C(10) and C(12), gelator molecules were stacked with their cyclohexyl rings in parallel, forming double anti-parallel chains of intermolecular hydrogen bonds using two pairs of >NH and >C=O groups. In case of C(6) and C(7), gelator molecules were stacked through a single chain of intermolecular hydrogen bonds using a pair of >NH and >C=O groups. The remaining pair of >NH and >C=O groups formed an intramolecular hydrogen bond.

Velocity modulation spectroscopy of molecular ions II: The millimeter/submillimeter-wave spectrum of TiF + ( X3Φr)

NASA Astrophysics Data System (ADS)

Halfen, D. T.; Ziurys, L. M.

2006-11-01

The pure rotational spectrum of the molecular ion TiF + in its 3Φr ground state has been measured in the range 327-542 GHz using millimeter-wave direct absorption techniques combined with velocity modulation spectroscopy. TiF + was made in an AC discharge from a mixture of TiCl 4, F 2 in He, and argon. Ten transitions of this ion were recorded. In every transition, fluorine hyperfine interactions, as well as the fine structure splittings, were resolved. The fine structure pattern was found to be regular with almost equal spacing in frequency between the three spin components, in contrast to TiCl +, which is perturbed in the ground state. The data were fit with a case ( a) Hamiltonian and rotational, fine structure, and hyperfine constants were determined. The bond length established for TiF +, r0 = 1.7775 Å, was found to be shorter than that of TiF, r0 = 1.8342 Å—also established from mm-wave data. The hyperfine parameters determined are consistent with a δ1π1 electron configuration with the electrons primarily located on the titanium nucleus. The nuclear spin-orbit constant a indicates that the unpaired electrons are closer to the fluorine nucleus in TiF + relative to TiF, as expected with the decrease in bond length for the ion. The shorter bond distance is thought to arise from increased charge on the titanium nucleus as a result of a Ti 2+F - configuration. A similar decrease in bond length was found for TiCl + relative to TiCl.

Effect of cutting temperature on hardness of SiC and diamond in the nano-cutting process of monocrystalline silicon

NASA Astrophysics Data System (ADS)

Wang, Jiachun; Li, Yuntao; Liu, Xiaoxuan; Lv, Maoqiang

2016-10-01

In the process of cutting silicon by natural diamond tools, groove wear happens on the flank face of cutting tool frequently.Scholars believe that one of the wear reasons is mechanical scratching effect by hard particles like SiC. To reveal the mechanical scratching mechanism, it is essential to study changes in the mechanical properties of hard particles and diamond, especially the effect of cutting temperature on hardness of diamond and hard particles. Molecular dynamics (MD) model that contact-zone temperature between tool and workpiece was calculated by dividing zone while nano-cutting monocrystalline silicon was established, cutting temperature values in different regions were computed as the simulation was carried out.On this basis, the models of molecular dynamics simulation of SiC and diamond were established separately with setting the initial temperature to room temperature. The laws of length change of C-C bond and Si-C bond varing with increase of simulation temperature were studied. And drawing on predecessors' research on theoretical calculation of hardness of covalent crystals and the relationship between crystal valence electron density and bond length, the curves that the hardness of diamond and SiC varing with bond length were obtained. The effect of temperature on the hardness was calculated. Results show that, local cutting temperature can reach 1300K.The rise in cutting temperature leaded to a decrease in the diamond local atomic clusters hardness,SiC local atomic clusters hardness increased. As the cutting temperature was more than 1100K,diamond began to soften, the local clusters hardness was less than that of SiC.

In-Situ Adhesive Bond Assessment

DTIC Science & Technology

2010-08-01

a list of AR coefficients. The use of the VCC metric , with appropriate extreme value statistics models as described in detail below, allowed...equivalent PZT with thickness equal to the MFC electrode spacing , a , and length equal to the MFC net electrode length, (p le), where p is the number of ...particular geometry of the test specimen and with MFC patches affixed to the

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singer, Jared W.; Yazaydin, A. O.; Kirkpatrick, Robert J.

Amorphous calcium carbonate (ACC) is a metastable precursor to crystalline CaCO{sub 3} phases that precipitates by aggregation of ion pairs and prenucleation clusters. We use {sup 43}Ca solid-state NMR spectroscopy to probe the local structure and transformation of ACC synthesized from seawater-like solutions with and without Mg{sup 2+} and computational molecular dynamics (MD) simulations to provide more detailed molecular-scale understanding of the ACC structure. The {sup 43}Ca NMR spectra of ACC collected immediately after synthesis consist of broad, featureless resonances with Gaussian line shapes (FWHH = 27.6 {+-} 1 ppm) that do not depend on Mg{sup 2+} or H{sub 2}Omore » content. A correlation between {sup 43}Ca isotropic chemical shifts and mean Ca-O bond distances for crystalline hydrous and anhydrous calcium carbonate phases indicates indistinguishable maximum mean Ca-O bond lengths of {approx}2.45 {angstrom} for all our samples. This value is near the upper end of the published Ca-O bond distance range for biogenic and synthetic ACCs obtained by Ca-X-ray absorption spectroscopy. It is slightly smaller than the values from the structural model of Mgfree ACC by Goodwin et al. obtained from reverse Monte Carlo (RMC) modeling of X-ray scattering data and our own computational molecular dynamics (MD) simulation based on this model. An MD simulation starting with the atomic positions of the Goodwin et al. RMC model using the force field of Raiteri and Gale shows significant structural reorganization during the simulation and that the interconnected carbonate/water-rich channels in the Goodwin et al. model shrink in size over the 2 ns simulation time. The distribution of polyhedrally averaged Ca-O bond distances from the MD simulation is in good agreement with the {sup 43}Ca NMR peak shape, suggesting that local structural disorder dominates the experimental line width of ACC.« less

Ultrafast Coulomb explosion of a diiodomethane molecule induced by an X-ray free-electron laser pulse.

PubMed

Takanashi, Tsukasa; Nakamura, Kosuke; Kukk, Edwin; Motomura, Koji; Fukuzawa, Hironobu; Nagaya, Kiyonobu; Wada, Shin-Ichi; Kumagai, Yoshiaki; Iablonskyi, Denys; Ito, Yuta; Sakakibara, Yuta; You, Daehyun; Nishiyama, Toshiyuki; Asa, Kazuki; Sato, Yuhiro; Umemoto, Takayuki; Kariyazono, Kango; Ochiai, Kohei; Kanno, Manabu; Yamazaki, Kaoru; Kooser, Kuno; Nicolas, Christophe; Miron, Catalin; Asavei, Theodor; Neagu, Liviu; Schöffler, Markus; Kastirke, Gregor; Liu, Xiao-Jing; Rudenko, Artem; Owada, Shigeki; Katayama, Tetsuo; Togashi, Tadashi; Tono, Kensuke; Yabashi, Makina; Kono, Hirohiko; Ueda, Kiyoshi

2017-08-02

Coulomb explosion of diiodomethane CH 2 I 2 molecules irradiated by ultrashort and intense X-ray pulses from SACLA, the Japanese X-ray free electron laser facility, was investigated by multi-ion coincidence measurements and self-consistent charge density-functional-based tight-binding (SCC-DFTB) simulations. The diiodomethane molecule, containing two heavy-atom X-ray absorbing sites, exhibits a rather different charge generation and nuclear motion dynamics compared to iodomethane CH 3 I with only a single heavy atom, as studied earlier. We focus on charge creation and distribution in CH 2 I 2 in comparison to CH 3 I. The release of kinetic energy into atomic ion fragments is also studied by comparing SCC-DFTB simulations with the experiment. Compared to earlier simulations, several key enhancements are made, such as the introduction of a bond axis recoil model, where vibrational energy generated during charge creation processes induces only bond stretching or shrinking. We also propose an analytical Coulomb energy partition model to extract the essential mechanism of Coulomb explosion of molecules from the computed and the experimentally measured kinetic energies of fragment atomic ions by partitioning each pair Coulomb interaction energy into two ions of the pair under the constraint of momentum conservation. Effective internuclear distances assigned to individual fragment ions at the critical moment of the Coulomb explosion are then estimated from the average kinetic energies of the ions. We demonstrate, with good agreement between the experiment and the SCC-DFTB simulation, how the more heavily charged iodine fragments and their interplay define the characteristic features of the Coulomb explosion of CH 2 I 2 . The present study also confirms earlier findings concerning the magnitude of bond elongation in the ultrashort X-ray pulse duration, showing that structural damage to all but C-H bonds does not develop to a noticeable degree in the pulse length of ∼10 fs.

Reliable bonding using indium-based solders

NASA Astrophysics Data System (ADS)

Cheong, Jongpil; Goyal, Abhijat; Tadigadapa, Srinivas; Rahn, Christopher

2004-01-01

Low temperature bonding techniques with high bond strengths and reliability are required for the fabrication and packaging of MEMS devices. Indium and indium-tin based bonding processes are explored for the fabrication of a flextensional MEMS actuator, which requires the integration of lead zirconate titanate (PZT) substrate with a silicon micromachined structure at low temperatures. The developed technique can be used either for wafer or chip level bonding. The lithographic steps used for the patterning and delineation of the seed layer limit the resolution of this technique. Using this technique, reliable bonds were achieved at a temperature of 200°C. The bonds yielded an average tensile strength of 5.41 MPa and 7.38 MPa for samples using indium and indium-tin alloy solders as the intermediate bonding layers respectively. The bonds (with line width of 100 microns) showed hermetic sealing capability of better than 10-11 mbar-l/s when tested using a commercial helium leak tester.

Reliable bonding using indium-based solders

NASA Astrophysics Data System (ADS)

Cheong, Jongpil; Goyal, Abhijat; Tadigadapa, Srinivas; Rahn, Christopher

2003-12-01

Low temperature bonding techniques with high bond strengths and reliability are required for the fabrication and packaging of MEMS devices. Indium and indium-tin based bonding processes are explored for the fabrication of a flextensional MEMS actuator, which requires the integration of lead zirconate titanate (PZT) substrate with a silicon micromachined structure at low temperatures. The developed technique can be used either for wafer or chip level bonding. The lithographic steps used for the patterning and delineation of the seed layer limit the resolution of this technique. Using this technique, reliable bonds were achieved at a temperature of 200°C. The bonds yielded an average tensile strength of 5.41 MPa and 7.38 MPa for samples using indium and indium-tin alloy solders as the intermediate bonding layers respectively. The bonds (with line width of 100 microns) showed hermetic sealing capability of better than 10-11 mbar-l/s when tested using a commercial helium leak tester.

Can You Party Your Way to Better Health? A Propensity Score Analysis of Block Parties and Health

PubMed Central

Dean, Lorraine T.; Hillier, Amy; Chau-Glendinning, Hang; Subramanian, SV; Williams, David R.; Kawachi, Ichiro

2015-01-01

While other indicators of social capital have been linked to health, the role of block parties on health in Black neighborhoods and on Black residents is understudied. Block parties exhibit several features of bonding social capital and are present in nearly 90% of Philadelphia’s predominantly Black neighborhoods. This analysis investigated: (1) whether or not block parties are an indicator of bonding social capital in Black neighborhoods; (2) the degree to which block parties might be related to self-rated health in the ways that other bonding social indicators are related to health; and (3) whether or not block parties are associated with average self-rated health for Black residents particularly. Using census tract-level indicators of bonding social capital and records of block parties from 2003 to 2008 for 381 Philadelphia neighborhoods (defined by census tracts), an ecological-level propensity score was generated to assess the propensity for a block party, adjusting for population demographics, neighborhood characteristics, neighborhood resources and violent crime. Results indicate that in multivariable regression, block parties were associated with increased bonding social capital in Black neighborhoods; however, the calculation of the average effect of the treatment on the treated (ATT) within each propensity score strata showed no effect of block parties on average self-rated health for Black residents. Block parties may be an indicator of bonding social capital in Philadelphia’s predominantly Black neighborhoods, but this analysis did not show a direct association between block parties and self-rated health for Black residents. Further research should consider what other health outcomes or behaviors block parties may be related to and how interventionists can leverage block parties for health promotion. PMID:26117555

Significantly shorter Fe–S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase

DOE PAGES

Krest, Courtney M.; Silakov, Alexey; Rittle, Jonathan; ...

2015-08-03

Cytochrome P450 (P450) and chloroperoxidase (CPO) are thiolate-ligated haem proteins that catalyse the activation of carbon hydrogen bonds. The principal intermediate in these reactions is a ferryl radical species called compound I. P450 compound I (P450-I) is significantly more reactive than CPO-I, which only cleaves activated C–H bonds. In this paper, to provide insight into the differing reactivities of these intermediates, we examined CPO-I and P450-I using variable-temperature Mössbauer and X-ray absorption spectroscopies. These measurements indicate that the Fe–S bond is significantly shorter in P450-I than in CPO-I. This difference in Fe–S bond lengths can be understood in terms ofmore » variations in the hydrogen-bonding patterns within the ‘cys-pocket’ (a portion of the proximal helix that encircles the thiolate ligand). Weaker hydrogen bonding in P450-I results in a shorter Fe–S bond, which enables greater electron donation from the axial thiolate ligand. Finally, this observation may in part explain P450's greater propensity for C–H bond activation.« less

Padded self-adhesive strap immobilization following newborn bladder exstrophy closure: the Utah straps.

PubMed

Wallis, M Chad; Oottamasathien, Siam; Wicher, Chris; Hadley, David; Snow, Brent W; Cartwright, Patrick C

2013-12-01

Several methods have been described for immobilization of the pelvis following bladder exstrophy closure, which can be challenging to manage. We hypothesized that immobilization can be significantly simplified using a modified mermaid wrap with padded Velcro® straps around the thigh and lower leg. We retrospectively reviewed all patients who underwent bladder exstrophy closure in the newborn period at our institution from 1990 through 2010. Patients with cloacal exstrophy and those who underwent delayed closure due to other medical conditions were excluded. We collected data on closure technique, length of stay and complications of the primary closure as outcomes. A total of 20 boys and 7 girls underwent closure of classic bladder exstrophy. Followup ranged from 2 to 22 years. Seven boys underwent complete primary repair and 13 underwent staged repair. All patients had the legs stabilized with a modified wrap technique using 2 lengths of Velcro straps lined with self-adhering open cell foam pads for 3 weeks. Complications of exstrophy closure included bladder dehiscence in 1 patient (4%) and incisional hernia in 2 (7%). Following complete primary repair urethrocutaneous fistula developed in 2 patients and urethral stricture in 2. Average length of stay for patients without significant prematurity was 15 days. Padded Velcro strap immobilization simplifies postoperative care, provides secure fixation, decreases length of stay, and enables parents to hold and bond with the child shortly after repair. We advocate this simplified technique, which can be applied with a rate of complications that is comparable to other procedures. Copyright © 2013 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2015-01-01

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

Electrostatically Embedded Many-Body Expansion for Neutral and Charged Metalloenzyme Model Systems.

PubMed

Kurbanov, Elbek K; Leverentz, Hannah R; Truhlar, Donald G; Amin, Elizabeth A

2012-01-10

The electrostatically embedded many-body (EE-MB) method has proven accurate for calculating cohesive and conformational energies in clusters, and it has recently been extended to obtain bond dissociation energies for metal-ligand bonds in positively charged inorganic coordination complexes. In the present paper, we present four key guidelines that maximize the accuracy and efficiency of EE-MB calculations for metal centers. Then, following these guidelines, we show that the EE-MB method can also perform well for bond dissociation energies in a variety of neutral and negatively charged inorganic coordination systems representing metalloenzyme active sites, including a model of the catalytic site of the zinc-bearing anthrax toxin lethal factor, a popular target for drug development. In particular, we find that the electrostatically embedded three-body (EE-3B) method is able to reproduce conventionally calculated bond-breaking energies in a series of pentacoordinate and hexacoordinate zinc-containing systems with an average absolute error (averaged over 25 cases) of only 0.98 kcal/mol.

Consequences of theory level choice evaluated with new tools from QTAIM and the stress tensor for a dipeptide conformer

NASA Astrophysics Data System (ADS)

Li, Jiahui; Xu, Tianlv; Ping, Yang; van Mourik, Tanja; Früchtl, Herbert; Kirk, Steven R.; Jenkins, Samantha

2018-03-01

QTAIM and the stress tensor were used to provide a detailed analysis of the topology of the molecular graph, BCP and bond-path properties, including the new introduced helicity length H, of a Tyr-Gly dipeptide conformer subjected to a torsion with four levels of theory; MP2, M06-2X, B3LYP-D3 and B3LYP and a modest-sized basis set, 6-31+G(d). Structural effects and bonding properties are quantified and reflect differences in the BSSE and lack of inclusion of dispersion effects in the B3LYP calculations. The helicity length H demonstrated that MP2 produced a unique response to the torsion suggesting future use as a diagnostic tool.

Determination of the crystal structure and composition of Li6Be4OH12 by the stochastic method.

PubMed Central

Pauling, L

1990-01-01

Because of the failure to find a structure for LiBeH3 with a face-centered unit cube with edge 5.09 A, the x-ray powder pattern has been reindexed for a body-centered unit cube with edge 7.24 A. Application of the principles of structural chemistry leads to the formula Li6Be4OH12 and to a structure involving Be4OH12 clusters formed by 4 BeOH3 tetrahedra with their O corner shared, Be--(H,O) bond length 1.59 A, and with the clusters joined to one another by Li with octahedral or rectangular-planar coordination of 6 H or 4 H, Li-H bond lengths about 1.92 A. PMID:11607052

Determination of the crystal structure and composition of Li6Be4OH12 by the stochastic method.

PubMed

Pauling, L

1990-01-01

Because of the failure to find a structure for LiBeH3 with a face-centered unit cube with edge 5.09 A, the x-ray powder pattern has been reindexed for a body-centered unit cube with edge 7.24 A. Application of the principles of structural chemistry leads to the formula Li6Be4OH12 and to a structure involving Be4OH12 clusters formed by 4 BeOH3 tetrahedra with their O corner shared, Be--(H,O) bond length 1.59 A, and with the clusters joined to one another by Li with octahedral or rectangular-planar coordination of 6 H or 4 H, Li-H bond lengths about 1.92 A.

Study on the Connecting Length of CFRP

NASA Astrophysics Data System (ADS)

Liu, Xiongfei; Li, Yue; Li, Zhanguo

2018-05-01

The paper studied the varying mode of shear stress in the connecting zone of CFRP. Using epoxy resin (EP) as bond material, performance of specimens with different connecting length of CFRP was tested to obtain the conclusion. CFRP-confined concrete column was tested subsequently to verify the conclusion. The results show that: (1) The binding properties of modified epoxy resin with CFRP is good; (2) As the connecting length increased, the ultimate tensile strength of CFRP increased as well in the range of the experiment parameters; (3) Tensile strength of CFRP can reach the ultimate strength when the connecting length is 90mm;(4) The connecting length of 90mm of CFRP meet the reinforcement requirements.

The role of amino acid side chains in stabilizing dipeptides: the laser ablation Fourier transform microwave spectrum of Ac-Val-NH2.

PubMed

León, I; Alonso, E R; Mata, S; Cabezas, C; Rodríguez, M A; Grabow, J-U; Alonso, J L

2017-09-20

The steric effects imposed by the isopropyl group of valine in the conformational stabilization of the capped dipeptide N-acetyl-l-valinamide (Ac-Val-NH 2 ) have been studied by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy. The rotational and quadrupole coupling constants of the two 14 N nuclei determined in this work show that this dipeptide exists as a mixture of C 7 and C 5 conformers in the supersonic expansion. The conformers are stabilized by a C[double bond, length as m-dash]OH-N intramolecular hydrogen bond closing a seven- or a five-membered ring, respectively. The observation of both conformers is in good agreement with previous results on the related dipeptides containing different residues, confirming that the polarity/non-polarity of the side chains of the amino acid is responsible for the conformational locking/unlocking. The voluminous isopropyl group is not able to prevent the less stable C 5 conformer from forming but it destabilizes the C[double bond, length as m-dash]OH-N interaction.

Crystal structure of cis-aqua­bis­(2,2′-bi­pyridine-κ2 N,N′)chlorido­chromium(III) tetra­chlorido­zincate determined from synchrotron data

PubMed Central

Moon, Dohyun; Ryoo, Keon Sang; Choi, Jong-Ha

2016-01-01

The structure of the title salt, [CrCl(C10H8N2)2(H2O)][ZnCl4], has been determined from synchrotron data. The CrIII ion is coordinated by four N atoms from two 2,2′-bi­pyridine (bipy) ligands, one O atom from a water mol­ecule and a chloride anion in a cis arrangement, displaying a distorted octa­hedral geometry. The tetra­hedral [ZnCl4]2− anion is slightly distorted owing to its involvement in O—H⋯Cl hydrogen bonding with the coordinating water mol­ecule. The Cr—N(bipy) bond lengths are in the range 2.0485 (13)–2.0632 (12) Å, while the Cr—Cl and Cr—(OH2) bond lengths are 2.2732 (6) and 1.9876 (12) Å, respectively. In the crystal, mol­ecules are stacked along the a axis. PMID:27006786

Bis{2-meth­oxy-6-[tris­(hydroxy­meth­yl)methyl­imino­meth­yl]phenolato-κ3 O,N,O′}manganese(II) dimethanol solvate hemihydrate

PubMed Central

Zhang, Xiutang; Wei, Peihai; Dou, Jianmin; Li, Bin; Hu, Bo

2009-01-01

In the title complex, [Mn(C12H16NO5)2]·2CH3OH·0.5H2O, the MnII atom has a distorted octa­hedral coordination geometry in which two N atoms from two 6-meth­oxy-2-[tris­(hydroxy­meth­yl)methyl­imino­meth­yl]phenolate ligands adopt a trans arrangement. The Mn—O(H) bonds (mean length 2.134 Å) are significantly longer than the Mn—O and Mn—N bonds (mean length 2.011 and 2.027 Å, respectively), and the dihedral angle between the mean planes through the aromatic rings of the two ligands is 76.8 (1)°. A complex network of O—H⋯O hydrogen bonds is formed between the complexes and the uncoordinated methanol and water mol­ecules. The C and O atoms of one C—OH group are disordered with equal occupancies. PMID:21582076

Modeling the intermolecular interactions: molecular structure of N-3-hydroxyphenyl-4-methoxybenzamide.

PubMed

Karabulut, Sedat; Namli, Hilmi; Kurtaran, Raif; Yildirim, Leyla Tatar; Leszczynski, Jerzy

2014-03-01

The title compound, N-3-hydroxyphenyl-4-methoxybenzamide (3) was prepared by the acylation reaction of 3-aminophenol (1) and 4-metoxybenzoylchloride (2) in THF and characterized by ¹H NMR, ¹³C NMR and elemental analysis. Molecular structure of the crystal was determined by single crystal X-ray diffraction and DFT calculations. 3 crystallizes in monoclinic P2₁/c space group. The influence of intermolecular interactions (dimerization and crystal packing) on molecular geometry has been evaluated by calculations performed for three different models; monomer (3), dimer (4) and dimer with added unit cell contacts (5). Molecular structure of 3, 4 and 5 was optimized by applying B3LYP method with 6-31G+(d,p) basis set in gas phase and compared with X-ray crystallographic data including bond lengths, bond angles and selected dihedral angles. It has been concluded that although the crystal packing and dimerization have a minor effect on bond lengths and angles, however, these interactions are important for the dihedral angles and the rotational conformation of aromatic rings. Copyright © 2013 Elsevier Inc. All rights reserved.

Spin-Orbit Effect on the Molecular Properties of TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4): A Density Functional Theory and Ab Initio Study.

PubMed

Moon, Jiwon; Kim, Joonghan

2016-09-29

Density functional theory (DFT) and ab initio calculations, including spin-orbit coupling (SOC), were performed to investigate the spin-orbit (SO) effect on the molecular properties of tellurium halides, TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4). SOC elongates the Te-X bond and slightly reduces the vibrational frequencies. Consideration of SOC leads to better agreement with experimental values. Møller-Plesset second-order perturbation theory (MP2) seriously underestimates the Te-X bond lengths. In contrast, B3LYP significantly overestimates them. SO-PBE0 and multireference configuration interactions with the Davidson correction (MRCI+Q), which include SOC via a state-interaction approach, give the Te-I bond length of TeI2 that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI4 is unlikely to be stable. The use of PBE0 including SOC is strongly recommended for predicting the molecular properties of Te-containing compounds.

Ab initio study on the structural and electronic properties of water surrounding a multifunctional nanoprobe

NASA Astrophysics Data System (ADS)

Xia, Xiuli; Shao, Yuanzhi

2018-02-01

We report the magneto-electric behavior of a dual-modality biomedical nanoprobe, a ternary nanosystem consisting of gold and gadolinia clusters and water molecules, with the effect of both nanoclusters on the structural and electronic properties of water. The hydrogen-oxygen bond lengths and angles as well as electronic charges of water molecules surrounding both nanoclusters were calculated using Hubbard U corrected density functional theory aided by molecular dynamics approach. The calculations reveal existence of a magneto-electric interaction between gold and gadolinium oxide nanoclusters, which influences the physical properties of surrounding water remarkably. A broader (narrower) distribution of Hsbnd O bond lengths (Hsbnd Osbnd H bond angles) was observed at the presence of either gold or gadolinia nanoclusters. The presence of Gd6O9 cluster leads to the larger charges of neighbour oxygen atoms. The distribution of oxygen atom charges becomes border when both Gd6O9 and Au13 clusters coexist. Ab initio calculation provides a feasible approach to explore the most essential interactions among functional components of a multimodal nanoprobe applied in aqueous environment.

Variation in leader length of bitterbrush

Treesearch

Richard L. Hubbard; David. Dunaway

1958-01-01

The estimation of herbage production and· utilization in browse plants has been a problem for many years. Most range technicians have simply estimated the average length of twigs or leaders. then expressed use by deer and livestock as a percentage thereof based on the estimated average length left after grazing. Riordan used this method on mountain mahogany (

Analysis of the bonding in XH3Cu+ (XB, Al, Ga) complexes

NASA Astrophysics Data System (ADS)

Corral, Inés; Mó, Otilia; Yáñez, Manuel

High-level density functional theory (DFT) calculations on XH3Cu+ (XB, Al, Ga) complexes show that the attachment of the metal cation to the base takes place through agostic-type interactions. These interactions that can be viewed as dative bonds from the σXH bonding orbitals of the base toward low-lying empty 4s orbitals of the metal cation, and back-donations from the lone pairs of the metal into the σ *XH antibonding orbitals of the neutral, are particularly favored when the XH bonds have a high X+δH-δ polarity. Accordingly, the AlH3 and GaH3 Cu+ binding energies are very similar, but much larger than that of BH3. Depopulation of the σXH bonding orbital and the concomitant population of the σ *XH antibonding orbital involved in the agostic interaction result in a significant weakening of the corresponding XH linkages, whose bond length increases and whose stretching frequency appears red-shifted.

3-[Bis(dimethyl­amino)­methyl­ene]-1,1-diphenyl­urea

PubMed Central

Tiritiris, Ioannis

2012-01-01

In the title compound, C18H22N4O, the C=N and C—N bond lengths in the CN3 unit are 1.3179 (11), 1.3551 (11) and 1.3737 (11) Å, indicating double- and single-bond character, respectively. The N—C—N angles are 115.91 (8), 118.20 (8) and 125.69 (8), showing a deviation of the CN3 plane from an ideal trigonal–planar geometry. The bonds between the N atoms and the terminal C-methyl groups all have values close to a typical single bond [1.4529 (12)–1.4624 (12) Å]. The dihedral angle between the phenyl rings is 79.63 (4)°. In the crystal, the mol­ecules are connected via weak C—H⋯O hydrogen bonds, generating chains along [100]. PMID:23284417

Linking microscopic and macroscopic response in disordered solids

NASA Astrophysics Data System (ADS)

Hexner, Daniel; Liu, Andrea J.; Nagel, Sidney R.

2018-06-01

The modulus of a rigid network of harmonic springs depends on the sum of the energies in each of the bonds due to an applied distortion such as compression in the case of the bulk modulus or shear in the case of the shear modulus. However, the distortion need not be global. Here we introduce a local modulus, Li, associated with changing the equilibrium length of a single bond, i , in the network. We show that Li is useful for understanding many aspects of the mechanical response of the entire system. It allows an efficient computation of how the removal of any bond changes the global properties such as the bulk and shear moduli. Furthermore, it allows a prediction of the distribution of these changes and clarifies why the changes of these two moduli due to removal of a bond are uncorrelated; these are the essential ingredients necessary for the efficient manipulation of network properties by bond removal.

Natural bond orbital analysis, electronic structure, non-linear properties and vibrational spectral analysis of L-histidinium bromide monohydrate: a density functional theory.

PubMed

Sajan, D; Joseph, Lynnette; Vijayan, N; Karabacak, M

2011-10-15

The spectroscopic properties of the crystallized nonlinear optical molecule L-histidinium bromide monohydrate (abbreviated as L-HBr-mh) have been recorded and analyzed by FT-IR, FT-Raman and UV techniques. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal were calculated with the help of density functional theory computations. The optimized geometric bond lengths and bond angles obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The natural bond orbital (NBO) analysis confirms the occurrence of strong intra and intermolecular N-H⋯O hydrogen bonding. Copyright © 2011 Elsevier B.V. All rights reserved.

Polyarylether composition and membrane

DOEpatents

Hung, Joyce; Brunelle, Daniel Joseph; Harmon, Marianne Elisabeth; Moore, David Roger; Stone, Joshua James; Zhou, Hongyi; Suriano, Joseph Anthony

2010-11-09

A composition including a polyarylether copolymer is provided. The copolymer includes a polyarylether backbone; and a sulfonated oligomeric group bonded to the polyarylether suitable for use as a cation conducting membrane. Method of bonding a sulfonated oligomeric group to the polyarylether backbone to form a polyarylether copolymer. The membrane may be formed from the polyarylether copolymer composition. The chain length of the sulfonated oligomeric group may be controlled to affect or control the ion conductivity of the membrane.

Topology of charge density of flucytosine and related molecules and characteristics of their bond charge distributions.

PubMed

Murgich, Juan; Franco, Héctor J; San-Blas, Gioconda

2006-08-24

The molecular charge distribution of flucytosine (4-amino-5-fluoro-2-pyrimidone), uracil, 5-fluorouracil, and thymine was studied by means of density functional theory calculations (DFT). The resulting distributions were analyzed by means of the atoms in molecules (AIM) theory. Bonds were characterized through vectors formed with the charge density value, its Laplacian, and the bond ellipticity calculated at the bond critical point (BCP). Within each set of C=O, C-H, and N-H bonds, these vectors showed little dispersion. C-C bonds formed three different subsets, one with a significant degree of double bonding, a second corresponding to single bonds with a finite ellipticity produced by hyperconjugation, and a third one formed by a pure single bond. In N-C bonds, a decrease in bond length (an increase in double bond character) was not reflected as an increase in their ellipticity, as in all C-C bonds studied. It was also found that substitution influenced the N-C, C-O, and C-C bond ellipticity much more than density and its Laplacian at the BCP. The Laplacian of charge density pointed to the existence of both bonding and nonbonding maxima in the valence shell charge concentration of N, O, and F, while only bonding ones were found for the C atoms. The nonbonding maxima related to the sites for electrophilic attack and H bonding in O and N, while sites of nucleophilic attack were suggested by the holes in the valence shell of the C atoms of the carbonyl groups.

Cellulosic nanowhiskers. Theory and application of light scattering from polydisperse spheroids in the Rayleigh-Gans-Debye regime.

PubMed

Braun, Birgit; Dorgan, John R; Chandler, John P

2008-04-01

Mathematical treatment of light scattering within the Rayleigh-Gans-Debye limit for spheroids with polydispersity in both length and diameter is developed and experimentally tested using cellulosic nanowhiskers (CNW). Polydispersity indices are obtained by fitting the theoretical formfactor to experimental data. Good agreement is achieved using a polydispersity of 2.3 for the length, independent of the type of acid used. Diameter polydispersities are 2.1 and 3.0 for sulfuric and hydrochloric acids, respectively. These polydispersities allow the determination of average dimensions from the z-average mean-square radius (z) and the weight-average molecular weight (M w) easily obtained from Berry plots. For cotton linter hydrolyzed by hydrochloric acid, the average length and diameter are 244 and 22 nm. This compares to average length and diameter of 272 and 13 nm for sulfuric acid. This study establishes a new light-scattering methodology as a quick and robust tool for size characterization of polydisperse spheroidal nanoparticles.

History-dependence of muscle slack length following contraction and stretch in the human vastus lateralis.

PubMed

Stubbs, Peter W; Walsh, Lee D; D'Souza, Arkiev; Héroux, Martin E; Bolsterlee, Bart; Gandevia, Simon C; Herbert, Robert D

2018-06-01

In reduced muscle preparations, the slack length and passive stiffness of muscle fibres have been shown to be influenced by previous muscle contraction or stretch. In human muscles, such behaviours have been inferred from measures of muscle force, joint stiffness and reflex magnitudes and latencies. Using ultrasound imaging, we directly observed that isometric contraction of the vastus lateralis muscle at short lengths reduces the slack lengths of the muscle-tendon unit and muscle fascicles. The effect is apparent 60 s after the contraction. These observations imply that muscle contraction at short lengths causes the formation of bonds which reduce the effective length of structures that generate passive tension in muscles. In reduced muscle preparations, stretch and muscle contraction change the properties of relaxed muscle fibres. In humans, effects of stretch and contraction on properties of relaxed muscles have been inferred from measurements of time taken to develop force, joint stiffness and reflex latencies. The current study used ultrasound imaging to directly observe the effects of stretch and contraction on muscle-tendon slack length and fascicle slack length of the human vastus lateralis muscle in vivo. The muscle was conditioned by (a) strong isometric contractions at long muscle-tendon lengths, (b) strong isometric contractions at short muscle-tendon lengths, (c) weak isometric contractions at long muscle-tendon lengths and (d) slow stretches. One minute after conditioning, ultrasound images were acquired from the relaxed muscle as it was slowly lengthened through its physiological range. The ultrasound image sequences were used to identify muscle-tendon slack angles and fascicle slack lengths. Contraction at short muscle-tendon lengths caused a mean 13.5 degree (95% CI 11.8-15.0 degree) shift in the muscle-tendon slack angle towards shorter muscle-tendon lengths, and a mean 5 mm (95% CI 2-8 mm) reduction in fascicle slack length, compared to the other conditions. A supplementary experiment showed the effect could be demonstrated if the muscle was conditioned by contraction at short lengths but not if the relaxed muscle was held at short lengths, confirming the role of muscle contraction. These observations imply that muscle contraction at short lengths causes the formation of bonds which reduce the effective length of structures that generate passive tension in muscles. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Rotational dynamics of coumarin-153 and 4-aminophthalimide in 1-ethyl-3-methylimidazolium alkylsulfate ionic liquids: effect of alkyl chain length on the rotational dynamics.

PubMed

Das, Sudhir Kumar; Sarkar, Moloy

2012-01-12

Rotational dynamics of two neutral organic solutes, coumarin-153 (C-153) and 4-aminophthalimide (AP), with only the latter having hydrogen-bond-donating ability, has been investigated in a series of 1-ethyl-3-methylimidazolium alkyl sulfate ionic liquids as a function of temperature. The ionic liquids differ only in the length of the linear alkyl side chain (alkyl = ethyl, butyl, hexyl, and octyl) on the anionic moiety. The present study has been undertaken to examine the role of alkyl side chains on the rotational dynamics of the two solutes in these ionic liquids. Analysis of the results using Stokes-Einstein-Debye hydrodynamic theory indicates that the rotational dynamics of C-153 lies between the stick and slip boundary condition in the ethyl analogue and finally reaches subslip condition as in case of the octyl substituent. The observed rotational behavior of C-153 has been explained on the basis of an increase in the size of the solvent, which offers lower friction for solute rotation. On the other hand, AP shows superstick behavior in the ethyl system and exceeds the stick limit in the octyl derivative. Superstick behavior of AP has been attributed to the specific hydrogen-bonding interaction between AP and the sulfate moiety. Proton NMR investigation confirms the hydrogen-bonding interaction between the N-H hydrogen of AP and the ionic liquid. The decrease in rotational coupling constant values for AP with increasing length of alkyl side chains has been attributed to the decrease in the solute-solvent-specific interaction with an increase in the alkyl side chain length on the sulfate moiety.

Influence of chain length and double bond on the aqueous behavior of choline carboxylate soaps.

PubMed

Rengstl, Doris; Diat, Olivier; Klein, Regina; Kunz, Werner

2013-02-26

In preceding studies, we demonstrated that choline carboxylates ChC(m) with alkyl chain lengths of m = 12 - 18 are highly water-soluble (for m = 12, soluble up to 93 wt % soap and 0 °C). In addition, choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concentration, the following phases were found: micellar phase (L(1)), discontinuous cubic phase (I(1)' and I(1)"), hexagonal phase (H(1)), bicontinuous cubic phase (V(1)), and lamellar phase (L(α)). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aqueous phase behavior of choline soaps with C(8) and C(10) chain-lengths (choline octanoate and choline decanoate) and with a C(18) chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologues mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar solution phase. In addition, choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better solubility in water and a decrease of the solubilization temperature. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar solution phase in the binary phase diagram of choline octanoate viscosity and conductivity measurements were also carried out.

LED Die-Bonded on the Ag/Cu Substrate by a Sn-BiZn-Sn Bonding System

NASA Astrophysics Data System (ADS)

Tang, Y. K.; Hsu, Y. C.; Lin, E. J.; Hu, Y. J.; Liu, C. Y.

2016-12-01

In this study, light emitting diode (LED) chips were die-bonded on a Ag/Cu substrate by a Sn-BixZn-Sn bonding system. A high die-bonding strength is successfully achieved by using a Sn-BixZn-Sn ternary system. At the bonding interface, there is observed a Bi-segregation phenomenon. This Bi-segregation phenomenon solves the problems of the brittle layer-type Bi at the joint interface. Our shear test results show that the bonding interface with Bi-segregation enhances the shear strength of the LED die-bonding joints. The Bi-0.3Zn and Bi-0.5Zn die-bonding cases have the best shear strength among all die-bonding systems. In addition, we investigate the atomic depth profile of the deposited Bi-xZn layer by evaporating Bi-xZn E-gun alloy sources. The initial Zn content of the deposited Bi-Zn alloy layers are much higher than the average Zn content in the deposited Bi-Zn layers.

Shear Bond Strengths and Morphological Evaluation of Filled and Unfilled Adhesive Interfaces to Enamel and Dentine

PubMed Central

Mortazavi, Vajihesadat; Fathi, Mohammadhosein; Ataei, Ebrahim; Khodaeian, Niloufar; Askari, Navid

2012-01-01

In this laboratory study shear bond strengths of three filled and one unfilled adhesive systems to enamel and dentine were compared. Forty-eight extracted intact noncarious human mandibular molars were randomly assigned to two groups of 24 one for bonding to enamel and the other for bonding to dentine. Buccal and lingual surfaces of each tooth were randomly assigned for application of each one of filled (Prime & Bond NT (PBNT), Optibond Solo Plus (OBSP), and Clearfil SE Bond (CSEB)) and unfilled (Single Bond (SB)) adhesive systems (n = 12). A universal resin composite was placed into the translucent plastic cylinders (3 mm in diameter and 2 mm in length) and seated against the enamel and dentine surfaces and polymerized for 40 seconds. Shear bond strength was determined using a universal testing machine, and the results were statistically analyzed using two-way ANOVA, one-way ANOVA, t-test, and Tukey HSD post hoc test with a 5% level of significance.There were no statistically significant differences in bond strength between the adhesive systems in enamel, but CSEB and SB exhibited significantly higher and lower bond strength to dentine, respectively, than the other tested adhesive systems while there were no statistically significant differences between PBNT and OBSP. PMID:23209471

On the interpretation of domain averaged Fermi hole analyses of correlated wavefunctions.

PubMed

Francisco, E; Martín Pendás, A; Costales, Aurora

2014-03-14

Few methods allow for a physically sound analysis of chemical bonds in cases where electron correlation may be a relevant factor. The domain averaged Fermi hole (DAFH) analysis, a tool firstly proposed by Robert Ponec in the 1990's to provide interpretations of the chemical bonding existing between two fragments Ω and Ω' that divide the real space exhaustively, is one of them. This method allows for a partition of the delocalization index or bond order between Ω and Ω' into one electron contributions, but the chemical interpretation of its parameters has been firmly established only for single determinant wavefunctions. In this paper we report a general interpretation based on the concept of excluded density that is also valid for correlated descriptions. Both analytical models and actual computations on a set of simple molecules (H2, N2, LiH, and CO) are discussed, and a classification of the possible DAFH situations is presented. Our results show that this kind of analysis may reveal several correlated assisted bonding patterns that might be difficult to detect using other methods. In agreement with previous knowledge, we find that the effective bond order in covalent links decreases due to localization of electrons driven by Coulomb correlation.

Reaction pathways of proton transfer in hydrogen-bonded phenol-carboxylate complexes explored by combined UV-vis and NMR spectroscopy.

PubMed

Koeppe, Benjamin; Tolstoy, Peter M; Limbach, Hans-Heinrich

2011-05-25

Combined low-temperature NMR/UV-vis spectroscopy (UVNMR), where optical and NMR spectra are measured in the NMR spectrometer under the same conditions, has been set up and applied to the study of H-bonded anions A··H··X(-) (AH = 1-(13)C-2-chloro-4-nitrophenol, X(-) = 15 carboxylic acid anions, 5 phenolates, Cl(-), Br(-), I(-), and BF(4)(-)). In this series, H is shifted from A to X, modeling the proton-transfer pathway. The (1)H and (13)C chemical shifts and the H/D isotope effects on the latter provide information about averaged H-bond geometries. At the same time, red shifts of the π-π* UV-vis absorption bands are observed which correlate with the averaged H-bond geometries. However, on the UV-vis time scale, different tautomeric states and solvent configurations are in slow exchange. The combined data sets indicate that the proton transfer starts with a H-bond compression and a displacement of the proton toward the H-bond center, involving single-well configurations A-H···X(-). In the strong H-bond regime, coexisting tautomers A··H···X(-) and A(-)···H··X are observed by UV. Their geometries and statistical weights change continuously when the basicity of X(-) is increased. Finally, again a series of single-well structures of the type A(-)···H-X is observed. Interestingly, the UV-vis absorption bands are broadened inhomogeneously because of a distribution of H-bond geometries arising from different solvent configurations.

Role of Short-Range Chemical Ordering in (GaN) 1–x (ZnO) x for Photodriven Oxygen Evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Dennis P.; Neuefeind, Joerg C.; Koczkur, Kallum M.

(GaN)1–x(ZnO)x (GZNO) is capable of visible-light driven water splitting, but its bandgap at x ≤ 0.15 (>2.7 eV) results in poor visible-light absorption. Unfortunately, methods to narrow its bandgap by incorporating higher ZnO concentrations are accompanied by extensive Urbach tailing near the absorption-edge, which is indicative of structural disorder or chemical inhomogeneities. We evaluated whether this disorder is intrinsic to the bond-length distribution in GZNO or is a result of defects introduced from the loss of Zn during nitridation. Here, the synthesis of GZNO derived from layered double hydroxide (LDH) precursors is described which minimizes Zn loss and chemical inhomogeneitiesmore » and enhances visible-light absorption. The average and local atomic structures of LDH-derived GZNO were investigated using X-ray and neutron scattering and are correlated with their oxygen evolution rates. An isotope-contrasted neutron-scattering experiment was conducted in conjunction with reverse Monte Carlo (RMC) simulations. We showed that a bond-valence bias in the RMC refinements reproduces the short-range ordering (SRO) observed in structure refinements using isotope-contrasted neutron data. The findings suggest that positional disorder of cation–anion pairs in GZNO partially arises from SRO and influences local bond relaxations. Furthermore, particle-based oxygen evolution reactions (OERs) in AgNO3 solution reveal that the crystallite size of GZNO correlates more than positional disorder with oxygen evolution rate. These findings illustrate the importance of examining the local structure of multinary photocatalysts to identify dominant factors in particulate-based photodriven oxygen evolution.« less

Fesbnd X (X = B, N) binary compounds: First-principles calculations of electronic structures, theoretic hardness and magnetic properties

NASA Astrophysics Data System (ADS)

Hui, Liangliang; Xie, Zhongjing; Li, Chunmei; Chen, Zhi-Qian

2018-04-01

The first-principles calculations are implemented to investigate the electronic structures, theoretic hardness and magnetic properties of iron borides and nitrides with four different crystal systems containing hexagonal (FeB2, ε-Fe3N), tetragonal (Fe2B, α″-Fe16N2), orthorhombic (α-FeB, θ-Fe3B, ζ-Fe2N), and cubic (zb-FeN, rs-FeN, γ‧-Fe4N, γ-Fe23B6) phase. The calculated lattice parameters using RPBE meet well with the experimental results. The cohesive energy and formation enthalpy values indicate the Fesbnd X (X = B, N) binary compounds are thermodynamically stable. Meanwhile, the h-FeB2 is most difficult phase for experimental synthesis among these interstitial compounds. Moreover, magnetic properties are discussed and show that the mean magnetic moments of o-Fe3B and c-Fe23B6 with the values of 2.227 μB and 2.256 μB per iron atom are approaching to that of pure iron (2.32 μB) while the c-Fe4N and t-Fe16N2 with the values of 2.51 and 2.48 μB are beyond that of pure α-Fe. The c-FeN phase shows nonmagnetic in zb-style while rs-type shows antiferromagnetic with a value of 2.52 μB. Furthermore, the average bonding length and Mulliken population combined with electronic structures are also analysed in this paper which provide that strong Fesbnd X and Xsbnd X covalent bonds are responsible for high hardness. Finally, the theoretic hardness of Xsbnd X, Fesbnd X and Fesbnd Fe bonds is predicted by semi empirical hardness theory.

The GAAS metagenomic tool and its estimations of viral and microbial average genome size in four major biomes.

PubMed

Angly, Florent E; Willner, Dana; Prieto-Davó, Alejandra; Edwards, Robert A; Schmieder, Robert; Vega-Thurber, Rebecca; Antonopoulos, Dionysios A; Barott, Katie; Cottrell, Matthew T; Desnues, Christelle; Dinsdale, Elizabeth A; Furlan, Mike; Haynes, Matthew; Henn, Matthew R; Hu, Yongfei; Kirchman, David L; McDole, Tracey; McPherson, John D; Meyer, Folker; Miller, R Michael; Mundt, Egbert; Naviaux, Robert K; Rodriguez-Mueller, Beltran; Stevens, Rick; Wegley, Linda; Zhang, Lixin; Zhu, Baoli; Rohwer, Forest

2009-12-01

Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses; however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS), a complete software package that provides improved estimates of community composition and average genome length for metagenomes in both textual and graphical formats. GAAS implements a novel methodology to control for sampling bias via length normalization, to adjust for multiple BLAST similarities by similarity weighting, and to select significant similarities using relative alignment lengths. In benchmark tests, the GAAS method was robust to both high percentages of unknown sequences and to variations in metagenomic sequence read lengths. Re-analysis of the Sargasso Sea virome using GAAS indicated that standard methodologies for metagenomic analysis may dramatically underestimate the abundance and importance of organisms with small genomes in environmental systems. Using GAAS, we conducted a meta-analysis of microbial and viral average genome lengths in over 150 metagenomes from four biomes to determine whether genome lengths vary consistently between and within biomes, and between microbial and viral communities from the same environment. Significant differences between biomes and within aquatic sub-biomes (oceans, hypersaline systems, freshwater, and microbialites) suggested that average genome length is a fundamental property of environments driven by factors at the sub-biome level. The behavior of paired viral and microbial metagenomes from the same environment indicated that microbial and viral average genome sizes are independent of each other, but indicative of community responses to stressors and environmental conditions.

26 CFR 1.142(a)(5)-1 - Exempt facility bonds: Sewage facilities.

Code of Federal Regulations, 2011 CFR

2011-04-01

...; however, for property treating wastewater reasonably expected to have an average daily raw wasteload... the extent the treatment is for wastewater having an average daily raw wasteload concentration of BOD...—(i) Exception to BOD limit. A facility treating wastewater with an average daily raw wasteload...

26 CFR 1.142(a)(5)-1 - Exempt facility bonds: Sewage facilities.

Code of Federal Regulations, 2012 CFR

2012-04-01

...; however, for property treating wastewater reasonably expected to have an average daily raw wasteload... the extent the treatment is for wastewater having an average daily raw wasteload concentration of BOD...—(i) Exception to BOD limit. A facility treating wastewater with an average daily raw wasteload...

26 CFR 1.142(a)(5)-1 - Exempt facility bonds: Sewage facilities.

Code of Federal Regulations, 2014 CFR

2014-04-01

...; however, for property treating wastewater reasonably expected to have an average daily raw wasteload... the extent the treatment is for wastewater having an average daily raw wasteload concentration of BOD...—(i) Exception to BOD limit. A facility treating wastewater with an average daily raw wasteload...

26 CFR 1.142(a)(5)-1 - Exempt facility bonds: Sewage facilities.

Code of Federal Regulations, 2013 CFR

2013-04-01

...; however, for property treating wastewater reasonably expected to have an average daily raw wasteload... the extent the treatment is for wastewater having an average daily raw wasteload concentration of BOD...—(i) Exception to BOD limit. A facility treating wastewater with an average daily raw wasteload...

26 CFR 1.142(a)(5)-1 - Exempt facility bonds: Sewage facilities.

Code of Federal Regulations, 2010 CFR

2010-04-01

...; however, for property treating wastewater reasonably expected to have an average daily raw wasteload... the extent the treatment is for wastewater having an average daily raw wasteload concentration of BOD...—(i) Exception to BOD limit. A facility treating wastewater with an average daily raw wasteload...

Chemical intuition for high thermoelectric performance in monolayer black phosphorus, α-arsenene and aW-antimonene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Bo; Zhang, Hao; Shao, Hezhu

Identifying materials with intrinsically high thermoelectric performance remains a challenge even with the aid of a high-throughput search. Here, using a chemically intuitive approach based on the bond-orbital theory, three anisotropic 2D group-V materials (monolayer black phosphorus, α-arsenene, and aW-antimonene) are identified as candidates for high thermoelectric energy conversion efficiency. Concepts, such as bond length, bond angle, and bond strength, are used to explain the trends in their electronic properties, such as the band gap and the effective mass. Our first principles calculations confirm that high carrier mobilities and large Seebeck coefficients can be obtained at the same time inmore » these materials, due to complex Fermi surfaces originating from the anisotropic structures. An intuitive understanding of how the bonding character affects phonon transport is also provided with emphasis on the importance of bonding strength and bond anharmonicity. High thermoelectric performance is observed in these materials. In conclusion, our approach provides a powerful tool to identify new thermoelectric materials and evaluate their transport properties.« less

Chemical intuition for high thermoelectric performance in monolayer black phosphorus, α-arsenene and aW-antimonene

DOE PAGES

Peng, Bo; Zhang, Hao; Shao, Hezhu; ...

2017-11-21

Identifying materials with intrinsically high thermoelectric performance remains a challenge even with the aid of a high-throughput search. Here, using a chemically intuitive approach based on the bond-orbital theory, three anisotropic 2D group-V materials (monolayer black phosphorus, α-arsenene, and aW-antimonene) are identified as candidates for high thermoelectric energy conversion efficiency. Concepts, such as bond length, bond angle, and bond strength, are used to explain the trends in their electronic properties, such as the band gap and the effective mass. Our first principles calculations confirm that high carrier mobilities and large Seebeck coefficients can be obtained at the same time inmore » these materials, due to complex Fermi surfaces originating from the anisotropic structures. An intuitive understanding of how the bonding character affects phonon transport is also provided with emphasis on the importance of bonding strength and bond anharmonicity. High thermoelectric performance is observed in these materials. In conclusion, our approach provides a powerful tool to identify new thermoelectric materials and evaluate their transport properties.« less

Crystal structure details of La- and Bi-substituted hydroxyapatites: Evidence for LaO{sup +} and BiO{sup +} with a very short metal–oxygen bond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazin, Pavel E., E-mail: kazin@inorg.chem.msu.ru; Pogosova, Mariam A.; Trusov, Lev A.

Crystal structures of substituted apatites with general formula Ca{sub 10−x}M{sub x}(PO{sub 4}){sub 6}(OH{sub 1−δ}){sub 2−x}O{sub x}, where M=La, Bi, 0≤x<2, were refined using high-resolution X-ray powder diffraction patterns. Individual positions for Ca{sup 2+} and M{sup 3+}-ions localized near Ca2-site were determined. The M{sup 3+}-ion was found shifted toward the hexagonal channel center with respect to the Ca{sup 2+}-ion, forming very short bond with the intrachannel O{sup 2−}, while leaving considerably longer distances to other oxygen atoms, which suggested the existence of a MO{sup +} ion. Distinct bands of stretching M–O modes were observed in the Raman and FT-IR spectra ofmore » the compounds. The bond lengths for BiO{sup +} and LaO{sup +} were estimated to be 2.05(1) and 2.09(1) Å correspondingly. The latter was almost 0.3 Å lower than the shortest La–O bond in La{sub 2}O{sub 3}. The realization of such a strong lanthanide–oxygen bond in a crystal lattice could provide a very high axial ligand field and might be implemented to develop high-energy-barrier single-molecule magnets as well as to tune properties of lanthanide-based luminophores. - Graphical abstract: A fragment of the La-for-Ca substituted apatite crystal structure focusing on the La–O bond. - Highlights: • Individual positions in the apatite crystal lattice for a doping atom (La, Bi) and Ca. • The doping atom shifts toward the center of the hexagonal channel. • BiO{sup +} and LaO{sup +} with estimated short bond lengths of 2.05 and 2.09 Å respectively.« less

The Bacillus subtilis Acyl Lipid Desaturase Is a Δ5 Desaturase

PubMed Central

Altabe, Silvia G.; Aguilar, Pablo; Caballero, Gerardo M.; de Mendoza, Diego

2003-01-01

Bacillus subtilis was recently reported to synthesize unsaturated fatty acids (UFAs) with a double bond at positions Δ5, Δ7, and Δ9 (M. H. Weber, W. Klein, L. Muller, U. M. Niess, and M. A. Marahiel, Mol. Microbiol. 39:1321-1329, 2001). Since this finding would have considerable importance in the double-bond positional specificity displayed by the B. subtilis acyl lipid desaturase, we have attempted to confirm this observation. We report that the double bond of UFAs synthesized by B. subtilis is located exclusively at the Δ5 position, regardless of the growth temperature and the length chain of the fatty acids. PMID:12730185

Quantum chemical calculations of Cr2O3/SnO2 using density functional theory method

NASA Astrophysics Data System (ADS)

Jawaher, K. Rackesh; Indirajith, R.; Krishnan, S.; Robert, R.; Das, S. Jerome

2018-03-01

Quantum chemical calculations have been employed to study the molecular effects produced by Cr2O3/SnO2 optimised structure. The theoretical parameters of the transparent conducting metal oxides were calculated using DFT / B3LYP / LANL2DZ method. The optimised bond parameters such as bond lengths, bond angles and dihedral angles were calculated using the same theory. The non-linear optical property of the title compound was calculated using first-order hyperpolarisability calculation. The calculated HOMO-LUMO analysis explains the charge transfer interaction between the molecule. In addition, MEP and Mulliken atomic charges were also calculated and analysed.

A DFT study of pure and lithium doped gold clusters

NASA Astrophysics Data System (ADS)

Rani, Babita

2018-05-01

First principles calculations on Aun and Aun-1Li (n=1-6) clusters are performed to understand the effect of size and composition on their structural and energy parameters. It has been found that binding energy increases continuously with increase in the size of pure Aun and doped Aun-1Li clusters and attains its maximum at n=6. Also, Li doping results in the improvement of relative stabilities of pure gold clusters, owing to higher bond strength (i.e. shorter bond length) of Au- Li bond as compared to Au-Au bonds. Moreover, Aun-1Li clusters are found to be more compact. Structural transformations are observed in case of gold clusters doped with Li atom which may affect their application in the field of catalysis.

Structural model of dioxouranium(VI) with hydrazono ligands.

PubMed

Mubarak, Ahmed T

2005-04-01

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of OUO groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the UO bond distances were calculated. The bond distances of these complexes were also investigated.

Non-covalent synthesis of supermicelles with complex architectures using spatially confined hydrogen-bonding interactions

PubMed Central

Li, Xiaoyu; Gao, Yang; Boott, Charlotte E.; Winnik, Mitchell A.; Manners, Ian

2015-01-01

Nature uses orthogonal interactions over different length scales to construct structures with hierarchical levels of order and provides an important source of inspiration for the creation of synthetic functional materials. Here, we report the programmed assembly of monodisperse cylindrical block comicelle building blocks with crystalline cores to create supermicelles using spatially confined hydrogen-bonding interactions. We also demonstrate that it is possible to further program the self-assembly of these synthetic building blocks into structures of increased complexity by combining hydrogen-bonding interactions with segment solvophobicity. The overall approach offers an efficient, non-covalent synthesis method for the solution-phase fabrication of a range of complex and potentially functional supermicelle architectures in which the crystallization, hydrogen-bonding and solvophobic interactions are combined in an orthogonal manner. PMID:26337527

Structural model of dioxouranium(VI) with hydrazono ligands

NASA Astrophysics Data System (ADS)

Mubarak, Ahmed T.

2005-04-01

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of O sbnd U sbnd O groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the U sbnd O bond distances were calculated. The bond distances of these complexes were also investigated.

Thermodynamic limits on the size and size distribution of nucleic acids synthesized in vitro: the role of pyrophosphate hydrolysis.

PubMed

Peller, L

1977-02-08

The free-energy change of phosphodiester bond formation from nucleoside triphosphates is more favorable than with nucleoside diphosphates as substrates. Base-stacking interactions can make significant contributions to both delta G degrees ' values. Pyrophosphate hydrolysis when it accompanies the former reaction dominates all thermodynamic considerations. Three experimental situations are discussed in which high-molecular-weight polynucleotides are synthesized without a strong driving force for covalent bond formation. For one of these, a kinetic scheme is presented which encompasses an early narrow Poisson distribution of chain lengths with ultimate passage to a disperse equilibrium population of chain sizes. Hydrolytic removal of pyrophosphate expands the time scale for this undesirable process by a factor of 10(9), while it enormously elevates the thermodynamic ceiling for the average degrees of polymerization in the other two examples. The electron micrographically revealed broad size population from an early study of partial replication of a T7 DNA template is found to adhere (fortuitously) to a disperse most probable representation. Some possible origins are examined for the branched structures in this product, as well as in a later investigation of replication of this nucleic acid. The achievement of both very high molecular weights and sharply peaked size distributions in polynucleotides synthesized in vitro will require coupling to inorganic pyrophosphatase action as in vivo.

Laser transmission welding of polylactide to aluminium thin films for applications in the food-packaging industry

NASA Astrophysics Data System (ADS)

Pagano, Nunziante; Campana, Giampaolo; Fiorini, Maurizio; Morelli, Raffaele

2017-06-01

Laser transmission welding is a suitable technology to join thin films of similar or dissimilar materials without any addition of chemical solvents or adhesives. This process represents a very important opportunity in the case of packaging applications (for example in food and pharmaceutical sectors) where the realisation of strong welds by avoiding the contact between the thermal source and the processed materials and, furthermore, without using any third material that could contaminate the contents, is reliable and relevant. The aim of this paper is to prove the feasibility of the laser transmission welding of polylactide to aluminium thin films by means of laser transmission welding through the use of a low power pulsed wave fibre laser. Laser joint samples were realised, analysed by optical microscopy to reveal possible defects and to evaluate the weld width and tested to measure the mechanical tensile strength. An accurate relationship between the joint quality and both the welding speed and the k-factor, which represents the delivered energy per unit length and affects the bonding mechanism at the interface, was determined. The achieved feasibility area is extremely narrow and possible only for the higher value of the average power. The joint tensile strength was proven to be in a proportional relationship with the effective bonded area and reached satisfactory values.

Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds

PubMed Central

Jafri, S. Hassan M.; Löfås, Henrik; Blom, Tobias; Wallner, Andreas; Grigoriev, Anton; Ahuja, Rajeev; Ottosson, Henrik; Leifer, Klaus

2015-01-01

Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with ω-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices. PMID:26395225

A new approach to process control using Instability Index

NASA Astrophysics Data System (ADS)

Weintraub, Jeffrey; Warrick, Scott

2016-03-01

The merits of a robust Statistical Process Control (SPC) methodology have long been established. In response to the numerous SPC rule combinations, processes, and the high cost of containment, the Instability Index (ISTAB) is presented as a tool for managing these complexities. ISTAB focuses limited resources on key issues and provides a window into the stability of manufacturing operations. ISTAB takes advantage of the statistical nature of processes by comparing the observed average run length (OARL) to the expected run length (ARL), resulting in a gap value called the ISTAB index. The ISTAB index has three characteristic behaviors that are indicative of defects in an SPC instance. Case 1: The observed average run length is excessively long relative to expectation. ISTAB > 0 is indicating the possibility that the limits are too wide. Case 2: The observed average run length is consistent with expectation. ISTAB near zero is indicating that the process is stable. Case 3: The observed average run length is inordinately short relative to expectation. ISTAB < 0 is indicating that the limits are too tight, the process is unstable or both. The probability distribution of run length is the basis for establishing an ARL. We demonstrate that the geometric distribution is a good approximation to run length across a wide variety of rule sets. Excessively long run lengths are associated with one kind of defect in an SPC instance; inordinately short run lengths are associated with another. A sampling distribution is introduced as a way to quantify excessively long and inordinately short observed run lengths. This paper provides detailed guidance for action limits on these run lengths. ISTAB as a statistical method of review facilitates automated instability detection. This paper proposes a management system based on ISTAB as an enhancement to more traditional SPC approaches.

26 CFR 1.149(d)-1 - Limitations on advance refundings.

Code of Federal Regulations, 2010 CFR

2010-04-01

...) The yield on all the investments (including investment property and tax-exempt bonds) in the refunding... are invested in tax-exempt bonds and a portion of the proceeds are invested in nonpurpose investments... nonpurpose investments in the refunding escrow, and the weighted average maturity of nonpurpose investments...

Electronegativity and the Bond Triangle

ERIC Educational Resources Information Center

Meek, Terry L.; Garner, Leah D.

2005-01-01

The usefulness of the bond triangle for categorizing compounds of the main-group elements may be extended by the use of weighted average electronegativities to allow distinction between compounds of the same elements with different stoichiometries. In such cases a higher valency for the central atom leads to greater covalent character and the…

78 FR 56842 - Arbitrage Restrictions on Tax-Exempt Bonds

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-16

... working capital. This accounting rule recognizes that sources of funds are fungible and treats bond..., DC 20044. Submissions may be hand delivered to: CC:PA:LPD:PR Monday through Friday between the hours.... Estimated total annual recordkeeping burden: 232 hours. Estimated average annual burden hours per respondent...

Quantum mechanics models of the methanol dimer: OH⋯O hydrogen bonds of β-d-glucose moieties from crystallographic data.

PubMed

Cintrón, Michael Santiago; Johnson, Glenn P; French, Alfred D

2017-04-18

The interaction of two methanol molecules, simplified models of carbohydrates and cellulose, was examined using a variety of quantum mechanics (QM) levels of theory. Energy plots for hydrogen bonding distance (H⋯O) and angle (OH⋯O) were constructed. All but two experimental structures were located in stabilized areas on the vacuum phase energy plots. Each of the 399 models was analyzed with Bader's atoms-in-molecules (AIM) theory, which showed a widespread ability by the dimer models to form OH⋯O hydrogen bonds that have bond paths and Bond Critical Points. Continuum solvation calculations suggest that a portion of the energy-stabilized structures could occur in the presence of water. A survey of the Cambridge Structural Database (CSD) for all donor-acceptor interactions in β-D-glucose moieties examined the similarities and differences among the hydroxyl groups and acetal oxygen atoms that participate in hydrogen bonds. Comparable behavior was observed for the O2H, O3H, O4H, and O6H hydroxyls, acting either as acceptors or donors. Ring O atoms showed distinct hydrogen bonding behavior that favored mid-length hydrogen bonds. Published by Elsevier Ltd.

Accurate gas-phase structure of para-dioxane by fs Raman rotational coherence spectroscopy and ab initio calculations

NASA Astrophysics Data System (ADS)

Den, Takuya; Menzi, Samuel; Frey, Hans-Martin; Leutwyler, Samuel

2017-08-01

p-Dioxane is non-polar, hence its rotational constants cannot be determined by microwave rotational coherence spectroscopy (RCS). We perform high-resolution gas-phase rotational spectroscopy of para-dioxane-h8 and -d8 using femtosecond time-resolved Raman RCS in a gas cell at T = 293 K and in a pulsed supersonic jet at T ˜130 K. The inertial tensor of p-dioxane-h8 is strongly asymmetric, leading to a large number of asymmetry transients in its RCS spectrum. In contrast, the d8-isotopomer is a near-oblate symmetric top that exhibits a much more regular RCS spectrum with few asymmetry transients. Fitting the fs Raman RCS transients of p-dioxane-h8 to an asymmetric-top model yields the ground-state rotational constants A0 = 5084.4(5) MHz, B0 = 4684(1) MHz, C0 = 2744.7(8) MHz, and (A0 + B0)/2 = 4884.5(7) MHz (±1 σ ). The analogous values for p-dioxane-d8 are A0 = 4083(2) MHz, B0 = 3925(4) MHz, C0 = 2347.1(6) MHz, and (A0 + B0)/2 = 4002.4(6) MHz. We determine the molecular structure with a semi-experimental approach involving the highly correlated coupled-cluster singles, doubles and iterated triples method and the cc-pCVXZ basis set series from double- to quadruple-zeta (X = D, T, Q). Combining the calculated vibrationally averaged rotational constants A0c a l c(X ) ,B0c a l c(X ) ,C0c a l c(X ) for increasing basis-set size X with non-linear extrapolation to the experimental constants A0e x p,B0e x p,C0e x p allows to determine the equilibrium ground state structure of p-dioxane. For instance, the equilibrium C-C and C-O bond lengths are re(CC) = 1.5135(3) Å and re(CO) = 1.4168(4) Å, and the four axial C-H bond lengths are 0.008 Å longer than the four equatorial ones. The latter is ascribed to the trans-effect (anomeric effect), i.e., the partial delocalization of the electron lone-pairs on the O atoms that are oriented trans, relative to the axial CH bonds.

A new copper(II) chelate complex with tridentate ligand: Synthesis, crystal and molecular electronic structure of aqua-(diethylenetriamine-N, N‧, N‧‧)-copper(II) sulfate monohydrate and its fire retardant properties

NASA Astrophysics Data System (ADS)

Lavrenyuk, H.; Mykhalichko, O.; Zarychta, B.; Olijnyk, V.; Mykhalichko, B.

2015-09-01

The crystals of a new aqua-(diethylenetriamine-N, N‧, N‧‧)-copper(II) sulfate monohydrate have been synthesized by direct interaction of solid copper(II) sulfate pentahydrate with diethylenetriamine (deta). The crystal structure of [Cu(deta)H2O]SO4ṡH2O (1) has been determined by X-ray diffraction methods at 100 K and characterized using X-ray powder diffraction pattern: space group P 1 bar, a = 7.2819(4), b = 8.4669(4), c = 8.7020(3) Å, α = 83.590(3), β = 89.620(4), γ = 84.946(4)°, Z = 2. The environment of the Cu(II) atom is a distorted, elongated square pyramid which consists of three nitrogen atoms of the deta molecule and oxygen atom of the water molecule in the basal plane of the square pyramid (the average lengths of the in-plane Cu-N and Cu-O bonds are 2.00 Å). The apical position of the coordination polyhedron is occupied by complementary oxygen atom of the sulfate anion (the length of the axial Cu-O bond is 2.421(1) Å). The crystal packing is governed by strong hydrogen bonds of O-H⋯O and N-H⋯O types. The ab initio quantum-chemical calculations have been performed by the restricted Hartree-Fock method with a basis set 6-31∗G using the structural data of [Cu(deta)H2O]SO4ṡH2O. It has been ascertained that the degenerate d-orbitals of the Cu2+ ion split under the co-action of both the square-pyramidal coordination and the chelation. It is significant that visually observed crystals color (blue-violet) of the [Cu(deta)H2O]SO4ṡH2O complex is in good agreement with the calculated value of wavelength of visible light (λ = 5735 Å) which is closely related to the energy of the absorbed photon (Δ = 2.161 eV). Furthermore, the stereo-chemical aspect of influence of the CuSO4 upon combustibility of modified epoxy-amine polymers has been scrutinized.

Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion

NASA Astrophysics Data System (ADS)

Singh, R.; Yadav, R. A.

2014-09-01

Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5sbnd C6 bond length increases and loses its double bond character while the C4sbnd C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled Nsbnd H stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled.

Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion.

PubMed

Singh, R; Yadav, R A

2014-09-15

Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5C6 bond length increases and loses its double bond character while the C4C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled NH stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled. Copyright © 2014 Elsevier B.V. All rights reserved.

Supramolecular structures for determination and identification of the bond lengths in novel uranyl complexes from their infrared spectra

NASA Astrophysics Data System (ADS)

El-Sonbati, A. Z.; Diab, M. A.; Morgan, Sh. M.; Seyam, H. A.

2018-02-01

Novel dioxouranium (VI) heterochelates with neutral bidentate compounds (Ln) have been synthesized. The ligands and the heterochelates [UO2(Ln)2(O2NO)2] were confirmed and characterized by elemental analysis, 1H NMR, UV.-Vis, IR, mass spectroscopy, X-ray diffraction and thermogravimetric analysis (TGA). IR spectral data suggest that the molecules of the Schiff base are coordinated to the central uranium atom (ON donor). The nitrato groups are coordinated as bidentate ligands. The thermodynamic parameters were calculated using Coats-Redfern and Horowitz-Metzger methods. The ligands (Ln) and their complexes (1-3) showed the υ3 frequency of UO22+ has been shown to be an excellent molecular probe for studying the coordinating power of the ligands. The values of υ3 of the prepared complexes containing UO22+ were successfully used to calculate the force constant, FUO (1n 10-8N/Å) and the bond length RUO (Å) of the Usbnd O bond. A strategy based upon both theoretical and experimental investigations has been adopted. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the Usbnd O bond distances from the values of the stretching and interaction force constants. The most probable correlation between Usbnd O force constant to Usbnd O bond distance were satisfactorily discussed in term of Badger's rule and the equations suggested by Jones and El-Sonbati. The effect of Hammett's constant is also discussed.

A virtual pebble game to ensemble average graph rigidity.

PubMed

González, Luis C; Wang, Hui; Livesay, Dennis R; Jacobs, Donald J

2015-01-01

The body-bar Pebble Game (PG) algorithm is commonly used to calculate network rigidity properties in proteins and polymeric materials. To account for fluctuating interactions such as hydrogen bonds, an ensemble of constraint topologies are sampled, and average network properties are obtained by averaging PG characterizations. At a simpler level of sophistication, Maxwell constraint counting (MCC) provides a rigorous lower bound for the number of internal degrees of freedom (DOF) within a body-bar network, and it is commonly employed to test if a molecular structure is globally under-constrained or over-constrained. MCC is a mean field approximation (MFA) that ignores spatial fluctuations of distance constraints by replacing the actual molecular structure by an effective medium that has distance constraints globally distributed with perfect uniform density. The Virtual Pebble Game (VPG) algorithm is a MFA that retains spatial inhomogeneity in the density of constraints on all length scales. Network fluctuations due to distance constraints that may be present or absent based on binary random dynamic variables are suppressed by replacing all possible constraint topology realizations with the probabilities that distance constraints are present. The VPG algorithm is isomorphic to the PG algorithm, where integers for counting "pebbles" placed on vertices or edges in the PG map to real numbers representing the probability to find a pebble. In the VPG, edges are assigned pebble capacities, and pebble movements become a continuous flow of probability within the network. Comparisons between the VPG and average PG results over a test set of proteins and disordered lattices demonstrate the VPG quantitatively estimates the ensemble average PG results well. The VPG performs about 20% faster than one PG, and it provides a pragmatic alternative to averaging PG rigidity characteristics over an ensemble of constraint topologies. The utility of the VPG falls in between the most accurate but slowest method of ensemble averaging over hundreds to thousands of independent PG runs, and the fastest but least accurate MCC.

Amperometric biosensor based on glassy carbon electrode modified with long-length carbon nanotube and enzyme

NASA Astrophysics Data System (ADS)

Furutaka, Hajime; Nemoto, Kentaro; Inoue, Yuki; Hidaka, Hiroki; Muguruma, Hitoshi; Inoue, Hitoshi; Ohsawa, Tatsuya

2016-05-01

An amperometric biosensor based on a glassy carbon electrode modified with long-length multiwalled carbon nanotubes (MWCNTs) and enzyme nicotinamide-adenine-dinucleotide-dependent glucose dehydrogenase (GDH) is presented. We demonstrate the effect of the MWCNT length on the amperometric response of the enzyme biosensor. The long length of MWCNT is 200 µm (average), whereas the normal length of MWCNT is 1 µm (average). The response of the long MWCNT-GDH electrode is 2 times more sensitive than that of the normal-length MWCNT-GDH electrode in the concentration range from 0.25-35 mM. The result of electrochemical impedance spectroscopy measurements suggest that the long-length MWCNT-GDH electrode formed a better electron transfer network than the normal-length one.

The human-animal bond in academic veterinary medicine.

PubMed

Rowan, Andrew N

2008-01-01

This article outlines the development of academic veterinary interest in the human-animal bond (HAB) and provides short summaries of the various centers currently studying the HAB at North American universities. Although most of these centers are at veterinary schools, the level of involvement by veterinarians is surprisingly low, considering how important a strong HAB is for the average veterinary practitioner (the stronger the bond, the more the client will be willing to pay for veterinary services).

A Comparison of Cocrystal Structure Solutions from Powder and Single Crystal Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

S Lapidus; P Stephens; K Arora

We demonstrate the effectiveness and accuracy of high resolution powder diffraction for determination of cocrystal structures through a double-blind study. Structures of 10 cocrystals of varying complexity were determined independently using single crystal and powder techniques. The two methodologies give identical molecular packing and hydrogen bond topology, and an rms difference in covalent bond lengths of 0.035 {angstrom}. Powder techniques are clearly sufficient to establish a complete characterization of cocrystal geometry.

Fixman compensating potential for general branched molecules

NASA Astrophysics Data System (ADS)

Jain, Abhinandan; Kandel, Saugat; Wagner, Jeffrey; Larsen, Adrien; Vaidehi, Nagarajan

2013-12-01

The technique of constraining high frequency modes of molecular motion is an effective way to increase simulation time scale and improve conformational sampling in molecular dynamics simulations. However, it has been shown that constraints on higher frequency modes such as bond lengths and bond angles stiffen the molecular model, thereby introducing systematic biases in the statistical behavior of the simulations. Fixman proposed a compensating potential to remove such biases in the thermodynamic and kinetic properties calculated from dynamics simulations. Previous implementations of the Fixman potential have been limited to only short serial chain systems. In this paper, we present a spatial operator algebra based algorithm to calculate the Fixman potential and its gradient within constrained dynamics simulations for branched topology molecules of any size. Our numerical studies on molecules of increasing complexity validate our algorithm by demonstrating recovery of the dihedral angle probability distribution function for systems that range in complexity from serial chains to protein molecules. We observe that the Fixman compensating potential recovers the free energy surface of a serial chain polymer, thus annulling the biases caused by constraining the bond lengths and bond angles. The inclusion of Fixman potential entails only a modest increase in the computational cost in these simulations. We believe that this work represents the first instance where the Fixman potential has been used for general branched systems, and establishes the viability for its use in constrained dynamics simulations of proteins and other macromolecules.

Influence of face-down and face-up bonding on the degree of polarization of superluminescent diode

NASA Astrophysics Data System (ADS)

Zhou, Shuai

2017-12-01

Face-down and face-up bonded polarization-insensitive buried heterojunction superluminescent diode has been studied in terms of thermal behavior and degree of polarization. Our studies have shown that the thermal rollover of current-power characteristic for face-down bonding was about 1.16 times higher than face-up configurations, and face-down bonding can offer higher heat transfer than face-up one. However, face-down bonding will cause more physical stress to the device, and the average value of degree of polarization for face-down bonding devices (35.3%) was much higher than face-up ones (-2.1%). After 48 h high temperature storage at 85∘C, the stress of face-down devices obtained a better relaxation due to the more stress accumulation.

A Sticky Chain Model of the Elongation and Unfolding of Escherichia coli P Pili under Stress

PubMed Central

Andersson, Magnus; Fällman, Erik; Uhlin, Bernt Eric; Axner, Ove

2006-01-01

A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke's law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding: elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-versus-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined. PMID:16361334

A sticky chain model of the elongation and unfolding of Escherichia coli P pili under stress.

PubMed

Andersson, Magnus; Fällman, Erik; Uhlin, Bernt Eric; Axner, Ove

2006-03-01

A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke's law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding: elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-versus-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined.

Synthesis, crystal structure and optical properties of BiMgVO 5

NASA Astrophysics Data System (ADS)

Benmokhtar, S.; El Jazouli, A.; Chaminade, J. P.; Gravereau, P.; Guillen, F.; de Waal, D.

2004-11-01

The new vanadate BiMgVO 5 has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P21/n, a=7.542(6) Å, b=11.615(5) Å, c=5.305(3) Å, β=107.38(5)°, wR2=0.0447, R=0.0255. The structure consists of [Mg 2O 10] and [Bi 2O 10] dimers sharing their corners with [VO 4] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.

Local structure of In0.5Ga0.5As from joint high-resolution and differential pair distribution function analysis

NASA Astrophysics Data System (ADS)

Petkov, V.; Jeong, I.-K.; Mohiuddin-Jacobs, F.; Proffen, Th.; Billinge, S. J. L.; Dmowski, W.

2000-07-01

High resolution total and indium differential atomic pair distribution functions (PDFs) for In0.5Ga0.5As alloys have been obtained by high energy and anomalous x-ray diffraction experiments, respectively. The first peak in the total PDF is resolved as a doublet due to the presence of two distinct bond lengths, In-As and Ga-As. The In differential PDF, which involves only atomic pairs containing In, yields chemical specific information and helps ease the structure data interpretation. Both PDFs have been fit with structure models and the way in that the underlying cubic zinc-blende lattice of In0.5Ga0.5As semiconductor alloy distorts locally to accommodate the distinct In-As and Ga-As bond lengths present has been quantified.

Depressing thermal conductivity of fullerene by caging rare gas

NASA Astrophysics Data System (ADS)

Li, Jian; Zheng, Dong-Qin; Zhong, Wei-Rong

2016-01-01

We have investigated the thermal conductivity of C60 and its derivatives caged with rare gas by using the nonequilibrium molecular dynamics method. It is reported that embedding C60 with different rare gas atoms has a significant impact on its thermal conductivity. We analyze the phenomenon through the phonon spectra of rare gas atom and the C-C bonds length of C60. When the number of atoms inside the C60 increases, the phonon spectra band width of rare gas expands and the length of C-C bonds becomes longer, which contributes to the depression of the thermal conductivity of C60. The method is applied to control the thermal conductivity of C60 chains, which maybe a kind of potential materials in thermal circuits. Our results also provide a controllable method for the thermal management in nanoscale materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, Kunyue; Chatterjee, Sabornie; Saito, Tomonori

Dielectric spectroscopy, rheology, and differential scanning calorimetry were employed to study the effect of chain-end hydrogen bonding on the dynamics of hydroxylterminated polydimethylsiloxane. We demonstrate that hydrogen bonding has a strong influence on both segmental and slower dynamics in the systems with low molecular weights. In particular, the decrease in the chain length leads to an increase of the glass transition temperature, viscosity, and fragility index, at variance with the usual behavior of nonassociating polymers. The supramolecular association of hydroxylterminated chains leads to the emergence in dielectric and mechanical relaxation spectra of the so-called Debye process traditionally observed in monohydroxymore » alcohols. Our analysis suggests that the hydroxyl-terminated PDMS oligomers may associate in brush-like or chain-like structures, depending on the size of their covalent chains. Finally, the effective length of the linear-associated chains was estimated from the rheological measurements.« less

In situ observation of electron beam-induced phase transformation of CaCO3 to CaO via ELNES at low electron beam energies.

PubMed

Golla-Schindler, Ute; Benner, Gerd; Orchowski, Alexander; Kaiser, Ute

2014-06-01

It is demonstrated that energy-filtered transmission electron microscope enables following of in situ changes of the Ca-L2,3 edge which can originate from variations in both local symmetry and bond lengths. Low accelerating voltages of 20 and 40 kV slow down radiation damage effects and enable study of the start and finish of phase transformations. We observed electron beam-induced phase transformation of single crystalline calcite (CaCO3) to polycrystalline calcium oxide (CaO) which occurs in different stages. The coordination of Ca in calcite is close to an octahedral one streched along the <111> direction. Changes during phase transformation to an octahedral coordination of Ca in CaO go along with a bond length increase by 5 pm, where oxygen is preserved as a binding partner. Electron loss near-edge structure of the Ca-L2,3 edge show four separated peaks, which all shift toward lower energies during phase transformation at the same time the energy level splitting increases. We suggest that these changes can be mainly addressed to the change of the bond length on the order of picometers. An important pre-condition for such studies is stability of the energy drift in the range of meV over at least 1 h, which is achieved with the sub-Ångström low-voltage transmission electron microscope I prototype microscope.

Theoretical characterization of the F(2)O(3) molecule by coupled-cluster methods.

PubMed

Huang, Ming-Ju; Watts, John D

2010-09-23

Coupled-cluster calculations with extended basis sets that include noniterative connected triple excitations (CCSD(T)) have been used to study the FOOOF isomer of F(2)O(3). Second-order Moller-Plessett perturbation theory (MP2) and density-functional theory (B3LYP functional) calculations have also been performed for comparison. Two local minima of similar energy, namely, conformers of C(2) and C(s) symmetry have been located. Structures, harmonic vibrational frequencies, and standard enthalpies and free energies of formation have been calculated. The calculated bond lengths of F(2)O(3) are more characteristic of those in F(2)O and a "normal" peroxide than the unusual bond lengths in F(2)O(2). Both conformers have equal F-O and O-O bond lengths, contrary to a recent suggestion of an unsymmetrical structure. The harmonic vibrational frequencies can aid possible identification of gaseous F(2)O(3). The calculated Δ(f)H° and Δ(f)G° are 110 and 173 kJ mol(-1), respectively. These values are based on extrapolation of CCSD(T) results with augmented triple- and quadruple-ζ basis sets and are expected to be within chemical accuracy (i.e., 1 kcal mol(-1) or 4 kJ mol(-1)). F(2)O(3) is calculated to be stable to decomposition to either FO + FOO or F(2) + O(3), but unstable to decomposition to its elements, to F(2)O(2) + (1)/(2)O(2), and to F(2)O + O(2).

Length estimations of presumed upward connecting leaders in lightning flashes to flat water and flat ground

NASA Astrophysics Data System (ADS)

Stolzenburg, Maribeth; Marshall, Thomas C.; Karunarathne, Sumedhe; Orville, Richard E.

2018-10-01

Using video data recorded at 50,000 frames per second for nearby negative lightning flashes, estimates are derived for the length of positive upward connecting leaders (UCLs) that presumably formed prior to new ground attachments. Return strokes were 1.7 to 7.8 km distant, yielding image resolutions of 4.25 to 19.5 m. No UCLs are imaged in these data, indicating those features were too transient or too dim compared to other lightning processes that are imaged at these resolutions. Upper bound lengths for 17 presumed UCLs are determined from the height above flat ground or water of the successful stepped leader tip in the image immediately prior to (within 20 μs before) the return stroke. Better estimates of maximum UCL lengths are determined using the downward stepped leader tip's speed of advance and the estimated return stroke time within its first frame. For 17 strokes, the upper bound length of the possible UCL averages 31.6 m and ranges from 11.3 to 50.3 m. Among the close strokes (those with spatial resolution <8 m per pixel), the five which connected to water (salt water lagoon) have UCL upper bound estimates averaging significantly shorter (24.1 m) than the average for the three close strokes which connected to land (36.9 m). The better estimates of maximum UCL lengths for the eight close strokes average 20.2 m, with slightly shorter average of 18.3 m for the five that connected to water. All the better estimates of UCL maximum lengths are <38 m in this dataset

Relationship between neighbor number and vibrational spectra in disordered colloidal clusters with attractive interactions

NASA Astrophysics Data System (ADS)

Yunker, Peter J.; Zhang, Zexin; Gratale, Matthew; Chen, Ke; Yodh, A. G.

2013-03-01

We study connections between vibrational spectra and average nearest neighbor number in disordered clusters of colloidal particles with attractive interactions. Measurements of displacement covariances between particles in each cluster permit calculation of the stiffness matrix, which contains effective spring constants linking pairs of particles. From the cluster stiffness matrix, we derive vibrational properties of corresponding "shadow" glassy clusters, with the same geometric configuration and interactions as the "source" cluster but without damping. Here, we investigate the stiffness matrix to elucidate the origin of the correlations between the median frequency of cluster vibrational modes and average number of nearest neighbors in the cluster. We find that the mean confining stiffness of particles in a cluster, i.e., the ensemble-averaged sum of nearest neighbor spring constants, correlates strongly with average nearest neighbor number, and even more strongly with median frequency. Further, we find that the average oscillation frequency of an individual particle is set by the total stiffness of its nearest neighbor bonds; this average frequency increases as the square root of the nearest neighbor bond stiffness, in a manner similar to the simple harmonic oscillator.

Capacity of MIMO free space optical communications using multiple partially coherent beams propagation through non-Kolmogorov strong turbulence.

PubMed

Deng, Peng; Kavehrad, Mohsen; Liu, Zhiwen; Zhou, Zhou; Yuan, Xiuhua

2013-07-01

We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law α, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.

Geometry, bonding and magnetism in planar triangulene graphene molecules with D3h symmetry: Zigzag Cm∗∗2+4m+1H3m+3 (m = 2, …, 15)

NASA Astrophysics Data System (ADS)

Philpott, Michael R.; Cimpoesu, Fanica; Kawazoe, Yoshiyuki

2008-12-01

Ab initio plane wave based all valence electron DFT calculations with geometry optimization are reported for the electronic structure of planar zigzag edged triangular shaped graphene molecules CH where the zigzag ring number m = 2, …, 15. The largest molecule C 286H 48 has a 3.8 nm side length and retains D3h symmetric geometry. The zone in the middle of the molecules, where the geometry and electronic properties resemble infinite single sheet graphite (graphene), expands with increasing ring number m, driving deviations in geometry, charge and spin to the perimeter. If a molecule is viewed as a set of nested triangular rings of carbon, then the zone where the lattice resembles an infinite sheet of graphene with CC = 142 pm, extends to the middle of the penultimate ring. The radial bonds joining the perimeter carbon atoms to the interior are long CC = 144 pm, except near the three apexes where the bonds are shorter. Isometric surfaces of the total charge density show that the two bonds joined at the apex have the highest valence charge. The perimeter CC bonds establish a simple pattern as the zigzag number increases, which shares some features with the zigzag edges in the D2h linear acenes C 4m+2H 2m+4 and the D6h hexangulenes CH6m but not the D6h symmetric annulenes (CH). The two CC bonds forming each apex are short (≈139 pm), next comes one long bond CC ≈ 142 pm and a middle region where all the CC bonds have length ≈141 pm. The homo-lumo gap declines from 0.53 eV at m = 2 to approximately 0.29 V at m = 15, the latter being larger than found for linear or hexagonal shaped graphenes with comparable edge lengths. Across the molecule the charge on the carbon atoms undergoes a small oscillation following the bipartite lattice. The magnitude of the charge in the same nested triangle decreases monotonically with the distance of the row from the center of the molecule. These systems are predicted to have spin polarized ground states with S = ½( m - 1), in accord with the theorems of Lieb for a bipartite lattice with unequal numbers of sub-lattice carbon atoms. The magnitude of the spin on the atoms increases monotonically from the center to the edges, this effect being greatest on the majority A-sub lattice atoms. The spins are delocalized, not confined to specific atoms as might result in geometries stabilized by islands of aromatic resonance. In the largest systems the magnetic non-bonding levels (NBL) occur as a narrowly distributed set of homos close to the Fermi level, separated from the lower lying valence bond manifold by a gap of about 1 eV. The NBL are a set of disjoint radical orbitals having charge only on atoms belonging to the A-lattice and this charge is concentrated on the perimeter and penultimate row atoms.

Femtosecond laser etching of dental enamel for bracket bonding.

PubMed

Kabas, Ayse Sena; Ersoy, Tansu; Gülsoy, Murat; Akturk, Selcuk

2013-09-01

The aim is to investigate femtosecond laser ablation as an alternative method for enamel etching used before bonding orthodontic brackets. A focused laser beam is scanned over enamel within the area of bonding in a saw tooth pattern with a varying number of lines. After patterning, ceramic brackets are bonded and bonding quality of the proposed technique is measured by a universal testing machine. The results are compared to the conventional acid etching method. Results show that bonding strength is a function of laser average power and the density of the ablated lines. Intrapulpal temperature changes are also recorded and observed minimal effects are observed. Enamel surface of the samples is investigated microscopically and no signs of damage or cracking are observed. In conclusion, femtosecond laser exposure on enamel surface yields controllable patterns that provide efficient bonding strength with less removal of dental tissue than conventional acid-etching technique.

Changes in average length of stay and average charges generated following institution of PSRO review.

PubMed Central

Westphal, M; Frazier, E; Miller, M C

1979-01-01

A five-year review of accounting data at a university hospital shows that immediately following institution of concurrent PSRO admission and length of stay review of Medicare-Medicaid patients, there was a significant decrease in length of stay and a fall in average charges generated per patient against the inflationary trend. Similar changes did not occur for the non-Medicare-Medicaid patients who were not reviewed. The observed changes occurred even though the review procedure rarely resulted in the denial of services to patients, suggesting an indirect effect of review. PMID:393658

Non-destructive testing of full-length bonded rock bolts based on HHT signal analysis

NASA Astrophysics Data System (ADS)

Shi, Z. M.; Liu, L.; Peng, M.; Liu, C. C.; Tao, F. J.; Liu, C. S.

2018-04-01

Full-length bonded rock bolts are commonly used in mining, tunneling and slope engineering because of their simple design and resistance to corrosion. However, the length of a rock bolt and grouting quality do not often meet the required design standards in practice because of the concealment and complexity of bolt construction. Non-destructive testing is preferred when testing a rock bolt's quality because of the convenience, low cost and wide detection range. In this paper, a signal analysis method for the non-destructive sound wave testing of full-length bonded rock bolts is presented, which is based on the Hilbert-Huang transform (HHT). First, we introduce the HHT analysis method to calculate the bolt length and identify defect locations based on sound wave reflection test signals, which includes decomposing the test signal via empirical mode decomposition (EMD), selecting the intrinsic mode functions (IMF) using the Pearson Correlation Index (PCI) and calculating the instantaneous phase and frequency via the Hilbert transform (HT). Second, six model tests are conducted using different grouting defects and bolt protruding lengths to verify the effectiveness of the HHT analysis method. Lastly, the influence of the bolt protruding length on the test signal, identification of multiple reflections from defects, bolt end and protruding end, and mode mixing from EMD are discussed. The HHT analysis method can identify the bolt length and grouting defect locations from signals that contain noise at multiple reflected interfaces. The reflection from the long protruding end creates an irregular test signal with many frequency peaks on the spectrum. The reflections from defects barely change the original signal because they are low energy, which cannot be adequately resolved using existing methods. The HHT analysis method can identify reflections from the long protruding end of the bolt and multiple reflections from grouting defects based on mutations in the instantaneous frequency, which makes weak reflections more noticeable. The mode mixing phenomenon is observed in several tests, but this does not markedly affect the identification results due to the simple medium in bolt tests. The mode mixing can be reduced by ensemble EMD (EEMD) or complete ensemble EMD with adaptive noise (CEEMDAN), which are powerful tools to used analyze the test signal in a complex medium and may play an important role in future studies. The HHT bolt signal analysis method is a self-adaptive and automatic process, which can be programed as analysis software and will make bolt tests more convenient in practice.

Asymptotically optimum multialternative sequential procedures for discernment of processes minimizing average length of observations

NASA Astrophysics Data System (ADS)

Fishman, M. M.

1985-01-01

The problem of multialternative sequential discernment of processes is formulated in terms of conditionally optimum procedures minimizing the average length of observations, without any probabilistic assumptions about any one occurring process, rather than in terms of Bayes procedures minimizing the average risk. The problem is to find the procedure that will transform inequalities into equalities. The problem is formulated for various models of signal observation and data processing: (1) discernment of signals from background interference by a multichannel system; (2) discernment of pulse sequences with unknown time delay; (3) discernment of harmonic signals with unknown frequency. An asymptotically optimum sequential procedure is constructed which compares the statistics of the likelihood ratio with the mean-weighted likelihood ratio and estimates the upper bound for conditional average lengths of observations. This procedure is shown to remain valid as the upper bound for the probability of erroneous partial solutions decreases approaching zero and the number of hypotheses increases approaching infinity. It also remains valid under certain special constraints on the probability such as a threshold. A comparison with a fixed-length procedure reveals that this sequential procedure decreases the length of observations to one quarter, on the average, when the probability of erroneous partial solutions is low.

HgCdTe Surface and Defect Study Program.

DTIC Science & Technology

1985-07-01

a! Td . - a,+ - , are the bonding and antibonding one electron energy states "- "𔃾 owing only to covalent and ionic interactions, . = T . . (U6 II .1...Group Meeting. Boulder CO. 1983; T. W. Jamet atid B. Fandvacncyforatin eerg) t inreae popotioal o a Ziack. 4bd . low inverse power of the average bond

Molecularly Tuning the Radicaloid N-H···O═C Hydrogen Bond.

PubMed

Lu, Norman; Chung, Wei-Cheng; Ley, Rebecca M; Lin, Kwan-Yu; Francisco, Joseph S; Negishi, Ei-Ichi

2016-03-03

Substituent effects on the open shell N-H···O═C hydrogen-bond has never been reported. This study examines how 12 functional groups composed of electron donating groups (EDG), halogen atoms and electron withdrawing groups (EWG) affect the N-H···O═C hydrogen-bond properties in a six-membered cyclic model system of O═C(Y)-CH═C(X)N-H. It is found that group effects on this open shell H-bonding system are significant and have predictive trends when X = H and Y is varied. When Y is an EDG, the N-H···O═C hydrogen-bond is strengthened; and when Y is an EWG, the bond is weakened; whereas the variation in electronic properties of X group do not exhibit a significant impact upon the hydrogen bond strength. The structural impact of the stronger N-H···O═C hydrogen-bond are (1) shorter H and O distance, r(H···O) and (2) a longer N-H bond length, r(NH). The stronger N-H···O═C hydrogen-bond also acts to pull the H and O in toward one another which has an effect on the bond angles. Our findings show that there is a linear relationship between hydrogen-bond angle and N-H···O═C hydrogen-bond energy in this unusual H-bonding system. In addition, there is a linear correlation of the r(H···O) and the hydrogen bond energy. A short r(H···O) distance corresponds to a large hydrogen bond energy when Y is varied. The observed trends and findings have been validated using three different methods (UB3LYP, M06-2X, and UMP2) with two different basis sets.

Energetic Analysis of Conjugated Hydrocarbons Using the Interacting Quantum Atoms Method.

PubMed

Jara-Cortés, Jesús; Hernández-Trujillo, Jesús

2018-07-05

A number of aromatic, antiaromatic, and nonaromatic organic molecules was analyzed in terms of the contributions to the electronic energy defined in the quantum theory of atoms in molecules and the interacting quantum atoms method. Regularities were found in the exchange and electrostatic interatomic energies showing trends that are closely related to those of the delocalization indices defined in the theory. In particular, the CC interaction energies between bonded atoms allow to rationalize the energetic stabilization associated with the bond length alternation in conjugated polyenes. This approach also provides support to Clar's sextet rules devised for aromatic systems. In addition, the H⋯H bonding found in some of the aromatic molecules studied was of an attractive nature, according to the stabilizing exchange interaction between the bonded H atoms. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Femtosecond x-ray scattering study of ultrafast photoinduced structural dynamics in solvated [ Co ( terpy ) 2 ] 2 +

DOE PAGES

Biasin, Elisa; van Driel, Tim Brandt; Kjær, Kasper S.; ...

2016-06-30

Here, we study the structural dynamics of photoexcited [Co(terpy) 2] 2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of themore » high spin state is established on a single-picosecond time scale and that this state has a lifetime of ~7 ps.« less

Ultrastable assembly and integration technology for ground- and space-based optical systems.

PubMed

Ressel, Simon; Gohlke, Martin; Rauen, Dominik; Schuldt, Thilo; Kronast, Wolfgang; Mescheder, Ulrich; Johann, Ulrich; Weise, Dennis; Braxmaier, Claus

2010-08-01

Optical metrology systems crucially rely on the dimensional stability of the optical path between their individual optical components. We present in this paper a novel adhesive bonding technology for setup of quasi-monolithic systems and compare selected characteristics to the well-established state-of-the-art technique of hydroxide-catalysis bonding. It is demonstrated that within the measurement resolution of our ultraprecise custom heterodyne interferometer, both techniques achieve an equivalent passive path length and tilt stability for time scales between 0.1 mHz and 1 Hz. Furthermore, the robustness of the adhesive bonds against mechanical and thermal inputs has been tested, making this new bonding technique in particular a potential option for interferometric applications in future space missions. The integration process itself is eased by long time scales for alignment, as well as short curing times.

Structural elucidation of antihemorrhage drug molecule Diethylammonium 2,5-dihydroxybenzene sulfonate - an insilico approach

NASA Astrophysics Data System (ADS)

Kumar, S. Anil; Bhaskar, BL

2018-02-01

Ab-initio computational study of antihemorrhage drug molecule diethylammonium 2,5-dihydroxybenzene sulfonate, popularly known as ethamsylate, has been attempted using Gaussian 09. The optimized molecular geometry has been envisaged using density functional theory method at B3LYP/6-311 basis set. Different geometrical parameters like bond lengths and bond angles were computed and compared against the experimental results available in literature. Fourier transform infrared scanning of the title molecule was performed and vibrational frequencies were also computed using Gaussian software. The presence of O-H---O hydrogen bonds between C6H5O5S- anions and N-H---O hydrogen bonds between anion and cation is evident in the computational studies also. In general, satisfactory agreement of concordance has been observed between computational and experimental results.

Molecular-dynamics simulation of polymethylene chain confined in cylindrical potentials. I. Nature of the conformational defects

NASA Astrophysics Data System (ADS)

Yamamoto, Takashi; Kimikawa, Yuichi

1992-10-01

The conformational motion of a polymethylene molecule constrained by a cylindrical potential is simulated up to 100 ps. The molecule consists of 60 CH2 groups and has variable bond lengths, bond angles, and dihedral angles. Our main concern here is the excitation and the dynamics of the conformational defects: kinks, jogs, etc. Under weaker constraint a number of gauche bonds are excited; they mostly form pairs such as gtḡ kinks or gtttḡ jogs. These conformational defects show no continuous drift in space. Instead they often annihilate and then recreate at different sites showing apparently random positional changes. The conformational defects produce characteristic strain fields around them. It seems that the conformational defects interact attractively through these strain fields. This is evidenced by remarkably correlated spatial distributions of the gauche bonds.

Queues with Choice via Delay Differential Equations

NASA Astrophysics Data System (ADS)

Pender, Jamol; Rand, Richard H.; Wesson, Elizabeth

Delay or queue length information has the potential to influence the decision of a customer to join a queue. Thus, it is imperative for managers of queueing systems to understand how the information that they provide will affect the performance of the system. To this end, we construct and analyze two two-dimensional deterministic fluid models that incorporate customer choice behavior based on delayed queue length information. In the first fluid model, customers join each queue according to a Multinomial Logit Model, however, the queue length information the customer receives is delayed by a constant Δ. We show that the delay can cause oscillations or asynchronous behavior in the model based on the value of Δ. In the second model, customers receive information about the queue length through a moving average of the queue length. Although it has been shown empirically that giving patients moving average information causes oscillations and asynchronous behavior to occur in U.S. hospitals, we analytically and mathematically show for the first time that the moving average fluid model can exhibit oscillations and determine their dependence on the moving average window. Thus, our analysis provides new insight on how operators of service systems should report queue length information to customers and how delayed information can produce unwanted system dynamics.

Piperidine-1-carboximidamide

PubMed Central

Tiritiris, Ioannis

2012-01-01

In the title compound, C6H13N3, the C=N and C—N bond lengths in the CN3 unit are 1.3090 (17), and 1.3640 (17) (C–NH2) and 1.3773 (16) Å, indicating double- and single-bond character, respectively. The N—C—N angles are 116.82 (12), 119.08 (11) and 124.09 (11)°, showing a deviation of the CN3 plane from an ideal trigonal–planar geometry. The piperidine ring is in a chair conformation. In the crystal, mol­ecules are linked by N—H⋯N hydrogen bonds, forming a two-dimensional network along the ac plane. PMID:23284550

On the CH...Cu agostic interaction: chiral copper(II) compounds with ephedrine and pseudoephedrine derivatives.

PubMed

Castro, Miguel; Cruz, Julián; López-Sandoval, Horacio; Barba-Behrens, Norah

2005-08-14

The ephedrine derivative, (H2ceph), yields [Cu(Hceph)2], showing a CH...Cu(II) agostic interaction; while in the analogous compound [Cu(Hcpse)2], with pseudoephedrine (H2cpse), that interaction is absent, despite the fact that these two diasteromers differ only in the orientation of the methyl and phenyl groups: erythro in H2ceph and threo in H2cpse. The X-ray crystal structure of [Cu(Hceph)2], indicates a Cu...HC length of 2.454 A and the theoretical study reveals the formation of a Cu...HC bond since the associated electronic density shows both a bond critical point and a bond ring critical point.