Superplastic Forming/Diffusion Bonding Without Interlayer of 5A90 Al-Li Alloy Hollow Double-Layer Structure

NASA Astrophysics Data System (ADS)

Jiang, Shaosong; Jia, Yong; Lu, Zhen; Shi, Chengcheng; Zhang, Kaifeng

2017-09-01

The hollow double-layer structure of 5A90 Al-Li alloy was fabricated by SPF/DB process in this study. The characteristics and mechanism of 5A90 Al-Li alloy with respect to superplasticity and diffusion bonding were investigated. Tensile tests showed that the optimal elongation of tensile specimens was 243.97% at the temperature of 400 °C and the strain rate of 0.001 s-1. Effect of the surface roughness, bonding temperature and bonding time to determine the microstructure and mechanical properties of diffusion bonding joints was investigated, and the optimum bonding parameters were 540 °C/2.5 h/Ra18. Through the finite element simulation, it could be found that the SPF/DB process of hollow double-layer structure was feasible. The hollow double-layer structure of 5A90 Al-Li alloy was manufactured, showing that the thickness distribution of the bonding area was uniform and the thinnest part was the round corner. The SEM images of diffusion bonding joints showed that sound bonding interfaces were obtained in which no discontinuity existed.

Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds.

PubMed

Choi, Jongwook; Choliy, Yuriy; Zhang, Xiawei; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

2009-11-04

(PCP)Ir (PCP = kappa(3)-C(6)H(3)-2,6-[CH(2)P(t-Bu)(2)](2)) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH(3))(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [k(CH(3))(OAr)/k(CD(3))(OAr) = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and alpha-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by beta-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp(3))-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.

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).

Using ambient ozone for assignment of double bond position in unsaturated lipids.

PubMed

Ellis, Shane R; Hughes, Jessica R; Mitchell, Todd W; in het Panhuis, Marc; Blanksby, Stephen J

2012-03-07

Unsaturated lipids deposited onto a range of materials are observed to react with the low concentrations of ozone present in normal laboratory air. Parent lipids and ozonolysis cleavage products are both detected directly from surfaces by desorption electrospray ionisation mass spectrometry (DESI-MS) with the resulting mass spectra providing clear evidence of the double bond position within these molecules. This serendipitous process has been coupled with thin-layer chromatography (TLC) to provide a simple but powerful approach for the detailed structural elucidation of lipids present in complex biological extracts. Lipid extracts from human lens were deposited onto normal phase TLC plates and then developed to separate components according to lipid class. Exposure of the developed plates to laboratory air for ca. 1 h prior to DESI-MS analysis gave rise to ozonolysis products allowing for the unambiguous identification of double bond positions in even low abundant, unsaturated lipids. In particular, the co-localization of intact unsaturated lactosylceramides (LacCer) with products from their oxidative cleavage provide the first evidence for the presence of three isomeric LacCer (d18:0/24:1) species in the ocular lens lipidome, i.e., variants with double bonds at the n-9, n-7 and n-5 positions.

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.

Determining Double Bond Position in Lipids Using Online Ozonolysis Coupled to Liquid Chromatography and Ion Mobility-Mass Spectrometry.

PubMed

Harris, Rachel A; May, Jody C; Stinson, Craig A; Xia, Yu; McLean, John A

2018-02-06

The increasing focus on lipid metabolism has revealed a need for analytical techniques capable of structurally characterizing lipids with a high degree of specificity. Lipids can exist as any one of a large number of double bond positional isomers, which are indistinguishable by single-stage mass spectrometry alone. Ozonolysis reactions coupled to mass spectrometry have previously been demonstrated as a means for localizing double bonds in unsaturated lipids. Here we describe an online, solution-phase reactor using ozone produced via a low-pressure mercury lamp, which generates aldehyde products diagnostic of cleavage at a particular double bond position. This flow-cell device is utilized in conjunction with structurally selective ion mobility-mass spectrometry. The lamp-mediated reaction was found to be effective for multiple lipid species in both positive and negative ionization modes, and the conversion efficiency from precursor to product ions was tunable across a wide range (20-95%) by varying the flow rate through the ozonolysis device. Ion mobility separation of the ozonolysis products generated additional structural information and revealed the presence of saturated species in a complex mixture. The method presented here is simple, robust, and readily coupled to existing instrument platforms with minimal modifications necessary. For these reasons, application to standard lipidomic workflows is possible and aids in more comprehensive structural characterization of a myriad of lipid species.

Bond additivity corrections for quantum chemistry methods

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

C. F. Melius; M. D. Allendorf

1999-04-01

In the 1980's, the authors developed a bond-additivity correction procedure for quantum chemical calculations called BAC-MP4, which has proven reliable in calculating the thermochemical properties of molecular species, including radicals as well as stable closed-shell species. New Bond Additivity Correction (BAC) methods have been developed for the G2 method, BAC-G2, as well as for a hybrid DFT/MP2 method, BAC-Hybrid. These BAC methods use a new form of BAC corrections, involving atomic, molecular, and bond-wise additive terms. These terms enable one to treat positive and negative ions as well as neutrals. The BAC-G2 method reduces errors in the G2 method duemore » to nearest-neighbor bonds. The parameters within the BAC-G2 method only depend on atom types. Thus the BAC-G2 method can be used to determine the parameters needed by BAC methods involving lower levels of theory, such as BAC-Hybrid and BAC-MP4. The BAC-Hybrid method should scale well for large molecules. The BAC-Hybrid method uses the differences between the DFT and MP2 as an indicator of the method's accuracy, while the BAC-G2 method uses its internal methods (G1 and G2MP2) to provide an indicator of its accuracy. Indications of the average error as well as worst cases are provided for each of the BAC methods.« less

Raman and FTIR spectroscopic studies on two hydroxylated tung oils (HTO) bearing conjugated double bonds

NASA Astrophysics Data System (ADS)

Zhuang, Yuwei; Ren, Zhiyong; Jiang, Lei; Zhang, Jiaxiang; Wang, Huafen; Zhang, Guobao

2018-06-01

Tung oil (TO) was used as a model compound to study two hydroxylated tung oils (HTO), prepared from TO by either aminolysis (HTO-am) or alcoholysis (HTO-al). Main bands in Raman and FTIR spectra were initially assigned based on the detailed analysis of the compound spectra before and after exposure to elevated temperature (200 °C). The effect of heat treatment in air on spectral bands, and especially on the changes associated with double bonds, were then investigated. In the present work, changes in spectral bands due to heat treatment were compared with those revealed in the previous work of others. The results show that the conjugated triene structure of TO has been retained during alcoholysis and aminolysis, to yield the HTOs studied; yet the change of the triene structure caused by heating is different among the three samples; the H-bonding strength between OH and Cdbnd O in HTO-am is higher than that in HTO-al; the changes in HTO vOH and vCdbnd O bands in FTIR caused by the present heat treatment were significant; for TO, there is a big difference between changes in spectra as caused by thermal exposure, compared to those caused by ageing under UV light or exposure to a catalyst. The present work has laid additional groundwork for further study of the reactions of such triply conjugated double bond structures under different ageing conditions.

A stable silicon(0) compound with a Si=Si double bond.

PubMed

Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; King, R Bruce; Schaefer, Henry F; von R Schleyer, Paul; Robinson, Gregory H

2008-08-22

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.

Adhesive-bonded double-lap joints. [analytical solutions for static load carrying capacity

NASA Technical Reports Server (NTRS)

Hart-Smith, L. J.

1973-01-01

Explicit analytical solutions are derived for the static load carrying capacity of double-lap adhesive-bonded joints. The analyses extend the elastic solution Volkersen and cover adhesive plasticity, adherend stiffness imbalance and thermal mismatch between the adherends. Both elastic-plastic and bi-elastic adhesive representations lead to the explicit result that the influence of the adhesive on the maximum potential bond strength is defined uniquely by the strain energy in shear per unit area of bond. Failures induced by peel stresses at the ends of the joint are examined. This failure mode is particularly important for composite adherends. The explicit solutions are sufficiently simple to be used for design purposes

Determination of Double Bond Positions in Polyunsaturated Fatty Acids Using the Photochemical Paternò-Büchi Reaction with Acetone and Tandem Mass Spectrometry.

PubMed

Murphy, Robert C; Okuno, Toshiaki; Johnson, Christopher A; Barkley, Robert M

2017-08-15

The positions of double bonds along the carbon chain of methylene interrupted polyunsaturated fatty acids are unique identifiers of specific fatty acids derived from biochemical reactions that occur in cells. It is possible to obtain direct structural information as to these double bond positions using tandem mass spectrometry after collisional activation of the carboxylate anions of an acetone adduct at each of the double bond positions formed by the photochemical Paternò-Büchi reaction with acetone. This reaction can be carried out by exposing a small portion of an inline fused silica capillary to UV photons from a mercury vapor lamp as the sample is infused into the electrospray ion source of a mass spectrometer. Collisional activation of [M - H] - yields a series of reverse Paternò-Büchi reaction product ions that essentially are derived from cleavage of the original carbon-carbon double bonds that yield an isopropenyl carboxylate anion corresponding to each double bond location. Aldehydic reverse Paternò-Büchi product ions are much less abundant as the carbon chain length and number of double bonds increase. The use of a mixture of D 0 /D 6 -acetone facilitates identification of these double bonds indicating product ions as shown for arachidonic acid. If oxygen is present in the solvent stream undergoing UV photoactivation, ozone cleavage ions are also observed without prior collisional activation. This reaction was used to determine the double bond positions in a 20:3 fatty acid that accumulated in phospholipids of RAW 264.7 cells cultured for 3 days.

Effect of additional etching and ethanol-wet bonding on the dentin bond strength of one-step self-etch adhesives

PubMed Central

Ahn, Joonghee; Jung, Kyoung-Hwa; Son, Sung-Ae; Hur, Bock; Kwon, Yong-Hoon

2015-01-01

Objectives This study examined the effects of additional acid etching on the dentin bond strength of one-step self-etch adhesives with different compositions and pH. The effect of ethanol wetting on etched dentin bond strength of self-etch adhesives was also evaluated. Materials and Methods Forty-two human permanent molars were classified into 21 groups according to the adhesive types (Clearfil SE Bond [SE, control]; G-aenial Bond [GB]; Xeno V [XV]; Beauti Bond [BB]; Adper Easy Bond [AE]; Single Bond Universal [SU]; All Bond Universal [AU]), and the dentin conditioning methods. Composite resins were placed on the dentin surfaces, and the teeth were sectioned. The microtensile bond strength was measured, and the failure mode of the fractured specimens was examined. The data were analyzed statistically using two-way ANOVA and Duncan's post hoc test. Results In GB, XV and SE (pH ≤ 2), the bond strength was decreased significantly when the dentin was etched (p < 0.05). In BB, AE and SU (pH 2.4 - 2.7), additional etching did not affect the bond strength (p > 0.05). In AU (pH = 3.2), additional etching increased the bond strength significantly (p < 0.05). When adhesives were applied to the acid etched dentin with ethanol-wet bonding, the bond strength was significantly higher than that of the no ethanol-wet bonding groups, and the incidence of cohesive failure was increased. Conclusions The effect of additional acid etching on the dentin bond strength was influenced by the pH of one-step self-etch adhesives. Ethanol wetting on etched dentin could create a stronger bonding performance of one-step self-etch adhesives for acid etched dentin. PMID:25671215

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)

Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with Double and Triple W-P and W-As Bonds.

PubMed

Andrews, Lester; Cho, Han-Gook; Fang, Zongtang; Vasiliu, Monica; Dixon, David A

2018-05-07

Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH 3 and HE═WH 2 molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH 3 to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W-H stretching region are assigned to the molecules with loss of H from W, E≡WH 2 . The electronic structure calculations show that the E≡WH 3 molecules have a W-E triple bond, the HE═WH 2 molecules have a W-E double bond, and the H 2 E-WH molecules have a W-E single bond. The formation of multiple E-W bonds leads to increasing stability for the isomers.

Characterization of Wax Esters by Electrospray Ionization Tandem Mass Spectrometry: Double Bond Effect and Unusual Product Ions

PubMed Central

Chen, Jianzhong; Green, Kari B; Nichols, Kelly K

2015-01-01

A series of different types of wax esters (represented by RCOOR′) were systematically studied by using electrospray ionization (ESI) collision-induced dissociation tandem mass spectrometry (MS/MS) along with pseudo MS3 (in-source dissociation combined with MS/MS) on a quadrupole time-of-flight (Q-TOF) mass spectrometer. The tandem mass spectra patterns resulting from dissociation of ammonium/proton adducts of these wax esters were influenced by the wax ester type and the collision energy applied. The product ions [RCOOH2]+, [RCO]+ and [RCO – H2O]+ that have been reported previously were detected; however, different primary product ions were demonstrated for the three wax ester types including: 1) [RCOOH2]+ for saturated wax esters, 2) [RCOOH2]+, [RCO]+ and [RCO – H2O]+ for unsaturated wax esters containing only one double bond in the fatty acid moiety or with one additional double bond in the fatty alcohol moiety, and 3) [RCOOH2]+ and [RCO]+ for unsaturated wax esters containing a double bond in the fatty alcohol moiety alone. Other fragments included [R′]+ and several series of product ions for all types of wax esters. Interestingly, unusual product ions were detected, such as neutral molecule (including water, methanol and ammonia) adducts of [RCOOH2]+ ions for all types of wax esters and [R′ – 2H]+ ions for unsaturated fatty acyl-containing wax esters. The patterns of tandem mass spectra for different types of wax esters will inform future identification and quantification approaches of wax esters in biological samples as supported by a preliminary study of quantification of isomeric wax esters in human meibomian gland secretions. PMID:26178197

Characterization of Wax Esters by Electrospray Ionization Tandem Mass Spectrometry: Double Bond Effect and Unusual Product Ions.

PubMed

Chen, Jianzhong; Green, Kari B; Nichols, Kelly K

2015-08-01

A series of different types of wax esters (represented by RCOOR') were systematically studied by using electrospray ionization (ESI) collision-induced dissociation tandem mass spectrometry (MS/MS) along with pseudo MS(3) (in-source dissociation combined with MS/MS) on a quadrupole time-of-flight (Q-TOF) mass spectrometer. The tandem mass spectra patterns resulting from dissociation of ammonium/proton adducts of these wax esters were influenced by the wax ester type and the collision energy applied. The product ions [RCOOH2](+), [RCO](+) and [RCO-H2O](+) that have been reported previously were detected; however, different primary product ions were demonstrated for the three wax ester types including: (1) [RCOOH2](+) for saturated wax esters, (2) [RCOOH2](+), [RCO](+) and [RCO-H2O](+) for unsaturated wax esters containing only one double bond in the fatty acid moiety or with one additional double bond in the fatty alcohol moiety, and (3) [RCOOH2](+) and [RCO](+) for unsaturated wax esters containing a double bond in the fatty alcohol moiety alone. Other fragments included [R'](+) and several series of product ions for all types of wax esters. Interestingly, unusual product ions were detected, such as neutral molecule (including water, methanol and ammonia) adducts of [RCOOH2](+) ions for all types of wax esters and [R'-2H](+) ions for unsaturated fatty acyl-containing wax esters. The patterns of tandem mass spectra for different types of wax esters will inform future identification and quantification approaches of wax esters in biological samples as supported by a preliminary study of quantification of isomeric wax esters in human meibomian gland secretions.

Tough, high performance, addition-type thermoplastic polymers

NASA Technical Reports Server (NTRS)

Pater, Ruth H. (Inventor)

1992-01-01

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites.

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.

Preparation of mesoporous alumina particles by spray pyrolysis and application to double bond migration of 2-butene.

PubMed

Song, Ki Chang; Kim, Joo Hyun; Kim, Jin Han; Jung, Kyeong Youl; Park, Young-Kwon; Jeon, Jong-Ki

2011-07-01

The objective of the present study is to investigate the catalytic performance of mesoporous alumina that were prepared via spray pyrolysis for double bond migration from 2-butene to 1-butene. The mesoporous alumina particles were prepared via spray pyrolysis by changing the types of organic surfactants and Al precursors. The texture and acidic properties of mesoporous alumina were analyzed through N2 adsorption, SEM, ammonia-temperature programmed desorption, and FT-IR of adsorbed pyridine. The morphologies and texture properties of the mesoporous alumina were found to have been strongly influenced by the combination of the Al precursor and the structure-directing agents. The mesoporous alumina samples had two kinds of acidic sites: a Lewis acid site and a H-bonded weak acid site. 1-Butene was produced selectively through double bond migration of 2-butene over all of the mesoporous alumina catalysts. The catalyst prepared by using a chloride compound as an aluminium precursor and CTAC as a structure-directing agent showed the highest activity in the double bond migration of 2-butene, which was attributed to its large surface area and an overall high amount of acid sites.

Integrated packaging of multiple double sided cooling planar bond power modules

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

Liang, Zhenxian

An integrated double sided cooled power module has one or multiple phase legs configuration including one or more planar power packages, each planar power package having an upper power switch unit and a lower power switch unit directly bonded and interconnected between two insulated power substrates, and further sandwiched between two heat exchangers via direct bonds. A segmented coolant manifold is interposed with the one or more planar power packages and creates a sealed enclosure that defines a coolant inlet, a coolant outlet and a coolant flow path between the inlet and the outlet. A coolant circulates along the flowmore » path to remove heat and increase the power density of the power module.« less

Substituent effects in double-helical hydrogen-bonded AAA-DDD complexes.

PubMed

Wang, Hong-Bo; Mudraboyina, Bhanu P; Wisner, James A

2012-01-27

Two series of DDD and AAA hydrogen-bond arrays were synthesized that form triply-hydrogen-bonded double-helical complexes when combined in CDCl(3) solution. Derivatization of the DDD arrays with electron-withdrawing groups increases the complex association constants by up to a factor of 30 in those arrays examined. Derivatization of the AAA arrays with electron donating substituents reveals a similar magnitude effect on the complex stabilities. The effect of substitution on both types of arrays are modeled quite satisfactorily (R(2) > 0.96 in all cases) as free energy relationships with respect to the sums of their Hammett substituent constants. In all, the complex stabilities can be manipulated over more than three orders of magnitude (>20 kJ mol(-1)) using this type of modification. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

42 CFR 489.66 - Additional requirements of the surety bond.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 42 Public Health 5 2011-10-01 2011-10-01 false Additional requirements of the surety bond. 489.66 Section 489.66 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) STANDARDS AND CERTIFICATION PROVIDER AGREEMENTS AND SUPPLIER APPROVAL Surety Bond...

Effects of double and triple bonds on the spatial representations of odorants in the rat olfactory bulb.

PubMed

Johnson, Brett A; Ong, Joan; Lee, Kaman; Ho, Sabrina L; Arguello, Spart; Leon, Michael

2007-02-01

Many naturally occurring volatile chemicals that are detected through the sense of smell contain unsaturated (double or triple) carbon-carbon bonds. These bonds can affect odors perceived by humans, yet in a prior study of unsaturated hydrocarbons we found only very minor effects of unsaturated bonds. In the present study, we tested the possibility that unsaturated bonds affect the recognition of oxygen-containing functional groups, because humans perceive odor differences between such molecules. We therefore compared spatial activity patterns across the entire glomerular layer of the rat olfactory bulb evoked by oxygen-containing odorants differing systematically in the presence, position, number, and stereochemistry of unsaturated bonds. We quantified activity patterns by mapping [(14)C]2-deoxyglucose uptake into anatomically standardized data matrices, which we compared statistically. We found that the presence and number of unsaturated bonds consistently affected activity patterns, with the largest effect related to the presence of a triple bond. Effects of bond saturation included a loss of activity in glomeruli strongly activated by the corresponding saturated odorants and/or the presence of activity in areas not stimulated by the corresponding saturated compounds. The position of double bonds also affected patterns of activity, but cis vs. trans configuration had no measurable impact in all five sets of stereoisomers that we studied. These results simultaneously indicate the importance of interactions between carbon-carbon bond types and functional groups in the neural coding of odorant chemical information and highlight the emerging concept that the rat olfactory system is more sensitive to certain types of chemical differences than others. (c) 2006 Wiley-Liss, Inc.

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.

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.

Exactly solvable Schrödinger equation with double-well potential for hydrogen bond

NASA Astrophysics Data System (ADS)

Sitnitsky, A. E.

2017-05-01

We construct a double-well potential for which the Schrödinger equation can be exactly solved via reducing to the confluent Heun's one. Thus the wave function is expressed via the confluent Heun's function. The latter is tabulated in Maple so that the obtained solution is easily treated. The potential is infinite at the boundaries of the final interval that makes it to be highly suitable for modeling hydrogen bonds (both ordinary and low-barrier ones). We exemplify theoretical results by detailed treating the hydrogen bond in KHCO3 and show their good agreement with literature experimental data.

Identification and cloning of an NADPH-dependent hydroxycinnamoyl-CoA double bond reductase involved in dihydrochalcone formation in Malus×domestica Borkh.

PubMed

Ibdah, Mwafaq; Berim, Anna; Martens, Stefan; Valderrama, Andrea Lorena Herrera; Palmieri, Luisa; Lewinsohn, Efraim; Gang, David R

2014-11-01

The apple tree (Malus sp.) is an agriculturally and economically important source of food and beverages. Many of the health beneficial properties of apples are due to (poly)phenolic metabolites that they contain, including various dihydrochalcones. Although many of the genes and enzymes involved in polyphenol biosynthesis are known in many plant species, the specific reactions that lead to the biosynthesis of the dihydrochalcone precursor, p-dihydrocoumaroyl-CoA (3), are unknown. To identify genes involved in the synthesis of these metabolites, existing genome databases of the Rosaceae were screened for apple genes with significant sequence similarity to Arabidopsis alkenal double bond reductases. Herein described are the isolation and characterization of a Malus hydroxycinnamoyl-CoA double bond reductase, which catalyzed the NADPH-dependent reduction of p-coumaroyl-CoA and feruloyl-CoA to p-dihydrocoumaroyl-CoA and dihydroferuloyl-CoA, respectively. Its apparent Km values for p-coumaroyl-CoA, feruloyl-CoA and NADPH were 96.6, 92.9 and 101.3μM, respectively. The Malus double bond reductase preferred feruloyl-CoA to p-coumaroyl-CoA as a substrate by a factor of 2.1 when comparing catalytic efficiencies in vitro. Expression analysis of the hydroxycinnamoyl-CoA double bond reductase gene revealed that its transcript levels showed significant variation in tissues of different developmental stages, but was expressed when expected for involvement in dihydrochalcone formation. Thus, the hydroxycinnamoyl-CoA double bond reductase appears to be responsible for the reduction of the α,β-unsaturated double bond of p-coumaroyl-CoA, the first step of dihydrochalcone biosynthesis in apple tissues, and may be involved in the production of these compounds. Copyright © 2014 Elsevier Ltd. All rights reserved.

The Existence of a Designer Al=Al Double Bond in the LiAl2 H4- Cluster Formed by Electronic Transmutation.

PubMed

Lundell, Katie A; Zhang, Xinxing; Boldyrev, Alexander I; Bowen, Kit H

2017-12-22

The Al=Al double bond is elusive in chemistry. Herein we report the results obtained via combined photoelectron spectroscopy and ab initio studies of the LiAl 2 H 4 - cluster that confirm the formation of a conventional Al=Al double bond. Comprehensive searches for the most stable structures of the LiAl 2 H 4 - cluster have shown that the global minimum isomer I possesses a geometric structure which resembles that of Si 2 H 4 , demonstrating a successful example of the transmutation of Al atoms into Si atoms by electron donation. Theoretical simulations of the photoelectron spectrum discovered the coexistence of two isomers in the ion beam, including the one with the Al=Al double bond. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

THP-1 macrophage lipid accumulation unaffected by fatty acid double bond geometric or positional configuration

USDA-ARS?s Scientific Manuscript database

Dietary fatty acid type alters atherosclerotic lesion progression and macrophage lipid accumulation. Incompletely elucidated are the mechanisms by which fatty acids differing in double-bond geometric or positional configuration alter arterial lipid accumulation. The objective of this study was to ev...

A Novel Multiscale Design of Interfaces for Polymeric Composites and Bonded Joints using Additive Manufacturing

DTIC Science & Technology

2016-09-13

AFRL-AFOSR-VA-TR-2016-0317 A Novel Multiscale Design of Interfaces for Polymeric Composites and Bonded Joints using Additive Manufacturing Pavana...Composites and Bonded Joints using Additive Manufacturing AWARD NO.: FA9550-15-1-0216 AGENCY NAME: The Air Force Office of Scientific Research (AFOSR), Ar...20 3 Additive Manufacturing for Bonded Composite Joints 21 3.1 Introduction

First-principles study on C=C defects near SiC/SiO2 interface: Defect passivation by double-bond saturation

NASA Astrophysics Data System (ADS)

Tajima, Nobuo; Kaneko, Tomoaki; Yamasaki, Takahiro; Nara, Jun; Schimizu, Tatsuo; Kato, Koichi; Ohno, Takahisa

2018-04-01

Thermally produced SiC/SiO2 stacking in SiC MOSFETs creates defect-related interfacial states in and around the band gap of SiC. These interfacial states can cause serious reliability problems such as threshold voltage shift, as well as efficiency problems such as channel mobility degradation. Carbon species having C=C double bonds have been suggested as one of the origins of these interfacial states. We have theoretically shown that this type of defect produces interfacial states in and around the band gap of SiC, and that they can be removed by saturating the C=C double bond by reactions with H2 and F2. The single-bond products of these reactions are found to be stable at regular device operation temperatures.

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.

Origin of the 900 cm{sup −1} broad double-hump OH vibrational feature of strongly hydrogen-bonded carboxylic acids

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

Van Hoozen, Brian L.; Petersen, Poul B.

2015-03-14

Medium and strong hydrogen bonds are common in biological systems. Here, they provide structural support and can act as proton transfer relays to drive electron and/or energy transfer. Infrared spectroscopy is a sensitive probe of molecular structure and hydrogen bond strength but strongly hydrogen-bonded structures often exhibit very broad and complex vibrational bands. As an example, strong hydrogen bonds between carboxylic acids and nitrogen-containing aromatic bases commonly display a 900 cm{sup −1} broad feature with a remarkable double-hump structure. Although previous studies have assigned this feature to the OH, the exact origin of the shape and width of this unusualmore » feature is not well understood. In this study, we present ab initio calculations of the contributions of the OH stretch and bend vibrational modes to the vibrational spectrum of strongly hydrogen-bonded heterodimers of carboxylic acids and nitrogen-containing aromatic bases, taking the 7-azaindole—acetic acid and pyridine—acetic acid dimers as examples. Our calculations take into account coupling between the OH stretch and bend modes as well as how both of these modes are affected by lower frequency dimer stretch modes, which modulate the distance between the monomers. Our calculations reproduce the broadness and the double-hump structure of the OH vibrational feature. Where the spectral broadness is primarily caused by the dimer stretch modes strongly modulating the frequency of the OH stretch mode, the double-hump structure results from a Fermi resonance between the out of the plane OH bend and the OH stretch modes.« less

Accurate characterization of wafer bond toughness with the double cantilever specimen

NASA Astrophysics Data System (ADS)

Turner, Kevin T.; Spearing, S. Mark

2008-01-01

The displacement loaded double cantilever test, also referred to as the "Maszara test" and the "crack opening method" by the wafer bonding community, is a common technique used to evaluate the interface toughness or surface energy of direct wafer bonds. While the specimen is widely used, there has been a persistent question as to the accuracy of the method since the actual specimen geometry differs from the ideal beam geometry assumed in the expression used for data reduction. The effect of conducting the test on whole wafer pairs, in which the arms of cantilevers are wide plates rather than slender beams, is examined in this work using finite element analysis. A model is developed to predict the equilibrium shape of the crack front and to develop a corrected expression for calculating interface toughness from crack length measurements obtained in tests conducted on whole wafer pairs. The finite element model, which is validated through comparison to experiments, demonstrates that using the traditional beam theory-based expressions for data reduction can lead to errors of up to 25%.

The covalently bound diazo group as an infrared probe for hydrogen bonding environments.

PubMed

You, Min; Liu, Liyuan; Zhang, Wenkai

2017-07-26

Covalently bound diazo groups are frequently found in biomolecular substrates. The C[double bond, length as m-dash]N[double bond, length as m-dash]N asymmetric stretching vibration (ν as ) of the diazo group has a large extinction coefficient and appears in an uncongested spectral region. To evaluate the solvatochromism of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band for studying biomolecules, we recorded the infrared (IR) spectra of a diazo model compound, 2-diazo-3-oxo-butyric acid ethyl ester, in different solvents. The width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band was linearly dependent on the Kamlet-Taft solvent parameter, which reflects the polarizability and hydrogen bond accepting ability of the solvent. Therefore, the width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band could be used to probe these properties for a solvent. We found that the position of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band was linearly correlated with the density of hydrogen bond donor groups in the solvent. We studied the relaxation dynamics and spectral diffusion of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band of a natural amino acid, 6-diazo-5-oxo-l-norleucine, in water using nonlinear IR spectroscopy. The relaxation and spectral diffusion time constants of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band were similar to those of the N[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band. We concluded that the position and width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N ν as band of the diazo group could be used to probe the hydrogen bond donating and accepting ability of a solvent, respectively. These results suggest that the diazo group could be used as a site-specific IR probe for the local hydration

27 CFR 19.959 - Additional provisions with respect to bonds.

Code of Federal Regulations, 2010 CFR

2010-04-01

... alcohol fuel plants. Construction, Equipment and Security ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Additional provisions with respect to bonds. 19.959 Section 19.959 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND...

42 CFR 489.66 - Additional requirements of the surety bond.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 42 Public Health 5 2010-10-01 2010-10-01 false Additional requirements of the surety bond. 489.66 Section 489.66 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN... of this subpart, remains effective and the Surety remains liable for unpaid claims, civil money...

In vitro bonding effectiveness of three different one-step self-etch adhesives with additional enamel etching.

PubMed

Batra, Charu; Nagpal, Rajni; Tyagi, Shashi Prabha; Singh, Udai Pratap; Manuja, Naveen

2014-08-01

To evaluate the effect of additional enamel etching on the shear bond strength of three self-etch adhesives. Class II box type cavities were made on extracted human molars. Teeth were randomly divided into one control group of etch and rinse adhesive and three test groups of self-etch adhesives (Clearfil S3 Bond, Futurabond NR, Xeno V). The teeth in the control group (n = 10) were treated with Adper™ Single Bond 2. The three test groups were further divided into two subgroups (n = 10): (i) self-etch adhesive was applied as per the manufacturer's instructions; (ii) additional etching of enamel surfaces was done prior to the application of self-etch adhesives. All cavities were restored with Filtek Z250. After thermocycling, shear bond strength was evaluated using a Universal testing machine. Data were analyzed using anova independent sample's 't' test and Dunnett's test. The failure modes were evaluated with a stereomicroscope at a magnification of 10×. Additional phosphoric acid etching of the enamel surface prior to the application of the adhesive system significantly increased the shear bond strength of all the examined self-etch adhesives. Additional phosphoric acid etching of enamel surface significantly improved the shear bond strength. © 2013 Wiley Publishing Asia Pty Ltd.

Evidence for cis-trans isomerization of a double bond in the fatty acids of the psychrophilic bacterium Vibrio sp. strain ABE-1.

PubMed

Morita, N; Shibahara, A; Yamamoto, K; Shinkai, K; Kajimoto, G; Okuyama, H

1993-02-01

Vibrio sp. strain ABE-1 was grown in a medium that contained as its stable isotope tracer either [2,2-2H2]cis-9-hexadecenoic or [2,2-2H2]trans-9-hexadecenoic acid. Gas chromatographic-mass spectrometric analysis of the cis-9-hexadecenoic and trans-9-hexadecenoic acid fractions from the cells revealed the formation of an intracellularly isomerized 2,2-2H2-fatty acid which differed from the tracer only in the geometrical configuration of the double bond. This observation shows that cis-trans isomerization without a shift in double-bond position between these two geometric hexadecenoic acid isomers can occur in the cells.

Evidence for cis-trans isomerization of a double bond in the fatty acids of the psychrophilic bacterium Vibrio sp. strain ABE-1.

PubMed Central

Morita, N; Shibahara, A; Yamamoto, K; Shinkai, K; Kajimoto, G; Okuyama, H

1993-01-01

Vibrio sp. strain ABE-1 was grown in a medium that contained as its stable isotope tracer either [2,2-2H2]cis-9-hexadecenoic or [2,2-2H2]trans-9-hexadecenoic acid. Gas chromatographic-mass spectrometric analysis of the cis-9-hexadecenoic and trans-9-hexadecenoic acid fractions from the cells revealed the formation of an intracellularly isomerized 2,2-2H2-fatty acid which differed from the tracer only in the geometrical configuration of the double bond. This observation shows that cis-trans isomerization without a shift in double-bond position between these two geometric hexadecenoic acid isomers can occur in the cells. PMID:8423164

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.

Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon Double Bonds.

PubMed

Bidange, Johan; Fischmeister, Cédric; Bruneau, Christian

2016-08-22

Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2.

PubMed

Takeshita, Tyler Y; Lindquist, Beth A; Dunning, Thom H

2015-07-16

There are many well-known differences in the physical and chemical properties of ozone (O3) and sulfur dioxide (SO2). O3 has longer and weaker bonds than O2, whereas SO2 has shorter and stronger bonds than SO. The O-O2 bond is dramatically weaker than the O-SO bond, and the singlet-triplet gap in SO2 is more than double that in O3. In addition, O3 is a very reactive species, while SO2 is far less so. These disparities have been attributed to variations in the amount of diradical character in the two molecules. In this work, we use generalized valence bond (GVB) theory to characterize the electronic structure of ozone and sulfur dioxide, showing O3 does indeed possess significant diradical character, whereas SO2 is effectively a closed shell molecule. The GVB results provide critical insights into the genesis of the observed difference in these two isoelectronic species. SO2 possesses a recoupled pair bond dyad in the a"(π) system, resulting in SO double bonds. The π system of O3, on the other hand, has a lone pair on the central oxygen atom plus a pair of electrons in orbitals on the terminal oxygen atoms that give rise to a relatively weak π interaction.

Activation of carbon-hydrogen bonds and dihydrogen by 1,2-CH-addition across metal-heteroatom bonds.

PubMed

Webb, Joanna R; Burgess, Samantha A; Cundari, Thomas R; Gunnoe, T Brent

2013-12-28

The controlled conversion of hydrocarbons to functionalized products requires selective C-H bond cleavage. This perspective provides an overview of 1,2-CH-addition of hydrocarbons across d(0) transition metal imido complexes and compares and contrasts these to examples of analogous reactions that involve later transition metal amide, hydroxide and alkoxide complexes with d(6) and d(8) metals.

Extended reaction scope of thiamine diphosphate dependent cyclohexane-1,2-dione hydrolase: from C-C bond cleavage to C-C bond ligation.

PubMed

Loschonsky, Sabrina; Wacker, Tobias; Waltzer, Simon; Giovannini, Pier Paolo; McLeish, Michael J; Andrade, Susana L A; Müller, Michael

2014-12-22

ThDP-dependent cyclohexane-1,2-dione hydrolase (CDH) catalyzes the CC bond cleavage of cyclohexane-1,2-dione to 6-oxohexanoate, and the asymmetric benzoin condensation between benzaldehyde and pyruvate. One of the two reactivities of CDH was selectively knocked down by mutation experiments. CDH-H28A is much less able to catalyze the CC bond formation, while the ability for CC bond cleavage is still intact. The double variant CDH-H28A/N484A shows the opposite behavior and catalyzes the addition of pyruvate to cyclohexane-1,2-dione, resulting in the formation of a tertiary alcohol. Several acyloins of tertiary alcohols are formed with 54-94 % enantiomeric excess. In addition to pyruvate, methyl pyruvate and butane-2,3-dione are alternative donor substrates for CC bond formation. Thus, the very rare aldehyde-ketone cross-benzoin reaction has been solved by design of an enzyme variant. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Estimation of strength in different extra Watson-Crick hydrogen bonds in DNA double helices through quantum chemical studies.

PubMed

Bandyopadhyay, D; Bhattacharyya, D

2006-10-15

It was shown earlier, from database analysis, model building studies, and molecular dynamics simulations that formation of cross-strand bifurcated or Extra Watson-Crick hydrogen (EWC) bonds between successive base pairs may lead to extra rigidity to DNA double helices of certain sequences. The strengths of these hydrogen bonds are debatable, however, as they do not have standard linear geometry criterion. We have therefore carried out detailed ab initio quantum chemical studies using RHF/6-31G(2d,2p) and B3LYP/6-31G(2p,2d) basis sets to determine strengths of several bent hydrogen bonds with different donor and acceptors. Interaction energy calculations, corrected for the basis set superposition errors, suggest that N-H...O type bent EWC hydrogen bonds are possible along same strands or across the strands between successive base pairs, leading to significant stability (ca. 4-9 kcal/mol). The N-H...N and C-H...O type interactions, however, are not so stabilizing. Hence, consideration of EWC N-H...O H-bonds can lead to a better understanding of DNA sequence directed structural features. Copyright (c) 2006 Wiley Periodicals, Inc.

Regioselective cis-trans isomerization of arachidonic double bonds by thiyl radicals: the influence of phospholipid supramolecular organization.

PubMed

Ferreri, Carla; Samadi, Abdelouahid; Sassatelli, Fabio; Landi, Laura; Chatgilialoglu, Chryssostomos

2004-02-04

Trans unsaturated fatty acids in humans may be originated by two different contributions. The exogenous track is due to dietary supplementation of trans fats and the endogenous path deals with free-radical-catalyzed cis-trans isomerization of fatty acids. Arachidonic acid residue (5c,8c,11c,14c-20:4), which has only two out of the four double bonds deriving from the diet, was used to differentiate the two paths and to assess the importance of a radical reaction. A detailed study on the formation of trans phospholipids catalyzed by the HOCH2CH2S* radical was carried out on L-alpha-phosphatidylcholine from egg lecithin and 1-stearoyl-2-arachidonoyl-L-alpha-phosphatidylcholine (SAPC) in homogeneous solution or in large unilamellar vesicles (LUVET). Thiyl radicals were generated from the corresponding thiol by either gamma-irradiation or UV photolysis, and the reaction course was followed by GC, Ag/TLC, and 13C NMR analyses. The isomerization was found to be independent of cis double bond location (random process) in i-PrOH solution. In the case of vesicles, the supramolecular organization of lipids produced a dramatic change of the isomerization outcome: (i) in egg lecithin, the reactivity of arachidonate moieties is higher than that of oleate and linoleate residues, (ii) in the linoleate residues of egg lecithin, the 9t,12c-18:2 isomer prevailed on the 9c,12t-18:2 isomer (3:1 ratio), and (iii) a regioselective isomerization of SAPC arachidonate residues occurred in the 5 and 8 positions. This effect of "positional preference" indicates that thiyl radicals entering the hydrophobic region of the membrane bilayer start to isomerize polyunsaturated fatty acid residues having the double bonds nearest to the membrane surfaces. We propose that arachidonic acid and its trans isomers can function as biomarkers in membranes for distinguishing the two trans fatty acid-forming pathways.

Assessing the issue of instability due to Michael adduct formation in novel chemical entities possessing a carbon-carbon double bond during early drug development--applicability of common laboratory analytical protocols.

PubMed

Polepally, Akshanth Reddy; Kumar, Venkata V Pavan; Bhamidipati, Ravikanth; Kota, Jagannath; Naveed, Shaik Abdul; Reddy, Karnati Harinder; Mamidi, Rao N V S; Selvakumar, N; Mullangi, Ramesh; Srinivas, Nuggehally R

2008-09-01

The discovery of small-molecule novel chemical entities (NCEs) is often a complex play between appropriate structural requirements and optimization of the desired efficacy, safety and pharmacokinetic properties. One of the typical structural variants such as having an active carbon-carbon double bond (alpha, beta-unsaturated carbonyl group) in xenobiotics may lead to stability issues. Such functionalities are extremely reactive, paving way to nucleophilic attack by endogenously occurring and ubiquitous nucleophiles like thiols. While it is easy to make a unilateral decision to not pursue the development of xenobiotics with such functionalities, we question the wisdom of such a decision. In this report, we present in vitro methodologies with appropriate examples to illustrate the ease of assessing the reactivity of the xenobiotics containing double bonds with a known nucleophile. The protocols involve simple reaction procedures followed by measurements using standard laboratory equipments (UV spectrophotometer, HPLC and LC-MS). Our data suggests that not all xenobiotics with carbon-carbon double bonds readily form a Michael's adduct product with glutathione. Hence, the criterion for dropping discovery compounds because of alpha,beta-unsaturated double bonds needs to be reconsidered.

Double addition of diethylamine to biacetylene (in Russian)

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

Trofimov, B.A.; Vavilova, A.N.

1986-03-01

Biacetylene reacts with an excess of diethylamine in dilute solutions of anhydrous acetonitrile, methanol, ethanol, and THF to form the diadduct 1,3-bis(diethyl-amino)-1,3-butadiene (lambda/sub max/ 325 nm). During concentration of the reaction mixture the latter undergoes hydration by the residual amounts of water in the 3-(diethylamino)-2-butenal. The spectral characteristics (UV, IR, PMR) of the intermediate reaction products are given. The kinetics of the stage of addition of the diethylamine and water to the monoadduct, 1-(diethylamino)-1-buten-3-yne, were studied. It was concluded that the addition of the nucleophile to the triple bond during its secondary amination and hydration is facilitated by the concertedmore » transfer of a proton.« less

Different Roles of Endo- and Exo-cyclic Double Bonds in Limonene Ozonolysis System: Effect of Water and OH Radical Scavengers

NASA Astrophysics Data System (ADS)

Gong, Y.; Li, H.; Chen, Z.

2017-12-01

Limonene, as an important monoterpene, has a high emission rate both from biogenic and anthropogenic sources. Its doubly unsaturated structure leads to a high potential for secondary organic aerosol formation and a detailed understanding of roles of endo- and exo-cyclic double bonds in limonene ozonolysis is in urgent need. This study provided new insights into the mechanism and effect of both unsaturated bonds oxidation. A low and a high ratio set of [O3]/[limonene] experiments in the presence or absence of OH scavenger (2-butanol or cyclohexane) in the relative humidity (RH) range of 0-90% were conducted. Molar yields of hydrogen peroxide (H2O2) and hydromethyl hydroperoxide (HMHP) both increased rapidly as RH rose from 0 to 50%, then reached a plateau above 70% RH, while peroxyformic acid (PFA) and peroxyacetic acid (PAA) kept increasing with RH. The ozonolysis of exocyclic double bonds showed larger capacity for producing these peroxides than endocyclic ones, resulting in significantly higher yields of H2O2, HMHP, PFA and PAA in limonene ozonolysis than α-pinene when ozone was sufficient. The SOA mass fraction of total peroxides was 50% at high [O3]/[limonene] ratio, whereas only 12% at low ratio. The gas-particle partitioning coefficient of undetected peroxides rose up from (0.8-2.0)×10-3m3μg-1 at 0% RH to (4.0-5.2)×10-3m3μg-1 at 90% RH, indicating some water-dependent channels contributed low-volatility peroxides formation. A box model was employed to simulate the reaction system, and the results obviously underestimated the yield of H2O2, whilst overestimated the yield of undetected peroxides. It is interesting to note that SOA produced at high [O3]/[limonene] ratio could generate considerable amount of H2O2 in the aqueous phase, which may be another source of H2O2 in cloud drops. To elucidate the mechanism further, the yield of OH radicals formed from endocyclic double bonds was found to be about 3 times larger than that from exocyclic double bonds

Shear bond strength of self-etch adhesives to enamel with additional phosphoric acid etching.

PubMed

Lührs, Anne-Katrin; Guhr, Silke; Schilke, Reinhard; Borchers, Lothar; Geurtsen, Werner; Günay, Hüsamettin

2008-01-01

This study evaluated the shear bond strength of self-etch adhesives to enamel and the effect of additional phosphoric acid etching. Seventy sound human molars were randomly divided into three test groups and one control group. The enamel surfaces of the control group (n=10) were treated with Syntac Classic (SC). Each test group was subdivided into two groups (each n=10). In half of each test group, ground enamel surfaces were coated with the self-etch adhesives AdheSe (ADH), Xeno III (XE) or Futurabond NR (FNR). In the remaining half of each test group, an additional phosphoric acid etching of the enamel surface was performed prior to applying the adhesives. The shear bond strength was measured with a universal testing machine at a crosshead speed of 1 mm/minute after storing the samples in distilled water at 37 degrees C for 24 hours. Fracture modes were determined by SEM examination. For statistical analysis, one-way ANOVA and the two-sided Dunnett Test were used (p>0.05). Additional phosphoric etching significantly increased the shear bond strength of all the examined self-etch adhesives (p<0.001). The highest shear bond strength was found for FNR after phosphoric acid etching. Without phosphoric acid etching, only FNR showed no significant differences compared to the control (SC). SEM evaluations showed mostly adhesive fractures. For all the self-etch adhesives, a slight increase in mixed fractures occurred after conditioning with phosphoric acid. An additional phosphoric acid etching of enamel should be considered when using self-etch adhesives. More clinical studies are needed to evaluate the long-term success of the examined adhesives.

CRADA/NFE-15-05761 Report: Additive Manufacturing of Isotropic NdFeB Bonded Permanent Magnets

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

Paranthaman, M. Parans

2016-07-18

The technical objective of this technical collaboration phase I proposal is to fabricate net shape isotropic NdFeB bonded magnets utilizing additive manufacturing technologies at the ORNL MDF. The goal is to form complex shapes of thermoplastic and/or thermoset bonded magnets without expensive tooling and with minimal wasted material. Two additive manufacturing methods; the binder jet process; and big area additive manufacturing (BAAM) were used. Binder jetting produced magnets with the measured density of the magnet of 3.47 g/cm 3, close to 46% relative to the NdFeB single crystal density of 7.6 g/cm 3 were demonstrated. Magnetic measurements indicate that theremore » is no degradation in the magnetic properties. In addition, BAAM was used to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm 3, and the room temperature magnetic properties are: Intrinsic coercivity Hci = 8.65 kOe, Remanence Br = 5.07 kG, and energy product (BH) max = 5.47 MGOe (43.50 kJ/m 3). This study provides a new pathway for preparing near-net shape bonded magnets for various magnetic applications.« less

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.

The effect of double-coating and times on the immediate and 6-month dentin bonding of universal adhesives.

PubMed

Pashaev, Diial; Demirci, Mustafa; Tekçe, Neslihan; Tuncer, Safa; Baydemir, Canan

2017-01-01

The purpose of this study was to evaluate the effect of double-application coats and times on microtensile bond strength (μTBS) and adhesive-dentin interfaces created by dentin adhesive systems after 6 months of storage in water. Two-hundred sixteen extracted non-carious human third molars were selected for the study. Single-Bond Universal (SU) and All-Bond Universal (AU), Adper Easy One (Eo) Self-Etch adhesive and Adper Single-Bond 2 (Sb) etch-and-rinse adhesive were applied to a flat dentin surface using three methods (1): dentin adhesives were applied as recommended by the manufacturers; (2): two consecutive coats of dentin adhesives were applied before photo-polymerization; and (3): a single coat of adhesive was applied but with twice the manufacturers recommended application time. Microtensile bond strength was determined either immediately or after 6 months of water storage. Data were analyzed using one-way analysis of variance and Tukey's post-hoc tests. At 24 h, groups 1, 2, and 3 exhibited statistically similar results for all dentin adhesive systems. For AU-Er, group 3 showed significantly higher bond strength than all group of AU-Se after 6 months. Universal adhesives seemed more stable against water degradation than traditional two-step etch-and-rinse and all-in-one systems within the 6-month period.

Catalytic coupling of sp2- and sp-hybridized carbon-hydrogen bonds with vinylmetalloid compounds.

PubMed

Marciniec, Bogdan

2007-10-01

In the Account given herein, it has been shown that silylative coupling of olefins, well-recognized as a new catalytic route for the activation of double bond C-H bond of olefins and double bond C-Si bond of vinylsilicon compounds with ethylene elimination, can be extended over both other vinylmetalloid derivatives (double bond C-E) (where E = Ge, B, and others) as well as the activation of triple bond C-H, double bond C aryl-H, and -O-H bond of alcohols and silanols. This general transformation is catalyzed by transition-metal complexes (mainly Ru and Rh) containing or initiating TM-H and/or TM-E bonds (inorganometallics). This new general catalytic route for the activation of double bond C-H and triple bond C-H as well as double bond C-E bonds called metallative coupling or trans-metalation (cross-coupling, ring-closing, and polycondensation) constitutes an efficient method (complementary to metathesis) for stereo- and regioselective synthesis of a variety of molecular and macromolecular compounds of vinyl-E (E = Si, B, and Ge) and ethynyl-E (E = Si and Ge) functionality, also potent organometallic reagents for efficient synthesis of highly pi-conjugated organic compounds. The mechanisms of the catalysis of this deethenative metalation have been supported by equimolar reactions of TM-H and/or TM-E with initial substances and reactions with deuterium-labeled reagents.

Bond additive modeling 10. Upper and lower bounds of bond incident degree indices of catacondensed fluoranthenes

NASA Astrophysics Data System (ADS)

Vukičević, Damir; Đurđević, Jelena

2011-10-01

Bond incident degree index is a descriptor that is calculated as the sum of the bond contributions such that each bond contribution depends solely on the degrees of its incident vertices (e.g. Randić index, Zagreb index, modified Zagreb index, variable Randić index, atom-bond connectivity index, augmented Zagreb index, sum-connectivity index, many Adriatic indices, and many variable Adriatic indices). In this Letter we find tight upper and lower bounds for bond incident degree index for catacondensed fluoranthenes with given number of hexagons.

Surface oxidation under ambient air--not only a fast and economical method to identify double bond positions in unsaturated lipids but also a reminder of proper lipid processing.

PubMed

Zhou, Ying; Park, Hyejung; Kim, Philseok; Jiang, Yan; Costello, Catherine E

2014-06-17

A simple, fast approach elucidated carbon-carbon double bond positions in unsaturated lipids. Lipids were deposited onto various surfaces and the products from their oxidation in ambient air were observed by electrospray ionization (ESI) mass spectrometry (MS). The most common oxidative products, aldehydes, were detected as transformations at the cleaved double bond positions. Ozonides and carboxylic acids were generated in certain lipids. Investigations of the conditions controlling the appearance of these products indicated that the surface oxidation depends on light and ambient air. Since the lipid oxidation was slower in a high concentration of ozone, singlet oxygen appeared to be a parallel oxidant for unsaturated lipids. The 3-hydroxyl group in the sphingoid base of sulfatides offered some protection from oxidation for the Δ4,5-double bond, slowing its oxidation rate relative to that of the isolated double bond in the N-linked fatty acyl chain. Direct sampling by thin-layer chromatography (TLC)-ESI-MS provides a powerful approach to elucidate detailed structural information on biological samples. Co-localization of the starting lipids and their oxidation products after TLC separation allowed assignment of the native unsaturation sites. Phosphatidylserine and N,N-dimethyl phosphatidylethanolamine isomers in a bovine brain total lipid extract were distinguished on the basis of their oxidation products. Meanwhile, the findings reported herein reveal a potential pitfall in the assignment of structures to lipids extracted from TLC plates because of artifactual oxidation after the plate development.

Photoisomerization around a fulvene double bond: coherent population transfer to the electronic ground state?

PubMed

Ioffe, Ilya; Dobryakov, Alexander L; Granovsky, Alexander A; Ernsting, Nikolaus P; Lustres, J Luis Pérez

2011-07-11

Photoisomerization around a central fulvene-type double bond is known to proceed through a conical intersection at the perpendicular geometry. The process is studied with an indenylidene-dihydropyridine model compound, allowing the use of visible excitation pulses. Transient absorption shows that 1) stimulated emission shifts to the red and loses oscillator strength on a 50 fs timescale, and 2) bleach recovery is highly nonexponential and not affected by solvent viscosity or methyl substitution at the dihydropyridine ring. Quantum-chemical calculations are used to explain point 1 as a result of initial elongation of the central C=C bond with mixing of S(2) and S(1) states. From point 2 it is concluded that internal conversion of S(1)→S(0) does not require torsional motion to the fully perpendicular state. The S(1) population appears to encounter a sink on the torsional coordinate before the conical intersection is reached. Rate equations cannot model the observed ground-state recovery adequately. Instead the dynamics are best described with a strongly damped oscillatory contribution, which could indicate coherent S(1)-S(0) population transfer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bond-rearrangement and ionization mechanisms in the photo-double-ionization of simple hydrocarbons (C 2H 4, C 2H 3F, and 1,1-C 2H 2F 2) near and above threshold

DOE PAGES

Gaire, B.; Gatton, A. S.; Wiegandt, F.; ...

2016-09-14

We have investigated bond-rearrangement driven by photo-double-ionization (PDI) near and above the double ionization threshold in a sequence of carbon-carbon double bonded hydrocarbon molecules: ethylene, fluoroethylene, and 1,1-difluoroethylene. We employ the kinematically complete cold target recoil ion momentum spectroscopy (COLTRIMS) method to resolve all photo-double-ionization events leading to two-ionic fragments. We observe changes in the branching ratios of different dissociative ionization channels depending on the presence of none, one, or two fluorine atoms. The role of the fluorine atom in the bond-rearrangement channels is intriguing as evident by the re-ordering of the threshold energies of the PDI in the fluorinatedmore » molecules. These effects offer a compelling argument that the electronegativity of the fluorine (or the polarity of the molecule) strongly influences the potential energy surfaces of the molcules and drives bond-rearrangement during the dissociation process. The energy sharing and the relative angle between the 3D-momentum vectors of the two electrons provide clear evidence of direct and indirect PDI processes.« less

48 CFR 28.106-3 - Additional bond and security.

Code of Federal Regulations, 2010 CFR

2010-10-01

... GENERAL CONTRACTING REQUIREMENTS BONDS AND INSURANCE Bonds and Other Financial Protections 28.106-3... described in 28.204 in lieu of corporate or individual surety, agencies shall use Standard Form 25...

A density functional theory for association of fluid molecules with a functionalized surface: fluid-wall single and double bonding.

PubMed

Haghmoradi, Amin; Wang, Le; Chapman, Walter G

2017-02-01

In this manuscript we extend Wertheim's two-density formalism beyond its first order to model a system of fluid molecules with a single association site close to a planar hard wall with association sites on its surface in a density functional theory framework. The association sites of the fluid molecules are small enough that they can form only one bond, while the wall association sites are large enough to bond with more than one fluid molecule. The effects of temperature and of bulk fluid and wall site densities on the fluid density profile, extent of association, and competition between single and double bonding of fluid segments at the wall sites versus distance from the wall are presented. The theory predictions are compared with new Monte Carlo simulation results and they are in good agreement. The theory captures the surface coverage over wide ranges of temperature and bulk density by introducing the effect of steric hindrance in fluid association at a wall site.

Big Area Additive Manufacturing of High Performance Bonded NdFeB Magnets

NASA Astrophysics Data System (ADS)

Li, Ling; Tirado, Angelica; Nlebedim, I. C.; Rios, Orlando; Post, Brian; Kunc, Vlastimil; Lowden, R. R.; Lara-Curzio, Edgar; Fredette, Robert; Ormerod, John; Lograsso, Thomas A.; Paranthaman, M. Parans

2016-10-01

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic properties are: intrinsic coercivity Hci = 688.4 kA/m, remanence Br = 0.51 T, and energy product (BH)max = 43.49 kJ/m3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. The present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.

Big area additive manufacturing of high performance bonded NdFeB magnets

DOE PAGES

Li, Ling; Tirado, Angelica; Nlebedim, I. C.; ...

2016-10-31

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic propertiesmore » are: intrinsic coercivity Hci = 688.4 kA/m, remanence B r = 0.51 T, and energy product (BH) max = 43.49 kJ/m 3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. As a result, the present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.« less

Big area additive manufacturing of high performance bonded NdFeB magnets

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

Li, Ling; Tirado, Angelica; Nlebedim, I. C.

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic propertiesmore » are: intrinsic coercivity Hci = 688.4 kA/m, remanence B r = 0.51 T, and energy product (BH) max = 43.49 kJ/m 3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. As a result, the present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.« less

Role of intramolecular hydrogen bonding in the excited-state intramolecular double proton transfer (ESIDPT) of calix[4]arene: A TDDFT study

NASA Astrophysics Data System (ADS)

Wang, Se; Wang, Zhuang; Hao, Ce

2016-01-01

The time-dependent density functional theory (TDDFT) method was performed to investigate the excited-state intramolecular double proton transfer (ESIDPT) reaction of calix[4] arene (C4A) and the role of the intramolecular hydrogen bonds in the ESIDPT process. The geometries of C4A in the ground state and excited states (S1, S2 and T1) were optimized. Four intramolecular hydrogen bonds formed in the C4A are strengthened or weakened in the S2 and T1 states compared to those in the ground state. Interestingly, upon excitation to the S1 state of C4A, two protons H1 and H2 transfer along the two intramolecular hydrogen bonds O1-H1···O2 and O2-H2···O3, while the other two protons do not transfer. The ESIDPT reaction breaks the primary symmetry of C4A in the ground state. The potential energy curves of proton transfer demonstrate that the ESIDPT process follows the stepwise mechanism but not the concerted mechanism. Findings indicate that intramolecular hydrogen bonding is critical to the ESIDPT reactions in intramolecular hydrogen-bonded systems.

Replacement of the double bond of antitubulin chalcones with triazoles and tetrazoles: Synthesis and biological evaluation.

PubMed

Mesenzani, Ornella; Massarotti, Alberto; Giustiniano, Mariateresa; Pirali, Tracey; Bevilacqua, Valentina; Caldarelli, Antonio; Canonico, Pierluigi; Sorba, Giovanni; Novellino, Ettore; Genazzani, Armando A; Tron, Gian Cesare

2011-01-15

In the chalcone scaffold, it is thought that the double bond is an important structural linker but it is likely not essential for the interaction with tubulin. Yet, it may be a potential site of metabolic degradation and interaction with biological nucleophiles. In this letter, we have replaced this olefinic portion of chalcones with two metabolically stable and chemically inert heterocyclic rings, namely triazole or tetrazole. Yet, our biologic data suggest that, unlike in other antitubulinic structures, the olephinic ring might not be merely a structural linker. Copyright © 2010 Elsevier Ltd. All rights reserved.

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

The structure of the ends of α-helices in globular proteins: effect of additional hydrogen bonds and implications for helix formation.

PubMed

Leader, David P; Milner-White, E James

2011-03-01

We prepared a set of about 2000 α-helices from a relational database of high-resolution three-dimensional structures of globular proteins, and identified additional main chain i ← i+3 hydrogen bonds at the ends of the helices (i.e., where the hydrogen bonding potential is not fulfilled by canonical i ← i+4 hydrogen bonds). About one-third of α-helices have such additional hydrogen bonds at the N-terminus, and more than half do so at the C-terminus. Although many of these additional hydrogen bonds at the C-terminus are associated with Schellman loops, the majority are not. We compared the dihedral angles at the termini of α-helices having or lacking the additional hydrogen bonds. Significant differences were found, especially at the C-terminus, where the dihedral angles at positions C2 and C1 in the absence of additional hydrogen bonds deviate substantially from those occurring within the α-helix. Using a novel approach we show how the structure of the C-terminus of the α-helix can emerge from that of constituent overlapping α-turns and β-turns, which individually show a variation in dihedral angles at different positions. We have also considered the direction of propagation of the α-helix using this approach. If one assumes that helices start as a single α-turn and grow by successive addition of further α-turns, the paths for growth in the N → C and C → N directions differ in a way that suggests that extension in the C → N direction is favored. Copyright © 2010 Wiley-Liss, Inc.

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).

Analysis of factors influencing the bond strength in roll bonding processes

NASA Astrophysics Data System (ADS)

Khaledi, Kavan; Wulfinghoff, Stephan; Reese, Stefanie

2018-05-01

Cold Roll Bonding (CRB) is recognized as an industrial technique in which the metal sheets are joined together in order to produce laminate metal composites. In this technique, a metallurgical bond resulting from severe plastic deformation is formed between the rolled metallic layers. The main objective of this paper is to analyse different factors which may affect the bond formation in rolling processes. To achieve this goal, first, an interface model is employed which describes both the bonding and debonding. In this model, the bond strength evolution between the metallic layers is calculated based on the film theory of bonding. On the other hand, the debonding process is modelled by means of a bilinear cohesive zone model. In the numerical section, different scenarios are taken into account to model the roll bonding process of metal sheets. The numerical simulation includes the modelling of joining during the roll bonding process followed by debonding in a Double Cantilever Beam (DCB) peeling test. In all simulations, the metallic layers are regarded as elastoplastic materials subjected to large plastic deformations. Finally, the effects of some important factors on the bond formation are numerically investigated.

A monotopic aluminum telluride with an Al=Te double bond stabilized by N-heterocyclic carbenes

PubMed Central

Franz, Daniel; Szilvási, Tibor; Irran, Elisabeth; Inoue, Shigeyoshi

2015-01-01

Aluminum chalcogenides are mostly encountered in the form of bulk aluminum oxides that are structurally diverse but typically consist of networks with high lattice energy in which the chalcogen atoms bridge the metal centres. This makes their molecular congeners difficult to synthesize because of a pronounced tendency for oligomerization. Here we describe the isolation of the monotopic aluminum chalcogenide (LDipN)AlTe(LEt)2 (LDip=1,3-(2,6-diisopropylphenyl)-imidazolin-2-imine, LEt=1,3-diethyl-4,5-dimethyl-imidazolin-2-ylidene). Unique features of (LDipN)AlTe(LEt)2 are the terminal position of the tellurium atom, the shortest aluminum–tellurium distance hitherto reported for a molecular complex and the highest bond order reported for an interaction between these elements, to the best of our knowledge. At elevated temperature (LDipN)AlTe(LEt)2 equilibrates with dimeric {(LDipN)AlTe(LEt)}2 in which the chalcogen atoms assume their common role as bridges between the metal centres. These findings demonstrate that (LDipN)AlTe(LEt)2 comprises the elusive Al=Te double bond in the form of an N-heterocyclic carbene-stabilized species. PMID:26612781

Big Area Additive Manufacturing of High Performance Bonded NdFeB Magnets

PubMed Central

Li, Ling; Tirado, Angelica; Nlebedim, I. C.; Rios, Orlando; Post, Brian; Kunc, Vlastimil; Lowden, R. R.; Lara-Curzio, Edgar; Fredette, Robert; Ormerod, John; Lograsso, Thomas A.; Paranthaman, M. Parans

2016-01-01

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic properties are: intrinsic coercivity Hci = 688.4 kA/m, remanence Br = 0.51 T, and energy product (BH)max = 43.49 kJ/m3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. The present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials. PMID:27796339

Big Area Additive Manufacturing of High Performance Bonded NdFeB Magnets.

PubMed

Li, Ling; Tirado, Angelica; Nlebedim, I C; Rios, Orlando; Post, Brian; Kunc, Vlastimil; Lowden, R R; Lara-Curzio, Edgar; Fredette, Robert; Ormerod, John; Lograsso, Thomas A; Paranthaman, M Parans

2016-10-31

Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm 3 , and the room temperature magnetic properties are: intrinsic coercivity H ci  = 688.4 kA/m, remanence B r  = 0.51 T, and energy product (BH) max  = 43.49 kJ/m 3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. The present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.

Hindered Csbnd N bond rotation in triazinyl dithiocarbamates

NASA Astrophysics Data System (ADS)

Jung, Taesub; Do, Hee-Jin; Son, Jongwoo; Song, Jae Hee; Cha, Wansik; Kim, Yeong-Joon; Lee, Kyung-Koo; Kwak, Kyungwon

2018-01-01

The substituent and solvent effects on the rotation around a Csbnd N amide bond were studied for a series of triazine dibenzylcarbamodithioates. The Gibbs free energies (ΔG‡) were measured to be 16-18 kcal/mol in DMSO-d6 and toluene-d8 using variable-temperature nuclear magnetic resonance (VT-1H NMR) spectroscopy. Density functional theory (DFT) calculations reproduced the experimental observations with various substituents, as well as solvents. From the detailed analysis of the DFT results, we found that the electron donating dibenzyl amine group increased the electron population on the triazinyl ring, which decreased the rotational barrier of the Csbnd N bond in the dithiocarbamate group attached to the triazinyl ring. The higher electron population on the triazine moiety stabilizes the partial double bond character of the Ssbnd C bond, which competitively excludes the double bond character of the Csbnd N bond. Therefore, the rotational dynamics of the Csbnd N bond in dithiocarbamates can be a sensitive probe to small differences in the electron population of substituents on sulfur.

Cooperative Metal+Ligand Oxidative Addition and Sigma-Bond Metathesis: A DFT Study

DOE PAGES

Lopez, Kent G.; Cundari, Thomas R.; Gary, J. Brannon

2018-01-17

A computational study of the experimentally proposed mechanism of alkyne diboration by a PDICo complex yielded two fundamental catalytic steps that undergo remarkable electronic changes, PDI = bis(imino)-pyridine. The reactions are envisaged via DFT (density functional theory) and MCSCF (multi-configuration self-consistent field) simulations as (i) a cooperative metal+ligand oxidative addition, and (ii) a sigma-bond metathesis induced ligand-to-metal charge transfer. Analysis of the bonding of pertinent intermediates/TSs also yielded important insight that may be illuminating with regards to the larger field of green catalysis that seeks to ennoble base metals through synergy with potentially redox non-innocent (RNI) ligands. For the presentmore » case, massive changes in electronic structure do not incur massive energetic penalties. Finally, in conjunction with previous research, one may postulate that structural and energetic “fluidity” among several electronic states of RNI-M 3d along the reaction coordinate is an essential signature of redox cooperativity and thus ennoblement.« less

Cooperative Metal+Ligand Oxidative Addition and Sigma-Bond Metathesis: A DFT Study

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

Lopez, Kent G.; Cundari, Thomas R.; Gary, J. Brannon

A computational study of the experimentally proposed mechanism of alkyne diboration by a PDICo complex yielded two fundamental catalytic steps that undergo remarkable electronic changes, PDI = bis(imino)-pyridine. The reactions are envisaged via DFT (density functional theory) and MCSCF (multi-configuration self-consistent field) simulations as (i) a cooperative metal+ligand oxidative addition, and (ii) a sigma-bond metathesis induced ligand-to-metal charge transfer. Analysis of the bonding of pertinent intermediates/TSs also yielded important insight that may be illuminating with regards to the larger field of green catalysis that seeks to ennoble base metals through synergy with potentially redox non-innocent (RNI) ligands. For the presentmore » case, massive changes in electronic structure do not incur massive energetic penalties. Finally, in conjunction with previous research, one may postulate that structural and energetic “fluidity” among several electronic states of RNI-M 3d along the reaction coordinate is an essential signature of redox cooperativity and thus ennoblement.« less

Low-lying singlet states of carotenoids having 8-13 conjugated double bonds as determined by electronic absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Peng; Nakamura, Ryosuke; Kanematsu, Yasuo; Koyama, Yasushi; Nagae, Hiroyoshi; Nishio, Tomohiro; Hashimoto, Hideki; Zhang, Jian-Ping

2005-07-01

Electronic absorption spectra were recorded at room temperature in solutions of carotenoids having different numbers of conjugated double bonds, n = 8-13, including a spheroidene derivatives, neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin. The vibronic states of 1Bu+(v=0-4), 2Ag-(v=0-3), 3Ag- (0) and 1Bu- (0) were clearly identified. The arrangement of the four electronic states determined by electronic absorption spectroscopy was identical to that determined by measurement of resonance Raman excitation profiles [K. Furuichi et al., Chem. Phys. Lett. 356 (2002) 547] for carotenoids in crystals.

Additional hydrogen bonds and base-pair kinetics in the symmetrical AMP-DNA aptamer complex.

PubMed Central

Nonin-Lecomte, S; Lin, C H; Patel, D J

2001-01-01

The solution structure of an adenosine monophosphate (AMP)-DNA aptamer complex has been determined previously [Lin, C. H., and Patel, D. J. (1997) Chem. Biol. 4:817-832]. On a symmetrical aptamer complex containing the same binding loop, but with better resolved spectra, we have identified two additional hydrogen bond-mediated associations in the binding loop. One of these involves a rapidly exchanging G imino proton. The phosphate group of the AMP ligand was identified as the acceptor by comparison with other aptamer complexes. Imino proton exchange measurements also yielded the dissociation constants of the stem and binding loop base pairs. This study shows that nuclear magnetic resonance-based imino proton exchange is a good probe for detection of weak hydrogen-bond associations. PMID:11721004

How many hydrogen-bonded α-turns are possible?

PubMed

Schreiber, Anette; Schramm, Peter; Hofmann, Hans-Jörg

2011-06-01

The formation of α-turns is a possibility to reverse the direction of peptide sequences via five amino acids. In this paper, a systematic conformational analysis was performed to find the possible isolated α-turns with a hydrogen bond between the first and fifth amino acid employing the methods of ab initio MO theory in vacuum (HF/6-31G*, B3LYP/6-311 + G*) and in solution (CPCM/HF/6-31G*). Only few α-turn structures with glycine and alanine backbones fulfill the geometry criteria for the i←(i + 4) hydrogen bond satisfactorily. The most stable representatives agree with structures found in the Protein Data Bank. There is a general tendency to form additional hydrogen bonds for smaller pseudocycles corresponding to β- and γ-turns with better hydrogen bond geometries. Sometimes, this competition weakens or even destroys the i←(i + 4) hydrogen bond leading to very stable double β-turn structures. This is also the reason why an "ideal" α-turn with three central amino acids having the perfect backbone angle values of an α-helix could not be localized. There are numerous hints for stable α-turns with a distance between the C(α)-atoms of the first and fifth amino acid smaller than 6-7 Å, but without an i←(i + 4) hydrogen bond.

Emergent Ising degrees of freedom above a double-stripe magnetic ground state [Emergent Ising degrees of freedom above double-stripe magnetism

DOE PAGES

Zhang, Guanghua; Flint, Rebecca

2017-12-27

Here, double-stripe magnetism [Q=(π/2,π/2)] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2Sb 2O families of superconductors. Double-stripe order is captured within a J 1–J 2–J 3 Heisenberg model in the regime J 3 >> J 2 >> J 1. Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π,π). Because the ground state is fourfold degenerate, modulo rotations in spin space,more » only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one.« less

Emergent Ising degrees of freedom above a double-stripe magnetic ground state [Emergent Ising degrees of freedom above double-stripe magnetism

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

Zhang, Guanghua; Flint, Rebecca

Here, double-stripe magnetism [Q=(π/2,π/2)] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2Sb 2O families of superconductors. Double-stripe order is captured within a J 1–J 2–J 3 Heisenberg model in the regime J 3 >> J 2 >> J 1. Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π,π). Because the ground state is fourfold degenerate, modulo rotations in spin space,more » only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one.« less

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

PubMed Central

Pauling, Linus

1978-01-01

An equation for the bond angles OC—M—CO for tetracarbonyl groups in which the transition metal atom M is enneacovalent, derived from the simple theory of hybrid sp3d5 bond orbitals, is tested by comparison of the calculated values of the angles with the experimental values reported for many compounds containing M(CO)4 groups, especially those with M = Fe, Mn, Re, Cr, or Mo. The importance of the energy of resonance of single bonds and double bonds in stabilizing octahedral complexes of chromium and manganese with carbonyl, phosphine, arsine, and thio groups is also discussed. PMID:16592490

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.

Tunable electroluminescent color for 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds

NASA Astrophysics Data System (ADS)

Cheng, Gang; Zhang, Yingfang; Zhao, Yi; Liu, Shiyong; Xie, Zengqi; Xia, Hong; Hanif, Muddasir; Ma, Yuguang

2005-07-01

Exciplex emission is observed in electroluminescent (EL) spectrum of an organic light-emitting device (OLED), where 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds (trans-DPDSB), (8-hydroxyquinoline) aluminum, and N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) are used as light-emitting, electron-transporting, and hole-transporting layers, respectively. This emission can be dramatically weakened by inserting a hole-injecting layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) between the hole-transporting layer and the anode. Consequently, EL color of this OLED is tuned from white to blue. This phenomenon may result from the improvement of hole injection, which shifts the major recombination zone from the NPB/trans-DPDSB interface to the trans-DPDSB layer.

Accurate bond energies of hydrocarbons from complete basis set extrapolated multi-reference singles and doubles configuration interaction.

PubMed

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

2011-12-09

Quantum chemistry has become one of the most reliable tools for characterizing the thermochemical underpinnings of reactions, such as bond dissociation energies (BDEs). The accurate prediction of these particular properties (BDEs) are challenging for ab initio methods based on perturbative corrections or coupled cluster expansions of the single-determinant Hartree-Fock wave function: the processes of bond breaking and forming are inherently multi-configurational and require an accurate description of non-dynamical electron correlation. To this end, we present a systematic ab initio approach for computing BDEs that is based on three components: 1) multi-reference single and double excitation configuration interaction (MRSDCI) for the electronic energies; 2) a two-parameter scheme for extrapolating MRSDCI energies to the complete basis set limit; and 3) DFT-B3LYP calculations of minimum-energy structures and vibrational frequencies to account for zero point energy and thermal corrections. We validated our methodology against a set of reliable experimental BDE values of CC and CH bonds of hydrocarbons. The goal of chemical accuracy is achieved, on average, without applying any empirical corrections to the MRSDCI electronic energies. We then use this composite scheme to make predictions of BDEs in a large number of hydrocarbon molecules for which there are no experimental data, so as to provide needed thermochemical estimates for fuel molecules. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nature of Bonding in Bowl-Like B36 Cluster Revisited: Concentric (6π+18π) Double Aromaticity and Reason for the Preference of a Hexagonal Hole in a Central Location.

PubMed

Li, Rui; You, Xue-Rui; Wang, Kang; Zhai, Hua-Jin

2018-05-04

The bowl-shaped C 6v B 36 cluster with a central hexagon hole is considered an ideal molecular model for low-dimensional boron-based nanosystems. Owing to the electron deficiency of boron, chemical bonding in the B 36 cluster is intriguing, complicated, and has remained elusive despite a couple of papers in the literature. Herein, a bonding analysis is given through canonical molecular orbitals (CMOs) and adaptive natural density partitioning (AdNDP), further aided by natural bond orbital (NBO) analysis and orbital composition calculations. The concerted computational data establish the idea of concentric double π aromaticity for the B 36 cluster, with inner 6π and outer 18π electron counting, which both conform to the (4n+2) Hückel rule. The updated bonding picture differs from existing knowledge of the system. A refined bonding model is also proposed for coronene, of which the B 36 cluster is an inorganic analogue. It is further shown that concentric double π aromaticity in the B 36 cluster is retained and spatially fixed, irrespective of the migration of the hexagonal hole; the latter process changes the system energetically. The hexagonal hole is a destabilizing factor for σ/π CMOs. The central hexagon hole affects substantially fewer CMOs, thus making the bowl-shaped C 6v B 36 cluster the global minimum. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Intramolecular hydrogen-bond activation for the addition of nucleophilic imines: 2-hydroxybenzophenone as a chemical auxiliary.

PubMed

Choubane, Houcine; Garrido-Castro, Alberto F; Alvarado, Cuauhtemoc; Martín-Somer, Ana; Guerrero-Corella, Andrea; Daaou, Mortada; Díaz-Tendero, Sergio; Carmen Maestro, M; Fraile, Alberto; Alemán, José

2018-03-29

The addition of nucleophilic imines, using 2-hydroxybenzophenone as a chemical auxiliary, is presented. An intramolecular six-membered ring via hydrogen bonding that enhances the reactivity and selectivity is the key of this strategy, which is supported by DFT calculations and experimental trials.

Synthesis and characterization of hydrogen-bond acidic functionalized graphene

NASA Astrophysics Data System (ADS)

Yang, Liu; Han, Qiang; Pan, Yong; Cao, Shuya; Ding, Mingyu

2014-05-01

Hexafluoroisopropanol phenyl group functionalized materials have great potential in the application of gas-sensitive materials for nerve agent detection, due to the formation of strong hydrogen-bonding interactions between the group and the analytes. In this paper, take full advantage of ultra-large specific surface area and plenty of carbon-carbon double bonds and hexafluoroisopropanol phenyl functionalized graphene was synthesized through in situ diazonium reaction between -C=C- and p-hexafluoroisopropanol aniline. The identity of the as-synthesis material was confirmed by transmission electron microscopy, Raman spectroscopy, ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy and thermo gravimetric analysis. The synthesis method is simply which retained the excellent physical properties of original graphene. In addition, the novel material can be assigned as an potential candidate for gas sensitive materials towards organophosphorus nerve agent detection.

Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

PubMed Central

Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

2015-01-01

Succinimide formation from aspartic acid (Asp) residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe) as a model compound, we propose the possibility that acetic acid (AA), which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition) to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds) occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism. PMID:25588215

Acetic acid can catalyze succinimide formation from aspartic acid residues by a concerted bond reorganization mechanism: a computational study.

PubMed

Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

2015-01-12

Succinimide formation from aspartic acid (Asp) residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe) as a model compound, we propose the possibility that acetic acid (AA), which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition) to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds) occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

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.

Double hetero-Michael addition of N-substituted hydroxylamines to quinone monoketals: synthesis of bridged isoxazolidines.

PubMed

Yin, Zhiwei; Zhang, Jinzhu; Wu, Jing; Liu, Che; Sioson, Kate; Devany, Matthew; Hu, Chunhua; Zheng, Shengping

2013-07-19

A general synthesis of bridged isoxazolidines from a double hetero-Michael addition of N-substituted hydroxylamines to quinone monoketals has been developed. The different addition order of N-benzylhydroxylamine and N-Boc hydroxylamine is also discussed. Moreover, the various functionalities in the isoxazolidine products allow facile derivatization.

Dianionic Carbon-Bridged Scandium-Copper/Silver Heterobimetallic Complexes: Synthesis, Bonding, and Reactivity.

PubMed

Wang, Chen; Xiang, Li; Yang, Yan; Fang, Jian; Maron, Laurent; Leng, Xuebing; Chen, Yaofeng

2018-04-11

Alkylidene-bridged scandium-copper/silver heterobimetallic complexes were synthesized and structurally characterized. The complexes contain different Sc-C and M-C (M=Cu I , Ag I ) bonds. The reactivity of the scandium-copper heterobimetallic complex was also studied, which reveals that the heterobimetallic complex is a reaction intermediate for the transmetalation of akylidene group from Sc III to Cu I . The scandium-copper heterobimetallic complex also undergoes an addition reaction with CO, resulting in the formation of a new C=C double bond. DFT calculations were used to study the bonding and the subsequent reactivity with CO of the scandium-copper heterobimetallic complex. It clearly demonstrates a cooperative effect between the two metal centers through the formation of a direct Sc⋅⋅⋅Cu interaction that drives the reactivity with CO. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Resolution of concerted versus sequential mechanisms in photo-induced double-proton transfer reaction in 7-azaindole H-bonded dimer

PubMed Central

Catalán, Javier; del Valle, Juan Carlos; Kasha, Michael

1999-01-01

The experimental and theoretical bases for a synchronous or concerted double-proton transfer in centro-symmetric H-bonded electronically excited molecular dimers are presented. The prototype model is the 7-azaindole dimer. New research offers confirmation of a concerted mechanism for excited-state biprotonic transfer. Recent femtosecond photoionization and coulombic explosion techniques have given rise to time-of-flight MS observations suggesting sequential two-step biprotonic transfer for the same dimer. We interpret the overall species observed in the time-of-flight experiments as explicable without conflict with the concerted mechanism of proton transfer. PMID:10411876

Nickel-Catalyzed Addition-Type Alkenylation of Unactivated, Aliphatic C-H Bonds with Alkynes: A Concise Route to Polysubstituted γ-Butyrolactones.

PubMed

Li, Mingliang; Yang, Yudong; Zhou, Danni; Wan, Danyang; You, Jingsong

2015-05-15

Through the nickel-catalyzed chelation-assisted C-H bond activation strategy, the addition-type alkenylation of unreactive β-C(sp(3))-H bonds of aliphatic amides with internal alkynes is developed for the first time to produce γ,δ-unsaturated carboxylic amide derivatives. The resulting alkenylated products can further be transformed into polysubstituted γ-butyrolactones with pyridinium chlorochromate (PCC).

78 FR 37277 - CDFI Bond Guarantee Program; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-20

... the CDFI Fund in the following format: no more than 40 single-sided pages; double spaced; 12 font size... mail to the attention of Lisa Jones, Program Manager, CDFI Bond Guarantee Program, CDFI Fund, U.S... to the attention of Lisa Jones, Program Manager, CDFI Bond Guarantee Program, CDFI Fund, 1801-6215...

Influence of laboratory degradation methods and bonding application parameters on microTBS of self-etch adhesives to dentin.

PubMed

Erhardt, Maria Carolina G; Pisani-Proença, Jatyr; Osorio, Estrella; Aguilera, Fátima S; Toledano, Manuel; Osorio, Raquel

2011-04-01

To evaluate the laboratory resistance to degradation and the use of different bonding treatments on resin-dentin bonds formed with three self-etching adhesive systems. Flat, mid-coronal dentin surfaces from extracted human molars were bonded according to manufacturer's directions and submitted to two challenging regimens: (A) chemical degradation with 10% NaOC1 immersion for 5 hours; and (B) fatigue loading at 90 N using 50,000 cycles at 3.0 Hz. Additional dentin surfaces were bonded following four different bonding application protocols: (1) according to manufacturer's directions; (2) acid-etched with 36% phosphoric acid (H3PO4) for 15 seconds; (3) 10% sodium hypochlorite (NaOClaq) treated for 2 minutes, after H3PO4-etching; and (4) doubling the application time of the adhesives. Two one-step self-etch adhesives (an acetone-based: Futurabond/FUT and an ethanol-based: Futurabond NR/FNR) and a two-step self-etch primer system (Clearfil SE Bond/CSE) were examined. Specimens were sectioned into beams and tested for microtensile bond strength (microTBS). Selected debonded specimens were observed under scanning electron microscopy (SEM). Data (MPa) were analyzed by ANOVA and multiple comparisons tests (alpha= 0.05). microTBS significantly decreased after chemical and mechanical challenges (P< 0.05). CSE showed higher microTBS than the other adhesive systems, regardless the bonding protocol. FUT attained the highest microTBS after doubling the application time. H3PO4 and H3PO4 + NaOCl pretreatments significantly decreased bonding efficacy of the adhesives.

Effect of prolonged heating on the asphalt-aggregate bond strength of HMA containing liquid anti-strip additives

DOT National Transportation Integrated Search

2008-09-01

In this study, an attempt was made to determine the effect of prolonged heating on the bond strength between : aggregate and asphalt that contained anti-strip additives (LOF 6500 and Morelife 2200). On account of the : substantial decrease of anti-st...

Q-Band Electron-Nuclear Double Resonance Reveals Out-of-Plane Hydrogen Bonds Stabilize an Anionic Ubisemiquinone in Cytochrome bo3 from Escherichia coli.

PubMed

Sun, Chang; Taguchi, Alexander T; Vermaas, Josh V; Beal, Nathan J; O'Malley, Patrick J; Tajkhorshid, Emad; Gennis, Robert B; Dikanov, Sergei A

2016-10-11

The respiratory cytochrome bo 3 ubiquinol oxidase from Escherichia coli has a high-affinity ubiquinone binding site that stabilizes the one-electron reduced ubisemiquinone (SQ H ), which is a transient intermediate during the electron-mediated reduction of O 2 to water. It is known that SQ H is stabilized by two strong hydrogen bonds from R71 and D75 to ubiquinone carbonyl oxygen O1 and weak hydrogen bonds from H98 and Q101 to O4. In this work, SQ H was investigated with orientation-selective Q-band (∼34 GHz) pulsed 1 H electron-nuclear double resonance (ENDOR) spectroscopy on fully deuterated cytochrome (cyt) bo 3 in a H 2 O solvent so that only exchangeable protons contribute to the observed ENDOR spectra. Simulations of the experimental ENDOR spectra provided the principal values and directions of the hyperfine (hfi) tensors for the two strongly coupled H-bond protons (H1 and H2). For H1, the largest principal component of the proton anisotropic hfi tensor T z' = 11.8 MHz, whereas for H2, T z' = 8.6 MHz. Remarkably, the data show that the direction of the H1 H-bond is nearly perpendicular to the quinone plane (∼70° out of plane). The orientation of the second strong hydrogen bond, H2, is out of plane by ∼25°. Equilibrium molecular dynamics simulations on a membrane-embedded model of the cyt bo 3 Q H site show that these H-bond orientations are plausible but do not distinguish which H-bond, from R71 or D75, is nearly perpendicular to the quinone ring. Density functional theory calculations support the idea that the distances and geometries of the H-bonds to the ubiquinone carbonyl oxygens, along with the measured proton anisotropic hfi couplings, are most compatible with an anionic (deprotonated) ubisemiquinone.

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.

A novel method combining additive manufacturing and alloy infiltration for NdFeB bonded magnet fabrication

DOE PAGES

Li, Ling; Tirado, Angelica; Conner, Benjamin S.; ...

2017-04-27

In this paper, binder jetting additive manufacturing technique is employed to fabricate NdFeB isotropic bonded magnets, followed by an infiltration process with low-melting point eutectic alloys [i.e., Nd 3Cu 0.25Co 0.75 (NdCuCo) and Pr 3Cu 0.25Co 0.75 (PrCuCo)]. Densification and mechanical strength improvement are achieved for the as-printed porous part. Meanwhile, the intrinsic coercivity H ci is enhanced from 732 to 1345 kA/m and 1233 kA/m after diffusion of NdCuCo and PrCuCo, respectively. This study presents a novel method for fabricating complex-shaped bonded magnets with promising mechanical and magnetic properties.

A novel method combining additive manufacturing and alloy infiltration for NdFeB bonded magnet fabrication

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

Li, Ling; Tirado, Angelica; Conner, Benjamin S.

In this paper, binder jetting additive manufacturing technique is employed to fabricate NdFeB isotropic bonded magnets, followed by an infiltration process with low-melting point eutectic alloys [i.e., Nd 3Cu 0.25Co 0.75 (NdCuCo) and Pr 3Cu 0.25Co 0.75 (PrCuCo)]. Densification and mechanical strength improvement are achieved for the as-printed porous part. Meanwhile, the intrinsic coercivity H ci is enhanced from 732 to 1345 kA/m and 1233 kA/m after diffusion of NdCuCo and PrCuCo, respectively. This study presents a novel method for fabricating complex-shaped bonded magnets with promising mechanical and magnetic properties.

Noble reaction features of bromoborane in oxidative addition of B-Br σ-bond to [M(PMe3)2] (M=Pt or Pd): theoretical study.

PubMed

Zeng, Guixiang; Sakaki, Shigeyoshi

2011-06-06

Through detailed calculations by density functional theory and second-order Møller-Plesset perturbation theory (MP2) to fourth-order Møller-Plesset perturbation theory including single, double, and quadruple excitations [MP4(SDQ)] methods, we investigated the oxidative addition of the B-Br bond of dibromo(trimethylsiloxy)borane [Br(2)B(OSiMe(3))] to Pt(0) and Pd(0) complexes [M(PMe(3))(2)] (M = Pt or Pd) directly yielding a trans bromoboryl complex trans-[MBr{BBr(OSiMe(3))}(PMe(3))(2)]. Two reaction pathways are found for this reaction: One is a nucleophilic attack pathway which directly leads to the trans product, and the other is a stepwise reaction pathway which occurs through successive cis oxidative addition of the B-Br bond to [M(PMe(3))(2)] and thermal cis-trans isomerization. In the Pt system, the former course occurs with a much smaller energy barrier (E(a) = 5.8 kcal/mol) than the latter one (E(a) = 20.7 kcal/mol), where the DFT-calculated E(a) value is presented hereafter. In the Pd system, only the latter course is found in which the rate-determining steps is the cis-trans isomerization with the E(a) of 15.1 kcal/mol. Interestingly, the thermal cis-trans isomerization occurs on the singlet potential energy surface against our expectation. This unexpected result is understood in terms of the strong donation ability of the boryl group. Detailed analyses of electronic processes in all these reaction steps as well as remarkable characteristic features of [Br(2)B(OSiMe(3))] are also provided. © 2011 American Chemical Society

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.

Controlled double emulsification utilizing 3D PDMS microchannels

NASA Astrophysics Data System (ADS)

Chang, Fu-Che; Su, Yu-Chuan

2008-06-01

This paper presents a PDMS emulsification device that is capable of generating water-in-oil-in-water double emulsions in a controlled manner. Specially designed 3D microchannels are utilized to steer the independently driven water- and oil-phase flows (especially to restrict the attachment of the middle oil-phase flow on the channel surfaces), and to break the continuous flows into monodisperse double emulsions. In addition to channel geometries and fluid flow rates, surfactants and osmotic agents are employed to facilitate the breakup process and stabilize the resulting emulsion structures. In the prototype demonstration, two-level SU-8 molds were fabricated to duplicate PDMS microstructures, which were surface treated and bonded irreversibly to form 3D microchannels. Throughout the emulsification trials, dripping was intentionally induced to generate monodisperse double emulsions with single or multiple aqueous droplets inside each oil drop. It is found that the overall and core sizes of the resulting double emulsions could be adjusted independently, mainly by varying the outer and inner fluid flow rates, respectively. As such, the presented double emulsification device could potentially realize the controllability on emulsion structure and size distribution, which is desired for a variety of biological and pharmaceutical applications.

31 CFR 315.91 - Additional requirements; bond of indemnity.

Code of Federal Regulations, 2010 CFR

2010-07-01

... (Continued) FISCAL SERVICE, DEPARTMENT OF THE TREASURY BUREAU OF THE PUBLIC DEBT REGULATIONS GOVERNING U.S. SAVINGS BONDS, SERIES A, B, C, D, E, F, G, H, J, AND K, AND U.S. SAVINGS NOTES Miscellaneous Provisions...

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing [Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing

DOE PAGES

Li, Ling; Jones, Kodey E.; Sales, Brian C.; ...

2018-04-03

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ~5.2 g/cm 3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performedmore » at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Lastly, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.« less

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing [Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing

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

Li, Ling; Jones, Kodey E.; Sales, Brian C.

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ~5.2 g/cm 3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performedmore » at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Lastly, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.« less

Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

PubMed

Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

2016-05-05

Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

An Ex-vivo Shear and tensile bond strengths of orthodontic molar tubes bonded using different techniques.

PubMed

Abu-Alhaija, Elham; Jaradat, Mohammad; Alwahadni, Ahed

2017-03-01

Molar bonding procedures need continuous improvement to be widely accepted clinically and eventually replace molar bands. The purpose of this study was to determine the effects of enamel micro-abrasion and silane coating of the base of molar tubes on shear and tensile bond strengths of orthodontic molar tubes. A total of 200 third molars were randomly allocated into five groups of 40 teeth as follows: group 1: molar tubes bonded to etched teeth (37% phosphoric acid gel; control group); group 2: molar tubes bonded to etched teeth (37% phosphoric acid) with the addition of silane to the base of molar tubes; group 3: molar tubes bonded to teeth pre-treated with 18% hydrochloric acid and pumice (micro-abrasion); group 4: molar tubes bonded to teeth pre-treated with microabrasion with the addition of silane to the base of molar tubes; group 5: molar tubes bonded to teeth pre-treated with microabrasion before conventional acid etching combined with the addition of silane to the base of molar tubes. The bond strength testing was performed using a computer control electromechanical universal testing machine. The highest mean shear and tensile bond strengths were recorded in group 5 (13.81±2.54MPa and 13.97±2.29 MPa, respectively). Micro-abrasion alone (group 3) and the combination of enamel micro-abrasion and the addition of silane (group 4) produced bond strength values comparable to the control. Enamel surface pre-treatment (micro abrasion) before conventional acid etching combined with the addition of silane to the base of the molar tube produced the highest bond strengths among all tested groups. Key words: Molar, shear strength, tensile strength, orthodontic appliances.

Emergent Ising degrees of freedom above a double-stripe magnetic ground state

NASA Astrophysics Data System (ADS)

Zhang, Guanghua; Flint, Rebecca

2017-12-01

Double-stripe magnetism [Q =(π /2 ,π /2 )] has been proposed as the magnetic ground state for both the iron-telluride and BaTi2Sb2O families of superconductors. Double-stripe order is captured within a J1-J2-J3 Heisenberg model in the regime J3≫J2≫J1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π ,π ) . Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one.

Energy and structure of bonds in the interaction of organic anions with layered double hydroxide nanosheets: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Tsukanov, A. A.; Psakhie, S. G.

2016-01-01

The application of hybrid and hierarchical nanomaterials based on layered hydroxides and oxyhydroxides of metals is a swiftly progressing field in biomedicine. Layered double hydroxides (LDH) possess a large specific surface area, significant surface electric charge and biocompatibility. Their physical and structural properties enable them to adsorb various kinds of anionic species and to transport them into cells. However, possible side effects resulting from the interaction of LDH with anions of the intercellular and intracellular medium need to be considered, since such interaction can potentially disrupt ion transport, signaling processes, apoptosis, nutrition and proliferation of living cells. In the present paper molecular dynamics is used to determine the energies of interaction of organic anions (aspartic acid, glutamic acid and bicarbonate) with a fragment of layered double hydroxide Mg/Al-LDH. The average number of hydrogen bonds between the anions and the hydroxide surface and characteristic binding configurations are determined. Possible effects of LDH on the cell resulting from binding of protein fragments and replacement of native intracellular anions with delivered anions are considered.

Hydroxyapatite-coated double network hydrogel directly bondable to the bone: Biological and biomechanical evaluations of the bonding property in an osteochondral defect.

PubMed

Wada, Susumu; Kitamura, Nobuto; Nonoyama, Takayuki; Kiyama, Ryuji; Kurokawa, Takayuki; Gong, Jian Ping; Yasuda, Kazunori

2016-10-15

We have developed a novel hydroxyapatite (HAp)-coated double-network (DN) hydrogel (HAp/DN gel). The purpose of this study was to determine details of the cell and tissue responses around the implanted HAp/DN gel and to determine how quickly and strongly the HAp/DN gel bonds to the bone in a rabbit osteochondral defect model. Immature osteoid tissue was formed in the space between the HAp/DN gel and the bone at 2weeks, and the osteoid tissue was mineralized at 4weeks. The push-out load of the HAp/DN gel averaged 37.54N and 42.15N at 4 and 12weeks, respectively, while the push-out load of the DN gel averaged less than 5N. The bonding area of the HAp/DN gel to the bone was above 80% by 4weeks, and above 90% at 12weeks. This study demonstrated that the HAp/DN gel enhanced osseointegration at an early stage after implantation. The presence of nanoscale structures in addition to osseointegration of HAp promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage. Recent studies have reported the development of various hydrogels that are sufficiently tough for application as soft supporting tissues. However, fixation of hydrogels on bone surfaces with appropriate strength is a great challenge. We have developed a novel, tough hydrogel hybridizing hydroxyapatite (HAp/DN gel), which is directly bondable to the bone. The present study demonstrated that the HAp/DN gel enhanced osseointegration in the early stage after implantation. The presence of nanoscale structures in addition to the osseointegration ability of hydroxyapatite promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Evaluation of Disulfide Bond Position to Enhance the Thermal Stability of a Highly Stable Single Domain Antibody

PubMed Central

Zabetakis, Dan; Olson, Mark A.; Anderson, George P.; Legler, Patricia M.; Goldman, Ellen R.

2014-01-01

Single domain antibodies are the small recombinant variable domains derived from camelid heavy-chain-only antibodies. They are renowned for their stability, in large part due to their ability to refold following thermal or chemical denaturation. In addition to refolding after heat denaturation, A3, a high affinity anti-Staphylococcal Enterotoxin B single domain antibody, possesses a melting temperature of ∼84°C, among the highest reported for a single domain antibody. In this work we utilized the recently described crystal structure of A3 to select locations for the insertion of a second disulfide bond and evaluated the impact that the addition of this second bond had on the melting temperature. Four double-disulfide versions of A3 were constructed and each was found to improve the melting temperature relative to the native structure without reducing affinity. Placement of the disulfide bond at a previously published position between framework regions 2 and 3 yielded the largest improvement (>6°C), suggesting this location is optimal, and seemingly provides a universal route to raise the melting temperature of single domain antibodies. This study further demonstrates that even single domain antibodies with extremely high melting points can be further stabilized by addition of disulfide bonds. PMID:25526640

Selective aliphatic carbon-hydrogen bond activation of protected alcohol substrates by cytochrome P450 enzymes.

PubMed

Bell, Stephen G; Spence, Justin T J; Liu, Shenglan; George, Jonathan H; Wong, Luet-Lok

2014-04-21

Protected cyclohexanol and cyclohex-2-enol substrates, containing benzyl ether and benzoate ester moieties, were designed to fit into the active site of the Tyr96Ala mutant of cytochrome P450cam. The protected cyclohexanol substrates were efficiently and selectively hydroxylated by the mutant enzyme at the trans C-H bond of C-4 on the cyclohexyl ring. The selectivity of oxidation of the benzoate ester protected cyclohexanol could be altered by making alternative amino acid substitutions in the P450cam active site. The addition of the double bond in the cyclohexyl ring of the benzoate ester protected cyclohex-2-enol has a debilitative effect on the activity of the Tyr96Ala mutant with this substrate. However, the Phe87Ala/Tyr96Phe double mutant, which introduces space at a different location in the active site than the Tyr96Ala mutant, was able to efficiently hydroxylate the C-H bonds of 1-cyclohex-2-enyl benzoate at the allylic C-4 position. Mutations at Phe87 improved the selectivity of the oxidation of 1-phenyl-1-cyclohexylethylene to trans-4-phenyl-ethenylcyclohexanol (92%) when compared to single mutants at Tyr96 of P450cam.

Formal oxidative addition of a C-H bond by a 16e iridium(i) complex involves metal-ligand cooperation.

PubMed

Kumar, Amit; Feller, Moran; Ben-David, Yehoshoa; Diskin-Posner, Yael; Milstein, David

2018-05-10

The first example of oxidative addition of a C-H bond to a square planar d8-Iridium complex, without any external additive, such as an acid, is described. Our mechanistic investigations show that metal-ligand cooperation through aromatization-dearomatization of the lutidine backbone is involved in this process, and that the actual C-H activation step occurs through an Ir(iii) intermediate.

An Ex-vivo Shear and tensile bond strengths of orthodontic molar tubes bonded using different techniques

PubMed Central

Alwahadni, Ahed

2017-01-01

Background Molar bonding procedures need continuous improvement to be widely accepted clinically and eventually replace molar bands. Material and Methods The purpose of this study was to determine the effects of enamel micro-abrasion and silane coating of the base of molar tubes on shear and tensile bond strengths of orthodontic molar tubes. A total of 200 third molars were randomly allocated into five groups of 40 teeth as follows: group 1: molar tubes bonded to etched teeth (37% phosphoric acid gel; control group); group 2: molar tubes bonded to etched teeth (37% phosphoric acid) with the addition of silane to the base of molar tubes; group 3: molar tubes bonded to teeth pre-treated with 18% hydrochloric acid and pumice (micro-abrasion); group 4: molar tubes bonded to teeth pre-treated with microabrasion with the addition of silane to the base of molar tubes; group 5: molar tubes bonded to teeth pre-treated with microabrasion before conventional acid etching combined with the addition of silane to the base of molar tubes. The bond strength testing was performed using a computer control electromechanical universal testing machine. Results The highest mean shear and tensile bond strengths were recorded in group 5 (13.81±2.54MPa and 13.97±2.29 MPa, respectively). Micro-abrasion alone (group 3) and the combination of enamel micro-abrasion and the addition of silane (group 4) produced bond strength values comparable to the control. Conclusions Enamel surface pre-treatment (micro abrasion) before conventional acid etching combined with the addition of silane to the base of the molar tube produced the highest bond strengths among all tested groups. Key words:Molar, shear strength, tensile strength, orthodontic appliances. PMID:28298990

Effect of NaCl addition during diafiltration on the solubility, hydrophobicity, and disulfide bonds of 80% milk protein concentrate powder.

PubMed

Mao, X Y; Tong, P S; Gualco, S; Vink, S

2012-07-01

We investigated the surface hydrophobicity index based on different fluorescence probes [1-anilinonaphthalene-8-sulfonic acid (ANS) and 6-propionyl-2-(N,N-dimethylamino)-naphthalene (PRODAN)], free sulfhydryl and disulfide bond contents, and particle size of 80% milk protein concentrate (MPC80) powders prepared by adding various amounts of NaCl (0, 50, 100, and 150 mM) during the diafiltration process. The solubility of MPC80 powder was not strictly related to surface hydrophobicity. The MPC80 powder obtained by addition of 150 mM NaCl during diafiltration had the highest solubility but also the highest ANS-based surface hydrophobicity, the lowest PRODAN-based surface hydrophobicity, and the least aggregate formation. Intermolecular disulfide bonds caused by sulfhydryl-disulfide interchange reactions and hydrophobic interactions may be responsible for the lower solubility of the control MPC80 powder. The enhanced solubility of MPC80 powder with addition of NaCl during diafiltration may result from the modified surface hydrophobicity, the reduced intermolecular disulfide bonds, and the associated decrease in mean particle size. Addition of NaCl during the diafiltration process can modify the strength of hydrophobic interactions and sulfhydryl-disulfide interchange reactions and thereby affect protein aggregation and the solubility of MPC powders. Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Enhanced production of a single domain antibody with an engineered stabilizing extra disulfide bond.

PubMed

Liu, Jinny L; Goldman, Ellen R; Zabetakis, Dan; Walper, Scott A; Turner, Kendrick B; Shriver-Lake, Lisa C; Anderson, George P

2015-10-09

Single domain antibodies derived from the variable region of the unique heavy chain antibodies found in camelids yield high affinity and regenerable recognition elements. Adding an additional disulfide bond that bridges framework regions is a proven method to increase their melting temperature, however often at the expense of protein production. To fulfill their full potential it is essential to achieve robust protein production of these stable binding elements. In this work, we tested the hypothesis that decreasing the isoelectric point of single domain antibody extra disulfide bond mutants whose production fell due to the incorporation of the extra disulfide bond would lead to recovery of the protein yield, while maintaining the favorable melting temperature and affinity. Introduction of negative charges into a disulfide bond mutant of a single domain antibody specific for the L1 antigen of the vaccinia virus led to approximately 3.5-fold increase of protein production to 14 mg/L, while affinity and melting temperature was maintained. In addition, refolding following heat denaturation improved from 15 to 70 %. It also maintained nearly 100 % of its binding function after heating to 85 °C for an hour at 1 mg/mL. Disappointingly, the replacement of neutral or positively charged amino acids with negatively charged ones to lower the isoelectric point of two anti-toxin single domain antibodies stabilized with a second disulfide bond yielded only slight increases in protein production. Nonetheless, for one of these binders the charge change itself stabilized the structure equivalent to disulfide bond addition, thus providing an alternative route to stabilization which is not accompanied by loss in production. The ability to produce high affinity, stable single domain antibodies is critical for their utility. While the addition of a second disulfide bond is a proven method for enhancing stability of single domain antibodies, it frequently comes at the cost of reduced

Urethane/Silicone Adhesives for Bonding Flexing Metal Parts

NASA Technical Reports Server (NTRS)

Edwards, Paul D.

2004-01-01

Adhesives that are blends of commercially available urethane and silicone adhesives have been found to be useful for bonding metal parts that flex somewhat during use. These urethane/silicone adhesives are formulated for the specific metal parts to be bonded. The bonds formed by these adhesives have peel and shear strengths greater than those of bonds formed by double-sided tapes and by other adhesives, including epoxies and neat silicones. In addition, unlike the bonds formed by epoxies, the bonds formed by these adhesives retain flexibility. In the initial application for which the urethane/silicone adhesives were devised, there was a need to bond spring rings, which provide longitudinal rigidity for inflatable satellite booms, with the blades that provide the booms axial strength. The problem was to make the bonds withstand the stresses, associated with differences in curvature between the bonded parts, that arose when the booms were deflated and the springs were compressed. In experiments using single adhesives (that is, not the urethane/ silicone blends), the bonds were broken and, in each experiment, it was found that the adhesive bonded well with either the ring or with the blade, but not both. After numerous experiments, the adhesive that bonded best with the rings and the adhesive that bonded best with the blades were identified. These adhesives were then blended and, as expected, the blend bonded well with both the rings and the blades. The two adhesives are Kalex (or equivalent) high-shear-strength urethane and Dow Corning 732 (or equivalent) silicone. The nominal mixture ratio is 5 volume parts of the urethane per 1 volume part of the silicone. Increasing the proportion of silicone makes the bond weaker but more flexible, and decreasing the proportion of silicone makes the bond stronger but more brittle. The urethane/silicone blend must be prepared and used quickly because of the limited working time of the urethane: The precursor of the urethane

Protein farnesyltransferase isoprenoid substrate discrimination is dependent on isoprene double bonds and branched methyl groups.

PubMed

Micali, E; Chehade, K A; Isaacs, R J; Andres, D A; Spielmann, H P

2001-10-16

Farnesylation is a posttranslational lipid modification in which a 15-carbon farnesyl isoprenoid is linked via a thioether bond to specific cysteine residues of proteins in a reaction catalyzed by protein farnesyltransferase (FTase). We synthesized the benzyloxyisoprenyl pyrophosphate (BnPP) series of transferable farnesyl pyrophosphate (FPP) analogues (1a-e) to test the length dependence of the isoprenoid substrate on the FTase-catalyzed transfer of lipid to protein substrate. Kinetic analyses show that pyrophosphates 1a-e and geranyl pyrophosphate (GPP) transfer with a lower efficiency than FPP whereas geranylgeranyl pyrophosphate (GGPP) does not transfer at all. While a correlation was found between K(m) and analogue hydrophobicity and length, there was no correlation between k(cat) and these properties. Potential binding geometries of FPP, GPP, GGPP, and analogues 1a-e were examined by modeling the molecules into the active site of the FTase crystal structure. We found that analogue 1d displaces approximately the same volume of the active site as does FPP, whereas GPP and analogues 1a-c occupy lesser volumes and 1e occupies a slightly larger volume. Modeling also indicated that GGPP adopts a different conformation than the farnesyl chain of FPP, partially occluding the space occupied by the Ca(1)a(2)X peptide in the ternary X-ray crystal structure. Within the confines of the FTase pocket, the double bonds and branched methyl groups of the geranylgeranyl chain significantly restrict the number of possible conformations relative to the more flexible lipid chain of analogues 1a-e. The modeling results also provide a molecular explanation for the observation that an aromatic ring is a good isostere for the terminal isoprene of FPP.

Influence of carbon conductive additives on electrochemical double-layer supercapacitor parameters

NASA Astrophysics Data System (ADS)

Kiseleva, E. A.; Zhurilova, M. A.; Kochanova, S. A.; Shkolnikov, E. J.; Tarasenko, A. B.; Zaitseva, O. V.; Uryupina, O. V.; Valyano, G. V.

2018-01-01

Electrochemical double-layer capacitors (EDLC) offer energy storage technology, highly demanded for rapid transition processes in transport and stationary applications, concerned with fast power fluctuations. Rough structure of activated carbon, widely used as electrode material because of its high specific area, leads to poor electrode conductivity. Therefore there is the need for conductive additive to decrease internal resistance and to achieve high specific power and high specific energy. Usually carbon blacks are widely used as conductive additive. In this paper electrodes with different conductive additives—two types of carbon blacks and single-walled carbon nanotubes—were prepared and characterized in organic electrolyte-based EDLC cells. Electrodes are based on original wood derived activated carbon produced by potassium hydroxide high-temperature activation at Joint Institute for High Temperatures RAS. Electrodes were prepared from slurry by cold-rolling. For electrode characterization cyclic voltammetry, impedance spectra analysis, equivalent series resistance measurements and galvanostatic charge-discharge were used.

Unveiling of novel regio-selective fatty acid double bond hydratases from Lactobacillus acidophilus involved in the selective oxyfunctionalization of mono- and di-hydroxy fatty acids.

PubMed

Kim, Kyoung-Rok; Oh, Hye-Jin; Park, Chul-Soon; Hong, Seung-Hye; Park, Ji-Young; Oh, Deok-Kun

2015-11-01

The aim of this study is the first time demonstration of cis-12 regio-selective linoleate double-bond hydratase. Hydroxylation of fatty acids, abundant feedstock in nature, is an emerging alternative route for many petroleum replaceable products thorough hydroxy fatty acids, carboxylic acids, and lactones. However, chemical route for selective hydroxylation is still quite challenging owing to low selectivity and many environmental concerns. Hydroxylation of fatty acids by hydroxy fatty acid forming enzymes is an important route for selective biocatalytic oxyfunctionalization of fatty acids. Therefore, novel fatty acid hydroxylation enzymes should be discovered. The two hydratase genes of Lactobacillus acidophilus were identified by genomic analysis, and the expressed two recombinant hydratases were identified as cis-9 and cis-12 double-bond selective linoleate hydratases by in vitro functional validation, including the identification of products and the determination of regio-selectivity, substrate specificity, and kinetic parameters. The two different linoleate hydratases were the involved enzymes in the 10,13-dihydroxyoctadecanoic acid biosynthesis. Linoleate 13-hydratase (LHT-13) selectively converted 10 mM linoleic acid to 13S-hydroxy-9(Z)-octadecenoic acid with high titer (8.1 mM) and yield (81%). Our study will expand knowledge for microbial fatty acid-hydroxylation enzymes and facilitate the designed production of the regio-selective hydroxy fatty acids for useful chemicals from polyunsaturated fatty acid feedstocks. © 2015 Wiley Periodicals, Inc.

Effects of single bond-ion and single bond-diradical form on the stretching vibration of Cdbnd N bridging bond in 4,4‧-disubstituted benzylidene anilines

NASA Astrophysics Data System (ADS)

Cao, Chao-Tun; Bi, Yakun; Cao, Chenzhong

2016-06-01

Fifty-seven samples of model compounds, 4,4‧-disubstituted benzylidene anilines, p-X-ArCH = NAr-p-Y were synthesized. Their infrared absorption spectra were recorded, and the stretching vibration frequencies νCdbnd N of the Cdbnd N bridging bond were determined. New stretching vibration mode was proposed by means of the analysis of the factors affecting νCdbnd N, that is there are mainly three modes in the stretching vibration of Cdbnd N bond: (I) polar double bond form Cdbnd N, (II) single bond-ion form C+-N- and (III) single bond-diradical form Crad -Nrad . The contributions of the forms (I) and (II) to the change of νCdbnd N can be quantified by using Hammett substituent constant (including substituent cross-interaction effects between X and Y groups), whereas the contribution of the form (III) can be quantified by employing the excited-state substituent constant. The most contribution of these three forms is the form (III), the next is the form (II), whose contribution difference was discussed with the viewpoint of energy requirements in vibration with the form (III) and form (II).

Diffusion bonding aeroengine components

NASA Astrophysics Data System (ADS)

Fitzpatrick, G. A.; Broughton, T.

1988-10-01

The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

Bonding temperature dependence of GaInAsP/InP laser diode grown on hydrophilically directly bonded InP/Si substrate

NASA Astrophysics Data System (ADS)

Aikawa, Masaki; Onuki, Yuya; Hayasaka, Natsuki; Nishiyama, Tetsuo; Kamada, Naoki; Han, Xu; Kallarasan Periyanayagam, Gandhi; Uchida, Kazuki; Sugiyama, Hirokazu; Shimomura, Kazuhiko

2018-02-01

The bonding-temperature-dependent lasing characteristics of 1.5 a µm GaInAsP laser diode (LD) grown on a directly bonded InP/Si substrate were successfully obtained. We have fabricated the InP/Si substrate using a direct hydrophilic wafer bonding technique at bonding temperatures of 350, 400, and 450 °C, and deposited GaInAsP/InP double heterostructure layers on this InP/Si substrate. The surface conditions, X-ray diffraction (XRD) analysis, photoluminescence (PL) spectra, and electrical characteristics after the growth were compared at these bonding temperatures. No significant differences were confirmed in X-ray diffraction analysis and PL spectra at these bonding temperatures. We realized the room-temperature lasing of the GaInAsP LD on the InP/Si substrate bonded at 350 and 400 °C. The threshold current densities were 4.65 kA/cm2 at 350 °C and 4.38 kA/cm2 at 400 °C. The electrical resistance was found to increase with annealing temperature.

Switching bonds in a DNA gel: an all-DNA vitrimer.

PubMed

Romano, Flavio; Sciortino, Francesco

2015-02-20

We design an all-DNA system that behaves like vitrimers, innovative plastics with self-healing and stress-releasing properties. The DNA sequences are engineered to self-assemble first into tetra- and bifunctional units which, upon further cooling, bind to each other forming a fully bonded network gel. An innovative design of the binding regions of the DNA sequences, exploiting a double toehold-mediated strand displacement, generates a network gel which is able to reshuffle its bonds, retaining at all times full bonding. As in vitrimers, the rate of bond switching can be controlled via a thermally activated catalyst, which in the present design is very short DNA strands.

Rate-dependent inverse-addition beta-selective mannosylation and contiguous sequential glycosylation involving beta-mannosidic bond formation.

PubMed

Chang, Shih-Sheng; Shih, Che-Hao; Lai, Kwun-Cheng; Mong, Kwok-Kong Tony

2010-05-03

The beta-selectivity of mannosylation has been found to be dependent on the addition rate of the mannosyl trichloroacetimidate donor in an inverse-addition (I-A) procedure. This rate dependent I-A procedure can improve the selectivity of direct beta-mannosylation and is applicable to orthogonal glycosylations of thioglycoside acceptors. Further elaboration of this novel procedure enables the development of the contiguous sequential glycosylation strategy, which streamlines the preparation of oligosaccharides invoking beta-mannosidic bond formation. The synthetic utility of the contiguous glycosylation strategy was demonstrated by the preparation of the trisaccharide core of human N-linked glycoproteins and the trisaccharide repeating unit of the O-specific polysaccharide found in the cellular capsule of Salmonelle bacteria.

Heat conduction in double-walled carbon nanotubes with intertube additional carbon atoms.

PubMed

Cui, Liu; Feng, Yanhui; Tan, Peng; Zhang, Xinxin

2015-07-07

Heat conduction of double-walled carbon nanotubes (DWCNTs) with intertube additional carbon atoms was investigated for the first time using a molecular dynamics method. By analyzing the phonon vibrational density of states (VDOS), we revealed that the intertube additional atoms weak the heat conduction along the tube axis. Moreover, the phonon participation ratio (PR) demonstrates that the heat transfer in DWCNTs is dominated by low frequency modes. The added atoms cause the mode weight factor (MWF) of the outer tube to decrease and that of the inner tube to increase, which implies a lower thermal conductivity. The effects of temperature, tube length, and the number and distribution of added atoms were studied. Furthermore, an orthogonal array testing strategy was designed to identify the most important structural factor. It is indicated that the tendencies of thermal conductivity of DWCNTs with added atoms change with temperature and length are similar to bare ones. In addition, thermal conductivity decreases with the increasing number of added atoms, more evidently for atom addition concentrated at some cross-sections rather than uniform addition along the tube length. Simultaneously, the number of added atoms at each cross-section has a considerably more remarkable impact, compared to the tube length and the density of chosen cross-sections to add atoms.

Infrared spectroscopy of phenol-(H2O)(n>10): structural strains in hydrogen bond networks of neutral water clusters.

PubMed

Mizuse, Kenta; Hamashima, Toru; Fujii, Asuka

2009-11-05

To investigate hydrogen bond network structures of tens of water molecules, we report infrared spectra of moderately size (n)-selected phenol-(H2O)n (approximately 10 < or = n < or = approximately 50), which have essentially the same network structures as (H2O)(n+1). The phenyl group in phenol-(H2O)(n) allows us to apply photoionization-based size selection and infrared-ultraviolet double resonance spectroscopy. The spectra show a clear low-frequency shift of the free OH stretching band with increasing n. Detailed analyses with density functional theory calculations indicate that this shift is accounted for by the hydrogen bond network development from highly strained ones in the small (n < approximately 10) clusters to more relaxed ones in the larger clusters, in addition to the cooperativity of hydrogen bonds.

Double stranded nucleic acid biochips

DOEpatents

Chernov, Boris; Golova, Julia

2006-05-23

This invention describes a new method of constructing double-stranded DNA (dsDNA) microarrays based on the use of pre-synthesized or natural DNA duplexes without a stem-loop structure. The complementary oligonucleotide chains are bonded together by a novel connector that includes a linker for immobilization on a matrix. A non-enzymatic method for synthesizing double-stranded nucleic acids with this novel connector enables the construction of inexpensive and robust dsDNA/dsRNA microarrays. DNA-DNA and DNA-protein interactions are investigated using the microarrays.

Dual resin bonded joints in polyetheretherketone (PEEK) matrix composites

NASA Astrophysics Data System (ADS)

Zelenak, Steve; Radford, Donald W.; Dean, Michael W.

1993-04-01

The paper describes applications of the dual resin (miscible polymer) bonding technique (Smiley, 1989) developed as an alternative to traditional bonding approaches to joining thermoplastic matrix composite subassemblies into structures. In the experiments, the performance of joint geometries, such as those that could be used to assemble large truss structures in space, are investigated using truss joint models consisting of woven carbon fiber/PEEK tubes of about 1 mm wall thickness. Specific process conditions and hand-held hardware used to apply heat and pressure were chosen to simulate a field asembly technique. Results are presented on tube/cruciform double lap shear tests, pinned-pinned tube compression tests, and single lap shear bond tests of joints obtained using the dual resin bonding technique.

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.

The extension of a DNA double helix by an additional Watson-Crick base pair on the same backbone.

PubMed

Kumar, Pawan; Sharma, Pawan K; Madsen, Charlotte S; Petersen, Michael; Nielsen, Poul

2013-06-17

Additional base pair: The DNA duplex can be extended with an additional Watson-Crick base pair on the same backbone by the use of double-headed nucleotides. These also work as compressed dinucleotides and form two base pairs with cognate nucleobases on the opposite strand. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dynamics of vibrational relaxation in the S 1 state of carotenoids having 11 conjugated CC bonds

NASA Astrophysics Data System (ADS)

Hörvin Billsten, Helena; Zigmantas, Donatas; Sundström, Villy; Polívka, Tomáš

2002-04-01

Transient absorption spectra and kinetics in the 470-650 nm region were recorded for lycopene, β-carotene and zeaxanthin, all carotenoids with 11 conjugated double bonds, in two solvents with different polarity. Analysis of the red wing of the carotenoid S 1-S n transition revealed presence of a pronounced shoulder at early delay times. The kinetics recorded at this low-energy shoulder of the S 1-S n transition yields an additional decay component of 500-800 fs in addition to the main S 1 decay. This dynamics is ascribed to a vibrational relaxation in the S 1 state of the carotenoids.

Local vibrational modes of the formic acid dimer - the strength of the double hydrogen bond

NASA Astrophysics Data System (ADS)

Kalescky, R.; Kraka, E.; Cremer, D.

2013-07-01

The 24 normal and 24 local vibrational modes of the formic acid dimer formed by two trans formic acid monomers to a ring (TT1) are analysed utilising preferentially experimental frequencies, but also CCSD(T)/CBS and ωB97X-D harmonic vibrational frequencies. The local hydrogen bond (HB) stretching frequencies are at 676 cm-1 and by this 482 and 412 cm-1 higher compared to the measured symmetric and asymmetric HB stretching frequencies at 264 and 194 cm-1. The adiabatic connection scheme between local and normal vibrational modes reveals that the lowering is due to the topology of dimer TT1, mass coupling, and avoided crossings involving the HṡṡṡOC bending modes. The HB local mode stretching force constant is related to the strength of the HB whereas the normal mode stretching force constant and frequency lead to an erroneous underestimation of the HB strength. The HB in TT1 is stabilised by electron delocalisation in the O=C-O units fostered by forming a ring via double HBs. This implies that the CO apart from the OH local stretching frequencies reflect the strength of the HB via their red or blue shifts relative to their corresponding values in trans formic acid.

Latex Clearing Protein—an Oxygenase Cleaving Poly(cis-1,4-Isoprene) Rubber at the cis Double Bonds

PubMed Central

Hiessl, Sebastian; Böse, Dietrich; Oetermann, Sylvia; Eggers, Jessica; Pietruszka, Jörg

2014-01-01

Gordonia polyisoprenivorans strain VH2, a potent rubber-degrading actinomycete, harbors two latex clearing proteins (Lcps), which are known to be essential for the microbial degradation of rubber. However, biochemical information on the exact role of this protein in the degradation of polyisoprene was lacking. In this study, the gene encoding Lcp1VH2 was heterologously expressed in strains of Escherichia coli, the corresponding protein was purified, and its role in rubber degradation was examined by measurement of oxygen consumption as well as by chromatographic and spectroscopic methods. It turned out that active Lcp1VH2 is a monomer and is responsible for the oxidative cleavage of poly(cis-1,4-isoprene) in synthetic as well as in natural rubber by the addition of oxygen (O2) to the cis double bonds. The resulting oligomers possess repetitive isoprene units with aldehyde (CHO-CH2—) and ketone (—CH2-CO-CH3) functional groups at the termini. Two fractions with average isoprene contents of 18 and 10, respectively, were isolated, thus indicating an endocleavage mechanism. The activity of Lcp1VH2 was determined by applying a polarographic assay. Alkenes, acyclic terpenes, or other rubber-like polymers, such as poly(cis-1,4-butadiene) or poly(trans-1,4-isoprene), are not oxidatively cleaved by Lcp1VH2. The pH and temperature optima of the enzyme are at pH 7 and 30°C, respectively. Furthermore, it was demonstrated that active Lcp1VH2 is a Cu(II)-containing oxygenase that exhibits a conserved domain of unknown function which cannot be detected in any other hitherto-characterized enzyme. The results presented here indicate that this domain might represent a new protein family of oxygenases. PMID:24928880

Concise synthesis of the bryostatin A-ring via consecutive C-C bond forming transfer hydrogenations.

PubMed

Lu, Yu; Krische, Michael J

2009-07-16

Under the conditions of C-C bond forming transfer hydrogenation, 1,3-propanediol 1 engages in double asymmetric carbonyl allylation to furnish the C(2)-symmetric diol 2. Double ozonolysis of 2 followed by TBS protection delivers aldehyde 3, which is subject to catalyst directed carbonyl reverse prenylation via transfer hydrogenation to deliver neopentyl alcohol 4 and, ultimately, the bryostatin A-ring 7. Through use of two consecutive C-C bond forming transfer hydrogenations, the Evans' bryostatin A-ring 7 is prepared in less than half the manipulations previously reported.

Adhesive-bonded scarf and stepped-lap joints

NASA Technical Reports Server (NTRS)

Hart-Smith, L. J.

1973-01-01

Continuum mechanics solutions are derived for the static load-carrying capacity of scarf and stepped-lap adhesive-bonded joints. The analyses account for adhesive plasticity and adherend stiffness imbalance and thermal mismatch. The scarf joint solutions include a simple algebraic formula which serves as a close lower bound, within a small fraction of a per cent of the true answer for most practical geometries and materials. Digital computer programs were developed and, for the stepped-lap joints, the critical adherend and adhesive stresses are computed for each step. The scarf joint solutions exhibit grossly different behavior from that for double-lap joints for long overlaps inasmuch as that the potential bond shear strength continues to increase with indefinitely long overlaps on the scarf joints. The stepped-lap joint solutions exhibit some characteristics of both the scarf and double-lap joints. The stepped-lap computer program handles arbitrary (different) step lengths and thickness and the solutions obtained have clarified potentially weak design details and the remedies. The program has been used effectively to optimize the joint proportions.

Preliminary assessment of metal-porcelain bonding strength of CoCrW alloy after 3wt.% Cu addition.

PubMed

Lu, Yanjin; Zhao, Chaoqian; Ren, Ling; Guo, Sai; Gan, Yiliang; Yang, Chunguang; Wu, Songquan; Lin, Junjie; Huang, Tingting; Yang, Ke; Lin, Jinxin

2016-06-01

In this work, a novel Cu-bearing CoCrW alloy fabricated by selective laser melting for dental application has been studied. For its successful application, the bonding strength of metal-porcelain is essential to be systematically investigated. Therefore, the aim of this study was to evaluate the metal-porcelain bonding strength of CoCrWCu alloy by three-point bending test, meanwhile the Ni-free CoCrW alloy was used as control. The oxygen content was investigated by an elemental analyzer; X-ray photoelectron spectroscopy (XPS) was used to analyze the surface chemical composition of CoCrW based alloy after preoxidation treatment; the fracture mode was investigated by X-ray energy spectrum analysis (EDS) and scanning electron microscope (SEM). Result from the oxygen content analysis showed that the content of oxygen dramatically increased after the Cu addition. And the XPS suggested that Co-oxidation, Cr2O3, CrO2, WO3, Cu2O and CuO existed on the preoxidated surface of the CoCrWCu alloy; the three-point bending test showed that the bonding strength of the CoCrWCu alloy was 43.32 MPa, which was lower than that of the CoCrW group of 47.65 MPa. However, the average metal-porcelain bonding strength is significantly higher than the minimum value in the ISO 9693 standard. Results from the SEM images and EDS indicated that the fracture mode of CoCrWCu-porcelain was mixed between cohesive and adhesive. Based on the results obtained in this study, it can be indicated that the Cu-bearing CoCrW alloy fabricated by the selective laser melting is a promising candidate for use in dental application. Copyright © 2016 Elsevier B.V. All rights reserved.

Double-stage nematic bond ordering above double stripe magnetism: Application to BaTi 2 Sb 2 O

DOE PAGES

Zhang, G.; Glasbrenner, J. K.; Flint, R.; ...

2017-05-01

Spin-driven nemore » maticity, or the breaking of the point-group symmetry of the lattice without long-range magnetic order, is clearly quite important in iron-based superconductors. From a symmetry point of view, nematic order can be described as a coherent locking of spin fluctuations in two interpenetrating Néel sublattices with ensuing nearest-neighbor bond order and an absence of static magnetism. In this paper, we argue that the low-temperature state of the recently discovered superconductor BaTi 2 Sb 2 O is a strong candidate for a more exotic form of spin-driven nematic order, in which fluctuations occurring in four Néel sublattices promote both nearest- and next-nearest-neighbor bond order. We develop a low-energy field theory of this state and show that it can have, as a function of temperature, up to two separate bond-order phase transitions, namely, one that breaks rotation symmetry and one that breaks reflection and translation symmetries of the lattice. The resulting state has an orthorhombic lattice distortion, an intra-unit-cell charge density wave, and no long-range magnetic order, all consistent with reported measurements of the low-temperature phase of BaTi 2 Sb 2 O . Finally, we then use density functional theory calculations to extract exchange parameters to confirm that the model is applicable to BaTi 2 Sb 2 O .« less

Double-stage nematic bond ordering above double stripe magnetism: Application to BaTi 2 Sb 2 O

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

Zhang, G.; Glasbrenner, J. K.; Flint, R.

Spin-driven nemore » maticity, or the breaking of the point-group symmetry of the lattice without long-range magnetic order, is clearly quite important in iron-based superconductors. From a symmetry point of view, nematic order can be described as a coherent locking of spin fluctuations in two interpenetrating Néel sublattices with ensuing nearest-neighbor bond order and an absence of static magnetism. In this paper, we argue that the low-temperature state of the recently discovered superconductor BaTi 2 Sb 2 O is a strong candidate for a more exotic form of spin-driven nematic order, in which fluctuations occurring in four Néel sublattices promote both nearest- and next-nearest-neighbor bond order. We develop a low-energy field theory of this state and show that it can have, as a function of temperature, up to two separate bond-order phase transitions, namely, one that breaks rotation symmetry and one that breaks reflection and translation symmetries of the lattice. The resulting state has an orthorhombic lattice distortion, an intra-unit-cell charge density wave, and no long-range magnetic order, all consistent with reported measurements of the low-temperature phase of BaTi 2 Sb 2 O . Finally, we then use density functional theory calculations to extract exchange parameters to confirm that the model is applicable to BaTi 2 Sb 2 O .« less

Isolation and characterization of a uranium(VI)-nitride triple bond

NASA Astrophysics Data System (ADS)

King, David M.; Tuna, Floriana; McInnes, Eric J. L.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Liddle, Stephen T.

2013-06-01

The nature and extent of covalency in uranium bonding is still unclear compared with that of transition metals, and there is great interest in studying uranium-ligand multiple bonds. Although U=O and U=NR double bonds (where R is an alkyl group) are well-known analogues to transition-metal oxo and imido complexes, the uranium(VI)-nitride triple bond has long remained a synthetic target in actinide chemistry. Here, we report the preparation of a uranium(VI)-nitride triple bond. We highlight the importance of (1) ancillary ligand design, (2) employing mild redox reactions instead of harsh photochemical methods that decompose transiently formed uranium(VI) nitrides, (3) an electrostatically stabilizing sodium ion during nitride installation, (4) selecting the right sodium sequestering reagent, (5) inner versus outer sphere oxidation and (6) stability with respect to the uranium oxidation state. Computational analyses suggest covalent contributions to U≡N triple bonds that are surprisingly comparable to those of their group 6 transition-metal nitride counterparts.

Correlated hydrogen bonding fluctuations and vibrational cross peaks in N-methyl acetamide: simulation based on a complete electrostatic density functional theory map.

PubMed

Hayashi, Tomoyuki; Mukamel, Shaul

2006-11-21

The coherent nonlinear response of the entire amide line shapes of N-methyl acetamide to three infrared pulses is simulated using an electrostatic density functional theory map. Positive and negative cross peaks contain signatures of correlations between the fundamentals and the combination state. The amide I-A and I-III cross-peak line shapes indicate positive correlation and anticorrelation of frequency fluctuations, respectively. These can be ascribed to correlated hydrogen bonding at C[double bond]O and N-H sites. The amide I frequency is negatively correlated with the hydrogen bond on carbonyl C[double bond]O, whereas the amide A and III are negatively and positively correlated, respectively, with the hydrogen bond on amide N-H.

High reliability bond program using small diameter aluminum wire

NASA Technical Reports Server (NTRS)

Macha, M.; Thiel, R. A.

1975-01-01

The program was undertaken to characterize the performance of small diameter aluminum wire ultrasonically bonded to conductors commonly encountered in hybrid assemblies, and to recommend guidelines for improving this performance. Wire, 25.4, 38.1 and 50.8 um (1, 1.5 and 2 mil), was used with bonding metallization consisting of thick film gold, thin film gold and aluminum as well as conventional aluminum pads on semiconductor chips. The chief tool for evaluating the performance was the double bond pull test in conjunction with a 72 hour - 150 C heat soak and -65 C to +150 C thermal cycling. In practice the thermal cycling was found to have relatively little effect compared to the heat soak. Pull strength will decrease after heat soak as a result of annealing of the aluminum wire; when bonded to thick film gold, the pull strength decreased by about 50% (weakening of the bond interface was the major cause of the reduction). Bonds to thin film gold lost about 30 - 40% of their initial pull strenth; weakening of the wire itself at the bond heel was the predominant cause. Bonds to aluminum substrate metallization lost only about 22%. Bonds between thick and thin film gold substrate metallization and semiconductor chips substantiated the previous conclusions but also showed that in about 20 to 25% of the cases, bond interface failure occurred at the semiconductor chip.

The Nature of the Idealized Triple Bonds Between Principal Elements and the σ Origins of Trans-Bent Geometries-A Valence Bond Study.

PubMed

Ploshnik, Elina; Danovich, David; Hiberty, Philippe C; Shaik, Sason

2011-04-12

We describe herein a valence bond (VB) study of 27 triply bonded molecules of the general type X≡Y, where X and Y are main element atoms/fragments from groups 13-15 in the periodic table. The following conclusions were derived from the computational data: (a) Single π-bond and double π-bond energies for the entire set correlate with the "molecular electronegativity", which is the sum of the X and Y electronegativites for X≡Y. The correlation with the molecular electronegativity establishes a simple rule of periodicity: π-bonding strength generally increases from left to right in a period and decreases down a column in the periodic table. (b) The σ frame invariably prefers trans bending, while π-bonding gets destabilized and opposes the trans distortion. In HC≡CH, the π-bonding destabilization overrides the propensity of the σ frame to distort, while in the higher row molecules, the σ frame wins out and establishes trans-bent molecules with 2(1)/2 bonds, in accord with recent experimental evidence based on solid state (29)Si NMR of the Sekiguchi compound. Thus, in the trans-bent molecules "less bonds pay more". (c) All of the π bonds show significant bonding contributions from the resonance energy due to covalent-ionic mixing. This quantity is shown to correlate linearly with the corresponding "molecular electronegativity" and to reflect the mechanism required to satisfy the equilibrium condition for the bond. The π bonds for molecules possessing high molecular electronegativity are charge-shift bonds, wherein bonding is dominated by the resonance energy of the covalent and ionic forms, rather than by either form by itself.

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.

eIF4E/Fmr1 double mutant mice display cognitive impairment in addition to ASD-like behaviors.

PubMed

Huynh, Thu N; Shah, Manan; Koo, So Yeon; Faraud, Kirsten S; Santini, Emanuela; Klann, Eric

2015-11-01

Autism spectrum disorder (ASD) is a group of heritable disorders with complex and unclear etiology. Classic ASD symptoms include social interaction and communication deficits as well as restricted, repetitive behaviors. In addition, ASD is often comorbid with intellectual disability. Fragile X syndrome (FXS) is the leading genetic cause of ASD, and is the most commonly inherited form of intellectual disability. Several mouse models of ASD and FXS exist, however the intellectual disability observed in ASD patients is not well modeled in mice. Using the Fmr1 knockout mouse and the eIF4E transgenic mouse, two previously characterized mouse models of fragile X syndrome and ASD, respectively, we generated the eIF4E/Fmr1 double mutant mouse. Our study shows that the eIF4E/Fmr1 double mutant mice display classic ASD behaviors, as well as cognitive dysfunction. Importantly, the learning impairments displayed by the double mutant mice spanned multiple cognitive tasks. Moreover, the eIF4E/Fmr1 double mutant mice display increased levels of basal protein synthesis. The results of our study suggest that the eIF4E/Fmr1 double mutant mouse may be a reliable model to study cognitive dysfunction in the context of ASD. Copyright © 2015 Elsevier Inc. All rights reserved.

Single and double C-Cl-activation of methylene chloride by P,N-ligand coordinated rhodium complexes.

PubMed

Blank, Benoît; Glatz, Germund; Kempe, Rhett

2009-02-02

Two in one: The simultaneous formation of bimetallic mu-methylene bridged Rh(III) complexes as well as dimeric Rh(III) complexes with terminal chloromethyl groups is observed for P,N-ligand stabilized Rh(I) complexes by C-Cl bond activation of methylene chloride. A mechanistic proposal for the formation of both activation products is also discussed. The synthesis of Rh(I) complexes with P-functionalized aminopyridine ligands is reported as well as the first simultaneous observation of a single and double activation of C-Cl bonds of methylene chloride affording both a dimeric Rh(III) complex bearing terminal CH(2)Cl groups in addition to a binuclear Rh(III) complex with a bridging mu-CH(2) group. The structures of the oxidative addition products were obtained by X-ray diffraction studies and NMR experiments were performed to elucidate some aspects of the reaction pathway.

Intramolecular competition between n-pair and π-pair hydrogen bonding: Microwave spectrum and internal dynamics of the pyridine–acetylene hydrogen-bonded complex

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

Mackenzie, Rebecca B.; Dewberry, Christopher T.; Leopold, Kenneth R., E-mail: A.C.Legon@bristol.ac.uk, E-mail: david.tew@bristol.ac.uk, E-mail: kleopold@umn.edu

2015-09-14

a-type rotational spectra of the hydrogen-bonded complex formed from pyridine and acetylene are reported. Rotational and {sup 14}N hyperfine constants indicate that the complex is planar with an acetylenic hydrogen directed toward the nitrogen. However, unlike the complexes of pyridine with HCl and HBr, the acetylene moiety in HCCH—NC{sub 5}H{sub 5} does not lie along the symmetry axis of the nitrogen lone pair, but rather, forms an average angle of 46° with the C{sub 2} axis of the pyridine. The a-type spectra of HCCH—NC{sub 5}H{sub 5} and DCCD—NC{sub 5}H{sub 5} are doubled, suggesting the existence of a low lying pairmore » of tunneling states. This doubling persists in the spectra of HCCD—NC{sub 5}H{sub 5}, DCCH—NC{sub 5}H{sub 5}, indicating that the underlying motion does not involve interchange of the two hydrogens of the acetylene. Single {sup 13}C substitution in either the ortho- or meta-position of the pyridine eliminates the doubling and gives rise to separate sets of spectra that are well predicted by a bent geometry with the {sup 13}C on either the same side (“inner”) or the opposite side (“outer”) as the acetylene. High level ab initio calculations are presented which indicate a binding energy of 1.2 kcal/mol and a potential energy barrier of 44 cm{sup −1} in the C{sub 2v} configuration. Taken together, these results reveal a complex with a bent hydrogen bond and large amplitude rocking of the acetylene moiety. It is likely that the bent equilibrium structure arises from a competition between a weak hydrogen bond to the nitrogen (an n-pair hydrogen bond) and a secondary interaction between the ortho-hydrogens of the pyridine and the π electron density of the acetylene.« less

The shortest Th-Th distance from a new type of quadruple bond.

PubMed

Hu, Han-Shi; Kaltsoyannis, Nikolas

2017-02-15

Compounds featuring unsupported metal-metal bonds between actinide elements remain highly sought after yet confined experimentally to inert gas matrix studies. Notwithstanding this paucity, actinide-actinide bonding has been the subject of extensive computational research. In this contribution, high level quantum chemical calculations at both the scalar and spin-orbit levels are used to probe the Th-Th bonding in a range of zero valent systems of general formula LThThL. Several of these compounds have very short Th-Th bonds arising from a new type of Th-Th quadruple bond with a previously unreported electronic configuration featuring two unpaired electrons in 6d-based δ bonding orbitals. H 3 AsThThAsH 3 is found to have the shortest Th-Th bond yet reported (2.590 Å). The Th 2 unit is a highly sensitive probe of ligand electron donor/acceptor ability; we can tune the Th-Th bond from quadruple to triple, double and single by judicious choice of the L group, up to 2.888 Å for singly-bonded ONThThNO.

Assessing the distinguishable cluster approximation based on the triple bond-breaking in the nitrogen molecule

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

Rishi, Varun; Perera, Ajith; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu

2016-03-28

Obtaining the correct potential energy curves for the dissociation of multiple bonds is a challenging problem for ab initio methods which are affected by the choice of a spin-restricted reference function. Coupled cluster (CC) methods such as CCSD (coupled cluster singles and doubles model) and CCSD(T) (CCSD + perturbative triples) correctly predict the geometry and properties at equilibrium but the process of bond dissociation, particularly when more than one bond is simultaneously broken, is much more complicated. New modifications of CC theory suggest that the deleterious role of the reference function can be diminished, provided a particular subset of termsmore » is retained in the CC equations. The Distinguishable Cluster (DC) approach of Kats and Manby [J. Chem. Phys. 139, 021102 (2013)], seemingly overcomes the deficiencies for some bond-dissociation problems and might be of use in quasi-degenerate situations in general. DC along with other approximate coupled cluster methods such as ACCD (approximate coupled cluster doubles), ACP-D45, ACP-D14, 2CC, and pCCSD(α, β) (all defined in text) falls under a category of methods that are basically obtained by the deletion of some quadratic terms in the double excitation amplitude equation for CCD/CCSD (coupled cluster doubles model/coupled cluster singles and doubles model). Here these approximate methods, particularly those based on the DC approach, are studied in detail for the nitrogen molecule bond-breaking. The N{sub 2} problem is further addressed with conventional single reference methods but based on spatial symmetry-broken restricted Hartree–Fock (HF) solutions to assess the use of these references for correlated calculations in the situation where CC methods using fully symmetry adapted SCF solutions fail. The distinguishable cluster method is generalized: 1) to different orbitals for different spins (unrestricted HF based DCD and DCSD), 2) by adding triples correction perturbatively (DCSD(T)) and

Addition of ArSSAr to dienes via intramolecular C-C bond formation initiated by a catalytic amount of ArS+.

PubMed

Matsumoto, Kouichi; Fujie, Shunsuke; Suga, Seiji; Nokami, Toshiki; Yoshida, Jun-ichi

2009-09-28

A catalytic amount of electrochemically generated "ArS+" ("ArS+" = ArS(ArSSAr)+) initiates a cation chain reaction of dienes that involves the addition of ArSSAr associated with stereoselective intramolecular carbon-carbon bond formation, and the direct (in-cell) electrolysis of a mixture of a diene and ArSSAr with a catalytic amount of electricity also effectively initiates the reaction.

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.

A valence bond study of three-center four-electron pi bonding: electronegativity vs electroneutrality.

PubMed

DeBlase, Andrew; Licata, Megan; Galbraith, John Morrison

2008-12-18

Three-center four-electron (3c4e) pi bonding systems analogous to that of the ozone molecule have been studied using modern valence bond theory. Molecules studied herein consist of combinations of first row atoms C, N, and O with the addition of H atoms where appropriate in order to preserve the 3c4e pi system. Breathing orbital valence bond (BOVB) calculations were preformed at the B3LYP/6-31G**-optimized geometries in order to determine structural weights, pi charge distributions, resonance energies, and pi bond energies. It is found that the most weighted VB structure depends on atomic electronegativity and charge distribution, with electronegativity as the dominant factor. By nature, these systems are delocalized, and therefore, resonance energy is the main contributor to pi bond energies. Molecules with a single dominant VB structure have low resonance energies and therefore low pi bond energies.

Bond Sensitivity to Silicone Contamination

NASA Technical Reports Server (NTRS)

Caldwell, G. A.; Hudson, W. D.; Hudson, W. D.; Cash, Stephen F. (Technical Monitor)

2003-01-01

Currently during fabrication of the Space Shuttle booster rocket motors, the use of silicone and silicone-containing products is prohibited in most applications. Many shop aids and other materials containing silicone have the potential, if they make contact with a bond surface, to transfer some of the silicone to the substrates being bonded. Such transfer could result in a reduction of the bond strength or even failure of the subsequent bonds. This concern is driving the need to understand the effect of silicones and the concentration needed to affect a given bond-line strength. Additionally, as silicone detection methods used for materials acceptance improve what may have gone unnoticed earlier is now being detected. Thus, realistic silicone limits for process materials (below which bond performance is satisfactory) are needed rather than having an absolute no silicone permitted policy.

High voltage electrochemical double layer capacitors using conductive carbons as additives

NASA Astrophysics Data System (ADS)

Michael, M. S.; Prabaharan, S. R. S.

We describe here an interesting approach towards electrochemical capacitors (ECCs) using graphite materials (as being used as conductive additives in rechargeable lithium-ion battery cathodes) in a Li + containing organic electrolyte. The important result is that we achieved a voltage window of >4 V, which is rather large, compared to the standard window of 2.5 V for ordinary electric double layer capacitors (DLCs). The capacitor performance was evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge techniques. From charge-discharge studies of the symmetrical device (for instance, SFG6 carbon electrode), a specific capacitance of up to 14.5 F/g was obtained at 16 mA/cm 2 current rate and at a low current rate (3 mA/cm 2), a higher value was obtained (63 F/g). The specific capacitance decreased about 25% after 1000 cycles compared to the initial discharge process. The performances of these graphites are discussed in the light of both double layer capacitance (DLC) and pseudocapacitance (battery-like behavior). The high capacitance obtained was not only derived from the current-transient capacitive behavior but is also attributed to pseudocapacitance associated with some kind of faradaic reaction, which could probably occur due to Li + intercalation/deintercalation reactions into graphitic layers of the carbons used. The ac impedance (electrochemical impedances spectroscopy, EIS) measurements were also carried out to evaluate the capacitor parameters such as equivalent series resistance (ESR) and frequency dependent capacitance ( Cfreq). Cyclic voltammetry measurements were also performed to evaluate the cycling behavior of the carbon electrodes and the non-rectangular shaped voltammograms revealed the non-zero time constant [ τ( RC)≠0] confirming that the current contains a transient as well as steady-state components.

NMR studies of double proton transfer in hydrogen bonded cyclic N,N'-diarylformamidine dimers: conformational control, kinetic HH/HD/DD isotope effects and tunneling.

PubMed

Lopez, Juan Miguel; Männle, Ferdinand; Wawer, Iwona; Buntkowsky, Gerd; Limbach, Hans-Heinrich

2007-08-28

Using dynamic NMR spectroscopy, the kinetics of the degenerate double proton transfer in cyclic dimers of polycrystalline (15)N,(15)N'-di-(4-bromophenyl)-formamidine (DBrFA) have been studied including the kinetic HH/HD/DD isotope effects in a wide temperature range. This transfer is controlled by intermolecular interactions, which in turn are controlled by the molecular conformation and hence the molecular structure. At low temperatures, rate constants were determined by line shape analysis of (15)N NMR spectra obtained using cross-polarization (CP) and magic angle spinning (MAS). At higher temperatures, in the microsecond time scale, rate constants and kinetic isotope effects were obtained by a combination of longitudinal (15)N and (2)H relaxation measurements. (15)N CPMAS line shape analysis was also employed to study the non-degenerate double proton transfer of polycrystalline (15)N,(15)N'-diphenyl-formamidine (DPFA). The kinetic results are in excellent agreement with the kinetics of DPFA and (15)N,(15)N'-di-(4-fluorophenyl)-formamidine (DFFA) studied previously for solutions in tetrahydrofuran. Two large HH/HD and HD/DD isotope effects are observed in the whole temperature range which indicates a concerted double proton transfer mechanism in the domain of the reaction energy surface. The Arrhenius curves are non-linear indicating a tunneling mechanism. Arrhenius curve simulations were performed using the Bell-Limbach tunneling model. The role of the phenyl group conformation and hydrogen bond compression on the barrier of the proton transfer is discussed.

A reversible fluorescent probe based on C[double bond, length as m-dash]N isomerization for the selective detection of formaldehyde in living cells and in vivo.

PubMed

Song, Xinyu; Han, Xiaoyue; Yu, Fabiao; Zhang, Jinjin; Chen, Lingxin; Lv, Changjun

2018-01-15

Formaldehyde (FA) is an endogenously produced reactive carbonyl species (RCS) through biological metabolic processes whose concentration is closely related to human health and disease. Noninvasive and real-time detection of FA concentration in organisms is very important for revealing the physiological and pathological functions of FA. Herein, we design and synthesize a reversible fluorescent probe BOD-NH 2 for the detection of FA in living cells and in vivo. The probe is composed of two moieties: the BODIPY fluorophore and the primary amino group response unit. The probe undergoes an intracellular aldimine condensation reaction with FA and forms imine (C[double bond, length as m-dash]N) which will result in C[double bond, length as m-dash]N isomerization and rotation to turn-off the fluorescence of the probe. It is important that the probe can show a reversible response to FA. The probe BOD-NH 2 has been successfully applied for detecting and imaging FA in the cytoplasm of living cells. BOD-NH 2 is capable of detecting fluctuations in the levels of endogenous and exogenous FA in different types of living cells. The probe can be used to visualize the FA concentration in fresh hippocampus and the probe can further qualitatively evaluate the FA concentrations in ex vivo-dissected organs. Moreover, BOD-NH 2 can also be used for imaging in mice. The above applications make our new probe a potential chemical tool for the study of physiological and pathological functions of FA in cells and in vivo.

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.

Heterobimetallic Complexes That Bond Vanadium to Iron, Cobalt, and Nickel.

PubMed

Clouston, Laura J; Bernales, Varinia; Cammarota, Ryan C; Carlson, Rebecca K; Bill, Eckhard; Gagliardi, Laura; Lu, Connie C

2015-12-21

Zero-valent iron, cobalt, and nickel were installed into the metalloligand V[N(o-(NCH2P((i)Pr)2)C6H4)3] (1, VL), generating the heterobimetallic trio FeVL (2), CoVL (3), and NiVL (4), respectively. In addition, the one-electron-oxidized analogues [FeVL]X ([2(ox)]X, where X(-) = BPh4 or PF6) and [CoVL]BPh4 ([3(ox)]BPh4) were prepared. The complexes were characterized by a host of physical methods, including cyclic voltammetry, X-ray crystallography, magnetic susceptibility, electronic absorption, NMR, electron paramagnetic resonance (EPR), and Mössbauer spectroscopies. The CoV and FeV heterobimetallic compounds have short M-V bond lengths that are consistent with M-M multiple bonding. As revealed by theoretical calculations, the M-V bond is triple in 2, 2(ox), and 3(ox), double in 3, and dative (Ni → V) in 4. The (d-d)(10) species, 2 and 3(ox), are diamagnetic and exhibit large diamagnetic anisotropies of -4700 × 10(-36) m(3)/molecule. Complexes 2 and 3(ox) are also characterized by intense visible bands at 760 and 610 nm (ε > 1000 M(-1) cm(-1)), respectively, which correspond to an intermetal (M → V) charge-transfer transition. Magnetic susceptibility measurements and EPR characterization establish S = (1)/2 ground states for (d-d)(9) 2(ox) and (d-d)(11) 3, while (d-d)(12) 4 is S = 1 based on Evans' method.

Stereochemistry of complexes with double and triple metal-ligand bonds: a continuous shape measures analysis.

PubMed

Alvarez, Santiago; Menjón, Babil; Falceto, Andrés; Casanova, David; Alemany, Pere

2014-11-17

To each coordination polyhedron we can associate a normalized coordination polyhedron that retains the angular orientation of the central atom-ligand bonds but has all the vertices at the same distance from the center. The use of shape measures of these normalized coordination polyhedra provides a simple and efficient way of discriminating angular and bond distance distortions from an ideal polyhedron. In this paper we explore the applications of such an approach to analyses of several stereochemical problems. Among others, we discuss how to discern the off-center displacement of the metal from metal-ligand bond shortening distortions in families of square planar biscarbene and octahedral dioxo complexes. The normalized polyhedron approach is also shown to be very useful to understand stereochemical trends with the help of shape maps, minimal distortion pathways, and ligand association/dissociation pathways, illustrated by the Berry and anti Berry distortions of triple-bonded [X≡ML4] complexes, the square pyramidal geometries of Mo coordination polyhedra in oxido-reductases, the coordination geometries of actinyl complexes, and the tetrahedricity of heavy atom-substituted carbon centers.

Ultra precision and reliable bonding method

NASA Technical Reports Server (NTRS)

Gwo, Dz-Hung (Inventor)

2001-01-01

The bonding of two materials through hydroxide-catalyzed hydration/dehydration is achieved at room temperature by applying hydroxide ions to at least one of the two bonding surfaces and by placing the surfaces sufficiently close to each other to form a chemical bond between them. The surfaces may be placed sufficiently close to each other by simply placing one surface on top of the other. A silicate material may also be used as a filling material to help fill gaps between the surfaces caused by surface figure mismatches. A powder of a silica-based or silica-containing material may also be used as an additional filling material. The hydroxide-catalyzed bonding method forms bonds which are not only as precise and transparent as optical contact bonds, but also as strong and reliable as high-temperature frit bonds. The hydroxide-catalyzed bonding method is also simple and inexpensive.

Photoinduced Intramolecular Bifurcate Hydrogen Bond: Unusual Mutual Influence of the Components.

PubMed

Sigalov, Mark V; Shainyan, Bagrat A; Sterkhova, Irina V

2017-09-01

A series of 7-hydroxy-2-methylidene-2,3-dihydro-1H-inden-1-ones with 2-pyrrolyl (3), 4-dimethylaminophenyl (4), 4-nitrophenyl (5), and carboxyl group (6) as substituents at the exocyclic double bond was synthesized in the form of the E-isomers (4-6) or predominantly as the Z-isomer (3) which in solution is converted to the E-isomer. The synthesized compounds and their model analogues were studied by NMR spectroscopy, X-ray analysis, and MP2 theoretical calculations. The E-isomers having intramolecular O-H···O═C hydrogen bond are converted by UV irradiation to the Z-isomers having bifurcated O-H···O···H-X hydrogen bond. Unexpected shortening (and, thus, strengthening) of the O-H···O═C component of the bifurcated hydrogen bond upon the formation of the C═O···H-X hydrogen bond was found experimentally, proved theoretically (MP2), and explained by a roundabout interaction of the H-donor (HX) and H-acceptor (C═O) via the system of conjugated bonds.

Investigation of ball bond integrity for 0.8 mil (20 microns) diameter gold bonding wire on low k die in wire bonding technology

NASA Astrophysics Data System (ADS)

Kudtarkar, Santosh Anil

Microelectronics technology has been undergoing continuous scaling to accommodate customer driven demand for smaller, faster and cheaper products. This demand has been satisfied by using novel materials, design techniques and processes. This results in challenges for the chip connection technology and also the package technology. The focus of this research endeavor was restricted to wire bond interconnect technology using gold bonding wires. Wire bond technology is often regarded as a simple first level interconnection technique. In reality, however, this is a complex process that requires a thorough understanding of the interactions between the design, material and process variables, and their impact on the reliability of the bond formed during this process. This research endeavor primarily focused on low diameter, 0.8 mil thick (20 mum) diameter gold bonding wire. Within the scope of this research, the integrity of the ball bond formed by 1.0 mil (25 mum) and 0.8 mil (20 mum) diameter wires was compared. This was followed by the evaluation of bonds formed on bond pads having doped SiO2 (low k) as underlying structures. In addition, the effect of varying the percentage of the wire dopant, palladium and bonding process parameters (bonding force, bond time, ultrasonic energy) for 0.8 mil (20 mum) bonding wire was also evaluated. Finally, a degradation empirical model was developed to understand the decrease in the wire strength. This research effort helped to develop a fundamental understanding of the various factors affecting the reliability of a ball bond from a design (low diameter bonding wire), material (low k and bonding wire dopants), and process (wire bonding process parameters) perspective for a first level interconnection technique, namely wire bonding. The significance of this research endeavor was the systematic investigation of the ball bonds formed using 0.8 mil (20 microm) gold bonding wire within the wire bonding arena. This research addressed low k

Hydrogen bonding in the mechanism of GDP-mannose mannosyl hydrolase

NASA Astrophysics Data System (ADS)

Mildvan, A. S.; Xia, Z.; Azurmendi, H. F.; Legler, P. M.; Balfour, M. R.; Lairson, L. L.; Withers, S. G.; Gabelli, S. B.; Bianchet, M. A.; Amzel, L. M.

2006-06-01

GDP-mannose mannosyl hydrolase (GDPMH) from E. coli catalyzes the hydrolysis of GDP-α- D-sugars to GDP and β- D-sugars by nucleophilic substitution with inversion at the anomeric C1 of the sugar, with general base catalysis by His-124. The 1.3 Å X-ray structure of the GDPMH-Mg 2+-GDP complex was used to model the complete substrate, GDP-mannose into the active site. The substrate is linked to the enzyme by 12 hydrogen bonds, as well as by the essential Mg 2+. In addition, His-124 was found to participate in a hydrogen bonded triad: His-124-NδH⋯Tyr-127-OH⋯Pro-120(C dbnd6 O). The contributions of these hydrogen bonds to substrate binding and to catalysis were investigated by site-directed mutagenesis. The hydrogen bonded triad detected in the X-ray structure was found to contribute little to catalysis since the Y127F mutation of the central residue shows only 2-fold decreases in both kcat and Km. The GDP leaving group is activated by the essential Mg 2+ which contributes at least 10 5-fold to kcat, and by nine hydrogen bonds, including those from Tyr-103, Arg-37, Arg-52, and Arg-65 (via an intervening water), each of which contribute factors to kcat ranging from 24- to 309-fold. Both Arg-37 and Tyr-103 bind the β-phosphate of the leaving GDP and are only 5.0 Å apart. Accordingly, the R37Q/Y103F double mutant shows partially additive effects of the two single mutants on kcat, indicating cooperativity of Arg-37 and Tyr-103 in promoting catalysis. The extensive activation of the GDP leaving group suggests a mechanism with dissociative character with a cationic oxocarbenium-like transition state and a half-chair conformation of the sugar ring, as found with glycosidase enzymes. Accordingly, Asp-22 which contributes 10 2.1- to 10 2.6-fold to kcat, is positioned to both stabilize a developing cationic center at C1 and to accept a hydrogen bond from the C2-OH of the mannosyl group, and His-88, which contributes 10 2.3-fold to kcat, is positioned to accept

Mobile phase additives for enhancing the chromatographic performance of astaxanthin on nonendcapped polymeric C30-bonded stationary phases.

PubMed

Kaiser, Philipp; Surmann, Peter; Fuhrmann, Herbert

2009-01-01

Astaxanthin shows peak deformation and reduced peak area response when eluted with methanol and methyl tert-butyl ether on nonendcapped polymeric C30-bonded HPLC phases. The present study tested different column manufacturers, column batches, and ten mobile phase additives including acids, bases, buffers, complexing and antioxidant agents for improvement of peak shape and peak area response. Concerning chromatographic benefits and feasibility, ammonium acetate was found to be the best additive followed by triethylamine for all columns tested. Variation of the mobile phase pH equivalent and the column temperature showed no synergistic effects on peak shape and peak area response. Results indicate that peak tailing and variation of peak area response are due to different on-column effects. Possible mechanisms of the observed phenomenon will be discussed.

Determinants of Interest Rates on Corporate Bonds of Mining Enterprises

NASA Astrophysics Data System (ADS)

Ranosz, Robert

2017-09-01

This article is devoted to the determinants of interest rates on corporate bonds of mining enterprises. The study includes a comparison between the cost of foreign capital as resulting from the issue of debt instruments in different sectors of the economy in relation to the mining industry. The article also depicts the correlation between the rating scores published by the three largest rating agencies: S&P, Moody's, and Fitch. The test was based on simple statistical methods. The analysis performed indicated that there is a dependency between the factors listed and the amount of interest rates on corporate bonds of global mining enterprises. Most significant factors include the rating level and the period for which the given series of bonds was issued. Additionally, it is not without significance whether the given bond has additional options. Pursuant to the obtained results, is should be recognized that in order to reduce the interest rate on bonds, mining enterprises should pay particular attention to the rating and attempt to include additional options in issued bonds. Such additional options may comprise, for example, an ability to exchange bonds to shares or raw materials.

Intrinsic bond strength of metal films on polymer substrates

NASA Technical Reports Server (NTRS)

Wheeler, Donald R.; Osaki, Hiroyuki

1990-01-01

A semiquantitative method for the measurement of the intrinsic bond strength between elastic substrates and elastic films that fail by brittle fracture is described. Measurements on a polyethylene terephthalate (PET)-Ni couple were used to verify the essential features of the analysis. It was found that the interfacial shear strength of Ni on PET doubled after ion etching.

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.

The effect of nitrogen incorporation on the bonding structure of hydrogenated carbon nitride films

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

Camero, M.; Buijnsters, J. G.; Gomez-Aleixandre, C.

2007-03-15

This work describes the composition and bonding structure of hydrogenated carbon nitride (a-CN{sub x}:H) films synthesized by electron cyclotron resonance chemical vapor deposition using as precursor gases argon, methane, and nitrogen. The composition of the films was derived from Rutherford backscattering and elastic recoil detection analysis and the bonding structure was examined by infrared (IR) spectroscopy and x-ray absorption near edge spectroscopy (XANES). By varying the nitrogen to methane ratio in the applied gas mixture, polymeric a-CN{sub x}:H films with N/C contents varying from 0.06 to 0.49 were obtained. Remarkably, the H content of the films ({approx}40 at. %) wasmore » rather unaffected by the nitrogenation process. The different bonding states as detected in the measured XANES C(1s) and N(1s) spectra have been correlated with those of a large number of reference samples. The XANES and IR spectroscopy results indicate that N atoms are efficiently incorporated into the amorphous carbon network and can be found in different bonding environments, such as pyridinelike, graphitelike, nitrilelike, and amino groups. The nitrogenation of the films results in the formation of N-H bonding environments at the cost of C-H structures. Also, the insertion of N induces a higher fraction of double bonds in the structure at the expense of the linear polymerlike chains, hence resulting in a more cross-linked solid. The formation of double bonds takes place through complex C=N structures and not by formation of graphitic aromatic rings. Also, the mechanical and tribological properties (hardness, friction, and wear) of the films have been studied as a function of the nitrogen content. Despite the major modifications in the bonding structure with nitrogen uptake, no significant changes in these properties are observed.« less

The Pariser-Parr-Pople model for trans-polyenes. I. Ab initio and semiempirical study of the bond alternation in trans-butadiene

NASA Astrophysics Data System (ADS)

Förner, Wolfgang

1992-03-01

Ab initio investigations of the bond alternation in butadiene are presented. The atomic basis sets applied range from minimal to split valence plus polarization quality. With the latter one the Hartree-Fock limit for the bond alternation is reached. Correlation is considered on Møller-Plesset many-body perturbation theory of second order (MP2), linear coupled cluster doubles (L-CCD) and coupled cluster doubles (CCD) level. For the smaller basis sets it is shown that for the bond alternation π-π correlations are essential while the effects of σ-σ and σ-π correlations are, though large, nearly independent of bond alternation. On MP2 level the variation of σ-π correlation with bond alternation is surprisingly large. This is discussed as an artefact of MP2. Comparative Su-Schrieffer-Heeger (SSH) and Pariser-Parr-Pople (PPP) calculations show that these models in their usual parametrizations cannot reproduce the ab initio results.

In vitro evaluation of an alternative method to bond molar tubes

PubMed Central

PINZAN-VERCELINO, Célia Regina Maio; PINZAN, Arnaldo; GURGEL, Júlio de Araújo; BRAMANTE, Fausto Silva; PINZAN, Luciana Maio

2011-01-01

Despite the advances in bonding materials, many clinicians today still prefer to place bands on molar teeth. Molar bonding procedures need improvement to be widely accepted clinically. Objective The purpose of this study was to evaluate the shear bond strength when an additional adhesive layer was applied on the occlusal tooth/tube interface to provide reinforcement to molar tubes. Material and methods Sixty third molars were selected and allocated to the 3 groups: group 1 received a conventional direct bond followed by the application of an additional layer of adhesive on the occlusal tooth/tube interface, group 2 received a conventional direct bond, and group 3 received a conventional direct bond and an additional cure time of 10 s. The specimens were debonded in a universal testing machine. The results were analyzed statistically by ANOVA and Tukey’s test (α=0.05). Results Group 1 had a significantly higher (p<0.05) shear bond strength compared to groups 2 and 3. No difference was detected between groups 2 and 3 (p>0.05). Conclusions The present in vitro findings indicate that the application of an additional layer of adhesive on the tooth/tube interface increased the shear bond strength of the bonded molar tubes. PMID:21437468

Hydrogen bonding in ionic liquids.

PubMed

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

2015-03-07

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

Facile and Promising Method for Michael Addition of Indole and Pyrrole to Electron-Deficient trans-β-Nitroolefins Catalyzed by a Hydrogen Bond Donor Catalyst Feist's Acid and Preliminary Study of Antimicrobial Activity

PubMed Central

Al Majid, Abdullah M. A.; Islam, Mohammad Shahidul; Barakat, Assem; Al-Agamy, Mohamed H. M.; Naushad, Mu.

2014-01-01

The importance of cooperative hydrogen-bonding effects has been demonstrated using novel 3-methylenecyclopropane-1,2-dicarboxylic acid (Feist's acid (FA)) as hydrogen bond donor catalysts for the addition of indole and pyrrole to trans-β-nitrostyrene derivatives. Because of the hydrogen bond donor (HBD) ability, Feist's acid (FA) has been introduced as a new class of hydrogen bond donor catalysts for the activation of nitroolefin towards nucleophilic substitution reaction. It has effectively catalyzed the Michael addition of indoles and pyrrole to β-nitroolefins under optimum reaction condition to furnish the corresponding Michael adducts in good to excellent yields (up to 98%). The method is general, atom-economical, convenient, and eco-friendly and could provide excellent yields and regioselectivities. Some newly synthesized compounds were for examined in vitro antimicrobial activity and their preliminary results are reported. PMID:24574906

Water interaction and bond strength to dentin of dye-labelled adhesive as a function of the addition of rhodamine B.

PubMed

Wang, Linda; Bim, Odair; Lopes, Adolfo Coelho de Oliveira; Francisconi-Dos-Rios, Luciana Fávaro; Maenosono, Rafael Massunari; D'Alpino, Paulo Henrique Perlatti; Honório, Heitor Marques; Atta, Maria Teresa

2016-01-01

This study investigated the effect of the fluorescent dye rhodamine B (RB) for interfacial micromorphology analysis of dental composite restorations on water sorption/solubility (WS/WSL) and microtensile bond strength to dentin (µTBS) of a 3-step total etch and a 2-step self-etch adhesive system. The adhesives Adper Scotchbond Multi-Purpose (MP) and Clearfil SE Bond (SE) were mixed with 0.1 mg/mL of RB. For the WS/WSL tests, cured resin disks (5.0 mm in diameter x 0.8 mm thick) were prepared and assigned into four groups (n=10): MP, MP-RB, SE, and SE-RB. For µTBS assessment, extracted human third molars (n=40) had the flat occlusal dentin prepared and assigned into the same experimental groups (n=10). After the bonding and restoration procedures, specimens were sectioned in rectangular beams, stored in water and tested after seven days or after 12 months. The failure mode of fractured specimens was qualitatively evaluated under optical microscope (x40). Data from WS/WSL and µTBS were assessed by one-way and three-way ANOVA, respectively, and Tukey's test (α=5%). RB increased the WSL of MP and SE. On the other hand, WS of both MP and SE was not affected by the addition of RB. No significance in µTBS between MP and MP-RB for seven days or one year was observed, whereas for SE a decrease in the µTBS means occurred in both storage times. RB should be incorporated into non-simplified DBSs with caution, as it can interfere with their physical-mechanical properties, leading to a possible misinterpretation of bonded interface.

Prediction of allosteric sites and mediating interactions through bond-to-bond propensities

NASA Astrophysics Data System (ADS)

Amor, B. R. C.; Schaub, M. T.; Yaliraki, S. N.; Barahona, M.

2016-08-01

Allostery is a fundamental mechanism of biological regulation, in which binding of a molecule at a distant location affects the active site of a protein. Allosteric sites provide targets to fine-tune protein activity, yet we lack computational methodologies to predict them. Here we present an efficient graph-theoretical framework to reveal allosteric interactions (atoms and communication pathways strongly coupled to the active site) without a priori information of their location. Using an atomistic graph with energy-weighted covalent and weak bonds, we define a bond-to-bond propensity quantifying the non-local effect of instantaneous bond fluctuations propagating through the protein. Significant interactions are then identified using quantile regression. We exemplify our method with three biologically important proteins: caspase-1, CheY, and h-Ras, correctly predicting key allosteric interactions, whose significance is additionally confirmed against a reference set of 100 proteins. The almost-linear scaling of our method renders it suitable for high-throughput searches for candidate allosteric sites.

Prediction of allosteric sites and mediating interactions through bond-to-bond propensities

PubMed Central

Amor, B. R. C.; Schaub, M. T.; Yaliraki, S. N.; Barahona, M.

2016-01-01

Allostery is a fundamental mechanism of biological regulation, in which binding of a molecule at a distant location affects the active site of a protein. Allosteric sites provide targets to fine-tune protein activity, yet we lack computational methodologies to predict them. Here we present an efficient graph-theoretical framework to reveal allosteric interactions (atoms and communication pathways strongly coupled to the active site) without a priori information of their location. Using an atomistic graph with energy-weighted covalent and weak bonds, we define a bond-to-bond propensity quantifying the non-local effect of instantaneous bond fluctuations propagating through the protein. Significant interactions are then identified using quantile regression. We exemplify our method with three biologically important proteins: caspase-1, CheY, and h-Ras, correctly predicting key allosteric interactions, whose significance is additionally confirmed against a reference set of 100 proteins. The almost-linear scaling of our method renders it suitable for high-throughput searches for candidate allosteric sites. PMID:27561351

Synthesis and Characterization of a Hyperbranched Hydrogen Bond Acidic Carbosilane Sorbent Polymer

DTIC Science & Technology

2010-01-01

double bond of HCSA2 (1) electrophilically attacks the ketone carbon of the HFA. The bonds are formed via a pericyclic mechanism which requires formation...val- ues for H, 3.1% and C, 35.4% compared with the theoretical weight percents of H, 2.2%, and C, 34.3%. Fluorine composi- tion numbers were...Srcic, S. Acta Chim Solv 2004, 51, 373–394. 43 Bhadury, P. S.; Dubey, V.; Singh, S.; Saxena, C. J. Fluorine Chem 2005, 126, 1252–1256. 44 Grate, J. W

Intramolecular hydrogen bonding in malonaldehyde and its radical analogues.

PubMed

Lin, Chen; Kumar, Manoj; Finney, Brian A; Francisco, Joseph S

2017-09-28

High level Brueckner doubles with triples correction method-based ab initio calculations have been used to investigate the nature of intramolecular hydrogen bonding and intramolecular hydrogen atom transfer in cis-malonaldehyde (MA) and its radical analogues. The radicals considered here are the ones that correspond to the homolytic cleavage of C-H bonds in cis-MA. The results suggest that cis-MA and its radical analogues, cis-MA RS , and cis-MA RA , both exist in planar geometry. The calculated intramolecular O-H⋯O=C bond in cis-MA is shorter than that in the radical analogues. The intramolecular hydrogen bond in cis-MA is stronger than in its radicals by at least 3.0 kcal/mol. The stability of a cis-malonaldehyde radical correlates with the extent of electron spin delocalization; cis-MA RA , in which the radical spin is more delocalized, is the most stable MA radical, whereas cis-MA RS , in which the radical spin is strongly localized, is the least stable radical. The natural bond orbital analysis indicates that the intramolecular hydrogen bonding (O⋯H⋯O) in cis-malonaldehyde radicals is stabilized by the interaction between the lone pair orbitals of donor oxygen and the σ * orbital of acceptor O-H bond (n → σ * OH ). The calculated barriers indicate that the intramolecular proton transfer in cis-MA involves 2.2 kcal/mol lower barrier than that in cis-MA RS .

26 CFR 1.6165-1 - Bonds where time to pay the tax or deficiency has been extended.

Code of Federal Regulations, 2010 CFR

2010-04-01

... exceeding double the amount of the tax with respect to which the extension is granted. Such bond shall be... 26 Internal Revenue 13 2010-04-01 2010-04-01 false Bonds where time to pay the tax or deficiency... THE TREASURY (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES Extensions of Time for Payment § 1.6165-1...

Shear Bond Strength of Orthodontic Brackets Bonded to Zirconium Crowns

PubMed Central

Mehmeti, Blerim; Azizi, Bleron; Kelmendi, Jeta; Iljazi-Shahiqi, Donika; Alar, Željko

2017-01-01

Background An increasing demand for esthetic restorations has resulted in an increased use of all-ceramic restorations, such as zirconium. However, one of the challenges the orthodontist must be willing to face is how to increase bond strength between the brackets and various ceramic restorations.Bond strength can beaffected bybracket type, by the material that bracketsaremade of, and their base surface design or retention mode. ​ Aim: of this study was to perform a comparative analysis of the shear bond strength (SBS) of metallic and ceramic orthodontic brackets bonded to all-zirconium ceramic surfaces used for prosthetic restorations, and also to evaluate the fracture mode of these two types of orthodontic brackets. Material and methods Twenty samples/semi-crowns of all-zirconium ceramic, on which orthodontic brackets were bonded, 10 metallic and 10 ceramic polycrystalline brackets, were prepared for this research. SBS has been testedby Universal Testing Machine, with a load applied using a knife edged rod moving at a fixed rate of 1 mm/min, until failure occurred. The force required to debond the brackets was recorded in Newton, then SBS was calculated to MPa. In addition, the samples were analyzed using a digital camera magnifier to determine Adhesive Remnant Index (ARI). Statistical data were processed using t-test, and the level of significance was set at α = 0.05. Results Higher shear bond strength values were observed in metallic brackets bonded to zirconium crowns compared tothoseof ceramic brackets, with a significant difference. During the test, two of the ceramic brackets were partially or totally damaged. Conclusion Metallic brackets, compared to ceramic polycrystalline brackets, seemed tocreate stronger adhesion with all-zirconium surfaces due to their better retention mode. Also, ceramic brackets showed higher fragility during debonding. PMID:28827846

Shear Bond Strength of Orthodontic Brackets Bonded to Zirconium Crowns.

PubMed

Mehmeti, Blerim; Azizi, Bleron; Kelmendi, Jeta; Iljazi-Shahiqi, Donika; Alar, Željko; Anić-Milošević, Sandra

2017-06-01

An increasing demand for esthetic restorations has resulted in an increased use of all-ceramic restorations, such as zirconium. However, one of the challenges the orthodontist must be willing to face is how to increase bond strength between the brackets and various ceramic restorations.Bond strength can beaffected bybracket type, by the material that bracketsaremade of, and their base surface design or retention mode. ​: A im: of this study was to perform a comparative analysis of the shear bond strength (SBS) of metallic and ceramic orthodontic brackets bonded to all-zirconium ceramic surfaces used for prosthetic restorations, and also to evaluate the fracture mode of these two types of orthodontic brackets. Twenty samples/semi-crowns of all-zirconium ceramic, on which orthodontic brackets were bonded, 10 metallic and 10 ceramic polycrystalline brackets, were prepared for this research. SBS has been testedby Universal Testing Machine, with a load applied using a knife edged rod moving at a fixed rate of 1 mm/min, until failure occurred. The force required to debond the brackets was recorded in Newton, then SBS was calculated to MPa. In addition, the samples were analyzed using a digital camera magnifier to determine Adhesive Remnant Index (ARI). Statistical data were processed using t-test, and the level of significance was set at α = 0.05. Higher shear bond strength values were observed in metallic brackets bonded to zirconium crowns compared tothoseof ceramic brackets, with a significant difference. During the test, two of the ceramic brackets were partially or totally damaged. Metallic brackets, compared to ceramic polycrystalline brackets, seemed tocreate stronger adhesion with all-zirconium surfaces due to their better retention mode. Also, ceramic brackets showed higher fragility during debonding.

Shear Bond Strength of Three Orthodontic Bonding Systems on Enamel and Restorative Materials.

PubMed

Hellak, Andreas; Ebeling, Jennifer; Schauseil, Michael; Stein, Steffen; Roggendorf, Matthias; Korbmacher-Steiner, Heike

2016-01-01

Objective. The aim of this in vitro study was to determine the shear bond strength (SBS) and adhesive remnant index (ARI) score of two self-etching no-mix adhesives (iBond ™ and Scotchbond ™ ) on different prosthetic surfaces and enamel, in comparison with the commonly used total etch system Transbond XT ™ . Materials and Methods . A total of 270 surfaces (1 enamel and 8 restorative surfaces, n = 30) were randomly divided into three adhesive groups. In group 1 (control) brackets were bonded with Transbond XT primer. In the experimental groups iBond adhesive (group 2) and Scotchbond Universal adhesive (group 3) were used. The SBS was measured using a Zwicki 1120 ™ testing machine. The ARI and SBS were compared statistically using the Kruskal-Wallis test ( P ≤ 0.05). Results . Significant differences in SBS and ARI were found between the control group and experimental groups. Conclusions . Transbond XT showed the highest SBS on human enamel. Scotchbond Universal on average provides the best bonding on all other types of surface (metal, composite, and porcelain), with no need for additional primers. It might therefore be helpful for simplifying bonding in orthodontic procedures on restorative materials in patients. If metal brackets have to be bonded to a metal surface, the use of a dual-curing resin is recommended.

Bonding without Tears.

ERIC Educational Resources Information Center

Akeroyd, F. Michael

1982-01-01

Discusses merits of using sigma-pi model of ethylene as a teaching aid in introductory organic chemistry. The nonmathematical treatment of sigma-pi bonding is then extended to such phenomena as conjugation, hyperconjugation, Markovnikoff addition, aromaticity, and aromatic substitution. (SK)

Heterobimetallic Complexes That Bond Vanadium to Iron, Cobalt, and Nickel

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

Clouston, Laura J.; Bernales, Varinia; Cammarota, Ryan C.

2015-12-21

Zero-valent iron, cobalt, and nickel were installed into the metalloligand V[N(o-(NCH2P(iPr)2)C6H4)3] (1, VL), generating the heterobimetallic trio FeVL (2), CoVL (3), and NiVL (4), respectively. In addition, the one-electron-oxidized analogues [FeVL]X ([2ox]X, where X– = BPh4 or PF6) and [CoVL]BPh4 ([3ox]BPh4) were prepared. The complexes were characterized by a host of physical methods, including cyclic voltammetry, X-ray crystallography, magnetic susceptibility, electronic absorption, NMR, electron paramagnetic resonance (EPR), and Mössbauer spectroscopies. The CoV and FeV heterobimetallic compounds have short M–V bond lengths that are consistent with M–M multiple bonding. As revealed by theoretical calculations, the M–V bond is triple in 2,more » 2ox, and 3ox, double in 3, and dative (Ni → V) in 4. The (d–d)10 species, 2 and 3ox, are diamagnetic and exhibit large diamagnetic anisotropies of -4700 × 10–36 m3/molecule. Complexes 2 and 3ox are also characterized by intense visible bands at 760 and 610 nm (ε > 1000 M–1 cm–1), respectively, which correspond to an intermetal (M → V) charge-transfer transition. Magnetic susceptibility measurements and EPR characterization establish S = 1/2 ground states for (d–d)9 2ox and (d–d)11 3, while (d–d)12 4 is S = 1 based on Evans’ method.« less

Quantum finance Hamiltonian for coupon bond European and barrier options.

PubMed

Baaquie, Belal E

2008-03-01

Coupon bond European and barrier options are financial derivatives that can be analyzed in the Hamiltonian formulation of quantum finance. Forward interest rates are modeled as a two-dimensional quantum field theory and its Hamiltonian and state space is defined. European and barrier options are realized as transition amplitudes of the time integrated Hamiltonian operator. The double barrier option for a financial instrument is "knocked out" (terminated with zero value) if the price of the underlying instrument exceeds or falls below preset limits; the barrier option is realized by imposing boundary conditions on the eigenfunctions of the forward interest rates' Hamiltonian. The price of the European coupon bond option and the zero coupon bond barrier option are calculated. It is shown that, is general, the constraint function for a coupon bond barrier option can -- to a good approximation -- be linearized. A calculation using an overcomplete set of eigenfunctions yields an approximate price for the coupon bond barrier option, which is given in the form of an integral of a factor that results from the barrier condition times another factor that arises from the payoff function.

Efficient synthesis of optically active 4-nitro-cyclohexanones via bifunctional thiourea-base catalyzed double-Michael addition of nitromethane to dienones.

PubMed

Wu, Bin; Liu, Guo-Gui; Li, Mei-Qiu; Zhang, Yong; Zhang, Shao-Yun; Qiu, Jun-Ru; Xu, Xiao-Ping; Ji, Shun-Jun; Wang, Xing-Wang

2011-04-07

Thiourea-modified cinchona alkaloids as bifunctional catalysts and a base could catalyze a stepwise [5+1] cyclization of divinyl ketones with nitromethane via double Michael additions, furnishing optically active 4-nitro-cyclohexanones with good yields, excellent diastereoselectivities (>20 : 1) and high enantiomeric ratios (up to 97 : 3).

Unconventional Tough Double-Network Hydrogels with Rapid Mechanical Recovery, Self-Healing, and Self-Gluing Properties.

PubMed

Jia, Haiyan; Huang, Zhangjun; Fei, Zhaofu; Dyson, Paul J; Zheng, Zhen; Wang, Xinling

2016-11-16

Hydrogels are polymeric materials that have a relatively high capacity for holding water. Recently, a double network (DN) technique was developed to fabricate hydrogels with a toughness comparable to rubber. The mechanical properties of DN hydrogels may be attributed to the brittle sacrificial bonding network of one hydrogel, facilitating stress dispersion, combined with ductile polymer chains of a second hydrogel. Herein, we report a novel class of tunable DN hydrogels composed of a polyurethane hydrogel and a stronger, dipole-dipole and H-bonding interaction reinforced (DHIR) hydrogel. Compared to conventional DN hydrogels, these materials show remarkable improvements in mechanical recovery, modulus, and yielding, with excellent self-healing and self-gluing properties. In addition, the new DN hydrogels exhibit excellent tensile and compression strengths and possess shape-memory properties, which make them promising for applications in engineering, biomedicine, and other domains where load bearing is required.

Water interaction and bond strength to dentin of dye-labelled adhesive as a function of the addition of rhodamine B

PubMed Central

WANG, Linda; BIM, Odair; LOPES, Adolfo Coelho de Oliveira; FRANCISCONI-DOS-RIOS, Luciana Fávaro; MAENOSONO, Rafael Massunari; D’ALPINO, Paulo Henrique Perlatti; HONÓRIO, Heitor Marques; ATTA, Maria Teresa

2016-01-01

ABSTRACT Objective This study investigated the effect of the fluorescent dye rhodamine B (RB) for interfacial micromorphology analysis of dental composite restorations on water sorption/solubility (WS/WSL) and microtensile bond strength to dentin (µTBS) of a 3-step total etch and a 2-step self-etch adhesive system. Material and Methods The adhesives Adper Scotchbond Multi-Purpose (MP) and Clearfil SE Bond (SE) were mixed with 0.1 mg/mL of RB. For the WS/WSL tests, cured resin disks (5.0 mm in diameter x 0.8 mm thick) were prepared and assigned into four groups (n=10): MP, MP-RB, SE, and SE-RB. For µTBS assessment, extracted human third molars (n=40) had the flat occlusal dentin prepared and assigned into the same experimental groups (n=10). After the bonding and restoration procedures, specimens were sectioned in rectangular beams, stored in water and tested after seven days or after 12 months. The failure mode of fractured specimens was qualitatively evaluated under optical microscope (x40). Data from WS/WSL and µTBS were assessed by one-way and three-way ANOVA, respectively, and Tukey’s test (α=5%). Results RB increased the WSL of MP and SE. On the other hand, WS of both MP and SE was not affected by the addition of RB. No significance in µTBS between MP and MP-RB for seven days or one year was observed, whereas for SE a decrease in the µTBS means occurred in both storage times. Conclusions RB should be incorporated into non-simplified DBSs with caution, as it can interfere with their physical-mechanical properties, leading to a possible misinterpretation of bonded interface. PMID:27556201

Isotope effects associated with tunneling and double proton transfer in the hydrogen bonds of benzoic acid

NASA Astrophysics Data System (ADS)

Xue, Q.; Horsewill, A. J.; Johnson, M. R.; Trommsdorff, H. P.

2004-06-01

The isotope effects associated with double proton transfer in the hydrogen bonds of benzoic acid (BA) dimers have been measured using field-cycling 1H NMR relaxometry and quasielastic neutron scattering. By studying mixed isotope (hydrogen and deuterium) samples, the dynamics of three isotopologues, BA-HH, BA-HD, and BA-DD, have been investigated. Low temperature measurements provide accurate measurements of the incoherent tunneling rate, k0. This parameter scales accurately with the mass number, m, according to the formula k0=(E/m)e-F√m providing conclusive evidence that the proton transfer process is a strongly correlated motion of two hydrons. Furthermore, we conclude that the tunneling pathway is the same for the three isotopologue species. Measurements at higher temperatures illuminate the through barrier processes that are mediated via intermediate or excited vibrational states. In parallel with the investigation of proton transfer dynamics, the theoretical and experimental aspects of studying spin-lattice relaxation in single crystals of mixed isotope samples are investigated in depth. Heteronuclear dipolar interactions between 1H and 2H isotopes contribute significantly to the overall proton spin-lattice relaxation and it is shown that these must be modeled correctly to obtain accurate values for the proton transfer rates. Since the sample used in the NMR measurements was a single crystal, full account of the orientation dependence of the spin-lattice relaxation with respect to the applied B field was incorporated into the data analysis.

Relationship between thin-film bond strength as measured by a scratch test, and indentation hardness for bonding agents.

PubMed

Kusakabe, Shusuke; Rawls, H Ralph; Hotta, Masato

2016-03-01

To evaluate thin-film bond strength between a bonding agent and human dentin, using a scratch test, and the characteristics and accuracy of measurement. One-step bonding agents (BeautiBond; Bond Force; Adper Easy Bond; Clearfil tri-S Bond) and two-step bonding agents (Cleafil SE Bond; FL-Bond II) were investigated in this study. Flat dentin surfaces were prepared for extracted human molars. The dentin surfaces were ground and bonding agents were applied and light cured. The thin-film bond strength test of the specimens was evaluated by the critical load at which the coated bonding agent failed and dentin appeared. The scratch mark sections were then observed under a scanning electron microscope. Indentation hardness was evaluated by the variation in depth under an applied load of 10gf. Data were compared by one-way ANOVA with the Scheffé's post hoc multiple comparison test (p<0.05). In addition, thin-film bond strength and indentation hardness were analyzed using analysis of correlation and covariance. The thin-film bond strength of two-step bonding agents were found to be significantly higher than that of one-step bonding agents with small standard deviations. Scratch marks consistently showed adhesive failure in the vicinity of the bonding agent/dentin interface. The indentation hardness showed a trend that two-step bonding agents have greater hardness than one-step bonding agents. A moderately significant correlation (r(2)=0.31) was found between thin-film bond strength and indentation hardness. Thin-film bond strength test is a valid and reliable means of evaluating bond strength in the vicinity of the adhesive interface and is more accurate than other methods currently in use. Further, the thin-film bond strength is influenced by the hardness of the cued bonding agent. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effects of surface preparation on the long-term durability of adhesively bonded composite joints

NASA Astrophysics Data System (ADS)

Bardis, Jason Dante

The long-term durability of adhesively bonded composite joints is critical to modern aircraft structures, which are increasingly adopting bonding as an alternative option to mechanical fastening. The effects of the surface preparation of the adherends are critical, affecting initial strength, long-term durability, fracture toughness, and failure modes of bonded joints. In this study, several potential factors are evaluated, with focus on the following: (1) Effects of possible chemical contamination from release fabrics, release films, and peel plies during adherend cure. (2) Chemical and mechanical effects of abrasion on the fracture toughness and failure mode. (3) Characterization of paste and film adhesives. There are several standard test methods used to evaluate specimen fracture, but the majority concentrate on bonded metals and interlaminar composite fracture. Testing concentrated on mode I tests; a custom double cantilever beam specimen was devised and utilized, and two forms of a wedge crack test (traveling and static) were also used. Additionally, single lap shear tests were run to contrast the mode I tests. Non-destructive testing included X-ray photography of crack fronts, energy dispersive spectroscopy and X-ray photoelectron spectroscopy surface chemistry analyses, and scanning electron microscope imaging of prepared surfaces. All mode I test methods tended to be in agreement in the ranking of different surface preparation methods. Test results revealed that release agents deposited on adherend surfaces during their cure cycle prevented proper adhesion. While mechanical abrasion did improve their fracture toughness and lower their contamination greatly, the test values did not reach the levels of samples that were not contaminated before bonding, and the interfacial modes of failure did not always change to desirable modes.

Intramolecular CH···O hydrogen bonds in the AI and BI DNA-like conformers of canonical nucleosides and their Watson-Crick pairs. Quantum chemical and AIM analysis.

PubMed

Yurenko, Yevgen P; Zhurakivsky, Roman O; Samijlenko, Svitlana P; Hovorun, Dmytro M

2011-08-01

The aim of this work is to cast some light on the H-bonds in double-stranded DNA in its AI and BI forms. For this purpose, we have performed the MP2 and DFT quantum chemical calculations of the canonical nucleoside conformers, relative to the AI and BI DNA forms, and their Watson-Crick pairs, which were regarded as the simplest models of the double-stranded DNA. Based on the atoms-in-molecules analysis (AIM), five types of the CH···O hydrogen bonds, involving bases and sugar, were detected numerically from 1 to 3 per a conformer: C2'H···O5', C1'H···O2, C6H···O5', C8H···O5', and C6H···O4'. The energy values of H-bonds occupy the range of 2.3-5.6 kcal/mol, surely exceeding the kT value (0.62 kcal/mol). The nucleoside CH···O hydrogen bonds appeared to "survive" turns of bases against the sugar, sometimes in rather large ranges of the angle values, pertinent to certain conformations, which points out to the source of the DNA lability, necessary for the conformational adaptation in processes of its functioning. The calculation of the interactions in the dA·T nucleoside pair gives evidence, that additionally to the N6H···O4 and N1···N3H canonical H-bonds, between the bases adenine and thymine the third one (C2H···O2) is formed, which, though being rather weak (about 1 kcal/mol), satisfies the AIM criteria of H-bonding and may be classified as a true H-bond. The total energy of all the CH···O nontraditional intramolecular H-bonds in DNA nucleoside pairs appeared to be commensurable with the energy of H-bonds between the bases in Watson-Crick pairs, which implies their possible important role in the DNA shaping.

26 CFR 1.149(g)-1 - Hedge bonds.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 26 Internal Revenue 2 2012-04-01 2012-04-01 false Hedge bonds. 1.149(g)-1 Section 1.149(g)-1...) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.149(g)-1 Hedge bonds... for purposes of section 149(g) and this section. In addition, the following terms have the following...

26 CFR 1.149(g)-1 - Hedge bonds.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Hedge bonds. 1.149(g)-1 Section 1.149(g)-1...) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.149(g)-1 Hedge bonds... for purposes of section 149(g) and this section. In addition, the following terms have the following...

26 CFR 1.149(g)-1 - Hedge bonds.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 26 Internal Revenue 2 2011-04-01 2011-04-01 false Hedge bonds. 1.149(g)-1 Section 1.149(g)-1...) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.149(g)-1 Hedge bonds... for purposes of section 149(g) and this section. In addition, the following terms have the following...

26 CFR 1.149(g)-1 - Hedge bonds.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 26 Internal Revenue 2 2013-04-01 2013-04-01 false Hedge bonds. 1.149(g)-1 Section 1.149(g)-1...) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.149(g)-1 Hedge bonds... for purposes of section 149(g) and this section. In addition, the following terms have the following...

26 CFR 1.149(g)-1 - Hedge bonds.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 2 2010-04-01 2010-04-01 false Hedge bonds. 1.149(g)-1 Section 1.149(g)-1...) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.149(g)-1 Hedge bonds... for purposes of section 149(g) and this section. In addition, the following terms have the following...

The reactivity of phosphagermaallene Tip(t-Bu)Ge=C=PMes* with doubly and triply bonded nitrogen compounds.

PubMed

Ghereg, Dumitru; Gornitzka, Heinz; Escudié, Jean; Ladeira, Sonia

2010-11-15

Phosphagermaallene Tip(t-Bu)Ge=C=PMes* (1; Mes* = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) gives, with N-benzylidenemethylamine and pivalonitrile, [2+2] cycloadditions between the Ge=C double bond and the C=N and C≡N unsaturations, leading to the formation of the corresponding four-membered heterocycles 2 and 9. With N-tert-butyl-α-phenylnitrone and benzonitrile oxide, [2+3] cycloadditions occur to form the five-membered ring derivatives 6 and 7. By treatment of 1 with derivatives which possess weak acidic hydrogens in α of the C=N or C≡N multiple bond, two types of reactions were observed: an ene reaction with methyl(benzylideneamino)acetate and a 1,2 addition with acetonitrile to afford azadienyl(germyl)ether (4) and 3-germa-1-phosphapropene (8), respectively. In the case of benzonitrile, phosphagermaallene 1 behaves as a 1,3-dipole, to give, via a cyclic phosphagermacarbene intermediate, the tricyclic derivative 10.

Water transport and desalination through double-layer graphyne membranes.

PubMed

Akhavan, Mojdeh; Schofield, Jeremy; Jalili, Seifollah

2018-05-16

Non-equilibrium molecular dynamics simulations of water-salt solutions driven through single and double-layer graphyne membranes by a pressure difference created by rigid pistons are carried out to determine the relative performance of the membranes as filters in a reverse osmosis desalination process. It is found that the flow rate of water through a graphyne-4 membrane is twice that of a graphyne-3 membrane for both single and double-layer membranes. Although the addition of a second layer to a single-layer membrane reduces the membrane permeability, the double-layer graphyne membranes are still two or three orders of magnitude more permeable than commercial reverse osmosis membranes. The minimum reduction in flow rate for double-layer membranes occurs at a layer spacing of 0.35 nm with an AA stacking configuration, while at a spacing of 0.6 nm the flow rate is close to zero due to a high free energy barrier for permeation. This is caused by the difference in the environments on either side of the membrane sheets and the formation of a compact two-dimensional layer of water molecules in the interlayer space which slows down water permeation. The distribution of residence times of water molecules in the interlayer region suggests that at the critical layer spacing of 0.6 nm, a cross-over occurs in the mechanism of water flow from the collective movement of hydrogen-bonded water sheets to the permeation of individual water molecules. All membranes are demonstrated to have a high salt rejection fraction and the double-layered graphyne-4 membranes can further increase the salt rejection by trapping ions that have passed through the first membrane from the feed solution in the interlayer space.

Double Charge Exchange Reactions and Double Beta Decay

NASA Astrophysics Data System (ADS)

Auerbach, N.

2018-05-01

The subject of this presentation is at the forefront of nuclear physics, namely double beta decay. In particular one is most interested in the neutrinoless process of double beta decay, when the decay proceeds without the emission of two neutrinos. The observation of such decay would mean that the lepton conservation symmetry is violated and that the neutrinos are of Majorana type, meaning that they are their own anti-particles. The life time of this process has two unknowns, the mass of the neutrino and the nuclear matrix element. Determining the nuclear matrix element and knowing the cross-section well will set limits on the neutrino mass. There is a concentrated effort among the nuclear physics community to calculate this matrix element. Usually these matrix elements are a very small part of the total strength of the transition operators involved in the process. There is no simple way to “calibrate” the nuclear double beta decay matrix element. The double beta decay is a double charge exchange process, therefore it is proposed that double charge exchange reactions using ion projectiles on nuclei that are candidates for double beta decay, will provide additional necessary information about the nuclear matrix elements.

Verification of surface preparation for adhesive bonding

NASA Technical Reports Server (NTRS)

Myers, Rodney S.

1995-01-01

A survey of solid rocket booster (SRB) production operations identified potential contaminants which might adversely affect bonding operations. Lap shear tests quantified these contaminants' effects on adhesive strength. The most potent contaminants were selected for additional studies on SRB thermal protection system (TPS) bonding processes. Test panels were prepared with predetermined levels of contamination, visually inspected using white and black light, then bonded with three different TPS materials over the unremoved contamination. Bond test data showed that white and black light inspections are adequate inspection methods for TPS bonding operations. Extreme levels of contamination (higher than expected on flight hardware) had an insignificant effect on TPS bond strengths because of the apparent insensitivity of the adhesive system to contamination effects, and the comparatively weak cohesive strength of the TPS materials.

Shear bond strength of orthodontic brackets bonded with different self-etching adhesives.

PubMed

Scougall Vilchis, Rogelio José; Yamamoto, Seigo; Kitai, Noriyuki; Yamamoto, Kohji

2009-09-01

The purpose of this study was to compare the shear bond strength (SBS) of orthodontic brackets bonded with 4 self-etching adhesives. A total of 175 extracted premolars were randomly divided into 5 groups (n = 35). Group I was the control, in which the enamel was etched with 37% phosphoric acid, and stainless steel brackets were bonded with Transbond XT (3M Unitek, Monrovia, Calif). In the remaining 4 groups, the enamel was conditioned with the following self-etching primers and adhesives: group II, Transbond Plus and Transbond XT (3M Unitek); group III, Clearfil Mega Bond FA and Kurasper F (Kuraray Medical, Tokyo, Japan); group IV, Primers A and B, and BeautyOrtho Bond (Shofu, Kyoto, Japan); and group V, AdheSE and Heliosit Orthodontic (Ivoclar Vivadent AG, Liechtenstein). The teeth were stored in distilled water at 37 degrees C for 24 hours and debonded with a universal testing machine. The adhesive remnant index (ARI) including enamel fracture score was also evaluated. Additionally, the conditioned enamel surfaces were observed under a scanning electron microscope. The SBS values of groups I (19.0 +/- 6.7 MPa) and II (16.6 +/- 7.3 MPa) were significantly higher than those of groups III (11.0 +/- 3.9 MPa), IV (10.1 +/- 3.7 MPa), and V (11.8 +/- 3.5 MPa). Fluoride-releasing adhesives (Kurasper F and BeautyOrtho Bond) showed clinically acceptable SBS values. Significant differences were found in the ARI and enamel fracture scores between groups I and II. The 4 self-etching adhesives yielded SBS values higher than the bond strength (5.9 to 7.8 MPa) suggested for routine clinical treatment, indicating that orthodontic brackets can be successfully bonded with any of these self-etching adhesives.

Reliable four-point flexion test and model for die-to-wafer direct bonding

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

Tabata, T., E-mail: toshiyuki.tabata@cea.fr; Sanchez, L.; Fournel, F.

2015-07-07

For many years, wafer-to-wafer (W2W) direct bonding has been very developed particularly in terms of bonding energy measurement and bonding mechanism comprehension. Nowadays, die-to-wafer (D2W) direct bonding has gained significant attention, for instance, in photonics and microelectro-mechanics, which supposes controlled and reliable fabrication processes. So, whatever the stuck materials may be, it is not obvious whether bonded D2W structures have the same bonding strength as bonded W2W ones, because of possible edge effects of dies. For that reason, it has been strongly required to develop a bonding energy measurement technique which is suitable for D2W structures. In this paper, bothmore » D2W- and W2W-type standard SiO{sub 2}-to-SiO{sub 2} direct bonding samples are fabricated from the same full-wafer bonding. Modifications of the four-point flexion test (4PT) technique and applications for measuring D2W direct bonding energies are reported. Thus, the comparison between the modified 4PT and the double-cantilever beam techniques is drawn, also considering possible impacts of the conditions of measures such as the water stress corrosion at the debonding interface and the friction error at the loading contact points. Finally, reliability of a modified technique and a new model established for measuring D2W direct bonding energies is demonstrated.« less

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).

Carbon-Hydrogen Bond Activation in Hydridotris(pyrazolyl)borate Platinum(IV) Complexes:  Comparison of Density Functionals, Basis Sets, and Bonding Patterns.

PubMed

Vastine, Benjamin Alan; Webster, Charles Edwin; Hall, Michael B

2007-11-01

The reaction mechanism for the cycle beginning with the reductive elimination (RE) of methane from κ(3)-TpPt(IV)(CH3)2H (1) (Tp = hydridotris(pyrazolyl)borate) and subsequent oxidative addition (OA) of benzene to form finally κ(3)-TpPt(IV)(Ph)2H (19) was investigated by density functional theory (DFT). Two mechanistic steps are of particular interest, namely the barrier to C-H coupling (barrier 1 - Ba1) and the barrier to methane release (barrier 2 - Ba2). For 31 density functionals, the calculated values for Ba1 and Ba2 were benchmarked against the experimentally reported values of 26 (Ba1) and 35 (Ba2) kcal·mol(-1), respectively. Specifically, the values for Ba1 and Ba2, calculated at the B3LYP/double-ζ plus polarization level of theory, are 24.6 and 34.3 kcal·mol(-1), respectively. Overall, the best performing functional was BPW91 where the mae associated with the calculated values of the two barriers is 0.68 kcal·mol(-1). The calculated B3LYP values of Ba1 ranged between 20 and 26 kcal·mol(-1) for 12 effective core potential basis sets for platinum and 29 all-electron basis sets for the first row elements. Polarization functions for the first row elements were important for accurate values, but the addition of diffuse functions to non-hydrogen (+) and hydrogen atoms (++) had little effect on the calculated values. Basis set saturation was achieved with APNO basis sets utilized for first-row atoms. Bader's "Atoms in Molecules" was used to analyze the electron density of several complexes, and the electron density at the Pt-Nax bond critical point (trans to the active site for C-H coupling) varied over a wider range than any of the other Pt-N bonds.

Shear Bond Strength of Three Orthodontic Bonding Systems on Enamel and Restorative Materials

PubMed Central

Ebeling, Jennifer; Schauseil, Michael; Stein, Steffen; Roggendorf, Matthias; Korbmacher-Steiner, Heike

2016-01-01

Objective. The aim of this in vitro study was to determine the shear bond strength (SBS) and adhesive remnant index (ARI) score of two self-etching no-mix adhesives (iBond™ and Scotchbond™) on different prosthetic surfaces and enamel, in comparison with the commonly used total etch system Transbond XT™. Materials and Methods. A total of 270 surfaces (1 enamel and 8 restorative surfaces, n = 30) were randomly divided into three adhesive groups. In group 1 (control) brackets were bonded with Transbond XT primer. In the experimental groups iBond adhesive (group 2) and Scotchbond Universal adhesive (group 3) were used. The SBS was measured using a Zwicki 1120™ testing machine. The ARI and SBS were compared statistically using the Kruskal–Wallis test (P ≤ 0.05). Results. Significant differences in SBS and ARI were found between the control group and experimental groups. Conclusions. Transbond XT showed the highest SBS on human enamel. Scotchbond Universal on average provides the best bonding on all other types of surface (metal, composite, and porcelain), with no need for additional primers. It might therefore be helpful for simplifying bonding in orthodontic procedures on restorative materials in patients. If metal brackets have to be bonded to a metal surface, the use of a dual-curing resin is recommended. PMID:27738633

Mapping quantitative trait loci with additive effects and additive x additive epistatic interactions for biomass yield, grain yield, and straw yield using a doubled haploid population of wheat (Triticum aestivum L.).

PubMed

Li, Z K; Jiang, X L; Peng, T; Shi, C L; Han, S X; Tian, B; Zhu, Z L; Tian, J C

2014-02-28

Biomass yield is one of the most important traits for wheat (Triticum aestivum L.)-breeding programs. Increasing the yield of the aerial parts of wheat varieties will be an integral component of future wheat improvement; however, little is known regarding the genetic control of aerial part yield. A doubled haploid population, comprising 168 lines derived from a cross between two winter wheat cultivars, 'Huapei 3' (HP3) and 'Yumai 57' (YM57), was investigated. Quantitative trait loci (QTL) for total biomass yield, grain yield, and straw yield were determined for additive effects and additive x additive epistatic interactions using the QTLNetwork 2.0 software based on the mixed-linear model. Thirteen QTL were determined to have significant additive effects for the three yield traits, of which six also exhibited epistatic effects. Eleven significant additive x additive interactions were detected, of which seven occurred between QTL showing epistatic effects only, two occurred between QTL showing epistatic effects and additive effects, and two occurred between QTL with additive effects. These QTL explained 1.20 to 10.87% of the total phenotypic variation. The QTL with an allele originating from YM57 on chromosome 4B and another QTL contributed by HP3 alleles on chromosome 4D were simultaneously detected on the same or adjacent chromosome intervals for the three traits in two environments. Most of the repeatedly detected QTL across environments were not significant (P > 0.05). These results have implications for selection strategies in wheat biomass yield and for increasing the yield of the aerial part of wheat.

Carbon-hydrogen bond activation, C-N bond coupling, and cycloaddition reactivity of a three-coordinate nickel complex featuring a terminal imido ligand.

PubMed

Mindiola, Daniel J; Waterman, Rory; Iluc, Vlad M; Cundari, Thomas R; Hillhouse, Gregory L

2014-12-15

The three-coordinate imidos (dtbpe)Ni═NR (dtbpe = (t)Bu2PCH2CH2P(t)Bu2, R = 2,6-(i)Pr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni-N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-(i)Pr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N-C coupled product keteneimine PhCH═C═N(2,6- (i)Pr2C6H3). Given the ability of the Ni═N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni═N{2,6-(i)Pr2C6H3} when this species is treated with HSn((n)Bu)3. Likewise, the microscopic reverse reaction--conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-(i)Pr2C6H3)} to the imido (dtbpe)Ni═N{2,6-(i)Pr2C6H3}--is promoted when using the radical Mes*O(•) (Mes* = 2,4,6-(t)Bu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni═N{2,6-(i)Pr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C-N and N-N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni═N{2,6-(i)Pr2C6H3}.

Carbon–Hydrogen Bond Activation, C–N Bond Coupling, and Cycloaddition Reactivity of a Three-Coordinate Nickel Complex Featuring a Terminal Imido Ligand

PubMed Central

2015-01-01

The three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu2PCH2CH2PtBu2, R = 2,6-iPr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-iPr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr2C6H3). Given the ability of the Ni=N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6-iPr2C6H3} when this species is treated with HSn(nBu)3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-iPr2C6H3)} to the imido (dtbpe)Ni=N{2,6-iPr2C6H3}—is promoted when using the radical Mes*O• (Mes* = 2,4,6-tBu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6-iPr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6-iPr2C6H3}. PMID:25437507

Electrical Bonding: A Survey of Requirement, Methods, and Specifications

NASA Technical Reports Server (NTRS)

Evans, R. W.

1998-01-01

This document provides information helpful to engineers imposing electrical bonding requirements, reviewing waiver requests, or modifying specifications on various space programs. Electrical bonding specifications and some of the processes used in the United States have been reviewed. This document discusses the specifications, the types of bonds, the intent of each, and the basic requirements where possible. Additional topics discussed are resistance versus impedance, bond straps, corrosion, finishes, and special applications.

Additional double-wall roof in single-wall, closed, convective incubators: Impact on body heat loss from premature infants and optimal adjustment of the incubator air temperature.

PubMed

Delanaud, Stéphane; Decima, Pauline; Pelletier, Amandine; Libert, Jean-Pierre; Stephan-Blanchard, Erwan; Bach, Véronique; Tourneux, Pierre

2016-09-01

Radiant heat loss is high in low-birth-weight (LBW) neonates. Double-wall or single-wall incubators with an additional double-wall roof panel that can be removed during phototherapy are used to reduce Radiant heat loss. There are no data on how the incubators should be used when this second roof panel is removed. The aim of the study was to assess the heat exchanges in LBW neonates in a single-wall incubator with and without an additional roof panel. To determine the optimal thermoneutral incubator air temperature. Influence of the additional double-wall roof was assessed by using a thermal mannequin simulating a LBW neonate. Then, we calculated the optimal incubator air temperature from a cohort of human LBW neonate in the absence of the additional roof panel. Twenty-three LBW neonates (birth weight: 750-1800g; gestational age: 28-32 weeks) were included. With the additional roof panel, R was lower but convective and evaporative skin heat losses were greater. This difference can be overcome by increasing the incubator air temperature by 0.15-0.20°C. The benefit of an additional roof panel was cancelled out by greater body heat losses through other routes. Understanding the heat transfers between the neonate and the environment is essential for optimizing incubators. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

Computational Study of Pincer Iridium Catalytic Systems: C-H, N-H, and C-C Bond Activation and C-C Coupling Reactions

NASA Astrophysics Data System (ADS)

Zhou, Tian

Computational chemistry has achieved vast progress in the last decades in the field, which was considered to be only experimental before. DFT (density functional theory) calculations have been proven to be able to be applied to large systems, while maintaining high accuracy. One of the most important achievements of DFT calculations is in exploring the mechanism of bond activation reactions catalyzed by organometallic complexes. In this dissertation, we discuss DFT studies of several catalytic systems explored in the lab of Professor Alan S. Goldman. Headlines in the work are: (1) (R4PCP)Ir alkane dehydrogenation catalysts are highly selective and different from ( R4POCOP)Ir catalysts, predicting different rate-/selectivity-determining steps; (2) The study of the mechanism for double C-H addition/cyclometalation of phenanthrene or biphenyl by (tBu4PCP)Ir(I) and ( iPr4PCP)Ir illustrates that neutral Ir(III) C-H addition products can undergo a very facile second C-H addition, particularly in the case of sterically less-crowded Ir(I) complexes; (3) (iPr4PCP)Ir pure solid phase catalyst is highly effective in producing high yields of alpha-olefin products, since the activation enthalpy for dehydrogenation is higher than that for isomerization via an allyl pathway; higher temperatures favor the dehydrogenation/isomerization ratio; (4) (PCP)Ir(H)2(N2H4) complex follows a hydrogen transfer mechanism to undergo both dehydrogenation to form N 2 and H2, as well as hydrogen transfer followed by N-N bond cleavage to form NH3, N2, and H2; (5) The key for the catalytic effect of solvent molecule in CO insertion reaction for RMn(CO)5 is hydrogen bond assisted interaction. The basicity of the solvent determines the strength of the hydrogen bond interaction during the catalytic path and determines the catalytic power of the solvent; and (6) Dehydrogenative coupling of unactivated C-H bonds (intermolecular vinyl-vinyl, intramolecular vinyl-benzyl) is catalyzed by precursors of the

Diffusion bonding of Ti-48Ni-2Mn-2Nb (at.%)

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

Godfrey, S.P.; Strangwood, M.; Threadgill, P.L.

The diffusion bonding behavior of Ti-48at. % Al-2at. % Mn-2at. %Nb has been studied as a function of temperature (in the range 1,200--1,350C), time (15--45 minutes) and starting microstructure (lamellar, duplex and near {gamma}) at constant bonding pressure of 10 MPa. It was found, that under the above conditions, small twin related {gamma} grains, approximately 10-20 {mu}m in size, nucleated at the original interface and grew into the matrix forming a double necklace grain structure. Particles of {alpha}{sub 2} were observed around the interface, the formation of {alpha}{sub 2} particles was believed to be related to oxygen partitioning and stabilizationmore » effects from dissolved oxide films during the bonding process. Evidence for this mechanism was obtained from parallel electron energy loss spectroscopy (PEELS), which identified oxygen partitioning in the (X2) particles. For the fully lamellar structure bonded at 1,250 C for 45 minutes the failure strength of the bond was found to be 250 MPa, approximately 50 MPa lower than the failure strength of the base material.« less

Ozone-induced dissociation on a traveling wave high-resolution mass spectrometer for determination of double-bond position in lipids.

PubMed

Vu, Ngoc; Brown, Jeffery; Giles, Kevin; Zhang, Qibin

2017-09-15

The position of C=C within fatty acyl chains affects the biological function of lipids. Ozone-induced dissociation mass spectrometry (OzID-MS) has great potential in determination of lipid double-bond position, but has generally been implemented on low-resolution ion trap mass spectrometers. In addition, most of the OzID-MS experiments carried out so far were focused on the sodiated adducts of lipids; fragmentation of the most commonly observed protonated ions generated in LC/MS-based lipidomics workflow has been less explored. Ozone generated in line from an ozone generator was connected to the trap and transfer gas supply line of a Synapt G2 high-resolution mass spectrometer. Protonated ions of different phosphatidylcholines (PC) were generated by electrospray ionization through direct infusion. Different parameters, including traveling wave height and velocity, trap entrance and DC potential, were adjusted to maximize the OzID efficiency. sn-positional isomers and cis/trans isomers of lipids were compared for their reactivity with ozone. Traveling wave height and velocity were tuned to prolong the encounter time between lipid ions and ozone, and resulted in improved OzID efficiency, as did increasing trapping region DC and entrance potential. Under optimized settings, at least 1000 times enhancement in OzID efficiency was achieved compared to that under default settings for monounsaturated PC standards. Monounsaturated C=C in the sn-2 PC isomer reacted faster with ozone than the sn-1 isomer. Similarly, the C=C in trans PC reacted faster than in cis PC. This is the first implementation of OzID in the trap and transfer region of a traveling wave enabled high-resolution mass spectrometer. The OzID reaction efficiency is significantly improved by slowing down ions in the trap region for their prolonged interaction with ozone. This will facilitate application of high-resolution OzID-MS in lipidomics. Copyright © 2017 John Wiley & Sons, Ltd.

Power module packaging with double sided planar interconnection and heat exchangers

DOEpatents

Liang, Zhenxian; Marlino, Laura D.; Ning, Puqi; Wang, Fei

2015-05-26

A double sided cooled power module package having a single phase leg topology includes two IGBT and two diode semiconductor dies. Each IGBT die is spaced apart from a diode semiconductor die, forming a switch unit. Two switch units are placed in a planar face-up and face-down configuration. A pair of DBC or other insulated metallic substrates is affixed to each side of the planar phase leg semiconductor dies to form a sandwich structure. Attachment layers are disposed on outer surfaces of the substrates and two heat exchangers are affixed to the substrates by rigid bond layers. The heat exchangers, made of copper or aluminum, have passages for carrying coolant. The power package is manufactured in a two-step assembly and heating process where direct bonds are formed for all bond layers by soldering, sintering, solid diffusion bonding or transient liquid diffusion bonding, with a specially designed jig and fixture.

Hydrogen Bond Acceptors and Additional Cationic Charges in Methylene Blue Derivatives: Photophysics and Antimicrobial Efficiency

PubMed Central

Felgenträger, Ariane; Maisch, Tim; Dobler, Daniel; Späth, Andreas

2013-01-01

Photodynamic inactivation of bacteria (PIB) by efficient singlet oxygen photosensitizers might be a beneficial alternative to antibiotics in the struggle against multiresistant bacteria. Phenothiazinium dyes belong to the most prominent classes of such sensitizers due to their intense absorption in the red-light region (λ abs, max ca. 600–680 nm, ε > 50000 L mol−1 cm−1), their low toxicity, and their attachment/penetration abilities. Except simple substituents like alkyl or hydroxyalkyl residues, nearly no modifications of the phenothiaziniums have been pursued at the auxochromic sites. By this, the properties of methylene blue derivatives and their fields of application are limited; it remains unclear if their potential antimicrobial efficacy may be enhanced, also to compete with porphyrins. We prepared a set of six mainly novel methylene blue derivatives with the ability of additional hydrogen bonding and/or additional cationic charges to study the substituents' effect on their activity/toxicity profiles and photophysical properties. Direct detection of singlet oxygen was performed at 1270 nm and the singlet oxygen quantum yields were determined. In suspensions with both, Gram-positive and Gram-negative bacteria, some derivatives were highly active upon illumination to inactivate S. aureus and E. coli up to 7 log10 steps (99.99999%) without inherent toxicities in the nonirradiated state. PMID:23509728

Analysis of bonded joints. [shear stress and stress-strain diagrams

NASA Technical Reports Server (NTRS)

Srinivas, S.

1975-01-01

A refined elastic analysis of bonded joints which accounts for transverse shear deformation and transverse normal stress was developed to obtain the stresses and displacements in the adherends and in the bond. The displacements were expanded in terms of polynomials in the thicknesswise coordinate; the coefficients of these polynomials were functions of the axial coordinate. The stress distribution was obtained in terms of these coefficients by using strain-displacement and stress-strain relations. The governing differential equations were obtained by integrating the equations of equilibrium, and were solved. The boundary conditions (interface or support) were satisfied to complete the analysis. Single-lap, flush, and double-lap joints were analyzed, along with the effects of adhesive properties, plate thicknesses, material properties, and plate taper on maximum peel and shear stresses in the bond. The results obtained by using the thin-beam analysis available in the literature were compared with the results obtained by using the refined analysis. In general, thin-beam analysis yielded reasonably accurate results, but in certain cases the errors were high. Numerical investigations showed that the maximum peel and shear stresses in the bond can be reduced by (1) using a combination of flexible and stiff bonds, (2) using stiffer lap plates, and (3) tapering the plates.

Bonding strategies for MIH-affected enamel and dentin.

PubMed

Krämer, Norbert; Bui Khac, Ngoc-Han Nana; Lücker, Susanne; Stachniss, Vitus; Frankenberger, Roland

2018-02-01

Aim of the present study was to evaluate resin composite adhesion to dental hard tissues affected by molar incisor hypomineralisation (MIH). 94 freshly extracted human molars and incisors (53 suffering MIH) were used. 68 teeth (35 with MIH) were used for μ-TBS tests in enamel and dentin, 26 (18 with MIH) for qualitative evaluation. Specimens were bonded with Clearfil SE Bond, Scotchbond Universal, and OptiBond FL. For MIH affected enamel, additional OptiBond FL groups with NaOCl and NaOCl+Icon were investigated. Beside fractographic analysis, also qualitative evaluations were performed using SEM at different magnifications as well as histological sectioning. Highest μ-TBS values were recorded with dentin specimens (ANOVA, mod. LSD, p<0.05). Results were independent of adhesive and dentin substrate (p>0.05). Pre-test failures did not occur in dentin specimens. Sound enamel specimens exhibited significantly higher μ-TBS values than MIH enamel (p<0.05). The two-step self-etch adhesive (Clearfil SE Bond) and the two-step etch-and-rinse adhesive (Scotchbond Universal) showed the lowest values in affected enamel specimens (p<0.05) with most pre-test failures (p<0.05). OptiBond FL on affected enamel showed better results than Clearfil SE Bond (p<0.05). An additional pre-treatment of affected enamel with NaOCl or NaOCl and Icon did not enhance enamel bonding (p>0.05), however, it caused less pre-test failures (p<0.05). Micromorphological analyses revealed that conventional phosphoric acid etching produces a much less pronounced etching pattern in affected enamel and a porous structure as weak link for the resin-enamel bond was identified. Bonding to porous hypomineralized MIH enamel is the limiting factor in adhesion to MIH teeth. MIH-affected dentin may be bonded conventionally. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Enamel shear bond strength of two orthodontic self-etching bonding systems compared to Transbond™ XT.

PubMed

Hellak, Andreas; Rusdea, Patrick; Schauseil, Michael; Stein, Steffen; Korbmacher-Steiner, Heike Maria

2016-11-01

The aim of this in vitro study was to compare the shear bond strength (SBS) and Adhesive Remnant Index (ARI) scores of two self-etching no-mix adhesives (Prompt L-Pop™ and Scotchbond™) for orthodontic appliances to the commonly used total etch system Transbond XT™ (in combination with phosphoric acid). In all, 60 human premolars were randomly divided into three groups of 20 specimens each. In group 1 (control), brackets were bonded with Transbond™ XT primer. Prompt L-Pop™ (group 2) and Scotchbond™ Universal (group 3) were used in the experimental groups. Lower premolar brackets were bonded by light curing the adhesive. After 24 h of storage, the shear bond strength (SBS) was measured using a Zwicki 1120 testing machine. The adhesive remnant index (ARI) was determined under 10× magnification. The Kruskal-Wallis test was used to statistically compare the SBS and the ARI scores. No significant differences in the SBS between any of the experimental groups were detected (group 1: 15.49 ± 3.28 MPa; group 2: 13.89 ± 4.95 MPa; group 3: 14.35 ± 3.56 MPa; p = 0.489), nor were there any significant differences in the ARI scores (p = 0.368). Using the two self-etching no-mix adhesives (Prompt L-Pop™ and Scotchbond™) for orthodontic appliances does not affect either the SBS or ARI scores in comparison with the commonly used total-etch system Transbond™ XT. In addition, Scotchbond™ Universal supports bonding on all types of surfaces (enamel, metal, composite, and porcelain) with no need for additional primers. It might therefore be helpful for simplifying bonding in orthodontic procedures.

Additional New Cytotoxic Triquinane-Type Sesquiterpenoids Chondrosterins K–M from the Marine Fungus Chondrostereum sp

PubMed Central

Huang, Lei; Lan, Wen-Jian; Deng, Rong; Feng, Gong-Kan; Xu, Qing-Yan; Hu, Zhi-Yu; Zhu, Xiao-Feng; Li, Hou-Jin

2016-01-01

By the method of 1H NMR prescreening and tracing the diagnostic proton signals of the methyl groups, three additional new triquinane-type sesquiterpenoids—chondrosterins K–M (1–3) and the known sesquiterpenoid anhydroarthrosporone (4)—were isolated from the marine fungus Chondrostereum sp. Their structures were elucidated on the basis of MS, 1D, and 2D NMR data. Chondrosterin K is a rare hirsutane sesquiterpenoid, in which a methyl group was migrated from C-2 to C-6 and has a double bond between C-2 and C-3. Compounds 1–3 showed significant cytotoxicities against various cancer cell lines in vitro. PMID:27571085

Halogen-bonding-triggered supramolecular gel formation

NASA Astrophysics Data System (ADS)

Meazza, Lorenzo; Foster, Jonathan A.; Fucke, Katharina; Metrangolo, Pierangelo; Resnati, Giuseppe; Steed, Jonathan W.

2013-01-01

Supramolecular gels are topical soft materials involving the reversible formation of fibrous aggregates using non-covalent interactions. There is significant interest in controlling the properties of such materials by the formation of multicomponent systems, which exhibit non-additive properties emerging from interaction of the components. The use of hydrogen bonding to assemble supramolecular gels in organic solvents is well established. In contrast, the use of halogen bonding to trigger supramolecular gel formation in a two-component gel (‘co-gel’) is essentially unexplored, and forms the basis for this study. Here, we show that halogen bonding between a pyridyl substituent in a bis(pyridyl urea) and 1,4-diiodotetrafluorobenzene brings about gelation, even in polar media such as aqueous methanol and aqueous dimethylsulfoxide. This demonstrates that halogen bonding is sufficiently strong to interfere with competing gel-inhibitory interactions and create a ‘tipping point’ in gel assembly. Using this concept, we have prepared a halogen bond donor bis(urea) gelator that forms co-gels with halogen bond acceptors.

Activation of a Carbon-Oxygen Bond of Benzofuran by Precoordination of Manganese to the Carbocyclic Ring: A Model for Hydrodeoxygenation.

PubMed

Zhang; Watson; Dullaghan; Gorun; Sweigart

1999-08-01

Stable unsaturated heterocycles such as benzofuran are difficult to remove from petroleum by conventional catalytic hydrotreating. However, in a model system, coordination of Mn(CO)(3)(+) to the aromatic ring of benzofuran activates the C-O bond towards insertion of [Pt(PPh(3))(2)] [Eq. (1)]. The insertion is preceded by precoordination to the furan C=C bond; thus, the 2,3-dihydro analogue of 1, which lacks this double bond, does not undergo insertion of the Pt moiety.

Room-temperature wafer bonding of LiNbO3 and SiO2 using a modified surface activated bonding method

NASA Astrophysics Data System (ADS)

Takigawa, Ryo; Higurashi, Eiji; Asano, Tanemasa

2018-06-01

In this paper, we report room-temperature bonding of LiNbO3 (LN) and SiO2/Si for the realization of a LN on insulator (LNOI)/Si hybrid wafer. We investigate the applicability of a modified surface activated bonding (SAB) method for the direct bonding of LN and a thermally grown SiO2 layer. The modified SAB method using ion beam bombardment demonstrates the room-temperature wafer bonding of LN and SiO2. The bonded wafer was successfully cut into 0.5 × 0.5 mm2 dies without interfacial debonding owing to the applied stress during dicing. In addition, the surface energy of the bonded wafer was estimated to be approximately 1.8 J/m2 using the crack opening method. These results indicate that a strong bond strength can be achieved, which may be sufficient for device applications.

Bonding measurement -Strength and fracture mechanics approaches.

PubMed

Anunmana, Chuchai; Wansom, Wiroj

2017-07-26

This study investigated the effect of cross-sectional areas on interfacial fracture toughness and bond strength of bilayered dental ceramics. Zirconia core ceramics were veneered and cut to produce specimens with three different cross-sectional areas. Additionally, monolithic specimens of glass veneer were also prepared. The specimens were tested in tension until fracture at the interface and reported as bond strength. Fracture surfaces were observed, and the apparent interfacial toughness was determined from critical crack size and failure stress. The results showed that cross-sectional area had no effect on the interfacial toughness whereas such factor had a significant effect on interfacial bond strength. The study revealed that cross-sectional area had no effect on the interfacial toughness, but had a significant effect on interfacial bond strength. The interfacial toughness may be a more reliable indicator for interfacial bond quality than interfacial bond strength.

Hydrothermal syntheses, characterizations and crystal structures of a new lead(II) carboxylate-phosphonate with a double layer structure and a new nickel(II) carboxylate-phosphonate containing a hydrogen-bonded 2D layer with intercalation of ethylenediamines

NASA Astrophysics Data System (ADS)

Song, Jun-Ling; Mao, Jiang-Gao; Sun, Yan-Qiong; Zeng, Hui-Yi; Kremer, Reinhard K.; Clearfield, Abraham

2004-03-01

Hydrothermal reactions of N, N-bis(phosphonomethyl)aminoacetic acid (HO 2CCH 2N(CH 2PO 3H 2) 2) with metal(II) salts afforded two new metal carboxylate-phosphonates, namely, Pb 2[O 2CCH 2N(CH 2PO 3)(CH 2PO 3H)]·H 2O ( 1) and {NH 3CH 2CH 2NH 3}{Ni[O 2CCH 2N(CH 2PO 3H) 2](H 2O) 2} 2 ( 2). Among two unique lead(II) ions in the asymmetric unit of complex 1, one is five coordinated by five phosphonate oxygen atoms from 5 ligands, whereas the other one is five-coordinated by a tridentate chelating ligand (1 N and 2 phosphonate O atoms) and two phosphonate oxygen atoms from two other ligands. The carboxylate group of the ligand remains non-coordinated. The bridging of above two types of lead(II) ions through phosphonate groups resulted in a <002> double layer with the carboxylate group of the ligand as a pendant group. These double layers are further interlinked via hydrogen bonds between the carboxylate groups into a 3D network. The nickel(II) ion in complex 2 is octahedrally coordinated by a tetradentate chelating ligand (two phosphonate oxygen atoms, one nitrogen and one carboxylate oxygen atoms) and two aqua ligands. These {Ni[O 2CCH 2N(CH 2PO 3H) 2][H 2O] 2} - anions are further interlinked via hydrogen bonds between non-coordinated phosphonate oxygen atoms to form a <800> hydrogen bonded 2D layer. The 2H-protonated ethylenediamine cations are intercalated between two layers, forming hydrogen bonds with the non-coordinated carboxylate oxygen atoms. Results of magnetic measurements for complex 2 indicate that there is weak Curie-Weiss behavior with θ=-4.4 K indicating predominant antiferromagnetic interaction between the Ni(II) ions. Indication for magnetic low-dimension magnetism could not be detected.

A remarkable enhancement of selectivity towards versatile analytes by a strategically integrated H-bonding site containing phase.

PubMed

Mallik, Abul K; Qiu, Hongdeng; Kuwahara, Yutaka; Takafuji, Makoto; Ihara, Hirotaka

2015-09-28

A double β-alanylated L-glutamide-derived organic phase has been newly designed and synthesized in such a way that integrated H-bonding (interaction) sites make it very suitable for the separation of versatile analytes, including shape-constrained isomers, and nonpolar, polar and basic compounds. The β-alanine residues introduced into two long-chain alkyl group moieties provide ordered polar groups through H-bonding among the amide groups.

Locally measuring the adhesion of InP directly bonded on sub-100 nm patterned Si.

PubMed

Pantzas, K; Le Bourhis, E; Patriarche, G; Troadec, D; Beaudoin, G; Itawi, A; Sagnes, I; Talneau, A

2016-03-18

A nano-scale analogue to the double cantilever experiment that combines instrumented nano-indentation and atomic force microscopy is used to precisely and locally measure the adhesion of InP bonded on sub-100 nm patterned Si using oxide-free or oxide-mediated bonding. Surface-bonding energies of 0.548 and 0.628 J m(-2), respectively, are reported. These energies correspond in turn to 51% and 57% of the surface bonding energy measured in unpatterned regions on the same samples, i.e. the proportion of unetched Si surface in the patterned areas. The results show that bonding on patterned surfaces can be as robust as on unpatterned surfaces, provided care is taken with the post-patterning surface preparation process and, therefore, open the path towards innovative designs that include patterns embedded in the Si guiding layer of hybrid III-V/Si photonic integrated circuits.

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

PubMed

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

2017-12-22

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

Energetics of short hydrogen bonds in photoactive yellow protein.

PubMed

Saito, Keisuke; Ishikita, Hiroshi

2012-01-03

Recent neutron diffraction studies of photoactive yellow protein (PYP) proposed that the H bond between protonated Glu46 and the chromophore [ionized p-coumaric acid (pCA)] was a low-barrier H bond (LBHB). Using the atomic coordinates of the high-resolution crystal structure, we analyzed the energetics of the short H bond by two independent methods: electrostatic pK(a) calculations and a quantum mechanical/molecular mechanical (QM/MM) approach. (i) In the QM/MM optimized geometry, we reproduced the two short H-bond distances of the crystal structure: Tyr42-pCA (2.50 Å) and Glu46-pCA (2.57 Å). However, the H atoms obviously belonged to the Tyr or Glu moieties, and were not near the midpoint of the donor and acceptor atoms. (ii) The potential-energy curves of the two H bonds resembled those of standard asymmetric double-well potentials, which differ from those of LBHB. (iii) The calculated pK(a) values for Glu46 and pCA were 8.6 and 5.4, respectively. The pK(a) difference was unlikely to satisfy the prerequisite for LBHB. (iv) The LBHB in PYP was originally proposed to stabilize the ionized pCA because deprotonated Arg52 cannot stabilize it. However, the calculated pK(a) of Arg52 and QM/MM optimized geometry suggested that Arg52 was protonated on the protein surface. The short H bond between Glu46 and ionized pCA in the PYP ground state could be simply explained by electrostatic stabilization without invoking LBHB.

Influence of Bond Coat on HVOF-Sprayed Gradient Cermet Coating on Copper Alloy

NASA Astrophysics Data System (ADS)

Ke, Peng; Cai, Fei; Chen, Wanglin; Wang, Shuoyu; Ni, Zhenhang; Hu, Xiaohong; Li, Mingxi; Zhu, Guanghong; Zhang, Shihong

2017-06-01

Coatings are required on mold copper plates to prolong their service life through enhanced hardness, wear resistance, and oxidation resistance. In the present study, NiCr-30 wt.%Cr3C2 ceramic-metallic (cermet) layers were deposited by high velocity oxy-fuel (HVOF) spraying on different designed bond layers, including electroplated Ni, HVOF-sprayed NiCr, and double-decker Ni-NiCr. Annealing was also conducted on the gradient coating (GC) with NiCr bond layer to improve the wear resistance and adhesion strength. Coating microstructure was investigated by scanning electron microscopy and x-ray diffraction analysis. Mechanical properties including microhardness, wear resistance, and adhesion strength of the different coatings were evaluated systematically. The results show that the types of metallic bond layer and annealing process had a significant impact on the mechanical properties of the GCs. The GCs with electroplated Ni bond layer exhibited the highest adhesion strength (about 70 MPa). However, the GC with HVOF-sprayed NiCr bond layer exhibited better wear resistance. The wear resistance and adhesion strength of the coating with NiCr metallic bond layer were enhanced after annealing.

Solid-Liquid Interdiffusion Bonding of Silicon Carbide to Steel for High Temperature MEMS Sensor Packaging and Bonding

NASA Astrophysics Data System (ADS)

Chan, Matthew Wei-Jen

Complex engineering systems ranging from automobile engines to geothermal wells require specialized sensors to monitor conditions such as pressure, acceleration and temperature in order to improve efficiency and monitor component lifetime in what may be high temperature, corrosive, harsh environments. Microelectromechanical systems (MEMS) have demonstrated their ability to precisely and accurately take measurements under such conditions. The systems being monitored are typically made from metals, such as steel, while the MEMS sensors used for monitoring are commonly fabricated from silicon, silicon carbide and aluminum nitride, and so there is a sizable thermal expansion mismatch between the two. For these engineering applications the direct bonding of MEMS sensors to the components being monitored is often required. This introduces several challenges, namely the development of a bond that is capable of surviving high temperature harsh environments while mitigating the thermally induced strains produced during bonding. This project investigates the development of a robust packaging and bonding process, using the gold-tin metal system and the solid-liquid interdiffusion (SLID) bonding process, to join silicon carbide substrates directly to type-316 stainless steel. The SLID process enables bonding at lower temperatures while producing a bond capable of surviving higher temperatures. Finite element analysis was performed to model the thermally induced strains generated in the bond and to understand the optimal way to design the bond. The cross-sectional composition of the bonds has been analyzed and the bond strength has been investigated using die shear testing. The effects of high temperature aging on the bond's strength and the metallurgy of the bond were studied. Additionally, loading of the bond was performed at temperatures over 415 °C, more than 100 °C, above the temperature used for bonding, with full survival of the bond, thus demonstrating the benefit of

Identification of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid in Pseudomonas sp. strain E-3.

PubMed

Okuyama, H; Enari, D; Shibahara, A; Yamamoto, K; Morita, N

1996-06-01

A cell-free extract of Pseudomonas sp. strain E-3 catalyzed the conversion of 9-cis-hexadecenoic acid [16:1(9c)] to 9-trans-hexadecenoic acid [16:1(9t)] in the free acid form and when 16:1(9c) was esterified to phosphatidylethanolamine (PE). The cytosolic fraction catalyzed the isomerizations of free 16:1(9c) by itself and of 16:1(9c) esterified to PE in the presence of the membrane fraction. Tracer experiments using [2,2-2H2]16:1(9c) demonstrated that the isomerization of free 16:1(9c) occurred independently of the isomerization of 16:1(9c) esterified to PE, indicating that this bacterium has two types of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid.

A high level Ab initio study of the anionic hydrogen-bonded complexes FH-CN-, FH-NC-, H2O-CN- and H2O-NC-

NASA Technical Reports Server (NTRS)

Lee, Timothy J.

1989-01-01

HF, H2O, CN- and their hydrogen-bonded complexes were studied using state-of-the-art ab initio quantum mechanical methods. A large Gaussian one particle basis set consisting of triple zeta plus double polarization plus diffuse s and p functions (TZ2P + diffuse) was used. The theoretical methods employed include self consistent field, second order Moller-Plesset perturbation theory, singles and doubles configuration interaction theory and the singles and doubles coupled cluster approach. The FH-CN- and FH-NC- and H2O-CN-, H2O-NC- pairs of complexes are found to be essentially isoenergetic. The first pair of complexes are predicted to be bound by approx. 24 kcal/mole and the latter pair bound by approximately 15 kcal/mole. The ab initio binding energies are in good agreement with the experimental values. The two being shorter than the analogous C-N hydrogen bond. The infrared (IR) spectra of the two pairs of complexes are also very similar, though a severe perturbation of the potential energy surface by proton exchange means that the accurate prediction of the band center of the most intense IR mode requires a high level of electronic structure theory as well as a complete treatment of anharmonic effects. The bonding of anionic hydrogen-bonded complexes is discussed and contrasted with that of neutral hydrogen-bonded complexes.

σ-Hole Bond vs π-Hole Bond: A Comparison Based on Halogen Bond.

PubMed

Wang, Hui; Wang, Weizhou; Jin, Wei Jun

2016-05-11

The σ-hole and π-hole are the regions with positive surface electrostatic potential on the molecule entity; the former specifically refers to the positive region of a molecular entity along extension of the Y-Ge/P/Se/X covalent σ-bond (Y = electron-rich group; Ge/P/Se/X = Groups IV-VII), while the latter refers to the positive region in the direction perpendicular to the σ-framework of the molecular entity. The directional noncovalent interactions between the σ-hole or π-hole and the negative or electron-rich sites are named σ-hole bond or π-hole bond, respectively. The contributions from electrostatic, charge transfer, and other terms or Coulombic interaction to the σ-hole bond and π-hole bond were reviewed first followed by a brief discussion on the interplay between the σ-hole bond and the π-hole bond as well as application of the two types of noncovalent interactions in the field of anion recognition. It is expected that this review could stimulate further development of the σ-hole bond and π-hole bond in theoretical exploration and practical application in the future.

Highly Stable Double-Stranded DNA Containing Sequential Silver(I)-Mediated 7-Deazaadenine/Thymine Watson-Crick Base Pairs.

PubMed

Santamaría-Díaz, Noelia; Méndez-Arriaga, José M; Salas, Juan M; Galindo, Miguel A

2016-05-17

The oligonucleotide d(TX)9 , which consists of an octadecamer sequence with alternating non-canonical 7-deazaadenine (X) and canonical thymine (T) as the nucleobases, was synthesized and shown to hybridize into double-stranded DNA through the formation of hydrogen-bonded Watson-Crick base pairs. dsDNA with metal-mediated base pairs was then obtained by selectively replacing W-C hydrogen bonds by coordination bonds to central silver(I) ions. The oligonucleotide I adopts a duplex structure in the absence of Ag(+) ions, and its stability is significantly enhanced in the presence of Ag(+) ions while its double-helix structure is retained. Temperature-dependent UV spectroscopy, circular dichroism spectroscopy, and ESI mass spectrometry were used to confirm the selective formation of the silver(I)-mediated base pairs. This strategy could become useful for preparing stable metallo-DNA-based nanostructures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4‧-dimethylaminoflavonol in ethanol solvent

NASA Astrophysics Data System (ADS)

Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

2015-02-01

Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4‧-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule.

Progress in cold roll bonding of metals

PubMed Central

Li, Long; Nagai, Kotobu; Yin, Fuxing

2008-01-01

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described. PMID:27877949

Enhanced rigid-bond restraints

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

Thorn, Andrea; Dittrich, Birger; Sheldrick, George M., E-mail: gsheldr@shelx.uni-ac.gwdg.de

2012-07-01

An extension is proposed to the rigid-bond description of atomic thermal motion in crystals. The rigid-bond model [Hirshfeld (1976 ▶). Acta Cryst. A32, 239–244] states that the mean-square displacements of two atoms are equal in the direction of the bond joining them. This criterion is widely used for verification (as intended by Hirshfeld) and also as a restraint in structure refinement as suggested by Rollett [Crystallographic Computing (1970 ▶), edited by F. R. Ahmed et al., pp. 167–181. Copenhagen: Munksgaard]. By reformulating this condition, so that the relative motion of the two atoms is required to be perpendicular to themore » bond, the number of restraints that can be applied per anisotropic atom is increased from about one to about three. Application of this condition to 1,3-distances in addition to the 1,2-distances means that on average just over six restraints can be applied to the six anisotropic displacement parameters of each atom. This concept is tested against very high resolution data of a small peptide and employed as a restraint for protein refinement at more modest resolution (e.g. 1.7 Å)« less

Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

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

Guan, Zhibin; Lu, Yixuan

A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact withmore » a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.« less

Hydrogen bond and halogen bond inside the carbon nanotube

NASA Astrophysics Data System (ADS)

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

2011-02-01

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.

The role of intra-domain disulfide bonds in heat-induced irreversible denaturation of camelid single domain VHH antibodies

PubMed Central

Akazawa-Ogawa, Yoko; Uegaki, Koichi; Hagihara, Yoshihisa

2016-01-01

Camelid-derived single domain VHH antibodies are highly heat resistant, and the mechanism of heat-induced VHH denaturation predominantly relies on the chemical modification of amino acids. Although chemical modification of disulfide bonds has been recognized as a cause for heat-induced denaturation of many proteins, there have been no mutagenesis studies, in which the number of disulfide bonds was controlled. In this article, we examined a series of mutants of two different VHHs with single, double or no disulfide bonds, and scrutinized the effects of these disulfide bond modifications on VHH denaturation. With the exception of one mutant, the heat resistance of VHHs decreased when the number of disulfide bonds increased. The effect of disulfide bonds on heat denaturation was more striking if the VHH had a second disulfide bond, suggesting that the contribution of disulfide shuffling is significant in proteins with multiple disulfide bonds. Furthermore, our results directly indicate that removal of a disulfide bond can indeed increase the heat resistance of a protein, irrespective of the negative impact on equilibrium thermodynamic stability. PMID:26289739

Temporal heating profile influence on the immediate bond strength following laser tissue soldering.

PubMed

Rabi, Yaron; Katzir, Abraham

2010-07-01

Bonding of tissues by laser heating is considered as a future alternative to sutures and staples. Increasing the post-operative bond strength remains a challenging issue for laser tissue bonding, especially in organs that have to sustain considerable tension or pressure. In this study, we investigated the influence of different temporal heating profiles on the strength of soldered incisions. The thermal damage following each heating procedure was quantified, in order to assess the effect of each heating profile on the thermal damage. Incisions in porcine bowel tissue strips (1 cmx4 cm) were soldered, using a 44% liquid albumin mixed with indocyanine green and a temperature controlled laser (830 nm) tissue bonding system. Heating was done either with a linear or a step temporal heating profile. The incisions were bonded by soldering at three points, separated by 2 mm. Set-point temperatures of T(set) = 60, 70, 80, 90, 100, 110, 150 degrees C and dwell times of t(d) = 10, 20, 30, 40 seconds were investigated. The bond strength was measured immediately following each soldering by applying a gradually increased tension on the tissue edges until the bond break. Bonds formed by linear heating were stronger than the ones formed by step heating: at T(set) = 80 degrees C the bonds were 40% stronger and at T(set) = 90 degrees C the bonds strength was nearly doubled. The bond strength difference between the heating methods was larger as T(set) increased. Linear heating produced stronger bonds than step heating. The difference in the bond strength was more pronounced at high set-point temperatures and short dwell times. The bond strength could be increased with either higher set-point temperature or a longer dwell time.

In Vitro Evaluation of Shear Bond Strength of Nanocomposites to Dentin

PubMed Central

Vellanki, Vinay Kumar; Shetty, Vikram K; Kushwah, Sudhanshu; Goyal, Geeta; Chandra, S.M. Sharath

2015-01-01

Aims: To compare the shear bond strength of nanocomposites to dentin using three different types of adhesive systems; and to test few specimens under Scanning Electron Microscope (SEM) for analysing whether the bond failure is adhesive or cohesive. Materials and Methods: Sixty human premolar teeth were selected and were randomly grouped, with 20 specimens in each group: group 1 - fluoride releasing dentin bonding agent; group 2 - antibacterial containing dentin bonding agent; and group 3 - one step conventional self etch adhesive. Each group was treated with its respective bonding agents, composite resin build up was done, and shear bond strengths were tested using Instron Universal testing machine. Few of the specimens were tested under SEM. Results: The results were statistically analysed using One-way ANOVA and paired t-test. It was observed that group 3 has the highest shear bond strength followed by group 2, and then group 1. Adhesive failures and mixed failures were most frequent types of failures as seen under SEM. Conclusion: Addition of antimicrobial agent decreases the bond strength of dentin bonding agent and addition of fluoride further decreases the bond strength. From SEM results it can be concluded that the zone of failure could not be defined and also that the failure mode was independent of the dentin bonding agent used. PMID:25738077

A novel addition polyimide adhesive

NASA Technical Reports Server (NTRS)

St.clair, T. L.; Progar, D. J.

1981-01-01

An addition polyimide adhesive, LARC 13, was developed which shows promise for bonding both titanium and composites for applications which require service temperatures in excess of 533 K. The LARC 13 is based on an oligomeric bis nadimide containing a meta linked aromatic diamine. The adhesive melts prior to polymerization due to its oligomeric nature, thereby allowing it to be processed at 344 kPa or less. Therefore, LARC 13 is ideal for the bonding of honeycomb sandwich structures. After melting, the resin thermosets during the cure of the nadic endcaps to a highly crosslinked system. Few volatiles are evolved, thus allowing large enclosed structures to be bonded. Preparation of the adhesive as well as bonding, aging, and testing of lap shear and honeycomb samples are discussed.

Enhanced photocatalytic degradation of Amaranth dye on mesoporous anatase TiO2: evidence of C-N, N[double bond, length as m-dash]N bond cleavage and identification of new intermediates.

PubMed

Naik, Amarja P; Salkar, Akshay V; Majik, Mahesh S; Morajkar, Pranay P

2017-07-01

The photocatalytic degradation mechanism of Amaranth, a recalcitrant carcinogenic azo dye, was investigated using mesoporous anatase TiO 2 under sunlight. Mesoporous anatase TiO 2 of a high photocatalytic activity has been synthesized using a sol-gel method and its photocatalytic activity for the degradation of Amaranth dye has been evaluated with respect to Degussa P25. The effect of bi-dentate complexing agents like oxalic acid, ethylene glycol and urea on the surface properties of TiO 2 catalyst has been investigated using TG-DTA, FTIR, HR-TEM, SAED, PXRD, EDS, UV-DRS, PL, BET N 2 adsorption-desorption isotherm studies and BJH analysis. The influence of catalyst properties such as the mesoporous network, pore volume and surface area on the kinetics of degradation of Amaranth as a function of irradiation time under natural sunlight has been monitored using UV-Vis spectroscopy. The highest rate constant value of 0.069 min -1 was obtained for the photocatalytic degradation of Amaranth using TiO 2 synthesized via a urea assisted sol-gel synthesis method. The effect of the reaction conditions such as pH, TiO 2 concentration and Amaranth concentration on the photodegradation rate has been investigated. The enhanced photocatalytic activity of synthesized TiO 2 in comparison with P25 is attributed to the mesoporous nature of the catalyst leading to increased pore diameter, pore volume, surface area and enhanced charge carrier separation efficiency. New intermediates of photocatalytic degradation of Amaranth, namely, sodium-3-hydroxynaphthalene-2,7-disulphonate, 3-hydroxynaphthalene, sodium-4-aminonaphthalenesulphonate and sodium-4-aminobenzenesulphonate have been identified using LC-ESI-MS for the very first time, providing direct evidence for simultaneous bond cleavage pathways (-C-N-) and (-N[double bond, length as m-dash]N-). A new plausible mechanism of TiO 2 catalysed photodegradation of Amaranth along with the comparison of its toxicity to that of its degradation

Atom and Bond Fukui Functions and Matrices: A Hirshfeld-I Atoms-in-Molecule Approach.

PubMed

Oña, Ofelia B; De Clercq, Olivier; Alcoba, Diego R; Torre, Alicia; Lain, Luis; Van Neck, Dimitri; Bultinck, Patrick

2016-09-19

The Fukui function is often used in its atom-condensed form by isolating it from the molecular Fukui function using a chosen weight function for the atom in the molecule. Recently, Fukui functions and matrices for both atoms and bonds separately were introduced for semiempirical and ab initio levels of theory using Hückel and Mulliken atoms-in-molecule models. In this work, a double partitioning method of the Fukui matrix is proposed within the Hirshfeld-I atoms-in-molecule framework. Diagonalizing the resulting atomic and bond matrices gives eigenvalues and eigenvectors (Fukui orbitals) describing the reactivity of atoms and bonds. The Fukui function is the diagonal element of the Fukui matrix and may be resolved in atom and bond contributions. The extra information contained in the atom and bond resolution of the Fukui matrices and functions is highlighted. The effect of the choice of weight function arising from the Hirshfeld-I approach to obtain atom- and bond-condensed Fukui functions is studied. A comparison of the results with those generated by using the Mulliken atoms-in-molecule approach shows low correlation between the two partitioning schemes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bonded exciplex formation: electronic and stereoelectronic effects.

PubMed

Wang, Yingsheng; Haze, Olesya; Dinnocenzo, Joseph P; Farid, Samir; Farid, Ramy S; Gould, Ian R

2008-12-18

As recently proposed, the singlet-excited states of several cyanoaromatics react with pyridine via bonded-exciplex formation, a novel concept in photochemical charge transfer reactions. Presented here are electronic and steric effects on the quenching rate constants, which provide valuable support for the model. Additionally, excited-state quenching in poly(vinylpyridine) is strongly inhibited both relative to that in neat pyridine and also to conventional exciplex formation in polymers, consistent with a restrictive orientational requirement for the formation of bonded exciplexes. Examples of competing reactions to form both conventional and bonded exciplexes are presented, which illustrate the delicate balance between these two processes when their reaction energetics are similar. Experimental and computational evidence is provided for the formation of a bonded exciplex in the reaction of the singlet excited state of 2,6,9,10-tetracyanoanthracene (TCA) with an oxygen-substituted donor, dioxane, thus expanding the scope of bonded exciplexes.

Robust Bonding of Tough Double Network Hydrogel to Bone

NASA Astrophysics Data System (ADS)

Nonoyama, Takayuki; Wada, Susumu; Kiyama, Ryuji; Kitamura, Nobuto; Kurokawa, Takayuki; Nakajima, Tasuku; Yasuda, Kazunori; Gong, Jian Ping

Tough Double Network (DN) hydrogels are one of candidates as next-generation artificial cartilage from the viewpoints of low friction, water storage capability and toughness. For practical use, the hydrogel must be strongly fixed at the joint. However, strong fixation of such hydrogel to other materials (tissues) has not been achieved yet because the surface property of hydrogel is almost equal to water due to its high water content. Therefore, robust adhesion for fixation and low friction for lithe motion are trade-off relation. Here, we report robust fixation of hydroxyapatite (HAp) mineralized DN hydrogel to the bone without any toxicity. HAp is main inorganic component of bone tissues and has osteoconductive capability. After 4 weeks implantation of HAp/DN gel into rabbit femoral groove, The robust fixation between bone and HAp/DN gel, more than strength of gel matrix, was achieved. The methodology is universal for new biomaterials, which should be fixed on bone, such as ligament and tendon systems.

Interlayer interaction in Ca-Fe layered double hydroxides intercalated with nitrate and chloride species

NASA Astrophysics Data System (ADS)

Al-Jaberi, Muayad; Naille, Sébastien; Dossot, Manuel; Ruby, Christian

2015-12-01

Ca-Fe layered double hydroxide (LDH) intercalated with chloride and nitrate ions has been synthesized with varying CaII:FeIII molar ratios of the initial solution. Phase pure LDH is observed with CaII:FeIII molar ratio of 2:1 and a mixture of LDH and Ca(OH)2 is formed for CaII:FeIII molar ratios higher than 2:1. Vibrational spectroscopies (Raman and IR) were used successfully to understand the interaction between the cationic and anionic sheets. The Raman bands positions at lower frequencies (150-600 cm-1) are intimately correlated to the nature of the divalent and trivalent ions but also to the nature of the anions. Indeed, a shift of ˜9 cm-1 is observed for the Raman double bands situated in the 300-400 cm-1 region when comparing Raman spectra of CaFe-LDH containing either nitrate or chloride ions. Two types of nitrate environments are observed namely free (non-hydrogen bonded) nitrate and nitrate hydrogen bonded to the interlayer water or to the 'brucite-like' hydroxyl surface. Multiple types of water structure are observed and would result from different hydrogen bond structures. Water bending modes are identified at 1645 cm-1 greater than the one observed for LDH intercalated with chloride anions (1618 cm-1), indicating that the water is strongly hydrogen bonded to the nitrate anions.

Laser Surface Preparation of Epoxy Composites for Secondary Bonding: Optimization of Ablation Depth

NASA Technical Reports Server (NTRS)

Palmieri, Frank L.; Hopkins, John; Wohl, Christopher J.; Lin, Yi; Connell, John W.; Belcher, Marcus A.; Blohowiak, Kay Y.

2015-01-01

Surface preparation has been identified as one of the most critical aspects of attaining predictable and reliable adhesive bonds. Energetic processes such as laser ablation or plasma treatment are amenable to automation and are easily monitored and adjusted for controlled surface preparation. A laser ablation process was developed to accurately remove a targeted depth of resin, approximately 0.1 to 20 micrometers, from a carbon fiber reinforced epoxy composite surface while simultaneously changing surface chemistry and creating micro-roughness. This work demonstrates the application of this process to prepare composite surfaces for bonding without exposing or damaging fibers on the surface. Composite panels were prepared in an autoclave and had a resin layer approximately 10 micrometers thick above the fiber reinforcement. These composite panels were laser surface treated using several conditions, fabricated into bonded panels and hygrothermally aged. Bond performance of aged, experimental specimens was compared with grit blast surface treated specimens using a modified double cantilever beam test that enabled accelerated saturation of the specimen with water. Comparison of bonded specimens will be used to determine how ablation depth may affect average fracture energies and failure modes.

Characterization of mode 1 and mixed-mode failure of adhesive bonds between composite adherends

NASA Technical Reports Server (NTRS)

Mall, S.; Johnson, W. S.

1985-01-01

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

De novo design of protein homo-oligomers with modular hydrogen bond network-mediated specificity

PubMed Central

Boyken, Scott E.; Chen, Zibo; Groves, Benjamin; Langan, Robert A.; Oberdorfer, Gustav; Ford, Alex; Gilmore, Jason; Xu, Chunfu; DiMaio, Frank; Pereira, Jose Henrique; Sankaran, Banumathi; Seelig, Georg; Zwart, Peter H.; Baker, David

2017-01-01

In nature, structural specificity in DNA and proteins is encoded quite differently: in DNA, specificity arises from modular hydrogen bonds in the core of the double helix, whereas in proteins, specificity arises largely from buried hydrophobic packing complemented by irregular peripheral polar interactions. Here we describe a general approach for designing a wide range of protein homo-oligomers with specificity determined by modular arrays of central hydrogen bond networks. We use the approach to design dimers, trimers, and tetramers consisting of two concentric rings of helices, including previously not seen triangular, square, and supercoiled topologies. X-ray crystallography confirms that the structures overall, and the hydrogen bond networks in particular, are nearly identical to the design models, and the networks confer interaction specificity in vivo. The ability to design extensive hydrogen bond networks with atomic accuracy is a milestone for protein design and enables the programming of protein interaction specificity for a broad range of synthetic biology applications. PMID:27151862

Directed-Backbone Dissociation Following Bond-Specific Carbon-Sulfur UVPD at 213 nm

NASA Astrophysics Data System (ADS)

Talbert, Lance E.; Julian, Ryan R.

2018-04-01

Ultraviolet photodissociation or UVPD is an increasingly popular option for tandem-mass spectrometry experiments. UVPD can be carried out at many wavelengths, and it is important to understand how the results will be impacted by this choice. Here, we explore the utility of 213 nm photons for initiating bond-selective fragmentation. It is found that bonds previously determined to be labile at 266 nm, including carbon-iodine and sulfur-sulfur bonds, can also be cleaved with high selectivity at 213 nm. In addition, many carbon-sulfur bonds that are not subject to direct dissociation at 266 nm can be selectively fragmented at 213 nm. This capability can be used to site-specifically create alaninyl radicals that direct backbone dissociation at the radical site, creating diagnostic d-ions. Furthermore, the additional carbon-sulfur bond fragmentation capability leads to signature triplets for fragmentation of disulfide bonds. Absorption of amide bonds can enhance dissociation of nearby labile carbon-sulfur bonds and can be used for stochastic backbone fragmentation typical of UVPD experiments at shorter wavelengths. Several potential applications of the bond-selective fragmentation chemistry observed at 213 nm are discussed. [Figure not available: see fulltext.

48 CFR 1228.106-1 - Bonds and bond-related forms.

Code of Federal Regulations, 2010 CFR

2010-10-01

... GENERAL CONTRACTING REQUIREMENTS BONDS AND INSURANCE Bonds and Other Financial Protections 1228.106-1 Bonds and bond-related forms. (b) Standard Form (SF) 25, Performance Bond, prescribed at (FAR) 48 CFR 28...) shall not be used by contractors when a performance bond is required. ...

Evaluation to the effect of B2O3-La2O3-SrO-Na2O-Al2O3 bonding agent on Ti6Al4V-porcelain bonding.

PubMed

Zhao, C Q; Wu, S Q; Lu, Y J; Gan, Y L; Guo, S; Lin, J J; Huang, T T; Lin, J X

2016-10-01

Low-fusing bonding agents have been widely applied in Ti-ceramics restorations. As an important category, borate bonding agents have great potentials in increasing Ti-porcelain bonding. The purpose of this study is to evaluate the effect of borate bonding agent with addition of Na2O and Al2O3 on Ti6Al4V-porcelain bonding. The thermal properties of borate bonding agent, such as glass transition temperature (Tg) and crystallization peak temperature (Tp), were investigated to establish the sintering process. And the coefficient of thermal expansion (CTE) was to evaluate the matching effect of porcelain to Ti6Al4V. The bond strength was analyzed by the three point bending test. The microscopic morphology of the borate bonding agent surface after sintering, the interface of Ti-borate bonding agent-porcelain, and the fracture mode after porcelains fracture, were studied to assess the influence of borate bonding agent on Ti6Al4V-ceramics. With the addition of Na2O and Al2O3, the porcelain residues were observed increased indication on the Ti6Al4V surface after porcelain fracture and the bond strength was acquired the maximum (49.45MPa) in the bonding agent composition of 75.70B2O3-5.92La2O3-11.84SrO-4.67Na2O-1.87Al2O3. Those results suggest that borate bonding agent is an effective way to improve the Ti6Al4V-ceramics bond strength. And the addition of Na2O and Al2O3 strengthen this effect. Copyright © 2016 Elsevier Ltd. All rights reserved.

Bonding in Some Zintl Phases: A Study by Tin-119 Mössbauer Spectroscopy

NASA Astrophysics Data System (ADS)

Asbrand, M.; Berry, F. J.; Eisenmann, B.; Kniep, R.; Smart, L. E.; Thied, R. C.

1995-09-01

The 119Sn Mössbauer parameters for a range of Zintl phase compounds are reported. The compounds containing tetrahedrally coordinated tin of composition M5SnX3 (M = Na, K; X = P, As, Sb) have chemical isomer shifts close to that of grey-tin and can be considered to be covalently bonded species. The layer structures of composition KSnX (X = As, Sb) and double-layer compounds M Sn2X2 (M = Na, Sr; X = As, Sb) have tin in a distorted octahedral environment. The chemical isomer shifts are closer to that of white-tin and can be interpreted in terms of metallic bonding.

Mechanism of Me–Re Bond Addition to Platinum(II) and Dioxygen Activation by the Resulting Pt–Re Bimetallic Center

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

Pichaandi, Kothanda Rama; Kabalan, Lara; Amini, Hashem

Unusual cis-oxidative addition of methyltrioxorhenium (MTO) to [PtMe 2(bpy)], (bpy = 2,2'-bipyridine) (1) is described. Addition of MTO to 1 first gives the Lewis acid–base adduct [(bpy)Me 2Pt–Re(Me)(O) 3] (2) and subsequently affords the oxidative addition product [(bpy)Me 3PtReO 3] (3). All complexes 1, MTO, 2, and 3 are in equilibrium in solution. The structure of 2 was confirmed by X-ray crystallography, and its dissociation constant in solution is 0.87 M. The structure of 3 was confirmed by extended X-ray absorption fine structure and X-ray absorption near-edge structure in tandem with one- and two-dimensional NMR spectroscopy augmented by deuterium andmore » 13C isotope-labeling studies. Kinetics of formation of compound 3 revealed saturation kinetics dependence on [MTO] and first-order in [Pt], complying with prior equilibrium formation of 2 with oxidative addition of Me–Re being the rate-determining step. Exposure of 3 to molecular oxygen or air resulted in the insertion of an oxygen atom into the platinum–rhenium bond forming [(bpy)Me 3PtOReO 3] (4) as final product. In conclusion, density functional theory analysis on oxygen insertion pathways leading to complex 4, merited on the basis of Russell oxidation pathway, revealed the involvement of rhenium peroxo species.'« less

Pauling bond strength, bond length and electron density distribution

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

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

2014-01-18

A power law regression equation, = 1.46(/r)-0.19, connecting the average experimental bond lengths, , with the average accumulation of the electron density at the bond critical point, , between bonded metal M and oxygen atoms, determined at ambient conditions for oxide crystals, where r is the row number of the M atom, is similar to the regression equation R(M-O) = 1.39(ρ(rc)/r)-0.21 determined for three perovskite crystals for pressures as high as 80 GPa. The two equations are also comparable with those, = 1.43( /r)-0.21, determined for a large number of oxide crystals at ambient conditions and = 1.39(/r)-0.22, determined formore » geometry optimized hydroxyacid molecules, that connect the bond lengths to the average Pauling electrostatic bond strength, , for the M-O bonded interactions. On the basis of the correspondence between the two sets of equations connecting ρ(rc) and the Pauling bond strength s with bond length, it appears that Pauling’s simple definition of bond strength closely mimics the accumulation of the electron density between bonded pairs of atoms. The similarity of the expressions for the crystals and molecules is compelling evidence that the M-O bonded interactions for the crystals and molecules 2 containing the same bonded interactions are comparable. Similar expressions, connecting bond lengths and bond strength, have also been found to hold for fluoride, nitride and sulfide molecules and crystals. The Brown-Shannon bond valence, σ, power law expression σ = [R1/(R(M-O)]N that has found wide use in crystal chemistry, is shown to be connected to a more universal expression determined for oxides and the perovskites, = r[(1.41)/]4.76, demonstrating that the bond valence for a bonded interaction is likewise closely connected to the accumulation of the electron density between the bonded atoms. Unlike the Brown-Shannon expression, it is universal in that it holds for the M-O bonded interactions for a relatively wide range of M atoms of the

Push-out bond strengths of two fiber post types bonded with different dentin bonding agents.

PubMed

Topcu, Fulya Toksoy; Erdemir, Ugur; Sahinkesen, Gunes; Mumcu, Emre; Yildiz, Esra; Uslan, Ibrahim

2010-05-01

The aim of this study was to evaluate the regional push-out bond strengths for two fiber-reinforced post types using three different dentin bonding agents. Sixty single-rooted extracted human first premolar teeth were sectioned below the cemento-enamel junction, and the roots were endodontically treated. Following standardized post space preparations, the roots were divided into two fiber-post groups (Glassix and Carbopost), and further divided into three subgroups of 10 specimens each for the bonding systems self-etching dentin bonding agents (Clearfil SE Bond and Optibond all-in-one), and total-etching dentin bonding agent (XP Bond). A dual-cure resin luting cement (Maxcem) was then placed in the post spaces and posts were then seated into the root canals polymerized through the cervical portion. The roots were then cut into 3-mm thick sections. Push-out tests were performed at a crosshead speed of 0.5 mm/min. The data were analyzed with multivariate ANOVA (alpha = 0.05). The morphology of interface between different dentin bonding agents from the cervical sections were analyzed with SEM. Glass fiber-reinforced posts demonstrated significantly higher push-out bond strengths than carbon fiber-reinforced posts (p < 0.001). Bond strength values decreased significantly from the cervical to the apical root canal regions (p < 0.001). Self-etching dentin adhesive Clearfil SE Bond and total-etching dentin adhesive XP Bond demonstrated similar bond strengths values and this was significantly higher compared with the Optibond all-in-one in cervical root canal region. In conclusion, in all root segments, the glass fiber-reinforced posts provided significantly increased post retention than the carbon fiber-reinforced posts, regardless of the adhesive used. (c) 2010 Wiley Periodicals, Inc.

Improved Method for the Synthesis of β-Carbonyl Silyl-1,3-Dithianes by the Double Conjugate Addition of 1,3-Dithiol to Propargylic Carbonyl Compounds

PubMed Central

Mukherjee, Sumit; Kontokosta, Dimitra; Patil, Aditi; Rallapalli, Sivakumar; Lee, Daesung

2009-01-01

Base-mediated double conjugate addition of 1,3-propane dithiol to various silylated propargylic aldehydes and ketones allows for an efficient and scalable synthesis of β-carbonyl silyl-1,3-dithianes. PMID:19877611

Mechanism for Si-Si Bond Rupture in Single Molecule Junctions.

PubMed

Li, Haixing; Kim, Nathaniel T; Su, Timothy A; Steigerwald, Michael L; Nuckolls, Colin; Darancet, Pierre; Leighton, James L; Venkataraman, Latha

2016-12-14

The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si-Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si-Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si-Si bond is ruptured using an applied voltage. We investigate this voltage induced Si-Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation of molecular vibrational modes by tunneling electrons leads to homolytic Si-Si bond rupture.

Halogen bonding (X-bonding): A biological perspective

PubMed Central

Scholfield, Matthew R; Zanden, Crystal M Vander; Carter, Megan; Ho, P Shing

2013-01-01

The concept of the halogen bond (or X-bond) has become recognized as contributing significantly to the specificity in recognition of a large class of halogenated compounds. The interaction is most easily understood as primarily an electrostatically driven molecular interaction, where an electropositive crown, or σ-hole, serves as a Lewis acid to attract a variety of electron-rich Lewis bases, in analogous fashion to a classic hydrogen bonding (H-bond) interaction. We present here a broad overview of X-bonds from the perspective of a biologist who may not be familiar with this recently rediscovered class of interactions and, consequently, may be interested in how they can be applied as a highly directional and specific component of the molecular toolbox. This overview includes a discussion for where X-bonds are found in biomolecular structures, and how their structure–energy relationships are studied experimentally and modeled computationally. In total, our understanding of these basic concepts will allow X-bonds to be incorporated into strategies for the rational design of new halogenated inhibitors against biomolecular targets or toward molecular engineering of new biological-based materials. PMID:23225628

IR-UV double resonance spectroscopic investigation of phenylacetylene-alcohol complexes. Alkyl group induced hydrogen bond switching.

PubMed

Singh, Prashant Chandra; Patwari, G Naresh

2008-06-12

The electronic transitions of phenylacetylene complexes with water and trifluoroethanol are shifted to the blue, while the corresponding transitions for methanol and ethanol complexes are shifted to the red relative to the phenylacetylene monomer. Fluorescence dip infrared (FDIR) spectra in the O-H stretching region indicate that, in all the cases, phenylacetylene is acting as a hydrogen bond acceptor to the alcohols. The FDIR spectrum in the acetylenic C-H stretching region shows Fermi resonance bands for the bare phenylacetylene, which act as a sensitive tool to probe the intermolecular structures. The FDIR spectra reveal that water and trifluoroethanol interact with the pi electron density of the acetylene C-C triple bond, while methanol and ethanol interact with the pi electron density of the benzene ring. It can be inferred that the hydrogen bonding acceptor site on phenylacetylene switches from the acetylene pi to the benzene pi with lowering in the partial charge on the hydrogen atom of the OH group. The most significant finding is that the intermolecular structures of water and methanol complexes are notably distinct, which, to the best of our knowledge, this is first such observation in the case of complexes of substituted benzenes.

Carbon–hydrogen bond activation, C–N bond coupling, and cycloaddition reactivity of a three-coordinate nickel complex featuring a terminal imido ligand

DOE PAGES

Mindiola, Daniel J.; Waterman, Rory; Iluc, Vlad M.; ...

2014-12-01

Here, the three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu 2PCH 2CH 2PtBu 2, R = 2,6- iPr 2C 6H 3, 2,4,6-Me 3C 6H 2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6- iPr 2C 6H 3, reductive carbonylation results in formation of the (dtbpe)Ni(CO) 2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr 2C 6H 3). Given the ability of the Ni=N bond to have biradical character as suggested bymore » theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6- iPr 2C 6H 3} when this species is treated with HSn( nBu) 3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6- iPr 2C 6H 3)} to the imido (dtbpe)Ni=N{2,6- iPr 2C 6H 3}—is promoted when using the radical Mes*O • (Mes* = 2,4,6- tBu 3C 6H 2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6- iPr 2C 6H 3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6- iPr 2C 6H 3}.« less

Carbon–hydrogen bond activation, C–N bond coupling, and cycloaddition reactivity of a three-coordinate nickel complex featuring a terminal imido ligand

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

Mindiola, Daniel J.; Waterman, Rory; Iluc, Vlad M.

Here, the three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu 2PCH 2CH 2PtBu 2, R = 2,6- iPr 2C 6H 3, 2,4,6-Me 3C 6H 2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6- iPr 2C 6H 3, reductive carbonylation results in formation of the (dtbpe)Ni(CO) 2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr 2C 6H 3). Given the ability of the Ni=N bond to have biradical character as suggested bymore » theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6- iPr 2C 6H 3} when this species is treated with HSn( nBu) 3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6- iPr 2C 6H 3)} to the imido (dtbpe)Ni=N{2,6- iPr 2C 6H 3}—is promoted when using the radical Mes*O • (Mes* = 2,4,6- tBu 3C 6H 2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6- iPr 2C 6H 3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6- iPr 2C 6H 3}.« less

The role of intra-domain disulfide bonds in heat-induced irreversible denaturation of camelid single domain VHH antibodies.

PubMed

Akazawa-Ogawa, Yoko; Uegaki, Koichi; Hagihara, Yoshihisa

2016-01-01

Camelid-derived single domain VHH antibodies are highly heat resistant, and the mechanism of heat-induced VHH denaturation predominantly relies on the chemical modification of amino acids. Although chemical modification of disulfide bonds has been recognized as a cause for heat-induced denaturation of many proteins, there have been no mutagenesis studies, in which the number of disulfide bonds was controlled. In this article, we examined a series of mutants of two different VHHs with single, double or no disulfide bonds, and scrutinized the effects of these disulfide bond modifications on VHH denaturation. With the exception of one mutant, the heat resistance of VHHs decreased when the number of disulfide bonds increased. The effect of disulfide bonds on heat denaturation was more striking if the VHH had a second disulfide bond, suggesting that the contribution of disulfide shuffling is significant in proteins with multiple disulfide bonds. Furthermore, our results directly indicate that removal of a disulfide bond can indeed increase the heat resistance of a protein, irrespective of the negative impact on equilibrium thermodynamic stability. © The Authors 2015. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

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.

Discrete component bonding and thick film materials study

NASA Technical Reports Server (NTRS)

Kinser, D. L.

1975-01-01

The results are summarized of an investigation of discrete component bonding reliability and a fundamental study of new thick film resistor materials. The component bonding study examined several types of solder bonded components with some processing variable studies to determine their influence upon bonding reliability. The bonding reliability was assessed using the thermal cycle: 15 minutes at room temperature, 15 minutes at +125 C 15 minutes at room temperature, and 15 minutes at -55 C. The thick film resistor materials examined were of the transition metal oxide-phosphate glass family with several elemental metal additions of the same transition metal. These studies were conducted by preparing a paste of the subject composition, printing, drying, and firing using both air and reducing atmospheres. The resulting resistors were examined for adherence, resistance, thermal coefficient of resistance, and voltage coefficient of resistance.

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)

Stereodivergent Aminocatalytic Synthesis of Z- and E-Trisubstituted Double Bonds from Alkynals.

PubMed

Marzo, Leyre; Luis-Barrera, Javier; Mas-Ballesté, Rubén; Ruano, José Luis García; Alemán, José

2016-11-07

A highly diastereoselective synthesis of trisubstituted Z- or E-enals, which are important intermediates in organic synthesis, as well as being present in natural products, is described using different alkynals and nucleophiles as starting materials. Diastereocontrol is mainly governed by the appropriate catalyst. Therefore, those reactions controlled by steric effects, such as the Jørgensen-Hayashi's catalyst, give access to E isomers, and those catalysts that facilitate hydrogen bonding, such as tetrazol-pyrrolidine Ley's catalyst, allow the synthesis of Z isomers. A stereochemical model based on DFT calculations is proposed. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Control of C-H Bond Activation by Mo-Oxo Complexes: pKa or Bond Dissociation Free Energy (BDFE)?

PubMed

Nazemi, Azadeh; Cundari, Thomas R

2017-10-16

A density functional theory (DFT) study (BMK/6-31+G(d)) was initiated to investigate the activation of benzylic carbon-hydrogen bonds by a molybdenum-oxo complex with a potentially redox noninnocent supporting ligand-a simple mimic of the active species of the enzyme ethylbenzene dehydrogenase (EBDH)-through deprotonation (C-H bond heterolysis) or hydrogen atom abstraction (C-H bond homolysis) routes. Activation free-energy barriers for neutral and anionic Mo-oxo complexes were high, but lower for anionic complexes than neutral complexes. Interesting trends as a function of substituents were observed that indicated significant H δ+ character in the transition states (TS), which was further supported by the preference for [2 + 2] addition over HAA for most complexes. Hence, it was hypothesized that C-H activation by these EBDH mimics is controlled more by the pK a than by the bond dissociation free energy of the C-H bond being activated. Therefore, the results suggest promising pathways for designing more efficient and selective catalysts for hydrocarbon oxidation based on EBDH active-site mimics.

Multiple bonds between transition metals and main-group elements. 73. Synthetic routes to rhenium(V) alkyl and rhenium(VII) alkylidyne complexes. X-ray crystal structures of (. eta. sup 5 -C sub 5 Me sub 5 )Re( double bond O)(CH sub 3 )(CH sub 2 C(CH sub 3 ) sub 3 ) and (. eta. sup 5 -C sub 5 Me sub 5 )(Br) sub 3 Re triple bond CC(CH sub 3 ) sub 3

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

Herrmann, W.A.; Felixberger, J.K.; Anwander, R.

1990-05-01

Dialkyloxo({eta}{sup 5}pentamethylcyclopentadienyl)rhenium(V) complexes ({eta}{sup 5}-C{sub 5}Me{sub 5})Re({double bond}O)(CH{sub 3})R{prime}(R{prime} = C{sub 2}H{sub 5}, CH{sub 2}Si(CH{sub 3}){sub 3}, CH{sub 2}C(CH{sub 3}){sub 3}), 1c-e, have become accessible through alkylation of ({eta}{sup 5}-C{sub 5}Me{sub 5})Re({double bond}O)(Cl)(CH{sub 3}) (7) with R{prime}MgCl. 1c-e are the first rhenium complexes containing different alkyl ligands. The neopentyl derivative 1e (R{prime} = CH{sub 2}C(CH{sub 3}){sub 3}) crystallizes in the orthorhombic space group Pbca with a = 960.7 (2), b = 2.844.5 (4), c = 1,260.7 (2) pm, and Z = 8. The X-ray crystal structure was refined to R{sub W} = 3.9%. The chiral molecule shows a distorted tetrahedralmore » geometry around the rhenium center. The tribromide 3b has been structurally characterized. Brown crystals of 3b belong to space group P2{sub 1}/c with unit cell dimensions a = 1,311.5 (2), b = 723.0 (1), c = 1,901.6 (2) pm, {beta} = 92.68 (1){degree}, and Z = 4. The structure exhibits a four-legged piano stool geometry with no trans influence of the neopentylidyne ligand to the bromine atom.« less

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 26 Internal Revenue 2 2012-04-01 2012-04-01 false Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds. 1.144-1 Section 1.144-1 Internal Revenue INTERNAL...) Tax Exemption Requirements for State and Local Bonds § 1.144-1 Qualified small issue bonds, qualified...

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 26 Internal Revenue 2 2013-04-01 2013-04-01 false Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds. 1.144-1 Section 1.144-1 Internal Revenue INTERNAL...) Tax Exemption Requirements for State and Local Bonds § 1.144-1 Qualified small issue bonds, qualified...

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 2 2010-04-01 2010-04-01 false Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds. 1.144-1 Section 1.144-1 Internal Revenue INTERNAL...) Tax Exemption Requirements for State and Local Bonds § 1.144-1 Qualified small issue bonds, qualified...

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds. 1.144-1 Section 1.144-1 Internal Revenue INTERNAL...) Tax Exemption Requirements for State and Local Bonds § 1.144-1 Qualified small issue bonds, qualified...

26 CFR 1.144-1 - Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 26 Internal Revenue 2 2011-04-01 2011-04-01 false Qualified small issue bonds, qualified student loan bonds, and qualified redevelopment bonds. 1.144-1 Section 1.144-1 Internal Revenue INTERNAL...) Tax Exemption Requirements for State and Local Bonds § 1.144-1 Qualified small issue bonds, qualified...

Mechanism for Si–Si Bond Rupture in Single Molecule Junctions

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

Li, Haixing; Kim, Nathaniel T.; Su, Timothy A.

The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si–Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si–Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si–Si bond is ruptured using an applied voltage. We investigate this voltage induced Si–Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation ofmore » molecular vibrational modes by tunneling electrons leads to homolytic Si–Si bond rupture.« less

The mechanism of addition to a CN triple bond. An ab initio study of the first stages of the Stephen, Gatterman and Houben-Hoesch reactions

NASA Astrophysics Data System (ADS)

Alagona, Giuliano; Tomasi, Jacopo

The mechanism of addition of HCl to the triple bond of RCN (R=H, CH,) is studied by means of ab initio SCF and CI calculations. Geometries and energies of minima (initial H-bonded complexes, products) and saddle points (transition state) are completed by a determination of the intrinsic reaction coordinate and of a relatively large portion of the energy hypersurface. The evolution of the electronic structure along the reaction coordinate is interpreted using localized orbitals. Particular attention is paid to the effect of chemical substitution, for which a new test, based on the electrostatic forces acting on nuclei along the reaction coordinate, has been employed. CI calculations performed over canonical and localized orbitals are compared to determine whether the latter formulation is more convenient for non-equilibrium geometries.

27 CFR 24.147 - Operations bond or unit bond.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Operations bond or unit... BUREAU, DEPARTMENT OF THE TREASURY LIQUORS WINE Establishment and Operations Bonds and Consents of Surety § 24.147 Operations bond or unit bond. Notwithstanding the provisions of § 24.146, each person...

Flip-chip bonded optoelectronic integration based on ultrathin silicon (UTSi) CMOS

NASA Astrophysics Data System (ADS)

Hong, Sunkwang; Ho, Tawei; Zhang, Liping; Sawchuk, Alexander A.

2003-06-01

We describe the design and test of flip-chip bonded optoelectronic CMOS devices based on Peregrine Semiconductor's 0.5 micron Ultra-Thin Silicon on sapphire (UTSi) technology. The UTSi process eliminates the substrate leakage that typically results in crosstalk and reduces parasitic capacitance to the substrate, providing many benefits compared to bulk silicon CMOS. The low-loss synthetic sapphire substrate is optically transparent and has a coefficient of thermal expansion suitable for flip-chip bonding of vertical cavity surface emitting lasers (VCSELs) and detectors. We have designed two different UTSi CMOS chips. One contains a flip-chip bonded 1 x 4 photodiode array, a receiver array, a double edge triggered D-flip flop-based 2047-pattern pseudo random bit stream (PRBS) generator and a quadrature-phase LC-voltage controlled oscillator (VCO). The other chip contains a flip-chip bonded 1 x 4 VCSEL array, a driver array based on high-speed low-voltage differential signals (LVDS) and a full-balanced differential LC-VCO. Each VCSEL driver and receiver has individual input and bias voltage adjustments. Each UTSi chip is mounted on different printed circuit boards (PCBs) which have holes with about 1 mm radius for optical output and input paths through the sapphire substrate. We discuss preliminary testing of these chips.

Significance of wood extractives for wood bonding.

PubMed

Roffael, Edmone

2016-02-01

Wood contains primary extractives, which are present in all woods, and secondary extractives, which are confined in certain wood species. Extractives in wood play a major role in wood-bonding processes, as they can contribute to or determine the bonding relevant properties of wood such as acidity and wettability. Therefore, extractives play an immanent role in bonding of wood chips and wood fibres with common synthetic adhesives such as urea-formaldehyde-resins (UF-resins) and phenol-formaldehyde-resins (PF-resins). Extractives of high acidity accelerate the curing of acid curing UF-resins and decelerate bonding with alkaline hardening PF-resins. Water-soluble extractives like free sugars are detrimental for bonding of wood with cement. Polyphenolic extractives (tannins) can be used as a binder in the wood-based industry. Additionally, extractives in wood can react with formaldehyde and reduce the formaldehyde emission of wood-based panels. Moreover, some wood extractives are volatile organic compounds (VOC) and insofar also relevant to the emission of VOC from wood and wood-based panels.

Electrical properties of Si-Si interfaces obtained by room temperature covalent wafer bonding

NASA Astrophysics Data System (ADS)

Jung, A.; Zhang, Y.; Arroyo Rojas Dasilva, Y.; Isa, F.; von Känel, H.

2018-02-01

We study covalent bonds between p-doped Si wafers (resistivity ˜10 Ω cm) fabricated on a recently developed 200 mm high-vacuum system. Oxide- and void free interfaces were obtained by argon (Ar) or neon (Ne) sputtering prior to wafer bonding at room temperature. The influence of the sputter induced amorphous Si layer at the bonding interface on the electrical behavior is accessed with temperature-dependent current-voltage measurements. In as-bonded structures, charge transport is impeded by a potential barrier of 0.7 V at the interface with thermionic emission being the dominant charge transport mechanism. Current-voltage characteristics are found to be asymmetric which can tentatively be attributed to electric dipole formation at the interface as a result of the time delay between the surface preparation of the two bonding partners. Electron beam induced current measurements confirm the corresponding asymmetric double Schottky barrier like band-alignment. Moreover, we demonstrate that defect annihilation at a low temperature of 400 °C increases the electrical conductivity by up to three orders of magnitude despite the lack of recrystallization of the amorphous layer. This effect is found to be more pronounced for Ne sputtered surfaces which is attributed to the lighter atomic mass compared to Ar, inducing weaker lattice distortions during the sputtering.

Contamination and Surface Preparation Effects on Composite Bonding

NASA Technical Reports Server (NTRS)

Kutscha, Eileen O.; Vahey, Paul G.; Belcher, Marcus A.; VanVoast, Peter J.; Grace, William B.; Blohowiak, Kay Y.; Palmieri, Frank L.; Connell, John W.

2017-01-01

Results presented here demonstrate the effect of several prebond surface contaminants (hydrocarbon, machining fluid, latex, silicone, peel ply residue, release film) on bond quality, as measured by fracture toughness and failure modes of carbon fiber reinforced epoxy substrates bonded in secondary and co-bond configurations with paste and film adhesives. Additionally, the capability of various prebond surface property measurement tools to detect contaminants and potentially predict subsequent bond performance of three different adhesives is also shown. Surface measurement methods included water contact angle, Dyne solution wettability, optically stimulated electron emission spectroscopy, surface free energy, inverse gas chromatography, and Fourier transform infrared spectroscopy with chemometrics analysis. Information will also be provided on the effectiveness of mechanical and energetic surface treatments to recover a bondable surface after contamination. The benefits and drawbacks of the various surface analysis tools to detect contaminants and evaluate prebond surfaces after surface treatment were assessed as well as their ability to correlate to bond performance. Surface analysis tools were also evaluated for their potential use as in-line quality control of adhesive bonding parameters in the manufacturing environment.

High-Q Wafer Level Package Based on Modified Tri-Layer Anodic Bonding and High Performance Getter and Its Evaluation for Micro Resonant Pressure Sensor.

PubMed

Wang, Liying; Du, Xiaohui; Wang, Lingyun; Xu, Zhanhao; Zhang, Chenying; Gu, Dandan

2017-03-16

In order to achieve and maintain a high quality factor (high-Q) for the micro resonant pressure sensor, this paper presents a new wafer level package by adopting cross-layer anodic bonding technique of the glass/silicon/silica (GSS) stackable structure and integrated Ti getter. A double-layer structure similar to a silicon-on-insulator (SOI) wafer is formed after the resonant layer and the pressure-sensitive layer are bonded by silicon direct bonding (SDB). In order to form good bonding quality between the pressure-sensitive layer and the glass cap layer, the cross-layer anodic bonding technique is proposed for vacuum package by sputtering Aluminum (Al) on the combination wafer of the pressure-sensitive layer and the resonant layer to achieve electrical interconnection. The model and the bonding effect of this technique are discussed. In addition, in order to enhance the performance of titanium (Ti) getter, the prepared and activation parameters of Ti getter under different sputtering conditions are optimized and discussed. Based on the optimized results, the Ti getter (thickness of 300 nm to 500 nm) is also deposited on the inside of the glass groove by magnetron sputtering to maintain stable quality factor (Q). The Q test of the built testing system shows that the number of resonators with a Q value of more than 10,000 accounts for more than 73% of the total. With an interval of 1.5 years, the Q value of the samples remains almost constant. It proves the proposed cross-layer anodic bonding and getter technique can realize high-Q resonant structure for long-term stable operation.

21 CFR 172.330 - Calcium pantothenate, calcium chloride double salt.

Code of Federal Regulations, 2010 CFR

2010-04-01

... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) FOOD ADDITIVES PERMITTED FOR DIRECT ADDITION TO FOOD FOR HUMAN CONSUMPTION Special Dietary and Nutritional Additives § 172.330 Calcium pantothenate, calcium chloride double salt. The food additive calcium chloride double salt of calcium pantothenate may...

21 CFR 172.330 - Calcium pantothenate, calcium chloride double salt.

Code of Federal Regulations, 2012 CFR

2012-04-01

... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) FOOD ADDITIVES PERMITTED FOR DIRECT ADDITION TO FOOD FOR HUMAN CONSUMPTION Special Dietary and Nutritional Additives § 172.330 Calcium pantothenate, calcium chloride double salt. The food additive calcium chloride double salt of calcium pantothenate may...

21 CFR 172.330 - Calcium pantothenate, calcium chloride double salt.

Code of Federal Regulations, 2013 CFR

2013-04-01

... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) FOOD ADDITIVES PERMITTED FOR DIRECT ADDITION TO FOOD FOR HUMAN CONSUMPTION Special Dietary and Nutritional Additives § 172.330 Calcium pantothenate, calcium chloride double salt. The food additive calcium chloride double salt of calcium pantothenate may...

21 CFR 172.330 - Calcium pantothenate, calcium chloride double salt.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Calcium pantothenate, calcium chloride double salt... FOOD FOR HUMAN CONSUMPTION Special Dietary and Nutritional Additives § 172.330 Calcium pantothenate, calcium chloride double salt. The food additive calcium chloride double salt of calcium pantothenate may...

THz quantum cascade lasers with wafer bonded active regions.

PubMed

Brandstetter, M; Deutsch, C; Benz, A; Cole, G D; Detz, H; Andrews, A M; Schrenk, W; Strasser, G; Unterrainer, K

2012-10-08

We demonstrate terahertz quantum-cascade lasers with a 30 μm thick double-metal waveguide, which are fabricated by stacking two 15 μm thick active regions using a wafer bonding process. By increasing the active region thickness more optical power is generated inside the cavity, the waveguide losses are decreased and the far-field is improved due to a larger facet aperture. In this way the output power is increased by significantly more than a factor of 2 without reducing the maximum operating temperature and without increasing the threshold current.

Effect of etching on bonding of a self-etch adhesive to dentine affected by amelogenesis imperfecta.

PubMed

Epasinghe, Don Jeevanie; Yiu, Cynthia Kar Yung

2018-02-01

Dentine affected by amelogenesis imperfecta (AI) is histologically altered due to loss of hypoplastic enamel and becomes hypermineralized. In the present study, we examined the effect of additional acid etching on microtensile bond strength of a self-etch adhesive to AI-affected dentine. Flat coronal dentine obtained from extracted AI-affected and non-carious permanent molars were allocated to two groups: (a) Clearfil SE Bond (control); and (b) Clearfil SE Bond and additional etching with 34% phosphoric acid for 15 seconds. The bonded teeth were sectioned into .8-mm 2 beams for microtensile bond strength testing, and stressed to failure under tension. The bond strength data were analyzed using two-way analysis of variance (dentine type and etching step) and Student-Newman-Keuls multiple comparison test (P<.05). Representative fractured beams from each group were examined under scanning electron microscopy. Both factors, dentine substrate (P<.001) and etching step (P<.05), and their interactions (P<.001), were statistically significant. Additional etching had an adverse effect on the bond strength of Clearfil SE Bond to normal dentine (P<.005), and no significant improvement was found for AI-affected dentine (P=.479). Additional acid etching does not improve the bond strength of a self-etch adhesive to AI-affected dentine. © 2017 John Wiley & Sons Australia, Ltd.

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

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

Colby, Denise; Bergman, Robert; Ellman, Jonathan

2010-05-13

Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the areamore » of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach

Adhesive bonding and performance testing of bonded wood products

Treesearch

Charles R. Frihart

2005-01-01

Despite the importance of durable wood bonds, the factors that lead to durability are not well understood, and the internal forces exerted upon the bondline are often overlooked. Durability requires that the bonded assembly resist dimensional changes of wood with fluctuation of wood moisture levels. Both bonding and bond breaking steps need to be understood at cellular...

Observing Double Stars

NASA Astrophysics Data System (ADS)

Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

2012-05-01

Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

C-H bond activation of hydrocarbons by an imidozirconocene complex.

PubMed

Hoyt, Helen M; Michael, Forrest E; Bergman, Robert G

2004-02-04

Monomeric imidozirconocene complexes of the type Cp2(L)Zr=NCMe3 (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon-hydrogen bonds of benzene, but not the C-H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C-H activation reactions has heretofore not been observed in imidometallocene systems. The M=NR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C-H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C-H bond. Products formed by activation of sp2 C-H bonds are generally more thermodynamically stable than those formed by activation of sp3 C-H bonds, and those resulting from reaction at primary C-H bonds are preferred over secondary sp3 C-H activation products. There is also evidence that thermodynamic selectivity among C-H bonds is sterically rather than electronically controlled.

Low-pressure, high-temperature thermal bonding of polymeric microfluidic devices and their applications for electrophoretic separation

NASA Astrophysics Data System (ADS)

Sun, Yi; Chian Kwok, Yien; Nguyen, Nam-Trung

2006-08-01

A new method for thermally bonding poly(methyl methacrylate) (PMMA) substrates has been demonstrated. PMMA substrates are first engraved by CO2-laser micromachining to form microchannels. Both channel width and depth can be adjusted by varying the laser power and scanning speed. Channel depths from 50 µm to 1500 µm and widths from 150 µm to 400 µm are attained. CO2 laser is also used for drilling and dicing of the PMMA parts. Considering the thermal properties of PMMA, a novel thermal bonding process with high temperature and low bonding pressure has been developed for assembling PMMA sheets. A high bonding strength of 2.15 MPa is achieved. Subsequent inspection of the cross sections of several microdevices reveals that the dimensions of the channels are well preserved during the bonding process. Electroosmotic mobility of the ablated channel is measured to be 2.47 × 10-4 cm2 V-1 s-1. The functionality of these thermally bonded microfluidic substrates is demonstrated by performing rapid and high-resolution electrophoretic separations of mixture of fluorescein and carboxyfluorescein as well as double-stranded DNA ladders (ΦX174-Hae III dsDNA digest). The performance of the CO2 laser ablated and thermally bonded PMMA devices compares favorably with those fabricated by other professional means.

21 CFR 172.330 - Calcium pantothenate, calcium chloride double salt.

Code of Federal Regulations, 2014 CFR

2014-04-01

... SERVICES (CONTINUED) FOOD ADDITIVES PERMITTED FOR DIRECT ADDITION TO FOOD FOR HUMAN CONSUMPTION Special Dietary and Nutritional Additives § 172.330 Calcium pantothenate, calcium chloride double salt. The food additive calcium chloride double salt of calcium pantothenate may be safely used in foods for special...

Enhancing integration of articular cartilage grafts via photochemical bonding.

PubMed

Arvayo, Alberto L; Wong, Ivan J; Dragoo, Jason L; Levenston, Marc E

2018-03-25

The integration of osteochondral grafts to native articular cartilage is critical as the lack of graft integration may lead to continued tissue degradation, poor load transfer and inadequate nutrient transport. Photochemical bonding promotes graft integration by activating a photosensitizer at the interface via a light source and avoids negative effects associated with other bonding techniques. We hypothesized that the bond strength depends on photosensitizer type and concentration in addition to light exposure. Photochemical bonding was evaluated using methylene blue (MB), a cationic phenothiazine photosensitizer, and two phthalocyanine photosensitizers, Al(III) phthalocyanine chloride tetrasulfonic acid (CASPc) and aluminum phthalocyanine chloride (AlPc). Exposure was altered by varying irradiation time for a fixed irradiance or by varying irradiance with a fixed irradiation time. MB was ineffective at producing bonding at the range of concentrations tested while CASPc produced a peak twofold bond strength increase over controls. AlPc produced substantial bonding at all concentrations with a peak 3.9-fold bond strength increase over controls. Parametric tests revealed that bond strength depended primarily on the total energy delivered to the bonding site rather than the rate of light delivery or light irradiance. Bond strength persisted for 1 week of in-vitro culture, which warrants further exploration for clinical applications. These studies indicate that photochemical bonding is a viable strategy for enhancing articular cartilage graft integration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Activation of carbon-hydrogen bonds via 1,2-addition across M-X (X = OH or NH(2)) bonds of d(6) transition metals as a potential key step in hydrocarbon functionalization: a computational study.

PubMed

Cundari, Thomas R; Grimes, Thomas V; Gunnoe, T Brent

2007-10-31

Recent reports of 1,2-addition of C-H bonds across Ru-X (X = amido, hydroxo) bonds of TpRu(PMe3)X fragments {Tp = hydridotris(pyrazolyl)borate} suggest opportunities for the development of new catalytic cycles for hydrocarbon functionalization. In order to enhance understanding of these transformations, computational examinations of the efficacy of model d6 transition metal complexes of the form [(Tab)M(PH3)2X]q (Tab = tris-azo-borate; X = OH, NH2; q = -1 to +2; M = TcI, Re(I), Ru(II), Co(III), Ir(III), Ni(IV), Pt(IV)) for the activation of benzene C-H bonds, as well as the potential for their incorporation into catalytic functionalization cycles, are presented. For the benzene C-H activation reaction steps, kite-shaped transition states were located and found to have relatively little metal-hydrogen interaction. The C-H activation process is best described as a metal-mediated proton transfer in which the metal center and ligand X function as an activating electrophile and intramolecular base, respectively. While the metal plays a primary role in controlling the kinetics and thermodynamics of the reaction coordinate for C-H activation/functionalization, the ligand X also influences the energetics. On the basis of three thermodynamic criteria characterizing salient energetic aspects of the proposed catalytic cycle and the detailed computational studies reported herein, late transition metal complexes (e.g., Pt, Co, etc.) in the d6 electron configuration {especially the TabCo(PH3)2(OH)+ complex and related Co(III) systems} are predicted to be the most promising for further catalyst investigation.

30 CFR 581.33 - Bonds and bonding requirements.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 2 2012-07-01 2012-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE... title. Prior to the approval of a Delineation, Testing, or Mining Plan, the bond amount shall be...

30 CFR 281.33 - Bonds and bonding requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 2 2011-07-01 2011-07-01 false Bonds and bonding requirements. 281.33 Section 281.33 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, REGULATION, AND ENFORCEMENT, DEPARTMENT OF..., Testing, or Mining Plan, the bond amount shall be adjusted, if appropriate, to cover the operations and...

30 CFR 581.33 - Bonds and bonding requirements.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 2 2013-07-01 2013-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE... title. Prior to the approval of a Delineation, Testing, or Mining Plan, the bond amount shall be...

30 CFR 581.33 - Bonds and bonding requirements.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 2 2014-07-01 2014-07-01 false Bonds and bonding requirements. 581.33 Section 581.33 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE... title. Prior to the approval of a Delineation, Testing, or Mining Plan, the bond amount shall be...

In vitro evaluation of an adhesive monomer as a bonding agent for orthodontic brackets to primary teeth and nickel-chromium ion crowns.

PubMed

Ergas, R P; Hondrum, S O; Mathieu, G P; Koonce, J D

1995-01-01

The adhesive monomer, Clearfil New Bond, was used to enhance the bond strength between orthodontic brackets and primary molars, premolars, and NiCr crowns. Twenty specimens of each had this dental adhesive applied according to the manufacturer's instructions in addition to a chemically cured composite material. The remaining specimens (20 each) were bonded without the adhesive monomer. Shear bond strengths were determined using a universal testing machine. Fracture sites were examined to determine the type of bond failure. All bond strengths were significantly increased with the addition of Clearfil New Bond (P < or = 0.0001). The shear bond strength to NiCr crowns with the addition of the adhesive monomer was 7.76 kg. This is comparable to the shear bond strength observed for primary molars (8.66 kg) and premolars (8.65 kg) without adhesive monomer. The observed decrease in adhesive bond failures with the addition of Clearfil New Bond indicated a stronger shear bond strength between the tooth surface and the bracket base. Clearfil New Bond can significantly increase the shear bond strength of orthodontic brackets to both primary molars and premolars. Additionally, it was shown that orthodontic brackets can be successfully bonded to Ni-Cr crowns at strengths comparable to primary or permanent enamel.

Reduction of unsaturated compounds under interstellar conditions: chemoselective reduction of C≡C and C=C bonds over C=O functional group

NASA Astrophysics Data System (ADS)

Jonusas, Mindaugas; Guillemin, Jean-Claude; Krim, Lahouari

2017-07-01

The knowledge of the H-addition reactions on unsaturated organic molecules bearing a triple or a double carbon-carbon bond such as propargyl or allyl alcohols and a CO functional group such as propynal, propenal or propanal may play an important role in the understanding of the chemical complexity of the interstellar medium. Why different aldehydes like methanal, ethanal, propynal and propanal are present in dense molecular clouds while the only alcohol detected in those cold regions is methanol? In addition, ethanol has only been detected in hot molecular cores. Are those saturated and unsaturated aldehyde and alcohol species chemically linked in molecular clouds through solid phase H-addition surface reactions or are they formed through different chemical routes? To answer such questions, we have investigated a hydrogenation study of saturated and unsaturated aldehydes and alcohols at 10 K. We prove through this experimental study that while pure unsaturated alcohol ices bombarded by H atoms lead to the formation of the corresponding fully or partially saturated alcohols, surface H-addition reactions on unsaturated aldehyde ices exclusively lead to the formation of fully saturated aldehyde. Such results show that in addition to a chemoselective reduction of C≡C and C=C bonds over the C=O group, there is no link between aldehydes and their corresponding alcohols in reactions involving H atoms in dense molecular clouds. Consequently, this could be one of the reasons why some aldehydes such as propanal are abundant in dense molecular clouds in contrast to the non-detection of alcohol species larger than methanol.

Hydroxide-catalyzed bonding

NASA Technical Reports Server (NTRS)

Gwo, Dz-Hung (Inventor)

2003-01-01

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

Layered Double Hydroxide Nanoplatelets with Excellent Tribological Properties under High Contact Pressure as Water-Based Lubricant Additives

PubMed Central

Wang, Hongdong; Liu, Yuhong; Chen, Zhe; Wu, Bibo; Xu, Sailong; Luo, Jianbin

2016-01-01

High efficient and sustainable utilization of water-based lubricant is essential for saving energy. In this paper, a kind of layered double hydroxide (LDH) nanoplatelets is synthesized and well dispersed in water due to the surface modification with oleylamine. The excellent tribological properties of the oleylamine-modified Ni-Al LDH (NiAl-LDH/OAm) nanoplatelets as water-based lubricant additives are evaluated by the tribological tests in an aqueous environment. The modified LDH nanoplatelets are found to not only reduce the friction but also enhance the wear resistance, compared with the water-based cutting fluid and lubricants containing other particle additives. By adding 0.5 wt% LDH nanoplatelets, under 1.5 GPa initial contact pressure, the friction coefficient, scar diameter, depth and width of the wear track dramatically decrease by 83.1%, 43.2%, 88.5% and 59.5%, respectively. It is considered that the sufficiently small size and the excellent dispersion of NiAl-LDH/OAm nanoplatelets in water are the key factors, so as to make them enter the contact area, form a lubricating film and prevent direct collision of asperity peaks. Our investigations demonstrate that the LDH nanoplatelet as a water-based lubricant additive has a great potential value in industrial application. PMID:26951794

Layered Double Hydroxide Nanoplatelets with Excellent Tribological Properties under High Contact Pressure as Water-Based Lubricant Additives.

PubMed

Wang, Hongdong; Liu, Yuhong; Chen, Zhe; Wu, Bibo; Xu, Sailong; Luo, Jianbin

2016-03-08

High efficient and sustainable utilization of water-based lubricant is essential for saving energy. In this paper, a kind of layered double hydroxide (LDH) nanoplatelets is synthesized and well dispersed in water due to the surface modification with oleylamine. The excellent tribological properties of the oleylamine-modified Ni-Al LDH (NiAl-LDH/OAm) nanoplatelets as water-based lubricant additives are evaluated by the tribological tests in an aqueous environment. The modified LDH nanoplatelets are found to not only reduce the friction but also enhance the wear resistance, compared with the water-based cutting fluid and lubricants containing other particle additives. By adding 0.5 wt% LDH nanoplatelets, under 1.5 GPa initial contact pressure, the friction coefficient, scar diameter, depth and width of the wear track dramatically decrease by 83.1%, 43.2%, 88.5% and 59.5%, respectively. It is considered that the sufficiently small size and the excellent dispersion of NiAl-LDH/OAm nanoplatelets in water are the key factors, so as to make them enter the contact area, form a lubricating film and prevent direct collision of asperity peaks. Our investigations demonstrate that the LDH nanoplatelet as a water-based lubricant additive has a great potential value in industrial application.

Method of bonding functional surface materials to substrates and applications in microtechnology and antifouling

DOEpatents

Feng, Xiangdong; Liu, Jun; Liang, Liang

1999-01-01

A simple and effective method to bond a thin coating of poly(N-isopropylacylamide) (NIPAAm) on a glass surface by UV photopolymerization, and the use of such a coated surface in nano and micro technology applications. A silane coupling agent with a dithiocarbamate group is provided as a photosensitizer, preferably, (N,N'-diethylamine)dithiocarbamoylpropyl-(trimethoxy)silane (DATMS). The thiocarbamate group of the sensitizer is then bonded to the glass surface by coupling the silane agent with the hydroxyl groups on the glass surface. The modified surface is then exposed to a solution of NIPAAm and a crosslinking agent which may be any organic molecule having an acrylamide group and at least two double bonds in its structure, such as N,N'-methylenebisacrylamide, and a polar solvent which may be any polar liquid which will dissolve the monomer and the crosslinking agent such as acetone, water, ethanol, or combinations thereof. By exposing the glass surface to a UV light, free radicals are generated in the thiocarbamate group which then bonds to the crosslinking agent and the NIPAAm. Upon bonding, the crosslinking agent and the NIPAAm polymerize to form a thin coating of PNIPAAm bonded to the glass. Depending upon the particular configuration of the glass, the properties of the PNIPAAm allow applications in micro and nano technology.

Sticker Bonding.

ERIC Educational Resources Information Center

Frazier, Laura Corbin

2000-01-01

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

Aligning, Bonding, and Testing Mirrors for Lightweight X-ray Telescopes

NASA Technical Reports Server (NTRS)

Chan, Kai-Wing; Zhang, William W.; Saha, Timo T.; McClelland, Ryan S.; Biskach, Michael P.; Niemeyer, Jason; Schofield, Mark J.; Mazzarella, James R.; Kolos, Linette D.; Hong, Melinda M.;

Method for joining metal by solid-state bonding

DOEpatents

Burkhart, L. Elkin; Fultz, Chester R.; Maulden, Kerry A.

1979-01-01

The present development is directed to a method for joining metal at relatively low temperatures by solid-state bonding. Planar surfaces of the metal workpieces are placed in a parallel abutting relationship with one another. A load is applied to at least one of the workpieces for forcing the workpieces together while one of the workpieces is relatively slowly oscillated in a rotary motion over a distance of about 1.degree.. After a preselected number of oscillations, the rotary motion is terminated and the bond between the abutting surfaces is effected. An additional load may be applied to facilitate the bond after terminating the rotary motion.

Single Molecule Junctions: A Laboratory for Chemistry, Mechanics and Bond Rupture

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

Hybertsen M. S.

Simultaneous measurement [1] of junction conductance and sustained force in single molecule junctions bridging metal electrodes provides a powerful tool in the quantitative study of the character of molecule-metal bonds. In this talk I will discuss three topics. First, I will describe chemical trends in link bond strength based on experiments and Density Functional Theory based calculations. Second, I will focus on the specific case of pyridine-linked junctions. Bond rupture from the high conductance junction structure shows a requires a force that exceeds the rupture force of gold point contacts and clearly indicates the role of additional forces, beyond themore » specific N-Au donor acceptor bond. DFT-D2 calculations with empirical addition of dispersion interactions illustrates the interplay between the donor-acceptor bonding and the non-specific van der Waals interactions between the pyridine rings and Au asperities. Third, I will describe recent efforts to characterize the diversity of junction structures realized in break-junction experiments with suitable models for the potential surfaces that are observed. [1] Venkataraman Group, Columbia University.« less

Competing Intramolecular vs. Intermolecular Hydrogen Bonds in Solution

PubMed Central

Nagy, Peter I.

2014-01-01

A hydrogen bond for a local-minimum-energy structure can be identified according to the definition of the International Union of Pure and Applied Chemistry (IUPAC recommendation 2011) or by finding a special bond critical point on the density map of the structure in the framework of the atoms-in-molecules theory. Nonetheless, a given structural conformation may be simply favored by electrostatic interactions. The present review surveys the in-solution competition of the conformations with intramolecular vs. intermolecular hydrogen bonds for different types of small organic molecules. In their most stable gas-phase structure, an intramolecular hydrogen bond is possible. In a protic solution, the intramolecular hydrogen bond may disrupt in favor of two solute-solvent intermolecular hydrogen bonds. The balance of the increased internal energy and the stabilizing effect of the solute-solvent interactions regulates the new conformer composition in the liquid phase. The review additionally considers the solvent effects on the stability of simple dimeric systems as revealed from molecular dynamics simulations or on the basis of the calculated potential of mean force curves. Finally, studies of the solvent effects on the type of the intermolecular hydrogen bond (neutral or ionic) in acid-base complexes have been surveyed. PMID:25353178

Halogen bonding, chalcogen bonding, pnictogen bonding, tetrel bonding: origins, current status and discussion.

PubMed

Brammer, Lee

2017-10-13

The role of the closing lecture in a Faraday Discussion is to summarise the contributions made to the Discussion over the course of the meeting and in so doing capture the main themes that have arisen. This article is based upon my Closing Remarks Lecture at the 203 rd Faraday Discussion meeting on Halogen Bonding in Supramolecular and Solid State Chemistry, held in Ottawa, Canada, on 10-12 th July, 2017. The Discussion included papers on fundamentals and applications of halogen bonding in the solid state and solution phase. Analogous interactions involving main group elements outside group 17 were also examined. In the closing lecture and in this article these contributions have been grouped into the four themes: (a) fundamentals, (b) beyond the halogen bond, (c) characterisation, and (d) applications. The lecture and paper also include a short reflection on past work that has a bearing on the Discussion.

Bonding resin thixotropy and viscosity influence on dentine bond strength.

PubMed

Niem, Thomas; Schmidt, Alexander; Wöstmann, Bernd

2016-08-01

To investigate the influence of bonding resin thixotropy and viscosity on dentine tubule penetration, blister formation and consequently on dentine bond strength as a function of air-blowing pressure (air-bp) intensity. Two HEMA-free, acetone-based, one-bottle self-etch adhesives with similar composition except disparate silica filler contents and different bonding resin viscosities were investigated. The high-filler-containing adhesive (G-Bond) featured a lower viscous bonding resin with inherent thixotropic resin (TR) properties compared to the low-filler-containing adhesive (iBond) exhibiting a higher viscous bonding resin with non-thixotropic resin (NTR) properties. Shear bond strength tests for each adhesive with low (1.5bar; 0.15MPa; n=16) and high (3.0bar; 0.30MPa; n=16) air-bp application were performed after specimen storage in distilled water (24h; 37.0±1.0°C). Results were analysed using a Student's t-test to identify statistically significant differences (p<0.05). Fracture surfaces of TR adhesive specimens were morphologically characterised by SEM. Statistically significant bond strength differences were obtained for the thixotropic resin adhesive (high-pressure: 24.6MPa, low-pressure: 9.6MPa). While high air-bp specimens provided SEM images revealing resin-plugged dentine tubules, resin tags and only marginally blister structures, low air-bp left copious droplets and open dentine tubules. In contrast, the non-thixotropic resin adhesive showed no significant bond strength differences (high-pressure: 9.3MPa, low-pressure: 7.6MPa). A pressure-dependent distinct influence of bonding resin thixotropy and viscosity on dentine bond strength has been demonstrated. Stronger adhesion with high air-bp application is explained by improved resin fluidity and facilitated resin penetration into dentine tubules. Filler particles used in adhesive systems may induce thixotropic effects in bonding resin layers, accounting for improved free-flowing resin properties. In

The fabrication of a double-layer atom chip with through silicon vias for an ultra-high-vacuum cell

NASA Astrophysics Data System (ADS)

Chuang, Ho-Chiao; Lin, Yun-Siang; Lin, Yu-Hsin; Huang, Chi-Sheng

2014-04-01

This study presents a double-layer atom chip that provides users with increased diversity in the design of the wire patterns and flexibility in the design of the magnetic field. It is more convenient for use in atomic physics experiments. A negative photoresist, SU-8, was used as the insulating layer between the upper and bottom copper wires. The electrical measurement results show that the upper and bottom wires with a width of 100 µm can sustain a 6 A current without burnout. Another focus of this study is the double-layer atom chips integrated with the through silicon via (TSV) technique, and anodically bonded to a Pyrex glass cell, which makes it a desired vacuum chamber for atomic physics experiments. Thus, the bonded glass cell not only significantly reduces the overall size of the ultra-high-vacuum (UHV) chamber but also conducts the high current from the backside to the front side of the atom chip via the TSV under UHV (9.5 × 10-10 Torr). The TSVs with a diameter of 70 µm were etched through by the inductively coupled plasma ion etching and filled by the bottom-up copper electroplating method. During the anodic bonding process, the electroplated copper wires and TSVs on atom chips also need to pass the examination of the required bonding temperature of 250 °C, under an applied voltage of 1000 V. Finally, the UHV test of the double-layer atom chips with TSVs at room temperature can be reached at 9.5 × 10-10 Torr, thus satisfying the requirements of atomic physics experiments under an UHV environment.

Ab initio simulations of bond breaking in sulfur crosslinked isoprene oligomer units

NASA Astrophysics Data System (ADS)

Gehrke, Sascha; Alznauer, Hans Tobias; Karimi-Varzaneh, Hossein Ali; Becker, Jörg August

2017-12-01

Sulfur crosslinked polyisoprene (rubber) is used in important material components for a number of technical tasks (e.g., in tires and sealings). If mechanical stress, like tension or shear, is applied on these material components, the sulfur crosslinks suffer from homolytic bond breaking. In this work, we have simulated the bond breaking mechanism of sulfur crosslinks between polyisoprene chains using Car-Parrinello molecular dynamic simulations and investigated the maximum forces which can be resisted by the crosslinks. Small model systems with crosslinks formed by chains of N = 1 to N = 6 sulfur atoms have been simulated with the slow growth-technique, known from the literature. The maximum force can be thereby determined from the calculated energies as a function of strain (elongation). The stability of the crosslink under strain is quantified in terms of the maximum force that can be resisted by the system before the crosslink breaks. As shown by our simulations, this maximum force decreases with the sulfur crosslink length N in a step like manner. Our findings indicate that in bridges with N = 1, 2, and 3 sulfur atoms predominantly, carbon-sulfur bonds break, while in crosslinks with N > 3, the breaking of a sulfur-sulfur bond is the dominant failure mechanism. The results are explained within a simple chemical bond model, which describes how the delocalization of the electrons in the generated radicals can lower their electronic energy and decrease the activation barriers. It is described which of the double bonds in the isoprene units are involved in the mechanochemistry of crosslinked rubber.

Composite Laser Ceramics by Advanced Bonding Technology

PubMed Central

Kamimura, Tomosumi; Honda, Sawao

2018-01-01

Composites obtained by bonding materials with the same crystal structure and different chemical compositions can create new functions that do not exist in conventional concepts. We have succeeded in bonding polycrystalline YAG and Nd:YAG ceramics without any interstices at the bonding interface, and the bonding state of this composite was at the atomic level, similar to the grain boundary structure in ceramics. The mechanical strength of the bonded composite reached 278 MPa, which was not less than the strength of each host material (269 and 255 MPa). Thermal conductivity of the composite was 12.3 W/mK (theoretical value) which is intermediate between the thermal conductivities of YAG and Nd:YAG (14.1 and 10.2 W/mK, respectively). Light scattering cannot be detected at the bonding interface of the ceramic composite by laser tomography. Since the scattering coefficients of the monolithic material and the composite material formed by bonding up to 15 layers of the same materials were both 0.10%/cm, there was no occurrence of light scattering due to the bonding. In addition, it was not detected that the optical distortion and non-uniformity of the refractive index variation were caused by the bonding. An excitation light source (LD = 808 nm) was collimated to 200 μm and irradiated into a commercial 1% Nd:YAG single crystal, but fracture damage occurred at a low damage threshold of 80 kW/cm2. On the other hand, the same test was conducted on the bonded interface of 1% Nd:YAG-YAG composite ceramics fabricated in this study, but it was not damaged until the excitation density reached 127 kW/cm2. 0.6% Nd:YAG-YAG composite ceramics showed high damage resistance (up to 223 kW/cm2). It was concluded that composites formed by bonding polycrystalline ceramics are ideal in terms of thermo-mechanical and optical properties. PMID:29425152

Effect of La2O3 addition on interface chemistry between 4YSZ top layer and Ni based alloy bond coat in thermal barrier coating by EB PVD.

PubMed

Park, Chan-Young; Yang, Young-Hwan; Kim, Seong-Won; Lee, Sung-Min; Kim, Hyung-Tae; Jang, Byung-Koog; Lim, Dae-Soon; Oh, Yoon-Suk

2014-11-01

The effect of a 5 mol% La2O3 addition on the forming behavior and compositional variation at interface between a 4 mol% Yttria (Y2O3) stabilized ZrO2 (4YSZ) top coat and bond coat (NiCrAlY) as a thermal barrier coating (TBC) has been investigated. Top coats were deposited by electron beam physical vapor deposition (EB PVD) onto a super alloy (Ni-Cr-Co-Al) substrate without pre-oxidation of the bond coat. Top coats are found to consist of dense columnar grains with a thin interdiffusion layer between metallic bond coats. In the as-received 4YSZ coating, a thin interdiffusion zone at the interface between the top and bond coats was found to consist of a Ni-Zr intermetallic compound with a reduced quantity of Y, Al or O elements. On the other hand, in the case of an interdiffusion area of 5 mol% La2O3-added 4YSZ coating, it was found that the complicated composition and structure with La-added YSZ and Ni-Al rich compounds separately. The thermal conductivity of 5 mol% La2O3-added 4YSZ coating (- 1.6 W/m x k at 1100 degrees C) was lower than a 4YSZ coating (- 3.2 W/m x k at 1100 degrees C) alone.

Ab Initio energetics of SiO bond cleavage.

PubMed

Hühn, Carolin; Erlebach, Andreas; Mey, Dorothea; Wondraczek, Lothar; Sierka, Marek

2017-10-15

A multilevel approach that combines high-level ab initio quantum chemical methods applied to a molecular model of a single, strain-free SiOSi bridge has been used to derive accurate energetics for SiO bond cleavage. The calculated SiO bond dissociation energy and the activation energy for water-assisted SiO bond cleavage of 624 and 163 kJ mol -1 , respectively, are in excellent agreement with values derived recently from experimental data. In addition, the activation energy for H 2 O-assisted SiO bond cleavage is found virtually independent of the amount of water molecules in the vicinity of the reaction site. The estimated reaction energy for this process including zero-point vibrational contribution is in the range of -5 to 19 kJ mol -1 . © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Fast and accurate predictions of covalent bonds in chemical space.

PubMed

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

2016-05-07

We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (∼1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H2 (+). Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

Fatigue life prediction of bonded primary joints

NASA Technical Reports Server (NTRS)

Knauss, J. F.

1979-01-01

The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.

Effect of light aging on silicone-resin bond strength in maxillofacial prostheses.

PubMed

Polyzois, Gregory; Pantopoulos, Antonis; Papadopoulos, Triantafillos; Hatamleh, Muhanad

2015-04-01

The aim of this study was to investigate the effect of accelerated light aging on bond strength of a silicone elastomer to three types of denture resin. A total of 60 single lap joint specimens were fabricated with auto-, heat-, and photopolymerized (n = 20) resins. An addition-type silicone elastomer (Episil-E) was bonded to resins treated with the same primer (A330-G). Thirty specimens served as controls and were tested after 24 hours, and the remaining were aged under accelerated exposure to daylight for 546 hours (irradiance 765 W/m(2) ). Lap shear joint tests were performed to evaluate bond strength at 50 mm/min crosshead speed. Two-way ANOVA and Tukey's test were carried out to detect statistical significance (p < 0.05). ANOVA showed that the main effect of light aging was the most important factor determining the shear bond strength. The mean bond strength values ranged from 0.096 to 0.136 MPa. The highest values were recorded for auto- (0.131 MPa) and photopolymerized (0.136 MPa) resins after aging. Accelerated light aging for 546 hours affects the bond strength of an addition-type silicone elastomer to three different denture resins. The bond strength significantly increased after aging for photo- and autopolymerized resins. All the bonds failed adhesively. © 2014 by the American College of Prosthodontists.

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.

Elucidating bonding preferences in tetrakis(imido)uranate(VI) dianions

NASA Astrophysics Data System (ADS)

Anderson, Nickolas H.; Xie, Jing; Ray, Debmalya; Zeller, Matthias; Gagliardi, Laura; Bart, Suzanne C.

2017-09-01

Actinyl species, [AnO2]2+, are well-known derivatives of the f-block because of their natural occurrence and essential roles in the nuclear fuel cycle. Along with their nitrogen analogues, [An(NR)2]2+, actinyls are characterized by their two strong trans-An-element multiple bonds, a consequence of the inverse trans influence. We report that these robust bonds can be weakened significantly by increasing the number of multiple bonds to uranium, as demonstrated by a family of uranium(VI) dianions bearing four U-N multiple bonds, [M]2[U(NR)4] (M = Li, Na, K, Rb, Cs). Their geometry is dictated by cation coordination and sterics rather than by electronic factors. Multiple bond weakening by the addition of strong π donors has the potential for applications in the processing of high-valent actinyls, commonly found in environmental pollutants and spent nuclear fuels.

Insight into hydrogen bonding of uranyl hydroxide layers and capsules by use of 1H magic-angle spinning NMR spectroscopy [Insight into the hydrogen bonding for uranyl hydroxides using 1H MAS NMR spectroscopy

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

Alam, Todd M.; Liao, Zuolei; Nyman, May

Solid-state 1H magic-angle spinning (MAS) NMR was used to investigate local proton environments in anhydrous [UO 2(OH) 2] (α-UOH) and hydrated uranyl hydroxide [(UO 2) 4O(OH) 6·5H 2O (metaschoepite). For the metaschoepite material, proton resonances of the μ 2-OH hydroxyl and interlayer waters were resolved, with two-dimensional (2D) double-quantum (DQ) 1H– 1H NMR correlation experiments revealing strong dipolar interactions between these different proton species. The experimental NMR results were combined with first-principles CASTEP GIPAW (gauge including projector-augmented wave) chemical shift calculations to develop correlations between hydrogen-bond strength and observed 1H NMR chemical shifts. Furthermore, these NMR correlations allowed characterization ofmore » local hydrogen-bond environments in uranyl U 24 capsules and of changes in hydrogen bonding that occurred during thermal dehydration of metaschoepite.« less

Insight into hydrogen bonding of uranyl hydroxide layers and capsules by use of 1H magic-angle spinning NMR spectroscopy [Insight into the hydrogen bonding for uranyl hydroxides using 1H MAS NMR spectroscopy

DOE PAGES

Alam, Todd M.; Liao, Zuolei; Nyman, May; ...

2016-04-27

Solid-state 1H magic-angle spinning (MAS) NMR was used to investigate local proton environments in anhydrous [UO 2(OH) 2] (α-UOH) and hydrated uranyl hydroxide [(UO 2) 4O(OH) 6·5H 2O (metaschoepite). For the metaschoepite material, proton resonances of the μ 2-OH hydroxyl and interlayer waters were resolved, with two-dimensional (2D) double-quantum (DQ) 1H– 1H NMR correlation experiments revealing strong dipolar interactions between these different proton species. The experimental NMR results were combined with first-principles CASTEP GIPAW (gauge including projector-augmented wave) chemical shift calculations to develop correlations between hydrogen-bond strength and observed 1H NMR chemical shifts. Furthermore, these NMR correlations allowed characterization ofmore » local hydrogen-bond environments in uranyl U 24 capsules and of changes in hydrogen bonding that occurred during thermal dehydration of metaschoepite.« less

Predicting Trigger Bonds in Explosive Materials through Wiberg Bond Index Analysis.

PubMed

Harper, Lenora K; Shoaf, Ashley L; Bayse, Craig A

2015-12-21

Understanding the explosive decomposition pathways of high-energy-density materials (HEDMs) is important for developing compounds with improved properties. Rapid reaction rates make the detonation mechanisms of HEDMs difficult to understand, so computational tools are used to predict trigger bonds-weak bonds that break, leading to detonation. Wiberg bond indices (WBIs) have been used to compare bond densities in HEDMs to reference molecules to provide a relative scale for the bond strength to predict the activated bonds most likely to break to trigger an explosion. This analysis confirms that X-NO2 (X=N,C,O) bonds are trigger linkages in common HEDMs such as TNT, RDX and PETN, consistent with previous experimental and theoretical studies. Calculations on a small test set of substituted tetrazoles show that the assignment of the trigger bond depends upon the functionality of the material and that the relative weakening of the bond correlates with experimental impact sensitivities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Long-range Coulomb forces and localized bonds.

PubMed

Preiser; Lösel; Brown; Kunz; Skowron

1999-10-01

The ionic model is shown to be applicable to all compounds in which the atoms carry a net charge and their electron density is spherically symmetric regardless of the covalent character of the bonding. By examining the electric field generated by an array of point charges placed at the positions of the ions in over 40 inorganic compounds, we show that the Coulomb field naturally partitions itself into localized regions (bonds) which are characterized by the electric flux that links neighbouring ions of opposite charge. This flux is identified with the bond valence, and Gauss' law with the valence-sum rule, providing a secure theoretical foundation for the bond-valence model. The localization of the Coulomb field provides an unambiguous definition of coordination number and our calculations show that, in addition to the expected primary coordination sphere, there are a number of weak bonds between cations and the anions in the second coordination sphere. Long-range Coulomb interactions are transmitted through the crystal by the application of Gauss' law at each of the intermediate atoms. Bond fluxes have also been calculated for compounds containing ions with non-spherical electron densities (e.g. cations with stereoactive lone electron pairs). In these cases the point-charge model continues to describe the distant field, but multipoles must be added to the point charges to give the correct local field.

Bond Issues.

ERIC Educational Resources Information Center

Pollack, Rachel H.

2000-01-01

Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

A comparison of shear bond strength of orthodontic brackets bonded with four different orthodontic adhesives

PubMed Central

Sharma, Sudhir; Tandon, Pradeep; Nagar, Amit; Singh, Gyan P; Singh, Alka; Chugh, Vinay K

2014-01-01

Objectives: The objective of this study is to compare the shear bond strength (SBS) of stainless steel (SS) orthodontic brackets bonded with four different orthodontic adhesives. Materials and Methods: Eighty newly extracted premolars were bonded to 0.022 SS brackets (Ormco, Scafati, Italy) and equally divided into four groups based on adhesive used: (1) Rely-a-Bond (self-cure adhesive, Reliance Orthodontic Product, Inc., Illinois, USA), (2) Transbond XT (light-cure adhesive, 3M Unitek, CA, USA), (3) Transbond Plus (sixth generation self-etch primer, 3M Unitek, CA, USA) with Transbond XT (4) Xeno V (seventh generation self-etch primer, Dentsply, Konstanz, Germany) with Xeno Ortho (light-cure adhesive, Dentsply, Konstanz, Germany) adhesive. Brackets were debonded with a universal testing machine (Model No. 3382 Instron Corp., Canton, Mass, USA). The adhesive remnant index (ARI) was recordedIn addition, the conditioned enamel surfaces were observed under a scanning electron microscope (SEM). Results: Transbond XT (15.49 MPa) attained the highest bond strength. Self-etching adhesives (Xeno V, 13.51 MPa; Transbond Plus, 11.57 MPa) showed clinically acceptable SBS values and almost clean enamel surface after debonding. The analysis of variance (F = 11.85, P < 0.0001) and Chi-square (χ2 = 18.16, P < 0.05) tests revealed significant differences among groups. The ARI score of 3 (i.e., All adhesives left on the tooth) to be the most prevalent in Transbond XT (40%), followed by Rely-a-Bond (30%), Transbond Plus with Transbond XT (15%), and Xeno V with Xeno Ortho (10%). Under SEM, enamel surfaces after debonding of the brackets appeared porous when an acid-etching process was performed on the surfaces of Rely-a-Bond and Transbond XT, whereas with self-etching primers enamel presented smooth and almost clean surfaces (Transbond Plus and Xeno V group). Conclusion: All adhesives yielded SBS values higher than the recommended bond strength (5.9-7–8 MPa), Seventh generation

Single and double carbon vacancies in pyrene as first models for graphene defects: A survey of the chemical reactivity toward hydrogen

NASA Astrophysics Data System (ADS)

Nieman, Reed; Das, Anita; Aquino, Adélia J. A.; Amorim, Rodrigo G.; Machado, Francisco B. C.; Lischka, Hans

2017-01-01

Graphene is regarded as one of the most promising materials for nanoelectronics applications. Defects play an important role in modulating its electronic properties and also enhance its chemical reactivity. In this work the reactivity of single vacancies (SV) and double vacancies (DV) in reaction with a hydrogen atom Hr is studied. Because of the complicated open shell electronic structures of these defects due to dangling bonds, multireference configuration interaction (MRCI) methods are being used in combination with a previously developed defect model based on pyrene. Comparison of the stability of products derived from Csbnd Hr bond formation with different carbon atoms of the different polyaromatic hydrocarbons is made. In the single vacancy case the most stable structure is the one where the incoming hydrogen is bound to the carbon atom carrying the dangling bond. However, stable Csbnd Hr bonded structures are also observed in the five-membered ring of the single vacancy. In the double vacancy, most stable bonding of the reactant Hr atom is found in the five-membered rings. In total, Csbnd Hr bonds, corresponding to local energy minimum structures, are formed with all carbon atoms in the different defect systems and the pyrene itself. Reaction profiles for the four lowest electronic states show in the case of a single vacancy a complex picture of curve crossings and avoided crossings which will give rise to a complex nonadiabatic reaction dynamics involving several electronic states.

Evidence of significant covalent bonding in Au(CN)(2)(-).

PubMed

Wang, Xue-Bin; Wang, Yi-Lei; Yang, Jie; Xing, Xiao-Peng; Li, Jun; Wang, Lai-Sheng

2009-11-18

The Au(CN)(2)(-) ion is the most stable Au compound known for centuries, yet a detailed understanding of its chemical bonding is still lacking. Here we report direct experimental evidence of significant covalent bonding character in the Au-C bonds in Au(CN)(2)(-) using photoelectron spectroscopy and comparisons with its lighter congeners, Ag(CN)(2)(-) and Cu(CN)(2)(-). Vibrational progressions in the Au-C stretching mode were observed for all detachment transitions for Au(CN)(2)(-), in contrast to the atomic-like transitions for Cu(CN)(2)(-), revealing the Au-C covalent bonding character. In addition, rich electronic structural information was obtained for Au(CN)(2)(-) by employing 118 nm detachment photons. Density functional theory and high-level ab initio calculations were carried out to understand the photoelectron spectra and obtain insight into the nature of the chemical bonding in the M(CN)(2)(-) complexes. Significant covalent character in the Au-C bonding due to the strong relativistic effects was revealed in Au(CN)(2)(-), consistent with its high stability.

27 CFR 19.318 - Addition of caramel to rum or brandy and addition of oak chips to spirits.

Code of Federal Regulations, 2010 CFR

2010-04-01

... or brandy and addition of oak chips to spirits. 19.318 Section 19.318 Alcohol, Tobacco Products and... PLANTS Production § 19.318 Addition of caramel to rum or brandy and addition of oak chips to spirits. Caramel possessing no material sweetening properties may be added to rum or brandy on bonded premises...

Probing Fe-V Bonding in a C3-Symmetric Heterobimetallic Complex.

PubMed

Greer, Samuel M; McKay, Johannes; Gramigna, Kathryn M; Thomas, Christine M; Stoian, Sebastian A; Hill, Stephen

2018-04-30

Direct metal-metal bonding of two distinct first-row transition metals remains relatively unexplored compared to their second- and third-row heterobimetallic counterparts. Herein, a recently reported Fe-V triply bonded species, [V( i PrNPPh 2 ) 3 FeI] (1; Kuppuswamy, S.; Powers, T. M.; Krogman, J. P.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C. M. Vanadium-iron complexes featuring metal-metal multiple bonds. Chem. Sci. 2013, 4, 3557-3565), is investigated using high-frequency electron paramagnetic resonance, field- and temperature-dependent 57 Fe nuclear gamma resonance (Mössbauer) spectroscopy, and high-field electron-electron double resonance detected nuclear magnetic resonance. From the use of this suite of physical methods, we have assessed the electronic structure of 1. These studies allow us to establish the effective g̃ tensors as well as the Fe/V electro-nuclear hyperfine interaction tensors of the spin S = 1 / 2 ground state. We have rationalized these tensors in the context of ligand field theory supported by quantum chemical calculations. This theoretical analysis suggests that the S = 1 / 2 ground state originates from a single unpaired electron predominately localized on the Fe site.

Fabrication of (PPC/NCC)/PVA composites with inner-outer double constrained structure and improved glass transition temperature.

PubMed

Cui, Shaoying; Li, Li; Wang, Qi

2018-07-01

Improving glass transition temperature (T g ) and mechanical property of the environment-friendly poly(propylene carbonate) via intermacromolecular complexation through hydrogen bonding is attractive and of great importance. A novel and effective strategy to prepare (polypropylene carbonate/nanocrystalline cellulose)/polyvinyl alcohol ((PPC/NCC)/PVA) composites with inner-outer double constrained structure was reported in this work. Outside the PPC phase, PVA, as a strong skeleton at microscale, could constrain the movement of PPC molecular chains by forming hydrogen bonding with PPC at the interface of PPC and PVA phases; inside the PPC phase, the rod-like NCC could restrain the flexible molecular chains of PPC at nanoscale by forming multi-hydrogen bonding with PPC. Under the synergistic effect of this novel inner-outer double constrained structure, T g , mechanical properties and thermal stability of (PPC/NCC)/PVA composite were significantly increased, e.g. T g of the composite researched the maximum value of 49.6 °C, respectively 15.6 °C, 5.7 °C and 4.2 °C higher than that of PPC, PPC/NCC and PPC/PVA composite. Copyright © 2018 Elsevier Ltd. All rights reserved.

Tunneling spectroscopy measurements on hydrogen-bonded supramolecular polymers.

PubMed

Vonau, François; Shokri, Roozbeh; Aubel, Dominique; Bouteiller, Laurent; Guskova, Olga; Sommer, Jens-Uwe; Reiter, Günter; Simon, Laurent

2014-07-21

We studied the formation of hydrogen-bonded supramolecular polymers of Ethyl Hexyl Urea Toluene (EHUT) on a gold (111) surface by low temperature scanning tunneling microscopy. Tunneling spectroscopy performed along an individual molecule embedded in a self-assembled layer revealed strong changes in the value of the HOMO-LUMO gap. A variation of the LUMO state is attributed to the effect of space charge accumulation resulting from anisotropic adhesion of the molecule. In addition, for specific tunneling conditions, changes induced through the formation of hydrogen bonds became visible in the differential conductance (dI/dV) maps; isolated molecules, hydrogen bonded dimers and supramolecular polymers of EHUT were distinguishable through their electronic properties.

Tunneling spectroscopy measurements on hydrogen-bonded supramolecular polymers

NASA Astrophysics Data System (ADS)

Vonau, François; Shokri, Roozbeh; Aubel, Dominique; Bouteiller, Laurent; Guskova, Olga; Sommer, Jens-Uwe; Reiter, Günter; Simon, Laurent

2014-06-01

We studied the formation of hydrogen-bonded supramolecular polymers of Ethyl Hexyl Urea Toluene (EHUT) on a gold (111) surface by low temperature scanning tunneling microscopy. Tunneling spectroscopy performed along an individual molecule embedded in a self-assembled layer revealed strong changes in the value of the HOMO-LUMO gap. A variation of the LUMO state is attributed to the effect of space charge accumulation resulting from anisotropic adhesion of the molecule. In addition, for specific tunneling conditions, changes induced through the formation of hydrogen bonds became visible in the differential conductance (dI/dV) maps; isolated molecules, hydrogen bonded dimers and supramolecular polymers of EHUT were distinguishable through their electronic properties.

Oxidative Addition and Reductive Elimination at Main-Group Element Centers.

PubMed

Chu, Terry; Nikonov, Georgii I

2018-04-11

Oxidative addition and reductive elimination are key steps in a wide variety of catalytic reactions mediated by transition-metal complexes. Historically, this reactivity has been considered to be the exclusive domain of d-block elements. However, this paradigm has changed in recent years with the demonstration of transition-metal-like reactivity by main-group compounds. This Review highlights the substantial progress achieved in the past decade for the activation of robust single bonds by main-group compounds and the more recently realized activation of multiple bonds by these elements. We also discuss the significant discovery of reversible activation of single bonds and distinct examples of reductive elimination at main-group element centers. The review consists of three major parts, starting with oxidative addition of single bonds, proceeding to cleavage of multiple bonds, and culminated by the discussion of reversible bond activation and reductive elimination. Within each subsection, the discussion is arranged according to the type of bond being cleaved or formed and considers elements from the left to the right of each period and down each group of the periodic table. The majority of results discussed in this Review come from the past decade; however, earlier reports are also included to ensure completeness.

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.

Effect of handpiece maintenance method on bond strength.

PubMed

Roberts, Howard W; Vandewalle, Kraig S; Charlton, David G; Leonard, Daniel L

2005-01-01

This study evaluated the effect of dental handpiece lubricant on the shear bond strength of three bonding agents to dentin. A lubrication-free handpiece (one that does not require the user to lubricate it) and a handpiece requiring routine lubrication were used in the study. In addition, two different handpiece lubrication methods (automated versus manual application) were also investigated. One hundred and eighty extracted human teeth were ground to expose flat dentin surfaces that were then finished with wet silicon carbide paper. The teeth were randomly divided into 18 groups (n=10). The dentin surface of each specimen was exposed for 30 seconds to water spray from either a lubrication-free handpiece or a lubricated handpiece. Prior to exposure, various lubrication regimens were used on the handpieces that required lubrication. The dentin surfaces were then treated with total-etch, two-step; a self-etch, two-step or a self-etch, one-step bonding agent. Resin composite cylinders were bonded to dentin, the specimens were then thermocycled and tested to failure in shear at seven days. Mean bond strength data were analyzed using Dunnett's multiple comparison test at an 0.05 level of significance. Results indicated that within each of the bonding agents, there were no significant differences in bond strength between the control group and the treatment groups regardless of the type of handpiece or use of routine lubrication.

Aging Effects of Environmentally-Friendly Cleaners on Adhesive Bond Integrity

NASA Technical Reports Server (NTRS)

Biegert, L. L.; Anderson, G. L.; Evans, K. B.; Olsen, B. D.; Weber, B. L.; McCool, A. A. (Technical Monitor)

2000-01-01

Because of the 1990 Clean Air Act Amendment many chlorinated solvents are being phased out of use in manufacturing industries. Replacement of the ODC (ozone- depleting chemicals) with less volatile, non-ozone depleting cleaners has been extensively studied over the past nine years at Thiokol Propulsion, Cordant Technologies. Many of the non-ODC cleaners contain compounds that can potentially degrade over time under conditions of high temperature, humidity and exposure to light. The chemical composition of environmentally conditioned cleaners and the subsequent effect on aluminum/amine-cured epoxy bond integrity as measured by Tapered Double Cantilever Beam were evaluated. From this study it is observed that moisture content increases for those cleaners containing polar compounds. Non-volatile residue content increases as stabilizers are depleted and the chemical compound limonene is oxidized. A change in aluminum/ amine-cured epoxy bond fracture toughness is observed as some of these cleaners age with increases in moisture and NVR content.

Forging Unsupported Metal-Boryl Bonds with Icosahedral Carboranes.

PubMed

Saleh, Liban M A; Dziedzic, Rafal M; Khan, Saeed I; Spokoyny, Alexander M

2016-06-13

In contrast to the plethora of metal-catalyzed cross-coupling methods available for the installation of functional groups on aromatic hydrocarbons, a comparable variety of methods are currently not available for icosahedral carboranes, which are boron-rich three-dimensional aromatic analogues of aryl groups. Part of this is due to the limited understanding of the elementary steps for cross-coupling involving carboranes. Here, we report our efforts in isolating metal-boryl complexes to further our understanding of one of these elementary steps, oxidative addition. Structurally characterized examples of group 10 M-B bonds featuring icosahedral carboranes are completely unknown. Use of mercurocarboranes as a reagent to deliver M-B bonds saw divergent reactivity for platinum and palladium, with a Pt-B bond being isolated for the former, and a rare Pd-Hg bond being formed for the latter. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method of bonding functional surface materials to substrates and applications in microtechnology and anti-fouling

DOEpatents

Feng, Xiangdong; Liu, Jun; Liang, Liang

2001-01-01

A simple and effective method to bond a thin coating of poly(N-isopropylacylamide) (NIPAAm) on a glass surface by UV photopolymerization, and the use of such a coated surface in nano and micro technology applications. A silane coupling agent with a dithiocarbamate group is provided as a photosensitizer preferably, (N,N'-diethylamine) dithiocarbamoylpropyl-(trimethoxy) silane (DATMS). The thiocarbamate group of the sensitizer is then bonded to the glass surface by coupling the silane agent with the hydroxyl groups on the glass surface. The modified surface is then exposed to a solution of NIPAAm and a crosslinking agent which may be any organic molecule having an acrylamide group and at least two double bonds in its structure, such as N, N'-methylenebisacrylamide, and a polar solvent which may be any polar liquid which will dissolve the monomer and the crosslinking agent such as acetone, water, ethanol, or combinations thereof. By exposing the glass surface to a UV light, free radicals are generated in the thiocarbamate group which then bonds to the crosslinking agent and the NIPAAm. Upon bonding, the crosslinking agent and the NIPAAm polymerize to form a thin coating of PNIPAAm bonded to the glass. Depending upon the particular configuration of the glass, the properties of the PNIPAAm allow applications in micro and nano technology.

Rapid adhesive bonding concepts

NASA Technical Reports Server (NTRS)

Stein, B. A.; Tyeryar, J. R.; Hodges, W. T.

1984-01-01

Adhesive bonding in the aerospace industry typically utilizes autoclaves or presses which have considerable thermal mass. As a consequence, the rates of heatup and cooldown of the bonded parts are limited and the total time and cost of the bonding process is often relatively high. Many of the adhesives themselves do not inherently require long processing times. Bonding could be performed rapidly if the heat was concentrated in the bond lines or at least in the adherends. Rapid adhesive bonding concepts were developed to utilize induction heating techniques to provide heat directly to the bond line and/or adherends without heating the entire structure, supports, and fixtures of a bonding assembly. Bonding times for specimens are cut by a factor of 10 to 100 compared to standard press bonding. The development of rapid adhesive bonding for lap shear specimens (per ASTM D1003 and D3163), for aerospace panel bonding, and for field repair needs of metallic and advanced fiber reinforced polymeric matrix composite structures are reviewed.

Recent advances in heterobimetallic palladium(II)/copper(II) catalyzed domino difunctionalization of carbon-carbon multiple bonds.

PubMed

Beccalli, Egle M; Broggini, Gianluigi; Gazzola, Silvia; Mazza, Alberto

2014-09-21

The double functionalization of carbon-carbon multiple bonds in one-pot processes has emerged in recent years as a fruitful tool for the rapid synthesis of complex molecular scaffolds. This review covers the advances in domino reactions promoted by the couple palladium(ii)/copper(ii), which was proven to be an excellent catalytic system for the functionalization of substrates.

Opioids and social bonding: naltrexone reduces feelings of social connection

PubMed Central

Ray, Lara A.; Irwin, Michael R.; Way, Baldwin M.; Eisenberger, Naomi I.

2016-01-01

Close social bonds are critical to a happy and fulfilled life and yet little is known, in humans, about the neurochemical mechanisms that keep individuals feeling close and connected to one another. According to the brain opioid theory of social attachment, opioids may underlie the contented feelings associated with social connection and may be critical to continued bonding. However, the role of opioids in feelings of connection toward close others has only begun to be examined in humans. In a double-blind, placebo-controlled, crossover study of naltrexone (an opioid antagonist), 31 volunteers took naltrexone for 4 days and placebo for 4 days (separated by a 10-day washout period). Participants came to the laboratory once on the last day of taking each drug to complete a task designed to elicit feelings of social connection. Participants also completed daily reports of feelings of social connection while on naltrexone and placebo. In line with hypotheses, and for the first time in humans, results demonstrated that naltrexone (vs placebo) reduced feelings of connection both in the laboratory and in daily reports. These results highlight the importance of opioids for social bonding with close others, lending support to the brain opioid theory of social attachment. PMID:26796966

Disulfide bond exchanges in integrins αIIbβ3 and αvβ3 are required for activation and post-ligation signaling during clot retraction.

PubMed

Mor-Cohen, Ronit; Rosenberg, Nurit; Averbukh, Yulia; Seligsohn, Uri; Lahav, Judith

2014-05-01

Integrin αIIbβ3 mediates platelet adhesion, aggregation and fibrin clot retraction. These processes require activation of αIIbβ3 and post-ligation signaling. Disulfide bond exchanges are involved in αIIbβ3 and αvβ3 activation. In order to investigate the role of integrin activation and disulfide bond exchange during αIIbβ3- and αvβ3-mediated clot retraction, we co-expressed in baby hamster kidney cells wild-type (WT) human αIIb and WT or mutated human β3 that contain single or double cysteine substitutions disrupting C523-C544 or C560-C583 bonds. Flow cytometry was used to measure surface expression and activation state of the integrins. Time-course of fibrin clot retraction was examined. Cells expressed WT or mutated human αIIbβ3 as well as chimeric hamster/human αvβ3. The αIIbβ3 mutants were constitutively active and the thiol blocker dithiobisnitrobenzoic acid (DTNB) did not affect their activation state. WT cells retracted the clot and addition of αvβ3 inhibitors decreased the retraction rate. The active mutants and WT cells activated by anti-LIBS6 antibody retracted the clot faster than untreated WT cells, particularly in the presence of αvβ3 inhibitor. DTNB substantially inhibited clot retraction by WT or double C523S/C544S mutant expressing cells, but minimally affected single C523S, C544S or C560S mutants. Anti-LIBS6-enhanced clot retraction was significantly inhibited by DTNB when added prior to anti-LIBS6. Both αIIbβ3 and αvβ3 contribute to clot retraction without prior activation of the integrins. Activation of αIIbβ3, but not of αvβ3 enhances clot retraction. Both αIIbβ3 activation and post-ligation signaling during clot retraction require disulfide bond exchange. Copyright © 2014 Elsevier Ltd. All rights reserved.

The marginal effect of bond insurance on hospital, tax-exempt bond yields.

PubMed

Carpenter, C E

1991-01-01

In response to changes in the health care environment and the tax-exempt bond market, many hospitals have purchased bond insurance and other forms of credit enhancement to lower the yields on their debt financings. This study of tax-exempt revenue bonds issued by hospitals from 1982-84 estimates that bond insurance lowers yields on hospital bonds by approximately 87 basis points and that bond insurance serves as a substitute measure of creditworthiness. The findings also suggest that the insured group of hospital bonds is more homogeneous than the uninsured group in terms of characteristics that affect the risks associated with hospital investments. Insured bonds seem to represent hospitals in an intermediate risk group.

Quasi-Monolithic Structures for Spaceflight Using Hydroxide-Catalysis Bonding

NASA Technical Reports Server (NTRS)

Preston, Alix; Thorpe, J. Ira; Miner, Linda

2012-01-01

Future space-based missions will take measurements of the universe with unprecedented results. To do this, these missions will require materials and bonding techniques with ever-increasing stability in order to make their measurements. As an example, the Laser Interferometer Space Antenna (LISA) will detect and observe gravitational waves in the 0.1 mHz to 1 Hz frequency range with strain sensitivities on the order of 10(exp -21) at its most sensitive frequency. To make these measurements, critical components such as the optical bench or telescope support structure, will need to have path-length stabilities of better than 1 pm/(square root)Hz. The baseline construction method for the LISA optical bench is to affix fused silica optical components to a Zerodur baseplate using hydroxide-catalysis bonding (HCB). HCB is a recently developed technique that allows the bonding of glasses, some metals, and silicon carbide with significant strength and stability with a bond thickness of less than a few micrometers. In addition, a wide range of surface profiles can be bonded using only a small amount of hydroxide solution. These characteristics make HCB ideal for adhering optical components in complex optical systems. In addition to being used to construct the LISA optical bench, the HCB technique shows great promise for constructing other structures such as hollow retroreflectors to be used for lunar laser ranging, or a visible nulling coronograph to be used for exo-planet detection. Here we present construction techniques that could be used to make an optical bench, hollow retroreflector, nulling coronograph, or other quasi-monolithic structures using HCB. In addition, we present dimensional stability results of an optical bench that was made using HCB, as well as HCB strength measurements.

Probing the structural evolution and bonding properties of PtnC2-/0 (n = 1-7) clusters by density functional calculations

NASA Astrophysics Data System (ADS)

Lu, Sheng-Jie

2018-05-01

We present a theoretical investigation on the structural evolution and bonding properties of PtnC2-/0 (n = 1-7) clusters using density functional theoretical calculations. The results showed that both anionic and neutral PtnC2 (n = 1-7) clusters primarily adopt 2D planar chain-shaped or ring-based structures. The two C atoms directly interact with each other to form a Csbnd C bond for n = 1-3, while the two C atoms are separated by the Pt atoms for n = 4-7, except for neutral Pt5C2. Pt4C2- anion and Pt4C2 neutral both show σ plus π double delocalized bonding patterns.

Stereocontrolled Additions to a Rigid Bicyclo [3.3.0] Octane Ring System

DTIC Science & Technology

2008-05-05

bridgehead carbon. The metals studied were palladium, platinum, and the Raney nickel catalyst . The catalysts themselves are usually absorbed on an...Catalytic Hydrogenation Reaction The Raney nickel catalyst yielded extremely pure product in a single isomeric form when the reaction was run with...ethyl acetate was 68.7%, a noted increase over that obtained with the Raney nickel catalyst . 31 Disappearance of the double bond peak again

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

46 CFR 171.106 - Wells in double bottoms.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 7 2014-10-01 2014-10-01 false Wells in double bottoms. 171.106 Section 171.106... PERTAINING TO VESSELS CARRYING PASSENGERS Additional Subdivision Requirements § 171.106 Wells in double bottoms. (a) This section applies to each vessel that has a well installed in a double bottom required by...

46 CFR 171.106 - Wells in double bottoms.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 7 2012-10-01 2012-10-01 false Wells in double bottoms. 171.106 Section 171.106... PERTAINING TO VESSELS CARRYING PASSENGERS Additional Subdivision Requirements § 171.106 Wells in double bottoms. (a) This section applies to each vessel that has a well installed in a double bottom required by...

46 CFR 171.106 - Wells in double bottoms.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 7 2013-10-01 2013-10-01 false Wells in double bottoms. 171.106 Section 171.106... PERTAINING TO VESSELS CARRYING PASSENGERS Additional Subdivision Requirements § 171.106 Wells in double bottoms. (a) This section applies to each vessel that has a well installed in a double bottom required by...

46 CFR 171.106 - Wells in double bottoms.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 7 2010-10-01 2010-10-01 false Wells in double bottoms. 171.106 Section 171.106... PERTAINING TO VESSELS CARRYING PASSENGERS Additional Subdivision Requirements § 171.106 Wells in double bottoms. (a) This section applies to each vessel that has a well installed in a double bottom required by...

Reliability improvement of 1 mil aluminum wire bonds for semiconductors, technical performance summary

NASA Technical Reports Server (NTRS)

1971-01-01

The reliability of semiconductor devices as influenced by the reliability of wire bonds used in the assembly of the devices is investigated. The specific type of failure dealt with involves fracture of wire bonds as a result of repeated flexure of the wire at the heel of the bond when the devices are operated in an on-off mode. The mechanism of failure is one of induced fracture of the wire. To improve the reliability of a chosen transistor, one-mil diameter wires of aluminum with various alloy additions were studied using an accelerated fatigue testing machine. In addition, the electroprobe was used to study the metallurgy of the wires as to microstructure and kinetics of the growth of insoluble phases. Thermocompression and ultrasonic bonding techniques were also investigated.

The coevolution of long-term pair bonds and cooperation.

PubMed

Song, Z; Feldman, M W

2013-05-01

The evolution of social traits may not only depend on but also change the social structure of the population. In particular, the evolution of pairwise cooperation, such as biparental care, depends on the pair-matching distribution of the population, and the latter often emerges as a collective outcome of individual pair-bonding traits, which are also under selection. Here, we develop an analytical model and individual-based simulations to study the coevolution of long-term pair bonds and cooperation in parental care, where partners play a Snowdrift game in each breeding season. We illustrate that long-term pair bonds may coevolve with cooperation when bonding cost is below a threshold. As long-term pair bonds lead to assortative interactions through pair-matching dynamics, they may promote the prevalence of cooperation. In addition to the pay-off matrix of a single game, the evolutionarily stable equilibrium also depends on bonding cost and accidental divorce rate, and it is determined by a form of balancing selection because the benefit from pair-bond maintenance diminishes as the frequency of cooperators increases. Our findings highlight the importance of ecological factors affecting social bonding cost and stability in understanding the coevolution of social behaviour and social structures, which may lead to the diversity of biological social systems. © 2013 The Authors. Journal of Evolutionary Biology © 2013 European Society For Evolutionary Biology.

Municipal Bond Insurance Might Enhance Your Next School Bond.

ERIC Educational Resources Information Center

Shapiro, Eric J.

1989-01-01

School systems with a rating of "A" or lower can save money by insuring their bonds because, in almost every instance, the reduced borrowing cost more than offsets the bond insurance premium. Included is a list compiled by Donna Harrington-Lueker of the four major players in the bond insurance field and elements to consider in choosing…

Comparative evaluation of shear bond strength of metallic brackets bonded with two different bonding agents under dry conditions and with saliva contamination.

PubMed

Khanehmasjedi, Mashallah; Naseri, Mohammad Ali; Khanehmasjedi, Samaneh; Basir, Leila

2017-02-01

This study compared the shear bond strength of metallic brackets bonded with Single Bond and Assure bonding agents under dry and saliva-contamination conditions. Sixty sound premolar teeth were selected, and stainless-steel brackets were bonded on enamel surfaces with Single Bond and Assure bonding agents under dry condition or with saliva contamination. Shear bond strength values of brackets were measured in a universal testing machine. The adhesive remnant index scores were determined after debonding of the brackets under a stereomicroscope. One-way analysis of variance (ANOVA) was used to analyze bond strength. Two-by-two comparisons were made with post hoc Tukey tests (p<0.001). Frequencies of adhesive remnant index scores were analyzed by Kruskal-Wallis test. Bond strength values of brackets to tooth structure were 9.29±8.56 MPa and 21.25±8.93 MPa with the use of Assure resin bonding agent under saliva-contamination and dry conditions, respectively. These values were 10.13±6.69 MPa and 14.09±6.6 MPa, respectively, under the same conditions with the use of Single Bond adhesive. Contamination with saliva resulted in a significant decrease in the bond strength of brackets to tooth structure with the application of Assure adhesive resin (p<0.001). There were no significant differences in the adhesive remnant index scores between the study groups. Application of Single Bond and Assure bonding agents resulted in adequate bond strength of brackets to tooth structures. Contamination with saliva significantly decreased the bond strength of Assure bonding agent compared with dry conditions. Copyright © 2016. Published by Elsevier Taiwan LLC.

Simultaneous bond degradation and bond formation during phenol-formaldehyde curing with wood

Treesearch

Daniel J. Yelle; John Ralph

2016-01-01

Bonding of wood using phenol–formaldehyde adhesive develops highly durable bonds. Phenol– formaldehyde is believed to form primary bonds with wood cell wall polymers (e.g., lignin). However, it is unclear how this adhesive interacts and bonds to lignin. Through wood solubilisation methodologies, earlywood and latewood bonded assemblies were characterized using two-...

Disulphide bonds in casein micelle from milk.

PubMed

Bouguyon, Edwige; Beauvallet, Christian; Huet, Jean-Claude; Chanat, Eric

2006-05-05

Mammary epithelial cells synthesised and secreted caseins, the major milk proteins in most mammals, as large aggregates called micelles into the alveolar lumen they surround. We investigated the implication of the highly conserved cysteine(s) of kappa-casein in disulphide bond formation in casein micelles from several species. Dimers were found in all milks studied, confirming previous observation in ruminants. More importantly, the study of interchain disulphide bridges in mouse and rat casein micelles revealed that any casein possessing a cysteine is engaged in disulphide bond interchange; these species express four or five cysteine-containing caseins, respectively. We found that the main rodent caseins form both homo- and heterodimers. Additionally, disulphide bond formation among milk proteins was specific since the interaction of the caseins with cysteine-containing whey proteins was not observed in native casein micelles.

First principles study of the electronic and magnetic structures and bonding properties of UCoC2 ternary, characteristic of C-C units

NASA Astrophysics Data System (ADS)

Matar, Samir F.

2013-03-01

The electronic structure of UCoC2, a di-carbide with the C-C units is examined from ab initio with an assessment of the properties of chemical bonding. The energy-volume equation of state shows large anisotropy effects due to C-C alignment along tetragonal c-axis leading to high linear incompressibility. Relevant features of selective bonding of uranium and cobalt with carbon at two different Wyckoff sites and strong C-C interactions are remarkable. The vibrational frequencies for C⋯C stretching modes indicate closer behavior to aliphatic C-C rather than Cdbnd C double bond. A ferromagnetic ground state is proposed from the calculations.

LIADA's Double Star Section: Studies Of Visual Double Star By Amateurs

NASA Astrophysics Data System (ADS)

Rica, F. M.; Benavides, R.; Masa, E.; Ling, J.

2007-08-01

LIADA's Double Star Section has as main goal to perform measures of relative astrometry of neglected and unconfirmed wide pairs, as well as to determine the astrophysical properties for their components and classify them, according to their nature, as phyisical, common origin, common proper motion or optical pairs. BVIJHK photometry, relative astrometry and kinematical data in addition to other astrophysical parameters, were obtained from literature to characterize the components and the stellar systems. VizieR, Simbad. Aladin and the "services abstract" tools were used from the website of Centre De Données Stellaires de Strasbourg (CDS). USNO catalogs (USNO-B1.0 and UCAC-2) in addition to ESA catalogs (Tycho-2 and HIPPARCOS) were often used. Spectral types, luminosity classes, absolute magnitudes, photometric distances were determined by using several tables, two colours and reduced proper motion diagrams. Astrophysical properties were corrected by reddening by using several maps. CCD cameras, micrometric eyepieces, photographic plates from Digitalized Sky Survey (DSS) and other surveys were used to perform our astrometric measures. According to their nature double stars are classified by using several professional criteria. Since 2001 LIADA has studied about 500 visual double stars, has discovered about 150 true binaries and several candidates to be white dwarfs, subdwarfs and nearby stars. Several orbits have been calculated. Our results were published in national and international journals such as Journal of Double Star Observations (JDSO), in Information Circulars edited by Commision 26 of IAU and our measures were included in WDS catalog. LIADA publish a circular twice a year with our results.

Effect of delayed polymerization time and bracket manipulation on orthodontic bracket bonding

NASA Astrophysics Data System (ADS)

Ponikvar, Michael J.

This study examined the effect of bracket manipulation in combination with delayed polymerization times on orthodontic bracket shear bond strength and degree of resin composite conversion. Orthodontics brackets were bonded to extracted third molars in a simulated oral environment after a set period of delayed polymerization time and bracket manipulation. After curing the bracket adhesive, each bracket underwent shear bond strength testing followed by micro-Raman spectroscopy analysis to measure the degree of conversion of the resin composite. Results demonstrated the shear bond strength and the degree of conversion of ceramic brackets did not vary over time. However, with stainless steel brackets there was a significant effect (p ≤ 0.05) of delay time on shear bond strength between the 0.5 min and 10 min bracket groups. In addition, stainless steel brackets showed significant differences related to degree of conversion over time between the 0.5 min and 5 min groups, in addition to the 0.5 min and 10 min groups. This investigation suggests that delaying bracket adhesive polymerization up to a period of 10 min then adjusting the orthodontic bracket may increase both shear bond strength and degree of conversion of stainless steel brackets while having no effect on ceramic brackets.

Antibacterial activity and ion release of bonding agent containing amorphous calcium phosphate nanoparticles

PubMed Central

Chen, Chen; Weir, Michael D.; Cheng, Lei; Lin, Nancy; Lin-Gibson, Sheng; Chow, Laurence C.; Zhou, Xuedong; Xu, Hockin H. K.

2015-01-01

Objectives Recurrent caries at the margins is a primary reason for restoration failure. The objectives of this study were to develop bonding agent with the double benefits of antibacterial and remineralizing capabilities, to investigate the effects of NACP filler level and solution pH on Ca and P ion release from adhesive, and to examine the antibacterial and dentin bond properties. Methods Nanoparticles of amorphous calcium phosphate (NACP) and a quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM) were synthesized. Scotchbond Multi-Purpose (SBMP) primer and adhesive served as control. DMADDM was incorporated into primer and adhesive at 5% by mass. NACP was incorporated into adhesive at filler mass fractions of 10%, 20%, 30% and 40%. A dental plaque microcosm biofilm model was used to test the antibacterial bonding agents. Calcium (Ca) and phosphate (P) ion releases from the cured adhesive samples were measured vs. filler level and solution pH of 7, 5.5 and 4. Results Adding 5% DMADDM and 10–40% NACP into bonding agent, and water-aging for 28 days, did not affect dentin bond strength, compared to SBMP control at 1 day (p > 0.1). Adding DMADDM into bonding agent substantially decreased the biofilm metabolic activity and lactic acid production. Total microorganisms, total streptococci, and mutans streptococci were greatly reduced for bonding agents containing DMADDM. Increasing NACP filler level from 10% to 40% in adhesive increased the Ca and P ion release by an order of magnitude. Decreasing solution pH from 7 to 4 increased the ion release from adhesive by 6–10 folds. Significance Bonding agents containing antibacterial DMADDM and remineralizer NACP were formulated to have Ca and P ion release, which increased with NACP filler level from 10% to 40% in adhesive. NACP adhesive was “smart” and dramatically increased the ion release at cariogenic pH 4, when these ions would be most-needed to inhibit caries. Therefore, bonding agent

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.

Double-double bend achromat cell upgrade at the Diamond Light Source: From design to commissioning

NASA Astrophysics Data System (ADS)

Bartolini, R.; Abraham, C.; Apollonio, M.; Bailey, C. P.; Cox, M. P.; Day, A.; Fielder, R. T.; Hammond, N. P.; Heron, M. T.; Holdsworth, R.; Kay, J.; Martin, I. P. S.; Mhaskar, S.; Miller, A.; Pulampong, T.; Rehm, G.; Rial, E. C. M.; Rose, A.; Shahveh, A.; Singh, B.; Thomson, A.; Walker, R. P.

2018-05-01

Diamond has recently successfully commissioned a major change in the lattice consisting of the substitution of a standard double-bend achromat (DBA) cell with a modified four-bend achromat (4BA) cell called "double-double bend achromat" (DDBA). This work stems from the original studies initiated in 2012 towards a Diamond upgrade and provides the benefit of an additional straight section in the ring available for insertion devices. This paper reviews the DDBA design and layout, the implications for technical subsystems, the associated engineering challenges and the main results of the commissioning completed in April 2017.

Active mineral additives of sapropel ashes

NASA Astrophysics Data System (ADS)

Khomich, V. A.; Danilina, E. V.; Krivonos, O. I.; Plaksin, G. V.

2015-01-01

The goal of the presented research is to establish a scientific rational for the possibility of sapropel ashes usage as an active mineral additive. The research included the study of producing active mineral additives from sapropels by their thermal treatment at 850900 °C and afterpowdering, the investigation of the properties of paste matrix with an ash additive, and the study of the ash influence on the cement bonding agent. Thermogravimetric analysis and X-ray investigations allowed us to establish that while burning, organic substances are removed, clay minerals are dehydrated and their structure is broken. Sapropel ashes chemical composition was determined. An amorphous ash constituent is mainly formed from silica of the mineral sapropel part and alumosilicagels resulted from clay minerals decomposition. Properties of PC 400 and PC 500A0 sparopel ash additives were studied. Adding ashes containing Glenium plasticizer to the cement increases paste matrix strength and considerably reduces its water absorption. X-ray phase analysis data shows changes in the phase composition of the paste matrix with an ash additive. Ash additives produce a pozzolanic effect on the cement bonding agent. Besides, an ash additive due to the alumosilicagels content causes transformation from unstable calcium aluminate forms to the stable ones.

Influence of hydrophilic pre-treatment on resin bonding to zirconia ceramics.

PubMed

Noro, Akio; Kameyama, Atsushi; Haruyama, Akiko; Takahashi, Toshiyuki

2015-01-01

Atmospheric plasma or ultraviolet (UV) treatment alters the surface characteristics of tetragonal zirconia polycrystal (TZP), increasing its hydrophilicity by reducing the contact angle against water to zero. This suggests that such treatment would increase the wettability of bonding resin. The purpose of this study was to determine how increasing the hydrophilicity of TZP through plasma irradiation, UV treatment, or application of ceramic primer affected initial bonding with resin composites. Here, the effect of each pre-treatment on the hydrophilicity of TZP surfaces was determined by evaluating change in shear bond strength. Plasma irradiation, UV, or ceramic primer pre-treatment showed no significant effect on bonding strength between TZP surfaces and resin composites. In addition, alumina blasting yielded no significant increase in bond strength. Plasma irradiation, UV treatment, or ceramic primer pre-treatment did not lead to significant increase in bond strength between TZP and resin composites.

Oxytocin promotes social bonding in dogs.

PubMed

Romero, Teresa; Nagasawa, Miho; Mogi, Kazutaka; Hasegawa, Toshikazu; Kikusui, Takefumi

2014-06-24

Recent evidence suggests that enduring social bonds have fitness benefits. However, very little is known about the neural circuitry and neurochemistry underlying the formation and maintenance of stable social bonds outside reproductive contexts. Oxytocin (OT), a neuropeptide synthetized by the hypothalamus in mammals, regulates many complex forms of social behavior and cognition in both human and nonhuman animals. Animal research, however, has concentrated on monogamous mammals, and it remains unknown whether OT also modulates social bonds in nonreproductive contexts. In this study we provide behavioral evidence that exogenous OT promotes positive social behaviors in the domestic dog toward not only conspecifics but also human partners. Specifically, when sprayed with OT, dogs showed higher social orientation and affiliation toward their owners and higher affiliation and approach behaviors toward dog partners than when sprayed with placebo. Additionally, the exchange of socio-positive behaviors with dog partners triggered the release of endogenous OT, highlighting the involvement of OT in the development of social relationships in the domestic dog. These data provide new insight into the mechanisms that facilitate the maintenance of close social bonds beyond immediate reproductive interest or genetic ties and complement a growing body of evidence that identifies OT as one of the neurochemical foundations of sociality in mammalian species.

Structural and electronic properties of double-walled boron nitride nanocones

NASA Astrophysics Data System (ADS)

Brito, E.; Silva, T. S.; Guerra, T.; Leite, L.; Azevedo, S.; Freitas, A.; Kaschny, J. R.

2018-01-01

First principles calculations were applied to study the structural and electronic properties of different configurations of double-walled boron nitride nanocones with a disclination angle of 60°. The analysis includes different rotation angles, distance between apexes, as well as distinct types of antiphase boundaries. The calculations indicate that the non-rotated configuration of double-walled nanocone with a defective line composed by C and N atoms, forming C-N bonds, is the most stable configuration. It was found that the yam angle, apexes distance and defective line composition present significant influence on the electronic properties of such structures. Moreover, analyzing the spin charge density, for the electronic states near the Fermi level, it was also found that the configuration with a defective line containing C atoms presents a net magnetic moment.

Can nature's design be improved upon? High strength, transparent nacre-like nanocomposites with double network of sacrificial cross links.

PubMed

Podsiadlo, Paul; Kaushik, Amit K; Shim, Bong Sup; Agarwal, Ashish; Tang, Zhiyong; Waas, Anthony M; Arruda, Ellen M; Kotov, Nicholas A

2008-11-20

The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa.

Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective

PubMed Central

Wolters, Lando P; Bickelhaupt, F Matthias

2012-01-01

We have carried out extensive computational analyses of the structure and bonding mechanism in trihalides DX⋅⋅⋅A− and the analogous hydrogen-bonded complexes DH⋅⋅⋅A− (D, X, A=F, Cl, Br, I) using relativistic density functional theory (DFT) at zeroth-order regular approximation ZORA-BP86/TZ2P. One purpose was to obtain a set of consistent data from which reliable trends in structure and stability can be inferred over a large range of systems. The main objective was to achieve a detailed understanding of the nature of halogen bonds, how they resemble, and also how they differ from, the better understood hydrogen bonds. Thus, we present an accurate physical model of the halogen bond based on quantitative Kohn–Sham molecular orbital (MO) theory, energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. It appears that the halogen bond in DX⋅⋅⋅A− arises not only from classical electrostatic attraction but also receives substantial stabilization from HOMO–LUMO interactions between the lone pair of A− and the σ* orbital of D–X. PMID:24551497

Flow in out-of-plane double S-bonds

NASA Technical Reports Server (NTRS)

Schmidt, M. C.; Whitelaw, J. H.; Yianneskis, M.

1986-01-01

Developing flows in two out-of-plane double S-bend configurations have been measured by laser-Doppler anemometry. The first duct had a rectangular cross-section 40mmx40mm at the inlet and consisted of a uniform area 22.5 deg. - 22.5 deg. S-duct upstream with a 22.5 deg.- 22.5 deg. S- diffuser downstream. The second duct had a circular cross-section and consisted of a 45 deg. - 45 deg. uniform area S-duct upstream with a 22.5 deg. -22.5 deg. S-diffuser downstream. In both configurations the ratio of the mean radius of curvature to the inlet hydraulic diameter was 7.0, the exit-to-inlet area ratio of the diffusers was 1.5 and the ducts were connected so that the centerline of the S-duct lay in a plane normal to that of the S-diffuser. Streamwise and cross-stream velocity components were measured in laminar flow for the rectangular duct and in turbulent flow for both configurations; measurements of the turbulence levels, cross-correlations and wall static pressures were also made in the turbulent flow cases. Secondary flows of the first kind are present in the first S-duct and they are complemented or counteracted by the secondary flows generated by the area expansion and by the curvature of the S-diffusers downstream. Cross-stream velocities with magnitudes up to 0.19 and 0.11 of the bulk velocity were measured in the laminar and turbulent flows respectively in the rectangular duct and six cross-flow vortices were evident at the exit of the duct in both flow cases. The turbulent flow in the circular duct was qualitatively similar to that in the rectangular configuration, but the cross-stream velocities measured at the exit plane were smaller in the circular geometry. The results are presented in sufficient detail and accuracy for the assessment of numerical calculation methods and are listed in tabular form for this purpose.

Carbon-fluorine bond activation coupled with carbon-hydrogen bond formation alpha to iridium: kinetics, mechanism, and diastereoselectivity.

PubMed

Garratt, Shaun A; Hughes, Russell P; Kovacik, Ivan; Ward, Antony J; Willemsen, Stefan; Zhang, Donghui

2005-11-09

Reactions of iridium(fluoroalkyl)hydride complexes CpIr(PMe(3))(CF(2)R(F))Y (R(F) = F, CF(3); Y = H, D) with LutHX (Lut = 2,6-dimethylpyridine; X = Cl, I) results in C-F activation coupled with hydride migration to give CpIr(PMe(3))(CYFR(F))X as variable mixtures of diastereomers. Solution conformations and relative diastereomer configurations of the products have been determined by (19)F{(1)H}HOESY NMR to be (S(C), S(Ir))(R(C), R(Ir)) for the kinetic diastereomer and (R(C), S(Ir))(S(C), R(Ir)) for its thermodynamic counterpart. Isotope labeling experiments using LutDCl/CpIr(PMe(3))(CF(2)R(F))H and CpIr(PMe(3))(CF(2)R(F))D/LutHCl) showed that, unlike a previously studied system, H/D exchange is faster than protonation of the alpha-CF bond, giving an identical mixture of product isotopologues from both reaction mixtures. The kinetic rate law shows a first-order dependence on the concentration of iridium substrate, but a half-order dependence on that of LutHCl; this is interpreted to mean that LutHCl dissociates to give HCl as the active protic source for C-F bond activation. Detailed kinetic studies are reported, which demonstrate that lack of complete diastereoselectivity is not a function of the C-F bond activation/H migration steps but that a cationic intermediate plays a double role in loss of diastereoselectivity; the intermediate can undergo epimerization at iridium before being trapped by halide and can also catalyze the epimerization of kinetic diastereomer product to thermodynamic product. A detailed mechanism is proposed and simulations performed to fit the kinetic data.

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.

Structure-spectrophotometric selectivity relationship in interactions of quercetin related flavonoids with double stranded and single stranded RNA

NASA Astrophysics Data System (ADS)

Piantanida, Ivo; Mašić, Lozika; Rusak, Gordana

2009-04-01

Interactions of five flavonoids with dsRNA and single stranded ssRNA were studied by UV/vis titrations. The results obtained supported the intercalative binding mode as a dominant interaction of studied flavonoids with dsRNA as well as major interaction with ssRNA. Furthermore, changes of the UV/vis spectra of flavonoids induced by addition of poly G or poly C, respectively, are significantly stronger than changes induced by double stranded poly G-poly C, pointing to essential role of the free poly G or poly C sequence (not hydrogen bonded in double helix). Exclusively poly G caused significant batochromic shift of the UV/vis maxima of all studied flavonoids, whereby the intensity of batochromic shift is nicely correlated to the number of OH groups of flavonoid. Unlikely to poly G, addition of poly A and poly U induced measurable changes only in the UV/vis spectra of flavonoids characterised by no OH (galangin) or three OH groups (myricetin) on the phenyl part of the molecule. Consequently, flavonoids with one- or two-OH groups on the phenyl part of the molecule (luteolin, fisetin, kaempferol) specifically differentiate between poly A, poly U (negligible changes in the UV/Vis spectra) and poly G (strong changes in the UV/Vis spectra) as well as poly C (moderate changes in the UV/Vis spectra).

Direction-dependent secondary bonds and their stepwise melting in a uracil-based molecular crystal studied by infrared spectroscopy and theoretical modeling

NASA Astrophysics Data System (ADS)

Szekrényes, Zsolt; Nagy, Péter R.; Tarczay, György; Maggini, Laura; Bonifazi, Davide; Kamarás, Katalin

2018-01-01

Three types of supramolecular interactions are identified in the three crystallographic directions in crystals of 1,4-bis[(1-hexylurac-6-yl) ethynyl]benzene, a uracil-based molecule with a linear backbone. These three interactions, characterized by their strongest component, are: intermolecular double H-bonds along the molecular axis, London dispersion interaction of hexyl chains connecting these linear assemblies, and π - π stacking of the aromatic rings perpendicular to the molecular planes. On heating, two transitions happen, disordering of hexyl chains at 473 K, followed by H-bond melting at 534 K. The nature of the bonds and transitions was established by matrix-isolation and temperature-dependent infrared spectroscopy and supported by theoretical computations.

Influence of cleaning methods on resin bonding to saliva-contaminated zirconia.

PubMed

Yoshida, Keiichi

2018-02-08

The aim of this study was to investigate the influence of different cleaning methods on the shear bond strengths of 2 resin cements to saliva-contaminated zirconia. After saliva contamination, alumina-blasted zirconia specimens were cleaned with 1 of 5 methods of water-rinsing (SA), K-etchant GEL phosphoric acid (PA), Ivoclean (IC), AD Gel (ADG), or additional alumina-blasting (AB). Alumina-blasted zirconia without saliva contamination was used as control group (Cont). Composite cylinders were bonded to the zirconia with 1 of 2 dual-cured resin cements. The bond strengths were measured by shear testing after 24 hours (TC0) and after thermal cycling at 4°C-60°C (TC10 000) and specimen surfaces were evaluated using X-ray photoelectron spectroscopy (XPS). Data were statistically analyzed using 3-way analysis of variance and Tukey test (α = 0.05). There were no significant differences in the bond strengths of 2 resin cements between the Cont ADG, and AB groups before and after TCs (P > .05). SA, PA, and IC groups did not exhibit durable resin bonding to zirconia. XPS showed that carbon and nitrogen increased in the SA group in comparison to the Cont group. The concentration of carbon in other 4 groups returned to the concentration range of the Cont group; however, nitrogen was not detected in the only AB group. Saliva contamination significantly reduced the bond strength of 2 resin cements to zirconia. Additional AB or cleaning with ADG resulted in effective cleaning of saliva contamination and preserved resin cement bond strength to zirconia. Saliva contamination occurs during clinical procedures for adjustment of zirconia ceramic restorations in the oral environment. AD Gel application is effective for removing saliva contaminants on the alumina-blasted zirconia surface beforehand by the dental laboratory instead of additional AB since AD Gel application and AB had a similar effect on the removal of organic components of saliva. © 2018 Wiley Periodicals

29 CFR 2580.412-19 - Term of the bond, discovery period, other bond clauses.

Code of Federal Regulations, 2010 CFR

2010-07-01

... SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules § 2580.412-19 Term of the bond, discovery... 29 Labor 9 2010-07-01 2010-07-01 false Term of the bond, discovery period, other bond clauses... new bond must be obtained each year. There is nothing in the Act that prohibits a bond for a term...

[The bonding mechanisms of base metals for metal-ceramic crown microstructure analysis of bonding agent and gold bond between porcelain and base metals].

PubMed

Wang, C C; Hsu, C S

1996-06-01

The use of base metal alloys for porcelain fused to a metal crown and bridges has increased recently because of lower price, high hardness, high tensile strength and high elastic modulus. The addition of beryllium to base metal alloys increased fluidity and improved casting fitness. Beryllium also controlled surface oxidation and bonding strength. The bonding agent and gold bonding agent also affected the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys were studied (two alloys contained beryllium element, another two did not). The purpose of this investigation was to study the microstructure between porcelain matrix, bonding agent and alloy matrix interfaces. A scanning electron micro-probe analyzer and energy dispersive X-ray spectroscopy (EDXS) were used to study the distribution of elements (Ni, Cr, Mo, Cu, O, Si, Sn, Al) in four base alloys. The following results were obtained: 1. The thickness of the oxidized layer of Rexillium III alloy and Unitbond alloy (contained beryllium) was thinner than Unibond alloy and Wiron 88 alloy (no beryllium). 2. The thickness of the oxidized layer of alloys in air (10 minutes and 30 minutes) was thinner in Unitbond (2.45 microns and 3.80 microns) and thicker in Wiron 88 (4.39 microns and 5.96 microns). 3. The thickness of the oxidized layer occurring for a duration of ten minutes (in vaccum) showed that the Rexillium III alloy was the thinnest (1.93 microns), and Wiron 88 alloy was the thickest (2.30 microns). But in thirty minutes (vacuum), Unitbond alloy was the thinnest (3.37 microns), and Wiron 88 alloy was the thickest (5.51 microns). 4. The intensity of Cr elements was increased obviously near the interface between Unitbond alloy, Wiron 88 alloy (no beryllium) and oxidized layer, but the intensity of Ni and Mo elements was slightly increased. The intensity of Cr element was not increased markedly between Rexillium III alloy, Unitbond alloy (beryllium) and oxidized

Hydrogen-bonded side chain liquid crystalline block copolymer: Molecular design, synthesis, characterization and applications

NASA Astrophysics Data System (ADS)

Chao, Chi-Yang

combinations were carried out to investigate the interplay between morphology, mesophase behavior and blend composition (molar ratios of proton acceptors to proton donors). A critical composition for mesophase formation was identified and the characteristics of the H-bonded complexes below the critical blend ratios were very different than those above. Hydrogen bonding was also used to direct microphase separation of miscible poly(hydroxystyrene-b-methyl methacrylate) diblock copolymer by adopting imidazolyl additives able to hydrogen bond with poly(hydroxystyrene). The miscibility between PHS and PMMA segments was diminished significantly by introducing small quantities of H-binding additives. The critical blend ratio for microphase separation was determined more by the molecular structure of the additives than the number of hydrogen bonds formed between PHS and additives.

Low-temperature poly(oxymethylene) direct bonding via self-assembled monolayer

NASA Astrophysics Data System (ADS)

Fu, Weixin; Ma, Bo; Kuwae, Hiroyuki; Shoji, Shuichi; Mizuno, Jun

2018-02-01

A direct bonding of poly(oxymethylene) (POM) was feasible at 100 °C by using self-assembled monolayer (SAM) as a surface modification method. (3-aminopropyl)triethoxysilane (APTES) and (3-glycidyloxypropyl)trimethoxysilane (GOPTS) were used in our work. X-ray photoelectron spectroscopy showed that both APTES and GOPTS modified the POM surface successfully. Bonding strength evaluation revealed that surface modification was affected by pretreatment (VUV/O3) process time. In addition, the bonding condition with highest strength had an average strength of 372 kPa. This technology is expected to be used in packaging for micro-/nano-electromechanical systems, such as biomedical devices.

Periodic trends in bond dissociation energies. A theoretical study.

PubMed

Mó, Otilia; Yáñez, Manuel; Eckert-Maksić, Mirjana; Maksić, Zvonimir B; Alkorta, Ibón; Elguero, José

2005-05-19

Bond dissociation energies (BDEs) of all possible A-X single bonds involving the first- and second-row atoms, from Li to Cl, where the free valences are saturated by hydrogens, have been estimated through the use of the G3-theory and at the B3LYP/6-311+G(3df,2pd)//B3LYP/6-31G(2df,p) DFT level of theory. BDEs exhibit a periodical behavior. The A-X (A = Li, Be, B, Na, Mg, Al, and Si) BDEs show a steady increase along the first and the second row of the periodic table as a function of the atomic number Z(X). For A-X bonds involving electronegative atoms (A = C, N, O, F, P, S, and Cl) the bond energies achieve a maximum around Z(X) = 5. The same behavior is observed when BDEs are plotted against the electronegativity chi(X) of the atom X. Thus, for A-X bonds (A = Li, Be, B, Na, Mg, Al, Si), the BDEs for a fixed A increases, grosso modo, as the electronegativity differences between X and A increase, with some exceptions, which reflect the differences in the relaxation energies of the radicals produced upon the bond cleavage. A similar trend, albeit less pronounced, is found for single A-X bonds, where A = C, N, O, F, P, S, and Cl. However, there is an additional feature embodied in the enhancement of the strength of the A-boron bonds due to the ability of boron to act as a strong electron acceptor. The trends in bond lengths and charge densities at the bond critical points are in line with the aforementioned behavior.