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## Shear bond strength of adhesive systems to enamel and dentin. Thermocycling influence

Dos Santos, Patrícia Aleixo; Garcia, Patrícia Petromilli Nordi Sasso; Palma-Dibb, Regina Guenka
Tipo: Artigo de Revista Científica Formato: 727-732
ENG
Relevância na Pesquisa
46.22%
Objectives: The purpose of the this study was to evaluate the influence of thermocycling on shear bond strength on bovine enamel and dentin surfaces of different adhesive systems. Methods: Thirty sound bovine incisors were sectioned in mesiodistal and inciso-cervical direction obtaining 60 incisal surfaces (enamel) and 60 cervical surfaces (dentin). Specimens were randomly assigned to 3 groups of equal size (n = 40), according to the adhesive system used: I-Single Bond; II-Prime & Bond NT/NRC; III-One Coat Bond. After 24-h storage in distilled water at 37 o C, each main group was divided into two subgroups: A- specimens tested after 24 h storage in distilled water at 37°C; B - specimens submitted to thermocycling (500 cycles). Shear bond strength tests were performed. Data were submitted to ANOVA and Tukey test. Results: Means (MPa) of different groups were: I-AE-16.96, AD-17.46; BE-21.60, BD-12.79; II-AE-17.20, AD-11.93; BE-20.67, BD-13.94; III-AE-25.66, AD-17.53; BE-24.20, BD-19.38. Significance: Thermocycling did not influence significantly the shear bond strength of the tested adhesive systems; enamel was the dental substrate that showed larger adhesive strength; One Coat Bond system showed the best adhesive strength averages regardless of substrate or thermocycling. © 2005 Springer Science + Business Media...

## Evaluation of the chemical interaction between carbon nanotubes functionalized with TGDDM tetrafunctional resin and hardener DDS

Edwards, E. R.; Kostov, K. G.; Botelho, E. C.
Tipo: Artigo de Revista Científica Formato: 197-203
ENG
Relevância na Pesquisa
46.15%
In this work, the chemical interaction between carbon nanotubes (MWCNT) functionalized with acyl chloride (SOCl2) and polymer chain tetrafuncional N,N,N′,N′-tetraglycidyl-4,4′- diaminodiphenylmethane (TGDDM) and hardener 4,4′diaminodiphenyl sulfone (DDS) has been monitored by Fourier transform infrared spectroscopy (FTIR) with a attenuated total reflectance (ATR) coupled. MWCNT were obtained from the pyrolysis of a mixture of camphor and ferrocene into a oven. The functionalization process was done by oxidative treatment in order to incorporate carboxylic group over the walls of MWCNT, before to be used SOCl2. The functionalized carbon nanotubes were evaluated by X-ray photoelectron spectroscopy (XPS), Raman and transmission electron microscopy (TEM). Nanostructured composites were processed by using epoxy resin with MWCNT in varying percentages. In this work it was observed that different percentages of functionalized nanotubes modify the interaction between the composite matrix and curing agent, where can be observed that in specimens with content less than 1 wt% MWCNT the chemical bond occurs preferentially from the opening of the SO double bond of the hardener and when is used MWCNT content higher than 1 wt% there is little chemical interaction with the SO bond of the hardener and most MWCNT binds to amine. © 2013 Elsevier Ltd.

## The nature of the chemical bond

Nascimento,Marco Antonio Chaer
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
66.3%
In this paper we briefly review the basic requirements that must be satisfied by any wave function representing many-electron systems. Following that, we examine the conditions under which the classical concepts of molecular structure, chemical structure and chemical bond can be translated into a quantum-mechanical language. Essential to this aim is the utilization of an independent particle model (IPM) for a many-electron system. In spite of the great popularity of the Hartree-Fock (HF) model only Valence-Bond (VB) type wave functions with optimized, singly occupied and non necessarily orthogonal atomic-like orbitals, can provide a quantum-mechanical translation of the classical concepts of chemical structure and chemical bond, although the HF model can still be useful for translating the concept of molecular structure. Finally, a quantum-dynamical-type of analysis allows us to conclude that, from the quantum mechanical point of view, the chemical bond is a consequence of interference effects. From the energetic point of view, the interference effect responsible for the bond formation manifests itself as a reduction of the kinetic energy of the electrons as the bond is formed.

## Electron energy-loss cross sections for the chemical bond overlap plasmon Of the hydrogen molecule

Malta,Oscar L.; Moura Jr.,Renaldo T.; Longo,Ricardo L.
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
56.11%
We examine the possibility of detecting the chemical bond overlap plasmon (CBOP) of the hydrogen molecule by electron inelastic scattering. The CBOP has been predicted to efficiently absorb and scatter electromagnetic radiation above the molecular ionization threshold in the cases of alkali halides. For the hydrogen molecule the quadrupole nature of the CBOP energy-loss cross section leads to cross section values with impacting electron energy dependence and an angular behavior which are totally distinguishable from the usual ionization, inter-band transitions and dissociation processes. Previously established relationships between the CBOP and the polarizability of the overlap region suggest this an a promising theoretical tool for quantifying covalency in the chemical bond.

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

Aragoni, M. Carla; Arca, Massimiliano; Devillanova, Francesco A.; Garau, Alessandra; Isaia, Francesco; Lippolis, Vito; Mancini, Annalisa
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.16%
The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3− and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat...

## The Bondons: The Quantum Particles of the Chemical Bond

Putz, Mihai V.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.14%
By employing the combined Bohmian quantum formalism with the U(1) and SU(2) gauge transformations of the non-relativistic wave-function and the relativistic spinor, within the Schrödinger and Dirac quantum pictures of electron motions, the existence of the chemical field is revealed along the associate bondon particle B̶ characterized by its mass (mB̶), velocity (vB̶), charge (eB̶), and life-time (tB̶). This is quantized either in ground or excited states of the chemical bond in terms of reduced Planck constant ħ, the bond energy Ebond and length Xbond, respectively. The mass-velocity-charge-time quaternion properties of bondons’ particles were used in discussing various paradigmatic types of chemical bond towards assessing their covalent, multiple bonding, metallic and ionic features. The bondonic picture was completed by discussing the relativistic charge and life-time (the actual zitterbewegung) problem, i.e., showing that the bondon equals the benchmark electronic charge through moving with almost light velocity. It carries negligible, although non-zero, mass in special bonding conditions and towards observable femtosecond life-time as the bonding length increases in the nanosystems and bonding energy decreases according with the bonding length-energy relationship Ebond[kcal/mol]×Xbond[A0]=182019...

## Carbon-nitrogen bond-forming reactions in supercritical and expanded-liquid carbon dioxide media : green synthetic chemistry with multiscale reaction and phase behavior modeling; Green synthetic chemistry with multiscale reaction and phase behavior modeling

Ciccolini, Rocco P
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 338 p.
ENG
Relevância na Pesquisa
46.14%
The goal of this work was to develop a detailed understanding of carbon-nitrogen (C-N) bond-forming reactions of amines carried out in supercritical and expanded-liquid carbon dioxide (CO2) media. Key motivations behind this study were the importance of nitrogen-containing compounds in the pharmaceutical and fine chemical industries and a growing commercial interest in utilizing environmentally-friendly syntheses and processing with cost-efficient, green solvents. The thermodynamics and reaction engineering characteristics associated with the synthesis of several model C-N bond-forming reactions were examined both experimentally and theoretically. Operating conditions and engineering correlations were identified that will facilitate process scale-up and potential commercialization of these and other fundamentally-important CO2-based processes. Amine chemistry in CO2-based media was complicated by the facility of nucleophilic amines to react with carbon dioxide to form carbamic acids, which sometimes interfered with desired reaction pathways. Experimental observations and a complimentary ab initio quantum chemical calculation study revealed that carbamic acid formation was suppressed when adding bulky N-substituents to primary amines and when operating at low pressures and/or high temperatures. With a firm understanding of amine-CO2 chemistry...

## Bond strengths between composite resin and auto cure glass ionomer cement using the co-cure technique

Knight, G.; McIntyre, J.; Mulyani
Fonte: Australian Dental Assn Inc Publicador: Australian Dental Assn Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.24%
Background: The clinical technique for sandwich restorations prescribes etching initially set auto cure glass ionomer cement (GIC) prior to placing a layer of resin bond to develop a weak mechanical bond between composite resin and GIC. Co-curing a resin modified glass ionomer cement (RMGIC) bond and composite resin to GIC may create a chemical bond and improve the bond strengths between these two materials. Methods: A total of 48 specimens were prepared, 12 in each of four categories. Capsulated GIC was placed into a mould and allowed to set for four minutes, etched for five seconds followed by placement of a resin bond and photo cured for five seconds over which a composite resin was puddled onto the resin bond and photo cured for 10 seconds. Capsulated GIC was placed into a mould and allowed to set for four minutes after which a sample of RMGIC (Riva LC) was prepared using twice the liquid powder ratio and painted over the surface of the set GIC using a micro brush. An increment of composite resin was added over the RMGIC and both materials were photo co-cured for 10 seconds. Capsulated GIC was placed into a mould and RMGIC (Riva LC) that had been prepared using twice the liquid powder was brushed over the GIC (prior to initial set) followed by the placement of a layer of composite resin and photo co-cured for 10 seconds. Capsulated GIC was placed into a mould and RMGIC (Fuji II LC) that had been prepared using twice the liquid powder was brushed over the GIC (prior to initial set) followed by the placement of a layer of composite resin and photo co-cured for 10 seconds. Shear testing of each of the samples was carried out and specimens were examined to determine the nature of the fracture. Selected samples were prepared for SEM investigation to observe the interfaces between the GIC and composite resin. Results: There were significantly lower bond strengths (P<0.05) amongst samples that had been etched and bonded (2.42MPa) compared to the other samples that had been co-cure bonded with RMGIC (6.48–7.05MPa). There were no significantdifferences amongst the bond strengths of the samples co-cure bonded with RMGIC. Specimens prepared by the ‘etch and bond’ technique failed adhesively and co-cured specimens failed cohesively within the GIC. SEM investigation showed chemical bonds between RMGIC bond and GIC and composite resin. Conclusions: The co-cured RMGIC bonding system eliminates several placement steps and produces a significantly stronger chemical bond between GIC and composite resin than the ‘etch and bond’ technique. RMGIC bond and composite resin may be co-cured to GIC either before or after initial set has occurred.; The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.

## The genesis of the quantum theory of the chemical bond

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.1%
An historical overview is given of the relevant steps that allowed the genesis of the quantum theory of the chemical bond, starting from the appearance of the new quantum mechanics and following later developments till approximately 1931. General ideas and some important details are discussed concerning molecular spectroscopy, as well as quantum computations for simple molecular systems performed within perturbative and variational approaches, for which the Born-Oppenheimer method provided a quantitative theory accounting for rotational, vibrational and electronic states. The novel concepts introduced by the Heitler-London theory, complemented by those underlying the method of the molecular orbitals, are critically analyzed along with some of their relevant applications. Further improvements in the understanding of the nature of the chemical bond are also considered, including the ideas of one-electron and three-electron bonds introduced by Pauling, as well as the generalizations of the Heitler-London theory firstly performed by Majorana, which allowed the presence of ionic structures into homopolar compounds and provided the theoretical proof of the stability of the helium molecular ion. The study of intermolecular interactions, as developed by London...

## The New Resonating Valence Bond Method for Ab-Initio Electronic Simulations

Sorella, Sandro; Zen, Andrea
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.2%
The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.

## A dynamical model of the chemical bond

Hofmann, Holger F.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.23%
A new approach to chemical bonding is introduced in order to provide an improved understanding of the connection between basic quantum mechanics and the covalent pair bond. It's focus is on the fact that the energy of the bond is largely given by the kinetic energy of the electrons, while the Coulomb forces are only comparable to the kinetic energy terms close to the atomic nuclei, where they define the shape and the size of the atomic orbitals. If atomic orbitals are used as a starting point, the kinetic energy operator is sufficient to determine the energy of the chemical bond. The simple mathematical structure of this operator allows a calculation of bond energy as a function of the distance between the atoms. For Gaussian wavefunctions, it is possible to calculate this bonding potential analytically, determining the bond length, the bond energy and the elasticity of the bond from only a single parameter, the width of the atomic wavefunction. It is shown that the results correspond surprisingly well with experimental values for diatomic molecules.; Comment: 9 pages RevTex and 3 figures, to be published in European Journal of Physics

## Are there missing bond paths in Trimethylenemethane-Iron-tri-carbonyl [(CO)3Fe-(C4H6)] complex?

Shahbazian, Shant
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.24%
In a recent paper [J. Organomet. Chem. (2013) doi: 10.1016 /j.jorganchem. 2013.03.047] analyzing the bonding mode of Trimethylenemethane (TMM) with some metal carbonyls, Mousavi and Frenking have declared the absence of bond paths, the so-called missed bond paths, between metal atoms and terminal carbon atoms in several complexes. In this communication, it is first demonstrated that the presupposition of the equivalence of a bond path and a chemical bond within the context of the quantum theory of atoms in molecules (QTAIM) is superficial and basically flawed which is not only against with the recent strict declaration on the contrary [R.F.W. Bader, J. Phys. Chem. A 113 (2009) 10396], but also in odd with the foundations of the QTAIM. Then, it is demonstrated that the so-called missed bond paths indeed appear in molecular graphs of some non-equilibrium geometries that are energetically quite accessible at room temperatures. To emphasize on the importance of this observation the term passionate neighbors is coined referring to the atomic basins that do not share an inter-atomic surface at the equilibrium geometry but are neighbors, share an inter-atomic surface, at non-equilibrium geometries accessible by nuclear vibrations. Using the delocalization index as well as other evidence from previous literature it is demonstrated that the QTAIM analysis is indeed compatible with the presence of chemical bonds between iron metal and terminal carbons in (CO)3Fe-TMM complex. Finally...

## A Corpuscular Picture of Electrons in Chemical Bond

Ando, Koji
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.12%
We introduce a theory of chemical bond with a corpuscular picture of electrons. It employs a minimal set of localized electron wave packets with 'floating and breathing' degrees of freedom and the spin-coupling of non-orthogonal valence-bond theory. It accurately describes chemical bonds in ground and excited states of spin singlet and triplet, in a distinct manner from conventional theories, indicating potential for establishing a dynamical theory of electrons in chemical bonds.; Comment: 4 pages, 4 figures

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

Ravaine, Boris; Porsev, Sergey G.; Derevianko, Andrei
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.06%
Heavy polar molecules offer a great sensitivity to the electron Electric Dipole Moment(EDM). To guide emerging searches for EDMs with molecular ions, we estimate the EDM-induced energy corrections for hydrogen halide ions $\mathrm{HBr}^{+}$ and $\mathrm{HI}^{+}$ in their respective ground $X ^2\Pi_{3/2}$ states. We find that the energy corrections due to EDM for the two ions differ by an unexpectedly large factor of fifteen. We demonstrate that a major part of this enhancement is due to a dissimilarity in the nature of the chemical bond for the two ions: the bond that is nearly of ionic character in $\mathrm{HBr}^{+}$ exhibits predominantly covalent nature in $\mathrm{HI}^{+}$. We conclude that because of this enhancement the HI$^+$ ion may be a potentially competitive candidate for the EDM search.; Comment: This manuscript has been accepted for publication in Physical Review Letters. The paper is now being prepared for publication

## Majorana, Pauling and the quantum theory of the chemical bond

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.02%
We discuss in detail very little known results obtained by Majorana as early as 1931, regarding the quantum theory of the chemical bond in homopolar molecules, based on the key concept of exchange interaction. After a brief historical overview of the quantum homopolar valence theory, we address the intriguing issues of the formation of the helium molecular ion, He2+, and of the accurate description of the hydrogen molecule, H2. For the first case, the group theory-inspired approach used by Majorana is contrasted with that more known followed by Pauling (and published few months after that of Majorana), while for the second case we focus on his proposal concerning the possible existence of ionic structures in homopolar compounds, just as in the hydrogen molecule. The novelty and relevance of Majorana's results in the modern research on molecular and chemical physics is emphasized as well.; Comment: amsart, 17 pages, no figures

## Concept of chemical bond and aromaticity based on quantum information theory

Szilvási, T.; Barcza, G.; Legeza, Ö.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.2%
Quantum information theory (QIT) emerged in physics as standard technique to extract relevant information from quantum systems. It has already contributed to the development of novel fields like quantum computing, quantum cryptography, and quantum complexity. This arises the question what information is stored according to QIT in molecules which are inherently quantum systems as well. Rigorous analysis of the central quantities of QIT on systematic series of molecules offered the introduction of the concept of chemical bond and aromaticity directly from physical principles and notions. We identify covalent bond, donor-acceptor dative bond, multiple bond, charge-shift bond, and aromaticity indicating unified picture of fundamental chemical models from ab initio.; Comment: 7 pages, 3 figures

## El enlace químico : una conceptualización poco comprendida

Riboldi, Liliana; Pliego, Óscar; Odetti, Héctor
Tipo: Article; info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Relevância na Pesquisa
46.14%
Este estudio describe las ideas sobre los enlaces químicos de un grupo de estudiantes que iban a comenzar la universidad y las de otro de estudiantes universitarios. Los resultados muestran distintas ideas con respecto a: procesos donde átomos iguales o distintos se agrupan, la posibilidad de que una unión química sea un proceso espontáneo, la estructura de sustancias unidas por enlace iónico o covalente y la causa de un enlace iónico. Resalta también el pobre grado de coherencia de las concepciones manifestada cuando los estudiantes usan una idea en un contexto pero no en otro similar. La investigación encuentra que las concepciones de los alumnos universitarios y preuniversitarios son las mismas en la mayoría de los casos.; This study describes the ideas about chemical bond of a group of students about to enter university studies and another already at university. The results show different ideas with respect to processes where similar or different atoms group, the possibility of a chemical bond being a spontaneous process, the structure of substances bonding by ionic or covalent bond, and the cause of ionic bond. The study also highlights the poor coherency shown when students use an idea in a certain context but not in another similar to the first. The research finds that the conceptions of university and pre-university students coincide in most cases.

## Variable Trends in R-X Bond Dissociation Energies (R = Me, Et, i -Pr, t -Bu)

Coote, Michelle; Pross, Andy; Radom, Leo
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.01%
(Equation presented) High level ab initio molecular orbital calculations confirm experimental indications that the effect of alkyl substituents (R = Me, Et, i-Pr, t-Bu) on R-X bond dissociation energies varies considerably according to the nature of X. A

## Mechanism of Phosphorus-Carbon Bond Cleavage by Lithium in Tertiary Phosphines. An Optimized Synthesis of 1,2-Bis(phenylphosphino)ethane

Dogan, John; Schulte, Jurgen; Swiegers, Gerhard; Wild, Stanley (Bruce)
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.14%
Conditions influencing the extent of P-C(aryl) vs P-C(alkyl) bond cleavage in the reaction of Ph2P(CH2)2PPh2 with lithium in THF have been investigated. The results complement and elucidate earlier work; they indicate that the mechanism of P-C bond cleavage in tertiary phosphines of this type involves a thermodynamic equilibrium between P-C(aryl) and P- C(alkyl) cleaved radicals and anions, followed by reaction and stabilization of these as lithium salts. The addition of water to the reaction mixture causes a reestablishment of the cleavage equilibrium prior to the formation of the secondary phosphines. A mechanism involving competitive release of leaving groups as the thermodynamically most stable anion or radical has been proposed. The preparation of (R*, R*)-(±)/(R*, S*)-PhP(H)(CH2)2P(H)Ph by this route has been optimized.

## Electrochemically informed synthesis and characterization of salts of the [Pt 2 ( μ-κAs,κC -C 6 H 3 -5-Me-2-AsPh 2 ) 4 ] + lantern complex containing a Pt?Pt bond of order

Bennett, Martin; Bhargava, Suresh Kumar; Boas, John; Boere, Rene; Bond, I A; Edwards, Alison; Guo, Si-Xuan; Hammerl, Anton; Pilbrow, John; Priver, Steven H; Schwerdtfeger, Peter
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.01%
Detailed electrochemical studies in dichloromethane (0.1 M Bu 4NPF6) on the oxidation of the half-lantern [Pt 2(κ2As,C-C6H3-5-Me-2-AsPh 2)2(μ-κAs,κC-C6H 3-5-Me-2-AsPh2)2] (1) and full-lantern [Pt 2(μ-κAs,κC-C6H3-5-Me-2-AsPh 2)4] (2) complexes revea