Search results for "bonding"
showing 10 items of 996 documents
Effect of endodontic treatment on fatigue resistance of fiber posts bonding
2003
Objectives: The aim of this study is to evaluate the effect of the endodontic treatment on the fatigue resistance of endodontic post adhesive interfaces. Materials and methods: 50 single-rooted human teeth have been severed at the cement-enamel junction and randomly assigned to 5 groups receiving different endodontic treatments as follows: 1) distilled water + gutta-percha (control); 2) NaOCl 5% + gutta-percha and Pulp Canal Sealer EWT (Kerr); 3) NaOCl 5% + gutta-percha and Top Seal (Dentsply-Maillefer); 4) NaOCl 5% and EDTA 10% (alternatively) + gutta-percha and Pulp Canal Sealer EWT; 5) NaOCl 5% and EDTA 10% (alternatively) + gutta-percha and Top Seal. Subsequently, Light-Post DT #2 quart…
Solubility and solvation features of native cyclodextrins in 1-ethyl-3-methylimidazolium acetate
2022
The comprehension of the mechanism entailing efficient solvation of cyclodextrins (CD) by green solvents is of great relevance to boost environmentally sustainable usages of smart supramolecular systems. Here, 1-ethyl-3- methylimidazolium acetate, an ecofriendly ionic liquid (IL), is considered as an excellent solvent for native CDs. This IL efficiently dissolves up to 40 wt.% β- and γ-CD already at ambient temperature and X-ray scattering indicates that CDs do not tend to detrimental flocculation under these drastic concentration conditions. Simu- lation techniques reveal the intimate mechanism of CD solvation by the ionic species: while the strong hydrogen bonding acceptor acetate anion i…
Three-dimensional solvation structure of ethanol on carbonate minerals
2020
Calcite and magnesite are important mineral constituents of the earth’s crust. In aqueous environments, these carbonates typically expose their most stable cleavage plane, the (10.4) surface. It is known that these surfaces interact with a large variety of organic molecules, which can result in surface restructuring. This process is decisive for the formation of biominerals. With the development of 3D atomic force microscopy (AFM) it is now possible to image solid–liquid interfaces with unprecedented molecular resolution. However, the majority of 3D AFM studies have been focused on the arrangement of water at carbonate surfaces. Here, we present an analysis of the assembly of ethanol – an o…
Calculation of proton activity in aqueous protolyte solutions
1980
Abstract A general and thermodynamically exact equation for the calculation of the proton (hydroxide ion) activity of aqueous solutions of monoprotic acidic (and basic) species is given. Under certain conditions, various approximate equations can be derived from the exact form; the applicability of these depends mainly on both the thermodynamic equilibrium constant, K p , of the protolytic reaction, and the stoichiometric concentration, C o , of the protolyte. Taking into account the mean ionic activity coefficients which are calculated by means of the Davies equation, diagrams are constructed exhibiting those combinations of K p and C o for which the respective approximations can be applie…
Recent advances on ionic liquid uses in separation techniques
2018
International audience; The molten organic salts with melting point below 100°C, commonly called ionic liquids (ILs) have found numerous uses in separation sciences due to their exceptional properties as non molecular solvents, namely, a negligible vapor pressure, a high thermal stability, and unique solvating properties due to polarity and their ionic character of molten salts. Other properties, such as viscosity, boiling point, water solubility, and electrochemical window, are adjustable playing with which anion is associated with which cation. This review focuses on recent development of the uses of ILs in separation techniques actualizing our 2008 article (same authors, J. Chromatogr. A…
Conformational analysis of α,β-dehydropeptide models at the HF and DFT levels
2004
Abstract The Ramachandran potential energy surfaces of N-acetyl-α,β-dehydroamino acid N′-monomethylamides Ac-ΔXaa-NHMe (ΔXaa=ΔAla, (Z)-ΔPhe; 1, 2) and N-acetyl-α,β-dehydroamino acid N′,N′-dimethylamides Ac-ΔXaa-NMe2 (ΔXaa=ΔAla, (Z)-ΔPhe, (Z)-ΔAbu; 3–5) were calculated at the HF/6-31G*//HF/3-21G level. The conformers localised were fully optimised at the DFT/B3LYP/6-31+G** level and their relative stabilities were analysed in terms of both π-conjugation and internal hydrogen bonding. The Ac-ΔXaa-NMe2 molecules reveal the low-energy conformer H/F, φ=−41±4°, ψ=128±4°, which is not too easily accessible for common amino acid residues. This conformer is stabilised by the bifurcated N2–CH3 O1 int…
Size-Dependent Structural Evolution and Chemical Reactivity of Gold Clusters
2006
Ground-state structures and other experimentally relevant isomers of Au(15) (-) to Au(24) (-) clusters are determined through joint first-principles density functional theory and photoelectron spectroscopy measurements. Subsequent calculations of molecular O(2) adsorption to the optimal cluster structures reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis of the underlying electronic structure shows that the chemical reactivity of the gold cluster anions can be elucidated in terms of a partial-jellium picture, where delocalized electrons occupying electronic shells move over the ionic skeleton, whose geometric structure is strongly infl…
Charge distribution and optical properties of and F centres in crystals
1997
Results of quantum chemical calculations for the and F centres in cubic and orthorhombic phases of a perovskite ferroelectric are presented and analysed in the light of existing experimental literature. It is shown that one (two) electrons of the and F centres, respectively, are considerably delocalized, even in the ground state of defects, over the two Nb atoms nearest to the O vacancy, and other close atoms. They resemble more electron defects in partly covalent crystals (the so-called centre) than F-type centres in ionic MgO crystals. We predict two or three absorption bands (depending on the crystalline phase) for each of the defects. The calculated absorption energies for the centre ar…
Self-assembled dendrimers with uniform structure
2008
Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH(2))(n)-C(O)-NH-(CH(2))(m)-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene () they form dendritic assemblies since the well …
An in vitro evaluation of two dentine adhesive systems to seal the pulp chamber using a glucose penetration model
2010
Objectives: To evaluate the sealing capability of Cavit TM G with or without Clearfil TM S3 Bond and Prime & Bond NT placed in the pulp chamber. Study Design: Forty single rooted premolars, extracted for orthodontic and periodontal reasons, with intact coronal surface and mature apices, were standardized to a length of 15 mm. The teeth were instrumented, filled with a gutta-percha master cone and divided into three groups to obturate the pulp chambers: Cavit TM G; Clearfil TM S3 Bond plus Cavit TM G and Prime & Bond® NT plus Cavit TM G. A glucose leakage model was used for evaluating the coronal microleakage. The Mann-Whitney test was used to evaluate the differences in the means of the glu…