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New Bonds (new + bond)
Selected AbstractsEffects of adhesive systems and luting agents on bonding of fiber posts to root canal dentinJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Francesca Monticelli Abstract The study evaluated the influence of different luting materials on the microtensile bond strength of glass fiber posts to root canal dentin. Thirty extracted maxillary premolars were endodontically treated, and the roots were prepared for post cementation using the FRC Postec system (Vivadent). Two luting materials (Multilink, Vivadent and Clearfil Photo Core, Kuraray) were used in combination with three adhesive: Multilink Primer (Vivadent), Clearfil Photo Bond, and Clearfil New Bond (Kuraray). A composite build-up was performed around the root to provide adequate gripping during testing. Specimens were cut to obtain beams with the post in the center and with the radicular dentin overlaid by the composite build-up on each side. Microtensile testing was performed with a universal testing machine at a cross-head speed of 0.5 mm/min. The failure mode was classified under a stereomicroscope and four representative beams of each group were selected for SEM analysis. Bond strength data that were analyzed with two-way ANOVA and Student-Newman-Keuls multiple comparisons tests revealed that adhesive systems, luting materials, and the interaction between these two factors significantly influenced the bond strength results (p < 0.01). Multilink applied with its own adhesive system obtained the best results, while the lowest bond strength was achieved with clearfil photo core in combination with multilink primer. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Vaginocervical stimulation of Ewes induces the rapid formation of a new bond with an alien young without interfering with a previous bondDEVELOPMENTAL PSYCHOBIOLOGY, Issue 6 2010F. Lévy Abstract Ewes form a selective olfactory memory for their lambs after 2,hr of mother,young interaction following parturition. Mothers will subsequently reject any strange lamb at suckling. The present study investigated whether artificial vaginocervical stimulation (VCS) allows the formation of a selective bond with an unfamiliar lamb and whether it interferes with the maintenance of the bond formed with the familiar lamb. At 2,hr postpartum, mothers were separated from their familiar lamb after having formed a selective bond with it and were given 10,min of mechanical VCS. In the "VCS,+,lamb" group (n,=,24) an unfamiliar lamb was left with the ewe for 2,hr whereas in the "VCS no lamb" group (n,=,26) the mother was left alone for the same period of time. Ewes of the "no VCS" group (n,=,14) did not receive any VCS. In the majority of animals of the "VCS,+,lamb" group (23/24) VCS induced a complete acceptance of the unfamiliar lamb without any disruption of the bond previously formed with the familiar lamb. VCS or 2,hr of separation did not disrupt the maintenance of the selective bond initially formed with the familiar lamb since all the ewes of the "VCS no lamb" and "no VCS" groups accepted it at suckling. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 52: 537,544, 2010. [source] Local HSAB principle in the conjugate addition of p -substituted thiophenols to cyclohexenoneINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2005Rocío Meza Abstract In the formation of new bonds through the Michel-type addition of thiolates to a ,,,-conjugate system, it is observed that the reaction takes place faster if the thio donor compound contains an electron-rich group or the enone acceptor is highly electron deficient. In contrast, the hard,soft acid,base (HSAB) principle predicts that this reaction is favored when a soft,soft interaction between the reactants takes place. Taking into account that softness is related to a barely electronegative atom of high polarizability, we consider it of interest to analyze the effect of charge transfer of a p -substituent on the softness of sulfur in thiophenols, as well as its impact in the conjugate addition to 2-cyclohexen-1-one. Experiments-in-competition, net charge of X-groups at the p -position of the aromatic ring, the global and local softness at sulfur, and the electrophilicity, obtained by density functional theory (DFT), led to the observation that the reaction is faster for electron attractor thiophenols. The softness at sulfur increases by delocalization of charge through the aromatic ring. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Domino Reaction of Acyclic ,,,-Dialkenoylketene S,S -Acetals and Diamines: Efficient Synthesis of Tetracyclic Thieno[2,3- b]thiopyran-Fused Imidazo[1,2- a]pyridine/Pyrido[1,2- a]pyrimidinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Fushun Liang Abstract A series of unusual fused tetraheterocyclic compounds 3, consisting of a thiopyran (ring A), a thiophene (ring B), a pyridine (ring C), and an imidazole or a pyrimidine (ring D) core, with a bridgehead nitrogen and an angular methyl group, were successfully synthesized by a catalyst-free, one-pot, two-component domino reaction of 4-(4-methyl-1,3-dithiol-2-ylidene)-1,7-bis(aryl/heteroaryl)hepta-1,6-diene-3,5-dione 2 and diamines. In this reaction, up to five new bonds were formed accompanied by the CS bond cleavage of the 1,3-dithiole ring of 2, with water as the only by-product. [source] Spectroscopic Properties and Local Structure of Eu3+ in Ge,Ga,S,CsBr (or CsCl) GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Woon Jin Chung Spectroscopic properties and local structure of Eu3+ in Ge,Ga,S,CsBr (or CsCl) glasses were investigated using fluorescence measurements and several spectroscopic methods. Fluorescence from Eu3+:5D0,7F2 was observed only from glasses with CsBr/Ga ratios greater than unity and disappeared at temperatures above 140 K. Phonon sideband (PSB) spectra revealed that Eu3+ ions are located next to halogen ions, which form part of well-structured complexes such as EuCl3, tetrahedral [GaS3/2Cl],, subunits and/or Ga2Cl6. These new bonds showed reduced coupling strength compared with Eu3+,S bonds in Ge,Ga,S glass. Fluorescence line narrowing experiments showed little site-to-site variation of Eu3+ ions. [source] Gold Catalysis: Tandem Reactions of Diyne,Diols and External Nucleophiles as an Easy Access to Tricyclic Cage-Like Structures,CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2010Stephen Abstract Different diyne,diols composed of two terminal homopropargylic alcohol groups were prepared by bi-directional synthesis. Subjection of the syn diastereomers to NAC,gold catalysts (NAC=nitrogen acyclic carbene) in the presence of external nucleophiles such as water or anilines provided substituted and highly rigid heterocyclic cages. The corresponding anti disastereomers polymerised. An intermediate of the reactions of the syn diastereomers could be isolated and even be characterised by crystal structure analysis. Overall, eight new bonds are formed in the reaction, which proceeds by a multistep sequence of highly selective hydroalkoxylations and hydrohydroxylation or hydroaminations. For furyl substituents and for internal alkynes competing reaction pathways could be identified. By the cross-coupling of a product with an iodoaryl substituent, the use of these cage compounds as geometrically defined linking groups by using orthogonal transition-metal-catalysed methodology, namely, gold and palladium catalysis, could be demonstrated. [source] One-Pot Catalytic Asymmetric Cascade Synthesis of Cycloheptane DerivativesCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2008Jan Vesely Dr. Abstract A regiospecific, highly chemo-, diastereo-, and enantioselective one-pot catalytic cascade synthesis of cycloheptane derivatives is presented. In this chiral-amine-catalyzed asymmetric process, six new bonds and five new stereocenters were formed with excellent stereocontrol (>25:1 d.r. and 98, >99,ee). [source] | |||||||||||||