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排序方式: 共有318条查询结果,搜索用时 15 毫秒
311.
The main objective of this work is to understand the effects caused by particle size, temperature, and sintering time on ceramic formation and development of its surface hardness (Vickers hardness Vk) in order to extend its use in medical applications. The ceramic consists of a biphasic calcium phosphates mixture (beta-tricalcium phosphate and hydroxylapatite) to which we have added zinc oxide, silica, and zirconia in order to improve the biological and mechanical profiles of this ceramic. The ceramization process is made by partial melting, which the melt agent is an amorphous aluminum phosphate added by small quantities to the last mixture. In fact, when the aluminum phosphate is under high temperature, it causes the formation of a melt which facilitates the adhesion of particles during the solidification process. In this study, we adopted an experimental strategy such as central composite design. This plan lets us optimize the mechanical hardness of the ceramic, involving a polynomial form derived from the Taylor–Mac Lorrain equation. The isoresponses curves obtained give us the estimated responses and empirical possibilities for obtaining ceramics with an optimum hardness, which can then be used for each type or intervention place in reconstructive surgery. 相似文献
312.
Dr. Robert Langer Ido Fuchs Dr. Matthias Vogt Dr. Ekambaram Balaraman Dr. Yael Diskin‐Posner Dr. Linda J. W. Shimon Yehoshoa Ben‐David Prof. Dr. David Milstein 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3407-3414
The synthesis and reactivity of ruthenium complexes containing the tetradentate phenanthroline‐based phosphine ligand 2,9‐bis((di‐tert‐butylphosphino)methyl)‐1,10‐phenanthroline (PPhenP) is described. The hydrido chloro complex [RuHCl(PPhenP)] ( 2 ) undergoes facile dearomatization upon deprotonation of the benzylic position, to give [RuH(PPhenP‐H)] ( 4 ). Addition of dihydrogen to 4 causes rearomatization of the phenanthroline moiety to trans‐[Ru(H)2(PPhenP)] ( 5 ), followed by hydrogenation of an aromatic heterocycle in the ligand backbone, to give a new dearomatized and deconjugated complex [RuH(PPhenP*‐H)] ( 6 ). These aromatization/deconjugation steps of the coordinated ligand were demonstrated to be reversible and operative in the dehydrogenation of primary alcohols without the need for a hydrogen acceptor. This aromatization/deconjugation sequence constitutes an unprecedented mode of a stepwise cooperation between the metal center and the coordinated ligand. 相似文献
313.
Montag M Efremenko I Cohen R Leitus G Shimon LJ Diskin-Posner Y Ben-David Y Martin JM Milstein D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(27):8183-8194
The crystal structure of the new cationic Rh(I) complex trans-[Rh(CO)(2)(L)(2)]BF(4) (L=alpha(2)-(diisopropylphosphino)isodurene) was found to exhibit a nonlinear OC-Rh-CO fragment and weak intramolecular C-H...Rh interactions. These interactions, which have also been shown to occur in solution, have been examined by density functional theory calculations and found to be inextricably linked to the presence of the distorted OC-Rh-CO fragment. This linkage has also been demonstrated by comparison with a highly similar Rh(I) complex, in which these C-H...Rh interactions are absent. Furthermore, the presence of these weak interactions has been shown to have a significant effect on the reactivity of the metal center. 相似文献
314.
Klerman Y Ben-Ari E Diskin-Posner Y Leitus G Shimon LJ Ben-David Y Milstein D 《Dalton transactions (Cambridge, England : 2003)》2008,(24):3226-3234
The cationic, pincer-type complexes [(SNS)Ir(COE)][BF4] (1) and [(SNS)Rh(COE)][BF4] (2) (SNS = 2,6-bis(t-butylthiomethy1)pyridine; COE = cyclooctene) complexes were prepared, and their structure and reactivity were studied. They are fluxional at room temperature as a result of "arm" hemilability, which can be frozen at low temperatures. Reaction of complex 1 with H2 resulted in a dimeric dihydride complex [(SNS)Ir(H2)]2[BF4]2 (3) in which the sulfur atoms bridge between two metal centers. The Rh complex 2 did not react with H2. Both the carbonyl complexes [(SNS)Ir(CO)][BF4] (5) and [(SNS)Rh(CO)][BF4] (6) show differences in the IR stretching frequencies in solution vs. solid states, which are a result of uncommon metal-metal interactions between square planar d8 systems in the solid state. Complexes 1, 3, 5 and 6 were structurally characterized by X-ray crystallography. A network of hydrogen bonds involving the BF4(-) counter anion and hydrogen atoms of complex 5 was observed. 相似文献
315.
Durán Pachón L Thathagar MB Hartl F Rothenberg G 《Physical chemistry chemical physics : PCCP》2006,8(1):151-157
The advantages of bimetallic nanoparticles as C-C coupling catalysts are discussed, and a simple, bottom-up synthesis method of core-shell Ni-Pd clusters is presented. This method combines electrochemical and 'wet chemical' techniques, and enables the preparation of highly monodispersed structured bimetallic nanoclusters. The double-anode electrochemical cell is described in detail. The core-shell Ni-Pd clusters were then applied as catalysts in the Hiyama cross-coupling reaction between phenyltrimethoxysilane and various haloaryls. Good product yields were obtained with a variety of iodo- and bromoaryls. We found that, for a fixed amount of Pd atoms, the core-shell clusters outperform both the monometallic Pd clusters and the alloy bimetallic Ni-Pd ones. THF is an excellent solvent for this process, with less than 2% homocoupling by-product. The roles of the stabiliser and the solvent are discussed. 相似文献
316.
One-pot Pd/C catalysed 'domino' HALEX and Sonogashira reactions: a ligand- and Cu-free alternative 总被引:1,自引:0,他引:1
The advantages of combining heterogeneous catalysis and aryl chloride substrates for cross-coupling are introduced. A heterogeneous Pd/C catalyst is used for activating aryl bromides and electron withdrawing aryl chlorides via a one-pot 'domino' HALEX-Sonogashira reaction. No ligand or co-catalyst is required, and the cross-coupling products are obtained in moderate to good yields. The influence of the solvent, base, iodide source and catalyst is evaluated. The catalyst is reusable for at least six consecutive reaction cycles. A variation on this reaction using catalytic amounts of KI is also proposed. 相似文献
317.
Diblock and multiblock copolymers composed of a poly(D,L-lactide) (PLA) or poly(trimethylene carbonate) (PTMC) core with a hydrophilic chain of poly(ethylene glycol) (PEG) were prepared. These copolymers, in which the core is connected to PEG through a polyfunctional molecule such as citric, mucic, or tartaric acid, may be used to form nanoparticles for drug delivery applications. Branched copolymers were prepared by direct amidation between the polyfunctional acid and methoxy PEGamine, followed by ring-opening polymerization of lactide or trimethyl carbonate to form the PLA and PTMC block copolymers. In addition, a complex multiblock copolymer of biotin-PEG-poly[lactic-co-(glycolic acid)] (PLGA) for application in an avidin-biotin system was prepared for possible design of nanospheres with targeting properties. Studies of drug release from polymeric systems containing multiblock copolymers and studies of polymer degradation were also performed. 相似文献
318.