Search results for "medium"
showing 10 items of 3746 documents
Synthesis of Highly Substituted 2-13C-Imidazolium Salts and Metal NHC Complexes for the Investigation of Electronic Unsymmetry by NMR
2013
Complexes of unsymmetrically substituted N-heterocyclic carbenes with NMR-active metals (Ag, Hg, Pt) with or without a 13C-label in the 2-position were synthesized by aldimine cross coupling and analyzed with respect to the scalar couplings between the metal center or C2 and the other ring atoms.
Polyaza[n]paracyclophanes as synthetic models of Zn containing enzymes. The role of a non coordinated nitrogen atom in the proximity of the metal
1997
Abstract 2,6,9,13-Tetraaza[14]paracyclophane ( 3, B323 ) represents a simple model for Zn containing enzymes like HCAII which possess additional reactive groups in the proximity of the metal center. The Zn 2+ . 3 complex shows notable catalytic activity for the hydrolysis of p -nitrophenyl acetate. Structural modifications of 3 which affect to the non coordinated nitrogen atom greatly modify the catalytic activity of the receptor.
ChemInform Abstract: New Crown Ether-Like Macrocycles Containing a Nitrophenol Unit. Synthesis and Metal Ion Effects on the Reactivity of Their Aceta…
2010
Solid State Analysis of Metal-Containing Polymers Employing Mossbauer Spectroscopy, Solid State NMR and F EI TOF MALDI MS
2010
Polymers in general and metal-containing polymers in particular are often sparingly soluble or insoluble, in contrast to small molecules. Thus, special significance is attached to characterization techniques that can be applied to the materials as solids. Here, three techniques are discussed that give structural information gained from the solid material. Mossbauer spectroscopy is a powerful technique that may give information on the structure about the metal-containing moiety for about 44 different nuclei. Its use in describing the structure of the product obtained from organotin dichlorides and the unsymmetrical ciprofloxacin is presented along with the reaction implications of the result…
Rigid polymer materials with hologram enhancement by molecular diffusion
2003
The principle of diffusional enhancement has been embodied in the rigid glassy polymer with phenanthrenequinone able to photochemically attach to surrounding macromolecules, thus forming a permanent grating. Owing to material stiffness, it does not suffer from shrinkage and can be made very thick; serving a basis for very stable spectrally selective elements. Replacement of commonly used acrylic glass by polycarbonate ensures further significant improvement of performance and stability of 3D holographic optical elements and memories.
Improved Preparations of Molybdenum Coordination Compounds from Tetrachlorobis(diethyl ether)molybdenum(IV)
2001
International audience; The reduction of MoCl5 with metallic tin in diethyl ether provides a rapid and convenient entry to [MoCl4(OEt2)2] This compound can be transformed easily and in high yields into a variety of other useful synthons. The loss of ether in the solid state affords a new and reactive form of MoCl4. Treatment with THF, PMe3 or LiOtBu affords [MoCl4(THF)2], [MoCl4(PMe3)3] or [Mo(OtBu)4] in high isolated yields. Treatment with metallic tin in THF affords [MoCl3(THF)3] All of these reactions can be carried out under simple experimental conditions and represent significant improvements relative to previously reported syntheses of the same compounds.
Partial Discharge Tests Using CIGRE Method II Upon Nanocomposite Epoxy Resins
2007
Nanocomposite polymers are becoming a new family of dielectric materials with promising insulating properties. In order to apply this technology to insulation systems, a study about the material longterm endurance (life) is needed. In this paper results from comparative life tests performed upon base and nanostructured epoxy resin samples are presented. The nanofiller is a organophillic-modified ultra-clean montmorillonite. Specimens were subjected to ageing under surface discharge phenomena using a standard electrode configuration, that is the CIGRE method II. Life data and partial discharge phase resolved patterns, acquired during time under stress, are presented and commented, in order t…
Bio-inspired Resorbable Calcium Phosphate-Polymer Nanocomposites for Bone Healing Devices with Controlled Drug Release
2011
In orthopedic research, increasing attention is being paid to bioresorbable composite materials as an attractive alternative to permanent metal bone healing devices. Typical composites consist of a biodegradable polyester matrix loaded with bioactive calcium phosphate ceramic particles (tricalcium phosphate, TCP or hydroxyapatite, HA) added to improve the biological response and mechanical properties of the neat polymer. The mechanical behavior of such particle-reinforced composites, however, falls far short of the expected performance in high-load bearing situations. Replicating some features of nacre—a strong and tough natural nanocomposite with a very high content of brittle inorganic ph…
Experimental Studies for Modelling the Phase Behaviour of Monomer/Polymer/Disc Composites
2010
Nanoparticles do not stabilize the mixtures of epoxy monomer (prepolymer)/thermoplastic modifier (PS) and the ones of thermoplastic modifier dispersed within cured epoxy matrix. A small amount of thermoplastic co-polymer poly(styrene-b-methyl methacrylate) [P(S-b-MMA)] of MMA 4-22 wt.%, mixed with PS, makes compatible the mixtures with monomer epoxy precursor and cured epoxy matrix. The mixtures of cured epoxy matrix with thermoplastic consisting of PS and P(S-b-MMA), with nanofil 1%, are stable: the instability produced by the nanofil is overcome by the stability provided by the co-polymer. A model by Balazs' group to explain the phase behaviour of polymer/clay composites is extended.