			Home About us Contact

Acceptor Properties (acceptor + property)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Steering the Surprisingly Modular ,-Acceptor Properties of N-Heterocyclic Carbenes: Implications for Gold Catalysis,

ANGEWANDTE CHEMIE, Issue 14 2010
Manuel Alcarazo Dr.
Geben und nehmen: Die ,-Akzeptoreigenschaften N-heterocyclischer Carbene (NHCs) werden oft als vernachlässigbar angesehen, können aber bis zu dem Punkt erhöht werden, an dem sie das Katalyseverhalten von Gold-NHC-Komplexen zu dominieren beginnen (siehe Schema). Da es leichter zu sein scheint, die ,-Acidität von NHCs einzustellen als ihre ,-Donoreigenschaften, muss die allgemeine Einschätzung dieser wichtigen Hilfsliganden revidiert werden. [source]

Synthesis of a [60] fullerene,Functionalized isotactic polypropylene derivative

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2008
Gerardo Martínez
Abstract The covalent attachment of [60] fullerene (C60) to isotactic polypropylene (i-PP) is achieved by direct reaction in 1,2,4-trichlorobenzene (TCB) solution in the presence of dicumyl peroxide (DCP). The chemically modified pendant C60/i-PP polymers are soluble in chlorinated solvents and have been characterized by ultraviolet,visible and fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, cyclic voltametry, and thermogravimetric analysis. From the results it can be concluded that the modification of i-PP by grafting via a free-radical reaction competes with the possibility of chain scission of i-PP due to the presence of DCP. The functionalized polymers crystallize in the monoclinic crystal modification, and have high crystallinity. The incorporation of C60 significantly enhances the thermal stability of the i-PP. Electrochemical measurements demonstrate good electron acceptor properties of the fullerenated i-PP samples. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6722,6733, 2008 [source]

Synthesis of a [60]fullerene-functionalized poly(vinyl chloride) derivative by stereospecific chemical modification of PVC

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007
Gerardo Martínez
Abstract The covalent attachment of [60]fullerene (C60) to two poly(vinyl chloride) (PVC) samples with different isotactic content is achieved by direct reaction in o -dichlorobenzene (o -DCB) solution in the presence of AIBN. The extent of fullerenation is controlled by varying the C60 feed ratio. The pendant C60 -chemically modified PVC polymers are soluble in tetrahydrofuran (THF) and have been characterized by UV,vis, NMR, FTIR, DSC, TGA, cyclic voltammetry, and SEM. The quantitative microstructural analysis after covalent attachment of the bulky C60 moiety to the PVC has been followed by 13C NMR spectroscopy. From the results it can be concluded that the modification of PVC by graft reaction through free radical reaction proceeds by a stereoselective mechanism. This conclusion has been confirmed on the basis of the increase of the glass-transition temperature (Tg) and the thermal stability of the C60 -chemical modified PVC samples. The fullerenated PVCs obtained show good electron acceptor properties, as evidenced by electrochemical investigations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5408,5419, 2007 [source]

Allosteric Tuning of the Intra-Cavity Binding Properties of a Calix[6]arene through External Binding to a ZnII Center Coordinated to Amino Side Chains

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007
Ulrich Darbost Dr.
Abstract Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of ZnII ion provides the dinuclear ,-hydroxo complex , XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species , one of which (X = Cl) has been characterized by XRD. A dicationic complex is obtained upon treatment of with a mixture of an alkylamine and a strong acid. Each of these ZnII complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO,, X,, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor , based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, ,-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo -coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment. [source]

Exploring the Dynamics of Calix[4]pyrrole: Effect of Solvent and Fluorine Substitution

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007
Ramón Blas Dr.
Abstract Molecular dynamics simulations show that calix[4]pyrrole (CP) and octafluorocalix[4]pyrrole (8F-CP) are extremely flexible molecules. CP mainly adopts the 1,3-alternate conformation in all the solvents, although the percentage of alternative conformations increases in polar solvents, especially those with good hydrogen-bonding acceptor properties. However, in the case of 8F-CP, the cone conformation is the most populated in some solvents. Transitions between conformers are common and fast, and both CP and 8F-CP can adopt the cone conformation needed for optimum interaction with anions more easily than would be predicted on the basis of previous gas-phase calculations. Furthermore, the present studies show that when a fluoride anion is specifically placed initially in close proximity to CP and 8F-CP in their respective 1,3-alternate conformations, an extremely fast change to the cone conformation is observed in both cases. The results suggest that preorganization does not represent a major impediment to anion-binding for either CP or 8F-CP, and that ion-induced conformational changes can follow different mechanisms depending on the solvent and the chemical substituents present on the calix[4]pyrrole beta-pyrrolic positions. [source]