Stoichiometric Conditions (stoichiometric + condition)

Distribution by Scientific Domains

Selected Abstracts

Hybrid Bioorganic,Inorganic Materials Prepared by Site-Specific Ligation of Peptides to Functionalized Polydisperse Silica Particles

Pascal Joly
Abstract We describe the synthesis of semicarbazide- or glyoxylyl-functionalized polydisperse silica particles and their use for the preparation of hybrid polypeptide,silica materials. The peptides were attached to the surface of functionalized silicas by site-specific ,-oxo hydrazone or semicarbazone ligation. The reaction of semicarbazide silicas with a model glyoxylyl peptide was found to be very efficient under stoichiometric conditions and led to ligation yields of about 90,%. The use of glyoxylyl silicas and of hydrazinoacetyl peptides led to lower yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Copper(II)-Catalyzed Aminooxygenation and Carboamination of N -Aryl-2-allylanilines


Abstract The scope of the intramolecular copper(II)-catalyzed carboamination and aminooxygenation reactions of olefins has been extended to include N -aryl-2-allylanilines. These substrates exhibit divergent reactivity under catalytic vs. stoichiometric conditions. [source]

The Heteropolytungstate Core {BW13O46}11, Derived as Monomer, Dimer, and Trimer

Nathalie Leclerc-Laronze Dr.
Abstract A study of the borotungstate system has led to the characterization of new, original compounds based on the unconventional Keggin derivative [H3BW13O46]8, ion (denoted as 1). [H3BW14O48]6, (2) and the dimer [H6B2W26O90]12, (3) crystallize as mixed cesium/ammonium salts and have been characterized by single-crystal X-ray diffraction analysis. Anion 2 reveals an unusual arrangement, consisting of an outer {W3O9} core grafted onto the monovacant [BW11O39]9, Keggin moiety and exhibits an unprecedented distorted square-pyramidal arrangement for a cis -{WO2} core. Elemental analysis, supported by bond distance analysis, is consistent with the presence of three protons distributed over the terminal oxygens of the outer {W3O7} capping fragment. The [H6B2W26O90]12, ion (3) is formally derived from the direct condensation of two [H3BW13O46]8, subunits. The cisoid arrangement of the two [BW11O39]9, subunits, coupled with the antiparallel arrangement of the two quasi-linear OW,,,OWOH2 chains within the central {W4O12} connecting group, breaks any symmetry, thereby resulting in a chiral compound. Polarography and pH-metric titrations reveal the formation of the monomeric precursor [H3BW13O46]8, (anion 1) under stoichiometric conditions. 183W NMR analysis of 2 and 3 in solution gives complex spectra, consistent with the presence of equilibria between several species. In the frame of this study, we also report on a structural re-investigation of the [H6B3W39O132]15, ion (4) based on reliable results obtained in the solid state by means of single-crystal X-ray diffraction analysis, and in solution by means of 1D and 2D COSY 183W NMR. X-ray diffraction analysis revealed the presence of three attached aquo ligands on the central {W6O15} connecting core, generating three OW,,,OWOH2 quasi-linear chains, which are responsible for the chirality of the trimeric assembly. This structural arrangement accounts for the 39-line 183W solution spectrum. The 2D COSY spectrum permits reliable assignments of the six strongly shielded resonances (around ,250 and ,400,ppm) to the six central W atoms, as well as additional assignments. The origin of such strong shielding for these particular W atoms is discussed on the basis of previously published results. Infrared data for compounds 1, 3, and 4 are also presented. [source]

Programming Heteropolymetallic Lanthanide Helicates: Thermodynamic Recognition of Different Metal Ions Along the Strands

Sébastien Floquet Dr.
Abstract Under stoichiometric conditions, the segmental tris-tridentate ligand L9 assembles with two different lanthanide metal ions Ln1 and Ln2 (Ln1, Ln2=La, Nd, Sm, Eu, Yb, Lu, Y) to give mixtures of the heterotrimetallic triple-stranded helicates [(Ln1)x(Ln2)3,x(L9)3]9+ (x=0,3) in acetonitrile. The combination of qualitative (ESI-MS) and quantitative (1H NMR) speciations provides a set of thermodynamic data that were analysed with various statistical chemical models. A satisfying description requires the consideration of different affinities for the terminal N6O3 sites (k) and for the central N9 site (k) for each specific lanthanide. The nontrivial dependence of these parameters on the ionic radius provides size-discriminating effects that favour the formation of heterotrimetallic helicates in which the central site is occupied by the larger metal of the pair. Combining the latter enthalpic driving forces with entropic contributions due to specific stoichiometric conditions allows partial selection (i.e., programming) of a specific heterotrimetallic species in solution, which can be isolated by crystallisation, as demonstrated for [Eu2.04La0.96(L9)3](CF3SO3)9(CH3NO2)9 (1, Eu2.04La0.96C207H222N48O51S9F27, monoclinic, P21/c, Z=4) in which the cation [EuLaEu(L9)3]9+ is the major component in the crystal. The scope and limitation of this approach is discussed together with the conditions for explicitly considering intermetallic interaction parameters uLn1Ln2 in more sophisticated chemical models. [source]