Search results for "force"

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

2004

Abstract Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤ P n sc ≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d ∼( M n sc ) 0.476 . The contour length of the cylindrical brush polymers per main chain monomer unit, l m , was determined to slightly vary with side chain molar mass M n sc according to l m ∼( M n sc ) 0.059 . The resulting values are much less than the maximum exte…

Two penta­de­hydro­peptides with different configurations of the ΔPhe residues

2009

Comparison of the crystal structures of two pentadehydropeptides containing DeltaPhe residues, namely (Z,Z)-N-(tert-butoxycarbonyl)glycyl-alpha,beta-phenylalanylglycyl-alpha,beta-phenylalanylglycine (or Boc(0)-Gly(1)-Delta(Z)Phe(2)-Gly(3)-Delta(Z)Phe(4)-Gly(5)-OH) methanol solvate, C(29)H(33)N(5)O(8) x CH(4)O, (I), and (E,E)-N-(tert-butoxycarbonyl)glycyl-alpha,beta-phenylalanylglycyl-alpha,beta-phenylalanylglycine (or Boc(0)-Gly(1)-Delta(E)Phe(2)-Gly(3)-Delta(E)Phe(4)-Gly(5)-OH), C(29)H(33)N(5)O(8), (II), indicates that the Delta(Z)Phe residue is a more effective inducer of folded structures than the Delta(E)Phe residue. The values of the torsion angles phi and psi show the presence of two …

Spectrophotometric determinations of binding constants between cyclodextrins and aromatic nitrogen substrates at various pH values

2001

The inclusion capacity of native β-cyclodextrin (1) and mono-(6-amino-6-deoxy)-β-cyclodextrin (2) versus aromatic compounds having a nitro or an amino group or both has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. Electrostatic and van der Waals interactions and the formation of a hydrogen bond between the donor amino group and the oxygen atom of the secondary hydroxyl group seem to be the more important contributions in determining complex stability. The inclusion capacity of two different cyclodextrins versus aromatic compounds has been investigated at three differ…

New perspectives for the design of molecular actuators: thermally induced collapse of single macromolecules from cylindrical brushes to spheres.

2004

Reactivity of the carbon-carbon double bond towards nucleophilic additions. A dft analysis

2004

Abstract The global and local electrophilicity indexes have been used to characterize the reactivity pattern of the CC double bond towards nucleophilic addition reactions. A wide family of molecules including ketones, esters, anhydrides, nitriles and nitrocompounds containing appropriate substitution on the CC double bond have been classified within an unique scale of reactivity. The predictive capability of the theoretical model is tested against a series of benzylidenemalononitriles and substituted α-nitrostilbenes.

The [3,3′-Co(1,2-C2B9H11)2]– anion as a platform for new materials: synthesis of its functionalized monosubstituted derivatives incorporating synthon…

2003

[3,3′-Co(8-C5H10O-1,2-C2B9H10)(1′,2′-C2B9H11)] (2) was synthesized by reaction of the caesium salt of [Co(C2B9H11)2]− with dimethyl sulfate in the presence of sulfuric acid as catalyst and tetrahydropyrane as solvent; the zwitterionic compound (2) yielded [3,3′-Co(8-C4H4N-(CH2)5-O-1,2-C2B9H10)(1′,2′-C2B9H11)]− (6), [3,3′-Co(8-C8H6N-(CH2)5-O-1,2-C2B9H10)(1′,2′-C2B9H11)]− (7), and [3,3′-Co(8-C12H8N-(CH2)5-O-1,2-C2B9H10)(1′,2′-C2B9H11)]− (8) through the nucleophilic addition of potassium pyrrolyl, indolyl and carbazolyl, respectively. The nucleophilic addition of the same salts on [3,3′-Co(8-C4H8O2-1,2-C2B9H10)(1′,2′-C2B9H11)] (1) yielded, respectively, [3,3′-Co(8-C4H4N-(CH2)2-O-(CH2)2-O-1,2-C…

Multiplicity of Reaction Pathways in the Processes of Oxygen Transfer to Secondary Amines by Mo(VI) and W(VI) Peroxo Complexes.

1996

Oxidation of N,N-benzylmethylamine, N,N-benzylisopropylamine, and N,N-benzyl-tert-butylamine by both anionic and neutral Mo(VI) and W(VI) oxodiperoxo complexes yields the corresponding nitrones quantitatively. The oxidation reactions employing anionic oxidants were performed in CHCl(3) and follow second-order kinetics, first order with respect to the amine and to the oxidant. The data were rationalized on the basis of a rate-determining nucleophilic attack of the amine onto the peroxide oxygen of the oxidant, with a transition state in which N-O bond formation and O-O bond cleavage occur in a concerted way (electrophilic oxygen transfer mechanism). This attack yields the corresponding hydro…

The synergy between the CsPbBr3 nanoparticle surface and the organic ligand becomes manifest in a demanding carbon–carbon coupling reaction

2020

We demonstrate here the suitability of CsPbBr3nanoparticles as photosensitizers for a demanding photoredox catalytic homo- and cross-coupling of alkyl bromides at room temperature by merely using visible light and an electron donor, thanks to the cooperative action between the nanoparticle surface and organic capping. Fil: Rosa-Pardo, Ignacio. Instituto de Ciencia Molecular; España. Universidad de Valencia; España Fil: Casadevall, Carla. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; España Fil: Schmidt, Luciana Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigac…

Analysis of plasticization and reprocessing effects on the segmental cooperativity of polylactide by dielectric thermal spectroscopy

2021

Abstract In the present study, the dielectric properties of both neat and plasticized polylactide submitted to repeated extrusion and injection processes to simulate recycling were analysed. The dielectric relaxation spectrum, consisting of β and α relaxation, revealed the relevance of both acryl-PEG based plasticization and thermo-mechanical degradation induced by repeated extrusion and grinding-injection reprocessing cycles on polylactide (PLA). The β-relaxation has its origin in the intramolecular local motions of pendant groups of the PLA backbone, while the α-relaxation is representative of the intermolecular large-scale segmental motions of the PLA backbone. The addition of acryl-PEG …

Pressure effect studies on spin crossover systems

2005

Abstract In the present review article we discuss the results of investigations of the influence of hydrostatic pressure (up to 1.2 GPa) on the spin transition behaviour in coordination compounds of 3d transition metal ions. The systems under investigation are mononuclear spin crossover compounds of iron(II) and chromium(II), dinuclear complexes of iron(II) exhibiting coexistence of intramolecular anti-ferromagnetic coupling and thermal spin crossover, and 1D, 2D and 3D polynuclear spin crossover complexes of iron(II). It is demonstrated that the application of hydrostatic pressure serves as a tool for modifying the ligand field strength in a controlled manner.