Search results for "BOND"
showing 10 items of 3527 documents
Hydrogen bonds in unpolar matrix — Comparison of complexation in polymeric and low molecular-weight systems
1991
By ene-reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with double bonds, polar 4-phenyl-1,2,4-triazolidine-3,5-dione (phenyl urazole) groups are introduced into unpolar matrices. Hydrogen-bond complexes are formed between two amide-like units. The temperature dependence of complex formation in dilute hydrocarbon medium is obtained from remperature-dependent IR spectra in the region of the C=O stretching vibration. Results obtained for a low molecular-weight model system are compared with modified polybutadienes, where the groups are attached statistically along the polymer backbone. The enthalpy and the entropy of complex formation (ΔH f =−28.6 kJ/mol; ΔS f =−52 J/mol K−1) obtained for the…
Reactions of Maleisomides with Alcohols
2004
Abstract New surfactants (surfmers) with various amide and ester groups next to C˭C double bonds have been obtained. Maleic acid amidesters (AE) with different hydrophobic groups at the nitrogen atom and hydrophilic substituents at oxygen atoms were synthesized starting with maleic isoimides. 1H KMR and IR spectra were used for their characterization. Some were further characterized for their critical micellar concentration (CMC). A few cationic and zwitterionic surfmers were also prepared from isoimide precursors and characterized. All these surfmers were applied in batch emulsion polymerization of styrene, and in core‐shell seeded copolymerization of styrene and butylacrylate to give late…
Influence of the irradiation parameters on the molecular modifications of an isotactic polypropylene gamma-irradiated under vacuum
2000
Isotactic polypropylene was irradiated under vacuum in a complete set of experimental conditions. The influence of the irradiation parameters, total absorbed dose, D, and dose rate, I, was analysed in order to verify the theoretical predictions of a simple kinetic model, already presented (Sarcinelli L, Valenza A, Spadaro G. Polymer 1997;38:2307), based on the rates of the main reactions occurring during irradiation, i.e. β-scission, addition to double bonds and termination. The concentration of free radicals and double bonds formed during irradiation is detected together with a comparison to their dependence on the irradiation parameters. A quantitative determination of the “inversion curv…
Cooperative structure formation by combination of covalent and association chain polymers: 4. Designing functional groups for supramolecular structur…
1991
Abstract A small number of polar functional groups are attached to polybutadiene by a polymer analogous reaction. Depending on their molecular structure, different degrees of supramolecular ordering result from the aggregation of these polar groups. In the case of phenylurazole units, which carry a single site for hydrogen-bond complexation, binary contacts are formed; whereas linear association chain structures are formed in the case of polybutadiene carrying phenylurazole units additionally substituted with a carboxy group in meta or para positions of the phenyl ring. In the latter case, association chains aggregate cooperatively to an ordered supramolecular structure. The different struc…
Hairy Aramide Rod−Coil Copolymers
2010
We have synthesized monodisperse “hairy rod oligomers” based on oligo(p-benzamide)s carrying alkyl side chains and conjugated them with polydisperse poly(ethylene glycol) (PEG) chains. The well-defined oligomers were synthesized from 4-amino-2-hexyloxybenzoic acid using a commercial peptide synthesizer. The PEG conjugated hairy rod−coil block copolymers self-assemble in polar and nonpolar organic solvents. The self-organization in solution was investigated by dynamic light scattering (DSL) and transmission electron microscopy (TEM) as a function of solvent, equilibration time, and polarity of the substrate. Individual fibers and fiberlike bundles of aggregates could be observed. As all hydr…
Microstructure analysis of biocompatible phosphoester copolymers
2013
Copolymers with varying compositions of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane (EEP) and 2-ethoxy-4-methyl-2-oxo-1,3,2-dioxaphospholane (EMEP) have been synthesized via 1,5,7-triazabicyclo[4.4.0]dec-5-ene-catalyzed anionic ring-opening polymerization. The molecular weights and comonomer ratios were well controlled and polymers with reasonable molecular weight distributions (<1.5) were obtained in all cases. The copolymers were investigated by 1H and 31P NMR spectroscopies to determine the underlying microstructure via detailed dyad analysis. The copolymers were found to be nontoxic to HeLa cells. Furthermore, the obtained copolymers of EEP and EMEP show thermoresponsive properties, i.e., exh…
Ion pair association in isodielectric mixtures at 25�C
1974
Conductance measurements of potassium perchlorate and iodide have been carried out on the following mixtures: methanol-ethylene carbonate, acetone-ethylene carbonate, acetonitrile-ethylene carbonate, sulfolane-ethylene carbonate, isodielectric with water; and in benzene-sulfolane, benzene-acetonitrile, ethanol-sulfolane, isodielectric with methanol. The extent of ionic association at a given concentration in two solvents of the same dielectric constant is greater in the aprotic solvent.
Die alkoholyse des triethylsilans katalysiert von [(CH3)3P]2Ru(CO)2Cl2
1983
Abstract [(CH 3 ) 3 Pl 2 Ru(CO) 2 Cl 2 is an effective catalyst for the reaction of alcohols with triethylsilane. The rate of this reaction varies with the substituents in the hydroxy compound; it is fastest for short primary alcohols. Even in the presence of groups which can be hydrosilated (CC triple or double bonds, as well as ketones), a hydroxy group reacts preferably and completely with the silane. Kinetic experiments have been performed with the system Et 3 SiH/CH 3 CH(OH)COOEt/Ru complex.
Comparison of Water Adsorption Properties of Cellulose and Cellulose Nanocrystals Studied by Near-Infrared Spectroscopy and Gravimetry
2017
The adsorption properties of water molecules on cellulose and cellulose nanocrystals (CNCs), isolated from defatted rice bran (DRB) by 55% sulfuric acid hydrolysis under sonication were investigated. The powdered samples of cellulose and CNCs were analysed by using near infrared spectroscopy (NIR) and gravimetry at 38% and 55% humidities. Small amounts of samples were dried under vacuum at 120°C and the NIR spectra of the dry samples and their spectra during the adsorption water molecules were measured by using an NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The quantitative adsorption of water molecules by the samples was determined by gravimetry. Second a…
Multiscale Simulations of SARS-CoV-2 3CL Protease Inhibition with Aldehyde Derivatives. Role of Protein and Inhibitor Conformational Dynamics in the …
2020
<p>We here investigate the mechanism of SARS-CoV-2 3CL protease inhibition by one of the most promising families of inhibitors, those containing an aldehyde group as warhead. These compounds are covalent inhibitors that inactivate the protease forming a stable hemithioacetal complex. Inhibitor 11a is a potent inhibitor that has been already tested in vitro and in animals. Using a combination of classical and QM/MM simulations we determined the binding mode of the inhibitor into the active site and the preferred rotameric state of the catalytic histidine. In the noncovalent complex the aldehyde group is accommodated into the oxyanion hole formed by the NH main chain groups of residues …