Search results for "Ethylene"
showing 10 items of 2589 documents
1,3-Dipolar cycloadditions of electrophilically activated benzonitrile N-oxides. Polar cycloaddition versus oxime formation.
2006
The reactions of electrophilically activated benzonitrile N-oxides (BNOs) toward 3-methylenephthalimidines (MPIs) have been studied using density functional theory (DFT) at the B3LYP/6-31G* level. For these reactions, two different channels allowing the formation of the [3 + 2] cycloadducts and two isomeric (E)- and (Z)-oximes have been characterized. The 1,3-dipolar cycloadditions take place along concerted but highly asynchronous transition states, while formation of the oximes is achieved through a stepwise mechanism involving zwitterionic intermediates. Both reactions are initiated by the nucleophilic attack of the methylene carbon of the MPIs to the carbon atom of the electrophilically…
Synthesis and Redox Behaviour of the Chalcogenocarbonyl Dianions, [(E)C(PPh2S)2]2−: Formation and Structures of Chalcogen−Chalcogen Bonded Dimers and…
2010
The lithium salts of the chalcogenocarbonyl dianions [(E)C(PPh(2)S)(2)](2-) (E=S (4 b), Se (4 c)) were produced through the reactions between Li(2)[C(PPh(2)S)(2)] and elemental chalcogens in the presence of tetramethylethylenediamine (TMEDA). The solid-state structure of {[Li(TMEDA)](2)[(Se)C(PPh(2)S)(2)]}-[{Li(TMEDA)}(2)4 c]-was shown to be bicyclic with the Li(+) cations bis-S,Se-chelated by the dianionic ligand. One-electron oxidation of the dianions 4 b and 4 c with iodine afforded the diamagnetic complexes {[Li(TMEDA)](2)[(SPh(2)P)(2)CEEC(PPh(2)S)(2)]} ([Li(TMEDA)](2)7 b (E=S), [Li(TMEDA)](2)7 c (E=Se)), which are formally dimers of the radical anions [(E)C(PPh(2)S)(2)](-) (.) (E=S (5 …
New cycloaddition reactions of 1-phenyl-4-vinylpyrazole
1986
Abstract 1-Phenyl-4-vinylpyrazole reacts with methyl propiolate and N-phenylmaleimide giving via the Diels-Alder 1:1 adducts, products (4) and (8), and also the 1:2 adducts (5), (6) and (9) resulting from an “ene” reaction of the initially forced cycloadducts. The obtention of the adducts (5) and (6) in equimolecular amounts is a good example of the non-regioselective character of the “ene” reaction. The reaction with tetracyanoethylene takes place through the olefinic substituent giving the π2 + π2 adduct (10).
PEG-benzofulvene copolymer hydrogels for antibody delivery.
2010
A new amphiphilic copolymer have been synthesized starting from the hydrosoluble polyaspartylhydrazide (PAHy) polymer, by grafting both hydrophilic PEG(2000) chains and hydrophobic palmitic acid (C(16)) moieties on polymer backbone, and the structure of obtained PAHy-PEG(2000)-C(16) copolymer have been characterized by 2D (1)H/(13)C NMR experiments. PAHy-PEG(2000)-C(16) copolymer showed the ability of self-assembling in aqueous media giving a core-shell structure and resulted potentially useful for encapsulating and dissolving hydrophobic drug. The formation of micellar core-shell structure has been investigated by 2D (1)H NMR NOESY experiments. The presence of cross-peaks for protons of C(…
Bone Scaffolds Based on Degradable Vaterite/PEG‐Composite Microgels
2019
Vaterite, a metastable modification of calcium carbonate, embedded in a flexible microgel packaging with adjustable mechanical properties, functionality, and biocompatibility, provides a powerful scaffolding for bone tissue regeneration, as it is easily convertible to bone-like hydroxyapatite (HA). In this study, the synthesis and physical analysis of a packaging material to encapsulate vaterite particles and osteoblast cells into monodisperse, sub-millimeter-sized microgels, is described whereby a systematic approach is used to tailor the microgel properties. The size and shape of the microgels is controlled via droplet-based microfluidics. Key requirements for the polymer system, such as …
Hemoglobin loaded polymeric nanoparticles: preparation and characterizations.
2011
In the present work polymeric nanoparticles based on Poly (maleic anhydride-alt-butyl vinyl ether) 5% grafted with m-PEG (2000) and 95% grafted with 2-methoxyethanol (VAM41-PEG) were loaded with human hemoglobin (Hb) and characterized from a physicochemical point of view. The assessment of structural and functional features of the loaded Hb was performed and the effect of the introduction of different reducing agents as aimed at minimizing Hb oxidation during the nanoparticles formulation process, was also investigated. Nanoparticles possessing an average diameter of 138 ± 10 nm and physicochemical features suitable for this kind of application were successfully obtained. Although the oxida…
Silver Oxide Mediated Monotosylation of Poly(ethylene glycol) (PEG): Heterobifunctional PEG via Polymer Desymmetrization
2017
Heterobifunctional poly(ethylene glycol)s (PEGs) are key structures for bioconjugation in the context of the “PEGylation” strategy to enhance blood circulation times of, for example, peptide drugs or “stealth” liposomes. The formation of heterobifunctional PEGs from symmetric PEG diols is challenging because of limited yields of the targeted monofunctional product and difficulties associated with separation steps. On the basis of a detailed comparison of reaction conditions, we have investigated a “polymer desymmetrization” strategy to maximize the yields of monofunctional PEG tosylate. The tosylation reaction in the presence of the heterogeneous catalyst silver oxide and potassium iodide i…
Characterization and biodistribution of Au nanoparticles loaded in PLGA nanocarriers using an original encapsulation process
2021
Due to their imaging and radiosensitizing properties, ultrasmall gadolinium chelate-coated gold nanoparticles (AuNP) represent a promising approach in the diagnosis and the treatment of tumors. However, their poor pharmacokinetic profile, especially their rapid renal clearance prevents from an efficient exploitation of their potential for medical applications. The present study focuses on a strategy which resides in the encapsulation of AuNP in large polymeric NP to avoid the glomerular filtration and then to prolong the vascular residence time. An original encapsulation procedure using the polyethyleneimine (PEI) was set up to electrostatically entrap AuNP in biodegradable poly(lactic-co-g…
Influence of Surface Charge and Polymer Coating on Internalization and Biodistribution of Polyethylene Glycol-Modified Iron Oxide Nanoparticles
2015
International audience; The aim of this study was to investigate the influence of the surface charge and coating of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) on their in vitro and in vivo behaviors. Neutral and negatively-charged PEG-based SPIONs were synthesized and compared to Resovist (R), a carboxydextran-based SPION currently used in clinics. Their cytotoxicity, cell internalization, and potential as contrast agents for magnetic resonance imaging were assessed. Neutral pegylated SPIONs were internalized less readily by the reticuloendothelial system and showed a lower uptake by the liver, compared to negatively-charged SPIONs (with carboxydextran and PEG). These results sugge…
Efficient Shielding of Polyplexes Using Heterotelechelic Polysarcosines
2018
Shielding agents are commonly used to shield polyelectrolyte complexes, e.g. polyplexes, from agglomeration, precipitation in complex media, like blood, and thus enhance their circulation times in vivo. Since up to now primarily poly(ethylene glycol) (PEG) has been investigated to shield non-viral carriers for systemic delivery, we report on the use of polysarcosine (pSar) as a potential alternative for steric stabilization. A redox-sensitive, cationizable lipo-oligomer structure (containing two cholanic acids attached via a bioreducible disulfide linker to an oligoaminoamide backbone in T-shape configuration) was equipped with azide-functionality by solid phase supported synthesis. After m…