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61.
The polymerization kinetics and mechanisms of model compounds (mono- and difunctional) characteristic of prepolymers of ATR (acetylene-terminated resins) have been studied by HPLC, FTIR, UV, NMR (liquid and solid) and HPLC in the temperature range of 150–220°C. Using monofunctional compounds, we were able to show that the thermal polymerization of acetylene functions is not a simple reaction. Initially, the majority of compounds formed have a low polymerization degree, followed by the formation of species with higher and progressive polymerization degrees. Spectroscopic techniques such as NMR and FTIR lead to the unambiguous determination of reaction conversion up to 95% in the case of bifunctional prepolymers. The understanding of network structures, on the other hand, is more delicate in polyaromatic systems, since the chains formed are very similar to the basic skeleton of the prepolymer. The kinetic curves obtained isothermally between 150–220°C have shown that while kinetic monitoring of the disappearance of the first 90% of ethynyl functions poses no particular problems, there is a considerable uncertainty for the last 10%, regardless of the technique chosen. We have demonstrated that me thermal properties are dependent on the molecular weight and the structure of the polymer. 相似文献
62.
Journal of Experimental and Theoretical Physics - In this study, we examine the underlying surface wave dynamics forming an octupole structure of vortices on the air–water interface. The... 相似文献
63.
Delphine Catel Olivier Payen Floris Chevallier Florence Mongin Philippe C. Gros 《Tetrahedron》2012,68(21):4018-4028
Butyl and dibutylmagnesiates incorporating chiral ligands have been prepared and their reactivity studied. The reagents were efficient to promote the clean bromine–magnesium exchange of azinyl bromides at room temperature and subsequent reaction with aldehydes affording pyridylcarbinols. (R,R)-TADDOL-based dibutylmagnesiate was the best reagent leading to acceptable to good enantioselectivities, depending on the substrate and on the aldehyde substitution. This is the first example of enantioselective addition of in situ generated pyridylmagnesiate to carbonyl electrophiles. 相似文献
64.
The reaction of various alcohols with cyanogen bromide, triphenylphosphine, and a base afforded the corresponding nitrile in satisfactory yields. 相似文献
65.
The use of light front coordinates in quantum field theories (QFT) always brought some problems and controversies. In this work we explore some aspects of its formalism with respect to the employment of dimensional regularization in the computation of the photon’s self-energy at the one-loop level and how the fermion propagator has an important role in the outcoming results. 相似文献
66.
Sébastien Bau Denis Bémer Florence Grippari Jean-Christophe Appert-Collin Dominique Thomas 《Journal of nanoparticle research》2014,16(10):1-13
The cysteamine-modified hyaluronic acid (HA) polymer was employed to coat quantum dots (QDs) through a convenient one-step reverse micelle method, with the final QDs hydrodynamic size of around 22.6 nm. The HA coating renders the QDs with very good stability in PBS for more than 140 days and resistant to large pH range of 2–12. Besides, the HA-coated QDs also show excellent fluorescence stability in BSA-containing cell culture medium. In addition, the cell culture assay indicates no significant cytotoxicity for MD-MB-231 breast cancer cells, and its targeting ability to cancer receptor CD44 has been demonstrated on two breast cancer cell lines. The targeting mechanism was further proved by the HA competition experiment. This work has established a new approach to help solve the stability and toxicity problems of QDs, and moreover render the QDs cancer targeting property. The current results indicate that the HA polymer-coated QDs hold the potential application for both in vitro and in vivo cancer imaging researches. 相似文献
67.
Stéphanie Gracia Cédric Marion Jullien Rey Florence Popowycz Stéphane Pellet-Rostaing Marc Lemaire 《Tetrahedron letters》2012,53(25):3165-3168
Horner-Wadsworth Emmons olefination followed by asymmetric hydrogenation allowed the first synthetic access to the chiral thiotryptophan with good enantiomeric excess. Oxazolidinone formation followed by a Pictet–Spengler condensation provided the benzothiophenic analog of Azatoxin. 相似文献
68.
A three-dimensional liquid chromatographic purification protocol based on sequential size-exclusion, anion-exchange and cation-exchange separation mechanisms was developed for the mapping of seleno compounds in aqueous yeast extracts. The method allowed the demonstration of the presence of more than 30 different seleno compounds. Semi-preparative size-exclusion and anion-exchange chromatography were optimized for maximum resolution using electrospray-compatible buffers in order to purify the compounds for mass spectrometric analysis. Molecular masses were attributed to many of the compounds on the basis of the selenium isotopic pattern in the electrospray mass spectra and of the collision-induced fragmentation patterns. Limitations preventing the ultimate identification of the selenium species detected are discussed. 相似文献
69.
Methylolation and condensation products formed in caprolactam-formaldehyde reaction mixtures have been identified using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Previously unreported side-products were also detected. All of the reaction products were separated by micellar electrokinetic chromatography (MEKC) and high performance liquid chromatography (HPLC), and the separation parameters, such as efficiency and distribution constants, obtained in the two techniques were compared. For quantification, the response factors for the monomers were determined using standard calibration and hydrolysis, whilst those for the condensation products were deduced from the values of the monomers. The accurate determination of the response factors was confirmed by checking the mass balance of a known mixture. 相似文献
70.
Florence Geneste Alec Moradpour Georges Dive Daniel Peeters Jacques Malthête Jean-Fran?ois Sadoc 《The Journal of organic chemistry》2002,67(2):605-607
The total number of possible retrosynthetic bisections of C(60) leads to nine different isometric C(30) fragments. These molecules include five chiral units, four of which derive from partitions corresponding to four distinct "Coupes du Roi". The energies, curvatures, and homodesmotic stabilization energies of the C(30) fragments are evaluated at the ab initio 6-31G level. 相似文献