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1.
Alexander Semenov Aurélia Charlot Rachel Auzély-Velty Marguerite Rinaudo 《Rheologica Acta》2007,46(5):541-568
Dynamics of associating polymer solutions above the reversible gelation point are studied. Each macromolecule consists of
a soluble backbone (B) and a small fraction of specific strongly interacting groups (A or C stickers) attached to B. A mixture
of B–A and B–C associating polymers with 1:1 stoichiometric ratio is considered. As a result of AC association, the polymers
reversibly gelate above the overlap concentration. It is shown that (1) the network strands are linear complexes (double chains)
of B–A and B–C; (2) “diffusion” of the network junction points is characterized by an apparent activation energy, which can
be significantly higher than the energy of one AC bond; (3) most importantly, the randomness of sticker distribution along
the chain can significantly slow down the network relaxation leading to a markedly non-Maxwellian viscoelastic behavior. The
theory elucidates the most essential features of rheological behavior of polysaccharide associating systems (with A = adamantyl
moiety, C = β-cyclodextrin, B = either chitosan or hyaluronan) including similar behavior of G
′ and G
″ in a wide frequency range, strong temperature dependence of the characteristic frequency ω
x
, and an extremely strong effect of added free stickers (fC) on the dynamics.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
2.
Methods for metal preconcentration are often described in the literature. However, purposes are often different, depending
on whether the methods are applied in environmental, clinical or technological fields. The respective method needs to be efficient,
give high sensitivity, and ideally also is selective which is useful when used in combination with atomic spectroscopy. This
review presents the actual tendencies in metal preconcentration using techniques such as Flame Atomic Absorption Spectrometry
(FAAS), Electrothermal Atomic Absorption Spectrometry (ETAAS), Hydride Generation Atomic Absorption Spectrometry (HGAAS),
Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
Procedures based on related to electrochemical, coprecipitation/precipitation, liquid–liquid and solid–liquid extraction and
atom trapping mechanisms are presented.
Correspondence: Department of Analytical Chemistry, Universidade Estadual de Campinas – UNICAMP, P.O. Box 6154, 13083-970
Campinas, Brazil. e-mail: zezzi@iqm.unicamp.br
Received December 20, 2001; accepted October 11, 2002 相似文献
3.
Murphy JA Commeureuc AG Snaddon TN McGuire TM Khan TA Hisler K Dewis ML Carling R 《Organic letters》2005,7(7):1427-1429
[reaction: see text] N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product. 相似文献
4.
Treatment of 2-methylphenols with chloro(diphenyl)-lambda(3)-iodane led to their regioselective dearomatizing 2-phenylation into cyclohexa-2,4-dienone derivatives via a proposed ligand coupling reaction. In the same vein of investigation, treatment of 2-methylanilines with the lambda(5)-iodane 2-iodoxybenzoic acid IBX reagent led to their regioselective dearomatization into previously undescribed ortho-quinol imines. 相似文献
5.
The ketals of bis(o-nitrophenyl)ethanediol and ketones or aldehydes are smoothly deprotected in neutral conditions by irradiation with 350 nm light. The chemical stability in basic, acidic, and oxidizing media makes this form of protection orthogonal to classical protecting groups. Both racemic and enantiopure forms are readily available in two steps from inexpensive starting materials. 相似文献
6.
Enantiospecific total synthesis of (-)-polyoxamic acid using 2,3-aziridino-gamma-lactone methodology
The non-natural enantiomer of polyoxamic acid was synthesized in six steps from 2,3-aziridino-gamma-lactone 7 with an overall yield of 10%. The key step of the strategy is a deprotection-protection sequence on the nitrogen atom of the aziridine ring required for aziridine activation toward nucleophilic ring opening. 相似文献
7.
Three standardised, capillary zone electrophoresis-electrospray ionisation mass spectrometry (CZE-ESI-MS) methods were developed for the analysis of six drug candidates and their respective process-related impurities comprising a total of 22 analytes with a range of functional groups and lipophilicities. The selected background electrolyte conditions were found to be: 60/40 v/v 10 mM ammonium formate pH 3.5/organic, 60/40 v/v 10 mM ammonium acetate pH 7.0/organic and 10 mM piperidine, pH 10.5, where the organic solvent is 50/50 v/v methanol/acetonitrile. The coaxial sheath flow consisted of either 0.1% v/v formic acid in 50/50 v/v methanol/water, or 10 mM ammonium acetate in 50/50 v/v methanol/water, depending on the mixture being analysed. Factor analysis and informational theory were used to quantify the orthogonality of the methods and predict their complementarities. The three selected CZE-ESI-MS methods allowed the identification of 21 out of 22 of all the drug candidates and their process-related impurities and provided orthogonality with four established high-performance liquid chromatography-mass spectrometry (HPLC-MS) methods. These methodologies therefore form the basis of a generic approach to impurity profiling of pharmaceutical drug candidates and can be applied with little or no analytical method development, thereby offering significant resource and time savings. 相似文献
8.
[reaction: see text] SIBX is a nonexplosive formulation of IBX that can be used as a suspension in a variety of standard organic solvents such as refluxing EtOAc and THF to oxidize safely alcohols into aldehydes and ketones. The use of hot THF is limited to the oxidation of allylic and benzylic alcohols. Most yields are comparable to those obtained with IBX or DMP. SIBX can also be used to perform oxygenative demethylation of 2-methoxyarenols into orthoquinones and catechols. 相似文献
9.
Dr. Aurélien Adenot Dr. Lucile Anthore-Dalion Dr. Emmanuel Nicolas Jean-Claude Berthet Dr. Pierre Thuéry Dr. Thibault Cantat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18047-18053
An air-tolerant Cu-catalyzed sulfonylative Hiyama cross-coupling reaction enabling the formation of diaryl sulfones is described. Starting from aryl silanes, DABSO and aryliodides, the reaction tolerates a large variety of polar functional groups (amines, ketones, esters, aldehydes). Control experiments coupled with DFT calculations shed light on the mechanism, characterized by the formation of a Cu(I)-sulfinate intermediate via fast insertion of a SO2 molecule. 相似文献
10.