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111.
Elizabeth Dinand Michel Vignon Henri Chanzy Laurent Heux 《Cellulose (London, England)》2002,9(1):7-18
The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with 13C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains. 相似文献
112.
Christian Chapuis Fabrice Robvieux Carole Cantatore Christine Saint‐Léger Laurent Maggi 《Helvetica chimica acta》2012,95(3):428-447
Treatment of cyclohexadecanone ( 1g ; with I2 (2.2 mol‐euqiv.) and KOH in MeOH) furnished the unsaturated (Z)‐ester 2g in 83% yield, via a stereospecific Favorskii rearrangement (Scheme 1). Further treatment with 3‐chloroperbenzoic acid (m‐CPBA) afforded the unreported epoxy ester 3g (88% yield), which was cleaved in 33% yield to Exaltone® (=cyclopentadecanone; 1f ) with NaOH in MeOH/H2O and then HCl at 65°. This methodology was similarly extended to higher (C17) and lower (C15 to C11) cyclic ketone analogues, as well as regioselectively to (?)‐(R)‐muscone ( 5c ) and homomuscone ( 5f ) (Scheme 2). Olfactive properties of the corresponding macrocyclic 1‐oxaspiro[2,n]alkanes and ‐alkenes 4 and 8 , resulting from a Corey? Chaykovsky oxiranylation, are also presented. 相似文献
113.
Armspach D Poorters L Matt D Benmerad B Balegroune F Toupet L 《Organic & biomolecular chemistry》2005,3(14):2588-2592
1,3-Bis[bis(4-tert-butylphenyl)chloromethyl]benzene and 1,3-bis[bis(4-anisyl)chloromethyl]benzene were employed as regioselective capping reagents for the preparation of C-6A,C-6B-bridged, permethylated alpha- and beta-CD derivatives; isolated yields up to 55% of proximally capped, methylated CDs were obtained, thus opening the way to the straightforward preparation of a wide range of A,B-functionalised CDs. As revealed by a single crystal X-ray diffraction study, the benzene-1,3-bis[bis(4-tert-butylphenyl)methyl] spacer is perfectly suited for A,B-capping of beta-cyclodextrin. 相似文献
114.
The binding of a chiral quaternary ammonium ion to a cyclopeptide containing aromatic amino acid subunits is affected not only by the configuration of the cation but also by the configuration of the chiral counterion. Analysis of the binding equilibria shows that complex formation involves interaction of the whole ion pair with the host indicating that steric requirements of the anion influence complex geometry and stability. 相似文献
115.
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117.
Luce VanderElst Audrey Sessoye Sophie Laurent RobertN. Muller 《Helvetica chimica acta》2005,88(3):574-587
The self‐diffusion (Dc) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution 1H‐NMR spectroscopy. The self‐diffusion coefficient of H2O (Dw) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10?9 and of 3.3 (±0.1)×10?9 m2 s?1 at 25 and 37°, respectively, for 'small' contrast agents (Mr 500–750 g/mol), and with the value of bulk H2O (2.2×10?9 and 2.9×10?9 m2 s?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of Dc for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τR) are very close to those already reported. However, differences in the electronic relaxation time (τSO) at very low field and in the correlation time (τV) related to electronic relaxation were found. 相似文献
118.
Jun-ichi Azuma Nam-Hun Kim Laurent Heux Roger Vuong Henri Chanzy 《Cellulose (London, England)》2000,7(1):3-19
The cellulose system of the viscous fibrous cellulosic polysaccharide (viscan) in the viscin tissue of the European mistletoe, Viscum album L., was analyzed by chemical and physicochemical techniques including sugar analysis, optical and transmission electron microscopy, X-ray and electron diffraction together with solid state CP/MAS 13C-NMR spectroscopy. The results confirmed that in the elongated thin viscin cells, the cellulose microfibrils (having a diameter of around 3 nm) were tightly coiled with their axes perpendicular to the long axis of the cell. Upon stretching these cells became deformed by more than a hundred fold. In such a deformation, the cellulose microfibrils became unwound to be perfectly aligned along the stretching direction. Based on solid-state CP/MAS 13C-NMR spectroscopic analysis of the viscin tissue, it was found that its cellulose consisted of I and I polymorphs in the ratio 1:1. 相似文献
119.