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921.
922.
Jumpei Kawada Yasuo Abe Toshifumi Yui Kenji Okuyama Kozo Ogawa 《Journal of carbohydrate chemistry》2013,32(5):559-571
ABSTRACT Spontaneous removal of monocarboxylic (formic, acetic, propionic or butyric) acids accompanying dehydration of the corresponding chitosan salts was observed from X-ray fiber diffraction diagrams obtained during the storage of these salts for a given period of time. The first three salts were prepared by immersing a tendon chitosan (a hydrated crystal) in an aqueous solution of respective monocarboxylic acid and 2-propanol. The salts showed similar fiber patterns not only to one another but also to the “Eight-fold” polymorph of the original chitosan, indicating that they are Type II salts, hydrated crystals, where the backbone chitosan molecule takes up an eight-fold helical conformation. The temperature required for the salt formation depended on the hydrophobicity of the acid, e.g., the chitosan formic acid salt could be prepared at room temperature, whereas, formation of the propionic acid salt was carried out at 4 °C. All the acids spontaneously evaporated accompanied by dehydration during storage of the salts, resulting in formation of anhydrous crystalline chitosan. Removal of the monocarboxylic acids was accelerated by increasing the hydrophobicity of the acid: at 100% relative humidity approximately 3 months for the formic, 1 month for the acetic and 3 weeks for the propionic acid salts. In the case of butyric acid the anhydrous polymorph of chitosan was obtained immediately after the reaction, suggesting that the water removing action of this acid was too fast to detect a Type II salt by the present X-ray method. The anhydrous crystals of chitosan were irreversibly prepared by annealing a hydrated crystal in water at a high temperature, such as 240 °C, leading to a little loss of orientation and to thermal decomposition of the sample specimen to some extent. But it was found that, through Type II salts of monocarboxylic acids, the hydrated crystals of chitosan can be dehydrated even at room temperature without any loss of orientation and decomposition of the chitosan specimen. 相似文献
923.
Takeshi Fukuda 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4743-4755
The control achievable by living radical polymerization (LRP) is based on a kinetic balance of the activation–deactivation reversible reactions, which are specific to LRP, with conventional elementary reactions such as initiation, propagation, and termination. This work describes, as plainly as possible, how chains grow and how their polydispersity evolves as they experience activation–deactivation cycles and how these processes can be quantitatively analyzed by gel permeation chromatography. A comprehensive probability theory on the polydispersity indices of LRP polymers is presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4743–4755, 2004 相似文献
924.
Abstract A series of cellobiose octaalkanoates, Cel-II-n (n is the carbon number of the alkyl chain), with n = 7–14 were prepared and their mesogenic properties examined by differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction. All of these compounds form enantiotropic discotic columnar phases, in which the columns are built up by a regular stacking of the cellobiose moieties and are packed in a two dimensional lattice. Homologues with n = 9–14 form the Dho phase only whilst the compound with n = 7 forms the Dro phase. The n = 8 compound forms the Dho phase at higher temperatures and the Dro phase at lower temperatures. Structural parameters obtained from X-ray diffraction studies are presented for both phases. 相似文献
925.
Takehito Nakano Yuka Ikemoto Yasuo Nozue 《Molecular Crystals and Liquid Crystals》2013,570(2):461-466
Abstract Magnetic and optical properties are investigated for K clusters incorporated into zeolite LTA at loading densities of K atoms, n, between 1.0 and 3.2 per cluster. No magnetic ordering is observed at n < 2. The spontaneous magnetization due to ferromagnetism is observed suddenly at n > 2. It is confirmed that the 1p-like quantum electronic state of K cluster plays an essential role in the ferromagnetic phase. 相似文献
926.
Yuka Ikemoto Takehito Nakano Momoko Kuno Yasuo Nozue 《Molecular Crystals and Liquid Crystals》2013,570(2):453-459
Abstract Na clusters are generated in zeolite FAU with Si-to-Al ratios of 2.8 (Y-type) and 1.25 (X-type). When the density of adsorbed Na atoms increases, the ESR spectrum with hyper-fine structures becomes narrow into a single line. In the IR absorption spectrum, no Drude-like absorption is observed at any adsorption densities of Na atoms. The ESR narrowing is explained by the mean field theory of the exchange narrowing given by Anderson and Weiss, by using the experimentally observed antiferromagnetic exchange coupling energy between magnetic moments of clusters. 相似文献
927.
Atsushi Narumi Harumi Kaga Kosei Kawasaki Yasuo Taniguchi Toshifumi Satoh Toyoji Kakuchi 《Journal of polymer science. Part A, Polymer chemistry》2001,39(23):4061-4067
Glucosyl styrene ( 1a ), maltosyl styrene ( 1b ), and maltohexaosyl styrene ( 1c ) were prepared by the glycosylation of 4‐vinylbenzyl alcohol with the corresponding glycosyl trichloroacetimidates with boron trifluoride diethyl ether complex. The copolymerizations of 1a – 1c with styrene were carried out with 2,2′‐azobis(2‐methylpropionitrile) as an initiator in dry N,N‐dimethylformamide at 60 °C, and this was followed by deacetylation to produce amphiphilic polystyrenes with glucose ( 3a ), maltose ( 3b ), and maltohexaose ( 3c ) as hydrophilic segments. 3 showed various solubility characteristics that were dependent on the content of glucose residues, especially within a range of 20–50 wt %. The solubility characteristics of 3 , related to the copolymer composition, indicated that the hydrophilic property was remarkably improved with an increased number of glucose units, that is, in the order 3a < 3b ? 3c . The results described in this article provide useful information for the design of glycoconjugated architectures with desired amphiphilic properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4061–4067, 2001 相似文献
928.
Noboru Watanabe Yohei Kamata Kota Yamauchi Yasuo Udagawa 《Journal of computational chemistry》2001,22(13):1315-1320
Total X‐ray scattering intensity σee(q) is very sensitive to electron correlation effects. In this study σee(q) of N2, CO, and N2O have been computed by the coupled cluster singles and doubles (CCSD) method and compared with configuration interaction singles and doubles (CISD) calculations as well as experimental observations. σee(q) curves by CCSD calculations are rather close to those by CISD, but although small, there still exist some discrepancies between calculated and observed values. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1315–1320, 2001 相似文献
929.
930.
We study numerically the director and orientational order parameter configurations in a nematic liquid crystal around a two-dimensional
spherical particle on the basis of the tensor order parameter formalism. To properly account for the large length scale difference
between the particle and the accompanying orientational defect, we devise an adaptive grid scheme in which the lattice spacing
is automatically and locally adjusted in response to the spatial gradient of the orientational order parameter. This adaptive
grid scheme is useful in studying dynamical as well as static orientational structures. We present a simulation result which
shows how a hedgehog defect of topological charge -1 becomes unstable in two dimensions, and splits into a defect pair of
topological charge -1/2, located symmetrically around the particle.
Received 14 September 2000 and Received in final form 27 December 2000 相似文献