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81.
Dhanpat Rai Mikazu Yui Dean A. Moore Gregg J. Lumetta Kevin M. Rosso Yuanxian Xia Andrew R. Felmy Frances N. Skomurski 《Journal of solution chemistry》2008,37(12):1725-1746
No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO2(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L−1) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations
of about 0.006 mol⋅L−1 or 0.018 mol⋅L−1. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations
were reached in < 29 days. X-ray diffraction, FTIR, and Raman analyses of the equilibrated solid phases showed that the Th
solids were amorphous ThO2(am) containing some adsorbed Si. The solubility of ThO2(am) at pH values ranging from 10 to 13.3 at fixed 0.018 mol⋅L−1 aqueous Si concentrations decreases rapidly with an increase in pH, and increases dramatically with an increase in Si concentrations
beyond about 0.003 mol⋅L−1 at fixed pH values > 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion
of one mixed-hydroxy-silica complex of Th [Th(OH)3(H3SiO4)32−]. Both models provided similar complexation constant values for the formation of this species. Density functional theory
calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable.
Predictions based on the fitted value of log 10
K
0=−18.5±0.7 for the ThO2(am) solubility reaction involving Th(OH)3(H3SiO4)32−[ThO2(am)+3H4SiO4+H2O↔Th(OH)3(H3SiO4)32−+2H+], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive
experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th. 相似文献
82.
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
83.
Regular helical structures of polysaccharides are most conveniently described by a set of the helix parameters; n for the number of chemical repeating units per turn and h in Å for the rise per unit along the helix axis. A two dimensional mapping of n-h values for possible helix models along with the potential energy surfaces allows one to estimate conformational accessibility of a given posaccharide.1-3 Recently, we have adopted the method to study an acidic heteropolysaccharide4 and a branching glucan.5 These polysaccharides involve two or three sets of backbone glycosidic linkages (Φ-Ψ), each of which varies independently, and, therefore, enormous multidimensional spaces must be explored. Their n-h maps were calculated based on the low energy Φ-Ψ values derived from MM36-8-generated, relaxed-residue potential energy maps9, 10 of the component disaccharides. The present assessment of helix models for the two heteropolymeric glucans is achieved by calculating n-h maps in a similar fashion. These glucans are the two poly(disaccharide)s, poly[(1→3)-α-D-maltotriose] (elsinan) and poly[(1→3)-β-D-cellotriose] (lichenan). In addition to single-stranded helices, three types of mutiple helices; double-parallel, and double-antiparallel, and triple helices have also been examined. 相似文献
84.
Ryosuke Matsuoka Tatsuto Yui Ryo Sasai Katsuhiko Takagi Haruo Inoue 《Molecular Crystals and Liquid Crystals》2013,570(2):333-338
Abstract Tetra-(4-sulfonatophenyl)porphyrinatotin(IV) aggregated efficiently in a clay (saponite) layer intercalated with a polyfluorinated surfactant, but no aggregation was observed in a hydrocarbon type surfactant-clay hybrid environment. Germanium(IV) porphyrins remained as monomers even in the polyfluorinated environment. 相似文献
85.
A computer docking study was carried out on the (110) crystal surface of the cellulose Iα crystal model for the carbohydrate
binding module (CBM) of cellobiohydrolase Cel6A, which is produced by the filamentous fungus Trichoderma reesei. Three-dimensional structures of the CBM were constructed by the homology modeling method using the Cel7A CBM, which is another
cellobiohydrolase from T. reesei, as a template, and refined by molecular dynamics calculations in the solution state. Among the three models tested, those
with three disulfide bonds were selected for a docking analysis. The binding free energy maps represented changes in non-covalent
interactions and solvation free energies with respect to the CBM position. These indicated two minimum positions within the
unit cell for both the parallel and antiparallel orientation modes of the CBM with respect to the cellulose fiber axis. Molecular
dynamics calculations under an explicit solvent system were performed for the four complex models derived from the minimum
positions of the binding free energy maps. The complex models with CBM in the parallel orientation had the lowest binding
energies. 相似文献
86.
Dr. Akihito Konishi Koki Horii Haruna Iwasa Yui Okada Dr. Ryohei Kishi Prof. Dr. Masayoshi Nakano Prof. Dr. Makoto Yasuda 《化学:亚洲杂志》2021,16(12):1553-1561
The singlet open-shell character and antiaromaticity are intriguing features in π-conjugated carbocycles. These two exhibit similar chemical and physical properties. However, they rarely coexist in the same molecule. Understanding the interrelation between the open-shell and antiaromatic characteristics in the same molecule is crucial to control the electronic properties. Herein we describe the synthesis and characterization of a new member of diareno[a,f]pentalene, benzo[a]naphtho[2,3-f]pentalene 6 . Unlike its isomer 5 with a closed-shell ground state, 6 exhibits an appreciable open-shell character and a moderate antiaromatic feature. The behaviors of the open-shell index (y0) against the difference of the proton chemical signal (Δδ(H1)) between pentalenide dianions/neutral pentalenes for our reported pentalenes 1 , 4 , 5 , and 6 give a thought-provoking conclusion about the interrelation between open-shell and antiaromatic characteristics in this series. The mode of the incorporated quinoidal moiety and the formal molecular symmetry are critical to balance these two characteristics. 相似文献
87.
As a feasible way for controlling the density of ligands in polyrotaxanes, azidated polyrotaxanes comprising PEG (MW = 3 000 and 20 000 g · mol−1) and mono‐, di‐, or triazidated α‐cyclodextrins are prepared in a water/DMSO solution in a one‐pot synthesis. The azidated polyrotaxanes are then allowed to conjugate with propargyl‐modified mannose as a ligand via click chemistry. As proven by FTIR spectroscopy and 1H NMR‐spectroscopy, mannose molecules are efficiently introduced into all of the azide moieties of the polyrotaxanes. The results verify the achievement of ligand‐density‐controlled polyrotaxanes. The functionalized polyrotaxanes can be utilized for a variety of biological applications.
88.
Angelov P Chau YK Fryer PJ Moloney MG Thompson AL Trippier PC 《Organic & biomolecular chemistry》2012,10(17):3472-3485
Biomimetic intramolecular aldol reactions on oxazolidine templates derived from serine may be used to generate densely functionalised pyroglutamates, which are simpler mimics of the right hand side of oxazolomycin. Some of the compounds from this sequence exhibit in vivo activity against S. aureus and E. coli, suggesting that pyroglutamate scaffolds may be useful templates for the development of novel antibacterials, and cheminformatic analysis has been used to provide some structure-activity data. 相似文献
89.
The colloid and radionuclide retardation experiments performed at NAGRA's Grimsel Test Site in Switzerland are part of an international collaboration program designed to collect in situ data on the impacts of colloids on radionuclide transport. In this work, breakthrough behaviors of trivalent americium (i.e., 241Am and 243Am) both in the absence and presence of bentonite colloids are analyzed with COLFRAC--a code that models colloid-facilitated solute transport in discretely-fractured, porous media. Model fits to the experimental results indicate that Am sorbed onto mobile colloids, which enhance Am transport relative to a non-sorbing tracer, 131I. Modelling results suggest that Am is kinetically sorbed onto both naturally occurring and exogenous bentonite colloids. Results also indicate that desorption of Am from colloids is slow with respect to the duration of the experiment. In addition, early colloid breakthrough compared to a conservative tracer suggests the effects of hydrodynamic chromatography. Overall, Am breakthrough curves suggest enhanced mobility due to co-transport with both naturally occurring and bentonite colloids. 相似文献
90.